Al-Alaoui operator and the new transformation polynomials for discretization of analogue systems

The “new transformation polynomials for discretization of analogue systems” was recently introduced. The work proposes that the discretization of 1/s ⁿ should be done independently rather than by raising the discrete representation of 1/s to the power n. Several examples are given in to back this idea. In this paper it is shown that the “new transformation polynomials for discretization of analogue systems” is exactly the same as the parameterized Al-Alaoui operator. In the following sections, we will show that the same results could be obtained with the parameterized Al-Alaoui operator. This research was supported, in part, by the University Research Board of the American University of Beirut.     

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.     

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.     

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]     

On a generalization of the wave digital filter concept

The design of digital filter structures imitating the behaviour of classical analogue networks has received considerable interest in the literature. Of particular interest has been the Wave Digital Filter first considered by Fettweis. We examine here a generalization in which the relationships between the voltages, currents and wave variables are considered as a linear transformation on the ABCD matrix of the analogue two-port network. The linear transformation is examined in some detail and conditions are derived which impose constraints on the elements of the matrices involved in the transformation. Finally a table giving thirteen transformations known to yield realizable digital filter structures is presented.     

Discontinuous Galerkin solver for Boltzmann-Poisson transients

We present results of a discontinuous Galerkin scheme applied to deterministic computations of the transients for the Boltzmann-Poisson system describing electron transport in semiconductor devices. The collisional term models optical-phonon interactions which become dominant under strong energetic conditions corresponding to nano-scale active regions under applied bias. The proposed numerical technique is a finite element method using discontinuous piecewise polynomials as basis functions on unstructured meshes. It is applied to simulate hot electron transport in bulk silicon, in a silicon n ⁺-n-n ⁺ diode and in a double gated 12 nm MOSFET. Additionally, the obtained results are compared to those of a high order WENO scheme simulation.     

Dielectric relaxation and variable-range-hopping conduction in BaSn1−x Cr x O3 system

The possibility of formation of a solid solution in the system BaSn_1−x Cr _x O₃ has been explored upto x ≤ 0.20. It has been confirmed that single phase solid solution forms upto x ≤ 0.10. Dielectric and conduction behaviour of single phase samples have been studied in the temperature range 400–610 K and frequency range 10 Hz–2 MHz. Two dielectric relaxation processes in two different frequency ranges have been observed. The temperature dependence of both dc and ac resistivity obey relation ρ = ρ _o exp(B/T^1/4), indicative of variable range hopping conduction mechanism. The activation energy for dc conduction is higher than that for relaxation time (τ) of low frequency dielectric relaxation process. It has been observed that activation energy for dielectric relaxation matches with activation energy for ac conductivity (at 100 kHz) for both the dielectric relaxation processes. Seebeck coefficient ‘α’ of the samples have been measured in the temperature range 350–650 K. Negative value of ‘α’ in the entire range of temperature measurement shows that conduction species are negatively charged. On the basis of value of activation energy for dc conduction and sign of Seebeck coefficient, conduction in the low temperature region (below 500 K) is attributed to hopping of weakly bonded electrons among Sn²⁺ ⇔ Sn⁴⁺ or Sn³⁺ ⇔ Sn⁴⁺ and that in the high temperature region (above 500 K) to hopping of doubly ionized oxygen vacancies .     

Design of stable two-dimensional analogue and digital filters with applications in image processing

A method is proposed for the frequency domain design of linear two-dimensional analogue and digital filters with guaranteed stability. The technique used is based on the result that the numerator and the denominator of the input immittance of a two-variable network (which is passive and lossy) are strictly Hurwitz polynomials. One of these strictly Hurwitz polynomials is assigned to the denominator of a two-variable analogue transfer function and the network elements are then used as the variables of optimization thereby guaranteeing the stability of the analogue transfer function. The transfer function of the corresponding two-dimensional discrete (digital) filter is obtained from the analogue transfer function by the bilinear transformation. Examples illustrating the versatility of the technique in designing 2D digital filters of arbitrary order approximating a given magnitude and group delay response are presented. These filters are used to process a simple binary image. The results obtained demonstrate the importance of linear phase in image processing applications. The method presented here can be extended to the design of stable m-dimensional analogue and digital filters.     

