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SUMMARY:Towards understanding of condensed matter via study granular syste
ms
DTSTART;VALUE=DATE-TIME:20191223T144500Z
DTEND;VALUE=DATE-TIME:20191223T150500Z
DTSTAMP;VALUE=DATE-TIME:20240520T143908Z
UID:indico-contribution-21-147@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Andrii Spivak (Odesa State Environmental University)
\nGranular materials under the external perturbations show a diversity of
structural transformations which characterized by different symmetries. Th
eir rigorous classification in terms of phase transitions seems very attra
ctable (nevertheless\, still questionable). Intriguing question is: can we
use the information extracted from studying of structural transformations
characters in granular materials to describe any details about the local
symmetry of the condensed matter\, which displayed during the typical phas
e–transformations? Here\, there are several analogies as well as discrep
ancies are waiting for us: Local structure\, Phase transitions\, Landau-Gi
nzburg kinetics\, Lindeman criteria for crystallization\, Equation of stat
e.\n$~~~~~~$We would like to outline some results of our research directed
to study of structurization\, which occurs during packing processes in ge
ntly agitated granular (micro-mechanical) systems [1-5]. The focus will be
done on developing and investigation of hard-spheres (discs) packing mode
ls. The results of this research\, in our opinion\, in principle can provi
de an understanding of some characters of the local structure and bulk pro
perties not only of granular matter\, but also a regular phases of condens
ed matter (e.g.\, molecular liquids and solutions\, colloids\, glasses). T
he problem of densest packing are formally belong to pure mathematical are
a. But inspite of this objectives to study structural and physical propert
ies of perturbed granular systems a variety of physical theoretical model
s which are partially based on phenomenological information (direct observ
ation) have been developed. The packing of hard-particles can be described
by geometric approach\, which provides a practical and universal methods
of quantitative characterization of the local (as well as global) packing
via symmetry categories.\n$~~~~~~$We will consider a packing of a large co
nglomeration of hard particles confined by a finite-sized container. Bound
aries as well as exclusion-volume effects (under the negligible dissipatio
n) would be described by simple packing parameters (like compactivity). Pr
operties of the states of such systems (for instance 2D hard discs) will b
e studied theoretically and after then compared with the results of direct
observations. Obtained results will be analyzed with respect to reminisce
nces with some properties of the typical phases of condensed matter.\n\n[1
]. Gerasimov O.I.\, Idomskyy V.A.\, Schram P.P.-J.M. Compaction of granula
r graphite in a vertically vibrating container with restricted geometry. C
ondens. Matter Phys. 4 (1)\, 161-164 (2001). DOI: https://doi.org/10.5488/
CMP.4.1.161\n[2]. Gerasimov O.I.\, Schram P.P.-J.M. Differential equation
of state of a model system with a singular measure: application to granula
r materials in steady states. Physica A 312 (1-2)\, 172-180 (2002). DOI: h
ttps://doi.org/10.1016/S0378-4371(02)00851-8\n[3]. Gerasymov O.I.\, Zagoro
dny A.G.\, Somov M.M. Toward the Analysis of the Structure of Granular Mat
erials. Ukr. J. Phys. 58 (1)\, 32-39 (2013). DOI: https://doi.org/10.1540
7/ujpe58.01.0032\n[4]. Gerasymov O.I.\, Spivak A.Ya. Kinetic model of comp
action in granular materials. Ukr. J. Phys. 60 (3)\, 253-257 (2015). DOI:
https://doi.org/10.15407/ujpe60.03.0253\n[5]. Schockmel J.\, Vandewalle N.
\, Opsomer E.\, Lumay G. Frustrated crystallization of a monolayer of magn
etized beads under geometrical confinement. Phys. Rev. E 95 (6)\, 062120
(2017). DOI: https://doi.org/10.1103/PhysRevE.95.062120\n\nhttps://indico.
