Nonlocal symmetries and negative hierarchies related to bilinear Bäcklund transformation
In this paper, nonlocal symmetries defined by bilinear Bäcklund transformation for bilinear potential KdV (pKdV) equation are obtained. By introducing an auxiliary variable which just satisfies the Schwartzian form of KdV (SKdV) equation, the nonlocal symmetry is localized and the Levi transformation is presented. Besides, based on three different types of nonlocal symmetries for potential KdV equation, three sets of negative pKdV hierarchies along with their bilinear forms are constructed. An impressive result is that the coefficients of the third type of (bilinear) negative pKdV hierarchy (N>0) are variable, which are obtained via introducing an arbitrary parameter by considering the translation invariance of the pKdV equation.
Explicit solutions from residual symmetry of the Boussinesq equation
Controllability of fractional-order Chua's circuit
Hybrid natural element method for large deformation elastoplasticity problems
We present the hybrid natural element method (HNEM) for two-dimensional elastoplastic large deformation problems. Sibson interpolation is adopted to construct the shape functions of nodal incremental displacements and incremental stresses. The incremental form of Hellinger-Reissner variational principle for elastoplastic large deformation problems is deduced to obtain the equation system. The total Lagrangian formulation is used to describe the discrete equation system. Compared with the natural element method (NEM), the HNEM has higher computational precision and efficiency in solving elastoplastic large deformation problems. Some numerical examples are selected to demonstrate the advantage of the HNEM for large deformation elastoplasticity problems.
Inverse problem of pulsed eddy current field of ferromagnetic plates
Approximate analytical solution of the Dirac equation with q-deformed hyperbolic Pöschl-Teller potential and trigonometric Scarf Ⅱ non-central potential
Spin transport properties of a Dresselhaus-polygonal quantum ring
We propose a theoretical method to investigate the effect of the Dresselhaus spin-orbit coupling (DSOC) on the spin transport properties of a regular polygonal quantum ring with an arbitrary number of segments. We find that the DSOC can break the time reversal symmetry of the spin conductance in a polygonal ring and that this property can be used to reverse the spin direction of electrons in the polygon with the result that a pure spin up or pure spin down conductance can be obtained by exchanging the source and the drain. When the DSOC is considered in a polygonal ring with Rashba spin-orbit coupling (RSOC) with symmetric attachment of the leads, the total conductance is independent of the number of segments when both of the two types of spin-orbit coupling (SOC) have the same value. However, the interaction of the two types of SOC results in an anisotropic and shape-dependent conductance in a polygonal ring with asymmetric attachment of the leads. The method we proposed to solve for the spin conductance of a polygon can be generalized to the circular model.
Measurement-induced nonlocality in the W and Greenberger-Horne-Zeilinger superposition states
Measurement-induced nonlocality (MIN) is a newly defined quantity to measure correlations in bipartite quantum states [Luo S and Fu S 2011 Phys. Rev. Lett. 106 120401]. MIN in the n-qubit W and Greenberger-Horne-Zeilinger (GHZ) superposition states is considered. It is revealed that n=3 and n≥ 4 states have very different characteristics, especially the monogamy relation about MIN, and the monogamy equality of MIN is held in all n-qubit W states (n≥ 3).
Topological phase transitions driven by next-nearest-neighbor hopping in noncentrosymmetric cold Fermi gases
We investigate the topological phase marked by the Thouless-Kohmoto-Nightingale-Nijs (TKNN) number and the phase transitions driven by the next nearest neighbor (NNN) hopping in noncentrosymmetric cold Fermi gases, both spin-singlet pairing and spin-triplet pairing are considered. There exists a critical t'c for the NNN hopping, at which the quantum phase transition occurs, and the system changes from an Abelian (non-Abelian) phase to a non-Abelian (Abelian) one. By numerically diagonalizing the Hamiltonian in the real space, the energy spectra with edge states for different topological phases and the Majorana zero modes are discussed. Although the spin-triplet pairing does not contribute to the gap closing and the phase diagram, it induces gapless states in the presence of a magnetic field, and the TKNN number in this region is still zero.
