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  • Articles  (71,573)
  • Oxford University Press  (59,522)
  • IOS Press  (12,051)
  • Mathematics  (65,093)
  • Energy, Environment Protection, Nuclear Power Engineering  (6,480)
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Years
  • 1
    Publication Date: 2020-10-09
    Description: Diffuse nutrient pollution from agriculture has been the concern of policymakers for several decades, and yet it remains a persistent environmental issue. The current approach to mitigating the problem is predominantly via command and control regulation within the Nitrates Directive and the Water Framework Directive. This article will set out how diffuse pollution can be considered a wicked policy problem which acts as an explanation of how it has eluded the current regulatory regime. It will further establish that the traditional planning process overlooked the complexity of the problem. Finally, it will illustrate the ineffectiveness of the current regulatory framework to mitigate the problem. This will be exemplified through the legal framework of Northern Ireland.
    Print ISSN: 0952-8873
    Electronic ISSN: 1464-374X
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Law
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  • 2
    Publication Date: 2020-10-09
    Description: This analysis explores new developments in judicial review of planning policy interpretation. It shows how the nature of policy, often contextual and judgment-dependent, has led the UK Supreme Court to rethink the standard of review applicable to this issue. By considering the recent decision in Samuel Smith as part of a trilogy of cases—including Tesco Stores and Hopkins Homes—this analysis reveals a change in judicial attitudes, away from the expansive judicial supervision upheld in Tesco Stores. Furthermore, this study reflects on how this change is related to two wider ideas. The first is the Court’s understanding of the law and policy divide in the planning field, whilst the second is to do with a pragmatic stance regarding the purpose of the planning system and the institutional role of the courts in it. Finally, this analysis shows how the new approach emphasises the distinctive character of policy in the planning context.
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Law
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  • 3
    Publication Date: 2015-08-16
    Description: Natural gas is an extremely important bridge fuel to a low-carbon energy economy for improving local air quality. Coal to synthetic natural gas (SNG) is an effective way to convert the high-carbon energy (coal) into the low-carbon energy with rich hydrogen (natural gas). For the modern coal to SNG industry, the high-temperature methanation (HTM) catalyst plays an important role, and the advanced evaluation process should necessitate the elimination of mass transfer effect. Some simple but effective model catalysts, such as slab and sphere, can be very helpful in defining the reaction conditions, and thus facilitating the evaluation process for real HTM catalysts. In this work, slab and sphere model catalysts were adopted to derive mass transfer and reaction-coupled equations, the numerical methods were used to solve the coupled equations for the concentration profiles in catalysts, and the effectiveness factors were accordingly calculated. By taking advantage of the Thiele module and the Weisz–Prater module , the criteria for the elimination of mass transfer effect in the HTM catalyst evaluation process were successfully defined. This work also complements the Weisz–Prater criterion by incorporating ‘negative reaction orders’.
    Keywords: Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 4
    Publication Date: 2015-08-16
    Description: The energy expended for conditioning buildings around the world is worryingly large and increasing every year. Currently, almost half of houses around the world use some type of energy-expensive conventional air-conditioning system. These systems are high emitters of gases such as carbon dioxide and so high contributors to climate change. Consequently, alternatives must be considered. Earth–air heat exchangers (EAHEs) and phase-change materials (PCMs) may be options; they have, however, limitations. This paper proposes a novel hybrid space-conditioning system combining EAHEs with PCMs, which uses surfaces as sources of heating or cooling to provide better temperature distribution across a space and comfort enhancement with low energy use. The idea is to use an EAHE to provide cool air to discharge the PCM, consequently helping to overcome most of the limitations of both strategies. Two of a series of experiments undertaken to test the proposed system are reported in this article. The EAHE + PCM system compared with a reference room could decrease temperature swings by up to 47%. The system was proved to work although further work is required to make it commercially viable.
    Keywords: Other low-carbon energy technologies
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 5
    Publication Date: 2015-08-16
    Description: The design of a future building with very high-energy efficiency demands from the architect to study the available solar resources in this urban environment. The purpose of the presented methodology is to study the variations in all components of the incident solar radiation daily, monthly and seasonally for all building facades. This is realized in the computer program 3D–SOLARIA. In the focus of the paper is the estimation of the background component of the incident diffuse solar irradiation on a building facade under orthogonally obstructed sky, using anisotropic sky view factors.
    Keywords: Sustainable/low carbon buildings
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 6
    Publication Date: 2015-08-16
    Description: The assessment of building envelope sustainability using existing building performance assessment methods is still a challenge and yet to be fully addressed. This is due to the single-dimensional nature and lack of integration of sustainable performance values. Besides, the issue of sustainability assessment in the building envelope requires considering many factors including life cycle considerations. As such, in an effort to develop an integrated approach that combines relevant sustainable development factors and life cycles, an integrated performance model (IPM) was developed. The IPM is an essential tool developed to aid the sustainable design of the residential building envelope that can reduce carbon emission and whole residential building energy consumption and ensure sustainable performance of the building envelope.
    Keywords: Sustainable/low carbon buildings
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 7
    Publication Date: 2015-08-16
    Description: The results and considerations on one self-consumption photovoltaic installation with net balance in Granada (South of Spain) are presented and discussed in this paper. The use of the building (one faculty) makes it optimal for this kind of consumption. Finally, the potential benefits and problems of self-consumption with net balance are presented.
    Keywords: Solar energy technologies
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 8
    Publication Date: 2015-08-16
    Description: Passive convective heat transfer enhancement can be achieved by improving the thermo-physical properties of the working fluid, changing flow geometry or both. This work presents a numerical study to investigate the combined effect of using helical coils and nanofluids on the heat transfer characteristics and pressure losses in turbulent flow regime. The developed computational fluid dynamics models were validated against published experimental data and empirical correlations. Results have shown that combining the effects of alumina (Al 2 O 3 ) nanoparticles and tube coiling could enhance the heat transfer coefficient by up to 60% compared with that of pure water in straight tube at the same Reynolds number. Also, results showed that the pressure drop in helical coils using Al 2 O 3 nanofluid for volume fraction of 3% was six times that of water in straight tubes (80% of the pressure drop increase is due to nanoparticles addition), while the effect of Reynolds number on the pressure drop penalty factor was found to be insignificant.
    Keywords: Other low-carbon energy technologies
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 9
    Publication Date: 2015-08-16
    Description: The demand for better indoor environment has led to a wide use of heating, ventilating and air conditioning (HVAC) systems. However, this demanding cannot be sustained without a strategy to reduce the energy consumption of HVAC systems. Employing advanced HVAC control is one of the strategies to maintain high-quality indoor thermal comfort with low energy consumption. This paper reviews the development of control technologies for HVAC systems. It summarizes the problems in existing reviews and gives a future perspective on HVAC control systems for occupant comfort and energy efficiency.
    Keywords: Built environment and low-carbon society
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 10
    Publication Date: 2015-08-05
    Description: We prove a spectral flow formula for one-parameter families of Hamiltonian systems under homoclinic boundary conditions, which relates the spectral flow to the relative Maslov index of a pair of curves of Lagrangians induced by the stable and unstable subspaces, respectively. Finally, we deduce sufficient conditions for bifurcation of homoclinic trajectories of one-parameter families of non-autonomous Hamiltonian vector fields.
    Print ISSN: 0024-6115
    Electronic ISSN: 1460-244X
    Topics: Mathematics
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  • 11
    Publication Date: 2015-08-05
    Description: We consider the Schur–Horn problem for normal operators in von Neumann algebras, which is the problem of characterizing the possible diagonal values of a given normal operator based on its spectral data. For normal matrices, this problem is well known to be extremely difficult, and in fact, it remains open for matrices of size greater than $3$ . We show that the infinite-dimensional version of this problem is more tractable, and establish approximate solutions for normal operators in von Neumann factors of type I $_\infty$ , II, and III. A key result is an approximation theorem that can be seen as an approximate multivariate analogue of Kadison's Carpenter Theorem.
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    Topics: Mathematics
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  • 12
    Publication Date: 2015-08-05
    Description: We study the rate of convergence to zero of the tail entropy of $C^\infty$ maps. We give an upper bound of this rate in terms of the growth in $k$ of the derivative of order $k$ and give examples showing the optimality of the established rate of convergence. We also consider the case of multimodal maps of the interval. Finally, we prove that homoclinic tangencies give rise to $C^r$ $(r\geqslant 2)$ robustly non- $h$ -expansive dynamical systems.
