bluuebunny/crossref_metadata_2025 huggingface dataset:
Generalised 3‐D ADI‐FDTD algorithm for the modeling of wave propagation in dispersive media
Authors: Prokopidis K.P. , Zografopoulos D.C.
Published: July 2017

A 3D alternating‐direction‐implicit finite‐difference time‐domain algorithm is presented for problems that involve material frequency dispersion described by generalised modified Lorentzian terms. The implementation exploits the auxiliary differential equations formulation and applies an order reduction technique in order to achieve synchronisation with the two‐step procedure. The efficiency of the proposed method is validated in a benchmark problem of a resonant metallic cavity filled with plasma.
Dynamic current mode logic based flip‐flop design for robust and low‐power security integrated circuits
Authors: Shen Jizhong , Geng Liang , Zhang Fan
Published: July 2017

Side‐channel analysis (SCA) is a powerful technique to reveal the secrets using detectable physical leakages from logic elements, which brings severe security threats to modern circuits. To alleviate this problem, applying cell‐level countermeasure is usually a suitable solution, which is mainly implemented as dual‐rail precharge logic. Mace et al. has the proposed dynamic current mode logic (DyCML) scheme as a novel technology to resist SCA, whose power consumption is constant regardless of the data processed. However, the DyCML‐based sequential elements are still in blank field. So, we have implemented a novel flip‐flop compatible with DyCML, whose enhanced security has been proved by corresponding simulations.
Comparison of conventional and regenerative electrostatic energy harvesters
Authors: Li Yin , Misra Manjusri , Gregori Stefano
Published: July 2017

This study presents a performance comparison of two green electrostatic energy harvesters based on force‐sensitive mechanically variable capacitors. A startup battery is required in the conventional electrostatic energy harvester to precharge the mechanically variable capacitor. This adds an extra element to the device and increases the harvester's size and weight. The proposed harvester does not need a startup battery, operates in a regenerative mode, and provides a similar output power. It has a compact size and can start from low voltages. The conventional and regenerative harvesters were developed using mechanically variable capacitors fabricated with renewable materials (i.e. nanocellulose and carbon‐coated nanocellulose). The flexible nanocellulose films and the cost‐effective fabrication process make the energy harvesters suitable for powering low‐power and wearable devices. The bio‐based materials further reduce the environmental impact of the devices. Prototypes of the two energy harvesters were built, and their performances were compared on the basis of simulation and measurement results. Both simulation and experimental results are shown to demonstrate the startup and scalable energy availability of the proposed regenerative electrostatic energy harvester for driving low‐power devices, such as wireless sensor networks.
Three‐phase qZ‐source inverter with fault tolerant capability
Authors: Pires Vitor Fernão , Foito Daniel , Cordeiro Armando
Published: July 2017

The requirement of three‐phase inverters with high reliability capability is considered important in several applications. Most of the adopted fault‐tolerant solutions use classical three‐phase voltage source inverters (VSI) with redundant controlled power devices or modified control strategies for acceptably degraded performance in the event of a failure yielding the loss of devices. This work proposes the use of a fault‐tolerant converter based on the quasi‐Z‐source inverter (qZSI). This inverter presents important features such as boost capability and not requires dead time circuits. These features associated to the proposed topology results in a converter with high reliability and fault‐tolerant capability. The proposed topology is designed to allow the reconfiguration of the converter after a power switch failure, using only two legs in the faulty mode. Additionally, this topology avoids extra inductors, capacitors and active power switches for the fault‐tolerant condition. A current controller associated to a vectorial voltage modulator is used to control the proposed topology, which results in three‐phase balanced AC currents with reduced total harmonic distortion even in faulty condition. The performance of this solution is confirmed through experimental results obtained from a laboratory prototype.
InBr3-Catalyzed Synthesis of Aryl 1,2-trans-Thio(seleno)glycosides
Authors: Yu Lan , Xue Weihua , Ma Teng , Li Changwei , Liang Haijing , Wang Zhaoyan
Published: July 2017

InBr3 is demonstrated to be an efficient catalyst for reactions of fully acetated aldoses with aryl mercaptans or selenophenol at room temperature, rapidly furnishing the corresponding thioglycosides or selenoglycosides with exclusively 1,2-trans-stereoselectivity. This bromide is an air- and moisture-stable Lewis acid and therefore the reactions can be performed in air atmosphere making the procedure simple to perform.
Regio- and Diastereoselective Samarium-Mediated Allylic Benzoate Reductions
Authors: O’Neil Gregory , Stockdale Trevor
Published: July 2017

A regio- and diastereoselective samarium(II)-mediated reduction of allylic benzoates is described. Yields for the reactions are generally high with diastereoselectivities up to 90:10 and in some cases only a single regioisomer was obtained. The stereoselectivity of the reaction is proposed to arise from chelation of a hydroxyl-stereocenter and starting alkene geometry, with protonation occurring intramolecularly by samarium-bound water.
Knee Osteoarthritis after Reconstruction of Isolated Anterior Cruciate Ligament Injuries: A Systematic Literature Review
Authors: Riccardo Compagnoni , Fabio Catani , Pietro Randelli
Published: July 2017

Purpose The aim of this review was to analyze the current literature on osteoarthritic evolution of knees without any combined meniscal or ligament lesions undergoing anterior cruciate ligament (ACL) reconstruction.

