Riassunto
Over the past ten years, the asymptotic theory of one-parameter semigroups of operators has witnessed an explosive development. A number oflong-standing open problems have recently been solved and the theory seems to have obtained a certain degree of maturity. These notes, based on a course delivered at the University of Tiibingen in the academic year 1994-1995, represent a first attempt to organize the available material, most of which exists only in the form of research papers. If A is a bounded linear operator on a complex Banach space X, then it is an easy consequence of the spectral mapping theorem exp(tO"(A)) = O"(exp(tA)), t E JR, and Gelfand's formula for the spectral radius that the uniform growth bound of the wt family {exp(tA)h~o, i. e. the infimum of all wE JR such that II exp(tA)II :::: Me for some constant M and all t 2: 0, is equal to the spectral bound s(A) = sup{Re A : A E O"(A)} of A. This fact is known as Lyapunov's theorem. Its importance resides in the fact that the solutions of the initial value problem du(t) =A () dt u t , u(O) = x, are given by u(t) = exp(tA)x. Thus, Lyapunov's theorem implies that the expo nential growth of the solutions of the initial value problem associated to a bounded operator A is determined by the location of the spectrum of A.
Contenuti
1. Spectral bound and growth bound.- 1.1. C0—semigroups and the abstract Cauchy problem.- 1.2. The spectral bound and growth bound of a semigroup.- 1.3. The Laplace transform and its complex inversion.- 1.4. Positive semigroups.- Notes.- 2. Spectral mapping theorems.- 2.1. The spectral mapping theorem for the point spectrum.- 2.2. The spectral mapping theorems of Greiner and Gearhart.- 2.3. Eventually uniformly continuous semigroups.- 2.4. Groups of non-quasianalytic growth.- 2.5. Latushkin - Montgomery-Smith theory.- Notes.- 3. Uniform exponential stability.- 3.1. The theorem of Datko and Pazy.- 3.2. The theorem of Rolewicz.- 3.3. Characterization by convolutions.- 3.4. Characterization by almost periodic functions.- 3.5. Positive semigroups on Lp-spaces.- 3.6. The essential spectrum.- Notes Ill.- 4. Boundedness of the resolvent.- 4.1. The convexity theorem of Weis and Wrobel.- 4.2. Stability and boundedness of the resolvent.- 4.3. Individual stability in B-convex Banach spaces.- 4.4. Individual stability in spaces with the analytic RNP.- 4.5. Individual stability in arbitrary Banach spaces.- 4.6. Scalarly integrable semigroups.- Notes.- 5. Countability of the unitary spectrum.- 5.1. The stability theorem of Arendt, Batty, Lyubich, and V?.- 5.2. The Katznelson-Tzafriri theorem.- 5.3. The unbounded case.- 5.4. Sets of spectral synthesis.- 5.5. A quantitative stability theorem.- 5.6. A Tauberian theorem for the Laplace transform.- 5.7. The splitting theorem of Glicksberg and DeLeeuw.- Notes.- Append.- Al. Fractional powers.- A2. Interpolation theory.- A3. Banach lattices.- A4. Banach function spaces.- References.- Symbols.
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