Electrophysiological correlates of high-level perception during spatial navigation

We studied the electrophysiological basis of object recognition by recording scalp\ud electroencephalograms while participants played a virtual-reality taxi driver game.\ud Participants searched for passengers and stores during virtual navigation in simulated\ud towns. We compared oscillatory brain activity in response to store views that were targets or\ud nontargets (during store search) or neutral (during passenger search). Even though store\ud category was solely defined by task context (rather than by sensory cues), frontal ...\ud \u

The role of proton precipitation in Jovian aurora: Theory and observation

It was proposed that the Jovian auroral emissions observed by Voyager spacecraft could be explained by energetic protons precipitating into the upper atmosphere of Jupiter. Such precipitation of energetic protons results in Doppler-shifted Lyman alpha emission that can be quantitatively analyzed to determine the energy flux and energy distribution of the incoming particle beam. Modeling of the expected emission from a reasonably chosen Voyager energetic proton spectrum can be used in conjunction with International Ultraviolet Explorer (IUE) observations, which show a relative lack of red-shifted Lyman alpha emission, to set upper limits on the amount of proton precipitation taking place in the Jovian aurora. Such calculations indicate that less than 10 percent of the ultraviolet auroral emissions at Jupiter can be explained by proton precipitation

Omega-3 Fatty Acids Improve Recovery, whereas Omega-6 Fatty Acids Worsen Outcome, after Spinal Cord Injury in the Adult Rat

Spinal cord injury (SCI) is a cause of major neurological disability, and no satisfactory treatment is currently available. Evidence suggests that polyunsaturated fatty acids (PUFAs) could target some of the pathological mechanisms that underlie damage after SCI. We examined the effects of treatment with PUFAs after lateral spinal cord hemisection in the rat. The ω-3 PUFAs α-linolenic acid and docosahexaenoic acid (DHA) injected 30 min after injury induced significantly improved locomotor performance and neuroprotection, including decreased lesion size and apoptosis and increased neuronal and oligodendrocyte survival. Evidence showing a decrease in RNA/DNA oxidation suggests that the neuroprotective effect of ω-3 PUFAs involved a significant antioxidant function. In contrast, animals treated with arachidonic acid, an ω-6 PUFA, had a significantly worse outcome than controls. We confirmed the neuroprotective effect of ω-3 PUFAs by examining the effects of DHA treatment after spinal cord compression injury. Results indicated that DHA administered 30 min after spinal cord compression not only greatly increased survival of neurons but also resulted in significantly better locomotor performance for up to 6 weeks after injury. This report shows a striking difference in efficacy between the effects of treatment with ω-3 and ω-6 PUFAs on the outcome of SCI, with ω-3 PUFAs being neuroprotective and ω-6 PUFAs having a damaging effect. Given the proven clinical safety of ω-3 PUFAs, our observations show that these PUFAs have significant therapeutic potential in SCI. In contrast, the use of preparations enriched in ω-6 PUFAs after injury could worsen outcome after SCI

Further Observational Evidence for a Critical Ionising Luminosity in Active Galaxies

We report the results of a survey for HI 21-cm absorption at redshifts of z > 2.6 in a new sample of radio sources with the Green Bank and Giant Metrewave Radio Telescopes. From a total of 25 targets, we report zero detections in the 16 for which optical depth limits could be obtained. Based upon the detection rate for z > 0.1 associated absorption, we would expect approximately four detections. Of the 11 which have previously not been searched, there is sufficient source-frame optical/ultra-violet photometry to determine the ionising photon rate for four. Adding these to the literature, the hypothesis that there is a critical rate of logQ = 56 ionising photons per second is now significant at ~7 sigma. This reaffirms our assertion that searching z > 3 active galaxies for which optical redshifts are available selects sources in which the ultra-violet luminosity is sufficient to ionise all of the neutral gas in the host galaxy.Comment: Accepted by MNRA

