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31.
嗅觉系统神经网络模型字符识别中的应用 总被引:1,自引:0,他引:1
Freeman在大量神经生理实验的基础上建立了生物嗅觉系统的非线性神经网络模型,即K系列模型.其中,KⅢ模型是一种混沌神经网络,它的模式识别机制与以往的人工神经网络完全不同,更接近实际生物神经系统的工作模式.研究通过对26个英文字符的学习、识别研究得出,系统相对于传统的神经网络有着很强的学习能力,学习5~6次就能有很好的识别能力,在10次达到最优学习效果,并与真实神经系统学习过程中的倒“U”曲线相对应. 相似文献
32.
R. Walter G. Schaechtelin L. C. Craig 《Cellular and molecular life sciences : CMLS》1974,30(3):306-308
Zusammenfassung Der Effekt von Na+-, NH4
+- und Ca++-Ionen auf die Blutdruckaktivität von Arginin-Vasopressom wurde untersucht und mit analogen Experimenten (Val5-Angiotensin II-Asp1--Amid) verglichen. Die Wirkungsweise der Ionen-induzierten Potenzierung von Vasopressin wird diskutiert.
Supported by USPHS Grant No. AM-13567.
Abbreviations used are: AVP, arginine-vasopressin; bp, blood pres sure; U, unit;n, number of experiments; , mean value; S.E. standard error;p, level of significance; NS, not significant. 相似文献
Supported by USPHS Grant No. AM-13567.
Abbreviations used are: AVP, arginine-vasopressin; bp, blood pres sure; U, unit;n, number of experiments; , mean value; S.E. standard error;p, level of significance; NS, not significant. 相似文献
33.
The Effects of Environmental Variables on Gas Exchange of Several Tree Species Under
Boreal Field Conditions 下载免费PDF全文
1994年和1995年夏季在加拿大Saskatchewan省PrinceAlbert市北部森林测定环境条件对欧洲杨(PopulustremuloidesMichx.),胶杨(PopulusbalsamiferaL.),榛子(CoryluscornutaMarsh.),短叶松(PinusbanksianaLamb.)和黑云杉(Piceamariana(Mil)BSP)气体交换的影响。气体交换率的测定使用便携式气体交换系统(LI-6200)。结果表明光合作用光流动量(PPFD)、气温(Ta)、蒸气压差(VPD)和体内二氧化碳浓度(Ci)均对气体交换有显著影响,但对不同树种影响程度不同。在大气二氧化碳浓度(Ca)和相对稳定的气温和蒸气压差下,欧洲杨比短叶松和黑云杉有较高光饱和点、同化量子产量(Φ)、在饱和PPFD下最高同化率(Pm)和较低的光补偿点(LCP)。对欧洲杨树,幼龄树比老龄树有较高光合能力,且生长季早期光合能力比后期高。欧洲杨和短叶松的气孔导度(gs)随PPFD增加而增加。但黑云杉gs不受PPFD影响。在高光强下(PPFD>1000μmol·m-2s-1),欧洲杨幼树被光叶片比曝光叶片表现较低的净二氧化 相似文献
34.
Marscher AP Jorstad SG D'Arcangelo FD Smith PS Williams GG Larionov VM Oh H Olmstead AR Aller MF Aller HD McHardy IM Lähteenmäki A Tornikoski M Valtaoja E Hagen-Thorn VA Kopatskaya EN Gear WK Tosti G Kurtanidze O Nikolashvili M Sigua L Miller HR Ryle WT 《Nature》2008,452(7190):966-969
Blazars are the most extreme active galactic nuclei. They possess oppositely directed plasma jets emanating at near light speeds from accreting supermassive black holes. According to theoretical models, such jets are propelled by magnetic fields twisted by differential rotation of the black hole's accretion disk or inertial-frame-dragging ergosphere. The flow velocity increases outward along the jet in an acceleration and collimation zone containing a coiled magnetic field. Detailed observations of outbursts of electromagnetic radiation, for which blazars are famous, can potentially probe the zone. It has hitherto not been possible to either specify the location of the outbursts or verify the general picture of jet formation. Here we report sequences of high-resolution radio images and optical polarization measurements of the blazar BL Lacertae. The data reveal a bright feature in the jet that causes a double flare of radiation from optical frequencies to TeV gamma-ray energies, as well as a delayed outburst at radio wavelengths. We conclude that the event starts in a region with a helical magnetic field that we identify with the acceleration and collimation zone predicted by the theories. The feature brightens again when it crosses a standing shock wave corresponding to the bright 'core' seen on the images. 相似文献
35.
