Considerations on the lubrication of spacecraft mechanisms

Space tribology and a number of precepts to guide designers in its application are discussed. Of the many techniques available all, without exception, have limitations in performance. Two processes are discussed in more detail and their limitations identified. Some performance results on a liquid space lubricant are given

GIOTTO's antenna de-spin mechanism: Ots lubrication and thermal vacuum performance

Except in the near Earth phase of GIOTTO's mission to Comet Halley, the HGA (high gain antenna) on board GIOTTO was the only designed means of up/down communications. The spacecraft spin stabilization required that the HGA be despun at the same rotational rate of nominally 15 rpm in order to keep the HGA pointing accurately to a Earth. A dual servomotor despin mechanism was designed and built by SEP of France for this purpose. The expected thermal environment suggested that dry lubrication was preferable to wet for the ball bearings but there existed no relevant data on the torque noise spectrum of candidate solid lubricants. Therefore ad hoc torque noise tests were run with two solid lubricants: ion plated lead film plus lead bronze cage (retainer) and a PTFE composite cage only. The lead lubrication showed the better spectrum up to the mission lifetime point so it was selected for continued test over some 20 times the Halley mission life, with periodic torque spectrum monitoring. The spectrum remained well within the pointing error budget over the 100 million revolutions covered

Time to plan and aggregate fluctuations

This article investigates the business cycle implications of the planning phase of business investment projects. Time to plan is built into a Kydland-Prescott time-to-build model, which assumes that investment projects take four periods to complete. In the Kydland-Prescott time-to-build model, resources for these projects flow uniformly across the four periods; in the time-to-plan model, few resources are used in the first period. The investigation determines that incorporating time to plan in this way improves the model's ability to account for three key features of U.S. business cycles: their persistence, or the fact that when output growth is above (or below) average, it tends to remain high (or low) for a few quarters; the fact that productivity leads hours worked over the business cycle; and the fact that business investment in structures and business investment in equipment lag output over the cycle.Business cycles

Autonomous power expert system

The goal of the Autonomous Power System (APS) program is to develop and apply intelligent problem solving and control technologies to the Space Station Freedom Electrical Power Systems (SSF/EPS). The objectives of the program are to establish artificial intelligence/expert system technology paths, to create knowledge based tools with advanced human-operator interfaces, and to integrate and interface knowledge-based and conventional control schemes. This program is being developed at the NASA-Lewis. The APS Brassboard represents a subset of a 20 KHz Space Station Power Management And Distribution (PMAD) testbed. A distributed control scheme is used to manage multiple levels of computers and switchgear. The brassboard is comprised of a set of intelligent switchgear used to effectively switch power from the sources to the loads. The Autonomous Power Expert System (APEX) portion of the APS program integrates a knowledge based fault diagnostic system, a power resource scheduler, and an interface to the APS Brassboard. The system includes knowledge bases for system diagnostics, fault detection and isolation, and recommended actions. The scheduler autonomously assigns start times to the attached loads based on temporal and power constraints. The scheduler is able to work in a near real time environment for both scheduling and dynamic replanning

USING CALLING ACTIVITY TO PREDICT CALLING ACTIVITY: A CASE STUDY WITH THE ENDANGERED HOUSTON TOAD (BUFO [ANAXYRUS] HOUSTONENSIS)

Understanding anuran calling activity patterns is important for maximizing efficiency and value of call survey data collection and analyses. Previous studies have primarily focused on identifying and quantifying abiotic variables that influence anuran calling activity, and investigating relationships between calling activity and population estimates. In this study we investigated the use of a predictor pond approach to guide call survey effort. In this approach, calling activity at a subset of breeding sites (e.g., ponds) is used as a predictor of calling activity at additional breeding sites, with the goal being to minimize sampling effort while simultaneously maximizing sampling efficiency. We explored the efficiency of this approach using call survey data collected on the endangered Houston Toad (Bufo [Anaxyrus] houstonensis) at 15 known breeding ponds over 9 survey years. We found that if calling activity at 3 predictor ponds was used to decide if additional call surveys would occur at the remaining 12 ponds, we would have hypothetically correctly assumed calling activity was not occurring at non-predictor ponds on 92.1% of survey nights, and we would have hypothetically detected 93.9% of the total number of detected individuals over the 9 survey years. We found the predictor pond approach performed well in our case study, and believe it could be a valuable tool for many anuran monitoring programs

Pilot study of the influence of self-coding on empathy within an introductory motivational interviewing training

