Buffer Structure Research Articles

Fast Realization of 3-D Space-Time Correlation Sea Clutter of Large-Scale Sea Scene Based on FPGA: From EM Model to Statistical Model

Memoryless nonlinear transform (MNLT) method was widely used in the statistical model for sea clutter simulations. When the radar scattering data sets were obtained, we can simulate large scene and long-time varying 3-D sea surface scattering using expended power spectral quickly and accurately. Compared with the personal computer platform, field-programmable gate array (FPGA) has the unique merit of energy efficiency, high performance and adaptability. In this article, we proposed a novel architecture for implementing the 3-D MNLT algorithm on FPGA using high-level synthesis. As the simulation size increases, the demand for storage resources will also increase rapidly, and the on-chip memory resource will be limited on FPGA. Aiming at these problems, we divided the 3-D space-time simulation into a 2-D spatial simulation and a 3-D temporal simulation, so that we can make full use of the off-chip memory. Our design employs multiple on-chip buffer structures to decrease the transfer time of internal and external data on the FPGA. We also design a dataflow inverse fast Fourier transform processing engine (PE). The dataflow implementation overlapped butterfly operation, increasing concurrency and the overall throughput of this PE. Experimental results show that we can obtain the same accuracy and higher efficiency on a Xilinx Zynq XC7Z100 SoC platform.

Pressure impact characteristic of vane type continuous rotary motor under different buffer structures

In order to solve the problem of pressure shock on the continuous rotary electro-hydraulic servo motor, the mathematical models of pressure gradient under the structure of pre-compressed chamber and U-shaped groove were established. The optimal structure dimensions of the pre-compressed chamber and the U-shaped groove were determined. The fluid models were established by Solidworks under the four structures of triangular groove, triangular groove with pre-compression chamber, U-shaped groove and U-shaped groove with pre-compression chamber. Simulation analysis of depressurization process of fluid models was performed based on FLUENT. The pressure nephograms of different buffer structures were compared and analyzed, and the pressure change curves and pressure gradient change curves in the process of depressurization were obtained. The results show that the optimal edge length of the pre-compressed chamber of continuous rotary electro-hydraulic servo motor is 20 mm in the process of decompression. The pressure reduction effect is the best when the width of the U-shaped groove is 1.5 mm and the depth is 1.65 mm. The U-shaped groove structure with pre-compression chamber is more conducive to alleviate the pressure shock phenomenon of the motor compared with different combine buffer structures.

A Mixed Parallel and Pipelined Efficient Architecture for Intra Prediction Scheme in HEVC

The complexity of intra prediction in High-Efficiency Video Coding (HEVC) is increased significantly due to the incorporation of inherent features like variable-sized quadtree partitioned coding units and 35 angular modes that help in achieving better compression. This paper presents an efficient hardware architecture for the intra prediction that supports and comprises the above aspects and achieves a higher throughput to support high definition (HD) videos. A compact reusable reference buffer structure is implemented to limit the buffer size to 1 KB. A dedicated arithmetic unit to take advantage of the parallelism present in the prediction algorithm is incorporated, which allows the reuse of multipliers to reduce hardware resources. The loading of reference samples to buffers for prediction causes significant delays which are eliminated in our design. The entire architecture functions as a pipelined unit with no data dependency and generates eight samples/clock cycle in parallel. The design is implemented on a Field Programmable Gate Array (FPGA) platform operating at a frequency of 110 MHz. This makes it possible to support 4 K videos at 30 frames per second, with the resource cost of 16 K logic gates and 122 registers.

Wide-range energy-efficient buffer-based voltage level-up converters for multi-supply voltage systems

The voltage level converters (LCs) are required to attain optimized power consumption by interfacing two or more supply voltage domains in Systems-on-Chip (SoC) applications. The voltage level-up conversion can be easily and effectively achieved by the use of buffer structures. Hence this article proposes two buffer-based LCs, namely transmission gate buffer level converter (TGBLC) and stacked PMOS buffer level converter (SPBLC), based on voltage stepping technique. The energy-efficient transmission gate (TG) and stacked PMOS (SP) structures are proposed to define voltage steps in the buffer and ensure a wider voltage conversion range with high speed. The LCs are implemented in 0.18 $$\mu $$ m technology and their performance metrics are verified using a Spectre circuit simulator. The simulation results show that TGBLC and SPBLC can convert a low input voltage of 600 and 550 mV to 1.8 V, respectively. For the target input voltage of 0.8 V with frequency of 1 MHz, the TGBLC and SPBLC exhibit an improved delay of 7.3 and 7.1 ns with an energy consumption of 9.66 and 6.66 pJ per transition, respectively. It is noted from the experimental results that the proposed LCs are suitable for applications where simplicity and energy efficiency/low power with a wider conversion range is preferred.

