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Department of Theoretical Physics, Tomsk State University, 1 Novosobornaya Sq., 634050 Tomsk, Russia
2
Laboratory for Theoretical Cosmology, International Centre of Gravity and Cosmos, Tomsk State University of Control Systems and Radioelectronics, 40 Lenina av., 634050 Tomsk, Russia
3
Division for Electronic Engineering, Tomsk Polytechnic University, 30 Lenina av., 634050 Tomsk, Russia
4
Laboratory of Quantum Electronics, V.E. Zuev Institute of Atmospheric Optics, Siberian Branch of the Russian Academy of Sciences, 1 Academician Zuev Sq., 634055 Tomsk, Russia
*
Authors to whom correspondence should be addressed.
We apply the original semiclassical approach to the kinetic ionization equation with the nonlocal cubic nonlinearity in order to construct the family of its asymptotic solutions. The approach proposed relies on an auxiliary dynamical system of moments of the desired solution to the kinetic equation and the associated linear partial differential equation. The family of asymptotic solutions to the kinetic equation is constructed using the symmetry operators acting on functions concentrated in a neighborhood of a point determined by the dynamical system. Based on these solutions, we introduce the nonlinear superposition principle for the nonlinear kinetic equation. Our formalism based on the Maslov germ method is applied to the Cauchy problem for the specific two-dimensional kinetic equation. The evolution of the ion distribution in the kinetically enhanced metal vapor active medium is obtained as the nonlinear superposition using the numerical–analytical calculations.
Kinetic equations are the theoretical footing for the dynamic phenomena of various nature that occur in physical systems of many interacting elements (particles). Examples of such system are diluted gases, gas discharges, a plasma, processes of coagulation [1], and biological systems such as, e.g., population systems [2,3,4]. In some systems, nonlocal collective (averaged) interactions of elements substantially contribute to dynamics. Such interactions are modeled by integral terms in kinetic equations that become integro-differential. In spatially heterogeneous kinetic phenomena, the interelement interactions occur along with the diffusion. Then, the model kinetic equation belongs to the class of reaction-diffusion (RD) equations. The study of RD equations with both local and nonlocal terms have formed an independent branch of mathematical physics.
Due to the mathematical complexity of the study of RD equation with nonlocal interactions, methods of computer modeling prevail here. However, the demand for the analytical methods stimulates the development of approximate and asymptotically exact solutions. For a number of RD kinetic equations with nonlocal interactions, one can succeed using the WKB–Maslov theory of semiclassical approximation or the Maslov complex germ method [5,6,7]. Based on the WKB–Maslov theory, the method of semiclassical asymptotics was developed for a generalized Fisher–Kolmogorov–Petrovskii–Piskunov equation (Fisher–KPP) with a quadratic nonlocal term in [8,9] and for the nonlocal Gross–Pitaevskii equation in [10,11].
In this work, using the results of [9,12], we construct semiclassical asymptotics for the model kinetic equation with the nonlocal cubic nonlinearity of the form
Here, t is a time, is a distribution function (e.g., the particle density in a system), . In a general case, the method under consideration is applicable for n-dimensional space, . The nonlinearity parameter and the small diffusion parameter D are introduced explicitly for the sake of convenience. The n-dimensional Laplace operator in the Cartesian space is denoted by . The coefficients and are smooth functions of their spatial arguments that grow not faster than polynomially at each point t.
In the physical two-dimensional or three-dimensional space, Equation (1) is considered as a model of the optical metal vapor active medium (MVAM) excited by an electrical discharge [12]. The MVAM is a mixture of a buffer inert gas and metal vapors in a gas discharge tube (GDT) (see [13,14] and references therein). In the active medium excited by an electrical discharge, the ionization and recombination processes are mainly caused by the inelastic electron impact. For typical pressures of a buffer gas and metal vapors, preferentially metal atoms are ionized in the mixture. The process of triple recombination of an ion with two electrons is responsible for the deionization (see, e.g., [15]). Such dense plasma formed by metal ions and electrons can be considered as quasineutral. The contracted electrical discharge generates ions and electrons localized in the neighborhood of the GDT center. It means that the concentration of the charges rapidly decreases with the distance from the GDT center. In [12,16], the description of the plasma kinetics under assumptions made was based on the following equation:
where are Cartesian coordinates of a point in or depending on the problem statement. The quantity is the kinetic coefficient for the electron impact ionization of neutral atoms with a concentration ( is an electron concentration). In the same sense, the coefficient meets the process of triple recombination of ions with a concentration . We assume the plasma to be dense so that the triple recombination dominates over the dielectronic recombination. The coefficient is an ambipolar diffusion coefficient. The dependence of , , , and on and t is due to their dependence on electron temperature that substantially depends on and t.
