‎In this manuscript, we compute the Bishop-Phelps-Bollobás modulus for functionals in classical Banach spaces‎, ‎such as Hilbert spaces‎, ‎spaces of continuous functions $c_0$ and $\ell_1$‎.

Starting from the finite adele ring $A_{\Bbb{Q}},$ we construct semigroup dynamical systems of $A_{\Bbb{Q}},$ acting on certain $C^{*}$-probability spaces. From such dynamical-systematic $C^{*}$-probability spaces, we construct Banach-space operators acting on the $C^{*}$-probability spaces and corresponding Banach $*$-probability spaces. In particular, we are interested in Banach-space operators whose free distributions are the (weighted-)semicircular law(s).

A Banach partial $*$-algebra is a locally convex partial $*$-algebra whose total space is a Banach space. A Banach partial $*$-algebra is said to be of type (B) if it possesses a generating family of multiplier spaces that are also Banach spaces. We describe the basic properties of these objects and display a number of examples, namely, $L^p$-like function spaces and spaces of operators on Hilbert scales or lattices. Finally we analyze the important cases of Banach quasi $*$-algebras and $CQ^*$-algebras.

If $G$ is a locally compact group, $CD(G)$ the algebra of convolution dominated operators on $L^2(G)$, then an important question is: Is $\mathbb {C}1+CD(G)$ (or $CD(G)$ if $G$ is discrete) inverse-closed in the algebra of bounded operators on $L^2(G)$?

In this note we answer this question in the affirmative, provided $G$ is such that one of the following properties is satisfied.

1. There is a discrete, rigidly symmetric, and amenable subgroup $H\subset G$ and a (measurable) relatively compact neighbourhood of the identity $U$, invariant under conjugation by elements of $H$, such that $\{hU\;:\;h\in H\}$ is a partition of $G$.

2. The commutator subgroup of $G$ is relatively compact. (If $G$ is connected, this just means that $G$ is an IN group.)

All known examples where $CD(G)$ is inverse-closed in $B(L^2(G))$ are covered by this.

Let $P_t$ $(a\le t\le b)$ be a function whose values are projections in a Banach space. The paper is devoted to bounded linear operators $A$ admitting the representation $$A=\int_a^b \phi(t)dP_{t}+V,$$ where $\phi(t)$ is a scalar function and $V$ is a compact quasi-nilpotent operator such that $P_tVP_t=VP_t$ $(a\le t\le b)$. We obtain norm estimates for the resolvent of $A$ and a bound for the spectral variation of $A$. In addition, the representation for the resolvents of the considered operators is established via multiplicative operator integrals. That representation can be considered as a generalization of the representation for the resolvent of a normal operator in a Hilbert space. It is also shown that the considered operators are Kreiss-bounded. Applications to integral operators in $L^p$ are also discussed. In particular, bounds for the upper and lower spectral radius of integral operators are derived.

In this study, the structure of fractional spaces generated by the two-dimensional neutron transport operator $A$ defined by formula $Au=\omega_{1}\frac{\partial u}{\partial x}+\omega _{2}\frac{\partial u}{\partial y}$ is investigated. The positivity of $A$ in $C\left( \mathbb{R}^{2}\right)$ and $L_{p}\left( \mathbb{R}^{2}\right)$, $1\leq p \lt \infty$, is established. It is established that, for any $0 \lt \alpha \lt 1$ and $1\leq p \lt \infty$, the norms of spaces $E_{\alpha ,p}\left( L_{p}\left( \mathbb{R}^{2}\right), A\right)$ and $E_{\alpha }\left( C\left( \mathbb{R}^{2}\right), A\right) , W_{p}^{\alpha } \left( \mathbb{R}^{2}\right)$ and $C^{\alpha }\left( \mathbb{R}^{2}\right)$ are equivalent, respectively. The positivity of the neutron transport operator in Hölder space $C^{\alpha }\left( \mathbb{R}^{2}\right)$ and Slobodeckij space $W_{p}^{\alpha }\left( \mathbb{R}^{2}\right)$ is proved. In applications, theorems on the stability of Cauchy problem for the neutron transport equation in Hölder and Slobodeckij spaces are provided.

In this paper, we generalize some inequalities for the approximation numbers of an element in a normed (Banach) algebra $X$ and, as an application, we present inequalities for the quasinorms of some ideals defined by means of the approximation numbers.

In particular, if $X=L(E)$ - the algebra of linear and bounded operators $T:E \to E$, where $E$ is a Banach space, we obtain inequalities for certain quasinorms of operators.

‎It is well-known that any compact Lie group appears as closed subgroup of a unitary group‎, ‎$G\subset U_N$‎. ‎The unitary group $U_N$ has a free analogue $U_N^+$‎, ‎and the study of the closed quantum subgroups $G\subset U_N^+$ is a problem of general interest‎. ‎We review here the basic tools for dealing with such quantum groups‎, ‎with all the needed preliminaries included‎, ‎and we discuss as well a number of more advanced topics‎.