Influence of the environmental noise on determining the period of a torsion pendulum
The environmental noise can restrict the accuracy of period estimation since the torsion pendulum is sensitive to weak forces. Two typical models for the environmental noise are proposed to make an evaluation. Generally, the stationary environmental noise is modeled as a white noise, and contributes to the period uncertainty as a function of the initial amplitude, the quality factor, the variance of noise and the time length. As to a sudden sharp disturbance acting on the pendulum, a narrow impulse model is constructed. It results in a sharp jump in the phase difference, which can be excluded with the 3σ criterion for a correction. An experimental data analysis for the measurement of the gravitational constant G with the time-of-swing method shows that the period uncertainty due to the environmental noise is about one and a half times the fundamental thermal noise limit. Though this result is dependent on the ambient environment, the analysis is instructive to improve the measurement accuracy of experiments.
Bifurcation behavior and coexisting motions in a time-delayed power system
Policy iteration optimal tracking control for chaotic systems by using an adaptive dynamic programming approach
Observer of a class of chaotic systems: An application to Hindmarsh-Rose neuronal model
Robust sliding mode control for fractional-order chaotic economical system with parameter uncertainty and external disturbance
Infrared transparent frequency selective surface based on iterative metallic meshes
Precision calculation of fine structure in helium and Li+
The fine structure constant α can be extracted from high-precision spectroscopy of the 23PJ fine structure splittings in helium and light helium-like ions. In this work, the 23PJ fine structure splittings of helium and Li+ ion are calculated, including relativistic and QED corrections of order mα4, mα4(m/M), mα5, mα5(m/M), and Douglas-Kroll operators of mα6 and mα6(m/M), which provide an independent verification for the previous calculations performed by Drake [Can. J. Phys. 80 1195 (2002)] and by Pachucki and Yerokhin [Phys. Rev. A 79 062516 (2009); Phys. Rev. Lett. 104 070403 (2010); Can. J. Phys. 89 1139 (2011)]. The results of the three groups agree with each other.
Compton profile of molecular hydrogen
The Compton profile of molecular hydrogen has been determined at an incident photon energy of 20 keV based on the third generation synchrotron radiation, and the statistical accuracy of 0.2% is achieved at pz=0. Different theoretical methods, i.e., the density functional method, and the Hartree-Fock method, were used to calculate the Compton profiles of hydrogen with different basis sets, and the theoretical calculations are in agreement with the experimental observation in the whole pz region. Compared with the HF calculation, the DFT-B3LYP ones are in better agreement with the present experiment, which indicates the electron correlation effect is very important to describe the wavefunction in the ground state of hydrogen.
Ellipticity-dependent ionization/dissociation of carbon dioxide in strong laser fields
Ionization and dissociation of linear triatomic molecules, carbon dioxide, are studied in 50-fs 800-nm strong laser fields using time-of-flight mass spectrometer. The yields of double charged ions CO22+ and various fragment ions (CO+, On+, and Cn+ (n=1, 2)) are measured as a function of ellipticity of laser polarization in the intensity range from 5.0× 1013 W/cm2 to 6.0× 1014 W/cm2. The results demonstrate that non-sequential double ionization, which is induced by laser-driven electron recollision, dominates double ionization of CO2 in the strong IR laser field with intensity lower than 2.0×1014 W/cm2. The electron recollision could also have contribution in strong-field multiple ionization and formation of fragments of CO2 molecules. The present study indicates that the intensity and ellipticity dependence of ions yields can be used to probe the complex dynamics of strong-field ionization/dissociation of polyatomic molecules.
