306 research outputs found

    Nonlocal long-range synchronization of planar Josephson junction arrays

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    We study arrays of planar Nb Josephson junctions with contacts to intermediate electrodes, which allow measurements of individual junctions and, thus, provide an insight into intricate array dynamics. We observe a robust phase-locking of arrays, despite a significant inter-junction separation. Several unusual phenomena are reported, such as a bi-stable critical current with re-entrant superconductivity upon switching of nearby junctions; and incorrect Shapiro steps, occurring at mixing frequencies between the external RF radiation and the internal Josephson frequency in nearby junctions. Our results reveal a surprisingly strong and long-range inter-junction interaction. It is attributed to nonlocality of planar junction electrodynamics, caused by the long-range spreading of stray electromagnetic fields. The nonlocality greatly enhances the high-frequency interjunction coupling and enables large-scale synchronization. Therefore, we conclude that planar geometry is advantageous for realization of coherent Josephson electronics.Comment: 8 pages, 5 figure

    Non-Metric Gravity I: Field Equations

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    We describe and study a certain class of modified gravity theories. Our starting point is Plebanski formulation of gravity in terms of a triple B^i of 2-forms, a connection A^i and a ``Lagrange multiplier'' field Psi^ij. The generalization we consider stems from presence in the action of an extra term proportional to a scalar function of Psi^ij. As in the usual Plebanski general relativity (GR) case, a certain metric can be constructed from B^i. However, unlike in GR, the connection A^i no longer coincides with the self-dual part of the metric-compatible spin-connection. Field equations of the theory are shown to be relations between derivatives of the metric and components of field Psi, as well as its derivatives, the later being in contrast to the GR case. The equations are of second order in derivatives. An analog of the Bianchi identity is still present in the theory, as well as its contracted version tantamount to energy conservation equation.Comment: 21 pages, no figures (v2) energy conservation equation simplified, note on reality conditions added (v3) minor change

    Treatment of ischemic stroke caused by dissection and occlusion of internal carotid artery in a young patient

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    The type and etiology of stroke in young patients are known to differ from those in elderly patients, that influences the diagnosis and treatment. Dissection of cerebral arteries holds the top position in the structure of the causes of ischemic stroke in children and young people below 45 years. Currently no clear guideline on the proper treatment of this pathology exists. The article presents the case of acute ischemic stroke in a young patient (the stroke was caused by the occlusion due to dissection of the internal carotid artery) successfully treated with radiosurgical method - stenting of the cervical part of the artery with the transition to petrous segment of the left carotid artery using combined proximal and distal protection of cerebral vessels. The control of patient's state and results of angiography and ultrasound demonstrate the favourable immediate and medium-term prognosis for the patient

    Clinical use of various endovascular stenting techniques in challenging coronary interventions

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    Aim. Development of an algorithm of actions for stenting of artery stenosis during challenging percutaneous coronary interventions (PCI) based on the analysis of the results of different endovascular techniques. Methods. We analyzed the experience of the department of radiologic endovascular diagnosis and treatment of Stavropol regional clinical hospital for endovascular surgical treatment of atherosclerosis of coronary arteries. The study included 317 cases of coronary interventions with technically impossible stent delivery to stenosis by standard method along the front-line guidewire and standard choice of the guide in case of distal TIMI 3 flow. For the study the patients were divided into 3 groups comparable by the number of subjects: 104, 113 and 100 respectively. For each group we determined different stages of enhancing support with consistent step-wise transition. The groups differed by the used methods of enhancing support and consistency of their use. Among other methods of support group 2 included the method of guide change and delivery of the second guidewire of enhanced support. At the same time groups 1 and 3 used these methods separately. Results. The smallest number of unsuccessful interventions was observed in group 2 compared to those of groups 1 and 3. The relative risk indicators also demonstrate the high effectiveness of tactics used in the group 2. Conclusion. The most preferable method for the necessary support when stent delivery distal to stenosis is impossible, is a choice of optimal guide and use of the second guidewire of enhanced support
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