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Spin polarization through a four-quantum-dot system is theoretically studied by considering the effects of Zeeman magnetic field, extrinsic Rashba spin–orbit interaction and external magnetic field. We analyze how the resonance and anti-resonance bands are formed by means of the mathematical formula. By adjusting the external magnetic field, the spin polarization can be converted between −100% and 100%, which suggests a physical scheme of an effective magnetically-controlled spin filter. The combined effect of external magnetic field and extrinsic Rashba spin–orbit interaction leads to spin-polarized oscillations. The introduction of the Zeeman magnetic field makes the system easier to be applied as a spin filter. This study provides theoretical insights into the realization of quantum computing, quantum information transmission and development of nanoscale quantum devices.

Antiresonance and its application in triple-quantum-dot systems are studied theoretically using nonequilibrium Green’s function method. The presence or absence of antiresonance point can be used to determine whether quantum dot impurity exists in the system. For a tri-quantum-dot ring, the conversion between 0 and 1 for the conductance can be realized by adjusting the energy levels of quantum dots, which makes the system applicable as a quantum switch. The coupling strength can be measured according to the energy level of the antiresonance point. Once the intradot Coulomb interactions are taken into account, three new Fano antiresonances emerge in the conductance spectrum. Under the action of the magnetic field, two antiresonance points disappear simultaneously. Our work sheds lights onto the design and implementation of new quantum functional devices for electronic measurements.

Twist measurement based on the transmission of fixed wavelength of a helical long-period fiber grating is studied. The single-mode fiber is spiraled by a welding machine. There are two resonance dips near 1473 nm and 1517 nm, with the pitch length around 782 μm. The experimental results show that the transmission near 1473 nm decreases along with contra-direction twist and increases along with co-direction twist. In contrast, the transmission near 1517 nm decreases along with co-direction twist and increases along with contra-direction twist. The relationships between the twist and the resonance wavelength, the twist and the transmission of resonance dips, the twist and the transmission of fixed wavelengths are studied, respectively. They all show linear relationship with the twist, and the slopes are about 100 nm·mm/rad, 36 dB·mm/rad, and 46 dB·mm/rad, respectively. The dual-wavelength ratio is studied, and the ratio also shows linear relationship with the twist. The twist sensitivity of I1463.3 nm/I1526.5 nm is about 0.79 each 0.01 rad/mm. This has great potential application in twist sensors.

This research involves a novel axial strain measurement of helical long-period grating by dual-wavelength ratio. The single-mode fiber is spirally processed via the commercial welding machine. There are two obvious resonance dips near 1473 and 1517 nm, with the pitch length around 782 μ m. The experimental results show that both the transmission of dip1 and dip2 rise along with increasing axial strain. The relationships between axial strain versus transmission of resonance dip and axial strain versus transmission of a fixed wavelength are studied separately. They are all linear change with axial strain. This indicates that the axial strain can be measured by the linear relationship between the transmission and axial strain. Furthermore, to eliminate the influence of light source, the dual-wavelength ratio is studied. The experimental results show that the ratio also changes linearly with axial strain. The fixed wavelength can be selected by a filter or a fiber Bragg grating, and the transmission intensity can be measured by a light intensity detector. This exploits a new way to devise high precision, low cost, and gains great potential application in the axial strain sensor.

In this work, we investigate the effect of cavity size on the change of the physical fields of diamond synthetic cavity and the mechanism of large cavity to improve the growth rate of the large single crystal diamond under high pressure and high temperature (HPHT) conditions. Finite element method (FEM) is used to simulate the temperature and convection field of the Φ15 and Φ10 cavity assemblies. Temperature simulation results indicate that the increase of cavity size leads to the increase of axial and radial temperature difference of catalyst. Convection simulation results show that the convection velocity and strength of the catalyst increases significantly with the increase of the cavity size. The increase of temperature difference and convection velocity and strength lead to the acceleration of crystal growth. The simulation results were perfectly validated by the synthetic experiments. This work not only elucidates the mechanism of large cavity to improve the growth rate, but also provides a theoretical reference for the application of the large-size cavity in the diamond synthetic industry.