Methods A PubMed/MEDLINE research was performed using the following keywords: “Anterior Cruciate Ligament Reconstruction” [Mesh] AND “Osteoarthritis, Knee” [Mesh]. Only English language literature and articles published after 2005 were included. Studies including concomitant meniscal tears, posterior cruciate or collateral ligament injuries, previous surgery in the affected knees, infections, osteochondral defects, loose bodies, synovial plica syndrome, and posteromedial or posterolateral corner injuries were not considered in this review.

Results Twelve studies were selected. These papers included 892 patients (mean age at the time of surgery was 22.3 years), with an average follow-up of 11 years. Imaging at follow-up was obtained with standard radiographs in nine studies, magnetic resonance imaging (MRI) in one study, and both X-rays and MRI in two studies. Eight studies reported osteoarthritic evolution, with different prevalence.

Conclusion Only few high-quality studies focused on these specific patients have been published. When reconstructed, isolated ACL-deficient knees have a low risk of osteoarthritic evolution, but mild signs of joint degeneration are reported by the current literature.

Level of Evidence Level IV, systematic review of level I to level IV studies.
Second Generation Needling Techniques for the Treatment of Chondral Defects in Animal Model
Authors: Zedde Pietro , Cudoni Sebastiano , Manunta Lucia , Passino Eraldo , Masala Gerolamo , Brunetti Antonio , Uboldi Francesco , Manunta Andrea
Published: July 2017

Purpose To compare the macroscopic, histological, and immunohistochemical characteristics of the repair tissue of chondral defects treated with microfracture and nanofracture in an ovine model.

Methods Full-thickness chondral lesions were created in the medial femoral condyle of both knees in four adult sheep and were treated with microfracture on one side and with nanofracture on the contralateral side. Chondral repair was assessed after 12 months by macroscopic, histological, and immunohistochemical analyses.

Results Histological cartilage repair significantly improved in the samples treated with nanofracture for cellular morphological characteristics and cartilage architecture. The immunohistochemical analysis showed a significantly higher immunoreactivity to type II collagen in the defects treated with nanofracture.

Conclusion Nanofracture provided better repair tissue than microfracture, with a more satisfactory cartilage architecture renovation and tissue having greater type II collagen content.

Clinical Relevance Mesenchymal stem cell stimulation is the most frequently used primary cartilage repair procedure. Nanofracture represents a novel technique to stimulate bone marrow that results into a successful repair of chondral defects.
How Do Obstetric and Neonatology Teams Communicate Prior to High-Risk Deliveries?
Authors: Suresh Gautham , Sundgren Nathan
Published: July 2017

Background Improving communication in healthcare improves the quality of care and patient outcomes, but communication between obstetric and neonatal teams before and during a high-risk delivery is poorly studied.

Study Design We developed a survey to study communication between obstetric and neonatal teams around the time of a high-risk delivery. We surveyed neonatologists from North America and asked them to answer questions about their institutions' communication practices.

Results The survey answers revealed variations in communication practices between responders. Most institutions relied on nursing to communicate obstetric information to the neonatal team. Although a minority of institutions used a standardized communication process to summon neonatology team or to communicate in the delivery room, these reported higher rates of information sharing and greater satisfaction with communication between services.

Conclusion Standardized communication procedures are an underutilized method of communication and have the potential to improve communication around high-risk deliveries.
The effect of pressure on the conductivity behavior of the (NH4)3H(SeO4)2 superprotonic crystal
Authors: Lindner Ł. , Zdanowska-Frączek M. , Pawłowski A. , Frączek Z. J. , Masłowski T.
Published: July 2017

The impedance spectra of (NH4)3 H(SeO4)2 in low and high-conductive phases under various thermodynamic conditions were analyzed. The measurements were performed by the ac admittance technique along the trigonal c axis of the crystal, i.e., along the direction perpendicular to the plane in which, in the superionic phases, a dynamically disordered H-bond network was formed. Activation energies and activation volumes were calculated for different phases of the (NH4)3 H(SeO4)2 crystal from the baric dependencies of dc conductivity and they were correlated with pressure coefficients of the phase transitions. The experimental results were analyzed within the classical hopping model, in terms of the strong proton–phonon coupling and polaronic effect.
First-principles characterization of native-defect-related optical transitions in ZnO
Authors: Lyons J. L. , Varley J. B. , Steiauf D. , Janotti A. , Van de Walle C. G.
Published: July 2017

We investigate the electrical and optical properties of oxygen vacancies (VO), zinc vacancies (VZn), hydrogenated VZn, and isolated dangling bonds in ZnO using hybrid functional calculations. While the formation energy of VO is high in n-type ZnO, indicating that this center is unlikely to form, our results for optical absorption signals associated with VO are consistent with those observed in irradiated samples, and give rise to emission with a peak at less than 1 eV. Under realistic growth conditions, we find that VZn is the lowest-energy native defect in n-type ZnO, acting as an acceptor that is likely to compensate donor doping. Turning to optical transitions, we first examine NO as a case study, since N-related transitions have been identified in experiments on ZnO. We also examine how hydrogen, often unintentionally present in ZnO, forms stable complexes with VZn and modifies its optical properties. Compared with isolated VZn, VZn-H complexes have charge-state transition levels lower in the band gap as well as have lower formation energies. These complexes also lead to characteristic vibrational frequencies which compare favorably with experiment. Oxygen dangling bonds show behavior mostly consistent with VZn, while zinc dangling bonds give rise to transition levels near the ZnO conduction-band minimum and emission peaking near 2.4 eV. We discuss our results in view of the available experimental literature.
Bulk saturable absorption in topological insulator thin films
Authors: Gopal Radha Krishna , Ambast Deepak K. S. , Singh Sourabh , Sarkar Jit , Pal Bipul , Mitra Chiranjib
Published: July 2017

