Dependence of the kinetics of liquid-phase photocatalyzed reactions on oxygen concentration and light intensity

The initial kinetics of the oxidation of 4-chlorophenol, 4-CP, photocatalyzed by titania films and aqueous dispersions were studied as a function of oxygen partial pressure, P-O2, and incident light intensity, I. The reaction conditions were such that the kinetics were independent of [4-CP] but strongly dependent on PO2-a situation that allowed investigation of the less-often studied kinetics of oxygen reduction. The observed kinetics fit a pseudo-steady-state model in which the oxygen is Langmuir-adsorbed on the titania photocatalyst particles before being reduced by photogenerated electrons. The maximum rate of photocatalysis depends directly on I-beta, where, beta = 1 for films and 0.7 for dispersions of titania, indicating that the kinetics are dominated by the surface reactions of the photogenerated electrons and holes for the films and by direct recombination for the powder dispersions. Using the pseudo-first-order model, for both titania films and dispersions, the apparent Langmuir adsorption constant, K-LH, derived from a Langmuir-Hinshelwood analysis of the kinetics, appears to be largely independent of incident light intensity, unlike KLH for 4-CP Consequently, similar values are obtained for the Langmuir adsorption constant, K-ads, extracted from a pseudosteady-state analysis of the kinetics for oxygen on TiO2 dispersions and films in aqueous solution (i.e., ca. 0.0265 +/- 0.005 kPa(-1)), and for both films and dispersions, oxygen appears to be weakly adsorbed on TiO2 compared with 4-CP, at a rate that would take many minutes to reach equilibrium. The value of Kads for oxygen on titania particles dispersed in solution is ca. 4.7 times lower than that reported for the dark Langmuir adsorption isotherm; possible causes for this difference are discussed. (c) 2006 Elsevier Inc. All rights reserved.

The kinetics of semiconductor photocatalysis: Light intensity effects

The kinetics of the photomineralisation of 4-chlorophenol, 4-CP, by oxygen, sensitized by TiO2 as a function of incident light intensity are described. Degussa P25 TiO2 in the form of either a thin film or a dispersion is used as the photocatalyst. With a TiO2 dispersion the initial rate of photomineralisation, R-i, depends upon I-0.64, implying that electron-hole recombination is the dominant process with respect to photogenerated holes (where R-i is expected proportional to I-0.5), but that the light intensities used spanned both the high (R-i expected proportional to I-0.5) and low (R-i expected proportional to I) intensity regimes. With a TiO2 film R-i is proportional to I indicating that the photocatalytically active particles of the TiO2 film are shielded in some way and so operate under low intensity conditions. Most significantly, it was also found that the apparent value of the Langmuir adsorption coefficient, K4-CP, as determined from the kinetic data, was not independent of I for either a TiO2, film or dispersion photocatalyst. Rather K4-CP increased with decreasing light intensity. A possible mechanism is suggested as a rationale for the observed light intensity effects reported.

DEPENDENCE OF LIGHT OUTPUT FROM NOMINALLY SMOOTH AL-OX-AU TUNNEL-JUNCTIONS ON ELECTRODE MORPHOLOGY

The light output from nominally smooth Al-Ox-Au tunnel junctions is observed to be substantially independent of the deposition rate of the Au film electrode. Films deposited quickly (2 nm s-1) and those deposited slowly (0.16 nm s-1) have similar spectral dependences and intensities. (This is in contrast to roughened films where those deposited quickly give out less light, especially towards the blue end of the spectrum.) The behaviour can be interpreted in terms of the ratio l(ph)/l(em) where l(ph) and l(em) are the mean free paths of surface plasmons between external photon emissions and internal electromagnetic absorptions respectively. Once l(ph)/l(em) exceeds 100, as it does on smooth films, grain size has little further effect on the spectral shape of the light output. In fast-deposited films there are two compensating effects on the output intensity: grain boundary scattering decreases it and greater surface roughness increases it.

Brightness variation distributions among main belt asteroids from sparse light curve sampling with Pan-STARRS 1

The rotational state of asteroids is controlled by various physical mechanisms including collisions, internal damping and the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. We have analysed the changes in magnitude between consecutive detections of ∼ 60,000 asteroids measured by the PanSTARRS 1 survey during its first 18 months of operations. We have attempted to explain the derived brightness changes physically and through the application of a simple model. We have found a tendency toward smaller magnitude variations with decreasing diameter for objects of 1 < D < 8 km. Assuming the shape distribution of objects in this size range to be independent of size and composition our model suggests a population with average axial ratios 1: 0.85 ± 0.13: 0.71 ± 0.13, with larger objects more likely to have spin axes perpendicular to the orbital plane.

