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This paper demonstrates low-leakage hydrogen plasma (HP) terminated GaN-on-GaN vertical p–n diodes. The leakage current was decreased by ∼800 times (at −600 V), and the breakdown voltage was nearly doubled with a p-GaN extension design. The devices showed a non-destructive breakdown voltage of 1.68 kV, a specific on-resistance (Ron) of 0.40 MΩ cm2, and a Baliga's figure of merit of 7.1 GW cm−2. These results indicate that HP termination with p-GaN extension is effective in reducing leakage and enhancing the breakdown capability of vertical GaN power diodes. [ABSTRACT FROM AUTHOR]

We report an overlapping sampling scheme to accelerate computational ghost imaging for imaging moving targets, based on reordering a set of Hadamard modulation matrices by means of a heuristic algorithm. The new condensed overlapped matrices are then designed to shorten and optimize encoding of the overlapped patterns, which are shown to be much superior to the random matrices. In addition, we apply deep learning to image the target, and use the signal acquired by the bucket detector and corresponding real image to train the neural network. Detailed comparisons show that our new method can improve the imaging speed by as much as an order of magnitude, and improve the image quality as well. [ABSTRACT FROM AUTHOR]

Crack free GaN films were grown on 1200×1200μm2 patterned Si (111) substrates and 36 light emitting diodes (LEDs) were fabricated in each pattern unit. Spatial distribution of the tensile stress in the pattern units and its influence on the LED performance are studied by micro-Raman and electroluminescence (EL). The Raman shift of the GaN E2 mode shows that the tensile stress is the maximum at the center, partially relaxed at the edge, and further relaxed at the corner. With the stress relaxation, the EL wavelength has a significant blue shift and the luminous intensity shows a great enhancement. [ABSTRACT FROM AUTHOR]

In abdomen computed tomography (CT), repeated radiation exposures are often inevitable for cancer patients who receive surgery or radiotherapy guided by CT images. Low-dose scans should thus be considered in order to avoid the harm of accumulative x-ray radiation. This work is aimed at improving abdomen tumor CT images from low-dose scans by using a fast dictionary learning (DL) based processing. Stemming from sparse representation theory, the proposed patch-based DL approach allows effective suppression of both mottled noise and streak artifacts. The experiments carried out on clinical data show that the proposed method brings encouraging improvements in abdomen low-dose CT images with tumors. [ABSTRACT FROM AUTHOR]

Memristor-based neuromorphic computing is expected to overcome the bottleneck of von Neumann architecture. An artificial synaptic device with continuous conductance variation is essential for implementing bioinspired neuromorphic systems. In this work, a memristor based on Pt/LiSiO x /TiN structure is developed to emulate an artificial synapse, which shows non-volatile multilevel resistance state memory behavior. Moreover, the high nonlinearity caused by abrupt changes in the set process is optimized by adjusting the initial resistance. 100 levels of continuously modulated conductance states are achieved and the nonlinearity factors are reduced to 1.31. The significant improvement is attributed to the decrease in the Schottky barrier height and the evolution of the conductive filaments. Finally, due to the improved linearity of the long-term potentiation/long-term depression behaviors in LiSiO x memristor, a robust recognition rate (∼94.58%) is achieved for pattern recognition with the modified National Institute of Standards and Technology handwriting database. The Pt/LiSiO x /TiN memristor shows significant potential in high-performance multilevel data storage and neuromorphic computing systems. [ABSTRACT FROM AUTHOR]

The x-ray exposure to patients has become a major concern in computed tomography (CT) and minimizing the radiation exposure has been one of the major efforts in the CT field. Due to plenty high-attenuation tissues in the human chest, under low-dose scan protocols, thoracic low-dose CT (LDCT) images tend to be severely degraded by excessive mottled noise and non-stationary streak artifacts. Their removal is rather a challenging task because the streak artifacts with directional prominence are often hard to discriminate from the attenuation information of normal tissues. This paper describes a two-step processing scheme called 'artifact suppressed large-scale nonlocal means' for suppressing both noise and artifacts in thoracic LDCT images. Specific scale and direction properties were exploited to discriminate the noise and artifacts from image structures. Parallel implementation has been introduced to speed up the whole processing by more than 100 times. Phantom and patient CT images were both acquired for evaluation purpose. Comparative qualitative and quantitative analyses were both performed that allows conclusion on the efficacy of our method in improving thoracic LDCT data. [ABSTRACT FROM AUTHOR]

We investigate the molecular environment of the Galactic supernova remnant (SNR) Kesteven 78 and perform an XMM-Newton X-ray spectroscopic study for the northeastern edge of the remnant. SNR Kes 78 is found to interact with the molecular clouds (MCs) at a systemic local standard of rest velocity of 81 km s-1. At around this velocity, the SNR appears to contact a long molecular strip in the northeast and a large cloud in the east as revealed in the 13CO line, which may be responsible for the radio brightness peak and the OH maser, respectively. The 12CO-line bright region morphologically matches the eastern bright radio shell in general, and the SNR is consistent in extent with a CO cavity. Broadened 12CO-line profiles discerned in the eastern maser region and the western clumpy molecular arc and the elevated 12CO (J = 2-1)/(J = 1-0) ratios along the SNR boundary may be signatures of shock perturbation in the molecular gas. The SNR--MC association places the SNR at a kinematic distance of 4.8 kpc. The X-rays arising from the northeastern radio shell are emitted by underionized hot (~1.5 keV), low-density (~0.1 cm-3) plasma with solar abundance, and the plasma may be of intercloud origin. The age of the remnant is inferred to be about 6 kyr. The size of the molecular cavity in Kes 78 implies an initial mass around 22 M⊙ for the progenitor. [ABSTRACT FROM AUTHOR]

