The effects of dietary phospholipids enriched with phosphatidylethanolamine on bile and red cell membrane lipids in humans

The role of phospholipids in biliary cholesterol solubilization and crystallization has only recently begun to be appreciated. Phospholipid vesicles are believed to be the metastable carrier from which cholesterol nucleates. Cholesterol crystallization is influenced by the phospholipid species in bile. Feeding rats and hamsters with diets enriched in phospholipids or their precursors, especially ethanolamine, resulted in reduced cholesterol saturation of bile. Although whole phospholipids are normal dietary constituents, the effects and safety of phospholipid components have not been tested in humans. In the present study, we have evaluated the effects of a dietary phospholipid mixture, enriched with phosphatidylethanolamine, on human bile and red blood cell membrane lipid composition. Five ambulatory volunteers having a chronic indwelling T-tube, with an intact enterohepatic circulation, were investigated. Thirty-six grams of phospholipids (54% phosphatidylethanolamine, 54% linoleyl acyl chains) were added to their daily diet for fourteen days. Biliary nucleation time, cholesterol carriers, as well as plasma, red blood cell membrane, and bile lipid compositions, were monitored. Following phospholipid supplementation, the proportion of linoleyl chains (18:2) in biliary phospholipids increased significantly from 31.1±1.2 to 37.7±5.3%, while that of oleyl chains (18:1) decreased from 11.4±1.6 to 9.6±1.1%. These changes were accompanied by an increase of linoleate and its metabolite, arachidonate, in red cell membranes. Phospholipid feeding did not cause any side effects, and no significant changes in biliary nucleation time, cholesterol, phospholipid, or bile salt concentrations, or in the distribution of cholesterol within micelles or vesicles. We conclude that phospholipid feeding is safe, and can be effective as a vehicle for lecithin fatty acyl chain modulation of bile and lipid membranes. These findings may provide a basis for a controlled modulation of biliary phospholipids to increase cholesterol solubility in bile.     

Microarray Analysis of Oligosaccharide‐Mediated Multivalent Carbohydrate–Protein Interactions and Their Heterogeneity

Carbohydrate–protein interactions (CPIs) are involved in a wide range of biological phenomena. Hence, the characterization and presentation of carbohydrate epitopes that closely mimic the natural environment is one of the long‐term goals of glycosciences. Inspired by the multivalency, heterogeneity and nature of carbohydrate ligand‐mediated interactions, we constructed a combinatorial library of mannose and galactose homo‐ and hetero‐glycodendrons to study CPIs. Microarray analysis of these glycodendrons with a wide range of biologically important plant and animal lectins revealed that oligosaccharide structures and heterogeneity interact with each other to alter binding preferences.     

Adiabatic flow distribution of gas and liquid in parallel pipes—Effect of additional restrictions

The distribution of gas and liquid among four parallel pipes was studied with and without orifice restrictions. The results show that the two phases may not be equally distributed among the pipes. It is shown that the two-phase flow mixture can “choose” to flow in one, two, three or in all four pipes depending on gas and liquid flow rates, on pipe inclination and on the orifice plate size. Addition of orifice plates expands the region of stability and the range of flow in all four pipes. The experimental results are in reasonable agreement with the analysis.     

Cloning and analysis of CoEXG1, a secreted 1,3-beta-glucanase of the yeast biocontrol agent Candida oleophila

Lytic enzymes may have a role in the biological control of fungi. The yeast biocontrol agent, Candida oleophila, is an excellent subject to research this matter. In the present study, CoEXG1, which encodes for a secreted 1,3-beta-glucanase, is the first gene to be cloned from C. oleophila. It was isolated from a partial genomic library and analysed. Its open reading frame and putative promoter were expressed in baker's yeast, Saccharomyces cerevisiae. The reading frame, expressed under the inducible GAL1 promoter, caused an increased secretion of beta-glucanase, and the putative promoter region activated the lacZ reporter gene, to which it was fused. Sequencing analysis revealed that CoEXG1 carries the signature pattern of the 5 glycohydrolases family and has a putative secretion leader, as well as a high degree of identity to yeast 1,3-beta-glucanases. The GenBank Accession No. of CoEXG1 is AF393806.     

