Diversity of the polar lipids of the food-borne pathogenListeria monocytogenes

Listeria monocytogenes is a Gram-positive bacterium that can adapt to high salinity and cold. Because the membrane lipids may play a role in its survival and adaptation, we have examined the polar lipids ofL. monocytogenes. Extraction of total lipids fromL. monocytogenes yielded 7±1 mg/mL wet cells. Polar lipids represented 64% of total lipids and contained 9% lipid-phosphorus. Polar lipids were separated into 14 components by two-dimensional thin-layer chromatography. Eight components (88% of polar lipids) contained lipid-phosphorus; among these was one major component (34% of polar lipids). Two other phospholipids were ninhydrin-positive components and accounted for 15% of the polar lipids. Orcinol staining revealed two glyco- or sulfo-lipids accounting for 9% of polar lipids. Five components (4% of polar lipids) were amino components free of phosphorus. The major component contained 46% of its fatty acids as 15:0anteiso, 24% as 17:0anteiso, and 11% as 15:0iso. The fatty acid profile of the remaining polar lipids was variable, consisting primarily of 16:0, 18:0, 15:0anteiso, and 17:0anteiso. Their unsaturation level was ≤20%; however, the major phosphoaminolipid component was 46% unsaturated. The ratios of 15:0anteiso/17:0anteiso and 15:0anteiso/15:0iso were similar in all classes, averaging 1.5 and 4.5, respectively. Since the adaptation process to stressful environments involves activation of a membrane transport system for the protectant glycine betaine, the membrane lipids may play a role in enabling transport.     

Effect of the spreading procedure on the formation of cationic–anionic mixed monolayers

Mixed monolayers of dioctadecyldimethylammonium bromide (DODAB) with sodium hexadecylsulfate (SHS) can be obtained by spreading both components at the interface, co-spread (1) or separately spread (2), or by incorporation of the water soluble surfactant SHS from the subphase (3). The most efficient procedure is co-spreading, when equimolar amounts are used. On the other hand, when the components are spread separately at the interface, or when SHS is adsorbed from the aqueous subphase, it is not possible to obtain an efficiency as high as that of co-spreading, even after 5 h. The equimolar composition at the interface can also be immediately obtained after solvent evaporation when SHS is added to the subphase in large excess to DODAB (9:1); alternatively, the same composition can be obtained from smaller excesses of SHS to DODAB, but only after larger time intervals. The composition of the mixed monolayers obtained by procedures 2 and 3 was estimated from the correlation compressibility–composition, obtained independently by co-spreading.     

Sampling Errors in the Estimation of Peak Wind-Induced Internal Forces in Low-Rise Structures

Peak values in time histories of wind effects may be obtained by using the entire information inherent in the time series of the wind effect, a method entailing the estimation of the probability distribution of the peak through the application of the classical Rice procedure extended for non-Gaussian time histories. We present estimates of the sampling errors inherent in this method. These are needed for structural reliability calculations and for decisions on the requisite length of wind tunnel pressure records, especially for database-assisted design. If based on the analysis of 1-h-long records generated by Monte Carlo simulation, typical sampling errors in the estimation of peaks of time histories corresponding to windstorms of 1-h duration are about 5%. If based on 30- or 20-min records, they are about 1.5 times or twice as large, respectively. Consideration of the sampling errors in reliability calculations entails an estimated increase in the requisite safety margins with respect to wind loading of roughly 2, 3, and 5% if 1-h, 30-min, or 20-min records are used, respectively.     

Wind speed estimation uncertainties: effects of climatological and micrometeorological parameters

To achieve structures that are risk-consistent, structural reliability methods must be used that account for uncertainties with respect to the relevant parameters affecting the estimation of wind effects. In this paper, we obtain measures of uncertainties in the estimation of the wind speeds upwind of structures. These uncertainties are due to incomplete knowledge with respect to the relevant extreme climatological and micrometeorological parameters. Advances in wind engineering and improvements in computational capabilities now make it possible to improve upon earlier estimates available in the literature. The work presented in this paper is a phase of a broader NIST project aimed at developing user-friendly software for the estimation of probabilities of failure of low-rise structures subjected to wind loads.     