Ab initio calculation of the total dielectronic recombination (DR) rate coefficient from the ground and the first excited states of Co-like gold is performed employing the relativistic distorted-wave approximation with configuration interaction. The DR contributions are explicitly taken into account from the relevant complexes of a Ni-like ion: 3d33/2 3d65/2n'l', 3p5 3d10n'l', 3s 3p63d10n'l', 3d8 4ln'l', 3p5 3d9 4ln'l' and 3s 3p6 3d9 4ln'l' with n' [?] 25, and 3d8 5ln'l' with n' [?] 9. The contributions from a higher n' complex are evaluated by an extrapolation procedure. The DR contributions mainly come from complex series 3d8 4ln'l' and 3p5 3d9 4ln'l'. The complex series 3p5 3d10n'l' and 3d8 5ln'l' also contribute significantly to the total DR rates at low and high electron temperatures, respectively. The l' and n' dependences of the partial rate coefficient are investigated. The possible important decays into autoionizing levels followed by radiative cascade (DAC) from the resonant levels are taken into account, as well as the resonant stabilizing and non-resonant stabilizing transitions. The inclusion of DAC transitions enlarges the total DR rate coefficients by a factor of about 10% and may break down the usual n'[?]3 scaling law of the partial DR rates along some complex series. To evaluate the high n' contributions from these complex series, the level-by-level extrapolation method is developed to include DAC effects. The total DR rate coefficients are fitted to an empirical formula. The present results are compared with those from the semiempirical Burgess-Merts approximation. The DR rate coefficients of Ni-like gold are also presented and compared to those of Co-like gold. In addition, some comments on the published DR data for the NiI isoelectronic sequence are drawn from the present calculation. [ABSTRACT FROM AUTHOR]

Based on the analysis of birefringence and leakage properties in rectangular lattice photonic crystal fibres (RLPCFs), we present a simple technique of improving the optical properties of the fibres by the introduction of a doped core. The advantage of a doped core is firstly investigated by the comparison of the mode profiles of RLPCFs with a pure silica core, an additional air-hole in the core and a down-doped silica core. The influence of doping level on that of birefringence and leakage losses of the fibres is also explored. Our numerical simulation indicates, for PCFs with a anisotropic cladding, increased birefringence and reduced leakage losses can be obtained by a down-doped core. The proposed technique also has the merit of enlarging the mode field without the reduction of birefringence, therefore, coupling light to the fibre will become easier. [ABSTRACT FROM AUTHOR]

A miniature device composed of anodic aluminum oxide membrane and aligned polypropylene submicron tubes is fabricated by a simple template method. When organic fluids are dripped on the membrane, the device floating on water could be propelled by organic fluid jetflow through the polymer tubes. The driving force is mainly attributed to the spreading of organic fluids on water surface. Compared to the motions driven by spreading fluids in bulk, the propulsion of this device is more efficient benefiting from the submicron-tube microstructure. This work may provide a feasible approach to enhance the efficiency of chemical driving movements. [ABSTRACT FROM AUTHOR]

The generation of hollow atoms will reduce the probability of light absorption and provide a high-quality diffraction image in the experiment. In this paper, we calculated the ionization rate of the Kr atom under x-ray free-electron laser (XFEL) using Hartree–Fock–Slater model and simulated the ionization model of Kr atom using Monte–Carlo method to determine the response of the hollow atom of Kr atom to the XFEL photon energy. Calculating the correlation between the total photoionization cross-section of the ground state of Kr atom and the photon energy, we determined three particular photon energies of 1.75 keV, 1.90 keV, and 14.30 keV. The dynamics simulation under the experimental condition's 17.50 keV photon energy was achieved by implementing the Monte–Carlo method and calibrating the photon flux modeling parameters. Consequently, our calculated data are more consistent with experimental phenomena than previous theoretical studies. The saturable absorption of Kr at 1.75 keV, 1.90 keV, 14.30 keV, and 17.50 keV energies was further investigated by using the optimized photon flux model theory. We compared the statistics on main ionization paths under those four specific photon energies and calculated the population changes of various Kr hollow atoms with different configurations. The results demonstrate that the population of hollow atoms produced at the critical ionization photon energy is high. Furthermore, the change of population with respect to position is smooth, which shows a significant difference between the generation mode of ions with low and high photon energies. The result is important for the study of medium- and high- Z element hollow atoms, which has substantial implications for the study of hollow atoms with medium and high charge states, as well as for the scaling of photon energy of free electron lasers. [ABSTRACT FROM AUTHOR]

We perform a molecular (CO and CN) line observation using the IRAM 30 m telescope toward two small regions near the western edge of supernova remnant (SNR) W50/SS 433. CO observation reveals spatial correspondence of two molecular clumps at the local-standard-of-rest (LSR) velocity around +53 , with multiwavelength local features of the W50/SS 433 system. One of the two clumps appears to be embedded in a void of diffuse radio and X-ray emission. Toward the two clumps, asymmetric broad-line profiles of the 12CO lines are obtained, which provide kinematic evidence of the association between the clumps and the jet-related gas. The 12CO J = 2–1/J = 1–0 line ratios (≳0.9) and the kinetic temperatures (∼30 K) of the clumps are distinctively higher than all those of the clumps at other LSR velocities along the same line of sight, which may be physical signatures of the association. We show that the clump coincident with the void can survive the thermal heating if it is surrounded by hot gas, with an evaporation timescale much larger than the age of SNR W50. We also show that the thermal equilibrium in the high-temperature clumps can be maintained by the heating of the penetrating environmental cosmic rays. CN (J = 3/1–1/2) line emission is detected in the two clumps, and the CN abundances derived are much higher than that in the interstellar molecular clouds (MCs) and that in the SNR-interacting MCs. [ABSTRACT FROM AUTHOR]

A substrate-free approach of semiconductor nanowire growth has been achieved by the aerotaxy technique previously. In this work, we propose an in situ method to monitor the size of nanowires through non-destructive optical-extinction measurements. Our work aims to build a theoretical look-up database of extinction spectra for a single nanowire of varying dimensions. We describe the origin of possible peaks in the spectra, for example due to nanowire-length dependent Fabry–Perot resonances and nanowire-diameter dependent TM and TE mode resonances. Furthermore, we show that the Au catalyst on top of the nanowire can be ignored in the simulations when the volume of the nanowire is an order of magnitude larger than that of the Au catalyst and the diameter is small compared to the incident wavelength. For the calculation of the extinction spectra, we use the finite element method, the discrete dipole approximation and the Mie theory. To compare with experimental measurements of randomly oriented nanowires, we perform an averaging over nanowire orientation for the modeled results. However, in the experiments, nanowires are accumulating on the quartz window of the measurement setup, which leads to increasing uncertainty in the comparison with the experimental extinction spectra. This uncertainty can be eliminated by considering both a sparse and a dense collection of nanowires on the quartz window in the optical simulations. Finally, we create a database of extinction spectra for a GaAs nanowire of varying diameters and lengths. This database can be used to estimate the diameter and the length of the nanowires by comparing the position of a peak and the peak-to-shoulder difference in the extinction spectrum. Possible tapering of nanowires can be monitored through the appearance of an additional peak at a wavelength of 700–800 nm. [ABSTRACT FROM AUTHOR]

