V-shaped Structures Research Articles

Operating resistance prediction of non-flat HEPA filters

The operating resistance of a high-efficiency particulate air (HEPA) filter is affected by the environment and cannot be obtained through the dust holding capacity (DHC) test in the laboratory. For non-flat HEPA filters, studies on the effect of non-uniform deposition of particles on operating resistance were insufficient. We proposed an equivalent permeability coefficient (EPC) method to calculate the operating resistance of the filter and took particle size distribution into account. After comparing with the DHC test data using Arizona test dust (A2 fine dust), it was proved that this method can achieve a relative error of <4%. We found >60% of the particles were deposited in the bottom 2/5 of the V-shaped structures. And the uneven deposition of particles could reduce the operating resistance. Then, we realized the optimal design of structural parameters of V-shape and cylinder filters. • Proposed a novel operating resistance prediction model of HEPA filters. • The uneven particle deposition is beneficial to reduce the operating resistance. • Optimized the structural parameters of the HEPA filters.

Heat transfer analysis of a PCM in shell-and-tube thermal energy storage unit with different V-shaped fin structures

This study provides an alternative solution to enhance melting performance of phase change material by designing a novel V-shaped fin. Nineteen cases with different V-shaped fins is designed, the effects of angle, length, number and arrangement of fins on heat transfer performance of heat storage unit were studied. The response surface method was used to optimize the structure. Assessments on the melting fraction, temperature field, velocity distribution, and uniformity for melting are made. Results demonstrate that due to the effect of natural convection, the upper part melting speed is accelerated, resulting in a significant difference in the heat storage efficiency between the upper and lower half regions. The melting time of the lower half of the heat storage unit without fins accounting for 62.5 % of the whole melting time. Based on the above analysis, more and longer fins should be considered to be arranged at the bottom of the heat storage unit to improve the heat storage performance of the system. As noticed, the structure parameters change of fins has a significant effect on reducing the melting time of the whole phase change material. It can be found that there are optimal values for the structure parameters. The optimal fin structure parameters (fin angle α = 55°, fin length L1 = 9 mm, fin number N = 5, branch angle β = 55°, and branch length L3 = 3) obtained. The heat storage efficiency of the optimal fin structure was 2.57 times that without fins, and the heat storage time was shortened by 61.05 %. To be conclusive, adding fins to a heat exchanger is more beneficial than no fins, saving more energy storage time.

Fabrication of sub-micrometer 3D structures for terahertz oscillators by electron beam gray-tone lithography

More and more novel applications are appearing in the almost-unexplored-up-to-recent-times frequency range of around 0.3–3 terahertz (THz), where sub-millimeter radio waves meet far-infrared optical waves. Resonant tunneling diodes (RTDs) are considered one of the promising compact and coherent room temperature signal sources for terahertz applications. In this work, the fabrication process and fabrication challenges for an RTD THz oscillator with a cylindrical resonant cavity are discussed. Successful fabrication of 3D metallic structures with a height of 2–5 μm and a feature size down to 0.5 μm was achieved by combining the traditional trilayer resist process with the dose-modulated (gray-tone) electron-beam (EB) lithography process. It was shown that two-step EB exposure could be used in thick (&amp;gt;2.4 μm) PMMA resist to achieve predictable and controllable fabrication of V-shaped metallic structures with lateral sizes down to 0.5 μm. Applicability of the described fabrication approach was proven by the measurement of oscillation characteristics for the fabricated RTD THz oscillators. Successful operation of the RTD oscillator devices confirms good electrical contact between the top contact of the RTD mesa structure and the RTD pillar structure as well as between the resonant cavity and antenna parts. The fabrication approach described in this work allowed us to eliminate parasitic capacitance formed around RTD mesa in the first fabrication trial and achieve a frequency increase of up to 200 GHz for RTD THz oscillators operating at frequencies 1.5–1.7 THz. The described fabrication approach may also be applicable for the fabrication of 3D metallic structures with a feature size less than 0.5 μm and a height more than 2 μm with EB energies above 50 keV.

