A high-speed gateable image pipeline

We present the performance of a high-speed gateable vacuum image pipeline, which permits individual images to be delayed and selected from continuous non-repetitive image stream. This device is composed of a vacuum tube equipped with a photocathode at one end, a phosphor screen at the other end, and a system of metal grids in between. Photoelectrons produced by the images focused on the photocathode, are guided by a uniform magnetic field, parallel to the tube axis. By changing the grid potentials, the drift time of the photoelectrons inside the tube can be varied from 0.35 to 1.5 μs. An image can then be selected by an external trigger with a time resolution in the range of 4–30 ns, depending on the delay time. The selected photoelectrons are finally accelerated onto the phosphor screen, set at 10 kV, where they reproduce the desired image. With a magnetic field of 0.1 T, a spatial resolution of 33 lp/mm was obtained. The high spatial and time resolution make this device an interesting tool for high-energy physics and astrophysics experiments, and for high-speed photography.     

Thermal and nonequilibrium responses of superconductors for radiation detectors

This work summarizes the progress in the study of the superconductor response to optical radiation and in the development of infrared detectors. The recent advances in the design of high-T _c superconducting radiation detectors using silicon microfabrication technology are emphasized. Thermal and optical properties important for the detector performance are discussed. The mechanism of the nonequilibrium optical response and its potential use to build fast and sensitive radiation detectors are described. Future challenges and opportunities in the development of high-T _c superconducting radiation detectors are highlighted.     

Matching with don't-cares and a small number of mismatches

In matching with don't-cares and k mismatches we are given a pattern of length m and a text of length n, both of which may contain don't-cares (a symbol that matches all symbols), and the goal is to find all locations in the text that match the pattern with at most k mismatches, where k is a parameter. We present new algorithms that solve this problem using a combination of convolutions and a dynamic programming procedure. We give randomized and deterministic solutions that run in time O(nk²logm) and O(nk³logm), respectively, and are faster than the most efficient extant methods for small values of k. Our deterministic algorithm is the first to obtain an O(polylog(k)⋅nlogm) running time.     

Computer-assisted single- or double-cut oblique osteotomies for the correction of lower limb deformities

Corrective osteotomy interventions on lower extremities are widely accepted procedures for restoring axial alignment of lower limbs. However, some studies reveal failure rates of up to 70 per cent in a 10 year time frame, which indicates that the success of corrective osteotomies depends on multiple factors. Based on a comprehensive review of error sources among conventional correction osteotomy interventions, a novel approach was developed in order to reduce these error sources among all clinical working steps (deformity determination, planning, and intra-operative realization). The article describes the implemented methodology for realizing optimal correction osteotomies based on a six-dimensional or 12-dimensional optimization module for single- and double-cut oblique osteotomies. The results show that the realized planning and navigation concept enables reduction in the error sources among the clinical working steps of correction osteotomy interventions.     

Superfast densification of nanocrystalline oxide powders by spark plasma sintering

Spark plasma sintering (SPS) is a newly discovered old technique which recently has been used for superfast densification of ceramic powders. Simultaneous application of pulsed high dc current densities and load is the necessary condition for rapid and full densification of ceramic powders by SPS. Commercial nanocrystalline magnesium oxide (nc-MgO) and yttrium aluminum garnet (nc-YAG) powders were densified to optical transparency using spark plasma sintering at distinctly different homologous temperatures (0.3 T _m for nc-MgO and 0.7 T _m for nc-YAG). The observed microstructure, density and grain size evolutions versus the SPS temperature were analyzed. The enhanced densification of the nc-MgO powder at the present SPS conditions was related to plastic deformation followed by diffusion processes. Densification of nc-YAG powder was described by the formation of viscous layer at the particle surfaces and corresponding densification by grain rotation and diffusion through the liquid phase. Densification by normal grain growth takes place at higher relative densities, regardless of the material.     

Effect of grain size on elastic modulus and hardness of nanocrystalline ZrO2-3 wt% Y2O3 ceramic

Dense nanocrystalline ZrO₂-3 wt% Y₂O₃ ceramics with grain sizes ranging between 23 to 130 nm were tested by ultrasonic pulse echo and Vickers hardness. The elastic modulus and hardness results were corrected for the residual porosity and the phase content. The corrected elastic moduli exhibited continuous decrease with decrease in the grain size. In contrast, no correlation was found between the corrected hardness and grain size. The percolative composite model was used to describe the changes in the elastic moduli in terms of percolation of the elastic wave through the intercrystalline phase at the percolation threshold. The absence of correlation with the hardness results was explained due to the other energy absorbing mechanisms such as microcracking beneath the indenter.     

