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61.
The authors compared the extent of development of the germ cells of the human fetus ovaries developing in the organ culture and of control ovaries obtained of fetuses of "equivalent" age. The capacity to enter the meiosis prophase under conditions of the organ culture was expressed by the germ cells of fetuses of 8-9 week of gestation, and older; only individual oocytes reached the leptotene stage in the explants of the ovaries of 7-8 week fetuses. The oocytes at the leptotene, zygotene and pachitene stage appeared in the culture at the same periods as in the organism. However, the percentage of cells of these stages in the explant was as a rule lower than in control ovaries. In case of pulse administration of thymidine-3H into the culture labeled oocytes at the zygotene stage appeared in 4, and at the pachitene stage - in 14 days. 相似文献
62.
Floris Bex Henry Prakken Chris Reed Douglas Walton 《Artificial Intelligence and Law》2003,11(2-3):125-165
This paper studies the modelling of legal reasoning about evidence within general theories of defeasible reasoning and argumentation. In particular, Wigmore's method for charting evidence and its use by modern legal evidence scholars is studied in order to give a formal underpinning in terms of logics for defeasible argumentation. Two notions turn out to be crucial, viz. argumentation schemes and empirical generalisations. 相似文献
63.
Chris Reed 《AI & Society》1997,11(1-2):138-154
The concept of argumentation in AI is based almost exclusively on the use of formal, abstract representations. Despite their
appealing computational properties, these abstractions become increasingly divorced from their real world counterparts, and,
crucially, lose the ability to express the rich gamut of natural argument forms required for creating effective text. In this
paper, the demands that socially situated argumentation places on knowledge representation are explored, and the various problems
with existing formalisations are discussed. Insights from argumentation theory and social psychology are then adduced as key
contributions to a notion of social context which is both computationally tractable and suitably expressive for handling the
complexities of argumentation found in natural language. 相似文献
64.
Solution of a Well-Field Design Problem with Implicit Filtering 总被引:1,自引:0,他引:1
Fowler Kathleen R. Kelley Carl T. Miller Cass T. Kees Christopher E. Darwin Robert W. Reese Jill P. Farthing Matthew W. Reed Mark S. C. 《Optimization and Engineering》2004,5(2):207-234
Problems involving the management of groundwater resources occur routinely, and management decisions based upon optimization approaches offer the potential to save substantial amounts of money. However, this class of application is notoriously difficult to solve due to non-convex objective functions with multiple local minima and both nonlinear models and nonlinear constraints. We solve a subset of community test problems from this application field using MODFLOW, a standard groundwater flow model, and IFFCO, an implicit filtering algorithm that was designed to solve problems similar to those of focus in this work. While sampling methods have received only scant attention in the groundwater optimization literature, we show encouraging results that suggest they are deserving of more widespread consideration for this class of problems. In keeping with our objectives for the community problems, we have packaged the approaches used in this work to facilitate additional work on these problems by others and the application of implicit filtering to other problems in this field. We provide the data for our formulation and solution on the web. 相似文献
65.
D Zhang I Botos FX Gomis-Rüth R Doll C Blood FG Njoroge JW Fox W Bode EF Meyer 《Canadian Metallurgical Quarterly》1994,91(18):8447-8451
The structure of the metalloproteinase and hemorrhagic toxin atrolysin C form d (EC 3.4.24.42), from the venom of the western diamondback rattlesnake Crotalus atrox, has been determined to atomic resolution by x-ray crystallographic methods. This study illuminates the nature of inhibitor binding with natural (< Glu-Asn-Trp, where < Glu is pyroglutamic acid) and synthetic (SCH 47890) ligands. The primary specificity pocket is exceptionally deep; the nature of inhibitor and productive substrate binding is discussed. Insights gained from the study of these complexes facilitate the design of potential drugs to treat diseases where matrix metalloproteinases have been implicated, e.g., arthritis and tumor metastasis. 相似文献
66.
