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1.
Crystallization and melting properties of triacylglycerols (TGs) in anhydrous goat's milk fat (AGMF) are investigated by X-ray diffraction as a function of temperature (XRDT) coupled with high-sensitivity differential scanning calorimetry (DSC), using synchrotron radiation and Microcalix. The polymorphic behavior of AGMF was monitored by varying the cooling rates between 5 and 1 degrees C/min from 45 to -20 degrees C with their subsequent melting at 1 degrees C/min. Quenching of AGMF at -20 degrees C was also examined to determine the metastable polymorphic form of AGMF. At intermediate cooling rates, TGs in AGMF crystallize, from about 18 degrees C in two different lamellar structures with triple chain length 3Lalpha stacking of 72 A and a double chain length 2Lalpha stacking of 48 A, which are correlated to two overlapped exothermic peaks recorded by DSC. A reversible transition sub alpha <--> alpha was observed. Subsequent heating at 1 degrees C/min shows numerous structural rearrangements before final melting. At fast cooling of AGMF (5 degrees C/min), similar unstable crystalline varieties are formed while three endotherms are recorded. Several new unstable lamellar structures are observed after quenching. All of these data are compared to those previously reported at slow cooling (0.1 degrees C/min) showing a relative stability of the structures formed. In spite of general similitude, the thermal and structural behavior of the goat's milk is more complex than that of the cow's milk.  相似文献   
2.
Ollivon  D.  Blanchard  M.  Garban  B. 《Water, air, and soil pollution》1999,115(1-4):429-444

PAHs produced by motor vehicle combustion were determined in the dusts from the substructures of a parisian car park. The high levels of benzo(ghi)perylene (bgp) and pyrene (pyr) expressed as ratios to fluoranthene (flu), were 1.73 and 1.23, respectively, which was typical of these exhausts. From these findings, bgp and pyr may be used as tracers for estimating the contamination fluctuations and transfer processes in rain waters and river waters, in a highly industrialized and urbanized area. During flood events, the pollution related to atmospheric scavenging alone was negligible as compared to that due to urban surface leaching, contrary to steady period events. During that last period, when the river contamination was low, about 40 ng L?1, and when mean bulk precipitation concentrations were about 350 ng L?1, minor precipitations might contribute less than 2% to river contamination, whereas heavy showers might induce a quite important pollution flush: PAH concentrations were twice higher and 26% of the inputs came from rain and 74% from runoff in the river Seine.

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3.
Concentrations of Cd, Cu, Ni, Pb and Zn were determined in bulk atmospheric deposition collected at five stations in the Seine River basin (France), to evaluate sources and fluxes of atmospheric trace metals. Bulk deposition (wet + dry) was sampled weekly from March 2001 to February 2002 for 4 sites and from March to December 2001 for the last one. The concentrations of the elements in bulk deposition (dissolved + particulate form) followed the order: Zn > Pb > Cu > Ni > Cd. Concentrations of Zn, Pb and Ni were highly correlated with one another, suggesting a common source, related to the combustion of coal and heavy fuel. Metal concentrations in bulk deposition did not exhibit a high degree of temporal variability over the annual cycle and were not obviously related to meteorological parameters (rainfall, wind). Estimates of the total annual direct atmospheric deposition of metals to the Seine Estuary ranged from 16 kg yr? 1 for Cd to 5600 kg yr? 1 for Zn. Loadings of Cd, Cu and Ni from direct atmospheric inputs were less than 1% of those contributed by the Seine River and loadings of Pb and Zn represented 1.27% and 1.56% of the Seine contribution. Direct atmospheric inputs are negligible compared to fluvial inputs, but the indirect atmospheric deposition to the estuary was not estimated. Based on these results, trace metal concentrations in Paris have decreased by a factor of 4.6 for Zn and by a factor of 50 for Ni from 1988 to 2001. Of particular interest is the continued decrease in bulk deposition of Pb during this period, underlining the impact of policy initiatives concerning the reduction of lead on emissions in France.  相似文献   
4.
