128,908 research outputs found
Inferring bulk self-assembly properties from simulations of small systems with multiple constituent species and small systems in the grand canonical ensemble
In this paper we generalize a methodology [T. E. Ouldridge, A. A. Louis, and
J. P. K. Doye, J. Phys.: Condens. Matter {\bf 22}, 104102 (2010)] for dealing
with the inference of bulk properties from small simulations of self-assembling
systems of characteristic finite size. In particular, schemes for extrapolating
the results of simulations of a single self-assembling object to the bulk limit
are established in three cases: for assembly involving multiple particle
species, for systems with one species localized in space and for simulations in
the grand canonical ensemble. Furthermore, methodologies are introduced for
evaluating the accuracy of these extrapolations. Example systems demonstrate
that differences in cluster concentrations between simulations of a single
self-assembling structure and bulk studies of the same model under identical
conditions can be large, and that convergence on bulk results as system size is
increased can be slow and non-trivial.Comment: Accepted by J. Chem. Phy
Limits of sympathetic cooling of fermions: The role of the heat capacity of the coolant
The sympathetic cooling of an initially degenerate Fermi gas by either an
ideal Bose gas below or an ideal Boltzmann gas is investigated. It is
shown that the efficiency of cooling by a Bose gas below is by no means
reduced when its heat capacity becomes much less than that of the Fermi gas,
where efficiency is measured by the decrease in the temperature of the Fermi
gas per number of particles evaporated from the coolant. This contradicts the
intuitive idea that an efficient coolant must have a large heat capacity. In
contrast, for a Boltzmann gas a minimal value of the ratio of the heat
capacities is indeed necessary to achieve T=0 and all of the particles must be
evaporated.Comment: 5 pages, 3 figure
Crossover from one to three dimensions for a gas of hard-core bosons
We develop a variational theory of the crossover from the one-dimensional
(1D) regime to the 3D regime for ultra-cold Bose gases in thin waveguides.
Within the 1D regime we map out the parameter space for fermionization, which
may span the full 1D regime for suitable transverse confinement.Comment: 4 pages, 2 figure
Structure and energetics of helium adsorption on nanosurfaces
The ground and excited state properties of small helium clusters, 4He_N,
containing nanoscale (~3-10 Angstroms) planar aromatic molecules have been
studied with quantum Monte Carlo methods. Ground state structures and energies
are obtained from importance-sampled, rigid-body diffusion Monte Carlo. Excited
state energies due to helium vibrational motion are evaluated using the
projection operator, imaginary time spectral evolution technique. We examine
the adsorption of N helium atoms (N less than or equal to 24) on a series of
planar aromatic molecules (benzene, naphthalene, anthracene, tetracene,
phthalocyanine). The first layer of helium atoms is well-localized on the
molecule surface, and we find well-defined localized excitations due to
in-plane vibrational motion of helium on the molecule surface. We discuss the
implications of these confined excitations for the molecule spectroscopy.Comment: 6 pages, 2 figures, QFS 2003 Symposium, submitted to J. Low Temp.
Phy
Magneto-controlled nonlinear optical materials
We exploit theoretically a magneto-controlled nonlinear optical material
which contains ferromagnetic nanoparticles with a non-magnetic metallic
nonlinear shell in a host fluid. Such an optical material can have anisotropic
linear and nonlinear optical properties and a giant enhancement of
nonlinearity, as well as an attractive figure of merit.Comment: 11 pages, 2 figures. To be published in Appl. Phys. Let
Structure and spectroscopy of doped helium clusters using quantum Monte Carlo techniques
We present a comparative study of the rotational characteristics of various
molecule-doped 4He clusters using quantum Monte Carlo techniques. The
theoretical conclusions obtained from both zero and finite temperature Monte
Carlo studies confirm the presence of two different dynamical regimes that
correlate with the magnitude of the rotational constant of the molecule, i.e.,
fast or slow rotors. For a slow rotor, the effective rotational constant for
the molecule inside the helium droplet can be determined by a microscopic
two-fluid model in which helium densities computed by path integral Monte Carlo
are used as input, as well as by direct computation of excited energy levels.
For a faster rotor, the conditions for application of the two-fluid model for
dynamical analysis are usually not fulfilled and the direct determination of
excitation energies is then mandatory. Quantitative studies for three molecules
are summarized, showing in each case excellent agreement with experimental
results
Nuclear condensation and the equation of state of nuclear matter
The isothermal compression of a dilute nucleonic gas invoking cluster degrees
of freedom is studied in an equilibrium statistical model; this clusterized
system is found to be more stable than the pure nucleonic system. The equation
of state (EoS) of this matter shows features qualitatively very similar to the
one obtained from pure nucleonic gas. In the isothermal compression process,
there is a sudden enhancement of clusterization at a transition density
rendering features analogous to the gas-liquid phase transition in normal
dilute nucleonic matter. Different observables like the caloric curves, heat
capacity, isospin distillation, etc. are studied in both the models. Possible
changes in the observables due to recently indicated medium modifications in
the symmetry energy are also investigated.Comment: 18 pages and 11 figures. Phys. Rev. C (in press
Noninteracting Fermions in infinite dimensions
Usually, we study the statistical behaviours of noninteracting Fermions in
finite (mainly two and three) dimensions. For a fixed number of fermions, the
average energy per fermion is calculated in two and in three dimensions and it
becomes equal to 50 and 60 per cent of the fermi energy respectively. However,
in the higher dimensions this percentage increases as the dimensionality
increases and in infinite dimensions it becomes 100 per cent. This is an
intersting result, at least pedagogically. Which implies all fermions are
moving with Fermi momentum. This result is not yet discussed in standard text
books of quantum statistics. In this paper, this fact is discussed and
explained. I hope, this article will be helpful for graduate students to study
the behaviours of free fermions in generalised dimensionality.Comment: To appear in European Journal of Physics (2010
Finite Temperature Phase Diagram in Rotating Bosonic Optical Lattice
Finite temperature phase boundary between superfluid phase and normal state
is analytically derived by studying the stability of normal state in rotating
bosonic optical lattice. We also prove that the oscillation behavior of
critical hopping matrix directly follows the upper boundary of Hofstadter
butterfly as the function of effective magnetic field.Comment: 10 pages, 2 figure
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