A Method To Determine Lake Depth and Water Availability on the North Slope of Alaska with Spaceborne Imaging Radar and Numerical Ice Growth Modelling

Spaceborne synthetic aperture radar (SAR) images and numerical ice growth modelling were used to determine maximum water depth and water availability in two areas of the North Slope in northwestern Alaska. SAR images obtained between September 1991 and May 1992 were used to identify when and how many lakes froze completely to the bottom, and how many lakes did not freeze completely to the bottom. At Barrow, on the coast, 60% of the lakes froze completely to the bottom in mid-January alone, and by the end of winter 77% of the lakes were completely frozen. In contrast, 100 km to the south in the 'B' Lakes region, only 23% of the lakes froze completely, and there was no sudden freezing of many lakes as occurred at Barrow. A physically based, numerical model was used to simulate ice growth on the lakes. The simulated maximum ice thickness is 2.2 m. Consequently, any lake where some part of the ice cover does not freeze to the bottom has some water more than 2.2 m deep. For those lakes where the ice cover had frozen completely at some time in the winter, the simulated ice growth curve provides the ice thickness at the time each lake had frozen completely to the bottom and thus the lake's maximum water depth. At Barrow, 60% of the lakes are between 1.4 and 1.5 m deep, and 23% are more than 2.2 m deep. At the 'B' Lakes, 77% of the lakes are more than 2.2 m deep. Thus, there is a considerable contrast in lake depth and water availability between the Barrow and the 'B' Lakes regions. This method is simple to implement, and the relatively inexpensive SAR data have good spatial and temporal coverage. This method could be used to determine lake depth and water availability on the entire North Slope and in other polar and subpolar areas where shallow lakes are common. On s'est servi d'images prises au radar à antenne latérale synthétique (RALS) spatioporté et d'une modélisation numérique de la formation de la glace pour déterminer la profondeur d'eau maximale et la disponibilité de cette eau dans deux régions du versant Nord dans le nord-est de l'Alaska. Des images RALS obtenues entre septembre 1991 et mai 1992 ont servi à identifier quand et comment un grand nombre de lacs avaient gelé sur toute leur profondeur et comment cela ne s'était pas produit pour bien d'autres. À Barrow, sur la côte, 60 p. cent des lacs avaient déjà gelé sur toute leur profondeur à la mi-janvier et, à la fin de l'hiver, 77 p. cent des lacs avaient complètement gelé. Par contre, à 100 km plus au sud, dans la région des lacs "B", seulement 23 p. cent des lacs avaient complètement gelé, et on n'observait pas l'engel soudain de nombreux lacs comme c'était le cas à Barrow. On s'est servi d'un modèle numérique fondé sur des critères physiques pour simuler la formation de la glace sur les lacs. L'épaisseur maximale de la glace simulée est de 2,2 m. En conséquence, tout lac où une partie du manteau glaciel n'atteint pas le fond a une profondeur supérieure à 2,2 m. Pour les lacs dont le manteau glaciel atteignait le fond à un moment quelconque de l'hiver, la courbe de formation simulée de la glace donne l'épaisseur de la glace au moment où chaque lac a gelé sur toute sa profondeur, et donc, la profondeur maximale de ce lac. À Barrow, 60 p. cent des lacs ont entre 1,4 et 1,5 m de profondeur et 23 p. cent ont plus de 2,2 m de profondeur. Dans la région des lacs "B", 77 p. cent des lacs ont plus de 2,2 m de profondeur. Il y a donc un fort contraste dans la profondeur des lacs et la disponibilité de l'eau entre la région de Barrow et celle des lacs "B". Cette méthode est facile à appliquer et les données RALS - relativement bon marché - offrent une bonne couverture spatiale et temporelle. On pourrait utiliser cette méthode pour déterminer la profondeur des lacs et la disponibilité de l'eau sur tout le versant Nord et dans d'autres zones polaires et subpolaires où se trouve un grand nombre de lacs peu profonds