Poly(ethylene oxide) Grafted to Silicon Surfaces: Grafting Density and Protein Adsorption

Poly(ethylene oxide) (PEO) polymer, in linear and star form, was covalently grafted to silicon surfaces, and the surfaces were tested for their ability to adsorb proteins. Linear PEG of molecular weight 3400, 10 000, and 20 000 g/mol and star PEO molecules were coupled via their terminal hydroxyl groups activated by tresyl chloride to aminosilane-treated silicon wafers. The amount of PEO coupled to the surface was varied by changing the concentration of the tresyl-PEO solution. The dry PEO thickness on the surface was measured using X-ray photoelectron spectroscopy (XPS) and ellipsometry, from which the grafting density was calculated. The PEO surfaces were exposed to solutions of each of three proteins: cytochrome-c, albumin, and fibronectin. The degree of adsorption of each protein was determined by XPS and ellipsometry and recorded as a function of PEO grafting density. All three proteins were found to reach zero adsorption at the highest grafting densities on all three PEG surfaces, which for all three PEG surfaces was a PEO content of 100 +/- 10 ng/cm2. On both star PEO surfaces, albumin and fibronectin decreased to zero adsorption at intermediate values of grafting density, whereas cytochrome-c continued to adsorb at all grafting densities, although with a decreasing trend. A physical model of the surface helped explain these protein adsorption results in terms of the spacing and degree of overlap of grafted PEO chains.     

Effect of lead on the uptake of nutrients by unicellular algae

From batch growth experiments carried out with the alga Selenastrum capricornutum Printz the evolution of uptake of nitrogen and phosphorus with time in the absence and presence of lead 1 × 10⁻⁶ M and at pH 7 and 4 has been considered. The change of pigments (chlorophylls a, b and vegetal carotenoids) with time, as well as the labile and total lead in the medium and in the alga and the fluorescence compounds released by the alga, have also been analysed.Relationships between phosphorus in the alga and the pigments and lead in the cell, as well as between phosphorus and fluorescence compounds exudated by each unit of the unicellular alga, have been examined in order to try to understand the biochemical mechanism.     

Uranium Recovery from Phosphoric Acid with Selective Resins

The synthesis and performance of resins selective for adsorbing uranium from wet-process phosphoric acid were studied. The resins' capacity for uranium was determined in batch experiments and in columns. The morphology of the resin was examined by scanning electron microscopy. The conditions of column loading and elution were found and the concentration of uranium in the eluent was increased more than 50-fold from 0.15 g/l to 5–7.     

Cobalt-Catalyzed Green Cross-Dehydrogenative C(sp<Superscript>2</Superscript>)-H/P-H Coupling Reactions

Joined electrolysis of arenes (benzene or coumarin derivatives) and diethyl-H-phosphonate (EtO)₂P(O)H in the presence of [CoCl₂(bpy)] catalyst (5%) in an ethanol-aqueous solution in reductive conditions allows obtaining the desired products in a single step by aromatic C–H bonds phosphonation with yields up to 70%. The only by-product is hydrogen; the reaction proceeds at room temperature and does not require specially added reducing agents and oxidants or other initiators. Radical mechanism has been confirmed for the catalytic reaction proceeding via bicobalt phosphonates with Co–P bond, the structure of which also has been identified.     

Dynamic graph summarization: a tensor decomposition approach

Due to the scale and complexity of todays’ social networks, it becomes infeasible to mine them with traditional approaches. A possible solution to reduce such scale and complexity is to produce a compact (lossy) version of the network that represents its major properties. This task is known as graph summarization, which is the subject of this research. Our focus is on time-evolving graphs, a more complex scenario where the dynamics of the network also should be taken into account. We address this problem using tensor decomposition, which enables us to capture the multi-way structure of the time-evolving network. This property is unique and is impossible to obtain with other approaches such as matrix factorization. Experimental evaluation on five real world networks implies promising results demonstrating that tensor decomposition is quite useful for summarizing dynamic networks.