Single Barrier Research Articles

Подавление волноводной рекомбинации за счет использования парных асимметричных барьеров в лазерных гетероструктурах

AbstractA semiconductor-laser design is proposed in which parasitic recombination in the waveguide region is suppressed by means of double asymmetric barriers adjacent to the active region. Double asymmetric barriers block the undesirable transport of one type of charge carrier while allowing the transport of the other type of carrier. The spacer in the double asymmetric barrier can serve to compensate the elastic strain introduced by the barrier layers as well as to control the energy spectrum of charge carriers and, thus, the transmission coefficient. By the example of a laser with Al_0.2Ga_0.8As waveguide layers, it is shown that the design with double asymmetric barriers makes it possible to suppress undesirable electron transport by a factor of 4 in comparison to the design using single asymmetric barriers.

The Study of Sand-blocking Characteristic and Flow Field Simulation Analysis of the Ring-shaped Sand-barrier

Aiming at the complexity of wind direction and irregular sand flow in a desert area, a combinatorial ring-shaped sand barrier is used. Stokes law of inertia force and centrifugal force and gravity sedimentation are used. With CFD fluid software Fluent, laminar flow model Equation and κ-ε turbulence model, the wind speed of the sand in the sand-gas-solid two-phase flow passing through the circular sand barrier is studied at different distances and different altitudes after the sand barrier, the wind speeds before and after the sand barrier are compared and analyzed . The mean minimum wind speed behind the single sand barrier was reduced by 32.5% -49.4% compared with that before the sand barrier. The wind speed at different height of the composite sand barrier was reduced by 30% -58.3% compared with the inlet wind speed, which solved the problem of irregular wind and sand control in the desert wind direction.

Investigation of sweep efficiency in surfactant-polymer flooding with an existing barrier between wells by using CMG (STARS) simulator

The effects of a single barrier existing between two wells on the chemical flooding are investigated with the assumed various shapes and sizes of the barrier by 3D numerical studies in STARS (CMG) software. The same injection schemes of surfactant and surfactant-polymer (SP) flooding are utilised for all barrier cases and the no barrier case. The simulated results show that in surfactant flooding, the small type barrier might give the positive effects on the flooding performances compared to no barrier case and bigger barrier cases, while the existence of a barrier completely influences negatively to the sweep efficiencies in SP flooding. However, for all barrier cases, the combined surfactant-polymer injection scheme always gives higher oil production than using single surfactant injection although the obstructive level by a barrier is higher in SP flooding. The changes of well configurations in terms of well locations and well patterns point out the unsuitable of installing horizontal wells in any case of barrier compared to vertical wells, instead the vertical injector should be installed closer to barrier than the vertical producer for achieving the better flooding performances. [Received: May 12, 2016; Accepted: October 21, 2016]

Structural-elastic determination of the force-dependent transition rate of biomolecules.

The force-dependent unfolding/refolding of protein domains and ligand-receptor association/dissociation are crucial for mechanosensitive functions, while many aspects of how force affects the transition rate still remain poorly understood. Here, we report a new analytical expression of the force-dependent rate of molecules for transitions overcoming a single barrier. Unlike previous models derived in the framework of Kramers theory that requires a presumed one-dimensional free energy landscape, our model is derived based on the structural-elastic properties of molecules which are not restricted by the shape and dimensionality of the underlying free energy landscape. Importantly, the parameters of this model provide direct information on the structural-elastic features of the molecules between their transition and initial states. We demonstrate the applications of this model by applying it to explain force-dependent transition kinetics for several molecules and predict the structural-elastic properties of the transition states of these molecules.

An empirical formula for coefficient of permeability and its application in theoretical wave-perforated structure interaction problems

The permeability characteristics of homogenous perforated plate have been estimated using measured pressure drops and velocities through pipe flow experiments. An empirical formula for coefficient of permeability is proposed for various values of porosity of plates, which is further used in a theoretical model to estimate the hydrodynamic characteristics of perforated plate, in terms of wave reflection and transmission. The empirical formula-based theoretical estimation of reflection and transmission coefficients is then validated with the experimental results obtained from wave tank tests, for single and double perforated vertical barriers.

