Single Barrier Research Articles

Degradation of sulfamethoxazole in aqueous solution by dielectric barrier discharge plasma combined with Bi2WO6 -rMoS2 nanocomposite: Mechanism and degradation pathway

The feasibility of pollutant removal in aqueous solution by dielectric barrier discharge plasma in combination with Bi2WO6-rMoS2 composite photocatalyst was investigated by choosing sulfamethoxazole (SMZ) as the model pollutant. In this study, Bi2WO6-rMoS2 catalysts were synthesized by a modified hydrothermal method and characterized by TEM, XRD, XPS. The results showed that the Bi2WO6 was well loaded on the surface of MoS2. The influences of the main operating parameters including discharge voltage, initial concentration, initial pH, mass ratios and dosages of Bi2WO6-rMoS2 on the removal efficiency of SMZ were studied. The results revealed that the initial concentration of 20 mg L−1 SMZ solution (100 mL) could be degraded by 97.6% with the addition of 0.08 g L−1 Bi2WO6-rMoS2 (1 wt%) at 9 kV after 21 min, compared with 72.5% by single dielectric barrier discharge plasma. Even after four cycling runs, Bi2WO6-rMoS2 (1 wt%) still remained high removal efficiency of SMZ. Moreover, the yields of hydrogen peroxide (H2O2) and Ozone (O3) in plasma discharge process were also investigated, and the results exhibited that adding Bi2WO6-rMoS2 could notably influence the amount of O3 and H2O2. Finally, ten intermediates of SMZ degradation were identified, and the proposed SMZ degradation pathways were deduced based on the detected intermediates.

Enhancement of Dissociation Kinetics of Biomolecules through the Use of Alternating Electric Fields

In this work we verify both theoretically and by simulation that an AC electric field, with a frequency much higher than the dissociation rate, can significantly accelerate the dissociation of biological molecules, such as DNA, under isothermal conditions. The cumulative effect of the AC field is shown to break a key bottleneck by reducing the entropy (and increasing the free energy of the local minimum) via alignment of the molecular dipole with the field. For DNA molecules, this dissociation mechanism is shown to follow a universal pathway of successive molecular alignment and base-pair breakage over each cycle. It is an activated process with a single barrier, which corresponds to the breaking of the first couple of base pairs at one end, and the cumulative work done by the AC field in repeated alignments of the DNA dipole is to reduce this barrier. We were able to derive frequency and amplitude dependence of the enhanced dissociation that is consistent with All-Atomic simulations, to demonstrate the existence of an optimum frequency with the highest dissociation rate (roughly corresponding to the inverse dipole decay time) and to show that the dissociation rate at high enhancement is a universal one with a weak logarithm dependence on the DNA length and sequence, in concordance with experiments. This suggests that the high electric field at gap junctions and ion channels may have a universal transient time to facilitate their synchronization.

A single gas barrier layer of high-density Al2O3 formed by neutral beam-assisted sputtering at room temperature

This paper reveals the formation of high-density Al2O3 thin films at low temperatures for inorganic gas barriers using neutral beam-assisted sputtering (NBAS). The NBAS induces an annealing effect even at room temperature through energetic neut.al particles, leading to an enhancement in the density of Al2O3 thin films. As a result, we obtained a water vapor transmission rate of 1.58 × 10−5 g/(m2·day) using a single layer of Al2O3 thin film at a thickness of 100 nm. In the NBAS, the energetic neutral particle bombardment of the thin film occurs during magnetron sputtering. The high-density Al2O3 gas barrier films formed by the NBAS show applicability to organic microelectronic devices, including organic light-emitting diodes.

Graft-implanted, enzyme responsive, tacrolimus-eluting hydrogel enables long-term survival of orthotopic porcine limb vascularized composite allografts: A proof of concept study.

