Guided Modes of Elliptical Metamaterial Waveguides

The propagation of guided electromagnetic waves in open elliptical metamaterial waveguide structures is investigated. The waveguide contains a negative-index media core, where the permittivity, $\epsilon$ and permeability $\mu$ are negative over a given bandwidth. The allowed mode spectrum for these structures is numerically calculated by solving a dispersion relation that is expressed in terms of Mathieu functions. By probing certain regions of parameter space, we find the possibility exists to have extremely localized waves that transmit along the surface of the waveguide

Mixed Linear Layouts of Planar Graphs

A $k$-stack (respectively, $k$-queue) layout of a graph consists of a total order of the vertices, and a partition of the edges into $k$ sets of non-crossing (non-nested) edges with respect to the vertex ordering. In 1992, Heath and Rosenberg conjectured that every planar graph admits a mixed $1$-stack $1$-queue layout in which every edge is assigned to a stack or to a queue that use a common vertex ordering. We disprove this conjecture by providing a planar graph that does not have such a mixed layout. In addition, we study mixed layouts of graph subdivisions, and show that every planar graph has a mixed subdivision with one division vertex per edge.Comment: Appears in the Proceedings of the 25th International Symposium on Graph Drawing and Network Visualization (GD 2017

Molecular hydrogen deficiency in HI-poor galaxies and its implications for star formation

We use a sample of 47 homogeneous and high sensitivity CO images taken from the Nobeyama and BIMA surveys to demonstrate that, contrary to common belief, a significant number (~40%) of HI-deficient nearby spiral galaxies are also depleted in molecular hydrogen. While HI-deficiency by itself is not a sufficient condition for molecular gas depletion, we find that H2 reduction is associated with the removal of HI inside the galaxy optical disk. Those HI-deficient galaxies with normal H2 content have lost HI mainly from outside their optical disks, where the H2 content is low in all galaxies. This finding is consistent with theoretical models in which the molecular fraction in a galaxy is determined primarily by its gas column density. Our result is supported by indirect evidence that molecular deficient galaxies form stars at a lower rate or have dimmer far infrared fluxes than gas rich galaxies, as expected if the star formation rate is determined by the molecular hydrogen content. Our result is consistent with a scenario in which, when the atomic gas column density is lowered inside the optical disk below the critical value required to form molecular hydrogen and stars, spirals become quiescent and passive evolving systems. We speculate that this process would act on the time-scale set by the gas depletion rate and might be a first step for the transition between the blue and red sequence observed in the color-magnitude diagram.Comment: 12 pages, 9 figures, accepted for publication in Ap

Graph Treewidth and Geometric Thickness Parameters

Consider a drawing of a graph $G$ in the plane such that crossing edges are coloured differently. The minimum number of colours, taken over all drawings of $G$, is the classical graph parameter "thickness". By restricting the edges to be straight, we obtain the "geometric thickness". By further restricting the vertices to be in convex position, we obtain the "book thickness". This paper studies the relationship between these parameters and treewidth. Our first main result states that for graphs of treewidth $k$, the maximum thickness and the maximum geometric thickness both equal $\lceil{k/2}\rceil$. This says that the lower bound for thickness can be matched by an upper bound, even in the more restrictive geometric setting. Our second main result states that for graphs of treewidth $k$, the maximum book thickness equals $k$ if $k \leq 2$ and equals $k+1$ if $k \geq 3$. This refutes a conjecture of Ganley and Heath [Discrete Appl. Math. 109(3):215-221, 2001]. Analogous results are proved for outerthickness, arboricity, and star-arboricity.Comment: A preliminary version of this paper appeared in the "Proceedings of the 13th International Symposium on Graph Drawing" (GD '05), Lecture Notes in Computer Science 3843:129-140, Springer, 2006. The full version was published in Discrete & Computational Geometry 37(4):641-670, 2007. That version contained a false conjecture, which is corrected on page 26 of this versio

Far infrared mapping of three Galactic star forming regions : W3(OH), S 209 & S 187

Three Galactic star forming regions associated with W3(OH), S209 and S187 have been simultaneously mapped in two trans-IRAS far infrared (FIR) bands centered at ~ 140 and 200 micron using the TIFR 100 cm balloon borne FIR telescope. These maps show extended FIR emission with structures. The HIRES processed IRAS maps of these regions at 12, 25, 60 & 100 micron have also been presented for comparison. Point-like sources have been extracted from the longest waveband TIFR maps and searched for associations in the other five bands. The diffuse emission from these regions have been quantified, which turns out to be a significant fraction of the total emission. The spatial distribution of cold dust (T < 30 K) for two of these sources (W3(OH) & S209), has been determined reliably from the maps in TIFR bands. The dust temperature and optical depth maps show complex morphology. In general the dust around S209 has been found to be warmer than that in W3(OH) region.Comment: Accepted for publication in Journal of Astrophysics and Astronomy (20 pages including 8 figures & 3 tables

