Single Barrier Research Articles

High Temperature Behavior Prediction Techniques for Non-Uniform Ni/SiC Schottky Diodes

Two characterization methods are compared in terms of their suitability for predicting the electrical behavior of non-uniform Ni/4H-SiC Schottky contacts up to 450°C, using data measured at lower temperatures. These techniques are based on the established Gaussian distribution of barrier heights model and a recently proposed discrete barrier distribution model, respectively. Two samples with different degrees of contact inhomogeneity are measured and their forward characteristics are fitted using both techniques. The Gaussian distribution approach is shown to accurately fit experimental data only for the nearly-uniform sample, while requiring the extraction of two separate barrier height values from measurements in the room-250°C range, only. When attempting to use this method to characterize the sample with strong non-uniformity, fitting accuracy (given by R2) drops under 90%. In contrast, the discrete barrier distribution technique is proven able to forecast the electrical behavior of both samples (with R2 > 99% in most cases), over the entire room-450°C range, using a single Schottky barrier for each device (1.61V, corresponding to a Ni2Si Schottky contact and 0.9V, afferent to a Ni metallization).

Cytokine Tuning of Intestinal Epithelial Function.

The intestine serves as both our largest single barrier to the external environment and the host of more immune cells than any other location in our bodies. Separating these potential combatants is a single layer of dynamic epithelium composed of heterogeneous epithelial subtypes, each uniquely adapted to carry out a subset of the intestine’s diverse functions. In addition to its obvious role in digestion, the intestinal epithelium is responsible for a wide array of critical tasks, including maintaining barrier integrity, preventing invasion by microbial commensals and pathogens, and modulating the intestinal immune system. Communication between these epithelial cells and resident immune cells is crucial for maintaining homeostasis and coordinating appropriate responses to disease and can occur through cell-to-cell contact or by the release or recognition of soluble mediators. The objective of this review is to highlight recent literature illuminating how cytokines and chemokines, both those made by and acting on the intestinal epithelium, orchestrate many of the diverse functions of the intestinal epithelium and its interactions with immune cells in health and disease. Areas of focus include cytokine control of intestinal epithelial proliferation, cell death, and barrier permeability. In addition, the modulation of epithelial-derived cytokines and chemokines by factors such as interactions with stromal and immune cells, pathogen and commensal exposure, and diet will be discussed.

Debris flow protection with flexible ring net barriers – 10 years of experience

AbstractFlexible ring net barriers against debris flow have been installed worldwide during the last 10 years mainly for the purpose of debris retention and a few as erosion control. An increasing number of client projects (40 barriers within Switzerland, more than 100 worldwide by 2017) shows the interest in this solution. This article highlights different special applications such as one single barrier providing a very large retention capacity, an example of several barriers in line and filled up barriers for erosion control. Advantages and challenges for the use of flexible ring net barriers are discussed on a technical and economic level and needs for maintenance and replacement works are addressed.

Shape optimized inclined single and double wall wave barriers for ground vibration mitigation

Stiff wave barriers are capable of reducing the transmission of ground vibrations. Most designs consist of a single vertical wall, although double walls are also being considered. This paper investigates the shape optimization (position, inclination, length and thickness) of these topologies in a two-dimensional setting, for a point source and a point receiver placed symmetrically with respect to the design domain. Three types of sources are studied: a single-frequency source, a broadband source and a harmonic source within a given frequency range. An economical constraint on the maximum material use is considered. A multi-region BEM methodology is used for evaluating the objective function and its gradient. Analytical expressions are presented for the sensitivities, providing a very effective simulation tool for this type of problem. It is found that significant improvement can be achieved by repositioning and inclining the walls when compared to the reference cases. It is also found that optimized double wall barriers outperform single wall barriers. The improvement is insignificant for sources which generate Rayleigh wavelengths similar to the design domain depth, but it greatly increases as frequency increases and the penetration depth decreases.

