Band offsets engineering at Cd_xZn_(1-x)S/Cu_2ZnSnS_4 heterointerface

Cd1-xZnxS/Cu2ZnSnS4 （CZTS）-based thin film solar cells usually use CdS as a buffer layer, but due to its smaller band gap （2.4 eV）, CdS film has been replaced with higher band gap materials. The cadmium zinc sulfide （CdZnS） ternary compound has a higher band gap than other compounds, which leads to a decrease in window absorption loss. In this paper, the band offsets at Cd1-xZnxS/CuzZnSnS4 （CZTS） heterointerface are calculated by the first-principles, density- functional and pseudopotential method. The band offsets at Cdl xZnxS/CZTS heterointerface are tuned by controlling the composition of Zn in Cd1-xZnxS alloy, the calculated valence band offsets are small, which is consistent with the commonanion rule. The favorable heterointerface of type-I with a moderate barrier height （〈 0.3 eV） can be obtained by controlling the composition of Zn in Cdl-xZnxS alloy between 0.25 and 0.375.

Fault diagnosis for down-hole conditions of sucker rod pumping systems based on the FBH-SC method

Dynamometer cards are commonly used to analyze down-hole working conditions of pumping systems in actual oil production. Nowadays, the traditional supervised learning methods heavily rely on the classification accuracy of the training samples. In order to reduce the errors of manual classification, an automatic clustering algorithm is proposed and applied to diagnose down-hole conditions of pumping systems. The spectral clustering （SC） is a new clustering algorithm, which is suitable for any data distribution. However, it is sensitive to initial cluster centers and scale parameters, and needs to predefine the cluster number. In order to overcome these shortcom- ings, we propose an automatic clustering algorithm, fast black hole-spectral clustering （FBH-SC）. The FBH algo- rithm is used to replace the K-mean method in SC, and a CritC index function is used as the target function to automatically choose the best scale parameter and clus- tering number in the clustering process. Different simulation experiments were designed to define the relationship among scale parameter, clustering number, CritC index value, and clustering accuracy. Finally, an example is given to validate the effectiveness of the proposed algorithm.

Spin-Selective Transport of Electron in a Quantum Dot under Magnetic Field

We study electronic spin-polarised transport in a system composed of a quantum dot(QD)connected to one normal metal electrode and one ferromagnetic one.The electrical current of each spin component and the spin accumulation on the QD are calculated by using the nonequilibrium Green's function method.We find that in the Coulomb blockade regime,the current spin polarisation can reach 100%under a strong magnetic field.Meanwhile,the spin accumulation on the QD approaches to unit,and thus the dot is occupied by electrons of one certain spin orientation.The system can operate as a spin injector from a normal metal reservoir to a semiconductor material,and may find real usage in solid state quantum information processes.

Monte Carlo study of the magnetic properties of spin liquid compound NiGa_2S_4

The magnetic properties of two-dimensional antiferromagnet NiGa2S4 have attracted much attention and yet some problems are far from being solved. We investigate the magnetic properties of NiGa2S4 by Monte Carlo simulations. A new spin-interacting model is proposed to describe the system, and the specific heat together with the doping effect of nonmagnetic impurity is studied by simulations. The double peaks of the specific heat as well as other behaviors are well reproduced. We also compare our results with those of other models, and the underlying physics is discussed.

Security Analysis of Subspace Network Coding

This paper analyzed the security of constant dimensional subspace code against wiretap attacks. The security was measured in the probability with which an eavesdropper guessed the source message successfully. With the methods of linear algebra and combinatorics, an analytic solution of the probability was obtained. Performance of subspace code was compared to several secure network coding schemes from the perspective of security, flexibility, complexity, and independence, etc. The comparison showed subspace code did not have perfect security, but it achieved probabilistic security with low complexity. As a result, subspace code was suitable to the applications with limited computation and moderate security requirement.

Finite Frequency Fuzzy H∞Control for Uncertain Active Suspension Systems With Sensor Failure

This paper investigates the problem of finite frequency fuzzy H_∞ control for uncertain active vehicle suspension systems, in which sensor failure is taken into account. TakagiSugeno(T-S) fuzzy model is established for considered suspension systems. In order to describe the sensor fault effectively, a corresponding model is introduced. A vital performance index,H_∞ performance, is utilized to measure the drive comfort. In the framework of Kalman-Yakubovich-Popov theory, the H_∞ norm from external perturbation to controlled output is optimized effectively in the frequency domain of 4 Hz-8 Hz to enhance ride comfort level. Meanwhile, three suspension constrained requirements, i.e., ride comfort level, manipulation stability,suspension deflection are also guaranteed. Furthermore, sufficient conditions are developed to design a fuzzy controller to guarantee the desired performance of active suspension systems. Finally, the proposed control scheme is applied to a quarter-vehicle active suspension, and simulation results are given to illustrate the effectiveness of the proposed approach.

