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P Coleman

Publications and source records attributed to P Coleman.

At least 19 recordsLinked to original sources
PubMed2006

Conserving many body approach to the infinite-U Anderson model.

Using a Luttinger-Ward scheme for interacting gauge particles, we present a conserving many body treatment of a family of fully screened infinite-U Anderson models that has a smooth crossover into the Fermi-liquid state, with a finite scattering phase shift at zero temperature and a Wilson ratio greater than 1. We illustrate our method, computing the temperature dependence of the thermodynamics, resistivity, and electron dephasing rate and discuss its future application to nonequilibrium quantum dots and quantum critical mixed valent systems.

Journal Article↗
PubMed2006

Schwinger boson approach to the fully screened Kondo model.

We apply the Schwinger boson scheme to the fully screened Kondo model and generalize the method to include antiferromagnetic interactions between ions. Our approach captures the Kondo crossover from local moment behavior to a Fermi liquid with a nontrivial Wilson ratio. When applied to the two-impurity model, the mean-field theory describes the "Varma-Jones" quantum phase transition between a valence bond state and a heavy Fermi liquid.

Journal Article↗
PubMed2006

The evolution of the emergency care practitioner role in England: experiences and impact.

BACKGROUND: The emergency care practitioner (ECP) is a generic practitioner who combines extended nursing and paramedic skills. The "new" role emerged out of changing workforce initiatives intended to improve staff career opportunities in the National Health Service and ensure that patients' health needs are assessed appropriately. OBJECTIVE: To describe the development of ECP Schemes in 17 sites, identify criteria contributing to a successful operational framework, analyse routinely collected data and provide a preliminary estimate of costs. METHODS: There were three methods used: (a) a quantitative survey, comprising a questionnaire to project leaders in 17 sites, and analysis of data collected routinely; (b) qualitative interpretation based on telephone interviews in six sites; and (c) an economic costing study. RESULTS: Of 17 sites, 14 (82.5%) responded to the questionnaire. Most ECPs (77.4%) had trained as paramedics. Skills and competencies have been extended through educational programmes, training, and assessment. Routine data indicate that 54% of patient contacts with the ECP service did not require a referral to another health professional or use of emergency transport. In a subset of six sites, factors contributing to a successful operational framework were strategic visions crossing traditional organisational boundaries and appropriately skilled workforce integrating flexibly with existing services. Issues across all schemes were patient safety, appropriate clinical governance, and supervision and workforce issues. On the data available, the mean cost per ECP patient contact is 24.00 pounds sterling, which is less than an ED contact of 55.00 pounds sterling. CONCLUSION: Indications are that the ECP schemes are moving forward in line with original objectives and could be having a significant impact on the emergency services workload.

Delivery of Health Care↗
PubMed2005

Nonequilibrium noise as a probe of the Kondo effect in mesoscopic wires.

We study the nonequilibrium noise in mesoscopic diffusive wires hosting magnetic impurities. We find that the shot-noise to current ratio develops a peak at intermediate source-drain biases of the order of the Kondo temperature. The enhanced impurity contribution at intermediate biases is also manifested in the effective distribution. The predicted peak represents an increased inelastic scattering rate at the nonequilibrium Kondo crossover.

Journal Article↗
PubMed2005

Anomalous conductance of a spin-1 quantum dot.

We interpret the recent observation of a zero-bias anomaly in spin-1 quantum dots in terms of an underscreened Kondo effect. Although spin-1 quantum dots are expected to undergo a two-stage quenching effect, in practice the log-normal distribution of Kondo temperatures leads to a broad temperature region dominated by underscreened Kondo physics. General arguments, based on the asymptotic decoupling between the partially screened moment and the leads, predict a singular temperature and voltage dependence of the conductance G and differential conductance g, resulting in dg/dT approximately 1/T and dG/dV approximately 1/V. Using a Schwinger boson approach, we show how these qualitative expectations are borne out in a detailed many body calculation.

Journal Article↗
PubMed2004

Hall-effect evolution across a heavy-fermion quantum critical point.

