ALBERT

Description: 〈p〉Publication date: Available online 1 November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Complexity〈/p〉 〈p〉Author(s): Robert J. Kunsch, Erich Novak, Daniel Rudolf〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We compute the integral of a function or the expectation of a random variable with minimal cost and use, for our new algorithm and for upper bounds of the complexity, i.i.d. samples. Under certain assumptions it is possible to select a sample size based on a variance estimation, or – more generally – based on an estimation of a (central absolute) 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="si1.gif"〉〈mi〉p〈/mi〉〈/math〉-moment. That way one can guarantee a small absolute error with high probability, the problem is thus called solvable. The expected cost of the method depends on the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="si1.gif"〉〈mi〉p〈/mi〉〈/math〉-moment of the random variable, which can be arbitrarily large. In order to prove the optimality of our algorithm we also provide lower bounds. These bounds apply not only to methods based on i.i.d. samples but also to general randomized algorithms. They show that – up to constants – the cost of the algorithm is optimal in terms of accuracy, confidence level, and norm of the particular input random variable. Since the considered classes of random variables or integrands are very large, the worst case cost would be infinite. Nevertheless one can define adaptive stopping rules such that for each input the expected cost is finite. We contrast these positive results with examples of integration problems that are not solvable.〈/p〉〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Computers in Industry, Volume 104〈/p〉 〈p〉Author(s): Jacques Bahi, Wiem Elghazel, Christophe Guyeux, Mourad Hakem, Kamal Medjaher, Noureddine Zerhouni〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Monitoring activities in industry may require the use of wireless sensor networks, for instance due to difficult access or hostile environment. But it is well known that this type of networks has various limitations like the amount of disposable energy. Indeed, once a sensor node exhausts its resources, it will be dropped from the network, stopping so to forward information about maybe relevant features towards the sink. This will result in broken links and data loss which impacts the diagnostic accuracy at the sink level. It is therefore important to keep the network's monitoring service as long as possible by preserving the energy held by the nodes. As packet transfer consumes the highest amount of energy comparing to other activities in the network, various topologies are usually implemented in wireless sensor networks to increase the network lifetime. In this paper, we emphasize that it is more difficult to perform a good diagnostic when data are gathered by a wireless sensor network instead of a wired one, due to broken links and data loss on the one hand, and deployed network topologies on the other hand. Three strategies are considered to reduce packet transfers: (1) sensor nodes send directly their data to the sink, (2) nodes are divided by clusters, and the cluster heads send the average of their clusters directly to the sink, and (3) averaged data are sent from cluster heads to cluster heads in a hop-by-hop mode, leading to an avalanche of averages. Their impact on the diagnostic accuracy is then evaluated. We show that the use of random forests is relevant for diagnostics when data are aggregated through the network and when sensors stop to transmit their values when their batteries are emptied. This relevance is discussed qualitatively and evaluated numerically by comparing the random forests performance to state-of-the-art PHM approaches, namely: basic bagging of decision trees, support vector machine, multinomial naive Bayes, AdaBoost, and Gradient Boosting. Finally, a way to couple the two best methods, namely the random forests and the gradient boosting, is proposed by finding the best hyperparameters of the former by using the latter.〈/p〉〈/div〉

Description: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Radiation Measurements, Volume 119〈/p〉 〈p〉Author(s): Alessio Parisi, Luana de Freitas Nascimento, Olivier Van Hoey, Patrice Mégret, Hisashi Kitamura, Satoshi Kodaira, Filip Vanhavere〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Lithium fluoride thermoluminescent radiation detectors with different dopant concentrations (〈sup〉7〈/sup〉LiF:Mg,Ti and 〈sup〉7〈/sup〉LiF:Mg,Cu,P) were exposed to 〈sup〉1〈/sup〉H and 〈sup〉4〈/sup〉He ions at the Heavy Ion Medical Accelerator in Chiba (HIMAC) in order to investigate their response to energetic light charged particles. Computer simulations with the Monte Carlo code PHITS were performed for a better interpretation of the experimental data. The results were compared with literature efficiency data and with the results of a recently developed microdosimetric efficiency model. In case of the main peak signal of 〈sup〉7〈/sup〉LiF:Mg,Ti detectors, the determined efficiency values are in good agreement with previous investigations. Discrepancies in the efficiency of high temperature signal due to well-known non-linearity effects are reported. For 〈sup〉7〈/sup〉LiF:Mg,Cu,P detectors, an anomalous thermoluminescence behavior in the low temperature part of the signal was found and discussed. Depending on the light quantification process, differences up to 30% in the dose assessment can be obtained, affecting also the relative efficiency determination process. An explanation of this phenomenon as a consequence of local migration of the charged carriers between the low temperature peaks and the main peak is presented. The implications of these findings on the use of LiF:Mg,Cu,P detectors in radiation environments characterized by the presence of 〈sup〉1〈/sup〉H and 〈sup〉4〈/sup〉He ions (i.e. space and proton therapy) are discussed. In order to avoid the occurrence of this anomalous behavior, it is advised to pre-heat the detectors after energetic light particle exposures.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 31 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Power Sources, Volume 408〈/p〉 〈p〉Author(s): Guoping Chen, Xiong Song, Suqing Wang, Xinzhi Chen, Haihui Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Lithium-sulfur (Li〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉S) batteries are attractive candidates for advanced energy storage devices. However, the low utilization of sulfur and the severe “shuttle effect” hinder the commercialization of Li〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉S batteries. Herein, we design an ultra-thin and lightweight two-dimensional (2D) molybdenum nitride nanosheets layer to modify Celgard (denoted as MoN〈sub〉x〈/sub〉/Celgard) separator to promote the electrochemical performance of Li〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉S batteries. Benefiting from the 2D polar molybdenum nitride nanosheets, the obtained molybdenum nitride layer can effectively suppress the shuttle effect via the synergistic effect of structural confinement and chemical absorption. Meanwhile, molybdenum nitride nanosheets layer possesses metallic and catalytic characteristics, which are beneficial for high sulfur utilization. Therefore, the Li〈img src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"〉S batteries using MoN〈sub〉x〈/sub〉/Celgard separator with multifunction exhibit high capacity and outstanding cycling performance. It delivers a high discharge capacity of 1298 mA h g〈sup〉−1〈/sup〉 at 0.1C and sustain a capacity of 566 mA h g〈sup〉−1〈/sup〉 after 500 cycles at 0.5C, corresponding with the capacity fading rate of only 0.063% per cycle.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 379〈/p〉 〈p〉Author(s): Takashi Shiroto, Naofumi Ohnishi, Yasuhiko Sentoku〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉For more than half a century, most of the plasma scientists have encountered a violation of the conservation laws of charge, momentum, and energy whenever they have numerically solved the first-principle equations of kinetic plasmas, such as the relativistic Vlasov–Maxwell system. This fatal problem is brought by the fact that both the Vlasov and Maxwell equations are indirectly associated with the conservation laws by means of some mathematical manipulations. Here we propose a quadratic conservative scheme, which can strictly maintain the conservation laws by discretizing the relativistic Vlasov–Maxwell system. A discrete product rule and summation-by-parts are the key players in the construction of the quadratic conservative scheme. Numerical experiments of the relativistic two-stream instability and relativistic Weibel instability prove the validity of our computational theory, and the proposed strategy will open the doors to the first-principle studies of mesoscopic and macroscopic plasma physics.〈/p〉〈/div〉

Description: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Radiation Measurements, Volume 119〈/p〉 〈p〉Author(s): Chen Wang, Shi-Lun Guo, Zhi-Yuan Chang, Guo-Rong Liu, Yong-Gang Zhao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Two parameter approach –a new technique has been devised and tested to identify and distinguish Pu–bearing particles from U-bearing particles. This technique can be used to select rare and microscopic Pu-bearing particles from environmental samples, such as in soil, water, air (aerosol) and swipe samples from the wall of buildings and surfaces of machines in nuclear factories. Some amount of Pu and U standard reference materials were respectively added to cellulose nitrate (CN) solution and dropped some quantity of the solution on mica plates and dried to from CN sheets. CR-39 track detectors were used to record tracks of α particles emitted from the Pu or U particles in CN sheets. After etching of CR-39 plates, α track stars were developed and can be seen under optical microscope. Tracks shapes of α particles in the stars were investigated. We found that at certain interval of etching time, the tip part of α tracks of Pu was very sharp, but the tip part of α tracks of U was blunted with spherical tips. The ratio Rt/Ro of the diameter (Rt) of tip point to the diameter (Ro) of the round track in center area of star is a superior parameter to identify Pu from U particles. The Rt/Ro measurements should be carried at a certain distance from the center point. The two parameter approach has been using in nuclear safeguards and nuclear forensics to analyze isotopic compositions and age of Pu samples.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 31 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Power Sources, Volume 408〈/p〉 〈p〉Author(s): Yilan Wu, Xin Fan, Rohit Ranaganathan Gaddam, Qinglan Zhao, Dongfang Yang, Xiaoming Sun, Chao Wang, X.S. Zhao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Sodium-ion capacitors with unique characteristics such as higher energy density than electrical double-layer capacitors, higher power density than rechargeable batteries, and abundant sodium resources represent current research trend in developing large-scale electrical energy storage technology. One of the key challenges presently facing the development of this technology is the imbalanced kinetics between the sluggish Faradaic sodium insertion in the anode and the fast capacitive ion adsorption on the cathode. Here we demonstrate the sol-gel synthesis of a novel, high-rate, stable composite anode material for sodium-ion capacitors (NICs). The composite consisted of Nb〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 nanoparticles embedded in a carbon matrix (denoted by m-Nb〈sub〉2〈/sub〉O〈sub〉5〈/sub〉/C). Sodium-ion capacitors employing the m-Nb〈sub〉2〈/sub〉O〈sub〉5〈/sub〉/C anode and a commercial activated carbon as the cathode showed an admirable performance, delivering high energy densities in a wide range of power densities (73 Wh kg〈sup〉−1〈/sup〉@250 W kg-1 and 16.8 Wh kg〈sup〉−1〈/sup〉@20 kW kg〈sup〉−1〈/sup〉). These favourable cell characteristics are attributed to the properties of the m-Nb〈sub〉2〈/sub〉O〈sub〉5〈/sub〉/C anode: the mesoporous structure that facilitates electron and ion transport, the presence of the niobium carbide interlayer between the Nb〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 nanoparticles and the surrounding graphitic carbon that additionally improves the electron conductivity, and the predominant capacitive charge storage mechanism.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0378775318311881-fx1.jpg" width="302" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 31 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Power Sources, Volume 408〈/p〉 〈p〉Author(s): Yuyan Zhang, Pei Tian, Kexun Li, Yi Liu, Zhaohui Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A highly active electrocatalyst is synthesized by employing melamine assisted metal-organic framework as the precursor. By pyrolyzing the hybrid at 350–800 °C, the precursor can be easily transferred into abundant iron and nitrogen co-doped carbon skeleton. The microbial fuel cell doped with the above treated sample at 600 °C achieves the maximum power density 2229 ± 10 mW m〈sup〉−2〈/sup〉, 257% and 36.6% higher than that of activated carbon and the control sample. The total resistance decreases by 53.8% from 18.16 Ω (activated carbon) to 8.39 Ω. The reaction process is testified to be four-electron transfer. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy prove the coexistence of divalent copper and C〈sub〉3〈/sub〉N〈sub〉4〈/sub〉 and the incorporation of nitrogen into the network formed active sites. Thus, the ideal results make the pyrolyzed hybrid at 600 °C a promising catalyst in microbial fuel cell.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Computers & Geosciences, Volume 122〈/p〉 〈p〉Author(s): Hassan Talebi, Ute Mueller, Raimon Tolosana-Delgado〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Ore deposits usually consist of ore materials with different discrete (e.g. rock and alteration types) and continuous (e.g. geochemical and mineral composition) features. Financial feasibility studies are highly dependent on the modelling of these features and their associated joint uncertainties. Few geostatistical techniques have been developed for the joint modelling of high-dimensional mixed data (continuous and categorical) or constrained data, such as compositional data. The compositional nature of the mineral and geochemical data induces several challenges for multivariate geostatistical techniques, because such data carry relative information and are known for spurious statistical and spatial correlation effects. This paper investigates the application of the direct sampling algorithm for joint modelling of compositional and categorical data. In some mining projects the amount of available data may be enormous in some parts of the deposit and if the density of measurements is sufficient, multivariate geospatial patterns can be derived from that data and be simulated (without model inference) at other undersampled areas of the deposit with similar characteristics. In this context, the direct sampling multiple-point simulation method can be implemented for this reconstruction process. The compositional nature of the data is addressed via implementing an isometric log-ratio transformation. The approach is illustrated through two case studies, one synthetic and one real. The accuracy of the results is checked against a set of validation data, revealing the potential of the proposed methodology for joint modelling of compositional and categorical information. The direct sampling technique can be considered as a smart move to assess the future risk and uncertainty of a resource by making use of all the information hidden within the early data.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 281〈/p〉 〈p〉Author(s): Yuan Chen, Xue-Rui Wei, Ru Sun, Yu-Jie Xu, Jian-Feng Ge〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Five cyanine dyes (〈strong〉1a-e〈/strong〉) with azonia unit have been prepared by the reaction of pyrido[1,2−a]pyrimidinium ions and suitable aldehydes. Before further research, their photo and thermal stabilities were determined in the first place. At least 88% absorption remained after 5 h irradiating illustrated all of these dyes had excellent photo stability. Meanwhile, the decomposition temperature of dyes was around 200 °C which demonstrated they had good thermal stability. Therefore, the good photo and thermal stability made them possible to be probes. Subsequently, the optical properties of probes toward nucleic acids had been measured. TheirOFF–ON fluorescent responses (〈strong〉1a〈/strong〉-〈strong〉d〈/strong〉) towards nucleic acids were investigated. In addition, confocal microscopy imaging of probe 〈strong〉1a〈/strong〉 in live HeLa cells indicated that probe 〈strong〉1a〈/strong〉 could image mitochondrial nucleic acid.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925400518319233-ga1.jpg" width="398" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 281〈/p〉 〈p〉Author(s): S. Pimenta, S. Cardoso, E.M.S. Castanheira, G. Minas〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper presents a CMOS optical microsystem with a 4 × 4 photodiodes array and their readout electronics, based on 16 light-to-frequency converters, and 16 high selective optical filters, for spectrophotometric measurement of diffuse reflectance and fluorescence signals, applied to the detection of gastrointestinal dysplasia. The photodiodes array is based on n+/p-epilayer junction silicon photodiodes. Their readout electronics outputs a digital signal, with a frequency proportional to the photodiode current, featuring a sensitivity of 26 Hz/nA at 550 nm, a spectral resolution of 9 MHz and a power consumption of 1 mW. The optical filters are based on 16 thin-film narrow-band 〈em〉Fabry-Perot〈/em〉 resonators, in which dielectric mirrors are used. They feature high transmittances and low full-width-half-maximum. Experimental measurements, using phantoms representative of the main absorbing, scattering and fluorescence properties of gastrointestinal tissues, proved the viability of the CMOS optical microsystem with the optical filters to extract those signals, when comparing the obtained results with commercial equipment. The implemented apparatus is ready to be used as a portable system on a surgery room to verify the total removing of gastrointestinal cancer tissue. Moreover, the developed approach is a step forward in the implementation of a gastrointestinal dysplasia detection miniaturized tool.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 281〈/p〉 〈p〉Author(s): Xueli Yang, Sufang Zhang, Qi yu, Liupeng Zhao, Peng Sun, Tianshuang Wang, Fangmeng Liu, Xu Yan, Yuan Gao, Xishuang Liang, Sumei Zhang, Geyu Lu〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this work, a novel branched heterostructural composite composed of nanorods ZnO backbone and SnO〈sub〉2〈/sub〉 branches was prepared via a facile one-step hydrothermal method. The morphology, structure and component of the SnO〈sub〉2〈/sub〉/ZnO composite was characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and elemental mapping analysis. The evolution process of the SnO〈sub〉2〈/sub〉/ZnO composite was observed by SEM that the SnO〈sub〉2〈/sub〉 branches gradually grow on ZnO backbones. The composite with novel heterostructure was applied as the sensing material for the fabrication of gas sensor, and their gas sensing properties were tested for response to various gases. Compared to pure ZnO gas sensors the branched SnO〈sub〉2〈/sub〉/ZnO gas sensor exhibited enhanced gas sensing properties toward ethanol, giving a response of 18.1–100 ppm.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 281〈/p〉 〈p〉Author(s): Qian Ma, Pin Li, Zhiqiang Gao, Sam Fong Yau Li〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A simple fluorescence biosensor for rapid and sensitive target microRNA (miRNA) quantification by branched rolling circle amplification (BRCA) is developed in this work. Target miRNA functions as primer to recognize and hybridize with a circle DNA template, initiating rolling circle amplification (RCA) by Phi29 DNA polymerase. The introduction of reverse primers complementary to the RCA products enables isothermal BRCA, in which a large amount of deoxynucleotide (dNTP) were consumed and same number of pyrophosphates (PPi) were produced. In this study, a simple and non-expensively synthesized terpyridine-based Zn(II) complex is utilized as fluorescent probe for selective detection of pyrophosphate (PPi) over dNTP. The PPi generated in this isothermal amplification process efficiently chelates to this terpyridine-Zn(II) complex, forming a highly fluorescent complex, terpyridine-Zn(II)-PPi, whose fluorescence intensity is closely related with the initial target miRNA concentration. The utilization of the isothermal BRCA amplification and direct monitoring of the DNA polymerization by-product, i.e. PPi, for non-label fluorescence detection of miRNA greatly simplify this sensor procedure. This sensor shows a linear response between the fluorescence intensity and the target miRNA concentration from 50 to 500 fM with a detection limit of 25 fM. This much-simplified sensor offers a sensitive and easy-to-use platform for miRNA quantification, and hence may significantly enhance the utilisation of miRNAs as biomarkers in drug discovery, clinical diagnosis and life science research.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S092540051831918X-ga1.jpg" width="245" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: Available online 14 August 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics〈/p〉 〈p〉Author(s): Mehdi Samiee, Mohsen Zayernouri, Mark M. Meerschaert〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We present the stability and error analysis of the unified Petrov–Galerkin spectral method, developed in [1], for linear fractional partial differential equations with two-sided derivatives and constant coefficients in any (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mn〉1〈/mn〉〈mo〉+〈/mo〉〈mi〉d〈/mi〉〈/math〉)-dimensional space-time hypercube, 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mi〉d〈/mi〉〈mo〉=〈/mo〉〈mn〉1〈/mn〉〈mo〉,〈/mo〉〈mn〉2〈/mn〉〈mo〉,〈/mo〉〈mn〉3〈/mn〉〈mo〉,〈/mo〉〈mo〉⋯〈/mo〉〈/math〉, subject to homogeneous Dirichlet initial/boundary conditions. Specifically, we prove the existence and uniqueness of the weak form and perform the corresponding stability and error analysis of the proposed method. Finally, we perform several numerical simulations to compare the theoretical and computational rates of convergence.〈/p〉〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 376〈/p〉 〈p〉Author(s): Giovanni Soligo, Alessio Roccon, Alfredo Soldati〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this work, we propose and test the validity of a modified Phase Field Method (PFM), which is specifically developed for large scale simulations of turbulent flows with large and deformable surfactant-laden droplets. The time evolution of the phase field, 〈em〉ϕ〈/em〉, and of the surfactant concentration field, 〈em〉ψ〈/em〉, are obtained from two Cahn–Hilliard-like equations together with a two-order-parameter Time-Dependent Ginzburg–Landau (TDGL) free energy functional. The modifications introduced circumvent existing limitations of current approaches based on PFM and improve the well-posedness of the model. The effect of surfactant on surface tension is modeled via an Equation Of State (EOS), further improving the flexibility of the approach. This method can efficiently handle topological changes, i.e. breakup and coalescence, and describe adsorption/desorption of surfactant. The capabilities of the proposed approach are tested in this paper against previous experimental results on the effects of surfactant on the deformation of a single droplet and on the interactions between two droplets. Finally, to appreciate the performances of the model on a large scale complex simulation, a qualitative analysis of the behavior of surfactant-laden droplets in a turbulent channel flow is presented and discussed.〈/p〉〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 376〈/p〉 〈p〉Author(s): Sergii V. Siryk〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We provide a careful Fourier analysis of the Guermond–Pasquetti mass lumping correction technique (Guermond and Pasquetti, 2013 [11]) applied to pure transport and convection–diffusion problems. In particular, it is found that increasing the number of corrections reduces the accuracy for problems with diffusion; however all the corrected schemes are more accurate than the consistent Galerkin formulation in this case. For the pure transport problems the situation is the opposite. We also investigate the differences between two numerical solutions – the consistent solution and the corrected ones, and show that increasing the number of corrections makes solutions of the corrected schemes closer to the consistent solution in all cases.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 377〈/p〉 〈p〉Author(s): Adam S. Jermyn〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Tensors are a natural way to express correlations among many physical variables, but storing tensors in a computer naively requires memory which scales exponentially in the rank of the tensor. This is not optimal, as the required memory is actually set not by the rank but by the mutual information amongst the variables in question. Representations such as the tensor tree perform near-optimally when the tree decomposition is chosen to reflect the correlation structure in question, but making such a choice is non-trivial and good heuristics remain highly context-specific. In this work I present two new algorithms for choosing efficient tree decompositions, independent of the physical context of the tensor. The first is a brute-force algorithm which produces optimal decompositions up to truncation error but is generally impractical for high-rank tensors, as the number of possible choices grows exponentially in rank. The second is a greedy algorithm, and while it is not optimal it performs extremely well in numerical experiments while having runtime which makes it practical even for tensors of very high rank.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 377〈/p〉 〈p〉Author(s): Lam H. Nguyen, Dominik Schillinger〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We describe a local iterative corrector scheme that significantly improves the accuracy of the multiscale finite element method (MsFEM). Our technique is based on the definition of a local corrector problem for each multiscale basis function that is driven by the residual of the previous multiscale solution. Each corrector problem results in a local corrector solution that improves the accuracy of the corresponding multiscale basis function at element interfaces. We cast the strategy of residual-driven correction in an iterative scheme that is straightforward to implement and, due to the locality of corrector problems, well-suited for parallel computing. We show that the iterative scheme converges to the best possible fine-mesh solution. Finally, we illustrate the effectiveness of our approach with multiscale benchmarks characterized by missing scale separation, including the microCT-based stress analysis of a vertebra with trabecular microstructure.〈/p〉〈/div〉

