3,918 research outputs found
Coherence properties and quantum state transportation in an optical conveyor belt
We have prepared and detected quantum coherences with long dephasing times at
the level of single trapped cesium atoms. Controlled transport by an "optical
conveyor belt" over macroscopic distances preserves the atomic coherence with
slight reduction of coherence time. The limiting dephasing effects are
experimentally identified and are of technical rather than fundamental nature.
We present an analytical model of the reversible and irreversible dephasing
mechanisms. Coherent quantum bit operations along with quantum state transport
open the route towards a "quantum shift register" of individual neutral atoms.Comment: 4 pages, 3 figure
Phase transitions and ordering of confined dipolar fluids
We apply a modified mean-field density functional theory to determine the
phase behavior of Stockmayer fluids in slitlike pores formed by two walls with
identical substrate potentials. Based on the Carnahan-Starling equation of
state, a fundamental-measure theory is employed to incorporate the effects of
short-ranged hard sphere - like correlations while the long-ranged
contributions to the fluid interaction potential are treated perturbatively.
The liquid-vapor, ferromagnetic liquid - vapor, and ferromagnetic liquid -
isotropic liquid first-order phase separations are investigated. The local
orientational structure of the anisotropic and inhomogeneous ferromagnetic
liquid phase is also studied. We discuss how the phase diagrams are shifted and
distorted upon varying the pore width.Comment: 15 pages including 8 figure
The Glass Transition and Liquid-Gas Spinodal Boundaries of Metastable Liquids
A liquid can exist under conditions of thermodynamic stability or
metastability within boundaries defined by the liquid-gas spinodal and the
glass transition line. The relationship between these boundaries has been
investigated previously using computer simulations, the energy landscape
formalism, and simplified model calculations. We calculate these stability
boundaries semi-analytically for a model glass forming liquid, employing
accurate liquid state theory and a first-principles approach to the glass
transition. These boundaries intersect at a finite temperature, consistent with
previous simulation-based studies.Comment: Minor text revisions. Fig.s 4, 5 update
Representation of spectral functions and thermodynamics
In this paper we study the question of effective field assignment to measured
or nonperturbatively calculated spectral functions. The straightforward
procedure is to approximate it by a sum of independent Breit-Wigner resonances,
and assign an independent field to each of these resonances. The problem with
this idea is that it introduces new conserved quantities in the free model (the
new particle numbers), therefore it changes the symmetry of the system. We
avoid this inconsistency by representing each quantum channel with a single
effective field, no matter how complicated the spectral function is.
Thermodynamical characterization of the system will be computed with this
representation method, and its relation to the independent resonance
approximation will be discussed.Comment: 15 pages, 9 figures, revtex
EvoBot: Towards a Robot-Chemostat for Culturing and Maintaining Microbial Fuel Cells (MFCs)
In this paper we present EvoBot, a RepRap open-source 3D-printer modified to operate like a robot for culturing and maintaining Microbial Fuel Cells (MFCs). EvoBot is a modular liquid handling robot that has been adapted to host MFCs in its experimental layer, gather data from the MFCs and react on the set thresholds based on a feedback loop. This type of robot-MFC interaction, based on the feedback loop mechanism, will enable us to study further the adaptability and stability of these systems. To date, EvoBot has automated the nurturing process of MFCs with the aim of controlling liquid delivery, which is akin to a chemostat. The chemostat is a well-known microbiology method for culturing bacterial cells under controlled conditions with continuous nutrient supply. EvoBot is perhaps the first pioneering attempt at functionalizing the 3D printing technology by combining it with the chemostat methods. In this paper, we will explore the experiments that EvoBot has carried out so far and how the platform has been optimised over the past two years
An alternative model for the electroweak symmetry breaking sector and its signature in future e-gamma colliders
We perform a preliminary study of the deviations from the Standard Model
prediction for the cross section for the process . We work in the context of a higgsless chiral lagrangian model that
includes an extra vector resonance and an anomalous coupling.
