Satellite systems for personal communications

A number of industry groups are planning to construct satellite systems that will provide a personal communications service (PCS) (typically voice, data, and fax) to users over small, hand-held, cellular-type telephones. Some of these systems (e.g., Iridium and Globalstar) will be constructed using satellites in low Earth orbit. Two (Ellipso and ICO) will employ medium Earth orbit (3-8-h period), and still others (ACeS and Agrani) will operate from geostationary altitude. The origin and evolution of mobile satellite communications is discussed first, including the Inmarsat system and several land-based mobile satellite systems in operation. The rival approaches to the PCS market are then described, and some of the technical challenges inherent in each are indicated. This paper concludes with speculation on the factors influencing the likelihood of business success for the various PCS systems     

Structure-activity relationships of alkyl- and alkoxy-substituted 1,4-dihydroquinoxaline-2,3-diones: potent and systemically active antagonists for the glycine site of the NMDA receptor

We report on a series of alkyl- and alkoxy-substituted 1,4-dihydroquinoxaline-2,3-diones (QXs), prepared as a continuation of our structure-activity relationship (SAR) study of QXs as antagonists for the glycine site of the N-methyl-D-aspartate (NMDA) receptor. The in vitro potency of these antagonists was determined by displacement of the glycine site radioligand [3H]-5,7-dichlorokynurenic acid ([3H]DCKA) in rat brain cortical membranes. In general, methyl is a good replacement for chloro or bromo in the 6-position, and alkoxy-substituted QXs have lower potencies than alkyl- or halogen-substituted QXs. Ethyl-substituted QXs are generally less potent than methyl-substituted QXs, especially in the 6-position of 5,6,7-trisubstituted QXs. Fusion of a ring system at the 6,7-positions results in QXs with low potency. Several methyl-substituted QXs are potent glycine site antagonists that have surprisingly high in vivo activity in the maximal electroshock (MES) test in mice. Among these, 7-chloro-6-methyl-5-nitro QX (14g) (IC50 = 5 nM) and 7-bromo-6-methyl-5-nitro QX (14f) (IC50 = 9 nM) are comparable in potency to 6,7-dichloro-5-nitro QX (2) (ACEA 1021) as glycine site antagonists. QX 14g has an ED50 value of 1.2 mg/kg iv in the mouse MES assay. Interestingly, alkyl QXs with log P values of 0.5 or less tend to be more bioavailable than QXs with higher log P values. QX 14g has 440-fold selectivity for NMDA vs alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, as determined electrophysiologically under steady-state conditions in oocytes expressing rat cerebral cortex poly(A)+ RNA. Overall, 14g was found to have the best combination of in vitro and in vivo potency of all the compounds tested in this and previous studies on the QX series.     

Can the ventilatory equivalent for carbon dioxide predict the severity of functional impairment in patients with cardiac insufficiency?

OBJECTIVE: To evaluate whether the changes in the ventilatory equivalent for carbon dioxide (VE/VCO2), during the early stages of cardiopulmonary exercise testing, can predict maximal oxygen consumption (VO2max) in patients with chronic heart failure. METHODS: We studied 38 patients (30 males, mean age 56 +/- 11 years) with chronic heart failure. All patients performed maximal symptom limited, treadmill exercise test with breath-by-breath respiratory gas analysis. They were divided in two groups according to their maximal oxygen consumption (group I-VO2max above 14 ml/kg/min and group II-VO2max below 14 ml/kg/min). In both groups, we analysed VE/VCO2 at rest, at the anaerobic threshold (AT) and at peak exercise, and the percentage of VE/VCO2 reduction from rest to AT. RESULTS: Eleven patients had a VO2max below 14 ml/kg/min (group II). At rest VE/VCO2 = 53 +/- 13 in group II versus 47 +/- 10 in group I (p = 0.048), at the AT VE/VCO2 = 46 +/- 12 in group II versus 36 +/- 7 in group I (p = 0.001) and at peak exercise VE/VCO2 = 46.2 +/- 13 in group II versus 36.2 +/- 6 in group I (p = 0.0002). There was a 24% reduction in the VE/VCO2, from rest to AT in group I, compared to a 16% reduction in group II (p = 0.004). A reduction in the VE/VCO2 from rest to AT less than 16% predicted a VO2max below 14 ml/kg/min with a sensitivity of 60% and a specificity of 93%. CONCLUSIONS: Patients with severe functional impairment have higher values of VE/VCO2 in all exercise stages. A reduction of VE/VCO2 from rest to anaerobic threshold of less than 16% is a high specific predictor of a VO2max below 14 ml/kg/min.     

Biocatalytic sulfur removal from fuels: applicability for producing low sulfur gasoline

Environmental regulations are driving R&D efforts to produce low sulfur fuels, including diesel fuel and gasoline for motor vehicles. Biocatalytic sulfur removal from fuels has potential applicability for producing low sulfur gasoline. Microbial biocatalysts have been identified that can biotransform sulfur compounds found in fuels, including ones that selectively remove sulfur from dibenzothiophene heterocyclic compounds. Most attention is give to the 4S pathway of Rhodococcus, which can remove sulfur from substituted and unsubstituted dibenzothiophenes, including sulfur compounds that hinder chemical catalysis and that resist removal by mild hydrotreatment. Various bioreactor and bioprocess designs are being tested for use with biocatalysts, including recombinant biocatalysts, for use in removing sulfur from fuels and feedstocks within the petroleum refinery stream. With bioprocess improvements that enhance biocatalyst stability, achieve faster kinetics, improve mass transfer limitations, temperature and solvent tolerance, as well as broaden substrate specificity to attack a greater range of heterocyclic compounds, biocatalysis may be a cost-effective approach to achieve the production of low sulfur gasoline. The challenge will be to accomplish these improvements by the time the regulations for low sulfur gasoline and other vehicle fuels go into effect in order to be competitive with emerging nonbiological desulfurization technologies.     