Evan J. Reed Marin Solja
i Mihai Ibanescu J. D. Joannopoulos 《Journal of Computer-Aided Materials Design》2005,12(1):1-15
We predict that reversed and anomalous non-relativistic Doppler shifts can be observed under some circumstances when light reflects from a shock wave front propagating through a photonic crystal, or material with a periodic modulation of the dielectric. This theoretical prediction is generalizable and applies to wave-like excitations in a variety of periodic media. An experimental observation of this effect has recently been made (Seddon, N. and Bearpark, T. Science, 302 (2003) 1537) and we provide a brief discussion of this experiment. 相似文献
67.
J. C. Roberts C. A. Parker J. F. Muth S. F. Leboeuf M. E. Aumer S. M. Bedair M. J. Reed 《Journal of Electronic Materials》2002,31(1):L1-L6
Metal-semiconductor-metal (MSM) photodetectors have been fabricated on InxGa1−xN epitaxial films grown by metalorganic chemical vapor deposition within the composition range 0≤x≤0.13. The dark current
and spectral response were measured for devices with a varying In mole fraction x. The devices, which had nominal finger widths
and finger spacing of 5 μm, were biased with modest voltages in the range 2≤Vbias≤5 V. In general, turn-on wave-length and dark current increased with increasing x. Turn-on wavelengths ranged from λ=370
nm to 430 nm and dark current densities ranged from Idark=2×10−2 A/cm2 (Vbias=5 V, x≈0.05) to 9×104 A/cm2 (Vbias=2 V, x≈0.13) depending on the In content, x, of the device active area. 相似文献
68.
Abstract In this study, a layered cuttings transport model is developed for high-angle and horizontal wells, which can be used for incompressible non-Newtonian fluids as well as compressible non-Newtonian fluids (i.e., foams). The effects of major drilling parameters, such as flow rate, rate of penetration, fluid density, viscosity, gas ratio, cuttings size, cuttings density, wellbore inclination and eccentricity of the drillsting on cuttings transport efficiency are analyzed. The major findings from this study are, the dominating parameter on wellbore cleaning is the flow rate, and, as the viscosity of the fluid is increased, the thickness of the cuttings bed developed in the wellbore is significantly increasing. Also, cuttings properties, fluid density, wellbore inclination and eccentricity have some influence on cuttings transport. 相似文献
69.
Harpreet S. Dhillon Jeong-O Jeong Dinesh Datla Michael Benonis R. Michael Buehrer Jeffrey H. Reed 《Analog Integrated Circuits and Signal Processing》2011,69(2-3):297-306
The main hurdle in the realization of dynamic spectrum access systems from the physical layer perspective is the reliable sensing of low power licensed users. One such scenario shows up in the unlicensed use of the TV bands where the TV band devices are required to sense extremely low power wireless microphones (WMs). The lack of technical standards among various wireless manufacturers and the resemblance of certain WM signals to narrow-band interference signals, such as spurious emissions, further aggravate the problem. Due to these uncertainties, it is extremely difficult to abstract the features of WM signals and hence develop robust sensing algorithms. To partly counter these challenges, we develop a two-stage sub-space algorithm that detects multiple narrow-band analog frequency-modulated signals generated by WMs. The performance of the algorithm is verified by using the real WM signals experimentally captured under low SNR conditions. The problem of differentiating between the WM and other narrow-band signals is left as future work. 相似文献
70.
H. J. Dai H. B. Dong N. D’Souza J.-C. Gebelin R. C. Reed 《Metallurgical and Materials Transactions A》2011,42(11):3439-3446
In this article, grain selection in spiral selectors during investment casting of single-crystal (SX) components is simulated using a cellular automaton grain structure model (CAFE) within a finite element thermal model (PROCAST). The models were validated against experimental observations and then were applied to model the effect of geometry of the spiral selectors on grain selection through a systematic approach. It was found that the efficiency of the spiral selector is significantly dependent on its geometry; the spiral becomes more efficient in selecting single grain with a smaller wax wire diameter; larger spiral rotation diameter, and smaller take-off angle. Recommendations for optimizing the spiral geometry are provided. 相似文献