The paper is devoted to the study of deformations of Artinian algebras and zero-dimensional germs of varieties. In particular, an approach is developed to solving the open problem about the ...nonexistence of rigid Artinian algebras; it is based essentially on the use of the canonical duality in the cotangent complex. Thus, it is shown that there are no rigid Gorenstein Artinian algebras and rigid almost complete intersections. The proof of the latter statement is based on the properties of the torsion functors. More precisely, the tensor product of the conormal and canonical modules of the corresponding Artinian algebra is calculated. In this case, the homology and cohomology groups of higher degrees are also found. Among other things, some estimates are obtained for the dimension of the spaces of the first lower and upper cotangent functors of Artinian algebras, and the relationship between them is described. In conclusion, several examples of nonsmoothable Artinian noncomplete intersections are examined, and some unusual properties of such algebras are discussed.
In the present investigation we revisit the widely-used locally-constant field approximation (LCFA) in the context of the pair-production phenomenon in strong electromagnetic backgrounds. By means of ...nonperturbative numerical calculations, we assess the validity of the LCFA considering several spatially homogeneous field configurations and a number of space-time-dependent scenarios. By studying the momentum spectra of particles produced, we identify the criteria for the applicability of the LCFA. It is demonstrated that the Keldysh parameter itself does not allow one to judge if the LCFA should perform accurately. In fact, the external field parameters must obey less trivial relations whose form depends on the field configuration. We reveal several generic properties of these relations which can also be applied to a broader class of other pair-production scenarios.
For a retarded nonlinear system with a Lipschitz nonlinearity on bounded sets outside the origin, this article proposes necessary conditions for application of the Lyapunov-Razumikhin method. The ...presented conditions are illustrated on the classes of linear and nonlinear homogeneous systems.
We investigate the phenomenon of electron-positron pair production from vacuum in the presence of a strong electric field superimposed by a weak but fast varying pulse which substantially increases ...the total particle yield. We employ a nonperturbative numerical technique and perform the calculations beyond the spatially-uniform-field approximation, i.e., dipole approximation, taking into account the coordinate dependence of the fast component. The analysis of the main characteristics of the pair-production process (momentum spectra of particles and total amount of pairs) reveals a number of important features which are absent within the previously used approximation. In particular, the structure of the momentum distribution is modified both qualitatively and quantitatively, and the total number of pairs created as well as the enhancement factor due to dynamical assistance become significantly smaller.
On the basis of the comparison method, sufficient conditions of polystability are derived for a class of nonlinear complex systems. The developed approach is applied for the stability analysis of ...mechanical systems composed of interacted subsystems with dissipative, gyroscopic and potential forces. Conditions of polystability of the trivial equilibrium positions of the considered systems are obtained. Two examples are given to demonstrate the effectiveness of the proposed results.
Cystic fibrosis transmembrane regulator (CFTR) is a dynamic membrane protein belonging to the ABC transporter family. It is unusual within this family as it is an ion channel, as opposed to a ...transporter. Activation of CFTR requires ATP and phosphorylation by PKA, and dysregulation of CFTR mediated salt and water homeostasis can lead to cystic fibrosis. Recent advancements in structural biological methods have led to more than 10 published CFTR structures, and, so far, all of these structures of CFTR, determined by cryo-EM, have been limited to detergent-purified protein preparations. To visualize CFTR in an environment that more closely represents its native membranous environment, we utilized two different lipoprotein particle encapsulation techniques: one in which the ion channel is first purified and then reconstituted using the membrane scaffolding protein Saposin A and another that uses the solubilizing polymer Sokalan CP9 (DIBMA) to extract CFTR directly from membranes. Structures derived from these types of preparations may better correlate to their function, for instance, the single-channel measurements from membrane vesicles.
We study the pair-production process in the presence of two counterpropagating linearly polarized short laser pulses. By means of a nonperturbative technique, we take into account the full coordinate ...dependence of the external field going beyond the dipole and standing-wave approximations. In particular, we analyze the momentum distribution of particles created. It is demonstrated that the spatial variations of the laser pulses may play a crucial role. The more accurate treatment reveals a number of prominent features: the pair-production probabilities become considerably smaller, the quantitative behavior of the momentum spectra changes dramatically, and the pulse shape effects become much less pronounced. The results of our study are expected to be very important for future theoretical and experimental investigations.
This paper is concerned with the problems of stability and stabilization for a class of nonlinear mechanical systems. It is assumed that considered systems are under the action of linear gyroscopic ...forces, nonlinear homogeneous positional forces and nonlinear homogeneous dissipative forces of positional–viscous friction. An approach to strict Lyapunov functions construction for such systems is proposed. With the aid of these functions, sufficient conditions of the asymptotic stability and estimates of the convergence rate of solutions are found. Moreover, systems with delay in the positional forces are studied, and new delay-independent stability conditions are derived. The obtained results are used for developing new approaches to the synthesis of stabilizing controls with delay in feedback law.
Operators of the form
f
⟼
x
β
f
(
x
α
) are treated. Among other things, it is proved that such an operator acts on the class of operator Lipschitz functions on (0,+∞) tending to zero at zero if and ...only if α + β = 1.