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  • 13
    Publication Date: 2015-08-05
    Description: Let ${{\mathscr {C}}}^0_{{{\mathfrak {g}}}}$ be the category of finite-dimensional integrable modules over the quantum affine algebra $U_{q}'({{\mathfrak {g}}})$ and let $R^{A_\infty }{\mbox {-}\mathrm {gmod}}$ denote the category of finite-dimensional graded modules over the quiver Hecke algebra of type $A_{\infty }$ . In this paper, we investigate the relationship between the categories ${{\mathscr {C}}}^0_{A_{N-1}^{(1)}}$ and ${{\mathscr {C}}}^0_{A_{N-1}^{(2)}}$ by constructing the generalized quantum affine Schur–Weyl duality functors ${\mathcal {F}}^{(t)}$ from $R^{A_\infty }{\mbox {-}\mathrm {gmod}}$ to ${{\mathscr {C}}}^0_{A_{N-1}^{(t)}}\ (t=1,2)$ .
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  • 14
    Publication Date: 2015-08-05
    Description: We present new constructions of complex and $p$ -adic Darmon points on elliptic curves over base fields of arbitrary signature. We conjecture that these points are global and present numerical evidence to support our conjecture.
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  • 15
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    Oxford University Press
    Publication Date: 2015-08-21
    Description: Individualized treatment rules recommend treatments on the basis of individual patient characteristics. A high-quality treatment rule can produce better patient outcomes, lower costs and less treatment burden. If a treatment rule learned from data is to be used to inform clinical practice or provide scientific insight, it is crucial that it be interpretable; clinicians may be unwilling to implement models they do not understand, and black-box models may not be useful for guiding future research. The canonical example of an interpretable prediction model is a decision tree. We propose a method for estimating an optimal individualized treatment rule within the class of rules that are representable as decision trees. The class of rules we consider is interpretable but expressive. A novel feature of this problem is that the learning task is unsupervised, as the optimal treatment for each patient is unknown and must be estimated. The proposed method applies to both categorical and continuous treatments and produces favourable marginal mean outcomes in simulation experiments. We illustrate it using data from a study of major depressive disorder.
    Print ISSN: 0006-3444
    Electronic ISSN: 1464-3510
    Topics: Biology , Mathematics , Medicine
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  • 16
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    Oxford University Press
    Publication Date: 2015-08-21
    Description: Sufficient dimension reduction in regression aims to reduce the predictor dimension by replacing the original predictors with some set of linear combinations of them without loss of information. Numerous dimension reduction methods have been developed based on this paradigm. However, little effort has been devoted to diagnostic studies within the context of dimension reduction. In this paper we introduce methods to check goodness-of-fit for a given dimension reduction subspace. The key idea is to extend the so-called distance correlation to measure the conditional dependence relationship between the covariates and the response given a reduction subspace. Our methods require minimal assumptions, which are usually much less restrictive than the conditions needed to justify the original methods. Asymptotic properties of the test statistic are studied. Numerical examples demonstrate the effectiveness of the proposed approach.
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  • 17
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    Oxford University Press
    Publication Date: 2015-08-21
    Description: We propose a geometric framework to assess sensitivity of Bayesian procedures to modelling assumptions based on the nonparametric Fisher–Rao metric. While the framework is general, the focus of this article is on assessing local and global robustness in Bayesian procedures with respect to perturbations of the likelihood and prior, and on the identification of influential observations. The approach is based on a square-root representation of densities, which enables analytical computation of geodesic paths and distances, facilitating the definition of naturally calibrated local and global discrepancy measures. An important feature of our approach is the definition of a geometric $\epsilon$ -contamination class of sampling distributions and priors via intrinsic analysis on the space of probability density functions. We demonstrate the applicability of our framework to generalized mixed-effects models and to directional and shape data.
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  • 18
    Publication Date: 2015-08-21
    Description: With the discovery of an increasing number of causal genes for complex human disorders, it is crucial to assess the genetic risk of disease onset for individuals who are carriers of these causal mutations and to compare the distribution of the age-at-onset for such individuals with the distribution for noncarriers. In many genetic epidemiological studies that aim to estimate causal gene effect on disease, the age-at-onset of disease is subject to censoring. In addition, the mutation carrier or noncarrier status of some individuals may be unknown, due to the high cost of in-person ascertainment by collecting DNA samples or because of the death of older individuals. Instead, the probability of such individuals’ mutation status can be obtained from various other sources. When mutation status is missing, the available data take the form of censored mixture data. Recently, various methods have been proposed for risk estimation using such data, but none is efficient for estimating a nonparametric distribution. We propose a fully efficient sieve maximum likelihood estimation method, in which we estimate the logarithm of the hazard ratio between genetic mutation groups using B-splines, while applying nonparametric maximum likelihood estimation to the reference baseline hazard function. Our estimator can be calculated via an expectation-maximization algorithm which is much faster than existing methods. We show that our estimator is consistent and semiparametrically efficient and establish its asymptotic distribution. Simulation studies demonstrate the superior performance of the proposed method, which is used to estimate the distribution of the age-at-onset of Parkinson's disease for carriers of mutations in the leucine-rich repeat kinase 2, LRRK2, gene.
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    Topics: Biology , Mathematics , Medicine
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  • 19
    Publication Date: 2015-08-21
    Description: Smoothing splines provide flexible nonparametric regression estimators. However, the high computational cost of smoothing splines for large datasets has hindered their wide application. In this article, we develop a new method, named adaptive basis sampling, for efficient computation of smoothing splines in super-large samples. Except for the univariate case where the Reinsch algorithm is applicable, a smoothing spline for a regression problem with sample size n can be expressed as a linear combination of n basis functions and its computational complexity is generally O ( n 3 ). We achieve a more scalable computation in the multivariate case by evaluating the smoothing spline using a smaller set of basis functions, obtained by an adaptive sampling scheme that uses values of the response variable. Our asymptotic analysis shows that smoothing splines computed via adaptive basis sampling converge to the true function at the same rate as full basis smoothing splines. Using simulation studies and a large-scale deep earth core-mantle boundary imaging study, we show that the proposed method outperforms a sampling method that does not use the values of response variables.
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  • 20
    Publication Date: 2015-08-21
    Description: We propose tests for nonlinear serial dependence in time series under the null hypothesis of general linear dependence, in contrast to the more widely studied null hypothesis of independence. The approach is based on combining an entropy dependence metric, which possesses many desirable properties and is used as a test statistic, with a suitable extension of surrogate data methods, a class of Monte Carlo distribution-free tests for nonlinearity, and a smoothed sieve bootstrap scheme. We show how, in the same way as the autocorrelation function is used for linear models, our tests can in principle be employed to detect the lags at which a significant nonlinear relationship is present. We prove the asymptotic validity of the proposed procedures and the corresponding inferences. The small-sample performance of the tests in terms of power and size is assessed through a simulation study. Applications to real datasets of different kinds are also presented.
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  • 21
    Publication Date: 2015-08-21
    Description: Contamination caused by outliers is inevitable in data analysis, and robust statistical methods are often needed. In this paper we develop a new approach for robust data analysis on the basis of scoring rules. A scoring rule is a discrepancy measure to assess the quality of probabilistic forecasts. We propose a simple method of estimating not only parameters in the statistical model but also the contamination ratio, i.e., the ratio of outliers. The outliers are detected based on the estimated contamination ratio. For this purpose, we use scoring rules with extended statistical models called unnormalized models. Regression problems are also considered. We study complex heterogeneous contamination wherein the contamination ratio in a response variable may depend on covariate variables, and propose a simple method to estimate a robust regression function and expected contamination ratio. Simulation studies demonstrate the effectiveness of our method.
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  • 22
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    Oxford University Press
    Publication Date: 2015-08-21
    Description: The sample covariance matrix, which is well known to be highly nonrobust, plays a central role in many classical multivariate statistical methods. A popular way of making such multivariate methods more robust is to replace the sample covariance matrix with some robust scatter matrix. The aim of this paper is to point out that multivariate methods often require that certain properties of the covariance matrix hold also for the robust scatter matrix in order for the corresponding robust plug-in method to be a valid approach, but that not all scatter matrices possess the desired properties. Plug-in methods for independent components analysis, observational regression and graphical modelling are considered in more detail. For each case, it is shown that replacing the sample covariance matrix with a symmetrized robust scatter matrix yields a valid robust multivariate procedure.
