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Energy barriers for point-defect reactions in 3C-SiC

Physical Review B 2013年第5期88卷 054105-054105页

作者： Ming-Jie Zheng Narasimhan Swaminathan Dane Morgan Izabela Szlufarska Materials Science and Engineering Department University of Wisconsin-Madison Madison Wisconsin USA Department of Mechanical Engineering Indian Institute of Technology Madras Chennai 600036 India Material Science Program University of Wisconsin-Madison Madison Wisconsin USA

Energy barriers of the key annealing reactions of neutral and charged point defects in SiC are calculated with ab initio density functional theory methods. In order to effectively search for the lowest energy migration paths the preliminary path is first established based on ab initio molecular dynamics (AIMD) simulations. The energy barrier of each hop is then calculated via climbing image nudged elastic band methods for paths guided by the AIMD simulations. The final paths and barriers are determined by comparing different pathways. The annealing reactions have important implications in understanding the amorphization, recovery, and other aspects of the radiation response of SiC. The results are compared with the literature data and experimental results on SiC recovery and amorphization. We propose that the C interstitial and Si antisite annealing reaction may provide a critical barrier that governs both the recovery stage III and amorphization processes.

关键词： SILICON carbide AB initio methods (Quantum mechanics) MOLECULAR dynamics AMORPHIZATION SIMULATED annealing (Mathematics)

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Low-power signal processing methodologies for implantable biosensing platforms

Low-power signal processing methodologies for implantable bi...

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2013 IEEE Signal Processing in Medicine and Biology Symposium, SPMB 2013

作者： Croce Jr., Robert A. Vaddiraju, Santhisagar Legassey, Allen Islam, Syed K. Papadimitrakopoulos, Fotios Jain, Faquir C. IBiorasis Inc. Technology Incubation Program Storrs CT 06269 United States Dept. of Chemistry Institute of Materials Science University of Connecticut Storrs CT 06269 United States Department of Electrical and Computer Engineering University of Connecticut Storrs CT 06269 United States Analog VLSI and Devices Laboratory Department of Electrical Engineering and Computer Science University of Tennessee Knoxville TN 37996 United States

ISBN: (纸本)9781479930074

This paper presents the design and implementation of highly-miniaturized, low-power CMOS signal conditioning schemes intended for use in a totally implantable biomedical sensor platform. Due to the thrust for the development implantable biomedical sensing systems for health management and disease prevention, there exists a need for signal processing schemes which occupy very little on-chip real estate and consume negligible amounts of power. In light of this, this paper presents both a CMOS current-to-frequency converter and voltage-tofrequency converter which have been designed primarily for use in implantable biosensing platforms and applications. Such designs can be implemented in stand-alone single sensor designs, or in tandem to create multi-analyte architectures. The versatility of employing current-to-frequency as well as voltageto- frequency signal transduction schemes presents an avenue for the integration with any electrochemical sensing element which has been fabricated in an amperometric or voltammetric fashion. Furthermore, we demonstrate the efficacy of both these circuit designs by integrating them together with high performance electrochemical implantable glucose and pH sensors. The low power consumption and miniature size of the amperometric and voltammetric signal processing units (0.25 mm2 and 18 IlW / 0.045 mm2 and 122 IlW, respectively) presents an ideal design for signal processing in implantable continuous metabolic monitoring devices.

关键词： Signal processing

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Deformation of Porous, Nanostructured Silver at Room Temperature and 150 °C

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MRS Online Proceedings Library 2013年第1期1513卷 1-6页

作者： Noiseau, Guillaume Becker, Michael F. Keto, John W. Kovar, Desiderio Materials Science and Engineering Graduate Program The University of Texas at Austin Austin USA Department of Electrical and Computer Engineering The University of Texas Austin USA Department of Physics The University of Texas Austin USA Department of Mechanical Engineering The University of Texas Austin USA

Porous, nanostructured silver samples were produced using a direct-write method where a nanoparticle aerosol consisting of particles with a mean size of approximately 5 nm were accelerated to speeds of approximately 1000 m/sec and impacted onto a translating substrate [1]. The impacting particles have sufficient energy to stick to the substrate, allowing patterned thick films to be directly written from the aerosol without a mask. Unlike other low temperature processing routes for achieving patterned films, no organics are added that can interfere with postdeposition processing. Typical films are 5- 100 μm thick, up to several centimeters long, and have an as-deposited relative densities as high as 70% of bulk Ag. Compression tests were carried out in steps at room temperature and at 150°C under constant displacement rates. Local strain and densification were measured by optical profilometry between each compression step. The results can be used as a starting point to better understand the mechanisms that govern plasticity, creep, and sintering in nanostructured, porous silver at low processing temperatures.

关键词： Ag densification nanoscale

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A bio-inspired hemispherical lens based on reflecting superposition compound eye optics

A bio-inspired hemispherical lens based on reflecting superp...

