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  • 1
    Publikationsdatum: 2016-07-15
    Beschreibung: Direct evidence of the relationship between the polymorphic phase transformation from monoclinic Cu 6 Sn 5 to hexagonal Cu 6 Sn 5 and stress accumulation/release in Cu 6 Sn 5 , formed at the interface between Sn-0.7Cu lead-free solder and their Cu substrates, has been obtained. To explore this challenging phenomenon, we developed an in situ heating/isothermal observation technique in ultrahigh-voltage transmission electron microscopy that enables the observation of thick samples (around 0.5  μ m) for solder joints, including Cu/Cu 3 Sn/Cu 6 Sn 5 /Sn-0.7Cu solder interfaces prepared by a focused ion beam milling technique. The results show evidence of stress creation and release events by imaging bend contours that may arise due to the polymorphic transformations of the Cu 6 Sn 5 phase and the associated volumetric change.
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  • 2
    Publikationsdatum: 2016-07-15
    Beschreibung: Effects of temperature and slag basicity on the reduction rate of iron oxide in molten synthetic electric arc furnace oxidizing slag by Al-40 wt.%Fe alloy was investigated. An alloy sample was dropped into molten slag in an MgO crucible. When the initial slag temperature was 1723 K, there was no reduction. However, when the initial slag temperature was 1773 K and the slag basicity was 1.1, the reduction was initiated and the temperature of the slag rapidly increased. When the slag basicity was 1.1, increasing the initial slag temperature from 1773 K to 1823 K increases the reaction rate. As the slag basicity increased from 1.1 to 1.4 at 1773 K, the reaction rate increased. From SEM analysis, it was found that an Al 2 O 3 or a spinel phase at the slag-metal interface inhibited the reaction at a lower temperature and a lower slag basicity.
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  • 3
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
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    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
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  • 4
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: This paper presents a method to estimate steady wind and a maneuvering strategy for loitering under a strong, steady wind. The wind estimation uses Global Positioning System velocity only through a novel filter design without airspeed measurement. The wind estimate is then used to guide the aircraft to crab in a direction perpendicular to the wind, thereby avoiding large changes in flight variables if an orbit-type maneuver is attempted. The proposed method is demonstrated through flight tests.
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    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
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  • 5
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: We propose biased estimators to find the direction of arrival of emitters present in the mainlobe of a spinning antenna-based electronic intelligence system. The proposed estimators were constructed by using Bayesian techniques and by performing a linear transformation and an affine transformation on the maximum likelihood estimator. From a Monte Carlo simulation and experimental results, we demonstrate that the proposed estimators outperform the limit set by the popular performance benchmark, the Cramer-Rao lower bound.
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  • 6
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: A new method was proposed for chirp signal detection and estimation built on the frame-based fast Fourier transform (FFT). The proposed method uses the peak frequency difference between FFT frames to detect a chirp signal and estimate chirp rate. This approach differs from conventional methods and is easy to implement. It generates more accurate chirp rate estimation especially under a low signal-to-noise ratio. Simulation and experimental data are used to verify the proposed methods.
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  • 7
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: The quasimaximum likelihood (QML) estimator of polynomial-phase signals (PPSs) is based on the maximization of the short-time Fourier transform and suffers from aliasing when signals are sampled below the Nyquist sampling rate. In this paper, a phase unwrapping procedure has been proposed as an additional step in the QML to estimate parameters of such signals. Statistical study has shown excellent performance of the proposed approach.
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  • 8
    Publikationsdatum: 2016-07-20
    Beschreibung: TiN and (Ti,Mg)N thin film coatings were deposited on Ti substrates by an arc-physical vapor deposition technique. The effect of cell presence on hydroxyapatite (HA) formation was investigated using surfaces with four different Mg contents (0, 8.1, 11.31, and 28.49 at.%). Accelerated corrosion above 10 at.% Mg had a negative effect on the performance in terms of both cell proliferation and mineralization. In the absence of cells, Mg-free TiN coatings and low-Mg (8.1 at.%)-doped (Ti,Mg)N surfaces led to an early HA deposition (after 7 days and 14 days, respectively) in cell culture medium (DMEM), but the crystallinity was low. More crystalline HA structures were obtained in the presence of the cells. HA deposits with an ideal Ca/P ratio were obtained at least a week earlier, at day 14, in TiN and low-Mg (8.1 at.%)-doped (Ti,Mg)N compared with that of high-Mg-containing surfaces (〉10 at.%). A thicker mineralized matrix was formed on low-Mg (8.1 at.%)-doped (Ti,Mg)N relative to that of the TiN sample. Low-Mg doping (〈10 at.%) into TiN coatings resulted in better cell proliferation and thicker mineralized matrix formation, so it could be a promising alternative for hard tissue applications.
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  • 9
    Publikationsdatum: 2016-07-22
    Beschreibung: The content of TiO 2 has an important influence on both the basic structure and the crystallization behavior of titanium-bearing blast furnace (BF) slag. The results of thermodynamic calculations show that, when the mass content of TiO 2 is smaller than 25%, CaTiO 3 increases as the content of TiO 2 increases. However, when the TiO 2 content is more than 25%, the CaTiO 3 content decreases and TiO 2 gradually increases. The results of a confocal laser scanning microscopy (CLSM) experiment show that, when the TiO 2 mass content is 10%, Ca 2 MgSi 2 O 7 and Ca 2 Al 2 SiO 7 are the main crystallized phases resulting from the molten slag. Furthermore, when the TiO 2 mass content is 20%, CaMgSi 2 O 6 , Ca(Ti,Mg,Al)(Si,Al) 2 O 7 and dendrite CaTiO 3 are the crystallized phases, while when the TiO 2 mass content increases to 30%, CaTiO 3 is the sole phase. The discrepancy between the CLSM results and the thermodynamic calculations occurs mainly due to the high melting point of the titanium-bearing BF slag. During the cooling process for the molten slag, CaTiO 3 is crystallized first, due to its high crystallization temperature. Furthermore, the molten slag is solidified in its entirety before the other phases crystallize.
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  • 10
    Publikationsdatum: 2016-07-22
    Beschreibung: Forest-derived biomaterials can play an integral role in a sustainable and renewable future. Research across a range of disciplines is required to develop the knowledge necessary to overcome the challenges of incorporating more renewable forest resources in materials, chemicals, and fuels. We focus on wood specifically because in our view, better characterization of wood as a raw material and as a feedstock will lead to its increased utilization. We first give an overview of wood structure and chemical composition and then highlight current topics in forest products research, including (1) industrial chemicals, biofuels, and energy from woody materials; (2) wood-based activated carbon and carbon nanostructures; (3) development of improved wood protection treatments; (4) massive timber construction; (5) wood as a bioinspiring material; and (6) atomic simulations of wood polymers. We conclude with a discussion of the sustainability of wood as a renewable forest resource.
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  • 11
    Publikationsdatum: 2016-07-22
    Beschreibung: The AA7050 alloy strips can be successfully prepared by semi-solid powder rolling. The effect and factors of particle size on the microstructure, relative density, and mechanical properties were discussed. The results show that coarse starting powders require less liquid to achieve high relative density, and the formed strips have lower elongation compared with that prepared with the fine starting powders. The strength is more related to defects, whereas elongation partially depends on the grain size. Additionally, the fracture mechanism of strips prepared with fine powders is the ductile fracture because many dimples are observed. For relative density, when the initial liquid fraction is lower than 10%, the difference of deformation degree is the main factor. When the liquid fraction is higher than 10–20%, premature solidification and more particle interfaces are the two main factors.
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  • 12
    Publikationsdatum: 2016-07-23
    Beschreibung: Based on FACTSage® software, this paper focuses on the thermodynamic calculations of selective carbothermal reactions of vanadium-bearing titanomagnetite concentrates for preparing iron-based wear-resistant material directly from vanadium-bearing titanomagnetite concentrates. The calculations show that it was most likely to generate metallic iron, titanium carbide and vanadium carbide among all possible carbothermal reactions of vanadium-bearing titanomagnetite concentrates in a vacuum of 10 Pa. The equilibrium composition calculations indicate that Fe 3 O 4 can be reduced to metallic iron by carbon above 400°C, FeTiO 3 can be converted into TiC by carbon above 800°C and V 2 O 5 can be converted into VC by carbon above 600°C in a vacuum of 10 Pa. The investigations demonstrated that the percentage of ferrous oxides reduced to metallic iron was about 96%, the conversion percentage of FeTiO 3 into TiC was about 75% and the conversion percentage of V 2 O 5 into VC was about 94% after the selective carbothermal reactions of vanadium-bearing titanomagnetite concentrates at 1300°C for 3 h in a vacuum of 10 Pa.
