Position Of Barrier Research Articles

Electrostatic field calculation in air gaps with a transverse layer of dielectric barrier

Abstract In this paper the influence of transverse layer of dielectric barrier to the electrostatic field strength of air gaps using a hyperbolic needle-to-plane configuration is investigated. A three dimensional field problem is presented for simulating the electrostatic field in the air gap. This is achieved by using the charge simulation method. Group of ring charges are used to simulate the needle surface. A genetic algorithm is used for optimum number, location, dimension and value of simulating ring charges. The used needle tip radius was 8 μm while the gap spacing varied from 0.3 cm to 50 cm. The optimum barrier position minimizes the maximum electrostatic field and the electric energy density at the needle tip and consequently maximizes the required breakdown value. The simulation result has been compared with available experimental observations. A good agreement is found between the numerical and experimental data.

Capture Collisions of Polyynide Anions with Hydrogen Atoms: Effect of the Ion Dipole, Quadrupole, and Anisotropic Polarizability

Classical capture rate constants are calculated for a molecular ion with a dipole moment, quadrupole moment, and anisotropic polarizability colliding with a neutral polarizable atom. The free-energy effective potential method is used to average the potential energy over the interaction angle. Numerical methods are used to calculate the effective potential from the full anisotropic induction potential energy function, to solve for the position of the centrifugal barrier, and to determine the thermal rate constants. The capture collision model is applied to the reactions of polyynide anions, HC4−, HC6−, and HC8−, with atomic hydrogen, which are of interest in astrophysical environments, using calculated multipole moments and anisotropic polarizabilities. The dipole moment, quadrupole moment, and polarizability of the ion each contribute significantly toward the total predicted classical capture collision rates for these systems.

Systematic study of deformation effects on fusion cross-sections using various proximity potentials

Abstract The influence of static quadrupole and hexadecapole (positive & negative) deformation of targets are studied using eleven different versions of nuclear potentials. The height and position of the interaction barrier for the reactions induced by spherical projectile (16O) on the deformed targets such as 166Er, 154Sm and 176Yb have been estimated. It is found that the nucleus-nucleus potential strongly depends on the value of the deformation parameters and orientation of the target. The experimental fusion cross-section of the reactions 16O + 176Yb, 16O +166Er and 16O +154Sm are investigated by applyingWong’s formula using various parameterizations of the proximity potential as well as an assessment of the results of a multi-dimensional barrier penetration model (BPM). The fusion cross-sections by Prox 77, Prox 88, Prox 00, Prox 00DP, Denisov DP, Bass 80, CW 76 and AW 95 potentials are found to be better than the rest in comparison to experimental data.

Experimental Investigations and Ageing Studies on Effects of Insulating Barriers in Transformer Oil during High Frequency High Voltage Transients in Inhomogeneous Field

Insulating barriers utilized in complex high voltage insulation systems has been exploited widely by manufacturers of power apparatus. Barriers have found utility in a variety of power apparatus for protection against direct lightning strokes, as an interface at the boundaries of composite insulation materials etc. Though investigations have been carried out by researchers on the breakdown characteristics, barrier position in the gap, influence of space charge etc these characteristics have been analyzed based on aspects pertinent to classical testing procedures only. Advent of high speed switching devices in power systems provides avenues to investigate the effect of insulation performance due to High Frequency High Voltage (HFHV) also. Further, uncharacteristic failures in oil filled distribution transformers have been reported indicated fast transients as the major cause for failures which was not revealed during classical laboratory testing. This research focuses on the influence and effects of solid insulating barriers placed in transformer oil due to HFHV in inhomogeneous fields. Test cell arrangement has been fabricated for carrying out experimental investigations to adhere international standards. Exhaustive experimentation has been performed to infer the influence of the position of barrier, nature of field and breakdown voltage, erosion characteristics of the barrier at an appropriate range of frequencies. A detailed comparison between HFHV and classical power frequency voltage has been carried out. The nature of ionization at the barrier interface and the subsequent increase in the breakdown voltage as explained by Double Electric Layer (DEL) theory has been cross validated. In addition, a study has also been carried out to assess and characterize the ageing of oil based on Dissolved Gas Analysis (DGA) analysis using Weibull distribution.

Systematic analysis of fusion barrier heights and positions for proton projectiles using the single folding model

The nuclear potentials between protons and different target nuclei are calculated by using the single folding model with the density-dependent nucleon-nucleon interaction. The fusion barrier heights and positions for proton projectiles fusing with different target nuclei with masses from 51 amu to 139 amu are systematically shown, with charge numbers and root-mean-square radii of the interacting nuclei. The parameterized formulas for the fusion barrier height and position are obtained for proton projectile fusing with the different nuclei. The calculated results of parameterized formulas are compared to empirical values, as well as those of the proximity potential and Akyüz-Winther (AW) potential. It is shown that the calculated results agree perfectly with theirs. The parameterized formulas can reproduce the exact barrier heights and positions for proton fusion systems.

