bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects on beam pattern performance for colocated multi‐input multi‐output radar transmitting correlated waveforms
Authors: Yang Jin , Chen Haowen , Qiu Zhaokun , Li Xiang , Zhuang Zhaowen
Published: August 2013

The authors investigate the role of correlated waveforms in transmit–receive beam pattern performance of colocated multi‐input multi‐output (MIMO) radar, which presents many advantages by waveform diversity. The mutual orthogonality among the transmitted waveforms is often assumed but cannot be achieved in practice due to the limitation of signal duration and hardware precision. The authors introduce a common model considering the waveform correlation and propose a matched processing structure for the next estimation of parameters. The sufficient statistic for direction estimation is derived, and the transmit–receive beam pattern related to the waveform correlation matrix is obtained. This work mainly studies the effects of transmitting correlated waveforms with all kinds of correlation forms on beam pattern level. By employing these theoretical results, four numerical examples are performed further to obtain both qualitative and quantificational analyses of MIMO radar transmit–receive beam pattern performance with respect to the changing of the cross‐correlation levels of the transmitted waveforms, which can provide a good guidance for orthogonal waveform design when considering MIMO radar beam patterns.
Approach to direct coning/sculling error compensation based on the sinusoidal modelling of IMU signal
Authors: Kang Chul Woo , Ik Cho Nam , Park Chan Gook
Published: August 2013

A direct coning mitigation algorithm based on the detection of a sinusoidal component in the gyro measurements is proposed. The coning error, which is one of dominant error sources affecting the accuracy of attitude computation in the inertial navigation system (INS), is induced by the sinusoidal motion such as a manoeuvre of vehicle or the vibration of a dithering of ring laser gyro. However, many researchers have developed coning error mitigation algorithms based on the higher‐order polynomial model and its correction terms are extracted from the gyro output without faithful consideration of the periodicity of motion. Hence, the authors first detect and estimate the sinusoidal components from gyro measurements, and then find the higher‐order correction terms from the estimated sinusoidal parameters. The authors also show that this algorithm can be applied to the mitigation of sculling error because of its duality to the coning motion. Simulation results show that the direct compensation algorithm works effectively for the navigation of vehicles with continuous and steady oscillations. Also, the rate table test with HG1700 inertial measurement unit (IMU) is conducted to show the effectiveness of proposed algorithm on real INS signal.
Complementary‐based chaotic phase‐coded waveforms design for MIMO radar
Authors: Jin Yang , Wang Hongqiang , Jiang Weidong , Zhuang Zhaowen
Published: August 2013

This study deals with orthogonal waveform design for multi‐input multi‐output (MIMO) radar. Chaos is introduced to generate orthogonal phase‐coded waveforms of arbitrary coded length for arbitrary number of transmitters. However, most of these chaos‐based waveforms suffer high range sidelobe level and intrapulse Doppler intolerance for pulse compression. A complementary transmitting structure is proposed for the MIMO radar to supress these high range sidelobes, and an adaptive clonal selection algorithm is introduced to search for the optimal complementary codes of the transmitted chaotic phase‐coded waveform. This algorithm proves that it is convergent in theory as well. A multiple hypotheses approach is introduced at the transmitters to estimate and then compensate for the intrapulse Doppler phase shift for MIMO radar pulse compression countering the intrapulse Doppler intolerance. Numerical simulations with four typical chaotic maps are carried out and compared with Deng's codes, which validate the proposed methods of this study.
Estimation of clutter degrees of freedom for airborne multiple‐input multiple‐output‐phased array radar
Authors: Xie Wenchong , Zhang Xichuan , Wang Yongliang , Zhu Yong
Published: August 2013

This study focuses on estimation of clutter degrees of freedom (DOFs) for airborne multiple‐input multiple‐output (MIMO)‐phased array radar. Firstly, two equivalent clutter models are presented, according to the transmitting subarray beampattern and synthetic‐phased centre, and based on the basic steering vector. Secondly, a convenient estimating rule of clutter DOFs for airborne MIMO‐phased array radar under arbitrary transmitting subarray structures is presented and proofed strictly. Finally, the simulated results indicate that airborne MIMO‐phased array radar is effective both in spatial selectivity and clutter suppression, and the clutter DOFs under arbitrary transmitted subarray structures can be estimated by the proposed rule exactly. The proposed models and rule are suitable for both conventional‐phased array radar and airborne MIMO radar with uniform or non‐uniform transmitting subarray and sparse array, and they are valuable for the improvement of space‐time adaptive processing algorithm performance.
Bistatic high range resolution profiles of precessing cone‐shaped targets
Authors: Ai Xiaofeng , Zou Xiaohai , Liu Jin , Li Yongzhen , Xiao Shunping
Published: August 2013