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  • 23
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    Oxford University Press
    Publication Date: 2015-08-21
    Description: So-called big data are likely to have complex structure, in particular implying that estimates of precision obtained by applying standard statistical procedures are likely to be misleading, even if the point estimates of parameters themselves may be reasonably satisfactory. While this possibility is best explored in the context of each special case, here we outline a fairly general representation of the accretion of error in large systems and explore the possible implications for the estimation of regression coefficients. The discussion raises issues broadly parallel to the distinction between short-range and long-range dependence in time series theory.
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  • 24
    Publication Date: 2015-08-21
    Description: This paper extends the classical two-regime threshold autoregressive model by introducing hysteresis to its regime-switching structure, which leads to a new model: the hysteretic autoregressive model. The proposed model enjoys the piecewise linear structure of a threshold model but has a more flexible regime switching mechanism. A sufficient condition is given for geometric ergodicity. Conditional least squares estimation is discussed, and the asymptotic distributions of its estimators and information criteria for model selection are derived. Simulation results and an example support the model.
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  • 25
    Publication Date: 2015-08-21
    Description: This paper points out an error in Davidov and Iliopoulos's ( Biometrika 100 , 778–80) proof of convergence of an iterative algorithm for the proportional likelihood ratio model. It is shown that the iterative algorithm increases the likelihood in each iteration and converges under mild additional conditions when the odds ratio function is bounded.
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  • 26
    Publication Date: 2015-08-21
    Description: Choosing the number of components in a finite mixture model is a challenging task. In this article, we study the behaviour of information criteria for selecting the mixture order, based on either the observed likelihood or the complete likelihood including component labels. We propose a new observed likelihood criterion called aic mix , which is shown to be order consistent. We further show that when there is a nontrivial level of classification uncertainty in the true model, complete likelihood criteria asymptotically underestimate the true number of components. A simulation study illustrates the potentially poor finite-sample performance of complete likelihood criteria, while aic mix and the Bayesian information criterion perform strongly regardless of the level of classification uncertainty.
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  • 27
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    Oxford University Press
    Publication Date: 2015-08-21
    Description: Outlier detection is an integral component of statistical modelling and estimation. For high-dimensional data, classical methods based on the Mahalanobis distance are usually not applicable. We propose an outlier detection procedure that replaces the classical minimum covariance determinant estimator with a high-breakdown minimum diagonal product estimator. The cut-off value is obtained from the asymptotic distribution of the distance, which enables us to control the Type I error and deliver robust outlier detection. Simulation studies show that the proposed method behaves well for high-dimensional data.
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  • 28
    Publication Date: 2015-08-21
    Description: This paper adopts a nonparametric Bayesian approach to testing whether a function is monotone. Two new families of tests are constructed. The first uses constrained smoothing splines with a hierarchical stochastic-process prior that explicitly controls the prior probability of monotonicity. The second uses regression splines together with two proposals for the prior over the regression coefficients. Via simulation, the finite-sample performance of the tests is shown to improve upon existing frequentist and Bayesian methods. The asymptotic properties of the Bayes factor for comparing monotone versus nonmonotone regression functions in a Gaussian model are also studied. Our results significantly extend those currently available, which chiefly focus on determining the dimension of a parametric linear model.
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  • 29
    Publication Date: 2015-08-21
    Description: The paper develops hierarchical empirical Bayes and benchmarked hierarchical empirical Bayes estimators of positive small area means under multiplicative models. The usual benchmarking requirement is that the small area estimates, when aggregated, should equal the direct estimates for the larger geographical areas. However, while estimating positive small area parameters, the conventional squared error or weighted squared error loss subject to the usual benchmark constraint may not produce positive estimators, so it is necessary to seek other loss functions. We consider a multiplicative model for the original data for estimating positive small area means, and suggest a variant of the Kullback–Leibler divergence as a loss function. The prediction errors of the suggested hierarchical empirical Bayes estimators are investigated asymptotically, and their second-order unbiased estimators are provided. Bootstrapped estimators of these prediction errors for both hierarchical empirical Bayes and benchmarked hierarchical empirical Bayes estimators are also given. The performance of the suggested procedures is investigated through simulation as well as with an example.
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  • 30
    Publication Date: 2015-08-21
    Description: Odds ratios can be estimated in case-control studies using standard logistic regression, ignoring the outcome-dependent sampling. In this paper we discuss an analogous result for treatment effects on the treated in matched cohort studies. Specifically, in studies where a sample of treated subjects is observed along with a separate sample of possibly matched controls, we show that efficient and doubly robust estimators of effects on the treated are computationally equivalent to standard estimators, which ignore the matching and exposure-based sampling. This is not the case for general average effects. We also show that matched cohort studies are often more efficient than random sampling for estimating effects on the treated, and derive the optimal number of matches for a given set of matching variables. We illustrate our results via simulation and in a matched cohort study of the effect of hysterectomy on the risk of cardiovascular disease.
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  • 31
    Publication Date: 2015-08-21
    Description: Current status data occur in contexts including demographic studies and tumorigenicity experiments. In such cases, each subject is observed only once and the failure time of interest is either left- or right-censored (Kalbfleisch & Prentice, 2002). Many methods have been developed for the analysis of such data (Huang, 1996; Sun, 2006), most of which assume that the failure time and the observation time are independent completely or given covariates. In this paper, we present a sieve maximum likelihood approach for current status data when independence does not hold. A copula model and monotone I-splines are used and the asymptotic properties of the resulting estimators are established. In particular, the estimated regression parameters are shown to be semiparametrically efficient. An illustrative example is provided.
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  • 32
    Publication Date: 2015-08-16
    Description: In buildings without mechanical ventilation, the fresh air needed by the occupants is supplied only by air infiltration or natural ventilation. Its quantification by analytical methods is difficult, and so experimental methods such as the tracer gas technique are very useful. In this work, several case studies are presented, where one may see the potential of this technique to detect small differences in building air tightness, due to different envelope elements, namely the type of window frames and location of blinds' boxes. The applicability of this technique to other spaces rather than buildings can also be analyzed. When dealing with mechanical ventilation, it is difficult to measure the duct air flow rate precisely, because of the minimum duct length necessary to obtain a good mixing of the tracer gas with the air, when conventional probes are used. Research was carried out with the development of new probes to overcome this situation, and results are also shown. With accurate measurements of air flow rates, it is possible to reduce CO 2 emissions due to air heating or cooling in buildings.
    Keywords: Built environment and low-carbon society
    Print ISSN: 1748-1317
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 33
    Publication Date: 2015-08-16
    Description: A number of factors influence the performance of an ejector, e.g. working fluid, geometry and operating conditions. In the present work, six low-environmental-impact working fluids were evaluated for their use in an ejector cooling system running on low-temperature thermal energy. The numerical analysis was based on a model applying the 1D constant-pressure mixing theory. Ejector performance was assessed for the temperatures of the generator, evaporator and condenser in the range of 80–120°C, 5–15°C and 25–40°C, respectively. The results indicated that owing to its high coefficient of performance and moderate operating pressures throughout the entire ejector cycle, isobutane is a good choice for a refrigerant. The area ratio required for running the ejector in critical mode, under changing operating conditions, varied in a significant range regardless of the selected refrigerant. This clearly indicates the importance of a variable geometry ejector design to strengthen the position of ejector cooling systems among other refrigeration technologies.
    Keywords: Other low-carbon energy technologies
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    Electronic ISSN: 1748-1325
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 34
    Publication Date: 2015-07-30
    Description: Energy security remains a vital issue for the European Union (EU), even more so in the wake of the events that unfolded in early 2014 in Ukraine. The EU’s already fragile position in the international energy arena in terms of security of supply appears to be more uncertain than ever after its umpteenth fallout with its historic energy supplier, Russia. This situation is untenable and calls for swift and decisive action to adequately tackle the issue once and for all. The article looks at the creation of a single EU energy market through integration of energy networks in the EU. It then examines various ways to diversify the EU’s energy supply, whether through increasing the import of liquefied natural gas, through its relations with the Eurasian Union, the promotion of renewable energy or the construction of alternative pipelines and energy routes. The article then offers an analysis of the latest developments of the Energy Charter Conference. The article concludes that from energy transit, to technology transfer, to investment protection, energy and trade present interplays across various fields. Improvements can be made to the EU trading system to ensure greater energy security and more efficient energy markets.
