A Model for Analyzing the Performance of Wireless Multi-Hop Networks using a Contention-based CSMA/CA Strategy

( Sajid M. Sheikh ),( Riaan Wolhuter ),( Herman A. Engelbrecht ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.5

Multi-hop networks are a low-setup-cost solution for enlarging an area of network coverage through multi-hop routing. Carrier sense multiple access with collision avoidance (CSMA/CA) is frequently used in multi-hop networks. Multi-hop networks face multiple problems, such as a rise in contention for the medium, and packet loss under heavy-load, saturated conditions, which consumes more bandwidth due to re-transmissions. The number of re-transmissions carried out in a multi-hop network plays a major role in the achievable quality of service (QoS). This paper presents a statistical, analytical model for the end-to-end delay of contention-based medium access control (MAC) strategies. These strategies schedule a packet before performing the back-off contention for both differentiated heterogeneous data and homogeneous data under saturation conditions. The analytical model is an application of Markov chain theory and queuing theory. The M/M/1 model is used to derive access queue waiting times, and an absorbing Markov chain is used to determine the expected number of re-transmissions in a multi-hop scenario. This is then used to calculate the expected end-to-end delay. The prediction by the proposed model is compared to the simulation results, and shows close correlation for the different test cases with different arrival rates.

Development of ENDF/B-VII.1 and its covariance component

M. Herman 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23

The US nuclear data community, coordinated by CSEWG, is preparing release of the ENDF/B-VII.1 library. This new release will address deficiencies identified in ENDF/B-VII.0, include improved evaluations for some 50-60 materials and provide covariances for more than 110 materials. The major players in this undertaking are LANL, BNL, ORNL, and LLNL. We summarize deficiencies in the ENDF/B-VII.0 and outline development of the new library. We concentrate on the BNL activities which aim in providing covariances for the materials important for the design of the innovative reactors. Finally we outline a futuristic approach, known as \emph{assimilation} that tries to link nuclear reaction theory and integral experiments.

International Cooperation in Nuclear Data Evaluation

M. Herman,J. Katakura,A. J. Koning,C. Nordborg 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23

The OECD Nuclear Energy Agency (NEA) is organising a co-operation between the major nuclear data evaluation projects in the world. The co-operation involves the ENDF, JEFF, and JENDL projects, and, owing to the collaboration with the International Atomic Energy Agency (IAEA), also the Russian BROND and the Chinese CENDL projects. The Working Party on international nuclear data Evaluation Cooperation (WPEC), comprised of about 20 core members, manages this co-operation and meets annually to discuss progress in each evaluation project and also related experimental activities. The WPEC assesses common needs for nuclear data improvements and these needs are then addressed by initiating joint evaluation efforts. The work is performed in specially established subgroups, consisting of experts from the participating evaluation projects. The outcome of these subgroups is published in reports, issued by the NEA. Current WPEC activities comprise for example a number of studies related tonuclear data uncertainties, including a review of methods for the combined use of integral experiments and covariance data, as well as evaluations of some of the major actinides, such as ^(235)U and ^(239)Pu. This paper gives an overview of current and planned activities within the WPEC.

Nuclear Data Target Accuracies for Generation-IV Systems Based on the Use of New Covariance Data

G. Palmiotti,M. Assawaroongruengchot,M. Salvatores,M. Herman,P. Oblozinsky,C. Mattoon,M. Pigni 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23

A target accuracy assessment using new available covariance data, the AFCI 1.2 covariance data, has been carried out. At the same time, the more theoretical issue of taking into account correlation terms in target accuracy assessment studies has been deeply investigated. The impact of correlation terms is very significant in target accuracy assessment evaluation and can produce very stringent requirements on nuclear data. For this type of study a broader energy group structure should be used, in order to smooth out requirements and provide better feedback information to evaluators and cross section measurement experts. The main difference in results between using BOLNA or AFCI 1.2 covariance data are related to minor actinides, minor Pu isotopes, structural materials (in particular Fe56), and coolant isotopes (Na23) accuracy requirements.

