240 research outputs found
Stability of the genetic code and optimal parameters of amino acids
The standard genetic code is known to be much more efficient in minimizing
adverse effects of misreading errors and one-point mutations in comparison with
a random code having the same structure, i.e. the same number of codons coding
for each particular amino acid. We study the inverse problem, how the code
structure affects the optimal physico-chemical parameters of amino acids
ensuring the highest stability of the genetic code. It is shown that the choice
of two or more amino acids with given properties determines unambiguously all
the others. In this sense the code structure determines strictly the optimal
parameters of amino acids. In the code with the structure of the standard
genetic code the resulting values for hydrophobicity obtained in the scheme
leave one out and in the scheme with fixed maximum and minimum parameters
correlate significantly with the natural scale. This indicates the co-evolution
of the genetic code and physico-chemical properties of amino acids.Comment: 9 pages, 3 figure
Genome packaging within icosahedral capsids and large-scale segmentation in viral genomic sequences
The assembly and maturation of viruses with icosahedral capsids must be
coordinated with icosahedral symmetry. The icosahedral symmetry imposes also
the restrictions on the cooperative specific interactions between genomic
RNA/DNA and coat proteins that should be reflected in quasi-regular
segmentation of viral genomic sequences. Combining discrete direct and double
Fourier transforms, we studied the quasi-regular large-scale segmentation in
genomic sequences of different ssRNA, ssDNA, and dsDNA viruses. The particular
representatives included satellite tobacco mosaic virus and the strains of
satellite tobacco necrosis virus, STNV-C, STNV-1, STNV-2, Escherichia phages
MS2, phiX174, alpha3, and HK97, and Simian virus 40. In all their genomes, we
found the significant quasi-regular segmentation of genomic sequences related
to the virion assembly and the genome packaging within icosahedral capsid. We
also found good correspondence between our results and available cryo-electron
microscopy data on capsid structures and genome packaging in these viruses.
Fourier analysis of genomic sequences provides the additional insight into
mechanisms of hierarchical genome packaging and may be used for verification of
the concepts of 3-fold or 5-fold intermediates in virion assembly. The results
of sequence analysis should be taken into account at the choice of models and
data interpretation. They also may be helpful for the development of antiviral
drugs.Comment: 55 pages, 14 figure
Statistics of genome architecture
The main statistical distributions applicable to the analysis of genome
architecture and genome tracks are briefly discussed and critically assessed.
Although the observed features in distributions of element lengths can be
equally well fitted by the different statistical approximations, the
interpretation of observed regularities may strongly depend on the chosen
scheme. We discuss the possible evolution scenarios and describe the main
characteristics obtained with different distributions. The expression for the
assessment of levels in hierarchical chromatin folding is derived and the
quantitative measure of genome architecture inhomogeneity is suggested. This
theory provides the ground for the regular statistical study of genome
architecture and genome tracks.Comment: 25 pages, 8 figures, 1 tabl
Three-dimensional Modeling of the Matter Flow Structure in Semidetached Binary Systems
Results of numerical simulations of matter flows in a semidetached binary
system similar to the low-mass X-ray binary X1822--371 are presented.
Three-dimensional modeling of the mass transfer gas dynamics makes it possible
to investigate gas streams in the system and to study the influence of a common
envelope. The presence of the common envelope leads to the absence of shock
interaction between the stream of matter flowing from the inner Lagrange point
and the gas in the accretion disk. The stream is deflected by the gas in the
common envelope and approaches the disk tangentially, so that it does not cause
any shock perturbation ("hot spot") on the disk. At the same time, the
interaction of the stream with the common envelope leads to the formation of an
extended shock wave along the edge of the stream. The observational
manifestation of this shock is estimated to be equivalent to that of a hot spot
in the disk. The calculated accretion disk parameters are presented.Comment: 9 pages, LaTeX, 6 EPS figures, using AAS2PP4 style (included
Driven-disk model for binaries with precessing donor star. Three-dimensional simulations
We present the results of three-dimensional numerical simulations of mass
transfer in semi-detached binary with a donor star whose rotation vector
precesses around the orbital rotation axis of the binary in the observer's
coordinate frame. The calculations support our previous model of flow without a
`hot spot'. Characteristic features of the flow in this model, such as the
formation of an circumbinary envelope, the absence of a `hot spot' at the edge
of the accretion disk, and the formation of a shock wave along the edge of the
stream, are also present in the solution for a binary with precessing donor
star. The parameters of accretion disk and of the structure of the near-disk
regions recur with the precessional period of the rotation axis of donor star.Comment: LaTeX, 10 page
Synthetic Doppler maps of gaseous flows in semidetached binaries based on the results of 3D gas dynamical simulations
We present synthetic Doppler maps of gaseous flows in semidetached binaries