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  • 13
    Publikationsdatum: 2016-07-27
    Beschreibung: Cellulose nanomaterials (CNs) are a new class of cellulose particles with properties and functionalities distinct from molecular cellulose and wood pulp, and as a result, they are being developed for applications that were once thought impossible for cellulosic materials. Momentum is growing in CN research and development, and commercialization in this field is happening because of the unique combination of characteristics (e.g., high mechanical properties, sustainability, and large-scale production potential) and utility across a broad spectrum of material applications (e.g. as an additive, self-sustaining structures, and template structures) that CNs offer. Despite the challenges typical for materials development, CN and near-CN production is ramping up with pilot scale to industry demonstration trials, and the first commercial products are starting to hit the marketplace. This review provides a broad overview of CNs and their capabilities that are enabling new application areas for cellulose-based materials.
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  • 14
    Publikationsdatum: 2016-07-28
    Beschreibung: Novel kinds of nanocomposites based on bisphenol A-aniline based polybenzoxazine matrix P(BA-a) and 0 wt.%–20 wt.% boron carbide (B 4 C) nanoparticles were produced and their properties were evaluated in terms of the nano-B 4 C content. The thermal conductivity of the P(BA-a) matrix was improved approximately three times from 0.18 W/m K to 0.86 W/m K at 20 wt.% nano-B 4 C loading, while its coefficient of thermal expansion (CTE) was deceased by 47% with the same nanofiller content. The microhardness properties were significantly improved by adding the B 4 C nanoparticles. At 20 wt.% of nano-B 4 C content, dynamic mechanical analysis (DMA) revealed a marked increase in the storage modulus and the glass transition temperature ( T g ) of the nanocomposites, reaching 3.9 GPa and 204°C, respectively. Hot water uptake tests showed that the water-resistance of the polybenzoxazine matrix was increased by filling with nano-B 4 C nano-filler. The morphological analysis reflected that the improvements obtained in the mechanical and thermal properties are related to the uniform dispersion of the nano-B 4 C particles and their strong adhesion to the P(BA-a) matrix.
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  • 15
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    Springer
    Publikationsdatum: 2016-07-28
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  • 16
    Publikationsdatum: 2016-07-28
    Beschreibung: This article investigates the development of porosity in titania-rich slag obtained by sintering via conventional and thermal plasma heating at 1000°C in inert atmosphere. The holder in the plasma reactor acted as the discharge anode confined within a hollow graphite cathode. Quantitative evaluation of the porosity in the conventionally sintered and plasma-sintered titania-rich slag was performed via pycnometry. Specifically, the physical dimension and morphology of the pores were characterized according to the area fraction, mean diameter, shape factor, and elongation factor. Under both conventional and thermal plasma heating conditions, porosity developed on the surface of titania-rich slag. The titania-rich slag obtained by two processes showed different porosity features in terms of the morphology and porosity. A lower porosity was observed in the plasma-sintered sample when compared with that obtained via conventional heating.
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  • 17
    Publikationsdatum: 2016-07-28
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  • 18
    Publikationsdatum: 2016-07-28
    Beschreibung: The solubility of lithium metal in molten LiCl–Li 2 O mixtures has been measured at various concentrations of Li 2 O ranging from 0 wt.% to 2.7 wt.% at a temperature of approximately 670–680°C. After contacting molten lithium with molten LiCl–Li 2 O for several hours to achieve equilibrium saturation, samples were taken by freezing the salt onto a room-temperature steel rod and dissolving in water for analysis. Both volume of hydrogen gas generated and volume of titrated HCl were measured to investigate two different approaches to calculating the lithium concentration. There appeared to be no effect of Li 2 O concentration on the Li solubility in the salt. But the results vary between different methods of deducing the amount of dissolved Li. The H 2 collection method is recommended, but care must be taken to ensure all of the H 2 has been included.
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  • 19
    Publikationsdatum: 2016-07-28
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  • 20
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    Springer
    Publikationsdatum: 2016-07-28
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  • 21
    Publikationsdatum: 2016-07-28
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  • 22
    Publikationsdatum: 2016-07-28
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  • 23
    Publikationsdatum: 2016-07-30
    Beschreibung: Decreasing pitch size in electronic packaging has resulted in a drastic decrease in solder volumes. The Sn grain crystallography and fraction of intermetallic compounds (IMCs) in small-scale solder joints evolve much differently at the smaller length scales. A cross-sectional study limits the morphological analysis of microstructural features to two dimensions. This study utilizes serial sectioning technique in conjunction with electron backscatter diffraction to investigate the crystallographic orientation of both Sn grains and Cu 6 Sn 5 IMCs in Cu/Pure Sn/Cu solder joints in three dimensional (3D). Quantification of grain aspect ratio is affected by local cooling rate differences within the solder volume. Backscatter electron imaging and focused ion beam serial sectioning enabled the visualization of morphology of both nanosized Cu 6 Sn 5 IMCs and the hollow hexagonal morphology type Cu 6 Sn 5 IMCs in 3D. Quantification and visualization of microstructural features in 3D thus enable us to better understand the microstructure and deformation mechanics within these small scale solder joints.
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  • 24
    Publikationsdatum: 2016-08-03
    Beschreibung: Free-standing NiCo 2 O 4 @Ni cathodes for aprotic lithium-oxygen batteries were synthesized through a simple hydrothermal process followed by heat treatment in the air. The morphology of the NiCo 2 O 4 deposit changed from nanosheet to nanowire with the increase of hydrothermal time. Further observation revealed that the nanosheet/nanowire NiCo 2 O 4 were assembled by nanoparticles with a size of 10–20 nm. The directional assembly of the nanoparticles were not affected by the reaction time. The influence of catalyst microstructure on the electrochemical performance of Li-O 2 batteries was studied. The results of battery tests in pure oxygen indicate that the cathode material with a high specific surface area, large pore volume and broad pore size distribution can facilitate the discharge reaction, leading to an improved cell performance. As a result, the cathode based on the NiCo 2 O 4 nanowire array delivered a specific discharge capacity of 1682 mAh g −1 at 30 mA g −1 and a stable cyclability of 50 cycles with a capacity limitation of 500 mAh g −1 .
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  • 25
    Publikationsdatum: 2016-08-06
    Beschreibung: The room temperature mechanical behavior of the fully bainitic steel grade 20CrMoVTiB410 was studied in the as-quenched and tempered conditions. The hardenability response of the steel during heat treatment was assessed. In the as-quenched condition itself, the steel exhibited a good combination of strength, ductility and toughness. Tempering the quenched steel till to 550°C, showed uniform mechanical properties. Tempering at 650°C showed secondary hardening behaviour, where the highest strength and least impact toughness was observed. Tempering at 700°C showed a sharp decrease in strength but with significant enhancement of toughness. The properties obtained were correlated with the microstructure and phase analysis was established using optical, scanning electron microscope, transmission electron microscope and x-ray diffraction techniques.
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  • 26
    Publikationsdatum: 2016-08-06
    Beschreibung: In present study, 6061- and A356-based nano-composites are fabricated by using the ultrasonic stirring technology (UST) in a coreless induction furnace. SiC nanoparticles are used as the reinforcement. Nanoparticles are added into the molten metal and then dispersed by ultrasonic cavitation and acoustic streaming assisted by electromagnetic stirring. The applied UST parameters in the current experiments are used to validate a recently developed magneto-hydro-dynamics (MHD) model, which is capable of modeling the cavitation and nanoparticle dispersion during UST processing. The MHD model accounts for turbulent fluid flow, heat transfer and solidification, and electromagnetic field, as well as the complex interaction between the nanoparticles and both the molten and solidified alloys by using ANSYS Maxwell and ANSYS Fluent. Molecular dynamics (MD) simulations are conducted to analyze the complex interactions between the nanoparticle and the liquid/solid interface. The current modeling results demonstrate that a strong flow can disperse the nanoparticles relatively well during molten metal and solidification processes. MD simulation results prove that ultrafine particles (10 nm) will be engulfed by the solidification front instead of being pushed, which is beneficial for nano-dispersion.
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  • 27
    Publikationsdatum: 2016-07-15
    Beschreibung: In this article, the wrinkling behavior and thickness distribution of 5A06 aluminum alloy sheets in an annealed state with thickness of 1.0 mm and 2.5 mm was numerically and experimentally investigated under different hydraulic pressures in the hydroforming of single-layer and double-layer sheets. Note that, in double-layer sheets hydroforming, an upper-aided sheet is needed. The upper, thicker sheet synchronously deforms with the lower, thinner sheet during hydroforming. When the double-layer sheets are separated, a thinner curved sheet part will be manufactured. As can be seen from the simulation and experimental results, the upper, thicker sheet could effectively suppress the wrinkles of the lower, thinner sheet and improve the thickness distribution due to the increasing anti-wrinkle ability of the formed sheet and the interfacial friction between the double-layer sheets. In addition, the maximum hydraulic pressure can be decreased via hydroforming of double-layer sheets; this approach reduces the drawing force for large sheet parts and meets the requirement of energy conservation.