Pixelated Microsized Quantum Dot Arrays Using Surface-Tension-Induced Flow.

Quantum dots (QDs) are semiconducting nanoparticles that exhibit unique fluorescent characteristics when excited by an ultraviolet light source. Owing to their highly saturated emissions, display panels using QDs as pixels have been presented. However, the complications of the nanofabrication procedure limit the industrial application of QDs. This study suggests a method to arrange high-aspect-ratio QD pixels by inducing both Laplace-pressure-driven capillary flow and thermally driven Marangoni flow. The evaporation of colloidal QDs induces a capillary flow that drives the QDs toward the inner tips of V-shaped structures. Additionally, the Marangoni flow arranges the gathered QDs at the tip; thus, they could form a high dune, overcoming the limitations of the existing capillary assembly method using evaporation. Using these phenomena, clover-shaped (assembly of V-shaped edges) templates were made to gather numerous QDs, and the clover with a 30° angle afforded the highest brightness among all the angle structures. Finally, by demonstrating a 100-cm2-sized QD microarray with high uniformity (98.6%), our method shows the feasibility of large-area fabrication, which has extensive application in manufacturing QD displays, anti-counterfeiting labels, and other QD-based optical devices.

Investigations of Rake and Rib Structures in Sand Traps to Prevent Sediment Transport in Hydropower Plants

In order to increase the lifespan of hydraulic turbines in hydropower plants, it is necessary to minimize damages caused by sediment erosion. One solution is to reduce the amount of sediments by improving the design of sand trap. In the present work, the effects on sand trap efficiency by installing v-shaped rake structures for flow distribution and rib structures for sediment trapping is investigated numerically using the SAS–SST turbulence model. The v-shaped rake structures are located in the diffuser near the inlet of the sand trap, while the ribs cover a section of the bed in the downstream end. Three-dimensional models of the sand trap in Tonstad hydropower plant are created. The present study showed that integrating rib type structure can reduce the total weight of sediments escaping the sand trap by 24.5%, which leads to an improved sand trap efficiency. Consequently, the head loss in the sand trap is increased by 1.8%. By additionally including the v-shaped rakes, the total weight of sediments escaping the sand trap is instead increased by 48.5%, thus worsening the sand trap efficiency. This increases head loss by 12.7%. The results also show that turbulent flow commencing at the sand trap diffuser prevents the downstream settling of sediments with a diameter of less than one millimeter. The hydraulic representation of the numerical model is validated by comparison with particle image velocimetry measurements of the flow field from scale experiments and ADCP measurements from the prototype. The tested rib design has not previously been installed in a hydropower plant, and can be recommended. The tested v-shaped rakes have been installed in existing hydropower plants, but this practice should be reconsidered.

Optimal design and photoelectric performance study of micro-lens light trapping structure for CIGS thin film solar cell in BIPV

In this paper, an optimal design method of micro-lens light trapping structure for thin film solar cells applied to building integrated photovoltaic (BIPV) is proposed. Under three common scenes of BIPV, including lighting roof, sunshade and building facade, the optimal design and photoelectric performance study of Copper Indium Gallium Selenium (CIGS) thin film solar cells with micro-lens light trapping structure are studied. Among the three kinds of micro-lens light trapping structures, V-shaped, semi-cylindrical and concave, the light capture performance of V-shaped micro-lens light trapping structure is the best. The V-shaped micro-lens light trapping structure with a vertex angle of 70° and a groove depth of 100 μm has the best light capture performance in lighting roof and sunshade scene, which can increase the annual radiation flux of the absorption layer incident surface by 4.45% and 2.84% respectively. The V-shaped micro-lens light trapping structure with a vertex angle of 60° and a groove depth of 200 μm has the best light capture performance in building facade scene, which can increase the annual radiation flux of the absorption layer incident surface by 7.63%. When the light source is vertically incident, these two V-shaped micro-lens light trapping structures can increase the short-circuit current density by 15.57% and 7.11% respectively.

