Spin-spin Correlation in Some Excited States of Transverse Ising Model

We consider the transverse Ising model in one dimension with nearest-neighbour interaction and calculate exactly the longitudinal spin-spin correlation for a class of excited states. These states are known to play an important role in the perturbative treatment of one-dimensional transverse Ising model with frustrated second-neighbour interaction. To calculate the correlation, we follow the earlier procedure of Wu, use Szego's theorem and also use Fisher-Hartwig conjecture. The result is that the correlation decays algebraically with distance ($n$) as $1/\surd n$ and is oscillatory or non-oscillatory depending on the magnitude of the transverse field.Comment: 5 pages, 1 figur

Framing the tax and health nexus: a neglected aspect of public health concern

Previous studies have described various associations between tax policy and health. Here we propose a unifying conceptual framework of ‘Five R’s’ to stimulate awareness about the importance of tax to health improvement. First, tax can improve representation and democratic accountability, and help make governments more responsive to the needs of its citizens. Second, tax can create a revenue stream for a universal pool of public finance for health care and other public services. Third, progressive taxation when combined with appropriate public spending can help redistribute wealth and income and mitigate social and health inequalities. Fourth, the re-pricing of harmful products (e.g. tobacco, alcohol and unhealthy food) can help reduce their consumption. Fifth, taxation provides a route by which certain harmful industries can be regulated. The paper also discusses the barriers that hinder the full potential for taxation to be used to improve health, including: weak tax administrations, large ‘shadow economies’, international trade liberalisation, tax avoidance, transfer pricing by transnational corporations and banking secrecy. We suggest that a greater awareness of the manifold associations between tax and health will encourage health practitioners to actively promote fairer and better taxation, thereby helping to improve health and reduce health inequalities

Health system constraints to optimal coverage of the prevention of mother-to-child HIV transmission programme in South Africa: lessons from the implementation of the national pilot programme

Background: It is three years since the government of South Africa began implementing a PMTCT programme. Over this period of time attempts have been made to scale up this programme across all provinces under routine health service conditions. Objectives: To report on the uptake and performance of South Africa\'s national pilot programme for preventing mother to child HIV transmission (PMTCT) and to identify health system constraints to optimal coverage. Methods: Routine programme data were collected from antenatal records and delivery registers at the pilot sites and interviews were conducted with health workers on site and with provincial programme managers. Results: Routine PMTCT programme data were collected from all 18 pilot sites for the period January to December 2002. During this period, of 84406 women attending the sites for first antenatal visits, 47267 (56%) agreed to an HIV test. 14340 (30%) of the women tested were HIV positive and of these 7853 (55%) were dispensed nevirapine. 7950 (99%) of infants born to women identified as being HIV positive received nevirapine syrup. 58% (4196/7237) of HIV positive women expressed an intention to exclusively formula feed, and 42% (3041/7237) intended to exclusively breastfeed. 1907 infants were due for 12 month HIV testing between January and December 2002, of these 949 (50%) infants were tested. Conclusions: Programme effectiveness was limited by the low rate of HIV test acceptance, poor delivery of nevirapine to mothers and inability to track mother-infant pairs postnatally for 12-month HIV testing of infants. Infant feeding intentions of mothers suggest inadequate counselling and possible negative effects of the provision of free formula milk. The poor perfor- mance of the main components of this programme will seriously reduce its operational effectiveness. There is a need for greater integration of VCT within antenatal care, a review of the current policy of providing free formula milk and an alternative model for mother-infant follow up. African Health Sciences Vol. 5 (3) 2005: pp. 213-21

Exact renormalization of the random transverse-field Ising spin chain in the strongly ordered and strongly disordered Griffiths phases

The real-space renormalization group (RG) treatment of random transverse-field Ising spin chains by Fisher ({\it Phys. Rev. B{\bf 51}, 6411 (1995)}) has been extended into the strongly ordered and strongly disordered Griffiths phases and asymptotically exact results are obtained. In the non-critical region the asymmetry of the renormalization of the couplings and the transverse fields is related to a non-linear quantum control parameter, $\Delta$, which is a natural measure of the distance from the quantum critical point. $\Delta$, which is found to stay invariant along the RG trajectories and has been expressed by the initial disorder distributions, stands in the singularity exponents of different physical quantities (magnetization, susceptibility, specific heat, etc), which are exactly calculated. In this way we have observed a weak-universality scenario: the Griffiths-McCoy singularities does not depend on the form of the disorder, provided the non-linear quantum control parameter has the same value. The exact scaling function of the magnetization with a small applied magnetic field is calculated and the critical point magnetization singularity is determined in a simple, direct way.Comment: 11 page

Griffiths-McCoy singularities in random quantum spin chains: Exact results through renormalization

