Fractionation of nitrogen isotopes by animals: a further complication to the use of variations in the natural abundance of ¹⁵N for tracer studies

A study of the fractionation of nitrogen isotopes in the diet by cattle is described and the results discussed. Compared with the diet, urine had a lower ratio of ¹⁵N to ¹⁴N, but faeces, blood and milk all had a higher ratio. It is argued that the use of natural ¹⁵N as a tracer in grazed ecosystems is more complicated than was at first thought

Denitrification by rhizobia: A possible factor contributing to nitrogen losses from soils

The intensive pastoral farming system on which New Zealand animal production is based is almost completely dependent upon the rhizobium-legurne symbiosis for the fixed nitrogen required for pasture production. The average annual fixation has been measured as 184 kg nitrogen/ha in developed lowland pastures Hoglund et cii., 1979 and about 13 kg nitrogen/ha in poorly developed bill country pastures (Grant and Lambert, 1979). From these figures it can be estimated that rhizobia in New Zealand pastures fix in excess of one million tonnes of nitrogen an nually. The current annual application of fertilizer nitrogen to pastures is about 12 500 tonnes (O'Connor, 1979)

Colonization of Heterodera glycines cysts by Fusarium solani form A, the cause of sudden death syndrome, and other fusaria in soybean fields in the midwestern and southern United States

La forme A du Fusarium solani et d'autres fusariums ont été isolés de kystes de l' Heterodera glycines désinfectés en surface et récoltés dans la rhizosphère de plants de soja ( Glycine max) présentant des symptômes du syndrome de la mort subite et récoltés dans des champs du centre-ouest et du sud des États-Unis. Deux formes du Fusarium solani, pathogènes du soja, ont été isolées : la forme A, responsable du syndrome de la mort subite, et la forme B, responsable d'une maladie des semis et d'un pourridié fusarien. La forme B du Fusarium solani a été isolée plus souvent que la forme A. La forme A du Fusarium solani était présente dans les kystes de 82 % des champs infestés de kystes et avec des plantes présentant des symptômes du syndrome de la mort subite, avec des fréquences maximale et moyenne (champs et années confondus) de respectivement 28 et 7 %. Ce champignon n'a pas été retrouvé dans les kystes de cinq champs exempts du syndrome de la mort subite. Des isolats de la forme B du F. solani ont été très fréquemment retrouvés dans les kystes de chacun de ces champs ; la forme B du F. solani était présente dans les kystes de 94 % des champs envahis de kystes et avec le syndrome de la mort subite, avec des fréquences maximale et moyenne (champs et années confondus) de respectivement 48 et 16 %. Le Fusarium oxysporum (l'espèce ayant la troisième fréquence moyenne d'isolement), le F. chlamydosporum, le F. equiseti, le F. moniliforme, et le F. pallidoroseum (syn. F. semitectum) ont aussi été isolés. En se basant sur les densités des populations de kystes dans le sol et les pourcentages de kystes colonisés par la forme A du F. solani, le maximum et la moyenne de kystes colonisés par 500 cm3 de sol de la rhizosphère étaient respectivement de 149 et 22. Une grande proportion de la forme A du Fusarium solani a survécu dans des kystes dans du sol entreposé durant 8 mois à approximativement 10 C, ce qui montre la possibilité d'une hibernation dans des kystes entre les saisons de croissance du soja. Le taux de survie de la forme A du Fusarium solani était faible dans des kystes dans du sol entreposé durant 20 mois. Le maximum et la moyenne de kystes par 500 cm3 de sol étaient plus élevés pour la forme B du F. solani, avec respectivement 700 et 82, que pour la forme A du F. solani. De plus, les taux de survie des kystes dans du sol entreposé durant 8 et 20 mois étaient aussi plus élevés. Les isolats de la forme A du F. solani provenant de kystes étaient aussi virulents sur le soja que des isolats provenant de racines malades.Fusarium solani form A and other fusaria were isolated from surface disinfested cysts of Heterodera glycines collected from the rhizosphere of soybean (Glycine max) plants symptomatic for sudden death syndrome, collected from fields in the midwestern and southern United States. Two forms of Fusarium solani pathogenic to soybean were isolated: form A, the cause of sudden death syndrome, and form B, the cause of seedling disease and root rot. Fusarium solani form B was more frequently isolated than form A. Fusarium solani form A occurred in cysts in 82% of the cystinfested fields containing plants symptomatic of sudden death syndrome, with maximum and average isolation frequencies (across fields and years) of 28 and 7%, respectively. This fungus was not found in cysts from five fields lacking sudden death syndrome. Isolates of F. solani form B were found in high frequency in cysts from each of those fields; F. solani form B occurred in cysts in 94% of the cyst-infested fields containing sudden death syndrome, with maximum and average isolation frequencies (across years and fields) of 48 and 16%, respectively. Fusarium oxysporum (the species with the third highest average isolation frequency), F. chlamydosporum, F. equiseti, F. moniliforme, and F. pallidoroseum (syn. F. semitectum) were also isolated. Based on cyst population densities occurring in soil and percentages of cysts colonized by F. solani form A, the maximum and average numbers of colonized cysts per 500 cm3 of rhizosphere soil were 149 and 22, respectively. Fusarium solani form A survived at a high rate in cysts in soil stored for 8 months at ca 10 C, indicating an ability to overwinter in cysts between soybean growing seasons. Fusarium solani form A had a poor survival rate in cysts in soil stored for 20 months. Compared to F. solani form A, maximum and average numbers of F. solani form B in cysts per 500 cm3 soil were higher, at 700 and 82, respectively. Furthermore, the survival rate of cysts in soil stored for 8 and 20 months was also higher. Isolates of F. solani form A from cysts were as virulent on soybean as isolates from diseased roots

