33 research outputs found
Towards a high precision calculation for the pion-nucleus scattering lengths
We calculate the leading isospin conserving few-nucleon contributions to pion
scattering on H, He, and He. We demonstrate that the strong
contributions to the pion-nucleus scattering lengths can be controlled
theoretically to an accuracy of a few percent for isoscalar nuclei and of 10%
for isovector nuclei. In particular, we find the -He scattering length
to be where the uncertainties are
due to ambiguities in the -N scattering lengths and few-nucleon effects,
respectively. To establish this accuracy we need to identify a suitable power
counting for pion-nucleus scattering. For this purpose we study the dependence
of the two-nucleon contributions to the scattering length on the binding energy
of H. Furthermore, we investigate the relative size of the leading two-,
three-, and four-nucleon contributions. For the numerical evaluation of the
pertinent integrals, aMonte Carlo method suitable for momentum space is
devised. Our results show that in general the power counting suggested by
Weinberg is capable to properly predict the relative importance of -nucleon
operators, however, it fails to capture the relative strength of - and
-nucleon operators, where we find a suppression by a factor of 5
compared to the predicted factor of 50. The relevance for the extraction of the
isoscalar -N scattering length from pionic H and He is discussed.
As a side result, we show that beyond the calculation of the -H
scattering length is already beyond the range of applicability of heavy pion
effective field theory.Comment: 24 pages, 14 figures, 10 table
Origin of micro-scale heterogeneity in polymerisation of photo-activated resin composites
Photo-activated resin composites are widely used in industry and medicine. Despite extensive chemical characterisation, the micro-scale pattern of resin matrix reactive group conversion between filler particles is not fully understood. Using an advanced synchrotron-based wide-field IR imaging system and state-of-the-art Mie scattering corrections, we observe how the presence of monodispersed silica filler particles in a methacrylate based resin reduces local conversion and chemical bond strain in the polymer phase. Here we show that heterogeneity originates from a lower converted and reduced bond strain boundary layer encapsulating each particle, whilst at larger inter-particulate distances light attenuation and monomer mobility predominantly influence conversion. Increased conversion corresponds to greater bond strain, however, strain generation appears sensitive to differences in conversion rate and implies subtle distinctions in the final polymer structure. We expect these findings to inform current predictive models of mechanical behaviour in polymer-composite materials, particularly at the resin-filler interface
Study of pallial neurogenesis in shark embryos and the evolutionary origin of the subventricular zone
The dorsal part of the developing telencephalon is one of the brain areas that has suffered most drastic changes throughout vertebrate evolution. Its evolutionary increase in complexity was thought to be partly achieved by the appearance of a new neurogenic niche in the embryonic subventricular zone (SVZ). Here, a new kind of amplifying progenitors (basal progenitors) expressing Tbr2, undergo a second round of divisions, which is believed to have contributed to the expansion of the neocortex. Accordingly, the existence of a pallial SVZ has been classically considered exclusive of mammals. However, the lack of studies in ancient vertebrates precludes any clear conclusion about the evolutionary origin of the SVZ and the neurogenic mechanisms that rule pallial development. In this work, we explore pallial neurogenesis in a basal vertebrate, the shark Scyliorhinus canicula, through the study of the expression patterns of several neurogenic markers. We found that apical progenitors and radial migration are present in sharks, and therefore, their presence must be highly conserved throughout evolution. Surprisingly, we detected a subventricular band of ScTbr2-expressing cells, some of which also expressed mitotic markers, indicating that the existence of basal progenitors should be considered an ancestral condition rather than a novelty of mammals or amniotes. Finally, we report that the transcriptional program for the specification of glutamatergic pallial cells (Pax6, Tbr2, NeuroD, Tbr1) is also present in sharks. However, the segregation of these markers into different cell types is not clear yet, which may be linked to the lack of layering in anamniotesThis work was supported by the Spanish Ministerio de EconomÃa y Competitividad-FEDER (BFU2014-5863-1P)S
Consensus recommendations on the use of 18F-FDG PET/CT in lung disease
Positron emission tomography (PET) with 18F-fluorodeoxyglucose (18F-FDG)
has been increasingly applied, predominantly in the research setting,
to study drug effects and pulmonary biology and
monitor disease progression and treatment outcomes
in lung diseases, disorders that interfere with gas exchange through
alterations
of the pulmonary parenchyma, airways and/or
vasculature. To date, however, there are no widely accepted standard
acquisition
protocols and imaging data analysis methods for
pulmonary 18F-FDG PET/CT in these diseases, resulting in
disparate approaches. Hence, comparison of data across the literature is
challenging.
To help harmonize the acquisition and analysis and
promote reproducibility, acquisition protocol and analysis method
details
were collated from seven PET centers. Based on
this information and discussions among the authors, the consensus
recommendations
reported here on patient preparation, choice of
dynamic versus static imaging, image reconstruction, and image analysis
reporting
were reached.
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An exploratory study to assess the knowledge, attitudes and practices of Lebanese residents towards acrylamide
Introduction
For years, heat treatment has been an essential method for ensuring mature food that meet the desired quality and safety characteristics. However, this process could lead to the formation of harmful compounds such as acrylamide. In this study we aimed to investigate the knowledge, attitudes and practices (KAPs) of the Lebanese population toward the potential risk associated with acrylamide.
Materials & methods
An online survey (n = 598) was conducted among residents in Lebanon aged 18 years and above. The survey was divided into five sections including participants’ sociodemographic characteristics, knowledge, attitude and practice sections, and some questions related to consumer’s preferences.
Results & discussion
The results showed that the majority of the participants had low food safety knowledge regarding acrylamide. Specifically, 82.9% of the consumers had no idea about the chemical, its formation, the foods with a high risk of acrylamide formation and the health risks associated with its exposure. Despite lack of knowledge, good domestic food practices (storage, pre-treatment) were noticed among participants. Moreover, the majority of consumers (> 80%) showed positive attitude towards proper acrylamide labeling. Participants with a bachelor’s degree appeared to have a more positive attitude toward food safety compared to those with no qualifications (p<0.001).
Conclusion
Despite the high consumption of acrylamide by the consumers in Lebanon through fried potatoes, bread, and coffee, the majority have no idea about acrylamide’s presence in food, its sources and its adverse health effects. Raising awareness among the public, involving policy makers in addressing the issue of clear labeling and encouraging the adoption of alternative practices to reduce acrylamide are all crucial to protect consumers’ health in Lebanon and promote healthier food consumption habits