971 research outputs found
Polar mesosphere summer echoes: a comparison of simultaneous observations at three wavelengths
On 5 July 2005, simultaneous observations of Polar Mesosphere Summer Echoes (PMSE) were made using the EISCAT VHF (224 MHz) and UHF (933 MHz) radars located near TromsΓΈ, Norway and the ALWIN VHF radar (53.5 MHz) situated on AndΓΈya, 120 km SW of the EISCAT site. During the short interval from 12:20 UT until 12:26 UT strong echoes at about 84 km altitude were detected with all three radars. The radar volume reflectivities were found to be 4&times;10<sup>&minus;13</sup> m<sup>&minus;1</sup>, 1.5&times;10<sup>&minus;14</sup> m<sup>&minus;1</sup> and 1.5&times;10<sup>&minus;18</sup> m<sup>&minus;1</sup> for the ALWIN, EISCAT-VHF and UHF radars, respectively. We have calculated the reflectivity ratios for each pair of radars and have compared them to ratios obtained from the turbulence-theory model proposed by Hill (1978a). We have tested different values of the turbulent energy dissipation rate &epsilon; and Schmidt number <i>S<sub>c</sub></i>, which are free parameters in the model, to try to fit theoretical reflectivity ratios to the experimental ones. No single combination of the parameters &epsilon; and <i>S<sub>c</sub></i> could be found to give a good fit. Spectral widths for the EISCAT radars were estimated from the spectra computed from the autocorrelation functions obtained in the experiment. After correction for beam-width broadening, the spectral widths are about 4 m/s for the EISCAT-VHF and 1.5&ndash;2 m/s for the UHF radar. However, according to the turbulence theory, the spectral widths in m/s should be the same for both radars. We also tested an incoherent scatter (IS) model developed by Cho et al. (1998), which takes into account the presence of charged aerosols/dust at the summer mesopause. It required very different sizes of particles for the EISCAT-VHF and UHF cases, to be able to fit the experimental spectra with model spectra. This implies that the IS model cannot explain PMSE spectra, at least not for monodisperse distributions of particles
Renormalized theory of the ion cyclotron turbulence in magnetic field--aligned plasma shear flow
The analytical treatment of nonlinear evolution of the shear-flow-modified
current driven ion cyclotron instability and shear-flow-driven ion cyclotron
kinetic instabilities of magnetic field--aligned plasma shear flow is
presented. Analysis is performed on the base of the nonlinear dispersion
equation, which accounts for a new combined effect of plasma turbulence and
shear flow. It consists in turbulent scattering of ions across the shear flow
with their convection by shear flow and results in enhanced nonlinear
broadening of ion cyclotron resonances. This effect is found to lead to the
saturation of ion cyclotron instabilities as well as to the development of
nonlinear shear flow driven ion cyclotron instability. 52.35.RaComment: 21 page
Quantitative relation between PMSE and ice mass density
Radar reflectivities associated with Polar Mesosphere Summer Echoes (PMSE)
are compared with measurements of ice mass density in the mesopause region.
The 54.5 MHz radar Moveable Atmospheric Radar for Antarctica (MARA), located
at the Wasa/Aboa station in Antarctica (73Β° S, 13Β° W) provided
PMSE measurements in December 2007 and January 2008. Ice mass density was
measured by the Solar Occultation for Ice Experiment (SOFIE). The radar
operated continuously during this period but only measurements close to local
midnight are used for comparison, to coincide with the local time of the
measurements of ice mass density. The radar location is at high geographic
latitude but low geomagnetic latitude (61Β°) and the measurements were
made during a period of very low solar activity. As a result, background
electron densities can be modelled based on solar illumination alone. We find
a close correlation between the time and height variations of radar
reflectivity and ice mass density, at all PMSE heights, from 80 km up to 95 km.
