Length Of Sheet Research Articles

Imaging of trabecular meshwork using Bessel–Gauss light sheet with fluorescence

Ocular imaging technology that holds promise for both fundamental investigation and clinical detection of glaucoma is still a challenging research area. A direct view of the trabecular meshwork (TM) with high resolution is not generally possible because the iridocorneal angle region is obstructed by the sclera overlap. The best approach to observe the aqueous outflow system (AOS) is therefore to view from the opposite angle. In this research work, we developed two imaging systems for the high resolution ex vivo studies of the AOS inside porcine eye, based on a Gaussian illuminated and a digitally scanned Bessel–Gauss beam light sheet fluorescence configurations. The digitally scanned Bessel–Gauss beam is able to overcome the trade-off between the length and thickness of the Gaussian light sheet to give better imaging performance. It has adequate spatial resolution to resolve critical anatomical structures such as the TM, thereby enabling objective information about the AOS. This non-contact and non-invasive imaging methodology with excellent safety profile is expected to be well received by vision researchers and clinicians in the evaluation and management of glaucoma.

Fractional statistical potential in graphene

In this work the fractional statistics is applied to an anyon gas in graphene to obtain the special features that the arbitrary phase interchange of the particle coordinates introduce in the thermodynamic properties. The electron gas is constituted by N anyons in the long wavelength approximation obeying fractional exclusion statistics and the partition function is analyzed in terms of a perturbation expansion up to first order in the dimensionless constant λ/L being L the length of the graphene sheet and λ=βℏvF the thermal wavelength. By considering the correct permutation expansion of the many-anyons wavefunction, taking into account that the phase changes with the number of inversions in each permutation, the statistical fermionic/bosonic potential is obtained and the intermediate statistical behavior is found. It is shown that “extra” fermonic and bosonic particles states appears and this “statistical particle” distribution depends on N. Entropy and specific heat is obtained up to first order in λ/L showing that the results obtained differs from those obtained in different approximation to the fractional exclusion statistics.

LASCO White-Light Observations of Eruptive Current Sheets Trailing CMEs

Many models of eruptive flares or coronal mass ejections (CMEs) involve formation of a current sheet connecting the ejecting CME flux rope with a magnetic loop arcade. However, there is very limited observational information on the properties and evolution of these structures, hindering progress in understanding eruptive activity from the Sun. In white-light images, narrow coaxial rays trailing the outward-moving CME have been interpreted as current sheets. Here, we undertake the most comprehensive statistical study of CME-rays to date. We use SOHO/LASCO data, which have a higher cadence, larger field of view, and better sensitivity than any previous coronagraph. We compare our results to a previous study of Solar Maximum Mission (SMM) CMEs, in 1984 – 1989, having candidate magnetic disconnection features at the CME base, about half of which were followed by coaxial bright rays. We examine all LASCO CMEs during two periods of minimum and maximum activity in Solar Cycle 23, resulting in many more events, \(\sim130\) CME-rays, than during SMM. Important results include: The occurrence rate of the rays is \(\sim11~\%\) of all CMEs during solar minimum, but decreases to \(\sim7~\%\) at solar maximum; this is most likely related to the more complex coronal background. The rays appear on average 3 – 4 hours after the CME core, and are typically visible for three-fourths of a day. The mean observed current sheet length over the ray lifetime is \(\sim12~R_{\odot}\), with the longest current sheet of \(18.5~R_{\odot}\). The mean CS growth rates are \(188~\mbox{km}\,\mathrm{s}^{-1}\) at minimum and \(324~\mbox{km}\,\mathrm{s}^{-1}\) at maximum. Outward-moving blobs within several rays, which are indicative of reconnection outflows, have average velocities of \(\sim350~\mbox{km}\,\mathrm{s}^{-1}\) with small positive accelerations. A pre-existing streamer is blown out in most of the CME-ray events, but half of these are observed to reform within \(\sim1\) day. The long lifetime and long lengths of the CME-rays challenge our current understanding of the evolution of the magnetic field in the aftermath of CMEs.