Defective Barrier on Voltage Optimization for Small Airgap

Aim: To investigate the effect of defective barrier on the optimum breakdown voltage, using positive and negative needle electrodes in an air medium of 10cm gap distance. Methodology: The barriers for the tests were placed at 2.5cm from the point electrode for each test. The defective barriers were created by having holes of 6mm, 8mm, 12mm and 20mm diameter at the centre of the barrier. For each barrier position the breakdown test for positive and negative polarity for needle electrodes were carried out. Also, tests were carried out with non defective barrier and with point-plane airgap (without barrier). Result: From the test without barrier the negative point electrode offered higher breakdown voltage (1.8 times), than the positive point. When with plain barrier the positive point was optimized to 1.6 times, while the negative point was lowered. The optimum breakdown voltage decreased gradually as the hole diameter increased and at 20mm hole diameter the effect was like the plain barrier. Conclusion: From the results, optimization is only effective with positive point’s electrode and it endures even with small opening within the ionization zone. It is necessary to check this in practical situations because the specified optimum voltage of an equipment may be lowered.

Relative importance of energy dependent diffuseness parameter and barrier position in the analysis of fusion excitation function data

We have investigated the relative importance of the energy dependence of diffuseness parameter and barrier position in the description of the fusion excitation function data of some heavy ion systems in near barrier energy region. The effects of the energy dependent diffuseness parameter are found to be much more prominent in comparison to those of barrier position.

Studying the mechanism of CD47-SIRPα interactions on red blood cells by single molecule force spectroscopy.

The interaction forces and binding kinetics between SIRPα and CD47 were investigated by single-molecule force spectroscopy (SMFS) on both fresh and experimentally aged human red blood cells (hRBCs). We found that CD47 experienced a conformation change after oxidation, which influenced the interaction force and the position of the energy barrier between SIRPα and CD47. Our results are significant for understanding the mechanism of phagocytosis of red blood cells at the single molecule level.

The effect of interface phonons on operating electron states in three-barrier resonant tunneling structure as an active region of quantum cascade detector

The Hamiltonian of electrons interacting with interface phonons in three-barrier resonant tunneling structure is established using the first principles within the models of effective mass and polarization continuum. Using the Green's functions method, the temperature shifts and decay rates of operating electron states are calculated depending on geometric design of three-barrier nano-structure GaAs/Al$_{x}$Ga$_{1-x}$As which is an active region of quantum cascade detector. It is established that independently of the temperature, the energy of quantum transition during the process of electromagnetic field absorption is a nonlinear weakly varying function of the position of the inner barrier with respect to the outer barriers of the structure.

Water dissociation on Ni(100) and Ni(111): Effect of surface temperature on reactivity

Water adsorption and dissociation on Ni(100) and Ni(111) surfaces are studied using density functional theory calculations. Water adsorbs on top site on both the surfaces, while H and OH adsorb on four fold hollow and three fold hollow (fcc) sites on Ni(100) and Ni(111), respectively. Transition states (TS) on both surfaces are identified using climbing image-nudged elastic band method. It is found that the barrier to dissociation on Ni(100) surface is slightly lower than that on Ni(111) surface. Dissociation on both the surfaces is exothermic, while the exothermicity on Ni(100) is large. To study the effect of lattice motion on the energy barrier, TS calculations are performed for various values of Q (lattice atom coordinate along the surface normal) and the change in the barrier height and position is determined. Calculations show that the energy barrier to reaction decreases with increasing Q and increases with decreasing Q on both the surfaces. Dissociation probability values at different surface temperatures are computed using semi-classical approximation. Results show that the influence of surface temperature on dissociation probability on the Ni(100) is significantly larger compared to that of Ni(111). Moreover, on Ni(100), a dramatic shift in energy barrier to lower incident energy values is observed with increasing surface temperature, while the shift is smaller in the case of Ni(111).

Effect of deformation and orientation on interaction barrier and fusion cross-sections using various proximity potentials

Abstract The effect of deformation and orientation on barrier height and barrier position is studied using different types of proximity potentials for some 52 colliding nuclei with mass asymmetry parameter in range of 0 to 0.96. Various proximity potentials like Prox 77, Prox 88, Prox 00, Bass 80 and Denisov DP are used to extract barrier characteristics. These potentials cover a wide range of barrier and have different isospin and asymmetry dependence. With the inclusion of deformations, the barrier height and barrier position gets modified along with a significant change in the curvature. In order to study the possible effect of these deformation and orientation dependent proximity potentials, application is made in the framework of Wong formula to O-, Ca- and Ni-based reactions in medium mass region in reference to available data on fusion cross-sections at around and above the Coulomb barrier energies. For 16 O- and 48 Ca-based reactions, Prox 77 gives better comparison with experimental data as compared to other potentials around the Coulomb barrier energies whereas for 64 Ni-based reactions Prox 88 seems close to the experimental data. At energies above the Coulomb barrier Bass 80 and Denisov DP compete with each other. Angular dependence of cross-section is also studied. It is observed that deformation and orientation degree of freedom plays a significant role in reaction dynamics.