A quantum critical point (QCP) develops in a material at absolute zero when a new form of order smoothly emerges in its ground state. QCPs are of great current interest because of their singular ability to influence the finite temperature properties of materials. Recently, heavy-fermion metals have played a key role in the study of antiferromagnetic QCPs. To accommodate the heavy electrons, the Fermi surface of the heavy-fermion paramagnet is larger than that of an antiferromagnet. An important unsolved question is whether the Fermi surface transformation at the QCP develops gradually, as expected if the magnetism is of spin-density-wave (SDW) type, or suddenly, as expected if the heavy electrons are abruptly localized by magnetism. Here we report measurements of the low-temperature Hall coefficient (R(H))--a measure of the Fermi surface volume--in the heavy-fermion metal YbRh2Si2 upon field-tuning it from an antiferromagnetic to a paramagnetic state. R(H) undergoes an increasingly rapid change near the QCP as the temperature is lowered, extrapolating to a sudden jump in the zero temperature limit. We interpret these results in terms of a collapse of the large Fermi surface and of the heavy-fermion state itself precisely at the QCP.

Journal Article↗
PubMed2004

Factors that influence the prevalence of acaricide resistance and tick-borne diseases.

This manuscript provides a summary of the results presented at a symposium organized to accumulate information on factors that influence the prevalence of acaricide resistance and tick-borne diseases. This symposium was part of the 19th International Conference of the World Association for the Advancement of Veterinary Parasitology (WAAVP), held in New Orleans, LA, USA, during August 10-14, 2003. Populations of southern cattle ticks, Boophilus microplus, from Mexico have developed resistance to many classes of acaricide including chlorinated hydrocarbons (DDT), pyrethroids, organophosphates, and formamidines (amitraz). Target site mutations are the most common resistance mechanism observed, but there are examples of metabolic mechanisms. In many pyrethroid resistant strains, a single target site mutation on the Na(+) channel confers very high resistance (resistance ratios: >1000x) to both DDT and all pyrethroid acaricides. Acetylcholine esterase affinity for OPs is changed in resistant tick populations. A second mechanism of OP resistance is linked to cytochrome P450 monooxygenase activity. A PCR-based assay to detect a specific sodium channel gene mutation that is associated with resistance to permethrin has been developed. This assay can be performed on individual ticks at any life stage with results available in a few hours. A number of Mexican strains of B. microplus with varying profiles of pesticide resistance have been genotyped using this test. Additionally, a specific metabolic esterase with permethrin-hydrolyzing activity, CzEst9, has been purified and its gene coding region cloned. This esterase has been associated with high resistance to permethrin in one Mexican tick population. Work is continuing to clone specific acetylcholinesterase (AChE) and carboxylesterase genes that appear to be involved in resistance to organophosphates. Our ultimate goal is the design of a battery of DNA- or ELISA-based assays capable of rapidly genotyping individual ticks to obtain a comprehensive profile of their susceptibility to various pesticides. More outbreaks of clinical bovine babesisois and anaplasmosis have been associated with the presence of synthetic pyrethroid (SP) resistance when compared to OP and amidine resistance. This may be the result of differences in the temporal and geographic patterns of resistance development to the different acaricides. If acaricide resistance develops slowly, herd immunity may not be affected. The use of pesticides for the control of pests of cattle other than ticks can affect the incidence of tick resistance and tick-borne diseases. Simple analytical models of tick- and tsetse-borne diseases suggest that reducing the abundance of ticks, by treating cattle with pyrethroids for example, can have a variety of effects on tick-borne diseases. In the worst-case scenario, the models suggest that treating cattle might not only have no impact on trypanosomosis but could increase the incidence of tick-borne disease. In the best-case, treatment could reduce the incidence of both trypanosomosis and tick-borne diseases Surveys of beef and dairy properties in Queensland for which tick resistance to amitraz was known were intended to provide a clear understanding of the economic and management consequences resistance had on their properties. Farmers continued to use amitraz as the major acaricide for tick control after the diagnosis of resistance, although it was supplemented with moxidectin (dairy farms) or fluazuron, macrocyclic lactones or cypermethrin/chlorfenvinphos.

Acaricides↗
PubMed2003

Spin dynamics from majorana fermions.