Phase transformation and microwave dielectric properties of BiPO4 ceramics

Monazite-type compounds, BiPO₄ polymorphs were prepared by the solid-state reaction method. The phase transformation and microwave dielectric properties of sintered ceramics were investigated using the X-ray powder diffraction (XRD) and a network analyzer, respectively. The low-temperature phase of BiPO₄ has monoclinic structure, and was transformed into the high-temperature phase with a slight distortion of monoclinic when it is heated above 600^∘C. The effect of the transformation on the microwave dielectric properties was examined. It was found that the dielectric properties of each phase were significantly different. In particular, the high-temperature phase sintered at 950^∘C has good microwave dielectric properties; the relative dielectric constant (ε _r ) = 22, the quality factor (Q× f) = 32,500 GHz and the temperature coefficient of resonant frequency (τ _f ) = − 79 ppm/ ^∘C.     

Diffusion-weighted imaging of the spine using radialk-space trajectories

Introduction Diffusion-weighted MR imaging (DWI) of the spine requires robust imaging methods, that are insensitive to susceptibility effects caused by the transition from bone to soft tissue and motion artifacts due to breathing, swallowing, and cardiac motion. The purpose of this study was to develop a robust imaging method suitable for DWI of the spine. Methods and subjects A radialk-space spin echo sequence has been implemented, which is sell-navigating because each acquisition line passes through the origin ofk-space. Influence of cardiac motion and associated flow of cerebrospinal fluid is minimized by cardiac gating with a finger photoplethysmograph. The sequence has been tested on a 1.5T system. Diffusion-weighted images of six normal volunteers were acquired in the sagittal plane with 4b values between 50 and 500 s mm⁻². Because of the symmetries of the cord, diffusion measurements in the head-foot (HF) or left-right (LR) directions were sufficient to measure the dominant effects of anisotropy. Results The apparent diffusion coefficients (ADCs) measured, respectively, in the LR and HF directions were (0.699 ± 0.050) × 10⁻³ and (1.805 ± 0.086) × 10⁻³ mm² s⁻¹ in the spinal cord. (1.588 ± 0.082) × 10⁻³ and (1.528 ± 0.052) × 10⁻³ mm² s⁻¹ in the intervertebral disks, and (0.346 ± 0.047) × 10⁻³ and (0.306 ± 0.035) × 10⁻³ mm² s⁻¹ in the vertebrae of the cervicothoraeic spine. Conclusion Diffusion-weighted spin echo sequences with radial trajectories ink-space provide a means of achieving robust, high quality diffusion-weighted imaging and measuring ADCs in the spine. The application of the diffusion-weighting gradients in different directions allows diffusion anisotropy to be measured.     

Generalized bessel polynomials with application to the design of bandpass filters with approximately flat group delay response

The continued fraction expansion of the ordinary Bessel polynomials is modified by replacing the complex frequency variable p by p/(1+γp), where γ=?0. The resulting polynomials, when a reactance transformation is applied, are capable of providing bandpass filters with an approximately flat group delay response.     

Free-carrier grating due to the optical phonon emission in InP n + nn + structures

Electron transport in 5 μm long InP n ⁺ nn ⁺ structure with the n-region doping of 10¹⁵cm⁻³ is theoretically investigated by the Monte Carlo Particle (MCP) technique at low lattice temperature (T = 10 K), when dominating scattering mechanism is the optical phonon emission. It is shown that at the constant bias a free-carrier grating (FCG) can be formed inside the n-region. The simple model of FCG formation is proposed and verified by MCP simulation of electron transport and noise in the considered InP structure.     

