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951.
A fast spin echo two-point Dixon (fast 2PD) technique was developed for efficient T2-weighted imaging with uniform water and fat separation. The technique acquires two interleaved fast spin echo images with water and fat in-phase and 180° out-of-phase, respectively, and generates automatically separate water and fat images for each slice. The image reconstruction algorithm uses an improved and robust region-growing scheme for phase correction and achieves consistency in water and fat identification between different slices by exploiting the intrinsic correlation between the complex images from two neighboring slices. To further lower the acquisition time to that of a regular fast spin echo acquisition with a single signal average, we combined the fast 2PD technique with sensitivity encoding (SENSE). Phantom experiments show that the fast 2PD and SENSE are complementary in scan efficiency and signal-to-noise ratio (SNR). In vivo data from scanning of clinical patients demonstrate that T2-weighted imaging with uniform and consistent fat separation, including breath-hold abdominal examinations, can be readily performed with the fast 2PD technique or its combination with SENSE. 相似文献
952.
Son DT 《Physical review letters》2005,94(17):175301
We construct a low-energy effective Lagrangian describing zero temperature supersolids. Galilean invariance imposes strict constraints on the form of the effective Lagrangian. We identify a topological term in the Lagrangian that couples superfluid and crystalline modes. For small superfluid fractions, this interaction term is dominant in problems involving defects. As an illustration, we compute the differential cross section of scatterings of low-energy transverse elastic phonons by a superfluid vortex. The result is model independent. 相似文献
953.
Several elements (V, Mo, Fe, Mn, Cd, Zn) as metallic impurities in pure uranium compounds were quantitatively determined by atomic absorption spectrometry. The effects of uranium and that of other factors on the absorption intensity of each element were studied. The analyzed samples were dissolved in 6 M nitric acid, and uranium was selectively extracted with tributylphosphate. The aqueous solution containing impurities was then evaporated and the obtained moist residues were dissolved in dilute hydrochloride acid or nitric acid. The sample solution was measured with a flame atomic absorption spectrometer under the optimum conditions, such as the maximum wavelength, suitable ratio of acetylene-air or acetylene-nitrogen oxide mixture, and some other parameters of the instrument. The analytical procedure was applied in laboratories belonging to Vietnam Atomic Energy Commission for the determination of these above-mentioned elements in synthesized uranium samples and in purified uranium oxide samples with high precision and accuracy. 相似文献
954.
柱胞鱼腥藻(Anabaenacylindrica)原生质球培养再生的初步研究郭厚良,宋文贞,于登洲(武汉大学生命科学学院,武汉,430072)陈贤均(咸宁医学院生物学教研室)关键词蓝藻,原生质球,培养,再生中图法分类号Q949.221967年,Big... 相似文献
955.
Van Son Nguyen Robert Kershaw Kirby Dwight Aaron Wold 《Journal of solid state chemistry》1981,36(2):241-245
Members of the system Cd2Ge1?xSixO4 where 0 ≤ x ≤ 0.4 have been prepared. These compounds were observed to crystallize with the olivine structure, space group Pbnm. The resistivity, Hall mobility, flat-band potential, band gaps, and stability were determined as functions of composition. The variation of these photoelectronic properties can be attributed to the reduction of the cell parameters with increasing silicon substitution. The substitution of silicon for germanium reduces the loss of photocurrent from 25% after 1 hr for x = 0.0 to only 6% after 22 hr for x = 0.4. 相似文献
956.
Epitaxial silicon carbide is likely to contain hydrogen and vacancies ( V); therefore, V+nH complexes are likely to influence its electronic properties. Using ab initio calculations we show that neutral and positive H atoms are trapped by carbon vacancies ( V(C)) in three-center bonds with two Si neighbors. The double positive charge state of V(C)+H is not stable in equilibrium and in the triply positive state H binds only to one of the Si neighbors. At most two H atoms can be accommodated by a single V(C). The V(C)+nH complexes have donor character and exhibit rather atypical vibration modes for Si-H bonds. Occupation levels and spin distributions were calculated and compared for V(C)+H and V(C). 相似文献
957.
958.
S.F. Son B.W. Asay E.M. Whitney H.L. Berghout 《Proceedings of the Combustion Institute》2007,31(2):2063-2070
There is little flame spread data for homogeneous energetic materials and no data for nitramines. We report the results of flame spread experiments of PBX 9501 (HMX (cyclotetramethylenetetranitramine) based explosive). The horizontal flame spread rate, Sf, is of the same order of magnitude as normal deflagration and varies nearly as the square root of pressure, as our scaling analysis presented here predicts. In the vertical orientation, the flame propagation downward was observed to be slightly faster than horizontal flame spread, presumably because of the melt layer flowing downward on the sample. In an accident scenario, a charge may be fractured or the surface roughened. Consequently, we also examined the effect of roughness. Minor roughness created by explosives machining was found to have a negligible affect on flame spread. However, more significant roughness can increase the rate between two and three times over normal flame spread for the conditions considered here. In addition we examine the effect of sample edges and configuration. Corners result in more favorable heat loss and therefore affect flame spread rate. We argue that the increased spread rate on edges and rough surfaces is because of favorable heat transfer convergence. 相似文献
959.
A novel scheme for fast conformational search has been developed by combining the replica exchange method (REM) with the generalized effective potential concept. The new method, referred to Q-REM [S. Jang et al. Phys. Rev. Lett. 91, 058305 (2003)], is expected to provide a useful alternative to the conventional REM for effective conformational sampling of complex systems. The authors have performed folding simulations of the Trp-cage miniprotein using Q-REM. All atom level simulations with generalized Born solvent access-area solvation model show that successful folding can be observed with much smaller number of replicas in Q-REM compared to the conventional REM. It can be concluded that the new method has potential to significantly improve sampling efficiency, allowing simulations of more challenging systems. 相似文献
960.
Hoang Viet Long Nguyen Thi Kim Son Nguyen Thi My Ha Le Hoang Son 《Fuzzy Optimization and Decision Making》2014,13(4):435-462
Fuzzy hyperbolic partial differential equation, one kind of uncertain differential equations, is a very important field of study not only in theory but also in application. This paper provides a theoretical foundation of numerical solution methods for fuzzy hyperbolic equations by considering sufficient conditions to ensure the existence and uniqueness of fuzzy solution. New weighted metrics are introduced to investigate the solvability for boundary valued problems of fuzzy hyperbolic equations and an extended result for more general classes of hyperbolic equations is initiated. Moreover, the continuity of the Zadeh’s extension principle is used in some illustrative examples with some numerical simulations for \(\alpha \) -cuts of fuzzy solutions. 相似文献