New transformation polynomials for discretization of analogue systems

The novel transformation polynomials for discretization of analogue systems have been presented. A generalization of some of the existing transformation methods has also been done. A comparative analysis, through the corresponding examples involving several known discretization methods, has been carried out. It has been demonstrated that the application of these transformation polynomials allows the reduction of discretization error compared to other approximation methods. The response to an arbitrary excitation of the discrete system obtained by these transformations is approximately equal to that of the original analogue system. The transformations are rational since variable s ^{− n} ,n ∈ N, transforms to the quotient of two linear functions of variable z.     

Dispersion and rheology of BaTiO3 nanoparticles in ethanol–isopropanol solvents

Barium titanate (BaTiO₃) nanoparticles were dispersed in ethanol–isopropanol mixtures and their rheological behaviors were examined in terms of surfactant concentration (0–5 wt.% of the solids) and volumetric solids loading () over a shear-rate () range 1 to 1,000 s⁻¹. An oxyethylene-based polymeric surfactant was used to facilitate the nanoparticle dispersion. A pronounced viscosity reduction, >95% when compared to the suspensions without the dispersant, resulted with a surfactant concentration of 4 wt.% at a constant shear rate of 100 s⁻¹. This finding was in parallel with a simultaneous reduction in the mean “floc” size of the suspensions. Shear-thinning flow character resulted over most of the shear-rate range examined, especially for the concentrated suspensions with ϕ ≥ 0.25. The concentrated suspensions were indeed flocculated. This increased instability was partly due to the compression of electrical double layer as the particulate solids became more crowded in the carrier solvents, and also to the increased “effective” solids concentration because of the preferential adsorption of the surfactant molecules on the nanoparticle surface.     

A numerical method for a transient quantum drift-diffusion model arising in semiconductor devices

This paper describes a numerical method for a transient quantum drift-diffusion model arising in semiconductor devices. The discretization method is presented with emphasis on adaptive time discretization. An adaptive time step algorithm is constructed by introducing the derivative of the free energy of the system, which has an essential property to understand the carrier behavior of the time-dependent problems. The algorithm is verified with switching characteristics of one-dimensional n⁺–n–n⁺ silicon diodes. It is shown that the time step is adapted to the switching characteristics. The new algorithm significantly reduces the total number of time steps.     

Anisotropic piezoelectric properties of 1–3 ceramic / polymer composites comprising rods with elliptic cross section

This paper is concerned with the study of effective piezoelectric properties of 1–3 ferroelectric ceramic / polymer composites. The aim of this paper is to show the role of a combination of the electromechanical properties of components and microgeometry of the 1–3 composite in determining its anisotropic piezoelectric response. The system of ceramic rods in the form of elliptic cylinders is an important microgeometric factor that influences the piezoelectric coefficients and their anisotropy. Examples of the piezoelectric response and anisotropy are analysed for the 1–3 composites based on either “soft” or “hard” ceramic and having either piezo-active or piezo-passive matrix. Combinations of the ceramic and polymer components are found that provide different volume-fraction dependences of the piezoelectric coefficients d_3j^* d_{3j}^{*} and g_3j^* g_{3j}^{*} : both monotonic, both non-monotonic, monotonic d_3j^* d_{3j}^{*} and non-monotonic g_3j^* g_{3j}^{*} , and vice versa. Examples of volume-fraction dependences of electromechanical coupling factors k_3j^* k_{3j}^{*} are also considered. A comparison of the effective piezoelectric coefficients calculated by the effective field method and the finite element method is carried out for different compositions in wide ranges of the ratio of semiaxes of the ellipse and of volume fractions of the components. Good agreement between data calculated by means of the aforementioned methods is obtained for the 1–3 structure comprising the elliptic cylinders.     

Induction motor rotor fault diagnosis method based on double PQ transformation

This paper presents a new rotor fault diagnosis method for induction motors which is based on the double PQ transformation. We construct the PQ transformation matrix with the positive sequence fundamental voltage components and their Hilbert transformation as elements. The active power P and the reactive power Q are obtained through the PQ transformation of the stator currents. As both P and Q are constant for a healthy motor, they are represented by a dot on the PQ plane. Whereas the P and Q for a rotor broken bar motor are represented by an ellipse because they comprise an additional frequency component 2sf _s (s is the slip and f _s is the supply frequency). Thus, by distinguishing these two different patterns, the rotor broken bar fault is detected. We use the major radius of the ellipse as the fault indicator and the distance between the point of no-load condition and the center of the ellipse on the PQ plane as its normalization value. We thus arrive at the fault severity factor which is fairly independent of the load level and the inertia value of the induction motors. Experimental results have demonstrated that the proposed method is effective in identifying the rotor-broken-bars fault and at determining the severity of the fault. Translated from Proceedings of the Chinese Society for Electrical Engineering, 2006, 26(13): 135–140 [译自: 中国电机工程学报]     