Assuming the quasineutrality of plasma, the concentrations of ions and electrons are the same, i.e.,
Then, for given and , Equation (2) becomes closed and determines the concentration for the given initial and boundary conditions.
To apply the method of semiclassical asymptotics borrowed from papers [9,12], we write Equation (2) in the nonlocal form (1). For the space or , the function is the probability density of a triple recombination due to the collision of an ion with two electrons. The ambipolar diffusion coefficient in Equation (2) is written as where D is the asymptotic small parameter.
In this work, following the method of semiclassical asymptotics [8,9], we have constructed approximate solutions of Equation (1) in an explicit analytical form for the special set of equation coefficients. The obtained expressions are leading terms of semiclassical expansion for the solutions of Equation (1) within the accuracy of in the following class of trajectory concentrated functions (TCF):
where is a generic element of the class ; ; the real function belongs to the Schwartz space in variables , smoothly depends on t, and regularly depends on as . The real smooth functions and , characterizing the class , regularly depend on as and are to be determined.
Note that the approach proposed can be useful for other models based on nonlinear equations similar to (2). Nonlinear kinetic equations arise in various areas such as cosmology models (see review [17]), superfluidity models [18], etc.
In the next section, we expound the main ideas of the our approach and basic notations, and we introduce the linear equation associated with the original kinetic equation whose solutions include the asymptotic solutions to the original kinetic equation. In Section 3, we obtain the particular solution to the associated linear equation for the special choice of equation coefficients in the two-dimensional case. In Section 4, the main object of Maslov theory, the germ, is obtained. Here, we present the symmetry operators to the associated linear equation and construct the family of its solutions. In Section 5, we apply the algebraic conditions on the solutions to the associated linear equation that allow us to obtain the countable set of new asymptotic solutions to the nonlinear kinetic equation. Moreover, the new method for constructing asymptotic solutions to the Cauchy problem for the kinetic equation based on the nonlinear superposition principle is proposed. In Section 6, the specific physically motivated example of the two-dimensional kinetic equation is considered. We illustrate the general formalism of our semiclassical approach by constructing the evolution of the initial ion distribution in the relaxing kinetically enhanced active medium. In Section 7, we conclude with some remarks.
2. Leading Term of Semiclassical Asymptotics for the Cauchy Problem Solution
In this section, we recapitulate the general scheme for the method of constructing the leading term of semiclassical asymptotics for Equation (1). The detailed description of this method can be found in [12].
According to [12], the following asymptotic estimates hold for functions from the class :
where , , ∇ is the gradient operator with respect to , , , is the -norm, is the scalar product of vectors, and k is the non-negative integer. In particular, (5) yields , . Here, means that , .
For simplicity, we will omit the parameter D in expressions where it does not cause confusion.
In view of the estimates (5), the asymptotic expansion of the coefficient in Equation (1) in powers of in a neighborhood of the trajectory allows us to transform Equation (1) to the approximate one with the given accuracy. The residual of the approximate equation has the estimate in the class , where is the highest power of accounted in the expansion. The leading term of asymptotics of the solution to (1) is determined by the expansion of up to . Following [12], the respective expansions in matrix notations can be written as
Here, , , , and are column vectors; is a transposed matrix; , , , and are row vectors of the form , , row vectors , have the analogous form; and are symmetric matrices of the form , , matrices , , , , ,, and have the analogous form.
The key point of the considered approach [12] is that the nonlocal nonlinearity enters into the approximate kinetic equation obtained with the help of an asymptotic expansion of (1) in the form of the moments of the solution , and dynamical equations that determine the evolution of these moments can be solved separately.
In order to construct the leading term of asymptotics, we need corresponding moments of up to the second order that are defined as follows
Here, is the symmetric matrix of the central second-order moments of the function . The first-order moment will determine the functional parameter of the class (4) as
Dynamical equations for the moments (7) are obtained by differentiation with respect to t, from the definitions (7), and using from (1). Taking into consideration expansions (6) and estimates (5) with accuracy of , we arrive at the following moment equations:
where is the identity matrix of size n, and the expression implies a product of matrices and .
