9,279 research outputs found
On the Path Integral Representation for Spin Systems
We propose a classical constrained Hamiltonian theory for the spin. After the
Dirac treatment we show that due to the existence of second class constraints
the Dirac brackets of the proposed theory represent the commutation relations
for the spin. We show that the corresponding partition function, obtained via
the Fadeev-Senjanovic procedure, coincides with the one obtained using coherent
states. We also evaluate this partition function for the case of a single spin
in a magnetic field.Comment: To be published in J.Phys. A: Math. and Gen. Latex file, 12 page
Testicular histopathology, semen analysis and FSH, predictive value of sperm retrieval: supportive counseling in case of reoperation after testicular sperm extraction (TESE)
Background: To provide indicators for the likelihood of sperm retrieval in patients undergoing testicular sperm extraction is a major issue in the management of male infertility by TESE. The aim of our study was to determine the impact of different parameters, including testicular histopathology, on sperm retrieval in case of reoperation in patients undergoing testicular sperm extraction. Methods: We retrospectively analyzed 486 patients who underwent sperm extraction for intracytoplasmic sperm injection and testicular biopsy. Histology was classified into: normal spermatogenesis; hypospermatogenesis (reduction in the number of normal spermatogenetic cells); maturation arrest (absence of the later stages of spermatogenesis); and Sertoli cell only (absence of germ cells). Semen analysis and serum FSH, LH and testosterone were measured. Results: Four hundred thirty patients had non obstructive azoospermia, 53 severe oligozoospermia and 3 necrozoospermia. There were 307 (63%) successful sperm retrieval. Higher testicular volume, lower levels of FSH, and better histological features were predictive for sperm retrieval. The same parameters and younger age were predictive factors for shorter time for sperm recovery. After multivariable analysis, younger age, better semen parameters, better histological features and lower values of FSH remained predictive for shorter time for sperm retrieval while better semen and histology remained predictive factors for successful sperm retrieval. The predictive capacity of a score obtained by summing the points assigned for selected predictors (1 point for Sertoli cell only, 0.33 points for azoospermia, 0.004 points for each FSH mIU/ml) gave an area under the ROC curve of 0.843. Conclusions: This model can help the practitioner with counseling infertile men by reliably predicting the chance of obtaining spermatozoa with testicular sperm extraction when a repeat attempt is planne
Sudden hearing loss as an early detector of multiple sclerosis: a systematic review
To evaluate whether Sudden Sensorineural Hearing Loss (S-SNHL) may be an early symptom of Multiple Sclerosis (MS). A systematic review was conducted using the following keywords: "Multiple sclerosis, hearing loss, sudden hearing loss, vertigo, tinnitus, magnetic resonance imaging, otoacoustic emission, auditory brainstem responses, white matter lesions, sensorineural hearing loss, symptoms of MS and otolaryngology, nerve disease and MS". Only the articles that included results of at least one auditory test and MRI were considered. We evaluated the prevalence of SNHL in patients with MS, the presence of different forms of SNHL (S-SNHL and Progressive SNHL (P-SNHL)) and their correlation with the stage of MS, the results of electrophysiological tests, and the location (if any) of MS lesions as detected by white matter hyperintensities in the MRI. We reviewed a total of 47 articles, which included 29 case reports, 6 prospective studies, 6 cohort studies, 4 case-control studies, and 2 retrospective studies. 25% of patients suffered from SNHL. S-SNHL typically occurred in the early stage of the disease (92% of patients) and was the only presenting symptom in 43% of female subjects. Instead, P-SNHL occurred in the late stage of MS (88% of patients). Auditory Brainstem Responses (ABR) were abnormal in all MS patients with S-SNHL. When S-SNHL appeared during the early stage of the disease, MS lesions were found in the brain in 60% of patients and in the Internal Auditory Canal in 40% of patients. ABR remained abnormal after recovery. S-SNHL can be an early manifestation of MS and should always be considered in the differential diagnosis of this condition, especially in women. The pathophysiology can be explained by the involvement of microglia attacking the central and/or peripheral auditory pathways as indicated by WMHs
One-electron self energies and spectral functions for the t-J model in the large-N limit
Using a recently developed perturbative approach, which considers Hubbard
operators as fundamental excitations, we have performed electronic self-energy
and spectral function calculations for the model on the square lattice.
We have found that the spectral functions along the Fermi surface are
isotropic, even close to the critical doping where the -density wave phase
takes place. Fermi liquid behavior with scattering rate and a
finite quasiparticle weight was obtained. decreases with decreasing
doping taking low values for low doping. Results are compared with other ones,
analytical and numerical like slave-boson and Lanczos diagonalization finding
agreement. We discuss our results in the light of recent experiments in
cuprates.Comment: 10 pages, 9 figures, accepted for publication in Phys. Rev.
Prediction of hearing recovery in sudden deafness treated with intratympanic steroids
The present study aims to obtain a probability model allowing the prediction of the auditory recovery in patients affected by sudden sensorineural hearing loss treated exclusively with intratympanic steroids. A monocentric retrospective chart review of three-hundred eighty-one patients has been performed. A Probit model was used to investigate the correlation between the success of the treatment (marked or total recovery according to Furuashi's criteria), and the delay between the onset of disease and the beginning of therapy. The age of the patients and the audiometric curve shapes were included in the analysis. Results show that delay is negatively correlated with the variable success. Considering the entire sample, each day of delay decreases by 3% the probability of success. The prediction model shows that for every day that passes from the onset of the disease the probability of success declines in absence of the medical treatment, hence we conclude that early treatment is strongly recommended
A remark on an overdetermined problem in Riemannian Geometry
Let be a Riemannian manifold with a distinguished point and
assume that the geodesic distance from is an isoparametric function.