Geological controls on the geometry of incised-valley fills: Insights from a global dataset of late-Quaternary examples

Incised valleys that develop due to relative sea-level change are common features of continental shelves and coastal plains. Assessment of the factors that control the geometry of incised-valley fills has hitherto largely relied on conceptual, experimental or numerical models, else has been grounded on case studies of individual depositional systems. Here, a database-driven statistical analysis of 151 late-Quaternary incised-valley fills has been performed, the aim being to investigate the geological controls on their geometry. Results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of incised-valley fills through their effect on the degree and rate of river incision, and on river size and mobility. The studied incised-valley fills developed along active margins are thicker and wider, on average, than those along passive margins, suggesting that tectonic setting exerts a control on the geometry of incised-valley fills, likely through effects on relative sea-level change and river behaviour, and in relation to distinct characteristics of basin physiography, water discharge and modes of sediment delivery. Valley-fill geometry is positively correlated with the associated drainage-basin size, confirming the dominant role of water discharge. Climate is also inferred to exert a potential control on valley-fill dimensions, possibly through modulations of temperature, peak precipitation, vegetation and permafrost, which would in turn affect water discharge, rates of sediment supply and valley-margin stability. Shelves with slope breaks that are currently deeper than 120 m contain incised-valley fills that are thicker and wider, on average, than those hosted on shelves with breaks shallower than 120 m. No correlation exists between valley-fill thickness and present-day coastal-prism convexity, which is measured as the difference in gradient between lower coastal plains and inner shelves. These findings challenge some concepts embedded in sequence stratigraphic thinking, and have significant implications for analysis and improved understanding of source-to-sink sediment route-ways, and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs

Constraints on R-parity violating supersymmetry from leptonic and semileptonic tau, B_d and B_s decays

We put constraints on several products of R-parity violating lambda lambda' and lambda' lambda' type couplings from leptonic and semileptonic tau, B_d and B_s decays. Most of them are one to two orders of magnitude better than the existing bounds, and almost free from theoretical uncertainties. A significant improvement of these bounds can be made in high luminosity tau-charm or B factories.Comment: 14 pages, latex. A few references added, two typos corrected. Version to be published in Physical Review

The influence of gene expression time delays on Gierer-Meinhardt pattern formation systems

There are numerous examples of morphogen gradients controlling long range signalling in developmental and cellular systems. The prospect of two such interacting morphogens instigating long range self-organisation in biological systems via a Turing bifurcation has been explored, postulated, or implicated in the context of numerous developmental processes. However, modelling investigations of cellular systems typically neglect the influence of gene expression on such dynamics, even though transcription and translation are observed to be important in morphogenetic systems. In particular, the influence of gene expression on a large class of Turing bifurcation models, namely those with pure kinetics such as the Gierer–Meinhardt system, is unexplored. Our investigations demonstrate that the behaviour of the Gierer–Meinhardt model profoundly changes on the inclusion of gene expression dynamics and is sensitive to the sub-cellular details of gene expression. Features such as concentration blow up, morphogen oscillations and radical sensitivities to the duration of gene expression are observed and, at best, severely restrict the possible parameter spaces for feasible biological behaviour. These results also indicate that the behaviour of Turing pattern formation systems on the inclusion of gene expression time delays may provide a means of distinguishing between possible forms of interaction kinetics. Finally, this study also emphasises that sub-cellular and gene expression dynamics should not be simply neglected in models of long range biological pattern formation via morphogens

Identification of quantitative trait loci for resistance against soybean sudden death syndrome caused by Fusarium tucumaniae

The objective of this work was to identify genomic regions that underlie resistance to Fusarium tucumaniae sp. nov., the causing agent of sudden death syndrome (SDS) in soybean in South America, using a population with a genetic background different from that previously reported for Fusarium virguliforme sp. nov. (F. solani f. sp. glycines), also responsible for SDS in soybean. Although major genes and quantitative trait loci (QTL) for SDS resistance have been identified, little is known about the same disease caused by Fusarium tucumaniae sp. nov., in South America. To identify genetic factors related to resistance to F. tucumaniae and DNA markers associated with them, a QTL analysis was performed using recombinant inbred lines. The map locations of the four loci, here identified, differed from those SDS resistance QTL previously described. It was screened a residual heterozygous line (RHL), which was heterozygous around the most effective QTL, RSDS1, and homozygous for the other genomic regions. The genetic effect of RSDS1 was confirmed using near-isogenic lines (NIL) derived from the RHL. The line which was homozygous for the Misuzudaizu genotype showed resistance levels comparable with that of the line homozygous for the Moshidou Gong 503 genotype

Quel rôle peut-on imputer aux banques à charte canadiennes dans la transmission des chocs monétaires des années quatre-vingt?

