Description of the fluctuating colloid-polymer interface

To describe the full spectrum of surface fluctuations of the interface between phase-separated colloid-polymer mixtures from low scattering vector q (classical capillary wave theory) to high q (bulk-like fluctuations), one must take account of the interface's bending rigidity. We find that the bending rigidity is negative and that on approach to the critical point it vanishes proportionally to the interfacial tension. Both features are in agreement with Monte Carlo simulations.Comment: 5 pages, 3 figures, 1 table. Accepted for publication in Phys. Rev. Let

ISO observations of obscured Asymptotic Giant Branch stars in the Large Magellanic Cloud

We present ISO photometric and spectroscopic observations of a sample of 57 bright Asymptotic Giant Branch stars and red supergiants in the Large Magellanic Cloud, selected on the basis of IRAS colours indicative of high mass-loss rates. PHOT-P and PHOT-C photometry at 12, 25 and 60 $\mu$m and CAM photometry at 12 $\mu$m are used in combination with quasi-simultaneous ground-based near-IR photometry to construct colour-colour diagrams for all stars in our sample. PHOT-S and CAM-CVF spectra in the 3 to 14 $\mu$m region are presented for 23 stars. From the colour-colour diagrams and the spectra, we establish the chemical types of the dust around 49 stars in this sample. Many stars have carbon-rich dust. The most luminous carbon star in the Magellanic Clouds has also a (minor) oxygen-rich component. OH/IR stars have silicate absorption with emission wings. The unique dataset presented here allows a detailed study of a representative sample of thermal-pulsing AGB stars with well-determined luminosities.Comment: 19 pages, 10 figures. Accepted for publication in Astronomy and Astrophysics Main Journa

Results from a prospective, randomized, controlled study evaluating the acceptability and effects of routine pre‐IVF counselling

BACKGROUND: The aim of this study was to evaluate a model of routine pre‐IVF counselling focusing on the narrative capacities of couples. The acceptability of counselling, the effects on emotional factors and the participants' assessments were considered. METHODS: The study included 141 consecutive childless couples preparing for their first IVF. Randomization was carried out through sealed envelopes attributing participants to counselled and non‐counselled groups and was accepted by 100 couples. Another 12 couples refused randomization because they wanted counselling and 29 because they did not. Questionnaires including the State‐Trait Anxiety Inventory, the Beck Depression Inventory and assessments of help were mailed to couples before IVF and counselling, and after the IVF outcome. RESULTS: Counselling was accepted by 79% (112/141) of couples. There was no significant effect of counselling on anxiety and depression scores which were within normal ranges at both times. Counselling provided help for 86% (75/87) of initially non‐demanding subjects and 96% (25/26) of those initially requesting a session. Help was noted in areas of psychological assistance, technical explanations and discussing relationships. CONCLUSIONS: This model of routine counselling centred on the narrative provides an acceptable form of psychological assistance for pre‐IVF couple

The exponential map for representations of Up,q(gl(2))U_{p,q}(gl(2))

For the quantum group $GL_{p,q}(2)$ and the corresponding quantum algebra $U_{p,q}(gl(2))$ Fronsdal and Galindo explicitly constructed the so-called universal $T$-matrix. In a previous paper we showed how this universal $T$-matrix can be used to exponentiate representations from the quantum algebra to get representations (left comodules) for the quantum group. Here, further properties of the universal $T$-matrix are illustrated. In particular, it is shown how to obtain comodules of the quantum algebra by exponentiating modules of the quantum group. Also the relation with the universal $R$-matrix is discussed.Comment: LaTeX-file, 7 pages. Submitted for the Proceedings of the 4th International Colloquium ``Quantum Groups and Integrable Systems,'' Prague, 22-24 June 199

Spatial division multiplexing for optical data center networks

P

O3/O7 Orientifold Truncations and Very Special Quaternionic-Kaehler Geometry

We study the orientifold truncation that arises when compactifying type II string theory on Calabi-Yau orientifolds with O3/O7-planes, in the context of supergravity. We look at the N=2 to N=1 reduction of the hypermultiplet sector of N=2 supergravity under the truncation, for the case of very special quaternionic-Kaehler target space geometry. We explicitly verify the Kaehler structure of the truncated spaces, and we study the truncated isometry algebra. For symmetric special quaternionic spaces, we give a complete overview of the spaces one finds after truncation. We also find new examples of dual Kaehler spaces, that give rise to flat potentials in N=1 supergravity.Comment: 25 pages, LaTeX, v2:curvature tensor of the dual symmetric spaces calculated, section 7 expanded, references added, v3:few typos fixed, version to appear in Class.Quantum Gravit