A TEM Study of AlN–AlGaN–GaN Multilayer Buffer Structures on Silicon Substrates

Two buffer structures based on AlxGa1 – xN solutions with silicon doping and without it have been studied by transmission electron microscopy. The structures have been grown on silicon substrates with the (111) orientation by metalorganic vapor-phase epitaxy with consistently decreasing Al content. A significant threading dislocation density reduction in the region of intermediate layers has been found at a change in the Al content from 32 to 23%. Phase decay and the phenomenon of compositional self-modulation in the AlxGa1 – xN layers in the direction of growth have been detected at an Al content equal to 32, 23, 12, and 4%. A model of the structure of layers in the region of composition modulation has been proposed.

Characterization of theCorynebacterium glutamicumdehydroshikimate dehydratase QsuB and its potential for microbial production of protocatechuic acid.

The dehydroshikimate dehydratase (DSD) from Corynebacterium glutamicum encoded by the qsuB gene is related to the previously described QuiC1 protein (39.9% identity) from Pseudomonas putida. Both QuiC1 and QsuB are two-domain bacterial DSDs. The N-terminal domain provides dehydratase activity, while the C-terminal domain has sequence identity with 4-hydroxyphenylpyruvate dioxygenase. Here, the QsuB protein and its N-terminal domain (N-QsuB) were expressed in the T7 system, purified and characterized. QsuB was present mainly in octameric form (60%), while N-QsuB had a predominantly monomeric structure (80%) in aqueous buffer. Both proteins possessed DSD activity with one of the following cofactors (listed in the order of decreasing activity): Co2+, Mg2+, Mn2+. The Km and kcat values for the QsuB enzyme (Km ~ 1 mM, kcat ~ 61 s-1) were two and three times higher than those for N-QsuB. 3,4-DHBA inhibited QsuB (Ki ~ 0.38 mM, Ki’ ~ 0.96 mM) and N-QsuB (Ki ~ 0.69 mM) enzymes via mixed and noncompetitive inhibition mechanism, respectively. E. coli MG1655ΔaroEPlac‒qsuB strain produced three times more 3,4-DHBA from glucose in test tube fermentation than the MG1655ΔaroEPlac‒n-qsuB strain. The C-terminal domain activity towards 3,4-DHBA was not established in vitro. This domain was proposed to promote protein oligomerization for maintaining structural stability of the enzyme. The dimer formation of QsuB protein was more predictable (ΔG = ‒15.8 kcal/mol) than the dimerization of its truncated version N-QsuB (ΔG = ‒0.4 kcal/mol).

Wet-Spinning Synthetic Fibers from Aggregate Glue: Aggregate Spidroin 1 (AgSp1).

Spidroin has the potential of wide applications in the biomedicine field as a natural biomaterial. Various synthetic fibers with outstanding mechanical properties have been produced from different spidroins. However, studies on the structural analysis or biomimetic exploration of aggregate spidroin (AgSp) remain scarce. Here, three recombinant AgSp1 spidroins (1RP, 1RC, 3RP) were constructed and expressed in Escherichia coli, followed by purification via coupling heating and ammonium sulfate precipitation. Circular dichroism (CD) spectrum-based secondary structural analysis shows that 1RP and 3RP have similar structures (mainly random coil) in water and PB buffer, while 1RC is mainly composed of α-helix structure and HFIP can change all of the recombinant AgSp1 into helix structure. Through the wet-spinning method, six types of synthetic fibers were produced from these three recombinant AgSp1 spidroins. Subsequently, the properties and structures of synthetic fibers were characterized by mechanical testing and ATR-FTIR. Synthetic fibers spun from 3RP have considerable tensile strength and extensibility (∼37.56 MPa and ∼4.5%, respectively). To the best of our knowledge, this is the first synthetic fiber obtained from AgSp spidroin. Our results demonstrated that AgSp1 can be regarded as an available source of spidroin for silklike fiber production and may provide valuable perspectives on the AgSp1 biomimetic process for certain applications.

