2,619 research outputs found
Optimal distinction between non-orthogonal quantum states
Given a finite set of linearly independent quantum states, an observer who
examines a single quantum system may sometimes identify its state with
certainty. However, unless these quantum states are orthogonal, there is a
finite probability of failure. A complete solution is given to the problem of
optimal distinction of three states, having arbitrary prior probabilities and
arbitrary detection values. A generalization to more than three states is
outlined.Comment: 9 pages LaTeX, one PostScript figure on separate pag
Convex probability domain of generalized quantum measurements
Generalized quantum measurements with N distinct outcomes are used for
determining the density matrix, of order d, of an ensemble of quantum systems.
The resulting probabilities are represented by a point in an N-dimensional
space. It is shown that this point lies in a convex domain having at most d^2-1
dimensions.Comment: 7 pages LaTeX, one PostScript figure on separate pag
Relativistic Doppler effect in quantum communication
When an electromagnetic signal propagates in vacuo, a polarization detector
cannot be rigorously perpendicular to the wave vector because of diffraction
effects. The vacuum behaves as a noisy channel, even if the detectors are
perfect. The ``noise'' can however be reduced and nearly cancelled by a
relative motion of the observer toward the source. The standard definition of a
reduced density matrix fails for photon polarization, because the
transversality condition behaves like a superselection rule. We can however
define an effective reduced density matrix which corresponds to a restricted
class of positive operator-valued measures. There are no pure photon qubits,
and no exactly orthogonal qubit states.Comment: 10 pages LaTe
Gravitating monopoles in SU(3) gauge theory
We consider the Einstein-Yang-Mills-Higgs equations for an SU(3) gauge group
in a spherically symmetric ansatz. Several properties of the gravitating
monopole solutions are obtained an compared with their SU(2) counterpart.Comment: 7 pages, Latex, 3 figure
The TRENDS High-Contrast Imaging Survey. VI. Discovery of a Mass, Age, and Metallicity Benchmark Brown Dwarf
The mass and age of substellar objects are degenerate parameters leaving the
evolutionary state of brown dwarfs ambiguous without additional information.
Theoretical models are normally used to help distinguish between old, massive
brown dwarfs and young, low mass brown dwarfs but these models have yet to be
properly calibrated. We have carried out an infrared high-contrast imaging
program with the goal of detecting substellar objects as companions to nearby
stars to help break degeneracies in inferred physical properties such as mass,
age, and composition. Rather than using imaging observations alone, our targets
are pre-selected based on the existence of dynamical accelerations informed
from years of stellar radial velocity (RV) measurements. In this paper, we
present the discovery of a rare benchmark brown dwarf orbiting the nearby
( pc), solar-type (G9V) star HD 4747 ([Fe/H]=)
with a projected separation of only AU (
0.6"). Precise Doppler measurements taken over 18 years reveal the companion's
orbit and allow us to place strong constraints on its mass using dynamics (). Relative photometry (,
, ) indicates that HD 4747 B is
most-likely a late-type L-dwarf and, if near the L/T transition, an intriguing
source for studying cloud physics, variability, and polarization. We estimate a
model-dependent mass of for an age of
Gyr based on gyrochronology. Combining astrometric measurements with RV data,
we calculate the companion dynamical mass () and orbit
() directly. As a new mass, age, and metallicity benchmark, HD
4747 B will serve as a laboratory for precision astrophysics to test
theoretical models that describe the emergent radiation of brown dwarfs.Comment: Accepted to Ap
The 1-soliton in the SO(3) gauged Skyrme model with mass term
The solitons of the SO(3) gauged Skyrme model with no pion-mass potential
were studied in Refs. {nl,jmp}. Here, the effects of the inclusion of this
potential are studied. In contrast with the (ungauged) Skyrme model, where the
effect of this potential on the solitons is marginal, here it turns out to be
decisive, resulting in very different dependence of the energy as a function of
the Skyrme coupling constant.Comment: new title, typos corrected, LaTeX, 8 pages, 4 figure
A condition for any realistic theory of quantum systems
In quantum physics, the density operator completely describes the state.
