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.     

Arctic freshwater forcing of the Younger Dryas cold reversal

The last deglaciation was abruptly interrupted by a millennial-scale reversal to glacial conditions, the Younger Dryas cold event. This cold interval has been connected to a decrease in the rate of North Atlantic Deep Water formation and to a resulting weakening of the meridional overturning circulation owing to surface water freshening. In contrast, an earlier input of fresh water (meltwater pulse 1a), whose origin is disputed, apparently did not lead to a reduction of the meridional overturning circulation. Here we analyse an ensemble of simulations of the drainage chronology of the North American ice sheet in order to identify the geographical release points of freshwater forcing during deglaciation. According to the simulations with our calibrated glacial systems model, the North American ice sheet contributed about half the fresh water of meltwater pulse 1a. During the onset of the Younger Dryas, we find that the largest combined meltwater/iceberg discharge was directed into the Arctic Ocean. Given that the only drainage outlet from the Arctic Ocean was via the Fram Strait into the Greenland-Iceland-Norwegian seas, where North Atlantic Deep Water is formed today, we hypothesize that it was this Arctic freshwater flux that triggered the Younger Dryas cold reversal.     

Nestin expression – a property of multi-lineage progenitor cells?

Tissue-specific progenitor cells are characterized by proliferation and differentiation, but, in contrast to embryonic stem (ES) cells, have limited capacities for self-renewal and no tumourigenic potential. These latter traits make progenitor cells an ideal source for regenerative cell therapies. In this review, we describe what is currently known about nestin, an intermediate filament first identified in neuroepithelial stem cells. During embryogenesis, nestin is expressed in migrating and proliferating cells, whereas in adult tissues, nestin is mainly restricted to areas of regeneration. We show that nestin is abundant in ES-derived progenitor cells that have the potential to develop into neuroectodermal, endodermal and mesodermal lineages. Although it remains unclear what factors regulate in vitro and in vivo expression of nestin, we conclude that nestin represents a characteristic marker of multi-lineage progenitor cells and suggest that its presence in cells may indicate multi-potentiality and regenerative potential.     

静电场与表面活性剂对液-液体系相间传质动力学特性的影响

在Lewis传质池外部施加不同方向的静电场激励,研究反萃传质体系Cu2 -HDEHP-CCl4/H2O在改变相主体搅拌速率、体系添加十二烷基硫酸钠、聚乙二醇辛基苯基醚、十六烷基三甲基溴化铵等条件时的传质动力学特性.研究发现:无静电场激励时,添加十二烷基硫酸钠可提高传质速率42.0%,但添加聚乙二醇辛基苯基醚降低传质速率45.5%,添加十六烷基三甲基溴化铵降低传质速率19.8%;无表面活性剂时,不同方向的静电场均显著加速传质过程,正向静电场增幅达到114%;在垂直静电场作用下,体系添加聚乙二醇辛基苯基醚传质速率降低28.0%;在减速静电场作用下,体系添加十六烷基三甲基溴化铵传质速率降低16.0%;但体系添加十二烷基硫酸钠时,传质速率均被加速,最高达64.0%;提高搅拌速率不仅可以影响相间流体力学层,还可以改变相间分散层结构.