Expansion-induced contribution to the precession of binary orbits

We point out the existence of new effects of global spacetime expansion on local binary systems. In addition to a possible change of orbital size, there is a contribution to the precession of elliptic orbits, to be added to the well-known general relativistic effect in static spacetimes, and the eccentricity can change. Our model calculations are done using geodesics in a McVittie metric, representing a localized system in an asymptotically Robertson-Walker spacetime; we give a few numerical estimates for that case, and indicate ways in which the model should be improved.Comment: revtex, 7 pages, no figures; revised for publication in Classical and Quantum Gravity, with minor changes in response to referees' comment

The star-formation histories of elliptical galaxies across the fundamental plane

We present the first results from a study designed to test whether, given high-quality spectrophotometry spanning the mid-UV--optical wavelength regime, it is possible to distinguish the metal content (Z) and star-formation history (sfh) of individual elliptical galaxies with sufficient accuracy to establish whether their formation history is linked to their detailed morphology and position on the Fundamental Plane. From a detailed analysis of UV-optical spectrophotometry of the `cuspy' elliptical galaxy NGC 3605 and the giant elliptical NGC 5018 we find that: 1) optical spectra with l > 3500 A may not contain sufficient data to robustly uncover all the stellar populations present in individual galaxies, even in such relatively passive objects as ellipticals, 2) the addition of the UV data approaching l = 2500 A holds the key to establishing well-constrained sfhs, from which we can infer a formation and evolution history which is consistent with their photometric properties, 3) despite the superficial similarity of their spectra, the two galaxies have very different `recent' sfhs -- the smaller, cuspy elliptical NGC 3605 contains a high-Z population of age ~= 1 Gyr, and has a position on the fundamental plane typical of the product of a low-z gas-rich merger (most likely at z ~ 0.08), while the giant elliptical NGC 5018, with a sub-solar secondary population, appears to have gained its more recent stars via mass transfer / accretion of gas from its spiral companion, 4) despite these differences in detailed history, more than 85% of the stellar mass of both galaxies is associated with an old (9-12 Gyr) stellar population of near-solar Z. This pilot study provides strong motivation for the construction and analysis of high-quality UV-optical spectra for a substantial sample of ellipticals spanning the Fundamental Plane.Comment: 11 pages, 10 figures, submitted to MNRAS, revised versio

Odd-parity perturbations of self-similar Vaidya spacetime

We carry out an analytic study of odd-parity perturbations of the self-similar Vaidya space-times that admit a naked singularity. It is found that an initially finite perturbation remains finite at the Cauchy horizon. This holds not only for the gauge invariant metric and matter perturbation, but also for all the gauge invariant perturbed Weyl curvature scalars, including the gravitational radiation scalars. In each case, `finiteness' refers to Sobolev norms of scalar quantities on naturally occurring spacelike hypersurfaces, as well as pointwise values of these quantities.Comment: 28 page

A note on behaviour at an isotropic singularity

The behaviour of Jacobi fields along a time-like geodesic running into an isotropic singularity is studied. It is shown that the Jacobi fields are crushed to zero length at a rate which is the same in every direction orthogonal to the geodesic. We show by means of a counter-example that this crushing effect depends crucially on a technicality of the definition of isotropic singularities, and not just on the uniform degeneracy of the metric at the singularity.Comment: 13 pp. plain latex. To appear in Classical and Quantum Gravit

Stationary states in Langevin dynamics under asymmetric L\'evy noises

Properties of systems driven by white non-Gaussian noises can be very different from these systems driven by the white Gaussian noise. We investigate stationary probability densities for systems driven by $\alpha$-stable L\'evy type noises, which provide natural extension to the Gaussian noise having however a new property mainly a possibility of being asymmetric. Stationary probability densities are examined for a particle moving in parabolic, quartic and in generic double well potential models subjected to the action of $\alpha$-stable noises. Relevant solutions are constructed by methods of stochastic dynamics. In situations where analytical results are known they are compared with numerical results. Furthermore, the problem of estimation of the parameters of stationary densities is investigated.Comment: 9 pages, 9 figures, 3 table

Controlling the Size and Shape of Polypeptide Colloidal Particles: Temperature Dependence of Particle Formation

A promising approach for developing new drug delivery vehicles is by using stimuli responsive hydrogel nanoparticles. Polypeptide surfactants designed in our lab have been shown to form micellar particles of varying sizes and shapes depending on the solution salt concentration. These responsive polypeptide surfactants consist of a small charged protein domain (foldon) with three elastin-like polypeptide (ELP) chains forming a three-armed star polymer. The size and shape of the micelles they form is dependent on the ratio of total ELP volume to head group area. By introducing linear ELP into the ELP-foldon solution, the total volume of ELP in the aggregate would be increased if the linear ELP is incorporated in the micelle. This method could control the particle size and shape. To determine if the linear and three-armed ELPs co-assemble, we have observed aggregation as a function of temperature using turbidity measurements in a UV-vis spectrometer. We have found that higher concentrations of linear ELP increases the difference in transition temperature between the linear and three-armed ELP. At these higher ratios, the linear ELP aggregates prior to micelle formation. When the ELP-foldon subsequently passes through its critical micelle temperature, they break down the linear ELP aggregates resulting in smaller colloidal emulsions. Light scattering will be used to characterize the size and shape of these aggregates.https://engagedscholarship.csuohio.edu/u_poster_2013/1016/thumbnail.jp

