A New Translation of and Guide to Newton's Principia

This paper discusses the emergence of new medical experimental specialties at the Medical School of Surgery (Escola Médico-Cirúrgica) and the Faculty of Medicine of Lisbon University (Faculdade de Medicina da Universidade de Lisboa) between 1897 and 1946, as a result of the activities of Marck Athias's (1875–1946) histophysiology research school. In 1897, Marck Athias, a Portuguese physician who had graduated from the Faculty of Medicine in Paris, founded a research school in Lisbon along the lines of Michael Foster's physiology research school in England and Franz Hofmeister's physiological chemistry school in Germany. His research programme was highly innovative in Portugal. Not only did it bring together many disciples and co-workers, but it branched out and created new medical specialties within Portuguese medical science. These new disciplinary areas grew out of the study of the histology of the nervous system but eventually expanded into normal and pathological histophysiology, physiological chemistry and experimental endocrinology. The esprit de corps that existed between research school members ensured the school's success and influence in various fields social and political as well as scientific. Athias's school was strongly influenced by positivist ideals and promoted a teaching and research style that sought inspiration in Humboldt's university model, thus helping to bring about a change in the dominant scientific ethos and to modernize scientific research in Portugal during the first half of the twentieth century.     

Increased soil emissions of potent greenhouse gases under increased atmospheric CO2

Increasing concentrations of atmospheric carbon dioxide (CO(2)) can affect biotic and abiotic conditions in soil, such as microbial activity and water content. In turn, these changes might be expected to alter the production and consumption of the important greenhouse gases nitrous oxide (N(2)O) and methane (CH(4)) (refs 2, 3). However, studies on fluxes of N(2)O and CH(4) from soil under increased atmospheric CO(2) have not been quantitatively synthesized. Here we show, using meta-analysis, that increased CO(2) (ranging from 463 to 780 parts per million by volume) stimulates both N(2)O emissions from upland soils and CH(4) emissions from rice paddies and natural wetlands. Because enhanced greenhouse-gas emissions add to the radiative forcing of terrestrial ecosystems, these emissions are expected to negate at least 16.6 per cent of the climate change mitigation potential previously predicted from an increase in the terrestrial carbon sink under increased atmospheric CO(2) concentrations. Our results therefore suggest that the capacity of land ecosystems to slow climate warming has been overestimated.     

Gut flora metabolism of phosphatidylcholine promotes cardiovascular disease

Metabolomics studies hold promise for the discovery of pathways linked to disease processes. Cardiovascular disease (CVD) represents the leading cause of death and morbidity worldwide. Here we used a metabolomics approach to generate unbiased small-molecule metabolic profiles in plasma that predict risk for CVD. Three metabolites of the dietary lipid phosphatidylcholine--choline, trimethylamine N-oxide (TMAO) and betaine--were identified and then shown to predict risk for CVD in an independent large clinical cohort. Dietary supplementation of mice with choline, TMAO or betaine promoted upregulation of multiple macrophage scavenger receptors linked to atherosclerosis, and supplementation with choline or TMAO promoted atherosclerosis. Studies using germ-free mice confirmed a critical role for dietary choline and gut flora in TMAO production, augmented macrophage cholesterol accumulation and foam cell formation. Suppression of intestinal microflora in atherosclerosis-prone mice inhibited dietary-choline-enhanced atherosclerosis. Genetic variations controlling expression of flavin monooxygenases, an enzymatic source of TMAO, segregated with atherosclerosis in hyperlipidaemic mice. Discovery of a relationship between gut-flora-dependent metabolism of dietary phosphatidylcholine and CVD pathogenesis provides opportunities for the development of new diagnostic tests and therapeutic approaches for atherosclerotic heart disease.     

Winter crude protein among accessions of fourwing saltbush grown in a uniform garden

Winter crude protein content was determined for the current year's growth of 43 accessions of fourwing saltbush ( Atriplex canescens ) grown on a uniform garden. The crude protein level varied among accessions from 6 percent to 14 percent of dry matter. Individual plants (215) ranged from 5.3 percent to 17.1 percent. The mean winter crude protein level was 9.6 percent. Because these data were generated on even-aged plants, it appears that genetic variation plays an important role in determining the level of crude protein in fourwing saltbush.     

