A Tandem Fluid Network with L\'evy Input in Heavy Traffic

In this paper we study the stationary workload distribution of a fluid tandem queue in heavy traffic. We consider different types of L\'evy input, covering compound Poisson, $\alpha$-stable L\'evy motion (with $1<\alpha<2$), and Brownian motion. In our analysis we separately deal with L\'evy input processes with increments that have finite and infinite variance. A distinguishing feature of this paper is that we do not only consider the usual heavy-traffic regime, in which the load at one of the nodes goes to unity, but also a regime in which we simultaneously let the load of both servers tend to one, which, as it turns out, leads to entirely different heavy-traffic asymptotics. Numerical experiments indicate that under specific conditions the resulting simultaneous heavy-traffic approximation significantly outperforms the usual heavy-traffic approximation

Heterogeneous chemistry related to Antarctic ozone depletion: Reaction of ClONO2 and N2O5 on ice surfaces

Laboratory studies of heterogeneous reactions of possible importance for Antarctic ozone depletion were performed. In particular, the reactions of chlorine nitrate (ClONO2) and dinitrogen pentoxide (N2O5) were investigated on ice and HCl/ice surfaces. These reactions occur on the surfaces of polar stratospheric clouds (PSCs) over Antarctica. One reaction transforms the stable chlorine reservoir species (ClONO2 and HCl) into photochemically active chlorine in the form of HOCl and Cl2. Condensation of HNO3 in the reactions removes odd nitrogen from the stratosphere, a requirement in nearly all models of Antarctic ozone depletion. Other reactions may also be important for Antarctic ozone depletion. Like the reactions of chlorine nitrate, these reactions deplete odd nitrogen through HNO3 condensation. In addition, one reaction converts a stable chlorine reservior species (HCl) into photochemically active chlorine (ClNO2). These reactions were studied with a modified version of a Knudsen cell flow reactor

Coarse-grained simulation of amphiphilic self-assembly

We present a computer simulation study of amphiphilic self assembly performed using a computationally efficient single-site model based on Gay-Berne and Lennard-Jones particles. Molecular dynamics simulations of these systems show that free self-assembly of micellar, bilayer and inverse micelle arrangements can be readily achieved for a single model parameterisation. This self-assembly is predominantly driven by the anisotropy of the amphiphile-solvent interaction, amphiphile-amphiphile interactions being found to be of secondary importance. While amphiphile concentration is the main determinant of phase stability, molecular parameters such as headgroup size and interaction strength also have measurable affects on system properties. </p

Thermoluminescence Dating of Late Pleistocene Sediments, St. Lawrence Lowland, Québec

This paper presents the results of a thermoluminescence (TL) dating program applied to waterlaid sediments of Late Pleistocene age, collected in the central St. Lawrence Lowland, in eastern Canada. The apparent TL ages were obtained using a partial bleach method (R-Gamma) in which the TL from light-sensitive traps is separated from the total TL. Fluvial (modern), marine (late-glacial) lacustrine (interstadial) and glacio-lacustrine (stadial) sediments yielded apparent ages ranging from 4 to 135 ka, and in general, these ages agreed with available stratigraphic evidence. Whilst testing the zeroing assumption, apparent TL ages obtained from modern fluvial and late glacial sediments suggest that laboratory overbleaching or insufficient natural bleaching may result in over-estimation of the apparent TL ages by 4-5 ka. All samples display anomalous fading, a problem that can be overcome by introducing a three month delay between artificial irradiation and glowing. Future research should focus on sediments for which the age as well as the sedimentology are well documented, such as the late glacial Champlain Sea sediments.Cet article présente les résultats d'un projet de datation par thermoluminescence (TL) de sédiments des basses terres du Saint-Laurent datant du Pléistocène supérieur. Les âges TL apparents ont été obtenus en utilisant une méthode de lessivage partiel (R-Gamma) par laquelle la TL émanant de pièges cristallins sensibles à la lumière a pu être séparée de la TL totale. Les sédiments, d'origines fluviatile (modernes), marine (tardiglaciaires), lacustre (interstadiaires) et glaciolacustre (stadiaires) ont livré des âges entre 4 et 135 ka et, erï général, les âges obtenus correspondent aux données stratigraphiques. Des expériences menées sur le phénomène de « remise à zéro » ont été menées sur des sédiments fluviatiles modernes et marins tardiglaciaires. Elles démontrent que, dans les cas où le lessivage solaire a pu être insuffisant ou le lessivage simulé en laboratoire trop intense, les âges TL apparents peuvent être surestimés de 4 à 5 ka. Tous les échantillons montrent un affaiblissement anormal du signal de thermoluminescence. Ce problème peut être résolu par l'introduction d'un délai de trois mois entre l'irradiation artificielle et la mesure de l'échantillon. À l'avenir la recherche devrait se faire sur des sédiments dont la chronologie et la sédimentologie sont bien connues, tels les sédiments tardiglaciaires champlainiens.Dieser Artikel stellt die Ergebnisse eines Datierungsprojekts mittles Thermoluminiszenz (TL) dar, angewandt auf angeschwemmte Sedimente aus dem spaten Pleistozàn, die in Ostkanada, in der zentralen Sankt-Lorenz Tiefebene gesammelt wurden. Die offensichtlichen TL-Alter wurden mittels einer partiellen Bleichmethode (R-Gamma) gewonnen, in welcher die TL der lichtempfindlichen Fallen von der totalen TL getrennt wurde. Die Sedimente von FIuB (modem), Meer (Spâtglazial), See (Interstadial) und Glazio-See (Stadial) lieferten offensichtliche Alter zwischen 4 bis 135 ka, und im allgemeinene stimmten dièse Alter mit den verfùgbaren stratigraphischen Zeugnissen ùberein. Wohingegen beim Testen mittels der 'NuII-Annahme' die offensichtlichen TL-Alter, die aus modernen FluBsedimenten und spaten glazialen Sedimenten gewonnen wurden, vermuten lassen, daB zu intensives Bleichen im Labor oder ungenùgendes Bleichen in der Natur zu einer Ùberschàtzung der offensichtlichen TL-Alter von 4 bis 5 ka fuhren. Allé Proben weisen eine anormale Abschwâchung des TL-Signals auf. Dies Problem kann durch die Einfùhrung eines Aufschubs von drei Monaten zwischen der kùnstlichen Bestrahlung und dem Messen der Probe gelôstwerden. Die kùnftige Forschung sollte sich auf Sedimente konzentrieren, deren Alter als auch Sédimentologie gut dokumentiert sind, wie z.B. die spàtglazialenChamplain-Meer-Sedimente

