On the thermoelastic analysis of solar cell arrays and related material properties

Accurate prediction of failure of solar cell arrays requires accuracy in the computation of thermally induced stresses. This was accomplished by using the finite element technique. Improved procedures for stress calculation were introduced together with failure criteria capable of describing a wide range of ductile and brittle material behavior. The stress distribution and associated failure mechanisms in the N-interconnect junction of two solar cell designs were then studied. In such stress and failure analysis, it is essential to know the thermomechanical properties of the materials involved. Measurements were made of properties of materials suitable for the design of lightweight arrays: microsheet-0211 glass material for the solar cell filter, and Kapton-H, Kapton F, Teflon, Tedlar, and Mica Ply PG-402 for lightweight substrates. The temperature-dependence of the thermal coefficient of expansion for these materials was determined together with other properties such as the elastic moduli, Poisson's ratio, and the stress-strain behavior up to failure

Differences observed in the graft compatibility between some cultivars of Muscadine grape (Vitis rotundifolia Michx.) and European grape (Vitis vinifera L. cv. Cabernet Sauvignon).

Well-known graft incompatibility between the Muscadine grape (Vitis rotundifolia MICHX.) and European grape (V. vinifera L.) is easily overcome with the green grafting method. But the results depend greatly on the genotypes of the Muscadine grape used. Typical symptoms of incompatibility appear after one year's growth when V. vinifera cv. Cabernet Sauvignon is grafted on Muscadine varieties like Carlos and Male. Other Muscadine varieties like Yuga and Noble do not show any symptom. These observations rule out the hypothesis that graft incompatibility between Muscadine grape and European grape was due to the existing structural and anatomical differences between these two species. Macroscopical and microscopical examination of the graft union lets us think that the observed symptoms can be related to a translocated incompatibility. The role of a hypothetical grafttransmissible factor is under investigation.Différences observées dans la compatibilité au greffage de quelques variétés de Muscadine (Vitis rotundifolia Michx.) avec Vitis vinifera L. cv. Cabernet SauvignonL'incompatibilité au greffage reconnue depuis longtemps entre la Muscadine (Vitis rotundifolia MICHX.) et la vigne européenne (V. vinifera L.) est facilement surmontable par la méthode de la greffe en vert. Mais les résultats varient en fonction de la variété de Muscadine utilisée. Des symptômes typiques d'incompatibilité se manifestent tardivement lorsque V. vinifera cv. Cabernet Sauvignon est greffé sur les variétés de Muscadine Carlos ou Male. A l'opposé, les variétés Yuga et Noble ne manifestent aucun symptôme. Ces observations permettent d'écarter l'hypothèse selon laquelle l 'incompatibilité au greffage entre V. rotundifolia et V. vinifera serait due aux différences anatomiques et structurales qui existent entre ces deux espèces. L'examen macroscopique et microscopique du point de greffe laisse penser que les symptômes observés peuvent être rattachés à une incompatibilité «de translocation». L'hypothèse d'un facteur viral responsable des différences observées d'incompatibilité au greffage est actuellement en cours de vérification

The Effects of Amplification Bias in Gravitational Microlensing Experiments

Although a source star is fainter than the detection limit imposed by crowding, it is still possible to detect an event if the star is located in the seeing disk of a bright star is and gravitationally amplified: amplification bias. Using a well-constrained luminosity function, I show that $\sim 40\%$ of events detected toward the Galactic bulge are affected by amplification bias and the optical depth might be overestimated by a factor $\sim 1.7$. In addition, I show that if one takes amplification bias into consideration, the observed time scale distribution matches significantly better, especially in the short time-scale region, with the distribution expected from a mass-spectrum model in which lenses are composed of the known stellar population plus an additional population of brown dwarfs than it is without the effect of the amplification bias.Comment: 16 pages including 4 figures, ApJ, submitte

Effect of some genetic and environmental factors on spontaneous polyembryony in grape (Vitis vinifera L.)

Variability of polyembryony was studied in 35 varieties of Vitis vinifera L. The observed frequency of twin seedlings is varying from O to 0.35 °/o with a mean of 0.054 %. Merlot is the most interesting variety.Polyembryony in grape is mainly under genetieal control and is a varietal characteristie. However, polyembryony is influenced by environmental factors: A low berry set, induced by climatie conditions or other factors, is generally correlated with a high frequency of twin seedlings.Differences observed in the kinetics of germination and influence of the length of chilling show that polyembryonie seeds are less fit to germinate than monoembryonie seeds. Optimal temperature for germination of polyembryonie seeds is 23 °C; higher temperatures increase the competition between polyembryos and the occurrence of "cryptie twins".Weakness and lethality of numerous plantlets obtained from polyembryonie seeds reduce strongly the probability of obtaining haploid plants. So far, only diploid seedlings were obtained, but apparent instability of the haploid condition in grape let us think that diploid homozygote seedlings originating from parthenogenetie development of cells of the embryo sac, could be produced by this way.Effet de quelques facteurs génétiques et du milieu sur la polyembryonie spontanéechez la vigne (Vitis vinifera L.)La variabilité du caractére «polyembryonie spontanée» été étudiée sur 35 cépages de V. vinifera L. La fréquence observée des plantules jumelles parmi les pépins germés varie de O à 0,35 0/o, avec une moyenne de 0,054 0/o. Merlot est la variété la plus intéressante à cet égard.La polyembryonie chez la vigne semble être une caractéristique variétale contrôlée génétiquement. Cependant, elle peut être influencée par certains facteurs du milieu: Un faible taux de nouaison, induit par les conditions climatiques ou tout autre facteur, est généralement corrélé avec une fréquence élevée de polyembryonie. Les différences observées dans les cinétiques comparées de germination, et l'influence de la durée de stratification des pépins au froid, montrent que les pépins polyembryonnés sont moins aptes à germer que les pépins monoembryonnés. La température optimale de germination des pépins polyembryonnés est 23 °C; une température plus haute augmente la compétition entre les embryons multiples, et accroît la fréquence des «jumeaux cachés».La faiblesse et la léthalité de nombreuses plantules issues des pépins polyembryonnés réduit fortement la probabilité d'obtenir des plantes haploïdes. Jusqu'à maintenant, seules des plantules diploïdes ont pu être obtenues. Cependant, l'instabilité apparente de l'état haploïde chez lo vigne laisse penser que des plantes diploïdes homozygotes, issues du développement parthénogénétique de cellules du sac embryonnaire, pourraient être produites par cette voie

