Field theoretical treatment of H-plane waveguide junctionswith anisotropic medium

A method based on the equivalence principle and cavity field expansions is used to analyze an H-plane waveguide junction containing an anisotropic (ferrite or composite ferrite) post. Using the equivalence principle, magnetic surface currents are introduced at the imaginary boundaries chosen between the central region of the junction and the waveguides. The electric displacement in the junction can be completely expressed in terms of a solenoidal set. On the other hand, the magnetic induction in the junction must be expressed in terms of a solenoidal set and an irrotational set. Continuing the tangential magnetic field at the imaginary boundaries leads to a matrix equation, the unknowns of which are the amplitudes of the scattered waveguide modes. Using this method, H-plane waveguide junctions with ferrite and composite ferrite posts are considered. The numerical results show excellent agreement with previously published experimental and theoretical results     

Coplanar waveguide with top and bottom shields in place ofair-bridges

A convenient technique for the elimination of the coupled slot-line mode in coplanar waveguide (CPW) nonsymmetric circuits is proposed. This technique simply uses top and/or bottom ground plane shields and avoids the more costly airbridges. These shields are easy to fabricate; however, they may slightly affect the propagation of the CPW mode in the form of power leakage into the parallel plate TEM mode. This effect can be avoided by restricting operation to lower frequencies. Numerical comparisons between the effect of the shields and the airbridges on a CPW filter are presented     

New two CFOA-based sinusoidal RC oscillators with buffered outlet

Using a unified representation for a class of buffered-outlet two current-feedback operational amplifier (CFOAs)-based sinusoidal oscillators, new circuits of this type can be systematically discovered. A catalogue of four circuit structures, each structure realizing nine oscillator circuits, is presented. Moreover, using the RC:CR transformation, additional nine oscillator circuits can be obtained from each structure. While each circuit requires five passive elements, some of the circuits enjoy one or more of the following attractive features: use of grounded capacitors, feasibility of absorbing the parasitic components of the CFOAs and orthogonal tuning of the frequency and the startup condition of oscillation.     

Hybrid image steganography method using Lempel Ziv Welch and genetic algorithms for hiding confidential data

Multidimensional Systems and Signal Processing - Digital images are commonly used in steganography due to the popularity of digital image transfer and exchange through the Internet. However, the...     

Synthesis,characterization, and supercapacitor studies of manganese (IV) oxide nanowires

One-dimensional manganese (IV) oxide (MnO₂) (～20 nm in average diameter) were synthesized by cathodic electrodeposition and heat treatment. The mechanism of electrodeposition and nanowire formation were discussed. The product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR). Nanowires with varying lengths and diameters were found in TEM and SEM images of the sample. The results of N₂ adsorption–desorption analysis indicated that the BET surface area of the MnO₂ nanowires was 157 m² g^?1 and the pore size distributions were 2.5 and 4.5 nm. The electrochemical performances of the prepared MnO₂ as an electrode material for supercapacitors were evaluated by cyclic voltammetry and galvanostatic charge/discharge measurements in a solution of 0.5 M Na₂SO₄. The higher specific capacitance of 318 F g^?1 and good capacity retention of 86% were achieved after 1000 charge–discharge cycles had been observed for the MnO₂ nanowires electrode.     

An analytical approach for the inverse scattering solution of radially inhomogeneous spherical bodies using higher order TE and TM illuminations

A novel method for the reconstruction of inhomogeneous permittivity profiles of spherical dielectric objects illuminated by higher order TE/sub mn/ and TM/sub mn/ spherical modes is presented. The overall technique is based on the derivation of Riccati-similar nonlinear differential equations in a spherical coordinate system for both TE and TM illuminations as a part of the direct problem formulation. These differential equations are then inverted using a quasi-linear approach to obtain a closed-form expression of the radially varying permittivity profile of spherical objects in terms of a spherical Fourier-Bessel transform of the measured spectral domain reflection coefficient data. To validate the proposed method, several examples with different mode illuminations and with different noise levels are considered for reconstructions. A good agreement between the actual and the reconstructed permittivity profiles even under high noisy conditions shows that our method is not much sensitive to the presence of noise in the reflection coefficient data.     

On the realization of the current controlled current-mode amplifier using the current controlled conveyor

The current controlled current-mode amplifier proposed by Fabre et al. (1996, IEEE Transactions on Circuits and Systems—I, 43, 82) is reanalysed to show that it can work not only under small signal conditions, as suggested by Fabre et al., but also under large signal conditions. Simulation results which confirm the theory presented are included.     

Analysis of TCP Vegas and TCP Reno

In this paper we use an analytic fluid approach in order to analyze the different features of both Vegas and Reno TCP versions. We then use simulations to confirm our analytic results. When the available bandwidth is high, indeed Vegas can retransmit less than one‐fifth as much data as Reno does, so that the higher the available bandwidth is, the more efficient Vegas is. However, under heavy congestion Vegas behaves like Reno and does not manage to make efficient use of its new mechanism for congestion detection. The analytic results that we obtain are the evolution of the window size, round trip times and their averages, and the average throughput. This revised version was published online in June 2006 with corrections to the Cover Date.     

Video compression using spatiotemporal regularity flow.

We propose a new framework in wavelet video coding to improve the compression rate by exploiting the spatiotemporal regularity of the data. A sequence of images creates a spatiotemporal volume. This volume is said to be regular along the directions in which the pixels vary the least, hence the entropy is the lowest. The wavelet decomposition of regularized data results in a fewer number of significant coefficients, thus yielding a higher compression rate. The directions of regularity of an image sequence depend on both its motion content and spatial structure. We propose the representation of these directions by a 3-D vector field, which we refer to as the spatiotemporal regularity flow (SPREF). SPREF uses splines to approximate the directions of regularity. The compactness of the spline representation results in a low storage overhead for SPREF, which is a desired property in compression applications. Once SPREF directions are known, they can be converted into actual paths along which the data is regular. Directional decomposition of the data along these paths can be further improved by using a special class of wavelet basis called the 3-D orthonormal bandelet basis. SPREF -based video compression not only removes the temporal redundancy, but it also compensates for the spatial redundancy. Our experiments on several standard video sequences demonstrate that the proposed method results in higher compression rates as compared to the standard wavelet based compression.     

A Simple Ultra-Wideband Suspended Stripline Bandpass Filter With Very Wide Stop-Band

This letter introduces a simple ultra-wideband suspended stripline filter with a pass-band from 3.1 to 10.6 GHz and a very wide stop-band up to more than 25 GHz. The filter is realized by capacitive coupling of a quasi-lumped low-pass filter to the I/O ports. Insertion loss in the pass-band is better than 0.5 dB. The filter has a length of 13.8 mm. Excellent agreement is achieved between measured and simulated results.