Design of a shielding collimator device for a small-angle monoenergetic neutron source

To obtain a small-angle monoenergetic neutron source,a shielding collimator device is designed for the neutron source generated by a neutron tube.The device is divided into the collimator and the capture cave.The collimator is made of three layers of stainless steel and borated polyethylene and is used to constrain neutrons in a small angle.The capture cave is used to increase the number of times neutron inelastic scattering occurs in the opposite direction of the radiation field,thereby reducing the proportion of scattered neutrons in the radiation field.Material thickness,aperture size,and the optimum structure of the capture cave were simulated using MCNP.The design features a neutron emission angle within a range of 3° and neutron fluxes in the radiation field,which are higher by two orders of magnitude than those outside the radiation field.This research has practical value for the generation of monoenergetic small-angle neutron sources and neutron applications.

Negative Thermal Expansion of the Dy_2Fe_(16)Cr Compound

Structural, thermal expansion, and magnetic properties of the Dy_2Fe_(16)Cr compound are investigated by means of x-ray diffraction and magnetization measurements. The Dy_2Fe_(16)Cr compound has a hexagonal Th_2Ni_(17)-type structure. There exists a negative thermal expansion resulting from a strong spontaneous magnetostriction in the magnetic state of the Dy_2Fe_(16)Cr compound. The average thermal expansion coefficient is-0.794 × 10^(-5)/K in the temperature range 292–407 K. The spontaneous magnetostrictive deformation and the Curie temperature are discussed.

Homocysteine-Induced Disturbances in DNA Methylation Contribute to Development of Stress-Associated Cognitive Decline in Rats

Chronic stress is generally accepted as the main risk factor in the development of cognitive decline;however,the underlying mechanisms remain unclear.Previous data have demonstrated that the levels of homocysteine(Hcy)are significantly elevated in the plasma of stressed animals,which suggests that Hcy is associated with stress and cognitive decline.To test this hypothesis,we analyzed the cognitive function,plasma concentrations of Hcy,and brain-derived neurotropic factor(BDNF)levels in rats undergoing chronic unpredicted mild stress(CUMS).The results showed that decreased cognitive behavioral performance and decreased BDNF transcription and protein expression were correlated with hyperhomocysteinemia(HHcy)levels in stressed rats.Diet-induced HHcy mimicked the cognitive decline and BDNF downregulation in the same manner as CUMS,while Hcy reduction(by means of vitamin B complex supplements)alleviated the cognitive deficits and BDNF reduction in CUMS rats.Furthermore,we also found that both stress and HHcy disturbed the DNA methylation process in the brain and induced DNA hypermethylation in the BDNF promoter.In contrast,control of Hcy blocked BDNF promoter methylation and upregulated BDNF levels in the brain.These results imply the possibility of a causal role of Hcy in stress-induced cognitive decline.We also used ten-eleven translocation(TET1),an enzyme that induces DNA demethylation,to verify the involvement of Hcy and DNA methylation in the regulation of BDNF expression and the development of stress-related cognitive decline.The data showed that TET1-expressing viral injection into the hippocampus inhibited BDNF promoter methylation and significantly mitigated the cognitive decline in HHcy rats.Taken together,novel evidence from the present study suggests that Hcy is likely involved in chronic stress-induced BDNF reduction and related cognitive deficits.In addition,the negative side-effects of HHcy may be associated with Hcy-induced DNA hypermethylation in the BDNF promoter.The results also suggest the possibility of Hcy as a target for therapy and the potential value of vitamin B intake in preventing stress-induced cognitive decline.

Three-dimensional topological insulators:case of quaternary Heusler compounds

The feasibility of converting quaternary Heusler compounds XX’MZ(X=Sc,La;X’=Sc,Y;M=Ru,Fe;Z=Pb)into three-dimensional topological insulators was investigated by first-principle calculations.It is found that the topological insulating state can be achieved in these quaternary Heusler compounds by the proper strain engineering or the substitution of elements.Most of these compounds investigated in this paper have a negative formation energy,which implies that they are possible to be synthesized in reality.