An improved model for soil ionization around grounding system and its application to stratified soil

An improved model for taking into account the effect of the soil ionization around grounding system under lightning strike is proposed in this paper. In this model, the soil ionization region is assumed to retain 7% of its pre-ionization resistivity, which is consistent with the experimental results on soil ionization found in literature (Trans. SA Inst. Electr. Eng. (1988) 63; AIEE Trans. 61 (1942) 349; Proc. IEE 121(2) (1974) 123) and our own laboratory experiments (Time domain modelling of the response of grounding systems subjected to lightning currents, Licenciate Thesis, Uppsala University, 2003). Compared with modelling the soil ionization as an increase in the size of the ground conductor, the model presented here will not overestimate the beneficial influence of the soil ionization in reducing the ground potential rise, especially in high resistivity soil. The model is also applied to study the transient behaviour of grounding conductors in stratified soil under lightning strike including soil ionization. It shows that making the grounding conductor to penetrate the lower resistivity soil layer could help to decrease the ground potential rise at the injection point several times.     

Stepped side shield writer for perpendicular recording

To increase the track density in hard disk drive (HDD), the write head fringing field should be controlled. The side shield is one of the candidates to reduce the fringing stray field. Although the wrap-around type [K. Nakamoto, et al., IEEE Trans. Magn. 41(10) (2005) 2914] and many other side shield structures [Y. Kanai, et al., IEEE Trans. Magn. 39(4) (2003) 1955; D.T. Wilton, D.J. Mapps, IEEE Trans. Magn. 29 (1993) 4182] were proposed, these side shield structures have a trade-off between the track edge field sharpness and the maximum write field strength on the center track. In this paper, we propose the new side shield writer called the stepped side shield (3S) head. The 3S head satisfies both the on-track write field strength and reduction of the adjacent track stray field. The track edge field sharpness is much improved especially in the high skew angle recording. We studied the 3S head effect by the statistic field simulation.     

Existence and global exponential stability of periodic solution to BAM neural networks with periodic coefficients and continuously distributed delays

By using the continuation theorem of coincidence degree theory and Liapunov function, we obtain some sufficient criteria to ensure the existence and global exponential stability of periodic solution to the bidirectional associative memory (BAM) neural networks with periodic coefficients and continuously distributed delays. These results improve and generalize the works of papers [J. Cao, L. Wang, Phys. Rev. E 61 (2000) 1825] and [Z. Liu, A. Chen, J. Cao, L. Huang, IEEE Trans. Circuits Systems I 50 (2003) 1162]. An example is given to illustrate that the criteria are feasible.     

Implementation and synchronization of 3x3 grid scroll chaotic circuits with analog programmable devices

The implementation of circuits with complex dynamics is a very challenging problem. In this paper we present a new chaotic circuit based on the dynamical equations introduced in IEEE Trans. Circuits Syst., I: Fundam. Theory Appl. 51, 2476-2490 (2004). This circuit has been realized by using programmable analog devices, and, in particular, field programmable analog arrays have been used to implement a two-dimensional 3x3 grid scroll chaotic attractor. The implementation of complex dynamics with low cost circuits is very appealing; moreover, the implementation of the chaotic attractor discussed in this paper is not present in the literature. The experimental results including the synchronization between two chaotic circuits show complete agreement with the simulation results reported in IEEE Trans. Circuits Syst., I: Fundam. Theory Appl. 51, 2476-2490 (2004).     