Another derivation of the geometrical KPZ relations

We give a physicist's derivation of the geometrical (in the spirit of Duplantier-Sheffield) KPZ relations, via heat kernel methods. It gives a covariant way to define neighborhoods of fractals in 2d quantum gravity, and shows that these relations are in the realm of conformal field theory

Motor Vehicle Accidents: The Most Common Cause of Traumatic Vertebrobasilar Ischemia

Background: Recent media exposure of strokes from chiropractic manipulation have focused attention on traumatic vertebrobasilar ischemia. However, chiropractic manipulation, while the easiest cause to recognize, is probably not the most common cause of this condition. Methods: We reviewed all consecutive cases of traumatic vertebrobasilar ischemia referred to a single neurovascular practice over 20 years, from the office files and hospital records. Results: There were 80 patients whose vertebrobasilar ischemia was attributed to neck trauma. Five were diagnosed as due to chiropractic manipulation, but the commonest attributed cause was motor vehicle accidents (MVAs), which accounted for 70 cases; one was a sports injury, and five were industrial accidents. In some cases neck pain from an MVA led to chiropractic manipulation, so the cause may have been compounded. In most vehicular cases the diagnosis had been missed, even denied, by the neurologists and neurosurgeons initially involved. The longest delay between the injury and the onset of delayed symptoms was five years. Conclusions: Traumatic vertebrobasilar ischemia is most often due to MVAs; the diagnosis is often missed, in part because of the delay between injury and onset of symptoms and, in part, we hypothesize, because of reluctance of doctors to be involved in medicolegal cases

Steady steps versus sudden shifts: Cooperation in (a)symmetric linear and step-level social dilemmas

Are groups of people better able to minimize a collective loss if there is a collective target that must be reached or if every small contribution helps? In this paper we investigate whether cooperation in social dilemmas can be increased by structuring the problem as a step-level social dilemma rather than a linear social dilemma and whether cooperation can be increased by manipulating endowment asymmetry between individuals. In two laboratory experiments using 'Public Bad' games, we found that that individuals defect less and are better able to minimize collective and personal costs in a step-level social dilemma than in a linear social dilemma. We found that the level of cooperation is not affected by an ambiguous threshold: even when participants cannot be sure about the optimal cooperation level, cooperation remains high in the step-level social dilemmas. We find mixed results for the effect of asymmetry on cooperation. These results imply that presenting social dilemmas as step-level games and reducing asymmetry can help solve environmental dilemmas in the long term

Exact averages of central values of triple product L-functions

We obtain exact formulas for central values of triple product L-functions averaged over newforms of weight 2 and prime level. We apply these formulas to non-vanishing problems. This paper uses a period formula for the triple product L-function proved by Gross and Kudla

Electric-field tuning of the valley splitting in silicon corner dots

We perform an excited state spectroscopy analysis of a silicon corner dot in a nanowire field-effect transistor to assess the electric field tunability of the valley splitting. First, we demonstrate a back-gate-controlled transition between a single quantum dot and a double quantum dot in parallel that allows tuning the device in to corner dot formation. We find a linear dependence of the valley splitting on back-gate voltage, from $880~\mu \text{eV}$ to $610~\mu \text{eV}$ with a slope of $-45\pm 3~\mu \text{eV/V}$ (or equivalently a slope of $-48\pm 3~\mu \text{eV/(MV/m)}$ with respect to the effective field). The experimental results are backed up by tight-binding simulations that include the effect of surface roughness, remote charges in the gate stack and discrete dopants in the channel. Our results demonstrate a way to electrically tune the valley splitting in silicon-on-insulator-based quantum dots, a requirement to achieve all-electrical manipulation of silicon spin qubits.Comment: 5 pages, 3 figures. In this version: Discussion of model expanded; Fig. 3 updated; Refs. added (15, 22, 32, 34, 35, 36, 37