25,744 research outputs found
Effect of mass asymmetry on the mass dependence of balance energy
We demonstrate the role of the mass asymmetry on the balance energy (Ebal) by
studying asymmetric reactions throughout the periodic table and over entire
colliding geometry. Our results, which are almost independent of the system
size and as well as of the colliding geometries indicate a sizeable effect of
the asymmetry of the reaction on the balance energy.Comment: Journal of Physics - Conference Series - Online end of March (2011
Probing Pair-Correlated Fermionic Atoms through Correlations in Atom Shot Noise
Pair-correlated fermionic atoms are created through dissociation of weakly
bound molecules near a magnetic-field Feshbach resonance. We show that
correlations between atoms in different spin states can be detected using the
atom shot noise in absorption images. Furthermore, using time-of-Flight imaging
we have observed atom pair correlations in momentum space
Observation of harmonic generation and nonlinear coupling in the collective dynamics of a Bose condensate
We report the observation of harmonic generation and strong nonlinear
coupling of two collective modes of a condensed gas of rubidium atoms. Using a
modified TOP trap we changed the trap anisotropy to a value where the frequency
of the m=0 high-lying mode corresponds to twice the frequency of the m=0
low-lying mode, thus leading to strong nonlinear coupling between these modes.
By changing the anisotropy of the trap and exciting the low-lying mode we
observed significant frequency shifts of this fundamental mode and also the
generation of its second harmonic.Comment: 4 pages,3 figure
An Investigation into the Critical Factors of on-site Waste Segregation in the UK Construction and Demolition Sector.
This paper provides an in-depth exploration into critical factors affecting the use of on-site waste segregation strategies in the UK C&D market. Utilising data from two separate survey questionnaires; this study confirms usage of on-site segregation strategies by many UK contractors where physical site space and project budgets allow. However, through assessment of stakeholder perceptions, this paper also identifies several key barriers that are impeding overall effectiveness. Amongst many factors, this study indicates how issues such as poor attitude and a lack of knowledge of the benefits amongst workers, could be having a profound effect on successful adaptation of ground level recycling initiatives. This research project then finishes by ranking existent barriers by importance, with the goal of suggesting proposals for overcoming these challenges. Ultimately, weighing the critical factors and prospective barriers to on-site segregation in the UK C&D sector, this study makes recommendation of multiple incentives, but suggests that enhanced training initiatives could be a crucial element for instigating long-term industry improvement in respect of recycling and on-site waste segregation strategies
Polarization and decoherence in a two-component Bose-Einstein Condensate
We theoretically investigate polarization properties of a two-component
Bose-Einstein condensate (BEC) and influence of decoherence induced by
environment on BEC polarization through introducing four BEC Stokes operators
which are quantum analog of the classical Stokes parameters for a light field.
BEC polarization states can be geometrically described by a Poincar\'{e} sphere
defined by expectation values of BEC Stokes operators. Without decoherence, it
is shown that nonlinear inter-atomic interactions in the BEC induce periodic
polarization oscillations whose periods depend on the difference between
self-interaction in each component and inter-component interaction strengths.
In particular, when inter-atomic nonlinear self-interaction in each BEC
component equals inter-component nonlinear interaction, Stokes vector
associated with Stokes operators precesses around a fixed axis in the dynamic
evolution of the BEC. The value of the processing frequency is determined by
the strength of the linear coupling between two components of the BEC. When
decoherence is involved, we find each component of the Stokes vector decays
which implies that decoherence depolarizes the BEC.Comment: 10 pages, 2 figure
Quadrupole collective modes in trapped finite-temperature Bose-Einstein condensates
Finite temperature simulations are used to study quadrupole excitations of a
trapped Bose-Einstein condensate. We focus specifically on the m=0 mode, where
a long-standing theoretical problem has been to account for an anomalous
variation of the mode frequency with temperature. We explain this behavior in
terms of the excitation of two separate modes, corresponding to coupled motion
of the condensate and thermal cloud. The relative amplitudes of the modes
depends sensitively on the temperature and on the frequency of the harmonic
drive used to excite them. Good agreement with experiment is found for
appropriate drive frequencies.Comment: 4 pages, 3 figure
The experimental observation of Beliaev damping in a Bose condensed gas
We report the first experimental observation of Beliaev damping of a
collective excitation in a Bose-condensed gas. Beliaev damping is not predicted
by the Gross-Pitaevskii equation and so this is one of the few experiments that
tests BEC theory beyond the mean field approximation. Measurements of the
amplitude of a high frequency scissors mode, show that the Beliaev process
transfers energy to a lower lying mode and then back and forth between these
modes. These characteristics are quite distinct from those of Landau damping,
which leads to a monotonic decrease in amplitude. To enhance the Beliaev
process we adjusted the geometry of the magnetic trapping potential to give a
frequency ratio of 2 to 1 between two of the scissors modes of the condensate.
The ratios of the trap oscillation frequencies and
were changed independently, so that we could investigate
the resonant coupling over a range of conditions.Comment: 4 pages including 5 fig
A Cellular Automata Model with Probability Infection and Spatial Dispersion
In this article, we have proposed an epidemic model by using probability
cellular automata theory. The essential mathematical features are analyzed with
the help of stability theory. We have given an alternative modelling approach
for the spatiotemporal system which is more realistic and satisfactory from the
practical point of view. A discrete and spatiotemporal approach are shown by
using cellular automata theory. It is interesting to note that both size of the
endemic equilibrium and density of the individual increase with the increasing
of the neighborhood size and infection rate, but the infections decrease with
the increasing of the recovery rate. The stability of the system around the
positive interior equilibrium have been shown by using suitable Lyapunov
function. Finally experimental data simulation for SARS disease in China and a
brief discussion conclude the paper
Structural Ordering and Symmetry Breaking in Cd_2Re_2O_7
Single crystal X-ray diffraction measurements have been carried out on
Cd_2Re_2O_7 near and below the phase transition it exhibits at Tc' ~195 K.
Cd_2Re_2O_7 was recently discovered as the first, and to date only,
superconductor with the cubic pyrochlore structure. Superlattice Bragg peaks
show an apparently continuous structural transition at Tc', however the order
parameter displays anomalously slow growth to ~Tc'/10, and resolution limited
critical-like scattering is seen above Tc'. High resolution measurements show
the high temperature cubic Bragg peaks to split on entering the low temperature
phase, indicating a (likely tetragonal) lowering of symmetry below Tc'.Comment: 4 pages, 4 figure
Evaporative Cooling of a Two-Component Degenerate Fermi Gas
We derive a quantum theory of evaporative cooling for a degenerate Fermi gas
with two constituents and show that the optimum cooling trajectory is
influenced significantly by the quantum statistics of the particles. The
cooling efficiency is reduced at low temperatures due to Pauli blocking of
available final states in each binary collision event. We compare the
theoretical optimum trajectory with experimental data on cooling a quantum
degenerate cloud of potassium-40, and show that temperatures as low as 0.3
times the Fermi temperature can now be achieved.Comment: 6 pages, 4 figure
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