411 research outputs found
Cryptands and bismacrocycles with cyanuric and isocyanuric units: synthesis and structural investigations
Hay synthesis of cryptands and bismacrocycles starting from tripodands with cyanuric and isocyanuric cores is reported. The structure of the compounds is revealed by X-ray diffraction, NMR spectrometry and MS investigations. DNMR experiments carried out with bismacrocycles indicated the flipping of the rings and the free-energy barrier for the conformational process could be determined in one case. (C) 2012 Elsevier Ltd. All rights reserved
Cryptorchidism in the orl rat is associated with muscle patterning defects in the fetal gubernaculum and altered hormonal signaling
Cryptorchidism, or undescended testis, is a common male genital anomaly of unclear etiology. Hormonal stimulation of the developing fetal gubernaculum by testicular androgens and insulin-like 3 (INSL3) is required for testicular descent. In studies of the orl fetal rat, one of several reported strains with inherited cryptorchidism, we studied hormone levels, gene expression in intact and hormone-stimulated gubernaculum, and imaging of the developing cremaster muscle facilitated by a tissue clearing protocol to further characterize development of the orl gubernaculum. Abnormal localization of the inverted gubernaculum was visible soon after birth. In the orl fetus, testicular testosterone, gubernacular androgen-responsive transcript levels, and muscle-specific gene expression were reduced. However, the in vitro transcriptional response of the orl gubernaculum to androgen was largely comparable to wild type (wt). In contrast, increases in serum INSL3, gubernacular INSL3-responsive transcript levels, expression of the INSL3 receptor, Rxfp2, and the response of the orl gubernaculum to INSL3 in vitro all suggest enhanced activation of INSL3/RXFP2 signaling in the orl rat. However, DNA sequence analysis did not identify functional variants in orl Insl3. Finally, combined analysis of the present and previous studies of the orl transcriptome confirmed altered expression of muscle and cellular motility genes, and whole mount imaging revealed aberrant muscle pattern formation in the orl fetal gubernaculum. The nature and prevalence of developmental muscle defects in the orl gubernaculum are consistent with the cryptorchid phenotype in this strain. These data suggest impaired androgen and enhanced INSL3 signaling in the orl fetus accompanied by defective cremaster muscle development
Interaction of quasilocal harmonic modes and boson peak in glasses
The direct proportionality relation between the boson peak maximum in
glasses, , and the Ioffe-Regel crossover frequency for phonons,
, is established. For several investigated materials . At the frequency the mean free path of the
phonons becomes equal to their wavelength because of strong resonant
scattering on quasilocal harmonic oscillators. Above this frequency phonons
cease to exist. We prove that the established correlation between
and holds in the general case and is a direct consequence of
bilinear coupling of quasilocal oscillators with the strain field.Comment: RevTex, 4 pages, 1 figur
Equilibration times in numerical simulation of structural glasses: Comparing parallel tempering and conventional molecular dynamics
Generation of equilibrium configurations is the major obstacle for numerical
investigation of the slow dynamics in supercooled liquid states. The parallel
tempering (PT) technique, originally proposed for the numerical equilibration
of discrete spin-glass model configurations, has recently been applied in the
study of supercooled structural glasses. We present an investigation of the
ability of parallel tempering to properly sample the liquid configuration space
at different temperatures, by mapping the PT dynamics into the dynamics of the
closest local potential energy minima (inherent structures). Comparing the PT
equilibration process with the standard molecular dynamics equilibration
process we find that the PT does not increase the speed of equilibration of the
(slow) configurational degrees of freedom.Comment: 5 pages, 3 figure
Numerical study of anharmonic vibrational decay in amorphous and paracrystalline silicon
The anharmonic decay rates of atomic vibrations in amorphous silicon (a-Si)
and paracrystalline silicon (p-Si), containing small crystalline grains
embedded in a disordered matrix, are calculated using realistic structural
models. The models are 1000-atom four-coordinated networks relaxed to a local
minimum of the Stillinger-Weber interatomic potential. The vibrational decay
rates are calculated numerically by perturbation theory, taking into account
cubic anharmonicity as the perturbation. The vibrational lifetimes for a-Si are
found to be on picosecond time scales, in agreement with the previous
perturbative and classical molecular dynamics calculations on a 216-atom model.
The calculated decay rates for p-Si are similar to those of a-Si. No modes in
p-Si reside entirely on the crystalline cluster, decoupled from the amorphous
matrix. The localized modes with the largest (up to 59%) weight on the cluster
decay primarily to two diffusons. The numerical results are discussed in
relation to a recent suggestion by van der Voort et al. [Phys. Rev. B {\bf 62},
8072 (2000)] that long vibrational relaxation inferred experimentally may be
due to possible crystalline nanostructures in some types of a-Si.Comment: 9 two-column pages, 13 figure
The evolution of vibrational excitations in glassy systems
The equations of the mode-coupling theory (MCT) for ideal liquid-glass
transitions are used for a discussion of the evolution of the
density-fluctuation spectra of glass-forming systems for frequencies within the
dynamical window between the band of high-frequency motion and the band of
low-frequency-structural-relaxation processes. It is shown that the strong
interaction between density fluctuations with microscopic wave length and the
arrested glass structure causes an anomalous-oscillation peak, which exhibits
the properties of the so-called boson peak. It produces an elastic modulus
which governs the hybridization of density fluctuations of mesoscopic wave
length with the boson-peak oscillations. This leads to the existence of
high-frequency sound with properties as found by X-ray-scattering spectroscopy
of glasses and glassy liquids. The results of the theory are demonstrated for a
model of the hard-sphere system. It is also derived that certain schematic MCT
models, whose spectra for the stiff-glass states can be expressed by elementary
formulas, provide reasonable approximations for the solutions of the general
MCT equations.Comment: 50 pages, 17 postscript files including 18 figures, to be published
in Phys. Rev.
A consensus-based framework for conducting and reporting osteoarthritis phenotype research
Background
The concept of osteoarthritis (OA) heterogeneity is evolving and gaining renewed interest. According to this concept, distinct subtypes of OA need to be defined that will likely require recognition in research design and different approaches to clinical management. Although seemingly plausible, a wide range of views exist on how best to operationalize this concept. The current project aimed to provide consensus-based definitions and recommendations that together create a framework for conducting and reporting OA phenotype research.
Methods
A panel of 25 members with expertise in OA phenotype research was composed. First, panel members participated in an online Delphi exercise to provide a number of basic definitions and statements relating to OA phenotypes and OA phenotype research. Second, panel members provided input on a set of recommendations for reporting on OA phenotype studies.
Results
Four Delphi rounds were required to achieve sufficient agreement on 11 definitions and statements. OA phenotypes were defined as subtypes of OA that share distinct underlying pathobiological and pain mechanisms and their structural and functional consequences. Reporting recommendations pertaining to the study characteristics, study population, data collection, statistical analysis, and appraisal of OA phenotype studies were provided.
Conclusions
This study provides a number of consensus-based definitions and recommendations relating to OA phenotypes. The resulting framework is intended to facilitate research on OA phenotypes and increase combined efforts to develop effective OA phenotype classification. Success in this endeavor will hopefully translate into more effective, differentiated OA management that will benefit a multitude of OA patients
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