Abstract
The neutron lifetime has been measured by comparing the decay rate with the reaction rate of $^3$He nuclei of a pulsed neutron beam from the spallation neutron source at the Japan Proton ...Accelerator Research Complex (J-PARC). The decay rate and the reaction rate were determined by simultaneously detecting electrons from the neutron decay and protons from the $^3$He(n,p)$^3$H reaction using a gas chamber, the working gas of which contains diluted $^3$He. The measured neutron lifetime was $898\,\pm\,10\,_{\rm stat}\,^{+15}_{-18}\,_{\rm sys}\,$s.
A new time projection chamber (TPC) was developed for neutron lifetime measurement using a pulsed cold neutron spallation source at the Japan Proton Accelerator Research Complex (J-PARC). Managing ...considerable background events from natural sources and the beam radioactivity is a challenging aspect of this measurement. To overcome this problem, the developed TPC has unprecedented features such as the use of polyether-ether-ketone plates in the support structure and internal surfaces covered with 6Li-enriched tiles to absorb outlier neutrons. In this paper, the design and performance of the new TPC are reported in detail.
Abstract
In a neutron lifetime measurement at the Japan Proton Accelerator Complex, the neutron lifetime is calculated from the neutron decay rate and the incident neutron flux. The flux is obtained ...by counting the protons emitted from the neutron absorption reaction of ^{3}{\rm He}$ gas, which is diluted in a mixture of working gas in a detector. Hence, it is crucial to determine the amount of ^{3}{\rm He}$ in the mixture. In order to improve the accuracy of the number density of the ^{3}{\rm He}$ nuclei, we have suggested using the ^{14}{\rm N}({\rm n},{\rm p}){}^{14}{\rm C}$ reaction as a reference because this reaction involves similar kinetic energy to the $^3$He(n,p)$^3$H reaction and a smaller reaction cross section to introduce reasonable large partial pressure. The uncertainty of the recommended value of the cross section, however, is not satisfied with our requirement. In this paper we report the most accurate experimental value of the cross section of the $^{14}$N(n,p)$^{14}$C reaction at a neutron velocity of 2200 m s$^{-1}$, measured relative to the $^3$He(n,p)$^3$H reaction. The result was 1.868 $\pm$ 0.003 (stat.) $\pm$ 0.006 (sys.) b. Additionally, the cross section of the $^{17}$O(n,$\alpha$)$^{14}$C reaction at the neutron velocity is also redetermined as 249 $\pm$ 6 mb.
Various natural and synthetic compounds including alkaloids, terpenoids and phenolics were tested for inhibition of the cell surface expression of intercellular adhesion molecule-1 (ICAM-1) and ...vascular cell adhesion molecule-1 (VCAM-1), both of which are crucial in the regulation of immune response and inflammation. Of 40 compounds tested, two compounds significantly downregulated the expression of VCAM-1 on murine endothelial cells (F-2) and ten compounds that of ICAM-1 on mouse myeloid leukemia cells (M1). Sanguinarine chloride (5) and isoliquiritigenin (13) were capable of lowering the levels of both ICAM-1 and VCAM-1. The structure-activity relationships study on chalcone and flavone derivatives related to 13 suggested that the inhibitory activity of the chalcone derivatives is attributable to the 4-hydroxy group as well as the possible coplanarity between the phenyl ring and the adjacent conjugated ketone.
From the cultures of the spore-derived mycobionts of the lichen Pyrenula japonica, two new xanthones, 1,8-dihydroxy-3-hydroxymethyl-5-methoxyxanthone and 1,2,8-trihydroxy-5-methoxy-3-methylxanthone, ...were isolated along with 1,7-dihydroxy-3-methylxanthone, 1,5,8-trihydroxy-3-methylxanthone, 1,8-dihydroxy-5-methoxy-3-methylxanthone, emodin and sclerotiorin. Their structures were determined by spectroscopic methods. Sclerotiorin was isolated for the first time from lichen mycobionts. Radical scavenging activities of the isolated xanthones were also studied.
Phytochemical study of the leaves and stems of Jasminum nudiflorum has led to the isolation of three secoiridoid glucosides, jasnudiflosides A-C (1-3). The structures of these compounds were ...elucidated on the basis of chemical and spectroscopic evidence.
The spore-derived mycobionts of the lichen Graphis prunicola, G. cognata and G. scripta were cultivated on a malt-yeast extract medium supplemented with 10% sucrose and their metabolites were ...investigated. Graphislactones A-D were isolated from the cultures of G. prunicola, while alternariol and graphislactones A and C were isolated from those of G. cognata. From the cultured mycobionts of G. scripta, a new 6H-dibenzob,dpyran-6-one derivative, graphislactone E with graphislactones A and C was obtained. On the other hand, cultivation of the mycobionts of G. prunicola on a malt-yeast extract medium supplemented with 2.5% sucrose and 0.25% sodium acetate produced two new metabolites, graphislactones E and F. Their structures were determined by spectroscopic methods. The biogenetic origin of the carbon skeleton in both compounds was verified by administering sodium 1-13C-acetate and sodium 1,2-13C(2)-acetate.
From the dried roots of Rauwolfia serpentina were isolated five new indole alkaloids, N(b)-methylajmaline (1), N(b)-methylisoajmaline (2), 3-hydroxysarpagine (3), yohimbinic acid (4), isorauhimbinic ...acid (5), a new iridoid glucoside, 7-epiloganin (6), and a new sucrose derivative, 6'-O-(3,4,5-trimethoxybenzoyl)glomeratose A (7), together with 20 known compounds. The structures of the new compounds were determined by spectroscopic and chemical means. The inhibitory activities of the selected alkaloids on topoisomerase I and II and their cytotoxicity against the human promyelocytic leukemia (HL-60) cell lines were assessed.
Five phenolic glycosides
1–
5 and an iridoid glucoside
6 were isolated, together with 22 known compounds, from the dried barks and woods of
Strychnos axillaris. The structures of the compounds were ...determined by spectroscopic and chemical means.
Five phenolic glycosides
1–
5 and an iridoid glucoside
6 were isolated, together with 22 known compounds, from the dried barks and woods of
Strychnos
axillaris. Their structures were determined by application of spectroscopic (NMR, MS) and chemical methodologies.
PDF
![6H-Dibenzo[b, d]pyran-6-one...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0031-9422/small "6H-Dibenzo[b, d]pyran-6-one derivatives from the cultured lichen mycobionts of Graphis spp. and their biosynthetic origin")