13,004 research outputs found
Postsettlement growth of two estuarine crab species, Chasmagnathus granulata and Cyrtograpsus angulatus (Crustacea, Decapoda, Grapsidae): laboratory and field observations
The estuarine grapsid crabs Chasmagnathus granulata and Cyrtograpsus angulatus belong to the most typical and dominant inhabitants of brackish coastal lagoons in southeastern South America. In a combined laboratory and field investigation of juvenile growth, we measured the increase in body size in these species under controlled conditions as well as in field experiments (in Mar Chiquita lagoon, Argentina), seasonal changes in size frequency distribution of a natural population, and growth related changes in selected morphometric traits of male and female juveniles (relations between carapace width, carapace length, propodus height and length of the cheliped, and pleon width). At 24°C, Cy. angulatus grew faster than Ch. granulata; it reached the crab-9 instar (C9; 13 mm carapace width) after 92 days, while Ch. granulata required 107 days to reach the C8 instar (7.4 mm). At 12°C, growth ceased in both species. The pleon begins to show sexual differences in the C5 (Cy. angulatus) and C8 instar (Ch. granulata), respectively, while the chelae differentiate earlier in Ch. granulata than in Cy. angulatus (in C4 vs C6). In the field, growth was maximal in summer, and was generally faster than in laboratory cultures. However, there is great individual variability in size (about 25% even in the first crab instar) and in size increments at ecdysis, increasing throughout juvenile growth. Our data indicate that, in the field, small-scale and short-term variations in feeding conditions, temperature, and salinity account for an extremely high degree of variability in the absolute and relative rates of growth as well as in the time to sexual differentiation
Thermopower of a superconducting single-electron transistor
We present a linear-response theory for the thermopower of a single-electron
transistor consisting of a superconducting island weakly coupled to two
normal-conducting leads (NSN SET). The thermopower shows oscillations with the
same periodicity as the conductance and is rather sensitive to the size of the
superconducting gap. In particular, the previously studied sawtooth-like shape
of the thermopower for a normal-conducting single-electron device is
qualitatively changed even for small gap energies.Comment: 9 pages, 3 figure
Rotational Heisenberg Inequalities
Since their discovery in 1927, the Heisenberg Inequalities have become an
icon of quantum mechanics. Often inappropriately referred to as the Uncertainty
Principle, these inequalities relating the standard deviations of the position
and momentum observables to Planck's constant are one of the cornerstones of
the quantum formalism even if the physical interpretation of quantum mechanics
remains still open to controversy nowadays. The Heisenberg Inequalities
governing translational motion are well understood. However, the corresponding
inequalities pertaining to rotational motion have not been established so far.
To fill this gap, we present here the Rotational Heisenberg Inequalities
relating the standard deviations of the orientation axis and orbital angular
momentum observables of an isolated molecule. The reason for choosing this
system is that a molecule separated from its environment corresponds to a bound
system preserving the orbital angular momentum.Comment: 6 pages, 2 figures. arXiv admin note: substantial text overlap with
arXiv:1412.211
Hanbury Brown and Twiss correlations in atoms scattered from colliding condensates
Low energy elastic scattering between clouds of Bose condensed atoms leads to
the well known s-wave halo with atoms emerging in all directions from the
collision zone. In this paper we discuss the emergence of Hanbury Brown and
Twiss coincidences between atoms scattered in nearly parallel directions. We
develop a simple model that explains the observations in terms of an
interference involving two pairs of atoms each associated with the elementary s
wave scattering process.Comment: Minor corrections. reference update
Single-hole transistor in p-type GaAs/AlGaAs heterostructures
A single-hole transistor is patterned in a p-type, C-doped GaAs/AlGaAs
heterostructure by AFM oxidation lithography. Clear Coulomb blockade resonances
have been observed at T=300 mK. A charging energy of ~ 1.5 meV is extracted
from Coulomb diamond measurements, in agreement with the lithographic
dimensions of the dot. The absence of excited states in Coulomb diamond
measurements, as well as the temperature dependence of Coulomb peak heights
indicate that the dot is in the multi-level transport regime. Fluctuations in
peak spacings larger than the estimated mean single-particle level spacing are
observed.Comment: 4 pages, 5 figure
From brain to earth and climate systems: Small-world interaction networks or not?
