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Particle transport, acceleration and energization are phenomena of major importance for both space and laboratory plasmas. Despite years of study, an accurate theoretical description of these effects is still lacking. Validating models with self-consistent, kinetic simulations represents today a new challenge for the description of weakly collisional, turbulent plasmas. We perform simulations of steady state turbulence in the 2.5-dimensional approximation (three-dimensional fields that depend only on two-dimensional spatial directions). The chosen plasma parameters allow to span different systems, going from the solar corona to the solar wind, from the Earth’s magnetosheath to confinement devices. To describe the ion diffusion we adapted the nonlinear guiding centre (NLGC) theory to the two-dimensional case. Finally, we investigated the local influence of coherent structures on particle energization and acceleration: current sheets play an important role if the ions’ Larmor radii are of the order of the current sheet’s size. This resonance-like process leads to the violation of the magnetic moment conservation, eventually enhancing the velocity-space diffusion.
Previous studies have highlighted the role of the brain reward and cognitive control systems in the etiology of anorexia nervosa (AN). In an attempt to disentangle the relative contribution of these systems to the disorder, we used functional magnetic resonance imaging (fMRI) to investigate hemodynamic responses to reward-related stimuli presented both subliminally and supraliminally in acutely underweight AN patients and age-matched healthy controls (HC).
fMRI data were collected from a total of 35 AN patients and 35 HC, while they passively viewed subliminally and supraliminally presented streams of food, positive social, and neutral stimuli. Activation patterns of the group×stimulation condition×stimulus type interaction were interrogated to investigate potential group differences in processing different stimulus types under the two stimulation conditions. Moreover, changes in functional connectivity were investigated using generalized psychophysiological interaction analysis.
AN patients showed a generally increased response to supraliminally presented stimuli in the inferior frontal junction (IFJ), but no alterations within the reward system. Increased activation during supraliminal stimulation with food stimuli was observed in the AN group in visual regions including superior occipital gyrus and the fusiform gyrus/parahippocampal gyrus. No group difference was found with respect to the subliminal stimulation condition and functional connectivity.
Increased IFJ activation in AN during supraliminal stimulation may indicate hyperactive cognitive control, which resonates with clinical presentation of excessive self-control in AN patients. Increased activation to food stimuli in visual regions may be interpreted in light of an attentional food bias in AN.
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.
An attempt was made to develop a simple but accurate method for making compressive strength tests on right circular cylinders. Compliant loading platens were designed to apply uniform normal stress without introducing significant interface radial shear stresses. The compliant platens gave reproducible results that agree well with results obtained by a precise conventional technique. Accurate results were obtained with simple specimen preparation, and with short specimens where the length-to-diameter ratio was less than unity. Platens were made from a rubber-like urethane which was molded in aluminum cylinders to provide lateral restraint. Uniaxial compression tests on cylindrical polycrystalline ice specimens were made to determine the characteristics of the platens. For 21 specimens with ends prepared on a lapping plate to obtain a mirror finish, the measured strength showed a variation of only 13% for length-to-diameter ratios from 0.74 to 2.5, with no systematic trend. Another 21 specimens with length-to-diameter ratios of about 2.35 were tested with various platens and various methods of specimen end preparation. The strength for specimens with saw-cut ends and for those with ends lapped showed very little difference when tested with the rubber platens.
Ice pile-up and ride-up are common occurrences along beaches in the sub-Arctic and Arctic. An understanding of the factors which lead to pile-up is important for design of a defensive strategy to prevent damage to coastal installations.
Since ice action on a sloping beach is complex, an experimental model study was undertaken to determine the factors which promote ice pile-up. The factors varied in this study were the freeboard, slope, and roughness of the beach. One experiment was performed to observe the effectiveness of a shore defense structure against ice ride-up.
Experiments were performed to determine the forces required to buckle a floating ice sheet pushing against structures of different widths. The characteristic length of each ice sheet was determined to enable a comparison to be made between the theoretical and experimental results.
Most of the experimental data points are within the range of the theoretical values of normalized buckling loads for frictionless and hinged boundary conditions, which represent the extreme situations for ice-structure contact. Thus, the agreement between the theoretical and experimental buckling loads is considered to be good. Photographs of the buckled ice sheets show a resemblance to the theoretical mode of buckling.
We present preliminary results on multi-wavelength observations of the Wolf-Rayet Blue Compact Dwarf Galaxy He2–10. These observations include Hα and continuum imaging, high-resolution Hα spectroscopy, high-resolution radio-continuum mapping at 6.3 and 3.5 cm and X-ray mapping. The deep Hα image reveals that the galaxy consists of a complex system of different star-forming knots surrounded by kpc-scale bubble-like and filamentary structures. The most interesting structure is a bipolar superbubble centered on the most intense star-formation knot. High-resolution spectroscopy of this structure indicates that it is expanding with a velocity in the range 75–250 km s−1. This kind of outflows is likely to be produced by the mechanical action of stellar winds and supernovae explosions in the intense starbursts that the galaxy hosts. This scenario is consistent with the finding of a very steep radio spectral index in the extended radio continuum emission (α = −0.59) that confirms the presence of a large number of supernova remnants in the galaxy.
We present a comparison between the latest Parkes radio surveys (Filipović et al. 1995, 1996, 1997) and Hα surveys of the Magellanic Clouds (Kennicutt & Hodge 1986). We have found 180 discrete sources in common for the Large Magellanic Cloud (LMC) and 40 in the field of the Small Magellanic Cloud (SMC). Most of these sources (95%) are HII regions and supernova remnants (SNRs). A comparison of the radio and Hα flux densities shows a very good correlation and we note that many of the Magellanic Clouds SNRs are embedded in HII regions.
