Double Valley Research Articles

A Study on the Temporal and Spatial Changes of Nitrogen Oxides in the Southwest Corner of Jingzhou City Wall

With the growth of people's consumption capacity, the production and consumption of energy are rapidly increasing every year, and the emissions of nitrogen oxides are also increasing. Nitrogen oxides include many types of compounds, such as nitric oxide (NO), nitrogen dioxide (NO2), nitrous oxide (N2O), etc. Except for nitrogen dioxide, the properties of other nitrogen oxides are extremely unstable. Therefore, in the actual atmosphere, nitric oxide (NO) and nitrogen dioxide (NO2) are usually collectively referred to as nitrogen oxides (NOx). This article measured and compared the nitrogen oxide concentration and other meteorological indicators in the public, commercial, and civilian areas at the southwest corner of the city wall in Jingzhou City in March and April 2022. The following conclusions were drawn: the mass concentration of nitrogen oxide pollutants was highest around noon and evening, and the concentration was relatively small before and after sunrise and afternoon, with a "double peak and double valley" distribution. The nitrogen oxide concentration began to decrease at night and reached the first valley in the early morning, then it gradually rises, reaching its peak around 8:00 and then showing a downward trend. A second trough will appear around 13:00, followed by a continuous increase in concentration, and finally a small peak will appear at 18:00.

Data-driven multi-valley dark solitons of multi-component Manakov Model using Physics-Informed Neural Networks

In this paper, we employ a Deep Learning technique, namely Physics-Informed Neural Network for solving multi-component Manakov models. In particular, we consider three and four-coupled nonlinear Schrödinger equations. We show that in the former case, one of the components and two others can carry, respectively, a double valley dark soliton and asymmetric bright solitons. In the four-component Manakov model, all four components are predicted by PINN with high accuracy in which the first component is shown to be a triple-valley dark soliton. We compare the results with the exact solutions and bring out the ability of Deep Learning in solving coupled systems of nonlinear partial differential equations with high accuracy. The performance of the PINN in approximating the solutions is estimated by taking the squared difference between the exact and predicted squared magnitude of the solutions. We have also computed the L2-norm errors for real, imaginary and absolute-value components of the solutions to emphasize the accuracy of PINN.

Simultaneous enhancement in electrical conductivity and Seebeck coefficient by single- to double-valley transition in a Dirac-like band

SnTe possesses a single- to double-valley transition in the conduction band minimum when a compressive strain is applied. Through a tight-binding analysis, it is shown that the variation of the band structure is attributed to the strain-induced delocalization of both the Sn-5s orbitals and Te-5p orbitals with different angular momenta. This effect can largely increase the electron density of states near the band edge and thus keep the Fermi level of the compressed SnTe closer to it, where the electrons have lower scattering rates. The strain-induced double valleys lead to simultaneous increases in the electrical conductivity and the Seebeck coefficient and thereby nearly four times the enhancement of the power factor at the doping concentration of 5×1019 cm–3. This work suggests a feasible concept that can be employed to promote the power factor of a Dirac semiconductor via manipulating the valley degeneracy in the conduction band minimum.

Exploring the detailed spatiotemporal characteristics of PM2.5: Generating a full-coverage and hourly PM2.5 dataset in the Sichuan Basin, China

Fine particulate matter (PM2.5) has received worldwide attention due to its threat to public health. In the Sichuan Basin (SCB), PM2.5 is causing heavy health burdens due to its high concentrations and population density. Compared with other heavily polluted areas, less effort has been made to generate a full-coverage PM2.5 dataset of the SCB, in which the detailed PM2.5 spatiotemporal characteristics remain unclear. Considering commonly existing spatiotemporal autocorrelations, the top-of-atmosphere reflectance (TOAR) with a high coverage rate and other auxiliary data were employed to build commonly used random forest (RF) models to generate accurate hourly PM2.5 concentration predictions with a 0.05° × 0.05° spatial resolution in the SCB in 2016. Specifically, with historical concentrations predicted from a spatial RF (S-RF) and observed at stations, an alternative spatiotemporal RF (AST-RF) and spatiotemporal RF (ST-RF) were built in grids with stations (type 1). The predictions from the AST-RF in grids without stations (type 2) and observations in type 1 formed the PM2.5 dataset. The LOOCV R2, RMSE and MAE were 0.94/0.94, 8.71/8.62 μg∕m3 and 5.58/5.57 μg∕m3 in the AST-RF/ST-RF, respectively. Using the produced dataset, spatiotemporal analysis was conducted for a detailed understanding of the spatiotemporal characteristics of PM2.5 in the SCB. The PM2.5 concentrations gradually increased from the edge to the center of the SCB in spatial distribution. Two high-concentration areas centered on Chengdu and Zigong were observed throughout the year, while another high-concentration area centered on Dazhou was only observed in winter. The diurnal variation had double peaks and double valleys in the SCB. The concentrations were high at night and low in daytime, which suggests that characterizing the relationship between PM2.5 and adverse health outcomes by daily means might be inaccurate with most human activities conducted in daytime.

