Study of gap conductance model for thermo mechanical fully coupled finite element model
Energy Technology Data Exchange (ETDEWEB)
Kim, Hyo Cha; Yang, Yong Sik; Kim, Dae Ho; Bang, Je Geon; Kim, Sun Ki; Koo, Yang Hyun [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2012-10-15
accurately, gap conductance model for thermomechanical fully coupled FE should be developed. However, gap conductance in FE can be difficult issue in terms of convergence because all elements which are positioned in gap have different gap conductance at each iteration step. It is clear that our code should have gap conductance model for thermo-mechanical fully coupled FE in three-dimension. In this paper, gap conductance model for thermomechanical coupled FE has been built using commercial FE code to understand gap conductance model in FE. We coded commercial FE code using APDL because it does not have iterative gap conductance model. Through model, convergence parameter and characteristics were studied.
Thermal conductivity model for powdered materials under vacuum based on experimental studies
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N. Sakatani
2017-01-01
Full Text Available The thermal conductivity of powdered media is characteristically very low in vacuum, and is effectively dependent on many parameters of their constituent particles and packing structure. Understanding of the heat transfer mechanism within powder layers in vacuum and theoretical modeling of their thermal conductivity are of great importance for several scientific and engineering problems. In this paper, we report the results of systematic thermal conductivity measurements of powdered media of varied particle size, porosity, and temperature under vacuum using glass beads as a model material. Based on the obtained experimental data, we investigated the heat transfer mechanism in powdered media in detail, and constructed a new theoretical thermal conductivity model for the vacuum condition. This model enables an absolute thermal conductivity to be calculated for a powder with the input of a set of powder parameters including particle size, porosity, temperature, and compressional stress or gravity, and vice versa. Our model is expected to be a competent tool for several scientific and engineering fields of study related to powders, such as the thermal infrared observation of air-less planetary bodies, thermal evolution of planetesimals, and performance of thermal insulators and heat storage powders.
Sari, I. M.
2017-02-01
Teacher plays a crucial role in Education. Helping students construct scientifically mental model is one of obligation of Physics Education Department of Teacher Education Institute that produce physics teacher. Excavating students’ mental model is necessary to be done in physics education. This research was first to identify 23 physics students’ mental model of heat and heat conduction. A series of semi-structured interviews was conducted to excavate the students’ understanding of heat and mental models on heat conduction. The students who involved in this study come from different level from sophomore to master degree in Physics Education Department. This study adopted a constant comparison method to obtain the patterns of the participants’ responses through the students’ writing, drawing and verbal utterances. The framework for assessing mental model and the instruments were adopted and adapted from Chiou and Anderson (2010). We also compared the students’ understanding of heat and mental models on heat conduction. The result shows that Heat is treated as Intrinsic property, material substances, and caloric flow. None of students expressed heat as transfer of thermal energy. Moreover, there are two kinds of students’ fundamental component of mental model in heat conduction were found: medium and molecules. Students understanding of heat and fundamental components of mental model in heat conduction are not resulted from running mental model.
Study on Unit Cell Models and the Effective Thermal Conductivities of Silica Aerogel.
Liu, He; Li, Zeng-Yao; Zhao, Xin-Peng; Tao, Wen-Quan
2015-04-01
In this paper, two modified unit cell models, truncated octahedron and cubic array of intersecting square rods with 45-degree rotation, are developed in consideration of the tortuous path of heat conduction in solid skeleton of silica aerogel. The heat conduction is analyzed for each model and the expressions of effective thermal conductivity of the modified unit cell models are derived. Considering the random microstructure of silica aerogel, the probability model is presented. We also discuss the effect of the thermal conductivity of aerogel backbone. The effective thermal conductivities calculated by the proposed probability model are in good agreement with available experimental data when the density of the aerogel is 110 kg/m3.
Summary report on UO_{2} thermal conductivity model refinement and assessment studies
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Liu, Xiang-Yang [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Cooper, Michael William Donald [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Mcclellan, Kenneth James [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Lashley, Jason Charles [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Byler, Darrin David [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Bell, B. D.C. [Imperial College, London (United Kingdom); Grimes, R. W. [Imperial College, London (United Kingdom); Stanek, Christopher Richard [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Andersson, David Ragnar [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-02-03
Uranium dioxide (UO_{2}) is the most commonly used fuel in light water nuclear reactors and thermal conductivity controls the removal of heat produced by fission, therefore, governing fuel temperature during normal and accident conditions. The use of fuel performance codes by the industry to predict operational behavior is widespread. A primary source of uncertainty in these codes is thermal conductivity, and optimized fuel utilization may be possible if existing empirical models were replaced with models that incorporate explicit thermal conductivity degradation mechanisms during fuel burn-up. This approach is able to represent the degradation of thermal conductivity due to each individual defect type, rather than the overall burn-up measure typically used which is not an accurate representation of the chemical or microstructure state of the fuel that actually governs thermal conductivity and other properties. To generate a mechanistic thermal conductivity model, molecular dynamics (MD) simulations of UO_{2} thermal conductivity including representative uranium and oxygen defects and fission products are carried out. These calculations employ a standard Buckingham type interatomic potential and a potential that combines the many-body embedded atom method potential with Morse-Buckingham pair potentials. Potential parameters for UO_{2+x} and ZrO_{2} are developed for the latter potential. Physical insights from the resonant phonon-spin scattering mechanism due to spins on the magnetic uranium ions have been introduced into the treatment of the MD results, with the corresponding relaxation time derived from existing experimental data. High defect scattering is predicted for Xe atoms compared to that of La and Zr ions. Uranium defects reduce the thermal conductivity more than oxygen defects. For each defect and fission product, scattering parameters are derived for application in both a Callaway model and the corresponding high
Shen, Hua; Zhu, Yong; Qin, Kai-Rong
2016-12-01
The electrical conductivity of pulsatile blood flow in arteries is an important factor for the application of the electrical impedance measurement system in clinical settings. The electrical conductivity of pulsatile blood flow depends not only on blood-flow-induced red blood cell (RBC) orientation and deformation but also on artery wall motion. Numerous studies have investigated the conductivity of pulsatile blood based on a rigid tube model, in which the effects of wall motion on blood conductivity are not considered. In this study, integrating Ling and Atabek's local flow theory and Maxwell-Fricke theory, we develop an elastic tube model to explore the effects of wall motion as well as blood flow velocity on blood conductivity. The simulation results suggest that wall motion, rather than blood flow velocity, is the primary factor that affects the conductivity of flowing blood in arteries.
Reviewing Instructional Studies Conducted Using Video Modeling to Children with Autism
Acar, Cimen; Diken, Ibrahim H.
2012-01-01
This study explored 31 instructional research articles written using video modeling to children with autism and published in peer-reviewed journals. The studies in this research have been reached by searching EBSCO, Academic Search Complete, ERIC and other Anadolu University online search engines and using keywords such as "autism, video modeling,…
Directory of Open Access Journals (Sweden)
Andreas N. Prokopiou
2015-01-01
Full Text Available This paper presents a computational model which estimates the postsynaptic conductance change of mammalian Type I afferent peripheral process when airborne acoustic waves impact on the tympanic membrane. A model of the human auditory periphery is used to estimate the inner hair cell potential change in response to airborne sound. A generic and tunable topology of the mammalian synaptic ribbon is generated and the voltage dependence of its substructures is used to calculate discrete and probabilistic neurotransmitter vesicle release. Results suggest an almost linear relationship between increasing sound level (in dB SPL and the postsynaptic conductance for frequencies considered too high for neurons to phase lock with (i.e., a few kHz. Furthermore coordinated vesicle release is shown for up to 300–400 Hz and a mechanism of phase shifting the subharmonic content of a stimulating signal is suggested. Model outputs suggest that strong onset response and highly synchronised multivesicular release rely on compound fusion of ribbon tethered vesicles.
Energy Technology Data Exchange (ETDEWEB)
Sanghavi, Rahul P.; Devanathan, Ramaswami; Nandasiri, Manjula I.; Kuchibhatla, Satyanarayana V N T; Kovarik, Libor; Thevuthasan, Suntharampillai; Prasad, Shalini
2011-12-12
Oxygen diffusion and ionic conductivity of samaria-doped ceria (SDC) thin films have been studied as a function of composition using experiment and atomistic simulation. SDC thin films were grown on Al2O3 (0001) substrates by oxygen plasma-assisted molecular beam epitaxy (OPA-MBE) technique. The experimental results show a peak in electrical conductivity of SDC at 15 mol% Sm2O3. The oxygen diffusion coefficient obtained from molecular dynamics simulation of the same system shows a peak at about 13 mol% Sm2O3. The activation energy for oxygen diffusion was found to be in the range from 0.8 to 1.0 eV by simulations depending on the Sm2O3 content, which compares well with the range from 0.6 to 0.9 eV given by the experimental work. The simulations also show that oxygen vacancies prefer Sm3+ ions as first neighbors over Ce4+ ions. The present results reveal that the optimum samaria content for ionic conductivity in single crystals of SDC is less than that in polycrystals, which can be related to the preferential segregation of dopant cations to grain boundaries in polycrystals.
Geomechanical/Geochemical Modeling Studies Conducted within theInternational DECOVALEX Project
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Birkholzer, J.T.; Rutqvist, J.; Sonnenthal, E.L.; Barr, D.; Chijimatsu, M.; Kolditz, O.; Liu, Q.; Oda, Y.; Wang, W.; Xie, M.; Zhang, C.
2005-10-19
The DECOVALEX project is an international cooperative project initiated by SKI, the Swedish Nuclear Power Inspectorate, with participation of about 10 international organizations. The general goal of this project is to encourage multidisciplinary interactive and cooperative research on modeling coupled thermo-hydro-mechanical-chemical (THMC) processes in geologic formations in support of the performance assessment for underground storage of radioactive waste. One of the research tasks, initiated in 2004 by the U.S. Department of Energy (DOE), addresses the long-term impact of geomechanical and geochemical processes on the flow conditions near waste emplacement tunnels. Within this task, four international research teams conduct predictive analysis of the coupled processes in two generic repositories, using multiple approaches and different computer codes. Below, we give an overview of the research task and report its current status.
Selected soil thermal conductivity models
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Rerak Monika
2017-01-01
Full Text Available The paper presents collected from the literature models of soil thermal conductivity. This is a very important parameter, which allows one to assess how much heat can be transferred from the underground power cables through the soil. The models are presented in table form, thus when the properties of the soil are given, it is possible to select the most accurate method of calculating its thermal conductivity. Precise determination of this parameter results in designing the cable line in such a way that it does not occur the process of cable overheating.
Roy Adaptation Model: integrative review of studies conducted in the light of the theory
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Lays Pinheiro de Medeiros
2015-04-01
Full Text Available Objective: to identify the scientific evidence about the components of the Roy Adaptation Model in the population studied in the light of this theory. Methods: this is an integrative literature review in databases of the Latin-American and Caribbean Center on Health Sciences Information, Medical Literature Analysis and Retrieval System Online, Spanish Bibliographic Index on Health Sciences, Nursing Database, PubMed Central, Cumulative Index to Nursing and Allied Health Literature, Web of Science, and SciVerse Scopus. The sample consists of 20 articles published between 2005 and 2013. Results: the three types of stimuli, 38 of 82 adaptive problems, the four adaptive modes, and the six steps of the nursing process were identified. Conclusion: there is need for further studies on this theory and that address the entire nursing process, culminating in the increase in specific nursing knowledge and affirmation of this science in health.
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Yu, Zhongqing; Devanathan, Ramaswami; Jiang, Weilin; Nachimuthu, Ponnusamy; Shutthanandan, V.; Saraf, Laxmikant V.; Wang, Chong M.; Kuchibhatla, Satyanarayana V N T; Thevuthasan, Suntharampillai
2010-03-12
Scandia-stabilized zirconia films were epitaxially grown on sapphire (0001) substrates by oxygen-plasma-assisted molecular beam epitaxy. The cubic phase was found to exist over a wider dopant concentration range than previously observed (4.6-17.6 mol% Sc2O3). The monoclinic phase was observed for dopant concentrations of 1.5 mol% and 22.5 mol %. An increase in the fraction of the monoclinic phase relative to the cubic phase decreased the ionic conductivity. The highest conductivity in the temperature range of 460-900 °C was observed for 9.9 mol % Sc2O3. Atomistic computer simulations show that the observed composition dependence can be related to changes in migration barriers for O2- ion transport with Sc3+ substitution of Zr4+ ions.
STUDIES ON ENHANCED CONDUCTIVITY OF STRETCHED CONDUCTING POLYMERS
Institute of Scientific and Technical Information of China (English)
WAN Meixiang
1995-01-01
A physical model of series of the conductivity on chain and the interchain conductivity between chains is proposed to explain enhanced conductivity of stretched conducting polymers.This model suggests that the enhanced conductivity for stretched conducting polymers might be due to increasing of the interchain conductivity between chains along the elongation direction after drawing processes if the conductivity on chain is assumed much larger than that of the interchain conductivity between chains. According to this model, it is expected that the temperature dependence of conductivity measured by four-probe method for stretched conducting polymers is controlled by a variation of the interchain conductivity between chains with temperature, which can be used to explain that a metallic temperature dependence of conductivity for stretched conducting polymers is not observed although the conductivity along the elongation direction is enhanced by two or three orders of magnitude.
A 1-D radiative conductive model to study the SOIR/VEx thermal profiles
Mahieux, Arnaud; Erwin, Justin T.; Chamberlain, Sarah; Robert, Séverine; Carine Vandaele, Ann; Wilquet, Valérie; Thomas, Ian; Yelle, Roger V.; Bertaux, Jean-Loup
2015-04-01
SOIR is an infrared spectrometer on board Venus Express that probes the Venus terminator region since 2006. The measurements are taken on the morning and evening sides of the terminator, covering all latitudes from the North Pole to the South Pole. Its wavelength range - 2.2 to 4.3 μm - allows a detailed chemical inventory of the Venus atmosphere [1-5], such as CO2, CO, H2O, HCl, HF, SO2 and aerosols. CO2 is detected from 70 km up to 165 km, CO from 70 km to 140 km, and the minor species typically below 110 km down to 70 km. Number density profiles of these species are computed from the measured spectra. Temperature profiles are obtained while computing the spectral inversion of the CO2 spectra combined with the hydrostatic law [6]. These temperature measurements show a striking permanent temperature minimum (at 125 km) and a weaker temperature maximum (over 100-115 km). The time variability of the CO2 density profiles spans over two orders of magnitude, and a clear trend is seen with latitude. The temperature variations are also important, of the order of 35 K for a given pressure level, but the latitude variation are small. Miss-RT, a 1D radiative transfer model has been developed to reproduce the SOIR terminator profiles, derived from the Mars thermosphere code presented in [7]. This model has been expanded to better account for the CO2, CO, and O non-LTE radiative heating and cooling processes which have to be considered in the dense atmosphere of Venus. Radiative cooling by minor species detected by SOIR (e.g. HCl, SO2, and H2O) are found to be small in comparison to the 15 μm CO2 cooling. Aerosol cooling in the 60-90km altitude range may be important to the thermal balance. There is a good agreement between the 1D model temperature profile and the mean SOIR temperature profile. Further we can suggest parameters that can be adjusted to improve the agreement between the model and measurements. The remaining differences can be attributed to the atmosphere
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Ho, T.T.Y.; Sahai, S.K. [Conoco Inc., Ponca City, OK (United States); Leadholm, R.H. [Conoco Inc., Houston, TX (United States); Senneseth, O. [Conoco Norway Inc., Stavanger (Norway); Jensen, R.P.
1998-12-31
The primary objective of this paper is to demonstrate the successful application of maturation modelling using velocity-based thermal conductivity in the whole cycle of hydrocarbon exploration (frontier, developing and mature) on the Halten Terrace, Offshore Norway. This seismic geochemical method, used as a critical technique for selecting a favourable block in the early stages of exploration in the early 80s, enabled Conoco and its partners to make the first oil discovery and the subsequent discovery of the giant Heidrun Field in the area north of the 62nd parallel. Additional data (modelling and measured) on the thermal conductivity and Ro values are now available, and provide an excellent opportunity to compare the original (pre-drilling) basin models and related modelling results of the early 80s with 1990s (post-drilling) state-of-the-art data and models. The results of the comparative study indicate that the velocity-based conductivity compares very well with measured data, particularly in an overpressured area where conventional porosity (modelled) based thermal conductivities were inadequate. The pre-drilling predicted values of heat flow, geothermal gradient and vitrinite reflectance (based on Arrhenius equation) and oil window limits also compared favourably with post-drilling measured results. Thus, the method of calculating thermal conductivity from seismic data provides a useful tool to integrate geochemistry and geophysical (seismic) data, to calibrate maturation models, and to enhance the value of geochemistry and basin modelling in hydrocarbon exploration. (Author)
Charge-transport model for conducting polymers
Dongmin Kang, Stephen; Jeffrey Snyder, G.
2016-11-01
The growing technological importance of conducting polymers makes the fundamental understanding of their charge transport extremely important for materials and process design. Various hopping and mobility edge transport mechanisms have been proposed, but their experimental verification is limited to poor conductors. Now that advanced organic and polymer semiconductors have shown high conductivity approaching that of metals, the transport mechanism should be discernible by modelling the transport like a semiconductor with a transport edge and a transport parameter s. Here we analyse the electrical conductivity and Seebeck coefficient together and determine that most polymers (except possibly PEDOT:tosylate) have s = 3 and thermally activated conductivity, whereas s = 1 and itinerant conductivity is typically found in crystalline semiconductors and metals. The different transport in polymers may result from the percolation of charge carriers from conducting ordered regions through poorly conducting disordered regions, consistent with what has been expected from structural studies.
Studies on Nanocomposite Conducting Coatings
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Amitava Bhattacharyya
2013-01-01
Full Text Available Nanocomposite conducting coatings can impart stable surface electrical conductivity on the substrate. In this paper, carbon nanofiber (CNF and nanographite (NG are dispersed in thermoplastic polyurethane matrix and coated on the surface of glass and polyethylene terephthalate (PET film. The nanoparticles dispersion was studied under TEM. The coating thicknesses were estimated. Further, their resistance and impedance were measured. It has been observed that the 5 wt% CNF dispersed nanocomposite coatings show good conductivity. The use of NG can bring down the amount of CNF; however, NG alone has failed to show significant improvement in conductivity. The nanocomposite coating on PET film using 2.5 wt% of both CNF and NG gives frequency-independent impedance which indicates conducting network formation by the nanoparticles. The study was carried out at different test distances on nanocomposite coated PET films to observe the linearity and continuity of the conducting network, and the result shows reasonable linearity in impedance over total test length (from 0.5 cm to 4.5 cm. The impedance of nanocomposite coatings on glass is not frequency independent and also not following linear increase path with distance. This indicates that the dispersion uniformity is not maintained in the coating solution when it was coated on glass.
Modeling liver electrical conductivity during hypertonic injection.
Castellví, Quim; Sánchez-Velázquez, Patricia; Moll, Xavier; Berjano, Enrique; Andaluz, Anna; Burdío, Fernando; Bijnens, Bart; Ivorra, Antoni
2017-05-30
Metastases in the liver frequently grow as scattered tumor nodules that neither can be removed by surgical resection nor focally ablated. Previously, we have proposed a novel technique based on irreversible electroporation that may be able to simultaneously treat all nodules in the liver while sparing healthy tissue. The proposed technique requires increasing the electrical conductivity of healthy liver by injecting a hypersaline solution through the portal vein. Aiming to assess the capability of increasing the global conductivity of the liver by means of hypersaline fluids, here, it is presented a mathematical model that estimates the NaCl distribution within the liver and the resulting conductivity change. The model fuses well-established compartmental pharmacokinetic models of the organ with saline injection models used for resuscitation treatments, and it considers changes in sinusoidal blood viscosity because of the hypertonicity of the solution. Here, it is also described a pilot experimental study in pigs in which different volumes of NaCl 20% (from 100 to 200 mL) were injected through the portal vein at different flow rates (from 53 to 171 mL/minute). The in vivo conductivity results fit those obtained by the model, both quantitatively and qualitatively, being able to predict the maximum conductivity with a 14.6% average relative error. The maximum conductivity value was 0.44 second/m, which corresponds to increasing 4 times the mean basal conductivity (0.11 second/m). The results suggest that the presented model is well suited for predicting on liver conductivity changes during hypertonic saline injection. Copyright © 2017 John Wiley & Sons, Ltd.
Conducting Simulation Studies in Psychometrics
Feinberg, Richard A.; Rubright, Jonathan D.
2016-01-01
Simulation studies are fundamental to psychometric discourse and play a crucial role in operational and academic research. Yet, resources for psychometricians interested in conducting simulations are scarce. This Instructional Topics in Educational Measurement Series (ITEMS) module is meant to address this deficiency by providing a comprehensive…
Llopis-Albert, C.; Capilla, J. E.
2010-09-01
SummaryMajor factors affecting groundwater flow through fractured rocks include the geometry of each fracture, its properties and the fracture-network connectivity together with the porosity and conductivity of the rock matrix. When modelling fractured rocks this is translated into attaining a characterization of the hydraulic conductivity ( K) as adequately as possible, despite its high heterogeneity. This links with the main goal of this paper, which is to present an improvement of a stochastic inverse model, named as Gradual Conditioning (GC) method, to better characterise K in a fractured rock medium by considering different K stochastic structures, belonging to independent K statistical populations (SP) of fracture families and the rock matrix, each one with its own statistical properties. The new methodology is carried out by applying independent deformations to each SP during the conditioning process for constraining stochastic simulations to data. This allows that the statistical properties of each SPs tend to be preserved during the iterative optimization process. It is worthwhile mentioning that so far, no other stochastic inverse modelling technique, with the whole capabilities implemented in the GC method, is able to work with a domain covered by several different stochastic structures taking into account the independence of different populations. The GC method is based on a procedure that gradually changes an initial K field, which is conditioned only to K data, to approximate the reproduction of other types of information, i.e., piezometric head and solute concentration data. The approach is applied to the Äspö Hard Rock Laboratory (HRL) in Sweden, where, since the middle nineties, many experiments have been carried out to increase confidence in alternative radionuclide transport modelling approaches. Because the description of fracture locations and the distribution of hydrodynamic parameters within them are not accurate enough, we address the
Directory of Open Access Journals (Sweden)
Krzysztof Buczkowski
2017-01-01
Full Text Available Tobacco smoking is the single most important modifiable factor in increased morbidity and premature mortality. Numerous factors—including genetics, personality, and environment—affect the development and persistence of tobacco addiction, and knowledge regarding these factors could improve smoking cessation rates. This study compared personality traits between never, former, and current smokers, using the Five-Factor Model of Personality in a country with a turbulent smoking reduction process.: In this cross-sectional study, 909 Polish adults completed the Revised Neuroticism-Extraversion-Openness Personality Inventory. Our results showed that current smokers’ scores for extraversion, one of the five global dimensions of personality, were higher relative to never smokers. Neuroticism, openness to experience, agreeableness, and conscientiousness did not differ significantly according to smoking status. Facet analysis, which described each dimension in detail, showed that current smokers’ activity and excitement seeking (facets of extraversion scores were higher relative to those of never and former smokers. In turn, current smokers’ dutifulness and deliberation (facets of conscientiousness scores were lower than those found in former and never smokers. Never smokers scored the highest in self-consciousness (a facet of neuroticism and compliance (a component of agreeableness. The study conducted among Polish individuals showed variation in personality traits according to their smoking status; however, this variation differed from that reported in countries in which efforts to reduce smoking had begun earlier relative to Poland. Knowledge regarding personality traits could be useful in designing smoking prevention and cessation programs tailored to individuals’ needs.
Buczkowski, Krzysztof; Basinska, Małgorzata A.; Ratajska, Anna; Lewandowska, Katarzyna; Luszkiewicz, Dorota; Sieminska, Alicja
2017-01-01
Tobacco smoking is the single most important modifiable factor in increased morbidity and premature mortality. Numerous factors—including genetics, personality, and environment—affect the development and persistence of tobacco addiction, and knowledge regarding these factors could improve smoking cessation rates. This study compared personality traits between never, former, and current smokers, using the Five-Factor Model of Personality in a country with a turbulent smoking reduction process.: In this cross-sectional study, 909 Polish adults completed the Revised Neuroticism-Extraversion-Openness Personality Inventory. Our results showed that current smokers’ scores for extraversion, one of the five global dimensions of personality, were higher relative to never smokers. Neuroticism, openness to experience, agreeableness, and conscientiousness did not differ significantly according to smoking status. Facet analysis, which described each dimension in detail, showed that current smokers’ activity and excitement seeking (facets of extraversion) scores were higher relative to those of never and former smokers. In turn, current smokers’ dutifulness and deliberation (facets of conscientiousness) scores were lower than those found in former and never smokers. Never smokers scored the highest in self-consciousness (a facet of neuroticism) and compliance (a component of agreeableness). The study conducted among Polish individuals showed variation in personality traits according to their smoking status; however, this variation differed from that reported in countries in which efforts to reduce smoking had begun earlier relative to Poland. Knowledge regarding personality traits could be useful in designing smoking prevention and cessation programs tailored to individuals’ needs. PMID:28134805
Buczkowski, Krzysztof; Basinska, Małgorzata A; Ratajska, Anna; Lewandowska, Katarzyna; Luszkiewicz, Dorota; Sieminska, Alicja
2017-01-27
Tobacco smoking is the single most important modifiable factor in increased morbidity and premature mortality. Numerous factors-including genetics, personality, and environment-affect the development and persistence of tobacco addiction, and knowledge regarding these factors could improve smoking cessation rates. This study compared personality traits between never, former, and current smokers, using the Five-Factor Model of Personality in a country with a turbulent smoking reduction process.: In this cross-sectional study, 909 Polish adults completed the Revised Neuroticism-Extraversion-Openness Personality Inventory. Our results showed that current smokers' scores for extraversion, one of the five global dimensions of personality, were higher relative to never smokers. Neuroticism, openness to experience, agreeableness, and conscientiousness did not differ significantly according to smoking status. Facet analysis, which described each dimension in detail, showed that current smokers' activity and excitement seeking (facets of extraversion) scores were higher relative to those of never and former smokers. In turn, current smokers' dutifulness and deliberation (facets of conscientiousness) scores were lower than those found in former and never smokers. Never smokers scored the highest in self-consciousness (a facet of neuroticism) and compliance (a component of agreeableness). The study conducted among Polish individuals showed variation in personality traits according to their smoking status; however, this variation differed from that reported in countries in which efforts to reduce smoking had begun earlier relative to Poland. Knowledge regarding personality traits could be useful in designing smoking prevention and cessation programs tailored to individuals' needs.
