Showing papers by "National Scientific and Technical Research Council published in 1991"
TL;DR: In this paper, a volume fraction transfer (VFT) scheme is proposed for grain reorientation due to twinning, which is also applied to the slip modes of Zr and Zr alloys, and a comparison of various predicted and experimental textures leads to the conclusion that twinning must be controlling texture development.
Abstract: In many polycrystals of less than cubic crystal symmetry, plastic deformation is dominated by twinning. In particular, we will treat the case of Zr and Zr alloys in detail. We propose a new method for modelling grain reorientation due to twinning, which is based on a Volume Fraction Transfer (VFT) scheme; the scheme is also applied to the slip modes. We find that this method predicts textures that are, when twinning is the dominant mode, considerably different from and in better agreement with experiment than the conventional schemes which reorient an entire grain when some criterion has been met. Various combinations of slip and twinning modes and of the associated critical stresses are systematically investigated for the case of rolling, tension and compression of Zr alloys. A comparison of various predicted and experimental textures leads to the conclusion that twinning must, indeed, be controlling texture development.
548 citations
TL;DR: The thermodynamic equilibrium involved in the steam reforming of ethanol to produce hydrogen has been examined over the following ranges: pressure 1-9 atm, temperature 400-800 K and water to ethanol feed ratio 0:1-10:1 as discussed by the authors.
265 citations
TL;DR: The morphology of a system consisting of a bisphenol A digrycidylether (DGEBA) based epoxy, cured with a cycloaliphatic diamine (4,4'-diamino-3,3'-dimethyldicyclohexylmethane, 3DCM), in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN), was studied as a function of the cure schedule and the initial rubber concentration.
Abstract: The morphology of a system consisting of a bisphenol A digrycidylether (DGEBA) based epoxy, cured with a cycloaliphatic diamine (4,4'-diamino-3,3'-dimethyldicyclohexylmethane, 3DCM), in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN), was studied as a function of the cure schedule and the initial rubber concentration
164 citations
TL;DR: In experiments simulating the conditions during sea ice melting, ice algae revealed a strong propensity to form aggregates, suggesting that ice algae released from the melting sea ice are subject to rapid sedimentation.
Abstract: Factors influencing the fate of ice algae released from melting sea ice were studied during a R V Polarstern cruise (EPOS Leg 2) to the northwestern Weddell Sea. The large-scale phytoplankton distribution patterns across the receding ice edge and small-scale profiling of the water column adjacent to melting ice floes indicated marked patchiness on both scales. The contribution of typical ice algae to the phytoplankton was not significant. In experiments simulating the conditions during sea ice melting, ice algae revealed a strong propensity to form aggregates. Differences in the aggregation potential were found for algal assemblages collected from the ice interior and the infiltration layer. Although all algal species collected from the ice were also found in aggregates, the species composition of dispersed and aggregated algae differed significantly. Aggregates were of a characteristic structure consisting of monospecific microaggregates which are likely to have formed in the minute brine pockets and channels within the ice. Sinking rates of aggregates were three orders of magnitude higher than those of dispersed ice algae. These observations, combined with the negligible seeding effect of ice algae found during this study, suggest that ice algae released from the melting sea ice are subject to rapid sedimentation. High grazing pressure at the ice edge of the investigation area is another factor eliminating ice algae released during melting.
156 citations
TL;DR: As in other arid ecosystems, plant species of north-eastern Patagonia showed phenological asynchrony among species in accordance with the ability of each species to exploit water and nutrients stored in different soil sub-spaces.
141 citations
TL;DR: The theropod families Abelisauridae and Noasauridae appear closely related because of shared derived characters such as the short anterior area of the maxilla, the small or absent preantorbital fenestra, the quadrate fused to the quadratojugal, and cervical vertebrae with vestigial neural spines and hypertrophied epipophyses.