Human airway smooth muscle maintain in situ cell orientation and phenotype when cultured on aligned electrospun scaffolds

Human airway smooth muscle (HASM) contraction plays a central role in regulating airway resistance in both healthy and asthmatic bronchioles. In vitro studies that investigate the intricate mechanisms that regulate this contractile process are predominantly conducted on tissue culture plastic, a rigid, 2D geometry, unlike the 3D microenvironment smooth muscle cells are exposed to in situ. It is increasingly apparent that cellular characteristics and responses are altered between cells cultured on 2D substrates compared with 3D topographies. Electrospinning is an attractive method to produce 3D topographies for cell culturing as the fibers produced have dimensions within the nanometer range, similar to cells' natural environment. We have developed an electrospun scaffold using the nondegradable, nontoxic, polymer polyethylene terephthalate (PET) composed of uniaxially orientated nanofibers and have evaluated this topography's effect on HASM cell adhesion, alignment, and morphology. The fibers orientation provided contact guidance enabling the formation of fully aligned sheets of smooth muscle. Moreover, smooth muscle cells cultured on the scaffold present an elongated cell phenotype with altered contractile protein levels and distribution. HASM cells cultured on this scaffold responded to the bronchoconstrictor bradykinin. The platform presented provides a novel in vitro model that promotes airway smooth muscle cell development toward a more in vivo-like phenotype while providing topological cues to ensure full cell alignment

The Shapes of Dirichlet Defects

If the vacuum manifold of a field theory has the appropriate topological structure, the theory admits topological structures analogous to the D-branes of string theory, in which defects of one dimension terminate on other defects of higher dimension. The shapes of such defects are analyzed numerically, with special attention paid to the intersection regions. Walls (co-dimension 1 branes) terminating on other walls, global strings (co-dimension 2 branes) and local strings (including gauge fields) terminating on walls are all considered. Connections to supersymmetric field theories, string theory and condensed matter systems are pointed out.Comment: 24 pages, RevTeX, 21 eps figure

Microlensing by natural wormholes: theory and simulations

We provide an in depth study of the theoretical peculiarities that arise in effective negative mass lensing, both for the case of a point mass lens and source, and for extended source situations. We describe novel observational signatures arising in the case of a source lensed by a negative mass. We show that a negative mass lens produces total or partial eclipse of the source in the umbra region and also show that the usual Shapiro time delay is replaced with an equivalent time gain. We describe these features both theoretically, as well as through numerical simulations. We provide negative mass microlensing simulations for various intensity profiles and discuss the differences between them. The light curves for microlensing events are presented and contrasted with those due to lensing produced by normal matter. Presence or absence of these features in the observed microlensing events can shed light on the existence of natural wormholes in the Universe.Comment: 16 pages, 24 postscript figures (3 coloured), revtex style, submitted to Phys. Rev.

Hippocampus, Amygdala and Basal Ganglia Based Navigation Control

In this paper we present a novel robot navigation system aimed at testing hypotheses about the roles of key brain areas in foraging behavior of rats. The key components of the control network are: 1. a Hippocampus inspired module for spatial localization based on associations between sensory inputs and places; 2. an Amygdala inspired module for the association of values with places and sensory stimuli; 3. a Basal Ganglia inspired module for the selection of actions based on the evaluated sensory inputs. By implementing this Hippocampus-Amygdala-Basal Ganglia based control network with a simulated rat embodiment we intend to test not only our understanding of the individual brain areas but especially the interaction between them. Understanding the neural circuits that allows rats to efficiently forage for food will also help to improve the ability of robots to autonomously evaluate and select navigation targets

