1,385 research outputs found
Simple Model for the Variation of Superfluid Density with Zn Concentration in YBCO
We describe a simple model for calculating the zero-temperature superfluid
density of Zn-doped YBa_2Cu_3O_{7-\delta} as a function of the fraction x of
in-plane Cu atoms which are replaced by Zn. The basis of the calculation is a
``Swiss cheese'' picture of a single CuO_2 layer, in which a substitutional Zn
impurity creates a normal region of area around it as
originally suggested by Nachumi et al. Here is the zero-temperature
in-plane coherence length at x = 0. We use this picture to calculate the
variation of the in-plane superfluid density with x at temperature T = 0, using
both a numerical approach and an analytical approximation. For ,
if we use the value = 18.3 angstrom, we find that the in-plane
superfluid decreases with increasing x and vanishes near in the
analytical approximation, and near in the numerical approach.
is quite sensitive to , whose value is not widely agreed upon.
The model also predicts a peak in the real part of the conductivity,
Re, at concentrations , and low frequencies,
and a variation of critical current density with x of the form near percolation, where is the in-plane
superfluid density.Comment: 19 pages including 6 figures, submitted to Physica
Dynamic Structure Factor of Liquid and Amorphous Ge From Ab Initio Simulations
We calculate the dynamic structure factor S(k,omega) of liquid Ge (l-Ge) at
temperature T = 1250 K, and of amorphous Ge (a-Ge) at T = 300 K, using ab
initio molecular dynamics. The electronic energy is computed using
density-functional theory, primarily in the generalized gradient approximation,
together with a plane wave representation of the wave functions and ultra-soft
pseudopotentials. We use a 64-atom cell with periodic boundary conditions, and
calculate averages over runs of up to 16 ps. The calculated liquid S(k,omega)
agrees qualitatively with that obtained by Hosokawa et al, using inelastic
X-ray scattering. In a-Ge, we find that the calculated S(k,omega) is in
qualitative agreement with that obtained experimentally by Maley et al. Our
results suggest that the ab initio approach is sufficient to allow approximate
calculations of S(k,omega) in both liquid and amorphous materials.Comment: 31 pages and 8 figures. Accepted for Phys. Rev.
A review of Ireland's waterbirds, with emphasis on wintering migrants and reference to H5N1 avian influenza
Ireland is characterised by its diversity and large abundance of wetlands, making it attractive to a wide variety of waterbirds throughout the year. This paper presents an overview of Ireland's waterbirds, including ecological factors relevant to the potential introduction, maintenance, transmission and spread of infectious agents, including the H5N1 avian influenza virus, in Ireland. Particular emphasis is placed on five groups of wintering migrants (dabbling and sieving wildfowl, grazing wildfowl, diving wildfowl, waders and gulls), noting that the H5N1 avian influenza virus has mainly been isolated from this subset of waterbirds. Ireland's wetlands are visited during the spring and summer months by hundreds of thousands of waterbirds which come to breed, predominantly from southern latitudes, and during the autumn and winter by waterbirds which come from a variety of origins (predominantly northern latitudes), and which are widely distributed and often congregate in mixed-species flocks. The distribution, feeding habits and social interactions of the five groups of wintering migrants are considered in detail. Throughout Ireland, there is interaction between different waterbird populations (breeding migrants, the wintering migrants and resident waterbird populations). There is also a regular and complex pattern of movement between feeding and roosting areas, and between wetlands and farmland. These interactions are likely to facilitate the rapid transmission and spread of the H5N1 avian influenza virus, if it were present in Ireland
A comparison of the metabolic effects of sustained strenuous activity in polar environments on men and women
This study investigates differences in pre- to post-expedition energy expenditure, substrate utilisation and body composition, between the all-male Spear17 (SP-17) and all-female Ice Maiden (IM) transantarctic expeditions (IM: N = 6, 61 days, 1700 km; SP-17: N = 5, 67 days, 1750 km). Energy expenditure and substrate utilisation were measured by a standardised 36 h calorimetry protocol; body composition was determined using air displacement plethysmography. Energy balance calculation were used to assess the physical challenge. There was difference in the daily energy expenditure (IM: 4,939 kcal day−1; SP-17: 6,461 kcal day−1, p = 0.004); differences related to physical activity were small, but statistically significant (IM = 2,282 kcal day−1; SP-17 = 3,174 kcal day−1; p = 0.004). Bodyweight loss was modest (IM = 7.8%, SP-17 = 6.5%; p > 0.05) as was fat loss (IM = 30.4%, SP-17 = 40.4%; p > 0.05). Lean tissue weight change was statistically significant (IM = − 2.5%, SP-17 = + 1.0%; p = 0.05). No difference was found in resting or sleeping energy expenditure, normalised to lean tissue weight (p > 0.05); nor in energy expenditure when exercising at 80, 100 and 120 steps min−1, normalised to body weight (p > 0.05). Similarly, no difference was found in the change in normalised substrate utilisation for any of the activities (p > 0.05). Analysis suggested that higher daily energy expenditures for the men in Spear-17 was the result of higher physical demands resulting in a reduced demand for energy to thermoregulate compared to the women in Ice Maiden. The lack of differences between men and women in the change in energy expenditure and substrate utilisation, suggests no sex difference in response to exposure to extreme environments
Assessing the reliability of retrospective reports of adverse childhood experiences among adolescents with documented childhood maltreatment
The literature suggests that childhood maltreatment
is related to a higher probability of developing psychopathology
and disease in adulthood. However, some authors have
questioned the reliability of self-reports of maltreatment, suggesting
that psychopathology at the time of evaluation affects
self-reports. We evaluated the reliability of the self-reports of
79 young adults who were identified in childhood by Child
Protective Services by comparing two moments of evaluation.