Background: Motivational interviewing (MI) is a framework for addressing behavior change that is often used by healthcare professionals. Expression of empathy during MI is associated with positive client outcomes, while absence of empathy may produce iatrogenic effects. Although training in MI is linked to increased therapeutic empathy in learners, no research has investigated individual training components' contribution to this increase. The objective of this study was to test whether a self-coding MI exercise using smartphones completed at hour 6 of an 8-h MI training was superior in engendering empathy to training as usual (watching an MI expert perform in a video clip for the same duration at the same point in the training). Methods: This was a pilot study at two sites using randomization and control groups with 1:1 allocation. Allocation was achieved via computerized assignment (site 1, United Kingdom) or facedown playing card distribution (site 2, United States). Participants were 58 students attending a university class at one of two universities, of which an 8-h segment was dedicated to a standardized MI training. Fifty-five students consented to participate and were randomized. The intervention was an MI self-coding exercise using smartphone recording and a standardized scoring sheet. Students were encouraged to reflect on areas of potential improvement based on their self-coding results. The main outcome measure was score on the Helpful Responses Questionnaire, a measure of therapeutic empathy, collected prior to and immediately following the 8-h training. Questionnaire coding was completed by 2 blinded external reviewers and assessed for interrater reliability, and students were assigned averaged empathy scores from 6 to 30. Analyses were conducted via repeated-measures ANOVA using the general linear model. Results: Fifty-five students were randomized, and 2 were subsequently excluded from analysis at site 2 due to incomplete questionnaires. The study itself was feasible, and overall therapeutic empathy increased significantly and substantially among students. However, the intervention was not superior to the control condition in this study. Conclusions: Replacing a single passive learning exercise with an active learning exercise in an MI training did not result in a substantive boost to therapeutic empathy. However, consistently with prior research, this study identified significant overall increases in empathy following introductory MI training. A much larger study examining the impact of selected exercises and approaches would likely be useful and informative

Statistical stability of equilibrium states for interval maps

We consider families of multimodal interval maps with polynomial growth of the derivative along the critical orbits. For these maps Bruin and Todd have shown the existence and uniqueness of equilibrium states for the potential $\phi_t:x\mapsto-t\log|Df(x)|$, for $t$ close to 1. We show that these equilibrium states vary continuously in the weak$^*$ topology within such families. Moreover, in the case $t=1$, when the equilibrium states are absolutely continuous with respect to Lebesgue, we show that the densities vary continuously within these families.Comment: More details given and the appendices now incorporated into the rest of the pape

Evidence for Correlated Titanium and Deuterium Depletion in the Galactic ISM

Current measurements indicate that the deuterium abundance in diffuse interstellar gas varies spatially by a factor of ~4 among sightlines extending beyond the Local Bubble. One plausible explanation for the scatter is the variable depletion of D onto dust grains. To test this scenario, we have obtained high signal-to-noise, high resolution profiles of the refractory ion TiII along seven Galactic sightlines with D/H ranging from 0.65 to 2.1x10^-5. These measurements, acquired with the recently upgraded Keck/HIRES spectrometer, indicate a correlation between Ti/H and D/H at the >95% c.l. Therefore, our observations support the interpretation that D/H scatter is associated with differential depletion. We note, however, that Ti/H values taken from the literature do not uniformly show the correlation. Finally, we identify significant component-to-component variations in the depletion levels among individual sightlines and discuss complications arising from this behavior.Comment: 4 pages; Accepted to Astrophysical Journal Letter

Neutron-Rich Nuclei in Heaven and Earth

An accurately calibrated relativistic parametrization is introduced to compute the ground state properties of finite nuclei, their linear response, and the structure of neutron stars. While similar in spirit to the successful NL3 parameter set, it produces an equation of state that is considerably softer -- both for symmetric nuclear matter and for the symmetry energy. This softening appears to be required for an accurate description of several collective modes having different neutron-to-proton ratios. Among the predictions of this model are a symmetric nuclear-matter incompressibility of K=230 MeV and a neutron skin thickness in 208Pb of Rn-Rp=0.21 fm. Further, the impact of such a softening on the properties of neutron stars is as follows: the model predicts a limiting neutron star mass of Mmax=1.72 Msun, a radius of R=12.66 km for a ``canonical'' M=1.4 Msun neutron star, and no (nucleon) direct Urca cooling in neutrons stars with masses below M=1.3 Msun.Comment: 4 pages, 3 tables, and no figure

A study of search directions in primal-dual interior-point methods for semidefinite programming

A study of search directions in primal-dual interior-point methods for semidefinite programmin