Trace metals: Cd, Cu, Cr, Ni, Pb and Zn and persistent organicpollutants: polycyclic aromatic hydrocarbons (PAHs) and polychlorobiphenyls (PCBs) were investigated in a fraction ofsediments characterized by a granulometry < 200 μm. Coresfrom 17 to 54 cm depth, were collected at two sites of theSeine river upstream (Port à l'Anglais) and downstream (Saint-Cloud) from Paris and at one site of the Marne river (Saint-Maurice). Marne river sediments displayed higher Cu andPb levels than those of the Seine river. Except for Cd and Cr,contents did not vary notably in the Seine river sediments.Metal contents, except Pb, were significantly correlated withthe sediment fraction which granulometry is < 50 μm,particularly at Port à l'Anglais (p < 0.001). Correlationcoefficients between Cr, Cu, Ni and Zn contents and clayfractions of the cores ranged from 0.85 to 0.99 at both sitesof the Seine river. PCB levels varied widely, ranging from 27to 689 μg kg-1 and were highly correlated with bothsediment fraction < 50μm and particulate organic carbon(POC) ratio. PAH levels ranged from 2.30 to 41.3 μg g-1 and displayed the highest values close to dams; theyshowed no correlations with sediment fraction < 50 μm and POC.  相似文献   
5.
The water vapor permeability of fat barrier films has been associated with structural characteristics such as polymorphism, crystal size, and chemical composition, among others. However, no mechanistic models have been proposed to describe this relationship. In this study, we have determined the effects of processing conditions on the structure and physicochemical characteristics of four fats and their relationship to water vapor permeability. Results suggest that the solids' volume fraction and the domain size of the fat crystals seem to be the most important factors controlling water vapor migration. Moreover, materials with relatively large crystalline domains will yield malleable films with relatively low storage and loss moduli and strain/stress at the limit of linearity high tan delta values. The structural effects on the permeability of fat films are related to the nanoscale of the material.  相似文献   
6.
The thermal and structural behaviors of anhydrous goat's milk fat (AGMF) have been determined as a function of temperature using a powerful technique allowing simultaneous time-resolved synchrotron X-ray diffraction as a function of temperature (XRDT) and high-sensivity differential scanning calorimetry (DSC) measurements from the same sample. This first paper, aiming at the characterization of the physical properties of AGMF, we examine crystalline organizations made by triacylglycerols (TG) upon slow cooling at /dT/dt/ = 0.1 degrees C/min from 45 to -20 degrees C in order to approach system equilibrium. Three overlapped exotherms were observed by DSC upon cooling, whereas four endotherms were found on the subsequent heating at 1 degrees C/min. XRDT evidenced that AGMF crystallizes under four different lamellar structures, two with double-chain length packings at 41.5 and 38.2 angstroms and two with triple-chain lengths of 72 and 64.7 angstroms stacking. Simultaneous wide-angle XRDT has shown that initial nucleation mainly occurs in a packing of beta' type from approximately 26 degrees C, although some transient presence of alpha was detected. The absence of polymorphic transition, on heating, until final melting (approximately 40 degrees C) demonstrated the relative stability of the structures formed.  相似文献   
7.
The chemical composition and properties of lipids, both triglycerides and phospholipids, play a major role in the functional and nutritional properties of food products. In this study, the suprastructure of fat, solid fat content, and crystallographic properties of triglycerides were investigated in hard-type cheeses from the microscopic scale to the molecular level using the combination of relevant techniques. Two industrial cheeses with different oiling off properties were compared with experimental cheeses manufactured in the laboratory. Microstructural analysis performed using confocal laser scanning microscopy showed that milk processing led to the disruption of fat globules with the formation of nonglobular fat. For a similar fatty acid composition, oiling off was mainly related to the fat in dry matter content and to the suprastructure of fat in cheese. An exogenous fluorescent phospholipid permitted the localization of milk phospholipids in the cheese matrix, which mainly remain around fat inclusions after disruption of the milk fat globule membrane, and to show heterogeneities. We also showed using differential scanning calorimetry that the suprastructure of fat did not affect the solid fat content in cheese at 4 degrees C: 71.6 +/- 4.9%. The organization of triglyceride molecules in fat crystals, elucidated at a molecular level using X-ray diffraction, corresponded to the coexistence of 2 lamellar structures (2L 40.5 angstroms and 3L 54.6 angstroms) with four polymorphic forms: alpha, two beta' and beta. A schematic representation of the multiscale organization of triglycerides and phospholipids in cheese is proposed.  相似文献   
8.
