The metric-valued Lebesgue differentiation theorem in measure spaces and its applicationsAdvances in Operator Theory - - 2023
Danka Lučić, Enrico Pasqualetto
We prove a version of the Lebesgue differentiation theorem for mappings that are defined on a measure space and take values into a metric space, with respect to the differentiation basis induced by a von Neumann lifting. As a consequence, we obtain a lifting theorem for the space of sections of a measurable Banach bundle and a disintegration theorem for vector measures whose target is a Banach spa...... hiện toàn bộ
Characterizations of extra-invariant spaces under the left translations on a Lie groupAdvances in Operator Theory - Tập 8 Số 3 - Trang 1-16 - 2023
Sarkar, Sudipta, Shukla, Niraj K.
In the context of a connected, simply connected nilpotent Lie group, whose representations are square-integrable modulo the center, we find characterization results of extra-invariant spaces under the left translations associated with the range functions. Consequently, the theory is valid for the Heisenberg group $${\mathbb {H}}^d,$$ a 2-step nilpotent Lie group.
Estimates of the best approximations of the functions of the Nikol’skii–Besov class in the generalized space of LorentzAdvances in Operator Theory - Tập 6 - Trang 1-36 - 2020
G. Akishev
In this paper, we consider the generalized Lorentz space of periodic functions of several variables and the Nikol’skii–Besov space of functions. The article establishes a sufficient condition for a function to belong from one generalized Lorentz space to another space in terms of the difference of the partial sums of the Fourier series of a given function. Exact in order estimates of the best appr...... hiện toàn bộ
Isomorphisms of $$AC(\sigma )$$ spaces for linear graphsAdvances in Operator Theory - Tập 5 Số 2 - Trang 474-488 - 2020
Al-shakarchi, Shaymaa, Doust, Ian
We show that among compact subsets of the plane which are drawings of linear graphs, two sets $$\sigma $$ and $$\tau $$ are homeomorphic if and only if the corresponding spaces of absolutely continuous functions (in the sense of Ashton and Doust) are isomorphic as Banach algebras. This gives an analogue for this class of sets to the well-known result of Gelfand and Kolmogorov for $$C(\varOmega )$$...... hiện toàn bộ
Two classes of operators related to the perturbation classes problemAdvances in Operator Theory - - 2023
Manuel González, Margot Salas-Brown
AbstractLet $${{\mathcal {S}}}{{\mathcal {S}}}$$
S
S
and $${{\mathcal {S}}}{{\mathcal {C}}}$$
S
C
be the strictly singular and the strictly cosingular operators acting between Banach spaces, and let $$P\Phi _+$$
P
Φ
+
and $$P\Phi _+$$
P
Φ
+
be the perturbation classes for the upper and the lower semi-Fredholm operators. We study two classes of operators $$\Phi {\mathcal {S}}$$
Φ
S
and $$\Phi {\mathcal {C}}$$
Φ
C
that satisfy $${{\mathcal {S}}}{{\mathcal {S}}}\subset \Phi {\mathcal {S}}\subset P\Phi _+$$
S
S
⊂
Φ
S
⊂
P
Φ
+
and $${{\mathcal {S}}}{{\mathcal {C}}}\subset \Phi {\mathcal {C}}\subset P\Phi _-.$$ hiện toàn bộ