Active innovation resistance: An empirical study on functional and psychological barriers to innovation adoption in different contexts

Active innovation resistance is considered to be a main driver of innovation rejection, and traditionally related to five product-specific adoption barriers driving this negative attitude formation. While recent literature introduced a more comprehensive typology encompassing nine functional and eight psychological barriers driving active innovation resistance, an empirical validation of this framework is still missing. In order to close this research gap, we employed a two-study design. First, we conducted a qualitative study to empirically evaluate whether the typology including 17 adoption barriers encompasses all possible negative, product driven reactions of consumers within new product evaluations. Second, we used a quantitative large-scale study to assess the relative importance of each single product-specific adoption barrier within new product evaluations in the context of product and mobile service innovation. Both studies confirm that innovations are commonly rejected owing to these 17 product-specific adoption barriers. However, our results also highlight that functional and psychological barriers vary in their effect on adoption intention depending on whether a new product or service gets evaluated. This study provides first empirical evidence in favor of applying a more comprehensive typology of product-specific barriers when assessing effects of active innovation resistance on consumers' adoption behavior in future research.

Spin-polarized charge transport in HgTe/CdTe quantum well topological insulator under a ferromagnetic metal strip

Electron tunneling through a single magnetic barrier in a HgTe topological insulator has been theoretically investigated. We find that the perpendicular magnetic field would not lead to spin-flip of the edge states due to the conservation of the angular moment. By tuning the magnetic field and the Fermi energy, the edge channels can be transited from switch-on states to switch-off states and the current from unpolarized states can be filtered to fully spin polarized states. These features offer us an efficient way to control charge/spin transport in a HgTe/CdTe quantum well, and pave a way to construct the nanoelectronic devices utilizing the topological edge states.

Potential barrier-induced dynamics of finite energy Airy beams in fractional Schrödinger equation

The dynamics of Airy beams modeled by the fractional Schrodinger equation (FSE) with the potential barrier are numerically investigated. Adjusting the Levy index provides a convenient way to control the diffraction of Airy beams which presents the non-diffraction and splitting property. It has been found that the total reflection of beams occurs when the depth of the single potential barrier exceeds the threshold, and that the number of reflected waves is influenced by the Levy index and the location of potential barrier. However, the periodic self-imaging phenomenon of Airy beams is shown under a symmetric potential barrier when the Levy index is equal to one, and the self-imaging period of the asymmetric Airy beams is analytically demonstrated and is as twice as that of symmetric Gaussian beams, moreover, the chaoticon of light field is formed during propagation as the Levy index increases. All the properties of Airy beams modeled by FSE confirm the potential application in optical manipulation.

Gender-Related Barriers to Service Access and uptake in nutrition programmes

Background
 Approximately 17 million children under five years suffer from Severe Acute Malnutrition (SAM). Although the most frequent barriers to service access in Community Management of Acute Malnutrition (CMAM) programmes have already been identified, there has been no analysis of the relationship between gender-related barriers and access to treatment.
 Approach
 The main objective is to review the key gender barriers to service access and uptake of treatment in CMAM programmes based on evidence gathered from coverage assessments carried out in Sub-Saharan Africa and Asia. A retrospective review of twenty-five coverage assessments was undertaken in 2013.
 Main findings
 Gender-related barriers were detected in 24 of the 25 coverage assessments. The main barriers detected were related to traditional gender roles: Women busy with duties (27.8%) followed by men control household expenditures and decision-making in the family (16.7%) and women sick (15.3%).
 Principal conclusions
 
