Evaluation of a Denuder-MOUDI-PUF Sampling System to Measure the Size Distribution of Semi-Volatile Polycyclic Aromatic Hydrocarbons in the Atmosphere

This study describes a field comparison conducted between 2 methods employing different MOUDI impactor configurations to evaluate their performance in sampling and measurement of the size distribution of 15 priority pollutant polycyclic aromatic hydrocarbons (PAHs). Samples were collected during 24 h periods approximately every 7th day, beginning at 8:00 AM, in 2 different sites of the Los Angeles Basin. One site was near Central Los Angeles in an area impacted by high vehicular traffic, whereas the other site was located about 60 km downwind of central Los Angeles (receptor site). Particle samples from about 43 m 3 of air were collected using collocated MOUDI impactors and classified in 3 aerodynamic diameter size intervals: 0-0.18 w m (ultrafine mode I), 0.18-2.5 w m (accumulation mode II), and 2.5-10 w m (coarse mode III). One MOUDI operated in the conventional mode, the other with a vapor trapping system that included an XAD-4 coated annular denuder placed upstream of the impactor and a polyurethane foam plug (PUF) placed in series behind the impactor. PAHs were separated and quantified by HPLC with fluorescence detection optimized for the highest sensitivity. The results showed that for both sites, using either sampling system, the size distributions obtained are similar for the less volatile PAHs (log [ p ° L ] h m 3.2), but different for the more volatile PAHs (log [ p ° L ] S m 2.06). In the central Los Angeles site, the largest PAH fraction was found in the 0-0.18 w m (mode I) size range, typical of primary emissions. At the downwind location, the largest fraction was in the 0.18-2.5 w m (mode II) size range, consistent with an "aged" aerosol. At both sites, albeit not statistically significant, the mean regular to denuded MOUDI mass ratios were 33-36% and 11-19% higher, respectively, for the more volatile and the less volatile PAH groups. Sampling with the regular MOUDI configuration is simpler and thus recommended for measurement of the size distribution of PAHs in either group.     

Spectral Solar Irradiance And Some Optical Properties For Various Polluted Atmospheres

Using ground-based spectroradiometric measurements taken over the Athens atmosphere during May 1995, the influence of gaseous pollutants and aerosol on the spectral radiant energy distribution was investigated. It was found that spectral measurements exhibited variations based on various polluted urban atmospheric conditions as determined via gaseous pollutants record analysis. The relative attenuations caused by gaseous pollutants and aerosol can exceed 27%, 17% and 16% in the global ultraviolet, visible and near-infrared portions of the solar spectrum respectively, as compared to “background” values. In contrast, an enhancement of the near-infrared diffuse component by 66%, was observed, while in visible and ultraviolet bands the relative increases reached 54% and 21% respectively. Experimental total Rayleigh-corrected and spectral aerosol optical depths were retrieved, representing differences in polluted air over the Athens atmosphere. The diffuse component accounts for more than 80% of the total radiation field under high polluted atmosphere. The observed differences of solar radiation between the Athens center and at a nearby suburban site are a manifestation of contrasting air properties provided mainly by automotive traffic.     

Childhood cancer: a two-year prospective study of the psychological adjustment of children and parents

OBJECTIVE: To follow prospectively the psychological adjustment of young children, parents, and families during the first 2 years after the children's diagnosis of cancer. METHOD: Children aged 2 to 5 years with cancer diagnoses and their parents and families (n = 38) were assessed immediately after diagnosis, 1 year after diagnosis, and 2 years after diagnosis. At each assessment, the psychological adjustment of the children and their families was compared with the adjustment of a cohort of children and families in the general community (n = 39). RESULTS: Children with cancer and their parents experienced significantly more emotional distress than children and parents in the community during the period immediately after diagnosis. However, the number of problems experienced by the children with cancer and their parents declined during the first year after the children's diagnosis and stabilized at a level comparable with that found among children and parents in the general community. CONCLUSION: Although the results are consistent with reports that suggest that in the longer term the prevalence of psychological problems among children with cancer is similar to that found among children in the general community, they also highlight the considerable distress experienced by children and parents during the period immediately after the children's diagnosis.     

Statistical analysis of wind speed and direction in Cyprus

The aim of this study is to establish the meteorological basis for the assessment of wind energy resources in Cyprus and to provide suitable data for evaluating the potential wind power. For this purpose the mean values, the systematic daily and annual variations, the frequency distributions and the estimation of the extreme values are determined. Predictions were also obtained from the WAsP model and, finally, the Wind Atlas of the island, in the form of contours of constant wind speed, was produced.     

A frequency-domain approach to shallow-water depth measurement

A new formulation for ocean-depth measurement using a frequency-domain approach is proposed. This technique uses two high-resolution eigensubspace methods to estimate the ocean depth from backscattered noisy data. The problem has been addressed both for real and complex attenuation coefficients by utilizing a double eigenstructure decomposition procedure on a Toeplitz as well as a Hankel matrix structure. The approach is similar to obtaining the best rational approximation that fits the actual measured data in a least-square sense     

Nonlinear Galerkin methods for a system of PDEs with Turing instabilities

We address and discuss the application of nonlinear Galerkin methods for the model reduction and numerical solution of partial differential equations (PDE) with Turing instabilities in comparison with standard (linear) Galerkin methods. The model considered is a system of PDEs modelling the pattern formation in vegetation dynamics. In particular, by constructing the approximate inertial manifold on the basis of the spectral decomposition of the solution, we implement the so-called Euler–Galerkin method and we compare its efficiency and accuracy versus the linear Galerkin methods. We compare the efficiency of the methods by (a) the accuracy of the computed bifurcation points, and, (b) by the computation of the Hausdorff distance between the limit sets obtained by the Galerkin methods and the ones obtained with a reference finite difference scheme. The efficiency with respect to the required CPU time is also accessed. For our illustrations we used three different ODE time integrators, from the Matlab ODE suite. Our results indicate that the performance of the Euler–Galerkin method is superior compared to the linear Galerkin method when either explicit or linearly implicit time integration scheme are adopted. For the particular problem considered, we found that the dimension of approximate inertial manifold is strongly affected by the lenght of the spatial domain. Indeeed, we show that the number of modes required to accurately describe the long time Turing pattern forming solutions increases as the domain increases.     