石油化工仪表防雷接地系统设计与实现

为了提高石油化工仪表的防雷安全性,进行防雷接地系统的优化设计,提出一种基于漏感和励磁电感增益分配和检波控制的防雷接地系统设计方法,基于麦克斯韦全电流定理,进行石油化工仪表防雷接地的电磁场分析,以双运放LM358放大器为核心进行石油化工仪表防雷接地系统电路设计,主要包括了交流放大器设计、滤波器设计、检波器设计和直流放大器设计,在检波设计中采用8阶高通滤波器(S3529)并联,提高防雷接地系统的输出运放性能,最后进行系统调试和电路测试,结果表明,采用该系统进行石油化工仪表防雷接地设计,防雷的阻带衰减大于51dB,对雷击信号具有较好的高通滤波和低通滤波性能,较好地保护了石油化工仪表安全。     

Mode Converter Synthesis by the Particle Swarm Optimization

Particle Swarm Optimization (PSO) is an effective, simple and promising method intended for the fast search in multi-dimensional space [Kennedy and Eberhart, "Particle Swarm Optimization", Proc. of the 1995 IEEE International Conference on Neural Networks, 1995]. Besides special testing problems a number of engineering tasks of electrodynamics were solved by the PSO successfully [Robinson and Rahmat-Samii, "Particle Swarm Optimization in Electromagnetics", IEEE Trans. Antennas Propag., 2004; Jin and Rahmat-Samii, "Parallel Particle Swarm Optimization and Finite-Difference Time-Domain (PSO/FDTD) Algorithm for Multband and Wide-Band Patch Antenna Designs", IEEE Trans. Antennas Propag., 2005]. On the other hand, the scattering matrix technique is a fast and accurate method of mode converter analysis. We illustrate PSO by a number of converter designs developed for high-power microwaves control: a matching horn for output maser section, a corrugated converter of linear-polarized hybrid modes, a TE₀₁ mitre bend.     

Numerical simulation of long laboratory sparks generated by positive switching impulses

A numerical methodology using two different leader channel criteria has been implemented. The methodology is based on Bondiou and Gallimberti's proposition [A. Bondiou, I. Gallimberti, Theoretical modelling of the development of the positive spark in long spark, J. Phys. D: Appl. Phys. 27 (1994) 1252–1266]. The leader channel criteria used are Rizk engineering criterion [Rizk, A model for switching impulse leader inception and breakdown of long air gaps, IEEE Trans. Power Deliv., 4(1) (1989)] and Local thermodynamic – L.T.E. – physical concept [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7–193]. The methodology was tested in three different cases; a deterministic case, a statistical variation and a typical constant level test. Deterministic calculation considered corona inception using stabilization corona electric field criterion of Gallimberti [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7–193] and the leader moving as segments. The statistical simulation has two different statistical delays, one at inception and the other due to the tortuous characteristics of the leader channel. The constant level test consists of 200 positive switching impulses with the same characteristics such as maximum applied voltage, time to crest and time to fall. Time to breakdown and breakdown voltage were found based on the results obtained from the constant level test characteristics. All the numerical results presented are based on experimental conditions reported in [Les Renardières Group, Research on long gap discharges at Les Renardières, Electra N 35 (1973)] from the world class research group namely Les Renardieres Group.     

DESIGN BUILDING AND PRELIMINARY TEST OF SMALL MSAC

A small MSAC, with effective area 7.4×8cm², has been designed, build and tested. Each grid wire is insolated with others. Energy resolution of the PA gap for X-ray detection is about 19% (FWHM) at 5.9 keV. Avalanche mechanism has been discussed.     

Transient lightning responses of grounding systems buried in horizontal multilayered earth with a hybrid method

Combined with the Fast Fourier Transform (FFT), a mathematical hybrid method for accurately computing the lightning response from grounding systems buried in multilayered earth model has been developed in this paper. In the method, electrical circuit consists of “T” typical of basic elements. To accelerate calculations of the method, quasi-static complex image method and closed form of Green's function and analytical formula for mutual induction and impedance coefficients were introduced into this method. With the inverse FFT, the method can be used for studying performances of transient lightning response from the grounding systems.     

