Ionization heating in rare-gas clusters under intense XUV laser pulses

The interaction of intense extreme ultraviolet (XUV) laser pulses ($\lambda=32\rm\,nm$, $I=10^{11-14}$\,W/cm$^2$) with small rare-gas clusters (Ar$_{147}$) is studied by quasi-classical molecular dynamics simulations. Our analysis supports a very general picture of the charging and heating dynamics in finite samples under short-wavelength radiation that is of relevance for several applications of free-electron lasers. First, up to a certain photon flux, ionization proceeds as a series of direct photoemission events producing a jellium-like cluster potential and a characteristic plateau in the photoelectron spectrum as observed in [Bostedt {\it et al.}, Phys. Rev. Lett. {\bf 100}, 013401 (2008)]. Second, beyond the onset of photoelectron trapping, nanoplasma formation leads to evaporative electron emission with a characteristic thermal tail in the electron spectrum. A detailed analysis of this transition is presented. Third, in contrast to the behavior in the infrared or low vacuum ultraviolet range, the nanoplasma energy capture proceeds via {\it ionization heating}, i.e., inner photoionization of localized electrons, whereas collisional heating of conduction electrons is negligible up to high laser intensities. A direct consequence of the latter is a surprising evolution of the mean energy of emitted electrons as function of laser intensity.Comment: figure problems resolve

Coefficient of tangential restitution for the linear dashpot model

The linear dashpot model for the inelastic normal force between colliding spheres leads to a constant coefficient of normal restitution, $\epsilon_n=$const., which makes this model very popular for the investigation of dilute and moderately dense granular systems. For two frequently used models for the tangential interaction force we determine the coefficient of tangential restitution $\epsilon_t$, both analytically and by numerical integration of Newton's equation. Although $\epsilon_n=$const. for the linear-dashpot model, we obtain pronounced and characteristic dependencies of the tangential coefficient on the impact velocity $\epsilon_t=\epsilon_t(\vec{g})$. The results may be used for event-driven simulations of granular systems of frictional particles.Comment: 12 pages, 12 figure

Expansion and Collapse in the Cosmic Web

We study the kinematics of the gaseous cosmic web at high redshift with Lyman alpha forest absorption in multiple QSO sightlines. Using a simple analytic model and a cosmological hydrodynamic simulation we constrain the underlying three-dimensional distribution of velocities from the observed line-of-sight distribution of velocity shear across the plane of the sky. The distribution is found to be in good agreement with the intergalactic medium (IGM) undergoing large scale motions dominated by the Hubble flow. Modeling the Lyman alpha clouds analytically and with a hydrodynamics simulation, the average expansion velocity of the gaseous structures causing the Lyman alpha forest in the lower redshift (z = 2) sample appears about 20 percent lower than the local Hubble expansion velocity. We interpret this as tentative evidence for some clouds undergoing gravitational collapse. However, the distribution of velocities is highly skewed, and the majority of clouds at redshifts from 2 to 3.8 expand typically about 5 - 20 percent faster than the Hubble flow. This behavior is explained if most absorbers in the column density range typically detectable are expanding filaments that stretch and drain into more massive nodes. We find no evidence for the observed distribution of velocity shear being significantly influenced by processes other than Hubble expansion and gravitational instability, like galactic winds. To avoid overly disturbing the IGM, winds may be old and/or limp by the time we observe them in the Lyman alpha forest, or they may occupy only an insignificant volume fraction of the IGM. (abridged)Comment: 63 pages, 26 figures, AAS Latex; ApJ, in pres

A Framework for Intranet-Based Information Systems (I-BIS) Applications

A recent survey of business executives showed that of 169 decision makers who responded to a survey by the Business Research Group, over fifty percent have either already implemented an internal web site or are in the process of developing such a site (Engler, 1996). These results were similar to those reported in InformationWeek, which showed that 49% of those firms responding to the survey already had direct Internet access for their employees. According to this same survey, this figure is expected to increase to 67% of these same firms by the spring of 1997 with another 10% of the firms testing the viability of such a connectivity policy (Yankelovich, 1996). Gantz (1986) reported that the microcomputer had achieved the same level of penetration into the corporate world (in terms of the percentage of employees with desktop access) in ten years that the telephone required 75 years to achieve. With these systems increasingly tied together in local or wide area networks, it is likely that a comparable level of penetration of Intranet-Based Information System (I-BIS) will occur in an even shorter time span. The rapid proliferation of network communication technology points to a need to measure how and where these systems are being implemented, and what results are being achieved. Recently published reports concerning Intranet-Based Information Systems (I-BIS) have cited return on investment values exceeding 1300% and direct payback time periods of six to twelve weeks (Campbell, 1996). While these systems have already been widely accepted and implemented, scant attention has been paid to rigorous research in relation to users\u27 acceptance and utilization of these systems or the perceived quality of these system

How to Find More Supernovae with Less Work: Object Classification Techniques for Difference Imaging

