1,538 research outputs found
Palatability of forage plants in North-west sheep pastures
A DECLINE in carrying capacity has occurred in large areas of the Pilbara district of the North-West, due to the decrease in palatable plants and the increase in unpalatable ones.
The relative palatability of the various species to sheep is therefore a matter of considerable importance to pastoralists
A non-Markovian quantum trajectory approach to radiation into structured continuum
We present a non-Markovian quantum trajectory method for treating atoms
radiating into a reservoir with a non-flat density of states. The results of an
example numerical simulation of the case where the free space modes of the
reservoir are altered by the presence of a cavity are presented and compared
with those of an extended system approach
Deriving Telescope Mueller Matrices Using Daytime Sky Polarization Observations
Telescopes often modify the input polarization of a source so that the
measured circular or linear output state of the optical signal can be
signficantly different from the input. This mixing, or polarization
"cross-talk", is defined by the optical system Mueller matrix. We describe here
an efficient method for recovering the input polarization state of the light
and the full 4 x 4 Mueller matrix of the telescope with an accuracy of a few
percent without external masks or telescope hardware modification. Observations
of the bright, highly polarized daytime sky using the Haleakala 3.7m AEOS
telescope and a coude spectropolarimeter demonstrate the technique.Comment: Accepted for publication in PAS
Glycerol monooleate/solvents systems for progesterone transdermal delivery: In vitro permeation and microscopic studies
A liberação transdérmica de muitos fármacos é dificultada pelas características de barreira do estrato córneo. Promotores químicos de absorção cutânea são capazes de interagir com os constituintes do estrato córneo, induzindo aumento temporário e reversível na permeabilidade da pele. O objetivo deste trabalho foi avaliar a influência de sistemas monoleína (monoleato de glicerol)/solventes na absorção percutânea de um fármaco lipofílico (a progesterona), através do estrato córneo de camundongos sem pelo, bem como o efeito da monoleína nas características estruturais do estrato córneo, por meio de microscopia eletrônica de varredura (SEM) e microscopia de varredura confocal a laser (CLSM). As alterações morfológicas observadas no estrato córneo de camundongos sem pelo sugerem efeito da monoleína na barreira da pele. E, ainda, o aumento no fluxo In vitro da progesterona, bem como na penetração in vivo do marcador fluorescente (fluoresceína), apontam a monoleína como potencial promotor de absorção cutânea. Os resultados obtidos mostraram que os sistemas monoleína/solventes provocaram alterações na estrutura do estrato córneo, que poderiam causar o aumento da permeação da progesterona através da pele de camundongos sem pelo, otimizando, deste modo, a liberação transdérmica deste fármaco.Transdermal delivery of most drugs is precluded by the barrier characteristics of the stratum corneum (SC). Chemical penetration enhancers are capable of interacting with SC constituents, inducing a temporary reversible increase in the skin permeability. The aim of this work was to assess the influence of glycerol monooleate (GMO)/solvents systems on percutaneous absorption across hairless mouse SC of a lipophilic drug, progesterone (PG), as well as its effect on the SC structural characteristics, by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). The morphological changes observed in the hairless mouse SC suggest a GMO effect on the skin barrier. In addition, the increase in the In vitro PG flux and in vivo penetration of a fluorescent label point towards GMO as a potential absorption enhancer. The results obtained showed that GMO/solvents systems provoked changes in the SC that could be causing increased permeation of PG across hairless mouse skin, optimising in this way the transdermal delivery of this drug
Resonance fluorescence spectrum in a weak squeezed field with an arbitrary bandwidth
We analyze the linewidth narrowing in the fluorescence spectrum of a two-level atom driven by a squeezed vacuum field of a finite bandwidth. It is found that the fluorescence spectrum in a low-intensity squeezed field can exhibit a (omega - omega(0))(-6) frequency dependence in the wings. We show that this fast fall-off behavior is intimately related to the properties of a narrow-bandwidth squeezed field and does not extend into the region of broadband excitation. We apply the Linear response model and find that the narrowing results from a convolution of the atom response with the spectrum of the incident field. On the experimental side, we emphasize that the linewidth narrowing is not sensitive to the solid angle of the squeezed modes coupled to the atom. We also compare the fluorescence spectrum with the quadrature-noise spectrum and find that the fluorescence spectrum for an off-resonance excitation does not reveal the noise spectrum. We show that this difference arises from the competing three-photon scattering processes. [S1050-2947(98)04308-X]
Adaptive single-shot phase measurements: The full quantum theory
The phase of a single-mode field can be measured in a single-shot measurement
by interfering the field with an effectively classical local oscillator of
known phase. The standard technique is to have the local oscillator detuned
from the system (heterodyne detection) so that it is sometimes in phase and
sometimes in quadrature with the system over the course of the measurement.