Abstract: The theropod families Abelisauridae and Noasauridae appear closely related because of shared derived characters such as the short anterior area of the maxilla, the small or absent preantorbital fenestra, the quadrate fused to the quadratojugal, and cervical vertebrae with vestigial neural spines and hypertrophied epipophyses. The families appear linked to Ceratosauridae and are interpreted as Ceratosauria. They are very different from the clade Allosauridae‐Tyrannosauridae as well as from other Laurasian theropods. The geographic distribution of the Abelisauridae possibly includes Africa, India, South America and southern Europe, and they are generally associated with titanosaurid sauropods. It is considered that they are endemic to Gondwana, and the presence of abelisaurids in Europe may be the result of a migratory event from Africa. It is suggested that the Baharija theropods may be more related to the abelisaurs than to the tyrannosaurs.
113 citations
TL;DR: It is shown that the membership problem has single exponential sequential and polynomial parallel complexity for unmixed ideals.
108 citations
TL;DR: It is concluded that leaves and ear compete for the nitrogen, and that a low level of carbohydrates in the flag leaf, due to a low source-sink ratio, delays leaf senescence.
Abstract: The relation between the source-sink ratio and nitrogen nutrition on grain yield of wheat (Triticum aestivum L. cv. Klein Chamaco) was studied in a greenhouse experiment. Plants were grown until anthesis in pots with soil fertilized with 0.16 mmol N per plant twice a week. At anthesis, all leaves but the flag leaf were excised in a group of plants. In another group the treatment consisted in a similar defoliation plus the longitudinal excision of half the ear, while a third group was left untouched as a control. At the same time, the N supply to half of the plants in each group was interrupted, while the other half continued receiving 16 mM N. The defoliated plants showed a longer functional life of the flag leaf than the control, retaining the chlorophyll, soluble proteins and total reduced nitrogen for a longer time. The ear-excised plants showed an intermediate behavior. The plants with the interrupted N supply showed a faster leaf senescence than the N supplied ones, and this coincided with an increase in the proteolytic activity and nitrogen transport to the ear. However there were no differences in ear weight between the two nitrogen treatments. It is concluded that leaves and ear compete for the nitrogen, and that a low level of carbohydrates in the flag leaf, due to a low source-sink ratio, delays leaf senescence.
101 citations
TL;DR: Data demonstrate that NS26 is processed to a 28-kDa polypeptide by addition of O-linked monosaccharide residues of N-acetylglucosamine.
98 citations
TL;DR: A phase separation model was used to simulate the morphologies obtained in a system consisting of a diepoxide based on bisphenol-A diglycidylether cured with a cycloaliphatic diamine, in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN).
Abstract: A phase separation model was used to simulate the morphologies obtained in a system consisting of a diepoxide based on bisphenol-A diglycidylether cured with a cycloaliphatic diamine, in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN). A detailed analysis of experimental factors affecting resulting morphologies was previously reported. The model, based on a thermodynamic description through a Flory–Huggins equation, and constitutive equations for polymerization and phase separation rates, could explain most of the observed trends. A nucleation-growth mechanism was believed to take place because of the very low values of interfacial tensions for this type of systems. Conditions which would lead to spinodal demixing are also discussed.
88 citations
TL;DR: In this paper, three different techniques based on component synthesis are discussed, corresponding respectively to fully consistent mass discretization, lumped mass discreteization and corotational approximation of inertia forces.
Abstract: The paper deals with substructuring for dynamic analysis of flexible multibody systems. Three different techniques based on component synthesis are discussed, corresponding respectively to fully consistent mass discretization, lumped mass discretization and corotational approximation of inertia forces. To simplify the computer implementation, only the lumped mass and corotational approximations have been considered in detail and programmed. Both approaches are validated on simple examples of rotating beams for which a full elastic model is available using a fully non-linear beam element. The computational efficiency of the corotational inertia approach is also demonstrated on the deployment of a large flexible satellite antenna.
TL;DR: In this article, the mechanical properties of a bisphenol A diglycidylether (DGEBA) expoxy, cured with a cycloaliphatic diamine (4,4′-diamino-3,3 dimethyldicyclohexyl-methane, 3DCM), in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN), was studied as a function of the cure schedule and the initial rubber concentration.
