Proper material constitutive models for concrete-filled tube ͑CFT͒ columns are proposed and verified by the nonlinear finite element program ABAQUS against experimental data. The cross sections of the CFT columns in the numerical analysis are categorized into three groups, i.e., circular section, square section, and square section stiffened by reinforcing ties. Via the numerical analyses, it is shown that for circular CFT columns, the tubes can provide a good confining effect to the concrete especially when the width-to-thickness ratio D/t is small ͑say D/tϽ40). For square CFT columns, the tubes do not provide a large confining effect to the concrete especially when the width-to-thickness ratio B/t is large ͑say B/tϾ30). The confining effect of square CFT columns with reinforcing ties is enhanced by the use of reinforcing ties especially when the tie spacing is small and the tie number ͑or tie diameter͒ is large.
This paper demonstrates the use of microlens projection lithography using gray-scale masks to fabricate arrays of microstructures in photoresist. In microlens projection lithography, an array of microlenses (diameter d ) 1-1000 µm) reduces a common, centimeter-scale pattern in an illuminated mask to a corresponding pattern of micrometer-scale images in its image plane. The pattern of intensity projected by the array of microlenses depends on the shape and gray-level distribution of the pattern on the illuminated mask and on the shape and pattern of the lenses. The distribution of intensity in the microimages could be adjusted using gray-scale masks. After the recording of this intensity distribution in layers of photoresist and developing, the developed resist showed arrays of 3D microstructures over areas larger than 10 cm 2 . We used these arrays of 3D microstructures as masters and cast transparent elastomer onto them to generate complementary replicas. For a specific microlens array and a fixed light source, the profile of the 3D microstructures generated by this method depended on the pattern on the illuminated mask and on the distance of the mask from the lens array. An appropriate mask with noncircular, gray-level patterns generated arrays of 3D microstructures that acted as lenses. This technique generates arrays of noncircular microlenses over areas larger than 10 cm 2 in a single exposure. LA015735B
Most commonly used methods for three-dimensional (3D) fluorescence microscopy make use of sectioning techniques that require that the object be physically scanned in a series of two-dimensional (2D) sections along the z axis. The main drawback in these approaches is the need for these sequential 2D scans. An alternative approach to fluorescence imaging in three dimensions has been developed that is based on optical scanning holography. This novel approach requires only a 2D scan to record 3D information. Holograms of 15-microm fluorescent latex beads with longitinal separation of ~2 mm have been recorded and reconstructed. To our knowledge, this is the first time holograms of fluorescent specimens have been recorded by an optical holographic technique.
High-quality p-GaN∕i-In0.1Ga0.9N∕n-GaN heterojunctional epilayers are grown on (0001)-oriented sapphire substrates by metal organic chemical vapor deposition. The Pendellösung fringes around the InGaN peak in high-resolution x-ray diffraction (HRXRD) confirm a sharp interface between InGaN and GaN films. The corresponding HRXRD and photoluminescence measurements demonstrate that there is no observable phase separation. The improvement in crystal quality yields high-performance photovoltaic cells with open-circuit voltage of around 2.1eV and fill factor up to 81% under standard AM 1.5 condition. The dark current-voltage measurements show very large shunt resistance, implying an insignificant leakage current in the devices and therefore achieving the high fill factor in the illuminated case.
Pulsed power accelerators compress electrical energy in space and time to provide versatile experimental platforms for high energy density and inertial confinement fusion science. The 80-TW “Z” pulsed power facility at Sandia National Laboratories is the largest pulsed power device in the world today. Z discharges up to 22 MJ of energy stored in its capacitor banks into a current pulse that rises in 100 ns and peaks at a current as high as 30 MA in low-inductance cylindrical targets. Considerable progress has been made over the past 15 years in the use of pulsed power as a precision scientific tool. This paper reviews developments at Sandia in inertial confinement fusion, dynamic materials science, x-ray radiation science, and pulsed power engineering, with an emphasis on progress since a previous review of research on Z in Physics of Plasmas in 2005.
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