Theory of continuum percolation III. Low density expansion

We use a previously introduced mapping between the continuum percolation model and the Potts fluid (a system of interacting s-states spins which are free to move in the continuum) to derive the low density expansion of the pair connectedness and the mean cluster size. We prove that given an adequate identification of functions, the result is equivalent to the density expansion derived from a completely different point of view by Coniglio et al. [J. Phys A 10, 1123 (1977)] to describe physical clustering in a gas. We then apply our expansion to a system of hypercubes with a hard core interaction. The calculated critical density is within approximately 5% of the results of simulations, and is thus much more precise than previous theoretical results which were based on integral equations. We suggest that this is because integral equations smooth out overly the partition function (i.e., they describe predominantly its analytical part), while our method targets instead the part which describes the phase transition (i.e., the singular part).Comment: 42 pages, Revtex, includes 5 EncapsulatedPostscript figures, submitted to Phys Rev

Probing Disordered Substrates by Imaging the Adsorbate in its Fluid Phase

Several recent imaging experiments access the equilibrium density profiles of interacting particles confined to a two-dimensional substrate. When these particles are in a fluid phase, we show that such data yields precise information regarding substrate disorder as reflected in one-point functions and two-point correlations of the fluid. Using Monte Carlo simulations and replica generalizations of liquid state theories, we extract unusual two-point correlations of time-averaged density inhomogeneities induced by disorder. Distribution functions such as these have not hitherto been measured but should be experimentally accessible.Comment: 10 pages revtex 4 figure

Barriers to mental health service use among distressed family caregivers of lung cancer patients

Although family caregivers of patients with lung and other cancers show high rates of psychological distress, they underuse mental health services. This qualitative study aimed to identify barriers to mental health service use among 21 distressed family caregivers of lung cancer patients. Caregivers had not received mental health services during the patient's initial months of care at a comprehensive cancer centre in New York City. Thematic analysis of interview data was framed by Andersen's model of health service use and Corrigan's stigma theory. Results of our analysis expand Andersen's model by providing a description of need variables (e.g. psychiatric symptoms), enabling factors (e.g. finances), and psychosocial factors associated with caregivers' non-use of mental health services. Regarding psychosocial factors, caregivers expressed negative perceptions of mental health professionals and a desire for independent management of emotional concerns. Additionally, caregivers perceived a conflict between mental health service use and the caregiving role (e.g. prioritising the patient's needs). Although caregivers denied stigma associated with service use, their anticipated negative self-perceptions if they were to use services suggest that stigma may have influenced their decision to not seek services. Findings suggest that interventions to improve caregivers' uptake of mental health services should address perceived barriers

The emergency use of endografts in the carotid circulation to control hemorrhage in potentially contaminated fields

We report our experience with the use of endoluminal grafts to control emergency bleeding in two patients with tracheoinnominate fistulas and three patients with carotid blowouts. Systemic infectious complications were not seen. However, rebleeding occurred in one patient, and extensive stent coverage to control bleeding was required in a second. Survival was usually limited by the patient’s cancer. There was one long-term survivor without cancer whose tracheostomy was placed for neurologic compromise. A review of the literature for similar cases identified 18 additional endografts placed for carotid blowout and 3 placed for tracheoinnominate fistulas. Overall, infectious complications occurred in only two patients, whereas rebleeding occurred in eight patients. On the basis of these findings, we believe that endografts are useful to control emergency hemorrhage in these two pathologies because treatment is usually palliative, given the poor survival secondary to the underlying disease. However, more extensive graft coverage may be necessary considering the erosive nature of these processes

Glass transition and effective potential in the hypernetted chain approximation

We study the glassy transition for simple liquids in the hypernetted chain (HNC) approximation by means of an effective potential recently introduced. Integrating the HNC equations for hard spheres, we find a transition scenario analogous to that of the long range disordered systems with ``one step replica symmetry breaking''. Our result agree qualitatively with Monte Carlo simulations of three dimensional hard spheres.Comment: 7 pages, 7 figures, Revtex fil

An experimental and analytical study of plasma closing switches filled with environmentally friendly gases

In recent years there has been a desire within the pulsed power community to find potential alternative gases to sulphur hexafluoride (SF6) for use within pulsed power systems. Within plasma closing switches (PCSs), the desire to use environmentally friendly gases has come as a result of environmental concerns over the emissions of currently used gases into the atmosphere and contributing to the global warming problem. One of the main issues in finding a suitable replacement gas or gases for use in PCSs is that the performance characteristics of a switch filled with an alternative gas or gas mixture should be comparable to the performance characteristics of conventional SF6-filled switches. The research presented in this paper is an expansion of previous work conducted and forms an experimental and analytical evaluation of breakdown characteristics in two commonly used PCS topologies (a two-electrode self-breakdown switch and a field distortion switch) when filled with different gases (air, oxygen-nitrogen mixtures, argon oxygen mixture, nitrogen and carbon dioxide) over a range of pressures from 0.1 MPa to 0.45 MPa and for a range of inter-electrode distances