Use of Covariance Matrices in a Consistent (Multiscale) Data Assimilation for Improvement of Basic Nuclear Parameters in Nuclear Reactor Applications: from Meters to Femtometers

G. Palmiotti,H. Hiruta,M. Salvatores,M. Herman,P. Oblozinsky,M. T. Pigni 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23

A new approach is proposed, the consistent data assimilation, that allows to link the integral data experiment results to basic nuclear parameters employed by evaluators to generate ENDF/B point energy files in order to improve them. A practical example is provided where the sodium neutron propagation experiments, EURACOS and JANUS-8, are used to improve via modifications of ^(23)Na nuclear parameters (like scattering radius, resonance parameters, Optical model parameters, Statistical Hauser-Feshbach model parameters, and Preequilibrium Exciton model parameters) the agreement of calculation versus experiments for a series of measured reaction rate detectors slopes. Future work involves comparison of results against a more traditional multigroup adjustments, and extension to other isotope of interest in the reactor community as ^(56)Fe, actinides, and fission products.

Adaptive Super Twisting Control of a Dual-rotor VTOL Flight System Under Model Uncertainties

Jorge M. Arizaga,Jose. R. Noriega,L. A. Garcia-Delgado,Herman Castaneda 제어·로봇·시스템학회 2021 International Journal of Control, Automation, and Vol.19 No.6

This paper addresses an adaptive super twisting control for a dual-rotor flight system subject to uncertainties. The system can perform vertical take-off and landing, roll and yaw movements. The dynamical model is described under the Euler-Lagrange approach, where a characterization of the thrust and the torque of the rotors is included. However, uncertainties such as friction and unmodeled dynamics remain. To overcome these problems, a class of adaptive sliding mode control is designed, which is robust to bounded uncertainties and external perturbations, offers reduced chattering, and not overestimate the control gain. Furthermore, the closed-loop stability is analyzed. Finally, simulation and experimental validation, and a comparison versus other standard control approaches illustrate the feasibility and usefulness of the proposed controller.

A new finite element procedure for fatigue life prediction of AL6061 plates under multiaxial loadings

Wasim Tarar,M.-H. Herman Shen,Tommy George,Charles Cross 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.35 No.5

An energy-based fatigue life prediction framework was previously developed by the authors for prediction of axial, bending and shear fatigue life at various stress ratios. The framework for the prediction of fatigue life via energy analysis was based on a new constitutive law, which states the following: the amount of energy required to fracture a material is constant. In the first part of this study, energy expressions that construct the constitutive law are equated in the form of total strain energy and the distortion energy dissipated in a fatigue cycle. The resulting equation is further evaluated to acquire the equivalent stress per cycle using energy based methodologies. The equivalent stress expressions are developed both for biaxial and multiaxial fatigue loads and are used to predict the number of cycles to failure based on previously developed prediction criterion. The equivalent stress expressions developed in this study are further used in a new finite element procedure to predict the fatigue life for two and three dimensional structures. In the second part of this study, a new Quadrilateral fatigue finite element is developed through integration of constitutive law into minimum potential energy formulation. This new QUAD-4 element is capable of simulating biaxial fatigue problems. The final output of this finite element analysis both using equivalent stress approach and using the new QUAD-4 fatigue element, is in the form of number of cycles to failure for each element on a scale in ascending or descending order. Therefore, the new finite element framework can provide the number of cycles to failure at each location in gas turbine engine structural components. In order to obtain experimental data for comparison, an Al6061-T6 plate is tested using a previously developed vibration based testing framework. The finite element analysis is performed for Al6061-T6 aluminum and the results are compared with experimental results.

