| 1. |
- Areschoug, Thomas, et al.
(författare)
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A Proline-Rich Region with a Highly Periodic Sequence in Streptococcal beta Protein Adopts the Polyproline II Structure and Is Exposed on the Bacterial Surface.
- 2002
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Ingår i: Journal of Bacteriology. - 0021-9193. ; 184:22, s. 6376-6383
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Tidskriftsartikel (refereegranskat)abstract
- Proline-rich regions have been identified in many surface proteins of pathogenic streptococci and staphylococci. These regions have been suggested to be located in cell wall-spanning domains and/or to be required for surface expression of the protein. Because little is known about these regions, which are found in extensively studied and biologically important surface proteins, we characterized the proline-rich region in one such protein, the beta protein of group B streptococci. The proline-rich region in beta, designated the XPZ region, has a proline at every third position, and the sequence is highly periodic in other respects. Immunochemical analysis showed that the XPZ region was not associated with the cell wall but was exposed on the bacterial surface. Moreover, characterization of a beta mutant lacking the XPZ region demonstrated that this region was not required for surface expression of the beta protein. Comparison of the XPZ region in different beta proteins showed that it varied in size but always retained the typical sequence periodicity. Circular dichroism spectroscopy indicated that the XPZ region had the structure of a polyproline II helix, an extended and solvent-exposed structure with exactly three residues per turn. Because of the three-residue sequence periodicity in the XPZ region, it is expected to be amphipathic and to have distinct nonpolar and polar surfaces. This study identified a proline-rich structure with unique properties that is exposed on the surface of an important human pathogen.
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| 2. |
- Avgustinovich, S. V., et al.
(författare)
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On intersection problem for perfect binary codes
- 2006
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Ingår i: Designs, Codes and Cryptography. - : Springer Science and Business Media LLC. - 0925-1022 .- 1573-7586. ; 39:3, s. 317-322
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Tidskriftsartikel (refereegranskat)abstract
- The main result is that to any even integer q in the interval 0 <= q <= 2(n+1-2) (log(n+1)), there are two perfect codes C-1 and C-2 of length n = 2(m) -1, m >= 4, such that vertical bar C-1 boolean AND C-2 vertical bar = q.
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| 3. |
- Avgustinovich, S. V., et al.
(författare)
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On partitions of an n-cube into nonequivalent perfect codes
- 2007
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Ingår i: Problems of Information Transmission. - : Pleiades Publishing Ltd. - 0032-9460 .- 1608-3253. ; 43:4, s. 310-315
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Tidskriftsartikel (refereegranskat)abstract
- We prove that for all n = 2(k)-1, k >= 5. there exists a partition of the set of all binary vectors of length n into pairwise nonequivalent perfect binary codes of length n with distance 3.
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| 4. |
- Avgustinovich, S. V., et al.
(författare)
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On the structure of symmetry groups of Vasil'ev codes
- 2005
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Ingår i: Problems of Information Transmission. - : Springer Science and Business Media LLC. - 0032-9460 .- 1608-3253. ; 41:2, s. 105-112
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Tidskriftsartikel (refereegranskat)abstract
- The structure of symmetry groups of Vasil'ev codes is studied. It is proved that the symmetry group of an arbitrary perfect binary non-full-rank Vasil'ev code of length n is always nontrivial; for codes of rank n - log(n + 1) + 1, an attainable upper bound on the order of the symmetry group is obtained.
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| 5. |
- Avgustinovich, S. V., et al.
(författare)
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The classification of some perfect codes
- 2004
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Ingår i: Designs, Codes and Cryptography. - 0925-1022 .- 1573-7586. ; 31:3, s. 313-318
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Tidskriftsartikel (refereegranskat)abstract
- Perfect 1-error correcting codes C in Z(2)(n), where n = 2(m) - 1, are considered. Let [C] denote the linear span of the words of C and let the rank of C be the dimension of the vector space [C]. It is shown that if the rank of C is n - m + 2 then C is equivalent to a code given by a construction of Phelps. These codes are, in case of rank n - m + 2, described by a Hamming code H and a set of MDS-codes D-h; h is an element of H, over an alphabet with four symbols. The case of rank n - m + 1 is much simpler: Any such code is a Vasil'ev code.
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| 6. |
- De Lucca, Anthony J., et al.
