中国科学院数学与系统科学研究院期刊网

Acta Mathematica Sinica 2006 Vol.22

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Convergence of Hybrid Steepest–Descent Methods for Generalized Variational Inequalities
Liu Chuan Zeng, N. C. Wong, J. C. Yao,
Acta Mathematica Sinica    2006, 22 (1): 1-12.   DOI: 10.1007/s10114-005-0608-3
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In this paper, we consider the generalized variational inequality GVI(F, g,C), where F and g are mappings from a Hilbert space into itself and C is the fixed point set of a nonexpansive mapping. We propose two iterative algorithms to find approximate solutions of the GVI(F, g,C). Strong convergence results are established and applications to constrained generalized pseudo–inverse are included.

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Tensor Product of Massey Products
Qi Bing Zheng
Acta Mathematica Sinica    2006, 22 (1): 13-22.   DOI: 10.1007/s10114-004-0525-x
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 In this paper, we interpret Massey products in terms of realizations (twitsting cochains) of certain differential graded coalgebras with values in differential graded algebras. In the case where the target algebra is the cobar construction of a differential graded commutative Hopf algebra, we construct the tensor product of realizations and show that the tensor product is strictly associative, and commutative up to homotopy.

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Rational Homotopy Theory and Nonnegative Curvature
Jian Zhong Pan, Shao Bing Wu
Acta Mathematica Sinica    2006, 22 (1): 23-26.   DOI: 10.1007/10.1007/s10114-004-0466-4
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 In this note, we answer positively a question by Belegradek and Kapovitch about the relation between rational homotopy theory and a problem in Riemannian geometry which asks that total spaces of which vector bundles over compact non–negative curved manifolds admit (complete) metrics with non–negative curvature.

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General Regular Variation of the n–th Order and 2nd Order Edgeworth Expansions of the Extreme Value Distribution (II)
Xiao Qian Wang, Shi Hong Cheng
Acta Mathematica Sinica    2006, 22 (1): 27-40.   DOI: 10.1007/s10114-005-0566-9
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In this part II the fundamental inequality of the third order general regular variation is proved and the second order Edgeworth expansion of the distribution of the extreme values is discussed.

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The Symmetry of Singular Hamiltonian Differential Operators and Properties of Deficiency Indices
Jian Gang Qi
Acta Mathematica Sinica    2006, 22 (1): 41-50.   DOI: 10.1007/s10114-005-0535-3
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  The symmetry of singular Hamiltonian differential operators is proved under the standard "definiteness condition", which is strictly weaker than the densely definite condition used by A. M. Krall. Meanwhile, some properties of deficiency indices are given.

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Lp–Solutions of Vector Refinement Equations with General Dilation Matrix
Song Li, Ruei Fang Hu, Xiang Qing Wang,
Acta Mathematica Sinica    2006, 22 (1): 51-58.   DOI: 10.1007/10.1007/s10114-004-0465-5
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The purpose of this paper is to investigate the solutions of refinement equations of the form

$$
            \varphi (x) = {\sum\limits_{\alpha  \in \mathbb{Z}^{s} } {a(\alpha )\varphi {\left( {Mx - \alpha } \right)},\;\;\;\;x \in \mathbb{R}^{s} } }\;,
            $$
where the vector of functions ? = (?1, . . . ,?r) T is in (L p (? s )) r , 0 < p ≤ ∞, a(α), α ∈ ? s ¸ is a finitely supported sequence of r× r matrices called the refinement mask, and M is an s × s integer matrix such that limn→ ∞ M n = 0. In this article, we characterize the existence of an L p –solution of the refinement equation for 0 < p ≤ ∞. Our characterizations are based on the p–norm joint spectral radius.
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On a Problem of D. H. Lehmer
Hua Ning Liu, Wen Peng Zhang
Acta Mathematica Sinica    2006, 22 (1): 61-68.   DOI: 10.1007/s10114-004-0464-6
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The main purpose of this paper is to use the Fourier expansion for character sums and the mean value theorem of Dirichlet L–functions to study the asymptotic property of the difference between a D. H. Lehmer number and its inverse modulo p (an odd prime). A interesting mean square value formula is also given.

