bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural model of FeoB, the iron transporter fromPseudomonas aeruginosa, predicts a cysteine lined, GTP-gated pore
Authors: Seyedmohammad Saeed , Fuentealba Natalia Alveal , Marriott Robert A.J. , Goetze Tom A. , Edwardson J. Michael , Barrera Nelson P. , Venter Henrietta
Published: March 2016

Iron is essential for the survival and virulence of pathogenic bacteria. The FeoB transporter allows the bacterial cell to acquire ferrous iron from its environment, making it an excellent drug target in intractable pathogens. The protein consists of an N-terminal GTP-binding domain and a C-terminal membrane domain. Despite the availability of X-ray crystal structures of the N-terminal domain, many aspects of the structure and function of FeoB remain unclear, such as the structure of the membrane domain, the oligomeric state of the protein, the molecular mechanism of iron transport, and how this is coupled to GTP hydrolysis at the N-terminal domain. In the present study, we describe the first homology model of FeoB. Due to the lack of sequence homology between FeoB and other transporters, the structures of four different proteins were used as templates to generate the homology model of full-length FeoB, which predicts a trimeric structure. We confirmed this trimeric structure by both blue-native-PAGE (BN-PAGE) and AFM. According to our model, the membrane domain of the trimeric protein forms a central pore lined by highly conserved cysteine residues. This pore aligns with a central pore in the N-terminal GTPase domain (G-domain) lined by aspartate residues. Biochemical analysis of FeoB from Pseudomonas aeruginosa further reveals a putative iron sensor domain that could connect GTP binding/hydrolysis to the opening of the pore. These results indicate that FeoB might not act as a transporter, but rather as a GTP-gated channel.
Vision‐based trajectory tracking for mobile robots using Mirage pose estimation method
Authors: Dinc Semih , Fahimi Farbod , Aygun Ramazan
Published: March 2016

Unmanned vehicles are autonomous robotic systems that are fully or partially controlled by an operator remotely from a station. In the last two decades, massive amount of advancements have been observed regarding unmanned vehicles for both military and civilian purposes. Today majority of these vehicles require human guidance even for basic missions, thus, minimising the human intervention on such systems is one of the emerging research topics. To serve this purpose, this study proposes a new trajectory tracking algorithm using Mirage pose estimation method. Mirage employs target pixel errors in two‐dimensional image plane and analytically calculates the robot's pose in three‐dimensional Euclidean space. Therefore, complex computations are not needed and undesirable Euclidean trajectories are avoided since the vehicle's pose is directly controlled. Both simulations and real experiments were performed to verify the effectiveness of the method. The results show that the proposed method is a feasible alternative for vision‐based Euclidean trajectory tracking with high accuracy and low complexity.
Optimisation of automatic face annotation system used within a collaborative framework for online social networks
Authors: Huang Shih‐Chia , Jiau Ming‐Kai , Jian Yu‐Hsiang
Published: March 2016

Recently, the development of automatic face annotation techniques in online social networks has become a promising research area for the purpose of management of the large numbers of photographs uploaded to social network platforms. In this study, the authors first construct the personalised pyramid database units for each member in the pyramid database access control module by effectively making use of various types of social network context to drastically reduce time expenditure and further boost the accuracy of face identification. Next, they train and optimise the personalised multiple‐kernel learning (MKL) classifier unit for each member, which utilises the MKL algorithm to locally adapt to each member, resulting in the production of high‐quality face identification results for the current owner in the MKL face recognition module. Experimental results demonstrate that their proposed face annotation approach provides a substantially higher level of efficacy and efficiency than other face annotation approaches for real‐life personal photographs with pose variations.
Estimation of fisheye camera external parameter based on second‐order cone programming
Authors: Zhu Haijiang , Zhang Fan , Zhou Jinglin , Wang Jing , Wang Xue Jing , Wang Xuan
Published: March 2016

Although second‐order cone programming (SOCP) has been applied to optimise camera parameters in computer vision, it is occasionally been used to refine fisheye camera external parameters as well. This study presents a fisheye camera external parameter estimation based on SOCP in convex optimisation. The homography constraint between two spherical images are first exploited to derive an equation with respect to a given error threshold. Then, the fisheye camera external estimation is transformed into an SOCP optimisation problem through reformulating the parameter estimation equation. The SOCP method has been implemented in Matlab and the optimisation toolbox has been made publicly available. The fisheye camera external parameter optimisation method has been validated by some experiments with synthetic and real data. Comparison experiments between the proposed method and other methods in the literature are also carried out, and the results show that the SOCP method is better for the corrected images.
Improvement of the power conversion efficiency of a personal computer
Authors: Huang Te , Bai Ying‐Wen , Kuan Hung‐Ming
Published: March 2016

Most low‐power PC design research focuses on the power consumption of devices in the system, in order to reduce the consumption of the peripheral components while the system is in the idle state. In this design, the power conversion efficiency of the multi‐phase pulse width modulation power regulator can be improved by using the auto‐phase switching control scheme. The external load‐sensing circuit is used to both monitor the output current and to change the regulator to a different operation method automatically. This design is dependent on the different loading to set the optimised operation phase. The power conversion efficiency can be maintained from 88.19 to 93.41%, when the load current is changed from 1.06 to 119 A.
Coupled inductor‐based single‐stage high gain DC–AC buck–boost inverter
Authors: Sreekanth T. , Lakshminarasamma N. , Mishra Mahesh Kumar
Published: March 2016