We present nonlinear optical absorption properties of pulsed laser deposited thin films of topological insulator (TI), Bi2Se3 on a quartz substrate, using an open aperture z-scan technique. We observed saturable absorption with a low saturation intensity in as deposited thin films. Past results from the literature are inconclusive in establishing whether the saturable absorption in TI is coming from surface states or the bulk. Specifically designed experiments with magnetically doped TI samples allow us to attribute the saturable absorption characteristic of TI to the bulk states. Detailed experimental procedures and possible explanation of observed results have been discussed.
Double Hall sensor structure reducing voltage offset
Authors: Oszwaldowski M. , El-Ahmar S.
Published: July 2017

In this paper, we report on the double Hall sensor structure (DHSS) in which the voltage offset can be effectively reduced. The DHSS is composed of two standard Hall sensors that are activated with two currents from electrically independent current sources. The operation principle of the DHSS is explained in detail, and the concluded properties of the DHSS are confirmed in the experimental part of the paper. The measurements are performed on DHSSs based on InSb thin films. The offset is reduced by about three orders of magnitude. The minimum value of the reduced offset obtained is 10 μV. It appears that the minimum reduced offset is limited by the electric noise. The advantage of DHSS is that it can be manufactured with the standard thin film technology enabling effective miniaturization of the system. The DHSS can effectively be used for the measurements of the Hall effect in ultra-thin layers containing the two dimensional electron gas, such as the epitaxial graphene.
Pulsed high magnetic field measurement with a rubidium vapor sensor
Authors: George S. , Bruyant N. , Béard J. , Scotto S. , Arimondo E. , Battesti R. , Ciampini D. , Rizzo C.
Published: July 2017

We present a new technique to measure pulsed magnetic fields based on the use of rubidium in gas phase as a metrological standard. We have therefore developed an instrument based on laser inducing transitions at about 780 nm (D2 line) in rubidium gas contained in a mini-cell of 3 mm × 3 mm cross section. To be able to insert such a cell in a standard high-field pulsed magnet, we have developed a fibred probe kept at a fixed temperature. Transition frequencies for both the π (light polarization parallel to the magnetic field) and σ (light polarization perpendicular to the magnetic field) configurations are measured by a commercial wavemeter. One innovation of our sensor is that in addition to the usual monitoring of the light transmitted by the Rb cell, we also monitor the fluorescence emission of the gas sample from a volume of 0.13 mm3. Our sensor has been tested up to about 58 T.
Guiding characteristics of guided waves in slab waveguide with hexagonal boron nitride
Authors: Xu Hailin , Wang Xi , Jiang Xing , Dai Xiaoyu , Xiang Yuanjiang
Published: July 2017

Due to the non-overlapping Reststrahlen bands, both type I and type II hyperbolic responses are available in hexagonal boron nitride (hBN), which can be used as the guiding medium or the cladding medium in the slab waveguide. The characteristics of guided waves in the slab waveguide with hBN are theoretically investigated, and the existence conditions of the guided and surface modes of waveguides in the two types of hyperbolic responses are analyzed by using the graphic method. It is shown that, in the type-Ι hyperbolicity of the hBN waveguide, both TE and TM guided modes are existent. In the type-ΙΙ hyperbolicity, both the guided and surface modes are existent for TM guided waves; however, the guided and surface modes of TE polarization are absent. In addition, the propagation constant and the normalized power versus the thickness of waveguide are showed and the cutoff thickness and the power localization are discussed.
Femtosecond response time measurements of a Cs2Te photocathode
Authors: Aryshev A. , Shevelev M. , Honda Y. , Terunuma N. , Urakawa J.
Published: July 2017

Success in design and construction of a compact, high-brightness accelerator system is strongly related to the production of ultra-short electron beams. Recently, the approach to generate short electron bunches or pre-bunched beams in RF guns directly illuminating a high quantum efficiency semiconductor photocathode with femtosecond laser pulses has become attractive. The measurements of the photocathode response time in this case are essential. With an approach of the interferometer-type pulse splitter deep integration into a commercial Ti:Sa laser system used for RF guns, it has become possible to generate pre-bunched electron beams and obtain continuously variable electron bunch separation. In combination with a well-known zero-phasing technique, it allows us to estimate the response time of the most commonly used Cs2Te photocathode. It was demonstrated that the peak-to-peak rms time response of Cs2Te is of the order of 370 fs, and thereby, it is possible to generate and control a THz sequence of relativistic electron bunches by a conventional S-band RF gun. This result can also be applied for investigation of other cathode materials and electron beam temporal shaping and further opens a possibility to construct wide-range tunable, table-top THz free electron laser.
Numerical analysis of temperature field improvement with nanoparticles designed to achieve critical power dissipation in magnetic hyperthermia
Authors: Tang Yundong , Flesch Rodolfo C. C. , Jin Tao
Published: July 2017