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Continuity for Maximal Multilinear Bochner–Riesz Operators on Hardy and Herz–Hardy Spaces
Lan Zhe Liu, Shan Zhen Lu
Acta Mathematica Sinica    2006, 22 (1): 69-76.   DOI: 10.1007/s10114-004-0488-y
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 Let 
$$
B^{A}_{{\delta , * }}
$$ be the maxiamal multilinear Bochner–Riesz operators generated by Bochner– Riesz operators and D α A ∈ Lipβ(|α| = m). The continuity of the operator on some Hardy and Herz type Hardy is obtained.

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An Improved Result for Positive Measure Reducibility of Quasi-periodic Linear Systems
Hai Long He, Jian Gong You
Acta Mathematica Sinica    2006, 22 (1): 77-80.   DOI: 10.1007/s10114-004-0473-5
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 In this paper, by the KAM method, under weaker small denominator conditions and nondegeneracy conditions, we prove a positive measure reducibility for quasi-periodic linear systems close to constant: X? = (A(λ) + F(?, λ))X, $$
\dot{\varphi } = \omega
$$ where the parameter λ ∈ (a, b), ω is a fixed Diophantine vector, which is a generalization of Jorba & Simó’s positive measure reducibility result.

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Fourier Method for an Over–Determined Elliptic System with Several Complex Variables
Dao Qing Dai
Acta Mathematica Sinica    2006, 22 (1): 87-94.   DOI: 10.1007/s10114-004-0472-6
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Two boundary value problems are investigated for an over–determined elliptic system with several complex variables in polydisc. Necessary and sufficient conditions for the existence of finitely many linearly independent solutions and finitely many solvability conditions are derived. Moreover, the boundary value problem for any number of complex variables is treated in a unified way and the essential difference between the case of one complex variable and that of several complex variables is revealed.

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Littlewood–Paley g–function on the Heisenberg Group
He Ping Liu, Rui Qin Ma
Acta Mathematica Sinica    2006, 22 (1): 95-100.   DOI: 10.1007/s10114-004-0469-1
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 We consider the g–function related to a class of radial functions which gives a characterization of the L p –norm of a function on the Heisenberg group.

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Lp-gradient Estimates of Symmetric Markov Semigroups for 1 < p ≤ 2
Ana Bela Cruzeiro, Xi Cheng Zhang
Acta Mathematica Sinica    2006, 22 (1): 101-104.   DOI: 10.1007/s10114-005-0538-0
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 For 1 < p ≤ 2, an L p -gradient estimate for a symmetric Markov semigroup is derived in a general framework, i. e. $$
{\left\| {\Gamma ^{{1/2}} {\left( {T_{t} f} \right)}} \right\|}_{p}  \leqslant \frac{{C_{p} }}
{{{\sqrt t }}}{\left\| f \right\|}_{p}
$$ , where Γ is a carré du champ operator. As a simple application we prove that Γ1/2((I-L)) is a bounded operator from L p to L p provided that 1 < p < 2 and $$
\frac{1}
{2} < \alpha  < 1
$$ . For any 1 < p < 2, q > 2 and $$
\frac{1}
{2} < \alpha  < 1
$$ , there exist two positive constants c q,α,C p,α such that ∥Df p C p,α∥(I - L)α f p , c q,α∥(I - L)1-α f q ≤ ∥Df q + ∥fq, where D is the Malliavin gradient ([2]) and L the Ornstein–Uhlenbeck operator.