Electric field effects during spark plasma sintering of ceramic nanoparticles

The effects of the applied electric field during the spark plasma sintering of ceramic nanoparticles were examined at various stages of the process. It was assumed that local intensification of the electric field arises due to the nanoscale structural features. Enhanced surface conductivity is expected in the nanoparticles during the heating, which otherwise are electrically non-conducting as a bulk. Percolation of the electric current at “optimal” electrical conductivity is obtained by fractal dimension. The defective nanoparticle surfaces experience charging–discharge cycles which lead to local breakdown and to plasma formation due to the ionized surface molecules. High local temperatures which evolved in a nonlinear fashion at the particle surfaces lead to enhanced sintering and densification kinetics, consistent with the flash sintering phenomenon. The contribution of the pondermotive force to the enhancement of the diffusion kinetics is discussed. Temperature windows for enhanced densification kinetics via plastic deformation or plasma-assisted processes are estimated for MgO, Al₂O₃, and YAG.     

Effect of La partial substitution for Zr on the Structural and electrochemical properties of Ti0.17Zr0.08-xLaxV0.35Cr0.1Ni0.3 (x = 0–0.04) electrode alloys

In order to elucidate the effects of metallic La addition on the performance of Ti–V-based hydrogen storage alloys as negative electrodes for nickel/metal-hydrides batteries, Ti_0.17Zr_0.08-xLa_xV_0.35Cr_0.1Ni_0.3 (x = 0, 0.01, 0.02, 0.03, 0.04) alloys were prepared and their structural and electrochemical properties were systematically investigated. X-ray powder diffraction (XRD) results showed that these alloys were mainly consisted of C14 Laves phase with a hexagonal structure, V-based solid solution phase with BCC structure and C15 Laves phase with a cubic structure. The electrochemical measurements indicated that the maximum discharge capacities of the alloy electrodes decreased from 337.3 mAh/g (x = 0) to 262.5 mAh/g (x = 0.04) and that the substitution of Zr with metallic La in the alloys had no obvious effect on the capacity retention rate (C₁₀₀/C_max, C₂₀₀/C_max). The high-rate dischargeability (HRD) of the alloy electrodes at the discharge current density of 800 mA/g first increased from 69.01% (x = 0) to 71.13% (x = 0.01) and then decreased to 65.35% (x = 0.04). In brief, the HRD was improved with an optimum La content in the alloy (x = 0.01). The electrochemical hydrogen kinetics of the alloy electrodes was further studied by means of electrochemical impedance spectroscopy, linear polarization, anodic polarization and potential-step measurements. The charge-transfer reaction resistance R_ct decreased for x = 0.01 with respect to x = 0 and then increased with the increase of x, while exchange current density I₀, limiting current density I_L and hydrogen diffusion coefficient D were all increased for x = 0.01 with respect to x = 0 and then decreased with the increase of x. The optimal content of La in Ti_0.17Zr_0.08-xLa_xV_0.35Cr_0.1Ni_0.3 alloys for negative electrodes in alkaline rechargeable secondary batteries is x = 0.01 in this study.     

Densification of nanocrystalline Y2O3 ceramic powder by spark plasma sintering

Nanocrystalline Y₂O₃ powders with 18 nm crystallite size were sintered using spark plasma sintering (SPS) at different conditions between 1100 and 1600 °C. Dense specimens were fabricated at 100 MPa and 1400 °C for 5 min duration. A maximum in density was observed at 1400 °C. The grain size continuously increased with the SPS temperature into the micrometer size range. The maximum in density arises from competition between densification and grain growth. Retarded densification above 1400 °C is associated with enhanced grain growth that resulted in residual pores within the grains. Analysis of the grain growth kinetics resulted in activation energy of 150 kJ mol^?1 and associated diffusion coefficients higher by 10³ than expected for Y³⁺ grain boundary diffusion. The enhanced diffusion may be explained by combined surface diffusion and particle coarsening during the heating up with grain boundary diffusion at the SPS temperature.     

The Effect of External Electrostatic Field Orientation on Aerosol Filtration by Granular Filters

The separation of fine aerosol particles by a packed granular-bed filter, enhanced by external electrostatic fields, was studied experimentally and theoretically. The filtration efficiencies of charged and neutralized aerosols were measured for external fields aligned with the air flow, transverse to the flow, and opposite to the flow. Theoretical models of electrostatically enhanced granular-bed filtration of micrometer and submicrometer particles were developed. Experimental results which demonstrate the relative merit of each configuration were presented and compared with the theory. The parallel-field configuration yielded the best filtration efficiency followed by the transverse configuration.