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1.
Susan T. Weintraub R. Neal Pinckard Timothy G. Heath Douglas A. Gage 《Journal of the American Society for Mass Spectrometry》1991,2(6):476-482
Direct derivatization of the acyl analogue of platelet-activating factor (acyl-PAF) with heptafluorobutyric anhydride results in replacement of the phosphocholine moiety with a heptafluorobutyryl (HFB) group. Electron capture (EC) mass spectrometric analysis of this compound that makes use of negative ion detection along with subsequent accurate mass measurement and tandem mass spectrometry studies revealed that in addition to expected fragmentation due to losses of elements of HF, ketene, and/or acetic acid, there is a rearrangement reaction between the HFB group and the substituent on carbon-2 of the glycerol backbone. For 2-acetyl isomers, this fragmentation yields a characteristic ion at m/z 237; for 1-acetyl isomers, the analogous ion is observed at [M-135]−, along with a corresponding carboxylate anion. The use of the HFB derivative is invaluable for analysis of PAF homologues and analogues because it provides detailed structural information in combination with the high sensitivity of a gas chromatography combined with EC-mass spectrometry assay. 相似文献
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Different methods for the interpretation of linear dichroic spectra of molecules incorporated in uniaxial matrices are discussed. A method based on the combination of both polarized absorption and emission measurements is described for the resolution of absorption and emission spectra into their different polarized components, and for the investigation of molecular distributions in the oriented matrix. The distributions of some planar molecules of different shapes incorporated in stretched polyethylene films are presented. 相似文献
4.
Kielas-Jensen Calvin Cichella Venanzio Casbeer David Manyam Satyanarayana Gupta Weintraub Isaac 《Journal of Optimization Theory and Applications》2021,191(2-3):899-916
Journal of Optimization Theory and Applications - A framework for monitoring a target modeled as Dubins car using multiple UAVs is proposed. The UAVs are subject to minimum and maximum speed,... 相似文献
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Jacob Sagiv 《Tetrahedron》1977,33(17):2303-2313
The influence of substitution on the benzenoid 1Lb, 1La and 1B transitions is studied by the technique of linear dichroism in stretched polyethylene films.The total intensity of the 1Lb system is resolved into induced and vibrational components and the influence of various substitution patterns on the magnitude and polarization of both components is analyzed quantitatively. As expected from theoretical considerations, the vibrational components like the induced intensity are found to be strongly affected by the substituent strength and the symmetry of substitution pattern. The previously accepted assumption, according to which the vibrational intensity is regarded as a constant, appears to be completely unrealistic when dealing with cases of strong substituents. A satisfactory quantitative treatment of both weak and strong substituents using the same simple theoretical approach seems possible only if the systematic variations observed in the vibrational intensity are not neglected.A qualitative analysis is given for the 1La, and 1B systems. The results are compared with available theoretical predictions and previous experimental data.Practical implications of the present new experimental information to the study of aromatic optical activity are discussed. 相似文献
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Brian A. Naughton Benson Sibanda Jory P. Weintraub Julia San Román Vafa Kamali 《Applied biochemistry and biotechnology》1995,54(1-3):65-91
A method of coculturing adult rat hepatic parenchymal cells (PC) and stromal cells in a three-dimensional framework of nylon
filtration screens or biodegradable polymer meshes was developed in our laboratory. Rat liver stroma, which includes vascular
and bile duct endothelial cells, fat-storing cells, fibroblasts, and Kupffer cells, were isolated by gradient centrifugation
afterin situ liver perfusion and expanded in monolayer culture prior to seeding onto nylon screens or bioresorbable polyglycolic acid
(PGA) polymers oriented into a felt-like construct. A second inoculum of freshly isolated PC was applied after the stromal
cells became established. Histological analyses revealed that PC proliferation occurred until all available space for expansion
within the template was exhausted. These cells retained their rounded morphology, and after 4–5 wk 7–9 “layers” of PC filled
the 140-μm deep template. Dioxin-inducible cytochrome P450 activity was detected for up to 58 d in culture, and albumin, fibrinogen,
transferrin, and soluble fibronectin were detected in the medium by enzyme-linked immunosorbent assay (ELISA) for 48 d in
vitro. Immunohistochemical analysis of sections through the cultures confirmed the presence of these proteins as well as cytokeratin
at the cellular level; the extracellular matrix stained for both collagen type III and laminin. Long-term PC proliferation
and function were enhanced by the presence of stromal cells as well as by a meshwork template whose geometry allows the interaction
of PC with stroma and matrix on several different planes. To permit transplantation, co-cultures of hepatic PC and stromal
cells were established on PGA felt constructs instead of nylon screens. After 24 d in vitro, these constructs were grafted
into sites in the mesentery, omentum, and sub-cutaneous tissues of adult Long-Evans rats. The growth of hepatocytes after
30 din situ was evident by histological analysis; grafts of co-cultures regenerated a liver-like architecture consisting of sinusoids
and putative biliary structures. In addition, PC at these extrahepatic graft sites were positive for albumin, transferrin,
and fibrinogen synthesis by immunohistochemistry. Graft survival was enhanced when recipients were subjected to 40% hepatectomy.
Hepatic PC:stromal cell cocultures may prove useful in the restoration of liver function either by direct transplantation
using PGA or similar templates, or as extracorporeal devices, using nylon screens. 相似文献
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This work addresses a tactical planning problem faced by a forestry firm, deciding which timber units to harvest and what
roads to build to obtain the greatest possible benefits. We include uncertainty in prices by means of utility theory. This
enables solutions to be found that the firm finds preferable to those obtained when risk aversion is ignored and makes it
possible to design insurance contracts that benefit the firm while also being attractive to an insurer. Two types of contract
are designed; one dependent on the firm’s operating result and the other independent of it. Metrics are then developed to
quantify the benefits conferred by a contract, demonstrating that the latter contract type dominates the former. These results
are then illustrated by applying them to a simplified planning problem of a forest owned by the Chilean forestry operator
Millalemu. 相似文献