Modified Grey Model Predictor Design Using Optimal Fractional-order Accumulation Calculus

The major advantage of grey system theory is that both incomplete information and unclear problems can be processed precisely. Considering that the modeling of grey model(GM) depends on the preprocessing of the original data,the fractional-order accumulation calculus could be used to do preprocessing. In this paper, the residual sequence represented by Fourier series is used to ameliorate performance of the fractionalorder accumulation GM(1,1) and improve the accuracy of predictor. The state space model of optimally modified GM(1,1)predictor is given and genetic algorithm(GA) is used to find the smallest relative error during the modeling step. Furthermore,the fractional form of continuous GM(1,1) is given to enlarge the content of prediction model. The simulation results illustrated that the fractional-order calculus could be used to depict the GM precisely with more degrees of freedom. Meanwhile, the ranges of the parameters and model application could be enlarged with better performance. The method of modified GM predictor using optimal fractional-order accumulation calculus is expected to be widely used in data processing, model theory, prediction control and related fields.

Generating and reversing spin accumulation by temperature gradient in a quantum dot attached to ferromagnetic leads

We propose to generate and reverse the spin accumulation in a quantum dot （QD） by using the temperature difference between the two ferromagnetic leads connected to the dot. The electrons are driven purely by the temperature gradient in the absence of an electric bias and a magnetic field. In the Coulomb blockade regime, we find two ways to reverse the spin accumulation. One is by adjusting the QD energy level with a fixed temperature gradient, and the other is by reversing the temperature gradient direction for a fixed value of the dot level. The spin accumulation in the QD can be enhanced by the magnitudes of both the leads＇ spin polarization and the asymmetry of the dot-lead coupling strengths. The present device is quite simple, and the obtained results may have practical usage in spintronics or quantum information processing.

Heat generation by spin-polarized current in a quantum dot connected to spin battery and ferromagnetic lead

We study theoretically the heat originated from electron-phonon coupling in a spintronic device composed of a semi- conductor quantum dot attached to one spin battery and one ferromagnetic lead. It is found that the phenomenon of the negative differential of the heat current, which has previously been predicted in the charge-based device, disappears due to the Pauli exclusion principle resulted from the presence of the spin battery. Under some conditions, huge heat in the heat generation induced by resonant phonon emitting processes also disappears in this spin-based device. Furthermore, we find that the ferromagnetism of the lead can be used to effectively adjust the magnitude of the heat current in different dot level ranges. The proposed system is realizable by current technology and may be useful in designing high-efficiency spintronic components.

Thermoelectric transport through a quantum dot with a magnetic impurity

We study the thermoelectric effect in a small quantum dot with a magnetic impurity in the Coulomb blockade regime. The electrical conductance, thermal conductance, thermopower, and the thermoelectrical figure of merit （FOM） are calcu- lated by using Green＇s function method. It is found that the peaks in the electrical conductance are split by the exchange coupling between the electron entering into the dot and the magnetic impurity inside the dot, accompanied by the decrease in the height of peaks. As a result, the resonances in the thermoelectric quantities, such as the thermal conductance, ther- mopower, and the FOM, are all split, opening some effective new working regions. Despite of the significant reduction in the height of the electrical conductance peaks induced by the exchange coupling, the values of the FOM and the ther-mopower can be as large as those in the case of zero exchange coupling. We also find that the thermoelectric efficiency, characterized by the magnitude of the FOM, can be enhanced by adjusting the left-right asymmetry of the electrode-dot coupling or by optimizing the system＇s temperature.

A Network Coding Based Cloud Storage Scheme

With this paper, we propose a network coding based cloud storage scheme. The storage system is in the form of an m * n data array. The n columns stand for n storage nodes, which are comprised of a part of systematic nodes storing source symbols and a part of nonsystematic nodes storing parity symbols. Every row of the data array is a (n, k) systematic Maximum Distance Separable (MDS) code. A source symbol is only involved in the encoding with the unique row;it locates at and is not used by other rows. Such a design significantly decreases the complexity of encoding and decoding. Moreover, in case of single node failures, we use interference alignment to further reduce repair bandwidth. Compared to some existing cloud storage schemes, our scheme significantly reduces resource consumption on storage, update bandwidth and repair bandwidth.