Abstract: The mechanical properties of a system consisting of a bisphenol A diglycidylether (DGEBA) expoxy, cured with a cycloaliphatic diamine (4,4′-diamino-3,3 dimethyldicyclohexyl-methane, 3DCM), in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN), was studied as a function of the cure schedule and the initial rubber concentration. Fracture toughness (KIc) and fracture energy (GIc) were increased, while Young's modulus and yield strength decreased slightly with increasing volume fraction of the dispersed phase. We show that there is no significant influence of the precure schedule and of the various observed particle diameters on the mechanical properties for a constant rubber volume fraction. In our case, the main deformation process in the rubber-modified epoxy networks is shear yielding while cavitation is negligible.
Journal Article•
TL;DR: In this paper, the authors derived the likely location of the separatrices, surfaces that separates cells of different field line connectivities, and of the separator which is the intersection of separatrices.
Abstract: By modeling the observed vertical magnetic field of an active region AR 2372 by the potential field of an ensemble of magnetic dipoles, the likely location of the separatrices, surfaces that separates cells of different field line connectivities, and of the separator which is the intersection of the separatrices, is derived. Four of the five off-band H-alpha kernels of a flare that occurred less than 20 minutes before obtaining the magnetogram are shown to have taken place near or at the separatrices. These H-alpha kernels are connected by field lines that pass near the separator. This indicates that the flare may have resulted from the interaction in the separator region of large scale magnetic structures.
01 Jan 1991
TL;DR: In this article, the authors present deux algorithms for computing composante irreductible and equidimensionnelle decompositions of a variete algebrique affine (ou projective), defined by un ensemble fini de polynomes.
Abstract: Resume. Nous decrivons dans cet article deux algorithmes qui construisent les decompositions irreductible et equidimensionnelle d’une variete algebrique affine (ou projective), definie par un ensemble fini de polynomes. Le premier calcule les composantes irreductibles, donc depend d’un algorithme de factorisation, et en consequence ne peut se paralleliser que partiellement, du moins a notre connaissance. Le second correspond aux composantes equidimensionelles, et est susceptible d’une parallelisation totale. Comme applications, le lecteur trouvera en appendice un calcul de la forme de Chow d’une variete projective quelconque, du a T. Krick et P. Solerno, et un calcul du degre d’une variete affine.
TL;DR: Serotonin inhibited in a concentration dependent way the LPS induced Tumor Necrosis Factor-α synthesis both, when added to the monocyte cultures from the beginning and when added together with the activating stimulus 8 hours before the end of the culture.
TL;DR: The Barro Negro site (23°S lat., 65°37′W long) in the Altiplano (Puna) of northwestern Argentina contains a well stratified sequence of remains of Hippidion, the American extinct horse, camelids, and archaeological materials, which is the focus of.
Abstract: The Barro Negro site (23°S lat., 65°37′W long.) in the Altiplano (Puna) of northwestern Argentina contains a well stratified sequence of remains of Hippidion, the American extinct horse, camelids, and archaeological materials, which is the focus of this study. In addition to establishing a reliable chronology, paleoenvironmental information was obtained based on analyses of pollen and stable isotopes (oxygen and carbon) from bone and marl. The data indicate that Hippidion was present at the site between 12,000 and 10,000 yr B. P., at a time when Altoandean grasslands had expanded to lower elevations. By 10,000 yr B.P., when modern semi-arid sub-puna scrub had replaced the Altoandean grasslands, only camelids (Lama or Vicugna) were present, simultaneous with the first evidence of local human occupation. This suggests that a climatic shift from cool and moist (winter rain regime) to warm and dry (summer rain regime) conditions took place simultaneously with the disappearance of the American horse and the appearance of camelids and man.
TL;DR: The findings indicate that the male adult vizcacha under natural conditions exhibits an annual reproductive cycle, and an increase in sexual activity as well as in the ability to secrete testosterone.
