Soap Bubbles in Outer Space: Interaction of a Domain Wall with a Black Hole

We discuss the generalized Plateau problem in the 3+1 dimensional Schwarzschild background. This represents the physical situation, which could for instance have appeared in the early universe, where a cosmic membrane (thin domain wall) is located near a black hole. Considering stationary axially symmetric membranes, three different membrane-topologies are possible depending on the boundary conditions at infinity: 2+1 Minkowski topology, 2+1 wormhole topology and 2+1 black hole topology. Interestingly, we find that the different membrane-topologies are connected via phase transitions of the form first discussed by Choptuik in investigations of scalar field collapse. More precisely, we find a first order phase transition (finite mass gap) between wormhole topology and black hole topology; the intermediate membrane being an unstable wormhole collapsing to a black hole. Moreover, we find a second order phase transition (no mass gap) between Minkowski topology and black hole topology; the intermediate membrane being a naked singularity. For the membranes of black hole topology, we find a mass scaling relation analogous to that originally found by Choptuik. However, in our case the parameter $p$ is replaced by a 2-vector $\vec{p}$ parametrizing the solutions. We find that $Mass\propto|\vec{p}-\vec{p}_*|^\gamma$ where $\gamma\approx 0.66$. We also find a periodic wiggle in the scaling relation. Our results show that black hole formation as a critical phenomenon is far more general than expected.Comment: 15 pages, Latex, 4 figures include

Coherent spin valve phenomena and electrical spin injection in ferromagnetic/semiconductor/ferromagnetic junctions

Coherent quantum transport in ferromagnetic/ semiconductor/ ferromagnetic junctions is studied theoretically within the Landauer framework of ballistic transport. We show that quantum coherence can have unexpected implications for spin injection and that some intuitive spintronic concepts which are founded in semi-classical physics no longer apply: A quantum spin-valve (QSV) effect occurs even in the absence of a net spin polarized current flowing through the device, unlike in the classical regime. The converse effect also arises, i.e. a zero spin-valve signal for a non-vanishing spin-current. We introduce new criteria useful for analyzing quantum and classical spin transport phenomena and the relationships between them. The effects on QSV behavior of spin-dependent electron transmission at the interfaces, interface Schottky barriers, Rashba spin-orbit coupling and temperature, are systematically investigated. While the signature of the QSV is found to be sensitive to temperature, interestingly, that of its converse is not. We argue that the QSV phenomenon can have important implications for the interpretation of spin-injection in quantum spintronic experiments with spin-valve geometries.Comment: 15 pages including 11 figures. To appear in PR

Characterising Probabilistic Processes Logically

In this paper we work on (bi)simulation semantics of processes that exhibit both nondeterministic and probabilistic behaviour. We propose a probabilistic extension of the modal mu-calculus and show how to derive characteristic formulae for various simulation-like preorders over finite-state processes without divergence. In addition, we show that even without the fixpoint operators this probabilistic mu-calculus can be used to characterise these behavioural relations in the sense that two states are equivalent if and only if they satisfy the same set of formulae.Comment: 18 page

A parton picture of de Sitter space during slow-roll inflation

It is well-known that expectation values in de Sitter space are afflicted by infra-red divergences. Long ago, Starobinsky proposed that infra-red effects in de Sitter space could be accommodated by evolving the long-wavelength part of the field according to the classical field equations plus a stochastic source term. I argue that--when quantum-mechanical loop corrections are taken into account--the separate-universe picture of superhorizon evolution in de Sitter space is equivalent, in a certain leading-logarithm approximation, to Starobinsky's stochastic approach. In particular, the time evolution of a box of de Sitter space can be understood in exact analogy with the DGLAP evolution of partons within a hadron, which describes a slow logarithmic evolution in the distribution of the hadron's constituent partons with the energy scale at which they are probed.Comment: 36 pages; uses iopart.cls and feynmp.sty. v2: Minor typos corrected. Matches version published in JCA

Spin injection into a ballistic semiconductor microstructure

A theory of spin injection across a ballistic ferromagnet-semiconductor-ferromagnet junction is developed for the Boltzmann regime. Spin injection coefficient $\gamma$ is suppressed by the Sharvin resistance of the semiconductor $r_N^*=(h/e^2)(\pi^2/S_N)$, where $S_N$ is the Fermi-surface cross-section. It competes with the diffusion resistances of the ferromagnets $r_F$, and $\gamma\sim r_F/r_N^*\ll 1$ in the absence of contact barriers. Efficient spin injection can be ensured by contact barriers. Explicit formulae for the junction resistance and the spin-valve effect are presented.Comment: 5 pages, 2 column REVTeX. Explicit prescription relating the results of the ballistic and diffusive theories of spin injection is added. To this end, some notations are changed. Three references added, typos correcte