We study the dynamics of a two-level crossing model with a parabolic separation of the diabatic energies. The solutions are expressed in terms of the tri-confluent Heun equations—the generalization of the confluent hypergeometric equations. We obtain analytical approximations for the state populations in terms of Airy and Bessel functions. Applicable expressions are derived for a large part of the parameter space. We also provide simple formulas which connect local solution in different time regimes. The validity of the analytical approximations is shown by comparing them to numerical simulations. [ABSTRACT FROM AUTHOR]

The China Fusion Engineering Test Reactor (CFETR) is the next device in the Chinese roadmap for the realization of fusion energy, and is currently in the design phase. In this work, the stability of alpha particle-driven Alfvén eigenmodes (AEs) is investigated using a gyrokinetic ion/fluid electron hybrid code. It is found that the toroidal mode numbers of the most unstable modes are and the linear growth rate of the mode is slightly higher than that of the and modes. The excitation threshold in central alpha particle beta of the most unstable mode is found to be about , which is substantially below the expected value of alpha particle beta () in CFETR. This result indicates that the high-n alpha particle-driven AEs are strongly unstable in CFETR, with many toroidal mode numbers simultaneously destabilized, at least for the CFETR design parameters considered in this work. Furthermore, a systematic study of parameter dependence has been carried out. It is found that the stability of AE with a single toroidal mode number is sensitive to the safety factor profile. However, the overall stability of AEs is much less sensitive to the value of when different toroidal mode numbers are considered simultaneously. It is shown that the normalized alpha particle gyro-radius and the alpha particle speed are two important parameters determining the alpha particle drive. The alpha particle drive is maximized for CFETR values of these two parameters. Finally, it is found that the alpha particle-driven AE’s growth rate decreases as the thermal ion temperature/density decreases/increases at fixed plasma pressure. [ABSTRACT FROM AUTHOR]

The Vela X pulsar wind nebula (PWN) is characterized by the extended radio nebula (ERN) and the central X-ray “cocoon.” We have interpreted the γ-ray spectral properties of the cocoon in the first paper; here, we account for the broadband photon spectrum of the ERN. Since the diffusive escape of the electrons from the TeV emitting region is expected to play an insignificant role in shaping the spectrum of the ERN, we attribute the GeV cutoff of the ERN to the reverse shock–PWN interaction. Due to the disruption of the reverse shock, most of the plasma of the PWN is driven into the ERN. During the subsequent reverberation phase, the ERN could be compressed by a large factor in radius, and the magnetic field in the ERN is thus significantly enhanced, burning off the high-energy electrons. We thus obtain the electron spectrum of the ERN, and the broadband spectrum of the ERN is explained satisfactorily. [ABSTRACT FROM AUTHOR]

Thermal properties of the diamond nanothread (DNT) forest array are studied using non-equilibrium molecular dynamics simulations. We find a strong anisotropic thermal property in this structure, i.e. the thermal conductivity in thread direction is over 300 times of that in the perpendicular direction. When subject to external strain, the thermal conductivity of the DNT forest decreases with increasing compressive/tensile strain in the thread direction, while thermal conductivity increases exponentially with increasing compressive strain in the perpendicular direction. The increase in thermal conductivity is attributed to the enhanced interactions among DNTs induced by compression. These results are explained by phonon spectra and structural deformation. Our findings show that diamond nanothread forest has a great potential application in the super-capacitors. [ABSTRACT FROM AUTHOR]

Kepler’s supernova remnant (SNR) is believed to result from a Type Ia supernova, but to be interacting with dense circumstellar material (CSM), which makes its progenitor system a mystery. Using the Chandra ACIS-S 741 ks effective exposure data and an advanced adaptive binning algorithm, we analyze the spectra from tessellated regions in Kepler’s SNR. For the first time, we map out the detailed spatial distributions of emission measure (EM), electron temperature, ionization parameter, and metal abundances for both the low- and high-temperature plasma components. The low-temperature plasma diverges into two branches in the temperature versus ionization parameter diagram, which appear to be spatially associated with the warm CSM dusts and the Si- and S-rich ejecta, respectively. We construct the probability distribution functions of abundance ratios of O and Mg to L-shell emitting Fe ([O]/[Fe]L and [Mg]/[Fe]L), and fit them with double Gaussians. Thereby, we distinguish the CSM from the ejecta: the CSM is characterized by and , while the ejecta by and . We estimate the total hydrogen mass of the shocked CSM as ∼1.4 M⊙ and the EM-weighted mean [Mg]/[O] = 1.14 ± 0.49, which can be reproduced with an asymptotic giant branch donor star with initial mass of ∼4 M⊙. The abundance ratios from the shocked ejecta are well compatible with the predicted results from spherical delayed-detonation models for Type Ia supernovae. We also find that the two “ears” of the remnant are dominated by Si- and S-rich ejecta, thus favoring a pre-explosion jets scenario. [ABSTRACT FROM AUTHOR]

It is necessary to reduce the currents of poloidal field (PF) coils as small as possible, during the static equilibrium design procedure of Experimental Advanced Superconductive Tokamak (EAST). The quasi-snowflake (QSF) divertor configuration is studied in this paper. Starting from a standard QSF plasma equilibrium, a new QSF equilibrium with 300 kA total plasma current is designed. In order to reduce the currents of PF6 and PF14, the influence of plasma shape on PF coil current distribution is analyzed. A fixed boundary equilibrium solver based on a non-rigid plasma model is used to calculate the flux distribution and PF coil current distribution. Then the plasma shape parameters are studied by the orthogonal method. According to the result, the plasma shape is redefined, and the calculated equilibrium shows that the currents of PF6 and PF14 are reduced by 3.592 kA and 2.773 kA, respectively. [ABSTRACT FROM AUTHOR]