Abstract: Seasonal changes in reproductive activity in the adult male vizcacha (Lagostomus maximus maximus), a South American rodent, were investigated. Monthly, for 2 yr, the animals were killed and decapitated during the night near their burrows in the vicinity of San Luis, Argentina. The testes, epididymides, and pineal glands were removed and used for biochemical and structural studies. Significant changes associated with seasonal cycles were found. 1) In July-August (winter in South America), a short hibernal period of sexual quiescence, decline in testicular and epididymal weights, arrest of spermatogenesis, and decrease of serum testosterone were observed. The gonads regressed during this period, with regression most pronounced in August. 2) During September-November (spring), a recovery period--without arrest of spermatogenesis--was observed, with significant expression of gonadal activity during April-May (autumn). In this season, gonadal weight was increased and spermatogenesis was complete. These results indicate an increase in sexual activity as well as in the ability to secrete testosterone. A gradual reduction of testicular activity appeared in June-July (early winter). Conversely, in this period, the pineal hydroxyindole-O-methyl transferase activity decreased in contrast to the highest values observed in winter. Our findings indicate that the male adult vizcacha under natural conditions exhibits an annual reproductive cycle. A possible relationship between increased pineal activity and gonadal regression is also suggested.
TL;DR: In this article, the authors identify the primary products of the reaction in order to propose a mechanistic explanation for the selective hydrogenation of ethyl acetate to ethanol and propose a reaction mechanism involving a single rhodium atom.
TL;DR: It is suggested that a selective involvement of specific portions of Brodmann's areas 4 and 6, and/or its subcortical projections, may account for the peculiar combination of segmental and prosodic deficits underlying the FAS.
Abstract: Four right-handed monolingual Spanish-speaking patients who developed a foreign accent syndrome (FAS) during the recovery period from a non-fluent aphasia or an aphemia are reported. The FAS resolved rapidly (within 2 months) in two patients, both with small stroke lesions in the posterior margin of the left middle frontal gyrus. In the other two patients, who had lesions involving the middle portion of the left precentral gyrus and the white matter underlying the right sensory-motor cortex, the FAS lasted more than 1 year. Phonetic and fundamental frequency (F0) analysis showed atypical articulatory and prosodic patterns in the two patients with a long-lasting FAS, but only abnormal prosodic features in the two recovered cases. These findings suggest that: (1) a selective involvement of specific portions of Brodmann's areas 4 and 6, and/or its subcortical projections, may account for the peculiar combination of segmental and prosodic deficits underlying the FAS; and (2) recovery seems to be rela...
TL;DR: In this article, a series of PdGe, Sb, PdSb, Sn, or Pb catalysts were tested in the gas-phase hydrogenation of 2-methyl-1-buten-3-yne (valylene) and 2-m-1,3-butadiene (isoprene).
TL;DR: The Late Pleistocene and Holocene loess deposits of the SE Buenos Aires province are composed of four allostratigraphic units that represent four episodes of loess deposition as mentioned in this paper.
Abstract: The Late Pleistocene and Holocene loess deposits of the SE Buenos Aires province are composed of four allostratigraphic units that represent four episodes of loess deposition. The first and the second episodes occurred in Late Pleistocene times. The second episode was followed by a soil forming interval (Early Holocene to Mid-Holocene times). The third episode took place at about 5000 yr BP, after the Holocene sea-level maximum when marine regression began. The fourth episode constitutes a historical event of only local significance. Loess shows a fairly constant granulometric and mineralogical composition. The modal fraction consists of very fine sand and coarse silt (3 to 5 phi). They are classified as sandy silts or silty sands. Three grain-size subpopulations are differentiated: coarse, medium and fine. The medium-size subpopulation, which is the most important, consists of most of the very fine sand and coarse silt. It is thought to be transported by modified saltation and short-term suspension during local dust-storms. The mineralogical composition of loess consists of a volcaniclastic assemblage derived mainly from reworked pyroclastic deposits, primary tephras and volcaniclastic sediments. The source area of these materials was located in the lower Colorado river valley about 400 km SW of the studied area. There was also a direct supply by volcanic ash falls.
