4,236 research outputs found
State-space based mass event-history model I: many decision-making agents with one target
A dynamic decision-making system that includes a mass of indistinguishable
agents could manifest impressive heterogeneity. This kind of nonhomogeneity is
postulated to result from macroscopic behavioral tactics employed by almost all
involved agents. A State-Space Based (SSB) mass event-history model is
developed here to explore the potential existence of such macroscopic
behaviors. By imposing an unobserved internal state-space variable into the
system, each individual's event-history is made into a composition of a common
state duration and an individual specific time to action. With the common state
modeling of the macroscopic behavior, parametric statistical inferences are
derived under the current-status data structure and conditional independence
assumptions. Identifiability and computation related problems are also
addressed. From the dynamic perspectives of system-wise heterogeneity, this SSB
mass event-history model is shown to be very distinct from a random effect
model via the Principle Component Analysis (PCA) in a numerical experiment.
Real data showing the mass invasion by two species of parasitic nematode into
two species of host larvae are also analyzed. The analysis results not only are
found coherent in the context of the biology of the nematode as a parasite, but
also include new quantitative interpretations.Comment: Published in at http://dx.doi.org/10.1214/08-AOAS189 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Functional imaging reveals working memory and attention interact to produce the attentional blink
Copyright @ 2012 Massachusetts Institute of Technology PressIf two centrally presented visual stimuli occur within approximately half a second of each other, the second target often fails to be reported correctly. This effect, called the attentional blink (AB; Raymond, J. E., Shapiro, K. L., & Arnell, K. M. Temporary suppression of visual processing in an RSVP task: An attentional blink? Journal of Experimental Psychology, Human Perception and Performance, 18, 849-860, 1992], has been attributed to a resource "bottleneck," likely arising as a failure of attention during encoding into or retrieval from visual working memory (WM). Here we present participants with a hybrid WM-AB study while they undergo fMRI to provide insight into the neural underpinnings of this bottleneck. Consistent with a WM-based bottleneck account, fronto-parietal brain areas exhibited a WM load-dependent modulation of neural responses during the AB task. These results are consistent with the view that WM and attention share a capacity-limited resource and provide insight into the neural structures that underlie resource allocation in tasks requiring joint use of WM and attention.This research was supported by a project grant (071944) from the Wellcome Trust to Kimron Shapiro
Frontal and parietal theta burst TMS impairs working memory for visual-spatial conjunctions
Open Access funded by Wellcome Trust Under a Creative Commons license Acknowledgments This research was supported by the Wellcome Trust (grant number 077185/Z/05/Z) and the Welsh Assembly Government through the Wales Institute of Cognitive Neuroscience.Peer reviewedPublisher PD
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The Use of In-Situ Simulation to Improve Safety in the Plastic Surgery Office: A Feasibility Study
Objective: Simulation-based interventions and education can potentially contribute to safer and more effective systems of care. We utilized in-situ simulation to highlight safety issues, regulatory requirements, and assess perceptions of safety processes by the plastic surgery office staff. Methods: A high-fidelity human patient simulator was brought to an office-based plastic surgery setting to enact a half-day full-scale, multidisciplinary medical emergency. Facilitated group debriefings were conducted after each scenario with special consideration of the principles of team training, communication, crisis management, and adherence to evidence-based protocols and regulatory standards. Abbreviated AHRQ Medical Office Safety Culture Survey was completed by the participants before and after the session. Results: The in-situ simulations had a high degree of acceptance and face validity according to the participants. Areas highlighted by the simulation sessions included rapid communication, delegation of tasks, location of emergency materials, scope of practice, and logistics of transport. The participant survey indicated greater awareness of patient safety issues following participation in simulation and debriefing exercises in 3 areas (P < 0.05): the need to change processes if there is a recognized patient safety issue (100% vs 75%), openness to ideas about improving office processes (100% vs 88%), and the need to discuss ways to prevent errors from recurring (88% vs 62%). Conclusions: Issues of safety and regulatory compliance can be assessed in an office-based setting through the short-term (half-day) use of in-situ simulation with facilitated debriefing and the review of audiovisual recordings by trained facilities inspectors
One loop renormalization of the four-dimensional theory for quantum dilaton gravity.
We study the one loop renormalization in the most general metric-dilaton
theory with the second derivative terms only. The general theory can be divided
into two classes, models of one are equivalent to conformally coupled with
gravity scalar field and also to general relativity with cosmological term. The
models of second class have one extra degree of freedom which corresponds to
dilaton. We calculate the one loop divergences for the models of second class
and find that the arbitrary functions of dilaton in the starting action can be
fine-tuned in such a manner that all the higher derivative counterterms
disappear on shell. The only structures in both classical action and
counterterms, which survive on shell, are the potential (cosmological) ones.
They can be removed by renormalization of the dilaton field which acquire the
nontrivial anomalous dimension, that leads to the effective running of the
cosmological constant. For some of the renormalizable solutions of the theory
the observable low energy value of the cosmological constant is small as
compared with the Newtonian constant. We also discuss another application of
our result.Comment: 21 pages, latex, no figures
Hydrodynamical winds from two-temperature plasma in X-ray binaries
Hydrodynamical winds from a spherical two-temperature plasma surrounding a
compact object are constructed. The mass-loss rate is computed as a function of
electron temperature, optical depth and luminosity of the sphere, the values of
which can be constrained by the fitting of the spectral energy distributions
for known X-ray binary systems. The sensitive dependence of the mass loss rate
with these parameters leads to the identification of two distinct regions in
the parameter space separating wind-dominated from non wind dominated systems.
A critical optical depth, tau_c, as a function of luminosity and electron
temperature, is defined which differentiates these two regions. Systems with
optical depths significantly smaller than tau_c are wind-dominated.
The results are applied to black hole candidate X-ray binary systems in the
hard spectral state (Cyg X-1, GX 339-4 and Nova Muscae), and it is found that
the inferred optical depth (tau) is similar to tau_c suggesting that they are
wind regulated systems. On the other hand, for X-ray binary systems containing
a neutron star (e.g., Cyg X-2) tau is much larger than tau_c indicating the
absence of significant hydrodynamical winds.Comment: 9 pages, 4 figures, Accepted for publication in MNRA
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