Projectile angular-differential cross sections for single electron transfer in fast He+-He collisions
Formation of hydrogen atom in 2s state in proton-sodium inelastic scattering
Fast-electron-impact ionization process by 3p of hydrogen-like ions in Debye plasmas
Morphology and structural stability of Pt-Pd bimetallic nanoparticles
The morphologies and structures of Pt-Pd bimetallic nanoparticles determine their chemical and physical properties. Therefore, a fundamental understanding of their morphologies and structural stabilities is of crucial importance to their applications. In this article, we have performed Monte Carlo simulations to systematically explore the structural stability and structural features of Pt-Pd alloy nanoparticles. Different Pt/Pd ratios, and particle sizes and shapes were considered. The simulated results reveal that the truncated octahedron, which has the remarkably lowest energy among all the considered shapes, exhibits the best structural stability while the tetrahedron has the worst invariably. Furthermore, all the structures of Pt-Pd alloy nanoparticles present Pd-rich in the outmost layer but Pt-rich in the sub-outmost layer. Especially, atomic distribution and chemical short-range order parameter were applied to further characterize the structural features of Pt-Pd alloy nanoparticles. This study provides a significant insight not only into the structural stability of Pt-Pd alloy nanoparticles with different compositions, and particle sizes and shapes but also to the design of bimetallic nanoparticles.
Implementation of ternary Shor's algorithm based on vibrational states of an ion in anharmonic potential
Drift effect on vacuum birefringence in a strong electric and magnetic field
As an important QED effect to detect the vacuum polarization, birefringence in the presence of a strong electric and magnetic field, E0⊥B0,E0≤cB0, is considered. The directional dependence of birefringence is obtained. In two special cases: E0 = 0 and E0 = cB0, our results are consistent with the previous ones. The refractive index of the probe wave propagating in the E0×B0 direction decreases with E0/cB0, while that in the -E0×B0 direction increases with E0/cB0. The physics of the direction dependence of birefringence maybe the E0×B0 drift velocity of the virtual electrons and positrons.
Spontaneous emission of “polarized” V-type three-level atoms strongly coupled with an optical cavity
Preparation of SiO2@Au nanorod array as novel surface enhanced Raman substrate for trace pollutants detection
Sensitive absorption measurements of hydrogen sulfide at 1.578 μm using wavelength modulation spectroscopy
First-principles study on linear and nonlinear optical properties of ZnGeP2
The study of the linear and nonlinear optical properties of ZnGeP2 based on density functional theory has been carried out. In order to get a more physical picture in the infrared region, terms which are considered as the phonon effect were added to the calculated refractive dispersion curves. The phonon-corrected calculation curves show excellent agreement with experimental refractive indexes, which gives a better comprehension of the linear optical proprieties in the transparent region. The static nonlinear optical susceptibility was investigated using approaches based on the “sum over states” and the 2n+1 theorem methods. Both of the results of these two methods reasonably coincided with the experimental results.
Attosecond pulse generation from two-electron harmonic emission spectrum
In this paper, we theoretically investigate the high-order harmonic generation and attosecond pulse generation when a two-electron He atom is exposed to the intense laser pulse. It shows that due to the two-electron double recombination mechanism, an extended plateau beyond the classical single-electron harmonic has been obtained on the two-electron harmonic spectrum. Further by using this two-electron harmonic extension scheme combined with the two-color field, two supercontinuum bandwidths with 200 eV have been obtained. As a result, a series of sub-60 as extreme ultraviolet (XUV) pulses have been directly generated.
Non-Gaussian quantum states generation and robust quantum non-Gaussianity via squeezing field
Frequency detection of self-adaption control based on chaotic theory
Time fractional dual-phase-lag heat conduction equation
Enhanced thermoelectric performance of TiO2-based hybrid materials by incorporating conducting polymer
High coercivity in large exchange-bias Co/CoO-MgO nano-granular films
We present a detailed study on the magnetic coercivity of Co/CoO-MgO core-shell systems, which exhibits a large exchange bias due to an increase of the uncompensated spin density at the interface between the CoO shell and the metallic Co core by replacing Co by Mg within the CoO shell. We find a large magnetic coercivity of 7120 Oe around the electrical percolation threshold of the Co/CoO core/shell particles, while samples with a smaller or larger Co metal volume fraction show a considerably smaller coercivity. Thus, this study may lead to a route to improving the magnetic properties of artificial magnetic material in view of potential applications.
