The sub-energetic gamma-ray burst GRB 031203 as a cosmic analogue to the nearby GRB 980425.

Over the six years since the discovery of the gamma-ray burst GRB 980425, which was associated with the nearby (distance approximately 40 Mpc) supernova 1998bw, astronomers have debated fiercely the nature of this event. Relative to bursts located at cosmological distance (redshift z approximately 1), GRB 980425 was under-luminous in gamma-rays by three orders of magnitude. Radio calorimetry showed that the explosion was sub-energetic by a factor of 10. Here we report observations of the radio and X-ray afterglow of the recent GRB 031203 (refs 5-7), which has a redshift of z = 0.105. We demonstrate that it too is sub-energetic which, when taken together with the low gamma-ray luminosity, suggests that GRB 031203 is the first cosmic analogue to GRB 980425. We find no evidence that this event was a highly collimated explosion viewed off-axis. Like GRB 980425, GRB 031203 appears to be an intrinsically sub-energetic gamma-ray burst. Such sub-energetic events have faint afterglows. We expect intensive follow-up of faint bursts with smooth gamma-ray light curves (common to both GRB 031203 and 980425) to reveal a large population of such events.

Determination of the Hubble constant.

Establishing accurate extragalactic distances has provided an immense challenge to astronomers since the 1920s. The situation has improved dramatically as better detectors have become available, and as several new, promising techniques have been developed. For the first time in the history of this difficult field, relative distances to galaxies are being compared on a case-by-case basis, and their quantitative agreement is being established. New instrumentation, the development of new techniques for measuring distances, and recent measurements with the Hubble Space telescope all have resulted in new distances to galaxies with precision at the +/-5-20% level. The current statistical uncertainty in some methods for measuring H(0) is now only a few percent; with systematic errors, the total uncertainty is approaching +/-10%. Hence, the historical factor-of-two uncertainty in the value of the H(0) is now behind us.

A distance to the galaxy NGC4258 from observations of Cepheid variable stars.

Cepheid variable stars pulsate in a way that is correlated with their intrinsic luminosity, making them useful as 'standard candles' for determining distances to galaxies; the potential systematic uncertainties in the resulting distances have been estimated to be only 8-10%. They have played a crucial role in establishing the extragalactic distance scale and hence the value of the Hubble constant. Here we report observations of Cepheids in the nearby galaxy NGC4258; the distance calculated from the Cepheids is 8.1 +/- 0.4 Mpc, where the uncertainty does not include possible systematic errors. There is an independently determined geometric distance to this galaxy of 7.2 +/- 0.5 Mpc, based on the observed proper motions of water masers orbiting the central black hole; the distances differ by 1.3sigma. If the maser-based distance is adopted and the Cepheid distance scale revised accordingly, the derived value of the Hubble constant would increase by 12 +/- 9%, while the expansion age of the Universe would decrease by the same amount.

Measuring cosmological parameters.

In this review, the status of measurements of the matter density (Omegam), the vacuum energy density or cosmological constant (OmegaLambda), the Hubble constant (H0), and the ages of the oldest measured objects (t0) are summarized. Three independent types of methods for measuring the Hubble constant are considered: the measurement of time delays in multiply imaged quasars, the Sunyaev-Zel'dovich effect in clusters, and Cepheid-based extragalactic distances. Many recent independent dynamical measurements are yielding a low value for the matter density (Omegam approximately 0.2-0.3). A wide range of Hubble constant measurements appear to be converging in the range of 60-80 km/sec per megaparsec. Areas where future improvements are likely to be made soon are highlighted-in particular, measurements of anisotropies in the cosmic microwave background. Particular attention is paid to sources of systematic error and the assumptions that underlie many of the measurement methods.

A combinatorial approach to materials discovery.

A method that combines thin film deposition and physical masking techniques has been used for the parallel synthesis of spatially addressable libraries of solid-state materials. Arrays containing different combinations, stoichiometries, and deposition sequences of BaCO(3), Bi(2)O(3), CaO, CuO, PbO, SrCO(3), and Y(2)O(3) were generated with a series of binary masks. The arrays were sintered and BiSrCaCuO and YBaCuO superconducting films were identified. Samples as small as 200 micrometers by 200 micrometers in size were generated, corresponding to library densities of 10,000 sites per square inch. The ability to generate and screen combinatorial libraries of solid-state compounds, when coupled with theory and empirical observations, may significantly increase the rate at which novel electronic, magnetic, and optical materials are discovered and theoretical predictions tested.

The neonate with unexpected acidemia.

We attempted to determine the etiology and clinical significance of unexpected acidemia in otherwise healthy neonates. A retrospective review was performed of the umbilical cord pH in 11,203 deliveries performed at Denver General Hospital, with an umbilical artery pH < 7.13 (3 SD below the mean) selected as the definition of neonatal acidemia. Among those neonates weighing > 2.5 kg with umbilical artery pH < 7.13, 76 were expected to have acidemia because of signs of severe fetal distress. There were 59 neonates with unexpected acidemia, having umbilical artery pH < 7.13, with no definite etiology found. In 96% of cases of unexpected acidemia, the neonates were discharged with their mothers, while 84% of the expected cases went home with their mothers. In excess of $880,000 was spent performing routine umbilical blood pH determinations without any apparent clinical or legal benefit. Routine umbilical blood gas studies on all neonates does not appear to be indicated for either clinical or legal reasons.

