High-Resolution Measurements of e+ + H2O Total Cross Section

Using a purely positron beam, the total cross section of positrons scattering from H2O has been measured for the first time with a high angular discrimination (≃1°) against forward scattered projectiles. Results are presented in the energy range (10-300) eV. Significant deviations from previous measurements are found which are, if ascribed entirely to the angular acceptances of various experimental systems, in quantitative accord with ab initio theoretical predictions of the differential elastic scattering cross section

Magnetic field-free measurements of the total cross section for positrons scattering from helium and krypton

An electrostatic beam has been used to perform scattering measurements with an angular-discrimination of $\lesssim 2^\circ$. The total cross sections of positrons scattering from helium and krypton have been determined in the energy range (10–300) eV. This work was initially stimulated by the investigations of Nagumo et al (2011 J. Phys. Soc. Japan 80 064301), the first positron field-free measurements performed with a similarly high resolution, which found significant discrepancies at low energies with most other experiments and theories. The present results show good agreement with theories and several other measurements, even those characterized by a much poorer angular discrimination, implying a small contribution from particles elastically scattered at forward angles, as theoretically predicted for He but not for Kr

Absolute differential positronium-formation cross sections

The first absolute experimental determinations of the differential cross-sections for the formation of ground-state positronium are presented for He, Ar, H2 and CO2 near 0○. Results are compared with available theories. The ratio of the differential and integrated cross-sections for the targets exposes the higher propensity for forward-emission of positronium formed from He and H2

Structural neuroimaging biomarkers for obsessive-compulsive disorder in the ENIGMA-OCD consortium: medication matters

No diagnostic biomarkers are available for obsessive-compulsive disorder (OCD). Here, we aimed to identify magnetic resonance imaging (MRI) biomarkers for OCD, using 46 data sets with 2304 OCD patients and 2068 healthy controls from the ENIGMA consortium. We performed machine learning analysis of regional measures of cortical thickness, surface area and subcortical volume and tested classification performance using cross-validation. Classification performance for OCD vs. controls using the complete sample with different classifiers and cross-validation strategies was poor. When models were validated on data from other sites, model performance did not exceed chance-level. In contrast, fair classification performance was achieved when patients were grouped according to their medication status. These results indicate that medication use is associated with substantial differences in brain anatomy that are widely distributed, and indicate that clinical heterogeneity contributes to the poor performance of structural MRI as a disease marker

Quantum suppression of antihydrogen formation in positronium-antiproton scattering

Calculation of antihydrogen formation from antiproton-positronium collisions, with the positroniun in excited states. Novelty is the extension to positronium states with principal quantum numbers 4 and 5 and the discovery that the increase in the cross section is muted over simple expectations due to a suppression effect.This effect is due to a centrifugal barrier-type effect, which markedly reduces the influence of the higher angular momentum components which typically provide the cross section enhancements at lower values of n

Notes for genera: basal clades of Fungi (including Aphelidiomycota, Basidiobolomycota, Blastocladiomycota, Calcarisporiellomycota, Caulochytriomycota, Chytridiomycota, Entomophthoromycota, Glomeromycota, Kickxellomycota, Monoblepharomycota, Mortierellomycota, Mucoromycota, Neocallimastigomycota, Olpidiomycota, Rozellomycota and Zoopagomycota)

Compared to the higher fungi (Dikarya), taxonomic and evolutionary studies on the basal clades of fungi are fewer in number. Thus, the generic boundaries and higher ranks in the basal clades of fungi are poorly known. Recent DNA based taxonomic studies have provided reliable and accurate information. It is therefore necessary to compile all available information since basal clades genera lack updated checklists or outlines. Recently, Tedersoo et al. (MycoKeys 13:1--20, 2016) accepted Aphelidiomycota and Rozellomycota in Fungal clade. Thus, we regard both these phyla as members in Kingdom Fungi. We accept 16 phyla in basal clades viz. Aphelidiomycota, Basidiobolomycota, Blastocladiomycota, Calcarisporiellomycota, Caulochytriomycota, Chytridiomycota, Entomophthoromycota, Glomeromycota, Kickxellomycota, Monoblepharomycota, Mortierellomycota, Mucoromycota, Neocallimastigomycota, Olpidiomycota, Rozellomycota and Zoopagomycota. Thus, 611 genera in 153 families, 43 orders and 18 classes are provided with details of classification, synonyms, life modes, distribution, recent literature and genomic data. Moreover, Catenariaceae Couch is proposed to be conserved, Cladochytriales Mozl.-Standr. is emended and the family Nephridiophagaceae is introduced

