John Furst

Extrapolation procedures in Mott electron polarimetry

In standard Mott electron polarimetry using thin gold film targets, extrapolation procedures must be used to reduce the experimentally measured asymmetries A to the values they would have for scattering from single atoms. These extrapolations involve the dependence of A on either the gold film thickness t or the maximum detected electron energy loss in the target ΔE. Using a concentric cylindrical‐electrode Mott polarimeter, we have studied and compared these two types of extrapolations over the electron energy range 20–100 keV. The potential systematic errors which can result from such procedures are analyzed in detail, particularly with regard to the use of various fitting functions in thickness extrapolations, and the failure of perfect energy‐loss discrimination to yield accurate polarizations when thick foils are used. A critical discussion of previous work on this subject is presented.

Vitamin D, folate, and potential early lifecycle environmental origin of significant adult phenotypes

Solar radiation early in pregnancy interacts with light sensitive vitamins to influence an embryos genetic profile. This influences both adult disease risk and may play a role in the evolution of skin colour.

Proton chemical shifts in some hydrogen bonded solids and a correlation with bond lengths

Using multipulse techniques, principal values of the proton nuclear magnetic resonance (NMR) chemical shift tensors were measured at room temperature for the monoclinic form of oxalic acid, potassium hydrogen oxalate, and potassium hydroxide. The isotropic and perpendicular shifts of the first two compounds, which are of medium hydrogen bond strength, were found to fit the linear correlation with O⋅⋅⋅O distance, RO⋅O, established by Rohlfing, Allen, and Ditchfield for medium and strongly O–H⋅⋅⋅O hydrogen bonded solids. Although KOH is very weakly hydrogen bonded, the shifts were also found to conform to the correlation, at least as well as does the other data, thus extending this to weakly hydrogen bonded solids. An empirical correlation of the isotropic and perpendicular shifts with exp(−RO⋅O/ρ), where RO⋅O is in A and ρ is 0.94 A, is given here which has better agreement with the data and has an interpretation in terms of a simple ionic model of an O–H⋅⋅⋅O bond.

Production of a high‐density state‐selected metastable neon beam

We have developed a high‐density source of metastable neon and have selectively quenched both metastable species using a standing‐wave dye laser. The source is compact, stable, and produces an average intensity of 3.6×1014 sr−1 s−1 and a density on target of 7.7×106 cm−3.

UV-associated decline in systemic folate: implications for human nutrigenetics, health, and evolutionary processes

The purpose of this study was to examine whether UV exposure alters folate status according to C677T‐MTHFR genotype, and to consider the relevance of this to human health and the evolutionary model of skin pigmentation.

Vitamin D Receptor Genotype Modulates the Correlation between Vitamin D and Circulating Levels of let-7a/b and Vitamin D Intake in an Elderly Cohort

Background and Aims: Circulating microRNAs (miRNAs) are linked to disease and are potential biomarkers. Vitamin D may modulate miRNA profiles, and vitamin D status has been linked to risk of disease, including cardiovascular disease and cancers. We hypothesise that genotypic variance influences these relationships. We examined the correlations between vitamin D intake and circulating levels of the miRNAs let-7a/b, and the involvement of two common vitamin D receptor (VDR) polymorphisms, BsmI and ApaI. Methods: Two hundred participants completed food frequency and supplement questionnaires, and were assayed for circulating let-7b expression by qPCR. Polymorphisms were detected using restriction fragment length polymorphism-PCR. Results: let-7b expression negatively correlated with vitamin D intake (rs = -0.20, p = 0.005). The magnitude and direction of correlation were maintained in the presence of the BsmI restriction site (rs = -0.27, p = 0.0005). However, in the absence of BsmI restriction site, the direction of the correlation was reversed (rs = +0.319, p = 0.0497). These correlations were significantly different (z-score = 2.64, p = 0.0085). The correlation between vitamin D intake and let-7a was only significant in those without the ApaI restriction site. Conclusions: The correlation between vitamin D intake and let-7a/b expression in this cohort varies with VDR genotype. This study highlights the importance of considering underlying genotypic variance in miRNA expression studies and in nutritional epigenetics generally.

Total cross sections for the production of metastable neon atoms by electron impact

Total cross sections have been measured for the production of the metastable 1s3 and 1s5 states in neon at incident electron energies from threshold to 500 eV. A time of flight technique was used to determine relative cross sections which were made absolute by comparison with the known cross sections for metastable production in helium. Reasonable agreement is found between the present results and those of Phillips et al. (1981) who used different techniques to measure relative cross sections and to normalise their data. This good agreement has implications for the mechanism of the excitation of the metastable states.

Vitamin D Beyond Metabolism

Interest in vitamin D and the VDR gene is increasing as putative roles in human health and evolutionary processes are explored. This review looks beyond the classic biochemistry that links vitamin D to calcium homeostasis; it explores how vitamin D interacts with light in a broader perspective than simple skin photosynthesis. It examines how the vitamin influences circadian rhythm, and how it may have helped drive the evolution of skin pigmentation. To this end, the nutrient–nutrient relationship with folate is also explored. The VDR gene is additionally examined as a factor in the evolutionary selection of skin depigmentation at higher latitudes to allow vitamin D synthesis. Evidence is given to show that VDR polymorphisms exhibit a latitudinal gradient in allele prevalence consistent with such a paradigm. Overall, the review examines new evo-devo ideas that link light-sensitive vitamins to human health/phenotype, both within and across the lifecycle.

Production of excited atomic hydrogen and deuterium from H2and D2photodissociation

We have measured the production of both Lya and Ha fluorescence from atomic H and D for the photodissociation of H 2 and D 2 by linearly polarized photons with energies between 24 and 60 eV. In this energy range, excited photofragments result primarily from he production of doubly excited molecular species which promptly autoionize or dissociate into two neutrals. Our data are compared with ab initio calculations of the dissociation process, in which both doubly excited state production and prompt ionization (non-resonant) channels are considered. Agreement between our experimental data and that of earlier work, and with our theoretical calculations, is qualitative at best.

Excitation of He 3(3)P and Ne 3p states by polarized electrons

Integrated Stokes parameters for the transitions in helium (388.9 nm) and neon (640.2 nm) and (626.7 nm) have been measured over the electron energy range from threshold to 300 eV after excitation by polarized electrons. The measured zero values of for both the He 388.9 and Ne 640.2 nm photons are consistent with the LS coupling of the upper states for each transition. Similarly, the measured non-zero values of for the 626.7 nm photons provide clear evidence of the breakdown of LS coupling for the Ne state due to the spin - orbit interaction of the atomic electrons. Non-zero values of the Stokes parameter indicate strong electron exchange effects, particularly near threshold. Negative ion resonances show considerable effects on the polarizations of the subsequent radiations. The effect of different core configurations on the alignment of excited states is discussed.