 Gender-related barriers are present in the majority of the nutrition programs, so if the aim is universal coverage, gender should be considered during the coverage assessment
 Initiatives contributing to gender equality would contribute to overcoming coverage barriers in CMAM programmes
 The traditional use of the CMAM model considered gender with regards to the impact that the intervention could have on gender relations. However gender is now shown to also be a key factor contributing to poor nutrition.
 Further research and assessments should include Gender Based Violence as a single barrier, or as a component of other barriers

Compositional Engineering To Improve the Stability of Lead Halide Perovskites: A Comparative Study of Cationic and Anionic Dopants

The instability of perovskite solar cells is the single greatest barrier to their commercialization. While a number of studies have now looked at the effect of perovskite composition on device stability, many of these have examined only a single compositional variable. With many of these studies having been carried out under different environmental conditions, and still others lacking environmental controls entirely, it is often difficult to compare the relative effect of various cationic or anionic dopants. To address this knowledge gap, we fabricated CH3NH3PbI3-based solar cells where either the methylammonium or iodide ions were replaced with 20 mol % of a dopant ion (ethylammonium, formamidinium, bromide, or chloride). We then assessed their stability either in a controlled 85% relative humidity environment or under 1 sun illumination in air; both conditions have been previously shown to rapidly decompose CH3NH3PbI3. Of the dopants studied, the formamidinium cations imparted the best moisture resistan...

Monodisperse measurement of the biotin-streptavidin interaction strength in a well-defined pulling geometry.

The widely used interaction of the homotetramer streptavidin with the small molecule biotin has been intensively studied by force spectroscopy and has become a model system for receptor ligand interaction. However, streptavidin’s tetravalency results in diverse force propagation pathways through the different binding interfaces. This multiplicity gives rise to polydisperse force spectroscopy data. Here, we present an engineered monovalent streptavidin tetramer with a single cysteine in its functional subunit that allows for site-specific immobilization of the molecule, orthogonal to biotin binding. Functionality of streptavidin and its binding properties for biotin remain unaffected. We thus created a stable and reliable molecular anchor with a unique high-affinity binding site for biotinylated molecules or nanoparticles, which we expect to be useful for many single-molecule applications. To characterize the mechanical properties of the bond between biotin and our monovalent streptavidin, we performed force spectroscopy experiments using an atomic force microscope. We were able to conduct measurements at the single-molecule level with 1:1-stoichiometry and a well-defined geometry, in which force exclusively propagates through a single subunit of the streptavidin tetramer. For different force loading rates, we obtained narrow force distributions of the bond rupture forces ranging from 200 pN at 1,500 pN/s to 230 pN at 110,000 pN/s. The data are in very good agreement with the standard Bell-Evans model with a single potential barrier at Δx0 = 0.38 nm and a zero-force off-rate koff,0 in the 10−6 s-1 range.

Efficacy of Tantalum Tungsten Alloys for Diffusion Barrier Applications

Traditionally either Niobium, Tantalum or a combination of both have been used as diffusion barriers in Nb3Sn Multi-filament wire. Vanadium has also been used successfully but the ultimate RRR of the copper is limited unless an external shell of Niobium is included. Niobium is preferred over Tantalum when alternating current losses are not an issue as the Niobium will react to form Nb3Sn. Pure Tantalum tends to deform irregularly requiring extra starting thickness to ensure good barrier qualities. Our evaluations showed Tantalum lightly alloyed with 3 wt% Tungsten is compatible with the wire drawing process while deforming as well as or better than pure Niobium. Ta3wt%W has been processed as a single barrier and as a distributed barrier to fine dimensions. In addition, the higher modulus and strength of the Tantalum Tungsten alloy improves the overall tensile properties of the wire.

Mid-wavelength infrared unipolar nBp superlattice photodetector

We report a Mid-Wavelength Infrared (MWIR) barrier photodetector based on the InAs/GaSb/AlSb type-II superlattice (T2SL) material system. The nBp design consists of a single unipolar barrier (InAs/AlSb SL) placed between a 4 µm thick p-doped absorber (InAs/GaSb SL) and an n-type contact layer (InAs/GaSb SL). At 80 K, the device exhibited a 50% cut-off wavelength of 5 µm, was fully turned-ON at zero bias and the measured QE was 50% (front side illumination with no AR coating) at 4.5 µm with a dark current density of 4.7 × 10−6 A/cm2 at Vb = 50 mV. At 150 K and Vb = 50 mV, the 50% cut-off wavelength increased to 5.3 µm, and the QE was 54% at 4.5 µm with a dark current of 5.0 × 10−4 A/cm2.

