Barrier Thickness Research Articles

The effect of flexible obstacles with different thicknesses on explosion propagation of premixed methane-air in a confined duct

The effect of flexible obstacles with varying thicknesses on the explosion characteristics of combustible gas in a simulated confined duct (cross section 80 mm × 80 mm, length 3 m) was experimentally investigated, aiming to reduce the huge losses caused by gas explosion accidents in the process industries and mining industries. In this paper, plant fiber membranes with an opening area of 0 and thicknesses of 0.105 mm, 0.210 mm, 0.315 mm, 0.420 mm, 0.525 mm, and 0.630 mm were selected as flexible obstacles. The thickness of the flexible obstacle determines the strength of its compressive resistance. The characteristics of overpressure and flame during methane explosions are analyzed and conclusions are drawn. Results indicate that several shock wave reflection processes occur before the diaphragm ruptures, resulting in turbulent flames. In addition, the explosion wave generated numerous shock reflections during the rupture process of the diaphragm, which was gradually discharged downstream of the pipe by ejection as the pressure wave accumulated in front of the diaphragm. It should be noted that the thickness of the flexible obstacle determines the pressure accumulation in front of the membrane. Generally, the thinner the flexible obstacle, the less intense the turbulent flame is induced by the flexible obstacle, decreasing the contact area between the unignited gas downstream of the pipeline and the turbulent flame area. In conclusion, with an increase in the thickness of the flexible barrier, it exhibits a mechanism of initially suppressing and subsequently enhancing the impact on methane explosions. The increase of the thickness of the flexible obstacle motivates the flame propagation speed, which leads to an increase of turbulence intensity and explosion intensity.

Resonant Tunneling Effects on the Double‐Barrier Electron Blocking Layer of a Nitride Deep‐UV Light‐Emitting Diode

The multi‐quantum‐barrier electron blocking layer (EBL) is reported to significantly improve efficiency by nearly 3 times over a single barrier in deep‐UV AlGaN light‐emitting diodes to deal with electron leakage. The improvement is usually attributed to the enhanced effective barrier height, and this article aims to explore the benefits of the tunneling effect by calculating the tunneling currents of electrons and holes through an Al0.6Ga0.4N/AlyGa1−yN double‐barrier EBL under external bias from opposite directions. The results show that the tunneling current for holes Jh is several orders of magnitude higher than that of the electrons Je as the barriers are with Al mole fraction y greater than 0.75 and thickness larger than 2 nm, which promises effective hole injection by tunneling without much electron leakage. Tunneling mechanism works better in EBL with higher and thicker barriers because the tunneling coefficients of light hole drop much slower than electrons due to its small effective mass. A proper distance between the barriers is needed to avoid electron leakage while holes tunnel through the EBL. Built‐in electric fields tilt the band to enlarge the peak‐to‐valley ratio. This work indicates that the tunneling effect substantially facilitates a multibarrier EBL to enhance carrier‐injection efficiency.

FXLMS with Multiple Error Switching for Active Noise-Cancelling Casings

Passive noise reduction methods require thick and heavy barriers to be effective for low frequencies and those clasical ones are thus not suitable for reduction of low frequency noise generated by devices. Active noise-cancelling casings, where casing walls vibrations are actively controlled, are an interesting alternative that can provide much higher low-frequency noise reduction. Such systems, compared to classical ANC systems, can provide not only local, but also global noise reduction, which is highly expected for most applications. For effective control of casing vibrations a large number of actuators is required. Additionally, a high number of error sensors, usually microphones that measure noise emission from the device, is also required. All actuators have an effect on all error sensors, and the control system must take into account all paths, from each actuator to each error sensor. The Multiple Error FXLMS has very high computational requirements. To reduce it a Switched-Error FXLMS, where only one error signal is used at the given time, have been proposed. This, however, significantly reduces convergence rate. In this paper an algorithm that uses multiple errors at once, but not all, is proposed. The performance of various algorithm variants is compared using simulations with the models obtained from real active-noise cancelling casing.