Finite Element Model of Cardiac Electrical Conduction.
Yin, John Zhihao
1994-01-01
In this thesis, we develop mathematical models to study electrical conduction of the heart. One important pattern of wave propagation of electrical excitation in the heart is reentry which is believed to be the underlying mechanism of some dangerous cardiac arhythmias such as ventricular tachycardia and ventricular fibrillation. We present in this thesis a new ionic channel model of the ventricular cardiac cell membrane to study the microscopic electrical properties of myocardium. We base our model on recent single channel experiment data and a simple physical diffusion model of the calcium channel. Our ionic channel model of myocardium has simpler differential equations and fewer parameters than previous models. Further more, our ionic channel model achieves better results in simulating the strength-interval curve when we connect the membrane patch model to form a one dimensional cardiac muscle strand. We go on to study a finite element model which uses multiple states and non-nearest neighbor interactions to include curvature and dispersion effects. We create a generalized lattice randomization to overcome the artifacts generated by the interaction between the local dynamics and the regularities of the square lattice. We show that the homogeneous model does not display spontaneous wavefront breakup in a reentrant wave propagation once the lattice artifacts have been smoothed out by lattice randomization with a randomization scale larger than the characteristic length of the interaction. We further develop a finite 3-D 3-state heart model which employs a probability interaction rule. This model is applied to the simulation of Body Surface Laplacian Mapping (BSLM) using a cylindrical volume conductor as the torso model. We show that BSLM has a higher spatial resolution than conventional mapping methods in revealing the underlying electrical activities of the heart. The results of these studies demonstrate that mathematical modeling and computer simulation are very
Model calculation of thermal conductivity in antiferromagnets
Energy Technology Data Exchange (ETDEWEB)
Mikhail, I.F.I., E-mail: ifi_mikhail@hotmail.com; Ismail, I.M.M.; Ameen, M.
2015-11-01
A theoretical study is given of thermal conductivity in antiferromagnetic materials. The study has the advantage that the three-phonon interactions as well as the magnon phonon interactions have been represented by model operators that preserve the important properties of the exact collision operators. A new expression for thermal conductivity has been derived that involves the same terms obtained in our previous work in addition to two new terms. These two terms represent the conservation and quasi-conservation of wavevector that occur in the three-phonon Normal and Umklapp processes respectively. They gave appreciable contributions to the thermal conductivity and have led to an excellent quantitative agreement with the experimental measurements of the antiferromagnet FeCl{sub 2}. - Highlights: • The Boltzmann equations of phonons and magnons in antiferromagnets have been studied. • Model operators have been used to represent the magnon–phonon and three-phonon interactions. • The models possess the same important properties as the exact operators. • A new expression for the thermal conductivity has been derived. • The results showed a good quantitative agreement with the experimental data of FeCl{sub 2}.
Conductive thermal modeling of Wyoming geothermal systems
Energy Technology Data Exchange (ETDEWEB)
Heasler, H.P.; Ruscetta, C.A.; Foley, D. (eds.)
1981-05-01
A summary of techniques used by the Wyoming Geothermal Resource Assessment Group in defining low-temperature hydrothermal resource areas is presented. Emphasis is placed on thermal modeling techniques appropriate to Wyoming's geologic setting. Thermal parameters discussed include oil-well bottom hole temperatures, heat flow, thermal conductivity, and measured temperature-depth profiles. Examples of the use of these techniques are from the regional study of the Bighorn Basin and two site specific studies within the Basin.
Nerve conduction and electromyography studies.
Kane, N M; Oware, A
2012-07-01
Nerve conduction studies (NCS) and electromyography (EMG), often shortened to 'EMGs', are a useful adjunct to clinical examination of the peripheral nervous system and striated skeletal muscle. NCS provide an efficient and rapid method of quantifying nerve conduction velocity (CV) and the amplitude of both sensory nerve action potentials (SNAPs) and compound motor action potentials (cMAPs). The CV reflects speed of propagation of action potentials, by saltatory conduction, along large myelinated axons in a peripheral nerve. The amplitude of SNAPs is in part determined by the number of axons in a sensory nerve, whilst amplitude of cMAPs reflects integrated function of the motor axons, neuromuscular junction and striated muscle. Repetitive nerve stimulation (RNS) can identify defects of neuromuscular junction (NMJ) transmission, pre- or post-synaptic. Needle EMG examination can detect myopathic changes in muscle and signs of denervation. Combinations of these procedures can establish if motor and/or sensory nerve cell bodies or peripheral nerves are damaged (e.g. motor neuronopathy, sensory ganglionopathy or neuropathy), and also indicate if the primary target is the axon or the myelin sheath (i.e. axonal or demyelinating neuropathies). The distribution of nerve damage can be determined as either generalised, multifocal (mononeuropathy multiplex) or focal. The latter often due to compression at the common entrapment sites (such as the carpal tunnel, Guyon's canal, cubital tunnel, radial groove, fibular head and tarsal tunnel, to name but a few of the reported hundred or so 'entrapment neuropathies').
Pornprasertsuk, Rojana
Because of the steep increase in oil prices, the global warming effect and the drive for energy independence, alternative energy research has been encouraged worldwide. The sustainable fuels such as hydrogen, biofuel, natural gas, and solar energy have attracted the attention of researchers. To convert these fuels into a useful energy source, an energy conversion device is required. Fuel cells are one of the energy conversion devices which convert chemical potentials into electricity. Due to their high efficiency, the ease to scale from 1 W range to megawatts range, no recharging requirement and the lack of CO2 and NOx emission (if H2 and air/O 2 are used), fuel cells have become a potential candidate for both stationary power generators and portable applications. This thesis has been focused primarily on solid oxide fuel cell (SOFC) studies due to its high efficiency, varieties of fuel choices, and no water management problem. At the present, however, practical applications of SOFCs are limited by high operating temperatures that are needed to create the necessary oxide-ion vacancy mobility in the electrolyte and to create sufficient electrode reactivities. This thesis introduces several experimental and theoretical approaches to lower losses both in the electrolyte and the electrodes. Yttria stabilized zirconia (YSZ) is commonly used as a solid electrolyte for SOFCs due to its high oxygen-ion conductivity. To improve the ionic conductivity for low temperature applications, an approach that involves dilating the structure by irradiation and introducing edge dislocations into the electrolyte was studied. Secondly, to understand the activation loss in SOFC, the kinetic Monte Carlo (KMC) technique was implemented to model the SOFC operation to determining the rate-limiting step due to the electrodes on different sizes of Pt catalysts. The isotope exchange depth profiling technique was employed to investigate the irradiation effect on the ionic transport in different
Directory of Open Access Journals (Sweden)
Beecham Jennifer
2011-10-01
Full Text Available Abstract Background Conduct disorders are the most common psychiatric disorders in children and may persist into adulthood in about 50% of cases. The costs to society are high and impact many public sector agencies. Parenting programmes have been shown to positively affect child behaviour, but little is known about their potential long-term cost-effectiveness. We therefore estimate the costs of and longer-term savings from evidence-based parenting programmes for the prevention of persistent conduct disorder. Methods A decision-analytic Markov model compares two scenarios: 1 a 5-year old with clinical conduct disorder receives an evidence-based parenting programme; 2 the same 5-year old does not receive the programme. Cost-savings analysis is performed by comparing the probability that conduct disorder persists over time in each scenario, adopting both a public sector and a societal perspective. If the intervention is successful in reducing persistent conduct disorder, cost savings may arise from reduced use of health services, education support, social care, voluntary agencies and from crimes averted. Results Results strongly suggest that parenting programmes reduce the chance that conduct disorder persists into adulthood and are cost-saving to the public sector within 5-8 years under base case conditions. Total savings to society over 25 years are estimated at £16,435 per family, which compares with an intervention cost in the range of £952-£2,078 (2008/09 prices. Conclusions Effective implementation of evidence-based parenting programmes is likely to yield cost savings to the public sector and society. More research is needed to address evidence gaps regarding the current level of provision, longer-term effectiveness and questions of implementation, engagement and equity.
Itinerant electron model and conductance of DNA
Institute of Scientific and Technical Information of China (English)
Zhen QU; Da-wei KANG; Xu-tuan GAO; Shi-jie XIE
2008-01-01
DNA (Deoxyribonucleic acid) has recently caught the attention of chemists and physicists.A major reason for this interest is DNA's potential use in nanoelectronie devices,both as a template for assembling nanocireuits and as an element of such circuits.However,the electronic properties of the DNA molecule remain very controversial. Charge-transfer reactions and conductivity measurements show a large variety of possible electronic behavior,ranging from Anderson and bandgap insulators to effective molecular wires and induced superconductors.In this review article,we summarize the wide-ranging experimental and theoretical results of charge transport in DNA.An itinerant electron model is suggested and the effect of the density of itinerant electrons on the conductivity of DNA is studied.Calculations show that a DNA molecule may show conductivity from insulating to metallic,which explains the controversial and profuse electric characteristics of DNA to some extent.
Gerke, Kirill; Khirevich, Siarhei; Sizonenko, Timofey; Karsanina, Marina; Umarova, Aminat; Korost, Dmitry; Matthai, Stephan; Mallants, Dirk
2016-04-01
To verify pore-scale modelling approach for determination of soil saturated hydraulic conductivity properties we scanned three cylindrical soil samples taken from A, Ah and B horizons using X-ray microtomography method. Resulting 3D soil images with resolutions of 15.25-20.96 μm were segmented into pores and solids and their maximum inscribed cube subvolumes were used as input data for three major pore-scale modelling methods to simulate saturated flow - lattice-Boltzmann method, finite-difference solution of the Stokes problem, and pore-network model. Provided that imaging resolution is high enough to capture the backbone of effective porosity and the main conducting pores all three methods resulted in simulated soil permeabilities close to experimental values for Ah and B samples. The resolution of A sample was not enough for an accurate modelling and we concluded that this soil requires multi-scale imaging to cover all relevant heterogeneities. We demonstrate that popular SWV method to choose segmentation threshold resulted in oversegmentation and order of magnitude higher permeability values. Careful manual thresholding combined with local segmentation algorithm provided much more accurate results. Detailed analysis of water retention curves showed that air-filled porosity at relevant pressure stages cannot be used for verification of the segmentation results. Representativity analysis by simulating flow in increasing soil volume up to 2.8 cm3 revealed no representative elementary volume (REV) within Ah sample and non-uniqueness of REV for B sample. The latter was explained by soil structure non-stationarity. We further speculate that structures soil horizons can exhibit no REV at all. We discuss numerous advantages of coupled imaging and pore-scale modelling approach and show how it can become a successor of the conventional soil coring method to parametrize large scale continuum models.
Measurement and modeling of unsaturated hydraulic conductivity
Perkins, Kim S.; Elango, Lakshmanan
2011-01-01
The unsaturated zone plays an extremely important hydrologic role that influences water quality and quantity, ecosystem function and health, the connection between atmospheric and terrestrial processes, nutrient cycling, soil development, and natural hazards such as flooding and landslides. Unsaturated hydraulic conductivity is one of the main properties considered to govern flow; however it is very difficult to measure accurately. Knowledge of the highly nonlinear relationship between unsaturated hydraulic conductivity (K) and volumetric water content is required for widely-used models of water flow and solute transport processes in the unsaturated zone. Measurement of unsaturated hydraulic conductivity of sediments is costly and time consuming, therefore use of models that estimate this property from more easily measured bulk-physical properties is common. In hydrologic studies, calculations based on property-transfer models informed by hydraulic property databases are often used in lieu of measured data from the site of interest. Reliance on database-informed predicted values with the use of neural networks has become increasingly common. Hydraulic properties predicted using databases may be adequate in some applications, but not others. This chapter will discuss, by way of examples, various techniques used to measure and model hydraulic conductivity as a function of water content, K. The parameters that describe the K curve obtained by different methods are used directly in Richards’ equation-based numerical models, which have some degree of sensitivity to those parameters. This chapter will explore the complications of using laboratory measured or estimated properties for field scale investigations to shed light on how adequately the processes are represented. Additionally, some more recent concepts for representing unsaturated-zone flow processes will be discussed.
Geneser, Sarah; Choe, Seungkeol; Kirby, Robert; Macleod, Robert
2005-01-01
Quantification of the sensitivity of the electro-cardiographic forward problem to various parameters can effectively direct the generalization of patient specific models without significant loss in accuracy. To this purpose we applied polynomial chaos based stochastic finite elements to assess the effect of variations in the distributions of tissue conductivity in a two-dimensional torso geometry generated from MRI scans and epicardial boundary conditions specified by intra-operatively recorded heart potentials. The polynomial chaos methodology allows sensitivity analysis of this type to be done in a fraction of the time required for a Monte Carlo analysis.
Thermal Conductivity Coefficient from Microscopic Models
Nemakhavhani, T E
2016-01-01
Thermal conductivity of hadron matter is studied using a microscopic transport model, which will be used to simulate ultra-relativistic heavy ion collisions at different energy densities, namely the Ultra-relativistic Quantum Molecular Dynamics (UrQMD). The molecular dynamics simulation is performed for a system of light mesons species (pion, rho, kaon) in a box with periodic boundary conditions. The equilibrium state is investigated by studying chemical equilibrium and thermal equilibrium of the system. Particle multiplicity equilibrates with time, and the energy spectra of different light mesons species have the same slopes and common temperatures when thermal equilibrium is reached. Thermal conductivity transport coefficient is calculated from the heat current - current correlations using the Green-Kubo relations.
Negm, Amro; Barontini, Stefano; Bacchi, Baldassare
2015-04-01
An experimental field was installed in Summer 2012 in a mountain environment (Cividate Camuno, Oglio river basin, Central Italian Alps, 274 m a.s.l.) in order to investigate the soil-water balance and the effectiveness of the eddy correlation technique to measure the evapotranspirative fluxes in a complex topography. The soil is young, shallow and anthropized, grown on the debris of a power plant workings. The genetic sequence is given by A, C and D horizons, as it is common in many Alpine sites. USDA textural classes are silty loam (A, up to 9 cm depth), loam (upper C, 9 to 22 cm), silty clay loam (lower C, 22 to 28 cm) and silty loam (D, deeper than 38 cm), with increasing gravel fraction (pebbles) with depth. Due to the meaningful pebbles presence, the sampled soil cores were disturbed and considered reliable only for porosity, grains size distribution, water content and soil-water retention relationships. In the field a single ring infiltrometer was used to estimate the soil conductivity at saturation. Two infiltration tests were performed, in view of sampling the A-layer and the upper 10 centimeters of the C-layer. The great soil heterogeneity in the upper layers does not merge the hypotheses of the classical approaches to determine the soil conductivity after infiltration tests, therefore a methodology based on inverse modelling was developed. After a preliminary estimate of the conductivities of the A-layer (Ks,A) and of the C-layer (Ks,C) based on the hypothesis of steady percolation at the end of the infiltration tests, a 2D axisymmetrical model was set up for both the tests with the FV-FD AdHydra code, which numerically solves the Richards equation. Then the two infiltration tests were used to iteratively fit both Ks,A (first test) and Ks,C (second test), using as an initial condition for the simulation of the second test the tensiometer-pressure potential map given as an output of the simulation of the first test. The procedure rapidly converged to
Hopping models for ion conduction in noncrystals
DEFF Research Database (Denmark)
Dyre, Jeppe; Schrøder, Thomas
2007-01-01
Ion conduction in noncrystals (glasses, polymers, etc) has a number of properties in common. In fact, from a purely phenomenological point of view, these properties are even more widely observed: ion conduction behaves much like electronic conduction in disordered materials (e.g., amorphous...... semiconductors). These universalities are subject of much current interest, for instance interpreted in the context of simple hopping models. In the present paper we first discuss the temperature dependence of the dc conductivity in hopping models and the importance of the percolation phenomenon. Next......, the experimental (quasi)universality of the ac conductivity is discussed. It is shown that hopping models are able to reproduce the experimental finding that the response obeys time-temperature superposition, while at the same time a broad range of activation energies is involved in the conduction process. Again...
Characterising and modelling extended conducted electromagnetic emission
CSIR Research Space (South Africa)
Grobler, Inus
2013-06-01
Full Text Available -1 2013 IEEE Energy Conversion Congress and Exposition Asia (ECCE Downunder), Melbourne, Australia, 3-6 June 2013 Characterising and Modelling Extended Conducted Electromagnetic Emission I Grobler1 and MN Gitau2 Department of Electrical...
Homogenized thermal conduction model for particulate foods
Energy Technology Data Exchange (ETDEWEB)
Chinesta, Francisco [Laboratoire de mecanique des systemes et des procedes, Ecole nationale superieure d' arts et metiers, 151 boulevard de l' Hopital, 75013, Paris (France); Torres, Rafael [Departamento de Ingenieria Mecanica, Universidad Politecnica de Valencia, Camino de Vera s/n. 46071, Valencia (Spain); Ramon, Antonio [AIMPLAS, Gustave Eiffel 4, 46980 Paterna, Valencia (Spain); Rodrigo, Mari Carmen; Rodrigo, Miguel [Instituto de Agroquimica y Tecnologia de Alimentos, Consejo Superior de Investigaciones Cientificas, Apartado de correos 73, 46100, Burjasot (Spain)
2002-12-01
This paper deals with the definition of an equivalent thermal conductivity for particulate foods. An homogenized thermal model is used to asses the effect of particulate spatial distribution and differences in thermal conductivities. We prove that the spatial average of the conductivity can be used in an homogenized heat transfer model if the conductivity differences among the food components are not very large, usually the highest conductivity ratio between the foods components is lower than 5. In the general case we propose to use a standard spatial homogenization procedure. Although the heterogeneity give rise to an anisotropic heat transfer behaviour, this effect is negligible when the food particles are randomly distributed. When we use pre-mixed particulate foods a statistical average can be defined from a small number of possible particle arrangements. (authors)
Modeling Classical Heat Conduction in FLAG
Energy Technology Data Exchange (ETDEWEB)
Ramsey, Scott D. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Hendon, Raymond Cori [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2015-01-12
The Los Alamos National Laboratory FLAG code contains both electron and ion heat conduction modules; these have been constructed to be directly relevant to user application problems. However, formal code verification of these modules requires quantitative comparison to exact solutions of the underlying mathematical models. A wide variety of exact solutions to the classical heat conduction equation are available for this purpose. This report summarizes efforts involving the representation of the classical heat conduction equation as following from the large electron-ion coupling limit of the electron and ion 3T temperature equations, subject to electron and ion conduction processes. In FLAG, this limiting behavior is quantitatively verified using a simple exact solution of the classical heat conduction equation. For this test problem, both heat conduction modules produce nearly identical spatial electron and ion temperature profiles that converge at slightly less than 2nd order to the corresponding exact solution.
Conducting pilot and feasibility studies.
Cope, Diane G
2015-03-01
Planning a well-designed research study can be tedious and laborious work. However, this process is critical and ultimately can produce valid, reliable study findings. Designing a large-scale randomized, controlled trial (RCT)-the gold standard in quantitative research-can be even more challenging. Even the most well-planned study potentially can result in issues with research procedures and design, such as recruitment, retention, or methodology. One strategy that may facilitate sound study design is the completion of a pilot or feasibility study prior to the initiation of a larger-scale trial. This article will discuss pilot and feasibility studies, their advantages and disadvantages, and implications for oncology nursing research. .
Energy Technology Data Exchange (ETDEWEB)
Arani, Ali Akbar Abbasian; Azemati, Ali Akbar; Rezaee, Mohammad [University of Kashan, Kashan (Iran, Islamic Republic of); Hadavand, Behzad Shirkavand [Islamic Azad University, Abadan (Iran, Islamic Republic of)
2017-05-15
Natural convection in enclosures containing nanofluids is important in physical and environmental applications. Different models for conduction have been developed because of the importance of this phenomenon in natural convection in enclosures. In this study, effects of conduction models of Chon, Corcione, Khanafer, and Koo and Kleinstreuer on the natural convection inside a trapezoidal enclosure with hot and cold walls are evaluated numerically. The enclosure contains Al{sub 2}O{sub 3}-water nanofluid with variable properties. Effects of the conduction models on fluid flow, natural convection, variations in volume fraction, and diameter of nanoparticles in the models, as well as the variations in the Rayleigh number, are examined. Results show that at Rayleigh numbers of 105 and 106, the maximum and minimum values of the average Nusselt number are obtained using the models of Khanafer and Chon, respectively. In all models, the average Nusselt number presents upward and downward trends when the volume fraction of nanoparticles increases but decreases when the di- ameter of the nanoparticles increases. At Ra = 105 in all models, as the volume fraction of nanoparticles increases, the nanofluid provides a higher average Nusselt number compared with the base fluid. By contrast, at Ra = 106, at volume fractions larger than 0.01 and using the model of Chon, the average Nusselt number of the nanofluid is lower compared with that of the base fluid.
Modeling of ion conductivity in Nafion membranes
Institute of Scientific and Technical Information of China (English)
YANG Zhen; PENG Xiaofeng; WANG Buxuan; LEE Duujong; DUAN Yuanyuan
2007-01-01
A theoretical investigation was conducted to describe the ion transport behavior in a Nafion Membrane of proton exchange membrane fuel cells (PEMFC).By analyzing the surface energy configuration of the ionic clusters in a Nafion membrane,an equivalent field intensity,Ee,was introduced to facilitate the analysis of surface resistance against ion conduction in the central region of clusters.An expression was derived for ionic conductivity incorporating the influence of surface resistance.A face-centered cubic (FCC)lattice model for a spatial cluster distribution was used to modify the effect of water content on ionic conductivity in the polymeric matrix,i.e.,the regions between clusters.Compared with the available empirical correlations,the new expression showed much better agreement with the available experimental results,which indicates the rationality to consider the structural influence on ion conduction in water-swollen Nation membranes.
Conductivity bounds in probe brane models
Ikeda, Tatsuhiko N; Nakai, Yuichiro
2016-01-01
We discuss upper and lower bounds on the electrical conductivity of finite temperature strongly coupled quantum field theories, holographically dual to probe brane models, within linear response. In a probe limit where disorder is introduced entirely through an inhomogeneous background charge density, we find simple lower and upper bounds on the electrical conductivity in arbitrary dimensions. In field theories in two spatial dimensions, we show that both bounds persist even when disorder is included in the bulk metric. We discuss the challenges with finding sharp lower bounds on conductivity in three or more spatial dimensions when the metric is inhomogeneous.
Recent progress on the Random Conductance Model
Biskup, Marek
2011-01-01
Recent progress on the understanding of the Random Conductance Model is reviewed and commented. A particular emphasis is on the results on the scaling limit of the random walk among random conductances for almost every realization of the environment, observations on the behavior of the effective resistance as well as the scaling limit of certain models of gradient fields with non-convex interactions. The text is an expanded version of the lecture notes for a course delivered at the 2011 Cornell Summer School on Probability.
Beecham Jennifer; Stevens Madeleine; Bonin Eva-Maria; Byford Sarah; Parsonage Michael
2011-01-01
Abstract Background Conduct disorders are the most common psychiatric disorders in children and may persist into adulthood in about 50% of cases. The costs to society are high and impact many public sector agencies. Parenting programmes have been shown to positively affect child behaviour, but little is known about their potential long-term cost-effectiveness. We therefore estimate the costs of and longer-term savings from evidence-based parenting programmes for the prevention of persistent c...
Bonin, Eva-Maria; Stevens, Madeleine; Beecham, Jennifer; Byford, Sarah; Parsonage, Michael
2011-01-01
Background\\ud \\ud Conduct disorders are the most common psychiatric disorders in children and may persist into adulthood in about 50% of cases. The costs to society are high and impact many public sector agencies. Parenting programmes have been shown to positively affect child behaviour, but little is known about their potential long-term cost-effectiveness. We therefore estimate the costs of and longer-term savings from evidence-based parenting programmes for the prevention of persistent con...
Soil hydraulic properties near saturation, an improved conductivity model
DEFF Research Database (Denmark)
Børgesen, Christen Duus; Jacobsen, Ole Hørbye; Hansen, Søren;
2006-01-01
The hydraulic properties near saturation can change dramatically due to the presence of macropores that are usually difficult to handle in traditional pore size models. The purpose of this study is to establish a data set on hydraulic conductivity near saturation, test the predictive capability...... of commonly used hydraulic conductivity models and give suggestions for improved models. Water retention and near saturated and saturated hydraulic conductivity were measured for a variety of 81 top and subsoils. The hydraulic conductivity models by van Genuchten [van Genuchten, 1980. A closed-form equation...... for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44, 892–898.] (vGM) and Brooks and Corey, modified by Jarvis [Jarvis, 1991. MACRO—A Model of Water Movement and Solute Transport in Macroporous Soils. Swedish University of Agricultural Sciences. Department of Soil Sciences...
Sinatkas, Georgios; Pitilakis, Alexandros; Zografopoulos, Dimitrios C.; Beccherelli, Romeo; Kriezis, Emmanouil E.
2017-01-01
Electro-optic waveguide modulators exploiting the carrier-induced epsilon-near-zero effect in transparent conducting oxides are comprehensively studied and evaluated using a rigorous multi-physics modeling framework. The examined amplitude modulators integrate indium tin oxide with two representative examples of the silicon-on-insulator technology, the silicon-rib and silicon-slot platform, with the latter design exhibiting superior performance, featuring μm modulation lengths, switching speeds exceeding 100 GHz, and a sub-pJ per bit of energy consumption. The effect of free carriers is rigorously introduced by combining the drift-diffusion model for the description of the carrier dynamics with near-infrared carrier-dependent permittivity models, leading to a seamless and physically consistent integration of solid-state physics and Maxwell wave theory on a unified finite-element platform.