A search for 21 cm HI absorption in AT20G compact radio galaxies

We present results from a search for 21 cm associated HI absorption in a sample of 29 radio sources selected from the Australia Telescope 20 GHz survey. Observations were conducted using the Australia Telescope Compact Array Broadband Backend, with which we can simultaneously look for 21 cm absorption in a redshift range of 0.04 < z < 0.08, with a velocity resolution of 7 km/s . In preparation for future large-scale H I absorption surveys we test a spectral-line finding method based on Bayesian inference. We use this to assign significance to our detections and to determine the best-fitting number of spectral-line components. We find that the automated spectral-line search is limited by residuals in the continuum, both from the band-pass calibration and spectral-ripple subtraction, at spectral-line widths of \Deltav_FWHM > 103 km/s . Using this technique we detect two new absorbers and a third, previously known, yielding a 10 per cent detection rate. Of the detections, the spectral-line profiles are consistent with the theory that we are seeing different orientations of the absorbing gas, in both the host galaxy and circumnuclear disc, with respect to our line-of-sight to the source. In order to spatially resolve the spectral-line components in the two new detections, and so verify this conclusion, we require further high-resolution 21 cm observations (~0.01 arcsec) using very long baseline interferometry.Comment: 16 pages, 8 figures and 5 tables; accepted for publication in MNRAS (version 2 based on proof corrections

Electron-impact ionization of atomic hydrogen at 2 eV above threshold

The convergent close-coupling method is applied to the calculation of fully differential cross sections for ionization of atomic hydrogen by 15.6 eV electrons. We find that even at this low energy the method is able to yield predictive results with small uncertainty. As a consequence we suspect that the experimental normalization at this energy is approximately a factor of two too high.Comment: 10 page

Adolescent Experiences With Intrauterine Devices: A Qualitative Study

PURPOSE: The purpose of this study was to improve understanding of adolescents\u27 reasons for choosing an intrauterine device (IUD) and to explore experiences that led to continuation or discontinuation of the levonorgestrel intrauterine system (LNG-IUS) and the copper IUD (copper IUD). METHODS: We conducted focus groups (FGs) with adolescents and young women who were current or former IUD users stratified by IUD type and 12-month IUD continuation or discontinuation. All subjects were participants from the Contraceptive CHOICE Project. FG data were supplemented with in-depth interviews (IDIs). Data collection was continued until thematic saturation was reached. Transcripts were independently coded by two researchers, and interrater reliability was calculated using a Kappa coefficient. Analysis followed a standard text-analysis approach. RESULTS: Thirteen FGs and seven IDIs were conducted with 43 young women. Effectiveness, duration of use, convenience, and potential bleeding changes emerged as themes for both choosing and continuing IUDs. Some women chose the LNG-IUS to achieve amenorrhea, whereas copper IUD users wanted a nonhormonal method and continued menses. Copper IUD users cited expulsion and bleeding irregularities as reasons for discontinuation, whereas LNG-IUS users reported bleeding irregularities and continued pain as reasons for removal. IUD users noted an adjustment period of weeks to months in which side effects were present before lessening. CONCLUSIONS: Effectiveness, duration of use, convenience, and potential changes in bleeding patterns drove adolescents\u27 choice and continuation of an IUD. Bleeding changes and pain contributed to IUD discontinuation. Discussion of effectiveness, duration and convenience, and anticipatory guidance regarding post-insertion side effects may be important in counseling young women about IUDs

Measurement of Relativistic Orbital Decay in the PSR B1534+12 Binary System

We have made timing observations of binary pulsar PSR B1534+12 with radio telescopes at Arecibo, Green Bank, and Jodrell Bank. By combining our new observations with data collected up to seven years earlier, we obtain a significantly improved solution for the astrometric, spin, and orbital parameters of the system. For the first time in any binary pulsar system, no fewer than five relativistic or "post-Keplerian" orbital parameters are measurable with useful accuracies in a theory-independent way. We find the orbital period of the system to be decreasing at a rate close to that expected from gravitational radiation damping, according to general relativity, although the precision of this test is limited to about 15% by the otherwise poorly known distance to the pulsar. The remaining post-Keplerian parameters are all consistent with one another and all but one of them have fractional accuracies better than 1%. By assuming that general relativity is the correct theory of gravity, at least to the accuracy demanded by this experiment, we find the masses of the pulsar and companion star each to be 1.339+-0.003 Msun and the system's distance to be d = 1.1+-0.2 kpc, marginally larger than the d ~ 0.7 kpc estimated from the dispersion measure. The increased distance reduces estimates of the projected rate of coalescence of double neutron-star systems in the universe, a quantity of considerable interest for experiments with terrestrial gravitational wave detectors such as LIGO.Comment: 17 pages, 4 figures, submitted to the Ap