Stability, Multistability, and Complexity Analysis in a Dynamic Duopoly Game with Exponential Demand Function

In this paper, a discrete-time dynamic duopoly model, with nonlinear demand and cost functions, is established. The properties of existence and local stability of equilibrium points have been verified and analyzed. The stability conditions are also given with the help of the Jury criterion. With changing of the values of parameters, the system shows some new and interesting phenomena in terms to stability and multistability, such as V-shaped stable structures (also called Isoperiodic Stable Structures) and different shape basins of attraction of coexisting attractors. The eye-shaped structures appear where the period-doubling and period-halving bifurcations occur. Finally, by utilizing critical curves, the changes in the topological structure of basin of attraction and the reason of “holes” formation are analyzed. As a result, the generation of global bifurcation, such as contact bifurcation or final bifurcation, is usually accompanied by the contact of critical curves and boundary.

What Produces Dust Polarization in the HH 212 Protostellar Disk at 878 μm: Dust Self-scattering or Dichroic Extinction?

Abstract We report the results of new dust polarization of a nearly edge-on disk in the HH 212 protostellar system, obtained with the Atacama Large Millimeter/submillimeter Array at ∼0.035″ (14 au) resolution in a continuum at λ ∼ 878 μm. Dust polarization is detected within ∼44 au of the central source, where a rotationally supported disk has formed. The polarized emission forms V-shaped structures opening to the east, and probably to the west, arising from the disk surfaces and arm structures further away in the east and west, which could be due to potential spiral arms excited in the outer disk. The orientations of the polarization are mainly parallel to the minor axis of the disk, with some in the western part tilting slightly away from the minor axis to form a concave shape with respect to the center. This tilting of the orientations of the polarization is expected from dust self-scattering, e.g., by 50−75 μm grains in a young disk. The intensity and degree of the polarization both peak near the central source with a small dip at the central source and decrease toward the edges. These decreases in the intensity and degree of polarization are expected from dichroic extinction by grains aligned by poloidal fields, but may also be consistent with dust self-scattering if the grain size decreases toward the edges. It is possible that both mechanisms are needed to produce the observed dust polarization, suggesting the presence of both grain growth and poloidal fields in the disk.

Structures of three MORN repeat proteins and a re-evaluation of the proposed lipid-binding properties of MORN repeats.

MORN (Membrane Occupation and Recognition Nexus) repeat proteins have a wide taxonomic distribution, being found in both prokaryotes and eukaryotes. Despite this ubiquity, they remain poorly characterised at both a structural and a functional level compared to other common repeats. In functional terms, they are often assumed to be lipid-binding modules that mediate membrane targeting. We addressed this putative activity by focusing on a protein composed solely of MORN repeats-Trypanosoma brucei MORN1. Surprisingly, no evidence for binding to membranes or lipid vesicles by TbMORN1 could be obtained either in vivo or in vitro. Conversely, TbMORN1 did interact with individual phospholipids. High- and low-resolution structures of the MORN1 protein from Trypanosoma brucei and homologous proteins from the parasites Toxoplasma gondii and Plasmodium falciparum were obtained using a combination of macromolecular crystallography, small-angle X-ray scattering, and electron microscopy. This enabled a first structure-based definition of the MORN repeat itself. Furthermore, all three structures dimerised via their C-termini in an antiparallel configuration. The dimers could form extended or V-shaped quaternary structures depending on the presence of specific interface residues. This work provides a new perspective on MORN repeats, showing that they are protein-protein interaction modules capable of mediating both dimerisation and oligomerisation.

Flat Cross-Shaped Piezoelectric Rotary Motor

A numerical and experimental investigation of a flat, cross-shaped piezoelectric rotary motor is presented. The design and configuration of the motor allow it to be mounted directly to the printed circuit board or integrated into the other system where mounting space is limited. The design of the motor is based on the cross-shaped stator with 16 piezo ceramic plates, which are glued on it. The rotor is placed at the center of the stator and consists of two hemispheres, a shaft, and a preloading spring. Special clamping of the stator was developed as well. It consists of four V-shaped beam structures that allow it to rigidly clamp the stator with reduced damping effect to vibrations. The operation principle of the motor is based on the first in-plane bending mode of the cross-shaped stator. The motor excitation is performed through four harmonic signals, which have a phase difference of π/2. A numerical investigation of the motor was conducted to optimize the geometrical parameters of the stator and to analyze the displacement characteristics of the contacting point. The prototype of the motor was made, and the electrical, as well as rotation speed characteristics of the motor, were measured. The results of the experimental investigation showed that the motor is able to provide a maximum rotation speed of 972.62 RPM at 200 Vp-p when the preload force of 22.65 mN was applied.

