排序方式: 共有119条查询结果,搜索用时 15 毫秒
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Zhang XM Fatemi M Kinnick RR Greenleaf JF 《The Journal of the Acoustical Society of America》2003,113(3):1249-1257
Coupled vibration of arterial tubes is analyzed with the wave propagation approach and first-order shear deformation theory. Both the interior and exterior fluids are considered as compressible so that acoustic waves can be generated and propagated in the fluids. Results obtained using the theory have been evaluated against those available in the literature and the agreement has been found to be good. The theory can be used for future research on the vibration and acoustics of arterial walls. Vibration experiments were carried out on a silicone rubber tube in a water tank with a novel ultrasound stimulated optical vibrometry system. This system uses the radiation force of ultrasound to vibrate the tube at low frequency and records the resulting response by a laser vibrometer. Both the excitation and measurement are remote and noncontact. The silicone rubber tube was chosen because it has mechanical properties close to those of arteries. The fundamental frequency is well excited by the radiation force and measured with the laser. The measured fundamental frequency is in good agreement with the present theory. 相似文献
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We have observed electronically excited states in alkali-halide cluster anions with one excess electron. Using photoelectron spectroscopy, we have found two narrow states in (KI)-2, (NaI)-2, and (NaCl)-2, consistent with a dipole-bound electron, while larger cluster anions exhibit a single broad excited state. In the larger systems, electronic excitation is often accompanied by vibrational excitation and thus a change in cluster temperature. Such temperature changes affect cluster structure and in some cases lead to rapid thermal isomerization. 相似文献
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Vibro-acoustography is an imaging method based on audio-frequency harmonic vibrations induced in the object by the radiation force of focused ultrasound. The purpose of this study is to investigate features of vibro-acoustography images and manifestation of various tissue structures and calcifications in such images. Our motivation for this study is to pave the way for further in vitro and in vivo applications of vibro-acoustography. Here, vibro-acoustography images of excised prostate and in vivo breast are presented and compared with images obtained with other modalities. Resulting vibro-acoustography images obtained with a 3 MHz ultrasound transducer and at a vibration frequency of 50-60 kHz show soft tissue structures, tissue borders, and microcalcifications with high contrast, high resolution, and no speckle. It is concluded that vibro-acoustography offers features that may be valuable for diagnostic purposes. 相似文献
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Geis E Kohl M Ziskin V Akdogan T Arenhövel H Alarcon R Bertozzi W Booth E Botto T Calarco J Clasie B Crawford CB DeGrush A Donnelly TW Dow K Farkhondeh M Fatemi R Filoti O Franklin W Gao H Gilad S Hasell D Karpius P Kolster H Lee T Maschinot A Matthews J McIlhany K Meitanis N Milner RG Rapaport J Redwine RP Seely J Shinozaki A Sirca S Sindile A Six E Smith T Steadman M Tonguc B Tschalaer C Tsentalovich E Turchinetz W Xiao Y Xu W Zhang C Zhou Z Zwart T;BLAST Collaboration 《Physical review letters》2008,101(4):042501
We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio GEn/GMn was extracted from the beam-target vector asymmetry AedV at four-momentum transfers Q2=0.14, 0.20, 0.29, and 0.42 (GeV/c)2. 相似文献
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An open metal site framework named UTSA‐16 was synthesized and modified as a high‐capacity adsorbent for reversible CO2 capture. Partial substitution of intrinsic Co2+ sites of UTSA‐16 with Ni2+ centres was realized in the molar composition range 0–75% Ni with the aim of increasing CO2 uptake. Synthesized bimetallic Nix‐UTSA‐16 (x = 0, 20, 50, 75) materials were characterized using various techniques to assess the influence of chemical composition on CO2 binding affinity and any subsequent physical change in morphology, crystal size and porosity on the total uptake. Experimental isotherm adsorption studies showed the following trend for CO2 adsorption capacity employing the Nix‐UTSA‐16 series: Ni20‐UTSA‐16 > UTSA‐16 > Ni50‐UTSA‐16 > Ni75‐UTSA‐16. According to the dynamic breakthrough CO2 profiles measured for a mixture of CO2 and CH4 (15/85 molar ratio), Ni20‐UTSA‐16 exhibited 2 times the breakthrough time with 1.5 times the loading capacity at 75 Nml min?1 feed flow rate, compared to the parent UTSA‐16. In addition, the Ni20‐UTSA‐16 bimetallic metal–organic framework exhibited lower isosteric heat of adsorption compared to UTSA‐16 (ΔHave = 28.54 versus 46.85 kJ mol?1). As a result, more than 95% of its capacity was restored by applying a partial vacuum for only 1 h at room temperature without involving any other time‐ and energy‐consuming regenerative step. 相似文献