Selective 3D ultrashort TE imaging: comparison of “dual-echo” acquisition and magnetization preparation for improving short-<Emphasis Type="Italic">T</Emphasis><Subscript>2</Subscript> contrast

Objective The objective of this study was to compare two different schemes for long-T ₂ component suppression in ultrashort echo-time (UTE) imaging. The aim was to increase conspicuity of short-T ₂ components accessible by the UTE technique. Materials and methods A “dual-echo” and a magnetization-preparation approach for long-T ₂ and fat suppression were implemented on clinical scanners. Both techniques were compared in 3D UTE exams on healthy volunteers regarding short-T ₂ Signal-to-noise ratio (SNR), long-T ₂ suppression quality, and scan efficiency. A quantitative SNR evaluation was performed using ankle scans of six volunteers. T ₂ suppression profiles were simulated for both approaches to facilitate interpretation of the observations. Results At 1.5 T, both techniques perform equally well in suppressing long-T ₂ components and fat. Magnetization preparation requires more shimming effort due to the use of narrow-band pulses, while the “dual-echo” technique requires a post-processing step to form a subtraction image. For scans with a short repetition time (TR), the “dual-echo” approach is much faster than the magnetization preparation, which depends on slow T ₁ recovery between preparation steps. The SNR comparison shows slightly higher short-T ₂ SNR for the “dual-echo” approach. At 3.0 T, magnetization preparation becomes more challenging due to stronger off-resonance effects. Conclusion Both techniques are well suited for long-T ₂ suppression and offer comparable short-T ₂ SNR. However, the “dual-echo” approach has strong advantages in terms of scan efficiency and off-resonance behavior.     

Picturing the elephant: Giant piezoelectric activity and the monoclinic phases of relaxor-ferroelectric single crystals

Understanding the relationship between the structure and “giant” piezoelectric properties of relaxor ferroelectric solid solutions (1–x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ [PMN–xPT] and (1–x)Pb(Zn_1/3Nb_2/3)O₃–xPbTiO₃ [PZN–xPT] is an extremely difficult task. In this article, three main paradigms are reviewed. In the first, the monoclinic phases present at the morphotropic phase boundary (MPB) are responsible for the giant piezoelectric response in that they allow, or at least facilitate, polarization rotation. In the second, a strong polarization rotation effect is explained by the large piezoelectric shear coefficients of zero-field rhombohedral and orthorhombic phases due to the near degeneracy at the MPB and the intrinsic softness of the relaxor state; zero-field monoclinic symmetries are explained by residually distorted rhombohedral and orthorhombic phases in the presence of internal stresses and/or residual bias fields. In the third, the monoclinic “phases” are composed of very finely twinned rhombohedral or tetragonal domains. In this “adaptive phase” model, based on that for ferroelastic martensites, the large electric-field induced strains are extrinsic in nature and result from the progressive switching of the component “nano-twins”; the ease of polarization rotation is explained by a high domain wall mobility. These paradigms remain to be mutually reconciled. The article includes a thorough review of the history of PMN–xPT and PZN–xPT single crystals and, particularly, the most important work done over the last decade.     

Indoor Location Algorithm Based on the Measurement of the Received Signal Strength

The “distance-loss” model is amended by inserting a random distance-estimation variable. The estimation error is very small; thus, it does not change the log-normal distribution of the shadowing factor in the model. Then, an iterative method is introduced to reduce the influence of shadowing, and the location estimation based on the received signal strength will be improved. Simulations show that this algorithm is effective. Translated from the Journal of Fudan University (Natural Science), 2004, 43(1): 72–76 (in Chinese)     

Effect of Concentration of SH U 555A Labeled Human Melanoma Cells on MR Spin Echo and Gradient Echo Signal Decay at 0.2, 1.5, and 3T

In the current study the effect of increasing concentrations of superparamagnetic iron oxide labeled cells on the MRI signal decay at magnetic field strengths of 0.2, 1.5, and 3 T was evaluated. The spin echo and gradient echo cellular transverse relaxivity was systematically studied for various concentrations (N = 1, 5, 10, 20, 40, and 80 cells/μl_gel) of homogeneously suspended SH U 555A labeled SK-Mel28 human melanoma cells. For all field strengths investigated a linear relationship between cellular transverse relaxation enhancement and cell concentration was found. In the spin echo case, the cellular relaxivities [i.e., d(ΔR ₂)/dN] were determined to 0.12 s⁻¹ (cell/μl)⁻¹ at 0.2 T, 0.16 s⁻¹ (cell/μl)⁻¹ at 1.5 T, and 0.17 s⁻¹ (cell/μl) at 3 T. In the gradient echo case, the calculated cellular relaxivities (i.e., d(ΔR ₂ ^* )/dN) were 0.51 s⁻¹ (cell/μl)⁻¹ at 0.2 T, 0.69 s⁻¹ (cell/μl)⁻¹ at 1.5 T, and 0.71 s⁻¹ (cell/μl)⁻¹ at 3 T. The proposed preparation technique has proven to be a simple and reliable approach to quantify effects of magnetically labeled cells in vitro. On the basis of this quantification well suited tissue specific models can be derived.     

