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Search Results: 1 - 10 of 87 matches for " Friedel "
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Anisotropy and magnetism of high temperature oxides superconductors
J. Friedel,M. Kohmoto
Physics , 1999,
Abstract: Phonon or electron mediated weak BCS attraction is enough to have high critical temperature if a van Hove anomaly is at work. This could apply to electron doped compounds and also to compounds with CuO$_2$ planes overdoped in holes, where $T_c$ decreases with increasing doping. If phonons dominate, it should lead to an anisotropic but mainly $s$ superconductive gap, as observed recently in overdoped LaSrCuO, and probably also in electron doped compounds. If electrons dominate, a $d$ gap should develop as observed in a number of cases. In the underdoped range, the observed decrease of $T_c$ with hole doping can be related in all cases to the development of antiferromagnetic fluctuations which produces a magnetic pseudogap, thus lowering the density of states at the Fermi level. The observed mainly $d$ superconductive gap then can be due to a prevalent superconductive coupling through antiferromagnetic fluctuations; it could also possibly be attributed to the same phonon coupling as in the overdoped range, now acting on Bloch functions scattered in the magnetic pseudogap. More systematic studies of superconductive gap anisotropy and of magnetic fluctuations would be in order.
CADRE: The CArma Data REduction pipeline
D. N. Friedel
Physics , 2013,
Abstract: The Combined Array for Millimeter-wave Astronomy (CARMA) data reduction pipeline (CADRE) has been developed to give investigators a first look at a fully reduced set of their data. It runs automatically on all data produced by the telescope as they arrive in the CARMA data archive. CADRE is written in Python and uses Python wrappers for MIRIAD subroutines for direct access to the data. It goes through the typical reduction procedures for radio telescope array data and produces a set of continuum and spectral line maps in both MIRIAD and FITS format. CADRE has been in production for nearly two years and this paper presents the current capabilities and planned development.
On the nature of antiferromagnetism in the CO_2 planes of oxide superconductors
J. Friedel,M. Kohmoto
Physics , 2002, DOI: 10.1140/epjb/e2002-00399-x
Abstract: Recent results on electrons and holes doped CuO 2 planes confirm the marked covalency of CuO bonding, suggesting a band picture of long and short range antiferromagnetism. The maxima of superconductive T c versus doping can be related to the crossing by the Fermi level of the edges of the pseudogap due to antiferromagnetic short range order (bonding edge for holes doping, antibonding one for electrons doping). The symmetry of the superconductive gap can be related to the Bragg scattering of electronic Bloch states near the edges of the AF pseudogap. Assuming a standard phonon coupling, one then predicts for commensurate AF a pure d symmetry of the superconductive gap for underdoped samples and d symmetry plus an ip contribution increasing linearly with overdoping. This seems in agreement with recent measurements of gap symmetry for YBCO, but should be more fully tested, especially for electron doped samples. The simple band approximation used here could no doubt be made more realistic by a specific inclusion of electron correlations and by a better description of AF short range order. Uncommensurate AF, as in LSCO, is not considered here.
Disclinations, dislocations and continuous defects: a reappraisal
Maurice Kleman,Jacques Friedel
Physics , 2007, DOI: 10.1103/RevModPhys.80.61
Abstract: Disclinations, first observed in mesomorphic phases, are relevant to a number of ill-ordered condensed matter media, with continuous symmetries or frustrated order. They also appear in polycrystals at the edges of grain boundaries. They are of limited interest in solid single crystals, where, owing to their large elastic stresses, they mostly appear in close pairs of opposite signs. The relaxation mechanisms associated with a disclination in its creation, motion, change of shape, involve an interplay with continuous or quantized dislocations and/or continuous disclinations. These are attached to the disclinations or are akin to Nye's dislocation densities, well suited here. The notion of 'extended Volterra process' takes these relaxation processes into account and covers different situations where this interplay takes place. These concepts are illustrated by applications in amorphous solids, mesomorphic phases and frustrated media in their curved habit space. The powerful topological theory of line defects only considers defects stable against relaxation processes compatible with the structure considered. It can be seen as a simplified case of the approach considered here, well suited for media of high plasticity or/and complex structures. Topological stability cannot guarantee energetic stability and sometimes cannot distinguish finer details of structure of defects.
Short Proof of Dirichlet's Principle
H. N. Friedel
Mathematics , 2010,
Abstract: A standard Hilbert-space proof of Dirichlet's principle is simplified, using an observation that a certain form of min-problem has unique solution, at a specified point. This solves Dirichlet's problem, after it is recast in the required form (using the Poincare/Friedrichs bound and Riesz representation). The solution's dependence on data is linear and continuous; and the solution is invariant under certain changes of data, away from the border of the region where Dirichlet's problem is given. If that region is regular enough for functions on it to have border-traces, then the problem can be stated and solved in terms of border-data.
