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991.
Pietro De Poi 《Mathematische Nachrichten》2005,278(4):363-378
In this article we study congruences of lines in ?n, and in particular of order one. After giving general results, we obtain a complete classification in the case of ?4 in which the fundamental surface F is in fact a variety, i.e. it is integral, and the congruence is the irreducible set of the trisecant lines of F. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
992.
993.
For each integer n l(n)=[(log n)/(log g(n))]\lambda(n)={{\rm log}\, n\over{\rm log}\, \gamma(n)}
be the index of composition of n, where
g(n)=?p|np\gamma(n)=\prod_{p\vert n}p
. For convenience, we write ?x £ n £ x+?xl(n)\sum_{x\le n\le x+\sqrt{x}}\lambda(n)
and
?n £ xl(n)\sum_{n\le x}\lambda(n)
, as well as for
?x £ n £ x+?x1/l(n)\sum_{x\le n\le x+\sqrt{x}}1/\lambda(n)
and
?n £ x1/l(n)\sum_{n\le x}1/\lambda(n)
. Finally we study the sum of running over shifted primes. 相似文献
994.
Email: csfvega{at}dm.uba.ar
Received on August 17, 2006; Accepted on September 8, 2007 Necessary conditions are proved for optimal control problemsinvolving an infinite horizon and terminal conditions at infinitywhose states are governed by Volterra integral equations withnon-linear time delay. 相似文献
995.
Under a suitable condition on n and p, the quasilinear equation at critical growth −Δpu=λ|u|p−2u+|u|p∗−2u is shown to admit a nontrivial weak solution for any λ?λ1. Nonstandard linking structures, for the associated functional, are recognized. 相似文献
996.
Jesús A. De Loera Edward D. Kim Shmuel Onn Francisco Santos 《Journal of Combinatorial Theory, Series A》2009,116(8):1306-1325
This paper discusses properties of the graphs of 2-way and 3-way transportation polytopes, in particular, their possible numbers of vertices and their diameters. Our main results include a quadratic bound on the diameter of axial 3-way transportation polytopes and a catalogue of non-degenerate transportation polytopes of small sizes. The catalogue disproves five conjectures about these polyhedra stated in the monograph by Yemelichev et al. (1984). It also allowed us to discover some new results. For example, we prove that the number of vertices of an m×n transportation polytope is a multiple of the greatest common divisor of m and n. 相似文献
997.
We develop a rigorous theory of non-local Poisson structures, built on the notion of a non-local Poisson vertex algebra. As an application, we find conditions that guarantee applicability of the Lenard–Magri scheme of integrability to a pair of compatible non-local Poisson structures. We apply this scheme to several such pairs, proving thereby integrability of various evolution equations, as well as hyperbolic equations. 相似文献
998.
Fernando Charro Guido De Philippis Agnese Di Castro Davi Máximo 《Calculus of Variations and Partial Differential Equations》2013,48(3-4):667-693
We prove L ∞ bounds and estimates of the modulus of continuity of solutions to the Poisson problem for the normalized infinity and p-Laplacian, namely $$\begin{array}{ll} -\Delta_p^N u=f\quad{\rm for } \; n < p \leq\infty.\end{array}$$ We are able to provide a stable family of results depending continuously on the parameter p. We also prove the failure of the classical Alexandrov–Bakelman–Pucci estimate for the normalized infinity Laplacian and propose alternate estimates. 相似文献
999.
Manlio De Domenico Mohammad Ali Ghorbani Oleg Makarynskyy Dina Makarynska Hakimeh Asadi 《Applied Mathematical Modelling》2013
Prediction of sea-level is an important task for navigation, coastal engineering and geodetic applications, as well as recreational activities. This study presents a comparison of Chaos theory and Auto-Regressive Integrated Moving Average (ARIMA) techniques for sea level modelling for daily, weekly, 10-day and monthly time scale at the Cocos (Keeling) islands from 1992 to 2001. The state space reconstruction of the unknown underlying process is directly employed from time series data, through Takens delay embedding method: optimal embedding dimension and delay time are obtained from false nearest neighbours and average mutual information techniques, respectively. Optimal values are then used for the estimation of the correlation dimension and the largest Lyapunov exponent, for inspecting possible signatures of chaotic dynamics. We find a positive Lyapunov exponent an evident feature of chaos. Indeed, the nonlinear prediction of sea level, in the period ranging from January 2001 to December 2001, is in an excellent agreement with the data for the same period, evidencing the nonlinear nature of the process. ARIMA method is also used for sea level modelling, for the same time scales; the performances of the two models are compared using such statistical indices as the root mean square error (RMSE) and correlation coefficient (CC). The comparative analyses show that the chaos theory model has a slight edge over ARIMA while both models are in principal acceptable. 相似文献
1000.
A unital in PG(2, q2) is a set of points such that each line meets in 1 or points. The well‐known example is the classical unital consisting of all absolute points of a unitary polarity of PG(2, q2). Unitals other than the classical one also exist in PG(2, q2) for every . Actually, all known unitals are of Buekenhout–Metz type [see F. Buekenhout, Geom Dedicata 5 (1976), 189–194, R. Metz, Geom Dedicata 8 (1979), 125–126.], and they can be obtained by a construction due to F. Buekenhout, (Geom Dedicata 5 (1976), 189–194).. The unitals constructed by R. D. Baker and G. L. Ebert (J Combin Theory Ser A 60 (1992), 67–84), and independently by J. W. P. Hirschfeld and T. Sz?nyi (Discrete Math 97 (1991), 229–242), are the union of q conics. Our Theorem 1.1 shows that this geometric property characterizes the Baker–Ebert–Hirschfeld–Sz?nyi unitals. © 2012 Wiley Periodicals, Inc. J. Combin. Designs 21: 101–111, 2013 相似文献