Degree distribution and robustness of cooperativecommunication network with scale-free model
The consistent Riccati expansion and new interaction solution for a Boussinesq-type coupled system
Starting from the Davey–Stewartson equation, a Boussinesq-type coupled equation system is obtained by using a variable separation approach. For the Boussinesq-type coupled equation system, its consistent Riccati expansion (CRE) solvability is studied with the help of a Riccati equation. It is significant that the soliton–cnoidal wave interaction solution, expressed explicitly by Jacobi elliptic functions and the third type of incomplete elliptic integral, of the system is also given.
Reweighted ensemble dynamics simulations: Theory, improvement, and application
Based on multiple parallel short molecular dynamics simulation trajectories, we designed the reweighted ensemble dynamics (RED) method to more efficiently sample complex (biopolymer) systems, and to explore their hierarchical metastable states. Here we further present an improvement to depress statistical errors of the RED and we discuss a few keys in practical application of the RED, provide schemes on selection of basis functions, and determination of the free parameter in the RED. We illustrate the application of the improvements in two toy models and in the solvated alanine dipeptide. The results show the RED enables us to capture the topology of multiple-state transition networks, to detect the diffusion-like dynamical behavior in an entropy-dominated system, and to identify solvent effects in the solvated peptides. The illustrations serve as general applications of the RED in more complex biopolymer systems.
Solutions of the D-dimensional Schrödinger equation with Killingbeck potential: Lie algebraic approach
Quantum correlation dynamics in a two-qubit Heisenberg XYZ model with decoherence
Quantum correlation dynamics in an anisotropic Heisenberg XYZ model under decoherence is investigated by making use of concurrence C and quantum discord (QD). Firstly, we show that both the concurrence and QD exhibit oscillation with time whereas a remarkable difference between them is presented: there is an “entanglement intermittently sudden death” phenomenon in the concurrence but not in the QD, which is valid for all the initial states of this system. Also, the interval time of entanglement sudden death is found to be strongly dependent on the initial states, the inhomogeneous magnetic field b and the anisotropic parameter △. Then, it implies that the steady concurrence and QD can be obtained in the long-time limit, which means that the environmental decoherence cannot entirely destroy the quantum correlation, the variation of the uniform magnetic field B and the anisotropic parameter can change the magnitude of the steady concurrence and QD evidently whereas the parameter b cannot. In addition, based on the analysis of the steady concurrence and QD with t→∞, we give the reason why the magnitude of the steady concurrence and QD is so complicated with the change of the parameters B and D, whereas the parameter b is independent of the steady concurrence and QD.
Statistical analysis of the temporal single-photon response of superconducting nanowire single photon detection
A new method to study the transient detection efficiency (DE) and pulse amplitude of superconducting nanowire single photon detectors (SNSPD) during the current recovery process is proposed–statistically analyzing the single photon response under photon illumination with a high repetition rate. The transient DE results match well with the DEs deduced from the static current dependence of DE combined with the waveform of a single-photon detection event. This proves that static measurement results can be used to analyze the transient current recovery process after a detection event. The results are relevant for understanding the current recovery process of SNSPDs after a detection event and for determining the counting rate of SNSPDs.
Effects of systematic phase errors on optimized quantum random-walk search algorithm
Oscillation of the spin-currents of cold atoms on a ring due to light-induced spin-orbit coupling
Analysis of field coupling to transmission lines with random rotation over the ground
Moment stability for a predator-prey model with parametric dichotomous noises
Study on a new chaotic bitwise dynamical system and its FPGA implementation
A circular zone counting method of identifying a Duffing oscillator state transition and determining the critical value in weak signal detection
A joint image encryption and watermarking algorithm based on compressive sensing and chaotic map
In this paper, a compressive sensing (CS) and chaotic map-based joint image encryption and watermarking algorithm is proposed. The transform domain coefficients of the original image are scrambled by Arnold map firstly. Then the watermark is adhered to the scrambled data. By compressive sensing, a set of watermarked measurements is obtained as the watermarked cipher image. In this algorithm, watermark embedding and data compression can be performed without knowing the original image; similarly, watermark extraction will not interfere with decryption. Due to the characteristics of CS, this algorithm features compressible cipher image size, flexible watermark capacity, and lossless watermark extraction from the compressed cipher image as well as robustness against packet loss. Simulation results and analyses show that the algorithm achieves good performance in the sense of security, watermark capacity, extraction accuracy, reconstruction, robustness, etc.
Dynamical characteristics of an HP memristor based on an equivalent circuit model in a chaotic oscillator
To develop real world memristor application circuits, an equivalent circuit model which imitates memductance (memory conductance) of the HP memristor is presented. The equivalent circuit can be used for breadboard experiments for various application circuit designs of memristor. Based on memductance of the realistic HP memristor and Chua's circuit a new chaotic oscillator is designed. Some basic dynamical behaviors of the oscillator, including equilibrium set, Lyapunov exponent spectrum, and bifurcations with various circuit parameters are investigated theoretically and numerically. To confirm the correction of the proposed oscillator an analog circuit is designed using the proposed equivalent circuit model of an HP memristor, and the circuit simulations and the experimental results are given.
