Regular coordinate systems for Schwarzschild and other spherical spacetimes

The continuation of the Schwarzschild metric across the event horizon is almost always (in textbooks) carried out using the Kruskal-Szekeres coordinates, in terms of which the areal radius r is defined only implicitly. We argue that from a pedagogical point of view, using these coordinates comes with several drawbacks, and we advocate the use of simpler, but equally effective, coordinate systems. One such system, introduced by Painleve and Gullstrand in the 1920's, is especially simple and pedagogically powerful; it is, however, still poorly known today. One of our purposes here is therefore to popularize these coordinates. Our other purpose is to provide generalizations to the Painleve-Gullstrand coordinates, first within the specific context of Schwarzschild spacetime, and then in the context of more general spherical spacetimes.Comment: 5 pages, 2 figures, ReVTeX; minor changes were made, new references were include

Healthcare Gaps in Migrant Farmer Populations

Various healthcare gaps have been identified in migrant farmer population, including preventative care, continuity of care for chronic conditions, occupational hazards and work related injury, and mental health services. Barriers to accessing care include lack of transportation, non-English speaking populations, and lack of education regarding US healthcare systems. For this project, flu vaccines were provided to migrant farmers at their homes throughout Vermont. Over 250 vaccines were provided by the Vermont Department of Health. Future directions include annual mobile flu clinics, continuing this model for Covid vaccines, and implementing a global health course for fourth year medical students aimed at addressing migrant farmer healthcare needs.https://scholarworks.uvm.edu/fmclerk/1696/thumbnail.jp

Stable self-similar blow-up dynamics for slightly L2L^2-supercritical generalized KdV equations

In this paper we consider the slightly $L^2$-supercritical gKdV equations $\partial_t u+(u_{xx}+u|u|^{p-1})_x=0$, with the nonlinearity $5<p<5+\varepsilon$ and $0<\varepsilon\ll 1$ . We will prove the existence and stability of a blow-up dynamic with self-similar blow-up rate in the energy space $H^1$ and give a specific description of the formation of the singularity near the blow-up time.Comment: 38 page

Effects of soil insecticide treatments on northern corn rootworm, Diabrotica barberi [Coleoptera : Chrysomelidae] populations and on corn yield

Durant 3 ans, des essais au champ ont permis d'evaluer les effets de trois insecticides appliqués au sol lors des semis sur les populations de la chrysomèle des racines du maïs (Diabrotica barberi). Dans chacune des parcelles, une cage d'émergence a été placée au-dessus d'un plant de maïs (Zea mays) et les populations d'adultes ont été suivies hebdomadairement. Les dommages faits par les larves aux racines de maïs ont été évalués et le rendement en grains a été déterminé à la fin de la saison de croissance des plantes. Les traitements insecticides ont réduit significativement le nombre d'adultes émergeant durant la première année seulement. La force d'arrachage était reliée négativement au nombre d'adultes émergeant par plant. Chaque année le rendement en grains des parcelles traitées n'était pas significativement différent de celui des parcelles non traitées. Les traitements insecticides peuvent donc réduire le nombre d'adultes émergeant sans toutefois augmenter les rendements.A 3-yr field study was conducted to determine the effects of three soil applied insecticides on northern corn rootworm (Diabrotica barberi) populations. In each plot, an emergence cage was placed over a corn (Zea mays) plant, and adult populations were monitored weekly. Larval damage to corn roots was evaluated and corn yield was recorded at the end of the growing season. Insecticide treatments significantly reduced the number of emerging adults in the first yr, but no difference was observed in the following yr. Root strength was negatively correlated to the number of emerging adults per plant. Each yr, corn yields in treated plots did not differ significantly from yield in untreated plots, which suggests that insecticide treatments can reduce the number of emerging adults without increasing yields

Giacobini-Zinner comet: Polarimetric and physical observations

The results of observations of the Giacobini-Zinner comet on 25 and 31 October 1959 are presented. The magnitude of the comet was measured photoelectrically in two spectral regions. The radius is on the order of one kilometer. The photoelectric measurements of comets 1959b and 1957c were used to measure the abundances of the CN and C2 radicals and of solid particles in the heads

