810 research outputs found
Electrostatic tailoring of magnetic interference in quantum point contact ballistic Josephson junctions
The magneto-electrostatic tailoring of the supercurrent in quantum point
contact ballistic Josephson junctions is demonstrated. An etched InAs-based
heterostructure is laterally contacted to superconducting niobium leads and the
existence of two etched side gates permits, in combination with the application
of a perpendicular magnetic field, to modify continuously the magnetic
interference pattern by depleting the weak link. For wider junctions the
supercurrent presents a Fraunhofer-like interference pattern with periodicity
h/2e whereas by shrinking electrostatically the weak link, the periodicity
evolves continuously to a monotonic decay. These devices represent novel
tunable structures that might lead to the study of the elusive Majorana
fermions.Comment: 4.5 pages, 4 color figure
Picocyanobacteria distribution in the Ebro Estuary (Spain)
The stratified estuary of the Ebro River is located on the Mediterranean coast of Spain. From samples obtained in 6 sampling campaigns between July 1999 and February 2000 from the last 18 km of Ebro River, the abundance of picocyanobacteria was estimated by epifluorescence microscopy. The abundance of picocyanobacteria reached 93.7 x106 cells Lâ1 in the river mouth (station R1) below the surface, in October 1999. In deeper layers of salt wedge area stations (near the river mouth), we could observe higher concentrations of marine cyanobacteria. This study offers comments about the abundance and distribution in cyanobacteria
Switching the sign of Josephson current through Aharonov-Bohm interferometry
We investigate the DC Josephson effect in a superconductor-normal
metal-superconductor junction where the normal region consists of a ballistic
ring. We show that a fully controllable -junction can be realized through
the electro-magnetostatic Aharonov-Bohm effect in the ring. The sign and the
magnitude of the supercurrent can be tuned by varying the magnetic flux and the
gate voltage applied to one arm, around suitable values. The implementation in
a realistic set-up is discussed.Comment: 4 pages, 3 figure
Living on the Edge: Settlement Patterns by the Symbiotic Barnacle \u3cem\u3eXenobalanus globicipitis\u3c/em\u3e on Small Cetaceans
The highly specialized coronulid barnacle Xenobalanus globicipitis attaches exclusively on cetaceans worldwide, but little is known about the factors that drive the microhabitat patterns on its hosts. We investigate this issue based on data on occurrence, abundance, distribution, orientation, and size of X. globicipitis collected from 242 striped dolphins (Stenella coeruleoalba) that were stranded along the Mediterranean coast of Spain. Barnacles exclusively infested the fins, particularly along the trailing edge. Occurrence, abundance, and density of X. globicipitis were significantly higher, and barnacles were significantly larger, on the caudal fin than on the flippers and dorsal fin. Barnacles were found more frequently and in greater numbers on the dorsal rather than ventral side of the caudal fin and on the central third of dorsal and ventral fluke surfaces. Nearly all examined individuals attached with their cirral fan oriented opposite to the fluke edge. We suggest that X. globicipitis may chemically recognize dolphins as a substratum, but fins, particularly the flukes, are passively selected because of creation of vortices that increase contact of cyprids with skin and early survival of these larvae at the corresponding sites. Cyprids could actively select the trailing edge and orient with the cirri facing the main direction of flow. Attachment on the dorsal side of the flukes is likely associated with asymmetrical oscillation of the caudal fin, and the main presence on the central segment of the flukes could be related to suitable water flow conditions generated by fluke performance for both settlement and nutrient filtration
Modelling the Canes Venatici I dwarf spheroidal galaxy
The aim of this work is to find a progenitor for Canes Venatici I (CVn I),
under the assumption that it is a dark matter free object that is undergoing
tidal disruption. With a simple point mass integrator, we searched for an orbit
for this galaxy using its current position, position angle, and radial velocity
in the sky as constraints. The orbit that gives the best results has the pair
of proper motions = -0.099 mas yr and = -0.147
mas yr, that is an apogalactic distance of 242.79 kpc and a perigalactic
distance of 20.01 kpc. Using a dark matter free progenitor that undergoes tidal
disruption, the best-fitting model matches the final mass, surface brightness,
effective radius, and velocity dispersion of CVn I simultaneously. This model
has an initial Plummer mass of 2.47 x M and a Plummer radius of
653 pc, producing a remnant after 10 Gyr with a final mass of 2.45 x 10
M, a central surface brightness of 26.9 mag arcsec, an effective
radius of 545.7 pc, and a velocity dispersion with the value 7.58 km s.
