9,214 research outputs found
Engineering the spatial confinement of exciton-polaritons in semiconductors
We demonstrate the spatial confinement of electronic excitations in a solid
state system, within novel artificial structures that can be designed having
arbitrary dimensionality and shape. The excitations under study are
exciton-polaritons in a planar semiconductor microcavity. They are confined
within a micron-sized region through lateral trapping of their photon
component. Striking signatures of confined states of lower and upper polaritons
are found in angle-resolved light emission spectra, where a discrete energy
spectrum and broad angular patterns are present. A theoretical model supports
unambiguously our observations
Theory and Phenomenology of Hadrons
This Dyson-Schwinger equation (DSE) aperc,u highlights recent applications to
mesons. It reports features of, and results for, pseudoscalar and scalar
bound-state residues in vacuum polarisations, and exhibits how a restoration of
chiral symmetry in meson trajectories could be manifest in a relationship
between them. It also touches on nucleon studies, emphasising the importance of
both scalar and axial-vector diquark correlations, and reporting the
calculation of mu_n G_E^n(Q^2)/G_M^n(Q^2). The value of respecting symmetries,
including Poincare' covariance, is stressed.Comment: 7 pages, 1 figure, contribution to proceedings of "18th International
IUPAP Conference on Few-Body Problems in Physics," Santos, Brazil, August
21-26, 200
Large Wilson loops with overlap and clover fermions: Two-loop evaluation of the b-quark mass shift and the quark-antiquark potential
We compute, to two loops in pertubation theory, the fermionic contribution to
rectangular RxT Wilson loops, for different values of R and T.
We use the overlap fermionic action. We also employ the clover action, for
comparison with existing results in the literature.
In the limit R, T -> Infinity our results lead to the shift in the b-quark
mass. We also evaluate the perturbative static potential as T -> Infinity.Comment: 24 pages, 14 figures, 14 table
Nonlinear Dynamic Phenomena in Macroscopic Tunneling
Numerical simulations of the NLSE (or GPE) are presented demonstrating
emission of short pulses of the matter (light) density formed in the course of
tunneling in wave-guided light and/or trapped BEC. The phenomenon is observed
under various conditions, for nonlinearities of different signs, zero
nonlinearity included. We study, both numerically and analytically, pulsations
of matter (light) remaining within the trap and use the results in order to
induce emission of sequential pulses by properly narrowing the trap. This
allows us to propose a mechanism for a realization of Atom Pulse Laser.Comment: 14 pages, 6 figure
Maternal Characteristics and Clinical Diagnoses Influence Obstetrical Outcomes in Indonesia
This Indonesian study evaluates associations between near-miss status/death with maternal demographic, health care characteristics, and obstetrical complications, comparing results using retrospective and prospective data. The main outcome measures were obstetric conditions and socio-economic factors to predict near-miss/death. We abstracted all obstetric admissions (1,358 retrospective and 1,240 prospective) from two district hospitals in East Java, Indonesia between 4/1/2009 and 5/15/2010. Prospective data added socio-economic status, access to care and referral patterns. Reduced logistic models were constructed, and multivariate analyses used to assess association of risk variables to outcome. Using multivariate analysis, variables associated with risk of near-miss/death include postpartum hemorrhage (retrospective AOR 5.41, 95 % CI 2.64–11.08; prospective AOR 10.45, 95 % CI 5.59–19.52) and severe preeclampsia/ eclampsia (retrospective AOR 1.94, 95 % CI 1.05–3.57; prospective AOR 3.26, 95 % CI 1.79–5.94). Associations with near-miss/death were seen for antepartum hemorrhage in retrospective data (AOR 9.34, 95 % CI 4.34–20.13), and prospectively for poverty (AOR 2.17, 95 % CI 1.33–3.54) and delivering outside the hospital (AOR 2.04, 95 % CI 1.08–3.82). Postpartum hemorrhage and severe preeclampsia/ eclampsia are leading causes of near-miss/death in Indonesia. Poverty and delivery outside the hospital are significant risk factors. Prompt recognition of complications, timely referrals, standardized care protocols, prompt hospital triage, and structured provider education may reduce obstetric mortality and morbidity. Retrospective data were reliable, but prospective data provided valuable information about barriers to care and referral patterns
Bethe-Salpeter equation and a nonperturbative quark-gluon vertex
A Ward-Takahashi identity preserving Bethe-Salpeter kernel can always be
calculated explicitly from a dressed-quark-gluon vertex whose diagrammatic
content is enumerable. We illustrate that fact using a vertex obtained via the
complete resummation of dressed-gluon ladders. While this vertex is planar, the
vertex-consistent kernel is nonplanar and that is true for any dressed vertex.
