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Six radio telescopes were operated as the first southern hemisphere VLBI array in April and May 1982. Observations were made at 2.3 and 8.4 Ghz. This array produced VLBI images of 28 southern hemisphere radio sources, high accuracy VLBI geodesy between southern hemisphere sites, and subarcsecond radio astrometry of celestial sources south of declination −45 degrees. This paper discusses only the astrophysical aspects of the experiment.
VLBI observations of the nucleus of Centaurus A were made in April, 1982 at two frequencies with an array of five Australian radio antennas as part of the Southern Hemisphere VLBI Experiment (SHEVE). Observations were undertaken at 2.29 GHz with all five antennas, while only two were operational at 8.42 GHz. The 2.29 GHz data yielded significant information on the structure of the nuclear jet. At 8.42 GHz a compact unresolved core was detected as well.
The Southern Hemisphere VLBI Experiment (SHEVE) program is aimed at producing high-resolution images of southern radio sources. The radio telescopes of the present SHEVE array are described below and some recent results presented.
Two important factors for understanding the physical nature of compact steep spectrum (CSS) radio sources are determining the correct radio morphological classification of these objects together with their characteristics in wavebands different from the radio (Fanti et al. 1995, A&A, 302, 317). Seven CSS sources (linear dimensions < 30kpc for Ho = 50 kms–1Mpc–1 and α > 0.5, S ≃ v–α) have been found in a complete sample of strong southern radio sources. This group of CSS sources is particularly interesting because some optical and X-ray information is already available as part of a more general study of southern radio sources (Morganti et al. & Siebert et al. these Proceedings). The spectra of all the sources were presented in Tadhunter et al. (1993, MNRAS, 263, 999.) Here we present VLBI observations for three of these sources (0252-71, 1306-09 and 1814-63). The remaining four have already been imaged with VLBI (King et al. these Proceedings).
PKS 1830–211 is the strongest known radio gravitational lens by almost an order of magnitude and has the potential to provide a measurement of H0, provided the lensing system can be parameterized. Attempts to identify optical counterparts, to measure redshifts, have so far proved unsuccessful and this has lead to radio and millimetre spectral line observations. We present our discovery of an absorption system at z = 0.19. A brief description is also made of our ATCA observations to measure the lensing time delay for this source.
PKS 1934–638 is an archetypal GPS source, peaking at 1.4 GHz and exhibits almost no flux density variability. VLBI images at frequencies of .843, 2.3, 4.8, & 8.4 were made with the southern hemisphere VLBI array and they reveal that the source is a 42 mas compact double. There is no detectable change in separation over the last 20 years, yielding an upper limit of ~ 0.03c ± 0.2c on any expansion velocity. The spectral shapes of the two components are remarkably similar, despite indications of finer structure on longer baselines. Magnetic field calculations indicate fields of a few mGauss and the results are consistent with equipartition.
From the combination of VLBI phase-referenced observations and Hipparcos satellite data, we have found evidence of a low-mass object orbiting the late-type star AB Doradus. The mass of the new object is near the hydrogen burning limit and will constitute a precise point for calibrating the low end of the main sequence. This represents the first detection of a low-mass stellar companion using the VLBI technique, which could become an important tool in future searches for planets and brown dwarfs orbiting other stars.
We are undertaking an observational program using the ATCA to monitor the intraday variability (IDV) of a sample of sources at 4.8 and 8.6 GHz. The sources were selected to include the known strong southern IDV sources plus a number of sources whose IDV was recently discovered. The present monitoring program will extend over a full year in order to search for any annual cycle that may be present in the long-term IDV characteristics of these sources. In this paper we discuss the observing strategy and data analysis, and present the first results from our observations.
This paper discusses the nonhermetic performance of polymer thin film coatings derived from 1,3-bis(2-bicyclo[4.2.0]octa-1,3,5-trien-3-ylethenyl)-1,1,3,3-tetramethyl disiloxane (mixed isomers, CAS 117732-87-3), known also as divinyl siloxane bis-benzocyclobutene or DVS bis-BCB. The stability of the dielectric constant and the mechanical properties have been examined before and during high temperature exposures of the polymer films to air for extended periods of time at high and low humidity. Infrared absorbance spectra and dielectric constant measurements have been correlated.
