scholarly journals Simulating pulsar glitches: an N-body solver for superfluid vortex motion in two dimensions

2020 ◽  
Vol 498 (1) ◽  
pp. 320-331
Author(s):  
G Howitt ◽  
A Melatos ◽  
B Haskell
Keyword(s):  
Waiting Times ◽  
Vortex Motion ◽  
Two Dimensions ◽  
Pitaevskii Equation ◽  
Lognormal Distributions ◽  
State Dependent ◽  
Stress Release Model ◽  
Before And After ◽  
Release Model ◽  
Stress Accumulation

ABSTRACT A rotating superfluid forms an array of quantized vortex lines that determine its angular velocity. The spasmodic evolution of the array under the influence of deceleration, dissipation, and pinning forces is thought to be responsible for the phenomenon of pulsar glitches, sudden jumps in the spin frequency of rotating neutron stars. We describe and implement an N-body method for simulating the motion of up to 5000 vortices in two dimensions and present the results of numerical experiments validating the method, including stability of a vortex ring and dissipative formation of an Abrikosov array. Vortex avalanches occur routinely in the simulations, when chains of unpinning events are triggered collectively by vortex–vortex repulsion, consistent with previous, smaller scale studies using the Gross–Pitaevskii equation. The probability density functions of the avalanche sizes and waiting times are consistent with both exponential and lognormal distributions. We find weak correlations between glitch sizes and waiting times, consistent with astronomical data and meta-models of pulsar glitch activity as a state-dependent Poisson process or a Brownian stress-accumulation process, and inconsistent with a threshold-triggered stress-release model with a single, global stress reservoir. The spatial distribution of the effective stress within the simulation volume is analysed before and after a glitch.

scholarly journals Long-term statistics of pulsar glitches triggered by a Brownian stress accumulation process

2020 ◽  
Vol 494 (3) ◽  
pp. 3383-3391 ◽  
Author(s):  
J B Carlin ◽  
A Melatos
Keyword(s):  
Cross Correlation ◽  
Waiting Times ◽  
Rotation Frequency ◽  
Critical Threshold ◽  
Accumulation Process ◽  
Meta Model ◽  
State Dependent ◽  
Brownian Process ◽  
Stress Accumulation

ABSTRACT A microphysics-agnostic meta-model of rotational glitches in rotation-powered pulsars is developed, wherein the globally averaged internal stress accumulates as a Brownian process between glitches, and a glitch is triggered once a critical threshold is surmounted. Precise, falsifiable predictions are made regarding long-term event statistics in individual pulsars. For example, the Spearman cross-correlation coefficient between the size of a glitch and the waiting time until the next glitch should exceed 0.25 in all pulsars. Among the six pulsars with the most recorded glitches, PSR J0537−6910 and PSR J0835−4510 are consistent with the predictions of the meta-model, while PSR J1740−3015 and PSR J0631+1036 are not. PSR J0534+2200 and PSR J1341−6220 are only consistent with the meta-model, if there exists an undetected population of small glitches with small waiting times, which we do not resolve. The results are compared with a state-dependent Poisson process, another microphysics-agnostic meta-model in the literature. The results are also applied briefly to recent pulse-to-pulse observations of PSRJ0835−4510, which appear to reveal evidence for a negative fluctuation in rotation frequency just prior to the 2016 glitch.

scholarly journals Evaluation of Emergency Health-Care Initiatives to Reduce Overcrowding in a Referral Medical Complex, Jeddah, Saudi Arabia

2021 ◽  
pp. 1-6
Author(s):  
Khalid Alabbasi ◽  
Estie Kruger ◽  
Marc Tennant
Keyword(s):  
Health Care ◽  
Primary Health Care ◽  
Public Hospital ◽  
Waiting Times ◽  
Care Centre ◽  
Health Care Centre ◽  
Transfer Policy ◽  
Primary Health ◽  
Before And After ◽  
Ed Visits

