Single Barrier Research Articles

Gate-controlled spin-valley-layer locking in bilayer transition-metal dichalcogenides.

The interplay between various internal degrees of freedom of electrons is of fundamental importance for designing high performance electronic devices. A particular instance of this interplay can be observed in bilayer TMDs due to the combined effect of spin-orbit and interlayer couplings. We study the transport of spin, valley and layer pseudospin, generally, through a magnetoelectric barrier in AB-stacked bilayer TMDs and demonstrate an electrically controllable platform for multifunctional and ultra-high-speed logic devices. Perfect spin and valley polarizations as well as good layer localization of electrons occur in a rather large range of Fermi energies for moderate electric and magnetic fields. Any number of these polarizations can be inverted by adjusting the two potential gates on the two layers. Furthermore, the conditions for the excellent polarizations are determined for the spin, valley and layer degrees of freedom, in terms of the adjustable system parameters. We discuss the individual electric and magnetic barriers and show that the single electric barrier acts as a bipolar pseudospin semiconductor with opposite polarizations for the conduction and valence bands. The results of this study pave the way for multifunctional pseudospintronic applications based on 2D materials.

Управление детонационным горением посредством предварительной подготовки газовой смеси

Using a detailed kinetic model of chemical interaction, numerical investigation of influence of a preliminary preparation of a stoichiometrical hydrogen-air mixture (decomposition of some volumes of molecular hydrogen and molecular oxygen gases into atomic gases) on characteristics of a propagating detonation wave has been carried out. It has been obtained that the preliminary partial dissociation of the gas mixture results in an essential decrease of the detonation cell size and a small increase of the self-sustained detonation wave propagation velocity. Due to the established detonation combustion features, preliminary preparation of the mixture can be used to prevent destruction of a detonation wave in channels with both a single transverse barrier and a barrier domain.

Experimental investigation of single microdischarges in a barrier corona arrangement with a cathodic metal pin

Microdischarges (MDs) in a sinusoidally driven barrier corona discharge, operated in dry air at atmospheric pressure, are investigated using time-correlated single photon counting (TC-SPC) technique, electrical measurements (applied voltage and current pulses) and ICCD images. In the current contribution, results of the cathodic pin half-cycle are presented. Results of the anodic pin half-cycle were presented in a previous study (Jahanbakhsh et al 2018 Plasma Sources Sci. Technol. 27 115011). In the cathodic pin half-cycle appearance phase and current pulse amplitude of the MDs have an erratic behavior. Hence, a statistical study of the current pulse amplitudes is conducted, and it is correlated to the phase-resolved spatio-temporal development of the MDs, obtained from TC-SPC recordings. This study indicates that the breakdown and development of the MDs is dependent on their inception phase, which is related to the discharge activity in preceding (anodic pin) half-cycles. It is shown that the MDs appearing at lower applied voltages are ignited with a positive streamer starting near the anode (dielectric), similar to single dielectric barrier discharge MDs. On the other hand, the inception of the MDs appearing at higher applied voltages takes place with a double-streamer mechanism starting near the tip of the cathode (pin). These MDs have similarities to transient sparks, in particular much higher current pulse amplitudes compared to single DBDs.

Postnatal PMTCT: Women’s Perception Barriers at a Johannesburg Health Centre, South Africa