‎Several numerical radius inequalities for operator matrices are‎ ‎proved by generalizing earlier inequalities‎. ‎In particular‎, ‎the‎ ‎following inequalities are obtained‎: ‎if $n$ is even‎, ‎‎ \[2w(T) \leq \max\{\| A_1 \|‎, ‎\| A_2 \|,\ldots‎, ‎\| A_n \|\}+\frac{1}{2}\displaystyle\sum_{k=0}^{n-1} \|‎~ ‎|A_{n-k}|^{t}|A_{k+1}^{*}|^{1-t} \|,\] ‎and if $n$ is odd‎,‎‎ \[2w(T) \leq \max\{\| A_1 \|,\| A_2 \|,\ldots,\| A_n \|\}‎+ ‎w\bigg(\widetilde{A}_{(\frac{n+1}{2})t}\bigg)‎+ ‎\frac{1}{2}\displaystyle\sum_{k=0}^{n-1} \|‎~ ‎|A_{n-k}|^{t}|A_{k+1}^{*}|^{1-t} \|,\] ‎for all $t\in [0‎, ‎1]$‎, ‎$ A_i$'s are bounded linear operators on the‎ ‎Hilbert space $\mathcal{H}$‎, ‎and $T$ is off diagonal matrix with entries ‎$‎A_1, \cdots, A_n‎$‎.‎

‎‎We consider exponential dichotomies on finite intervals and show that if the constants in the notion of an exponential dichotomy are chosen appropriately and uniformly on those intervals‎, ‎then there exists an exponential dichotomy on the whole line‎. ‎We consider the general case of a nonautonomous dynamics that need not be invertible‎. ‎Moreover‎, ‎we consider both cases of discrete and continuous time‎.

‎‎‎A differential identity on the hypergeometric function ${}_2F_1(a,b;c;z)$ unifying and extending certain spectral results on the scale of‎ ‎Gegenbauer and Jacobi polynomials and leading to a new class of hypergeometric related scalars $\mathsf{c}_j^m(a,b,c)$ and‎ ‎polynomials $\mathscr{R}_m=\mathscr{R}_m(X)$ is established‎. ‎The Laplace-Beltrami operator on a compact rank one symmetric‎ ‎space is considered next‎, ‎and for operators of the Laplace transform type by invoking an operator trace relation‎, ‎the Maclaurin spectral‎ ‎coefficients of their Schwartz kernel are fully described‎. ‎Other related representations as well as extensions of the differential‎ ‎identity to the generalized hypergeometric function ${}_pF_q(\textbf{a}; \textbf{b}; z)$ are formulated and proved‎.

‎In this paper, we introduce a new class of operators in lattice-normed spaces‎. ‎We say that an orthogonally additive operator $T$ from a lattice-normed space $(V,E)$ to a lattice-normed space‎ ‎$(W,F)$ is dominated‎, ‎if there exists a positive orthogonally additive operator $S$ from $E$ to $F$ such that $\vert Tx \vert \leq S \vert x \vert$ for any element $x$ of $(V,E)$‎. ‎We show that under some mild‎ ‎conditions‎, ‎a dominated orthogonally additive operator has an exact dominant and obtain formulas for calculating the exact dominant of a dominated orthogonally additive operator‎. ‎In the last part of the‎ ‎paper we consider laterally-to-order continuous operators‎. ‎We prove that a dominated orthogonally additive operator is laterally-to-order continuous if and only if the same is its exact dominant‎.

‎‎We introduce and investigate a new notion of the approximation property $AP_{[c]},$‎ ‎where $c= (c_n)$ is an arbitrary positive real sequence‎, ‎tending to infinity‎. ‎Also‎, ‎we study the corresponding notion of $[c]$-nuclear operators in Banach spaces‎. ‎Some characterization of the $AP_{[c]}$ in terms of tensor products‎, ‎as well as‎ ‎sufficient conditions for a Banach space to have the $AP_{[c]},$ are given‎. ‎We give also sufficient conditions for a positive answer to the question‎: ‎When it follows from the $[c]$-nuclearity of an adjoint operator the nuclearity of‎ ‎the operator itself‎. ‎Obtained results are applied then to the study of properties‎ ‎of nuclear operators in some spaces of analytical functions‎. ‎Many examples are given‎.

‎The classical Lebesgue's theorem is generalized‎, ‎and it is proved that under some conditions on the summability function $\theta$‎, ‎the $\ell_1$-$\theta$-means of a function $f$ from the Wiener amalgam space $W(L_1,\ell_\infty)(\R^d)\supset L_1(\R^d)$ converge to $f$ at each modified strong Lebesgue point and thus almost everywhere‎. ‎The $\theta$-summability contains the Weierstrass‎, ‎Abel‎, ‎Picard‎, ‎Bessel‎, Fejér‎, ‎de La Vallée-Poussin‎, ‎Rogosinski‎, ‎and Riesz summations‎.

‎‎In this paper‎, ‎we consider different notions of openness for the scalar multiplication on sequence spaces and spaces of continuous functions‎. ‎We apply existing techniques to derive weak openness of multiplication on spaces of differentiable functions‎, ‎endowed with a large collection of quasi-algebra norms‎.