A new piecewise linear Chen system of fractional-order: Numerical approximation of stable attractors
Mittag-Leffler synchronization of fractional-order uncertain chaotic systems
An efficient three-party password-based key agreement protocol using extended chaotic maps
Optimization of combined endoreversible Carnot heat engines with different objectives
Theoretical models for designing a 220-GHz folded waveguide backward wave oscillator
In-situ measurement of magnetic field gradient in a magnetic shield by a spin-exchange relaxation-free magnetometer
Globally accurate ab initio based potential energy surface of H2O+(X4A")
Two-photon spectrum of 87Rb using optical frequency comb
Exploring photocurrent output from donor/acceptor bulk-heterojunctions by monitoring exciton quenching
Ramsey-CPT spectrum with the Faraday effect and its application to atomic clocks
Rydberg excitation of neutral nitric oxide molecules instrong UV and near-IR laser fields
Photodetachment microscopy of H- in the magnetic field near different dielectric surfaces
Scaling law of single ion-atom impact ionization cross sections of noble gases from He to Xe at strong perturbative energies
Multiple ionization of Ne induced by 10 keV/u-500 keV/u Cq+ (q=1-3) ions
Conditions for formation and trapping of the two-ion Coulomb cluster in the dissipative optical superlattice
Conditions have been studied under which a polychromatic optical superlattice can form and trap the Coulomb cluster of two strongly interacting ions. In our previous work (Krasnov I V and Kamenshchikov L P 2014 Opt. Comm. 312 192) this new all-optical method of obtaining and confining the Coulomb clusters was demonstrated by numerical simulations for special values of the optical superlattice parameters and in the case of Yb ions. In the present paper the conditions are explicitly formulated, under which the long-lived two-ion cluster in the superlattice cell is formed. The peculiarity of these conditions is the renormalization of the ion–ion Coulomb interaction. Notably, the renormalized Coulomb force is determined by the effective charge which depends on the light field parameters and can strongly differ from the “bare” ion charge. This result can be accounted for by the combined manifestation of the quantum fluctuations of optical forces, nonlinear dependence of these forces on the velocity, and non-Maxwellian (Tsallis type) velocity distribution of the ions in the optical superlattice. Explicit analytical formulas are also obtained for the parameters of the optical two-ion cluster.
Achieving a multi-band metamaterial perfect absorber via a hexagonal ring dielectric resonator
Improved autonomous star identification algorithm
Electrically tunable holographic polymer templated blue phase liquid crystal grating
Algebraic and group treatments to nonlinear displaced number statesand their nonclassicality features: A new approach
Multiple frequency conversion via atomic spin coherence of storing a light pulse
Electromagnetic field quantization and input-output relation for anisotropic magnetodielectric metamaterial
A scheme for two-photon lasing with two coupled flux qubits in circuit quantum electrodynamics
We theoretically study the system of a superconducting transmission line resonator coupled to two interacting superconducting flux qubits. It is shown that under certain conditions the resonator mode can be tuned to two-photon resonance between the ground state and the highest excited state while the middle excited states are far-off resonance. Furthermore, we study the steady-state properties of the flux qubits and resonator, such as the photon statistics, the spectrum and squeezing of the resonator, and demonstrate that two-photon laser can be implemented with current experimental technology.
High coupling efficiency and low signal light loss (2+1)× 1 coupler
A long-term frequency-stabilized erbium-fiber-laser-based optical frequency comb with an intra-cavity electro-optic modulator
Single, composite, and ceramic Nd:YAG 946-nm lasers
Graded doping low internal loss 1060-nm InGaAs/AlGaAsquantum well semiconductor lasers
Stability analysis for flow past a cylinder via lattice Boltzmann method and dynamic mode decomposition
A combination of the lattice Boltzmann method and the most recently developed dynamic mode decomposition is proposed for stability analysis. The simulations are performed on a graphical processing unit. Stability of the flow past a cylinder at supercritical state, Re=50, is studied by the combination for both the exponential growing and the limit cycle regimes. The Ritz values, energy spectrum, and modes for both regimes are presented and compared with the Koopman eigenvalues. For harmonic-like periodic flow in the limit cycle, global analysis from the combination gives the same results as those from the Koopman analysis. For transient flow as in the exponential growth regime, the combination can provide more reasonable results. It is demonstrated that the combination of the lattice Boltzmann method and the dynamic mode decomposition is powerful and can be used for stability analysis for more complex flows.
Experimental study on spectrum and multi-scale nature of wall pressure and velocity in turbulent boundary layer
A novel simulation method for positive corona current pulses
High-order optical vortex harmonics generated by relativistic femtosecond laser pulse
Two-dimensional numerical study of an atmospheric pressurehelium plasma jet with dual-power electrode
In this paper, the characteristics of an atmospheric pressure helium plasma jet generated by a dual-power electrode (DPE) configuration are investigated by using a two-dimensional fluid model. The effect of a needle electrode on the discharge is studied by comparing the results of the DPE configuration with those of the single ring electrode configuration. It is found that the existence of the needle leads to the generation of a helium plasma jet with a higher propagation velocity, higher species density, and larger discharge width. Furthermore, the influences of the needle radius and needle-to-ring discharge gap on the generation of a plasma jet are also studied. The simulation results indicate that the needle electrode has an evident influence on the plasma jet characteristics.
