排序方式: 共有47条查询结果,搜索用时 15 毫秒
21.
We report structural data on liquid iron at pressures up to 58 GPa measured by x-ray scattering in a laser heated diamond anvil cell. The determined structure factor preserves essentially the same shape along the melting curve. Our data demonstrate that liquid iron at high pressures is a close-packed hard-sphere liquid. The results place important constraints on the thermodynamic and transport properties of liquid iron and the melting curve of iron. 相似文献
22.
R. J. Rivers 《International Journal of Theoretical Physics》2000,39(7):1779-1802
Kibble and Zurek have provided a unifying causal picture for the appearance ofclassical defects like cosmic strings or vortices at the onset of phase transitionsin relativistic QFT and condensed matter systems, respectively. In condensedmatter the predictions are partially supported by agreement with experiments insuperfluid helium. We provide an alternative picture for the initial appearanceof defects that supports the experimental evidence. When the original predictionsfail, this is understood, in part, as a consequence of thermal fluctuations (noise),which play a comparable role in both condensed matter and QFT. 相似文献
23.
N. Datta-Gupta D. Malakar Lesa Rice Sheila Rivers 《Journal of heterocyclic chemistry》1987,24(3):629-632
A complete series of five phenyl/4-benzyloxyphenyl 5,10,15,20-substituted porphyrin has been synthesized, characterized by analysis, Rf values, and proton-nmr spectroscopy (pmr). Their physicochemical properties, namely ir spectra, absorption spectra, emission spectra, excited state life-times, pK3 values, reduction potentials, and kinetics of Cu(+2) insertion, have been determined. Attempts have been made to correlate these physicochemical properties with the structures of the porphyrins. 相似文献
24.
Rivers RJ 《Physical review letters》2000,84(6):1248-1251
We examine the Zurek scenario for the production of vortices in quenches of liquid 4He in the light of recent experiments. Extending our previous results to later times, we argue that short wavelength thermal fluctuations make vortices poorly defined until after the transition has occurred. Further, if and when vortices appear, it is plausible that they will decay faster than anticipated from turbulence experiments, irrespective of quench rates. 相似文献
25.
Syntheses, structures and luminescent properties of new lanthanide-based coordination polymers based on 1,4-benzenedicarboxylate (bdc) 总被引:1,自引:0,他引:1
Yang XP Jones RA Rivers JH Lai RP 《Dalton transactions (Cambridge, England : 2003)》2007,(35):3936-3942
Reaction of 1,4-benzenedicarboxylic acid (1,4-H(2)BDC) with EuCl(3).6H(2)O in MeOH in the presence of Et(3)N and MeCN gives a mixture of the 3-D metal-organic-framework (MOF) materials [Eu(2)(1,4-BDC)(3)(MeOH)(4)].8MeOH () and 2-D [Eu(1,4-BDC)(MeOH)(4)].Cl.MeOH.0.25H(2)O (). Similar reactions afforded the isomorphous Gd () and Tb () analogs of . Reaction of 1,4-H(2)BDC with Ln(NO(3))(3).6H(2)O under similar conditions gave [Ln(BDC)NO(3)(MeOH)(2)].MeCN.H(2)O (Ln = Eu () and Gd ()), which have 2-D framework structures. The structures of were determined by single crystal X-ray crystallographic studies and the luminescence properties of and in DMF solution were determined. 相似文献
26.
Norimasa Nishiyama Yanbin Wang Tetsuo Irifune Takeshi Sanehira Mark L. Rivers Steve R. Sutton David Cookson 《Journal of synchrotron radiation》2009,16(6):742-747
A modified Drickamer anvil apparatus has been developed to combine with monochromatic synchrotron radiation for high‐pressure X‐ray diffraction and radiography in the GSECARS bending‐magnet station, 13‐BM‐D, at the Advanced Photon Source, Argonne, USA. Using this experimental set‐up, deformation experiments can be carried out at pressures in excess of 30 GPa at high temperatures. Differential stresses and total axial strains of polycrystalline platinum and Mg2SiO4 ringwoodite have been measured up to 32 GPa at room temperature using tungsten carbide anvils. The total axial strain of the platinum increases with pressure and reaches about 55% at the highest pressure. A test run using a composite sintered diamond anvil system was performed. The use of X‐ray‐tranparent anvils enables the entire Debye rings to be observed up to 10° 2θ. With high‐energy photons (65–70 keV), this allows a coverage in Q (= 2π sinθ/λ) to about 3 Å?1, thus making it possible to evaluate hydrostatic pressure and differential stress in crystalline minerals using diffraction. This, coupled with the ability to determine axial strain, allows deformation studies to be performed to pressures above 30 GPa. 相似文献
27.
Jon M. Friedrich Mark L. Rivers Michael A. Perlowitz Zachary Meinhart Vanessa V. Ramirez 《Particle & Particle Systems Characterization》2012,29(1):35-42
We show that synchrotron x‐ray microtomography (μCT) followed by digital data extraction can be used to examine the size distribution and particle morphologies of the polydisperse (750 to 2450 μm diameter) particle size standard NIST 1019b. Our size distribution results are within errors of certified values with data collected at 19.5 μm/voxel. One of the advantages of using μCT to investigate the particles examined here is that the morphology of the glass beads can be directly examined. We use the shape metrics aspect ratio and sphericity to examine of individual standard beads morphologies as a function of spherical equivalent diameters. We find that the majority of standard beads possess near‐spherical aspect ratios and sphericities, but deviations are present at the lower end of the size range. The majority (> 98 %) of particles also possess an equant form when examined using a common measure of equidimensionality. Although the NIST 1019b standard consists of loose particles, we point out that an advantage of μCT is that coherent materials comprised of particles can be examined without disaggregation. 相似文献
28.
The Chiral Phase Transition in QCD is studied analytically by looking at truncations of the Schwinger-Dyson equation for the quark self-mass. We find that the usual implementation of the gluon propagator at non-zero temperature is far too simple. When the gluons are given the correct qualitative non-zero temperature behaviour, the calculation of the critical temperature changes significantly. 相似文献
29.
R. J. Rivers F. C. Lombardo F. D. Mazzitelli 《International Journal of Theoretical Physics》2002,41(11):2145-2160
Classical defects (monopoles, vortices, etc.) are a characteristic consequence of many phase transitions of quantum fields. Most likely these include transitions in the early universe and such defects would be expected to be present in the universe today. We continue our analysis of the onset of classical behavior after a second-order phase transition in quantum field theory and show how defects appear after such transitions. 相似文献
30.