607 research outputs found

    On the expressive power of read-once determinants

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    We introduce and study the notion of read-kk projections of the determinant: a polynomial f∈F[x1,
,xn]f \in \mathbb{F}[x_1, \ldots, x_n] is called a {\it read-kk projection of determinant} if f=det(M)f=det(M), where entries of matrix MM are either field elements or variables such that each variable appears at most kk times in MM. A monomial set SS is said to be expressible as read-kk projection of determinant if there is a read-kk projection of determinant ff such that the monomial set of ff is equal to SS. We obtain basic results relating read-kk determinantal projections to the well-studied notion of determinantal complexity. We show that for sufficiently large nn, the n×nn \times n permanent polynomial PermnPerm_n and the elementary symmetric polynomials of degree dd on nn variables SndS_n^d for 2≀d≀n−22 \leq d \leq n-2 are not expressible as read-once projection of determinant, whereas mon(Permn)mon(Perm_n) and mon(Snd)mon(S_n^d) are expressible as read-once projections of determinant. We also give examples of monomial sets which are not expressible as read-once projections of determinant

    Effet magnéto-optique et optique des couches minces à base de ferrite de cobalt

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    Cette Ă©tude a pour but la mesure des effets magnĂ©to-optiques (rotation Faraday) en fonction du champ magnĂ©tique appliquĂ© et en fonction de la longueur d’onde, ainsi que la mesure de la transmittance (effet optique) des couches minces Ă  base de ferrite de cobalt. Les rĂ©sultats montrent une forte rotation Faraday spĂ©cifique avec des cycles d'hystĂ©rĂ©sis et des spectres de transmittance d'une bonne transparence dans la gamme TĂ©lĂ©com (≈1550 nm).Mots-clĂ©s: ferrite de cobalt, sol-gel, couches minces, rotation Faraday, transmittance. Magneto-optical effect and optical thin films cobalt ferriteThis study was designed to measure the magneto-optical effect (Faraday rotation) according to the applied magnetic field and a function of the wavelength and the transmittance measurement (optical effect) thin film based on cobalt ferrite. The results show a high specific Faraday rotation with hysteresis cycles and transmittance spectra of a good transparency in the range Telecom (≈1550 nm).Keywords: cobalt ferrite, sol-gel thin films, Faraday rotation, transmittance

    Review: Towards the agroecological management of ruminants, pigs and poultry through the development of sustainable breeding programmes. II. Breeding strategies

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    Agroecology uses ecological processes and local resources rather than chemical inputs to develop productive and resilient livestock and crop production systems. In this context, breeding innovations are necessary to obtain animals that are both productive and adapted to a broad range of local contexts and diversity of systems. Breeding strategies to promote agroecological systems are similar for different animal species. However, current practices differ regarding the breeding of ruminants, pigs and poultry. Ruminant breeding is still an open system where farmers continue to choose their own breeds and strategies. Conversely, pig and poultry breeding is more or less the exclusive domain of international breeding companies which supply farmers with hybrid animals. Innovations in breeding strategies must therefore be adapted to the different species. In developed countries, reorienting current breeding programmes seems to be more effective than developing programmes dedicated to agroecological systems that will struggle to be really effective because of the small size of the populations currently concerned by such systems. Particular attention needs to be paid to determining the respective usefulness of cross-breeding v. straight breeding strategies of well-adapted local breeds. While cross-breeding may offer some immediate benefits in terms of improving certain traits that enable the animals to adapt well to local environmental conditions, it may be difficult to sustain these benefits in the longer term and could also induce an important loss of genetic diversity if the initial pure-bred populations are no longer produced. As well as supporting the value of within-breed diversity, we must preserve between-breed diversity in order to maintain numerous options for adaptation to a variety of production environments and contexts. This may involve specific public policies to maintain and characterize local breeds (in terms of both phenotypes and genotypes), which could be used more effectively if they benefited from the scientific and technical resources currently available for more common breeds. Last but not least, public policies need to enable improved information concerning the genetic resources and breeding tools available for the agroecological management of livestock production systems, and facilitate its assimilation by farmers and farm technicians

    Etude des propriétés magnéto-optiques des couches minces à base de ferrite de cobalt obtenues par voie sol-gel

