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

Exact solution of a 2d random Ising model

The model considered is a d=2 layered random Ising system on a square lattice with nearest neighbours interaction. It is assumed that all the vertical couplings are equal and take the positive value J while the horizontal couplings are quenched random variables which are equal in the same row but can take the two possible values J and J-K in different rows. The exact solution is obtained in the limit case of infinite K for any distribution of the horizontal couplings. The model which corresponds to this limit can be seen as an ordinary Ising system where the spins of some rows, chosen at random, are frozen in an antiferromagnetic order. No phase transition is found if the horizontal couplings are independent random variables while for correlated disorder one finds a low temperature phase with some glassy properties.Comment: 10 pages, Plain TeX, 3 ps figures, submitted to Europhys. Let

The Transition of CCS from Fossil Fuel CO2 Control to Negative Emissions

The last decade’s major investments in CCUS as a fossil fuel control technology have brought the field to the point that it is effective and readily designed. However even more rapid development of renewable technology is likely to keep CCUS from being a major player in world electric generation as investment in clean electricity from wind and solar is more cost effective and lower risk. However, at least 25% of the ultimate reductions in carbon emissions, and then any required atmospheric remediation through negative emissions, will require those same technologies in slightly different approaches. Much smaller scale capture plants will be required for industrial emissions and for biofuel plants. Fortunately a number of industrial players are already developing technology at this scale. The development of low carbon fuel standards is a huge innovation driver in this space. California regulations will, in the future, permit carbon capture on biofuels to be included in carbon footprint calculations. That market is designed to maintain a price of $100/ton for CO2, and current prices hover around that point. This confluence of new small carbon capture technology and innovative means for providers to get paid for capture will create a new generation of carbon capture, and ultimately negative emissions technologies. Challenges include CO2 transportation and underground storage when the sources are smaller than today’s power plant plans. This talk will focus on the US market for small scale-capture driven by biofuel production, and the approaches that carbon capture providers are taking to make their technology appropriate at this scale

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

Localization transitions in non-Hermitian quantum mechanics

We study the localization transitions which arise in both one and two dimensions when quantum mechanical particles described by a random Schr\"odinger equation are subjected to a constant imaginary vector potential. A path-integral formulation relates the transition to flux lines depinned from columnar defects by a transverse magnetic field in superconductors. The theory predicts that the transverse Meissner effect is accompanied by stretched exponential relaxation of the field into the bulk and a diverging penetration depth at the transition.Comment: 4 pages (latex) with 3 figures (epsf) embedded in the text using the style file epsf.st

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

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

Universality of liquid-gas Mott transitions at finite temperatures

We explain in a consistent manner the set of seemingly conflicting experiments on the finite temperature Mott critical point, and demonstrate that the Mott transition is in the Ising universality class. We show that, even though the thermodynamic behavior of the system near such critical point is described by an Ising order parameter, the global conductivity can depend on other singular observables and, in particular, on the energy density. Finally, we show that in the presence of weak disorder the dimensionality of the system has crucial effects on the size of the critical region that is probed experimentally.Comment: 4 pages, 3 figure