Thermal conductivity modeling of water containing metal oxide nanoparticles
Institute of Scientific and Technical Information of China (English)
Ahmad Azari
2015-01-01
The nano particles have demonstrated great potential to improve the heat transfer characteristics of heat transfer fluids. Possible parameters responsible for this increase were studied. The heat transfer profile in the nanolayer region was combined with other parameters such as volume fraction, particle radius thermal conductivity of the fluid, particle and nanolayer, to formulate a thermal conductivity model. Results predicting the thermal conductivity of nanofluids using the model were compared with experimental results as well as studies by other researchers. The comparison of the results obtained for the CuO/water and TiO2/water nanofluids studied shows that the correlation proposed is in closest proximity in predicting the experimental results for the thermal conductivity of a nanofluid. Also, a parametric study was performed to understand how a number of factors affect the thermal conductivity of nanofluids using the developed correlation.
Graphene Nanoribbon Conductance Model in Parabolic Band Structure
Directory of Open Access Journals (Sweden)
Mohammad Taghi Ahmadi
2010-01-01
Full Text Available Many experimental measurements have been done on GNR conductance. In this paper, analytical model of GNR conductance is presented. Moreover, comparison with published data which illustrates good agreement between them is studied. Conductance of GNR as a one-dimensional device channel with parabolic band structures near the charge neutrality point is improved. Based on quantum confinement effect, the conductance of GNR in parabolic part of the band structure, also the temperature-dependent conductance which displays minimum conductance near the charge neutrality point are calculated. Graphene nanoribbon (GNR with parabolic band structure near the minimum band energy terminates Fermi-Dirac integral base method on band structure study. While band structure is parabola, semiconducting GNRs conductance is a function of Fermi-Dirac integral which is based on Maxwell approximation in nondegenerate limit especially for a long channel.
Multiscale Modeling of UHTC: Thermal Conductivity
Lawson, John W.; Murry, Daw; Squire, Thomas; Bauschlicher, Charles W.
2012-01-01
We are developing a multiscale framework in computational modeling for the ultra high temperature ceramics (UHTC) ZrB2 and HfB2. These materials are characterized by high melting point, good strength, and reasonable oxidation resistance. They are candidate materials for a number of applications in extreme environments including sharp leading edges of hypersonic aircraft. In particular, we used a combination of ab initio methods, atomistic simulations and continuum computations to obtain insights into fundamental properties of these materials. Ab initio methods were used to compute basic structural, mechanical and thermal properties. From these results, a database was constructed to fit a Tersoff style interatomic potential suitable for atomistic simulations. These potentials were used to evaluate the lattice thermal conductivity of single crystals and the thermal resistance of simple grain boundaries. Finite element method (FEM) computations using atomistic results as inputs were performed with meshes constructed on SEM images thereby modeling the realistic microstructure. These continuum computations showed the reduction in thermal conductivity due to the grain boundary network.
Modeling of the RF system for the normal conducting linac
Institute of Scientific and Technical Information of China (English)
GENG Zhe-Qiao; HOU Mi; PEI Guo-Xi
2008-01-01
To study the new RF control methods, a mathematic model of the RF system for the normal conducting linac is built and implemented with the software of Matlab. The model contains some typical units of the RF system, such as the klystron, the SLED and the traveling wave accelerating tube. Finally, the model is used to study the working point of the SLED and the adaptive feed forward algorithm for the RF control system. Simulation shows that the model works well as expected.
DC electrical conductivity study of cerium doped conducting glass systems
Barde, R. V.; Waghuley, S. A.
2013-06-01
The glass samples of composition 60V2O5-5P2O5-(35-x)B2O3-xCeO2, (1 ≤ x ≤ 5) were prepared by the conventional melt quench method. The samples were characterized by X-ray diffraction and thermo gravimetric-differential thermal analysis. The glass transition temperature and crystallization temperature determined from TG-DTA analysis. The DC electrical conductivity has been carried out in the temperature range 303-473 K. The maximum conductivity and minimum activation energy were found to be 0.039 Scm-1 and 0.15 eV at 473 K for x=1, respectively.
Sensory nerve conduction studies in neuralgic amyotrophy.
van Alfen, Nens; Huisman, Willem J; Overeem, S; van Engelen, B G M; Zwarts, M J
2009-11-01
Neuralgic amyotrophy is a painful, episodic peripheral nerve disorder localized to the brachial plexus. Sensory symptoms occur in 80% of the patients. We assessed the frequency of abnormalities in sensory nerve conduction studies of the lateral and medial antebrachial cutaneous, radial sensory, median sensory, and ulnar sensory nerves in 112 patients. Sensory nerve conduction studies showed abnormalities in nerves, even when the nerve was clinically affected. The lateral and medial antebrachial cutaneous nerves were most often abnormal, in 15% and 17% of nerves. No correlation with the presence or localization of clinical deficits was found. Brachial plexus sensory nerve conduction studies seem to be of little diagnostic value in neuralgic amyotrophy. Our findings also indicate that some sensory lesions may be in the nerve roots instead of the plexus. An examination of normal sensory nerve conduction studies does not preclude neuralgic amyotrophy as a diagnosis.
A D-region conductivity model from EISCAT VHF measurements
Directory of Open Access Journals (Sweden)
K. Schlegel
Full Text Available An easy-to-use model to evaluate conductivities at high and middle latitudes in the height range 70–100 km is presented. It is based on electron density profiles obtained with the EISCAT VHF radar during 11 years and on the neutral atmospheric model MSIS95. The model uses solar zenith angle, geomagnetic activity and season as input parameters. It was mainly constructed to study the properties of Schumann resonances that depend on such conductivity profiles.
Key words. Meteorology and atmospheric dynamics (middle atmospheric dynamics – Ionosphere (modeling and forecasting; ionosphere-atmosphere interaction
A Simple Holographic Model of Nonlinear Conductivity
Horowitz, Gary T; Santos, Jorge E
2013-01-01
We present a simple analytic gravitational solution which describes the holographic dual of a 2+1-dimensional conductor which goes beyond the usual linear response. In particular it includes Joule heating. We find that the nonlinear frequency-dependent conductivity is a constant. Surprisingly, the pressure remains isotropic. We also apply an electric field to a holographic insulator and show that there is a maximum electric field below which it can remain an insulator. Above this critical value, we argue that it becomes a conductor due to pair creation of charged particles. Finally, we study 1+1 and 3+1 dimensional conductors at the nonlinear level; here exact solutions are not available and a perturbative analysis shows that the current becomes time dependent, but in a way that is captured by a time-dependent effective temperature.
Energy Technology Data Exchange (ETDEWEB)
Kang, Hyung-sun; Koh, Young Ha; Jin, Jae Sik [Chosun College of Science and Technology, Gwangju (Korea, Republic of)
2017-06-15
The aim of this study is to understand the phonon transfer characteristics of a silicon thin film transistor. For this purpose, the Joule heating mechanism was considered through the electron-phonon interaction model whose validation has been done. The phonon transport characteristics were investigated in terms of phonon mean free path for the variations in the device power and silicon layer thickness from 41 nm to 177 nm. The results may be used for developing the thermal design strategy for achieving reliability and efficiency of the silicon-on-insulator (SOI) transistor, further, they will increase the understanding of heat conduction in SOI systems, which are very important in the semiconductor industry and the nano-fabrication technology.
Quantum Ising model coupled with conducting electrons
Energy Technology Data Exchange (ETDEWEB)
Yamashita, Yasufumi; Yonemitsu, Kenji [Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585 (Japan); Graduate University for Advanced studies, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585 (Japan)
2005-01-01
The effect of photo-doping on the quantum paraelectric SrTiO{sub 3} is studied by using the one-dimensional quantum Ising model, where the Ising spin describes the effective lattice polarization of an optical phonon. Two types of electron-phonon couplings are introduced through the modulation of transfer integral via lattice deformations. After the exact diagonalization and the perturbation studies, we find that photo-induced low-density carriers can drastically alter quantum fluctuations when the system locates near the quantum critical point between the quantum para- and ferro-electric phases.
Quantum Ising model coupled with conducting electrons
Yamashita, Yasufumi; Yonemitsu, Kenji
2005-01-01
The effect of photo-doping on the quantum paraelectric SrTiO3 is studied by using the one-dimensional quantum Ising model, where the Ising spin describes the effective lattice polarization of an optical phonon. Two types of electron-phonon couplings are introduced through the modulation of transfer integral via lattice deformations. After the exact diagonalization and the perturbation studies, we find that photo-induced low-density carriers can drastically alter quantum fluctuations when the system locates near the quantum critical point between the quantum para- and ferro-electric phases.
Abkari, A.; Chaabane, I.; Guidara, K.
2016-09-01
In the present work, the synthesis and characterization of the Bis(4-acetylanilinium) tetrachlorocuprate(II) compound are presented. The structure of this compound is analyzed by X-ray diffraction which confirms the formation of single phase and is in good agreement the literature. Indeed, the Thermo gravimetric Analysis (TGA) shows that the decomposition of the compound is observed in the range of 420-520 K. However, the differential thermal analysis (DTA) indicates the presence of a phase transition at T=363 k. Furthermore, the dielectric properties and AC conductivity were studied over a temperature range (338-413 K) and frequency range (200 Hz-5 MHz) using complex impedance spectroscopy. Dielectric measurements confirmed such thermal analyses by exhibiting the presence of an anomaly in the temperature range of 358-373 K. The complex impedance plots are analyzed by an electrical equivalent circuit consisting of resistance, constant phase element (CPE) and capacitance. The activation energy values of two distinct regions are obtained from log σT vs 1000/T plot and are found to be E=1.27 eV (Tdependence of ac conductivity, σac, has been analyzed by Jonscher's universal power law σ(ω)=σdc+Aωs. The value of s is to be temperature-dependent, which has a tendency to increase with temperature and the non-overlapping small polaron tunneling (NSPT) model is the most applicable conduction mechanism in the title compound. Complex impedance spectra of [C8H10NO]2CuCl4 at different temperatures.
Theoretical studies of ionic conductivity of crosslinked chitosan membranes
Energy Technology Data Exchange (ETDEWEB)
Chavez, Ernesto Lopez [Programa de Ingenieria Molecular y Nuevos Materiales, Universidad Autonoma de la Ciudad de Mexico, Fray Servando Teresa de Mier 92, 1er. Piso, Col Centro, Mexico D.F. CP 06080 (Mexico); Oviedo-Roa, R.; Contreras-Perez, Gustavo; Martinez-Magadan, Jose Manuel [Instituto Mexicano del Petroleo, Eje Central Lazaro Cardenas Norte 152, Col. San Bartolo Atepehuacan, CP 07730 Mexico D.F. (Mexico); Castillo-Alvarado, F.L. [Escuela Superior de Fisica y Matematicas del Instituto Politecnico Nacional, Edificio 9 de la UPALM, Colonia Lindavista, Mexico D.F. CP 07738 (Mexico)
2010-11-15
Ionic conductivity of crosslinked chitosan membranes was studied using techniques of molecular modeling and simulation. The COMPASS force field was used. The simulation allows the description of the mechanism of ionic conductivity along the polymer matrix. The theoretical results obtained are compared with experimental results for chitosan membranes. The analysis suggests that the conduction mechanism is portrayed by the overlapping large Polaron tunneling model. In addition, when the chitosan membrane was crosslinked with an appropriate degree of crosslinking its ionic conductivity, at room temperature, was increased by about one order of magnitude. The chitosan membranes can be used as electrolytes in solid state batteries, electric double layer capacitors and fuel cells. (author)
Sensory nerve conduction studies in neuralgic amyotrophy.
Alfen, N. van; Huisman, W.J.; Overeem, S.; Engelen, B.G.M. van; Zwarts, M.J.
2009-01-01
Neuralgic amyotrophy is a painful, episodic peripheral nerve disorder localized to the brachial plexus. Sensory symptoms occur in 80% of the patients. We assessed the frequency of abnormalities in sensory nerve conduction studies of the lateral and medial antebrachial cutaneous, radial sensory, medi
Simple Predictive Models for Saturated Hydraulic Conductivity of Technosands
DEFF Research Database (Denmark)
Arthur, Emmanuel; Razzaghi, Fatemeh; Møldrup, Per
2012-01-01
Accurate estimation of saturated hydraulic conductivity (Ks) of technosands (gravel-free, coarse sands with negligible organic matter content) is important for irrigation and drainage management of athletic fields and golf courses. In this study, we developed two simple models for predicting Ks......-connectivity parameter (m) obtained for pure coarse sand after fitting to measured Ks data was 1.68 for both models and in good agreement with m values obtained from recent solute and gas diffusion studies. Both the modified K-C and R-C models are easy to use and require limited parameter input, and both models gave...
Challenges in conducting psychiatry studies in India
Directory of Open Access Journals (Sweden)
Saifuddin Kharawala
2011-01-01
Full Text Available A large number of psychiatry studies are conducted in India. Psychiatry studies are complex and present unique challenges in the Indian setting. Ethical issues pertaining to the risk of worsening of illness, use of placebo and validity of informed consents are commonly faced. Site selection can be difficult due to the relative paucity of ICH-GCP (International Conference on Harmonisation - Good Clinical Practice trained psychiatry investigators in India. Recruitment can be challenging due to issues such as strict eligibility criteria, (lack of availability of caregiver, illness-related considerations, etc. Assessment of the consent capacity of patients is not simple, while structured assessments are not commonly employed. As the illness fluctuates, the consent capacity may change, thus requiring continued assessment of consent capacity. Study patients run the risk of worsening of illness and suicide due to exposure to inactive treatments; this risk is counterbalanced by use of appropriate study designs, as well as the indirect psychotherapeutic support received. Psychiatry studies are associated with a high placebo response. This necessitates conduct of placebo-controlled studies despite the attendant difficulties. Also, the high placebo response is often the cause of failed trials. Rating scales are essential for assessment of drug response. Some rating instruments as well as some rater training procedures may not be suitable for the Indian setting. Technological advancements may increase the procedural complexity but improve the quality of ratings. Psychiatry studies present monitors and auditors with unique scenarios too. Utilization of psychiatry specific training and expertise is recommended to ensure successful conduct of these studies in India.
Jung, Yong-Woon; Lu, Benzhuo; Mascagni, Michael
2009-12-01
The biophysical mechanisms underlying the relationship between the structure and function of the KcsA K(+) channel are described. Because of the conciseness of electrodiffusion theory and the computational advantages of a continuum approach, the Nernst-Planck (NP) type models, such as the Goldman-Hodgkin-Katz and Poisson-NP (PNP) models, have been used to describe currents in ion channels. However, the standard PNP (SPNP) model is known to be inapplicable to narrow ion channels because it cannot handle discrete ion properties. To overcome this weakness, the explicit resident ions NP (ERINP) model was formulated, which applies a local explicit model where the continuum model fails. Then, the effects of the ERI Coulomb potential, the ERI induced potential, and the ERI dielectric constant for ion conductance were tested in the ERINP model. The current-voltage (I-V) and current-concentration (I-C) relationships determined in the ERINP model provided biologically significant information that the traditional continuum model could not, explicitly taking into account the effects of resident ions inside the KcsA K(+) channel. In addition, a mathematical analysis of the K(+) ion dynamics established a tight structure-function system with a shallow well, a deep well, and two K(+) ions resident in the selectivity filter. Furthermore, the ERINP model not only reproduced the experimental results with a realistic set of parameters, but it also reduced CPU costs.
Local electric conductive property of Si nanowire models
Directory of Open Access Journals (Sweden)
Yuji Ikeda
2012-12-01
Full Text Available Local electric conductive properties of Si nanowire models are investigated by using two local electric conductivity tensors, σ↔ ext (r⃗ and σ↔ int (r⃗, defined in Rigged QED. It is emphasized that σ↔ int (r⃗ is defined as the response of electric current to the actual electric field at a specific point and does not have corresponding macroscopic physical quantity. For the Si nanowire models, there are regions which show complicated response of electric current density to electric field, in particular, opposite and rotational ones. Local conductivities are considered to be available for the study of a negative differential resistance (NDR, which may be related to this opposite response. It is found that σ↔ int (r⃗ shows quite different pattern from σ↔ ext (r⃗, local electric conductivity defined for the external electric field. The effects of impurities are also studied by using the model including a Ge atom, in terms of the local response to electric field. It is found that the difference from the pristine model is found mainly around the Ge atom.
Undergraduate Study of Thermal Conductivity of Metals
Directory of Open Access Journals (Sweden)
Ferrari T. B.
2002-01-01
Full Text Available In this work we analyze an undergraduate experiment used to determine the thermal conductivity of metals (K. We introduce few modifications in order to offer the student the chance to explore dierent models, learning the basic scientiffic method of developing appropriate and improved explanations for each experiment in order to better link theory and empirical results. Semi-empirical corrections are introduced in the system in order to check the experimental results according to previously reported K values. As specific cases we use copper [K = 0.92 cal /(°C s cm], aluminum [K = 0.49 cal /(°C s cm] and brass [K = 0.26 cal /(°C s cm] cylinders.
Trapping in the random conductance model
Biskup, M; Rozinov, A; Vandenberg-Rodes, A
2012-01-01
We consider random walks on $\\Z^d$ among nearest-neighbor random conductances which are i.i.d., positive, bounded uniformly from above but whose support extends all the way to zero. Our focus is on the detailed properties of the paths of the random walk conditioned to return back to the starting point at time $2n$. We show that in the situations when the heat kernel exhibits subdiffusive decay --- which is known to occur in dimensions $d\\ge4$ --- the walk gets trapped for a time of order $n$ in a small spatial region. This shows that the strategy used earlier to infer subdiffusive lower bounds on the heat kernel in specific examples is in fact dominant. In addition, we settle a conjecture concerning the worst possible subdiffusive decay in four dimensions.
Trapping in the Random Conductance Model
Biskup, M.; Louidor, O.; Rozinov, A.; Vandenberg-Rodes, A.
2013-01-01
We consider random walks on ℤ d among nearest-neighbor random conductances which are i.i.d., positive, bounded uniformly from above but whose support extends all the way to zero. Our focus is on the detailed properties of the paths of the random walk conditioned to return back to the starting point at time 2 n. We show that in the situations when the heat kernel exhibits subdiffusive decay—which is known to occur in dimensions d≥4—the walk gets trapped for a time of order n in a small spatial region. This shows that the strategy used earlier to infer subdiffusive lower bounds on the heat kernel in specific examples is in fact dominant. In addition, we settle a conjecture concerning the worst possible subdiffusive decay in four dimensions.
Microscale Heat Conduction Models and Doppler Feedback
Energy Technology Data Exchange (ETDEWEB)
Hawari, Ayman I. [North Carolina State Univ., Raleigh, NC (United States); Ougouag, Abderrafi [Idaho National Lab. (INL), Idaho Falls, ID (United States)
2015-01-22
The objective of this project is to establish an approach for providing the fundamental input that is needed to estimate the magnitude and time-dependence of the Doppler feedback mechanism in Very High Temperature reactors. This mechanism is the foremost contributor to the passive safety of gas-cooled, graphite-moderated high temperature reactors that use fuel based on Tristructural-Isotropic (TRISO) coated particles. Therefore, its correct prediction is essential to the conduct of safety analyses for these reactors. Since the effect is directly dependent on the actual temperature reached by the fuel during transients, the underlying phenomena of heat deposition, heat transfer and temperature rise must be correctly predicted. To achieve the above objective, this project will explore an approach that accounts for lattice effects as well as local temperature variations and the correct definition of temperature and related local effects.
Modelling electrolyte conductivity in a water electrolyzer cell
DEFF Research Database (Denmark)
Caspersen, Michael; Kirkegaard, Julius Bier
2012-01-01
An analytical model describing the hydrogen gas evolution under natural convection in an electrolyzer cell is developed. Main purpose of the model is to investigate the electrolyte conductivity through the cell under various conditions. Cell conductivity is calculated from a parallel resistor app...... for electrolyte conductivity from combinations of pressure, current density and electrolyte width among others....
Study on the Thermal Conductivity Model of Hollow Beads Insulating Mortar%玻化微珠保温砂浆导热系数模型研究
Institute of Scientific and Technical Information of China (English)
龚建清; 张婵韬
2014-01-01
Based on the minimum thermal resistance theory and homogenization method,the effective thermal conductivity of hollow beads insulating mortar was estimated.With ANSYS imitating the heat transmission of the 2D unit model of hollow beads insulating mortar,we can find it will bring about calcu-lation errors by considering the extreme cases of the transverse thermal resistance of resistance network. Compared with the effective thermal conductivity of 3D unit cell model calculated by ANSYS with three kinds of theoretical calculating value,it is more accurate than the effective thermal conductivity of unit cal-culated by the model of effective thermal resistance average.A model was built by assuming transverse thermal resistance infinitesimal and infinite.Final laboratory finding also confirms this conclusion.With only 0.2% deviation between the experiment values and the calculation of theoretical model,it is feasible to estimate the effective thermal conductivity of hollow bead insulating mortar.%基于最小热阻力法则和均匀化方法估算了玻化微珠保温砂浆的等效导热系数.用ANSYS模拟玻化微珠保温砂浆二维单元胞体的热传导，发现对热阻网络的横向热阻的极端考虑会给计算结果带来误差.用 ANSYS 计算的三维单元体模型的等效导热系数值与3种理论计算值进行比较，发现用假设横向热阻无穷小与假设横向热阻无穷大求得的单元体等效热阻的平均值作为单元体的等效热阻来求单元体等效导热系数更精确，最后实验也验证了这一结论.实验值与本文提出的理论模型计算值偏差仅为0.2%，证明用该方法来估算玻化微珠保温砂浆的导热系数是可行的.
Organizational aspects of conducting of bioequivalence study
Directory of Open Access Journals (Sweden)
Khokhlov A.L.
2014-03-01
Full Text Available Aim: to evaluate the organizational aspects of conducting bioequivalence study in Russia on the example of one of the clinical centers, Yaroslavl. Material and methods. On the basis of the Municipal Autonomous institution of health care of the Yaroslavl region Clinical hospital №2 (CH, clinical base of the Department of clinical pharmacology of YSMA was held 93 bioequivalence studies and pharmacokinetics in the period from 2011 to 2014, of which 15 studies of foreign sponsors and 78 of domestic producers. Result.: The studies involved 48 volunteers of both sexes from the database of clinical center CH №2. There were 698 females (48.6% and 739 males (51.4%. The average age of the volunteers was 26,37 years. In each study there were from 18 to 103 volunteers, depending on the design of the research Protocol. At the same time Russian studies ranged about 18-24 volunteers, about 30-103 volunteers abroad. The number of doubles in domestic studies ranged from 2 to 6 persons, and foreign — from 6 to 12 people. 10-15% from the whole number of subjects were not included into the study. Conclusion. In Russia bioequivalence of medicines for more than ten years is the main requirement of medico-biological control generic drugs. Regardless of the manufacturer to the generic drugs are exactly the same as the original drugs, must meet the following requirements: quality efficiency and safety. In connection with the increase in recent years of bioequivalence studies of medicines, require close monitoring of the quality of these studies on the territory of the Russian Federation.
Electrochemical Study of Conductive Gel Polymer
Institute of Scientific and Technical Information of China (English)
Zhaohui Li; Jing Jiang; Gangtie Lei
2005-01-01
@@ 1Introduction Conventional ion-conducting polymer consists of electrolyte salt and polymer matrix, so-called salt-inpolymer. It possesses lower conductivity because the migration of ions depends on the motion of polymer segmental. To increase the ionic conductivity, a kind of gel polymer film (GPF) was prepared by in situ polymerization of methyl methacrylate (MMA) monomer in room-temperature ionic liquid(RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6). Due to immeasurably low vapor pressure, high ionic conductivity, and greater thermal and electrochemical stability, BMIPF6 is suitable electrolyte salts for ion-conducting polymer.
Functional mathematical model of dual pathway AV nodal conduction.
Climent, A M; Guillem, M S; Zhang, Y; Millet, J; Mazgalev, T N
2011-04-01
Dual atrioventricular (AV) nodal pathway physiology is described as two different wave fronts that propagate from the atria to the His bundle: one with a longer effective refractory period [fast pathway (FP)] and a second with a shorter effective refractory period [slow pathway (SP)]. By using His electrogram alternance, we have developed a mathematical model of AV conduction that incorporates dual AV nodal pathway physiology. Experiments were performed on five rabbit atrial-AV nodal preparations to develop and test the presented model. His electrogram alternances from the inferior margin of the His bundle were used to identify fast and slow wave front propagations. The ability to predict AV conduction time and the interaction between FP and SP wave fronts have been analyzed during regular and irregular atrial rhythms (e.g., atrial fibrillation). In addition, the role of dual AV nodal pathway wave fronts in the generation of Wenckebach periodicities has been illustrated. Finally, AV node ablative modifications have been evaluated. The model accurately reproduced interactions between FP and SP during regular and irregular atrial pacing protocols. In all experiments, specificity and sensitivity higher than 85% were obtained in the prediction of the pathway responsible for conduction. It has been shown that, during atrial fibrillation, the SP ablation significantly increased the mean HH interval (204 ± 39 vs. 274 ± 50 ms, P AV node mechanisms and should be considered as a step forward in the studies of AV nodal conduction.