The dynamic properties, including hysteresis loop and dielectric susceptibility, of a ferroelectric heterostructure composed by two different films have been discussed, by means of a Landau–Devonshire theory in combination with Landau–Khalatnikov dynamic equation. The surface transition layer within each component film and a ferroelectric coupling at the interface between two films are taken into account. A parameter is introduced to describe the differences of physical properties between two constituent films. The results show that if the ferroelectric interfacial coupling is large enough, the system will lead to the severe hysteresis phenomenon for hysteresis loop and four peaks of the curve for dielectric susceptibility versus the electric field.

Employing the nonequilibrium Green’s function technique, electron transport characteristics through a laterally coupled triple-quantum-dot chain are investigated. The conductance versus electron energy is numerically calculated. Two anti-resonance points change into two anti-resonance bands with increasing the size of triple-quantum-dot chain. The widths of two anti-resonance bands are the same and can be regulated via adjusting the inter-dot tunneling coupling strength in the main chain or its attachment. Spin-polarized window emerges due to Zeeman splitting as an external magnetic flux is introduced. Our studies demonstrate that the system can be used as a quantum switch or an efficient spin filtering.

Layered Ruddlesden-Popper La2NiO4+δ (LNO) is reported to possess excellent oxygen surface and bulk transport properties, but its application as the cathode of solid oxide fuel cells is restrained by the relatively poor electrocatalytic activity. Here, we report the incorporation of highly ion-conducting Er-stabilized Bi2O3 (ESB) into LNO and assemble the LNO-ESB composite cathode directly on zirconia electrolyte film using a facile electrochemical polarization approach. The results show the presence of ESB remarkably reduces the contact resistance at the electrode/electrolyte interface and enhances the electrocatalytic activity and cation stability of LNO. The cell with the LNO-ESB cathode generates a peak power density of 852 mW cm-2 at 750°C with reasonable operating stability over 200 h. This work demonstrates the feasibility of incorporating ESB to promote the layered nickelate cathodes for intermediate temperature solid oxide fuel cells. Published version

A presentation based on the helical long-period grating (H-LPFG) affected by the change of temperature and twist has been demonstrated. There are two resonant peaks near 1451 nm (resonant peak 1) and 1519 nm (resonant peak 2) when the pitch length is about 757 μm. The resonant peak 1 is caused by second-order diffraction coupling between the fundamental mode and the LP110 cladding mode, and the resonant peak 2 is caused by first-order diffraction coupling between the fundamental mode and the LP15 cladding mode. Their temperature sensitivities are 72 pm/℃ and 45 pm/℃, respectively. The resonant peak 1 twist sensitivities are − 138 nm·mm/rad with co-direction twist and 133 nm·mm/rad with contrary-direction twist, but the resonant peak 2 is insensitive to twist. This indicates that at the resonant peak 2, the H-LPFG can measure temperature without cross-impact by twist. Therefore, this can be applied to measure temperature and twist at the same time.

The thermoelectric transport properties of a parallel-coupled double quantum dot (PCDQD) system with side-coupled quantum dots (QDs) is investigated by using the Keldysh non-equilibrium Green's function technique. The thermoelectric quantities, including the thermal conductance, thermopower, and thermoelectric figure of merit denoted by ZT, are sensitive to the inter-dot coupling strength. With the help of side-coupled QD, unusual double Fano resonances are created in the conductance spectra to largely enhance the thermoelectric effect at low-temperature. Benefited from the coexistence of local bipolar effect and Fano resonance, the ZT can be improved by one-fold higher than that of original PCDQD system. Moreover, when the asymmetry parameter α, which indicates the geometric arrangement of coupled QDs with a given lead, takes appropriate value, the optimization of ZT can be achieved at high temperature. Our work suggests that the side-coupled QDs scheme holds promise for the designing of high-efficiency thermoelectric conversion devices.

