Autonomous underwater vehicles (AUVs) have many scientific, military, and commercial applications because of their potential capabilities and significant cost-performance improvements over traditional means for perfor...
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Autonomous underwater vehicles (AUVs) have many scientific, military, and commercial applications because of their potential capabilities and significant cost-performance improvements over traditional means for performing search and survey. The development of a reliable sampling platform requires a thorough system design and many costly at-sea trials during which systems specifications can be validated. modeling and simulation provides a cost-effective measure to carry out preliminary component, system (hardware and software), and mission testing and verification, thereby reducing the number of potential failures in at-sea trials. An accurate simulation can help engineers to find hidden errors in the AUV embedded software and gain insights into the AUV operations and dynamics. This paper reviews our research work on real-time physics-based modeling and simulation for our AUVs. The modeling component includes vehicle dynamics, environment and sensor characteristics. The simulation component consists of stand-alone versus hardware-in-the-loop (HIL) implementation, for both single as well as multiple vehicles. In particular, implementation issues with regard to multitasking system resources will be addressed. The main contribution of this paper is to present the rationale for our simulation architecture and the lessons learned.
Uncontrolled and spontaneous decomposition of methane hydrates in ocean floors can pose risks and potential problems, including damage to equipment that extracts fuel from underwater" tanks. Since one of the main...
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Uncontrolled and spontaneous decomposition of methane hydrates in ocean floors can pose risks and potential problems, including damage to equipment that extracts fuel from underwater" tanks. Since one of the main factors in hydrate decompositions is their heat up by oil and gas extraction and transportation pipes, this heating and decomposition of it are examined in this, paper. After introduction to control volume and mathematical modeling, the developed equations of math model were solved via orthogonal collocation and finite element method and the results were compared. The results concluded to decomposed hydrate volume, released gas volume and its relevant pressure on sediment layer. In this research, the effect of gas flow velocity in pipes, porosity of sediment layers and thermal conductivity constant in pipes on two important parameter of volume of hydrate and its decomposition pattern were studied and it was realized that rising gas velocity in pipe could increase the volume of decomposed hydrate. A side of this enhancing the porosity leads to reduce the radius and volume of decomposed hydrate. Furthermore enhancing the porosity could increase conduction coefficient of heat transfer in gas media, as the increased velocity of gas shows similar effect on heat transfer rate and hydrate decomposition. (C) 2016 Elsevier B.V. All rights reserved.
This article presents a modeling and simulation methodology to analyze the performance of voice quality when sent over the available bit rate service in asynchronous transfer mode networks. Sources can modify the rate...
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This article presents a modeling and simulation methodology to analyze the performance of voice quality when sent over the available bit rate service in asynchronous transfer mode networks. Sources can modify the rate at which they send traffic to the network based on the feedback carried in the resource management cells. This is achieved by changing the encoding level. As the contention increases to network resources-bandwidth in this case-sources start reducing the rate at which they generate and send traffic. The efficiency of the scheme under different scheduling/drop policies and other operating conditions and environments is evaluated using simulationmodeling. Furthermore, sensitivity analysis is applied to different parameters, such as queue size and averaging interval length, to investigate their impact on the performance metrics. Results show that limiting the load to 41 % of the link capacity results in an acceptable quality.
Under thermal constraints of process technology, discontinuous stable/metastable high strained layer configurations in Si/SiGe/Si HBT arrays can partly relax via misfit dislocation generation. The physical modeling of...
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Under thermal constraints of process technology, discontinuous stable/metastable high strained layer configurations in Si/SiGe/Si HBT arrays can partly relax via misfit dislocation generation. The physical modeling of creep in SiGe layer stacks proposed here is able to predict their coherency and relaxation behavior and to provide guidance for device simulation. (C) 1998 Elsevier Science B.V.
Biodegradation kinetics of different polyaromatic sulfur heterocyclic compounds (PASHs): thiophene (Th), benzothiophene (BT), and dibenzothiophene (DBT) in a series of batch experiments were investigated as mono-, bin...
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Biodegradation kinetics of different polyaromatic sulfur heterocyclic compounds (PASHs): thiophene (Th), benzothiophene (BT), and dibenzothiophene (DBT) in a series of batch experiments were investigated as mono-, binary-, and tertiary-substrate systems to study the substrates interaction effect and capabilities of Bacillus sphaericus HN1 to utilize PASHs as sole carbon and energy source in mono-and multi-substrate systems. A multiple comparison test was performed for growth of microorganism and substrate biodegradation to obtain pairwise comparison between the three studied systems. Both tests ANOVA1 and Kruskal-Wallis showed that there was a highly statistically significant difference in growth of HN1 between negative control (free of PASHs) and all other treatments (p = 2.2105e-7 and 9.303e-4, respectively). Although, there was a statistically significant difference for biodegradation of DBT in mono- and binary- substrate systems within the time interval 96-168 h (p < 0.05), but there was a nonstatistically significant difference in the biodegradation of both Th and BT in the three studied systems (p > 0.05). A multi-substrate form of the Monod kinetic model was applied to predict the substrate interactions in binary- and tertiary-substrate systems using the Monod parameters derived from the mono- substrate systems. simulation of the applied models to describe and estimate the biodegradation kinetics of the three studied PASHs in the different investigated systems was performed and the validity of the models was confirmed.
We study the collective vibrational breathing modes in the Raman spectrum of multiwalled carbon nanotubes (MCNTs). First, a bond polarization theory and the spectral moment's method (SMM) are used to calculate the...