Instead, in classical physics the mean value of every physical quantity is
evaluated by means of a probability distribution. We study the possibility to
describe pure quantum states and events with classical probability
distributions and conditional probabilities and prove that the distributions
can not be quadratic functions of the quantum state. Some examples are
considered. Finally, we deal with the exponential complexity problem of quantum
physics and introduce the concept of classical dimension for a quantum system
African American Race and Prevalence of Atrial Fibrillation:A Meta-Analysis
Background. It has been observed that African American race is associated with a lower prevalence of atrial fibrillation (AF) compared to Caucasian race. To better quantify the association between African American race and AF, we performed a meta-analysis of published studies among different patient populations which reported the presence of AF by race. Methods. A literature search was conducted using electronic databases between January 1999 and January 2011. The search was limited to published studies in English conducted in the United States, which clearly defined the presence of AF in African American and Caucasian subjects. A meta-analysis was performed with prevalence of AF as the primary endpoint. Results. In total, 10 studies involving 1,031,351 subjects were included. According to a random effects analysis, African American race was associated with a protective effect with regard to AF as compared to Caucasian race (odds ratio 0.51, 95% CI 0.44 to 0.59, P < 0.001). In subgroup analyses, African American race was significantly associated with a lower prevalence of AF in the general population, those hospitalized or greater than 60 years old, postcoronary artery bypass surgery patients, and subjects with heart failure. Conclusions. In a broad sweep of subjects in the general population and hospitalized patients, the prevalence of AF in African Americans is consistently lower than in Caucasians
Quality in quality improvement research--a new benchmark.
CITATION: Scales DC, Dainty K, Hales B, Pinto R, Fowler RA, Adhikari NK, Zwarenstein M: A multifaceted intervention for quality improvement in a network of intensive care units: a cluster randomized trial. JAMA 2011, 305:363-72. CONTEXT: Evidence-based practices improve intensive care unit (ICU) outcomes, but eligible patients may not receive them. Community hospitals treat most critically ill patients but may have few resources to devote to quality improvement. OBJECTIVE: To determine the effectiveness of a multicenter quality improvement program to increase delivery of 6 evidence-based ICU practices. DESIGN, SETTING, AND PARTICIPANTS: Pragmatic, cluster-randomized trial among 15 community hospital ICUs in Ontario, Canada. A total of 9269 admissions occurred during the trial (November 2005 to October 2006) and 7141 admissions during a decay-monitoring period (December 2006 to August 2007). INTERVENTION: The authors implemented a videoconference-based forum including audit and feedback, expert-led educational sessions, and dissemination of algorithms to sequentially improve delivery of 6 practices. The ICUs were randomized into 2 groups. Each group received this intervention, targeting a new practice every 4 months, while acting as control for the other group, in which a different practice was targeted in the same period. MAIN OUTCOMES: The primary outcome was the summary ratio of odds ratios (ORs) for improvement in adoption (determined by daily data collection) of all 6 practices during the trial in intervention vs control ICUs. RESULTS: Overall, adoption of the targeted practices was greater in intervention ICUs than in controls (summary ratio of ORs, 2.79; 95% confidence interval [CI], 1.00-7.74). Improved delivery in intervention ICUs was greatest for semi recumbent positioning to prevent ventilator-associated pneumonia (90.0% of patient-days in last month vs. 50.0% in first month; OR, 6.35; 95% CI, 1.85-21.79) and precautions to prevent catheter-related bloodstream infection (70.0% of patients receiving central lines vs. 10.6%; OR, 30.06; 95% CI, 11.00-82.17). Adoption of other practices, many with high baseline adherence, changed little. CONCLUSION: In a collaborative network of community ICUs, a multi-faceted quality improvement intervention improved adoption of care practices
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