Description: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Radiation Measurements, Volume 119〈/p〉 〈p〉Author(s): Larisa Grigorjeva, Aleksejs Zolotarjovs, Donats Millers, Krisjanis Smits, Peter Krug, Johannes Stollenwerk, Alan Osman, Thomas Tenostendarp〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉For many years doped α-Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 has attracted interest as a dosimeter for personal, environment monitoring and food control. The alumina single crystal growth is a difficult process; however, materials in form of powders, ceramics and coating are possible to obtain. In this study for the first time Cr doped α-Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 powders were prepared by DC reactive magnetron sputtering followed by milling and oxidation. The morphology and phase analysis was performed; content of residual impurities was determined and thermostimulated glow curves were measured after different x-ray irradiation times (radiation doses). The prepared powder shows the dosimetry properties up to 20 kGy dose.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 377〈/p〉 〈p〉Author(s): Brody Bassett, Brian Kiedrowski〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The meshless local Petrov–Galerkin (MLPG) method is applied to the steady-state and 〈em〉k〈/em〉-eigenvalue neutron transport equations, which are discretized in energy using the multigroup approximation and in angle using the discrete ordinates approximation. To prevent oscillations in the neutron flux, the MLPG transport equation is stabilized by the streamline upwind Petrov–Galerkin (SUPG) method. Global neutron conservation is enforced by using moving least squares basis and weight functions and appropriate SUPG parameters. The cross sections in the transport equation are approximated in accordance with global particle balance and without constraint on their spatial dependence or the location of the basis and weight functions. The equations for the strong-form meshless collocation approach are derived for comparison to the MLPG equations. The method of manufactured solutions is used to verify the resulting MLPG method in one, two and three dimensions. Results for realistic problems, including two-dimensional pincells, a reflected ellipsoid and a three-dimensional problem with voids, are verified by comparison to Monte Carlo simulations.〈/p〉〈/div〉

Description: 〈p〉Publication date: Available online 28 May 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics〈/p〉 〈p〉Author(s): Frederic Gibou, David Hyde, Ron Fedkiw〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We present a review on numerical methods for simulating multiphase and free surface flows. We focus in particular on numerical methods that seek to preserve the discontinuous nature of the solutions across the interface between phases. We provide a discussion on the Ghost-Fluid and Voronoi Interface methods, on the treatment of surface tension forces that avoid stringent time step restrictions, on adaptive grid refinement techniques for improved efficiency and on parallel computing approaches. We present the results of some simulations obtained with these treatments in two and three spatial dimensions. We also provide a discussion of Machine Learning and Deep Learning techniques in the context of multiphase flows and propose several future potential research thrusts for using deep learning to enhance the study and simulation of multiphase flows.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈/p〉〈/div〉 〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0021999118303371-gr001.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉

Description: 〈p〉Publication date: Available online 26 October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics〈/p〉 〈p〉Author(s): Xiaodong Liu, Jiguang Sun〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Inverse scattering has been an active research area for the past thirty years. While very successful in many cases, progress has lagged when only 〈em〉limited-aperture〈/em〉 measurement is available. In this paper, we perform some elementary study to recover data that can not be measured directly. In particular, we aim at recovering the 〈em〉full-aperture〈/em〉 far field data from 〈em〉limited-aperture〈/em〉 measurement. Due to the reciprocity relation, the multi-static response matrix (MSR) has a symmetric structure. Using the Green's formula and single layer potential, we propose two schemes to recover 〈em〉full-aperture〈/em〉 MSR. The recovered data is tested by a recently proposed direct sampling method and the factorization method. Numerical results show that it is possible to, at least, partially recover the missing data and consequently improve the reconstruction of the scatterer.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 377〈/p〉 〈p〉Author(s): D. Reiser, J. Romazanov, Ch. Linsmeier〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The problem of constructing Monte-Carlo solutions of drift-diffusion systems corresponding to Fokker–Planck equations with sources and sinks is revisited. Firstly, a compact formalism is introduced for the specific problem of stationary solutions. This leads to identification of the dwell time as the key quantity to characterize the system and to obtain a proper normalization for statistical analysis of numerical results. Secondly, the question of appropriate track length estimators for drift-diffusion systems is discussed for a 1D model system. It is found that a simple track length estimator can be given only for pure drift motion without diffusion. The stochastic nature of the diffusive part cannot be appropriately described by the path length of simulation particles. Further analysis of the usual situation with inhomogeneous drift and diffusion coefficients leads to an error estimate based on particle trajectories. The result for limits in grid cell size and time step used for the construction of Monte-Carlo trajectories resembles the Courant-Friedrichs-Lewy and von Neumann conditions for explicit methods.〈/p〉〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 376〈/p〉 〈p〉Author(s): Dinshaw S. Balsara, Roger Käppeli〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The time-dependent equations of computational electrodynamics (CED) are evolved consistent with the divergence constraints on the electric displacement and magnetic induction vector fields. Respecting these constraints has proved to be very useful in the classic finite-difference time-domain (FDTD) schemes. As a result, there has been a recent effort to design finite volume time domain (FVTD) and discontinuous Galerkin time domain (DGTD) schemes that satisfy the same constraints and, nevertheless, draw on recent advances in higher order Godunov methods. This paper catalogues the first step in the design of globally constraint-preserving DGTD schemes. The algorithms presented here are based on a novel DG-like method that is applied to a Yee-type staggering of the electromagnetic field variables in the faces of the mesh. The other two novel building blocks of the method include constraint-preserving reconstruction of the electromagnetic fields and multidimensional Riemann solvers; both of which have been developed in recent years by the first author.〈/p〉 〈p〉The resulting DGTD scheme is linear, at least when limiters are not applied to the DG scheme. As a result, it is possible to carry out a von Neumann stability analysis of the entire suite of DGTD schemes for CED at orders of accuracy ranging from second to fourth. The analysis requires some simplifications in order to make it analytically tractable, however, it proves to be extremely instructive. A von Neumann stability analysis is a necessary precursor to the design of a full DGTD scheme for CED. It gives us the maximal CFL numbers that can be sustained by the DGTD schemes presented here at all orders. It also enables us to understand the wave propagation characteristics of the schemes in various directions on a Cartesian mesh. We find that constraint-preserving DGTD schemes permit CFL numbers that are competitive with conventional DG schemes. However, like conventional DG schemes, the CFL of DGTD schemes decreases with increasing order. To counteract that, we also present constraint-preserving PNPM schemes for CED. We find that the third and fourth order constraint-preserving DGTD and P1PM schemes have some extremely attractive properties when it comes to low-dispersion, low-dissipation propagation of electromagnetic waves in multidimensions. Numerical accuracy tests are also provided to support the von Neumann stability analysis. We expect these methods to play a role in those problems of engineering CED where exceptional precision must be achieved at any cost.〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 377〈/p〉 〈p〉Author(s): Yinghe Qi, Jiacai Lu, Ruben Scardovelli, Stéphane Zaleski, Grétar Tryggvason〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In spite of considerable progress, computing curvature in Volume of Fluid (VOF) methods continues to be a challenge. The goal is to develop a function or a subroutine that returns the curvature in computational cells containing an interface separating two immiscible fluids, given the volume fraction in the cell and the adjacent cells. Currently, the most accurate approach is to fit a curve (2D), or a surface (3D), matching the volume fractions and finding the curvature by differentiation. Here, a different approach is examined. A synthetic data set, relating curvature to volume fractions, is generated using well-defined shapes where the curvature and volume fractions are easily found and then machine learning is used to fit the data (training). The resulting function is used to find the curvature for shapes not used for the training and implemented into a code to track moving interfaces. The results suggest that using machine learning to generate the relationship is a viable approach that results in reasonably accurate predictions.〈/p〉〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 376〈/p〉 〈p〉Author(s): Mani Razi, Robert M. Kirby, Akil Narayan〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, we introduce a novel approach for the construction of multi-fidelity surrogate models with “discrete” fidelity levels. The notion of a discrete level of fidelity is in contrast to a mathematical model, for which the notion of refinement towards a high-fidelity model is relevant to sending a discretization parameter toward zero in a continuous way. Our notion of discrete fidelity levels encompasses cases for which there is no notion of convergence in terms of a fidelity parameter that can be sent to zero or infinity. The particular choice of how levels of fidelity are defined in this framework paves the way for using models that may have no apparent physical or mathematical relationship to the target high-fidelity model. However, our approach requires that models can produce results with a common set of parameters in the target model. Hence, fidelity level in this work is not directly representative of the degree of similarity of a low-fidelity model to a target high-fidelity model. In particular, we show that our approach is applicable to competitive ecological systems with different numbers of species, discrete-state Markov chains with a different number of states, polymer networks with a different number of connections, and nano-particle plasmonic arrays with a different number of scatterers. The results of this study demonstrate that our procedure boasts computational efficiency and accuracy for a wide variety of models and engineering systems.〈/p〉〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 376〈/p〉 〈p〉Author(s): Hasan Almanasreh〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this work we will treat the spurious eigenvalues obstacle that appears in the computation of the radial Dirac eigenvalue problem using numerical methods. The treatment of the spurious solution is based on applying Petrov–Galerkin finite element method. The significance of this work is the employment of just continuous basis functions, thus the need of a continuous function which has a continuous first derivative as a basis, as in [2], [3], is no longer required. The Petrov–Galerkin finite element method for the Dirac eigenvalue problem strongly depends on a stability parameter, 〈em〉τ〈/em〉, that controls the size of the diffusion terms added to the finite element formulation for the problem. The mesh-dependent parameter 〈em〉τ〈/em〉 is derived based on the given problem with the particular basis functions.〈/p〉〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 376〈/p〉 〈p〉Author(s): S.B. Adrian, F.P. Andriulli, T.F. Eibert〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We present a Calderón preconditioner for the electric field integral equation (EFIE), which does not require a barycentric refinement of the mesh and which yields a Hermitian, positive definite (HPD) system matrix allowing for the usage of the conjugate gradient (CG) solver. The resulting discrete equation system is immune to the low-frequency and the dense-discretization breakdown and, in contrast to existing Calderón preconditioners, no second discretization of the EFIE operator with Buffa–Christiansen (BC) functions is necessary. This preconditioner is obtained by leveraging on spectral equivalences between (scalar) integral operators, namely the single layer and the hypersingular operator known from electrostatics, on the one hand, and the Laplace–Beltrami operator on the other hand. Since our approach incorporates Helmholtz projectors, there is no search for global loops necessary and thus our method remains stable on multiply connected geometries. The numerical results demonstrate the effectiveness of this approach for both canonical and realistic (multi-scale) problems.〈/p〉〈/div〉

