On the structure Jacobi operator of a real hypersurface in complex projective space

We prove the non-existence of a certain family of real hypersurfaces in complex projective space. From this result we classify real hypersurfaces whose structure Jacobi operator satisfies a condition that generalizes parallelness.     

On the Riemannian curvature tensor of a real hypersurface in a complex projective space

We consider real hypersurfaces M in complex projective space equipped with both the Levi–Civita and generalized Tanaka–Webster connections and classify them when the covariant derivatives associated with both connections, either in the direction of the structure vector field or any direction of the maximal holomorphic distribution, coincide when applying to the Riemannian curvature tensor of the real hypersurface.     

<Emphasis Type="Italic">A</Emphasis><Subscript>2</Subscript>-continued fraction representation of real numbers and its geometry

We study the geometry of representations of numbers by continued fractions whose elements belong to the set A ₂ = {α₁, α₂} (A ₂-continued fraction representation). It is shown that, for α₁α₂ ≤ 1/2 , every point of a certain segment admits an A ₂-continued fraction representation. Moreover, for α₁α₂ = 1/2, this representation is unique with the exception of a countable set of points. For the last case, we find the basic metric relation and describe the metric properties of a set of numbers whose A ₂-continued fraction representation does not contain a given combination of two elements. The properties of a random variable for which the elements of its A ₂-continued fraction representation form a homogeneous Markov chain are also investigated.     

Bar-invariant bases of the quantum cluster algebra of type <Emphasis Type=Italic>A</Emphasis><Stack><Subscript>2</Subscript><Superscript>(2)</Superscript></Stack>

We construct bar-invariant ℤ[q ^±1/2]-bases of the quantum cluster algebra of the valued quiver A ₂⁽²⁾, one of which coincides with the quantum analogue of the basis of the corresponding cluster algebra discussed in P. Sherman, A. Zelevinsky: Positivity and canonical bases in rank 2 cluster algebras of finite and affine types, Moscow Math. J., 4, 2004, 947–974.     

Restrictions of modules over classical groups to subgroups of type <Emphasis Type="Italic">A</Emphasis><Subscript>2</Subscript> in characteristic 2

Restrictions of irreducible modules over classical groups to subsystem subgroups of type A ₂ in characteristic 2 are studied. The composition factors (without their multiplicities) for restrictions of such modules with 2-restricted highest weights are found. Bibliography: 7 titles.     

On characterizations of real hypersurface in complex space form with Codazzi type structure Lie operator

In this paper, we prove that if $(\nabla _{X} L_{\xi })Y= (\nabla _{Y} L_{\xi })X$ holds on $M$ , then $M$ is a Hopf hypersurface, where $L_\xi $ denote the induced operator from the Lie derivative with respect to the structure vector field $\xi $ . We characterize such Hopf hypersurfaces of $M_n(c)$ .     

Interpolation of operators of weak type (ϕ<Subscript>0</Subscript>, ψ<Subscript>0</Subscript>, ϕ<Subscript>1</Subscript>, ψ<Subscript>1</Subscript>) in Lorentz spaces

We prove theorems on interpolation of quasilinear operators of weak type (ϕ₀, ψ₀, ϕ₀, ψ₁) in Lorentz spaces. The operators under study are analogs of the Calderón operator and the Benett operator for concave and convex functions ϕ₀(t), ψ₀(t), ϕ₁(t), and ψ₁(t). __________ Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 57, No. 11, pp. 1490–1507, November, 2005.     

Scalar curvature of a certain CR-submanifold of complex projective space

We study an n-dimensional, compact, minimal CR-submanifold of CR-dimension n − 1 and give a sufficient condition for the submanifold to be a tube over a totally geodesic complex subspace. Dedicated to Professor U-Hang Ki on his 60th birthday This work is supported by the research grant of the Catholic University of Taegu-Hyosung in 1996.     

