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排序方式: 共有217条查询结果,搜索用时 171 毫秒
101.
Thode A Skinner J Scott P Roswell J Straley J Folkert K 《The Journal of the Acoustical Society of America》2010,128(5):2681-2694
Passive acoustic towed linear arrays are increasingly used to detect marine mammal sounds during mobile anthropogenic activities. However, these arrays cannot resolve between signals arriving from the port or starboard without vessel course changes or multiple cable deployments, and their performance is degraded by vessel self-noise and non-acoustic mechanical vibration. In principle acoustic vector sensors can resolve these directional ambiguities, as well as flag the presence of non-acoustic contamination, provided that the vibration-sensitive sensors can be successfully integrated into compact tow modules. Here a vector sensor module attached to the end of a 800 m towed array is used to detect and localize 1813 sperm whale "clicks" off the coast of Sitka, AK. Three methods were used to identify frequency regimes relatively free of non-acoustic noise contamination, and then the active intensity (propagating energy) of the signal was computed between 4-10 kHz along three orthogonal directions, providing unambiguous bearing estimates of two sperm whales over time. These bearing estimates are consistent with those obtained via conventional methods, but the standard deviations of the vector sensor bearing estimates are twice those of the conventionally-derived bearings. The resolved ambiguities of the bearings deduced from vessel course changes match the vector sensor predictions. 相似文献
102.
We study grain-boundary fluctuations in two-dimensional colloidal crystals in real space and time using video microscopy. The experimentally obtained static and dynamic correlation functions are very well described by expressions obtained using capillary wave theory. This directly leads to values for the interfacial stiffness and the interface mobility, the key parameters in curvature-driven grain-boundary migration. Furthermore, we show that the average grain-boundary position exhibits a one-dimensional random walk as recently suggested by computer simulations [Z. T. Trautt, M. Upmanyu, and A. Karma, Science 314, 632 (2006)]. The interface mobility determined from the mean-square displacement of the average grain-boundary position is in good agreement with values inferred from grain-boundary fluctuations. 相似文献
103.
104.
Tuhin Roychowdhury Dhruv Shah Varun Jain Dhananjay I. Patel Berg Dodson William Skinner James N. Hilfiker Stacey J. Smith Matthew R. Linford 《Surface and interface analysis : SIA》2020,52(7):433-441
In this work, copper and tungsten were sputtered onto silicon wafers by direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS). The resulting films were characterized by energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and X-ray diffraction (XRD). By EDX and XPS, all the sputtered films showed only the expected metal peaks. By XPS, the surfaces sputtered by DCMS were richer in oxygen than those produced by HiPIMS. By AFM, the surfaces were quite smooth. The root mean square (RMS) roughness values are as follows: 0.83 nm (W, HiPIMS), 1.10 nm (W, DCMS), 0.85 nm (Cu, HiPIMS), and 1.78 nm (Cu, DCMS). By SEM, the HiPIMS films exhibited smaller grain sizes, which was confirmed by XRD. The crystallite sizes estimated by XRD are as follows: 4 nm (W, body-centered cubic, HiPIMS), 13 nm (W, body-centered cubic, DCMS), 7 nm (W, cubic, HiPIMS), 14 nm (W, cubic, DCMS), 25 nm (Cu, HiPIMS), and 35 nm (Cu, DCMS). By SE, the HiPIMS surfaces showed higher refractive indices, which suggested that they were denser and less oxidized than the DCMS surfaces. 相似文献
105.
106.
Pyrolysis of a dilute mixture of neopentane (2,2-dimethylpropane) has been studied behind incident shock waves at an average pressure of 0.35 atm; the reaction was followed by absorption spectroscopy for H atoms. In the temperature range 1230–1455 K, the rate constant for dissociation of neopentane to t-butyl and methyl radicals is 1.1 E 13 exp(?62 kcal/RT) s?1. These data and some of the literature results, between 1000 and 1450 K, can be fitted by an RRKM model of the hindered Gorin type, with five active internal rotors in the complex. To match our data with other literature data down to 800 K, a vibrational model was more satisfactory, but this did not fit very low pressure pyrolysis data in the 1000–1100 K range. Apparently, the VLPP data are too high because of heterogeneous processes or chain reactions. 相似文献
107.
