New data on the ternary fission of 252Cf from the Gammasphere facility

Ternary fission of ²⁵²Cf was studied at Gammasphere using eight ΔE×E particle telescopes. Helium, beryllium, boron, and carbon light charged particles (LCPs) emitted with kinetic energy more than 9, 21, 26, and 32 MeV, respectively, were identified. The 3368-keV γ transition from the first 2⁺ excited state in ¹⁰Be was found and the population probability ratio N(2⁺)/N(0⁺) = 0.160 ± 0.025 was estimated. No evidence was found for 3368-keV γ rays emitted from a triple molecular state. For the first time, charge distributions are obtained for ternary fission fragments emitted with helium, beryllium, and carbon LCPs.     

Alkylation d'enamines par les halogeno-5 ene-3 ynes-1

The alkylation of several enamines of cyclanones with 5-halogeno 3-ene 1-ynes 1 gives a mixture of isomeric ketones 3 and 4. The composition of this mixture is independent of the enamine but is related to the nature of the halide 1. The primary halides lead essentially to ketones 3 and the secondary halides give predominantly 4. Both ketones are always formed via an initial C-alkylation; a mechanism taking account of the experimental results is proposed.     

Heterocyclisation de diols βγ′-alleniques.

The silver nitrate assisted cyclization of the entitled diols $\text{3}$ leads, depending on the substitution of the allenic linkage, specifically to dihydropyranes $\text{4}$, when R is alkyl or to an equimolecular mixture of $\text{4}$ and its tetrahydrofuranyl isomer $\text{5}$ when R is hydrogen.     

Mass spectrometry in structural and stereochemical problems—CLXXXIV: Charge localization in fragment ions of amino ketones and esters

The mass spectral fragmentation of a number of specially synthesized amino esters and ketones has been studied in which the distance between the two functionalities has been varied. The principal fragments formed following initial ionization are the even-electron immonium ions a and b. Further fragmentation of ion a in the amino esters occurs via non-specific processes. Therefore it is difficult to establish the degree of mobility of the positive charge in the fragment ions, notably whether the species with the charge present on the oxygen atom makes a significant contribution to the fragmentation. The β-(IIb) and γ-(IV) amino ketones show no McLafferty rearrangements after α-fission, thus demonstrating that uncoupling of the carbonyl π electrons is not a feasible trigger in lieu of charge localization.     

A Simple and Environmentally Benign Nitration of Pyrazoles by Impregnated Bismuth Nitrate

We report herein a facile, rapid, and environmentally friendly synthesis of nitropyrazoles in good yields using silica‐bismuth nitrate and silica‐sulfuric acid‐bismuth nitrate at room temperature for the first time. The relatively non‐toxic nature, ease of handling, easy availability, and low cost make the present procedure attractive for the nitration of a wide variety of diazoles in the drug and pharmaceutical industries.     

Analytical predictions of shapes of laminar diffusion flames in microgravity and earth gravity

Flame shape is an important observed characteristic of flames that can be used to scale flame properties such as heat release rates and radiation. Flame shape is affected by fuel type, oxygen levels in the oxidiser, inverse burning and gravity. The objective of this study is to understand the effect of high oxygen concentrations, inverse burning, and gravity on the predictions of flame shapes. Flame shapes are obtained from recent analytical models and compared with experimental data for a number of inverse and normal ethane flame configurations with varying oxygen concentrations in the oxidiser and under earth gravity and microgravity conditions. The Roper flame shape model was extended to predict the complete flame shapes of laminar gas jet normal and inverse diffusion flames on round burners. The Spalding model was extended to inverse diffusion flames. The results show that the extended Roper model results in reasonable predictions for all microgravity and earth gravity flames except for enhanced oxygen normal diffusion flames under earth gravity conditions. The results also show trends towards cooler flames in microgravity that are in line with past experimental observations. Some key characteristics of the predicted flame shapes and parameters needed to describe the flame shape using the extended Roper model are discussed.     

An fMRI study of magnitude comparison and exact addition in children

By contrast to the adult literature, in which a consistent parietofrontal network for number processing has been identified, the data from studies of number processing in children have been less consistent, probably due to differences in study design and control conditions. Number processing was examined using functional magnetic resonance imaging in 18 right-handed children (8–12 years) from the Cape Coloured community in Cape Town, South Africa, using Proximity Judgment and Exact Addition (EA) tasks. The findings were consistent with the hypothesis that, as in adults, the anterior horizontal intraparietal sulcus (HIPS) plays a major role in the representation and manipulation of quantity in children. The posterior medial frontal cortex, believed to be involved in performance monitoring in more complex arithmetic manipulations in adults, was extensively activated even for relatively simple symbolic number processing in the children. Other areas activated to a greater degree in the children included the left precentral sulcus, which may mediate number knowledge and, for EA, the head of the caudate nucleus, which is part of a fronto-subcortical circuit involved in the behavioral execution of sequences. Two regions that have been linked to number processing in adults — the angular gyrus and posterior superior parietal lobule — were not activated in the children. The data are consistent with the inference that although the functional specialization of the anterior HIPS may increase as symbolic number processing becomes increasingly automatic, this region and other elements of the parietofrontal network identified in adults are already reliably and robustly activated by middle childhood.     

Functional connectivity between task-positive and task-negative brain areas and its relation to working memory performance

Functional brain imaging studies have identified a set of brain areas typically activated during cognitive tasks (task-positive brain areas) and another set of brain areas typically deactivated during cognitive tasks (task-negative brain areas). Negative correlations, or anticorrelations, between task-positive and task-negative brain areas have been reported at rest. Furthermore, the strength of these anticorrelations appears to be related to cognitive function. However, studies examining anticorrelations have typically employed global regression or similar analysis steps that force anticorrelated relationships to exist between brain areas. Therefore the validity of these findings has been questioned. Here we examine anticorrelations between a task-negative region in the medial frontal gyrus/anterior cingulate cortex and dorsolateral prefrontal cortex, a classic task-positive area, using an analysis that does not include global regression. Instead, we control for whole-brain correlations in the group-level analysis. Using this approach, we demonstrate that the strength of the functional connection between the medial frontal cortex and the dorsolateral prefrontal cortex is related to cognitive function and that this relationship is not an artifact of global regression.