Characterization of Propellant Flow and Bias Required to Initiate an Arc Discharge in a Heaterless Hollow Cathode

Heaterless hollow cathodes provide an opportunity to reduce complexity and improve reliability in electric propulsion systems. While removal of the heater has little effect on steady-state operation of a hollow cathode, it has a considerable effect on the ignition process. To successfully integrate a heaterless hollow cathode into a spaceflight electric propulsion system, it will be necessary to establish definitive requirements for the propellant feed and electrical subsystems so that ignition of a plasma discharge can be achieved reliably. The aim of this research was to form a better understanding of these requirements by performing an investigation of the propellant flow and voltage conditions required for the ignition of a plasma arc discharge. This aim was achieved by performing discharge initiation experiments using both a specially designed experimental apparatus and a functional heaterless hollow cathode assembly. It was demonstrated that there is a distinct difference in the voltage required to initiate a plasma discharge between two common electric propulsion propellants, xenon and krypton, which suggests that the developmental testing of heaterless hollow cathodes needs to be performed with the appropriate propellant gas species. Heaterless hollow cathode ignition experiments showed that the keeper orifice diameter has a strong effect on the voltage required to ignite a plasma discharge at a given propellant mass flow rate, while the effect of keeper-cathode separation distance was only strong at flow rates below 25 sccm (Xe)

Planetary Science Technology Infusion Study: Findings and Recommendations Status

The Planetary Science Division (PSD) within the National Aeronautics and Space Administrations (NASA) Science Mission Directorate (SMD) at NASA Headquarters sought to understand how to better realize a scientific return on spacecraft system technology investments currently being funded. In order to achieve this objective, a team at NASA Glenn Research Center was tasked with surveying the science and mission communities to collect their insight on technology infusion and additionally sought inputs from industry, universities, and other organizations involved with proposing for future PSD missions. This survey was undertaken by issuing a Request for Information (RFI) activity that requested input from the proposing community on present technology infusion efforts. The Technology Infusion Study was initiated in March 2013 with the release of the RFI request. The evaluation team compiled and assessed this input in order to provide PSD with recommendations on how to effectively infuse new spacecraft systems technologies that it develops into future competed missions enabling increased scientific discoveries, lower mission cost, or both. This team is comprised of personnel from the Radioisotope Power Systems (RPS) Program and the In-Space Propulsion Technology (ISPT) Program staff.The RFI survey covered two aspects of technology infusion: 1) General Insight, including: their assessment of barriers to technology infusion as related to infusion approach; technology readiness; information and documentation products; communication; integration considerations; interaction with technology development areas; cost-capped mission areas; risk considerations; system level impacts and implementation; and mission pull. 2) Specific technologies from the most recent PSD Announcements of Opportunities (AOs): The Advanced Stirling Radioisotope Generator (ASRG), aerocapture and aeroshell hardware technologies, the NASA Evolutionary Xenon Thruster (NEXT) ion propulsion system, and the Advanced Materials Bi-propellant Rocket (AMBR) engine.This report will present the teams Findings from the RFI inputs and the recommendations that arose from these findings. Methodologies on the findings and recommendations development are discussed

Dynamic concentration of motors in microtubule arrays

We present experimental and theoretical studies of the dynamics of molecular motors in microtubule arrays and asters. By solving a convection-diffusion equation we find that the density profile of motors in a two-dimensional aster is characterized by continuously varying exponents. Simulations are used to verify the assumptions of the continuum model. We observe the concentration profiles of kinesin moving in quasi two-dimensional artificial asters by fluorescent microscopy and compare with our theoretical results.Comment: 4pages, 4 figures revte

