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Proper design of wireless personal and local area networks requires accurate characterization of radio wave propagation in indoor environments. The Shooting-and-Bouncing-Ray tracing (SBR) method, which uses Geometrical Optics (GO) approximation, has been widely used for indoor propagation modeling [1-2]  

In this study, in order to maximize the reaction rate of neutron activation (NA), an approach using combination of the MCNP code, the feed-forward neural network with the Bayesian regularization (FFNN-BR) learning algorithm, and the genetic algorithm (GA) is proposed. The MCNP code calculates the reaction rates based on the different moderator dimensions/ target positions. The calculated reaction rates with appropriate features (i.e. RT, R2S, and Z2S) are applied for training of the FFNN-BR. The trained neural network is utilized for estimating the reaction rates of the generated individuals by the GA. The results show that the trained neural network estimates the reaction rates with... 

In this study, a method for transient analysis of availability and survivability of a system with the standby components is presented. The availability and survivability of the standby systems is evaluated in two cases, the standby systems with the identical components and the standby systems with the non-identical components. In this study the Markov models, eigen vectors and eigen values for analyzing the transient availability and survivability of the system are employed. The method is implemented through an algorithm which is tested in MATLAB (matrix laboratory) programming environment. The new method enjoys a stronger mathematical foundation and more flexibility for analyzing the... 

This study presents a new ray tracing acceleration technique for site-specific propagation modelling in indoor environments. It overcomes one of the major problems regarding the computational efficiency of shooting-and-bouncing-ray (SBR) method, that is most of the rays emitted from the source do not reach the receiver whereas all of them must be traced. Our proposed method solves this problem in a two-step procedure based on the idea of line search theory. In the first step, called the bracketing phase, the solid angles around the transmitter that transport electromagnetic power to the receiver are determined. In the second step, called the sectioning or zoom phase, the accuracy is improved... 

Site-specific ultrawideband propagation modeling involves dealing with frequency variations of the propagation mechanisms and antenna patterns in the ray tracing program. Typically, electromagnetic field calculations have to be performed in a lot of frequencies to accurately construct the frequency response of the channel at a receiving point. This imposes a heavy computational burden on ray tracing specially in calculating the coverage map or finding the statistics of channel parameters where the number of receiving locations is large. In this paper, the computational complexity of ray tracing in ultrawideband propagation modeling is reduced by using cubic B-spline interpolation. The... 

This study presents the modified wavefront decomposition method as a new ray-tracing acceleration technique for indoor propagation modelling. In this method, the exact propagation paths of the rays that reach the receiver after multiple reflections and/or refractions are calculated. Thus, the electromagnetic field at the receiver is obtained with a high accuracy. When only reflections are considered, our method simplifies to the multiple image theory or shooting and bouncing ray/image approach already available in the literature. However, the modified wavefront decomposition method calculates the exact propagation paths toward the receiver even if the rays encounter multiple refractions or a... 

In site-specific ultrawideband propagation modelling, electromagnetic field calculations need to be performed by ray tracing at numerous frequencies of the band in order to properly include the frequency variations of the propagation mechanisms and antenna patterns. This is computationally intensive especially in calculating the coverage map or finding the statistics of the channel parameters where field calculations need to be carried out at a lot of receiver locations. In this study, the cubic B-spline function is incorporated in ray tracing to increase the computational efficiency of site-specific ultrawideband propagation modelling. This function can accurately reconstruct a signal from... 

This paper presents an efficient way for overcoming the inaccurate path error encountered in ray tracing for site-specific indoor propagation modeling. The source is modeled using triangular ray tubes each of which consists of three rays which do not lie in the same plane. Each possible source ray inside an arbitrary ray tube is expanded in terms of the three rays defining that ray tube. The variations of the expansion coefficients during the intersections of the ray tubes with dielectric media are derived and used for correcting the paths of the rays toward the receiver. A verification example is presented which proves that the presented method has the ability to be efficiently used in... 

In ray-tracing-based propagation modelling, the electromagnetic field at the receiver is obtained by coherent summation of the fields of multipath components. It is therefore crucial to accurately calculate the phase of the electromagnetic field of each ray. In practice, when preparing the plan of the environment for ray tracing simulation, the lateral positions of the walls may not be included accurately in the database. This alters the phases of the fields as well as the delays of arrival of multipath components which may consequently lead to less accurate results. In this study, the sensitivity of ray tracing results to this type of geometrical inaccuracy is investigated through the... 