Effect of deposition parameters on structural and mechanicalproperties of niobium nitride synthesized by plasma focus device
Current-voltage characteristics of hydrogen DC plasma torches with different sizes in an external axial magnetic field
Evolution of magnetically rotating arc into large area arc plasma
An arc channel tends to shrink due to its conductivity increasing with the increase of temperature. In this study, to generate large area arc plasma, we construct a magnetically rotating arc plasma generator, which mainly consists of a lanthanide tungsten cathode (13 mm in diameter), a concentric cylindrical graphite anode chamber (60 mm in diameter) and a solenoid coil for producing an axial magnet field. By controlling the cold gas flow, the magnetically rotating arc evolves from constricted mode to diffuse mode, which almost fills the whole arc chamber cross section. Results show that the diffuse arc plasma has better uniformity and stability. The formation mechanism of large area arc plasma is discussed in this paper.
Implicit electrostatic particle-in-cell/Monte Carlo simulation for the magnetized plasma: Algorithms and application in gas-inductive breakdown
Band structures of elastic waves in two-dimensional eight-fold solid-solid quasi-periodic phononic crystals
Combined with the supercell method, band structures of the anti-plane and in-plane modes of two-dimensional (2D) eight-fold solid–solid quasi-periodic phononic crystals (QPNCs) are calculated by using the finite element method. The influences of the supercell on the band structure and the wave localization phenomenon are discussed based on the modal distributions. The reason for the appearance of unphysical bands is analyzed. The influence of the incidence angle on the transmission spectrum is also discussed.
Low-temperature phase transformation from nanotube to sp3 superhard carbon phase
Numerous new carbon allotropes have been uncovered by compressing carbon nanotubes based on our computational investigation. The volume compression calculations suggest that these new phases have a very high anti-compressibility with a large bulk modulus (B0). The predicted B0 of new phases is larger than that of c-BN (373 GPa) and smaller than that of diamond (453 GPa). All of the predicted structures are superhard transparent materials with a larger band gap and possess the covalent characteristics with sp3-hybridized electronic states. The simulated results will help us better understand the structural phase transition of cold-compressed carbon nanotubes.
Structural and magnetic transition in stainless steel Fe-21Cr-6Ni-9Mn up to 250 GPa
Room temperature damping correlated to the microstructures in Cu-20.4Al-8.7Mn
Dynamic strength behavior of a Zr-based bulk metallic glassunder shock loading
Dynamic strength behavior of Zr51Ti5Ni10Cu25Al9 bulk metallic glass (BMG) up to 66 GPa was investigated in a series of plate impact shock-release and shock-reload experiments. Particle velocity profiles measured at the sample/LiF window interface were used to estimate the shear stress, shear modulus, and yield stress in shocked BMG. Beyond confirming the previously reported strain-softening of shear stress during the shock loading process for BMGs, it is also shown that the softened Zr-BMG still has a high shear modulus and can support large yield stress when released or reloaded from the shocked state, and both the shear modulus and the yield stress appear as strain-hardening behaviors. The work provides a much clearer picture of the strength behavior of BMGs under shock loading, which is useful to comprehensively understand the plastic deformation mechanisms of BMGs.
Synthesis mechanism of nanoporous Sn3O4 nanosheets by hydrothermal process without any additives
Nanoporous anorthic-phase Sn3O4 nanosheets are successfully fabricated via a hydrothermal process without any additives. With the pH value of the precursor increasing from 2.0 to 11.8, the valence of the precursor changes from mixed valence (the ratio of Sn2+ to Sn4+ is 2.7:1) to pure bivalent, and the product transformed from Sn3O4 to SnO mesocrystals. When doping SbCl3 to the alkaline precursor, the valence of the precursor shows mixed valence with the ratio of Sn2+ to Sn4+ being 2.6:1 and Sn3O4 is synthesized after the hydrothermal process. The valence state of Sn species in the precursor is the key factor of the formation of Sn3O4. The synthesis mechanism is discussed and proposed. These experimental results expand the knowledge base that can be used to guide technological applications of intermediate tin oxide materials.
Mechanical properties of copper nanocube under three-axial tensile loadings
The mechanical properties of copper nanocubes by molecular dynamics are investigated in this paper. The , ,  nanocubes are created, and their energies, yield stresses, hydrostatic stresses, Mises stresses, and the relationships between them and strain are analyzed. Some concepts of the microscopic damage mechanics are introduced, which are the basis of studying the damage mechanical properties by molecular dynamics. The  nanocube exhibits homogeneity and isotropy and achieves a balance easily. The  nanocube presents transverse isotropy. The  nanocube shows the complexity and anisotropy because the orientation sizes in three directions are different. The broken point occurs on a surface, but the other two do not. The  orientation model will be an ideal model for studying the microscopic damage theory.