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2013 17th International Conference on Solid-State Sensors, Actuators and Microsystems, TRANSDUCERS and EUROSENSORS 2013

作者： Huang, C.-C. Aldalali, B. Wu, X. Jiang, H. Department of Electrical and Computer Engineering University of Wisconsin - Madison Madison WI United States McPherson Eye Research Institute University of Wisconsin-Madison Madison WI United States Materials Science Program University of Wisconsin-Madison Madison WI United States Department of Biomedical Engineering University of Wisconsin - Madison Madison WI United States

ISBN: (纸本)9781467359818

This paper presents the design and fabrication of a 3-dimensional (3-D), hemispherical lens based on reflecting superposition compound eye (RSCE) optics. The configuration of our hemispherical lens, similar to that of natural RSCEs, consists of a large-area array of reflective, high aspect-ratio, micro-square-tubes fabricated on a transparent, flexible and hemispherical polydimethylsiloxane (PDMS) membrane via a peeling micro-printing process. The dimensions of the micro-square-tubes are on the order of tens of microns. Unlike ordinary lenses, our RSCE device focuses light based on reflection rather than refraction. The hemispherical RSCE lens was able to focus a collimated and a non-collimated light source, respectively, with a focal length of 1.5 cm. The imaging performance was consistent with theoretic prediction based on the geometric optics model and ray-tracing technique. The device also achieved a wide field of view (FOV) of up to 100°. © 2013 IEEE.

关键词： Light

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Reactivity of Ti-B, Cr-S, and Mn-S powder systems during explosively-driven collapse

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Journal of Physics: Conference Series 2014年第18期500卷

作者： M Serge P H Chiu A J Higgins V F Nesterenko Mechanical Engineering Department McGill University Montreal QC H3A 0C3 Canada Department of Mechanical and Aerospace Engineering UCSD La Jolla CA 92093-0411 USA Materials Science and Engineering Graduate Program UCSD La Jolla CA 92093-0411 USA

Metal-metal and metal-sulfur reactive powder mixtures have been previously tested for initiation of reaction via planar, normal-shock loading. In addition to reacting under shock, such powder mixtures may undergo exothermic reaction from other types of mechanical loading. The thick-walled cylinder technique was performed on samples of Ti-B (1:2 molar ratio), Cr-S (1.15:1 molar ratio), and Mn-S (1:1 molar ratio). These experiments were aimed to determine the effect of large shear strains exerted on reactive metal powder mixtures and to establish the relative effectiveness of shear loading in comparison to shock loading for initiating reaction. Recovered samples were analyzed via SEM and XRD to determine the degree of reaction.

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Optimal conditions for high current proton irradiations at the university of Wisconsin's ion beam laboratory

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AIP Conference Proceedings 2013年第1期1525卷 649-653页

作者： C. J. Wetteland K. G. Field T. J. Eiden T. J. Gerczak B. R. Maier O. Albakri K. Sridharan T. R. Allen Materials Science Program University of Wisconsin Madison WI 53706 USA Department of Engineering Physics University of Wisconsin Madison WI 53706 USA

The National Electrostatics Corporation's (NEC) Toroidal Volume Ion Source (TORVIS) source is known for exceptionally high proton currents with minimal service downtime as compared to traditional sputter sources. It has been possible to obtain over 150μA of proton current from the source, with over 70μA on the target stage. However, beam fluxes above ∼1×1017/m2-s may have many undesirable effects, especially for insulators. This may include high temperature gradients at the surface, sputtering, surface discharge, cracking or even disintegration of the sample. A series of experiments were conducted to examine the role of high current fluxes in a suite of ceramics and insulating materials. Results will show the optimal proton irradiation conditions and target mounting strategies needed to minimize unwanted macro-scale damage, while developing a procedure for conducting preliminary radiation experiments.

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Selective surface functionalization at regions of high local curvature in graphene

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Chemical Communications 2013年第7期49卷 677-679页

作者： Wu, Qingzhi Wu, Yaping Hao, Yufeng Geng, Jianxin Charlton, Matthew Chen, Shanshan Ren, Yujie Ji, Hengxing Li, Huifeng Boukhvalov, Danil W. Piner, Richard D. Bielawski, Christopher W. Ruoff, Rodney S. State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Biomedical Materials and Engineering Center Wuhan University of Technology Wuhan 430070 China Department of Mechanical Engineering Department of Materials Science Department of Engineering Program The University of Texas at Austin Austin TX 78712 1 University Station C2200 United States Department of Chemistry and Biochemistry The University of Texas at Austin Austin TX 78712 1 University Station A1590 United States School of Computational Sciences Korea Institute for Advanced Study Seoul 130-722 South Korea ) School of Chemical and Biological Engineering Seoul National University Seoul 151-742 South Korea

Monolayer graphene was deposited on a Si wafer substrate decorated with SiO2 nanoparticles (NPs) and then exposed to aryl radicals that were generated in situ from their diazonium precursors. Using micro-Raman mapping, the aryl radicals were found to selectively react with the regions of graphene that covered the NPs. The enhanced chemical reactivity was attributed to the increased strain energy induced by the local mechanical deformation of the graphene. © The Royal Society of Chemistry.

