Critical properties of a continuous family of XY noncollinear magnets

Monte Carlo methods are used to study a family of three dimensional XY frustrated models interpolating continuously between the stacked triangular antiferromagnets and a variant of this model for which a local rigidity constraint is imposed. Our study leads us to conclude that generically weak first order behavior occurs in this family of models in agreement with a recent nonperturbative renormalization group description of frustrated magnets.Comment: 5 pages, 3 figures, minor changes, published versio

Genetic heterogeneity of white-tailed deer: management lessons from a long-term study

Genetic data from a long-term (16-year) study of white-tailed deer (Odocoileus virginianus) on the U.S. Department of Energy\u27s Savannah River Site (SRS) were examined to evaluate spatial and temporal genetic heterogeneity in this species. Based on our analyses of the long-term data set, three major findings emerged, all of which have important implications for management of white-tailed deer: (1) There exists significant spatial genetic heterogeneity in white-tailed deer based on analyses of allozyme frequencies and mtDNA haplotypes. This heterogeneity exists on a much smaller spatial scale than would be expected for such a large and potentially mobile species as 0. virginianus. (2) The genetic structure of white-tailed deer at SRS is temporally dynamic and significant heterogeneity exists within demographic units such as age and sex classes. (3) Levels of genetic variation, as measured by multilocus heterozygosity, are frequently correlated to characteristics that are important determinants of ecological function in white-tailed deer populations. These findings are evaluated in the context of a general management model for 0. virginianus that is also applicable to other wildlife species

Localization of the paranodal protein Caspr in the mammalian retina

Purpose: The retina has the demanding task of encoding all aspects of the visual scene within the space of one fixation period lasting only a few hundred milliseconds. To accomplish this feat, information is encoded in specialized parallel channels and passed on to numerous central nuclei via the optic nerve. These parallel channels achieve specialization in at least three ways: the synaptic networks in which they participate, the neurotransmitter receptors expressed and the types and locations of ion channels or transporters used. Subcellular localization of receptors, channels and transporters is made yet more complex in the retina by the double duty many retinal processes serve. In the present work, we show that the protein Caspr (Contactin Associated Protein), best known for its critical role in the localization of voltage-gated ion channels at the nodes of Ranvier, is present in several types of retinal neurons including amacrine, bipolar, horizontal, and ganglion cells. Methods: Using standard double label immunofluorescence protocols, we characterized the pattern of Caspr expression in the rodent retina. Results: Caspr labeling was observed through much of the retina, including horizontal, bipolar, amacrine, and ganglion cells. Among amacrine cells, Caspr was observed in AII amacrine cells through co-localization with Parvalbumin and Disabled-1 in rat and mouse retinas, respectively. An additional amacrine cell type containing Calretinin also co-localized with Caspr, but did not co-localize with choline-acetyltransferase. Nearly all cells in the ganglion cell layer contain Caspr, including both displaced amacrine and ganglion cells. In the outer retina, Caspr was co-localized with PKC labeling in rod bipolar cell dendrites. In addition, Caspr labeling was found inside syntaxin-4 'sandwiches' in the outer plexiform layer, most likely indicating its presence in cone bipolar cell dendrites. Finally, Caspr was co-localized in segments of horizontal cell dendrites labeled with Calbindin-D28k. Conclusions: Caspr is best known for its role in organizing the localization of different voltage-gated ion channels in and around nodes of Ranvier. As neuronal processes in the retina often play a dual role involving both input and output, it is possible that the localization of Caspr in the retina will help us decipher the way retinal cells localize ion channels in their processes to increase computational capacity

Field-theory results for three-dimensional transitions with complex symmetries

We discuss several examples of three-dimensional critical phenomena that can be described by Landau-Ginzburg-Wilson $\phi^4$ theories. We present an overview of field-theoretical results obtained from the analysis of high-order perturbative series in the frameworks of the $\epsilon$ and of the fixed-dimension d=3 expansions. In particular, we discuss the stability of the O(N)-symmetric fixed point in a generic N-component theory, the critical behaviors of randomly dilute Ising-like systems and frustrated spin systems with noncollinear order, the multicritical behavior arising from the competition of two distinct types of ordering with symmetry O($n_1$) and O($n_2$) respectively.Comment: 9 pages, Talk at the Conference TH2002, Paris, July 200

