Reducing Crop Production Cost

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Theoretical Isochrones with Extinction in the K Band. II. J - K versus K

We calculate theoretical isochrones in a consistent way for five filter pairs near the J and K band atmospheric windows (J-K, J-K', J-Ks, F110W-F205W, and F110W-F222M) using the Padova stellar evolutionary models of Girardi et al. We present magnitude transformations between various K-band filters as a function of color. Isochrones with extinction of up to 6 mag in the K band are also presented. As found for the filter pairs composed of H & K band filters, we find that the reddened isochrones of different filter pairs behave as if they follow different extinction laws, and that the extinction curves of Hubble Space Telescope NICMOS filter pairs in the color-magnitude diagram are considerably nonlinear. Because of these problems, extinction values estimated with NICMOS filters can be in error by up to 1.3 mag. Our calculation suggests that the extinction law implied by the observations of Rieke et al for wavelengths between the J and K bands is better described by a power-law function with an exponent of 1.66 instead of 1.59, which is commonly used with an assumption that the transmission functions of J and K filters are Dirac delta functions.Comment: Published in PASP, 118, 62 (Jan. 2006

X-43D Conceptual Design and Feasibility Study

NASA s Next Generation Launch Technology (NGLT) Program, in conjunction with the office of the Director of Defense Research and Engineering (DDR&E), developed an integrated hypersonic technology demonstration roadmap. This roadmap is an integral part of the National Aerospace Initiative (NAI), a multi-year, multi-agency cooperative effort to invest in and develop, among other things, hypersonic technologies. This roadmap contains key ground and flight demonstrations required along the path to developing a reusable hypersonic space access system. One of the key flight demonstrations required for systems that will operate in the high Mach number regime is the X-43D. As currently conceived, the X-43D is a Mach 15 flight test vehicle that incorporates a hydrogen-fueled scramjet engine. The purpose of the X-43D is to gather high Mach number flight environment and engine operability information which is difficult, if not impossible, to gather on the ground. During 2003, the NGLT Future Hypersonic Flight Demonstration Office initiated a feasibility study on the X-43D. The objective of the study was to develop a baseline conceptual design, assess its performance, and identify the key technical issues. The study also produced a baseline program plan, schedule, and cost, along with a list of key programmatic risks

Paleoeskimo Demography and Holocene Sea-level History, Gulf of Boothia, Arctic Canada

Surveys in six areas along the Gulf of Boothia produced large collections of radiocarbon samples from raised beaches that yield six new relative sea-level curves and information on Holocene bowhead whale ranges. In addition, on the lower beaches, we documented 482 Paleoeskimo dwelling features spanning about 3500 years (4200–800 14C years BP). Spatial densities of sites are only about half those reported by us from adjacent regions, but other attributes are remarkably similar. On the basis of feature elevation, corroborated by radiocarbon dates, Paleoeskimo occupation appears to have passed through a series of boom-and-bust cycles, the first being the most prominent. After the first peopling about 4200 BP, populations rose between about 3900 and 3600 BP to their all-time maximum, which was followed by a dramatic crash. Population recoveries after the initial crash were small and perhaps temporary. A final increase between 1900 (1500) and 800 14C years BP was followed by the disappearance of the Paleoeskimo. No compelling evidence yet points to the cause of the population declines; climate change and resource over-exploitation are equally plausible. The frequency distributions of dwelling sizes and numbers of dwellings per site closely resemble those in adjacent regions, suggesting similar social dynamics. Specifically, dispersed nuclear families or small extended families characterized Paleoeskimo settlement patterns for most of the year, but annual aggregations involved 100 or more people. The only significant architectural change coincides with the arrival of Late Dorset people bringing distinctive triangular midpassages and soapstone lamp supports.Des levés réalisés dans six régions situées le long du golfe de Boothia ont permis de recueillir de vastes collections d’échantillons au carbone 14 provenant de plages surélevées. Les résultats découlant de ces levés produisent six nouvelles résonances relatives du niveau de la mer de même que des renseignements sur le parcours des baleines de l’Holocène. Par ailleurs, dans le cas des plages inférieures, nous avons répertorié 482 caractéristiques d’habitations paléoesquimaudes s’étendant sur environ 3 500 ans (de 4200 à 800 14C années BP). Les densités spatiales des sites ne constituent environ que la moitié des densités qui nous avons repérées dans des régions adjacentes, mais les autres attributs sont remarquablement semblables. En ce qui a trait à l’élévation des caractéristiques, corroborée par la datation par le carbone 14, l’occupation paléoesquimaude semble avoir traversé une série de cycles d’expansion et de ralentissement, le premier de ces cycles étant le plus éminent. Après le premier peuplement vers 4200 BP, les populations se sont élevées entre 3900 et 3600 BP pour atteindre leur summum de tous les temps, ce qui a été suivi par un déclin dramatique. Les reprises de population après le déclin initial étaient minces, voire peut-être temporaires. Une dernière augmentation entre 1900 (1500) et 800 14C années BP a été suivie de la disparition des Paléoesquimaux. À ce jour, aucune preuve évidente ne nous laisse comprendre les déclins de population. Le changement climatique et la surexploitation des ressources sont des causes toutes aussi plausibles les unes que les autres. La distribution statistique relativement à la taille des habitations et au nombre d’habitations par site s’apparente de près à celle des régions adjacentes, ce qui laisse entrevoir une dynamique sociale semblable. Plus précisément, des familles nucléaires dispersées ou de petites familles étendues caractérisaient les modèles de peuplement des Paléoesquimaux pendant la plus grande partie de l’année, bien que les rassemblements annuels regroupaient une centaine de personnes ou plus. Le seul changement architectural important coïncide avec l’arrivée du peuple du Dorset tardif ayant mis en valeur des couloirs triangulaires distinctifs et des supports à lampes en saponite

