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BEGIN:VEVENT
SUMMARY:Modeling of activation and deactivation processes in postsynaptic
membrane
DTSTART;VALUE=DATE-TIME:20181204T112500Z
DTEND;VALUE=DATE-TIME:20181204T114500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-8@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleksii Kulish (Taras Shevchenko National University
of Kyiv)\nModern technologies are increasingly turning to the issue of mo
deling nerve impulse transmission mechanisms to create artificial simulato
rs. Despite the fact that the basic principles of the specialized contact
zone between two neurons (chemical synapse) are known\, there still a lot
questions are open.\nIn this paper\, we research the issue of building a p
hysical model of the process of activation and deactivation of the postsyn
aptic membrane in a chemical synapse. Based on the diffusion process\, con
sidering the interaction of choline with receptors on the postsynaptic mem
brane\, we obtained a temporary dependence of activated receptors on the p
ostsynaptic membrane. The relationship between the activation time of the
postsynaptic membrane and the number of activated receptors was also analy
zed. The work also calculated the space-time distribution of the anti - me
diator (choline) in the synaptic cleft.\nWe hope that the results obtained
in the work will help to better understand the processes occurring during
the transmission of the nerve signal and will give impetus to further res
earch in the field of medical preparations and the construction of artific
ial neural networks.\n\nhttps://indico.bitp.kiev.ua/event/2/contributions/
8/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Blocking of DNA sites of specific recognition by hydrogen peroxide
molecules in the process of ion beam therary
DTSTART;VALUE=DATE-TIME:20181204T104500Z
DTEND;VALUE=DATE-TIME:20181204T110500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-26@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleksii Zdorevskyi (Bogolyubov Institute for Theoret
ical Physics)\nAfter irradiation of cancer cells in the ion beam therapy m
ethod the concentration of hydrogen peroxide in the cell medium grows sign
ificantly. But the role of hydrogen peroxide molecules in ion beam therapy
has not been determined yet. We assume that interaction of peroxide molec
ules with DNA atomic groups can block the genetic information of the cance
r cell and lead to its neutralization. To understand the possibility of DN
A deactivation in the cell\, in the present study the formation of complex
es of hydrogen peroxide with DNA specific recognition atomic groups is con
sidered. Using atom-atom potential functions method and quantum-chemical a
pproach\, based on density functional theory\, the spatial configurations
and energy minima for the complexes of peroxide and water molecules with n
ucleic bases are studied. The obtained data allows us to formulate a new\,
different from the already known\, mechanism of the ion irradiation actio
n on living cells\, that can be the key factor in the ion beam therapy tre
atment.\n\nhttps://indico.bitp.kiev.ua/event/2/contributions/26/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Linear-in-gradients hydrodynamic equations for a system with small
interaction
DTSTART;VALUE=DATE-TIME:20181204T084500Z
DTEND;VALUE=DATE-TIME:20181204T090500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-14@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Vyacheslav Gorev (National Mining University)\nThe s
ystem under consideration is a one-component weakly non-uniform gas with s
mall potential interaction. The investigation is based on the kinetic equa
tion in the case of small interaction with a nonlocal collision integral [
1]. In [2] it is shown that the system kinetic energy is not conserved on
the basis of the nonlocal collision integral. So the system temperature sh
ould be defined on the basis on the total system energy rather than the ki
netic one. The following hydrodynamic equations are obtained up to the fir
st order in small gradients and the second order in small interaction:\n\n
$ \\frac{{\\partial n}}{{\\partial t}} = - n\\frac{{\\partial {\\upsilon
_n}}}{{\\partial {x_n}}} - {\\upsilon _n}\\frac{{\\partial n}}{{\\partial
{x_n}}}\, \\quad \\frac{{\\partial {\\upsilon _n}}}{{\\partial t}} = - {\
\upsilon _l}\\frac{{\\partial {\\upsilon _n}}}{{\\partial {x_l}}} + \\left
[ { - \\frac{T}{{nm}} - \\frac{1}{m}V\\left( {k = 0} \\right) + } \\right.
$\n\n$ \\left. { + \\frac{1}{{2{\\pi ^2}mT}}\\left( {A + \\frac{B}{3}} \\
right)} \\right]\\frac{{\\partial n}}{{\\partial {x_n}}} + \\left[ { - \\f
rac{1}{m} - \\frac{n}{{4{\\pi ^2}m{T^2}}}\\left( {A + \\frac{B}{3}} \\righ
t)} \\right]\\frac{{\\partial T}}{{\\partial {x_n}}}\, $\n\n$ \\frac{{\\pa
rtial T}}{{\\partial t}} = \\left[ { - \\frac{2}{3}T + \\frac{n}{{9{\\pi ^
2}T}}\\left( {A + \\frac{B}{2}} \\right)} \\right]\\frac{{\\partial {\\ups
ilon _n}}}{{\\partial {x_n}}} - {\\upsilon _n}\\frac{{\\partial T}}{{\\par
tial {x_n}}}\, $\n\n$ A = \\int\\limits_0^\\infty {dk} {k^2}{V^2}\\left(
k \\right)\, \\quad B = \\int\\limits_0^\\infty {dk{k^3}V\\left( k \\righ
t)\\frac{{\\partial V\\left( k \\right)}}{{\\partial k}}} $\n\nwhere $n$ i
s the particle number density\, $\\upsilon_l$ is the velocity\, $T$ is the
temperature\, and $V(k)$ is the Fourier transform of the system pair pote
ntial. In fact\, these equations are non-dissipative hydrodynamic equation
s and in the leading-in-interaction order they coincide with corresponding
equations in the framework of standard hydrodynamics. The obtained equati
ons may be a basis for the investigation of the system dissipative hydrody
namics and system kinetic coefficients. \n\n[1] A.I. Akhiezer and S.V. Pel
etminsky\, Methods of Statistical Physics\, Oxford\, Pergamon Press\, 1981
\, 376 p.\n[2] V.N. Gorev and A.I. Sokolovsky\, Visnik Dnipropetrovs'kogo
Universitetu. Seria Fizika\, radioelektronika\, 25\, issue 24\, 14 (2017).
