Multiple routes to mammalian diversity

The radiation of the mammals provides a 165-million-year test case for evolutionary theories of how species occupy and then fill ecological niches. It is widely assumed that species often diverge rapidly early in their evolution, and that this is followed by a longer, drawn-out period of slower evolutionary fine-tuning as natural selection fits organisms into an increasingly occupied niche space. But recent studies have hinted that the process may not be so simple. Here we apply statistical methods that automatically detect temporal shifts in the rate of evolution through time to a comprehensive mammalian phylogeny and data set of body sizes of 3,185 extant species. Unexpectedly, the majority of mammal species, including two of the most speciose orders (Rodentia and Chiroptera), have no history of substantial and sustained increases in the rates of evolution. Instead, a subset of the mammals has experienced an explosive increase (between 10- and 52-fold) in the rate of evolution along the single branch leading to the common ancestor of their monophyletic group (for example Chiroptera), followed by a quick return to lower or background levels. The remaining species are a taxonomically diverse assemblage showing a significant, sustained increase or decrease in their rates of evolution. These results necessarily decouple morphological diversification from speciation and suggest that the processes that give rise to the morphological diversity of a class of animals are far more free to vary than previously considered. Niches do not seem to fill up, and diversity seems to arise whenever, wherever and at whatever rate it is advantageous.     

A Philosophy for the Social Sciences: Realism, Pragmatism, or neither?

Philosophers of science seek to discover theessential features of science. Having donethis, these features are then proffered as a`benchmark' against which any putative sciencecan be assessed for its scientificity. Socialscientists, in particular, are much concernedwith achieving the status of genuine science.When considering the status of the socialsciences, philosophers of science also seek todiscern the essential, and differentiating,characteristics of the object of study, namely,social phenomena as such. This paper provides acritical examination of two apparentlydiametrically opposed approaches to philosophyof science, namely, realism and pragmatism. Thestance of `immanent critique' is adopted. Thisstance seeks to evaluate the success of aphilosophical programme entirely by thestandards that are internal to that programme.The conclusion reached, from this point ofview, is that realism is unrealistic, andpragmatism lacks practical utility.     

中医名词英译:应用系统化原则的翻译模式

虽然近几十年来中医已广受西方国家的欢迎,但还未有规范化的中医英文词汇.中国传统医学的词汇极为庞大复杂,在<中医大词典>[1]中即收词逾30000个,因此,在任何译入语中制定对应词汇必然工程浩大,规范化的过程亦将极为复杂.曾经有许多中医汉英双语词表问世,但其所用的翻译方法不一,而且在翻译法则上大都缺乏系统化的总纲领.大部分英文教科书和临床文献都不采用已出版之双语词汇表中的词汇,而大部分西方翻译人员顶多在其出版物中附上名词双语对照简表.值此中国科学技术名词审定委员会致力于中医词汇英译规范化之际,本人愿意就中医词汇的英译提出个人的翻译模式.此一模式的产生系参酌其他领域的翻译实务,并已经由中医现代与古典文献的英译实务所建立的词汇体系加以检视.     

Wave acceleration of electrons in the Van Allen radiation belts

The Van Allen radiation belts are two regions encircling the Earth in which energetic charged particles are trapped inside the Earth's magnetic field. Their properties vary according to solar activity and they represent a hazard to satellites and humans in space. An important challenge has been to explain how the charged particles within these belts are accelerated to very high energies of several million electron volts. Here we show, on the basis of the analysis of a rare event where the outer radiation belt was depleted and then re-formed closer to the Earth, that the long established theory of acceleration by radial diffusion is inadequate; the electrons are accelerated more effectively by electromagnetic waves at frequencies of a few kilohertz. Wave acceleration can increase the electron flux by more than three orders of magnitude over the observed timescale of one to two days, more than sufficient to explain the new radiation belt. Wave acceleration could also be important for Jupiter, Saturn and other astrophysical objects with magnetic fields.     

Mutations in a Sar1 GTPase of COPII vesicles are associated with lipid absorption disorders

Dietary fat is an important source of nutrition. Here we identify eight mutations in SARA2 that are associated with three severe disorders of fat malabsorption. The Sar1 family of proteins initiates the intracellular transport of proteins in COPII (coat protein)-coated vesicles. Our data suggest that chylomicrons, which vastly exceed the size of typical COPII vesicles, are selectively recruited by the COPII machinery for transport through the secretory pathways of the cell.     

Downward pumping of magnetic flux as the cause of filamentary structures in sunspot penumbrae

The structure of a sunspot is determined by the local interaction between magnetic fields and convection near the Sun's surface. The dark central umbra is surrounded by a filamentary penumbra, whose complicated fine structure has only recently been revealed by high-resolution observations. The penumbral magnetic field has an intricate and unexpected interlocking-comb structure and some field lines, with associated outflows of gas, dive back down below the solar surface at the outer edge of the spot. These field lines might be expected to float quickly back to the surface because of magnetic buoyancy, but they remain submerged. Here we show that the field lines are kept submerged outside the spot by turbulent, compressible convection, which is dominated by strong, coherent, descending plumes. Moreover, this downward pumping of magnetic flux explains the origin of the interlocking-comb structure of the penumbral magnetic field, and the behaviour of other magnetic features near the sunspot.     

Prediction intervals for growth curve forecasts

Since growth curves are often used to produce medium- to long-term forecasts for planning purposes, it is obviously of value to be able to associate an interval with the forecast trend. The problems in producing prediction intervals are well described by Chatfield. The additional problems in this context are the intrinsic non-linearity of the estimation procedure and the requirement for a prediction region rather than a single interval. The approaches considered are a Taylor expansion of the variance of the forecast values, an examination of the joint density of the parameter estimates, and bootstrapping. The performance of the resultant intervals is examined using simulated data sets. Prediction intervals for real data are produced to demonstrate their practical value.