TL;DR: In this article, the thermodynamic analysis of the water-foodstuff equilibrium is reviewed, showing how partial molar and integral enthalpies and entropies can be obtained and indicating how to manipulate the experimental data for this purpose.
Abstract: The thermodynamic analysis of the water-foodstuff equilibrium is reviewed, showing how partial molar and integral enthalpies and entropies can be obtained and indicating how to manipulate the experimental data for this purpose. The need for accurate and precise data is stressed and one experimental approach is recommended. Experimental results of desorption of water from Granny Smith apples provide information which is consistent from the thermodynamical standpoint. It is noted that the value of monolayer thickness corresponding to a minimum in integral entropy is substantially different from the value predicted by the BET equation.
TL;DR: The data demonstrated that chagasic IgG interacting with cardiac muscarinic cholinergic receptor triggers the biological effects associated with Chagas' myocarditis, including decrement of atria contractility, inhibition of cAMP and activation of the turnover of phosphoinositides via phospholipase C.
TL;DR: Cerro La China, within the Tandilia Range, has a long archaeological record in which three different human occupations were identified as discussed by the authors, and the geoarchaeological approach allowed us to correlate the archaeosedimentary columns at Site 2 and Site 3 and place the local stratigraphy in a regional context.
Abstract: Cerro La China, within the Tandilia Range, has a long archaeological record in which three different human occupations were identified. The geoarchaeological approach allowed us to correlate the archaeosedimentary columns at Site 2 and Site 3 and place the local stratigraphy in a regional context.
The archaeologically rich stratigraphic sequence is composed of three episodes of loess deposition. The first bears a 10,600 yr B.P. Paleoindian occupation with Fishtail or Fell's Cave Stemmed points. It is followed by a soil-forming interval which ended about 5000 yr B.P. with an erosive episode. The second event of loess deposition continued through an unknown span of time until a new soil-forming interval started; it includes triangular stemless medium size projectile points corresponding to a different human group. By the sixteenth century another erosive event interrupted the soil-forming interval. After this, the third short-term eolian episode occurred and bears the most recent archaeological occupation marked by small triangular stemless points.
TL;DR: Bis(tributyltin)oxide acts as a mild, neutral and chemoselective ester cleavage reagent for a variety of carboxylic esters with good to excellent yields as mentioned in this paper.
TL;DR: Tintinnid species-specific assemblages show a coherent distributional pattern and well defined environment-related trends; most clearly differentiated preferences are exhibited by Laackmanniella prolongata (closely associated with ice-covered areas), Cymatocylis affinis/convallaria (oligotrophic open-ocean waters), and Codonellopsis balechi (coastal regions).