Two stage conversion systems (TSCSs) normally use either boost converter or high gain dc–dc converter along with dc–ac inverter in order to transfer power from low input voltage dc source to high voltage ac load. When these TSCSs operate at extremely low input voltages, the boost converter has to operate at extremely high duty ratios. This in turn results in more losses and reverse recovery problems. Usage of high gain dc–dc converter results in more number of components, increase in control complexity and decrease in reliability. Single‐stage conversion systems (SSCSs) are formed by merging both dc–dc and dc–ac conversion processes. These SSCSs have advantages like low loss, more compactness and less reverse recovery problems. In this study, a high gain coupled inductor‐based single‐phase SSCS is presented. This SSCS topology has many desirable features such as high gain, less switching losses, free from leakage inductance adverse effects and compact. Principle of operation, steady‐state analysis and design of the proposed topology are described in detail. MATLAB simulation results of the proposed topology and experimental results using DSP28335‐based experimental setup are presented to validate the proposed scheme.
Five‐phase travelling wave induction heater for continuous heating of flat material
Authors: Al‐Shaikhli Ali K. , Humod Abdul‐Rahim T. , Hasan Fadhil A.
Published: March 2016

This study proposed a novel travelling wave induction heating system with five‐phase exciting current. The proposed system used special exciting current to obtain a homogeneous eddy current density, which affects the temperature pattern over the material surface. Five‐phase system has been attracted from many industrial applications due to its inherent features compared to the three‐phase system. An even number of phases is not preferred because the poles exchange with each other. A comparison investigation with other traditional methods is represented to realise the features of the proposed method. A finite‐element method simulation is represented by using ANSYS 15®; the simulation results show that the proposed system gives superior performance of energy transferred, uniform heat distribution and higher power factor over that of the traditional three‐phase system. Moreover, it performs identical eddy current, power densities, temperature and efficiency to that of the six‐phase system with profits of reduction in size, weight, cost and winding copper losses.
Tangent hyperbolic circular frequency diverse array radars
Authors: Saeed Sarah , Qureshi Ijaz Mansoor , Khan Waseem , Salman Ayesha
Published: March 2016

Frequency diverse array (FDA) with uniform frequency offset (UFO) has been in spot light of research for past few years. Not much attention has been devoted to non‐UFOs in FDA. This study investigates tangent hyperbolic (TH) function for frequency offset selection scheme in circular FDAs (CFDAs). Investigation reveals a three‐dimensional single‐maximum beampattern, which promises to enhance system detection capability and signal‐to‐interference plus noise ratio. Furthermore, by utilising the versatility of TH function, a highly configurable type array system is achieved, where beampatterns of three different configurations of FDA can be generated, just by adjusting a single function parameter. This study further examines the utility of the proposed TH‐CFDA in some practical radar scenarios.
Phase transition and critical behaviors of spin-orbital coupling spinel compound CdV2O4
Authors: Wang Li , Sun Duohua , Wang Rongjuan , Zhu Yuanyuan , Lu Zhihong , Xiong Rui , Liu Yong , Shi Jing
Published: March 2016

The temperature dependent susceptibility and specific heat of spinel compound CdV2O4 were investigated. The structural transition accompanied with orbital order appearing at 89.6 K is confirmed to be a first order transition, while the magnetic transitions at 30.2 K is revealed to be a second order one. For the paramagnetism-antiferromagnetic transition, the width of critical region was estimated to be about 1.5 K by differentiating with Gaussian fluctuation. In critical region, the critical behavior of specific heat was compared with renormalization-group theory. Critical exponent α and critical amplitude ratio (A+/A−) fitting to the data was found to be −0.017 and 1.26, respectively. The value of A+/A− shows the critical behavior of CdV2O4's deviates from 3D-Heisenberg and shifts to 3D-XY. The analysis of specific heat in low temperature range gives out that Debye temperature ΘD for CdV2O4 is estimated to be 190 K.
Early-time radiation flux symmetry optimization and its effect on gas-filled hohlraum ignition targets on the National Ignition Facility
Authors: Milovich J. L. , Dewald E. L. , Pak A. , Michel P. , Town R. P. J. , Bradley D. K. , Landen O. , Edwards M. J.
Published: March 2016

