3,036 research outputs found
Diffusive counter dispersion of mass in bubbly media
We consider a liquid bearing gas bubbles in a porous medium. When gas bubbles
are immovably trapped in a porous matrix by surface-tension forces, the
dominant mechanism of transfer of gas mass becomes the diffusion of gas
molecules through the liquid. Essentially, the gas solution is in local
thermodynamic equilibrium with vapor phase all over the system, i.e., the
solute concentration equals the solubility. When temperature and/or pressure
gradients are applied, diffusion fluxes appear and these fluxes are faithfully
determined by the temperature and pressure fields, not by the local solute
concentration, which is enslaved by the former. We derive the equations
governing such systems, accounting for thermodiffusion and gravitational
segregation effects which are shown not to be neglected for geological
systems---marine sediments, terrestrial aquifers, etc. The results are applied
for the treatment of non-high-pressure systems and real geological systems
bearing methane or carbon dioxide, where we find a potential possibility of the
formation of gaseous horizons deep below a porous medium surface. The reported
effects are of particular importance for natural methane hydrate deposits and
the problem of burial of industrial production of carbon dioxide in deep
aquifers.Comment: 10 pages, 5 figures, 1 table, Physical Review
Classical simulation of measurement-based quantum computation on higher-genus surface-code states
We consider the efficiency of classically simulating measurement-based
quantum computation on surface-code states. We devise a method for calculating
the elements of the probability distribution for the classical output of the
quantum computation. The operational cost of this method is polynomial in the
size of the surface-code state, but in the worst case scales as in the
genus of the surface embedding the code. However, there are states in the
code space for which the simulation becomes efficient. In general, the
simulation cost is exponential in the entanglement contained in a certain
effective state, capturing the encoded state, the encoding and the local
post-measurement states. The same efficiencies hold, with additional
assumptions on the temporal order of measurements and on the tessellations of
the code surfaces, for the harder task of sampling from the distribution of the
computational output.Comment: 21 pages, 13 figure
The phase diagram of the lattice Calogero-Sutherland model
We introduce a {\it lattice} version of the Calogero Sutherland model adapted
to describe pairwise interacting steps with discrete positions on a
vicinal surface. The configurational free energy is obtained within a transfer
matrix method. The full phase diagram for attractive and for repulsive
interaction is deduced. For attraction, critical temperatures of faceting
transitions are found to depend on step density.Comment: latex PRBCalogSuth.tex, 6 files, 4 pages [SPEC-S00/900
Probing microscopic origins of confined subdiffusion by first-passage observables
Subdiffusive motion of tracer particles in complex crowded environments, such
as biological cells, has been shown to be widepsread. This deviation from
brownian motion is usually characterized by a sublinear time dependence of the
mean square displacement (MSD). However, subdiffusive behavior can stem from
different microscopic scenarios, which can not be identified solely by the MSD
data. In this paper we present a theoretical framework which permits to
calculate analytically first-passage observables (mean first-passage times,
splitting probabilities and occupation times distributions) in disordered media
in any dimensions. This analysis is applied to two representative microscopic
models of subdiffusion: continuous-time random walks with heavy tailed waiting
times, and diffusion on fractals. Our results show that first-passage
observables provide tools to unambiguously discriminate between the two
possible microscopic scenarios of subdiffusion. Moreover we suggest experiments
based on first-passage observables which could help in determining the origin
of subdiffusion in complex media such as living cells, and discuss the
implications of anomalous transport to reaction kinetics in cells.Comment: 21 pages, 3 figures. Submitted versio
Quantization of Superflow Circulation and Magnetic Flux with a Tunable Offset
Quantization of superflow-circulation and of magnetic-flux are considered for
systems, such as superfluid He-A and unconventional superconductors, having
nonscalar order parameters. The circulation is shown to be the anholonomy in
the parallel transport of the order parameter. For multiply-connected samples
free of distributed vorticity, circulation and flux are predicted to be
quantized, but generically to nonintegral values that are tunably offset from
integers. This amounts to a version of Aharonov-Bohm physics. Experimental
settings for testing these issues are discussed.Comment: 5 two-column pages, ReVTeX, figure available upon request (to
[email protected]
Velocity vector (3D) measurement for spherical objects using an electro-optical device
The present paper describes a procedure to measure the velocity vector (3D) of a spherical
object using an electro-optical device configured as a single large detection area optical
barrier. The proposed procedure allows a measurement accuracy up to 0.1% in some cases
and presents several advantages in relation to other measurement procedures like image
processing, doppler-radar and some other electro-optical devices. The procedure is independent
of the relative position of the measurement device in relation to the object trajectory.
The fact of using a single optical barrier reduces the space required in the movement
direction and increase the cases where the device can be used. A prototype has been built
and tested.Lluna Gil, E.; Santiago-Praderas, V.; Defez Garcia, B.; Dunai, L.; Peris Fajarnes, G. (2011). Velocity vector (3D) measurement for spherical objects using an electro-optical device. Measurement. 44(9):1723-1729. doi:10.1016/j.measurement.2011.07.006S1723172944
Nuclear structure studies with the 7Li(e,e'p) reaction
Experimental momentum distributions for the transitions to the ground state
and first excited state of 6He have been measured via the reaction
7Li(e,e'p)6He, in the missing momentum range from -70 to 260 MeV/c. They are
compared to theoretical distributions calculated with mean-field wave functions
and with variational Monte Carlo (VMC) wave functions which include strong
state-dependent correlations in both 7Li and 6He. These VMC calculations
provide a parameter-free prediction of the momentum distribution that
reproduces the measured data, including its normalization. The deduced summed
spectroscopic factor for the two transitions is 0.58 +/- 0.05, in perfect
agreement with the VMC value of 0.60. This is the first successful comparison
of experiment and ab initio theory for spectroscopic factors in p-shell nuclei.Comment: 4 pages, 3 figure
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