Temperature dependence of microwave resistances of n++np++ Si X band IMPATT diode

The change of both microwave negative resistance (R) and its parasitic series resistance (R_s) on the rise of junction temperature in the range of 100–220 °C of HP n⁺⁺np⁺⁺ Si IMPATT [M. Mitra, M. Das, S. Kar, S.K. Roy, IEEE Trans. Electron. Dev. 40 (1993) 1890] diode at X band (8–12 GHz) have been simulated. The studies followed by Gummel–Blue Technique [H.K. Gummel, J.L. Blue, IEEE Trans. Electron. Dev. 14 (1967) 569] show that for a constant experimental bias current of 25 mA [Mitra et al., 1993], for which the space charge effect is not prominent, the values of negative conductance and negative resistance degrade taking into account the changes in the ionization rates and drift velocities due to rise of temperature. Also observed that the critical series resistance increases with the increase of temperature up to 2.23 Ω, slightly higher than the realistic limit of 2 Ω [Mitra et al., 1993].     

Orthogonal bi-pulse UWB: Timing and (de)modulation

In this paper, we propose a novel orthogonal bi-pulse ultra-wideband (UWB) system, which uses an even pulse and an odd pulse to convey information symbols in an alternating manner. Due to the orthogonality of these pulses, their corresponding received waveforms remain orthogonal after propagating through multipath channels. Then we consider two major challenges in the realization of our proposed UWB system: timing synchronization and symbol demodulation. In particular, the idea of timing with dirty template (TDT) in [L. Yang, G.B. Giannakis, Timing Ultra-Wideband signals with dirty templates, IEEE Trans. on Commun. 53 (11) (2005) 1952–1963] is employed for timing synchronization and the noncoherent scheme in [L. Yang, G.B. Giannakis, A. Swami, Noncoherent Ultra-Wideband (de)modulation, IEEE Trans. Commun. 55 (4) (2007) 810–819] is used to bypass channel estimation. Both of these techniques are characterized by correlating adjacent waveform segments. In the implementation of these techniques, we will gradually reveal the advantages of our proposed system. The correlation of adjacent waveform segments only contains the information of a single symbol. This enables a significant enhancement of the synchronization speed of TDT when no training sequence is transmitted. For the same reason, our demodulation approach completely mitigates the inter-symbol interference (ISI) in the second paper referred to, above, and entails a simple demodulator even in the presence of unknown timing errors. Simulations are also carried out to corroborate our analysis.     

Planar superstrate for dual-frequency RHCP-LHCP array

Patch antennas are low profile, lightweight and most suitable for aerospace and mobile applications. In recent years Fabry–Pérot cavities and meta-surfaces have been used as superstrates to improve the radiation performance of planar antennas (Saenz et al., IEEE Trans. Antennas Propag. 56(4), 2008; Iriarte et al., IEEE Trans. Antennas Propag. 57(1), 2009) such as directivity, mutual coupling on array configuration and bandwidth. These structures usually work for a single polarization and frequency band, while an increasing number of applications require multifrequency operation. In this paper a Fabry–Pérot cavity that works with dual-polarized and dual-frequency patch antennas (rectangular patch excited orthogonally) is proposed in order to design high-directivity dual-frequency RHCP-LHCP Arrays.     

Surface treatment of aluminum by high current pulsed electron beam

The development of advanced technology based on the interaction of high current pulsed electron beam (HCPEB) with solid materials is very important at present time [R. Stark, J. Christiansen, et al., IEEE Trans. Plasma Sci. 23 (3) (1995) 258–264; T. Witke, A. Lenk, B. Schultrich, IEEE Trans. Plasma Sci. 24 (1) (1996) 61–62]. When the concentrated electron flux are acting on a material, superfast processes such as heating, melting, and solidification, as well as dynamic stresses induced in the processes impart surface layer with improved physical, chemical and mechanical properties unattainable with conventional surface treatment methods. This paper reports on an investigation on pure aluminum treated by “Nadezhda-2” HCPEB device. The extreme surface is melted to a depth of about 1 μm at the input energy density of 3 J/cm². Craters, micrometers in size, are formed in the melted surface. Vacancy and dislocations are significantly increased near the surface as a result of the electron bombardment. Based on the microhardness distribution measured on the cross-section, it has been established that the thickness of the modified layer is several hundreds of micrometers beneath the surface, significantly greater than that of the heat-affected zone. The experimental results are compared with those obtained by solving numerically the heat and stress equations, with finite difference and finite element methods, taking into account of the processes of melting and changing of physics parameters related to changing temperature. Satisfactory agreement between experimental and theoretical data is obtained.     

