5,661 research outputs found
Miniaturized Circular-Waveguide Probe Antennas Using Metamaterial Liners
This work presents the radiation performance of open-ended circular-waveguide
probe antennas that have been miniaturized by the introduction of thin
metamaterial liners. The liners introduce an HE mode well below the
natural cutoff frequency, which provides substantial gain improvements over a
similarly sized waveguide probe. A new feeding arrangement employing a
shielded-loop source embedded inside the miniaturized waveguide is developed to
efficiently excite the HE mode and avoid the excitation of other modes
across the frequency reduced band while maintaining the antenna's compactness.
A metamaterial-lined circular-waveguide probe antenna operating over 42% below
its natural cutoff frequency is designed to provide a radiation efficiency of
up to 28.8%. A simple, printed-circuit implementation of the metamaterial liner
based on inductively loaded wires is proposed and its dispersion features are
discussed.Comment: The manuscript has been revised for publication as a 6 page
communication in the IEEE Transactions on Antennas and Propagation. This
included a reduction of material in the theory section, removal of all
discussion on anisotropic theory, and introduction of a novel excitation
sourc
Analog-digital simulation of transient-induced logic errors and upset susceptibility of an advanced control system
A simulation study is described which predicts the susceptibility of an advanced control system to electrical transients resulting in logic errors, latched errors, error propagation, and digital upset. The system is based on a custom-designed microprocessor and it incorporates fault-tolerant techniques. The system under test and the method to perform the transient injection experiment are described. Results for 2100 transient injections are analyzed and classified according to charge level, type of error, and location of injection
Radiation reaction in the 2.5PN waveform from inspiralling binaries in circular orbits
In this Comment we compute the contributions of the radiation reaction force
in the 2.5 post-Newtonian (PN) gravitational wave polarizations for compact
binaries in circular orbits. (i) We point out and correct an inconsistency in
the derivation of Arun, Blanchet, Iyer, and Qusailah. (ii) We prove that all
contributions from radiation reaction in the 2.5PN waveform are actually
negligible since they can be absorbed into a modification of the orbital phase
at the 5PN order.Comment: 7 pages, no figures, submitted to CQ
Fission-fusion dynamics and group-size dependent composition in heterogeneous populations
Many animal groups are heterogeneous and may even consist of individuals of
different species, called mixed-species flocks. Mathematical and computational
models of collective animal movement behaviour, however, typically assume that
groups and populations consist of identical individuals. In this paper, using
the mathematical framework of the coagulation-fragmentation process, we develop
and analyse a model of merge and split group dynamics, also called
fission-fusion dynamics, for heterogeneous populations that contain two types
(or species) of individuals. We assume that more heterogeneous groups
experience higher split rates than homogeneous groups, forming two daughter
groups whose compositions are drawn uniformly from all possible partitions. We
analytically derive a master equation for group size and compositions and find
mean-field steady-state solutions. We predict that there is a critical group
size below which groups are more likely to be homogeneous and contain the
abundant type/species. Despite the propensity of heterogeneous groups to split
at higher rates, we find that groups are more likely to be heterogeneous but
only above the critical group size. Monte-Carlo simulation of the model show
excellent agreement with these analytical model results. Thus, our model makes
a testable prediction that composition of flocks are group-size dependent and
do not merely reflect the population level heterogeneity. We discuss the
implications of our results to empirical studies on flocking systems.Comment: 19 pages, 8 figure
Free-Space Imaging Beyond the Diffraction Limit Using a Veselago-Pendry Transmission-Line Superlens
Focusing using conventional lenses relies on the collection and interference
of propagating waves, but discounts the evanescent waves that decay rapidly
from the source. Since these evanescent waves contain the finest details of the
source, the image suffers a loss of resolution and is referred to as
'diffraction-limited'. Superlensing is the ability to create an image with fine
features beyond the diffraction limit, and can be achieved with a
'Veselago-Pendry' lens made from a metamaterial. Such a Veselago-Pendry
superlens for imaging in free space must be stringently designed to restore
both propagating and evanescent waves, but meeting these design conditions