Background: Maximising women’s participation and ensuring optimal outcomes will require that the women’s perception barriers to postnatal prevention of Mother-to-Child Transmission (PMTCT) programme of HIV be addressed. However, little is known about women’s perception barriers to postnatal PMTCT programme of HIV and how these barriers affect the women’s health seeking behavior and uptake. Objective: This study sought to explore the women’s perception barriers to postnatal PMTCT programme at a Johannesburg Community Health Centre during April-May, 2016. Methods: A qualitative study on 30 women (aged 20 - 39 years) was conducted at a Johannesburg community health (CHC), South Africa, during May-June 2016, after obtaining their consent. The data was analysed thematically to understand women’s perception barriers to postnatal PMTCT programme. Results: The study found that inadequate counselling was perceived to be the single key health service barrier to PMTCT programme. At the individual level, adherence to ART was considered the leading women’s barriers to the postnatal PMTCT. Exclusive breastfeeding was, however, perceived as important women’s barriers to the postnatal PMTCT. Inadequate emotional support from families and community was a noteworthy women’s perception barrier to the programme. Conclusion: The study makes two recommendations: firstly, the staff, programme managers and health policy makers need to be aware of the women’s perception barriers to the postnatal PMTCT programme. Secondly, the programme should be strengthened by addressing perception barriers to the programme to enhance women participation to ensure optimal outcomes for women and their infants.

Prostanoids regulate vascular permeability

In normal condition, vasculature transports only small molecules such as nutrients across vascular wall. When inflammation occurs, inflammatory stimuli increase the permeability of vessel, which induces the extravasation of molecules larger than 40 kDa including plasma proteins. These extravasated molecules cause further inflammation by promoting the infiltration of inflammatory cells and the production of inflammatory mediators. Although it is known that vascular hyper-permeability plays an important role in inflammation, the detailed mechanism of vascular permeability regulation is still unclear. It is known that vascular permeability is controlled by two types of cells: endothelial cells and vascular mural cells. Endothelial cells cover the luminal side of vascular wall in a single layer and form endothelial barrier. Vascular mural cells regulate the blood flow volume of the downstream tissue by contracting or relaxing vascular wall. Endothelial barrier enhancement and vasocontraction suppress the vascular permeability, while endothelial barrier disruption and vasorelaxation promote it. Vascular permeability is regulated by the balance between the response of endothelial cells and vascular mural cells. Prostanoids are cell membrane-derived lipid mediators which bind to each specific G protein-coupled receptor (GPCR), prostanoid receptors. Recently, several studies showed that prostanoids regulate vascular permeability by acting on endothelial cells and/or vascular mural cells. In this review, we would like to describe the role of each prostanoid in vascular permeability by focusing on the characteristics of each specific receptor.

A QCM-based rupture event scanning technique as a simple and reliable approach to study the kinetics of DNA duplex dissociation.

Rupture Event Scanning (REVS) is applied for the first time within an approach based on dynamic force spectroscopy. Using model DNA duplexes containing 20 pairs of oligonucleotides including those containing single mismatches, we demonstrated the possibility of reliable determination of the kinetic parameters of dissociation of biomolecular complexes: barrier positions, the rate constants of dissociation, and the lifetime of complexes. Within this approach, mechanical dissociation of DNA duplexes occurs according to a mechanism similar to unzipping. It is shown that this process takes place by overcoming a single energy barrier. In the case where a mismatch is located at the farthest duplex end from the QCM surface, a substantial decrease in the position of the barrier between the bound and unbound states is observed. We suppose that this is due to the formation of an initiation complex containing 3-4 pairs of bases, and this is sufficient for starting duplex unzipping.

A mechanistic explanation of the inhibitory role of the protein corona on liposomal gene expression

The past three decades have witnessed fast advances in the use of cationic liposome-DNA complexes (lipoplexes) for gene delivery applications. However, no lipoplex formulation has reached into the clinical practice so far. The primary drawback limiting clinical use of lipoplexes is the lack of mechanistic understanding of their low transfection efficiency (TE) in vivo. In physiological environments, lipoplexes are coated by a protein corona (PC) that mediates the interactions with the cell machinery. Here we show that the formation of PC can change the interactions of multicomponent (MC) lipoplexes with our cell model (i.e., HeLa). At the highest lipoplex concentration, the formation of PC can reduce the TE of MC lipoplexes from 60% to <5%. Combining dynamic light scattering and synchrotron small-angle X-ray scattering (SAXS), we clarify that the formation of PC modifies physical-chemical properties of MC lipoplexes so as to affect their TE. Moreover, we examined single transfection barriers by a combination of fluorescence-activated cell sorting, single-cell real-time fluorescence confocal microscopy, and synchrotron SAXS. We demonstrate that PC formation has the ability to modify the relative contribution of caveolae-mediated endocytosis and macropinocytosis in lipoplexes uptake, in favor of the latter, increasing accumulation of PC-decorated lipoplexes into degradative lysosomal compartments. Finally, we report evidences that PC reduces the structural stability of lipoplexes against solubilization by cellular lipids, likely favoring premature DNA release and cytosolic digestion by DNAase. These combined effects revealed here offer a comprehensive mechanistic explanation on the reason behind reduction in gene expression of MC lipoplexes.

