1,792 research outputs found
Relativistic continuum-continuum coupling in the dissociation of halo nuclei
A relativistic coupled-channels theory for the calculation of dissociation
cross sections of halo nuclei is developed. A comparison with non-relativistic
models is done for the dissociation of B projectiles. It is shown that
neglecting relativistic effects leads to seizable inaccuracies in the
extraction of the astrophysical S-factor for the proton+beryllium radiative
capture reaction.Comment: 4 pages, 2 figures, version accepted for publication at Physics
Review Letter
Determination of S17 from 8B breakup by means of the method of continuum-discretized coupled-channels
The astrophysical factor for 7Be(p,\gamma)8B at zero energy, S17(0), is
determined from an analysis of 208Pb(8B, p+7Be)208Pb at 52 MeV/nucleon by means
of the method of continuum-discretized coupled-channels (CDCC) taking account
of all nuclear and Coulomb breakup processes. The asymptotic normalization
coefficient (ANC) method is used to extract S17(0) from the calculated
breakup-cross-section. The main result of the present paper is S17(0)=20.9
+2.0/-1.9 eV b. The error consists of 8.4% experimental systematic error and
the error due to the ambiguity in the s-wave p-7Be scattering length. This
value of S17(0) differs from the one extracted with the first-order
perturbation theory including Coulomb breakup by dipole transitions: 18.9 +/-
1.8 eV b. It turns out that the difference is due to the inclusion of the
nuclear and Coulomb-quadrupole transitions and multi-step processes of
all-order in the present work. The p-7Be interaction potential used in the CDCC
calculation is also used in the ANC analysis of 7Be(p,\gamma)8B. The value of
S17(0)=21.7 +0.62/-0.55 eV b obtained is consistent with the previous one
obtained from a precise measurement of the p-capture reaction cross section
extrapolated to zero incident energy, S17(0)=22.1 +/- 0.6 (expt) +/- 0.6 (theo)
eV b, where (theo) stands for the error in the extrapolation. Thus, the
agreement between the values of S17(0) obtained from direct 7Be(p,\gamma)8B and
indirect 8B-breakup measurements is significantly improved.Comment: 13 pages, 9 figures, published in PR
Light hypernuclei in four-body cluster models
Detailed structure calculations in Be, H,
Li, H and Li are performed
within the framework of the microscopic two-, three- and four-body cluster
models using the Gaussian Expansion Method.Comment: 14 pages, 19 figures. To be published in Phys. Rev.
Spin-Orbit Assisted Variable-Range Hopping in Strong Magnetic Fields
It is shown that in the presence of strong magnetic fields, spin-orbit
scattering causes a sharp increase in the effective density of states in the
variable-range hopping regime when temperature decreases. This effect leads to
an exponential enhancement of the conductance above its value without
spin-orbit scattering. Thus an experimental study of the hopping conductivity
in a fixed, large magnetic field, is a sensitive tool to explore the spin-orbit
scattering parameters in the strongly localized regime.Comment: 9 pages + 2 figures (enclosed), Revte
Quantum limits of super-resolution in reconstruction of optical objects
We investigate analytically and numerically the role of quantum fluctuations
in reconstruction of optical objects from diffraction-limited images. Taking as
example of an input object two closely spaced Gaussian peaks we demonstrate
that one can improve the resolution in the reconstructed object over the
classical Rayleigh limit. We show that the ultimate quantum limit of resolution
in such reconstruction procedure is determined not by diffraction but by the
signal-to-noise ratio in the input object. We formulate a quantitative measure
of super-resolution in terms of the optical point-spread function of the
system.Comment: 23 pages, 7 figures. Submitted to Physical Review A e-mail:
[email protected]
Evidence of ratchet effect in nanowires of a conducting polymer
Ratchet effect, observed in many systems starting from living organism to
artificially designed device, is a manifestation of motion in asymmetric
potential. Here we report results of a conductivity study of Polypyrrole
nanowires, which have been prepared by a simple method to generate a variation
of doping concentration along the length. This variation gives rise to an
asymmetric potential profile that hinders the symmetry of the hopping process
of charges and hence the value of measured resistance of these nanowires become
sensitive to the direction of current flow. The asymmetry in resistance was
found to increase with decreasing nanowire diameter and increasing temperature.
The observed phenomena could be explained with the assumption that the spatial
extension of localized state involved in hopping process reduces as the doping
concentration reduces along the length of the nanowires.Comment: Revtex, two column, 4 pages, 10 figure
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