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A characterization of health care workers' exposures to magnetic fields in the 40-1000 Hz range was performed in a multistory research hospital and single-story outpatient surgery unit. Area survey, source, and personal measurements of broadband and frequency-specific magnetic flux densities were performed with frequency analyzer dosimeters; the background static field was measured with a portable magnetometer. Dosimetry measurements were cross-referenced to workers' time/activity patterns. Spot measurements of magnetic flux density in the research hospital varied between 0.8 mG (.08 microT) and 65 mG (6.5 microT). Workers' time-weighted average exposures ranged from 1.2 mG (0.12 microT) to 10.4 mG (1.04 microT), with peak exposures ranging from 8.9 mG (0.89 microT) to 103.7 mG (10.37 microT). Frequency spectra of the exposures were variable and included harmonic bands as well as 60 Hz. The background static magnetic field in the hospital varied between 250 mG (25 microT) and 480 mG (48 microT) suggesting shielding of the geomagnetic field from building materials. These results indicate that health care workers are exposed to 40-1000 Hz magnetic fields during routine patient care. The fields are characterized by a switching (on/off, in/out) pattern of occurrence, variable frequencies that include 60 Hz and harmonic bands, and peak excursions that may occur at regular intervals. These characteristics vary both within and among job categories, suggesting that job title may be a poor surrogate for exposure classification. Although limited in scope, the results indicate that spot measurement of broadband or 60-Hz magnetic fields, or summary indices such as time-weighted average, mean or median, are insufficient to characterize occupational exposures.

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The in vivo and in vitro accessory cell requirements of class I major histocompatability complex (MHC) antigen-restricted cytotoxic T-lymphocyte (CTL) responses were determined using cell-depletion experiments coupled with active immunizations using ovalbumin (OVA) as the immunogen and saponin adjuvant (QS-21). To paralyze macrophage activity in vivo, C57BL/6 mice were treated with particulate silica or carrageenan. In vivo depletion of helper T-lymphocytes was accomplished by treatment with GK1.5 rat monoclonal antibody, which is specific for the murine CD4 antigen, and by genetic depletion of class II MHC antigens. Following treatments, the mice were immunized with formulations containing OVA alone or mixed with QS-21 saponin adjuvant, which induces MHC class I antigen-restricted CTL responses. In vivo treatment to paralyze macrophages abrogated these CTL responses but not antigen-specific antibody or lymphocyte proliferative responses. Depletion of CD4+ T-lymphocytes had no effect on CTL responses but significantly reduced proliferation and antibody responses. In vitro depletion and reconstitution experiments were done to compare the contributions of different antigen-presenting cells (APC), specifically dendritic cells (DC) and macrophages. Again, the requirement for macrophages was absolute but there was no indication that DC were involved. These data suggest that antigen processing and presentation functions are critical to the induction of CTL and that they are a function of macrophages but that CD4+ helper T-lymphocyte functions are not required.

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In situ nightside electric field observations from the Pioneer Venus Orbiter have been interpreted as evidence of extensive lightning in the lower atmosphere of Venus. The scenario, including proposed evidence of clustering of lightning over surface highland regions, has encouraged the acceptance of currently active volcanic output as part of several investigations of the dynamics and chemistry of the atmosphere and the geology of the planet. However, the correlation between the 100-hertz electric field events attributed to lightning and nightside ionization troughs resulting from the interaction of the solar wind with the ionosphere indicates that the noise results from locally generated plasma instabilities and not from any behavior of the lower atmosphere. Furthermore, analysis of the spatial distribution of the noise shows that it is not clustered over highland topography, but rather occurs at random throughout the latitude and longitude regions sampled by the orbiter during the first 5 years of operation, from 1978 to 1984. Thus the electric field observations do not identify lightning and do not provide a basis for inferring the presence of currently active volcanic output. In the absence of known evidence to the contrary, it appears that Venus is no longer active.

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The Bennett radio-frequency ion mass spectrometer on the Pioneer Venus orbiter is returning the first direct composition evidence of the processes responsible for the formation and maintenance of the nightside ionosphere. Early results from predusk through the nightside in the solar zenith angle range 63 degrees (dusk) to 120 degrees (dawn) reveal that, as on the dayside, the lower nightside ionosphere consists of F(1)and F(2) layers dominated by O(2)(+) and O(+), respectively. Also like the dayside, the nightside composition includes distributions of NO(+), C(+), N(+), H(+), He(+), CO(2)(+), and 28(+) (a combination of CO(+) and N(2)(+)). The surprising abundance of the nightside ionosphere appears to be maintained by the transport of O(+) from the dayside, leading also to the formation of O(2)(+) through charge exchange with CO(2). Above the exobase, the upper nightside ionosphere exhibits dramatic variability in apparent response to variations in the solar wind and interplanetary magnetic field, with the ionopause extending to several thousand kilometers on one orbit, followed by the complete rertnoval of thermal ions to altitudes below 200 kilometers on the succeeding orbit, 24 hours later. In the upper ionosphere, considerable structure is evident in many of the nightside ion profiles. Also evident are horizontal ion drifts with velocities up to the order of 1 kilometer per second. Whereas the duskside ionopause is dominated by O(+) H(+) dominates the topside on the dawnside of the antisolar point, indicating two separate regions for ion depletion in the magnetic tail regions.

RESUMEN

The first in situ measurements of the composition of the ionosphere of Venus are provided by independent Bennett radio-frequency ion mass spectrometers on the Pioneer Venus bits and orbiter spacecraft, exploring the dawn and duskside regions, respectively. An extensive composition of ion species, rich in oxygen, nitrogen, and carbon chemistry is idenitified. The dominant topside ion is O(+), with C(+), N(+), H(+), and He(+) as prominent secondary ions. In the lower ionosphere, the ionzization peak or F(1) layer near 150 kilometers reaches a concentration of about 5 x l0(3) ions per cubic centimeter, and is composed of the dominant molecular ion, O(2)(+), with NO(+), CO(+), and CO(2)(+), constituting less than 10 percent of the total. Below the O(+) peak near 200 kilometers, the ions exhibit scale heights consistent with a neutral gas temperature of about 180 K near the terminator. In the upper ionosphere, scale heights of all species reflect the effects of plasma transport, which lifts the composition upward to the often abrupt ionopause, or thermal ion boundary, which is observed to vary in height between 250 to 1800 kilometers, in response to solar wind dynamics.

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Bennett radio-frequency ion mass spectrometers have returned the first in situ measurements of the Venus dayside ion composition, including evidence of pronounced structural variability resulting from a dynamic interaction with the solar wind. The ionospheric envelope, dominated above 200 kilometers by O(+), responds dramatically to variations in the solar wind pressure, Which is observed to compress the thermal ion distributions from heights as great as 1800 kilometers inward to 280 kilometers. At the thermal ion boundary, or ionopause, the ambient ions are swept away by the solar wind, such that a zone of accelerated suprathermnal plasma is encountered. At higher altitudes, extending outward on some orbits for thousands of kilometers to the bows shock, energetic ion currents are detected, apparently originating from the shocked solar wind plasma. Within the ionosphere, observations of pass-to-pass differences in the ion scale heights are indicative of the effects of ion convection stimlulated by the solar wind interaction.