A new finite element procedure for fatigue life prediction of AL6061 plates under multiaxial loadings

Tarar, Wasim,Herman Shen, M.H.,George, Tommy,Cross, Charles Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.35 No.5

An energy-based fatigue life prediction framework was previously developed by the authors for prediction of axial, bending and shear fatigue life at various stress ratios. The framework for the prediction of fatigue life via energy analysis was based on a new constitutive law, which states the following: the amount of energy required to fracture a material is constant. In the first part of this study, energy expressions that construct the constitutive law are equated in the form of total strain energy and the distortion energy dissipated in a fatigue cycle. The resulting equation is further evaluated to acquire the equivalent stress per cycle using energy based methodologies. The equivalent stress expressions are developed both for biaxial and multiaxial fatigue loads and are used to predict the number of cycles to failure based on previously developed prediction criterion. The equivalent stress expressions developed in this study are further used in a new finite element procedure to predict the fatigue life for two and three dimensional structures. In the second part of this study, a new Quadrilateral fatigue finite element is developed through integration of constitutive law into minimum potential energy formulation. This new QUAD-4 element is capable of simulating biaxial fatigue problems. The final output of this finite element analysis both using equivalent stress approach and using the new QUAD-4 fatigue element, is in the form of number of cycles to failure for each element on a scale in ascending or descending order. Therefore, the new finite element framework can provide the number of cycles to failure at each location in gas turbine engine structural components. In order to obtain experimental data for comparison, an Al6061-T6 plate is tested using a previously developed vibration based testing framework. The finite element analysis is performed for Al6061-T6 aluminum and the results are compared with experimental results.

Effect of Film Thickness on Structural, Electrical, and Optical Properties of Sol-Gel Deposited Layer-by-layer ZnO Nanoparticles

S. S. Shariffudin,M. Salina,S. H. Herman,M. Rusop 한국전기전자재료학회 2012 Transactions on Electrical and Electronic Material Vol.13 No.2

The structural, electrical, and optical properties of layer-by-layer ZnO nanoparticles deposited using sol-gel spin coating technique were studied and now presented. Thicknesses of the thin films were varied by increasing the number of deposited layers. As part of our characterization process, XRD and FE-SEM were used to characterize the structural properties, current-voltage measurements for the electrical properties, and UV-Vis spectra and photoluminescence spectra for the optical properties of the ZnO thin films. ZnO thin films with thicknesses ranging from 14.2 nm to 62.7 nm were used in this work. Film with thickness of 42.7 nm gave the lowest resistivity among all,1.39×10-2 Ω·cm. Photoluminescence spectra showed two peaks which were in the UV emission centered at 380 nm,and visible emission centered at 590 nm. Optical transmittance spectra of the samples indicated that all films were transparent (>88%) in the visible-NIR range. The optical band gap energy was estimated to be 3.21~3.26 eV, with band gap increased with the thin film thickness.

Effect of Film Thickness on Structural, Electrical, and Optical Properties of Sol-Gel Deposited Layer-by-layer ZnO Nanoparticles

Shariffudin, S.S.,Salina, M.,Herman, S.H.,Rusop, M. The Korean Institute of Electrical and Electronic 2012 Transactions on Electrical and Electronic Material Vol.13 No.2

The structural, electrical, and optical properties of layer-by-layer ZnO nanoparticles deposited using sol-gel spin coating technique were studied and now presented. Thicknesses of the thin films were varied by increasing the number of deposited layers. As part of our characterization process, XRD and FE-SEM were used to characterize the structural properties, current-voltage measurements for the electrical properties, and UV-Vis spectra and photoluminescence spectra for the optical properties of the ZnO thin films. ZnO thin films with thicknesses ranging from 14.2 nm to 62.7 nm were used in this work. Film with thickness of 42.7 nm gave the lowest resistivity among all, $1.39{\times}10^{-2}{\Omega}{\cdot}cm$. Photoluminescence spectra showed two peaks which were in the UV emission centered at 380 nm, and visible emission centered at 590 nm. Optical transmittance spectra of the samples indicated that all films were transparent (>88%) in the visible-NIR range. The optical band gap energy was estimated to be 3.21~3.26 eV, with band gap increased with the thin film thickness.