Achieving ignition on the National Ignition Facility (NIF) is tied to our ability to control and minimize deviations from sphericity of the capsule implosion. Low-mode asymmetries of the hot spot result from the combined effect of radiation drive asymmetries throughout the laser pulse and initial roughness on the capsule surface. In this paper, we report on simulations and experiments designed to assess, measure, and correct the drive asymmetries produced by the early-time (≈first 2 ns or “picket”) period of the laser pulse. The drive asymmetry during the picket is commonly thought to introduce distortions in the hot-spot shape at ignition time. However, a more subtle effect not previously considered is that it also leads to an asymmetry in shock velocity and timing, thereby increasing the fuel adiabat and reducing the margin for ignition. It is shown via hydrodynamic simulations that minimizing this effect requires that the early-time asymmetry be kept below 7.5% in the second Legendre mode (P2), thus keeping the loss of performance margin below ≈10% for a layered implosion. Asymmetries during the picket of the laser pulse are measured using the instantaneous self-emission of a high-Z re-emission sphere in place of an ignition capsule in a hohlraum with large azimuthal diagnostic windows. Three dimensional simulations using the code HYDRA (to capture the effect of non-azimuthal hohlraum features) coupled to a cross-beam energy transfer model [Michel et al., Phys. Plasmas 17, 056305 (2010)] are used to establish the surrogacy of the re-emit target and to assess the early-time drive symmetry. Calculations using this model exhibit the same sensitivity to variations in the relative input powers between the different cones of NIF beams as measured for the “Rev5” CH target [Haan et al., Phys Plasmas 18, 051001 (2011)] and reported by Dewald et al. [Phys. Rev. Lett. 111, 235001 (2013)]. The same methodology applied to recently improved implosions using different hohlraum geometries and picket powers show good agreement with experimental data.
Two-fluid and finite Larmor radius effects on helicity evolution in a plasma pinch
Authors: Sauppe J. P. , Sovinec C. R.
Published: March 2016

The evolution of magnetic energy, helicity, and hybrid helicity during nonlinear relaxation of a driven-damped plasma pinch is compared in visco-resistive magnetohydrodynamics and two-fluid models with and without the ion gyroviscous stress tensor. Magnetic energy and helicity are supplied via a boundary electric field which initially balances the resistive dissipation, and the plasma undergoes multiple relaxation events during the nonlinear evolution. The magnetic helicity is well conserved relative to the magnetic energy over each event, which is short compared with the global resistive diffusion time. The magnetic energy decreases by roughly 1.5% of its initial value over a relaxation event, while the magnetic helicity changes by at most 0.2% of the initial value. The hybrid helicity is dominated by magnetic helicity in low-β pinch conditions and is also well conserved. Differences of less than 1% between magnetic helicity and hybrid helicity are observed with two-fluid modeling and result from cross helicity evolution. The cross helicity is found to change appreciably due to the first-order finite Larmor radius effects which have not been included in contemporary relaxation theories. The plasma current evolves towards the flat parallel current state predicted by Taylor relaxation theory but does not achieve it. Plasma flow develops significant structure for two-fluid models, and the flow perpendicular to the magnetic field is much more substantial than the flow along it.
The steady-state and transient electron transport within bulk zinc-blende indium nitride: The impact of crystal temperature and doping concentration variations
Authors: Siddiqua Poppy , O'Leary Stephen K.
Published: March 2016

Within the framework of a semi-classical three-valley Monte Carlo electron transport simulation approach, we analyze the steady-state and transient aspects of the electron transport within bulk zinc-blende indium nitride, with a focus on the response to variations in the crystal temperature and the doping concentration. We find that while the electron transport associated with zinc-blende InN is highly sensitive to the crystal temperature, it is not very sensitive to the doping concentration selection. The device consequences of these results are then explored.
Symmetry breaking in hexagonal and cubic polymorphs of BaTiO3
Authors: Hashemizadeh Sina , Biancoli Alberto , Damjanovic Dragan
Published: March 2016

BaTiO3 appears in cubic and hexagonal variants, both of which are centrosymmetric. Samples of cubic BaTiO3 are known to exhibit breaking of the centric symmetry locally and globally. It has been proposed that the local symmetry breaking originates in polar regions, the precursors of the ferroelectric phase. Origins of the macroscopic symmetry breaking, which are not well understood, have been previously tentatively correlated with inhomogeneities in the samples, such as strain gradients that may align or redistribute objects such as charged point defects or polar regions making material macroscopically polar. No such data are available for BaTiO3 with hexagonal symmetry. We compare dielectric, elastic, and pyroelectric properties of the two materials in polycrystalline form. In contrast to cubic BaTiO3, hexagonal BaTiO3 does not exhibit macroscopic pyroelectric response at room temperature. This is consistent with apparent absence of polar regions in the hexagonal material, and the fact that in hexagonal BaTiO3, strain rather than polarization is the order parameter for the phase transition into ferroelectric-ferroelastic phase. The thermally stimulated currents measured in hexagonal and cubic BaTiO3, however, show that both materials exhibit noncentric macroscopic symmetry. This result supports the idea that extrinsic factors, such as strain gradients, which are apparently common for both materials, may break the macroscopic symmetry, which may then lead to alignment and redistribution of polar regions or charged defects.
Analysis of structural correlations in a model binary 3D liquid through the eigenvalues and eigenvectors of the atomic stress tensors
Authors: Levashov V. A.
Published: March 2016

It is possible to associate with every atom or molecule in a liquid its own atomic stress tensor. These atomic stress tensors can be used to describe liquids’ structures and to investigate the connection between structural and dynamic properties. In particular, atomic stresses allow to address atomic scale correlations relevant to the Green-Kubo expression for viscosity. Previously correlations between the atomic stresses of different atoms were studied using the Cartesian representation of the stress tensors or the representation based on spherical harmonics. In this paper we address structural correlations in a 3D model binary liquid using the eigenvalues and eigenvectors of the atomic stress tensors. This approach allows to interpret correlations relevant to the Green-Kubo expression for viscosity in a simple geometric way. On decrease of temperature the changes in the relevant stress correlation function between different atoms are significantly more pronounced than the changes in the pair density function. We demonstrate that this behaviour originates from the orientational correlations between the eigenvectors of the atomic stress tensors. We also found correlations between the eigenvalues of the same atomic stress tensor. For the studied system, with purely repulsive interactions between the particles, the eigenvalues of every atomic stress tensor are positive and they can be ordered: λ1 ≥ λ2 ≥ λ3 ≥ 0. We found that, for the particles of a given type, the probability distributions of the ratios (λ2/λ1) and (λ3/λ2) are essentially identical to each other in the liquids state. We also found that λ2 tends to be equal to the geometric average of λ1 and λ3. In our view, correlations between the eigenvalues may represent “the Poisson ratio effect” at the atomic scale.
Characteristics of undulatory locomotion in granular media
Authors: Peng Zhiwei , Pak On Shun , Elfring Gwynn J.
Published: March 2016

