92 research outputs found
A weakly random Universe?
The cosmic microwave background (CMB) radiation is characterized by
well-established scales, the 2.7 K temperature of the Planckian spectrum and
the amplitude of the temperature anisotropy. These features were
instrumental in indicating the hot and equilibrium phases of the early history
of the Universe and its large scale isotropy, respectively. We now reveal one
more intrinsic scale in CMB properties. We introduce a method developed
originally by Kolmogorov, that quantifies a degree of randomness (chaos) in a
set of numbers, such as measurements of the CMB temperature in some region.
Considering CMB as a composition of random and regular signals, we solve the
inverse problem of recovering of their mutual fractions from the temperature
sky maps. Deriving the empirical Kolmogorov's function in the Wilkinson
Microwave Anisotropy Probe's maps, we obtain the fraction of the random signal
to be about 20 per cent, i.e. the cosmological sky is a weakly random one. The
paper is dedicated to the memory of Vladimir Arnold (1937-2010).Comment: 4 pages, 3 figs, A & A (Lett) in press; to match the published
versio
Low flow enhances platelet activation after acute experimental arterial injury
AbstractPurpose: Vascular smooth muscle cell (VSMC) proliferation and migration to the subintima or intimal hyperplasia (IH) occur after arterial injury and are thought to be induced by mitogenic factors released from activated platelets. Because low flow (LF) and shear have been attributed to the localization and progression of IH, we postulated that hemodynamic factors may regulate the degree of platelet activation, as measured by plasma thromboxane B2 (TXB2) and platelet-derived growth factor-AB (PDGF-AB) release at regions of experimental arterial injury. Methods: The right common carotid artery (CCA) was subjected to balloon injury in 18 New Zealand White male rabbits. Flow in the injured CCA was reduced by out-flow ligation (LF group, n = 6) or increased by ligation of the left CCA (high flow [HF] group, n = 6). In six other animals, flow was preserved (normal flow [NF] group). Mean blood flow and pressure in the right CCA were measured thereafter at 10 and 30 minutes. Plasma TXB2 and PDGF-AB levels were determined with the enzyme-linked immunosorbent assay method in each animal with blood samples taken systematically before injury (baseline) and in the distal CCA at similar time points. Results: At 10 minutes, mean blood flow was reduced from 20 ± 2 ml/min in the NF group to 7 ± 1 ml/min in the LF group animals (p < 0.01) and increased to 32 ± 2 ml/min in the HF group animals (p < 0.05). Mean arterial blood pressure did not differ among the groups. Hemodynamic parameters were similar at 10 and 30 minutes. TXB2 levels were more than fourfold greater in the LF group than in the HF and NF groups at both time points (p < 0.05). In addition, there was a twofold increase in plasma PDGF-AB level at 10 minutes in the LF group compared with baseline levels (p < 0.05). Conclusion: Platelet activation at regions of acute vascular injury was determined to be flow dependent. Upregulated platelet activity in low flow conditions may be due to increased platelet exposure time to subendothelial collagen and is greatly attenuated if normal or increased flow is present.(J Vasc Surg 1998;27:910-8.
Options for Scaling up Community-Based Health Insurance for Rural Communities in Armenia
This paper summarises the results of a study which examined international experience with regard to community-based health financing (CBHF) schemes, scaling up CBHF schemes, and the feasibility of scaling up community-based health insurance (CBHI) in Armenia. It was based on a literature review of international experience and qualitative research in Armenia. The recommendations derived from this study have relevance both for Armenia and for the use of CBHI schemes as a tool for promoting pro-poor health system reform in low-resource settings more generally
Cooperative effects in nuclear excitation with coherent x-ray light
The interaction between super-intense coherent x-ray light and nuclei is
studied theoretically. One of the main difficulties with driving nuclear
transitions arises from the very narrow nuclear excited state widths which
limit the coupling between laser and nuclei. In the context of direct
laser-nucleus interaction, we consider the nuclear width broadening that occurs
when in solid targets, the excitation caused by a single photon is shared by a
large number of nuclei, forming a collective excited state. Our results show
that for certain isotopes, cooperative effects may lead to an enhancement of
the nuclear excited state population by almost two orders of magnitude.
