1,722,106 research outputs found
Elastic-plastic analysis of crack propagation with branching
No full textA numerical procedure is described for the elastic-plastic finite element analysis of crack propagation with branching. Constraint equations are used to model crack closing and sliding. Constraint conditions are imposed by using a penalty method for the self-similar crack propagation and an elimination method for the off-axis propagation. The contact condition is examined during plasticity iterations. The use of multiple constraints at the crack branching point to determine the mode of contact is discussed in detail. The method is then applied to (i) the self-similar crack growth in a single-edge notch specimen, (ii) the self-similar propagation followed by interfacial splitting in a center-cracked 0 degrees composite plate, and (iii) the bifurcation of a crack in a compact tension specimen.X11sciescopu
Nature of an intermediate non-Fermi liquid state in Ge-substituted YbRh2Si2: Fermionized skyrmions, Lifshitz transition, skyrmion liquid, and Gruneisen ratio
No full textWe propose a skyrmion liquid state for the non-Fermi liquid (NFL) phase in Ge-substituted YbRh2Si2, where skyrmions form their Fermi surface, argued to result from the strongly coupled nature between skyrmions and itinerant electrons. The fermionized skyrmion theory identifies the antiferromagnetic (AF) transition with the Lifshitz transition, where the quantum critical point (QCP) is characterized by the dynamical critical exponent z = 2. Nonlocal interactions between skyrmions allow a critical line above the AF QCP, which originates from the Kondo-coupling effect with itinerant electrons. This critical line is described by the skyrmion liquid state, which results in Landau damping for spin fluctuations, thus characterized by z = 3. As a result, the Gruneisen ratio is predicted to change from similar to T-1 at the AF QCP to similar to T-2/3 in the NFL phase.open110sciescopu
Stoner Instability Revisited: Emergence of Local Quantum Criticality?
No full textWe revisit Stoner instability, an old problem but in a modern point of view. An idea is to extract out dynamics of directional fluctuations of spins explicitly, resorting to the CP1 representation and integrating over their amplitude fluctuations. As a result, we derive an effective field theory for ferromagnetic quantum phase transitions in terms of bosonic spinons and fermionic holons. We show that this effective field theory reproduces overdamped spin dynamics in a paramagnetic Fermi liquid and magnon spectrum in a ferromagnetic Fermi liquid. An interesting observation is that the velocity of spinons becomes zero, approaching the ferromagnetic quantum critical point, which implies emergence of local quantum criticality. Based on this scenario, we predict the omega/T scaling behavior near ferromagnetic quantum criticality beyond the conventional scenario of the weak-coupling approach.X1111sciescopu
From gas phase clusters to nanomaterials: An overview of theoretical insights
No full textSince theoretical investigations of gas phase clusters enable the evaluation of intrinsic molecular properties and intermolecular interactions, one can predict the macroscopic properties of bulk matter, from a microscopic determination of the properties of individual atoms, molecules, or clusters. Based on the insights obtained from theoretical investigations of the properties of a large number of cluster systems (ranging from simple water clusters to large pi-systems), we have investigated the properties of various novel molecular systems including endo/exohedral fullerenes, nanotori,nonlinear optical materials, ionophores/receptors, polypeptides, enzymes, organic nanotubes, nanowires, and electronic and nano-mechanical molecular devices. The present mini-review highlights some of the interesting results obtained in the course of our extensive theoretical investigations of clusters and nanomaterials.X1131sciescopuskc
Emergence of localized magnetic moments near antiferromagnetic quantum criticality
No full textWe revisit an antiferromagnetic quantum phase transition with Q = 2k(F), where Q is an ordering wave vector and k(F) is a Fermi momentum. Reformulating the Hertz-Moriya-Millis theory within the strong-coupling approach to diagonalize the spin-fermion coupling term and performing the scaling analysis for an effective-field theory with quantum corrections in the Eliashberg approximation, we propose an interacting fixed point for this antiferromagnetic quantum phase transition, where antiferromagnetic spin fluctuations become locally critical to interact with renormalized electrons. The emergence of local quantum criticality suggests a mechanism of omega/T scaling for antiferromagnetic quantum criticality, generally forbidden in the context of the Hertz-Moriya-Millis theory.open110sciescopu
MACROMOLECULAR MODELING AND NMR DISTANCE GEOMETRY REFINEMENT - CONOTOXIN G1 IN SOLVENT
No full textX116sci
Role of axion electrodynamics in a Weyl metal: Violation of Wiedemann-Franz law
No full textRecently, enhancement of the longitudinal magnetoelectrical conductivity (LMEC) has been observed in Bi1-xSbx around x similar to 3% under E parallel to B (E, external electric field and B, external magnetic field) [Phys. Rev. Lett. 111, 246603 (2013)], where an enhancement factor proportional to B-2 is suggested to result from the E . B term. In the present study, we show that this B-2 enhancement is not limited on the LMEC, where both the Seebeck and thermal conductivities in the longitudinal setup (E parallel to B) are predicted to show essentially the same enhancement proportional to B-2. In particular, the B-2 enhancement factor of the LMEC turns out to differ from that of the longitudinal thermal conductivity, responsible for the breakdown of the Wiedemann-Franz (WF) law, which means that anomalous currents flowing through the dissipationless channel differ from each other. Since the breakdown of the WF law appears in spite of the existence of electron quasiparticles, regarded to be a purely topological character (chiral anomaly), the Weyl metallic state cannot be identified with the Landau Fermi-liquid fixed point. We propose the violation of the WF law as another hallmark of the Weyl metallic phase, which originates from axion electrodynamics.open111415sciescopu