关键词： GRAPHENE synthesis MONOMOLECULAR films SILICON wafers NANOPARTICLES -- Spectra DIAZONIUM compounds RAMAN effect

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Variation of Hardness and Modulus across the Thickness of Zr-Cu-Al Metallic Glass Ribbons

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MRS Online Proceedings Library (OPL) 2013年第1期1520卷 mrsf12-1520-nn10-06-mrsf12-1520-nn10-06页

作者： Z. Humberto Melgarejo J.E. Jakes J. Hwang Y.E. Kalay M.J. Kramer P.M. Voyles D.S. Stone Materials Science Program University of Wisconsin-Madison Madison WI 53706 U.S.A. Performance Enhanced Biopolymers United States Forest Service Forest Products Laboratory Madison WI 53726 U.S.A. Ames Laboratory (DOE) Ames Iowa 50011 USA and Department of Materials Science and Engineering Iowa State University Ames IA 50011 U.S.A. Department of Materials Science and Engineering and Materials Science Program University of Wisconsin-Madison Madison WI 53706 U.S.A.

We investigate through-thickness hardness and modulus of Zr50Cu45Al5 metallic glass melt-spun ribbon. Because of their thinness, the ribbons are challenging to measure, so we employ a novel nanoindentation based-method to remove artifacts caused by ribbon flexing and edge effects. Hardness and modulus vary approximately linearly across the thickness but, unlike bulk ingots, the side of the ribbon that cooled most quickly had the highest hardness and modulus. This “inverse” variation may be caused by the fast-moving solidification front, which might conceivably, for instance, push free volume in advance of it. Annealing near Tg causes both hardness and modulus to increase and become more uniform across the thickness.

关键词： hardness nano-indentation amorphous

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P-type and undoped InGaN across the entire alloy composition range

P-type and undoped InGaN across the entire alloy composition...

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10th Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2013

作者： Wang, Ke Araki, T. Yu, K.M. Katsuki, T. Mayer, M.A. Alarcon-Llado, E. Ager, J.W. Walukiewicz, W. Nanishi, Y. Department of Photonics Ritsumeikan University 1-1-1 Noji Higashi Kusatsu Shiga 525-8577 Japan Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley CA 94720 United States WCU Hybrid Materials Program Dept. of Materials Science and Engineering Seoul National University 151-744 Korea Republic of

We report a systematic study on undoped and Mg-doped InGaN grown by molecular beam epitaxy. Various experiments have been combined to demonstrate p-type InGaN across the entire alloy composition range. © 2013 IEEE.

ISBN: (纸本)9781467364751

关键词： Semiconductor alloys

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Use of microseismicity for determining the structure of the fracture network of large-scale porous media

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Physical Review E 2013年第3期87卷 032152-032152页

作者： Tayeb A. Tafti Muhammad Sahimi Fred Aminzadeh Charles G. Sammis Mork Family Department of Chemical Engineering and Materials Science and the Petroleum Engineering Program University of Southern California Los Angeles California 90089-1211 USA Department of Earth Sciences University of Southern California Los Angeles California 90089 USA

We show that microseismic events—earthquakes with small magnitudes—can be fruitfully used to gain insight into the properties of the fracture network of large-scale porous media, such as oil, gas, and geothermal reservoirs. As an example, we analyze extensive data for the Geysers geothermal field in northeast California. Injection of cold water into the reservoir to produce steam leads to microseismic events. It is demonstrated that the analysis can also lead to insight into whether the fractures are of tectonic type or induced by injection of cold water. To demonstrate this we estimate, using the catalogue of the microseismic events, the fractal dimension Df of the spatial distribution of hypocenters of the events in three seismic clusters associated with the injection of cold water into the field, as well as the b values in the Gutenberg-Richter frequency-magnitude distribution. The fractal dimensions are all in a narrow range centered around Df≃2.57±0.06, comparable to the measured fractal dimension of fracture sets in the greywacke reservoir rock. For most cases the b values are about b≃1.3±0.1, consistent with the Aki relation, Df=2b. Both Df and b are significantly higher than those commonly observed for regional tectonic seismicity or aftershock sequences for which Df≈2 and b≈1 are typical. Our results do not imply that no tectonic triggering exists in the reservoir, but rather that the overpressure allows the activation of less favorably oriented fractures that produce an increase in both b and Df. The estimate Df≈2 for tectonic seismicity has been interpreted as indicating that most tectonic events occur on the subset of near-vertical faults—because they have lower normal stress—or that they occur on the backbone of the fracture and fault network, the multiply connected part of the network that enables finite shear strain. Our results lend support to the latter. The results that the entire fracture network, and not just its backbone, is active at the Geyser

关键词： Hydraulic fracturing

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