Channel Half Research Articles

Structure of the Vacuolar H+-ATPase Rotary Motor Reveals New Mechanistic Insights

SummaryVacuolar H+-ATPases are multisubunit complexes that operate with rotary mechanics and are essential for membrane proton transport throughout eukaryotes. Here we report a ∼1 nm resolution reconstruction of a V-ATPase in a different conformational state from that previously reported for a lower-resolution yeast model. The stator network of the V-ATPase (and by implication that of other rotary ATPases) does not change conformation in different catalytic states, and hence must be relatively rigid. We also demonstrate that a conserved bearing in the catalytic domain is electrostatic, contributing to the extraordinarily high efficiency of rotary ATPases. Analysis of the rotor axle/membrane pump interface suggests how rotary ATPases accommodate different c ring stoichiometries while maintaining high efficiency. The model provides evidence for a half channel in the proton pump, supporting theoretical models of ion translocation. Our refined model therefore provides new insights into the structure and mechanics of the V-ATPases.

Large Eddy Simulation of Turbulent Channel Flow Using Smagorinsky Model and Effects of Smagorinsky Constants

A large eddy simulation (LES) of a turbulent channel flow is performed by using the Smagorinsky subgrid scale model and the effects of Smagorinsky constants in LES are discussed. The computation is performed in the domain of δ δ 2 δ 2 π × × π with 32 64 32 × × grid points at a Reynolds number Reτ = 590 based on the channel half width, δ and wall shear velocity, uτ. The performance of the Smagorinsky model is tested in LES for three values of Smagorinsky constant, CS = 0.065, 0.1 and 0.13, and for all three cases the computed essential turbulence statistics of the flow field are compared with Direct Numerical Simulation (DNS) data. Comparing the results with those from DNS data throughout the whole calculation domain we have found that turbulence statistics for CS = 0.065 show reasonable agreement with the DNS data. Agreements as well as discrepancies are discussed. The behavior of the flow structures in the computed flow field has also been discussed.

DSMC Simulation of Non-Premixed Combustion of H2/O2 in a Y-shaped Microchannel

Combustion at the microscale shows an immeasurable potential in the fields of energy utilization and microelectromechanical systems (MEMS) due to its novel combustion characteristics. Studying the mechanism of this kind of combustion is of great significance for deepening the understanding of microcombustion phenomena and designing related devices. In this article, the non-premixed combustion of H2/O2 in a two-dimensional Y-shaped microchannel with a height of 10 μm was numerically studied using the direct simulation Monte Carlo (DSMC) method. The total collision energy (TCE) model and a kinetic mechanism including six species and seven reversible reactions were employed. Predicted distributions of velocity, temperature, heat flux, and components inside the microchannel are presented and analyzed. Influences of the Knudsen number and wall surface conditions on the combustion characteristics are discussed. The results show that the exothermic reaction mainly takes place in the junction area of the branch channels and in the first half of the main channel, and the wall heat flux at the microscale is much higher than that at the conventional scale. This is helpful to effectively heat and ignite the gaseous H2/O2 mixture. Moreover, the conversions and distributions of individual components in the flow field are mainly controlled by the chemical kinetics; the Kn number and different wall conditions have a sophisticated influence on the combustion process.

Doping modulated carbon nanotube synapstors for a spike neuromorphic module.

A doping-modulated carbon nanotube (CNT) electronic device, called a "synapstor," emulates the function of a biological synapse. The CNT synapstor has a field-effect transistor structure with a random CNT network as its channel. An aluminium oxide (Al2 O3 ) film is deposited over half of the CNT channel in the synapstor, converting the covered part of the CNT from p-type to n-type, forming a p-n junction in the CNT channel and increasing the Schottky barrier between the n-type CNT and its metal contact. This scheme significantly improves the postsynaptic current (PSC) from the synapstor, extends the tuning range of the plasticity, and reduces the power consumption of the CNT synapstor. A spike neuromorphic module is fabricated by integrating the CNT synapstors with a Si-based "soma" circuit. Spike parallel processing, memory, and plasticity functions of the module are demonstrated. The module could potentially be integrated and scaled up to emulate a biological neural network with parallel high-speed signal processing, low power consumption, memory, and learning capabilities.