Observers for a Class of Chaotic Systems

The design of observers for a class of practical physical chaotic systems is discussed. By using only one state variable and its time derivatives, a control law is constructed to achieve the synchronization between the investigated chaotic systems and their observers, and the results are proved theoretically. Several observers of chaotic systems are designed by using this method. Translated from “Observers for a Class of Chaotic Systems” published in Journal of Southwest China Normal University (Natural Science), 2004, 29(1): 53–57 (in Chinese)     

Exploration of Na<Superscript>+</Superscript>,K<Superscript>+</Superscript>-ATPase ion permeation pathways <Emphasis Type="Italic">via</Emphasis> molecular dynamic simulation and electrostatic analysis

Biologically-inspired nanodevices can serve as “natural” alternatives to conventional semiconductor devices in many applications from information storage to mechanical rotors. In this work we consider an ATP-powered transmembrane protein, the Na⁺,K⁺-ATPase, which has appealing functionality but still lacks an “atomistic” picture capable of elucidating its operation. The vast collection of experimental literature on the Na⁺,K⁺-ATPase gives a unique advantage to this protein in developing and validating computational tools. We have performed extensive molecular dynamic simulations of the Na⁺,K⁺-ATPase in an accurate biological environment, followed by time-averaged electrostatic analysis, to investigate the ion-binding loci and access/egress pathways that cations may take through the protein as they are transported across the membrane.     

The segmentation algorithm for handwritten numeral strings in bank-check recognition

In this paper, an integrated system of segmenting unconstrained handwritten numeral strings with unknowing number of digits is proposed, which consists of the extraction of connected components based on vertical projection and isolated components analysis, the length estimation of connected components using syntax analysis and waveform analysis and the segmentation of unconstrained connected handwritten numeral strings using innovative reverse “drop-falling” algorithm. This segmentation system which has promising results is then incorporated into a complete bank check character recognition system. Translated from Journal of Beijing University of Posts and Telecommunications, 2006, 29(1): 13–16 [译自: 北京邮电大学学报]     

Efficient time integration of the Boltzmann-Poisson system applied to semiconductor device simulation

This paper presents new efficient methods for performing the time integration of finite-difference WENO approximations of the Boltzmann-Poisson system applied to semiconductor device simulation. The developed methods are based on local time-step schemes for hyperbolic conservation laws which permit the use of different time increments at different positions in space. A strategy to dynamically adapt the space-time grid according to the actual stability criteria imposed by the CFL-condition is proposed. The resulting numerical schemes are used to simulate the electron transport in a n⁺−n−n⁺ silicon diode and in a silicon MESFET. Several numerical tests and comparisons with computations performed with TVD Runge-Kutta type algorithms prove the efficiency of the presented time integration methods.     

Silicon-on-insulator non-volatile memories with second-bit effect

In this paper we propose an analytical approach to investigate the electrostatic impact of very small charged regions in the gate dielectric of dual bit non-volatile memories (NVMs) Silicon-On-Insulator (SOI) cells. This original model is based on the surface potential approach and allows to investigate the behavior of NVMs in subthreshold working condition. It is particularly accurate for charged region, as small as L ₂ = 10 nm and up to a charge density of Q = 10¹³ cm⁻² and it is complementarity to another approach proposed for bulk devices [1]. Relevant consequences of the asymmetric charging of the storage layer on the electrical characteristics of discrete-trap memories are thoroughly analyzed: the importance of Short Channel Effects (SCEs) for the performance of these cells is highlighted. Moreover a method for extracting an “effective” distribution of charges from the transfer characteristics is derived.     

