5,777 research outputs found
Message passing and Monte Carlo algorithms: connecting fixed points with metastable states
Mean field-like approximations (including naive mean field, Bethe and Kikuchi
and more general Cluster Variational Methods) are known to stabilize ordered
phases at temperatures higher than the thermodynamical transition. For example,
in the Edwards-Anderson model in 2-dimensions these approximations predict a
spin glass transition at finite . Here we show that the spin glass solutions
of the Cluster Variational Method (CVM) at plaquette level do describe well
actual metastable states of the system. Moreover, we prove that these states
can be used to predict non trivial statistical quantities, like the
distribution of the overlap between two replicas. Our results support the idea
that message passing algorithms can be helpful to accelerate Monte Carlo
simulations in finite dimensional systems.Comment: 6 pages, 6 figure
The metal abundance of circumnuclear star forming regions in early type spirals. Spectrophotometric observations
We have obtained long-slit observations in the optical and near infrared of
12 circumnuclear HII regions (CNSFR) in the early type spiral galaxies NGC
2903, NGC 3351 and NGC 3504 with the aim of deriving their chemical abundances.
Only for one of the regions, the [SIII] 6312 \AA was detected
providing, together with the nebular [SIII] lines at 9069,
9532 \AA, a value of the electron temperature of T([SIII])= 8400K. A semi-empirical method for the derivation of abundances in
the high metallicity regime is presented.
We obtain abundances which are comparable to those found in high metallicity
disc HII regions from direct measurements of electron temperatures and
consistent with solar values within the errors. The region with the highest
oxygen abundance is R3+R4 in NGC 3504, 12+log(O/H) = 8.85, about 1.5 solar if
the solar oxygen abundance is set at the value derived by Asplund et al.
(2005), 12+log(O/H) = 8.660.05. Region R7 in NGC 3351 has the
lowest oxygen abundance of the sample, about 0.6 times solar. In all the
observed CNSFR the O/H abundance is dominated by the O/H contribution,
as is also the case for high metallicity disc HII regions. For our observed
regions, however, also the S/S ratio is larger than one, contrary to
what is found in high metallicity disc HII regions for which, in general, the
sulphur abundances are dominated by S/H...Comment: 24 pages, 19 figures, accepted by MNRA
Ripples in Tapped or Blown Powder
We observe ripples forming on the surface of a granular powder in a container
submitted from below to a series of brief and distinct shocks. After a few
taps, the pattern turns out to be stable against any further shock of the same
amplitude. We find experimentally that the characteristic wavelength of the
pattern is proportional to the amplitude of the shocks. Starting from
consideration involving Darcy's law for air flow through the porous granulate
and avalanche properties, we build up a semi-quantitative model which fits
satisfactorily the set of experimental observations as well as a couple of
additional experiments.Comment: 7 pages, four postscript figures, submitted PRL 11/19/9
Carbon-fiber tips for scanning probe microscopes and molecular electronics experiments
We fabricate and characterize carbon-fiber tips for their use in combined
scanning tunneling and force microscopy based on piezoelectric quartz tuning
fork force sensors. An electrochemical fabrication procedure to etch the tips
is used to yield reproducible sub-100-nm apex. We also study electron transport
through single-molecule junctions formed by a single octanethiol molecule
bonded by the thiol anchoring group to a gold electrode and linked to a carbon
tip by the methyl group. We observe the presence of conductance plateaus during
the stretching of the molecular bridge, which is the signature of the formation
of a molecular junction.Comment: Conference Proceeding (Trends in NanoTechnology 2011, Tenerife
SPAIN); Nanoscale Research Letters, (2012) 7:25
Conjuncture Analysis of the Manufacturing Industry in Mexico. A Methodologic Proposal and Applications
In this work I use the Box-Jenkins methodology and extensions of the same one in order to make a conjuncture analysis of the manufacturing industry of Mexico to make a reliable prognosis about this industry.Box-Jenkins; industria; manufactura; Mexico; Pronóstico
Convergence and Regional Economic Growth in Mexico: 1970-1995
This paper studies absolute and conditional convergence (alfa and beta-convergence too,) in Mexico over the period 1970-1995. I use the neoclassical growth model and a cross-section data for empirics. I find evidence of conditional convergence (near at traditional 2% rate) for full period but different rates for other periods. I find also a faster convergence rate for "poor" states than the "rich" ones. Finally, our results point to significant impact of the human capital variables on economic growth.Convergence; Economic Growth; Mexico; human capital; convergencia; crecimiento economico; capital humano;
Approaching ultra-strong coupling in Transmon circuit-QED using a high-impedance resonator
In this experiment, we couple a superconducting Transmon qubit to a
high-impedance microwave resonator. Doing so leads to a large
qubit-resonator coupling rate , measured through a large vacuum Rabi
splitting of MHz. The coupling is a significant fraction of the
qubit and resonator oscillation frequencies , placing our system close
to the ultra-strong coupling regime ( on resonance).
Combining this setup with a vacuum-gap Transmon architecture shows the
potential of reaching deep into the ultra-strong coupling
with Transmon qubits
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