Natural Isomorphism from a Linear Map's Image to Complement of Nullspace
H. N. Friedel
Mathematics , 2011,
Abstract: There is a natural isomorphism from image to complement of nullspace, for a bounded linear map from a real Banach space onto a closed subspace of a real Hilbert space. This generalizes Riesz representation (self-duality of Hilbert space). The isomorphism helps solve the pressure equation of fluid dynamics.
Self-Adjoint Extension of Symmetric Maps
H. N. Friedel
Mathematics , 2011,
Abstract: A densely-defined symmetric linear map from/to a real Hilbert space extends to a self-adjoint map. Extension is expressed via Riesz representation. For a case including Friedrichs extension of a strongly monotone map, self-adjoint extension is unique, and equals closure of the given map.
Influence of degree correlations on network structure and stability in protein-protein interaction networks
Caroline C Friedel, Ralf Zimmer
BMC Bioinformatics , 2007, DOI: 10.1186/1471-2105-8-297
Abstract: For each PPI network, we simulated uncorrelated, positively and negatively correlated reference networks. Here, a simple model was developed which can create different types of degree correlations in a network without changing the degree distribution. Differences in static properties associated with degree correlations were compared by analyzing the network characteristics of the original PPI and reference networks. Dynamics were compared by simulating the effect of a selective deletion of hubs in all networks.Considerable differences between the network types were found for the number of components in the original networks. Negatively correlated networks are fragmented into significantly less components than observed for positively correlated networks. On the other hand, the selective deletion of hubs showed an increased structural tolerance to these deletions for the positively correlated networks. This results in a lower rate of interaction loss in these networks compared to the negatively correlated networks and a decreased disintegration rate. Interestingly, real PPI networks are most similar to the randomly correlated references with respect to all properties analyzed. Thus, although structural properties of networks can be modified considerably by degree correlations, biological PPI networks do not actually seem to make use of this possibility.All biological processes of a cell such as proliferation, signal transduction or apoptosis are shaped by proteins interacting specifically with each other and building more or less transient complexes. To understand these processes, determining the underlying protein interactions is of vital importance. The advent of high-throughput methods such as yeast two-hybrid (Y2H) has made it possible to determine protein interactions on a large scale. This development has lead to the determination of several large-scale species-specific protein-protein interaction networks in the last years [1-7].Apart from biological implicatio
Inferring topology from clustering coefficients in protein-protein interaction networks
Caroline C Friedel, Ralf Zimmer
BMC Bioinformatics , 2006, DOI: 10.1186/1471-2105-7-519
Abstract: In this paper, we investigate the effect of limited sampling on average clustering coefficients and how this can help to more confidently exclude possible topology models for the complete interactome. Both analytical and simulation results for different network topologies indicate that partial sampling alone lowers the clustering coefficient of all networks tremendously. Furthermore, we extend the original sampling model by also including spurious interactions via a preferential attachment process. Simulations of this extended model show that the effect of wrong interactions on clustering coefficients depends strongly on the skewness of the original topology and on the degree of randomness of clustering coefficients in the corresponding networks.Our findings suggest that the complete interactome is either highly skewed such as e.g. in scale-free networks or is at least highly clustered. Although the correct topology of the interactome may not be inferred beyond any reasonable doubt from the interaction networks available, a number of topologies can nevertheless be excluded with high confidence.Since protein-protein interactions are of fundamental importance for all processes taking place in a cell, great efforts have been devoted to the systematic identification of protein interactions for a number of organisms. To generate large-scale protein interaction maps, two methods are commonly used: (i) yeast two-hybrid (Y2H) [1-7] and (ii) affinity purification followed by mass spectrometry (e.g. Co-immuno-precipitation (Co-IP) [8] or tandem affinity purification (TAP) [9-11]). Both of these methods are prone to spurious interactions (false positives) due to self-activators (Y2H), protein contaminants (affinity purification) or non-specific interactions. Based on expression data and information about paralogues, the fraction of correct high-throughput interactions has been estimated at 30–50% [12]. In addition to false positives, high-throughput experiments are characteriz
Dynamic coexistence of various configurations: clusters vs.nuclei
V. Z. Kresin,J. Friedel
Physics , 2011, DOI: 10.1209/0295-5075/93/13002
Abstract: The presence of energy shells in metallic clusters and atomic nuclei leads to a peculiar relation between the number of particles N and the structure, and this leads to a strong correlation between the energy spectrum and N. An analysis of experimental data leads to the conclusion that, in addition to the static Jahn-Teller effect, the dynamic effect leading to the quantum coexistence of different configurations (quantum oscillations) plays an important role. Such suggested coexistence is an essential feature of clusters as well as nuclei, both finite Fermi systems.
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