4,149 research outputs found
Spin susceptibility of interacting electrons in one dimension: Luttinger liquid and lattice effects
The temperature-dependent uniform magnetic susceptibility of interacting
electrons in one dimension is calculated using several methods. At low
temperature, the renormalization group reaveals that the Luttinger liquid spin
susceptibility approaches zero temperature with an infinite slope
in striking contrast with the Fermi liquid result and with the behavior of the
compressibility in the absence of umklapp scattering. This effect comes from
the leading marginally irrelevant operator, in analogy with the Heisenberg spin
1/2 antiferromagnetic chain. Comparisons with Monte Carlo simulations at higher
temperature reveal that non-logarithmic terms are important in that regime.
These contributions are evaluated from an effective interaction that includes
the same set of diagrams as those that give the leading logarithmic terms in
the renormalization group approach. Comments on the third law of thermodynamics
as well as reasons for the failure of approaches that work in higher dimensions
are given.Comment: 21 pages, latex including 5 eps figure
Editorial: Crosstalk between intonation and lexical tones: Linguistic, cognitive and neuroscience perspectives
The interplay between categorical and continuous aspects of the speech signal remains central and yet controversial in the fields of phonetics and phonology. The division between phonological abstractions and phonetic variations has been particularly relevant to the unraveling of diverse communicative functions of pitch in the domain of prosody. Pitch influences vocal communication in two major but fundamentally different ways, and lexical and intonational tones exquisitely capture these functions. Lexical tone contrasts convey lexical meanings as well as derivational meanings at the word level and are grammatically encoded as discrete structures. Intonational tones, on the other hand, signal post-lexical meanings at the phrasal level and typically allow gradient pragmatic variations. Since categorical and gradient uses of pitch are ubiquitous and closely intertwined in their physiological and psychological processes, further research is warranted for a more detailed understanding of their structural and functional characterisations. This Research Topic addresses this matter from a wide range of perspectives, including first and second language acquisition, speech production and perception, structural and functional diversity, and working with distinct languages and experimental measures. In the following, we provide a short overview of the contributions submitted to this topi
Invariants of Triangular Lie Algebras
Triangular Lie algebras are the Lie algebras which can be faithfully
represented by triangular matrices of any finite size over the real/complex
number field. In the paper invariants ('generalized Casimir operators') are
found for three classes of Lie algebras, namely those which are either strictly
or non-strictly triangular, and for so-called special upper triangular Lie
algebras. Algebraic algorithm of [J. Phys. A: Math. Gen., 2006, V.39, 5749;
math-ph/0602046], developed further in [J. Phys. A: Math. Theor., 2007, V.40,
113; math-ph/0606045], is used to determine the invariants. A conjecture of [J.
Phys. A: Math. Gen., 2001, V.34, 9085], concerning the number of independent
invariants and their form, is corroborated.Comment: LaTeX2e, 16 pages; misprints are corrected, some proofs are extende
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Update of Atlas of Major Texas Oil Reservoirs Data Base and Atlas of Major Texas Gas Reservoirs Data Base
Updating both the "Atlas of Major Texas Oil Reservoirs: Database" (Holtz and others, 1991) and the "Atlas of Major Texas Gas Reservoirs: Database" (Garrett and others, 1991) centered on updating cumulative production data current to December 31, 1992, for reservoirs already in the database and adding new significant-sized reservoirs (cumulative production greater than 1 million barrels of oil equivalent) to the databases. Addition of new reservoirs to the database resulted in the modification of existing plays or the determination of new plays. Play boundaries were also modified to accommodate the additional reservoirs. Oil and gas production data used for the cumulative production update and the determination of significant-sized reservoirs were obtained from Dwight's Energy data. For reservoirs already included in the Atlas databases, annual production values were added to the cumulative production already determined by the Bureau of Economic Geology (BEG) or reported by the Railroad Commission of Texas. For new reservoirs, the cumulative production values reported by Dwight's Energy data were applied. Oil reservoirs originally listed in both databases because of large gas production were combined and now are listed only in the updated Oil Atlas database.Bureau of Economic Geolog
Can we build on social movement theories to develop and improve community‐based participatory research? a framework synthesis review
A long‐standing challenge in community‐based participatory research (CBPR) has been to anchor practice and evaluation in a relevant and comprehensive theoretical framework of community change. This study describes the development of a multidimensional conceptual framework that builds on social movement theories to identify key components of CBPR processes. Framework synthesis was used as a general literature search and analysis strategy. An initial conceptual framework was developed from the theoretical literature on social movement. A literature search performed to identify illustrative CBPR projects yielded 635 potentially relevant documents, from which eight projects (corresponding to 58 publications) were retained after record and full‐text screening. Framework synthesis was used to code and organize data from these projects, ultimately providing a refined framework. The final conceptual framework maps key concepts of CBPR mobilization processes, such as the pivotal role of the partnership; resources and opportunities as necessary components feeding the partnership's development; the importance of framing processes; and a tight alignment between the cause (partnership's goal), the collective action strategy, and the system changes targeted. The revised framework provides a context‐specific model to generate a new, innovative understanding of CBPR mobilization processes, drawing on existing theoretical foundations