Using the Majorana fermion representation of spin-1/2 local moments, we show how the dynamic spin correlation and susceptibility are obtained directly from the one-particle Majorana propagator. We illustrate our method by applying it to the spin dynamics of a nonequilibrium quantum dot, computing the voltage-dependent spin relaxation rate and showing that, at weak coupling, the fluctuation-dissipation relation for the spin of a quantum dot is voltage dependent. We confirm the voltage-dependent Curie susceptibility recently found by Parcollet and Hooley [Phys. Rev. B 66, 085315 (2002)]].

Journal Article↗
PubMed2003

The break-up of heavy electrons at a quantum critical point.

The point at absolute zero where matter becomes unstable to new forms of order is called a quantum critical point (QCP). The quantum fluctuations between order and disorder that develop at this point induce profound transformations in the finite temperature electronic properties of the material. Magnetic fields are ideal for tuning a material as close as possible to a QCP, where the most intense effects of criticality can be studied. A previous study on the heavy-electron material YbRh2Si2 found that near a field-induced QCP electrons move ever more slowly and scatter off one another with ever increasing probability, as indicated by a divergence to infinity of the electron effective mass and scattering cross-section. But these studies could not shed light on whether these properties were an artefact of the applied field, or a more general feature of field-free QCPs. Here we report that, when germanium-doped YbRh2Si2 is tuned away from a chemically induced QCP by magnetic fields, there is a universal behaviour in the temperature dependence of the specific heat and resistivity: the characteristic kinetic energy of electrons is directly proportional to the strength of the applied field. We infer that all ballistic motion of electrons vanishes at a QCP, forming a new class of conductor in which individual electrons decay into collective current-carrying motions of the electron fluid.

Journal Article↗
PubMed2003

Developing integrated CAM services in Primary Care Organisations.

OBJECTIVES: To explore policy development and the provision of integrated NHS CAM therapy services following the reorganisation of UK primary care services in 1999. DESIGN: Structured survey interviews with Chairpersons in a stratified random sample of 72 Primary Care Organisations (PCOs) in England in 1999 and 2000; semi-structured telephone interviews with purposive samples of (i) providers of primary care CAM services (mostly General Practitioners), and (ii) Commissioners of primary care services in two purposive sub-samples of PCOs involved in positive policy formation in relation to CAM. RESULTS: By the end of 2000, it is estimated that 85% of PCOs in England (95% CI 78-91%) had discussed CAM at board level, and 37% (95% CI 26-48%) had at least one CAM policy in place. The dominant strategy that emerged was a policy of "provide and review", particularly in practices that had managed their own budgets under the previous fundholding system. We found that a small number of PCOs were developing area-wide services. Positive influences or "drivers" for CAM policy formation were identified as: existing services, local enthusiasm and expertise, patient demand, a willingness to consider the wider evidence-base for CAM, and a perception that complementary therapies could help the PCOs to meet national NHS targets. Negative influences included: the cost of ensuring equitable access to services, a perception that CAM lacks the credibility required for public funding, the need to prioritize services and the need to direct funding towards meeting national and local health objectives. CONCLUSIONS: Opportunities for development of integrated NHS services are most likely to occur where CAM provision is seen as a potential solution to an NHS problem. Locality-based, integrated CAM services that are responsive to NHS priorities may offer a model for the future development of CAMs in primary care.

Complementary Therapies↗
PubMed2003

Trends in access to complementary or alternative medicines via primary care in England: 1995-2001 results from a follow-up national survey.

A prior national survey of one in eight randomly selected general practices in England estimated that 39% of general practices [95% confidence interval (CI) 35-43%] provided some access to complementary or alternative medicine (CAM) therapies in 1995. A repeat survey, conducted in 2001, estimated that one in two practices in England now offer their patients some access to CAMs (95% CI 46-52%). The change was due to increased provision in-house; the proportion of practices making NHS referrals remained unchanged. The proportion of services supported by patient payments rose from 26 to 42%.

Complementary Therapies↗
PubMed2003

Early detection of hepatitis B surface antigen--prototype of a new fully automated HBsAg microparticle enzyme immunoassay (MEIA).