82‐1: Invited Paper: Large Area Thin Film Encapsulation from Bendable to Rollable and Foldable

Single layer barrier layer and multi‐layer barrier/buffer/barrier layers thin film encapsulation (TFE) were developed by large area PECVD. The barrier performances as well as mechanical bending flexibility were demonstrated.

Numerical simulation of tunneling through arbitrary potential barriers applied on MIM and MIIM rectenna diodes

With the continuous miniaturization of electronic devices, quantum-mechanical effects such as tunneling become more effective in many device applications. In this paper, a numerical simulation tool is developed under a MATLAB environment to calculate the tunneling probability and current through an arbitrary potential barrier comparing three different numerical techniques: the finite difference method, transfer matrix method, and transmission line method. For benchmarking, the tool is applied to many case studies such as the rectangular single barrier, rectangular double barrier, and continuous bell-shaped potential barrier, each compared to analytical solutions and giving the dependence of the error on the number of mesh points. In addition, a thorough study of the J − V characteristics of MIM and MIIM diodes, used as rectifiers for rectenna solar cells, is presented and simulations are compared to experimental results showing satisfactory agreement. On the undergraduate level, the tool provides a deeper insight for students to compare numerical techniques used to solve various tunneling problems and helps students to choose a suitable technique for a certain application.

Barriers to the Circular Economy: Evidence From the European Union (EU)

The circular economy concept is much discussed in the European Union (EU), but only limited progress has been accomplished so far regarding its implementation. Most scholarly studies blame this on various technological barriers. Our work rebuts these studies. We present the first large-N-study on circular economy barriers in the EU (208 survey respondents, 47 expert interviews). We find that cultural barriers, particularly a lack of consumer interest and awareness as well as a hesitant company culture, are considered the main circular economy barriers by businesses and policy-makers. These are driven by market barriers which, in turn, are induced by a lack of synergistic governmental interventions to accelerate the transition towards a circular economy. Meanwhile, not a single technological barrier is ranked among the most pressing circular economy barriers, according to our research. Overall, our work suggests that circular economy is a niche discussion among sustainable development professionals at this stage. Significant efforts need to be undertaken for the concept to maintain its momentum.

Maximum Thrust of Single Dielectric Barrier Discharge Thruster at Low Pressure

The theoretical thrust mechanism of a single dielectric barrier discharge plasma thruster at low pressure is studied. A theoretical thrust model is proposed to establish that the thrust increases to a maximum and then drops steadily as the pressure monotonically increases over a pressure range from 10 to 90 kPa. A formula for revealing the relationships among the pressure, permittivity, dielectric thickness, and operating voltage is derived from the model. This formula shows that a higher operating voltage and smaller ratio of dielectric thickness to permittivity can lead to a higher pressure at the point of maximum thrust. The theoretical results are consistent with the experimental results. The results can be used to determine the optimal operating pressure for a single dielectric barrier discharge thruster.

Effect of Fluid Intake on Hydration Status and Skin Barrier Characteristics in Geriatric Patients: An Explorative Study

Background/Aim: Inadequate fluid intake is assumed to be a trigger of water-loss dehydration, which is a major health risk in aged and geriatric populations. Thus, there is a need to search for easy to use diagnostic tests to identify dehydration. Our overall aim was to investigate whether skin barrier parameters could be used for predicting fluid intake and/or hydration status in geriatric patients. Methods: An explorative observational comparative study was conducted in a geriatric hospital including patients aged 65 years and older. We measured 3-day fluid intake, skin barrier parameters, Overall Dry Skin Score, serum osmolality, cognitive and functional health, and medications. Results: Forty patients were included (mean age 78.45 years and 65% women) with a mean fluid intake of 1,747 mL/day. 20% of the patients were dehydrated and 22.5% had an impending dehydration according to serum osmolality. Multivariate analysis suggested that skin surface pH and epidermal hydration at the face were associated with fluid intake. Serum osmolality was associated with epidermal hydration at the leg and skin surface pH at the face. Fluid intake was not correlated with serum osmolality. Diuretics were associated with high serum osmolality. Conclusions: Approximately half of the patients were diagnosed as being dehydrated according to osmolality, which is the current reference standard. However, there was no association with fluid intake, questioning the clinical relevance of this measure. Results indicate that single skin barrier parameters are poor markers for fluid intake or osmolality. Epidermal hydration might play a role but most probably in combination with other tests.

