748 research outputs found
Interaction effects between impurities in low dimensional spin-1/2 antiferromagnets
We are considering the interplay between several non-magnetic impurities in
the spin-1/2 Heisenberg antiferromagnet in chains, ladders and planes by
introducing static vacancies in numerical quantum Monte Carlo simulations. The
effective potential between two and more impurities is accurately determined,
which gives a direct measure of the quantum correlations in the systems. Large
effective interaction potentials are an indication of strong quantum
correlations in the system and reflect the detailed nature of the valence bond
ground states. In two-dimensions (2D) the interactions are smaller, but can
still be analyzed in terms of valence bonds.Comment: 8 pages, 6 figures, accepted by Europhys. Lett. The latest pdf file
is available at http://www.physik.uni-kl.de/eggert/papers/interact2d.pd
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The Janus-faced Nature of miR-22 in Hematopoiesis: Is It an Oncogenic Tumor Suppressor or Rather a Tumor-Suppressive Oncogene?
An open-label clinical trial to investigate the efficacy and safety of corifollitropin alfa combined with hCG in adult men with hypogonadotropic hypogonadism
Subject disposition. (EPS 1138 kb
Quantum Phase Transition of Randomly-Diluted Heisenberg Antiferromagnet on a Square Lattice
Ground-state magnetic properties of the diluted Heisenberg antiferromagnet on
a square lattice are investigated by means of the quantum Monte Carlo method
with the continuous-time loop algorithm. It is found that the critical
concentration of magnetic sites is independent of the spin size S, and equal to
the two-dimensional percolation threshold. However, the existence of quantum
fluctuations makes the critical exponents deviate from those of the classical
percolation transition. Furthermore, we found that the transition is not
universal, i.e., the critical exponents significantly depend on S.Comment: RevTeX, 4 pages including 5 EPS figure
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Classical Correlation-Length Exponent in Non-Universal Quantum Phase Transition of Diluted Heisenberg Antiferromagnet
Critical behavior of the quantum phase transition of a site-diluted
Heisenberg antiferromagnet on a square lattice is investigated by means of the
quantum Monte Carlo simulation with the continuous-imaginary-time loop
algorithm. Although the staggered spin correlation function decays in a power
law with the exponent definitely depending on the spin size , the
correlation-length exponent is classical, i.e., . This implies that
the length scale characterizing the non-universal quantum phase transition is
nothing but the mean size of connected spin clusters.Comment: 4 pages, 3 figure
Vegetation history and agriculture in the cover-sand area west of Breda (province of Noord-Brabant, The Netherlands)
Rare region effects at classical, quantum, and non-equilibrium phase transitions
Rare regions, i.e., rare large spatial disorder fluctuations, can
dramatically change the properties of a phase transition in a quenched
disordered system. In generic classical equilibrium systems, they lead to an
essential singularity, the so-called Griffiths singularity, of the free energy
in the vicinity of the phase transition. Stronger effects can be observed at
zero-temperature quantum phase transitions, at nonequilibrium phase
transitions, and in systems with correlated disorder. In some cases, rare
regions can actually completely destroy the sharp phase transition by smearing.
This topical review presents a unifying framework for rare region effects at
weakly disordered classical, quantum, and nonequilibrium phase transitions
based on the effective dimensionality of the rare regions. Explicit examples
include disordered classical Ising and Heisenberg models, insulating and
metallic random quantum magnets, and the disordered contact process.Comment: Topical review, 68 pages, 14 figures, final version as publishe
Weed finds as indicators for the cultivation regime of the early Neolithic Bandkeramik culture?
FSH treatment improves sperm DNA damage in men with idiopathic infertility carriers of the FSH receptor p.N680S homozygous N genotype: an interim analysis
Study question: To assess whether in men with idiopathic infertility, the sperm DNA fragmentation (sDF) improves depending on the FSH receptor (FSHR) genotype as assessed by the non-synonymous polymorphisms (SNP) rs6166 (wild type or p.N680S).
Summary answer: FSH treatment improves sDF in a subgroup of idiopathic infertile men, although 40% of these men do not show any significant improve- ment. The response of sDF, a surrogate marker of sperm quality, together with the evaluation of FSHR SNP p.N680S might be useful to predict the response to FSH treatment.
What is known already: FSH is fundamental for spermatogenesis and is em- pirically used to treat male idiopathic infertility. Several studies suggest that sDF could be a candidate predictor of response to FSH treatment, in terms of probability to conceive. Furthermore, it is widely accepted that the FSHR SNP p.N680S influences ovarian response in women and testicular volume in men. Study design, size, duration: Multicenter, longitudinal, prospective, open-la- bel, two-arms clinical trial. Subjects enrolled were idiopathic infertile men and received 150 IU of recombinant FSH (Gonal f®) every other day for 12 weeks and were then followed-up for further 12 weeks after FSH-withdrawal. Patients were evaluated at baseline and at the end of the two phases. Participants/materials, setting, methods: Eighty-eight men with idiopathic male infertility carrier of the homozygous FSHR p.N680S N or S genotype, FSH 15%, were enrolled. 66 patients completed the sDF analysis. sDF was centrally evaluated by TUNEL/PI assay coupled to flow cy- tometry, resolving two different sperm populations, namely: PIbrighter and PIdimmer.
Main results and the role of chance: Thirty-seven men (56%) were carriers of the p.N680S homozygous-N and 29 (44%) of the homozygous-S genotype, respectively. Total sDF (PIbrighter + PIdimmer) was significantly lower at the end of the study in patients carriers of the p.N680S-N allele than patients carri- ers of p.N680S-S allele (p = 0.008). Only in patients carriers of the p.N680S-N allele, total sDF decreased significantly from baseline to the end of the study (p = 0.021) and this decrease was entirely sustained by the sperm population containing vital sperms (i.e., PIbrighter fraction) (p = 0.008). PIdimmer frac- tion, including only non-vital sperms, was significantly higher in patients car- riers of the p.N680S-S allele than in carriers of N allele (p = 0.018). Total sDF was inversely related to total sperm number (p = 0.020) and progressive sperm motility (p = 0.014).
Limitations, reason for caution: The statistical power of the results obtained so far is 86.9%, with alpha-error 0.05. This is an interim-analysis.
Wider implications of the findings: The study suggests that FSH treatment induces a significant improvement of total sDF in men carriers of the p.N680S homozygous N allele. This sDF decrease awaits confirmation, since the study will be completed by June 2015.
Study funding/competing interest(s): Funding by commercial/corporate company(ies) – The study was supported by unrestricted grant by Merck Serono.
Trial registration number: EudraCT number 2010-020240-35.
Keywords: FSH treatment, male infertility, Sperm-DNA fragmentatio
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