A Pathway to Thin GaAs Virtual Substrate on On‐Axis Si (001) with Ultralow Threading Dislocation Density

With recent developments in high‐speed and high‐power electronics and Si‐based photonic integration, the concept of monolithic III–V/Si integration through epitaxial methods is gaining momentum. However, the performance and reliability of epitaxially grown devices are still limited by defects in the semiconductor material, especially the threading dislocation density (TDD). Herein, a novel “asymmetric step‐graded filter” structure grown by molecular beam epitaxy (MBE) is proposed based on a systematic study of the commonly used techniques for threading dislocation reduction for high‐quality GaAs on Si (001) growth. The proposed structure greatly enhances the plastic relaxation in the filter layers. A surface TDD lower than 2 × 106 cm−2 is achieved with a total buffer thickness of only 2.55 μm. This provides a clear pathway to further reduce defect density down to the theoretical limit in the 105 cm−2 regime with a thin buffer structure.

Impact of Varied Buffer Layer Designs on Single-Event Response of 1.2-kV SiC Power MOSFETs

In this article, the single-event response of the 1.2-kV silicon-carbide (SiC) power MOSFETs with varied buffer layer designs is investigated by the 2-D numerical simulations. The structural parameters of the buffer layers are compared and analyzed to understand the transient response after the heavy ion strike and the related physical mechanisms comprehensively. Simulation results reveal that an optimized single buffer structure can be acquired by using a relatively thicker buffer layer (T $\mu \text{m}$ ) and a moderate doping concentration (D cm−3). It demonstrates that the single-event-burnout (SEB) performance can be improved significantly under the worst case bias conditions [a drain bias voltage of 1.2 kV and a linear energy transfer (LET) of 1 pC/ $\mu \text{m}$ ]. In addition, the optimized structural combinations adopted in the dual or triple buffer layers can strengthen the SEB performance further. The simulation results show that a step electric field distribution is established inside the optimized dual or triple buffers, where the electric field peak is mitigated from 3 to 2.2 MV/cm. Moreover, the excess carrier generation is suppressed and the local temperature rise is weakened during the transient electrothermal process. Consequently, the structure with the optimal buffer layer designs can enlarge the SEB safe operating area (SOA) from 30%–50% to 100% rated breakdown voltage at high LET bias, which makes the SiC power MOSFETs used in aerospace and aviation power electronic systems become possible.

Construction of a secondary conductive and buffer structure towards high-performance Si anodes for Li-ion batteries

Nowadays, Silicon (Si) is known as the next generation anode of lithium ion batteries (LIBs), owing to its high theoretical capacity, low lithium storage potential and natural abundance. However, the huge volume expansion and poor conductivity of silicon anodes restrict their practical application due to their poor cyclability and unsatisfied rate performances. Herein, to improve the electrochemical performance of silicon anodes, a facile one-step injection pyrolysis was used to construct a novel secondary conductive and buffer structure where Si nanoparticles are conformally coated by the interconnected onion-like carbon and then are anchored in graphene nanosheets (GNS) skeleton. The synergy of interconnected ordered onion-like carbon coating layer and GNS favors for promoting fast electron transfers and improving electrochemical kinetics, which benefits for achieving an excellent rate performance. Additionally, layer-by-layer strain relaxation by onion-like carbon and flexible GNS hierarchically buffer the substantial variation in volume of Si and then endow the composite with good cyclability. Specifically, the anode of GNS@OLC-Si shows high reversible capacity of 1129.3 mAh g−1 after 300 cycles at a current density of 0.5 A g−1. In rate performance test, the capacity retention of the GNS@OLC-Si is high especially at high current density (66.2% at 2 A g−1). Hence, a new secondary structure is successfully designed to accelerate the diffusion kinetics and buffer the volume change of Si, thereby achieving stable cyclabilities and rate performances.

Simulation design of a high-breakdown-voltage p-GaN-gate GaN HEMT with a hybrid AlGaN buffer layer for power electronics applications

We propose a novel GaN high-breakdown-voltage high-electron-mobility transistor (HB-HEMT) with a p-GaN gate and hybrid AlGaN buffer to improve the breakdown voltage and Baliga’s figure of merit. The hybrid AlGaN buffer is composed of a horizontally arranged AlaGa1−aN zone and an AlbGa1−bN zone, each having different Al compositions a and b. The proposed HB-HEMT is simulated using the Silvaco technology computer-aided design (TCAD) tool ATLAS, considering the polarization model, low-field mobility, high-field mobility, and Selberherr’s impact ionization model to simulate the direct-current (DC), breakdown, and C–V properties of the proposed HB-HEMT. The breakdown voltage of the HB-HEMT is significantly improved by introducing the hybrid AlGaN buffer structure, which can effectively modulate the electric field distributions within the channel and the buffer. A high breakdown voltage (1450 V), a low specific on-state resistance (0.47 mΩ cm2), and a high Baliga’s figure of merit (4.47 GW/cm2) are obtained at the same time with an Lgd (gate-to-drain distance) of 6 µm, a distance from the gate to the AlaGa1−aN/AlbGa1−bN interface of 4 µm, and Al compositions of a = 0.25 and b = 0.1. The simulated C–V results also reveal that the GaN HB-HEMT shows better switching characteristics than the conventional GaN HEMT with a p-GaN gate.