Non-monotonic variation with salt concentration of the second virial coefficient in protein solutions

The osmotic virial coefficient $B_2$ of globular protein solutions is calculated as a function of added salt concentration at fixed pH by computer simulations of the ``primitive model''. The salt and counter-ions as well as a discrete charge pattern on the protein surface are explicitly incorporated. For parameters roughly corresponding to lysozyme, we find that $B_2$ first decreases with added salt concentration up to a threshold concentration, then increases to a maximum, and then decreases again upon further raising the ionic strength. Our studies demonstrate that the existence of a discrete charge pattern on the protein surface profoundly influences the effective interactions and that non-linear Poisson Boltzmann and Derjaguin-Landau-Verwey-Overbeek (DLVO) theory fail for large ionic strength. The observed non-monotonicity of $B_2$ is compared to experiments. Implications for protein crystallization are discussed.Comment: 43 pages, including 17 figure

A white humpback whale (Megaptera novaeangliae) in the Atlantic Ocean, Svalbard, Norway, August 2012

A white humpback whale (Megaptera novaeangliae) was observed on several occasions off Svalbard, Norway, during August 2012. The animal was completely white, except for a few small dark patches on the ventral side of its fluke. The baleen plates were light-coloured, but the animal's eyes had normal (dark) colouration. This latter characteristic indicates that the animal was not an albino; it was a leucistic individual. The animal was a full-sized adult and was engaged in “bubble-feeding”, together with 15–20 other humpback whales, each time it was seen. Subsequent to these sightings, polling of the marine mammal science community has resulted in the discovery of two other observations of white humpback whales in the Barents Sea area, one in 2004 and another in 2006; in both cases the observed individuals were adult animals. It is likely that all of these sightings are of the same individual, but there is no genetic or photographic evidence to confirm this suggestion. The rarity of observations of such white individuals suggests that they are born at very low frequencies or that the ontogenetic survival rates of the colour morph are low

Anthropogenic Space Weather

Anthropogenic effects on the space environment started in the late 19th century and reached their peak in the 1960s when high-altitude nuclear explosions were carried out by the USA and the Soviet Union. These explosions created artificial radiation belts near Earth that resulted in major damages to several satellites. Another, unexpected impact of the high-altitude nuclear tests was the electromagnetic pulse (EMP) that can have devastating effects over a large geographic area (as large as the continental United States). Other anthropogenic impacts on the space environment include chemical release ex- periments, high-frequency wave heating of the ionosphere and the interaction of VLF waves with the radiation belts. This paper reviews the fundamental physical process behind these phenomena and discusses the observations of their impacts.Comment: 71 pages, 35 figure

Chronology of Dune Development in the White River Badlands, Northern Great Plains, USA

Aeolian dune field chronologies provide important information on drought history on the Great Plains. The White River Badlands (WRB) dunes are located approximately 60 km north of the Nebraska Sand Hills (NSH), in the western section of the northern Great Plains. Clifftop dunes, sand sheets, and stabilized northwest-southeast trending parabolic dunes are found on upland mesas and buttes, locally called tables. The result of this study is a dune stabilization history determined from samples collected from stratigraphic exposures and dune crests. Thirty-seven OSL ages, from this and previous investigations, show three periods of dune activity: 1) ∼21,000 years ago to 12,000 years ago (a), 2) ∼9 to 6 ka, and 3) post-700 a. Stratigraphic exposures and low-relief dune forms preserve evidence of late Pleistocene and middle Holocene dune development, while high-relief dune crests preserve evidence of late Holocene dune development. Results of 12 OSL ages from the most recent dune activation event indicate that Medieval Climate Anomaly (MCA) droughts and Little Ice Age (LIA) droughts caused dune reactivation on the tables. Dune reactivation was accompanied by other drought-driven geomorphological responses in the WRB, including fluvial incision of the prairie and formation of sod tables. Regional significance of the MCA and LIA droughts is supported by similarities in the aeolian chronologies of the NSH at 700–600 a and some western Great Plains dune fields at 420–210 a. Aerial photographs of the WRB show little activity during the Dust Bowl droughts of the 1930s

Model-Based Verification, Optimization, Synthesis and Performance Evaluation of Real-Time Systems

International audienceThis article aims at providing a concise and precise Travellers Guide, Phrase Book or Reference Manual to the timed automata modeling formalism introduced by Alur and Dill [8, 9]. The paper gives comprehensive definitions of timed automata, priced (or weighted) timed automata, and timed games and highlights a number of results on associated decision problems related to model checking, equivalence checking, optimal scheduling, the existence of winning strategies, and then statistical model checking