Dynamics of a hyperbolic system that applies at the onset of the oscillatory instability

A real hyperbolic system is considered that applies near the onset of the oscillatory instability in large spatial domains. The validity of that system requires that some intermediate scales (large compared with the basic wavelength of the unstable modes but small compared with the size of the system) remain inhibited; that condition is analysed in some detail. The dynamics associated with the hyperbolic system is fully analysed to conclude that it is very simple if the coefficient of the cross-nonlinearity is such that , while the system exhibits increasing complexity (including period-doubling sequences, quasiperiodic transitions, crises) as the bifurcation parameter grows if ; if then the system behaves subcritically. Our results are seen to compare well, both qualitatively and quantitatively, with the experimentally obtained ones for the oscillatory instability of straight rolls in pure Rayleigh - Bénard convection

Adaptive motor control and learning in a spiking neural network realised on a mixed-signal neuromorphic processor

Neuromorphic computing is a new paradigm for design of both the computing hardware and algorithms inspired by biological neural networks. The event-based nature and the inherent parallelism make neuromorphic computing a promising paradigm for building efficient neural network based architectures for control of fast and agile robots. In this paper, we present a spiking neural network architecture that uses sensory feedback to control rotational velocity of a robotic vehicle. When the velocity reaches the target value, the mapping from the target velocity of the vehicle to the correct motor command, both represented in the spiking neural network on the neuromorphic device, is autonomously stored on the device using on-chip plastic synaptic weights. We validate the controller using a wheel motor of a miniature mobile vehicle and inertia measurement unit as the sensory feedback and demonstrate online learning of a simple 'inverse model' in a two-layer spiking neural network on the neuromorphic chip. The prototype neuromorphic device that features 256 spiking neurons allows us to realise a simple proof of concept architecture for the purely neuromorphic motor control and learning. The architecture can be easily scaled-up if a larger neuromorphic device is available.Comment: 6+1 pages, 4 figures, will appear in one of the Robotics conference

Gravitational perturbations of the Schwarzschild spacetime: A practical covariant and gauge-invariant formalism

We present a formalism to study the metric perturbations of the Schwarzschild spacetime. The formalism is gauge invariant, and it is also covariant under two-dimensional coordinate transformations that leave the angular coordinates unchanged. The formalism is applied to the typical problem of calculating the gravitational waves produced by material sources moving in the Schwarzschild spacetime. We examine the radiation escaping to future null infinity as well as the radiation crossing the event horizon. The waveforms, the energy radiated, and the angular-momentum radiated can all be expressed in terms of two gauge-invariant scalar functions that satisfy one-dimensional wave equations. The first is the Zerilli-Moncrief function, which satisfies the Zerilli equation, and which represents the even-parity sector of the perturbation. The second is the Cunningham-Price-Moncrief function, which satisfies the Regge-Wheeler equation, and which represents the odd-parity sector of the perturbation. The covariant forms of these wave equations are presented here, complete with covariant source terms that are derived from the stress-energy tensor of the matter responsible for the perturbation. Our presentation of the formalism is concluded with a separate examination of the monopole and dipole components of the metric perturbation.Comment: 21 page

Experimental study of a liquid Xenon PET prototype module

A detector using liquid Xenon in the scintillation mode is studied for Positron Emission Tomography (PET). The specific design aims at taking full advantage of the liquid Xenon properties. It does feature a promising insensitive to any parallax effect. This work reports on the performances of the first LXe prototype module, equipped with a position sensitive PMT operating in the VUV range (178 nm).Comment: Proc. of the 7th International Workshops on Radiation Imaging Detectors (IWORID-7), Grenoble, France 4-7 July 200

Note on flat foliations of spherically symmetric spacetimes

It is known that spherically symmetric spacetimes admit flat spacelike foliations. We point out a simple method of seeing this result via the Hamiltonian constraints of general relativity. The method yields explicit formulas for the extrinsic curvatures of the slicings.Comment: 4 pages, to appear in PRD, reference added, typos correcte