We present theoretically the quantum electronic transport through an interferometer asymmetrically coupled with triple quantum dots. Using the Keldysh non-equilibrium Green’s function method, the photon-assisted transport properties through the asymmetric quantum system are numerically analyzed. The sidebands of the photon-assisted tunneling process appear when driven by the time-modulated field. The average current spectra are simulated as a function of quantum dot energy to understand the roles of side-coupling strength and time-modulated field in sideband effect and electron tunneling. This is helpful in future design of the basic structures required for quantum computation applications.

We theoretically study the average current through a ring embedded with multiple quantum dots in each arm subjected to a time-dependent external field. A current resonance band can be observed in a six-quantum-dot system. In the presence of a time-dependent external field, mutual transformation occurs between the resonance band and antiresonance band, indicating an effective optically-controlled quantum switch can be realized in a wider quantum dot’s energy regime. As the Zeeman effect is introduced, the conversion between 100 and − 100% for spin polarization $$p$$ p can be realized by adjusting the frequency of time-dependent external field, suggesting a physical scheme of an optically-controlled spin filter. The present work sheds lights onto the design and quantum computation of future nano-devices.

The influence of interface structure on the photoelectric properties of InGaN light-emitting diodes grown on (0001) polar, (11–22) semi-polar, and (11–20) nonpolar planes is studied. Nonpolar and semi-polar interface structures are characterized by reduced polarization-related electric fields and suppressed QCSE. The energy bands of the structures grown on these orientations are undistorted, and QWs have more rectangular shapes. Consequently, these structures do not undergo separation of the electron and hole wavefunctions typical of c-plane structures. The simulation results suggest that potoelectric properties and efficiency drop is markedly improved when the polar interface structure is replaced by nonpolar or semi-polar interface structures.

The electrical and optical properties of InGaN LEDs with different threading dislocation densities (TDDs) were investigated. LEDs with low TDDs exhibited low forward voltage and high injection efficiency compared with LEDs with high TDDs. The effect of TDDs on the electrical properties of InGaN LEDs was attributed to efficient carrier injection into the QWs brought about by increased transverse carrier mobility in the InGaN layer resulting from reductions in carrier scattering around dislocation cores. In terms of optical properties, LEDs with low TDDs exhibited high peak efficiency and substantial efficiency droops under increased current densities, whereas LEDs with high TDDs showed low peak efficiency and minimal droops under the same condition. These trends can be explained by the correlations of high TDDs with increased dominance of nonradiative recombination and pronounced suppression of peak efficiency under low current densities.

In this paper, several four-quantum-dot topological structures are designed. The influence of the interdot coupling strength and intradot Coulomb interactions on the conductance is discussed. The location of the anti-resonance band can be manipulated by tuning the interdot coupling strength, which suggests a physical scheme of an effective quantum switch. The Fano anti-resonance peak may evolve into a resonance peak. For the particular value of the interdot coupling strength, two Fano anti-resonances collapse and bound states in the continuum are formed. Moreover, many-body effect makes the number of anti-resonance bands increase. This study provides a theoretical basis for the design of quantum computing devices.

Using the non-equilibrium Keldysh Green's function technique, electron transport properties through a two-terminal linear tri-quantum-dot molecule Aharonov-Bohm (A-B) interference are investigated. The conductance as a function of electron energy is numerically calculated. The influence of magnetic flux and interdot coupling strength on the conductance is researched. Fano resonances emerge in the conductance spectrum, and two bound states in the continuum form simultaneously when the interdot couplings take appropriate values. A conductance dip is observed and evolves into an antiresonance band with increasing magnetic flux. The system can be designed as a quantum switch by adjusting the intramolecular couplings.