Description: 〈p〉Publication date: Available online 21 February 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics〈/p〉 〈p〉Author(s): Mehdi Samiee, Mohsen Zayernouri, Mark M. Meerschaert〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We develop a unified Petrov–Galerkin spectral method for a class of fractional partial differential equations with two-sided derivatives and constant coefficients of the form 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mmultiscripts〉〈mrow〉〈mi mathvariant="script"〉D〈/mi〉〈/mrow〉〈mrow〉〈mi〉t〈/mi〉〈/mrow〉〈none〉〈/none〉〈none〉〈/none〉〈mrow〉〈mn〉2〈/mn〉〈mi〉τ〈/mi〉〈/mrow〉〈mprescripts〉〈/mprescripts〉〈mrow〉〈mn〉0〈/mn〉〈/mrow〉〈none〉〈/none〉〈/mmultiscripts〉〈mi〉u〈/mi〉〈mo〉+〈/mo〉〈msubsup〉〈mrow〉〈mo〉∑〈/mo〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈mo〉=〈/mo〉〈mn〉1〈/mn〉〈/mrow〉〈mrow〉〈mi〉d〈/mi〉〈/mrow〉〈/msubsup〉〈mo stretchy="false"〉[〈/mo〉〈msub〉〈mrow〉〈msub〉〈mrow〉〈mi〉c〈/mi〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉l〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msub〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉a〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msub〉〈msubsup〉〈mrow〉〈mi mathvariant="script"〉D〈/mi〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉x〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈msub〉〈mrow〉〈mi〉μ〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msubsup〉〈mi〉u〈/mi〉〈mo〉+〈/mo〉〈msub〉〈mrow〉〈msub〉〈mrow〉〈mi〉c〈/mi〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉r〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msub〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉x〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msub〉〈msubsup〉〈mrow〉〈mi mathvariant="script"〉D〈/mi〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉b〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈msub〉〈mrow〉〈mi〉μ〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msubsup〉〈mi〉u〈/mi〉〈mo stretchy="false"〉]〈/mo〉〈mo〉+〈/mo〉〈mi〉γ〈/mi〉〈mspace width="0.2em"〉〈/mspace〉〈mspace width="0.2em"〉〈/mspace〉〈mi〉u〈/mi〉〈mo〉=〈/mo〉〈msubsup〉〈mrow〉〈mo〉∑〈/mo〉〈/mrow〉〈mrow〉〈mi〉j〈/mi〉〈mo〉=〈/mo〉〈mn〉1〈/mn〉〈/mrow〉〈mrow〉〈mi〉d〈/mi〉〈/mrow〉〈/msubsup〉〈mo stretchy="false"〉[〈/mo〉〈msub〉〈mrow〉〈msub〉〈mrow〉〈mi〉κ〈/mi〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉l〈/mi〉〈/mrow〉〈mrow〉〈mi〉j〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msub〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉a〈/mi〉〈/mrow〉〈mrow〉〈mi〉j〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msub〉〈msubsup〉〈mrow〉〈mi mathvariant="script"〉D〈/mi〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉x〈/mi〉〈/mrow〉〈mrow〉〈mi〉j〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈msub〉〈mrow〉〈mi〉ν〈/mi〉〈/mrow〉〈mrow〉〈mi〉j〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msubsup〉〈mi〉u〈/mi〉〈mo〉+〈/mo〉〈msub〉〈mrow〉〈msub〉〈mrow〉〈mi〉κ〈/mi〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉r〈/mi〉〈/mrow〉〈mrow〉〈mi〉j〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msub〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉x〈/mi〉〈/mrow〉〈mrow〉〈mi〉j〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msub〉〈msubsup〉〈mrow〉〈mi mathvariant="script"〉D〈/mi〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉b〈/mi〉〈/mrow〉〈mrow〉〈mi〉j〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈msub〉〈mrow〉〈mi〉ν〈/mi〉〈/mrow〉〈mrow〉〈mi〉j〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msubsup〉〈mi〉u〈/mi〉〈mo stretchy="false"〉]〈/mo〉〈mo〉+〈/mo〉〈mi〉f〈/mi〉〈/math〉, where 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mn〉2〈/mn〉〈mi〉τ〈/mi〉〈mo〉∈〈/mo〉〈mo stretchy="false"〉(〈/mo〉〈mn〉0〈/mn〉〈mo〉,〈/mo〉〈mn〉2〈/mn〉〈mo stretchy="false"〉)〈/mo〉〈/math〉, 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mn〉2〈/mn〉〈mi〉τ〈/mi〉〈mo〉≠〈/mo〉〈mn〉1〈/mn〉〈/math〉, 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.gif" overflow="scroll"〉〈mn〉2〈/mn〉〈msub〉〈mrow〉〈mi〉μ〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈/msub〉〈mo〉∈〈/mo〉〈mo stretchy="false"〉(〈/mo〉〈mn〉0〈/mn〉〈mo〉,〈/mo〉〈mn〉1〈/mn〉〈mo stretchy="false"〉)〈/mo〉〈/math〉 and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.gif" overflow="scroll"〉〈mn〉2〈/mn〉〈msub〉〈mrow〉〈mi〉ν〈/mi〉〈/mrow〉〈mrow〉〈mi〉j〈/mi〉〈/mrow〉〈/msub〉〈mo〉∈〈/mo〉〈mo stretchy="false"〉(〈/mo〉〈mn〉1〈/mn〉〈mo〉,〈/mo〉〈mn〉2〈/mn〉〈mo stretchy="false"〉)〈/mo〉〈/math〉, in a (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si6.gif" overflow="scroll"〉〈mn〉1〈/mn〉〈mo〉+〈/mo〉〈mi〉d〈/mi〉〈/math〉)-dimensional 〈em〉space–time〈/em〉 hypercube, 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si7.gif" overflow="scroll"〉〈mi〉d〈/mi〉〈mo〉=〈/mo〉〈mn〉1〈/mn〉〈mo〉,〈/mo〉〈mn〉2〈/mn〉〈mo〉,〈/mo〉〈mn〉3〈/mn〉〈mo〉,〈/mo〉〈mo〉⋯〈/mo〉〈/math〉, subject to homogeneous Dirichlet initial/boundary conditions. We employ the eigenfunctions of the fractional Sturm–Liouville eigen-problems of the first kind in [1], called 〈em〉Jacobi poly-fractonomial〈/em〉s, as temporal bases, and the eigen-functions of the boundary-value problem of the second kind as temporal test functions. Next, we construct our spatial basis/test functions using Legendre polynomials, yielding mass matrices being independent of the spatial fractional orders (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si8.gif" overflow="scroll"〉〈msub〉〈mrow〉〈mi〉μ〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈/msub〉〈mo〉,〈/mo〉〈mspace width="0.2em"〉〈/mspace〉〈msub〉〈mrow〉〈mi〉ν〈/mi〉〈/mrow〉〈mrow〉〈mi〉j〈/mi〉〈/mrow〉〈/msub〉〈mo〉,〈/mo〉〈mspace width="0.2em"〉〈/mspace〉〈mi〉i〈/mi〉〈mo〉,〈/mo〉〈mspace width="0.2em"〉〈/mspace〉〈mi〉j〈/mi〉〈mo〉=〈/mo〉〈mn〉1〈/mn〉〈mo〉,〈/mo〉〈mn〉2〈/mn〉〈mo〉,〈/mo〉〈mo〉⋯〈/mo〉〈mo〉,〈/mo〉〈mi〉d〈/mi〉〈/math〉). Furthermore, we formulate a novel unified fast linear solver for the resulting high-dimensional linear system based on the solution of generalized eigen-problem of spatial mass matrices with respect to the corresponding stiffness matrices, hence, making the complexity of the problem optimal, i.e., 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si9.gif" overflow="scroll"〉〈mi mathvariant="script"〉O〈/mi〉〈mo stretchy="false"〉(〈/mo〉〈msup〉〈mrow〉〈mi〉N〈/mi〉〈/mrow〉〈mrow〉〈mi〉d〈/mi〉〈mo〉+〈/mo〉〈mn〉2〈/mn〉〈/mrow〉〈/msup〉〈mo stretchy="false"〉)〈/mo〉〈/math〉. We carry out several numerical test cases to examine the CPU time and convergence rate of the method. The corresponding stability and error analysis of the Petrov–Galerkin method are carried out in [2].〈/p〉〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 376〈/p〉 〈p〉Author(s): Ruilian Du, Yubin Yan, Zongqi Liang〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A new high-order finite difference scheme to approximate the Caputo fractional derivative 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mfrac〉〈mrow〉〈mn〉1〈/mn〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈/mrow〉〈/mfrac〉〈mo stretchy="true" maxsize="2.4ex" minsize="2.4ex"〉(〈/mo〉〈mspace width="0.2em"〉〈/mspace〉〈mmultiscripts〉〈mrow〉〈mi〉D〈/mi〉〈/mrow〉〈mrow〉〈mi〉t〈/mi〉〈/mrow〉〈mrow〉〈mi〉α〈/mi〉〈/mrow〉〈mprescripts〉〈/mprescripts〉〈mrow〉〈mn〉0〈/mn〉〈/mrow〉〈mrow〉〈mi〉C〈/mi〉〈/mrow〉〈/mmultiscripts〉〈mi〉f〈/mi〉〈mo stretchy="false"〉(〈/mo〉〈msub〉〈mrow〉〈mi〉t〈/mi〉〈/mrow〉〈mrow〉〈mi〉k〈/mi〉〈/mrow〉〈/msub〉〈mo stretchy="false"〉)〈/mo〉〈mo〉+〈/mo〉〈mspace width="0.2em"〉〈/mspace〉〈mmultiscripts〉〈mrow〉〈mi〉D〈/mi〉〈/mrow〉〈mrow〉〈mi〉t〈/mi〉〈/mrow〉〈mrow〉〈mi〉α〈/mi〉〈/mrow〉〈mprescripts〉〈/mprescripts〉〈mrow〉〈mn〉0〈/mn〉〈/mrow〉〈mrow〉〈mi〉C〈/mi〉〈/mrow〉〈/mmultiscripts〉〈mi〉f〈/mi〉〈mo stretchy="false"〉(〈/mo〉〈msub〉〈mrow〉〈mi〉t〈/mi〉〈/mrow〉〈mrow〉〈mi〉k〈/mi〉〈mo〉−〈/mo〉〈mn〉1〈/mn〉〈/mrow〉〈/msub〉〈mo stretchy="false"〉)〈/mo〉〈mo stretchy="true" maxsize="2.4ex" minsize="2.4ex"〉)〈/mo〉〈/math〉, 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mi〉k〈/mi〉〈mo〉=〈/mo〉〈mn〉1〈/mn〉〈mo〉,〈/mo〉〈mn〉2〈/mn〉〈mo〉,〈/mo〉〈mo〉…〈/mo〉〈mo〉,〈/mo〉〈mi〉N〈/mi〉〈/math〉, with the convergence order 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si160.gif" overflow="scroll"〉〈mi〉O〈/mi〉〈mo stretchy="false"〉(〈/mo〉〈mi mathvariant="normal"〉Δ〈/mi〉〈msup〉〈mrow〉〈mi〉t〈/mi〉〈/mrow〉〈mrow〉〈mn〉4〈/mn〉〈mo〉−〈/mo〉〈mi〉α〈/mi〉〈/mrow〉〈/msup〉〈mo stretchy="false"〉)〈/mo〉〈/math〉, 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.gif" overflow="scroll"〉〈mi〉α〈/mi〉〈mo〉∈〈/mo〉〈mo stretchy="false"〉(〈/mo〉〈mn〉1〈/mn〉〈mo〉,〈/mo〉〈mn〉2〈/mn〉〈mo stretchy="false"〉)〈/mo〉〈/math〉 is obtained when 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si123.gif" overflow="scroll"〉〈msup〉〈mrow〉〈mi〉f〈/mi〉〈/mrow〉〈mrow〉〈mo〉‴〈/mo〉〈/mrow〉〈/msup〉〈mo stretchy="false"〉(〈/mo〉〈msub〉〈mrow〉〈mi〉t〈/mi〉〈/mrow〉〈mrow〉〈mn〉0〈/mn〉〈/mrow〉〈/msub〉〈mo stretchy="false"〉)〈/mo〉〈mo〉=〈/mo〉〈mn〉0〈/mn〉〈/math〉, where Δ〈em〉t〈/em〉 denotes the time step size. Based on this scheme we introduce a finite difference method for solving fractional diffusion wave equation with the convergence order 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si6.gif" overflow="scroll"〉〈mi〉O〈/mi〉〈mo stretchy="false"〉(〈/mo〉〈mi mathvariant="normal"〉Δ〈/mi〉〈msup〉〈mrow〉〈mi〉t〈/mi〉〈/mrow〉〈mrow〉〈mn〉4〈/mn〉〈mo〉−〈/mo〉〈mi〉α〈/mi〉〈/mrow〉〈/msup〉〈mo〉+〈/mo〉〈msup〉〈mrow〉〈mi〉h〈/mi〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈/mrow〉〈/msup〉〈mo stretchy="false"〉)〈/mo〉〈/math〉, where 〈em〉h〈/em〉 denotes the space step size. Numerical examples are given to show that the numerical results are consistent with the theoretical results.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 377〈/p〉 〈p〉Author(s): Jie Du, Yang Yang〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Local discontinuous Galerkin (LDG) methods are popular for convection-diffusion equations. In LDG methods, we introduce an auxiliary variable 〈em〉p〈/em〉 to represent the derivative of the primary variable 〈em〉u〈/em〉, and solve them on the same mesh. It is well known that the maximum-principle-preserving (MPP) LDG method is only available up to second-order accuracy. Recently, we introduced a new algorithm, and solve 〈em〉u〈/em〉 and 〈em〉p〈/em〉 on different meshes, and obtained stability and optimal error estimates. In this paper, we will continue this approach and construct MPP third-order LDG methods for convection-diffusion equations on overlapping meshes. The new algorithm is more flexible and does not increase any computational cost. Numerical evidence will be given to demonstrate the accuracy and good performance of the third-order MPP LDG method.〈/p〉〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 376〈/p〉 〈p〉Author(s): Yunchang Seol, Yu-Hau Tseng, Yongsam Kim, Ming-Chih Lai〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, a two-dimensional immersed boundary method is developed to simulate the dynamics of Newtonian vesicle in viscoelastic Oldroyd-B fluid under shear flow. The viscoelasticity effect of extra stress is well incorporated into the immersed boundary formulation using the indicator function. Our numerical methodology is first validated in comparison with theoretical results in purely Newtonian fluid, and then a series of numerical experiments is conducted to study the effects of different dimensionless parameters on the vesicle motions. Although the tank-treading (TT) motion of Newtonian vesicle in Oldroyd-B fluid under shear flow can be observed just like in Newtonian fluid, it is surprising to find that the stationary inclination angle can be negative without the transition to tumbling (TB) motion. Moreover, the inertia effect plays a significant role that is able to turn the vesicle back to positive inclination angle through TT-TB-TT transition as the Reynolds number increases. To the best of our knowledge, this is the first numerical work for the detailed investigations of Newtonian vesicle dynamics suspended in viscoelastic Oldroyd-B fluid. We believe that our numerical results can be used to motivate further studies in theory and experiments for such coupling vesicle problems.〈/p〉〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Computers & Geosciences, Volume 122〈/p〉 〈p〉Author(s): Seth Goodman, Ariel BenYishay, Zhonghui Lv, Daniel Runfola〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Interdisciplinary use of geospatial data requires the integration of data from a breadth of sources, and frequently involves the harmonization of different methods of sampling, measurement, and technical data types. These integrative efforts are often inhibited by fundamental geocomputational challenges, including a lack of memory efficient or parallel processing approaches to traditional methods such as zonal statistics. GeoQuery (〈a href="http://geoquery.org/" target="_blank"〉geoquery.org〈/a〉) is a dynamic web application which utilizes a High Performance Computing cluster and novel parallel geospatial data processing methods to overcome these challenges. Through an online interface, GeoQuery users can request geospatial data - which spans categories including geophysical, environmental and social measurements - to be aggregated to user-selected units of analysis (e.g., subnational administrative boundaries). Once a request has been processed, users are provided with permanent links to access their customized data and documentation. Datasets made available through GeoQuery are reviewed, prepared, and provisioned by geospatial data specialists, with processing routines tailored for each dataset. The code used and steps taken while preparing datasets and processing user requests are publicly available, ensuring transparency and replicability of all data and processes. By mediating the complexities of working with geospatial data, GeoQuery reduces the barriers to entry and the related costs of incorporating geospatial data into research across disciplines. This paper presents the technology and methods used by GeoQuery to process and manage geospatial data and user requests.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Computers & Geosciences, Volume 123〈/p〉 〈p〉Author(s): Pouyan Pirnia, François Duhaime, Yannic Ethier, Jean-Sébastien Dubé〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The thermal, mechanical and hydrodynamic behaviour of porous media in geoscience applications is usually modelled through the finite-element (FEM) or finite-difference methods. These continuum models tend to perform poorly when modelling phenomena that are essentially dependent on behaviour at the particle scale or phenomena that are not accurately described by partial differential equations (PDE), such as internal erosion and filtration. The discrete nature of granular materials can be modelled through the discrete-element method (DEM). However, in some instances, DEM models would benefit from an interface with continuum models to solve coupled PDEs or to model phenomena that occur at a different scale. This paper introduces ICY, an interface between COMSOL Multiphysics, a commercial finite-element engine, and YADE, an open-source discrete-element code. The interface is centred on a JAVA class. It was verified using the simple example of a sphere falling in water according to Stokes’ law. For this example, the drag force was calculated in COMSOL and body forces (gravity, buoyancy and drag) on the sphere were summed in YADE. The paper also presents an application example for the interface based on the modelling of internal erosion tests.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0098300417313213-fx1.jpg" width="334" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 31 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Power Sources, Volume 408〈/p〉 〈p〉Author(s): Guiping Ren, Yuan Sun, Anhuai Lu, Yan Li, Hongrui Ding〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Anode electron transfer efficiency is one of the main bottlenecks in determining the performance of microbial fuel cells (MFCs). Here, we report for the first time a novel design of a silicon solar cell equipped MFC with one-dimensional TiO〈sub〉2〈/sub〉/Fe〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 photoanode and conventional bioanode to overcome the constraints of using traditional anodes. The novel MFC has the maximum power density of 638.3 mW m〈sup〉−2〈/sup〉, which is nearly 7.6 times higher than that of general MFCs (84.2 mW m〈sup〉−2〈/sup〉). In addition, the novel MFC achieves 90.9% removal of hexavalent chromium Cr(VI) with concentration of 50 ppm within 13.5 h, and this rate is significantly high at 3.67 g m〈sup〉−3〈/sup〉 h〈sup〉−1〈/sup〉. Efficient microbial oxidation and photoelectrocatalysis are realized after constructing the SSC with double-anode MFC, thereafter leading to enhanced electron transfer to the external circuit. In addition, the electrons are driven by the built-in electric field in silicon solar cell, in which system barriers are resolved at the same time. Power output and Cr(VI) reduction efficiency are both remarkably enhanced. Such a novel MFC strategy provides new directions for designing new systems that can increase the efficiency of MFCs by utilizing solar energy economically, which further suggest great potential in environmental remediation.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0378775318311893-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 31 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Power Sources, Volume 408〈/p〉 〈p〉Author(s): Xiumei Guo, Nana Bai, Yan Tian, Ligang Gai〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Flexible all-solid-state supercapacitors with specific energy higher than 1 mW h cm〈sup〉−3〈/sup〉 after long-term cycles remain a hot research topic in energy storage systems. In this paper, free-standing reduced graphene oxide/polypyrrole films are produced at the ice/ethanol interface following by hydrogen iodide reduction. The reduced graphene oxide/polypyrrole films are featured with high specific surface area, three-dimensional porosity, and tunable thickness and electronic conductivity. The typical flexible all-solid-state supercapacitor based on reduced graphene oxide/polypyrrole films exhibits a high volumetric specific capacitance of 17.3 F cm〈sup〉−3〈/sup〉 and a high specific energy of 2.40 mW h cm〈sup〉−3〈/sup〉 with corresponding specific power of 136.1 mW cm〈sup〉−3〈/sup〉 at a current density of 3 mA cm〈sup〉−2〈/sup〉 (ca. 10 A g〈sup〉−1〈/sup〉). After 10,000 cycles at 3 mA cm〈sup〉−2〈/sup〉, the capacitance retention of the typical flexible supercapacitor retains 73.2%. The enhanced electrochemical properties of the flexible supercapacitors are attributed to the high specific surface area, three-dimensional porosity, and the synergistic effect between reduced graphene oxide and polypyrrole with respect to the composite films.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0378775318311911-fx1.jpg" width="500" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 378〈/p〉 〈p〉Author(s): Oscar P. Bruno, Martín Maas〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper introduces a fast algorithm, applicable throughout the electromagnetic spectrum, for the numerical solution of problems of scattering by periodic surfaces in two-dimensional space. The proposed algorithm remains highly accurate and efficient for challenging configurations including randomly rough surfaces, deep corrugations, large periods, near grazing incidences, and, importantly, Wood-anomaly resonant frequencies. The proposed approach is based on use of certain “shifted equivalent sources” which enable FFT acceleration of a Wood-anomaly-capable quasi-periodic Green function introduced recently (Bruno and Delourme (2014) [4]). The Green-function strategy additionally incorporates an exponentially convergent shifted version of the classical 〈em〉spectral〈/em〉 series for the Green function. While the computing-cost asymptotics depend on the asymptotic configuration assumed, the computing costs rise at most linearly with the size of the problem for a number of important rough-surface cases we consider. In practice, single-core runs in computing times ranging from a fraction of a second to a few seconds suffice for the proposed algorithm to produce highly-accurate solutions in some of the most challenging contexts arising in applications.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 379〈/p〉 〈p〉Author(s): Denis S. Grebenkov, Sergey D. Traytak〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The generalized method of separation of variables (GMSV) is applied to solve boundary value problems for the Laplace operator in three-dimensional domains with disconnected spherical boundaries (e.g., an arbitrary configuration of non-overlapping partially reactive spherical sinks or obstacles). We consider both exterior and interior problems and all most common boundary conditions: Dirichlet, Neumann, Robin, and conjugate one. Using the translational addition theorems for solid harmonics to switch between the local spherical coordinates, we obtain a semi-analytical expression of the Green function as a linear combination of partial solutions whose coefficients are fixed by boundary conditions. Although the numerical computation of the coefficients involves series truncation and solution of a system of linear algebraic equations, the use of the solid harmonics as basis functions naturally adapted to the intrinsic symmetries of the problem makes the GMSV particularly efficient, especially for exterior problems. The obtained Green function is the key ingredient to solve boundary value problems and to determine various characteristics of stationary diffusion such as reaction rate, escape probability, harmonic measure, residence time, and mean first passage time, to name but a few. The relevant aspects of the numerical implementation and potential applications in chemical physics, heat transfer, electrostatics, and hydrodynamics are discussed.〈/p〉〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 AEU - International Journal of Electronics and Communications, Volume 98〈/p〉 〈p〉Author(s): Ahmed H. Fouad, Ahmed G. Radwan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper theorizes the possibilities of generalizing a memristor based ternary adder circuit, to a memristor based multi-valued logic adder. The proposition tries to achieve the theoretical advantages of processing different numbering systems, increasing the density, and decreasing the processing time, by utilizing the memristor properties and dynamics. This is done using a memristor cell based circuit structure. The memristor is quantized to more levels in order to accommodate more values of logic being processed. Quinary numbering system is used to demonstrate the generalization, then a process of generalization is shown. Circuit modifications can be made to process different numbering systems.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 AEU - International Journal of Electronics and Communications, Volume 98〈/p〉 〈p〉Author(s): Ziqiang Xu, Jiahao Liu, Si Huang, Yuanxun Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A gain-enhanced low profile substrate integrated waveguide (SIW) cavity-backed slot antenna is presented in this paper. By etching three parallel transverse slots on the center and both edges of the rectangular SIW cavity as the radiating elements, higher resonance mode of TE〈sub〉410〈/sub〉 can be excited to achieve gain enhancement. Radiating mechanism and parameter effects of the three radiating slots have been investigated. Using the proposed multi-slot structures, an antenna is designed, fabricated and characterized, respectively. The fabricated antenna demonstrated a gain of 9.2 dBi, a front-to-back ratio of 17 dB, and a maximum cross-polarized radiation level of −19.7 dB at 10 GHz. Furthermore, the proposed antenna constructed using a single-layer printed circuit board (PCB) yields a better radiation performance and configuration advantage over that of the conventional planar antenna by taking advantage of the TE〈sub〉410〈/sub〉 cavity resonance.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 377〈/p〉 〈p〉Author(s): Samar Chehade, Audrey Kamta Djakou, Michel Darmon, Gilles Lebeau〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Non Destructive Examination (NDE) of industrial structures requires the modeling of specimen geometry echoes generated by the surfaces (entry, backwall …) of inspected blocks. For that purpose, the study of plane wave diffraction by a wedge is of great interest. The work presented here is preliminary research to model the case of an elastic wave diffracted by a wedge in the future, for which there exist various modeling approaches but the numerical aspects have only been developed for wedge angles lower than 〈em〉π〈/em〉. The spectral functions method has previously been introduced to solve the 2D diffraction problem of an immersed elastic wedge for angles lower than 〈em〉π〈/em〉. As a first step, the spectral functions method has been developed here for the diffraction on an acoustic wave by a stress-free wedge, in 2D and for any wedge angle, before studying the elastic wave diffraction from a wedge. In this method, the solution to the diffraction problem is expressed in terms of two unknown functions called the spectral functions. These functions are computed semi-analytically, meaning that they are the sum of two terms. One of them is determined exactly and the other is approached numerically, using a collocation method. A successful numerical validation of the method for all wedge angles is proposed, by comparison with the GTD (Geometrical Theory of Diffraction) solution derived from the exact Sommerfeld integral.〈/p〉〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Ultramicroscopy, Volume 196〈/p〉 〈p〉Author(s): A. del Moral, J.C. González-Rosillo, A. Gómez, T. Puig, X. Obradors〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Enabling temperature dependent experiments in Atomic Force Microscopy is of great interest to study materials and surface properties at the nanoscale. By studying Curie temperature of multiferroic materials, temperature dependent phase transitions on crystalline structures or resistive switching phenomena are only a few examples of applications. We present an equipment capable of cooling samples using a thermoelectric cooling stage down to −61.4〈code〉 〈/code〉°C in a 15 × 15 mm〈sup〉2〈/sup〉 sample plate. The equipment uses a four-unit thermoelectric stack to achieve maximum temperature range, with low electrical and mechanical noise. The equipment is installed into a Keysight 5500LS Atomic Force Microscopy maintaining its compatibility with all Electrical and Mechanical modes of operation. We study the contribution of the liquid cooling pump vibration into the cantilever static deflection noise and the temperature dependence of the cantilever deflection. A La〈sub〉0.7〈/sub〉Sr〈sub〉0.3〈/sub〉MnO〈sub〉3-y〈/sub〉 thin film sample is used to demonstrate the performance of the equipment and its usability by analyzing the resistive switching phenomena associated with this oxide perovskite.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0304399118301049-fx1.jpg" width="301" alt="Image, graphical abstract" title="Image, graphical abstract"〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 31 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Power Sources, Volume 408〈/p〉 〈p〉Author(s): Muhammad Rauf, Jing-Wen Wang, Peixin Zhang, Waheed Iqbal, Junle Qu, Yongliang Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The exploration of cheap and stable electrocatalysts with high activity towards oxygen reduction reaction in the acidic and alkaline medium is a vital activity for large-scale applications of fuel cells. In recent years, one-dimensional nanofibrous electrode materials with high surface area and specific porosities have been drawing great attention in energy conversion devices such as fuel cells and metal-air batteries. Nanofibers with a one-dimensional nanostructure can be produced by electrospinning, which has been considered as a particularly low-cost and versatile method. In this review, we summarize the properties of electrospun nanofibers and the recent progress in designing of non-precious nanostructured electrocatalysts for oxygen reduction reaction in fuel cells. More importantly, we also highlight the interesting nanostructures, new synthetic approaches, and the electrocatalytic performance including active sites and stability of electrospun-based electrocatalysts. In addition, we describe the research challenges and future developmental perspectives of electrospun materials in energy technology.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 31 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Power Sources, Volume 408〈/p〉 〈p〉Author(s): Yijie Xu, Dustin Bauer, Mechthild Lübke, Thomas E. Ashton, Yun Zong, Jawwad A. Darr〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Sodium titanate nanopowder (nominal formula Na〈sub〉1.5〈/sub〉H〈sub〉0.5〈/sub〉Ti〈sub〉3〈/sub〉O〈sub〉7〈/sub〉) was directly synthesized using a continuous hydrothermal flow synthesis process using a relatively low base concentration (4 M NaOH) in process. The as-made titanate nanomaterials were characterised using powder X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, Brunauer–Emmett–Teller analysis and transmission electron microscopy, and evaluated as potential electrode materials for Li-ion and Na-ion batteries. Cyclic voltammetry studies on half-cells revealed that the sodium titanate nanomaterial stored charge primarily through a combination of pseudocapacitive and diffusion-limited processes in both systems. Electrochemical cycling tests at a high specific current of 1000 mA g〈sup〉−1〈/sup〉, revealed that the Li-ion and Na-ion cells retained relatively high specific capacities after 400 cycles of 131 and 87 mAh g〈sup〉−1〈/sup〉, respectively. This study demonstrates the potential of CHFS-made sodium titanate nanopower as an anode material for both Li- and Na-ion cell chemistries.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0378775318311406-fx1.jpg" width="428" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 31 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Power Sources, Volume 408〈/p〉 〈p〉Author(s): Yannick Garsany, Robert W. Atkinson, Benjamin D. Gould, Karen E. Swider-Lyons〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We present a method for preparing laboratory-scale proton exchange membrane fuel cells (PEMFCs) that have high power and high current densities despite their low platinum loadings. This performance is achieved with membrane electrode assemblies featuring a commercial PtCo catalyst supported on high surface area carbon and a short-side chain, low equivalent weight ionomer binder in the cathode catalyst layer; these are then compressed with dry-laid paper type gas diffusion media. The PEMFCs with a Pt loading of 0.08 mg〈sub〉Pt〈/sub〉 cm〈sup〉−2〈/sup〉 produced comparatively high power to similarly loaded state-of-the-art PEMFCs. This methodology can be used for further research on high performance catalyst layers.〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0378775318311819-fx1.jpg" width="341" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 281〈/p〉 〈p〉Author(s): Ganesan Muthusankar, Chellakannu Rajkumar, Shen-Ming Chen, Rajendran Karkuzhali, Gopalakrishnan Gopu, Arumugam Sangili, Nallathambi Sengottuvelan, Raman Sankar〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We report a simple preparation of novel nanocomposite for the sensitive determination of riboflavin (RF) in real samples. Nitrogen-doped carbon quantum dots/SnO〈sub〉2〈/sub〉 (N-CQD/SnO〈sub〉2〈/sub〉) nanocomposite was prepared using sonochemical approach and applied as a voltammetric sensor for the sensitive determination of RF for the first time. The crystallographic phase, functional groups, surface analysis, and elemental distribution were examined using XRD, FT-IR, HR-TEM and EDS spectroscopic techniques respectively. This N-CQD/SnO〈sub〉2〈/sub〉 nanocomposite-modified electrode shows a fast and sensitive electrochemical response to RF sensing with a good sensitivity (2.496 μA μM〈sup〉−1〈/sup〉 cm〈sup〉-2〈/sup〉), wide linear range (0.05–306 μM), low detection limit (8 nM) and excellent anti-interference ability. Furthermore, the developed sensor was investigated in commercial riboflavin tablets and milk powder and obtained results are quite satisfactory.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925400518319221-ga1.jpg" width="329" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 AEU - International Journal of Electronics and Communications, Volume 98〈/p〉 〈p〉Author(s): Meenakshi Awasthi, Madhav J. Nigam, Vijay Kumar〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, energy efficiency for cooperative spectrum sensing in cognitive radio network is investigated and optimized. The novel mathematical formulation of energy efficiency maximization problem by considering number of secondary users, sensing time, and transmission time as design parameters with protection of primary user from SU transmission has been done. In order to solve the formulated problem, first the optimal expression for number of secondary users is formulated, then, an iterative sub optimal algorithm is proposed to obtain optimal sensing and transmission time. Numerical results and illustrative plots demonstrate the correctness and optimality of the proposed algorithm and show the improved performance over the state of arts.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 281〈/p〉 〈p〉Author(s): Aritz Ozcariz, Dafne A. Piña-Azamar, Carlos R. Zamarreño, René Dominguez, Francisco J. Arregui〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This work presents the experimental demonstration of lossy mode resonance generation by means of aluminum doped zinc oxide thin-films. The use of such material may allow to optimize the performance of LMR-based sensors, obtaining good sensitivity at lower costs than other overlays, such as those including indium. The refractometric response of the fabricated devices is explored in different spectral regions. One refractometer working in the near infrared region was fabricated, obtaining a sensitivity of 2280 nm/RIU. A second refractometer working in the visible light spectrum was also fabricated. This second device allows to observe rough refractive index variations with the naked eye as a change of the color of the light propagating through the fiber, simplifying the setup needed for its use.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 281〈/p〉 〈p〉Author(s): Ling Yang, Hengjia Ni, Chenglong Li, Xiya Zhang, Kai Wen, Yuebin Ke, Huijuan Yang, Weimin Shi, Suxia Zhang, Jianzhong Shen, Zhanhui Wang〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Antibody-based sensors are the most widely used for screening antibiotic residues in food samples. However, these sensors always suffer from cross-reacting antibiotics which are able to bind the employed antibodies in a manner similar to the target, thus resulting in inaccurate quantification. In this study, we developed a highly specific and sensitive chemiluminescence aptasensor for sulfamethazine (SMZ) by employing the supernormal selectivity of a new selected aptamer. Four SMZ-specific aptamers (〈em〉K〈sub〉d〈/sub〉〈/em〉 ranging from 79 to 274 nM) were selected 〈em〉in vitro〈/em〉 by MB-SELEX with an intentional counter selection to avoid the recognition other sulfonamides, which is impossible to achieve in the corresponding procedure of antibody production. The binding mechanism of aptamers for SMZ was further analyzed and clarified with molecular simulation and docking. Under optimum conditions, the chemiluminescence aptasensor based on the highest affinity aptamer named SA07 provided a limit of detection of 0.92 ng/mL with negligible cross-reactivity with the 27 tested sulfonamides. The developed aptasensor was applied to milk samples, and achieved good accuracy and precision. These results demonstrated that the integration of an aptamer and chemiluminescence in a sensor platform is a promising method for the sensitive, specific, rapid and accurate detection of antibiotic residues of interest in food samples.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925400518319208-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 281〈/p〉 〈p〉Author(s): Łukasz Janicki, Jan Misiewicz, Marcin Siekacz, Henryk Turski, Joanna Moneta, Sandeep Gorantla, Czesław Skierbiszewski, Robert Kudrawiec〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Modulation spectroscopy was applied to study the N-polar GaN surface barrier height dependency on ambient gas type in GaN/GaN:Si and GaN/AlGaN/GaN heterostructures. The built-in electric field in the undoped layer of the GaN/GaN:Si structure was determined by an analysis of a Franz-Keldysh oscillation present in spectra and used to calculate the surface barrier in presence of various gases. A barrier of 0.35 eV in air and N〈sub〉2〈/sub〉+O〈sub〉2〈/sub〉 (82:18 ratio) mixture ambient was determined while in vacuum, N〈sub〉2〈/sub〉, Ar and SF〈sub〉6〈/sub〉 it amounted to 0.20 eV. No effect of humidity on the surface barrier was observed. The GaN channel built-in electric field of the GaN/AlGaN/GaN heterostructure was also determined from optical studies. It was then used as a parameter in a self-consistent solution of Schrödinger-Poisson equations in order to calculate the surface barrier for this structure in air and vacuum ambient, and the results matched those obtained for the UN + structure. This indicated that the electronic state of surface behaves in the same way irrespectively of the structure design. Calculated carrier concentration of the GaN/AlGaN/GaN heterostructure shows a significant dependency on the surface barrier indicating a possible application in gas sensing. The response time was also studied showing a fast (〈10 s) barrier increase in presence of oxygen and a much slower decrease when oxygen was removed.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 281〈/p〉 〈p〉Author(s): Jiaoyan Qiu, Yujie Zhang, Chen Dong, Yunlong Huang, Li Sun, Huimin Ruan, Hongsen Wang, Xing Li, Aiguo Wu〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Potassium ions (K〈sup〉+〈/sup〉) play an important role in biological organisms. Therefore, efficient and sensitive detection of K〈sup〉+〈/sup〉 in biological complex samples is crucial for disease diagnosis. Herein, we propose a novel sensor based on crown ether (4-aminobenzo-18-crown-6, ABC) modified Au NPs for rapid colorimetric detection of K〈sup〉+〈/sup〉. Recognition of K〈sup〉+〈/sup〉 and constitution of the aggregates are posed by a sandwich complex of 2:1 between ABC moiety and K〈sup〉+〈/sup〉. Based on the aggregation mechanism, this colorimetric detection method has superior selectivity and anti-interference ability for potassium ions (K〈sup〉+〈/sup〉) compared with other ions. There is a good linear relationship (R〈sup〉2〈/sup〉 = 0.9979) in the range of 0–200 μM K〈sup〉+〈/sup〉 concentration and this detection method can be successfully applied in the detection of K〈sup〉+〈/sup〉 in real urine samples.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925400518319166-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 281〈/p〉 〈p〉Author(s): Hui-Min Wang, Chen-Chen Wang, Ai-Jun Wang, Lu Zhang, Xiliang Luo, Pei-Xin Yuan, Jiu-Ju Feng〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Electrochemiluminescence (ECL) has attracted significant interest because of its superior properties and potential applications in bioanalysis, and therefore many luminescent nanomaterials have been developed. Herein, well-defined Pd nanocones (Pd NCs) were facilely obtained by a one-pot hydrothermal method with poly-〈span〉l〈/span〉-lysine (PLL) as a green protecting ligand, which were mainly characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Then, the as-obtained Pd NCs were first explored as an anodic ECL emitter, where tripropylamine (TPA) worked as the coreactant to boost the ECL emission. The possible ECL mechanism of Pd NCs/TPA system was extensively explored by ECL and electrochemical techniques. Briefly, the ECL emission underwent the oxidation-reduction route, in which both Pd NCs and TPA were initially oxidized, and then the oxidized TPA lost an proton to form reducing agent (TPA〈sup〉·〈/sup〉) strongly reacted with the oxidized Pd NCs generating Pd NCs* for the emission. Furthermore, using dopamine (DA) as an ECL quencher, an ultrasensitive sensor was constructed for DA detection. The fabricated ECL sensor shows high sensitivity and selectivity, good stability, and wide linear range with the low detection limit of 0.46 pM. It offers a new avenue to exploit ECL illuminant and enriches the ECL emission theory.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925400518319300-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 281〈/p〉 〈p〉Author(s): Matteo Tonezzer, Jae-Hun Kim, Jae-Hyoung Lee, Salvatore Iannotta, Sang Sub Kim〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The detection of volatile compounds is important for a broad variety of applications. Metal oxide gas nanosensors are tiny, inexpensive devices that can be integrated into any application, but they lack selectivity. On the other hand, electronic noses consisting of sensors arrays comprised of different active materials are complex as well as expensive to fabricate and use. This paper presents a novel approach using Pt-decorated tin oxide (SnO〈sub〉2〈/sub〉) nanowires at different working temperatures to produce a virtual sensor array exploiting the thermal fingerprints of the different gases. With only one nanostructured material (Pt-SnO〈sub〉2〈/sub〉) and 5 temperature values, the system could qualitatively and quantitatively discriminate all the gasestested (all reducing gases). The sensor could detect selectively which gas is present (with an accuracy of 100%) at what concentration (with an overall average error of approximately 14%, down to 3.7% for benzene). The results showed that single metal oxide resistive nanosensors could achieve a good level of real selectivity exploiting the thermal fingerprints from a temperature gradient.〈/p〉〈/div〉