On the threshold of magnetic island width in nonlinear mutual destabilization of tearing mode and ion temperature gradient mode

Nonlinear multi-scale interactions between the tearing mode and the ion temperature gradient (ITG) mode are investigated by means of numerical simulations in a self-consistent 5-field Landau-fluid model. It is observed that there exists a threshold of magnetic island width in the nonlinear evolution of interaction, above which the ITG turbulence can enhance the island growth significantly. Dependence of the threshold on basic plasma parameters is deeply analyzed. It is found that the higher ion viscosity may raise the threshold through its effect on the E×B drift and the diamagnetic drift of electron density gradient in different ways, both of which play a synergetic role in determining the threshold. Moreover, the effects of plasma resistivity, gradient length of equilibrium current sheet as well as magnetic shear of field line on the threshold are discussed based on the analyses of the initial growth rate of islands.

해상 폐기물매립지 경사식 호안에서의 차수시트 설치에 따른 침투거동 분석

해상 폐기물매립지에서 내부 침출수의 외부 유출을 방지하기 위하여 차수공이 필수적으로 요구된다. 이를 위해 경사식 호안의 경우에는 사면부에 차수시트가 설치된다. 사면부에 설치된 차수시트의 하부 지반에서의 연장설치범위에 따른 침투차단효과를 평가하기 위하여 SEEP/W를 이용하여 침투해석을 실시하였다. 해석결과, 해저지반에 저투수성 지층이 분포되어 있으면 차수시트를 호안 사면끝단으로부터 점토층 상부면으로 1m 이상 연장하여 설치하여야 침투방지에 효과가 있는 것으로 나타났다. 하부지반에 투수성이 큰 사질토층이 존재하는 경우에는 폭 1m 이상을 저투수성으로 개량하고 차수시트를 1m 이상 연장하여 설치하는 것이 효과적인 것으로 나타났다. In order to prevent leakage of leachate in offshore landfill, hydraulic barrier is indispensable. In the case of rubble mound revetment at offshore landfill, HDPE sheet in slope should be installed. In this study, seepage analysis were performed to evaluate seepage and flow in the seabed and revetment according to extended length of HDPE sheet by using SEEP/W. Results show that, in the case of low permeability layer is distributed where extended length of HDPE sheet was more than 1m, seepage flux in seabed and revetment was greatly reduced. In order to prevent seepage in seabed and revetment in the case of sand layer of high permeability is existed above low permeable layer, extended length of HDPE sheet and impermeable improvement width of permeable layer should be more than 1m at seabed.

Fast reconnection in relativistic plasmas: the magnetohydrodynamics tearing instability revisited

Fast reconnection operating in magnetically dominated plasmas is often invoked in models for magnetar giant flares, for magnetic dissipation in pulsar winds, or to explain the gamma-ray flares observed in the Crab nebula, hence its investigation is of paramount importance in high-energy astrophysics. Here we study, by means of two dimensional numerical simulations, the linear phase and the subsequent nonlinear evolution of the tearing instability within the framework of relativistic resistive magnetohydrodynamics, as appropriate in situations where the Alfven velocity approaches the speed of light. It is found that the linear phase of the instability closely matches the analysis in classical MHD, where the growth rate scales with the Lundquist number S as S^-1/2, with the only exception of an enhanced inertial term due to the thermal and magnetic energy contributions. In addition, when thin current sheets of inverse aspect ratio scaling as S^-1/3 are considered, the so-called "ideal" tearing regime is retrieved, with modes growing independently on S and extremely fast, on only a few light crossing times of the sheet length. The overall growth of fluctuations is seen to solely depend on the value of the background Alfven velocity. In the fully nonlinear stage we observe an inverse cascade towards the fundamental mode, with Petschek-type supersonic jets propagating at the external Alfven speed from the X-point, and a fast reconnection rate at the predicted value R~(ln S)^-1.

Empirical Correlation of the Primary Stability Variable of Liquid Jet and Liquid Sheet Under Acoustic Field

The investigation focuses on optimizing the length of wind-pipe that transmits acoustic energy from the compression driver to the cavity of twin-fluid atomizers. To accomplish this objective, the primary variable of stability, that is, the breakup length of liquid jet and sheet under acoustic perturbations has been experimentally characterized for a range of wind-pipe length and liquid velocity. The analysis considers liquid phase Weber number in the range of 0.7–8, and the results are compared with primary breakup data without acoustic perturbations. The range of Weber number tested belongs to Rayleigh breakup zone, so that inertia force is negligible compared to surface tension force. It shows the existence of unique stability functions based on dimensionless products up to an optimum wind-pipe length, which extends greater for liquid sheet configuration. The present results may find relevance in atomizer design that utilizes acoustic source to enhance liquid column breakup processes.

