3,922 research outputs found
Three-dimensional theory of stimulated Raman scattering
We present a three-dimensional theory of stimulated Raman scattering
(SRS) or superradiance. In particular we address how the spatial and temporal
properties of the generated SRS beam, or Stokes beam, of radiation depends on
the spatial properties of the gain medium. Maxwell equations for the Stokes
field operators and of the atomic operators are solved analytically and a
correlation function for the Stokes field is derived. In the analysis we
identify a superradiating part of the Stokes radiation that exhibit beam
characteristics. We show how the intensity in this beam builds up in time and
at some point largely dominates the total Stokes radiation of the gain medium.
We show how the SRS depends on geometric factors such as the Fresnel number and
the optical depth, and that in fact these two factors are the only factors
describing the coherent radiation.Comment: 21 pages 14 figure
Metformin and other glucose-lowering drug initiation and rates of community-based antibiotic use and hospital-treated infections in patients with type 2 diabetes: a Danish nationwide population-based cohort study
OBJECTIVE: Data on early risk of infection in patients receiving their first treatment for type 2 diabetes are limited. We examined rates of community-based antibiotic use and hospital-treated infection in initiators of metformin and other glucose-lowering drugs (GLDs). DESIGN: Population-based cohort study using medical databases. SETTING: General practice and hospitals in Denmark. PARTICIPANTS: 131 949 patients with type 2 diabetes who initiated pharmacotherapy with a GLD between 2005 and 2012. EXPOSURE: Initial GLD used for pharmacotherapy. MAIN OUTCOME MEASURES: We computed rates and adjusted HRs of community-based antibiotic use and hospital-treated infection associated with choice of initial GLD with reference to metformin initiation, using an intention-to-treat approach. RESULTS: The rate of community-based antibiotic use was 362 per 1000 patient-years at risk (PYAR) and that for hospital-treated infection was 51 per 1000 PYAR. Compared with metformin, the risk of hospital-treated infection was slightly higher in sulfonylurea initiators (HR 1.12, 95% CI 1.08 to 1.16) and substantially higher in insulin initiators (HR 1.63, 95% CI 1.54 to 1.72) initiators after adjustment for comorbid conditions, comedications and other confounding factors. In contrast, virtually no difference was observed for overall community-based antibiotic use (HR 1.02, 95% CI 1.01 to 1.04, for sulfonylurea initiators; and 1.04, 95% CI 1.01 to 1.07, for insulin initiators). CONCLUSIONS: Rates of community-based antibiotic treatment and hospitalisation for infection were high in patients receiving their first treatment for type 2 diabetes and differed with the choice of initial GLD used for pharmacotherapy
Preparation of spin squeezed atomic states by optical phase shift measurement
In this paper we present a state vector analysis of the generation of atomic
spin squeezing by measurement of an optical phase shift. The frequency
resolution is improved when a spin squeezed sample is used for spectroscopy in
place of an uncorrelated sample. When light is transmitted through an atomic
sample some photons will be scattered out of the incident beam, and this has a
destructive effect on the squeezing. We present quantitative studies for three
limiting cases: the case of a sample of atoms of size smaller than the optical
wavelength, the case of a large dilute sample and the case of a large dense
sample.Comment: 18 page
Age at Puberty and the Emerging Obesity Epidemic
Background: Recent studies have shown that puberty starts at younger ages than previously. It has been hypothesized that the increasing prevalence of childhood obesity is contributing to this trend. The purpose of this study was to analyze the association between prepubertal body mass index (BMI) and pubertal timing, as assessed by age at onset of pubertal growth spurt (OGS) and at peak height velocity (PHV), and the secular trend of pubertal timing given the prepubertal BMI. Methodology/Principal Findings: Annual measurements of height and weight were available in all children born from 1930 to 1969 who attended primary school in the Copenhagen municipality; 156,835 children fulfilled the criteria for determining age at OGS and PHV. The effect of prepubertal BMI at age seven on these markers of pubertal development within and between birth cohorts was analyzed. BMI at seven years was significantly inversely associated with age at OGS and PHV. Dividing the children into five levels of prepubertal BMI, we found a similar secular trend toward earlier maturation in all BMI groups. Conclusion/Significance: The heavier both boys and girls were at age seven, the earlier they entered puberty. Irrespective of level of BMI at age seven, there was a downward trend in the age at attaining puberty in both boys and girls, whic
Multi-particle entanglement of hot trapped ions
We propose an efficient method to produce multi-particle entangled states of
ions in an ion trap for which a wide range of interesting effects and
applications have been suggested. Our preparation scheme exploits the
collective vibrational motion of the ions, but it works in such a way that this
motion need not be fully controlled in the experiment. The ions may, e.g., be
in thermal motion and exchange mechanical energy with a surrounding heat bath
without detrimental effects on the internal state preparation. Our scheme does
not require access to the individual ions in the trap.Comment: 4 pages, including 3 figures. To appear in Phys. Rev. Lett. This
paper previously appeared under the name "Schrodingers cat in a hot trap".
The paper has been revised according to Phys. Rev. policy on Schrodinger
cats. No cats were harmed during the production of this manuscrip
Capacitive coupling of atomic systems to mesoscopic conductors
We describe a technique that enables a strong, coherent coupling between
isolated neutral atoms and mesoscopic conductors. The coupling is achieved by
exciting atoms trapped above the surface of a superconducting transmission line
into Rydberg states with large electric dipole moments, that induce voltage
fluctuations in the transmission line. Using a mechanism analogous to cavity
quantum electrodynamics an atomic state can be transferred to a long-lived mode
of the fluctuating voltage, atoms separated by millimeters can be entangled, or
the quantum state of a solid state device can be mapped onto atomic or photonic
states.Comment: 4 pages, including one figure. v2: Improved discussion of surface
effect
Many-particle entanglement with Bose--Einstein condensates
We propose a method to produce entangled states of several particles starting
from a Bose-Einstein condensate. In the proposal, a single fast pulse
is applied to the atoms and due to the collisional interaction, the subsequent
free time evolution creates an entangled state involving all atoms in the
condensate. The created entangled state is a spin-squeezed state which could be
used to improve the sensitivity of atomic clocks.Comment: 4 pages. Minor modification
Universal Behavior of One-Dimensional Gapped Antiferromagnets in Staggered Magnetic Field
We study the properties of one-dimensional gapped Heisenberg antiferromagnets
in the presence of an arbitrary strong staggered magnetic field. For these
systems we predict a universal form for the staggered magnetization curve. This
function, as well as the effect the staggered field has on the energy gaps in
longitudinal and transversal excitation spectra, are determined from the
universal form of the effective potential in O(3)-symmetric 1+1--dimensional
field theory. Our theoretical findings are in excellent agreement with recent
neutron scattering data on R_2 Ba Ni O_5 (R = magnetic rare earth) linear-chain
mixed spin antiferromagnets.Comment: 4 pages, 2 figure
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