Properties of sound attenuation around a two-dimensional underwater vehicle with a large cavitation number
Linear and nonlinear optical properties of Sb-doped GeSe2 thin films
Progress in bulk GaN growth
Three main technologies for bulk GaN growth, i.e., hydride vapor phase epitaxy (HVPE), Na-flux method, and ammonothermal method, are discussed. We report our recent work in HVPE growth of GaN substrate, including dislocation reduction, strain control, separation, and doping of GaN film. The growth mechanisms of GaN by Na-flux and ammonothermal methods are compared with those of HVPE. The mechanical behaviors of dislocation in bulk GaN are investigated through nano-indentation and high-space resolution surface photo-voltage spectroscopy. In the last part, the progress in growing some devices on GaN substrate by homo-epitaxy is introduced.
Design of patterned sapphire substrates for GaN-based light-emitting diodes
A new method for patterned sapphire substrate (PSS) design is developed and proven to be reliable and cost-effective. As progress is made with LEDs' luminous efficiency, the pattern units of PSS become more complicated, and the effect of complicated geometrical features is almost impossible to study systematically by experiments only. By employing our new method, the influence of pattern parameters can be systematically studied, and various novel patterns are designed and optimized within a reasonable time span, with great improvement in LEDs' light extraction efficiency (LEE). Clearly, PSS pattern design with such a method deserves particular attention. We foresee that GaN-based LEDs on these newly designed PSSs will achieve more progress in the coming years.
Metal-organic-vapor phase epitaxy of InGaN quantum dots and their applications in light-emitting diodes
InGaN quantum dot is a promising optoelectronic material, which combines the advantages of low-dimensional and wide-gap semiconductors. The growth of InGaN quantum dots is still not mature, especially the growth by metal–organic–vapor phase epitaxy (MOVPE), which is challenge due to the lack of 、itin-situ monitoring tool. In this paper, we reviewed the development of InGaN quantum dot growth by MOVPE, including our work on growth of near-UV, green, and red InGaN quantum dots. In addition, we also introduced the applications of InGaN quantum dots on visible light emitting diodes.
Progress in research of GaN-based LEDs fabricated on SiC substrate
The influence of buffer layer growth conditions on the crystal quality and residual stress of GaN film grown on silicon carbide substrate is investigated. It is found that the AlGaN nucleation layer with high growth temperature can efficiently decrease the dislocation density and stress of the GaN film compared with AlN buffer layer. To increase the light extraction efficiency of GaN-based LEDs on SiC substrate, flip-chip structure and thin film flip-chip structure were designed and optimized. The fabricated blue LED had a maximum wall-plug efficiency of 72% at 80 mA. At 350 mA, the output power, the Vf, the dominant wavelength, and the wall-plug efficiency of the blue LED were 644 mW, 2.95 V, 460 nm, and 63%, respectively.
Status of GaN-based green light-emitting diodes
GaN-based blue light emitting diodes (LEDs) have undergone great development in recent years, but the improvement of green LEDs is still in progress. Currently, the external quantum efficiency (EQE) of GaN-based green LEDs is typically 30%, which is much lower than that of top-level blue LEDs. The current challenge with regard to GaN-based green LEDs is to grow a high quality InGaN quantum well (QW) with low strain. Many techniques of improving efficiency are discussed, such as inserting AlGaN between the QW and the barrier, employing prestrained layers beneath the QW and growing semipolar QW. The recent progress of GaN-based green LEDs on Si substrate is also reported: high efficiency, high power green LEDs on Si substrate with 45.2% IQE at 35 A/cm2, and the relevant techniques are detailed.
Transient thermal analysis as measurement method for IC package structural integrity
Practices of IC package reliability testing are reviewed briefly, and the application of transient thermal analysis is examined in great depth. For the design of light sources based on light emitting diode (LED) efficient and accurate reliability testing is required to realize the potential lifetimes of 10^5 h. Transient thermal analysis is a standard method to determine the transient thermal impedance of semiconductor devices, e.g. power electronics and LEDs. The temperature of the semiconductor junctions is assessed by time-resolved measurement of their forward voltage (Vf). The thermal path in the IC package is resolved by the transient technique in the time domain. This enables analyzing the structural integrity of the semiconductor package. However, to evaluate thermal resistance, one must also measure the dissipated energy of the device (i.e., the thermal load) and the k-factor. This is time consuming, and measurement errors reduce the accuracy. To overcome these limitations, an innovative approach, the relative thermal resistance method, was developed to reduce the measurement effort, increase accuracy and enable automatic data evaluation. This new way of evaluating data simplifies the thermal transient analysis by eliminating measurement of the k-factor and thermal load, i.e. measurement of the lumen flux for LEDs, by normalizing the transient Vf data. This is especially advantageous for reliability testing where changes in the thermal path, like cracks and delaminations, can be determined without measuring the k-factor and thermal load. Different failure modes can be separated in the time domain. The sensitivity of the method is demonstrated by its application to high-power white InGaN LEDs. For detailed analysis and identification of the failure mode of the LED packages, the transient signals are simulated by time-resolved finite element (FE) simulations. Using the new approach, the transient thermal analysis is enhanced to a powerful tool for reliability investigation of semiconductor packages in accelerated lifetime tests and for inline inspection. This enables automatic data analysis of the transient thermal data required for processing a large amount of data in production and reliability testing. Based on the method, the integrity of LED packages can be tested by inline, outgoing inspection and the lifetime prediction of the products is improved.
