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排序方式: 共有105条查询结果,搜索用时 15 毫秒
1.
Scientometrics - Using a selection of general science journals, general medical journals and specialized medical journals, this paper analyses four indicators of epistemic community formation:... 相似文献
2.
We present an Extended Quadratic Frobenius Primality Test (EQFT), which is related to the Miller-Rabin test and to several
other known probabilistic tests. EQFT takes time equivalent to about two or three Miller-Rabin tests, but has a much smaller
error probability, namely 256/331776t for t iterations of the test in the worst case. We also give bounds on the average-case behaviour of the test: consider
the algorithm that repeatedly chooses random odd k bit numbers, subjects them to t iterations of our test and outputs the
first one found that passes all tests. We obtain numeric upper bounds for the error probability of this algorithm as well
as a general closed expression bounding the error. For instance, it is at most 2-155 for k = 500, t = 2. Compared with earlier similar results for the Miller-Rabin test, the results indicate that our test in
the average case has the effect of nine Miller-Rabin tests. We also give bounds for the error in case a prime is sought by
incremental search from a random starting point. 相似文献
3.
We present the first fully dynamic algorithm for computing the characteristic polynomial of a matrix. In the generic symmetric case, our algorithm supports rank-one updates in O(n2logn) randomized time and queries in constant time, whereas in the general case the algorithm works in O(n2klogn) randomized time, where k is the number of invariant factors of the matrix. The algorithm is based on the first dynamic algorithm for computing normal forms of a matrix such as the Frobenius normal form or the tridiagonal symmetric form. The algorithm can be extended to solve the matrix eigenproblem with relative error 2−b in additional O(nlog2nlogb) time. Furthermore, it can be used to dynamically maintain the singular value decomposition (SVD) of a generic matrix. Together with the algorithm, the hardness of the problem is studied. For the symmetric case, we present an Ω(n2) lower bound for rank-one updates and an Ω(n) lower bound for element updates. 相似文献
4.
5.
Kinetics of tyre char oxidation under combustion conditions 总被引:1,自引:0,他引:1
Morten Boberg Larsen Morten Linde Hansen Lars Skaarup-Jensen Flemming Frandsen 《Fuel》2007,86(15):2343-2350
Combustion of tyre char particles with diameters between 102 and 212 μm was performed in an experimental laboratory reactor, at temperatures between 750 and 850 °C, in an oxidative atmosphere with up to 10 vol.% O2 at 1 bar. The observed char combustion time varied from about 9 s at 750 °C to about 4 s at 850 °C. Under these conditions the experimental data indicated increasing mass transfer resistance with temperature. A diffusion reaction model was employed to study the effects of simultaneous mass transfer and kinetics in the experiments. An intrinsic reaction rate for tyre char combustion was estimated and comparison with literature data revealed good agreement. 相似文献
6.
Tove Faber Frandsen 《Scientometrics》2008,74(3):439-451
This paper presents a study of possible changes in patterns of document types in economics journals since the mid-1980s. Furthermore,
the study includes an analysis of a possible relation between the profile of a journal concerning composition of document
types and factors such as place of publication and JIF. The results provide little evidence that the journal editors have
succeeded in manipulating the distribution of document types. Furthermore, there is little support for the hypothesis that
journal editors decrease the number of publications included in the calculation of JIF or for that matter for the hypothesis
that journal editors increase the number of publications not included in the calculation of JIF. The results of the analyses
show that there is a clear distinction of journals based on place of publication and JIF 相似文献
7.
Release to the gas phase of metals, S and Cl during combustion of dedicated waste fractions 总被引:1,自引:0,他引:1
Anne Juul Pedersen Simone C. van Lith Flemming J. Frandsen Steinunn D. Steinsen Lilian B. Holgersen 《Fuel Processing Technology》2010,91(9):1062-4971
The release to the gas phase of inorganic elements such as alkali metals, Cl, S, and heavy metals in Waste-to-Energy (WtE) boilers is a challenge. Besides the risk of harmful emissions to the environment, inorganic elements released from the grate may cause severe ash deposition and corrosion problems in the boiler, subsequently leading to decreased overall efficiency and costly, unscheduled shut-downs. The objective of this study was to obtain quantitative data on the release of inorganic elements from dedicated, well-characterized waste fractions; in order to understand the release pattern and the link to the formation of fly ash and aerosols in full-scale waste incinerators. The release of metals, S and Cl from four dedicated waste fractions was quantified as a function of temperature in a lab-scale fixed-bed reactor. The waste fractions comprised chromated copper arsenate (CCA) impregnated wood, shoes, automotive shredder waste and PVC (poly-vinyl-chloride). The waste fractions were characterized by use of wet chemical analysis, and, based on the chemical composition of the initial fuel sample and the ash residue after the experiments; the release of inorganic elements was quantified. The lab-scale release results were then compared with results from a related, full-scale partitioning study, in which test runs with the addition of similar, dedicated waste fractions to a base-load waste had been performed in a grate-fired WtE boiler. In general, the elements Al, Ca, Cr, Cu, Fe, Mg, Si and Ti were not released, in consistency with the non-volatile nature of these elements. The elements Pb, Zn, Cl, S, Na, K and As, on the other hand, were released to a significant extent, and the release pattern was found to be both temperature dependent and fuel specific. Possible release mechanisms were discussed in relation to the chemical characteristics of each fuel, and some of the same release mechanisms as previously suggested for e.g. biomass-based fuels in the literature also seemed to apply for the present waste fractions. 相似文献
8.