Building solids inside nano-space: from confined amorphous through confined solvate to confined ‘metastable’ polymorph

The nanocrystallisation of complex molecules inside mesoporous hosts and control over the resulting structure is a significant challenge. To date the largest organic molecule crystallised inside the nano-pores is a known pharmaceutical intermediate – ROY (259.3 g mol1). In this work we demonstrate smart manipulation of the phase of a larger confined pharmaceutical – indomethacin (IMC, 357.8 g mol1), a substance with known conformational flexibility and complex polymorphic behaviour. We show the detailed structural analysis and the control of solid state transformations of encapsulated molecules inside the pores of mesoscopic cellular foam (MCF, pore size ca. 29 nm) and controlled pore glass (CPG, pore size ca. 55 nm). Starting from confined amorphous IMC we drive crystallisation into a confined methanol solvate, which upon vacuum drying leads to the stabilised rare form V of IMC inside the MCF host. In contrast to the pure form, encapsulated form V does not transform into a more stable polymorph upon heating. The size of the constraining pores and the drug concentration within the pores determine whether the amorphous state of the drug is stabilised or it recrystallises into confined nanocrystals. The work presents, in a critical manner, an application of complementary techniques (DSC, PXRD, solid-state NMR, N2 adsorption) to confirm unambiguously the phase transitions under confinement and offers a comprehensive strategy towards the formation and control of nano-crystalline encapsulated organic solids

Mapping the submillimeter spiral wave in NGC 6946

We have analysed SCUBA 850\mum images of the (near) face-on spiral galaxy NGC 6946, and found a tight correlation between dust thermal emission and molecular gas. The map of visual optical depth relates well to the distribution of neutral gas (HI+H2) and implies a global gas-to-dust ratio of 90. There is no significant radial variation of this ratio: this can be understood, since the gas content is dominated by far by the molecular gas. The latter is estimated through the CO emission tracer, which is itself dependent on metallicity, similarly to dust emission. By comparing the radial profile of our visual optical depth map with that of the SCUBA image, we infer an emissivity (dust absorption coefficient) at 850\mum that is 3 times lower than the value measured by COBE in the Milky Way, and 9 times lower than in NGC 891. A decomposition of the spiral structure half way out along the disk of NGC 6946 suggests an interarm optical depth of between 1 and 2. These surprisingly high values represent 40-80% of the visual opacity that we measure for the arm region (abridged).Comment: 12 pages, 9 figures, accepted in A&

Mycobacterium tuberculosis Responds to Chloride and pH as Synergistic Cues to the Immune Status of its Host Cell

PubMed ID: 23592993This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

AzTEC millimeter survey of the COSMOS field - III. Source catalog over 0.72 sq. deg. and plausible boosting by large-scale structure

We present a 0.72 sq. deg. contiguous 1.1mm survey in the central area of the COSMOS field carried out to a 1sigma ~ 1.26 mJy/beam depth with the AzTEC camera mounted on the 10m Atacama Submillimeter Telescope Experiment (ASTE). We have uncovered 189 candidate sources at a signal-to-noise ratio S/N >= 3.5, out of which 129, with S/N >= 4, can be considered to have little chance of being spurious (< 2 per cent). We present the number counts derived with this survey, which show a significant excess of sources when compared to the number counts derived from the ~0.5 sq. deg. area sampled at similar depths in the Scuba HAlf Degree Extragalactic Survey (SHADES, Austermann et al. 2010). They are, however, consistent with those derived from fields that were considered too small to characterize the overall blank-field population. We identify differences to be more significant in the S > 5 mJy regime, and demonstrate that these excesses in number counts are related to the areas where galaxies at redshifts z < 1.1 are more densely clustered. The positions of optical-IR galaxies in the redshift interval 0.6 < z < 0.75 are the ones that show the strongest correlation with the positions of the 1.1mm bright population (S > 5 mJy), a result which does not depend exclusively on the presence of rich clusters within the survey sampled area. The most likely explanation for the observed excess in number counts at 1.1mm is galaxy-galaxy and galaxy-group lensing at moderate amplification levels, that increases in amplitude as one samples larger and larger flux densities. This effect should also be detectable in other high redshift populations.Comment: 21 pages, 17 figures, accepted for publication in MNRA