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41.
42.
Kerdock codes (Kerdock, Inform Control 20:182–187, 1972) are a well-known family of non-linear binary codes with good parameters
admitting a linear presentation in terms of codes over the ring (see Nechaev, Diskret Mat 1:123–139, 1989; Hammons et al., IEEE Trans Inform Theory 40:301–319, 1994). These codes have been
generalized in different directions: in Calderbank et al. (Proc Lond Math Soc 75:436–480, 1997) a symplectic construction
of non-linear binary codes with the same parameters of the Kerdock codes has been given. Such codes are not necessarily equivalent.
On the other hand, in Kuzmin and Nechaev (Russ Math Surv 49(5), 1994) the authors give a family of non-linear codes over the
finite field F of q = 2
l
elements, all of them admitting a linear presentation over the Galois Ring R of cardinality q
2 and characteristic 22. The aim of this article is to merge both approaches, obtaining in this way new families of non-linear codes over F that can be presented as linear codes over the Galois Ring R. The construction uses symplectic spreads.
相似文献
43.
We study the pure braid groups of the real projective plane , and in particular the possible splitting of the Fadell–Neuwirth short exact sequence , where n ≥ 2 and m ≥ 1, and p
* is the homomorphism which corresponds geometrically to forgetting the last m strings. This problem is equivalent to that of the existence of a section for the associated fibration of configuration spaces. Van Buskirk proved (1966, Trans. Am. Math. Soc., 122:81–97) that p and p
* admit a section if n = 2 and m = 1. Our main result in this paper is to prove that there is no section if n ≥ 3. As a corollary, it follows that n = 2 and m = 1 are the only values for which a section exists. As part of the proof, we derive a presentation of : this appears to be the first time that such a presentation has been given in the literature.
相似文献
44.
“化学反应速率”综合体现了微粒观、实验观及科学本质观等化学基本观念,是提高学生科学素养的重要载体。从内容选取、内容编排与内容呈现3个方面对英国索尔特高级化学课程教材与国内化学教材中“化学反应速率”相关内容的编写进行比较,并简要阐述几点对化学教材编写和化学教学的启示。 相似文献
45.
Given a family of Calabi-Yau varieties over the punctured disc or over the field of Laurent series, we show that, after a finite base change, the family can be extended across the origin while keeping the canonical class trivial. More generally, we prove similar extension results for families whose log-canonical class is semi-ample. We use these to show that the Berkovich and essential skeleta agree for smooth varieties over C((t)) with semi-ample canonical class. 相似文献
46.
In this article, we investigate Programming Evaluation and Review Technique networks with independently and generally distributed activity durations. For any path in this network, we select all the activities related to this path such that the completion time of the sub-network (only consisting of all the related activities) is equal to the completion time of this path. We use the elapsed time as the supplementary variables and model this sub-network as a Markov skeleton process, the state space is related to the sub-network structure. Then use the backward equation to compute the distribution of the sub-network's completion time, which is an important rule in project management and scheduling. 相似文献
47.
Let R be a Noetherian ring and M be a finitely generated R-module. Let I(M) be the first nonzero Fitting ideal of M. The main result of this paper asserts that when I(M) = Q is a regular maximal ideal of R, then M?R∕Q⊕P, for some projective R-module P of constant rank if and only if T(M)?QM. As a consequence, it is shown that if M is an Artinian R-module and I(M) = Q is a regular maximal ideal of R, then M?R∕Q. 相似文献
48.
A robust method of determining the sign map and skeletons for ESPI images is introduced in this paper. ESPI images have high speckle noise which makes it difficult to obtain the fringe information, especially from a single image. To overcome the effects of high speckle noise, local directional computing windows are designed according to the fringe directions. Then by calculating the gradients from the filtered image in directional windows, sign map and good skeletons can be determined robustly. Based on the sign map, single image phase-extracting methods such as quadrature transform can be improved. And based on skeletons, fringe phases can be obtained directly by normalization methods. Experiments show that this new method is robust and effective for extracting phase from a single ESPI fringe image. 相似文献
49.
Ligulasagitins A-E (1-5), five new eremophilane-derived metabolites possibly formed via a Diels-Alder reaction in the biosynthetic process, were isolated from Ligularia sagitta Maxim. Among them 1 and 2 possess a novel C19 skeleton, 4 and 5 are two novel dimeric eremophilane type derivatives. Their structures were determined by extensive spectroscopic analysis and the structure of 2 was also confirmed by a single-crystal X-ray diffraction analysis. Furthermore, 4 and 5 showed weak cytotoxic activity against HL-60 (human promyelocytic leukemia) cells. 相似文献
50.
Mai Thanh Thi Nguyen 《Tetrahedron letters》2004,45(46):8519-8522
A novel dimeric methanodibenzoxocinone, named neosappanone A (1), possessing a unique unprecedented novel carbon framework, has been isolated from the heartwood of Caesalpinia sappan L. of Vietnam, and its structure was elucidated on the basis of spectroscopic analysis. Neosappanone A (1) competitively inhibited xanthine oxidase in a concentration-dependent manner (IC50, 29.7 μM; Ki, 16.3 μM). 相似文献