Semigroup representation of the Vlasov evolution

1998 ◽  
Vol 59 (4) ◽  
pp. 611-618 ◽  
Author(s):  
I. PRIGOGINE ◽  
T. PETROSKY
Keyword(s):  
Hilbert Space ◽  
Real Axis ◽  
Vlasov Equation ◽  
Spectral Representation ◽  
Decay Rates ◽  
Landau Damping ◽  
The Real ◽  
Rigged Hilbert Space ◽  
Time Symmetry ◽  
Friedrichs Model

The well-known van Kampen–Case treatment of the Vlasov equation leads to a spectrum on the real axis. In this paper we show that, by going to a ‘rigged’ Hilbert space, we can derive a spectral representation that is complex and breaks time symmetry. This leads to a semigroup description in which the decay rates due to the Landau damping appear explicitly in the spectrum. Moreover, we can then define an entropy. In this way, the relation between Landau damping and irreversibility is made explicit. The analogy with the well-known Friedrichs model is stressed.

scholarly journals The spectra of compact operators in Hilbert spaces

1965 ◽  
Vol 7 (1) ◽  
pp. 34-38
Author(s):  
T. T. West
Keyword(s):  
Hilbert Space ◽  
Unit Circle ◽  
Real Axis ◽  
Complex Plane ◽  
Hilbert Spaces ◽  
Compact Operators ◽  
Conformal Mappings ◽  
The Real ◽  
Finite Set

In [2] a condition, originally due to Olagunju, was given for the spectra of certain compact operators to be on the real axis of the complex plane. Here, by using conformal mappings, this result is extended to more general curves. The problem divides naturally into two cases depending on whether or not the curve under consideration passes through the origin. Discussion is confined to the prototype curves C0 and C1. The case of C0, the unit circle of centre the origin, is considered in § 3; this problem is a simple one as the spectrum is a finite set. In § 4 results are given for C1 the unit circle of centre the point 1, and some results on ideals of compact operators, given in § 2, are needed. No attempt has been made to state results in complete generality (see [2]); this paper is kept within the framework of Hilbert space, and particularly simple conditions may be given if the operators are normal.

MEASUREMENT, IRREVERSIBILITY AND DECOHERENCE IN QUANTUM MECHANICS

1994 ◽  
Vol 09 (22) ◽  
pp. 3913-3924
Author(s):  
BELAL E. BAAQUIE
Keyword(s):  
Hilbert Space ◽  
Quantum Mechanics ◽  
Quantum System ◽  
Quantum Measurement ◽  
State Vector ◽  
Space Time ◽  
Measuring Apparatus ◽  
Rigged Hilbert Space ◽  
Friedrichs Model ◽  
Time Irreversibility

We review Prigogine's model of quantum measurement. The measuring apparatus is considered to be an unstable quantum system with its state vector belonging to a rigged Hilbert space. Time irreversibility arises due to the dissipative nature of the measuring apparatus (an unstable quantum system) which induces decoherence in the system being measured. Friedrichs' model is used to concretely illustrate these ideas.

The Fourier–Plancherel transform as a spectral representation of a rigged Hilbert space

1987 ◽  
Vol 101 (3) ◽  
pp. 567-573
Author(s):  
B. Fishel
Keyword(s):  
Hilbert Space ◽  
Lebesgue Measure ◽  
Spectral Representation ◽  
Adjoint Operator ◽  
Rigged Hilbert Space ◽  
Cyclic Vectors ◽  
Generalized Translation ◽  
Translation Operators

In ‘Generalized Translation Operators…’ [3] algebras associated with a self-adjoint operator were investigated. Examples were given in the cases, inter alia, of the operators Mt and i d/dt in the space L2(ℝ, m) (m = Lebesgue measure). This paper shows that by suitably rigging the space the examples can be seen as natural generalizations of certain familiar algebras. The rigging enables us to introduce, rigorously, into L2(ℝ,m) the improper elements used by Akhiezer and Glazman [1] as cyclic vectors for Mt and i d/dt in order to identify the Fourier–Plancherel transform with a spectral representation of the space.