In an exemplifying model the rainbow-ladder truncation of the gap and
Bethe-Salpeter equations yields many results; e.g., pi- and rho-meson masses,
that are changed little by including higher-order corrections. Repulsion
generated by nonplanar diagrams in the vertex-consistent Bethe-Salpeter kernel
for quark-quark scattering is sufficient to guarantee that diquark bound states
do not exist.Comment: 16 pages, 12 figures, REVTEX
Quantum-fluid dynamics of microcavity polaritons
Semiconductor microcavities offer a unique system to investigate the physics
of weakly interacting bosons. Their elementary excitations, polaritons--a
mixture of excitons and photons--behave, in the low density limit, as bosons
that can undergo a phase transition to a regime characterised by long range
coherence. Condensates of polaritons have been advocated as candidates for
superfluidity; and the formation of vortices as well as elementary excitations
with a linear dispersion are actively sought after. In this work, we have
created and set in motion a macroscopically degenerate state of polaritons and
let it collide with a variety of defects present in the sample. Our experiments
show striking manifestations of a coherent light-matter packet that displays
features of a superfluid, although one of a highly unusual character as it
involves an out-of-equilibrium dissipative system where it travels at
ultra-fast velocity of the order of 1% the speed of light. Our main results are
the observation of i) a linear polariton dispersion accompanied with
diffusion-less motion, ii) flow without resistance when crossing an obstacle,
iii) suppression of Rayleigh scattering and iv) splitting into two fluids when
the size of the obstacle is comparable with the size of the wavepacket. This
work opens the way to the investigation of new phenomenology of
out-of-equilibrium condensates.Comment: 22 pages, 5 figure
A surface-patterned chip as a strong source of ultracold atoms for quantum technologies
Laser-cooled atoms are central to modern precision measurements. They are also increasingly important as an enabling technology for experimental cavity quantum electrodynamics, quantum information processing and matter–wave interferometry. Although significant progress has been made in miniaturizing atomic metrological devices, these are limited in accuracy by their use of hot atomic ensembles and buffer gases. Advances have also been made in producing portable apparatus that benefits from the advantages of atoms in the microkelvin regime. However, simplifying atomic cooling and loading using microfabrication technology has proved difficult. In this Letter we address this problem, realizing an atom chip that enables the integration of laser cooling and trapping into a compact apparatus. Our source delivers ten thousand times more atoms than previous magneto-optical traps with microfabricated optics and, for the first time, can reach sub-Doppler temperatures. Moreover, the same chip design offers a simple way to form stable optical lattices. These features, combined with simplicity of fabrication and ease of operation, make these new traps a key advance in the development of cold-atom technology for high-accuracy, portable measurement devices
Shape Selectivity by Guest- Driven Restructuring of a Porous Material
A flexible metal-organic framework selectively sorbs para- (pX) over meta-xylene (mX) by synergic restructuring around pX coupled with generation of unused void space upon mX loading. The nature of the structural change suggests more generally that flexible structures which are initially mismatched in terms of fit and capacity to the preferred guest are strong candidates for effective molecular separations
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