BackgroundCurrently, patients receiving vascularized composite allotransplantation (VCA) grafts must take long-term systemic immunosuppressive therapy to prevent immunologic rejection. The morbidity and mortality associated with these medications is the single greatest barrier to more patients being able to receive these life-enhancing transplants. In contrast to solid organs, VCA, exemplified by hand or face transplants, allow visual diagnosis of clinical acute rejection (AR), directed biopsy and targeted graft therapies. Local immunosuppression in VCA could reduce systemic drug exposure and limit adverse effects. This proof of concept study evaluated, in a large animal forelimb VCA model, the efficacy and tolerability of a novel graft-implanted enzyme-responsive, tacrolimus (TAC)—eluting hydrogel platform, in achieving long-term graft survival.MethodsOrthotopic forelimb VCA were performed in single haplotype mismatched mini-swine. Controls (n = 2) received no treatment. Two groups received TAC hydrogel: high dose (n = 4, 91 mg TAC) and low dose (n = 4, 49 mg TAC). The goal was to find a dose that was tolerable and resulted in long-term graft survival. Limbs were evaluated for clinical and histopathological signs of AR. TAC levels were measured in serial blood and skin tissue samples. Tolerability of the dose was evaluated by monitoring animal feeding behavior and weight.ResultsControl limbs underwent Banff Grade IV AR by post-operative day six. Low dose TAC hydrogel treatment resulted in long-term graft survival time to onset of Grade IV AR ranging from 56 days to 93 days. High dose TAC hydrogel also resulted in long-term graft survival (24 to 42 days), but was not well tolerated.ConclusionGraft-implanted TAC-loaded hydrogel delays the onset of Grade IV AR of mismatched porcine forelimb VCA grafts, resulting in long term graft survival and demonstrates dose-dependent tolerability.

Barriers to Research among Faculty at a Health Sciences University

Research in the health sciences is needed in order to continue to improve patient care. A survey was distributed to investigate barriers to research among Dentistry, Nursing and Allied Health Professionals academic faculty at a public health sciences university in the United States. Among the 86 faculty respondents, the majority (58%) of faculty identified “lack of time for me to do research” to be the single largest barrier to their own research activity and this item had a higher mean score than all other barriers to research examined. Lack of time was significantly more problematic among female faculty (p=0.006). Research resources were a greater barrier than relevance of research (p<0.001). Respondents noted that clinical duties are frequently a higher priority than research among health sciences faculty, presumably due to shortages in funding and resources. Given the importance of research to the future quality of patient care, efforts should be made to protect health science faculty members’ time and to provide the resources necessary to conduct meaningful research.

Minimum Cost Deployment of Bistatic Radar Sensor for Perimeter Barrier Coverage.

Perimeter barriers can provide intrusion detection for a closed area. It is efficient for practical applications, such as coastal shoreline monitoring and international boundary surveillance. Perimeter barrier coverage construction in some regions of interest with irregular boundaries can be represented by its minimum circumcircle and every point on the perimeter can be covered. This paper studies circle barrier coverage in Bistatic Radar Sensor Network (BRSN) which encircles a region of interest. To improve the coverage quality, it is required to construct a circle barrier with a predefined width. Firstly, we consider a BR deployment problem to constructing a single BR circular barrier with minimum threshold of detectability. We study the optimized BR placement patterns on the single circular ring. Then the unit costs of the BR sensor are taken into account to derive the minimum cost placement sequence. Secondly, we further consider a circular BR barrier with a predefined width, which is wider than the breadth of Cassini oval sensing area with minimum threshold of detectability. We propose two segment strategies to efficiently divide a circular barrier to several adjacent sub-ring with some appropriate width: Circular equipartition strategy and an adaptive segmentation strategy. Finally, we propose approximate optimization placement algorithms for minimum cost placement of BR sensor for circular barrier coverage with required width and detection threshold. We validate the effectiveness of the proposed algorithms through theory analysis and extensive simulation experiments.

Universal Kinetics of the Onset of Cell Spreading on Substrates of Different Stiffness

When plated onto substrates, cell morphology and even stem-cell differentiation are influenced by the stiffness of their environment. Stiffer substrates give strongly spread (eventually polarized) cells with strong focal adhesions and stress fibers; very soft substrates give a less developed cytoskeleton and much lower cell spreading. The kinetics of this process of cell spreading is studied extensively, and important universal relationships are established on how the cell area grows with time. Here, we study the population dynamics of spreading cells, investigating the characteristic processes involved in the cell response to the substrate. We show that unlike the individual cell morphology, this population dynamics does not depend on the substrate stiffness. Instead, a strong activation temperature dependence is observed. Different cell lines on different substrates all have long-time statistics controlled by the thermal activation over a single energy barrier ΔG ≈ 18 kcal/mol, whereas the early-time kinetics follows a power law ∼t5. This implies that the rate of spreading depends on an internal process of adhesion complex assembly and activation; the operational complex must have five component proteins, and the last process in the sequence (which we believe is the activation of focal adhesion kinase) is controlled by the binding energy ΔG.