A quantitative expression relating radar reflectivities to ice mass
density is found, including an empirical dependence on background electron
density. Using this relation, we can use PMSE reflectivities as a proxy for
ice mass density, and estimate the daily variation of ice mass density from
the daily variation of PMSE reflectivities. According to this proxy, ice mass
density is maximum around 05:00β07:00 LT, with lower values around local noon, in
the afternoon and in the evening. This is consistent with the small number of
previously published measurements and model predictions of the daily
variation of noctilucent (mesospheric) clouds and in contrast to the daily
variation of PMSE, which has a broad daytime maximum, extending from 05:00 LT to
15:00 LT, and an evening-midnight minimum
ΠΡΡΠ°ΠΆΠ΅Π½ΠΈΠ΅ ΠΈΠ΄Π΅Π½ΡΠΈΡΠ½ΠΎΡΡΠΈ ΡΡΡΡΠΊΠΈΡ ΡΠ΅ΡΠ΅Π· ΡΠ°ΡΠΏΠΎΠ·Π½Π°Π²Π°Π½ΠΈΠ΅ Π°Π²ΡΠΎΡΡΠ½ΠΎΠΈΠΌΠΏΠ»ΠΈΠΊΠ°ΡΡΡ (Π½Π° ΠΏΡΠΈΠΌΠ΅ΡΠ΅ Π°Π½Π°Π»ΠΈΠ·Π° Π°Π²ΡΠΎΡΡΠ½ΠΎΠΈΠΌΠΏΠ»ΠΈΠΊΠ°ΡΡΡ ΠΎ ΡΡΡΡΠΊΠΎΠΌ ΡΠ°Π·Π³ΠΎΠ²ΠΎΡΠ΅ / Π±Π΅ΡΠ΅Π΄Π΅)
The article is devoted to the study of the problem of national identity of modern Russian people through its reflection in the Russian language. The consideration of the problem of national identity is connected with the question of who can be attributed to the Russians today. It is believed that one of the key conditions for the formation of a national-cultural identity is the assimilation of the values and norms of its sociocultural community, which can be reflected in language in the form of stable expressions (proverbs, sayings, idioms, etc.), and in the form of ethno-implicatures ( auto-ethno-implicatures). If the stable expressions characterizing a particular nation (ethnic group, nation), including Russians, are studied well enough, then research on ethno-implicatures (especially auto-ethno-implicatures) is clearly insufficient. It is assumed that through the recognition of auto-ethno-implicatures, it is possible to determine