Mapping global, diffuse and beam solar radiation over Zimbabwe

A database for long-term monthly radiation over Zimbabwe is developed. The meteorological raw data inputs are long-term monthly average records of pyranometer-measured hemispherical radiation, monthly average sunshine records, and satellite-measured hemispherical records over a 2-year period. The sunshine records are incorporated into the database by use of Angstrom-type correlations developed for Zimbabwe, and the short-term satellite data are ‘cultured to long-term ground-measurement basis by means of an empirically derived correlation’ and a ‘time series factor’. Diffuse radiation values are generated from the resulting hemispherical radiation database by a locally developed correlation of the monthly average diffuse fraction of hemispherical radiation with monthly average clearness index. Normal beam radiation is computed from the hemispherical and diffuse radiation using two different methods. The two methods are found to agree generally to within 7%. The results are presented as country-border-contained isolines of radiation. The sensitivity of beam radiation to the accuracy of estimating diffuse radiation is inspected. The sensitivity is quite high, about 1:1 for months and locations with very low clearness. This translates to an almost equal sensitivity of insolation available to tracking tilted apertures, underscoring the importance of developing a local diffuse fraction-clearness index correlation rather than relying on a correlation developed elsewhere.     

Low On-Resistance High-Breakdown Normally Off AlN/GaN/AlGaN DHFET on Si Substrate

Ultrathin-barrier normally off AlN/GaN/AlGaN double-heterostructure field-effect transistors using an in situ SiN cap layer have been fabricated on 100-mm Si substrates for the first time. The high 2DEG density in combination with an extremely thin barrier layer leads to enhancement-mode devices with state-of-the-art combination of specific on-resistance that is as low as 1.25 $hbox{m}Omegacdothbox{cm}^{2}$ and breakdown voltage of 580 V at ${V}_{rm GS} = hbox{0} hbox{V}$ . Despite the 2-$muhbox{m}$ gate length used, the transconductance peaks above 300 mS/mm. Furthermore, pulsed measurements show that the devices are dispersion free up to high drain voltage ${V}_{rm DS} = hbox{50} hbox{V}$. More than 200 devices have been characterized in order to confirm the reproducibility of the results.      

MT™-compatible connectorisation of VCSEL and RCLED arrays to plastic optical fibre ribbon for low cost parallel datalinks

For the realisation of MT™-compatible direct connectorised modules, a PMMA-based interconnection scheme, using index alignment is developed. Plastic pieces are accurately positioned with respect to the chips and then fixed with epoxy, following an index-alignment strategy. Alignment accuracies in the range of 5–10 μm have been achieved, which is sufficient to have good coupling efficiencies in view of the relaxed alignment tolerances when coupling to small diameter (125 μm) plastic optical fibre. The chips are assembled in commercially available packages, which are then mounted on PCB boards. First coupling measurements on fully assembled modules, using a red (670 nm) 1×8 VCSEL-array and an infrared (980 nm) 1×8 RCLED (resonant cavity LED) array, are successfully carried out.     

Further results on generalized Hamming weights for Goethals andPreparata codes over Z4

This article contains results on the generalized Hamming weights (GHW) for the Goethals and Preparata codes over Z₄. We give an upper bound on the rth generalized Hamming weights d_r(m,j) for the Goethals code G_m(j) of length 2^m over Z ₄, when m is odd. We also determine d_3.5(m,j) exactly. The upper bound is shown to be tight up to r=3.5. Furthermore, we determine the rth generalized Hamming weight d_r(m) for the Preparata code of length 2^m over Z₄ when r=3.5 and r=4     

Supported Lipid Bilayer on Nanocrystalline Diamond: Dual Optical and Field‐Effect Sensor for Membrane Disruption

It is demonstrated that a good biomimetic model lipid membrane with dynamic fluidity can be established on optically transparent nanocrystalline diamond (OTND) with surface roughness below 10 nm. Maigainin II, an antimicrobial peptide, is chosen to investigate the permeation of artificial bacterial membranes constructed on OTND. Due to the unique combination of optical transparency and highly sensitive surface conducting channel, intrinsic OTND affords the possibility of dual‐mode sensing based on optical and field effect properties. This opens up new possibilities for making integrated biomolecule–semiconductor microdevices, or sensors where the binding of biomolecules can be tracked using confocal microscopy whilst the associated changes in charge density during membrane perforation can be tracked using the space charge effect in the semiconductor. Such a synergistic approach may provide a powerful methodology for the screening of specific bactericidal activity on biomimetic membrane systems.     