Objective: Cuffless blood-pressure (BP) estimation has attracted widespread interest owing to its potential for long-term, non-invasive BP monitoring. But it is still impractical in clinical settings, mainly owing to ongoing challenges with respect to accuracy in hypertensive patients. To better estimate the BP, the current study proposes a new cuffless estimation method that includes a sympathetic tone, which has been reported with a varied pattern in hypertensive patients. Approach: First, the heart-rate variability of all subjects is investigated, and a new parameter, the heart-rate power spectrum ratio (HPSR), is proposed to indicate BP dynamics under sympathetic regulation. Then, a new BP estimation model is constructed by integrating HPSP with the pulse transit time (PTT) and photoplethysmography intensity ratio. The estimation accuracy is further evaluated by making comparisons with the standard sphygmomanometer BP on 60 subjects (29 hypertensive and 31 normotensive). Main results: A significant increase in HPSR was observed in hypertensive patients compared to normotensive subjects. Of the 60 subjects, the estimation accuracy was 0.73  ±  10.04 mmHg for systolic BP (SBP) and 0.90  ±  7.10 mmHg for diastolic BP (DBP) in hypertensive patients, which is comparable to 0.54  ±  7.52 mmHg for SBP and 0.82  ±  6.20 mmHg for DBP in normotensive subjects. Furthermore, the proposed method overperformed the traditional PTT-based algorithm by reducing the 3 mmHg error in the standard deviation in hypertensive patients. Significance: The results of the current study demonstrate that the inclusion of factors associated with autonomic activities in the BP estimation model would improve the BP estimation accuracy, especially for hypertensive subjects. [ABSTRACT FROM AUTHOR]

Diffuse soft X-ray line emission is commonly used to trace the thermal and chemical properties of the hot interstellar medium, as well as its content, in nearby galaxies. Although resonant-line scattering complicates the interpretation of the emission, it also offers an opportunity to measure the kinematics of the medium. We have implemented a direct Monte Carlo simulation scheme that enables us to account for the resonant scattering (RS) effect in the medium, in principle, with arbitrary spatial, thermal, chemical, and kinematic distributions. Here we apply this scheme via dimensionless calculation to an isothermal, chemically uniform, and spherically symmetric medium with a radial density distribution characterized by a β-model. This application simultaneously accounts for both optical depth-dependent spatial distortion and intensity change of the resonant-line emission due to the scattering, consistent with previous calculations. We further apply the modeling scheme to the O vii and O viii emission line complex observed in the XMM-Newton RGS spectrum of the M31 bulge. This modeling, although with various limitations due to its simplicity, shows that the RS could indeed account for much of the spatial distortion of the emission, as well as the relative intensities of the lines, especially the large forbidden-to-resonant-line ratio of the O vii Heα triplet. We estimate the isotropic turbulence Mach number of the medium in M31 as ∼0.17 for the first time and the line-emitting gas temperature as ∼2.3 × 106 K. We conclude that the RS may in general play an important role in shaping the soft X-ray spectra of diffuse hot gas in normal galaxies. [ABSTRACT FROM AUTHOR]

We present a new millimeter CO-line observation toward supernova remnant (SNR) CTB 87, which was regarded purely as a pulsar wind nebula (PWN), and an optical investigation of a coincident surrounding superbubble. The CO observation shows that the SNR delineated by the radio emission is projectively covered by a molecular cloud (MC) complex at to . Both the symmetric axis of the radio emission and the trailing X-ray PWN appear projectively to be along a gap between two molecular gas patches at −58 to . Asymmetric broad profiles of 12CO lines peaked at are found at the eastern and southwestern edges of the radio emission. This represents a kinematic signature consistent with an SNR–MC interaction. We also find that a superbubble, ∼37′ in radius, appears to surround the SNR from H i 21 cm ( to ), WISE mid-IR, and optical extinction data. We build a multi-band photometric stellar sample of stars within the superbubble region and find 82 OB star candidates. The likely peak distance in the stars’ distribution seems consistent with the distance previously suggested for CTB 87. We suggest the arc-like radio emission is mainly a relic of the part of the blast wave that propagates into the MC complex and is now in a radiative stage while the other part of the blast wave has been expanding into the low-density region in the superbubble. This scenario naturally explains the lack of X-ray emission related to the ejecta and blast wave. The SNR–MC interaction also favors a hadronic contribution to the γ-ray emission from the CTB 87 region. [ABSTRACT FROM AUTHOR]

Nowadays, massive amounts of data have been accumulated in various and wide fields, it has become today one of the central issues in interdisciplinary fields to analyze existing data and extract as much useful information as possible from data. It is often that the output data of systems are measurable while dynamic structures producing these data are hidden, and thus studies to reveal system structures by analyzing available data, i.e., reconstructions of systems become one of the most important tasks of information extractions. In the past, most of the works in this respect were based on theoretical analyses and numerical verifications. Direct analyses of experimental data are very rare. In physical science, most of the analyses of experimental setups were based on the first principles of physics laws, i.e., so-called top-down analyses. In this paper, we conducted an experiment of “Boer resonant instrument for forced vibration” (BRIFV) and inferred the dynamic structure of the experimental set purely from the analysis of the measurable experimental data, i.e., by applying the bottom-up strategy. Dynamics of the experimental set is strongly nonlinear and chaotic, and itʼs subjects to inevitable noises. We proposed to use high-order correlation computations to treat nonlinear dynamics; use two-time correlations to treat noise effects. By applying these approaches, we have successfully reconstructed the structure of the experimental setup, and the dynamic system reconstructed with the measured data reproduces good experimental results in a wide range of parameters. [ABSTRACT FROM AUTHOR]

Semiconductor nanowire arrays are a promising candidate for next generation solar cells due to enhanced absorption and reduced material consumption. However, to optimize their performance, time consuming three-dimensional (3D) opto-electronics modeling is usually performed. Here, we develop an accurate one-dimensional (1D) modeling method for the analysis. The 1D modeling is about 400 times faster than 3D modeling and allows direct application of concepts from planar pn-junctions on the analysis of nanowire solar cells. We show that the superposition principle can break down in InP nanowires due to strong surface recombination in the depletion region, giving rise to an IV-behavior similar to that with low shunt resistance. Importantly, we find that the open-circuit voltage of nanowire solar cells is typically limited by contact leakage. Therefore, to increase the efficiency, we have investigated the effect of high-bandgap GaP carrier-selective contact segments at the top and bottom of the InP nanowire and we find that GaP contact segments improve the solar cell efficiency. Next, we discuss the merit of p-i-n and p–n junction concepts in nanowire solar cells. With GaP carrier selective top and bottom contact segments in the InP nanowire array, we find that a p–n junction design is superior to a p-i-n junction design. We predict a best efficiency of 25% for a surface recombination velocity of 4500 cm s−1, corresponding to a non-radiative lifetime of 1 ns in p–n junction cells. The developed 1D model can be used for general modeling of axial p–n and p-i-n junctions in semiconductor nanowires. This includes also LED applications and we expect faster progress in device modeling using our method. [ABSTRACT FROM AUTHOR]