GaN substrate and GaN homo-epitaxy for LEDs: Progress and challenges
After a brief review on the progresses in GaN substrates by ammonothermal method and Na-flux method and hydride vapor phase epitaxy (HVPE) technology, our research results of growing GaN thick layer by a gas flow-modulated HVPE, removing the GaN layer through an efficient self-separation process from sapphire substrate, and modifying the uniformity of multiple wafer growth are presented. The effects of surface morphology and defect behaviors on the GaN homo-epitaxial growth on free standing substrate are also discussed, and followed by the advances of LEDs on GaN substrates and prospects of their applications in solid state lighting.
Phosphor-free white light-emitting diodes
The multiple color-matching schemes that could improve the color rendering index for phosphor-free white LEDs are discussed. Then we review a few of the recent research directions for phosphor-free white LEDs, which include the development of monolithic GaN-based white LEDs and hybrid integrated GaN-based and AlGaInP-based white LEDs. These development paths will pave the way toward commercial application of phosphor-free white LEDs in the coming years.
Progress and prospects of GaN-based LEDs using nanostructures
Progress with GaN-based light emitting diodes (LEDs) that incorporate nanostructures is reviewed, especially the recent achievements in our research group. Nano-patterned sapphire substrates have been used to grow an AlN template layer for deep-ultraviolet (DUV) LEDs. One efficient surface nano-texturing technology, hemisphere-cones-hybrid nanostructures, was employed to enhance the extraction efficiency of InGaN flip-chip LEDs. Hexagonal nanopyramid GaN-based LEDs have been fabricated and show electrically driven color modification and phosphor-free white light emission because of the linearly increased quantum well width and indium incorporation from the shell to the core. Based on the nanostructures, we have also fabricated surface plasmon-enhanced nanoporous GaN-based green LEDs using AAO membrane as a mask. Benefitting from the strong lateral SP coupling as well as good electrical protection by a passivation layer, the EL intensity of an SP-enhanced nanoporous LED was significantly enhanced by 380%. Furthermore, nanostructures have been used for the growth of GaN LEDs on amorphous substrates, the fabrication of stretchable LEDs, and for increasing the 3-dB modulation bandwidth for visible light communication.
Structural, electronic, and magnetic properties in FeAlAun (n=1-6) clusters: A first-principles study
First principles study on d0 half-metallic properties of full-Heusler compounds RbCaX2 (X=C, N, and O)
A first-principles approach is employed to study the structural, electronic, and magnetic properties of RbCaX2 (X=C, N, and O) full-Heusler compounds. It is observed that RbCaN2 and RbCaO2 are new d0 half-metals with an integer magnetic moment of 3 μB and 1 μB in their ferrimagnetic ground states, respectively, while RbCaC2 is a common metallic compound. Analysis of the density of states of these compounds indicates that the magnetic moment and furthermore, the half-metallicity primarily originate from the spin-polarization of the p-like states of N and O atoms. The half-metallic (HM) gaps of RbCaN2 and RbCaO2 are notably large; thus, the half-metallicity is robust against lattice distortion. Such materials are suitable to be grown on various semiconductor substrates. In addition, for RbCaN2 and RbCaO2, four possible terminations of the surface are also calculated.
Low-temperature physical properties and electronic structures of Ni3Sb, Ni5Sb2, NiSb2, and NiSb
We report the results of low temperature resistivity and magnetization measurements on polycrystalline samples of four Ni–Sb compounds, Ni3Sb, Ni5Sb2, NiSb, and NiSb2. Resistivity measurements revealed that these compounds exhibit a metallic type of electrical conductivity. Temperature dependences of the resistivities were well fitted by the generalized Bloch–Grüneisen formula with an exponent of n=3, indicating that the s–d interband scattering is the dominant scattering mechanism. The magnetic susceptibilities of Ni5Sb2, NiSb, and NiSb2 are almost independent of temperature (above 150 K), exhibiting Pauli paramagnetic behavior. The temperature dependences of the susceptibilities were fitted using the Curie–Weiss law. Ni3Sb was found to have a paramagnetic–ferromagnetic phase transition at 229 K.First-principles calculations have been performed to investigate the electronic structures and physical properties of these Ni–Sb alloys. The calculation of the band structure predicted that Ni3Sb, Ni5Sb2, NiSb, and NiSb2 have characteristics of metal, and the ground state of Ni3Sb is ferromagnetic. The electrical and magnetic properties observed experimentally are consistent with that predicted by the first-principle electronic structure calculations.