Magnetic nanoparticle (MNP) hyperthermia is a promising emerging therapy for cancer treatment that is minimally invasive and has been successfully used to treat different types of tumors. The power dissipation of MNPs, which is one of the most important factors during a hyperthermia treatment, is determined by the properties of MNPs and characteristics of the magnetic field. This paper proposes a method based on the finite element analysis for determining the value of the power dissipation of particles (PDP) that can maximize the average temperature of the tumor during treatment and at the same time guarantee that the maximum temperature is within the therapeutic range. The application of the critical PDP value can improve the effectiveness of the treatment since it increases the average temperature in the tumor region while limiting the damage to the healthy tissue that surrounds it. After the critical PDP is determined for a specific model, it is shown how the properties of the MNPs can be chosen to achieve the desired PDP value. The transient behavior of the temperature distribution for two different models considering blood vessels is analyzed as a case study, showing that the presence of a blood vessel inside the tumor region can significantly decrease the uniformity of the temperature field and also increase the treatment duration given its cooling effects. To present a solution that does not depend upon a good model of the tumor region, an alternative method that uses MNPs with low Curie temperature is proposed, given the temperature self-regulating properties of such MNPs. The results demonstrate that the uniformity of the temperature field can be significantly increased by combining the optimization procedure proposed in this paper with the use of low-Curie-temperature MNPs.
Drift and separation in collisionality gradients
Authors: Ochs I. E. , Rax J. M. , Gueroult R. , Fisch N. J.
Published: July 2017

We identify a single-particle drift resulting from collisional interactions with a background species, in the presence of a collisionality gradient and background net flow. We analyze this drift in different limits, showing how it reduces to the well known impurity pinch for high-Zi impurities. We find that in the low-temperature, singly ionized limit, the magnitude of the drift becomes mass-dependent and energy-dependent. By solving for the resulting diffusion-advection motion, we propose a mass-separation scheme that takes advantage of this drift, and analyze the separative capability as a function of collisionally dissipated energy.
Generation of highly symmetric, cylindrically convergent shockwaves in water
Authors: Bland S. N. , Krasik Ya. E. , Yanuka D. , Gardner R. , MacDonald J. , Virozub A. , Efimov S. , Gleizer S. , Chaturvedi N.
Published: July 2017

We report on pulsed power driven, exploding copper wire array experiments conducted to generate cylindrical convergent shockwaves in water employing μs risetime currents >550 kA in amplitude and with stored energies of >15 kJ—a substantial increase over previous results. The experiments were carried out on the recently constructed Mega-Ampere-Compression-and-Hydrodynamics facility at Imperial College London in collaboration with colleagues of Technion, Israel. 10 mm diameter arrays consisting of 60 × 130 μm wires were utilized, and the current and voltage diagnostics of the load region suggested that ∼8 kJ of energy was deposited in the wires (and the load region close to the wires) during the experiments, resulting in the formation of dense, highly resistive plasmas that rapidly expanded driving the shockwaves in water. Laser-backlit framing images of the shockfront were obtained at radii <0.25 mm for the first time, and there was strong evidence that even at radii <0.1 mm this front remains stable, resulting in a convergence ratio of >50:1. Framing images and streak photographs showed that the velocity of the shockwave reached ∼7.5 km s−1 at 0.1 mm from the axis. 2D hydrodynamic simulations that match the experimentally obtained implosion trajectory suggest that pressures >1 Mbar are produced within 10 μm of the axis along with water densities of 3gcm−3 and temperatures of many 1000 s of Kelvin. Under these conditions, Quotidian Equation of State suggests that a strongly coupled plasma with an ionization fraction of ∼0.7 would be formed. The results represent a “stepping stone” in the application of the technique to drive different material samples into high pressure, warm dense matter regimes with compact, university scale generators, and provide support in scaling the technique to multi-mega ampere currents.
Noise radiated by low-Reynolds number flows past a hemisphere at Ma = 0.3
Authors: Yao Hua-Dong , Davidson Lars , Eriksson Lars-Erik
Published: July 2017

Flows past a hemisphere and their noise generation are investigated at the Reynolds numbers (Re) of 1000 and 5000. The Mach number is 0.3. The computational method of the flows is large eddy simulation. The noise is computed using the Ffowcs Williams and Hawkings Formulation 1C (F1C). An integral surface with an open end is defined for the F1C. The end surface is removed to reduce the numerical contamination that is introduced by vortices passing this surface. However, the contamination cannot be completely reduced since a discontinuity of the flow quantities still exists at the open surface boundary. This problem is solved using a surface correction method, in which a buffer zone is set up at the end of the integral surface. The transformation of flow structures due to Re is explored. Large coherent structures are observable at low Re, whereas they diminish at high Re. A large amount of small-scale turbulent vortices occur in the latter case. It is found that these characteristics of the flows have an important influence on the noise generation in regard to the noise spectra. In the flows studied in this work, the fluctuating pressure on the walls is a negligible noise contributor as compared with the wake.
Breakdown conditions of short air-insulated gaps under alternating non-uniform electric fields
Authors: Chen Yong , Zheng Yuesheng , Miao Xiren
Published: July 2017