Formulations of the DVS bis-BCB prepolymer with a polymeric oxidation inhibitor are predicted to yield polymer films which display less than a 10% change in the dielectric constant after 40 years in air at 85°C. These films have excellent potential for use as the dielectric coating layer in nonhermetic packaging applications for Multi Chip Module (MCM) circuits.
Carbon films deposited by filtered cathodic arc show a high compressive stress which limits their thickness because of delamination. We study three methods of relieving the stress in these films. We first determine the dependence of the stress on DC bias up to bias voltages of 1200V and show that the formula of Davis provides a good fit to the data including the stress maximum in the region of 150–200V and the progressive decrease in stress at higher voltages. In the second method, plasma immersion ion implantation (PIII) was used to create multilayer of alternating high density, high stress (PIII on) films and lower density, low stress (PIII off) films. This method enabled thicker structures to be produced. In the third method we made multilayers using amorphous silicon and carbon layers. Annealing of these layers showed that the stress could be reduced to very low values because of the ability of the silicon layers to absorb compressive stress by contracting after the annealing step. The microstructural effects of PIII were studied by transmission and scanning electron microscopy.
This paper investigates the prognostic value of flash visual evoked potentials (VEPs) recorded in preterm infants at birth and at term age with respect to severe neurological outcome. Flash VEPs were recorded in 81 preterm infants at birth (i.e. <35 weeks' gestation) and repeated in 56 of these infants at term age. The preterm infants were assigned to either a healthy or at-risk subgroup based on clinical birth factors. Normal ranges of flash-VEP latencies, amplitudes, and number of components present were obtained from the subgroup of healthy preterm infants and from 68 term infants tested postnatally. The flash-VEP results of the entire preterm group were compared with the normal ranges and any abnormalities noted. Seven preterm infants in the at-risk group died, six of whom had abnormal flash VEPs before term age. Of the five infants from the at-risk group diagnosed with cerebral palsy (CP), three had abnormal flash VEPs before term age. Thus the sensitivity and specificity of the flash VEP with respect to survival was 86% and 89% respectively, and with respect to the development of CP was 60% and 92%. The abnormal features of the flash VEP associated with adverse outcomes comprised a delayed N3 component before term age and the absence of a positive component (P2) at term age.
Single photon emission tomography (SPET) with the lipophilic blood flow marker 99mTc-hexamethyl propyleneamine oxime (99mTc-HMPAO) has been used to determine regional uptake of radiolabel into brain regions of patients with presenile Alzheimer's disease and Korsakoff's psychosis, and age-matched controls. Using occipital cortical uptake as reference area, the pattern of relative regional cerebral blood flow (rCBF) was determined in other cortical areas and basal ganglia. In Alzheimer's disease, reduction in rCBF occurred most strikingly in posterior temporal and parietal areas. By contrast, in Korsakoff's psychosis, posterior temporal rCBF was maintained, although there was a trend to reduced tracer uptake in other cortical areas. These impairments of flow were correlated with impairments of neuropsychological function. In Alzheimer's disease, left posterior temporal and left parietal regions in particular showed rCBF to be strongly correlated with most aspects of cognitive function. In Korsakoff's psychosis, however, impaired flow in frontal regions was correlated with impaired performance on tests of memory and orientation. The findings in Alzheimer's disease show quantitative parallels with those from studies using Positron Emission Tomography (PET), and extend our understanding of the relationship between cognition and regional brain function in dementia. The findings in Korsakoff's psychosis offer the first direct evidence linking frontal lobe dysfunction with the cognitive impairment seen in the disorder.
Twenty-seven diabetic men with erectile impotence were given physical and psychosexual assessments. Physical assessment included vascular and neurological evaluation. Psychosexual assessment was by means of a semi-structured interview. Seven potent diabetic men formed a control group. Patients with erectile failure Had a varied clinical picture which differed from the stereotype of diabetic impotence: morning erections were preserved in over a half (55 per cent), eight patients (30 per cent) had intact spontaneous erections, and sexual interest was reduced in 12 patients (44 per cent). In 13 patients (48 per cent) ejaculation was disturbed and a further four patients (15 per cent) described unusual disorders of sexual function.
Within the group there were no differences in clinical picture between those with and without autonomic neuropathy, retinopathy or potential psychogenic factors.
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