Preparation and characterization of thin films of NbO2

Thin films of NbO₂, with thicknesses ranging from 1000 to 20 000 Å, were prepared by r.f. sputtering powder targets of NbO₂ in a reducing atmosphere of 90vol.%Ar–10vol.%H. Transmission electron microscopy and X-ray diffraction studies of self-supported films indicate that the as-deposited material was amorphous. Compositional analysis, derived from interpretation of Rutherford back-scattering spectra and neutron activation analysis of films deposited onto vitreous carbon substrates, indicates a high degree of stoichiometry. The variation in the electrical conductivity with the rate of deposition is reported, and also a comparison is made between the electrical conductivity of the amorphous and crystalline phases of films of NbO₂.     

Comparison of three coupled gas chromatographic detectors (MS, MIP-AES, ICP-TOFMS) for organolead speciation analysis

An automatic unit for the screening of rainwater is used for the determination of organolead compounds using different detectors coupled to a gas chromatograph. A systematic overview is given of the advantages and disadvantages of several detectors (electron ionization mass spectrometry, EI-MS; microwave induced plasma atomic emission spectrometry, MIP-AES; and inductively coupled plasma time-of-flight mass spectrometry, ICP-TOFMS, for the speciation of organolead compounds on the basis of sensitivity, selectivity and reliability. C60 fullerene and RP-C18 were used as sorbent materials for these compounds. The primary assets of the fullerene sorbent, as compared to C18 sorbent, are high sensitivity and selectivity resulting from efficient adsorption due to large surface area and interstitial volume. Among the detection systems, GC/ ICP-TOFMS is the most sensitive, with absolute detection limits of approximately 15 fg of organolead compounds (as lead) using 5-mL sample volumes. Except for diethyllead, similar sensitivities were obtained by MIP-AES. GC/MS is intrinsically the most specific option, because the species are detected directly from molecular information. The precision is similar for all detectors. The screening of rainwater from different locations showed that samples collected in countries in which leaded gasolines are now banned contain organolead species at concentrations below 2 pg/ mL, levels that can be detected only for sample volumes of 25 mL and using MIP-AES or ICP-TOFMS as detectors, their determination being impossible by GC/MS.     

Targeting RNA with small-molecule drugs: therapeutic promise and chemical challenges

Researchers' increasing awareness of the essential role played by RNA in many biological processes and in the progression of disease makes the discovery of new RNA targets an emerging field in drug discovery. Since most existing pharmacologically active compounds bind proteins, RNA provides nearly untapped opportunities for pharmacological development. The elucidation of the structure of the ribosome and other cellular and viral RNA motifs creates the opportunity for discovering new drug-like compounds that inhibit RNA function. However, further advances in understanding the chemistry and structure of RNA recognition are needed before these promises are fulfilled.     

Chemoenzymatic synthesis of biotinylated nucleotide sugars as substrates for glycosyltransferases

The enzymatic oxidation of uridine 5'-diphospho-alpha-D-galactose (UDP-Gal) and uridine 5'-diphospho-N-acetyl-alpha-D-galactosamine (UDP-GalNAc) with galactose oxidase was combined with a chemical biotinylation step involving biotin-epsilon-amidocaproylhydrazide in a one-pot synthesis. The novel nucleotide sugar derivatives uridine 5'-diphospho-6-biotin-epsilon-amidocaproylhydrazino-alpha-D-galactose (UDP-6-biotinyl-Gal) and uridine 5'-diphospho-6-biotin-epsilon-amidocaproylhydrazino-N-acetyl-alpha-D-galactosamine (UDP-6-biotinyl-GalNAc) were synthesized on a 100-mg scale and characterized by mass spectrometry (fast atom bombardment and matrix-assisted laser desorption/ionization time of flight) and one/two dimensional NMR spectroscopy. It could be demonstrated for the first time, by use of UDP-6-biotinyl-Gal as a donor substrate, that the human recombinant galactosyltransferases beta3Gal-T5, beta4Gal-T1, and beta4Gal-T4 mediate biotinylation of the neoglycoconjugate bovine serum albumin-p-aminophenyl N-acetyl-beta-D-glucosaminide (BSA-(GlcNAc)17) and ovalbumin. The detection of the biotin tag transferred by beta3Gal-T5 onto BSA-(GlcNAc)17 with streptavidin-enzyme conjugates gave detection limits of 150 pmol of tagged GlcNAc in a Western blot analysis and 1 pmol of tagged GlcNAc in a microtiter plate assay. The degree of Gal-biotin tag transfer onto agalactosylated hybrid N-glycans present at the single glycosylation site of ovalbumin was dependent on the Gal-T used (either beta3Gal-T5, beta4Gal-T4, or beta4Gal-T1), which indicates that the acceptor specificity may direct the transfer of the Gal-biotin tag. The potential of this biotinylated UDP-Gal as a novel donor substrate for human galactosyltransferases lies in the targeting of distinct acceptor structures, for example, under-galactosylated glycoconjugates, which are related to diseases, or in the quality control of glycosylation of recombinant and native glycoproteins.     

