Solid-state spun fibers and yarns from 1-mm long carbon nanotube forests synthesized by water-assisted chemical vapor deposition

We report continuous carbon nanotube (CNT) fibers and yarns dry-drawn directly from water-assisted chemical vapor deposition (CVD) grown forests with about 1-mm height. As-drawn CNT fibers exist as aerogel and can be transformed into more compact fibers through twisting or densification with a volatile organic liquid. CNT fibers are characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, Raman microscopy, and wide-angle X-ray diffraction. Mechanical properties and electrical conductivity of the post-treated CNT fibers are investigated. The resulting fibers show the work of rupture of 30 J/g and DC electrical conductivity of 5.0 × 10⁴ S/m.     

Effective Suppression of Conducted Electro Magnetic Interference in DC-DC Boost Converter Using Field Programmable Gate Array Based Chaotic Pulse Width Modulation Switching

Abstract—In recent years, electro-magnetic interference on DC-DC converters is seen as serious problem as it limits the capability of the DC-DC converter. It is popular to use analog circuits to suppress electro-magnetic interference; however, a cheap analog circuit suffers from numerous drawbacks, including inaccurate pulse generation, carrier frequency limitation, and degraded performance due to aging. Conversely, high-performance digital circuits are capable of providing accurate pulses compared to analog circuits. In this article, a field-programmable gate array is used to generate accurate chaotic pulse-width modulation pulses for DC-DC converters. A spread spectrum technique based on randomized carrier frequency modulation with fixed duty ratio is proposed for gating pulse generation, implemented using a field-programmable gate array for electro-magnetic interference suppression. A hardware prototype is built in the laboratory for the proposed method and tested. The performance of the proposed method estimated through simulation study is validated via experimental results.     

Intermetallic and void formation in gold wirebonds to aluminum films

Gold ball bonds attached to either pure Al films or Al films with Cu and Si additions were annealed at temperatures in the range 77–277°C for periods of up to 3,000 h and then shear tested. The resulting fracture surfaces were observed to change progressively with time and temperature of annealing. The intermetallic phases and voids present after each annealing treatment were characterized by microscopic examination of the bond cross sections. Shear test results are discussed in terms of the observed microstructures.     

Mesenteric ischemia secondary to cocaine abuse: case reports and literature review

In summary, we report two cases of mesenteric ischemia following cocaine abuse in young women. In such cases it is always difficult to prove a direct causal relationship between the abuse of cocaine and mesenteric ischemia. Both our patients were relatively young (in their thirties) and did not have any history of atherosclerosis, and their urine toxicity screens were positive for the use of cocaine. Cocaine-related hospital visits are on the increase. Mesenteric ischemia should be considered in the differential diagnosis when evaluating a young patient with a history of cocaine abuse presenting with an acute abdomen.     

Novel geodesic splitting on paraboloid of revolution with applications to ray-theoretic analysis

Computer simulations have shown a novel geodesic splitting on the paraboloid of revolution leading to a multiplicity of surface ray paths. Such a phenomenon would have wide ramifications for wave propagation problems in general, besides applications in target-detection problems and the computational requirements of ray-theoretic formulations such as the UTD, in computing the antenna characteristics in the high-frequency domain.<>     

Grain orientation studies in YBCO superconductors by molten salt synthesis

The molten salt or the flux method is utilized in this study to fabricate a grainoriented YBa₂Cu₃O_7−x superconductor. The formation of YBa₂Cu₃O_7−x in the presence of molten salts of Na, K, Li belonging to chloride and iodide systems does not appear feasible due to the instability of the superconducting phase in these salt systems. Studies using the “green phase,” Y₂BaCuO₅, as seed crystals suggest a two-stage approach in the formation of YBa₂Cu₃O_7−x . The process uses Y₂BaCuO₅ formed by molten salt synthesis which has been observed to be stable in water and against most of the salts. The 211 crystals can be mixed with oxides and converted to 123. Analysis of X-ray data and SEM micrographs indicates a certain degree of grain orientation, which can be further enhanced by tape-casting or not-forging.     

