1,385 research outputs found
Invariant Form of BK-factorization and its Applications
Invariant form of BK-factorization is presented, it is used for factorization
of the LPDOs equivalent under gauge transformation and for construction of
approximate factorization simplifying numerical simulsations with corresponding
LPDEs of higher orderComment: 11 pages, 7 figure
Nonlinear acoustic waves in channels with variable cross sections
The point symmetry group is studied for the generalized Webster-type equation
describing non-linear acoustic waves in lossy channels with variable cross
sections. It is shown that, for certain types of cross section profiles, the
admitted symmetry group is extended and the invariant solutions corresponding
to these profiles are obtained. Approximate analytic solutions to the
generalized Webster equation are derived for channels with smoothly varying
cross sections and arbitrary initial conditions.Comment: Revtex4, 10 pages, 2 figure. This is an enlarged contribution to
Acoustical Physics, 2012, v.58, No.3, p.269-276 with modest stylistic
corrections introduced mainly in the Introduction and References. Several
typos were also correcte
Excitonic Instability and Pseudogap Formation in Nodal Line Semimetal ZrSiS
Electron correlation effects are studied in ZrSiS using a combination of
first-principles and model approaches. We show that basic electronic properties
of ZrSiS can be described within a two-dimensional lattice model of two nested
square lattices. High degree of electron-hole symmetry characteristic for ZrSiS
is one of the key features of this model. Having determined model parameters
from first-principles calculations, we then explicitly take electron-electron
interactions into account and show that at moderately low temperatures ZrSiS
exhibits excitonic instability, leading to the formation of a pseudogap in the
electronic spectrum. The results can be understood in terms of
Coulomb-interaction-assisted pairing of electrons and holes reminiscent to that
of an excitonic insulator. Our finding allows us to provide a physical
interpretation to the unusual mass enhancement of charge carriers in ZrSiS
recently observed experimentally.Comment: 6 pages, 4 figures. Final versio
Interaction of Kelvin waves and nonlocality of energy transfer in superfluids
We argue that the physics of interacting Kelvin Waves (KWs) is highly nontrivial and cannot be understood on the basis of pure dimensional reasoning. A consistent theory of KW turbulence in superfluids should be based upon explicit knowledge of their interactions. To achieve this, we present a detailed calculation and comprehensive analysis of the interaction coefficients for KW turbuelence, thereby, resolving previous mistakes stemming from unaccounted contributions. As a first application of this analysis, we derive a local nonlinear (partial differential) equation. This equation is much simpler for analysis and numerical simulations of KWs than the Biot-Savart equation, and in contrast to the completely integrable local induction approximation (in which the energy exchange between KWs is absent), describes the nonlinear dynamics of KWs. Second, we show that the previously suggested Kozik-Svistunov energy spectrum for KWs, which has often been used in the analysis of experimental and numerical data in superfluid turbulence, is irrelevant, because it is based upon an erroneous assumption of the locality of the energy transfer through scales. Moreover, we demonstrate the weak nonlocality of the inverse cascade spectrum with a constant particle-number flux and find resulting logarithmic corrections to this spectrum
Optical models of the molecular atmosphere
The use of optical and laser methods for performing atmospheric investigations has stimulated the development of the optical models of the atmosphere. The principles of constructing the optical models of molecular atmosphere for radiation with different spectral composition (wideband, narrowband, and monochromatic) are considered in the case of linear and nonlinear absorptions. The example of the development of a system which provides for the modeling of the processes of optical-wave energy transfer in the atmosphere is presented. Its physical foundations, structure, programming software, and functioning were considered
Finite-Dimensional Turbulence of Planetary Waves
Finite-dimensional wave turbulence refers to the chaotic dynamics of
interacting wave `clusters' consisting of finite number of connected wave
triads with exact three-wave resonances. We examine this phenomenon using the
