Periodic variations in the colours of the classical T Tauri star RW Aur A

The classical T Tauri star RW Aur A is an irregular variable with a large amplitude in all photometric bands. In an extended series of photometric data we found small-amplitude periodic variations in the blue colours of the star, with a period of 2.64 days. The period was relatively stable over several years. The amplitude of the periodic signal is 0.21 mag in U-V, 0.07 mag in B-V, and about 0.02 mag in V-R and V-I. No periodicity was found in the V magnitude. The relevance of this photometric period to the recently discovered periodicity in spectral features of the star is discussed, and the hypothesis of a hot spot is critically considered.Comment: 5 pages, 8 figures, uses new aa.cls, accepted for publication in Astronomy and Astrophysic

Firms, Nonprofits, and Cooperatives: A Theory of Organizational Choice

Abstract This paper formalizes the difference between firms, nonprofits, and cooperatives and identifies optimal organizational choice. In a model of quality provision, we find a clear ranking of quality produced: Firms provide lowest and nonprofits highest levels of quality. Efficiency, however, depends on the competitive environment, the decision making process and technology. Cooperatives are optimal when decision making costs are low. Else, cooperatives are increasingly dominated by either nonprofits or firms (depending on the incremental costs of quality production). Finally, changes in the competitive environment affect organizational choice: Increased competition induces a shift towards firm organization and away from nonprofits.Theory of the Firm;Cooperatives;Nonprofits;Organizational Choice;organizational change

X-ray Emission from the Weak-lined T Tauri Binary System KH 15D

The unique eclipsing, weak-lined T Tauri star KH 15D has been detected as an X-ray source in a 95.7 ks exposure from the Chandra X-ray Observatory archives. A maximum X-ray luminosity of 1.5 x 10^{29} erg s$^{-1}$ is derived in the 0.5--8 keV band, corresponding to L_{X}/L_bol = 7.5 x 10^{-5}. Comparison with samples of stars of similar effective temperature in NGC 2264 and in the Orion Nebula Cluster shows that this is about an order of magnitude low for a typical star of its mass and age. We argue that the relatively low luminosity cannot be attributed to absorption along the line of sight but implies a real deficiency in X-ray production. Possible causes for this are considered in the context of a recently proposed eccentric binary model for KH 15D. In particular, we note that the visible component rotates rather slowly for a weak-lined T Tauri star and has possibly been pseudosynchronized by tidal interaction with the primary near periastron

Thermal Evaluation of High Voltage Hermetic Motors Experiencing Recurrent Insulation Failures

A high voltage hermetic compressor motor design developed for chiller applications has shown recurrent insulation failures in certain stator end-turn regions. Initial investigations found discoloration of failed coil insulation and suggested that the stator coils over heated during operation at rated load. Thermal modeling was conducted to develop an understanding of the causes of the unacceptably high motor failure rate so that corrective actions could be taken for future motor designs. This paper presents thermal modeling efforts for predicting steady-state temperature distributions within the stator coil in the end-turn region under full-load electrical heating and a refrigerant cooling environment. Insulation thermal conductivity and coil surface convection heat transfer coefficient were identified as two critical heat transfer parameters which dictate the effectiveness of coil heat dissipation. Thermal analysis results have been correlated with measured temperature dependent insulation thermal conductivities and stator coil surface temperatures measured in motor cooling tests. The results of thermal evaluation indicate that the premature motor failures are likely caused by excessive conductor heating due to high operating current density in a non-uniform coolant distribution.Center for Electromechanic

Profiles of Strong Permitted Lines in Classical T Tauri Stars

We present a spectral analysis of 30 T Tauri stars observed with the Hamilton echelle spectrograph over more than a decade. One goal is to test magnetospheric accretion model predictions. Observational evidence previously published supporting the model, such as emission line asymmetry and a high frequency of redshifted absorption components, are considered. We also discuss the relation between different line forming regions and search for good accretion rate indicators. In this work we confirm several important points of the models, such as the correlation between accretion and outflow, broad emission components that are mostly central or slightly blueshifted and only the occasional presence of redshifted absorption. We also show, however, that the broad emission components supposedly formed in the magnetospheric accretion flow only partially support the models. Unlike the predictions, they are sometimes redshifted, and are mostly found to be symmetric. The published theoretical profiles do not have a strong resemblance to our observed ones. We emphasize the need for accretion models to include a strong turbulent component before their profiles will match the observations. The effects of rotation, and the outflow components, will also be needed to complete the picture.Comment: 25 pages including 9 figures, 3 tables, accepted for publication in the Astronomical Journa

Radiative corrections to the pressure and the one-loop polarization tensor of massless modes in SU(2) Yang-Mills thermodynamics

We compute the one-loop polarization tensor $\Pi$ for the on-shell, massless mode in a thermalized SU(2) Yang-Mills theory being in its deconfining phase. Postulating that SU(2)$_{\tiny{CMB}}\stackrel{\tiny{today}}=U(1)_Y$, we discuss $\Pi$'s effect on the low-momentum part of the black-body spectrum at temperatures $\sim 2... 4$ $T_{\tiny{CMB}}$ where $T_{\tiny{CMB}}\sim 2.73$K. A table-top experiment is proposed to test the above postulate. As an application, we point out a possible connection with the stability of dilute, cold, and old innergalactic atomic hydrogen clouds. We also compute the two-loop correction to the pressure arising from the instantaneous massless mode in unitary-Coulomb gauge, which formerly was neglected, and present improved estimates for subdominant corrections.Comment: 25 pages, 17 figs, v4: consequences of a modification of the evolution equation for the effectice coupling implemented, no qualitative change of the physic

Regional and Structural Impacts of Alternative Dairy Policy Options

Milk and dairy product prices have fallen to their lowest levels in 3 years following the record highs of 2004 and 2005. The large government stockpiles of non-fat dry milk are gone, but threaten to build again as non-fat dry milk and cheese prices decline nearer the support price level. A new farm bill is scheduled to be written in 2007. The Milk Income Loss Contract (MILC) program included in the last farm bill was only authorized through September 2005. Subsequent legislation reinstated the MILC program through August 2007. WTO negotiations are on-going and could influence U.S. farm programs 1/. Dairy’s role in the U.S. amber box limit of $19.1 billion may necessitate some possible trade-offs with other commodities. Dairy counts about$4.2 billion toward the annual amber box limit, but actual spending only averages about $1 billion (Outlaw, et al). The pressure of low prices, WTO negotiations, MILC continuation, and a new farm bill has created the potential for a number of options and alternatives for dairy policy. This paper examines the regional and structural impacts of 3 dairy policy options: MILC continuation, a target price/deficiency payment program, and an increase in the support price. All three options are designed to spend$400 million in amber box payments per year. The analysis uses representative dairy farms in major milk producing regions of the country developed by the AFPC for policy analysis.Agribusiness, Agricultural and Food Policy, Livestock Production/Industries,