918 research outputs found
Работы Ю.С. Колесова по дифференциальным уравнениям
The article describes the most interesting, in the author's opinion, results obtained by Yu.S. Kolesov, devoted to differential equations (common, functional-differential, with partial derivatives) and their applications to the mathematical ecology, radiophysics, automatic regulation, mechanics.Описываются наиболее интересные, по мнению автора, результаты Ю.С. Колесова, посвященные дифференциальным уравнениям (обыкновенным, функционально-дифференциальным, с частными производными) и их приложениям к математической экологии, радиофизике, автоматическому регулированию, механике
Snowmelt onset hinders bromine monoxide heterogeneous recycling in the Arctic
Reactive bromine radicals (bromine atoms, Br, and bromine monoxide, BrO) deplete ozone and alter tropospheric oxidation chemistry during the Arctic springtime (February–June). As spring transitions to summer (May–June) and snow begins to melt, reactive bromine events cease and BrO becomes low in summer. In this study, we explore the relationship between the end of the reactive bromine season and snowmelt timing. BrO was measured by Multi‐AXis Differential Optical Absorption Spectrometer at Utqiaġvik (Barrow), AK, from 2012 to 2016 and on drifting buoys deployed in Arctic sea ice from 2011 to 2016, a total of 13 site and year combinations. The BrO seasonal end date (SED) was objectively determined and was compared to surface‐air‐temperature‐derived melt onset date (MOD). The SED was highly correlated with the MOD (N = 13, R2 = 0.983, RMS = 1.9 days), and BrO is only observed at subfreezing temperatures. In subsets of these sites and years where ancillary data were available, we observed that snowpack depth reduced and rain precipitation occurred within a few days of the SED. These data are consistent with snowpack melting hindering BrO recycling, which is necessary to maintain enhanced BrO concentrations. With a projected warmer Arctic, a shift to earlier snowmelt seasons could alter the timing and role of halogen chemical reactions in the Arctic with impacts on ozone depletion and mercury deposition.Plain Language SummaryReactive bromine events in the Arctic are common in spring and deplete ozone and cause mercury deposition. These events are affected by snow and ice, which are changing in the Arctic; therefore, we need to understand how environmental conditions affect reactive bromine chemistry. We find that the reactive bromine season ends when snowpack begins to melt. Through these full seasonal observations, we find that reactive bromine events occur to warmer temperatures than previously reported, with 0°C being the observed threshold above which reactive bromine is absent. We also find that snow appears necessary for reactive bromine chemistry and rain stops this chemistry. Earlier snowmelt in a warmer Arctic would end the reactive bromine season earlier, decreasing late springtime ozone depletion and mercury deposition.Key PointsSnowmelt onset hinders reactive bromine heterogeneous recycling and ends season of reactive bromine eventsReactive bromine events occur at subfreezing air temperatures but not at higher temperaturesSnow appears necessary for reactive bromine heterogeneous recycling, and rainwater can terminate this chemistryPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138295/1/jgrd53947_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138295/2/jgrd53947.pd
Chaotic Friedmann-Robertson-Walker Cosmology
We show that the dynamics of a spatially closed Friedmann - Robertson -
Walker Universe conformally coupled to a real, free, massive scalar field, is
chaotic, for large enough field amplitudes. We do so by proving that this
system is integrable under the adiabatic approximation, but that the
corresponding KAM tori break up when non adiabatic terms are considered. This
finding is confirmed by numerical evaluation of the Lyapunov exponents
associated with the system, among other criteria. Chaos sets strong limitations
to our ability to predict the value of the field at the Big Crunch, from its
given value at the Big Bang. (Figures available on request)Comment: 28 pages, 11 figure
Exponential-Potential Scalar Field Universes I: The Bianchi I Models
We obtain a general exact solution of the Einstein field equations for the
anisotropic Bianchi type I universes filled with an exponential-potential
scalar field and study their dynamics. It is shown, in agreement with previous
studies, that for a wide range of initial conditions the late-time behaviour of
the models is that of a power-law inflating FRW universe. This property, does
not hold, in contrast, when some degree of inhomogeneity is introduced, as
discussed in our following paper II.Comment: 16 pages, Plain LaTeX, 1 Figure to be sent on request, to appear in
Phys. Rev.