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Boundedness of Some Marcinkiewicz Integral Operators Related to Higher Order Commutators on Hardy Spaces
Shan Zhen Lu, Li Fang Xu
Acta Mathematica Sinica    2006, 22 (1): 105-114.   DOI: 10.1007/s10114-005-0545-1
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In this paper, the authors study the boundedness properties of $$
\mu ^{m}_{{\Omega ,b}}
$$ generated by the function b ∈ Lip β (?n)(0 < β ≤ 1/m) and the Marcinkiewicz integrals operator μ Ω . The boundednesses are established on the Hardy type spaces $$
H^{p}_{{b^{m} ,s}} {\left( {\mathbb{R}^{n} } \right)}
$$ and the Herz–Hardy type spaces $$
H_{{b^{m} }} \dot{K}^{{\alpha ,p}}_{q} {\left( {\mathbb{R}^{n} } \right)}
$$ .

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Discreteness of Flux Groups
Yong Seung Cho, Myung Im Lim
Acta Mathematica Sinica    2006, 22 (1): 115-122.   DOI: 10.1007/s10114-004-0480-6
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Let (M, ω) be a closed symplectic 2n–dimensional manifold. Donaldson in his paper showed that there exist 2m–dimensional symplectic submanifolds (V 2 m , ω) of (M,ω), 1 ≤ mn – 1, with (m – 1)–equivalent inclusions. On the basis of this fact we obtain isomorphic relations between kernel of Lefschetz map of M and kernels of Lefschetz maps of Donaldson submanifolds V 2 m , 2 ≤ mn−1. Then, using this relation, we show that the flux group of M is discrete if the action of π1(M) on π2(M) is trivial and there exists a retraction r : MV , where V is a 4–dimensional Donaldson submanifold. And, in the symplectically aspherical case, we investigate the flux groups of the manifolds.

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The Quotient Category of a Graded Morita–Takeuchi Context
F. Castaño Iglesias*, C. N?st?sescu**
Acta Mathematica Sinica    2006, 22 (1): 123-130.   DOI: 10.1007/s10114-004-0501-5
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In this paper, we offer a graded equivalence between the quotient categories defined by any graded Morita–Takeuchi context via certain modifications of the graded cotensor functors. As a consequence, we show a commutative diagram that establish the relation between the closed objects of the categories gr C and M C , where C is a graded coalgebra.

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On t–Dimension over Strong Mori Domains
Fang Gui Wang
Acta Mathematica Sinica    2006, 22 (1): 131-138.   DOI: 10.1007/s10114-005-0539-z
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In this note we prove that if R is a strong Mori domain with t–dim R = n and with countably many prime v–ideals, then there is a chain of rings between R and R w


            $$
            R_{1}  = R \subset R_{2}  \subset  \cdots  \subset R_{n}  \subseteq R^{w}
            $$

such that each R i is also a strong Mori domain and t–dim Rk = nk + 1 for k = 1, 2, . . . , n.

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Boundary Dilatation and Asymptotical Hamilton Sequences
Na Sun, Sheng Jian Wu
Acta Mathematica Sinica    2006, 22 (1): 139-142.   DOI: 10.1007/s10114-004-0474-4
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In this paper, we study the boundary dilatation of quasiconformal mappings in the unit disc. By using Strebel mapping by heights theory we show that an asymptotical Hamilton sequence is determined by a quasisymmetric function

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Cited: Baidu(1)
Precise Asymptotics in the Law of the Iterated Logarithm of Moving-Average Processes
Yun Xia Li, Li Xin Zhang
Acta Mathematica Sinica    2006, 22 (1): 143-156.   DOI: 10.1007/s10114-005-0542-4
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In this paper, we discuss the moving-average process $$
X_{k}  = {\sum\nolimits_{i =  - \infty }^\infty  {\alpha _{{i + k}} \varepsilon _{i} } }
$$ , where {α i ;-∞ < i < ∞} is a doubly infinite sequence of identically distributed φ-mixing or negatively associated random variables with mean zeros and finite variances, {α i ;-∞ < i < ∞} is an absolutely summable sequence of real numbers. Set $$
S_{n}  = {\sum\nolimits_{k = 1}^n {X_{k} ,n \geqslant 1} }
$$ . Suppose that $$
\sigma ^{2}  = E\varepsilon ^{2}_{1}  + 2{\sum\nolimits_{k = 2}^\infty  {E\varepsilon _{1} \varepsilon _{k} } } > 0
$$ . We prove that for any $$
\delta  \geqslant 0,\;{\text{if}}\;E{\left[ {\varepsilon ^{2}_{1} {\left( {\log \;\log {\left| {\varepsilon _{1} } \right|}} \right)}^{{\delta  - 1}} } \right]} < \infty
$$ ,