Comparison of ochratoxin A and deoxynivalenol in organically and conventionally produced beers sold on the Belgian market.

Beer was chosen as a cereal-derived and homogeneous product for a comparison of organic and conventional production methods in terms of mycotoxin contamination levels. Ochratoxin A (OTA, a storage mycotoxin) and deoxynivalenol (DON, a field mycotoxin) were assessed by HPLC in organically and conventionally produced beers sold in Belgium. Immunoaffinity column (OchraTest and DONPrep) purification was used prior to HPLC analysis. For in-house validation, recovery experiments, carried out with the spiked beers in the ranges of 50-200 ng OTA l-1 and 20-100 microg DON l-1, led to the overall averages of 91% (RSD = 10%, n = 9) and 93% (RSD = 5%, n = 27), respectively. Organic beers collected during 2003-2004 were more frequently OTA-contaminated (95%, n = 40) than their conventional counterparts (50%, n = 40). Conventional beers were OTA-contaminated at a mean concentration of 25 ng l-1 (range: 19-198 ng l-1), while organic beers contained a mean level of 182 ng l-1 (range: 18-1134 ng l-1). High OTA contamination above the limit of 200 ng l-1 (up to 1134 ng l-1) occasionally occurred in organically produced beers. A complementary survey performed with the same brands in 2005 did not confirm this accidental presence of excessive OTA loads (range: 3-67 ng l-1 for 10 conventional beers and 19-158 ng l-1 for 10 organic beers). Establishing a maximum of 3 microg OTA kg-1 in malt, the application of the regulation EC No. 466/2001 (entered in force before the last sampling) may be related to the observed improvement. The overall incidence of DON was 67 and 80% in conventional and organic beers, respectively. DON concentrations ranged from 2 to 22 microg DON l-1 (mean = 6 microg DON l-1) in conventional beers, while organic beers ranged from 2 to 14 microg DON l-1 (mean=4 microg DON l-1). Thus, DON in beers does not appear to be a major matter of concern. From the statistical tests, it was concluded that the variation between different batches was significant (P < 0.0001), in contrast to that observed between different brands, showing a lack of homogeneity in the raw materials. This occurs either in organically or in conventionally produced materials. Considering these results, an optimized frequency of controls according to European Regulations EC No 466/2001 and EC No 856/2005 should be recommended to reject the irregular batches.     

From surface science to nanotechnology

This overview sketches the historical development of surface science through nanoscience toward nanotechnology. It spans about 50 years of evolution and emphasizes the multidisciplinary nature of this field, as well as its closely-knit interactions with technology, scientific disciplines, phenomena and techniques. A series of examples is given, drawn mainly from work performed in Berkeley, to highlight various stages in the field: surfaces, interfaces, clusters, thin films, superlattices, nanostructures and “bionano”.     

A method for predicting long-term average performance of photovoltaic systems

A method for predicting the long-term average conventional energy displaced by a photovoltaic system comprising of a photovoltaic array, a storage battery, some power conditioning equipment with maximum power tracking capability and an auxiliary power facility, is described. System simulation is done over the average day of the month. Average hourly energy flows are estimated from a knowledge of array test parameters, monthly average hourly ambient temperature and monthly average daily hemispherical radiation. The monthly average diffuse component of radiation can be predicted from the hemispherical radiation by the use of an appropriate empirical correlation relating the monthly average diffuse fraction to monthly average clearness index. Hourly average radiation values are estimated from daily values using a statistical model. The condition that there should be no net battery energy gain during the average day enables the correct setting of the battery energy level at the beginning of the day. For a given hourly load profile, for example a constant 24 h-per-day load, a chart relating annual solar fraction with array and storage battery size, for a given location and set of array test parameters, can be plotted as a basis for design and economic optimisation of the system.