Mathematical formulae for neutron self-shielding properties of media in an isotropic neutron field

The complexity of the neutron transport phenomenon throws its shadows on every physical system wherever neutron is produced or used. In the current study, an ab initio derivation of the neutron self-shielding factor to solve the problem of the decrease of the neutron flux as it penetrates into a material placed in an isotropic neutron field. We have employed the theory of steady-state neutron transport, starting from Stuart's formula. Simple formulae were derived based on the integral cross-section parameters that could be adopted by the user according to various variables, such as the neutron flux distribution and geometry of the simulation at hand. The concluded formulae of the self-shielding factors comprise an inverted sigmoid function normalized with a weight representing the ratio between the macroscopic total and scattering cross-sections of the medium. The general convex volume geometries are reduced to a set of chord lengths, while the neutron interactions probabilities within the volume are parameterized to the epithermal and thermal neutron energies. The arguments of the inverted-sigmoid function were derived from a simplified version of neutron transport formulation. Accordingly, the obtained general formulae were successful in giving the values of the experimental neutron self-shielding factor for different elements and different geometries.Comment: 14 pages, 5 figures, 1 graphical abstract, 73 references, and 2 tables, include improvement of illustration and story-telling writing styl

Stimulated perturbation on the neutron flux distribution in the mutually-dependent source-to-absorber geometry

The complexity of the neutron transport phenomenon throws its shadows on every physical system wherever neutron is produced or absorbed. The Monte Carlo N-Particle Transport Code (MCNP) was used to investigate the flux perturbations in the neutron field caused by an absorber. The geometry of the present experiment was designed to reach a simulation of an isotopic neutron field. The neutron source was a ${}^{241}$AmBe with the production physics of neutrons is dependent only on alpha-beryllium interaction and is independent of what happened to the neutron after it was generated. The geometries have been designed to get a volume of uniform neutron densities within a spherical volume of radius 15 cm in every neutron energy group up to 10 MeV. Absorbers of different dimensions were placed within the volume to investigate the field perturbation. Different neutron absorbers were used to correlate the phenomenon to the integral cross-section of the absorber. Flux density inside and outside the absorber samples was determined, while the spatial neutron flux distribution produced by the AmBe source without an absorber was taken as a reference. This study displayed that absorbers of various dimensions perturb the neutron field in a way that is dependent on the absorption and scattering cross-sections, particularly in the neutron resonance region. Unlike the simple picture of reducing the number density of neutrons, the perturbation was found to influence the moderation of neutrons in the medium, significantly above 1 MeV.Comment: 10 pages, 13 figures, 26 reference

Cloning and Functional Studies of a Splice Variant of CYP26B1 Expressed in Vascular Cells

Background: All-trans retinoic acid (atRA) plays an essential role in the regulation of gene expression, cell growth and differentiation and is also important for normal cardiovascular development but may in turn be involved in cardiovascular diseases, i.e. atherosclerosis and restenosis. The cellular atRA levels are under strict control involving several cytochromes P450 isoforms (CYPs). CYP26 may be the most important regulator of atRA catabolism in vascular cells. The present study describes the molecular cloning, characterization and function of atRA-induced expression of a spliced variant of the CYP26B1 gene. Methodology/Principal Findings: The coding region of the spliced CYP26B1 lacking exon 2 was amplified from cDNA synthesized from atRA-treated human aortic smooth muscle cells and sequenced. Both the spliced variant and full length CYP26B1 was found to be expressed in cultured human endothelial and smooth muscle cells, and in normal and atherosclerotic vessel. atRA induced both variants of CYP26B1 in cultured vascular cells. Furthermore, the levels of spliced mRNA transcript were 4.5 times higher in the atherosclerotic lesion compared to normal arteries and the expression in the lesions was increased 20-fold upon atRA treatment. The spliced CYP26B1 still has the capability to degrade atRA, but at an initial rate one-third that of the corresponding full length enzyme. Transfection of COS-1 and THP-1 cells with the CYP26B1 spliced variant indicated either an increase or a decrease in the catabolism of atRA, probably depending on the expression of other atRA catabolizing enzymes in the cells. Conclusions/Significance: Vascular cells express the spliced variant of CYP26B1 lacking exon 2 and it is also increased in atherosclerotic lesions. The spliced variant displays a slower and reduced degradation of atRA as compared to the full-length enzyme. Further studies are needed, however, to clarify the substrate specificity and role of the CYP26B1 splice variant in health and disease

A systematic review and meta-analysis of the prevalence of childhood undernutrition in North Africa.

