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Biomedical subjects

T G Brown

Publications and source records attributed to T G Brown.

At least 19 recordsLinked to original sources
PubMed2003

Polarization-vortex-driven second-harmonic generation.

Polarization vortices exist in the focus of a class of vector beams, the lowest order of which possess full vector symmetry about the axis of propagation of the beam. At high numerical apertures these beams are known to exhibit large, local, longitudinal fields in the focal region. At an interface these fields can be many times stronger than the largest available transverse component and are therefore candidates for a variety of different experiments in surface physics. The observation of vortex-driven surface second-harmonic generation at smooth metal and semiconductor surfaces and thin films is reported. By comparing the response to that of a purely transverse field, we show that the smooth surface responds primarily to the longitudinal field component.

Journal Article↗
PubMed2001

Longitudinal field modes probed by single molecules.

We demonstrate that a strong longitudinal, nonpropagating field is generated at the focus of a radially polarized beam mode. This field is localized in space and its energy density exceeds the energy density of the transverse field by more than a factor of 2. Single molecules with fixed absorption dipole moments are used to probe the longitudinal field. Vice versa, it is demonstrated that orientations of single molecules are efficiently mapped out in three dimensions by using a radially polarized beam as the excitation source. We also show that there is no momentum or energy transport associated with the longitudinal field.

Journal Article↗
PubMed2000

Nonperturbative analysis of cross coupling in corrugated metal films.

There has been a recent renewal of interest in anomalously high energy transfer through otherwise opaque metal film geometries. One of the earliest such systems, that of surface plasmon cross coupling in a sinusoidally corrugated continuous metal film, was studied by Gruhlke et al. [Phys. Rev. Lett. 56, 2838 (1986)]. We show that it is possible to use a nonperturbative method to accurately predict this coupling, and we use this method to analyze both intrinsic coupling in symmetric structures and grating-assisted cross coupling in asymmetric structures.

Journal Article↗
PubMed1999

Violent substance abusers in domestic violence treatment.

Although substance abuse is frequently encountered in men receiving services in violence treatment settings, systematic study of these 'dual-problem' men has lagged. This study had two main objectives: (1) the characterization of psychoactive substance abuse disorders in a naturalistic sample of men in domestic violence treatment; and (2) clarification of the role of substance abuse on the sociodemographic, personality, psychosocial, and abuse characteristics of dual-problem men. Fifty-three adult men who were attending domestic violence treatment were recruited. They were administered the Addiction Severity Index, the Conflicts Tactics Scale, Structured Clinical Diagnostic Interview, the 16PF and the Symptoms Checklist-90. Partners, when available, were asked to provide corroboration. Sixty-three percent of the men had a current diagnosis of psychoactive substance abuse or dependence, while 92.5% had a lifetime diagnosis. Of the former, the majority was diagnosed as multiply dependent on alcohol and other drugs. As the severity of the substance abuse increased, so too did the dangerousness and frequency of abusive behaviors. Moreover, dual-problem men reported more hostility, apprehension, frustration and suspiciousness and past arrests than did their violence-only cohorts as well as a history of multiple (unsuccessful) treatments for substance abuse. These findings suggest that the trend toward multiple drug complaints seen in other clinical milieus is also being confronted in conjugal violence settings. In addition to the greater therapeutic challenge such dual-problem men present, these findings speak to the need to investigate integrated treatment approaches to improve the outlook of men grappling with both conjugal violence and multiple substance abuse problems.

Adult↗
PubMed1997

The effect of vocalization on the heart rate response to mental arithmetic.

The heart rate (HR) responses to verbal and nonverbal mental arithmetic tasks were studied in twenty undergraduate males. The two problem-sets were presented in counterbalanced order to the subjects. Greater HR responses to verbal, in contrast to nonverbal, arithmetic were only observed when the verbal arithmetic task was presented first. The peak (maximal) HR response was also the highest when the verbal arithmetic was presented first to the subjects. It is concluded that physiological or mechanical components of vocalization do not affect the HR response to mental arithmetic. However, certain psychological components, including test-anxiety or motivation, may increase the HR when subjects have to provide verbal answers during a first exposure to a challenge. This effect dissipates during the second exposure to the challenge due to habituation.

Adult↗
PubMed1993

Aerobic fitness does not influence directly heart rate reactivity to mental stress.

Thirty-seven aerobically high and low fit male and female university students, selected on the basis of estimated aerobic capacity, completed a set of hard as well as a set of easy mental arithmetic tasks for 90 seconds in a counterbalanced order with a 10 min rest period between the tasks. Heart rate (HR) reactivity to either task was independent of aerobic fitness level. Although subjectively rated as more challenging, HR responses to the hard arithmetic task were not greater than that seen to the easy task. These results do not support the conjecture that aerobic fitness level may mediate HR response to acute mental challenge. The overall implications of these results are discussed in relation to the literature concerning aerobic fitness and mental stress.

Adult↗
PubMed1983

Electron-nuclear double resonance of copper complexes of human transferrin.

Electron-nuclear double resonance (ENDOR) spectroscopy has been used to study ligand and copper hyperfine interactions in Cu(II) complexes of human transferrin. A nearly isotropic superhyperfine interaction of the Cu(II) spin with a single 14N nucleus was identified, and the principal values of its tensor were estimated. All principal values of the copper hyperfine tensor were also directly measured for the first time. Resonances from at least two exchangeable protons were observed, but their origin could not be ascertained. At physiological pH, and in the presence of bicarbonate, ENDOR spectra of the two metal-binding sites were virtually indistinguishable.

Copper↗
PubMed1979

Electron-nuclear double resonance of the hydrogen peroxide compound of cytochrome c peroxidase: identification of the free radical site with a methionyl cluster.

The results of electron-nuclear double resonance and electron paramagnetic resonance (EPR) studies on the hydrogen peroxide compound of yeast cytochrome c peroxidase are inconsistent with previous proposals for the source of the EPR signal in this compound, in particular with its identification with an aromatic amino acid radical such as would arise by oxidation of a tryptophanyl side chain. The present observations lead us to propose that the EPR signal is associated with a cluster containing at least one methionine and in which proximate side chains share the charge created by loss of one electron.

Binding Sites↗