Location of the Hydrophobic Surfactant Proteins, SP-B and SP-C, in Fluid-Phase Bilayers.

The hydrophobic surfactant proteins, SP-B and SP-C, promote rapid adsorption by the surfactant lipids to the surface of the liquid that lines the alveolar air sacks of the lungs. To gain insights into the mechanisms of their function, we used X-ray diffuse scattering (XDS) and molecular dynamics (MD) simulations to determine the location of SP-B and SP-C within phospholipid bilayers. Initial samples contained the surfactant lipids from extracted calf surfactant with increasing doses of the proteins. XDS located protein density near the phospholipid headgroup and in the hydrocarbon core, presumed to be SP-B and SP-C, respectively. Measurements on dioleoylphosphatidylcholine (DOPC) with the proteins produced similar results. MD simulations of the proteins with DOPC provided molecular detail and allowed direct comparison of the experimental and simulated results. Simulations used conformations of SP-B based on other members of the saposin-like family, which form either open or closed V-shaped structures. For SP-C, the amino acid sequence suggests a partial α-helix. Simulations fit best with measurements of XDS for closed SP-B, which occurred at the membrane surface, and SP-C oriented along the hydrophobic interior. Our results provide the most definitive evidence yet concerning the location and orientation of the hydrophobic surfactant proteins.

Effect of Strains and V-Shaped Pit Structures on the Performance of GaN-Based Light-Emitting Diodes

Strains and V-shaped pits are essential factors for determining the efficiency of GaN-based light-emitting diodes (LEDs). In this study, we systematically analyzed GaN LED structures on patterned sapphire substrates (PSSs) with two types of growth temperature employed for prestrained layers and three different thickness of n-type GaN layers by using cathodoluminescence (CL), microphotoluminescence (PL), and depth-resolved confocal Raman spectroscopy. The results indicated that V-pits formation situation can be analyzed using CL. From the emission peak intensity ratio of prestrained layers and multiple quantum wells (MQWs) in the CL spectrum, information regarding strain relaxation between prestrained layers and MQWs was determined. Furthermore, micro-PL and depth-resolved confocal Raman spectroscopy were employed to validate the results obtained from CL measurements. The growth conditions of prestrained layers played a dominant role in the determination of LED performance. The benefit of the thick layer of n-GaN was the strain reduction, which was counteracted by an increase in light absorption in thick n-type doped layers. Consequently, the most satisfactory LED performance was observed in a structure with relatively lower growth temperature of prestrained layers that exhibited larger V-pits, leading to higher strain relaxation and thinner n-type GaN layers, which prevent light absorption caused by n-type GaN layers.

Study on the influence of interphase spacers on ice shedding of three-phase iced eight-bundled transmission lines

Sudden ice shedding from three-phase iced eight-bundled transmission lines with inverted-triangle arrangement was numerically and experimentally modeled. The staggered-arrangement groups and compact-arrangement groups (including triangular and V-shaped structures) of interphase spacers were considered to investigate the inhibition effects on ice shedding. Based on the similarity theory, a modification method was proposed to determine the natural frequency similarity between model and prototype. According to the dynamic tension, interphase distance, and jumping height, the reduction rate of dynamic tension, interphase-distance ratio, reduction rate of jumping height, and comprehensive reduction rates were determined for different arrangements of the interphase spacers. The inhibition effects of different factors on ice shedding were discussed for different lines, including the position and number of transmission lines for the ice-shedding phase and the various possible arrangements of interphase spacers. Deicing schemes for the different line configurations were proposed, and the best arrangement of interphase spacers was selected for each case. The present study provides a theoretical foundation for selecting an appropriate arrangement of interphase spacers during ice shedding.

