Enlarged Gap Research Articles

Femtosecond laser-induced ultrafast electron dynamics and band gap renormalization in InSb

Studying ultrafast dynamical processes is essential for understanding light-matter coupling, which is crucial for the optoelectronic and photonic applications of semiconductor materials. Herein, we investigate the evolution of electron population near the conduction band minimum (CBM) and band gap in InSb (100) crystal under different laser fluences using time- and angle-resolved photoelectron spectra (TrARPES). In contrast to the pump-fluence-independent fast growth process (FP) of the electron population, the slow process (SP) is fluence sensitive, which is similar to the temperature-dependent behavior observed in InSb (110). In addition, we observe a band gap enlargement with increasing the photoexcitation flux. Comprehensive analysis reveals that these observed diverse results are attributed to the laser-tunable dielectric function on the surface of InSb. Our findings not only enhance the understanding of laser-semiconductor interactions but also broaden the potential applications in the field of optoelectronic and photonic devices.

RE(HSeO3)(SeO3)(H2O)·(H2O) (RE = Y, Gd): Two Rare-Earth Selenite Nonlinear Optical Crystals with Wide Band Gaps.

The band gap is one of the significant parameters for nonlinear optical (NLO) materials, which is the key factor in their application band in laser technology. This study reports the synthesis of two rare-earth selenite NLO crystals, namely, RE(HSeO3)(SeO3)(H2O)·(H2O) (RE = Y, Gd), utilizing the hydrothermal technique. The two compounds are isostructural, and both belong to the orthorhombic chiral space group of P212121 and possess three-dimensional structures consisting of two-dimensional rare-earth selenite layers connected by hydrogen bonds (O-H··O). These two compounds exhibit a moderate second harmonic generation intensity of 0.5/0.8 × KDP and wide energy band gaps reaching 4.8 eV. Comprehensive density functional theory analyses based on first-principles were carried out to unravel the relationship between the structural and corresponding properties. This work provides an approach for band gap enlargement in rare-earth selenite systems and is beneficial to the design of future NLO materials.

The wall between urban and rural: How does the urban-rural electricity gap inhibit the human development index

Based on the Instrumental Variables - Generalized Method of Moments (IV-GMM) model, this paper explores the relationship, heterogeneity, and mechanisms between the urban-rural electricity gap and the human development index for 176 countries during 2000–2020. The key findings are as follows: (1) Urban-rural electricity gap is harmful to the improvement of the human development index; an enlarged gap in electricity accessibility between urban and rural is detrimental to sustainable human development. (2) Urban-rural electricity gap is more harmful to the increase of human development index in low-income countries and low governance efficiency countries. Also, the heterogeneity exists in different quantiles, and their nexus is closer in countries with lower levels of human development index. (3) Income inequality and energy poverty act as mechanisms, which means that the urban-rural electricity gap inhibits the human development index by exacerbating income inequality and energy poverty.

Experiment investigation on secondary flow loss and flow control mechanisms in a variable compressor cascade with penny cavities

Variable Stator Vanes (VSVs) with penny cavities are an important method to improve the efficiency of compressors. However, the annular and radial gaps in VSVs introduce complex flow structures, posing challenges in enhancing compressor efficiency. This article employs low-speed wind tunnel experiments to study the impact mechanisms of VSVs' adjustment angle and radial gap size on secondary flow losses and implements single-hole suction as a means of flow control to reduce total pressure loss. The results indicate that radial gap leakage has a certain inhibitory effect on annular gap leakage at general adjustment angles. Total pressure loss decreases initially as the radial gap increases but once the radial gap further enlarges and dominates the loss components, the total pressure loss increases proportionally with the radial gap. At extreme adjustment angles, where the lateral pressure gradient is significant, radial gap leakage intensity is high and comprises the major part of the loss, leading to an increase in total pressure loss in proportion to radial gap enlargement. Additionally, single-hole suction is effective under various conditions, with the potential to reduce total pressure loss by up to 19.4 %. These findings provide guidance for the application of VSVs in further improving compressor efficiency.

