Nuclear medium modifications of the NN interaction via quasielastic (p⃗,p⃗′\vec p,\vec p ') and (p⃗,n⃗\vec{p},\vec{n}) scattering

Within the relativistic PWIA, spin observables have been recalculated for quasielastic ($\vec p,\vec p '$) and ($\vec p,\vec n$) reactions on a $^{40}$Ca target. The incident proton energy ranges from 135 to 300 MeV while the transferred momentum is kept fixed at 1.97 fm^{-1}. In the present calculations, new Horowitz-Love--Franey relativistic NN amplitudes have been generated in order to yield improved and more quantitative spin observable values than before. The sensitivities of the various spin observables to the NN interaction parameters, such as (1) the presence of the surrounding nuclear medium, (2) a pseudoscalar versus a pseudovector interaction term, and (3) exchange effects, point to spin observables which should preferably be measured at certain laboratory proton energies, in order to test current nuclear models. This study also shows that nuclear medium effects become more important at lower proton energies ($\leq$ 200 MeV). A comparison to the limited available data indicates that the relativistic parametrization of the NN scattering amplitudes in terms of only the five Fermi invariants (the SVPAT form) is questionable.Comment: 10 pages, 6 Postscript figures, uses psfig.sty and article.sty, submitted to Phys. Rev.

Test, test, test for COVID-19 antibodies:the importance of sensitivity, specificity and predictive powers

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody tests of varying specificity and sensitivity are now available. For informing individuals whether they have had coronavirus disease 2019 (COVID-19), they need to be very accurate. For measuring population prevalence of past infection, the numbers of false positives and negatives need to be roughly equal. With a series of worked examples for a notional population of 100,000 people, we show that even test systems with a high specificity can yield a large number of false positive results, especially where the population prevalence is low. For example, at a true population prevalence of 5%, using a test with 99% sensitivity and specificity, 16% of positive results will be false and thus 950 people will be incorrectly informed they have had the infection. Further confirmatory testing may be needed. Giving false reassurance on which personal or societal decisions might be based could be harmful for individuals, undermine public confidence and foster further outbreaks

Rapid deconvolution of low-resolution time-of-flight data using Bayesian inference

CITATION: Pieterse, C. L., et al. 2019. Rapid deconvolution of low-resolution time-of-flight data using Bayesian inference. The Journal of Chemical Physics, 151:244307, doi:10.1063/1.5129343.The original publication is available at https://aip.scitation.orgThe deconvolution of low-resolution time-of-flight data has numerous advantages, including the ability to extract additional information from the experimental data. We augment the well-known Lucy-Richardson deconvolution algorithm using various Bayesian prior distributions and show that a prior of second-differences of the signal outperforms the standard Lucy-Richardson algorithm, accelerating the rate of convergence by more than a factor of four, while preserving the peak amplitude ratios of a similar fraction of the total peaks. A novel stopping criterion and boosting mechanism are implemented to ensure that these methods converge to a similar final entropy and local minima are avoided. Improvement by a factor of two in mass resolution allows more accurate quantification of the spectra. The general method is demonstrated in this paper through the deconvolution of fragmentation peaks of the 2,5-dihydroxybenzoic acid matrix and the benzyltriphenylphosphonium thermometer ion, following femtosecond ultraviolet laser desorption.https://aip.scitation.org/doi/10.1063/1.5129343Publisher's versio

Rapid deconvolution of low-resolution time-of-flight data using Bayesian inference

CITATION: Pieterse, C. L., et al. 2019. Rapid deconvolution of low-resolution time-of-flight data using Bayesian inference. The Journal of Chemical Physics, 151:244307, doi:10.1063/1.5129343.The original publication is available at https://aip.scitation.orgThe deconvolution of low-resolution time-of-flight data has numerous advantages, including the ability to extract additional information from the experimental data. We augment the well-known Lucy-Richardson deconvolution algorithm using various Bayesian prior distributions and show that a prior of second-differences of the signal outperforms the standard Lucy-Richardson algorithm, accelerating the rate of convergence by more than a factor of four, while preserving the peak amplitude ratios of a similar fraction of the total peaks. A novel stopping criterion and boosting mechanism are implemented to ensure that these methods converge to a similar final entropy and local minima are avoided. Improvement by a factor of two in mass resolution allows more accurate quantification of the spectra. The general method is demonstrated in this paper through the deconvolution of fragmentation peaks of the 2,5-dihydroxybenzoic acid matrix and the benzyltriphenylphosphonium thermometer ion, following femtosecond ultraviolet laser desorption.https://aip.scitation.org/doi/10.1063/1.5129343Publisher's versio