Effect of major lifestyle risk factors, independent and jointly, on life expectancy with and without cardiovascular disease: results from the Consortium on Health and Ageing Network of Cohorts in Europe and the United States (CHANCES)

Seldom have studies taken account of changes in lifestyle habits in the elderly, or investigated their impact on disease-free life expectancy (LE) and LE with cardiovascular disease (CVD). Using data on subjects aged 50+ years from three European cohorts (RCPH, ESTHER and Tromsø), we used multi-state Markov models to calculate the independent and joint effects of smoking, physical activity, obesity and alcohol consumption on LE with and without CVD. Men and women aged 50 years who have a favourable lifestyle (overweight but not obese, light/moderate drinker, non-smoker and participates in vigorous physical activity) lived between 7.4 (in Tromsø men) and 15.7 (in ESTHER women) years longer than those with an unfavourable lifestyle (overweight but not obese, light/moderate drinker, smoker and does not participate in physical activity). The greater part of the extra life years was in terms of "disease-free" years, though a healthy lifestyle was also associated with extra years lived after a CVD event. There are sizeable benefits to LE without CVD and also for survival after CVD onset when people favour a lifestyle characterized by salutary behaviours. Remaining a non-smoker yielded the greatest extra years in overall LE, when compared to the effects of routinely taking physical activity, being overweight but not obese, and drinking in moderation. The majority of the overall LE benefit is in disease free years. Therefore, it is important for policy makers and the public to know that prevention through maintaining a favourable lifestyle is "never too late".

Synechococcus sp. PCC 7002 CpcB lyase null mutations alter phycocyanin chromophore function and, consequently, affect the redistribution of excitation energy via the light state transition /

Phycobilisomes are the major light harvesting complexes for cyanobacteria and phycocyanin is the primary phycobiliprotein of the phycobilisome rod. The phycocyanobilin lyases responsible for chromophorylating the phycocyanin p subunit (CpcB) have been recently identified in the cyanobacterium Synechococcus sp. PCC 7002. Surprisingly, mutants missing the CpcB lyases were nevertheless capable of producing pigmented phycocyanin. 10K absorbance measurements revealed that the energy states of the p phycocyanin chromophores were only subtly shifted; however, 77K steady state fluorescence emission spectroscopy showed excitation energy transfer involving the targeted chromophores to be highly disrupted. Such evidence suggests that phycobilin orientation within the binding domain is specifically modified. We hypothesized that alternate, less specific lyases are able to act on the p binding sites. A phycocyanin linker-polypeptide deficient mutant was similarly characterized. The light state transition, a short term adaptation of the photosynthetic light harvesting apparatus resulting in the redistribution of excitation energy among the photo systems, was shown to be dominated by the reallocation of phycocyanin-absorbed excitation energy. Treatment with a high M phosphate buffer effectively prevented the redistribution of both chlorophyll a- and phycobilisome- absorbed excitation energy, suggesting that the two effects are not strictly independent. The mutant strains required a larger redistribution of excitation energy between light states, perhaps to compensate for their loss in phycobilisome antenna function.

Robust decoupled visual servoing based on structured light

This paper focuses on the problem of realizing a plane-to-plane virtual link between a camera attached to the end-effector of a robot and a planar object. In order to do the system independent to the object surface appearance, a structured light emitter is linked to the camera so that 4 laser pointers are projected onto the object. In a previous paper we showed that such a system has good performance and nice characteristics like partial decoupling near the desired state and robustness against misalignment of the emitter and the camera (J. Pages et al., 2004). However, no analytical results concerning the global asymptotic stability of the system were obtained due to the high complexity of the visual features utilized. In this work we present a better set of visual features which improves the properties of the features in (J. Pages et al., 2004) and for which it is possible to prove the global asymptotic stability

On-line prediction of cheese making using backscatter of near infrared indices light

The potential of a fibre optic sensor, detecting light backscatter in a cheese vat during coagulation and syneresis, to predict curd moisture, fat loses and curd yield was examined. Temperature, cutting time and calcium levels were varied to assess the strength of the predictions over a range of processing conditions. Equations were developed using a combination of independent variables, milk compositional and light backscatter parameters. Fat losses, curd yield and curd moisture content were predicted with a standard error of prediction (SEP) of +/- 2.65 g 100 g(-1) (R-2 = 0.93), +/- 0.95% (R-2 = 0.90) and +/- 1.43% (R-2 = 0.94), respectively. These results were used to develop a model for predicting curd moisture as a function of time during syneresis (SEP = +/- 1.72%; R-2 = 0.95). By monitoring coagulation and syneresis, this sensor technology could be employed to control curd moisture content, thereby improving process control during cheese manufacture. (c) 2007 Elsevier Ltd. All rights reserved..

The global distribution of phytoplankton size spectrum and size classes from their light-absorption spectra derived from satellite data