Description: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Computers & Geosciences, Volume 123〈/p〉 〈p〉Author(s): Timothy J. Naegeli, Jason Laura〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper we present an extension to the Large Crater Clustering (LCC) tool set which places a cone of uncertainty around the trajectories of secondary impact craters to determine potential locations of source craters. The LCC tool set was a first step in the spatial quantification of primary and secondary cratering processes, which allows planetary geologists to accurately estimate the geologic age of a celestial surface. This work builds on the LCC tool set by accounting for the ambiguity of flight path trajectories through a Python script that leverages ArcGIS's ArcPy library. We chronicle the mechanics of the script, which creates geodetically correct cones then counts them within equally sized cells of a vector grid. We describe the process that was used to derive the shape of the cone and provide parameters for the sizes of the cones and the grid. We demonstrate that the cone of uncertainty has the ability to compensate for error in secondary crater trajectories by introducing deviation in the trajectory bearing and comparing the predicted primary crater location. We use two study areas on Mars as well as the entire lunar surface to illustrate the usefulness of the extension as an aid to human interpretation of back-projections.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 377〈/p〉 〈p〉Author(s): Hong Fang, Yikun Hu, Caihui Yu, Ming Tie, Jie Liu, Chunye Gong〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The mesh deformation method based on radial basis functions (RBF) has many advantages and is widely used. RBF based mesh deformation method mainly has two steps: data reduction and displacement interpolation. The data reduction step includes solving interpolation weight coefficients and searching for the node with the maximum interpolation error. The data reduction schemes based on greedy algorithm is used to select an optimum reduced set of surface mesh nodes. In this paper, a parallel mesh deformation method based on parallel data reduction and displacement interpolation is proposed. The proposed recurrence Choleskey decomposition method (RCDM) can decrease the computational cost of solving interpolation weight coefficients from 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mi〉O〈/mi〉〈mrow〉〈mo stretchy="true"〉(〈/mo〉〈msubsup〉〈mrow〉〈mi〉N〈/mi〉〈/mrow〉〈mrow〉〈mi〉c〈/mi〉〈/mrow〉〈mrow〉〈mn〉4〈/mn〉〈/mrow〉〈/msubsup〉〈mo stretchy="true"〉)〈/mo〉〈/mrow〉〈/math〉 to 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mi〉O〈/mi〉〈mrow〉〈mo stretchy="true"〉(〈/mo〉〈msubsup〉〈mrow〉〈mi〉N〈/mi〉〈/mrow〉〈mrow〉〈mi〉c〈/mi〉〈/mrow〉〈mrow〉〈mn〉3〈/mn〉〈/mrow〉〈/msubsup〉〈mo stretchy="true"〉)〈/mo〉〈/mrow〉〈/math〉, where 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈msub〉〈mrow〉〈mi〉N〈/mi〉〈/mrow〉〈mrow〉〈mi〉c〈/mi〉〈/mrow〉〈/msub〉〈/math〉 denotes the number of support nodes. The technology of parallel computing is used to accelerate the searching for the node with the maximum interpolation error and displacement interpolation. The combination of parallel data reduction and parallel interpolation can greatly improve the efficiency of mesh deformation. Two typical deformation problems of the ONERA M6 and DLR-F6 wing-body-Nacelle-Pylon configuration are taken as the test cases to validate the proposed approach and can get up to 19.57 times performance improvement with the proposed approach. Finally, the aeroelastic response of HIRENASD wing-body configuration is used to verify the efficiency and robustness of the proposed method.〈/p〉〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 376〈/p〉 〈p〉Author(s): Daniil Bochkov, Frederic Gibou〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We present two finite volume schemes to solve a class of Poisson-type equations subject to Robin boundary conditions in irregular domains with 〈em〉piecewise smooth〈/em〉 boundaries. The first scheme results in a symmetric linear system and produces second-order accurate numerical solutions with first-order accurate gradients in the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈msup〉〈mrow〉〈mi〉L〈/mi〉〈/mrow〉〈mrow〉〈mo〉∞〈/mo〉〈/mrow〉〈/msup〉〈/math〉-norm (for solutions with two bounded derivatives). The second scheme is nonsymmetric but produces second-order accurate numerical solutions as well as second-order accurate gradients in the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈msup〉〈mrow〉〈mi〉L〈/mi〉〈/mrow〉〈mrow〉〈mo〉∞〈/mo〉〈/mrow〉〈/msup〉〈/math〉-norm (for solutions with three bounded derivatives). Numerical examples are given in two and three spatial dimensions.〈/p〉〈/div〉