Experimental study and analysis on the rising motion of grains in a vertically-vibrated pipe
Frequency-dependent friction in pipelines
Enhancement of third harmonic generation in air filamentation using obstacles
The intensity of third harmonic emission in air filamentation disturbed by copper fibers and alcohol droplets has been investigated experimentally. Enhancement of the third harmonic emission up to more than one order of magnitude has been observed. The physical mechanism of third harmonic enhancement is attributed to suppression of the destructive interference by comparison of the experimental results and it is closely related to the type, size, and relative position of the obstacles.
Low field induced giant anisotropic magnetocaloric effect in DyFeO3 single crystal
We have investigated the anisotropic magnetocaloric effect and the rotating field magnetic entropy in DyFeO3 single crystal. A giant rotating field entropy change of -ΔSMR=16.62 J/kg·K was achieved from b axis to c axis in bc plane at 5 K for a low field change of 20 kOe. The large anisotropic magnetic entropy change is mainly accounted for the 4f electron of rare-earth Dy3+ ion. The large value of rotating field entropy change, together with large refrigeration capacity and negligible hysteresis, suggests that the multiferroic ferrite DyFeO3 singlecrystal could be a potential material for anisotropic magnetic refrigeration at low field, which can be realized in the practical application around liquid helium temperature region.
New layered metal oxides as positive electrode materials for room-temperature sodium-ion batteries Hot!
In order to achieve better Na storage performance, most layered oxide positive electrode materials contain toxic and expensive transition metals Ni and/or Co, which are also widely used for lithium-ion batteries. Here we report a new quaternary layered oxide consisting of Cu, Fe, Mn, and Ti transition metals with O3-type oxygen stacking as a positive electrode for room-temperature sodium-ion batteries. The material can be simply prepared by a high-temperature solidstate reaction route and delivers a reversible capacity of 94 mAh/g with an average storage voltage of 3.2 V. This paves the way for cheaper and non-toxic batteries with high Na storage performance.
Modeling of nonlinear envelope solitons in strongly coupled dusty plasmas: Instability and collision
Start-up phase plasma discharge design of a tokamak via control parameterization method
A tunable magnetically insulated transmission line oscillator Hot!
A tunable magnetically insulated transmission line oscillator (MILO) is put forward and simulated. When the MILO is driven by a 430 kV, 40.6 kA electron beam, high-power microwave is generated with a peak output power of 3.0 GW and frequency of 1.51 GHz, and the relevant power conversion efficiency is 17.2%. The 3-dB tunable frequency range (the relative output power is above half of the peak output power) is 2.25-0.825 GHz when the outer radius of the slow-wave structure (SWS) vanes ranges from 77 mm to 155 mm, and the 3-dB tuning bandwidth is 92%, which is sufficient for the aim of large-scale tuning and high power output.
Synthesis and performance of Zn-Ni-P thin films
Flexural wave band-gaps in phononic metamaterial beam with hybrid shunting circuits
Two-dimensional arsenic monolayer sheet predicted from first-principles
Using first-principles calculations, we investigate the two-dimensional arsenic nanosheet isolated from bulk gray arsenic. Its dynamical stability is confirmed by phonon calculations and molecular dynamics analyzing. The arsenic sheet is an indirect band gap semiconductor with a band gap of 2.21 eV in the hybrid HSE06 functional calculations. The valence band maximum (VBM) and the conduction band minimum (CBM) are mainly occupied by the 4p orbitals of arsenic atoms, which is consistent with the partial charge densities of VBM and CBM. The charge density of the VBM G point has the character of a π bond, which originates from p orbitals. Furthermore, tensile and compressive strains are applied in the armchair and zigzag directions, related to the tensile deformations of zigzag and armchair nanotubes, respectively. We find that the ultimate strain in zigzag deformation is 0.13, smaller than 0.18 of armchair deformation. The limit compressive stresses of single-layer arsenic along armchair and zigzag directions are -4.83 GPa and -4.76 GPa with corresponding strains of -0.15 and -0.14, respectively.