Spin Stiffness of Stacked Triangular Antiferromagnets

We study the spin stiffness of stacked triangular antiferromagnets using both heat bath and broad histogram Monte Carlo methods. Our results are consistent with a continuous transition belonging to the chiral universality class first proposed by Kawamura.Comment: 5 pages, 7 figure

The experience of long-term opiate maintenance treatment and reported barriers to recovery: A qualitative systematic review

Background/Aim: To inform understanding of the experience of long-term opiate maintenance and identify barriers to recovery. Methods: A qualitative systematic review. Results: 14 studies in 17 papers, mainly from the USA (65%), met inclusion criteria, involving 1,088 participants. Studies focused on methadone prescribing. Participants reported stability; however, many disliked methadone. Barriers to full recovery were primarily ‘inward focused'. Conclusion: This is the first review of qualitative literature on long-term maintenance, finding that universal service improvements could be made to address reported barriers to recovery, including involving ex-users as positive role models, and increasing access to psychological support. Treatment policies combining harm minimisation and abstinence-orientated approaches may best support individualised recovery

Comprehensive Analysis of the 16p11.2 Deletion and Null Cntnap2 Mouse Models of Autism Spectrum Disorder

Autism spectrum disorder comprises several neurodevelopmental conditions presenting symptoms in social communication and restricted, repetitive behaviors. A major roadblock for drug development for autism is the lack of robust behavioral signatures predictive of clinical efficacy. To address this issue, we further characterized, in a uniform and rigorous way, mouse models of autism that are of interest because of their construct validity and wide availability to the scientific community. We implemented a broad behavioral battery that included but was not restricted to core autism domains, with the goal of identifying robust, reliable phenotypes amenable for further testing. Here we describe comprehensive findings from two known mouse models of autism, obtained at different developmental stages, using a systematic behavioral test battery combining standard tests as well as novel, quantitative, computer-vision based systems. The first mouse model recapitulates a deletion in human chromosome 16p11.2, found in 1% of individuals with autism. The second mouse model harbors homozygous null mutations in Cntnap2, associated with autism and Pitt-Hopkins-like syndrome. Consistent with previous results, 16p11.2 heterozygous null mice, also known as Del(7Slx1b-Sept1)4Aam weighed less than wild type littermates displayed hyperactivity and no social deficits. Cntnap2 homozygous null mice were also hyperactive, froze less during testing, showed a mild gait phenotype and deficits in the three-chamber social preference test, although less robust than previously published. In the open field test with exposure to urine of an estrous female, however, the Cntnap2 null mice showed reduced vocalizations. In addition, Cntnap2 null mice performed slightly better in a cognitive procedural learning test. Although finding and replicating robust behavioral phenotypes in animal models is a challenging task, such functional readouts remain important in the development of therapeutics and we anticipate both our positive and negative findings will be utilized as a resource for the broader scientific community

Critical thermodynamics of three-dimensional chiral model for N > 3

The critical behavior of the three-dimensional $N$-vector chiral model is studied for arbitrary $N$. The known six-loop renormalization-group (RG) expansions are resummed using the Borel transformation combined with the conformal mapping and Pad\'e approximant techniques. Analyzing the fixed point location and the structure of RG flows, it is found that two marginal values of $N$ exist which separate domains of continuous chiral phase transitions $N > N_{c1}$ and $N N > N_{c2}$ where such transitions are first-order. Our calculations yield $N_{c1} = 6.4(4)$ and $N_{c2} = 5.7(3)$. For $N > N_{c1}$ the structure of RG flows is identical to that given by the $\epsilon$ and 1/N expansions with the chiral fixed point being a stable node. For $N < N_{c2}$ the chiral fixed point turns out to be a focus having no generic relation to the stable fixed point seen at small $\epsilon$ and large $N$. In this domain, containing the physical values $N = 2$ and $N = 3$, phase trajectories approach the fixed point in a spiral-like manner giving rise to unusual crossover regimes which may imitate varying (scattered) critical exponents seen in numerous physical and computer experiments.Comment: 12 pages, 3 figure