Let be a bounded domain, with , and consider
the problem in with on ,
where is the -Laplacian of . We prove that if the normal
derivative of along the boundary of is a
function of satisfying suitable conditions, then must be a
geodesic ball. In particular, our result applies to open balls of
equipped with a rotationally symmetric metric of the form
, where is the standard metric of the sphere.Comment: 8 pages. This paper has been written for possible publication in a
special volume dedicated to the conference "Geometric Properties for
Parabolic and Elliptic PDE's. 4th Italian-Japanese Workshop", organized in
Palinuro in May 201
Genome-wide signatures of population bottlenecks and diversifying selection in European wolves
Genomic resources developed for domesticated species provide powerful tools for studying the evolutionary history of their wild relatives. Here we use 61K single-nucleotide polymorphisms (SNPs) evenly spaced throughout the canine nuclear genome to analyse evolutionary relationships among the three largest European populations of grey wolves in comparison with other populations worldwide, and investigate genome-wide effects of demographic bottlenecks and signatures of selection. European wolves have a discontinuous range, with large and connected populations in Eastern Europe and relatively smaller, isolated populations in Italy and the Iberian Peninsula. Our results suggest a continuous decline in wolf numbers in Europe since the Late Pleistocene, and long-term isolation and bottlenecks in the Italian and Iberian populations following their divergence from the Eastern European population. The Italian and Iberian populations have low genetic variability and high linkage disequilibrium, but relatively few autozygous segments across the genome. This last characteristic clearly distinguishes them from populations that underwent recent drastic demographic declines or founder events, and implies long-term bottlenecks in these two populations. Although genetic drift due to spatial isolation and bottlenecks seems to be a major evolutionary force diversifying the European populations, we detected 35 loci that are putatively under diversifying selection. Two of these loci flank the canine platelet-derived growth factor gene, which affects bone growth and may influence differences in body size between wolf populations. This study demonstrates the power of population genomics for identifying genetic signals of demographic bottlenecks and detecting signatures of directional selection in bottlenecked populations, despite their low background variability.Heredity advance online publication, 18 December 2013; doi:10.1038/hdy.2013.122
Pulso mínimo de agua para la emergencia de plántulas de tres especies de gramíneas perennes nativas del Monte Central (Argentina), influenciado por el efecto de la sombra y la estación del año
In deserts, seedling emergence occurs only
after precipitation threshold has been exceeded,
however, the presence of trees modifies microenvironmental
conditions that might affect the
effectiveness of a water pulse. In the Monte
desert, Prosopis flexuosa trees generate
different micro-environmental conditions that
might influence grass seedlings establishment.
The objective of this work was: a) to know
the effective minimum water input event that
triggers the emergence of native perennial
grass seedlings; b) to relate this fact with the
effect of the shade of P. flexuosa canopy and
the seasonal temperatures. Three important
forage species of the Monte were studied:
Pappophorum caespitosum and Trichloris crinita,
with C4, and Jarava ichu, with C3 metabolism.
Each season, seeds of these species were sown
in pots placed at two light conditions: shade
(similar to P. flexuosa cover) and open area, and
with seven irrigation treatments (0, 10, 20, 30,
40, 2*10 and 3*10 mm). J. ichu did not emerge
in any of the treatments. Significant seedling
emergence was registered for P. caespitosum
and T. crinita in shade conditions with 40 mm
irrigation treatment in summer. Since 40 mm
precipitation events are infrequent in the Monte,
seedling emergence for these species would
be restricted to exceptional rainy years. The
facilitating effect of P. flexuosa shade would be
important during the hot season.En los desiertos, la emergencia de las
plántulas se produce cuando un evento de
precipitación excede un valor umbral. La
presencia de árboles modifica las condiciones
micro ambientales y en consecuencia, la
efectividad de los eventos de lluvia. En el
Monte, las condiciones generadas por Prosopis
flexuosa (algarrobo) afectarían el establecimiento
de las gramíneas. El objetivo del trabajo fue:
a) conocer el evento mínimo de agua necesario
para desencadenar la emergencia de gramíneas
perennes; b) relacionarlo con la influencia de
la sombra del algarrobo y las temperaturas
estacionales. Se trabajó con tres especies nativas
de gramíneas forrajeras perennes: Pappophorum
caespitosum, Trichloris crinita, (C4), y Jarava
ichu (C3). En cada estación del año, semillas de
las tres especies fueron sembradas en macetas
bajo dos condiciones lumínicas: sombra (similar
a la sombra de P. flexuosa) y área abierta y con
siete niveles de riego (0, 10, 20, 30, 40, 2*10 y
3*10 mm). Jarava ichu no emergió en ningún
tratamiento. En el verano se obtuvo emergencia
significativa de T. crinita y P. caespitosum solo
en los tratamientos de 40 mm y a la sombra.
Debido a que en el Monte los eventos de
precipitación de 40 mm son infrecuentes, la
emergencia de estas especies ocurriría en los
años excepcionalmente lluviosos. El efecto
facilitador de la sombra del algarrobo sería de
importancia en la estación cálida.Fil: Greco, Silvina A..
Universidad Nacional de Cuyo. Facultad de Ciencias AgrariasFil: Sartor, Carmen E..
Universidad Nacional de Cuyo. Facultad de Ciencias AgrariasFil: Villagra, Pablo E..
Universidad Nacional de Cuyo. Facultad de Ciencias Agraria
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