Dynamics of Vesicle Suspensions in Shear Flow Between Walls

The behaviour of a vesicle suspension in a simple shear flow between plates (Couette flow) was investigated experimentally in parabolic flight and sounding rocket experiments by Digital Holographic Microscopy. The lift force which pushes deformable vesicles away from walls was quantitatively investigated and is found to be rather well described by a theoretical model by Olla (J Phys II (France) 7:1533, 1997). At longer shearing times, vesicles reach a steady distribution about the center plane of the shear flow chamber, through a balance between the lift force and shear induced diffusion due to hydrodynamic interactions between vesicles. This steady distribution was investigated in the BIOMICS experiment in the MASER 11 sounding rocket. The results allow an estimation of self-diffusion coefficients in vesicle suspensions and reveal possible segregation phenomena in polydisperse suspensions.     

Binary search trees with binary comparison cost

We introduce a new variant of the cost measure usually associated with binary search trees. This cost measure BCOST, results from the observation that during a search, a decision to branch left need require only one binary comparison, whereas branching right or not branching at all requires two binary comparisons. This is in contrast with the standard cost measure TCOST, which assumes an equal number of comparisons is required for each of the three possible actions. With BCOST in mind we re-examine its effect with respect to minimal and maximal BCOST trees, minimal and maximal BCOST-height trees, and introduce a class of BCOST-height balanced trees, which have a logarithmically maintainable stratified subclass. Finally, a number of other issues are briefly touched upon.This work was partially supported by NATO Grant GR 155.81, Natural Sciences and Engineering Research Council of Canada Grant No. A-5692, and National Science Foundation Grant No. MCS-8116522.     

An oscillation-driven neural network for the simulation of an olfactory system

Understanding the nonlinear dynamics of an olfactory bulb (OB) is essential for the modelling of the brain and nervous system. We have analysed the nature of odour-receptor interactions and the conditions controlling neural oscillations. This analysis is the basis for the proposed biologically plausible three-tiered model of an oscillation-driven neural network (ODNN) with three non-linearities. The layered architecture of the bulb is viewed as a composition of different processing stages performing specific computational tasks. The presented three-tiered model of the olfactory system (TTOS) contains the sensory, olfactory bulb and anterior nucleus tiers. The number of excitatory (mitral/tufted) cells differs from the number of inhibitory (granule) cells, which improves the cognitive ability of the model. The odour molecules are first received at the sensory layer, where receptor neurons spatio-temporally encode them in terms of spiking frequencies. Neurons expressing a specific receptor project to two or more topographically fixed glomeruli in the OB and create a sensory map. Excitatory postsynaptic potentials are formed in the primary dendrite of mitral cells and are encoded in an exclusive way to present them to the coupled non-linear oscillatory model of the next mitral-granule layer. In a noisy background, our model functions as an associative memory, although it operates in oscillatory mode. While feed-forward networks and recurrent networks with symmetric connections always converge to static states, learning and pattern retrieval in an asymmetrically connected neural network based on oscillations are not well studied. We derive the requirements under which a state is stable and test whether a given equilibrium state is stable against noise. The ODNN demonstrates its capability to discriminate odours by using nonlinear dendro-dendritic interactions between neurons. This model allows us to visualise and analyse how the brain is able to encode information from countless molecules with different odour receptors.     

