PubMed Health⌕ Search

Biomedical subjects

P G Evans

Publications and source records attributed to P G Evans.

15 recordsLinked to original sources
PubMed2006

Shear modulus and plasticity of a driven charge density wave.

We have probed the effects of transverse variations in pinning strength on charge-density-wave (CDW) structure in NbSe3 by x-ray micro-beam diffraction. In ribbonlike crystals having a large longitudinal step in thickness, the CDW first depins on the thick side of the step, causing rotations of the CDW wave vector. By measuring these rotations as a function of position and electric field, the corresponding shear strains are determined, allowing the CDW's shear modulus to be estimated. These results demonstrate the usefulness of x-ray microdiffraction as a tool in studying collective dynamics in electronic crystals.

Journal Article↗
PubMed2005

Internal contamination of gloves: routes and consequences.

The effect of internal glove contamination was investigated using N-methyl pyrrolidone (NMP) as a biological marker to assess systemic absorption when wearing internally contaminated gloves, and when not wearing gloves but subjected to the same challenge contaminant. The routes by which the insides of gloves become contaminated were also investigated. The area of dermal contamination was quantified using a fluorescent tracer dye and a surface monitoring fluorimeter. The main routes of internal glove contamination were found to be self-contamination, cuff entry and failed gloves. Wearing internally contaminated gloves led to higher systemic absorption than was gained from the equivalent skin contamination when not wearing gloves. Repeat wetting of fingers with aqueous NMP, when gloves were not worn, gave higher systemic absorption than the equivalent continuous exposure, probably due to the low volatility of NMP leading to increased concentration and longer residence time on the skin.

Environmental Monitoring↗
PubMed2004

Crystallization of charge holes in the spin ladder of Sr14Cu24O41.

Determining the nature of the electronic phases that compete with superconductivity in high-transition-temperature (high-T(c)) superconductors is one of the deepest problems in condensed matter physics. One candidate is the 'stripe' phase, in which the charge carriers (holes) condense into rivers of charge that separate regions of antiferromagnetism. A related but lesser known system is the 'spin ladder', which consists of two coupled chains of magnetic ions forming an array of rungs. A doped ladder can be thought of as a high-T(c) material with lower dimensionality, and has been predicted to exhibit both superconductivity and an insulating 'hole crystal' phase in which the carriers are localized through many-body interactions. The competition between the two resembles that believed to operate between stripes and superconductivity in high-T(c) materials. Here we report the existence of a hole crystal in the doped spin ladder of Sr14Cu24O41 using a resonant X-ray scattering technique. This phase exists without a detectable distortion in the structural lattice, indicating that it arises from many-body electronic effects. Our measurements confirm theoretical predictions, and support the picture that proximity to charge ordered states is a general property of superconductivity in copper oxides.

Journal Article↗
PubMed2004

Probing large area surface plasmon interference in thin metal films using photon scanning tunneling microscopy.

The interference of surface plasmons can provide important information regarding the surface features of the hosting thin metal film. We present an investigation of the interference of optically excited surface plasmons in the Kretschmann configuration in the visible spectrum. Large area surface plasmon interference regions are generated at several wavelengths and imaged with the photon scanning tunneling microscope. Furthermore, we discuss the non-retarded dispersion relations for the surface plasmons in the probe-metal system modeled as confocal hyperboloids of revolution in the spheroidal coordinate systems.

Journal Article↗
PubMed2003

A toolkit for dermal risk assessment and management: an overview.

The European Research project RISKOFDERM (QLK4-CT-1999-01107) has two major goals. One is the development of a conceptual model for dermal risk assessment for regulatory purposes, such as the registration of new chemicals. The other goal is to develop a simple-to-use toolkit for assessment and management of health risks from occupational dermal exposure. This toolkit was constructed by analysing the major determinants of dermal hazard and dermal exposure. The results were combined in the form of a decision-tree that leads the user of the toolkit through a number of questions on the hazardous properties of the chemical in use, and on the exposure situation. The toolkit translates the information given by the user into broad data categories of hazard and exposure that lead to a rough estimate of health risk from dermal exposure. This is done separately for local skin effects and skin allergy on the one hand, and systemic effects after skin penetration on the other hand. After going through the decision-tree, the user is advised to act to control the risk, and to read general information on dermal exposure and a statement describing the uncertainty of the risk estimate produced by the toolkit. The final version of the toolkit will be available for use on portable or stationary computers and runs the decision algorithms in the background so that the non-expert user only will see the judgements, the recommendations and the general information. The toolkit will be evaluated before release by experts on the various elements included in the toolkit and by field experts in its practical use. The toolkit is an attempt to adapt elements of exact science to a situation where the necessary input data are of limited quality and are only estimates. The toolkit does not claim to give precise answers based on imprecise information. The purpose is to enable the user to estimate the order of magnitude of hazard, exposure and risk, and to encourage the user to deal with the issues of dermal hazard, exposure and control.

Humans↗
PubMed2002

X-ray microdiffraction images of antiferromagnetic domain evolution in chromium.

Magnetic x-ray diffraction combined with x-ray focusing optics was used to image individual antiferromagnetic spin density wave domains in a chromium single crystal at the micron scale. The cross section for nonresonant magnetic x-ray scattering depends on the antiferromagnetic modulation vector and spin polarization direction and allows these quantities to be extracted independently. The technique was used to show that the broadening of the nominally first-order "spin-flip" transition at 123 kelvin, at which the spins rotate by 90 degrees C, originates at the walls between domains with orthogonal modulation vectors. During cooling, the transition begins at these walls and progresses inward. The modulation vector domains are themselves unchanged.