Low bias electron transport properties of the graphene-Ge2Sb2Te5 heterostructure device

We explore the performance improvement of ultra-scaled phase-change memory (PCM) device with graphene- Ge2Sb2Te5 (GST) heterostructure by means of first-principle simulations of electron transport. We compare the tunneling probability of single-barrier(SB) and double barrier(DB) heterostructures and show that the use of DB can have a significant impact on the ON/OFF conductance ratio of the device. The reason for this is that the graphene layers in the middle of the single potential barrier, forming the double potential barrier, perform as an operative phase randomizer and destroy the coherence of the electrons that carry out the transport. Hence, the electric current and conductivity decrease in the amorphous phase and the ON/OFF conductance ratio sharply increases. The results of this work offer great potential to obtain a high ON/OFF ratio in ultra-scaled PCM devices.

An Urgent Need for Data to Drive Decision Making: Rationale for the Canadian Registry for Amyloidosis Research

Recent developments in cardiac amyloidosis have raised awareness of the disease and have advanced diagnostic and treatment strategies. Novel therapies may vastly improve the prognosis of the disease but will be associated with significant costs. Data are needed to inform clinical decisions and to drive resource allocation within the health care system. Many aspects of disease management are unlikely to be addressed by clinical trials and are better suited to nonrandomized cohort studies, but the limited numbers of patients in any single centre present barriers to high-quality observational research. Disease registries offer opportunities to assemble large numbers of patients from multiple institutions for adequately powered observational studies, to recruit patients for randomized clinical trials; to provide real-world effectiveness and safety data, to study cost-effectiveness of novel therapies, and to engage patients in the collection of patient-reported outcome data. Existing amyloidosis registries have limitations. Canada is an ideal setting for a national amyloidosis registry, with ethnic diversity, relatively few academic centres, access to advanced diagnostic and therapeutic options, and a track record of collaboration among institutions. The Canadian Registry for Amyloidosis Research aims to capitalize on this opportunity and provide high-quality data to inform clinical practice and health care policy in Canada and beyond.

Tunneling through Double Electrostatic Barriers in Strained Graphene

Herein, the electronic structure of Dirac fermions scattered by double barrier potential in graphene under strain effect is studied. It is shown that traction and compression strains can be used to generate fermion beam collimation, 1D transport channels, surface states, and confinement. The corresponding transmission probability and conductance at zero temperature are calculated and their numerical computations are performed taking into account various alterations of physical parameters, enabling the analysis of some important features of the system. It is shown that the transmissions satisfy three symmetry relations depending on the incident angle and strain parameters, while the conductance is reduced compared to that of the strained single barrier.

Beam manipulations with barrier buckets in the CERN PS

A barrier bucket scheme is being considered to reduce losses during the Multi-Turn Extraction from the CERN Proton Synchrotron to the Super Proton Synchrotron for the fixed- target physics programme. For effective loss reduction, the extraction kicker has to be triggered during the gap at the time of the longitudinal barrier. Initial beam studies at injection energy and with low intensity beams allowed to fully qualify an existing wide-band cavity to generate one or multiple beam synchronous pulses per turn. Bunch-length stretching and shortening have been exercised with barriers moving in azimuth with respect to the beam. The encouraging results obtained at injection energy guided the implementation of a de-bunching manipulation at higher energy to move all bunches into a single barrier bucket. Beam measurements at a momentum of 14GeV/c, varying intensity and the width of the barrier, demonstrate that a quasi-constant longitudinal line density and an almost fully depleted gap can be achieved at highest intensities. The contribution summarises the results of the beam studies at high energy together with some observations related to the Multi-Turn Extraction.

