Covariant action for a string in doubled yet gauged spacetime

The section condition in double field theory has been shown to imply that a physical point should be one-to-one identified with a gauge orbit in the doubled coordinate space. Here we show the converse is also true, and continue to explore the idea of `spacetime being doubled yet gauged'. Introducing an appropriate gauge connection, we construct a string action, with an arbitrary generalized metric, which is completely covariant with respect to the coordinate gauge symmetry, generalized diffeomorphisms, world-sheet diffeomorphisms, world-sheet Weyl symmetry and O(D,D) T-duality. A topological term previously proposed in the literature naturally arises and a self-duality condition follows from the equations of motion. Further, the action may couple to a T-dual background where the Riemannian metric becomes everywhere singular.Comment: 1+29 pages; v2) Refs added. minor changes. To appear in Nuclear Physics

Topological Twisting of Multiple M2-brane Theory

Bagger-Lambert-Gustavsson theory with infinite dimensional gauge group has been suggested to describe M5-brane as a condensation of multiple M2-branes. Here we perform a topological twisting of the Bagger-Lambert-Gustavsson theory. The original SO(8) R-symmetry is broken to SO(3)XSO(5), where the former may be interpreted as a diagonal subgroup of the Euclidean M5-brane world-volume symmetry SO(6), while the latter is the isometry of the transverse five directions. Accordingly the resulting action contains an one-form and five scalars as for the bosonic dynamical fields. We further lift the action to a generic curved three manifold. In order to make sure the genuine topological invariance, we construct an off-shell formalism such that the scalar supersymmetry transformations are nilpotent strictly off-shell and independent of the metric of the three manifold. The one loop partition function around a trivial background yields the Ray-Singer torsion. The BPS equation involves an M2-brane charge density given by a Nambu-Goto action defined in an internal three-manifold.Comment: 20 pages, no figure; Refs added, minor improvement, to appear in JHE

Supersymmetric Double Field Theory: Stringy Reformulation of Supergravity

We construct a supersymmetric extension of double field theory that realizes the ten-dimensional Majorana-Weyl local supersymmetry. In terms of a stringy differential geometry we proposed earlier, our action consists of five simple terms -- two bosonic plus three fermionic -- and manifests not only diffeomorphism and one-form gauge symmetry of B-field, but also O(10,10) T-duality as well as a direct product of two local Lorentz symmetries, SO(1,9) \times SO(9,1). A gauge fixing that identifies the double local Lorentz groups reduces our action to the minimal supergravity in ten dimensions.Comment: Initally submitted to PRL on 28th November 2011. 5+4 pages (Five pages of publication in PRD Rapid Communications plus Four pages of Appendix). v4) Typo in Eq.(34) fixed, Erratum to be published in journal. cf. http://www.newton.ac.uk/programmes/BSM/seminars/021611301.htm

The Solar-Type Contact Binary BX Pegasi Revisited

We present the results of new CCD photometry for the contact binary BX Peg, made during three successive months beginning on September 2008. As do historical light curves, our observations display an O'Connell effect and the November data by themselves indicate clear evidence for very short-time brightness disturbance. For these variations, model spots are applied separately to the two data set of Group I (Sep.--Oct.) and Group II (Nov.). The former is described by a single cool spot on the secondary photosphere and the latter by a two-spot model with a cool spot on the cool star and a hot one on either star. These are generalized manifestations of the magnetic activity of the binary system. Twenty light-curve timings calculated from Wilson-Devinney code were used for a period study, together with all other minimum epochs. The complex period changes of BX Peg can be sorted into a secular period decrease caused dominantly by angular momentum loss due to magnetic stellar wind braking, a light-travel-time (LTT) effect due to the orbit of a low-mass third companion, and a previously unknown short-term oscillation. This last period modulation could be produced either by a second LTT orbit with a period of about 16 yr due to the existence of a fourth body or by the effect of magnetic activity with a cycle length of about 12 yr.Comment: 23 pages, including 6 figures and 8 tables, accepted for publication in PAS

Multidimensional item response theory: A SAS MDIRT macro and empirical study of PIAT math test.

Even though unidimensional item response theory (IRT) provides a better framework for practical test settings than classical test theory (CTT), theoretical and empirical evidence shows that most response data violate the assumption of unidimensionality. There are several computer programs dedicated to estimating parameters based on the multidimensional perspective (MIRT). However, their accessibility is still costly, and they are not easy to use. In this paper, we present a SAS macro called MDIRT-FIT, to increase accessibility to the benefits obtained from this recent measurement theory development. The program is developed to estimate parameters based on a compensatory multidimensional item response theory (MIRT) model for dichotomous data. The full information item factor analysis model with an EM algorithm suggested in Bock & Aitken (1988) is implemented in the SAS programs. The estimation program written in SAS/IMLRTM provides both parameters of MIRT and parameters of the factor analysis model with their associated standard errors and overall model fit statistics. The maximum number of latent traits that can be estimated with this program is limited to five latent dimensions because of both computational burden and practical sufficiency. The accuracy and stability of the SAS macro is examined by utilizing simulated data of examinees' responses. The PIAT math test, a subset of the Peabody Individual Achievement Test, was examined to validate the comparability of the SAS macro to TESTFACT which is widely used for estimating parameters of MIRT models

Assessment of an Initial Roadmap for Protein-Protein-Small Molecule Networks in the Brain of Alzheimer’s Disease

Alzheimer’s disease (AD) is one of the fatal and leading causes of death. Amyloid-beta (Abeta) and transition metal ions [which can bind each other and may influence peptide aggregation, producing toxic oligomeric Abeta species, and reactive oxygen species (ROS)] have been suggested to be involved in AD pathogenesis. In addition, there may be interactions of Abeta with other proteins [i.e., human serum albumin (HSA), S100 proteins]. Unfortunately, a clear relationship between Abeta, metal ions, and other proteins in AD etiology has not been identified. In order to understand the role of metal-associated Abeta (metal–Abeta) species in AD, several chemical tools have been studied and presented their abilities toward A-beta. The structural moieties responsible for such reactivities, however, are not completely elucidated. To gain a better understanding of structure-interaction-reactivity relationships between small molecules and metal-free Abeta or metal–Abeta, naturally occurring flavonoids (morin, quercetin, galangin, and luteolin) with structural variations (i.e., the number and position of hydroxyl functionality) and two series of rationally designed chemical reagents were investigated. Four flavonoids in this study could significantly modulate aggregation pathways of metal–Abeta over metal-free Abeta and mediate Abeta-linked cytotoxicity to different extents. The variations of hydroxyl groups within a flavonoid backbone can modify their reactivity toward Abeta species. In addition, the motif of N1,N1-dimethylbenzene-1,4-diamine could be considered to be essential for targeting and modulating Abeta aggregation pathways and scavenging free radicals. Moreover, we have examined the interactions of Abeta with other proteins (i.e., HSA, S100 proteins) with and without metal ions and their influence on the peptide aggregation. HSA and S100 proteins could alter the Abeta aggregation pathways by directly binding to Abeta followed by formation of complexes which possibly are less toxic than protein-free Abeta aggregates. Taken together, the studies described in this thesis demonstrate the pivotal functionalities of chemical tools for their reactivity toward metal-free and metal-bound Abeta, as well as present the initial information on a link of protein–protein–small molecule (metal) networks to AD etiology. Our overall results and observations will be able to provide insight into new discovery of chemical tools and therapeutics toward AD.PhDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/116719/1/hyuckjin_1.pd