Step-like Form Research Articles

Quantum capacitance of quasi-2D-crystals

Results of research in the quantum capacitance [Formula: see text] of quasi-2D-crystals are presented. The detected extraordinary behavior of [Formula: see text] manifests itself in the existence of such energy ranges in which it is practically equal to zero. The causes for the existence of such ranges are: (a) dimensional quantization as a result of the nanoscale of the van der Waals gap, (b) a certain value of the width of the allowed zone in the plane of the layers, which is determined by the value of the effective mass. Intercalation and external electric field are effective factors capable of changing the position of ranges. Thus, in a system connected in a series of electrostatic and quantum capacitances, the resulting capacitance will significantly depend on the [Formula: see text] behavior. Comparative analyses of structures, chemical bonds, majority of coinciding characteristics of physical quantities in graphite, transition metal dichalcogenides (TMD), and layered crystals A3B6 allow us to assert that the obtained qualitative conclusions can be applied for each of them. Calculations of density of states (DOS) of quasi-2D crystals performed by authors within the framework of the improved Kohn–Sham density functional theory (DFT), namely the DFT taking into account the van der Waals forces in it, show a step-like form of DOS qualitatively similar to ours.

Deformation Behaviour and Damage Evolution of Carbonaceous Phyllite under Cyclic Triaxial Loading.

Rocks present complex deformation behaviours and damage processes under triaxial cyclic loading-a subject not yet sufficiently researched. This paper performed triaxial multistage constant-amplitude cyclic loading experiments under different confining stresses on carbonaceous phyllite. The degradation process is analysed by investigating the variation of elastic modulus ES, Poisson's ratio υ, irreversible strain εirr and energy. Moreover, the rock's failure mode is explored from both macro and micro perspectives. The results showed that the increase in stress level caused the decrease of ES in a step-like form, and the constant-amplitude cyclic loading in each stress level caused a slow decrease of ES, while the υ increased with stress level and constant-amplitude cycles in a similar form. εirr accumulated rapidly at first and then slowly at each stress level; the stress level and irreversible axial strain are related by an exponential function. In terms of energy evolution analysis, the damage to rock can be represented by the cumulative damage energy, there were deceleration accumulations and stability accumulation stages of damage at all stress levels, and an acceleration accumulation stage occurred when the rock was close to failure. The failures of rock under cyclic loading are mainly shear failures, accompanied by grain crushing.

Tunable NIR absorption in a Ge2Sb2Te5-based 1D asymmetric nonlinear hybrid nanostructure

The absorption behaviors of a photonic nonlinear (NL) Kerr multilayer doped by a 30 nm-Ge2Sb2Te5 (GST) absorbing film are investigated theoretically in the near-infrared region. One can reconfigure the GST from the amorphous-to-crystalline state via the thermo-optical effect, which changes its absorption in a step-like form. Once the external light intensity increases, the resonant wavelength is red-shifted with a strong bending, yielding optical bistability due to the Kerr-NL effect. Moreover, for the input light with an appropriate non-resonant wavelength, the nonreciprocal absorption of the maximum contrast of 0.5 is realized in some ranges of intensities thanks to the localized electric field around the GST layer in only one direction. These features of the considered structure can provide a suitable platform for designing the near-infrared absorption diodes and optical switches.

Stability analysis of traveling wave solutions of a generalized Korteweg–de Vries–Burgers equation with variable dissipation parameter

We consider traveling wave solutions of a generalized Korteweg–de Vries–Burgers equation. The dissipation coefficient depends on coordinate and time and has a smoothed step-like form at every instant of time. Small-scale processes of dissipation and dispersion determine the solution of the traveling wave problem in the high-gradient region. The flux function is non-convex and has two inflection points. It is shown that traveling wave solutions with the same wave speed can converge to the three different limiting values behind the wave. The Evans function technique is used to conduct linear stability analysis. We demonstrate that traveling wave solutions can be linearly stable for each of the three possible cases. Thus, we found linearly stable solutions in the form of a traveling wave, which correspond to admissible discontinuities in hyperbolic model. These discontinuities have the same speed but different states behind them.

