Discovery of 40Mg and 42Al suggests neutron drip-line slant towards heavier isotopes

A fundamental question in nuclear physics is what combinations of neutrons and protons can make up a nucleus. Many hundreds of exotic neutron-rich isotopes have never been observed; the limit of how many neutrons a given number of protons can bind is unknown for all but the lightest elements, owing to the delicate interplay between single particle and collective quantum effects in the nucleus. This limit, known as the neutron drip line, provides a benchmark for models of the atomic nucleus. Here we report a significant advance in the determination of this limit: the discovery of two new neutron-rich isotopes--40Mg and 42Al--that are predicted to be drip-line nuclei. In the past, several attempts to observe 40Mg were unsuccessful; moreover, the observation of 42Al provides an experimental indication that the neutron drip line may be located further towards heavier isotopes in this mass region than is currently believed. In stable nuclei, attractive pairing forces enhance the stability of isotopes with even numbers of protons and neutrons. In contrast, the present work shows that nuclei at the drip line gain stability from an unpaired proton, which narrows the shell gaps and provides the opportunity to bind many more neutrons.     

雷公藤红素缓解刀豆蛋白A诱导的小鼠急性肝损伤作用及其机制

将36只同一批次体重无明显差异的7周龄C57雄鼠随机分为6组,每组6只,即对照组,模型组,地塞米松(dexamethasone, DXM)组及雷公藤红素(celastrol, Cel)低、中、高剂量组(1.5、3、6 mg/kg),连续灌胃7 d后尾静脉注射20 mg/kg刀豆蛋白A(concanavalin A, ConA),地塞米松(0.5 mg/kg)于刀豆蛋白给药前1 h腹腔注射.注射8 h后处死小鼠,取其血清分别检测白介素-6(IL-6)、白介素-10(IL-10)、肿瘤坏死因子-α(tumor necrosis factor-α,TNF-α)和丙氨酸氨基转移酶(ALT)及天冬氨酸转移酶(AST)的含量.取小鼠肝脾称重计算脏器系数,苏木精-伊红(HE)染色观察肝组织病理改变,用实时定量PCR法(RT-qPCR法)检测肝组织中相关基因mRNA的表达水平,流式细胞术检测脾脏中巨噬细胞的极化方向,从而研究雷公藤红素对刀豆蛋白A诱导的小鼠急性肝损伤的保护作用及其机制.结果显示:相较于正常组,模型组小鼠的肝组织明显发生急性肝炎,其小叶结构紊乱,肝细胞结构破坏,汇管区炎症细胞浸润,雷公藤...     

Mitotic response and sister chromatid exchanges in lymphocytes cultured in sera from different sources

Summary The numbers of sister chromatid exchanges in lymphocytes grown in varying concentrations of serum from different sources indicated that some sera contain a factor, probably introduced as a contaminant, which induces SCEs. Sera from 6 animals showed no evidence of a difference in baseline SCE levels due to the donor of the serum.Research sponsored by U.S. Department of Energy contract number DE-ACO5-760R00242 with The University of Tennessee.