676 research outputs found
Einbettungsprobleme in der Differentialgaloistheorie
Die Differentialgaloistheorie ist analog zur gewoehnlichen Galoistheorie aufgebaut. Statt Polynomgleichungen ueber Koerpern studiert man lineare Differentialgleichungen ueber einem Differentialkoerper K mit Konstantenkoerper C. Wir nehmen an, dass C algebraisch abgeschlossen und von Charakteristik 0 ist. Die Begriffe "Galoiserweiterung" und "Galoisgruppe" und der Hauptsatz der Galoistheorie haben eine Entsprechung in der Differentialgaloistheorie. Auch Einbettungsprobleme koennen wie in der gewoehnlichen Galoistheorie definiert werden. Zuerst verallgemeinern wir den Begriff eines Frattini-Einbettungsproblems von endlichen auf lineare algebraische Gruppen. Dies erlaubt die Zerlegung eines Einbettungsproblems in ein zerfallendes und ein Frattini-Einbettungsproblem wie in der gewoehnlichen Galoistheorie. Als Hauptresultat fuer zusammenhaengende Einbettungsprobleme erhalten wir: --- Im Fall K=C(t) hat jedes zusammenhaengende Einbettungsproblem eine eigentliche Loesung. --- Wir koennen sogar mehr zeigen: Ist der Transzendenzgrad von K ueber C endlich, dann hat jedes zusammenhaengende, effektive Einbettungsproblem eine eigentliche Loesung. Hier ist die Effektivitaet eine technische Bedingung, die im Fall K=C(t) automatisch erfuellt ist. Diese Resultate koennen fuer einige nicht zusammenhaengende Einbettungsprobleme verallgemeinert werden. Hiermit kann das inverse Problem ueber Funktionenkoerper geloest werden: --- Ist K ein Funktionenkoerper in endlich vielen Variablen ueber C, dann kann jede lineare algebraische Gruppe als Differentialgaloisgruppe ueber K realisiert werden. --
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Rethinking How We Use LibGuides: Assessing Content and Creating a Consistent Experience
Re-think it: Libraries for a New Age is a national conference that brings together academic, public and K-12 librarians, administrators, technologists, architects, designers, furniture manufacturers, and educators. Participants gathered to collectively re-think the increasingly important role libraries play in the communities they serve. The conference was held January 8-10, 2018 at the University of Texas and other locations in Austin. In its second edition, Re-think it 2018 is co-hosted by The UT Libraries, the Austin Public Library, the Austin Community College Library Services, and seven additional local library partners.UT Librarie
The Chinese theatre
This item was digitized by the Internet Archive. Thesis (M.A.)--Boston Universityhttps://archive.org/details/thechinesetheatr00obe
The most widely recognized mushroom: Chemistry of the genus Amanita
Abstract: Many review papers have been published on mushrooms of the genus Amanita, as these are well known to both scientific and lay audiences, probably due to the toxic and/or hallucinogenic properties of some species. This article aims to supplement the content of previous reviews by categorizing all of the natural products isolated from any species in the genus Amanita. These compounds are subdivided into six major structural types, and references are provided for all species that have been examined chemically
Discovery of anticancer agents of diverse natural origin
A collaborative multidisciplinary research project is described in which new natural product anticancer drug leads are obtained from a diverse group of organisms, constituted by tropical plants, aquatic cyanobacteria, and filamentous fungi. Information is provided on how these organisms are collected and processed. The types of bioassays are indicated in which crude extracts of these acquisitions are tested. Progress made in the isolation of lead bioactive secondary metabolites from three tropical plants is discussed
Pyrrolizidine alkaloids from Echium glomeratum (Boraginaceae).
