8,211 research outputs found
Hodograph Method and Numerical Integration of Two Hyperbolic Quasilinear Equations. Part I. The Shallow Water Equations
In paper [S.I. Senashov, A. Yakhno. 2012. SIGMA. Vol.8. 071] the variant of
the hodograph method based on the conservation laws for two hyperbolic
quasilinear equations of the first order is described. Using these results we
propose a method which allows to reduce the Cauchy problem for the two
quasilinear PDE's to the Cauchy problem for ODE's. The proposed method is
actually some similar method of characteristics for a system of two hyperbolic
quasilinear equations. The method can be used effectively in all cases, when
the linear hyperbolic equation in partial derivatives of the second order with
variable coefficients, resulting from the application of the hodograph method,
has an explicit expression for the Riemann-Green function. One of the method's
features is the possibility to construct a multi-valued solutions. In this
paper we present examples of method application for solving the classical
shallow water equations.Comment: 19 pages, 5 figure
Hodograph Method and Numerical Solution of the Two Hyperbolic Quasilinear Equations. Part III. Two-Beam Reduction of the Dense Soliton Gas Equations
The paper presents the solutions for the two-beam reduction of the dense
soliton gas equations (or Born-Infeld equation) obtained by analytical and
numerical methods. The method proposed by the authors is used. This method
allows to reduce the Cauchy problem for two hyperbolic quasilinear PDEs to the
Cauchy problem for ODEs. In some respect, this method is analogous to the
method of characteristics for two hyperbolic equations. The method is
effectively applicable in all cases when the explicit expression for the
Riemann-Green function for some linear second order PDE, resulting from the use
of the hodograph method for the original equations, is known. The numerical
results for the two-beam reduction of the dense soliton gas equations, and the
shallow water equations (omitting in the previous papers) are presented. For
computing we use the different initial data (periodic, wave packet).Comment: 22 pages, 11 figures. arXiv admin note: substantial text overlap with
arXiv:1503.0176
Mathematical Model of a pH-gradient Creation at Isoelectrofocusing. Part II. Numerical Solution of the Stationary Problem
The mathematical model describing the natural textrm{pH}-gradient arising
under the action of an electric field in an aqueous solution of ampholytes
(amino acids) is constructed and investigated. This paper is the second part of
the series papers \cite{Part1,Part3,Part4} that are devoted to pH-gradient
creation problem. We present the numerical solution of the stationary problem.
The equations system has a small parameter at higher derivatives and the
turning points, so called stiff problem. To solve this problem numerically we
use the shooting method: transformation of the boundary value problem to the
Cauchy problem. At large voltage or electric current density we compare the
numerical solution with weak solution presented in Part 1.Comment: 14 pages, 8 figure
Modeling of zonal electrophoresis in plane channel of complex shape
The zonal electrophoresis in the channels of complex forms is considered
mathematically with the use of computations. We show that for plane S-type
rectangular channels stagnation regions can appear that cause the strong
variations of the spatial distribution of an admixture. Besides, the shape of
an admixture zone is strongly influenced by the effects of electromigration and
by a convective mixing. Taking into account the zone spreading caused by
electromigration, the influence of vertex points of cannel walls, and
convection would explain the results of electrophoretic experiments, which are
difficult to understand otherwise.Comment: 13 pages, 10 figure
Rotating electrohydrodynamic flow in a suspended liquid film
The mathematical model of a rotating electrohydrodynamic flow in a thin
suspended liquid film is proposed and studied. The motion is driven by the
given difference of potentials in one direction and constant external
electrical field \vE_\text{out} in another direction in the plane of a film.
To derive the model we employ the spatial averaging over the normal coordinate
to a film that leads to the average Reynolds stress that is proportional to
|\vE_\text{out}|^3. This stress generates tangential velocity in the vicinity
of the edges of a film that, in turn, causes the rotational motion of a liquid.
