3,417 research outputs found
Gas purged dry box glove Patent
Gas purged dry box glove reducing permeation of air or moisture into dry box or isolator by diffusion through glov
Double gloves reduce contamination of dry box atmosphere
Pair of encased low permeability hand gloves between which an inert gas circulates reduces dry box contamination. This innovation is applicable to dry boxes using radioactive and alkali metal compounds, submicron powders, and liquid metals
Colour reverse learning and animal personalities: the advantage of behavioural diversity assessed with agent-based simulations
Foraging bees use colour cues to help identify rewarding from unrewarding flowers, but as conditions change, bees may require behavioural flexibility to reverse their learnt preferences. Perceptually similar colours are learnt slowly by honeybees and thus potentially pose a difficult task to reverse-learn. Free-flying honeybees (N = 32) were trained to learn a fine colour discrimination task that could be resolved at ca. 70% accuracy following extended differential conditioning, and were then tested for their ability to reverse-learn this visual problem multiple times. Subsequent analyses identified three different strategies: ‘Deliberative-decisive’ bees that could, after several flower visits, decisively make a large change to learnt preferences; ‘Fickle- circumspect’ bees that changed their preferences by a small amount every time they encountered evidence in their environment; and ‘Stay’ bees that did not change from their initially learnt preference. The next aim was to determine if there was any advantage to a colony in maintaining bees with a variety of decision-making strategies. To understand the potential benefits of the observed behavioural diversity agent-based computer simulations were conducted by systematically varying parameters for flower reward switch oscillation frequency, flower handling time, and fraction of defective ‘target’ stimuli. These simulations revealed that when there is a relatively high frequency of reward reversals, fickle-circumspect bees are more efficient at nectar collection. However, as the reward reversal frequency decreases the performance of deliberative-decisive bees becomes most efficient. These findings show there to be an evolutionary benefit for honeybee colonies with individuals exhibiting these different strategies for managing resource change. The strategies have similarities to some complex decision-making processes observed in humans, and algorithms implemented in artificial intelligence systems
Shell structure in neutron-rich Ca and Ni nuclei under semi-realistic mean fields
Shell structure in the neutron-rich Ca and Ni nuclei is investigated by the
spherical Hartree-Fock calculations with the semi-realistic interactions.
Specific ingredients of the effective interaction, particularly the tensor
force, often play a key role in the dependence of the neutron shell
structure. Such examples are found in N=32 and N=40; N=32 becomes magic or
submagic in Ca while its magicity is broken in Ni, and N=40 is
submagic (though not magic) in Ni but not in Ca. Comments are
given on the doubly magic nature of Ni. We point out that the loose
binding can lead to a submagic number N=58 in Ni, assisted by the weak
pair coupling.Comment: 14 pages including 5 figures, to appear in Physical Review C (Rapid
Communication
Hamiltonian approach to QCD in Coulomb gauge - a survey of recent results
I report on recent results obtained within the Hamiltonian approach to QCD in
Coulomb gauge. Furthermore this approach is compared to recent lattice data,
which were obtained by an alternative gauge fixing method and which show an
improved agreement with the continuum results. By relating the Gribov
confinement scenario to the center vortex picture of confinement it is shown
that the Coulomb string tension is tied to the spatial string tension. For the
quark sector a vacuum wave functional is used which explicitly contains the
coupling of the quarks to the transverse gluons and which results in
variational equations which are free of ultraviolet divergences. The
variational approach is extended to finite temperatures by compactifying a
spatial dimension. The effective potential of the Polyakov loop is evaluated
from the zero-temperature variational solution. For pure Yang--Mills theory,
the deconfinement phase transition is found to be second order for SU(2) and
first order for SU(3), in agreement with the lattice results. The corresponding
critical temperatures are found to be and , respectively. When quarks are included, the deconfinement
transition turns into a cross-over. From the dual and chiral quark condensate
one finds pseudo-critical temperatures of and , respectively, for the deconfinement and chiral transition.Comment: Talk given by H. Reinhardt at "5th Winter Workshop on
Non-Perturbative Quantum Field Theory", 22-24 March 2017, Sophia-Antipolis,
France. arXiv admin note: text overlap with arXiv:1609.09370,
arXiv:1510.03286, arXiv:1607.0814
Self-Consistent Pushing and Cranking Corrections to the Meson Fields of the Chiral Quark-Loop Soliton
We study translational and spin-isospin symmetry restoration for the
two-flavor chiral quark-loop soliton. Instead of a static soliton at rest we
consider a boosted and rotating hedgehog soliton. Corrected classical meson
fields are obtained by minimizing a corrected energy functional which has been
derived by semi-classical methods ('variation after projection'). We evaluate
corrected meson fields in the region 300 MeV \le M \le 600 MeV of constituent
quark masses M and compare them with the uncorrected fields. We study the
effect of the corrections on various expectation values of nuclear observables
such as the root-mean square radius, the axial-vector coupling constant,
magnetic moments and the delta-nucleon mass splitting.Comment: 19 pages, LaTeX, 7 postscript figures included using 'psfig.sty', to
appear in Int.J.Mod.Phys.
