Branching mechanism of intergranular crack propagation in three dimensions

We investigate the process of slow intergranular crack propagation by the finite element method model, and show that branching is induced by partial arresting of crack front owing to the geometrical randomness of grain boundaries. A possible scenario for branching instability of crack propagation in disordered continuum medium is also discussed.Comment: 4 pages, submitted to Phys.Rev.E; v2:corrected typos v3: final version to be publishe

Color Glass Condensate and BFKL dynamics in deep inelastic scattering at small x

The proton structure function F_2(x,Q^2) for x < 0.01 and 0.045< Q^2 < 45 GeV^2, measured in the deep inelastic scattering at HERA, can be well described within the framework of the Color Glass Condensate.Comment: 4 pages, 1 figure, incl. IOP style files. Talk given at the 17th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2004), Oakland, CA USA, 11-17 Jan 200

Two Langevin equations in the Doi-Peliti formalism

A system-size expansion method is incorporated into the Doi-Peliti formalism for stochastic chemical kinetics. The basic idea of the incorporation is to introduce a new decomposition of unity associated with a so-called Cole-Hopf transformation. This approach elucidates a relationship between two different Langevin equations; one is associated with a coherent-state path-integral expression and the other describes density fluctuations. A simple reaction scheme $X \rightleftarrows X+X$ is investigated as an illustrative example.Comment: 14page

Role of heating and current-induced forces in the stability of atomic wires

We investigate the role of local heating and forces on ions in the stability of current-carrying aluminum wires. We find that heating increases with wire length due to a red shift of the frequency spectrum. Nevertheless, the local temperature of the wire is relatively low for a wide range of biases provided good thermal contact exists between the wire and the bulk electrodes. On the contrary, current-induced forces increase substantially as a function of bias and reach bond-breaking values at about 1 V. These results suggest that local heating promotes low-bias instabilities if dissipation into the bulk electrodes is not efficient, while current-induced forces are mainly responsible for the wire break-up at large biases. We compare these results to experimental observations.Comment: 4 pages, 4 figure

Proteins to Order Use of Synthetic DNA to Generate Site-Specific Mutations

The ability to cause specific changes in the amino acid sequences of proteins would greatly advance studies on the influence of protein structure on biochemical function. If the desired changes can once be made in the nucleic acid which encodes the protein, one can use cloning in an appropriate microorganism to produce essentially limitless quantities of the mutant protein. We describe here the application of oligonucleotide-directed site-specific mutagenesis to accomplish this objective for the enzyme B-lactamase, the gene for which is contained in the plasmid pBR322. The method uses a procedure to screen for mutant clones which depends on the DNA in the various colonies and not on the properties of the mutant protein; the method can, therefore, be widely applied and does not require, in each separate case, the development of a screening procedure which depends on some phenotypic difference between mutant and wild-type protein

Chemical Equilibration and Transport Properties of Hadronic Matter near TcT_c

We discuss how the inclusion of Hagedorn states near $T_c$ leads to short chemical equilibration times of proton anti-proton pairs, $K\bar{K}$ pairs, and $\Lambda\bar{\Lambda}$ pairs, which indicates that hadrons do not need to be "born" into chemical equilibrium in ultrarelativistic heavy ion collisions. We show that the hadron ratios computed within our model match the experimental results at RHIC very well. Furthermore, estimates for $\eta/s$ near $T_c$ computed within our resonance gas model are comparable to the string theory viscosity bound $\eta/s=1/4\pi$. Our model provides a good description of the recent lattice results for the trace anomaly close to $T_c=196$ MeV.Comment: 4 pages, 3 figures, to appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse

A possible phase diagram of a t-J ladder model

We investigate a t-J ladder model by numerical diagonalization method. By calculating correlation functions and assuming the Luttinger liquid relation, we obtained a possible phase diagram of the ground state as a function of J/t and electron density $n$. We also found that behavior of correlation functions seems to consist with the prediction of Luttinger liquid relation. The result suggests that the superconducting phase appear in the region of $J/t \displaystyle{ \mathop{>}_{\sim}} 0.5$ for high electron density and $J/t \displaystyle{ \mathop{>}_{\sim}} 2.0$ for low electron density.Comment: Latex, 10 pages, figures available upon reques

Statistical Physics and Light-Front Quantization

Light-front quantization has important advantages for describing relativistic statistical systems, particularly systems for which boost invariance is essential, such as the fireball created in a heavy ion collisions. In this paper we develop light-front field theory at finite temperature and density with special attention to quantum chromodynamics. We construct the most general form of the statistical operator allowed by the Poincare algebra and show that there are no zero-mode related problems when describing phase transitions. We then demonstrate a direct connection between densities in light-front thermal field theory and the parton distributions measured in hard scattering experiments. Our approach thus generalizes the concept of a parton distribution to finite temperature. In light-front quantization, the gauge-invariant Green's functions of a quark in a medium can be defined in terms of just 2-component spinors and have a much simpler spinor structure than the equal-time fermion propagator. From the Green's function, we introduce the new concept of a light-front density matrix, whose matrix elements are related to forward and to off-diagonal parton distributions. Furthermore, we explain how thermodynamic quantities can be calculated in discretized light-cone quantization, which is applicable at high chemical potential and is not plagued by the fermion-doubling problem.Comment: 30 pages, 3 figures; v2: Refs. added, minor changes, accepted for publication in PR

Dynamical Chiral Symmetry Breaking on the Light Front I. DLCQ Approach

Dynamical chiral symmetry breaking in the DLCQ method is investigated in detail using a chiral Yukawa model closely related to the Nambu-Jona-Lasinio model. By classically solving three constraints characteristic of the light-front formalism, we show that the chiral transformation defined on the light front is equivalent to the usual one when bare mass is absent. A quantum analysis demonstrates that a nonperturbative mean-field solution to the ``zero-mode constraint'' for a scalar boson (sigma) can develop a nonzero condensate while a perturbative solution cannot. This description is due to our identification of the ``zero-mode constraint'' with the gap equation. The mean-field calculation clarifies unusual chiral transformation properties of fermionic field, which resolves a seemingly inconsistency between triviality of the null-plane chiral charge Q_5|0>=0 and nonzero condensate. We also calculate masses of scalar and pseudoscalar bosons for both symmetric and broken phases, and eventually derive the PCAC relation and nonconservation of Q_5 in the broken phase.Comment: Revised version to appear in Phys. Rev. D. 19 pages, 4 figures, REVTEX. Derivation of the PCAC relation is given. Its relation to the nonconservation of chiral charge is clarified. 1 figure and some references adde

One-Dimensional S=1 Spin-Orbital Model with Uniaxial Single-Ion Anisotropy

We investigate ground-state properties of a one-dimensional S=1 spin-orbital model with or without uniaxial single-ion anisotropy. By means of the density matrix renormalization group method, we compute the ground-state energy, the magnetization curves and the correlation functions. We discuss how the ground-state properties depend on the two exchange couplings for orbital and spin sectors. The phase diagram obtained is compared with that for the S=1/2 model. We also address the effect of uniaxial single-ion anisotropy.Comment: 7 pages, 10 figures, accepted for publication in J. Phys. Soc. Jp