Domain wall generation by fermion self-interaction and light particles

A possible explanation for the appearance of light fermions and Higgs bosons on the four-dimensional domain wall is proposed. The mechanism of light particle trapping is accounted for by a strong self-interaction of five-dimensional pre-quarks. We obtain the low-energy effective action which exhibits the invariance under the so called \tau-symmetry. Then we find a set of vacuum solutions which break that symmetry and the five-dimensional translational invariance. One type of those vacuum solutions gives rise to the domain wall formation with consequent trapping of light massive fermions and Higgs-like bosons as well as massless sterile scalars, the so-called branons. The induced relations between low-energy couplings for Yukawa and scalar field interactions allow to make certain predictions for light particle masses and couplings themselves, which might provide a signature of the higher dimensional origin of particle physics at future experiments. The manifest translational symmetry breaking, eventually due to some gravitational and/or matter fields in five dimensions, is effectively realized with the help of background scalar defects. As a result the branons acquire masses, whereas the ratio of Higgs and fermion (presumably top-quark) masses can be reduced towards the values compatible with the present-day phenomenology. Since the branons do not couple to fermions and the Higgs bosons do not decay into branons, the latter ones are essentially sterile and stable, what makes them the natural candidates for the dark matter in the Universe.Comment: 34 pages, 2 figures, JHEP style,few important refs. adde

Chronic exposure to environmental temperature attenuates the thermal sensitivity of salmonids

Metabolism, the biological processing of energy and materials, scales predictably with temperature and body size. Temperature effects on metabolism are normally studied via acute exposures, which overlooks the capacity for organisms to moderate their metabolism following chronic exposure to warming. Here, we conduct respirometry assays in situ and after transplanting salmonid fish among different streams to disentangle the effects of chronic and acute thermal exposure. We find a clear temperature dependence of metabolism for the transplants, but not the in-situ assays, indicating that chronic exposure to warming can attenuate salmonid thermal sensitivity. A bioenergetic model accurately captures the presence of fish in warmer streams when accounting for chronic exposure, whereas it incorrectly predicts their local extinction with warming when incorporating the acute temperature dependence of metabolism. This highlights the need to incorporate the potential for thermal acclimation or adaptation when forecasting the consequences of global warming on ecosystems

Demonstration of a solid deuterium source of ultra-cold neutrons

Ultra-cold neutrons (UCN), neutrons with energies low enough to be confined by the Fermi potential in material bottles, are playing an increasing role in measurements of fundamental properties of the neutron. The ability to manipulate UCN with material guides and bottles, magnetic fields, and gravity can lead to experiments with lower systematic errors than have been obtained in experiments with cold neutron beams. The UCN densities provided by existing reactor sources limit these experiments. The promise of much higher densities from solid deuterium sources has led to proposed facilities coupled to both reactor and spallation neutron sources. In this paper we report on the performance of a prototype spallation neutron-driven solid deuterium source. This source produced bottled UCN densities of 145 +/-7 UCN/cm3, about three times greater than the largest bottled UCN densities previously reported. These results indicate that a production UCN source with substantially higher densities should be possible

Magnetic Field Generation in Stars

Enormous progress has been made on observing stellar magnetism in stars from the main sequence through to compact objects. Recent data have thrown into sharper relief the vexed question of the origin of stellar magnetic fields, which remains one of the main unanswered questions in astrophysics. In this chapter we review recent work in this area of research. In particular, we look at the fossil field hypothesis which links magnetism in compact stars to magnetism in main sequence and pre-main sequence stars and we consider why its feasibility has now been questioned particularly in the context of highly magnetic white dwarfs. We also review the fossil versus dynamo debate in the context of neutron stars and the roles played by key physical processes such as buoyancy, helicity, and superfluid turbulence,in the generation and stability of neutron star fields. Independent information on the internal magnetic field of neutron stars will come from future gravitational wave detections. Thus we maybe at the dawn of a new era of exciting discoveries in compact star magnetism driven by the opening of a new, non-electromagnetic observational window. We also review recent advances in the theory and computation of magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo theory. These advances offer insight into the action of stellar dynamos as well as processes whichcontrol the diffusive magnetic flux transport in stars.Comment: 41 pages, 7 figures. Invited review chapter on on magnetic field generation in stars to appear in Space Science Reviews, Springe

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results