Thermomechanical analysis of the formation of hot cracks in remote laser welded aluminium fillet welds

Remote laser welding of high strength aluminum alloys is still a field of extensive research due to the hot cracking phenomena. Recent research activities have been focused on center-line hot cracks in welds that are located close to the edge of the material. To avoid this type of crack from occurring, a fillet weld joint design could be utilized. However, within the fillet welds there are still transverse hot cracks present on a microscopic scale. This paper presents a thermomechanical analysis of the formation of transverse hot cracks in EN AW-6082 alloy fillet welds. In order to calculate the local deformation near the mush zone, a welding simulation based on the finite element method was created. The simulation was able to depict different settings for the welding speed, laser power, beam position, protruding length of the lower sheet, and the sheet thickness. For this purpose, an automated method for heat source calibration was developed based on image processing of polish of cross sections of different weld seams. As a result, it was possible to investigate the influencing factors on the formation of local strain and strain rate during the hot crack sensitive temperature range. It was found that the welding speed and laser power significantly increased the strain rate, but had no effect on the strain. In addition, it was determined that the position of the laser beam caused a major difference in the formation of strain and strain rate if weld seams changed from partial penetration to full penetration. Full penetration welds had lower strain and strain rate. The protruding length of the lower sheet and the sheet thickness had a minor impact on strain and strain rate. By linking the computerized results of strain and strain rate with data obtained from experiments on the hot crack susceptibility, a hot cracking criteria based on strain rate was found.

“Ideal” tearing and the transition to fast reconnection in the weakly collisional MHD and EMHD regimes

AbstractThis paper discusses the transition to fast growth of the tearing instability in thin current sheets in the collisionless limit where electron inertia drives the reconnection process. It has been previously suggested that in resistive MHD there is a natural maximum aspect ratio (ratio of sheet length and breadth to thickness) which may be reached for current sheets with a macroscopic length L, the limit being provided by the fact that the tearing mode growth time becomes of the same order as the Alfvén time calculated on the macroscopic scale. For current sheets with a smaller aspect ratio than critical the normalized growth rate tends to zero with increasing Lundquist number S, while for current sheets with an aspect ratio greater than critical the growth rate diverges with S. Here we carry out a similar analysis but with electron inertia as the term violating magnetic flux conservation: previously found scalings of critical current sheet aspect ratios with the Lundquist number are generalized to include the dependence on the ratio , where de is the electron skin depth, and it is shown that there are limiting scalings which, as in the resistive case, result in reconnecting modes growing on ideal time scales. Finite Larmor radius effects are then included, and the rescaling argument at the basis of “ideal” reconnection is proposed to explain secondary fast reconnection regimes naturally appearing in numerical simulations of current sheet evolution.

Characterization of FRP Uwrap Anchors for Externally Bonded FRP-Reinforced Concrete Elements: An Experimental Study

AbstractWhile the majority of U-shape wrapping (Uwrap) studies have focused on the mechanism of the shear-strengthening effect, very few studies have been devoted to the use of Uwraps as anchorage for longitudinal fiber-reinforced polymer (FRP) sheets or plates. This investigation therefore focuses on the anchor effect of the carbon-fiber-reinforced polymer (CFRP) Uwrap on externally bonded FRP-reinforced concrete elements. Based on selected parameters from the preliminary study, a parametric study was conducted on concrete blocks with an attached FRP sheet with and without Uwraps. Pull-out tests were conducted on these specimens. Slips along the length of the FRP sheet and debonding propagation in the region under the Uwrap were observed using a linear variable differential transformer (LVDT) and strain gauges. Among the tested specimens, the FRP Uwraps with a 45° angle without an edge distance maximizes the benefit of the anchoring effect. Two factors were found to control the Uwrap performance: the str...

Experimental Study on Failure Mode of Concrete Beams Strengthened with FRP Sheet

The failure mode of the FRP reinforced concrete beam with different sheet length was investigated by experiments. The results indicate that, more cracks distributed on the bottom of the beam in the failure process of the FRP reinforced concrete structure. The effect of the FRP sheet length is considered to be an important factor not only to significantly influence the loading capacity but also to control the maximum deflection of the concrete beam. In addition, the loading capacity is increased and maximum deflection of the concrete beam is also increased with the increasing of the FRP sheet length. It showed that FRP strengthened beams failed prematurely in a brittle and sudden manner due to debonding between FRP and concrete substrate and therefore the full strength of the FRP sheet cannot be sufficiently utilized.