Optical Properties of Plasmonic Nanoantennas Based on Arrays of Interacting V-Shaped Structures in the Mid-IR Range

Polarization-selected IR transmission, IR reflection, and IR absorption spectra of arrays of V-shaped gold structures are experimentally studied for various structure periods. To form a local region of the enhanced electromagnetic field in subwavelength nanogaps, arrays with unit cells consisting of two V-shaped structures, facing each other by acute angles with gaps of 0, 50, 100 nm were also used. The results of comparison of spectral data with measurements of dimensional parameters using atomic-force microscopy and scanning electron microscopy are presented. The possibility of using the fabricated structures to achieve the effect of surface-enhanced IR absorption by quantum dots is shown.

$Ka$ -Band Symmetric V-Shaped Meander-Line Slow Wave Structure

A symmetric configuration of two V-shaped microstrip meander-line slow wave structures (MLSWSs) is studied for application in Ka -band traveling-wave tubes (TWTs). Simulated dispersion characteristics and coupling impedance are presented for an optimized design. Particle-in-cell (PIC) simulation results show that for a 3.6-kV, 50-mA sheet-beam, the output power can potentially reach 28 W at 32 GHz with a gain of 28- and a 3-dB bandwidth of about 25% centered at 32 GHz. The proposed configuration is realized by first microfabricating a number of V-shaped MLSWSs on a 4” quartz wafer and then laser-dicing individual SWSs. A metal enclosure with waveguide input-output couplers is fabricated to house the SWSs and facilitate measurements. With two of the SWSs placed symmetrically inside the metal enclosure, the measured S11 for a 150-period symmetric MLSWS is better than -15 dB over 24-40 GHz. The reasons for the measured S21 being higher than expected are identified and verified by measurements on another set of SWSs which is fabricated using printed-circuit technique. An assembly that can be used for hot-tests is also presented.

Heat Transfer and Turbulent Flow Structure in Channels With Miniature V-Shaped Rib-Dimple Hybrid Structures on One Wall

An experimental and numerical study has been conducted on heat transfer and turbulent flow structure in channels with novel hybrid structures with miniature V-shaped ribs and dimples on one wall. One miniature V-shaped rib was arranged immediately upstream each individual dimple to form the hybrid structure, which aims at inducing additional near-wall secondary flow interacting with the dimple vortex flow and further improving the heat transfer. Steady-state convective heat transfer experiments were done to obtain the heat transfer and pressure loss of the turbulent flow over the surfaces with the miniature V rib-dimples for the Reynolds numbers from 18,700 to 60,000. In addition, the turbulent flow structure in the V rib-dimpled channels has been predicted by carrying out numerical computations. The experimental results indicated that the overall heat transfer enhancement of the miniature V rib-dimpled channels can be increased by up to about 60.0% compared with the counterpart of the dimpled only channel, and by about 23.0% compared with the counterpart of the miniature V ribbed only channel. The miniature V ribs showed appreciable effects on the heat transfer and pressure loss characteristics for the turbulent flow over the V rib-dimpled surfaces. The numerical computations showed that the miniature V rib upstream each dimple produced strong near-wall downwashing secondary flow, which significantly changed the flow patterns and intensified the turbulent flow mixing inside and outside the dimple and above the surrounding wall. These unique near-wall flow characteristics generated a significant heat transfer improvement in both the magnitude and the uniformity.

Fish under pressure: Examining behavioural responses of Iberian barbel under simulated hydropeaking with instream structures.