An elementary proof of the <Emphasis Type="Italic">A</Emphasis><Subscript>2</Subscript> bound

A martingale transform T, applied to an integrable locally supported function f, is pointwise dominated by a positive sparse operator applied to |f|, the choice of sparse operator being a function of T and f. As a corollary, one derives the sharp A _p bounds for martingale transforms, recently proved by Thiele-Treil-Volberg, as well as a number of new sharp weighted inequalities for martingale transforms. The (very easy) method of proof (a) only depends upon the weak-L ¹ norm of maximal truncations of martingale transforms, (b) applies in the vector valued setting, and (c) has an extension to the continuous case, giving a new elementary proof of the A ² bounds in that setting.     

A characterization of totally <Emphasis Type="Italic">η</Emphasis>-umbilical real hypersurfaces and ruled real hypersurfaces of a complex space form

We give a characterization of totally η-umbilical real hypersurfaces and ruled real hypersurfaces of a complex space form in terms of totally umbilical condition for the holomorphic distribution on real hypersurfaces. We prove that if the shape operator A of a real hypersurface M of a complex space form M ⁿ (c), c ≠ 0, n ⩾ 3, satisfies g(AX, Y) = ag(X, Y) for any X, Y ∈ T ₀(x), a being a function, where T ₀ is the holomorphic distribution on M, then M is a totally η-umbilical real hypersurface or locally congruent to a ruled real hypersurface. This condition for the shape operator is a generalization of the notion of η-umbilical real hypersurfaces.     

Characterizing projective general unitary groups PGU<Subscript>3</Subscript>(<Emphasis Type="Italic">q</Emphasis><Superscript>2</Superscript>) by their complex group algebras

Let G be a finite group. Let X ₁(G) be the first column of the ordinary character table of G. We will show that if X ₁(G) = X1(PGU₃(q ²)), then G ? PGU₃(q ²). As a consequence, we show that the projective general unitary groups PGU₃(q ²) are uniquely determined by the structure of their complex group algebras.     

Intrinsic normalizations of a nonholonomic hypersurface with <Emphasis Type="Italic">m</Emphasis>-dimensional generators in affine space <Emphasis Type="Italic">A</Emphasis><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

We consider some intrinsic normalizations of a nonholonomic hypersurface with m-dimensional generators in the n-dimensional affine spaced. Published in Lietuvos Matematikos Rinkinys, Vol. 47, No. 3, pp. 532–562, October–December, 2007.     

Regularity for weakly (K<Subscript>1</Subscript>, K<Subscript>2</Subscript>)-quasiregular mappings

In this paper, we first give the definition of weakly (K₁,K₂-quasiregular mappings, and then by using the Hodge decomposition and the weakly reverse Hölder inequality, we obtain their regularity property: For anyq ₁ that satisfies\(0< K_1 n^{(n + 4)/2} 2^{n + 1} \times 100^{n^2 } [2^{3n/2} (2^{5n} + 1)](n - q_1 )< 1\), there existsp ₁=p ₁(n,q ₁,K ₁,K ₂)>n, such that any (K₁, K₂)-quasiregular mapping\(f \in W_{loc}^{1,q_1 } (\Omega ,R^n )\) is in fact in\(W_{loc}^{1,p_1 } (\Omega , R^n )\). That is, f is (K₁,K₂)-quasiregular in the usual sense.     

Power Sums Related to Semigroups S(d<Subscript>1</Subscript>, d<Subscript>2</Subscript>, d<Subscript>3</Subscript>)

The explicit formulas for the sums of positive powers of the integers unrepresentable by the triple of integers , are derived.     

Geodesics on real hypersurfaces of type A 2 in a complex space form

In this paper, we study geodesics with null structure torsions on real hypersurfaces of type A ₂ in a complex space form. These geodesics give a nice family of helices of order 3 generated by Killing vector fields on the ambient complex space form. Author’s address: Toshiaki Adachi, Department of Mathematics, Nagoya Institute of Technology, Nagoya 466-8555, Japan     

A characterization of the finite simple group L<Subscript>16</Subscript>(2) by its prime graph

In this paper as the main result we prove that the projective special linear group L ₁₆(2) is uniquely determined by its prime graph. In fact we give a positive answer to an open problem arose in Zavarnitsin (Algebra Logic 43(4), 220–231, 2006) and we obtain a first example of a finite group with connected prime graph which is uniquely determined by its prime graph. This research was in part supported by a grant from IPM (No. 86200023).