L-shaped Channels Research Articles

Curvature-mediated programming of liquid crystal microflows.

Despite the recognized role of liquid crystal microfluidics in generating programmable, self-organized and guided flow properties, to date, the flow behavior of LCs within curved channels remains unexplored. Using experiments and numerical simulations, we demonstrate that the curvature of microscale conduits allow programming of liquid crystal (LC) flows. Focusing on a nematic LC flowing through U- and L-shaped channels - two simple yet fundamental curved flow paths - with rectangular cross-section, our results reveal that the curvature of flow path can trigger transverse flow-induced director gradients. The emergent director field feeds back into the flow field, ultimately leading to LC flows controlled by the channel curvature. This curvature-mediated flow control, identified by polarizing optical microscopy and supported by the nematofluidic solutions, offers concepts in LC microfluidic valves, wherein the throughput distribution is determined by the Ericksen number and variations in local curvature. Finally, this work leverages curvature to amplify (suppress) LC transport through flow-aligned (homeotropic) regions emerging within channels with bends, in a programmable manner. Our results demonstrating the dependence of the dynamic flow-director coupling on the local curvature will have far-reaching ramifications in advancing the understanding of LC-based passive and active biological systems under real life geometrical constraints.

Analytical investigation of rectangular steel pipe shear connector

Rectangular steel pipe (RSP) which is a new kind of connector in a composite slab of steel–concrete has been proposed. Research on the shear properties of RSPs is limited, but such data are needed if RSPs are to be used as shear connectors in composite slabs. Here, a nonlinear finite-element (FE) model that accounts for the nonlinear material properties and the RSP–concrete interface is proposed. A comparison between the finite element method (FEM) results and the static push-out test data showed good agreement in terms of shear stiffness, shear capacity, and failure mode. This verified FE model was then used in a parametric study to investigate the effects of constraint in push-out test, concrete stiffness, concrete compressive strength, RSP dimensions, RSP thickness, and RSP welding length on RSP shear capacity. The analytical results showed that constraint, concrete strength, RSP dimensions, RSP thickness, and welding length all affected RSP shear capacity, whereas concrete stiffness showed light effects. The shear capacity obtained using the FE model was compared with the calculated result using the Japan Society of Civil Engineers (JSCE) equations for the shear capacity of L-shaped channels.

Effect of channel length to the frequency response of Si-based Self-Switching Diodes using two-dimensional simulation

A planar nanodevice, known as the self-switching diode (SSD) which can be exploited as a high-speed rectifier in a wide range of applications. The non-linearity in the I-V characteristic of the SSD structure has been aimed for rectification application at GHz frequencies is reported. In this work simulation has been conducted on Si-based SSD structure with 230 nm L-shaped channels using ATLAS device simulator under the channel length range of 0.5 μm to 1.3 μm. Furthermore, the validity of the cut-off frequency has also been described using a theoretical value of f t at zero bias. The results showed that the optimization in the channel length of the SSD can assist the high cut-off frequency of SSD rectifying behavior to efficiently operate as microwave rectifier.

Design of a novel antisymmetric coil array for parallel transmit cardiac MRI in pigs at 7 T.

The design, simulation, assembly and testing of a novel dedicated antisymmetric transmit/receive (Tx/Rx) coil array to demonstrate the feasibility of cardiac magnetic resonance imaging (cMRI) in pigs at 7 T was described. The novel antisymmetric array is composed of eight elements based on mirrored and reversed loop orientations to generate varying B1+ field harmonics for RF shimming. The central four loop elements formed together a pair of antisymmetric L-shaped channels to allow good decoupling between all neighboring elements of the entire array. The antisymmetric array was compared to a standard symmetric rectilinear loop array with an identical housing dimension. Both arrays were driven in the parallel transmit (pTx) mode forming an 8-channel transmit and 16-channel receive (8Tx/16Rx) coil array, where the same posterior array was combined with both anterior arrays. The hardware and imaging performance of the dedicated cardiac arrays were validated and compared by means of electromagnetic (EM) simulations, bench-top measurements, phantom, and ex-vivo MRI experiments with 46 kg female pig. Combined signal-to-noise ratio (SNR), geometry factor (g-factor), noise correlation maps, and high resolution ex-vivo cardiac images were acquired with an in-plane resolution of 0.3 mm × 0.3 mm using both arrays. The novel antisymmetric array enhanced the SNR within the heart by about two times and demonstrated good decoupling and improved control of the B1+ field distributions for RF shimming compared to the standard coil array. Parallel imaging with acceleration factor (R) up to 4 was possible using the novel antisymmetric coil array while maintaining the mean g-factor within the heart region of 1.13.