Measure and analysis of 4H-SiC Schottky barrier height with Mo contacts

Current–voltage (I–V) and capacitance–voltage (C–V) characteristics of Schottky Mo/4H-SiC diodes have been measured and analyzed as a function of temperature between 80 and 400 K. The I–V characteristics significantly deviate from ideal characteristics predicted by the thermionic emission model because of the inhomogeneity of Schottky contact. After a brief review of the different existing models, the main parameters (ideality factor, barrier height, and effective Richardson constant) of both diodes have been extracted in the frame of a Gaussian barrier height distribution model, whose mean and standard deviation are linearly dependent on voltage and temperature, as well as in the context of the potential fluctuation model. The results are compared with the values extracted by C–V and the values in the literature. A link is established between these two models. Diodes of different I–V characteristics, either identified as single barrier or double barrier, have been analyzed by Deep Level Transient Spectroscopy (DLTS) to investigate the deep level defects present. No noticeable difference has been found.

Modeling Neisseria meningitidis Infection in Mice: Methods and Logistical Considerations for Nasal Colonization and Invasive Disease.

The single greatest barrier to studying the lifestyle of Neisseria meningitidis stems from its exquisite adaptation to life in humans, a specialization which prevents it from infecting other animals. This barrier to modeling meningococcal infection has been overcome by the provision of factors that allow the meningococci to overcome one or more aspects of host restriction, including the use of mice expressing receptors that allow mucosal colonization and/or the inclusion of serum factors that facilitate meningococcal replication during disseminated meningococcal disease. Here we discuss these advances, consider variables that influence the outcome of infection, and detail the technical requirements to establish robust and reproducible nasal colonization or sepsis. Once established, these models can then be used to study the meningococcal lifestyle and the immune response during infection, and to facilitate development of novel drug or vaccine-based approaches to intervene in meningococcal carriage and disease.

Numerical algorithm for discrete barrier option pricing in a Black-Scholes model with stationary process

In this article, we propose a numerical algorithm for computing price of discrete single and double barrier option under the emph{Black-Scholes} model. In virtue of some general transformations, the partial differential equations of option pricing in different monitoring dates are converted into simple diffusion equations. The present method is fast compared to alternative numerical methods presented in previous papers.

Water wave scattering by three thin vertical barriers with middle one partially immersed and outer two submerged

The problem of oblique water wave scattering by three thin vertical barriers in deep water is investigated here assuming linear theory. The geometrical configurations of the three barriers are such the inner(middle) barrier is partially immersed and the two outer barriers are completely submerged and extend infinitely downwards. A system of three simultaneous integral equations of first kind involving differences of velocity potentials across the barriers has been obtained in the mathematical analysis by employing Havelock’s expansion of water wave potential alongwith Havelock’s inversion formulae. Approximate numerical solutions of these integral equations are obtained by using single-term Galerkin approximations where the single term is chosen to be the exact solution of the integral equation obtained for a single vertical barrier in deep water for normal incidence of surface waves. Fairely accurate numerical estimates for the reflection and transmission coefficients are obtained by solving this system of linear equations. These estimates satisfy the energy identity, thereby justifying the validity of the present method. Due to energy identity, the behaviour of reflection coefficient is discussed by depicting it graphically against wavenumber. Existence of zeros of reflection coefficient is observed only when the two outer barriers are identical i.e. they are submerged from the same depth below the mean free surface. Some earlier results for two completely submerged barriers and a single barrier are recovered as special cases for a particular set of values of the parameters involved in the problem. This provides another check on the correctness of the present method.

Tunable parallel barriers using Helmholtz resonator

Parallel barriers are widely adopted to control environmental noise, but their performance may be inferior to that of a single barrier owing to the formation of multiple reflection waves between the parallel barriers. To improve the performance of parallel barriers, single or multiple Helmholtz resonators (HRs) are proposed to be mounted on the barrier surface. An acoustic interaction occurs between the HR and open cavity formed by the rigid ground and a pair of barriers, whereby the acoustic modal response within the open cavity is significantly suppressed and the diffraction wave at the barrier top edge is reduced. A semi-analytical model for dealing with acoustic coupling between the open cavity and HRs in a two-dimensional configuration is established in order to understand the sound suppression mechanism within the shadow zone. This model is also helpful for generating a noise control strategy that involves varying the dominant modal response at the target frequency. With the optimal position of a single HR, the insertion loss of about 10 dB around the target frequency can be controlled, while less influence is exerted on the off-target frequency. Comparisons are conducted between the data predicted using the present model and the numerical results obtained using the boundary element method, and the agreement between them is observed. Furthermore, experimental results demonstrate that the use of HRs for reducing noise in the shadow zone is feasible.