    Print ISSN: 1754-9957
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    Topics: Energy, Environment Protection, Nuclear Power Engineering , Law , Economics
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  • 35
    Publication Date: 2015-07-30
    Description: Despite the Egyptian authorities’ great hopes for the fledging shale gas industry in Egypt, it appears that it could be difficult for Egypt to realize these lofty ambitions, at least in the near future. The Egyptian shale gas industry faces technical challenges as well as a critical lack of detailed regulations regarding the exploration for and the production of shale gas. There is also a lack of guidance over the manner in which foreign investments can be made in the industry.
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  • 36
    Publication Date: 2015-08-05
    Description: We introduce a new framework for the analysis of the stability of solitons for the one-dimensional Gross–Pitaevskii equation. In particular, we establish the asymptotic stability of the black soliton with zero speed.
    Print ISSN: 0024-6115
    Electronic ISSN: 1460-244X
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  • 37
    Publication Date: 2015-08-05
    Description: Let $k$ and $n$ be positive even integers. For a cuspidal Hecke eigenform $h$ in the Kohnen plus space of weight $k-n/2+1/2$ for $\varGamma _0(4),$ let $I_n(h)$ be the Duke–Imamo $\bar {{\text {g}}}$ lu–Ikeda lift of $h$ in the space of cusp forms of weight $k$ for ${\rm Sp}_n({{\bf{Z}}}),$ and $f$ be the primitive form of weight $2k-n$ for ${\rm SL}_2({{\bf{Z}}})$ corresponding to $h$ under the Shimura correspondence. We then express the ratio $\displaystyle {\langle I_n(h), I_n(h) \rangle / \langle h, h \rangle }$ of the period of $I_n(h)$ to that of $h$ in terms of special values of certain $L$ -functions of $f$ . This proves the conjecture proposed by Ikeda concerning the period of the Duke–Imamo $\bar {{\text {g}}}$ lu–Ikeda lift.
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  • 38
    Publication Date: 2015-06-05
    Description: We study the homological finiteness properties ${\rm FP}_m$ of wreath products $\Gamma = H \wr _X G$ . We show that, when $H$ has infinite abelianization, $\Gamma$ is of type ${\rm FP}_m$ if and only if both $G$ and $H$ have type ${\rm FP}_m$ and $G$ acts (diagonally) on $X^i$ with stabilizers of type ${\rm FP}_{m-i}$ and with finitely many orbits for all $1 \leq i \leq m$ . If furthermore $H$ is torsion-free, we give a criterion for $\Gamma$ to be Bredon- ${\rm FP}_m$ with respect to the class of finite subgroups of $\Gamma$ . Finally, when $H$ has infinite abelianization and $\chi : \Gamma \to \mathbb {R}$ is a non-zero homomorphism with $\chi (H) = 0$ , we classify when $[\chi ]$ belongs to the Bieri–Neumann–Strebel–Renz invariant $\Sigma ^m(\Gamma , \mathbb {Z})$ .
    Print ISSN: 0033-5606
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  • 39
    Publication Date: 2015-06-05
    Description: We investigate the logarithmic bundles associated to arrangements of hypersurfaces with a fixed degree in a smooth projective variety. We then specialize to the case when the variety is a quadric hypersurface and a multiprojective space to prove a Torelli-type theorem in some cases.
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  • 40
    Publication Date: 2015-06-05
    Description: We study the higher differentiability of the very weak solution of the Cauchy–Dirichlet problem associated to the linear parabolic system with Hölder continuous coefficients and L 1 right-hand side of the form $$\begin{align*} \dfrac{\partial u}{\partial t} -{\rm div}(A(x,t)Du) & = \mu \quad \mbox{in } \Omega \,{\times}\,]0, T[,\\ u & = 0 \quad \mbox{on } \partial \Omega \,{\times}\,]0, T[,\\ u & = 0 \quad \mbox{on } \Omega \times \{ 0\}. \end{align*}$$
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  • 41
    Publication Date: 2015-06-09
    Description: This article evaluates 186 papers, published between 1978 and 2013 in 16 representative scientific journals, related to maintenance and reliability problems that were tackled from a multi-criteria (MC) perspective. An overview and insights are presented. This study may be useful to researchers and others concerned with maintenance and reliability who seek not only to understand the potential of MC and multi-objective models but also to develop and apply an MC decision model to help solve a real problem in these areas. There are some discussions on some principles for the application of MC in maintenance and reliability and some guidance on how to choose a suitable MC method is given, based on previous applications.
    Print ISSN: 1471-678X
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  • 42
    Publication Date: 2015-06-09
    Description: A credit-linked note (CLN) is a type of credit derivative, constructed with a bond and an embedded credit default swap, which allows the issuer to transfer a specific credit risk to credit investors. In this paper, we model CLNs with and without counterparty risk in the reduced-form framework. For CLNs with counterparty risk, we consider two different scenarios, i.e. the issuer of CLNs and reference assets have either positive correlation or negative correlation. Assuming the interest rate follows the Cox–Ingersoll–Ross (CIR) model (Cox et al ., 1985) and the default events mainly depend on the interest rate, we model the two different correlations. Explicit formulas for value functions are obtained through a partial differential equation approach. In addition, counterparty valuation adjustment and the dependence on related parameters are also investigated.
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  • 43
    Publication Date: 2015-08-16
    Description: The thermal performance of a disc-shaped heat generation body with cooling channels is investigated by using constructal theory based on previous model of heat convection on a disc and previous analytical method of heat conduction on a disc. By taking minimum dimensionless maximum thermal resistance as optimization objective, the optimal aspect ratio of the elemental sector in the radial-pattern disc is obtained for the specified power pumping of the elemental sector; the optimal width ratio of the first-order and elemental cooling channels and the optimal dimensionless radius of the elemental sector are obtained for the specified power pumping of the disc. There exists a critical radius of the disc to determine whether the radial-pattern design and branched-pattern design should be adopted. These conclusions are different from those obtained by Wechsatol et al. 's model, and the essential reason for these differences is that the power pumping is specified in this article, but not the specified flow rate number in Wechsatol et al. 's model. Finally, the assumption about the heat capacity of the coolant and the thermal conductivity of the disc is validated. An analytical method is introduced in this article, which can provide another thought for the constructal optimization of disc with heat convection. The optimal constructs of the discs are obtained for the specified power pumping, which provides some different guidelines for the design of disc with heat convection.
    Keywords: Other low-carbon energy technologies
    Print ISSN: 1748-1317
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  • 44
    Publication Date: 2015-08-16
    Description: In this paper, solar box cookers with ordinary and finned absorber plates are theoretically investigated in terms of thermodynamic performance parameters. For a typical summer and winter day, temperatures of solar cooker components such as glass cover, internal air, absorber plate, cooking vessel and the liquid are determined theoretically versus time. The analysis is carried out for conventional and finned absorber plates, and accuracy of the results is verified by a previously published experimental work. Energy and exergy efficiencies of box-type solar cookers are plotted versus time for various cases. The methodology presented in this paper enables to make a preliminary evaluation of ordinary and modified solar box cookers with respect to changes in main environmental parameters such as temperature and illumination intensity. Some recommendations are also made to enhance the power outputs of the aforementioned solar cookers.
    Keywords: Solar energy technologies
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  • 45
    Publication Date: 2015-08-16
    Description: The sun is the more plentiful source of natural power that we have in the Earth. However, the amount of radiation reaching the Earth's surface depends on astronomical and climatic factors. One of the factors exerting a greater influence is cloudiness. For that reason, it is important to quantify its influence on solar radiation. According to that, in this work, a prototype to capture images of the celestial vault is designed and implemented to be able to measure parameters related to the cloud properties and, later, to determine their influence on solar radiation.
    Keywords: Solar energy technologies
    Print ISSN: 1748-1317
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  • 46
    Publication Date: 2015-08-16
    Description: Under transient climatic conditions, solar water heaters using heat pipes are more effective at capturing incident solar radiation than other equivalent sized solar water heaters. The cost must be reduced to improve uptake of such systems. To investigate two methods were considered by this study: thermosyphon fluid flow and reflective concentrators. A physical reconfigurable laboratory model of the manifold and associated condensers of a heat-pipe-evacuated tube system were fabricated; fluid circulation was via thermosyphonic action, particle imaging velocimetry derived velocity maps and the use of concentrators was simulated. When condenser spacing was doubled, the Nusselt number increased by 43%, the velocity by 55% but the heat transfer efficiency of the model manifold decreased by 9%. Potential annual energy savings of 10 207 GWh could be realized if such systems could be successfully fabricated.
