On level crossings for a general class of piecewise-deterministic Markov processes

We consider a piecewise-deterministic Markov process governed by a jump intensity function, a rate function that determines the behaviour between jumps, and a stochastic kernel describing the conditional distribution of jump sizes. We study the point process of upcrossings of a level $b$ by the Markov process. Our main result shows that, under a suitable scaling $\nu(b)$, the point process converges, as $b$ tends to infinity, weakly to a geometrically compound Poisson process. We also prove a version of Rice's formula relating the stationary density of the process to level crossing intensities. This formula provides an interpretation of the scaling factor $\nu(b)$. While our proof of the limit theorem requires additional assumptions, Rice's formula holds whenever the (stationary) overall intensity of jumps is finite.Comment: 25 page

Optimization of nanostructured permalloy electrodes for a lateral hybrid spin-valve structure

Ferromagnetic electrodes of a lateral semiconductor-based spin-valve structure are designed to provide a maximum of spin-polarized injection current. A single-domain state in remanence is a prerequisite obtained by nanostructuring Permalloy thin film electrodes. Three regimes of aspect ratios $m$ are identified by room temperature magnetic force microscopy: (i) high-aspect ratios of $m \ge 20$ provide the favored remanent single-domain magnetization states, (ii) medium-aspect ratios $m \sim 3$ to $m \sim 20$ yield highly remanent states with closure domains and (iii) low-aspect ratios of $m \le 3$ lead to multi-domain structures. Lateral kinks, introduced to bridge the gap between micro- and macroscale, disturb the uniform magnetization of electrodes with high- and medium-aspect ratios. However, vertical flanks help to maintain a uniformly magnetized state at the ferromagnet-semiconcuctor contact by domain wall pinning.Comment: revised version, major structural changes, figures reorganized,6 pages, 8 figures, revte

Hemotropic mycoplasmas in little brown bats (Myotis lucifugus).

BackgroundHemotropic mycoplasmas are epicellular erythrocytic bacteria that can cause infectious anemia in some mammalian species. Worldwide, hemotropic mycoplasmas are emerging or re-emerging zoonotic pathogens potentially causing serious and significant health problems in wildlife. The objective of this study was to determine the molecular prevalence of hemotropic Mycoplasma species in little brown bats (Myotis lucifugus) with and without Pseudogymnoascus (Geomyces) destrucans, the causative agent of white nose syndrome (WNS) that causes significant mortality events in bats.MethodsIn order to establish the prevalence of hemotropic Mycoplasma species in a population of 68 little brown bats (Myotis lucifugus) with (n = 53) and without (n = 15) white-nose syndrome (WNS), PCR was performed targeting the 16S rRNA gene.ResultsThe overall prevalence of hemotropic Mycoplasmas in bats was 47%, with similar (p = 0.5725) prevalence between bats with WNS (49%) and without WNS (40%). 16S rDNA sequence analysis (~1,200 bp) supports the presence of a novel hemotropic Mycoplasma species with 91.75% sequence homology with Mycoplasma haemomuris. No differences were found in gene sequences generated from WNS and non-WNS animals.ConclusionsGene sequences generated from WNS and non-WNS animals suggest that little brown bats could serve as a natural reservoir for this potentially novel Mycoplasma species. Currently, there is minimal information about the prevalence, host-specificity, or the route of transmission of hemotropic Mycoplasma spp. among bats. Finally, the potential role of hemotropic Mycoplasma spp. as co-factors in the development of disease manifestations in bats, including WNS in Myotis lucifugus, remains to be elucidated

Palm pairs and the general mass-transport principle

We consider a lcsc group G acting properly on a Borel space S and measurably on an underlying sigma-finite measure space. Our first main result is a transport formula connecting the Palm pairs of jointly stationary random measures on S. A key (and new) technical result is a measurable disintegration of the Haar measure on G along the orbits. The second main result is an intrinsic characterization of the Palm pairs of a G-invariant random measure. We then proceed with deriving a general version of the mass-transport principle for possibly non-transitive and non-unimodular group operations first in a deterministic and then in its full probabilistic form.Comment: 26 page

Paleohydrology, Sedimentology, and Geochemistry of Two Meromictic Saline Lakes in Southern Saskatchewan