Catching Common Cold Virus with a Net: Pyridostatin Forms Filaments in Tris Buffer That Trap Viruses-A Novel Antiviral Strategy?

The neutrophil extracellular trap (ET) is a eukaryotic host defense machinery that operates by capturing and concentrating pathogens in a filamentous network manufactured by neutrophils and made of DNA, histones, and many other components. Respiratory virus-induced ETs are involved in tissue damage and impairment of the alveolar–capillary barrier, but they also aid in fending off infection. We found that the small organic compound pyridostatin (PDS) forms somewhat similar fibrillary structures in Tris buffer in a concentration-dependent manner. Common cold viruses promote this process and become entrapped in the network, decreasing their infectivity by about 70% in tissue culture. We propose studying this novel mechanism of virus inhibition for its utility in preventing viral infection.

Aerodynamic effect of cross passages at the entrance section of a high-speed railway tunnel in a region with mountains and canyons

The environmental characteristics of difficult mountainous regions has ruled out the easy installation of buffer structures in tunnels. To address this problem, we proposed the installation of cross passages in an entrance section to alleviate the aerodynamic effects of a high-speed train entering the tunnel. In this study, a slide rail high-speed train experimental aerodynamic model was established based on the same principles. By combining the aerodynamic model experiments with a numerical simulation, the effect of cross passage on the generation and propagation of compression waves and micro-pressure waves was investigated. The simulation was capable of predicting the behavior of compression waves and verifying the correctness of the model at a low cost. The results showed that the installation of cross passages could reduce the peak pressure of the initial compression wave, modulate the pressure fluctuation in the tunnel and reduce the micro-pressure wave. For a train speed of 350 ​km/h and a tunnel cross-sectional area of 100 ​m2, the cross passage with the best modulation effect had a length of 10 ​m and a cross-sectional area of 20 ​m2. This cross passage was located at a distance of 10–20 ​m from the tunnel opening.

Epitaxial growth and characterization of dual-sided Y2O3 buffer layer for superconducting coated conductors

In this work, a dual-sided buffer template, which allows the deposition of YB2Cu3O7-δ (YBCO) coated conductors on both sides, has been proposed and investigated. Theoretically, in contrast to traditional YBCO structure on one side, the performance of critical current in YBCO films has been improved by two times. In this buffer structure, the dual-sided Y2O3 films were grown on a flexible metal template by a home-made reel-to-reel dynamic direct current sputtering system and the film growth parameters were systematically investigated. The microstructure were characterized by in situ reflection high-energy electron diffraction monitoring in real time during the deposition stage. X-ray diffraction, and atomic force microscopy were used to detect the biaxial texture and surface morphology, respectively. What's more, by the application of stopping and range of ions in matter software, it helped us to understand the influence of deposition parameter to the growth rate of Y2O3 films. Finally, the biaxial texture of dual-sided Y2O3 film yielded out-of-plane texture of Δω = 4.2° and in-plane texture of ΔΦ = 5.2° for one side, as well as Δω = 5° and ΔΦ = 5.3° for the second side. Subsequently, the dual-sided YBCO superconducting films were coated on the above Y2O3 buffer layer by low-cost metal-organic chemical vapor deposition method with critical current of 30 A/cm and 60 A/cm for each side.

Cathodoluminescence Study of Dislocations in Step-Graded InGaP Buffer Layers of Metamorphic Single-Junction InGaAs Solar Cells

Epitaxial growth of lattice-mismatched materials is useful for solar cells, but lattice dislocations must be controlled for best device performance. It has been shown that metamorphic growth enables fabrication of InGaAs p–n junctions with good performances on GaAs substrates due to the insertion of buffer layers. Here, we investigate misfit and threading dislocations inside the step-graded InGaP buffer layers of a single-junction InGaAs solar cell by cathodoluminescence microscopy. Prior to measurement, the device edges were polished at various angles (less than 10° with respect to the substrate surface). By using this technique, cross sections of very thin layers can be directly imaged with a resolution that allows us to observe misfit and threading dislocations. In the present device, the densities of the two types of dark lines depend on the position in the buffer structure. In particular, near the InGaAs base layer, the density of the dark lines extending in the [110] direction is higher than that of the dark lines extending in the [1-10] direction. We believe that this difference in the dark line density is related to the surface morphology.