Let us consider Equation (9) as the system where the aggregate of moments
is substituted for the set of independent variables , and that are not related to the function in the general case. Thus, the resulting system can be treated as an independent dynamical system. According to [12], this system is termed the Einstein–Ehrenfest (EE) system of the second order for the nonlocal kinetic Equation (1) in the class of TCF (4). The second order of the system implies that we preserve the terms of order not higher than .
Let the general solution of this system be
where is a set of arbitrary integration constants. Then, the substitution of the expansion (6) into Equation (1) with the replacement of moments (10) by the general solution (11) yields the following linear equation:
where the linear operator is given by
Equations (12) and (13) in [12] are termed the associated linear equation for Equation (1).
Let us pose the Cauchy problem for Equation (1) in the class of TCF (4):
Next, we impose a restriction on the integration constants involved in the general solutions (11). The restriction is given by the following algebraic condition:
which yields . Here, is the aggregate of the moments (10) that is determined by the initial condition as
Let us consider the Cauchy problem for the associated linear Equations (12) and (13) with the initial condition
According to [9,12], the solution of the Cauchy problem for Equation (1) with the initial condition (14) and the solutions of the Cauchy problems (12), (17) in the class of TCF are related as follows:
3. Semiclassical Asymptotics in a Two-Dimensional Plane-Parallel Case
In this section, based on the method proposed in the previous section, we will obtain an explicit expression for a family of asymptotic solutions for the special case of Equation (1) analogous to the one considered in [12].
Let us consider the problem in the plane orthogonal to the GDT axis. Let be Cartesian coordinates in this plane and the coefficients in (1) be given by
where the functions and are assumed to be monotone decreasing and increasing, respectively, and the parameter characterizes the nonlocality of the nonlinearity kernel , .
For functions (19), Equations (8) and (9) yield . The identity also holds in a more general case for the problem with the symmetric configuration of a GDT. We choose the origin of coordinates so that . It leads to . Ions are usually localized on the GDT axis, which is taken as the origin of coordinates in our case. Then, .
In the case under consideration, Equation (9) reads
Here, we denoted
where is a diagonal -matrix, diagonal elements of the matrix characterize the degree of localization (dispersion) of the initial axial ion distribution with respect to , and , is the identity -matrix.
where and c is an arbitrary integration constant, . Note that and .
Thus, the relation (20) for with and the relation (22) for yield the general solution of the EE system with arbitrary integration constant :
where the set of integration constants reads
Let us proceed to the construction of the family of particular solutions for the kinetic equation. For the two-dimensional case under consideration, , with the coefficients (19), Equation (1) can be written as
where is a two-dimensional Laplace operator. In view of (5) and (6), Equation (25) reads
Next, we obtain the associated linear Equation (12) from Equation (26) by the replacement of moments , of the required solution by the general solutions of the dynamical EE system (23).
which allows us to write the associated linear Equation (12) as
We are looking for the particular solutions of Equation (28) in the form of the Gaussian function:
where is a normalization constant that is related to the initial number of ions. The multiplier is introduced for convenience. Note that this multiplier does not contradict the ansatz (4) since it can be included in the function as the summand . The term as , so it does not violate the regularity of with respect to as .
Equation (30) determines the functions and through quadratures:
The matrix Riccati equation in (30) can be represented as the linear system by the substitution:
where and are nondegenerate matrices that satisfy the following matrix linear system of differential equations:
4. Countable Set of Solutions to the Associated Linear Equation
In this section, we describe the approach to constructing the family of solutions of the associated linear Equation (28) based on solutions of the system (33).
Denote . Since the coefficients in the system (33) are scalar, the matrices and can be sought in the diagonal form:
where and , , are scalar functions.
Note that the matrix is also diagonal is this case:
The equations for functions and are identical. Hence, these functions can differ only due to their different initial condition. Let us consider the system of equations for the functions and ,
whose solutions for different initial conditions determine the matrices and and, correspondingly, the matrix . The system (37) was coined “the variational system” in [9].
The system (37) has two linearly independent solutions. Let us denote them by the following formulae:
These solutions are determined by the following initial conditions:
For the functions , , the numbers that determine the initial conditions by
can be different in a general case.
Now, we can construct the family of solutions to Equation (28) based on the particular solution (29). For this purpose, we use the well-known quantum mechanics method widely used in various problems [19,20,21].
Denote the two-dimensional symplectic identity matrix as . Introduce the two-dimensional column vectors
Following the general Maslov complex germ method, the linear -dimensional space with the basis vectors and is called the germ . In our case, the germ is chosen to be real, since we seek the real solutions to (25). The pair , where is the trajectory (the time-dependent 0-dimensional manifold) , determines the set of asymptotic solutions to Equation (25). In order to construct such solutions, we present the symmetry operators associated with the vectors , and with the vectors , .