Structural phase transitions of tellurium nanoplates under pressure
In situ high-pressure angle dispersive x-ray diffraction experiments using synchrotron radiation on Te nanoplates were carried out with a diamond anvil cell at room temperature. The results show that Te-I with a trigonal structure transforms to triclinic Te-Ⅱ at about 4.9 GPa, Te-Ⅱ transforms to monoclinic Te-Ⅲ at about 8.0 GPa, Te-Ⅲ turns to rhombohedral Te-IV at about 23.8 GPa, and Te-IV changes to body centered cubic Te-V at 27.6 GPa. The bulk moduli B0 of Te nanoplates are higher than those of Te bulk materials.
Strain analysis of free-standing strained silicon-on-insulator nanomembrane
Water-assisted highly enhanced crystallographic etching of graphene by iron catalysts Hot!
We report the assisted role of water vapor in crystallographic cutting of graphene via iron catalysts in reduced atmosphere. Without water, graphene can be tailored with smooth trenches composed of straight lines with angles of 60° or 120° between two adjacent trenches. After the addition of water, new chacteristics are found: such as almost no iron particles can be detected along the trenches; each trench becomes longer and lots of graphene nanoribbons can be generated. The underlying mechanism is proposed and discussed, which is attributed to stimulating and lengthening of the catalytic activity of iron particles by water vapor.
Dynamic resistive switching in a three-terminal device based on phase separated manganites
Electrical bistable devices using composites of zinc sulfide nanoparticles and poly-(N-vinylcarbazole)
Spin and valley filter in strain engineered silicene
New SOI power device with multi-region high-concentration fixed interface charge and the model of breakdown voltage
Two-dimensional metallic behavior at polar MgO/BaTiO3 (110) interfaces
Majorana fermion realization and relevant transport processes in a triple-quantum dot system
Nonequilibrium electronic transports through a system hosting three quantum dots hybridized with superconductors are investigated. By tuning the relative positions of the dot levels, we illustrate the existence of Majorana fermions and show that the Majorana feimions will either survive separately on single dots or distribute themselves among different dots with tunable probabilities. As a result, different physical mechanisms appear, including local Andreev reflection (LAR), cross Andreev reflection (CAR), and cross resonant tunneling (CRT). The resulting characteristics may be used to reveal the unique properties of Majorana fermions. In addition, we discuss the spin-polarized transports and find a pure spin current and a spin filter effect due to the joint effect of CRT and CAR, which is important for designing spintronic devices.
Influences of fringing capacitance on threshold voltage and subthreshold swing of a GeOI metal-oxide-semiconductor field-effect transistor
Models of threshold voltage and subthreshold swing, including the fringing-capacitance effects between the gate electrode and the surface of the source/drain region, are proposed. The validity of the proposed models is confirmed by the good agreement between the simulated results and the experimental data. Based on the models, some factors impacting the threshold voltage and subthreshold swing of a GeOI metal-oxide-semiconductor field-effect transistor (MOSFET) are discussed in detail and it is found that there is an optimum thickness of gate oxide for definite dielectric constant of gate oxide to obtain the minimum subthreshold swing. As a result, it is shown that the fringing-capacitance effect of a short-channel GeOI MOSFET cannot be ignored in calculating the threshold voltage and subthreshold swing.
Improvement of the off-state breakdown voltage with field plate and low-density drain in AlGaN/GaN high-electron mobility transistors
We present an AlGaN/GaN high-electron mobility transistor (HEMT) device with both field plate (FP) and low-density drain (LDD). The LDD is realized by the injection of negatively charged fluorine (F-) ions under low power in the space between the gate and the drain electrodes. With a small-size FP and a LDD length equal to only 31% of the gate-drain spacing, the device effectively modifies the electric field distribution and achieves a breakdown voltage enhancement up to two times when compared with a device with only FP.
