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The electronic and phononic properties of [V.sub.2]A1C have been extensively studied using ab initio pseudopotential density functional theory. Our investigations revealed that the longest V-V bond and its least variations have led to the stiffer c axis. The nearly unchanged net charge of the C atom under pressure has led to nearly unchanged overlapped populations along the C-V bond. The obvious charge transfer of V → Al has induced significant variations of the overlapped populations along Al-V and V-V bonds. An anomalous variation of charge transfer between V and Al atoms and V-V bond populations at about 700 GPa has been revealed, which may relate to its structural instability at about 731 GPa. Previously calculated structural instability at about 731 GPa has been successfully confirmed by the present phonon dispersion curve. The bonding natures are also studied by the electron density difference, electron density of states, and the energy band structure. PACS Nos.: 63.20.D-, 71.20.-b, 71.15.Mb. Nous avons fait une etude en profondeur des proprietes de [V.sub.2]A1C en utilisant la theorie de la fonctionnelle de densite avec pseudo-potentiel ab initio. Notre etude revele que le plus grand lien V-V et sa petite variation sont responsables de la forte rigidite de l'axe c. La charge nette de l'atome C ne change pratiquement pas sous la pression, indiquant une constance des populations de recouvrement dans le lien C-V. L'evident transfert de charges V → Al induit des variations significatives des populations de recouvrement dans les liens V-Al et V-V. Nous notons une variation anomale de transfert de charges entre les atomes V et Al autour de 700 GPa, ce qui pourrait etre relie a l'instabilite structurelle observee a 731 GPa. Des calculs anterieurs de cette instabilite structurelle a 731 GPa ont ete confirmes avec succes par notre courbe de dispersion des phonons. Nous etudions egalement la nature des liens a l'aide de la difference dans la densite electronique, de la densite d'etats electroniques et de la structure des bandes d'energie. [Traduit par la Redaction], 1. Introduction The [M.sub.n+1]A[X.sub.n] phases, where M is an early transition metal, A is an A-group element (mostly IIIA and IVA elements), X is either C or N, and n [...]

The systematic trends of electronic structure and optical properties of Ru[O.sub.2] consisting of its four phases have been studied by using norm-conserving pseudopotential within the generalized gradient approximation for the exchange- correlation potential. The total density of states (DOS) and energy band structure investigations revealed that the fluorite phase possesses the broadest conduction bandwidth (0-30 eV) and the pyrite phase possesses the narrowest conduction bandwidth (0-5 eV). Study on partial DOS we found that O 2p electrons of the fluorite phase present a significant shift towards the Fermi level and Ru s and p electrons of the rutile phase contribute little to the orbital energy level formation. For the first time, we found that the norm-conserving pseudopotential failed to obtain the normal DOS and energy band distributions for a rutile Ru atom below about -10 eV, whereas such missing electronic distributions could be obtained successfully using an ultrasoft pseudo potential. Investigations on the optical properties further found that the rutile and Ca[Cl.sub.2]-type phases behave more similarly and the fluorite phase shows the most sensitive response in the whole radiation reaction region. The electron energy loss function revealed that the pyrite phase corresponds to the least relative intensity. PACS Nos: 63.20.dk, 71.20.-b, 78.20.Ci Nous utilisons un pseudo-potentiel a norme conservee dans l'approximation du gradient generalise pour obtenir le potentiel d'echange-correlation, afin d'etudier les tendances systematiques de la structure electronique et des proprietes optiques du Ru[O.sub.2], incluant ses quatre phases. La densite totale d'etats (DOS) et la structure de la bande d'energie revelent que la phase fluorite possede la plus grande largeur de bande de valence (0-30 eV) et que la phase pyrite possede la plus etroite (-20-0 eV). Etudiant les DOS partielles, nous trouvons que les electrons 2p de O dans la phase fluorite montrent un deplacement marque vers le niveau de Fermi, alors que les electrons s et p du Ru dans la phase rutile contribuent peu aux niveaux d'energie orbitaux. Pour la premiere fois, nous trouvons que le pseudo-potentiel a norme conservee echoue a obtenir la DOS normale et les distributions de bande d'energie pour le Ru rutile sous -10 eV, alors que de telles distributions sont obtenues avec succes a partir de pseudo-potentiels ultra mous. Etudiant les proprietes optiques, nous trouvons que les phases rutile et du type Ca[Cl.sub.2] sont plus proches et que la phase fluorite a la reponse la plus sensible sur toute la region de reaction radiative. La fonction de perte d' energie electronique revele que la phase pyrite a la plus faible intensite relative. [Traduit par la Redaction], 1. Introduction The low resistivity and reactivity of Ru[O.sub.2] has made it technologically important as a strip-line conductor in integrated circuits, as a diffusion barrier in contact metallizations, etc. [1, [...]

