Über die orientierung und den dynamischen formfaktor von kettenförmigen aerosolteilchen in ladungsspektrometern     

W. Stöber  C. Boose  V. Prodi 《Water, air, and soil pollution》1974,3(4):493-506

Electron microscopic inspection of chain aggregates of submicron latex spheres deposited in a change spectrometer reveals a preferred orientation of the chain aggregates with their polar axis almost perpendicular to the sampling surface. It is concluded that the polar axis of the aggregates tends towards a position parallel to the electric field while the aggregates move along the field lines during precipitation. This conclusion is supported by the measurement of the dynamic shape factors of the aggregates. The values are slightly higher than theoretical ones available for prolate spheroids of corresponding elongation and orientation. Analogous results are known from a study of centrifugal precipitation where the motion of the chain aggregates tends to be perpendicular to their polar axis. This explains why dynamic shape factors of chain aggregates as obtained in centrifugal and electrical precipitation experiments are significantly different. Values are given for chain aggregates containing up to eight spheres.  相似文献   

Formation of modified fatty acids and oxyphytosterols during refining of low erucic acid rapeseed oil   总被引：4，自引：0，他引：4  

Lambelet P  Grandgirard A  Gregoire S  Juaneda P  Sebedio JL  Bertoli C 《Journal of agricultural and food chemistry》2003,51(15):4284-4290

Formation of trans fatty acids and cyclic fatty acid monomers was investigated during refining of low erucic acid rapeseed oil. The first steps of the refining process, that is, degumming, neutralization, and bleaching, hardly modified the fatty acid profile. In contrast, deodorization produced substantial quantities of trans fatty acids (>5% of total fatty acids) and small amounts of cyclic fatty acid monomers (650 mg of cyclic fatty acid monomers/kg of oil) when severe conditions (5-6 h at 250 degrees C) were used. Alpha-linolenic acid was the main precursor of cyclic fatty acid monomers. The influence of deodorization on the chemical composition of low erucic acid rapeseed oil was studied additionally. Whereas free fatty acids, peroxides, and tocopherols decreased, neither total polar compounds nor oxyphytosterols changed during deodorization. Oxyphytosterols were identified by GC-MS. Three oxyphytosterols not yet observed in oil were tentatively identified as 6beta-hydroxycampestanol, 6beta-hydroxysitostanol, and 6beta-hydroxybrassicastanol. Brassicasterol oxides were the most abundant oxyphytosterols.  相似文献   

Managing small remnants of native forest to increase biodiversity within plantation landscapes in the south west of Western Australia   总被引：1，自引：0，他引：1  

Robert D. Archibald  Michael D. Craig  Katarzyna Bialkowski  Chris Howe  Treena I. Burgess  Giles E.St.J. Hardy 《Forest Ecology and Management》2011,261(7):1254-1264

Recent expansion of industrial-scale plantations into agricultural areas in Australia has the potential to assist biodiversity conservation by rehabilitating ecosystems at the landscape scale and reducing edge effects, isolation and disturbance within remnants of native vegetation. However, the efficient management of remnants for biodiversity within a plantation estate requires knowledge of both the causes and the consequences of remnant degradation. With this in mind, we examined key ecosystem features and processes relating to soil chemistry, decomposition, native tree health and regeneration and vertebrate abundance, within small forest remnants (1-4 ha) embedded within Eucalyptus globulus plantations in south west Western Australia. Soil nutrient enrichment was significantly associated with a scale of vegetation modification in order from: (1) intact forest, (2) remnants with native understorey (UDN), (3) remnants with exotic understorey (UDE), (4) plantation and (5) pasture. We propose that, in this region, UDE remnants will often remain in a degraded state even after plantation establishment and the cessation of stock grazing. This is due, in part, to more rapid rates of nutrient turnover sustaining higher nutrient availability in the soil following the replacement of ligneous understorey plants with annual ones. Cotton strips placed in surface soils were often disintegrated in UDE remnants and largely intact in UDN remnants, indicating that decomposition was accelerated in the former. Continued tree decline and regeneration failure within UDE remnants will also reinforce the UDE condition. There was less canopy seed set and little or no seedling establishment in UDE remnants compared to UDN remnants. Therefore, management interventions to assist native tree regeneration in UDE remnants are needed. Fauna trapping highlighted the desirability of retaining, and preferably restoring, small remnants in plantations. Small native mammals were found exclusively in remnants and fewer introduced Mus musculus were present in UDN remnants. Higher numbers of native lizards were found in UDN remnants, but this result was not significant (marginally).  相似文献   

Cellular uptake and efflux of trans-piceid and its aglycone trans-resveratrol on the apical membrane of human intestinal Caco-2 cells     

Henry C  Vitrac X  Decendit A  Ennamany R  Krisa S  Mérillon JM 《Journal of agricultural and food chemistry》2005,53(3):798-803