Electron transport characteristics through a system consisting of a series of triangular quantum dot rings are studied utilizing the non-equilibrium Green’s function. In the presence of a magnetic field, an additional anti-resonance point occurs in the conductance spectrum. As the number of triangular quantum dot rings increases, two anti-resonance points evolve into two well-defined insulating bands. The insulating band disappears as the magnetic flux takes an appropriate value, and therefore, an effective magnetically-controlled quantum switch can be achieved. If a Zeeman magnetic field is introduced, a spin-polarized window (SPW) can be formed, suggesting a physical scheme of a spin filtering. As the intradot Coulomb interactions are taken into consideration, more SPWs can be obtained. This work sheds lights onto the design of future quantum devices.

We design a four-quantum-dot system subjected to a time-dependent external field. The average current through the quantum dot system is obtained by using the method of non-equilibrium Green's function. By adjusting either the amplitude or frequency of the time-dependent external field, the average current can be converted between zero and non-zero. Based on this property, the system can be designed as an optically-controlled quantum switch device. When the asymmetric time-dependent external field is irradiated to the left and right electrodes, negative current can be observed in the current spectrum, i.e., the photon-electron pumping effect. The present work sheds lights onto design and quantum computation of future nano-devices.

We report the conductance and average current through a triple-quantum-dot interferometer coupled with two ferromagnetic leads using the nonequilibrium Green’s function. The results show that the interference between the resonant process and the non-resonant process leads to the formation of Fano resonance. More Fano resonances can be observed by applying a time-dependent external field. As a Zeeman magnetic field is applied, the spin-up electron transport is depressed in a certain range of electron energy levels. A spin-polarized pulse device can be realized by adjusting the spin polarization parameters of ferromagnetic leads. Moreover, the I–V characteristic curves show that under the influence of Fano resonance, the spin polarization is significantly enhanced by applying a relatively large reverse bias voltage. These results strongly suggest that the spin-polarized pulse device can be potentially applied as a spin-dependent quantum device.

Using first-principles density functional theory, we predict a hexagonal structure of boron carbide with two shells, which consists of the sp2 hybridized boron and carbon in (001) plane and the pz–pz (σ) bonding carbon along [001] direction. The calculated results show that the structure is thermodynamically stable and possesses lower formation energy than other candidates. In addition, the quasiparticle calculations within the GW approximation reveal that the boron carbide, which is a two dimensional insulator, exhibits the indirect band gap of 2.4 eV and large exciton bonding energy of 1.35 eV. In optical absorption spectra, a bright Frenkel class bound exciton has been discovered at about 2.98 eV, which is desirable for light emitting applications. Besides, the piezoelectric coefficient (e22) of −2.38×10−10 Cm−1 is predicted for monolayer boron carbide, which indicates that the monolayer boron carbide is a potential candidate for piezoelectric applications in the nanoelectromechanical systems.

T-shape double quantum dot molecule A–B interference with the action of time-dependent external field is designed. Using the Keldysh non-equilibrium Green's function method, spin-dependent average current as a function of quantum dot energy is obtained. The magnitude and position of average current resonance peaks can be controlled by adjusting interdot coupling strength, frequency and amplitude of time-dependent electric field. The conversion between zero and non-zero value for average current can be realized under the condition with or without the action of time-dependent external field, respectively, which is the basis for the design of controlled quantum switch. Under the combined action of the external magnetic flux and Rashba spin–orbit coupling strength, the spin-polarized average current can be observed. Dc current–voltage characteristics are researched.

A four quantum dots structure is designed. The influence of the interdot coupling strength, energy levels of quantum dots, magnetic flux and intradot Coulomb interactions on the conductance is discussed. An antiresonance point exactly emerges at the location of the energy level of side-coupled quantum dots (SCQD). The conversion between resonance band and antiresonance band can be achieved as parallel-coupled di-quantum dots with or without SCQD, which suggests a physical scheme of an effective quantum switch. The Breit–Wigner resonant and Fano antiresonant peaks may merge into one resonant band. By means of the mathematical formula, we analyze how the resonance band is formed. By varying intradot Coulomb interaction, the resonance band may evolve into a Fano antiresonance with an ultra-narrow width. This study provides theoretical basis for the design of quantum computing devices.

