Analyzation, design, fabrication and testing of a foil bearing rotor support system quarterly technical report, period ending 21 aug. 1965

High speed rotor support system with foil bearin

The Ages of Pre-main-sequence Stars

The position of pre-main-sequence or protostars in the Hertzsprung--Russell diagram is often used to determine their mass and age by comparison with pre-main-sequence evolution tracks. On the assumption that the stellar models are accurate, we demonstrate that, if the metallicity is known, the mass obtained is a good estimate. However, the age determination can be very misleading because it is significantly (generally different by a factor of two to five) dependent on the accretion rate and, for ages less than about one million years, the initial state of the star. We present a number of accreting protostellar tracks that can be used to determine age if the initial conditions can be determined and the underlying accretion rate has been constant in the past. Because of the balance established between the Kelvin-Helmholtz, contraction timescale and the accretion timescale a pre-main-sequence star remembers its accretion history. Knowledge of the current accretion rate, together with an H--R-diagram position gives information about the rate of accretion in the past but does not necessarily improve any age estimate. We do not claim that ages obtained by comparison with these particular accreting tracks are likely to be any more reliable than those from comparisons with non-accreting tracks. Instead we stress the unreliability of any such comparisons and use the disparities between various tracks to estimate the likely errors in age and mass estimates. We also show how a set of coeval accreting objects do not appear coeval when compared with non-accreting tracks. Instead accreting pre-main-sequence stars of around a solar mass are likely to appear older than those of either smaller or larger mass.Comment: Accepted by MNRA

Analyzation, design, fabrication, and testing of a foil bearing rotor support system Quarterly technical report, period ending 21 Feb. 1966

Design, fabrication, and testing of foil bearing rotor support syste

Externally Fed Accretion onto Protostars

The asymmetric molecular emission lines from dense cores reveal slow, inward motion in the clouds' outer regions. This motion is present both before and after the formation of a central star. Motivated by these observations, we revisit the classic problem of steady, spherical accretion of gas onto a gravitating point mass, but now include self-gravity of the gas and impose a finite, subsonic velocity as the outer boundary condition. We find that the accretion rate onto the protostar is lower than values obtained for isolated, collapsing clouds, by a factor that is the Mach number of the outer flow. Moreover, the region of infall surrounding the protostar spreads out more slowly, at a speed close to the subsonic, incoming velocity. Our calculation, while highly idealized, provides insight into two longstanding problems -- the surprisingly low accretion luminosities of even the most deeply embedded stellar sources, and the failure so far to detect spatially extended, supersonic infall within their parent dense cores. Indeed, the observed subsonic contraction in the outer regions of dense cores following star formation appears to rule out a purely hydrodynamic origin for these clouds.Comment: accepted by MNRA

On the unique possibility to increase significantly the contrast of dark resonances on D1 line of 87^{87}Rb

We propose and study, theoretically and experimentally, a new scheme of excitation of a coherent population trapping resonance for D1 line of alakli atoms with nuclear spin $I=3/2$ by bichromatic linearly polarized light ({\em lin}$||${\em lin} field) at the conditions of spectral resolution of the excited state. The unique properties of this scheme result in a high contrast of dark resonance for D1 line of $^{87}$Rb.Comment: 9 pages, 7 figures. This material has been partially presented on ICONO-2005, 14 May 2005, St. Petersburg, Russia. v2 references added; text is changed a bi

Chemical Control of Weeds in South Dakota

There are now many chemicals on the market that have possibilities for use in a weed control program. Many of these chemicals are being tested and several can be used in controlling weeds. This bulletin explains the use and value of the more important chemicals. Recommendations are based on experimental results from cooperative tests in South Dakota and the results reported at the North Central Weed Control Conference. The tests in South Dakota include plots established throughout the state in 1945 and 1947, and at the Weed Research Farm at Scotland, which was begun in 1946

Cultural Methods of Noxious Weed Control in South Dakota

This outline has been prepared as a guide for field workers in weed control; for county, township, and neighborhood supervisors and for farmers cooperating in the program. The control measures presented here are based on the latest information available from weed control research and proven field applications. A choice of methods and procedures is presented that will fit practically all situations. It is assumed that local practices will be kept within the limits of recommendations outlined. Each of the eight weeds listed as noxious will be considered and recommendations for the use of intensive cultivation with various crops will be outlined for each weed. The choice of procedure to be adopted will depend on several factors, namely: (1) extent of infestation; (2) value and productivity of the land; (3) availability of material, equipment, and manpower; (4) adaptability of control practices, and (5) adaptability of crops. If chemicals are to be used, Experiment Station Circular No. 69 should be obtained. The recommendations given in that publication should be followed closely. Colored plates of the noxious weeds which show pictures and give characteristics of these weeds are also available. Copies of the Circular No. 69 or the colored plates can be obtained from the County Agent\u27s office or from the Bulletin Department at South Dakota State College, Brookings, South Dakota. Some cultural practices that are recommended for weed control involve long periods of intensive cultivation. Those that leave the soil barren during the winter are conducive to soil erosion. ln areas where this condition is a hazard the practice should be modified to conform with recommended soil conservation practices

Chemical Control of Weeds in South Dakota

There are now many chemicals on the market that have possibilities for use in weed control. This circular explains the use and value of the more important chemicals. Recommendations are based on experimental results from cooperative tests in South Dakota and from those reported at the North Central Weed Control Conference. The tests in South Dakota include 49 sets of plots established throughout the state from 1945 to 1950, work conducted at the Weed Research Farm at Scotland from 1946 to 1950, work conducted at Brookings from 1947 to 1951 and at a Weed Research Farm near Gary which was established in 1950

Endogenous Market Structures and the Gains from Foreign Direct Investment

This paper discusses the gains from liberalizing foreign direct investment (FDI) in a two country setting with endogenous market structures. Two different scenarios are investigated. In the first scenario, headquarters are run in the domestic country only and the FDI regime is compared to the intersectoral trade case. If multinational and national firms coexist, market concentration occurs and FDI is welfare improving for the foreign country, but welfare declining for the domestic country. In the second scenario, headquarters are run in both countries and the FDI regime is compared to the intraindustry trade case. This regime switch leads to mutual welfare gains, irrespective of market structure effects.

The Nature of Class I Sources: Periodic Variables in Orion

We present a quantitative, empirically based argument that at least some Class I sources are low-mass, pre-main-sequence stars surrounded by spatially extended envelopes of dusty gas. The source luminosity arises principally from stellar gravitational contraction, as in optically visible pre-main-sequence stars that lack such envelopes. We base our argument on the fact that some Class I sources in Orion and other star-forming regions have been observed by Spitzer to be periodic variables in the mid-infrared, and with periods consistent with T Tauri rotation rates. Using a radiative transfer code, we construct a variety of dust envelopes surrounding rotating, spotted stars, to see if an envelope that produces a Class I SED at least broadly matches the observed modulations in luminosity. Acceptable envelopes can either be spherical or flattened, and may or may not have polar cavities. The key requirement is that they have a modest equatorial optical depth at the Spitzer waveband of 3.6 ${\mu}$m, typically ${\tau_{3.6}}$ ${\approx}$ 0.6. The total envelope mass, based on this limited study, is at most about 0.1 $\text{M}_{\odot}$, less than a typical stellar mass. Future studies should focus on the dynamics of the envelope, to determine whether material is actually falling onto the circumstellar disk.Comment: 17 pages, 16 figures. Additional light curve figures and associated data table referred to in Appendix B available as online dat