911 resultados para Branch and bound method


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A large number of evidences correlate elevated levels of homocysteine (Hcys) with a higher cardiovascular diseases (CVDs) risk, especially, atherosclerosis. Similarly, abnormal low levels of the vitamins B6, B9 and B12 are associated to an instability in the methionine cycle with an over production of Hcys. Thus, biomedical sciences are looking forward for a cheaper, faster, precise and accurate analytical methodology to quantify these compounds in a suitable format for the clinical environment. Therefore the objective of this study was the development of a simple, inexpensive and appropriate methodology to use at the clinical level. To achieve this goal, a procedure integrating a digitally controlled (eVol®) microextraction by packed sorbent (MEPS) and an ultra performance liquid chromatography (UPLC) coupled to a photodiode array detector (PDA) was developed to identify and quantify Hcys vitamins B6, B9 and B12. Although different conditions were assayed, we were not able to combine Hcys with the vitamins in the same analytical procedure, and so we proceeded to the optimization of two methods differing only in the composition of the gradient of the mobile phase and the injected volume. It was found that MEPS did not bring any benefit to the quantification of the Hcys in the plasma. Therefore, we developed and validate an alternative method that uses the direct injection of treated plasma (reduced and precipitated). This same method was evaluated in terms of selectivity, linearity, limit of detection (LOD), limit of quantification (LOQ), matrix effect and precision (intra-and inter-day) and applied to the determination of Hcys in a group composed by patients presenting augmented CVD risk. Good results in terms of selectivity and linearity (R2> 0.9968) were obtained, being the values of LOD and LOQ 0.007 and 0.21 mol / L, respectively. The intra-day precision (1.23-3.32%), inter-day precision (5.43-6.99%) and the recovery rate (82.5 to 93.1%) of this method were satisfactory. The matrix effect (>120%) was, however, higher than we were waiting for. Using this methodology it was possible to determine the amount of Hcys in real plasma samples from individuals presenting augmented CVD risk. Regarding the methodology developed for vitamins, despite the optimization of the extraction technique and the chromatographic conditions, it was found that the levels usually present in plasma are far below the sensitivity we obtained. Therefore, further optimizations of the methodology developed are needed. As conclusion, part of the objectives of this study was achieved with the development of a quick, simple and cheaper method for the quantification of Hcys.

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Two cores, Site 1089 (ODP Leg 177) and PS2821-1, recovered from the same location (40°56'S; 9°54'E) at the Subtropical Front (STF) in the Atlantic Sector of the Southern Ocean, provide a high-resolution climatic record, with an average temporal resolution of less than 600 yr. A multi-proxy approach was used to produce an age model for Core PS2821-1, and to correlate the two cores. Both cores document the last climatic cycle, from Marine Isotopic Stage 6 (MIS 6, ca. 160 kyr BP, ka) to present. Summer sea-surface temperatures (SSSTs) have been estimated, with a standard error of ca. +/-1.16°C, for the down core record by using Q-mode factor analysis (Imbrie and Kipp method). The paleotemperatures show a 7°C warming at Termination II (last interglacial, transition from MIS 6 to MIS 5). This transition from glacial to interglacial paleotemperatures (with maximum temperatures ca. 3°C warmer than present at the core location) occurs earlier than the corresponding shift in delta18O values for benthic foraminifera from the same core; this suggests a lead of Southern Ocean paleotemperature changes compared to the global ice-volume changes, as indicated by the benthic isotopic record. The climatic evolution of the record continues with a progressive temperature deterioration towards MIS 2. High-frequency, millennial-scale climatic instability has been documented for MIS 3 and part of MIS 4, with sudden temperature variations of almost the same magnitude as those observed at the transitions between glacial and interglacial times. These changes occur during the same time interval as the Dansgaard-Oeschger cycles recognized in the delta18Oice record of the GRIP and GISP ice cores from Greenland, and seem to be connected to rapid changes in the STF position in relation to the core location. Sudden cooling episodes ('Younger Dryas (YD)-type' and 'Antarctic Cold Reversal (ACR)-type' of events) have been recognized for both Termination I (ACR-I and YD-I events) and II (ACR-II and YD-II events), and imply that our core is located in an optimal position in order to record events triggered by phenomena occurring in both hemispheres. Spectral analysis of our SSST record displays strong analogies, particularly for high, sub-orbital frequencies, to equivalent records from Vostok (Antarctica) and from the Subtropical North Atlantic ocean. This implies that the climatic variability of widely separated areas (the Antarctic continent, the Subtropical North Atlantic, and the Subantarctic South Atlantic) can be strongly coupled and co-varying at millennial time scales (a few to 10-ka periods), and eventually induced by the same triggering mechanisms. Climatic variability has also been documented for supposedly warm and stable interglacial intervals (MIS 1 and 5), with several cold events which can be correlated to other Southern Ocean and North Atlantic sediment records.