TURBULENT RECONNECTION IN RELATIVISTIC PLASMAS AND EFFECTS OF COMPRESSIBILITY

We report turbulence effects on magnetic reconnection in relativistic plasmas using 3-dimensional relativistic resistive magnetohydrodynamics simulations. We found reconnection rate became independent of the plasma resistivity due to turbulence effects similarly to non-relativistic cases. We also found compressible turbulence effects modified the turbulent reconnection rate predicted in non-relativistic incompressible plasmas; The reconnection rate saturates and even decays as the injected velocity approaches to the Alfv\'en velocity. Our results indicate the compressibility cannot be neglected when compressible component becomes about half of incompressible mode occurring when the Alfv\'en Mach number reaches about $0.3$. The obtained maximum reconnection rate is around $0.05$ to $0.1$, which will be able to reach around $0.1$ to $0.2$ if injection scales are comparable to the sheet length.

Visualization studies of the spray from swirl injectors under elevated ambient pressure

This paper presents the results of a visualization study on spray formed by swirl injectors with different geometries under elevated ambient pressure. A spray test facility with an ambient pressure chamber was constructed, and sprays were recorded using a high-speed camera. The parameters of the spray characteristics, e.g. the spray cone angle and breakup length of liquid sheet, were measured, and the effects of the ambient pressure and injector geometrical parameters on the spray were obtained. Experimental results indicated that when other parameters in the swirl injector remained constant, the increase of ambient pressure caused a decrease in the spray cone angle and the breakup length of liquid sheets. However, the mass flow rates remained nearly constant. An increase in nozzle diameter increased the spray cone angle, and the variation of breakup length according to nozzle diameter was somewhat irregular. The increase in the diameter of the tangential inlet reduced the spray cone angle; the breakup length scarcely varied.

Experimental study on the influence of liquid and air boundary conditions on a planar air-blasted liquid sheet, Part I: Liquid and air thicknesses

This experimental study is devoted to the influence of the air and liquid thicknesses on an air-blasted atomizer. The flow configuration corresponds to a planar liquid sheet sheared on both sides by two high velocity airflows. Using planar laser induced fluorescence, back lighting visualizations and light diffraction, flapping frequency, breakup length of the liquid sheet and droplet sizes resulting from the atomization process are measured. The results show that the influence of each fluid thickness depends on the investigated flow characteristic. Thus, breakup length is strongly correlated to liquid flow rate, whereas flapping frequency depends mainly on airflow conditions, characterized by the vorticity thickness. Concerning final droplet sizes, both previous parameters must be taken into account, leading to a correlation based on breakup length and oscillation frequency.

Spin- and valley-dependent transport properties for metal-silicene-metal junctions

Detailed knowledge relating to the interactions between silicene and normal metal is crucial to understanding silicene growth on metal surfaces and metal/silicene interfaces in nanoelectronic devices. In this work, we study the valley- and spin-dependent transport properties of a metal/silicene/metal junction (MSM) with end and side metal-silicene contacts, respectively, where the central silicene sheet is simultaneously in proximity to a ferromagnet and a perpendicular electric field. By connecting the wave amplitudes obeying the lattice Schrodinger equation for the interfaces within the tight-binding model, the tunable conductance of both end-contacted (EC) and side contacted (SC) MSM junctions have been calculated. The current through MSM junctions is spin and valley polarized due to the coupling between valley and spin degrees of freedom, and the conductance and polarization show oscillating behavior as a function of the length of the silicene sheet. In particular, we find that the full spin and valley polarized conductance can be achieved by introducing proper electric and exchange fields. Further, the conductance is heavily dependent on the hopping integrals of simple metal, silicene and metal/silicene interfaces for EC junctions, and as long as the hopping integrals satisfy certain condition (with suitable incident energy) there is no difference in the transport between EC and SC junctions. The findings here may be meaningful in understanding the nature of metal/silicene interfaces.