We report our independent GeV γ-ray study of the young shell-type supernova remnant (SNR) Kes 73, which harbors a central magnetar, and CO-line millimeter observations toward the SNR. Using 7.6 years of Fermi-LAT observation data, we detected an extended γ-ray source (“source A”) with centroid on the west of the SNR, with a significance of 21σ in 0.1–300 GeV and an error circle of 5.′4 in angular radius. The γ-ray spectrum cannot be reproduced by a pure leptonic emission or a pure emission from the magnetar, and thus a hadronic emission component is needed. The CO-line observations reveal a molecular cloud (MC) at VLSR ∼ 90 km s−1, which demonstrates morphological correspondence with the western boundary of the SNR brightened in multiwavelength. The 12CO (J = 2 − 1)/12CO (J = 1 − 0) ratio in the left (blue) wing 85–88 km s−1 is prominently elevated to ∼1.1 along the northwestern boundary, providing kinematic evidence of the SNR-MC interaction. This SNR-MC association yields a kinematic distance 9 kpc to Kes 73. The MC is shown to be capable of accounting for the hadronic γ-ray emission component. The γ-ray spectrum can be interpreted with a pure hadronic emission or a magnetar+hadronic hybrid emission. In the case of pure hadronic emission, the spectral index of the protons is 2.4, very similar to that of the radio-emitting electrons, essentially consistent with the diffusive shock acceleration theory. In the case of magnetar+hadronic hybrid emission, a magnetic field decay rate ≳1036 erg s−1 is needed to power the magnetar’s curvature radiation. [ABSTRACT FROM AUTHOR]

The coupling efficiency of the beam combination and the fiber-coupled module is limited due to the large vertical divergent angle of conventional semiconductor laser diodes. We present a high coupling efficiency module using photonic-band-crystal (PBC) laser diodes with narrow vertical divergent angles. Three PBC single-emitter laser diodes are combined into a fiber with core diameter of 105 μm and numerical aperture of 0.22. A high coupling efficiency of 94.4% is achieved and the brightness is calculated to be 1.7 MW/(cmsr) with the injection current of 8 A. [ABSTRACT FROM AUTHOR]

This paper proposes a concise and effective approach termed discriminative feature representation (DFR) for low dose computerized tomography (LDCT) image processing, which is currently a challenging problem in medical imaging field. This DFR method assumes LDCT images as the superposition of desirable high dose CT (HDCT) 3D features and undesirable noise-artifact 3D features (the combined term of noise and artifact features induced by low dose scan protocols), and the decomposed HDCT features are used to provide the processed LDCT images with higher quality. The target HDCT features are solved via the DFR algorithm using a featured dictionary composed by atoms representing HDCT features and noise-artifact features. In this study, the featured dictionary is efficiently built using physical phantom images collected from the same CT scanner as the target clinical LDCT images to process. The proposed DFR method also has good robustness in parameter setting for different CT scanner types. This DFR method can be directly applied to process DICOM formatted LDCT images, and has good applicability to current CT systems. Comparative experiments with abdomen LDCT data validate the good performance of the proposed approach. [ABSTRACT FROM AUTHOR]

Photolithography has long been a critical technology for nanoscale manufacturing, especially in the semiconductor industry. However, the diffractive nature of light has limited the continuous advance of optical lithography resolution. To overcome this obstacle, near-field scanning optical lithography (NSOL) is an alternative low-cost technique, whose resolution is determined by the near-field localization that can be achieved. Here, we apply the newly-developed backside milling method to fabricate bowtie apertures with a sub-15 nm gap, which can substantially improve the resolution of NSOL. A highly confined electric near field is produced by localized surface plasmon excitation and nanofocusing of the closely-tapered gap. We show contact lithography results with a record 16 nm resolution (FWHM). This photolithography scheme promises potential applications in data storage, high-speed computation, energy harvesting, and other nanotechnology areas. [ABSTRACT FROM AUTHOR]

Kes 79 (G33.6+0.1) is an aspherical thermal composite supernova remnant (SNR) observed across the electromagnetic spectrum and showing an unusual highly structured morphology, in addition to harboring a central compact object (CCO). Using the CO J = 1–0, J = 2–1, and J = 3–2 data, we provide the first direct evidence and new morphological evidence to support the physical interaction between the SNR and the molecular cloud in the local standard of rest velocity . We revisit the 380 ks XMM-Newton observations and perform a dedicated spatially resolved X-ray spectroscopic study with careful background subtraction. The overall X-ray-emitting gas is characterized by an under-ionized () cool ( keV) plasma with solar abundances, plus an under-ionized () hot ( keV) plasma with elevated Ne, Mg, Si, S, and Ar abundances. The X-ray filaments, spatially correlated with the 24 IR filaments, are suggested to be due to the SNR shock interaction with dense gas, while the halo forms from SNR breaking out into a tenuous medium. Kes 79 appears to have a double-hemisphere morphology viewed along the symmetric axis. Projection effect can explain the multiple-shell structures and the thermal composite morphology. The high-velocity, hot ( keV) ejecta patch with high metal abundances, together with the non-uniform metal distribution across the SNR, indicate an asymmetric SN explosion of Kes 79. We refine the Sedov age to 4.4–6.7 kyr and the mean shock velocity to 730 . Our multi-wavelength study suggests a progenitor mass of ∼15–20 solar masses for the core-collapse explosion that formed Kes 79 and its CCO, PSR J1852+0040. [ABSTRACT FROM AUTHOR]