Malanchi I Peinado H Kassen D Hussenet T Metzger D Chambon P Huber M Hohl D Cano A Birchmeier W Huelsken J 《Nature》2008,452(7187):650-653
Continuous turnover of epithelia is ensured by the extensive self-renewal capacity of tissue-specific stem cells. Similarly, epithelial tumour maintenance relies on cancer stem cells (CSCs), which co-opt stem cell properties. For most tumours, the cellular origin of these CSCs and regulatory pathways essential for sustaining stemness have not been identified. In murine skin, follicular morphogenesis is driven by bulge stem cells that specifically express CD34. Here we identify a population of cells in early epidermal tumours characterized by phenotypic and functional similarities to normal bulge skin stem cells. This population contains CSCs, which are the only cells with tumour initiation properties. Transplants derived from these CSCs preserve the hierarchical organization of the primary tumour. We describe beta-catenin signalling as being essential in sustaining the CSC phenotype. Ablation of the beta-catenin gene results in the loss of CSCs and complete tumour regression. In addition, we provide evidence for the involvement of increased beta-catenin signalling in malignant human squamous cell carcinomas. Because Wnt/beta-catenin signalling is not essential for normal epidermal homeostasis, such a mechanistic difference may thus be targeted to eliminate CSCs and consequently eradicate squamous cell carcinomas. 相似文献
36.
澳大利亚及斯洛文尼亚稻绿蝽(Nezara viridula)外生殖器微细结构电镜观察 总被引:2,自引:0,他引:2
齐宝瑛 《内蒙古师范大学学报(自然科学版)》2000,29(1)
澳大利亚和斯洛文尼亚的稻绿蝽因不完全的生殖隔离而曾被认为是两个不同的但互为姊妹的种群 .作者对采自于澳大利亚和斯洛文尼亚的稻绿蝽的雄性、雌性外生殖器及触角节上的感觉毛进行了解剖比较和扫描电子显微镜下的观察研究 ,旨在从外生殖器及触角感觉器等方面找出支持该观点的证据 .研究证明 ,上述几种器官的微细结构在两个种群间并无显著的差异 ,不存在将二者分为姊妹种的依据 .故两个群体间生殖隔离现象与外生殖器的结构无关 . 相似文献
37.
Walter E. Gross 《Annals of science》2013,70(5):407-427
Early geological investigations in the St David's area (Pembrokeshire) are described, particularly the work of Murchison. In a reconnaissance survey in 1835, he regarded a ridge of rocks at St David's as intrusive in unfossiliferous Cambrian; and the early Survey mapping (chiefly the work of Aveline and Ramsay) was conducted on that assumption, leading to the publication of maps in 1845 and 1857. The latter represented the margins of the St David's ridge as ‘Altered Cambrian’. So the supposedly intrusive ‘syenite’ was regarded as younger, and there was no Precambrian. These views were challenged by a local doctor, Henry Hicks, who developed an idea of the ex-Survey palaeontologist John Salter that the rocks of the ridge were stratified and had formed a Precambrian island, round which Cambrian sediments (now confirmed by fossil discoveries) had been deposited. Hicks subsequently proposed subdivision of his Precambrian into ‘Dimetian’, ‘Pebidian’, and (later) ‘Arvonian’, and he attempted correlations with rocks in Shropshire, North Wales, and even North America, seeking to develop the neo-Neptunist ideas of Sterry Hunt. The challenge to the Survey's work was countered in the 1880s by the Director General, Geikie, who showed that Hicks's idea of stratification in the Dimetian was mistaken. A heated controversy developed, several amateur geologists, supported by a group of Cambridge Sedgwickians, forming a coalition of ‘Archaeans’ against the Survey. Geikie was supported by Lloyd Morgan. Attention focused particularly on Ogof Lle-sugn Cave and St Non's Arch, with theory/controversy-ladenness of observations evident on both sides. Evidence from an eyewitness student record of a Geological Society meeting reveals the ‘sanit`ized’ nature of the official summary of the debate in QJGS. Field mapping early in the twentieth century by J. F. N. Green allowed a compromise consensus to be achieved, but Green's evidence for unconformity between the Cambrian and the Dimetian, obtained by excavation, can no longer be verified, and his consensual history of the area may need revision. Unconformity between the Cambrian and the Pebidian tuffs is not in doubt, however, and Precambrian at St David's is accepted. The study exhibits features of geological controversy and the British geological community in the nineteenth century. It also furnishes a further instance of the great influence of Murchison in nineteenth-century British geology and the side-effects of his controversy with Sedgwick. 相似文献
38.
39.
P Walter 《Experientia》1991,47(2):178-181
Some recent evidence on the benefits and hazards of elevated dosages of vitamins is summarized. Special emphasis is given on the safety of vitamins A, D, K1 and B6. Furthermore, the possibly beneficial effects of vitamins for athletic performance as well as the preventive potential of antioxidative vitamins and of carotenoids against cancer are discussed. 相似文献
40.
Walter Krämer 《Journal of forecasting》2017,36(7):854-858
We compare the accuracy of default predictions as, for instance, produced by professional rating agencies. We extend previous results on partial orderings to nonidentical sets of obligors and show that the calibration requirement virtually rules out the possibility of some partial orderings and that the partial ordering based on the ROC curve is most easily achieved in practice. As an example, we show for more than 5,000 firms rated by Moody's and S&P that these ratings cannot be ranked according to their grade distributions given default or nondefault, but that Moody's dominate S&P with respect to the ROC criterion and the Gini curve. 相似文献