(isotropic n = epsilon_r = mu_r = -1) has proven difficult and has made its
realization elusive. We demonstrate free-space imaging with a resolution over
three times better than the diffraction limit at microwave frequencies using a
Veselago-Pendry metamaterial superlens based on the negative-refractive-index
transmission-line (NRI-TL) approach, which affords precise control over its
electromagnetic properties and is also less susceptible to losses than other
approaches. A microwave superlens can be particularly useful for illumination
and discrimination of closely spaced buried objects over practical distances by
way of back-scattering, e.g. in tumour or landmine detection, or for targeted
irradiation/hyperthermia.Comment: 19 pages, 7 figures, submitted to IEEE Transactions on Antennas and
Propagatio
Magnetic anomalies in single crystalline ErPd2Si2
Considering certain interesting features in the previously reported 166Er
Moessbauer effect and neutron diffraction data on the polycrystalline form of
ErPd2Si2 crystallizing in ThCr2Si2-type tetragonal structure, we have carried
out magnetic measurements (1.8 to 300 K) on the single crystalline form of this
compound. We observe significant anisotropy in the absolute values of
magnetization (indicating that the easy axis is c-axis) as well as in the
features due to magnetic ordering in the plot of magnetic susceptibility (chi)
versus temperature (T) at low temperatures. The chi(T) data reveal that there
is a pseudo-low dimensional magnetic order setting in at 4.8 K, with a
three-dimensional antiferromagnetic ordering setting in at a lower temperature
(3.8 K). A new finding in the chi(T) data is that, for H//, but not for
H//, there is a broad shoulder in the range 8-20 K, indicative of the
existence of magnetic correlations above 5 K as well, which could be related to
the previously reported slow-relaxation-dominated Moessbauer spectra.
Interestingly, the temperature coefficient of electrical resistivity is found
to be isotropic; no feature due to magnetic ordering could be detected in the
electrical resistivity data at low temperatures, which is attributed to
magnetic Brillioun-zone boundary gap effects. The results reveal complex nature
of the magnetism of this compound
Higher signal harmonics, LISA's angular resolution, and dark energy
It is generally believed that the angular resolution of the Laser
Interferometer Space Antenna (LISA) for binary supermassive black holes (SMBH)
will not be good enough to identify the host galaxy or galaxy cluster. This
conclusion, based on using only the dominant harmonic of the binary SMBH
signal, changes substantially when higher signal harmonics are included in
assessing the parameter estimation problem. We show that in a subset of the
source parameter space the angular resolution increases by more than a factor
of 10, thereby making it possible for LISA to identify the host galaxy/galaxy
cluster. Thus, LISA's observation of certain binary SMBH coalescence events
could constrain the dark energy equation of state to within a few percent,
comparable to the level expected from other dark energy missions.Comment: 15 pages, no figures. Final version to appear in Phys. Rev.
Probing the non-linear structure of general relativity with black hole binaries
Observations of the inspiral of massive binary black holes (BBH) in the Laser
Interferometer Space Antenna (LISA) and stellar mass binary black holes in the
European Gravitational-Wave Observatory (EGO) offer an unique opportunity to
test the non-linear structure of general relativity. For a binary composed of
two non-spinning black holes, the non-linear general relativistic effects
depend only on the masses of the constituents. In a recent letter, we explored
the possibility of a test to determine all the post-Newtonian coefficients in
the gravitational wave-phasing.
However, mutual covariances dilute the effectiveness of such a test. In this
paper, we propose a more powerful test in which the various post-Newtonian
coefficients in the gravitational wave phasing are systematically measured by
treating three of them as independent parameters and demanding their mutual
consistency. LISA (EGO) will observe BBH inspirals with a signal-to-noise ratio
of more than 1000 (100) and thereby test the self-consistency of each of the
nine post-Newtonian coefficients that have so-far been computed, by measuring
the lower order coefficients to a relative accuracy of
(respectively, ) and the higher order coefficients to a relative
accuracy in the range -0.1 (respectively, -1).Comment: 5 pages, 4 figures. Revised version, accepted for publication in
Phys. Rev
Quality control of molluscan shellfish products
Since the molluscan shellfish filter large
quantities of water during their feeding process,
there are chances of accumulation of toxic heavy
metals in their body, if the environment is
polluted with toxic metals
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