Entropy-driven phase transition in a polydisperse hard-rods lattice system

We study a system of rods on the 2d square lattice, with hard-core exclusion. Each rod has a length between 2 and N. We show that, when N is sufficiently large, and for suitable fugacity, there are several distinct Gibbs states, with orientational long-range order. This is in sharp contrast with the case N=2 (the monomer-dimer model), for which Heilmann and Lieb proved absence of phase transition at any fugacity. This is the first example of a pure hard-core system with phases displaying orientational order, but not translational order; this is a fundamental characteristic feature of liquid crystals

Phases of supersymmetric O(N) theories

We perform a global renormalization group study of O(N) symmetric Wess-Zumino theories and their phases in three euclidean dimensions. At infinite N the theory is solved exactly. The phases and phase transitions are worked out for finite and infinite short-distance cutoffs. A distinctive new feature arises at strong coupling, where the effective superfield potential becomes multi-valued, signalled by divergences in the fermion-boson interaction. Our findings resolve the long-standing puzzle about the occurrence of degenerate O(N) symmetric phases. At finite N, we find a strongly-coupled fixed point in the local potential approximation and explain its impact on the phase transition. We also examine the possibility for a supersymmetric Bardeen-Moshe-Bander phenomenon, and relate our findings with the spontaneous breaking of supersymmetry in other models.Comment: 23 pages, 18 figure

Some records of wood-inhabiting fungi on Fagus sylvatica in northern Spain

Es presenta una llista d'algunes recol·leccions interessants de macromicets sobre Fagus, fetes en algunes prospeccions a Astúries i Navarra, en novembre de 2005 . Pel cap baix, Antrodiella fissiliformis, Nemania carbonacea y Phellinus cavicola representen les primeres citacions per a l 'estat espanyol. Des del punt de vista de l' interès per a la conservació de la biodiversitat fúngica, les reserves integrals de Lizardoia i Aztaparreta, a Navarra, es consideren d'especial importància per a la conservació dels fongs saproxílics fagícoles del sud-oest d'Europa. Aquest treball vol estimular també l 'estudi continuat dels fongs lignícoles a les fagedes de l 'estat espanyol.A list is given of some interesting records of lignicolous macrofungi found on Fagus during some excursions in Asturias and Navarra in November 2005 . At least Antrodiella fissiliformis, Nemania carbonacea and Phellinus cavicola represent frrst records for the country. In a conservation perspective, the strict forest reserves Lizardoia and Aztaparreta in Navarra are considered to be important for the conservation of saproxylic fungi on beech in south western Europe. It is our hope that the paper will inspire to continued studies of wood-inhabiting fungi in beech forests in Spain.Se presenta una lista de algunos allaazgos interesantes de macromicetes lignícolas sobre Fagus, realizados durante las prospecciones en Asturias y Navarra, en noviembre de 2005. Por lo menos Antrodiella fissiliformis, Nemania carbonacea y Phellinus cavicola representan primeras citas para España. desde una prespectiva de la conservación de la biodiversidad fúngica, las reservas integrales de L izardoia i Aztaparreta, en Navarra, se consideran de especial importancia para la conservación de los hongos saproxílicos fagícolas en el sudoeste de Europa. Este trabajo esta orientado también a fomentar el estudio continuado de los hongos lignícolas en los hayedos de España

Some records of wood-inhabiting fungi on Fagus sylvatica in northern Spain

Es presenta una llista d'algunes recol·leccions interessants de macromicets sobre Fagus, fetes en algunes prospeccions a Astúries i Navarra, en novembre de 2005 . Pel cap baix, Antrodiella fissiliformis, Nemania carbonacea y Phellinus cavicola representen les primeres citacions per a l 'estat espanyol. Des del punt de vista de l' interès per a la conservació de la biodiversitat fúngica, les reserves integrals de Lizardoia i Aztaparreta, a Navarra, es consideren d'especial importància per a la conservació dels fongs saproxílics fagícoles del sud-oest d'Europa. Aquest treball vol estimular també l 'estudi continuat dels fongs lignícoles a les fagedes de l 'estat espanyol.Se presenta una lista de algunos allaazgos interesantes de macromicetes lignícolas sobre Fagus, realizados durante las prospecciones en Asturias y Navarra, en noviembre de 2005. Por lo menos Antrodiella fissiliformis, Nemania carbonacea y Phellinus cavicola representan primeras citas para España. desde una prespectiva de la conservación de la biodiversidad fúngica, las reservas integrales de L izardoia i Aztaparreta, en Navarra, se consideran de especial importancia para la conservación de los hongos saproxílicos fagícolas en el sudoeste de Europa. Este trabajo esta orientado también a fomentar el estudio continuado de los hongos lignícolas en los hayedos de España.A list is given of some interesting records of lignicolous macrofungi found on Fagus during some excursions in Asturias and Navarra in November 2005 . At least Antrodiella fissiliformis, Nemania carbonacea and Phellinus cavicola represent frrst records for the country. In a conservation perspective, the strict forest reserves Lizardoia and Aztaparreta in Navarra are considered to be important for the conservation of saproxylic fungi on beech in south western Europe. It is our hope that the paper will inspire to continued studies of wood-inhabiting fungi in beech forests in Spain