A micromechanical model for effective conductivity in granular electrode structures
Ott, Julia; Völker, Benjamin; Gan, Yixiang; McMeeking, Robert M.; Kamlah, Marc
2013-10-01
Optimization of composition and microstructure is important to enhance performance of solid oxide fuel cells (SOFC) and lithium-ion batteries (LIB). For this, the porous electrode structures of both SOFC and LIB are modeled as a binary mixture of electronic and ionic conducting particles to estimate effective transport properties. Particle packings of 10 000 spherical, binary sized and randomly positioned particles are created numerically and densified considering the different manufacturing processes in SOFC and LIB: the sintering of SOFC electrodes is approximated geometrically, whereas the calendering process and volume change due to intercalation in LIB are modeled physically by a discrete element approach. A combination of a tracking algorithm and a resistor network approach is developed to predict the connectivity and effective conductivity for the various densified structures. For SOFC, a systematic study of the influence of morphology on connectivity and conductivity is performed on a large number of assemblies with different compositions and particle size ratios between 1 and 10. In comparison to percolation theory, an enlarged percolation area is found, especially for large size ratios. It is shown that in contrast to former studies the percolation threshold correlates to varying coordination numbers. The effective conductivity shows not only an increase with volume fraction as expected but also with size ratio. For LIB, a general increase of conductivity during the intercalation process was observed in correlation with increasing contact forces. The positive influence of calendering on the percolation threshold and the effective conductivity of carbon black is shown. The anisotropy caused by the calendering process does not influence the carbon black phase.
Non-Michaelis-Menten kinetics model for conductance of low-conductance potassium ion channels.
Tolokh, Igor S; Tolokh, Illya I; Cho, Hee Cheol; D'Avanzo, Nazzareno; Backx, Peter H; Goldman, Saul; Gray, C G
2005-02-01
A reduced kinetics model is proposed for ion permeation in low-conductance potassium ion channels with zero net electrical charge in the selectivity filter region. The selectivity filter is assumed to be the only conductance-determining part of the channel. Ion entry and exit rate constants depend on the occupancy of the filter due to ion-ion interactions. The corresponding rates are assumed slow relative to the rates of ion motion between binding sites inside the filter, allowing a reduction of the kinetics model of the filter by averaging the entry and exit rate constants over the states with a particular occupancy number. The reduced kinetics model for low-conductance channels is described by only three states and two sets of effective rate constants characterizing transitions between these states. An explicit expression for the channel conductance as a function of symmetrical external ion concentration is derived under the assumption that the average electrical mobility of ions in the selectivity filter region in a limited range of ion concentrations does not depend on these concentrations. The simplified conductance model is shown to provide a good description of the experimentally observed conductance-concentration curve for the low-conductance potassium channel Kir2.1, and also predicts the mean occupancy of the selectivity filter of this channel. We find that at physiological external ion concentrations this occupancy is much lower than the value of two ions observed for one of the high-conductance potassium channels, KcsA.
Institute of Scientific and Technical Information of China (English)
WAN Meixiang
1989-01-01
Method of VSC (Voltage Shorted Compaction ) can be used to determine the intrinsic temperature dependence of conductivity of polycrystalline compaction .The experimental conditions and technical key for preparation of VSC device and its physical model as well as its applications in conducting polymers are discussed in detail.
Cacciani, Francesca; Zaniboni, Massimiliano
2015-01-01
Initiation and maintenance of atrial fibrillation (AF) is often associated with pharmacologically or pathologically induced bradycardic states. Even drugs specifically developed in order to counteract cardiac arrhythmias often combine their action with bradycardia and, in turn, with development of AF, via still largely unknown mechanisms. This study aims to simulate action potential (AP) conduction between sinoatrial node (SAN) and atrial cells, either arranged in cell pairs or in a one-dimensional strand, where the relative amount of SAN membrane is made varying, in turn, with junctional resistance. The source-sink relationship between the two membrane types is studied in control conditions and under different simulated chronotropic interventions, in order to define a safety factor for pacemaker-to-atrial AP conduction (SASF) for each treatment. Whereas antiarrhythmic-like interventions which involve downregulation of calcium channels or of calcium handling decrease SASF, the simulation of Ivabradine administration does so to a lesser extent. Particularly interesting is the increase of SASF observed when downregulation GKr, which simulates the administration of class III antiarrhythmic agents and is likely sustained by an increase in ICaL. Also, the increase in SASF is accompanied by a decreased conduction delay and a better entrainment of repolarization, which is significant to anti-AF strategies. PMID:26229960
Directory of Open Access Journals (Sweden)
Francesca Cacciani
2015-01-01
Full Text Available Initiation and maintenance of atrial fibrillation (AF is often associated with pharmacologically or pathologically induced bradycardic states. Even drugs specifically developed in order to counteract cardiac arrhythmias often combine their action with bradycardia and, in turn, with development of AF, via still largely unknown mechanisms. This study aims to simulate action potential (AP conduction between sinoatrial node (SAN and atrial cells, either arranged in cell pairs or in a one-dimensional strand, where the relative amount of SAN membrane is made varying, in turn, with junctional resistance. The source-sink relationship between the two membrane types is studied in control conditions and under different simulated chronotropic interventions, in order to define a safety factor for pacemaker-to-atrial AP conduction (SASF for each treatment. Whereas antiarrhythmic-like interventions which involve downregulation of calcium channels or of calcium handling decrease SASF, the simulation of Ivabradine administration does so to a lesser extent. Particularly interesting is the increase of SASF observed when downregulation GKr, which simulates the administration of class III antiarrhythmic agents and is likely sustained by an increase in ICaL. Also, the increase in SASF is accompanied by a decreased conduction delay and a better entrainment of repolarization, which is significant to anti-AF strategies.
Electrochemical Corrosion Studies in Low Conductivity Media
1990-11-01
E.o (2) and the Tafel slopes: B - bbc/2.3(b + b,). (3) A Qomputer program has been devloped and tested earlier which allows simultaneous determinacion ...conductance of a solution made up of ions of high equivalent conductance, which is the case here. A Bode plot (log IZI vs log f) representation of
Conductivity studies on microwave synthesized glasses
Indian Academy of Sciences (India)
Asha Rajiv; M Sudhakara Reddy; R Viswanatha; Jayagopal Uchil; C Narayana Reddy
2015-08-01
Conductivity measurements have been made on 2O5 − (100 − ) [0.5 Na2O + 0.5 B2O3] (where 10 ≤ ≤ 50) glasses prepared by using microwave method. DC conductivity () measurements exhibit temperature-and compositional-dependent trends. It has been found that conductivity in these glasses changes from the predominantly ‘ionic’ to predominantly ‘electronic’ depending upon the chemical composition. The dc conductivity passes through a deep minimum, which is attributed to network disruption. Also, this nonlinear variation in dc and activation energy can be interpreted using ion–polaron correlation effect. Electron paramagnetic resonance (EPR) and impedance spectroscopic techniques have been used to elucidate the nature of conduction mechanism. The EPR spectra reveals, in least modified (25 Na2O mol%) glasses, conduction is due to the transfer of electrons via aliovalent vanadium sites, while in highly modified (45 Na2O mol%) glasses Na+ ion transport dominates the electrical conduction. For highly modified glasses, frequency-dependent conductivity has been analysed using electrical modulus formalism and the observations have been discussed.
Study on conductance of supersaturated chloride microdroplets
Institute of Scientific and Technical Information of China (English)
HE KeJuan; CHENG Hua; ZHU YanYing; WANG LiangYu; ZHANG YunHong
2009-01-01
By using the measuring system previously designed by the authors,the conductance of KCI,NaCl and NH4Cl microdroplets is obtained in the whole measuring RH range,especially in the supersaturation region,which cannot be acquired from the bulk solutions and fills the gap of lack of experimental data of conductance under the supersaturated state.The ERH and DRH of these three kinds of microdroplets observed from a microscope are 80.5% and 95.4% (KCI),75.7% and 93.3% (NaCl),and 69.9% and 96.6% (NH4Cl),respectively.In addition,it can be found from the dependence of conductance on RH that conductance is very sensitive to the existence of water molecules inside the microdroplet and the threshold of the deliquescence process can be predicted by the variation of conductance.
Study on conductance of supersaturated chloride microdroplets
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
By using the measuring system previously designed by the authors, the conductance of KCl, NaCl and NH4Cl microdroplets is obtained in the whole measuring RH range, especially in the supersaturation region, which cannot be acquired from the bulk solutions and fills the gap of lack of experimental data of conductance under the supersaturated state. The ERH and DRH of these three kinds of microdroplets observed from a microscope are 80.5% and 95.4% (KCl), 75.7% and 93.3% (NaCl), and 69.9% and 96.6% (NH4Cl), respectively. In addition, it can be found from the dependence of conductance on RH that conductance is very sensitive to the existence of water molecules inside the microdroplet and the threshold of the deliquescence process can be predicted by the variation of conductance.
Measurement and modeling of unsaturated hydraulic conductivity: Chapter 21
Perkins, Kim S.; Elango, Lakshmanan
2011-01-01
The unsaturated zone plays an extremely important hydrologic role that influences water quality and quantity, ecosystem function and health, the connection between atmospheric and terrestrial processes, nutrient cycling, soil development, and natural hazards such as flooding and landslides. Unsaturated hydraulic conductivity is one of the main properties considered to govern flow; however it is very difficult to measure accurately. Knowledge of the highly nonlinear relationship between unsaturated hydraulic conductivity (K) and volumetric water content () is required for widely-used models of water flow and solute transport processes in the unsaturated zone. Measurement of unsaturated hydraulic conductivity of sediments is costly and time consuming, therefore use of models that estimate this property from more easily measured bulk-physical properties is common. In hydrologic studies, calculations based on property-transfer models informed by hydraulic property databases are often used in lieu of measured data from the site of interest. Reliance on database-informed predicted values with the use of neural networks has become increasingly common. Hydraulic properties predicted using databases may be adequate in some applications, but not others.
Excitation model of pacemaker cardiomyocytes of cardiac conduction system
Grigoriev, M.; Babich, L.
2015-11-01
Myocardium includes typical and atypical cardiomyocytes - pacemakers, which form the cardiac conduction system. Excitation from the atrioventricular node in normal conditions is possible only in one direction. Retrograde direction of pulses is impossible. The most important prerequisite for the work of cardiomyocytes is the anatomical integrity of the conduction system. Changes in contractile force of the cardiomyocytes, which appear periodically, are due to two mechanisms of self-regulation - heterometric and homeometric. Graphic course of the excitation pulse propagation along the heart muscle more accurately reveals the understanding of the arrhythmia mechanism. These models have the ability to visualize the essence of excitation dynamics. However, they do not have the proper forecasting function for result estimation. Integrative mathematical model enables further investigation of general laws of the myocardium active behavior, allows for determination of the violation mechanism of electrical and contractile function of cardiomyocytes. Currently, there is no full understanding of the topography of pacemakers and ionic mechanisms. There is a need for the development of direction of mathematical modeling and comparative studies of the electrophysiological arrangement of cells of atrioventricular connection and ventricular conduction system.
Configurational Model for Conductivity of Stabilized Fluorite Structure Oxides
DEFF Research Database (Denmark)
Poulsen, Finn Willy
1981-01-01
The formalism developed here furnishes means by which ionic configurations, solid solution limits, and conductivity mechanisms in doped fluorite structures can be described. The present model differs markedly from previous models but reproduces qualitatively reality. The analysis reported...
Multiscale Modeling of Thermal Conductivity of Polymer/Carbon Nanocomposites
Clancy, Thomas C.; Frankland, Sarah-Jane V.; Hinkley, Jeffrey A.; Gates, Thomas S.
2010-01-01
Molecular dynamics simulation was used to estimate the interfacial thermal (Kapitza) resistance between nanoparticles and amorphous and crystalline polymer matrices. Bulk thermal conductivities of the nanocomposites were then estimated using an established effective medium approach. To study functionalization, oligomeric ethylene-vinyl alcohol copolymers were chemically bonded to a single wall carbon nanotube. The results, in a poly(ethylene-vinyl acetate) matrix, are similar to those obtained previously for grafted linear hydrocarbon chains. To study the effect of noncovalent functionalization, two types of polyethylene matrices. -- aligned (extended-chain crystalline) vs. amorphous (random coils) were modeled. Both matrices produced the same interfacial thermal resistance values. Finally, functionalization of edges and faces of plate-like graphite nanoparticles was found to be only modestly effective in reducing the interfacial thermal resistance and improving the composite thermal conductivity
Model for electrical conductivity of muscle meat during Ohmic heating
Sman, van der R.G.M.
2017-01-01
A model is presented for predicting the electrical conductivity of muscle meat, which can be used for the evaluation of Ohmic heating. The model computes the conductivity as a function of composition, temperature and microstructure. The muscle meat is thought to be composed of protein, water, salt.
Rock thermal conductivity as key parameter for geothermal numerical models
Di Sipio, Eloisa; Chiesa, Sergio; Destro, Elisa; Galgaro, Antonio; Giaretta, Aurelio; Gola, Gianluca; Manzella, Adele
2013-04-01
The geothermal energy applications are undergoing a rapid development. However, there are still several challenges in the successful exploitation of geothermal energy resources. In particular, a special effort is required to characterize the thermal properties of the ground along with the implementation of efficient thermal energy transfer technologies. This paper focuses on understanding the quantitative contribution that geosciences can receive from the characterization of rock thermal conductivity. The thermal conductivity of materials is one of the main input parameters in geothermal modeling since it directly controls the steady state temperature field. An evaluation of this thermal property is required in several fields, such as Thermo-Hydro-Mechanical multiphysics analysis of frozen soils, designing ground source heat pumps plant, modeling the deep geothermal reservoirs structure, assessing the geothermal potential of subsoil. Aim of this study is to provide original rock thermal conductivity values useful for the evaluation of both low and high enthalpy resources at regional or local scale. To overcome the existing lack of thermal conductivity data of sedimentary, igneous and metamorphic rocks, a series of laboratory measurements has been performed on several samples, collected in outcrop, representative of the main lithologies of the regions included in the VIGOR Project (southern Italy). Thermal properties tests were carried out both in dry and wet conditions, using a C-Therm TCi device, operating following the Modified Transient Plane Source method.Measurements were made at standard laboratory conditions on samples both water saturated and dehydrated with a fan-forced drying oven at 70 ° C for 24 hr, for preserving the mineral assemblage and preventing the change of effective porosity. Subsequently, the samples have been stored in an air-conditioned room while bulk density, solid volume and porosity were detected. The measured thermal conductivity
Structural and Electrical Study of Conducting Polymers
Shaktawat, Vinodini; Dixit, Manasvi; Saxena, N. S.; Sharma, Kananbala
2010-06-01
Pure and oxalic acid doped conducting polymers (polyaniline and polypyrrole) were chemically synthesized using ammonium persulfate (APS) as an oxidant. These samples were characterized through Scanning Electron Microscopy (SEM), which provides information about the surface topography of polymers. I-V characteristics have been recorded at room temperature as well as in the temperature range from 313 K to 463 K. So obtained characteristic curves were found to be linear. Temperature dependence of conductivity suggests a semiconducting nature in polyaniline samples with increase in temperature, whereas oxalic acid doped polypyrrole sample suggests a transition from semiconducting to metallic nature with the increase of temperature.
Numerical Modelling of Electric Conductance of a thin Sheet
Directory of Open Access Journals (Sweden)
Mojmir Kollar
2006-01-01
Full Text Available In this paper the numeric modelling of total resistance of a thin sheet, with local conductivity in randomlydistributed grains higher then is that of the basic matrix, is presented. The 2D model is formed by a structure of longitudinaland transversal conductors interconnected in nodes of a square net. In all nodes, using iteration procedure, the potential isdetermined from which the conductance of sheet is computed between two touching electrodes. The described model can beused to imitate the behaviour of heterogeneous thin conducting sheets prepared by different techniques. The model wasverified in some cases where the net resistance is well known from the theory.
Neuroscience Investigations: An Overview of Studies Conducted
Reschke, Millard F.
1999-01-01
The neural processes that mediate human spatial orientation and adaptive changes occurring in response to the sensory rearrangement encountered during orbital flight are primarily studied through second and third order responses. In the Extended Duration Orbiter Medical Project (EDOMP) neuroscience investigations, the following were measured: (1) eye movements during acquisition of either static or moving visual targets, (2) postural and locomotor responses provoked by unexpected movement of the support surface, changes in the interaction of visual, proprioceptive, and vestibular information, changes in the major postural muscles via descending pathways, or changes in locomotor pathways, and (3) verbal reports of perceived self-orientation and self-motion which enhance and complement conclusions drawn from the analysis of oculomotor, postural, and locomotor responses. In spaceflight operations, spatial orientation can be defined as situational awareness, where crew member perception of attitude, position, or motion of the spacecraft or other objects in three-dimensional space, including orientation of one's own body, is congruent with actual physical events. Perception of spatial orientation is determined by integrating information from several sensory modalities. This involves higher levels of processing within the central nervous system that control eye movements, locomotion, and stable posture. Spaceflight operational problems occur when responses to the incorrectly perceived spatial orientation are compensatory in nature. Neuroscience investigations were conducted in conjunction with U. S. Space Shuttle flights to evaluate possible changes in the ability of an astronaut to land the Shuttle or effectively perform an emergency post-landing egress following microgravity adaptation during space flights of variable length. While the results of various sensory motor and spatial orientation tests could have an impact on future space flights, our knowledge of
40 CFR 160.130 - Conduct of a study.
2010-07-01
... 40 Protection of Environment 23 2010-07-01 2010-07-01 false Conduct of a study. 160.130 Section... LABORATORY PRACTICE STANDARDS Protocol for and Conduct of a Study § 160.130 Conduct of a study. (a) The study... the conduct of a study, except those that are generated by automated data collection systems, shall be...
Thermal Conductivity of the Potential Repository Horizon Model Report
Energy Technology Data Exchange (ETDEWEB)
J. Ramsey
2002-08-29
The purpose of this report is to assess the spatial variability and uncertainty of thermal conductivity in the host horizon for the proposed repository at Yucca Mountain. More specifically, the lithostratigraphic units studied are located within the Topopah Spring Tuff (Tpt) and consist of the upper lithophysal zone (Tptpul), the middle nonlithophysal zone (Tptpmn), the lower lithophysal zone (Tptpll), and the lower nonlithophysal zone (Tptpln). The Tptpul is the layer directly above the repository host layers, which consist of the Tptpmn, Tptpll, and the Tptpln. Current design plans indicate that the largest portion of the repository will be excavated in the Tptpll (Board et al. 2002 [157756]). The main distinguishing characteristic among the lithophysal and nonlithophysal units is the percentage of large scale (cm-m) voids within the rock. The Tptpul and Tptpll, as their names suggest, have a higher percentage of lithophysae than the Tptpmn and the Tptpln. Understanding the influence of the lithophysae is of great importance to understanding bulk thermal conductivity and perhaps repository system performance as well. To assess the spatial variability and uncertainty of thermal conductivity, a model is proposed that is functionally dependent on the volume fraction of lithophysae and the thermal conductivity of the matrix portion of the rock. In this model, void space characterized as lithophysae is assumed to be air-saturated under all conditions, while void space characterized as matrix may be either water- or air-saturated. Lithophysae are assumed to be air-saturated under all conditions since the units being studied are all located above the water table in the region of interest, and the relatively strong capillary forces of the matrix will, under most conditions, preferentially retain any moisture present in the rock.
Bayesian Model Averaging of Artificial Intelligence Models for Hydraulic Conductivity Estimation
Nadiri, A.; Chitsazan, N.; Tsai, F. T.; Asghari Moghaddam, A.
2012-12-01
This research presents a Bayesian artificial intelligence model averaging (BAIMA) method that incorporates multiple artificial intelligence (AI) models to estimate hydraulic conductivity and evaluate estimation uncertainties. Uncertainty in the AI model outputs stems from error in model input as well as non-uniqueness in selecting different AI methods. Using one single AI model tends to bias the estimation and underestimate uncertainty. BAIMA employs Bayesian model averaging (BMA) technique to address the issue of using one single AI model for estimation. BAIMA estimates hydraulic conductivity by averaging the outputs of AI models according to their model weights. In this study, the model weights were determined using the Bayesian information criterion (BIC) that follows the parsimony principle. BAIMA calculates the within-model variances to account for uncertainty propagation from input data to AI model output. Between-model variances are evaluated to account for uncertainty due to model non-uniqueness. We employed Takagi-Sugeno fuzzy logic (TS-FL), artificial neural network (ANN) and neurofuzzy (NF) to estimate hydraulic conductivity for the Tasuj plain aquifer, Iran. BAIMA combined three AI models and produced better fitting than individual models. While NF was expected to be the best AI model owing to its utilization of both TS-FL and ANN models, the NF model is nearly discarded by the parsimony principle. The TS-FL model and the ANN model showed equal importance although their hydraulic conductivity estimates were quite different. This resulted in significant between-model variances that are normally ignored by using one AI model.
Model for thermal conductivity of CNT-nanofluids
Indian Academy of Sciences (India)
H E Patel; K B Anoop; T Sundararajan; Sarit K Das
2008-06-01
This work presents a simple model for predicting the thermal conductivity of carbon nanotube (CNT) nanofluids. Effects due to the high thermal conductivity of CNTs and the percolation of heat through it are considered to be the most important reasons for their anomalously high thermal conductivity enhancement. A new approach is taken for the modeling, the novelty of which lies in the prediction of the thermal behaviour of oil based as well as water based CNT nanofluids, which are quite different from each other in thermal characteristics. The model is found to correctly predict the trends observed in experimental data for different combinations of CNT nanofluids with varying concentrations.
Precise methods for conducted EMI modeling,analysis,and prediction
Institute of Scientific and Technical Information of China (English)
2008-01-01
Focusing on the state-of-the-art conducted EMI prediction, this paper presents a noise source lumped circuit modeling and identification method, an EMI modeling method based on multiple slope approximation of switching transitions, and dou-ble Fourier integral method modeling PWM conversion units to achieve an accurate modeling of EMI noise source. Meanwhile, a new sensitivity analysis method, a general coupling model for steel ground loops, and a partial element equivalent circuit method are proposed to identify and characterize conducted EMI coupling paths. The EMI noise and propagation modeling provide an accurate prediction of conducted EMI in the entire frequency range (0―10 MHz) with good practicability and generality. Finally a new measurement approach is presented to identify the surface current of large dimensional metal shell. The proposed analytical modeling methodology is verified by experimental results.
Precise methods for conducted EMI modeling,analysis, and prediction
Institute of Scientific and Technical Information of China (English)
MA WeiMing; ZHAO ZhiHua; MENG Jin; PAN QiJun; ZHANG Lei
2008-01-01
Focusing on the state-of-the-art conducted EMI prediction, this paper presents a noise source lumped circuit modeling and identification method, an EMI modeling method based on multiple slope approximation of switching transitions, and dou-ble Fourier integral method modeling PWM conversion units to achieve an accurate modeling of EMI noise source. Meanwhile, a new sensitivity analysis method, a general coupling model for steel ground loops, and a partial element equivalent circuit method are proposed to identify and characterize conducted EMI coupling paths. The EMI noise and propagation modeling provide an accurate prediction of conducted EMI in the entire frequency range (0-10 MHz) with good practicability and generality. Finally a new measurement approach is presented to identify the surface current of large dimensional metal shell. The proposed analytical modeling methodology is verified by experimental results.
Height-integrated conductivity in auroral substorms - 2. Modeling
DEFF Research Database (Denmark)
Gjerløv, Jesper Wittendorff; Hoffman, R.A.
2000-01-01
Calculations of height-integrated conductivity from 31 individual Dynamics Explorer (DE 2) substorm crossings presented by Gjerloev and Hoffman [this issue] are used to compile empirical models of the height-integrated Pedersen and Hall conductivities (conductances) in a bulge-type auroral substorm....... Global auroral images obtained by Dynamics Explorer 1 (DE 1) were used to select substorms displaying a typical bulge-type emission pattern and each individual DE 2 pass was positioned with respect to key features in the observed emission pattern. The conductances were calculated for each DE 2 pass using...... electron precipitation data and a monoenergetic conductance model. All passes were divided into six different sectors, and average conductance profiles were carefully deduced for each of these sectors. Using a simple boxcar filter, smoothed average sector passes were calculated and from linear...
Multiscale modeling of thermal conductivity of polycrystalline graphene sheets.
Mortazavi, Bohayra; Pötschke, Markus; Cuniberti, Gianaurelio
2014-03-21
We developed a multiscale approach to explore the effective thermal conductivity of polycrystalline graphene sheets. By performing equilibrium molecular dynamics (EMD) simulations, the grain size effect on the thermal conductivity of ultra-fine grained polycrystalline graphene sheets is investigated. Our results reveal that the ultra-fine grained graphene structures have thermal conductivity one order of magnitude smaller than that of pristine graphene. Based on the information provided by the EMD simulations, we constructed finite element models of polycrystalline graphene sheets to probe the thermal conductivity of samples with larger grain sizes. Using the developed multiscale approach, we also investigated the effects of grain size distribution and thermal conductivity of grains on the effective thermal conductivity of polycrystalline graphene. The proposed multiscale approach on the basis of molecular dynamics and finite element methods could be used to evaluate the effective thermal conductivity of polycrystalline graphene and other 2D structures.
Nuts and bolts of conducting feasibility studies.
Tickle-Degnen, Linda
2013-01-01
Many factors can affect the successful implementation and validity of intervention studies. A primary purpose of feasibility and pilot studies is to assess the potential for successful implementation of the proposed main intervention studies and to reduce threats to the validity of these studies. This article describes a typology to guide the aims of feasibility and pilot studies designed to support the development of randomized controlled trials and provides an example of the studies underlying the development of one rehabilitation trial. The purpose of most feasibility and pilot studies should be to describe information and evidence related to the successful implementation and validity of a planned main trial. Null hypothesis significance testing is not appropriate for these studies unless the sample size is properly powered. The primary tests of the intervention effectiveness hypotheses should occur in the main study, not in the studies that are serving as feasibility or pilot studies.
Institute of Scientific and Technical Information of China (English)
潘和平; 王家映; 樊政军; 马勇; 柳建华; 李明强
2001-01-01
Shaly sands reservoir is one of the most distributive types of the oil(gas)-bearing reservoirs discovered in China, and low resistivity oil(gas)-bearing reservoirs are mostly shaly sands reservoirs. Therefore, shaly sands reservoir conductive model is the key to evaluate low resistivity oil(gas)-bearing reservoirs using logging information. Some defects were found when we studied the clay distribution type conductive model, dual-water conductive model, conductive rock matrix model, etc. Some models could not distinguish the conductive path and nature of microporosity water and clay water and some models did not consider the clay distribution type and the mount of clay volume. So, we utilize the merits,overcome the defects of the above models, and put forward a new shaly sands conductive model-dual water clay matrix conductive model (DWCMCM) in which dual water is the free water and the microporosity water in shaly sands and the clay matrix(wet clay) is the clay grain containing water. DWCMCM is presented here, the advantages of which can tell the nature and conductive path from different water (microporosity water and freewater), in consid-eration of the clay distribution type and the mount of clay volume in shaly sands. So, the results of logging interpretation in the oil(gas)-bearing reservoirs in the north of Tarim Basin area, China with DWCMCM are better than those interpreted by the above models.