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  • 28
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: In this paper, a direct approach of designing robust weighted fusion steady-state Kalman predictors with uncertain noise variances is presented. Based on the steady-state Kalman filtering theory, using the minimax robust estimation principle, the local and six weighted fusion robust steady-state Kalman predictors are proposed based on the worst case systems with the conservative upper bounds of noise variances. They include the three robust weighted state fusers, two robust weighted measurement fusers, and a modified robust covariance intersection (CI) fuser. Their actual prediction error variances are guaranteed to have the corresponding minimal upper bounds for all admissible uncertainties. A Lyapunov equation approach for robustness analysis and the concept of the robust accuracy are presented and their robust accuracy relations are proved. A simulation example verifies the accuracy relations and robustness.
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  • 29
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: In multitarget tracking, the problem of track labeling (assigning labels to tracks) is an ongoing research topic. The existing literature, however, lacks an appropriate measure of uncertainty related to the assigned labels that has a sound mathematical basis as well as clear practical meaning to the user. This is especially important in a situation where well separated targets move in close proximity with each other and thereafter separate again; in such a situation, it is well known that there will be confusion on target identities, also known as "mixed labeling." In this paper, we specify comprehensively the necessary assumptions for a Bayesian formulation of the multitarget tracking and labeling (MTTL) problem to be meaningful.We provide a mathematical characterization of the labeling uncertainties with clear physical interpretation.We also propose a novel labeling procedure that can be used in combination with any existing (unlabeled)MTT algorithm to obtain a Bayesian solution to the MTTL problem. One advantage of the resulting solution is that it readily provides the labeling uncertainty measures. Using the mixed labeling phenomenon in the presence of two targets as our test bed, we show with simulation results that an unlabeled multitarget sequential Monte Carlo (M-SMC) algorithm that employs sequential importance resampling (SIR) augmented with our labeling procedure performs much better than its "naive" extension, the labeled SIR M-SMC filter.
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  • 30
    Publikationsdatum: 2016-07-19
    Beschreibung: Track-before-detect methods jointly detect and track one or several targets from raw sensor measurements. They often require the computation of the measurement likelihood conditional on the hidden state, which depends on the complex amplitudes of the targets. Since these amplitudes are unknown and fluctuate over time, this likelihood must be marginalized over the complex amplitude (i.e., phase and modulus). It has been demonstrated that this marginalization can be done analytically over the phase in the monotarget case. In this article, we first propose to extend the marginalization to the modulus in a monotarget setting, and we show that closed forms can be obtained for fluctuations of type Swerling 1 and 3. Second, we demonstrate that, in a multitarget setting, a closed form can be obtained for the Swerling 1 case. For Swerling 0 and 3 models, we propose some approximation to alleviate the computation. Since many articles consider the case of squared modulus measurements, we also consider this specific case in monoand multitarget settings with Swerling 0, 1, and 3 fluctuations. Finally, we compare the performance in estimation and detection for the different cases studied, and we show the gain, both in detection and estimation, of the complex measurement method over the squared modulus method, for any fluctuation model.
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  • 31
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: When a bistatic inverse synthetic aperture radar (ISAR) system fails to collect complete radar cross section (RCS) datasets, bistatic ISAR (Bi-ISAR) images are usually corrupted using the conventional Fourier transform (FT)-based imaging algorithm. To overcome this problem, this paper proposes a new Bi-ISAR image reconstruction method that includes three steps: suboptimal estimation of parameters regarding the bistatic angle in the Bi-ISAR signal model via an orthogonal matching pursuit-type group-searching scheme, Bi-ISAR signal reconstruction using the estimated parameters, and Bi-ISAR image generation using the FT-based imaging algorithm applied to the reconstructed Bi-ISAR signal. To validate the reconstruction capability of the proposed method, bistatic-scattered field data using the physical optics technique as well as the point-scatterer model are used for Bi-ISAR image reconstruction. The results show that the proposed sparse-recovery-interpolation approach based on the Bi-ISAR signal model reconstruction combined with the classical FT-based algorithm can yield high reconstruction accuracy for incomplete bistatic RCS data compared to conventional numerical interpolation methods and existing direct sparse reconstruction techniques.
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  • 32
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: Bistatic inverse synthetic aperture radar (ISAR) is an efficient geometric configuration of ISAR to image targets traveling along radar transmitter's line of sight, but it has the problem of defocusing and distortion because of the time-varying bistatic angle. In this paper, we derive the defocusing term and the distortion term by expanding the bistatic angle using first-order Taylor expansion. In addition, necessary constraints to neglect the defocusing term are provided via point spread function analysis, and a novel method to eliminate distortion based on linked scatterers is proposed. Simulation results validate our theoretical analysis and show the effectiveness of our method.
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  • 33
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: Micro-Doppler (MD)-based target classification capabilities of automotive radars can provide high reliability and short latency to future active safety automotive features. A large number of pedestrians surrounding a vehicle in practical urban scenarios mandate prioritization of their treatment level. Distinguishing between relevant pedestrians that are crossing the street or are within the vehicle path and those that are on the sidewalks and are moving along the vehicle route can significantly minimize the number of vehicle-to-pedestrian accidents. This work proposes a novel technique for estimating a pedestrian direction of motion that treats pedestrians as complex distributed targets and utilizes their MD radar signatures. The MD signatures are shown to be indicative of pedestrian direction of motion, and a supervised regression is used to estimate the mapping between the directions of motion and the corresponding MD signatures. In order to achieve higher regression performance, a state-of-the-art sparse dictionary learning-based feature extraction algorithm was adopted from the field of computer vision by drawing a parallel between the Doppler effect and the video temporal gradient. The performance of the proposed approach is evaluated in practical automotive scenario simulations, where a walking pedestrian is observed by a multiple-input/multiple-output automotive radar with a two-dimensional rectangular array. The simulated data was generated using the statistical Boulic-Thalman human locomotion model. Accurate direction of motion estimation was achieved by using support vector regression and multilayer perceptron-based regression algorithms. The results show that the direction estimation error is less than 10° in 95% of the tested cases for pedestrian at a range of 100 m from the radar.
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  • 34
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: This paper proposes a novel phase synchronization technique that enables beamforming with multiple resource-limited spacecraft in space and capitalizes on their spatial geometry. The proposed technique employs an external beacon to obviate the need for explicit time synchronization and reduces the accuracy requirements on localization. Results show that subcentimeter (subnanosecond)-level phase synchronization can be achieved with localization accuracy in the order of meters.
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  • 35
    Publikationsdatum: 2016-07-19
    Beschreibung: The use of chirp signals in modern radar and ranging systems have numerous benefits. They are extensively used to improve signal-to-noise ratio and range resolution. The performance capabilities of these signals are directly related to their time-bandwidth product, i.e., the duration and bandwidth of the pulse. Ultra-wideband chirp signals are further desirable because they span a large bandwidth, making them resistant to narrowband environmental interference. The accurate detection and measurement of high chirp signals is difficult due to the necessity of a high-sampling analog-digital converter, a target measurement platform with high computational power, and a time-of-arrival (TOA) estimator with high temporal resolution. The difficulty of the problem is further compounded with the requirement that no a priori knowledge of the signal, noise, or operating environment is known. This paper presents a practical approach and implementation of a high linear chirp rate receiver and TOA estimator pair capable of detecting and measuring stationary radio frequency pulses as well as linear chirp rates up to 1.18 GHz in 400 ns. The high-resolution TOA algorithm and linear chirp receiver have been prototyped, synthesized, and placed and routed for a Virtex 6 SX475 FPGA.
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  • 36
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: In this paper, an impact angle control guidance law, which considers simultaneously the impact angle and seeker's look angle constraints, is proposed for a constant speed missile against a stationary target. An optimal control theory with state variable inequality constraint is used to design the guidance law, for which a control energy performance index with the weighting function of the range-to-go is minimized. Various forms of guidance and trajectory shaping are possible by selecting a proper gain of the weighting function. To handle the seeker's look angle limits when the missile trajectory is highly curved by controlling the impact angle, the proposed guidance law generates three types of acceleration commands as the guidance phases: the first acceleration command for an initial guidance phase makes an initial seeker's look angle reach the maximum look angle; the second one for a midguidance phase maintains the maximum look angle; the final one for a terminal guidance phase intercepts the target with the desired impact angle. The performance of the proposed guidance law was investigated with nonlinear simulations for various engagement conditions.
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  • 37
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: This paper presents a means of near asteroid hovering of a rigid spacecraft in the asteroid body-fixed frame with parameter variations and external disturbances. An adaptive finite-time control scheme is proposed, where the upper bounds of the parametric uncertainties and disturbances are not required for controller design. The detailed design principles and a rigorous stability analysis are provided. Finally, a body-fixed hovering maneuver is employed in numerical simulation to verify the effectiveness of the proposed strategy.