Thermal cycling behavior of La2Zr2O7 thermal barrier coatings by plasma spraying of an amorphous and crystalline precursors

Single layer thermal barrier coatings (TBCs) of La2Zr2O7 (LZ) and double layer YSZ/LZ TBCs produced from amorphous (LZA) and crystalline (LZC) feedstock were deposited by atmospheric plasma spray (APS) technique. Thermal cycling behaviors, phase structures and cross-sectional morphologies before and after thermal cycling tests of these coatings were studied in detail. Microstructural properties of three different types of coatings affect thermal cycling lifetime of the coatings. The thermal cyclic test results indicate that the thermal cycling lifetime of LZC/YSZ double layer TBCs is longer than that of single layer LZA and LZC TBCs due to the fact that there are improvements in the sintering resistance ability, thermal expansion mismatch between the ceramic layer and the metallic substrate at high temperature, and thermal insulation effect of DLC (double layer coating) LZ/8YSZ TBCs. The thermal cycling tests indicated that the YSZ/LZC coating has a lifetime of 400 cycles which is longer than single layer LZA and LZC coating. The failure of LZC and LZA coatings mainly results from excessive growth of thermally grown oxide layer, the thermal expansion mismatch between ceramic top coatings and bond coat and thermal stresses accumulated during thermal cycling tests.

In silico synthesis of carbon molecular sieves for high-performance air separation

We performed nonequilibrium molecular dynamics simulations of the chemical vapor deposition (CVD) of hydrocarbons on a precursor-activated carbon model with a slit-like pore (in silico CVD simulation) to explore design guidelines for the synthesis of high-performance carbon molecular sieves (CMSs) for air-separation purposes. The dependence of the CVD process on gas species was investigated using “united-atom” hydrocarbons mimicking ethylene, benzene, toluene, and mesitylene. The obtained CMS models were then used to evaluation the diffusion rate constants of O2 and N2 using the transition state theory. We also constructed idealized carbon pore structures that extracted the characteristics of the CMS models obtained via the in silico CVD simulations to understand the relation between the size and geometry of pore mouths, diffusion rate constants, and kinetic O2 selectivity. We found that most of the simulated results were supported by experimental evidence. Furthermore, we conclude that a high-performance CMS for air separation requires the development of thin amorphous carbon at the pore mouths of the precursor-activated carbon by CVD, which provides a single energy barrier for O2 diffusion and effectively prevents the formation of multiple energy barriers.

Repeal and Replace? A Note of Caution for Medical School Curriculum Reformers.

The sudden, dramatic collapse of the seven-year struggle in Congress to repeal and replace the Affordable Care Act holds important lessons for all would-be reformers, including those advocating fundamental changes in medical education. In this Invited Commentary, the author draws parallels between reform initiatives in health policy and those in medical education, highlighting that, in both settings, stakeholders rarely support "repeal" in the absence of a superior replacement, even when they view the status quo as deeply flawed.For more than three decades, reformers have worked to overhaul the preclerkship medical school curriculum. The author compares two broad categories of these reform initiatives. First, pedagogical reforms largely preserve existing curricular content, instead seeking to maximize active learning principles from educational psychology. By contrast, content reformers attribute the traditional curriculum's shortcomings mainly to what students are taught, rather than how they learn, and seek to swap out significant portions of the existing basic science curriculum to make room for more clinically relevant material. While pedagogical innovations currently dominate reform efforts, few medical education research studies have rigorously proved the impact of different teaching strategies on the outcome of greatest interest to future patients and the public at large: Do new teaching methods yield better doctors?The persistent reliance of residency programs on United States Medical Licensing Examination Step 1 scores in the resident selection process constitutes the single greatest barrier to fundamental paradigm shifts in undergraduate medical education. The author concludes by proposing a solution to overcome this barrier.

Application of plasma for efficient H2 production: A realism of copper electrode in single dielectric barrier discharge reactor

Effective transformation of moisture into hydrogen in argon containing 100% relative humidity employing dielectric barrier discharge cold plasma is reported. The coaxial reactor with a common outer Pyrex tube having an inner diameter of 14 mm accompanied by a central electrode combination is employed for H2 generation through water splitting. Three different central electrodes such as Pyrex (double dielectric surfaces), copper (Cu), and stainless steel (SS) [single dielectric (SD) surface] are used separately, investigating the H2 production efficiency with the variation of gas residence time (GRT), electric field, working frequency, electrode surface, and discharge gas-gap (GG). Optimal electric fields 3.5, 1.7, and 1.3 kV mm−1 at 14.5 kHz are required for the highest H2 production at 45 s GRT for Pyrex, SS, and Cu reactors, respectively. The utmost H2 productions 2500 and 4500 ppmv are observed with 100 mm long, 4 mm GG and 290 mm long, 2 mm GG Cu SD reactors, respectively.