This study focuses on the bistatic high range resolution profiles (HRRPs) of precessing targets and considers how to utilise bistatic HRRPs for feature extraction. The movement model of the slippery bistatic scattering centres of precessing targets and the wideband bistatic echo model are introduced firstly. The dynamic simulation method of the bistatic HRRPs of the precessing target is presented using the bistatic scattering coefficients obtained via electromagnetic calculations, and the simulation results validate the theoretical analysis. Furthermore, the characteristics of the bistatic HRRP are analysed and show that the bistatic HRRP generally reflects the projection of the target onto the bisector of the bistatic angle, except that the bistatic angle is so wide that the bistatic HRRP is quite different from the monostatic HRRP. This research is helpful for imaging, and identifying precessing targets in the bistatic radar.
Adaptive robust Kalman filter for relative navigation using global position system
Authors: Li Wei , Gong Deren , Liu Meihong , Chen Ji'an , Duan Dengping
Published: August 2013

An adaptive robust Kalman filter algorithm is derived to account for both process noise and measurement noise uncertainty. The adaptive algorithm estimates process noise covariance based on the recursive minimisation of the difference between residual covariance matrix given by the filter and that calculated from time‐averaging of the residual sequence generated by the filter at each time step. A recursive algorithm is proposed based on both Massachusetts Institute of Technology (MIT) rule and typical non‐linear extended Kalman filter equations for minimising the difference. The measurement update using a robust technique to minimise a criterion function originated from Huber filter. The proposed adaptive robust Kalman filter has been successfully implemented in relative navigation using global position system for spacecraft formation flying in low earth orbit, with real‐orbit perturbations and non‐Gaussian random measurement errors. The numerical simulation results indicate that the proposed adaptive robust filter can provide better relative navigation performance in terms of accuracy and robustness as compared with previous filter algorithms.
Compressive high‐range‐resolution radar imaging using dynamic dictionaries
Authors: Hu Lei , Shi Zhiguang , Zhou Jianxiong , Fu Qiang
Published: August 2013

Compressive sensing theory suggests that accurate reconstruction of a signal can be achieved using its highly undersampled measurements, provided that the signal is sparse in an a priori known dictionary. For the range imaging problem in wideband radar, this dictionary is typically taken to be a DFT basis. However, since practical target scatterers do not lie exactly in the frequency lattice of the discrete Fourier transform (DFT) basis, there is always mismatch between the assumed DFT basis and the actual dictionary for sparsity. To address this, the authors consider the radar echo sparsifying dictionary as refinable and develop a compressive imaging approach using dynamic dictionaries. The approach treats the frequency gridding points as adjustable parameters of the sparsifying Fourier dictionary and achieves dynamical dictionary refinement via iterative optimisation of these parameters. To achieve joint image formation and dictionary refinement, the approach utilises the variational expectation‐maximisation algorithm to iteratively perform a two‐step process, that is, estimating sparse backscattering coefficients given a dictionary and then updating the dictionary to better fit the data sparsity model. The experimental results based on both synthetic and anechoic chamber data demonstrate that the approach improves the precision in range estimation and suppresses spurious spikes in the constructed profiles.
Ghost image cancellation algorithm through numeric beamforming for multi‐antenna radar imaging
Authors: Vermesan Irina , Carsenat David , Decroze Cyril , Reynaud Sébastien
Published: August 2013

In this study, a new approach is proposed for accurate target identification, required by the phased array radar systems that are employed in through‐the‐wall imaging applications. In radar imaging, the effects of the multipath propagation are materialised in fake impressions of the true target, known as ghost images. The developed algorithm removes these ambiguities related to the existence of a target by cancelling, in the final radar image, the ghost images by means of improving the global signal‐to‐spurious‐ratio (SSR) and the target‐to‐ghost‐ratio (TGR) that characterise the real target signature. The development of the approach is based on beamforming and on coherent signal processing upon the returned signal and clutters, for a phased array monostatic radar system. The performances of the algorithm are measured in terms of both the global SSR gain and the TGR and they are verified through simulations and measurements in scenarios that quantify the robustness of the approach. The obtained numerical results concerning the global SSR gain and the TGR certify that the proposed method improves the target localisation and removes the ghost images for radars that operate in rich scattering environments. In the end, the limitations of the approach are also presented.
Waveform design for wideband radar target recognition based on eigensubspace projection
Authors: Jiu Bo , Liu Hongwei , Chen Bo , Liu Zheng
Published: August 2013

Transmission waveform design based on the target and the surrounding environment plays an important role in wideband target recognition radar, which could be helpful to enlarge the separation between the received echoes of different targets. However, precise prior knowledge of target–radar orientation is usually difficult to obtain, whereas target impulse response is sensitive to target–radar orientation. Therefore that has become a barrier for the waveform design. In this study, the authors propose an eigensubspace projection‐based method to enlarge the separation between the received echoes of different targets with additive coloured Gaussian noise, after analysing the upper bound on the error probability of multi‐target recognition. Numerical results show that the proposed method is able to improve the recognition rates effectively.
Joint systematic error estimation algorithm for radar and automatic dependent surveillance broadcasting
Authors: You He , Hongwei Zhu , Xiaoming Tang
Published: August 2013

