Substrate-Controlled Magnetism: Fe nanowires on vicinal Cu surfaces

Here we present a novel approach to control magnetic interactions in atomic-scale nanowires. Our ab initio calculations demonstrate the possibility to tune magnetic properties of Fe nanowires formed on vicinal Cu surfaces. Both intrawire and interwire magnetic exchange parameters are extracted from DFT calculations. This study suggests that the effective interwire magnetic exchange parameters exhibit Ruderman--Kittel--Kasuya--Yosida-like (RKKY) oscillations as a function of Fe interwire separation. The choice of vicinal Cu surface offers possibilities for controlling the magnetic coupling. Furthermore, an anisotropic Heisenberg model was used in Monte Carlo simulations to examine the stability of these magnetic configurations at finite temperature. The predicted critical temperatures of the Fe nanowires on Cu(422) and Cu(533) surfaces are well-above room temperature

Low-velocity impact craters in ice and ice-saturated sand with implications for Martian crater count ages

We produced a series of decimeter-sized impact craters in blocks of ice near 0°C and −70°C and in ice-saturated sand near −70°C as a preliminary investigation of cratering in materials analogous to those found on Mars and the outer solar system satellites. The projectiles used were standard 0.22 and 0.30 caliber bullets fired at velocities between 0.3 and 1.5 km/s, with kinetic energies at impact between 10^9 and 4×10^(10) ergs. Crater diameters in the ice-saturated sand were ∼2 times larger than craters in the same energy and velocity range in competent blocks of granite, basalt and cement. Craters in ice were ∼3 times larger. If this dependence of crater size on strength persists to large hypervelocity impact craters, then surfaces of geologic units composed of ice or ice-saturated soil would have greater crater count ages than rocky surfaces with identical influx histories. The magnitude of the correction to crater counts required by this strength effect is comparable to the magnitudes of corrections required by variations in impact velocity and surface gravity used in determining relative interplanetary chronologies. The relative sizes of craters in ice and ice-saturated sand imply that the tensile strength of ice-saturated sand is a strong inverse function of temperature. If this is true, then Martian impact crater energy versus diameter scaling may also be a function of latitude

Improved Sequential MAP estimation of CABAC encoded data with objective adjustment of the complexity/efficiency tradeoff

International audienceThis paper presents an efficient MAP estimator for the joint source-channel decoding of data encoded with a context adaptive binary arithmetic coder (CABAC). The decoding process is compatible with realistic implementations of CABAC in standards like H.264, i.e., handling adaptive probabilities, context modeling and integer arithmetic coding. Soft decoding is obtained using an improved sequential decoding technique, which allows to obtain various tradeoffs between complexity and efficiency. The algorithms are simulated in a context reminiscent of H264. Error detection is realized by exploiting on one side the properties of the binarization scheme and on the other side the redundancy left in the code string. As a result, the CABAC compression efficiency is preserved and no additional redundancy is introduced in the bit stream. Simulation results outline the efficiency of the proposed techniques for encoded data sent over AWGN and UMTS-OFDM channels

Multiscale imaging of HIV-1 transmission in humanized mice

HIV transmission within lymphoid tissues remains incompletely characterized at the level of individual cells and virions. Here we visually describe our approach to understanding HIV-1 dissemination at different levels of volume and resolution within lymphoid tissues from HIV-1-infected humanized mice. We combined tissue clearing techniques, immunostaining, and light sheet fluorescence microscopy to visualize large-volumes of intact tissue with single-cell resolution from HIV-1-infected humanized mice. In parallel, we imaged adjacent regions of tissue using electron microscopy and electron tomography to gain 3D ultrastructural information about the same tissue samples. This approach can provide spatial information about the density and distribution of target cells, HIV-1-infected cells, and individual budding and free-virions within lymphoid tissues. Multiscale imaging of HIV-1 infected tissues from humanized mice can provide insight into the biological mechanisms of HIV-1 transmission through the correlation of global pathology with structural details and these methods are directly translatable to other animal models and human clinical samples

Comparing Physiological Responses While Walking on a Standard Motorized Treadmill and Curve Treadmill

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Six-week Pilates Program Improved Postural Stability, Balance, and Isometric Back Strength in College-aged Athletes

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The Effects of Caffeine on Maximal Anaerobic Exercise

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Experimental simulation of volcanic steam blasts and jets at high pressure ratios

End-member compositions of plumes from volcanic eruptions range from nearly pure steam to heavily particle-laden gas flows. In all cases, if the plumes erupt from a high-pressure reservoir, they are initially supersonic jets that may have complex internal flow structures not easily documented in the field. In the laboratory, some properties of volcanic jets can be investigated with particle-laden flows, but other properties can only be investigated in optically transparent flows. We examine the relation of unsteady jet structure to reservoir conditions for optically transparent flows. We have developed an experimental shock tube facility capable of achieving pressure ratios up to ~150 with reservoirs of different shapes. Time-resolved schlieren visualization is combined with pitot pressure measurements to interrogate the structure of the underexpanded jet flow. We have done preliminary experiments at a pressure ration of 40 with air, with two reservoirs that are 12.6 and 20 cm in length. These initially produce well-defined supersonic jets that have properties (shape of the underexpanded jet; barrel shocks, Mach disk shocks) which we have bench-marked against other experiments and simulations. Estimated durations of the supersonic portions of the flow from pressure decay calculations are ~45 and ~75 ms, respectively. On these time-scales, the experimental jets collapse; the plume boundary and internal barrel shocks tighten and the Mach disk shock moves toward the vent, until subsonic conditions occur

Unsteady high-pressure flow experiments with applications to explosive volcanic eruptions

Motivated by the hypothesis that volcanic blasts can have supersonic regions, we investigate the role of unsteady flow in jets from a high-pressure finite reservoir. We examine the processes for formation of far-field features, such as Mach disk shocks, by using a shock tube facility and numerical experiments to investigate phenomena to previously unobtained pressure ratios of 250:1. The Mach disk shock initially forms at the edges of the vent and moves toward the centerline. The shock is established within a few vent diameters and propagates downstream toward the equilibrium location as the jet develops. The start-up process is characterized by two different timescales: the duration of supersonic flow at the nozzle exit and the formation time of the Mach disk shock. The termination process also is characterized by two different timescales: the travel time required for the Mach disk shock to reach its equilibrium position and the time at which the Mach disk shock begins significantly to collapse away from its equilibrium position. The critical comparisons for the formation of steady state supersonic regions are between the two start-up timescales and the termination timescales. We conclude that for typical vulcanian eruptions and the Mount St. Helens directed blast, the Mach disk shock could have formed near the vent, and that there was time for it to propagate a distance comparable to its equilibrium location. These experiments provide a framework for analysis of short-lived volcanic eruptions and data for benchmarking simulations of jet structures in explosive volcanic blasts