Identifying Barriers to Preemptive Kidney Transplantation in a Living Donor Transplant Cohort.

BackgroundDespite substantial evidence demonstrating clear benefit, rates of preemptive kidney transplantation (PreKTx) remain low in the United States. Our goal was to identify barriers to PreKTx.MethodsUsing a telephone-administered questionnaire including questions about barriers, timing of referral, timing of education, we retrospectively studied first living donor kidney transplant recipients (2006-2010) at Mayo Clinic, Rochester, MN. Of 235 patients, 145 (62%) responded to the questionnaire (74 PreKTx and 71 non-PreKTx). We compared categorical data with Fisher exact test and median times with Wilcoxon rank sum test.ResultsPolycystic kidney disease (PCKD), longer median time between diagnosis and transplant, and time between education about transplant and transplant correlated with PreKTx (P < 0.01). The presence of at least 1 patient-identified barrier (lack of referral, financial barriers, medical barriers, no identified living donor and donor evaluation delays) was associated with non-PreKTx (0.034) though no single barrier predominated. Age, education level, insurance status and source of referral (primary care, nephrology, and nonphysician referral) were not associated with the rate of PreKTx. Univariate logistic regression identified white race, PCKD, and increased time from diagnosis as factors favoring PreKTx; PCKD and increased time remained significant factors after multivariate analysis.ConclusionsEven among a patient population that is primarily white, educated, and has a spouse or first-degree relative donor, PreKTx rates remain concerningly low. Increased time between diagnosis or education and transplant are predictors of PreKTx. Greater emphasis on transplant education earlier in the stages of chronic kidney disease and community outreach from transplant centers may help to increase the rate of PreKTx.

Temperature- and concentration-dependent hydrogen diffusivity in palladium from statistically-averaged molecular dynamics simulations

Solid-state hydrogen storage materials undergo complex phase transformations in which kinetics are often limited by hydrogen diffusion that significantly changes during hydrogen uptake and release. Here we perform robust statistically-averaged molecular dynamics simulations to obtain a well-converged analytical expression for hydrogen diffusivity in bulk palladium that is valid throughout all stages of the reaction. Our studies confirm the experimentally observed dependence of the diffusivity on concentration and temperature and elucidate the underlying physics. Whereas at low hydrogen concentrations, a single dilute hopping barrier dominates, at high hydrogen concentrations, diffusion exhibits multiple hopping barriers corresponding to hydrogen-rich and hydrogen-poor local environments.

Parametric study of a DBD plasma actuation based on the Suzen-Huang model

Since the introduction of Suzen-Huang (SH) model in 2005, a huge number of publications discussing various aspects of this model has been reported. Most of these studies, till date are mainly focused on flow analyses in the framework of a Single Dielectric Barrier Discharge (SDBD) plasma actuator. This paper extends the application of the SH model to analyze the effects of some geometrical and electrical parameters of DBD plasma actuators in flow control applications. In some earlier experimental studies, it has been reported that a thick dielectric (a few mm) enhances the plasma extension resulting in an improvement of the electro-hydrodynamic (EHD) body force and the resulting ionic wind. Various parameters influence the electro-mechanical characteristics of DBD actuators such as - the dielectric thickness, the distance between both electrodes, the magnitude, the frequency and the waveform of the applied voltage The aim of this paper is to highlight the effects of these parameters on the ionic wind and EHD body force induced by the plasma discharge. It was observed that there is an optimal thickness of the dielectric layer for each configuration of actuator; above or below that optimal thickness, there is depreciation in the performance of the actuator. Thus, this paper summarizes the significance of the geometrical parameters for DBD plasma actuators. The optimal gap between the electrodes was found to be equal to zero which is in agreement with experimental observations. It is shown that with the increase in gap beyond 1 mm, the induced ionic wind velocity was significantly reduced. It is concluded that these two geometrical parameters play a fundamental role in optimization of the DBD actuator configurations. The applied voltage frequencies in the range from 1 to 4 kHz did not show significant performance variations in our DBD actuators configurations. Increasing the voltage amplitude leads to a better gain in terms of EHD force as reported in experimental studies. It is shown that square waveform of the applied voltage gives higher induced velocities compared to sinus or triangular waveform.