Energy evolution in time-dependent harmonic oscillator
The theory of adiabatic invariants has a long history, and very important
implications and applications in many different branches of physics,
classically and quantally, but is rarely founded on rigorous results. Here we
treat the general time-dependent one-dimensional harmonic oscillator, whose
Newton equation cannot be solved in general. We
follow the time-evolution of an initial ensemble of phase points with sharply
defined energy at time and calculate rigorously the distribution of
energy after time , which is fully (all moments, including the
variance ) determined by the first moment . For example,
, and all
higher even moments are powers of , whilst the odd ones vanish
identically. This distribution function does not depend on any further details
of the function and is in this sense universal. In ideal
adiabaticity , and the variance is
zero, whilst for finite we calculate , and for the
general case using exact WKB-theory to all orders. We prove that if is of class (all derivatives up to and including the order
are continuous) , whilst for class it is known to be exponential .Comment: 26 pages, 5 figure
Multiconfigurational Hartree-Fock theory for identical bosons in a double well
Multiconfigurational Hartree-Fock theory is presented and implemented in an
investigation of the fragmentation of a Bose-Einstein condensate made of
identical bosonic atoms in a double well potential at zero temperature. The
approach builds in the effects of the condensate mean field and of atomic
correlations by describing generalized many-body states that are composed of
multiple configurations which incorporate atomic interactions. Nonlinear and
linear optimization is utilized in conjunction with the variational and
Hylleraas-Undheim theorems to find the optimal ground and excited states of the
interacting system. The resulting energy spectrum and associated eigenstates
are presented as a function of double well barrier height. Delocalized and
localized single configurational states are found in the extreme limits of the
simple and fragmented condensate ground states, while multiconfigurational
states and macroscopic quantum superposition states are revealed throughout the
full extent of barrier heights. Comparison is made to existing theories that
either neglect mean field or correlation effects and it is found that
contributions from both interactions are essential in order to obtain a robust
microscopic understanding of the condensate's atomic structure throughout the
fragmentation process.Comment: 21 pages, 13 figure
Quantum Dynamics of Solitons in Strongly Interacting Systems on Optical Lattices
Mean-field dynamics of strongly interacting bosons described by hard core
bosons with nearest-neighbor attraction has been shown to support two species
of solitons: one of Gross-Pitaevskii (GP-type) where the condensate fraction
remains dark and a novel non-Gross-Pitaevskii-type (non-GP-type) characterized
by brightening of the condensate fraction. Here we study the effects of quantum
fluctuations on these solitons using the adaptive time-dependent density matrix
renormalization group method, which takes into account the effect of strong
correlations. We use local observables as the density, condensate density and
correlation functions as well as the entanglement entropy to characterize the
stability of the initial states. We find both species of solitons to be stable
under quantum evolution for a finite duration, their tolerance to quantum
fluctuations being enhanced as the width of the soliton increases. We describe
possible experimental realizations in atomic Bose Einstein Condensates,
polarized degenerate Fermi gases, and in systems of polar molecules on optical
lattices
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