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Biomedical subjects

J S Harris

Publications and source records attributed to J S Harris.

At least 19 recordsLinked to original sources
PubMed2006

Optical parametric generation of a mid-infrared continuum in orientation-patterned GaAs.

We have generated an ultrabroad mid-infrared continuum by using single-pass optical parametric generation (OPG) in orientation-patterned GaAs (OP-GaAs). The spectrum spans more than an octave, from 4.5 to 10.7 microm, measured 20 dB down from the peak. The 17.5 mm long, 0.5 mm thick, all-epitaxially-grown OP-GaAs sample with a 166.6-microm quasi-phase-matching period was pumped with 3.1-3.3 microm wavelength, 1 ps pulses up to 2 microJ in energy. The OPG threshold was observed at 55 nJ pump energy with the pump polarized along the [111] crystal direction. The slope efficiency near threshold was 51%, and the external conversion efficiency was as high as 15%.

Journal Article↗
PubMed2005

Highly spin-polarized room-temperature tunnel injector for semiconductor spintronics using MgO(100).

The spin polarization of current injected into GaAs from a CoFe/MgO(100) tunnel injector is inferred from the electroluminescence polarization from GaAs/AlGaAs quantum well detectors. The polarization reaches 57% at 100 K and 47% at 290 K in a 5 T perpendicular magnetic field. Taking into account the field dependence of the luminescence polarization, the spin injection efficiency is at least 52% at 100 K, and 32% at 290 K. We find a nonmonotonic temperature dependence of the polarization which can be attributed to spin relaxation in the quantum well detectors.

Journal Article↗
PubMed2004

Optical parametric oscillation in quasi-phase-matched GaAs.

We demonstrate an optical parametric oscillator (OPO) based on GaAs. The OPO utilizes an all-epitaxially-grown orientation-patterned GaAs crystal that is 0.5 mm thick, 5 mm wide, and 11 mm long, with a domain reversal period of 61.2 microm. Tuning either the near-IR pump wavelength between 1.8 and 2 microm or the temperature of the GaAs crystal allows the mid-IR output to be tuned between 2.28 and 9.14 microm, which is limited only by the spectral range of the OPO mirrors. The pump threshold of the singly resonant OPO is 16 microJ for the 6-ns pump pulses, and the photon conversion slope efficiency reaches 54%. We also show experimentally the possibility of pump-polarization-independent frequency conversion in GaAs.

Journal Article↗
PubMed2003

Photocurrent, rectification, and magnetic field symmetry of induced current through quantum dots.

We report mesoscopic dc current generation in an open chaotic quantum dot with ac excitation applied to one of the shape-defining gates. For excitation frequencies large compared to the inverse dwell time of electrons in the dot (i.e., GHz), we find mesoscopic fluctuations of induced current that are fully asymmetric in the applied perpendicular magnetic field, as predicted by recent theory. Conductance, measured simultaneously, is found to be symmetric in field. In the adiabatic (i.e., MHz) regime, in contrast, the induced current is always symmetric in field, suggesting its origin is mesoscopic rectification.

Journal Article↗
PubMed2001

A computational study of tetrahedrene: strained alkene or dicarbene?

A computational study of tetrahedrene at the RCCD/cc-pVDZ level led to a singlet-state structure with a lowest energy vibrational mode of 660 cm(-1). The corresponding triplet state was found to be ca. 37 kcal/mol lower in energy than the singlet state. The heat of formation of the singlet state was estimated to be 270 kcal/mol. An isomeric singlet bicyclic dicarbene bis-bicyclo[1.1.0]cyclobutylidene was found to be approximately 94 kcal/mol lower in energy than tetrahedrene.

Journal Article↗
PubMed2001

Decoherence in nearly isolated quantum dots.

Decoherence in nearly isolated GaAs quantum dots is investigated using the change in the average Coulomb blockade peak height when time-reversal symmetry is broken. The normalized change in the average peak height approaches the predicted universal value of 1/4 at temperatures well below the single-particle level spacing, T < Delta, but is greatly suppressed for T > Delta, suggesting that inelastic scattering or other dephasing mechanisms dominate in this regime.

Journal Article↗
PubMed2001

Spin degeneracy and conductance fluctuations in open quantum dots.

The dependence of conductance fluctuations on parallel magnetic field is used as a probe of spin degeneracy in open GaAs quantum dots. The variance of fluctuations at high parallel field is reduced from the low-field variance (with broken time-reversal symmetry) by factors ranging from roughly 2 in a 1 microm (2) dot to greater than 4 in 8 microm (2) dots. The factor of 2 is expected for Zeeman splitting of spin-degenerate channels. A possible explanation for the larger suppression based on field-dependent spin-orbit scattering is proposed.

Journal Article↗
PubMed2001

A comparison of health needs and personal health goals of Army Reserve Military and civilian employees.

