Development of a direct evaporation bismuth Hall thruster

Hall thrusters have been under active development around the world since the 1960’s. Thrusters using traditional propellants such as xenon have been flown on a variety of satellite orbit raising and maintenance missions with an excellent record. To expand the mission envelope, it is necessary to lower the specific impulse of the thrusters but xenon and krypton are poor performers at specific impulses below 1,200 seconds. To enhance low specific impulse performance, this dissertation examines the development of a Hall-effect thruster which uses bismuth as a propellant. Bismuth, the heaviest non-radioactive element, holds many advantages over noble gas propellants from an energetics as well as a practical economic standpoint. Low ionization energy, large electron-impact crosssection and high atomic mass make bismuth ideal for low-specific impulse applications. The primary disadvantage lies in the high temperatures which are required to generate the bismuth vapors. Previous efforts carried out in the Soviet Union relied upon the complete bismuth vaporization and gas phase delivery to the anode. While this proved successful, the power required to vaporize and maintain gas phase throughout the mass flow system quickly removed many of the efficiency gains expected from using bismuth. To solve these problems, a unique method of delivering liquid bismuth to the anode has been developed. Bismuth is contained within a hollow anode reservoir that is capped by a porous metallic disc. By utilizing the inherent waste heat generated in a Hall thruster, liquid bismuth is evaporated and the vapors pass through the porous disc into the discharge chamber. Due to the high temperatures and material compatibility requirements, the anode was fabricated out of pure molybdenum. The porous vaporizer was not available commercially so a method of creating a refractory porous plate with 40-50% open porosity was developed. Molybdenum also does not respond well to most forms of welding so a diffusion bonding process was also developed to join the molybdenum porous disc to the molybdenum anode. Operation of the direct evaporation bismuth Hall thruster revealed interesting phenomenon. By utilizing constant current mode on a discharge power supply, the discharge voltage settles out to a stable operating point which is a function of discharge current, anode face area and average pore size on the vaporizer. Oscillations with a 40 second period were also observed. Preliminary performance data suggests that the direct evaporation bismuth Hall thruster performs similar to xenon and krypton Hall thrusters. Plume interrogation with a Retarding Potential Analyzer confirmed that bismuth ions were being efficiently accelerated while Faraday probe data gave a view of the ion density in the exhausted plume.

Using a Prediction and Option Generation Paradigm to Understand Decision Making

In many complex and dynamic domains, the ability to generate and then select the appropriate course of action is based on the decision maker's "reading" of the situation--in other words, their ability to assess the situation and predict how it will evolve over the next few seconds. Current theories regarding option generation during the situation assessment and response phases of decision making offer contrasting views on the cognitive mechanisms that support superior performance. The Recognition-Primed Decision-making model (RPD; Klein, 1989) and Take-The-First heuristic (TTF; Johnson & Raab, 2003) suggest that superior decisions are made by generating few options, and then selecting the first option as the final one. Long-Term Working Memory theory (LTWM; Ericsson & Kintsch, 1995), on the other hand, posits that skilled decision makers construct rich, detailed situation models, and that as a result, skilled performers should have the ability to generate more of the available task-relevant options. The main goal of this dissertation was to use these theories about option generation as a way to further the understanding of how police officers anticipate a perpetrator's actions, and make decisions about how to respond, during dynamic law enforcement situations. An additional goal was to gather information that can be used, in the future, to design training based on the anticipation skills, decision strategies, and processes of experienced officers. Two studies were conducted to achieve these goals. Study 1 identified video-based law enforcement scenarios that could be used to discriminate between experienced and less-experienced police officers, in terms of their ability to anticipate the outcome. The discriminating scenarios were used as the stimuli in Study 2; 23 experienced and 26 less-experienced police officers observed temporally-occluded versions of the scenarios, and then completed assessment and response option-generation tasks. The results provided mixed support for the nature of option generation in these situations. Consistent with RPD and TTF, participants typically selected the first-generated option as their final one, and did so during both the assessment and response phases of decision making. Consistent with LTWM theory, participants--regardless of experience level--generated more task-relevant assessment options than task-irrelevant options. However, an expected interaction between experience level and option-relevance was not observed. Collectively, the two studies provide a deeper understanding of how police officers make decisions in dynamic situations. The methods developed and employed in the studies can be used to investigate anticipation and decision making in other critical domains (e.g., nursing, military). The results are discussed in relation to how they can inform future studies of option-generation performance, and how they could be applied to develop training for law enforcement officers.

