1,734 research outputs found
Many-particle correlations in non-equilibrium Luttinger liquid
We develop an operator-based approach to the problem of Luttinger liquid
conductor in a non-equilibrium stationary state. We show that the
coherent-state many-body fermionic density matrix as well as all fermionic
correlation functions out of equilibrium are given by one-dimensional
functional determinants of the Fredholm type. Thus, the model constitutes a
remarkable example of a many-body problem where all the correlation functions
can be evaluated exactly. On the basis of the general formalism we investigate
four-point correlation functions of the fermions coming out of the Luttinger
liquid wire. Obtained correlations in the fermionic distribution functions
represent the combined effect of interaction and non-equilibrium conditions.Comment: 23 pages,7 figure
Indications of Universal Excess Fluctuations in Nonequilibrium Systems
The fluctuation in electric current in nonequilibrium steady states is
investigated by molecular dynamics simulation of macroscopically uniform
conductors. At low frequencies, appropriate decomposition of the spectral
intensity of current into thermal and excess fluctuations provides a simple
picture of excess fluctuations behaving as shot noise. This indicates that the
fluctuation-dissipation relation may be violated in a universal manner by the
appearance of shot noise for a wide range of systems with particle or momentum
transport.Comment: 4 pages, 4 figures; title changed, major revision; to appear in J.
Phys. Soc. Jp
A healthy start : promoting mental health and well-being in the early primary school years
This study was in part funded by the University of Malta.Mental health problems in children represent a significant international health concern, with up to one in five children using mental health services during the course of any given year. Identifying the processes of what prevents social, emotional and behaviour difficulties (SEBD) and promotes healthy development from an early age can make a significant contribution to the promotion of positive mental health in children. This article describes a longitudinal study which sought to identify the risk and promotive factors as young children move from the early to junior years in primary school. Multilevel analysis was used to identify the individual, classroom, school, home and community factors that predict change in SEBD and in prosocial behaviour in the early school years. It also calculated the cumulative effect of the various risk and promotive factors on the pupilsā well-being and mental health. The article presents the windows of vulnerability and opportunity for young childrenās healthy development, proposing a trajectory for healthy development in early and middle childhood.peer-reviewe
Exponential Time Complexity of Weighted Counting of Independent Sets
We consider weighted counting of independent sets using a rational weight x:
Given a graph with n vertices, count its independent sets such that each set of
size k contributes x^k. This is equivalent to computation of the partition
function of the lattice gas with hard-core self-repulsion and hard-core pair
interaction. We show the following conditional lower bounds: If counting the
satisfying assignments of a 3-CNF formula in n variables (#3SAT) needs time
2^{\Omega(n)} (i.e. there is a c>0 such that no algorithm can solve #3SAT in
time 2^{cn}), counting the independent sets of size n/3 of an n-vertex graph
needs time 2^{\Omega(n)} and weighted counting of independent sets needs time
2^{\Omega(n/log^3 n)} for all rational weights x\neq 0.
We have two technical ingredients: The first is a reduction from 3SAT to
independent sets that preserves the number of solutions and increases the
instance size only by a constant factor. Second, we devise a combination of
vertex cloning and path addition. This graph transformation allows us to adapt
a recent technique by Dell, Husfeldt, and Wahlen which enables interpolation by
a family of reductions, each of which increases the instance size only
polylogarithmically.Comment: Introduction revised, differences between versions of counting
independent sets stated more precisely, minor improvements. 14 page
The meeting problem in the quantum random walk
We study the motion of two non-interacting quantum particles performing a
random walk on a line and analyze the probability that the two particles are
detected at a particular position after a certain number of steps (meeting
problem). The results are compared to the corresponding classical problem and
differences are pointed out. Analytic formulas for the meeting probability and
its asymptotic behavior are derived. The decay of the meeting probability for
distinguishable particles is faster then in the classical case, but not
quadratically faster. Entangled initial states and the bosonic or fermionic
nature of the walkers are considered
In search of Coulsonās lost theorem
In HĆ¼ckel theory, the bond number is the sum of the orders of the Ļ bonds incident on a given carbon center. From the work of Coulson and his school, it has been believed for over 70 years that the bond number has a maximum of 3āÆāÆā and that this bound is realized by exactly one conjugated framework, that of the trimethylenemethane radical. Search of published literature and archived correspondence failed to find any formal proof of these two statements. Here, we provide a new formula for bond number that leads to an easily checked proof of both. The bond number of graphene is 1.574 597ā¦ (90.9% of the mathematical limit), and this value appears to act as a separator for the classes of metallic and semiconducting single-walled nanotubes, as defined within HĆ¼ckel theory
Mott insulator phases and first-order melting in BSCCO crystals with periodic surface holes
We measured the effects of periodic surface holes, created using a focused
ion beam, on the phase diagram of the vortex matter in high-T_c
Bi_2Sr_2CaCu_2O_{8+\delta} crystals. Differential magneto-optical measurements
show that the irreversibility line is shifted to higher fields and
temperatures, with respect to the pristine melting line. The irreversibility
line displays weak field dependence between integer matching fields indicating
multiple-flux-quanta pinning at holes. We find reduced equilibrium
compressibility of the vortex matter at integer matching fields, which is
strong evidence for the existence of thermodynamic Mott insulator phases.
Shaking with a transverse ac field surprisingly reveals first-order melting
that is not shifted with respect to the pristine melting line and that seems to
occur within the Mott insulator regions. This melting is understood to be the
first-order transition in the bulk of the crystal beneath the surface holes.
The transition is visible at the surface, despite the reduced vortex
compressibility in the top layer.Comment: 11 pages, 8 figures. To appear in Physical Review
Staphylococcal pelvic and rectal infection in a neonate
An infant with neonatal staphylococcal infection had evidence of pelvic inflammation, peritonitis and proctitis which resulted in narrowing of the rectosigmoid, uterectasis, pyelocaliectasis, and partial obstruction of the inferior vena cava. Appropriate treatment resulted in resolution of these findings.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46724/1/247_2004_Article_BF00973969.pd
seeMotif: exploring and visualizing sequence motifs in 3D structures
Sequence motifs are important in the study of molecular biology. Motif discovery tools efficiently deliver many function related signatures of proteins and largely facilitate sequence annotation. As increasing numbers of motifs are detected experimentally or predicted computationally, characterizing the functional roles of motifs and identifying the potential synergetic relationships between them are important next steps. A good way to investigate novel motifs is to utilize the abundant 3D structures that have also been accumulated at an astounding rate in recent years. This article reports the development of the web service seeMotif, which provides users with an interactive interface for visualizing sequence motifs on protein structures from the Protein Data Bank (PDB). Researchers can quickly see the locations and conformation of multiple motifs among a number of related structures simultaneously. Considering the fact that PDB sequences are usually shorter than those in sequence databases and/or may have missing residues, seeMotif has two complementary approaches for selecting structures and mapping motifs to protein chains in structures. As more and more structures belonging to previously uncharacterized protein families become available, combining sequence and structure information gives good opportunities to facilitate understanding of protein functions in large-scale genome projects. Available at: http://seemotif.csie.ntu.edu.tw,http://seemotif.ee.ncku.edu.tw or http://seemotif.csbb.ntu.edu.tw
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