Undulatory locomotion is ubiquitous in nature and observed in different media, from the swimming of flagellated microorganisms in biological fluids, to the slithering of snakes on land, or the locomotion of sandfish lizards in sand. Despite the similarity in the undulating pattern, the swimming characteristics depend on the rheological properties of different media. Analysis of locomotion in granular materials is relatively less developed compared with fluids partially due to a lack of validated force models but recently a resistive force theory in granular media has been proposed and shown useful in studying the locomotion of a sand-swimming lizard. Here we employ the proposed model to investigate the swimming characteristics of a slender filament, of both finite and infinite length, undulating in a granular medium and compare the results with swimming in viscous fluids. In particular, we characterize the effects of drifting and pitching in terms of propulsion speed and efficiency for a finite sinusoidal swimmer. We also find that, similar to Lighthill’s results using resistive force theory in viscous fluids, the sawtooth swimmer is the optimal waveform for propulsion speed at a given power consumption in granular media. The results complement our understanding of undulatory locomotion and provide insights into the effective design of locomotive systems in granular media.
Dean instability of nanofluids with radial temperature and concentration non-uniformity
Authors: Avramenko A. A. , Tyrinov A. I. , Shevchuk I. V. , Dmitrenko N. P.
Published: March 2016

The paper focuses on an investigation into instability of Dean flows of nanofluids in curved channels restricted by two concentric cylinders. The flow is caused by a constant azimuthal pressure gradient. Critical values of the Dean number, which serves as the instability criterion, were found numerically by the collocation method. Functional dependencies of the critical Dean number on the ratio between the radii of the concave and convex walls (0.1…0.99), as well as dimensionless parameters describing the temperature gradient (−3…6), the relative density of the nanoparticles (0…4), the ratio of the Brownian and thermophoretic diffusion (0.1…0.9), Prandtl (0.1…10) and Schmidt (10…100) number were revealed. It was shown that an increase in the relative density of the nanoparticles, the ratio of the Brownian and thermophoretic diffusion, and Schmidt number causes instability under conditions of either positive or negative temperature gradients. An increase in the Prandtl number enforces flow stability for the negative temperature gradient and deteriorates stability for the positive temperature gradient. In light of the complexity of the physical problem in the present paper, only axisymmetric perturbations are considered as the first step to be further developed in future investigations.
Structural design and optimization of near-ultraviolet light-emitting diodes with wide wells
Authors: Kuo Yen-Kuang , Chen Fang-Ming , Chang Jih-Yuan , Shih Ya-Hsuan
Published: March 2016

The characteristics of the near-ultraviolet (NUV) light-emitting diodes (LEDs) with wide (14-nm-thick) and narrow (2-nm-thick) wells under the situations of different numbers of wells and degree of polarization are systematically investigated. The simulation results show that the Auger recombination can be efficiently suppressed with the increase of number of wells in NUV LEDs. For the LEDs with wide wells, the quantum-confined Stark effect and Shockley–Read–Hall recombination play an important role when the number of wells increases, especially when the LED is under low current injection or high degree of polarization. In order to take the advantage of using wide wells, it is proposed that the quaternary Al0.1In0.05Ga0.85N barriers be used in wide-well NUV LEDs along with the use of Al0.3Ga0.7N/Al0.1Ga0.9N superlattice electron-blocking layer to mitigate the polarization effect and electron overflow. With this band-engineering structural design, the optical performance of the wide-well NUV LEDs is much better than its thin-well counterpart even under the situation of high degree of polarization.
Tunability, dielectric, and piezoelectric properties of Ba(1−x)CaxTi(1−y)ZryO3 ferroelectric thin films
Authors: Daumont C. J. M. , Simon Q. , Le Mouellic E. , Payan S. , Gardes P. , Poveda P. , Negulescu B. , Maglione M. , Wolfman J.
Published: March 2016

Tunable ferroelectric capacitors, which exhibit a decrease of the dielectric permittivity (ϵ) under electric field, are widely used in electronics for RF tunable applications (e.g., antenna impedance matching). Current devices use barium strontium titanate as the tunable dielectric, and the need for performance enhancement of the tunable element is the key for device improvement. We report here on libraries of Ba0.97Ca0.03Ti1−xZrxO3 thin films (0 ≤ x ≤ 27%) with a thickness of about 130 nm deposited on IrO2/SiO2/Si substrates using combinatorial pulsed laser deposition allowing for gradients of composition on one sample. A total of 600 capacitors on a single sample were characterized in order to statistically investigate the dielectric properties. We show that the tunabilty is maximum at intermediate compositions, reaching values up to 60% for an electric field of about 400 kV cm−1. We attribute the high tunability in the intermediate compositions to the paraelectric-ferroelectric phase transition, which is brought down to room temperature by the addition of Zr. In addition, the piezoelectric coefficient is found to be decreasing with increasing Zr content.
Comment on “Analysis of single-layer metamaterial absorber with reflection theory” [J. Appl. Phys. 117, 154906 (2015)]
Authors: Tung Nguyen Thanh
Published: March 2016