Comparison of negative streamer development in synthetic ester and mineral oil in a point-sphere gap divided by a pressboard barrier

This article presents the results of the studies on development of negative streamers in synthetic ester and mineral oil with electrode system using a pressboard barrier. The tests were performed at standard lightning impulse voltage in point-sphere electrode configuration as reference system and a 5 mm thick pressboard barrier placed in different locations between the point and the sphere. Introducing pressboard between the electrodes allowed to relate the observations to the real insulating systems where long oil gaps are divided on shorter by insulating barriers. It was done to show whether pressboard barrier changes the streamers behavior in the considered electrode gap distance what is important from the viewpoint of assessment of dielectric properties of alternative liquids versus mineral oils. The results showed that the pressboard barrier for both liquids tested prevents breakdown. In addition, the barrier causes reduction of the propagation velocity of the streamers in synthetic ester, which is benefit in relation to the results concerning free liquid gaps.

Efficient alternating current electroluminescence of CBP: Ir(ppy)3 in the tandem devices with ladder barrier layers

In this paper, alternating current-driven organic light-emitting diodes (AC-OLEDs) with different structures are reported, which can be driven under forward and reverse biases by using a bipolar functionality emission layer of CBP: Ir(ppy)3. The maximum current efficiencies (CEs) under forward and reverse DC biases of prepared symmetric devices with ladder barrier layers are 9.6 and 13.6 cd A−1, respectively. The mechanism and the reason for efficiency improvement are discussed by changing the thickness of barrier layers from 0, 5, 7.5 to 10 nm respectively. The differences in EL spectra of different devices are explained by FDTD simulation. The distance from the metal electrode to the light source influences the light extraction, which results in the spectrum difference for devices with different thicknesses of ladder barriers or working under different biases. The current density decreases along with the increasing thickness of barrier layers, and the highest current efficiency is achieved when the thickness is 7.5 nm. Then an effective method to further develop AC-driven tandem devices is proposed.

Theoretical study of the electronic and optical properties of ZnO/MgO rock salt superlattices

An analysis of some electronic and optical properties of rock salt (RS) ZnO/MgO superlattices related to potential applications in optoelectronics and electronics is carried out.In order to find possible light emission mechanisms, the electronic band structure, projected and k-resolved projected density of states and optical parameters such as the refractive index, reflection and absorption coefficients are calculated.We show that the bandgap of the RS ZnO/MgO superlattice is indirect for all considered thicknesses of quantum wells and barriers. Despite the indirect character of the bandgap, other features of the studied superlattice, such as the flat character of the top of the valence band and the bottom of the conduction band, combined with strong electron-phonon coupling and high exciton binding energy, may indicate the possibility of light emission similar to that in hexagonal BN.

Modeling and simulation of an insulated-gate HEMT using p-SnO2 gate for high VTH design

In this paper, we proposed a novel recess-free insulated-gate High Electron Mobility Transistor (HEMT) with p-SnO2 gate realizing high threshold voltage (VTH) over 2 V. p-SnO2 is used as the gate material instead of traditional Ni/Au gate. Owing to the high work function of the p-SnO2 (both wide bandgap and large electron affinity (χ)), the 2DEG channel under the gate region can be deeply depleted realizing high VTH even with thick AlGaN barrier over 10 nm, which also ensures high channel mobility. An analytical model is presented and verified by experimentally calibrated TCAD simulation. Results show that for a 25 nm Al2O3, VTH of the proposed HEMT reaches 3.1 V with p-SnO2 doping NA = 5 × 1019 cm−3, which is ∼2.5 V higher than that of a conventional MIS-HEMT with the same parameters. Moreover, the specific on-resistance (Ron,sp) of the proposed HEMT is only 1.31 mΩ cm2, which is reduced by 54.8% compared with that of a recessed-gate MIS-HEMT with the same VTH of ∼2.2 V.