Define the operators
These operators satisfy the following commutation relations:
We define the normalization multiplier as . Then, we have
and
For the diagonal matrix (35), the solution (29) can be written as
Here, , and the functions are solutions of the system (37) with initial conditions (40).
For the two-dimensional case, the operators (48) read
and the commutators are as follows:
It can be shown that the operators nullify the function of the form (50)
and that operators commute with the operator of Equation (28):
It means that the operators are the symmetry operators for Equation (28). Hence, the action of the operators on generates the family of new solutions to Equation (28). Let us define this family of solutions by
Here, is the two-dimensional multi-index, , , , are normalization coefficients.
The solutions to (55) can be written in the explicit form. Define
In view of the formula for the Hermitian polynomials [22]
The set (58) is the parametric family of solutions to the associated linear Equation (28). Our next task is to find a countable set of asymptotic solutions to the kinetic Equation (25) among these solutions with the free parameter .
5. Algebraic Conditions and Solutions of the Kinetic Equation
In this section, we construct solutions to Equation (26) with help of the solutions (58) to the associated linear equation (28). For this, we impose the algebraic conditions (15) and (16) on arbitrary integration constants that are included in the solution of the EE system. Then, we have
where
The functions are the leading terms of asymptotics for solutions to the original nonlocal kinetic Equation (25) with accuracy of .
Next, we obtain the constants (60) in an explicit form. Let us write the solutions to (58) in the form
In order to obtain the moments for the whole set of solutions , we use the representation of the Hermitian polynomial through the generating function [22]:
Then, the generating function for solutions (61) is given as follows,
From (7), one can see that and are linear functionals with respect to . This property allows us to obtain moments and of the functions (61) with the help of respective generating functions derived from (63). Introduce the following functions:
Here, the subscripts indicate the number of a matrix element.
Straightforward calculations of integral in the formulae (64) yield
The formula for can be obtained from one for (65) by the formal interchanging in all subscripts. In view of (64), the expansion of functions (65) in powers of , yields the following expression for moments:
Thus, among the obtained solutions to the associated linear Equation (28), only those ones with even indices , generate the asymptotic solutions to the kinetic Equation (25).
Note that functions (66) are particular solutions to the EE system (20). Hence, the solutions to the EE system (20) are determined by the solutions to the variational system (36). It is a corollary of the fact shown in [12] that the leading term of asymptotics for the function uniquely defines the functions , within accuracy of .
Substituting into the formulae (66) and taking into account (40) and (31), we obtain the following initial conditions for moments included in the integration constants :
Thus, the functions (59) with the constants of the form (67) and (68) determine a countable set of solutions to Equation (26) that are the leading terms of semiclassical asymptotics for the kinetic Equation (25).
Note that the solution in Equation (58) for changes its sign in the space due to the properties of Hermitian polynomials. For the main physical applications, the function is positive definite (e.g., it corresponds to the ion concentration in the model of the MVAM kinetics). Therefore, the functions are rather of interest not by themselves but as a basis for the expansion of positive definite functions. In such interpretation, the function is a “mode” of the physical state involving in its expansion. In order to clarify the meaning of this statements, let us describe the nonlinear superposition principle for semiclassical solutions of Equation (25).
It can be seen that the following orthogonality condition holds for the functions :
Let us expand the initial condition (17) in functions :
Then, the initial condition corresponds to the following solution to the associated linear Equation (28):
In order to obtain the asymptotic solution of the original kinetic Equation (25), we must impose the algebraic condition . The integration constants for the function (72) are given by
where .
Thus, a set of the integration constants is determined by a set of expansion coefficients of an initial condition with respect to functions , i.e., expansion coefficients nonlinearly determine the asymptotic solution to the nonlinear kinetic Equation (25) with the initial condition . The nonlinearity of this superposition principle is caused by the nonlinear dependence of the functions included in (73) (in particular, the solutions of the variational system) on the integration constants in (74).
Although the solutions of the associated linear equation , , do not correspond to any asymptotic solutions of the kinetic equation in themselves, the functions , , and given by (69) enter into the expansion (73) subject to . Thus, we can construct asymmetrical solutions with respect to spatial variables (not odd and not even) to the nonlinear kinetic equation with the help of the nonlinear superposition principle.