Study of the conductivity of irradiated dielectrics
Energy Technology Data Exchange (ETDEWEB)
Maslov, V.V.; Ivanov, N.V.; Shelenin, A.V.
1977-01-01
The processes of ionization of air, metals and dielectrics arising from Gamma irradiation are analyzed. The effect of these processes on the measurement of the electrical conductivity of the dielectrics which are irradiated is evaluated. The maximum current which can be carried by an ionized gas is proportional to the radiation dose, gas pressure and reciprocal gas temperature. It is much more difficult to define the voltage developing between the two metal objects exposed to ionizing radiation due to such factors as the variation in resistance with dose, difficulty in defining the coefficient characterizing the accumulated charge, which depends on the nature of the metal, its shape, thickness and many other factors. Results of a simple calculation are presented in tabular form for aluminum. In some cases the voltage which develops is proportional to dose, in other cases--to the square root of dose, in still other cases--somewhere in between. 3 tables, 6 references.
Investigating Student Understanding of Quantum Mechanics Spontaneous Models of Conductivity
Wittmann, M C; Redish, E F; Wittmann, Michael C.; Steinberg, Richard N.; Redish, Edward F.
2002-01-01
Students are taught several models of conductivity, both at the introductory and the advanced level. From early macroscopic models of current flow in circuits, through the discussion of microscopic particle descriptions of electrons flowing in an atomic lattice, to the development of microscopic non-localized band diagram descriptions in advanced physics courses, they need to be able to distinguish between commonly used, though sometimes contradictory, physical models. In investigations of student reasoning about models of conduction, we find that students often are unable to account for the existence of free electrons in a conductor and create models that lead to incorrect predictions and responses contradictory to expert descriptions of the physics. We have used these findings as a guide to creating curriculum materials that we show can be effective helping students to apply the different conduction models more effectively.
Noise Modeling From Conductive Shields Using Kirchhoff Equations.
Sandin, Henrik J; Volegov, Petr L; Espy, Michelle A; Matlashov, Andrei N; Savukov, Igor M; Schultz, Larry J
2010-10-01
Progress in the development of high-sensitivity magnetic-field measurements has stimulated interest in understanding the magnetic noise of conductive materials, especially of magnetic shields based on high-permeability materials and/or high-conductivity materials. For example, SQUIDs and atomic magnetometers have been used in many experiments with mu-metal shields, and additionally SQUID systems frequently have radio frequency shielding based on thin conductive materials. Typical existing approaches to modeling noise only work with simple shield and sensor geometries while common experimental setups today consist of multiple sensor systems with complex shield geometries. With complex sensor arrays used in, for example, MEG and Ultra Low Field MRI studies, knowledge of the noise correlation between sensors is as important as knowledge of the noise itself. This is crucial for incorporating efficient noise cancelation schemes for the system. We developed an approach that allows us to calculate the Johnson noise for arbitrary shaped shields and multiple sensor systems. The approach is efficient enough to be able to run on a single PC system and return results on a minute scale. With a multiple sensor system our approach calculates not only the noise for each sensor but also the noise correlation matrix between sensors. Here we will show how the algorithm can be implemented.
Validation of conducting wall models using magnetic measurements
Hanson, J. M.; Bialek, J.; Turco, F.; King, J.; Navratil, G. A.; Strait, E. J.; Turnbull, A.
2016-10-01
The impact of conducting wall eddy currents on perturbed magnetic field measurements is a key issue for understanding the measurement and control of long-wavelength MHD stability in tokamak devices. As plasma response models have growth in sophistication, the need to understand and resolve small changes in these measurements has become more important, motivating increased fidelity in simulations of externally applied fields and the wall eddy current response. In this manuscript, we describe thorough validation studies of the wall models in the mars-f and valen stability codes, using coil-sensor vacuum coupling measurements from the DIII-D tokamak (Luxon et al 2005 Fusion Sci. Technol. 48 807). The valen formulation treats conducting structures with arbitrary three-dimensional geometries, while mars-f uses an axisymmetric wall model and a spectral decomposition of the problem geometry with a fixed toroidal harmonic n. The vacuum coupling measurements have a strong sensitivity to wall eddy currents induced by time-changing coil currents, owing to the close proximities of both the sensors and coils to the wall. Measurements from individual coil and sensor channels are directly compared with valen predictions. It is found that straightforward improvements to the valen model, such as refining the wall mesh and simulating the vertical extent of the DIII-D poloidal field sensors, lead to good agreement with the experimental measurements. In addition, couplings to multi-coil, n = 1 toroidal mode perturbations are calculated from the measurements and compared with predictions from both codes. The toroidal mode comparisons favor the fully three-dimensional simulation approach, likely because this approach naturally treats n > 1 sidebands generated by the coils and wall eddy currents, as well as the n = 1 fundamental.
Fractional Heat Conduction Models and Thermal Diffusivity Determination
Directory of Open Access Journals (Sweden)
Monika Žecová
2015-01-01
Full Text Available The contribution deals with the fractional heat conduction models and their use for determining thermal diffusivity. A brief historical overview of the authors who have dealt with the heat conduction equation is described in the introduction of the paper. The one-dimensional heat conduction models with using integer- and fractional-order derivatives are listed. Analytical and numerical methods of solution of the heat conduction models with using integer- and fractional-order derivatives are described. Individual methods have been implemented in MATLAB and the examples of simulations are listed. The proposal and experimental verification of the methods for determining thermal diffusivity using half-order derivative of temperature by time are listed at the conclusion of the paper.
AC-conductance of a non-local Thirring model
Energy Technology Data Exchange (ETDEWEB)
Trobo, Marta Liliana; Von Reichenbach, Maria Cecilia [Universidad Nacional de La Plata (UNLP) (Argentina); Barci, Daniel G. [Universidade do Estado do Rio de Janeiro (UERJ), RJ (Brazil)]|[Illinois Univ., Urbana, IL (United States); Medeiros Neto, J.F. de [Universidade Estadual de Santa Cruz (UESC), Ilheus, BA (Brazil)
2000-07-01
Full text follows: In recent years renewed interest has arisen in the study of low dimensional field theories. In particular, research on the one dimensional (1-d) fermionic gas has been very active, mainly due to the actual nano-fabrication of the so called quantum wires and their relevance for low dimensional condensed matter physics as, for instance, the quantum Hall effect and high-T{sub c} superconductivity. Experimental and theoretical investigations of the AC-transport phenomena in nano-structures are of profound scientific interest since they provide insight into the behavior of quantum systems. In this frame, we consider a field theoretical approach that can be used to describe a system of 1-d strongly correlated particles in the low transferred momentum limit. We study a non-local and non-covariant version of the Thirring model where the fermionic densities and currents are coupled through bilocal, distance-dependent potentials which describe the forward scattering processes. We apply the functional bosonization formalism, a very useful technique to understand the non-perturbative regime of strongly correlated one-dimensional fermionic systems, to this non local Thirring like model (NLTM). We are interesting in the transport properties of the system, in particular in the AC-conductance. To this end, we consider a NLTM in the presence of an external electromagnetic field. We obtain the AC-conductance of the model in terms of non-local potentials used to describe the interactions between fermionic currents. We also analyze the transport properties in the case in which weak couplings between fermionic currents and localized impurities are taken into account. (author)
Modelling of diffusion and conductivity relaxation of oxide ceramics
Preis, Wolfgang
2016-12-01
A two-dimensional square grain model has been applied to simulate simultaneously the diffusion process and relaxation of the dc conduction of polycrystalline oxide materials due to a sudden change of the oxygen partial pressure of the surrounding gas phase. The numerical calculations are performed by employing the finite element approach. The grains are squares of equal side length (average grain size) and the grain boundaries may consist of thin slabs of uniform thickness. An additional (space charge) layer adjacent to the grain boundary cores (thin slabs) either blocking (depletion layer) or highly conductive for electronic charge carriers may surround the grains. The electronic transport number of the mixed ionic-electronic conducting oxide ceramics may be close to unity (predominant electronic conduction). If the chemical diffusion coefficient of the neutral mobile component (oxygen) of the grain boundary core regions is assumed to be higher by many orders of magnitude than that in the bulk, the simulated relaxation curves for mass transport (diffusion) and dc conduction can deviate remarkably from each other. Deviations between the relaxation of mass transport and dc conduction are found in the case of considerably different electronic conductivities of grain boundary core regions, space charge layers, and bulk. On the contrary, the relaxation curves of mass transport and electronic conductivity are in perfect coincidence, when either effective medium diffusion occurs or the effective conductivity is unaffected by the individual conductivities of core regions and possible space charge layers, i.e. the grain boundary resistivity is negligible.
Inverse modeling for heat conduction problem in human abdominal phantom.
Huang, Ming; Chen, Wenxi
2011-01-01
Noninvasive methods for deep body temperature measurement are based on the principle of heat equilibrium between the thermal sensor and the target location theoretically. However, the measurement position is not able to be definitely determined. In this study, a 2-dimensional mathematical model was built based upon some assumptions for the physiological condition of the human abdomen phantom. We evaluated the feasibility in estimating the internal organs temperature distribution from the readings of the temperature sensors arranged on the skin surface. It is a typical inverse heat conduction problem (IHCP), and is usually mathematically ill-posed. In this study, by integrating some physical and physiological a-priori information, we invoked the quasi-linear (QL) method to reconstruct the internal temperature distribution. The solutions of this method were improved by increasing the accuracy of the sensors and adjusting their arrangement on the outer surface, and eventually reached the state of converging at the best state accurately. This study suggests that QL method is able to reconstruct the internal temperature distribution in this phantom and might be worthy of a further study in an anatomical based model.
The optimization model of the heat conduction structure
Institute of Scientific and Technical Information of China (English)
Yongcun Zhang; Shutian Liu
2008-01-01
An optimization model considering a novel thermal performance index to be the objective function is proposed for minimizing the highest temperature in this paper. Firstly, the performance of the conventional heat conduction optimization model, with the dissipation of heat transport potential capacity as the objective function, is evaluated by a one-dimensional heat conduction problem in a planar plate exchanger. Then, a new thermal performance index, named the geometric average temperature, is introduced. The new heat conduction optimization model, with the geometric average temperature as the objective function, is developed and the corresponding finite element formula is presented. The results show that the geometric average temperature is an ideal thermal performance index and the solution of the new model is close to the theoretical optimal solution.
Deng, Dong-dong; Gong, Ying-lan; Shou, Guo-fa; Jiao, Pei-feng; Zhang, Heng-gui; Ye, Xue-song; Xia, Ling
2012-01-01
In order to better understand biatrial conduction, investigate various conduction pathways, and compare the differences between isotropic and anisotropic conductions in human atria, we present a simulation study of biatrial conduction with known/assumed conduction pathways using a recently developed human atrial model. In addition to known pathways: (1) Bachmann’s bundle (BB), (2) limbus of fossa ovalis (LFO), and (3) coronary sinus (CS), we also hypothesize that there exist two fast conducti...
Model Hamiltonian for the conductivity oscillations of magnetic multilayers
Weissmann, Mariana; Llois, Ana Maria; Kiwi, Miguel; Ramirez, Ricardo
1997-03-01
The behavior of the electrical conductivity as a function of layer thickness of the superlattice systems Ni/Co, Ni/Cu and Pd/Ag is studied. Experimentally an oscillatory dependence was found for the first two, while the latter exhibited a monotonous behavior. In our previous calculations we found that, in these superlattices, the current is carried by the sp--character electrons, which are quite insensitive to the interfaces. Therefore, to interpret the experimentally observed resistivity oscillations, we suggest a scattering mechanism of these carriers against d--character quantum well states that are present in only one of the superlattice materials, when the well state energy is close to E_F. To explore the validity of this mechanism we have put forward a model Hamiltonian which, for reasonable values of the parameters, leads to results in good agreement with experiments.
Current fluctuations in a two dimensional model of heat conduction
Pérez-Espigares, Carlos; Garrido, Pedro L.; Hurtado, Pablo I.
2011-03-01
In this work we study numerically and analytically current fluctuations in the two-dimensional Kipnis-Marchioro-Presutti (KMP) model of heat conduction. For that purpose, we use a recently introduced algorithm which allows the direct evaluation of large deviations functions. We compare our results with predictions based on the Hydrodynamic Fluctuation Theory (HFT) of Bertini and coworkers, finding very good agreement in a wide interval of current fluctuations. We also verify the existence of a well-defined temperature profile associated to a given current fluctuation which depends exclusively on the magnitude of the current vector, not on its orientation. This confirms the recently introduced Isometric Fluctuation Relation (IFR), which results from the time-reversibility of the dynamics, and includes as a particular instance the Gallavotti-Cohen fluctuation theorem in this context but adds a completely new perspective on the high level of symmetry imposed by timereversibility on the statistics of nonequilibrium fluctuations.
Mathematical modeling of mechanical vibration assisted conductivity imaging
Ammari, Habib; Kwon, Hyeuknam; Seo, Jin Keun; Woo, Eung Je
2014-01-01
This paper aims at mathematically modeling a new multi-physics conductivity imaging system incorporating mechanical vibrations simultaneously applied to an imaging object together with current injections. We perturb the internal conductivity distribution by applying time-harmonic mechanical vibrations on the boundary. This enhances the effects of any conductivity discontinuity on the induced internal current density distribution. Unlike other conductivity contrast enhancing frameworks, it does not require a prior knowledge of a reference data. In this paper, we provide a mathematical framework for this novel imaging modality. As an application of the vibration-assisted impedance imaging framework, we propose a new breast image reconstruction method in electrical impedance tomography (EIT). As its another application, we investigate a conductivity anomaly detection problem and provide an efficient location search algorithm. We show both analytically and numerically that the applied mechanical vibration increas...
Modeling Interfacial Thermal Boundary Conductance of Engineered Interfaces
2014-08-31
involving carbon materials. Determined scaling laws for conductivity of carbon nanotube networks [11]. Modified the DMM to predict hBD at metal–graphite...111, 084310 (2012). 11A. N. Volkov and L. V. Zhigilei, “Scaling laws and mesoscopic modeling of thermal conductivity in carbon nanotube materials...instead from an algebraic expression that accurately reproduces the MD results but with negligible computational expense. This permitted a large
Percolative model of proton conductivity of Nafion {sup registered} membranes
Energy Technology Data Exchange (ETDEWEB)
Costamagna, Paola; Grosso, Simone; Di Felice, Renzo [DICheP, Department of Chemical and Process Engineering ' G.B. Bonino' , University of Genoa, Via Opera Pia 15, 16145 Genoa (Italy)
2008-04-01
A model is proposed for the simulation of Nafion {sup registered} proton conductivity, where it is assumed that proton conduction occurs only in the water present in the membrane pores. Water is considered to be present in the pores due to two different phenomena: adsorption and capillary condensation. In the latter case, the pore is flooded and proton conduction occurs throughout the whole pore section. The conditions under which capillary condensation occurs are simulated in the model through the Kelvin-Cohan equation for condensation. The Kelvin-Cohan equation is a function of RH, temperature and the pore radius; the larger the pore, the higher the RH for which capillary condensation takes place. If the conditions for capillary condensation are not satisfied, then water is present in the pore due to adsorption under the form of a water layer which covers the pore walls and provides a path for proton conduction. In this case, the modified Brunauer-Emmet-Teller (BET) equation has been used in the model to simulate the thickness of the water layer. In both cases of capillary condensation and adsorption, the conductance g of a pore has then been calculated through the formula g = {kappa}S/l, where {kappa} is the proton conductivity of water, S the cross-section of the pore volume which is occupied by water, and l is the pore length. Pores of different size are present in the membrane (data of pore size distribution have been extracted from the literature); connectivity of the water layers present in the different pores is necessary in order to achieve a continuous path of proton conduction through the membrane, which is a percolation problem. To this end, the structure of the membrane pores has been simulated in the model through the effective medium approximation (EMA). The simulation results of proton conductivity of the membrane show good agreement with literature experimental data, even when varying the RH operating conditions. (author)
Random resistor network model of minimal conductivity in graphene.
Cheianov, Vadim V; Fal'ko, Vladimir I; Altshuler, Boris L; Aleiner, Igor L
2007-10-26
Transport in undoped graphene is related to percolating current patterns in the networks of n- and p-type regions reflecting the strong bipolar charge density fluctuations. Finite transparency of the p-n junctions is vital in establishing the macroscopic conductivity. We propose a random resistor network model to analyze scaling dependencies of the conductance on the doping and disorder, the quantum magnetoresistance and the corresponding dephasing rate.
Schwinger effect and negative differential conductivity in holographic models
Directory of Open Access Journals (Sweden)
Shankhadeep Chakrabortty
2015-01-01
Full Text Available The consequences of the Schwinger effect for conductivity are computed for strong coupling systems using holography. The one-loop diagram on the flavor brane introduces an O(λNc imaginary part in the effective action for a Maxwell flavor gauge field. This in turn introduces a real conductivity in an otherwise insulating phase of the boundary theory. Moreover, in certain regions of parameter space the differential conductivity is negative. This is computed in the context of the Sakai–Sugimoto model.
Physical mechanisms of nonlinear conductivity: A model analysis
Heuer, Andreas; Lühning, Lars
2014-03-01
Nonlinear effects are omnipresent in thin films of ion conducting materials showing up as a significant increase of the conductivity. For a disordered hopping model general physical mechanisms are identified giving rise to the occurrence of positive or negative nonlinear effects, respectively. Analytical results are obtained in the limit of high but finite dimensions. They are compared with the numerical results for 3D up to 6D systems. A very good agreement can be found, in particular for higher dimensions. The results can also be used to rationalize previous numerical simulations. The implications for the interpretation of nonlinear conductivity experiments on inorganic ion conductors are discussed.
OTTEN, E; HULLIGER, M; SCHEEPSTRA, KA
1995-01-01
The general mathematical model of Frankenhaeuser and Huxley, which describes the generation of action potentials in myelinated nerve fibres, has been used as a kernel for a model of a sensory nerve ending. Two types of modifications were implemented. First, the four original permeability constants (
DEFF Research Database (Denmark)
Henriksen, J H
1985-01-01
compatible with increased sinusoidal wall tightening and fibrosis in the interstitial space of the liver. The model presented supports the so-called 'lymph-imbalance' theory of ascites formation according to which a relatively insufficient lymph drainage is important in the pathogenesis of hepatic ascites....
A Model for Conducting and Assessing Interdisciplinary Undergraduate Dissertations
Engström, Henrik
2015-01-01
This paper presents an effort to create a unified model for conducting and assessing undergraduate dissertations, shared by all disciplines involved in computer game development at a Swedish university. Computer game development includes technology-oriented disciplines as well as disciplines with aesthetical traditions. The challenge has been to…
Modelling and measurement of high switching frequency conducted EMI
CSIR Research Space (South Africa)
Grobler, Inus
2013-11-01
Full Text Available to perform the analyses of the model, presented as a very easy and reliable tool. The common mode effect of electrically non-conductive polymer heatsinks was presented and tested as a remedy to reduce the increased common mode noise levels due to higher...
Physical-Statistical Model of Thermal Conductivity of Nanofluids
Directory of Open Access Journals (Sweden)
B. Usowicz
2014-01-01
Full Text Available A physical-statistical model for predicting the effective thermal conductivity of nanofluids is proposed. The volumetric unit of nanofluids in the model consists of solid, liquid, and gas particles and is treated as a system made up of regular geometric figures, spheres, filling the volumetric unit by layers. The model assumes that connections between layers of the spheres and between neighbouring spheres in the layer are represented by serial and parallel connections of thermal resistors, respectively. This model is expressed in terms of thermal resistance of nanoparticles and fluids and the multinomial distribution of particles in the nanofluids. The results for predicted and measured effective thermal conductivity of several nanofluids (Al2O3/ethylene glycol-based and Al2O3/water-based; CuO/ethylene glycol-based and CuO/water-based; and TiO2/ethylene glycol-based are presented. The physical-statistical model shows a reasonably good agreement with the experimental results and gives more accurate predictions for the effective thermal conductivity of nanofluids compared to existing classical models.
Ruhlin, C. L.; Rauch, F. J., Jr.; Waters, C.
1982-01-01
The model was a 1/6.5-size, semipan version of a wing proposed for an executive-jet-transport airplane. The model was tested with a normal wingtip, a wingtip with winglet, and a normal wingtip ballasted to simulate the winglet mass properties. Flutter and aerodynamic data were acquired at Mach numbers (M) from 0.6 to 0.95. The measured transonic flutter speed boundary for each wingtip configuration had roughly the same shape with a minimum flutter speed near M=0.82. The winglet addition and wingtip mass ballast decreased the wing flutter speed by about 7 and 5 percent, respectively; thus, the winglet effect on flutter was more a mass effect than an aerodynamic effect.
Institute of Scientific and Technical Information of China (English)
Dong-dong DENG; Ying-lan GONG; Guo-fa SHOU; Pei-feng JIAO; Heng-gui ZHANG; Xue-song YE; Ling XIA
2012-01-01
In order to better understand biatrial conduction,investigate various conduction pathways,and compare the differences between isotropic and anisotropic conductions in human atria,we present a simulation study of biatrial conduction with known/assumed conduction pathways using a recently developed human atrial model.In addition to known pathways:(1) Bachmann's bundle (BB),(2) limbus of fossa ovalis (LFO),and (3) coronary sinus (CS),we also hypothesize that there exist two fast conduction bundles that connect the crista terminalis (CT),LFO,and CS.Our simulation demonstrates that use of these fast conduction bundles results in a conduction pattern consistent with experimental data.The comparison of isotropic and anisotropoic conductions in the BB case showed that the atrial working muscles had small effect on conduction time and conduction speed,although the conductivities assigned in anisotropic conduction were two to four times higher than the isotropic conduction.In conclusion,we suggest that the hypothesized intercaval bundles play a significant role in the biatrial conduction and that myofiber orientation has larger effects on the conduction system than the atrial working muscles.This study presents readers with new insights into human atrial conduction.
Oxygen reduction kinetics on mixed conducting SOFC model cathodes
Energy Technology Data Exchange (ETDEWEB)
Baumann, F.S.
2006-07-01
The kinetics of the oxygen reduction reaction at the surface of mixed conducting solid oxide fuel cell (SOFC) cathodes is one of the main limiting factors to the performance of these promising systems. For ''realistic'' porous electrodes, however, it is usually very difficult to separate the influence of different resistive processes. Therefore, a suitable, geometrically well-defined model system was used in this work to enable an unambiguous distinction of individual electrochemical processes by means of impedance spectroscopy. The electrochemical measurements were performed on dense thin film microelectrodes, prepared by PLD and photolithography, of mixed conducting perovskite-type materials. The first part of the thesis consists of an extensive impedance spectroscopic investigation of La0.6Sr0.4Co0.8Fe0.2O3 (LSCF) microelectrodes. An equivalent circuit was identified that describes the electrochemical properties of the model electrodes appropriately and enables an unambiguous interpretation of the measured impedance spectra. Hence, the dependencies of individual electrochemical processes such as the surface exchange reaction on a wide range of experimental parameters including temperature, dc bias and oxygen partial pressure could be studied. As a result, a comprehensive set of experimental data has been obtained, which was previously not available for a mixed conducting model system. In the course of the experiments on the dc bias dependence of the electrochemical processes a new and surprising effect was discovered: It could be shown that a short but strong dc polarisation of a LSCF microelectrode at high temperature improves its electrochemical performance with respect to the oxygen reduction reaction drastically. The electrochemical resistance associated with the oxygen surface exchange reaction, initially the dominant contribution to the total electrode resistance, can be reduced by two orders of magnitude. This &apos
Studies of Electronic Conduction in Some Small Gallium Arsenic Based.
Whittington, Geoffrey
Available from UMI in association with The British Library. Requires signed TDF. This thesis describes experimental investigations of the physics involved with low temperature electronic conduction in three different semiconductor systems. The research relies upon technological advances in fabrication of such semiconductor samples. The first work deals with the effects of quantum interference of electrons in some submicron size, heavily doped Gallium Arsenide wire samples. The interesting effect of aperiodic fluctuations in the magnetoresistance of these samples is studied, making use of recently formulated theory on the subject, and with experimental data taken over the magnetic field range 0 to 10 tesla. The results verify the connection between the mean amplitude of the fluctuations and the field correlation period, in terms of the correlation function introduced in the theory. The second work is on the impurity-assisted tunnelling conduction in a magnetic field of three thin rm n^{+}/n^{-}/n^ {+} GaAs sandwich layer structures. The conduction of the system is shown to be determined by impurities lying in the centre of the middle layer. This allows the connection to be made between the conductivity of the system in a magnetic field, and the field-dependent shape of the donor electron wavefunction. The relative variation in resistance with angle to an applied magnetic field was measured, and is shown to be in agreement with predictions based on calculations of the shape of a normalised hydrogenic state wavefunction in high magnetic fields. The third work concerns the tunnelling conduction of a symmetrical GaAs/(AlGa)As/GaAs hetero-barrier system. The current-voltage characteristics at low temperature are fully modelled for applied voltages up to 180mV, using conventional theory of tunnelling and a position-dependent effective mass in the barrier. Low current oscillations in the Fowler-Nordheim tunnelling regime, corresponding to quantum reflection at the
Thermal scale modeling of radiation-conduction-convection systems.
Shannon, R. L.