Psychological and physical symptoms were tested to evaluate
their interference with the reports. We found good to excellent
agreement, with no significant correlation between the changes
in self-reported experiences and the changes in physical and
psychological symptoms, suggesting that the reliability of
reports is not related to the health state at the time of the report
Defending the genome from the enemy within:mechanisms of retrotransposon suppression in the mouse germline
The viability of any species requires that the genome is kept stable as it is transmitted from generation to generation by the germ cells. One of the challenges to transgenerational genome stability is the potential mutagenic activity of transposable genetic elements, particularly retrotransposons. There are many different types of retrotransposon in mammalian genomes, and these target different points in germline development to amplify and integrate into new genomic locations. Germ cells, and their pluripotent developmental precursors, have evolved a variety of genome defence mechanisms that suppress retrotransposon activity and maintain genome stability across the generations. Here, we review recent advances in understanding how retrotransposon activity is suppressed in the mammalian germline, how genes involved in germline genome defence mechanisms are regulated, and the consequences of mutating these genome defence genes for the developing germline
Destabilizers of the thymidylate synthase homodimer accelerate its proteasomal degradation and inhibit cancer growth
Cofactor-mediated conformational control in the bifunctional kinase/RNase Ire1
<p>Abstract</p> <p>Background</p> <p>Ire1 is a signal transduction protein in the endoplasmic reticulum (ER) membrane that serves to adjust the protein-folding capacity of the ER according to the needs of the cell. Ire1 signals, in a transcriptional program, the unfolded protein response (UPR) via the coordinated action of its protein kinase and RNase domains. In this study, we investigated how the binding of cofactors to the kinase domain of Ire1 modulates its RNase activity.</p> <p>Results</p> <p>Our results suggest that the kinase domain of Ire1 initially binds cofactors without activation of the RNase domain. RNase is activated upon a subsequent conformational rearrangement of Ire1 governed by the chemical properties of bound cofactors. The conformational step can be selectively inhibited by chemical perturbations of cofactors. Substitution of a single oxygen atom in the terminal β-phosphate group of a potent cofactor ADP by sulfur results in ADPβS, a cofactor that binds to Ire1 as well as to ADP but does not activate RNase. RNase activity can be rescued by thiophilic metal ions such as Mn<sup>2+ </sup>and Cd<sup>2+</sup>, revealing a functional metal ion-phosphate interaction which controls the conformation and RNase activity of the Ire1 ADP complex. Mutagenesis of the kinase domain suggests that this rearrangement involves movement of the αC-helix, which is generally conserved among protein kinases. Using X-ray crystallography, we show that oligomerization of Ire1 is sufficient for placing the αC-helix in the active, cofactor-bound-like conformation, even in the absence of cofactors.</p> <p>Conclusions</p> <p>Our structural and biochemical evidence converges on a model that the cofactor-induced conformational change in Ire1 is coupled to oligomerization of the receptor, which, in turn, activates RNase. The data reveal that cofactor-Ire1 interactions occur in two independent steps: binding of a cofactor to Ire1 and subsequent rearrangement of Ire1 resulting in its self-association. The pronounced allosteric effect of cofactors on protein-protein interactions involving Ire1's kinase domain suggests that protein kinases and pseudokinases encoded in metazoan genomes may use ATP pocket-binding ligands similarly to exert signaling roles other than phosphoryl transfer.</p
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