Enhancement of islanding-detection of distributed generation systems via wavelet transform-based approaches

In this paper, a wavelet transform-based approach is proposed to detect the occurrence of islanding events in distributed generation systems. Thanks to time–frequency localization capabilities exhibited by wavelet transform, the approach embedded with this transform technique has grasped the appearance of the islanding event in a highly effective manner. Moreover, for those regions which are in need of a better visualization, the proposed approach would serve as an efficient aid such that the mains power disconnection can be better distinguished. To validate the feasibility of this approach, the method has been validated through several scenarios. Test results supported the effectiveness of the method for the application considered.     

Enhanced electron emission from phosphorus-doped diamond-cladsilicon field emitter arrays

Undoped and phosphorus (P)-doped diamond-clad Si field emitter arrays have been successfully fabricated using microwave plasma chemical vapor deposition (MPCVD) technology. The electron emission from the blunt diamond-clad microtips are much higher than those for the pure Si tips with sharp curvature due to a lower work function. Furthermore, the characteristics of emission current against applied voltage for the P-doped diamond-clad tips show superior emission at lower field to the undoped ones. After the examination of Auger electron spectroscopy (AES) and electrical characteristics of as-grown diamond, such a significant enhancement of the electron emission from the P-doped diamond-clad tips is attributed to a higher electron conductivity and defect densities     

Parallel transport: a new transport layer paradigm for enabling Internet quality of service

The transport layer in the network protocol stack serves as a liaison between the application and the underlying network. Any quality of service provided by the network thus has to be effectively translated by the transport layer protocol in order to be enjoyed by the applications. In this article, we argue for a fundamental rethinking of the transport layer design to facilitate such QoS delivery. We identify the key requirement for a QoS enabling transport layer protocol as the ability to effectively handle multiplicity in terms of user differentiation levels, network resources, and service models. However, TCP, the transport layer protocol predominantly used in the Internet, is unable to support such multiplicity due to its single-state design. We extend TCP to a parallel transport layer protocol called parallel TCP (pTCP) that can tackle the different dimensions of multiplicity, and hence enable varying classes of QoS to applications. We discuss the applicability of pTCP in three specific domains with different levels of network support for QoS, and present simulation results substantiating our arguments.     

Conservatism of the gap metric

It is shown by way of simple examples that the gap metric may be inappropriate for quantifying the uncertainty for lightly damped systems, e.g. flexible structures such as spacecraft and aircraft. Two plants having otherwise identical transfer functions, except that their zeros on the imaginary axis are located slightly apart due to perturbations, are usually considered very close, i.e. their closed-loop characteristics under most stabilizing feedbacks are very similar. However, it is demonstrated that when the gap is used to quantify the plant perturbations, the computed gap may be large. Consequently, the stability of the perturbed plant with a stabilizing controller designed for the nominal plant cannot be guaranteed via the existing stability theorems using the gap metric     

Calculation of wall heat transfer in pipeexpansion turbulent flows

A new modified low-Reynolds-number k-ε turbulence [Chang, Hsieh and Chen (CHC)] model, which possesses the proper near-wall limiting behaviors and is free of the singular defect occurring near the reattachment point when applied to separated flows, is examined for use in wall heat transfer problems in flow with pipe expansion geometry. Another eight low-Reynolds-number k-ε models, found in open literature, are also examined in this study. Attention is specifically focused on the flow region surrounding the reattachment point. Comparative results show that only the CHC model and the model developed by Abe et al. [Abe, Kondoh and Nagano (AKN model)] can yield satisfactory distributions of the Nusselt number along the wall. However, the CHC model adopted the same model constants as conventionally used for the standard k-ε model. Thus, the CHC model is more universal than the AKN model.     

Stateful session handoff for mobile WWW

This paper proposes a web session handoff system that can hand over not only stateless but also stateful sessions between homogenous and heterogeneous user devices to enable uninterrupted and seamless web access. The proposed system adopts a proxy-based approach and an optional client-assisted scheme in order to track and hand over session information. In the proposed system, a session is registered at a User Agent Proxy (UAP) and then tracked by the UAP so that the session can be handed over from one device via the UAP to another device. In addition to session information tracked by a UAP, the UAP can hand over more comprehensive session information by using the client-assisted scheme. Compared with client-based approaches, our design has several advantages, such as less modification to user devices, practicability, and fault tolerance. We have implemented a UAP on a PC and client programs for both PC and PDA. The implementation can successfully hand over between PC and PDA a stateful session for online shopping applications.