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  • 38
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: In global navigation satellite system (GNSS) receivers, the acquisition process is the first stage of the signal processing module. It consists of assessing the presence of GNSS signals and providing a rough estimation of the incoming signal parameters: the Doppler frequency and the code delay. However, the presence of bit sign transitions affects receiver performance in signal acquisition detection. This article focuses on the bit transition and its impact on the acquisition performance by providing a general mathematical study and an illustration for two GNSS signals: the global positioning system legacy civil signal (GPS L1 C/A) and Galileo E1 open service (OS). This study is applicable to a terrestrial user in a constraint environment. Furthermore, the presented results are mathematical models of the probability of detection in the presence of bit sign transitions (only one potential bit sign transition per integration interval), and potential uncertainties on the Doppler frequency and code delay. These do not result from empirical acquisition of real signals.
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  • 39
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: This paper investigates the problem of ground vehicle tracking with ground-moving target indicator (GMTI) radar. In practice, the movement of ground vehicles may involve several different maneuvering types (acceleration, deceleration, standstill, etc.). Consequently, the GMTI radar may lose measurements when the radial velocity of the ground vehicle is below a threshold, i.e., falling into the Doppler blind region. In this paper, to incorporate the information gathered from normal measurements and knowledge on the Doppler blindness constraint, we develop an enhanced particle filtering method for which the importance distributions are inspired by a recent noise-related Doppler blind (NRDB) filtering algorithm for GMTI tracking. Specifically, when constructing the importance distributions, the proposed particle filter takes the advantages of the efficient NRDB algorithm by applying the extended Kalman filter and its generalization for interval-censored measurements. In addition, the linearization and Gaussian approximations in the NRDB algorithm are corrected by the weighting process of the developed filtering method to achieve a more accurate GMTI tracking performance. The simulation results show that the proposed method substantially outperforms the existing methods for the GMTI tracking problem.
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  • 40
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: Sets that are defined either from closed contours or from a set of points are generic descriptors for several kinds of objects in binary images. In this paper, we derive a novel model in the space of sets and design an observer for the proposed model to estimate the depth and orientation of planar objects from a camera. This problem is well known as "structure from motion." When the objects are only partially projected on the image plane of the camera, our model makes object depth and orientation estimation possible without feature tracking and matching between distinct image frames (i.e., the so-called correspondence problem), which is an advantage over the image moments-based model. However, the proposed model fails in some situations (the failures can be seen as brief instabilities), and it is not always continuous. To compensate for these drawbacks, we designed a fast observer based on L 1 control theory with a binary signal for the proposed model. Stability analysis with respect to a certain asymptotic instability ratio is also presented in this paper. The effectiveness of the proposed model and observer is demonstrated through simulations and experimental results.
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  • 41
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: Presents the front cover/table of contents for this issue of this publication.
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  • 42
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: A novel differential vector phase locked loop (DVPLL) is derived that takes global navigation satellite system (GNSS) code-phase and carrier-phase measurements from a base station and uses them to maintain a position with centimeter-level accuracy directly in the vector tracking loop of a rover receiver. The navigation filter uses five state variables, three position and two clock states, to create the replica code and carrier measurements for a static test. There are no individual channel states or feedback mechanisms. Closing the individual loops solely through the navigation filter makes this a purely vector method. For short baselines, where differential atmospheric errors are small, the DVPLL can be used on single-frequency data. An L1-only live-sky static test was performed using the method, resulting in a three-dimensional accuracy of 1.3 mm for a zero-baseline and 5.3 mm for an 18.5 m baseline.
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  • 43
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: An adaptive actuator failure and disturbance compensation scheme is developed for attitude tracking control of spacecraft. The proposed scheme consists of a composite parameter adaptation design that incorporates an adaptive backstepping feedback control law and an adaptive feedforward actuator failure compensator; it can guarantee the overall closed-loop system stability and asymptotic tracking. Illustrative simulation results of an application to a spacecraft model show that the designed actuator failure compensation controller ensures system stability and tracking performance.
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  • 44
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: Track-before-detect (TBD) is a popular incoherent energy integration technique aimed at improving detectability of weak targets. A number of studies are available in the literature demonstrating its efficacy against disturbance (whether noise or clutter), but most of them refer to synthetic data, i.e., relying on computer simulations. In this paper, we tackle the problem of assessing the TBD performance with real data and in a particularly severe clutter environment, i.e., sea-clutter. Precisely, using a set of real data from a ground-based sea-search radar, we implement TBD directly on the plot-lists coming from the radar plot extractor (this be can done with acceptable complexity by using an ad hoc dynamic programming algorithm), and demonstrate its effectiveness in reducing sea-clutter. As a further contribution, we also develop an improved decision logic for plot confirmation.
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  • 45
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: The concept of more electric aircraft leads to increases in the amount of electrical loads, as well as the power consumed in the aircraft of the future. To utilize the power feeders, more symmetric, load balancing methods can be applied to swap loads between different phases of an alternating current (AC) feeder, or even between different power feeders. If the load balancing system reacts to measurement data during the flight in real time, the cable power losses and return network power losses, too, are reduced. In addition, the rate of power management interventions decreases. The load balancing problem in three-phase systems is a mixed-integer nonlinear nondifferentiable optimization problem, which is typically solved by elaborate and time-consuming nonreal-time optimization algorithms. The AC loads in aircraft have different power factors, which result in currents described by complex numbers. To determine a load swapping scheme in real time starting from a given load allocation with sparse swapping, new heuristics are presented. One heuristic is specially designed to solve the phase swapping problem by shifting single-phase loads between phases of a feeder. Another heuristic, based on the first one, is enhanced to more than one three-phase feeder and considers the swapping of single-phase and three-phase loads. The heuristics are tested by simulations of a comprehensive case study based on real measurement data from a modern passenger aircraft. To prove the efficiency of the new concepts, a test bench has been built, and several experiments successfully conducted.
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  • 46
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: The probability hypothesis density (PHD) filter is an efficient algorithm for multitarget tracking in the presence of nonlinearities and/or non-Gaussian noise. The sequential Monte Carlo (SMC) and Gaussian mixture (GM) techniques are commonly used to implement the PHD filter. Recently, a new implementation of the PHD filter using B-splines with the capability to model any arbitrary density functions using only a few knots was proposed. The spline PHD (SPHD) filter was found to be more robust than the SMC-PHD filter because it does not suffer from degeneracy, and it was better than the GM-PHD implementation in terms of estimation accuracy, albeit with a higher computational complexity. In this paper, we propose a multiple model extension to the SPHD filter to track multiple maneuvering targets. Simulation results are presented to demonstrate the effectiveness of the new filter.
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  • 47
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: This paper proposes an optimal control framework for the climb and descent economy modes of a flight management system (FMS) yielding a solution that can be implemented in real-time flights below the drag divergence Mach number. The problem is formulated as the optimization of a functional that trades off the fuel- and time-related costs of a flight as a function of a (crew-supplied) parameter called the cost index. The work builds on previous research of the authors for the cruise phase and extends it to the climb and descent phases of flight. More specifically, for both climb and descent, it is found that suboptimal solutions can be obtained as the positive real roots of a fifth-degree polynomial lying inside the flight envelope, which can be found using fast-converging algorithms such as Newton's method. The main contributions of this work are threefold. First, the proposed method gives physical insight because there is an analytical expression for each coefficient of the polynomial. Second, this approach eliminates the need to have a performance database in the system, thus making its implementation faster in real-time. Third, the solution exhibits the same behavior of airborne FMS units as a function of the cost index, which is justified in this paper based on Bellman's principle of optimality. This justification is an important theoretical contribution of the paper. A validation of the approximate solution is obtained using the shooting method to compute the optimal trajectories and compare them against the proposed suboptimal solution. Simulation results show that, for an Airbus A320 model and for a Gulfstream-IV aircraft model, the relative error of the suboptimal trajectories when compared to the optimal trajectories is small for climb and descent trajectories, respectively.
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  • 48
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: An X-band, 15-W-class gallium nitride (GaN) solid-state power amplifier (SSPA) for the 50-kg-class ultrasmall deep-space probe PROCYON has been demonstrated in deep space for the first time. PROCYON was launched on December 3, 2014, as a subpayload of the Hayabusa 2 spacecraft. The GaN SSPA consists of three-stage, single-end amplifiers. The final-stage GaN high-power amplifier, which dominates the characteristics of the SSPA, achieves a maximum drain efficiency of 55.8% at 8.4 GHz. The fabricated SSPA using this GaN high-power amplifier has dimensions of 150 x 120 x 62 mm and weighs 1.5 kg, and its space applicability was confirmed through space environmental tests. For more than 2450 h of continuous operation in deep space, the GaN SSPA has achieved an average output power of 41.7 dBm (14.8 W), with standard deviation of 0.12 dB, maximum overall efficiency of 35.7%, and average efficiency of 33.8%. To the authors' knowledge, this is the highest efficiency of all proven X-band onboard SSPAs.
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  • 49
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: In this paper, an adaptive cubature Kalman filter (ACKF) is proposed to improve the performance of the conventional cubature Kalman filter. The ACKF uses a new cubature rule that combines a third-degree spherical rule with an adaptive higher degree radial rule along the directions of larger uncertainty. More accurate and robust results can be obtained with slightly more cubature points than the conventional third-degree cubature Kalman filter (CKF). Compared with other high-degree Gaussian filters, ACKF uses much fewer points but maintains very close performance. A target tracking problem is used to demonstrate the effectiveness of the proposed filter.