InP nanowire arrays with axial p-i-n junctions are promising devices for next-generation photovoltaics, with a demonstrated efficiency of 13.8%. However, the short-circuit current in such arrays does not match their absorption performance. Here, through combined optical and electrical modeling, we study how the absorption of photons and separation of the resulting photogenerated electron–hole pairs define and limit the short-circuit current in the nanowires. We identify how photogenerated minority carriers in the top n segment (i.e. holes) diffuse to the ohmic top contact where they recombine without contributing to the short-circuit current. In our modeling, such contact recombination can lead to a 60% drop in the short-circuit current. To hinder such hole diffusion, we include a gradient doping profile in the n segment to create a front surface barrier. This approach leads to a modest 5% increase in the short-circuit current, limited by Auger recombination with increased doping. A more efficient approach is to switch the n segment to a material with a higher band gap, like GaP. Then, a much smaller number of holes is photogenerated in the n segment, strongly limiting the amount that can diffuse and disappear into the top contact. For a 500 nm long top segment, the GaP approach leads to a 50% higher short-circuit current than with an InP top segment. Such a long top segment could facilitate the fabrication and contacting of nanowire array solar cells. Such design schemes for managing minority carriers could open the door to higher performance in single- and multi-junction nanowire-based solar cells. [ABSTRACT FROM AUTHOR]

As the power conversion efficiencies of organic solar cells (OSCs) have been improved continuously in recent years, more attention will be paid to the industrial production and practical application of OSCs. However, there are still many problems to be solved in the process of large-scale production. Among them, reducing the costs of the materials and enhancing the film-thickness tolerance of the active layer are the two key points. Therefore, it is urgent to develop organic semiconductor materials which are easy to synthesize and suitable for the construction of high-efficiency, thick-film OSCs. In this work, we have focused on the (E)âˆ'2-[2-(thiophen-2-yl)vinyl]thiophene (TVT) unit because of its unique coplanar structure. And we noticed that TVT was mostly used as an electron-donating unit in the previous reports. However, we have modified TVT into electron-withdrawing unit by the introduction of fluorine atoms/ester groups. And two new donorâ€"acceptor (Dâ€"A) copolymers have been obtained by combining the electron-withdrawing TVT unit with benzo[2,1-b:4,5-b′]dithiophene (BDT) unit. Among them, the polymer based on the ester modified TVT unit presents excellent photovoltaic performance by virtue of its good solubility and preferable molecular stacking mode, and the corresponding devices also show extraordinarily high-thickness tolerance. The emergence of this new electron-withdrawing TVT unit will undoubtedly further promote the development of low-cost, high-efficiency, thick-film OSCs. [ABSTRACT FROM AUTHOR]

Whether the progenitors of SNe Ia are single-degenerate or double-degenerate white dwarf (WD) systems is a highly debated topic. To address the origin of Tycho’s Type Ia supernova remnant (SNR), SN 1572, we have carried out a 12CO J = 2–1 mapping and a 3 mm line survey toward the remnant using the IRAM 30 m telescope. We show that Tycho is surrounded by a clumpy molecular bubble at a local standard of rest velocity of , which expands at a speed of and has a mass of (at the distance of 2.5 kpc). Enhanced 12CO J = 2–1 line emission relative to 12CO J = 1–0 emission and possible line broadenings (in velocity range −64 to −60 km s−1) are found at the northeastern boundary of the SNR, where the shell is deformed and decelerated. These features, combined with the morphological correspondence between the expanding molecular bubble and Tycho, suggest that the SNR is associated with the bubble at the velocity range −66 to −57 km s−1. The most plausible origin for the expanding bubble is the fast outflow (with velocity of hundreds km s−1) driven from the vicinity of a WD as it accreted matter from a nondegenerate companion star. The SNR has been expanding in the low-density wind-blown bubble, and the shock wave has just reached the molecular cavity wall. This is the first unambiguous detection of an expanding bubble driven by the progenitor of a Type Ia SNR, which constitutes evidence for a single-degenerate progenitor for this SN Ia. [ABSTRACT FROM AUTHOR]

According to the electromagnetic field distributions, there exist two kinds of coupled spoof surface plasmon polaritons (SSPPs), the symmetric and anti-symmetric modes, in the three-dimensional (3D) subwavelength spoof–insulator–spoof (SIS) waveguide. We study the dispersion and excitation of the two kinds of coupled SSPPs supported by the 3D SIS waveguide. The evolution of the dispersion with the thickness and gap width of the waveguide is numerically investigated, and we give a theoretical analysis according to the coupling mechanism. Specially, based on the coupling mechanism, we design a zipper structure, through which the excitation and propagation of the anti-symmetric coupled modes can be realized effectively. [ABSTRACT FROM AUTHOR]

RX J1713.7−3946 is a prototype in the γ-ray-bright supernova remnants (SNRs) and is in continuing debates on its hadronic versus leptonic origin of the γ-ray emission. We explore the role played by the diffusive relativistic protons that escape from the SNR shock wave in the γ-ray emission, apart from the high-energy particles’ emission from the inside of the SNR. In the scenario that the SNR shock propagates in a clumpy molecular cavity, we consider that the γ-ray emission from the inside of the SNR may arise either from the inverse Compton scattering or from the interaction between the trapped energetic protons and the shocked clumps. The dominant origin between them depends on the electron-to-proton number ratio. The diffusive protons that escaped from the shock wave during the expansion history can provide an outer hadronic γ-ray component by bombarding the surrounding dense matter. The broadband spectrum can be well explained by this two-zone model, in which the γ-ray emission from the inside governs the TeV band, while the outer emission component substantially contributes to the GeV γ-rays. The two-zone model can also explain the TeV γ-ray radial brightness profile that significantly stretches beyond the nonthermal X-ray-emitting region. In the calculation, we present a simplified algorithm for Li & Chen's “accumulative diffusion” model for escaping protons and apply the Markov Chain Monte Carlo method to constrain the physical parameters. [ABSTRACT FROM AUTHOR]