Total internal reflection-based optofluidic waveguides fabricated in aerogels

Liquid-core optofluidic waveguides based on total internal reflection of light were built in water-filled cylindrical microchannels fabricated in hydrophobic silica aerogels. Silica aerogels with densities ranging from 0.15 to 0.39 g/cm3 were produced by aging of alcogels in tetraethylorthosilicate solution for various time periods, followed by supercritical extraction of the solvent from the alcogel network. Subsequently, the resulting hydrophilic aerogel samples were made hydrophobic by hexamethyldisilazane vapor treatment. The synthesized samples retained their low refractive index (below ~1.09) and, hence, they could serve as suitable optical cladding materials for aqueous waveguide cores (refractive index n core = 1.33). Hydrophobic silica aerogel samples produced by the above technique also had low absorption coefficients in the visible part of the spectrum. Fabrication of microchannels in aerogel blocks by manual drilling preserving nanoporous and monolithic structure of aerogels was demonstrated for the first time. Long channels (up to ~7.5 cm) with varying geometries such as straight and inclined L-shaped channels could be fabricated. Multimode optofluidic waveguides prepared by filling the channels in the drilled aerogel monoliths with water yielded high numerical aperture values (~0.8). Efficient guiding of light by total internal reflection in the water-filled channels in aerogels was visually revealed and characterized by monitoring the channel output. The presented technique is expected to open up further possibilities for creating three-dimensional networks of liquid channels in aerogels for optofluidic applications.

Numerical solution of the Ericksen–Leslie dynamic equations for two-dimensional nematic liquid crystal flows

A finite difference method for solving nematic liquid crystal flows under the effect of a magnetic field is developed. The dynamic equations of nematic liquid crystals, given by the Ericksen–Leslie dynamic theory, are employed. These are expressed in terms of primitive variables and solved employing the ideas behind the GENSMAC methodology (Tomé and McKee, 1994; Tomé et al., 2002) [38,41]. These equations are nonlinear partial differential equations consisting of the mass conservation equation and the balance laws of linear and angular momentum. By employing fully developed flow assumptions an analytic solution for steady 2D-channel flow is found. The resulting numerical technique was then, in part, validated by comparing numerical solutions against this analytic solution. Convergence results are presented. To demonstrate the capabilities of the numerical method, the flow of a nematic liquid crystal through various complex geometries are then simulated. Results are obtained for L-shaped channels and planar 4:1 contraction for several values of Reynolds and Ericksen numbers.

Model and simulation of water penetration in water-assisted injection molding

Water penetration behavior in the polymer melt is an important part of water-assisted injection molding (WAIM) technology. Based on the traditional injection molding model, an improved WAIM mathematical model was proposed, in which shear stress transportation κ–ω turbulent model was used to reflect the turbulent characteristics of water and predict the cooling of the melt by the water. In addition, the free interface of water/melt two-phase flow was tracked by volume of fluid, and the distribution of temperature, velocity, and pressure were calculated by computational fluid dynamics method. The results showed that in the long straight water channel, water penetration was uniform and smooth, and wall thickness difference is small. However, it was easy to produce water fingering in variable cross-section and L-shaped water channels. The fingering could effectively be reduced by the smooth transition of size and fillet. Reasonable fillet radius made the distribution of residual wall thickness of the inner and outer relatively uniform, but the wall thickness difference was inevitable. The fast cooling of the melt by the water was verified, so the cycle time could be shortened effectively.

