Bulk and shear relaxation in glasses and highly viscous liquids

The ratio between the couplings of a relaxational process to compression and shear, respectively, is calculated in the Eshelby picture of structural rearrangements within a surrounding elastic matrix, assuming a constant density of stable structures in distortion space. The result is compared to experimental data for the low-temperature tunneling states in glasses and to Prigogine-Defay data at the glass transition from the literature.Comment: 6 pages, 2 figures, 53 references; version after understanding the Prigogine-Defay ratio at the glass transition in the accompanying paper arXiv:1203.3555 [cond-mat.dis-nn

Essential Tremor, the Cerebellum, and Motor Timing: Towards Integrating Them into One Complex Entity

Essential tremor (ET) is the most common movement disorder in humans. It is characterized by a postural and kinetic tremor most commonly affecting the forearms and hands. Isolated head tremor has been found in 1–10% of patients, suggesting that ET may be a composite of several phenotypes. The exact pathophysiology of ET is still unknown. ET has been repeatedly shown as a disorder of mild cerebellar degeneration, particularly in postmortem studies. Clinical observations, electrophysiological, volumetric and functional imaging studies all reinforce the fact that the cerebellum is involved in the generation of ET. However, crucial debate exists as to whether ET is a neurodegenerative disease. Data suggesting that it is neurodegenerative include postmortem findings of pathological abnormalities in the brainstem and cerebellum, white matter changes on diffusion tensor imaging, and clinical studies demonstrating an association with cognitive and gait changes. There is also conflicting evidence against ET as a neurodegenerative disease: the improvement of gait abnormalities with ethanol administration, lack of gray matter volume loss on voxel-based morphometry, failure to confirm the prominent presence of Lewy bodies in the locus ceruleus, and other pathological findings. To clarify this issue, future research is needed to describe the mechanism of cellular changes in the ET brain and to understand the order in which they occur. The cerebellum has been shown to be involved in the timing of movement and sensation, acting as an internal timing system that provides the temporal representation of salient events spanning hundreds of milliseconds. It has been reported that cerebellar timing function is altered in patients with ET, showing an increased variability of rhythmic hand movements as well as diminished performance during predictive motor timing task. Based on current knowledge and observations, we argue that ET is essentially linked with cerebellar degeneration, or at least cerebellar dysfunction, together with disturbance of motor timing. We explain the context of our current understanding on this topic, highlighting possible clinical consequences for patients suffering from ET and future research directions

Solution of classical stochastic one dimensional many-body systems

We propose a simple method that allows, in one dimension, to solve exactly a wide class of classical stochastic many-body systems far from equilibrium. For the sake of illustration and without loss of generality, we focus on a model that describes the asymmetric diffusion of hard core particles in the presence of an external source and instantaneous annihilation. Starting from a Master equation formulation of the problem we show that the density and multi-point correlation functions obey a closed set of integro-differential equations which in turn can be solved numerically and/or analyticallyComment: 2 figure

Relaxation kinetics of biological dimer adsorption models

We discuss the relaxation kinetics of a one-dimensional dimer adsorption model as recently proposed for the binding of biological dimers like kinesin on microtubules. The non-equilibrium dynamics shows several regimes: irreversible adsorption on short time scales, an intermediate plateau followed by a power-law regime and finally exponential relaxation towards equilibrium. In all four regimes we give analytical solutions. The algebraic decay and the scaling behaviour can be explained by mapping onto a simple reaction-diffusion model. We show that there are several possibilities to define the autocorrelation function and that they all asymptotically show exponential decay, however with different time constants. Our findings remain valid if there is an attractive interaction between bound dimers.Comment: REVTeX, 6 pages, 5 figures; to appear in Europhys. Letters; a Java applet showing the simulation is accessible at http://www.ph.tum.de/~avilfan/rela