The efficiency of sampling very high resolution images for area estimation in the European Union

Very high resolution (VHR) images are a valuable information source to estimate land cover area and land cover change. When full coverage of a region with VHR images is not affordable, a sample of images can be considered. Square grids provide a practical sampling frame for VHR images. When using a land cover map as pseudo-truth, the sampling variance is easily assessed but may be overestimated if the land cover map has a coarse resolution. To estimate the potential sampling variance of a cluster sampling scheme, we propose a method based on intra-cluster correlation (ICC) computed from a correlogram. The ‘equivalent number of points’ is a useful indicator to quantify cost-efficiency of sites of a given size. We obtained poor efficiency results for area estimation of major land cover types in the European Union (EU) with a sample of 10 km?×?10 km sites, but results are more encouraging for classes with a more scattered layout or for land cover change.     

Adaptative state-space model predictive control of a parabolic-trough field

Model Predictive control algorithms for trough solar plants make use of solar radiation measurements and the overall efficiency knowledge which are very useful in order to reject disturbances. However, direct solar radiation, mirror reflectivity and metal absorptance which affect overall efficiency, can only be measured locally. In this paper, an adaptative model predictive control using an unscented Kalman filter (UKF) to estimate both the effective solar radiation and the metal–fluid temperature profiles is proposed. The control algorithm is validated by tests with real data taken from the ACUREX field of the PSA in Almería (Spain).     

Wavelet power,entropy and bispectrum applied to AE signals for damage identification and evaluation of corroded galvanized steel

Acoustic emission (AE) signals obtained from scratch tests on hot dip galvanized samples with different corrosion levels were processed by wavelet transform (WT) analysis. Wavelet power was distributed in different frequency bands, according to damage mechanisms. The frequency bands were automatically obtained by searching for the relative minima of the wavelet entropy of signals and appropriate clustering methods. Correlation between the different mechanisms was corroborated by bispectrum analysis (BA). The damage evaluation entailed studying the evolution of the wavelet power in a specific frequency band, which corresponded to the fracture of the zeta phase columns of the galvanized coating. Results showed damage to increase along with the level of corrosion, but adherence was not dramatically affected in the studied corrosion range. The application of two signal-processing techniques, WT and BA, contributed to the consistency of our results. Besides the addressed technological application, we could demonstrate that that signal-processing techniques, when applied carefully, and results classified with care, are able to contribute to what is certainly an important problem, specially in cases like the treated here, where a complete physical theory relating damage and AE is not yet available.     

Radiographic findings in Pneumocystis carinii pneumonia and its complications in HIV patients

Despite their increasing representation in the population, little is known about the neuropsychological test performance of the oldest old, particularly those who live in residential settings. Limited published data and clinical experience suggest that this group is more likely to perform in the impaired range on standardized tests when cut-offs developed with younger groups are used. We examined the Dementia Rating Scale (DRS) performance of 82 nondemented nursing home residents, aged 80 to 99, with a mean education level of 11 years. Using published norms and cutoffs, a large percentage of this sample performed in the impaired range, particularly on the initiation and conceptualization subtests and on the total score. Education, but not age, was significantly related to performance in this sample. Percentages of patients misclassified were substantial in all groups, but were higher in those with less than 13 years of education. Using a lower total-score cutoff of 110 reduced the percentage of misclassifications markedly. We recommend the development and use of revised cutoff scores for the evaluation of very elderly nursing home residents.     

European Minor Constituent Radiometer: A New Millimeter Wave Receiver for Atmospheric Research

EMCOR is a heterodyne receiver for the frequency range of 201 to 210 GHz. It has been designed for ground-based measurements of various minor constituents of the stratosphere involved in ozone chemistry. Since the aim was the detection of faint spectral lines, a superconducting tunnel junction has been chosen as mixer element and special care has been taken in developing the calibration unit of the system. The front-end is completed by a quasi-optical system, a solid state local oscillator with electronic tuning and a HEMT pre-amplifier. In the back-end an acousto-optical spectrometer is employed to analyse the signal. A PC controls the whole system. The instrument has been installed at a high mountain site in the Swiss Alps.     

Practical Application of New Simulation Methods for the Elimination of Geometric Instabilities in Centerless Grinding

Elimination of geometric lobing in centerless grinding has been extensively investigated. Several models have been successfully developed, but no practical tool has been implemented on machines to ease the setting up of the machine to ensure stable conditions. This paper describes a software tool which has been developed for setting up and optimization of centerless plunge grinding processes to avoid geometric instabilities. The software generates stability maps showing the stable and non-stable geometric configurations and the number of lobes generated in non-stable conditions. Complementary time domain models quantitatively predict the evolution of the profile error for each geometric configuration.