Establishment and Evaluation of a Mice Model of High-Altitude Cerebral Edema

To establish an animal model of high-altitude cerebral edema (HACE), to explore the altitude and oxygen partial pressure conditions that can lead to obvious clinical manifestations of HACE, and to lay the foundation for further research of the pathogenic mechanisms and intervention strategies of HACE. Male BALB/c mice of 8 weeks old were randomly assigned to Control and HACE groups. The Control group (n=10) was treated with normobaric and normoxic conditions, while the HACE groups were placed in hypobaric hypoxic (HH) chambers for the durations of 6 h, 12 h, 24 h, 48 h and 72 h, respectively, receiving treatments of simulated HH conditions at the altitudes of 4000 m (n=10 for each group receiving different durations of HH treatment), 5000 m (n=10 for each group receiving different durations of HH treatment), and 6000 m (n=10 for each group receiving different durations of HH treatment). HE staining was performed to observe the morphological changes of the brain tissue and the appropriate simulated altitude conditions were selected accordingly for the construction and evaluation of the best HACE model. The HACE model was evaluated in the following ways, the mouse brain was weighed and the cerebral edema was measured accordingly, Evans blue (EB) was injected to determine the permeability of the blood-brain barrier (BBB), and the cell apoptosis was determined by immunofluorescence staining. There were no deaths in the groups treated with the HH conditions of the altitudes of 4000 m and 5000 m, while the mortality in the 6000 m altitude treatment groups was 12.2%. HE staining showed no significant changes in brain morphology or structure in the group receiving HH treatment for the altitude of 4000 m. A small amount of brain cell edema was observed in the groups receiving 48 h and 72 h of HH treatment for the altitude of 5000 m. The groups receiving HH treatment for the altitude of 6000 m demonstrated the most prominent modeling effect. HE staining showed increased volume and swelling of brain cells in all the 6000 m groups, especially in the 24 h, 48 h and 72 h treatment groups. In all the 6000 m groups, cell arrangement disorder, gap enlargement, and nuclear contraction were observed. Evaluation of the modeling effect demonstrated that, in the HACE mice model constructed with the HH conditions for the altitude of 6000 m, cerebral edema and EB permeability increased after 12 h HH treatment and there was no obvious apoptosis in the modeling groups receiving different durations of treatment. The HACE model can be established effectively by simulating conditions at the altitude of 6000 m (the atmospheric pressure being 47.19 kPa and the oxygen partial pressure being 9.73 kPa) with a HH chamber.

Investigation of a Realistic Flap Modeling Using a Combination of Chimera Method and Grid Deformation on a Wing Fuselage Configuration

AbstractFlap deflections of an aircraft wing for active load alleviation within CFD simulations are realized using pure grid deformation due to time saving and low modeling complexity. In this case, spanwise gaps are neglected, which are present in reality during a flap deflection. Another possibility to realize the deflections is the combination of pure grid deformation and Chimera method, which allows the modeling of the gap between flap and wing or consecutive flaps. The overall aim of this work is the analysis of the aerodynamic effects caused by the different modeling approaches realizing leading and trailing edge flap deflections. The comparison of the modeling methods is investigated on the DLR LEISA configuration, which is a generic wing‐fuselage configuration. For active gust load alleviation, the leading edge flaps are deflected downward and the trailing edge flaps are deflected upward. Due to the downward deflection of the leading edge flaps, vortices are formed using the combined Chimera method as a result of the gap consideration. These vortices lead to a local drag increase resulting in a difference between both modeling methods in the spanwise as well as global drag coefficient. With the pure grid deformation these vortices do not occur. Due to the upward trailing edge deflection, the combined Chimera method leads to a pressure compensation via the effective gap enlargement, which is not present in the pure grid deformation. Overall, the combined Chimera method offers a good possibility to model the induced drag as well as the pressure compensation at a large flap deflection.