the current national values of modern Russians, as well as to trace their changes. This is possible, in our opinion, with the help of a series of linguistic and sociolinguistic experiments. The article presents the results of a linguistic experiment aimed at recognizing auto-ethno-implicatures of one of the key values / traits of Russians, according to researchers, β the sincerity of relations, the need for close social relations, expressed in such a thing as βRussian conversationβ.ΠΠ°ΡΡΠΎΡΡΠ°Ρ ΡΡΠ°ΡΡΡ ΠΏΠΎΡΠ²ΡΡΠ΅Π½Π° ΠΈΠ·ΡΡΠ΅Π½ΠΈΡ ΠΏΡΠΎΠ±Π»Π΅ΠΌΡ Π½Π°ΡΠΈΠΎΠ½Π°Π»ΡΠ½ΠΎΠΉ ΠΈΠ΄Π΅Π½ΡΠΈΡΠ½ΠΎΡΡΠΈ ΡΠΎΠ²ΡΠ΅ΠΌΠ΅Π½Π½ΡΡ
ΡΡΡΡΠΊΠΈΡ
Π»ΡΠ΄Π΅ΠΉ ΡΠ΅ΡΠ΅Π· Π΅Ρ ΠΎΡΡΠ°ΠΆΠ΅Π½ΠΈΠ΅ Π² ΡΡΡΡΠΊΠΎΠΌ ΡΠ·ΡΠΊΠ΅. Π Π°ΡΡΠΌΠΎΡΡΠ΅Π½ΠΈΠ΅ ΠΏΡΠΎΠ±Π»Π΅ΠΌΡ Π½Π°ΡΠΈΠΎΠ½Π°Π»ΡΠ½ΠΎΠΉ ΠΈΠ΄Π΅Π½ΡΠΈΡΠ½ΠΎΡΡΠΈ ΡΠ²ΡΠ·Π°Π½ΠΎ Ρ Π²ΠΎΠΏΡΠΎΡΠΎΠΌ ΠΎ ΡΠΎΠΌ, ΠΊΠΎΠ³ΠΎ ΡΠ΅Π³ΠΎΠ΄Π½Ρ ΠΌΠΎΠΆΠ½ΠΎ ΠΎΡΠ½Π΅ΡΡΠΈ ΠΊ ΡΡΡΡΠΊΠΈΠΌ. Π‘ΡΠΈΡΠ°Π΅ΡΡΡ, ΡΡΠΎ ΠΎΠ΄Π½ΠΈΠΌ ΠΈΠ· ΠΊΠ»ΡΡΠ΅Π²ΡΡ
ΡΡΠ»ΠΎΠ²ΠΈΠΉ ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΡ Π½Π°ΡΠΈΠΎΠ½Π°Π»ΡΠ½ΠΎ-ΠΊΡΠ»ΡΡΡΡΠ½ΠΎΠΉ ΠΈΠ΄Π΅Π½ΡΠΈΡΠ½ΠΎΡΡΠΈ ΡΠ²Π»ΡΠ΅ΡΡΡ ΡΡΠ²ΠΎΠ΅Π½ΠΈΠ΅ ΡΠ΅Π½Π½ΠΎΡΡΠ΅ΠΉ ΠΈ Π½ΠΎΡΠΌ ΡΠ²ΠΎΠ΅ΠΉ ΡΠΎΡΠΈΠΎΠΊΡΠ»ΡΡΡΡΠ½ΠΎΠΉ ΠΎΠ±ΡΠ½ΠΎΡΡΠΈ, ΠΊΠΎΡΠΎΡΡΠ΅ Π² ΡΠ·ΡΠΊΠ΅ ΠΌΠΎΠ³ΡΡ ΠΎΡΡΠ°ΠΆΠ°ΡΡΡΡ ΠΊΠ°ΠΊ Π² Π²ΠΈΠ΄Π΅ ΡΡΡΠΎΠΉΡΠΈΠ²ΡΡ
Π²ΡΡΠ°ΠΆΠ΅Π½ΠΈΠΉ (ΠΏΠΎΡΠ»ΠΎΠ²ΠΈΡ, ΠΏΠΎΠ³ΠΎΠ²ΠΎΡΠΎΠΊ, ΡΡΠ°Π·Π΅ΠΎΠ»ΠΎΠ³ΠΈΠ·ΠΌΠΎΠ² ΠΈ Ρ. ΠΏ.), ΡΠ°ΠΊ ΠΈ Π² ΡΠΎΡΠΌΠ΅ ΡΡΠ½ΠΎΠΈΠΌΠΏΠ»ΠΈΠΊΠ°ΡΡΡ (Π°Π²ΡΠΎΡΡΠ½ΠΎΠΈΠΌΠΏΠ»ΠΈΠΊΠ°ΡΡΡ). ΠΡΠ»ΠΈ ΡΡΡΠΎΠΉΡΠΈΠ²ΡΠ΅ Π²ΡΡΠ°ΠΆΠ΅Π½ΠΈΡ, Ρ
Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΠ·ΡΡΡΠΈΠ΅ ΡΠΎΡ ΠΈΠ»ΠΈ ΠΈΠ½ΠΎΠΉ Π½Π°ΡΠΎΠ΄ (ΡΡΠ½ΠΎΡ, Π½Π°ΡΠΈΡ), Π² ΡΠΎΠΌ ΡΠΈΡΠ»Π΅ ΠΈ ΡΡΡΡΠΊΠΈΡ
, ΠΈΠ·ΡΡΠ΅Π½Ρ Π΄ΠΎΡΡΠ°ΡΠΎΡΠ½ΠΎ Ρ
ΠΎΡΠΎΡΠΎ, ΡΠΎ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΠΉ ΡΡΠ½ΠΎΠΈΠΌΠΏΠ»ΠΈΠΊΠ°ΡΡΡ (ΠΎΡΠΎΠ±Π΅Π½Π½ΠΎ Π°Π²ΡΠΎΡΡΠ½ΠΎΠΈΠΌΠΏΠ»ΠΈΠΊΠ°ΡΡΡ) ΠΏΠΎΠΊΠ° ΡΠ²Π½ΠΎ Π½Π΅Π΄ΠΎΡΡΠ°ΡΠΎΡΠ½ΠΎ. ΠΡΠ΅Π΄ΠΏΠΎΠ»Π°Π³Π°Π΅ΡΡΡ, ΡΡΠΎ ΡΠ΅ΡΠ΅Π· ΡΠ°ΡΠΏΠΎΠ·Π½Π°Π²Π°Π½ΠΈΠ΅ Π°Π²ΡΠΎΡΡΠ½ΠΎΠΈΠΌΠΏΠ»ΠΈΠΊΠ°ΡΡΡ ΠΌΠΎΠΆΠ½ΠΎ ΠΎΠΏΡΠ΅Π΄Π΅Π»ΠΈΡΡ Π΄Π΅ΠΉΡΡΠ²ΡΡΡΠΈΠ΅ Π½Π°ΡΠΈΠΎΠ½Π°Π»ΡΠ½ΡΠ΅ ΡΠ΅Π½Π½ΠΎΡΡΠΈ ΡΠΎΠ²ΡΠ΅ΠΌΠ΅Π½Π½ΡΡ