Double spin-glass-like behavior and antiferromagnetic superexchange interaction between Fe3+ ions in α-Ga2-xFexO3 (0 ≤ x ≤ 0.4)
Single phase of Fe3+-doped α-Ga2-xFexO3 (α -GFxO, x=0.1, 0.2, 0.3, 0.4) is synthesized by treating the β -Ga2-xFexO3 (β -GFxO) precursors at high temperatures and high pressures. Rietveld refinements of the X-ray diffraction data show that the lattice constants increase monotonically with the increase of Fe3+ content. Calorimetric measurements show that the temperature of the phase transition from α -GFxO to β -GFxO increases, while the associated enthalpy change decreases upon increasing Fe3+ content. The optical energy gap deduced from the reflectance measurement is found to decrease monotonically with the increase in Fe3+ content. From the measurements of magnetic field-dependent magnetization and temperature-dependent inverse molar susceptibility, we find that the superexchange interaction between Fe3+ ions is antiferromagnetic. Remnant magnetization is observed in the Fe3+-doped α -GFxO and is attributed to the spin glass in the magnetic sublattice. At high Fe3+ doping level (x=0.4), two evident peaks are observed in the image part of the AC susceptibility χ" ac. The frequency dependence in intensity of these two peaks as well as two spin freezing temperatures observed in the DC magnetization measurements of α -GF0.4O is suggested to be the behavior of two spin glasses.
Magnetic properties and magnetocaloric effects in HoPd intermetallic
Reduction of defect-induced ferromagnetic stability in passivated ZnO nanowires
Tailoring the structural and magnetic properties of Cu-doped ZnO by c-axis pressure
Effect of optimized aging processing on properties of the sintered Dy-doped Nd-Fe-B permanent magnet
Fabrication and magnetocrystalline anisotropy of NiCo(002) films
A series of 30-nm-thick epitaxial NixCo1-x (002) alloy films are fabricated by DC magnetron sputtering. MgO (002) and SrTiO3 (002) single substrates are used for x>0.5 and x<0.5, respectively. The magnetocrystalline anisotropy of NixCo1-x (002) alloy films is studied in the entire composition region for 0≤x≤ 1.0. When x decreases, the cubic magnetic anisotropy constant K1 changes sign from negative to positive at x=0.96 and becomes negative again at x= 0.79. It becomes more negative as x decreases from 0.79 to 0. The uniaxial anisotropy Ku is smaller than the K1 by a factor of two orders.
Current-induced magnetic soliton solutions in a perpendicular ferromagnetic anisotropy nanowire
Magnon density distribution can be affected by the spin-transfer torque in a perpendicular ferromagnetic anisotropy nanowire. We obtain the analytical expression for the critical current condition. For the cases of below and above the critical value, the magnon density distribution admits bright and dark soliton states, respectively. Moreover, we discuss two-soliton collision properties that are modulated by the current. Each magnetic soliton exhibits no changes in both velocity and width before and after the collision.
Quantitative calculations of polarizations arising from the symmetric and antisymmetric exchange strictions in Tm-doped GdMnO3
The ferroelectric polarization and phase diagram in Tm-doped GdMnO3 are studied by means of Monte Carlo simulation based on the Mochizuki-Furukawa model. Our work well reproduces the low temperature polarization at various substitution levels observed experimentally. It is demonstrated that the Tm-doping can control the multiferroic behaviors through modulating the spin structures, resulting in the flop of the electric polarization. In addition, the polarization in the ab-plane cycloidal spin phase arises from comparable contributions of the symmetric exchange striction and antisymmetric exchange striction, leading to much bigger polarization than that in the bc-plane cycloidal spin phase where only the contribution of the latter striction is available. The phase diagram obtained in our simulation is helpful for clarifying the multiferroic properties in doped manganite systems and other related multiferroics.