\n\nhttps://indico.bitp.kiev.ua/event/2/contributions/14/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Reconstructed potentials of the 2-field model of dark energy with
canonical and non-canonical kinetic terms
DTSTART;VALUE=DATE-TIME:20181204T130000Z
DTEND;VALUE=DATE-TIME:20181204T132000Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-3@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Olga Sergijenko (Taras Shevchenko National Universit
y of Kyiv)\nWe generalize quintom to include the tachyonic kinetic term al
ong with the classical one. For the spatially flat\, homogeneous and isotr
opic Universe with Friedmann-Robertson-Walker metric of 4-space we discuss
in detail the reconstruction of the scalar fields potential $U(\\phi\,\\x
i)$. Such a reconstruction cannot be done unambiguously\, so we consider 3
simplest forms of $U(\\phi\,\\xi)$: the product of $\\Phi(\\phi)$ and $\\
Xi(\\xi)$\, the sum of $\\Phi(\\phi)$ and $\\Xi(\\xi)$ and this sum to the
$\\kappa$th power. We present the maps of reconstructed potentials for th
e Chevallier-Polarski-Linder parametrization of the equation of state para
meter and the set of cosmological parameters obtained from the latest Plan
ck data.\n\nhttps://indico.bitp.kiev.ua/event/2/contributions/3/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The 3.5 keV dark matter candidate line in the Galactic bulge regio
n
DTSTART;VALUE=DATE-TIME:20181204T132000Z
DTEND;VALUE=DATE-TIME:20181204T134000Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-5@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Denys Savchenko (Bogolyubov Institute for Theoretica
l Physics of the NAS of Ukraine)\nThe 3.5 keV line\, discovered in early 2
014 in the spectra of different cosmic objects\, draws large attention as
being the dark matter signal candidate. Much effort was performed since th
en to determine it's nature. The one conclusion to point out is that the d
ark matter signal is by now the only explanation consistent with all the o
bservational data available.\nWe are presenting the detection of the 3.5 k
eV line in the stacked spectra of the XMM-Newton observation of the Galact
ic bulge region. The line was detected significantly in the several annulu
s regions around Galactic center. Being interpreted as dark matter decay l
ine\, this allows us to determine the inner halo profile slope. \nWe also
briefly discuss the perspectives of the planned experiments in frames of o
ur restrictions on signal parameters.\n\nhttps://indico.bitp.kiev.ua/event
/2/contributions/5/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Features of light coupling in low-loss 2D periodic structures supp
orting phonon polariton
DTSTART;VALUE=DATE-TIME:20181205T110500Z
DTEND;VALUE=DATE-TIME:20181205T112500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-11@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Yuliia Mankovska (Taras Shevchenko National Universi
ty of Kyiv)\nUnderstanding of light-matter interaction in a wide frequency
range is an important fundamental problem with significant potential appl
ied impacts. For instance\, Plasmonics is a rapidly developing field at th
e boundary of physical optics and condensed matter physics with many prosp
ective applications. However\, the use of plasmons is limited from a pract
ical point of view because their spectral signature is in the visible and
near infrared region\, where metals have strong absorption leading to high
losses. From this point of view\, the use of low-loss materials\, like po
lar dielectrics\, is promising. Particularly\, in such materials surface p
honon polaritons can be easily excited from the infrared to the terahertz
frequencies resulting in a strong coupling of light and optical phonons in
the crystal.\nIn this report\, we studied features of light localization
in low loss 2D periodic structures formed by a polar crystal. Specifically
\, we considered a periodic structure of silicon carbide nanodisks on a cr
ystalline silicon substrate. We numerically solved Maxwell equations with
appropriate boundary conditions. The strong dependence of phonon polariton
spectral resonances with the period of the array was theoretically reveal
ed. Furthermore\, experimental reflectivity measurements on the fabricated
structure confirmed these tendencies.\n\nhttps://indico.bitp.kiev.ua/even
t/2/contributions/11/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Solitons of Korteweg–de Vries equation and Bogoliubov transforma
tions
DTSTART;VALUE=DATE-TIME:20181204T080000Z
DTEND;VALUE=DATE-TIME:20181204T084500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-29@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Mykola Iorgov (Bogolyubov Institute for Theoretical
Physics)\nhttps://indico.bitp.kiev.ua/event/2/contributions/29/
LOCATION:Bogolyubov Institute for Theoretical Physics of the National Acad
emy of Sciences of Ukraine 422
URL:https://indico.bitp.kiev.ua/event/2/contributions/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Non-congruent phase transitions in strongly interacting matter wit
hin the Quantum van der Waals model
DTSTART;VALUE=DATE-TIME:20181205T144000Z
DTEND;VALUE=DATE-TIME:20181205T150000Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-31@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Roman Poberezhnyuk (Bogolubov Institute for Theoreti
cal Physics)\nThe non-congruent liquid-gas phase transition (LGPT) in asym
metric nuclear matter is studied using the recently developed Quantum van
der Waals model in the grand canonical ensemble. Different values of the e
lectric-to-baryon charge ratio\, $Q/B$\, are considered. This non-congruen
t LGPT exhibits several features which are not present in the congruent LG
PT of symmetric nuclear matter. These include a continuous phase transform
ation\, a change in the location of the critical point\, and the separatio
n of the critical point and the endpoints. The effects which are associate
d with the non-congruent LGPT become negligible for the following cases: w
hen $Q/B$ approaches its limiting values\, $0.5$ or $0$\, or if quantum st
atistical effects can be neglected. The latter situation is realized when
the particle degeneracy attains large values. The skewness and kurtosis of
the baryonic and electric charges fluctuations where calculated along the
chemical free-out curve of nucleus-nucleus collisions within Quantum van
der Waals - Hadron Resonance Gas model. Due to the existence of the non-co
ngruent LGPT\, all four quantities demonstrate large deviations from the I
deal Hadron Resonance Gas baseline.\n\nhttps://indico.bitp.kiev.ua/event/2
/contributions/31/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Boundary conditions for the superconducting junctions at temperatu
res close to critical
DTSTART;VALUE=DATE-TIME:20181205T100500Z
DTEND;VALUE=DATE-TIME:20181205T102500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-19@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleksandr Pastukh (Lesya Ukrainka Eastern European N
ational University)\nTo calculate the current-phase relation in supercondu
cting junctions\, it is necessary to investigate the spatial behavior of t
he order parameter in the superconducting regions of the junction. In the
case of temperatures close to the critical one\, the Ginzburg-Landau theor
