Molecular Hydrodynamics: Vortex Formation and Sound Wave Propagation

In the present study, quantitative feasibility tests of the hydrodynamic description of a two-dimensional fluid at the molecular level are performed, both with respect to length and time scales. Using high-resolution fluid velocity data obtained from extensive molecular dynamics simulations, we computed the transverse and longitudinal components of the velocity field by the Helmholtz decomposition and compared them with those obtained from the linearized Navier-Stokes (LNS) equations with time-dependent transport coefficients. By investigating the vortex dynamics and the sound wave propagation in terms of these field components, we confirm the validity of the LNS description for times comparable to or larger than several mean collision times. The LNS description still reproduces the transverse velocity field accurately at smaller times, but it fails to predict characteristic patterns of molecular origin visible in the longitudinal velocity field. Based on these observations, we validate the main assumptions of the mode-coupling approach. The assumption that the velocity autocorrelation function can be expressed in terms of the fluid velocity field and the tagged particle distribution is found to be remarkably accurate even for times comparable to or smaller than the mean collision time. This suggests that the hydrodynamic-mode description remains valid down to the molecular scale

Survey for Transiting Extrasolar Planets in Stellar Systems. II. Spectrophotometry and Metallicities of Open Clusters

We present metallicity estimates for seven open clusters based on spectrophotometric indices from moderate-resolution spectroscopy. Observations of field giants of known metallicity provide a correlation between the spectroscopic indices and the metallicity of open cluster giants. We use \chi^2 analysis to fit the relation of spectrophotometric indices to metallicity in field giants. The resulting function allows an estimate of the target-cluster giants' metallicities with an error in the method of \pm0.08 dex. We derive the following metallicities for the seven open clusters: NGC 1245, [m/H]=-0.14\pm0.04; NGC 2099, [m/H]=+0.05\pm0.05; NGC 2324, [m/H]=-0.06\pm0.04; NGC 2539, [m/H]=-0.04\pm0.03; NGC 2682 (M67), [m/H]=-0.05\pm0.02; NGC 6705, [m/H]=+0.14\pm0.08; NGC 6819, [m/H]=-0.07\pm0.12. These metallicity estimates will be useful in planning future extra-solar planet transit searches since planets may form more readily in metal-rich environments.Comment: 38 pages, including 12 figures. Accepted for publication in A

Calabi-Yau Orbifolds and Torus Coverings

The theory of coverings of the two-dimensional torus is a standard part of algebraic topology and has applications in several topics in string theory, for example, in topological strings. This paper initiates applications of this theory to the counting of orbifolds of toric Calabi-Yau singularities, with particular attention to Abelian orbifolds of C^D. By doing so, the work introduces a novel analytical method for counting Abelian orbifolds, verifying previous algorithm results. One identifies a p-fold cover of the torus T^{D-1} with an Abelian orbifold of the form C^D/Z_p, for any dimension D and a prime number p. The counting problem leads to polynomial equations modulo p for a given Abelian subgroup of S_D, the group of discrete symmetries of the toric diagram for C^D. The roots of the polynomial equations correspond to orbifolds of the form C^D/Z_p, which are invariant under the corresponding subgroup of S_Ds. In turn, invariance under this subgroup implies a discrete symmetry for the corresponding quiver gauge theory, as is clearly seen by its brane tiling formulation.Comment: 33 pages, 5 figures, 7 tables; version published on JHE

Environmental Influences on Juvenile Fish Abundances in a River-Dominated Coastal System

We investigated the influence of climatic and environmental factors on variations in juvenile abundances of marine fishes in a river-dominated coastal system of the north-central Gulf of Mexico, where an elevated primary productivity sustains fisheries of high economic importance. Fish were collected monthly with an otter trawl at three stations near Mobile Bay from 1982 to 2007. Fish sizes were used to isolate juvenile stages within the data set, and monthly patterns in juvenile fish abundance and size were then used to identify seasonal peaks for each species. The average numbers of juvenile fish collected during these seasonal peaks in each year were used as indices of annual juvenile abundances and were related to corresponding seasonal averages of selected environmental factors via a combination of principal components analysis and co-inertia analysis. Factors contributing the most to explain interannual variations in juvenile fish abundances were river discharge and water temperature during early spring–early summer, wind speed and North Atlantic Oscillation index during late fall–winter, and atmospheric pressure and wind speed during summer–fall. For example, juvenile abundances of southern kingfish Menticirrhus americanus during summer–fall were positively associated with atmospheric pressure and negatively associated with wind speed during this period. Southern kingfish juvenile abundances during late fall–winter were also negatively associated with wind speed during the same period and were positively associated with river discharge during early spring–early summer. Juvenile abundances of the Atlantic croaker Micropogonias undulatus during early spring–early summer were negatively associated with river discharge and North Atlantic Oscillation during late fall–winter. Overall, the importance of river discharge for many of the species examined emphasizes the major role of watershed processes for marine fisheries production in coastal waters of the north-central Gulf of Mexico