Controlling the Size and Shape of Polypeptide Colloidal Particles: Temperature Dependence of Particle Formation

A promising approach for developing new drug delivery vehicles is by using stimuli responsive hydrogel nanoparticles. Polypeptide surfactants designed in our lab have been shown to form micellar particles of varying sizes and shapes depending on the solution salt concentration. These responsive polypeptide surfactants consist of a small charged protein domain (foldon) with three elastin-like polypeptide (ELP) chains forming a three-armed star polymer. The size and shape of the micelles they form is dependent on the ratio of total ELP volume to head group area. By introducing linear ELP into the ELP-foldon solution, the total volume of ELP in the aggregate would be increased if the linear ELP is incorporated in the micelle. This method could control the particle size and shape. To determine if the linear and three-armed ELPs co-assemble, we have observed aggregation as a function of temperature using turbidity measurements in a UV-vis spectrometer. We have found that higher concentrations of linear ELP increases the difference in transition temperature between the linear and three-armed ELP. At these higher ratios, the linear ELP aggregates prior to micelle formation. When the ELP-foldon subsequently passes through its critical micelle temperature, they break down the linear ELP aggregates resulting in smaller colloidal emulsions. Light scattering will be used to characterize the size and shape of these aggregates.https://engagedscholarship.csuohio.edu/u_poster_2013/1016/thumbnail.jp

A Characterisation of Strong Wave Tails in Curved Space-Times

A characterisation of when wave tails are strong is proposed. The existence of a curvature induced tail (i.e. a Green's function term whose support includes the interior of the light-cone) is commonly understood to cause backscattering of the field governed by the relevant wave equation. Strong tails are characterised as those for which the purely radiative part of the field is backscattered. With this definition, it is shown that electromagnetic waves in asymptotically flat space-times and fields governed by tail-free propagation have weak tails, but minimally coupled scalar fields in a cosmological scenario have strong tails.Comment: 17 pages, Revtex, to appear in Classical and Quantum Gravit

Macular Pigment and Visual Function in Patients With Glaucoma: The San Diego Macular Pigment Study.

PurposeAlthough recent studies have shown that macular pigment (MP) is significantly lower in glaucoma patients, this relationship merits further investigation.MethodsThis cross-sectional study included 85 glaucoma patients and 22 controls. All subjects had standard automated perimetry (SAP) and retinal nerve fiber layer (RNFL) thickness measurements. Intake of lutein (L) and zeaxanthin (Z) was estimated using a novel dietary screener. The Heidelberg Spectralis dual-wavelength autofluorescence (AF) technology was employed to study the relationship between MP and glaucoma. The association between MP volume and glaucoma was investigated using linear regression models accounting for potential confounding factors.ResultsGlaucoma patients had significantly worse SAP mean deviation (MD) and lower RNFL thickness in the study eye compared to control subjects (P < 0.001 for both). MP (volume) was comparable between groups (P = 0.436). In the univariable model, diagnosis of glaucoma was not associated with MP volume (R2 = 1.22%; P = 0.257). Dietary intake of L and Z was positively and significantly related to MP in the univariable (P = 0.022) and multivariable (P = 0.020) models.ConclusionsThese results challenge previous studies that reported that glaucoma is associated with low MP. Dietary habits were found to be the main predictor of MP in this sample. Further research is merited to better understand the relationship between glaucoma, MP, and visual performance in these patients

On the importance of disc chemistry in the formation of protoplanetary disc rings

Radial substructures have now been observed in a wide range of protoplanetary discs (PPDs), from young to old systems, however their formation is still an area of vigorous debate. Recent magnetohydrodynamic (MHD) simulations have shown that rings and gaps can form naturally in PPDs when non-ideal MHD effects are included. However these simulations employ ad-hoc approximations to the magnitudes of the magnetic diffusivities in order to facilitate ring growth. We replace the parametrisation of these terms with a simple chemical network and grain distribution model to calculate the non-ideal effects in a more self-consistent way. We use a range of grain distributions to simulate grain formation for different disc conditions. Including ambipolar diffusion, we find that large grain populations (> 1{\mu}m), and those including a population of very small polyaromatic hydrocarbons (PAHs) facilitate the growth of periodic, stable rings, while intermediate sized grains suppress ring formation. Including Ohmic diffusion removes the positive influence of PAHs, with only large grain populations still producing periodic ring and gap structures. These results relate closely to the degree of coupling between the magnetic field and the neutral disc material, quantified by the non-dimensional Elsasser number {\Lambda} (the ratio of magnetic forces to Coriolis force). For both the ambipolar-only and ambipolar-ohmic cases, if the total Elsasser number is initially of order unity along the disc mid-plane, ring and gap structures may develop.Comment: Accepted for publication in MNRAS, 19 pages, 13 figure