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  • 50
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-07-19
    Beschreibung: We propose a simple method for estimating crystal oscillator g-sensitivity in inertially aided Global Navigation Satellite System (GNSS) receivers. It does not require any specific equipment, like GNSS signal simulators or rate tables. The method is based on analyzing closed-loop phase tracking errors. This enables us to utilize the actual GNSS signal as the frequency reference, despite the presence of an unknown Doppler shift in it. The method has been successfully applied to the calibration of an oven-controlled crystal oscillator.
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  • 51
    Publikationsdatum: 2016-07-20
    Beschreibung: Manual attribution of crystallographic phases from high-throughput x-ray diffraction studies is an arduous task, and represents a rate-limiting step in high-throughput exploration of new materials. Here, we demonstrate a semi-supervised machine learning technique, SS-AutoPhase, which uses a two-step approach to identify automatically phases from diffraction data. First, clustering analysis is used to select a representative subset of samples automatically for human analysis. Second, an AdaBoost classifier uses the labeled samples to identify the presence of the different phases in diffraction data. SS-AutoPhase was used to identify the metallographic phases in 278 diffraction patterns from a FeGaPd composition spread sample. The accuracy of SS-AutoPhase was 〉82.6% for all phases when 15% of the diffraction patterns were used for training. The SS-AutoPhase predicted phase diagram showed excellent agreement with human expert analysis. Furthermore it was able to determine and identify correctly a previously unreported phase.
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  • 52
    Publikationsdatum: 2016-07-23
    Beschreibung: The present work focuses on the processing of cathode active material of spent lithium ion batteries to improve the recovery of constituent metals using reducing agents. Reductants enhance the solubility of metals, which hitherto have been solubilised to a lesser extent using only acid as leaching agent. Thus, we have investigated sulfuric acid leaching in the presence of sodium bisulfite comparing its efficiency with hydrogen peroxide. By simple acid leaching using 1 M H 2 SO 4 at 368 K and 50 g/L pulp density, 93.4% Li, 66.2% Co, 96.3% Ni and 50.2% Mn were recovered in 240 min. In the presence of 5% H 2 O 2 as a reducing agent at 368 K with 1 M H 2 SO 4 and 50 g/L pulp density, the leaching of cobalt (79.2%) and manganese (84.6%) were significantly improved in 240 min. With the addition of 0.075 M NaHSO 3 as a reducing agent, ~96.7% Li, 91.6% Co, 96.4% Ni and 87.9% Mn were recovered under similar conditions. Sodium bisulfite addition results in better recovery of cobalt and manganese by reducing them to their lower oxidation states. The HSC evaluation of thermodynamic feasibility vis-à-vis x-ray diffraction and scanning electron microscopy characterization of residues generated by leaching with hydrogen peroxide and sodium bisulfite substantiates the governing mechanism.
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  • 53
    Publikationsdatum: 2016-07-27
    Beschreibung: This paper investigated the non-isothermal crystallization kinetics of the spinel crystals in vanadium slags containing high CaO content. Experiments were performed in combination with theoretical calculation to address this issue, and statistical analyses based on the Crystal Size Distribution theory. The results indicate that low cooling rate and high CaO content benefit the growth of spinel crystals. The growth mechanism is revealed to be controlled by interface reactions and diffusion at the cooling rates of 5 K/min and 15 K/min, respectively. However, at higher temperatures (〉1673 K), the growth of spinel crystals is controlled by nucleation. While the temperature is decreased to 1523 K at the cooling rate of 5 K/min, the mean diameter of spinel crystals could reach 36.44 μm. Experimental results combining with theoretical reveal that low cooling rate benefits spinels growth, especially for the interval of 1523 K–1200 K.
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  • 54
    Publikationsdatum: 2016-08-03
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  • 55
    Publikationsdatum: 2016-08-03
    Beschreibung: To maximize the recovery of iron and copper from copper slag, the modification process by adding a compound additive (a mixture of hematite, pyrite and manganous oxide) and optimizing the cooling of the slag was studied. The phase reconstruction mechanism of the slag modification process was revealed by thermodynamic calculations, x-ray diffraction, optical microscopy and scanning electron microscopy. The results show that the synergy between the burnt lime and the compound additive promotes the generation of target minerals, such as magnetite and copper matte. In addition, the multifunctional compound additive is able to improve the fluidity of the molten slag, which facilitates the coalescence and growth of fine particles of the target minerals. As a result, the percentage of iron distributed in the form of magnetite increased from 32.9% to 65.1%, and that of the copper exiting in the form of metallic copper and copper sulfide simultaneously increased from 80.0% to 90.3%. Meanwhile, the grains of the target minerals in the modified slag grew markedly to a mean size of over 50 μm after slow cooling. Ultimately, the beneficiation efficiency of copper and iron was improved because of the ease with which the target minerals could be liberated.
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  • 56
    Publikationsdatum: 2016-08-03
    Beschreibung: The high cost and time typically expended in the successful deployment of new materials into high-performance commercial products is attributable to multiple factors. The most significant of these include the heavy reliance on experiments, the persisting disconnect between multiscale experiments and multiscale models, the lack of a broadly accessible data and knowledge infrastructure that can support the implementation of a holistic systems approach, and the lack of a suitable framework for facilitating and enhancing the critically needed cross-disciplinary collaborations. The emerging discipline of materials data science and informatics (MDSI) promises to address these key technology gaps. The potential benefits to the materials innovation enterprise that could accrue from an aggressive adoption of the novel concepts and toolsets offered by MDSI are examined. A specific vision is expounded for the role of MDSI in bridging the large gap that exists between the multiscale materials experiments and the multiscale materials models.
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  • 57
    Publikationsdatum: 2016-08-03
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  • 58
    Publikationsdatum: 2016-08-03
    Beschreibung: Greenhouse gas (GHG) generation is inherent in the production of aluminium by a technology that uses carbon anodes. Most of those GHG are composed of CO 2 produced by redox reaction that occurs in the cell. However, a significant fraction of the annual GHG production is composed of perfluorocarbons (PFC) resulting from anode effects (AE). Multiple investigations have shown that tetrafluoromethane (CF 4 ) can be generated under low-voltage conditions in the electrolysis cells, without global anode effect. The aim of this paper is to find a quantitative relationship between monitored cell parameters and the emissions of CF 4 . To achieve this goal, a predictive algorithm has been developed using seven cell indicators. These indicators are based on the cell voltage, the noise level and other parameters calculated from individual anode current monitoring. The predictive algorithm is structured into three different steps. The first two steps give qualitative information while the third one quantitatively describes the expected CF 4 concentration at the duct end of the electrolysis cells. Validations after each step are presented and discussed. Finally, a sensitivity analysis was performed to understand the effect of each indicator on the onset of low-voltage PFC emissions. The standard deviation of individual anode currents was found to be the dominant variable. Cell voltage, noise level, and maximum individual anode current also showed a significant correlation with the presence of CF 4 in the output gas of an electrolysis cell.
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  • 59
    Publikationsdatum: 2016-08-03
    Beschreibung: The study of material failure with digital analytics is in its infancy and offers a new perspective to advance our understanding of damage initiation and evolution in metals. In this article, we study the failure of aluminum using data-enabled methods, statistics and data mining. Through the use of tension tests, we establish a multivariate acoustic-data matrix of random damage events, which typically are not visible and are very difficult to measure due to their variability, diversity and interactivity during damage processes. Aluminium alloy 6061-T651 and single crystal aluminium with a (111) orientation were evaluated by comparing the collection of acoustic signals from damage events caused primarily by slip in the single crystal and multimode fracture of the alloy. We found the resulting acoustic damage-event data to be large semi-structured volumes of Big Data with the potential to be mined for information that describes the materials damage state under strain. Our data-enabled analyses has allowed us to determine statistical distributions of multiscale random damage that provide a means to quantify the material damage state.
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  • 60
    Publikationsdatum: 2016-08-03
    Beschreibung: A two-stage sequential heavy reduction (HR) method, in which the reduction amount was increased both before and after the solidification end, is presented to simultaneously improve the homogeneity and compactness of the continuous casting bloom. With bearing steel GCr15 chosen as the specific research steel, a three-dimensional thermal–mechanical finite element model was developed to simulate and analyze the thermal and mechanical behaviors of the continuous casting bloom during the HR process. In order to ensure the accuracy of the simulation, the constitutive model parameters were derived from the experimental results. The predicted temperature distribution and shell thickness were verified using a thermal infrared camera and nail shooting results, respectively. The real measured relationship between the HR pressure and amount were applied to verify the mechanical model. The explorative application results showed that the quality of the bloom center and compactness of rolled bars have both been significantly improved after the HR was applied.