Polychoral performance practice and maestro di cappella conducting

Abstract This article disputes some basic questions concerning the coordination of seventeenth century sacred music, approaching the phenomenon through a musical species of particular interest, though largely unstudied from a performance practice point of view. Roman polychorality with its specific performing conditions offers an illuminating perspective on principles of musical direction and interaction which differ significantly from our modern access path towards these topics. The inquiry ranges from basics of performance (such as sheet music, rehearsals, direction technics, models and stylistic conditioning of the performers) over the concrete role of the maestro di cappella as well as the tactus as cornerstones of sacred music practice, up to the philosophical content the particular 'system of values', shining though this overall picture, seems to represent. On this groundwork the essay opens a discussion on conventions which have remained literally unchallenged by generations of researchers and performers.

Can a novel web-based computer test predict poor simulated driving performance? A pilot study with healthy and cognitive-impaired participants

BACKGROUND Driving a car is a complex instrumental activity of daily living and driving performance is very sensitive to cognitive impairment. The assessment of driving-relevant cognition in older drivers is challenging and requires reliable and valid tests with good sensitivity and specificity to predict safe driving. Driving simulators can be used to test fitness to drive. Several studies have found strong correlation between driving simulator performance and on-the-road driving. However, access to driving simulators is restricted to specialists and simulators are too expensive, large, and complex to allow easy access to older drivers or physicians advising them. An easily accessible, Web-based, cognitive screening test could offer a solution to this problem. The World Wide Web allows easy dissemination of the test software and implementation of the scoring algorithm on a central server, allowing generation of a dynamically growing database with normative values and ensures that all users have access to the same up-to-date normative values. OBJECTIVE In this pilot study, we present the novel Web-based Bern Cognitive Screening Test (wBCST) and investigate whether it can predict poor simulated driving performance in healthy and cognitive-impaired participants. METHODS The wBCST performance and simulated driving performance have been analyzed in 26 healthy younger and 44 healthy older participants as well as in 10 older participants with cognitive impairment. Correlations between the two tests were calculated. Also, simulated driving performance was used to group the participants into good performers (n=70) and poor performers (n=10). A receiver-operating characteristic analysis was calculated to determine sensitivity and specificity of the wBCST in predicting simulated driving performance. RESULTS The mean wBCST score of the participants with poor simulated driving performance was reduced by 52%, compared to participants with good simulated driving performance (P<.001). The area under the receiver-operating characteristic curve was 0.80 with a 95% confidence interval 0.68-0.92. CONCLUSIONS When selecting a 75% test score as the cutoff, the novel test has 83% sensitivity, 70% specificity, and 81% efficiency, which are good values for a screening test. Overall, in this pilot study, the novel Web-based computer test appears to be a promising tool for supporting clinicians in fitness-to-drive assessments of older drivers. The Web-based distribution and scoring on a central computer will facilitate further evaluation of the novel test setup. We expect that in the near future, Web-based computer tests will become a valid and reliable tool for clinicians, for example, when assessing fitness to drive in older drivers.

Is choking under pressure a consequence of skill-focus or increased distractibility? Results from a tennis serve task

It has been repeatedly demonstrated that athletes often choke in high pressure situations because anxiety can affect attention regulation and in turn performance. There are two competing theoretical approaches to explain the negative anxiety-performance relationship. According to skillfocus theories, anxious athletes’ attention is directed at how to execute the sport-specific movements which interrupts execution of already automatized movements in expert performers. According to distraction theories, anxious athletes are distractible and focus less on the relevant stimuli. We tested these competing assumptions in a between-subject design, as semi-professional tennis players were either assigned to an anxiety group (n = 25) or a neutral group (n = 28), and performed a series of second tennis serves into predefined target areas. As expected, anxiety was negatively related to serve accuracy. However, mediation analyses with the bootstrapping method revealed that this relationship was fully mediated by self-reported distraction and not by skill-focus.

