1,571 research outputs found
Adsorption on carbon nanotubes: quantum spin tubes, magnetization plateaus, and conformal symmetry
We formulate the problem of adsorption onto the surface of a carbon nanotube
as a lattice gas on a triangular lattice wrapped around a cylinder. This model
is equivalent to an XXZ Heisenberg quantum spin tube. The geometric frustration
due to wrapping leads generically to four magnetization plateaus, in contrast
to the two on a flat graphite sheet. We obtain analytical and numerical results
for the magnetizations and transition fields for armchair, zig-zag and chiral
nanotubes. The zig-zags are exceptional in that one of the plateaus has
extensive zero temperature entropy in the classical limit. Quantum effects lift
up the degeneracy, leaving gapless excitations which are described by a
conformal field theory with compactification radius quantized by the tube
circumference.Comment: 5 pages, 6 figure
Long term monitoring of bright TeV Blazars with the MAGIC telescope
The MAGIC telescope has performed long term monitoring observations of the
bright TeV Blazars Mrk421, Mrk501 and 1ES1959+650. Up to 40 observations, 30 to
60 minutes each have been performed for each source evenly distributed over the
observable period of the year. The sensitivity of MAGIC is sufficient to
establish a flux level of 25% of the Crab flux for each measurement. These
observations are well suited to trigger multiwavelength ToO observations and
the overall collected data allow an unbiased study of the flaring statistics of
the observed AGNs.Comment: 4 pages, 4 figures, to appear in the proceedings of the 30th
International Cosmic Ray Conference, Merida, July 200
First contemporary case of human infection with Cryptococcus gattii in Puget Sound: Evidence for spread of the Vancouver Island outbreak
We report a case of cryptococcosis due to C. gattii which appears to have been acquired in the Puget Sound region, Washington State. Genotyping confirmed identity to the predominant Vancouver Island genotype. This is the first documented case of human disease by the major Vancouver Island emergence strain acquired within the United States
Plastic Flow, Voltage Bursts, and Vortex Avalanches in Superconductors
We use large-scale parallel simulations to compute the motion of
superconducting magnetic vortices during avalanches triggered by small field
increases. We find that experimentally observable voltage bursts correspond to
pulsing vortex movement along branched channels or winding chains, and relate
vortex flow images to features of statistical distributions. As pin density is
increased, a crossover occurs from interstitial motion in narrow easy-flow
winding channels with typical avalanche sizes, to pin-to-pin motion in broad
channels, characterized by a very broad distribution of sizes. Our results are
consistent with recent experiments.Comment: 4 pages, Latex, 4 figures included. Movies available at
http://www-personal.engin.umich.edu/~nor
Corazonin Neurons Function in Sexually Dimorphic Circuitry That Shape Behavioral Responses to Stress in Drosophila
All organisms are confronted with dynamic environmental changes that challenge homeostasis, which is the operational definition of stress. Stress produces adaptive behavioral and physiological responses, which, in the Metazoa, are mediated through the actions of various hormones. Based on its associated phenotypes and its expression profiles, a candidate stress hormone in Drosophila is the corazonin neuropeptide. We evaluated the potential roles of corazonin in mediating stress-related changes in target behaviors and physiologies through genetic alteration of corazonin neuronal excitability. Ablation of corazonin neurons confers resistance to metabolic, osmotic, and oxidative stress, as measured by survival. Silencing and activation of corazonin neurons lead to differential lifespan under stress, and these effects showed a strong dependence on sex. Additionally, altered corazonin neuron physiology leads to fundamental differences in locomotor activity, and these effects were also sex-dependent. The dynamics of altered locomotor behavior accompanying stress was likewise altered in flies with altered corazonin neuronal function. We report that corazonin transcript expression is altered under starvation and osmotic stress, and that triglyceride and dopamine levels are equally impacted in corazonin neuronal alterations and these phenotypes similarly show significant sexual dimorphisms. Notably, these sexual dimorphisms map to corazonin neurons. These results underscore the importance of central peptidergic processing within the context of stress and place corazonin signaling as a critical feature of neuroendocrine events that shape stress responses and may underlie the inherent sexual dimorphic differences in stress responses
A compact and light-weight refractive telescope for the observation of extensive air showers
A general purpose instrument for imaging of Cherenkov light or fluorescence
light emitted by extensive air showers is presented. Its refractive optics
allows for a compact and light-weight design with a wide field-of-view of
12{\deg}. The optical system features a 0.5 m diameter Fresnel lens and a
camera with 61 pixels composed of Winston cones and large-sized 6x6 mm photo
sensors. As photo sensors, semi conductor light sensors (SiPMs) are utilized.
The camera provides a high photon detection efficiency together with robust
operation. The enclosed optics permit operation in regions of harsh
environmental conditions. The low price of the telescope allows the production
of a large number of telescopes and the application of the instrument in
various projects, such as FAMOUS for the Pierre Auger Observatory, HAWC's Eye
for HAWC or IceAct for IceCube. In this paper the novel design of this
telescope and first measurements are presented.Comment: Submitted to JINST, second (minor) revisio
Methane cycling dynamics in sediments of Alaskan Arctic Foothill lakes
We measured aspects of sediment methane (CH4) cycling dynamics in 3 shallow (mean depth, z = 2.1 m) and 3 deep (z = 6.5 m) Alaskan Arctic Foothill lakes to establish reference data to evaluate future climate-mediated changes in these systems and to identify lake-size-dependent differences in rates and controls on CH4 production and consumption or sensitivity to changing climate. The mean sedimentation rate and sediment oxygen (O2) penetration depth were significantly higher and lower, respectively, in shallow versus deep lakes. The molar carbon to nitrogen (C:N) ratio of 12 for sedimenting material across lakes indicated a dominance by phytodetritus. Pore water dissolved organic C and CH4 concentrations were higher in shallow than in deep lakes at comparable depths below the sediment surface. The average area-based rate of methanogenesis was significantly higher in shallow lakes, exceeding the mean of deep lakes by a factor of 4; however, the mean potential area-based rate of CH4 oxidation was comparable between lake classes due to the reduced sediment O2 penetration depth in shallow lakes. All lake sediments responded similarly to chemical amendments. Hydrogen addition significantly stimulated rates of methanogenesis relative to unamended controls, while rates were unchanged by alternate electron acceptors (SO42−, Fe3+, NO3−, Mn4+), suggesting that other microbial groups did not compete with methanogens for common substrates or produce toxic intermediates. Across all lakes, 30% of assimilated CH4 was converted to methanotophic biomass, and methanotrophic C production could be as much as 23% of epipelic primary production, pointing to the potential importance of CH4-derived C in Arctic lacustrine food webs
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