Two stilbenes (trans-piceid and its aglycone trans-resveratrol) were investigated in the uptake across the apical membrane of the human intestinal cell line Caco-2 in order to determine their mechanisms of transport. The uptake was quantified using a reverse phase high-performance liquid chromatography method with fluorescence detection. The rate of cellular accumulation in the cells was found to be higher for trans-resveratrol than for trans-piceid. In addition, trans-resveratrol uses passive transport to cross the apical membrane of the cells, whereas the transport of trans-piceid is likely active. With regard to the mechanisms of transport, the involvement of the active transporter SGLT1 in the absorption of trans-piceid was deduced using various inhibitors directly or indirectly exploiting the activity of this transporter (glucose, phlorizin, and ouabain). Moreover, we investigated the involvement of the multidrug-related protein 2 (MRP2), an efflux pump present on the apical membrane, in stilbene efflux by Caco-2 cells. The effect of MK-571 (an MRP inhibitor) seems to implicate MRP2 as responsible for apical efflux of trans-piceid and trans-resveratrol.  相似文献   

Directional Differences in Pigeon Homing     

Kramer G  Pratt JG  VON St Paul U 《Science (New York, N.Y.)》1956,123(3191):329-330

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Generating solitons by phase engineering of a bose-einstein condensate     

Denschlag J  Simsarian JE  Feder DL  Clark CW  Collins LA  Cubizolles J  Deng L  Hagley EW  Helmerson K  Reinhardt WP  Rolston SL  Schneider BI  Phillips WD 《Science (New York, N.Y.)》2000,287(5450):97-101

Quantum phase engineering is demonstrated with two techniques that allow the spatial phase distribution of a Bose-Einstein condensate (BEC) to be written and read out. A quantum state was designed and produced by optically imprinting a phase pattern onto a BEC of sodium atoms, and matter-wave interferometry with spatially resolved imaging was used to analyze the resultant phase distribution. An appropriate phase imprint created solitons, the first experimental realization of this nonlinear phenomenon in a BEC. The subsequent evolution of these excitations was investigated both experimentally and theoretically.  相似文献   

Low-level radiation     

Stöhrer G 《Science (New York, N.Y.)》1996,274(5292):1450a

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Absence of duplication of chromosome 21 genes in familial and sporadic Alzheimer's disease   总被引：8，自引：0，他引：8  

P H St George-Hyslop  R E Tanzi  R J Polinsky  R L Neve  D Pollen  D Drachman  J Growdon  L A Cupples  L Nee  R H Myers 《Science (New York, N.Y.)》1987,238(4827):664-666

The possibility that Alzheimer's disease (AD) is caused by overexpression or duplication of one or more genes on chromosome 21 has been raised by the observation of AD-like neuropathologic changes in individuals with Down syndrome and by the mapping of both the defect for familial AD and the amyloid beta protein gene to this autosome. Possible duplication on chromosome 21 was investigated in both familial and sporadic AD by means of restriction fragment length polymorphisms for the amyloid and SODI loci, as well as for DNA markers in the vicinity of the familial AD defect and in the critical Down syndrome region of chromosome 21. No evidence of increased DNA dosage was observed in either brain or leukocytes of patients with inherited or sporadic forms of AD. Duplication of these regions is therefore not a frequent event in either form of AD. Furthermore, no significant allelic association was detected between AD and any of the loci, including the amyloid and SODI genes, providing no support for the hypothesis that defects in these specific genes are the primary cause of AD.  相似文献   

Occurrence of isoprenoid Fatty acids in the green river shale     

Eglinton G  Douglas AG  Maxwell JR  Ramsay JN  Ställberg-Stenhagen S 《Science (New York, N.Y.)》1966,153(3740):1133-1135

The most abundant free fatty acids present in a sample of shale from the Green River Formation (Eocene, about 60 x 10(6) years) from Sulfur Creek are the acylic C(19) and C(20) isoprenoid acids. The dominance of these acids parallels the abundance of the corresponding hydrocarbons pristane and phytane.  相似文献   

Oncogenic purine derivatives: evidence for a possible proximate oncogen     

G St?hrer  G B Brown 《Science (New York, N.Y.)》1970,167(925):1622-1624

Two additional urinary metabolites of the chemical oncogen 3-hydroxyxanthine are now identified as 8-chloroxanthine and 8-methylmercaptoxanthine. Such products are thought to be derived from a reactive intermediate which can be tentatively considered to be a proximate oncogen. Since each of these 8-substituted xanthines has also been obtained in vitro by reactions of 3-acetoxyxanthine with chloride ion or methionine, their production in vivo can be explained as resulting through the metabolic formation of an activated ester with a reactivity similar to that of the chemical model.  相似文献