Effects of starting microstructure and billet orientations on the texture evolution and the mechanical behavior of Mg–3Al–1Zn rolled plate by half channel angular extrusion (HCAE)

Abstract A single pass of half-channel angular extrusion (HCAE), an unconventional severe plastic deformation process of an Mg–3Al–1Zn rolled plate, was performed at 523 K with six different starting textures with respect to three inter-perpendicular specimens along RD, TD, and ND in two types of initial plates such as as-rolled and twin-induced. In order to investigate the texture development and corresponding changes of mechanical properties, an EBSD OIM analysis and tensile tests at room temperature of HCAE-processed samples were carried out. The results show that the strength and ductility of Mg–3Al–1Zn can both be improved by controlling the initial microstructure in the HCAE process.

Large eddy simulation of smooth–rough–smooth transitions in turbulent channel flows

We describe a high Reynolds number large-eddy-simulation (LES) study of turbulent flow in a long channel of length 128 channel half heights, δ, with the walls consisting of roughness strips where the long stream-wise extent invites a full relaxation of the mean velocities within each strip. The channel is stream-wise periodic and strips are oriented transverse to the flow resulting in repeated transitions between smooth and rough surfaces along the stream-wise direction. The present LES uses a wall model that contains Colebrook’s empirical formula as a roughness correction to both the local and dynamic calculation of the friction velocity and also the LES wall boundary condition. This operates point-wise across wall surfaces, and hence changes in the outer flow can be viewed as a response to the temporally and/or spatially variant roughness distribution. At the wall surface, dynamically calculated levels of time- and span-wise-averaged friction velocity uτ‾(x) over/undershoot and then fully recover towards their smooth or rough state over a stream-wise distance of order 10–30δ depending on both roughness and Reynolds number. Also, the initial response rate in uτ‾ shows Reynolds number and roughness dependence over both transitions. The growth rate of the internal boundary layer (IBL), defined by the abrupt change in stream-wise turbulent intensity, is found to grow as x0.70 on average over multiple simulation conditions for the case of a smooth-to-rough transition, which agrees with the experimental results of Antonia and Luxton (1971) [1] and Efros and Krogstad (2011) [2]. IBL profiles demonstrate a good collapse on δ/log(Reτ∗), where Reτ∗ is the local Reynolds number based on uτ‾ at the point of full recovery.

A dynamic forcing scheme incorporating backscatter for hybrid simulation

In this paper, a dynamic forcing scheme incorporating backscatter is proposed in order to remove the artificial buffer layer in a hybrid Reynolds-averaged Navier-Stokes (RANS)/large-eddy simulation (LES) approach. In contrast to previous forcing techniques, the proposed forcing is determined dynamically from the flow field itself, and does not require any extraction of turbulent fields from reference direct numerical simulation (DNS) or high-resolution LES databases. Transport equations for the resolved turbulent stresses and kinetic energy are introduced to investigate the effects of dynamic forcing on reduction of the thickness and impact of the artificial buffer layer. The proposed forcing model has been tested in the context of turbulent channel flows with Reynolds numbers Reτ = 650 and 1020 (based on the wall friction velocity and half channel height). In order to validate the hybrid RANS/LES approach, flow statistics obtained from the simulations have been thoroughly compared against the available DNS data.

유한요소해석을 이용한 HCAE 공정의 가공 경로가 AZ61 마그네슘 합금의 변형 특성에 미치는 영향에 대한 연구

Half channel angular extrusion(HCAE) is the integration of equal channel angular extrusion(ECAE), which is a wellknown severe plastic deformation(SPD) method, with conventional forward extrusion in order to increase the strain per pass and effectiveness of the grain refinement. In the current study, the effects of processing routes during HCAE(Routes A, B, and C) on the strain distribution of the specimens have been investigated for an AZ61 Mg alloy by using three-dimensional finite element analysis. Comparisons with the results from a multi-pass of ECAE are made.