<b><i>Purpose:</i></b> Excessive delays and emergency department (ED) overcrowding have become an increasingly major problem for public health worldwide. This study was to assess the key strategies adopted by an ED, at a public hospital in Jeddah, to reduce delays and streamline patient flow. <b><i>Materials and Methods:</i></b> This study was a service evaluation for a Saudi patient population of all age-groups who attended the ED of a public hospital for the period between June 2016 and July 2019. The Saudi initiative to reduce the ED visits at the King Abdullah Medical Complex hospital has started on August 7, 2018. The initiative was to apply an urgency transfer policy which outlines the procedures to follow when patients arrive to the ED where they are reviewed based on the Canadian Triage and Acuity Scale (CTAS). Patients with less-urgent conditions (category 4 and 5) are referred to a primary health-care practice (where a family medicine consultant is available). Patients with urgent conditions (category 1–3) are referred to a specialized health-care centre if the service is not currently provided. To test the effectiveness of ED initiative on reducing the overcrowd, data were categorized into before and after the initiative. The bivariate analysis χ<sup>2</sup> tests and 2 sample <i>t</i>-tests were run to explore the relationship of gender and age with dependent variable emergency. <b><i>Results:</i></b> A total of 233,998 patients were included in this study, 61.8% of them were males and the average age of ED patients were 35.5 ± 18.6 years. The majority of cases were those classified as “less urgent” (CTAS 4), which accounted for 65.4%. Number of ED visits before and after the initiative was 67 and 33%, respectively. ED waiting times after the initiative have statistically significantly decreased across all acuity levels compared to ED waiting times before the initiative. <b><i>Conclusion and Implication:</i></b> The findings suggest that the majority of patients arrive to the ED with less-urgent conditions and arrived by walking-in. The number of cases attending the ED significantly decreased following the introduction of the urgency transfer policy. Referral for less-urgent patients to primary health-care centre may be an important front-end operational strategy to relieve congestion.

scholarly journals Anticipated help-seeking for cancer symptoms before and after the coronavirus pandemic: results from the Onco-barometer population survey in Spain

2021 ◽  
Author(s):  
Dafina Petrova ◽  
Marina Pollán ◽  
Miguel Rodriguez-Barranco ◽  
Dunia Garrido ◽  
Josep M. Borrás ◽  
...  
Keyword(s):  
Poisson Regression ◽  
Help Seeking ◽  
Regression Models ◽  
Population Survey ◽  
Waiting Times ◽  
Perceived Barriers ◽  
Older Individuals ◽  
Cancer Symptoms ◽  
Before And After ◽  
Diagnostic Delays

Abstract Background The patient interval—the time patients wait before consulting their physician after noticing cancer symptoms—contributes to diagnostic delays. We compared anticipated help-seeking times for cancer symptoms and perceived barriers to help-seeking before and after the coronavirus pandemic. Methods Two waves (pre-Coronavirus: February 2020, N = 3269; and post-Coronavirus: August 2020, N = 1500) of the Spanish Onco-barometer population survey were compared. The international ABC instrument was administered. Pre–post comparisons were performed using multiple logistic and Poisson regression models. Results There was a consistent and significant increase in anticipated times to help-seeking for 12 of 13 cancer symptoms, with the largest increases for breast changes (OR = 1.54, 95% CI 1.22–1–96) and unexplained bleeding (OR = 1.50, 1.26–1.79). Respondents were more likely to report barriers to help-seeking in the post wave, most notably worry about what the doctor may find (OR = 1.58, 1.35–1.84) and worry about wasting the doctor’s time (OR = 1.48, 1.25–1.74). Women and older individuals were the most affected. Conclusions Participants reported longer waiting times to help-seeking for cancer symptoms after the pandemic. There is an urgent need for public interventions encouraging people to consult their physicians with symptoms suggestive of cancer and counteracting the main barriers perceived during the pandemic situation.