The breakdown conditions of short air-insulated gaps under alternating non-uniform electric fields are investigated for providing an accurate prediction of the breakdown voltages of commonly used electrode systems. The breakdown voltages with the tip radius of the highly stressed electrode varying between 0.1 cm and 2 cm and the gap distance ranging from 1 cm to 5 cm were experimentally investigated, and the breakdown electric field distributions in inter-electrode gaps were analyzed by a finite element method. An abnormal phenomenon was observed that the breakdown voltage increased in a highly non-uniform electric field with the same gap distance. For different electrode arrangements, the breakdown conditions could not be characterized by the relationship between the maximum breakdown electric field at the electrode tip and the field non-uniform coefficient. Therefore, a combined breakdown criterion was proposed by introducing a geometrical parameter of the electrode system. The breakdown conditions can be, respectively, evaluated by the streamer inception criterion and a fitting formula when the value of the geometric parameter is on opposite sides of a critical value.
Differential carrier lifetime and transport effects in electrically injected III-nitride light-emitting diodes
Authors: Rashidi A. , Nami M. , Monavarian M. , Aragon A. , DaVico K. , Ayoub F. , Mishkat-Ul-Masabih S. , Rishinaramangalam A. , Feezell D.
Published: July 2017

This work describes a small-signal microwave method for determining the differential carrier lifetime and transport effects in electrically injected InGaN/GaN light-emitting diodes (LEDs). By considering the carrier diffusion, capture, thermionic escape, and recombination, the rate equations are used to derive an equivalent small-signal electrical circuit for the LEDs, from which expressions for the input impedance and modulation response are obtained. The expressions are simultaneously fit to the experimental data for the input impedance and modulation response for nonpolar InGaN/GaN micro-LEDs on free-standing GaN substrates. The fittings are used to extract the transport related circuit parameters and differential carrier lifetimes. The dependence of the parameters on the device diameter and current density is reported. We also derive approximations for the modulation response under low and high injection levels and show that the transport of carriers affects the modulation response of the device, especially at low injection levels. The methods presented are relevant to the design of high-speed LEDs for visible-light communication.
Spreading of electron scale magnetic reconnection with a wave number dependent speed due to the propagation of dispersive waves
Authors: Jain Neeraj , Büchner Jörg
Published: July 2017

In this work, we study electron scale spreading of localized magnetic reconnection in the presence of a guide magnetic field, however, without the influence of ions and cross-scale coupling. These fundamental physics studies will help to understand the coupling of the electron scale spreading with the ion scales in real systems. An electron-magnetohydrodynamic (EMHD) model is employed to model the physics at electron scales. Three dimensional EMHD simulations and linear eigen mode analysis are performed for different guide field strengths. The simulations show a wave-like bi-directional spreading of magnetic reconnection at electron scales. The electron scale spreading, however, unlike the ion scale spreading by Alfvén waves, is caused by the uni- and bi-directional propagation of the dispersive flow induced and whistler wave modes, respectively. The dispersive nature of the two wave modes makes the spreading-speed dependent on the wave numbers of the unstable tearing mode, which depend on the thickness of the electron current sheet and the strength of the guide field. A model of the speed of spreading is developed, in which the spreading-speeds parallel and anti-parallel to the guide field are given by linear combinations of the group speeds of the two wave modes. The model prediction of the spreading speeds agrees well with the speeds obtained from the simulation results. For small guide fields, the spreading is asymmetric being faster in the direction of the electron flow. On increasing the guide field, the spreading becomes increasingly symmetric, with the speeds of the order of electron Alfvén speed in the guide magnetic field, due to the dominance of the whistler group speed in determining the speed of the spreading. As a consequence of the asymmetric spreading, the chain of alternate X- and O-points, formed due the growth of oblique tearing modes, extends farther in the direction of electron flow as compared to that in the direction of the guide magnetic field.
Mesh-free Hamiltonian implementation of two dimensional Darwin model
Authors: Siddi Lorenzo , Lapenta Giovanni , Gibbon Paul
Published: July 2017

A new approach to Darwin or magnetoinductive plasma simulation is presented, which combines a mesh-free field solver with a robust time-integration scheme avoiding numerical divergence errors in the solenoidal field components. The mesh-free formulation employs an efficient parallel Barnes-Hut tree algorithm to speed up the computation of fields summed directly from the particles, avoiding the necessity of divergence cleaning procedures typically required by particle-in-cell methods. The time-integration scheme employs a Hamiltonian formulation of the Lorentz force, circumventing the development of violent numerical instabilities associated with time differentiation of the vector potential. It is shown that a semi-implicit scheme converges rapidly and is robust to further numerical instabilities which can develop from a dominant contribution of the vector potential to the canonical momenta. The model is validated by various static and dynamic benchmark tests, including a simulation of the Weibel-like filamentation instability in beam-plasma interactions.
Correlating the silicon surface passivation to the nanostructure of low-temperature a-Si:H after rapid thermal annealing
Authors: Macco Bart , Melskens Jimmy , Podraza Nikolas J. , Arts Karsten , Pugh Christopher , Thomas Owain , Kessels Wilhelmus M. M.
Published: July 2017