    Keywords: Solar energy technologies
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  • 47
    Publication Date: 2015-08-16
    Description: This paper presents the results of two field studies to examine the differences in ambient temperatures in a micro-scale environment (at distances of 50–200 m between measuring points) in two different climates during typical summer weather conditions at two similar sites in terms of construction and activities. The analysis considered the land use around the measuring locations split into three categories (built, green and open) as well as climatic conditions and studied the effect of these on ambient temperature at each measuring location. It was found that, similarly to macro-scale studies at the urban level, measuring locations with a higher green cover have a lower ambient temperature compared with measuring locations with a higher built and/or open land cover. The results provide measured evidence in two different climates that small green areas distributed within the urban environment can provide a reduction in the ambient temperature thus contributing to the mitigation of urban heat island.
    Keywords: Built environment and low-carbon society
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  • 48
    Publication Date: 2015-08-16
    Description: Capillary pump loop (CPL) is a two-phase heat transfer device considered as a useful solution for thermal control applications in spacecrafts, satellites and electronic components. The purpose of this paper is to study various aspects of the working state of the CPL evaporator. A two-dimensional computational model was developed in order to analyze the flow and the phase transformation inside a cylindrical evaporator. At the present analysis, different cases were studied by changing liquid saturation temperature, inclination angle of the evaporator and the length of the porous heated wick. Water, ammonia, acetone and freon-134 were used as working liquids for numerical experiments. Results present the evaporator capability to vaporize each working liquid and find out its possibility of dry-out causing failure. This information is useful in choosing the best working liquid for an evaporator, enabling bigger amounts of heat to be transferred.
    Keywords: Other low-carbon energy technologies
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  • 49
    Publication Date: 2015-08-16
    Description: In recent years, the concept of green building is becoming popular in China. Architects and engineers have the opportunity to actually implement green building practices. This paper reveals the failure of a naturally ventilated LEED-certified townhouse development project in China mentioned in recent research. The house owners made great alterations for the purpose of decoration, which removed or minimized the effectiveness of natural ventilation elements in the original design. The research shows that the houses show ‘International Style’ because the natural ventilation design principles were not fully applied in the design and the localized natural ventilation strategies were not fully considered by means of computational simulation in the design stage. Also, the lack of communication between designers and the owners caused the removal of most natural ventilation elements of these houses during the occupancy period. The authors advocate three criteria to avoid failures of natural ventilation design: localized/ climate adaptive design, relationship among design elements and design intention awareness.
    Keywords: Sustainable/low carbon buildings
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  • 50
    Publication Date: 2015-08-16
    Description: In the present paper, design of solar chimney (SC) and earth-to-air heat exchanger (EAHE) to meet the thermal need of flat buildings are studied regarding adaptive thermal comfort criteria. Investigation on the effects of geometric features shows that the design of SC with the air gap and outlet sizes of 0.2 m and also EAHE with the diameter and length of 0.5 and 25.0 m reveals better performance. Thermal comfort analysis shows that the SC is capable to power the underground heating system during few hours of the sunny days even at the ambient temperature as low as 0°C and the heating demand of 1000 W without needing the auxiliary devices. In addition, the required numbers of SCs and the underground air channels are strongly influenced by environmental outdoor conditions and heating demand of building and are approximately calculated by: $$\hbox{ room }\phantom{\rule{0.08em}{0ex}}\hbox{ volume/50 }\phantom{\rule{0.08em}{0ex}}\hbox{ and }\phantom{\rule{0.08em}{0ex}}\hbox{ 2 }\times (\hbox{ room }\phantom{\rule{0.08em}{0ex}}\hbox{ volume/50 })+\hbox{ 1, }$$ respectively.
    Keywords: Other low-carbon energy technologies
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  • 51
    Publication Date: 2015-08-16
    Description: Daylighting has an important role in sustainable architecture as it affects the energy consumption in a building. Especially for an office building, daylight helps not only to reduce the load on artificial lighting but also to promote work efficiency through promoting good human health, well-being and user comfort. The objective of this research is to develop an innovative façade design strategy that comes from the development of digital technology and dynamic daylight performance measuring methods. Thus, the various parameters are studied through the computational process of cellular automata (CA) to generate the several alternative opening patterns on the building façade. Each CA design value was tested under static and dynamic sky condition to analyze the quality and quantity of daylight and visual comfort throughout the year. The results were compared to find an optimum alternative design in terms of the daylighting design criteria, from building code, standard and design guidelines for the office building. Finally, research of an adaptive façade design strategy was concluded with the results from the above hybridization of generative and performative design methodology. This study discovers the architectural design approach from the CA and it will make not only progress in building façade esthetics, but also human comfort with building sustainability.
    Keywords: Sustainable/low carbon buildings
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  • 52
    Publication Date: 2015-09-15
    Description: This paper presents the development of an adaptive state estimator and an output controller based on the attractive ellipsoid method (AEM) for a class of uncertain non-linear systems (quasi-Lipschitz with external perturbations). The proposed method guarantees that, under a specific persistent excitation condition, the controlled system trajectories converge to an ellipsoid having a smaller trace of the corresponding inverse ellipsoidal matrix comparing to classical AEM without adaptation. An underactuated vertical double pendulum is considered as an experimental illustrative example of the suggested approach.
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  • 53
    Publication Date: 2015-09-15
    Description: In this paper, non-linear time-varying systems with slowly varying parameters are considered. Using slowly varying control Lyapunov function and considering a cost function, a controller (with closed-form structure) is presented which guarantees asymptotic stability of the closed-loop non-linear slowly varying system. Moreover, the Hamilton–Jacobi–Bellman equation is analysed to show that the proposed controller is a sub-optimal controller and the response of the closed-loop system may be very close to its optimal solution. Additionally, in order to show the applicability of the proposed method, it is applied to the time-varying inertia pendulum, which is one of the famous benchmarks among the non-linear time-varying systems. Then, the efficiency of the designed controller is compared with that of a numerical optimal controller, which is called, ‘receding horizon generalization of point-wise min-norm controller’. Simulation results demonstrate the applicability and efficiency of the proposed method.
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  • 54
    Publication Date: 2015-09-15
    Description: This paper addresses the problem of designing a static output feedback sliding mode control algorithm for linear MIMO systems with mismatched parameter uncertainties and matched perturbations. Once the system is in the sliding mode, the proposed output-dependent sliding variable can guarantee robust stability of the closed-loop system. The existence condition of the sliding variable is determined by solving the coupled algebraic Riccati equations which are involved with the original system parameters. The developed control law having the min–max property can guarantee that the system states are globally driven to and are finally maintained on the sliding variable in finite time. The high-gain control problem can be effectively avoided. The feasibility of the proposed method is demonstrated by simulation results.
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  • 55
    Publication Date: 2015-09-15
    Description: The objective of this paper is to study the notion of regional observability of a distributed parameter system governed by semilinear hyperbolic equations. This original concept is interested in the reconstruction of the state only on a subregion of the boundary of the system evolution domain . We give definition and some properties of this notion and we show that under some hypothesis, the regional boundary observability is guarantied. We use the analytical case by sectorial property of the considered dynamic operator and converted to a fixed point problem, and we show that it is possible to reconstruct such a state on a desired subregion . This approach leads to interesting results which are performed through numerical example and simulations.
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  • 56
    Publication Date: 2015-09-15
    Description: This paper deals with the distributed robust output regulation problem for the multi-agent systems with general nonlinear dynamics and uncertainty parameters. Assume that the information of active leaders or environmental disturbances cannot be completely measurable for all other agents. By employing the centre manifold theory and characteristics of the agents’ communication, the nonlinear distributed dynamic feedback controllers are designed to make the agents asymptotically track the references or reject the disturbance signals, which are generated by the exosystem. Two numerical examples are provided to show the effectiveness of the main results.
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  • 57
    Publication Date: 2015-09-15
    Description: This paper investigates event-triggered leaderless and leader-following consensus problems of multi-agent systems under jointly connected topology. A state-dependent event condition is proposed for each agent, which only relies on its own state and the last sampled data of itself and its neighbours. Based on the Lyapunov technique and algebraic graph theory, the designed event-triggered control strategies are proved to solve the leaderless and leader-following consensus problems when the topology is jointly connected. Moreover, such strategies can exclude Zeno-behaviour. Simulations illustrate the effectiveness of the theoretical results.
