Phase Diagrams of Bi1-xSbx Thin Films with Different Growth Orientations

A closed-form model is developed to evaluate the band-edge shift caused by quantum confinement for a two-dimensional non-parabolic carrier-pocket. Based on this model, the symmetries and the band-shifts of different carrier-pockets are evaluated for BiSb thin films that are grown along different crystalline axes. The phase diagrams for the BiSb thin film systems with different growth orientations are calculated and analyzed

Variation in Leaf Structure and Function in Quercus Douglasii Trees Differing in Root Architecture and Drought History

Seasonal changes in leaf specific mass, nitrogen, chlorophyll, and photosynthetic properties were measured for two groups of spatially intermixed Quercus douglasii trees with different drought histories and apparently different root architectures. One group, referred to as \u27\u27high-psi(pd) trees, included trees with low amounts of fine root biomass in the upper 50 cm of soil and high predawn xylem pressure potentials (psi(pd)) during summer drought. These two characteristics indicate that trees in this group have deep roots, which may reach the water table. The second group, referred to as \u27\u27low-psi(pd) trees, had three to five times higher fine root biomass in the upper 50 cm of soil and low psi(pd) during summer drought. These two characteristics indicate that these trees may not have access to the water table and are dependent on shallow soil moisture, which decreases rapidly during the rainless summers of central California. In the spring, after the full expansion of new leaves, but prior to significant divergence in psi(pd) between the groups, leaf area per leaf, leaf specific mass, chlorophyll per leaf area, incident quantum yield, leaf respiration rate, and irradiance at light compensation were lower for low-psi(pd) trees than for trees with high psi(pd). Nitrogen per leaf area did not differ between the groups. Net photosynthetic capacity at 2000 mu mol m(-2) s(-1) (A(max)) per leaf area was similar among all trees in the spring, but A(max)/leaf mass during the spring was higher for trees that eventually would develop low seasonal psi(pd). Since differences existed between new cohorts of leaves produced in the spring before summer drought, when psi(pd) was similar, we suggest that some leaf characteristics of Q. douglasii trees are determined by the de ree of drought exposure experienced in previous years, or by genetic variation within the species. During the rainless summer and fall seasons, A(max)/leaf area, A(max)/leaf mass, and total leaf chlorophyll/leaf mass decreased more rapidly in trees with low psi(pd) than in trees with high psi(pd), so that from August to the beginning of leaf senescence in October, leaves of high-psi(pd) trees had higher A(max)/leaf area, A(max)/leaf mass, and total leaf chlorophyll/leaf mass than those of low-psi(pd) trees. Overall, variations in root architecture and summer psi(pd), for Q. douglasii were correlated with substantial differences in morphological and physiological leaf characteristics. This apparent coordination of aboveground and belowground organs may explain, in part, how Q. douglasii tolerates the exceptionally broad range of topography and soil moisture conditions in which it occurs

Effects of Regional Origin and Genotype on Intraspecific Root Communication in the Desert Shrub Ambrosia Dumosa (Asteraceae)

Previous work has shown that the contact inhibition that occurs among roots of Ambrosia dumosa shrubs has a self/nonself recognition capability. In the current study, we investigated some of the geographic and genotypic dimensions of this recognition capability by using root observation chambers to observe the effects of encounters of individual roots on root elongation rates. We measured such effects in encounters between roots of plants from the same region and compared these to effects in encounters between roots of plants from two different regions. We also measured effects of encounters between roots of plants from the same clones and compared these to effects of encounters of roots of plants from different clones. Roots of plants from the same region (population) showed the usual \u27\u27nonself\u27\u27 precipitous decline in elongation rates following contact, but when roots of plants from different regions contacted each other, elongation rates continued unchanged. When roots of separate plants from the same clone contacted each other, the same \u27\u27nonself\u27\u27 precipitous decline in elongation rates as seen in encounters between roots of plants of different clones from the same region occurred. Meanwhile, in these same experiments \u27\u27self\u27\u27 contacts between sister roots connected to the same plants resulted in no changes in elongation rates. Thus, differences between individuals from two geographically separate populations of Ambrosia dumosa may be sufficient to thwart the \u27\u27nonself,\u27\u27 population-level recognition of similarity apparently necessary for contact inhibition. Furthermore, the \u27\u27self\u27\u27 recognition mechanism, which precludes contact inhibition between two roots on the same plant, appears to be physiological rather than genetic in nature

Local softness, softness dipole and polarizabilities of functional groups: application to the side chains of the twenty amino acids

The values of molecular polarizabilities and softnesses of the twenty amino acids were computed ab initio (MP2). By using the iterative Hirshfeld scheme to partition the molecular electronic properties, we demonstrate that the values of the softness of the side chain of the twenty amino acid are clustered in groups reflecting their biochemical classification, namely: aliphatic, basic, acidic, sulfur containing, and aromatic amino acids . The present findings are in agreement with previous results using different approximations and partitioning schemes [P. Senet and F. Aparicio, J. Chem. Phys. 126,145105 (2007)]. In addition, we show that the polarizability of the side chain of an amino acid depends mainly on its number of electrons (reflecting its size) and consequently cannot be used to cluster the amino acids in different biochemical groups, in contrast to the local softness. Our results also demonstrate that the global softness is not simply proportional to the global polarizability in disagreement with the intuition that "a softer moiety is also more polarizable". Amino acids with the same softness may have a polarizability differing by a factor as large as 1.7. This discrepancy can be understood from first principles as we show that the molecular polarizability depends on a "softness dipole vector" and not simply on the global softness

Direct angiotensin AT2 receptor stimulation using a novel AT2 receptor agonist, compound 21, evokes neuroprotection in conscious hypertensive rats

Background: In this study, the neuroprotective effect of a novel nonpeptide AT2R agonist, C21, was examined in a conscious model of stroke to verify a class effect of AT2R agonists as neuroprotective agents. Methods and Results: Spontaneously hypertensive rats (SHR) were pre-treated for 5 days prior to stroke with C21 alone or in combination with the AT2R antagonist PD123319. In a separate series of experiments C21 was administered in a series of 4 doses commencing 6 hours after stroke. A focal reperfusion model of ischemia was induced in conscious SHR by administering endothelin-1 to the middle cerebral artery (MCA). Motor coordination was assessed at 1 and 3 days after stroke and post mortem analyses of infarct volumes, microglia activation and neuronal survival were performed at 72 hours post MCA occlusion. When given prior to stroke, C21 dose dependently decreased infarct volume, which is consistent with the behavioural findings illustrating an improvement in motor deficit. During the pre-treatment protocol C21 was shown to enhance microglia activation, which are likely to be evoking protection by releasing brain derived neurotrophic factor. When drug administration was delayed until 6 hours after stroke, C21 still reduced brain injury. Conclusion: These results indicate that centrally administered C21 confers neuroprotection against stroke damage. This benefit is likely to involve various mechanisms, including microglial activation of endogenous repair and enhanced cerebroperfusion. Thus, we have confirmed the neuroprotective effect of AT2R stimulation using a nonpeptide compound which highlights the clinical potential of the AT2R agonists for future development