Some remarks on rotation theorems for complex polynomials
For any complex polynomial P having all its zeros in the unit disk, we estimate the rate of change of the argument P (z) when the point z runs through the boundary of this disk.
math.CV↗
arXiv subjects
V. N. Dubinin
Publications and source records attributed to V. N. Dubinin.
Optimal Green energy points on the circles in d-space
We give two precise estimates for the Green energy of a discrete charge, concentrated in the points on the circles, with respect to the concentric rotation domain in the d-dimensional Euclidean space, d>2.The proof is based on the application of a dissymmetrization, extremal metrics approach and an asymptotic formula for the condenser capacities in the case when some of its plates contract to given points.
math.AP↗
Distortion and critical values of the finite Blaschke product
We establish a sharp upper bound for the absolute value of the derivative of the finite Blaschke product, provided that the critical values of this product lie in a given disk.
math.CV↗
Four-point distortion theorem for complex polynomials
We prove a theorem on distortion of cross ratio of four points under the mapping effected by a complex polynomial with restricted critical values. Its corollaries include inequalities involving the absolute value and certain coefficients of a polynomial. In particular, an exact lower bound is established for maximal moduli of critical values of polynomials $P$ of degree $n$ normalized by $P(0)=0$, $P'(0)\ne0$.
math.CV↗
On the lemniscate components containing no critical points of a polynomial except for its zeros
We prove a sharp inequality for the modulus of the logarithmic derivative of a polynomial in the lemniscate components containing no critical points.
math.CV↗
Lower Bound for the Discrete Norm of a Polynomial on the Circle
We give a new lower bound for the discrete norm of a polynomial on the circle
math.CV↗
Steiner symmetrization and the initial coefficients of univalent functions
We study the behavior of the initial coefficients of univalent functions under the Steiner symmetrization, and give some applications to functions of class Σ.
math.CV↗
An extremal decomposition problem for harmonic measure
Let $E$ be a continuum in the closed unit disk $|z|\le 1$ of the complex $z$-plane which divides the open disk $|z| < 1$ into $n\ge 2$ pairwise non-intersecting simply connected domains $D_k,$ such that each of the domains $D_k$ contains some point $a_k$ on a prescribed circle $|z| = ρ, 0 <ρ<1, k=1,...,n\,. $ It is shown that for some increasing function $Ψ\,$ independent of $E$ and the choice of the points $a_k,$ the mean value of the harmonic measures $$ Ψ^{-1}\[ \frac{1}{n} \sum_{k=1}^{k} Ψ(ω(a_k,E, D_k))] $$ is greater than or equal to the harmonic measure $ω(ρ, E^*, D^*)\,,$ where $E^* = \{z: z^n \in [-1,0] \}$ and $D^* =\{z: |z|<1, |{\rm arg} z| < π/n\} \,.$ This implies, for instance, a solution to a problem of R.W. Barnard, L. Cole, and A. Yu. Solynin concerning a lower estimate of the quantity $\inf_{E} \max_{k=1,...,n} ω(a_k,E, D_k)\,$ for arbitrary points of the circle $|z| = ρ\,.$ These authors stated this hypothesis in the particular case when the points are equally distributed on the circle $|z| = ρ\,.$
math.CV↗
Two-sided bounds for the logarithmic capacity of multiple intervals
Potential theory on the complement of a subset of the real axis attracts a lot of attention both in function theory and applied sciences. The paper discusses one aspect of the theory - the logarithmic capacity of closed subsets of the real line. We give simple but precise upper and lower bounds for the logarithmic capacity of multiple intervals and a lower bound valid also for closed sets comprising an infinite number of intervals. Using some known methods to compute the exact values of capacity we demonstrate graphically how our estimates compare with them. The main machinery behind our results are separating transformation and dissymmetrization developed by V.N. Dubinin and a version of the latter by K. Haliste as well as some classical symmetrization and projection result for logarithmic capacity. The results of the paper improve some previous achievements by A.Yu. Solynin and K. Shiefermayr.
math.CV↗
On conformal moduli of polygonal quadrilaterals
The change of conformal moduli of polygonal quadrilaterals under some geometric transformations is studied. We consider the motion of one vertex when the other vertices remain fixed, the rotation of sides, polarization, symmetrization, and averaging transformation of the quadrilaterals. Some open problems are formulated.
math.CV↗