A Novel Approach for the Determination of Sorption Equilibria and Sorption Enthalpy Used for MOF Aluminium Fumarate with Water

Adsorption chillers offer an environmentally friendly solution for the valorisation of waste or solar heat for cooling demands. A recent application is high efficiency data centre cooling, where heat from CPUs is used to drive the process, providing cooling for auxiliary loads. The metal organic framework aluminium fumarate with water is potentially a suitable material pair for this low temperature driven application. A targeted heat exchanger design is a prerequisite for competitiveness, requiring, amongst other things, a sound understanding of adsorption equilibria and adsorption enthalpy. A novel method is employed for their determination based on small isothermal and isochoric state changes, applied with an apparatus developed initially for volume swing frequency response measurement, to samples with a binder-based adsorbent coating. The adsorption enthalpy is calculated through the Clausius–Clapeyron equation from the obtained slopes of the isotherm and isobar, while the absolute uptake is determined volumetrically. The isotherm confirms the step-like form known for aluminium fumarate, with a temperature dependent inflection point at p rel ≈ 0.25, 0.28 and 0.33 for 30 °C, 40 °C and 60 °C. The calculated differential enthalpy of adsorption is 2.90 ± 0.05 MJ/kg (52.2 ± 1.0 kJ/mol) on average, which is about 10–15% higher than expected by a simple Dubinin approximation.

水下爆炸冲击作用下悬浮隧道响应参数分析

To investigate the dynamic responses of submerged floating tunnels (SFTs) subjected to near-field non-contact explosions, the SFT was simplified as a constant-section-and-stiffness Bernoulli-Euler elastic-support beam to establish the SFT dynamic model under underwater shock load. The differential equation for the vibration was resolved with the Galerkin method. The displacement, velocity and acceleration were analyzed for the SFT, the influences of the explosive quantity, the blasting distance and the vertical stiffness of anchor cables were discussed, and the results were also used to analyze the damage of tunnels and human bodies. The results show that, the impact of the blasting distance on the kinematic parameters of the SFT is significant. Moreover, the maximum displacement of the tunnel decreases in inverse proportion to the blasting distance. Compared with those of the blasting distance of 10 m, the displacements of the tunnel body of 20m and 30 m decrease by 50.7% and 66.6%, respectively. The impact of the explosive quantity on the kinematic parameters of the SFT is significant. Also, the maximum displacement of the tunnel decreases approximately in a low-order power function with the explosive quantity. Compared with those of the explosive of 20 kg, the displacements of the tunnel body of 40 kg and 60 kg increase by 29.8% and 51.3%, respectively. The impact of the vertical stiffness of anchor cables on the kinematic parameters of the SFT is significant. Besides, the maximum displacement of the tunnel decreases approximately in a step-like form with the vertical stiffness of anchor cables. Compared with those of the vertical anchor stiffness of 5×105 N/m, the maximum displacement of the tunnel body of 5×10⁶ N/m and 5×10⁷ N/m decrease by 53.0% and 86.2%, respectively. However, there is an efficiently acting interval for the anchor cable stiffness. The stiffness has significant influence on the displacement of the tunnel body within the interval, but has little influence outside the interval (large or small).

Рассеяние электронов и дырок глубокими примесями в полупроводниковых гетероструктурах с квантовыми ямами

Electron and hole scattering by deep impurities in gallium arsenide heterostructures with two quantum wells under arbitrary doping profile was considered within the strongly localized potential approximation. The de-pendence of scattering rate on the carrier energy was shown to reproduce the step-like form of the density of states for size quantization subbands of the heterostructure accounting for the contribution of the overlap integral of the carrier wave functions. For hole subbands of negative effective mass the scattering rates at the subband edges have singularities common for one-dimensional systems.

Two-body problem for two-dimensional electrons in the Bernervig-Hughes-Zhang model

We study the two-body problem for two-dimensional electron systems in a symmetrized Bernevig-Hughes-Zhang model which is widely used to describe topological and conventional insulators. The main result is that two interacting electrons can form bound states with the energy in the gap of the band spectrum. The pairing mechanism can be interpreted as the formation of a negative reduced effective mass of two electrons. The problem is complicated because the relative motion of the electrons is coupled to the center-of-mass motion. We consider the case of zero total momentum. Detail calculations are carried out for the repulsive interaction potential of steplike form. The states are classified according to their spin structure and two-particle basis functions that form a given bound state. We analyze the spectra and electronic structure of the bound states in the case of both topological and trivial phases and especially focus on effects originating from the band inversion and the coupling of the electron and hole bands. In the trivial phase and the topological phase with the large coupling parameter $a$, the bound state spectra are qualitatively similar. However, when $a$ is less a certain value, the situation changes dramatically. In the topological phase, new states arise with a higher binding energy at lower interaction potential, which evidences that the band inversion can favor pairing the electrons.