Description: 〈p〉Publication date: Available online 19 October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics〈/p〉 〈p〉Author(s): Mandeep Deka, Shuvayan Brahmachary, Ramakrishnan Thirumalaisamy, Amaresh Dalal, Ganesh Natarajan〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We describe a new and simple strategy based on the Gauss divergence theorem for obtaining centroidal gradients on unstructured meshes. Unlike the standard Green–Gauss (SGG) reconstruction which requires face values of quantities whose gradients are sought, the proposed approach reconstructs the gradients using the normal derivative(s) at the faces. The new strategy, referred to as the Modified Green–Gauss (MGG) reconstruction results in consistent gradients which are at least first-order accurate on arbitrary polygonal meshes. We show that the MGG reconstruction is linearity preserving independent of the mesh topology and retains the consistent behaviour of gradients even on meshes with large curvature and high aspect ratios. The gradient accuracy in MGG reconstruction depends on the accuracy of discretisation of the normal derivatives at faces and this necessitates an iterative approach for gradient computation on non-orthogonal meshes. Numerical studies on different mesh topologies demonstrate that MGG reconstruction gives accurate and consistent gradients on non-orthogonal meshes, with the number of iterations proportional to the extent of non-orthogonality. The MGG reconstruction is found to be consistent even on meshes with large aspect ratio and curvature with the errors being lesser than those from linear least-squares reconstruction. A non-iterative strategy in conjunction with MGG reconstruction is proposed for gradient computations in finite volume simulations that achieves the accuracy and robustness of MGG reconstruction at a cost equivalent to that of SGG reconstruction. The efficacy of this strategy for fluid flow problems is demonstrated through numerical investigations in both incompressible and compressible regimes. The MGG reconstruction may, therefore, be viewed as a novel and promising blend of least-squares and Green–Gauss based approaches which can be implemented with little effort in open-source finite-volume solvers and legacy codes.〈/p〉〈/div〉