y [1] is used for this purpose. However\, to apply this theory there is ne
cessary to find the corresponding boundary conditions for the Ginzburg-Lan
dau equation. Boundary condition can be found using the Wiener–Hopf meth
od [2-3]\, however\, use of this method for complicated superconducting ju
nctions is problematic.\nIn our investigation\, the problem of finding bou
ndary conditions for the $\\\\$Ginzburg-Landau equation\, was considered i
n the case of different superconducting junctions. In particular\, superco
nducting junctions\, combining tunnel effects and the proximity effect\, w
ith nonmagnetic impurities in superconducting regions were investigated. F
or finding the boundary condition for the Ginzburg-Landau equation the met
hod of quasiorthogonality to asymptotics was used [4]. In addition\, there
were no restrictions on the values of the electron transmission coefficie
nt and the thickness of the normal layer.\nIt has been shown that the boun
dary condition for the Ginzburg-Landau equation contains unknown constants
for the calculation of which the quasiorthogonality to the asymptotics me
thod was used. This method proved to be quite effective for complicated su
perconducting systems which contain the combination of dielectric layer an
d normal layer. In addition\, boundary conditions obtained using this meth
od\, are valid for the arbitrary concentration of nonmagnetic impurities.\
n \n[1] A. V. Svidzinskii\, Spatially Innhomogeneous Problems in the Theor
y of Superconductivity\, Nauka\, Moscow (1982).\n[2] R.O. Zaitsev Boundary
conditions for the superconductivity equations at temperatures close to c
ritical // Sov. Phys. JETP 21\, 1178 (1965).\n[3] A. Barone\, Yu. N. Ovchi
nnikov Boundary conditions and critical current of SNS junctions // Zh. Ek
sp. Teor. Fiz. 77\, 1463 (1979).\n[4] A. V. Svidzinsky\, and V. E. Sakhnyu
k\, Condens. Matter Phys. 3\, 683 (2000).\n\nhttps://indico.bitp.kiev.ua/e
vent/2/contributions/19/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:An effective theory for Heisenberg antiferromagnet on one-dimensio
nal frustrated lattices at high magnetic fields
DTSTART;VALUE=DATE-TIME:20181205T090500Z
DTEND;VALUE=DATE-TIME:20181205T092500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-7@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Olesia Krupnitska (Institute for Condensed Matter Ph
ysics\, NAS of Ukraine)\nWe consider the spin-1/2 antiferromagnetic Heisen
berg model on one-dimen-sional frustrated lattices (double tetrahedra chai
n [1]\, deformed octahedral chain [2]) placed in an external magnetic fiel
d with almost dispersionless (almost flat) lowest magnon band. The main go
al of our study is to develop a systematic theory for the low-temperature
high-field properties of these models\, using the localized magnons approa
ch [3\,4]. We construct an effective description of one-dimensional chains
with triangular and quadrangular traps by means of the localized magnons
concept within the strong coupling approximation. The obtained effective m
odels are much simpler than the initial ones: firstly\, the effective mode
ls have smaller number of sites and secondly\, and most importantly\, they
are unfrustrated. As a result\, one can apply well elaborated methods of
the quantum spin systems theory to discuss the properties of the initial
frustrated quantum antiferromagnets at high fields and low temperatures. W
e perform extensive exact diagonalization calculations to check the validi
ty of the obtained effective Hamiltonians by comparison with the initial m
odels.\n\n[1] M. Maksymenko\, O. Derzhko and J. Richter\, Acta Physica Pol
onica A **119**\, 860 (2011)\; Eur. Phys. J. B **84**\, 397 (2011).\n[2] J
. Strečka et al.\, Phys. Rev. B **95**\, 224415 (2017)\; Physica B **536*
*\, 364 (2018).\n[3] J. Schulenburg et al.\, Phys. Rev. Lett. **88**\, 167
207 (2002).\n[4] O. Derzhko\, J. Richter\, and M. Maksymenko\, Int. J. Mod
. Phys. B **29**\, 1530007\n(2015).\n\nhttps://indico.bitp.kiev.ua/event/2
/contributions/7/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Relation between firing statistics of spiking neuron with delayed
feedback and without feedback
DTSTART;VALUE=DATE-TIME:20181204T102500Z
DTEND;VALUE=DATE-TIME:20181204T104500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-30@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Olha Shchur (Bogolyubov Institute for Theoretical Ph
ysics of the National Academy of Sciences of Ukraine)\nWe consider a class
of spiking neuronal models with threshold 2\, defined by a set of conditi
ons typical for basic threshold-type models\, such as the leaky integrate-
and-fire or the binding neuron model and also for some artificial neurons.
A neuron is fed with a Poisson process. Each output impulse is applied to
the neuron itself after a finite delay $\\Delta$. This impulse is identi
cal to those delivered from the input stream. We derive a general relation
which allows calculating exactly the probability density function (pdf) $
p(t)$ of output interspike intervals of a neuron with feedback based on kn
own pdf $p^0(t)$ for the same neuron without feedback\, intensity of the i
nput stream and the properties of the feedback line (the $\\Delta$ value)
.\n In addition to this\, we calculate exactly the model-independent ini
tial segment of pdf $p(t)$ for a neuron with feedback that is the same for
any neuron satisfying the imposed conditions. Also\, relations between mo
ments of pdf $p(t)$ for a neuron with feedback and pdf $p^0(t)$ for the s
ame neuron without feedback are derived. The obtained expressions are chec
ked numerically by means of Monte Carlo simulation.\nThe course of $p(t)$
has a $\\delta$-function peculiarity\, which makes it impossible to approx
imate $p(t)$ by Poisson or another simple stochastic process.\n\nhttps://i
ndico.bitp.kiev.ua/event/2/contributions/30/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:21-cm observations and warm dark matter models
DTSTART;VALUE=DATE-TIME:20181204T134000Z
DTEND;VALUE=DATE-TIME:20181204T140000Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-27@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Anton Rudakovskyi (Bogolyubov Institute for Theoreti
cal Physics)\nRecent report of 21-cm absorption signal by EDGES experiment
has raised considerable interest in the dark matter (DM) community. Takin
g the reported EDGES result at face value\, a number of forthcoming pape
rs constrained masses of DM particles and their interaction strengths wi
th Standard Model particles.\nHowever\, the connection between the formati
on of structures and 21-cm signal requires knowledge of parameters that de
scribe star formation and radiation at early times.\nWe use the recent mea
surements by EDGES to demonstrate that the robust warm dark matter (WDM) b
ounds are in fact weaker than those given by the Lyman-$\\alpha$ forest me
thod and other structure formation bounds.\nWe also show that resonantly p
roduced 7 keV sterile neutrino dark matter model is consistent with these
data.\n\nhttps://indico.bitp.kiev.ua/event/2/contributions/27/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/27/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tumour growth model: Lie symmetries and exact solutions
