Further Observations and Analysis of the Rapidly Pulsating Subdwarf B Star EC 20117-4014

We present the results of further observations and the subsequent analysis of the rapidly pulsating subdwarf B star EC 20117-4014. Despite our efforts, the only pulsations detected were those already reported by O'Donoghue et al., at 137.3, 142.1, and 157.4 s. We attempted a detailed asteroseismological analysis by thoroughly exploring the four-dimensional parameter space defining our equilibrium stellar structures [Teff, logg, M*, logq(H)] in search of models that could account precisely for the three observed periodicities. We were able to isolate just two potential families of optimal models, one of which is to be preferred on the basis of the period fit achieved and the surface gravity inferred. To proceed, we used external constraints on the effective temperature from published independent optical spectroscopy. Unfortunately, the contamination of the optical spectrum of EC 20117-4014 made it hard to quantify the uncertainties on the estimated spectroscopic temperature of ~34,800 K, and consequently, we adopted the conservative point of view that the true value would lie somewhere in the rather broad interval 32,800-36,800 K. Despite this limitation, leading to less accurate estimates of structural parameters than has been possible before for isolated pulsating EC 14026 stars, we still find that our asteroseismological exercise has been quite fruitful. Indeed, on the basis of our current models, we find that EC 20117-4014 would have a (logarithmic) surface gravity in the range 5.848-5.864 dex, a total mass in the range 0.50-0.59 Msolar, and a (logarithmic) fractional mass of its H envelope in the interval from -4.10 to -4.25 dex. From these primary parameters, we obtained useful estimates of secondary quantities such as the radius, the luminosity, the absolute visual magnitude, and the distance

ENGINEERING AN OLEOGINOUS YEAST FOR THE PRODUCTION OF BIODIESEL

poster abstractThere are economic and social interests in replacing the current energy dependence we have on petroleum-based oleochemicals. Yarrowia lipolytica, an oleaginous yeast, has the ability to metabolize unique carbon sources, particularly hydrocarbons and to accumulate large amounts of lipids which could be developed into a source of biodiesel. The ability of Y. lipolytica to accumulate triacylglycerols in lipid droplets and the complete sequencing of its genome make Y. lipolytica a viable organism to genetically engineer for the production of large quantities of biodiesel precursors. The purpose of this project is to genetically modify Y. lipolytica to further increase its production of triacylglycerols by knocking out genes that encode enzymes involved in the β-oxidation of fatty acids. This genetic modification will be accomplished by using homologous recombination to disrupt the genes POX3-5 and POT1. The 5’ and 3’ untranslated regions of POX3-5 and POT1 were amplified by polymerase chain reaction and cloned to allow a drug resistance gene to be introduced between them. Following cloning, these genes will be knocked out from the Y. lipolytica genome using drug resistance as a marker. The disruption of these genes is expected to increase the accumulation of triacylglycerols in Y. lipolytica lipid droplets versus the wild-type. Progress towards the goals of this project will be reported

Non linear equation of state and effective phantom divide in brane models

Here, DGP model of brane-gravity is analyzed and compared with the standard general relativity and Randall-Sundrum cases using non-linear equation of state. Phantom fluid is known to violate the weak energy condition. In this paper, it is found that this characteristic of phantom energy is affected drastically by the negative brane-tension $\lambda$ of the RS-II model. It is found that in DGP model strong energy condition(SEC) is always violated and the universe accelerates only where as in RS-II model even SEC is not violated for $1 < \rho/\lambda < 2$ and the universe decelerates

Graviton Resonances in E+ E- -> MU+ MU- at Linear Colliders with Beamstrahlung and ISR Effects

Electromagnetic radiation emitted by the colliding beams is expected to play an important role at the next generation of high energy e^+ e^- linear collider(s). Focusing on the simplest process e+e- -> mu+ mu-, we show that radiative effects like initial state radiation (ISR) and beamstrahlung can lead to greatly-enhanced signals for resonant graviton modes of the Randall-Sundrum model.Comment: 20 pages Latex, 7 eps figure

String Theoretic Bounds on Lorentz-Violating Warped Compactification

We consider warped compactifications that solve the 10 dimensional supergravity equations of motion at a point, stabilize the position of a D3-brane world, and admit a warp factor that violates Lorentz invariance along the brane. This gives a string embedding of ``asymmetrically warped'' models which we use to calculate stringy (\alpha') corrections to standard model dispersion relations, paying attention to the maximum speeds for different particles. We find, from the dispersion relations, limits on gravitational Lorentz violation in these models, improving on current limits on the speed of graviton propagation, including those derived from field theoretic loops. We comment on the viability of models that use asymmetric warping for self-tuning of the brane cosmological constant.Comment: 20pg, JHEP3; v2 additional references, slight change to intro; v3. added referenc

Pulsating hot O subdwarfs in ω Centauri: mapping a unique instability strip on the extreme horizontal branch