ΡΡΡΡΠΊΠΈΡ
, Π° ΡΠ°ΠΊΠΆΠ΅ ΠΏΡΠΎΡΠ»Π΅Π΄ΠΈΡΡ ΠΈΡ
ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΡ. ΠΡΠΎ Π²ΠΎΠ·ΠΌΠΎΠΆΠ½ΠΎ ΡΠ΄Π΅Π»Π°ΡΡ, Π½Π° Π½Π°Ρ Π²Π·Π³Π»ΡΠ΄, Ρ ΠΏΠΎΠΌΠΎΡΡΡ ΡΠ΅ΡΠΈΠΈ Π»ΠΈΠ½Π³Π²ΠΈΡΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΈ ΡΠΎΡΠΈΠΎΠ»ΠΈΠ½Π³Π²ΠΈΡΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΠΊΡΠΏΠ΅ΡΠΈΠΌΠ΅Π½ΡΠΎΠ². Π ΡΡΠ°ΡΡΠ΅ ΠΏΡΠΈΠ²ΠΎΠ΄ΡΡΡΡ ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΡ Π»ΠΈΠ½Π³Π²ΠΈΡΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΡΠΊΡΠΏΠ΅ΡΠΈΠΌΠ΅Π½ΡΠ°, Π½Π°ΠΏΡΠ°Π²Π»Π΅Π½Π½ΠΎΠ³ΠΎ Π½Π° ΡΠ°ΡΠΏΠΎΠ·Π½Π°Π²Π°Π½ΠΈΠ΅ Π°Π²ΡΠΎΡΡΠ½ΠΎΠΈΠΌΠΏΠ»ΠΈΠΊΠ°ΡΡΡΡ ΠΎΠ΄Π½ΠΎΠΉ ΠΈΠ· ΠΊΠ»ΡΡΠ΅Π²ΡΡ
ΡΠ΅Π½Π½ΠΎΡΡΠ΅ΠΉ / ΡΠ΅ΡΡ ΡΡΡΡΠΊΠΈΡ
, ΠΏΠΎ ΠΌΠ½Π΅Π½ΠΈΡ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°ΡΠ΅Π»Π΅ΠΉ, β Π΄ΡΡΠ΅Π²Π½ΠΎΡΡΠΈ ΠΎΡΠ½ΠΎΡΠ΅Π½ΠΈΠΉ, ΠΏΠΎΡΡΠ΅Π±Π½ΠΎΡΡΠΈ Π² Π±Π»ΠΈΠ·ΠΊΠΈΡ
ΡΠΎΡΠΈΠ°Π»ΡΠ½ΡΡ
ΠΎΡΠ½ΠΎΡΠ΅Π½ΠΈΡΡ
, Π²ΡΡΠ°ΠΆΠ΅Π½Π½ΠΎΠΉ Π² ΡΠ°ΠΊΠΎΠΌ ΡΠ²Π»Π΅Π½ΠΈΠΈ, ΠΊΠ°ΠΊ Β«ΡΡΡΡΠΊΠΈΠΉ ΡΠ°Π·Π³ΠΎΠ²ΠΎΡ / Π±Π΅ΡΠ΅Π΄Π°Β»
Polynomial formulations as a barrier for reduction-based hardness proofs
The Strong Exponential Time Hypothesis (SETH) asserts that for every
there exists such that -SAT requires time
. The field of fine-grained complexity has leveraged SETH to
prove quite tight conditional lower bounds for dozens of problems in various
domains and complexity classes, including Edit Distance, Graph Diameter,
Hitting Set, Independent Set, and Orthogonal Vectors. Yet, it has been
repeatedly asked in the literature whether SETH-hardness results can be proven
for other fundamental problems such as Hamiltonian Path, Independent Set,
Chromatic Number, MAX--SAT, and Set Cover.
In this paper, we show that fine-grained reductions implying even
-hardness of these problems from SETH for any , would
imply new circuit lower bounds: super-linear lower bounds for Boolean
series-parallel circuits or polynomial lower bounds for arithmetic circuits
(each of which is a four-decade open question).