Rearrangeability of 7-stage 16 × 16 shuffle exchange networks

It has long been an outstanding conjecture that any (2n − 1)-stage shuffle exchange network (Omega network) is rearrangeable for 2 ⁿ × 2 ⁿ . Many researchers have failed to prove this conjecture, including a recent one established by Hasan. However, nobody has pointed out its fallacy. Therefore, as one of the objectives, this paper shall clarify this fact. Since the case of n = 3 has been proven by many researchers [1,2], this paper uses a constructive approach to prove that when n = 4, the 7-stage 16 × 16 shuffle exchange network is also rearrangeable. The paper also presents the model of a balanced tree to avoid internal conflict, the representation of permutations using a connection graph and loop graph, and the concepts of symmetry graph and identical transform. Based on graphic composition and bipartition, the permutations 16 × 16 are divided into five classes, with five assignment algorithms proposed. These algorithms are simpler, clearer and easier to program. The techniques used for n = 4 may provide hints for the general case of n > 4. __________ Translated from Acta Electronica Sinica, 2007, 35(10): 1875–1885 [译自: 电子学报]     

Short-echo-time magnetic resonance phase-shift velocity mapping for assessment of heart valve and great vessel stenoses: three years' experience

Shortening the echo times of magnetic resonance (MR) sequences used for phase-shift velocity mapping to 3.6 ms has extended use of the technique to measurement of velocities in turbulent, poststenotic jet flows. We used a 0.5-T MR machine and field even-echo rephasing (FEER) sequences with 3.6 ms echo times for jet velocity mapping.In vitro trials used continuous flow through a phantom with a 6-mm stenosis. Fifteen patients with mitral and/or aortic valve stenosis and 20 patients with repaired aortic coarctation were studied prospectively, with Doppler ultrasonic measurement of peak jet velocity performed independently on the same day. The clinical contribution of MR jet velocity mapping, used during a 3-year period in 306 patients with congenital and acquired disease of heart valves, great vessels, and conduits, was assessed retrospectively. The 3.6-ms sequence allowed accurate measurement of jet velocities up to 6 m s^–1 in vitro (r=0.996). Prospective studies in patients showed good agreement between MR and Doppler measurements of peak velocity:n=38; range, 1.2–6.1 m s^–1; mean, 2.7 m s^–1; mean of differences (Doppler-MR), 0.22 ms^–1; standard deviation of differences, ±0.38 m s^–1 (±14%). MR jet velocity mapping proved particularly valuable for assessment and localization of stenoses at sites where ultrasonic access was limited. The technique represents a diagnostic advance which can obviate the need for catheterization in selected cases.     

Lead-free piezoelectric ceramics: Alternatives for PZT?

Investigations in the development of lead-free piezoelectric ceramics have recently claimed comparable properties to the lead-based ferroelectric perovskites, represented by Pb(Zr,Ti)O₃, or PZT. In this work, the scientific and technical impact of these materials is contrasted with the various families of “soft” and “hard” PZTs. On the scientific front, the intrinsic nature of the dielectric and piezoelectric properties are presented in relation to their respective Curie temperatures (T _C) and the existence of a morphotropic phase boundary (MPB). Analogous to PZT, enhanced properties are noted for MPB compositions in the (Na,Bi)TiO₃-BaTiO₃ and ternary system with (K,Bi)TiO₃, but offer properties significantly lower. The consequences of a ferroelectric to antiferroelectric transition well below T _C further limits their usefulness. Though comparable with respect to T _C, the high levels of piezoelectricity reported in the (K,Na)NbO₃ family are the result of enhanced polarizability associated with the orthorhombic-tetragonal polymorphic phase transition being compositionally shifted downward. As expected, the properties are strongly temperature dependent, while degradation occurs through the thermal cycling between the two distinct ferroelectric domain states. Extrinsic contributions arising from domains and domain wall mobility were determined using high field strain and polarization measurements. The concept of “soft” and “hard” lead-free piezoelectrics were discussed in relation to donor and acceptor modified PZTs, respectively. Technologically, the lead-free materials are discussed in relation to general applications, including sensors, actuators and ultrasound transducers.

Closed-form solutions to fractional-order linear differential equations

The definitions and properties of widely used fractional-order derivatives are summarized in this paper. The characteristic polynomials of the fractional-order systems are pseudo-polynomials whose powers of the complex variable are non-integers. This kind of systems can be approximated by high-order integer-order systems, and can be analyzed and designed by the sophisticated integer-order systems methodology. A new closed-form algorithm for fractional-order linear differential equations is proposed based on the definitions of fractional-order derivatives, and the effectiveness of the algorithm is illustrated through examples. __________ Translated from Journal of Northeastern University (Natural Science), 2007, 28(1): 10–13 [译自: 东北大学学报(自然科学版)]     

Novel anomaly detection approach for telecommunication network proactive performance monitoring

The mode of telecommunication network management is changing from “network oriented” to “subscriber oriented”. Aimed at enhancing subscribers’ feeling, proactive performance monitoring (PPM) can enable a fast fault correction by detecting anomalies designating performance degradation. In this paper, a novel anomaly detection approach is the proposed taking advantage of time series prediction and the associated confidence interval based on multiplicative autoregressive integrated moving average (ARIMA). Furthermore, under the assumption that the training residual is a white noise process following a normal distribution, the associated confidence interval of prediction can be figured out under any given confidence degree 1 - α by constructing random variables satisfying t distribution. Experimental results verify the method’s effectiveness.