In a recent paper, Xiong et al. [J. Appl. Phys. 117, 154906 (2015)] presented the simulated results of a Jerusalem-cross structure in an attempt to elaborate their proposed reflection theory for metamaterial absorbers. Noting that even at non-resonant frequencies the real part of the permeability shows an over-high average value and its imaginary part drops abruptly from positivity to negativity, we argue that their simulated results are unphysical, resulting from an incomplete understanding of the retrieval procedure.
Shock compression response of highly reactive Ni + Al multilayered thin foils
Authors: Kelly Sean C. , Thadhani Naresh N.
Published: March 2016

The shock-compression response of Ni + Al multilayered thin foils is investigated using laser-accelerated thin-foil plate-impact experiments over the pressure range of 2 to 11 GPa. The foils contain alternating Ni and Al layers (parallel but not flat) of nominally 50 nm bilayer spacing. The goal is to determine the equation of state and shock-induced reactivity of these highly reactive fully dense thin-foil materials. The laser-accelerated thin-foil impact set-up involved combined use of photon-doppler-velocimetry to monitor the acceleration and impact velocity of an aluminum flyer, and VISAR interferometry was used to monitor the back free-surface velocity of the impacted Ni + Al multilayered target. The shock-compression response of the Ni + Al target foils was determined using experimentally measured parameters and impedance matching approach, with error bars identified considering systematic and experimental errors. Meso-scale CTH shock simulations were performed using real imported microstructures of the cross-sections of the multilayered Ni + Al foils to compute the Hugoniot response (assuming no reaction) for correlation with their experimentally determined equation of state. It was observed that at particle velocities below ∼150 m/s, the experimentally determined equation of state trend matches the CTH-predicted inert response and is consistent with the observed unreacted state of the recovered Ni + Al target foils from this velocity regime. At higher particle velocities, the experimentally determined equation of state deviates from the CTH-predicted inert response. A complete and self-sustained reaction is also seen in targets recovered from experiments performed at these higher particle velocities. The deviation in the measured equation of state, to higher shock speeds and expanded volumes, combined with the observation of complete reaction in the recovered multilayered foils, confirmed via microstructure characterization, is indicative of the occurrence of shock-induced chemical reaction occurring in the time-scale of the high-pressure state. TEM characterization of recovered shock-compressed (unreacted) Ni + Al multilayered foils exhibits distinct features of constituent mixing revealing jetted layers and inter-mixed regions. These features were primarily observed in the proximity of the undulations present in the alternating layers of the Ni + Al starting foils, suggesting the important role of such instabilities in promoting shock-induced intermetallic-forming reactions in the fully dense highly exothermic multilayered thin foils.
Orientation-dependent mechanical behavior and phase transformation of mono-crystalline silicon
Authors: Sun Jiapeng , Ma Aibin , Jiang Jinghua , Han Jing , Han Ying
Published: March 2016

We perform a large-scale molecular dynamics simulation of nanoindentation on the (100), (110), and (111) oriented silicon surface to investigate the orientation-dependent mechanical behavior and phase transformation of monocrystalline silicon. The results show both the remarkable anisotropic mechanical behavior and structure phase transformation of monocrystalline silicon. The mechanical behavior of the (110) and (111) oriented surfaces are similar (has a high indentation modulus, low critical indentation depth for the onset of plastic deformation) but quite different from the (100) oriented surface. The mechanical behavior is carefully linked to the phase transformation. The formation of crystalline bct5 phase and β-Si phase is the fundamental phase transformation mechanism for (100) oriented surface. But, a large number of amorphous silicon can be found beneath the indenter for (110) and (111) oriented surface beside the bct5 phase and β-Si phase. The β-Si phase region is relatively small for (110) and (111) oriented surface, even cannot be detected for (111) oriented surface. This result highlights the dominating role of the amorphous transformation in the mechanical behavior of monocrystalline silicon. Additionally, our results indicate that the high pressure phases form a symmetrical, anisotropic pattern on the indented surface for all three oriented surface which is linked to the active {111}〈110〉 slip systems.
Efficient sampling over rough energy landscapes with high barriers: A combination of metadynamics with integrated tempering sampling
Authors: Yang Y. Isaac , Zhang Jun , Che Xing , Yang Lijiang , Gao Yi Qin
Published: March 2016