Remediation of an aquifer polluted with dissolved tetrachloroethylene by an array of wells filled with activated carbon

In this work, an array of deep passive wells filled with activated carbon, namely a Discontinuous Permeable Adsorptive Barrier (PAB-D), has been proposed for the remediation of an aquifer contaminated by tetrachloroethylene (PCE). The dynamics of the aquifer in the particular PAB-D configuration chosen, including the contaminant transport in the aquifer and the adsorption onto the barrier material, has been accurately performed by means of a computer code which allows describing all the phenomena occurring in the aquifer, simultaneously.A PAB-D design procedure is presented and the main dimensions of the barrier (number and position of passive wells) have been evaluated. Numerical simulations have been carried out over a long time span to follow the contaminant plume and to assess the effectiveness of the remediation method proposed. The model results show that this PAB-D design allows for a complete remediation of the aquifer under a natural hydraulic gradient, the PCE concentrations flowing out of the barrier being always lower than the corresponding Italian regulation limit.Finally, the results have been compared with those obtained for the design of a more traditional continuous barrier (PAB-C) for the same remediation process.

Formation and preservation of an overstepped segmented lagoon complex on a high‐energy continental shelf

AbstractThe duration of shoreline occupation at a given sea‐level, coastal response to sea‐level change and the controls on preservation of various shoreline elements can be recognized by detailed examination of submerged shorelines on the continental shelf. Using bathymetric and seismic observations, this article documents the evolution and preservation of an incised valley and lithified barrier complex between −65 m and −50 m mean sea‐level on a wave‐dominated continental shelf. The barrier complex is preserved as a series of aeolianite or beachrock ridges backed by laterally extensive back‐barrier sediments. The ridges include prograded cuspate lagoonal shoreline features similar to those found in contemporary lagoons. The incised valley trends shore‐parallel behind the barrier complex and records an early phase of valley filling, followed by a phase of extensive lagoonal sedimentation beyond the margins of the incised bedrock valley. Sea‐level stability at the outer barrier position (ca −65 m) enabled accumulation of a substantial coastal barrier that remained intact during a phase of subsequent slow sea‐level rise to −58 m when the lagoon formed. These lagoonal sediments are stripped seawards by bay ravinement processes which caused the formation of several prograded marginal cuspate features. An abrupt rise in sea‐level to −40 m, correlated with melt‐water pulse 1B, enabled the preservation of thick lagoonal sediments at the top of the incised valley fill and preservation on the sea bed of the cemented core of the barriers. This situation is unique to subtropical coastlines where early diagenesis is possible. The overlying sandy sediment from the uncemented upper portion of the barriers is dispersed by ravinement, partly burying the ridges and protecting the underlying sediments. The high degree of barrier or shoreline preservation is attributed to rapid overstepping of the shoreline, early cementation in favourable climatic conditions and the protection of the barrier cores by sand sheet draping.

New methods for the condition monitoring of level crossings

Level crossings represent a high risk for railway systems. This paper demonstrates the potential to improve maintenance management through the use of intelligent condition monitoring coupled with reliability centred maintenance (RCM). RCM combines advanced electronics, control, computing and communication technologies to address the multiple objectives of cost effectiveness, improved quality, reliability and services. RCM collects digital and analogue signals utilising distributed transducers connected to either point-to-point or digital bus communication links. Assets in many industries use data logging capable of providing post-failure diagnostic support, but to date little use has been made of combined qualitative and quantitative fault detection techniques. The research takes the hydraulic railway level crossing barrier (LCB) system as a case study and develops a generic strategy for failure analysis, data acquisition and incipient fault detection. For each barrier the hydraulic characteristics, the motor's current and voltage, hydraulic pressure and the barrier's position are acquired. In order to acquire the data at a central point efficiently, without errors, a distributed single-cable Fieldbus is utilised. This allows the connection of all sensors through the project's proprietary communication nodes to a high-speed bus. The system developed in this paper for the condition monitoring described above detects faults by means of comparing what can be considered a ‘normal’ or ‘expected’ shape of a signal with respect to the actual shape observed as new data become available. ARIMA (autoregressive integrated moving average) models were employed for detecting faults. The statistical tests known as Jarque–Bera and Ljung–Box have been considered for testing the model.