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  • 58
    Publication Date: 2015-09-15
    Description: By the theory of Sturm–Liouville eigenvalue problems, it is shown that the stability of one-dimensional wave equations with variable coefficients coupled with an ordinary differential equation (ODE) system on general tree-shaped networks is equivalent to that of its subsystem (called the base system). Thus, it is proved that the coupled system can arrive at asymptotical stability, if, for every interior vertex of the subsystem, the spectra of any two edges joined one common interior vertex of the subsystem are disjoint. Especially, the coupled system with one fixed root is exponentially stable. In the end, a star with three edges and a tree-shaped networks with 10 edges are given to verify the theoretical results.
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  • 59
    Publication Date: 2015-09-15
    Description: This paper studies the H consensus problem of multi-agent systems by means of a simultaneous stabilization approach. It is shown that the H consensus design problem for n coupled agents can be equivalently characterized as a problem of the simultaneous H stabilization of n – 1 independent subsystems. A new consensus analysis condition is obtained by investigating the corresponding simultaneous H stabilization problem. Based upon the analysis condition, a necessary and sufficient condition is derived to guarantee the consensus of multi-agent systems with a prescribed H performance, where the controller gain matrix is not coupled with the Lyapunov matrices, but parametrized by a positive-definite matrix. Iterative convex optimization approaches are further developed to solve the synthesis condition and to choose the initial values. Finally, a numerical example is given to show the applicability of the results.
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  • 60
    Publication Date: 2015-09-15
    Description: This article is concerned with the controllability of damped second-order impulsive neutral integrodifferential systems with infinite delay in Banach spaces. A set of sufficient conditions for the controllability of such systems are formulated by using a fixed point analysis approach. In particular, the compactness condition on the cosine family of operators appearing in various literatures is not required here. At last, an example is given to illustrate the obtained result.
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  • 61
    Publication Date: 2015-09-15
    Description: We consider an approximation scheme using hybrid functions for solving time-delayed optimal control problems with terminal inequality constraints. Using a Páde approximation, the problem is first transformed into one without a time-delayed argument. A computational method based on hybrid functions in time-domain is then proposed for solving the obtained non-delay optimal control problem. Hybrid functions integral operational matrix and direct collocation method are utilized to find the approximated optimal trajectory and the optimal control law of the original problem. Numerical results are also given to demonstrate the efficiency of the method.
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  • 62
    Publication Date: 2015-09-15
    Description: This paper investigates the problem of D-stability performance of an L 2 point formation control system with parametric uncertainties. A Quasi linear parameter varying (QLPV) model is introduced for the L 2 point formation flying, based on which a nonlinear control strategy is developed via the polynomial eigenstructure assignment (PEA) approach. The designed controller can guarantee the closed-loop system with invariant performance over a wide range of conditions due to its special structure with varying parameters. The robust D-stability of the multiple input and multiple output (MIMO) system is also addressed. It is shown that the D-stability performance of the L 2 point formation control system with parametric uncertainties can be ensured by using PEA controller. Finally, a simulation of formation flying is performed to illustrate the effectiveness of the proposed control approach.
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  • 63
    Publication Date: 2015-09-15
    Description: This paper considers an optimal control problem for switched stochastic systems. The controlled parameter consists of the switching times, and the cost criterion has the form of the mixed integral and endpoint cost terms of performance functions defined on the system's state trajectory. An approach to finding the optimal switching times is proposed. First, we derive the derivative of the cost with respect to the switching time for one switching time case. Then, for the problem with multi-switching times, we present the corresponding gradient formula. The obtained formulas have an especially simple form and can be directly used in gradient descent algorithms to locate the optimal switching instants. Finally, the validity of the proposed method is demonstrated by two numerical examples.
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  • 64
    Publication Date: 2015-09-19
    Description: We compute the algebraic $K$ -theory of the non-commutative ring $k\langle x_1,\ldots ,x_n \rangle /(m^a)$ when $k$ is a perfect field of positive characteristic and $m=(x_1,\ldots ,x_n)$ . We express the answer in terms of the truncation poset Witt vectors developed in Angeltveit [‘Witt vectors and truncation posets’, Preprint, 2014, arXiv:1409.4156].
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  • 65
    Publication Date: 2015-09-19
    Description: In this paper, we investigate the exactness of the Grassmannian Bernstein-Gel’fand-Gel’fand complexes introduced in a previous work of the author, and obtain some inequalities between some Hodge numbers of some irregular varieties. In particular, we obtain sharp lower bounds for the Hodge numbers of smooth subvarieties of Abelian varieties, as well as some improvements of results of Lazarsfeld-Popa and Lombardi concerning threefolds and fourfolds.
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  • 66
    Publication Date: 2015-09-19
    Description: We prove that every finitely presented group with positive first $\ell ^2$ -Betti number that virtually surjects onto $\mathbb Z$ is acylindrically hyperbolic. In particular, this implies acylindrical hyperbolicity of finitely presented residually finite groups with positive first $\ell ^2$ -Betti number as well as groups of deficiency at least $2$ .
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  • 67
    Publication Date: 2015-09-19
    Description: We give an elementary proof of Iyama–Yoshino's classification of rigid maximal Cohen-Macaulay modules on Veronese embeddings in $\mathbb P ^9$ .
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  • 68
    Publication Date: 2015-09-19
    Description: The virtual dimensions of both framed and unframed SU(2) magnetic monopoles on asymptotically conic 3-manifolds are obtained by computing the index of a Fredholm extension of the associated deformation complex. The unframed dimension coincides with the one obtained by Braam for conformally compact 3-manifolds. The computation follows from the application of a Callias-type index theorem.
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  • 69
    Publication Date: 2015-09-19
    Description: Let $f : (\mathbb {C}^n, 0) \rightarrow (\mathbb {C}, 0)$ be a semiquasihomogeneous function. We give a formula for the local Łojasiewicz exponent ${\mathcal L}_0 (f)$ of $f$ , in terms of weights of $f$ . In particular, in the case of a quasihomogeneous (QH) isolated singularity $f$ , we generalize a formula for ${\mathcal L}_0 (f)$ of Krasiłski, Oleksik and Płoski from 3 to $n$ dimensions. This was previously announced in the paper [ 19 ] of Tan, Yau and Zuo [Łojasiewicz inequality for weighted homogeneous polynomial with isolated singularity, Proc. Amer. Math. Soc. 138 (2010) 3975–3984], but as a matter of fact it was not proved correctly there, as noted by the AMS reviewer Tadeusz Krasiłski. As a consequence of our result, we obtain that the Łojasiewicz exponent is invariant in topologically trivial families of singularities coming from a QH germ. This is an affirmative partial answer to Teissier's conjecture.
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  • 70
    Publication Date: 2015-09-19
    Description: We show that the complement of the closure of the coamoeba of a variety of codimension $k + 1$ is $k$ -convex, in the sense of Gromov and Henriques. This generalizes a result of Nisse for hypersurface coamoebas. We use this to show that the complement of the nonarchimedean coamoeba of a variety of codimension $k + 1$ is $k$ -convex.
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  • 71
    Publication Date: 2015-09-19
    Description: We prove an analog of Lagrange's theorem for continued fractions on the Heisenberg group: points with an eventually periodic continued fraction expansion are those that satisfy a particular type of quadratic form, and vice-versa.
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  • 72
    facet.materialart.
    Unknown
    Oxford University Press
    Publication Date: 2015-09-19
    Description: Let $(M^n, g)$ be a compact $n$ -dimensional ( $n\geq 2$ ) manifold with nonnegative Ricci curvature, and if $n\geq 3,$ then we assume that $(M^n, g)\times \mathbb {R}$ has nonnegative isotropic curvature. The lower bound of the Ricci flow's existence time on $(M^n, g)$ is proved. This provides an alternative proof for the uniform lower bound of a family of closed Ricci flows' maximal existence times, which was first proved by E. Cabezas-Rivas and B. Wilking. We also get an interior curvature estimate for $n= 3$ under ${\rm Rc}\geq 0$ assumption among others. Combining these results, we proved the short-time existence of the Ricci flow on a large class of three-dimensional open manifolds, which admit some suitable exhaustion covering and have nonnegative Ricci curvature.
