Measuring the Effectiveness of Checkoff Programs

Marketing, Q13, M31, M37,

FRW Cosmology in F(R,T) gravity

In this paper, we consider a theory of gravity with a metric-dependent torsion namely the $F(R,T)$ gravity, where $R$ is the curvature scalar and $T$ is the torsion scalar. We study a geometric root of such theory. In particular we give the derivation of the model from the geometrical point of view. Then we present the more general form of $F(R,T)$ gravity with two arbitrary functions and give some of its particular cases. In particular, the usual $F(R)$ and $F(T)$ gravity theories are the particular cases of the $F(R,T)$ gravity. In the cosmological context, we find that our new gravitational theory can describes the accelerated expansion of the universe.Comment: 14 page

WIYN Open Cluster Study XVI: Optical/Infrared Photometry and Comparisons With Theoretical Isochrones

We present combined optical/near-IR photometry (BVIK) for six open clusters - M35, M37, NGC 1817, NGC 2477, NGC 2420, and M67. The open clusters span an age range from 150 Myr to 4 Gyr and have metal abundances from [Fe/H] = -0.3 to +0.09 dex. We have utilized these data to test the robustness of theoretical main sequences constructed by several groups as denoted by the following designations - Padova, Baraffe, Y^2, Geneva, and Siess. The comparisons of the models with the observations have been performed in the [Mv, (B-V)o], [Mv, (V-I)o], and [Mv, (V-K)o] colour-magnitude diagrams as well as the distance-independent [(V-K)o, (B-V)o] and [(V-K)o, (V-I)o] two-colour diagrams. We conclude that none of the theoretical models reproduce the observational data in a consistent manner over the magnitude and colour range of the unevolved main sequence. In particular, there are significant zeropoint and shape differences between the models and the observations. We speculate that the crux of the problem lies in the precise mismatch between theoretical and observational colour-temperature relations. These results underscore the importance of pursuing the study of stellar structure and stellar modelling with even greater intensity.Comment: Accepted for publication in MNRAS. 12 pages, 37 figures, 4 tables. High resolution figures available from http://www.astro.ufl.edu/~aaron/opt_ir_figs

The Sand-Dwelling Predatory Mayfly \u3ci\u3ePseudiron Centralis\u3c/i\u3e in Michigan (Ephemeroptera: Pseudironidae)

(excerpt) An examination of samples of Ephemeroptera larvae taken from 19 sites on the Pere Marquette River, Mason County, Michigan in October, 1990 and May, 1991 by A. G. B. Primack (Indiana University, Bloomington) revealed the presence of Pseudiron centralis McDunnough. This species was taken at seven sites between State Highway M37 and Rainbow Rapids, east of Ludington

Angular Momentum Transport In Solar-Type Stars: Testing the Timescale For Core-Envelope Coupling

We critically examine the constraints on internal angular momentum transport which can be inferred from the spin down of open cluster stars. The rotation distribution inferred from rotation velocities and periods are consistent for larger and more recent samples, but smaller samples of rotation periods appear biased relative to vsini studies. We therefore focus on whether the rotation period distributions observed in star forming regions can be evolved into the observed ones in the Pleiades, NGC2516, M34, M35, M37, and M50 with plausible assumptions about star-disk coupling and angular momentum loss from magnetized solar-like winds. Solid body models are consistent with the data for low mass fully convective stars but highly inconsistent for higher mass stars where the surface convection zone can decouple for angular momentum purposes from the radiative interior. The Tayler-Spruit magnetic angular momentum transport mechanism, commonly employed in models of high mass stars, predicts solid-body rotation on extremely short timescales and is therefore unlikely to operate in solar-type pre-MS and MS stars at the predicted rate. Models with core-envelope decoupling can explain the spin down of 1.0 and 0.8 solar mass slow rotators with characteristic coupling timescales of 55+-25 Myr and 175+-25 Myr respectively. The upper envelope of the rotation distribution is more strongly coupled than the lower envelope of the rotation distribution, in accord with theoretical predictions that the angular momentum transport timescale should be shorter for more rapidly rotating stars. Constraints imposed by the solar rotation curve are also discussed (Abridged)Comment: 42 pages, 16 figures, submitted to Ap

Dark Energy in F(R,T) Gravity

Since the discovery of cosmic acceleration, modified gravity theories play an important role in the modern cosmology. In particular, the well-known F(R)-theories reached great popularity motivated by the easier formalism and by the prospect to find a final theories of gravity for the dark scenarios. In the present work, we study some generalizations of F(R)and F(T) gravity theories. At the beginning, we briefly review the formalism of such theories. Then, we will consider one of their generalizations, the so-called F(R,T)-theory. The point-like Lagrangian is explicitly presented. Based on this Lagrangian, the field equations of F(R,T)-gravity are found. For the specific model $F(R,T)=\mu R+\nu T,$ the corresponding exact solutions are derived. Furthermore, we will consider the physical quantities associated to such solutions and we will find how for some values of the parameters the expansion of our universe can be accelerated without introducing any dark component.Comment: 16 pages, 1 figure. typos corrected, new results adde

A non-commutative algorithm for multiplying 5x5 matrices using 99 multiplications

We present a non-commutative algorithm for multiplying 5x5 matrices using 99 multiplications. This algorithm is a minor modification of Makarov's algorithm which exhibit the previous best known bound with 100 multiplications