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141.
We here propose the concept of enhanced evanescent tunneling (EET). Our analysis indicates that by means of a suitable control field, the transmission of evanescent waves across a forbidden gap can be enhanced by several orders of magnitude-well beyond the ordinary frustrated total internal reflection case. We show how such a phenomenon can be used to probe both the amplitude and phase of the evanescent portion of the angular spectrum, thereby allowing target superresolution. In principle EET can be manifested in other areas of physics where wave tunneling is involved. 相似文献
142.
Hossein Hodaei Mohammad‐Ali Miri Absar U. Hassan William E. Hayenga Matthias Heinrich Demetrios N. Christodoulides Mercedeh Khajavikhan 《Laser \u0026amp; Photonics Reviews》2016,10(3):494-499
Conventional techniques for transverse mode discrimination rely on introducing differential external losses to the different competing mode sets, enforcing single‐mode operation at the expense of additional losses to the desirable mode. We show how a parity‐time (PT) symmetric design approach can be employed to achieve single mode lasing in transversely multi‐moded microring resonators. In this type of system, mode selectivity is attained by judiciously utilizing the exceptional point dynamics arising from a complex interplay of gain and loss. The proposed scheme is versatile, robust to deviations from PT symmetry such as caused by fabrication inaccuracies or pump inhomogeneities, and enables a stable operation considerably above threshold while maintaining spatial and spectral purity. The experimental results presented here were obtained in InP‐based semiconductor microring arrangements and pave the way towards an entirely new class of chip‐scale semiconductor lasers that harness gain/loss contrast as a primary mechanism of mode selectivity.
143.
We introduce a new class of (2+1)D spatial and (3+1)D spatiotemporal waves that tend to autofocus in an abrupt fashion. While the maximum intensity of such a radial wave remains almost constant during propagation, it suddenly increases by orders of magnitude right before its focal point. These waves can be generated through the use of radially symmetric Airy waves or by appropriately superimposing Airy wave packets. Possible applications of such abruptly focusing beams are also discussed. 相似文献
144.
Apostolos Kuiroukidis Demetrios B. Papadopoulos 《International Journal of Theoretical Physics》2006,45(1):64-78
We consider brane cosmologies within the context of five-dimensional effective actions with higher curvature corrections. The actions are compatible with bulk string amplitude calculations from heterotic string theory. We find wrapped solutions that satisfy the field equations in an approximate but acceptable manner given their complexity, where the internal, four-dimensional, scale factor is naturally inflating, having an exponential De-Sitter form. The temporal dependence of the metric components is nontrivial so that this metric cannot be factored as in a conformally flat case. The effective Planck mass is finite and the brane solutions can localize four-dimensional gravity while the four-dimensional gravitational constant varies with time. The Hubble constant can be freely specified through the initial value of the scalar field, to conform with recent data. 相似文献
145.
Demetrios D. Dionysiou 《International Journal of Theoretical Physics》1974,10(5):355-362
The energy and angular momentum carried by gravitational waves of anN-body system has been extensively studied by the author. In this paper the linear momentum, within general relativity, is investigated by studying waves emitted from a source consisting ofN-particles moving under their own gravitation. 相似文献
146.
We consider the dynamical stability of a class of static, spherically symmetric solutions of the nonsymmetric gravitational theory. We numerically reproduce the Wyman solution and generate new solutions for the case where the theory has a nontrivial fundamental length scale -1. By considering spherically symmetric perturbations of these solutions we show that the Wyman solutions are generically unstable. 相似文献
147.
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149.
Demetrios N. Nicolaides Konstantinos E. Litinas Ioannis Vrasidas Konstantina C. Fylaktakidou 《Journal of heterocyclic chemistry》2004,41(4):499-503
The unexpected formation of 3‐aryl‐5‐arylamino‐1,2,4‐oxadiazoles took place, when arylamidoximes reacted thermally with ethoxycarbonylmethylene(triphenyl)phosphorane. Furoxans, nitriles, ureas were also isolated suggesting aryl cyanide oxides as intermediates. 3‐Aryl‐5‐arylamino‐1,2,4‐oxadiazoles were formed via an aryl migration from the carbon atom to the nitrogen atom of the amidoxime, and the structure was further proved from the X‐ray crystal structure of the N‐(4‐bromobenzoyl) derivative. 相似文献
150.
Demetrios Christodoulou 《Communications in Mathematical Physics》1984,93(2):171-195
The behaviour of the outgoing light rays in the gravitational collapse of an inhomogeneous spherically symmetric dust cloud is analyzed. It is shown that, for an open subset of initial density distributions, the first singular event, which occurs at the center of symmetry, is the vertex of an infinity of future null geodesic cones which intersect future null infinity. The frequency of the corresponding light rays is infinitely redshifted.Part of this work was done when the author was a Visiting Professor at the Department of Mathematics, University of Paris 6, Paris, FranceOn leave of absence from Max Planck Institute for Astrophysics, D-8046 Garching, Federal Republic of Germany 相似文献