HBsAg is the most important serological marker of acute and chronic hepatitis B infection. Therefore, sensitivity of the currently used detection systems for HBsAg is of major importance for blood screening, diagnosis of HBV infection and therapy monitoring of HBV infected individuals. A Prototype Microparticle Enzyme Immunoassay (MEIA) for qualitative determination of hepatitis B surface antigen (HBsAg) has recently been developed for the fully automated AxSYM analyzer with the intention to provide a test displaying improved sensitivity when compared to the currently marketed HBsAg assays. The present study was conducted to demonstrate sensitivity of the new Prototype AxSYM HBsAg MEIA and the corresponding, fully automated Prototype AxSYM HBsAg Confirmatory MEIA. Analytical sensitivity of the Prototype AxSYM HBsAg MEIA was assessed by testing quantitative HBsAg panels. Sensitivity for HBsAg subtypes ad and ay was found to be 0.15 ng/ml and 0.09 ng/ml, respectively. The detection level for HBsAg subtype ad Standard provided by the Paul Ehrlich Institute was estimated to be 0.03 PEI U/ml. Analysis of hepatitis B seroconversion panels suggests that the new Prototype AxSYM HBsAg MEIA significantly reduces the seroconversion window when being compared to other highly sensitive commercial HBsAg assays. The corresponding Prototype AxSYM HBsAg Confirmatory MEIA demonstrated the ability to confirm low titer seroconverters found reactive with the Prototype AxSYM HBsAg Screening MEIA.

Hepatitis B↗
PubMed2002

LiV2O4: frustration induced heavy fermion metal.

We propose a two-stage spin-quenching scenario for the unusual heavy fermion state realized in the mixed valent metal LiV2O4. In this theory, local valence fluctuations are responsible for the formation of partially quenched, spin-1 / 2 moments below room temperature. Frustration of the intersite spin couplings then drives the system to produce the heavy Fermi liquid seen at low temperatures. The anomalous resistivity and the sign change of the Hall constant can be understood naturally within this model, which also predicts a unique symmetry for the heavy quasiparticle bands that may be observed in de Haas-van Alphen experiments.

Journal Article↗
PubMed2002

Hidden orbital order in the heavy fermion metal URu(2)Si(2).

When matter is cooled from high temperatures, collective instabilities develop among its constituent particles that lead to new kinds of order. An anomaly in the specific heat is a classic signature of this phenomenon. Usually the associated order is easily identified, but sometimes its nature remains elusive. The heavy fermion metal URu(2)Si(2) is one such example, where the order responsible for the sharp specific heat anomaly at T(0) = 17 K has remained unidentified despite more than seventeen years of effort. In URu(2)Si(2), the coexistence of large electron electron repulsion and antiferromagnetic fluctuations leads to an almost incompressible heavy electron fluid, where anisotropically paired quasiparticle states are energetically favoured. Here we develop a proposal for the nature of the hidden order in URu(2)Si(2). We show that incommensurate orbital antiferromagnetism, associated with circulating currents between the uranium ions, can account for the local fields and entropy loss observed at the 17 K transition. We make detailed predictions for the outcome of neutron scattering measurements based on this proposal, so that it can be tested experimentally.

Journal Article↗
PubMed2002

The economic impact of foot and mouth disease control and eradication in the Philippines.

The authors evaluate the impact of foot and mouth disease (FMD) and control of the disease in the Philippines using cost-benefit analysis. A scenario in which FMD control is maintained at recent levels with continued presence of the disease is compared to scenarios in which a publicly funded programme achieves eradication by 2005 (current policy objective), 2007 and 2010. Under varying assumptions regarding the development of exports of livestock products following eradication, estimated benefit-cost ratios for the investment in eradication range from 1.6 (2010, no exports) to 12.0 (2005, export of 5,000 tons each of low-value and high-value livestock products annually), indicating eradication to be an economically viable investment. The commercial swine sector is estimated to capture 84% of the benefits generated by the public investment in eradication, versus 4% by backyard swine producers. The implications of these results within the context of regional efforts to control FMD in South-East Asia are explored.

Animals↗