A new acceleration technique is presented for shooting and bouncing ray tracing in indoor environments. Tracing just a few rays, the algorithm finds the solid angles around the transmitter that transport electromagnetic power to the receiver. The accuracy is then improved by iteratively increasing the tessellation frequency of the source in the power-transporting solid angles. No rays will be sent through non-power-transporting solid angles, which results in significant reduction of the simulation time. An example of applying the method for studying indoor radio wave propagation is presented and the results are compared with a very high-resolution fully three-dimensional (3D) ray tracing... 

This paper applies the method of decomposition of wavefronts to ray tube tracing model. Energy ray tubes which are emitted from the source are modeled by three rays and the method of decomposition of wavefronts iteratively improves the accuracy of ray tracing. Comparison with applying the method of decomposition of wavefronts to conventional ray tracing is made afterwards. It is observed that by applying the method of decomposition of wavefronts to ray tube model, the accuracy of ray tracing can be improved much more efficiently and the simulation time decreases to almost a half. ©2009 IEEE  

This paper presents a new efficient and accurate method to overcome the double-counting problem of ray tracing in indoor environments. The conventional method of modeling the transmitter using an icosahedron inscribed in the unit sphere is used. The separation angle distribution of the source rays over the faces of the icosahedron is calculated prior to the start of the tracing procedure. These angles are used to cancel the double-counting problem in the post processing stage. To validate our proposed method, an electromagnetic problem that has analytical solution is presented and the ray tracing results are compared to this solution. The simulation results agree with analytical solution... 

A new acceleration technique for the ray tracing algorithm was presented in this paper. Instead of reducing the number of intersection tests, our proposed method finds the solid angles around the transmitter that transport electromagnetic power to the receiver. Then, high-resolution rays are sent out only in these solid angles and the procedure continues iteratively. Since a few rays are traced in each iteration, high resolution can be achieved within acceptable amount of time  

The complex dielectric constants of building materials are present in the reflection, transmission and diffraction coefficients of the ray tracing formulation. Any deviation of the dielectric constants included in ray tracing simulation from the actual material properties may be a source of inaccuracy of the simulation results. This paper explores the sensitivity of ray tracing results to the inaccuracy of the dielectric constants of building materials. To do this, the real and imaginary parts of the dielectric constants are considered as random variables to account for the present uncertainty. The propagation of uncertainty in the ray tracing simulation is then obtained by means of the... 

The plan of the environment used in a ray tracing simulation is not usually in exact accordance with the actual environment plan. Errors on the order of several centimeters may be present in describing the lateral wall positions. Such errors are comparable to the wavelength in indoor wireless applications and hence, can severely alter the phases of multipath components and lead to inaccurate electromagnetic field at the receiver. In this paper, the impact of this type of geometrical errors on the ray tracing results is investigated. Lateral wall positions are considered as random variables to account for possible geometrical errors. The statistical moments of some channel parameters are... 

Ray tracing has been widely accepted as a versatile and reliable method for indoor propagation modeling. Several published articles have addressed the computational efficiency and reliability as the most challenging problems of ray tracing and have presented various solutions. Such challenges are discussed in this paper and some possible solutions are presented  

In this study, the Geant4 toolkit is utilized to present a new approach for simulation of the D-T interaction. The neutron production cross-section and the energy/angle distribution of neutrons produced as the D-T data libraries are incorporated in the Geant4, and their performance is evaluated. The spectra shape of the produced neutrons of the D-T interaction simulated by the Geant4 show good agreement compared to the results of the comparative codes (i.e. MCUNED, ENEA-JSI, and DDT). However, some differences are observed, especially, in angular range of 90-95 degrees. The reason for these differences as well as the results of the proposed approach in comparison with the results of the... 

Ease of use, high flexibility and variety of applications have made wireless sensor networks very popular. Node placement in a sensor network is very critical since it affects important network attributes such as coverage, lifetime, and reliability. Therefore, controlled node placement is necessary for achieving specific network features with minimum number of nodes. Since node placement is an NP-hard problem, many placement algorithms have been proposed based on heuristic and meta-heuristic methods. Most of those algorithms assume a uniform event pattern (UEP) throughout the area under investigation. However, in practice some networks deal with non-uniform event pattern (NEP). Optimization... 

The wide range of wireless sensor network applications has made it an interesting subject for many studies. One area of research is the controlled node placement in which the location of nodes is not random but predetermined. Controlled node placement can be very effective when either the price of the sensor nodes is high or the sensor coverage is of a specific type and it is necessary to provide special characteristics such as coverage, lifetime, reliability, delay, efficiency or other performance aspects of a wireless sensor network by using the minimum number of nodes. Since node placement algorithms are NP-Hard problems, and characteristics of a network are often in conflict with each...