Identity of the major triacylglycerols in ovine milk fat

Ovine milk fat obtained from milk collected from five different flocks was studied to determine its triacylglycerol (TAG) composition using a combination of gas chromatography/mass spectrometry. One hundred and thirty-four molecular species of TAG were identified, but not all could be quantified because some peaks contained more than one species of TAG. Fifty-one per cent of the identified species were trisaturated TAGs, 31% as monounsaturated TAGs and 18% as polyunsaturated TAGs. In terms of chain length, 58 of the TAGs identified (43% of the total) contained short-chain (C4 and C6) fatty acids (FAs), 94 (70%) contained medium-chain FAs (C8–C14) and 112 (84%) were composed of long-chain FAs (C16–C18). One hundred and twenty nine chromatographic peaks were detected. The sum of the 35 peaks, each representing>1 mol% of the TAGs, was 75% of total TAGs. Five peaks, each with>3.5 mol% included trisaturated and monounsaturated TAGs; quantitatively, the largest of these peaks (4.5 mol% of the total TAGs) contained two esterified monounsaturated TAGs with C4: 4,16,18:1 or 4,18,16:1, with the former being present at the highest levels. Comparison of the experimental values of TAG composition in ovine milk with the theoretical values derived from the experimental FA content showed that the distribution of the FAs in the TAGs was not random. The TAGs containing a short-chain FA were synthesized preferentially to those TAGs containing three medium- or three long-chain FAs. Our results for ewes’ milk were very similar to those for cows’ and goats’ milk despite the quantitative differences in the TAG profiles of the different species.     

Chiral gas chromatographic separation of 2-oxabicyclo[3.3.0]octane derivatives and their synthetic precursors

Chiral GC separation of (+/-)-2-allyl-2-carboethoxycyclopentanone (9) and the alcohols (+/-)-3-(hydroxymethyl)-5-carboethoxy-2-oxabicyclo[3.3.0]octane (7), (+/-)-2-allyl-2-carboethoxycyclopentanol (8), and their acetylated and trifluoroacetylated derivatives were investigated on three derivatized beta-cyclodextrins (CDs) diluted in SE-54 or 1701-OH: 2,3,6-tri-O-methyl-beta-CD (PMCD); 2,3-di-O-methyl-6-O-(tert-butyldimethylsilyl)-beta-CD (DIMETBCD); 2,3-di-O-acetyl-6-O-(tert-butyldimethylsilyl)-beta-CD (DIACTBCD). The understanding of these chiral separations is extremely relevant, since cyclopentanic and bicyclic cyclopentanic rings are common structural features of many important natural products and new pharmaceutical drugs. In general DIMETBCD diluted in SE-54 showed the best chiral resolution to alcohols 7 and 8 and only DIACTBCD showed enantioselectivity to 9. Hydrogen bonds prediction and dipole moments data were obtained by molecular modeling calculations for 7ab and 8ab and Ac and TFA derivatives. Comparison of these data with the chromatographic parameters for the related compounds were used to explain the differences of their elution orders and diastereo- and enantiomeric separations on the above chiral stationary phases (CSPs). The results suggest that the CSPs enantioselectivities are not affected by the carboethoxy-functionalized cyclopentanic and bicyclic cyclopentanic rings themselves but mainly by the functional group on the other stereogenic center.     

Objective data alignment and chemometric analysis of comprehensive two-dimensional separations with run-to-run peak shifting on both dimensions.

Data from comprehensive two-dimensional (2-D) separation techniques, such as comprehensive 2-D gas chromatography (GC x GC), liquid chromatography/liquid chromatography (LC x LC) and liquid chromatography/ capillary electrophoresis (LC x CE) can be readily analyzed by various chemometric methods to increase chemical analysis capabilities. A retention time alignment, preprocessing method is presented that objectively corrects for run-to-run retention time variations on both separation dimensions of comprehensive 2-D separations prior to application of chemometric data analysis algorithms. The 2-D alignment method corrects for run-to-run shifting of a sample data matrix relative to a standard data matrix on both separation time axes in an independent, stepwise fashion. After 2-D alignment, the generalized rank annihilation method (GRAM) is successfully applied, substantiating the performance of the alignment method. The alignment method should have important implications, because most 2-D separation techniques exhibit, in the context of chemometric data analysis, considerable run-to-run retention time shifting on both dimensions. Even when there are only three to four points/peak, that is, with three to four separations on the second dimension (column 2) per peak width from the first dimension (column 1), the 2-D alignment coupled with GRAM provides dependable analyte peak identification capabilities and adequate quantitative precision for unresolved analyte peaks. Thus, the 2-D alignment algorithm is applicable to lower data density conditions, which broadens the scope of chemometric analysis to high-speed 2-D separations.     

