The atmospheric X-ray imaging spectrometer (AXIS) instrument: Quantifying energetic particle precipitation through bremsstrahlung X-ray imaging

The Atmospheric X-ray Imaging Spectrometer (AXIS) described in this work is a compact, wide field-of-view, hard x-ray imager. The AXIS instrument will fly onboard the Atmospheric Effects of Precipitation through Energetic X-rays (AEPEX) 6U CubeSat mission and will measure bremsstrahlung x-ray photons in the 50-240 keV range with cadmium-zinc-telluride (CZT) detectors using coded aperture optics. AXIS will measure photons generated by energetic particle precipitation for the purpose of determining the spatial scales of precipitation and estimating electron precipitation characteristics. This paper describes the design and testing of the AXIS instrument, including a summary of simulations performed that motivate the shielding, optics, and mechanical design. Testing and characterization is reported that validates the instrument design and shows that the instrument design meets or exceeds the measurement requirements necessary for AEPEX mission success.

Near-fatal heat stroke during the 1995 heat wave in Chicago

BACKGROUND

In July 1995, Chicago sustained a heat wave that resulted in more than 600 excess deaths, 3300 excess emergency department visits, and a substantial number of intensive care unit admissions for near-fatal heat stroke.

OBJECTIVE

To describe the clinical features of patients admitted to an intensive care unit with near-fatal classic heat stroke. Patients were followed for 1 year to assess delayed functional outcome and mortality.

DESIGN

Observational study.

SETTING

Intensive care units in the Chicago area.

PATIENTS

58 patients admitted to the hospital from 12 July to 20 July 1995 who met the case definition of classic heat stroke.

MEASUREMENTS

The data collection tool was designed to compile demographic and survival data and to permit analysis of organ system function by abstracting data on physical examination findings, electrocardiography and echocardiography results, fluid resuscitation, radiography results, and laboratory findings. Data on functional status at discharge and at 1 year were collected by using a modified Stanford Health Assessment Questionnaire.

RESULTS

Patients experienced multiorgan dysfunction with neurologic impairment (100%), moderate to severe renal insufficiency (53%), disseminated intravascular coagulation (45%), and the acute respiratory distress syndrome (10%). Fifty-seven percent of patients had evidence of infection on admission. In-hospital mortality was 21%. Most survivors recovered near-normal renal, hematologic, and respiratory status, but disability persisted, resulting in moderate to severe functional impairment in 33% of patients at hospital discharge. At 1 year, no patient had improved functional status, and an additional 28% of patients had died.

CONCLUSIONS

Near-fatal classic heat stroke is associated with multiorgan dysfunction. A high percentage of patients had infection at presentation. A high mortality rate was observed during acute hospitalization and at 1 year. In addition, substantial functional impairment at discharge persisted 1 year. The degree of functional disability correlated highly with survival at 1 year.

Preferential completion of human immunodeficiency virus type 1 proviruses initiated with tRNA3Lys rather than tRNA1,2Lys

All retroviral genomes contain a nucleotide sequence designated as the primer binding site (PBS) which is complementary to the tRNA used for initiation of reverse transcription. For human immunodeficiency virus type 1 (HIV-1), all naturally occurring genomes have a PBS complementary to tRNA3Lys. However, within HIV-1 virions, there are approximately equal amounts of tRNA1Lys, tRNA2Lys, and tRNA3Lys. We have used an endogenous reverse transcription-PCR technique specific for the tRNA species within isolated HIV-1 virions to demonstrate that in addition to tRNA3Lys, tRNA1Lys and tRNA2Lys could be used for initiation of HIV-1 reverse transcription. Using a single-round infection assay which employed an HIV-1 genome with a gpt gene encoding xanthine-guanine phosphoribosyl transferase in place of the env gene, we generated cell lines resistant to mycophenolic acid. Analysis of the U5-PBS from single-cell clones revealed PBS complementary to tRNA3Lys, not tRNA1Lys or tRNA2Lys. A mutant HIV-1 genome was then created which would favor the completion of reverse transcription with tRNA1,2Lys. Using this provirus in the complementation system, we again found only genomes with a PBS complementary to tRNA3Lys from proviral DNA isolated from gpt-resistant single-cell colonies. Finally, infection of cells with a mutant HIV genome with a PBS complementary to tRNA1,2Lys resulted in gpt- resistant cell colonies which contained integrated provirions with a PBS complementary to tRNA1,2Lys. The results of these studies suggest that the selection of tRNA3Lys for initiation of HIV-1 reverse transcription occurs both at the initiation and at a postinitiation step in reverse transcription prior to integration of the proviral DNA.