Asymptotics for hitting times

In this paper we characterize possible asymptotics for hitting times in aperiodic ergodic dynamical systems: asymptotics are proved to be the distribution functions of subprobability measures on the line belonging to the functional class {6pt} {-3mm}(A){6mm}F={F:R\to [0,1]:\left\lbrack \matrixF is increasing, null on ]-\infty, 0]; \noalignF is continuous and concave; \noalignF(t)\le t for t\ge 0.\right.}. {6pt} Note that all possible asymptotics are absolutely continuous.Comment: Published at http://dx.doi.org/10.1214/009117904000000883 in the Annals of Probability (http://www.imstat.org/aop/) by the Institute of Mathematical Statistics (http://www.imstat.org

Attractive regular stochastic chains: perfect simulation and phase transition

We prove that uniqueness of the stationary chain, or equivalently, of the $g$-measure, compatible with an attractive regular probability kernel is equivalent to either one of the following two assertions for this chain: (1) it is a finitary coding of an i.i.d. process with countable alphabet, (2) the concentration of measure holds at exponential rate. We show in particular that if a stationary chain is uniquely defined by a kernel that is continuous and attractive, then this chain can be sampled using a coupling-from-the-past algorithm. For the original Bramson-Kalikow model we further prove that there exists a unique compatible chain if and only if the chain is a finitary coding of a finite alphabet i.i.d. process. Finally, we obtain some partial results on conditions for phase transition for general chains of infinite order.Comment: 22 pages, 1 pseudo-algorithm, 1 figure. Minor changes in the presentation. Lemma 6 has been remove

Partial Disorder and Metal-Insulator Transition in the Periodic Anderson Model on a Triangular Lattice

Ground state of the periodic Anderson model on a triangular lattice is systematically investigated by the mean-field approximation. We found that the model exhibits two different types of partially disordered states: one is at half filling and the other is at other commensurate fillings. In the latter case, the kinetic energy is lowered by forming an extensive network involving both magnetic and nonmagnetic sites, in sharp contrast to the former case in which the nonmagnetic sites are rather isolated. This spatially extended nature of nonmagnetic sites yields a metallic partially-disordered state by hole doping. We discuss the mechanism of the metal-insulator transition by the change of electronic structure.Comment: 4 pages, 4 figures, accepted for publication in J. Phys. Soc. Jp

AUTOMATIC CLEANING MACHINE FOR RF POWER COUPLERS

http://accelconf.web.cern.ch/AccelConf/SRF2011/papers/tupo011.pdfInternational audienceCouplers are technological devices that permit RF power matching between RF source and cavities. An high cleaning quality requirement especially for the coupler cold part directly linked to the cavity is needed. Even if the actual coupler preparation procedure at LAL works well, contamination risks remain due to the handling, no repeatability and a too long time duration (5 days) which is not acceptable for machines like ILC where around 16000 couplers would be prepared. Our challenge is to suppress these weak points, in designing an automatic coupler cleaning machine which give us a lower contamination risk, a fulthe cleaning and only 3 hours of process

Production of 3-hydroxypropionaldehyde using a two-step process with Lactobacillus reuteri

3-Hydroxypropionaldehyde (3-HPA) produced by Lactobacillus reuteri is a broad-spectrum antimicrobial substance of glycerol conversion. The aim of the present work was to optimize 3-HPA production by Lb. reuteri ATCC 53608 using a two-step process. The first step was the production of Lb. reuteri cells in optimal conditions. Cells were then harvested by centrifugation and suspended in glycerol solution, which the resting cells bioconverted to 3-HPA. The effect of biomass concentration, temperature, glycerol concentration, anaerobic/micro-aerophilic conditions, and incubation time was studied for high 3-HPA production. 3-HPA accumulation was limited by the death of cells in contact with high concentrations of 3-HPA. However, a very high 3-HPA concentration of 235±3mM was obtained after 45min of incubation at 30°C in 400mM glycerol for an initial free-cell concentration of 1.6±0.3×1010 viablecells/ml. A high viability was maintained at low temperatures in the range 5-15°C, but with a slightly lower yield of 3-HPA at 5°C compared with higher temperatures, up to 37°C. Successive 1-h incubations of Lb. reuteri cells in 200mM glycerol at 15°C to tentatively reuse the cells resulted in decreasing 3-HPA concentrations at the end of each cycle, with two successful production cycles yielding high 3-HPA concentrations of 147±1mM and 128±2m