High-Performance Poly-Si Thin-Film Transistors With L-Fin Channels

For the first time, we construct poly-Si thin-film transistors (TFTs) with novel L-shaped poly-Si fin channels (poly-Si TFTs with L-fin channels, called LFin-TFTs). The L-fin channels of LFin-TFTs are similar to the multiple-gated fin channels of FinFETs. The LFin-TFTs exhibit a low supply gate voltage (3 V), a good subthreshold swing (SS) ~ 190 mV/dec, and a high on/off current ratio (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> )>; 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> =1 V) without hydrogen-related plasma treatments. After Ni salicidation, the devices exhibit steep SS ~ 148 mV/dec and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ~ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> . After NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> plasma treatment, the characteristics of the devices are further improved. The LFin-TFTs have steeper SS ~ 132 mV/dec, higher (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> )>; 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> , and threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ) ~ 0.036 V.

Flow Induced Unstable Structure of Liquid Crystalline Polymer Solution in L-Shaped Slit Channels

An experimental study has been conducted on unstable structures induced in two-dimensional slit flows of liquid crystalline polymer solution. 50wt% aqueous solution of hydroxyl-propylcellulose (HPC) was utilized as a test fluid and its flow behavior in L-shaped slit channels with a cross section of 1mm height and 16mm width was measured optically. The inner corner of the L-shaped channel was rounded off in order to clarify the influence of the radius of curvature on the unstable behavior. A conversing curved channel was also tested. The flow patterns of the HPC solution in the channels were visualized with two crossed polarizers and we observed that typical wavy textures generated in the upstream of the corner almost disappeared after the corner flow. However, an unstable texture was developed again only from the inner corner in downstream flow. The fluctuation of the orientation angle and dichroism were also measured with a laser opto-rheometric system and it was found that the unstable behaviors of the HPC solution have periodic oscillatory characteristics at a typical frequency. In the inner side flow after the corner, the periodic motion became larger toward the downstream and then higher harmonic oscillations were superimposed. Larger rounding off of the inner corner suppressed the redevelopment of unstable behavior, and it is considered that the rapid regrowth of unstable behavior was caused by rapid deceleration at the corner flow. Moreover, the unstable structure was stabilized with an accelerated (elongated) region in the corner flow and the converging channel was helpful to obtain a stable structure in the downstream region.

A Numerical Computation of Heat and Fluid Flow in L-Shaped Curved Channels

A numerical analysis of steady, hydrodynamically and thermally fully developed, incompressible laminar flow with constant physical properties is presented. Two different geometrical cases of L-shaped channels are considered: right-curved and left-curved. The solution of the discretized continuity, momentum, and energy equations was obtained by using an elliptic Fortran program based on the SIMPLE algorithm. Solutions are obtained for Dean number ranges from 4.1 to 210.6 with dimensionless radius of curvature of 100, and Prandtl number of 0.7. The secondary flow streamlines, the isotherms, average Nusselt numbers, and friction factors are presented depending on Dean number and L-shaped channel orientation. As a result, it is observed that the secondary flows resulting from centrifugal forces change the distribution of the velocity and the temperature fields. In addition, it is determined that channel orientation has a profound effect on the flow and temperature fields.

FORAGING ANTS AREN'T CONFUSED BY A CLIMB

Without fail, desert ants make a beeline for their nests after a meandering foraging trip - and they manage this without spotting any landmarks or sniffing any scent trails. `It's amazing what these animals can do with a brain that's only a tenth of a milligram', says Bernhard Ronacher. To find out how desert ants measure distances on their long marches in search of food,Ronacher teamed up with Rüdiger Wehner of the University of Zürich and Gunnar Grah of Humboldt University in Berlin to test desert ants in hilly terrain (p. 4005).Desert ants use dead reckoning (path integration) to make their way home,which means that they must be able to measure both the direction and distance they've travelled from the nest. But what distance information do ants gather on their journeys across a hilly landscape - do they project their trajectories onto the horizontal plane as they travel over undulating terrain to measure the ground distance they've covered (`as the crow flies'), or do they measure the actual distance walked, which is much longer than the ground distance if the ants travel up and down hills?To find out, the team travelled to Wehner's field site on saltpans near Maharès, Tunisia. They trained three groups of desert ants to walk from their nest to a food site through L-shaped aluminium channels. The first group walked a straight stretch on the ground, then for the second leg of their trip they took a right-angled turn up a steep incline, walked another short straight stretch and then down a steep incline to ground level, where a bowl filled with biscuit crumbs awaited their arrival. The second group stayed at ground level, with the second leg of their L-shaped trip covering the same ground distance that the first group had travelled. Finally, the third group also walked along the ground, but the second leg of their journey was much longer, covering the same walking distance as the first group.The angle at which the ants subsequently set off for home would reveal whether the climbing ants (the first group) had gauged the ground or the walking distance during their L-shaped journey. Would climbing ants act like ants that had travelled the ground distance or like ants that had travelled the walking distance? When each ant had secured a treat from the bowl and held the crumb in its jaws for the homeward journey, the team scooped the unsuspecting insect into a box and took it to a flat field some distance away. To determine which direction an ant considered to be homeward bound, the team placed the ant on a grid painted on the ground and traced its movements on a piece of grid paper. They found that the ants that had climbed up the steep slopes set off at the same angle as the second group of ants, which had travelled the same ground distance as the first group. But the third group of ants, which had covered the first group's walking distance, took off at a completely different angle. Ants from the first two groups also travelled similar distances before they began circling to search for the nest entrance. The team concluded that ants measure the ground distance as they walk across hills, and don't measure the total distance walked. Importantly, desert ants incorporate this information into their path integration to calculate the correct angle to take a beeline back to the nest. If these ants ever find themselves crossing desert dunes, they certainly won't get lost on the way home.