Systematic error of radar cannot be accurately determined solely with the use of an automatic dependent surveillance broadcasting (ADS‐B) device. This is largely, because of the device's inability to obtain the exact transmitting time of ADS‐B data packets. In order to study and establish an efficient and accurate error registration algorithm for radars based on the ADS‐B system, a joint systematic error estimation model of the radar and ADS‐B was built. The authors showed that when receiving time is known, the time difference between radar measuring time and ADS‐B data transmitting time is consistently biased, a feature that can be used to calculate the systematic error of the ADS‐B receiving system. Then, they established an error estimation model based on the joint systematic error of the radar and ADS‐B. The generalised least squares estimation method was adopted to solve the model. Finally, data samples verified the accuracy and effectiveness of the error registration algorithm.
Multipath error mitigation using self‐encoded spread spectrum for navigation
Authors: Duraisamy Poomathi , Mee Jang Won , Nguyen Lim
Published: August 2013

Self‐encoded spread spectrum (SESS) is a novel modulation technique that acquires its spreading sequence from the random input data stream rather than using the traditional pseudo‐random‐code generators. It has been shown that the memory in SESS can improve the system performance significantly in fading channel. In this study the authors analyse the tracking error of SESS system in the presence of multipath Rayleigh fading channels. Code Shuffling is introduced to randomise the spreading code, which in turn mitigates the effect of reflected path component and enhances the accuracy and performance of iterative detection (ID) against multipath effects. The performance comparison of SESS with C/A code is investigated with the main focus on short multipath delay scenarios. The results demonstrate that ID can significantly mitigate the pseudorange multipath error without any bandwidth expansion.
Phenomenology of Doppler forward scatter radar for surface targets observation
Authors: Gashinova Marina , Daniel Liam , Sizov Vladimir , Hoare Edward , Cherniakov Mikhail
Published: August 2013

In this study, the forward scatter Doppler phase signature formation is analysed to show the rationale for the forward scatter radar in the true sense of the meaning, where a target actually crosses the baseline; so the advantage of the main shadow lobe is taken and, therefore a forward scatter effect occurs to enhance signal to clutter ratio. The modelling approach suggested is based on the consideration of the Doppler phase signature as a result of superposition of the direct path signal and the shadow radiation signal. It is shown that the target signature may be represented as a Doppler signature of a point‐like target specified by its trajectory and speed, which is modulated according to forward scatter cross‐section of an actual extended target specified by its silhouette at each moment of motion. The proposed model may be recommended to provide matched filtering in coherent processing. Finally, the approach is verified experimentally using calibrated targets with conductive and absorbing coating in the controlled environment and maritime targets in the real sea conditions.
Multipath mitigation techniques based on time reversal concept and superresolution algorithms for inverse synthetic aperture radar imaging
Authors: de Arriba‐Ruiz Imanol , Muñoz‐Ferreras Jose M. , Pérez‐Martínez Félix
Published: August 2013

Radar imaging based on static high‐resolution coherent radar is widely known as inverse synthetic aperture radar (ISAR) imaging. This ‘all‐weather’ system is able to provide slant‐range – Doppler images of non‐cooperative targets whose motion is unknown. Conventional ISAR systems are designed for imaging targets with a direct line of sight of sensors. For this reason, they have a reduced performance in today's complex scenarios – such as urban environments – where secondary returned waveforms are added to directly reflected echoes coming from targets. They are known as ghost artefacts since they obscure true targets when using the standard range‐Doppler algorithm (RDA). In this study, an innovative multipath mitigation technique is presented, in which ‘time reversal (TR)’ concept is implemented in ISAR images, leading to ‘TR‐ISAR algorithm’. For this purpose, a pre‐processing algorithm is previously needed so as to solve the geometric problem related to multipath. Finally, superresolution algorithms provide us with the tools to mitigate the spurious component that arises during the averaging process carried out by TR‐ISAR. The authors’ conclusion is that imaging quality after employing superresolution approaches is clearly improved. As a proof‐of‐concept, real data from high‐resolution radar have been used to verify the proposed method.
Multiple model tracking of manoeuvring targets accounting for standoff jamming information
Authors: Hou Jing , Li X. Rong , Jing Zhanrong
Published: August 2013

An Interacting Multiple Model (IMM) algorithm for manoeuvring target tracking in the presence of standoff jammer is proposed. In the IMM, the conventional Gaussian likelihood is replaced with a Gaussian sum (GS) likelihood, derived from a sensor model accounting for both the measurements and jamming information. Thus, the model‐conditioned posterior probability density function of the state is also a weighted sum of Gaussians but with recalculated weights. As a result of the combination of multiple models and jamming information, the proposed approach has a significant performance improvement when both manoeuvre and jamming occur. Simulation results show that the proposed approach outperforms the original IMM algorithm as well as the GS filters with only one model in terms of track loss and track accuracy.
Three-dimensional instability in the flow past two side-by-side square cylinders
Authors: Choi Choon-Bum , Yang Kyung-Soo
Published: August 2013