Persistence of Tall Fescue and Cattle Grazing Preference as Affected by Endophyte Status

Endophyte-infected (E+) grasses often exhibit increased survival, growth and resistance to herbivory compared to uninfected counterparts. Latch (1997) proposed a strategy for cultivar improvement of infecting elite cultivars with strains of Neotyphodium coenophialum that are non-toxic to livestock, but still able to convey the persistence advantage shown with wild-type, toxic endophyte. The strategy of re-infecting tall fescue (Lolium arundinaceum (Schreb.) Darbysh.) cultivars with naturally occurring, non-ergot-producing endophytes appears promising for removing animal toxicity symptoms and retaining agronomic performance (Bouton et al., 2002; Hill et al., 2002). The objective of this study was to compare the effect of endophyte status on grazing preference and persistence of tall fescue stand

Stroke Caregiver Outcomes from the Telephone Assessment and Skill-Building Kit (TASK)

Purpose: Stroke caregivers often express the need for information about stroke and assistance with stroke-related care in the early discharge period. The Telephone Assessment and Skill-Building Kit (TASK) is an 8-week program that addresses caregiver needs. This study explored the efficacy of the TASK program in improving stroke caregiver outcomes. Method: Guided by a conceptual model, 6 outcomes (optimism, task difficulty, threat appraisal, depressive symptoms, life changes, general health perceptions) were measured in 40 caregivers randomized to the TASK (n = 21) or an attention control group (n = 19). Data were analyzed using analysis of covariance (ANCOVA), controlling for baseline scores and minutes spent with the nurse. Results: Significant increases in optimism at 4 weeks, 8 weeks, and 12 weeks were found, with medium effect sizes for the TASK group relative to the control group (p < .05). Significant improvements in task difficulty at 4 weeks, and threat appraisal at both 8 weeks and 12 weeks were also found (p < .05). Conclusion: Caregivers receiving the TASK intervention improved in optimism, task difficulty, and threat appraisal. Further testing of an enhanced version of the TASK program is warranted, with attention directed toward more distal stroke caregiver outcomes

Content Validity and Satisfaction With a Stroke Caregiver Intervention Program

Background and Purpose Establishing evidence of content validity and satisfaction is an integral part of intervention research. The purpose of this article is to describe content validity and satisfaction relative to the Telephone Assessment and Skill-Building Kit (TASK), an 8-week follow-up program based on individualized assessment of stroke caregiver needs. Design and Methods The TASK intervention enables caregivers to develop skills based on assessment of their own needs. During the development of the TASK program, 10 experts rated the validity of the TASK intervention components for accuracy, feasibility, acceptability, and problem relevance. After incorporating feedback from the experts, a randomized controlled clinical trial was instituted using a convenience sample of 40 stroke caregivers to determine satisfaction (usefulness, case of use, and acceptability) with the TASK intervention (n=21) compared with an attention control group (n=19). Data collection occurred between March 2005 and June 2006. Data were analyzed using descriptive statistics, independent sample t tests, and content analysis. Findings Expert ratings on a 1 to 5 scale, with 5 being strongly agree, provided evidence of content validity (accuracy 4.71, feasibility 4.46, acceptability 4.40, problem relevance 4.67). Caregivers in the TASK group scored significantly higher than the attention control group on all satisfaction measures (usefulness p=.02; ease of use p=.02; acceptability p=.05). Qualitative comments from caregivers provided further evidence of satisfaction. Conclusions Evidence of content validity and user satisfaction for the TASK intervention relative to an attention control group was found. Clinical Relevance The TASK program may be a viable telephone-based program that can be implemented by nurses to support family caregivers during the first few months after stroke survivors are discharged home

Effect of applied field and rate of voltage rise on surface breakdown of oil-immersed polymers

In sub-systems of high-voltage, pulsed-power machines, the introduction of a solid into bulk liquid insulation located between two conductors is often necessary to provide mechanical support. Breakdown events on or around the surface of the solid can result in permanent damage to the insulation system. Described in the present paper are experimental results pertaining to surface breakdown of five different solid dielectrics held between plane-parallel electrodes immersed in mineral oil. The effect of varying level of peak applied field from 200 kV/cm (dV/dt 70 kV/µs) to 1 MV/cm (dV/dt 350 kV/µs) is investigated, and the breakdown voltages and times to breakdown are compared to those for an open oil gap. The time to breakdown is shown to be reduced by the introduction of a solid spacer into the gap. Rexolite and Torlon samples suffered significant mechanical damage, and consistently showed lower breakdown voltage than the other materials - average streamer propagation velocity up to 125 km/s was implied by the short times to breakdown. Although ultra-high molecular weight polyethylene yielded the longest times to breakdown of the five types of liquid-solid gap, breakdown events could be initiated at lower levels of applied field for spacers of this material than those with permittivity closely matched to that of the surrounding mineral oil. Polypropylene and low-density polyethylene are concluded to provide the most stable performance in mineral oil. Due to the similarity of the applied voltage wave-shape (1/6.5 µs) to short-tail lightning impulses, the results may also be of interest to high-voltage system designers in the power industry