On compressive radial tidal forces

Radial tidal forces can be compressive instead of disruptive, a possibility that is frequently overlooked in high level physics courses. For example, radial tidal compression can emerge in extended stellar systems containing a smaller stellar cluster. For particular conditions the tidal field produced by this extended mass distribution can exert on the cluster it contains compressive effects instead of the common disruptive forces. This interesting aspect of gravity can be derived from standard relations given in many textbooks and introductory courses in astronomy and can serve as an opportunity to look closer at some aspects of gravitational physics, stellar dynamics, and differential geometry. The existence of compressive tides at the center of huge stellar systems might suggest new evolutionary scenarios for the formation of stars and primordial galactic formation processes.Comment: 22 pages, 2 figure

The Utilization of the STOP-Bang Questionnaire for Identification of Surgical Patients at Risk for Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is a breathing disorder that if left untreated during the perioperative period can lead to deleterious complications. Considering there remains a significant amount of Americans undiagnosed, it is of utmost importance that adult surgical patients undergoing elective procedures be appropriately screened to detect OSA risk in order to decrease adverse events through individualized interventions during the surgical phases. Polysomnography testing is the diagnostic standard, but its complexity in the perioperative setting renders it impractical. The STOP-Bang questionnaire is a validated screening tool that can be utilized as an alternative in this population to accurately identify at risk patients. At a local urban hospital in Pennsylvania, a data analytics team determined that a 1.6% annual compliance rate exists with this risk stratification tool amongst anesthesia providers. The aim of this quality improvement (QI) project is to increase overall compliance of the STOP-Bang questionnaire via incorporation into the preoperative nursing assessment and ultimately, increase detection of OSA risk in the undiagnosed surgical population at this healthcare institution. Post implementation data was analyzed and it was revealed that STOP-Bang compliance increased at an upwards of 62.2% over a 4–week period. It was also shown that 14.8% of the surgical population was identified as intermediate to high-risk for OSA development. The STOP-Bang questionnaire is well documented for its reliability, precision, and ability to aid in provider identification of surgical patients at risk for OSA. Considering the specialized, individualized, and careful management OSA patients require to prevent perioperative complications, screening with the STOP-Bang questionnaire is recommended

Free Energy Minimizers for a Two--Species Model with Segregation and Liquid-Vapor Transition

We study the coexistence of phases in a two--species model whose free energy is given by the scaling limit of a system with long range interactions (Kac potentials) which are attractive between particles of the same species and repulsive between different species.Comment: 32 pages, 1 fig, plain tex, typeset twic

Robot swarm democracy: the importance of informed individuals against zealots

Abstract: In this paper we study a generalized case of best-of-n model, which considers three kind of agents: zealots, individuals who remain stubborn and do not change their opinion; informed agents, individuals that can change their opinion, are able to assess the quality of the different options; and uninformed agents, individuals that can change their opinion but are not able to assess the quality of the different opinions. We study the consensus in different regimes: we vary the quality of the options, the percentage of zealots and the percentage of informed versus uninformed agents. We also consider two decision mechanisms: the voter and majority rule. We study this problem using numerical simulations and mathematical models, and we validate our findings on physical kilobot experiments. We find that (1) if the number of zealots for the lowest quality option is not too high, the decision-making process is driven toward the highest quality option; (2) this effect can be improved increasing the number of informed agents that can counteract the effect of adverse zealots; (3) when the two options have very similar qualities, in order to keep high consensus to the best quality it is necessary to have higher proportions of informed agents

Shock Profiles for the Asymmetric Simple Exclusion Process in One Dimension

The asymmetric simple exclusion process (ASEP) on a one-dimensional lattice is a system of particles which jump at rates $p$ and $1-p$ (here $p>1/2$) to adjacent empty sites on their right and left respectively. The system is described on suitable macroscopic spatial and temporal scales by the inviscid Burgers' equation; the latter has shock solutions with a discontinuous jump from left density $\rho_-$ to right density $\rho_+$, $\rho_-<\rho_+$, which travel with velocity $(2p-1)(1-\rho_+-\rho_-)$. In the microscopic system we may track the shock position by introducing a second class particle, which is attracted to and travels with the shock. In this paper we obtain the time invariant measure for this shock solution in the ASEP, as seen from such a particle. The mean density at lattice site $n$, measured from this particle, approaches $\rho_{\pm}$ at an exponential rate as $n\to\pm\infty$, with a characteristic length which becomes independent of $p$ when $p/(1-p)>\sqrt{\rho_+(1-\rho_-)/\rho_-(1-\rho_+)}$. For a special value of the asymmetry, given by $p/(1-p)=\rho_+(1-\rho_-)/\rho_-(1-\rho_+)$, the measure is Bernoulli, with density $\rho_-$ on the left and $\rho_+$ on the right. In the weakly asymmetric limit, $2p-1\to0$, the microscopic width of the shock diverges as $(2p-1)^{-1}$. The stationary measure is then essentially a superposition of Bernoulli measures, corresponding to a convolution of a density profile described by the viscous Burgers equation with a well-defined distribution for the location of the second class particle.Comment: 34 pages, LaTeX, 2 figures are included in the LaTeX file. Email: [email protected], [email protected], [email protected]