Approximate formulae for numerical inversion of Laplace transforms

Most methods for the numerical calculation of inverse Laplace transformations f(t) = L⁻¹[F(s)] have serious limitations concerning the class of functions F(s) that can be inverted or the achievable accuracy. The procedures described in the paper can be used to invert rational as well as irrational or transcendental functions of the complex variable s. The required accuracy of the results can be enhanced without changing the algorithm, only at the cost of a longer computation time. The described methods were verified with many examples including transients in lumped/distributed systems with sections of lossy multiconductor transmission lines or with distributed RC elements. © 1998 John Wiley & Sons, Ltd.     

Piezoelectric micromachined ultrasonic transducers with thick PZT sol gel films

The fabricated micro machined ultrasonic transducers (pMUT) was based on piezoelectric laminated plates operating at flexural modes. The fabricated bimorph pMUT transducers were composed of 5-layers. A 4 μm thick lead zirconate titanate (PZT) thin film deposited by a sol–gel method was used. The piezoelectric layer exhibited a capacitance corresponding to a permitivity of ɛ _r = 1,200. The electromechanical coupling coefficient (k ²) and quality factor (Q) were measured as k ² = 4.4% and Q = 145 in air for a low frequency transducer (240 kHz). The effect of DC bias voltage on frequency and k ² has been studied. The 16.9 MHz transducer yielded values of Q = 25 in air and k ² = 3%.     

On constructing complex grid multi‐wing hyperchaotic system: Theoretical design and circuit implementation

This paper further investigates some novel methods for generating complex grid multi‐wing hyperchaotic attractors from four‐dimensional (4D) quadratic hyperchaotic systems, based on our previous works. First, a modified double‐wing hyperchaotic Lü system by using non‐uniform variable scaling transformation is obtained, and n‐wing hyperchaotic system equipped with a duality‐symmetric multi‐segment quadratic function is also constructed. Then, by switching control in the z direction, mirror symmetry conversion and rotation transformation, three classes of n × m‐wing hyperchaotic systems are respectively realized. Finally, two types of improved module‐based circuits are designed for generating various grid multi‐wing hyperchaotic attractors. One characteristic of the proposed approaches lies in their generality, which is also suitable for constructing 4D grid multi‐wing hyperchaotic Lorenz and Chen systems. Both numerical simulation and circuit implementation have demonstrated the feasibility and effectiveness of the proposed approaches. Copyright © 2010 John Wiley & Sons, Ltd.     

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)]     

Defects and transport in Gd-doped BaPrO3

The electrical conductivity of BaPr_1−x Gd_xO_3−δ has been characterized by means of the four-point van der Pauw technique at 200–1100 °C as a function of pO₂ and pH₂O. The contributions from ionic charge carriers were investigated by the EMF of concentration cells and the H⁺/D⁺ isotope effect on the total conductivity. BaPr_1−x Gd _x O_3−δ is predominately a p-type electronic conductor under oxidizing conditions, while ionic conduction is barely measurable. Gd(III) substituted for Pr(IV) is charge compensated mainly by electron holes, with protons and oxygen vacancies contributing significantly but as minority defects only at low temperatures (wet conditions) and at high temperatures, respectively. The conductivity behaviour has been modelled under these assumptions to extract thermodynamic parameters for the defect reactions at play. The practical use of this material is limited by its poor chemical stability.     

Photoresist patterned thick-film piezoelectric elements on silicon

A fundamental limitation of screen printing is the achievable alignment accuracy and resolution. This paper presents details of a thick-resist process that improves both of these factors. The technique involves exposing/developing a thick resist to form the desired pattern and then filling the features with thick film material using a doctor blading process. Registration accuracy comparable with standard photolithographic processes has been achieved resulting in minimum feature sizes of <50 μm and a film thickness of 100 μm. Piezoelectric elements have been successfully poled on a platinised silicon wafer with a measured d ₃₃ value of 60 pCN⁻¹.