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261.
The calculated rate of events in some of the existing solar neutrino detectors is directly proportional to the rate of the
7Be(p, γ)8B reaction measured in the laboratory at low energies. However, the low-energy cross sections of this reaction are quite uncertain
as various measurements differ from each other by 30–40%. The Coulomb dissociation process which reverses the radiative capture
by the dissociation of 8B in the Coulomb field of a target, provides an alternate way of accessing this reaction. While this method has several advantages
(like large breakup cross sections and flexibility in the kinematics), the difficulties arise from the possible interference
by the nuclear interactions, uncertainties in the contributions of the various multipoles and the higher order effects, which
should be considered carefully. We review the progress made so far in the experimental measurements and theoretical analysis
of the breakup of 8B and discuss the current status of the low-energy cross sections (or the astrophysical S-factor) of the 7Be(p, γ)8B reaction extracted therefrom. The future directions of the experimental and theoretical investigations are also suggested.
Work supported by EPSRC, UK, grant nos J/95867 and L/94574. 相似文献
262.
C. Blaas P. Weinberger L. Szunyogh J. Kudrnovský V. Drchal P. M. Levy C. Sommers 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(2):245-250
The functional dependence of the giant magnetoresistance (GMR) with respect to the relative angle between the orientations
of the magnetization in the magnetic slabs of a trilayer system is calculated by using the Kubo-Greenwood formula for electrical
transport together with the fully-relativistic spin-polarized screened Korringa-Kohn-Rostoker method for semi-infinite systems
and the coherent potential approximation. It is found that the functional dependence of the GMR is essentially of the form
.
Received 30 November 1998 相似文献
263.
D. Cassettari A. Chenet R. Folman A. Haase B. Hessmo P. Krüger T. Maier S. Schneider T. Calarco J. Schmiedmayer 《Applied physics. B, Lasers and optics》2000,70(5):721-730
A large variety of trapping and guiding potentials can be designed by bringing cold atoms close to charged or current carrying
material objects. We describe the basic principles of constructing microscopic traps and guides and how to load atoms into
them. The simplicity and versatility of these methods will allow for miniaturization and integration of atom optical elements
into matter-wave quantum circuits on Atom Chips. These could form the basis for robust and widespread applications in atom optics, ranging from fundamental studies in mesoscopic
physics to possibly quantum information systems.
Received: 20 December 1999 / Revised version: 7 March 2000 / Published online: 5 April 2000 相似文献
264.
Symmetric rotating octode field cages do not allow simultaneous particle trapping and electrorotation. Laser-trapped particles
can stably be held in inhomogeneous rotating electric fields. Therefore, in a combination of laser tweezers and field-cage
(electro-optical cage) dielectric single-particle spectroscopy (DSPS) of particles and cells can be carried out at low electric
field strength. The electro-optical cage overcomes the limitation of low enough effective particle conductivity ensuring repelling
dielectrophoretic forces in conventional field cages. At low power, forces in field cages and laser tweezers hardly interfere
and can be used to calibrate each other.
Received: 3 May 1999 / Revised version: 16 August 1999 / Published online: 27 October 1999 相似文献
265.
P. Rosenbusch J.A. Retter B.V. Hall E.A. Hinds F. Lison D. Haubrich D. Meschede 《Applied physics. B, Lasers and optics》2000,70(5):661-663
We have demonstrated that a cobalt single crystal can be used to make a remarkably smooth retro-reflector for cold paramagnetic
atoms. The crystal is cut so that its surface lies in the (0001) plane and the atoms are reflected by the magnetic field above
the surface due to the self-organized pattern of magnetic domains in the material. We find that the reflectivity for suitably
polarized atoms exceeds 90% and may well be unity. We use the angular spread of a reflected atom cloud to measure the roughness
of the mirror. We find that the angular variation of the equivalent hard reflecting surface is (3.1±0.3°)rms for atoms dropped
onto the mirror from a height of 2 cm.
Received: 29 November 1999 / Revised version: 24 February 2000 / Published online: 5 April 2000 相似文献
266.
267.
利用相对论模型势方法计算了Be^+离子和Li原子的波函数、能级和振子强度,进一步得到了基态的电偶极极化率和超极化率,并详细地分析了不同中间态对基态超极化率的贡献.对于Be^+离子,电偶极极化率和超极化率与已有的理论结果符合得非常好.对于Li原子,电偶极极化率与已有的理论结果符合得很好,但是不同理论方法计算给出的超极化率差别非常大,最大的差别超过了一个数量级.通过分析不同中间态对Li原子基态超极化率的贡献,解释了不同理论结果之间有较大差异的原因. 相似文献
268.
269.
The influence of an applied stress on discontinuous precipitation (DP) in a Cu–2.1 wt % Be alloy aged at 300°C was examined. A compressive stress accelerates the growth of DP cells, which consist of lamellae of the precipitated γ phase and the solute-depleted α phase, but a tensile stress does not essentially change it. The cell growth rates along the loading direction under the compressive and tensile stress are identical to those along the direction perpendicular to the loading direction under the same stress. Both the compressive and tensile stresses have no influence on the incubation time to initiate DP. From measurements of the specimen length change and investigations of the distribution of γ variants in cells in a particular case, specific γ variants among crystallographically equivalent ones are found to be formed, depending on the sense of the applied stress. This result, together with the dependence of the cell growth rate on the sense of the applied stress, can be well understood through the interaction energy between the external stress and the misfit strains of discontinuous γ precipitates. 相似文献
270.
《Physics and Chemistry of Liquids》2012,50(3):399-402
Two decades ago, Perrot and March [F. Perrot and N.H. March, Phys. Rev. A. 41, 4521 (1990)] used electron theory to derive an oscillatory pair potential between the beryllium nuclei in liquid metal beryllium. They predict a first minimum at 2.1?Å, followed by a larger repulsive hump at 2.8?Å. Here, we compare and contrast this result for liquid beryllium with the recent ab initio work by Koput and the present quantum Monte Carlo (QMC) calculation on the beryllium dimer in free space. Koput situates the minimum in the potential curve for the free-space dimer at 2.4?Å and it is quite similar in depth to that for liquid metallic beryllium. Our QMC curve is similar, with the minimum at 2.33?Å. They are tabulated in this letter. 相似文献