Army active and reserve component personnel must be ready for rapid mobilization as world conflicts increase in number and intensity. Department of Defense civilian employees also need to be available to work long hours to maintain troop support. Healthy lifestyles are key to the physical and mental readiness demanded by this kind of work. The purpose of this descriptive study was to assess health and readiness by examining the health needs, identified through health risk appraisals, and personal health goals of military personnel and civilians (N = 90) employed at a large Army Reserve command headquarters located in the southern part of the country. Prominent health needs included reducing the number of saturated fats found in the diets of military personnel and increasing the frequency of exercise for civilian employees. Weight loss constituted the primary personal health goal for 53% of all employees. Initial health promotion activities should incorporate assessment information into the design of command-sponsored programs. Focusing on health needs as well as personal health goals may enhance the early success of such programs.

Adult↗
PubMed2000

Evidence-based design: the ACOEM Practice Guidelines Dissemination Project.

A steering committee and investigators from the American College of Occupational and Environmental Medicine (ACOEM) designed and carried out the ACOEM Practice Guidelines Dissemination Project to encourage adoption of the ACOEM Occupational Medicine Practice Guidelines. The project also involved research on guideline acceptance as well as potential improvements and additions to the guidelines. To increase guideline adoption and use in improving the appropriateness and consistency of practice and case management, the design was based on existing research on guideline format, education, and adoption efforts. This article summarizes that information and the needs assessment done prior to case-based guidelines training. Other articles in this issue report on guideline adoption and use and the results of the market research on the ACOEM guidelines.

Diffusion of Innovation↗
PubMed2000

Acceptance and self-reported use of national occupational medicine practice guidelines.

The authors conducted a survey to ascertain post-training attitudes and self-reported use of the American College of Occupational and Environmental Medicine occupational medicine practice guidelines. Trainees were surveyed 3 to 4 months after completing a case-based practice ACOEM occupational practice guidelines seminar. Of 96 physician respondents, 95% reported that the guidelines improved their practice in some manner. Fifty-two percent of physicians thought that guideline use decreased medical costs. Seventy-one percent reported that their care complied with the guidelines in 70% or more of their cases; however, "actually considering the guidelines in particular cases" was reported by only 47%. Discussion of cases was frequent (92%) and involved physicians, patients, and other health care providers. We concluded that physicians' attitudes toward the guidelines are positive and that reported compliance is high. Guidelines are discussed frequently.

Attitude of Health Personnel↗
PubMed2000

Beliefs about and use of occupational medicine practice guidelines by case managers and insurance adjusters.

Workers' compensation case managers and adjusters have increased their use of practice guidelines recently, partly in response to state regulations. However, informally reported rates of use are not as high as desired for the best managed care practices and the greatest reductions in lost work time. Although there are several studies of physicians' use of guidelines, there are few if any studies about case managers' and adjusters' beliefs about, and utilization of, either general medical or occupational medical practice guidelines. Information about attitudes, beliefs about practice guidelines, and actual use should help developers make the guidelines more usable and bring about more effective interaction among case managers, adjusters, treating physicians, and other health professionals. This article reports on pre- and post-training surveys of a cohort of case managers and adjusters who participated in a case-based guideline training course. It then compares their responses to those of the physicians whose cases they might manage.

Case Management↗
PubMed2000

Suggested improvements in practice guidelines: market research to support clinical quality improvement.

The American College of Occupational and Environmental Medicine's Practice Guideline Dissemination Project included market research to better understand the wants and needs of physicians, case managers, and insurance adjusters who used the guidelines. We used structured and open-ended survey questions and focus groups administered to a cohort of physicians, adjusters, and case managers trained as part of the project. Respondents were generally satisfied with the format and contents of the guidelines. They requested additional material on case management and facilitation of effective treatment and return to work by other health professionals. They also suggested a variety of formats to improve the accessibility of the guidelines. The suggestions may be used in new product development or for guideline revisions.

Attitude of Health Personnel↗
PubMed1999

The effect of curing light intensity and test temperature on the dynamic mechanical properties of two polymer composites.

The dynamic modulus of elasticity of two composite materials cured by three light intensities was investigated using a dynamic thermal and mechanical analyser at 37 degrees C and 60 degrees C. The lowest light intensity, 180 mW/cm2, was found to be unsatisfactory in that specimens were weak and mostly untestable. The higher intensities, 350 and 700 mW/cm2, cured the materials to slightly different extents with the elevated temperatures of testing leading to post-cure maturation of the materials. An interesting finding was that one material had a significantly higher modulus when tested at 37 degrees C in comparison with that found at 60 degrees C. In one material the higher light intensity resulted in significantly higher modulus values and these values were increased by post-curing. In the other material the higher light intensity did not result in higher modulus figures at either test temperature, and lower test temperature resulted in better post-cure maturation. These findings are most likely to be caused by differences in base monomer and activator/initiator concentrations. The results indicate that optimum polymerization may not be achieved in all materials by the same method, in particular, high curing light intensities may not achieve the most desirable results.

Acrylic Resins↗