Using an inductively coupled plasma, hydrogenated amorphous silicon (a-Si:H) films have been prepared at very low temperatures (<50 °C) to provide crystalline silicon (c-Si) surface passivation. Despite the limited nanostructural quality of the a-Si:H bulk, a surprisingly high minority carrier lifetime of ∼4 ms is demonstrated after a rapid thermal annealing treatment. Besides the excellent level of surface passivation, the main advantage of the low-temperature approach is the facile suppression of undesired epitaxial growth. The correlation between the a-Si:H nanostructure and the activation of a-Si:H/c-Si interface passivation, upon annealing, has been studied in detail. This yields a structural model that qualitatively describes the different processes that take place in the a-Si:H films during annealing. The presented experimental findings and insights can prove to be useful in the further development of very thin a-Si:H passivation layers for use in silicon heterojunction solar cells.
Thermal conductivity of cross-linked polyethylene from molecular dynamics simulation
Authors: Xiong Xue , Yang Ming , Liu Changlin , Li Xiaobo , Tang Dawei
Published: July 2017

The thermal conductivity of cross-linked bulk polyethylene is studied using molecular dynamics simulation. The atomic structure of the cross-linked polyethylene (PEX) is generated through simulated bond formation using LAMMPS. The thermal conductivity of PEX is studied with different degrees of crosslinking, chain length, and tensile strain. Generally, the thermal conductivity increases with the increasing degree of crosslinking. When the length of the primitive chain increases, the thermal conductivity increases linearly. When the polymer is stretched along one direction, the thermal conductivity increases in the stretched direction and decreases in the direction perpendicular to it. However, the thermal conductivity varies slightly when the polymer is stretched in three directions simultaneously.
Tuning the transport behavior of centimeter-scale WTe2 ultrathin films fabricated by pulsed laser deposition
Authors: Gao Ming , Zhang Minhao , Niu Wei , Chen Yequan , Gu Min , Wang Haoyu , Song Fengqi , Wang Peng , Yan Shicheng , Wang Fengqiu , Wang Xinran , Wang Xuefeng , Xu Yongbing , Zhang Rong
Published: July 2017

We report on an avenue to obtain the centimeter-scale, uniform, and high-quality WTe2 ultrathin films by a pulsed laser deposition technique and the post-annealing under the tellurium (Te) vapor. The WTe2 ultrathin films showed the typical metallic behavior when Te vacancies were mostly eliminated. Magnetoresistance measurements showed that WTe2 ultrathin films underwent the competition between weak localization and weak antilocalization that could be modulated by the amount of Te vacancies. Our study may open an avenue to improve the charge transport of WTe2 for its two-dimensional device applications.
Synthesis of nitrogen-doped graphene via pentachloropyridine as the sole solid source
Authors: Wan J. X. , You Y. , Xu Y. L. , Wang C. , Zhang P. B. , Jiang X. Y. , Fang X. H. , Yang L. Y. , Chen X. Y.
Published: July 2017

The substitution of nitrogen atoms in the lattice plane of the graphene can adjust the electronic properties of the graphene to translate it from the half-metal to the n-type semiconductor. Here, we report a practicable growth of nitrogen-doped graphene films with the nitrogen atoms doped content of 4.4–7.5% by the sole solid precursor based chemical vapor deposition method. After the post-annealing process at high temperature, the morphology and crystallization quality of the nitrogen-doped graphene film were considerably improved. The as-synthesized nitrogen-doped graphene films exhibit typical n-type behavior with the electron carrier density of approximately 6.55 × 1012 cm−2 and the Hall mobility of around 522 cm2V−1 s−1.
High free carrier concentration in p-GaN grown on AlN substrates
Authors: Sarkar Biplab , Mita Seiji , Reddy Pramod , Klump Andrew , Kaess Felix , Tweedie James , Bryan Isaac , Bryan Zachary , Kirste Ronny , Kohn Erhard , Collazo Ramon , Sitar Zlatko
Published: July 2017

A high free hole concentration in III-nitrides is important for next generation optoelectronic and high power electronic devices. The free hole concentration exceeding 1018 cm−3 and resistivity as low as 0.7 Ω cm are reported for p-GaN layers grown by metalorganic vapor phase epitaxy on single crystal AlN substrates. Temperature dependent Hall measurements confirmed a much lower activation energy, 60–80 mV, for p-GaN grown on AlN as compared to sapphire substrates; the lowering of the activation energy was due to screening of Coulomb potential by free carriers. It is also shown that a higher doping density (more than 5 × 1019 cm−3) can be achieved in p-GaN/AlN without the onset of self-compensation.
Ionic transport properties in AgCl under high pressures
Authors: Wang Jia , Zhang Guozhao , Liu Hao , Wang Qinglin , Shen Wenshu , Yan Yalan , Liu Cailong , Han Yonghao , Gao Chunxiao
Published: July 2017

Ionic transport behaviors of silver chloride (AgCl) have been revealed with impedance spectra measurement under high pressures up to 20.4 GPa. AgCl always presented ionic conducting under experimental pressures, but electronic conduction can coexist with ionic conduction within the pressure range from 6.7 to 9.3 GPa. The ionic conductivity of AgCl decreases by three orders of magnitude under compression, indicating that Ag+ ion migrations are suppressed by high pressure. A parameter, fW, was defined as the starting frequency at which Ag+ ions begin to show obvious long-distance diffusion in AgCl. fW showed a similar trend with the ionic conductivity under high pressures, indicating that the speed of Ag+ ion diffusion slows down as the pressure increases. Unlike AgI, Ag+ ion diffusion in AgCl is controlled by the indirect-interstitial mechanism. Due to stronger ionic bonds and larger lattice deformation, Ag+ ion diffusion in the rigid Cl− lattice is more difficult than in the I− lattice under high pressures.
Toward achieving flexible and high sensitivity hexagonal boron nitride neutron detectors
Authors: Maity A. , Grenadier S. J. , Li J. , Lin J. Y. , Jiang H. X.
Published: July 2017