Interaction between oblique waves and multiple bottom-standing flexible porous barriers near a rigid wall

The interaction between oblique surface waves and multiple bottom-standing flexible porous barriers under the combined effects of a neighboring rigid vertical wall and a step of arbitrary profile on the bottom is investigated. The problem is analyzed under the assumptions of small-amplitude water waves and structural response. The solutions are found using the methods of least-squares approximation, eigenfunction expansion and multi-mode approximation associated with the modified mild-slope equation. To keep the barriers at a desired position of interest, clamped-free or clamped-moored edge conditions are considered. Effects of various wave and structural parameters are studied for single, double and multiple barriers by looking into the reflection coefficient, wave force exerted on the rigid wall, free-surface elevations, and plate deflection of the barriers. The model is validated by comparing with results available in the literature for the special case of wave interaction with single and double rigid porous barriers near a rigid wall in the presence of a vertical step. The study reveals that the presence of multiple flexible porous barriers may effectively reduce the wave reflection and wave force exerted on the rigid wall. Further, full and nearly zero wave reflection can be found in the case of single and/or multiple barriers.

Concerted-asynchronous reaction path of the excited-state double proton transfer in the 7-azaindole homodimer and 6H-indolo[2,3-b]quinoline/7-azaindole heterodimer

Reaction path of the excited-state double proton transfer (ESDPT) in the homodimer of 7-azaindole (7AI2 homodimer) and heterodimer of 6H-indolo[2,3-b]quinoline and 7-azaindole (6HIQ-7AI heterodimer) is computationally studied by means of intrinsic reaction coordinate (IRC) calculations. The IRC path determined at the TDDFT level predicts the concerted-asynchronous mechanism for the ESDPT in 6HIQ-7AI as well as in 7AI2, where the N–H⋯N hydrogen bonds exhibit asymmetric structures along the reaction path with a single energy barrier. The IRC calculations at the CIS level, however, exhibits a local minimum for single-proton-transferred intermediate, suggesting the stepwise mechanism. Single-point energy calculations at the RI-CC2 level reproduce the TDDFT results, but do not the CIS results. On the basis of potential-energy profiles calculated against intermolecular distance, the discrepancy between the TDDFT and CIS methods is likely attributed to the underestimation of intermolecular interaction energy in the latter method due to the lack of dynamical electron correlation.

Feasibility of ambient vibration screening by periodic geofoam-filled trenches

Single in-filled trench barriers have been widely investigated to mitigate ground vibrations. However, investigations on the application of multiple rows of in-filled trenches are very limited. This paper investigates the attenuation of surface waves by periodic geofoam-filled trenches in single-phased elastic soil deposits. First, a field test of train-induced ground vibration is carried out, from which the corresponding acceleration record and main frequency are obtained. Second, attenuation zones for surface waves in periodic geofoam-filled trenches are studied based on the periodic theory of solid-state physics. Finally, a numerical model for ambient vibration isolation is built under the conditions of plane strain, and the responses are performed both in frequency domain and in time domain by finite element method. The screening effectiveness of the proposed wave barrier is studied by conducting an extensive dimensionless parameter investigation. Results show that the proposed periodic geofoam-filled trenches can attenuate surface waves effectively, when the frequencies of surface waves are located in the attenuation zones. The present study provides a new concept for designing periodic in-filled trench barriers to mitigate ground vibrations.

