389 research outputs found
Potential Harmonics Expansion Method for Trapped Interacting Bosons : Inclusion of Two-Body Correlation
We study a system of identical interacting bosons trapped by an external
field by solving ab initio the many-body Schroedinger equation. A complete
solution by using, for example, the traditional hyperspherical harmonics (HH)
basis develops serious problems due to the large degeneracy of HH basis,
symmetrization of the wave function, calculation of the matrix elements, etc.
for large . Instead of the HH basis, here we use the "potential harmonics"
(PH) basis, which is a subset of HH basis. We assume that the contribution to
the orbital and grand orbital [in -dimensional space of the reduced
motion] quantum numbers comes only from the interacting pair. This implies
inclusion of two-body correlations only and disregard of all higher-body
correlations. Such an assumption is ideally suited for the Bose-Einstein
condensate (BEC), which is extremely dilute. Unlike the hyperspherical
variables in HH basis, the PH basis involves only three {\it{active}}
variables. It drastically reduces the number of coupled equations and
calculation of the potential matrix becomes tremendously simplified, as it
involves integrals over only three variables for any . One can easily
incorporate realistic atom-atom interactions in a straight forward manner. We
study the ground and excited state properties of the condensate for both
attractive and repulsive interactions for various particle number.Comment: 36 pages, 7 included figures, plain late
The parity-violating asymmetry in the 3He(n,p)3H reaction
The longitudinal asymmetry induced by parity-violating (PV) components in the
nucleon-nucleon potential is studied in the charge-exchange reaction 3He(n,p)3H
at vanishing incident neutron energies. An expression for the PV observable is
derived in terms of T-matrix elements for transitions from the {2S+1}L_J=1S_0
and 3S_1 states in the incoming n-3He channel to states with J=0 and 1 in the
outgoing p-3H channel. The T-matrix elements involving PV transitions are
obtained in first-order perturbation theory in the hadronic weak-interaction
potential, while those connecting states of the same parity are derived from
solutions of the strong-interaction Hamiltonian with the
hyperspherical-harmonics method. The coupled-channel nature of the scattering
problem is fully accounted for. Results are obtained corresponding to realistic
or chiral two- and three-nucleon strong-interaction potentials in combination
with either the DDH or pionless EFT model for the weak-interaction potential.
The asymmetries, predicted with PV pion and vector-meson coupling constants
corresponding (essentially) to the DDH "best values" set, range from -9.44 to
-2.48 in units of 10^{-8}, depending on the input strong-interaction
Hamiltonian. This large model dependence is a consequence of cancellations
between long-range (pion) and short-range (vector-meson) contributions, and is
of course sensitive to the assumed values for the PV coupling constants.Comment: 19 pages, 15 tables, revtex
Condenser-free contrast methods for transmitted-light microscopy
Phase contrast microscopy allows the study of highly transparent yet detail-rich specimens by producing intensity contrast from phase objects within the sample. Presented here is a generalized phase contrast illumination schema in which condenser optics are entirely abrogated, yielding a condenser- free yet highly effective method of obtaining phase contrast in transmitted-light microscopy. A ring of light emitting diodes (LEDs) is positioned within the light-path such that observation of the objective back focal plane places the il- luminating ring in appropriate conjunction with the phase ring. It is demonstrated that true Zernike phase contrast is obtained, whose geometry can be flexibly manipulated to provide an arbitrary working distance between illuminator and sample. Condenser-free phase contrast is demonstrated across a range of magnifications (4–100×), numerical apertures (0.13–1.65NA) and conventional phase positions. Also demonstrated is condenser-free darkfield microscopy as well as combinatorial contrast including Rheinberg illumination and simultaneous, colour-contrasted, brightfield, darkfield and Zernike phase contrast. By providing enhanced and arbitrary working space above the preparation, a range of concurrent imaging and electrophysiological techniques will be technically facilitated. Condenser-free phase contrast is demonstrated in conjunction with scanning ion conductance microscopy (SICM), using a notched ring to admit the scanned probe. The compact, versatile LED illumination schema will further lend itself to novel next-generation transmitted-light microscopy designs. The condenser-free illumination method, using rings of independent or radially-scanned emitters, may be exploited in future in other electromagnetic wavebands, including X-rays or the infrared
Bandwidth enhancement for parametric amplifiers operated in chirped multi-beam mode
In this paper we discuss the bandwidth enhancement that can be achieved in
multi-Joule optical parametric chirped pulse amplification (OPCPA) systems
exploiting the tunability of parametric amplification. In particular, we
consider a pair of single pass amplifiers based on potassium dideuterium
phosphate (DKDP), pumped by the second harmonic of Nd:glass and tuned to
amplify adjacent regions of the signal spectrum. We demonstrate that a
bandwidth enhancement up to 50% is possible in two configurations; in the first
case, one of the two amplifiers is operated near its non-collinear broadband
limit; to allow for effective recombination and recompression of the outgoing
signals this configuration requires filtering and phase manipulation of the
spectral tail of the amplified pulses. In the second case, effective
recombination can be achieved simply by spectral filtering: in this
configuration, the optimization of the parameters of the amplifiers (pulse,
crystal orientation and crystal length) does not follow the recipes of
non-collinear OPCPA.Comment: 11 pages, 5 figures. To appear in Opt.Com
A comparative evaluation of interest point detectors and local descriptors for visual SLAM
Abstract In this paper we compare the behavior of different interest points detectors and descriptors under the
conditions needed to be used as landmarks in vision-based simultaneous localization and mapping (SLAM).