Note that our functions contain two free positive parameters, and . The change of these parameters yields us a new family of the asymptotic solutions (59) or a new basis (69) for the nonlinear superposition principle. For example, the solution is invariant under the interchanging for and is not invariant for . The parameters , determine the localization area of the functions and with respect to , . The nonlinear superposition principle can be applied to the given initial condition under any positive , . However, the more the localization area of the initial condition differs from the localization area of the functions determined by , , the slower the series (72) converges. The slow convergence of the series (72) leads to the slow convergence of the series (73) for . Yet, it is not clear how to compare the localization area of two multipeak functions in a general case. It can be completed in the particular case though, which is illustrated in the next section. We can draw an analogy for the parameters , with the scaling factor (dilations) of the wavelets [23], since both the functions (69) and their Fourier transform with respect to are localized functions at each fixed t with the localization area determined by , . The proposed rule of thumb for the choice of , corresponds to the value of dilations for the peak of the wavelet image.
6. Example of the Semiclassical Two-Dimensional Distribution
In this section, we construct the semiclassical solutions to Equation (25) with the initial condition
where , . For such constraints for the parameters , , , and , the function does not take on negative values. If , then the initial distribution (75) has a minimum at the center . The minimum of the ion distribution described by Equation (25) is physically realizable by the addition of hydrogen into the metal vapor active medium (by creating the so-called kinetically enhanced active medium) [24,25,26].
Let us apply the nonlinear superposition principle to the initial condition (75). Note that
Let the value of the parameter be considered optimal when the coefficients converge to zero, as is the most rapid. It corresponds to the minimum value of the following function:
The function reaches its minimum at
We use this value of hereinafter. Note that the search of the value of corresponding to the the most rapid convergence can be more complicated in the general case. However, it is not crucial to obtain the exact value of corresponding to the least for large . Hence, it can be done using some approximations for (e.g., [27]).
The initial conditions for the EE system (20) can be obtained either by the substitution of the coefficients (79) into the formulae (74) or by the substitution of the initial condition (75) into the relations (16). Both ways yield
The EE system (20) is integrable for the coefficients in Equation (25) of the form
The general solutions to the EE system for the coefficients in (83) were obtained in [12]. This case is treated as the model of the plasma relaxation. Let us illustrate the solutions corresponding to the initial condition (75) for this case. Note that the variational system (37) is not integrable for such coefficients as far as we know. It is a remarkable fact, since the analytical solutions of the EE system, which are quite cumbersome though, can be expressed in terms of the solutions of the variational system by analogy with (66). For our example, we use the solution to the EE system from [12] and construct the solutions to the variational system (37) numerically. Note that the variational system (37) is the system of linear differential equations with constant-sign coefficients. The subsequent calculations are presented for , , , , , , , , , , , , . Figure 1 shows the evolution of for two values of . The physical meaning of this function is the total number of ions in the active medium. Figure 2 shows the solutions of the variational system. We provide the plot of these solutions just for one value of , since the difference between these plots for and is barely perceptible due to the little difference in . The sign of was reverted for compactness of the figure. The values of the expansion coefficients are presented in Table 1. Note that they tend to zero rapidly as increases due to the optimal choice of and they equal zero for odd or . Figure 3 shows the asymptotic evolution of the initial ion distribution (75) constructed as the proposed nonlinear superposition in the weak diffusion approximation with an accuracy of .
Note that does not tend to nonzero constant. In a general case, this constant can be negative, which leads to the zero value of at some point . At this point, the condition of nondegeneracy of the matrix (34) is violated. It is worthy of discussion how it affects the solutions . It can be shown that the functions (66) have the removable discontinuity at this point. The same is true for the solutions in (58). Hence, the asymptotic solutions regularly depend on t in a neighborhood of the point . It means that if we construct the germ from the point to a point left of the point and then we construct the germ after the point , the resulting asymptotic solutions , , and , , generated by the germ and , respectively, determine the continuous asymptotic evolution of the initial state for both and . Therefore, the formal constraint of the nondegeneracy of the matrix (34) can be bypassed. Note that the error of the semiclassical solutions usually grows over time. It can result in an adverse effect when the semiclassical solution jumps from the asymptotics for one exact solution to another at a sufficiently large time (see the work [28]). Therefore, the estimate of the period of time where the asymptotics are valid is the subject to study separately and is to be obtained in every particular case.
Figure 1 illustrates that the ion distribution with the less pronounced minimum at the GDT center relaxes faster. However, Figure 3 shows that both distributions tend to the Gauss-like profile over time. It means that their evolution will be similar on large times. Hence, the difference is significant only at the initial stage of the relaxation.
