466 research outputs found
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, and permeability
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 -stack (respectively, -queue) layout of a graph consists of a total
order of the vertices, and a partition of the edges into 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
-stack -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
Graph Treewidth and Geometric Thickness Parameters
Consider a drawing of a graph in the plane such that crossing edges are
coloured differently. The minimum number of colours, taken over all drawings of
, 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 , the maximum
thickness and the maximum geometric thickness both equal .
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 , the maximum book thickness equals if and equals if . 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
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
Connectivity of Sensor ~etworks with Power Control
Abstract-We consider a sensor network with an average of n nodes randomly placed over a region of unit area. We assume that each node is equipped with a wireless transceiver, and are interested in the minimum transmit power required for maintaining connectivity of the network when power control is employed (i.e., each node can choose a power level for transmissiol} independent of any other node). We show that the average power gain per node (th.e ratio of the transmit power required without and with power control) increases with the number of nodes n as (log n)o:l 2 , where a is the path loss exponent
Early growth response gene-2 (Egr-2) regulates the development of B and T cells
The study was supported by Arthritis Research UK.
Copyright @ 2011 Li et al.BACKGROUND: Understanding of how transcription factors are involved in lymphocyte development still remains a challenge. It has been shown that Egr-2 deficiency results in impaired NKT cell development and defective positive selection of T cells. Here we investigated the development of T, B and NKT cells in Egr-2 transgenic mice and the roles in the regulation of distinct stages of B and T cell development. METHODS AND FINDINGS: The expression of Egr1, 2 and 3 were analysed at different stages of T and B cell development by RT-PCT and results showed that the expression was strictly regulated at different stages. Forced expression of Egr-2 in CD2+ lymphocytes resulted in a severe reduction of CD4+CD8+ (DP) cells in thymus and pro-B cells in bone marrow, which was associated with reduced expression of Notch1 in ISP thymocytes and Pax5 in pro-B cells, suggesting that retraction of Egr-2 at the ISP and pro-B cell stages is important for the activation of lineage differentiation programs. In contrast to reduction of DP and pro-B cells, Egr-2 enhanced the maturation of DP cells into single positive (SP) T and NKT cells in thymus, and immature B cells into mature B cells in bone marrow. CONCLUSIONS: Our results demonstrate that Egr-2 expressed in restricted stages of lymphocyte development plays a dynamic, but similar role for the development of T, NKT and B cells.This article is provided by the Brunel Open Access publishing fund
Clinical- and cost-effectiveness of LDL particle-guided statin therapy: A simulation study
AbstractWe used the Archimedes Model, a mathematical simulation model (Model) to estimate the clinical- and cost-effectiveness of using LDL particle concentration (LDL-P) as an adjunct or alternative to LDL cholesterol (LDL-C) to guide statin therapy. LDL-P by NMR has been shown to be a better measure of cardiovascular disease (CVD) risk than LDL-C, and may therefore be a better gauge of the need for and response to statin treatment. Using the Model, we conducted a virtual clinical trial comparing the use of LDL-C alone, LDL-P alone, and LDL-C and LDL-P together to guide treatment in the general adult population, and in high-risk, dyslipidemic subpopulations. In the general population, the 5-year major adverse cardiovascular event (MACE) relative risk reduction (RRR) of LDL-P alone compared to the control arm (LDL-C alone) was 5.0% (95% CI, 4.7–5.3; p p p p In the general population, the costs per quality-adjusted life year (QALY) associated with the use of LDL-P alone were 8913 at 20 years and 25,505 at 20 years with the use of both markers. In high-risk subpopulations, the use of LDL-P alone was cost-saving at 5 years; whereas the cost per QALY for the use of both markers was 859 at 20 years for high-risk dyslipidemics, 649 at 20 years for diabetics, and 7268 at 20 years for patients with prior CHD. In conclusion, the model estimates that using LDL-P to guide statin therapy may reduce the risk of CVD events to a greater extent than does the use of LDL-C alone and maybe cost-effective or cost-saving for high-risk patients
Sampling device for the quantitative assessment of prawn and fish seed resources in the estuarine areas
The need for a suitable and efficient sampler for the quantitative assessment of prawn and fish seed resources of the estuarine areas was very much felt during the field surveys. Dragging or pushing a net was baset with several difficulties in the estuaries and backwaters. To overcome these, several devices such as drag nets, trolley type pushing nets, scoops, traps, etc were tried and finally a simple and at the same time efficient sampler was adopted
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
Effective surface albedo due to snow cover of the surrounding area
Albedo inversion techniques are investigated in this work. Several methods are applied to spectral irradiance data from a measurement campaign held in the German Alps during the spring of 1999. One first method is based on the comparison of measurements of absolute levels of UV irradiance with model calculations. The second method takes advantage of changes in the spectral slope of spectral UV irradiance, which is a function of the surface albedo. In the third method, the surrounding area is partitioned into snow-covered and snow-free regions, and the effective albedo estimated by applying a higher or lower reflectivity to each facet before integrating over the surroundings. We present sensitivity analysis, the differences and the correlations between the various methods as well as the results for the different locations
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