In order to efficiently overcome high free energy barriers embedded in a complex energy landscape and calculate overall thermodynamics properties using molecular dynamics simulations, we developed and implemented a sampling strategy by combining the metadynamics with (selective) integrated tempering sampling (ITS/SITS) method. The dominant local minima on the potential energy surface (PES) are partially exalted by accumulating history-dependent potentials as in metadynamics, and the sampling over the entire PES is further enhanced by ITS/SITS. With this hybrid method, the simulated system can be rapidly driven across the dominant barrier along selected collective coordinates. Then, ITS/SITS ensures a fast convergence of the sampling over the entire PES and an efficient calculation of the overall thermodynamic properties of the simulation system. To test the accuracy and efficiency of this method, we first benchmarked this method in the calculation of ϕ − ψ distribution of alanine dipeptide in explicit solvent. We further applied it to examine the design of template molecules for aromatic meta-C—H activation in solutions and investigate solution conformations of the nonapeptide Bradykinin involving slow cis-trans isomerizations of three proline residues.
Visible light broadband perfect absorbers
Authors: Jia X. L. , Meng Q. X. , Yuan C. X. , Zhou Z. X. , Wang X. O.
Published: March 2016

The visible light broadband perfect absorbers based on the silver (Ag) nano elliptical disks and holes array are studied using finite difference time domain simulations. The semiconducting indium silicon dioxide thin film is introduced as the space layer in this sandwiched structure. Utilizing the asymmetrical geometry of the structures, polarization sensitivity for transverse electric wave (TE)/transverse magnetic wave (TM) and left circular polarization wave (LCP)/right circular polarization wave (RCP) of the broadband absorption are gained. The absorbers with Ag nano disks and holes array show several peaks absorbance of 100% by numerical simulation. These simple and flexible perfect absorbers are particularly desirable for various potential applications including the solar energy absorber.
A novel calibration method for non-orthogonal shaft laser theodolite measurement system
Authors: Wu Bin , Yang Fengting , Ding Wen , Xue Ting
Published: March 2016

Non-orthogonal shaft laser theodolite (N-theodolite) is a new kind of large-scale metrological instrument made up by two rotary tables and one collimated laser. There are three axes for an N-theodolite. According to naming conventions in traditional theodolite, rotary axes of two rotary tables are called as horizontal axis and vertical axis, respectively, and the collimated laser beam is named as sight axis. And the difference between N-theodolite and traditional theodolite is obvious, since the former one with no orthogonal and intersecting accuracy requirements. So the calibration method for traditional theodolite is no longer suitable for N-theodolite, while the calibration method applied currently is really complicated. Thus this paper introduces a novel calibration method for non-orthogonal shaft laser theodolite measurement system to simplify the procedure and to improve the calibration accuracy. A simple two-step process, calibration for intrinsic parameters and for extrinsic parameters, is proposed by the novel method. And experiments have shown its efficiency and accuracy.
Photoconductivity of transparent perovskite semiconductor BaSnO3 and SrTiO3 epitaxial thin films
Authors: Park Jisung , Kim Useong , Char Kookrin
Published: March 2016

We measured the photoconductivity of transparent semiconductor BaSnO3 and compared it with that of SrTiO3. Epitaxial BaSnO3 and SrTiO3 films were grown on MgO substrates to exclude any contribution to photoconductivity from the substrate due to its large bandgap. In spite of the same perovskite structure and similar bandgap sizes (3.1–3.2 eV), the photoconductive behaviors of the two materials are quite different in terms of their magnitude and time dependence. The photoconductivity of BaSnO3 persists for many hours after removal from light exposure, whereas the photoconductivity of SrTiO3 shows little persistent conductivity. In addition, the photoconductivity of BaSnO3 increases to a value over 25 times higher than that of SrTiO3, after 3 h of illuminations. The spectral photoconductive responses of both BaSnO3 and SrTiO3 show their highest peaks below 400 nm, suggesting that the electron-hole pair generation is the main mechanism of the photoconductivity for the both materials. The large persistent photoconductivity of BaSnO3 seems related with deep level defects with relatively large barriers for charge trapping and detrapping.
Improved approach to measure the direct flexoelectric coefficient of bulk polyvinylidene fluoride
Authors: Lu Jianfeng , Lv Jiangyan , Liang Xu , Xu Minglong , Shen Shengping
Published: March 2016

We experimentally studied the built-in polarization induced effective piezoelectric constant and direct flexoelectric coefficient in α-phase bulk polyvinylidene fluoride (PVDF). This phenomenon was detected and discussed based on the compression of a truncated cone. An improved mechanical formulation of flexoelectricity was presented and discussed in this study, and the experiment was carried out based on the charge measurement. From the experiment study, a flexoelectric coupling coefficient 202.3 V was calculated from the flexoelectric coefficient μ11=1.6×10−8C/m for bulk polyvinylidene fluoride. We measured the flexoelectric response of bulk PVDF with consideration of the residual piezoelectric contributions and geometry-dependent calibration, which affect the flexoelectric measurement.
Atomistic nature in band-to-band tunneling in two-dimensional silicon pn tunnel diodes
Authors: Tabe Michiharu , Tan Hoang Nhat , Mizuno Takeshi , Muruganathan Manoharan , Anh Le The , Mizuta Hiroshi , Nuryadi Ratno , Moraru Daniel
Published: March 2016