example of atmospheric planetary (Rossby) waves. It is shown that the dynamics
of the clusters is determined by the types of connections between neighboring
triads within a cluster; these correspond to substantially different scenarios
of energy flux between different triads. All the possible cases of the energy
cascade termination are classified. Free and forced chaotic dynamics in the
clusters are investigated: due to the huge fluctuations of the energy exchange
between resonant triads these two types of evolution have a lot in common. It
is confirmed that finite-dimensional wave turbulence in finite wave systems is
fundamentally different from kinetic wave turbulence in infinite systems; the
latter is described by wave kinetic equations that account for interactions
with overlapping quasi-resonances of finite amplitude waves. The present
results are directly applicable to finite-dimensional wave turbulence in any
wave system in finite domains with 3-mode interactions as encountered in
hydrodynamics, astronomy, plasma physics, chemistry, medicine, etc.Comment: 29 pages, 21 figures, submitted to PR
On Formation of Anthrasemiquinone in the Conditions of Wood Alkaline Pulping
Electron spin resonance (ESR) and electronic absorbance
spectral experiments demonstrate that reversible temperature
variation of anion-radica1 concentration in the system anthraqui;
none (AQ) - anthrasemiquinone (AS) - anthrahydroquinone
(AHQ) in aqueous alka1i is a property of that system and not of
the more complicated catalyst-wood system. Lignin model compounds
present in low concentrations have no influence on this variation. A raise of radical concentration is accompanied by a change of the solution colour from red into yellow. In pulping conditions AQ can be reduced either by the hydrocarbon or by the lignin component of wood, probably also by numerous organic compounds and even by the alka1i itself. As a result of this process, an AQ-AS-AHQ system is being formed
Dinamika rastitel'nosti natsional'nogo parka "Orlovskoye polesye" v pozdnem golotsene = Vegetation dynamics in the "Orlovskoye Polesye" National Park in Late Holocene (in Russian)
The paper presents the first results of palaeobotanical study of the late Holocene peat deposits within the territory of the "Orlovskoye Polesye” National Park. Data obtained show, that mixed pine-broad leaved forests dominated the area during the past 3500 years. The early agricultural colonization of the territory by humans caused vegetation disturbances and led to a reduction of the proportion of a broadleaved trees in forest stands since 1600 years BP. During the last several centuries, the increased human impact resulted in further degradation of broadleaved forests and expansion of secondary forest stands.
(Text in Russian!
Histone H1 Plays a Role in Heterochromatin Formation and VSG Expression Site Silencing in Trypanosoma brucei
The African sleeping sickness parasite Trypanosoma brucei evades the host immune system through antigenic variation of its variant surface glycoprotein (VSG) coat. Although the T. brucei genome contains ∼1500 VSGs, only one VSG is expressed at a time from one of about 15 subtelomeric VSG expression sites (ESs). For antigenic variation to work, not only must the vast VSG repertoire be kept silent in a genome that is mainly constitutively transcribed, but the frequency of VSG switching must be strictly controlled. Recently it has become clear that chromatin plays a key role in silencing inactive ESs, thereby ensuring monoallelic expression of VSG. We investigated the role of the linker histone H1 in chromatin organization and ES regulation in T. brucei. T. brucei histone H1 proteins have a different domain structure to H1 proteins in higher eukaryotes. However, we show that they play a key role in the maintenance of higher order chromatin structure in bloodstream form T. brucei as visualised by electron microscopy. In addition, depletion of histone H1 results in chromatin becoming generally more accessible to endonucleases in bloodstream but not in insect form T. brucei. The effect on chromatin following H1 knock-down in bloodstream form T. brucei is particularly evident at transcriptionally silent ES promoters, leading to 6–8 fold derepression of these promoters. T. brucei histone H1 therefore appears to be important for the maintenance of repressed chromatin in bloodstream form T. brucei. In particular H1 plays a role in downregulating silent ESs, arguing that H1-mediated chromatin functions in antigenic variation in T. brucei
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