Social network to inform and prevent the spread of cocoa swollen shoot virus disease in Ghana

The cocoa swollen shoot virus disease is a major factor limiting cocoa (Theobroma cacao L.) productivity for West African farmers. The only treatment against this disease is to cut infected trees and replant with disease-free planting material. Research has recommended the prevention measures: (i) cordon sanitaire (leaving 10-m-wide cocoa-free zone around cocoa), (ii) barrier cropping, (iii) using partly tolerant hybrids, and (iv) removing specific alternative host tree species. Here, we evaluate the current adoption of these measures and identify their adoption constraints. We conducted a quantitative survey with 396 farmers in the Eastern and Western Regions of Ghana, held six focus group discussions and hosted a multi-stakeholder validation workshop with 31 key actors in the cocoa value chain. Our results indicate that the adoption of prevention measure against the disease remains limited. Farmers with a more extensive social network (number of family members/close friends who already adopted a particular measure), a larger farm size, more secure land tenure rights, and more knowledge about the measures were more likely to adopt them, especially barrier cropping, hybrid seedlings, and removing alternative host trees. Lack of knowledge about the measures was the single biggest barrier for their adoption, with 51% of the participating farmers not even being aware of any prevention measures. Here, we show for the first time that the social network is the main information source for farmers, which agrees with the finding that the flow of information between farmers and other stakeholders is a critical factor affecting knowledge spread and consequently adoption. Our results provide crucial insights for the elaboration of an implementation action plan to boost the dissemination of feasible prevention measures against the cocoa swollen shoot virus disease in Ghana in order to efficiently cover farmers’ needs for information (technical advice) and inputs (access to hybrid seedlings).

A novel method to mitigate residual stress in CVD diamond film on steel substrates with a single intermediate layer

Direct deposition of CVD diamond on steel produces useless diamond film which delaminates on cooling from deposition temperature [1–9]. The majority of current research efforts focus on single and multiple intermediate layers for CVD diamond deposition on steel substrate. There are many excellent diffusional barriers to transition metals migration from bulk to substrate surface to form graphitic sp2 bonds. However, there is no practical solution to the thermal expansion coefficient (TEC) mismatch between diamond and steels. In this work we use a vanadium carbide thermodiffused coating as the intermediate layer between diamond and AISI O1 steel substrate. It acts as a diffusional barrier and mitigates diamond residual stress after cooling from CVD temperature. Increasing vanadium carbide layer thickness creates a transition zone that attenuates diamond residual stress. Up to now, the vanadium carbide is the only single layer barrier able to inhibit graphitic phase formation and mitigate residual stress in diamond films to the level of 0.54 GPa.

Interrupted Pressure-Jump NMR Experiments Reveal Resonances of On-Pathway Protein Folding Intermediate.

Previous pressure-jump NMR experiments on a pressure-sensitized double mutant of ubiquitin showed evidence that its folding occurs via two parallel, comparably efficient pathways: a single barrier and a two-barrier pathway. An interrupted folding NMR experiment is introduced, where for a brief period the pressure is dropped to atmospheric conditions (1 bar), followed by a jump back to high pressure for signal detection. Conventional, forward sampling of the indirect dimension during the low-pressure period correlates the 15N or 13C' chemical shifts of the unfolded protein at 1 bar to the 1H frequencies of both the unfolded and folded proteins at high pressure. Remarkably, sampling the data of the same experiment in the reverse direction yields the frequencies of proteins present at the end of the low-pressure interval, which include unfolded, intermediate, and folded species. Although the folding intermediate 15N shifts differ strongly from natively folded protein, its 13C' chemical shifts, which are more sensitive probes for secondary structure, closely match those of the folded protein and indicate that the folding intermediate must have a structure that is quite similar to the native state.

Metal contact and carrier transport in single crystalline CH3NH3PbBr3 perovskite

Organic-inorganic perovskites have arrived at the forefront of solar technology due to their impressive carrier lifetimes and superior optoelectronic properties. By having the cm-sized perovskite single crystal and employing device patterning techniques, and the transfer length method (TLM), we are able to get the insight into the metal contact and carrier transport behaviors, which is necessary for maximizing device performance and efficiency. In addition to the metal work function, we found that the image force and interface charge pinning effects also affect the metal contact, and the studied single crystal CH3NH3PbBr3 features Schottky barriers of 0.17 eV, 0.38 eV, and 0.47 eV for Au, Pt, and Ti electrodes, respectively. Furthermore, the surface charges lead to the thermally activated transport from 207 K to 300 K near the perovskite surface. In contrast, from 120 K to 207 K, the material exhibited three-dimensional (3D) variable range hopping (VRH) carrier transport behavior. Understanding these fundamental contact and transport properties of perovskite will enable future electronic and optoelectronic applications.