The proposed model is aimed to explain the experimental observations of the
\emph{liquid film motor} (see arXiv:0805.0490v2).Comment: 12 pages, 9 figures. (Submitted to Phys. Rev. E
Mathematical Model of a pH-gradient Creation at Isoelectrofocusing
The mathematical model describing the stationary natural pH-gradient arising
under the action of an electric field in an aqueous solution of ampholytes
(amino acids) is constructed and investigated. The model is a part of a more
general model of the isoelectrofocusing process. Investigation is based on the
approximation of a weak solution by the piecewise continuous non-smooth
functions. The method can be used for solving classes of problems for ODEs with
a small parameter at higher derivatives and the turning points.Comment: 29 pages, 6 figure
Mathematical Model of a pH-gradient Creation at Isoelectrofocusing. Part IV. Theory
The mathematical model describing the non-stationary natural pH-gradient
arising under the action of an electric field in an aqueous solution of
ampholytes (amino acids) is constructed. The model is a part of a more general
model of the isoelectrofocusing (IEF) process. The presented model takes into
account: 1) general Ohm's law (electric current flux includes the diffusive
electric current); 2) dissociation of water; 3) difference between isoelectric
point (IEP) and isoionic point (PZC -- point of zero charge). We also study the
Kohlraush's function evolution and discuss the role of the Poisson-Boltzmann
equation.Comment: 15 pages, 1 figur
Interactions between discontinuities for binary mixture separation problem and hodograph method
The Cauchy problem for first-order PDE with the initial data which have a
piecewise discontinuities localized in different spatial points is completely
solved. The interactions between discontinuities arising after breakup of
initial discontinuities are studied with the help of the hodograph method. The
solution is constructed in analytical implicit form. To recovery the explicit
form of solution we propose the transformation of the PDEs into some ODEs on
the level lines (isochrones) of implicit solution. In particular, this method
allows us to solve the Goursat problem with initial data on characteristics.
The paper describes a specific problem for zone electrophoresis (method of the
mixture separation). However, the method proposed allows to solve any system of
two first-order quasilinear PDEs for which the second order linear PDE, arising
after the hodograph transformation, has the Riemann-Green function in explicit
form.Comment: 19 pages, 11 figure
Modeling dynamics of entangled physical systems with superconducting quantum computer
We implement several quantum algorithms in real five-qubit superconducting
quantum processor IBMqx4 to perform quantum computation of the dynamics of
spin-1/2 particles interacting directly and indirectly through the boson field.
Particularly, we focus on effects arising due to the presence of entanglement
in the initial state of the system. The dynamics is implemented in a digital
way using Trotter expansion of evolution operator. Our results demonstrate that
dynamics in our modeling based on real device is governed by quantum
interference effects being highly sensitive to phase parameters of the initial
state. We also discuss limitations of our approach due to the device
imperfection as well as possible scaling towards larger systems.Comment: 11 page
Algorithmic simulation of far-from-equilibrium dynamics using quantum computer
We point out that superconducting quantum computers are prospective for the
simulation of the dynamics of spin models far from equilibrium, including
nonadiabatic phenomena and quenches. The important advantage of these machines
is that they are programmable, so that different spin models can be simulated
in the same chip, as well as various initial states can be encoded into it in a
controllable way. This opens an opportunity to use superconducting quantum
computers in studies of fundamental problems of statistical physics such as the
absence or presence of thermalization in the free evolution of a closed quantum
system depending on the choice of the initial state as well as on the
integrability of the model. In the present paper, we performed
proof-of-principle digital simulations of two spin models, which are the
central spin model and the transverse-field Ising model, using 5- and 16-qubit
superconducting quantum computers of the IBM Quantum Experience. We found that
these devices are able to reproduce some important consequences of the symmetry
of the initial state for the system's subsequent dynamics, such as the
excitation blockade. However, lengths of algorithms are currently limited due
to quantum gate errors. We also discuss some heuristic methods which can be
used to extract valuable information from the imperfect experimental data.Comment: 26 pages. arXiv admin note: substantial text overlap with
arXiv:1710.0965
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