Voltage-controlled magnetic tunnel junctions with synthetic ferromagnet free layer sandwiched by asymmetric double MgO barriers

Memory and computing applications utilizing voltage-controlled magnetic random-access memory (MRAM) require perpendicular magnetic tunnel junctions (pMTJs) capable of high thermal stability and large write efficiency at advanced technology nodes. We first discuss the scaling requirements for voltage-controlled MRAM to replace various existing memory applications at an advanced CMOS technology node, including cell size, thermal stability, interfacial perpendicular magnetic anisotropy (PMA), and voltage-controlled magnetic anisotropy (VCMA). For replacing volatile memories including SRAM, eDRAM, and DRAM, we employ the retention relaxation technique along with a DRAM-style refresh scheme in the analysis. To enhance both PMA and VCMA at scaled nodes, we explore pMTJs with asymmetric double MgO barriers sandwiching a synthetic ferromagnet (SyF) free layer. In a thin MgO/SyF free layer/thick MgO/fixed layer MTJ stack, the SyF free layer is realized in various ways: single layer (X = Ta, W, Mo, Ir) and bilayers (X = Ta/W, Mo/Ir) of heavy metals insertions in CoFeB/X/CoFeB and Co2FeAl/X/Co2FeAl structures, and multiple insertions in [CoFeB/X]n/CoFeB structures for n = 1–4. A VCMA coefficient of 36 fJ (V m)−1 is achieved in a MgO/CoFeB/Ta/CoFeB/MgO-based MTJ which is comparable to that of the single MgO barrier MTJ. We find PMA enhancement, although with VCMA reduction for an increasing number n of [CoFeB/X]n repetitions. In addition, we demonstrate large TMR of 78%, large interfacial PMA of 1.45 mJ m−2, and VCMA of 65 fJ (V m)−1 in a MgO/Co2FeAl/W/Co2FeAl/MgO-based MTJ annealed above 400 °C.

Opportunities for tidal range projects beyond energy generation: Using Mersey barrage as a case study

Currently there is renewed interest in harnessing the vast tidal resource to combat the twin challenges of climate change and energy security. However, within the UK no tidal barrage proposals have passed the development stage, this is due to a combination of high cost and environmental concerns. This paper demonstrates how a framework, such as the North West Hydro Resource Model can be applied to tidal barrages, with the Mersey barrage as a case study. The model materialised in order to provide developers with a tool to successfully identify the capacity of hydropower schemes in a specific location. A key feature of the resource model is the understanding that there is no single barrier to the utilisation of small hydropower but several obstacles, which together impede development. Thus, this paper contributes in part to a fully holistic treatment of tidal barrages, recognising that apart from energy generation, other environmental, societal and economic opportunities arise and must be fully investigated for robust decision-making. This study demonstrates how considering the societal needs of the people and the necessity for compensatory habitats, for example, an organic architectural design has developed, which aims to enhance rather than detract from the Mersey.

The Evolving Concept of the Blood Brain Barrier (BBB): From a Single Static Barrier to a Heterogeneous and Dynamic Relay Center.