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  • 73
    Publication Date: 2015-09-19
    Description: Given any $\varepsilon 〉 0$ , we construct an orthonormal system of $n_k$ uniformly bounded polynomials of degree at most $k$ on the unit sphere in $\mathbb {R}^{m+1}$ where $n_k$ is bigger than $1-\varepsilon $ times the dimension of the space of polynomials of degree at most $k$ . Similarly, we construct an orthonormal system of sections of powers $A^k$ of a positive holomorphic line bundle on a compact Kähler manifold with cardinality bigger than $1-\varepsilon $ times the dimension of the space of global holomorphic sections to $A^k$ .
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  • 74
    Publication Date: 2015-09-19
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  • 75
    Publication Date: 2015-09-19
    Description: We prove that if $\mu $ is a Radon measure on the Heisenberg group $\mathbb {H}^n$ such that the density $\Theta ^s(\mu ,\cdot )$ , computed with respect to the Korányi metric $d_H$ , exists and is positive and finite on a set of positive $\mu $ measure, then $s$ is an integer. The proof relies on an analysis of uniformly distributed measures on $(\mathbb {H}^n,d_H)$ . We provide a number of examples of such measures, illustrating both the similarities and the striking differences of this sub-Riemannian setting from its Euclidean counterpart.
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  • 76
    Publication Date: 2015-09-19
    Description: Let $d 〉 1$ be an integer. In 1986, Shen defined a class of weight modules $F^\alpha _b(V)$ over the Witt algebra $\mathcal {W}_d$ for $\alpha \in {\mathbb C} ^d$ , $b\in {{\mathbb C}}$ , and an irreducible module $V$ over the general linear Lie algebra $\mathfrak {gl} _d$ on which the identity matrix acts as multiplication by $b$ . In 1996, Eswara Rao determined necessary and sufficient conditions for these modules to be irreducible when $V$ is finite-dimensional. In this note, we will determine necessary and sufficient conditions for all these modules $F^\alpha _b(V)$ to be irreducible where $V$ is not necessarily finite-dimensional. In this way, we obtain a large new family of irreducible $\mathcal {W}_d$ -modules with infinite-dimensional weight spaces.
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  • 77
    Publication Date: 2015-09-19
    Description: Using the Bockstein spectral sequence developed previously by the authors, we compute the ring $ER(n)^\ast (BO(q))$ explicitly. We then use this calculation to show that the ring spectrum $MO[2^{n+1}]$ is $ER(n)$ -orientable (but not $ER(n+1)$ -orientable), where $MO[2^{n+1}]$ is defined as the Thom spectrum for the self-map of $BO$ given by multiplication by $2^{n+1}$ .
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  • 78
    Publication Date: 2015-09-19
    Description: The commuting probability of a finite group is defined to be the probability that two randomly chosen group elements commute. Let ${{\mathcal P}}\subset (0,1]$ be the set of commuting probabilities of all finite groups. We prove that every point of ${{\mathcal P}}$ is nearly an Egyptian fraction of bounded complexity. As a corollary, we deduce two conjectures of Keith Joseph from 1977: all limit points of ${{\mathcal P}}$ are rational, and ${{\mathcal P}}$ is well ordered by $ 〉 $ . We also prove analogous theorems for bilinear maps of abelian groups.
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  • 79
    Publication Date: 2015-09-19
    Description: The class of elastic bodies, that is bodies incapable of dissipation in whatever motion that they undergo, has been significantly enlarged recently (see Rajagopal 2003, On implicit constitutive theories. Appl. Math. , 48 , 279–319; Rajagopal 2007, The elasticity of elasticity. Z. Angew. Math. Phys. 58 , 309–317; Rajagopal, K. R. & Srinivasa, A. R. 2007, On the response of non-dissipative solids. Proc. R. Soc. Lond. A , 463 , 357–367). The new classes include fully implicit constitutive relations for the stress and the deformation gradient, and the interesting sub-class wherein the Cauchy–Green tensor or the linearized strain tensor bears a non-linear relationship to the stress. While a fully thermodynamic treatment of such elastic bodies, when defined through implicit constitutive relations between the Piola stress and the Green–St. Venant strain, within a 3D framework has been carried out (see Rajagopal, K. R. & Srinivasa, A. R. 2007, On the response of non-dissipative solids, Proc. R. Soc. Lond. A , 463 , 357–367), other possible implicit relationships between other stress and kinematic measures have not been investigated. This paper is devoted to the determination of the consequences of thermodynamics on the new class of elastic bodies, when they are expressed through implicit relations for different stress and stretch/strain measures.
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  • 80
    Publication Date: 2015-09-19
    Description: This work investigates the existence and non-existence of travelling wave solutions for Kolmogorov-type delayed lattice reaction–diffusion systems. Employing the cross iterative technique coupled with the explicit construction of upper and lower solutions in the theory of quasimonotone dynamical systems, we can find two threshold speeds $c^* $ and $c_* $ with $c^* \geq c_* 〉 0.$ If the wave speed is greater than $c^* ,$ then we establish the existence of travelling wave solutions connecting two different equilibria. On the other hand, if the wave speed is smaller than $c_* ,$ we further prove the non-existence result of travelling wave solutions. Finally, several ecological examples including one-species, two-species and three-species models with various functional responses and time delays are presented to illustrate the analytical results.
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  • 81
    Publication Date: 2015-09-19
    Description: In this paper, sufficient criteria for global asymptotic stability of a general stochastic non-autonomous Lotka–Volterra system with infinite delays are established. Then these criteria are applied to a competitive system, a predator–prey system and a cooperative system to demonstrate their applicability and effectiveness. Some recent results are extended and improved.
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  • 82
    Publication Date: 2015-09-19
    Description: In the paper, the problem of existence of almost periodic solutions to non-linear impulsive systems of Caputo fractional order is addressed. Sufficient conditions for stability of almost periodic solutions are also established. The investigations are carried out by using of a fractional comparison principle and the Lyapunov's function method. We apply our results to an impulsive cellular neural network model of fractional order.
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  • 83
    Publication Date: 2015-09-20
    Description: We prove the $L_p$ Poincaré inequalities with constant $C\sqrt {p}$ for $1$ -cocycles on countable discrete groups under Bakry–Émery's $\Gamma _2$ -criterion. These inequalities determine an analog of subgaussian behavior for 1-cocycles. Our theorem improves some of our previous results in this direction, and in particular implies Efraim and Lust-Piquard's Poincaré-type inequalities for the Walsh system. The key new ingredient in our proof is a decoupling argument. As complementary results, we also show that the spectral gap inequality implies the $L_p$ Poincaré inequalities with constant $C{p}$ under some conditions in the noncommutative setting. New examples which satisfy the $\Gamma _2$ -criterion are provided as well.
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  • 84
    Publication Date: 2015-09-20
    Description: A real irrational toric variety $X$ is an analytic subset of the simplex associated to a finite configuration of real vectors. The positive torus acts on $X$ by translation, and we consider limits of sequences of these translations. Our main result identifies all possible Hausdorff limits of translations of $X$ as toric degenerations using elementary methods and the geometry of the secondary fan of the vector configuration. This generalizes work of García-Puente et al. , who used algebraic geometry and work of Kapranov, Sturmfels and Zelevinsky, when the vectors were integral.
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  • 85
    Publication Date: 2015-09-20
    Description: In this paper, we show how to construct examples of closed manifolds with explicitly computed irrational, even transcendental $L^2$ Betti numbers, defined via the universal covering. We show that every non-negative real number shows up as an $L^2$ -Betti number of some covering of a compact manifold, and that many computable real numbers appear as an $L^2$ -Betti number of a universal covering of a compact manifold (with a precise meaning of computable given below). In algebraic terms, for many given computable real numbers (in particular for many transcendental numbers) we show how to construct a finitely presented group and an element in the integral group ring such that the $L^2$ -dimension of the kernel is the given number. We follow the method pioneered by Austin [‘Rational group ring elements with kernels having irrational dimension’, Proc. London Math. Soc. (3) 107 (2013) 1424–1448], but refine it to get explicit calculations which make the above statements possible.