1972-01-01
Investigation of thermal scale modeling applied to radiation-conduction-convection systems with particular emphasis on the spacecraft cabin atmosphere/cabin wall thermal interface. The 'modified material preservation,' 'temperature preservation,' 'scaling compromises,' and 'Nusselt number preservation' scale modeling techniques and their inherent limitations and problem areas are described. The compromised scaling techniques of mass flux preservation and heat transfer coefficient preservation show promise of giving adequate thermal similitude while preserving both gas and temperature in the scale model. The use of these compromised scaling techniques was experimentally demonstrated in tests of full scale and 1/4 scale models. Correlation of test results for free and forced convection under various test conditions shows the effectiveness of these scaling techniques. It is concluded that either mass flux or heat transfer coefficient preservation may result in adequate thermal similitude depending on the system to be modeled. Heat transfer coefficient preservation should give good thermal similitude for manned spacecraft scale modeling applications.
The regular conducting fluid model for relativistic thermodynamics
Carter, Brandon
2012-01-01
The "regular" model presented here can be considered to be the most natural solution to the problem of constructing the simplest possible relativistic analogue of the category of classical Fourier--Euler thermally conducting fluid models as characterised by a pair of equations of state for just two dependent variables (an equilibrium density and a conducting scalar). The historically established but causally unsatisfactory solution to this problem due to Eckart is shown to be based on an ansatz that is interpretable as postulating a most unnatural relation between the (particle and entropy) velocities and their associated momenta, which accounts for the well known bad behaviour of that model which has recently been shown to have very pathological mixed-elliptic-hyperbolic comportments. The newer (and more elegant) solution of Landau and Lifshitz has a more mathematically respectable parabolic-hyperbolic comportment, but is still compatible with a well posed initial value problem only in such a restricted limi...
Thermal conductivity modeling of circular-wire nanocomposites
Hsieh, Tse-Yang; Yang, Jaw-Yen
2010-08-01
A phonon Boltzmann equation solver using multiblock-structured grid system is developed and applied to study transverse thermal transport in silicon-germanium circular-wire nanocomposite (silicon nanowires embedded in germanium host matrix). Past studies usually assume geometric simplification for the circular-wire nanocomposite, so the heat transfer is actually modeled in a square-wire nanocomposite. To demonstrate geometry effect, phonon transport in both the circular-wire and square-wire nanocomposites are investigated with various wire spacings, volume fractions, and dimensions. In ballistic phonon transport, due to the smoothness of circular shape, the circular wire imposes less thermal resistance than the square wire. Nevertheless, in the geometric simplification, the wire spacing of the square-wire nanocomposite is larger than that of the circular-wire nanocomposite. The usual geometric simplification can overestimate the thermal conductivity of the circular-wire nanocomposite. The obtained results can provide essential information for the development of bulk-nanostructured thermoelectric devices.
Energy Technology Data Exchange (ETDEWEB)
Midttoemme, Kirsti
1997-12-31
The thermal conductivity of sedimentary rocks is an important parameter in basin modelling as the main parameter controlling the temperature within a sedimentary basin. This thesis presents measured thermal conductivities, mainly on clay- and mudstone. The measured values are compared with values obtained by using thermal conductivity models. Some new thermal conductivity models are developed based on the measured values. The values obtained are less than most previously published values. In a study of unconsolidated sediments a constant deviation was found between thermal conductivities measured with a needle probe and a divided bas apparatus. Accepted thermal conductivity models based on the geometric mean model fail to predict the thermal conductivity of clay- and mudstone. Despite this, models based on the geometric mean model, where the effect of porosity is taken account of by the geometric mean equation, seem to be the best. Existing models underestimate the textural influence on the thermal conductivity of clay- and mudstone. The grain size was found to influence the thermal conductivity of artificial quartz samples. The clay mineral content seems to be a point of uncertainty in both measuring and modelling thermal conductivity. A good universal thermal conductivity model must include many mineralogical and textural factors. Since this is difficult, different models restricted to specific sediment types and textures are suggested to be the best solution to obtain realistic estimates applicable in basin modelling. 243 refs., 64 figs., 31 tabs.
A thermal conductivity model for U-Si compounds
Energy Technology Data Exchange (ETDEWEB)
Zhang, Yongfeng [Idaho National Lab. (INL), Idaho Falls, ID (United States); Andersson, Anders David Ragnar [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-02-02
U_{3}Si_{2} is a candidate for accident tolerant nuclear fuel being developed as an alternative to UO_{2} in commercial light water reactors (LWRs). One of its main benefits compared to UO_{2} is higher thermal conductivity that increases with temperature. This increase is contrary to UO_{2}, for which the thermal conductivity decreases with temperature. The reason for the difference is the electronic origin of thermal conductivity in U_{3}Si_{2}, as compared to the phonon mechanism responsible for thermal transport in UO_{2}. The phonon thermal conductivity in UO_{2} is unusually low for a fluorite oxide due to the strong interaction with the spins in the paramagnetic phase. The thermal conductivity of U_{3}Si_{2} as well as other U-Si compounds has been measured experimentally [1-4]. However, for fuel performance simulations it is also critical to model the degradation of the thermal conductivity due to damage and microstructure evolution caused by the reactor environment (irradiation and high temperature). For UO_{2} this reduction is substantial and it has been the topic of extensive NEAMS research resulting in several publications [5, 6]. There are no data or models for the evolution of the U_{3}Si_{2} thermal conductivity under irradiation. We know that the intrinsic thermal conductivities of UO_{2} (semi-conductor) and U_{3}Si_{2} (metal) are very different, and we do not necessarily expect the dependence on damage to be the same either, which could present another advantage for the silicide fuel. In this report we summarize the first step in developing a model for the thermal conductivity of U-Si compounds with the goal of capturing the effect of damage in U_{3}Si_{2}. Next year, we will focus on lattice damage. We will also attempt to assess the impact of fission gas bubbles.
A micro-convection model for thermal conductivity of nanofluids
Indian Academy of Sciences (India)
Hrishikesh E Patel; T Sundararajan; T Pradeep; A Dasgupta; N Dasgupta; Sarit K Das
2005-11-01
Increase in the specific surface area as well as Brownian motion are supposed to be the most significant reasons for the anomalous enhancement in thermal conductivity of nanofluids. This work presents a semi-empirical approach for the same by emphasizing the above two effects through micro-convection. A new way of modeling thermal conductivity of nanofluids has been explored which is found to agree excellently with a wide range of experimental data obtained by the present authors as well as the data published in literature.
Atomistic Modeling of Thermal Conductivity of Epoxy Nanotube Composites
Fasanella, Nicholas A.; Sundararaghavan, Veera
2016-05-01
The Green-Kubo method was used to investigate the thermal conductivity as a function of temperature for epoxy/single wall carbon nanotube (SWNT) nanocomposites. An epoxy network of DGEBA-DDS was built using the `dendrimer' growth approach, and conductivity was computed by taking into account long-range Coulombic forces via a k-space approach. Thermal conductivity was calculated in the direction perpendicular to, and along the SWNT axis for functionalized and pristine SWNT/epoxy nanocomposites. Inefficient phonon transport at the ends of nanotubes is an important factor in the thermal conductivity of the nanocomposites, and for this reason discontinuous nanotubes were modeled in addition to long nanotubes. The thermal conductivity of the long, pristine SWNT/epoxy system is equivalent to that of an isolated SWNT along its axis, but there was a 27% reduction perpendicular to the nanotube axis. The functionalized, long SWNT/epoxy system had a very large increase in thermal conductivity along the nanotube axis (~700%), as well as the directions perpendicular to the nanotube (64%). The discontinuous nanotubes displayed an increased thermal conductivity along the SWNT axis compared to neat epoxy (103-115% for the pristine SWNT/epoxy, and 91-103% for functionalized SWNT/epoxy system). The functionalized system also showed a 42% improvement perpendicular to the nanotube, while the pristine SWNT/epoxy system had no improvement over epoxy. The thermal conductivity tensor is averaged over all possible orientations to see the effects of randomly orientated nanotubes, and allow for experimental comparison. Excellent agreement is seen for the discontinuous, pristine SWNT/epoxy nanocomposite. These simulations demonstrate there exists a threshold of the SWNT length where the best improvement for a composite system with randomly oriented nanotubes would transition from pristine SWNTs to functionalized SWNTs.
Wu, Johnny; Witkiewitz, Katie; McMahon, Robert J; Dodge, Kenneth A
2010-10-01
Conduct problems, substance use, and risky sexual behavior have been shown to coexist among adolescents, which may lead to significant health problems. The current study was designed to examine relations among these problem behaviors in a community sample of children at high risk for conduct disorder. A latent growth model of childhood conduct problems showed a decreasing trend from grades K to 5. During adolescence, four concurrent conduct problem and substance use trajectory classes were identified (high conduct problems and high substance use, increasing conduct problems and increasing substance use, minimal conduct problems and increasing substance use, and minimal conduct problems and minimal substance use) using a parallel process growth mixture model. Across all substances (tobacco, binge drinking, and marijuana use), higher levels of childhood conduct problems during kindergarten predicted a greater probability of classification into more problematic adolescent trajectory classes relative to less problematic classes. For tobacco and binge drinking models, increases in childhood conduct problems over time also predicted a greater probability of classification into more problematic classes. For all models, individuals classified into more problematic classes showed higher proportions of early sexual intercourse, infrequent condom use, receiving money for sexual services, and ever contracting an STD. Specifically, tobacco use and binge drinking during early adolescence predicted higher levels of sexual risk taking into late adolescence. Results highlight the importance of studying the conjoint relations among conduct problems, substance use, and risky sexual behavior in a unified model. Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.
DSC and conductivity studies on PVA based proton conducting gel electrolytes
Indian Academy of Sciences (India)
S L Agrawal; Arvind Awadhia
2004-12-01
An attempt has been made in the present work to prepare polyvinyl alcohol (PVA) based proton conducting gel electrolytes in ammonium thiocyanate (NH4SCN) solution and characterize them. DSC studies affirm the formation of gels along with the presence of partial complexes. The cole–cole plots exhibit maximum ionic conductivity (2.58 × 10-3 S cm-1) for gel samples containing 6 wt% of PVA. The conductivity of gel electrolytes exhibit liquid like nature at low polymer concentrations while the behaviour is seen to be affected by the formation of PVA–NH4SCN complexes upon increase in polymer content beyond 5 wt%. Temperature dependence of ionic conductivity exhibits VTF behaviour.
Asymmetric Heat Conduction in One-Dimensional Hard-Point Model with Mass Gradient
Institute of Scientific and Technical Information of China (English)
LI Hai-Bin; NIE Qing-Miao; XIN Xiao-Tian
2009-01-01
The heat conduction in a one-dimensional (1D) hard-point model with mass gradient is studied. Using numerical simulation, we find an asymmetric heat conduction in this model with greater heat current in the direction of mass increase. The increase of temperature gradient, mass gradient and system size are found to enhance the asymmetric heat conduction. Based on the collision dynamic of a hard-point particle, we give a qualitative explanation for the underlying mechanism of asymmetric effect.
Holographic conductivity of 1+1 dimensional systems in soft wall model
Bhatnagar, Neha
2016-01-01
We study the optical conductivity of 1+1 dimensional systems using soft wall model in the bottom up approach of AdS/CFT (anti-de Sitter/conformal field theory) duality. We find the numerical results for optical conductivity and investigate the system using holographic model in the probe limit. The dependence of conductivity on chemical potential is also investigated. Further, we extend the soft wall model as a `no-wall' model by eliminating the dilaton background and study the response of the system in a simplified approach.
Bi-Spectrum Scattering Model for Conducting Randomly Rough Surface
Institute of Scientific and Technical Information of China (English)
刘宁; 李宗谦
2002-01-01
A scattering model is developed to predict the scattering coefficient of a conducting randomly rough surface by analyzing the randomly rough surface in the spectral domain using the bi-spectrum method. For common randomly rough surfaces without obvious two-scale characteristics, a scale-compression filter can divide the auto-correlation spectrum into two parts with different correlation lengths. The Kirchhoff approximation and the small perturbation method are used to obtain the surface field, then a bistatic scattering model, the bi-spectrum model (BSM), is used to derive an explicit expression from the surface field. Examples using the integral equation model (IEM), finite difference of the time domain (FDTD) method, and BSM show that the BSM accuracy is acceptable and its range of validity is similar to IEM. BSM can also be extended to a scattering model for dielectric randomly rough surfaces.
18 CFR 5.15 - Conduct of studies.
2010-04-01
... to the facts of the case, a demonstration that: (1) Approved studies were not conducted as provided... met with the approved study methodology; (3) Why the request was not made earlier; (4) Significant... 18 Conservation of Power and Water Resources 1 2010-04-01 2010-04-01 false Conduct of studies....
Molecular Models for Conductance in Junctions and Electrochemical Electron Transfer
Mazinani, Shobeir Khezr Seddigh
This thesis develops molecular models for electron transport in molecular junctions and intra-molecular electron transfer. The goal is to identify molecular descriptors that afford a substantial simplification of these electronic processes. First, the connection between static molecular polarizability and the molecular conductance is examined. A correlation emerges whereby the measured conductance of a tunneling junction decreases as a function of the calculated molecular polarizability for several systems, a result consistent with the idea of a molecule as a polarizable dielectric. A model based on a macroscopic extension of the Clausius-Mossotti equation to the molecular domain and Simmon's tunneling model is developed to explain this correlation. Despite the simplicity of the theory, it paves the way for further experimental, conceptual and theoretical developments in the use of molecular descriptors to describe both conductance and electron transfer. Second, the conductance of several biologically relevant, weakly bonded, hydrogen-bonded systems is systematically investigated. While there is no correlation between hydrogen bond strength and conductance, the results indicate a relation between the conductance and atomic polarizability of the hydrogen bond acceptor atom. The relevance of these results to electron transfer in biological systems is discussed. Hydrogen production and oxidation using catalysts inspired by hydrogenases provides a more sustainable alternative to the use of precious metals. To understand electrochemical and spectroscopic properties of a collection of Fe and Ni mimics of hydrogenases, high-level density functional theory calculations are described. The results, based on a detailed analysis of the energies, charges and molecular orbitals of these metal complexes, indicate the importance of geometric constraints imposed by the ligand on molecular properties such as acidity and electrocatalytic activity. Based on model calculations of
Modeling of thermal conductivity of stainless-steelmaking dust pellets
Institute of Scientific and Technical Information of China (English)
彭兵; 彭及; 余笛
2004-01-01
The thermal conductivity of stainless-steelmaking dust pellets, an important parameter for the direct recycling of the dust, is naturally of interest to metallurgists. The measurement of central temperature and surface temperature was taken in a furnace. The physical model and calculation model for the heating process were set up to check the thermal conductivity of the dust pellets. The physical structure parameters δ and λ of the basic unit are 0.92 and 0.45 based on the calculation. The temperature in the pellet can be expressed in a linear equation a5 Tp =a1 TN +a2 TM +a4. This is convenient to determine the central temperature of a pellet in the direct recycling process.
A Simple Model for Oxygen Conduction in Some Perovskite Compounds
Totsuji, Chieko
1996-01-01
A simple model for oxygen ion conduction in perovskite compounds is proposed. The potential for an oxygen ion is calculated as the sum of the long range Coulomb potential and short range repulsive potential in a cubic lattice. The activation energy is estimated as the difference in the values of potential at the barrier and at the stable site. When appropriate conditions are satisfied, the activation energy has a minimum as a function of lattice constant in accordance with recent experiments.
Electronic conductivity studies on oxyhalide glasses containing TMO
Energy Technology Data Exchange (ETDEWEB)
Vijayatha, D. [R& D Center, Bharatiar University, Coimbatore, Tamil Nadu (India); Department of Physics, Gurunanak Institute of Technology, Hyderabad -040 (India); Viswanatha, R. [Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012 (India); Sujatha, B. [Department of Electronics and Communcation, MSRIT, Bangalore 560054 (India); Narayana Reddy, C., E-mail: nivetejareddy@gmail.com [Department of Physics, Sree Siddaganga College of Arts, Science and Commerce, Tumkur 572102 (India)
2016-05-06
Microwave-assisted synthesis is cleaner, more economical and much faster than conventional methods. The development of new routes for the synthesis of solid materials is an integral part of material science and technology. The electronic conductivity studies on xPbCl{sub 2} – 60 PbO – (40-x) V{sub 2}O{sub 5} (1 ≥ x ≤ 10) glass system has been carried out over a wide range of composition and temperature (300 K to 423 K). X-ray diffraction study confirms the amorphous nature of the samples. The Scanning electron microscopic studies reveal the formation of cluster like morphology in PbCl{sub 2} containing glasses. The d.c conductivity exhibits Arrhenius behaviour and increases with V{sub 2}O{sub 5} concentration. Analysis of the results is interpreted in view Austin-Mott’s small polaron model of electron transport. Activation energies calculated using regression analysis exhibit composition dependent trend and the variation is explained in view of the structure of lead-vanadate glass.
Effective Thermal Conductivity Modeling of Sandstones: SVM Framework Analysis
Rostami, Alireza; Masoudi, Mohammad; Ghaderi-Ardakani, Alireza; Arabloo, Milad; Amani, Mahmood
2016-06-01
Among the most significant physical characteristics of porous media, the effective thermal conductivity (ETC) is used for estimating the thermal enhanced oil recovery process efficiency, hydrocarbon reservoir thermal design, and numerical simulation. This paper reports the implementation of an innovative least square support vector machine (LS-SVM) algorithm for the development of enhanced model capable of predicting the ETCs of dry sandstones. By means of several statistical parameters, the validity of the presented model was evaluated. The prediction of the developed model for determining the ETCs of dry sandstones was in excellent agreement with the reported data with a coefficient of determination value ({R}2) of 0.983 and an average absolute relative deviation of 0.35 %. Results from present research show that the proposed LS-SVM model is robust, reliable, and efficient in calculating the ETCs of sandstones.
Transport studies of conducting, semiconducting and photoconducting star polymers
Ferguson, John Baker
Star polymers are studied for their transport properties in the highly conducting state doped with NOPF6 and iodine, the undoped semiconducting state and the photoconducting state. Doped star polymers exhibit variable range hopping of charge carriers. Transport dimensionality and conductivity depend intricately on the processing conditions for doping and casting films. The highest conducting diffusion doped film (room temperature conductivity 50 S/cm) exhibits 2-dimensional variable range for all doping levels. Polymers doped in solution, then cast to form films have 1.4 dimensional variable range hopping for the highest conducting samples with 10 S/cm at room temperature. The hopping dimensionality varies as the conductivity decreases. The doped star polymers remain on the insulator side of the insulator metal transition with localized carriers as revealed with Kramer-Kronig analysis. Optical and near infrared absorbance and photoluminescence reveal the core of the star polymers exist in a solid state solution of the arms with similar absorbance and luminescence for both solution and films. The arms retain the optical properties of their linear analogs indicating the core and arms do not interact quantum mechanically to produce a new state. Excitons created by absorption in the wider band gap cores rapidly migrate to the arms. Photoconductive time of flight mobility measurements reveal an almost field independent mobility at room temperature. This is due to a unique cancellation of on diagonal and off diagonal disorder in the Bassler disorder formalism. The cores introduce heterogeneous regions with a net lower mobility predicted by correlated disorder models. Space charge limited current reveals trap densities several orders of magnitude higher than the carrier density. Photovoltaic performance of star polymer and fullerene blend devices with both 20 nm and 100 nm thick layers are investigated. The thin devices have low open circuit voltages due to space charge
Electrical conduction and dielectric studies of ZnO pellets
Energy Technology Data Exchange (ETDEWEB)
Chaari, Mariem, E-mail: m_chaari@yahoo.fr [Laboratory of Composite Ceramic and Polymer Materials (LaMaCoP), Scientific Faculty of Sfax, Route of the Soukra Km 4, Sfax 3038 (Tunisia); Matoussi, Adel [Laboratory of Composite Ceramic and Polymer Materials (LaMaCoP), Scientific Faculty of Sfax, Route of the Soukra Km 4, Sfax 3038 (Tunisia)
2012-09-01
A series of Zinc Oxide pellets sintered at different temperatures was studied by means of dielectric spectroscopy in the wide frequency range of 1-10{sup 6} Hz and temperature interval from -100 Degree-Sign C to 30 Degree-Sign C. Electrical conductivity was analysed using Jonsher's universal power law, and the values of s were found to decrease with the increase in temperature, which agrees well with the correlation barrier hopping (CBH) model. As the temperature increased, energy activation E{sub dc} became less than 0.39 eV and dc conductivity ({sigma}{sub dc}) values in the range of 1.9 Multiplication-Sign 10{sup -14}-9.7 Multiplication-Sign 10{sup -10} {Omega} m{sup -1} were observed. The dielectric modulus showed ionic polarisation at the intermediate and high frequencies related to oxygen interstitial O{sub i}, oxygen vacancy V{sub O} and Zinc interstitial Zn{sub i}. At low frequency, it revealed a Maxwell-Wagner-Sillars relaxation with barrier heights of grain boundaries between 0.74 and 0.88 eV for all the studied pellets.
Numerical Model for Conduction-Cooled Current Lead Heat Loads
White, M J; Brueck, H D; 10.1063/1.4706965
2012-01-01
Current leads are utilized to deliver electrical power from a room temperature junction mounted on the vacuum vessel to a superconducting magnet located within the vacuum space of a cryostat. There are many types of current leads used at laboratories throughout the world, however, conduction-cooled current leads are often chosen for their simplicity and reliability. Conduction-cooled leads have the advantage of using common materials, have no superconducting/normal state transition, and have no boil-off vapor to collect. The XFEL (X-Ray Free Electron Laser) magnets are operated at 2 K, which makes vapor-cooled current leads impractical due to the sub-atmospheric bath pressure. This paper presents a numerical model for conduction-cooled current lead heat loads. This model takes into account varying material and fluid thermal properties, varying thicknesses along the length of the lead, heat transfer in the circumferential and longitudinal directions, electrical power dissipation, and the effect of thermal inte...
Current amplification models of sensorineurall and conductive hearing loss
Directory of Open Access Journals (Sweden)
Ostojić Sanja
2012-01-01
Full Text Available The main function of a hearing aid is to improve auditory and language abilities of hearing impaired users. The amplification model has to be adapted according to age, degree and type of hearing loss. The goal of this paper is to analyze the current amplification models of sensorineural and conductive hearing loss which can provide a high quality of speech perception and sounds at any degree of hearing loss. The BAHA is a surgically implantable system for treatment of conductive hearing loss that works through direct bone conduction. BAHA is used to help people with chronic ear infections, congenital external auditory canal atresia and single sided deafness who cannot benefit from conventional hearing aids. The last generation of hearing aid for sensorineural hearing loss is cochlear implant. Bimodal amplification improves binaural hearing. Hearing aids alone do not make listening easier in all situations. The things that can interfere with listening are background noises, distance from a sound and reverberation or echo. The device used most often today is the Frequency Modulated (FM system.
Electromagnetic characterization of the CFRPs anisotropic conductivity: modeling and measurements
Menana, H.; Féliachi, M.
2011-02-01
This work deals with the characterization of the conductivity tensor of a carbon fiber reinforced polymer composite (CFRP) thin plate. We propose a contactless method based on the eddy current non destructive testing technique. The used eddy current sensor consists of a ferrite torus on which a winding is wound. The torus is of a rectangular section and contains a thin air-gap in which the thin CFRP plate is inserted. We developed analytical relations giving the longitudinal and transversal conductivities of the CFRP plate as functions of the impedances variations of the eddy current sensor, corresponding to the orientations of the carbon fibers parallel and transverse to the direction of the torus width which is much greater than its thickness. The analytical relations are developed by inverting interpolation functions of curves giving the variations of the sensor impedances as functions of the longitudinal and transversal conductivities of the CFRP plate. These curves are obtained by a numerical model based on a simplified integro-differential formulation in terms of the electric vector potential in the CFRP plate, coupled to the magnetic circuit equations in the ferrite torus. The modeling results are supported by measurements.
Quasiperiodicity route to chaos in cardiac conduction model
Quiroz-Juárez, M. A.; Vázquez-Medina, R.; Ryzhii, E.; Ryzhii, M.; Aragón, J. L.
2017-01-01
It has been suggested that cardiac arrhythmias are instances of chaos. In particular that the ventricular fibrillation is a form of spatio-temporal chaos that arises from normal rhythm through a quasi-periodicity or Ruelle-Takens-Newhouse route to chaos. In this work, we modify the heterogeneous oscillator model of cardiac conduction system proposed in Ref. [Ryzhii E, Ryzhii M. A heterogeneous coupled oscillator model for simulation of ECG signals. Comput Meth Prog Bio 2014;117(1):40-49. doi:10.1016/j.cmpb.2014.04.009.], by including an ectopic pacemaker that stimulates the ventricular muscle to model arrhythmias. With this modification, the transition from normal rhythm to ventricular fibrillation is controlled by a single parameter. We show that this transition follows the so-called torus of quasi-periodic route to chaos, as verified by using numerical tools such as power spectrum and largest Lyapunov exponent.
Modeling of Thermal Conductivity of Graphite Nanosheet Composites
Lin, Wei; Zhang, Rongwei; Wong, C. P.
2010-03-01
Recent experiments demonstrated a very high thermal conductivity in graphite nanosheet (GNS)/epoxy nanocomposites; however, theoretical analysis is lacking. In this letter, an effective medium model has been used to analyze the effective thermal conductivity of the GNS/polymer nanocomposites and has shown good validity. Strong influences of the aspect ratio and the orientation of the GNS are evident. As expected, interfacial thermal resistance still plays a role in determining the overall thermal transport in the GNS/polymer nanocomposites. In comparison with the interfacial thermal resistance between carbon nanotubes and polymers, the interfacial thermal resistance between GNS and polymers is about one order of magnitude lower, the reason for which is discussed.
Conductivity models for the North Perth Basin, Western Australia
Hoskin, T. E.; Regenauer-Lieb, K.; Jones, A. G.