Additionally, an update of previous estimates for nuclear excited state
population and signal photons taking into account the experimental advances of
the x-ray coherent light sources is given. The presented values are an
improvement by orders of magnitude and are encouraging for the future prospects
of nuclear quantum optics.Comment: 22 pages, 4 figures, 5 tables; updated to the published version, one
additional results tabl
The power spectrum of the cosmic microwave background Kolmogorov maps: possible clue to correlation of voids
The power spectrum is obtained for the Kolmogorov stochasticity parameter map
for WMAP's cosmic microwave background (CMB) radiation temperature datasets.
The interest for CMB Kolmogorov map is that it can carry direct information
about voids in the matter distribution, so that the correlations in the
distribution of voids have to be reflected in the power spectrum. Although
limited by the angular resolution of the WMAP, this analysis shows the
possibility of acquiring this crucial information via CMB maps. Even the
already obtained behavior, some of which is absent in the simulated maps, can
influence the development of views on the void correlations at the large-scale
web formation.Comment: A & A (Lett.) (accepted), 4 pages, 3 fig
Kolmogorov cosmic microwave background sky
A new map of the sky representing the degree of randomness in the cosmic
microwave background (CMB) temperature has been obtained. The map based on
estimation of the Kolmogorov stochasticity parameter clearly distinguishes the
contribution of the Galactic disk from the CMB and reveals regions of various
degrees of randomness that can reflect the properties of inhomogeneities in the
Universe. For example, among the high randomness regions is the southern
non-Gaussian anomaly, the Cold Spot, with a stratification expected for the
voids. Existence of its counterpart, a Northern Cold Spot with almost identical
randomness properties among other low-temperature regions is revealed. By its
informative power, Kolmogorov's map can be complementary to the CMB temperature
and polarization sky maps.Comment: A & A (in press), to match the published version, 4 pages, 5 figs, 2
Table
Optical transition radiation in fused quartz under external acoustic field
In the present paper we have investigated the optical transition radiation in a plate excited by a longitudinal acoustic wave. The spectral-angular density of the radiated energy is calculated. The numerical examples are given for
a plate of fused quartz. These results show that the acoustic waves allow to control the parameters of the radiation. In particular, new resonance peaks appear in the
spectral distribution of the radiation intensity. The height of the peaks can be tuned by choosing the parameters of the acoustic wave
Plane-mirroring anomaly in the cosmic microwave background maps
The plane-mirror symmetry previously noticed in the Cosmic Microwave
Background (CMB) temperature anisotropy maps of Wilkinson Microwave Anisotropy
Probe is shown to possess certain anomalous properties. The degree of the
randomness determined by the Kolmogorov stochasticity parameter in the both
symmetry regions appears to have identical values which, however, essentially
differ from the corresponding values for other sky regions. If the mirroring
were of cosmological origin, this would imply either additional randomizing
properties in those directions of the Universe or their different line-of-sight
depth. This analysis also provides a way to test the hypothesis of a link
between the nature of dark energy and inhomogeneities.Comment: A & A (Lett.) in press; 3 pages, 2 fig
American Cochlear Implant Alliance Task Force guidelines for clinical assessment and management of adult cochlear implantation for single-sided deafness
The indications for cochlear implantation have expanded to include individuals with profound sensorineural hearing loss in the impaired ear and normal hearing (NH) in the contralateral ear, known as single-sided deafness (SSD). There are additional considerations for the clinical assessment and management of adult cochlear implant candidates and recipients with SSD as compared to conventional cochlear implant candidates with bilateral moderate to profound sensorineural hearing loss. The present report reviews the current evidence relevant to the assessment and management of adults with SSD. A systematic review was also conducted on published studies that investigated outcomes of cochlear implant use on measures of speech recognition in quiet and noise, sound source localization, tinnitus perception, and quality of life for this patient population. Expert consensus and systematic review of the current literature were combined to provide guidance for the clinical assessment and management of adults with SSD
Experimental investigation of optical transition radiation in amorphous quartz
Optical transition radiation (OTR) in amorphous quartz is investigated experimentally for electrons with energies 7.5MeV. It is shown that the Cherenkov radiation and OTR can be separated at specific conditions. The linear
polarization of OTR is investigated and it is shown that the polarization is radial. The results of measurements for the spectral distribution of OTR have shown the maximum intensity of radiation at the wavelengths in the range 320–500 nm
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