The Northern Great Plains of western Canada contain numerous saline and hypersaline lakes. Most of these lakes are shallow (< 3 m) and exhibit playa characteristics. Some, however, are relatively deep, permanent water bodies. The sediment records of these deep perennial saline lakes offer an excellent opportunity to evaluate key paleohydrologic and hydrochemical parameters. Variations in these parameters may, in turn, be interpreted with respect to climatic fluctuations in the region. Waldsea and Deadmoose lakes, located in south-central Saskatchewan, are both presently meromictic, with saline Mg-Na-SO4-CI waters overlying denser hypersaline brines of similar composition. The modern sediments of the lakes consist of a mixture of organic matter, finegrained detrital elastics (mainly clay minerals, carbonate minerals, quartz, and feldspars), and finely crystalline endogenic/authigenic precipitates (aragonite, gypsum, calcite, pyrite, and mirabilite). Variations in mineralogy and chemistry of sediment cores from the morphologically simple Waldsea basin show that the lake was much shallower and more saline about 4000 years ago. Although water levels have since generally increased in the basin giving rise to higher organic productivity and greater inorganic carbonate precipitation, there is also evidence of several hydrologie reversals during the last 2000 years. The stratigraphy preserved in nearby Deadmoose Lake is much more complex because of the irregular basin morphology. Lower water levels about 1000 years ago created several isolated but still relatively deep lakes in the Deadmoose basin.Les grandes plaines du nord de l'ouest du Canada contiennent de nombreux lacs salés et hypersalés. La plupart de ces lacs sont peu profonds (< 3 m) et offrent les caractéristiques des playas. D'autres, par contre, sont des plans d'eau permanents relativement profonds. Les données sédimentologiques de ces derniers permettent d'évaluer certains paramètres clés de paléohydrologie et d'hydrochimie. Les variations qu'offrent ces paramètres peuvent à leur tour être interprétées en fonction des fluctuations climatiques qu'a connues la région. Les lacs Waldsea et Deadmoose, dans le centre-sud de la Saskatchewan, sont méromictiques et leurs eaux composées de Mg-Na-So4-Cl recouvrent une saumure hypersaline plus dense, mais de composition semblable. Les sédiments actuels de ces lacs consistent en un mélange de matière organique, de roches détritiques à grains fins (surtout des minéraux argileux et carbonates ainsi que des quartz et des feldspaths) et de calcaires de précipitation cristallins à grains fins endogènes et authigènes (aragonite, gypse, calcite, pyrite et mirabilite). La minéralogie et la chimie des sédiments contenus dans les carottes recueillies dans le bassin du lac Waldsea, de morphologie simple, montrent des variations qui indiquent que le lac était beaucoup moins profond et plus salé il y a 4000 ans. Bien que, de façon générale, les niveaux lacustres se soient haussés depuis, ce qui a donné lieu à une production accrue de matière organique et à une plus forte précipitation des carbonates inorganiques, on trouve les témoins de plusieurs inversions de nature hydrologique depuis les 2000 dernières années. Non loin, au lac Deadmoose, la stratigraphie est beaucoup plus complexe en raison de la morphologie irrégulière du bassin. Il y a 1000 ans environ, les bas niveaux lacustres ont été à l'origine de la formation de plusieurs lacs isolés et relativement profonds dans le bassin Deadmoose.den nôrdlichen groBen Ebenen von West-Kanada gibt es zahlreiche salzhaltige und hypersalzhaltige Seen. Die meisten dieser Seen sind seicht (< 3 m) und zeigen Pfannen Charakteristika. Einige hingegen sind relativ tiefe permanente Wasserspiegel. Die Sediment-Belege dieser tiefen, bestândigen Salz-Seen bieten eine ausgezeichnete Gelegenheit, die paleohydrologischen und hydrochemischen Schlùssel-Parameter zu bewerten. Variationen dieser Parameter kônnen ihrerseits interpretiert werden in Bezug auf die klimatischen Fluktuationen in dieser Region. Die Seen Waldsea und Deadmoose, die im sùdlichen Zentrum von Saskatchewan liegen, sind gegenwârtig beide meromiktisch, mit salinen Mg-Na-SO4-Cl Wassern, welche dichtere, hypersaline Salzlaken âhnlicher Zusammensetzung ùberlagern. Die gegenwàrtigen Sedimente dieser Seen bestehen aus einer Mischung von organischem Material, feinkôrnigen Trùmmergesteinen (hauptsàchlich Lehm-Minerale, Karbonat-Minerale, Quartz und Feldspate), und fein kristallinen endogenen/ authigenen Niederschlàgen (Aragonit, Gipsstein, Kalkspat, Pyrit und Mirabilit). Variationen in der Minéralogie und Chemie der Sediment-Keme von dem morphologisch einfachen Waldsea-Becken zeigen, dafî der See vor etwa 4000 Jahren viel seichter und saliner war. Obwohl die Wasserspiegel seitdem im Allgemeinen in dem Becken angestiegen sind, was zu hôherer organischer Produktivitàt und vestârktem inorganischem Karbonat-Niederschlag fùhrte, findet man auch Belege fur einige hydrologische Umschwùnge wâhrend der letzten 2000 Jahre. Die im nahegelegenen Deadmoose-See erhaltene Stratigraphie ist viel komplexer auf Grund der unregelmàfîigen Morphologie des Beckens. Niedrigere Wasserspiegel vor ungefâhr 1000 Jahren fùhrten zu einigen isolierten, aber immer noch relativ tiefen Seen im Deadmoose-Becken

Suppressed spin dephasing for 2D and bulk electrons in GaAs wires due to engineered cancellation of spin-orbit interaction terms

We report a study of suppressed spin dephasing for quasi-one-dimensional electron ensembles in wires etched into a GaAs/AlGaAs heterojunction system. Time-resolved Kerr-rotation measurements show a suppression that is most pronounced for wires along the [110] crystal direction. This is the fingerprint of a suppression that is enhanced due to a strong anisotropy in spin-orbit fields that can occur when the Rashba and Dresselhaus contributions are engineered to cancel each other. A surprising observation is that this mechanisms for suppressing spin dephasing is not only effective for electrons in the heterojunction quantum well, but also for electrons in a deeper bulk layer.Comment: 5 pages, 3 figure