A large-NcN_c PNJL model with explicit ZNc_{N_c} symmetry

A PNJL model is built, in which the Polyakov-loop potential is explicitly Z$_{N_c}$-symmetric in order to mimic a Yang-Mills theory with gauge group SU($N_c$). The physically expected large-$N_c$ and large-$T$ behaviours of the thermodynamic observables computed from the Polyakov-loop potential are used to constrain its free parameters. The effective potential is eventually U(1)-symmetric when $N_c$ is infinite. Light quark flavours are added by using a Nambu-Jona-Lasinio (NJL) model coupled to the Polyakov loop (the PNJL model), and the different phases of the resulting PNJL model are discussed in 't Hooft's large-$N_c$ limit. Three phases are found, in agreement with previous large-$N_c$ studies. When the temperature $T$ is larger than some deconfinement temperature $T_d$, the system is in a deconfined, chirally symmetric, phase for any quark chemical potential $\mu$. When $T<T_d$ however, the system is in a confined phase in which chiral symmetry is either broken or not. The critical line $T_\chi(\mu)$, signalling the restoration of chiral symmetry, has the same qualitative features than what can be obtained within a standard $N_c=3$ PNJL model.Comment: To appear in Phys Rev

Electronic states and magnetic excitations in LiV2O4: Exact diagonalization study

Motivated by recent inelastic neutron scattering experiment we examine magnetic properties of LiV2O4. We consider a model which describes the half-filled localized A1g spins interacting via frustrated antiferromagnetic Heisenberg exchange and coupled by local Hund's interaction with the 1/8-filled itinerant Eg band, and study it within an exact diagonalization scheme. In the present study we limited the analysis to the case of the cluster of two isolated tetrahedrons. We obtained that both the ground state structure and low-lying excitations depend strongly on the value of the Hund's coupling which favors the triplet states. With increasing temperature the triplet states become more and more populated which results in the formation of non-zero residual magnetic moment. We present the temperature dependence of calculated magnetic moment and of the spin-spin correlation functions at different values of Hund's coupling and compare them with the experimental results.Comment: 7 pages. 6 eps figure

Unique Spin Dynamics and Unconventional Superconductivity in the Layered Heavy Fermion Compound CeIrIn_5:NQR Evidence

We report measurements of the ^{115}In nuclear spin-lattice relaxation rate (1/T_1) between T=0.09 K and 100 K in the new heavy fermion (HF) compound CeIrIn_5. At 0.4 K < T < 100 K, 1/T_1 is strongly T-dependent, which indicates that CeIrIn_5 is much more itinerant than known Ce-based HFs. We find that 1/T_1T, subtracting that for LaIrIn_5, follows a 1/(T+\theta)^{3/4} variation with \theta=8 K. We argue that this novel feature points to anisotropic, due to a layered crystal structure, spin fluctuations near a magnetic ordering. The bulk superconductivity sets in at 0.40 K below which the coherence peak is absent and 1/T_1 follows a T^3 variation, which suggests unconventional superconductivity with line-node gap.Comment: minor changes, appeared in PRL (4 pages, 4 figures

Fine structure of the isoscalar giant quadrupole resonance in 40Ca due to Landau damping?

The fragmentation of the Isoscalar Giant Quadrupole Resonance (ISGQR) in 40Ca has been investigated in high energy-resolution experiments using proton inelastic scattering at E_p = 200 MeV. Fine structure is observed in the region of the ISGQR and its characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The experimental scales are well described by Random Phase Approximation (RPA) and second-RPA calculations with an effective interaction derived from a realistic nucleon-nucleon interaction by the Unitary Correlation Operator Method (UCOM). In these results characteristic scales are already present at the mean-field level pointing to their origination in Landau damping, in contrast to the findings in heavier nuclei and also to SRPA calculations for 40Ca based on phenomenological effective interactions, where fine structure is explained by the coupling to two-particle two-hole (2p-2h) states.Comment: Phys. Lett. B, in pres