From gyroscopic to thermal motion: a crossover in the dynamics of molecular superrotors

Localized heating of a gas by intense laser pulses leads to interesting acoustic, hydrodynamic and optical effects with numerous applications in science and technology, including controlled wave guiding and remote atmosphere sensing. Rotational excitation of molecules can serve as the energy source for raising the gas temperature. Here, we study the dynamics of energy transfer from the molecular rotation to heat. By optically imaging a cloud of molecular superrotors, created with an optical centrifuge, we experimentally identify two separate and qualitatively different stages of its evolution. The first non-equilibrium "gyroscopic" stage is characterized by the modified optical properties of the centrifuged gas - its refractive index and optical birefringence, owing to the ultrafast directional molecular rotation, which survives tens of collisions. The loss of rotational directionality is found to overlap with the release of rotational energy to heat, which triggers the second stage of thermal expansion. The crossover between anisotropic rotational and isotropic thermal regimes is in agreement with recent theoretical predictions and our hydrodynamic calculations

Transverse "resistance overshoot" in a Si/SiGe two-dimensional electron gas in the quantum Hall effect regime

We investigate the peculiarities of the "overshoot" phenomena in the transverse Hall resistance R_{xy} in Si/SiGe. Near the low magnetic field end of the quantum Hall effect plateaus, when the filling factor \nu approaches an integer i, R_{xy} overshoots the normal plateau value h/ie^2. However, if magnetic field B increases further, R_{xy} decreases to its normal value. It is shown that in the investigated sample n-Si/Si_{0.7}Ge_{0.3}, overshoots exist for almost all \nu. Existence of overshoot in R_{xy} observed in different materials and for different \nu, where splitting of the adjacent Landau bands has different character, hints at the common origin of this effect. Comparison of the experimental curves R_{xy}(\nu) for \nu = 3 and \nu = 5 with and without overshoot showed that this effect exist in the whole interval between plateaus, not only in the region where R_{xy} exceeds the normal plateau value.Comment: 3 pages, 5 EPS figure

An Introduction to Pervasive Interface Automata

Pervasive systems are often context-dependent, component based systems in which components expose interfaces and offer one or more services. These systems may evolve in unpredictable ways, often through component replacement. We present pervasive interface automata as a formalism for modelling components and their composition. Pervasive interface automata are based on the interface automata of Henzinger et al, with several significant differences. We expand their notion of input and output actions to combinations of input, output actions, and callable methods and method calls. Whereas interfaces automata have a refinement relation, we argue the crucial relation in pervasive systems is component replacement, which must include consideration of the services offered by a component and assumptions about the environment. We illustrate pervasive interface autmotata and component replacement with a small case study of a pervasive application for sports predictions

Religious Relationships with the Environment in a Tibetan Rural Community : Interactions and Contrasts with Popular Notions of Indigenous Environmentalism

Acknowledgments: We thank Beijing Forestry University, our field assistants Tashi Rabden, Pema Dechin, Tsewang Chomtso and Gele Chopel for their invaluable help, the Forest Bureau of Daocheng county for permission and support, and the people of Samdo for their hospitality and participation. The research was funded by the ESRC and the World Pheasant Association. This paper is a contribution to Imperial College’s Grand Challenges in Ecosystems and the Environment initiative. Two anonymous reviewers gave valuable comments on the manuscript.Peer reviewedPublisher PD

Experimental evidence that predator range expansion modifies alpine stream community structure

Climate change is projected to facilitate altitudinal range expansions of ‘lowland’ taxa, creating novel species interactions. However, how range shifts will alter biotic interactions and community structure in alpine streams is not well understood. In the Pyrénées, climate-induced physicochemical habitat change is hypothesized to facilitate the colonization of high-altitude streams by Perla grandis, a carnivorous stonefly. A field-based experiment was conducted in mesocosm channels beside a hillslope spring (2000 m asl) in the Taillon-Gabiétous catchment, French Pyrénées. The influence of P. grandis predation on community structure, feeding trait composition, body-size spectrum, and algal chlorophyll a concentration was examined. Gut contents were analyzed and used to identify consumed prey. Total invertebrate density was not significantly reduced by P. grandis, but Baetis spp. densities were depressed in the treatment channels through a combination of direct consumption and predator avoidance (emigration/drift). However, despite fewer grazers in the predator treatment channels, the magnitude of the trophic cascade effect on basal resources (measured as chlorophyll a density) was comparable between treatment and control channels. The results of this experiment suggest that size/species-specific predation, intraguild predation, and interference competition are the likely mechanisms that altered the body-size spectrum in treatment channels. In synergy with climate-driven physicochemical habitat change, the extinction risk of some range-restricted taxa (prey and other predators) could be increased where P. grandis colonization occurs. Hence, conservation efforts are required to ensure that additional anthropogenic stressors (e.g., nutrient enrichment, cattle trampling, hydropower development, ski runs, and tourism) are limited to minimize further pressures on these unique and sensitive habitats

A Mesolithic settlement site at Howick, Northumberland: a preliminary report

Excavations at a coastal site at Howick during 2000 and 2002 have revealed evidence for a substantial Mesolithic settlement and a Bronze Age cist cemetery. Twenty one radiocarbon determinations of the earlier eighth millennium BP (Cal.) indicate that the Mesolithic site is one of the earliest known in northern Britain. An 8m core of sediment was recovered from stream deposits adjacent to the archaeological site which provides information on local environmental conditions. Howick offers a unique opportunity to understand aspects of hunter-gatherer colonisation and settlement during a period of rapid palaeogeographical change around the margins of the North Sea basin, at a time when it was being progressively inundated by the final stages of the postglacial marine transgression. The cist cemetery will add to the picture of Bronze Age occupation of the coastal strip and again reveals a correlation between the location of Bronze Age and Mesolithic sites which has been observed elsewhere in the region

Positive practices : solution-focused and narrative therapeutic techniques with children with sexually harmful behaviours

This article explores the use of solution-focused and Narrative Therapeutic approaches with a boy who had sexually harmful behaviours. The paper will highlight the practical challenges of working with someone who is 'problem-saturated' through institutionalisation and who is also subjected to powerful discourses claiming the 'truth' about him. The use of solution-focused and Narrative Therapeutic principles and approaches will be demonstrated in the work described, in a way that allows the reader to reflect on how these may differ from modernist understandings and responses to this behaviour

Vesicles in solutions of hard rods

The surface free energy of ideal hard rods near curved hard surfaces is determined to second order in curvature for surfaces of general shape. In accordance with previous results for spherical and cylindrical surfaces it is found that this quantity is non-analytical when one of the principal curvatures changes signs. This prohibits writing it in the common Helfrich form. It is shown that the non-analytical terms are the same for any aspect ratio of the rods. These results are used to find the equilibrium shape of vesicles immersed in solutions of rod-like (colloidal) particles. The presence of the particles induces a change in the equilibrium shape and to a shift of the prolate-oblate transition in the vesicle phase diagram, which are calculated within the framework of the spontaneous curvature model. As a consequence of the special form of the energy contribution due to the rods these changes cannot be accounted for by a simple rescaling of the elastic constants of the vesicle as for solutions of spherical colloids or polymers.Comment: 11 pages, 7 figures, submitted to Phys. Rev.