We follow the formation and evolution of bars in N-body simulations of disc galaxies with gas and/or a triaxial halo. We find that both the relative gas fraction and the halo shape play a major role in the formation and evolution of the bar. In gas-rich simulations, the disc stays near-axisymmetric much longer than in gas-poor ones, and, when the bar starts growing, it does so at a much slower rate. Due to these two effects combined, large-scale bars form much later in gas-rich than in gas-poor discs. This can explain the observation that bars are in place earlier in massive red disc galaxies than in blue spirals. We also find that the morphological characteristics in the bar region are strongly influenced by the gas fraction. In particular, the bar at the end of the simulation is much weaker in gas-rich cases. The quality of our simulations is such as to allow us to discuss the question of bar longevity because the resonances are well resolved and the number of gas particles is sufficient to describe the gas flow adequately. In no case did we find a bar which was destroyed.Halo triaxiality has a dual influence on bar strength. In the very early stages of the simulation it induces bar formation to start earlier. On the other hand, during the later, secular evolution phase, triaxial haloes lead to considerably less increase of the bar strength than spherical ones. The shape of the halo evolves considerably with time. We confirm previous results of gas-less simulations that find that the inner part of an initially spherical halo can become elongated and develop a halo bar. However we also show that, on the contrary, in gas rich simulations, the inner parts of an initially triaxial halo can become rounder with time. The main body of initially triaxial haloes evolves towards sphericity, but in initially strongly triaxial cases it stops well short of becoming spherical. Part of the angular momentum absorbed by the halo generates considerable rotation of the halo particles that stay located relatively near the disc for long periods of time. Another part generates halo bulk rotation, which, contrary to that of the bar, increases with time but stays small. Thus, in our models there are two nonaxisymmetric components rotating with different pattern speeds, namely the halo and the bar, so that the resulting dynamics have strong similarities to the dynamics of double bar systems.

Independent short-term effects of photosynthetic photon flux density (PPFD) of 50-400 µmol m -2 s -1 , external CO 2 concentration (C a ) of 85-850 cm 3 m -3 , and vapor pressure deficit (VPD) of 0.9-2.2 kPa on net photosynthetic rate (P N ), stomatal conductance (g s ), leaf internal CO 2 concentration (C i ), and transpiration rates (E) were investigated in three cacao genotypes. In all these genotypes, increasing PPFD from 50 to 400 µmol m -2 s -1 increased P N by about 50 %, but further increases in PPFD up to 1 500 µmol m -2 s -1 had no effect on P N . Increasing C a significantly increased P N and C i while g s and E decreased more strongly than in most trees that have been studied. In all genotypes, increasing VPD reduced P N , but the slight decrease in g s and the slight increase in C i with increasing VPD were non-significant. Increasing VPD significantly increased E and this may have caused the reduction in P N . The unusually small response of g s to VPD could limit the ability of cacao to grow where VPD is high. There were no significant differences in gas exchange characteristics (g s , C i , E) among the three cacao genotypes under any measurement conditions.

Background: Theobroma cacao L., is a tree originated from the tropical rainforest of South America. It is one of the major cash crops for many tropical countries. T. cacao is mainly produced on smallholdings, providing resources for 14 million farmers. Disease resistance and T. cacao quality improvement are two important challenges for all actors of cocoa and chocolate production. T. cacao is seriously affected by pests and fungal diseases, responsible for more than 40% yield losses and quality improvement, nutritional and organoleptic, is also important for consumers. An international collaboration was formed to develop an EST genomic resource database for cacao.

Preparation of high-quality proteins from cacao vegetative organs is difficult due to very high endogenous levels of polysaccharides and polyphenols. In order to establish a routine procedure for the application of proteomic and biochemical analysis to cacao tissues, three new protocols were developed; one for apoplastic washing fluid (AWF) extraction, and two for protein extraction--under denaturing and nondenaturing conditions. The first described method allows a quick and easy collection of AWF--using infiltration-centrifugation procedure--that is representative of its composition in intact leaves according to the smaller symplastic contamination detected by the use of the hexose phosphate isomerase marker. Protein extraction under denaturing conditions for 2-DE was remarkably improved by the combination of chemically and physically modified processes including phenol, SDS dense buffer and sonication steps. With this protocol, high-quality proteins from cacao leaves and meristems were isolated, and for the first time well-resolved 1-DE and 2-DE protein patterns of cacao vegetative organs are shown. It also appears that sonication associated with polysaccharide precipitation using tert-butanol was a crucial step for the nondenaturing protein extraction and subsequent enzymatic activity detection. It is expected that the protocols described here could help to develop high-level proteomic and biochemical studies in cacao also being applicable to other recalcitrant plant tissues.

No abstract

Observed galaxy clusters often exhibit X-ray morphologies suggestive of recent interaction with an infalling subcluster. Abell 3376 is a nearby (z = 0.046) massive galaxy cluster whose bullet-shaped X-ray emission indicates that it may have undergone a recent collision. It displays a pair of Mpc-scale radio relics and its brightest cluster galaxy is located 970h −1 70 kpc away from the peak of X-ray emission, where the second brightest galaxy lies. We attempt to recover the dynamical history of Abell 3376. We perform a set of N -body adiabatic hydrodynamical simulations using the SPH code Gadget-2. These simulations of binary cluster collisions are aimed at exploring the parameter space of possible initial configurations. By attempting to match X-ray morphology, temperature, virial mass and X-ray luminosity, we set approximate constraints on some merger parameters. Our best models suggest a collision of clusters with mass ratio in the range 1/6-1/8, and having a subcluster with central gas density four times higher than that of the major cluster. Models with small impact parameter (b < 150 kpc), if any, are preferred. We estimate that Abell 3376 is observed approximately 0.5 Gyr after core passage, and that the collision axis is inclined by i ≈ 40 • with respect to the plane of the sky. The infalling subcluster drives a supersonic shock wave that propagates at almost 2600 km/s, implying a Mach number as high as M ∼ 4; but we show how it would have been underestimated as M ∼ 3 due to projection effects.

No abstract

Shaded perennial agroforestry systems contain relatively high quantities of soil carbon (C) resulting from continuous deposition of plant residues; however, the extent to which the C is sequestered in soil will depend on the extent of physical protection of soil organic C (SOC). The main objective of this study was to characterize SOC storage in relation to soil fraction-size classes in cacao (Theobroma cacao L.) agroforestry systems (AFSs). Two shaded cacao systems and an adjacent natural forest in reddish-yellow Oxisols in Bahia, Brazil were selected. Soil samples were collected from four depth classes to 1 m depth and separated by wet-sieving into three fraction-size classes (>250 microm, 250-53 microm, and <53 microm)-corresponding to macroaggregate, microaggregate, and silt-and-clay size fractions-and analyzed for C content. The total SOC stock did not vary among systems (mean: 302 Mg/ha). On average, 72% of SOC was in macroaggregate-size, 20% in microaggregate-size, and 8% in silt-and-clay size fractions in soil. Sonication of aggregates showed that occlusion of C in soil aggregates could be a major mechanism of C protection in these soils. Considering the low level of soil disturbances in cacao AFSs, the C contained in the macroaggregate fraction might become stabilized in the soil. The study shows the role of cacao AFSs in mitigating greenhouse gas (GHG) emission through accumulation and retention of high amounts of organic C in the soils and suggests the potential benefit of this environmental service to the nearly 6 million cacao farmers worldwide.