The synthesis telescopes at Fleurs and Molonglo have been used to map 50 supernova remnants. Additional specialized software to process the maps has been developed, and Parkes observations have been used to supply short spacing information missing from the maps.
The Molonglo Observatory synthesis telescope (MOST) of the University of Sydney (Mills 1981) produces maps of the 843 MHz continuum emission from fields of width 23′, 46′ or 70′ arc. The telescope comprises two co-linear east-west cylindrical paraboloids each 2186λ in length and separated by a gap of 43λ. For each paraboloid a phasing network (Durdin et al. 1984) generates a comb of 64 contiguous fan beams. Mapping is accomplished in real time during a 12-h observation by overlaying, in the map plane, the instantaneous cross-correlations of corresponding beams. The synthesized point-source response (beam) produced by this method has a width of 43″ (E-W) by 43″ cosec δ (N-S).
8.4 GHz linear polarization maps, obtained with the Parkes radio telescope, are presented for six southern supernova remnants. These results are compared with published and unpublished polarization maps at 5 GHz to derive the magnetic field direction and Faraday rotation measure distribution.
These results are part of a program to map the magnetic fields in galactic supernova remnants and complement our program to obtain high-resolution maps of galactic SNRs using the Molonglo Observatory Synthesis Telescope; five new Molonglo maps are presented here.
We present preliminary results from a number of deep radio polarization surveys being made of the Magellanic Clouds at 2.3 GHz, 4.75 GHz and 8.55 GHz. Extended and linearly polarized radio emission has been found at 2.3 and 4.75 GHz from both the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). However, as the analysis of these data is not yet complete we present only some of the 4.75 GHz results at this time.
At the centre of the Parkes 64—m radio telescope a region of diameter 17 m has recently been resurfaced to improve its efficiency at high frequencies. The first measurements using this section have been made at 22 GHz, in observations of both continuum sources and water tfapour masers. For these observations the receiver front-end used a mixer cooled in liquid nitrogen, followed by a 5 GHz cryogenic parametric amplifier as a second stage. The option of switching against an offset horn was available and the total system
noise temperature was ∽ 750 K.
In March 1963 a paper by Hazard, Mackey and Shimmins in Nature, announced an accurate position for the radio source 3C 273. This was subsequently identified as the first known quasar. Through an innocent editorial mistake, the affiliation of the first author was wrongly attributed. This caused long-term animosity between the Physics Department of the University of Sydney and the CSIRO Division of Radiophysics.
Several extragalactic HI surveys using a λ21 cm 13-beam focal plane array will begin in early 1997 using the Parkes 64 m telescope. These surveys are designed to detect efficiently nearby galaxies that have failed to be identified optically because of low optical surface brightness or high optical extinction. We discuss scientific and technical aspects of the multibeam receiver, including astronomical objectives, feed, receiver and correlator design and data acquisition. A comparison with other telescopes shows that the Parkes multibeam receiver has significant speed advantages for any large-area λ21 cm galaxy survey in the velocity range range 0–14000 km s−1.
VLBI observations of the nucleus of Centaurus A have been made at three southern hemisphere observatories. Since Centaurus A is the nearest active galaxy, VLBI investigations are important because the physical processes in the nucleus can be studied in greater linear detail than in other similar galaxies. Previous VLBI observations of Centaurus A have been hampered by its southerly declination (−43°) and the sparsity of VLBI capability in the southern hemisphere, leading to only scattered single point u, v coverage. This paper presents results from the early stages of development of a southern hemisphere VLBI network.
PILOT (the Pathfinder for an International Large Optical Telescope) is a proposed 2.5-m optical/infrared telescope to be located at Dome C on the Antarctic plateau. Conditions at Dome C are known to be exceptional for astronomy. The seeing (above ∼30 m height), coherence time, and isoplanatic angle are all twice as good as at typical mid-latitude sites, while the water-vapour column, and the atmosphere and telescope thermal emission are all an order of magnitude better. These conditions enable a unique scientific capability for PILOT, which is addressed in this series of papers. The current paper presents an overview of the optical and instrumentation suite for PILOT and its expected performance, a summary of the key science goals and observational approach for the facility, a discussion of the synergies between the science goals for PILOT and other telescopes, and a discussion of the future of Antarctic astronomy. Paper II and Paper III present details of the science projects divided, respectively, between the distant Universe (i.e. studies of first light, and the assembly and evolution of structure) and the nearby Universe (i.e. studies of Local Group galaxies, the Milky Way, and the Solar System).
The incidence of myocardial infarctions and influenza follow similar seasonal patterns. To determine if acute myocardial infarctions (AMIs) and ischaemic strokes are associated with influenza activity, we built time-series models using data from the Nationwide Inpatient Sample. In these models, we used influenza activity to predict the incidence of AMI and ischaemic stroke. We fitted national models as well as models based on four geographical regions and five age groups. Across all models, we found consistent significant associations between AMIs and influenza activity, but not between ischaemic strokes and influenza. Associations between influenza and AMI increased with age, were greatest in those aged >80 years, and were present in all geographical regions. In addition, the natural experiment provided by the second wave of the influenza pandemic in 2009 provided further evidence of the relationship between influenza and AMI, because both series peaked in the same non-winter month.