We consider recent reports on small-world topologies of interaction networks
derived from the dynamics of spatially extended systems that are investigated
in diverse scientific fields such as neurosciences, geophysics, or meteorology.
With numerical simulations that mimic typical experimental situations we have
identified an important constraint when characterizing such networks:
indications of a small-world topology can be expected solely due to the spatial
sampling of the system along with commonly used time series analysis based
approaches to network characterization
Elliptic aspects of statistical mechanics on spheres
Our earlier results on the temperature inversion properties and the
ellipticisation of the finite temperature internal energy on odd spheres are
extended to orbifold factors of odd spheres and then to other thermodynamic
quantities, in particular to the specific heat. The behaviour under modular
transformations is facilitated by the introduction of a modular covariant
derivative and it is shown that the specific heat on any odd sphere can be
expressed in terms of just three functions. It is also shown that the free
energy on the circle can be written elliptically.Comment: 22 pages. JyTe
Explicit coercivity estimates for the linearized Boltzmann and Landau operators
We prove explicit coercivity estimates for the linearized Boltzmann and
Landau operators, for a general class of interactions including any
inverse-power law interactions, and hard spheres. The functional spaces of
these coercivity estimates depend on the collision kernel of these operators.
They cover the spectral gap estimates for the linearized Boltzmann operator
with Maxwell molecules, improve these estimates for hard potentials, and are
the first explicit coercivity estimates for soft potentials (including in
particular the case of Coulombian interactions). We also prove a regularity
property for the linearized Boltzmann operator with non locally integrable
collision kernels, and we deduce from it a new proof of the compactness of its
resolvent for hard potentials without angular cutoff.Comment: 32 page
Cognitive performance in multiple system atrophy
The cognitive performance of a group of patients with multiple system atrophy (MSA) of striato-nigral predominance was compared with that of age and IQ matched control subjects, using three tests sensitive to frontal lobe dysfunction and a battery sensitive to memory and learning deficits in Parkinson's disease and dementia of the Alzheimer type. The MSA group showed significant deficits in all three of the tests previously shown to be sensitive to frontal lobe dysfunction. Thus, a significant proportion of patients from the MSA group failed an attentional set-shifting test, specifically at the stage when an extra-dimensional shift was required. They were also impaired in a subject-ordered test of spatial working memory. The MSA group showed deficits mostly confined to measures of speed of thinking, rather than accuracy, on the Tower of London task. These deficits were seen in the absence of consistent impairments in language or visual perception. Moreover, the MSA group showed no significant deficits in tests of spatial and pattern recognition previously shown to be sensitive to patients early in the course of probable Alzheimer's disease and only a few patients exhibited impairment on the Warrington Recognition Memory Test. There were impairments on other tests of visual memory and learning relative to matched controls, but these could not easily be related to fundamental deficits of memory or learning. Thus, on a matching-to-sample task the patients were impaired at simultaneous but not delayed matching to sample, whereas difficulties in a pattern-location learning task were more evident at its initial, easier stages. The MSA group showed no consistent evidence of intellectual deterioration as assessed from their performance on subtests of the Wechsler Adult Intelligence Scale (WAIS) and the National Adult Reading Test (NART). Consideration of individual cases showed that there was some heterogeneity in the pattern of deficits in the MSA group, with one patient showing no impairment, even in the face of considerable physical disability. The results show a distinctive pattern of cognitive deficits, unlike those previously seen using the same tests in patients with Parkinson's and Alzheimer's diseases, and suggesting a prominent frontal-lobe-like component. The implications for concepts of 'subcortical' dementia and 'fronto-striatal' cognitive dysfunction are considered
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