Preliminary study for the development of radiation safety evaluation methodology for industrial kV-rated radiation generator facilities

BackgroundThis study aims to develop an evaluator that can quickly and accurately evaluate the shielding of low-energy industrial radiation generators. MethodsWe used PyQt to develop a graphical user interface (GUI)-based program and employed the calculation methodology reported in the National Council on Radiation Protection and Measurements (NCRP)-49 for shielding calculations. We gathered the necessary factors for shielding evaluation using two libraries designed for Python, pandas and NumPy, and processed them into a database. We verified the effectiveness of the proposed program by comparing the results with those from safety reports of six domestic facilities. ResultsAfter verifying the effectiveness of the program using the NCRP-49 example, we obtained an average error rate of 1.73%. When comparing the facility safety report and results obtained using the program, we found that the error rate was between 1.09% and 6.51%. However, facilities that did not use a defined shielding methodology were underestimated by 31.82% compared with the program (the final barrier thickness satisfied the shielding standard). ConclusionThe developed program provides a fast and accurate shielding evaluation that can assist personnel that work in radiation generator facilities and government officials in reviewing safety.

Electrically Driven Site-Controlled Single Photon Source.

Single photon sources are fundamental building blocks for quantum communication and computing technologies. In this work, we present a device geometry consisting of gold pillars embedded in a van der Waals heterostructure of graphene, hexagonal boron nitride, and tungsten diselenide. The gold pillars serve to both generate strain and inject charge carriers, allowing us to simultaneously demonstrate the positional control and electrical pumping of a single photon emitter. Moreover, increasing the thickness of the hexagonal boron nitride tunnel barriers restricts electroluminescence but enables electrical control of the emission energy of the site-controlled single photon emitters, with measured energy shifts reaching 40 meV.

Spin transport characteristics modulated by the GeBi interlayer in Y3Fe5O12/GeBi/Pt heterostructures

For the past few years, germanium-based semiconductor spintronics has attracted considerable interest due to its potential for integration into mainstream semiconductor technology. The main challenges in the development of modern semiconductor spintronics are the generation, detection, and manipulation of spin currents. Here, the transport characteristics of a spin current generated by spin pumping through a GeBi semiconductor barrier in Y3Fe5O12/GeBi/Pt heterostructures were investigated systematically. The effective spin-mixing conductance and inverse spin Hall voltage to quantitatively describe the spin transport characteristics were extracted. The spin-injection efficiency in the Y3Fe5O12/GeBi/Pt heterostructures is comparable to that of the Y3Fe5O12/Pt bilayer, and the inverse spin Hall voltage exponential decays with the increase in the barrier thickness. Furthermore, the band gap of the GeBi layer was tuned by changing the Bi content. The spin-injection efficiency at the YIG/semiconductor interface and the spin transportation within the semiconductor barrier are related to the band gap of the GeBi layer. Our results may be used as guidelines for the fabrication of efficient spin transmission structures and may lead to further studies on the impacts of different kinds of barrier materials.

A feasible path for the use of ferromagnetic josephson junctions in quantum circuits: The ferro-transmon

We discuss the capabilities of ferromagnetic (F) Josephson junctions (JJs) in a variety of layouts and configurations. The main goal is to demonstrate the potential of these hybrid JJs to disclose new physics and the possibility to integrate them in superconducting classical and quantum electronics for various applications. The feasible path towards the use of ferromagnetic Josephson junctions in quantum circuits starts from experiments demonstrating macroscopic quantum tunneling in NbN/GdN/NbN junctions with ferro-insulator barriers and with triplet components of the supercurrent, supported by a self-consistent electrodynamic characterization as a function of the barrier thickness. This has inspired further studies on tunnel ferromagnetic junctions with a different layout and promoted the first generation of ferromagnetic Al-based JJs, specifically Al/AlOx/Al/Py/Al. This layout takes advantage of the capability to integrate the ferromagnetic layer in the junction without affecting the quality of the superconducting electrodes and of the tunnel barrier. The high quality of the devices paves the way for the possible implementation of Al tunnel-ferromagnetic JJs in superconducting quantum circuits. These achievements have promoted the notion of a novel type of qubit incorporating ferromagnetic JJs. This qubit is based on a transmon design featuring a tunnel JJ in parallel with a ferromagnetic JJ inside a SQUID loop capacitively coupled to a superconducting readout resonator. The effect of an external RF field on the magnetic switching processes of ferromagnetic JJs has been also investigated.