Hexagonal boron nitride (h-BN) detectors have demonstrated the highest thermal neutron detection efficiency to date among solid-state neutron detectors at about 51%. We report here the realization of h-BN neutron detectors possessing one order of magnitude enhancement in the detection area but maintaining an equal level of detection efficiency of previous achievement. These 3 mm × 3 mm detectors were fabricated from 50 μm thick freestanding and flexible 10B enriched h-BN (h-10BN) films, grown by metal organic chemical vapor deposition followed by mechanical separation from sapphire substrates. Mobility-lifetime results suggested that holes are the majority carriers in unintentionally doped h-BN. The detectors were tested under thermal neutron irradiation from californium-252 (252Cf) moderated by a high density polyethylene moderator. A thermal neutron detection efficiency of ∼53% was achieved at a bias voltage of 200 V. Conforming to traditional solid-state detectors, the realization of h-BN epilayers with enhanced electrical transport properties is the key to enable scaling up the device sizes. More specifically, the present results revealed that achieving an electrical resistivity of greater than 1014 Ω⋅cm and a leakage current density of below 3 × 10−10 A/cm2 is needed to fabricate large area h-BN detectors and provided guidance for achieving high sensitivity solid state neutron detectors based on h-BN.
Refractive index sensing based on semiconductor nanowire lasers
Authors: Wu Xiaoqin , Chen Qiushu , Xu Peizhen , Tong Limin , Fan Xudong
Published: July 2017

We demonstrate a refractive index (RI) sensor based on semiconductor nanowire lasers. It is shown that the TE01 mode is responsible for lasing and sensing with the lasing threshold of 3 μJ/mm2 and the lasing peak width as narrow as 0.22 nm. A RI sensitivity of 21.2 nm/RIU (refractive index units), a figure of merit of approximately 100, and an RI detection limit of 1.4×10−3 RIU are achieved.
Ambipolar field-effect transistors by few-layer InSe with asymmetry contact metals
Authors: Lin Chang-Yu , Ulaganathan Rajesh Kumar , Sankar Raman , Chou Fang-Cheng
Published: July 2017

Group IIIA−VIA layered semiconductors (MX, where M = Ga and In, X = S, Se, and Te) have attracted tremendous interest for their anisotropic optical, electronic, and mechanical properties. In this study, we demonstrated that metal and InSe junctions can lead to carrier behaviors in few-layered InSe FETs. These results indicate that the polarity of few-layered InSe FETs can be determined by using metals with different work functions. We adopted FET S/D metal contacts with asymmetric work functions to reduce the Schottky barriers of electrons and holes, and discovered that few-layered InSe FETs with carefully selected metal contacts can achieve ambipolar behaviors. These results indicate that group IIIA−VIA layered semiconductor FETs with asymmetry contact metals have great potential for applications in photovoltaic devices, optical sensors, and CMOS inverter circuits.
Note: Density functional theory for uniformly charged hard-sphere ions
Authors: Jang Seanea , Shin Ghi Ryang , Kim Soon-Chul
Published: July 2017

The density function theory has been proposed for studying the structural properties of electrolytes containing uniformly charged hard-spherical ions. The calculated result shows good agreement with the corresponding Monte Carlo simulation data of Bohinc et al. [J. Chem. Phys. 145, 234901 (2016)]. The results confirm that the attraction between like-charged planar surfaces is the results of the intra-ionic correlation and depends strongly on the charge distribution of hard-sphere ions.
Relative functional and optical absorption cross-sections of PSII and other photosynthetic parameters monitored in situ, at a distance with a time resolution of a few seconds, using a prototype light induced fluorescence transient (LIFT) device
Authors: Osmond Barry , Chow Wah Soon , Wyber Rhys , Zavafer Alonso , Keller Beat , Pogson Barry J. , Robinson Sharon A.
Published: July 2017