우리나라의 학교대지 조성 특성과 개선방안 연구

In this study, the characteristics and the composition of the school groundrevels in Korea to identify the problem, were compared with Japan, where in geographic and culturally similar environment the composition of the school groundrevels analyzed. The spatial extent of this study is the development of metropolitan areas and small city within 10 years (range time) survey of the 34 elementary schools were analyzed. The results are as follows: First, the school groundrevels are flat step-like form of the composition for the same level of barrier-free should be provided. Second, if the lower places in slopes where to place buildings and playgrounds are placed in high places. Third, the external space and the interior space of the connection is the concept of fault tolerance and eliminate need for stairs. This study is a part of the urban Newtown and there are limitations to generalize the results. Therefore, this result on the general guidance of school groundrevel composition in order to objectify an additional studies are required.

Threshold character of temperatures on deuterium thermal desorption in Mg-V composite grown atom-by-atom

The plasma evaporation-sputtering method was applied to make composite materials of the Mg-V system. The ion-implanted deuterium desorption temperature variations as a function of the component concentration were studied. It has been established that, by introducing vanadium into magnesium, the deuterium desorption temperature can be appreciably decreased (to 300-330 K) in comparison with the case of deuterium desorption from magnesium (~800 K). A step-like form of the curve of deuterium desorption temperature evidences on the presence of two different structure states of the Mg-V system depending on the ratio of components. The deuterium temperature decrease can be caused by filamentary inclusions formed, in the process of composite making and annealing, by the insoluble component (vanadium) atoms providing the deuterium diffusion from the sample at a lower temperature (channels for deuterium diffusion through the surface barrier). A necessary high diffusion mobility of deuterium is provided by the amorphous state of Mg83+xVx samples. The deuterium desorption data obtained on the example of Mg-V and Mg-Zr composites provide support for further research into hydrogen storage materials containing low-soluble chemical elements in the alloy components.

Threshold character of temperatures on deuterium desorption from the Mg-Zr composite

The plasma evaporation-sputtering method was used to manufacture composite materials of the Mg-Zr system. The ion-implanted deuterium desorption temperature variations depending on the component concentrations were studied. It has been established that the introduction of a Zr impurity to magnesium leads to the significant decrease of the deuterium desorption temperature (∼400K) as compared to the release from Mg samples. A step-like form of the curve of the deuterium desorption temperature testifies to presence of two various structural conditions at composite Mg-Zr depending on the relation of components. The hydrogen desorption data obtained using Mg-Zr composites can be used for the further invrstigations into the hydrogen storage materials containing chemical elements with a low solubility in the alloy components.

Influence of Ge nanocrystals and radiation defects on C–V characteristics in Si-MOS structures

Metal-Oxide-Semiconductor (MOS) structures containing 74Ge nanocrystals (NC-Ge) imbedded inside the SiO_2 layer were studied for their capacitance characterization. Ge atoms were introduced by implantation of 74Ge+ ions with energy of 150 keV into relatively thick (~640nm) amorphous SiO_2 films. The experimental characterization included room temperature measurements of capacitance-voltage (C-V) dependences at high frequencies (100 kHz and 1 MHz). Four groups of MOS structures have been studied: The 1st - "initial" samples, without Ge atoms (before ion implantation). The 2nd - "implanted" samples, after Ge+ ion implantation but before annealing, with randomly distributed Ge atoms within the struggle layer. The 3rd - samples after formation of Ge nanocrystals by means of annealing at 800 degree C ("NC-Ge" samples), and the 4th - "final" samples: NC-Ge samples that were subjected by an intensive neutron irradiation in a research nuclear reactor with the integral dose up to 10^20 neutrons/cm^2 followed by the annealing of radiation damage. It is shown that in "initial" samples, the C-V characteristics have a step-like form of "S-shape", which is typical for MOS structures in the case of high frequency. However, in "implanted" and "NC-Ge" samples, C-V characteristics have "U-shape" despite the high frequency operation, In addition, "NC-Ge" samples exhibit a large hysteresis which may indicate charge trapping at the NC-Ge. Combination of the "U-shape" and hysteresis characteristics allows us to suggest a novel 4-digits memory retention unit. "Final" samples indicate destruction of the observed peculiarities of C-V characteristics and recurrence to the C-V curve of "initial" samples.