DTSTART;VALUE=DATE-TIME:20181205T140000Z
DTEND;VALUE=DATE-TIME:20181205T142000Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-6@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Vasyl' Davydovych (Institute of Mathematics\, NAS o
f Ukraine)\nWe examine the tumour growth model proposed in [1]. In the 2D
case\, the governing equations after some simplifications take the form \n
$\\begin{array} {l}\n \\alpha_t + \\left(\\alpha u^1\\right)_{x}+\\left(
\\alpha u^2\\right)_{y}=\n S(\\alpha)\, \\\n u^1_{x} + u^2_{y} = \\nabla
\\cdot\\left(D(\\alpha)\\nabla p\\right)\, \\\\\n \\Big[(2+\\lambda)\\al
pha u^1_{x} + \\lambda \\alpha u^2_{y}\\Big]_x + \\Big[\\alpha u^1_{y} + \
\alpha u^2_{x}\\Big]_y =\n p_x + (\\alpha\\Sigma(\\alpha))_x\, \\hskip1.2
cm (1)\\\\\n \\Big[\\alpha u^1_{y} + \\alpha u^2_{x}\\Big]_x +\\Big[(2+\
\lambda)\\alpha u^2_{y} +\n \\lambda \\alpha u^1_{x}\\Big]_y = p_y + (\\
alpha\\Sigma(\\alpha))_y\, \n \\end{array}$ \nwhere $D\, \\ S$ and $\\Sig
ma$ are some functions and their typical forms are listed in [1]. Assuming
that the tumour boundary is prescribed by a curve $\\Gamma(t\,x\,y)=0$\,
where $\\Gamma$ is an unknown function\, the boundary сonditions have th
e form\n$\\begin{array} {l}\n u^1\\Gamma_{x}+ u^2\\Gamma_{y}= -\\Gamma_t
\, \\quad p=0\, \\\\\n \\Big[(2+\\lambda) u^1_{x} + \\lambda u^2_{y}\\Bi
g]\\Gamma_x + \\Big[ u^1_{y} + u^2_{x}\\Big]\\Gamma_y = 0\, \\hskip3.5cm
(2)\\\\\n \\Big[ u^1_{y} + u^2_{x}\\Big]\\Gamma_x +\\Big[(2+\\lambda) u^
2_{y} + \\lambda u^1_{x}\\Big]\\Gamma_y = 0.\n \\end{array}$\nSo\, we ha
ve the nonlinear boundary value problem (1)-(2) with the unknown moving bo
undary $\\Gamma(t\,x\,y)=0$.\nUsing the definition proposed in [2] and ass
uming $\\Gamma$ to be a closed curve for any $t\\geq 0$\, we examined the
Lie symmetry and constructed the exact solutions of the boundary value pro
blem (1)-(2). For instance\, the following statement takes place:\n*The sy
stem of nonlinear PDEs (1) with arbitrary functions $D\, \\ S$ and $\\Si
gma$ is invariant with respect to the infinite-dimensional Lie algebra ge
nerated by the Lie symmetry operators\n $\\begin{array} {l}\n \\partial_
t\, \\quad F(t) \\partial_p\, \\quad\n G_g = g(t)\\partial_x + \\dot
g\\partial_{u^1}\, \\quad G_h = h(t)\\partial_y + \\dot h\\partial_{u^2}
\\\\\n J_f = f(t) \\Big[y\\partial_x - x\\partial_y +(u^2+\\frac{\\dot
f}{f}y)\\partial_{u^1} -\n (u^1+\\frac{\\dot f}{f}x)\\partial_{u^2}\\B
ig].\n \\end{array}$ \n Here $ F\, f\, g\, $ and $h$ are arbitrary sm
ooth functions and the upper dot means differentiation with respect to tim
e.*\n\n [1] H. Byrne\, J.R. King\, D.L.S. McElwain\, L. Preziosi. A two-p
hase model of solid tumour growth. *Appl. Math. Letters.* **16** (2003) 5
67-573.\n [2] R. Cherniha\, S. Kovalenko. Lie symmetries and reductions of
multi-dimensional boundary value problems of the Stefan type. *J. Phys. A
: Math. Theor.* **44** (2011) 485202 (25 pp.)\n\nhttps://indico.bitp.kiev.
ua/event/2/contributions/6/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The influence of inhomogeneities on physical characteristics of fe
rromagnetic clusters inside of antiferromagnetic matrix in an external fie
ld
DTSTART;VALUE=DATE-TIME:20181204T092500Z
DTEND;VALUE=DATE-TIME:20181204T094500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-17@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleksii Kryvchikov (B. Verkin ILTPE of NASU)\nThe pr
oblem of the influence of an external field on the magnetic moments of fer
romagnetic clusters surrounded by an antiferromagnet is studied in this pa
per. Clusters interact with each other magneticaly. In the case of strong
anisotropy such a system can be described by a one-dimensional Ising model
with a random exchange in the presence of an effective local field. The i
nhomogeneity of the interface between clusters and an antiferromagnet repr
esents the random effective field. The ground state of such a model turns
out to be the set of domains of different lengths in fields smaller than t
he saturation field. In contrast to the one-dimensional Ising model in a h
omogeneous field\, linear dependence of the magnetization on the external
field in the presence of a random effective field in the region of small f
ields is observed. The magnitude of the exchange bias of the magnetization
curve depends on the average of the random effective field\, and the slop
e of the curve depends on the variance of the random effective field. The
use of such a model allows drawing conclusions about the properties of the
boundary between subsystems from experimental data. The results obtained
within the framework of such model allow to estimate the properties of the
boundary between subsystems basing on experimental data. A formula that e
stimates the quality of the interface in the case of the cylindrical geome
try of the sample is obtained.\n\nhttps://indico.bitp.kiev.ua/event/2/cont
ributions/17/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Constraints on the excess energy in low-mass systems
DTSTART;VALUE=DATE-TIME:20181204T140000Z
DTEND;VALUE=DATE-TIME:20181204T142000Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-1@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Iurii Babyk (Main Astronomical Observatory of NAS of
Ukraine)\nWe present the $K-T$ scaling relation of the individual galaxie
s (mostly early-type galaxies)\, groups\, and clusters. The given relation
is based on 168 targets observed with $Chandra$ X-ray Observatory. We der
ive entropy at $R_{2500}$ and build $K_{2500}-T$ relation covering 0.3 --
15.0 keV of temperature and 10$^{12}$ -- 10$^{15} M_{\\odot}$ of total mas
s bands. We find that entropy at $R_{2500}$ scales with averaged temperatu
re as $K_{2500} \\propto T^{0.68\\pm0.05}$\, leading to the break of a sel
f-similar model. We compare our measurements with previous results and fin
d precise agreement with $K-T$ relations obtained for entropies at $R_{200
}$ and $R_{500}$ radii. The break of the self-similar model indicates the
presence of non-gravitational processes at the cores of low- and high-mass
systems which provide an additional heating that is known as entropy exce
ss in $K-T$ relation. We show that AGN feedback is likely mechanism produc
ing this additional heating. We also show that active nuclei in low-mass s
ystems are better able to prevent the significant level of star formation
due to enough cooling nearby the nucleus to maintain the energetic feedbac
k loop by measuring the level of heating per gas particle in hot atmospher
es of low- and high-mass systems. In addition\, using radio flux and lumin
osity we build the entropy-cavity power relation\, finding a weak correlat
ion of $K_{2500} \\propto P_{cav}^{0.25\\pm0.5}$.\n\nhttps://indico.bitp.k
iev.ua/event/2/contributions/1/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Atomic charges for reproducing the dependence of molecular dipole
moment on conformation
DTSTART;VALUE=DATE-TIME:20181204T110500Z
DTEND;VALUE=DATE-TIME:20181204T112500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-24@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Tymofii Nikolaienko (Taras Shevchenko National Unive
rsity of Kyiv)\nA modification of the principal component regression model
is proposed for obtaining a fixed set of atomic charges (referred to as d