(författare)
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Antifungal Properties of Wheat Histones (H1-H4) and Purified Wheat Histone H1
- 2011
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 59:13, s. 6933-6939
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Tidskriftsartikel (refereegranskat)abstract
- Wheat (Triticum spp.) histones H1, H2, H3, and H4 were extracted, and H1 was further purified. The effect of these histones on specific fungi that may or may not be pathogenic to wheat was determined. These fungi included Aspergillus flavus, Aspergillus fumigatus, Aspergillus niger, Fusarium oxysporum, Fusarium verticillioides, Fusarium solani, Fusarium graminearum, Penicillium digitatum, Penicillium italicum, and Greeneria uvicola. Non-germinated and germinating conidia of these fungi were bioassayed separately. The non-germinated and germinating conidia of all Fusarium species were highly susceptible to the mixture (H1-H4) as well as pure H1, with viability losses of 99-100% found to be significant (p <0.001) at <= 10 mu M or less for the histone mixture and pure H1. F. graminearum was the most sensitive to histone activity. The histones were inactive against all of the non-germinated Penicillium spp. conidia. However, they significantly reduced the viability of the germinating conidia of the Penicillium spp. conidia, with 95% loss at 2.5 mu M. Non-germinated and germinating conidia viability of the Aspergillus spp. and G. uvicola were unaffected when exposed to histones up to 10 mu M. Results indicate that Fusarium spp. pathogenic to wheat are susceptible to wheat histones, indicating that these proteins may be a resistance mechanism in wheat against fungal infection.
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| 7. |
- El-Zanati, S., et al.
(författare)
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Partitions of the 8-Dimensional Vector Space Over GF(2)
- 2010
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Ingår i: Journal of combinatorial designs (Print). - : Wiley. - 1063-8539 .- 1520-6610. ; 18:6, s. 462-474
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Tidskriftsartikel (refereegranskat)abstract
- Let V=V(n,q) denote the vector space of dimension n over GF(q). A set of subspaces of V is called a partition of V if every nonzero vector in V is contained in exactly one subspace of V. Given a. partition P of V with exactly a(i) subspaces of dimension i for 1 <= i <= n, we have Sigma(n)(i=1) a(i)(q(i)-1) = q(n)-1, and we call the n-tuple (a(n), a(n-1), ..., a(1)) the type of P. In this article we identify all 8-tuples (a(8), a(7), ..., a(2), 0) that are the types of partitions of V(8,2).
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| 8. |
- Guzeltepe, Murat, et al.
(författare)
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Perfect Mannheim, Lipschitz and Hurwitz weight codes
- 2014
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Ingår i: Mathematical Communications. - 1331-0623 .- 1848-8013. ; 19:2, s. 253-276
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Tidskriftsartikel (refereegranskat)abstract
- The set of residue classes modulo an element pi in the rings of Gaussian integers, Lipschitz integers and Hurwitz integers, respectively, is used as alphabets to form the words of error correcting codes. An error occurs as the addition of an element in a set E to the letter in one of the positions of a word. If epsilon is a group of units in the original rings, then we obtain the Mannheim, Lipschitz and Hurwitz metrics, respectively. Some new perfect 1-error-correcting codes in these metrics are constructed. The existence of perfect 2-error-correcting codes is investigated by computer search.
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| 9. |
- Heden, Olof
(författare)
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A full rank perfect code of length 31
- 2006
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Ingår i: Designs, Codes and Cryptography. - : Springer Science and Business Media LLC. - 0925-1022 .- 1573-7586. ; 38:1, s. 125-129
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Tidskriftsartikel (refereegranskat)abstract
- A full rank perfect 1-error correcting binary code of length 31 with a kernel of dimension 21 is described. This was the last open case of the rank-kernel problem of Etzion and Vardy.
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| 10. |
- Heden, Olof
(författare)
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A maximal partial spread of size 45 in PG(3,7)
- 2001
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Ingår i: Designs, Codes and Cryptography. - 0925-1022 .- 1573-7586. ; 22:3, s. 331-334
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Tidskriftsartikel (refereegranskat)abstract
- An example of a maximal partial spread of size 45 in PG(3, 7) is given. This example show's that a conjecture of Bruen and Thas from 1976 is false. It also shows that an upper bound for the number of lines of a maximal partial spread, given by Blockhuis in 1994, cannot be improved in general.
