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41.
N. S. Petrosky R. A. Tassava C. L. Olsen 《Cellular and molecular life sciences : CMLS》1980,36(5):601-603
Summary Amputated, denervatedAmbystoma forelimbs undergo cellular dedifferentiation and slight resorption through 12 days post-amputation. Subsequently, as limb stumps become re-innervated, there occur mitosis, blastema formation, and regeneration. The initial increase in the mitotic index in once-denervated limb stumps is closely correlated with the presence of ingrowing nerve fibres.This work was supported by grant PCM 76-11807 from the National Science Foundation. 相似文献
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43.
Chaos in an enzyme reaction 总被引:2,自引:0,他引:2
Dynamic systems are usually thought to have either monotonic or periodic behaviour. Although the possibility of other types of behaviour has been recognised for many years, the existence of non-monotonic, non-periodic behaviour in dynamic systems has been firmly established only recently. It is termed chaotic behaviour. A review on the rapidly expanding literature on chaos in discrete model systems described by difference equations has been published by May. R?ssler, on the other hand, has discussed a few published works on systems of differential equations with chaotic solutions, and he has proposed a three-component chemical model system which he argues has chaotic solutions [figure see text]. The argument is based on a theorem by Li and Yorke. Here we report the finding of chaotic behaviour as an experimental result in an enzyme system (peroxidase). Like R?ssler we base our identification of chaos on the theorem by Li and Yorke. 相似文献
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45.
Michel M. Dacorogna Cindy L. Gauvreau Ulrich A. Müller Richard B. Olsen Olivier V. Pictet 《Journal of forecasting》1996,15(3):203-227
A forecasting model based on high-frequency market makers quotes of financial instruments is presented. The statistical behaviour of these time series leads to discussion of the appropriate time scale for forecasting. We introduce variable time scales in a general way and define the new concept of intrinsic time. The latter reflects better the actual trading activity. Changing time scale means forecasting in two steps, first an intrinsic time forecast against physical time, then a price forecast against intrinsic time. The forecasting model consists, for both steps, of a linear combination of non-linear price-based indicators. The indicator weights are continuously re-optimized through a modified linear regression on a moving sample of past prices. The out-of-sample performance of this algorithm is reported on a set of important FX rates and interest rates over many years. It is remarkably consistent. Results for short horizons as well as techniques to measure this performance are discussed. 相似文献
46.
Erler J Birge N Kortelainen M Nazarewicz W Olsen E Perhac AM Stoitsov M 《Nature》2012,486(7404):509-512
In 2011, 100 new nuclides were discovered. They joined the approximately 3,000 stable and radioactive nuclides that either occur naturally on Earth or are synthesized in the laboratory. Every atomic nucleus, characterized by a specific number of protons and neutrons, occupies a spot on the chart of nuclides, which is bounded by 'drip lines' indicating the values of neutron and proton number at which nuclear binding ends. The placement of the neutron drip line for the heavier elements is based on theoretical predictions using extreme extrapolations, and so is uncertain. However, it is not known how uncertain it is or how many protons and neutrons can be bound in a nucleus. Here we estimate these limits of the nuclear 'landscape' and provide statistical and systematic uncertainties for our predictions. We use nuclear density functional theory, several Skyrme interactions and high-performance computing, and find that the number of bound nuclides with between 2 and 120 protons is around 7,000. We find that extrapolations for drip-line positions and selected nuclear properties, including neutron separation energies relevant to astrophysical processes, are very consistent between the models used. 相似文献
47.
The sexual imprinting of a Barn Owl ( Tyto alba ) on humans is reported. 相似文献
48.
Coagulation factor VIIa (FVIIa) is an atypical member of the trypsin family of serine proteases. It fails to attain spontaneously
its catalytically competent conformation and requires its protein cofactor tissue factor (TF) to accomplish this. Over a number
of years, this unique behaviour of FVIIa has prompted investigations of the TF-induced activation mechanism and the zymogenicity
determinants in factor VIIa. Factor VIIa has gained additional interest in the past decade because of its development into
a clinically useful haemostatic agent. Here, we present an overview of the current knowledge about the TF-induced allosteric
activation of FVIIa and the various molecular approaches to enhance the intrinsic activity and efficacy of FVIIa.
Received 18 October 2007; received after revision 12 November 2007; accepted 14 November 2007 相似文献
49.
Goetz W Bertelsen P Binau CS Gunnlaugsson HP Hviid SF Kinch KM Madsen DE Madsen MB Olsen M Gellert R Klingelhöfer G Ming DW Morris RV Rieder R Rodionov DS de Souza PA Schröder C Squyres SW Wdowiak T Yen A 《Nature》2005,436(7047):62-65
The ubiquitous atmospheric dust on Mars is well mixed by periodic global dust storms, and such dust carries information about the environment in which it once formed and hence about the history of water on Mars. The Mars Exploration Rovers have permanent magnets to collect atmospheric dust for investigation by instruments on the rovers. Here we report results from M?ssbauer spectroscopy and X-ray fluorescence of dust particles captured from the martian atmosphere by the magnets. The dust on the magnets contains magnetite and olivine; this indicates a basaltic origin of the dust and shows that magnetite, not maghemite, is the mineral mainly responsible for the magnetic properties of the dust. Furthermore, the dust on the magnets contains some ferric oxides, probably including nanocrystalline phases, so some alteration or oxidation of the basaltic dust seems to have occurred. The presence of olivine indicates that liquid water did not play a dominant role in the processes that formed the atmospheric dust. 相似文献
50.
Grimwood J Gordon LA Olsen A Terry A Schmutz J Lamerdin J Hellsten U Goodstein D Couronne O Tran-Gyamfi M Aerts A Altherr M Ashworth L Bajorek E Black S Branscomb E Caenepeel S Carrano A Caoile C Chan YM Christensen M Cleland CA Copeland A Dalin E Dehal P Denys M Detter JC Escobar J Flowers D Fotopulos D Garcia C Georgescu AM Glavina T Gomez M Gonzales E Groza M Hammon N Hawkins T Haydu L Ho I Huang W Israni S Jett J Kadner K Kimball H Kobayashi A Larionov V Leem SH Lopez F Lou Y Lowry S 《Nature》2004,428(6982):529-535
Chromosome 19 has the highest gene density of all human chromosomes, more than double the genome-wide average. The large clustered gene families, corresponding high G + C content, CpG islands and density of repetitive DNA indicate a chromosome rich in biological and evolutionary significance. Here we describe 55.8 million base pairs of highly accurate finished sequence representing 99.9% of the euchromatin portion of the chromosome. Manual curation of gene loci reveals 1,461 protein-coding genes and 321 pseudogenes. Among these are genes directly implicated in mendelian disorders, including familial hypercholesterolaemia and insulin-resistant diabetes. Nearly one-quarter of these genes belong to tandemly arranged families, encompassing more than 25% of the chromosome. Comparative analyses show a fascinating picture of conservation and divergence, revealing large blocks of gene orthology with rodents, scattered regions with more recent gene family expansions and deletions, and segments of coding and non-coding conservation with the distant fish species Takifugu. 相似文献