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A growing interest in constellations of small satellites has recently emerged due to the increasing capability of these platforms and their reduced time and cost of development. However, in the absence of dedicated launch services for these systems, alternative methods for the deployment of these constellations must be considered which can take advantage of the availability of secondary-payload launch opportunities. Furthermore, a means of exploring the effects and tradeoffs in corresponding system architectures is required. This paper presents a methodology to integrate the deployment of constellations of small satellites into the wider design process for these systems. Using a method of design-space exploration, enhanced understanding of the tradespace is supported , whilst identification of system designs for development is enabled by the application of an optimisation process. To demonstrate the method, a simplified analysis framework and a multiobjective genetic algorithm are implemented for three mission case-studies with differing application. The first two cases, modelled on existing constellations, indicate the benefits of design-space exploration, and possible savings which could be made in cost, system mass, or deployment time. The third case, based on a proposed Earth observation nanosatellite constellation, focuses on deployment following launch using a secondary-payload opportunity and demonstrates the breadth of feasible solutions which may not be considered if only point-designs are generated by a priori analysis. These results indicate that the presented method can support the development of future constellations of small satellites by improving the knowledge of different deployment strategies available during the early design phases and through enhanced exploration and identification of promising design alternatives.
The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescopes and partner observatories as part of Australian-based and Australian-led research programs. We report early- to late-time multi-wavelength observations, including optical imaging and spectroscopy, mid-infrared imaging, radio imaging, and searches for fast radio bursts. Our optical spectra reveal that the transient source emission cooled from approximately 6 400 K to 2 100 K over a 7-d period and produced no significant optical emission lines. The spectral profiles, cooling rate, and photometric light curves are consistent with the expected outburst and subsequent processes of a binary neutron star merger. Star formation in the host galaxy probably ceased at least a Gyr ago, although there is evidence for a galaxy merger. Binary pulsars with short (100 Myr) decay times are therefore unlikely progenitors, but pulsars like PSR B1534+12 with its 2.7 Gyr coalescence time could produce such a merger. The displacement (~2.2 kpc) of the binary star system from the centre of the main galaxy is not unusual for stars in the host galaxy or stars originating in the merging galaxy, and therefore any constraints on the kick velocity imparted to the progenitor are poor.
Recent Hα surveys such as SHS and IPHAS have improved the completeness of the Galactic planetary nebula (PN) census. We now know of ∼3000 PNe in the Galaxy, but this is far short of most estimates, typically ~25 000 or more for the total population. The size of the Galactic PN population is required to derive an accurate estimate of the chemical enrichment rates of nitrogen, carbon, and helium. In addition, a high PN count (>20 000) is strong evidence that most main-sequence stars of mass 1–8 M⊙ will go through a PN phase, while a low count (<10 000) argues that special conditions (e.g. close binary interactions) are required to form a PN. We describe a technique for finding hundreds more PNe using the existing data collections of the digital sky surveys, thereby improving the census of Galactic PNe.
Having surveyed ≈ 10% of the sky, we have identified more than 130 PN candidates by surveying multicolour Digitized Sky Survey (DSS), Sloan Digitized Sky Survey (SDSS), and combined [O III], Hα and [S II] images. In a first imaging and spectroscopy campaign, 51 objects were identified as true and probable PNe. This work presents an additional 17 probable or possible PNe identified since that study. The majority of these candidates are situated at Galactic latitudes |b| > 5^, with the exception of seven objects located closer to the Galactic plane. Using the techniques described here that do not require any new survey data, we anticipate that many more PNe are waiting to be found, perhaps as many as 90.
The Salmonella Reference Centre in Johannesburg received 14059 strains of human origin between 1979 and 1984. A significant proportion (6·3%) proved to belong to subspecies II. The majority were cultured from faecal material, usually associated with symptoms related to the gastrointestinal tract. They comprised 884 isolates, represented by 203 serotypes, of which 45 were new serotypes.
The poor hygienic conditions found in many rural areas, together with possible contamination of food and water by wild animals, may contribute to the greater frequency of human S.II infections and the widespread occurrence of unusual serotypes in man in this geographic region.
A survey was undertaken of the occurrence, serotype, antimicrobial sensitivity and plasmid content of members of the tribe Proteeae in the environment of two calf-rearing units in the county of Avon in South West England. Examples of the following species were found: Proteus mirabilis, Prot. vulgaris, Prot. vulgaris Biogroup 2, Morganella morganii, Providencia stuartii, Prov. alcalifaciens and Prov. rettgeri. A wide range of sero types was found, many having been previously reported from nosocomial isolates. A total of 15% of isolates carried plasmids; six pairs of isolates were identified which had identical sero typesbut different patterns of plasmid carriage. The antimicrobial sensitivity of the isolates was generally similar to isolates of Proteeae from humans. Although no truly aminoglycosideresistantisolates were found, some isolates of Prov. stuartii and Prov. rettgeri had MIC's higher than the other isolates to gentamicin and netilmicin, suggesting the presence of lowlevels of the enzyme AAC 2′. The study demonstrates that there is a considerable diversityof species and types of Proteeae associated with calves and their environment. It seems likely that a potential cause of colonization of the human gut by Proteeae is the consumption of meat.