Beeping a maximal independent set

We consider the problem of computing a maximal independent set (MIS) in an extremely harsh broadcast model that relies only on carrier sensing. The model consists of an anonymous broadcast network in which nodes have no knowledge about the topology of the network or even an upper bound on its size. Furthermore, it is assumed that an adversary chooses at which time slot each node wakes up. At each time slot a node can either beep, that is, emit a signal, or be silent. At a particular time slot, beeping nodes receive no feedback, while silent nodes can only differentiate between none of its neighbors beeping, or at least one of its neighbors beeping. We start by proving a lower bound that shows that in this model, it is not possible to locally converge to an MIS in sub-polynomial time. We then study four different relaxations of the model which allow us to circumvent the lower bound and find an MIS in polylogarithmic time. First, we show that if a polynomial upper bound on the network size is known, it is possible to find an MIS in $\mathcal O (\log ^3 n)$ time. Second, if we assume sleeping nodes are awoken by neighboring beeps, then we can also find an MIS in $\mathcal O (\log ^3 n)$ time. Third, if in addition to this wakeup assumption we allow sender-side collision detection, that is, beeping nodes can distinguish whether at least one neighboring node is beeping concurrently or not, we can find an MIS in $\mathcal O (\log ^2 n)$ time. Finally, if instead we endow nodes with synchronous clocks, it is also possible to find an MIS in $\mathcal O (\log ^2 n)$ time.     

Common2 extended to stacks and unbounded concurrency

This paper extends Common2, the family of objects that implement and are wait-free implementable from 2 consensus objects, in two ways: First, the stack object is shown to be in the family, refuting a conjecture to the contrary [6]. Second, Common2 is investigated in the unbounded concurrency model, whereas until now it was considered only in an n-process model. We show that the fetch-and-add, test-and-set , and stack objects are in Common2 even with respect to this stronger notion of wait-free implementation. Our constructions rely on a wait-free implementation of immediate snapshots in the unbounded concurrency model, which was previously not known to be possible. The introduction of unbounded concurrency to the study of Common2 opens several directions of research: are there objects that have n-process implementations but are not unbounded concurrency implementable? We conjecture that swap is such an object. Additionally, the hope is that a queue impossibility proof, which eludes us in the n-process model, will be easier to establish in the unbounded concurrency model.     

Drawing directed graphs using quadratic programming

We describe a new method for visualization of directed graphs. The method combines constraint programming techniques with a high performance force-directed placement (FDP) algorithm. The resulting placements highlight hierarchy in directed graphs while retaining useful properties of FDP; such as emphasis of symmetries and preservation of proximity relations. Our algorithm automatically identifies those parts of the digraph that contain hierarchical information and draws them accordingly. Additionally, those parts that do not contain hierarchy are drawn at the same quality expected from a nonhierarchical, undirected layout algorithm. Our experiments show that this new approach is better able to convey the structure of large digraphs than the most widely used hierarchical graph-drawing method. An interesting application of our algorithm is directional multidimensional scaling (DMDS). DMDS deals with low-dimensional embedding of multivariate data where we want to emphasize the overall flow in the data (e.g., chronological progress) along one of the axes.     

Solute dispersion in oscillating electro-osmotic flow with boundary mass exchange

Mass transfer in an oscillatory electro-osmotic flow (EOF) is theoretically studied, for the case of a cylindrical tube with a reactive wall. An expression for the dispersion coefficient, reflecting the time-averaged mass flux of an electrically neutral solute, is derived analytically. Under the influence of a reversible solute-wall mass exchange, the dispersion coefficient exhibits a complex dependence on the various parameters representing the effects of the electric double-layer thickness, oscillation frequency, solution transport properties, solute partitioning, and reaction kinetics. Our results suggest that, in the presence of a reversible mass exchange at the wall, an oscillatory EOF may be used for separation of species. It is found that optimal conditions for separation are achieved for a thin double-layer, where an inert solute, or one with slow exchange kinetics, experiences virtually no dispersion while the dispersion is maximized for the reactive solute exhibiting fast kinetics.