A “4π-type” study of the reaction p(d,pp)n at Ed = 26.5 MeV

Experimental data on the three-nucleon reaction p(d, pp)n at E_d = 26.5 MeV obtained with the multidetector system BOL, covering most of the phase space, are presented. The data are compared with Faddeev calculations using a local S-wave potential for the nucleon-nucleon interaction. The calculated cross sections, which are in general not sensitive to the precise choice of the nucleon-nucleon potential, agree well with the data over the major part of phase space. We have, though, discovered a region in phase space with a strong discrepancy. In the same region, around a neutron c.m. angle of 140°, the calculations are sensitive to the N-N potential. Theoretical and experimental angular distributions in the p-n recoil c.m. subsystem for proton- neutron energies below 0.5 MeV agree in absolute magnitude, both being isotropic. For larger relative energies, a discrepancy develops, part of which might be related to missing higher par- tial wave components in the N-N interaction, rather than to Coulomb or S-wave scattering effects. The total breakup cross section has been deduced from the data as 169 ± 36 mb.     

On the magnetic threshold for the alignment of a twisted nematic crystal

A computation of the capacitance and the optical transmission between parallel polarizers of a twisted nematic liquid crystal in a magnetic field shows that the “optical threshold” occurs at a higher value of the field strength than the “capacitive threshold”.     

Determination of silicon in natural and pollution aerosols by 14-MeV neutron activation analysis

The determination of silicon via the ²⁸Si(n,p)²⁸ Al reaction by means of 14-MeV neutrons is applied to the analysis of pollution and natural aerosols. A Whatman 41 filter (40 cm²) on which airborne particulate material has been collected is compressed into a 3 × 12.7 mm pellet. Standards are prepared in the same way from clean filters spiked with a silicate solution. After a 50-s irradiation and a 75-s decay time, the sample is counted for 2 min with 5” × 5” NaI(Tl) well detector. The 1.779-MeV photopeak of ²⁸Al is measured with a single channel sealer chain or with a multichannel analyser. The reproducibility, sensitivity and liability to interference from other elements were investigated for both counting systems. The homogeneity of the pellets and the filters was checked. The overall precision of one single-channel determination was estimated to be 3.5% after a 24-h high-volume sampling time. Samples collected in urban, industrial and remote areas with concentrations ranging from 0.05 to 15 μg Si m^-3 air were analysed and the results are discussed.     

A critical study of the application of graphite-furnace non-flame atomic absorption spectrometry to the deter-mination of trace base metals in complex heavy-matrix sample solutions

Because of the extravagant claims made for the usefulness of non-flame atomic absorption spectroscopy, a critical evaluation of its performance in heavy matrix solutions, for selected trace heavy metals, was made. Studies of physical and chemical interference problems are presented for a range of inorganic and organic matrices. Often quoted remedies (e.g. selective volatilization, standard addition etc.) for solution of the more serious problems were found to be of little help in most cases. The influence of variables such as nature and flow rate of purge gas, ashing temperature and atomization temperature are also evaluated. Analyses for Cd, Cu, Pb, Zn, Ni, Co were done on samples by flame and nonflame methods in high solids solutions. While there appears to be an advantage to the non-flame method in dealing with sample solutions of high organic content, no advantage is apparent for either technique with highly inorganic matrices.     

Moving backward noisily

We discuss the fundamental physical differences and the mathematical interconnections of counterintuitive transport and response properties in Brownian motion far from equilibrium. After reviewing the ubiquity of such effects in physical and other systems, we illustrate the general properties on paradigmatic models for both individually and collectively acting Brownian particles.     

The use of multivariate MR imaging intensities versus metabolic data from MR spectroscopic imaging for brain tumour classification

This study investigated the value of information from both magnetic resonance imaging and magnetic resonance spectroscopic imaging (MRSI) to automated discrimination of brain tumours. The influence of imaging intensities and metabolic data was tested by comparing the use of MR spectra from MRSI, MR imaging intensities, peak integration values obtained from the MR spectra and a combination of the latter two. Three classification techniques were objectively compared: linear discriminant analysis, least squares support vector machines (LS-SVM) with a linear kernel as linear techniques and LS-SVM with radial basis function kernel as a nonlinear technique. Classifiers were evaluated over 100 stratified random splittings of the dataset into training and test sets. The area under the receiver operating characteristic (ROC) curve (AUC) was used as a global performance measure on test data. In general, all techniques obtained a high performance when using peak integration values with or without MR imaging intensities. For example for low- versus high-grade tumours, low- versus high-grade gliomas and gliomas versus meningiomas, the mean test AUC was higher than 0.91, 0.94, and 0.99, respectively, when both MR imaging intensities and peak integration values were used. The use of metabolic data from MRSI significantly improved automated classification of brain tumour types compared to the use of MR imaging intensities solely.     

Kinetic study of the degradation of a potential local anesthetic drug in serum using the DNA-based electrochemical biosensor

DNA-drug association interaction at the DNA modified screen-printed electrode for 1-methyl-2-piperidinoethylester of 2-hexoxyphenylcarbamic acid was found leading to an accumulation of the drug within the DNA layer. A procedure for the determination of drug in blood serum matrix using the protein precipitation and voltammetric measurement of the electroactive drug with the DNA biosensor was obtained and an effort was done to apply it for an assay of the drug enzymatic degradation in human and rabbit sera at 37 degrees C.     

First principles calculation of the interdiffusion coefficient in binary alloys

The atomic mechanisms of diffusion in alloys are complex due to the variations of migration energies with environment and the correlations induced by short-range order between the different components. We present a first-principles approach for calculating vacancy-mediated diffusion coefficients in crystalline binary alloys and apply it to obtain the interdiffusion coefficient of Al(1-x)Lix. The rigorous treatment of atomic migration indicates that short- and long-range order induces strongly correlated migration mechanisms that deviate from random walk behavior.