Structure of the specific combining ability between two species of Eucalyptus. II. A clustering approach and a multiplicative model

International audienceThe Eucalyptus breeding program of URPPI (a partnership between CIRAD-Fore t, Centre National de la Recherche Forestie re du Congo, and Unite dÕAforestation Industrielle du Congo) consists of a re- ciprocal recurrent selection scheme developed in the Congo between the two species Eucalyptus urophylla and Eucalyptus grandis. Two approaches are proposed in order to model and predict the speciÞc combining ability (SCA) between these species. The clustering ap- proach uses a simultaneous clustering procedure of the two species based on SCA and reveals heterotic groups coherent with the geographical origins of E. urophylla genotypes. The second approach uses a multiplicative model to partition the SCA into three multiplicative terms explaining 95% of the interactio

Structure of the specific combining ability between two species of Eucalyptus. I. RAPD data

International audienceWithin the context of the reciprocal recurrent selection scheme developed in 1989 by CIRAD-Fore t on Eucalyptus, RAPD essays were performed to assess the genetic diversity in the two species E. urophylla and E. grandis. The molecular markers were split into two parts: the speciÞc markers (present with di¤erent fre- quencies in the two species) and the common markers (present with similar frequencies in the two species). The study analyses the structure of genetic diversity within and between the two species of Eucalyptus. Dif- ferent genetic distances are worked out for use in pre- diction equations of the individual tree trunk volume of hybrids at 38 months. Each distance is expressed as the sum of the general genetic distance and the speciÞc genetic distance. The general genetic distance based on the double presence plus the double absence of bands seems to be an interesting co-variate to use in a factor regression model. Through this model the distance calculated between species explains the general com- bining ability (GCA) and the speciÞc combining ability (SCA) of the phenotypic character with a global coe¦c- ient of determination of 81.6

Yb-Yb correlations and crystal-field effects in the Kondo insulator YbB12 and its solid solutions

We have studied the effect of Lu substitution on the spin dynamics of the Kondo insulator YbB12 to clarify the origin of the spin-gap response previously observed at low temperature in this material. Inelastic neutron spectra have been measured in Yb1-xLuxB12 compounds for four Lu concentrations x = 0, 0.25, 0.90 and 1.0. The data indicate that the disruption of coherence on the Yb sublattice primarily affects the narrow peak structure occurring near 15-20 meV in pure YbB12, whereas the spin gap and the broad magnetic signal around 38 meV remain almost unaffected. It is inferred that the latter features reflect mainly local, single-site processes, and may be reminiscent of the inelastic magnetic response reported for mixed-valence intermetallic compounds. On the other hand, the lower component at 15 meV is most likely due to dynamic short-range magnetic correlations. The crystal-field splitting in YbB12 estimated from the Er3+ transitions measured in a Yb0.9Er0.1B12 sample, has the same order of magnitude as other relevant energy scales of the system and is thus likely to play a role in the form of the magnetic spectral response.Comment: 16 pages in pdf format, 9 figures. v. 2: coauthor list updated; extra details given in section 3.2 (pp. 6-7); one reference added; fig. 5 axis label change

Theory for Magnetic Anisotropy of Field-Induced Insulator-to-Metal Transition in Cubic Kondo Insulator YbB_{12}

Magnetization and energy gap of Kondo insulator YbB_{12} are calculated theoretically based on the previously proposed tight-binding model composed of Yb 5d$\epsilon$ and 4f $\Gamma_8$ orbitals. It is found that magnetization curves are almost isotropic, naturally expected from the cubic symmetry, but that the gap-closing field has an anisotropy: the gap closes faster for the field in (100) direction than in (110) and (111) directions, in accord with the experiments. This is qualitatively understood by considering the maximal eigenvalues of the total angular momentum operators projected on each direction of the magnetic field. But the numerical calculation based on the band model yields better agreement with the experiment.Comment: 4 pages, 4 figures, to appear in J. Phys. Soc. Jp

Study of water pollution by agricultural inputs: case of five intensive agriculture areas in Burkina Faso

Pour optimiser les rendements (agricoles), l’agriculture intensive nécessite une utilisation massive d’intrants agricoles dont les engrais chimiques, potentiellement sources de pollution des ressources en eau. La région du Sud - Ouest du Burkina, dont font partie les zones concernées par la présente étude, connaît une agriculture intensive du coton. Il est fait usage dans les champs de coton, d’engrais à base essentiellement d’azote, de phosphate, de potassium, mais également d’urée, de chlorure de potassium et de nitrate d’ammonium. Un total de 42 échantillons d’eau de surface, de puits et de forages ont fait l’objet d’analyses, afin d’évaluer l’impact de ces engrais sur la qualité des ressources en eau de consommation des populations sur une année. Eu égard à la nature des fertilisants utilisés, les paramètres essentiels suivants ont été ciblés : Nitrates, nitrites, ortho-phosphates, ammonium, potassium, conductivité électrique et dureté totale. Il ressort de ces investigations que les eaux de puits, pendant la saison hivernale, présentent des teneurs plus importantes en nitrates et potassium avec des valeurs maximales respectives de 178 mg/L (plus de 3 fois la valeur limite admise par l’OMS pour les eaux de consommation) et 55 mg/L pour une norme admise par l’OMS de 10 mg/L en potassium. Les ortho-phosphates, forme soluble du phosphore et les nitrites, présentent des teneurs inférieures aux normes admises. S’agissant des ions ammonium, un seul puits par sa position en aval d’un WC et d’un parc d’animaux, a donné des valeurs supérieures à la norme qui est fixée à 1,5 mg/L, atteignant ainsi 20 mg/L de N-NH+4. Les échantillons d’eau de forages sont exempts de toute contamination, alors que 33% des prélèvements d’eau de surface ont donné des teneurs dépassant la valeur limite admise seulement en potassium. Globalement, 61% des échantillons d’eau de puits sont contaminés par les nitrates, 67% par le potassium et 17% donnent des teneurs supérieures à la norme en ammonium. Ce qui permet d’en déduire qu’il y a une infiltration de pollution dans la nappe superficielle qui alimente les puits. La conductivité électrique et la dureté totale sans être excessives présentent les valeurs les plus importantes pour les mêmes sites que sont les puits, avec des valeurs maximales respectives de 1252 μS/cm et 202 mg/L de CaCO3

