Performance analysis of equal-gain diversity receivers over generalized Gamma fading channels

Generalized Gamma (GG) distribution is a generic model that covers many well-known fading distributions as special cases. This paper deals with the performance analysis of L-branch equal gain combining (EGC) receivers operating over GG fading channels. For these receivers and by using convergent infinite series approach, the probability of error (P_e) can be formulated in the form of an infinite series. The coefficients of P_e series can be derived by calculating complicated integrations over the fading envelope distribution. In this paper, it is shown that the required integrations for the case of GG distribution have a complex closed-form in terms of Meijer's G function, and then, a new approximation method is developed for computation of them. The proposed method only needs mean and variance of the fading envelope; hence it has low complexity and eliminates the need for calculation of complex functions. The presented numerical examples show that the developed method can approximate the required parameters and also the individual coefficients accurately and this accuracy increases with the increase of L. The proposed method is applied to analyze the probability of error performance of the L-branch EGC receiver with both coherent phase shift keying (CPSK) and frequency shift keying (CFSK) modulation schemes under different GG channel conditions. Also the effect of gain unbalance between diversity branches on the probability of error is investigated.     

New robust and efficient ant colony algorithms: Using new interpretation of local updating process

Two new efficient and robust ant colony algorithms are proposed. These algorithms contain two new and reasonable local updating rules that make them more efficient and robust. While going forward from start point to end point of a tour, the ants’ freedom to make local changes on links is gradually restricted. This idea is implemented in two different forms, leaving two new algorithms, KCC-Ants and ELU-Ants. To evaluate the new algorithms, we run them along with the old one on the standard TSP library, where in almost all of the cases the proposed algorithms had better solutions and even for some problem samples found the optimal solution.     

An approximate analytical framework for performance analysis of equal gain combining technique over independent Nakagami,Rician and Weibull fading channels

In this paper, an approximate analytical method for performance analysis of equal gain combiner (EGC) receiver over independent Nakagami and Rician fading channels is presented. We use a convergent infinite series approach which makes it possible to describe the probability of error of EGC receiver in the form of an infinite series. In this paper, we develop a new approximation method for computation of the required coefficients in this series which lets us to derive simple analytical closed-form expressions with good accuracy compared with the exact results existing in the literatures. Our proposed approximation method only needs the mean and the variance of the fading envelope, which are known for various fading distributions, and hence, bypasses the required integration over the fading envelope distribution while computing the required coefficients. This feature lets us to extend our approximation method for performance analysis of EGC receiver over independent Weibull fading channels where the required integration has not any closed-form or tabulated solutions. To give an application of our developed method, we analyze the probability of error of an EGC receiver for binary, coherent PSK (CPSK) modulation over independent Nakagami, Rician and weibull fading channels and study the effect of the fading conditions on the system performance.     

The modified Beckmann-Kirchhoff scattering theory for rough surface analysis

This paper focusses on how reflectance models based on scattering theory and reported in the physics literature can be used for making estimates of surface roughness parameters using reflectance measurements obtained with a digital camera. We commence by reviewing the Beckmann-Kirchhoff (B-K) scatter theory, and the recent modification to it by Vernold and Harvey. We show how this model can be used to estimate surface roughness parameters for dielectric surfaces using pixel brightness measurements. Using the roughness parameter measurements we compare the model with reflectance measurements from the CUReT database. This comparison shows that the Vernold-Harvey modification of the B-K model gives a better fit to data than the Oren-Nayar model for certain types of rough surface.     

A simple approach for determining detonation velocity of high explosive at any loading density

A simple empirical relationship is introduced between detonation velocity at any loading density and chemical composition of high explosive as well as its gas phase heat of formation, which is calculated by group additivity rules. The present work may be applied to any explosive that contains the elements of carbon, hydrogen, nitrogen and oxygen with no difficulties. The new correlation can easily be applied for determining detonation velocity of explosives with loading densities less than 1g/cm3 as well as greater than 1g/cm3. Calculated detonation velocities by this procedure for both pure and explosive formulations show good agreement with respect to measured detonation velocity over a wide range of loading density.     

A Hybrid Approach to Nonconformance Tracking and Recovery

The nonconformance diagnosis problem has been a major issue facing industry and academia over the years. Research has been carried out on technologies for different aspects of nonconformance diagnosis such as nonconformance monitoring, prediction, prevention, classification, tracking, and recovery. Despite these advances, nonconformance tracking and recovery still receive many concerns due to the fact that they are knowledge intensive and experience-based tasks, which in complex manufacturing environments can sometimes be beyond the capabilities of skilled operators and engineers. In addition, the existing systems for nonconformance tracking and recovery are usually special purpose systems. They lack the capabilities to migrate to new working domains. This paper proposes a generic intelligent nonconformance tracking and recovery (GINTR) system. In conjunction with computational intelligent techniques such as Artificial Neural Networks (ANN) and Genetic Algorithm (GA), the system identifies the root causes of a nonconformance and provides timely corrective actions. The drive towards designing such a system is motivated by the need to implement a generic base of system capabilities that is reliable, economical, scalable, and provides a stable foundation for migrating the system to different domains.     

THERMOCAPILLARY MIGRATION OF SLIGHTLY DEFORMED DROPLETS

A small viscous droplet which is suspended in an immiscible liquid in a zero-gravity environment can be made to migrate by subjecting the system to an external temperature gradient. This so-called thermocapillary migration occurs since the surface tension of the interface is a function of temperature. If inertial effects are negligible and the interface is clean, the shape of the migrating droplet remains spherical. However, when inertial effects are significant or when surfactants are present at the interface, the droplet assumes a prolate or oblate spheroidal shape. In this work we calculate the change in the net migration velocity of the droplet which results from such a deformation. This is done by solving the requisite viscous flow problem in the deformed geometry by perturbation, in conjunction with a generalization of the so-called Lorentz reciprocal theorem which simplifies the calculations. It is found that the migration velocity could increase, decrease or remain unchanged depending on the values of certain controlling parameters.     

Numerical methods for transient solutions of machine repair problems

This paper reviews and compares two types of numerical methods of computing transient probabilities of finite Markovian queues (particularly the machine repair problem). A brief review of each method is followed by numerical examples of small and moderate size machine repair problems. The results demonstrate the feasibility of applying numerical techniques for obtaining transient solutions to Markovian queueing problems.     

Stresses in buried conduits caused by freezing front

A laboratory experiment modeling the buried conduit problem was performed to study the stress changes in the conduit as a result of frost penetration in the soil. The model consisted of a large-scale soil container insulated on all sides except the top. The level and temperature of the ground water in the container, and the end restraints of the buried conduit, could be controlled. The model was placed in a cold room where the air temperature could be reduced to ?25°C. The experimental results, supplemented by the available field data, demonstrate the influence of soil freezing on pipe bending stresses. Maximum frost depth, which can vary with the rate of freezing even for comparable air freezing indexes, is a significant soil thermal parameter that correlates with pipe stresses. Availability of ground water significantly increases pipe stresses while pipe-end restraints tend to decrease them slightly. The results suggest that the water expulsion by the advancing freezing front causes loss of soil stiffness due to the increased pore water pressures and decreased effective stresses in the soil.