Neutron-Deuteron System and Photon Polarization Parameter at Thermal Neutron Energies

Effective Field Theory(EFT) is, the unique, model independent and systematic low-energy version of QCD for processes involving momenta below the pion mass. A low-energy photo-nuclear observable in three-body systems, photon polarization parameter at thermal neutron energies is calculated by using pionless EFT up to next-to-next to leading order(N$^2$LO). In order to make a comparative study of this model, we compared our results for photon polarization parameter with the realistic Argonne $v_{18}$ two-nucleon and Urbana IX or Tucson-Melbourne three-nucleon interactions. Three-body currents give small but significant contributions to some of the observables in the neutron-deuteron radiative capture cross section at thermal neutron energies. In this formalism the three-nucleon forces are needed up to N$^2$LO for cut-off independent results. Our result converges order by order in low energy expansion and also cut-off independent at this order.Comment: 10 pages, 3 figures, 2 table

Dynamical Cusp Regeneration

After being destroyed by a binary supermassive black hole, a stellar density cusp can regrow at the center of a galaxy via energy exchange between stars moving in the gravitational field of the single, coalesced hole. We illustrate this process via high-accuracy N-body simulations. Regeneration requires roughly one relaxation time and the new cusp extends to a distance of roughly one-fifth the black hole's influence radius, with density rho ~ r^{-7/4}; the mass in the cusp is of order 10% the mass of the black hole. Growth of the cusp is preceded by a stage in which the stellar velocity dispersion evolves toward isotropy and away from the tangentially-anisotropic state induced by the binary. We show that density profiles similar to those observed at the center of the Milky Way and M32 can regenerate themselves in several Gyr following infall of a second black hole; the presence of density cusps at the centers of these galaxies can therefore not be used to infer that no merger has occurred. We argue that Bahcall-Wolf cusps are ubiquitous in stellar spheroids fainter than M_V ~ -18.5 that contain supermassive black holes, but the cusps have not been detected outside of the Local Group since their angular sizes are less than 0.1". We show that the presence of a cusp implies a lower limit of \~10^{-4} per year on the rate of stellar tidal disruptions, and discuss the consequences of the cusps for gravitational lensing and the distribution of dark matter on sub-parsec scales.Comment: Accepted for publication in The Astrophysical Journa

Research on new techniques for the analysis of manual control systems Progress report, 16 Jun. - 15 Dec. 1968

Parameter estimation for continuous input-output systems with internal sampling in human controller model

Long-Term Evolution of Massive Black Hole Binaries. III. Binary Evolution in Collisional Nuclei

[Abridged] In galactic nuclei with sufficiently short relaxation times, binary supermassive black holes can evolve beyond their stalling radii via continued interaction with stars. We study this "collisional" evolutionary regime using both fully self-consistent N-body integrations and approximate Fokker-Planck models. The N-body integrations employ particle numbers up to 0.26M and a direct-summation potential solver; close interactions involving the binary are treated using a new implementation of the Mikkola-Aarseth chain regularization algorithm. Even at these large values of N, two-body scattering occurs at high enough rates in the simulations that they can not be simply scaled to the large-N regime of real galaxies. The Fokker-Planck model is used to bridge this gap; it includes, for the first time, binary-induced changes in the stellar density and potential. The Fokker-Planck model is shown to accurately reproduce the results of the N-body integrations, and is then extended to the much larger N regime of real galaxies. Analytic expressions are derived that accurately reproduce the time dependence of the binary semi-major axis as predicted by the Fokker-Planck model. Gravitational wave coalescence is shown to occur in <10 Gyr in nuclei with velocity dispersions below about 80 km/s. Formation of a core results from a competition between ejection of stars by the binary and re-supply of depleted orbits via two-body scattering. Mass deficits as large as ~4 times the binary mass are produced before coalescence. After the two black holes coalesce, a Bahcall-Wolf cusp appears around the single hole in one relaxation time, resulting in a nuclear density profile consisting of a flat core with an inner, compact cluster, similar to what is observed at the centers of low-luminosity spheroids.Comment: 21 page

Bias, the Brain, and Student Evaluations of Teaching

Student evaluations of teaching are a common fixture at American law schools, but they harbor surprising biases. Extensive psychology research demonstrates that these assessments respond overwhelmingly to a professor’s appearance and nonverbal behavior; ratings based on just thirty seconds of silent videotape correlate strongly with end-of-semester evaluations. The nonverbal behaviors that influence teaching evaluations are rooted in physiology, culture, and habit, allowing characteristics like race and gender to affect evaluations. The current process of gathering evaluations, moreover, allows social stereotypes to filter students’ perceptions, increasing risks of bias. These distortions are inevitable products of the intuitive, “system one” cognitive processes that the present process taps. The cure for these biases requires schools to design new student evaluation systems, such as ones based on facilitated group discussion, that enable more reflective, deliberative judgments. This article draws upon research in cognitive decision making, both to present the compelling case for reforming the current system of evaluating classroom performance and to illuminate the cognitive processes that underlie many facets of the legal system

Research on new techniques for the analysis of manual control systems Progress report, 15 Dec. 1968 - 15 Jun. 1969

Decision processes of human manual controllers, neuromuscular system, and stochastic processe

Texas Citrus Market Promotion.

2 p

Our Sacrifice Shall Not Be Required: Examining Maternal Ambivalence and Refusal in Black Motherhood

This thesis articulates motherhood as both a liberal and black humanist formation that conditions black women to mother and attempts to untether maternity from the black female body. By centering maternal ambivalence—the desire and distaste for motherhood—in selected works by black women, this thesis argues that black motherhood is an ambivalent site for some black women. Motherhood can be a site of joy and displeasure; sacrifice and refusal; life and death