scholarly journals Heisenberg–Weyl Groups and Generalized Hermite Functions

Symmetry ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 1060
Author(s):  
Enrico Celeghini ◽  
Manuel Gadella ◽  
Mariano A. del del Olmo
Keyword(s):  
Hilbert Space ◽  
Fourier Transform ◽  
Heisenberg Group ◽  
Real Line ◽  
Hermite Functions ◽  
Unitary Representations ◽  
Weyl Groups ◽  
The Real ◽  
Symmetry Properties ◽  
The Fourier Transform

We introduce a multi-parameter family of bases in the Hilbert space L2(R) that are associated to a set of Hermite functions, which also serve as a basis for L2(R). The Hermite functions are eigenfunctions of the Fourier transform, a property that is, in some sense, shared by these “generalized Hermite functions”. The construction of these new bases is grounded on some symmetry properties of the real line under translations, dilations and reflexions as well as certain properties of the Fourier transform. We show how these generalized Hermite functions are transformed under the unitary representations of a series of groups, including the Weyl–Heisenberg group and some of their extensions.

On Graeffe's Method for Complex Roots of Algebraic Equations

1924 ◽  
Vol 22 (2) ◽  
pp. 83-87 ◽  
Author(s):  
S. Brodetsky ◽  
G. Smeal
Keyword(s):  
Nineteenth Century ◽  
Real Axis ◽  
Practical Method ◽  
Algebraic Equations ◽  
Argand Diagram ◽  
Considerable Difficulty ◽  
The Real ◽  
Real Roots ◽  
Bipolar Coordinates ◽  
Complex Roots

The only really useful practical method for solving numerical algebraic equations of higher orders, possessing complex roots, is that devised by C. H. Graeffe early in the nineteenth century. When an equation with real coefficients has only one or two pairs of complex roots, the Graeffe process leads to the evaluation of these roots without great labour. If, however, the equation has a number of pairs of complex roots there is considerable difficulty in completing the solution: the moduli of the roots are found easily, but the evaluation of the arguments often leads to long and wearisome calculations. The best method that has yet been suggested for overcoming this difficulty is that by C. Runge (Praxis der Gleichungen, Sammlung Schubert). It consists in making a change in the origin of the Argand diagram by shifting it to some other point on the real axis of the original Argand plane. The new moduli and the old moduli of the complex roots can then be used as bipolar coordinates for deducing the complex roots completely: this also checks the real roots.

Interaction between a nanocrack with surface elasticity and a screw dislocation

2016 ◽  
Vol 22 (2) ◽  
pp. 131-143 ◽  
Author(s):  
Xu Wang ◽  
Hui Fan
Keyword(s):  
Screw Dislocation ◽  
Real Axis ◽  
Analytical Study ◽  
Logarithmic Singularity ◽  
Surface Elasticity ◽  
Spontaneous Generation ◽  
The Real ◽  
Crack Tips ◽  
Interaction Problem ◽  
The Continuum

In the present analytical study, we consider the problem of a nanocrack with surface elasticity interacting with a screw dislocation. The surface elasticity is incorporated by using the continuum-based surface/interface model of Gurtin and Murdoch. By considering both distributed screw dislocations and line forces on the crack, we reduce the interaction problem to two decoupled first-order Cauchy singular integro-differential equations which can be numerically solved by the collocation method. The analysis indicates that if the dislocation is on the real axis where the crack is located, the stresses at the crack tips only exhibit the weak logarithmic singularity; if the dislocation is not on the real axis, however, the stresses exhibit both the weak logarithmic and the strong square-root singularities. Our result suggests that the surface effects of the crack will make the fracture more ductile. The criterion for the spontaneous generation of dislocations at the crack tip is proposed.

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