The blood–brain barrier (BBB) helps maintain a tightly regulated microenvironment for optimal central nervous system (CNS) homeostasis and facilitates communications with the peripheral circulation. The brain endothelial cells, lining the brain’s vasculature, maintain close interactions with surrounding brain cells, e.g., astrocytes, pericytes and perivascular macrophages. This function facilitates critical intercellular crosstalk, giving rise to the concept of the neurovascular unit (NVU). The steady and appropriate communication between all components of the NVU is essential for normal CNS homeostasis and function, and dysregulation of one of its constituents can result in disease. Among the different brain regions, and along the vascular tree, the cellular composition of the NVU varies. Therefore, differential cues from the immediate vascular environment can affect BBB phenotype. To support the fluctuating metabolic and functional needs of the underlying neuropil, a specialized vascular heterogeneity is required. This is achieved by variances in barrier function, expression of transporters, receptors, and adhesion molecules. This mini-review will take you on a journey through evolving concepts surrounding the BBB, the NVU and beyond. Exploring classical experiments leading to new approaches will allow us to understand that the BBB is not merely a static separation between the brain and periphery but a closely regulated and interactive entity. We will discuss shifting paradigms, and ultimately aim to address the importance of BBB endothelial heterogeneity with regard to the function of the BBB within the NVU, and touch on its implications for different neuropathologies.

Transition dipole moments and probabilities of the CCl radicals

This work studies the transition dipole moments and properties of 12 electronic states. These states are X2Π, A2Δ, B2Σ+, C2Π, 12Σ−, 22Σ−, a4Σ−, b4Π, 14Σ+, 14Δ, 24Π, and 24Σ−; they originate from the first dissociation limit of the carbon monochloride radical. The potential energy curves were calculated using the complete active space self-consistent field method, followed by the valence internally contracted multireference configuration interaction approach. The B2Σ+ state has a double well and C2Π a single barrier. The radiative lifetimes of the vibrational levels are in the order of 10−7 s for the A2Δ state, and 10−7 and 10−5 s for the first and second wells of the B2Σ+ state, respectively, suggesting that the spontaneous emissions originated from the two states can easily occur. The radiative lifetimes are long for C2Π, b4Π, 14Δ, 14Σ+, and 24Π states and the Einstein A coefficients are small for the emissions originated from these states, indicating that the spontaneous emissions generated from these states are difficult to measure through spectroscopy. The 12Σ−, 22Σ−, and 24Σ− states are repulsive. Furthermore, the spectroscopic parameters and vibrational levels were evaluated. For the A2Δ – X2Π and B2Σ+ – X2Π systems, the Einstein A coefficients of the vibronic emissions are large, indicating that the emissions from the two systems can be easily detected by spectroscopy. The spectral range of the spontaneous emissions was evaluated for certain transitions.

Switching Performance Comparison With Low Switching Energy Due to Initial Temperature Increment in CoFeB/MgO-Based Single and Double Barriers

Spin-transfer torque magnetic random-access memory (STT-MRAM) based on a single-barrier magnetic tunnel junction (SBMTJ) and a double-barrier magnetic tunnel junction (DBMTJ) has evolved along with a low switching current and low energy consumption to obtain a high areal density and a fast switching speed. The increment of initial temperature, ${T}_{{\text {in}}}$ , in STT-MRAM can achieve low switching energy, ${E}_{{\text {SW}}}$ . However, this leads to an unavoidable decrease in $\Delta $ and switching efficiency. In this paper, SBMTJ and DBMTJ were analyzed in terms of the switching efficiency factor with ${E}_{{\text {SW}}}$ reduction by increasing the ${T}_{{\text {in}}}$ . The switching temperature, ${T}_{{\text {SW}}}$ , was investigated using a finite-element method simulation. The results show that the DBMTJ(A) and SBMTJ with the same MgO layer thickness of 0.9 nm provide a higher switching current, ${I}_{{\text {C}}}$ , than the DBMTJ(B) with a MgO layer thickness of 1.3 nm. The ${T}_{{\text {SW}}}$ in a DBMTJ(A) is higher than that in an SBMTJ, while ${T}_{{\text {SW}}}$ for a DBMTJ(B) is the smallest because of its low ${I}_{{\text {C}}}$ . The DBMTJ(A) and DBMTJ(B) can be applied in a higher temperature range than the SBMTJ at a $\Delta $ of 40. In addition, the STT efficiency factor, $\Delta /{I}_{{\text {C0}}}$ , for a DBMTJ is better than the factor for an SBMTJ. Although the temperature increment would cause an undesirable reduction in $\Delta $ , it can reach a low ${E}_{{\text {SW}}}$ for the requirement of a fast write access time. Therefore, the control device for increasing the ${T}_{{\text {in}}}$ in the MTJs is attractive and should be promoted in the advancement of memory technology.

