10,933 research outputs found
Devices and architectures for large scale integrated silicon photonics circuits
We present DWDM nanophotonics architectures based on microring resonator modulators and detectors. We focus on two implementations: an on chip interconnect for multicore processor (Corona) and a high radix network switch (HyperX). Based on the requirements of these applications we discuss the key constraints on the photonic circuits' devices and fabrication techniques as well as strategies to improve their performance
Application of multiple resistive superconducting fault-current limiters for fast fault detection in highly interconnected distribution systems
Superconducting fault-current limiters (SFCLs) offer several benefits for electrical distribution systems, especially with increasing distributed generation and the requirements for better network reliability and efficiency. This paper examines the use of multiple SFCLs in a protection scheme to locate faulted circuits, using an approach which is radically different from typical proposed applications of fault current limitation, and also which does not require communications. The technique, referred to as “current division discrimination” (CDD), is based upon the intrinsic inverse current-time characteristics of resistive SFCLs, which ensures that only the SFCLs closest to a fault operate. CDD is especially suited to meshed networks and particularly when the network topology may change over time. Meshed networks are expensive and complex to protect using conventional methods. Simulation results with multiple SFCLs, using a thermal-electric superconductor model, confirm that CDD operates as expected. Nevertheless, CDD has limitations, which are examined in this paper. The SFCLs must be appropriately rated for the maximum system fault level, although some variation in actual fault level can be tolerated. For correct coordination between SFCLs, each bus must have at least three circuits that can supply fault current, and the SFCLs should have identical current-time characteristics
Information measures and cognitive limits in multilayer navigation
Cities and their transportation systems become increasingly complex and
multimodal as they grow, and it is natural to wonder if it is possible to
quantitatively characterize our difficulty to navigate in them and whether such
navigation exceeds our cognitive limits. A transition between different
searching strategies for navigating in metropolitan maps has been observed for
large, complex metropolitan networks. This evidence suggests the existence of
another limit associated to the cognitive overload and caused by large amounts
of information to process. In this light, we analyzed the world's 15 largest
metropolitan networks and estimated the information limit for determining a
trip in a transportation system to be on the order of 8 bits. Similar to the
"Dunbar number," which represents a limit to the size of an individual's
friendship circle, our cognitive limit suggests that maps should not consist of
more than about connections points to be easily readable. We also show
that including connections with other transportation modes dramatically
increases the information needed to navigate in multilayer transportation
networks: in large cities such as New York, Paris, and Tokyo, more than
of trips are above the 8-bit limit. Multimodal transportation systems in large
cities have thus already exceeded human cognitive limits and consequently the
traditional view of navigation in cities has to be revised substantially.Comment: 16 pages+9 pages of supplementary materia
Superconducting fault current limiter application in a power-dense marine electrical system
Power-dense, low-voltage marine electrical systems have the potential for extremely high fault currents. Superconducting fault current limiters (SFCLs) have been of interest for many years and offer an effective method for reducing fault currents. This is very attractive in a marine vessel in terms of the benefits arising from reductions in switchgear rating (and consequently size, weight and cost) and damage at the point of fault. However, there are a number of issues that must be considered prior to installation of any SFCL device(s), particularly in the context of marine applications. Accordingly, this study analyses several such issues, including: location and resistance sizing of SFCLs; the potential effects of an SFCL on system voltage, power and frequency; and practical application issues such as the potential impact of transients such as transformer inrush. Simulations based upon an actual vessel are used to illustrate discussions and support assertions. It is shown that SFCLs, even with relatively small impedances, are highly effective at reducing prospective fault currents; the impact that higher resistance values has on fault current reduction and maintaining the system voltage for other non-faulted elements of the system is also presented and it is shown that higher resistance values are desirable in many cases. It is demonstrated that the exact nature of the SFCL application will depend significantly on the vessel’s electrical topology, the fault current contribution of each of the generators, and the properties of the SFCL device, such as size, weight, critical current value and recovery time
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