Nonstationary properties of postural sway.

Postural sway during quite stance is usually assumed to be a stationary stochastic process. We tested this assumption by investigating the time invariance of the average value and variance of the postural sway of three subjects. The sway was measured with a force plate under three conditions: subject standing on two feet with eyes open; subject standing on two feet with eyes closed; and subject standing on one foot with eyes open. Data were collected in 1 min runs. More than 50 min of data were collected for each subject under each test condition. The data were averaged across all runs for each subject and condition. Trends were found to be present in the data. In addition, there were initial transient increases in the second-order moments about the trends. The transient changes in first- and second-order moments usually disappeared during the first 20 s. In light of these findings, we can reject the hypothesis that postural sway is a stationary process. The results imply that the usual methods to parameterize postural sway have to be either changed or reinterpreted.

A retrospective review of the efficacy and safety of prostaglandin E2 with premature rupture of the membranes at term.

OBJECTIVE: The purpose of this study was to assess rates of endometritis, clinical chorioamnionitis, cesarean delivery, and neonatal sepsis from the records of patients with premature rupture of the membranes (PROM) and an unfavorable cervix treated with vaginal prostaglandin (PG) E2 in comparison with those in the literature. METHODS: Using a computer data base at Denver General Hospital, we identified 146 women with PROM and cervical dilatation of 2 cm or less at term who were treated with PGE2 gel or suppositories. The records were reviewed to identify rates of maternal and neonatal infection and complications, as well as cesarean delivery. RESULTS: The cesarean rate was 12%. Chorioamnionitis developed in 6.8% of the study group and endometritis in 2%. Neonatal complications were limited to two with low Apgar scores (less than 7 at 5 minutes), one with microbiologically confirmed sepsis, and two with positive urine counterimmunoelectrophoresis for group B streptococcus. The only instance of neonatal sepsis occurred in a patient with rupture of membranes longer than 24 hours. CONCLUSIONS: The use of vaginal PGE2 suppositories for induction of labor and cervical ripening in term patients with PROM was accompanied by a high rate of vaginal delivery and a low rate of maternal and neonatal complications in a city hospital setting.

The association of maternal low birthweight and infant low birthweight in a racially mixed population.

The association between maternal low birthweight (LBW) and infant low birthweight has been explored in previous studies in mainly middle and upper income, Caucasian populations. This study investigated whether the association found in these populations is true in a racially mixed, low socio-economic group. A case-control methodology was used and estimates of association were derived by means of logistic regression analyses. Data were gathered for 167 LBW infant-mother dyads and 338 adequate weight infant-mother controls matched on race and parity. The odds of a LBW infant having a LBW mother were 80% more likely than for adequate weight infants (OR = 1.80, 95% CI 1.14-2.84). This association was stronger for Hispanic women and their infants than for Black or non-Hispanic White women and their infants. Women who were both preterm and LBW had the higher estimate of risk for infant LBW than women who were LBW due to intrauterine growth retardation (IUGR). As found in previous research, the estimate of association between maternal LBW and infant LBW was greater for those infants who were LBW due to IUGR than those who were LBW due to being premature. The question of whether maternal LBW is also associated with increased risk of neonatal mortality and morbidity is as yet left unanswered.

Progression of exencephaly to anencephaly in the human fetus--an ultrasound perspective.

Exencephaly as a precursor of anencephaly is well delineated in animal studies. In humans, a similar though unproven embryologic sequence is postulated. In the case reported, serial ultrasound studies allowed us to identify a 16-week human exencephalic fetus and observe the cephalic changes during its progression to a classic anencephalic appearance.

Comparison of umbilical artery pH and 5-minute Apgar score in the low-birth-weight and very-low-birth-weight infant.

The division between "normal" and low Apgar scores is based largely on data obtained from term newborns and may not apply to the premature infant. Umbilical artery pH has been suggested as a better indicator of intrapartum asphyxia. We examined the charts of 558 infants with birth weights less than or equal to 2500 gm with respect to umbilical artery pH, 5-minute Apgar scores, and birth weight percentiles. A positive correlation between birth weight and 5-minute Apgar score was noted. No such relationship existed between birth weight and umbilical artery pH. Within birth weight groups, small-for-gestational-age infants have higher Apgar scores and lower umbilical artery pH values than their appropriate-for-gestational age counterparts.

Cross-modal functions in alcoholism and aging.

