72 research outputs found
Публікації Я. Новицького на сторінках «Катеринославських губернських відомостей»
Pulsed-field-gradient nuclear magnetic resonance (NMR) combined with time-resolved chemically induced dynamic nuclear polarization (TR-CIDNP) was applied to study the reduction of guanosyl radicals in reactions with the proteins hen egg white lysozyme (HEWL) and bovine a-lactalbumin (BLA) in their native state.Guanosyl radicalswere generated photochemically in the reaction of guanosine-50-monophosphate with photosensitizer, triplet-excited 2,20-dipyridyl. In this reaction, at pH 5 guanosyl cation radical is formed, which deprotonates to yield the neutral guanosyl radical. To minimize the contribution of the cation radical, phosphate buffer was added, which accelerates the deprotonation of guanosyl cation radical. From model simulations of CIDNP kinetics the rate constants of the reduction were found to be (3.1 ± 0.5) 9 107 M-1s-1 for HEWL and (1.6 ± 0.4) 9 107 M-1s-1 for BLA. Also, experiments were carried out at the conditions for denatured HEWL, i.e., at 50 C in the presence of 10 M urea-d4. The rate constant of the reduction of guanosyl radical in this case was (3.6 ± 0.5) 9 108 M-1s-1
Exactly solvable model of dissipative vortex tunneling
I consider the problem of vortex tunneling in a two-dimensional
superconductor. The vortex dynamics is governed by the Magnus force and the
Ohmic friction force. Under-barrier motion in the vicinity of the saddle point
of the pinning potential leads to a model with quadratic Hamiltonian which can
be analytically diagonalized. I find the dependence of the tunneling
probability on the normal state quasiparticle relaxation time with a
minimum at , where is the level spacing of the
quasiparticle bound states inside the vortex core. The results agree
qualitatively with the available experimental data.Comment: RevTeX, 6 pages, 2 figures. Published versio
UHECR Acceleration in Dark Matter Filaments of Cosmological Structure Formation
A mechanism for proton acceleration to ~10^21eV is suggested. It may operate
in accretion flows onto thin dark matter filaments of cosmic structure
formation. The flow compresses the ambient magnetic field to strongly increase
and align it with the filament. Particles begin the acceleration by the ExB
drift with the accretion flow. The energy gain in the drift regime is limited
by the conservation of the adiabatic invariant p_perp^2/B. Upon approaching the
filament, the drift turns into the gyro-motion around the filament so that the
particle moves parallel to the azimuthal electric field. In this 'betatron'
regime the acceleration speeds up to rapidly reach the electrodynamic limit
for an accelerator with magnetic field and the orbit radius
(Larmor radius). The periodic orbit becomes unstable and the particle
slings out of the filament to the region of a weak (uncompressed) magnetic
field, which terminates the acceleration.
The mechanism requires pre-acceleration that is likely to occur in structure
formation shocks upstream or nearby the filament accretion flow. Previous
studies identify such shocks as efficient proton accelerators to a firm upper
limit ~10^19.5 eV placed by the catastrophic photo-pion losses. The present
mechanism combines explosive energy gain in its final (betatron) phase with
prompt particle release from the region of strong magnetic field. It is this
combination that allows protons to overcome both the photo-pion and the
synchrotron-Compton losses and therefore attain energy 10^21 eV. A requirement
on accelerator to reach a given E_max placed by the accelerator energy
dissipation \propto E_{max}^{2}/Z_0 due to the finite vacuum impedance Z_0 is
circumvented by the cyclic operation of the accelerator.Comment: 34 pages, 10 figures, to be published in JCA
Direct evidence of nonstationary collisionless shocks in space plasmas
Collisionless shocks are ubiquitous throughout the universe: around stars, supernova remnants, active galactic
nuclei, binary systems, comets, and planets. Key information is carried by electromagnetic emissions from particles
accelerated by high Mach number collisionless shocks. These shocks are intrinsically nonstationary, and the
characteristic physical scales responsible for particle acceleration remain unknown. Quantifying these scales is crucial, as it affects the fundamental process of redistributing upstream plasma kinetic energy into other degrees of
freedom—particularly electron thermalization. Direct in situ measurements of nonstationary shock dynamics have
not been reported. Thus, the model that best describes this process has remained unknown. Here, we present
direct evidence demonstrating that the transition to nonstationarity is associated with electron-scale field
structures inside the shock ramp
Contributions to the cross shock electric field at supercritical perpendicular shocks: Impact of the pickup ions
A particle-in-cell code is used to examine contributions of the pickup ions
(PIs) and the solar wind ions (SWs) to the cross shock electric field at the
supercritical, perpendicular shocks. The code treats the pickup ions
self-consistently as a third component. Herein, two different runs with
relative pickup ion density of 25% and 55% are presented in this paper. Present
preliminary results show that: (1) in the low percentage (25%) pickup ion case,
the shock front is nonstationary. During the evolution of this perpendicular
shock, a nonstationary foot resulting from the reflected solar wind ions is
formed in front of the old ramp, and its amplitude becomes larger and larger.
At last, the nonstationary foot grows up into a new ramp and exceeds the old
one. Such a nonstationary process can be formed periodically. hen the new ramp
begins to be formed in front of the old ramp, the Hall term mainly contributed
by the solar wind ions becomes more and more important. The electric field Ex
is dominated by the Hall term when the new ramp exceeds the old one.