Little research has focused on delineating the specific predictors of emotional over-involvement (EOI) and critical comments (CC) in the early course of psychosis. The purpose of this study was to investigate the differential relationships of EOI and CC with relevant predictors in relatives of first-episode psychosis (FEP) patients.
Baseline patient-related factors including psychotic symptoms, depression and duration of untreated psychosis (DUP) and carer attributes comprising CC, EOI, burden of care and carers' stress and depression were assessed in a cohort of 63 remitted FEP patients and their relatives. Carers were reassessed at 7 months follow-up.
Baseline analysis showed that EOI was more strongly correlated with family stress compared with CC, whereas CC yielded a stronger association with DUP than EOI. Carers' CC at follow-up was not significantly predicted by either baseline family stress, burden of care or patient-related variables. Conversely, baseline EOI predicted both family stress and burden of care at 7 months follow-up. Finally, family burden of care at follow-up was a function of baseline EOI and patients' depressive symptoms.
This study provides preliminary support to the postulate that EOI and CC may be influenced by separate factors early in the course of psychosis and warrant future research and therapeutic interventions as separate constructs. Implications for family interventions in the early phase of psychosis and the prevention of CC and EOI are discussed.
The multi-disciplinary team of Becker and colleagues elegantly present their findings addressing aspects of the impact on Fijian schoolgirls of exposure to Western television (Becker et al, 2002, this issue). These findings support the notion that such exposure has generated disordered eating, underlying body dissatisfaction and intergenerational conflicts within the family that may, in part, be fuelling the process. Focusing on the expected escalation of such disordered eating in this population under these circumstances, their study was naturalistic in capitalising on the recent introduction of television to Fiji, with the first survey of these schoolgirls taking place within 1 month of its advent. The second survey was 3 years later in 1998. The authors point out that the traditional Fijian culture has ‘supported robust appetites and body shapes'.
In this paper we consider group actions on generalized treelike structures (termed
‘pretrees’) defined simply in terms of betweenness relations. Using a result of Levitt,
we show that if a countable group admits an archimedean action on a median pretree,
then it admits an action by isometries on an ℝ-tree. Thus the theory of isometric
actions on ℝ-trees may be extended to a more general setting where it merges naturally
with the theory of right-orderable groups. This approach has application also
to the study of convergence group actions on continua.
Recognition of the additional social handicaps and distress that people with mental illnesses experience as a result of prejudice.
To determine opinions of the British adult population concerning those with mental illnesses as baseline data for a campaign to combat stigmatisation.
Survey of adults (n=1737 interviewed; 65% response) regarding seven types of common mental disorders. Responses evaluated concerned eight specified perceptions.
Respondents commonly perceived people with schizophrenia, alcoholism and drug addiction as unpredictable and dangerous. The two latter conditions were also viewed as self-inflicted. People with any of the seven disorders were perceived as hard to talk with. Opinions about effects of treatment and prognosis suggested reasonable knowledge. About half the respondents reported knowing someone with a mental illness.
Negative opinions indiscriminately overemphasise social handicaps that can accompany mental disorders. They contribute to social isolation, distress and difficulties in employment faced by sufferers. A campaign against stigma should take account of the differences in opinions about the seven disorders studied.
Venezuelan politics presents a puzzle to students of Latin America, and to anyone concerned with the comparative analysis of democratization and democracy. As the major countries of Latin America (and the majority of scholars) worked their way from authoritarianism through “transitions”to democracy and hopefully toward democracy’s consolidation, Venezuela moved in the opposite direction. After decades of political stability and social peace, beginning in 1987 Venezuela’s democratic order was shaken by widespread unrest and citizen disaffection, the decay of key parties and state institutions, attempted coups, and the impeachment and removal of the president in 1993.
Records of ill people being stigmatised exist over the centuries, especially individuals with mental disorders and related mental health problems. Ingredients of such stigmatisation include a belief that such disorders are often self-inflicted and resistant to change. Also, the perceptions that those with them are dangerous and present major difficulties in social interaction (Hayward & Bright, 1997). Such stigmatisation then takes many behavioural forms, including abuse and social distancing. These same disorders are common and, overall, they comprise the largest group of health problems in the country today. For a century or more the public has been protected by the existence of mental hospitals. With their closure and the emphasis now on community care, public concern seems to be mounting and stigmatisation of those afflicted worsening.
The question as to whether anorexia nervosa as an illness has transformed itself was partially addressed in an investigation into the possible change over time in age of onset, age of presentation and the derived variable, delay between onset and presentation. These three variables were examined in 827 patients diagnosed as suffering with anorexia nervosa, who had attended the Eating Disorders Unit at the Middlesex and St George's Hospitals from 1960 to 1990. This analysis revealed a stable age of onset but a lengthening in duration of illness and associated increase of age at presentation. However, investigation of data obtained from two other tertiary referral centres revealed stability of all three variables over time.
The overall conclusion was that there has been no change in the age of onset of anorexia nervosa during the past 30 years. The increasing delay in presentation to the eating disorders clinic is most likely attributable to a change in the practice of patient referrals to a national tertiary referral centre.