Waiting times for M/M systems under state-dependent processor sharing

2008 ◽  
Vol 59 (3-4) ◽  
pp. 297-319 ◽  
Author(s):  
Andreas Brandt ◽  
Manfred Brandt
Keyword(s):  
Waiting Times ◽  
Processor Sharing ◽  
State Dependent

A Stress Release Model in Egypt

Geotectonics ◽  
2020 ◽  
Vol 54 (1) ◽  
pp. 106-112
Author(s):  
Kh. A. Omar ◽  
O. Mangira
Keyword(s):  
Stress Release ◽  
Stress Release Model ◽  
Release Model

scholarly journals Derivation of the Time Dependent Gross–Pitaevskii Equation in Two Dimensions

2019 ◽  
Vol 372 (1) ◽  
pp. 1-69 ◽  
Author(s):  
Maximilian Jeblick ◽  
Nikolai Leopold ◽  
Peter Pickl
Keyword(s):  
Schrödinger Equation ◽  
Nonlinear Schrödinger Equation ◽  
Schrodinger Equation ◽  
Particle System ◽  
Nonlinear Schrodinger Equation ◽  
Two Dimensions ◽  
Pitaevskii Equation ◽  
Nonlinear Schrödinger ◽  
Cubic Nonlinear Schrödinger Equation ◽  
Reduced Density

Abstract We present microscopic derivations of the defocusing two-dimensional cubic nonlinear Schrödinger equation and the Gross–Pitaevskii equation starting from an interacting N-particle system of bosons. We consider the interaction potential to be given either by $$W_\beta (x)=N^{-1+2 \beta }W(N^\beta x)$$Wβ(x)=N-1+2βW(Nβx), for any $$\beta >0$$β>0, or to be given by $$V_N(x)=e^{2N} V(e^N x)$$VN(x)=e2NV(eNx), for some spherical symmetric, nonnegative and compactly supported $$W,V \in L^\infty ({\mathbb {R}}^2,{\mathbb {R}})$$W,V∈L∞(R2,R). In both cases we prove the convergence of the reduced density corresponding to the exact time evolution to the projector onto the solution of the corresponding nonlinear Schrödinger equation in trace norm. For the latter potential $$V_N$$VN we show that it is crucial to take the microscopic structure of the condensate into account in order to obtain the correct dynamics.

scholarly journals Insensitive Bounds for the Moments of the Sojourn Times in M/GI Systems Under State-Dependent Processor Sharing

2010 ◽  
Vol 42 (01) ◽  
pp. 246-267 ◽  
Author(s):  
Andreas Brandt ◽  
Manfred Brandt
Keyword(s):  
Waiting Times ◽  
The State ◽  
Single Server ◽  
Processor Sharing ◽  
Actual Number ◽  
Service Capacity ◽  
State Dependent ◽  
Poisson Arrivals ◽  
Service Times ◽  
The Given

We consider a system with Poisson arrivals and independent and identically distributed service times, where requests in the system are served according to the state-dependent (Cohen's generalized) processor-sharing discipline, where each request receives a service capacity that depends on the actual number of requests in the system. For this system, we derive expressions as well as tight insensitive upper bounds for the moments of the conditional sojourn time of a request with given required service time. The bounds generalize and extend corresponding results, recently given for the single-server processor-sharing system in Cheung et al. (2006) and for the state-dependent processor-sharing system with exponential service times by the authors (2008). Analogous results hold for the waiting times. Numerical examples for the M/M/m-PS and M/D/m-PS systems illustrate the given bounds.

On the statistics of the linked stress release model

2001 ◽  
Vol 38 (A) ◽  
pp. 176-187 ◽  
Author(s):  
Mark Bebbington ◽  
David S. Harte
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Numerical Analysis ◽  
Large Scale ◽  
Point Processes ◽  
Information Criterion ◽  
Stress Release ◽  
Stress Release Model ◽  
Using Data ◽  
Release Model

The paper reviews the formulation of the linked stress release model for large scale seismicity together with aspects of its application. Using data from Taiwan for illustrative purposes, models can be selected and verified using tools that include Akaike's information criterion (AIC), numerical analysis, residual point processes and Monte Carlo simulation.

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