Symmetries of Abelian Orbifolds

Using the Polya Enumeration Theorem, we count with particular attention to C^3/Gamma up to C^6/Gamma, abelian orbifolds in various dimensions which are invariant under cycles of the permutation group S_D. This produces a collection of multiplicative sequences, one for each cycle in the Cycle Index of the permutation group. A multiplicative sequence is controlled by its values on prime numbers and their pure powers. Therefore, we pay particular attention to orbifolds of the form C^D/Gamma where the order of Gamma is p^alpha. We propose a generalization of these sequences for any D and any p.Comment: 75 pages, 13 figures, 30 table

MOx/CNTs Hetero-Structures for Gas Sensing Applications: Role of CNTs Defects

n/

The TAOS Project Stellar Variability I. Detection of Low-Amplitude delta Scuti Stars

We analyzed data accumulated during 2005 and 2006 by the Taiwan-American Occultation Survey (TAOS) in order to detect short-period variable stars (periods of <~ 1 hour) such as delta Scuti. TAOS is designed for the detection of stellar occultation by small-size Kuiper Belt Objects (KBOs) and is operating four 50cm telescopes at an effective cadence of 5Hz. The four telescopes simultaneously monitor the same patch of the sky in order to reduce false positives. To detect short-period variables, we used the Fast Fourier Transform algorithm (FFT) inasmuch as the data points in TAOS light-curves are evenly spaced. Using FFT, we found 41 short-period variables with amplitudes smaller than a few hundredths of a magnitude and periods of about an hour, which suggest that they are low-amplitude delta Scuti stars (LADS). The light-curves of TAOS delta Scuti stars are accessible online at the Time Series Center website (http://timemachine.iic.harvard.edu)Comment: Accepted for publication in A

Syntheses of 3-[(Alkylamino)methylene]-6-methyl-1Hpyridine-2,4-diones, Fluorescence Probes 3-Substituted 7-Methyl-6H-pyrano[3,2-c]pyridine-2,5-diones, and Tetrahydro-6H-2,10-dioxa-9-azaanthracen-1-ones

Various condensation and ring-closing reactions were used for the syntheses of 3-[(alkylamino)methylene]-6-methylpyridine-2,4(1H,3H)-diones, bicyclic pyridinones, and tricyclic morpholinopyrones. For instance, 3-[(dialkylamino)methylene]-6-methylpyridine-2,4(1H,3H)-diones were synthesized from the condensation of dialkylamines and 3-formyl-4-hydroxy-6-methylpyridin-2(1H)-one. 3-Formyl-4-hydroxy-6-methylpyridin-2(1H)-one, derived from 3-formyl-4-hydroxy-6-methylpyridin-2(1H)-one, was used to construct a number of bicyclic pyridinones via a one-pot Knoevenagal and intramolecular lactonization reaction. Tricyclic morpholinopyrones were assembled from a dialkylation reaction involving a dinucleophile, 3-amino-4-hydroxy-6-methyl-2H-pyran-2-one, and a dielectrophile, trans-3,6-dibromocyclohexene. Depending on the reaction conditions, isomers of the tricyclic molecules can be selectively produced, and their chemical structures were unequivocally determined using single-crystal X-ray analyses and 2D COSY spectroscopy. The fluorescently active bicyclic pyridinone compounds show longer absorption (368–430 nm; maximum) and emission wavelengths (450–467 nm) than those of 7-amino-4-methylcoumarin (AMC; λ[subscript abs,max] = 350 nm; λ[subscript em] = 430 nm) suggesting these molecules, such as 3-(2-aminoacetyl)-7-methyl-2H-pyrano[3,2-c]pyridine-2,5(6H)-dione, can be employed as fluorescence activity based probes for tracing biological pathways

Counting Orbifolds

We present several methods of counting the orbifolds C^D/Gamma. A correspondence between counting orbifold actions on C^D, brane tilings, and toric diagrams in D-1 dimensions is drawn. Barycentric coordinates and scaling mechanisms are introduced to characterize lattice simplices as toric diagrams. We count orbifolds of C^3, C^4, C^5, C^6 and C^7. Some remarks are made on closed form formulas for the partition function that counts distinct orbifold actions.Comment: 69 pages, 9 figures, 24 tables; minor correction