Theoretical study of mutual control mechanism between magnetization and polarization in multiferroic materials
Influence of strain distribution on the morphology evolution of a Ge/GeO2 core/shell nanoparticle confined in ultrathin Al2O3 thinfilm by surface oxidation
Phase transformation and morphology tuning of β-NaYF4: Yb3+, Er3+ nanocrystals through K+ ions codoping
Improvement of electron injection of organic light-emitting devices by inserting a thin aluminum layer into cesium carbonate injection layer
We investigate the electron injection effect of inserting a thin aluminum (Al) layer into cesium carbonate (Cs2CO3) injection layer. Two groups of organic light-emitting devices (OLEDs) are fabricated. For the first group of devices based on Alq3, we insert a thin Al layer of different thickness into Cs2CO3 injection layer, and the device's maximum current efficiency of 6.5 cd/A is obtained when the thickness of the thin Al layer is 0.4 nm. However, when the thickness of Al layer is 0.8 nm, the capacity of electron injection is the strongest. To validate the universality of this approach, then we fabricate another group of devices based on another blue emitting material. The maximum current efficiency of the device without and with a thin Al layer is 4.51 cd/A and 4.84 cd/A, respectively. Inserting a thin Al layer of an appropriate thickness into Cs2CO3 layer can result in the reduction of electron injection barrier, enhancement of the electron injection, and improvement of the performance of OLEDs. This can be attributed to the mechanism that thermally evaporated Cs2CO3 decomposes into cesium oxides, the thin Al layer reacts with cesium oxides to form Al-O-Cs complex, and the amount of the Al-O-Cs complex can be controlled by adjusting the thickness of the thin Al layer.
Effect of helium implantation on SiC and graphite
Effects of FeNi-phosphorus-carbon system on crystal growth of diamond under high pressure and high temperature conditions
Modeling and experiments of N-doped vanadium oxide prepared by a reactive sputtering process
An original numerical model, based on the standard Berg model, is used to simulate the growth mechanism of N-doped VOx deposited with changing oxygen flow in the reactive gas mixture. In order to compare with the numerical model, N-doped VOx films are prepared by reactive magnetron sputtering from a metallic vanadium target immersed in a reactive gas mixture of Ar+O2+N2. Both experimental and numerical results show that the addition of N2 to the process alleviates the hysteresis effect with respect to the oxygen supply. Film compositions obtained from the XPS analysis are compared to the numerical results and the agreement is satisfactory. The results also show that the compound of VN is only found at very low O concentration because of the replacement reaction of VN by O2 atoms with higher oxygen flow rate.
Energy-band alignment of atomic layer deposited (HfO2)x(Al2O3)1-x gate dielectrics on 4H-SiC
We study a series of (HfO2)x(Al2O3)1-x/4H-SiC MOS capacitors. It is shown that the conduction band offset of HfO2 is 0.5 eV and the conduction band offset of HfAlO is 1.11-1.72 eV. The conduction band offsets of (HfO2)x(Al2O3)1-x are increased with the increase of the Al composition, and the (HfO2)x(Al2O3)1-x offer acceptable barrier heights (> 1 eV) for both electrons and holes. With a higher conduction band offset, (HfO2)x(Al2O3)1-x/4H-SiC MOS capacitors result in a ～ 3 orders of magnitude lower gate leakage current at an effective electric field of 15 MV/cm and roughly the same effective breakdown field of ～ 25 MV/cm compared to HfO2. Considering the tradeoff among the band gap, the band offset, and the dielectric constant, we conclude that the optimum Al2O3 concentration is about 30% for an alternative gate dielectric in 4H-SiC power MOS-based transistors.
Theoretical prediction of energy dependence for D+BrO→DBr+O reaction: The rate constant and product rotational polarization
A novel integrated ultraviolet photodetector based on standard CMOS process
High performance silicon waveguide germanium photodetector
High-performance Ge-on-SOI p-i-n waveguide photodetectors with different sizes were fabricated. The performances, in terms of dark-current, photo current responsivity and 3-dB bandwidth, were well studied. A responsivity of 0.842 A/W at 1550 nm and dark current of 70 nA was measured from this detector at -1 V. The detector with a size of 4 μm× 10 μm demonstrated an optical band width of 19 GHz at -5 V for 1550 nm. Both the experimental results and the finite-difference time domain simulation show that, when the device size is above a certain threshold, the absorption is not sensitively dependent on such designing parameters as the width and length of the photodetector.