2013-12-01
Exploration for geothermal resources in the North Perth basin, Western Australia, led to acquisition of new, high resolution Magnetotelluric (MT) and Audio-Magnetotelluric (AMT) data, the first of its kind in the area. Electromagnetic (EM) techniques are widely used in geothermal exploration and ground water investigations and they are well suited for application in the Perth basin. Two east-west transects investigating the structure of the onshore basin and its eastern margin, the Darling Fault Zone, are compared with existing geological models and geophysical data. Down-hole temperature data and depth-to-basement models were used to define areas of investigation in the basin, but there are limited geophysical data available. 1D, 2D and 3D modeling of electromagnetic data have been used to produce new conductivity models using existing data to constrain modelling. EM data complement existing gravity and seismic data and support published models in the upper 4-6km. However in deeper parts of the basin, MT data provide additional information allowing for revision of depth-to-basement. In addition to this, we clearly identify a conductivity anomaly associated with the Darling Fault Zone and are able to image this anomaly penetrating into the upper mantle. Fault zone conductors have been imaged on other lithosphere faults around the world, with one explanation being fluids in the enhanced permeability of the damage zone. Evidence to explain the fault zone conductor of the Darling Fault is presented and discussed as it could have significant implications in the identification of new areas, prospective for geothermal resources in the basin.
Preclinical models of conduct disorder - principles and pharmacologic perspectives.
Haller, Jozsef
2016-05-26
The translational value of preclinical research was recently enhanced by abnormal aggression models, which focus on deviant behaviors induced by the exposure of rodents to etiological factors of aggression-related psychopathologies. Prompted by similar trials in other psychiatric disorders, here we investigate models of abnormal aggression from the perspective of DSM5 criteria. After proposing principles based on which analogies can be established between psychopathology symptoms and rodent behavioral dysfunctions, we show that rodents submitted to abnormal aggression models fulfill basic criteria of aggression-related psychopathologies; moreover, some models can be considered specific to particular disorders e.g. conduct disorder. We also show that abnormal and species-typical aggressions differ in terms of both brain mechanisms and pharmacological responsiveness, which mimics differences observed in psychiatric disorders. We conclude that evaluating abnormal aggression models from a DSM5 perspective is not only possible but also worthwhile, and such models may contribute to the development of novel treatment strategies not only for aggression as a symptom but also for specific aggression-related disorders or multi-symptom clusters at least. Copyright © 2016 Elsevier Ltd. All rights reserved.
In vitro burn model illustrating heat conduction patterns using compressed thermal papers.
Lee, Jun Yong; Jung, Sung-No; Kwon, Ho
2015-01-01
To date, heat conduction from heat sources to tissue has been estimated by complex mathematical modeling. In the present study, we developed an intuitive in vitro skin burn model that illustrates heat conduction patterns inside the skin. This was composed of tightly compressed thermal papers with compression frames. Heat flow through the model left a trace by changing the color of thermal papers. These were digitized and three-dimensionally reconstituted to reproduce the heat conduction patterns in the skin. For standardization, we validated K91HG-CE thermal paper using a printout test and bivariate correlation analysis. We measured the papers' physical properties and calculated the estimated depth of heat conduction using Fourier's equation. Through contact burns of 5, 10, 15, 20, and 30 seconds on porcine skin and our burn model using a heated brass comb, and comparing the burn wound and heat conduction trace, we validated our model. The heat conduction pattern correlation analysis (intraclass correlation coefficient: 0.846, p < 0.001) and the heat conduction depth correlation analysis (intraclass correlation coefficient: 0.93, p < 0.001) showed statistically significant high correlations between the porcine burn wound and our model. Our model showed good correlation with porcine skin burn injury and replicated its heat conduction patterns.
Institute of Scientific and Technical Information of China (English)
余勇; 吴小平
2010-01-01
The generalized mixture rule(GMR)is usually applied in determining mechanical properties such as the rheological property and Young's modulus of multi-phase rocks.However,it is rarely used to determine electrical conductivity of multi-phase rocks presently.In this paper,we calculate the effective conductivity using the 3D finite element method for a large number of two-phase medium stochastic models.The GMR is then employed as an effective conductivity model to fit the data.It shows a very close relationship between the parameter J of GMR and the ratio of conductivities of the two phases.We obtain the equations of the parameter J with the ratio of conductivity of two phases for the first time.On this basis,we can quickly predict(or calculate)the effective conductivity of any twophase medium stochastic model.The result is much more accurate than two other available effective conductivity models for the stochastic medium,which are the random model and effective medium theory model,laying a solid base for detailed evaluation of oil reservoirs.
Hybrid fluid/kinetic model for parallel heat conduction
Energy Technology Data Exchange (ETDEWEB)
Callen, J.D.; Hegna, C.C.; Held, E.D. [Univ. of Wisconsin, Madison, WI (United States)
1998-12-31
It is argued that in order to use fluid-like equations to model low frequency ({omega} < {nu}) phenomena such as neoclassical tearing modes in low collisionality ({nu} < {omega}{sub b}) tokamak plasmas, a Chapman-Enskog-like approach is most appropriate for developing an equation for the kinetic distortion (F) of the distribution function whose velocity-space moments lead to the needed fluid moment closure relations. Further, parallel heat conduction in a long collision mean free path regime can be described through a combination of a reduced phase space Chapman-Enskog-like approach for the kinetics and a multiple-time-scale analysis for the fluid and kinetic equations.
Conductive polymer foams with carbon nanofillers – Modeling percolation behavior
Directory of Open Access Journals (Sweden)
O. Maxian
2017-05-01
Full Text Available A new numerical model considering nanofiller random distribution in a porous polymeric matrix was developed to predict electrical percolation behavior in systems incorporating 1D-carbon nanotubes (CNTs and/or 2D-graphene nanoplatelets (GNPs. The numerical model applies to porous systems with closed-cell morphology. The percolation threshold was found to decrease with increasing porosity due to filler repositioning as a result of foaming. CNTs were more efficient in forming a percolative network than GNPs. High-aspect ratio (AR and randomly oriented fillers were more prone to form a network. Reduced percolation values were determined for misaligned fillers as they connect better in a network compared to aligned ones. Hybrid CNT-GNP fillers show synergistic effects in forming electrically conductive networks by comparison with single fillers.
Stenroos, Matti; Hauk, Olaf
2013-11-01
The conductivity profile of the head has a major effect on EEG signals, but unfortunately the conductivity for the most important compartment, skull, is only poorly known. In dipole modeling studies, errors in modeled skull conductivity have been considered to have a detrimental effect on EEG source estimation. However, as dipole models are very restrictive, those results cannot be generalized to other source estimation methods. In this work, we studied the sensitivity of EEG and combined MEG+EEG source estimation to errors in skull conductivity using a distributed source model and minimum-norm (MN) estimation. We used a MEG/EEG modeling set-up that reflected state-of-the-art practices of experimental research. Cortical surfaces were segmented and realistically-shaped three-layer anatomical head models were constructed, and forward models were built with Galerkin boundary element method while varying the skull conductivity. Lead-field topographies and MN spatial filter vectors were compared across conductivities, and the localization and spatial spread of the MN estimators were assessed using intuitive resolution metrics. The results showed that the MN estimator is robust against errors in skull conductivity: the conductivity had a moderate effect on amplitudes of lead fields and spatial filter vectors, but the effect on corresponding morphologies was small. The localization performance of the EEG or combined MEG+EEG MN estimator was only minimally affected by the conductivity error, while the spread of the estimate varied slightly. Thus, the uncertainty with respect to skull conductivity should not prevent researchers from applying minimum norm estimation to EEG or combined MEG+EEG data. Comparing our results to those obtained earlier with dipole models shows that general judgment on the performance of an imaging modality should not be based on analysis with one source estimation method only.
Normal thermal conduction in lattice models with asymmetric harmonic interparticle interactions
Institute of Scientific and Technical Information of China (English)
Zhong Yi; Zhang Yong; Wang Jiao; Zhao Hong
2013-01-01
We study the thermal conduction behaviors of one-dimensional lattice models with asymmetric harmonic interparticle interactions.Normal thermal conductivity that is independent of system size is observed when the lattice chains are long enough.Because only the harmonic interactions are involved,the result confirms,without ambiguity,that asymmetry plays a key role in normal thermal conduction in one-dimensional momentum conserving lattices.Both equilibrium and nonequilibrium simulations are performed to support the conclusion.
Steady States and Universal Conductance in a Quenched Luttinger Model
Langmann, Edwin; Lebowitz, Joel L.; Mastropietro, Vieri; Moosavi, Per
2016-05-01
We obtain exact analytical results for the evolution of a 1+1-dimensional Luttinger model prepared in a domain wall initial state, i.e., a state with different densities on its left and right sides. Such an initial state is modeled as the ground state of a translation invariant Luttinger Hamiltonian {H_{λ}} with short range non-local interaction and different chemical potentials to the left and right of the origin. The system evolves for time t > 0 via a Hamiltonian {H_{λ'}} which differs from {H_{λ}} by the strength of the interaction. Asymptotically in time, as {t to &infty}; , after taking the thermodynamic limit, the system approaches a translation invariant steady state. This final steady state carries a current I and has an effective chemical potential difference {μ+ - μ-} between right- (+) and left- (-) moving fermions obtained from the two-point correlation function. Both I and {μ+ - μ-} depend on {λ} and {λ'} . Only for the case {λ = λ' = 0} does {μ+ - μ-} equal the difference in the initial left and right chemical potentials. Nevertheless, the Landauer conductance for the final state, {G = I/(μ+ - μ-)} , has a universal value equal to the conductance quantum {e^2/h} for the spinless case.
Steady States and Universal Conductance in a Quenched Luttinger Model
Langmann, Edwin; Lebowitz, Joel L.; Mastropietro, Vieri; Moosavi, Per
2017-01-01
We obtain exact analytical results for the evolution of a 1+1-dimensional Luttinger model prepared in a domain wall initial state, i.e., a state with different densities on its left and right sides. Such an initial state is modeled as the ground state of a translation invariant Luttinger Hamiltonian {H_{λ}} with short range non-local interaction and different chemical potentials to the left and right of the origin. The system evolves for time t > 0 via a Hamiltonian {H_{λ'}} which differs from {H_{λ}} by the strength of the interaction. Asymptotically in time, as {t to ∞}, after taking the thermodynamic limit, the system approaches a translation invariant steady state. This final steady state carries a current I and has an effective chemical potential difference {μ+ - μ-} between right- (+) and left- (-) moving fermions obtained from the two-point correlation function. Both I and {μ+ - μ-} depend on {λ} and {λ'}. Only for the case {λ = λ' = 0} does {μ+ - μ-} equal the difference in the initial left and right chemical potentials. Nevertheless, the Landauer conductance for the final state, {G = I/(μ+ - μ-)}, has a universal value equal to the conductance quantum {e^2/h} for the spinless case.
Numerical heat conduction in hydrodynamical models of colliding hypersonic flows
Parkin, E R
2010-01-01
Hydrodynamical models of colliding hypersonic flows are presented which explore the dependence of the resulting dynamics and the characteristics of the derived X-ray emission on numerical conduction and viscosity. For the purpose of our investigation we present models of colliding flow with plane-parallel and cylindrical divergence. Numerical conduction causes erroneous heating of gas across the contact discontinuity which has implications for the rate at which the gas cools. We find that the dynamics of the shocked gas and the resulting X-ray emission are strongly dependent on the contrast in the density and temperature either side of the contact discontinuity, these effects being strongest where the postshock gas of one flow behaves quasi-adiabatically while the postshock gas of the other flow is strongly radiative. Introducing additional numerical viscosity into the simulations has the effect of damping the growth of instabilities, which in some cases act to increase the volume of shocked gas and can re-he...
Institute of Scientific and Technical Information of China (English)
LEI Xin; XU Wei-jun; LIU Chun-liang; LIANG Zhi-hu
2007-01-01
The forming and activation of the conductive films are studied experimentally. The power supply,a peak-to-peak 30 V triangle profile voltage,is applied to three kinds of conductive films that contain 0.25%,0.5%,and 1% of palladium respectively. In the experiments we contrasted the values of related parameter in different conditions,observed the lumi nous spots on the anode panel,dealt with and analyzed the related data,and compared the positions and the amount of the luminous spots. We have gotten the conclusion that there is a threshold value Uth. The emission current Ie will increase rapidly when the device voltage Uf is greater than Uth. And the emission current Ie could be controlled by the device voltage Uf.The positions of the luminous spots on the anode panel are related with the device voltage Uf.
A two-parameter nondiffusive heat conduction model for data analysis in pump-probe experiments
Ma, Yanbao
2014-12-01
Nondiffusive heat transfer has attracted intensive research interests in last 50 years because of its importance in fundamental physics and engineering applications. It has unique features that cannot be described by the Fourier law. However, current studies of nondiffusive heat transfer still focus on studying the effective thermal conductivity within the framework of the Fourier law due to a lack of a well-accepted replacement. Here, we show that nondiffusive heat conduction can be characterized by two inherent material properties: a diffusive thermal conductivity and a ballistic transport length. We also present a two-parameter heat conduction model and demonstrate its validity in different pump-probe experiments. This model not only offers new insights of nondiffusive heat conduction but also opens up new avenues for the studies of nondiffusive heat transfer outside the framework of the Fourier law.
Totally Asymmetric Limit for Models of Heat Conduction
De Carlo, Leonardo; Gabrielli, Davide
2017-08-01
We consider one dimensional weakly asymmetric boundary driven models of heat conduction. In the cases of a constant diffusion coefficient and of a quadratic mobility we compute the quasi-potential that is a non local functional obtained by the solution of a variational problem. This is done using the dynamic variational approach of the macroscopic fluctuation theory (Bertini et al. in Rev Mod Phys 87:593, 2015). The case of a concave mobility corresponds essentially to the exclusion model that has been discussed in Bertini et al. (J Stat Mech L11001, 2010; Pure Appl Math 64(5):649-696, 2011; Commun Math Phys 289(1):311-334, 2009) and Enaud and Derrida (J Stat Phys 114:537-562, 2004). We consider here the convex case that includes for example the Kipnis-Marchioro-Presutti (KMP) model and its dual (KMPd) (Kipnis et al. in J Stat Phys 27:6574, 1982). This extends to the weakly asymmetric regime the computations in Bertini et al. (J Stat Phys 121(5/6):843-885, 2005). We consider then, both microscopically and macroscopically, the limit of large externalfields. Microscopically we discuss some possible totally asymmetric limits of the KMP model. In one case the totally asymmetric dynamics has a product invariant measure. Another possible limit dynamics has instead a non trivial invariant measure for which we give a duality representation. Macroscopically we show that the quasi-potentials of KMP and KMPd, which are non local for any value of the external field, become local in the limit. Moreover the dependence on one of the external reservoirs disappears. For models having strictly positive quadratic mobilities we obtain instead in the limit a non local functional having a structure similar to the one of the boundary driven asymmetric exclusion process.
Polyaniline Conducting Electroactive Polymers Thermal and Environmental Stability Studies
Directory of Open Access Journals (Sweden)
Reza Ansari
2006-01-01
Full Text Available In the current studies, polyaniline (PANi was prepared both chemical and electrochemically in the presence of different bronsted acids from aqueous solutions. The effect of thermal treatment on electrical conductivity, and thermal stability of the PANi conducting polymers were investigated using 4-point probe and TGA techniques respectively. It was found that polymer prepared by CV method is more thermally stable than those prepared by the other electrochemical techniques. In this paper we have also reviewed some fundamental information about synthesis, general properties, diverse applications, thermal and environmental stability of polyaniline conducting polymers.
Thermal conductivity of penta-graphene from molecular dynamics study.
Xu, Wen; Zhang, Gang; Li, Baowen
2015-10-21
Using classical equilibrium molecular dynamics simulations and applying the original Tersoff interatomic potential, we study the thermal transport property of the latest two dimensional carbon allotrope, penta-graphene. It is predicted that its room-temperature thermal conductivity is about 167 W/mK, which is much lower than that of graphene. With normal mode decomposition, the accumulated thermal conductivity with respect to phonon frequency and mean free path is analyzed. It is found that the acoustic phonons make a contribution of about 90% to the thermal conductivity, and phonons with mean free paths larger than 100 nm make a contribution over 50%. We demonstrate that the remarkably lower thermal conductivity of penta-graphene compared with graphene results from the lower phonon group velocities and fewer collective phonon excitations. Our study highlights the importance of structure-property relationship and provides better understanding of thermal transport property and valuable insight into thermal management of penta-graphene.
Point Contacts in Modeling Conducting 2D Planar Structures
Thiel, David V; Hettenhausen, Jan; Lewis, Andrew
2015-01-01
Use of an optimization algorithm to improve performance of antennas and electromagnetic structures usually ends up in planar unusual shapes. Using rectangular conducting elements the proposed structures sometimes have connections with only one single point in common between two neighboring areas. The single point connections (point crossing) can affect the electromagnetic performance of the structure. In this letter, we illustrate the influence of point crossing on dipole and loop antennas using MoM, FDTD, and FEM solvers. Current distribution, radiation pattern, and impedance properties for different junctions are different. These solvers do not agree in the modeling of the point crossing junctions which is a warning about uncertainty in using such junctions. However, solvers agree that a negligible change in the junction would significantly change the antenna performance. We propose that one should consider both bridging and chamfering of the conflicting cells to find optimized structures. This reduces the ...
APPLICATION OF NUMERICAL SIMULATION TO STUDY ON THERMAL CONDUCTION
Institute of Scientific and Technical Information of China (English)
C. Zhu; Z. Xu; D.E. Wu
2004-01-01
In this paper, using computer simulation and mathematic experiment method to solve the simplified one dimensional thermal conduction equation and to obtain the temperature distribution in a metal bar when its one end was heated. According to principle of hot expansion, a holograph of temperature distribution in the bar by laser holotechnique was taken. The results of numerical simulation and experiments are in good agreement and a new method for study on thermal conduction by laser holo-technique was found.
Studies and Properties of Ceramics with High Thermal Conductivity
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The sintering technology of the AlN ceramics power were discussed. It is discussed that the compound sintering aids is consistent with the enhancement of the the thermal conductivity of AlN ceramics, and sintering technics is helped to the improvement of density. It is analyzed how to sinter machinable AlN ceramics with high thermal conductivity. And the microstructure of compound ceramics based on AlN was studied.
Parabolic Anderson Model in a Dynamic Random Environment: Random Conductances
Erhard, D.; den Hollander, F.; Maillard, G.
2016-06-01
The parabolic Anderson model is defined as the partial differential equation ∂ u( x, t)/ ∂ t = κ Δ u( x, t) + ξ( x, t) u( x, t), x ∈ ℤ d , t ≥ 0, where κ ∈ [0, ∞) is the diffusion constant, Δ is the discrete Laplacian, and ξ is a dynamic random environment that drives the equation. The initial condition u( x, 0) = u 0( x), x ∈ ℤ d , is typically taken to be non-negative and bounded. The solution of the parabolic Anderson equation describes the evolution of a field of particles performing independent simple random walks with binary branching: particles jump at rate 2 d κ, split into two at rate ξ ∨ 0, and die at rate (- ξ) ∨ 0. In earlier work we looked at the Lyapunov exponents λ p(κ ) = limlimits _{tto ∞} 1/t log {E} ([u(0,t)]p)^{1/p}, quad p in {N} , qquad λ 0(κ ) = limlimits _{tto ∞} 1/2 log u(0,t). For the former we derived quantitative results on the κ-dependence for four choices of ξ : space-time white noise, independent simple random walks, the exclusion process and the voter model. For the latter we obtained qualitative results under certain space-time mixing conditions on ξ. In the present paper we investigate what happens when κΔ is replaced by Δ𝓚, where 𝓚 = {𝓚( x, y) : x, y ∈ ℤ d , x ˜ y} is a collection of random conductances between neighbouring sites replacing the constant conductances κ in the homogeneous model. We show that the associated annealed Lyapunov exponents λ p (𝓚), p ∈ ℕ, are given by the formula λ p({K} ) = {sup} {λ p(κ ) : κ in {Supp} ({K} )}, where, for a fixed realisation of 𝓚, Supp(𝓚) is the set of values taken by the 𝓚-field. We also show that for the associated quenched Lyapunov exponent λ 0(𝓚) this formula only provides a lower bound, and we conjecture that an upper bound holds when Supp(𝓚) is replaced by its convex hull. Our proof is valid for three classes of reversible ξ, and for all 𝓚
A protocol for conducting rainfall simulation to study soil runoff.
Kibet, Leonard C; Saporito, Louis S; Allen, Arthur L; May, Eric B; Kleinman, Peter J A; Hashem, Fawzy M; Bryant, Ray B
2014-04-03
Rainfall is a driving force for the transport of environmental contaminants from agricultural soils to surficial water bodies via surface runoff. The objective of this study was to characterize the effects of antecedent soil moisture content on the fate and transport of surface applied commercial urea, a common form of nitrogen (N) fertilizer, following a rainfall event that occurs within 24 hr after fertilizer application. Although urea is assumed to be readily hydrolyzed to ammonium and therefore not often available for transport, recent studies suggest that urea can be transported from agricultural soils to coastal waters where it is implicated in harmful algal blooms. A rainfall simulator was used to apply a consistent rate of uniform rainfall across packed soil boxes that had been prewetted to different soil moisture contents. By controlling rainfall and soil physical characteristics, the effects of antecedent soil moisture on urea loss were isolated. Wetter soils exhibited shorter time from rainfall initiation to runoff initiation, greater total volume of runoff, higher urea concentrations in runoff, and greater mass loadings of urea in runoff. These results also demonstrate the importance of controlling for antecedent soil moisture content in studies designed to isolate other variables, such as soil physical or chemical characteristics, slope, soil cover, management, or rainfall characteristics. Because rainfall simulators are designed to deliver raindrops of similar size and velocity as natural rainfall, studies conducted under a standardized protocol can yield valuable data that, in turn, can be used to develop models for predicting the fate and transport of pollutants in runoff.
Thin inclusion approach for modelling of heterogeneous conducting materials
Energy Technology Data Exchange (ETDEWEB)
Lavrov, Nikolay [Davenport University, 4801 Oakman Boulevard, Dearborn, MI 48126 (United States); Smirnova, Alevtina; Gorgun, Haluk; Sammes, Nigel [University of Connecticut, Department of Materials Science and Engineering, Connecticut Global Fuel Center, 44 Weaver Road, Unit 5233, Storrs, CT 06269 (United States)
2006-04-21
Experimental data show that heterogeneous nanostructure of solid oxide and polymer electrolyte fuel cells could be approximated as an infinite set of fiber-like or penny-shaped inclusions in a continuous medium. Inclusions can be arranged in a cluster mode and regular or random order. In the newly proposed theoretical model of nanostructured material, the most attention is paid to the small aspect ratio of structural elements as well as to some model problems of electrostatics. The proposed integral equation for electric potential caused by the charge distributed over the single circular or elliptic cylindrical conductor of finite length, as a single unit of a nanostructured material, has been asymptotically simplified for the small aspect ratio and solved numerically. The result demonstrates that surface density changes slightly in the middle part of the thin domain and has boundary layers localized near the edges. It is anticipated, that contribution of boundary layer solution to the surface density is significant and cannot be governed by classic equation for smooth linear charge. The role of the cross-section shape is also investigated. Proposed approach is sufficiently simple, robust and allows extension to either regular or irregular system of various inclusions. This approach can be used for the development of the system of conducting inclusions, which are commonly present in nanostructured materials used for solid oxide and polymer electrolyte fuel cell (PEMFC) materials. (author)
Nerve conduction and excitability studies in peripheral nerve disorders
DEFF Research Database (Denmark)
Krarup, Christian; Moldovan, Mihai
2009-01-01
PURPOSE OF REVIEW: The review is aimed at providing information about the role of nerve excitability studies in peripheral nerve disorders. It has been known for many years that the insight into peripheral nerve pathophysiology provided by conventional nerve conduction studies is limited. Nerve...
Institute of Scientific and Technical Information of China (English)
孙宇瑞; 汪懋华
2001-01-01
针对一种土壤电导率的测量方法--"电流-电压四端法"，从理论上深入探讨了该方法的测量原理，建立了对应的数学模型。关于Wenner分布、Schlumberger分布和 Polar dipole分布3种测量组态计算公式的正确性也通过实验进行了检验。%The measurement of soil electrical conductivity has been increasingly gaining attentions because precision farming technologies rely on accurate field maps of the soil characteristics that affect field. In this paper, a mathematical model for four-electrode measurement method was developed. The discussion concerned with the model consists of three steps. At first, the behavior of single current electrode at a depth of field was treated. Secondly, a combination of two current electrodes at a depth of field was analyzed and some formulas used for different configurations of electrodes were developed. At last, a lemma associated with this model was proven. In addition, some experiment results and a general conclusion referring to this study were presented.
Concurrent adversities among adolescents with conduct problems: the NAAHS study.
Reigstad, Bjørn; Kvernmo, Siv
2016-10-01
Several studies have confirmed that maltreatment and abuse in childhood are related to conduct problems. Less is known about such relationships with concurrent adversities in adolescence and, also, when compared with other severe adversities and possible multiple additive effects. The study encompassed a community population of 4881 adolescents 15-16 years of age 50.1 % boys and 49.9 % girls. Youth with and without conduct problem scores within the deviant range on the Strength and Difficulties Questionnaire (SDQ) was compared on 12 concurrent adversities. Based on self-reports, 4.4 % of the adolescents had conduct problem scores within the deviant range and more girls (5.1 %) than boys (3.7 %). In the deviant conduct problem group, 65.1 % had experienced two or more concurrent adversities compared with 26.3 % of youths in the non-deviant group (OR 5.23, 95 % CI 3.91-7.01). Likewise, the deviant conduct problem group was from 1.71 to 8.43 times more at the risk of experiencing the different adversities. Parental mental health problems and experiences of violence were multivariately strongest associated with conduct problem scores within the deviant range on the SDQ. A strong multiple additive relationship with adversities was found. Two-thirds of youth with SDQ conduct problem scores within the deviant range reported two or more concurrent adversities. Clinicians should seek information about kinds and amount of possible traumatic adversities in youth with conduct problems and offer evidence based treatment.
