10,195 research outputs found
Phase transitions, entanglement and quantum noise interferometry in cold atoms
We show that entanglement monotones can characterize the pronounced
enhancement of entanglement at a quantum phase transition if they are sensitive
to long-range high order correlations. These monotones are found to develop a
sharp peak at the critical point and to exhibit universal scaling. We
demonstrate that similar features are shared by noise correlations and verify
that these experimentally accessible quantities indeed encode entanglement
information and probe separability.Comment: 4 pages 4 figure
Some aspects of analytical chemistry as applied to water quality assurance techniques for reclaimed water: The potential use of X-ray fluorescence spectrometry for automated on-line fast real-time simultaneous multi-component analysis of inorganic pollutants in reclaimed water
The potential use of isotopically excited energy dispersive X-ray fluorescence (XRF) spectrometry for automated on line fast real time (5 to 15 minutes) simultaneous multicomponent (up to 20) trace (1 to 10 parts per billion) analysis of inorganic pollutants in reclaimed water was examined. Three anionic elements (chromium 6, arsenic and selenium) were studied. The inherent lack of sensitivity of XRF spectrometry for these elements mandates use of a preconcentration technique and various methods were examined, including: several direct and indirect evaporation methods; ion exchange membranes; selective and nonselective precipitation; and complexation processes. It is shown tha XRF spectrometry itself is well suited for automated on line quality assurance, and can provide a nondestructive (and thus sample storage and repeat analysis capabilities) and particularly convenient analytical method. Further, the use of an isotopically excited energy dispersive unit (50 mCi Cd-109 source) coupled with a suitable preconcentration process can provide sufficient sensitivity to achieve the current mandated minimum levels of detection without the need for high power X-ray generating tubes
Effects of random localizing events on matter waves: formalism and examples
A formalism is introduced to describe a number of physical processes that may
break down the coherence of a matter wave over a characteristic length scale l.
In a second-quantized description, an appropriate master equation for a set of
bosonic "modes" (such as atoms in a lattice, in a tight-binding approximation)
is derived. Two kinds of "localizing processes" are discussed in some detail
and shown to lead to master equations of this general form: spontaneous
emission (more precisely, light scattering), and modulation by external random
potentials. Some of the dynamical consequences of these processes are
considered: in particular, it is shown that they generically lead to a damping
of the motion of the matter-wave currents, and may also cause a "flattening" of
the density distribution of a trapped condensate at rest.Comment: v3; a few corrections, especially in Sections IV and
Stimuli-responsive behavior of PNiPAm microgels under interfacial confinement
The volume phase transition of microgels is one of the most paradigmatic
examples of stimuli-responsiveness, enabling a collapse from a highly swollen
microgel state into a densely coiled state by an external stimulus. Although
well characterized in bulk, it remains unclear how the phase transition is
affected by the presence of a confining interface. Here, we demonstrate that
the temperature-induced volume phase transition of poly(N-isopropylacrylamide)
microgels, conventionally considered an intrinsic molecular property of the
polymer, is in fact largely suppressed when the microgel is adsorbed to an
air/liquid interface. We further observe a hysteresis in core morphology and
interfacial pressure between heating and cooling cycles. Our results, supported
by molecular dynamics simulations, reveal that the dangling polymer chains of
microgel particles, spread at the interface under the influence of surface
tension, do not undergo any volume phase transition, demonstrating that the
balance in free energy responsible for the volume phase transition is
fundamentally altered by interfacial confinement. These results imply that
important technological properties of such systems, including the
temperature-induced destabilization of emulsions does not occur via a decrease
in interfacial coverage of the microgels
Thermodynamics of quantum degenerate gases in optical lattices
The entropy-temperature curves are calculated for non-interacting Bose and
Fermi gases in a 3D optical lattice. These curves facilitate understanding of
how adiabatic changes in the lattice depth affect the temperature, and we
demonstrate regimes where the atomic sample can be significantly heated or
cooled by the loading process. We assess the effects of interactions on a Bose
gas in a deep optical lattice, and show that interactions ultimately limit the
extent of cooling that can occur during lattice loading.Comment: 6 pages, 4 figures. Submitted to proceedings of Laser Physics 2006
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Diffusion of hydrogen interstitials in the near-surface region of Pd(111) under the influence of surface coverage and external static electric fields
Past scanning tunneling microscopy (STM) experiments of H manipulation on
Pd(111), at low temperature, have shown that it is possible to induce
diffusion of surface species as well as of those deeply buried under the
surface. Several questions remain open regarding the role of subsurface site
occupancies. In the present work, the interaction potential of H atoms with
Pd(111) under various H coverage conditions is determined by means of density
functional theory calculations in order to provide an answer to two of these
questions: (i) whether subsurface sites are the final locations for the H
impurities that attempt to emerge from bulk regions, and (ii) whether
penetration of the surface is a competing route of on-surface diffusion during
depletion of surface H on densely covered Pd(111). We find that a high H
coverage has the effect of blocking resurfacing of H atoms travelling from
below, which would otherwise reach the surface fcc sites, but it hardly alters
deeper diffusion energy barriers. Penetration is unlikely and restricted to
high occupancies of hcp hollows. In agreement with experiments, the Pd lattice
expands vertically as a consequence of H atoms being blocked at subsurface
sites, and surface H enhances this expansion. STM tip effects are included in
the calculations self-consistently as an external static electric field. The
main contribution to the induced surface electric dipoles originates from the
Pd substrate polarisability. We find that the electric field has a non-
negligible effect on the H-Pd potential in the vicinity of the topmost Pd
atomic layer, yet typical STM intensities of 1-2âVĂ
â1 are insufficient to
invert the stabilities of the surface and subsurface equilibrium sites
Improving the family orientation process in Cuban Special Schools trough Nearest Prototype classification
Cuban Schools for children with Affective â Behavioral Maladies (SABM) have as goal to accomplish a major change in children behavior, to insert them effectively into society. One of the key elements in this objective is to give an adequate orientation to the childrenâs families; due to the family is one of the most important educational contexts in which the children will develop their personality. The family orientation process in SABM involves clustering and classification of mixed type data with non-symmetric similarity functions. To improve this process, this paper includes some novel characteristics in clustering and prototype selection. The proposed approach uses a hierarchical clustering based on compact sets, making it suitable for dealing with non-symmetric similarity functions, as well as with mixed and incomplete data. The proposal obtains very good results on the SABM data, and over repository databases
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