Transient dynamic analysis of higher order sandwich and composite arches

A higher order refined model with isoparametric elements is proposed to study the transient dynamic response of laminated arches/curved beams. The strain field is modeled through cubic axial, cubic transverse shear and linear transverse normal strain components. As the cross-sectional warping is accurately modeled by this theory, the shear correction factor is rendered redundant. The stress–strain relationship is derived from an orthotropic lamina in a three-dimensional state of stress, so that angle-ply laminates can be studied through one-dimensional elements. Consistent mass matrix is constituted for the equation of motion, which is solved by Newmark integration scheme. The higher order formulation is validated with available results and subsequently applied to arches with various curvatures, aspect ratios, boundary conditions, loadings and lamination schemes to evaluate its transient dynamic performance and suitable conclusions are drawn.     

Analysis and simulation of a solar water pump for lift irrigation

A solar water pump for lift irrigation, which was shown to be economically viable, was proposed by Rao and Rao [5]. A “modified pump” is suggested, which is suitable for village water supply. The thermodynamic analysis of the pumps is presented. Though the solar water pump is intended to be operated with flat-plate collectors, it is analysed whether the pump could be run more efficiently when coupled with concentrating collectors. The analysis is also applicable for bellow actuated solar water pumps.Preliminary experimental studies showed that the heat losses are 2–3 times the theoretical energy requirement and the losses to the water tank shell accounted for a major part of the total heat losses. To reduce these losses, it is proposed that the inner surface of the water tank shell be lined with a resin bonded cork insulation. A method to evaluate the heat losses to the shell with insulation by solving the unsteady state heat conduction equation for a composite cylindrical body with time varying convective boundary conditions is presented. The heat losses are reduced to 5–15 per cent of the theoretical energy requirement with the use of the internal insulation. The major problem encountered in operating the pump was the inadequate condensation of the working fluid, which resulted in failure of the suction of water into the water tank. To ensure proper suction of water, the conditions to be maintained are analysed. The presence of water vapor and air in the spent vapor has to be taken into consideration while designing the condenser.An algorithm to evaluate the year round performance of the water-cooled pump for any location, given the lift and collector area, is presented. The cost of the water-cooled pump is compared with the costs of other types of solar water pumps and it is shown that the pump under consideration costs several times less than the other ones. The conditions at which the pump will be economical vis-a-vis diesel and electrical pumps are presented.     

A review on current trends in potential use of metal-organic framework for hydrogen storage

Hydrogen can be a promising clean energy carrier for the replenishment of non-renewable fossil fuels. The set back of hydrogen as an alternative fuel is due to its difficulties in feasible storage and safety concerns. Current hydrogen adsorption technologies, such as cryo-compressed and liquefied storage, are costly for practical applications. Metal-organic frameworks (MOFs) are crystalline materials that have structural versatility, high porosity and surface area, which can adsorb hydrogen efficiently. Hydrogen is adsorbed by physisorption on the MOFs through weak van der Waals force of attraction which can be easily desorbed by applying suitable heat or pressure. The strategies to improve the MOFs surface area, hydrogen uptake capacities and parameters affecting them are studied. Hydrogen spill over mechanism is found to provide high-density storage when compared to other mechanisms. MOFs can be used as proton exchange membranes to convert the stored hydrogen into electricity and can be used as electrodes for the fuel cells. In this review, we addressed the key strategies that could improve hydrogen storage properties for utilizing hydrogen as fuel and opportunities for further growth to meet energy demands.     

Joint segmentation and reconstruction of hyperspectral data with compressed measurements

This work describes numerical methods for the joint reconstruction and segmentation of spectral images taken by compressive sensing coded aperture snapshot spectral imagers (CASSI). In a snapshot, a CASSI captures a two-dimensional (2D) array of measurements that is an encoded representation of both spectral information and 2D spatial information of a scene, resulting in significant savings in acquisition time and data storage. The reconstruction process decodes the 2D measurements to render a three-dimensional spatio-spectral estimate of the scene and is therefore an indispensable component of the spectral imager. In this study, we seek a particular form of the compressed sensing solution that assumes spectrally homogeneous segments in the two spatial dimensions, and greatly reduces the number of unknowns, often turning the underdetermined reconstruction problem into one that is overdetermined. Numerical tests are reported on both simulated and real data representing compressed measurements.