Christine J. Frandsen Karla S. Brammer Kunbae Noh Laura S. Connelly Seunghan Oh Li-Han Chen Sungho Jin 《Materials science & engineering. C, Materials for biological applications》2011,31(8):1716-1722
Electrochemical formation of tunable nanoscale oxide layers on biomedical metallic surfaces has recently drawn much attention in biomaterials research. In this study, we report on the cellular response to a unique vertically aligned, laterally spaced nanotube nanostructure made of zirconium oxide (ZrO2) fabricated by anodization. The growth, morphology, and functionality of osteoblasts cultured on ZrO2 nanotubes have been investigated. The initial adhesion and spreading was considerably improved on the nanotube surface as compared to a flat zirconium (Zr) surface without a nanostructure. The morphology of the adhered cells on the nanotube surface elicited a highly organized cytoskeleton with crisscross patterned actin, which was lacking on the flat Zr. Increased alkaline phosphatase activity levels and the formation of calcified extracellular matrix implied improved osteoblast functionality and mineralization on the nanotube substrate. This in vitro study suggests that the ZrO2 nanotubes provided an enhanced osteoblast response and demonstrated their apparent role in providing a platform for bone growth. 相似文献
9.
Monoclonal mouse IgG1 and IgG3 antibodies were developed to the food mutagens, 2-amino-1-methyl-6-phenylimidazo[4,5-b] pyridine (PhIP) and 2-amino-3,4,8-trimethylimidazo[4,4-f] quinoxaline (4,8-DiMeIQx) in order to make specific and sensitive detection and purification systems suitable for biological samples. The antibodies were developed with the strategy that cross-reaction with analogues modified in the N2-position was desirable. Competitive enzyme-linked immunosorbent assays (ELISA) with 50% inhibition by 0.4-6 pmol food mutagen were developed. The epitopes recognized by the antibodies have been characterized by ELISA using 52 synthetic analogues and metabolites of PhIP, 4,8-DiMeIQx, and other food mutagens. One of the anti-PhIP antibodies only recognizes PhIP and those PhIP-analogues which have minor modifications in the N2-amino group, whereas the other, 7B7-1, is less stringent and also recognizes several other modified metabolites, including bulky adducts at the N2-amino group e.g. the major guanine and deoxyguanosine adducts isolated from PhIP-modified DNA. The antibodies to DiMeIQx also recognize the food mutagens 2-amino-3,4-dimethylimidazo[4,5-f]quinoxaline (4-MeIQx), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (8-MeIQx), and the corresponding quinolines (4-MeIQ and 8-MeIQ). Two of these antibodies only bind analogues with minor modifications in the free amino group, whereas analogues with major modifications in this position, including a deoxyguanosine adduct, react with the third antibody. Urine samples and faecal extracts from 3H-PhIP or 2-14C-DiMeIQx dosed rats were analysed by these ELISA assays, and high correlations between radioactivity and response in the ELISA assays were observed. Urine samples and faecal extracts from 3H-PhIP-dosed rats were purified on an affinity column containing the less stringent anti-PhIP antibody, 7B7-1. The affinity column was found by high performance liquid chromatography (HPLC) analysis to concentrate exclusively labelled material. This affinity column also bound PhIP-related materials from dilute samples of acid hydrolysed PhIP-DNA with high efficiency. Only approximately 40% of the 4,8-DiMeIQx related materials found in dilute acid hydrolysed samples of 4,8-DiMeIQx-DNA was bound by an affinity column containing the less stringent anti-4,8-DiMeIQx antibody, 2C5-1. We conclude that our anti-PhIP and anti-DiMeIQx antibodies can be used to determine the presence of these food mutagens and some of their activated or conjugated metabolites in complex biological samples. 相似文献
10.
Scientometrics - The existence of gender disparities in academia is well documented. Many explanations have been proposed and productivity is one of the most used variables to explain a possible... 相似文献