Practical fixed-time adaptive fuzzy control of uncertain nonlinear systems with time-varying asymmetric constraints: a unified barrier function based approach

A practical fixed-time adaptive fuzzy control strategy is investigated for uncertain nonlinear systems with time-varying asymmetric constraints and input quantization. To overcome the difficulties of designing controllers under the state constraints, a unified barrier function approach is employed to construct a coordinate transformation that maps the original constrained system to an equivalent unconstrained one, thus relaxing the time-varying asymmetric constraints upon system states and avoiding the feasibility check condition typically required in the traditional barrier Lyapunov function based control approach. Meanwhile, the “explosion of complexity” problem in the traditional backstepping approach arising from repeatedly derivatives of virtual controllers is solved by using the command filter method. It is verified via the fixed-time Lyapunov stability criterion that the system output can track a desired signal within a small error range in a predetermined time, and that all system states remain in the constraint range. Finally, two simulation examples are offered to demonstrate the effectiveness of the proposed strategy.

Simulation of Tube Forming Process in Mannesmann Mill

The finite element method(FEM)is used for simulation of the tube piercing process in Mannesmann mill.The numerical model is described with taking into consideration thermal phenomena in metal during forming. The simulated results visualize dynamic distributions of mean stresses,temperature,velocity and shear stresses, especially inside the workpiece.On the basis of the basic parameters,the phenomenon in the piercing process is analyzed.The model is verified by comparing the values of calculated force parameters of the piercing process and those measured in laboratory conditions.

Large Negative Differential of Heat Generation in a Two-Level Quantum Dot Coupled to Ferromagnetic Leads

Heat current exchanged between a two-level quantum dot(QD) and a phonon reservoir coupled to it is studied within the nonequilibrium Green's function method. We consider that the QD is connected to the left and right ferromagnetic leads. It is found that the negative differential of the heat generation(NDHG) phenomenon,i.e.,the intensity of the heat generation decreases with increasing bias voltage,is obviously enhanced as compared to that in single-level QD system. The NDHG can emerge in the absence of the negative differential conductance of the electric current,and occurs in different bias voltage regions when the magnetic moments of the two leads are arranged in parallel or antiparallel configurations. The characteristics of the found phenomena can be understood by examining the change of the electron number on the dot.

Dynamical Properties of a Diluted Dipolar-Interaction Heisenberg Spin Glass

Up to now the chirality is seldom studied in the diluted spin glass although many investigations have been performed on the site-ordered Edwards-Anderson model. By simulation, we investigate the dynamicaJ properties of both the spin-glass and the chiral-glass phases in a diluted dipolar system, which was manifested to have a spin-glass transition by recent numerical study. By scaling we find that both phases have the same aging behavior and closer aging parameterμ. Similarly, the domains grow in the same way and both phases have a closer barrier exponent g2. It means that both the spins and the chirality have the same dynamical properties and they may freeze at the same temperature.

Robust H-infinity filtering for uncertain discrete-time systems using parameter-dependent Lyapunov functions

This paper deals with H-infinity filtering of discrete-time systems with polytopic uncertainties. The un- certain parameters are supposed to reside in a polytope. By using the parameter-dependent Lyapunov function approach and introducing some slack matrix variables, a new sufficient condition for the H-infinity filter design is presented in terms of solutions to a set of linear matrix inequalities （LMIs）. In contrast to the existing results for H-infinity filter design, the main advantage of the proposed design method is the reduced conservativeness. An example is provided to demonstrate the effectiveness of the proposed method.

Heat Generation by Electric Current in a Quantum Dot Molecular Coupled to Ferromagnetic Leads

We study the properties of the heat flow generated by electric current in a quantum dot(QD) molecular sandwiched between two ferromagnetic leads. The heat is exchanged between the QD and the phonon reservoir coupled to it. We find that when the leads' magnetic moments are in parallel configuration, the total heat generation is independent on the leads' spin-polarization regardless of the magnitude of the intradot Coulomb interaction. This behavior is similar to that of the electronic current. In the antiparallel configuration, however, the influences of the leads' ferromagnetism on the heat generation are quite different from those on the electric current. Under the conditions of weak intradot Coulomb interaction and small bias voltage, the heat generation is monotonously suppressed by increasing leads' spin-polarization.Whereas for sufficient large intradot Coulomb interaction and bias voltage, the heat generation shows non-monotonous behavior due to the electron-phonon interaction and the spin accumulation induced on the dot. Furthermore, the magnitude of the negative differential of the heat generation previously found in a QD connected to nonmagnetic leads can be weakened by the increase of the spin-polarization of the ferromagnetic leads.