Characterization of Bipolar Transport in Hf(Te1−xSex)2 Thermoelectric Alloys

Control of bipolar conduction is essential to improve the high-temperature thermoelectric performance of materials for power generation applications. Recently, Hf(Te1−xSex)2 alloys have gained much attention due to their potential use in thermoelectric power generation. Increasing the Se alloying content significantly increases the band gap while decreasing its carrier concentration. These two factors affect bipolar conduction substantially. In addition, the weighted mobility ratio is estimated from the experimental electronic transport properties of Hf(Te1−xSex)2 alloys (x = 0.0, 0.025, 0.25, 0.5, 1.0) by using the Two-Band model. From the bipolar thermal conductivity also calculated using the Two-Band model, we find that it peaks near x = 0.5. The initial bipolar conductivity increase of x < 0.5 is mostly due to the decrease in the weighted mobility ratio and carrier concentration with increasing x. For x > 0.5, the drop in the bipolar conductivity can be understood with significant band gap enlargement.

Measuring capacity utilization under the constraints of energy consumption and CO2 emissions using meta-frontier DEA: A case of China's non-ferrous metal industries

Currently, China's non-ferrous metal industry (NMI) still has the problem of overcapacity, measuring its capacity utilization (CU) and revealing its determinants is an important way to resolve the overcapacity problem of China's NMI. Using the panel data of China's 29 NMIs, this paper constructs a meta-frontier data envelopment analysis (DEA) to measure CU by taking into account the energy consumption and CO2 emissions constraints, and decompose the CU into four parts: technical efficiency, technology gap, scale efficiency, and equipment utilization. The main findings indicate that during the period of 2004–2017, the CU of China's NMI is generally low. Non-ferrous metal alloy manufacturing and rolling processing has the highest CU, while non-ferrous metals mining and dressing shows the lowest CU. From the dynamic perspective, mining and dressing experienced CU decrease, while other two sub-industries achieved CU increase. Technical inefficiency and technology gap enlargement are two main barriers of China's NMIs' CU. Besides, among 29 NMIs, there are only ten industries witnessed a CU improvement, while the remaining nineteen industries all experienced decrease of CU. CU and its determinants across China's 29 NMIs are quite different. Thus, the policies to improve CU should be made tailored to each industry's features.

An Open-Shell Superatom Cluster Ta10- with Enhanced Stability by United d-d π Bonds and d-Orbital Superatomic States.

We carried out a comprehensive study on the gas-phase reactions of Tan- (n = 5-27) with nitrogen using a customized reflection time-of-flight mass spectrometer coupled with a velocity map imaging apparatus (Re-TOFMS-VMI). Among the studied tantalum clusters, Ta10- exhibits prominent mass abundance indicative of its unique inertness. DFT calculation results revealed a D4d bipyramidal prolate structure of the most stable Ta10-, which was verified by photoelectron spectroscopy experiments. The calculations also unveiled that Ta10- has the largest HOMO-LUMO gap and second-order difference of binding energy among the studied clusters. This is associated with its well-organized superatomic orbitals, which consist of both 6s and 5d orbitals of tantalum atoms, allowing for splitting of superatomic 1D and 2P orbitals and an enlarged gap between the singly occupied molecular orbital (SOMO) and unoccupied β counterpart, which brings forth stabilization energy pertaining to Jahn-Teller distortion. Also, the SOMO exhibits a united d-d π orbital pattern that embraces the central Ta8- moiety.

Enlargement of band gaps on thermal wave crystals by using heterostructures

Thermal wave crystals are periodic structures that support temperature wave oscillations. In these lattices, band gaps exist for heat flow due to interference phenomena. In this work, we demonstrate how heterostructures—a stack of two different lattices—can be used to increase band gaps. We investigate two distinct periodic structures. The first is a biological composite made up of stratum-like and dermal-like materials where we have found a band gap enlargement from 1.93 to 10.08 Hz. The second is composed of two semiconductors, silicon (Si) and germanium (Ge), where we have designed a heterostructure with a band gap ranging 0.096 to 0.17 Thz. The design of heterostructures to increase band gaps is especially useful when there is a low contrast of material parameters, as is the case of semiconductors.