Note that our method is applicable for the linear case (). For and , the method proposed yields the exact solution to the kinetic equation.
7. Conclusions
Within the framework of the approach presented in [12], we have constructed a countable family of asymptotic solutions to the two-dimensional kinetic Equation (25) with the nonlocal cubic nonlinearity. The approach proposed can be generalized for n-dimensional space. We have considered the two-dimensional problem for the sake of simplicity in order to demonstrate our method and to give its physical interpretation. The constructed asymptotic solutions correspond to the weak diffusion approximation. The approach is based on the solutions to the Cauchy problem to the nonlinear dynamical system (the Einstein–Ehrenfest system) (9) and (20). These solutions generate the linear parabolic Equations (13) and (28) associated with the nonlinear kinetic equation. Solutions of this associated linear equation subject to the algebraic condition (15) yield the asymptotic solutions (58) and (59) to the original nonlinear kinetic equation. The family of the asymptotic solutions is constructed based on the set of skew-orthogonal, linearly independent solutions to the system of linear ODEs (37) (the variational system). Such asymptotic solutions form the orthogonal basis for the nonlinear superposition principle that allows one to construct the asymptotic evolution of arbitrary initial distribution (17) expanded into the series with respect to the basis formed by the functions (58). The nonlinearity of the superposition principle is caused by the necessity of solving the nonlinear dynamical system (9) and (20) with initial conditions (16) determined by the initial distribution. Note that the functions with determined from (74) form an orthogonal basis for the nonlinear superposition principle, while the functions with given by (67) and (68), which determine independent asymptotic solutions to the nonlinear kinetic equation, are not orthogonal in the general case.
This work extends the results of our work [12] where the asymptotic evolution operator of the kinetic Equation (25) was constructed via the Green function of the associated linear equation. Here, we construct the asymptotic solutions with the help of the symmetry operators (51) for the associated linear equation based on the nonlinear superposition principle. It allows us to study the properties of the asymptotic solutions through the properties of the variational system (37) that generates the Maslov germ on the zero-dimensional manifold and the symmetry operators. Moreover, we have found the relation (66) between the solutions to the Einstein–Ehrenfest system and the variational system. It means that our approach can yield analytical solutions expressed in terms of the solutions to the system of the linear ODEs (37) only. However, in the considered specific case, the nonlinear dynamical system admits the analytical solutions, while the variational system (37) is solved numerically. Note that the asymptotic evolution operator in [12] and the nonlinear superposition principle yield the exact solutions to the associated linear Equation (28), i.e., they yield the same asymptotic solutions for the given initial condition. However, the approach proposed here broadens the possibilities of analysis for these solutions. In addition, the nonlinear superposition principle leads to the expressions with free parameters that can be chosen so that the functional series (73) converges rapidly. Hence, in some cases, the study of the solutions (73) can be practically reduced to the study of the first few terms of the series. It makes the analysis of such solutions even easier, especially when the solutions are numerical–analytical.
The future prospects for this work are related to the study of a more complex two-component kinetic model. We plan to generalize the approach [29] for the latter problem.
Author Contributions
Conceptualization, A.V.S. and A.E.K.; methodology, A.V.S. and A.E.K.; validation, A.V.S. and A.E.K.; formal analysis, A.V.S. and A.E.K.; investigation, A.V.S. and A.E.K. and S.A.S.; writing—original draft preparation, A.V.S. and A.E.K.; writing—review and editing, A.V.S. and A.E.K.; visualization, A.E.K. and S.A.S.; software, A.E.K. and S.A.S.;supervision, A.V.S.; funding acquisition, A.V.S. and A.E.K. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by the Russian Foundation for Basic Research (RFBR) and Tomsk region grant number 19-41-700004.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
Not applicable.
Acknowledgments
The work is supported by Tomsk Polytechnic University under the International Competitiveness Improvement Program; by IAO SB RAS, Russia, project no. 121040200025-7.
Conflicts of Interest
The authors declare no conflict of interest.