Efficient calculation of the electrostatic interactions including repulsive force between charged molecules in a biomolecule system or charged particles in a colloidal system is necessary for the molecular scale or particle scale mechanical analyses of these systems. The electrostatic repulsive force depends on the mid-plane potential between two charged particles. Previous analytical solutions of the mid-plane potential, including those based on simplified assumptions and modern mathematic methods, are reviewed. It is shown that none of these solutions applies to wide ranges of inter-particle distance from 0 to 10 and surface potential from 1 to 10. Three previous analytical solutions are chosen to develop a semi-analytical solution which is proven to have more extensive applications. Furthermore, an empirical closed-form expression of mid-plane potential is proposed based on plenty of numerical solutions. This empirical solution has extensive applications, as well as high computational efficiency. [ABSTRACT FROM AUTHOR]

Reducing the radiation in computerized tomography is today a major concern in radiology. Low dose computerized tomography (LDCT) offers a sound way to deal with this problem. However, more severe noise in the reconstructed CT images is observed under low dose scan protocols (e.g. lowered tube current or voltage values). In this paper we propose a Gamma regularization based algorithm for LDCT image reconstruction. This solution is flexible and provides a good balance between the regularizations based on l0-norm and l1-norm. We evaluate the proposed approach using the projection data from simulated phantoms and scanned Catphan phantoms. Qualitative and quantitative results show that the Gamma regularization based reconstruction can perform better in both edge-preserving and noise suppression when compared with other norms. [ABSTRACT FROM AUTHOR]

Hadronic emission from supernova remnant (SNR)–molecular cloud (MC) association systems has been widely regarded as a probe of shock-accelerated cosmic-ray protons. Here, we report on the detection of a γ-ray emission source with a significance of in 0.2–300 GeV, projected to lie to the northwest of the thermal composite SNR Kesteven 41, using 5.6 years of Fermi-Large Area Telescope (LAT) observation data. No significant long-term variability in the energy range 0.2–300 GeV is detected around this source. The error circle, in radius, covers the 1720 MHz OH maser and is essentially consistent with the location of the MC with which the SNR interacts. The source emission has an exponential cutoff power-law spectrum with a photon index of 1.9 ± 0.1 and a cutoff energy of , and the corresponding 0.2–300 GeV luminosity is at a distance of 12 kpc. There is no radio pulsar in the circle responsible for the high γ-ray luminosity. While the inverse Compton scattering scenario would lead to difficulty in the electron energy budget, the source emission can naturally be explained by the hadronic interaction between the relativistic protons accelerated by the shock of SNR Kesteven 41 and the adjacent northwestern MC. In this paper, we present a list of Galactic thermal composite SNRs detected at GeV γ-ray energies by Fermi-LAT. [ABSTRACT FROM AUTHOR]

The high-quality light curves from the Kepler space telescope make it possible to analyze the optical variability of active galactic nuclei (AGNs) with unprecedented time resolution. Studying the asymmetry in variations could provide independent constraints on physical models for AGN variability. In this paper, we use Kepler observations of 19 sources to perform analyses of the variability asymmetry of AGNs. We apply smoothing correction to light curves to deduct their bias toward high-frequency variability asymmetry caused by long-term variations that have been poorly sampled due to the limited length of light curves. A parameter β based on structure functions is introduced to quantitively describe the asymmetry and its uncertainty is measured using extensive Monte Carlo simulations. Individual sources show no evidence of asymmetry at timescales of days and there is no general trend toward positive or negative asymmetry over the whole sample. Stacking the data from all 19 AGNs, we derive an averaged of 0.00 ± 0.03 and −0.02 ± 0.04 over timescales of 1 ∼ 5 days and 5 ∼ 20 days, respectively, which are statistically consistent with zero. Quasars and Seyfert galaxies show similar asymmetry parameters. Our results indicate that short-term optical variations in AGNs are highly symmetric. [ABSTRACT FROM AUTHOR]

The physical nature of thermal composite supernova remnants (SNRs) remains controversial. We have revisited the archival XMM-Newton and Chandra data of the thermal composite SNR Kesteven 41 (Kes 41 or G337.8–0.1) and performed a millimeter observation toward this source in the 12CO, 13CO, and C18O lines. The X-ray emission, mainly concentrated toward the southwestern part of the SNR, is characterized by distinct S and Ar He-like lines in the spectra. The X-ray spectra can be fitted with an absorbed nonequilibrium ionization collisional plasma model at a temperature of 1.3-2.6 keV and an ionization timescale of 0.1-1.2 × 1012 cm–3 s. The metal species S and Ar are overabundant, with 1.2-2.7 and 1.3-3.8 solar abundances, respectively, which strongly indicate the presence of a substantial ejecta component in the X-ray-emitting plasma of this SNR. Kes 41 is found to be associated with a giant molecular cloud (MC) at a systemic local standard of rest velocity of –50 km s–1 and confined in a cavity delineated by a northern molecular shell, a western concave MC that features a discernible shell, and an H I cloud seen toward the southeast of the SNR. The birth of the SNR in a preexisting molecular cavity implies a mass of ≳ 18 M☼ for the progenitor if it was not in a binary system. Thermal conduction and cloudlet evaporation seem to be feasible mechanisms to interpret the X-ray thermal composite morphology, and the scenario of gas reheating by the shock reflected from the cavity wall is quantitatively consistent with the observations. An updated list of thermal composite SNRs is also presented in this paper. [ABSTRACT FROM AUTHOR]

Over the past decade, two-dimensional semiconductors (2DSCs) have aroused wide interest due to their extraordinary electronic, magnetic, optical, mechanical, and thermal properties, which hold potential in electronic, optoelectronic, thermoelectric applications, and so forth. The field-effect transistor (FET), a semiconductor gated with at least three terminals, is pervasively exploited as the device geometry for these applications. For lack of effective and stable substitutional doping techniques, direct metal contact is often used in 2DSC FETs to inject carriers. A Schottky barrier (SB) generally exists in the metal–2DSC junction, which significantly affects and even dominates the performance of most 2DSC FETs. Therefore, low SB or Ohmic contact is highly preferred for approaching the intrinsic characteristics of the 2DSC channel. In this review, we systematically introduce the recent progress made in theoretical prediction of the SB height (SBH) in the 2DSC FETs and the efforts made both in theory and experiments to achieve low SB contacts. From the comparison between the theoretical and experimentally observed SBHs, the emerging first-principles quantum transport simulation turns out to be the most powerful theoretical tool to calculate the SBH of a 2DSC FET. Finally, we conclude this review from the viewpoints of state-of-the-art electrode designs for 2DSC FETs. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are carried out to study atomic diffusion in the explosive welding process of Ni50Ti50—Cu (at.%). By using a hybrid method which combines molecular dynamics simulation and classical diffusion theory, the thickness of the diffusion layer and the atomic concentration distribution across the welding interface are obtained. The results indicate that the concentration distribution curves at different times have a geometric similarity. According to the geometric similarity, the atomic concentration distribution at any time in explosive welding can be calculated. Ni50Ti50—Cu explosive welding and scanning electron microscope experiments are done to verify the results. The simulation results and the experimental results are in good agreement. [ABSTRACT FROM AUTHOR]