Calendar 2015

Item does not contain fulltextBACKGROUND: Children of patients with young onset dementia (YOD) who are confronted with a parent who has a progressive disease, often assist in caregiving tasks, which may have a great impact on their lives. The objective of the present study is to explore the experiences of children living with a young parent with dementia with a specific focus on the children's needs. METHODS: Semi-structured interviews with 14 adolescent children between the ages of 15 and 27 years of patients with YOD were analyzed using inductive content analysis. Themes were identified based on the established codes. RESULTS: The emerging categories were divided into three themes that demonstrated the impact of dementia on daily life, different ways of coping with the disease, and children's need for care and support. The children had difficulties managing all of the responsibilities and showed concerns about their future. To deal with these problems, they demonstrated various coping styles, such as avoidant or adaptive coping. Although most children were initially reluctant to seek professional care, several of them expressed the need for practical guidance to address the changing behavior of their parent. The children felt more comfortable talking to someone who was familiar with their situation and who had specific knowledge of YOD and the available services. CONCLUSION: In addition to practical information, more accessible and specific information about the diagnosis and the course of YOD is needed to provide a better understanding of the disease for the children. These findings underline the need for a personal, family-centered approach

Telefonisch Interview Cognitieve Status (TICS): psychometrische aspecten

Het Telefonisch Interview Cognitieve Status (TICS) is een telefonisch screeningsinstrument voor dementie bij ouderen. Hoewel in buitenlands onderzoek de psychometrische kwaliteiten zijn beschreven, zijn deze voor de Nederlandse versie onbekend. In deze studie wordt de Nederlandse versie van de TICS gepresenteerd en worden de betrouwbaarheid en de validiteit beschreven bij 51 patiënten die afkomstig zijn van het Diagnostisch Onderzoekscentrum voor Psychogeriatrische patiënten (N=24) en de Geheugenpoli (N=27) van het Academisch Ziekenhuis Maastricht. De Pearson correlatie en de intraclass correlatie voor de test-hertestbetrouwbaarheid bedroegen respectievelijk 0,93 en 0,92. De Pearson correlatie en de intraclass correlatie voor de interbeoordelaarsbetrouwbaarheid bedroegen respectievelijk 0,91 en 0,90. De sensitiviteit en de specificiteit zijn onderzocht door de verschillende afkappunten op de TICS te vergelijken met het afkappunt 23/24 op de Mini Mental State Examination (MMSE) en de diagnose dementie volgens de DSM-IV. Bij het afkappunt 26/27 op de TICS bedroegen de sensitiviteit en de specificiteit in alle gevallen 0,80 of meer. Het percentage onder de ROC bedroeg 90% en 93% met de MMSE, respectievelijk de diagnose dementie als criterium. Conclusie: de TICS is acceptabel voor het screenen op dementie bij ouderen. De TICS kan vooral efficiënt of bruikbaar zijn in onderzoekssituaties waar een persoonlijk contact niet mogelijk is

Optimizing the use of expert panel reference diagnoses in diagnostic studies of multidimensional syndromes

__Abstract__ Background: In the absence of a gold standard, a panel of experts can be invited to assign a reference diagnosis for use in research. Available literature offers limited guidance on assembling and working with an expert panel for this purpose. We aimed to develop a protocol for an expert panel consensus diagnosis and evaluated its applicability in a pilot project. Methods: An adjusted Delphi method was used, which started with the assessment of clinical vignettes by 3 experts individually, followed by a consensus discussion meeting to solve diagnostic discrepancies. A panel facilitator ensured that all experts were able to express their views, and encouraged the use of argumentation to arrive at a specific diagnosis, until consensus was reached by all experts. Eleven vignettes of patients suspected of having a primary neurodegenerative disease were presented to the experts. Clinical information was provided stepwise and included medical history, neurological, physical and cognitive function, brain MRI scan, and follow-up assessments over 2 years. After the consensus discussion meeting, the procedure was evaluated by the experts. Results: The average degree of consensus for the reference diagnosis increased from 52% after individual assessment of the vignettes to 94% after the consensus discussion meeting. Average confidence in the diagnosis after individual assessment was 85%. This did not increase after the consensus discussion meeting. The process evaluation led to several recommendations for improvement of the protocol. Conclusion: A protocol for attaining a reference diagnosis based on expert panel consensus was shown feasible in research practice

Description and dosimetric verification of the PEREGRINE Monte Carlo dose calculation system for photon beams incident on a water phantom

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134919/1/mp1551.pd