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  • 61
    Publikationsdatum: 2016-08-03
    Beschreibung: The mass of automotive components has a direct influence on several aspects of vehicle performance, including both fuel consumption and tailpipe emissions, but the real environmental benefit has to be evaluated considering the entire life of the products with a proper life cycle assessment. In this context, the present paper analyzes the environmental burden connected to the production of a safety-relevant aluminum high-pressure die-casting component for commercial vehicles (a suspension cross-beam) considering all the phases connected to its manufacture. The focus on aluminum high-pressure die casting reflects the current trend of the industry and its high energy consumption. This work shows a new method that deeply analyzes every single step of the component’s production through the implementation of a wide database of primary data collected thanks to collaborations of some automotive supplier companies. This energy analysis shows significant environmental benefits of aluminum recycling.
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  • 62
    Publikationsdatum: 2016-08-05
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  • 63
    Publikationsdatum: 2016-08-05
    Beschreibung: Nearly 400 million years of evolution and field-testing by the natural world has given humans thousands of wood types, each with unique structure–property relationships to study, exploit, and ideally, to manipulate, but the slow growth of trees makes them a recalcitrant experimental system. Variations in wood features of two genotypes of peach ( Prunus persica L.) trees, wild-type and crinkle-leaf, were examined to elucidate the nature of weak wood in crinkle-leaf trees. Crinkle-leaf is a naturally-occurring mutation in which wood strength is altered in conjunction with an easily observed ‘crinkling’ of the leaves’ surface. Trees from three vigor classes (low growth rate, average growth rate, and high growth rate) of each genotype were sampled. No meaningful tendency of dissimilarities among the different vigor classes was found, nor any pattern in features in a genotype-by-vigor analysis. Wild-type trees exhibited longer vessels and fibers, wider rays, and slightly higher specific gravity. Neither cell wall mechanical properties measured with nanoindentation nor cell wall histochemical properties were statistically or observably different between crinkle-leaf and wild-type wood. The crinkle-leaf mutant has the potential to be a useful model system for wood properties investigation and manipulation if it can serve as a field-observable vegetative marker for altered wood properties.
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  • 64
    Publikationsdatum: 2016-07-08
    Beschreibung: As the size of databases has significantly increased, whether through high throughput computation or through informatics-based modeling, the challenge of selecting the optimal material for specific design requirements has also arisen. Given the multiple, and often conflicting, design requirements, this selection process is not as trivial as sorting the database for a given property value. We suggest that the materials selection process should minimize selector bias, as well as take data uncertainty into account. For this reason, we discuss and apply decision theory for identifying chemical additions to Ni-base alloys. We demonstrate and compare results for both a computational array of chemistries and standard commercial superalloys. We demonstrate how we can use decision theory to select the best chemical additions for enhancing both property and processing, which would not otherwise be easily identifiable. This work is one of the first examples of introducing the mathematical framework of set theory and decision analysis into the domain of the materials selection process.
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  • 65
    Publikationsdatum: 2016-06-22
    Beschreibung: Al-4.5wt.%Cu-5wt.%TiB 2 in situ composite, fabricated by stir casting through a mixed salt reaction route process, needs further processing to exclude casting defects. Mushy state rolling has been developed as an easy and energy-efficient method for microstructural refinement and improvement in mechanical properties. It has been carried out at 621°C and 632°C with 20 vol.% and 30 vol.% of liquid, respectively, for up to 5% reduction in thickness. Mushy state rolling of the as-cast composite gives rise to a bimodal microstructure, which consists of very fine equiaxed grains adjacent to the rolled surface and comparatively larger elongated grains away from the rolled surface of the sample. Microhardness of the mushy state rolled sample has been observed to decrease gradually from edge to center of the rolled sample. The presence of the dislocation tangles and subgrains formed by dynamic recovery within solid-state deformed elongated grains and formation of recrystallized grains just adjacent to the second-phase particles have been examined with the help of electron backscattered diffraction and transmission electron microscopy analysis.
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  • 66
    Publikationsdatum: 2016-06-22
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  • 67
    Publikationsdatum: 2016-06-22
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  • 68
    Publikationsdatum: 2016-06-22
    Beschreibung: The effect of anisotropic hardening models on springback of an S-rail part was investigated. Two advanced constitutive models based on distortional and kinematic hardening, which captured the Bauschinger effect, transient hardening, and permanent softening during strain path change, were implemented in a finite element (FE) code. In-plane compression–tension tests were performed to identify the model parameters. The springback of the S-rail after forming a 980 MPa dual-phase steel sheet sample was measured and analyzed using different hardening models. The comparison between experimental and FE results demonstrated that the advanced anisotropic hardening models, which are particularly suitable for non-proportional loading, significantly improved the springback prediction capability of an advanced high strength steel.
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  • 69
    Publikationsdatum: 2016-06-22
    Beschreibung: A recent Critical Materials Strategy report highlighted the supply chain risk associated with neodymium and dysprosium, which are used in the manufacturing of neodymium-iron-boron permanent magnets (PM). In response, the Critical Materials Institute is developing innovative strategies to increase and diversify primary production, develop substitutes, reduce material intensity and recycle critical materials. Our goal in this paper is to propose an economic model to quantify the impact of one of these strategies, material intensity reduction. Technologies that reduce material intensity impact the economics of magnet manufacturing in multiple ways because of: (1) the lower quantity of critical material required per unit PM, (2) more efficient use of limited supply, and (3) the potential impact on manufacturing cost. However, the net benefit of these technologies to a magnet manufacturer is an outcome of an internal production decision subject to market demand characteristics, availability and resource constraints. Our contribution in this paper shows how a manufacturer’s production economics moves from a region of being supply-constrained, to a region enabling the market optimal production quantity, to a region being constrained by resources other than critical materials, as the critical material intensity changes. Key insights for engineers and material scientists are: (1) material intensity reduction can have a significant market impact, (2) benefits to manufacturers are non-linear in the material intensity reduction, (3) there exists a threshold value for material intensity reduction that can be calculated for any target PM application, and (4) there is value for new intellectual property (IP) when existing manufacturing technology is IP-protected.
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  • 70
    Publikationsdatum: 2016-06-22
    Beschreibung: As the demand for personal electronic devices, wind turbines, and electric vehicles increases, the world becomes more dependent on rare earth elements. Given the volatile, Chinese-concentrated supply chain, global attempts have been made to diversify supply of these materials. However, the overall effect of supply diversification on the entire supply chain, including increasing low-value rare earth demand, is not fully understood. This paper is the first attempt to shed some light on China’s supply chain from both demand and supply perspectives, taking into account different Chinese policies such as mining quotas, separation quotas, export quotas, and resource taxes. We constructed a simulation model using Powersim Studio that analyzes production (both legal and illegal), production costs, Chinese and rest-of-world demand, and market dynamics. We also simulated new demand of an automotive aluminum-cerium alloy in the US market starting from 2018. Results showed that market share of the illegal sector has grown since 2007–2015, ranging between 22% and 25% of China’s rare earth supply, translating into 59–65% illegal heavy rare earths and 14–16% illegal light rare earths. There will be a shortage in certain light and heavy rare earths given three production quota scenarios and constant demand growth rate from 2015 to 2030. The new simulated Ce demand would require supply beyond that produced in China. Finally, we illustrate revenue streams for different ore compositions in China in 2015.
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  • 71
    Publikationsdatum: 2016-06-22
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  • 72
    Publikationsdatum: 2016-05-10
    Beschreibung: Metal films on polymer substrates are commonly used in flexible electronic devices and may be exposed to large deformations during application. For flexible electronics, the main requirement is to remain conductive while stretching and compressing. Therefore, the electro-mechanical behaviour of 200-nm-thick Cu films on polyimide with two different microstructures (as-deposited and annealed) were studied by executing in situ fragmentation experiments with x-ray diffraction, under an atomic force microscope, and with 4-point probe resistance measurements in order to correlate the plastic deformation with the electrical behaviour. The three in situ techniques clearly demonstrate different behaviours controlled by the microstructure. Interestingly, the as-deposited film with a bi-modal microstructure is more suited for flexible electronic applications than an annealed film with homogenous 1- µ m-sized grains. The as-deposited film reaches a higher yield stress, with unchanged electrical conductivity, and does not show extensive surface deformation during straining.
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  • 73
    facet.materialart.
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    Springer
    Publikationsdatum: 2016-05-10
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  • 74
    facet.materialart.
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: Straight line motion is a fundamental target motion. Its modeling has been well studied for unconstrained targets (e.g., air targets). However, existing straight line motion models cannot be directly used for tracks constrained on a straight line, which has wide application, e.g., in ground target tracking. In this paper, modeling of the target motion constrained on a straight line is considered. First, linear equality constraints imposed by the straight line are set up explicitly. Then both direct elimination and along-track motion projection are applied to obtain two forms of constrained motion models. Connections between the two forms are studied. For the first form, conditions that guarantee the traditional linear Gaussian assumption are obtained. For the second form, conditions under which the motion along each axis is similar to the along-track motion are obtained. Supporting numerical examples are also provided.