Electrochemical Separation of Porous Anodic Aluminum Oxide with Thick Barrier Layers

We investigated an electrochemical separation method for anodic aluminum oxide (AAO) films possessing thicker barrier layers by electrolysis in sodium chloride (NaCl) and ethylene glycol (EG) solution and subsequent fabrication of through-hole AAO membranes by immersion in phosphoric acid (H3PO4) solution. The AAO films with different barrier layer thicknesses were formed on the aluminum surface by anodizing in sulfuric, oxalic, and H3PO4 solutions at up to 130 V. The AAO-covered aluminum specimens were immersed in NaCl/EG solution, and then constant voltage electrolysis at 10 V higher than the anodizing voltage was performed for the separation of AAO from the aluminum surface. Many nanoscale paths were formed throughout the barrier alumina layer in the initial stage of electrolysis, and then the aluminum substrate electrochemically dissolved through these narrow paths during electrolysis. Although the AAO film formed by anodizing at 130 V was partially fractured by electrolysis, the AAO films formed at up to 80 V were uniformly separated from the aluminum surface. As the separated AAO membrane was immersed in H3PO4 aqueous solution after electrolysis, the barrier layer with narrow paths preferentially dissolved into the solution, and a through-hole AAO membrane could be successfully obtained.

Design and simulation of T‐gate AlN/β‐Ga2O3 HEMT for DC, RF and high‐power nanoelectronics switching applications

AbstractIn this paper, we report DC and RF analysis of a T‐gate AlN/β‐Ga2O3 high electron mobility transistors (HEMTs) by optimizing the gate‐drain distance (LGD) and two T‐gate dimensions given by the—head‐length (LHL) and the foot‐length (LFL). A two‐dimensional (2‐D) physics‐based device simulator attuned with experimental results is used to perform the analysis. The AlN/β‐Ga2O3 HEMT achieves a high two‐dimensional electron gas (2DEG) density of ~3 × 1013 cm−2, which is attributed to large spontaneous as well as piezoelectric polarization components of the 10 nm AlN thick barrier layer. 2DEG density is also numerically validated using widely used polarization model for III nitrides. It is demonstrated that a highly scaled, both lateral and vertical, device with optimized T‐gate dimensions achieves higher blocking voltage (VBR), low on‐resistance (RON), higher cut‐off frequency (fT) and higher maximum oscillation frequency (fMAX), simultaneously. Consequently, AlN/β‐Ga2O3 HEMT achieves a low specific‐on resistance (RON,sp) of 0.1 mΩ cm2 and an off‐state breakdown voltage of 904 V, which corresponds to the record power figure‐of‐merit (PFoM) of ~8172 MW/cm2. Furthermore, fT of 73 GHz and fMAX of 142 GHz are estimated. These results—low power conduction loss along with higher blocking voltage, and superior RF parameters show the potential of the analyzed device T‐gate AlN/β‐Ga2O3 HEMT for high‐power switching and RF applications.

Radiotherapy Infrastructure Shielding Calculations: software development for shielding calculations in a linear accelerator radiotherapy room.

