Baffle aperture design study of hollow cathode equipped ion thrusters

A simple theoretical model which can be used as an aid in the design of the baffle aperture region of a hollow cathode equipped ion thruster was developed. An analysis of the ion and electron currents in both the main and cathode discharge chambers is presented. From this analysis a model of current flow through the aperture, which is required as an input to the design model, was developed. This model was verified experimentally. The dominant force driving electrons through the aperture was the force due to the electrical potential gradient. The diffusion process was modeled according to the Bolm diffusion theory. A number of simplifications were made to limit the amount of detailed plasma information required as input to the model to facilitate the use of the model in thruster design. This simplified model gave remarkably consistant results with experimental results obtained with a given thruster geometry over substantial changes in operating conditions. The model was uncertain to about a factor of two for different thruster cathode region geometries. The design usefulness was limited by this factor of two uncertainty and by the accuracy to which the plasma parameters required as inputs to the model were specified

PIPE Dreams? The Performance of Companies Issuing Equity Privately

Private Investments in Public Equity (PIPEs) have become an important source of financing for young, publicly traded firms whose poor operating performance may limit alternative financing options. We propose that firms are motivated to sell these securities to minimize costs associated with asymmetric information. We find that both the security structure and the investor composition of a PIPE security matter in the subsequent performance of the issuing firm. Poor post-issuance performance is associated with securities where investors obtain significant repricing rights, which protect them from future stock price declines. Furthermore, companies that obtain financing from hedge funds tend to under-perform companies that obtain financing from other institutional investors. We argue that hedge funds act as investors of last resort, playing an important role in the market for young, high-risk firms with substantial asymmetric information. Hedge funds are willing to fund such high-risk companies because they can protect against possible price declines in the issuing companies by either negotiating PIPE securities with repricing rights or by entering into short positions of the underlying stocks of the issuing companies.

Studies on Housing of Pregnant Sows in Groups and Individually

End of Project ReportIntensive methods of sow housing and their effects on health and welfare have become a topic of intense debate. In the EU the use of tethers for pregnant sows must be phased out by 2006. At pre s e n t there are no plans to ban stalls for pregnant sows. In 1997 the EU released a report on sow housing which was critical of stalls but did not recommend a ban (SVC, 1997). Some member countries have introduced more stringent legislation. The UK government has banned the use of both stalls and tethers for pregnant sows fro m January 1, 1999. Sweden has also imposed a ban on both stalls and tethers, and the Netherlands and De n m a rk have announced restrictions on when individual penning may be used. • This study included a comparison of pregnant gilts in loose housing (groups of 4) and in individual stalls from early pregnancy. Behaviour and skin lesions were monitored both during pregnancy and in the farrowing house. Stalled gilts tended to have higher skin lesion scores. Salivary cortisol levels in stalled gilts showed evidence of a chronic stress response. Loose gilts showed more distress when confined in the farrowing crate pre - f a r rowing than did gilts which had been housed in stalls in pregnancy. • Comparison of two group housing systems namely, groups of four with 3.0m2 per sow and groups of eight with 2.2m2 per sow showed a higher level of aggression in the larger group. Both treatments had free-access stalls with full length partitions but the groups of eight had a smaller communal lying area and they spent a greater proportion of their time in the stalls

Models of planetary rings

The Voyager occultations provide several uniform and high quality data sets for Saturn, Uranus, and Neptune. These data are intercompared, and theoretical models for the particle sizes and the particle transport are developed. The major topics covered include: ring size distribution, torques and resonances, and satellite wakes

Patient perspectives of managing fatigue in ankylosing spondylitis, and views on potential interventions: a qualitative study