Electrokinetic diffusioosmosis of viscoelastic Phan-Thien–Tanner liquids in slit microchannels

This research presents a theoretical/numerical investigation on electrokinetic diffusioosmotic flows of viscoelastic Phan-Thien–Tanner liquids in slit microchannels subjected to general wall zeta potentials. Based on a unidirectional lubricating flow analysis, numerical solutions to the effective viscosity, first normal stress difference, flow velocity field, and volume flow rate are obtained and expressed in terms of the spatial coordinate, half channel width to Debye length ratio, diffusivity difference parameter, wall zeta potential, and a combined elongation viscosity and Deborah number parameter (in short, Deborah number). Results of our parametric studies show that the respective strengths of the shear thinning and normal stress effects can be increased as the Deborah number is increased. Moreover, the respective strengths of the flow velocity and volume flow rate are increased as the Deborah number is increased regardless of the flow velocity and flow rate being directed towards upstream or downstream. Finally, based on the diffusivity difference parameter and zeta potential parametric pairs, the parametric regimes available for the volume flow rate to be directed towards downstream (upstream) are increased (reduced) as the value of the Deborah number parameter is reduced.

Cytoplasmic Loops of Subunits C and A in E. Coli F1Fo ATP Synthase Interact to Gate H+ Transport to the Cytoplasm

Rotary catalysis in F1Fo ATP synthase is powered by proton transport through the membrane-embedded Fo sector, which functions like a proton-driven turbine. Proton binding and release occur in the middle of the membrane at Asp61 on the second transmembrane helix (TMH) of subunit c, which folds in a hairpin-like structure with two transmembrane helices (TMHs). Previously, the aqueous accessibility of Cys substitutions in the TM regions of subunits c and a were probed by testing the inhibitory effects of Ag+ or Cd+2 on function, and defined two half-channels leading to the proton binding site at cAsp61. The half channel from the periplasm lies in the center of a four-helix bundle in subunit a. We show here that the gating of protons from the periplasmic half channel to the Asp61 binding site requires repositioning of helices at the aAsn214/aGln252 site of interaction between TMH4 and TMH5. In addition we show that Ag+ and Cd2+ sensitive Cys substitutions on the proton transporting pathway to the cytoplasm extend into the polar loop of subunit c. Further, Ag+ and Cd2+ sensitive Cys substitutions that are directly involved in proton transport through Fo are also found in two cytoplasmic loops of subunit a. We show here that Cys substitutions in the hairpin loop of subunit c and the two loops of subunit a, each of which are directly implicated in proton transport, can be cross-linked to each other. We suggest that the three loops pack as a single domain that serves to gate proton release to the cytoplasm.

2P241 アナベナセンサリーロドプシンの細胞質側で生じる光誘起プロトン移動反応の解析(18A. 光生物:視覚・光受容,ポスター,第52回日本生物物理学会年会(2014年度))

2P241 アナベナセンサリーロドプシンの細胞質側で生じる光誘起プロトン移動反応の解析(18A. 光生物:視覚・光受容,ポスター,第52回日本生物物理学会年会(2014年度))

Challenges and Directions in Mobile Device Packaging

Mobile devices such as phones, tablets and subnotebooks are driving innovation in device packaging. These devices currently are jammed full of advanced capabilities, such as HD video, GPS, WLAN, cellular, touchscreens, Bluetooth, and dual cameras - with significantly more functionality than “sophisticated” notebooks. These features drive demand for mobile devices and provide significant challenges to the packaging community for solutions such as thinner packages while still controlling warpage, new materials, both polymers and solders, as well as innovative structures moving into 2.5 and 3D. Solving these challenges allows innovation to drive demand for mobile devices, providing a providing a platform for many innovative uses that are still being tapped, such as entertainment, video recording, web access, computer vision, augmented reality, all readable, recognizable, locatable, addressable, and controllable through the internet, the Internet of Things (IOT) concept. This talk will discuss current and future innovations to address these formidable issues in the mobile environment. Many extreme temperature applications such as power converters and motor drivers operate from power rails that are floating, noisy and have extremely high voltages. Typically the logic signal is only a few volts but is must be transmitted in an environment with hundreds or thousands of volts of common mode voltage. In some cases isolation is required for safety reasons to prevent leakage currents that could present an electrical shock hazard. For example the ground reference for a high side driver of an all N channel half bridge is referenced to the switch pin and switches between ground and the power rail within a few nanoseconds. At normal operating temperatures there are many specialized components such as opto-isolators, capacitive coupled devices and devices with integrated high frequency transformers that transmit logic signals across the isolation barrier. These specialized integrated circuits that provide isolation may not function reliably at elevated temperatures; those that do tend to be expensive. With special consideration of the system partitioning, it may be possible to avoid the need for galvanic isolation at extreme temperatures. It may be possible to provide the isolation in a remote more benign environment and send the isolated signal down a cable with appropriate impedance matching. When galvanic isolation at extreme temperatures is necessary, there must be temperature considerations for the components used. For example, when designing pulse transformers, the temperature effects on the magnetic core material properties such as permeability and frequency response must be considered as well as the Curie temperature. Modulation of the logic signals can help to reduce transformer size. Since the isolated driver functions typically require power, a novel method of winding the transformer is discussed; this method allows the drive signal to be transferred across the isolation barrier in the same transformer core that is used to provide isolated power to the driver. This paper addresses these topics and provides several alternative solutions to the problem of galvanic signal isolation at extreme temperatures.

