Choice of Observing Schedules for Astrometric Planet Searches

The Space Interferometry Mission (SIM) will make precise astrometric measurements that can be used to detect planets around nearby stars. Since observational time will be extremely valuable, it is important to consider how the choice of the observing schedule influences the efficiency of SIM planet searches. We have conducted Monte Carlo simulations of astrometric observations to understand the effects of different scheduling algorithms. We find that the efficiency of planet searches is relatively insensitive to the observing schedule for most reasonable observing schedules.Comment: 29 pages, 9 figures, 2 tables, to be published in PAS

The Effects of Multiple Companions on the Efficiency of the SIM Planet Searches

The Space Interferometry Mission (SIM) is expected to make precise astrometric measurements that can be used to detect low mass planets around nearby stars. Since most nearby stars are members of multiple star systems, many stars will have a measurable acceleration due to their companion, which must be included when solving for astrometric parameters and searching for planetary perturbations. Additionally, many of the stars with one radial velocity planet show indications of additional planets. Therefore, astrometric surveys like SIM must be capable of detecting planets and measuring orbital parameters in systems with multiple stellar and/or planetary companions. We have conducted Monte Carlo simulations to investigate how the presence of multiple companions affects the sensitivity of an astrometric survey such as SIM. We find that the detection efficiency for planets in wide binary systems is relatively unaffected by the presence of a binary companion, if the planetary orbital period is less than half the duration of the astrometric survey. For longer orbital periods, there are significant reductions in the sensitivity of an astrometric survey. Additionally, we find that the signal required to detect a planet can be increased significantly due to the presence of an additional planet orbiting the same star. Fortunately, adding a modest number of precision radial velocity observations significantly improves the sensitivity for many multiple planet systems. Thus, the combination of radial velocity observations and astrometric observations by SIM will be a particularly valuable for studying multiple planet systems.Comment: 45 pages, 16 figures, 1 table, to appear in PAS

Thermal comfort guidelines for production spaces within multi-storey garment factories located in Bangladesh

This research presents extensive field data on indoor thermal conditions along with workers' comfort votes taken at their workstations within three existing multi-storied garment factories during the three seasons (cool-dry, hot-dry and warm-humid) of Bangladesh. The main objective of the study was to observe the impact of thermal conditions on workers’ indoor thermal perception during each season of a year and from this identify thermal comfort guidelines (e.g. neutral temperatures, comfort ranges, preferred airspeeds and directions) to execute their production work comfortably. Subjective votes were collected from a total of 908 workers with the thermal data, physiological data and adaptive measures recorded simultaneously. Statistical analyses revealed that workers can accept a wider and relatively higher comfort range than the predicted band during cool-dry and hot-dry seasons, for instance, 22.7–29.1 °C and 22.3–30.4 °C respectively. A narrower comfort band (e.g. 28.7–30.9 °C), close to the predicted range, was found during the warm-humid season, which can be maintained by reducing radiant temperature and elevating airspeed. Further analyses indicated that workers prefer a mean airspeed of 0.3  m/s and comfort range of 0–3.0  m/s specific to their activities preferably from inlets located on south, north and east facades while upward and downward air movement, from for example ceiling fans, causes a rise of air temperature in the occupational zone and thermal discomfort. This research also suggested that the maximum distances of workstations from the ventilation inlets (windows) should be maintained at 12–18 m for sufficient cross ventilation, personal controls and adaptive opportunities to help maintain preferred thermal condition

Parallel Algorithm for Solving Kepler's Equation on Graphics Processing Units: Application to Analysis of Doppler Exoplanet Searches

[Abridged] We present the results of a highly parallel Kepler equation solver using the Graphics Processing Unit (GPU) on a commercial nVidia GeForce 280GTX and the "Compute Unified Device Architecture" programming environment. We apply this to evaluate a goodness-of-fit statistic (e.g., chi^2) for Doppler observations of stars potentially harboring multiple planetary companions (assuming negligible planet-planet interactions). We tested multiple implementations using single precision, double precision, pairs of single precision, and mixed precision arithmetic. We find that the vast majority of computations can be performed using single precision arithmetic, with selective use of compensated summation for increased precision. However, standard single precision is not adequate for calculating the mean anomaly from the time of observation and orbital period when evaluating the goodness-of-fit for real planetary systems and observational data sets. Using all double precision, our GPU code outperforms a similar code using a modern CPU by a factor of over 60. Using mixed-precision, our GPU code provides a speed-up factor of over 600, when evaluating N_sys > 1024 models planetary systems each containing N_pl = 4 planets and assuming N_obs = 256 observations of each system. We conclude that modern GPUs also offer a powerful tool for repeatedly evaluating Kepler's equation and a goodness-of-fit statistic for orbital models when presented with a large parameter space.Comment: 19 pages, to appear in New Astronom

Observational Constraints on Trojans of Transiting Extrasolar Planets

Theoretical studies predict that Trojans are likely a frequent byproduct of planet formation and evolution. We present a novel method of detecting Trojan companions to transiting extrasolar planets which involves comparing the time of central eclipse with the time of the stellar reflex velocity null. We demonstrate that this method offers the potential to detect terrestrial-mass Trojans using existing ground-based observatories. This method rules out Trojan companions to HD 209458b and HD 149026b more massive than ~13 Earth masses and \~25 Earth masses at a 99.9% confidence level. Such a Trojan would be dynamically stable, would not yet have been detected by photometric or spectroscopic monitoring, and would be unrecognizable from radial velocity observations alone. We outline the future prospects for this method, and show that the detection of a "Hot Trojan" of any mass would place a significant constraint on theories of orbital migration.Comment: 6 pages, 2 figures, 1 table, accepted to ApJL. Added references, new transiting planets to table; minor correction

The Nichols Wing Cutting Equipment

Described here is wing cutting equipment for the economical production of metal wings for wind tunnel models. The machine will make any size of constant-section wing or strut up to one-sixth inch chord by 36-inch span and up to a thickness of one and one-quarter inches. It cuts a smooth, true model that is accurate to within two-thousandths of an inch on any ordinate. The holding jaws are so designed as to leave the model free of chip marks, and the only hand finishing necessary after the cutting is a rub with amunite to remove burrs. The actual change on ordinate in this finishing rub is less than .0002 inches

Rotational equilibrium of C2 in interstellar clouds

In this work the understanding of the rotational equilibrium of C2 in interstellar clouds is updated. It is critical for this equilibrium to be well understood if C2 is to be used as a probe of the physical conditions in these clouds. Although new data continues to be published, the model was last updated in 1987. In this work, new data is collected and incorporated into the model using the program Radex, which will provide a standard format for sharing data, facilitate future updates, and enable the model to quickly run for a grid of temperature and density conditions

Thermal reactor

A thermal reactor apparatus and method of pyrolyticaly decomposing silane gas into liquid silicon product and hydrogen by-product gas is disclosed. The thermal reactor has a reaction chamber which is heated well above the decomposition temperature of silane. An injector probe introduces the silane gas tangentially into the reaction chamber to form a first, outer, forwardly moving vortex containing the liquid silicon product and a second, inner, rewardly moving vortex containing the by-product hydrogen gas. The liquid silicon in the first outer vortex deposits onto the interior walls of the reaction chamber to form an equilibrium skull layer which flows to the forward or bottom end of the reaction chamber where it is removed. The by-product hydrogen gas in the second inner vortex is removed from the top or rear of the reaction chamber by a vortex finder. The injector probe which introduces the silane gas into the reaction chamber is continually cooled by a cooling jacket