38,649 research outputs found
Pathology of Schwinger boson mean field theory for Heisenberg spin models
We have re-analyze the Schwinger boson mean field theory (SBMFT) for
Heisenberg spin models on the cubic lattice. We find that the second order
phase transition point for magnetic ordering previously reported corresponds to
a local maximum of the free energy functional. For both ferromagnetic and
antiferromagnetic Heisenberg models with spin , where ,
the mean field transitions are first order from the magnetically long-ranged
ordered phase to the completely uncorrelated phase. In addition to erroneously
giving a first order transition for magnetic ordering, the mean field theory
does not include a phase with finite short-range correlation, thus negating one
of the prime advantages of SBMFT. The relevance of these pathologies to other
situations beyond the cubic lattice is discussed.Comment: 15 pages including 6 postscript figure
Theory for spin and orbital orderings in high temperature phase in
Motivated by the recent neutron diffraction experiment on , we
consider a microscopic model where each ion is occupied by two 3d
electrons of parallel spins with two fold degenerate orbital configurations.
The mean field classical solutions of the spin-orbital superexchange model
predicts an antiferro-orbital ordering at a higher temperature followed by a
C-type antiferromagnetic spin ordering at a lower temperature. Our results are
qualitatively consistent with the observed orbital phase transition at and the spin phase transition at in .Comment: 7 pages, 3 figures and 2 tables. Accepted to be published in PR
Uncovering the expression patterns of chimeric transcripts using surveys of affymetrix GeneChips.
BACKGROUND: A chimeric transcript is a single RNA sequence which results from the transcription of two adjacent genes. Recent studies estimate that at least 4% of tandem human gene pairs may form chimeric transcripts. Affymetrix GeneChip data are used to study the expression patterns of tens of thousands of genes and the probe sequences used in these microarrays can potentially map to exotic RNA sequences such as chimeras. RESULTS: We have studied human chimeras and investigated their expression patterns using large surveys of Affymetrix microarray data obtained from the Gene Expression Omnibus. We show that for six probe sets, a unique probe mapping to a transcript produced by one of the adjacent genes can be used to identify the expression patterns of readthrough transcripts. Furthermore, unique probes mapping to an intergenic exon present only in the MASK-BP3 chimera can be used directly to study the expression levels of this transcript. CONCLUSIONS: We have attempted to implement a new method for identifying tandem chimerism. In this analysis unambiguous probes are needed to measure run-off transcription and probes that map to intergenic exons are particularly valuable for identifying the expression of chimeras
Identifying Web Tables - Supporting a Neglected Type of Content on the Web
The abundance of the data in the Internet facilitates the improvement of
extraction and processing tools. The trend in the open data publishing
encourages the adoption of structured formats like CSV and RDF. However, there
is still a plethora of unstructured data on the Web which we assume contain
semantics. For this reason, we propose an approach to derive semantics from web
tables which are still the most popular publishing tool on the Web. The paper
also discusses methods and services of unstructured data extraction and
processing as well as machine learning techniques to enhance such a workflow.
The eventual result is a framework to process, publish and visualize linked
open data. The software enables tables extraction from various open data
sources in the HTML format and an automatic export to the RDF format making the
data linked. The paper also gives the evaluation of machine learning techniques
in conjunction with string similarity functions to be applied in a tables
recognition task.Comment: 9 pages, 4 figure
Iatrogenic superior mesenteric artery syndrome
We have carefully read the article "Superior mesenteric artery syndrome: an uncommon cause of intestinal obstruction" by José BarquÃn-Yagüez et al. and we would like to report one case with the same diagnosis but with another etiology.info:eu-repo/semantics/publishedVersio
Nonlinear c-axis transport in Bi_2Sr_2CaCu_2O_(8+d) from two-barrier tunneling
Motivated by the peculiar features observed through intrinsic tunneling
spectroscopy of BiSrCaCuO mesas in the normal state,
we have extended the normal state two-barrier model for the c-axis transport
[M. Giura et al., Phys. Rev. B {\bf 68}, 134505 (2003)] to the analysis of
curves. We have found that the purely normal-state model reproduces all
the following experimental features: (a) the parabolic -dependence of
in the high- region (above the conventional pseudogap temperature),
(b) the emergence and the nearly voltage-independent position of the "humps"
from this parabolic behavior lowering the temperature, and (c) the crossing of
the absolute curves at a characteristic voltage . Our
findings indicate that conventional tunneling can be at the origin of most of
the uncommon features of the c axis transport in
BiSrCaCuO. We have compared our calculations to
experimental data taken in severely underdoped and slightly underdoped
BiSrCaCuO small mesas. We have found good agreement
between the data and the calculations, without any shift of the calculated
dI/dV on the vertical scale. In particular, in the normal state (above
) simple tunneling reproduces the experimental dI/dV quantitatively.
Below quantitative discrepancies are limited to a simple rescaling of
the voltage in the theoretical curves by a factor 2. The need for such
modifications remains an open question, that might be connected to a change of
the charge of a fraction of the carriers across the pseudogap opening.Comment: 7 pages, 5 figure
Dynamically generated dimension reduction and crossover in a spin orbital model
We study a spin orbital model in which the spin-spin interaction couples
linearly to the orbital isospin. Fluctuations drive the transition from
paramagnetic state to C type ordered state into a strongly first order one, as
observed in . At T=0, there is a FOCS to FOGS transition. Close to the
transition point, the system shows dynamically generated dimension reduction
and crossover, resulting in one or more spin reentrant transitions.Comment: Submitted to PRL. 4 pages and one figur
Why do patients with myositis die? A retrospective analysis of a single-centre cohort
OBJECTIVES: Causes of death in inflammatory myopathies have rarely been studied. We have assessed a cohort of myositis patients followed in a single centre over a 37-year period, reviewing the mortality rate, causes of death and predictors of poor prognosis.
METHODS: We performed a single-centre, retrospective study on patients aged ≥16 years fulfilling 3 or 4 of the Bohan and Peter criteria, noting their demographic data, clinical features, serology, treatment and outcome.
RESULTS: Of 97 patients identified, 74.2% were female. The mean age at diagnosis was 40.5 years (SD 13.2). 38.1% had adult-onset dermatomyositis, 36.1% adult-onset polymyositis and 25.8% overlap myositis. 96.9% had upper and lower limb involvement (UL+/LL+) and 62.9% had a highest CK≥10 times the upper limit of normal. 33% had significant infection(s). The disease course was chronic persistent in 29.9%, relapsing and remitting in 34% and monophasic in 36.1%. All received steroids and 92.8% other immunosuppressant(s). The median follow-up was 9 years (IQR 11.5). The estimated cumulative proportion survival at 5, 10, 15 and 20 years were 94.6%, 82.2%, 72,1% and 66.1%, respectively. 24.7% of patients died, mostly due to infection (29.2%). In univariate analysis, lung involvement (HR 1.78, p=0.013), infection (HR 4.18, p=0.003) and UL+/LL+ (HR 0.13, p=0.010) were statistically significantly associated with the risk of death. In the multivariate analysis infection (HR 3.68, p=0.009) and UL+/LL+ (HR 0.16, p=0.027) were statistically significantly associated with survival.
CONCLUSIONS: A good long-term survival is reported. Nevertheless, careful follow-up of myositis patients is important
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