Stability and Control Characteristics at Subsonic Speeds of a Flat-Top Arrowhead Wing-Body Combination

A wind-tunnel investigation was made to determine the longitudinal- and lateral-stability derivatives of a flat-top wing-body configuration at Mach numbers from 0.22 to 0.90 and Reynolds numbers of 3.5 and 17 million. The wing had a leading-edge sweepback of 78.9 deg and a cathedral of 45 deg on the outer panels. The tests included the determination of the effectiveness of elevon and rudder controls and also an investigation of ground effects. The model was tested at angles of attack up to 28 deg and angles of sideslip up to 18 deg. The dynamic response of this configuration has been determined from the wind-tunnel data for a simulated airplane having a wing loading of 17.7 pounds per square foot. The longitudinal data show a forward shift in aerodynamic center of 10 percent of the mean aerodynamic chord as the lift coefficient is increased above 0.1. Although flown in the lift range of decreasing stability, the simulated airplane did not encounter pitch-up in maneuvers initiated from steady level flight with zero static margin unless a load factor of 2.2 was exceeded. This maneuver margin was provided by a large value of pitching moment due to pitching velocity. The number of cycles to damp the Dutch roll mode to half amplitude, the time constants of the roll subsidence and spiral divergence modes, and control effectiveness in roll are computed. The lateral stability is shown to be positive but is marginal in meeting the military specifications for today's aircraft. An analog computer study has been made in five degrees of freedom (constant velocity) which illustrates that the handling characteristics are satisfactory. Several programed rolling maneuvers and coordinated turns also illustrate the handling qualities of the airplane

Integrated Laboratory Demonstrations of Multi-Object Adaptive Optics on a Simulated 10-Meter Telescope at Visible Wavelengths

One important frontier for astronomical adaptive optics (AO) involves methods such as Multi-Object AO and Multi-Conjugate AO that have the potential to give a significantly larger field of view than conventional AO techniques. A second key emphasis over the next decade will be to push astronomical AO to visible wavelengths. We have conducted the first laboratory simulations of wide-field, laser guide star adaptive optics at visible wavelengths on a 10-meter-class telescope. These experiments, utilizing the UCO/Lick Observatory's Multi-Object / Laser Tomography Adaptive Optics (MOAO/LTAO) testbed, demonstrate new techniques in wavefront sensing and control that are crucial to future on-sky MOAO systems. We (1) test and confirm the feasibility of highly accurate atmospheric tomography with laser guide stars, (2) demonstrate key innovations allowing open-loop operation of Shack-Hartmann wavefront sensors (with errors of ~30 nm) as will be needed for MOAO, and (3) build a complete error budget model describing system performance. The AO system maintains a performance of 32.4% Strehl on-axis, with 24.5% and 22.6% at 10" and 15", respectively, at a science wavelength of 710 nm (R-band) over the equivalent of 0.8 seconds of simulation. The MOAO-corrected field of view is ~25 times larger in area than that limited by anisoplanatism at R-band. Our error budget is composed of terms verified through independent, empirical experiments. Error terms arising from calibration inaccuracies and optical drift are comparable in magnitude to traditional terms like fitting error and tomographic error. This makes a strong case for implementing additional calibration facilities in future AO systems, including accelerometers on powered optics, 3D turbulators, telescope and LGS simulators, and external calibration ports for deformable mirrors.Comment: 29 pages, 11 figures, submitted to PAS

Most Asked Agronomic Questions

Exact date of bulletin unknown.PDF pages: 4