Home About us Contact
|
Home About us Contact | ||
|
|
||
Average Lifetime (average + lifetime)
Selected AbstractsTime-resolved fluorescence analysis of the recombinant photosystem II antenna complex CP29FEBS JOURNAL, Issue 2 2001Effects of zeaxanthin, phosphorylation Nonradiative dissipation of excitation energy is the major photoprotective mechanism in plants. The formation of zeaxanthin in the antenna of photosystem II has been shown to correlate with the onset of nonphotochemical quenching in vivo. We have used recombinant CP29 protein, over-expressed in Escherichia coli and refolded in vitro with purified pigments, to obtain a protein indistinguishable from the native complex extracted from thylakoids, binding either violaxanthin or zeaxanthin together with lutein. These recombinant proteins and the native CP29 were used to measure steady-state chlorophyll fluorescence emission and fluorescence decay kinetics. We found that the presence of zeaxanthin bound to CP29 induces a ,,35% decrease in fluorescence yield with respect to the control proteins (the native and zeaxanthin-free reconstituted proteins). Fluorescence decay kinetics showed that four components are always present but lifetimes (,) as well as relative fluorescence quantum yields (rfqy) of the two long-lived components (,3 and ,4) are modified by the presence of zeaxanthin. The most relevant changes are observed in the rfqy of ,3 and in the average lifetime (, 2.4 ns with zeaxanthin and 3.2,3.4 ns in the control proteins). When studied in vitro, no significant effect of acidic pH (5.2,5.3) is observed on chlorophyll a fluorescence yield or kinetics. The data presented show that recombinant CP29 is able to bind zeaxanthin and this protein-bound zeaxanthin induces a significant quenching effect. [source] Implications of tropical cyclone power dissipation indexINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2008Liguang Wu Abstract Upward trends in the power dissipation index (PDI) in the North Atlantic (NA) and western North Pacific (WNP) basins and increases in the number and proportion of intense hurricanes (categories 4 and 5) in all tropical cyclone basins have been reported in recent studies. These changes have been arguably viewed as evidence of the responses of tropical cyclone intensity to the increasing tropical sea surface temperature (SST) over the past 30 years. Using the historical best-track datasets from 1975 to 2004, how the annual frequency, lifetime and intensity of tropical cyclones contribute to the changes in the annual accumulated PDI is examined. As the SST warmed in the NA, WNP and eastern North Pacific (ENP) basins over the past 30 years, the annual accumulated PDI trended upward significantly only in the NA basin, where the decreased vertical wind shear and warming ocean surface may have allowed more storms to form and to form earlier or dissipate later, increasing the lifetime and annual frequency of tropical cyclones. The moderate increase in the annual accumulated PDI in the WNP basin was primarily due to the significant increase in the average intensity. There are no significant trends in the accumulated PDI, average intensity, average lifetime, and annual frequency in the ENP basin. Copyright © 2007 Royal Meteorological Society [source] Metapopulation dynamics across gradients , the relation between colonization and extinction in shaping the range edgeOIKOS, Issue 10 2009Beáta Oborny We study the dynamics of a metapopulation in which the rates of colonization and/or extinction change along an environmental gradient. Spatially explicit simulations are applied to compare two cases: in parent-dependent colonization (PDC) the rate of colonization is limited by the production of new individuals; in offspring-dependent colonization (ODC) it is limited by the success of establishment of the offspring. Thus, PDC depends on the quality of the parent's site, while ODC is dependent on the offspring's site. We combine PDC and ODC in a spatially implicit model. We study the steady-state distribution of a metapopulation, and ask whether the local densities of occupied sites at each position x along the gradient could be predicted from the local rates of colonization c(x) and extinction e(x). This prediction is not trivial, since the sites are connected, enabling a flow of individuals from more favorable to less favorable sites. The results show that at ODC a single parameter, c(x)/e(x), is sufficient for the prediction. Therefore, different species and geographic regions can be directly compared by appropriate rescaling: choosing the local average lifetime of occupancy, 1/e(x), for a time unit at each point along the gradient. This permits generalizations about the shape of range edges, and can help to predict the position of the boundary of a species' distribution. At PDC, rescaling is not possible: the whole profile of c(x) and e(x) along the gradient has to be taken into consideration. Nevertheless, rescaling gives a good approximation when the parent-dependent component of colonization does not change abruptly across space. [source] Fluorescence Lifetime Spectroscopy of Glioblastoma Multiforme,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2004Laura Marcu ABSTRACT Fluorescence spectroscopy of the endogenous emission of brain tumors has been researched as a potentially important method for the intraoperative localization of brain tumor margins. We investigated the use of time-resolved, laser-induced fluorescence spectroscopy for demarcation of primary brain tumors by studying the time-resolved spectra of gliomas. The fluorescence of human brain samples (glioblastoma multiforme, cortex and white matter: six patients, 23 sites) was induced ex vivo with a pulsed nitrogen laser (337 nm, 3 ns). The time-resolved spectra were detected in a 360,550 nm wavelength range using a fast digitizer and gated detection. Parameters derived from both the spectral- (intensities from narrow spectral bands) and the time domain (average lifetime) measured at 390 and 460 nm were used for tissue characterization. We determined that high-grade gliomas are characterized by fluorescence lifetimes that varied with the emission wavelength (>3 ns at 390 nm, <1 ns at 460 nm) and their emission is overall longer than that of normal brain tissue. Our study demonstrates that the use of fluorescence lifetime not only improves the specificity of fluorescence measurements but also allows a more robust evaluation of data collected from brain tissue. Combined information from both the spectraland the time domain can enhance the ability of fluorescencebased techniques to diagnose and detect brain tumor margins intraoperatively. [source] Composition influence on positron annihilation parameters in ZnO-based nanocrystal semiconductor powdersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007L. C. Damonte Abstract Zn1,xMgxO powders at various compositions were obtained by mechanical milling from the binary oxides. The progressive incorporation of Mg atoms into the ZnO lattice was monitored by X-ray diffraction (XRD). The evolution of annihilation parameters with milling time and composition were analyzed and related to the possible types of mechanical and substitutional induced defect present. It was concluded that the average lifetime constitute a useful parameter to sense the complete cation substitution in the wurtzite structure. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||