The brightest pure-H ultracool white dwarf
We report the identification of LSR J0745+2627 in the United Kingdom InfraRed
Telescope Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) as a cool
white dwarf with kinematics and age compatible with the thick-disk/halo
population. LSR J0745+2627 has a high proper motion (890 mas/yr) and a high
reduced proper motion value in the J band (H_J=21.87). We show how the
infrared-reduced proper motion diagram is useful for selecting a sample of cool
white dwarfs with low contamination. LSR J0745+2627 is also detected in the
Sloan Digital Sky Survey (SDSS) and the Wide-field Infrared Survey Explorer
(WISE). We have spectroscopically confirmed this object as a cool white dwarf
using X-Shooter on the Very Large Telescope. A detailed analysis of its
spectral energy distribution reveals that its atmosphere is compatible with a
pure-H composition model with an effective temperature of 3880+-90 K. This
object is the brightest pure-H ultracool white dwarf (Teff<4000 K) ever
identified. We have constrained the distance (24-45 pc), space velocities and
age considering different surface gravities. The results obtained suggest that
LSR J0745+2627 belongs to the thick-disk/halo population and is also one of the
closest ultracool white dwarfs.Comment: 5 pages, 7 figures, accepted for publication in A&A Letter
Invariants of Lie Algebras with Fixed Structure of Nilradicals
An algebraic algorithm is developed for computation of invariants
('generalized Casimir operators') of general Lie algebras over the real or
complex number field. Its main tools are the Cartan's method of moving frames
and the knowledge of the group of inner automorphisms of each Lie algebra.
Unlike the first application of the algorithm in [J. Phys. A: Math. Gen., 2006,
V.39, 5749; math-ph/0602046], which deals with low-dimensional Lie algebras,
here the effectiveness of the algorithm is demonstrated by its application to
computation of invariants of solvable Lie algebras of general dimension
restricted only by a required structure of the nilradical.
Specifically, invariants are calculated here for families of real/complex
solvable Lie algebras. These families contain, with only a few exceptions, all
the solvable Lie algebras of specific dimensions, for whom the invariants are
found in the literature.Comment: LaTeX2e, 19 page
Infinite families of superintegrable systems separable in subgroup coordinates
A method is presented that makes it possible to embed a subgroup separable
superintegrable system into an infinite family of systems that are integrable
and exactly-solvable. It is shown that in two dimensional Euclidean or
pseudo-Euclidean spaces the method also preserves superintegrability. Two
infinite families of classical and quantum superintegrable systems are obtained
in two-dimensional pseudo-Euclidean space whose classical trajectories and
quantum eigenfunctions are investigated. In particular, the wave-functions are
expressed in terms of Laguerre and generalized Bessel polynomials.Comment: 19 pages, 6 figure
Magnetic and pair correlations of the Hubbard model with next-nearest-neighbor hopping
A combination of analytical approaches and quantum Monte Carlo simulations is
used to study both magnetic and pairing correlations for a version of the
Hubbard model that includes second-neighbor hopping as a
model for high-temperature superconductors. Magnetic properties are analyzed
using the Two-Particle Self-Consistent approach. The maximum in magnetic
susceptibility as a function of doping appears both at finite
and at but for two totally different physical reasons. When
, it is induced by antiferromagnetic correlations while at
it is a band structure effect amplified by interactions.
Finally, pairing fluctuations are compared with -matrix results to
disentangle the effects of van Hove singularity and of nesting on
superconducting correlations. The addition of antiferromagnetic fluctuations
increases slightly the -wave superconducting correlations despite the
presence of a van Hove singularity which tends to decrease them in the
repulsive model. Some aspects of the phase diagram and some subtleties of
finite-size scaling in Monte Carlo simulations, such as inverted finite-size
dependence, are also discussed.Comment: Revtex, 8 pages + 15 uuencoded postcript figure
Evidence from K2 for rapid rotation in the descendant of an intermediate-mass star
Using patterns in the oscillation frequencies of a white dwarf observed by
K2, we have measured the fastest rotation rate, 1.13(02) hr, of any isolated
pulsating white dwarf known to date. Balmer-line fits to follow-up spectroscopy
from the SOAR telescope show that the star (SDSSJ0837+1856, EPIC 211914185) is
a 13,590(340) K, 0.87(03) solar-mass white dwarf. This is the highest mass
measured for any pulsating white dwarf with known rotation, suggesting a
possible link between high mass and fast rotation. If it is the product of
single-star evolution, its progenitor was a roughly 4.0 solar-mass
main-sequence B star; we know very little about the angular momentum evolution
of such intermediate-mass stars. We explore the possibility that this rapidly
rotating white dwarf is the byproduct of a binary merger, which we conclude is
unlikely given the pulsation periods observed.Comment: 5 pages, 4 figure, 1 table; accepted for publication in The
Astrophysical Journal Letter
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