Self-assembled organic nanotubes and self-synthesized silver subnanowire arrays in an ambient solution phase
No full textWe review our recent work on the synthesis and characterization of metallic subnanowire arrays. Previous attempts to synthesize metallic systems of nanodimensions have been fraught with several problems. These include difficulty in synthesis, high temperatures and high pressures involved in the synthesis, low stabilities, susceptibility to external degrading factors, etc. In an attempt to circumvent these problems, our approach involved a novel strategy both of synthesizing and stabilizing the subnanowires. Thus we initially designed unusual organic systems, whose properties can be fine-tuned by either electrochemical or photochemical means. In the course of this process. we noted that organic nanotubes formed by the non-tubular subunits of electrochemically and photochemically active calix[4]hydroquinone (CHQ) possess infinitely long one-dimensional hydrogen-bond arrays. Based on simple electro/photochemistry uniform and ultrathin silver nanowires can be self-synthesized inside these organic CHQ nanotubes. These subnanowires, which are extremely long and have widths corresponding to the fee lattice constant of the bulk silver metal (0.4 nm), are stable for long periods Of time under ambient conditions, Based on both experimental and theoretical analysis of these ultra-thin silver subnanowires, we believe that they could serve as model systems for investigating wide-ranging and exciting one-dimensional physical phenomena (as a quantum wire) and also be employed as possible nanoconnectors in potential nanoelectronic devices. (C) 2002 Elsevier Science B.V. All rights reserved.X1124sciescopu
Emergent gauge fields and their nonperturbative effects in correlated electrons
No full textThe history of modern condensed matter physics may be regarded as the competition and reconciliation between Stoner's and Anderson's physical pictures, where the former is based on momentum-space descriptions focusing on long wave-length fluctuations while the latter is based on real-space physics emphasizing emergent localized excitations. In particular, these two view points compete with each other in various nonperturbative phenomena, which range from the problem of high T-C superconductivity, quantum spin liquids in organic materials and frustrated spin systems, heavy-fermion quantum criticality, metal-insulator transitions in correlated electron systems such as doped silicons and two-dimensional electron systems, the fractional quantum Hall effect, to the recently discussed Fe-based superconductors. An approach to reconcile these competing frameworks is to introduce topologically nontrivial excitations into the Stoner's description, which appear to be localized in either space or time and sometimes both, where scattering between itinerant electrons and topological excitations such as skyrmions, vortices, various forms of instantons, emergent magnetic monopoles, and etc. may catch nonperturbative local physics beyond the Stoner's paradigm. In this review paper, we discuss nonperturbative effects of topological excitations on dynamics of correlated electrons. First, we focus on the problem of scattering between itinerant fermions and topological excitations in antiferromagnetic doped Mott insulators, expected to be relevant for the pseudogap phase of high T-C cuprates. We propose that nonperturbative effects of topological excitations can be incorporated within the perturbative framework, where an enhanced global symmetry with a topological term plays an essential role. In the second part, we go on to discuss the subject of symmetry protected topological states in a largely similar light. While we do not introduce itinerant fermions here, the nonperturbative dynamics of topological excitations is again seen to be crucial in classifying topologically nontrivial gapped systems. We point to some hidden links between several effective field theories with topological terms, starting with one-dimensional physics, and subsequently finding natural generalizations to higher dimensions.1122sciescopu
Structures and spectra of iodide-water clusters I-(H2O)(n=1-6): An ab initio study
No full textTo investigate the structures of I-(H2O)(n = 1-6), extensive ab initio calculations have been carried out. Owing to very flexible potential surfaces of the system (in particular for n = 5 and 6), the lowest energy structures are characterized from various possible low-lying energy conformers. In contrast to some previously reported structures, we find a new lowest energy structure (followed by a few low-lying energy conformers) for n = 5 and four nearly isoenergetic conformers for n=6. These conformers have surface and near-surface structures with the coordination number of 4. The present results provide the information of possible structures in recent profuse experiments of infrared spectra of I-(H2O)(n = 1-6) and charge transfer from the excited iodide ion to water molecules. Our predicted ionization potentials and OH stretching frequencies are in good agreement with the experimental data available, while only the cases of the OH frequencies for n = 4 and the ionization potential for n = 5 need consideration of conformational change by the temperature effect. (C) 2001 American Institute of Physics.open11113sciescopu
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