Flexural and compression behavior for steel structures strengthened with Carbon Fiber Reinforced Polymers (CFRPs) sheet

This paper presents the experimental results of flexural and compression steel members strengthened with carbon fiber reinforced polymers (CFRP) sheets. In the flexural test, the five specimens were fabricated and the test parameters were the number of CFRP ply and the ratio of partial-length bonded CFRP sheets of specimen. The CFRP sheet strengthened steel beam had failure mode: CFRP sheet rupture at the mid span of steel beams. A maximum increase of 11.3% was achieved depending on the number of CFRP sheet ply and the length of CFRP sheet. In the compression test, the nine specimens were fabricated and the main parameters were: width-thickness ratio (b/t), the number of CFRP ply, and the length of the specimen. From the tests, for short columns it was observed that two sides would typically buckle outward and the other two sides would buckle inward. Also, for long columns, overall buckling was observed. A maximum increase of 57% was achieved in axial-load capacity when 3 layers of CFRP were used to wrap HSS columns of b/t = 60 transversely.

Effect of bonded lengths and wrappings on energy capacity and debonding strain of reinforced concrete beams strengthened with carbon‐fiber‐reinforced polymer

In this study, a series of flexural tests were performed to evaluate the energy capacity and debonding strain of reinforced concrete beams strengthened with a carbon‐fiber‐reinforced polymer (CFRP). Seven reinforced concrete beams were fabricated and loaded up to failure in a three‐point bending test. The type of CFRP laminate (plate or sheet), bonded length (1.44 or 2.16 m), and wrapping of the CFRP sheet were selected as the key test variables. The test results showed that beams strengthened with CFRP sheets were more effective than those strengthened with CFRP plates. The CFRP‐strengthened beams showed an elastic energy greater than that of the control beam, but the opposite result was obtained for the plastic energy. The average debonding strains of the CFRP plates and sheets were 4,309 and 11,649 μ, respectively, which corresponded to 21.5% and 77.1% of their respective ultimate tensile. POLYM. COMPOS., 38:1418–1426, 2017. © 2015 Society of Plastics Engineers

The thickness of glaciers

Basic formulae and results of glacier physics appearing in glaciology textbooks can be derived from first principles introduced in algebra-based first year physics courses. We discuss the maximum thickness of alpine glaciers and ice sheets and the relation between maximum thickness and length of an ice sheet. Knowledge of ordinary differential equations allows one to derive also the local ice thickness.

Characterization of Near-Field Spray of Nongelled- and Gelled-Impinging Doublets at High Pressure

Atomization mechanism of gelled propellants in an impinging jet flowfield is significantly different from that of nongelled liquid propellants and is not clearly understood. This study explores the effect of liquid fluid properties such as viscosity and surface tension on the liquid sheet breakup with a special emphasis on the effect of ambient pressure. A rheologically matched non-Newtonian fluid that is nonreactive and nontoxic is used as a simulant for the gelled hypergolic propellants. Near-field spray characteristics such as the sheet formation and breakup length of the liquid sheet are experimentally determined using shadowgraph. Various sheet breakup regimes have been identified for both nongelled and gelled simulants over a range of flow conditions. For all fluids, the breakup length is found to decrease as the ambient pressure increases. Near-field imaging and its analysis show that the ambient pressure affects jet surface dynamics before impingement by increasing the jet surface disturbance length scale and sheet dynamics after impingement by shortening the surface wavelength, resulting in shorter breakup length with the increase of ambient pressure.

Hybrid Energy Storage Devices Based on Monolithic Electrodes Containing Well-defined TiO2 Nanotube Size Gradients

Well-defined TiO2 nanotube size gradient thin films, manufactured using a bipolar electrochemistry approach, can be used as versatile monolithic hybrid electrodes for energy storage devices. The nanotube size distribution within the gradients can readily be controlled by altering the bipolar current and/or the length of the bipolar titanium sheet. As the electrochemical properties of the gradient electrodes can be carefully tailored by modifying the nanotube size gradient, this approach provides new possibilities for the manufacturing of hybrid electrodes with integrated energy and power density gradients. The free-standing anatase TiO2 nanotube size gradient electrodes provide unprecedented capacities at cycling rates from C/5 (i.e. 162μAhcm−2 or 169mAhg−1) to 50C (i.e. 40μAhcm−2 or 42mAhg−1). It is likewise shown that the size gradient electrodes facilitate fundamental studies of the charge/discharge process of TiO2 based electrodes. The results demonstrate that the different shapes of charge and discharge curves of TiO2 nanotube electrode can be explained by inherent differences between the lithiation and delithiation processes.