<p>Background: Fatigue is a major component of living with ankylosing spondylitis (AS), though it has been largely over-looked, and currently there are no specific agreed management strategies.</p> <p>Methods: This qualitative exploratory study involved participants who are members of an existing population-based ankylosing spondylitis (PAS) cohort. Participants residing in South West Wales were invited to participate in a focus group to discuss; (1) effects of fatigue, (2) self-management strategies and (3) potential future interventions. The focus groups were audio-recorded and the transcripts were analysed using thematic analysis.</p> <p>Results: Participants consisted of 3 males/4 females (group 1) and 4 males/3 females (group 2), aged between 35 and 73 years (mean age 53 years). Three main themes were identified: (1) The effects of fatigue were multi-dimensional with participants expressing feelings of being ‘drained’ (physical), ‘upset’ (emotional) and experiencing ‘low-mood’ (psychological); (2) The most commonly reported self-management strategy for fatigue was a balanced combination of activity (exercise) and rest. Medication was reluctantly taken due to side-effects and worries over dependency; (3) Participants expressed a preference for psychological therapies rather than pharmacological for managing fatigue. Information on Mindfulness-Based Stress Reduction (MBSR) was received with interest, with recommendations for delivery in a group format with the option of distance-based delivery for people who were not able to attend a group course.</p> <p>Conclusions: Patients frequently try and manage their fatigue without any formal guidance or support. Our research indicates there is a need for future research to focus on psychological interventions to address the multi-faceted aspects of fatigue in AS.</p&gt

High-Power Solar Electric Propulsion for Future NASA Missions

NASA has sought to utilize high-power solar electric propulsion as means of improving the affordability of in-space transportation for almost 50 years. Early efforts focused on 25 to 50 kilowatt systems that could be used with the Space Shuttle, while later efforts focused on systems nearly an order of magnitude higher power that could be used with heavy lift launch vehicles. These efforts never left the concept development phase in part because the technology required was not sufficiently mature. Since 2012 the NASA Space Technology Mission Directorate has had a coordinated plan to mature the requisite solar array and electric propulsion technology needed to implement a 30 to 50 kilowatt solar electric propulsion technology demonstration mission. Multiple solar electric propulsion technology demonstration mission concepts have been developed based on these maturing technologies with recent efforts focusing on an Asteroid Redirect Robotic Mission. If implemented, the Asteroid Redirect Vehicle will form the basis for a capability that can be cost-effectively evolved over time to provide solar electric propulsion transportation for a range of follow-on mission applications at power levels in excess of 100 kilowatts

Challenges to discussing palliative care with people experiencing homelessness: a qualitative study

OBJECTIVES: To explore the views and experiences of people who are homeless and those supporting them regarding conversations and approaches to palliative care SETTING: Data were collected between October 2015 and October 2016 in homeless hostels and day centres and with staff from primary and secondary healthcare providers and social care services from three London boroughs. PARTICIPANTS: People experiencing homelessness (n=28), formerly homeless people (n=10), health and social care providers (n=48), hostel staff (n=30) and outreach staff (n=10). METHODS: In this qualitative descriptive study, participants were recruited to interviews and focus groups across three London boroughs. Views and experiences of end-of-life care were explored with people with personal experience of homelessness, health and social care professionals and hostel and outreach staff. Saturation was reached when no new themes emerged from discussions. RESULTS: 28 focus groups and 10 individual interviews were conducted. Participants highlighted that conversations exploring future care preferences and palliative care with people experiencing homelessness are rare. Themes identified as challenges to such conversations included attitudes to death; the recovery focused nature of services for people experiencing homelessness; uncertainty regarding prognosis and place of care; and fear of negative impact. CONCLUSIONS: This research highlights the need for a different approach to supporting people who are homeless and are experiencing advanced ill health, one that incorporates uncertainty and promotes well-being, dignity and choice. We propose parallel planning and mapping as a way of working with uncertainty. We acknowledge that these approaches will not always be straightforward, nor will they be suitable for everyone, yet moving the focus of conversations about the future away from death and dying, towards the present and the future may facilitate conversations and enable the wishes of people who are homeless to be known and explored