$$
            {\mathop {\lim }\limits_{ \in  \searrow o} } \in ^{{2\delta  + 2}} {\sum\limits_{n = 1}^\infty  {\frac{{{\left( {\log \;\log \;n} \right)}^{\delta } }}
            {{n\;\log \;n}}} }P{\left\{ {{\left| {S_{n} } \right|} \geqslant \varepsilon \tau {\sqrt {2n\;\log \;\log \;n} }} \right\}} = \frac{1}
            {{{\left( {\delta  + 1} \right)}{\sqrt \pi  }}}\Gamma {\left( {\delta  + 3/2} \right)},
            $$

, and if $$
E{\left[ {\varepsilon ^{2}_{1} {\left( {\log {\left| {\varepsilon _{1} } \right|}} \right)}^{{\delta  - 1}} } \right]} < \infty
$$ ,

$$
            {\mathop {\lim }\limits_{ \in  \searrow o} } \in ^{{2\delta  + 2}} {\sum\limits_{n = 1}^\infty  {\frac{{{\left( {\log \;n} \right)}\delta }}
            {n}} }P{\left\{ {{\left| {S_{n} } \right|} \geqslant \varepsilon \tau {\sqrt {n\;\log \;n} }} \right\}} = \frac{{\mu ^{{{\left( {2\delta  + 2} \right)}}} }}
            {{\delta  + 1}}\tau ^{{2\delta  + 2}} ,
            $$

where $$
\tau  = \sigma  \cdot {\sum\nolimits_{i =  - \infty }^\infty  {\alpha _{i} ,\Gamma {\left(  \cdot  \right)}} }
$$ is a Gamma function and μ(2δ+2) stands for the (2δ + 2)-th absolute moment of the standard normal distribution.

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A Moment Characterization of B–Valued Generalized Functionals of White Noise
Cai Shi Wang, Zhi Yuan Huang
Acta Mathematica Sinica    2006, 22 (1): 157-168.   DOI: 10.1007/s10114-004-0523-z
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 Kernel theorems are established for Banach space–valued multilinear mappings. A moment characterization theorem for Banach space–valued generalized functionals of white noise is proved by using the above kernel theorems. A necessary and sufficient condition in terms of moments is given for sequences of Banach space–valued generalized functionals of white noise to converge strongly. The integration is also discussed of functions valued in the space of Banach space–valued generalized functionals.

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Semi–Fredholm Spectrum and Weyl's Theorem for Operator Matrices
Xiao Hong Cao, Mao Zheng Guo, Bin Meng,
Acta Mathematica Sinica    2006, 22 (1): 169-178.   DOI: 10.1007/s10114-004-0505-1
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When A ∈ B(H) and B ∈ B(K) are given, we denote by M C an operator acting on the Hilbert space H ⊕ K of the form $$
M_{C}  = {\left( {\begin{array}{*{20}c}
{A} & {C}  \\
{0} & {B}  \\
\end{array} } \right)}
.$$ In this paper, first we give the necessary and sufficient condition for M C to be an upper semi-Fredholm (lower semi–Fredholm, or Fredholm) operator for some C ∈ B(K,H). In addition, let $$
\sigma _{{SF_{ + } }}
$$ (A) ={λ ∈ ? : A − λI is not an upper semi-Fredholm operator} be the upper semi–Fredholm spectrum of A ∈ B(H) and let 
$$
\sigma _{{SF_{ - } }}
$$ (A) = {λ ∈ ? : A − λI is not a lower semi–Fredholm operator} be the lower semi–Fredholm spectrum of A. We show that the passage from 
$$
\sigma _{{SF_{ ±} }} {\left( A \right)} \cap \sigma _{{SF_{ ±} }} {\left( B \right)}\;{\text{to}}\;\sigma_{{SF_{±} }} {\left( {M_{C} } \right)}
$$ is accomplished by removing certain open subsets of $$
\sigma _{{SF_{ - } }} {\left( A \right)} \cap \sigma_{{SF_{ + } }} {\left( B \right)}
$$ from the former, that is, there is an equality