Geometric structure and formation mechanism of Lintong-Chang’an fault zone

The results from investigation of large quantity of fault outcrops and artificial earthquakes suggest that the Lintong-Chang’an fault zone mainly consists of two faults. One is the Majie-Nianwan fault that separates a branch of Wangjiabian-Houjiawan fault on the right bank of the Bahe River; the other is the Hujiagou-Shoupazhang fault that separates a branch of Zhongdicun-Tangjiazhai fault in Tongrenyuan and Shaolingyuan. As tensional dip-slip normal faults, the faults distribute with approximately parallel equal intervals in local regions and the profiles drop in a step-like form to the northwest, presenting a Y-shape combination. The result from deep seismic reflection indicates that the fault is about 5∼8 km in depth, which is not only a basement fault, but also a listric normal fault in the deep stratum. The Lintong-Chang’an fault is a typical outstretching rift system under the NS-trending tension stress field. At the same time, affected by the sinistral strike slip of the Yuxia-Tieluzi fault, the fault extends like a broom from the northeast to the southwest.

Quasi-two-dimensional carriers in dilute-magnetic-semiconductor quantum wells under in-plane magnetic field

Due to the competition between spatial and magnetic confinement, the density of states (DOS) of a quasi-two-dimensional system deviates from the ideal step-like form both quantitatively and qualitatively. We study how this affects the spin-subband populations and the spin polarization as functions of the temperature, T, and the in-plane magnetic field, B, for narrow to wide dilute-magnetic-semiconductor quantum wells (QWs). We focus on the QW width, the magnitude of the spin–spin exchange interaction, and the sheet carrier concentration dependence. We look for ranges where the system is completely spin polarized. Increasing T, the carrier spin splitting, U 0 σ , decreases, while on increasing B, U 0 σ increases. Moreover, due to the DOS modification, all energetically higher subbands become gradually depopulated.

Deformed Wigner crystal in a one-dimensional quantum dot

The spatial Fourier spectrum of the electron density distribution in a finite 1D system and the distribution function of electrons over single-particle states are studied in detail to show that there are two universal features in their behavior, which characterize the electron ordering and the deformation of Wigner crystal by boundaries. The distribution function has a $\delta$-like singularity at the Fermi momentum $k_F$. The Fourier spectrum of the density has a step-like form at the wavevector $2k_F$, with the harmonics being absent or vanishing above this threshold. These features are found by calculations using exact diagonalization method. They are shown to be caused by Wigner ordering of electrons, affected by the boundaries. However the common Luttinger liquid model with open boundaries fails to capture these features, because it overestimates the deformation of the Wigner crystal. An improvement of the Luttinger liquid model is proposed which allows one to describe the above features correctly. It is based on the corrected form of the density operator conserving the particle number.

An investigation into the electrical properties of finite carbon nanotubes in the presence of polar molecules

This study employs quantum transport theory to investigate the electrical properties of zigzag carbon nanotubes with different hopping integrals. It is found that the current-bias voltage profiles have a step-like form, in which each step corresponds to the voltage bias at which the energy imparted to the electrons is sufficient to cause them to hop between neighboring atoms. In carbon nanotubes with a length of several nanometers, the normalized-current-voltage profiles exhibit prominent peaks as the hopping integral decreases and distinct troughs as the hopping integral increases. In longer nanotubes, the current changes by several orders of magnitude in these peak and trough regions of the current–voltage curves. Furthermore, the peaks and troughs appear at lower values of the bias voltage. The results presented in this study suggest that semi-conducting zigzag nanotubes with an appropriate bias have the potential for use as ion or polar molecule absorption sensors.

Spin-subband populations and spin polarization of quasi-two-dimensional carriers under an in-plane magnetic field

Under an in-plane magnetic field, the density of states of quasi-two-dimensional carriers deviates from the occasionally stereotypic step-like form both quantitatively and qualitatively. Here we study how this affects the spin-subband populations and the spin-polarization as functions of the temperature, $T$, and the in-plane magnetic field, $B$, for narrow to wide dilute-magnetic-semiconductor quantum wells. We examine a wide range of material and structural parameters, focusing on the quantum well width, the magnitude of the spin-spin exchange interaction, and the sheet carrier concentration. Generally, increasing $T$, the carrier spin-splitting, ${U}_{o\ensuremath{\sigma}}$, decreases, augmenting the influence of the ``minority''-spin carriers. Increasing $B$, ${U}_{o\ensuremath{\sigma}}$, increases and, accordingly, carriers populate ``majority''-spin subbands while they abandon ``minority''-spin subbands. Furthermore, in line with the density of states modification, all energetically higher subbands become gradually depopulated. We also indicate the ranges where the system is completely spin-polarized.