ipole-derived charges) optimized for reproducing the dipole moment of a co
nformationally rich $\\\\$ molecule\, i.e.\, a molecule with multiple loca
l minima on the potential energy surface. The method requires geometry of
the conformers\, their dipole moments and APT charges (which only depend o
n the derivatives of the dipole moments with respect to the atomic coordin
ates) in each of the conformers as input data\, and produces a single set
of fixed charges suitable for accurate representation of both the dipole m
oment vector of all conformers and its variations resulting from small cha
nges in molecular geometry (e.g.\, caused by vibrations) [1]. The peculiar
feature of the method is that it requires neither adjustable empirical pa
rameters\, nor averaging over conformers or any other post-processing of t
he obtained charges. The input data used in the proposed method are obtain
ed from ab initio calculations which also do not require empirical paramet
ers.\nThe proposed method has been applied to canonical 2'-deoxyribonucleo
tides\, the model DNA monomers\, and the dipole-derived charges have been
shown to outperform both the averaged APT and RESP charges in reproducing
the dipole moments of large sets of conformers\, thus demonstrating a pote
ntial usefulness of the dipole-derived charges as a 'reference point' for
modeling polarization effects in conformationally rich molecules\, paramet
erizing non-polarizable force fields and for developing novel polarizable
force fields for classical MD simulations.\n\n[1] T.Yu.Nikolaienko and L.A
.Bulavin\, Phys. Chem. Chem. Phys\, 20\, 2890-2903 (2018).\n\nhttps://indi
co.bitp.kiev.ua/event/2/contributions/24/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:On consistency of classical homogenization $\\\\$ models for the p
ermittivity of statistically homogeneous mixtures
DTSTART;VALUE=DATE-TIME:20181205T130000Z
DTEND;VALUE=DATE-TIME:20181205T132000Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-15@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Andrii Semenov (Odessa I.I.Mechnikov National Univer
sity)\nThe standard effective-medium methods to electrodynamic homogenizat
ion of heterogeneous media can be divided into two classes: symmetrical an
d asymmetrical. They are assumed to be independent and applicable to diffe
rent types of systems\, making a basis for different further modifications
that take into account specific features of a given system. Despite the f
act that these modifications are able to restore experimental data rather
well\, various authors note that the basic assumptions behind the methods
are not consistent.\nThe goal of this report is to scrutinize these two ho
mogenization methods\, their consistency\, and ranges of validity. To obta
in the most general results\, a simple system of impenetrable dielectric b
alls embedded in a uniform host medium has been considered. For its analys
is\, a generalized differential scheme was developed for the effective qua
sistatic permittivity of macroscopically homogeneous and isotropic dielect
ric mixtures [1]. The scheme is based upon the compact group approach (CGA
) [2] reformulated in a way that allows one to analyze the role of differe
nt contributions to the effective permittivity of the system and modify it
for different system structures.\nIt is shown that within the CGA\, the o
nly physically consistent homogenization type is symmetrical effective-med
ium homogenization. Applicability of this approach to the core-shell model
and the description of numerical and experimental data for conductivity o
f composite electrolytes was demonstrated in [3]. The asymmetrical (differ
ential) homogenization type can be obtained by replacing the electromagnet
ic interaction between previously added constituents and those being added
by the interaction of the latter with recursively formed effective medium
. Under this assumption\, each portion of inclusions has different polariz
ation\, and the previously added portions do not interact with the new one
s. This can be valid only for narrow concentration ranges and low contrast
constituents\, even for the generalized versions of the original mixing r
ules\, as can be proved using the Hashin-Shtrikman bounds. Therefore\, the
asymmetric approach is approximate in the long-wave limit\, and one shoul
d be cautious when using the differential models since they can lead to un
predictable errors and wrong results.\n\n[1] A. K. Semenov\, *J. Phys. Com
mun.*\, **2** (2018) 035045.\n[2] M. Ya. Sushko\, *Zh. Eksp. Teor. Fiz.*\,
**132** (2007) 478 [*JETP* **105** (2007) 426]\; *Phys. Rev. E* **96** (2
017) 062121.\n[3] M. Ya. Sushko\, A. K. Semenov\, *arXiv*:1810.11892 [cond
-mat.mtrl-sci].\n\nhttps://indico.bitp.kiev.ua/event/2/contributions/15/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Physics of singular self-adjoint extensions of one-dimensional Dir
ac operator
DTSTART;VALUE=DATE-TIME:20181205T134000Z
DTEND;VALUE=DATE-TIME:20181205T140000Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-18@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Dmitry Panchenko (Odessa I.I.Mechnikov National Univ
ersity)\nWe consider boundary conditions (self-adjoint extensions) corresp
onding to point-like interactions for one-dimensional Dirac operator. Taki
ng the non-relativistic limit we show how all possible point-like interact
ions for one-dimensional Schrödinger operator of free spinless particle c
an be obtained from the Dirac Hamiltonian. In case of spin-1/2 we show tha
t there are boundary conditions with spin-flop mechanism. We suggest the p
hysical interpretation these point-like extensions in terms of the Rashba
(spin-orbital) coupling.\n\nhttps://indico.bitp.kiev.ua/event/2/contributi
ons/18/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The electroweak phase transition in a spontaneously magnetized vac
uum
DTSTART;VALUE=DATE-TIME:20181205T142000Z
DTEND;VALUE=DATE-TIME:20181205T144000Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-20@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Pavlo Minaiev (Oles Honchar Dnipro National Universi
ty)\nWe investigate the electroweak phase transition in the Standard Model
s with accounting for the spontaneous vacuum magnetization. It is known th
at for the mass of Higgs boson grater then 75 GeV\, the electroweak phase
transition is second order. But according to Sakharov's conditions for the
formation of the baryon asymmetry of the Universe\, it should be strong f
irst order. The spontaneously generated fields are temperature dependent a
nd they have an influence on the phase transition.\nChromomagnetic fields
$B_3$ and $B_8$ have to be created spontaneously in the gluon sector of QC
D at temperature $T > T_d$ higher the deconfinement temperature $T_d$. Usu
al magnetic field $H$ should also be spontaneously generated because of qu
ark-loop. For $T$ near $T_{EW}$\, this field should be present too\, so th
ey can change the behavior of phase transition.\nThe critical temperature
for the electroweak phase transition is estimated in Standart model and in
the scalar theory. The field strengths $B_3(T)$\, $B_8(T)$ and $H(T)$ at
relevant temperatures are also estimated.\n\nhttps://indico.bitp.kiev.ua/e