Journal Article↗
PubMed2001

Comment on "Mie scattering from a sonoluminescing bubble with high spatial and temporal resolution".

A key parameter underlying the existence of sonoluminescence (or SL) is the time dependence of the radius R(t) of the collapsing bubble from which SL originates. With regard to the use of light scattering to measure this quantity, we wish to note that we disagree with the statement of Gompf and Pecha-highly compressed water causes the minimum in scattered light to occur 700 ps before SL-and that this effect leads to an overestimate of the bubble wall velocity. We discuss potential artifacts in their experimental arrangement and reply to their criticisms of our experiments on Mie scattering.

Journal Article↗
PubMed2001

Personal protective equipment and dermal exposure.

Personal protective equipment (PPE) should only be used as a control measure when other measures are inappropriate or are inadequate by themselves. The person undertaking a risk assessment must exercise his or her judgment to take into account the protection afforded by the PPE. There is, therefore, considerable scope for differences in approach and it would seem sensible to eliminate these differences and ensure consistency, where possible, by reaching agreement on the attenuating effect of PPE. However, there is growing evidence that the levels of protection indicated by laboratory-based tests may not be achieved in real use situations. Studies of workplace protection suggest that the spread of contaminants inside protective clothing, including gloves, is commonplace and significant. Insufficient attention may have been paid to the effect of factors such as temperature differentials on the permeation of chemical agents through protective materials. To investigate this, a test cell was designed and built to measure the breakthrough times and subsequent permeation rate of solvents through glove materials where the temperature inside and outside the glove was representative of those that can occur in the workplace. Two chemical solvents were tested against two different glove materials at three different temperature conditions. The differences between the breakthrough times and permeation rates were measured and compared to manufacturer's test data. The practical implications are considered for risk of health and safety to the wearer.

Gloves, Protective↗
PubMed2001

Development and validation of a monoclonal based immunoassay for the measurement of fungal alpha-amylase: focus on peak exposures.

The inhalation of flour dust has been implicated in the induction of sensitisation and elicitation of respiratory symptoms, such as asthma in bakers. In addition to the cereal allergens present in wheat flour, enzymes in flour improvers, in particular fungal alpha-amylase, are now known to be a significant cause of respiratory allergy in the baking industry.A monoclonal antibody based enzyme-linked immunoassay (ELISA) was developed using two monoclonal antibodies that recognised two distinct epitopes of the fungal alpha-amylase enzyme. The ELISA had an inter-assay variation of 12.0% at 1360 pg/ml and 12.8% at 564 pg/ml and intra-assay variation of 4.9% at 1340 pg/ml and 6.1% at 504 pg/ml. The assay had a sensitivity of 200 pg/ml. Competitive inhibition assays confirmed that the monoclonal antibodies had no cross reactivity with other enzymes used in the baking industry and could distinguish added fungal alpha-amylase from cereal amylase. We assessed the levels of exposure to dust, total protein and fungal alpha-amylase in four UK bakeries ranging in size and technical capabilities. Within the bakeries we surveyed, workers were exposed to variable levels of inhalable dust (0.8-39.8 mg/m3), total protein (0-5.7 mg/m3) and fungal alpha-amylase (0-29.8 ng/m3). Consecutive 15 min personal samples taken over a 1 h period demonstrated that the ELISA could measure fungal alpha-amylase exposure in such a 15 min period. Short term peak exposures to fungal alpha-amylase could be identified which may contribute to the sensitisation in individuals who appear to have low exposure levels if measured over a full shift period.

Antibodies, Monoclonal↗
PubMed1976

Loss or persistence of the differentiated state of simian virus 40-induced hamster tumor cells before and after serial passage in culture.

The transformed cells that arise from among the hamster epithelial and mesenchymal cells exposed to SV40 in vitro are, as a rule, fibroblastoid and pleomorphic rather than epithelioid. Moreover, the neoplasms that these transformed cells induce in the allogeneic host are spindle cell sarcomas and pleomorphic sarcomas rather than carcinomas. Since this phenomenon may result from cellular dedifferentiation in culture, to the extent that the anaplastic morphology and lack of specialized function can no longer suggest the cell or origin, we investigated the fate of the differentiated state of cells of three types of SV40-induced hamster tumors before and after serial passage in vitro. The tumors evaluated were three reticulum cell sarcomas, three osteogenic sarcomas, and two lymphosarcomas of B-cell origin. Our data demonstrate that reticulum cell sarcoma cells lose their morphological differentiation soon after the original tumors are dissociated into cell suspensions but preserve their phagocytic activity throughout their in vitro passage. Osteogenic sarcoma cells lose their differentiated phenotype and their capacity to form osteoid during but not before their serial passage in culture. Lymphosarcoma cells preserve their lymphoid morphology and their ability to produce immunoglobulin even after many in vitro passages. These results indicate that, in many types of SV40-induced tumors, neoplastic cell dedifferentiation, following serial passage in culture, is responsible to a great extent for the emergence of new cell phenotypes lacking in morphological and functional features characteristic of the cells originally transformed by SV40.

Animals↗