The sensorial, functional, and nutritional properties of goat dairy products result from the specific fatty acid composition of goat's milk fat. However, information on the physical and thermal properties of goat's milk fat is scarce. In this study, crystallization of triacylglycerols (TG) in goat's milk fat globules was investigated using polarized light microscopy and the coupling of time-resolved synchrotron radiation X-ray diffraction (XRD) and high-sensitivity differential scanning calorimetry (DSC). The molecular organization of the solid fat phase was characterized for cooling rates between 3 and 0.1 degrees C/min. Quenching of goat's milk fat globules from 50 to -8 degrees C and 4 degrees C was also examined to identify the most unstable polymorphic forms of TG. Then, the melting behavior of fat crystals was studied on subsequent heating at 1 degrees C/min. Triple chain length (3L: 68.6-70 A) and double chain length (2L: 37-45.4 A) structures were characterized and 5 polymorphic forms, alpha, sub-alpha, beta' 1, beta' 2, and beta were identified. Polymorphic transitions were observed within goat's milk fat globules as a function of time after quenching and as a function of temperature on heating. From a technological point of view, this work will contribute to a better understanding of the rheological properties as well as on the flavor evolutions of goat's milk-based products.  相似文献   
9.
Sixteen EPA chosen polycyclic aromatic hydrocarbons (PAH) were studied in the sediments and the suspended matter of the River Seine to determine existing pollution. Analyses were carried out by HPLC with coupled fluorimetric and UV detectors. PAH contents were found to be highly variable depending on many factors such as anthropogenic activities, weather and flow rate of the river, and occasionally they rose to alarming levels. Contents of 16 PAH ranged from 1.5 to 7.4 μg g?1 in the sediments, but a peak at 60.7 μg g?1. In the suspended matter the contents were usually below 10 μg g?1. From these results and taking into account the mean content of suspended matter in the river downstream from Paris, the total adsorbed PAH concentration in the river Seine should be about 60 ng l?1. Evidence has been established that storm drain discharges are a major source of pollution.  相似文献   
10.
Atmospheric nitrogen species (NH4-N and (NO3+NO2)-N) were determined in weekly samples of atmospheric bulk deposition (dry plus wet), collected in France at seven sites over the course of a year. Rural, semi-rural and industrialised-urban sites were chosen in the Seine river watershed from the Seine estuary to upstream from Paris. Mean NH4-N concentrations varied from 0.7 to 1.7 mg L-1. Mean (NO3+NO2)-N concentrations were approximately 0.5 mg L-1 for all sites except Paris (0.7 mg L-1), which has a local impact on the fallout contamination from urban emissions. The relation between concentration and rainfall amount obeys a power law, in the form of y = ax b. When the nitrogen sources are very local, this relationship turns into a dilution law. Annual atmospheric nitrogen deposition (NH4-N+(NO3+NO2)-N) was calculated and varied from 7.8 kg ha-1 yr-1 in the neighbourhood of a rural town to 17.3 kg ha-1 yr-1 in a very industrialised harbour. 58% of the atmospheric nitrogen deposition occurred during ‘spring + summer’ period. The total nitrogen atmospheric input to the Seine estuary, via direct deposition + indirect input via the watershed, was estimated to about 5% of the total nitrogen load within the Seine river basin.  相似文献   
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