Phase Segregation Dynamics in Particle Systems with Long Range Interactions I: Macroscopic Limits

We present and discuss the derivation of a nonlinear non-local integro-differential equation for the macroscopic time evolution of the conserved order parameter of a binary alloy undergoing phase segregation. Our model is a d-dimensional lattice gas evolving via Kawasaki exchange dynamics, i.e. a (Poisson) nearest-neighbor exchange process, reversible with respect to the Gibbs measure for a Hamiltonian which includes both short range (local) and long range (nonlocal) interactions. A rigorous derivation is presented in the case in which there is no local interaction. In a subsequent paper (part II), we discuss the phase segregation phenomena in the model. In particular we argue that the phase boundary evolutions, arising as sharp interface limits of the family of equations derived in this paper, are the same as the ones obtained from the corresponding limits for the Cahn-Hilliard equation.Comment: amstex with macros (included in the file), tex twice, 20 page

Detailed study of the microwave emission of the supernova remnant 3C 396

We have observed the supernova remnant 3C~396 in the microwave region using the Parkes 64-m telescope. Observations have been made at 8.4 GHz, 13.5 GHz, and 18.6 GHz and in polarisation at 21.5 GHz. We have used data from several other observatories, including previously unpublished observations performed by the Green Bank Telescope at 31.2 GHz, to investigate the nature of the microwave emission of 3C 396. Results show a spectral energy distribution dominated by a single component power law emission with $\alpha=(-0.364 \pm 0.017)$. Data do not favour the presence of anomalous microwave emission coming from the source. Polarised emission at 21.5 GHz is consistent with synchrotron-dominated emission. We present microwave maps and correlate them with infrared (IR) maps in order to characterise the interplay between thermal dust and microwave emission. IR vs. microwave TT plots reveal poor correlation between mid-infrared and microwave emission from the core of the source. On the other hand, a correlation is detected in the tail emission of the outer shell of 3C 396, which could be ascribed to Galactic contamination.Comment: published in MNRA

YORP and Yarkovsky effects in asteroids (1685) Toro, (2100) Ra-Shalom, (3103) Eger, and (161989) Cacus

The rotation states of small asteroids are affected by a net torque arising from an anisotropic sunlight reflection and thermal radiation from the asteroids' surfaces. On long timescales, this so-called YORP effect can change asteroid spin directions and their rotation periods. We analyzed lightcurves of four selected near-Earth asteroids with the aim of detecting secular changes in their rotation rates that are caused by YORP. We use the lightcurve inversion method to model the observed lightcurves and include the change in the rotation rate $\mathrm{d} \omega / \mathrm{d} t$ as a free parameter of optimization. We collected more than 70 new lightcurves. For asteroids Toro and Cacus, we used thermal infrared data from the WISE spacecraft and estimated their size and thermal inertia. We also used the currently available optical and radar astrometry of Toro, Ra-Shalom, and Cacus to infer the Yarkovsky effect. We detected a YORP acceleration of $\mathrm{d}\omega / \mathrm{d} t = (1.9 \pm 0.3) \times 10^{-8}\,\mathrm{rad}\,\mathrm{d}^{-2}$ for asteroid Cacus. For Toro, we have a tentative ($2\sigma$) detection of YORP from a significant improvement of the lightcurve fit for a nonzero value of $\mathrm{d}\omega / \mathrm{d} t = 3.0 \times 10^{-9}\,\mathrm{rad}\,\mathrm{d}^{-2}$. For asteroid Eger, we confirmed the previously published YORP detection with more data and updated the YORP value to $(1.1 \pm 0.5) \times 10^{-8}\,\mathrm{rad}\,\mathrm{d}^{-2}$. We also updated the shape model of asteroid Ra-Shalom and put an upper limit for the change of the rotation rate to $|\mathrm{d}\omega / \mathrm{d} t| \lesssim 1.5 \times 10^{-8}\,\mathrm{rad}\,\mathrm{d}^{-2}$. Ra-Shalom has a greater than $3\sigma$ Yarkovsky detection with a theoretical value consistent with observations assuming its size and/or density is slightly larger than the nominally expected values

Influence of temperature on the quality factors of shredded carrots

A mathematical model was developed in order to describe the effect of temperature on the degradation process of shredded carrots. Shredded carrots were stored in an air flux system in the range of temperature 0 degrees-20 degrees C. Storage time varied with temperature to observe the complete decay of pH and colour over time. The experimental data collected at 10 degrees C were used to validate the model. The evolution of the pH over time was reasonably well describes by a Weibull equation, while a first order equation described the colour change. The rate constants of both models varied with temperature according to an Arrhenius - type relationship with activation energy equal to 71 +/- 2 KJ/mol for the pH, and 89 +/- 5 KJ/mol for the colour