Stripe rust, caused by Puccinia striiormis Westend f. sp. tritici, is one of the most important foliar diseases of wheat (Triticum aestivum L.) worldwide. Stripe rust resistance genes Yr27, Yr31, YrSp, YrV23, and YrCN19 on chromosome 2BS confer resistance to some or all Chinese P. striiormis f. sp. tritici races CYR31, CYR32, SY11-4, and SY11-14 in the greenhouse. To screen microsatellite (SSR) markers linked with YrCN19, Fl, FZ, and F3 populations derived from cross Ch377/CN19 were screened with race CYR32 and 35 SSR primer pairs. Linkage analysis indicated that the single dominant gene YrCN19 in cultivar CN19 was linked with SSR markers Xgwm410, Xgwm374, Xwmc477, and Xgwm382 on chromosome 2BS with genetic distances of 0.3, 7.9, 12.3, and 21.2 cM, respectively. Crosses of CN19 with wheat lines carrying other genes on chromosome 2B showed that all were located at different loci. YrCN19 is thus different from the other reported Yr genes in chromosomal location and resistance response and was therefore named Yr41. Prospects and strategies of using Yr41 and other Yr genes in wheat improvement for stripe rust resistance are discussed. Key words: microsatellite (SSR), stripe rust, wheat, gene mapping. La rouille jaune, causee par le Puccinia striiformis f. sp. tritici (PST), est l'une des plus importantes maladies foliaires chez le ble (Triticum aestivum L.) dans le monde. Les genes de resistance a la rouille jaune Yr27, Yr31, YrSp, YrV23 et YrCN19 sur le chromosome 2BS conferent la resistance a certaines ou toutes les races chinoises du PST (CYR31, CYR32, SY11-4 et SY11-14) en serre. Pour identifier des marqueurs microsatellites (SSR) lies au gene YrCN19, des populations Fl, FZ et F3 derivees du croisement Ch377/CN19 ont ete inoculees avec la race CYR32 et genotypees avec 35 paires d'amorces SSR. Une analyse de liaison genetique a revele que, chez le cultivar CN19, le gene dominant YrCN19 est lie aux marqueurs Xgwm410, Xgwm374, Xwmc477 et Xgwm382 sur le chromosome 2BS, respectivement a 0,3, 7,9, 12,3 et 21,2 cM. Des croisements entre CN19 et des lignees de ble portant d'autres genes de resistance sur le chromosome 2B ont montre que ces genes etaient situes a d'autres locus. Le gene YrCN19 est ainsi different des autres genes Yr connus tant pour ce qui est de sa position chromosomique que pour sa resistance. Pour ces raisons, il a ete nomme Yr41. Les auteurs discutent des perspectives et strategies en vue de l'exploitation du gene Yr41 et d'autres genes Yr en amelioration genetique du ble pour la resistance a la rouille jaune. Mots-cles : microsatellite (SSR), rouille jaune, ble, cartographie genetique. [Traduit par la Redaction], Introduction Wheat stripe rust, caused by Puccinia striiformis Westend f. sp. tritici (PST), is one of the most devastating diseases of wheat (Triticum aestivum L.) worldwide, especially in wheat-growing areas [...]