Abstract: Microplankton was sampled with a centrifugal suction pump in the surface layer (approx. 9 m) of the Bellingshausen Sea and the Bransfield Strait in March 1987, and concentrated with a 26μm-mesh net. Bulk microplanktonic settling volumes were assessed, silicoflagellates and large thecate dinoflagellates were counted, and tintinnids were counted and identified to species. Average (and maximum) values for the entire area surveyed were as follows, settling volume: 6.7 (43.3) ml/m3; silicoflagellates: 674 (7777) ind./l, 0.57 (6.54) mg C/m3; dinoflagellates: 109 (1321) ind./l, 1.40 (16.98) mg C/m3; tintinnids: 52 (589) ind./l, 1.15 (9.87) mg C/m3. The three geographic zones defined objectively on the basis of tintinnid specific assemblages also differed sharply in their surface salinity, overall microplanktonic abundance and bulk settling volume. The Bransfield Strait, with lowest settling volume values (2.1 ml/m3) and cell concentrations, was characterized by the dominance of Cymatocylis affinis/convallaria. In waters around the tip of the Antarctic Peninsula microplanktonic settling volumes averaged 4.6 ml/m3, cell concentrations were intermediate, and 79% of the tintinnids were represented by Codonellopsis balechi. The Bellingshausen Sea was characterized by the lowest salinities and the highest settling volumes (8.7 ml/m3) and cell counts; Laackmanniella spp. and Cymatocylis drygalskii, f. typica dominated this area. Almost all biological variables were significantly intercorrelated, and showed strong and mostly significant negative correlations with surface salinity, yet relationships between enhanced standing stock and ice meltwater were not obvious; rather, highest microplanktonic concentrations seemed to be due to ice-associated growth. Extremely high spatial correlations were found between the tintinnids and the dinoflagellates (r2: 0.941), suggesting the existence of close links between these two groups. Tintinnid species-specific assemblages show a coherent distributional pattern and well defined environment-related trends; most clearly differentiated preferences are exhibited by Laackmanniella prolongata (closely associated with ice-covered areas), Cymatocylis affinis/convallaria (oligotrophic open-ocean waters), and Codonellopsis balechi (coastal regions).
TL;DR: It is concluded that functional beta-adrenoceptors are absent in these lymphoma cells, and the possible implication of alternative transmission pathways and original neuroendocrine control in tumor lymphoid cells is discussed.
TL;DR: In Tierra del Fuego, the Holocene mean sea-level fluctuation reworked much pre-Wisconsin glacial drift into sand/gravel beaches and spits, and sand/mud tidal flats.
TL;DR: The anatomy of a new articulated enantiornithine bird skeleton from the Late Cretaceous of Patagonia clearly indicates a capacity for powered flight, approaching that of modern birds.
Abstract: The anatomy of a new articulated enantiornithine bird skeleton from the Late Cretaceous of Patagonia clearly indicates a capacity for powered flight, approaching that of modern birds. Enantiornithines possess some of the synapomorphies of the Ornithurae, although they retain plesiomorphic states for many other characters, mainly in the hind limb. Such a mosaic character combination suggests a sister-group relationship between Enantiornithes and Ornithurae. Derived features of the pectoral girdle are here considered as diagnostic for a major avian clade, the Ornithopectae, comprising all known birds other than Archaeopteryx. The combination of derived and primitive traits in the fore and hind limbs and their girdles in early ornithopectines reflects mosaic evolution, with flight-related modifications of the fore limb and pectoral girdle preceding those in the hind limb and pelvic girdle.
TL;DR: The ability of phospholipase A2 from porcine pancreas to degrade all of the available dilauroylphosphatidylcholine in mixed monolayers with galactocerebroside, sulfatide, or ganglioside GM1 was investigated at different constant surface pressures.
Abstract: The ability of phospholipase A2 from porcine pancreas to degrade all of the available dilauroylphosphatidylcholine in mixed monolayers with galactocerebroside, sulfatide, or ganglioside GM1 was investigated at different constant surface pressures. Under the conditions used the interfacial glycosphingolipid composition was continuously enriched as the enzyme action proceeded. The total percentage of phospholipid degradation depends on the surface pressure and on the type of glycosphingolipid. The presence of sulfatide activates the enzyme while galactocerebroside and ganglioside GM1 are inhibitory. The extent of phospholipid hydrolysis is independent of the effect of glycosphingolipids on the enzyme velocity. This is so when the latter is measured either in conditions of constant glycosphingolipid composition and zero-order kinetics [Bianco, I.D., Fidelio, G.D., & Maggio, B. (1989) Biochem. J. 258, 95-99] or under variable surface composition as in the present work. The modulation of phospholipase A2 activity by glycosphingolipids operates at two independent levels. One controls the rate of enzyme activity, and the other modulates the total extent of substrate degradation. This depends on the initial interaction of the enzyme with the interface. The glycosphingolipid effect on the activity is different depending on whether the enzyme has access to the substrate from the subphase or is already adsorbed to the lipid interface.