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排序方式: 共有74条查询结果,搜索用时 15 毫秒
31.
We study the connections between the linear topological structure of James spaces generated by a partially ordered index-set and the set-theoretic properties of that set.  相似文献   
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Scientific discovery with the James Webb Space Telescope   总被引:1,自引:0,他引:1  
For the past 400 years, astronomers have sought to observe and interpret the Universe by building more powerful telescopes. These incredible instruments extend the capabilities of one of our most important senses, sight, towards new limits such as increased sensitivity and resolution, new dimensions such as exploration of wavelengths across the full electromagnetic spectrum, new information content such as analysis through spectroscopy, and new cadences such as rapid time-series views of the variable sky. The results from these investments, from small to large telescopes on the ground and in space, have completely transformed our understanding of the Universe; including the discovery that Earth is not the centre of the Universe, that the Milky Way is one among many galaxies in the Universe, that relic cosmic background radiation fills all space in the early Universe, that that the expansion rate of the Universe is accelerating, that exoplanets are common around stars, that gravitational waves exist, and much more. For modern astronomical research, the next wave of breakthroughs in fields ranging over planetary, stellar, galactic, and extragalactic science motivate a general-purpose observatory that is optimised at near- and mid-infrared wavelengths, and that has much greater sensitivity, resolution, and spectroscopic multiplexing than all previous telescopes. This scientific vision, from measuring the composition of rocky worlds in the nearby Milky Way galaxy to finding the first sources of light in the Universe to other topics at the forefront of modern astrophysics, motivates the state-of-the-art James Webb Space Telescope (Webb). In this review paper, I summarise the design and technical capabilities of Webb and the scientific opportunities that it enables.  相似文献   
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We introduce a generalized James constant J(a,X) for a Banach space X, and prove that, if J(a,X)<(3+a)/2 for some a∈[0,1], then X has uniform normal structure. The class of spaces X with J(1,X)<2 is proved to contain all u-spaces and their generalizations. For the James constant J(X) itself, we show that X has uniform normal structure provided that , improving the previous known upper bound at 3/2. Finally, we establish the stability of uniform normal structure of Banach spaces.  相似文献   
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The mystery of whether or not Werner Heisenberg gave Niels Bohr a drawing that Bohr came to believe was that of a German nuclear weapon, is discussed and resolved.  相似文献   
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An EPR study of the photoexcited triplet state of porphyrins, Chl a and the covalently linked dimer of Zn pyrochlorophyllide a, in a liquid crystal, is reported The metalloporphyrins interact to form excimers The low intramolecular energy transfer rate in the dimer (? 106s?1) suggests that the unfolded form predominates.  相似文献   
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左占飞  唐春雷 《数学学报》2017,60(3):383-388
首先利用James常数J(X)给出了Jordan-von Neumann型常数C_(-∞)(X)的一个估计式,然后由此式说明确实存在C_(-∞)(X)C_Z(X)的例子,最后利用C_(-∞)(X)和Benavides常数R(a,X)的关系,得到了空间具有正规结构的充分条件,并通过一些例子说明我们的结论严格推广了一些文献中的结果.  相似文献   
38.
Let η be a regular cardinal. It is proved, among other things, that: (i) if J(η) is the corresponding long James space, then every closed subspace YJ(η), with Dens (Y) = η, has a copy of 𝓁2(η) complemented in J(η); (ii) if Y is a closed subspace of the space of continuous functions C([1, η]), with Dens (Y) = η, then Y has a copy of c0(η) complemented in C([1, η]). In particular, every nonseparable closed subspace of J1) (resp. C([1, ω1])) contains a complemented copy of 𝓁21) (resp.c01)). As consequence, we give examples (J1), C([1, ω1]), C(V), V being the “long segment”) of Banach spaces X with the hereditary density property (HDP) (i.e., for every subspace YX we have that Dens (Y) = w*–Dens (Y*)), in spite of these spaces are not weakly Lindelof determined (WLD).  相似文献   
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ABSTRACT

We present a necessary and sufficient condition for the norm-parallelism of bounded linear operators on a Hilbert space. We also give a characterization of the Birkhoff–James orthogonality for Hilbert space operators. Moreover, we discuss the connection between norm-parallelism to the identity operator and an equality condition for the Davis–Wielandt radius. Some other related results are also discussed.  相似文献   
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