Two experiments were performed to measure separate aspects of cross-modal functions in normal and alcoholic research participants: matching, and utilization of concepts. In Experiment 1, cross-modal equivalence-matching was measured, i.e. the ability to select in a second modality (e.g. vision), the same stimulus that was first presented in a different modality (e.g. touch). Experiment 2 measured cross-modal transfer of information about stimulus dimensions, i.e. the ability to recognize and use the concepts of texture and form, based upon prior experience solving tactual problems, to solve visual problems. Fifty-five normal and alcoholic research participants comprised the following five groups: 13 young normals (YN) and 10 young alcoholics (YA), 28-48 years of age; 13 older normals (ON) and 14 older alcoholics (OA), 50-71 years of age; and 5 alcoholic Korsakoff patients (K), 55-68 years of age. Separate subgroups of 9 age-matched ONs and 9 OAs were devised for purposes of statistical analyses of data involving the 5 Ks. Results of the experiments indicated that aging is associated with decline in tactual discrimination ability. Further, cross-modal functions appear to be compromised by alcoholic Korsakoff's disease, and--to a lesser extent--by the combined effects of alcoholism and normal chronological aging. Brain mechanisms important for normal cross-modal functions are discussed.

Comparison of vestibulo-ocular reflex (VOR) modification methods in cats.

The vestibulo-ocular reflex (VOR) has been measured and optically modified in several animal species. The VOR gain can be increased optokinetically by rotating the animal's visual surround opposite to the animal's direction of rotation or a VOR increase can result from the use of magnifying lenses. We describe here a comparison of three methods for producing VOR increases in cats: (i) optokinetic drum; (ii) a pair of 2.2 x telescopic lenses; (iii) Fresnel lens goggles. The animals were put through several preliminary calibrations followed by a sequence of VOR modification periods alternating with 10 testing periods. The results of the comparison in 4 cats show that the Fresnel lens system produces a greater and more stable VOR gain increase than the other two methods.

The future of clinical engineering in the 1990's.

The problems in hospitals which led to the development of the clinical engineering profession are described along with recent changes in the hospital environment. The authors discuss how the profession is adapting to these changes. Also discussed is the tendency for BMETs to move into clinical engineering roles.

Vestibulo-ocular reflex adaptation in cats before and after depletion of norepinephrine.

The vestibulo-ocular reflex (VOR) operates to stabilize the eyes in space during movements of the head. The system has been described as having a gain of approximately -1 since stimulation of the semi-circular canals brought about by head movements will have the effect of causing the eyes to rotate an equal amount in the opposite direction. Change in the gain of the VOR has been put forth as a model to study plasticity in the central nervous system. Since numerous studies have implicated norepinephrine (NE) in neuroplasticity and modifiability of neural circuits, we attempted to determine the effect of NE depletion (via 6-hydroxydopamine (6-OHDA) intra-cisternal injection) on the modifiability of the VOR. We have found that cats increase the gain of their VOR over a four hour period when rotated in the horizontal plane in a manner equal but opposite to the rotation of a surrounding opto-kinetic drum. The entire group of animals manifests a statistically significant decrement in their ability to increase VOR gain when central stores of norepinephrine are depleted via intra-cisternal injection of 6-OHDA. Individual animals manifest a wide variety of gain changes (0.98 to 1.62). We have found that there were two groups of cats--high and low gain modifiers. The greatest reduction in VOR gain increase after NE depletion was observed in the high gain modifiers. No difference was observed in the low gain modifiers. These same animals tested for VOR modification after amphetamine injection, produced similar results. Alertness during the VOR modification task, as estimated by saccadic eye movement counts, was unchanged after NE depletion NE levels, measured by HPLC-EC, after depletion were reduced to the greatest extent in the cerebellum. There was also a substantial reduction of NE in the visual cortex with less of a reduction in the brain stem.

Selection of movement patterns during functional tasks in humans.

These experiments examine the role of vision and step height in the selection of a simple binary choice of movement pattern by human subjects. The subjects selected a heel strike movement pattern (HS) (as used during level surface locomotion) or a toe strike movement pattern (TS) (as used during stair descent). The functional task involved descending a step of adjustable height followed by level surface walking under vision and nonvision conditions. Triceps surae and tibialis anterior electromyographic (EMG) activity, ankle angle position, and vertical force were examined. As step height was increased, there was an indistinct threshold at which subjects switched from landing with a HS movement pattern to a TS movement pattern. The tibialis anterior and triceps surae precontact EMG burst and subsequent ankle movement for HS and TS trials appear to be part of preprogrammed movement patterns, which are presumably of central origin. The particular mixture of voluntary, stereotypic, and reflex actions for any specified movement is based on the intent or functional outcome desired. The switching to the TS movement pattern as step height increased presumably results in the most efficient and stable movement.

Effect of myoelectric signal processing on the relationship between muscle force and processed EMG.

The relationship between the force generated by an isometrically contracting muscle and the associated myoelectric signal has been the subject of extensive investigation in the past and conflicting results were reported regarding this relationship. The objective of the present study was to investigate some of the sources that may lead to such conflicting results. Two possible sources were examined. The first was the variability in the force-EMG relationship resulting from processing the EMG signal with different EMG signal processing techniques and the second was the variability in the force-EMG relation obtained from repeated muscle contractions. The results of the study indicate that slight variations in the force-EMG relationships can be attributed to the selection of different processing techniques. However, the variability in the force-EMG relation, obtained by using different EMG signal processors, was found to be significantly smaller than the variability in this relationship obtained from repeated muscle contractions.