We find that this cross section can provide interesting constraints on the free
parameters of the model once it is measured in future colliders.Comment: LaTex , 14 pages, 5 figures not included but available as postscript
files upon request, NUB-3086/94-T
Direct observation of the formation of polar nanoregions in Pb(MgNb)O using neutron pair distribution function analysis
Using neutron pair distribution function (PDF) analysis over the temperature
range from 1000 K to 15 K, we demonstrate the existence of local polarization
and the formation of medium-range, polar nanoregions (PNRs) with local
rhombohedral order in a prototypical relaxor ferroelectric
Pb(MgNb)O. We estimate the volume fraction of the PNRs as a
function of temperature and show that this fraction steadily increases from 0 %
to a maximum of 30% as the temperature decreases from 650 K to 15 K.
Below T200 K the PNRs start to overlap as their volume fraction reaches
the percolation threshold. We propose that percolating PNRs and their
concomitant overlap play a significant role in the relaxor behavior of
Pb(MgNb)O.Comment: 4 pages, 3 figure
Equation of state of fully ionized electron-ion plasmas
Thermodynamic quantities of Coulomb plasmas consisting of point-like ions
immersed in a compressible, polarizable electron background are calculated for
ion charges Z=1 to 26 and for a wide domain of plasma parameters ranging from
the Debye-Hueckel limit to the crystallization point and from the region of
nondegenerate to fully degenerate nonrelativistic or relativistic electrons.
The calculations are based on the linear-response theory for the electron-ion
interaction, including the local-field corrections in the electronic dielectric
function. The thermodynamic quantities are calculated in the framework of the
N-body hypernetted-chain equations and fitted by analytic expressions. We
present also accurate analytic approximations for the free energy of the ideal
electron gas at arbitrary degeneracy and relativity and for the excess free
energy of the one-component plasma of ions (OCP) derived from Monte Carlo
simulations.
The extension to multi-ionic mixtures is discussed within the framework of
the linear mixing rule. These formulae provide a completely analytic, accurate
description of the thermodynamic quantities of fully ionized electron-ion
Coulomb plasmas, a useful tool for various applications from liquid state
theory to dense stellar matter.Comment: 13 pages, 2 tables, 7 figures, REVTeX using epsf.sty. To be published
in Phys. Rev. E, vol. 58 (1998
The 2-D electron gas at arbitrary spin polarizations and arbitrary coupling strengths: Exchange-correlation energies, distribution functions and spin-polarized phases
We use a recent approach [Phys. Rev. Letters, {\bf 84}, 959 (2000)] for
including Coulomb interactions in quantum systems via a classical mapping of
the pair-distribution functions (PDFs) for a study of the 2-D electron gas. As
in the 3-D case, the ``quantum temperature'' T_q of a classical 2-D Coulomb
fluid which has the same correlation energy as the quantum fluid is determined
as a function of the density parameter r_s. Spin-dependent exchange-correlation
energies are reported. Comparisons of the spin-dependent pair-distributions and
other calculated properties with any available 2-D quantum Monte Carlo (QMC)
results show excellent agreement, strongly favouring more recent QMC data. The
interesting novel physics brought to light by this study are: (a) the
independently determined quantum-temperatures for 3-D and 2-D are found to be
approximately the same, (i.e, universal) function of the classical coupling
constant Gamma. (b) the coupling constant Gamma increases rapidly with r_s in
2-D, making it comparatively more coupled than in 3-D; the stronger coupling in
2-D requires bridge corrections to the hyper- netted-chain method which is
adequate in 3-D; (c) the Helmholtz free energy of spin-polarized and
unpolarized phases have been calculated. The existence of a spin-polarized 2-D
liquid near r_s = 30, is found to be a marginal possibility. These results
pertain to clean uniform 2-D electron systems.Comment: This paper replaces the cond-mat/0109228 submision; the new version
include s more accurate numerical evaluation of the Helmholtz energies of the
para- and ferromagentic 2D fluides at finite temperatures. (Paper accepted
for publication in Phys. Rev. Lett.
- …