7,744 research outputs found
Observation of a parity oscillation in the conductance of atomic wires
Using a scanning tunnel microscope or mechanically controlled break
junctions, atomic contacts of Au, Pt and Ir are pulled to form chains of atoms.
We have recorded traces of conductance during the pulling process and averaged
these for a large amount of contacts. An oscillatory evolution of conductance
is observed during the formation of the monoatomic chain suggesting a
dependence on even or odd numbers of atoms forming the chain. This behaviour is
not only present in the monovalent metal Au, as it has been previously
predicted, but is also found in the other metals which form chains suggesting
it to be a universal feature of atomic wires
Exact relativistic models of thin disks around static black holes in a magnetic field
The exact superposition of a central static black hole with surrounding thin
disk in presence of a magnetic field is investigated. We consider two models of
disk, one of infinite extension based on a Kuzmin-Chazy-Curzon metric and other
finite based on the first Morgan-Morgan disk. We also analyze a simple model of
active galactic nuclei consisting of black hole, a Kuzmin-Chazy-Curzon disk and
two rods representing jets, in presence of magnetic field. To explain the
stability of the disks we consider the matter of the disk made of two
pressureless streams of counterrotating charged particles (counterrotating
model) moving along electrogeodesic. Using the Rayleigh criterion we derivate
for circular orbits the stability conditions of the particles of the streams.
The influence of the magnetic field on the matter properties of the disk and on
its stability are also analyzed.Comment: 17 pages, 14 figures. arXiv admin note: text overlap with
arXiv:gr-qc/0409109 by other author
Bose-Einstein Condensate Driven by a Kicked Rotor in a Finite Box
We study the effect of different heating rates of a dilute Bose gas confined
in a quasi-1D finite, leaky box. An optical kicked-rotor is used to transfer
energy to the atoms while two repulsive optical beams are used to confine the
atoms. The average energy of the atoms is localized after a large number of
kicks and the system reaches a nonequilibrium steady state. A numerical
simulation of the experimental data suggests that the localization is due to
energetic atoms leaking over the barrier. Our data also indicates a correlation
between collisions and the destruction of the Bose-Einstein condensate
fraction.Comment: 7 pages, 8 figure
Effects on Berry Shrinkage in Vitis vinifera. L cv. ‘Merlot’ From Changes in Canopy/Root Ratio: A Preliminary Approach
A trial was conducted to find a possible relationship between the canopy/root ratio and the incidence and severity of premature berry shrinkage, and to propose an alternative to avoid this phenomenon in ‘Merlot’ grapevines. The ratio was changed by cutting foliage at a certain height 15 days before véraison, and by delaying the removal of trunk shoots. Treatments were the control (T1), 50% foliage area of control (T2), 75% foliage area of control (T3), and delayed trunk shoot removal (T4). Foliage area and the canopy/root ratio were lower in the T2 and T3 treatments. T4 was ineffective in changing the parameters. The incidence of berry shrinkage was lower for the T2 and T3 treatments, with the percentage of affected plants dropping from the 52% of the control to 22.9% and 31.3% for T2 and T3 respectively, and from 52.4% of the affected bunches to 16.6% and 21.2% for the same treatments respectively. The percentage of affected bunches falling into the range of moderate to severe damage fell from the 24% of the control to 5.2% and 3.9% for T2 and T3 respectively. Therefore, it is possible to avoid the incidence and severity of berry shrinkage by decreasing the canopy/root ratio in ‘Merlot’ grapevines
Prolactin responses to stress induced by a competitive swimming effort
Purpose:The aim of the present study was to investigate the changes in prolactin (PRL) plasma concentrations induced by competitive swimming practice. Methods:Twenty-three males, 13 trained swimmers (experimental group) and 10 sedentary and healthy students (age-matched control group) took part in this investigation. The swimmers were assessed at three points: basal conditions, pre-and post-swimming competition (100 m freestyle), whereas subjects from the control group only undertook the basal trial. The variables analysed were: several body composition measures, anxiety level (STAI questionnaire), PRL and lactic acid concentrations. Results:No statistical differences were observed in PRL basal levels between groups. An evident PRL response to pre-competition psychological stress was observed in the experimental group, since the PRL plasma concentration rosefrom 4.02±0.53 ng/ml (basal conditions) to 5.52±0.53 ng/ml (p≤0.05). The PRL response to the competitive effort produced an important increase in its plasma concentration (10.07±1.59 ng/ml), showed statistical differences from pre-competition (p≤0.01) and from basal conditions (p≤0.001). A significant rise in plasma lactate levels just at the end of the effort was found, although it did not correlate with PRL levels in the same situation. Conclusion:While we observed a remarkable response of PRL to psychological and physiological stress induced by a short term competitive effort in swimming, no changes in PRL basal levels were exhibitedwith swim training. More research is needed to clarify these findings
Wannier-Stark ladders in one-dimensional elastic systems
The optical analogues of Bloch oscillations and their associated
Wannier-Stark ladders have been recently analyzed. In this paper we propose an
elastic realization of these ladders, employing for this purpose the torsional
vibrations of specially designed one-dimensional elastic systems. We have
measured, for the first time, the ladder wave amplitudes, which are not
directly accessible either in the quantum mechanical or optical cases. The wave
amplitudes are spatially localized and coincide rather well with theoretically
predicted amplitudes. The rods we analyze can be used to localize different
frequencies in different parts of the elastic systems and viceversa.Comment: 10 pages, 6 figures, accepted in Phys. Rev. Let
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