Furthermore, it is matching the position angle and ellipticity of the projected
object in the sky.Comment: 11 pages, 14 figures, accepted by A&
Anthocyanins are Key Regulators of Drought Stress Tolerance in Tobacco
Abiotic stresses will be one of the major challenges for worldwide food supply in the near future. Therefore, it is important to understand the physiological mechanisms that mediate plant responses to abiotic stresses. When subjected to UV, salinity or drought stress, plants accumulate specialized metabolites that are often correlated with their ability to cope with the stress. Among them, anthocyanins are the most studied intermediates of the phenylpropanoid pathway. However, their role in plant response to abiotic stresses is still under discussion. To better understand the effects of anthocyanins on plant physiology and morphogenesis, and their implications on drought stress tolerance, we used transgenic tobacco plants (AN1), which over-accumulated anthocyanins in all tissues. AN1 plants showed an altered phenotype in terms of leaf gas exchanges, leaf morphology, anatomy and metabolic profile, which conferred them with a higher drought tolerance compared to the wild-type plants. These results provide important insights for understanding the functional reason for anthocyanin accumulation in plants under stress
Hard-disk computer simulations -- a historic perspective
We discuss historic pressure computations for the hard-disk model performed
since 1953, and compare them to results that we obtain with a powerful
event-chain Monte Carlo and a massively parallel Metropolis algorithm. Like
other simple models in the sciences, such as the Drosophila model of biology,
the hard-disk model has needed monumental effort to be understood. In
particular, we argue that the difficulty of estimating the pressure has not
been fully realized in the decades-long controversy over the hard-disk
phase-transition scenario. We present the physics of the hard-disk model, the
definition of the pressure and its unbiased estimators, several of which are
new. We further treat different sampling algorithms and crucial criteria for
bounding mixing times in the absence of analytical predictions. Our definite
results for the pressure, for up to one million disks, may serve as benchmarks
for future sampling algorithms. A synopsis of hard-disk pressure data as well
as different versions of the sampling algorithms and pressure estimators are
made available in an open-source repository.Comment: 21 pages, 13 figures, open-source repositor
Biochemical, Physiological and Anatomical Mechanisms of Adaptation of Callistemon citrinus and Viburnum lucidum to NaCl and CaCl2 Salinization
Callistemon citrinus and Viburnum lucidum are very appreciated and widespread ornamental shrubs for their abundant flowering and/or brilliant foliage. The intrinsic tolerance to drought/salinity supports their use in urban areas and in xeriscaping. Despite adaptive responses of these ornamental species to sodium chloride (NaCl) have been extensively explored, little is known on the effects of other salt solution, yet iso-osmotic, on their growth, mineral composition and metabolism. The present research aimed to assess responses at the biochemical, physiological and anatomical levels to iso-osmotic salt solutions of NaCl and CaCl2 to discriminate the effects of osmotic stress and ion toxicity. The two ornamental species developed different salt-tolerance mechanisms depending on the salinity sources. The growth parameters and biomass production decreased under salinization in both ornamental species, independently of the type of salt, with a detrimental effect of CaCl2 on C. citrinus. The adaptive mechanisms adopted by the two ornamental species to counteract the NaCl salinity were similar, and the decline in growth was mostly related to stomatal limitations of net CO2 assimilation rate, together with the reduction in leaf chlorophyll content (SPAD index). The stronger reduction of C. citrinus growth compared to V. lucidum, was due to an exacerbated reduction in net photosynthetic rate, driven by both stomatal and non stomatal limitations. In similar conditions, V. lucidum exhibited other additional adaptive response, such as modification in leaf functional anatomical traits, mostly related to the reduction in the stomata size allowing plants a better control of stomata opening than in C. citrinus. However, C. citrinus plants displayed an increased ability to retain higher Cl- levels in leaves than in roots under CaCl2 salinity compared to V. lucidum, thus, indicating a further attempt to counteract chloride toxicity through an increased vacuolar compartmentalization and to take advantages of them as chip osmotica
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