Insights from a Comprehensive Commercial Lithium Ion Battery Cycling and Aging Study

The single largest barrier to adoption of electrochemical storage in the grid is often stated to be the value of a battery over the life of the system. To ensure long-term system safety and reliability, batteries must be selected based on application specific requirements and performance characteristics. Our approach to addressing the uncertainty in the performance and cycle life of commercially viable lithium ion batteries for grid storage has been to design studies with multiple chemistries, and conduct long term life cycle evaluations with systematically varied cycling conditions. Namely, we initiated a large-scale, multi-year cycling study of commercial LiFePO4/LFP, LiNixCoyAl1-x-y­O2/NCA, and LiNixMnyCo1-x-yO2/NMC cells. This study looks at chemistry specific influences on efficiency and cycle life under variables that include discharge rate, depth of discharge (DoD) and temperature, and is complemented by a calendar aging study. The source of differences in aging behavior was investigated through electrochemical impedance spectroscopy and differential capacity analysis. We compare results to literature to identify the degree to which variations may be expected with manufacturer and version, as products can see manufacturing changes year to year. Understanding variations is critical for lifetime assessment and economic evaluation that is meaningful for installed systems. We further look at how these best-case scenario results from single cell studies may be used as a baseline in moving toward understanding aging in module and system configurations. The overarching goal is to begin to effectively understand laboratory cell studies in a context applicable to grid storage systems.Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Finite-element analysis of strains in seepage barriers of the earth dam

This paper presents the strain profiles obtained along the height of the seepage barriers of the earth dam. The seepage barriers are employed in the permeable dam section in order to obstruct the seepage of water from upstream to downstream and thereby reducing the risk of piping. A total of 36 finite-element simulations were carried out in the study, wherein the combination and placement of the cut-off walls in the earth dam section were varied. The results include the horizontal, vertical and shear strain profiles and their variation along the height of barriers with respect to its position for different reservoir conditions, such as high reservoir and 5 d drawdown conditions. By the adoption of single barrier in the dam section, the strain values were found to be on the higher side when compared with the near-end barrier in double-configuration system under high reservoir conditions, whereas for the drawdown conditions, the magnitude of the strains in the barrier were more or less the same. The higher strain levels induced in the barrier could cause cracking of the barrier, thereby impairing the function of the barrier.

Role of Bloch waves in baryon-number violating processes

In the Bloch-wave approach to estimate the baryon-number-violating scattering cross section in the standard electroweak theory in the laboratory, we clarify the relation between the single sphaleron barrier and multiple (near periodic) sphaleron barrier cases. We explain how a realistic consideration modifies/corrects the idealized Bloch wave and the resonant tunneling approximation. The basic approach is in part analogous to the well-known triple-$\alpha$ process to form carbon in nucleosynthesis.

Mitigation of ground vibrations induced by high speed railways using double geofoam barriers: Centrifuge modeling

This paper presents a study of the propagation and mitigation of ground vibrations induced by high speed railways using 8 centrifuge tests. In the reported tests here, geofoam is used as a barrier in various locations and arrangements (single and double) to mitigate ground vibrations. The results show that the surface waves guide the propagation pattern of ground vibrations induced by high speed railways and also reveal that geofoam is a proper material for the mitigation of such ground vibrations. While the use of single geofoam barriers can reduce ground vibrations by up to 54.5%, their performance at low input frequencies are undesirable. Double geofoam barriers are used and tested in various locations to eliminate such inconvenient effects and improve the mitigation of ground vibrations. The results show that double geofoam barriers can mitigate the vibrations by about 14%–35% more than a single geofoam barrier and undesirable performances for the mentioned low input frequencies are also eliminated.