Performing ‘Readings’: The Interplay of Theatre And Digital Comics In Tezuka

The article investigates the intriguing interplay of digital comics and live-action elements in a detailed performance analysis of TeZukA (2011) by choreographer Sidi Larbi Cherkaoui. This dance theatre production enacts the life story of Osamu Tezuka and some of his famous manga characters, interweaving performers and musicians with large-scale projections of the mangaka’s digitised comics. During the show, the dancers perform different ‘readings’ of the projected manga imagery: e.g. they swipe panels as if using portable touchscreen displays, move synchronously to animated speed lines, and create the illusion of being drawn into the stories depicted on the screen. The main argument is that TeZukA makes visible, demonstrates and reflects upon different ways of delivering, reading and interacting with digital comics. In order to verify this argument, the paper uses ideas developed in comics and theatre studies to draw more specifically on the use of digital comics in this particular performance.

Critical indicators associated with negative performance in a selectively manned unit

Introduction. Selectively manned units have a long, international history, both military and civilian. Some examples include SWAT teams, firefighters, the FBI, the DEA, the CIA, and military Special Operations. These special duty operators are individuals who perform a highly skilled and dangerous job in a unique environment. A significant amount of money is spent by the Department of Defense (DoD) and other federal agencies to recruit, select, train, equip and support these operators. When a critical incident or significant life event occurs, that jeopardizes an operator's performance; there can be heavy losses in terms of training, time, money, and potentially, lives. In order to limit the number of critical incidents, selection processes have been developed over time to “select out” those individuals most likely to perform below desired performance standards under pressure or stress and to "select in" those with the "right stuff". This study is part of a larger program evaluation to assess markers that identify whether a person will fail under the stresses in a selectively manned unit. The primary question of the study is whether there are indicators in the selection process that signify potential negative performance at a later date. ^ Methods. The population being studied included applicants to a selectively manned DoD organization between 1993 and 2001 as part of a unit assessment and selection process (A&S). Approximately 1900 A&S records were included in the analysis. Over this nine year period, seventy-two individuals were determined to have had a critical incident. A critical incident can come in the form of problems with the law, personal, behavioral or family problems, integrity issues, and skills deficit. Of the seventy-two individuals, fifty-four of these had full assessment data and subsequent supervisor performance ratings which assessed how an individual performed while on the job. This group was compared across a variety of variables including demographics and psychometric testing with a group of 178 individuals who did not have a critical incident and had been determined to be good performers with positive ratings by their supervisors.^ Results. In approximately 2004, an online pre-screen survey was developed in the hopes of preselecting out those individuals with items that would potentially make them ineligible for selection to this organization. This survey has aided the organization to increase its selection rates and save resources in the process. (Patterson, Howard Smith, & Fisher, Unit Assessment and Selection Project, 2008) When the same prescreen was used on the critical incident individuals, it was found that over 60% of the individuals would have been flagged as unacceptable. This would have saved the organization valuable resources and heartache.^ There were some subtle demographic differences between the two groups (i.e. those with critical incidents were almost twice as likely to be divorced compared with the positive performers). Upon comparison of Psychometric testing several items were noted to be different. The two groups were similar when their IQ levels were compared using the Multidimensional Aptitude Battery (MAB). When looking at the Minnesota Multiphasic Personality Inventory (MMPI), there appeared to be a difference on the MMPI Social Introversion; the Critical Incidence group scored somewhat higher. When analysis was done, the number of MMPI Critical Items between the two groups was similar as well. When scores on the NEO Personality Inventory (NEO) were compared, the critical incident individuals tended to score higher on Openness and on its subscales (Ideas, Actions, and Feelings). There was a positive correlation between Total Neuroticism T Score and number of MMPI critical items.^ Conclusions. This study shows that the current pre-screening process is working and would have saved the organization significant resources. ^ If one was to develop a profile of a candidate who potentially could suffer a critical incident and subsequently jeopardize the unit, mission and the safety of the public they would look like the following: either divorced or never married, score high on the MMPI in Social Introversion, score low on MMPI with an "excessive" amount of MMPI critical items; and finally scores high on the NEO Openness and subscales Ideas, Feelings, and Actions.^ Based on the results gleaned from the analysis in this study there seems to be several factors, within psychometric testing, that when taken together, will aid the evaluators in selecting only the highest quality operators in order to save resources and to help protect the public from unfortunate critical incidents which may adversely affect our health and safety.^