based on the results of 3D gas dynamical simulations. Using of gas dynamical
calculations alongside with Doppler tomography technique permits to identify
main features of the flow on the Doppler maps without solution of ill-posed
inverse problem. Comparison of synthetic tomograms with observations makes
possible both to refine the gas dynamical model and to interpret the
observational data.Comment: To be published in Proceedings of International Workshop "Hot Points
in Astrophysics", Dubna, Russia, August 22-26, 200
The Influence of Parameters on the Flow Structure in Semidetached Binary Systems: 3D Numerical Simulation
The basic parameters determining the flow pattern for a nonviscous,
non-heat-conducting gas in a semidetached binary system without a magnetic
field are identified. Three-dimensional gas-dynamical modeling of the mass
transfer enables investigation of the influence of these parameters on the
structure of gas flows. The parameter on which the flow pattern depends most
strongly is the adiabatic index . The effect of other parameters is
small, and only leads to unimportant quantitative changes in the solutions
obtained. The main properties of flows typical of semidetached binaries without
magnetic fields are summarized.Comment: 16 pages, LaTeX, 8 EPS figures, using AAS2PP4 style, accepted by
Astron. Report
Detection of large-scale noisy multi-periodic patterns with discrete double Fourier transform
In many processes, the variations in underlying characteristics can be
approximated by noisy multi-periodic patterns. If large-scale patterns are
superimposed by a noise with long-range correlations, the detection of
multi-periodic patterns becomes especially challenging. To solve this problem,
we developed a discrete double Fourier transform (DDFT). DDFT is based on the
equidistance property of harmonics generated by multi-periodic patterns in the
discrete Fourier transform (DFT) spectra. As the large-scale patterns generate
long enough equidistant series, they can be detected by the iteration of the
primary DFT. DDFT is defined as Fourier transform of intensity spectral
harmonics or of their functions. It comprises widely used cepstrum transform as
a particular case. We present also the relevant analytical criteria for the
assessment of statistical significance of peak harmonics in DDFT spectra in the
presence of noise. DDFT technique was tested by extensive numerical
simulations. The practical applications of DDFT technique are illustrated by
the analysis of variations in solar wind speed related to solar rotation and by
the study of large-scale multi-periodic patterns in DNA sequences. The latter
application can be considered as generic example for the general spectral
analysis of symbolic sequences. The results are compared with those obtained by
the cepstrum transform. The mutual combination of DFT and DDFT provides an
efficient technique to search for noisy large-scale multi-periodic patterns.Comment: 45 pages, 15 figure
Large-scale chromosome folding versus genomic DNA sequences: A discrete double Fourier transform technique
Using state-of-the-art techniques combining imaging methods and
high-throughput genomic mapping tools leaded to the significant progress in
detailing chromosome architecture of various organisms. However, a gap still
remains between the rapidly growing structural data on the chromosome folding
and the large-scale genome organization. Could a part of information on the
chromosome folding be obtained directly from underlying genomic DNA sequences
abundantly stored in the databanks? To answer this question, we developed an
original discrete double Fourier transform (DDFT). DDFT serves for the
detection of large-scale genome regularities associated with domains/units at
the different levels of hierarchical chromosome folding. The method is
versatile and can be applied to both genomic DNA sequences and corresponding
physico-chemical parameters such as base-pairing free energy. The latter
characteristic is closely related to the replication and transcription and can
also be used for the assessment of temperature or supercoiling effects on the
chromosome folding. We tested the method on the genome of Escherichia coli K-12
and found good correspondence with the annotated domains/units established
experimentally. As a brief illustration of further abilities of DDFT, the study
of large-scale genome organization for bacteriophage PHIX174 and bacterium
Caulobacter crescentus was also added. The combined experimental, modeling, and
bioinformatic DDFT analysis should yield more complete knowledge on the
chromosome architecture and genome organization.Comment: 37 pages, 9 figure
Three-dimensional modeling of mass transfer in close binary systems with non-synchronous rotation
We present the results of three-dimensional numerical simulations of mass
transfer in semi-detached binary systems in which the mass-losing star is
rotating. The cases of aligned and misaligned non-synchronous rotation of the
donor star are considered; the resulting flow patterns are compared to the
synchronous case. The main properties of the flow, such as the formation of an
circumbinary envelope, the absence of a "hot spot" on the edge of the accretion
disk, and the formation of a shock wave along the flow edge, are qualitatively
similar to those obtained earlier. For the case of misaligned, non-synchronous
rotation, the behavior of the disk and surrounding matter in established flow
regime reflects changes in the boundary conditions at the surface of the donor
star; in other words, a "driven disk" model is realized in the calculations.Comment: LaTeX, 22 pages, accepted for publication in Astronomy Report
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