Experimental Investigation of Powder-mixed Dielectrics for Electrical Discharge Machining

The addition of various micro/nanopowders in the EDM dielectric results in superior machining performance over the conventional pure liquid dielectrics. While most of the experimental studies on powder-mixed dielectrics in EDM have used conductive or semi-conductive powders, a few have shown merit in using non-conductive powders as well. However, unlike conductive powders, the specific mechanisms through which the non-conductive powders and their concentration affect the EDM process is poorly understood. The research presented in this paper investigates the effect of non-conductive powders and their concentration on the machining performance of powder-mixed dielectric-based EDM (PMEDM) in terms of material removal rate, tool wear, and surface roughness. Experiments are conducted with Alumina and SiC powder added to DI water at three different concentrations. It is observed that the material removal rate (MRR) and tool wear rate (TWR) of PMEDM is higher than conventional EDM with pure dielectric, while the electrode wear ratio is lower. The machined surface finish is smoother in PMEDM than conventional EDM. In Alumina-based PMEDM, an increase in the powder concentration leads to inter-electrode gap enlargement due to increased electrical conductivity, and leads to higher pulse frequency, stable machining conditions and improved MRR. In addition, dispersion of discharge energy due to the powder results in a better surface finish. The conductivity of SiC-mixed dielectric remains unaffected with changes in powder concentration, leading to no significant improvements in MRR. However, the energy dispersion mechanism leads to a smoother surface as the powder concentration increases.

Titanium dioxide nanoparticles perturb the blood-testis barrier via disruption of actin-based cell adhesive function.

As one of the most commonly used nanoparticles, titanium dioxide nanoparticles (TiO2-NPs) are widely used as coating reagents in cosmetics, medicine and other industries. The increasing risk of exposure to TiO2-NPs raises concerns about their safety. In this study, we investigated the mechanism by which TiO2-NPs cross the blood-testis barrier (BTB). TM-4 cells were selected as an in vitro Sertoli cell model of BTB. Cell viability, cell morphological changes, apoptosis, oxidative damage, and the expression levels of actin regulatory and tight junction (TJ) proteins were assessed in TM-4 cells treated with 3-nm and 24-nm TiO2-NPs. Cells treated with 3-nm TiO2-NPs exhibited increased cytotoxicity and decreased Annexin II expression, whereas cells treated with 24-nm TiO2-NPs exhibited increased Arp 3 and c-Src expression. Both TiO2-NPs induced significant oxidative stress, decreased the expression of TJ proteins (occludin, ZO-1 and claudin 5), damaged the TJ structure, and exhibited enlarged gaps between TM-4 cells. Our results indicated that both TiO2-NPs crossed the BTB by disrupting actin-based adhesive junctions of TM-4 cells; however, apoptosis was not observed. Our results provide new insights into how TiO2-NPs cross the BTB.

RESEARCH OF RELIABILITY OF WORK AND MEANS OF DIAGNOSIS OF TECHNICAL CONDITION OF FUEL EQUIPMENT

The fuel system must provide an uninterrupted supply of fuel for the engine to operate in all possible modes of operation. Diesel fuel can be contaminated during transportation and subsequent storage, it can get dust from the air. Clogging of diesel fuel is also possible during engine operation, especially if the fuel tank is refueled at the same time as the technological operation. It is established in the article that mechanical impurities (mainly small particles of silica and alumina) harmful to the system get into diesel fuel. These particles have a very high hardness, equal to or even greater than the hardness of steels used in the manufacture of fuel equipment parts. Getting into the gap between the plunger and the sleeve of the fuel pump, such particles can get stuck in it and during the operation of the pump will erase the surface of the plunger and the sleeve. The jamming of the particles at the time of fuel supply under the action of pressure, the sleeve of the fuel pump is deformed. Larger particles can penetrate into this enlarged gap (it can be two to three times larger than the initial one, which is 2 to 3 μm). After cutting and pressure drop, the sleeve is tightened and clamps the particles that have penetrated into the gap. As a result, as the parts of the plunger pair wear, the radial gap between them increases, the leaks increase and the supply pressure decreases. For reliable operation of the engine constant and thorough cleaning of fuel is necessary therefore in fuel system for this purpose necessarily include fuel filters. Every third case of engine repair is associated with the failure of fuel equipment. Operation is often characterized by conditions when individual units, the engine as a whole work to partial disability without sufficient preventive measures.