References
Mitrophanov, A.; Wolberg, A.; Reifman, J. Kinetic model facilitates analysis of fibrin generation and its modulation by clotting factors: Implications for hemostasis-enhancing therapies. Mol. BioSyst.2014, 10, 2347–2357. [Google Scholar] [CrossRef] [PubMed] [Green Version]
Murray, J. Mathematical Biology; Interdisciplinary Applied Mathematics; Springer: New York, NY, USA, 2002. [Google Scholar]
Gluzman, S.; Karpeyev, D. Modern Problems in Applied Analysis. In Trends in Mathematics; chapter Perturbative expansions and critical phenomena in random structured media; Springer International Publishing AG: Cham, Switzerland, 2018; pp. 117–134. [Google Scholar] [CrossRef]
Aranson, I.; Tsimring, L. Theory of self-assembly of microtubules and motors. Phys. Rev. E Stat. Nonlinear Soft Matter Phys.2006, 74. [Google Scholar] [CrossRef] [PubMed] [Green Version]
Maslov, V. Operational Methods; Mir Publishers: Moscow, Russia, 1976. [Google Scholar]
Maslov, V. The Complex WKB Method for Nonlinear Equations. I. Linear Theory; Birkhauser: Basel, Switzerland, 1994. [Google Scholar]
Belov, V.V.; Dobrokhotov, S.Y. Semiclassical Maslov asymptotics with complex phases. I. General approach. Theor. Math. Phys.1992, 92, 843–868. [Google Scholar] [CrossRef]
Trifonov, A.Y.; Shapovalov, A.V. The one-dimensional Fisher-Kolmogorov equation with a nonlocal nonlinearity in a semiclassical approximation. Russ. Phys. J.2009, 52, 899–911. [Google Scholar] [CrossRef]
Shapovalov, A.V.; Trifonov, A.Y. An application of the Maslov complex germ method to the one-dimensional nonlocal Fisher-KPP equation. Int. J. Geom. Methods Mod. Phys.2018, 15, 1850102. [Google Scholar] [CrossRef]
Shapovalov, A.V.; Kulagin, A.E.; Trifonov, A.Y. The Gross–Pitaevskii equation with a nonlocal interaction in a semiclassical approximation on a curve. Symmetry2020, 12, 201. [Google Scholar] [CrossRef] [Green Version]
Shapovalov, A.; Kulagin, A. Semiclassical approach to the nonlocal kinetic model of metal vapor active media. Mathematics2021, 9, 2995. [Google Scholar] [CrossRef]
Little, C. Metal Vapor Lasers: Physics, Engineering & Applications; John Willey & Sons Ltd.: Chichester, UK, 1998; p. 620. [Google Scholar]
Sabotinov, N. Gas Lasers; chapter Metal Vapor Lasers; CRC Press: Boca Raton, FL, USA, 2007. [Google Scholar]
Gurevich, A.V.; Pitaevskii, L.P. Recombination coefficient in a dense low-temperature plasma. Sov. Phys. JETP1964, 19, 870–871. [Google Scholar]
Torgaev, S.N.; Kulagin, A.E.; Evtushenko, T.G.; Evtushenko, G.S. Kinetic modeling of spatio-temporal evolution of the gain in copper vapor active media. Opt. Commun.2019, 440, 146–149. [Google Scholar] [CrossRef]
Bamba, K.; Capozziello, S.; Nojiri, S.; Odintsov, S. Dark energy cosmology: The equivalent description via different theoretical models and cosmography tests. Astrophys. Space Sci.2012, 342, 155–228. [Google Scholar] [CrossRef] [Green Version]
Pitaevskii, L.; Stringari, S. Bose-Einstein Condensation and Superfluidity; Oxford University Press: Oxford, UK, 2016. [Google Scholar]
Malkin, M.; Manko, V. Dynamic Symmetries and Coherent States of Quantum Systems; Nauka: Moscow, Russia, 1979. [Google Scholar]
Perelomov, A. Generalized Coherent States and Their Applications; Theoretical and Mathematical Physics; Springer: Berlin, Germany, 1986. [Google Scholar]
Obukhov, V.V. Algebra of the Symmetry Operators of the Klein–Gordon–Fock Equation for the Case When Groups of Motions G3 Act Transitively on Null Subsurfaces of Spacetime. Symmetry2022, 14, 346. [Google Scholar] [CrossRef]
Beitmen, G.; Erdei, A. Higher Transcendental Functions; MC Graw Hill: New York, NY, USA, 1953; Volume 2. [Google Scholar]
Daubechies, I. Ten Lectures on Wavelets; CBMS-NSF Regional Conference Series in Applied Mathematics; Society for Industrial and Applied Mathematics: Philadelphia, PA, USA, 1992. [Google Scholar]
Boichenko, A.M.; Evtushenko, G.S.; Zhdaneev, O.V.; Yakovlenko, S.I. Theoretical analysis of the mechanisms of influence of hydrogen additions on the emission parameters of a copper vapour laser. Quantum Electron.2003, 33, 1047–1058. [Google Scholar] [CrossRef]
Boichenko, A.; Evtushenko, G.; Torgaev, S. Effect of hydrogen additives on characteristics of the CuBr laser. Phys. Wave Phenom.2011, 19, 189–201. [Google Scholar] [CrossRef]
Gluzman, S. Padé and Post-Padé Approximations for Critical Phenomena. Symmetry2020, 12, 1600. [Google Scholar] [CrossRef]
Bagrov, V. Strange approximate solutions to the Schrödinger equation. J. Mosc. Phys. Soc.1998, 8, 191–195. [Google Scholar]
Shapovalov, A.V.; Trifonov, A.Y. Approximate solutions and symmetry of a two-component nonlocal reaction-diffusion population model of the Fisher-KPP type. Symmetry2019, 11, 366. [Google Scholar] [CrossRef] [Green Version]
Figure 1.
