Academic literature on the topic 'Igbo knowledge systems'

Recently, long short-term memory (LSTM) networks have been widely adopted to help with fault diagnosis for power systems. However, the parameters of LSTM networks are determined by prior knowledge and experience and thereby not capable of dealing with unexpected faults in volatile environments. In this paper, we propose and apply an improved grey wolf optimization (IGWO) algorithm to optimize the parameters of LSTM networks, aiming to circumvent the drawback of empirical LSTM parameters and enhance the fault diagnosis accuracy for on-load tap changers (OLTCs). The composite multiscale weighted permutation entropy and energy entropy yielded by the grasshopper optimization algorithm and variational mode decomposition (GOA-VMD) method are used as the inputs of LSTM networks. The IGWO algorithm is applied in an iterative manner to optimize the relevant super arithmetic of the LSTM. In this way, an IGWO-LSTM combination model is constructed to classify different faults diagnosed in OLTCs. Experimental results verify the diagnosis performance superiority of the proposed method over several widely used comparison benchmarks

Frontiers advance and retreat, both figuratively and literally. At this moment they are advancing in three ways relevant to the subject of this book and the ongoing project on which it is based. First, after more than a century of reductionist hegemony, various science communities worldwide increasingly recognize the need to improve complementary, synthesis understanding—a way of putting the reductionist pieces of the problem back together again in order to understand how the ‘whole’ system works and to identify the emergent properties that follow from the complex interactions of the pieces. Synthesis understanding is not, of course, new. In the late eighteenth century, Immanuel Kant argued for it as one of the pillars of science in the reorganization of knowledge in the European academy (Turner 2002a) and designated geography as one of the ‘synthesis sciences’. Its contemporary rediscovery, however, rests in the science of global environmental change (Lawton 2001; Steffen et al. 2002), especially efforts to model complex systems, such as those in ocean–atmosphere–land interactions, and has been expanded by emerging research agendas seeking to couple human and environment systems, often registered under the label of ‘sustainability science’ (e.g. Kates et al. 2001; NRC 1999). Second, within these developments landuse and land-cover change (or, simply, land change) is singled out because of its centrality to a wide range of environmental concerns, including global climate change, regional–local hydrological impacts, biodiversity, and, of course, human development and ecosystem integrity (e.g. Brookfield 1995; NRC 2000; Watson et al. 2001). The need to advance an integrated land-change science is also increasingly recognized, one in which human, ecological, and remote sensing and geographical information systems (GIS) sciences are intertwined in problem-solving (Liverman et al. 1998; Klepeis and Turner 2001; Turner 2002b). And central to this effort is the need to advance geographically (spatially) explicit land-change models that can explain and project coupled human-ecological systems, and thus serve a wide range of research and assessment constituencies, from carbon to biodiversity to human vulnerability (IGBP 1999; Irwin and Geoghegan 2001; Kates et al. 2001; Liverman et al. 1998; Veldkamp and Lambin 2001). These two developments—synthesis science and integrated land science directed towards geographically explicit land-change models—constitute the broader intellectual and research frontiers to which this work contributes.

Abstract Insulated Gate Bipolar Transistor (IGBT) is one of the basic electronic components of rail and electric vehicle traction systems. They are used for switching and can perform this task very quickly. Regarding its operation, thermal modelling of IGBT modules is vital for obtaining temperature distribution for these components and thermal resistances of the entire IGBT as well. Nowadays, Computational Fluid Dynamics (CFD) is a robust and advantageous tool for modelling fluid flow and heat transfer problems that can be adopted to the thermal design of such critical components to better understand the effects of the design variables on the thermal-hydraulic performance of IGBT. This study is about conjugate heat transfer in a heat sink with diode and IGBT chips as heat sources and investigates the effect of minichannel porosity on Nusselt number (Nu) and the pumping power at several inlet Reynolds number (Re). The CFD analysis have been conducted parametrically and revealed that with increasing Re, both Nu and pumping powers increased significantly, indicating that heat transfer enhancement as well as power consumption are dominated by the flowrate. It is also shown that low minichannel porosities provide higher Nu and pumping power as well. The parametric studies provided a knowledge about the thermal-hydraulic performance of the IGBT and assisted to understand the effects of the governing parameters on the target functions.

Traveling wave (TW) optical amplifiers with high CW gains and wide band widths have recently been demonstrated at both 1.5 μm [1] and 1.3 μm [2] wavelengths. The use of optical amplifiers in ultra-high bit rate systems, such as those using optical time division multiplexing [3], requires knowledge of their gain characteristics for short (picosecond) optical pulse inputs. The amplification of short pulses has been demonstrated previously in various experiments using both GaAlAs and InGaAsP amplifiers [4-8]. All reported experiments used pulse repetition rates below 100 MHz. Moreover, only one past experiment [8] used an InGaAsP TW amplifier, but the pulses used were not very short (45-90 ps). We report here on the use of a 1.3-μm TW optical amplifier for amplification of picosecond pulses at a high repetition rate. We demonstrate distortionless amplification of 12-ps pulses at a repetition rate of 4 GHz. The amplifier gain was measured to be ~ 10 dB, corresponding to a chip gain of 21 dB, at a facet peak output power of 0.25 W.

Power semiconductor devices such as MOSFET/IGBT and PiN diodes are widely used as basic components for supporting infrastructure in the field of electronics, including in power conversion, industrial equipment, railways, and automobiles. Recently, increasing attention has been paid to silicon carbide (SiC) as a wide-band-gap semiconductor suitable for use in power devices with low loss and high breakdown voltage. However, basic knowledge of the material properties and reliability of SiC devices, and particularly the influence of mechanical stress on device characteristics, is still incomplete. In this paper, we evaluated the effect of mechanical stress on the electrical characteristics of SiC devices. In order to investigate the effect of stress on the SiC device characteristic, we propose a simple evaluation method using four-point bending, which is a classical method capable of applying uniaxial stress to a device. With this method, we evaluated the stress in a SiC device using residual stress measurement by Raman spectroscopy and stress simulation based on the finite element method. Our proposed experimental method is as follows. First, the SiC device was bonded with AuGe solder to a metal plate [phosphor bronze; Young’s modulus: 105 GPa; Poisson’s ratio: 0.33; dimensions: 100 mm (W) × 12 mm (L) × 2 mm (T)], and aluminum wire (wire radius: 200 μm) was also bonded to the device. Second, the prepared device was placed on the specially designed four-point bending apparatus for mechanical stress experiments. Finally, the sample was bent in compression or tension in the in-plane direction by the four-point system. The SiC device was subjected to compression or tensile stress via the metal plate. The electrical characteristics of the SiC-MOSFET were measured with a curve tracer in our proposed system. Id−Vds characteristics changed linearly as stress was applied to the device. As a result, the on-resistance was increased by 7.6% by applying a tensile stress of 300 MPa and was decreased by 1.0% by applying a compressive stress of 100 MPa at room temperature, respectively. A power device circuit with multiple chips was also simulated by SPICE based on the experimental results to confirm the effects of stress on SiC devices in a power module. Simulated MOSFET model contains stress factors obtained from experimental results. The circuit was simulated by electro-thermal coupled analysis using a one-dimensional model of the electric circuit and thermal circuit constructed in SPICE. The results show that the proposed method is powerful simulation method for power device design.