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991.
P. Cren C.F. Roos A. Aclan J. Dalibard D. Guéry-Odelin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(1):107-116
We demonstrate experimentally the continuous and pulsed loading of a slow and cold atomic beam into a magnetic guide. The
slow beam is produced using a vapor loaded laser trap, which ensures two-dimensional magneto-optical trapping, as well as
cooling by a moving molasses along the third direction. It provides a continuous flux larger than 109 atoms/s with an adjustable mean velocity ranging from 0.3 to 3 m/s, and with longitudinal and transverse temperatures smaller
than 100 μK. Up to 3×108 atoms/s are injected into the magnetic guide and subsequently guided over a distance of 40 cm.
Received 19 February 2002 Published online 28 June 2002 相似文献
992.
993.
J. R. Schroeder B. Hammouda R. A. Bubeck J. W. Chang 《Journal of Polymer Science.Polymer Physics》1991,29(13):1607-1612
Small-angle neutron scattering (SANS) has been used to investigate macromolecular orientation of uniaxially hot-stretched partially deuterated polystyrene. Principle radii of gyration and degree of eccentricity were measured over a range of hot-stretch temperatures, strain rates, and external draw ratios (EDR). Results show affine deformation for EDR <4 and an increase in the degree of local molecular orientation with increasing rate of strain and decreasing stretching temperature. It also is found that although the macromolecules follow the external stretching affinely on average, they do not deform uniformly. 相似文献
994.
The postulates of the double core model of binary fission are examined against the two well-known charge division mechanisms
of fission, namelyucd andecd. An analytic expression of the modifieducd formula is obtained. Radiochemical distribution of mass and charge, formulated from the model, is found to agree satisfactorily
with available experimental results. Finally, the most probable charge and mass values of the radiochemical heavy and light
products, the average number of neutron andβ-emissions per fragment, are calculated, and found to agree with experimental observations. 相似文献
995.
Barry J. Bauer 《Journal of polymer science. Part A, Polymer chemistry》2004,42(17):3070-3080
A practical method of calculating the small-angle scattering intensity and the density correlation function from the phase size distribution is presented for a sample with a random two-phase morphology. The correlation function can be calculated in terms of joint probability distribution functions of the phase size distributions of the two individual phases with information from the chord length distribution. The phase size distribution is approximated as a weighted sum of exponentials, which is then transformed analytically into the correlation function and hence the small-angle scattering for any combination of phase size distributions of the two phases. This represents an extension of the Debye method for materials with more complex phase size distributions. The inverse problem of calculating the phase size distributions from the small-angle scattering requires a thermodynamic model or simplifying approximation. An example of the reverse transformation is given for a nanoporous polymer thin film. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3070–3080, 2004 相似文献
996.
997.
We present a calculation of the neutrino-nucleon scattering cross-section which takes into account the nuclear correlations
in the relativistic random phase approximation (RPA). Our approach is based on a quantum-hadrodynamics model with exchange
of σ, ω, π, ρ and δ mesons. In view of applications to neutrino transport in the final stages of supernova explosion and proto-neutron
star cooling, we study the evolution of the neutrino mean free path as a function of density, proton-neutron asymmetry and
temperature. Special attention was paid to the issues of renormalization of the Dirac sea, residual interactions in the tensor
channel, coupling to the delta-meson and meson mixing. In contrast with the results of other authors, we find that the neutral-current
process is not sensitive to the strength g' of the residual contact interaction. As a consequence, it is found that RPA corrections with respect to the mean-field approximation
amount to only 10% to 15% at high density.
Received: 27 June 2001 / Accepted: 14 January 2002 相似文献
998.
Taleyarkhan等人是否测到了热核中子 总被引:1,自引:0,他引:1
对声致发光这一尚不清楚的非平衡态复杂过程,以平衡态近似作为上限,通过对Taleyarkhan等人实验数据的分析和氘氘聚变反应的反应率的计算,指出Taleyarkhan等人实验中测得的中子不是热核中子,今后实验中如能测到大于-10^8n/s的有效中子产生率才能显示“气泡核聚变”的反应温度达到了10^6-10^7K。 相似文献
999.
With scattering methods we are able to detect the elementary diffusion jump. This is a report on investigations with methods
working in the time domain, i.e., nuclear resonant scattering of synchrotron radiation and neutron spin echo. The accent of
this paper is on diffusion in ordered alloys. We finish with an outlook on what will be possible with the upcoming potential
of future synchrotron sources.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
1000.
Using Lexan polycarbonate plastic as the fission fragment track detectors, the fragment angular distributions have been measured
in the cases of fission of232Th and238U induced by alpha particles of various energies ranging from 40 to 70MeV obtained from the 88″ variable energy cyclotron
at Calcutta. The center-of-mass angular distributions have been calculated and fitted by a series of Legendre polynomials.
TheW(10°)/W(90°) ratios (defined as anisotropy) were measured at several energies for both the targets. These data are utilized in calculation
of the energy dependence ofK
0
2
, the standard deviation of the distribution in the angular momentum projection on the nuclear symmetry axis at the saddle
point. Values of Γ
f
/Γ
η
, i.e. the ratio of the fission width to neutron emission width have been determined for232Th and238U nuclei. The integral cross-section for alpha induced fission in each target was determined by numerical integration of the
respective center-of-mass angular differential cross-sections. The results were compared with similar data available in the
literature which served to resolve some of the discrepancies observed in earlier measurements. The results were also compared
with theoretical cross-sections. 相似文献