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| 11. |
- Heden, Olof
(författare)
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A note on the symmetry group of full rank perfect binary codes
- 2012
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Ingår i: Discrete Mathematics. - : Elsevier BV. - 0012-365X .- 1872-681X. ; 312:19, s. 2973-2977
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Tidskriftsartikel (refereegranskat)abstract
- It is proved that the size of the symmetry group Sym(C) of every full rank perfect 1-error correcting binary code C of length n is less than or equal to 2|Sym( Hn)|(n+1), where Hn is a Hamming code of the same length.
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| 12. |
- Heden, Olof
(författare)
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A remark on full rank perfect codes
- 2006
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Ingår i: Discrete Mathematics. - : Elsevier BV. - 0012-365X .- 1872-681X. ; 306:16, s. 1975-1980
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Tidskriftsartikel (refereegranskat)abstract
- Any full rank perfect 1-error correcting binary code of length n = 2(k) - 1 and with a kernel of dimension n - log(n + 1) - m, where in is sufficiently large, may be used to construct a full rank perfect 1-error correcting binary code of length 2(m) - 1 and with a kernel of dimension n - log(n + 1) - k. Especially we may construct full rank perfect 1-error correcting binary codes of length n = 2(m) - 1 and with a kernel of dimension n - log(n + 1) - 4 for nt = 6, 7,..., 10. This result extends known results on the possibilities for the size of a kernel of a full rank perfect code.
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| 13. |
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| 14. |
- Heden, Olof
(författare)
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A SURVEY of the DIFFERENT TYPES of VECTOR SPACE PARTITIONS
- 2012
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Ingår i: Discrete Mathematics, Algorithms and Applications (DMAA). - : World Scientific Publishing Co. Pte Ltd. - 1793-8309 .- 1793-8317. ; 4:1
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Tidskriftsartikel (refereegranskat)abstract
- A vector space partition is here a collection P of subspaces of a finite vector space V(n, q), of dimension n over a finite field with q elements, with the property that every non-zero vector is contained in a unique member of P. Vector space partitions relate to finite projective planes, design theory and error correcting codes. In the first part of the paper I will discuss some relations between vector space partitions and other branches of mathematics. The other part of the paper contains a survey of known results on the type of a vector space partition, more precisely: the theorem of Beutelspacher and Heden on T-partitions, rather recent results of El-Zanati et al. on the different types that appear in the spaces V(n, 2), for n ≤ 8, a result of Heden and Lehmann on vector space partitions and maximal partial spreads including their new necessary condition for the existence of a vector space partition, and furthermore, I will give a theorem of Heden on the length of the tail of a vector space partition. Finally, I will also give a few historical remarks.
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| 15. |
- Heden, Olof, et al.
(författare)
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Bruen chains in PG(3, p(k)) k >= 2
- 2000
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Ingår i: Discrete Mathematics. - 0012-365X .- 1872-681X. ; 214:3-Jan, s. 251-253
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Tidskriftsartikel (refereegranskat)abstract
- The Bruen chains of PC(3,q) for q = 9, 25 and 27 are described. They were found by a computer search. In the case q = 49 no chains have been found yet.
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| 16. |
- Heden, Olof, et al.
(författare)
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Extremal sizes of subspace partitions
- 2012
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Ingår i: Designs, Codes and Cryptography. - : Springer Science and Business Media LLC. - 0925-1022 .- 1573-7586. ; 64:3, s. 265-274
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Tidskriftsartikel (refereegranskat)abstract
- A subspace partition I of V = V(n, q) is a collection of subspaces of V such that each 1-dimensional subspace of V is in exactly one subspace of I . The size of I is the number of its subspaces. Let sigma (q) (n, t) denote the minimum size of a subspace partition of V in which the largest subspace has dimension t, and let rho (q) (n, t) denote the maximum size of a subspace partition of V in which the smallest subspace has dimension t. In this article, we determine the values of sigma (q) (n, t) and rho (q) (n, t) for all positive integers n and t. Furthermore, we prove that if n a parts per thousand yen 2t, then the minimum size of a maximal partial t-spread in V(n + t -1, q) is sigma (q) (n, t).
