Spatial variation in nitrogen dioxide in three European areas

In order to estimate the spatial variation within well-defined study areas, nitrogen dioxide was measured with diffusion samplers (Palmes tube) in 40-42 sites each in Germany (Munich), the Netherlands and Sweden (Stockholm County). Each site was measured over four 2-week periods during 1 year (spring 1999 to summer 2000). In each country, one reference site was measured during all periods and the results were used to adjust for seasonal variability, to improve the estimates of the annual average. Comparisons between the chemiluminescence method (European reference method) and Palmes tube measurement indicated a good agreement in Germany (with a ratio of 1.0 for Palmes tube/chemiluminescence) but underestimation for Palmes tube measurement in the Netherlands and Sweden (0.8 for both countries). The r2 values were between 0.86 and 0.90 for all three countries. The annual average values for NO2 for different sampling sites were between 15.9 and 50.6 (mean 28.8 microg/m3) in Germany, between 12.1 and 50.8 (mean 28.9 microg/m3) in the Netherlands and between 6.1 and 44.7 (mean 18.5 microg/m3) in Sweden. Comparing spatial variation between similar sites in the three countries, we did not find any significant differences between annual average levels for urban traffic sites. In Sweden, annual average levels in urban background and suburban backgrounds sites were about 8 microg/m3 lower than comparable sites in Germany and the Netherlands. Comparing site types within each country only urban traffic sites and suburban background sites differed in Germany. In the Netherlands and Sweden, the urban traffic sites differed from all other sites and in Sweden also the urban background sites differed from the other background sites. The observed contribution from local traffic was similar in the Netherlands and Sweden (10 and 8 microg/m3, corresponding to 26-27% of the NO2 concentration found in the urban traffic sites). In Germany, the contribution from local traffic was only 3 microg/m3, corresponding to 9% of the NO2 concentration found in the urban traffic sites. The spatial variation was substantially larger for NO2 than the variation for PM2.5 and similar to PM2.5 absorbance, measured in the same locations.     

Strategies for stereocontrol at C1 or C2 in syntheses of α-glucosaminides

The C1 and C2 stereocenters of α-glucosaminides can be prepared by establishing the stereocenters in either order. For the former, a C2-azido glucosyl donor is prepared first, and the restraining effect of a 4,6-O-benzylidene ring is used to induce α-coupling. For the latter, the C1 linkage is prepared first by use of an n-pentenyl-manno-1,2-orthoester donor which ensures (a) clean α-coupling and (b) a convenient C2-ester. The C2-ester is replaced with a triflate leaving group, and nucleophilic displacement is effected by use of a hypervalent silicon azide.     

On the validity of the cosine projection in wind-driven rain calculations on buildings

Wind-driven rain (WDR) is one of the most important boundary conditions governing the hygrothermal performance and the durability of building facades. Information concerning the quantity of WDR falling onto building facades is an essential requirement as a boundary condition for Heat–Air–Moisture transfer analyses and for building facade design. The quantity of WDR can be calculated with either semi-empirical methods (such as the WDR relationship) or numerical simulation methods that are based on Computational Fluid Dynamics (CFD). The WDR relationship is most often used. It applies the cosine projection to take into account the effect of varying wind direction on the WDR quantity or intensity. Up to now, the validity of the cosine projection for WDR calculations has not yet been investigated. Its use was suggested in the past and it has been adopted for all semi-empirical WDR calculations since then. Also, in the recently developed numerical simulation methods, it is tempting to apply the cosine projection to reduce the computational expense. In the present paper, the validity of the cosine projection is investigated based on 3D numerical simulations of WDR with CFD. It will be shown that the cosine projection, although generally accepted, is not valid and that it can give rise to significant errors.     