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  • 86
    Publication Date: 2015-09-20
    Description: In this paper, it is proved that one can find imaginary quadratic fields with class number not divisible by a specified prime $l$ and with certain specified splitting conditions at a finite number of primes. Such existence theorems are useful in the arithmetic of elliptic curves and, potentially, also in certain lifting problems for reducible two-dimensional Galois representations. The methods used are a blend of geometry and the theory of modular forms, especially the trace formula.
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  • 87
    Publication Date: 2015-09-20
    Description: Gronwall area formula can be used to express the area of the filled Julia set of connected quadratic Julia sets. Using parabolic enrichment, it is shown that there is no approximation of this formula by partial sums which is uniform along the boundary of the main cardioid of the Mandelbrot set.
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  • 88
    Publication Date: 2015-09-20
    Description: Investigating properties of two-dimensional Dirac operators coupled to an electric and a magnetic field (perpendicular to the plane) requires in general unbounded (vector-) potentials. If the system has a certain symmetry, then the fields can be described by one-dimensional potentials $V$ and $A$ . Assuming that $|A| 〈 |V|$ outside some arbitrary large ball, we show that absolutely continuous states of the effective Dirac operators spread ballistically. These results are based on well-known methods in spectral dynamics together with certain new Hilbert–Schmidt bounds. We use Lorentz boosts to derive these new estimates.
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  • 89
    Publication Date: 2015-09-20
    Description: We show that if $p$ is an odd prime and $G$ is a finite group satisfying the condition that $p^2$ divides the degree of no irreducible character of $G$ , then $|G:\mathbf {O}_p (G)|_p \le p^4,$ where $\mathbf {O}_p (G)$ is the largest normal $p$ -subgroup of $G$ , and if $P$ is a Sylow $p$ -subgroup of $G$ , then $P''$ is subnormal in $G$ . Our investigations suggest that if $p^a$ is the largest power of $p$ dividing the degrees of irreducible characters of $G$ , then $|G:\mathbf {O}_p(G)|_p$ is bounded by $p^{f(a)},$ where $f (a)$ is a function in $a$ and $P^{(a+1)}$ is subnormal in $G$ .
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  • 90
    Publication Date: 2015-09-20
    Description: Let the circle act effectively in a Hamiltonian fashion on a compact symplectic manifold $(M, \omega )$ . Assume that the fixed point set $M^{S^1}$ has exactly two components, $X$ and $Y$ , and that $\dim (X) + \dim (Y) +2 = \dim (M)$ . We first show that $X$ , $Y$ and $M$ are simply connected. Then we show that, up to $S^1$ -equivariant diffeomorphism, there are finitely many such manifolds in each dimension. Moreover, we show that in low dimensions, the manifold is unique in a certain category. We use techniques from both areas of symplectic geometry and geometric topology.
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  • 91
    Publication Date: 2015-09-20
    Description: In this article, we study optimization problems ruled by fractional diffusion operators with volume constraints. By means of penalization techniques, we prove existence of solutions. We also show that every solution is locally of class $C^{0,\alpha }$ (optimal regularity), and that the free boundary is a $C^{1,\gamma }$ surface, up to an $\mathcal {H}^{n-1}$ -negligible set.
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  • 92
    Publication Date: 2015-09-20
    Description: Let $\psi$ and $F$ be positive-definite forms with integral coefficients of equal degree. Using the circle method, we establish an asymptotic formula for the number of identical representations of $\psi$ by $F$ , provided that $\psi$ is everywhere locally representable and the number of variables of $F$ is large enough. In the quadratic case, this supersedes a recent result due to Dietmann and Harvey. Another application addresses the number of primitive linear spaces contained in a hypersurface.
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  • 93
    Publication Date: 2015-09-20
    Description: We explain how the work of Johnson-Leung and Roberts on lifting Hilbert modular forms for real quadratic fields to Siegel modular forms can be adapted to imaginary quadratic fields. For this, we use archimedean results from Harris, Soudry and Taylor and replace the global arguments of Roberts by the non-vanishing result of Takeda. As an application of our lifting result, we exhibit an abelian surface $B$ defined over $\mathbb {Q}$ , which is not a restriction of scalars of an elliptic curve and satisfies the paramodularity Conjecture of Brumer and Kramer.
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  • 94
    Publication Date: 2015-09-20
    Description: Hassett's moduli spaces of weighted stable curves form an important class of alternate modular compactifications of the moduli space of smooth curves with marked points. In this article, we define a tropical analog of these moduli spaces, and show that the naive set-theoretic tropicalization map can be identified with a natural deformation retraction onto the non-Archimedean skeleton. This result generalizes work of Abramovich, Caporaso, and Payne treating the Deligne–Knudsen–Mumford compactification of the moduli space of smooth curves with marked points. We also study tropical analogs of the tautological maps, investigate the dependence of the tropical moduli spaces on the weight data, and consider the example of Losev–Manin spaces.
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  • 95
    facet.materialart.
    Unknown
    Oxford University Press
    Publication Date: 2015-09-22
    Description: We present a proof system for the provability logic GLP in the formalism of nested sequents and prove the cut elimination theorem for it. As an application, we obtain the reduction of GLP to its important fragment called J syntactically.
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  • 96
    Publication Date: 2015-09-22
    Description: Intuitionistic sentential logic is shown to be sound and complete with respect to a semantics centered around extensions of atomic bases (i.e. sets of inference rules for atomic sentences). The result is made possible through a non-standard interpretation of disjunction, whereby, roughly speaking, a disjunction is taken to hold just in case every atomic sentence that follows from each of the disjuncts separately holds; it is argued that this interpretation makes good sense provided that rules in atomic bases are conceived of as being accepted hypothetically rather than categorically.
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  • 97
    Publication Date: 2015-09-22
    Description: Motivated by both established and new applications, we study navigational query languages for graphs (binary relations). The simplest language has only the two operators union and composition, together with the identity relation. We make more powerful languages by adding any of the following operators: intersection; set difference; projection; coprojection; converse; transitive closure; and the diversity relation. All these operators map binary relations to binary relations. We compare the expressive power of all resulting languages, both for binary-relation queries as well as for boolean queries. In the absence of transitive closure, a complete Hasse diagram of relative expressiveness has already been established [ 8 ]. Moreover, it has already been shown that for boolean queries over a single edge label, transitive closure does not add any expressive power when only projection and diversity may be present [ 11 ]. In the present article, we now complete the Hasse diagram in the presence of transitive closure, both for the case of a single edge label, as well as for the case of at least two edge labels. The main technical results are the following: (1) In contrast to the above-stated result [ 11 ] transitive closure does add expressive power when coprojection is present. (2) Transitive closure also adds expressive power as soon as converse is present. (3) Conversely, converse adds expressive power in the presence of transitive closure. In particular, the converse elimination result from [ 8 ] no longer works in the presence of transitive closure. (4) As a corollary, we show that the converse elimination result from [ 8 ] necessitates an exponential blow-up in the degree of the expressions.
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  • 98
    Publication Date: 2015-09-22
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  • 99
    Publication Date: 2015-09-22
    Description: Many authors have argued that, when performing simultaneous statistical test procedures, one should seek for solutions that lead to decisions that are consistent and, consequently, easier to communicate to practitioners of statistical methods. In this way, the set of hypotheses that are rejected and the set of hypotheses that are not rejected by a testing procedure should be consistent from a logic standpoint. For instance, if hypothesis A implies hypothesis B , a procedure that rejects B should also reject A , a property not always met by multiple test procedures. We contribute to this discussion by exploring how far one can go in constructing coherent procedures while still preserving statistical optimality. This is done by studying four types of logical consistency relations. We show that although the only procedures that satisfy more than (any) two of these properties are simple tests based on point estimation, it is possible to construct various interesting methods that fulfil one or two of them while preserving different statistical optimality criteria. This is illustrated with several Bayesian and frequentist examples. We also characterize some of these properties under a decision-theoretic framework.
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  • 100
    Publication Date: 2015-09-22
    Description: Derivationists, those wishing to explain the correctness and rigour of informal proofs in terms of associated formal proofs, are generally held to be supported by the success of the project of translating informal proofs into computer-checkable formal counterparts. I argue, however, that this project is a false friend for the derivationists because there are too many different associated formal proofs for each informal proof, leading to a serious worry of overgeneration. I press this worry primarily against Azzouni's derivation-indicator account, but conclude that overgeneration is a major obstacle to a successful account of informal proofs in this direction.
    Print ISSN: 0031-8019
    Electronic ISSN: 1744-6406
    Topics: Mathematics , Philosophy
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