917 research outputs found
Spectral multiplicity for powers of weakly mixing automorphisms
We study the behavior of maximal multiplicities for the powers of
a weakly mixing automorphism . For some special infinite set we show the
existence of a weakly mixing rank-one automorphism such that
and for all . Moreover, the cardinality
of the set of spectral multiplicities for is not bounded. We have
and , , . We
also construct another weakly mixing automorphism with the following
properties: for but ,
all powers have homogeneous spectrum, and the set of limit points of
the sequence is infinite
Sub-wavelength imaging: Resolution enhancement using metal wire gratings
An experimental evidence of subwavelength imaging with a "lens", which is a
uniaxial negative permittivity wire medium slab, is reported. The slab is
formed by gratings of long thin parallel conducting cylinders. Taking into
account the anisotropy and spatial dispersion in the wire medium we
theoretically show that there are no usual plasmons that could be exited on
surfaces of such a slab, and there is no resonant enhancement of evanescent
fields in the slab. The experimentally observed clear improvement of the
resolution in the presence of the slab is explained as filtering out the
harmonics with small wavenumbers. In other words, the wire gratings (the wire
medium) suppress strong traveling-mode components increasing the role of
evanescent waves in the image formation. This effect can be used in near-field
imaging and detection applications.Comment: 12 pages, 6 figure
Photoconductivity of CdS-CdSe granular films: influence of microstructure
We study experimentally the photoconductivity of CdS-CdSe sintered granular
films obtained by the screen printing method. We mostly focus on the
dependences of photoconductivity on film's microstructure, which varies with
changing heat-treatment conditions. The maximum photoconductivity is found for
samples with compact packing of individual grains, which nevertheless are
separated by gaps. Such a microstructure is typical for films heat-treated
during an intermediate (optimal) time. In order to understand whether the
dominant mechanism of charge transfer is identical with the one in
monocrystals, we perform temperature measurements of photoresistance.
Corresponding curves have the same peculiar nonmonotonic shape as in CdSe
monocrystals, from which we conclude that the basic mechanism is also the same.
It is suggested that the optimal heat-treatment time appears as a result of a
competition between two mechanisms: improvement of film's connectivity and its
oxidation. Photoresistance is also measured in vacuum and in helium atmosphere,
which suppress oxygen and water absorption/chemisorption at intergrain
boundaries. We demonstrate that this suppression increases photoconductivity,
especially at high temperatures.Comment: 12 pages, 8 figures, final versio
New SERS-active junction based on cerium dioxide facet dielectric films for biosensing
Further enhance of the Raman scattering is the priority for the development of the modern molecular diagnostic methods. Expected increasing in detection sensitivity of the biological and chemical agents provides substantial progress in such areas as: proteomics (discovery of new disease markers), pharmacokinetics of drugs, analysis of toxins and infections agents, drug analysis, food safety, and environmental safety.
In this paper we investigated the possibility of the facet structures, based on cerium dioxide to further enhance the SERS signal. During the studies a new metamaterial was developed. The metamaterial is based on the facet cerium dioxide films and plasmonic nanoparticles that are immobilized on its surface. The new metamaterial provides additional SERS signal amplification factor of 211. Thus developed material offers the prospect of increasing the sensitivity and selectivity of biochemical and immunological analysis
Circulation of Highly Pathogenic Avian Flu Virus in the Russian Federation in 2014-2015
Given are the data on the circulation of highly pathogenic flu virus, A/H5, within the last two years. Discussed is the current state of the situation on H5 flu in the territory of the Russian Federation, where during 2014-2015, for the first time since 2010, registered has been the isolation of highly pathogenic flu virus, H5N1 and H5N8 subtypes. It is demonstrated that the territory of Russia plays a significant role in trans-continental transfer of flu viruses by wild birds from South-Eastern Asia into Europe and North America. Moreover, an assumption is made that a continued circulation of highly pathogenic viruses in the territory of the country is quiet possible
Sputtered NbN Films for Ultrahigh Performance Superconducting Nanowire Single-Photon Detectors
Nowadays ultrahigh performance superconducting nanowire single-photon
detectors are the key elements in a variety of devices from biological research
to quantum communications and computing. Accurate tuning of superconducting
material properties is a powerful resource for fabricating single-photon
detectors with a desired properties. Here, we report on the major theoretical
relations between ultrathin niobium nitride (NbN) films properties and
superconducting nanowire single-photon detectors characteristics, as well as
ultrathin NbN films properties dependence on reactive magnetron sputtering
recipes. Based on this study we formulate the exact requirements to ultrathin
NbN films for ultrahigh performance superconducting nanowire single-photon
detectors. Then, we experimentally study ultrathin NbN films properties
(morphology, crystalline structure, critical temperature, sheet resistance) on
silicon, sapphire, silicon dioxide and silicon nitride substrates sputtered
with various recipes. We demonstrate ultrathin NbN films (obtained with more
than 100 films deposition) with a wide range of critical temperature from 2.5
to 12.1 K and sheet resistance from 285 to 2000 ~/sq, as well as
investigate a sheet resistance evolution over for more than 40\% within two
years. Finally, we found out that one should use ultrathin NbN films with
specific critical temperature near 9 K and sheet resistance of 400 ~/sq
for ultrahigh performance SNSPD.Comment: The following article has been submitted to APL Materials. After it
is published, it will be found at https://pubs.aip.org/aip/apm. Copyright
2023 Author(s). This article is distributed under a Creative Commons
Attribution (CC BY) Licens
Overview of the Epidemiological Situation on Highly Pathogenic Avian Influenza Virus in Russia in 2018
Analyzed was modern epidemiological situation on highly pathogenic avian flu in 2018. Prognosis for possible further distribution of viruses in the territory of Russia was made. In 2018, the situation on highly pathogenic avian flu in Russia was challenging. This was due to the spread of the viruses clade 2.3.4.4, which caused multiple outbreaks among wild birds and poultry in European part of Russia. In addition, A/H5N6 avian influenza virus circulation was for the first time detected in the Saratov Region during routine avian influenza virus surveillance. In May, 2018 two different lineages of avian influenza A/H9N2 were isolated during the outbreaks that occurred at several poultry plants in Primorsk Territory and Amur Region of Russia. Subsequently, that virus subtype continued spreading in Russia, which was recorded by detection of the A/H9N2 influenza virus in wild birds in the Khabarovsk and Tomsk Regions of Russia. Thus, it is shown yet again that the territory of Russia plays an important geographical role in the spread of avian influenza viruses
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