The onset of the three-dimensional (3D) instability in the flow past two side-by-side square cylinders has been studied via Floquet stability analysis. The gap between the two cylinders is the key parameter that alters flow topology, leading to change of stability characteristics. Depending on the gap, four distinct flow patterns have been identified for base flow. For each pattern of base flow, distinctive Floquet modes of 3D instability have been found. The spatial and temporal characteristics of the Floquet modes are similar to those of mode A or mode B of the single square cylinder case, namely, odd or even Reflection-Translation symmetries. Six distinct Floquet modes have been identified in total, and the spatial and temporal characteristics of each mode are described in detail. The criticality of Floquet modes, including their critical Reynolds number and the associated dominant spanwise wave number, is presented for each gap considered in the current study. For a small gap, the flow past the two cylinders resembles that of a single object, resulting in an approximately doubled characteristic length. Consequently, the critical Reynolds number becomes low with a small gap between the two cylinders. When the two cylinders are moderately apart, the interaction between the two wakes diminishes, and the criticality of 3D instabilities approaches that of the single cylinder case. Coexisting 3D instabilities for a specific base-flow topology are also noticed with a moderate gap. Neutral stability curves are computed and presented for some selected values of the gap.
Wohlleben effect in YRh4B4
Authors: Terekhov A. V.
Published: August 2013

The Wohlleben effect (a positive response in the temperature dependence of the magnetization in the superconducting state during FC measurements) is observed in the superconductor YRh4B4 in a magnetic field H = 10 Oe for the first time. The positive response disappears in a field of 20 Oe and a diamagnetic response develops and increases as the magnetic field is raised.
Dielectric properties of (CuO, CaO2, and BaO)y/CuTl-1223 composites
Authors: Mumtaz M. , Kamran M. , Nadeem K. , Jabbar Abdul , Khan Nawazish A. , Saleem Abida , Tajammul Hussain S. , Kamran M.
Published: August 2013

We synthesized (CuO, CaO2, and BaO)y/Cu0.5Tl0.5Ba2Ca2Cu3O10−δ (y = 0, 5%, 10%, 15%) composites by solid-state reaction and characterized them by x-ray diffraction, scanning electron microscopy, dc-resistivity, and Fourier transform infrared spectroscopy. Frequency and temperature dependent dielectric properties, such as real and imaginary parts of the dielectric constant, dielectric loss, and ac-conductivity of these composites were studied by capacitance and conductance measurements as a function of frequency (10 kHz to 10 MHz) and temperature (78 to 300 K). X-ray diffraction analysis reveals that the characteristic behavior of the superconductor phase and the structure of Cu0.5Tl0.5Ba2Ca2Cu3O10−δ are nearly undisturbed by doping with nanoparticles. Scanning electron microscopy images show the improvement in the intergranular linking between the superconducting grains occurring with increasing nanoparticle concentration. Microcracks are healed up with these nanoparticles, and superconducting volume fraction is also increased. Dielectric properties of these composites strongly depend on the frequency and temperature. Zero resistivity critical temperature and dielectric properties show opposite trends with the addition of nanoparticles to the Cu0.5Tl0.5Ba2Ca2Cu3O10−δ superconductor matrix.
Angular magnetic breakdown oscillations in organic conductors
Authors: Galbova O. , Kirichenko O. V. , Peschansky V. G.
Published: August 2013

The dependence of the magnetoresistance oscillations in layered organic conductors with a multisheet Fermi surface on the angle between the magnetic field and the normal to the layers is studied theoretically in the condition of possible magnetic breakdown between different sheets of the Fermi surface. It is shown that the distance between separate cavities of the Fermi surface in momentum space can be determined from the periods of magnetic breakdown oscillations.
Experimental low-temperature heat capacity of one-dimensional xenon adsorbate chains in the grooves of carbon c-SWNT bundles
Authors: Bagatskii M. I. , Manzhelii V. G. , Sumarokov V. V. , Barabashko M. S.
Published: August 2013

The experimental studies of the heat capacity of 1D chains of xenon atoms adsorbed in the outer grooves of bundles of closed single-walled carbon nanotubes CXe have been first made at temperature range 2–30 K with the adiabatic calorimeter. The experimental data CXe have been compared with theory [A. Šiber, Phys. Rev. B 66, 235414 (2002)]. The experimental and theoretical heat capacity curves are close below 8 K. Above 8 K the experimental curve CXe(T) exceeds the theoretical one and excess capacity ΔCXe(T) increases monotonously with temperature. We assume that the ΔCXe(T) caused mainly by the increase of the distance between the neighboring xenon atoms in the chain with increasing temperature.
Six-parameters deformations of fourth order Peregrine breather solutions of the nonlinear Schrödinger equation
Authors: Gaillard Pierre
Published: August 2013

We construct solutions of the focusing nonlinear Schrödinger (NLS) equation as a quotient of two determinants. This formulation gives in the case of the order 4, new deformations of the Peregrine breather with 6 real parameters. We construct families of quasi-rational solutions of the NLS equation and describe the apparition of multi-rogue waves. With this method, we construct the analytical expressions of deformations of the Peregrine breather of order 4 with 6 real parameters and plot different types of rogue waves.
Boundary based on exchange symmetry theory for multilevel simulations. I. Basic theory
Authors: Shiga Motoyuki , Masia Marco
Published: August 2013

