Development of a method of analysis for pentachlorophenol in liver

Pentachlorophenol (PCP) has been used for many years as an all purpose fungicide and pesticide. Its widespread use, especially in the wood preservation industry, has led to there being detectable levels within the food chain. It is therefore necessary to be able to detect and quantify levels present in plants and animals to ensure that tolerance is met. Detectable levels of PCP have been found in the liver of pigs in the Netherlands by the Food Inspection Service, Amsterdam in the range 0.01- 1.2 mg/kg (median 0.06 mg/kg). It was the purpose of this project to optimise the procedure for the quantification of PCP in the liver of cattle, sheep and chickens. Much of the work has been done on improving the efficiency of the derivatisation step. Parameters that appear to have no influence on the efficiency of the derivatisation step are the age and volume of acetic anhydride used, the temperature of and the time taken for the derivatisation procedure, the amount of Na2SO4 used in the drying step. Parameters that have an influence on the efficiency of the derivatisation step are the order in which the components are added together (acetic anhydride should be added to the mixture of the sample and the K2C03 ) , and the volume and the molarity of the K2C03. The optimum result was obtained using 80 ml 0.1M K2C03. The derivatised PCP (dPCP) was stable in the injector of the gas chromatography (GC) system, also during storage in the refrigerator for at least one month. Recovery experiments with liver spiked at the 1 mg/kg level show results better than 80 % (CV 2.5 % (n=3)) The coefficient of variation for the repeatability in a liver at the 0.05 mg/kg level was 18.8 % (n=6) and at the 0.01 mg/kg level 55.3 % (n=4)

Content of pentachlorophenol in liver of cattle, sheep, pigs and chickens

Pentachlorophenol (PCP) has been used for many years as an all purpose fungicide and pesticide. Its widespread use, especially in the wood preservation industry, has led to its presence in the food chain. It is therefore necessary to detect and quantify levels present in plants and animals to see if the levels are of concern. Detectable levels of PCP have be found in the liver of pigs in the Netherlands by the Food Inspection Service, Amsterdam in the range 0.01 - 1.2 mg/kg (median 0.06 mg/kg). It was the purpose of this project to measure PCP in the liver of cattle, sheep, pigs and chickens

Semiquantitative theory of electronic Raman scattering from medium-size quantum dots

A consistent semiquantitative theoretical analysis of electronic Raman scattering from many-electron quantum dots under resonance excitation conditions has been performed. The theory is based on random-phase-approximation-like wave functions, with the Coulomb interactions treated exactly, and hole valence-band mixing accounted for within the Kohn-Luttinger Hamiltonian framework. The widths of intermediate and final states in the scattering process, although treated phenomenologically, play a significant role in the calculations, particularly for well above band gap excitation. The calculated polarized and unpolarized Raman spectra reveal a great complexity of features and details when the incident light energy is swept from below, through, and above the quantum dot band gap. Incoming and outgoing resonances dramatically modify the Raman intensities of the single particle, charge density, and spin density excitations. The theoretical results are presented in detail and discussed with regard to experimental observations.Comment: Submitted to Phys. Rev.

Resonant Raman scattering off neutral quantum dots

Resonant inelastic (Raman) light scattering off neutral GaAs quantum dots which contain a mean number, N=42, of electron-hole pairs is computed. We find Raman amplitudes corresponding to strongly collective final states (charge-density excitations) of similar magnitude as the amplitudes related to weakly collective or single-particle excitations. As a function of the incident laser frequency or the magnetic field, they are rapidly varying amplitudes. It is argued that strong Raman peaks should come out in the spin-density channels, not related to valence-band mixing effects in the intermediate states.Comment: Accepted in Physical Review

Tests of sunspot number sequences: 1. Using ionosonde data

More than 70 years ago it was recognised that ionospheric F2-layer critical frequencies [foF2] had a strong relationship to sunspot number. Using historic datasets from the Slough and Washington ionosondes, we evaluate the best statistical fits of foF2 to sunspot numbers (at each Universal Time [UT] separately) in order to search for drifts and abrupt changes in the fit residuals over Solar Cycles 17-21. This test is carried out for the original composite of the Wolf/Zürich/International sunspot number [R], the new “backbone” group sunspot number [RBB] and the proposed “corrected sunspot number” [RC]. Polynomial fits are made both with and without allowance for the white-light facular area, which has been reported as being associated with cycle-to-cycle changes in the sunspot number - foF2 relationship. Over the interval studied here, R, RBB, and RC largely differ in their allowance for the “Waldmeier discontinuity” around 1945 (the correction factor for which for R, RBB and RC is, respectively, zero, effectively over 20 %, and explicitly 11.6 %). It is shown that for Solar Cycles 18-21, all three sunspot data sequences perform well, but that the fit residuals are lowest and most uniform for RBB. We here use foF2 for those UTs for which R, RBB, and RC all give correlations exceeding 0.99 for intervals both before and after the Waldmeier discontinuity. The error introduced by the Waldmeier discontinuity causes R to underestimate the fitted values based on the foF2 data for 1932-1945 but RBB overestimates them by almost the same factor, implying that the correction for the Waldmeier discontinuity inherent in RBB is too large by a factor of two. Fit residuals are smallest and most uniform for RC and the ionospheric data support the optimum discontinuity multiplicative correction factor derived from the independent Royal Greenwich Observatory (RGO) sunspot group data for the same interval

Probabilistic solar wind and geomagnetic forecasting using an analogue ensemble or "Similar Day" approach

Effective space-weather prediction and mitigation requires accurate forecasting of near-Earth solar-wind conditions. Numerical magnetohydrodynamic models of the solar wind, driven by remote solar observations, are gaining skill at forecasting the large-scale solar-wind features that give rise to near-Earth variations over days and weeks. There remains a need for accurate short-term (hours to days) solar-wind forecasts, however. In this study we investigate the analogue ensemble (AnEn), or “similar day”, approach that was developed for atmospheric weather forecasting. The central premise of the AnEn is that past variations that are analogous or similar to current conditions can be used to provide a good estimate of future variations. By considering an ensemble of past analogues, the AnEn forecast is inherently probabilistic and provides a measure of the forecast uncertainty. We show that forecasts of solar-wind speed can be improved by considering both speed and density when determining past analogues, whereas forecasts of the out-of-ecliptic magnetic field [ BNBN ] are improved by also considering the in-ecliptic magnetic-field components. In general, the best forecasts are found by considering only the previous 6 – 12 hours of observations. Using these parameters, the AnEn provides a valuable probabilistic forecast for solar-wind speed, density, and in-ecliptic magnetic field over lead times from a few hours to around four days. For BNBN , which is central to space-weather disturbance, the AnEn only provides a valuable forecast out to around six to seven hours. As the inherent predictability of this parameter is low, this is still likely a marked improvement over other forecast methods. We also investigate the use of the AnEn in forecasting geomagnetic indices Dst and Kp. The AnEn provides a valuable probabilistic forecast of both indices out to around four days. We outline a number of future improvements to AnEn forecasts of near-Earth solar-wind and geomagnetic conditions