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Static System (static + system)
Selected AbstractsSampling in the Great Lakes for pharmaceuticals, personal care products, and endocrine-disrupting substances using the passive polar organic chemical integrative samplerENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2010Hongxia Li Abstract The passive polar organic chemical integrative sampler in the pharmaceutical configuration (i.e., pharmaceutical-POCIS) was calibrated for sampling at water temperatures of 5, 15 and 25°C to determine the influence of temperature on chemical-specific sampling rates (RS), thus providing more robust estimates of the time-weighted average concentrations of pharmaceuticals and personal care products (PPCPs) and endocrine-disrupting substances (EDS) in surface water. The effect of water temperature and flow on the RS of these analytes was evaluated in the laboratory with a static system. The loss of the test compounds from water by uptake into POCIS was linear over an 8-d period, and these experimental data yielded RS values in the range of 0.07 to 2.46 L/d across the temperature range for the 30 compounds tested. Water temperature and flow influenced POCIS uptake rates, but these effects were relatively small, which is consistent with the theory for uptake into POCIS samplers. Therefore, under a narrow range of water temperatures and flows, it may not be necessary to adjust the RS for POCIS. Except for acidic drugs and sulfonamide antibiotics, RS values were positively correlated with octanol,water partition coefficients (log KOW) of the test compounds. A linear relationship was also observed between RS and chromatographic retention times on a C18 reversed-phase column. These observations may provide a rapid method for estimating the RS of additional chemicals in the POCIS. The application of the RS to POCIS deployed for one month in Lake Ontario, Canada, during the summers of 2006 and 2008 yielded estimates of PPCP and EDS concentrations that are consistent with conventional concentration measurements of these compounds in Lake Ontario surface water. Environ. Toxicol. Chem. 2010;29:751,762. © 2009 SETAC [source] agr -Genotyping and transcriptional analysis of biofilm-producing Staphylococcus aureusFEMS IMMUNOLOGY & MEDICAL MICROBIOLOGY, Issue 1 2007Viviana Cafiso Abstract We investigated the correlation between biofilm production and the accessory-gene-regulator (agr) in 29 strains isolated from catheter-associated infections compared to a control group (30 isolates). All strains were tested for their ability to produce biofilm in a static system, and their agr genotype was determined. ScaI-restriction fragment length polymorphism for agr -typing showed that strong biofilm-producing strains belong to agr - type II. We found two new agr -variants, and sequence analysis of the three PCR products revealed the insertion of IS256 within the agr- locus. Biofilm production was assessed and correlated with agr functionality, with the expression of the ica -operon and of two transcriptional regulators, sarA and rsbU. Our data show that agr -II strains produce large amounts of biofilm, possess a defective agr -system show early transcription of icaA and are defective in haemolysin activity, icaR transcription, and in the expression of the ,B activator rsbU. Strains with agrIII are medium biofilm producers, have an inactive agr -system, but express icaAR and rsbU in the late- and postexponential growth phases. In agrI,IV- and -IA-variants, medium or weak biofilm production was found. In these strains, the agr -locus was fully functional, rsbU- icaR and icaA were found in the late- and/or postexponential phases. Biofilm production was not affected by sarA. [source] The mechanisms of the homogeneous, unimolecular, elimination kinetics of several , -substituted diethyl acetals in the gas-phaseJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2010José R. Mora Abstract The rates of gas-phase elimination of several , -substituted diethyl acetals have been determined in a static system and seasoned with allyl bromide. The reactions, inhibited with toluene, are homogeneous, unimolecular, and follow first-order law kinetics. These elimination processes involve two parallel reactions. The first parallel reaction yields ethanol and the corresponding ethyl vinyl ether. The latter product is an unstable intermediate and further decomposes to ethylene and the corresponding substituted aldehyde. The second parallel reaction gives ethane and the corresponding ethyl ester. The kinetics has been measured over the temperature range of 370,441,°C and pressure range of 23,160,torr. The rate coefficients are given by the following Arrhenius equations: The differences in the rates of ethanol formation may be attributed to electronic transmission of the , -substituent. The comparative kinetic and thermodynamic parameters of the parallel reactions suggest two different concerted polar four-membered cyclic transition state types of mechanisms. Copyright © 2010 John Wiley & Sons, Ltd. [source] Experimental and theoretical studies of the elimination kinetics of 3-hydroxy-3-methyl-2-butanone in the gas phaseJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2005Mariana Graterol Abstract The kinetics of the gas-phase elimination of 3-hydroxy-3-methyl-2-butanone was investigated in a static system, seasoned with allyl bromide, and in the presence of the free chain radical inhibitor toluene. The working temperature and pressure range were 439.6,489.3°C and 81,201.5,Torr (1,Torr,=,133.3,Pa), respectively. The reaction was found to be homogeneous, unimolecular and to follow a first-order rate law. The products of elimination are acetone and acetaldehyde. The temperature dependence of the rate coefficients is expressed by the following equation: log[k1(s,1)],=,(13.05±0.53),(229.7±5.3),kJ,mol,1 (2.303RT),1. Theoretical estimations of the mechanism of this elimination suggest a molecular mechanism of a concerted non-synchronous four-membered cyclic transition-state process. An analysis of bond order and natural bond orbital charges suggests that the bond polarization of C(OH),C(O),, in the