We study low-temperature transport properties of two-dimensional (2D) Si tunnel diodes, or Si Esaki diodes, with a lateral layout. In ordinary Si Esaki diodes, interband tunneling current is severely limited because of the law of momentum conservation, while nanoscale Esaki diodes may behave differently due to the dopants in the narrow depletion region, by atomistic effects which release such current limitation. In thin-Si lateral highly doped pn diodes, we find clear signatures of interband tunneling between 2D-subbands involving phonon assistance. More importantly, the tunneling current is sharply enhanced in a narrow voltage range by resonance via a pair of a donor- and an acceptor-atom in the pn junction region. Such atomistic behavior is recognized as a general feature showing up only in nanoscale tunnel diodes. In particular, a donor-acceptor pair with deeper ground-state energies is likely to be responsible for such a sharply enhanced current peak, tunable by external biases.
Electrical characterization of all-optical helicity-dependent switching in ferromagnetic Hall crosses
Authors: El Hadri M. S. , Pirro P. , Lambert C.-H. , Bergeard N. , Petit-Watelot S. , Hehn M. , Malinowski G. , Montaigne F. , Quessab Y. , Medapalli R. , Fullerton E. E. , Mangin S.
Published: March 2016

We present an experimental study of all-optical helicity-dependent switching (AO-HDS) of ferromagnetic Pt/Co/Pt heterostructures with perpendicular magnetic anisotropy. The sample is patterned into a Hall cross and the AO-HDS is measured via the anomalous Hall effect. This all-electrical probing of the magnetization during AO-HDS enables a statistical quantification of the switching ratio for different laser parameters, such as the threshold power to achieve AO-HDS and the exposure time needed to reach complete switching at a given laser power. We find that the AO-HDS is a cumulative process, a certain number of optical pulses is needed to obtain a full and reproducible helicity-dependent switching. The deterministic switching of the ferromagnetic Pt/Co/Pt Hall cross provides a full “opto-spintronic device,” where the remanent magnetization can be all-optically and reproducibly written and erased without the need of an external magnetic field.
Anisotropy of electron Compton profiles of graphite investigated by electron energy-loss spectroscopy
Authors: Feng Zhenbao , Sakurai Yoshiharu , Liu Jianfang , Su Dangsheng , Schattschneider Peter
Published: March 2016

We report the high-resolution electron Compton profiles of graphite along three main crystallographic directions of [101¯0], [112¯0], and [0001] by recording electron energy-loss spectra at a large momentum transfer using a transmission electron microscope. A significant anisotropy is observed. The experimental results are in good agreement with theoretical calculations that use the full-potential linearized augmented plane wave method based on the local-density approximation. Electron Compton scattering from solids (ECOSS) is shown to be a sensitive probe of the binding structure in a material. ECOSS should be considered as a viable technique to determine the electron momentum distribution in nano-materials because of its short recording time and high momentum resolution.
High temperature Raman investigation of few-layer MoTe2
Authors: Zhang Hongguang , Zhou Wei , Li Xuefei , Xu Jun , Shi Yi , Wang Baigeng , Miao Feng
Published: March 2016

We present a Raman investigation of the temperature effect of single and few layer MoTe2 at an electronic device working temperature range from 300 K to 500 K. We observe linear frequency red-shifts with increasing temperature for the first order Raman active E12g, A1g, Raman inactive B12g mode, and the second order ω2 mode, which can be attributed to the anharmonic effect of the interatomic potential energy. The temperature coefficients of the out-of-plane vibrational B12g modes and inplane vibrational E12g modes are similarly around −0.013 cm−1/K, while lower than that of out-of-plane vibration A1g mode at −0.009 cm−1/K. The temperature coefficient of ω2 mode is −0.00521 cm−1/K, approximately half of those of the first order modes, and the temperature coefficient of transverse acoustic TA (M) mode is indirectly deduced as −0.0102 cm−1/K, which shows the corresponding Mo-Te stretching bonds of TA (M) mode behavior similarly to those of optical Raman vibrations. Our work thus provides temperature dependent lattice vibration information of MoTe2 and could be potentially useful in future optoelectronic devices based on MoTe2 related two dimensional materials.
Isotopic gas analysis through Purcell cavity enhanced Raman scattering
Authors: Petrak B. , Cooper J. , Konthasinghe K. , Peiris M. , Djeu N. , Hopkins A. J. , Muller A.
Published: March 2016

Purcell enhanced Raman scattering (PERS) by means of a doubly resonant Fabry-Perot microcavity (mode volume ≈ 100 μm3 and finesse ≈ 30 000) has been investigated as a technique for isotopic ratio gas analysis. At the pump frequency, the resonant cavity supports a buildup of circulating power while simultaneously enabling Purcell spontaneous emission rate enhancement at the resonant Stokes frequency. The three most common isotopologues of CO2 gas were quantified, and a signal was obtained from 13C16O2 down to a partial pressure of 2 Torr. Due to its small size and low pump power needed (∼10 mW) PERS lends itself to miniaturization. Furthermore, since the cavity is resonant with the emission frequency, future improvements could allow it to serve as its own spectral analyzer and no separate spectroscopic device would be needed.
Long wavelength optical response of graphene-MoS2 heterojunction
Authors: Kwak Joon Young , Hwang Jeonghyun , Calderon Brian , Alsalman Hussain , Spencer Michael G.
Published: March 2016

