Flux Attractors and Generating Functions

We use the flux attractor equations to study IIB supergravity compactifications with ISD fluxes. We show that the attractor equations determine not just the values of moduli fields, but also the masses of those moduli and the gravitino. We then show that the flux attractor equations can be recast in terms of derivatives of a single generating function. We also find a simple expression for this generating function in terms of the gravitino mass, with both quantities considered as functions of the fluxes. For a simple prepotential, we explicitly solve the attractor equations. We conclude by discussing a thermodynamic interpretation of this generating function, and possible implications for the landscape.Comment: 43 pages. v2, references added and typos correcte

Instantaneous Pair Theory for High-Frequency Vibrational Energy Relaxation in Fluids

Notwithstanding the long and distinguished history of studies of vibrational energy relaxation, exactly how it is that high frequency vibrations manage to relax in a liquid remains somewhat of a mystery. Both experimental and theoretical approaches seem to say that there is a natural frequency range associated with intermolecular motions in liquids, typically spanning no more than a few hundred cm^{-1}. Landau-Teller-like theories explain how a solvent can absorb any vibrational energy within this "band", but how is it that molecules can rid themselves of superfluous vibrational energies significantly in excess of these values? We develop a theory for such processes based on the idea that the crucial liquid motions are those that most rapidly modulate the force on the vibrating coordinate -- and that by far the most important of these motions are those involving what we have called the mutual nearest neighbors of the vibrating solute. Specifically, we suggest that whenever there is a single solvent molecule sufficiently close to the solute that the solvent and solute are each other's nearest neighbors, then the instantaneous scattering dynamics of the solute-solvent pair alone suffices to explain the high frequency relaxation. The many-body features of the liquid only appear in the guise of a purely equilibrium problem, that of finding the likelihood of particularly effective solvent arrangements around the solute. These results are tested numerically on model diatomic solutes dissolved in atomic fluids (including the experimentally and theoretically interesting case of I_2 in Xe). The instantaneous pair theory leads to results in quantitative agreement with those obtained from far more laborious exact molecular dynamics simulations.Comment: 55 pages, 6 figures Scheduled to appear in J. Chem. Phys., Jan, 199

Examination of teacher–child interactions in early childhood education programmes in the United Arab Emirates

© 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group. Teacher–child interactions provide an important context for children’s development and learning. The study explored how teacher- and classroom-level factors were associated with quality of teacher–child interactions in the United Arab Emirates (UAE). We also investigated associations between teacher–child interactions and child outcomes. Teacher–child interactions were observed in 60 kindergarten classrooms using the Classroom Assessment Scoring System, for the first time with this population. Pre-academic skills (letter and number knowledge), behavioural regulation (assessed with the Head-Toes-Knees-Shoulders task), and stress response physiology (assessed with salivary cortisol levels) were measured in a sample of 115 five-year-old children, recruited from 22 of the 60 classrooms. Results provided moderate evidence for a three-domain structure of teacher–child interactions. Some differences in the quality of teacher–child interactions were related to teachers’ years of experience. Correlational findings suggest links between quality of emotional support with children’s pre-academic skills and behavioural regulation. Results are also discussed in relation to similar international studies to highlight any unique findings to the UAE context

Why TiSe2_2 is a band insulator

In its crystalline form, TiSe$_2$ is thought to be an insulator with a bandgap of ~0.1-0.2 eV. This materials system has attracted a much interest because of its rich array of unique properties. It forms a charge density wave (CDW) in both bulk and monolayer form, and there has been wide speculation that TiSe$_2$ is a rare realisation of an excitonic insulator. Using a self-consistent form of many body perturbation theory, we establish that TiSe$_2$ is a band insulator, but it is only nonmetallic as a consequence of fluctuations in nuclear positions about its nominally high-symmetry (P-3m1) phase. Below 200 K, TiSe$_2$ undergoes a transition to a charge density-wave (P-3c1) phase, which activates coupling between states near the Fermi level and causes a gap to form. Above 200 K the nominal P-3m1 symmetry represents only a time average of the true configuration. Dynamics in the nuclear configuration are responsible for TiSe$_2$ being nonmetallic. We demonstrate this through a combination of molecular dynamics and the Self-consistent Quasiparticle Approximation. We further establish that ladder diagrams included in the polarizability (which includes the mechanism needed to form an excitonic insulator) are of little importance

The structure of the hydrated electron. Part 2. A mixed quantum classical molecular dynamics - embedded cluster density functional theory: single-excitation configuration interaction study

Adiabatic mixed quantum/classical molecular dynamics simulations were used to generate snapshots of the hydrated electron (e-) in liquid water at 300 K. Water cluster anions that include two complete solvation shells centered on the e- were extracted from these simulations and embedded in a matrix of fractional point charges designed to represent the rest of the solvent. Density functional theory and single-excitation configuration interaction methods were then applied to these embedded clusters. The salient feature of these hybrid calculations is significant transfer (ca. 0.18) of the excess electron's charge density into the O 2p orbitals in OH groups forming the solvation cavity. We used the results of these calculations to examine the structure of the molecular orbitals, the density of states, the absorption spectra in the visible and ultraviolet, the hyperfine coupling (hfc) tensors, and the IR and Raman spectra of the e-. The calculated hfc tensors were used to compute the EPR and ESEEM spectra for the e- that compared favorably to the experimental spectra of trapped e- in alkaline ice. The calculated vibrational spectra of the e- are consistent with the red-shifted bending and stretching frequencies observed in resonance Raman experiments. The model also accounts for the VIS and 190-nm absorption bands of the e-. Thus, our study suggests that to explain several important experimentally observed properties of the e-, many-electron effects must be accounted for.Comment: 68 pages, 12 figures + 16 more figures in the supplement (included) submitted to J Phys Chem