This work aimed to develop and validate software that calculates the shielding thickness required for a radiotherapy room with a linear accelerator utilising geometric and dosimetric data. The software "Radiotherapy Infrastructure Shielding Calculations" (RISC) was developed using MATLAB programming. It does not require the installation of the MATLAB platform, and the user only needs to download and install the application, which displays a graphical user interface (GUI). The GUI includes empty cells to insert numerical values for several parameters to calculate the proper shielding thickness. The GUI comprises two main interfaces, one for the primary and one for the secondary barrier calculation. The interface of the primary barrier is divided into four tabs: (a) primary radiation, (b) patient scattered and leakage radiation, (c) IMRT techniques and (d) the shielding cost calculations. The interface of the secondary barrier includes three tabs: (a) patient scattered and leakage radiation, (b) IMRT techniques and (c) the shielding cost calculations. Each tab consists of two sections: one for input and one for output of the necessary data. The RISC is based on the methods and formulae of the NCRP 151 and calculates the primary and secondary barrier thickness for ordinary concrete with a density of 2.35g/cm3 and the cost for a radiotherapy room with a linear accelerator that performs conventional or IMRT techniques. Calculations can be performed for photon energies of 4, 6, 10, 15, 18, 20, 25 and 30 MV of a dual-energy linear accelerator, while instantaneous dose rate (IDR) calculations are also performed. The RISC has been validated using all comparative examples of NCRP 151 and the calculations from shielding reports of the Varian IX linear accelerator at Methodist Hospital of Willowbrook and Elekta Infinity at the University Hospital of Patras. The RISC is accompanied by two text files: (a) "Terminology," extensively describing all parameters, and (b) "User's Manual," providing useful instructions to the user. The RISC is user-friendly, simple, fast and precise, providing accurate shielding calculations and quickly and easily reproducing different shielding scenarios for a radiotherapy room with a linear accelerator. Additionally, it could be used during the educational process of shielding calculations by graduate students or trainee medical physicists. As a future work, the RISC will be updated with new features such as skyshine radiation, door shielding, and other types of machines and shielding materials.

A model to predict the rear face damage caused by non‐deforming projectile impact on plain and steel fiber reinforced concrete barriers

AbstractThis paper presents a model for evaluation of the rear face damage in concrete barriers subjected to impact of non‐deforming projectiles. This is an improved and extended version of a previously published model, which now covers both plain and steel fiber reinforced concrete (SFRC) barriers. The rear face damaged area commonly measured in tests is characterized by an equivalent diameter, evaluated by the model. Calibration and then validation are based on published experimental data. Different sets of experiments, of plain concrete and SFRC, reported by different researchers, were used for the model's calibration and for its validation. The calibrated model's predictions show reasonable agreement with the reported experimental results, especially in view of their considerable scatter. The main findings from a parametric study of the model's predictions refer to the influence on the rear face damage (at barrier thickness lower than the scabbing limit thickness) of including steel fibers in the concrete mix, the barrier thickness, impact level, and the projectile diameter. The model's predictions demonstrate the lower extent of damage in SFRC barriers, compared to plain concrete. The use of the model enables quantitative assessment of this damage and of its reduction in SFRC barriers.

Arrangement of capillary barrier made of injected solution to prevent subgrade frost heaving

The problem of road pavement deterioration due to the forces of frost heave on operating roads remains highly relevant for many regions of Russia.One of the effective methods for regulating the magnitude of frost heave in the roadbed of highways under unfavorable soil-climatic conditions is the installation of a capillary barrier. This method, using injection methods for soil transformation, has been previously justified by the authors based on field and laboratory research.However, for practical implementation of the proposed method, the key unresolved research tasks are the determination of the calculated depth of the capillary barrier within the roadbed and its optimal thickness.In this regard, the aim of the research is to provide a calculated justification for the boundaries of the capillary barrier made from injected solution to prevent frost heave in the roadbed.The methodological basis of the study includes theoretical research methods such as abstraction, analysis, and synthesis.The article formulates the condition for transitioning from an "open" freezing system to a "closed" system and proposes criteria for creating a capillary barrier. A solution is obtained to determine the maximum thickness of the capillary barrier, which depends on the properties of its material and the coefficient of moisture conductivity. The solution to the problem of locating the capillary barrier within the structure of the operating roadbed is presented, based on correlating the zone of intensive moisture transfer with the isotherms of temperatures in the freezing massif.

Oblique wave interaction with an infinite trench in presence of a bottom-standing thick rectangular barrier

Oblique wave interaction with an infinite trench in presence of a bottom-standing thick rectangular barrier

Improving the subseasonal variability of the Indian summer monsoon in a climate model