The prototype light-induced fluorescence transient (LIFT) instrument provides continuous, minimally intrusive, high time resolution (~2 s) assessment of photosynthetic performance in terrestrial plants from up to 2 m. It induces a chlorophyll fluorescence transient by a series of short flashes in a saturation sequence (180 ~1μs flashlets in <380 μs) to achieve near-full reduction of the primary acceptor QA, followed by a relaxation sequence (RQA; 90 flashlets at exponentially increasing intervals over ~30 ms) to observe kinetics of QA re-oxidation. When fitted by the fast repetition rate (FRR) model (Kolber et al. 1998) the QA flash of LIFT/FRR gives smaller values for FmQA from dark adapted leaves than FmPAM from pulse amplitude modulated (PAM) assays. The ratio FmQA/FmPAM resembles the ratio of fluorescence yield at the J/P phases of the classical O-J-I-P transient and we conclude that the difference simply is due to the levels of PQ pool reduction induced by the two techniques. In a strong PAM-analogous WL pulse in the dark monitored by the QA flash of LIFT/FRR φPSIIWL ≈ φPSIIPAM. The QA flash also tracks PQ pool reduction as well as the associated responses of ETR QA → PQ and PQ → PSI, the relative functional (σPSII) and optical absorption (aPSII) cross-sections of PSII in situ with a time resolution of ~2 s as they relax after the pulse. It is impractical to deliver strong WL pulses at a distance in the field but a longer PQ flash from LIFT/FRR also achieves full reduction of PQ pool and delivers φPSIIPQ ≈ φPSIIPAM to obtain PAM-equivalent estimates of ETR and NPQ at a distance. In situ values of σPSII and aPSII from the QA flash with smaller antenna barley (chlorina-f2) and Arabidopsis mutants (asLhcb2–12, ch1–3 Lhcb5) are proportionally similar to those previously reported from in vitro assays. These direct measurements are further validated by changes in antenna size in response to growth irradiance. We illustrate how the QA flash facilitates our understanding of photosynthetic regulation during sun flecks in natural environments at a distance, with a time resolution of a few seconds.
Quantifying individual and collective influences of soil properties on crop yield
Authors: Whetton Rebecca , Zhao Yifan , Mouazen Abdul M.
Published: July 2017

Quantification of the agronomic influences of soil properties, collected at high sampling resolution, on crop yield is essential for site specific soil management. The objective of this study was to implement a novel Volterra Non-linear Regressive with eXogenous inputs (VNRX) model accounting for the linear and non-linear variability (VNRX-LN) to quantify causal factors affecting wheat yield in a 22-ha field with a waterlogging problem in Bedfordshire, UK. The VNRX-LN model was applied using high-resolution data of eight key soil properties (total nitrogen (TN), organic carbon, pH, available phosphorous, magnesium (Mg), calcium, moisture content and cation exchange capacity (CEC)). The data were collected with an on-line (tractor mounted) visible and near infrared spectroscopy sensor and used as multiple-input to the VNRX-LN model, whereas crop yield represented the single-output in the system. Results showed that the largest contributors to wheat yield were CEC, Mg and TN, with error reduction ratio contribution values of 14.6%, 4.69% and 1% respectively. The overall contribution of the soil properties considered in this study equalled 23.21%. This was attributed to a large area of the studied field having been waterlogged, which masked the actual effect of soil properties on crop yield. It is recommended that VNRX-LN is validated on a larger number of fields, where other crop yield affecting parameters e.g., crop disease, pests, drainage, topography and microclimate conditions should be taken into account.
Protein diversity in discrete structures at the distal tip of the trypanosome flagellum
Authors: Varga Vladimir , Moreira-Leite Flavia , Portman Neil , Gull Keith
Published: July 2017

Significance

The distal end of the eukaryotic flagellum/cilium has critical functions, yet due to its small dimensions and association of tip structures with the axoneme is rather intractable to studying. We have developed biochemical approaches to identify a cohort of proteins specific for the flagellum tip structures. We sublocalized these proteins into individual structures. Using functional studies, we elucidated how the identified proteins contribute to the function of the flagella connector, the mobile membrane junction at the tip of the trypanosome flagellum.
Effect of directional pulling on mechanical protein degradation by ATP-dependent proteolytic machines
Authors: Olivares Adrian O. , Kotamarthi Hema Chandra , Stein Benjamin J. , Sauer Robert T. , Baker Tania A.
Published: July 2017

Significance

Directional degradation is an important feature of energy-dependent intracellular proteolysis in all cells. Proteolytic machines can unravel protein substrates from either terminus depending on the site of initial recognition. Here, we use single-molecule optical trapping to probe how the bacterial AAA+ proteases ClpXP and ClpAP mechanically degrade a model substrate, titin
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, from the N terminus. N-terminal unfolding of this substrate is often accomplished with one or a few power strokes and is much faster than C-terminal unfolding, although translocation is only mildly affected by the direction. Our results highlight the paramount role of local stability in protein degradation and provide clues as to how the placement of degradation signals on a substrate may evolve to minimize the energetic cost of degradation.
BRCT-domain protein BRIT1 influences class switch recombination
Authors: Yen Wei-Feng , Chaudhry Ashutosh , Vaidyanathan Bharat , Yewdell William T. , Pucella Joseph N. , Sharma Rahul , Liang Yulong , Li Kaiyi , Rudensky Alexander Y. , Chaudhuri Jayanta
Published: July 2017

Significance

Class switch recombination (CSR), a B-cell–specific reaction essential for optimal antibody responses, proceeds through the deliberate generation of DNA breaks. Although these breaks are obligatory intermediates of class switching, their improper resolution not only impairs immune responses but also promotes oncogenic translocations. The pathways and mechanisms that participate in the repair of such lesions are yet to be fully elucidated. In this work, we have identified a BRCT domain containing protein BRIT1 as an effector of the DNA repair phase of CSR. We show that B cells lacking BRIT1 are impaired in undergoing class switching due to an inability to repair DNA breaks efficiently. This work thus has significant implications in both immunity and cancer.
The Junior Faculty Networking Cohort: Filling a gap in support for our community
Authors: Gordon Sharona E.
Published: July 2017

JGP, in partnership with the Society of General Physiologists, announces a new networking and mentoring program for junior faculty.