Hydropeaking is the rapid change in the water flow downstream of a hydropower plant, driven by changes in daily electricity demand. These fluctuations may produce negative effects in freshwater fish. To minimize these impacts, previous studies have proposed habitat enhancement structures as potential mitigation measures for salmonids. However, the recommendation of these mitigation measures for cyprinids remains scarce and their effects unknown. In this study, the effects of potential habitat mitigation structures under simulated hydropeaking and base-flow conditions are examined for Iberian barbel (Luciobarbus bocagei) in an indoor flume. Solid triangular pyramids and v-shaped structures were evaluated as potential flow-refuging areas and compared with a configuration without structures. A novel, interdisciplinary approach is applied to investigate individual and group responses to rapidly changing flows, by assessing physiological (glucose and lactate), movement behaviour (structure use, sprints and drifts) and the pressure distribution using a fish-inspired artificial lateral line flow sensor. The major findings of this study are four-fold: 1) Under hydropeaking conditions, the v-shaped structures triggered a lactate response and stimulated individual structure use, whereas solid structures did not elicit physiological adjustments and favoured individual and group structure use. Overall, both solid structures and their absence stimulated sprints and drifts. 2) The hydrodynamic conditions created in hydropeaking did not always reflect increased physiological responses or swimming activity. 3) Each event-structure combination resulted in unique hydrodynamic conditions which were reflected in the different fish responses. 4) The most relevant flow variable measured was the pressure asymmetry, which is caused by the vortex size and shedding frequency of the structures. Considering the non-uniform nature of hydropeaking events, and the observation that the fish responded differently to specific flow event-structure combinations, a diverse set of instream structures should be considered for habitat-based hydropeaking mitigation measures for Iberian barbel.

Progressive collapse of steel frame-brace structure under a column-removal scenario

Progressive collapse attracted more attention of researchers in recent years, mainly due to the increasing number of terrorist incidents worldwide. Based on the GSA and DOD design guidelines, structural resistance mechanisms to progressive collapse of steel frame, V-shaped and X-shaped braced frame structures are studied by a comparative analysis. The results show that the robustness index (RI) of steel braced frame structure is significantly greater than steel frame structure, and the X-shaped brace is greater than the V-shaped brace. Furthermore, static pushdown and nonlinear dynamic analysis are performed to study dynamic effects attributed to a column removed. The results show that the ultimate failure modes are generally similar by these two analytical method. The presence of the column bracing reduces the dynamic displacement response for a column removed instantly, and the X-shaped brace is better than the V-shaped brace.

Controlling gold helices with DNA

Plasmonics The plasmonic properties of gold nanoparticles can be exploited by creating arrays that control their spacing and orientation to induce chiral optical properties. Lan et al. attached gold nanorods to V-shaped hinged DNA origami structures, thereby allowing the DNA origami to self-assemble along their edges and create staircase helical structures. By interchanging the spacer that sets the hinge angle of the V with a longer spacer, they converted the helix into an extended structure with a different circular-dichroism spectrum. Alternatively, the authors show that a fixed spacer can be used and additional DNA strands attached at the hinge and at the ends of the V structures. These strands could then be reversibly displaced by ones that cause the helix to switch handedness. J. Am. Chem. Soc. 140 , 11763 (2018).

Structural evolution and bonding properties of Au2Sin-/0 (n = 1-7) clusters: Anion photoelectron spectroscopy and theoretical calculations.

The photoelectron spectra of Au2Sin- (n = 1-7) clusters were measured, and the structural evolution and bonding properties of Au2Si1-7- anions and their corresponding neutral counterparts were investigated by theoretical calculations. The two Au atoms in Au2Si1-7-/0 prefer to occupy low coordinate sites and form fewer Au-Si bonds. The aurophilic interaction is fairly weak in these clusters. The most stable structures of both Au2Sin- anions and Au2Sin neutrals can be described as the two Au atoms interacting with the Sin frameworks. The most stable isomers of Au2Sin- anions are in spin doublet states, while those of the neutral clusters are in spin singlet states. The lowest-lying isomers of Au2Si1-/0 have C2v symmetric V-shaped structures. The global minimum of the Au2Si2- anion has a D2h symmetric planar rhombus structure, while that of the Au2Si2 neutral adopts a C2v symmetric dibridged structure. In Au2Si3-/0, the two Au atoms independently interact with the different Si-Si bonds of the Si3 triangular structure. The global minima of Au2Si4-7-/0 primarily adopt prismatic based geometries. Interestingly, Au2Si6-/0 have significant 3D aromaticity and possess σ plus π double bonding characters, which play important roles in their structural stability.