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Trapping Mechanisms (trapping + mechanism)
Selected AbstractsCompetition between Host Aggregates and Isolated Guest Chromophores in Trapping Excitons in Polybenzazole Copolymers and BlendsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 24 2006Shanfeng Wang Abstract Summary: Host,guest systems have been prepared using the blends and copolymers consisting of the host molecule poly(p -phenylene benzobisoxazole) (PBO) with a higher bandgap of 2.93 eV and the guest molecule poly(2,5-thienylbenzobisoxazole) (PBOT) with a lower bandgap of 2.57 eV. These systems have been investigated using photoluminescence (PL) spectra and time-resolved PL decay dynamics. Both PBOT-PBO copolymers and PBOT/PBO blends with the PBOT compositions less than 20% demonstrate higher intensities and narrower bandwidths in solid-state emission compared to that of PBOT, as well as larger fractions of the shorter lifetime component in PL decay dynamics. A general scheme on intrachain and interchain exciton migration and trapping mechanism has been proposed to interpret the phenomena in both solutions and thin films. Particularly, a competition in trapping exciton between PBO aggregates and isolated PBOT chromophores has been revealed. General scheme of exciton migration and trapping paths for host (D: donor),guest (A: acceptor) systems involving the isolated chromophores (A and D) and aggregates (AA and DD) in both ground state and excited state marked without or with an asterisk. [source] Specificity and reactive loop length requirements for crmA inhibition of serine proteasesPROTEIN SCIENCE, Issue 2 2005Lisa D. Tesch Abstract The viral serpin, crmA, is distinguished by its small size and ability to inhibit both serine and cysteine proteases utilizing a reactive loop shorter than most other serpins. Here, we characterize the mechanism of crmA inhibition of serine proteases and probe the reactive loop length requirements for inhibition with two crmA reactive loop variants. P1 Arg crmA inhibited the trypsin-like proteases, thrombin, and factor Xa, with moderate efficiencies (,102,104 M,1sec,1), near equimolar inhibition stoichiometries, and formation of SDS-stable complexes which were resistant to dissociation (kdiss ,10,7 sec,1), consistent with a serpin-type inhibition mechanism. Trypsin was not inhibited, but efficiently cleaved the variant crmA as a substrate (kcat/KM of ,106 M,1 sec,1). N-terminal sequencing confirmed that the P1 Arg,P1,Cys bond was the site of cleavage. Altering the placement of the Arg in a double mutant P1 Gly-P1,Arg crmA resulted in minimal ability to inhibit any of the trypsin family proteases. This variant was cleaved by the proteases ,10-fold less efficiently than P1 Arg crmA. Surprisingly, pancreatic elastase was rapidly inhibited by wild-type and P1 Arg crmAs (105,106 M,1sec,1), although with elevated inhibition stoichiometries and higher rates of complex dissociation. N-terminal sequencing showed that elastase attacked the P1,Cys,P2,Ala bond, indicating that crmA can inhibit proteases using a reactive loop length similar to that used by other serpins, but with variations in this inhibition arising from different effective P2 residues. These results indicate that crmA inhibits serine proteases by the established serpin conformational trapping mechanism, but is unusual in inhibiting through either of two adjacent reactive sites. [source] Algorithm for determining optimum sequestration depth of CO2 trapped by residual gas and solubility trapping mechanisms in a deep saline formationGEOFLUIDS (ELECTRONIC), Issue 4 2008C. K. LIN Abstract An algorithm is proposed here for determining the optimum sequestration depth (in terms of depth corresponding to maximum net income per unit rock volume) in a saline formation for CO2 trapped by residual gas and solubility trapping mechanisms. The Peng,Robinson equation of state was used to determine the density and fugacity of sequestered CO2 and the compression energy required for CO2 injection. Geochemist's Workbench®, a commercial geochemical software package, was used to estimate CO2 solubility in groundwater. Operational costs and CO2 emissions due to compression energy consumption were estimated. A hypothetical reference case was constructed to illustrate the proposed algorithm, assuming constant values of geothermal gradient, hydrostatic pressure gradient, sweep efficiency and initial groundwater chemistry, with a depth-dependent porosity and porosity-dependent saturation of residual gas. In general, the algorithm was illustrated successfully for the hypothetical reference case and produced the following results. The depth corresponding to maximum trapping capacity was approximately 3000 m, but the depth representing maximum net income was approximately 1300 m. CO2 emissions due to compression energy consumption per unit mass of CO2 sequestration cannot be ignored, but may be <0.15, even down to a depth of 7000 m. Both the trapping capacity and net income of CO2 sequestration decreased with geothermal gradient, but the corresponding optimum depths increased with geothermal gradient. [source] The role of spatio-temporal heterogeneity in the establishment and maintenance of Suaeda maritima in salt marshesJOURNAL OF VEGETATION SCIENCE, Issue 1 2002Marc Tessier Tutin et al. (1964,1980) Abstract. The effects of disturbance and microtopography on the organization and dynamics of plant communities were studied in a European salt marsh located in the Bay of Mont St. Michel, France. The existence of seed trapping mechanisms was also tested. The study took place in the lower and middle marsh plant communities dominated by the perennials Puccinellia maritima and Halimione portulacoides, respectively and associated with the annual Suaeda maritima. Three treatments were used in series of plots placed in each community: (1) vegetation removal and root destruction to a depth of 10 cm and refilling, (2) non-remnant herbicide treatment without vegetation removal and (3) creation of depressions (20 cm deep). These treatments were compared with adjacent control plots. The first year of the experiment showed that the perennials facilitated the establishment of Suaeda by trapping its seeds. Estimation of cover, density and biomass over 5 yr following the disturbances showed that in the first 2 yr Suaeda dominated the disturbed plots. Thereafter Suaeda was gradually eliminated by competitive exclusion after ca. 3 yr in the zone originally dominated by Puccinellia maritima and after 4 yr in the zone occupied by Halimione portulacoides. Depressions constituted refuge habitats for Suaeda by limiting competition with the perennials but also led to a high risk of mortality with temporal fluctuations in density. Despite a period of investigation limited to 5 yr, our study demonstrated that natural disturbances of various types occurred and influenced the dynamics of Suaeda, Halimione and Puccinellia. We deduced that natural disturbances and microtopography are responsible for the maintenance of the habitat in a state of non-equilibrium by favouring the establishment of both spatial and temporal environmental heterogeneity. These conditions appear to be particularly favourable for the maintenance of annual species such as Suaeda maritima. [source] | ||||||||||