Undernutrition (stunting, wasting and underweight) among children remains a public health concern in North Africa, especially following recent conflicts in the region. Therefore, this paper systematically reviews and meta-analyses the prevalence of undernutrition among children under five in North Africa to determine whether efforts to reduce undernutrition are on track to achieving the Sustainable Development Goals (SDGs) by 2030. Eligible studies published between 1st January 2006 and 10th April 2022 were searched for, using five electronic bibliographic databases (Ovid MEDLINE, Web of Science, Embase (Ovid), ProQuest and CINAHL). The JBI critical appraisal tool was used, and a meta-analysis was conducted using the 'metaprop' command in STATA, to estimate the prevalence of each undernutrition indicator in the seven North African countries (Egypt, Sudan, Libya, Algeria, Tunisia, Morocco, and Western Sahara). Due to the significant heterogeneity among studies (I2 >50%), a random effect model and sensitivity analysis were conducted to examine the effect of outliers. Out of 1592 initially identified, 27 met the selection criteria. The prevalence of stunting, wasting and being underweight were 23.5%, 7.9% and 12.9%, respectively. Significant variations between the countries with the highest rates of stunting and wasting were reported in Sudan (36%, 14.1%), Egypt (23.7%, 7.5%), Libya (23.1%, 5.9%), and Morocco (19.9%, 5.1%). Sudan also had the highest prevalence of underweight (24.6%), followed by Egypt (7%), Morocco (6.1%), and Libya (4.3%) with more than one in ten children in Algeria and Tunisia having stunted growth. In conclusion, undernutrition is widespread in the North African region, particularly in Sudan, Egypt, Libya, and Morocco, making it challenging to meet the SDGs by 2030. Nutrition monitoring and evaluation in these countries is highly recommended

A systematic review and meta-analysis of the prevalence of childhood undernutrition in North Africa

Undernutrition (stunting, wasting and underweight) among children remains a public health concern in North Africa, especially following recent conflicts in the region. Therefore, this paper systematically reviews and meta-analyses the prevalence of undernutrition among children under five in North Africa to determine whether efforts to reduce undernutrition are on track to achieving the Sustainable Development Goals (SDGs) by 2030. Eligible studies published between 1st January 2006 and 10th April 2022 were searched for, using five electronic bibliographic databases (Ovid MEDLINE, Web of Science, Embase (Ovid), ProQuest and CINAHL). The JBI critical appraisal tool was used, and a meta-analysis was conducted using the ‘metaprop’ command in STATA, to estimate the prevalence of each undernutrition indicator in the seven North African countries (Egypt, Sudan, Libya, Algeria, Tunisia, Morocco, and Western Sahara). Due to the significant heterogeneity among studies (I2 >50%), a random effect model and sensitivity analysis were conducted to examine the effect of outliers. Out of 1592 initially identified, 27 met the selection criteria. The prevalence of stunting, wasting and being underweight were 23.5%, 7.9% and 12.9%, respectively. Significant variations between the countries with the highest rates of stunting and wasting were reported in Sudan (36%, 14.1%), Egypt (23.7%, 7.5%), Libya (23.1%, 5.9%), and Morocco (19.9%, 5.1%). Sudan also had the highest prevalence of underweight (24.6%), followed by Egypt (7%), Morocco (6.1%), and Libya (4.3%) with more than one in ten children in Algeria and Tunisia having stunted growth. In conclusion, undernutrition is widespread in the North African region, particularly in Sudan, Egypt, Libya, and Morocco, making it challenging to meet the SDGs by 2030. Nutrition monitoring and evaluation in these countries is highly recommended