We present the results of applying new object classification techniques to difference images in the context of the Nearby Supernova Factory supernova search. Most current supernova searches subtract reference images from new images, identify objects in these difference images, and apply simple threshold cuts on parameters such as statistical significance, shape, and motion to reject objects such as cosmic rays, asteroids, and subtraction artifacts. Although most static objects subtract cleanly, even a very low false positive detection rate can lead to hundreds of non-supernova candidates which must be vetted by human inspection before triggering additional followup. In comparison to simple threshold cuts, more sophisticated methods such as Boosted Decision Trees, Random Forests, and Support Vector Machines provide dramatically better object discrimination. At the Nearby Supernova Factory, we reduced the number of non-supernova candidates by a factor of 10 while increasing our supernova identification efficiency. Methods such as these will be crucial for maintaining a reasonable false positive rate in the automated transient alert pipelines of upcoming projects such as PanSTARRS and LSST.Comment: 25 pages; 6 figures; submitted to Ap

Chiral sedimentation of extended objects in viscous media

We study theoretically the chirality of a generic rigid object's sedimentation in a fluid under gravity in the low Reynolds number regime. We represent the object as a collection of small Stokes spheres or stokeslets, and the gravitational force as a constant point force applied at an arbitrary point of the object. For a generic configuration of stokeslets and forcing point, the motion takes a simple form in the nearly free draining limit where the stokeslet radius is arbitrarily small. In this case, the internal hydrodynamic interactions between stokeslets are weak, and the object follows a helical path while rotating at a constant angular velocity $\omega$ about a fixed axis. This $\omega$ is independent of initial orientation, and thus constitutes a chiral response for the object. Even though there can be no such chiral response in the absence of hydrodynamic interactions between the stokeslets, the angular velocity obtains a fixed, nonzero limit as the stokeslet radius approaches zero. We characterize empirically how $\omega$ depends on the placement of the stokeslets, concentrating on three-stokeslet objects with the external force applied far from the stokeslets. Objects with the largest $\omega$ are aligned along the forcing direction. In this case, the limiting $\omega$ varies as the inverse square of the minimum distance between stokeslets. We illustrate the prevalence of this robust chiral motion with experiments on small macroscopic objects of arbitrary shape.Comment: 35 pages, 10 figures; Section VII.A redone and other edits made for clarity. Accepted by Phys. Rev.

Spatiotemporal Distribution of Waterfowl Disease Outbreaks in Kansas, USA

Causes and impacts of disease outbreaks in wild bird populations are rarely studied beyond documentation of large epizootic events. In Kansas, USA, a central disease surveillance and reporting protocol currently does not exist within the Kansas Department of Wildlife, Parks and Tourism, which has led to a lack of available knowledge of disease occurrences that could be used to predict and manage future outbreaks. We compiled historic records of documented waterbird disease outbreaks in Kansas from 1967–2014 and related the frequency of outbreaks with light geese (Ross’s goose [Anser rossii]; Snow goose [A. caerulescens]) populations from 1970–2014. We found 32 reports across 16 counties that documented various outbreaks of avian cholera, avian botulism, aspergillosis, renal coccidiosis, West Nile, aflatoxicosis, and mycotoxicosis across multiple waterbird taxa. Avian cholera and avian botulism represented nearly 70% of documented disease outbreaks. Frequency of disease outbreaks increased across the time period with a positive relationship between annual Midwinter Waterfowl Survey counts of light geese and number of reported of avian cholera outbreaks in Kansas. Changes in the continental abundance and distribution of light geese has resulted in increasing residence times in Kansas during winter, potentially increasing risk and severity of avian cholera outbreaks. Disease mitigation efforts by the Kansas Department of Wildlife, Parks and Tourism (KDWPT) should strategically plan for future avian disease outbreaks

Spatiotemporal Distribution of Waterfowl Disease Outbreaks in Kansas, USA

Causes and impacts of disease outbreaks in wild bird populations are rarely studied beyond documentation of large epizootic events. In Kansas, USA, a central disease surveillance and reporting protocol currently does not exist within the Kansas Department of Wildlife, Parks and Tourism, which has led to a lack of available knowledge of disease occurrences that could be used to predict and manage future outbreaks. We compiled historic records of documented waterbird disease outbreaks in Kansas from 1967–2014 and related the frequency of outbreaks with light geese (Ross’s goose [Anser rossii]; Snow goose [A. caerulescens]) populations from 1970–2014. We found 32 reports across 16 counties that documented various outbreaks of avian cholera, avian botulism, aspergillosis, renal coccidiosis, West Nile, aflatoxicosis, and mycotoxicosis across multiple waterbird taxa. Avian cholera and avian botulism represented nearly 70% of documented disease outbreaks. Frequency of disease outbreaks increased across the time period with a positive relationship between annual Midwinter Waterfowl Survey counts of light geese and number of reported of avian cholera outbreaks in Kansas. Changes in the continental abundance and distribution of light geese has resulted in increasing residence times in Kansas during winter, potentially increasing risk and severity of avian cholera outbreaks. Disease mitigation efforts by the Kansas Department of Wildlife, Parks and Tourism (KDWPT) should strategically plan for future avian disease outbreaks