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  • 75
    facet.materialart.
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: Training sets for supervised classification tasks are usually limited in scope and only contain examples of a few classes. In practice, classes that were not seen in training are given labels that are always incorrect. Open set recognition (OSR) algorithms address this issue by providing classifiers with a rejection option for unknown samples. In this work, we introduce a new OSR algorithm and compare its performance to other current approaches for open set image classification.
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  • 76
    facet.materialart.
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: We propose a fast method of ultrawideband (UWB) radar imaging that can be applied to a moving target, having in mind such application as concealed weapon detection. We demonstrate the performance of the proposed method using simulations and measurements with static and moving targets. We also compare the computational complexity of the proposed method with that of a conventional method to clarify the feasibility of applying the proposed method to the intended real-time systems.
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  • 77
    facet.materialart.
    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: Nutation and precession parameter estimation is of great importance for attitude estimation of spin-stabilized space targets. In this paper, we propose a novel method to estimate the nutation and precession parameters of a rigid-body object from the one-dimensional high-resolution radial-range measurements. First, we elaborately derive the kinematic equations and one-dimensional radial-projection model of the precession-with-nutation object, where fixed-point and slipping scatterers are separately taken into account. Second, by using the radial-range trajectories of multiple scatterers, we employ the factorization-based algorithm to obtain the motion reconstruction. Third, we estimate the nutation and precession parameters based on the reconstructed motion and the spectrum analysis of the associated trajectories. Moreover, the l1-norm-based one-dimensional trajectory-recovering technique is developed to deal with the incomplete radial-range trajectories caused by the shadowing effect, specularity, and so on. Finally, experiments are carried out on the electromagnetic analysis data to verify the proposed model and parameter-estimation method.
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  • 78
    facet.materialart.
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: Reductionism and holism are two worldviews underlying the fields of linear and nonlinear signal processing, respectively. Conventional radar resolution theory is motivated by the former view, and it is violated by nonlinear phase modulation induced by dispersive scattering typically associated with extended targets. Motivated by the latter view, this paper offers a new insight into the process of feature extraction for target-recognition applications in single-channel imagery output from synthetic aperture radar processors. Two novel frameworks for holism-based feature extraction are presented. The first framework is based solely on the often-ignored phase chip. The second framework uses the complex-valued 2-D synthetic aperture radar chip after it is transformed into a 1-D vector. Representative features are introduced under each framework. Further, for comparison purposes, baseline features from the power-detected chip are also considered. Three feature sets are extracted from the real-world MSTAR data set and used separately and combinatorially to design multiple instances of an eight-class support vector machine classifier. A classification accuracy of 93.42% is achieved for the holism-based features. This is in comparison to 73.63% for the baseline features. Using Fisher scoring to measure the information contained in each feature, top-ranked features from the first and second holism-based frameworks, respectively, are found to be 7 and 160 times those of the baseline features. Because the nonlinear phenomenon is resolution dependent, our proposed approach is expected to achieve even greater accuracy for synthetic aperture radar sensors with higher resolution.
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  • 79
    facet.materialart.
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: This paper presents a blending principle of tail fins and reaction jets to achieve a fast response for a dual-controlled missile under a slew-rate limit. The blending principle can be categorized as controlling either the net force or the net moment according to how the two actuators cooperate with each other. When compared with controlling the net moment, controlling the net force of aerodynamic lift and jet thrust allows direct control of the acceleration, thus enabling a much faster response but at the expense of large control effort. In this work, for the initial transient period a force controller is designed to achieve fast response under the slew-rate limit, then the transition control is proposed, which begins with force control and makes a transition to moment control to reduce the control usage. This transition does not involve switching from one controller to the other. Rather, the angle of attack is properly shaped corresponding to the desired moment, allowing a smooth and stable transition from force control to moment control. The smooth transition by the proposed strategy from force control to moment control is demonstrated with nonlinear missile dynamics. The proposed approach shows a very fast response, while its input usage is almost same as the conventional moment control.
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  • 80
    facet.materialart.
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: In this correspondence, fractional negative-order moments are used to estimate the K-clutter plus noise parameters. Combining the fractional positive and negative moments, we aim to improve the accuracy of the estimation outcomes. This is achieved through the reduction of the effect of the two first intensity moments involved in the equation of the unknown parameters. For instance, the proposed fractional positive- and negative-order moments??? estimator, given in terms of two confluent hypergeometric functions, is solved numerically to yield the shape parameter. Using single pulse and multiple pulses in various clutter plus noise scenarios, we show, via both simulated and IPIX real data, a comparison of the new estimator with the estimators based on the higher-order moments, the fractional positive-order moments, the [zlog(z)], and the constrained maximum likelihood.
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  • 81
    facet.materialart.
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: Presents a listing of the editors and their technical areas of specialty for the publication.
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  • 82
    facet.materialart.
    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: Presents the front cover/table of contents for this issue of this publication.
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  • 83
    facet.materialart.
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: To separate the received signals in a multiple-input multiple-output (MIMO) radar, the transmitted signals should be orthogonal or have a low cross-correlation level. Some other properties, such as low autocorrelation sidelobes, high range resolution, and good Doppler tolerance are also desired. However, they are difficult to achieve simultaneously. In general, an improved criterion is at the cost of another degraded one. In this paper, we propose a piecewise linear frequency modulation (PLFM) waveform for the MIMO radar. The transmitted signals are pulse trains, including diversified subpulses, which are divided into three segments with controllable durations and bandwidths. The duration sequence of the second segment is obtained by the genetic algorithm to optimize the cross correlation. Theoretical analyses and numerical results are presented to illustrate the properties of the proposed PLFM waveform. Compared with the polyphase coding and the discrete frequency coding waveforms, the PLFM waveform has a lower cross-correlation level and higher degrees of freedom. The relationship of the bandwidths among different segments can be used to adjust the sidelobe peak and the main lobe width of the autocorrelation function.
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  • 84
    facet.materialart.
    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: In sky-wave over-the-horizon radar (OTHR), it is quite difficult to handle the issues of target location (ground range) and height (altitude) estimation due to their joint effect on group range. This work addresses the joint estimation of target location and height by the means of multipath propagation of OTHR signals and structure of a two-dimensional (2D) array. Usually, the multipath signal results from ionosphere propagation in OTHR and can be produced in multi-input???multi-output (MIMO) radar by transmitting signals of various carrier frequencies. A 2D array provides the potential of elevation resolution, which is related to ground and slant ranges. By the multi-quasi-parabolic (MQP) ionospheric model, we formulate the multipath propagation and signal model for the OTHR with a target at location r and height h. Moreover, the joint maximum-likelihood estimates (MLEs) of r and h are derived, and the joint Fisher information matrix (FIM) is calculated. With the so-obtained FIM, the estimability is analyzed; that is: r and h are estimable if and only if either a multipath signal or 2D array is available. The joint Cramer-Rao bound (CRB) is computed and discussed for accuracy improvement. Additionally, the estimability is also extended to the joint estimation of target location, height, and velocity.
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  • 85
    facet.materialart.
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: We propose an observer for attitude and position estimation of a rigid body using translational and angular velocity measurements together with a single landmark. Under an observability condition depending on landmark position, global and asymptotic convergence of attitude and position estimation errors to zero is achieved. We extend the observer for the case of nonideal velocity measurements. Simulation examples demonstrate convergence properties of the observer in the face of noise and bias in velocity measurements.
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  • 86
    Publikationsdatum: 2016-05-27
    Beschreibung: Reconfigurable adaptive amplifiers are expected to be a critical component of future adaptive and cognitive radar transmitters. This paper details an algorithm to simultaneously optimize input power and load reflection coefficient of a power amplifier device to obtain the largest power-added efficiency (PAE) possible under a predefined constraint on adjacent-channel power ratio (ACPR). The vector-based search relies on estimation of the PAE and ACPR gradients in the three-dimensional power Smith tube. Accurate convergence to the optimum impedance in the Smith chart is demonstrated in simulation and measurement search experiments requiring between 20 and 60 experimental queries. This paper presents a fast search to jointly optimize the input power level and load impedance. This method is feasible for future implementation in real-time reconfigurable power amplifiers.
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    Digitale ISSN: 1557-9603
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 87
    facet.materialart.
    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: The augmented ideal proportional navigation guidance law is derived as the closed-loop nonlinear optimal feedback solution for maneuvering target interception. The derived guidance law minimizes a performance index that is similar to the range-weighted control energy of relative motion. The optimal solution is obtained without any linearization of the engagement kinematics or assumption of a near-collision course condition. A method to implement the optimal guidance solution for a constant-speed pursuer is also proposed.
    Print ISSN: 0018-9251
    Digitale ISSN: 1557-9603
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 88
    facet.materialart.