Explorations on properties of ε′ phase and new crystalline phase of Fe3Ge alloy under high pressures

We calculated the lattice dynamics, elasticity, electron spin polarizability P(EF), and electron specific heat coefficient γ of the L12-Fe3Ge crystalline alloy under high pressure using first-principles method based on density functional theory. By comparing the lattice dynamics and elasticity of the ferromagnetic and non-magnetic systems, it can be found that the spontaneous magnetization of the system induces the dynamic stability of the system at low pressure (less than 6 GPa). Furthermore, the magnetostriction induced by the spontaneous magnetization enhances the elastic modulus of the system. With the increase of pressure, in the pressure range of 130-290 GPa where the spin magnetic moment of the system decreases sharply, the elastic modulus exhibits an abnormal behavior, which leads to double peaks in Poisson's ratio v and Pugh's ratio B/G, correspondingly, double valleys appear in shear modulus G, Young's modulus E and Debye temperature ΘD, which are associated with dynamic instability in the 130-290 GPa. Finally, for the phonon spectrum at 260 GPa with a significant imaginary frequency, the metastable orthogonal Fmmm structure is obtained using the soft mode phase transition theory. After comparing the enthalpy differences with different structures, it is found that the ferromagnetic Fmmm structure is a metastable phase, which is dynamic stable at 0 GPa and 260 GPa.

Spatiotemporal distribution of negative air ion and PM2.5 in urban residential areas

Urban environments are characterised by high pollution levels, which adversely affect the physiology, psychology and behaviour of the urban residents. In this study, on-site measurements and air quality evaluations were performed in urban residential areas. The negative air ion (NAI) concentration, fine particulate matter (PM2.5) concentration, temperature and relative humidity were measured in different seasons. Both PM2.5 and the NAI concentrations changed significantly with seasons. The PM2.5 concentration was the highest in winter, intermediate in autumn and the lowest in summer, while the NAI concentration showed an opposite trend. The overall changes in NAI and PM2.5 concentrations showed a trend of double peaks and double valleys, and there was a substantial difference between rainy days versus sunny days. The NAI concentration was positively correlated with temperature and relative humidity, and the influence of relative humidity on NAI was greater than that of temperature. There were notable spatial differences in the intensity of impact by different pollution sources. Based on these results, suggestions were made for optimising the layout of residential buildings and the rationalisation of traffic networks, with the aim of increasing NAI concentrations and reducing PM2.5 concentrations. This would help reduce the pollution levels in urban residential areas.

The preliminary value of vector flow mapping on assessment of left intraventricular pressure difference in patients with paroxysmal atrial fibrillation

This study aims to explore the intraventricular pressure difference (IVPD) within left ventricle in patients with paroxysmal atrial fibrillation (PAF) by using the relative pressure imaging (RPI) of vector flow mapping (VFM). Twenty patients with paroxysmal atrial fibrillation (PAF) and thirty control subjects were enrolled in the study. Systolic and diastolic IVPD derived from VFM within left ventricle and conventional echocardiographic parameters were analyzed. It was found that the B-A IVPD of left ventricle in PAF patients showed the same pattern as controls-single peak and single valley during systole and double peaks and double valleys during diastole. Basal IVPD was the main component of base to apex IVPD (B-A IVPD). The isovolumetric systolic IVPD was associated with early systolic IVPD, early systolic IVPD was associated with late systolic IVPD, and late systolic IVPD was associated with isovolumic diastolic IVPD (all P < 0.05). The B-A IVPD and basal IVPD during isovolumetric systole, early systole, late systole and isovolumetric diastole in PAF patients significantly decreased (all P < 0.05). The study shows that the B-A IVPD pattern of the PAF group is the same as controls, but systolic B-A IVPD and basal IVPD are significantly reduced in PAF patients. VFM-derived RPI can evaluate left ventricular IVPD in PAF patients, providing a visually quantitative method for evaluating left ventricular hemodynamic mechanics in the patients with PAF.