Influences of spark plasma sintering temperature on the microstructures and thermoelectric properties of (Sr0.95Gd0.05)TiO3 ceramics
(Sr0.95Gd0.05)TiO3 (SGTO) ceramics are successfully prepared via spark plasma sintering (SPS) respectively at 1548, 1648, and 1748 K by using submicron-sized SGTO powders synthesized from a sol–gel method. The densities, microstructures, and thermoelectric properties of the SGTO ceramics are studied. Though the Seebeck coefficient shows no obvious difference in the case that SPS temperatures range from 1548 K to 1648 K, the electrical conductivity and the thermal conductivity increase remarkably due to the increase in grain size and density. The sample has a density higher than 98% theoretical density as the sintering temperature increases up to 1648 K and shows average grain sizes increasing from ～ 0.7 μm to 7 μm until 1748 K. As a result, the maximum of the dimensionless figure of merit of ～ 0.24 is achieved at ～ 1000 K for the samples sintered at 1648 K and 1748 K, which was ～ 71% larger than that (0.14 at ～ 1000 K) for the sample sintered at 1548 K due to the enhancement of the power factor.
Effect of de-trapping on carrier transport process in semi-insulating CdZnTe
The effect of de-trapping on the carrier transport process in the CdZnTe detector is studied by laser beam-induced transient current (LBIC) measurement. Trapping time, de-trapping time, and mobility for electrons are determined directly from transient waveforms under various bias voltages. The results suggest that an electric field strengthens the capture and emission effects in trap center, which is associated with field-assisted capture and the Poole–Frenkel effect, respectively. The electron mobility is calculated to be 950 cm2/V·s and the corresponding electron mobility-lifetime product is found to be 1.32× 10-3 cm2/V by a modified Hecht equation with considering the surface recombination effect. It is concluded that the trapping time and de-trapping time obtained from LBIC measurement provide direct information concerning the transport process.
Formation of two-dimensional electron gas at AlGaN/GaN heterostructure and the derivation of its sheet density expression
Disorder-enhanced nuclear spin relaxation at Landau level filling factor one Hot!
The nuclear spin relaxation rate (1/T1) is measured for GaAs two-dimensional (2D) electron systems in the quantum Hall regime with an all-electrical technique for agitating and probing the nuclear spins. A “tilted plateau” feature is observed near the Landau level filling factor ν=1 in 1/T1 versus ν. Both the width and magnitude of the plateau increase with decreasing electron density. At low temperatures, 1/T1 exhibits an Arrhenius temperature dependence within the tilted plateau regime. The extracted energy gaps are up to two orders of magnitude smaller than the corresponding charge transport gaps. These results point to a nontrivial mechanism for the disorder-enhanced nuclear spin relaxation, in which microscopic inhomogeneities play a key role for the low energy spin excitations related to skyrmions.
Finite size effects on the quantum spin Hall state in HgTe quantum wells under two different types of boundary conditions
Enhanced ultraviolet photoresponse based on ZnO nanocrystals/Pt bilayer nanostructure
Stability of conductance oscillations in carbon atomic chains
Possible magnetic structures of EuZrO3
Influences of P doping on magnetic phase transition and structure in MnCoSi ribbon
Radio-frequency-heating capability of silica-coated manganese ferrite nanoparticles
MnFe2O4 nanoparticles (NPs) with various sizes and tight size-distribution were synthesized by a chemical solution-phase method. The as-synthesized NPs were coated with a silica shell of 4 nm–5 nm in thickness, enabling the water-solubility and biocompatibility of the NPs. The MnFe2O4 NPs with a size of less than 18 nm exhibit superparamagnetic behavior with high saturated magnetization. The capacity of the heat production was enhanced by increasing particle sizes and radio frequency (RF) field strengths. MnFe2O4/SiO2 NPs with 18-nm magnetic cores showed the highest heat-generation ability under an RF field. These MnFe2O4/SiO2 NPs have great potentiality to cancer treatments, controlled drug releases, and remote controls of single cell functions.
Preparation and piezoelectric properties of potassium sodium niobate glass ceramics
Magnetic and ferroelectric properties of Zn and Mn co-doped BaTiO3
Hydrothermal synthesis of Yb3+, Tm3+ co-doped Gd6MoO12 and its upconversion properties
2.0-μm emission and energy transfer of Ho3+/Yb3+ co-doped LiYF4 single crystal excited by 980 nm
Effects of the ion-beam voltage on the properties of the diamond-like carbon thin film prepared by ion-beam sputtering deposition
Influence factors and mechanism of emission of ZnS:Cu nanocrystals
The influence of phonon bath on the control of single photon
Giant enhancement of Kerr rotation in two-dimensional Bismuth iron garnet/Ag photonic crystals
Electronic structure of transition metal dichalcogenides PdTe2 and Cu0.05PdTe2 superconductors obtained by angle-resolved photoemission spectroscopy Hot!