Axially Symmetric Bianchi I Yang-Mills Cosmology as a Dynamical System
We construct the most general form of axially symmetric SU(2)-Yang-Mills
fields in Bianchi cosmologies. The dynamical evolution of axially symmetric YM
fields in Bianchi I model is compared with the dynamical evolution of the
electromagnetic field in Bianchi I and the fully isotropic YM field in
Friedmann-Robertson-Walker cosmologies. The stochastic properties of axially
symmetric Bianchi I-Einstein-Yang-Mills systems are compared with those of
axially symmetric YM fields in flat space. After numerical computation of
Liapunov exponents in synchronous (cosmological) time, it is shown that the
Bianchi I-EYM system has milder stochastic properties than the corresponding
flat YM system. The Liapunov exponent is non-vanishing in conformal time.Comment: 18 pages, 6 Postscript figures, uses amsmath,amssymb,epsfig,verbatim,
to appear in CQ
On the Cosmology of Massive Vector Fields with SO(3) Global Symmetry
A relevant reference ([14]) has been added.Comment: 19 pages, plain tex, DF/IST-3/92 and DFFCUL 03-5/199
Qualitative Analysis of Viscous Fluid Cosmological Models satisfying the Israel-Stewart theory of Irreversible Thermodynamics
Isotropic and spatially homogeneous viscous fluid cosmological models are
investigated using the truncated Israel-Stewart theory of irreversible
thermodynamics to model the bulk viscous pressure. The governing system of
differential equations is written in terms of dimensionless variables and a set
of dimensionless equations of state is then utilized to complete the system.
The resulting dynamical system is analyzed using geometric techniques from
dynamical systems theory to find the qualitative behaviour of the
Friedmann-Robertson-Walker models with bulk viscosity. In these models there
exists a free parameter such that the qualitative behaviour of the models can
be quite different (for certain ranges of values of this parameter) from that
found in models satisfying the Eckart theory studied previously. In addition,
the conditions under which the models inflate are investigated.Comment: 29 pages, 8 Encapsulated PostScript Figures, uses the IOP style file
On the Stability of the Einstein Static Universe
We show using covariant techniques that the Einstein static universe
containing a perfect fluid is always neutrally stable against small
inhomogeneous vector and tensor perturbations and neutrally stable against
adiabatic scalar density inhomogeneities so long as c_{s}^2>1/5, and unstable
otherwise. We also show that the stability is not significantly changed by the
presence of a self-interacting scalar field source, but we find that spatially
homogeneous Bianchi type IX modes destabilise an Einstein static universe. The
implications of these results for the initial state of the universe and its
pre-inflationary evolution are also discussed.Comment: some additional comments and references; version to appear in Class.
Quant. Gra
Evolution of the Bianchi I, the Bianchi III and the Kantowski-Sachs Universe: Isotropization and Inflation
We study the Einstein-Klein-Gordon equations for a convex positive potential
in a Bianchi I, a Bianchi III and a Kantowski-Sachs universe. After analysing
the inherent properties of the system of differential equations, the study of
the asymptotic behaviors of the solutions and their stability is done for an
exponential potential. The results are compared with those of Burd and Barrow.
In contrast with their results, we show that for the BI case isotropy can be
reached without inflation and we find new critical points which lead to new
exact solutions. On the other hand we recover the result of Burd and Barrow
that if inflation occurs then isotropy is always reached. The numerical
integration is also done and all the asymptotical behaviors are confirmed.Comment: 22 pages, 12 figures, Self-consistent Latex2e File. To be published
in Phys. Rev.
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