Density-matrix renormalization group method for the conductance of one-dimensional correlated systems using the Kubo formula

We improve the density-matrix renormalization group (DMRG) evaluation of the Kubo formula for the zero-temperature linear conductance of one-dimensional correlated systems.The dynamical DMRG is used to compute the linear response of a finite system to an applied AC source-drain voltage, then the low-frequency finite-system response is extrapolated to the thermodynamic limit to obtain the DC conductance of an infinite system. The method is demonstrated on the one-dimensional spinless fermion model at half filling. Our method is able to replicate several predictions of the Luttinger liquid theory such as the renormalization of the conductance in an homogeneous conductor, the universal effects of a single barrier, and the resonant tunneling through a double barrier.

Optimal Design of Wound Field Synchronous Reluctance Machines to Improve Torque by Increasing the Saliency Ratio

This paper proposes an optimal design for a salient pole wound field synchronous machine (WFSM) with a single flux barrier to improve torque performance and obtain a wide operating range, simultaneously. The proposed WFSM motor can effectively decrease $q$ -axis inductance to improve the saliency ratio ( $X_{d}/X_{q})$ and increase the reluctance torque. To maximize the saliency ratio and improve the torque characteristics, the single flux barrier is optimized, considering the magnetic saturation that uses Kriging method based on Latin hypercube sampling and a genetic algorithm. The 2-D finite element analysis results by the aid of JMAG-Designer shows that the saliency ratio $X_{d}/X_{q}$ , the reluctance torque, and the total torque of the optimal model are increased by 9.27%, 20.45%, and 6.17%, respectively, compared with those of the basic model. Finally, the performance of the optimal motor is verified through an experimental test, which indicates good agreement with the simulation results.

Intestinal Barrier Interactions with Specialized CD8 T Cells.

The trillions of microorganisms that reside in the gastrointestinal tract, essential for nutrient absorption, are kept under control by a single cell barrier and large amounts of immune cells. Intestinal epithelial cells (IECs) are critical in establishing an environment supporting microbial colonization and immunological tolerance. A large population of CD8+ T cells is in direct and constant contact with the IECs and the intraepithelial lymphocytes (IELs). Due to their location, at the interphase of the intestinal lumen and external environment and the host tissues, they seem ideally positioned to balance immune tolerance and protection to preserve the fragile intestinal barrier from invasion as well as immunopathology. IELs are a heterogeneous population, with a large innate-like contribution of unknown specificity, intercalated with antigen-specific tissue-resident memory T cells. In this review, we provide a comprehensive overview of IEL physiology and how they interact with the IECs and contribute to immune surveillance to preserve intestinal homeostasis and host-microbial relationships.

Structural insight into a partially unfolded state preceding aggregation in an intracellular lipid-binding protein.

Human ileal bile acid-binding protein (I-BABP) has a key role in the intracellular transport and metabolic targeting of bile salts. Similar to other members of the family of intracellular lipid-binding proteins (iLBPs), disorder-order transitions and local unfolding processes are thought to mediate ligand entry and release in human I-BABP. To gain insight into the stability of various protein regions, the temperature response of human I-BABP was investigated using NMR, CD and fluorescence spectroscopy, as well as molecular dynamics (MD) simulations. A joint analysis of NMR thermal melting and relaxation dispersion data indicates a complex pattern of internal dynamics with a dominating single barrier and a likely presence of rapidly exchanging conformational substates on both sides of the barrier. Moreover, our residue-specific analysis uncovers a partially unfolded U* state in which part of the helical region with three proximate β-strands contains a substantial amount of residual structure, whereas several segments of the C-terminal half exhibit a high susceptibility to temperature elevation. Cluster analysis of atomic temperature responses indicates a thermodynamic coupling between distant protein sites including the bottom of the β-barrel, the E-F region and part of the helical cap. MD simulations up to 1μs show correlated motions in the same protein regions and together with the NMR data suggest a role for the highly dynamic D-E turn and E-F region in the initiation of unfolding. The response of human I-BABP to temperature elevation is discussed in the context of the folding/unfolding behaviour of different members of the iLBP family.