Detection of fractional solitons in quantum spin Hall systems

We propose two experimental setups that allow for the implementation and the detection of fractional solitons of the Goldstone-Wilczek type. The first setup is based on two magnetic barriers at the edge of a quantum spin Hall system for generating the fractional soliton. If then a quantum point contact is created with the other edge, the linear conductance shows evidence of the fractional soliton. The second setup consists of a single magnetic barrier covering both edges and implementing a long quantum point contact. In this case, the fractional soliton can unambiguously be detected as a dip in the conductance without the need to control the magnetization of the barrier.

Geomorphic impact and assessment of flexible barriers using multi-temporal LiDAR data: The Portainé mountain catchment (Pyrenees)

Multi-temporal digital elevation models (DEMs) obtained from airborne LiDAR surveys are widely used to detect geomorphic changes in time and quantify sediment budgets. However, they have been rarely applied to study the geomorphic impact of engineering structures in mountain settings. In this study, we assessed the influence and behavior of flexible sediment retention barriers in the Portainé catchment (Spanish Pyrenees), using three LiDAR data sets (2009, 2011 and 2016) that covered a 7-year period. Densely forested mountainous areas present some limitations for reliable DEM analysis due to spatial variabilities in data precision, accuracy and point density. A new methodological approach for robust uncertainty analysis along channels, based on changes in cross-sectional elevations, was used to discriminate noise from real geomorphic changes. The obtained results indicated that erosion occurs along most reaches covering a large area, whereas deposition is localized in specific areas such as those upstream of sediment retention barriers and in the debris cone. Despite the presence of 15 flexible sediment retention barriers, the channels presented net degradation during both 2009–2011 and 2011–2016, with 2838 and 147 m3 of material exported from the basin, respectively. For the same periods, the barriers retained 33% and 25% of the total deposition (up to 1300 m3 per barrier), respectively, but also induced lateral and downstream incision, the latter reaching 703 m3 for a single barrier. We detected a horizontal displacement of the net of up to 1.2 m in filled barriers, resulting from net flexion. The interference of the natural river evolution by defense measures has resulted in a complex erosion-deposition pattern. The presented methods show high potential for the hydrogeomorphic study of mountain catchments, especially for a high-resolution assessment of flexible barriers or other engineering structures in remote areas.

The role of carrier gas flow in roll-to-roll AP-PECVD synthesized silica moisture barrier films

Moisture barrier films are deposited on a polymer foil by roll-to-roll Atmospheric Pressure Plasma Enhanced CVD reactor using a N2, O2, TEOS gas mixture. The film microstructure and permeation properties are studied as a function of the carrier gas flow rate with both static and dynamic film transport. The microstructure is analyzed by spatially resolved attenuated total reflectance (ATR)-FTIR and correlated with the vertical density gradient obtained in the dynamic films and the moisture barrier performance. It is shown that by varying the carrier gas flow rate the vertical density gradient, or the network porosity, can be tuned by governing the convective transport inside the reactor consequently densifying the inorganic film at fixed energy cost (i.e. Yasuda parameter) of the process. Moreover, adopting the bilayer architecture allows to achieve the same moisture barrier properties of 2 · 10−3 g·m−2·day−1 (40 °C, 90% RH) at only half the film thickness of a single layer barrier films, which consequently leads to a throughput increase of almost two times.

