16,524 research outputs found
Changes in the measured image separation of the gravitational lens system, PKS 1830-211
We present eight epochs of 43 GHz, dual-polarisation VLBA observations of the
gravitational lens system PKS 1830-211, made over fourteen weeks. A bright,
compact ``core'' and a faint extended ``jet'' are clearly seen in maps of both
lensed images at all eight epochs.
The relative separation of the radio centroid of the cores (as measured on
the sky) changes by up to 87 micro arcsec between subsequent epochs.
A comparison with the previous 43 GHz VLBA observations (Garrett et al. 1997)
made 8 months earlier show even larger deviations in the separation of up to
201 micro arcsec. The measured changes are most likely produced by changes in
the brightness distribution of the background source, enhanced by the
magnification of the lens. A relative magnification matrix that is applicable
on the milliarcsecond scale has been determined by relating two vectors (the
``core-jet'' separations and the offsets of the polarised and total intensity
emission) in the two lensed images. The determinant of this matrix,
-1.13 +/-0.61, is in good agreement with the measured flux density ratio of
the two images. The matrix predicts that the 10 mas long jet, that is clearly
seen in previous 15 and 8.4 GHz VLBA observations (Garrett et al. 1997,
Guirado et al. 1999), should correspond to a 4 mas long jet trailing to the
south-east of the SW image. The clear non-detection of this trailing jet is a
strong evidence for sub-structure in the lens and may require more realistic
lens models to be invoked, e.g. Nair & Garrett (2000).Comment: 8 pages, 5 figure
Carrier mobility and scattering lifetime in electric double-layer gated few-layer graphene
We fabricate electric double-layer field-effect transistor (EDL-FET) devices
on mechanically exfoliated few-layer graphene. We exploit the large capacitance
of a polymeric electrolyte to study the transport properties of three, four and
five-layer samples under a large induced surface charge density both above and
below the glass transition temperature of the polymer. We find that the carrier
mobility shows a strong asymmetry between the hole and electron doping regime.
We then employ ab-initio density functional theory (DFT) calculations to
determine the average scattering lifetime from the experimental data. We
explain its peculiar dependence on the carrier density in terms of the specific
properties of the electrolyte we used in our experiments.Comment: 6 pages, 3 figure
Strong Domination Index in Fuzzy Graphs
Topological indices play a vital role in the area of graph theory and fuzzy
graph (FG) theory. It has wide applications in the areas such as chemical graph
theory, mathematical chemistry, etc. Topological indices produce a numerical
parameter associated with a graph. Numerous topological indices are studied due
to its applications in various fields. In this article a novel idea of
domination index in a FG is defined using weight of strong edges. The strong
domination degree (SDD) of a vertex u is defined using the weight of minimal
strong dominating set (MSDS) containing u. Idea of upper strong domination
number, strong irredundance number, strong upper irredundance number, strong
independent domination number, and strong independence number are explained and
illustrated subsequently. Strong domination index (SDI) of a FG is defined
using the SDD of each vertex. The concept is applied on various FGs like
complete FG, complete bipartite and r-partite FG, fuzzy tree, fuzzy cycle and
fuzzy stars. Inequalities involving the SDD and SDI are obtained. The union and
join of FG is also considered in the study. Applications for SDD of a vertex is
provided in later sections. An algorithm to obtain a MSDS containing a
particular vertex is also discussed in the article
Domination Index in Graphs
The concepts of domination and topological index hold great significance
within the realm of graph theory. Therefore, it is pertinent to merge these
concepts to derive the domination index of a graph. A novel concept of the
domination index is introduced, which utilizes the domination degree of a
vertex. The domination degree of a vertex a is defined as the minimum
cardinality of a minimal dominating set that includes a. The idea of domination
degree and domination index is conducted of graphs like complete graphs,
complete bipartite, r partite graphs, cycles, wheels, paths, book graphs,
windmill graphs, Kragujevac trees. The study is extended to operation in
graphs. Inequalities involving domination degree and already established graph
parameters are discussed. An application of domination degree is discussed in
facility allocation in a city. Algorithm to find a MDS containing a particular
vertex is also discussed in the study
Hyperfine interaction and electronic spin fluctuation study on SrLaFeCoO (x = 0, 1, 2) by high-resolution back-scattering neutron spectroscopy
The study of hyperfine interaction by high-resolution inelastic neutron
scattering is not very well known compared to the other competing techniques
viz. NMR, M\"ossbauer, PACS etc. Also the study is limited mostly to
magnetically ordered systems. Here we report such study on
SrLaFeCoO (x = 0, 1, 2) of which first (SrFeCoO with x
= 0) has a canonical spin spin glass, the second (SrLaFeCoO with x = 1) has
a so-called magnetic glass and the third (LaFeCoO with x = 2) has a
magnetically ordered ground state. Our present study revealed clear inelastic
signal for SrLaFeCoO, possibly also inelastic signal for SrFeCoO
below the spin freezing temperatures but no inelastic signal at all
for for the magnetically ordered LaFeCoO in the neutron scattering
spectra. The broadened inelastic signals observed suggest hyperfine field
distribution in the two disordered magnetic glassy systems and no signal for
the third compound suggests no or very small hyperfine field at the Co nucleus
due to Co electronic moment. For the two magnetic glassy system apart from the
hyperfine signal due only to Co, we also observed electronic spin fluctuations
probably from both Fe and Co electronic moments. \end{abstract
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