Shear thickening of cornstarch suspensions as a re-entrant jamming transition

We study the rheology of cornstarch suspensions, a dense system of non-Brownian particles that exhibits shear thickening, i.e. a viscosity that increases with increasing shear rate. Using MRI velocimetry we show that the suspension has a yield stress. From classical rheology it follows that as a function of the applied stress the suspension is first solid (yield stress), then liquid and then solid again when it shear thickens. The onset shear rate for thickening is found to depend on the measurement geometry: the smaller the gap of the shear cell, the lower the shear rate at which thickening occurs. Shear thickening can then be interpreted as the consequence of the Reynolds dilatancy: the system under flow wants to dilate but instead undergoes a jamming transition because it is confined, as confirmed by measurement of the dilation of the suspension as a function of the shear rate

A Hopf lemma for the regional fractional Laplacian

We provide a Hopf boundary lemma for the regional fractional Laplacian (-Delta)(Omega)(s), with Omega subset of R-N a bounded open set. More precisely, given u a pointwise or weak super-solution of the equation (-Delta)(Omega)(s)u = c(x)u in Omega, we show that the ratio u(x)/(dist(x, partial derivative Omega))(2s-1) is strictly positive as x approaches the boundary partial derivative Omega of Omega. We also prove a strong maximum principle for distributional super-solutions

Angular momentum distribution of hot gas and implications for disk galaxy formation

We study the angular momentum profiles both for dark matter and for gas within virialized halos, using a statistical sample of halos drawn from cosmological hydrodynamics simulations. Three simulations have been analyzed, one is the ``non-radiative'' simulation, and the other two have radiative cooling. We find that the gas component on average has a larger spin and contains a smaller fraction of mass with negative angular momentum than its dark matter counterpart in the non-radiative model. As to the cooling models, the gas component shares approximately the same spin parameter as its dark matter counterpart, but the hot gas has a higher spin and is more aligned in angular momentum than dark matter, while the opposite holds for the cold gas. After the mass of negative angular momentum is excluded, the angular momentum profile of the hot gas component approximately follows the universal function originally proposed by Bullock et al. for dark matter, though the shape parameter $\mu$ is much larger for hot gas and is comfortably in the range required by observations of disk galaxies. Since disk formation is related to the distribution of hot gas that will cool, our study may explain the fact that the disk component of observed galaxies contains a smaller fraction of low angular momentum material than dark matter in halos.Comment: 30 pages, 12 figures, 4 tables, accepted for publication in Ap

Caracterisation agromorphologique, chimique et biochimique des noix brutes de trois provenances d’anacardiers (Anacardium occidentale L.) au Sud du Senegal

La sécurité alimentaire est l’une des préoccupations majeures des hommes dans le monde. Pour l’atteindre, les populations rurales tirent une grande partie de leurs alimentations dans les Produits Forestiers Non Ligneux. Anacardium occidentale L., une espèce agroforestière très prisée n’est pas en reste. Cependant, des études sur la valeur alimentaire et nutritionnelle de ses noix sont limitées et restent parcellaires. L’objectif de cette recherche est d’évaluer les teneurs en éléments nutritifs des noix brutes de Anacardium occidentale L. collectées à Ziguinchor, Sédhiou et Kolda. Pour ce faire, dans chaque zone, trois kilogrammes de noix ont été prélevées de manière aléatoire dans différents lieux de stockage. Puis les mensurations ont porté sur 450 noix par provenance. Les noix ont été ensuite décortiquées puis soumises à une analyse minérale (chimique et biochimique). Une analyse uni et multivariée a été effectuée à l’aide de XLSTAT 6.0. L’analyse a montré l’existence d’une variabilité des caractéristiques entre les provenances. Une corrélation forte, significative mais négative a été détectée entre le poids des amandes et la cellulose brute, ce qui signifierait que les amandes de petite taille sont plus sucrées. A travers cette étude, plusieurs possibilités s’offrent aux différents acteurs de la chaine de valeur anacarde. English title: Agromorphological, chemical and biochemical characterization of <I>Anacardium occidentale L.</I> in Sud Senegal Food security is one of the major concerns of people around the world. To achieve this, rural populations derive a large part of their food from Non-Wood Forest Products. Anacardium occidentale L., a highly prized agroforestry species, is not to be outdone. However, studies on the food and nutritional value of its nuts are limited and remain fragmented. The objective of this research is to evaluate the nutrient content of raw nuts of Anacardium occidentale L. collected in Ziguinchor, Sédhiou and Kolda. To do this, in each area, three kilograms of nuts were taken at random from  different storage locations. Then the measurements were carried out on 450 nuts per provenance. The nuts were then shelled and then subjected to mineral analysis (chemical and biochemical). Univariate and multivariate analysis was performed using XLSTAT 6.0. The analysis showed the  existence of variability in characteristics between provenances. A strong, significant but negative correlation was detected between the weight of the almonds and the crude fiber, which would mean that the small almonds are sweeter. Through this study, several possibilities are available to the various players in the cashew value chain