固体的电子结构和磁光性质

本书是一本关于固体化合物和多层材料的电子结构、光学、磁光学、X射线磁圆二向色性等的理论研究的新著作。     

Independent genome-wide scans identify a chromosome 18 quantitative-trait locus influencing dyslexia.

Developmental dyslexia is defined as a specific and significant impairment in reading ability that cannot be explained by deficits in intelligence, learning opportunity, motivation or sensory acuity. It is one of the most frequently diagnosed disorders in childhood, representing a major educational and social problem. It is well established that dyslexia is a significantly heritable trait with a neurobiological basis. The etiological mechanisms remain elusive, however, despite being the focus of intensive multidisciplinary research. All attempts to map quantitative-trait loci (QTLs) influencing dyslexia susceptibility have targeted specific chromosomal regions, so that inferences regarding genetic etiology have been made on the basis of very limited information. Here we present the first two complete QTL-based genome-wide scans for this trait, in large samples of families from the United Kingdom and United States. Using single-point analysis, linkage to marker D18S53 was independently identified as being one of the most significant results of the genome in each scan (P< or =0.0004 for single word-reading ability in each family sample). Multipoint analysis gave increased evidence of 18p11.2 linkage for single-word reading, yielding top empirical P values of 0.00001 (UK) and 0.0004 (US). Measures related to phonological and orthographic processing also showed linkage at this locus. We replicated linkage to 18p11.2 in a third independent sample of families (from the UK), in which the strongest evidence came from a phoneme-awareness measure (most significant P value=0.00004). A combined analysis of all UK families confirmed that this newly discovered 18p QTL is probably a general risk factor for dyslexia, influencing several reading-related processes. This is the first report of QTL-based genome-wide scanning for a human cognitive trait.     

<Emphasis Type="Italic">Newton's Argument for Proposition 1 of the</Emphasis> Principia

The first proposition of the Principia records two fundamental properties of an orbital motion: the Fixed Plane Property (that the orbit lies in a fixed plane) and the Area Property (that the radius sweeps out equal areas in equal times). Taking at the start the traditional view, that by an orbital motion Newton means a centripetal motion – this is a motion ``continually deflected from the tangent toward a fixed center' – we describe two serious flaws in the Principia's argument for Proposition 1, an argument based on a polygonal impulse approximation. First, the persuasiveness of the argument depends crucially on the validity of the Impulse Assumption: that every centripetal motion can be represented as a limit of polygonal impulse motions. Yet Newton tacitly takes the Impulse Assumption for granted. The resulting gap in the argument for Proposition 1 is serious, for only a nontrivial analysis, involving the careful estimation of accumulating local errors, verifies the Impulse Assumption. Second, Newton's polygonal approximation scheme has an inherent and ultimately fatal disability: it does not establish nor can it be adapted to establish the Fixed Plane Property. Taking then a different view of what Newton means by an orbital motion – namely that an orbital motion is by definition a limit of polygonal impulse motions – we show in this case that polygonal approximation can be used to establish both the fixed plane and area properties without too much trouble, but that Newton's own argument still has flaws. Moreover, a crucial question, haunted by error accumulation and planarity problems, now arises: How plentiful are these differently defined orbital motions? Returning to the traditional view, that Newton's orbital motions are by definition centripetal motions, we go on to give three proofs of the Area Property which Newton ``could have given' – two using polygonal approximation and a third using curvature – as well as a proof of the Fixed Plane Property which he ``almost could have given.' (Received August 14, 2002) Published online March 26, 2003 Communicated by G. Smith     

2009年的突破

<正>每年的12月,《科学》的编辑们都会面临这样一个挑战:全球科技界在即将过去的一年中完成了哪些令人瞩目的研究,以评选出我们的"年度突破"。这一挑战令人鼓舞,展示了科研领域持续而进步的喜人进展。涉及2009年入选的突破范围令人惊讶,从脉冲星(脉冲星