Ground plane impact on quadrifilar helix antenna performance with respect to deployment heights

Quadrifilar helix antenna (QHA) has its applications in satellite communications. This paper presents the performance optimisation of input and radiation characteristics of QHA in the presence of infinite and finite metallic ground planes. For the infinite ground plane, it has been observed that input parameters such as impedance and voltage standing wave ratio (VSWR) are stable, and the antenna has broader half power beamwidth (HPBW). Smaller metallic platforms that act as finite ground planes produce better 3‐dB axial ratio beamwidth and boresight axial ratio. Deployment of QHA on smaller metallic platforms such as nanosatellites and CubeSats enhances the circularly polarised beamwidth of the antenna with improved boresight axial ratio. However, on large low earth orbit (LEO) satellites, stable input characteristics and broader HPBW have been achieved at the cost of narrow circularly polarised beamwidth and degraded boresight axial ratio.     

System-level reliability assessment of mixed-signal convergent microsystems

The next-generation convergent microsystems, based on system-on-package (SOP) technology, require up-front system-level design-for-reliability approaches and appropriate reliability assessment methodologies to guarantee the reliability of digital, optical, and radio frequency (RF) functions, as well as their interfaces. Systems approach to reliability requires the development of: i) physics-based reliability models for various failure mechanisms associated with digital, optical, and RF Functions, and their interfaces in the system; ii) design optimization models for the selection of suitable materials and processing conditions for reliability, as well as functionality; and iii) system-level reliability models understanding the component and functional interaction. This paper presents the reliability assessment of digital, optical, and RF functions in SOP-based microsystems. Upfront physics-based design-for-reliability models for various functional failure mechanisms are presented to evaluate various design options and material selection even before the prototypes are made. Advanced modeling methodologies and algorithms to accommodate material length scale effects due to enhanced system integration and miniaturization are presented. System-level mixed-signal reliability is discussed thorough system-level reliability metrics relating component-level failure mechanisms to system-level signal integrity, as well as statistical aspects.     

A new radix-2/8 FFT algorithm for length-q/spl times/2/sup m/ DFTs

In this paper, a new radix-2/8 fast Fourier transform (FFT) algorithm is proposed for computing the discrete Fourier transform of an arbitrary length N=q/spl times/2/sup m/, where q is an odd integer. It reduces substantially the operations such as data transfer, address generation, and twiddle factor evaluation or access to the lookup table, which contribute significantly to the execution time of FFT algorithms. It is shown that the arithmetic complexity (multiplications+additions) of the proposed algorithm is, in most cases, the same as that of the existing split-radix FFT algorithm. The basic idea behind the proposed algorithm is the use of a mixture of radix-2 and radix-8 index maps. The algorithm is expressed in a simple matrix form, thereby facilitating an easy implementation of the algorithm, and allowing for an extension to the multidimensional case. For the structural complexity, the important properties of the Cooley-Tukey approach such as the use of the butterfly scheme and in-place computation are preserved by the proposed algorithm.     

New windowing techniques for variable-size block motioncompensation

The conventional overlapped block motion compensation (OBMC) technique, although effective in reducing the blocking effect for fixed-size partitioned frames, cannot be readily used for a frame partitioned region-wise or using variable-size blocks. The generalised OBMC (GOBMC) method, even though generally applicable, is not very effective in reducing the blocking effect and prediction error. Two windowing techniques are presented to reduce the blocking effect for a frame partitioned region-wise or using variable-size blocks. In the first technique, a virtual re-partitioning operation is employed, which maps a partitioned frame into its corresponding fully partitioned frame at the bottom level of the quadtree so that each resulting block has eight neighbouring blocks. In the second technique, the virtual re-partitioning operation for a given block (region) is carried out adaptively and performed locally; however, blocks (regions) need not always be virtually partitioned to the bottom level. Compared to the GOBMC method, the proposed techniques make use of more pixels in the close vicinity of boundaries of the regions in the windowing operation. Simulation results are included of applying the proposed techniques on a number of MPEG video sequences. These results indicate that the proposed techniques are superior to the GOBMC method in terms of reducing the prediction error as well as the blocking effect     

Bit-serial window partitioning algorithm for stack filtering

The authors introduce a new bit-serial algorithm for stack filtering, designated as the bit-serial window partitioning algorithm. It is shown that the proposed algorithm can achieve very important savings over the conventional bit-serial binary-tree search algorithm, in terms of the computational speed. This improved efficiency is obtained by evaluating the Boolean function at thresholds corresponding to the sample values within the filter window, and by taking advantage of the ordering information associated with the threshold sequences     

Prospects and challenges of using hydropower for electricity generation in Lebanon

In a region characterized by low water resources, Lebanon stands as an exceptional country in the Middle East. Several waterways present ample opportunity for utilization of hydropower. Before the civil war, several projects were undertaken to generate electricity through hydropower. A total installed capacity of 283 MW has aided Lebanon in supplementing its need of electricity from local renewable sources, thus reducing the overall bill of imported energy. The available hydropower generation constitutes currently 4–7% of the electricity generation depending on rainfall, with future plans expected to install another 205 MW of capacity. This use is in competition with water diversion for irrigation. Four different scenarios were analyzed to indicate the share of hydropower in the total production of electricity, with and without future irrigation and power projects, indicating that, by 2020, hydropower's share of electricity generation will vary between a maximum of 6.9% and a minimum of 1.2% depending on government plans regarding water use. Current value of potential energy available when water from the Litani river is used for hydropower is estimated to be around 20 cents per m³. Water uses planned should take this value into account.     

A Molecular Dynamics Study of Description Models for Shear Viscosity in Nanochannels: Mixtures and Effect of Temperature

Equilibrium molecular dynamics simulation was utilized to calculate the shear viscosity of monoatomic molecules liquid flow confined in a nanochannel in the pure state and their binary mixtures. The pure flow viscosity data of argon, krypton, and xenon were used to predict their binary mixture viscosities using prediction methods proposed in the literature. Each method was evaluated by comparison of its results with those obtained by validated molecular dynamics simulation at different temperatures. In addition, correlative methods for mixture viscosity estimation and temperature dependence models were evaluated and corresponding model parameters were obtained. Moreover, the relations representing mixture parameter values as a function of the pure ones were determined and evaluated according to their accuracy.     

Analytical expressions for intermodulation distortion of a MESFET small-signal amplifier using the nonlinear Volterra series

Using the nonlinear Volterra series representation, analytical expressions for the third-order intermodulation distortion power and intercept point for a MESFET small-signal amplifier are derived when its equivalent circuit is bilateral and includes the gate-to-drain capacitance (C_gd) explicitly as a nonlinear element. Previously developed analytical expressions treated C_gd as a linear element or incorporated it as a part of gate-to-source and drain-to-source capacitances (C_gs and C_ds). These new analytical expressions are then compared with experimental data and good agreement is obtained. The analytical expressions are also used to study the variation of intermodulation distortion with input power and frequency, and the effect of the individual nonlinear elements in the MESFET’s equivalent circuit.     

Multilayer Partially Homomorphic Encryption Text Steganography (MLPHE-TS): A Zero Steganography Approach

Wireless Personal Communications - This paper presents a Multilayer Partially Homomorphic Encryption Text Steganography, an invisible approach for covert communication. Existing text-based schemes...