vent/2/contributions/20/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Equilibrium states of antiferromagnetic ring-shaped and helix-shap
ed spin chains with hard-tangential anisotropy
DTSTART;VALUE=DATE-TIME:20181205T084500Z
DTEND;VALUE=DATE-TIME:20181205T090500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-12@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Denys Kononenko (Taras Shevchenko National Universit
y of Kyiv)\nFor the last decade\, active research on magnetic nanosystems
of curved geometry was motivated by their outstanding properties and great
application potential [1]. For instance\, recent theoretical studies of l
ow-dimensional magnets with complex geometry propose a description of fasc
inating geometry-induced effects including pattern formation and magnetoch
iral effects in quasi-one-dimensional wires [2]\, for review see [1]. Desp
ite these advances in the study of curvilinear low-dimensional ferromagnet
s\, significant knowledge gaps exist in the study of curvilinear antiferro
manetic systems.\nThe purpose of the current study is the theoretical inve
stigation of equilibrium states in antiferromagnetic ring-shaped and helix
-shaped spin chains with hard-tangential anisotropy. For this purpose we u
se both analytical methods and computer spin-lattice simulations in SLaSi
software package [3]. In our study\, we consider two sublattice antiferrom
agnet in the frame of the sigma-model approach where its statics and dyna
mics are described in terms of Neel vector only. \nWe analytically show t
hat the global energy minimum of the antiferromagnetic ring-shaped spin ch
ain is reached when Neel vector is perpendicular to the ring plane. An equ
ilibrium phase diagram is constructed for the antiferromagnetic helix-shap
ed spin chain: (i) a quasi-binormal state is realized in the case of relat
ively large curvatures and (ii) spatial-periodic state is typical in the o
pposite case. Both states are described analytically and well confirmed by
SLaSi.\nStability regions of both ground states are determined using spin
-lattice simulator SLaSi.\n\n[1] R. Streubel\, P. Fischer\, F. Kronast\, V
. P. Kravchuk\, D. D. Sheka\, Y. Gaididei\, O. G. Schmidt and D. Makarov\
, J. Phys. D\, 49\, 363001\, (2016). \n[2] D. D. Sheka\, V. P. Kravchuk\,
Y. Gaididei\, J. Phys. A\, 48\, 125202\, (2015).\n[3] http://slasi.knu.ua
/\n\nhttps://indico.bitp.kiev.ua/event/2/contributions/12/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:µ-Bose-Einstein condensate dark matter model
DTSTART;VALUE=DATE-TIME:20181204T142000Z
DTEND;VALUE=DATE-TIME:20181204T144000Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-4@indico.bitp.kiev.ua
DESCRIPTION:Speakers: M.V. Khelashvili (Bogolubov Institute for Theoretica
l Physics)\nIt is known that the Bose-Einstein condensate (BEC) based Dark
Matter (DM) model solves several problems of Cold Dark Matter model on th
e small scales\, including core-cusp problem. In turn\, there are some dif
ficulties that arise in the framework of BEC DM\, like overestimated a bit
(up to 20%) prediction of halo mass in comparison with the values derived
from observations. In ref. [1]\, the extended (via µ-deformation) µ-BEC
DM model is proposed. The µ-deformed gas has the properties similar to o
rdinary Bose gas endowed with an additional attraction between its particl
es\, incorporated [2] by the deformation parameter µ. We prove the possib
ility of BEC-like phase tran¬sition using the tools of thermodynamical (R
uppeiner) geometry\, through analysis of singularities of scalar curvature
in the thermodynamical parameters space. It is shown that the critical t
emperature of BEC-like transition is higher in the considered µ-Bose gas
than in the ordinary Bose case. Moreover\, dependence on the parameter µ
gives us certain freedom enabling to treat the weak points of BEC DM mode
l\, e.g. the overestimated value of DM halo mass. \n\n[1] A.M. Gavrilik\
, I.I. Kachurik\, M.V. Khelashvili\, A.V. Nazarenko Condensate of µ-Bose
gas as a model of dark matter. Physica A: V.506\, pp. 835-843 (2018)\n[2]
A.P. Rebesh\, I.I. Kachurik\, A.M. Gavrilik Elements of μ-calculus and th
ermodynamics of μ-Bose gas model\, Ukr. J. Phys. V. 58\, no.12\, pp. 1182
-1191 (2013)\n\nhttps://indico.bitp.kiev.ua/event/2/contributions/4/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Calculation of thermodynamic potential for Bose system near conden
sate point
DTSTART;VALUE=DATE-TIME:20181204T100500Z
DTEND;VALUE=DATE-TIME:20181204T102500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-25@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Kseniia Haponenko (Oles Honchar Dnipro National Univ
ersity)\nBose system in the presence of the condensate is investigated in
the Bogolyubov model of the separated condensate (see about in [1]). In th
is state occupation number ${{n}_{0}}$ of one-particle state with momentu
m ${p}=0$ is macroscopic one. In this model the system is described by the
statistical operator\n\n$\nw({{n}_{0}})={{e}^{\\beta [\\Omega ({{n}_{0}})
-\\hat{H}({{n}_{0}})+\\mu \\hat{N}({{n}_{0}})]}}\, \\quad \\mathrm{S
p}w({{n}_{0}})=1\n $\n\nwhere operators $\\hat{H}({{n}_{0}})$\, $\\hat{N}(
{{n}_{0}})$ are given by Hamiltonian of the system $\\hat{H}$ and operator
of particle number $\\hat{N}$ after substitution $n_{0}^{1/2}$ instead of
the Bose operators ${{a}_{0}}$\, ${{a}_{0}}^{+}$ ($\\beta $\,$\\mu $ are
the reverse temperature and the chemical potential). According to Bogolyub
ov equilibrium value $n_{0}^{o}$ of the occupation number $n_{0}^{{}}$ can
be found from the minimum condition of the thermodynamic potential $\\Ome
ga ({{n}_{0}})$ i.e. it is the non-equilibrium one of the system. Near tra
nsition point from normal state to the state with the condensate occupatio
n number $n_{0}^{{}}$ is small in comparison with the total number of part
icles and the potential $\\Omega ({{n}_{0}})$ can be calculated in a pertu
rbation theory in powers of $n_{0}^{1/2}$.\nThe purpose of this paper is c
alculating of the potential $\\Omega ({{n}_{0}})$ in a modified thermodyna
mic perturbation theory with small parameter $n_{0}^{{}}$. The obtained ex
pression for $\\Omega ({{n}_{0}})$ can be used as the potential Landau in
his theory of the phase transitions of the second kind for the system unde
r consideration. The statistical operator $w({{n}_{0}})$ can be written in
the form $w({{n}_{0}})=\\exp \\beta \\\,[F-({{\\mathbf{\\hat{H}}}_{0}}+{{
{\\hat{U}}}_{1}}+{{{\\hat{U}}}_{2}})]$ where the operators ${{{\\hat{U}}}_
{1}}\\sim n_{0}^{1/2}\, {{{\\hat{U}}}_{2}}\\sim{{n}_{0}}$. The calculation
is substantially simplified by the fact that the independent on ${{n}_{0}
}$ operator ${{\\mathbf{\\hat{H}}}_{0}}$ commutes with the operator of the
number of particles. It is shown that only integer powers of this number
are present in expansion of the potential. Relatively compact expressions
for the coefficients of this series are obtained because operators describ
ing the interaction in the system commutate under T-product. For a Bose ga
s they are calculated in an additional perturbation theory in interaction
between particles. An analyze of the results with connection to the Landau
theory of phase transitions is given. \n\n[1] Akhiezer\, A.I. Methods of
Statistical Physics [Text] / A.I. Akhiezer\, A.I. and S.V. Peletminskii.