Adsorption dynamics and interfacial properties of thiol-based cobalt terpyridine monolayers

Spontaneously adsorbed monolayers of [Co(ttp-CH₂-SH)₂](PF₆)₂ have been formed on platinum microelectrodes by exposure to micromolar solutions of the complex in 0.1 M TBABF₄ in acetonitrile, ttp-CH₂-SH is 4′-(p-(thiolmethyl)-phenyl)-2,2′:6′,2″-terpyridine. Resonance Raman spectroscopy on roughened polycrystalline platinum macro electrodes show that the molecule undergoes adsorption through the sulphur atom onto the platinum surface. The monolayers show reversible and well defined cyclic voltammetry when switched between Co²⁺ and Co³⁺ forms, with a peak to peak splitting of 0.040 ± 0.005 V up to 200 V s⁻¹ and an FWHM of 0.138 ± 0.010 V. Adsorption is irreversible leading to the maximum surface coverage, 6.3 ± 0.3 × 10⁻¹¹ mol cm⁻² for 2.5 ≤ [Co(ttp-CH₂-SH)₂] ≤ 10 μM. The rate of monolayer formation appears to be controlled not by mass transport or interfacial binding but by surface diffusion of the complex. The surface diffusion coefficient is 5.5 ± 1.1 × 10⁻⁷ cm² s⁻¹ indicating that prior to formation of an equilibrated monolayer, the adsorbates have significant mobility on the surface. The electron transfer process across the monolayer-electrode interface has been probed by high speed chronoamperometry and the standard heterogeneous electron transfer rate constant, k°, is approximately 3.06 ± 0.03 × 10⁴ s⁻¹. The reorganization energy is at least 18.5 kJ mol⁻¹.     

A simple and precise method for the routine determination of platelet-activating factor in blood and urine

A simple and precise method is described for the measurement of platelet-activating factor (PAF) in blood and urine. The method involves the isolation of PAF from blood samples by two successive steps. In the first step, blood proteins are precipitated with ethanol and the “free” PAF, i.e. the PAF which is extractable with ethanol, is recovered. In the second step, “bound” PAF, i.e., PAF not extractable with ethanol, is extracted from the protein precipitate with chloroform/methanol/water. The extraction of PAF from urine samples requires only the ethanol extraction step. “Free” and “bound” PAF are then each fractionated by silicic acid column chromatography, and the methanol/water eluent containing PAF is then further fractionated by high-performance liquid chromatography using an isocratic solvent system of acetonitrile/methanol/water. PAF is then quantitated by measuring its ability to induce platelet aggregation in an aggregometer. Application of the method to blood and urine samples from twenty-three healthy volunteers revealed PAF levels in blood of 140–480 pg/mL (630–254.4 pg “free” PAF/mL and 64–225.6 pg “bound” PAF/mL), and of 1.2–4.0 pg PAF/mL in urine. The method overcomes various technical problems and was shown to be very precise. It should prove useful for monitoring PAF levels in various disease conditions.     

High‐solids mar resistant clearcoats prepared from an isophthalate‐based oligoester and a melamine resin. Study and characterization of mar resistance with scanning probe microscopy method

A new series of high‐solids [low‐VOC (volatile organic compound)content] mar resistant clearcoats (CL‐series) were prepared upon crosslinking of a new‐synthesized hydroxyl‐terminated isophthalate‐based liquid oligoester (L‐311) with an hexakis(methoxymethylol)melamine (HMMM) resin, via an acid‐catalyzed etherification reaction. The chemical, physical, and mechanical properties of the CL‐clearcoats were compared to those of a reference clearcoat (CRO). An attempt was made to investigate the effect that the amounts of catalyst and melamine resin had on the clearcoats' physical, chemical, and mechanical properties, and moreover, to correlate these properties to the films chemical structures. The new‐formulated high‐solids clearcoats (CL‐series) presented enhanced processability and higher NVW values (lower VOC content) than the reference clearcoat CRO, and their properties (pencil hardness, knoop hardness, adhesion, impact resistance, solvent and gasoline resistance, mar resistance, and flexibility) were better or comparable to those of the CRO. More specifically, the mar resistance of the CL‐clearcoats series was investigated by applying both the crockmeter test and a novel method that employed a modified scanning probe microscope. In addition, we identified and characterized the different responses of the CRO and certain CL‐clearcoats to marring stress. The experimental data regarding the mar resistance of the new‐formulated clearcoats fully justified our polymer design strategy, verifying our expectations for the possibility of preparing glossy, high‐solids mar‐resistant clearcoats that could present enhanced processability and solvent resistance, relatively high pencil hardness, and at the same time very good elastic recovery to marring stress. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1317–1333, 2002     

Differentiation between conformational transitions of polymers and the transition observed near the theta conditions

Summary The differentiation between the conformational transitions of polymers and the transition observed near the conditions has been investigated. The conformational transitions are related with side-group effects and vanish under the influence of an appropriate amount of a polar solvent. In the contrary, the transition observed in the vicinity of the temperature is related with chain-backbone effects. The addition of a polar solvent shifts this transition to a different temperature in accordance with the resulted change of the temperature of the system.