High-Speed Force Spectroscopy of Lipid Bilayer Rupture

Supported Lipid Bilayers (SLBs) are simple biological membrane models widely used for fundamental studies. Atomic Force Microscopy (AFM)-based Force Spectroscopy is an ideal technique to investigate the mechanical properties of SLBs at the nanoscale, their elastic constants but also their resistance to failure. The mechanical rupture of the lipid bilayer by the AFM tip has been used extensively as a hallmark of its mechanical stability, usually by measuring the forces required to break the bilayer probed at different velocities. Being a stochastic process, rupture forces generally increases linearly with the logarithm of the loading rate, defining a characteristic dynamic force spectrum. Thanks to the miniaturization of the cantilever and piezoelectric elements, High-Speed AFM (HS-AFM) allows reaching tip velocities in the millimeter per second range with microsecond time resolution (1), covering a wider dynamic force spectrum. Here, we apply HS-AFM force spectroscopy to access six decades of indentation velocities on supported lipid bilayers. We also assess the possible contribution of the cantilever resonance frequency to the force spectrum. The preliminary dynamic force spectrum of DOPC can be interpreted with a single energy barrier although possibly followed by an outer state. The outcomes allow us to evaluate the validity of general theoretical developments applied in the field (2). 1.Rico F, Gonzalez L, Casuso I, Puig-Vidal M, & Scheuring S (2013) High-Speed Force Spectroscopy Unfolds Titin at the Velocity of Molecular Dynamics Simulations. Science 342(6159):741-743. 2.Butt HJ & Franz V (2002) Rupture of molecular thin films observed in atomic force microscopy. I. Theory. Physical Review E 66(3).

Suppression of Recombination in the Waveguide of a Laser Heterostructure by Means of Double Asymmetric Barriers

A 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 Al0.2Ga0.8As 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.

Experimental evidences of quantum confined 2D indirect excitons in single barrier GaAs/AlAs/GaAs heterostructure using photocapacitance at room temperature

We investigated excitonic absorptions in a GaAs/AlAs/GaAs single barrier heterostructure using both photocapacitance and photocurrent spectroscopies at room temperature. Photocapacitance spectra show well defined resonance peaks of indirect excitons formed around the Γ-AlAs barrier. Unlike DC-photocurrent spectra, frequency dependent photocapacitance spectra interestingly red shift, sharpen up, and then decrease with increasing tunneling at higher biases. Such dissimilarities clearly point out that different exciton dynamics govern these two spectral measurements. We also argue why such quantum confined dipoles of indirect excitons can have thermodynamically finite probabilities to survive even at room temperature. Finally, our observations demonstrate that the photocapacitance technique, which was seldom used to detect excitons in the past, is useful for selective detection and experimental tuning of relatively small numbers (∼1011/cm2) of photo-generated indirect excitons having large effective dipole moments in this type of quasi-two dimensional heterostructures.

Straightforward Probing of Polarization and Spin-Resolved Transmission through Potential Barriers in Silicene

The low-energy physics of silicene is described by Dirac electrons with a strong spin-orbit interaction and its band structure can be controlled by an external electric field Ez. We evaluate the electronic transmission through single and double barriers in silicene as a function of the angle of incidence θ, the electron energy E, and the strength of the field Ez. We find a spin-resolved transmission, reflected in the polarization P, and a conductance qualitatively different in some ranges of E than that in graphene. P exhibits quasiperiodic resonances versus θ in double-barrier structures.

Influence of SDBD plasma aerodynamic actuation on flow control by AC power supply and AC-DC power supply

In this paper, the excitation effect of single dielectric barrier discharge plasma actuator (SDBD) is compared by using AC power supply and AC-DC power supply. AC-DC power supply is based on the AC power supply, just adding DC component. The flow measurement is carried out by PIV technique. Results show that the excitation effect of AC power supply and AC-DC power supply increases by the increase of voltage, the range of speed field excited by AC power is greater than that of AC-DC power supply. For x direction maximum speed, excited by AC power supply is close to AC-DC, and for y direction maximum speed, AC power supply is greater than AC-DC power supply. So the excitation effect of AC power supply is better than that of AC-DC power supply for SDBD.