We present the results of an extensive survey for rapid pulsators among Extreme Horizontal Branch (EHB) stars in ω Cen. The observations performed consist of nearly 100 h of time-series photometry for several off-centre fields of the cluster, as well as low-resolution spectroscopy for a partially overlapping sample. We obtained photometry for some 300 EHB stars, for around half of which we are able to recover light curves of sufficient quality to either detect or place meaningful non-detection limits for rapid pulsations. Based on the spectroscopy, we derive reliable values of log g, Teff and log N(He) /N(H) for 38 targets, as well as good estimates of the effective temperature for another nine targets, whose spectra are slightly polluted by a close neighbour in the image. The survey uncovered a total of five rapid variables with multi-periodic oscillations between 85 and 125 s. Spectroscopically, they form a homogeneous group of hydrogen-rich subdwarf O stars clustered between 48 000 and 54 000 K. For each of the variables we are able to measure between two and three significant pulsations believed to constitute independent harmonic oscillations. However, the interpretation of the Fourier spectra is not straightforward due to significant fine structure attributed to strong amplitude variations. In addition to the rapid variables, we found an EHB star with an apparently periodic luminosity variation of ~2700 s, which we tentatively suggest may be caused by ellipsoidal variations in a close binary. Using the overlapping photometry and spectroscopy sample we are able to map an empirical ω Cen instability strip in log g − Teff space. This can be directly compared to the pulsation driving predicted from the Montréal “second-generation” models regularly used to interpret the pulsations in hot B subdwarfs. Extending the parameter range of these models to higher temperatures, we find that the region where p-mode excitation occurs is in fact bifurcated, and the well-known instability strip between 29 000−36 000 K where the rapid subdwarf B pulsators are found is complemented by a second one above 50 000 K in the models. While significant challenges remain at the quantitative level, we believe that the same κ-mechanism that drives the pulsations in hot B subdwarfs is also responsible for the excitation of the rapid oscillations observed in the ω Cen variables. Intriguingly, the ω Cen variables appear to form a unique class. No direct counterparts have so far been found either in the Galactic field, nor in other globular clusters, despite dedicated searches. Conversely, our survey revealed no ω Cen representatives of the rapidly pulsating hot B subdwarfs found among the field population, though their presence cannot be excluded from the limited sample

The Spectral Zeta Function for Laplace Operators on Warped Product Manifolds of the type I×fNI\times_{f} N

In this work we study the spectral zeta function associated with the Laplace operator acting on scalar functions defined on a warped product of manifolds of the type $I\times_{f} N$ where $I$ is an interval of the real line and $N$ is a compact, $d$-dimensional Riemannian manifold either with or without boundary. Starting from an integral representation of the spectral zeta function, we find its analytic continuation by exploiting the WKB asymptotic expansion of the eigenfunctions of the Laplace operator on $M$ for which a detailed analysis is presented. We apply the obtained results to the explicit computation of the zeta regularized functional determinant and the coefficients of the heat kernel asymptotic expansion.Comment: 29 pages, LaTe

Friedmann-like equations for High Energy Area of Universe

In this paper, evolution of the high energy area of universe, through the scenario of 5 dimensional (5D) universe, has been studied. For this purpose, we solve Einstein equations for 5D metric and 5D perfect fuid to derive Friedmann-like equations. Then we obtain the evolution of scale factor and energy density with respect to both space-like and time-like extra dimensions. We obtain the novel equations for the space-like extra dimension and show that the matter with zero pressure cannot exist in the bulk. Also, for dark energy fuid and vacuum fluid, we have both accelerated expansion and contraction in the bulk.Comment: 9 pages, Accepted to publication in IJTP 26 June 2012. arXiv admin note: substantial text overlap with arXiv:1202.497

Improved tests of extra-dimensional physics and thermal quantum field theory from new Casimir force measurements

We report new constraints on extra-dimensional models and other physics beyond the Standard Model based on measurements of the Casimir force between two dissimilar metals for separations in the range 0.2--1.2 $\mu$m. The Casimir force between an Au-coated sphere and a Cu-coated plate of a microelectromechanical torsional oscillator was measured statically with an absolute error of 0.3 pN. In addition, the Casimir pressure between two parallel plates was determined dynamically with an absolute error of $\approx 0.6$ mPa. Within the limits of experimental and theoretical errors, the results are in agreement with a theory that takes into account the finite conductivity and roughness of the two metals. The level of agreement between experiment and theory was then used to set limits on the predictions of extra-dimensional physics and thermal quantum field theory. It is shown that two theoretical approaches to the thermal Casimir force which predict effects linear in temperture are ruled out by these experiments. Finally, constraints on Yukawa corrections to Newton's law of gravity are strengthened by more than an order of magnitude in the range 56 nm to 330 nm.Comment: Revtex 4, 35 pages, 14 figures in .gif format, accepted for publication in Phys. Rev.

Ultrarelativistic black hole in an external electromagnetic field and gravitational waves in the Melvin universe

We investigate the ultrarelativistic boost of a Schwarzschild black hole immersed in an external electromagnetic field, described by an exact solution of the Einstein-Maxwell equations found by Ernst (the ``Schwarzschild-Melvin'' metric). Following the classical method of Aichelburg and Sexl, the gravitational field generated by a black hole moving ``with the speed of light'' and the transformed electromagnetic field are determined. The corresponding exact solution describes an impulsive gravitational wave propagating in the static, cylindrically symmetric, electrovac universe of Melvin, and for a vanishing electromagnetic field it reduces to the well known Aichelburg-Sexl pp-wave. In the boosting process, the original Petrov type I of the Schwarzschild-Melvin solution simplifies to the type II on the impulse, and to the type D elsewhere. The geometry of the wave front is studied, in particular its non-constant Gauss curvature. In addition, a more general class of impulsive waves in the Melvin universe is constructed by means of a six-dimensional embedding formalism adapted to the background. A coordinate system is also presented in which all the impulsive metrics take a continuous form. Finally, it is shown that these solutions are a limiting case of a family of exact gravitational waves with an arbitrary profile. This family is identified with a solution previously found by Garfinkle and Melvin. We thus complement their analysis, in particular demonstrating that such spacetimes are of type II and belong to the Kundt class.Comment: 11 pages, REVTeX