Large Eddy Simulation of Turbulent Channel Flow at Reτ = 590

A large eddy simulation of a plane turbulent channel flow is performed by using the third order Low- Storage Runge-Kutta method in time and second order Finite Difference formulation in space with staggered grid at a Reynolds number 590 based on the channel half width and wall shear velocity. The computation is performed in a domain where streamwise and spanwise directions are periodic with 32

Direct numerical simulation of a turbulent channel flow by an improved vortex in cell method

Purpose – This study is concerned with the direct numerical simulation (DNS) of a turbulent channel flow by an improved vortex in cell (VIC) method. The paper aims to discuss these issues. Design/methodology/approach – First, two improvements for VIC method are proposed to heighten the numerical accuracy and efficiency. A discretization method employing a staggered grid is presented to ensure the consistency among the discretized equations as well as to prevent the numerical oscillation of the solution. A correction method for vorticity is also proposed to compute the vorticity field satisfying the solenoidal condition. Second, the DNS for a turbulent channel flow is conducted by the improved VIC method. The Reynolds number based on the friction velocity and the channel half width is 180. Findings – It is highlighted that the simulated turbulence statistics, such as the mean velocity, the Reynolds shear stress and the budget of the mean enstrophy, agree well with the existing DNS results. It is also shown that the organized flow structures in the near-wall region, such as the streaks and the streamwise vortices, are favourably captured. These demonstrate the high applicability of the improved VIC method to the DNS for wall turbulent flows. Originality/value – This study enables the VIC method to perform the DNS for wall turbulent flows.

Obstruction of Transmembrane Helical Movements in Subunit a Blocks Proton Pumping by F1Fo ATP Synthase

Subunit a plays a key role in promoting H(+) transport-coupled rotary motion of the subunit c ring in F1Fo ATP synthase. H(+) binding and release occur at Asp-61 in the middle of the second transmembrane helix (TMH) of Fo subunit c. H(+) are thought to reach cAsp61 via aqueous half-channels formed by TMHs 2-5 of subunit a. Movements of TMH4 and TMH5 have been proposed to facilitate protonation of cAsp61 from a half channel centered in a four helix bundle at the periplasmic side of subunit a. The possible necessity of these proposed TMH movements was investigated by assaying ATP driven H(+) pumping function before and after cross-linking paired Cys substitutions at the center of TMHs within subunit a. The cross-linking of the Cys pairs aG218C/I248C in TMH4 and TMH5, and aL120C/H245C in TMH2 and TMH5, inhibited H(+) pumping by 85-90%. H(+) pumping function was largely unaffected by modification of the same Cys residues in the absence of cross-link formation. The inhibition is consistent with the proposed requirement for TMH movements during the gating of periplasmic H(+) access to cAsp61. The cytoplasmic loops of subunit a have been implicated in gating H(+) release to the cytoplasm, and previous cross-linking experiments suggest that the chemically reactive regions of the loops may pack as a single domain. Here we show that Cys substitutions in these domains can be cross-linked with retention of function and conclude that these domains need not undergo large conformational changes during enzyme function.

Control of Wall Turbulence by Spinning Discs

This article is an extension to a previous paper of ours. It summarizes the main findingsand complements flow visualisations. An active technique for friction drag reduction in a turbulentchannel flow is studied by direct numerical simulations. The flow is modified by the steady rotationof rigid flush-mounted discs, located next to one another on the walls. The effect of the disc motionon the friction drag is investigated at a Reynolds number of Rτ =180, based on the friction velocity ofthe stationary-wall case and the half channel height. We compute a maximum drag reduction of 23%and a maximum net power saved of 10%, calculated by taking into account the power needed to rotatethe discs. The new Reynolds stress term induced by the disc rotation and generated by the velocitycomponents of the time averaged flow is shown to be instrumental for drag reduction.