– Oxford: Pergamon Press\, 1981. – 450 p.\n\nhttps://indico.bitp.kiev.
ua/event/2/contributions/25/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ground-state phases of frustrated bilayer quantum Heisenberg antif
erromagnets
DTSTART;VALUE=DATE-TIME:20181205T092500Z
DTEND;VALUE=DATE-TIME:20181205T094500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-16@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Vasyl Baliha (Institute for Condensed Matter Physics
of the NASU)\nWe consider the quantum antiferromagnetic Heisenberg model
on the square-lattice and honeycomb-lattice bilayers in the absence of an
external magnetic field. We use a variational approach to construct the gr
ound-state phase diagrams of such model on different bilayers. For simplic
ity\, we choose two one-parameter variational wave functions\, which can d
escribe states of model in two regions with different relationships betwee
n lattice parameters. We calculate variational energies and compare them.
This allows us to find borders between different states\, where one of the
variational energies is minimal. Finally\, we construct ground-state phas
e diagrams in different coordinates. At the end of this study we compare
our findings with the earlier results obtained by more sophisticated appro
aches [1\, 2]. We observe good agreement with these results. This studies
were performed together with O. Derzhko\, J. Richter and O. Götze.\n\n[1]
H. Zhang et al.\, Phys. Rev. B 93\, 235150 (2016)\;\n[2] J. Stapmanns et
al.\, Phys. Rev. Lett. 121\, 127201 (2018).\n\nhttps://indico.bitp.kiev.ua
/event/2/contributions/16/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:The third sound as an electric field generator
DTSTART;VALUE=DATE-TIME:20181205T104500Z
DTEND;VALUE=DATE-TIME:20181205T110500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-10@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Aleksandr Konstantinov (B.Verkin Institute for Low T
emperature Physics and Engineering of the National Academy of Sciences of
Ukraine)\nIt is predicted that oscillations of temperature during propaga
tion of third sound in a thin superfluid film cause appearance of an alter
nating electric field in the surrounding space\, i.e. the third sound acts
as a generator of the electric field [1].\nAs known\, the helium atoms ha
ve no dipole\, quadrupole and other multipole moments. The situation chang
es in the vicinity of the wall. Interaction of helium with the container w
alls leads to the emergence of a nonzero average dipole moment of the heli
um atoms directed along the normal to the wall. This leads to polarization
of the film. Oscillations of its surface are accompanied by polarization
oscillations\, which cause the appearance of the electric fields over the
film. Specificity of a superfluid film is associated with the ability to c
ause oscillations of the film surface by periodically heating the film bou
ndary. As a result\, due to the anomalously large thermomechanical effect\
, a small temperature difference $\\Delta T$ leads to large fluctuations i
n film height and electrical potential $\\Delta \\varphi$. It turns out th
at the differential thermal e.m.f. $\\Delta \\varphi/\\Delta T$ exceeds i
ts value for typical metals. The predicted effect can be considered as an
electrical analogue of the fountain effect.\nUsing the method of I.E. Dzya
loshinskii\, the average electric field over the system "atom-solid" was c
alculated. It is shown that this electrical field is equivalent to the fie
ld of the dipole moment of the atom (induced by substrate) and its image.
The polarization of the system\, associated with its inhomogeneity (analog
ue of the flexoelectric effect)\, was also considered. It has been establi
shed that the flexoelectric effect leads only to a small renormalization o
f the dipole moment induced by the substrate. The equations describing the
propagation of the third sound through the film have been solved. The eff
ects of evaporation and condensation of helium atoms were taken into accou
nt. The relationship between oscillating parts of the height and temperatu
re of the film was found for the low-temperature and high-temperature regi
ons. For helium film covering a hollow cylinder on the outside or inside\,
an analytical expression for the electric field in space has been found.
The coefficient of proportionality between the electric potential and the
oscillating part of the film temperature (differential thermal e.m.f) was
calculated.\n[1] S. I. Shevchenko and A. M. Konstantinov\, J. Low Temp. Ph
ys. (2018).\n\nhttps://indico.bitp.kiev.ua/event/2/contributions/10/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Features of thermal transport in strained and compressed crystalli
ne silicon
DTSTART;VALUE=DATE-TIME:20181205T132000Z
DTEND;VALUE=DATE-TIME:20181205T134000Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-9@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Oleksii Nepochatyi (Faculty of Physics\, Taras Shevc
henko National University of Kyiv)\nTuning of thermal properties of variou
s materials is a key challenge in material research. First and foremost\,
such necessity arises because of continuous miniaturization of constitute
components of various devises. As a result\, issue connected with ameliora
tion of heat management started to be more and more crucial. Therefore\, a
ny possibilities of increasing or reduction of thermal conductivity in sem
iconductor material are very important. \nOne of the possibilities for var
iation of thermal transport is the change of elastic properties of the med
ia. Particularly\, it is well-known that straining and compression of crys
talline silicon lead to modification of heat conduction. However\, one nee
ds more physical insight regarding phonon transport for efficient manipula
tion of heat fluxes.\nIn our study\, we consider thermal conductivity of s
trained and compressed silicon as a function of strain and temperature. We
use ab-initio equilibrium molecular dynamics approach for evaluation of t
hermal conductivity. Additionally\, we extracted phonon density of states
and dispersion curves from molecular dynamics simulations. These data were
utilized for direct calculations of thermal conductivity with the use of
kinetic theory approach. Comparison of molecular dynamics simulation and
direct approach allows us to decompose different factors affecting the the
rmal conductivity of strained/$\\\\$compressed silicon.\n\nhttps://indico.