Molecular markers for discriminating Streptococcus pyogenes and S. dysgalactiae subspecies equisimilis

Given the increasing aetiological importance of Streptococcus dysgalactiae subspecies equisimilis in diseases which are primarily attributed to S. pyogenes, molecular markers are essential to distinguish these species and delineate their epidemiology more precisely. Many clinical microbiology laboratories rely on agglutination reactivity and biochemical tests to distinguish them. These methods have limitations which are particularly exacerbated when isolates with mixed properties are encountered. In order to provide additional distinguishing parameters that could be used to unequivocally discriminate these two common pathogens, we assess here three molecular targets: the speB gene, intergenic region upstream of the scpG gene (IRSG) and virPCR. Of these, the former two respectively gave positive and negative results for S. pyogenes, and negative and positive results for S. dysgalactiae subsp. equisimilis. Thus, a concerted use of these nucleic acid-based methods is particularly helpful in epidemiological surveillance to accurately assess the relative contribution of these species to streptococcal infections and diseases

Formation Mechanism of Hybridization Gap in Kondo Insulators based on a Realistic Band Model and Application to YbB12_{12}

A new LDA+U band calculation is performed on the Kondo insulator material YbB$_{12}$ and an energy gap of about 0.001Ryd is obtained. Based on this, a simple tight-binding model with 5d$\epsilon$ and 4f $\Gamma_8$ orbitals on Yb atoms and the nearest neighbor $\sigma$-bonds between them is constructed with a good agreement to the above the LDA+U calculation near the gap. The density of states is also calculated and the shape is found to be very asymmetric with respect to the gap. A formation mechanism of the gap is clarified for the first time in a realistic situation with the orbital degeneracies in both conduction bands and the f states. This model can be a useful starting point for incorporating the strong correlation effect, and for understanding all the thermal, thermoelectric, transport and magnetic properties of YbB$_{12}$.Comment: 15 pages, 15 figures, to appear in J. Phys. Soc. Jpn. Vol. 72 No. 5 (2003

Excitonic Bound State in the Extended Anderson Model with c-f Coulomb Interaction

The Anderson model with the Coulomb interaction between the local and conduction electrons is studied in the semiconducting phase. Based on a perturbation theory from the atomic limit, leading contributions for the c-f Coulomb interaction are incorporated as a vertex correction to hybridization. An analytical solution shows that the effective attraction in the intermediate states leads to a bound state localized at the local electron site. Self-consistent equations are constructed as an extension of the non-crossing approximation (NCA) to include the vertex part yielding the bound state. A numerical calculation demonstrates the excitonic bound state inside the semiconducting gap for single-particle excitations, and a discontinuity at the gap edge for magnetic excitations.Comment: 15 pages, 20 figures, submitted to J. Phys. Soc. Jp

Indirect and direct energy gaps in the Kondo semiconductor YbB12

Optical conductivity [$\sigma(\omega)$] of the Kondo semiconductor YbB$_{12}$ has been measured over wide ranges of temperature ($T$=8$-$690 K) and photon energy ($\hbar \omega \geq$ 1.3 meV). The $\sigma(\omega)$ data reveal the entire crossover of YbB$_{12}$ from a metallic electronic structure at high $T$ into a semiconducting one at low $T$. Associated with the gap development in $\sigma(\omega)$, a clear onset is newly found at $\hbar\omega$=15 meV for $T \leq$ 20 K. The onset energy is identified as the gap width of YbB$_{12}$ appearing in $\sigma(\omega)$. This gap in \sigma(\omega)$is interpreted as the indirect gap, which has been predicted in the band model of Kondo semiconductor. On the other hand, the strong mid-infrared (mIR) peak observed in$\sigma(\omega)$ is interpreted as arising from the direct gap. The absorption coefficient around the onset and the mIR peak indeed show characteristic energy dependences expected for indirect and direct optical transitions in conventional semiconductors.Comment: 4 pages, 3 figures, submitted to J. Phys. Soc. Jp

Fabrication and mechanical testing of a new sandwich structure with carbon fiber network core

The aim is the fabrication and mechanical testing of sandwich structures including a new core material known as fiber network sandwich materials. As fabrication norms for such a material do not exist as such, so the primary goal is to reproduce successfully fiber network sandwich specimens. Enhanced vibration testing diagnoses the quality of the fabrication process. These sandwich materials possess low structural strength as proved by the static tests (compression, bending), but the vibration test results give high damping values, making the material suitable for vibro-acoustic applications where structural strength is of secondary importance e.g., internal panelling of a helicopter