The layered transition metal chalcogenides have been a fertile land in solid state physics for many decades. Various MX2-type transition metal dichalcogenides, such as WTe2, IrTe2, and MoS2, have triggered great attention recently, either for the discovery of novel phenomena or some extreme or exotic physical properties, or for their potential applications. PdTe2 is a superconductor in the class of transition metal dichalcogenides, and superconductivity is enhanced in its Cu-intercalated form, Cu0.05PdTe2. It is important to study the electronic structures of PdTe2 and its intercalated form in order to explore for new phenomena and physical properties and understand the related superconductivity enhancement mechanism. Here we report systematic high resolution angle-resolved photoemission (ARPES) studies on PdTe2 and Cu0.05PdTe2 single crystals, combined with the band structure calculations. We present in detail for the first time the complex multi-band Fermi surface topology and densely-arranged band structure of these compounds. By carefully examining the electronic structures of the two systems, we find that Cu-intercalation in PdTe2 results in electron-doping, which causes the band structure to shift downwards by nearly 16 meV in Cu0.05PdTe2. Our results lay a foundation for further exploration and investigation on PdTe2 and related superconductors.
Toward the complete relational graph of fundamental circuit elements Hot!
A complete and harmonized fundamental circuit relational graph with four linear and four memory elements is constructed based on some newly defined elements, which provides a guide to developing novel circuit functionalities in the future. In addition to resistors, capacitors, and inductors, which are defined in terms of a linear relationship between charge q, current i, voltage v, and magnetic flux φ, Chua proposed in 1971 a fourth linear circuit element to directly relate φ and q. A nonlinear resistive device defined in memory i–v relation and dubbed memristor, was later attributed to such an element and has been realized in various material structures. Here we clarify that the memristor is not the true fourth fundamental circuit element but the memory extension to the concept of resistor, in analogy to the extension of memcapacitor to capacitor and meminductor to inductor. Instead, a two-terminal device employing the linear ME effects, termed transtor, directly relates φ and q and should be recognized as the fourth linear element. Moreover, its memory extension, termed memtranstor, is proposed and analyzed here.
Curvature-induced lipid segregation
We investigate how an externally imposed curvature influences lipid segregation on two-phase-coexistent membranes. We show that the bending-modulus contrast of the two phases and the curvature act together to yield a reduced effective line tension. On largely curved membranes, a state of multiple domains (or rafts) forms due to a mechanism analogous to that causing magnetic-vortex formation in type-II superconductors. We determine the criterion for such a multi-domain state to occur; we then calculate respectively the size of the domains formed on cylindrically and spherically curved membranes.
Gate-dependent photoresponse in self-assembled graphene p-n junctions
The intrinsic photocurrent generation mechanism of a self-assembled graphene p–n junction operating at 1.55 μ is investigated experimentally. It is concluded that both a photovoltage effect and a photothermoelectric effect contribute to the final photocurrent. The photocurrent signal at the p–n junction was found to be dominated by photothermoelectric current, arising from different self-assembled doping levels.
Silicon nanowire formed via shallow anisotropic etching Si-ash-trimming for specific DNA and electrochemical detection
A functionalized silicon nanowire field-effect transistor (SiNW FET) was fabricated to detect single molecules in the pM range to detect disease at the early stage with a sensitive, robust, and inexpensive method with the ability to provide specific and reliable data. The device was designed and fabricated by indented ash trimming via shallow anisotropic etching. The approach is a simple and low-cost technique that is compatible with the current commercial semiconductor standard CMOS process without an expensive deep reactive ion etcher. Specific electric changes were observed for DNA sensing when the nanowire surface was modified with a complementary captured DNA probe and target DNA through an organic linker (–OCH2CH3) using organofunctional alkoxysilanes (3-aminopropyl) triethoxysilane (APTES). With this surface modification, a single specific target molecule can be detected. The simplicity of the sensing domain makes it feasible to miniaturize it for the development of a cancer detection kit, facilitating its use in both clinical and non-clinical environments to allow non-expert interpretation. With its novel electric response and potential for mass commercial fabrication, this biosensor can be developed to become a portable/point of care biosensor for both field and diagnostic applications.
Wavelength-tunable prism-coupled external cavity passively mode-locked quantum-dot laser
A wavelength-tunable mode-locked quantum dot laser using an InAs/GaAs quantum-dot gain medium and a discrete semiconductor saturable absorber mirror is demonstrated. A dispersion prism, which has lower optical loss and less spectral narrowing than a blazed grating, is used for wavelength selection and tuning. A wavelength tuning range of 45.5 nm (from 1137.3 nm to 1182.8 nm) under 140-mA injection current in the passive mode-locked regime is achieved. The maximum average power of 19 mW is obtained at the 1170.3-nm wavelength, corresponding to the single pulse energy of 36.5 pJ.
Modeling the reactive sputter deposition of Ti-doped VOx thin films
Theoretical investigation on isomer formation probability and free energy of small C clusters
A theoretical exploration of the influencing factors for surface potential
Generic meminductive characteristics ofswitched reluctance machines
The meminductive system can be regarded as the generalization of the meminductor. This paper focuses on exploring the generic meminductive characteristics of the switched reluctance machine (SRM). The dynamical equations of SRM systems are derived and discussed in comparison with the typical constitutive relation equations of the meminductive system. Memory ability and pinched hysteresis loop (PHL) are taken as the indicative fingerprints to draw forth the theoretically comparative analysis. Based on the theoretical analysis, in addition to simulation and experimental confirmation, it can be concluded that from the viewpoint of circuit, SRM can be considered as a generic meminductive system.