In this paper, we lay the foundations for a new method that allows multilevel simulations of a diffusive system, i.e., a system where a flux of particles through the boundaries might disrupt the primary region. The method is based on the use of flexible restraints that maintain the separation between inner and outer particles. It is shown that, by introducing a bias potential that accounts for the exchange symmetry of the system, the correct statistical distribution is preserved. Using a toy model consisting of non-interacting particles in an asymmetric potential well, we prove that the method is formally exact, and that it could be simplified by considering only up to a couple of particle exchanges without a loss of accuracy. A real-world test is then made by considering a hybrid MM*/MM calculation of cesium ion in water. In this case, the single exchange approximation is sound enough that the results superimpose to the exact solutions. Potential applications of this method to many different hybrid QM/MM systems are discussed, as well as its limitations and strengths in comparison to existing approaches.
Noisy continuous time random walks
Authors: Jeon Jae-Hyung , Barkai Eli , Metzler Ralf
Published: August 2013

Experimental studies of the diffusion of biomolecules within biological cells are routinely confronted with multiple sources of stochasticity, whose identification renders the detailed data analysis of single molecule trajectories quite intricate. Here, we consider subdiffusive continuous time random walks that represent a seminal model for the anomalous diffusion of tracer particles in complex environments. This motion is characterized by multiple trapping events with infinite mean sojourn time. In real physical situations, however, instead of the full immobilization predicted by the continuous time random walk model, the motion of the tracer particle shows additional jiggling, for instance, due to thermal agitation of the environment. We here present and analyze in detail an extension of the continuous time random walk model. Superimposing the multiple trapping behavior with additive Gaussian noise of variable strength, we demonstrate that the resulting process exhibits a rich variety of apparent dynamic regimes. In particular, such noisy continuous time random walks may appear ergodic, while the bare continuous time random walk exhibits weak ergodicity breaking. Detailed knowledge of this behavior will be useful for the truthful physical analysis of experimentally observed subdiffusion.
Thermal imaging of standing spin waves
Authors: An T. , Yamaguchi K. , Uchida K. , Saitoh E.
Published: August 2013

A simple method for the spatial imaging of standing spin-wave modes is demonstrated. We observed instantaneous temperature-rise images on a polycrystalline ferrimagnetic insulator Y3Fe5O12 slab using an infrared camera immediately after exciting magnetostatic standing spin-wave modes. We found that a wavy temperature distribution appears before the temperature distribution on the sample is smoothed by heat conduction. The distribution is consistent with the result of a calculation based on the Landau-Lifshitz-Gilbert equation using the effective demagnetization coefficient of the slab. This result proves that the method can image the spatially distributed patterns of standing spin waves.
Effects of grain-boundary potential barrier height and its fluctuation on conductivity of polycrystalline semiconductors in the ionized-impurity-scattering dominated case
Authors: Kajikawa Y.
Published: August 2013

We propose a new conduction model based on an energy filtering model for thermionic emission over non-uniform grain-boundary barriers in polycrystalline semiconductors of arbitrary degeneracy in which the relaxation time of carriers is dominated by ionized-impurity scattering. It is shown that the non-linear curves of Arrhenius plots of electrical conductivity in several polycrystalline samples of different semiconductors (FeS2, WO3, SnO2, ZnO) in literature are well fitted using the model with the mean value and the standard deviation of the grain-boundary potential barrier height and the concentration of ionized impurities as the three fitting parameters.
Surface-enhanced Raman spectroscopic studies of the Au-pentacene interface: A combined experimental and theoretical investigation
Authors: Adil D. , Guha S.
Published: August 2013

It has recently been shown [D. Adil and S. Guha, J. Phys. Chem. C 116, 12779 (2012)]10.1021/jp3031804 that a large enhancement in the Raman intensity due to surface-enhanced Raman scattering (SERS) is observed from pentacene when probed through the Au contact in organic field-effect transistors (OFET) structures. Here, the SERS spectrum is shown to exhibit a high sensitivity to disorder introduced in the pentacene film by Au atoms. The Raman signature of the metal-semiconductor interface in pentacene OFETs is calculated with density-functional theory by explicitly considering the Au-pentacene interaction. The observed enhancement in the 1380 cm−1 and the 1560 cm−1 regions of the experimental Raman spectrum of pentacene is successfully modeled by Au-pentacene complexes, giving insights into the nature of disorder in the pentacene sp2 network. Finally, we extend our previous work on high-operating voltage pentacene OFETs to low-operating voltage pentacene OFETs. No changes in the SERS spectra before and after subjecting the OFETs to a bias stress are observed, concurrent with no degradation in the threshold voltage. This shows that bias stress induced performance degradation is, in part, caused by field-induced structural changes in the pentacene molecule. Thus, we confirm that the SERS spectrum can be used as a visualization tool for correlating transport properties to structural changes, if any, in organic semiconductor based devices.
Depth profiles of oxygen precipitates in nitride-coated silicon wafers subjected to rapid thermal annealing
Authors: Voronkov V. V. , Falster R. , Kim TaeHyeong , Park SoonSung , Torack T.
Published: August 2013