Models of Disk Evolution: Confrontation with Observations

We present simple models for disk evolution based on two different approaches: a forward approach based on predictions generic to hierarchical models for structure formation (e.g., Mo, Mao, & White 1998) and a backwards approach based on detailed modeling of the Milky Way galaxy (e.g., Bouwens, Cayon, & Silk 1997). We normalize these models to local observations and predict high-redshift luminosities, sizes, circular velocities, and surface brightnesses. Both approaches yield somewhat similar predictions for size, surface brightness, and luminosity evolution though they clearly differ in the amount of number evolution. These predictions seem to be broadly consistent with the high-redshift observations of Simard et al. (1999), suggesting that the B-band surface brightness of disks has indeed evolved by ~1.5 mag from z~0 to z~1 similar to the models and is not an artifact of selection effects as previously claimed. We also find a lack of low surface brightness galaxies in several high redshift samples relative to model predictions based on local samples (de Jong & van der Kruit 1994; Mathewson, Ford, & Buchhorn 1992).Comment: 34 pages, 9 figures, accepted to Ap

GMRT detection of HI 21 cm associated absorption towards the z=1.2 red quasar 3C 190

We report the GMRT detection of associated HI 21 cm-line absorption in the z=1.1946 red quasar 3C 190. Most of the absorption is blue-shifted with respect to the systemic redshift. The absorption, at $\sim$ 647.7 MHz, is broad and complex, spanning a velocity width of $\sim$ 600 \kms. Since the core is self-absorbed at this frequency, the absorption is most likely towards the hotspots. Comparison of the radio and deep optical images reveal linear filaments in the optical which overlap with the brighter radio jet towards the south-west. We therefore suggest that most of the HI 21 cm-line absorption could be occurring in the atomic gas shocked by the south-west jet.Comment: 8 pages, 1 fugure. To appear in Journal of Astrophysics and Astronom

Etude de l’activité antioxydante des extraits des feuilles de Vitex doniana (Verbenacea)

L’objectif de la présente étude était d’évaluer l’activité antioxydante des extraits des feuilles de Vitex doniana par spectrophotométrie en utilisant les méthodes de piégeage des radicaux libres 2,2-diphényl-1- picryl-hydrazyle (DPPH•) et acide 2,2’-azino-bis-(3-éthylbenzothiazoline-6-sulfonique) (ABTS+•). Une extraction éthanolique des feuilles de Vitex doniana a été effectuée au Soxhlet. L’extrait sec recueilli a été redissout dans de l’eau puis fractionné en utilisant successivement de l’hexane, du dichlorométhane et de l’acétate d’éthyle. Les propriétés antioxydantes de l’extrait éthanolique et celles de ses différentes fractions ont été évaluées aux concentrations de 2,5 ; 10 ; 100 et 200 μg/mL. Les pourcentages d’inhibition (PI) expriment l’effet antioxydant mesuré. L’extrait éthanolique et ses différentes fractions ont présenté une activité de piégeage des deux radicaux libres. Lors des tests d’inhibition de l’absorbance du radical DPPH•, les PI ont varié de (18,15±0,01)% pour la fraction hexanique (2,5 μg/mL) à (92,45±0,01)% pour la fraction d’acétate d’éthyle (100 μg/mL). Avec le radical ABTS+•, les PI ont varié de (52,76±0,05)% pour la fraction hexanique (2,5 μg/mL) à (98,27±0,12)% pour la fraction d’acétate d’éthyle (100 μg/mL). Ainsi, l’extrait éthanolique des feuilles de Vitex doniana et ses différentes fractions possèdent un pouvoir antioxydant significatif.Mots clés : Activité antioxydante, DPPH, ABTS, Vitex doniana