Defects introduced by helium irradiation at different temperatures in W and W-5wt%Re alloy

W and W-5wt%Re alloy were irradiated by 50 keV helium ions at RT, 200 °C, 350 °C and 500 °C to investigate the influence of temperature on the microdefects and surface morphology in the sample. The microdefects in the subsurface region and the surface damage caused by irradiation were characterized by Doppler broadening spectroscopy (DBS) of slow positron beam, transmission electron microscope (TEM) and scanning electron microscopy (SEM), respectively. The results show that a large number of vacancy-type defects were produced after helium ions irradiation, especially at 500 °C, the vacancy-type defects of W alloy are higher than that of W-5wt%Re alloy, which indicated that Re restricted the behavior of vacancy-type defects in tungsten to some extent. The surface irradiation damage such as crystal gap enlargement, grain fell off and pores were observed at different irradiation temperatures. Compared with the coral-like structure observed in W, the circular objects and Hilly-gully structure were observed in W-5wt%Re alloy, and both of them increased and grew with the increase of irradiation temperature. It was speculated that the presence of Re led to the difference by analyzing the formation mechanism of the coral-like structure and the Hilly-gully structure.

The electronic and optical properties of the Fe,Co,Ni and Cu doped ZnO monolayer photocatalyst

The structural, electronic, and optical properties of optimized Fe, Co, Ni and Cu doped ZnO monolayer in a two-dimensional honeycomb structure are analyzed based on the density functional theory. The stability is testified by analysis of phonon dispersion curves. The variations of electronic and optical properties of Fe, Co, Ni and Cu doped ZnO monolayer under in-plane and out-of-plane strain effect are also investigated. The results show that tunable band structures and optical properties of Fe, Co, Ni and Cu doped ZnO monolayer, such as indirect–direct band gap transition, shrink and enlargement of band gaps can be achieved by applying strain, which indicates a possible new route for tailoring the electronic properties of ultrathin nanofilms through strain engineering.

Revealing the pattern and evolution of global green development between different income groups: A global meta-frontier by-production technology approach

A clear understanding of the overall pattern of global green development and the green development discrepancies among countries has a bearing on how each country participates in global environmental governance, which is more conducive to promoting the process of global green development in the future. This study constructed a global meta-frontier by-production technology model to evaluate the green total-factor productivity (GTFP), and studied the discrepancies of green development process and their growth sources for a sample of 163 countries (or regions) during the period 1990–2017. The results indicate that global GTFP witnessed remarkable growth before financial crisis occurred in 2007, but showed a slow growth trend after a decline during the financial crisis. The performance of GTFP exhibits significant regional disparity and dynamic change disparity. GTFP was the highest in high-income group, while lower than 0.55 in the upper middle-income and lower middle-income group in all years. Technological gap between regions was the principal factor leading to this result. Dynamically, among all countries covered in this study, there are twenty-five countries (or regions) experienced GTFP decline. Technological gap enlargement was the most important factor causing their GTFP decline, followed by the resource allocation inefficiency.