Silicon wafers, coated with a silicon nitride layer and subjected to high temperature Rapid Thermal Annealing (RTA) in Ar, show—upon a subsequent two-step precipitation anneal cycle (such as 800 °C + 1000 °C)—peculiar depth profiles of oxygen precipitate densities. Some profiles are sharply peaked near the wafer surface, sometimes with a zero bulk density. Other profiles are uniform in depth. The maximum density is always the same. These profiles are well reproduced by simulations assuming that precipitation starts from a uniformly distributed small oxide plates originated from RTA step and composed of oxygen atoms and vacancies (“VO2 plates”). During the first step of the precipitation anneal, an oxide layer propagates around this core plate by a process of oxygen attachment, meaning that an oxygen-only ring-shaped plate emerges around the original plate. These rings, depending on their size, then either dissolve or grow during the second part of the anneal leading to a rich variety of density profiles.
A model for calculating impact ionization transition rate in wurtzite GaN for use in breakdown voltage simulation
Authors: Kodama Kazuki , Tokuda Hirokuni , Kuzuhara Masaaki
Published: August 2013

A model for calculating impact ionization transition rate (IITR) in wurtzite GaN has been developed for use in breakdown voltage simulations. The characteristic feature of the model is to calculate energy-dependent IITR by taking a conduction band index into account. Depending on the band index, the IITR values calculated by the proposed model show spreading by three orders of magnitude in the electron energy range from 6.5 to 8 eV, while this spreading is totally disregarded in the conventional model. An impact ionization coefficient is calculated based on a full band Monte Carlo simulation which incorporates IITRs by the proposed model. The calculated impact ionization coefficients by the proposed model exhibit better agreements with those by the rigorous model. The proposed model is applied to the calculation of breakdown characteristics for AlGaN/GaN HEMTs and demonstrates a higher breakdown voltage by about 30% than that by the conventional model.
Identification of dominant recombination mechanisms in narrow-bandgap InAs/InAsSb type-II superlattices and InAsSb alloys
Authors: Olson B. V. , Shaner E. A. , Kim J. K. , Klem J. F. , Hawkins S. D. , Flatté M. E. , Boggess T. F.
Published: August 2013

Minority carrier lifetimes in doped and undoped mid-wave infrared InAs/InAsSb type-II superlattices (T2SLs) and InAsSb alloys were measured from 77–300 K. The lifetimes were analyzed using Shockley-Read-Hall (SRH), radiative, and Auger recombination, allowing the contributions of the various recombination mechanisms to be distinguished and the dominant mechanisms identified. For the T2SLs, SRH recombination is the dominant mechanism. Defect levels with energies of 130 meV and 70 meV are determined for the undoped and doped T2SLs, respectively. The alloy lifetimes are limited by radiative and Auger recombination through the entire temperature range, with SRH not making a significant contribution.
Copper multilayers for the investigation of subsurface impurity redistribution and resultant microstructure
Authors: Rizzolo Michael , Novak Steve , Dunn Kathleen A.
Published: August 2013

Electroplating copper for semiconductor interconnects incorporates impurities, which have long been implicated as inhibiting recrystallization in fine features. In this study, a multilayer structure with intentional impurity fluctuations was plated with a microfluidic device to investigate how varying concentrations influenced the final microstructure. The distribution of impurities was analyzed using Secondary Ion Mass Spectrometry depth profiling, which found the bands of impurities were preserved at room temperature despite grain growth proceeding throughout the entire thickness of the film. Therefore, impurity variations of these magnitudes are not expected to be the major pinning force for recrystallizing grains in fine features.
Importance of configurational contributions to the free energy of nanoclusters
Authors: Posselt M.
Published: August 2013

An effective simulation method based on the Wang-Landau Monte Carlo algorithm is used in order to demonstrate the significance of the configurational contributions to the free energy of embedded nanoclusters. Starting from the most stable cluster configuration the simulation provides all geometrically different, but simply connected and sufficiently compact configurations of a nanocluster of a given size and the respective formation energies. The knowledge of these data allows the calculation of the free formation and free binding energy of the cluster at T ≠ 0. The method is applied to coherent Cu clusters in bcc-Fe. It is shown that even at moderate temperatures the configurational contributions to the free formation and binding energy must not be neglected. The dependence of the monomer free binding energy on clusters size is found to change significantly with increasing temperature which has a considerable effect on the pathway of cluster evolution. Therefore, present investigations provide an essential contribution to the improvement of the input parameters for object kinetic Monte Carlo simulations and rate theory used in multi-scale simulations of the nanostructure evolution. The calculation scheme developed in this work is rather general and applicable to many types of embedded nanoclusters. Compared to the method of overlapping distributions hitherto used in some cases to determine the configurational part of the free energy the new method has major advantages. Various tests are performed in order verify the presented approach and to compare with the results of the other calculation procedure. A roadmap is proposed to include the vibrational contributions to the free energy of the clusters within the framework of the method employed in this work.
Angular momentum transport in astrophysics and in the lab
Authors: Ji Hantao , Balbus Steven
Published: August 2013