Lipid polymorphism and protein-lipid interactions

Non-lamellar-forming lipids play an important role in determining the physical properties of membranes. They affect the activity of membrane proteins and peptides. In addition, peptides which lyse membranes as well as those which promote membrane fusion facilitate the formation of non-lamellar phases, either micelles, cubic or hexagonal phases. The relationship of these diverse effects on membrane curvature is discussed in relation to the function of certain peptides and proteins. Specific examples of ionophoric peptides, cytotoxic peptides and viral fusion peptides are given. In addition, we compare the modulation of the rate of photoisomerisation of an integral membrane protein, rhodopsin, by non-lamellar-forming lipids with the effects of these lipids on an amphitropic protein, protein kinase C. Among these diverse systems it is frequently observed that the modulation of biological activity can be described in terms of the effect of the peptide or protein on the relative stability of lamellar and non-lamellar structures.     

Is bone turnover a determinant of bone mass in rheumatoid arthritis?

OBJECTIVE: The aim of this study was to measure ultrasound (US) densitometric parameters [Broadband Ultrasound Attenuation (BUA), Speed of Sound (SOS), and stiffness of the os calcis] in patients with inflammatory bowel disease (IBD) and to compare the results with those obtained with conventional x-ray absorptiometry (DXA) of the lumbar spine. METHODS: Twenty-two patients with Crohn's disease (13 with ileal and nine with ileocolonic disease), 11 patients with ulcerative colitis (eight with left-sided and three with pancolitis), and 18 healthy controls. US densitometry of the right heel and DXA of the lumbar spine were performed within the same day. RESULTS: Compared to controls, IBD patients had significantly lower values with both methods, US and DXA. Forty-nine percent of patients had a lumbar T score below -1. Calcaneal SOS and stiffness of these patients were significantly reduced (p < 0.03 and p < 0.05, respectively). Positive significant correlations were found between lumbar DXA and calcaneal US parameters. Lumbar bone density and calcaneal US stiffness correlated inversely with the lifetime prednisone intake (p < 0.03 andp < 0.05, respectively), but not with age or duration of disease. A cut-off level of 80 dB/MHz for calcaneal BUA predicted axial osteopenia correctly in 74%, but some underestimation of spinal BMD was observed, especially in female patients with Crohn's disease. CONCLUSION: US evaluation of the os calcis gives results similar to those of conventional DXA and therefore may be used for screening IBD patients for axial osteoporosis. Because US does not expose patients to radiation, repeated measurements are possible and may be used to assess short term variations and the effect of treatment of IBD-associated bone disease.     

Is access to medical care associated with receipt of HIV testing and counselling?

Lack of timely HIV testing leads to missed prevention opportunities and poor prevention counselling may be related to further disease spread. We examined the association of self-reported access to medical care with receiving HIV testing and preventive counselling services among a sample of patients with HIV disease prior to hospitalization. We conducted a cross-sectional interview of 217 Los Angeles patients hospitalized with HIV-related illness between 1992 and 1993 and abstracted clinical data from the medical record. Eighty-four per cent of patients received HIV testing prior to hospitalization, but only 33% received preventive counselling services. Only 48% of all patients rated outpatient medical care as somewhat or very easy to obtain. Controlling for severity of illness, better access to outpatient medical care (OR = 1.48; 95% CI = 1.02-2.15), having a regular source of care (OR = 3.40; 95% CI = 1.29-8.97) and non-homosexual mode of HIV transmission (OR = 0.31; 0.12-0.83) were associated with receiving HIV testing services prior to hospitalization. Having a regular source of care (OR = 3.55; 95% CI = 1.37-9.22), being VA (Veterans' Administration) insured (OR = 6.16; 1.46-26.05), older age (OR = 0.95; 95% CI = 0.90-0.99) and having a CD4 count between 101-200 (OR = 0.19; 95% CI = 0.06-0.63) were associated with receiving HIV counselling. Limited self-reported access to medical care is associated with fewer patients receiving HIV testing and counselling. Improving timeliness of HIV testing may require removing the barriers to medical care.     

Effect of evaluator and resident gender on the American Board of Internal Medicine evaluation scores

OBJECTIVE: To examine the effects of resident and attending physician gender on the evaluation of residents in an internal medicine training program. DESIGN: Cross-sectional study. SETTING: Large urban academic internal medicine residency program. PARTICIPANTS: During their first 2 years of training, 132 residents (85 men, 47 women) received a total of 974 evaluations from 255 attending physicians (203 men, 52 women) from 1989 to 1995. MEASUREMENTS: The primary measurements were the numerical portions of the American Board of Internal Medicine evaluation form. Separate analyses were performed for each of the nine evaluation dimensions graded on a scale of 1 to 9. The primary outcome was the difference in the average scores received by each resident from male versus female attending physicians. RESULTS: Compared with female trainees, male residents received significantly higher scores from male attending physicians than from female attending physicians in six of the nine dimensions: clinical judgment, history, procedures, relationships, medical care, and overall. Similar trends, not reaching conventional levels of statistical significance, were observed in the other three categories: medical knowledge, physical exam, and attitude. These differences ranged from 0.24 to 0.60 points, and were primarily due to higher grading of male residents by male attending physicians than by female attending physicians. CONCLUSIONS: In one academic training program, we found a significant interaction in the grading process between the gender of internal medicine residents and the gender of their attending evaluators. This study raises the possibility that subtle aspects of gender bias may exist in medical training programs.