Rotation of dust clusters in an unmagnetized dusty plasma under different gas pressures is experimentally studied. Clusters containing different numbers of charged dust grains are found in different horizontal planes. The mechanism behind the dust rotation is investigated by using molecular dynamics simulations. The experimental and simulation results show that the radial confinement potential plays an important role in determining the properties of the cluster rotation under given gas pressure or temperature. [ABSTRACT FROM AUTHOR]

p-type gallium nitride (GaN) layers were regrown on etched surfaces on free-standing GaN substrates by metalorganic chemical vapor deposition with different growth rates by adjusting trimethylgallium flow rates. The roughness of the samples increases almost linearly with the growth rate, with an increase rate of 0.6 nm (μm h−1) −1. The screw dislocation density of the samples increases significantly when the growth rate is higher than 0.5 μm h−1. When the magnesium (Mg) doping concentration is higher than 7.0 × 1019 cm−3, transmission electron microscopy images clearly show the regrowth interfaces, and Mg precipitate occur in high-doping p-GaN layers. Under the same bis(cyclopentadienyl)magnesium (Cp2Mg) flow rate, the Mg doping concentration decreases with the growth rate. The samples with different growth rates show different electroluminescence spectra. The emission peak at 2.8 eV is due to the transition from the deep donor level to the Mg acceptor level. And the intensity of this peak drops with increasing growth rate due to reduction of Mg acceptors. Transitions related to defect levels appears with increasing growth rate due to an increased screw dislocation density. [ABSTRACT FROM AUTHOR]

A novel kind of terahertz directional optical fibre coupler is proposed. The coupling characteristics and operation bandwidth of the three-core photonic crystal fibre coupler are investigated. Numerical results show that it is possible to achieve a broadband terahertz fibre coupler with a small fibre length of a few centimetres. In addition, a modified configuration, which can achieve a wider bandwidth and lower absorption loss, is proposed. [ABSTRACT FROM AUTHOR]

In this paper we study the characteristic or generating function of a certain discontinuous linear statistic of the Laguerre unitary ensembles and show that this is a particular fifth Painlevé transcendent in the variable t, the position of the discontinuity. The proof of the ladder operators adapted to orthogonal polynomial with discontinuous weight announced sometime ago [13] is presented here, followed by the nonlinear difference equations satisfied by two auxiliary quantities and the derivation of the Painlevé equation. [ABSTRACT FROM AUTHOR]

The coupling characteristics of a three-core photonic crystal fiber (PCF) and its application as a broadband directional coupler are investigated. Numerical investigations demonstrated that broadband directional coupling with spectral width as large as 425 nm and polarization-dependent loss lower than 0.06 dB could be achieved in the proposed fiber coupler. In addition, the proposed fiber shows large tolerance to the variation of the fiber parameters. In particular, the fiber allows at least 4% deviation of the air-hole diameters and 10% deviation from the proposed length of 27 mm. [ABSTRACT FROM AUTHOR]

A novel low-cost, high-volume fabrication method for glass microlens arrays was developed by combining compression molding and thermal reflow processes. This fabrication process includes three major steps--i.e., fabrication of glassy carbon molds with arrays of micro size holes, glass compression molding to create micro cylinders on a glass substrate, and reheating to form microlens arrays. As compared to traditional polymer microlens arrays, glass microlens arrays are more reliable and therefore may be used in more critical applications. In this research, microlens arrays with different surface geometries were successfully fabricated on a P-SK57 (Tg = 493 °C) glass substrate using a combination of the compression molding and thermal reflow processes. The major parameters that influence the final lens shape, including reheating temperature and holding time, were studied to establish a suitable fabrication process. A numerical simulation method was developed to evaluate the fabrication process. Finally, both surface geometry and optical performance of the fabricated glass microlens arrays were analyzed. [ABSTRACT FROM AUTHOR]

III-nitrides and beta-phase gallium oxide (β-Ga2O3) are currently two intensively investigated wide bandgap semiconductor materials for power electronics. Due to the relatively low lattice mismatch between the two material systems and the availability of bulk AlN, GaN and β-Ga2O3 substrates, epitaxial growth of III-nitrides on β-Ga2O3 or vice versa has been realized. However, the design of power devices by integrating the two material systems is still lacking. Here we numerically investigate an AlN/β-Ga2O3 heterostructure by taking advantage of polarization-induced doping to realize high-performance enhancement-mode transistors. Induced by polarization effects at the AlN/β-Ga2O3 interface, a 2-dimensional electron gas concentration can reach up to 8.1 × 1019 cm−3 in the channel. On top of the channel, a p-GaN gate was introduced and eventually a normally-off AlN/β-Ga2O3 field-effect transistor with tunable positive threshold voltages was realized. Furthermore, we inserted an unintentionally doped GaN back barrier layer to suppress the drain leakage current. Eventually, the transfer and output characteristics of the proposed device with different structural parameters were further investigated and analyzed in the pursuit of high-performance III-nitrides/Ga2O3-based power devices. [ABSTRACT FROM AUTHOR]

GaAs multiple concentric nano-ring structures (CNRs) are prepared with multistep crystallization procedures by droplets epitaxy on GaAs (001) to explore the influence of different initial crystallization temperatures on CNRs morphology. Atomic force microscope (AFM) images show that GaAs nanostructures are more likely to form elliptical rings due to diffusion anisotropy. Meanwhile, with the increase of initial crystallization temperature, the inner ring height and density of CNRs are increased, and outer rings are harder to form. In addition, the mechanism of formation of CNRs is discussed by classical nucleation theory and diffusion theory. The method can be used to calculate the diffusion activation energy of gallium atoms (0.7±0.1 eV) on the GaAs (001) surface conveniently. [ABSTRACT FROM AUTHOR]