We evaluate the repeatability of the detectors, as well as the invariance and distinctiveness of the descriptors,
under different perceptual conditions using sequences of images representing planar objects as well as 3D scenes.
We believe that this information will be useful when selecting an appropriat
Proton-He elastic scattering at low energies
We present new accurate measurements of the differential cross section
and the proton analyzing power for proton-He
elastic scattering at various energies. A supersonic gas jet target has been
employed to obtain these low energy cross section measurements. The
distributions have been measured at = 0.99, 1.59,
2.24, 3.11, and 4.02 MeV. Full angular distributions of have been
measured at = 1.60, 2.25, 3.13, and 4.05 MeV. This set of
high-precision data is compared to four-body variational calculations employing
realistic nucleon-nucleon (NN) and three-nucleon (3N) interactions. For the
unpolarized cross section the agreement between the theoretical calculation and
data is good when a potential is used. The comparison between the
calculated and measured proton analyzing powers reveals discrepancies of
approximately 50% at the maximum of each distribution. This is analogous to the
existing `` Puzzle'' known for the past 20 years in nucleon-deuteron
elastic scattering.Comment: 22 pages, 9 figures, to be published in Physical Review C, corrected
reference 4
Experimental verification of the Heisenberg uncertainty principle for hot fullerene molecules
The Heisenberg uncertainty principle for material objects is an essential
corner stone of quantum mechanics and clearly visualizes the wave nature of
matter. Here we report a demonstration of the Heisenberg uncertainty principle
for the most massive, complex and hottest single object so far, the fullerene
molecule C70 at a temperature of 900 K. We find a good quantitative agreement
with the theoretical expectation: dx * dp = h, where dx is the width of the
restricting slit, dp is the momentum transfer required to deflect the fullerene
to the first interference minimum and h is Planck's quantum of action.Comment: 4 pages, 4 figure
Calculation of the Alpha--Particle Ground State within the Hyperspherical Harmonic Basis
The problem of calculating the four--nucleon bound state properties for the
case of realistic two- and three-body nuclear potentials is studied using the
hyperspherical harmonic (HH) approach. A careful analysis of the convergence of
different classes of HH functions has been performed. A restricted basis is
chosen to allow for accurate estimates of the binding energy and other
properties of the 4He ground state. Results for various modern two-nucleon and
two- plus three-nucleon interactions are presented. The 4He asymptotic
normalization constants for separation in 2+2 and 1+3 clusters are also
computed.Comment: 29 pages, 4 figures, 11 tables, revtex
Space-Time Approach to Scattering from Many Body Systems
We present scattering from many body systems in a new light. In place of the
usual van Hove treatment, (applicable to a wide range of scattering processes
using both photons and massive particles) based on plane waves, we calculate
the scattering amplitude as a space-time integral over the scattering sample
for an incident wave characterized by its correlation function which results
from the shaping of the wave field by the apparatus. Instrument resolution
effects - seen as due to the loss of correlation caused by the path differences
in the different arms of the instrument are automatically included and analytic
forms of the resolution function for different instruments are obtained. The
intersection of the moving correlation volumes (those regions where the
correlation functions are significant) associated with the different elements
of the apparatus determines the maximum correlation lengths (times) that can be
observed in a sample, and hence, the momentum (energy) resolution of the
measurement. This geometrical picture of moving correlation volumes derived by
our technique shows how the interaction of the scatterer with the wave field
shaped by the apparatus proceeds in space and time. Matching of the correlation
volumes so as to maximize the intersection region yields a transparent,
graphical method of instrument design. PACS: 03.65.Nk, 3.80 +r, 03.75, 61.12.BComment: Latex document with 6 fig
Algebraic Model for scattering in three-s-cluster systems. I. Theoretical Background
A framework to calculate two-particle matrix elements for fully
antisymmetrized three-cluster configurations is presented. The theory is
developed for a scattering situation described in terms of the Algebraic Model.
This means that the nuclear many-particle state and its asymptotic behaviour
are expanded in terms of oscillator states of the intra-cluster coordinates.
The Generating Function technique is used to optimize the calculation of matrix
elements. In order to derive the dynamical equations, a multichannel version of
the Algebraic Model is presented.Comment: 20 pages, 1 postscript figure, submitted to Phys. Rev.
- …