Commentary on "Alternative Strategies for Identifying High-Performing Charter Schools in Texas"

In the last few years policy makers and practitioners nationally have shown much interest in identifying, recognizing, and replicating successful charter schools, many of which are showing that they can educate low-income and otherwise at-risk students remarkably well. However past efforts to identify high performing schools have been problematic. Using these systematic, rigorous value-added methods, the authors identify 44 Open Enrollment charter schools that merit a “high-performer” rating. Nearly all of those campuses identified serve a disadvantaged student population. The article also finds that most of those high performers are highly cost-effective, earning high ratings on the cost-efficiency measures. The authors argue for more widespread use of value-added modeling in the state accountability system. The approach taken to identifying high-performers is sensible and fair, but any formulaic approach to school labels comes with some limitations.

Historia de un joven músico belga : anécdotas y testimonios sobre Julio Perceval en Bruselas y en Buenos Aires

Este artículo está dedicado a Julio Perceval (1903-1963) músico de origen belga que se radicó en la Argentina en 1926. Se ha enfocado en las etapas de su formación en Bruselas y su desarrollo profesional en Buenos Aires por medio de testimonios aportados por quienes compartieron el periodo de búsquedas juveniles del compositor. Para reconstruir el ambiente musical en la etapa belga han sido consultados trabajos de Robert Wangermée, en tanto que para conocer sus relaciones con colegas e intérpretes en Buenos Aires se ha contado con material del Archivo donado por la familia del músico a la Facultad de Artes y Diseño de la UNCuyo.

Recuerdos, espejos y lugares en el teatro comunitario argentino contemporáneo : Memoria colectiva, identidades y espacios público en las prácticas del Grupo de Teatro Popular de Sansinea [2010-2012]

La tesis de maestría 'Recuerdos, espejos y lugares en el teatro comunitario argentino contemporáneo. Memoria colectiva, identidades, y espacio público en las prácticas del Grupo de Teatro Popular de Sansinena [2010-2012]', indaga en las operaciones de memoria, la constitución de identidades y los procesos construcción/ reapropiación del espacio público, que tienen lugar en las prácticas de este grupo de teatro. Dentro del proceso de creación colectiva de la obra, se reconstruyen interpretaciones del pasado compartido, tensiones que dan cuenta de las lógicas que estructuran la selección de los hechos a contar, valores y representaciones que visibilizan un modo de percibir/ construir las identidades. El Grupo de Teatro Popular de Sansinena, la primera organización social que existe en el pueblo, configura un experiencia colectiva novedosa, que instaura nuevas lógicas de sociabilidad, genera vínculos con el 'afuera' y reivindica la bandera de resistencia y el reclamo de visibilización a través de la práctica cultural. Dentro de las dinámicas relacionales que atraviesan el grupo, observamos ciertas tendencias jerárquicas en los vínculos entre la directora y los vecinos que conforman el grupo 'lo que se percibe como una dificultad a superar- estructuradas en el fuerte liderazgo construido por la directora. Una Legitimidad configurada sobre los saberes reconocidos, virtudes heredadas y capacidades comprobadas en la práctica, que se perciben en los testimonios de los vecinos-actores. La conformación del Grupo de Teatro Comunitario de Rivadavia -compuesto por doscientos vecinos de seis pueblos del Partido de Rivadavia (incluido Sansinena)-, da cuenta de los alcances de este fenómeno, que deberá seguir estudiándose desde diversas perspectivas, a fin de visibilizar la relevancia que esta práctica cultural adquiere, tanto a nivel local como nacional

En los albores de la celestinesca : Sobre el "Romance nuevamente hecho de Calisto y Melibea" en el pliego suelto de 1513