Description: 〈p〉Publication date: Available online 18 July 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics〈/p〉 〈p〉Author(s): Marvin Bohm, Andrew R. Winters, Gregor J. Gassner, Dominik Derigs, Florian Hindenlang, Joachim Saur〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The first paper of this series presents a discretely entropy stable discontinuous Galerkin (DG) method for the resistive magnetohydrodynamics (MHD) equations on three-dimensional curvilinear unstructured hexahedral meshes. Compared to other fluid dynamics systems such as the shallow water equations or the compressible Navier–Stokes equations, the resistive MHD equations need special considerations because of the divergence-free constraint on the magnetic field. For instance, it is well known that for the symmetrization of the ideal MHD system as well as the continuous entropy analysis a non-conservative term proportional to the divergence of the magnetic field, typically referred to as the Powell term, must be included. As a consequence, the mimicry of the continuous entropy analysis in the discrete sense demands a suitable DG approximation of the non-conservative terms in addition to the ideal MHD terms.〈/p〉 〈p〉This paper focuses on the 〈em〉resistive〈/em〉 MHD equations: Our first contribution is a proof that the resistive terms are symmetric and positive-definite when formulated in entropy space as gradients of the entropy variables, which enables us to show that the entropy inequality holds for the resistive MHD equations. This continuous analysis is the key for our DG discretization and guides the path for the construction of an approximation that discretely mimics the entropy inequality, typically termed 〈em〉entropy stability〈/em〉. Our second contribution is a detailed derivation and analysis of the discretization on three-dimensional curvilinear meshes. The discrete analysis relies on the summation-by-parts property, which is satisfied by the DG spectral element method (DGSEM) with Legendre–Gauss–Lobatto (LGL) nodes. Although the divergence-free constraint is included in the non-conservative terms, the resulting method has no particular treatment of the magnetic field divergence errors, which might pollute the solution quality. Our final contribution is the extension of the standard resistive MHD equations and our DG approximation with a divergence cleaning mechanism that is based on a generalized Lagrange multiplier (GLM).〈/p〉 〈p〉As a conclusion to the first part of this series, we provide detailed numerical validations of our DGSEM method that underline our theoretical derivations. In addition, we show a numerical example where the entropy stable DGSEM demonstrates increased robustness compared to the standard DGSEM.〈/p〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 376〈/p〉 〈p〉Author(s): James F. Kelly, Harish Sankaranarayanan, Mark M. Meerschaert〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper develops appropriate boundary conditions for the two-sided fractional diffusion equation, where the usual second derivative in space is replaced by a weighted average of positive (left) and negative (right) fractional derivatives. Mass preserving, reflecting boundary conditions for two-sided fractional diffusion involve a balance of left and right fractional derivatives at the boundary. Stable, consistent explicit and implicit Euler methods are detailed, and steady state solutions are derived. Steady state solutions for two-sided fractional diffusion equations using both Riemann–Liouville and Caputo flux are computed. For Riemann–Liouville flux and reflecting boundary conditions, the steady-state solution is singular at one or both of the end-points. For Caputo flux and reflecting boundary conditions, the steady-state solution is a constant function. Numerical experiments illustrate the convergence of these numerical methods. Finally, the influence of the reflecting boundary on the steady-state behavior subject to both the Riemann–Liouville and Caputo fluxes is discussed.〈/p〉〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 376〈/p〉 〈p〉Author(s): N. Saini, C. Kleinstreuer〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉All natural and a growing number of manufactured solid particles are non-spherical. Interesting fluid–particle dynamics applications include the transport of granular material, piling of seeds or grains, inhalation of toxic aerosols, use of nanofluids for enhanced cooling or improved lubrication, and optimal drug-targeting of tumors. A popular approach for computer simulations of such scenarios is the multi-sphere (MS) method, where any non-spherical particle is represented by an assemblage of spheres. However, the MS approach may lead to multiple sphere-to-sphere contact points during collision, and subsequently to erroneous particle transport and deposition. In cases where non-spherical particles can be approximated as ellipsoids with arbitrary aspect ratios, a new theory for particle transport, collision and wall interaction is presented which is more accurate computationally and more efficient than the MS method. In general, with the new ellipsoidal particle interaction (EPI) model, contact points and planes of ellipsoids, rather than spheres, are obtained based on a geometric potential algorithm. Then, interaction forces and torques of the colliding particles are determined via inscribed ‘pseudo-spheres’, employing the soft-particle approach. The off-center forces and moments are then transferred to the mass center of the ellipsoids to solve the appropriate translatory and angular equations of motion. Considering ellipses to illustrate the workings and predictive power of the new collision model, turbulent fluid–particle flow with the EPI model in a 2-D channel is simulated and compared with 3-D numerical benchmark results which relied on the MS method. The 2-D concentrations of micron particles with different aspect ratios matched closely with the 3-D cases. However, interesting differences occurred when comparing the particle-velocity profiles for which the 2-D EPI model generated somewhat larger particle velocities due to out-of-plane collisions, slightly higher particle–wall interactions, and two-way coupling effects.〈/p〉〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 376〈/p〉 〈p〉Author(s): Kyongmin Yeo, Igor Melnyk〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We present a deep learning model, DE-LSTM, for the simulation of a stochastic process with an underlying nonlinear dynamics. The deep learning model aims to approximate the probability density function of a stochastic process via numerical discretization and the underlying nonlinear dynamics is modeled by the Long Short-Term Memory (LSTM) network. It is shown that, when the numerical discretization is used, the function estimation problem can be solved by a multi-label classification problem. A penalized maximum log likelihood method is proposed to impose a smoothness condition in the prediction of the probability distribution. We show that the time evolution of the probability distribution can be computed by a high-dimensional integration of the transition probability of the LSTM internal states. A Monte Carlo algorithm to approximate the high-dimensional integration is outlined. The behavior of DE-LSTM is thoroughly investigated by using the Ornstein–Uhlenbeck process and noisy observations of nonlinear dynamical systems; Mackey–Glass time series and forced Van der Pol oscillator. It is shown that DE-LSTM makes a good prediction of the probability distribution without assuming any distributional properties of the stochastic process. For a multiple-step forecast of the Mackey–Glass time series, the prediction uncertainty, denoted by the 95% confidence interval, first grows, then dynamically adjusts following the evolution of the system, while in the simulation of the forced Van der Pol oscillator, the prediction uncertainty does not grow in time even for a 3,000-step forecast.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 379〈/p〉 〈p〉Author(s): Christopher Eldred, Thomas Dubos, Evaggelos Kritsikis〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The rotating shallow water (RSW) equations are the usual testbed for the development of numerical methods for three-dimensional atmospheric and oceanic models. However, an arguably more useful set of equations are the thermal shallow water equations (TSW), which introduce an additional thermodynamic scalar but retain the single layer, two-dimensional structure of the RSW. As a stepping stone towards a three-dimensional atmospheric dynamical core, this work presents a quasi-Hamiltonian discretization of the thermal shallow water equations using compatible Galerkin methods, building on previous work done for the shallow water equations. Structure-preserving or quasi-Hamiltonian discretizations methods, that discretize the Hamiltonian structure of the equations of motion rather than the equations of motion themselves, have proven to be a powerful tool for the development of models with discrete conservation properties. By combining these ideas with an energy-conserving Poisson time integrator and a careful choice of Galerkin spaces, a large set of desirable properties can be achieved. In particular, for the first time total mass, buoyancy and energy are conserved to machine precision in the fully discrete model.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 377〈/p〉 〈p〉Author(s): Fang Qing, Xijun Yu, Zupeng Jia〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The MoF (Moment of Fluid) method is an accurate approach for interface reconstruction in numerical simulation of multi-material fluid flow. So far, most works focus on improving its accuracy and efficiency, such as developing analytic reconstruction method and deducing the iteration schemes based on high order derivatives of the objective function. In this paper, we mainly concern on improving its robustness, especially for severely deformed polygonal meshes, in which case the objective function has multiple minimum value points. By using an efficient method for solving multiple roots of the nonlinear equation in large scope, a new algorithm is developed to enhance robustness of the MoF method. The main idea of this algorithm is as follows. The first derivative of the objective function is continuous, so the minimum value points of the objective function must be the zero points of the first derivative. Instead of finding the zero points of the first derivative directly, we turn to calculating the minimum value points (also zero points) of the square of the first derivative, which is a convex function on a neighborhood of each zero point. Applying the properties of convex function, the neighbor of each extreme minimum point of it can be obtained efficiently. Then each zero point of the square of the first derivative can be obtained using the iterative formula in its neighbor. Finally, by comparing the values of the objective function at these zero points of the first derivative, the global minimum value point of the objective function can be found and is the desired solution. The new algorithm only uses the first derivative of the objective function. It doesn't need an initial guess for the solution, which has to be carefully chosen in previous works. Numerical results are presented to demonstrate the accuracy and robustness of this new algorithm. The results show that it is applicable to severely deformed polygonal mesh, even with concave cells.〈/p〉〈/div〉

Description: 〈p〉Publication date: Available online 22 March 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics〈/p〉 〈p〉Author(s): Savio Poovathingal, Eric C. Stern, Ioannis Nompelis, Thomas E. Schwartzentruber, Graham V. Candler〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Micro scale simulations are performed of flow through porous (pyrolyzing) thermal protection system (TPS) materials using the direct simulation Monte Carlo (DSMC) method. DSMC results for permeability are validated with computational fluid dynamics (CFD) calculations and theory, for simple porous geometries under continuum flow conditions. An artificial fiber-microstructure generation code FiberGen is used to create triangulated surface geometry representative of FiberForm® (FiberForm) material. DSMC results for permeability of FiberForm are validated for a range of pressures (transitional flow conditions) and agree with experimental measurements. Numerical uncertainty is determined to be within 2% if sufficiently large portions of the microstructure are included in the computation. However, small variations in fiber size and angle bias can combine to give 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mo〉+〈/mo〉〈mn〉30〈/mn〉〈mtext〉%〈/mtext〉〈/math〉 uncertainty when comparing with experimental permeability data. X-ray microtomography scans of FiberForm are used to create microstructure geometry for incorporation within DSMC simulations of coupled oxygen diffusion and gas-surface chemistry in the presence of a blowing pyrolysis gas. In-depth penetration of atomic oxygen is limited to 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mn〉0.2〈/mn〉〈mtext〉–〈/mtext〉〈mn〉0.4〈/mn〉〈/math〉 mm for the range of Knudsen number and pyrolysis gas conditions studied.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 279〈/p〉 〈p〉Author(s): Wallans T.P. dos Santos, Hatem M.A. Amin, Richard G. Compton〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A multilayer Carbon Black (CB) modified Glassy Carbon Electrode (GCE) is proposed, developed and optimized for Adsorptive Stripping Voltammetry (AdSV). The thick (up to 1000 monolayers) multilayer CB modification offers a significant enhancement in sensitivity for AdSV but not diffusive voltammetry. The detection of the stimulant selegiline, which is a prohibited drug for athletes in sports competitions, is used as model for application of the proposed electrochemical method in saliva samples. The analytical performance of the CB-GCE for detection of seligeline in authentic saliva samples revealed a limit of detection of 0.12 μmol L〈sup〉−1〈/sup〉 which is sufficiently low to allow a possible application of this fast method in the doping control of this drug.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 279〈/p〉 〈p〉Author(s): G.N. Gerasimov, V.F. Gromov, M.I. Ikim, O.J. Ilegbusi, L.I. Trakhtenberg〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The structure and conductometric sensing properties to hydrogen of In〈sub〉2〈/sub〉O〈sub〉3〈/sub〉-CeO〈sub〉2〈/sub〉 and SnO〈sub〉2〈/sub〉-CeO〈sub〉2〈/sub〉 nanocomposites were investigated. Addition of small amounts of CeO〈sub〉2〈/sub〉 to In〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 nanocrystals is shown to result in a significant increase in the sensor response. On the other hand, addition of CeO〈sub〉2〈/sub〉 to SnO〈sub〉2〈/sub〉 matrix produces a sharp decrease in the sensor response, and at 3 wt% CeO〈sub〉2〈/sub〉 concentration, the response of the SnO〈sub〉2〈/sub〉-CeO〈sub〉2〈/sub〉 composite to hydrogen is practically absent. The difference between the sensor response of In〈sub〉2〈/sub〉O〈sub〉3〈/sub〉-CeO〈sub〉2〈/sub〉 and SnO〈sub〉2〈/sub〉-CeO〈sub〉2〈/sub〉 composites is shown to be mainly due to the different interactions between the CeO〈sub〉2〈/sub〉 additives and the In〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 or SnO〈sub〉2〈/sub〉 matrix crystals in the composites. The probable mechanisms of the CeO〈sub〉2〈/sub〉 effect on sensor response of the composites are discussed.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 279〈/p〉 〈p〉Author(s): Xin Ting Zheng, Walter L. Goh, Peter Yeow, David P. Lane, Farid J. Ghadessy, Yen Nee Tan〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Improved chemical library screens for drug modulators of a target protein are vital to advance precision medicine. Here, we describe an ultrasensitive dynamic light scattering (DLS) based biosensor using gold nanoparticles as plasmon-enhanced sensing probes to rapidly screen anticancer compounds. The nanobiosensor which consists of DNA-conjugated dumbbell-shaped gold nanoprobes can detect protein activities in drug-treated cells. We have validated the utility of our nanosensor to screen for compounds known to reactivate mutated tumor suppressor protein p53 for DNA binding in complex cellular context, which leads to significant increases in the hydrodynamic size of the nanoprobes through DLS measurement. This unique nanoplasmonic biosensor not only significantly enhances the DLS signal for specific biomolecular binding, but also effectively suppresses the background noise from irrelevant entities, which greatly improves sensitivity and reduces consumption of both sample and probe. In addition, a competition assay designed to evaluate the relative DNA binding affinities of p53 using the same sensing probes allows a concomitant assessment of responsive p53 pathways downstream or cell fate. Most critically, this nanosensor enables direct interrogation of endogenous protein activities following drug treatment in live cells, allowing simultaneous on-target validation during phenotypic screens. This DLS-based nanobiosensor is broadly applicable to other DNA binding molecules and/or proteins, and holds great potential for high-throughput screening campaigns utilizing both conventional and fragment-based compound libraries in drug discovery.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925400518317234-ga1.jpg" width="485" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Solid-State Electronics, Volume 150〈/p〉 〈p〉Author(s): Ji-Hee Yang, Da-Jeong Yun, Seong-Min Kim, Do-Kyun Kim, Myung-Han Yoon, Gi-Heon Kim, Sung-Min Yoon〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉To realize highly-functional flexible nonvolatile memories, the organic/inorganic hybrid structures were introduced as suitable approaches to exploit both advantages of flexibility of organic materials and the electrical performance of inorganic materials. Electrically conductive poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) thin film was transferred on plastic poly(ethylene naphthalate) (PEN) substrates and then patterned by conventional photo-lithography process through the optimization of the surface properties in terms of the enhanced interaction between the PEDOT:PSS and the PEN substrate. The gate-stack structure of the charge-trap memory thin-film transistors was designed to be Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 blocking/ZnO charge-trap/Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 tunneling/In-Ga-Zn-O active/PEDOT:PSS source-drain layers. The fabricated device showed the nonvolatile memory operations including charge-trap-assisted memory window. However, the long-tapered rough patterns of PEDOT:PSS and damaged back-channel on organic barrier were demonstrated to be feasible origins for some drawbacks including the high contact resistance of the fabricated prototype device. Appropriate ideas for further improvements memory device characteristics was also suggested.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 30 August 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation〈/p〉 〈p〉Author(s): Péter Kutas〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We propose an algorithm for finding zero divisors in quaternion algebras over quadratic number fields, or equivalently, solving homogeneous quadratic equations in three variables over 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mi mathvariant="double-struck"〉Q〈/mi〉〈mo stretchy="false"〉(〈/mo〉〈msqrt〉〈mrow〉〈mi〉d〈/mi〉〈/mrow〉〈/msqrt〉〈mo stretchy="false"〉)〈/mo〉〈/math〉 where 〈em〉d〈/em〉 is a square-free integer. The algorithm is randomized and runs in polynomial time if one is allowed to call oracles for factoring integers.〈/p〉〈/div〉

Description: 〈p〉Publication date: May–June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 92〈/p〉 〈p〉Author(s): Maria Alberich-Carramiñana, Josep Àlvarez Montaner, Guillem Blanco〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We provide an algorithm that allows to describe the minimal log-resolution of an ideal in a smooth complex surface from the minimal log-resolution of its generators. In order to make this algorithm effective we present a modified version of the Newton–Puiseux algorithm that computes the Puiseux decomposition of a product of not necessarily reduced or irreducible elements together with their algebraic multiplicity in each factor.〈/p〉〈/div〉

Description: 〈p〉Publication date: March–April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 91〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: Available online 15 June 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation〈/p〉 〈p〉Author(s): Wayne Eberly〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Initial findings in a study of the automatic selection of algorithms for matrix computations are reported. These include the presentation and analysis of algorithms for the detection and certification of matrix properties allowing the reliable use of a variety of special-purpose algorithms for sparse and structured matrix computations.〈/p〉〈/div〉