TREATMENT OF THE INLET BOUNDARY CONDITIONS IN NATURAL-CONVECTION FLOWS IN OPEN-ENDED CHANNELS

The present work deals with the numerical solution of elliptic flows encountered in open-ended channels. The important question of applying boundary conditions for pressure and velocity for these flows is considered and a new method for the application of boundary conditions at the channel inlet is proposed. It is shown that the flow reversal at the channel outlet, which appears when nonsymmetric flow conditions are present, is strongly dependent on the entrance boundary conditions for pressure. Results for the straight channel in situations where flow reversal is present are reported for a wide range of Rayleigh numbers. Solutions for L-shaped channels are also reported with the aim of demonstrating the application of the model to arbitrary channels. It is shown that for certain flow situations the use of an elliptic formulation is imperative in order to predict correctly the flow behavior in open-ended channels.

An efficient cut-based algorithm on minimizing the number of L-shaped channels for safe routing ordering

Because definition of L-shaped channels in a floorplan graph breaks all the cyclic precedence constraints in a building block layout, routing space in a layout can be fully separated and defined as straight and L-shaped channels to guarantee a safe routing ordering. However, L-shaped channel routing is more difficult than straight channel routing. Hence, it is necessary for the completion of detailed routing to minimize the number of L-shaped channels in channel definition of a floorplan graph. In this paper, based on a geometrical topology of a floorplan graph and precedence relations in a channel precedence graph, cuts in a floorplan graph are classified into S-cuts, redundant L-cuts, balanced L-cuts, nonminimal L-cuts, noncritical L-cuts and critical L-cuts. An efficient cut-based algorithm on minimizing the number of L-shaped channels in channel definition of a floorplan graph is proposed, and the time complexity of our cut-based algorithm is proved to be in O(n) time, where n is the number of line segments in a floorplan graph. Finally, several examples have been tested on Dai's algorithm [1985], Cai's algorithm [1993] and our cut-based algorithm, respectively. The experimental results show that our cut-based algorithm defines fewer L-shaped channels in a floorplan graph than Dai's algorithm and Cai's algorithm to guarantee a safe routing ordering.

Numerical Simulation of Nematic Liquid Crystalline Flow in Two-Dimensional L-Shaped Channels.

Finite difference solutions to the Leslie-Ericksen equations were obtained for flows in two-dimensional L-shaped channels with various contraction ratios of the upstream to downstream channel width. A streamline shift toward the outer wall occurs upstream of the reentrant corner. Such behavior is similar to that of viscoelastic fluids. With increasing contraction ratio, the streamline shift occurs further upstream. The effect of the wall anchoring angle for the director is remarkable ; for example, when the anchoring angle along the downstream walls is set to be opposite to the main flow direction, a distortion of streamlines is produced in the corner region and the director moves to the downstream region upside down. At small Ericksen numbers, the orientation angle for the director is varied over a wide area so as to suppress its local deformation. In contrast, when the Ericksen number is large, the director profile in the upstream region is retained close to the corner region where the director turns rapidly to the downstream direction.

