1,701 research outputs found
Generalized Entanglement as a Natural Framework for Exploring Quantum Chaos
We demonstrate that generalized entanglement [Barnum {\em et al.}, Phys. Rev.
A {\bf 68}, 032308 (2003)] provides a natural and reliable indicator of quantum
chaotic behavior. Since generalized entanglement depends directly on a choice
of preferred observables, exploring how generalized entanglement increases
under dynamical evolution is possible without invoking an auxiliary coupled
system or decomposing the system into arbitrary subsystems. We find that, in
the chaotic regime, the long-time saturation value of generalized entanglement
agrees with random matrix theory predictions. For our system, we provide
physical intuition into generalized entanglement within a single system by
invoking the notion of extent of a state. The latter, in turn, is related to
other signatures of quantum chaos.Comment: clarified and expanded version accepted by Europhys. Let
Degenerate dispersive equations arising in the study of magma dynamics
An outstanding problem in Earth science is understanding the method of
transport of magma in the Earth's mantle. Models for this process, transport in
a viscously deformable porous media, give rise to scalar degenerate,
dispersive, nonlinear wave equations. We establish a general local
well-posedness for a physical class of data (roughly ) via fixed point
methods. The strategy requires positive lower bounds on the solution. This is
extended to global existence for a subset of possible nonlinearities by making
use of certain conservation laws associated with the equations. Furthermore, we
construct a Lyapunov energy functional, which is locally convex about the
uniform state, and prove (global in time) nonlinear dynamic stability of the
uniform state for any choice of nonlinearity. We compare the dynamics to that
of other problems and discuss open questions concerning a larger range of
nonlinearities, for which we conjecture global existence.Comment: 27 Pages, 7 figures are not present in this version. See
http://www.columbia.edu/~grs2103/ for a PDF with figures. Submitted to
Nonlinearit
Multicenter evaluation of computer automated versus traditional surveillance of hospital-acquired bloodstream infections
Objective.Central line–associated bloodstream infection (BSI) rates are a key quality metric for comparing hospital quality and safety. Traditional BSI surveillance may be limited by interrater variability. We assessed whether a computer-automated method of central line–associated BSI detection can improve the validity of surveillance.Design.Retrospective cohort study.Setting.Eight medical and surgical intensive care units (ICUs) in 4 academic medical centers.Methods.Traditional surveillance (by hospital staff) and computer algorithm surveillance were each compared against a retrospective audit review using a random sample of blood culture episodes during the period 2004–2007 from which an organism was recovered. Episode-level agreement with audit review was measured with κ statistics, and differences were assessed using the test of equal κ coefficients. Linear regression was used to assess the relationship between surveillance performance (κ) and surveillance-reported BSI rates (BSIs per 1,000 central line–days).Results.We evaluated 664 blood culture episodes. Agreement with audit review was significantly lower for traditional surveillance (κ [95% confidence interval (CI)] = 0.44 [0.37–0.51]) than computer algorithm surveillance (κ [95% CI] [0.52–0.64]; P = .001). Agreement between traditional surveillance and audit review was heterogeneous across ICUs (P = .001); furthermore, traditional surveillance performed worse among ICUs reporting lower (better) BSI rates (P = .001). In contrast, computer algorithm performance was consistent across ICUs and across the range of computer-reported central line–associated BSI rates.Conclusions.Compared with traditional surveillance of bloodstream infections, computer automated surveillance improves accuracy and reliability, making interfacility performance comparisons more valid.Infect Control Hosp Epidemiol 2014;35(12):1483–1490</jats:sec
From Cancer to Diarrhea: The Moving Target of Public Concern about Environmental Health Risks
Public concern about the environment can be unpredictable because it is influenced by numerous factors. Environmental health issues often emerge as important because the public is worried about their health especially when it comes to cancer. Public fear of cancer from environmental exposures is reinforced by many of the US regulations that set pollutant limits based on reducing the risk of cancers rather than other health outcomes. While fear of cancer will never dissipate, recent foodborne outbreaks are contributing to raising public awareness of the health effects from microbes. This paper adds to the dialogue about the challenges of enhancing public understanding of environmental health issues. Internal factors, such as worry, that contribute to public outrage are sometimes more important than external factors such as the media. In addition, relying on the media to inform the public about imminent public health risks may be an ineffective approach to enhancing understanding. In the end, scientists and risk communicators are forced to compete with politicians who are often very effective at manipulating public understanding of risk
Photometric Redshifts of Quasars
We demonstrate that the design of the Sloan Digital Sky Survey (SDSS) filter
system and the quality of the SDSS imaging data are sufficient for determining
accurate and precise photometric redshifts (``photo-z''s) of quasars. Using a
sample of 2625 quasars, we show that photo-z determination is even possible for
z<=2.2 despite the lack of a strong continuum break that robust photo-z
techniques normally require. We find that, using our empirical method on our
sample of objects known to be quasars, approximately 70% of the photometric
redshifts are correct to within delta z = 0.2; the fraction of correct
photometric redshifts is even better for z>3. The accuracy of quasar
photometric redshifts does not appear to be dependent upon magnitude to nearly
21st magnitude in i'. Careful calibration of the color-redshift relation to
21st magnitude may allow for the discovery of on the order of 10^6 quasars
candidates in addition to the 10^5 quasars that the SDSS will confirm
spectroscopically. We discuss the efficient selection of quasar candidates from
imaging data for use with the photometric redshift technique and the potential
scientific uses of a large sample of quasar candidates with photometric
redshifts.Comment: 29 pages, 8 figures, submitted to A
On non-local variational problems with lack of compactness related to non-linear optics
We give a simple proof of existence of solutions of the dispersion manage-
ment and diffraction management equations for zero average dispersion,
respectively diffraction. These solutions are found as maximizers of non-linear
and non-local vari- ational problems which are invariant under a large
non-compact group. Our proof of existence of maximizer is rather direct and
avoids the use of Lions' concentration compactness argument or Ekeland's
variational principle.Comment: 30 page
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