This enables both quadratures of the system to be measured, from which the
phase can be estimated. One of us [H.M. Wiseman, Phys. Rev. Lett. 75, 4587
(1995)] has shown recently that it is possible to make a much better estimate
of the phase by using an adaptive technique in which a resonant local
oscillator has its phase adjusted by a feedback loop during the single-shot
measurement. In Ref.~[H.M. Wiseman and R.B. Killip, Phys. Rev. A 56, 944] we
presented a semiclassical analysis of a particular adaptive scheme, which
yielded asymptotic results for the phase variance of strong fields. In this
paper we present an exact quantum mechanical treatment. This is necessary for
calculating the phase variance for fields with small photon numbers, and also
for considering figures of merit other than the phase variance. Our results
show that an adaptive scheme is always superior to heterodyne detection as far
as the variance is concerned. However the tails of the probability distribution
are surprisingly high for this adaptive measurement, so that it does not always
result in a smaller probability of error in phase-based optical communication.Comment: 17 pages, LaTeX, 8 figures (concatenated), Submitted to Phys. Rev.
Decoherence and Entanglement in Two-mode Squeezed Vacuum States
I investigate the decoherence of two-mode squeezed vacuum states by analyzing
the relative entropy of entanglement. I consider two sources of decoherence:
(i) the phase damping and (ii) the amplitude damping due to the coupling to the
thermal environment. In particular, I give the exact value of the relative
entropy of entanglement for the phase damping model. For the amplitude damping
model, I give an upper bound for the relative entropy of entanglement, which
turns out to be a good approximation for the entanglement measure in usual
experimental situations.Comment: 5 pages, RevTex, 3 eps figure
Broadband teleportation
Quantum teleportation of an unknown broadband electromagnetic field is
investigated. The continuous-variable teleportation protocol by Braunstein and
Kimble [Phys. Rev. Lett. {\bf 80}, 869 (1998)] for teleporting the quantum
state of a single mode of the electromagnetic field is generalized for the case
of a multimode field with finite bandwith. We discuss criteria for
continuous-variable teleportation with various sets of input states and apply
them to the teleportation of broadband fields. We first consider as a set of
input fields (from which an independent state preparer draws the inputs to be
teleported) arbitrary pure Gaussian states with unknown coherent amplitude
(squeezed or coherent states). This set of input states, further restricted to
an alphabet of coherent states, was used in the experiment by Furusawa {\it et
al.} [Science {\bf 282}, 706 (1998)]. It requires unit-gain teleportation for
optimizing the teleportation fidelity. In our broadband scheme, the excess
noise added through unit-gain teleportation due to the finite degree of the
squeezed-state entanglement is just twice the (entanglement) source's squeezing
spectrum for its ``quiet quadrature.'' The teleportation of one half of an
entangled state (two-mode squeezed vacuum state), i.e., ``entanglement
swapping,'' and its verification are optimized under a certain nonunit gain
condition. We will also give a broadband description of this
continuous-variable entanglement swapping based on the single-mode scheme by
van Loock and Braunstein [Phys. Rev. A {\bf 61}, 10302 (2000)]Comment: 27 pages, 7 figures, revised version for publication, Physical Review
A (August 2000); major changes, in parts rewritte
Narrowband frequency tunable light source of continuous quadrature entanglement
We report the observation of non-classical quantum correlations of continuous
light variables from a novel type of source. It is a frequency non-degenerate
optical parametric oscillator below threshold, where signal and idler fields
are separated by 740MHz corresponding to two free spectrum ranges of the
parametric oscillator cavity. The degree of entanglement observed, - 3.8 dB, is
the highest to-date for a narrowband tunable source suitable for atomic quantum
memory and other applications in atomic physics. Finally we use the latter to
visualize the Einstein-Podolsky-Rosen paradox.Comment: 11 pages, 9 figures, LaTe
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