High efficiency, large-active-area superconducting nanowire single-photon detectors
Niobium nitride superconducting nanowire single-photon detectors were fabricated on thermally oxidized silicon substrates with large active areas of 30 μm × 30 μm. To achieve non-constricted detectors, we improved the film growth and electron beam lithography process to fabricate uniform 100-nm wide NbN nanowires with a fill factor of 50%. The devices showed 72.4% system detection efficiency (SDE) at 100-Hz dark count rate (DCR) and 74-ps timing jitter, measured at the fiber communication wavelength of 1550 nm. The highest SDE which is 81.2% when the DCR is ～700 c/s appears at the wavelength of 1650 nm.
Non-ideal effect in 4H—SiC bipolar junction transistor with double Gaussian-doped base
Influences of stress on the properties of GaN/InGaN multiple quantum well LEDs grown on Si (111) substrates
The influences of stress on the properties of InGaN/GaN multiple quantum wells (MQWs) grown on silicon substrate were investigated. The different stresses were induced by growing InGaN and AlGaN insertion layers (IL) respectively before the growth of MQWs in metal–organic chemical vapor deposition (MOCVD) system. High resolution x-ray diffraction (HRXRD) and photoluminescence (PL) measurements demonstrated that the InGaN IL introduced an additional tensile stress in n-GaN, which released the strain in MQWs. It is helpful to increase the indium incorporation in MQWs. In comparison with MQWs without the IL, the wavelength shows a red-shift. AlGaN IL introduced a compressive stress to compensate the tensile stress, which reduces the indium composition in MQWs. PL measurement shows a blue-shift of wavelength. The two kinds of ILs were adopted to InGaN/GaN MQWs LED structures. The same wavelength shifts were also observed in the electroluminescence (EL) measurements of the LEDs. Improved indium homogeneity with InGaN IL, and phase separation with AlGaN IL were observed in the light images of the LEDs.
Investigation of L10 FePt-based soft/hard composite bit-patterned media by micromagnetic simulation
The soft/hard composite patterned media have potential to be the next generation of magnetic recording, but the composing modes of soft and hard materials have not been investigated systematically. L10 FePt-based soft/hard composite patterned media with an anisotropic constant distribution are studied by micromagnetic simulation. Square arrays and hexagonal arrays with various pitch sizes are simulated for two composing types: the soft layer that encloses the hard dots and the soft layer that covers the whole surface. It is found that the soft material can reduce the switching fields of bits effectively for all models. Compared with the first type, the second type of models possess low switching fields, narrow switching field distributions, and high gain factors due to the introduction of inter-bit exchange coupling. Furthermore, the readout waveforms of the second type are not deteriorated by the inter-bit soft layers. Since the recording density of hexagonal arrays are higher than that of square arrays with the same center-to-center distances, the readout waveforms of hexagonal arrays are a little worse, although other simulation results are similar for these two arrays.
Design and optimization of terahertz directional coupler based on hybrid-cladding hollow waveguide with low confinement loss
Experimental research on the feature of an x-ray Talbot-Lau interferometer versus tube accelerating voltage
X-ray Talbot–Lau interferometer has been used most widely to perform x-ray phase-contrast imaging with a conventional low-brilliance x-ray source, and it yields high-sensitivity phase and dark-field images of samples producing low absorption contrast, thus bearing tremendous potential for future clinical diagnosis. In this work, by changing the accelerating voltage of the x-ray tube from 35 kV to 45 kV, x-ray phase-contrast imaging of a test sample is performed at each integer value of the accelerating voltage to investigate the characteristic of an x-ray Talbot–Lau interferometer (located in the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Japan) versus tube voltage. Experimental results and data analysis show that within a range this x-ray Talbot–Lau interferometer is not sensitive to the accelerating voltage of the tube with a constant fringe visibility of ～ 44%. This x-ray Talbot–Lau interferometer research demonstrates the feasibility of a new dual energy phase-contrast x-ray imaging strategy and the possibility to collect a refraction spectrum.
Cosine fitting radiography and computed tomography
Stair evacuation simulation based on cellular automataconsidering evacuees' walk preferences
As a physical model, the cellular automata (CA) model is widely used in many areas, such as stair evacuation. However, existing CA models do not consider evacuees' walk preferences nor psychological status, and the structure of the basic model is unapplicable for the stair structure. This paper is to improve the stair evacuation simulation by addressing these issues, and a new cellular automata model is established. Several evacuees' walk preference and how evacuee's psychology influences their behaviors are introduced into this model. Evacuees' speeds will be influenced by these features. To validate this simulation, two fire drills held in two high-rise buildings are video-recorded. It is found that the simulation results are similar to the fire drill results. The structure of this model is simple, and it is easy to further develop and utilize in different buildings with various kinds of occupants.