Alveolar sacs and the expirograms of He and SF6: a model study

In 1975, Hansen and Ampaya described alveolated outpouchings in the walls of the acinar ducts, which were observed in all airway generations within the acini. These structures were called alveolar sacs, and they appear to contain the larger fraction (56%) of the acinar volume. The total depth of an alveolar sac including its alveoli (approximately 0.32 mm) is comparable to the mean length of an acinar duct (0.18 to 0.97 mm). Therefore, the alveolar sacs contribute to the asymmetric morphology of the acini. In this paper we investigate the impact of this aspect of the alveolar sacs on the shape of the expirograms of He and SF6. To that end, single-breath washout experiments were simulated with two different mathematical lung models. The one model is an airway model in which the alveolar sacs are modelled explicitly by separate compartments. The expirograms obtained with this model are compared to those obtained with a conventional axisymmetric airway model which is used as a reference model. In this model the volumes of the alveolar sacs are added to those of the acinar ducts; i.e., both air spaces are represented by the same compartments. The washout of He and SF6 was simulated for three different breathing maneuvers corresponding to ventilatory conditions at rest and at exercise. Comparison of the expirograms obtained with the two models showed no differences between their shapes when identical dimensions are used for the lengths and cross sections of the alveolar ducts in the two models. We conclude that the contribution of the alveolar sacs to the asymmetric morphologic structure of the acini has no consequences for the shape of the expirograms of He and SF6.     

Thymus lotocephalus wild plants and in vitro cultures produce different profiles of phenolic compounds with antioxidant activity

We compared the phenolic metabolites and antioxidant activities of Thymus lotocephalus G. López & R. Morales wild plants and in vitro cultures using different extraction solvents. HPLC-DAD analysis allowed the identification and quantification of phenolic (caffeic and rosmarinic) acids and flavones (luteolin and apigenin) in extracts from both sources. The in vitro cultures accumulated large amounts of rosmarinic acid. However, extracts from both sources were able to neutralise free radicals in different test systems (TEAC and ORAC assays), to form complexes with Fe(2+) and to protect mouse brains against Fe(2+)-induced lipid peroxidation. The solvent significantly influenced the phenolic content and antioxidant activity of the extracts, water/ethanol being the most efficient for the extraction of antioxidant phytochemicals. We conclude that in vitro cultures of T. lotocephalus represent a promising alternative for the production of valuable natural antioxidants and an efficient tool for the in vitro biosynthesis of rosmarinic acid, therefore avoiding the need to exploit populations of wild plants.     

Ditopic Cyclodextrin‐Based Receptors: New Perspectives in Aqueous Organometallic Catalysis

The mass transfer properties of mono‐ and ditopic β‐cyclodextrin‐based receptors have been evaluated in a biphasic palladium‐catalyzed Tsuji–Trost reaction and compared to one of the best mass‐transfer promoters, namely the randomly methylated β‐cyclodextrin. While monotopic receptors appeared to be poor mass‐transfer promoters of long alkyl chain allyl carbonates or urethanes, cooperative effects have been evidenced with ditopic cyclodextrin‐based receptors, opening new perspectives in aqueous organometallic catalysis.     

Season and location–specific nitrous oxide emissions in an almond orchard in California

Almonds are an important commodity in California and account for around 15% of the state’s fertilizer nitrogen (N) consumption. Motivated by strong correlations typically observed between fertilizer N inputs and emissions of the potent greenhouse gas and ozone depleting molecule nitrous oxide (N₂O), this study aimed to characterize spatial and temporal patterns in N₂O emissions in an almond orchard under typical agronomic management. N₂O fluxes were measured for a total of 2.5 years, including 3 growing seasons and 2 dormant seasons. Measurements targeted two functional locations, defined as tree rows and tractor rows. In conjunction with the flux measurements, we determined driving variables including soil ammonium (NH₄ ⁺) and nitrate (NO₃ ^?), dissolved organic carbon (DOC), soil water-filled pore space (WFPS), soil pH, air temperature and precipitation. Cumulative annual N₂O emissions were low (0.65 ± 0.07 and 0.53 ± 0.19 kg N₂O–N ha^?1 year^?1 in year 1 and 2, respectively), likely due to the coarse soil texture and microject sprinkler irrigation and fertigation system. Emission factors (EF), conservatively calculated as the ratio of N₂O emitted to fertilizer N applied, were 0.25 ± 0.03% and 0.19 ± 0.07% for year 1 and 2, respectively, which is below the IPCC EF range of 0.3–3%. Correlation analyses between N₂O and driving variables suggested that overall N₂O production was limited by microbial activity and nitrification was likely the major source process, but specific drivers of N₂O emissions varied between seasons and functional locations.