Reversing the direction of polarization current is essential for reversible solid oxide cells technologies, but its effect on cobaltite based perovskite oxygen electrodes is largely unknown. Herein, we report the operating stability and microstructure at the electrode/electrolyte interface of La0.57Sr0.38Co0.18Fe0.72Nb0.1O3-δ (LSCFN) oxygen electrodes assembled on barrier-layer-free Y2O3 ZrO2 electrolyte under cyclic anodic/cathodic polarization mode at 0.5 A cm−2 and 750 °C. During the cyclic polarization, the electrocatalytic activity of LSCFN electrode is drastically deteriorated in cathodic mode, but the performance loss is largely recoverable in anodic mode. This is due to the fact that the surface segregation of Sr and accumulation at the electrode/electrolyte interface by cathodic polarization can be remarkably mitigated by anodic polarization. The time period in each cycle plays a key role in determining the accumulation of Sr species at the electrode/electrolyte interface. A full cell operating in a time period of 12 h fuel-cell/12 h electrolysis is reversible for a duration of 240 h, in contrast to the performance degradation in a shorter time period of 4 h fuel cell/4 h electrolysis. The present study sheds lights on applying cobaltite based perovskite oxygen electrodes on barrier-layer-free YSZ electrolyte for reliable solid oxide cells.

Electron transport through a triple-quantum-dot ring in various kinds of dot-lead coupling configurations has been investigated using the nonequilibrium Green’s function technique. The conductance is numerically calculated as a function of the dots’ levels. The appearance of Fano resonance and the formation of bound state in the continuum strongly depend on the configuration of dot-lead coupling strengths. Moreover, a striking conductance dip is found and the conductance spectrum can be interchanged by tuning extra magnetic flux.

A three-quantum-dot spin filter based on nonequilibrium Greenʼs function technique is proposed with external magnetic flux, Rashba spin orbit interaction, and intradot coulomb interaction taken into consideration. Numerical results indicate a spin filter can be made efficient by adjusting external magnetic flux and Rashba spin orbit interaction. Moreover, the formation of a resonance band is discussed through calculation. It is observed that the possibility of transition from one peak to other three peaks in the conductance spectrum increases with increasing interdot coupling strength.

Based on the transverse Ising model within the framework of the mean-field approximation, a ferroelectric bilayer film composed of two different slabs, with the surface transition layer within each constituent slab and a ferroelectric interfacial coupling between two slabs, is investigated. The influence of the surface transition layer on the pyroelectric properties of a bilayer film is discussed in detail. The results show that the pyroelectric properties of a bilayer film embody show some interesting phenomena on account of the presence of surface transition layer.

Using the generalized Ginzburg-Landau-Devonshire theory, the characteristics of phase transformation of a ferroelectric thin film with surface layers are investigated. We study the effect of the surface layer on the properties (coercive field, critical thickness) of a ferroelectric thin film. Our theoretical results show that the surface layer is likely to answer for the emergence of phase transformation.

Employing the non-equilibrium Green’s function technique, we have obtained the formula for dc current of two one-dimensional multi-quantum dot arrays, which couple to each other via tunneling coupling between two quantum dots connected to four leads, respectively. The retarded Green’s function is a staircase type, terminating at the four leads. Furthermore, the four quantum dots case is demonstrated. The influence of inter-dot coupling strength and quantum dot energy level on the transmission probability for TL, TM and TN branches is investigated. A non-resonant band is observed. By adjusting energy levels of quantum dots, a resonance emerges in the region of the non-resonance band. The system can be used as a quantum switch.