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Deep-sea sediment samples from three Ocean Drilling Program (ODP) Leg 112 sites on the Peru continental margin were investigated, using a number of organic geochemical and organic petrographic techniques, for amounts and compositions of the organic matter preserved. Preliminary results include mass accumulation rates of organic carbon at Site 679 and characteristics of the organic facies for sediments from Sites 679, 681, and 684. Organic-carbon contents are high, with few exceptions. Particularly high values were determined in the Pliocene interval at Site 684 (4%-7.5%) and in the early Pliocene to Quaternary section of Hole 679D (2%-9%). Older sediments at this site have distinctively lower organic-carbon contents (0.2%-2.5%). Mass accumulation rates of organic matter at Site 679 are 0.02 to 0.07 g carbon/cm**2/k.y. for late Miocene to early Pliocene sediments and higher by a factor of 5 to 10 in the Quaternary sediments. The organic matter in all samples has a predominantly marine planktonic and bacterial origin, with minor terrigenous contribution. Organic particle sizes are strikingly small, so that only a minor portion is covered by visual maceral analysis. Molecular organic-geochemical data were obtained for nonaromatic hydrocarbons, aromatic hydrocarbons (including sulfur compounds), alcohols, ketones, esters, and carboxylic acids. Among the total extractable lipids, long-chain unsaturated ketones from Prymnesiophyte algae strongly predominate among the gas chromatography (GC) amenable components. Steroids are major constituents of the ketone and free- and bound-alcohol fractions. Perylene is the most abundant aromatic hydrocarbon, whereas in the nonaromatic hydrocarbon fractions, long-chain n-alkanes from higher land plants predominate, although the total terrigenous organic matter proportion in the sediments is small.

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A simple, reliable, and efficient method has been elaborated for direct determination of isotopic composition of authigenic uranium in siliceous lacustrine sediments. The method is based on studying kinetics of selective extraction of authigenic uranium from sediments by weak solutions of ammonium hydrocarbonate followed by ICP-MS analysis of nuclides. To estimate contamination of authigenic uranium by terrigenous one contents of 232Th and some other clastogenic elements in the extracts were measured simultaneously. Selectivity of extraction of authigenic uranium from the sediments treated with 1% NH4HCO3 solution appeared to be no worse than 99%. The method was applied to analysis of isotopic composition of authigenic uranium at several key horizons of the earlier dated core from the Baikal Lake. Measurements directly show that 234U/238U values in Baikal water varied depending on climate, which contradicts existing hypotheses. Measured 234U/238U ratios in water of the paleo-Baikal match corresponding values reconstructed from isotopic data for total uranium in the sediments on supposition that U/Th ratio is constant in terrigenous fraction of the sediments. Direct experimental determination of total and authigenic nuclides in sediments enhances potentiality of the method for 234U-230Th dating of non-carbonate lacustrine sediments including those from the Baikal Lake within intervals corresponding to periods of glaciation, when sediments were rich in terrigenous components. Portions of terrigenous and authigenic uranium are well separated and we can study variability of sources of terrigenous matter and refine the earlier model for reconstructing climate humidity in the East Siberia.

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A letter from Mr. Reid to Dr. Hales concerning the nature of Tar and a method of obtainig it's Medical Virtues, free from it's hurtful Oils: Whereby also the strength of each dose may be the better ascertained.

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Two tables mounted on boards and bound.

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This work is considered a forgery by Dr. Montague R. James in his Apocryphal New Testament, Oxford, 1924, p. 90.

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First published under title: Progressive and practical method for the study of the French language.

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Issued and bound with v. 3: Tullidge, E.W. The history of Salt Lake City and its founders.

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The 1917 edition has title: List of maps and publications issued by the Topographical surveys branch and available for distribution.