Modification of the Marching Cubes Algorithm to Obtain a 3D Representation of a Planar Image

Programming and Computer Software - The registration of a 3D model over an image can be seen as the alignment of visual correspondences extracted from these two data. This is a challenging task and...     

Effect of temperature uncertainty on polymer electrolyte fuel cell performance

The temperature of operation is a key parameter in determining the performance and durability of a polymer electrolyte fuel cell (PEFC). Controlling temperature and understanding its distribution and dynamic response is vital for effective operation and design of better systems. The sensitivity to temperature means that uncertainty in this parameter leads to variable response and can mask other factors affecting performance. It is important to be able to determine the impact of temperature uncertainly and quantify how much PEFC operation is influenced under different operating conditions. Here, a simple lumped mathematical model is used to describe PEFC performance under temperature uncertainty. An analytical approach gives a measure of the sensitivity of performance to temperature at different nominal operating temperatures and electrical loadings. Whereas a statistical approach, using Monte Carlo stochastic sampling, provides a ‘probability map’ of PEFC polarisation behaviour. As such, a polarisation ‘area’ or ‘band’ is considered as opposed to a polarisation ‘curve’. Results show that temperature variation has the greatest effect at higher currents and lower nominal operating temperatures. Thermal imaging of a commercial air-cooled stack is included to illustrate the temporal and spatial temperature variation experienced in real systems.     

Effect of nitrogen content in amorphous SiCxNyOz thin films deposited by low temperature reactive magnetron co-sputtering technique

Amorphous silicon oxycarbonitride (SiC_xN_yO_z) films have been deposited on Si substrates by low temperature reactive magnetron co-sputtering of silicon and graphite targets in mixed Ar/N₂ atmosphere. Our studies are focused on the influence of nitrogen incorporation on deposition rate, film composition, film structure, chemical bonds, and electrical resistivity of SiC_xN_yO_z films investigated by profilometry, Rutherford Backscattering Spectrometry (RBS), X-ray diffraction (XRD), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and four-point probe method. RBS results show that all samples contain significant amounts of oxygen (up to 16 at.%) which led to the formation of SiC_xN_yO_z. Further, XPS results show that most of this oxygen is located in the film surface. With the addition of N₂ gas in the plasma, the carbon, and nitrogen contents in the films increase. The increased carbon content is due to the contribution of chemically driven sputtering of the graphite target and the reduction of the sputtering rate of the silicon target owing to poisoning by nitrogen. Raman spectra suggest that the films contain amorphous phases and that the a-C clusters suffer a graphitization with increased N₂ gas flow rate. The XRD analysis confirmed the amorphous structure of these films. According to the XPS analysis, the increase in nitrogen content leads to an increase in SiN and CN bonds, decreasing the SiC, SiSi, and CC bonds. Finally, the films electrical resistivity depends mainly on the nitrogen content, which makes it possible to obtain semiconductor or insulator SiC_xN_yO_z films only by adjusting the N₂ concentration in the gas phase during the deposition process.     

Impurity profiling to match a nerve agent to its precursor source for chemical forensics applications

Chemical forensics is a developing field that aims to attribute a chemical (or mixture) of interest to its source by the analysis of the chemical itself or associated material constituents. Herein, for the first time, trace impurities detected by gas chromatography/mass spectrometry and originating from a chemical precursor were used to match a synthesized nerve agent to its precursor source. Specifically, six batches of sarin (GB, isopropyl methylphosphonofluoridate) and its intermediate methylphosphonic difluoride (DF) were synthesized from two commercial stocks of 97% pure methylphosphonic dichloride (DC); the GB and DF were then matched by impurity profiling to their DC stocks from a collection of five possible stocks. Source matching was objectively demonstrated through the grouping by hierarchal cluster analysis of the GB and DF synthetic batches with their respective DC precursor stocks based solely upon the impurities previously detected in five DC stocks. This was possible because each tested DC stock had a unique impurity profile that had 57% to 88% of its impurities persisting through product synthesis, decontamination, and sample preparation. This work forms a basis for the use of impurity profiling to help find and prosecute perpetrators of chemical attacks.     

Tin-coupled styrene-butadiene rubbers (SBRs). Relationship between coupling type and properties

Following the development of new SBRs for tyre applications, several kinds of tin-polymer bonds (styryl-, butadienyl-, isoprenyl- and α-methylstyryltin) have been studied, in both branched and linear chains. Dynamic-mechanical properties of the carbon black vulcanizates have been analyzed to establish a relationship between structural parameters of polymers and compound properties. The filler-polymer interaction parameter, defined by a ratio of mechanical and dynamic terms, has been used for the evaluation of the compounds. The introduction of different types of tin-polymer bonds, in branched and linear chains of the SBRs, implies an improvement in the hysteresis properties of the vulcanizates as well as a modification of the interaction parameter.