We have obtained the formula for dc current of a four-terminal quantum dot arrays consisting of six quantum dots, by using the nonequilibrium Keldysh Green's function technique. The transmission probability T ( ω ) as a function of electron energy ω and the differential conductance as a function of the chemical potential of the input terminal are numerically calculated.

Making use of the equation of motion method and Keldysh Green function technique, we obtain a general current formula for a quantum-dot-ring with one of the dots connected to two electron reservoirs under a DC bias voltage. The transmission probability T ( ω ) as a function of electron ω curve is presented, which displays oscillation structure. The resonant states of the system are found to distribute within an interval centered at e 0 (the dot energy level) with a width of two times the tunnel coupling amplitude between two neighboring dots, the number of the resonant peaks agrees with N (the number of the dots) when inter-dot tunnel coupling is sufficiently large and an odd–even behavior appears at the Fermi energy.

The nonequilibrium Keldysh Green function technique is used to study the electronic transport property of a four-quantum-dot ring system in a four-terminal configuration. A general formula for the current under dc bias is obtained; the linear conductance characteristic is numerically studied.

Using the non-equilibrium Green’s function technique, conductance through a parallel-coupled double quantum dot (PCDQD) with a side-coupled quantum dot system is investigated. The evolution of the conductance strongly depends on the coupling between the side-coupled quantum dot and PCDQD. Moreover, the conductance as a function of the level of side-couple quantum dot is investigated. Numerical results indicate the lineshape of Fano resonance can be modulated by adjusting the interdot coupling strength.

Online product quality detection is an effective process of product quality control. It can be fused into the machine tool by rebuilding and updating the machine tool. It can also be realized by changing the process of the product line, feeding back the testing results to the machine tool or the operating persons and applying it to the current machining system or to grade the products. The implement of parameter comparison of the processed cam and the standard cam based on wavelet filtering, cubic spline interpolation, long signal correlation is proposed. The theory and methodology of realizing high precision measurement with cheap but good in anti-shock and anti-pollution sensors is stressed, especially how to get rid of the risk caused by poor surface quality and local deformation, reach higher precision and achieve the purpose of quality control.

The thermoelectric and the thermospin transport properties, including electrical conductivity, Seebeck coefficient, thermal conductivity, and thermoelectric figure of merit, of a parallel coupled double-quantum-dot Aharonov—Bohm interferometer are investigated by means of the Green function technique. The periodic Anderson model is used to describe the quantum dot system, the Rashba spin—orbit interaction and the Zeeman splitting under a magnetic field are considered. The theoretical results show the constructive contribution of the Rashba effect and the influence of the magnetic field on the thermospin effects. We also show theoretically that material with a high figure of merit can be obtained by tuning the Zeeman splitting energy only.

Using the nonequilibrium Keldysh Green function technique, the influence of intradot Coulomb interactions on conductance for a parallel-coupled triple quantum dot system is investigated. The conductance as a function of electron energy is numerically calculated. The combined effect of the intradot Coulomb interaction and the magnetic flux leads to an intricate conductance lineshape. Moreover, both the magnetic flux and the interdot coupling strength may modulate the Fano effect.

Based on the Green's function technique and the equation of motion approach, this paper theoretically studies the thermoelectric effect in parallel coupled double quantum dots (DQDs), in which Rashba spin—orbit interaction is taken into account. Rashba spin—orbit interaction contributions, even in a magnetic field, are exhibited obviously in the double quantum dots system for the thermoelectric effect. The periodic oscillation of thermopower can be controlled by tunning the Rashba spin—orbit interaction induced phase. The interesting spin-dependent thermoelectric effects will arise which has important influence on thermoelectric properties of the studied system.

We design a coupled-quantum-dot bridge of two quantum-dot arrays coupled to each other via one quantum dot between two quantum-dot arrays, connected to four electron reservoirs. By using the nonequilibrium Green's function, the current formula of the system is obtained. The transmission probability T(ω) as a function of electron energy ω is numerically calculated.