1,316 research outputs found
Theory of impedance networks: The two-point impedance and LC resonances
We present a formulation of the determination of the impedance between any
two nodes in an impedance network. An impedance network is described by its
Laplacian matrix L which has generally complex matrix elements. We show that by
solving the equation L u_a = lambda_a u_a^* with orthonormal vectors u_a, the
effective impedance between nodes p and q of the network is Z = Sum_a [u_{a,p}
- u_{a,q}]^2/lambda_a where the summation is over all lambda_a not identically
equal to zero and u_{a,p} is the p-th component of u_a. For networks consisting
of inductances (L) and capacitances (C), the formulation leads to the
occurrence of resonances at frequencies associated with the vanishing of
lambda_a. This curious result suggests the possibility of practical
applications to resonant circuits. Our formulation is illustrated by explicit
examples.Comment: 21 pages, 3 figures; v4: typesetting corrected; v5: Eq. (63)
correcte
A case study of early galaxy cluster with the Athena X-IFU
Context: Observations of the hot gas in distant clusters of galaxies, though
challenging, are key to understand the role of intense galaxy activity,
super-massive black hole feedback and chemical enrichment in the process of
massive halos assembly. Aims: We assess the feasibility to retrieve, using
X-ray hyperspectral data only, the thermodymamical hot gas properties and
chemical abundances of a galaxy cluster of mass M500=7 x , extracted from the Hydrangea hydrodynamical simulation. Methods: We
create mock X-ray observations of the future X-ray Integral Field Unit (X-IFU)
onboard the Athena mission. By forward-modeling the measured 0.4-1 keV surface
brightness, the projected gas temperature and abundance profiles, we
reconstruct the three-dimensional distribution for the gas density, pressure,
temperature and entropy. Results: Thanks to its large field-of-view, high
throughput and exquisite spectral resolution, one X-IFU exposure lasting 100ks
enables reconstructing density and pressure profiles with 20% precision out to
a characteristic radius of R500, accounting for each quantity's intrinsic
dispersion in the Hydrangea simulations. Reconstruction of abundance profiles
requires both higher signal-to-noise ratios and specific binning schemes. We
assess the enhancement brought by longer exposures and by observing the same
object at later evolutionary stages (). Conclusions: Our analysis
highlights the importance of scatter in the radially binned gas properties,
which induces significant effects on the observed projected quantities. The
fidelity of the reconstruction of gas profiles is sensitive to the degree of
gas components mixing along the line-of-sight. Future analyses should aim at
involving dedicated hyper-spectral models and fitting methods that are able to
grasp the complexity of such three-dimensional, multi-phase, diffuse gas
structures.Comment: 15 pages, 11 figures, 3 tables. Accepted for publication in A&
Statistics of level spacing of geometric resonances in random binary composites
We study the statistics of level spacing of geometric resonances in the
disordered binary networks. For a definite concentration within the
interval , numerical calculations indicate that the unfolded level
spacing distribution and level number variance have the
general features. It is also shown that the short-range fluctuation and
long-range spectral correlation lie between the profiles of the
Poisson ensemble and Gaussion orthogonal ensemble (GOE). At the percolation
threshold , crossover behavior of functions and is
obtained, giving the finite size scaling of mean level spacing and
mean level number , which obey the scaling laws, and .Comment: 11 pages, 7 figures,submitted to Phys. Rev.
Avian malaria is absent in juvenile colonial herons (Ardeidae) but not Culex pipiens mosquitoes in the Camargue, Southern France
Apicomplexan blood parasites Plasmodium and Haemoproteus (together termed âAvian malariaâ) and Leucocytozoon are widespread, diverse vector-transmitted blood parasites of birds, and conditions associated with colonial nesting in herons (Ardeidae) and other waterbirds appear perfect for their transmission. Despite studies in other locations reporting high prevalence of parasites in juvenile herons, juvenile Little Egrets (Egretta garzetta) previously tested in the Camargue, Southern France, had a total absence of malaria parasites. This study tested the hypotheses that this absence was due to insufficient sensitivity of the tests of infection; an absence of infective vectors; or testing birds too early in their lives. Blood was sampled from juveniles of four species shortly before fledging: Little Egret (n = 40), Cattle Egret (Bubulcus ibis; n = 40), Black-crowned Night-Heron (Nycticorax nycticorax, n = 40), and Squacco Heron (Ardeola ralloides; n = 40). Sensitive nested-Polymerase Chain Reaction was used to test for the presence of parasites in both birds and host-seeking female mosquitoes captured around the colonies. No malaria infection was found of in any of the heron species. Four different lineages of Plasmodium were detected in pooled samples of female Culex pipiens mosquitoes, including two in potentially infective mosquitoes. These results confirm that the absence of malaria parasites previously demonstrated in Little Egret is not due to methodological limitations. Although the prevalence of infection in mosquitoes was low, conditions within the colonies were suitable for transmission of Plasmodium. These colonial heron species may have evolved strategies for resisting malaria infection through physiological or behavioral mechanisms
Infrared Studies of the Onset of Conductivity in Ultra-Thin Pb Films
In this paper we report the first experimental measurement of the infrared
conductivity of ultra-thin quenched-condensed Pb films. For dc sheet
resistances such that the ac conductance increases with
frequency but is in disagreement with the predictions of weak localization. We
attribute this behavior to the effects of an inhomogeneous granular structure
of these films, which is manifested at the very small probing scale of infrared
measurements. Our data are consistent with predictions of two-dimensional
percolation theory.Comment: Submitted to Physical Review Letter
Comparison of the properties of two fossil groups of galaxies with the normal group NGC 6034 based on multiband imaging and optical spectroscopy
We collected multiband imaging and spectroscopy for two fossil groups (RX
J1119.7+2126 and 1RXS J235814.4+150524) and one normal group (NGC 6034). We
computed photometric redshifts in the central zones of each group, combining
previous data with the SDSS five-band data. For each group we investigated the
red sequence (RS) of the color-magnitude relation and computed the luminosity
functions, stellar population ages and distributions of the group members.