An adjusted temperature wall function for turbulent forced convective heat transfer for bluff bodies in the atmospheric boundary layer

Accurate convective heat transfer predictions are required in building engineering and environmental studies on urban heat islands, building energy performance, building-envelope durability or conservation and (natural) ventilation of buildings. When applying computational fluid dynamics (CFD) for these computationally-expensive studies at high-Reynolds numbers, wall functions are mostly used to model the boundary-layer region. In this study, an adjustment to the standard temperature wall function is proposed for forced convective heat transfer at surfaces of typical wall-mounted bluff bodies in turbulent boundary layers, such as the atmospheric boundary layer, at moderate to high Reynolds numbers. The methodology to determine this customised temperature wall function (CWF) from validated numerical data of CFD simulations using low-Reynolds number modelling (LRNM) is explained, where a logarithmic- law behaviour is found. The performance of this CWF is evaluated for several bluff-body configurations. Standard wall functions (SWFs) yield deviations of about 40% for the convective heat transfer coefficient, compared to LRNM. With the CWF however, these deviations are reduced to about 10% or lower. The CWF therefore combines increased (wall-function) accuracy for convective heat transfer predictions with the typical advantage of wall functions compared to LRNM, being a lower grid resolution in the near-wall region, which increases computational economy and facilitates grid generation. Furthermore, this CWF can be easily implemented in existing CFD codes, and is implemented in the commercial CFD code Fluent in this study.     

High-resolution wind-driven rain measurements on a low-rise building—experimental data for model development and model validation

With the specific intention to provide experimental data for model development and model validation, a new measurement setup for wind, rain and wind-driven rain (WDR) has been designed and installed at the Laboratory of Building Physics (Katholieke Universiteit Leuven). This paper focuses on the new measurement setup and on the obtained measurement results. The CFD-based design and the installation of the measurement setup are outlined and samples of the database containing the wind, rain and high-resolution WDR measurements are provided and discussed. This paper also provides the link to a website from which the experimental WDR database can be downloaded. Finally, the use of these data to determine WDR coefficients and their use in WDR assessment are briefly addressed.     

A nanopositioner for scanning probe microscopy: the KoalaDrive

We present a new type of piezoelectric nanopositioner called KoalaDrive which can have a diameter less than 2.5 mm and a length smaller than 10 mm. The new operating principle provides a smooth travel sequence and avoids shaking which is intrinsic to nanopositioners based on inertial motion with sawtooth driving signals. In scanning probe microscopy, the KoalaDrive can be used for the coarse approach of the tip or sensor towards the sample. Inserting the KoalaDrive in a piezo tube for xyz-scanning integrates a complete scanning tunneling microscope (STM) inside a 4 mm outer diameter piezo tube of <10 mm length. The use of the KoalaDrive makes the scanning probe microscopy design ultracompact and accordingly leads to a high mechanical stability. The drive is UHV, low temperature, and magnetic field compatible. The compactness of the KoalaDrive allows building a multi-tip STM as small as a single tip STM.     

Characterization of surface carbon formed during the conversion of methane to benzene over Mo/H-ZSM-5 catalysts

During the conversion of methane to benzene in the absence of oxygen over a 2 wt% Mo/H-ZSM-5 catalyst at 700°C, three different types of surface carbon have been observed by X-ray photoelectron spectroscopy: adventitious or graphitic-like C (284.6 eV), carbidic-like C (282.7 eV), and hydrogen-poor sp-type C (283.2 eV), where the C 1s binding energies for the respective forms of carbon are given in parentheses. Pretreatment of the catalyst at 700°C in CO also resulted in a strong signal at 283.2 eV; thus, the species responsible for this signal appears to be different from the usual aromatic-type coke. The coke with dominantly sp hybridization is concentrated on the external surface of the zeolite and is responsible for the gradual deactivation of the catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ge/Si Core/Shell Quantum Dots in an Alumina Matrix: Influence of the Annealing Temperature on the Optical Properties

Semiconductors - Structures with Ge/Si nanoparticles (quantum dots) in an aluminum-oxide matrix are of interest due to the combination of two basic semiconductors and the use of a matrix with a...