Specific heat of single crystal MgB_2: a two-band superconductor with two different anisotropies

Heat-capacity measurements of a 39 microgramm MgB_2 single crystal in fields up to 14 T and below 3 K allow the determination of the low-temperature linear term of the specific heat, its field dependence and its anisotropy. Our results are compatible with two-band superconductivity, the band carrying the small gap being isotropic, that carrying the large gap having an anisotropy of ~ 5. Three different upper critical fields are thus needed to describe the superconducting state of MgB2.Comment: 4 pages, 4 figures - V2: Bibliography updated and some typo corrected. One reference added - V3: version accepted for publication in PRL, changes made in the tex

In vitro propagation of Vitis x Muscadinia hybrids by microcuttings or axillary budding

Research Not

Green-grafting between Muscadine grape (Vitis rotundifolia Michx.) and bunch grapes (Euvitis spp.) as a tool for physiological and pathological investigations

Well-known graft incompatibility between Muscadine grapes (V. rotundifolia Michx.) and bunch grapes (Euvitis spp.), seems to be easily overcome with the greengrafting method. Attempts at reciprocal graftings between V. rotundifolia and V. rupestris, using this method, have been successful. However, the number of successful unions is comparatively lesser when V. rotundifolia is used as scion.These results are discussed according to the differences of anatomical structure between the two species. The possibility of a delayed incompatibility cannot be ruled out, however, the interest in the method is not to use directly V. rotundifolia as rootstock, but to make easy tests of the value of this species as parent in interspecific breeding programs.Le greffage en vert entre la Muscadine (Vitis rotundifolia Michx.) et les vignes vraies (Euvitis spp.) comme moyen d'études physiologiques et pathologiquesL'incompatibilité au greffage reconnue depuis longtemps entre les espèces de la section Muscadinia et les espèces de la section Euvitis du genre Vitis semble être facilement surmontable par la technique du greffage en vert. Des essais de greffages réciproques entre V . rotundifolia et V. rupestris ont été couronnés de succès en employant cette méthode. Toutefois, le taux de reprise est comparativement moins élevé lorsque V . rotundifolia est utilisé comme greffon.Ces résultats sont discutés en fonction des différences de structure anatomique entre les deux espèces. L'éventualité d'une incompatibilité retardée ne peut pas être écartée, mais l'utilité de cette méthode n'est pas tant de permettre une utilisation directe de V . rotundifolia comme porte-greffe, que de faciliter la réalisation de t ests visant à mieux préciser les aptitudes de cette espèce comme géniteur dans un programme d'hybridation

Inheritance of seedlessness in grapevine (Vitis vinifera L.)

Despite considerable efforts made by breeders for over 70 years, inheritance of seedlessness in grapevine is not clearly defined. None of the numerous hypotheses proposed until now is satisfying, whether they are based on recessive or dominant genes. We measured precisely the phenotypic expression of the seeded/seedless character in a progeny obtained by crossing two partially seedless selections and using in ovulo and in vitro culture to rescue embryos. We propose the hypothesis that inheritance of seedlessness in grapevine is based on a complex system whereby the expression of three independently inherited recessive genes is controlled by a dominant regulator gene. This hypothesis was compared to other results published in the scientific literature and appeared coherent enough to be used as a theoretical basis for further work on seedlessness inheritance in grapevine. Attempts to explain the control of seedlessness involve interactions with endogenous gibberellins. The consequences of such a model for the development of breeding programs for seedless table grapes, and particularly for the use of molecular biology techniques, are discussed

Calorimetric Investigation of CeRu2Ge2 up to 8 GPa

We have developed a calorimeter able to give a qualitative picture of the specific heat of a sample under high pressure up to approximately 10 GPa. The principle of ac-calorimetry was adapted to the conditions in a high pressure clamp. The performance of this technique was successfully tested with the measurement of the specific heat of CeRu2Ge2 in the temperature range 1.5 K<T<12 K. The phase diagram of its magnetic phases is consistent with previous transport measurements.Comment: 5 pages, 4 figure