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| 17. |
- Heden, Olof
(författare)
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Full rank perfect codes and alpha-kernels
- 2009
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Ingår i: Discrete Mathematics. - : Elsevier BV. - 0012-365X .- 1872-681X. ; 309:8, s. 2202-2216
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Tidskriftsartikel (refereegranskat)abstract
- A perfect 1-error correcting binary code C, perfect code for short, of length n = 2(m) - 1 has full rank if the linear span < C > of the words of C has dimension n as a vector space over the finite field F-2. There are just a few general constructions of full rank perfect codes, that are not given by recursive methods using perfect codes of length shorter than n. In this study we construct full rank perfect codes, the so-called normal alpha-codes, by first finding the superdual of the perfect code. The superdual of a perfect code consists of two matrices G and T in which simplex codes play an important role as subspaces of the row spaces of the matrices G and T. The main idea in our construction is the use of alpha-words. These words have the property that they can be added to certain rows of generator matrices of simplex codes such that the result will be (other) sets of generator matrices for simplex codes. The kernel of these normal alpha-codes will also be considered. It will be proved that any subspace, of the kernel of a normal alpha-code, that satisfies a certain property will be the kernel of another perfect code, of the same length n. In this way, we will be able to relate some of the full rank perfect codes of length n to other full rank perfect codes of the same length n.
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| 18. |
- Heden, Olof, et al.
(författare)
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Intersections of perfect binary codes
- 2010
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Ingår i: Proceedings - 2010 IEEE Region 8 International Conference on Computational Technologies in Electrical and Electronics Engineering, SIBIRCON-2010. - 9781424476268 ; , s. 52-54
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Konferensbidrag (refereegranskat)abstract
- Intersections of perfect binary codes are investigated. In 1998 Etzion and Vardy proved that the intersection number η(C;D), for any two distinct perfect codes C and D, is always in the range 0 ≤η(C;D) ≤2 n-log(n+1)-2(n-1)/2; where the upper bound is attainable. We improve the upper bound and show that the intersection number 2n-log(n+1) -2(n-1)/2 is "sporadic". We also find a large class of intersection numbers for perfect binary codes of length 15 and for any admissible n >15 a new set of intersection numbers for perfect codes of length n.
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| 19. |
- Heden, Olof
(författare)
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Linear maps of perfect codes and irregular C-partitions
- 2015
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Ingår i: Discrete Mathematics. - : Elsevier BV. - 0012-365X .- 1872-681X. ; 338:3, s. 149-163
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Tidskriftsartikel (refereegranskat)abstract
- The concept of an irregular C-partition of binary space into perfect 1-error-correcting codes is defined. Three distinct constructions of irregular C-partitions are presented. The relation between irregular C-partitions and linear maps, that map perfect codes to perfect codes, is discussed
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| 20. |
- Heden, Olof
(författare)
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Maximal partial spreads and the modular n-queen problem III
- 2002
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Ingår i: Discrete Mathematics. - 0012-365X .- 1872-681X. ; 243:3-Jan, s. 135-150
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Tidskriftsartikel (refereegranskat)abstract
- Maximal partial spreads in PG(3, q) q = p(k), p odd prime and q greater than or equal to 7, are constructed for any integer n in the interval (q(2) + 1)/2 + 6 less than or equal to n less than or equal to (5q(2) + 4q - 1)/8 in the case q + 1 0, +/-2, +/-4, +/-6, +/-10, 12 (mod 24). In all these cases. maximal partial spreads of the size (q(2) + 2 + n have also been constructed for some small values of the integer n. These values depend on q and are mainly n = 3 and n = 4. Combining these results with previous results of the author and with that of others we can conclude that there exist maximal partial spreads in PG(3, q), q = p(k) where p is an odd prime and q greater than or equal to 7, of size n for any integer n in the interval (q(2) + 1) /2 + 6 less than or equal to n less than or equal to q(2) - q + 2.
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| 21. |
- Heden, Olof
(författare)
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Maximal partial spreads in PG(3,5)
- 2000
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Ingår i: Ars combinatoria. - 0381-7032. ; 57, s. 97-101
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Tidskriftsartikel (refereegranskat)abstract
- Maximal partial spreads of the sizes 13, 14, 15,..., 22 and 26 are described. They were found by using a computer. The computer also made a complete search for maximal partial spreads of size less then or equal to 12. No such maximal partial spreads were found.
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| 22. |
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| 23. |
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| 24. |
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| 25. |
- Heden, Olof
(författare)
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On kernels of perfect codes
- 2010
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Ingår i: Discrete Mathematics. - : Elsevier BV. - 0012-365X .- 1872-681X. ; 310:21, s. 3052-3055
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that there exists a perfect one-error-correcting binary code with a kernel which is not contained in any Hamming code.
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