Cette recherche s’inscrit dans la foulée de nombreux travaux entrepris suite aux publications de Bernanke et Blinder (1988, 1992) ayant remis à l’avant-plan le rôle joué par le système bancaire dans la transmission de la politique monétaire. Nous proposons d’examiner la dynamique inhérente à certains postes du bilan des banques à charte canadiennes suite aux mouvement des principaux taux d’intérêt, habituellement jugés révélateurs des conditions monétaires du moment. Pour ce faire, nous avons recours à un modèle VAR hebdomadaire comportant à la fois, des éléments de l’actif et du passif des banques ainsi que les taux de rendement associés à divers instruments financiers. Cependant, dans le but de bien encadrer cette analyse, nous développons un modèle formel du comportement d’une banque où les seuls changements aux postes de son bilan suite aux mouvements de taux d’intérêt sont dictés par des ajustements de portefeuille visant à tirer avantage des écarts se creusant entre ceux-ci. Ce modèle théorique est soumis aux variations de taux d’intérêt issues du modèle empirique VAR. Les mouvements observés aux postes du bilan de cette banque « témoin » fournissent un guide utile permettant d’interpréter de façon éclairée les résultats empiriques obtenus. À cet égard, l’exercice proposé montre qu’il est possible d’établir un parallèle assez étroit entre l’évolution des postes du bilan de la banque hypothétique et celle captée par le modèle VAR et ainsi apporte un certain support à l’approche traditionnelle sur le rôle joué par les banques dans la transmission des chocs monétaires.This paper can be seen as a contribution to a growing literature initiated by Bernanke and Blinder (1988, 1992) which have examined the role played by the banking system in the transmission of monetary policy. We propose to study the dynamic behaviour of the balance sheet of Canadian chartered banks following a shock to some key interest rates which are good indicators of the prevailing monetary conditions. More specifically, we estimate a weekly VAR model which comprises key asset and liabilities elements as well as rates of return on major financial instruments. However, to guide this empirical inquiry, we set up a model of a representative bank which adjusts its balance sheet elements according to the interest rate spreads arising in the financial markets. This theoretical model is then subjected to the same interest rate shocks than those imposed on the VAR model: the adjustments observed in this laboratory will prove quite useful to assess the significance of the empirical results uncovered by the VAR model. Overall, we find that both approaches give rise to quite similar dynamic responses which tends to support the traditional role of the banking sector in the transmission of monetary policy

Study of the B^0 Semileptonic Decay Spectrum at the Upsilon(4S) Resonance

We have made a first measurement of the lepton momentum spectrum in a sample of events enriched in neutral B's through a partial reconstruction of B0 --> D*- l+ nu. This spectrum, measured with 2.38 fb**-1 of data collected at the Upsilon(4S) resonance by the CLEO II detector, is compared directly to the inclusive lepton spectrum from all Upsilon(4S) events in the same data set. These two spectra are consistent with having the same shape above 1.5 GeV/c. From the two spectra and two other CLEO measurements, we obtain the B0 and B+ semileptonic branching fractions, b0 and b+, their ratio, and the production ratio f+-/f00 of B+ and B0 pairs at the Upsilon(4S). We report b+/b0=0.950 (+0.117-0.080) +- 0.091, b0 = (10.78 +- 0.60 +- 0.69)%, and b+ = (10.25 +- 0.57 +- 0.65)%. b+/b0 is equivalent to the ratio of charged to neutral B lifetimes, tau+/tau0.Comment: 14 page, postscript file also available at http://w4.lns.cornell.edu/public/CLN

Radiative Decay Modes of the D0D^{0} Meson

Using data recorded by the CLEO-II detector at CESR we have searched for four radiative decay modes of the $D^0$ meson: $D^0\to\phi\gamma$, $D^0\to\omega\gamma$, $D^0\to\bar{K}^{*}\gamma$, and $D^0\to\rho^0\gamma$. We obtain 90% CL upper limits on the branching ratios of these modes of $1.9\times 10^{-4}$, $2.4\times 10^{-4}$, $7.6\times 10^{-4}$ and $2.4\times 10^{-4}$ respectively.Comment: 15 page postscript file, postscript file also available through http://w4.lns.cornell.edu/public/CLN