For evolving astrophysical accretion disks to concentrate their mass and still conserve angular momentum, turbulent flows are crucial. Those flows cannot be directly observed, so to understand them better physicists are creating them in modest-sized laboratory experiments.
Drilling to Earth’s mantle
Authors: Umino Susumu , Nealson Kenneth , Wood Bernard
Published: August 2013

Half a century after the first efforts to drill through oceanic crust failed, geoscientists are ready to try again.
Coffee rings and coffee disks: Physics on the edge
Authors: Yunker Peter J. , Durian Douglas J. , Yodh Arjun G.
Published: August 2013

The stains left by drying coffee would look quite different—both microscopically and macroscopically—if the suspended grounds weren’t roughly spherical.
Induction of autophagy during in vitro maturation improves the nuclear and cytoplasmic maturation of porcine oocytes
Authors: Song Bong-Seok , Kim Ji-Su , Kim Young-Hyun , Sim Bo-Woong , Yoon Seung-Bin , Cha Jae-Jin , Choi Seon-A , Yang Hae-Jun , Mun Seong-Eun , Park Young-Ho , Jeong Kang-Jin , Huh Jae-Won , Lee Sang-Rae , Kim Sang-Hyun , Kim Sun-Uk , Chang Kyu-Tae
Published: August 2013

While a critical role of autophagy in mammalian early embryogenesis has been demonstrated, few studies have been conducted regarding the role of autophagy in in vitro maturation (IVM) of immature oocytes. In the present study we investigated the effect of rapamycin, a chemical autophagy inducer, on the nuclear and cytoplasmic maturation of porcine oocytes. Rapamycin treatment led to increased expression of LC3-II, an autophagy marker. Compared with the control group, as well as the 5 and 10 nM rapamycin treatment groups, the rate of MII oocyte production was higher in the 1 nM rapamycin treatment group, indicating improvement in nuclear maturation. In the analyses of cytoplasmic maturation, we found that the level of p34cdc2, a cytoplasmic maturation marker, and the monospermic fertilisation rate were higher in the 1 nM rapamycin treatment group than in the other groups. Moreover, the beneficial effect of 1 nM rapamycin on cytoplasmic maturation of MII oocytes was further evidenced by increases in blastocyst formation rate, total cell number and cell survival. In the blastocyst embryos, anti-apoptotic Bcl-xL transcript levels were elevated in the 1 nM rapamycin-treated group, whereas pro-apoptotic Bax transcript levels were decreased. Collectively, these results suggest that induction of autophagy during IVM contributes to enhancement of the nuclear and cytoplasmic maturation of porcine oocytes.
Reducing deformation anisotropy to achieve ultrahigh strength and ductility in Mg at the nanoscale
Authors: Yu Qian , Qi Liang , Mishra Raja K. , Li Ju , Minor Andrew M.
Published: August 2013

In mechanical deformation of crystalline materials, the critical resolved shear stress (CRSS;
τ
CRSS
) is the stress required to initiate movement of dislocations on a specific plane. In plastically anisotropic materials, such as Mg,
τ
CRSS
for different slip systems differs greatly, leading to relatively poor ductility and formability. However,
τ
CRSS
for all slip systems increases as the physical dimension of the sample decreases to approach eventually the ideal shear stresses of a material, which are much less anisotropic. Therefore, as the size of a sample gets smaller, the yield stress increases and
τ
CRSS
anisotropy decreases. Here, we use in situ transmission electron microscopy mechanical testing and atomistic simulations to demonstrate that
τ
CRSS
anisotropy can be significantly reduced in nanoscale Mg single crystals, where extremely high stresses (∼2 GPa) activate multiple deformation modes, resulting in a change from basal slip-dominated plasticity to a more homogeneous plasticity. Consequently, an abrupt and dramatic size-induced “brittle-to-ductile” transition occurs around 100 nm. This nanoscale change in the CRSS anisotropy demonstrates the powerful effect of size-related deformation mechanisms and should be a general feature in plastically anisotropic materials.
BslA is a self-assembling bacterial hydrophobin that coats the
Bacillus subtilis
biofilm
Authors: Hobley Laura , Ostrowski Adam , Rao Francesco V. , Bromley Keith M. , Porter Michael , Prescott Alan R. , MacPhee Cait E. , van Aalten Daan M. F. , Stanley-Wall Nicola R.
Published: August 2013