The optical response of graphene-MoS2 heterojunctions is investigated. Spatial resolution photoresponse maps obtained using multiple bias conditions are measured and analyzed by exciting the graphene-MoS2 heterojunction area, MoS2, and Ti-MoS2 junction on the same device with an 800 nm wavelength Ti-Sapphire raster scanning laser. It is found that a large photothermal electric (PTE) effect is the dominant mechanism for photoresponse in a graphene-MoS2 heterojunction. Responsivities of 0.139 mA/W and 0.019 mA/W on the graphene-MoS2 heterojunction area and 0.457 mA/W and 0.032 mA/W on the Ti-MoS2 junction area are observed with and without a bias, respectively, using a 430 μW laser. Current enhancement due to laser illumination is observed as far as 14 μm from the edge of the graphene-MoS2 heterojunction. Voltage generated by the PTE effect lowers the Schottky barrier junction, enabling more current flow during laser excitation. Photothermal-generated voltages of 0.22–0.47 mV and 31.8–37.9 mV are estimated at the graphene-MoS2 heterojunction and the Ti-MoS2 junction, respectively.
Enhanced photoelectrochemical and photocatalytic activity in visible-light-driven Ag/BiVO4 inverse opals
Authors: Fang Liang , Nan Feng , Yang Ying , Cao Dawei
Published: March 2016

BiVO4 photonic crystal inverse opals (io-BiVO4) with highly dispersed Ag nanoparticles (NPs) were prepared by the nanosphere lithography method combining the pulsed current deposition method. The incorporation of the Ag NPs can significantly improve the photoelectrochemical and photocatalytic activity of BiVO4 inverse opals in the visible light region. The photocurrent density of the Ag/io-BiVO4 sample is 4.7 times higher than that of the disordered sample without the Ag NPs, while the enhancement factor of the corresponding kinetic constant in photocatalytic experiment is approximately 3. The improved photoelectrochemical and photocatalytic activity is benefited from two reasons: one is the enhanced light harvesting owing to the coupling between the slow light and localized surface plasmon resonance effect; the other is the efficient separation of charge carriers due to the Schottky barriers.
Infrared absorption of thin films MoSi2/SiNx micro-bridge
Authors: Jiang Bo , Su Yan , He Yong , Wang Kaiying
Published: March 2016

In this paper, we report the infrared absorption and opto-electrical characteristics of multilayered thin films of MoSi2/SiNx with a micro-bridge structure. The thin films of MoSi2 deposited by radio frequency magnetron sputtering exhibit a relatively smooth surface (RMS roughness <1 nm, ∼0.98 Å/s), on which their square resistance is linearly increased from 340 to 550 Ω/sq. as the thickness decreases from 32 to 16 nm. Fourier transform infrared spectroscopy analysis indicates that the thin film MoSi2 with a thickness of ∼24 nm (450 Ω/sq.) presents the maximum infrared absorption on nearly dielectric thin film SiNx. Optical simulation verifies that the resistivity of the nearly dielectric thin film SiNx has an important influence on the infrared absorption of the thin film MoSi2. This work provides the physical understanding regarding the building of micro-bridges with the high infrared absorption.
Communication: Generalized canonical purification for density matrix minimization
Authors: Truflandier Lionel A. , Dianzinga Rivo M. , Bowler David R.
Published: March 2016

A Lagrangian formulation for the constrained search for the N-representable one-particle density matrix based on the McWeeny idempotency error minimization is proposed, which converges systematically to the ground state. A closed form of the canonical purification is derived for which no a posteriori adjustment on the trace of the density matrix is needed. The relationship with comparable methods is discussed, showing their possible generalization through the hole-particle duality. The appealing simplicity of this self-consistent recursion relation along with its low computational complexity could prove useful as an alternative to diagonalization in solving dense and sparse matrix eigenvalue problems.
Indium-bump-free antimonide superlattice membrane detectors on silicon substrates
Authors: Zamiri M. , Klein B. , Schuler-Sandy T. , Myers S. , Dahiya V. , Cavallo F. , Krishna S.
Published: March 2016

We present an approach to realize antimonide superlattices on silicon substrates without using conventional Indium-bump hybridization. In this approach, PIN superlattices are grown on top of a 60 nm Al0.6Ga0.4Sb sacrificial layer on a GaSb host substrate. Following the growth, the individual pixels are transferred using our epitaxial-lift off technique, which consists of a wet-etch to undercut the pixels followed by a dry-stamp process to transfer the pixels to a silicon substrate prepared with a gold layer. Structural and optical characterization of the transferred pixels was done using an optical microscope, scanning electron microscopy, and photoluminescence. The interface between the transferred pixels and the new substrate was abrupt, and no significant degradation in the optical quality was observed. An Indium-bump-free membrane detector was then fabricated using this approach. Spectral response measurements provided a 100% cut-off wavelength of 4.3 μm at 77 K. The performance of the membrane detector was compared to a control detector on the as-grown substrate. The membrane detector was limited by surface leakage current. The proposed approach could pave the way for wafer-level integration of photonic detectors on silicon substrates, which could dramatically reduce the cost of these detectors.
Combined fluorescence and phosphorescence lifetime imaging
Authors: Shcheslavskiy V. I. , Neubauer A. , Bukowiecki R. , Dinter F. , Becker W.
Published: March 2016

We present a lifetime imaging technique that simultaneously records the fluorescence and phosphorescence lifetime images in confocal laser scanning systems. It is based on modulating a high-frequency pulsed laser synchronously with the pixel clock of the scanner, and recording the fluorescence and phosphorescence signals by multidimensional time-correlated single photon counting board. We demonstrate our technique on the recording of the fluorescence/phosphorescence lifetime images of human embryonic kidney cells at different environmental conditions.