17,736 research outputs found
Rejuvenation and Memory in model Spin Glasses in 3 and 4 dimensions
We numerically study aging for the Edwards-Anderson Model in 3 and 4
dimensions using different temperature-change protocols. In D=3, time scales a
thousand times larger than in previous work are reached with the SUE machine.
Deviations from cumulative aging are observed in the non monotonic time
behavior of the coherence length. Memory and rejuvenation effects are found in
a temperature-cycle protocol, revealed by vanishing effective waiting times.
Similar effects are reported for the D=3$site-diluted ferromagnetic Ising model
(without chaos). However, rejuvenation is reduced if off-equilibrium
corrections to the fluctuation-dissipation theorem are considered. Memory and
rejuvenation are quantitatively describable in terms of the growth regime of
the spin-glass coherence length.Comment: Extended protocols. Accepted in Phys. Rev. B. 10 postscript figure
Discovery of a wide companion near the deuterium burning mass limit in the Upper Scorpius association
We present the discovery of a companion near the deuterium burning mass limit
located at a very wide distance, at an angular separation of 4.6+/-0.1 arcsec
(projected distance of ~ 670 AU) from UScoCTIO108, a brown dwarf of the very
young Upper Scorpius association. Optical and near-infrared photometry and
spectroscopy confirm the cool nature of both objects, with spectral types of M7
and M9.5, respectively, and that they are bona fide members of the association,
showing low gravity and features of youth. Their masses, estimated from the
comparison of their bolometric luminosities and theoretical models for the age
range of the association, are 60+/-20 and 14^{+2}_{-8} MJup, respectively. The
existence of this object around a brown dwarf at this wide orbit suggests that
the companion is unlikely to have formed in a disk based on current planet
formation models. Because this system is rather weakly bound, they did not
probably form through dynamical ejection of stellar embryos.Comment: 10 pages, including 4 figures and 2 table
Three-dimensional Heisenberg spin glass under a weak random anisotropy
We perform a finite-size scaling study of the three-dimensional Heisenberg spin glass in the presence of weak random anisotropic interactions, up to lattice sizes L = 32. Anisotropies have a major impact on the phase transition. The chiral-glass susceptibility does not diverge due to a large anomalous dimension. It follows that the anisotropic spin glass belongs to a Universality Class different from the isotropic model, which questions the applicability of the chirality scenario
Quantum Renormalization Group for 1 Dimensional Fermion Systems
Inspired by the superblock method of White, we introduce a simple
modification of the standard Renormalization Group (RG) technique for the study
of quantum lattice systems. Our method which takes into account the effect of
Boundary Conditions(BC), may be regarded as a simple way for obtaining first
estimates of many properties of quantum lattice systems. By applying this
method to the 1-dimensional free and interacting fermion system, we obtain the
ground state energy with much higher accuracy than the standard RG. We also
calculate the density-density correlation function in the free-fermion case
which shows good agreement with the exact result.Comment: LaTex file, 1 PS figur
The spin glass transition of the three dimensional Heisenberg spin glass
It is shown, by means of Monte Carlo simulation and Finite Size Scaling
analysis, that the Heisenberg spin glass undergoes a finite-temperature phase
transition in three dimensions. There is a single critical temperature, at
which both a spin glass and a chiral glass orderings develop. The Monte Carlo
algorithm, adapted from lattice gauge theory simulations, makes possible to
thermalize lattices of size L=32, larger than in any previous spin glass
simulation in three dimensions. High accuracy is reached thanks to the use of
the Marenostrum supercomputer. The large range of system sizes studied allow us
to consider scaling corrections.Comment: 4 pages, 4 Postscript figures, version to be published in Physical
Review Letter
IFLA WLIC 2012 in Helsinki, Finland: a first-time experience
This article is about the experience of two Filipino young students / new professionals (librarians) in their participation in the IFLA World Library and Information Congress (WLIC) 2012, in Helsinki, Finland
Keeper of Memories
During the pandemic, I, as a librarian and archivist, decided to reflect on the deaths and the tributes given to deceased friends and [well-known] personalities. This article is the output of this process. It talks about us, on memories, death and remembering
Digitizing the Archives: Trends, Innovations, and Best Practices
This presentation aimed to discuss pressing issues and concerns that necessitate the digitization of archival materials; to present latest technologies in digitization; and to cite practical and innovative projects involving digitization in special and academic library setting
Binary frequency of planet-host stars at wide separations: A new brown dwarf companion to a planet-host star
The aim of the project is to improve our knowledge on the multiplicity of
planet-host stars at wide physical separations.
We cross-matched approximately 6200 square degree area of the Southern sky
imaged by the Visible Infrared Survey Telescope for Astronomy (VISTA)
Hemisphere Survey (VHS) with the Two Micron All Sky Survey (2MASS) to look for
wide common proper motion companions to known planet-host stars. We
complemented our astrometric search with photometric criteria.
We confirmed spectroscopically the co-moving nature of seven sources out of
16 companion candidates and discarded eight, while the remaining one stays as a
candidate. Among these new wide companions to planet-host stars, we discovered
a T4.5 dwarf companion at 6.3 arcmin (~9000 au) from HIP70849, a K7V star which
hosts a 9 Jupiter mass planet with an eccentric orbit. We also report two new
stellar M dwarf companions to one G and one metal-rich K star. We infer stellar
and substellar binary frequencies for our complete sample of 37 targets of
5.4+/-3.8% and 2.7+/-2.7% (1 sigma confidence level), respectively, for
projected physical separations larger than ~60-160 au assuming the range of
distances of planet-host stars (24-75 pc). These values are comparable to the
frequencies of non planet-host stars. We find that the period-eccentricity
trend holds with a lack of multiple systems with planets at large
eccentricities (e > 0.2) for periods less than 40 days. However, the lack of
planets more massive than 2.5 Jupiter masses and short periods (<40 days)
orbiting single stars is not so obvious due to recent discoveries by
ground-based transit surveys and space missions.Comment: Accepted for publication in A&A, 13 pages, 5 figures, 3 tables,
optical spectra will be available at CDS Strasbour
Spin and chirality orderings of the one-dimensional Heisenberg spin glass with the long-range power-law interaction
The ordering of the one-dimensional Heisenberg spin glass interacting via the
long-range power-law interaction is studied by Monte Carlo simulations.
Particular attention is paid to the possible occurrence of the ``spin-chirality
decoupling'' for appropriate values of the power-law exponent \sigma. Our
result suggests that, for intermediate values of , the chiral-glass
order occurs at finite temperatures while the standard spin-glass order occurs
only at zero temperature.Comment: Proceedings of the Highly Frustrated Magnetism (HFM2006) conference.
To appear in a special issue of J. Phys. Condens. Matte
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