AbstractMany global climate models, including the Climate Forecast System version 2 (CFSv2), have a biased representation of subseasonal modes of variability of the Indian summer monsoon. For instance, they simulate a weaker summer mean monsoon low‐pressure systems (LPS) climatology, faster than observed northward propagation of monsoon intraseasonal oscillations (MISOs), and a systematic dry bias over Indian landmass. The Bay of Bengal (BoB), with its shallow mixed layers and unique thermal stratification, significantly modulates the convective activity in this region at subseasonal‐to‐seasonal timescales through modulation of sea surface temperature. The highly stratified upper ocean in the BoB is due to the enormous freshwater it receives from rains and rivers. A river routing model is coupled to the CFSv2 to account for the riverine freshwater and the improvements in modelling the upper‐ocean structure are analysed. Model simulations indicate that inclusion of temporally varying riverine freshwater improves the upper‐ocean state in the BoB and the observed mixed‐layer temperature gradients in the Bay are simulated reasonably after incorporating the time varying river runoff. This resulted in increased LPS lifetime and track density, and enhanced rainfall over central India. Better representation of the upper‐ocean stratification in the model leads to larger post‐convection shoaling of mixed layers at intraseasonal timescales, thereby forming thick barrier layers. Enhanced air–sea interactions restricted to the shallow mixed layer are associated with stronger vorticity, specific humidity and low‐level convergence to the north of the intraseasonal convection band. This enhanced low‐level moisture convergence north of the convection centre results in realistic northward propagation of MISO and aids LPS activity. It is demonstrated that better simulation of the upper‐ocean structure in coupled climate models can improve the representation of subseasonal modes of monsoon variability. These results bear important implications for operational forecasting.

An Eddy Current Testing Method Based on Magnetic Induction Intensity for Detecting Cracks in Steel Bridge Decks

Steel bridge decks are prone to fatigue cracking due to long-term wheel loading with high cyclic stress. Fatigue cracks threaten the safety of the bridge and even cause collapse, making crack detection very important. Crack detection with little influence on traffic is difficult due to the pavement. To confirm the feasibility of eddy current testing (ECT) for steel bridge fatigue cracks, the key parameters were calculated. The validity of the parameters was verified preliminarily using the finite-element method. An eddy current movement detection device was set up, and a prefabricated crack test was conducted. The influences of crack size and barrier thickness on the detection signal were discussed. The results show that the sampled signal of magnetic induction intensity is more obvious than voltage, and can be used for crack detection. When the direction of a crack is perpendicular to the direction of detected motion, the amplitude of magnetic induction intensity is positively correlated with the width and depth. Crack detection with a 20-mm-thick barrier layer is possible. The barrier layers weaken the strength of the sampled signal, but the variation law of the intensity with crack parameters is consistent with that of no barrier.

Spin Solar Cell Phenomenon on a Single-Molecule Magnet (SMM) Impacted CoFeB-Based Magnetic Tunnel Junctions

The single-molecule magnet (SMM) is demonstrated here to transform conventional magnetic tunnel junctions (MTJs), a memory device used in present-day computers, into solar cells. For the first time, we demonstrated an electronic spin-dependent solar cell effect on an SMM-transformed MTJ under illumination from unpolarized white light. We patterned cross-junction-shaped devices to form a CoFeB/MgO/CoFeB-based MTJ. The MgO barrier thickness at the intersection between the two exposed junction edges was less than the SMM extent, which enabled the SMM molecules to serve as channels to conduct spin-dependent transport. The SMM channels yielded a region of long-range magnetic ordering around these engineered molecular junctions. Our SMM possessed a hexanuclear [Mn6(μ3-O)2(H2N-sao)6(6-atha)2(EtOH)6] [H2N-saoH = salicylamidoxime, 6-atha = 6-acetylthiohexanoate] complex and thioesters end groups to form bonds with metal films. SMM-doped MTJs were shown to exhibit a solar cell effect and yielded ≈80 mV open-circuit voltage and ≈10 mA/cm2 saturation current density under illumination from one sun equivalent radiation dose. A room-temperature Kelvin Probe AFM (KPAFM) study provided direct evidence that the SMM transformed the electronic properties of the MTJ’s electrodes over a lateral area in excess of several thousand times larger in extent than the area spanned by the molecular junctions themselves. The decisive factor in observing this spin-photovoltaic effect is the formation of SMM spin channels between the two different ferromagnetic electrodes, which in turn is able to catalyze the long-range transformation in each electrode around the junction area.