Systems Engineering of a Nuclear-Electric Spacecraft

Studies have shown that nuclear-electric propulsion systems will provide superior payload capability and unique advantages over chemical systems for high-energy deep-space missions. Conceptual design studies of unmanned spacecraft employing nuclear-electric propulsion systems have been undertaken to determine some of the major integration problems. Early recognition of these problems will help to stimulate the development effort that will be required to bring these systems into fruitful utilization. Typical designs under consideration for interplanetary missions for the next decade employ a nuclear reactor providing thermal energy to a turbogeneration system which, in turn, supplies electrical power to an ion engine for primary propulsion and additional utility power for guidance and control, powered-flight radio transmission, instrumentation, et cetera. The major systems and components which form a complete spacecraft are listed in this Report, and a review of the significant physical and operational characteristics of these various systems and components which affect spacecraft integration is made. Conceptual.configurations and detailed weight studies for a 60-kilowatts-electric Venus-capture spacecraft and a 1-megawattelectric Jupiter-capture spacecraft are shown to illustrate typical physical arrangements based on the various hardware constraints. From these configurations, the major development goals are ascertained and summarized

The impact of increased food availability on reproduction in a long-distance migratory songbird: implications for environmental change?

Many populations of migratory songbirds are declining or shifting in distribution. This is likely due to environmental changes that alter factors such as food availability that may have an impact on survival and/or breeding success. We tested the impact of experimentally supplemented food on the breeding success over three years of northern wheatears (Oenanthe oenanthe), a species in decline over much of Europe. The number of offspring fledged over the season was higher for food-supplemented birds than for control birds. The mechanisms for this effect were that food supplementation advanced breeding date, which, together with increased resources, allowed further breeding attempts. While food supplementation did not increase the clutch size, hatching success or number of chicks fledged per breeding attempt, it did increase chick size in one year of the study. The increased breeding success was greater for males than females; males could attempt to rear simultaneous broods with multiple females as well as attempting second broods, whereas females could only increase their breeding effort via second broods. Multiple brooding is rare in the study population, but this study demonstrates the potential for changes in food availability to affect wheatear breeding productivity, primarily via phenotypic flexibility in the number of breeding attempts. Our results have implications for our understanding of how wheatears may respond to natural changes in food availability due to climate changes or changes in habitat management

Choosing Your Moment: Interruptions in Multimedia Annotation.

In a cooperative mixed-initiative system, timely and effective dialogue between the system and user is important to ensure that both sides work towards producing the most effective results, and this is affected by how disruptive any interruptions are as the user completes their primary task. A disruptive interaction means the user may become irritated with the system, or might take longer to deal with the interruption and provide information that the system needs to continue. Disruption is influenced both by the nature of the interaction and when it takes place in the context of the user’s progress through their main task. We describe an experiment based on a prototype cooperative video annotation system designed to explore the impact of interruptions, in the form of questions posed by the system that the user must address. Our findings demonstrate a preference towards questions presented in context with the content of the video, rather than at the natural opportunities presented by transitions in the video. This differs from previous research which concentrates on interruptions in the form of notifications

Pretreatment with Naltrindole exhibits robust cardioprotection in an isolated rat heart model of ischemia-reperfusion injury

Previously, a novel three-amino acid peptide (tripeptide) that is structurally similar to other amino acid-based delta and kappa-opioid receptor agonists (the predominant opioid receptor subtypes in heart tissue) demonstrated a significant reduction in infarct size and improved cardiac function when administered during preconditioning in isolated rat hearts using the Langendorf model. The cardioprotective effects of tripeptide were blocked by naloxone (NX, broad-spectrum opioid antagonist) and nor-binaltorphine (BNI, kappa-opioid receptor antagonist), whereas naltrindole (NTI, delta-opioid receptor antagonist) seemed to augment the effects of tripeptide. To determine whether the cardioprotective effects of the combination were due to tripeptide or NTI, the effects of NTI and other opioid antagonists were evaluated individually in the same model. Therefore, the goal was to evaluate the effects of NTI, BNI, and NX independently. Hearts isolated from male Sprague-Dawley rats (~300g) were subjected to global ischemia (I, 30min)/reperfusion (R, 50min). NX (10 μM, n=6), BNI (5 μM, n=7), NTI (5 μM, n=8), or Krebs’ buffer control (control n=10) were given to the hearts 5 min prior to ischemia and during the first 5 min of reperfusion in a Langendorf model, perfused at a constant pressure of 80mmHg. Left ventricular (LV) functional indices were measured using an indwelling pressure transducer-tipped catheter. At the end of reperfusion (50min), hearts were frozen, sectioned (2 mm), and stained with 1% triphenyltetrazolium chloride (TTC). To determine infarct size, the weight of infarcted tissue was compared to total tissue at risk. All data were evaluated using ANOVA Student-Newman-Keuls post-hoc analysis. Control (untreated) hearts showed an elevated final LV end-diastolic pressure (LVEDP) of 60 ± 5 mmHg compared to an average initial baseline of 8 ± 1 mmHg (similar in all groups) and a mean infarct size of 36 ± 3% at 50 min post-reperfusion. NX and BNI demonstrated no significant cardioprotective effects compared to control with final LVEDP measures of 64 ± 8 mmHg and 61 ± 2 mmHg, respectively. Infarct size for NX (35 ± 5%) and BNI (36 ± 5%) treated hearts were similar to control hearts. By contrast, NTI significantly improved final LVEDP (17 ± 3mmHg) to near baseline values and reduced infarct size to 7 ± 2% compared to all groups (p\u3c 0.01). The results indicate that pretreatment with NTI can prevent I/R injury and restore post-reperfused heart function to near pre-ischemic levels. In future studies, we will evaluate the cardioprotective effects of NTI in an acute in vivo heart I/R model. In separate studies, we will attempt to determine the mechanism of action of NTI preconditioning, specifically whether cardioprotection is indeed mediated via delta receptor antagonism or via some other mechanism

Transition Matrix Monte Carlo Reweighting and Dynamics

We study an induced dynamics in the space of energy of single-spin-flip Monte Carlo algorithm. The method gives an efficient reweighting technique. This dynamics is shown to have relaxation times proportional to the specific heat. Thus, it is plausible for a logarithmic factor in the correlation time of the standard 2D Ising local dynamics.Comment: RevTeX, 5 pages, 3 figure