Stellar populations in gas-rich galaxy mergers II. Feedback effects of Type Ia and II supernovae

We numerically investigate chemodynamical evolution of major disk-disk galaxy mergers in order to explore the origin of mass-dependent chemical, photometric, and spectroscopic properties observed in elliptical galaxies. We particularly investigate the dependence of the fundamental properties on merger progenitor disk mass (M_d). Main results obtained in this study are the following three. (1) More massive (luminous) ellipticals formed by galaxy mergers between more massive spirals have larger metallicity (Z) and thus show redder colors: The typical metallicity ranges from ~ 1.0 solar abundance (Z~ 0.02) for ellipticals formed by mergers with M_d = 10^10 M_solar to ~ 2.0 solar (Z ~ 0.04) for those with M_d = 10^12 M_solar. (2) The absolute magnitude of negative metallicity gradients developed in galaxy mergers is more likely to be larger for massive ellipticals. Absolute magnitude of metallicity gradient correlates with that of age gradient in ellipticals in the sense that an elliptical with steeper negative metallicity gradient is more likely to show steeper age gradient. (3) Both M/L_B and M/L_K, where M, L_B, and L_K are total stellar mass of galaxy mergers, B-band luminosity, and K-band one, respectively, depend on galactic mass in such a way that more massive ellipticals have larger M/L_B and smaller M/L_K.Comment: 58 pages 16 figures, ApJ in press (March 1999 issue

Galaxy Number Counts in the Subaru Deep Field: Multi-band Analysis in a Hierarchical Galaxy Formation Model

Number counts of galaxies are re-analyzed using a semi-analytic model (SAM) of galaxy formation based on the hierarchical clustering scenario. Faint galaxies in the Subaru Deep Field (SDF) and the Hubble Deep Field (HDF) are compared with our model galaxies. We have determined the astrophysical parameters in the SAM that reproduce observations of nearby galaxies, and used them to predict the number counts and redshifts of faint galaxies for three cosmological models, the standard cold dark matter (CDM) universe, a flat lambda-CDM, and an open CDM. The novelty of our SAM analysis is the inclusion of selection effects arising from the cosmological dimming of surface brightness of high-z galaxies, and from the absorption of visible light by internal dust and intergalactic HI clouds. As was found in our previous work, in which the UV/optical HDF galaxies were compared with our model galaxies, we find that our SAM reproduces counts of near-IR SDF galaxies in low-density models, and that the standard CDM universe is not preferred, as suggested by other recent studies. Moreover, we find that simple prescriptions for (1) the timescale of star formation being proportional to the dynamical time scale of the formation of galactic disks, (2) the size of galactic disks being rotationally supported with the same specific angular momentum as that of surrounding dark halo, and (3) the dust optical depth being proportional to the metallicity of cold gas, cannot completely explain all of observed data. Improved prescriptions incorporating mild z-dependence for those are suggested from our SAM analysis.Comment: 16 pages, 13 figures, to appear in Ap

Dynamical Properties of z~2 Star Forming Galaxies and a Universal Star Formation Relation

We present the first comparison of the dynamical properties of different samples of z~1.4-3.4 star forming galaxies from spatially resolved imaging spectroscopy from SINFONI/VLT integral field spectroscopy and IRAM CO millimeter interferometry. Our samples include 16 rest-frame UV-selected, 16 rest-frame optically-selected and 13 submillimeter galaxies (SMGs). We find that restframe UV- and optically bright (K<20) z~2 star forming galaxies are dynamically similar, and follow the same velocity-size relation as disk galaxies at z~0. In the theoretical framework of rotating disks forming from dissipative collapse in dark matter halos, the two samples require a spin parameter ranging from 0.06 to 0.2. In contrast bright SMGs have larger velocity widths and are much more compact. Hence, SMGs have lower angular momenta and higher matter densities than either of the UV- or optically selected populations. This indicates that dissipative major mergers may dominate the SMGs population, resulting in early spheroids, and that the majority of UV/optically bright galaxies have evolved less violently [...]. These early disks may later evolve into spheroids via disk instabilities or mergers. Because of their small sizes and large densities, SMGs lie at the high surface density end of a universal (out to z=2.5) "Schmidt-Kennicutt" relation between gas surface density and star formation rate surface density with a slope of ~1.7.Comment: 14 pages, 3 figures, accepted for publication in ApJ, minor typos correcte