$$
            \sigma_{{SF_{± } }} {\left( A \right)} \cup \sigma _{{SF_{ ±} }} {\left( B \right)} = \sigma_{{SF_{±} }} {\left( {M_{C} } \right)} \cup {\fancyscript G},$$

where $${\fancyscript G}$$ is the union of certain of the holes in $$
\sigma_{{SF_{± } }} {\left( {M_{C} } \right)}
$$ which happen to be subsets of 
$$
\sigma_{{SF_{ - } }} {\left( A \right)} \cap \sigma_{{SF_{ + } }} {\left( B \right)}
.$$ Weyl's theorem and Browder's theorem are liable to fail for 2 × 2 operator matrices. In this paper, we also explore how Weyl's theorem, Browder's theorem, a–Weyl's theorem and a–Browder's theorem survive for 2 × 2 upper triangular operator matrices on the Hilbert space.

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Additive Maps Preserving Similarity of Operators on Banach Spaces
Jin Chuan Hou, Xiu Ling Zhang
Acta Mathematica Sinica    2006, 22 (1): 179-186.   DOI: 10.1007/s10114-005-0564-y
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 Let X be an infinite–-dimensional complex Banach space and denote by ?(X) the algebra of all bounded linear operators acting on X. It is shown that a surjective additive map Φ from ?(X) onto itself preserves similarity in both directions if and only if there exist a scalar c, a bounded invertible linear or conjugate linear operator A and a similarity invariant additive functional φ on ?(X) such that either Φ(T) = cATA −1 + φ(T)I for all T, or Φ(T) = cAT*A −1 + φ(T)I for all T. In the case where X has infinite multiplicity, in particular, when X is an infinite–dimensional Hilbert space, the above similarity invariant additive functional φ is always zero.

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p–adic Transcendence and p–adic Transcendence Measures for the Values of Mahler Type Functions
Tian Qin Wang
Acta Mathematica Sinica    2006, 22 (1): 187-194.   DOI: 10.1007/s10114-005-0534-4
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 We prove the p–adic transcendence and p–adic transcendence measures for the values of some Mahler type functions.

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Second Order Nonlinear Evolution Inclusions II: Structure of the Solution Set
Nikolaos S. Papageorgiou, Nikolaos Yannakakis
Acta Mathematica Sinica    2006, 22 (1): 195-206.   DOI: 10.1007/s10114-004-0509-x
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We continue the work initiated in [1] (Second order nonlinear evolution inclusions I: Existence and relaxation results. Acta Mathematics Science, English Series, 21(5), 977-966 (2005)) and study the structural properties of the solution set of second order evolution inclusions which are defined in the analytic framework of the evolution triple. For the convex problem we show that the solution set is compact R δ , while for the nonconvex problem we show that it is path connected. Also we show that the solution set is closed only if the multivalued nonlinearity is convex valued. Finally we illustrate the results by considering a nonlinear hyperbolic problem with discontinuities.

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A Generalization of a Theorem of Liao
Xiong Ping Dai, Zuo Ling Zhou
Acta Mathematica Sinica    2006, 22 (1): 207-210.   DOI: 10.1007/s10114-005-0617-2
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Let X be a metrizable space and let ?:? × XX be a continuous flow on X. For any given {φt}–invariant Borel probability measure, this paper presents a {? t }–invariant Borel subset of X satisfying the requirements of the classical ergodic theorem for the continuous flow (X, {? t }). The set is more restrictive than the ones in the literature, but it might be more useful and convenient, particularly for non–uniformly hyperbolic systems and skew–product flows.