MOVPE and characterization of InAsN/GaAs multiple quantum wells

InAsN/GaAs multiple quantum wells (MQWs) were grown on GaAs (0 0 1) substrates by metalorganic vapor phase epitaxy (MOVPE) using 1,1-dimethylhydrazine (DMHy) and tertiarybutylarsine (TBAs) as the N and As precursors, respectively. The photoluminescence (PL) peaks of the MQWs clearly show a red shift with increasing DMHy flow rates. This result is opposite to that of the InAsN thin film whose absorption edge shows a blue shift due to the Burstein–Moss (B–M) effect (or band filling effect) caused by the high electron concentration associated with the N incorporation. The red shift of the PL peak is attributed to the huge bandgap bowing appearing with the N incorporation, because in contrast to the result of bulk InAsN, the step-like functional form of the two-dimensional density of states of quantum wells suppresses the B–M effect even in the case of a rise in residual carrier concentration. With increasing DMHy flow rate, the increase of the Stokes shift between the PL and photoluminescence excitation (PLE) peaks was observed. As a result of the excitation power dependence of the PL spectrum, it was found that the Stokes shift is attributed to the compositional fluctuation. These results indicate that the incorporation of the N into InAs in the MOVPE growth of InAsN induces a bandgap reduction due to the bandgap bowing, and the increase of the N content in the InAsN alloy causes the compositional fluctuation.

Modulation of cosmic rays in cycle 23: Some striking features

The evolutions of the mid-latitude cosmic ray (CR) neutron monitor intensities and interplanetary and solar indices for 1996–2003 (rising phase of solar cycle 23) showed the following: (1) Monthly values: Most of the solar indices started increasing by July 1997 and reached a first peak near July 2000, a second peak near October 2001, and a third minor peak near September 2002. However, CR remained at an almost steady level up to March 1998, suffered a sharp decline during March–May 1998, remained almost steady up to July 1999, decreased thereafter almost smoothly up to July 2000 (first trough), and fluctuated thereafter to have a second trough in September 2002. The solar open magnetic flux (<45° solar latitude) and IMF B component did not change fully parallel to the solar indices. (2) Daily values: CR depressions mostly coincided well with geomagnetic Dst, but sometimes, the two were dissimilar. Also, CR and many other parameters showed oscillations with peak spacings of 7–27 days. (3) Hourly values: cosmic rays showed (Forbush) decreases evolving in a very similar way to geomagnetic Dst, particularly when the IMF B was large. We do not think that the idea that the long-term modulation in step-like form is caused by the propagating diffusive barriers “Global” MIRs (GMIRs) (e.g., Burlaga, L.F., McDonald, F.B., Ness, N.F., 1993. CR modulation and the distant heliospheric magnetic field: Voyager 1 and 2 observations from 1986 to 1989, near 11 AU. J. Geophys. Res. 98, 1–11) and the alternative suggestion (e. g., Cane, H.V., Wibberenz, G., Richardson, I.G., von Rosenvinge, T.T., 1999. CR modulation and the solar magnetic field. Geophys. Res. Lett. 26, 565–568) that the step-like changes (medium-term events, lasting about an year) were related to a fundamental process at the Sun, are mutually exclusive. Both the processes are operative simultaneously, only that the relationship with near-Earth IMF is more spectacular as it occurs with considerable CR changes in a short time (hours to few days). During the absence of near-Earth events, the effects of GMIRs are seen clearly as slow CR decreases lasting for several days.

Spin polarization and magnetization of conduction-band dilute-magnetic-semiconductor quantum wells with non-step-like density of states

We study the magnetization, M, and the spin polarization, ζ, of n-doped non-magnetic-semiconductor (NMS)/narrow to wide dilute-magnetic-semiconductor (DMS)/n-doped NMS quantum wells, as a function of the temperature, T, and the in-plane magnetic field, B. Under such conditions the density of states (DOS) deviates from the occasionally stereotypic step-like form, both quantitatively and qualitatively. The DOS modification causes an impressive fluctuation of M in cases of vigorous competition between spatial and magnetic confinement. At low T, the enhanced electron spin-splitting, Uoσ, acquires its bigger value. At higher T, Uoσ decreases, augmenting the influence of the spin-up electrons. Increasing B, Uoσ increases and accordingly electrons populate spin-down subbands while they abandon spin-up subbands. Furthermore, due to the DOS modification, all energetically higher subbands become gradually depopulated.