Lightly Doped t-J Three-Leg Ladders - an Analog for the Underdoped Cuprates

The three-leg ladder has one odd-parity and two even-parity channels. At low doping these behave quite differently. Numerical calculations for a t-J model show that the initial phase upon hole doping has two components - a conducting Luttinger liquid in the odd-parity channel, coexisting with an insulating (i.e. undoped) spin liquid phase in the even-parity channels. This phase has a partially truncated Fermi surface and violates the Luttinger theorem. This coexistence of conducting fermionic and insulating paired bosonic degrees of freedom is similar to the recent proposal of Geshkenbein, Ioffe, and Larkin for the underdoped spin-gap normal phase of the cuprates. A mean field approximation is derived which has many similarities to the numerical results. One difference however is an induced hole pairing in the odd-parity channel at arbitrary small dopings, similar to that proposed by Geshkenbein, Ioffe, and Larkin for the two-dimensional case. At higher dopings, we propose that a quantum phase transition will occur as holes enter the even-parity channels, resulting in a Luther-Emery liquid with hole pairing with essentially d-wave character. In the mean field approximation a crossover occurs which we interpret as a reflection of this quantum phase transition deduced from the numerical results.Comment: RevTex, 36 pages with 16 figure

Small Amplitude Reciprocating Wear Performance of Diamond-like Carbon Films: Dependence of Film Composition and Counterface Material

Small amplitude (50 μm) reciprocating wear of hydrogen-containing diamond-like carbon (DLC) films of different compositions has been examined against silicon nitride and polymethyl-methacrylate (PMMA) counter-surfaces, and compared with the performance of an uncoated steel substrate. Three films were studied: a DLC film of conventional composition, a fluorine-containing DLC film (F-DLC), and silicon-containing DLC film. The films were deposited on steel substrates from plasmas of organic precursor gases using the Plasma Immersion Ion Implantation and Deposition (PIIID) process, which allows for the non-line-of-sight deposition of films with tailored compositions. The amplitude of the resistive frictional force during the reciprocating wear experiments was monitored in situ, and the magnitude of film damage due to wear was evaluated using optical microscopy, optical profilometry, and atomic force microscopy. Wear debris was analyzed using scanning electron microscopy and energy dispersive spectroscopy. In terms of friction, the DLC and silicon-containing DLC films performed exceptionally well, showing friction coefficients less than 0.1 for both PMMA and silicon nitride counter-surfaces. DLC and silicon-containing DLC films also showed significant reductions in transfer of PMMA compared with the uncoated steel. The softer F-DLC film performed similarly well against PMMA, but against silicon nitride, friction displayed nearly periodic variations indicative of cyclic adhesion and release of worn film material during the wear process. The results demonstrate that the PIIID films achieve the well-known advantageous performance of other DLC films, and furthermore that the film performance can be significantly affected by the addition of dopants. In addition to the well-established reduction of friction and wear that DLC films generally provide, we show here that another property, low adhesiveness with PMMA, is another significant benefit in the use of DLC films

Critical Properties of Spectral Functions for the 1D Anisotropic t-J Models with an Energy Gap

We exactly calculate the momentum-dependent critical exponents for spectral functions in the one-dimensional anisotropic t-J models with a gap either in the spin or charge excitation spectrum. Our approach is based on the Bethe ansatz technique combined with finite-size scaling techniques in conformal field theory. It is found that the spectral functions show a power-law singularity, which occurs at frequencies determined by the dispersion of a massive spin (or charge) excitation.We discuss how the nontrivial contribution of a massive excitation controls the singular behavior in optical response functions.Comment: 4 pages, REVTeX, 2 figures(available upon request), accepted for publication in JPSJ 66 (1997) No.

New integrable extension of the Hubbard chain with variable range hopping

New integrable variant of the one-dimensional Hubbard model with variable-range correlated hopping is studied. The Hamiltonian is constructed by applying the quantum inverse scattering method on the infinite interval at zero density to the one-parameter deformation of the L-matrix of the Hubbard model. By construction, this model has Y(su(2))$\oplus$Y(su(2)) symmetry in the infinite chain limit. Multiparticle eigenstates of the model are investigated through this method.Comment: 25 pages, LaTeX, no figure

The Supersymmetric t-J Model with a Boundary

An open supersymmetric t-J chain with boundary fields is studied by means of the Bethe Ansatz. Ground state properties for the case of an almost half-filled band and a bulk magnetic field are determined. Boundary susceptibilities are calculated as functions of the boundary fields. The effects of the boundary on excitations are investigated by constructing the exact boundary S-matrix. From the analytic structure of the boundary S-matrices one deduces that holons can form boundary bound states for sufficiently strong boundary fields.Comment: 23 pages of revtex, discussion on analytic structure of holon S-matrix change