NVU dynamics. I. Geodesic motion on the constant-potential-energy hypersurface

An algorithm is derived for computer simulation of geodesics on the constant potential-energy hypersurface of a system of N classical particles. First, a basic time-reversible geodesic algorithm is derived by discretizing the geodesic stationarity condition and implementing the constant potential energy constraint via standard Lagrangian multipliers. The basic NVU algorithm is tested by single-precision computer simulations of the Lennard-Jones liquid. Excellent numerical stability is obtained if the force cutoff is smoothed and the two initial configurations have identical potential energy within machine precision. Nevertheless, just as for NVE algorithms, stabilizers are needed for very long runs in order to compensate for the accumulation of numerical errors that eventually lead to "entropic drift" of the potential energy towards higher values. A modification of the basic NVU algorithm is introduced that ensures potential-energy and step-length conservation; center-of-mass drift is also eliminated. Analytical arguments confirmed by simulations demonstrate that the modified NVU algorithm is absolutely stable. Finally, simulations show that the NVU algorithm and the standard leap-frog NVE algorithm have identical radial distribution functions for the Lennard-Jones liquid

Hybrid systems: a real-time interface to control engineering

This paper gives an introduction to a general hybrid systems model for definition of system requirements and a corresponding software architecture together with an example of their specialization for use in implementing a modeswitching controller for a hydraulic cylinder. 1. Introduction An important application area for real-time computing is embedded systems where the computing system provides intelligent control of a mechanical, chemical etc. plant or device. The software requirements for such applications depend heavily on the properties of the plant. These properties are usually investigated by control engineers that base their work on the theory of dynamic systems [3, 9]. The mathematical tool for this work is thus mathematical analysis, in particular the theory of differential equations. If the models are linear differential equations, there are standard techniques for implementing a corresponding discrete, sampled system in the form of a computer program, and the work for the s..

Failure of Mean Field Theory at Large N

We study strongly coupled lattice QCD with $N$ colors of staggered fermions in 3+1 dimensions. While mean field theory describes the low temperature behavior of this theory at large $N$, it fails in the scaling region close to the finite temperature second order chiral phase transition. The universal critical region close to the phase transition belongs to the 3d XY universality class even when $N$ becomes large. This is in contrast to Gross-Neveu models where the critical region shrinks as $N$ (the number of flavors) increases and mean field theory is expected to describe the phase transition exactly in the limit of infinite $N$. Our work demonstrates that close to second order phase transitions infrared fluctuations can sometimes be important even when $N$ is strictly infinite.Comment: 4 pages, 3 figure

Using Alphabet Knowledge to Track the Emergent Literacy Skills of Children in Head Start

Having strong alphabet knowledge early in life is a powerful predictor of long-term reading and academic outcomes. Upon tracking the alphabet knowledge of 172 children enrolled in their first year of Head Start, we identified that most of the children could name fewer than 10 letters at the beginning of the academic year. Approximately, one third of the children with low alphabet knowledge in fall made significant progress and demonstrated mastery of 10 or more letters in spring. For the children who started the year knowing fewer than 10 letters, receptive vocabulary was the best predictor of who would make gains in alphabet knowledge throughout the year. In addition, most children who entered Head Start knowing fewer than 10 letters knew letters from their first names and the letters A, B, or O. Implications for the management of emergent literacy skills for children at-risk for academic difficulties are discussed

Spectral microscopic mechanisms and quantum phase transitions in a 1D correlated problem

In this paper we study the dominant microscopic processes that generate nearly the whole one-electron removal and addition spectral weight of the one-dimensional Hubbard model for all values of the on-site repulsion $U$. We find that for the doped Mott-Hubbard insulator there is a competition between the microscopic processes that generate the one-electron upper-Hubbard band spectral-weight distributions of the Mott-Hubbard insulating phase and finite-doping-concentration metallic phase, respectively. The spectral-weight distributions generated by the non-perturbative processes studied here are shown elsewhere to agree quantitatively for the whole momentum and energy bandwidth with the peak dispersions observed by angle-resolved photoelectron spectroscopy in quasi-one-dimensional compounds.Comment: 18 pages, 2 figure