110 research outputs found
Multiscale Modeling of Stress-Mediated Diffusion in Silicon - Volume Tensors
No full textABSTRACTIn a previous paper, we presented a general theoretical treatment of the effect of stress on defect diffusion in Si (M. S. Daw, W. Windl, N. N. Carlson, M. Laudon, and M. P. Masquelier, to be published in Phys. Rev. B). In this paper, we discuss the calculation of the parameters governing the stress dependence of the diffusivity, which are volume quantities, and present the fully anisotropic volume tensor for vacancy formation in Si.</jats:p
Evidence for a pathogenic role of different mutations at codon 188 of PRNP
No full textClinical and pathological changes in familial Creutzfeldt-Jakob disease (CJD) cases may be similar or indistinguishable from sporadic CJD. Therefore determination of novel mutations in PRNP remains of major importance. We identified two different rare mutations in codon 188 of the prion protein gene (PRNP) in four patients suffering from a disease clinically very similar to the major subtype of sporadic CJD. Both mutations result in an exchange of the amino acid residue threonine for a highly basic residue, either arginine (T188R) or lysine (T188K). The T188R mutation was found in one patient and the T188K mutation in three patients. The prevalence of mutations at codon 188 of PRNP was tested in 593 sporadic CJD cases and 735 healthy individuals. Neither mutation was found. The data presented here argue in favor of T188K being a pathogenic mutation causing genetic CJD. Since one individual with this mutation, who is the father of a clinically affected patient with T188K mutation, is now 79 years old and shows no signs of disease, this mutation is likely associated with a penetrance under 100%. Further observations will have to show whether T188R is a pathogenic mutation
2ND-ORDER RAMAN-SPECTRA OF DIAMOND FROM AB-INITIO PHONON CALCULATIONS
No full textThe second-order Raman spectra of diamond and silicon have been calculated using ab initio phonons and phenomenological polarizability coefficients. The sharp peak in the spectrum of diamond near the two-phonon cutoff is explained by a maximum in the vibrational density of states; this maximum originates from the uppermost phonon branch whose frequencies are calculated to have a minimum at the Brillouin-zone center. This frequency minimum as well as the sharp Raman peak are unique to diamond and do not occur for the other group-IV semiconductors. In our calculation based on harmonic ab initio lattice dynamics neither two-phonon bound states nor polarizability matrix element effects are needed to explain the peak, and we feel that the longstanding controversy about its origin has been resolved
AB-INITIO LATTICE-DYNAMICS OF DIAMOND
No full textWe present a first principles calculation of lattice dynamical properties of diamond. Our calculations have been performed using density-functional perturbation theory together with plane-wave expansion and nonlocal pseudopotentials. As a first step we have evaluated the equilibrium structure of diamond via the minimization of the total energy. Then, harmonic phonon dispersion curves and phonon eigenvectors have been evaluated within the linear-response framework. As a by-product of the calculation we have also obtained the internal-strain parameter. Furthermore, we have also tested the validity of the ab initio calculation for describing properties beyond the harmonic approximation. Using the quasiharmonic approximation we have calculated the thermal expansion coefficient and the mode Gruneisen parameter dispersion curves. Where experimental data are available, good agreement is found with our theoretical predictions
Investigations of the cellular trafficking of prion proteins in living cells using GFP chimerae
No full textInvestigations of the cellular trafficking of prion proteins in living cells using GFP chimerae
No full textAb initio phonon calculations in solids
No full textWe present some applications of a first-principles approach to the study of the vibrational properties of crystals. The ab initio lattice dynamics is studied by means of a perturbative approach to the density-functional theory. The validity of this method is investigated performing the calculation of the phonon frequencies of crystals with different structure and bonding properties. The results obtained are in excellent agreement with the available experimental data
Activation of phosphatidylinositol in 3-kinase by cellular prion protein and its role cell survival
No full textThe cellular prion protein (PrPC) is thought to be involved in protection against cell death, however the exact Cellular mechanisms involved are still controversial. Herein we present data that strongly indicate a functional link between PrPC-expression and phosphatidylinositol 3-kinase (Pl 3-kinase) activation, a protein kinase that plays a pivotal role in cell survival. Both Mouse neuroblastoma N2a cells and immortalized murine hippocampal neuronal cell lines expressing wild-type PrPC had significantly higher Pl 3-kinase activity levels than their respective controls. Moreover, PI 3-kinase activity was found to be elevated in brain lysates from wild-type mice as compared to prion protein-knockout mice. Recruitment of Pl 3-kinase by PrPC was shown to contribute to cellular survival toward oxidative stress by using 3-morpholinosydnonimine (SIN-1) and Serum deprivation. Moreover, both PI 3-kinase activation and cytoprotection by PrPC appeared to rely oil copper binding to the N-terminal octapeptide of PrPC. Thus, we propose a model in which the interaction of copper(II) with the N-terminal domain of PrPC enables transduction of a signal to PI 3-kinase: the latter. in turn, mediates downstream regulation Of Cell Survival. (c) 2005 Elsevier Inc. All rights reserved
Caprine prion gene polymorphisms are associated with decreased incidence of classical scrapie in goat herds in the United Kingdom
No full textAbstract The application of genetic breeding programmes to eradicate transmissible spongiform encephalopathies in goats is an important aim for reasons of animal welfare as well as human food safety and food security. Based on the positive impact of Prnp genetics on sheep scrapie in Europe in the past decade, we have established caprine Prnp gene variation in more than 1100 goats from the United Kingdom and studied the association of Prnp alleles with disease phenotypes in 150 scrapie-positive goats. This investigation confirms the association of the Met142 encoding Prnp allele with increased resistance to preclinical and clinical scrapie. It reveals a novel association of the Ser127 encoding allele with a reduced probability to develop clinical signs of scrapie in goats that are already positive for the accumulation of disease-specific prion protein in brain or periphery. A United Kingdom survey of Prnp genotypes in eight common breeds revealed eleven alleles in over thirty genotypes. The Met142 encoding allele had a high overall mean allele frequency of 22.6%, whereas the Ser127 encoding allele frequency was considerably lower with 6.4%. In contrast, a well known resistance associated allele encoding Lys222 was found to be rare (0.9%) in this survey. The analysis of Prnp genotypes in Mexican Criollas goats revealed nine alleles, including a novel Phe to Leu substitution in codon 201, confirming that high genetic variability of Prnp can be found in scrapie-free populations. Our study implies that it should be feasible to lower scrapie prevalence in goat herds in the United Kingdom by genetic selection.</p
Determination of the Si Young's modulus between room and melt temperature using the impulse excitation technique
No full textStress induced by the thermal gradients near the meltsolid interface affects the intrinsic point defect properties and the quality of single crystal Si grown from a melt. Also during device processing, stress in the Si substrate influences point defect behavior during thermal treatments. To be able to simulate and control the stress distribution one needs to know the elastic constants of single crystal Si at high temperatures. In the present study, the vibrational properties of single crystal Si samples are studied between room and melt temperature using the impulse excitation technique.
From the measurements, the temperature dependent Young’s moduli Eijk of moderately doped Czochralski-grown Si samples are extracted in the 100, 110 and 111 crystallographic directions. Close to the melt temperature, very high Young’s moduli values between 110 and 160 GPa are obtained, depending on the crystallographic direction. Empiric expressions are derived for the temperature dependence of E100, E110 and E111 and of the elastic compliances s11 and s12 +s44/2, useful for application in process simulation.status: Publishe
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