Interactions of positrons & positronium with matter

The aim of this work is to help and advance the understanding of the interaction of positrons and positronium (Ps) with matter. Knowledge of these interactions has a wide range of applications in many fields including medical imaging, galactic astronomy and condensed matter physics. An electrostatic beam of positrons has been used with a tungsten mesh moderator and a tungsten foil remoderator. The beam has been characterised to have a beam divergence of ∼ 1 degree and energy resolution of 1%. The system has been applied to the measurements of the positron total cross section for He. Despite improved absolute angular resolution and a truly field-free interaction region, similarity with previous magnetic beam measurements with poorer angular resolution and theories has been found, in contrast with the only previous electrostatic beam measurements. The collimated Ps production efficiency from Ar and Xe has been measured down to 1.4eV, enabling Ps scattering experiments to be performed in a new energy range. The total cross sections for Ps scattering from Ar, Xe, O2 and CF4 have been measured between 1.4 and 120eV. In comparison with the total cross section for equivelocity electrons, an enhancement in the Ps scattering is observed centred at ∼ 5 eV. For Ar and Xe, in contrast to theoretical predictions, the Ps total cross section is found to be not inconsistent with the Ramsauer-Townsend minima for electrons. The absolute differential Ps formation cross section near 0 degrees has been determined for Ar, Kr and Xe and compared with theory. In analogy with a semi-empirical scaling previously found for the integral Ps formation cross section, similarities in shape of the scaled differential Ps formation cross sections have been found between Ar, Kr and Xe and, separately, from those of He and H2 . An exponential relationship has been found between the maximum differential Ps formation cross section and the Ps formation threshold

Positronium production and scattering below its break-up threshold

Recent findings on the similarity between electron and positronium scattering at the same velocity [Brawley et al. Science 330 (2010) 789] have guided us towards the realization of a detectable flux of positronium atoms at beam energies five times lower than previously obtained, enabling total cross sections to be measured in the energy range \sim(1 -- 7)\,eV for the first time. In collision with Ar and Xe, the total cross-sections of positronium are found to be smallest at the lowest energy probed, approaching those of the Ramsauer-Townsend minima for electron projectiles. Additional structure has been observed in the case of positronium scattering at incident energies around 5\,eV

Viability of preserved Cryptosporidium baileyi oocysts

The present study was undertaken to determine the viability and infectivity of oocysts of Cryptosporidium baileyi that had been stored from 1 to 40 months at 4℃ preserved in 2.5% potassium dichromate solution. Oocysts of C. baileyi were purified from the feces of experimentally infected chickens using discontinuous sucrose gradients. Subsequently, the purified oocysts were suspended in 2.5% potassium dichromate solution at a concentration of 1 × 107 organism/ml, and their viabilities were assessed by nucleic acid staining, histologic examination, and infectivity to 2-day-old chickens. All chickens inoculated with oocysts that had been stored for 1-18 months developed patent infections, while chickens infected with older oocysts remained uninfected. Between 5.8% and 82.2% of the oocysts, stored at 4℃ in 2.5% potassium dichromate solution, were found to be viable, as determined by nucleic acid staining. Parasite colonization in the bursa of Fabricius was detected in the microvillus border of bursal epithelium. The finding that C. baileyi oocysts remain infective to chickens for at least 18 months offers important time-saving advantages to investigators who frequently require large numbers of oocysts