bitp.kiev.ua/event/4/contributions/147/
LOCATION:Bogolyubov Institute for Theoretical Physics of the National Acad
emy of Sciences of Ukraine 322
URL:https://indico.bitp.kiev.ua/event/4/contributions/147/
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SUMMARY:The influence of the three-particle interaction on critical phenom
ena of the Bose-Hubbard Model
DTSTART;VALUE=DATE-TIME:20191223T142500Z
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DTSTAMP;VALUE=DATE-TIME:20240520T143908Z
UID:indico-contribution-21-141@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleksii Kryvchikov (B.Verkin Institute for Low Tempe
rature Physics and Engineering of the National Academy of Sciences of Ukra
ine)\nThe critical behavior of a mixture of two types of ultracold bosons
on the optical lattice was studied. The system can be described by the Bos
e-Hubbard model. It is known that the system can be in a superfluid or in
a Mott insulator state\, depending on the hopping parameter and chemical p
otential. The interaction between different types of particles drastically
changes the phase diagram. In particular\, the transitions between mixed
and superfluid states appear. The presence of a three-particle interaction
leads to an increase in the Mott insulator region of the phase diagram. I
n particular\, bosons with a higher hopping value can be still in the Mott
insulator phase. The results are obtained in the framework of the mean-fi
eld approximation for a wide range of parameters.\n\nhttps://indico.bitp.k
iev.ua/event/4/contributions/141/
LOCATION:Bogolyubov Institute for Theoretical Physics of the National Acad
emy of Sciences of Ukraine 322
URL:https://indico.bitp.kiev.ua/event/4/contributions/141/
END:VEVENT
BEGIN:VEVENT
SUMMARY:First passage time distribution for spiking neuron with fast inhib
itory feedback stimulated with renewal stream
DTSTART;VALUE=DATE-TIME:20191223T150500Z
DTEND;VALUE=DATE-TIME:20191223T152500Z
DTSTAMP;VALUE=DATE-TIME:20240520T143908Z
UID:indico-contribution-21-140@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Olha Shchur (Bogolyubov Institute for Theoretical Ph
ysics of the National Academy of Sciences of Ukraine\, Kyiv)\nWe consider
a class of spiking neuron models defined by a set of conditions typical f
or basic threshold-type models\, such as leaky integrate-and-fire model an
d some artificial neurons. A series of impulses\, representing a point re
newal process\, is applied to a neuron. Each output impulse is fed back to
the neuron after a fixed time delay\, $\\Delta$. This impulse acts as an
impulse received through a fast inhibitory (GABA$_a$) synapse.\n$~~~~~~~~
$In our previous work [1]\, we have obtained a general relation in case of
input Poisson stream for calculating exactly the probability density func
tion (PDF) $p(t)$ for the distribution of the first passage time of crossi
ng the threshold.\n$~~~~~~~~$In the present work\, we have obtained a simi
lar results but applicable in case of any renewal input stream. The calcul
ation is based on the known PDF $p^0(t)$ for the same neuron without feedb
ack and the PDF of interspike intervals for input stream\, $p^{in}(t)$.\n
\n[1]. Vidybida\, A.\, Shchur\, O. Relation between firing statistics of s
piking neuron with delayed fast inhibitory feedback and without feedback\,
*Fluctuation and Noise Letters*\, 17(01):1850005 (2018).\n\nhttps://indic
o.bitp.kiev.ua/event/4/contributions/140/
LOCATION:Bogolyubov Institute for Theoretical Physics of the National Acad
emy of Sciences of Ukraine 322
URL:https://indico.bitp.kiev.ua/event/4/contributions/140/
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SUMMARY:Transverse energy transfer by Alfven waves in toroidal plasmas
DTSTART;VALUE=DATE-TIME:20191223T140500Z
DTEND;VALUE=DATE-TIME:20191223T142500Z
DTSTAMP;VALUE=DATE-TIME:20240520T143908Z
UID:indico-contribution-21-159@indico.bitp.kiev.ua
DESCRIPTION:Speakers: M.H. Tyshchenko (Institute for Nuclear Research of t
he National Academy of Sciences of Ukraine\, Kyiv)\nDestabilized magnetohy
drodynamic (MHD) eigenmodes can transfer the energy and momentum from the
region where particles (e.g.\, fast ions) drive the plasma instability to
another region\, where the destabilized waves are damped. This phenomenon
named “spatial channeling” (SC) was predicted in [1\,2]. A key element
of the SC is that the energy and momentum of particles driving the instab
ility are transferred by the waves (eigenmodes)\, not by the diffusion or
heat conduction. In this work the physics of the transverse energy transfe
r by Alfven waves in toroidal plasmas is elucidated. It is found that\, in
contrast to the classical Alfven waves in infinite plasmas\, the Alfven w
aves in toroidal systems produce plasma compression due to coupling with f
ast magnetoacoustic waves\, which provides the energy transfer. The radial
group velocities of the traveling waves constituting the Global Alfven Ei
genmodes and Toroidicity-induced Alfven Eigenmodes are calculated. It is s
hown that equation for Alfven eigenmodes derived in the approximation of v
anishing wave field along the equilibrium magnetic field reproduce the lon
gitudinal magnetic field of the wave and lead to correct transverse energy
flux. The obtained results explain how Alfven eigenmodes can provide the
spatial energy channeling. The results of this work are published in [3].
\nThis work was supported by the Project No. PL15/18 of the National Acade
my of Sciences of Ukraine and the Project No. 6392 of the Science and Tech
nology Center in Ukraine (STCU).\n\n[1] Ya. I. Kolesnichenko\, Yu. V. Yako
venko\, and V. V. Lutsenko\, Phys. Rev. Lett. **104**\, 075001 (2010)\n[2]
Ya. I. Kolesnichenko\, Yu. V. Yakovenko\, V. V. Lutsenko\, R. B. White\,
and A. Weller\, et al.\, Nucl. Fusion **50**\, 084011 (2010)\n[3] Ya. I.Ko
lesnichenko\, Yu. V. Yakovenko\, and M. H. Tyshchenko\, Phys. Plasmas **25
**\, 122508 (2018)\n\nhttps://indico.bitp.kiev.ua/event/4/contributions/15
9/
LOCATION:Bogolyubov Institute for Theoretical Physics of the National Acad
emy of Sciences of Ukraine 322
URL:https://indico.bitp.kiev.ua/event/4/contributions/159/
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