Biofilms represent the predominant mode of microbial growth in the natural environment.
Bacillus subtilis
is a ubiquitous Gram-positive soil bacterium that functions as an effective plant growth-promoting agent. The biofilm matrix is composed of an exopolysaccharide and an amyloid fiber-forming protein, TasA, and assembles with the aid of a small secreted protein, BslA. Here we show that natively synthesized and secreted BslA forms surface layers around the biofilm. Biophysical analysis demonstrates that BslA can self-assemble at interfaces, forming an elastic film. Molecular function is revealed from analysis of the crystal structure of BslA, which consists of an Ig-type fold with the addition of an unusual, extremely hydrophobic “cap” region. A combination of in vivo biofilm formation and in vitro biophysical analysis demonstrates that the central hydrophobic residues of the cap are essential to allow a hydrophobic, nonwetting biofilm to form as they control the surface activity of the BslA protein. The hydrophobic cap exhibits physiochemical properties remarkably similar to the hydrophobic surface found in fungal hydrophobins; thus, BslA is a structurally defined bacterial hydrophobin. We suggest that biofilms formed by other species of bacteria may have evolved similar mechanisms to provide protection to the resident bacterial community.
Relocating the active-site lysine in rhodopsin and implications for evolution of retinylidene proteins
Authors: Devine Erin L. , Oprian Daniel D. , Theobald Douglas L.
Published: August 2013

Type I and type II rhodopsins share several structural features including a G protein-coupled receptor fold and a highly conserved active-site Lys residue in the seventh transmembrane segment of the protein. However, the two families lack significant sequence similarity that would indicate common ancestry. Consequently, the rhodopsin fold and conserved Lys are widely thought to have arisen from functional constraints during convergent evolution. To test for the existence of such a constraint, we asked whether it were possible to relocate the highly conserved Lys296 in the visual pigment bovine rhodopsin. We show here that the Lys can be moved to three other locations in the protein while maintaining the ability to form a pigment with 11-
cis
-retinal and activate the G protein transducin in a light-dependent manner. These results contradict the convergent hypothesis and support the homology of type I and type II rhodopsins by divergent evolution from a common ancestral protein.
A Validated Questionnaire to Assess the Knowledge of Psychiatric Aspects of Alcohol Use Disorder
Authors: Jaworowski Sol , Walter Garry , Soh Nerissa , Freier Dror Yossi , Mergui Joseph , Gropp Cornelius , Haber Paul S.
Published: August 2013

Background

To the best of our knowledge, there is no validated instrument for measuring knowledge of psychiatric aspects of alcohol use disorder (AUD) amongst medical students. Our aim was to develop an instrument for this purpose and to describe the instrument's psychometric properties. We also investigated whether the instrument could demonstrate a significant change in scores following an educational intervention consisting of a 60-minute PowerPoint lecture on AUD, associated handouts, and role-plays.

Methods

The Knowledge of Psychiatric Aspects of Alcohol Questionnaire (KPAAQ) was developed from the Kaplan and Saddock textbook synopsis chapter on alcohol related disorders. The questionnaire included 6 categories of clinically relevant material: metabolism of alcohol, short-term effects of alcohol, long-term effects of alcohol, AUD, alcohol withdrawal, and alcohol use in pregnancy. The KPAAQ was administered to 75 medical students in Years 4 and 5 from the Hebrew University in Jerusalem, Israel, during a relevant clinical rotation. Following the initial administration of the KPAAQ, the students attended a 60-minute lecture (in Hebrew) based on material from the University of Sydney's learning module on alcohol. The KPAAQ was readministered to the students immediately following the lecture.

Results

The KPAAQ demonstrated good reliability (Cronbach α =.92 for all questions) and validity r(209) =.674, P <.001. Knowledge of alcohol and alcoholism significantly increased after the educational intervention ( F(2, 154) = 151.60, P <.001). Post hoc comparisons using the Scheffe test revealed a significant positive change in knowledge after students received the intervention (mean difference = 33, P <.001).

Conclusions

These initial findings suggest that the KPAAQ is a reliable and valid instrument for assessing medical student knowledge of psychiatric aspects of AUD over 6 clinical categories.
The Measurement of School-to-work Transitions as Processes
Authors: Brzinsky-Fay Christian
Published: August 2013

Measuring individual transitions means capturing a process with a specific time dimension. The established analysis of school-to-work transitions focuses on single status changes, such as those between education and unemployment. As longitudinal datasets became increasingly available, the periodical character of transitions has deserved attention, mostly in terms of studies that used event history models. But even these kinds of studies continued to focus on single status changes, which are not determined by theory but by the respective research question, or by data availability. Hence, the analysis of micro-level transitions remains selective, because there is no common idea how to explore them. As a result, school-to-work transition research is in danger to overlook important aspects of this life-course trajectory. This paper argues that the reason is the missing theoretical definition of a transition. Given the growing complexity of school-to-work transitions, the status change concept becomes inappropriate for their analysis. The predominance of hypothesis-testing methods together with an underrepresentation of explorative methods lead to a disregard of the process character of school-to-work transitions. This considerably limits the gain of new scientific insights. Recent methodological developments regarding the explorative analysis of longitudinal processes, namely sequence analysis, offer the possibility to cope with the complexity of school-to-work transitions. The paper aims at comparing the advantages and drawbacks of two methods in analysing transitions, and advocates a combined research design between explorative and hypothesis-testing methods.