    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: The use of Global Positioning System (GPS) observables provides the primary and advantageous technique for satellite orbit determination in low earth orbit (LEO), in particular when onboard autonomy is required. A wide range of LEO spacecraft equipped with GPS receivers have been launched into space for different applications. Aiming at determining the position and velocity of the satellite in real-time, a consider Kalman filter (CKF)-based reduced-dynamic orbit determination (RDOD) is introduced in this paper. In the CKF, orbit dynamic model is simplified to meet the space-borne computational limitations. The atmospheric drag and solar radiation pressure coefficients are considered rather than estimated in the conventional RDOD strategy. Only a lower order and degree of an earth gravity model is used in the orbit model. However, the propagation of the covariance of the consider parameters is able to absorb the unmodeled and dismodeled perturbations. Therefore, the filter could become convergent with desirable orbit determination performance. The CKF-RDOD method is implemented with a set of the Gravity Recovery and Climate Experiment flight data. The solutions indicate that this proposed method could achieve satisfactory precision orbit determination with approximately 1.5 m level of three-dimensional root-mean-square error using GPS broadcast messages in real-time scenarios.
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    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 89
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    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: Using a colocated multiple input/multiple output (MIMO) radar system, we consider the problem of joint design of amplitudes and frequency-hopping codes for frequency-hopping waveforms. The joint design method yields better combined code and amplitude matrices that result in improved performance over that of separate designs. We propose a game theory framework for the joint design. First, we present the MIMO radar signal model and the sparse representation. Then the problem formulation is constructed based on sparse recovery and the ambiguity function of the MIMO radar system for frequency-hopping waveforms. For amplitude design, we propose two strategies: amplitude design with separate constraints and amplitude design by fusing all transmitters. We formulate a novel game model and propose two joint design algorithms, one applying a noncooperative scheme and the other applying a cooperative scheme. Owing to the extremely large size of the feasible set of the discrete code, we propose to use these algorithms to obtain the ??-approximate equilibrium. We demonstrate the improvement of the resulting codes and amplitudes through numerical examples.
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    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 90
    facet.materialart.
    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: The effect of platform skin return on multiple-element retrodirective cross-eye jamming (MRCJ) system is investigated, allowing the differences between multiple jammer loops to be considered. The jammer antennas employ a linear array with a common center. The median value of the total cross-eye gain and the jamming-to-signal ratio (JSR) are derived to explore their relationship. Simulation results demonstrate the performance of MRCJ in the presence of platform skin return.
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    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 91
    facet.materialart.
    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: Large-scale and high-dimensional data are the main difficulties for Mach number prediction in a wind tunnel system. To solve these issues, based on the multivariate fuzzy Taylor theorem, the Feature Subsets Ensemble (FSE) method has been proposed. However, data sampled from measurements have noise. The FSE uses the entire data set at least once, and for data with noise this property may reduce the generalization of Mach number prediction. In this paper, a Modified Feature Subsets Ensemble (MFSE) method is proposed to overcome the limitation of the FSE on noisy data by introducing the bootstrap to the feature subsets. The bootstrap has the potential to avoid noise. In addition, the generating procedure of the bootstrap replications is straightforward, simple, and quick, which keeps the complexity of the MFSE low. Experiments show that the MFSE outperforms the FSE and the Random Forest method, particularly on high-noise data sets. For all three working conditions, on both the low- and the high-noise testing sets, only the MFSE estimator meets the requirements of forecasting speed, accuracy, and generalization of Mach number prediction.
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    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 92
    facet.materialart.
    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: This paper provides new integrity and continuity risk evaluation methods for fault detection and exclusion (FDE) using receiver autonomous integrity monitoring (RAIM). These methods are developed for both solution separation (SS) and Chi-squared RAIM: they capture the fact that exclusion enables continuity risk reduction in exchange for a higher integrity risk. The two approaches are implemented in an example advanced RAIM (ARAIM) application for worldwide vertical guidance of aircraft using multiconstellation Global Navigation Satellite Systems (GNSS).
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    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 93
    facet.materialart.
    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: The simultaneous use of multiple retrodirective cross-eye jammers is analyzed for both the case where the jammer loops point in different directions and when they point in the same direction. In both cases, the use of multiple cross-eye jammer loops is shown to lead to significantly increased angular errors in the threat radar under certain conditions. Alternatively, the sum-channel return can be increased to reduce the jammer-to-signal ratio requirements for each jammer loop.
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    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 94
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    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: In Brazil, almost all fires are caused by human activities, and for very different reasons: cleaning pastures, preparation for planting, removal of excess undergrowth, hand harvesting of cane sugar, vandalism, etc. Identifying fire occurrence promptly can assist and minimize the negative impact on the affected area. This article presents an onboard fuzzy logic approach for identifying and detecting active fire spots in the Brazilian Amazon forest considering the separability of fire spectral characteristics.
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    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 95
    facet.materialart.
    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: We proposed a dual smoothing superresolution direction-of-arrival (DOA) estimation for multitarget detection with two-channel frequency modulated continuous-wave (FMCW) radar. For the conventional superresolution FMCW radar, the number of detectable targets for DOA estimation is limited by the number of RX antenna arrays. To enable DOA estimation for more targets than the number of receiving channels, we propose exploiting a dual shift invariant structure of dual smoothed matrix. We implemented two-channel FMCW radar and tested the performance of the proposed method.
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    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 96
    facet.materialart.
    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: This paper proposes an invariant ellipsoid-based method for the controller design and gain synthesis of a low-cost quadrotor autonomous ship deck landing system subjected to wind disturbance and measurement noise. This method optimizes the quadrotor performance, hence achieving soft landing. A complete control architecture for the quadrotor is also presented. Simulations are performed using a realistic ship deck model in the presence of measurement noise and wind disturbance with a quadrotor.
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    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 97
    facet.materialart.
    Unbekannt
    Institute of Electrical and Electronics Engineers (IEEE)
    Publikationsdatum: 2016-05-27
    Beschreibung: Spacecraft attitude control using only magnetic torques is a time-varying system. Many designs have been proposed using linear quadratic regulator (LQR) and H∞ formulations. The existence of the solutions depends on the controllability of the linear time-varying systems, which has not been established. In this paper, the conditions of controllability for this linear time-varying system is derived.
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    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Maschinenbau
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
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    Unbekannt
    Springer
    Publikationsdatum: 2016-05-12
    Print ISSN: 1047-4838
    Digitale ISSN: 1543-1851
    Thema: Maschinenbau
    Publiziert von Springer
    Standort Signatur Erwartet Verfügbarkeit
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  • 99
    Publikationsdatum: 2016-05-12
    Beschreibung: As the manufacturing time, quality, and cost associated with additive manufacturing (AM) continue to improve, more and more businesses and consumers are adopting this technology. Some of the key benefits of AM include customizing products, localizing production and reducing logistics. Due to these and numerous other benefits, AM is enabling a globally distributed manufacturing process and supply chain spanning multiple parties, and hence raises concerns about the reliability of the manufactured product. In this work, we first present a brief overview of the potential risks that exist in the cyber-physical environment of additive manufacturing. We then evaluate the risks posed by two different classes of modifications to the AM process which are representative of the challenges that are unique to AM. The risks posed are examined through mechanical testing of objects with altered printing orientation and fine internal defects. Finite element analysis and ultrasonic inspection are also used to demonstrate the potential for decreased performance and for evading detection. The results highlight several scenarios, intentional or unintentional, that can affect the product quality and pose security challenges for the additive manufacturing supply chain.
    Print ISSN: 1047-4838
    Digitale ISSN: 1543-1851
    Thema: Maschinenbau
    Publiziert von Springer
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
    Publikationsdatum: 2016-05-12
    Beschreibung: To promote the application of high strength steels in automobile bodies, the practicability of hot hydroforming of tube by resistance heating is illustrated. From the results of experiments conducted to measure temperature distributions of the tube during the forming process, a method to improve temperature uniformity has been proposed and achieved. Validity was evaluated by examining the effects of hot gas forming on the microstructure and hardness. Results indicate an obvious temperature difference along the axial direction for two cross-sectional shapes: the temperature in the middle zone of the tube is higher than that at its ends. Both thermal convection and cross-sectional shape have only a limited effect on the temperature distribution. The main reason for non-uniform temperature distribution is the heat transition between the electrodes and the tube ends. The temperature difference decreased as the heating rate increased. In contrast, the temperature distribution was even along the circumferential direction for both cross-sectional shapes. Adjusting the contact resistance is a useful method of reducing the temperature difference. In this study, the temperature difference was successfully decreased to 20°C, while reaching a maximum temperature of 750°C, which is adequate for both forming and quenching. A rectangular component was formed to validate the practicality and efficiency of tube hot hydroforming by resistance heating. The hardness and microstructure met the requirements of 22MnB5, which demonstrates both the forming efficiency and quantity advantages of hot gas hydroforming by resistance heating.
    Print ISSN: 1047-4838
    Digitale ISSN: 1543-1851
    Thema: Maschinenbau
    Publiziert von Springer
    Standort Signatur Erwartet Verfügbarkeit
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