Mechanism of modified Yupingfeng naristillae in protecting the nasal mucosal epithelial barrier during allergic rhinitis

ObjectivesModified Yupingfeng naristillae (MYN) is an intranasal traditional Chinese medicinal preparation used to treat allergic rhinitis (AR) by repairing the nasal mucosal epithelial barrier. In this study, the mechanism underlying the effect of MYN was explored to provide a scientific reference for the development and application of new Chinese medicines. MethodsRat models of AR were randomly divided into the normal, AR and MYN groups. After 14 days of intervention, nasal mucosae were collected for histopathological examination. Quantitative real-time PCR was used to detect claudin-1 mRNA and zona occludens-1 (ZO-1) mRNA. Results(1) MYN could improve the swelling, shedding and gap enlargement of the nasal mucosal epithelium and promote the expression of claudin-1 mRNA (P<0.05). However, it did not show a significant regulatory effect on ZO-1 mRNA (P>0.05). (2) MYN could significantly inhibit inflammatory cell infiltration and eosinophil numbers in the nasal mucosa. ConclusionsMYN repairs the nasal mucosal epithelial barrier by upregulating the transcription of claudin-1 and reduces nasal inflammatory infiltration.

Silicon dots films deposited by spin-coating as a generated carrier addition layer of third generation photovoltaics

In this work, silicon ink composing of silicon powder and zinc oxide solution was formulated and spin-coated on quartz and n/p-Si substrates followed by drying the films under atmosphere at the temperature of 550 ​°C. The results showed that this top-addition layer could be the highly promising layer for photo-generating carriers in third-generation photovoltaics to enhance blue-light absorption. X-ray diffraction and scanning electron microscopy techniques were used to study the presence of silicon and zinc oxide nano-crystallites. The thin films consisting of different energy bandgap of Si nanocrystals (~100 ​nm) with narrow bandgap and spherical ZnO:Bi nanocrystal (~20 ​nm) with wider bandgap could be obtained from the evidence of bandgap enlargement. The band gaps of the thin films were tunable by adjusting silicon dots density in ZnO:Bi film. Energy upshift of light absorption edge depended on the silicon dots density was observed in the range 1.6–3.3 ​eV related band gap enlargement by Tauc plot. Under illumination, a high photocurrent gain of the thin film comprised of low Si dots density coated on a quartz substrate was about 103 times higher compared with its dark current. This result is agreeably explained in terms of its lower superficial trap states at the interface between silicon and zinc oxide matrix. The composite layer can be applied to a third-generation solar cell with the efficiency 1.50% higher than that with a typical crystalline-Si solar cell.

Investigation on substrate effect on physical characteristics of CuO- sprayed thin films suitable for photovoltaic application: Ag/ZnO:Sn (n)/CuO (p)/SnO2:F

ABSTRACT In this paper to compare the growth and optoelectronic properties of copper oxide (CuO) materials suitable for advanced application, CuO layers were synthesized on glass and SnO2:F). The X-ray diffraction analysis showed that CuO nanoparticles were formed in pure monoclinic structure where crystallite size decreases from 37.39 to 33.44 nm when the substrate changed, respectively, from glass to SnO2:F/glass. This crystallite size reduction was related to the energy band gap (Eg) enlargement from 1.455 to 1.525 eV due to the quantum confinement effect. Eg values were almost equal to the theoretical one for converting solar energy into electrical energy and CuO may be used as an absorber material in photovoltaic devices. Electrical characteristics were studied using the impedance spectroscopy technique at room temperature and confirmed by the Hall Effect measurements. CuO/SnO2:F/glass thin films have best electrical parameters and consequently the Ag/ZnO:Sn(n)/CuO(p)/SnO2:F photocell was elaborated and its J-V characteristics were analyzed.

Structural transition from marcasite to pyrite phase in FeSe2 under high pressure: a first-principles study

Based on density functional theory, first-principles simulations and calculations are carried out to study the structural stability and electronic properties of FeSe2 under high pressure. Present theoretical calculations not only reproduce successfully the lattice constants, bulk modulus, and indirect band gap of both the marcasite and pyrite phases at ambient conditions, but also predict a first-order phase transition from the marcasite to pyrite structure at 9 GPa under compression. Based on elastic constants and phonon spectra calculations and detailed analysis of the geometry structures, a possible mechanism of the structural transformation from marcasite to pyrite structure is presented. Furthermore, pressure-induced band gap enlargement is observed in the marcasite phase, which is benefit for the optical applications. By contrast, the band gap of the pyrite phase gradually decreases along with the compression, and finally closes up due to the broadening of bandwidths.