Coaxial Electrospun Fibermat of Poly(AM/DAAM)/ADH and PCL: Versatile Platform for Functioning Active Enzymes

Abstract In this study, we prepared and characterized enzyme (α-chymotrypsin or lactase)-encapsulating core-shell fibermats by electrospinning. The hydrophilic copolymer of acrylamide (AM) and diacetone acrylamide (DAAM), poly(AM/DAAM), was used as the base material to obtain the core unit of nanofibers. During electrospinning, poly(AM/DAAM) was crosslinked with the bifunctional crosslinker adipic acid dihydrazide (ADH) in the presence of enzyme molecules. The cores were wrapped with hydrophobic poly(ε-caprolactone) (PCL) layers as shell unit. Different from the fibermats of only poly(AM/DAAM)/ADH, the core-shell fibermat of poly(AM/DAAM)/ADH and PCL exhibited sufficient mechanical strength and stability of the stacked nanofibrous structure in a neutral-pH buffer. Furthermore, when the PCL-shell thickness was controlled to be less than 150 nm, the encapsulated enzymes exhibited an apparent activity of >70–80% for low-molecular weight substrates in an immersion buffer. These results indicate that the core-shell fibermats of poly(AM/DAAM)/ADH and PCL (or other hydrophobic polymer) could be used as effective enzyme-immobilizing platforms.

Buffering Effect of Overlying Sand Layer Technology for Dealing with Rockfall Disaster in Tunnels and a Case Study

Abstract An overlying sand layer combined with a concrete arch operates as a buffering structure for dealing with rockfall disasters in tunnel construction, especially through karst and weak strata...

Using hole injection layers for decreased metastability and higher performance in Cu(In,Ga)Se2 devices

Modifications to the buffer structure in Cu(In,Ga)Se2 (CIGS) solar cells are examined in terms of power conversion efficiency and metastability. Varying amounts of thin hole-injecting layers are introduced at different locations in the CIGS/Zn(O,S) device structure. It is found that such layers simultaneously increase performance and decrease metastability. The most effective variant produces devices without metastability and with higher efficiency than the CdS-only controls. The most effective location for hole injection is found to be between the Zn(O,S) buffer and the transparent conductor. At this location, passivation of the CIGS surface is not a function of the hole injection layer, and thus a variety of materials with appropriate band-edge energies should achieve the same purpose.

Tuning Mechanism through Buffer Dependence of Hydrogen Evolution Catalyzed by a Cobalt Mini-enzyme.

Cobalt-mimochrome VI*a (CoMC6*a) is a synthetic mini-protein that catalyzes aqueous proton reduction to hydrogen (H2). In buffered water, there are multiple possible proton donors, complicating the elucidation of the mechanism. We have found that the buffer pKa and sterics have significant effects on activity, evaluated via cyclic voltammetry (CV). Protonated buffer is proposed to act as the primary proton donor to the catalyst, specifically through the protonated amine of the buffers that were tested. At a constant pH of 6.5, catalytic H2 evolution in the presence of buffer acids with pKa values ranging from 5.8 to 11.6 was investigated, giving rise to a potential-pKa relationship that can be divided into two regions. For acids with pKa values of ≤8.7, the half-wave catalytic potential (Eh) changes as a function of pKa with a slope of -128 mV/pKa unit, and for acids with pKa of ≥8.7, Eh changes as a function of pKa with a slope of -39 mV/pKa unit. In addition, a series of buffer acids were synthesized to explore the influence of steric bulk around the acidic proton on catalysis. The catalytic current in CV shows a significant decrease in the presence of the sterically hindered buffer acids compared to those of their parent compounds, also consistent with the added buffer acid acting as the primary proton donor to the catalyst and showing that acid structure in addition to pKa impacts activity. These results demonstrate that buffer acidity and structure are important considerations when optimizing and evaluating systems for proton-dependent catalysis in water.

Monolayer of PtSe2 on Pt(1 1 1): is it metallic or insulating?

Motivated by the recent synthesis of a PtSe2 monolayer by direct selenization of a Pt(1 1 1) substrate and in order to reproduce ARPES experimental results, we investigate if the PtSe2 film could have grown directly on top of the Pt substrate or if some buffer structure separates both of them. We calculate the electronic properties for different growth possibilities and come to the conclusion that the experimental outcome is not compatible with the growth of a PtSe2 monolayer directly on top of the Pt(1 1 1) substrate.