The Ma-Dasgupta-Hu renormalization group (RG) scheme is used to study singular quantities in the Griffiths phase of random quantum spin chains. For the random transverse-field Ising spin chain we have extended Fisher's analytical solution to the off-critical region and calculated the dynamical exponent exactly. Concerning other random chains we argue by scaling considerations that the RG method generally becomes asymptotically exact for large times, both at the critical point and in the whole Griffiths phase. This statement is checked via numerical calculations on the random Heisenberg and quantum Potts models by the density matrix renormalization group method.Comment: 4 pages RevTeX, 2 figures include

Influence of rare regions on magnetic quantum phase transitions

The effects of quenched disorder on the critical properties of itinerant quantum magnets are considered. Particular attention is paid to locally ordered rare regions that are formed in the presence of quenched disorder even when the bulk system is still in the nonmagnetic phase. It is shown that these local moments or instantons destroy the previously found critical fixed point in the case of antiferromagnets. In the case of itinerant ferromagnets, the critical behavior is unaffected by the rare regions due to an effective long-range interaction between the order parameter fluctuations.Comment: 4 pp., REVTe

Movement and habitat ecology of protected species in North Carolina

Reptiles and amphibians are declining worldwide, especially from global climate change and habitat loss and fragmentation. Conservation efforts for imperiled species usually involve habitat protection, but are only effective if biologists and land managers have a thorough understanding of a species’ habitat requirements. This prerequisite knowledge is complicated for many herpetofauna because they utilize different habitats throughout their lifetime, such as separate breeding and non breeding habitats. Thus, multiple habitats must be studied and protected for conservation to be successful. This research aimed to better understand the habitat ecology of two protected herpetofaunal species in North Carolina to enhance future conservation. The first species, mountain chorus frogs (Pseudacris brachyphona), are small, terrestrial frogs, and a state species of special concern. Like many amphibians their breeding habitat has been studied, but little is known about their post breeding habitat. Nineteen individuals from two breeding sites were tracked by radio telemetry for approximately 25 days as they left their breeding site to examine their post breeding habitat. Breeding pools were surrounded closely by field and orchard habitats, and more distantly by forest. Frogs traveled 11.4 475.6 m from their breeding site, and no macrohabitat selection was detected among available habitats. However, the majority of individuals from the breeding site nearest the forest entered the forest, and the farthest traveling individuals from the other breeding site did as well. Mountain chorus frogs likely continued moving after 25 days, and were selecting forest habitat. I measured percent cover of vegetation within 1 m2 plots in all habitats, and forest had significantly greater leaf litter and canopy cover than did field and orchard. Likewise, there were significantly more burrows available in the forest than in other habitats. These habitat characteristics would provide greater protection from predators and desiccation in the forest, which could explain preference for forest. The second species studied, the bog turtle (Glyptemys muhlenbergii), is a small freshwater species, that is both federally- and state threatened. The majority of its habitat in the southeastern United States is small wetlands in livestock pastures, dominated by emergent vegetation (rushes and sedges) and with little shrub and canopy cover. I followed the movements of six turtles using radio telemetry from May October 2015 in a unique bog turtle wetland. This site is in Nantahala National Forest, has likely had little human disturbance for 80 years, and approximately half of the wetland is shrub/scrub habitat. Resident turtles significantly preferred shrub/scrub habitat with 68% of locations within this habitat type. I located two nests, both in emergent habitat. Shrub/scrub had significantly greater abundance of deep mud, which could explain turtles’ preference for this habitat. Bog turtles frequently burrow down into mud, and deeper mud might be easier to move through. Females had greater mean daily movement rates and home ranges (8.3 m/day, 0.6064 ha) than males (5.0 m/day, 0.4458 ha), which might be due to nesting migrations to emergent habitat. Thus, bog turtles will utilize shrub/scrub habitat where available, but nest in emergent habitat, likely due to its better thermal environment for offspring development

Dynamical Correlation Functions for One-Dimensional Quantum Spin Systems: New Results Based on a Rigorous Approach

We present new results on the time‐dependent correlation functions Ξ n (t) =4〈S ξ 0(t)S ξ n 〉, ξ=x,y at zero temperature of the one‐dimensional S=1/2 isotropic X Y model (h=γ=0) and of the transverse Ising model (TI) at the critical magnetic field (h=γ=1). Both models are characterized by special cases of the Hamiltonian H=−J∑ l [(1+γ)S x l S x l+1 +(1−γ)S y l S y l+1 +h S z l ]. We have derived exact results on the long‐time asymptotic expansions of the autocorrelation functions (ACF’s) Ξ0(t) and on the singularities of their frequency‐dependent Fourier transforms Φξξ 0(ω). We have also determined the latter functions by high‐precision numerical calculations. The functions Φξξ 0(ω), ξ=x,y have singularities at the infinite sequence of frequencies ω=mω0, m=0, 1, 2, 3, ... where ω0=J for the X Y model and ω0=2J for the TI model. In both models the singularities in Φ x x 0 (ω) for m=0, 1 are divergent, whereas the nonanalyticities at higher frequencies become increasingly weaker. We point out that the nonanalyticities at ω≠0 are intrinsic features of the discrete quantum chain and have therefore not been found in the context of a continuum analysis