Radiative lifetime of barbell excitons in semiparabolic double quantum wells under intense laser fields

The binding energy and optical properties of barbell excitons in GaAs–Ga1−xAlxAs semiparabolic double quantum wells under intense laser fields are investigated. Calculations are performed within the effective mass and envelope-function approximations, including the conduction band nonparabolicity. The dependence of the binding energy, oscillator strength and exciton absorption spectrum on the laser field in symmetric and asymmetric quantum wells is studied by using a finite difference method. It is shown that the exciton radiative lifetime can be tuned to a large extent by a proper choice of the structure design (double well size, middle barrier position and its thickness) as well as by varying the laser field intensity.

The Influence of the Dependence of Surface Energy Coefficient to Temperature in the Proximity Model

We introduce a new surface energy coefficient in proximity formalism, which is dependent on temperature, and apply it to a systematic study of barrier height and position. This proximity model can effectively predict the barrier heights and positions, as well as the fusion cross sections, over a wide range of incident energies, especially in light-heavy nuclei interaction.

Inter-ELM pedestal evolution on MAST and impact of resonant magnetic perturbations

The peak pressure gradient in the pedestal (dPe/dψ) on MAST varies little between edge localized modes (ELMs), although it varies between discharges due factors such as gas fuelling and plasma current. The pressure pedestal width in flux space on the high-field side (HFS), both during the inter-ELM period and amongst different plasma discharges is consistent with a scaling of . In flux space very similar dPe/dψ and Δpe are observed on the HFS and low-field side (LFS) in single null configuration. This symmetry is broken by the application of resonant magnetic perturbations (RMPs). During ELM mitigation by application of RMPs changes in the edge transport barrier position and width are observed. These changes are dependent on the intensity of the RMP and on the toroidal location with respect to the RMP phase. An outward displacement of up to 30 mm and increase in the edge pedestal width of up to 50% with respect to the coils case off are observed. Increased particle transport causes a decrease in ne,ped, and hence Pe,ped, as is observed on other devices. The combination of an increase in Δpe on the LFS and decrease in Pe,ped results in significantly reduced LFS dPe/dψ when these perturbations are applied to the plasma edge. A decrease in dPe/dψ on the HFS is also observed due to RMP; however, this decrease is caused solely by the Pe,ped decrease whilst no expansion of Δpe on the HFS is observed.

Systematic study of Coulomb barrier of reactions induced by loosely bound projectiles using proximity potential

Abstract Using eight different versions of the nuclear potential, we have calculated the height and position of the Coulomb barrier for reactions induced by loosely bound projectiles, 6Li, 7Li and 9Be. A total of 13 reactions have been studied and by comparing the results with the empirical values, we found the prediction of all the potentials quite satisfactory as they could reproduce the empirical values within 5% on average. The potentials Bass 80, BW 91 and AW 95 can determine the experimental barrier within 2 % on average. For the reaction 6Li + 152Sm the deviations from the empirical values are unusually large. On applying the correction of the Coulomb potential for the deformed target 152Sm the new values obtained are found to be closer to the empirical values. Applying Wongʼs formula the fusion cross-sections for four reactions are compared with the results of single BPM. The fittings of the fusion cross-section for the potentials of CW 76, BW 91 and Bass 80 are better than the rest.

A case study on acoustic performance and construction costs of noise barriers

In the study, the barriers used for reducing traffic noise are being examined in means of performance and construction cost. First a noise prediction is made in the sample highway under certain traffic conditions in order to determine the noise barrier requirement and the results are confirmed by measurement. According to the noise prediction equations used in Turkey, Germany and Canada, the effects of heavy vehicle ratio, average traffic flow speed and hourly total vehicle quantity change on noise level and barrier requirement are examined, so assessment can be made for highways having different traffic specifications than the sample highway. In the continuation of the study, the working principle of noise barriers and effects of barrier position and height on reducing noise are researched in order to determine the construction costs of barriers in Turkey and Canada at different heights and made from different materials. Key words: Highway, noise barrier, noise prediction, performance, construction cost.

Interaction spatial barrier distributions for the proton-halo system 8B+58Ni

Radial barrier distributions for the proton-halo system 8B+58Ni are obtained by the use of Woods-Saxon polarization potentials calculated from a fit to elastic scattering angular distribution data. The strength, diffuseness and reduced radii of the polarization potentials, besides fitting the data, are such that reproduce the barrier height and position as extracted from a Wong's fit to the universal behavior of reduced interaction cross sections for halo systems. It is found that, for the proton-halo system 8B+58Ni, the interaction barrier height VI and the interaction barrier radius RI result correspondingly lower and larger than the Coulomb nominal barrier height VB and barrier position RB as expected from Barrier Penetration Models and double folding density dependent interactions such as the São Paulo Potential. It is also shown that, the determined energy dependent polarization potentials, besides satisfying the dispersion relation, present a behavior consistent with the Breakup Threshold Anomaly. Keywords. Nuclear Reactions, weakly bound nuclei, threshold anomaly.