Furthermore, an extended and stationary foot in pickup ion gyro-scale is
located upstream of the nonstationary/self-reforming region within the shock
front, and is always dominated by the Lorentz term contributed by the pickup
ions; (2) in the high percentage (55%) pickup ion case, the amplitude of the
stationary foot is increased as expected. One striking point is that the
nonstationary region of the shock front evidenced by the self-reformation
disappears. Instead, a stationary extended foot dominated by Lorentz term
contributed by the pickup ions, and a tationary ramp dominated by Hall term
contributed by the solar wind ions are clearly evidenced. The significance of
the cross electric field on ion dynamics is also discussed.Comment: 11 pages, 6 figs and 1 table. This paper will be published in the
journal: Astrophysics and Space Scienc
Nonlinear ion-acoustic (IA) waves driven in a cylindrically symmetric flow
By employing a self-similar, two-fluid MHD model in a cylindrical geometry,
we study the features of nonlinear ion-acoustic (IA) waves which propagate in
the direction of external magnetic field lines in space plasmas. Numerical
calculations not only expose the well-known three shapes of nonlinear
structures (sinusoidal, sawtooth, and spiky or bipolar) which are observed by
numerous satellites and simulated by models in a Cartesian geometry, but also
illustrate new results, such as, two reversely propagating nonlinear waves,
density dips and humps, diverging and converging electric shocks, etc. A case
study on Cluster satellite data is also introduced.Comment: accepted by AS
Gamma-Ray Bursts: The Underlying Model
A pedagogical derivation is presented of the ``fireball'' model of gamma-ray
bursts, according to which the observable effects are due to the dissipation of
the kinetic energy of a relativistically expanding wind, a ``fireball.'' The
main open questions are emphasized, and key afterglow observations, that
provide support for this model, are briefly discussed. The relativistic outflow
is, most likely, driven by the accretion of a fraction of a solar mass onto a
newly born (few) solar mass black hole. The observed radiation is produced once
the plasma has expanded to a scale much larger than that of the underlying
``engine,'' and is therefore largely independent of the details of the
progenitor, whose gravitational collapse leads to fireball formation. Several
progenitor scenarios, and the prospects for discrimination among them using
future observations, are discussed. The production in gamma- ray burst
fireballs of high energy protons and neutrinos, and the implications of burst
neutrino detection by kilometer-scale telescopes under construction, are
briefly discussed.Comment: In "Supernovae and Gamma Ray Bursters", ed. K. W. Weiler, Lecture
Notes in Physics, Springer-Verlag (in press); 26 pages, 2 figure
What is the Oxygen Isotope Composition of Venus? The Scientific Case for Sample Return from Earth’s “Sister” Planet
Venus is Earth’s closest planetary neighbour and both bodies are of similar size and mass. As a consequence, Venus is often described as Earth’s sister planet. But the two worlds have followed very different evolutionary paths, with Earth having benign surface conditions, whereas Venus has a surface temperature of 464 °C and a surface pressure of 92 bar. These inhospitable surface conditions may partially explain why there has been such a dearth of space missions to Venus in recent years.The oxygen isotope composition of Venus is currently unknown. However, this single measurement (Δ17O) would have first order implications for our understanding of how large terrestrial planets are built. Recent isotopic studies indicate that the Solar System is bimodal in composition, divided into a carbonaceous chondrite (CC) group and a non-carbonaceous (NC) group. The CC group probably originated in the outer Solar System and the NC group in the inner Solar System. Venus comprises 41% by mass of the inner Solar System compared to 50% for Earth and only 5% for Mars. Models for building large terrestrial planets, such as Earth and Venus, would be significantly improved by a determination of the Δ17O composition of a returned sample from Venus. This measurement would help constrain the extent of early inner Solar System isotopic homogenisation and help to identify whether the feeding zones of the terrestrial planets were narrow or wide.Determining the Δ17O composition of Venus would also have significant implications for our understanding of how the Moon formed. Recent lunar formation models invoke a high energy impact between the proto-Earth and an inner Solar System-derived impactor body, Theia. The close isotopic similarity between the Earth and Moon is explained by these models as being a consequence of high-temperature, post-impact mixing. However, if Earth and Venus proved to be isotopic clones with respect to Δ17O, this would favour the classic, lower energy, giant impact scenario.We review the surface geology of Venus with the aim of identifying potential terrains that could be targeted by a robotic sample return mission. While the potentially ancient tessera terrains would be of great scientific interest, the need to minimise the influence of venusian weathering favours the sampling of young basaltic plains. In terms of a nominal sample mass, 10 g would be sufficient to undertake a full range of geochemical, isotopic and dating studies. However, it is important that additional material is collected as a legacy sample. As a consequence, a returned sample mass of at least 100 g should be recovered.Two scenarios for robotic sample return missions from Venus are presented, based on previous mission proposals. The most cost effective approach involves a “Grab and Go” strategy, either using a lander and separate orbiter, or possibly just a stand-alone lander. Sample return could also be achieved as part of a more ambitious, extended mission to study the venusian atmosphere. In both scenarios it is critical to obtain a surface atmospheric sample to define the extent of atmosphere-lithosphere oxygen isotopic disequilibrium. Surface sampling would be carried out by multiple techniques (drill, scoop, “vacuum-cleaner” device) to ensure success. Surface operations would take no longer than one hour.Analysis of returned samples would provide a firm basis for assessing similarities and differences between the evolution of Venus, Earth, Mars and smaller bodies such as Vesta. The Solar System provides an important case study in how two almost identical bodies, Earth and Venus, could have had such a divergent evolution. Finally, Venus, with its runaway greenhouse atmosphere, may provide data relevant to the understanding of similar less extreme processes on Earth. Venus is Earth’s planetary twin and deserves to be better studied and understood. In a wider context, analysis of returned samples from Venus would provide data relevant to the study of exoplanetary systems
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