Polarization transfer observables for quasielastic proton-nucleus scattering in terms of a complete Lorentz invariant representation of the NN scattering matrix

For the calculation of polarization transfer observables for quasielastic scattering of protons on nuclei, a formalism in the context of the Relativistic Plane Wave Impulse Approximation is developed, in which the interaction matrix is expanded in terms of a complete set of 44 independent invariant amplitudes. A boson-exchange model is used to predict the 39 amplitudes which were omitted in the formerly used five-term parameterization(the SPVAT form) of the nucleon-nucleon scattering matrix. Use of the complete set of amplitudes eliminates the arbitrariness of the five-term representation.Comment: 29 pages, 2 figure

Monitoring stimulated darkening from UV-C light on different bean genotypes by NMR spectroscopy.

The use of UV-C cool white light on bean (Phaseolus vulgaris L.) seeds significantly increases the biochemical seed coat post-harvest darkening process, whilst preserving seed germination. The aim of this work consists in monitoring the effect caused by the incidence of UV-C light on different bean genotypes using NMR spectroscopy. The genotype samples named IAC Alvorada; TAA Dama; BRS Estilo and BRS Pérola from the Agronomic Institute (IAC; Campinas; SP; Brazil) were evaluated. The following two methodologies were used: a prolonged darkening, in which the grain is placed in a room at a controlled temperature (298 K) and humidity for 90 days, simulating the supermarket shelf; an accelerated darkening, where the grains are exposed to UV-C light (254 nm) for 96 h. The experiments were performed using the following innovative time-domain (TD) NMR approaches: the RK-ROSE pulse sequence; one- and two-dimensional high resolution (HR) NMR experiments ( 1H; 1H-1H COSY and 1H-13C HSQC); chemometrics tools, such as PLS-DA and heat plots. The results suggest that the observed darkening occurs on the tegument after prolonged (90 days) and accelerated (96 h) conditions. In addition, the results indicate that phenylalanine is the relevant metabolite within this context, being able to participate in the chemical reactions accounted for by the darkening processes. Additionally, it is possible to confirm that a UV-C lamp accelerates oxidative enzymatic reactions and that the NMR methods used were a trustworthy approach to monitor and understand the darkening in bean seeds at metabolite level

Afrikaans adaptation of the children’s hope scale: Validation and measurement invariance

The overarching aim of this study was to validate the Afrikaans version of Snyder’s (1997) Children’s Hope Scale in a sample of children from Cape Town, South Africa. Within this process, the study aimed to test the measurement invariance across the English and Afrikaans language versions. The study used a cross-sectional survey design, with a two-stage stratified random sample of 1022 children between the ages of 11- to 12-years-old. We selected the participants from 15 schools located in low and middle socio-economic status communities in the Cape Town Metropole. We used confirmatory factor analysis to analyse the data. The results indicated a good fit for the overall model using the pooled sample (X2 = 35.692; df = 7; p =.00; CFI =.984; RMSEA =.063; SRMR =.023). Multi-group confirmatory factor analysis further demonstrated the tenability of metric and scalar invariance

Detectie van plantenpathogenen en –aantasters

Nederland speelt internationaal een belangrijke rol in productie en handel van plantaardig materiaal. Hierin zijn vaak ongewenste veroorzakers van quarantaine- (Q) en kwaliteitsziekten (K) en -plagen een storende factor. Om de (fytosanitaire) kwaliteit van verhandeld (met name ook geëxporteerd) plantmateriaal ook in de toekomst te kunnen blijven garanderen, en eigen teelten te vrijwaren van ongewenste organismen is het van groot belang vroegtijdig deze plantenpathogenen te kunnen detecteren en te identificeren. Hiervoor zijn gevalideerde onderzoekmethoden noodzakelijk, die geschikt zijn voor routinematig gebruik door het bedrijfsleven, de keuringsdiensten en de NVWA. De hier voorgestelde intensieve samenwerking tussen kennisinstellingen, overheid en keuringslaboratoria is noodzakelijk om de agrarische sector toekomstbestendig te houden. Daarnaast dient naast aandacht voor nieuwe ontwikkelingen ook aandacht besteedt te worden aan kwaliteitsborging en efficiëntie verbetering van bestaande technieken zodat de taken van de keuringsdiensten beter uitgevoerd kunnen worden