Aspects of Scalar Field Dynamics in Gauss-Bonnet Brane Worlds

The Einstein-Gauss-Bonnet equations projected from the bulk to brane lead to a complicated Friedmann equation which simplifies to $H^2 \sim \rho^q$ in the asymptotic regimes. The Randall-Sundrum (RS) scenario corresponds to $q=2$ whereas $q=2/3$ & $q=1$ give rise to high energy Gauss-Bonnet (GB) regime and the standard GR respectively. Amazingly, while evolving from RS regime to high energy GB limit, one passes through a GR like region which has important implications for brane world inflation. For tachyon GB inflation with potentials $V(\phi) \sim \phi^p$ investigated in this paper, the scalar to tensor ratio of perturbations $R$ is maximum around the RS region and is generally suppressed in the high energy regime for the positive values of $p$. The ratio is very low for $p>0$ at all energy scales relative to GB inflation with ordinary scalar field. The models based upon tachyon inflation with polynomial type of potentials with generic positive values of $p$ turn out to be in the $1 \sigma$ observational contour bound at all energy scales varying from GR to high energy GB limit. The spectral index $n_S$ improves for the lower values of $p$ and approaches its scale invariant limit for $p=-2$ in the high energy GB regime. The ratio $R$ also remains small for large negative values of $p$, however, difference arises for models close to scale invariance limit. In this case, the tensor to scale ratio is large in the GB regime whereas it is suppressed in the intermediate region between RS and GB. Within the frame work of patch cosmologies governed by $H^2 \sim \rho^q$, the behavior of ordinary scalar field near cosmological singularity and the nature of scaling solutions are distinguished for the values of $q 1$.Comment: 15 pages, 10 eps figures; appendix on various scales in GB brane world included and references updated; final version to appear in PR

Chronology protection in stationary three-dimensional spacetimes

We study chronology protection in stationary, rotationally symmetric spacetimes in 2+1 dimensional gravity, focusing especially on the case of negative cosmological constant. We show that in such spacetimes closed timelike curves must either exist all the way to the boundary or, alternatively, the matter stress tensor must violate the null energy condition in the bulk. We also show that the matter in the closed timelike curve region gives a negative contribution to the conformal weight from the point of view of the dual conformal field theory. We illustrate these properties in a class of examples involving rotating dust in anti-de Sitter space, and comment on the use of the AdS/CFT correspondence to study chronology protection.Comment: 20 pages. V2: minor corrections, Outlook expanded, references added, published versio

Leadership Department Newsletter - June 2015

https://digitalcommons.andrews.edu/ldn-2015/1004/thumbnail.jp

Observational Constraints on Disk Heating as a Function of Hubble Type

Current understanding of the secular evolution of galactic disks suggests that this process is dominated by two or more heating mechanisms, which increase the random motions of stars in the disk. In particular, the gravitational influence of giant molecular clouds and irregularities in the spiral potential have been proposed to explain the observed velocity dispersions in the solar neighborhood. Each of these mechanisms acts on different components of the stellar velocities, which affects the ratio of the vertical and radial components of the stellar velocity dispersion since the relative strengths of giant molecular clouds and spiral irregularities vary with Hubble type. A study of this ratio as function of Hubble type has the potential to provide strong constraints on disk heating mechanisms. We present major and minor axis stellar kinematics for four spiral galaxies of Hubble type from Sa to Sbc, and use the data to infer the ratios sigma_z/sigma_R in the galaxy disks. The results combined with two galaxies studied previously and with Milky Way data show that the ratio is generally in the range 0.5 - 0.8. There is a marginally significant trend of decreasing ratio with advancing Hubble type, consistent with the predictions of disk heating theories. However, the errors on individual measurements are large, and the absence of any trend is consistent with the data at the 1-sigma level. As a byproduct of our study, we find that three of the four galaxies in our sample have a central drop in their stellar line-of-sight velocity dispersion, a phenomenon that is increasingly observed in spiral galaxies. [ABRIDGED]Comment: 24 pages, LaTeX, 5 Postscript figures, to appear in AJ (Dec 2003