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The abc –conjecture for Algebraic Numbers
Jerzy Browkin
Acta Mathematica Sinica    2006, 22 (1): 211-222.   DOI: 10.1007/s10114-005-0624-3
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The abc–conjecture for the ring of integers states that, for every ε > 0 and every triple of relatively prime nonzero integers (a, b, c) satisfying a + b = c, we have max(|a|, |b|, |c|) ≤ rad(abc)1 + ε with a finite number of exceptions. Here the radical rad(m) is the product of all distinct prime factors of m.

In the present paper we propose an abc–conjecture for the field of all algebraic numbers. It is based on the definition of the radical (in Section 1) and of the height (in Section 2) of an algebraic number. From this abc–conjecture we deduce some versions of Fermat's last theorem for the field of all algebraic numbers, and we discuss from this point of view known results on solutions of Fermat's equation in fields of small degrees over ?.
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On the Solvability of Implicit Functional Equations with Applications to Discontinuous Differential Equations
S. Heikkilä
Acta Mathematica Sinica    2006, 22 (1): 223-232.   DOI: 10.1007/s10114-005-0558-9
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 In this paper we shall study the solvability of discontinuous functional equations, and apply the so-obtained results to discontinuous implicit initial value problems in ordered Banach spaces. The proofs are based on fixed point results in ordered spaces proved recently by the author. A concrete example is solved to demonstrate the obtained results.

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Naturally Full Functors in Nature
A. Ardizzoni, C. Menini, S. Caenepeel, G. Militaru
Acta Mathematica Sinica    2006, 22 (1): 233-250.   DOI: 10.1007/s10114-005-0561-1
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 We introduce and discuss the notion of a naturally full functor. The definition is similar to the definition of a separable functor; a naturally full functor is a functorial version of a full functor, while a separable functor is a functorial version of a faithful functor. We study the general properties of naturally full functors. We also discuss when functors between module categories and between categories of comodules over a coring are naturally full.

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Singular Integrals with Bilinear Phases
Elena Prestini
Acta Mathematica Sinica    2006, 22 (1): 251-260.   DOI: 10.1007/s10114-005-0562-0
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We prove the boundedness from L p (T 2) to itself, 1 < p < ∞, of highly oscillatory singular integrals Sf(x, y) presenting singularities of the kind of the double Hilbert transform on a non–rectangular domain of integration, roughly speaking, defined by |y'| > |x'|, and presenting phases λ(Ax+By) with 0 ≤ A, B ≤ 1 and λ ≥ 0. The norms of these oscillatory singular integrals are proved to be independent of all parameters A, B and λ involved. Our method extends to a more general family of phases. These results are relevant to problems of almost everywhere convergence of double Fourier and Walsh series.

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The Maximal Graded Left Quotient Algebra of a Graded Algebra1)
Gonzalo Aranda Pino, Mercedes Siles Molina,
Acta Mathematica Sinica    2006, 22 (1): 261-270.   DOI: 10.1007/s10114-005-0622-5
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We construct the maximal graded left quotient algebra of every graded algebra A without homogeneous total right zero divisors as the direct limit of graded homomorphisms (of left A–modules) from graded dense left ideals of A into a graded left quotient algebra of A. In the case of a superalgebra, and with some extra hypothesis, we prove that the component in the neutral element of the group of the maximal graded left quotient algebra coincides with the maximal left quotient algebra of the component in the neutral element of the group of the superalgebra.

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Weil Modules and Gauge Bundles
Miroslav Kureš
Acta Mathematica Sinica    2006, 22 (1): 271-278.   DOI: 10.1007/s10114-005-0616-3
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Finite dimensional modules over Weil algebras are investigated and corresponding gauge bundle functors, from the category of vector bundles into the category of fibered manifolds, are determined. The equivalence of the two definitions of gauge Weil functors is proved and a number of geometric examples is presented, including a new description of vertical Weil bundles.

