Deterministic annealing, constrained clustering, and optimization

In previous work the authors (Phys. Rev. Let., vol.65, p.945-8, 1990) proposed the concept of deterministic annealing for the problem of clustering and vector quantization. This approach is summarized. The authors extend the clustering method to the constraint clustering method. Adding constraints to the deterministic annealing mechanism expands the variety of optimization problems which can be solved by this method. A brief presentation of the clustering approach is given. Two examples to which the constraint clustering approach can be applied are included

DNA double-strand breaks induce H2Ax phosphorylation domains in a contact-dependent manner

Formation of γH2Ax serves as a checkpoint for double-strand break (DSB) repair pathways. Here the authors reveal via integrated chromatin analysis that γH2Ax domains are established by chromosomal contacts with the DSB site

Interplay of spin and orbital ordering in the layered colossal magnetoresistance manganite La2-2xSr1+2xMn2O7 (0.5<=x<=1.0)

The crystallographic and magnetic phase diagram of the n=2 layered manganite La2-2xSr1+2xMn2O7 in the region x=>0.5 has been studied using temperature dependent neutron powder diffraction. The magnetic phase diagram reveals a progression of ordered magnetic structures generally paralleling that of 3-D perovskites with similar electronic doping: A (0.5 C (0.75 G (0.90<=x<=1.0). However, the quasi-2-D structure amplifies this progression to expose features of manganite physics uniquely accessible in the layered systems: (a) a "frustrated" region between the A and C regimes where no long-range magnetic order is observed; (b) magnetic polytypism arising from weak inter-bilayer magnetic exchange in the Type-C regime; and (c) a tetragonal to orthorhombic phase transition whose temperature evolution directly measures ordering of d3y2-r2 orbitals in the a-b plane. This orbital-ordering transition is precursory to Type-C magnetic ordering, where ferromagnetic rods lie parallel to the b-axis. These observations support the notion that eg orbital polarisation is the driving force behind magnetic spin ordering. Finally, in the crossover region between Type-C and Type-G states, we see some evidence for the development of local Type-C clusters embedded in a Type-G framework, directly addressing proposals of similar short-range magnetic ordering in highly-doped La1-xCaxMnO3 perovskites.Comment: 32 pages, 13 figures, submitted to Phys. Rev.

Ground state properties and energy parameters of the Anderson lattice system, CeAl2

Des mesures de magnétostriction et d'expansion thermique de CeAl2 dans la phase et au voisinage de la phase antiferromagnétique (AF) ont établi, en premier lieu, la frontière de la phase AF dans le diagramme H-T, en second lieu, la nature de la réorientation des domaines AF et l'évolution du paramètre d'ordre AF dans un champ magnétique ainsi que les fluctuations au-dessus de TN, et, finalement, que l'échange magnétique est ferromagnétique pour un champ magnétique élevé. Des mesures de diffusion inélastique de neutrons révèlent une nouvelle particularité à 17,5 meV qui n'a pas encore été expliquée.Magnetostriction and thermal expansion measurements on CeAl2 in and near the antiferromagnetic (AF) phase have established (1) the AF phase boundary in the H-T plane ; (2) the nature of the reorientation of the AF domains in field, the evolution of the AF order parameter in field and the nature of the AF fluctuations above TN ; and (3) that the magnetic exchange between Ce atoms is ferromagnetic in large fields. Inelastic neutron scattering measurements reveal a new and yet unexplained feature at 17.5 meV

Two-dimensional Rayleigh model of vapor bubble evolution

The understanding of vapor bubble generation in an aqueous tissue near a fiber tip has required advanced two dimensional (2D) hydrodynamic simulations. For 1D spherical bubble expansion a simplified and useful Rayleigh-type model can be applied. For 2D bubble evolution, such a model does not exist. The present work proposes a Rayleigh-type model for 2D bubble expansion that is faster and simpler than the 2D hydrodynamic simulations. The model is based on a flow potential representation of the hydrodynamic motion controlled by a Laplace equation and a moving boundary condition. We show that the 1D Rayleigh equation is a specific case of our model. The Laplace equation is solved for each time step by a finite element solver using a triangulation of the outside bubble region by a fast unstructured mesh generator. Two problems of vapor bubbles generated by short-pulse lasers near a fiber tip-are considered: (a) the outside region has no boundaries except the fiber, (b) the fiber and the bubble are confined in a long channel, which simulates a fiber in a vessel wall. Our simulations for problems of type (a) include features of bubble evolution as seen in experiments, including a collapse away from the fiber tip. A different behavior was obtained for problems of type (b) when the channel boundary is close to the fiber. In this case the bubble� s expansion and collapse are both extremely slow in the direction normal to this boundary and distortion of the bubble is observed

Packet Size Distribution: an Aside?

For multimedia traffic like VBR video, knowledge of the average loss probability is not sufficient to determine the impact of loss on the perceived visual quality and on the possible ways of improving it, for example by forward error correction (FEC) and error concealment. In this paper we investigate how the packet size distribution affects the packet loss process, the distribution of the number of packets lost in a block of packets and the related FEC performance. We presen