Assessing the interaction of seismically loaded adjacent valleys using time-domain approach

Amplification or attenuation of seismic waves while passing through the soil medium can be due to soil type and its stratification or local topographic effects. Such aspects have been theoretically explained in many researches by means of ground response analysis. The results of seismic ground response analysis provide the necessary and realistic information for seismic design of structures and soil-structure interaction problems. In present study, two-dimensional finite element method is applied to evaluate the ground response of valley environments and estimation their interaction effects using time-domain approach. In this regard different cases include free field condition, single valley and double valleys environments are considered. Numerical simulations of seismic wave propagation for these cases are carried out and compared with each other. The results show that irregular topography can greatly amplify the seismic waves. On the other hand, if there are adjacent topographies, due to interaction of them, the amplification effect can be substantially increased. This amplification can be attenuated by moving away from the valley center to free field conditions.

Analysis of Pollution Characteristics and Influencing Factors of Main Pollutants in the Atmosphere of Shenyang City

Air pollution is one of the most concerning environmental problems in cities. Hourly data on pollutant concentrations from 11 automatic atmospheric monitoring stations and meteorological data in Shenyang from 2017 to 2019 were used to analyze the spatio-temporal variation rules of CO (carbon monoxide), SO2 (sulfur dioxide), NO2 (nitrogen dioxide), O3 (ozone), PM2.5 and PM10 (PM particles with an aerodynamic diameters of not more than 2.5 µm and 10 µm) and their relationships with meteorological parameters. Meanwhile, the regional transmission route of pollutants was analyzed by the hybrid single particle Lagrangian integrated trajectory (HYSPLIT) model. The results showed that the concentration of O3 in the northern area of the city was higher than that in the south; CO, SO2 and NO2 were relatively high in the urban center; and PM2.5 and PM10 were relatively high in the southwest. The average concentration of pollutants was lowest in 2019. The concentration of O3 was the highest in spring, while CO showed no significant variations between different seasons. The remaining pollutant concentrations appeared to be high in winter and low in summer. The cumulative concentrations of the six pollutants were the highest in March, and relatively low in July–September. The diurnal concentration variations of O3, CO and SO2 exhibited a “single peak,” while others showed a “double peak and double valley.” Temperature was positively correlated with O3 concentration and negatively correlated with others. Wind speed was negatively correlated with the concentration of PM2.5, NO2, and O3. The air quality of the main urban area in spring and summer was mainly affected by the coastal air flow, while it was mostly affected by the northwest air flow in autumn and winter.

Experimental investigation of nitrogen flow boiling heat transfer in a single mini-channel

Flow boiling heat transfer of nitrogen at high subcritical pressure conditions in a single vertical mini-channel with the diameter of 2.0 mm was experimentally investigated. The tested mass flux varied from 530 to 830 kg/(m2·s), the inlet pressure ranged from 630 to 1080 kPa, and the heat flux ranged from 0 to 223.2 kW/m2. Effects of the mass flux and the inlet pressure on the nitrogen boiling curve were examined. Results showed that within the limited test conditions, the merging of three boiling curves indicates the dominance of nucleate boiling and the inlet pressure has a positive enhancement on heat transfer performance. Three heat transfer trends were identified with increasing heat flux. At low heat fluxes, the heat transfer coefficient increases first and then decreases with vapour quality. At intermediate heat fluxes, the heat transfer coefficient versus the vapour quality presents an inverted “U” shape. At high heat fluxes, a double valley shape was observed and the partial dry-out in intermittent flow and annular flow helps to interpret the phenomenon. The increasing inlet pressure increases the heat transfer coefficient over a wide range of vapour quality until the partial dry-out inception. The lower surface tension and lower latent heat of evaporation enhance the nucleate boiling for higher inlet pressure. A modified experimental correlation (mean absolute error (MAE)=19.3%) was proposed on the basis of the Tran correlation considering both the nucleate boiling and the partial dry-out heat transfer mechanism.

An overlapping peak separation algorithm based on multiorder differential method and genetic algorithm for magnetic eddy current signal of a defect cluster

AbstractSafety assessment plays a vital role in the operation of oil and gas production systems, and data processing is important for the analysis of defects to make correct diagnosis. Therefore, the research to find a reliable data processing method is carried out. The magnetic eddy current signal detected of the defect is generally an abnormal data of “one peak and double valley” type. When the distance between the two defects is close, the leakage magnetic fields of the two defects interfere with each other. In order to facilitate the extraction of the characteristics of such anomalous data, it is necessary to separate the overlapping abnormal data. In this article, the above methods for identifying and processing anomaly detection data of complex defects are studied. The data fitting method is used to find the most suitable fitting function, and the accuracy of overlapping peak separation is optimized by the improved peak separation method based on GA algorithm. The results show that the Gaussian function is most suitable for fitting prediction of the “defective cluster” detection data after separation. The overlapped peak separation result optimized by GA algorithm has less error with the actual data. Therefore, the relevant features of the separated data can accurately reflect the defect related information and effectively improve the pipeline safety assessment.