On minimizing the number of L-shaped channels in building-block layout (VLSI)

Given a building-block layout of rectangular modules, the routing area is to be decomposed into straight and L-shaped channels and routed in a certain order. Since straight channels are easier to route and channel routers usually produce near-optimal results, it is desirable to minimize the number of L-shaped channels used in such a decomposition. An algorithm for minimizing the number of L-shaped channels used in the routing area decomposition is presented. The algorithm is based on a careful study of the structure of layouts of rectangular modules and a transformation of the original problem to a graph theoretical problem. For examples of up to 136 channels, the algorithm took less than one tenth of a second on a SUN SPARC station 1 to finish the computation and obtained up to 29% reduction in the mumber of L-shaped channels over the results produced by the algorithm of W.M. Dai et al. (1985). >

Channel ordering for VLSI layout with rectilinear modules

The authors present a channel-ordering algorithm for VLSI layout with rectilinear modules. Existing approaches for layout with rectangular modules using only straight and L-shaped channels are no longer applicable. In general, rectilinear channels are needed. An important class of channels, called staircase channels, is introduced. This algorithm produces a feasible channel ordering which minimizes the usage of nonstaircase channels and minimizes the number of corners in a channel. >

Design and fabrication of composite components; the spring-forward phenomenon

When subjected to a change in temperature, continuous fibre reinforced plastics, because of their highly anisotropic nature, distort in shape as well as size. For a channel of L-shaped cross section, differential in-plane to thickness contraction causes the enclosed angle to decrease upon cooling in what is referred to as the spring-forward phenomenon. When curved sections are incorporated into three-dimensional articles, such as a ‘top hat’ component, restraint of the edge results in stress build-up and distortion in the structure. The spring-forward effect is studied analytically and numerically for L-shaped cross section channels and the predictions are compared to experimental measurements. The modelling techniques are also applied to a ‘top hat’ component formed from continuous carbon fibre-reinforced PEEK composite of quasi-isotropic lay-up. Predicted deformations are compared to those measured for manufactured components. Using finite element modelling methods the effect of the spring-forward phenomenon during forming of composite components can be anticipated and accounted for in forming tool design.

A Block Interconnection Algorithm for Hierarchical Layout System

A block interconnection algorithm for a general cell VLSI is described, which consists of a number of procedures such as a global router with signal delays taken into account, a router for power and ground, a block positioning scheme to minimize the chip size, a channel construction scheme with the use of L-shaped channels, and a grid-free channel router. The algorithm has been employed in a layout design system SMILE for general cell VLSI's for more than one year. Some of the experimental results are also shown.

Generation of reverse flow of viscoelastic fluid upstream of re-entrant corner in two-dimensional L-shaped channel.

Viscoelastic flows are experimentally studied using two-dimensional L-shaped channels. Velocity and pressure distributions have been measured for various Reynolds numbers and for various channel widths on the downstream side in order to clarify the cause and the conditions under which the reverse flow is generated upstream of the re-entrant corner. The present experiment shows that the reverse flow is largest in size when the Reynolds number is nearly equal to unity and the channel width downstream of the re-entrant corner is a quarter of that upstream of it. Pressure distributions on the channel wall rise in the flow direction in the upstream vicinity of the re-entrant corner. This pressure rise takes the maximum in value and in extent under the same conditions as the reverse flow. It is considered that the normal stress effect, peculiar to viscoelastic fluids, causes the generation of the reverse flow and the pressure rise upstream of the re-entrant corner.

Routing Region Definition and Ordering Scheme for Building-Block Layout

We present a new routing region definition and ordering (RRDO) scheme for building block layout. Given an arbitrary placement of rectangular blocks (including the case with cycles in the channel precedence constraints), without modifying the placement, our scheme defines and orders channels so that when a new channel is being routed, its width can be expanded or contracted without destroying the previously routed channels. The cycles in the channel precedence constraints are broken by introducing a new kind of channel--the L-shaped channels. Unlike switchboxes, L-shaped channels can be expanded or contracted to permit the completion of routing without rerouting other existing channels. An efficient greedy RRDO algorithm has been implemented, which tries to generate as few L-shaped channels as possible since L-shaped channels are harder to route than straight channels. Our algorithm represents routing regions by a floor plan graph, for which we provide a precise definition and a construction algorithm. The experimental results of the RRDO algorithm are promising.