Performance improvement of GaN-based light-emitting diodes transferred from Si (111) substrate onto electroplating Cu submount with embedded wide p-electrodes
Crack-free GaN/InGaN multiple quantum wells (MQWs) light-emitting diodes (LEDs) are transferred from Si substrate onto electroplating Cu submount with embedded wide p-electrodes. The vertical-conducting n-side-up configuration of the LED is achieved by using the through-hole structure. The widened embedded p-electrode covers almost the whole transparent conductive layer (TCL), which could not be applied in the conventional p-side-up LEDs due to the electrode-shading effect. Therefore, the widened p-electrode improves the current spreading property and the uniformity of luminescence. The working voltage and series resistance are thereby reduced. The light output of embedded wide p-electrode LEDs on Cu is enhanced by 147% at a driving current of 350 mA, in comparison to conventional LEDs on Si.
Closed-loop control of epileptiform activities in a neural population model using a proportional-derivative controller
Epilepsy is believed to be caused by a lack of balance between excitation and inhibitation in the brain. A promising strategy for the control of the disease is closed-loop brain stimulation. How to determine the stimulation control parameters for effective and safe treatment protocols remains, however, an unsolved question. To constrain the complex dynamics of the biological brain, we use a neural population model (NPM). We propose that a proportional-derivative (PD) type closed-loop control can successfully suppress epileptiform activities. First, we determine the stability of root loci, which reveals that the dynamical mechanism underlying epilepsy in the NPM is the loss of homeostatic control caused by the lack of balance between excitation and inhibition. Then, we design a PD type closed-loop controller to stabilize the unstable NPM such that the homeostatic equilibriums are maintained; we show that epileptiform activities are successfully suppressed. A graphical approach is employed to determine the stabilizing region of the PD controller in the parameter space, providing a theoretical guideline for the selection of the PD control parameters. Furthermore, we establish the relationship between the control parameters and the model parameters in the form of stabilizing regions to help understand the mechanism of suppressing epileptiform activities in the NPM. Simulations show that the PD-type closed-loop control strategy can effectively suppress epileptiform activities in the NPM.
Some regularity on how to locate electrodes for higher fECG SNRs
Boron implanted emitter for n-type silicon solar cell
The effects of ion doses on the properties of boron implanted Si for n-type solar cell application were investigated with doses ranging from 5× 1014 cm-2 to 2× 1015 cm-2 and a subsequent two-step annealing process in a tube furnace. With the help of the TCAD process simulation tool, knowledge on diffusion kinetics of dopants and damage evolution was obtained by fitting SIMS measured boron profiles. Due to insufficient elimination of the residual damage, the implanted emitter was found to have a higher saturation current density (J0e) and a poorer crystallographic quality. Consistent with this observation, Voc, Jsc, and the efficiency of the all-implanted p+-n-n+ solar cells followed a decreasing trend with an increase of the implantation dose. The obtained maximum efficiency was 19.59% at a low dose of 5× 1014 cm-2. The main efficiency loss under high doses came not only from increased recombination of carriers in the space charge region revealed by double-diode parameters of dark I-V curves, but also from the degraded minority carrier diffusion length in the emitter and base evidenced by IQE data. These experimental results indicated that clusters and dislocation loops had appeared at high implantation doses, which acted as effective recombination centers for photogenerated carriers.
A new collision avoidance model for pedestrian dynamics
A new cellular automaton for signal controlled traffic flow based on driving behaviors
Correlation between the magic wavelengths and the polarization direction of the linearly polarized laser in the Ca+ optical clock Hot!
The magic wavelengths for different Zeeman components are measured based on the 40Ca+ optical clock. The dynamic dipole polarizability of a non-zero angular moment level has correlation with the polarization direction of the linearly polarized laser beam, and we show that the four hyperfine structure levels of 4s1/2, m = ± 1/2 and 3d5/2, m = ± 1/2 for 40Ca+ have the same dynamic dipole polarizability at the magic wavelength and a certain polarization direction. In addition, the existence of a specific direction of polarization may provide a new idea for improving the precision of magic wavelength measurement in experiment.