Spectroscopy allowed us to investigate the large-scale surroundings of these
groups and the substructure levels in 1RXS J235814.4+150524 and NGC 6034. The
large-scale environment of 1RXS J235814.4+150524 is poor, though its galaxy
density map shows a clear signature of the surrounding cosmic web. RX
J1119.7+2126 appears to be very isolated, while the cosmic environment of NGC
6034 is very rich. At the group scale, 1RXS J235814.4+150524 shows no
substructure. Galaxies with recent stellar populations seem preferentially
located in the group outskirts. A RS is discernable for all three groups in a
color-magnitude diagram. The luminosity functions based on photometric redshift
selection and on statistical background subtraction have comparable shapes, and
agree with the few points obtained from spectroscopic redshifts. These
luminosity functions show the expected dip between first and second brightest
galaxies for the fossil groups only. Their shape is also regular and relatively
flat at faint magnitudes down to the completeness level for RX J1119.7+2126 and
NGC 6034, while there is a clear lack of faint galaxies for 1RXS
J235814.4+150524. RX J1119.7+2126 is definitely classified as a fossil group;
1RXS J235814.4+150524 also has properties very close to those of a fossil
group, while we confirm that NGC 6034 is a normal group.Comment: Accepted in A&A, english-improved, 5 jpeg figures, and shortened
abstrac
Segregated tunneling-percolation model for transport nonuniversality
We propose a theory of the origin of transport nonuniversality in disordered
insulating-conducting compounds based on the interplay between microstructure
and tunneling processes between metallic grains dispersed in the insulating
host. We show that if the metallic phase is arranged in quasi-one dimensional
chains of conducting grains, then the distribution function of the chain
conductivities g has a power-law divergence for g -> 0 leading to nonuniversal
values of the transport critical exponent t. We evaluate the critical exponent
t by Monte Carlo calculations on a cubic lattice and show that our model can
describe universal as well nonuniversal behavior of transport depending on the
value of few microstructural parameters. Such segregated tunneling-percolation
model can describe the microstructure of a quite vast class of materials known
as thick-film resistors which display universal or nonuniversal values of t
depending on the composition.Comment: 8 pages, 5 figures (Phys. Rev. B - 1 August 2003)(fig1 replaced
MLVA Subtyping of Genovar E Chlamydia trachomatis Individualizes the Swedish Variant and Anorectal Isolates from Men who Have Sex with Men
This study describes a new multilocus variable number tandem-repeat (VNTR) analysis (MLVA) typing system for the discrimination of Chlamydia trachomatis genovar D to K isolates or specimens. We focused our MLVA scheme on genovar E which predominates in most populations worldwide. This system does not require culture and therefore can be performed directly on DNA extracted from positive clinical specimens. Our method was based on GeneScan analysis of five VNTR loci labelled with fluorescent dyes by multiplex PCR and capillary electrophoresis. This MLVA, called MLVA-5, was applied to a collection of 220 genovar E and 94 non-E genovar C. trachomatis isolates and specimens obtained from 251 patients and resulted in 38 MLVA-5 types. The genetic stability of the MLVA-5 scheme was assessed for results obtained both in vitro by serial passage culturing and in vivo using concomitant and sequential isolates and specimens. All anorectal genovar E isolates from men who have sex with men exhibited the same MLVA-5 type, suggesting clonal spread. In the same way, we confirmed the clonal origin of the Swedish new variant of C. trachomatis. The MLVA-5 assay was compared to three other molecular typing methods, ompA gene sequencing, multilocus sequence typing (MLST) and a previous MLVA method called MLVA-3, on 43 genovar E isolates. The discriminatory index was 0.913 for MLVA-5, 0.860 for MLST and 0.622 for MLVA-3. Among all of these genotyping methods, MLVA-5 displayed the highest discriminatory power and does not require a time-consuming sequencing step. The results indicate that MLVA-5 enables high-resolution molecular epidemiological characterisation of C. trachomatis genovars D to K infections directly from specimens
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