bitp.kiev.ua/event/2/contributions/9/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dirac and Weyl semimetals
DTSTART;VALUE=DATE-TIME:20181205T080000Z
DTEND;VALUE=DATE-TIME:20181205T084500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-28@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Eduard Gorbar (Bogolyubov Institute for Theoretical
Physics)\nLecture\n\nhttps://indico.bitp.kiev.ua/event/2/contributions/28/
LOCATION:Bogolyubov Institute for Theoretical Physics of the National Acad
emy of Sciences of Ukraine 422
URL:https://indico.bitp.kiev.ua/event/2/contributions/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Towards the problem of the Nesterenko’s soliton waves propagatio
n in nonlinear inhomogeneous Hertzian chains
DTSTART;VALUE=DATE-TIME:20181204T090500Z
DTEND;VALUE=DATE-TIME:20181204T092500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-22@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Andrii Spivak (Odesa State Environmental University)
\nWe consider theoretically the problem of the pulse transmission along 1D
vertical chain of hard spheres\, which interact with each other by pair-w
ise nonlinear Hertz law [1-3]. System is subject into gravity and therefor
e became inhomogeneous [2\,3]. We show\, that being excited form the bound
ary (from the top)\, system is able to exhibit complex multimode dynamics
of pulse propagation. After long-wave approximation has been used to study
the dynamics of week perturbation\, in the lowest approximation\, resulte
d governing equation is satisfy by either singular solutions\, or combinat
ions of cylindrical waves [2]. In the higher approximation we obtaine nonl
inear equation of motion (generalized in form of Bussinesq equation) which
bring us to solution of Nesterenko-type soliton [1] with a negligible dif
ferences in the amplitudes\, and dispersions.\nWe conclude that initially
weekly nonlinear and inhomogeneous chain\, already in the linear approxima
tion\, is able to transmit either normal or singular modes\, whenever\, th
e accounting\, of the nonlinearity leads to familiar Nesterenko-type solit
on’s [1].\nTherefore under the appropriate values of the parameters (non
linearity\, inhomogeneity\, signal amplitudes) linearized Hertzian chain s
upport both discontinuous as well as quasinormal mode scenarios of pulse t
ransmission.\n\n[1] Nesterenko\, V.F. Propagation of nonlinear compression
pulses in granular media. J. Appl. Mech. Tech. Phys. 24 (1) (1984) 733-74
3\; Translated from : Zh. Prikl. Mekh. Tekh. Fiz. (5) (1983) 136-148. [Rus
sian] \n[2] Sen\, S.\, Hong\, J.\, Bang\, J.\, Avalos\, E.\, and Doney\, R
. Solitary waves in the granular chain. Physics Reports 462 (2) (2008) 21-
66.\n[3] Gerasymov\, O.I. and Vandewalle\, N. On the exact solutions of th
e problem of impulsive propagation in an inhomogeneous granular chain. Dop
ov. Nac. acad. nauk Ukr. (8) (2012) 67-72. [Ukrainian]\n\nhttps://indico.b
itp.kiev.ua/event/2/contributions/22/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:A current density dependence on phase differences in layered super
conducting structures of SISIS type
DTSTART;VALUE=DATE-TIME:20181205T102500Z
DTEND;VALUE=DATE-TIME:20181205T104500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-13@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Arsen Shutovskyi (Lesya Ukrainka Eastern European Na
tional University)\nThe explored layered superconducting structure contain
s three massive superconductors separated by two thin insulator films. Wit
hout loss of generality we may consider that the superconductors are diffe
rent. An insulator film is mathematically expressed via the Dirac delta fu
nction [1]. An order parameter and a current density depend on an applicat
e\, because we have a one dimensional problem.\nAccording to the supercond
uctivity theory every physical quantity can be calculated using the Green
function method [2]. The Green functions satisfy the closed system of line
ar differential equations. The mentioned equations have the second derivat
ive in the configuration representation. Using the Fourier transform we ha
ve constructed the closed system of linear matrix differential equations i
n the t-representation [3]. The obtained equations have only the first der
ivative. Since a momentum is close to the Fermi momentum our calculations
become rather simplified. Solving the linear matrix differential equations
in the t-representation we have introduced the undefined integration cons
tants. These constants can be defined through application of Green functio
n continuity. This means that we need to have a boundary condition. An ord
er parameter as a complex function is usually defined by magnitude and pha
se. The model with a piecewise constant order parameter allows to suppose
that the outside superconductors have equal order parameter magnitudes and
unequal order parameter phases. The inside superconductor has a zero orde
r parameter phase. The order parameter magnitude of the inside superconduc
tor is not necessary equal to the order parameter magnitudes of the outsid
e superconductors.\nSubstituting the obtained integration constants into t
he Green functions we have obtained the current density dependence on an a
pplicate. Calculating the current density on the junction we have obtained
the current density expression as a phase difference function.\n\n[1] С
відзинський А. В. Математичні методи тео
ретичної фізики. У 2-х т. – Вид. 4-те\, допов
н. і переробл. – К.: І-нт теорет. фізики ім.
М. М. Боголюбова\, 2009.\n[2] Свидзинский А. В.
Пространственно-неоднородные задачи те
ории сверхпроводимости. – М.: Наука\, 1982.
– 310 с.\n[3] Свідзинський А. В. Мікроскопічн
а теорія надпровідності: монографія. – Л
уцьк: ВНУ ім. Лесі Українки\, 2011. – 422 с.\n\nht
tps://indico.bitp.kiev.ua/event/2/contributions/13/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/13/
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SUMMARY:Influence of correlated hopping on the optical conductivity spectr
a
DTSTART;VALUE=DATE-TIME:20181205T112500Z
DTEND;VALUE=DATE-TIME:20181205T114500Z
DTSTAMP;VALUE=DATE-TIME:20200807T155625Z
UID:indico-contribution-2-21@indico.bitp.kiev.ua
DESCRIPTION:Speakers: Danylo Dobushovskyi (Institute for Condensed Matter
Physics of the National Academy of Sciences of Ukraine)\nOptical conductiv
ity spectra are studied for the Falicov-Kimball model with correlated hopp
ing on the Bethe lattice. An expression for the current-current correlatio
n function is derived using dynamical mean field theory. Besides\, the Nyq
uist plots were built and used to distinguish different contributions in t
he optical conductivity spectra. \n In the metallic phase without correlat
ed hopping\, both the current-current correlation function $\\chi(\\Omega)
$ and optical conductivity $\\sigma(\\Omega)$ display Drude peak at low fr
equencies. The shape of Drude peak is described by the Debye relaxation eq
uation \n\n$\\chi_{\\text{D}}(\\Omega) = \\chi_{\\infty} + \\frac{\\chi_0-
\\chi_{\\infty}}{1-\\Omega\\tau_{\\text{D}}}$\n\nOn the other hand in the
presence of small correlated hopping\, the shape of Drude peak deviates f
rom the Debye relaxation peak\, and an additional wide peak is observed on
the optical conductivity spectra and on Nyquist plot when Fermi level is
in the vicinity of the two particle resonance [1]. At larger values of the
correlated hopping parameter\, the density of states contains three bands
[1] and the corresponding optical spectra and Nyquist plots display a mor
e complicated shape with additional peaks. For the case of strong local co
rrelations\, the overall picture strongly depends on the doping level. For
a small doping\, when the chemical potential is placed in the wide lower
Hubbard band the obtained results are much closer to the case of the doped
Mott insulator without correlated hopping\, whereas for a large doping\,
when the chemical potential is placed in the narrow upper Hubbard band\, t
he spectral weight of the Drude peak is strongly reduced and it is separat
ed by a gap from the charge-transfer peak.\n\n[1] D.A. Dobushovskyi\, A.M.
Shvaika\, V. Zlatic\, Phys. Rev. B. 95\, 125133 (2017).\n\nhttps://indico
.bitp.kiev.ua/event/2/contributions/21/
LOCATION:
URL:https://indico.bitp.kiev.ua/event/2/contributions/21/
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