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We study the collective vibrational breathing modes in the Raman spectrum of multiwalled carbon nanotubes (MCNTs). First, a bond polarization theory and the spectral moment's method (SMM) are used to calculate the non-resonant Raman frequencies of the breathing-like modes (BLMs) and the tangentiallike ones (TLMs). Second, the Raman active modes of MCNTs are computed for different diameters and numbers of layers. The obtained low frequency modes in MCNTs can be identified to each single-walled carbon nanotubes. These modes that originate from the radial breathing ones of the individual walls are strongly coupled through the concentric tube-tube van der Waals interaction. The calculated BLMs in the low-frequency region are compared with the experimental Raman data obtained from other studies. Finally, special attention is given to the comparison with Raman data on MCNTs composed of six layers. (C) 2013 Elsevier B.V. All rights reserved.
We developed a plasma etching simulation with our new concept in order to predict the distribution of plasma-induced damage during contact hole etching of SiO2 over Si substrate using fluorocarbon plasma (C4F8/O-2/Ar)...
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We developed a plasma etching simulation with our new concept in order to predict the distribution of plasma-induced damage during contact hole etching of SiO2 over Si substrate using fluorocarbon plasma (C4F8/O-2/Ar). Our model included plasma database, gas transport (direct and indirect fluxes of ions and radicals), surface reaction considering depth effect, and damage distribution. We could demonstrate how to evolve the Si damage in main and overetching steps, which is realistically difficult to measure. Our results show that polymer thickness, overetching time, and etched profile should be carefully controlled to reduce physical damage. (C) 2012 The Japan Society of Applied Physics
The design of the next generation of aeronautical vehicles is driven by the vastly increased cost of fuel and the resultant imperative for greater fuel efficiency. Carbon fiber composites have been used in aeronautica...
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The design of the next generation of aeronautical vehicles is driven by the vastly increased cost of fuel and the resultant imperative for greater fuel efficiency. Carbon fiber composites have been used in aeronautical structures to lower weight due to their superior stiffness and strength-to-weight properties. However, carbon composite material behavior under dynamic ballistic impact and blast loading conditions is relatively unknown. For aviation safety consideration, a computational constitutive model has been used to characterize the progressive failure behavior of carbon laminated composite plates subjected to ballistic impact and blast loading conditions. Using a meso-mechanics approach, a laminated composite is represented by a collection of selected numbers of representative unidirectional layers with proper layup configurations. The damage progression in a unidirectional layer is assumed to be governed by the strain-rate-dependent layer progressive failure model using the continuum damage mechanics approach. The composite failure model has been successfully implemented within LS-DYNA (R) as a user-defined material subroutine. In this paper, the ballistic limit velocity (V-50) was first established for a series of laminates by ballistic impact testing. Correlation of the predicted and measured V-50 values has been conducted to validate the accuracy of the ballistic modeling approach for the selected carbon composite material. A series of close-in shock hole blast tests on carbon composite panels were then tested and simulated using the LS-DYNA (R) Arbitrary-Lagrangian-Eulerian (ALE) method integrated with the Army Research Laboratory (ARL) progressive failure composite model. The computational constitutive model has been validated to characterize the progressive failure behavior in carbon laminates subjected to close-in blast loading conditions with reasonable accuracy. The availability of this modeling tool will greatly facilitate the development of carbon
A polymer electrolyte membrane (PEM) fuel cell is analyzed by applying the conservation principle to the electrode backing, catalyst layers and polymer electrolyte. The conservation equations used are the conservation...
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A polymer electrolyte membrane (PEM) fuel cell is analyzed by applying the conservation principle to the electrode backing, catalyst layers and polymer electrolyte. The conservation equations used are the conservation of species, momentum and energy, with the Nernst-Planck equation used for the electrolyte. Oxygen reduction at the cathode is modeled using the Butler-Volmer equation while the adsorption, desorption and electrooxidation of hydrogen and CO at the anode are modeled by the Tafel-Volmer and "reactant-pair "mechanism, respectively. Temperature variations within the cell are minimized by decreasing current density or increasing temperature. An increase in pressure increases the cell voltage at low current density, but decreases the cell voltage at high current density. The electrochemical kinetics model used for the adsorption, desorption and electro-oxidation of hydrogen and CO is validated with published, experimental data.
During the past decades significant progress has been made in our understanding of the importance of age-appropriate development of new drug therapies in children. Importantly, several regulatory initiatives in Europe...
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During the past decades significant progress has been made in our understanding of the importance of age-appropriate development of new drug therapies in children. Importantly, several regulatory initiatives in Europe and the US have provided a framework for a rationale. In the US, most notably the enactment of the Best Pharmaceuticals for Children Act (BPCA) and Product Research and Equity Act (PREA) has facilitated the studying of on-patent and off-patent drugs in children. The biggest challenge in pediatric studies is defining a safe and effective dose or dose range in a patient population that can span from premature neonates to adolescents. From a mechanism-based perspective, advances in the science of quantitative pharmacology and pharmacometrics have resulted in the development of model-based approaches to better describe and understand important age-related factors influencing drug disposition and response in pediatric patients. The application of modeling and simulation has been shown to result in better estimates of pediatric doses as evidenced by several studies, although the optimal approach is still being debated. The extrapolation of efficacy findings from adults to the pediatric population has streamlined the development process especially for studies in older children. However, a focus on developmental changes in neonates and infants as well as further developing a paradigm for conducting pharmacodynamic studies in neonates, infants, and children remain important unmet needs. In this overview we will review current approaches for age-appropriate dose selection and highlight ongoing efforts to define exposure-response and clinical outcome relationships across the pediatric age spectrum.
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