20,423 research outputs found
Wobbling of a liquid column between unequal discs
One of the most puzzling results of an experiment on the stability of long liquid columns under microgravity, performed aboard Spacelab-D2 in 1993 and named STACO, aiming at the analysis of deformations of nearly cylindrical liquid columns under several mechanical disturbances, is revisited here. It corresponds to the unexplained breakage of an 85 mm long liquid bridge of low viscosity silicone oil, established between unequal discs of 30 and 28 mm, intended to counterbalance the expected deformation by residual acceleration found in previous flights, and left idle because the vibrations and oscillations to be applied afterwards were not started, for fear of premature breakage. A detailed image analysis is performed to extract the maximum amount of data, to be able to check against available theories for axisymmetric and non-axisymmetric deformations of a liquid column
Effect of van der Waals forces on the stacking of coronenes encapsulated in a single-wall carbon nanotube and many-body excitation spectrum
We investigate the geometry, stability, electronic structure and optical
properties of C24H12 coronenes encapsulated in a single-wall (19,0) carbon
nanotube. By an adequate combination of advanced electronic-structure
techniques, involving weak and van derWaals interaction, as well as many-body
effects for establishing electronic properties and excitations, we have
accurately characterized this hybrid carbon nanostructure, which arises as a
promising candidate for opto-electronic nanodevices. In particular, we show
that the structure of the stacked coronenes inside the nanotube is
characterized by a rotation of every coronene with respect to its neighbors
through van derWaals interaction, which is of paramount importance in these
systems. We also suggest a tentative modification of the system in order this
particular rotation to be observed experimentally. A comparison between the
calculated many-body excitation spectrum of the systems involved reveals a
pronounced optical red-shift with respect to the coronene-stacking gas-phase.
The origin of this red-shift is explained in terms of the confinement of the
coronene molecules inside the nanotube, showing an excellent agreement with the
available experimental evidence
Time-Delayed transfer functions simulations for LMXBs
Recent works (Steeghs & Casares 2002, Casares et al. 2003, Hynes et al. 2003)
have demonstrated that Bowen flourescence is a very efficient tracer of the
companion star in LMXBs. We present a numerical code to simulate time-delayed
transfer functions in LMXBs, specific to the case of reprocessing in emission
lines. The code is also able to obtain geometrical and binary parameters by
fitting observed (X-ray + optical) light curves using simulated annealing
methods. In this work we present the geometrical model for the companion star
and the analytical model for the disc and show synthetic time-delay transfer
functions for different orbital phases and system parameters.Comment: Contribution presented at the conference "Interacting Binaries:
Accretion, Evolution and Outcomes", held in Cefalu, Sicily (Italy) in July
2004. To be published by AIP (American Institute of Physics), eds. L. A.
Antonelli, L. Burderi, F. D'Antona, T. Di Salvo, G.L. Israel, L. Piersanti,
O. Straniero, A. Tornambe. 4 pages, 4 figure
Effect of the number of vortices on the torque scaling in Taylor-Couette flow
Torque measurements in Taylor-Couette flow, with large radius ratio and large
aspect ratio, over a range of velocities up to a Reynolds number of 24 000 are
presented. Following a specific procedure, nine states with distinct number of
vortices along the axis were found and the aspect ratio of the vortices were
measured. The relationship between the speed and the torque for a given number
of vortices is reported. In the turbulent Taylor vortex flow regime, at
relatively high Reynolds number, a change in behaviour is observed
corresponding to intersections of the torque-speed curves for different states.
Before each intersection, the torque for a state with larger number of vortices
is higher. After each intersection, the torque for a state with larger number
of vortices is lower. The exponent, from the scaling laws of the torque, always
depends on the aspect ratio of the vortices. When the Reynolds number is
rescaled using the mean aspect ratio of the vortices, only a partial collapse
of the exponent data is found.Comment: 11 pages, 6 figure
Charge control in laterally coupled double quantum dots
We investigate the electronic and optical properties of InAs double quantum
dots grown on GaAs (001) and laterally aligned along the [110] crystal
direction. The emission spectrum has been investigated as a function of a
lateral electric field applied along the quantum dot pair mutual axis. The
number of confined electrons can be controlled with the external bias leading
to sharp energy shifts which we use to identify the emission from neutral and
charged exciton complexes. Quantum tunnelling of these electrons is proposed to
explain the reversed ordering of the trion emission lines as compared to that
of excitons in our system.Comment: 4 pages, 4 figures submitted to PRB Rapid Com
Using network science to analyze football passing networks: dynamics, space, time and the multilayer nature of the game
From the diversity of applications of Network Science, in this Opinion Paper
we are concerned about its potential to analyze one of the most extended group
sports: Football (soccer in U.S. terminology). As we will see, Network Science
allows addressing different aspects of the team organization and performance
not captured by classical analyses based on the performance of individual
players. The reason behind relies on the complex nature of the game, which,
paraphrasing the foundational paradigm of complexity sciences "can not be
analyzed by looking at its components (i.e., players) individually but, on the
contrary, considering the system as a whole" or, in the classical words of
after-match interviews "it's not just me, it's the team".Comment: 7 pages, 1 figur
Wetland restoration and nitrate reduction: the example of the periurban wetland of Vitoria-Gasteiz (Basque Country, North Spain)
Changes in land use and agricultural intensification caused wetlands on the quaternary aquifer of Vitoria-Gasteiz (Basque Country) to disappear some years ago and nitrate concentration in groundwaters increased very quickly. The Basque Government recently declared the East Sector of this aquifer a Vulnerable Zone according to the 91/676/CEE European Directive. Recently, the wetlands have been restored through the closure of the main drainage ditches, the consequent elevation of the water table and the abondonment of agricultural practices near the wetlands. This is the case of the Zurbano wetland. Restoration has allowed the recovery of its biogeochemical function, which has reduced nitrate concentrations in waters. Nitrate concentrations which exceed 50 mg l–1 in groundwaters entering into the wetland are less than 10 mg l–1 at the outlet. Conditions in the wetland are conducive to the loss of nitrates: organic matter rich wetted soils, clay presence allowing a local semiconfined flow and very low hydraulic gradient. Water quality monitoring at several points around the wetland showed the processes involved in nitrate loss, although some aspects still remain unresolved. However, during storm events, the wetland effectively reduces the nitrate concentration entering the Alegria River, the most important river on the quaternary aquifer
Diffusion in infinite and semi-infinite lattices with long-range coupling
We prove that for a one-dimensional infinite lattice, with long-range
coupling among sites, the diffusion of an initial delta-like pulse in the bulk,
is ballistic at all times. We obtain a closed-form expression for the mean
square displacement (MSD) as a function of time, and show some cases including
finite range coupling, exponentially decreasing coupling and power-law
decreasing coupling. For the case of an initial excitation at the edge of the
lattice, we find an approximate expression for the MSD that predicts ballistic
behavior at long times, in agreement with numerical results.Comment: 4 pages, 5 figures, submitted for publicatio
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