Description: 〈p〉Publication date: March–April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 91〈/p〉 〈p〉Author(s): Alexandru Dimca, Gabriel Sticlaru〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We describe an algorithm computing the monodromy and the pole order filtration on the Milnor fiber cohomology of any reduced projective plane curve 〈em〉C〈/em〉. The relation to the zero set of Bernstein–Sato polynomial of the defining homogeneous polynomial for 〈em〉C〈/em〉 is also discussed. When 〈em〉C〈/em〉 has some non-weighted homogeneous singularities, then we have to assume that a conjecture holds in order to get some of our results. In all the examples computed so far this conjecture holds.〈/p〉〈/div〉

Description: 〈p〉Publication date: March–April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 91〈/p〉 〈p〉Author(s): Simon Hampe, Michael Joswig, Benjamin Schröter〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We describe a new method for computing tropical linear spaces and more general duals of polyhedral subdivisions. This is based on an algorithm of Ganter for finite closure systems.〈/p〉〈/div〉

Description: 〈p〉Publication date: May–June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 92〈/p〉 〈p〉Author(s): Jinwang Liu, Dongmei Li, Weijun Liu〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉We consider the following two problems: Let 〈em〉f〈/em〉 and 〈em〉g〈/em〉 be two polynomials over a field 〈em〉K〈/em〉.〈/p〉 〈dl〉 〈dt〉P1.〈/dt〉 〈dd〉〈p〉When is 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mo stretchy="false"〉{〈/mo〉〈mi〉f〈/mi〉〈mo〉+〈/mo〉〈mi〉s〈/mi〉〈mo〉,〈/mo〉〈mi〉g〈/mi〉〈mo〉+〈/mo〉〈mi〉t〈/mi〉〈mo stretchy="false"〉}〈/mo〉〈/math〉 a Gröbner basis for all 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mi〉s〈/mi〉〈mo〉,〈/mo〉〈mi〉t〈/mi〉〈mo〉∈〈/mo〉〈mi〉K〈/mi〉〈/math〉?〈/p〉〈/dd〉 〈dt〉P2.〈/dt〉 〈dd〉〈p〉When is 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mo stretchy="false"〉{〈/mo〉〈msup〉〈mrow〉〈mi〉f〈/mi〉〈/mrow〉〈mrow〉〈mi〉λ〈/mi〉〈/mrow〉〈/msup〉〈mo〉,〈/mo〉〈msup〉〈mrow〉〈mi〉g〈/mi〉〈/mrow〉〈mrow〉〈mi〉σ〈/mi〉〈/mrow〉〈/msup〉〈mo stretchy="false"〉}〈/mo〉〈/math〉 a Gröbner basis for all 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.gif" overflow="scroll"〉〈mi〉λ〈/mi〉〈mo〉,〈/mo〉〈mi〉σ〈/mi〉〈mo〉∈〈/mo〉〈mi mathvariant="double-struck"〉N〈/mi〉〈/math〉?〈/p〉〈/dd〉 〈/dl〉 We provide a simpler proof of Hoon's criterion for P1 and a new criterion for P2. The two criteria are applied to the theory of Gröbner bases under composition.〈/div〉

Description: 〈p〉Publication date: May–June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 92〈/p〉 〈p〉Author(s): Rok Požar〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Let 〈em〉U〈/em〉 be a finitely presented group with a normal subgroup 〈em〉F〈/em〉, and let 〈em〉H〈/em〉 be a finite group. We present an effective method for constructing all 〈em〉U〈/em〉-stable epimorphisms from 〈em〉F〈/em〉 onto 〈em〉H〈/em〉; that is, epimorphisms whose kernels are normal in 〈em〉U〈/em〉. Our strategy is an adaptation of the algorithm for determining all epimorphisms from a finitely presented group onto a finite group. As an application, we construct all admissible regular graph covering projections with a given deck transformation group.〈/p〉〈/div〉

Description: 〈p〉Publication date: January–February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 90〈/p〉 〈p〉Author(s): Pascal Schreck, Pascal Mathis〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In most cases in geometry, applying analytic or algebraic tools on coordinates helps to solve some difficult problems. For instance, proving that a geometrical construction problem is solvable using ruler and compass is often impossible within a synthetic geometry framework. But in an analytic geometry framework, it is a direct application of Galois theory after performing triangularizations. However, these algebraic tools lead to a large amount of computation. Their implementation in modern Computer Algebra Systems (CAS) are still too time consuming to provide an answer in a reasonable time. In addition, they require a lot of memory space which can grow exponentially with the size of the problem. Fortunately, some geometrical properties can be used to setup the algebraic systems so that they can be more efficiently computed. These properties turn polynomials into new ones so as to reduce both the degrees and the number of monomials. The present paper promotes this approach by considering two corpora of geometric construction problems, namely Wernick's and Connely's lists. These lists contain about 280 problems. The purpose is to determine their status i.e. whether they are constructible or not with ruler and compass. Some of these problems had unknown status that will be settled in this paper. More generally, the status of all problems of these corpora are fully automatically given by an approach combining geometry and algebra.〈/p〉〈/div〉

Description: 〈p〉Publication date: May–June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 92〈/p〉 〈p〉Author(s): Grégoire Lecerf〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In their 1996 article, Lickteig and Roy introduced a fast “divide and conquer” variant of the subresultant algorithm which avoids coefficient growth in defective cases. The present article concerns the complexity analysis of their algorithm over effective rings endowed with the partially defined division routine. We achieve essentially the same kind of complexity bound as over effective fields. As a consequence we obtain new convenient complexity bounds for gcds, especially when coefficients are in abstract polynomial rings where evaluation/interpolation schemes are not supposed to be available.〈/p〉〈/div〉

Description: 〈p〉Publication date: March–April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 91〈/p〉 〈p〉Author(s): Xavier Allamigeon, Stéphane Gaubert, Mateusz Skomra〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Helton and Nie conjectured that every convex semialgebraic set over the field of real numbers can be written as the projection of a spectrahedron. Recently, Scheiderer disproved this conjecture. We show, however, that the following result, which may be thought of as a tropical analogue of this conjecture, is true: over a real closed nonarchimedean field of Puiseux series, the convex semialgebraic sets and the projections of spectrahedra have precisely the same images by the nonarchimedean valuation. The proof relies on game theory methods.〈/p〉〈/div〉

Description: 〈p〉Publication date: March–April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 91〈/p〉 〈p〉Author(s): Michela Ceria〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The aim of this paper is to count 0-dimensional stable and strongly stable ideals in 2 and 3 variables, given their (constant) affine Hilbert polynomial 〈em〉p〈/em〉, by means of a bijection between these ideals and some integer partitions of 〈em〉p〈/em〉, which can be counted via determinantal formulas. This will be achieved by the 〈em〉Bar Code〈/em〉, a bidimensional diagram that allows to represent any finite set of terms 〈em〉M〈/em〉 and desume many properties of the corresponding monomial ideal 〈em〉I〈/em〉, if 〈em〉M〈/em〉 is an order ideal.〈/p〉〈/div〉

Description: 〈p〉Publication date: May–June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 92〈/p〉 〈p〉Author(s): Scott McCallum, Adam Parusiński, Laurentiu Paunescu〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In 1994 Lazard proposed an improved method for cylindrical algebraic decomposition (CAD). The method comprised a simplified projection operation together with a generalized cell lifting (that is, stack construction) technique. For the proof of the method's validity Lazard introduced a new notion of valuation of a multivariate polynomial at a point. However a gap in one of the key supporting results for his proof was subsequently noticed. In the present paper we provide a complete validity proof of Lazard's method. Our proof is based on the classical parametrized version of Puiseux's theorem and basic properties of Lazard's valuation. This result is significant because Lazard's method can be applied to any finite family of polynomials, without any assumption on the system of coordinates. It therefore has wider applicability and may be more efficient than other projection and lifting schemes for CAD.〈/p〉〈/div〉

Description: 〈p〉Publication date: March–April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 91〈/p〉 〈p〉Author(s): Thomas Bauer, Sandra Di Rocco, David Schmitz, Tomasz Szemberg, Justyna Szpond〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In the present note we show that the union of 〈em〉r〈/em〉 general lines and one fat line in 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈msup〉〈mrow〉〈mi mathvariant="double-struck"〉P〈/mi〉〈/mrow〉〈mrow〉〈mn〉3〈/mn〉〈/mrow〉〈/msup〉〈/math〉 imposes independent conditions on forms of sufficiently high degree 〈em〉d〈/em〉, where the bound is independent of the number of lines. This extends former results of Hartshorne and Hirschowitz on unions of general lines, and of Aladpoosh on unions of general lines and one double line.〈/p〉〈/div〉

Description: 〈p〉Publication date: January–February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 90〈/p〉 〈p〉Author(s): Manfred Schmidt-Schauß, David Sabel, Yunus D.K. Kutz〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The problem of nominal unification where variables are allowed for atoms, and computing a complete set of unifiers is considered. The complexity is shown to be NP-complete, while for special cases there are polynomial time algorithms. The main result is a novel algorithm to compute a complete set of unifiers which performs lazy guessing of equality or disequality of atom-variables, runs in NP time, and the collecting variant has more chances to keep the complete set of unifiers small. Applications of this algorithm are in reasoning about program transformations in higher order functional languages. We also present a variant of the unification algorithm that delays guessing and checking solvability, and produces a single most general unifier.〈/p〉〈/div〉

Description: 〈p〉Publication date: Available online 19 June 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation〈/p〉 〈p〉Author(s): Angel Blasco, Sonia Pérez-Díaz〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Let 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mi mathvariant="script"〉P〈/mi〉〈mo stretchy="false"〉(〈/mo〉〈mi〉t〈/mi〉〈mo stretchy="false"〉)〈/mo〉〈mo〉∈〈/mo〉〈msup〉〈mrow〉〈mi mathvariant="double-struck"〉P〈/mi〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈/mrow〉〈/msup〉〈mo stretchy="false"〉(〈/mo〉〈mi mathvariant="double-struck"〉K〈/mi〉〈mo stretchy="false"〉(〈/mo〉〈mi〉t〈/mi〉〈mo stretchy="false"〉)〈/mo〉〈mo stretchy="false"〉)〈/mo〉〈/math〉 be a rational projective parametrization of a plane curve 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si138.gif" overflow="scroll"〉〈mi mathvariant="script"〉C〈/mi〉〈/math〉. In this paper, we introduce the notion of 〈em〉limit point〈/em〉, 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈msub〉〈mrow〉〈mi〉P〈/mi〉〈/mrow〉〈mrow〉〈mi〉L〈/mi〉〈/mrow〉〈/msub〉〈/math〉, of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si147.gif" overflow="scroll"〉〈mi mathvariant="script"〉P〈/mi〉〈mo stretchy="false"〉(〈/mo〉〈mi〉t〈/mi〉〈mo stretchy="false"〉)〈/mo〉〈/math〉, and some remarkable properties of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈msub〉〈mrow〉〈mi〉P〈/mi〉〈/mrow〉〈mrow〉〈mi〉L〈/mi〉〈/mrow〉〈/msub〉〈/math〉 are obtained. In particular, if the singularities of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si138.gif" overflow="scroll"〉〈mi mathvariant="script"〉C〈/mi〉〈/math〉 are 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si174.gif" overflow="scroll"〉〈msub〉〈mrow〉〈mi〉P〈/mi〉〈/mrow〉〈mrow〉〈mn〉1〈/mn〉〈/mrow〉〈/msub〉〈mo〉,〈/mo〉〈mo〉…〈/mo〉〈mo〉,〈/mo〉〈msub〉〈mrow〉〈mi〉P〈/mi〉〈/mrow〉〈mrow〉〈mi〉n〈/mi〉〈/mrow〉〈/msub〉〈/math〉 and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈msub〉〈mrow〉〈mi〉P〈/mi〉〈/mrow〉〈mrow〉〈mi〉L〈/mi〉〈/mrow〉〈/msub〉〈/math〉 (all of them ordinary) and their respective multiplicities are 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si175.gif" overflow="scroll"〉〈msub〉〈mrow〉〈mi〉m〈/mi〉〈/mrow〉〈mrow〉〈mn〉1〈/mn〉〈/mrow〉〈/msub〉〈mo〉,〈/mo〉〈mo〉…〈/mo〉〈mo〉,〈/mo〉〈msub〉〈mrow〉〈mi〉m〈/mi〉〈/mrow〉〈mrow〉〈mi〉n〈/mi〉〈/mrow〉〈/msub〉〈/math〉 and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si182.gif" overflow="scroll"〉〈msub〉〈mrow〉〈mi〉m〈/mi〉〈/mrow〉〈mrow〉〈mi〉L〈/mi〉〈/mrow〉〈/msub〉〈/math〉, we show that 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si8.gif" overflow="scroll"〉〈mi〉T〈/mi〉〈mo stretchy="false"〉(〈/mo〉〈mi〉s〈/mi〉〈mo stretchy="false"〉)〈/mo〉〈mo〉=〈/mo〉〈msubsup〉〈mrow〉〈mo〉∏〈/mo〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈mo〉=〈/mo〉〈mn〉1〈/mn〉〈/mrow〉〈mrow〉〈mi〉n〈/mi〉〈/mrow〉〈/msubsup〉〈msub〉〈mrow〉〈mi〉H〈/mi〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉P〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msub〉〈msup〉〈mrow〉〈mo stretchy="false"〉(〈/mo〉〈mi〉s〈/mi〉〈mo stretchy="false"〉)〈/mo〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉m〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈/mrow〉〈/msub〉〈mo〉−〈/mo〉〈mn〉1〈/mn〉〈/mrow〉〈/msup〉〈msub〉〈mrow〉〈mi〉H〈/mi〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉P〈/mi〉〈/mrow〉〈mrow〉〈mi〉L〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msub〉〈msup〉〈mrow〉〈mo stretchy="false"〉(〈/mo〉〈mi〉s〈/mi〉〈mo stretchy="false"〉)〈/mo〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉m〈/mi〉〈/mrow〉〈mrow〉〈mi〉L〈/mi〉〈/mrow〉〈/msub〉〈mo〉−〈/mo〉〈mn〉1〈/mn〉〈/mrow〉〈/msup〉〈/math〉, where 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si9.gif" overflow="scroll"〉〈mi〉T〈/mi〉〈mo stretchy="false"〉(〈/mo〉〈mi〉s〈/mi〉〈mo stretchy="false"〉)〈/mo〉〈/math〉 is the univariate resultant of two polynomials obtained from 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si147.gif" overflow="scroll"〉〈mi mathvariant="script"〉P〈/mi〉〈mo stretchy="false"〉(〈/mo〉〈mi〉t〈/mi〉〈mo stretchy="false"〉)〈/mo〉〈/math〉, and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si10.gif" overflow="scroll"〉〈msub〉〈mrow〉〈mi〉H〈/mi〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉P〈/mi〉〈/mrow〉〈mrow〉〈mn〉1〈/mn〉〈/mrow〉〈/msub〉〈/mrow〉〈/msub〉〈mo stretchy="false"〉(〈/mo〉〈mi〉s〈/mi〉〈mo stretchy="false"〉)〈/mo〉〈mo〉,〈/mo〉〈mo〉…〈/mo〉〈mo〉,〈/mo〉〈msub〉〈mrow〉〈mi〉H〈/mi〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉P〈/mi〉〈/mrow〉〈mrow〉〈mi〉n〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msub〉〈mo stretchy="false"〉(〈/mo〉〈mi〉s〈/mi〉〈mo stretchy="false"〉)〈/mo〉〈mo〉,〈/mo〉〈msub〉〈mrow〉〈mi〉H〈/mi〉〈/mrow〉〈mrow〉〈msub〉〈mrow〉〈mi〉P〈/mi〉〈/mrow〉〈mrow〉〈mi〉L〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/msub〉〈mo stretchy="false"〉(〈/mo〉〈mi〉s〈/mi〉〈mo stretchy="false"〉)〈/mo〉〈/math〉 are the 〈em〉fibre functions〈/em〉 of the singularities. The fibre function of a point 〈em〉P〈/em〉 is a polynomial 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si11.gif" overflow="scroll"〉〈msub〉〈mrow〉〈mi〉H〈/mi〉〈/mrow〉〈mrow〉〈mi〉P〈/mi〉〈/mrow〉〈/msub〉〈mo stretchy="false"〉(〈/mo〉〈mi〉s〈/mi〉〈mo stretchy="false"〉)〈/mo〉〈/math〉 whose roots are the fibre of 〈em〉P〈/em〉. Thus, a complete classification of the singularities of a given plane curve, via the factorization of a resultant, is obtained.〈/p〉〈/div〉

