Crafting a Class: The Trade Off Between Merit Scholarships and Enrolling Lower-Income Students

[Excerpt] It is well-known that test scores are correlated with students’ socio-economic backgrounds. Hence to the extent that colleges are successful in “buying” higher test score students, one should expect that their enrollment of students from families in the lower tails of the family income distribution should decline. However, somewhat surprisingly, there have been no efforts to test if this is occurring. Our paper presents such a test. While institutional level data on the dollar amounts of merit scholarships offered by colleges and universities are not available, data are available on the number of National Merit Scholarship (henceforth NMS) winners attending an institution on scholarships that have been funded by the institution itself, rather than the National Merit Scholarship Corporation (henceforth NMSC). These institutional scholarships are awarded to high test score students only if they attend the institution. Our research strategy is to estimate if an increase in the number of recipients of these scholarships at an institution is associated with a decline in the number of students from lower and lower middle income families attending the institution, other factors held constant. We measure the number of these students by the number of Pell Grant recipients attending the institution

Phase diagram of two-species Bose-Einstein condensates in an optical lattice

The exact macroscopic wave functions of two-species Bose-Einstein condensates in an optical lattice beyond the tight-binding approximation are studied by solving the coupled nonlinear Schrodinger equations. The phase diagram for superfluid and insulator phases of the condensates is determined analytically according to the macroscopic wave functions of the condensates, which are seen to be traveling matter waves.Comment: 13 pages, 2 figure

An efficient mixed variational reduced order model formulation for non-linear analyses of elastic shells

The Koiter-Newton method had recently demonstrated a superior performance for non-linear analyses of structures, compared to traditional path-following strategies. The method follows a predictor-corrector scheme to trace the entire equilibrium path. During a predictor step a reduced order model is constructed based on Koiter's asymptotic post-buckling theory which is followed by a Newton iteration in the corrector phase to regain the equilibrium of forces. In this manuscript, we introduce a robust mixed solid-shell formulation to further enhance the efficiency of stability analyses in various aspects. We show that a Hellinger-Reissner variational formulation facilitates the reduced order model construction omitting an expensive evaluation of the inherent fourth order derivatives of the strain energy. We demonstrate that extremely large step sizes with a reasonable out-of-balance residual can be obtained with substantial impact on the total number of steps needed to trace the complete equilibrium path. More importantly, the numerical effort of the corrector phase involving a Newton iteration of the full order model is drastically reduced thus revealing the true strength of the proposed formulation. We study a number of problems from engineering and compare the results to the conventional approach in order to highlight the gain in numerical efficiency for stability problems

Critical surface band gap of repulsive Casimir interaction between three dimensional topological insulators at finite temperature

We generalize the calculation of Casimir interaction between topological insulators with opposite topological magnetoelectric polarizabilities and finite surface band gaps to finite Temperature cases. We find that finite temperature quantitatively depress the repulsive peak and enlarge the critical surface gap $m_c$ for repulsive Casimir force. However the universal property $m_c a \sim 1/2$ is still valid for various oscillation strength, temperature region and topological magnetoelectric polarizabilities.Comment: 7 pages, 4 figure

Spin-dependent transport in a quasiballistic quantum wire

We describe the transport properties of a 5 $\mu$m long one-dimensional (1D) quantum wire. Reduction of conductance plateaux due to the introduction of weakly disorder scattering are observed. In an in-plane magnetic field, we observe spin-splitting of the reduced conductance steps. Our experimental results provide evidence that deviation from conductance quantisation is very small for electrons with spin parallel and is about 1/3 for electrons with spin anti-parallel. Moreover, in a high in-plane magnetic field, a spin-polarised 1D channel shows a plateau-like structure close to $0.3 \times e^2/h$ which strengthens with {\em increasing} temperatures. It is suggested that these results arise from the combination of disorder and the electron-electron interactions in the 1D electron gas.Comment: 4 pages, 5 figures, latex to be published in Phys. Rev. B (15/3/2000

Simulation and detection of Dirac fermions with cold atoms in an optical lattice

We propose an experimental scheme to simulate and observe relativistic Dirac fermions with cold atoms in a hexagonal optical lattice. By controlling the lattice anisotropy, one can realize both massive and massless Dirac fermions and observe the phase transition between them. Through explicit calculations, we show that both the Bragg spectroscopy and the atomic density profile in a trap can be used to demonstrate the Dirac fermions and the associated phase transition.Comment: 4 pages; Published versio

Resonant Excitation of Graphene K-Phonon and Intra-Landau-Level Excitons in Magneto-Optical Spectroscopy

Precise infrared magnetotransmission experiments have been performed in magnetic fields up to 32 T on a series of multilayer epitaxial graphene samples. We observe changes in the spectral features and broadening of the main cyclotron transition when the incoming photon energy is in resonance with the lowest Landau level separation and the energy of a K point optical phonon. We have developed a theory that explains and quantitatively reproduces the frequency and magnetic field dependence of the phenomenon as the absorption of a photon together with the simultaneous creation of an intervalley, intra-Landau-level exciton, and a K phonon.Comment: Main manuscript (5 pages); Supplementary Material (18 pages