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A Note on Linear Extension of Into–Isometries Between Two Unit Spheres of Atomic ALp–Space (0 < p < ∞)
Guang Gui Ding
Acta Mathematica Sinica    2006, 22 (1): 279-282.   DOI: 10.1007/s10114-005-0636-z
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 In this paper, we shall present a short and simple proof on the isometric linear extension problem of into–isometries between two unit spheres of atomic abstract L p –spaces (0 < p < ∞).

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On Two–stage Estimate Based on Independent Estimate of Covariance Matrix
Su Ju Yin, Song Gui Wang
Acta Mathematica Sinica    2006, 22 (1): 283-288.   DOI: 10.1007/s10114-005-0650-1
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 When an independent estimate of covariance matrix is available, we often prefer two–stage estimate (TSE). Expressions of exact covariance matrix of the TSE obtained by using all and some covariables in covariance adjustment approach are given, and a necessary and sufficient condition for the TSE to be superior to the least square estimate and related large sample test is also established. Furthermore the TSE, by using some covariables, is expressed as weighted least square estimate. Basing on this fact, a necessary and sufficient condition for the TSE by using some covariables to be superior to the TSE by using all covariables is obtained. These results give us some insight into the selection of covariables in the TSE and its application.

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Universal Similarity Factorization Equalities over Generalized Clifford Algebras
Yong Ge Tian
Acta Mathematica Sinica    2006, 22 (1): 289-300.   DOI: 10.1007/s10114-005-0552-2
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For any element a in a generalized 2 n –dimensional Clifford algebra $${\fancyscript C}$$ ? n ( $${\Bbb F}$$ ) over an arbitrary field $${\Bbb F}$$ of characteristic not equal to two, it is shown that there exits a universal invertible matrix P n over $${\fancyscript C}$$ ? n ( $${\Bbb F}$$ ) such that $$
P^{{ - 1}}_{n} D_{a} P_{n}  = \phi {\left( a \right)} \in F^{{2^{n}  \times 2^{n} }}
$$ , where ?(a) is a matrix representation of a over and D a is a diagonal matrix consisting of a or its conjugate.

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The Density of Linear Symplectic Cocycles with Simple Lyapunov Spectrum in \fancyscript GUnknown control sequence '\fancyscript'IC(X, SL(2,?))
Xiong Ping Dai
Acta Mathematica Sinica    2006, 22 (1): 301-310.   DOI: 10.1007/s10114-005-0571-z
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Let (X, $${\mathfrak{S}}$$ (X), $${\mathfrak{m}})$$ be a probability space with σ-algebra , $${\mathfrak{S}}$$ (X) and probability measure $${\mathfrak{m}}.$$ The set V in $${\mathfrak{S}}$$ is called P-admissible, provided that for any positive integer n and positive-measure set V n $${\mathfrak{S}}$$ contained in V , there exists a Z n $${\mathfrak{S}}$$ such that Z n V n and 0 < $${\mathfrak{m}}$$ (Z n ) < 1/n. Let T be an ergodic automorphism of (X, $${\mathfrak{S}})$$ preserving $${\mathfrak{m}},$$ and A belong to the space of linear measurable symplectic cocycles

$${\fancyscript G}$$ IC (X, SL(2,?)) := {A : XSL(2,?)| log ∥A ±1(x)∥ ∈ $${\Bbb L}$$ 1(X, $${\mathfrak{m}}).$$
We prove that for any P–admissible set V and ε > 0, there exists a B$${\fancyscript G}$$ IC (X, SL(2,?)) such that
max{∥A(x) − B(x)∥, ∥A −1(x) − B −1(x)∥} < ε for all xV, A(x) = B(x) for all xX \ V,
and B has the simple Lyapunov spectrum over the system (X, $${\mathfrak{m}},$$ T).
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