Quaternary Stratigraphy in Northwestern Maine: A Progress Report

A preliminary Quaternary stratigraphy for northwestern Maine can be assembled from interpretation of ice-flow indicators (dispersal and erosional), exposed sections, and drill-hole logs. Evidence from the ice-flow indicators delineates at least four regions each with different ice-flow histories. The distribution of these regions may result from an eastward invasion of Laurentide source ice during the early portion of the late Wisconsinan and subsequent development of a local ice dome during the closing portion of the Late Wisconsinan substage. Exposed sections contribute the following probable sequence of events to the stratigraphy: 1) deposition of alluvial fans, 2) deposition of a gray compact till beneath eastward flowing (Laurentide) ice, 3) deposition of a brown till beneath northward flowing local ice, 4) deglaciation by a southward retreating ice margin. These events appear continuous and have all been provisionally assigned a Late Wisconsinan age. Drill-hole logs confirm the sequence derived from the exposed sections and allow extension of the Quaternary stratigraphy. The drill-log data show three associated groups of sediments that may in turn result from at least three separate ice margin advances and recessions. The uppermost group of sediments is correlated with those found in exposed sections. The position of the drill-hole logs in an over-deepened basin suggest erosion by at least one even earlier glaciation.À partir de l'interprétation des indicateurs de l'écoulement glaciaire (de dispersion et d'érosion), des coupes naturelles et des résultats des forages, on a tenté d'établir la stratigraphie préliminaire du Quaternaire pour le nord du Maine. Les renseignements tirés des indicateurs de l'écoulement glaciaire ont permis de circonscrire au moins quatre régions, chacune d'elles présentant un processus différent d'écoulement glaciaire. La répartition des régions est probablement le résultat de la progression vers l'est des glaces laurentidiennes au début du Wisconsinien supérieur et de la formation subséquente d'un dôme local à la fin du Wisconsinien supérieur. Les coupes naturelles ont permis de reconstituer la séquence d'événements suivante : 1 ) formation de cônes de déjection; 2) dépôt d'un till gris compact sous une des glaces laurentidiennes s'écoulant vers l'est; 3) dépôt d'un till brun sous les glaces locales s'écoulant vers le nord; 4) déglaciation résultant du retrait de la marge glaciaire vers le sud. Ces événements semblent s'être déroulés de façon continue; on les attribue du moins provisoirement au Wisconsinien supérieur. Les résultats des forages confirment la séquence reconstituée grâce aux coupes naturelles et permettent même de prolonger la stratigraphie du Quaternaire. Les données de forage démontrent la présence de trois groupes associés de sédiments qui, à leur tour, sont le résultat d'au moins trois récurrences et trois récessions de la marge glaciaire. Le groupe supérieur correspond aux sédiments observés dans les coupes. Les résultats de forage dans un bassin surcreusé laissont croire qu'au moins une glaciation antérieure y a laissé des traces d'érosion.Eine vorlàufige Stratigraphie fur Nord-West Maine im Quatemar kann durch Interpretation der Eis-FluB Indikatoren (Dispersion und Erosion), der natùrlichen Schnitte und der Bohrergebnisse erstellt werden. Durch die Eis-RuB Indikatoren ergeben sich mindestens vier Gebiete mit jeweils unterschiedlicher Eis-FluB Vergangenheit. Die Verteilung dieser Gebiete hat wohl ihren Ursprung im Eindringen von Laurentischem Quell-Eis in ôstlicher Richtung wàhrend des Beginns des spàten Wisconsin und der darauf folgenden Entwicklung eines lokalen Eis-Doms wàhrend der AbschluBphase des spâten Wisconsin. Die natùrlichen Schnitte ergeben die folgende môgliche Abfolge der Ereignisse fur die Stratigraphie; 1) Ablagerung von Alluvialkegeln, 2) Ablagerung eines grauen kompakten Tills unter ostwàrts flieBendem (Laurentischem) Eis, 3) Ablagerung eines braunen Tills unter nordwârts flieBendem lokalem Eis, 4) Enteisung durch die sùdwàrts zurùckweichende Eisgrenze. Dièse Ereignisse scheinen kontinuierlich abgelaufen zu sein und sind aile vorlàufig dem spâten Wisconsin zugeschrieben worden. Die Bohrergebnisse bestàtigen die aus den natùrlichen Schnitten gewonnene Abfolge und erlauben eine Ausdehnung der Stratigraphie des Quatemar. Die Bohrdaten zeigen drei Gruppen von Sedimenten, die ihrerseits ihren Ursprung in mindestens drei unterschiedlichen VorstoB- und Rùckzugs-Phasen der Eisgrenze haben. Die oberste Gruppe der Sedimente steht in Wechselbeziehung mit den in den natùrlichen Schnitten gefundenen Sedimenten. Bohrergebnissg in einom ùbGrtieften Becken lassen vermuten, daB zumindest eine frùhre Vereisung Erosionsspuren hinterlassen hat