The methanolic extract of the whole plant of Echium glomeratum Poir. (Boraginaceae) has afforded five pyrrolizidine alkaloids, three that were (7S, 8R)-petranine (1), (7S, 8S)-petranine (2), and (7R, 8R)-petranine (3a) or (7R, 8S)-petranine (3b), comprising a tricyclic pyrrolizidine alkaloids subclass; and two that were known but to the species: 7-angeloylretronecine (4) and 9-angeloylretronecine (5). All compounds were tested against a human tumor panel for cytotoxicity; no activity was observed (EC50 values > 20 µg/ml)
Tumor Cell Growth Inhibition by Several Annonaceous Acetogenins in an in Vitro Disk Diffusion Assay
The cell inhibition activities of several Annonaceous acetogenins, covering the three major structural classes of bis-adjacent, bis-non-adjacent, and single tetrahydrofuran (THF) ring compounds and their respective ketolactone rearrangement products, were tested in an in vitro disk diffusion assay against three murine (P388, PO3, and M17/Adr) and two human (H8 and H125) cancerous cell lines as well as a non-cancerous immortalized rat GI epithelial cell line (I18). The results demonstrate a dose-dependent inhibition of cancerous cell growth, while non-cancerous cell growth is not inhibited by the same dosages. All of the acetogenins, irrespective of their various structural types, inhibit the growth of adriamycin resistant tumor cells and non-resistant tumor cells at the same levels of potency. These results show that the Annonaceous acetogenins are an extremely potent class of compounds, and their inhibition of cell growth can be selective for cancerous cells and also effective for drug resistant cancer cells, while exhibiting only minimal toxicity to ‘normal’ non-cancerous cells
Novel Strategies for the Discovery of Plant-Derived Anticancer Agents.
Work has continued on the investigation of plants, collected mainly from tropical rainforests, as potential sources of new cancer chemotherapeutic agents. About 400 primary samples are obtained each year, with the chloroform-soluble extract of each being screened against a battery of in vitro assays housed at the three consortial sites in our current National Cooperative Drug Discovery Group (NCDDG) research project. An HPLC-MS dereplication procedure designed to screen out “nuisance” compounds has been refined. Several hundred secondary metabolites that are active in one or more of the primary assays utilized have been obtained in the project to date, and are representative of wide chemical diversity. Some of these are also active in various in vivo assays, inclusive of the hollow fiber assay, which was installed recently as part of our collaborative research effort. A number of bioactive compounds of interest to the project are described
Comparative SAR Evaluations of Annonaceous Acetogenins for Pesticidal Activity
The activities of 44 Annonaceous acetogenins, which were originally isolated by monitoring plant fractionations with the brine shrimp lethality test (BST), were evaluated in the yellow fever mosquito larvae microtiter plate (YFM) assay. The results clearly demonstrate that most acetogenins have pesticidal properties. The structure–activity relationships indicate that the compounds bearing adjacent bis-THF (tetrahydrofuran) rings with three hydroxyl groups are the most potent. Bullatacin (1) and trilobin (7) gave the best activities against YFM with LC50 values of 0·10 and 0·67 mg litre-1, respectively. Compounds showing LC50 values below 1·0 mg litre-1 in this assay are usually considered significant as new lead candidates for pesticidal development. In the BST, the corresponding LC50 values were 1·6×10-3 (1) and 9·7×10-3 (7) mg litre-1. This is the first report of pesticidal structure–activity relationships for a series of Annonaceous acetogenins which are known to act, at least in part, as potent inhibitors of mitochondrial NADH: ubiquinone oxidoreductase
Mapping of sample collection data: GIS tools for the natural product researcher
Scientists engaged in the research of natural products often either conduct field collections themselves or collaborate with partners who do, such as botanists, mycologists, or SCUBA divers. The information gleaned from such collecting trips (e.g. longitude/latitude coordinates, geography, elevation, and a multitude of other field observations) have provided valuable data to the scientific community (e.g., biodiversity), even if it is tangential to the direct aims of the natural products research, which are often focused on drug discovery and/or chemical ecology. Geographic Information Systems (GIS) have been used to display, manage, and analyze geographic data, including collection sites for natural products. However, to the uninitiated, these tools are often beyond the financial and/or computational means of the natural product scientist. With new, free, and easy-to-use geospatial visualization tools, such as Google Earth, mapping and geographic imaging of sampling data are now within the reach of natural products scientists. The goals of the present study were to develop simple tools that are tailored for the natural products setting, thereby presenting a means to map such information, particularly via open source software like Google Earth
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