Pieniazek PA Tainter CJ Skinner JL 《Journal of the American Chemical Society》2011,133(27):10360-10363
Phase-sensitive vibrational sum-frequency experiments on the water surface, using isotopic mixtures of water and heavy water, have recently been performed. The experiments show a positive feature at low frequency in the imaginary part of the susceptibility, which has been difficult to interpret, and impossible to reproduce using two-body (pairwise-additive) water simulation models. We have reparameterized a new three-body simulation model for liquid water, and with this model we calculate the imaginary part of the sum-frequency susceptibility, finding good agreement with experiment for dilute HOD in D(2)O. Theoretical analysis provides a molecular-level structural interpretation of these new and exciting experiments. In particular, we do not find evidence of any special ice-like ordering at the surface of liquid water. 相似文献
108.
Maingi R Kaye SM Skinner CH Boyle DP Canik JM Bell MG Bell RE Gray TK Jaworski MA Kaita R Kugel HW LeBlanc BP Mansfield DK Osborne TH Sabbagh SA Soukhanovskii VA 《Physical review letters》2011,107(14):145004
Lithium wall coatings have been shown to reduce recycling, improve energy confinement, and suppress edge localized modes in the National Spherical Torus Experiment. Here, we show that these effects depend continuously on the amount of predischarge lithium evaporation. We observed a nearly monotonic reduction in recycling, decrease in electron transport, and modification of the edge profiles and stability with increasing lithium. These correlations challenge basic expectations, given that even the smallest coatings exceeded that needed for a nominal thickness of the order of the implantation range. 相似文献
109.
B. Skinner T. Chen B. I. Shklovskii 《Journal of Experimental and Theoretical Physics》2013,117(3):579-592
In the three-dimensional topological insulator (TI), the physics of doped semiconductors exists literally side-by-side with the physics of ultrarelativistic Dirac fermions. This unusual pairing creates a novel playground for studying the interplay between disorder and electronic transport. In this mini-review, we focus on the disorder caused by the three-dimensionally distributed charged impurities that are ubiquitous in TIs, and we outline the effects it has on both the bulk and surface transport in TIs. We present self-consistent theories for Coulomb screening both in the bulk and at the surface, discuss the magnitude of the disorder potential in each case, and present results for the conductivity. In the bulk, where the band gap leads to thermally activated transport, we show how disorder leads to a smaller-than-expected activation energy that gives way to variable-range hopping at low temperatures. We confirm this enhanced conductivity with numerical simulations that also allow us to explore different degrees of impurity compensation. For the surface, where the TI has gapless Dirac modes, we present a theory of disorder and screening of deep impurities, and we calculate the corresponding zero-temperature conductivity. We also comment on the growth of the disorder potential in passing from the surface of the TI into the bulk. Finally, we discuss how the presence of a gap at the Dirac point, introduced by some source of time-reversal symmetry breaking, affects the disorder potential at the surface and the mid-gap density of states. 相似文献
110.
A. G. Hunt T. E. Skinner R. P. Ewing B. Ghanbarian-Alavijeh 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,80(4):411-432
A recently introduced theory of solute transport in porous media is tested
by comparison with experiment. The solute transport is predicted using an
adaptation of the cluster statistics of percolation theory to critical path
analysis together with knowledge of how the structure of such percolation
clusters affects the time of transport across them. Only the effects of a
single scale of medium heterogeneity are incorporated, and a minimal amount
of information regarding the structure of the medium is required. This
framework is used to find effectively the distributions of solute velocities
and travel distances and thus generate arrival time distributions. The
comparison with experiment focuses on the dispersivity (the ratio of the
second to the first moment of the spatial solute distribution). The
predictions of the theory in the absence of diffusion are verified by
comparing with over 2200 experiments over length scales from a few microns
to 100 km. At larger length scales (centimeters on up) about 95% of the
data lie within our predicted bounds. At smaller length scales approximately
99.8% of the data lie where we predict. These comparisons are not trivial
as the typical values of the dispersivity increase by ten orders of
magnitude over ten orders of magnitude of length scale. Noteworthy is that
the classical advection-dispersion (ADE) equation predicts that the
dispersivity should be independent of length scale! This agreement with
experiment requires rethinking of the relevance of diffusion and multi-scale
heterogeneity and would also appear to signal the complete inappropriateness
of using the classical ADE or any of its derivatives to model solute
transport. 相似文献