The absorption spectra of phytoplankton in the visible domain hold implicit information on the phytoplankton community structure. Here we use this information to retrieve quantitative information on phytoplankton size structure by developing a novel method to compute the exponent of an assumed power-law for their particle-size spectrum. This quantity, in combination with total chlorophyll-a concentration, can be used to estimate the fractional concentration of chlorophyll in any arbitrarily-defined size class of phytoplankton. We further define and derive expressions for two distinct measures of cell size of mixed populations, namely, the average spherical diameter of a bio-optically equivalent homogeneous population of cells of equal size, and the average equivalent spherical diameter of a population of cells that follow a power-law particle-size distribution. The method relies on measurements of two quantities of a phytoplankton sample: the concentration of chlorophyll-a, which is an operational index of phytoplankton biomass, and the total absorption coefficient of phytoplankton in the red peak of visible spectrum at 676 nm. A sensitivity analysis confirms that the relative errors in the estimates of the exponent of particle size spectra are reasonably low. The exponents of phytoplankton size spectra, estimated for a large set of in situ data from a variety of oceanic environments (~ 2400 samples), are within a reasonable range; and the estimated fractions of chlorophyll in pico-, nano- and micro-phytoplankton are generally consistent with those obtained by an independent, indirect method based on diagnostic pigments determined using high-performance liquid chromatography. The estimates of cell size for in situ samples dominated by different phytoplankton types (diatoms, prymnesiophytes, Prochlorococcus, other cyanobacteria and green algae) yield nominal sizes consistent with the taxonomic classification. To estimate the same quantities from satellite-derived ocean-colour data, we combine our method with algorithms for obtaining inherent optical properties from remote sensing. The spatial distribution of the size-spectrum exponent and the chlorophyll fractions of pico-, nano- and micro-phytoplankton estimated from satellite remote sensing are in agreement with the current understanding of the biogeography of phytoplankton functional types in the global oceans. This study contributes to our understanding of the distribution and time evolution of phytoplankton size structure in the global oceans.

From the Reliable and Unselfish to the Versatile and Independent : - desired qualities in two Swedish curricula

The process in which girls and boys are constructed and construct themselves to pupils takes place in a context where conceptions of “the good pupil” are distinctly manifested in national school documents. In different types of texts concerning school and education, the image of the pupil that society wants to create emerges. Documents from early childhood education up to university level prioritise qualities such as independence, initiative, accountability and freedom to make ones own choices. Qualities or competencies that are preferred during a certain period change as time passes and society develops. The idea of the democratic subject is not the same today as it was 25 years ago. The purpose of this article is to emphasise and compare different desired qualities described in two Swedish national curricula, competencies that pupils in the compulsory school are supposed to develop. The discussion encompasses the political ideas of the pupil during a period of twenty-five years in light of changes in Western societies during the last decades.

Culture-dependent and culture-independent characterization of microorganisms associated with Aedes aegypti (Diptera: Culicidae) (L.) and dynamics of bacterial colonization in the midgut

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Activation of Ca2+-independent membrane-damaging activity in Lys49-phospholipase A(2) promoted by amphiphilic molecules

Association of class-II phospholipase A(2) (PLA(2)) with aggregated phospholipid substrate results in elevated levels of the Ca2+-dependent hydrolytic activity. The Asp49 residue participates in coordination of the Ca2+ ion cofactor, however, in Lys49-PLA(2) homologues (Lys49-PLA(2)S), substitution of the Asp49 by Lys results in loss of Ca2+ binding and lack of detectable phospholipid hydrolysis. Nevertheless, Lys49-PLA2S cause Ca2+-independent damage of liposome membranes. Bothropstoxin-I is a homodimeric Lys49-PLA(2) from the venom of Bothrops jararacussu, and in fluorescent marker release and dynamic light scattering experiments with DPPC liposomes we demonstrate activation of the Ca2+-independent membrane damaging activity by similar to4 molecules of sodium dodecyl sulphate (SDS) per protein monomer. Activation is accomparlied by significant changes in the intrinsic tryptophan fluorescence emission (ITFE) and near UV circular dichroism (UVCD) spectra of the protein. Subsequent binding of 7-10 SDS molecules results in further alterations in the ITFE and far UVCD spectra. Reduction in the rate of N-bromosuccinimide modification of Trp77 at the dimer interface suggests that initial binding of SDS to this region accompanies the activation of the membrane damaging activity. 1-anilinonaphthalene-8-sulphonic acid binding studies indicate that subsequent SDS binding to the active site is concomitant with the second structural transition. These results provide insights in the structural basis of amphiphile/protein coupling in class-II PLA(2)s. (C) 2004 Published by Elsevier B.V.

A constraint on the x dependence of the light antiquarks ratio

We perform a careful study on the effect of the Pauli blocking to the light antiquark structure of the proton sea. We develop the formal expressions for the antiquark distributions, highlighting the role played by quark statistics and the vacuum structure. Ratios involving the antiquarks are calculated. In particular, it is found that Delta(d) over bar (x)/Delta(u) over bar (x) should be negative and x independent. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Neutron-neutron correlation in the halo dissociation of light exotic nuclei

We present model results for the two-halo-neutron correlation functions, C-nn, for the dissociation process of light exotic nuclei modelled as two neutrons and a core. A minimum is predicted for C-nn as a function of the relative momentum of the two neutrons, p(nn), due to the coherence of the neutrons in the halo and final state interaction. Studying the systems Be-14, Li-11, and He-6 within this model, we show that the numerical asymptotic limit, C-nn-> 1, occurs only for p(nn)greater than or similar to 400 MeV/c, while such limit is reached for much lower values of p(nn) in an independent particle model as the one used in the analysis of recent experimental data. Our model is consistent with data once the experimental correlation function is appropriately normalized.

Universal aspects of light halo nuclei

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)