Considerations in applying clustering techniques to speaker-independent word recognition.

Recent work at Bell Laboratories has demonstrated the utility of applying sophisticated pattern recognition techniques to obtain a set of speaker-independent word templates for an isolated word recognition system [Levinson et al.,IEEE Trans. Acoust. Speech Signal Process. ASSP-27 (2), 134--141 (1979); Rabiner et al., IEEE Trans. Acoust. Speech Signal Process.(in press)]. In these studies, it was shown that a careful experimenter could guide the clustering algorithms to choose a small set of templates that were representative of a large number of replications for each word in the vocabulary. Subsequent word recognition tests verified that the templates chosen were indeed representative of a fairly large population of talkers. Given the success of this approach, the next important step is to investigate fully automatic techniques for clustering multiple versions of a single word into a set of speaker-independent word templates. Two such techniques are described in this paper. The first method uses distance data (between replications of a word) to segment the population into stable clusters. The word template is obtained as either the cluster minimax, or as an averaged version of all the elements in the cluster. The second method is a variation of the one described by Rabiner [IEEE Trans. Acoust. Speech Signal Process. ASSP-26 (3), 34--42 (1978)] in which averaging techniques are directly combined with the nearest neighbor rule to simultaneously define both the word template (i.e., the cluster center) and the elements in the cluster. Experimental data show the first method to be superior to the second method when three or more clusters per word are used in the recognition task.     

Comparison of results for the effective height and atmospheric electric field distribution surrounding a parallelepiped building with Franklin's rod and lightning protection rod JUS N. B4. 811

Atmospheric electric field distribution in the surroundings of building with lightning protection rod with and without horizontal circular loop is determined in this paper. Lightning protection rod having a circular loop is Serbian national standard (JUS N. B4. 811). The effective height of the building with lightning protection rod, as an important parameter for defining protection area, is also determined. Using the results it is noticed that lightning protection rod having a horizontal circular loop (JUS N. B4. 811) is better than Franklin's lightning protection rod, with equal height, for protecting buildings.     

Experimental subwavelength localization of scatterers by decomposition of the time reversal operator interpreted as a covariance matrix

The D.O.R.T. method (French acronym for Decomposition of the Time Reversal Operator) is an active remote sensing technique using arrays of antennas for the detection and localization of scatterers [Prada et at., J. Acoust. Soc. Am. 99, 2067-2076 (1996)]. The analogy between the time reversal operator and the covariance matrix used for classical sources separation in passive remote sensing [Bienvenu et al., IEEE Trans. ASSP 31, 1235-1247 (1983)] is established. Then, an experiment of subwavelength detection and localization of point-like scatterers with a linear array of transducers is presented. Using classical estimators in reception like Maximum-Likelihood and Multiple Signal Characterization (MUSIC), two point-like scatterers separated by lambda/3 and placed at 100lambda from the array of transducers are resolved. In these experiments, the role of multiple scattering and the existence of additional eigenvectors associated with dipolar and monopolar radiation of each scatterer is discussed.     

Attack structural vulnerability of power grids: A hybrid approach based on complex networks

Power grids have been studied as a typical example of real-world complex networks. Different from previous methods, this paper proposes a hybrid approach for structural vulnerability analysis of power transmission networks, in which a DC power flow model with hidden failures is embedded into the traditional error and attack tolerance methodology to form a new scheme for power grids vulnerability assessment and modeling. The new approach embodies some important characteristics of power transmission networks. Furthermore, the simulation on the standard IEEE 118 bus system demonstrates that a critical region might exist and when the power grid operates in the region, it is vulnerable to both random and intentional attacks. Finally, a brief theoretical analysis is presented to explain the new phenomena.