sense of C(OH),+&·C(O),,, is rate limiting in the elimination reaction. The rate coefficients obtained experimentally are in reasonably good agreement with the theoretical calculations. The mechanism of 3-hydroxy-3-methyl-2-butanone elimination is described. Copyright © 2005 John Wiley & Sons, Ltd. [source] Kinetics of elimination of several heterocyclic carbamates in the gas phase,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2002Yannely Brusco Abstract The kinetics of the gas-phase elimination of several heterocyclic carbamates were determined in a static system over the temperature range 190.0,409.7,°C and the pressure range 26.5,125,Torr (1,Torr,=,133.3,Pa). The reactions in seasoned vessels, with the free radical inhibitor cyclohexene and/or toluene always present, are homogeneous and unimolecular and obey a first-order rate law. The observed rate coefficients are represented by the following Arrhenius equations: for tert -butyl-1-pyrrolidine carboxylate, log k1 (s,1),=,(11.36,±,0.31) ,(145.4,±,3.1)kJ,mol,1 (2.303RT),1; for 1-(tert -butoxycarbonyl)-2-pyrrolidinone, log k1 (s,1),=,(11.54,±,0.29) ,(140.8,±,2.8)kJ,mol,1 (2.303RT),1; for tert -butyl-1-pyrrole carboxylate, log k1 (s,1),=,(12.12,±,0.05) ,(145.2,±,1.0),kJ,mol,1 (2.303RT),1; and for 1-ethylpiperazine carboxylate, log k1 (s,1),=,(12.05,±,0.19) ,(188.2,±,4.6),kJ,mol,1 (2.303RT),1. The saturated heterocyclic carbamates show a decrease in rates of elimination due to electronic factors. Heterocyclic carbamates with a nitrogen atom able to delocalize its electrons with ,-bonds present in the ring were found to enhance the rates due to resonance interactions. Copyright © 2002 John Wiley & Sons, Ltd. [source] Verstärken von Stahlbetonstützen mit textilbewehrtem BetonBETON- UND STAHLBETONBAU, Issue 10 2009Regine Ortlepp Dr.-Ing. Versuche; Bewehrung Abstract Der Aufsatz beschreibt die Ergebnisse experimenteller Untersuchungen zur Wirkung einer Textilbetonverstärkung an 2 m langen Stützen mit und ohne innen liegender Stahlbewehrung. Die Verstärkung mit textilbewehrtem Beton wurde auf zwei verschiedene Weisen ausgeführt, sowohl als vollständige Umwicklung über die gesamte Länge der Stützen als auch als teilweise Verstärkung über eine Länge von 30 cm in den Lasteinleitungsbereichen. Die einzelnen Anteile am Tragverhalten der verstärkten Stützen wurden untersucht. Ein einfaches Berechnungsmodell wird angegeben. Strengthening of Columns using Textile Reinforced Concrete (TRC) In the context of rehabilitation and repair works or in the course of usage changes of existing buildings the planning engineer frequently is confronted with the task of strengthening the loadbearing structure. This can become necessary, for example, if live loads are increased because of changes of use or if the structural safety of a building must be restored after a fire or earthquake. Particularly columns represent important components and elements of the static system for many buildings, whose main task is bearing normal forces. The results of experimental tests on the effect of a strengthening from textile reinforced concrete at 2 m long columns, both with and without internal steel reinforcement, are described in this article. The strengthening with textile reinforced concrete was made both wrapping round completely along the full height of the columns and partly wrapping round the columns along 300 mm in the load introduction ranges. Related to the unstrengthened reference columns ultimate load increasings by up to 85% could thereby be achieved. The individual components of the load bearing properties are analysed. A simple calculation model is indicated. [source] Relativistically expanding cylindrical electromagnetic fieldsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2009K. N. Gourgouliatos ABSTRACT We study relativistically expanding electromagnetic fields of cylindrical geometry. The fields emerge from the side surface of a cylinder and are invariant under translations parallel to the axis of the cylinder. The expansion velocity is in the radial direction and is parametrized by v=R/(ct). We consider force-free magnetic fields by setting the total force the electromagnetic field exerts on the charges and the currents equal to zero. Analytical and semi-analytical separable solutions are found for the relativistic problem. In the non-relativistic limit, the mathematical form of the equations is similar to equations that have already been studied in static systems of the same geometry. [source] Maintenance of pluripotency in mouse embryonic stem cells cultivated in stirred microcarrier culturesBIOTECHNOLOGY PROGRESS, Issue 2 2010Paulo A. N. Marinho Abstract The development of efficient and reproducible culture systems for embryonic stem (ES) cells is an essential pre-requisite for regenerative medicine. Culture scale-up ensuring maintenance of cell pluripotency is a central issue, because large amounts of pluripotent cells must be generated to warrant that differentiated cells deriving thereof are transplanted in great amounts and survive the procedure. This study aimed to develop a robust scalable cell expansion system, using a murine embryonic stem cell line that is feeder-dependent and adapted to serum-free medium, thus representing a more realistic model for human ES cells. We showed that high concentrations of murine ES cells can be obtained in stirred microcarrier-based spinner cultures, with a 10-fold concentration of cells per volume of medium and a 5-fold greater cell concentration per surface area, as compared to static cultures. No differences in terms of pluripotency and differentiation capability were observed between cells grown in traditional static systems and cells that were replated onto the traditional system after being expanded on microcarriers in the stirred system. This was verified by morphological analyses, quantification of cells expressing important pluripotency markers (Oct-4, SSEA-1, and SOX2), karyotype profile, and the ability to form embryoid bodies with similar sizes, and maintaining their intrinsic ability to differentiate into all three germ layers. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] | ||||||||||