Description: 〈p〉Publication date: March–April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 91〈/p〉 〈p〉Author(s): Hannah Markwig, Bernard Mourrain, Giorgio Ottaviani〈/p〉

Description: 〈p〉Publication date: Available online 17 July 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation〈/p〉 〈p〉Author(s): Cristina Bertone, Francesca Cioffi, Davide Franco〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉A classical approach to investigate a closed projective scheme 〈em〉W〈/em〉 consists of considering a general hyperplane section of 〈em〉W〈/em〉, which inherits many properties of 〈em〉W〈/em〉. The inverse problem that consists in finding a scheme 〈em〉W〈/em〉 starting from a possible hyperplane section 〈em〉Y〈/em〉 is called a 〈em〉lifting problem〈/em〉, and every such scheme 〈em〉W〈/em〉 is called a 〈em〉lifting〈/em〉 of 〈em〉Y〈/em〉. Investigations in this topic can produce methods to obtain schemes with specific properties. For example, any smooth point for 〈em〉Y〈/em〉 is smooth also for 〈em〉W〈/em〉.〈/p〉 〈p〉We characterize all the liftings of 〈em〉Y〈/em〉 with a given Hilbert polynomial by a parameter scheme that is obtained by gluing suitable affine open subschemes in a Hilbert scheme and is described through the functor it represents. We use constructive methods from Gröbner and marked bases theories. Furthermore, by classical tools we obtain an analogous result for equidimensional liftings. Examples of explicit computations are provided.〈/p〉 〈/div〉

Description: 〈p〉Publication date: May–June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 92〈/p〉 〈p〉Author(s): James East, Attila Egri-Nagy, James D. Mitchell, Yann Péresse〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Using a variant of Schreier's Theorem, and the theory of Green's relations, we show how to reduce the computation of an arbitrary subsemigroup of a finite regular semigroup to that of certain associated subgroups. Examples of semigroups to which these results apply include many important classes: transformation semigroups, partial permutation semigroups and inverse semigroups, partition monoids, matrix semigroups, and subsemigroups of finite regular Rees matrix and 0-matrix semigroups over groups. For any subsemigroup of such a semigroup, it is possible to, among other things, efficiently compute its size and Green's relations, test membership, factorize elements over the generators, find the semigroup generated by the given subsemigroup and any collection of additional elements, calculate the partial order of the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mi mathvariant="script"〉D〈/mi〉〈/math〉-classes, test regularity, and determine the idempotents. This is achieved by representing the given subsemigroup without exhaustively enumerating its elements. It is also possible to compute the Green's classes of an element of such a subsemigroup without determining the global structure of the semigroup.〈/p〉〈/div〉

Description: 〈p〉Publication date: May–June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 92〈/p〉 〈p〉Author(s): Ivan Marin〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We prove two new cases of the Broué–Malle–Rouquier freeness conjecture for the Hecke algebras associated to complex reflection groups, using methods inspired by non-commutative Gröbner bases. These two cases are the complex reflection groups of rank 2 called 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈msub〉〈mrow〉〈mi〉G〈/mi〉〈/mrow〉〈mrow〉〈mn〉20〈/mn〉〈/mrow〉〈/msub〉〈/math〉 and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si16.gif" overflow="scroll"〉〈msub〉〈mrow〉〈mi〉G〈/mi〉〈/mrow〉〈mrow〉〈mn〉21〈/mn〉〈/mrow〉〈/msub〉〈/math〉 in the Shephard and Todd classification. This reduces the number of remaining unproven cases to 3.〈/p〉〈/div〉

Description: 〈p〉Publication date: January–February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Symbolic Computation, Volume 90〈/p〉 〈p〉Author(s): Adnan Rashid, Osman Hasan〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉To study the dynamical behavior of the engineering and physical systems, we often need to capture their continuous behavior, which is modeled using differential equations, and perform the frequency-domain analysis of these systems. Traditionally, Fourier transform methods are used to perform this frequency domain analysis using paper-and-pencil based analytical techniques or computer simulations. However, both of these methods are error prone and thus are not suitable for analyzing systems used in safety-critical domains, like medicine and transportation. In order to provide an accurate alternative, we propose to use higher-order-logic theorem proving to conduct the frequency domain analysis of these systems. For this purpose, the paper presents a higher-order-logic formalization of Fourier transform using the HOL-Light theorem prover. In particular, we use the higher-order-logic based formalizations of differential, integral, transcendental and topological theories of multivariable calculus to formally define Fourier transform and reason about the correctness of its classical properties, such as existence, linearity, time shifting, frequency shifting, modulation, time scaling, time reversal and differentiation in time domain, and its relationships with Fourier Cosine, Fourier Sine and Laplace transforms. We use our proposed formalization for the formal verification of the frequency response of a generic n-order linear system, an audio equalizer and a MEMs accelerometer, using the HOL-Light theorem prover.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 281〈/p〉 〈p〉Author(s): Xiaoying Wang, Yanqun Shan, Miao Gong, Xin Jin, liangrui Lv, Meng Jiang, Jun Xu〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A novel electrochemical sensor for ochratoxin A (OTA) based on the hairpin aptamer (HA) and double report DNA was constructed successfully. In the work, HA was chosen as the OTA recognition element and immobilized on the gold electrode (GE) 〈em〉via〈/em〉 Au-S. Au nanoparticles (AuNPs) labeled double report DNA (rDNA1 and rDNA2) were symmetrically hybridized with HA simultaneously. Compared to the single report DNA, the strategy can dramatically increase the amount of AuNPs on the electrode surface and the stability of the HA to prevent lodging. The signal amplification was further implemented by using trithiocyanuric acid (TCA) to aggregate the AuNPs. Thus, it was observed that the differential pulse voltammetry (DPV) response of AuNPs was significantly amplified 〈em〉via〈/em〉 multiple signal amplification strategy. When OTA was present, the HA was specifically combined with OTA to form the OTA-HA complex, which caused double report DNA to detach from the electrode, resulting in the decrease of the DPV response. The proposed electrochemical aptasensor can sensitively detect low concentrations of OTA by monitoring the OTA-dependent DPV intensity change. Under the optimized conditions, it exhibited wide linear ranges from 1 pg mL〈sup〉−1〈/sup〉 to 1 ng mL〈sup〉−1〈/sup〉 with a low detection limit of 0.5 pg mL〈sup〉−1〈/sup〉. The work provides a new idea for the various mycotoxins and even other substances detection at trace level.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925400518319257-ga1.jpg" width="334" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 AEU - International Journal of Electronics and Communications, Volume 98〈/p〉 〈p〉Author(s): Daljeet Singh, Hem Dutt Joshi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, the closed form expressions of symbol error rate (SER) are derived for a space time block coded OFDM system subject to carrier frequency offset (CFO) under frequency-selective generalized fading scenarios. Apart from this, the effect of imperfect channel state information (CSI) is also taken into account for error rate analysis. The derived expressions are valid for any family of fading PDFs and the results of zero CFO with perfect CSI are found to be a special case. Numerical results are verified by extensive simulations.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: January–June 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 SoftwareX, Volume 7〈/p〉 〈p〉Author(s): Martin Masek, Chiou Peng Lam, Cameron Tranthim-Fryer, Bas Jansen, Kevin Baptist〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We present a software package for analysing body positions of a subject when they are lying or sleeping in their bed. The software is designed to interface to inexpensive sensors, such as the Microsoft Kinect, and is thus suitable for monitoring at the subjects own home, rather than a dedicated sleep lab. The system is invariant to bed clothing and levels of ambient lighting. Analysis time for a single night session is under five minutes, a significant improvement over the 30–60 min analysis time reported in the literature.〈/p〉〈/div〉

Description: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Pattern Recognition, Volume 87〈/p〉 〈p〉Author(s): Jimin Xiao, Yanchun Xie, Tammam Tillo, Kaizhu Huang, Yunchao Wei, Jiashi Feng〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Person search in real-world scenarios is a new challenging computer version task with many meaningful applications. The challenge of this task mainly comes from: (1) unavailable bounding boxes for pedestrians and the model needs to search for the person over the whole gallery images; (2) huge variance of visual appearance of a particular person owing to varying poses, lighting conditions, and occlusions. To address these two critical issues in modern person search applications, we propose a novel Individual Aggregation Network (IAN) that can accurately localize persons by learning to minimize intra-person feature variations. IAN is built upon the state-of-the-art object detection framework, i.e., faster R-CNN, so that high-quality region proposals for pedestrians can be produced in an online manner. In addition, to relieve the negative effect caused by varying visual appearances of the same individual, IAN introduces a novel center loss that can increase the intra-class compactness of feature representations. The engaged center loss encourages persons with the same identity to have similar feature characteristics. Extensive experimental results on two benchmarks, i.e., CUHK-SYSU and PRW, well demonstrate the superiority of the proposed model. In particular, IAN achieves 77.23% mAP and 80.45% top-1 accuracy on CUHK-SYSU, which outperform the state-of-the-art by 1.7% and 1.85%, respectively.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Sensors and Actuators B: Chemical, Volume 281〈/p〉 〈p〉Author(s): Tingting Zhou, Rui Zhang, Yubing Wang, Tong Zhang〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The key challenge to develop gas sensors with high performances lies in the novel design of superior functional materials for effective reactions between target gases and sensing layers. Metal–organic frameworks (MOFs) have emerged as versatile candidates for preparation of ideal nanostructured materials with controllable composition, various structures and tunable pore size. Herein, a series of Fe–based and Fe/Ni–based one–dimensional (1D) nanostructures using MOFs as templates were prepared systematically. As a result of the hollow structure and nanohybrid features, the optimized α–Fe〈sub〉2〈/sub〉O〈sub〉3〈/sub〉/NiFe〈sub〉2〈/sub〉O〈sub〉4〈/sub〉 nanotubes can exhibit high specific surface area (118.03 m〈sup〉2〈/sup〉 g〈sup〉−1〈/sup〉) and provide a mass of active sites compared to individual components (α–Fe〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 nanowires and NiFe〈sub〉2〈/sub〉O〈sub〉4〈/sub〉 nanowires), which is beneficial to improve the response (R〈sub〉a〈/sub〉/R〈sub〉g〈/sub〉 = 23) to acetone vapors. In addition, the smart design also endows the sensor based on α–Fe〈sub〉2〈/sub〉O〈sub〉3〈/sub〉/NiFe〈sub〉2〈/sub〉O〈sub〉4〈/sub〉 nanotubes with good selectivity, fast response time (4 s) and long–term stability (30 days). In this work, the advantages of 1D hollow heterogeneous materials will provide a new perspective of MOF–derived nanostructures for the particular application in acetone gas sensors.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0925400518319014-ga1.jpg" width="329" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 376〈/p〉 〈p〉Author(s): A. Belme, F. Alauzet, A. Dervieux〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We present a goal-oriented error analysis for the calculation of low Reynolds steady compressible flows with anisotropic mesh adaptation. The error analysis is of 〈em〉a priori〈/em〉 type. Its central principle is to express the right-hand side of the error equation, often referred as the local error, as a function of the interpolation error of a collection of fields present in the nonlinear Partial Differential Equations. This goal-oriented error analysis is the extension of [39] done for inviscid flows to laminar viscous flows by adding viscous terms. The main benefits of this approach, in comparison to other error estimates in the literature, is that the optimal anisotropy of the mesh directly appears in the error analysis and is not obtained from an ad hoc variable nor a local analysis. As a consequence, an optimum is obtained and the convergence of the mesh adaptive process is very fast, 〈em〉i.e.,〈/em〉 generally the convergence is obtained after 5 to 10 mesh adaptation cycle. Then, using the continuous mesh framework, an optimal metric is analytically obtained from the error estimation. Applications to mesh adaptive calculations of flows past airfoils are presented.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 375〈/p〉 〈p〉Author(s): Pablo Miguel Ramos, Nikos Ch. Karayiannis, Manuel Laso〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A new algorithmic approach is presented for the generation and successive equilibration of polymer configurations under conditions of extreme confinement where the inter-wall distance, in at least one dimension, approaches the diameter of the spherical monomers. It significantly improves on the Monte Carlo (MC) protocol described in Karayiannis and Laso (2008) [126]. The algorithm is designed to generate highly confined packings of freely-jointed chains of hard spheres of uniform size. Spatial confinement is achieved by including flat, parallel impenetrable walls in one or more dimensions of the simulation box. The present MC scheme allows the systematic study of the effect of chain length, polydispersity, volume fraction, bond tolerance (gap), cell aspect ratio and level of confinement on the short- and long-range structure of polymer chains near and far from the confining planes. In the present study we focus on the efficiency of the MC protocol in generating, equilibrating, and configurationally decorrelating chain assemblies with average lengths ranging from 〈em〉N〈/em〉 = 12 to 1000 monomers and at volume fractions from dilute up to the maximally random jammed (MRJ) state. Starting from cubic amorphous cells filled with polymer chains, the MC algorithm is able to reach quasi 2-d (plate-like) and 1-d (tube-like) states under conditions of extreme confinement and/or cell aspect ratio where the inter-wall distance approaches the diameter of beads forming the chains. A comparison with corresponding bulk packings shows the similarities and differences produced by extreme spatial confinement.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉Snapshots of computer-generated athermal polymer configurations under full confinement with increasing cell aspect ratio starting from 3-d cubic cells and leading to 2-d templates.〈/p〉〈/div〉 〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0021999118305850-gr001.jpg" width="452" alt="Graphical abstract for this article" title=""〉〈/figure〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Computational Physics, Volume 375〈/p〉 〈p〉Author(s): Gaddiel Y. Ouaknin, Nabil Laachi, Kris Delaney, Glenn H. Fredrickson, Frederic Gibou〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We introduce a level-set strategy to find the geometry of confinement that will guide the self-assembly of block copolymers to a given target design in the context of lithography. The methodology is based on a shape optimization algorithm, where the level-set normal velocity is defined as the pressure field computed through a self-consistent field theory simulation. We present numerical simulations that demonstrate that this methodology is capable of finding guiding templates for a variety of target arrangements of cylinders and thus is an effective approach to the inverse directed self-assembly problem.〈/p〉〈/div〉

Description: 〈p〉Publication date: October 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Complexity, Volume 48〈/p〉 〈p〉Author(s): Alexander E. Litvak, Anna Lytova, Konstantin Tikhomirov, Nicole Tomczak-Jaegermann, Pierre Youssef〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Let 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="si1.gif"〉〈mi〉d〈/mi〉〈/math〉 be a (large) integer. Given 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="si2.gif"〉〈mi〉n〈/mi〉〈mo〉≥〈/mo〉〈mn〉2〈/mn〉〈mi〉d〈/mi〉〈/math〉, let 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="si3.gif"〉〈msub〉〈mrow〉〈mi〉A〈/mi〉〈/mrow〉〈mrow〉〈mi〉n〈/mi〉〈/mrow〉〈/msub〉〈/math〉 be the adjacency matrix of a random directed 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="si1.gif"〉〈mi〉d〈/mi〉〈/math〉-regular graph on 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="si5.gif"〉〈mi〉n〈/mi〉〈/math〉 vertices, with the uniform distribution. We show that the rank of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="si3.gif"〉〈msub〉〈mrow〉〈mi〉A〈/mi〉〈/mrow〉〈mrow〉〈mi〉n〈/mi〉〈/mrow〉〈/msub〉〈/math〉 is at least 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="si7.gif"〉〈mi〉n〈/mi〉〈mo〉−〈/mo〉〈mn〉1〈/mn〉〈/math〉 with probability going to one as 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="si5.gif"〉〈mi〉n〈/mi〉〈/math〉 grows to infinity. The proof combines the well known method of simple switchings and a recent result of the authors on delocalization of eigenvectors of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll" altimg="si3.gif"〉〈msub〉〈mrow〉〈mi〉A〈/mi〉〈/mrow〉〈mrow〉〈mi〉n〈/mi〉〈/mrow〉〈/msub〉〈/math〉.〈/p〉〈/div〉