Characteristic features of the magnetoresistance related to structured defects in graphene on SiC (0001)

The structural characteristics of the graphene being grown on SiC (0001) were measured by Raman spectroscopy and Kelvin-probe microscopy. According to these data a single-layer graphene with a small amount (∼20%) of inclusions of double-layer islands with submicrometer dimensions was formed. Transport properties of graphitized silicon carbide are controlled by graphene layer heavily doped with electrons. In low magnetic fields at low temperatures, a negative magnetoresistance is observed due to the weak localization. A transition of the magnetoresistance from weak localization to weak antilocalization (the latter is a manifestation of the isospin in graphene and strong intervalley scattering ) was observed with increasing temperature (T > 150 K) for the first time in graphene grown on SiC (0001). The possible candidate for such intensive intervalley scattering can be the interphase boundaries separating the single-layered graphene and the islands of the double-layer graphene with high momentum transfer. A pronounced pattern of Shubnikov--de Haas oscillations was observed in strong magnetic fields (up to 30 T). This pattern demonstrates a 4-fold degeneration of the carrier spectrum due to the double spin degeneration and double valley degeneration and shows a manifestation of the Berry phase, which is somewhat different from the ‘ideal’ value of π.

Transition between Electron Localization and Antilocalization and Manifestation of the Berry Phase in Graphene on a SiC Surface

It is shown that the transport properties of graphitized silicon carbide are controlled by a surface graphene layer heavily doped with electrons. In weak magnetic fields and at low temperatures, a negative magnetoresistance is observed due to weak localization. A crossover in the magnetoresistance from weak localization to weak antilocalization (the latter is the manifestation of the isospin in graphene) is observed for the first time in samples of this kind at elevated temperatures. A pronounced pattern of Shubnikov–de Haas oscillations is observed in strong magnetic fields (up to 30 T). This pattern demonstrated fourfold carrier spectrum degeneracy due to the double spin and double valley degeneracies. Also, the manifestation of the Berry phase is observed. The effective electron mass is estimated to be m* = 0.08m0, which is characteristic of graphene with a high carrier concentration.

Переход между электронной локализацией и антилокализацией, а также проявление фазы Берри в графене на поверхности SiC

AbstractIt is shown that the transport properties of graphitized silicon carbide are controlled by a surface graphene layer heavily doped with electrons. In weak magnetic fields and at low temperatures, a negative magnetoresistance is observed due to weak localization. A crossover in the magnetoresistance from weak localization to weak antilocalization (the latter is the manifestation of the isospin in graphene) is observed for the first time in samples of this kind at elevated temperatures. A pronounced pattern of Shubnikov–de Haas oscillations is observed in strong magnetic fields (up to 30 T). This pattern demonstrated fourfold carrier spectrum degeneracy due to the double spin and double valley degeneracies. Also, the manifestation of the Berry phase is observed. The effective electron mass is estimated to be m * = 0 . 08 m _0, which is characteristic of graphene with a high carrier concentration.

Dynamics of soil water reservoir of wheat field in rain-fed area of the Loess Tableland, China

Soil reservoir is the basis of stable grain production and sustainable development in dry farming area. Based on the long-term field experiment, this paper investigated the changes of soil moisture in wheat field located in the rain-fed Changwu Tableland, and analyzed the interannual and annual variation characteristics and dynamics trends of soil reservoir from 2012 to 2015. The results showed that the vertical distribution curves of average soil water content were double peaks and double valleys: first peak and valley occurred in the 10-20 and 50 cm soil layer, respectively, while for the second peak and valley, the corresponding soil layer was the 100 and 280 cm soil layer. Soil reservoir did not coincide with precipitation for all yearly precipitation patterns but lagged behind. Yearly precipitation patterns had a great influence on the interannual and annual dynamic changes of soil reservoir. Compared with rainy year, the depth of soil moisture consumption decreased and supplementary effect of precipitation on soil moisture became obvious under effects of drought year and normal year. In rainy year, soil reservoir had a large surplus (84.2 mm), water balance was compensated; in normal year, it had a slight surplus (9.5 mm), water balance was compensated; while in drought year, it was slightly deficient (1.5 mm), water balance was negatively compensated. The dynamics of soil water in winter wheat field in the rain-fed Changwu Tableland could be divided into four periods: seedling period, slow consumption period, large consumption period, and harvest period, the order of evapotranspiration was large consumption period> seedling period> harvest period> slow consumption period.