The plot of the function for various . It illustrates the relaxation of the total number of ions for two initial distributions according to the analytic formula derived in [12] and (82).
Figure 1.
The plot of the function for various . It illustrates the relaxation of the total number of ions for two initial distributions according to the analytic formula derived in [12] and (82).
Figure 2.
The plot of the solutions to (37) and (39) for . The solutions are obtained numerically.
Figure 2.
The plot of the solutions to (37) and (39) for . The solutions are obtained numerically.
Figure 3.
The plot of the function in the section . It illustrates the evolution of the ion distribution according to the formula in (73).
Figure 3.
The plot of the function in the section . It illustrates the evolution of the ion distribution according to the formula in (73).
Table 1.
The values of the coefficient for , and two values of .
Table 1.
The values of the coefficient for , and two values of .
0
1
2
3
4
0
1
2
3
4
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
2
0
0
0
0
3
0
0
0
0
0
0
0
0
0
0
4
0
0
0
0
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Shapovalov, A.V.; Kulagin, A.E.; Siniukov, S.A.
Family of Asymptotic Solutions to the Two-Dimensional Kinetic Equation with a Nonlocal Cubic Nonlinearity. Symmetry2022, 14, 577.
https://doi.org/10.3390/sym14030577
AMA Style
Shapovalov AV, Kulagin AE, Siniukov SA.
Family of Asymptotic Solutions to the Two-Dimensional Kinetic Equation with a Nonlocal Cubic Nonlinearity. Symmetry. 2022; 14(3):577.
https://doi.org/10.3390/sym14030577
Chicago/Turabian Style
Shapovalov, Alexander V., Anton E. Kulagin, and Sergei A. Siniukov.
2022. "Family of Asymptotic Solutions to the Two-Dimensional Kinetic Equation with a Nonlocal Cubic Nonlinearity" Symmetry 14, no. 3: 577.
https://doi.org/10.3390/sym14030577
APA Style
Shapovalov, A. V., Kulagin, A. E., & Siniukov, S. A.
(2022). Family of Asymptotic Solutions to the Two-Dimensional Kinetic Equation with a Nonlocal Cubic Nonlinearity. Symmetry, 14(3), 577.
https://doi.org/10.3390/sym14030577
Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.
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Shapovalov, A.V.; Kulagin, A.E.; Siniukov, S.A.
Family of Asymptotic Solutions to the Two-Dimensional Kinetic Equation with a Nonlocal Cubic Nonlinearity. Symmetry2022, 14, 577.
https://doi.org/10.3390/sym14030577
AMA Style
Shapovalov AV, Kulagin AE, Siniukov SA.
Family of Asymptotic Solutions to the Two-Dimensional Kinetic Equation with a Nonlocal Cubic Nonlinearity. Symmetry. 2022; 14(3):577.
https://doi.org/10.3390/sym14030577
Chicago/Turabian Style
Shapovalov, Alexander V., Anton E. Kulagin, and Sergei A. Siniukov.
2022. "Family of Asymptotic Solutions to the Two-Dimensional Kinetic Equation with a Nonlocal Cubic Nonlinearity" Symmetry 14, no. 3: 577.
https://doi.org/10.3390/sym14030577
APA Style
Shapovalov, A. V., Kulagin, A. E., & Siniukov, S. A.
(2022). Family of Asymptotic Solutions to the Two-Dimensional Kinetic Equation with a Nonlocal Cubic Nonlinearity. Symmetry, 14(3), 577.
https://doi.org/10.3390/sym14030577
Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.