Relaxation of Spatially Advancing Coherent Structures in a Turbulent Curved Channel Flow

A direct numerical simulation is made for the incompressible turbulent flow in the 180 deg curved channel with a long straight portion connected to its exit port. An examination is made for how the organized coherent vortex grows and decays in the curved channel: the radius ratio of 0.92, the aspect ratio of 7.2, and the succeeding straight section length of 75 times the channel half width. The 1552 × 91 × 128 ( = 18,427,136) grids are allocated to the computational domain. The frictional-velocity-based Reynolds number is kept at 150 to resolve the long domain including curved and straight regions. In contrast to that the coherent vortex grows along the concave wall, the vortex remains strong in the convex-wall side after the curvature accompanying a tail of the small-scale turbulence near the convex wall. The dissimilarity between the onset and disappearing of the coherent vortex essentially comes from the mean pressure gradient, which aids or averts the near-wall fluid oppositely between the curvature inlet and the exit. The mean flow is decelerated near the inlet of the convex wall to destabilize the flow and to trigger the onset of the coherent vortex. Contrary, the mean flow is accelerated near the exit of the convex wall to weaken the coherent vortex, and is decelerated near the exit of the concave wall to enhance the turbulence. Therefore, the turbulence enhancement and attenuation occurs oppositely between the inlet and exit of the curvature, and the coherent vortex draws a wake in the convex-side rather than the concave-side where it starts.

Electroosmotic Flow and Heat Transfer in Microchannels: A Closed Form Solution

In this paper, an analysis has been conducted to explore the momentun and thermal transport characterastics of electroosmotic liquid flow in a microchannel under imposed constant wall heat flux boundary condition. The present formulation shows that the problem is governed by three parameters, namely, the length scale ratio (ratio of Debye length to half channel height), the Joule heating parameter (ratio of Joule heating to surface heat flux), and the Brinkman number. A closed form solution of the problem was obtained and the impact of viscous dissipation on the heat transfer behavior was investigated. Analytical exact solutions of dimensionless velocity and temperature profiles, normalized local velocity, volume flow rate, friction coefficient, mean fluid temperature, and the fully-developed Nusselt number were obtained as functions of the governing parameters. Especially, the effects of length scale ratio on major flow parameters (including the normalized local velocity, friction coefficient, and volumetric flow rate) were examined. Also, the viscous dissipation effect on thermal transport characteristics was discussed in depth.

Evolution of the microstructure and mechanical properties of AZ61 alloy processed by half channel angular extrusion (HCAE), a novel severe plastic deformation process

A new concept of severe plastic deformation (SPD) process is introduced. The proposed process, named half channel angular extrusion (HCAE), which is the integration of equal channel angular extrusion (ECAE) and the conventional forward extrusion process in order to enhance the formability and mechanical properties of Mg alloys. This paper focuses on the performance of HCAE process with extruded AZ61 alloy at elevated temperature in grain refinement and the improvement of mechanical properties, and this performance was evaluated through an OIM experiment using EBSD. The results show that the proposed HCAE process not only improves the efficiency of the SPD process with only one pass but also increase the elongation and hardness dramatically.

Turbulent drag reduction through rotating discs

AbstractAn active technique for friction drag reduction in a turbulent channel flow is studied by direct numerical simulations. The flow modification is induced by the steady rotation of rigid flush-mounted discs, located next to one another on the walls. The effect of the disc motion on the turbulent drag is investigated at a Reynolds number of ${R}_{\tau } = 180$, based on the friction velocity of the stationary-wall case and the half channel height. For a fixed maximum disc tip velocity, drag reduction can be achieved when the disc diameter is larger than a threshold, while below this threshold the drag increases. A maximum drag reduction of 23% is computed. The net power saved, obtained by taking into account the power spent to enforce the rotational motion against the fluid viscous resistance, is found to be positive and reach 10%. The disc-flow parameters required for commercial aircraft flight conditions and flows over high-speed trains and ship hulls are estimated and future implementations based on existing micro-electromagnetic motor and micro-air turbine technologies are discussed.