Double valley Dirac fermions for 3D and 2D Hg1−xCdxTe with strong asymmetry

In this paper the possibility to bring about the double-valley Dirac fermions in some quantum structures is predicted. These quantum structures are: strained 3D Hg1−xCdxTe topological insulator (TI) with strong interface inversion asymmetry and the asymmetric Hg1−xCdxTe double quantum wells (DQW). The numerical analysis of the dispersion relation for 3D TI Hg1−xCdxTe for the proper Cd (x)-content of the Hg1−xCdxTe compound clearly shows that the inversion symmetry breaking together with the unaxial tensile strain causes the splitting of each of the Dirac nodes (two belonging to two interfaces) into two in the proximity of the Γ-point. Similar effects can be obtained for asymmetric Hg1−xCdxTe DQW with the proper content of Cd and proper width of the quantum wells. The aim of this work is to explore the inversion symmetry breaking in 3D TI and 2D DQW mixed HgCdTe systems. It is shown that this symmetry breaking leads to the dependence of carriers energy on quasi-momentum similar to that of Weyl fermions.

Electronic structure for a topological insulator with a smoothly varying step on surface

We study the penetration depth (PD) of surface state into the bulk, the local density of states (LDOS) and the spin-polarized STM tip tunneling conductance (TG) for a smoothly varying step described by an asymptotic model, on the surface of a three-dimensional (3D) topological insulator (TI). Using curvilinear coordinates for calculation, we find that the PD shows two peaks near step edges with maximum surface curvature and a dip value of flat surface at step middle with zero curvature. In contrast, the LDOS exhibits a double valley (dip) pattern, in which it rapidly declines from the highest value for flat surface to the dip value near step edges, and then shows a small peak at step middle. This interesting small peak is in good agreement with experimentally observed LDOS peak within a step of definite span on a 3D TI surface. Moreover, the calculated surface spin-polarized STM tip TG also confirms the LDOS qualitatively. The findings here may provide a further understanding of 3D TI surface with step line defects.

HOT DEFORMATION BEHAVIOR OF A HIGH STRENGTH CONTAINER STEEL COMPOUNDED WITH Nb-B

Hot deformation behaviors of high strength container steel compounded with Nb-B have been systematically studied through high temperature compression tests on the Gleeble-1500 thermal-mechanical simulator. In the present deformation conditions, there are different relationships between the strain hardening exponent (n) and the true strain (e) under different strain rates at the deformation temperature of 1423 K; n-ecurves have single peak and single valley at the strain rates of 0.1 s~(-1) and 1s~(-1), while n-ecurves have double peaks and double valleys at the strain rates of 5 s~(-1) and 15 s~(-1).During the heat work-hardening process, dislocation strengthening, twin strengthening and precipitation strengthening are the major work-hardening mechanisms of the tested steel. According to Zener-Hollomon and Ludwik equation, the experimental data have been regressed by using nonlinear method, the apparent deformation activation energy (Q) and stress exponent (n) were obtained to be about (428.188±20.109) kJ/mol and 4.923 in the temperature range of 1123 K—1423 K, respectively. Finally, an expression of Z parameter, hot deformation equation and dynamic recrystallization model diagram of the tested steel are established.

Enhancement of Energy Harvested from a Random Vibration Source by Magnetic Coupling of a Piezoelectric Cantilever

It is demonstrated experimentally that the energy harvested from a random noise source by a piezoelectric cantilever can be substantially enhanced by introducing a magnetic coupling force. The coupled cantilever responds to a 1/f vibration spectrum (‘pink noise’) with chaotic motion that on average has larger amplitude than the non-chaotic motion of an uncoupled cantilever. A 50% increase in output voltage was observed in the coupled cantilever compared to the uncoupled cantilever. Calculations show that the magnetic force transforms the quadratic spring potential of the cantilever into a double valley of two potential wells. Fluctuations between the two potential minima increase the amplitude of the cantilever motion over a range of vibration frequencies.

Probing Pauli blocking with shot noise in resonant tunneling diodes: Experiment and theory

The Pauli exclusion principle is one of the fundamental tenets of quantum mechanics and determines the structure of matter at the atomic and molecular levels. Here, we show that Pauli blocking, a consequence of the exclusion principle according to which electron transitions are inhibited if the arrival state is occupied by another electron, has an observable effect on shot noise in resonant tunneling diodes. We measure a double valley feature in the plot of the noise suppression factor (the ``Fano'' factor) as a function of the applied voltage, which has been theoretically predicted a few years ago but has never been observed, and which suggests that Pauli blocking must be considered in the evaluation of transport in mesoscopic and nanoelectronic devices.