El Romance nueuamente hecho de Calisto y Melibea, pliego suelto impreso en 1513 (Jacobo Cromberger, Sevilla), un "romance-cuento" (según Menéndez Pidal) de 680 versos octosilábicos, atestigua una pronta transformación genérica: de la prosa dramática de Celestina a un poema narrativo con narrador extradiegético. La trama concisa incluye los típicos motivos narrativos del romancero hispánico (por ejemplo, el protagonista como un cazador) y acentúa el tema del pecado y el castigo (tomado de los paratextos de Celestina), también presente en los primeros pliegos sueltos cantados por ciegos. Existen evidencias de que el texto base ha sido la Comedia, no la Tragicomedia. Este texto temprano debería ser considerado un hito en la historia de la celestinesca

La intertextualidad en la copla popular de México

La intertextualidad en la lírica tradicional y popular surge como resultado de dos fenómenos: el surgimiento de una canción nueva (canciones contrahechas), en especial como parodia de la primera, y cuando una canción menciona a otra, creando una complicidad entre los intérpretes y el público durante la performance

Recuerdos, espejos y lugares en el teatro comunitario argentino contemporáneo : Memoria colectiva, identidades y espacios público en las prácticas del Grupo de Teatro Popular de Sansinea [2010-2012]

La tesis de maestría 'Recuerdos, espejos y lugares en el teatro comunitario argentino contemporáneo. Memoria colectiva, identidades, y espacio público en las prácticas del Grupo de Teatro Popular de Sansinena [2010-2012]', indaga en las operaciones de memoria, la constitución de identidades y los procesos construcción/ reapropiación del espacio público, que tienen lugar en las prácticas de este grupo de teatro. Dentro del proceso de creación colectiva de la obra, se reconstruyen interpretaciones del pasado compartido, tensiones que dan cuenta de las lógicas que estructuran la selección de los hechos a contar, valores y representaciones que visibilizan un modo de percibir/ construir las identidades. El Grupo de Teatro Popular de Sansinena, la primera organización social que existe en el pueblo, configura un experiencia colectiva novedosa, que instaura nuevas lógicas de sociabilidad, genera vínculos con el 'afuera' y reivindica la bandera de resistencia y el reclamo de visibilización a través de la práctica cultural. Dentro de las dinámicas relacionales que atraviesan el grupo, observamos ciertas tendencias jerárquicas en los vínculos entre la directora y los vecinos que conforman el grupo 'lo que se percibe como una dificultad a superar- estructuradas en el fuerte liderazgo construido por la directora. Una Legitimidad configurada sobre los saberes reconocidos, virtudes heredadas y capacidades comprobadas en la práctica, que se perciben en los testimonios de los vecinos-actores. La conformación del Grupo de Teatro Comunitario de Rivadavia -compuesto por doscientos vecinos de seis pueblos del Partido de Rivadavia (incluido Sansinena)-, da cuenta de los alcances de este fenómeno, que deberá seguir estudiándose desde diversas perspectivas, a fin de visibilizar la relevancia que esta práctica cultural adquiere, tanto a nivel local como nacional

En los albores de la celestinesca : Sobre el "Romance nuevamente hecho de Calisto y Melibea" en el pliego suelto de 1513

El Romance nueuamente hecho de Calisto y Melibea, pliego suelto impreso en 1513 (Jacobo Cromberger, Sevilla), un "romance-cuento" (según Menéndez Pidal) de 680 versos octosilábicos, atestigua una pronta transformación genérica: de la prosa dramática de Celestina a un poema narrativo con narrador extradiegético. La trama concisa incluye los típicos motivos narrativos del romancero hispánico (por ejemplo, el protagonista como un cazador) y acentúa el tema del pecado y el castigo (tomado de los paratextos de Celestina), también presente en los primeros pliegos sueltos cantados por ciegos. Existen evidencias de que el texto base ha sido la Comedia, no la Tragicomedia. Este texto temprano debería ser considerado un hito en la historia de la celestinesca

La intertextualidad en la copla popular de México

La intertextualidad en la lírica tradicional y popular surge como resultado de dos fenómenos: el surgimiento de una canción nueva (canciones contrahechas), en especial como parodia de la primera, y cuando una canción menciona a otra, creando una complicidad entre los intérpretes y el público durante la performance