We also extend this barrier result to the class of parameterized problems.
Namely, for every we conditionally rule out fine-grained reductions
implying SETH-based lower bounds of for a number of problems
parameterized by the solution size .
Our main technical tool is a new concept called polynomial formulations. In
particular, we show that many problems can be represented by relatively
succinct low-degree polynomials, and that any problem with such a
representation cannot be proven SETH-hard (without proving new circuit lower
bounds)
Computations with polynomial evaluation oracle: ruling out superlinear SETH-based lower bounds
The field of fine-grained complexity aims at proving conditional lower bounds
on the time complexity of computational problems. One of the most popular
assumptions, Strong Exponential Time Hypothesis (SETH), implies that SAT cannot
be solved in time. In recent years, it has been proved that
known algorithms for many problems are optimal under SETH. Despite the wide
applicability of SETH, for many problems, there are no known SETH-based lower
bounds, so the quest for new reductions continues.
Two barriers for proving SETH-based lower bounds are known. Carmosino et al.
(ITCS 2016) introduced the Nondeterministic Strong Exponential Time Hypothesis
(NSETH) stating that TAUT cannot be solved in time even if
one allows nondeterminism. They used this hypothesis to show that some natural
fine-grained reductions would be difficult to obtain: proving that, say, 3-SUM
requires time under SETH, breaks NSETH and this, in turn,
implies strong circuit lower bounds. Recently, Belova et al. (SODA 2023)
introduced the so-called polynomial formulations to show that for many NP-hard
problems, proving any explicit exponential lower bound under SETH also implies
strong circuit lower bounds.
We prove that for a range of problems from P, including -SUM and triangle
detection, proving superlinear lower bounds under SETH is challenging as it
implies new circuit lower bounds. To this end, we show that these problems can
be solved in nearly linear time with oracle calls to evaluating a polynomial of
constant degree. Then, we introduce a strengthening of SETH stating that
solving SAT in time is difficult even if one has
constant degree polynomial evaluation oracle calls. This hypothesis is stronger
and less believable than SETH, but refuting it is still challenging: we show
that this implies circuit lower bounds
Semantic features of the phraseological units with the component light within the artistic discourse
Conduct lexical and semantic analysis on the concept light in the artistic discourse of postmodern fictio
Fresnel scatter revisited-comparison of 50 MHz radar and radiosondes in the Arctic, the Tropics and Antarctica
High-resolution radiosondes and calibrated radars operating close to 50 MHz, are used to examine the relationship between the strength of radar scatter and refractive index gradient. Three radars are used, in Kiruna in Arctic Sweden, at Gadanki in southern India and at the Swedish/Finnish base Wasa/Aboa in Queen Maud Land, Antarctica. Calibration is accomplished using the daily variation of galactic noise measured at each site. Proportionality between radar scatter strength and the square of the mean gradient of potential refractive index, M2, is found in the upper troposphere and lower stratosphere at all three sites, confirming previously reported results from many VHF radars. If the radar scatter is interpreted as Fresnel scatter, the constant of proportionality between radar scatter and M2 is found to be the same, within the calibration uncertainties, for all three radars. The radiosondes show evidence of distinct layering with sharp gradients, extending over 10s of kilometers horizontally, but the scatter is found to be two orders of magnitude weaker than would be expected from true Fresnel scatter from such layers. Using radar reflectivities resolved to a few 100 ms, we show that this is due to strong temporal variability in the scattering conditions, possibly due to undulations of the scattering layers. The constancy of the radar scatter β M2 relationship between the different sites suggests an unexpected uniformity in these perturbations between very different regions of the globe
The bubbles of matter from multiskyrmions
The multiskyrmions with large baryon number B given by rational map (RM)
ansaetze can be described reasonably well within the domain wall approximation,
or as spherical bubbles with energy and baryon number density concentrated at
their boundary. A special class of profile functions is considered
approximating the true profile and domain wall behaviour at the same time. An
upper bound is obtained for the masses of RM multiskyrmions which is close to
the calculated masses, especially at large B. The gap between rigorous upper
and lower bounds for large B multiskyrmions is less than 4%. The basic
properties of such bubbles of matter are investigated, some of them being of
universal character, i.e. they do not depend on baryon number of configuration
and on the number of flavors. As a result, the lagrangian of the Skyrme type
models provides field theoretical realization of the bag model of special kind.Comment: 7 pages, no figure
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