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    Ce travail est consacrĂ© Ă  l'Ă©tude des propriĂ©tĂ©s magnĂ©to-optiques (rotation Faraday) de couches minces Ă  base de ferrite de cobalt obtenues par voie sol-gel. La contribution de la mĂ©thode sol-gel utilisĂ©e est trĂšs importante et cela permet d’obtenir des couches minces ayant une bonne qualitĂ© optique. Cette dĂ©marche nĂ©cessite juste l’utilisation de liquides magnĂ©tiques ou ferro fluides, de prĂ©curseurs de silice (pas cher) et d’un substrat de verre. Le but est d’obtenir des couches minces et Ă©tudier leurs propriĂ©tĂ©s magnĂ©to-optiques. Les courbes obtenues Ă  la longueur d’onde de 820 nm prĂ©sentent des cycles d’hystĂ©rĂ©sis avec des rotations rĂ©manentes de 40, 60 et 81°/cm. Ces rĂ©sultats prĂ©sentent une excellente rotation Faraday de 212, 318 et 340°/cm Ă  la longueur d’onde de 820 nm. Ceci montre la forte potentialitĂ© de la matrice sol-gel dopĂ©e.Mots-clĂ©s: nanoparticules magnĂ©tiques, ferrite de cobalt, sol-gel, couches minces, rotation Faraday. Study of themagneto-optical properties of thin films cobalt ferrite obtainedby the sol-gel This work is devoted to the study of magneto-optical (Faraday rotation) of thin cobalt ferrite layers obtained by sol-gel. The contribution of the sol-gel method is very important and it allows obtaining thin film shaving a good optical quality. This requires only the use of magnetic fluids or ferro fluids, silica precursors (cheap) and a glass substrate. The goal is to obtain thin layers and study their magneto-optical properties. The curves obtained for the wave length of 820 nm have hysteresis loops with retentive rotations of 40, 60 and 81°/ cm. These results show excellentFaradayrotation 212, 318 and 340°/cm ata wave length of 820 nm. This shows the high potential of the doped sol-gel matrix.Keywords: agnetic nanoparticles, cobalt ferrite, sol-gel, thin films, Faraday rotation

    A new approach to local hardness

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    The applicability of the local hardness as defined by the derivative of the chemical potential with respect to the electron density is undermined by an essential ambiguity arising from this definition. Further, the local quantity defined in this way does not integrate to the (global) hardness - in contrast with the local softness, which integrates to the softness. It has also been shown recently that with the conventional formulae, the largest values of local hardness do not necessarily correspond to the hardest regions of a molecule. Here, in an attempt to fix these drawbacks, we propose a new approach to define and evaluate the local hardness. We define a local chemical potential, utilizing the fact that the chemical potential emerges as the additive constant term in the number-conserving functional derivative of the energy density functional. Then, differentiation of this local chemical potential with respect to the number of electrons leads to a local hardness that integrates to the hardness, and possesses a favourable property; namely, within any given electron system, it is in a local inverse relation with the Fukui function, which is known to be a proper indicator of local softness in the case of soft systems. Numerical tests for a few selected molecules and a detailed analysis, comparing the new definition of local hardness with the previous ones, show promising results.Comment: 30 pages (including 6 figures, 1 table

    Negotiations of minority ethnic rugby league players in the Cathar country of France

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    This article is based on new empirical, qualitative research with minority ethnic rugby league players in the southwest of France. Drawing on similar research on rugby league in the north and the south of England, the article examines how rugby league, traditionally viewed as a white, working-class male game (Collins, 2006; Denham, 2004; Spracklen, 1995, 2001) has had to re-imagine its symbolic boundaries as they are constituted globally and locally to accommodate the needs of players from minority ethnic backgrounds. In particular, the article examines the sense in which experiences of minority ethnic rugby league players in France compare with those of their counterparts in England (Spracklen, 2001, 2007), how rugby league is used in France to construct identity, and in what sense the norms associated with the imaginary community of rugby league are replicated or challenged by the involvement of minority ethnic rugby league players in France. Questions about what it means to be (provincial, national) French (Kumar, 2006) are posed, questions that relate to the role of sport in the construction of Frenchness, and in particular the role of rugby league (and union). © Copyright ISSA and SAGE Publications

    A cost comparison of rasburicase versus dialysis in the management of children with acute leukaemia and lymphoma at a South African centre

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    Background: Tumour lysis syndrome is a common complication of haematological malignancies and has historically been managed with hyperhydration, urine alkalinisation and allopurinol with renal dialysis reserved for patients in acute renal failure. Rasburicase has been shown to drastically reduce the need for dialysis; however, its use is limited in developing countries owing to its cost and availability. Aim: This retrospective analysis aimed to compare the cost to state per patient of rasburicase compared to dialysis in the management and prevention of tumour lysis syndrome in paediatric patients presenting with haematological malignancies admitted to Red Cross War Memorial Children’s Hospital (RCWMCH). Setting: Red Cross War Memorial Children’s Hospital. Methods: Patients from two consecutive 35 month periods, before and after the availability of rasburicase at RCWMCH, were grouped according to treatment modality, and the cumulative costs of hospitalisation, dialysis and drug administration were compared. Results: The groups were comparable in mean age and gender. The mean total length of hospital stay was 10.04 days shorter for the rasburicase group than the dialysis group with the average cost per patient in the rasburicase group being R40 989.64 lower than the dialysis group. Conclusion: The use of rasburicase results in a significant per patient cost saving when compared to dialysis, which often requires intensive care admission, and results in extended hospitalisation. The study supports the continued use of rasburicase as an essential adjunct in the management and prevention of tumour lysis syndrome, reaffirming its use as a cost-effective and efficient drug
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