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41.
Muharem Avdispahi 《Mathematische Nachrichten》2019,292(4):691-693
We correct the exponent in the error term of the prime geodesic theorem for hyperbolic 3‐manifolds 1 and in Park's theorem for higher dimensions [ 3 , 2 ]. 相似文献
42.
Alberto Cattaneo 《Mathematische Nachrichten》2019,292(10):2137-2152
We study automorphisms of the Hilbert scheme of n points on a generic projective K3 surface S, for any . We show that is either trivial or generated by a non‐symplectic involution and we determine numerical and divisorial conditions which allow us to distinguish between the two cases. As an application of these results we prove that, for any , there exist infinitely many admissible degrees for the polarization of the K3 surface S such that admits a non‐natural involution. This provides a generalization of the results of [7] for . 相似文献
43.
《Journal of Pure and Applied Algebra》2019,223(11):4677-4688
In this paper, we prove a conjecture by T. Suzuki, which says if a smooth Fano manifold satisfies some positivity condition on its Chern characters, then it can be covered by rational N-folds. We prove this conjecture by using purely combinatorial properties of Bernoulli numbers. 相似文献
44.
We show that the only rational homology spheres which can admit almost complex structures occur in dimensions two and six. Moreover, we provide infinitely many examples of six-dimensional rational homology spheres which admit almost complex structures, and infinitely many which do not. We then show that if a closed almost complex manifold has sum of Betti numbers three, then its dimension must be a power of two. 相似文献
45.
Yunshyong Chow 《Journal of Difference Equations and Applications》2013,19(2):169-187
We investigate asymptotic dynamics of the classical Leslie–Gower competition model when both competing populations are subject to Allee effects. The system may possess four interior steady states. It is proved that for certain parameter regimes both competing populations may either go extinct, coexist or one population drives the other population to extinction depending on initial conditions. 相似文献
46.
In this paper, we present the general analytic solution to the zero curvature equation for rigid three-dimensional CR-manifolds. The solutions are uniquely determined by one function and four real parameters. 相似文献
47.
A high‐order element based adaptive mesh refinement strategy for three‐dimensional unstructured grid
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Adaptive mesh refinement (AMR) shows attractive properties in automatically refining the flow region of interest, and with AMR, better prediction can be obtained with much less labor work and cost compared to manually remeshing or the global mesh refinement. Cartesian AMR is well established; however, AMR on hybrid unstructured mesh, which is heavily used in the high‐Reynolds number flow simulation, is less matured and existing methods may result in degraded mesh quality, which mostly happens in the boundary layer or near the sharp geometric features. User intervention or additional constraints, such as freezing all boundary layer elements or refining the whole boundary layer, are required to assist the refinement process. In this work, a novel AMR strategy is developed to handle existing difficulties. In the new method, high‐order unstructured elements are first generated based on the baseline mesh; then the refinement is conducted in the parametric space; at last, the mesh suitable for the solver is output. Generating refined elements in the parametric space with high‐order elements is the key of this method and this helps to guarantee both the accuracy and robustness. With the current method, 3‐dimensional hybrid unstructured mesh of huge size and complex geometry can be automatically refined, without user intervention nor additional constraints. With test cases including the 2‐dimensional airfoil and 3‐dimensional full aircraft, the current AMR method proves to be accurate, simple, and robust. 相似文献
48.
Spontaneous excitation of a circularly accelerated atom coupled with vacuum Dirac field fluctuations
We study the spontaneous excitation of a circularly accelerated atom coupled with vacuum Dirac field fluctuations by separately calculating the contribution to the excitation rate of vacuum fluctuations and a cross term which involves both vacuum fluctuations and radiation reaction, and demonstrate that although the spontaneous excitation for the atom in its ground state would occur in vacuum, such atoms in circular motion do not perceive a pure thermal radiation as their counterparts in linear acceleration do since the transition rates of the atom do not contain the Planckian factor characterizing a thermal bath. We also find that the contribution of the cross term that plays the same role as that of radiation reaction in the scalar and electromagnetic fields cases differs for atoms in circular motion from those in linear acceleration. This suggests that the conclusion drawn for atoms coupled with the scalar and electromagnetic fields that the contribution of radiation reaction to the mean rate of change of atomic energy does not vary as the trajectory of the atom changes from linear acceleration to circular motion is not a general trait that applies to the Dirac field where the role of radiation reaction is played by the cross term. 相似文献
49.
Li Wei Bin Zhang Yan Zhou Li Qiang Junyan Zhang 《Surface and interface analysis : SIA》2013,45(8):1233-1237
Fluorine‐doped hydrogenated carbon film was grown by chemical vapor deposition technique using CH4 and CF4 as feedstock, with a pulse DC‐bias power supply. The structure of as‐deposited film was characterized by transmission electron microscopy and Raman spectra. The results suggested that the film could be considered as composite thin film with curved graphitic structures embedded in amorphous carbon matrix. The mechanical properties and friction coefficient were tested by TI 950 TriboIndenter and UMT‐2 at humidity of 30%, respectively. The results showed that the film exhibited high hardness (~11.04 GPa), good elasticity recovery(~83%) and ultra‐low coefficient of friction (~0.01). Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
50.