Metal insulator transition and Froehlich conductivity in the Su-Schrieffer-Heeger model
Michielsen, Kristel; Raedt, Hans De
1996-01-01
A quantum molecular dynamics technique is used to study the single-particle density of states, Drude weight, optical conductivity and flux quantization in the Su-Schrieffer-Heeger (SSH) model. Our simulation data show that the SSH model has a metal-insulator transition away from half-filling. In the
Metal-insulator transition and Frohlich conductivity in the Su-Schrieffer-Heeger model
Michielsen, K.F L; de Raedt, H.A.
1996-01-01
A quantum molecular dynamics technique is used to study the single-particle density of states, Drude weight, optical conductivity and flux quantization in the Su-Schrieffer-Heeger (SSH) model. Our simulation data show that the SSH model has a metal-insulator transition away from half-filling. In the
Directory of Open Access Journals (Sweden)
S. Kalia
2014-04-01
Full Text Available Gum ghatti-cl-poly(acrylamide-aniline interpenetrating network (IPN was synthesized by a two-step aqueous polymerization method, in which aniline monomer was absorbed into the network of gum ghatti-cl-poly(acrylamide and followed by a polymerization reaction between aniline monomers. Initially, semi-IPN based on acrylamide and gum ghatti was prepared by free-radical copolymerization in aqueous media with optimized process parameters, using N,N'-methylenebis-acrylamide, as cross-linker and ammonium persulfate, as an initiator system. Optimum reaction conditions affording maximum percentage swelling were: solvent [mL] =12, Acrylamide (AAm [mol•L–1] = 1.971, Ammonium peroxydisulfate (APS [mol•L–1] = 0.131•10–1, N,N'-methylene-bis-acrylamide (MBA [mol•L–1] = 0.162•10–1, reaction time [min] = 210, temperature [°C] = 100 and pH = 7.0. The resulting IPN was doped with different protonic acids. The effect of the doping has been investigated on the conductivity and surface morphology of the IPN hydrogel. The maximum conductivity was observed with 1.5N HClO4 concentration. The morphological, structural and electrical properties of the candidate polymers were studied using scanning electron micrscopy (SEM, Fourier transform infrared spectroscopy FTIR and two-probe method, respectively.
Low thermal conductivity of graphyne nanotubes from molecular dynamics study
Hu, Ming; Jing, Yuhang; Zhang, Xiaoliang
2015-04-01
It is well known that carbon nanotubes (CNTs) possess ultrahigh thermal conductivity that is comparable to bulk diamond. However, no research has studied the possible low thermal conductivity of different CNTs so far. By performing nonequilibrium molecular dynamic simulations, we reveal that the perfect graphyne nanotube (GNT) exhibits an unprecedentedly low thermal conductivity (below 10 W/mK at room temperature), which is generally two orders of magnitude lower than that of ordinary CNTs and even lower than the values reported for defected, doped, and chemically functionalized CNTs. By performing phonon polarization and spectral energy density analysis, we observe that the ultralow thermal conductivity stems from the unique atomic structure of the GNT, consisting of the weak acetylenic linkage (s p C-C bonds) and the strong hexagonal ring (s p2 C-C bonds), which results in a large vibrational mismatch between these two components, and thus induces significantly inefficient heat transfer. Moreover, the thermal transport in GNT with a large number of acetylenic linkages is dominated by the low frequency longitudinal modes in the linkage. Such strong confinement of the low frequency thermal energy results in the extremely low thermal conductivity due to the flattened phonon dispersion curves (low phonon group velocities). The exploration of the abnormal thermal transport of GNTs paves the way for design and application of the relevant devices that could benefit from the ultralow thermal conductivity, such as thermoelectrics for energy conversion.
Modeling of Thermal Conductivity of CVI-Densified Composites at Fiber and Bundle Level
Directory of Open Access Journals (Sweden)
Kang Guan
2016-12-01
Full Text Available The evolution of the thermal conductivities of the unidirectional, 2D woven and 3D braided composites during the CVI (chemical vapor infiltration process have been numerically studied by the finite element method. The results show that the dual-scale pores play an important role in the thermal conduction of the CVI-densified composites. According to our results, two thermal conductivity models applicable for CVI process have been developed. The sensitivity analysis demonstrates the parameter with the most influence on the CVI-densified composites’ thermal conductivity is matrix cracking’s density, followed by volume fraction of the bundle and thermal conductance of the matrix cracks, finally by micro-porosity inside the bundles and macro-porosity between the bundles. The obtained results are well consistent with the reported data, thus our models could be useful for designing the processing and performance of the CVI-densified composites.
Lombardozzi, Danica; Sparks, Jed P; Bonan, Gordon; Levis, Samuel
2012-07-01
Industrialization has significantly altered atmospheric chemistry by increasing concentrations of chemicals such as nitrogen oxides (NO( x )) and volatile organic carbon, which react in the presence of sunlight to produce tropospheric ozone (O(3)). Ozone is a powerful oxidant that causes both visual and physiological damage to plants, impairing the ability of the plant to control processes like photosynthesis and transpiration. Damage to photosynthesis and stomatal conductance does not always occur at the same rate, which generates a problem when using the Ball-Berry model to predict stomatal conductance because the calculations directly rely on photosynthesis rates. The goals of this work were to develop a modeling framework to modify Ball-Berry stomatal conductance predictions independently of photosynthesis and to test the framework using experimental data. After exposure to elevated O(3) in open-top chambers, photosynthesis and stomatal conductance in tulip poplar changed at different rates through time. We were able to accurately model observed photosynthetic and stomatal conductance responses to chronic O(3) exposure in a Ball-Berry framework by adjusting stomatal conductance in addition to photosynthesis. This led to a significant improvement in the modeled ability to predict both photosynthesis and stomatal conductance responses to O(3).
Modeling geomagnetic induction hazards using a 3-D electrical conductivity model of Australia
Wang, Liejun; Lewis, Andrew M.; Ogawa, Yasuo; Jones, William V.; Costelloe, Marina T.
2016-12-01
The surface electric field induced by external geomagnetic source fields is modeled for a continental-scale 3-D electrical conductivity model of Australia at periods of a few minutes to a few hours. The amplitude and orientation of the induced electric field at periods of 360 s and 1800 s are presented and compared to those derived from a simplified ocean-continent (OC) electrical conductivity model. It is found that the induced electric field in the Australian region is distorted by the heterogeneous continental electrical conductivity structures and surrounding oceans. On the northern coastlines, the induced electric field is decreased relative to the simple OC model due to a reduced conductivity contrast between the seas and the enhanced conductivity structures inland. In central Australia, the induced electric field is less distorted with respect to the OC model as the location is remote from the oceans, but inland crustal high-conductivity anomalies are the major source of distortion of the induced electric field. In the west of the continent, the lower conductivity of the Western Australia Craton increases the conductivity contrast between the deeper oceans and land and significantly enhances the induced electric field. Generally, the induced electric field in southern Australia, south of latitude -20°, is higher compared to northern Australia. This paper provides a regional indicator of geomagnetic induction hazards across Australia.
Self-consistent modeling of terahertz waveguide and cavity with frequency-dependent conductivity
Huang, Y. J.; Chu, K. R.; Thumm, M.
2015-01-01
The surface resistance of metals, and hence the Ohmic dissipation per unit area, scales with the square root of the frequency of an incident electromagnetic wave. As is well recognized, this can lead to excessive wall losses at terahertz (THz) frequencies. On the other hand, high-frequency oscillatory motion of conduction electrons tends to mitigate the collisional damping. As a result, the classical theory predicts that metals behave more like a transparent medium at frequencies above the ultraviolet. Such a behavior difference is inherent in the AC conductivity, a frequency-dependent complex quantity commonly used to treat electromagnetics of metals at optical frequencies. The THz region falls in the gap between microwave and optical frequencies. However, metals are still commonly modeled by the DC conductivity in currently active vacuum electronics research aimed at the development of high-power THz sources (notably the gyrotron), although a small reduction of the DC conductivity due to surface roughness is sometimes included. In this study, we present a self-consistent modeling of the gyrotron interaction structures (a metallic waveguide or cavity) with the AC conductivity. The resulting waveguide attenuation constants and cavity quality factors are compared with those of the DC-conductivity model. The reduction in Ohmic losses under the AC-conductivity model is shown to be increasingly significant as the frequency reaches deeper into the THz region. Such effects are of considerable importance to THz gyrotrons for which the minimization of Ohmic losses constitutes a major design consideration.
Nerve conduction studies after decompression in painful diabetic polyneuropathy
Macare van Maurik, JFM; Franssen, Hessel; Millin, Daniel W.; Peters, Edgar J G; Kon, Moshe
2015-01-01
Purpose: To investigate the influence of nerve decompression at potential entrapment sites in the lower extremity in painful diabetic polyneuropathy on nerve conduction study variables. Methods: Forty-two patients with painful diabetic polyneuropathy were included in this prospective randomized cont
FIBULAR MOTOR NERVE CONDUCTION STUDIES AND ANKLE SENSORIMOTOR CAPACITIES*
Richardson, James K.; Allet, Lara; Kim, Hogene; Ashton-Miller, James A.
2012-01-01
Introduction Nerve conduction studies provide information regarding the status of the peripheral nerve, but relationships with sensorimotor capacities that influence mobility have not been defined. Methods A secondary analysis was conducted of data from 41 older subjects (20 women, age 69.1 ± 8.3 years), 25 with diabetic neuropathy of varying severity, and 16 without diabetes or neuropathy. Measurements included routine fibular motor nerve conduction studies and laboratory-based determination of ankle inversion/eversion proprioceptive thresholds and ankle inversion/eversion motor function. Results Independent of age, fibular amplitude correlated robustly with ankle inversion/eversion proprioceptive thresholds (R2 = .591, p < .001), moderately with ankle inversion and eversion rates of torque generation (R2 = .216; p = .004 and R2 = .200; p = .006, respectively), and more strongly when fibular motor amplitude was normalized for body mass index (R2 = .350; p < .001 and R2 = .275; p = .001). Discussion Fibular motor amplitude was strongly associated with ankle sensorimotor capacities that influence lateral balance and recovery from perturbations during gait. The results suggest that nerve conduction study measures have potential for an expanded clinical role in evaluating mobility function in the population studied. PMID:23225524
40 CFR 792.130 - Conduct of a study.
2010-07-01
... 40 Protection of Environment 31 2010-07-01 2010-07-01 true Conduct of a study. 792.130 Section 792.130 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) TOXIC SUBSTANCES CONTROL ACT... the specimen in a manner that precludes error in the recording and storage of data. (d) In animal...
Comparative study of thermal conductivity in crystalline and amorphous nanocomposite
Juangsa, Firman Bagja; Muroya, Yoshiki; Ryu, Meguya; Morikawa, Junko; Nozaki, Tomohiro
2017-06-01
Silicon nanocrystals (SiNCs)/polystyrene (PS) nanocomposite has been observed to have a significant decrease in thermal conductivity in terms of the SiNC fraction with unspecified factors remained unclear. In this paper, amorphous silicon nanoparticles (a-SiNPs) with a mean diameter of 6 nm and PS nanocomposites were synthesized, and their thermal conductivity, including the density and specific heat, was compared with our previous work which investigated well-crystalized SiNPs (6 nm) and PS nanocomposite. The difference between amorphous and crystalline structure is insignificant, but phonon scattering at SiNPs and PS boundary is the key influencing factor of thermal conductivity reduction. The effective thermal conductivity models for nanocomposite revealed that the thermal boundary resistance, explained by Kapitza principle, is estimated to be 4 × 10-7 m2K/W, showing the significant effect of nanostructured heterogenic surface resistance on overall heat transfer behavior. Preservation of unique properties nanoscale materials and low-cost fabrication by silicon inks process at room temperature give the promising potential of SiNPs based heat transfer management.
Mössbauer study of conductive oxide glass
Matsuda, Koken; Kubuki, Shiro; Nishida, Tetsuaki
2014-10-01
Heat treatment of barium iron vanadate glass, BaO - Fe2O3- V2O5, at temperatures higher than crystallization temperature causes a marked decrease in resistivity (ρ) from several MΩcm to several Ωcm. 57Fe Mössbauer spectrum of heat-treated vanadate glass shows a marked decrease in quadrupole splitting (Δ) of FeIII, reflecting a structural relaxation, i.e., an increased symmetry of "distorted" FeO4 and VO4 tetrahedra which are connected to each other by sharing corner oxygen atoms. Structural relaxation of 3D-network of vanadate glass accompanies a decrease in the activation energy for the conduction, reflecting a decreased energy gap between the donor level and conduction band. A marked increase in the conductivity was observed in CuO- or Cu2O -containing barium iron vanadate glass after heat treatment at 450 °C for 30 min or more. "n-type semiconductor model combined with small polaron hopping theory" was proposed in order to explain the high conductivity.
Mössbauer study of conductive oxide glass
Energy Technology Data Exchange (ETDEWEB)
Matsuda, Koken; Kubuki, Shiro [Tokyo Metropolitan University, Hachi-Oji, Tokyo 192-0397 (Japan); Nishida, Tetsuaki, E-mail: nishida@fuk.kindai.ac.jp [Kinki University, Iizuka, Fukuoka 820-8555 (Japan)
2014-10-27
Heat treatment of barium iron vanadate glass, BaO‐Fe{sub 2}O{sub 3}‐V{sub 2}O{sub 5}, at temperatures higher than crystallization temperature causes a marked decrease in resistivity (ρ) from several MΩcm to several Ωcm. {sup 57}Fe Mössbauer spectrum of heat-treated vanadate glass shows a marked decrease in quadrupole splitting (Δ) of Fe{sup III}, reflecting a structural relaxation, i.e., an increased symmetry of 'distorted' FeO{sub 4} and VO{sub 4} tetrahedra which are connected to each other by sharing corner oxygen atoms. Structural relaxation of 3D-network of vanadate glass accompanies a decrease in the activation energy for the conduction, reflecting a decreased energy gap between the donor level and conduction band. A marked increase in the conductivity was observed in CuO- or Cu{sub 2}O-containing barium iron vanadate glass after heat treatment at 450 °C for 30 min or more. 'n-type semiconductor model combined with small polaron hopping theory' was proposed in order to explain the high conductivity.
Conductivity studies in SnO–NaPO3 glasses
Indian Academy of Sciences (India)
M Harish Bhat; Munia Ganguli; K J Rao
2003-06-01
Na+ ion conductivity has been studied in SnO.NaPO3 glasses, which have been prepared over a wide range of compositions using a microwave melting technique. D.c. activation barriers seem to reflect the structural changes in system. A.c. conductivity analysis has revealed that while the power law exponent, , seem to bear correlation to the structural changes, the exponent of the stretched exponential function describing the dielectric relaxation is largely insensitive to the structure. Possible importance of the correlation of transport property to the variation of available non-bridging oxygen (NBO) atoms in the structure is discussed.
Conductivity and dielectric studies on LiCeO_2
Institute of Scientific and Technical Information of China (English)
M.Prabu; S.Selvasekarapandian; A.R.Kulkarni; G.Hirankumar; C.Sanjeeviraja
2010-01-01
LiCeO2 was prepared by a solid-state reaction method using microwave heat treatment and identified by X-ray diffractometry.LiCeO2 has monoclinic crystal structure whose conductivity and dielectric properties were studied over a range of frequency(42 Hz to 1 MHz) and temperatures(30-500 °C) using ac technique of complex impedance analyzer HIOKI 3532.Combined impedance and modulus plots were used as tools to analyze the sample behaviour as a function of frequency at different temperatures.The d.c.conductivity...
Universality of AC conductivity: Random site-energy model with Fermi statistics
Pasveer, W. F.; Bobbert, P. A.; Michels, M. A. J.
2006-10-01
The universality of the frequency-dependent (AC) conduction of many disordered solids in the extreme-disorder limit has been demonstrated experimentally. Theoretically, this universality has been established with different techniques and for various models. A popular model that has been extensively investigated and for which AC universality was established is the symmetric random-barrier model without Fermi statistics. However, for the more realistic model of random site-energies and Fermi statistics AC universality has never been rigorously established. In the present work we perform a numerical study of the latter model for a regular lattice in two dimensions. In addition, we allow for variable-range hopping. Our main conclusion is that AC universality appears to hold for this realistic model. The obtained master curve for the conductivity and the one obtained for the random-barrier model in two dimensions appear to be the same.
FTIR AND IONIC CONDUCTIVITY STUDIES ON BLEND POLYMER ELECTROLYTES
Directory of Open Access Journals (Sweden)
J. Senthil
2011-08-01
Full Text Available Investigations on structural and conductivity properties of solid polymer complexes have attracted a high degree of attention. The main applications of solid polymer electrolytes (SPEs are found in varioussecondary batteries and energy conversion units. In view of the abundant resources, low costs and relatively low reactivity of magnesium, solid-state batteries using magnesium metal are worthy of investigations. The polymer electrolytes were prepared using poly methyl methacrylate (PMMA, poly vinyl chloride (PVC and magnesium chloride (MgCl2 by solvent casting technique. The complex formation and ionic conductivity were characterized by Fourier Transform Infra Red spectroscopy (FTIR and impedance spectroscopy respectively.The FTIR studies provide the evidence of interaction of cation Mg2+ with the polymers. The maximum conductivity found for PMMA-MgCl2 is 0.57 x 10-7 Scm-1 at room temperature.
Bentonite electrical conductivity: a model based on series–parallel transport
Lima, Ana T.
2010-01-30
Bentonite has significant applications nowadays, among them as landfill liners, in concrete industry as a repairing material, and as drilling mud in oil well construction. The application of an electric field to such perimeters is under wide discussion, and subject of many studies. However, to understand the behaviour of such an expansive and plastic material under the influence of an electric field, the perception of its electrical properties is essential. This work serves to compare existing data of such electrical behaviour with new laboratorial results. Electrical conductivity is a pertinent parameter since it indicates how much a material is prone to conduct electricity. In the current study, total conductivity of a compacted porous medium was established to be dependent upon density of the bentonite plug. Therefore, surface conductivity was addressed and a series-parallel transport model used to quantify/predict the total conductivity of the system. © The Author(s) 2010.
Energy Technology Data Exchange (ETDEWEB)
Benjamin Michael Meyer
2003-05-31
As time progresses, the world is using up more of the planet's natural resources. Without technological advances, the day will eventually arrive when these natural resources will no longer be sufficient to supply all of the energy needs. As a result, society is seeing a push for the development of alternative fuel sources such as wind power, solar power, fuel cells, and etc. These pursuits are even occurring in the state of Iowa with increasing social pressure to incorporate larger percentages of ethanol in gasoline. Consumers are increasingly demanding that energy sources be more powerful, more durable, and, ultimately, more cost efficient. Fast Ionic Conducting (FIC) glasses are a material that offers great potential for the development of new batteries and/or fuel cells to help inspire the energy density of battery power supplies. This dissertation probes the mechanisms by which ions conduct in these glasses. A variety of different experimental techniques give a better understanding of the interesting materials science taking place within these systems. This dissertation discusses Nuclear Magnetic Resonance (NMR) techniques performed on FIC glasses over the past few years. These NMR results have been complimented with other measurement techniques, primarily impedance spectroscopy, to develop models that describe the mechanisms by which ionic conduction takes place and the dependence of the ion dynamics on the local structure of the glass. The aim of these measurements was to probe the cause of a non-Arrhenius behavior of the conductivity which has been seen at high temperatures in the silver thio-borosilicate glasses. One aspect that will be addressed is if this behavior is unique to silver containing fast ion conducting glasses. more specifically, this study will determine if a non-Arrhenius correlation time, {tau}, can be observed in the Nuclear Spin Lattice Relaxation (NSLR) measurements. If so, then can this behavior be modeled with a new single
Energy Technology Data Exchange (ETDEWEB)
Meyer, Benjamin Michael [Iowa State Univ., Ames, IA (United States)
2003-01-01
As time progresses, the world is using up more of the planet's natural resources. Without technological advances, the day will eventually arrive when these natural resources will no longer be sufficient to supply all of the energy needs. As a result, society is seeing a push for the development of alternative fuel sources such as wind power, solar power, fuel cells, and etc. These pursuits are even occurring in the state of Iowa with increasing social pressure to incorporate larger percentages of ethanol in gasoline. Consumers are increasingly demanding that energy sources be more powerful, more durable, and, ultimately, more cost efficient. Fast Ionic Conducting (FIC) glasses are a material that offers great potential for the development of new batteries and/or fuel cells to help inspire the energy density of battery power supplies. This dissertation probes the mechanisms by which ions conduct in these glasses. A variety of different experimental techniques give a better understanding of the interesting materials science taking place within these systems. This dissertation discusses Nuclear Magnetic Resonance (NMR) techniques performed on FIC glasses over the past few years. These NMR results have been complimented with other measurement techniques, primarily impedance spectroscopy, to develop models that describe the mechanisms by which ionic conduction takes place and the dependence of the ion dynamics on the local structure of the glass. The aim of these measurements was to probe the cause of a non-Arrhenius behavior of the conductivity which has been seen at high temperatures in the silver thio-borosilicate glasses. One aspect that will be addressed is if this behavior is unique to silver containing fast ion conducting glasses. more specifically, this study will determine if a non-Arrhenius correlation time, τ, can be observed in the Nuclear Spin Lattice Relaxation (NSLR) measurements. If so, then can this behavior be modeled with a new single
Krøigård, Thomas; Gaist, David; Otto, Marit; Højlund, Dorthe; Selmar, Peter E; Sindrup, Søren H
2014-08-01
The reproducibility of variables commonly included in studies of peripheral nerve conduction in healthy individuals has not previously been analyzed using a random effects regression model. We examined the temporal changes and variability of standard nerve conduction measures in the leg. Peroneal nerve distal motor latency, motor conduction velocity, and compound motor action potential amplitude; sural nerve sensory action potential amplitude and sensory conduction velocity; and tibial nerve minimal F-wave latency were examined in 51 healthy subjects, aged 40 to 67 years. They were reexamined after 2 and 26 weeks. There was no change in the variables except for a minor decrease in sural nerve sensory action potential amplitude and a minor increase in tibial nerve minimal F-wave latency. Reproducibility was best for peroneal nerve distal motor latency and motor conduction velocity, sural nerve sensory conduction velocity, and tibial nerve minimal F-wave latency. Between-subject variability was greater than within-subject variability. Sample sizes ranging from 21 to 128 would be required to show changes twice the magnitude of the spontaneous changes observed in this study. Nerve conduction studies have a high reproducibility, and variables are mainly unaltered during 6 months. This study provides a solid basis for the planning of future clinical trials assessing changes in nerve conduction.
Model for predicting thermal conductivity using transient hot wire method
Kumar, Sublania Harish; Singh K., J.; Somani A., K.
2016-05-01
The use of the hot wire method for estimating the thermal conductivity measurement has recently known a significant increase. However, this method is theoretically not applicable to materials. Thermal conductivity values are necessary whenever a heat transfer problem is to be evaluated.
Structure-conductivity studies in polymer electrolytes containing multivalent cations
Aziz, M
1996-01-01
force microscopy (AFM). DSC evidences helped to explain the texture of the iron samples during the drying process, and showed transitions between low melting, PEO and high melting spherulites, and VTPM is able to visualise the spherulites present in the samples. AFM has successfully imaged the as cast PEO sub 8 :FeBr sub 2 sample and the surface effect causing extra resistance in the impedance spectra could be seen. Conductivity studies were carried out using a.c. impedance spectra. Fe(ll) samples exhibit the typical semicircle-spike plot but the Fe(lll) samples displayed an extra semicircle before the spike reflecting a surface effect. This is also manifested in the Arrhenius plots of the same samples where a dip was shown at 100 deg C. From the conductivity studies on the iron systems it was found that for the dry samples the optimum conductivity was observed in PEO sub 8 :FeBr sub x irrespective of the valence state of the cation. For the air-cast samples the optimum conductivity composition depends on the...
Method and results of studying conduction measuring transducers
Energy Technology Data Exchange (ETDEWEB)
Dunaevskii, I.G.; Korotkov, B.N.; Povkh, I.L.; Cheplyukov, V.G.
1977-01-01
The method and results are given for determining the sensitivity of conduction measuring transducers with a local magnetic field. The results were obtained by frequency-dependent gradation on a model pulsation velocity gauge--a thermoanemometer. The effect of measuring a transducer's diameter, inter-electrode distance and nose line forms on its spatial resolution capacity was estimated. Adjustment functions were obtained for these transducers. A concept was formulated for measuring transducers belonging to the same class. 5 references, 5 figures.
Singh, Nikhilendra
A novel approach for the electrodeposition of conducting polymers and conducting polymer-inorganic composite materials is presented. The approach shows that conducting polymers, such as polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) can be electrodeposited by the application of a cathodic bias that generates an oxidizing agent, NO+, via the in-situ reduction of nitrate anions. This new cathodic polymerization method allows for the deposition of PPy and PEDOT as three dimensional, porous films composed of spherical polymer particles. The method is also suitable for the co-deposition of inorganic species producing conducting polymer-inorganic composite electrodes. Such composites are used as high surface area electrodes in Li-ion batteries, electrochemical hydrogen evolution and in the development of various other conducting polymer-inorganic composite electrodes. New Sn-PPy and Sb-PPy composite electrodes where Sn and Sb nanoparticles are well dispersed among the PPy framework are reported. These structures allow for decreased stress during expansion and contraction of the active material (Sn, Sb) during the alloying and de-alloying processes of a Li-ion battery anode, significantly alleviating the loss of active material due to pulverization processes. The new electrochemical synthesis mechanism allows for the fabrication of Sn-PPy and Sb-PPy composite electrodes directly from a conducting substrate and eliminates the use of binding materials and conducting carbon used in modern battery anodes, which significantly simplifies their fabrication procedures. Platinum (Pt) has long been identified as the most efficient catalyst for electrochemical water splitting, while nickel (Ni) is a cheaper, though less efficient alternative to Pt. A new morphology of PPy attained via the aforementioned cathodic deposition method allows for the use of minimal quantities of Pt and Ni dispersed over a very high surface area PPy substrate. These composite electrodes
Experimental Study on Aero Conductivity of Porous Media
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
To study the variation pattern of aero conductivity of different porous media under low pressure conditions, three kinds of media are selected.These include sandy clay loam, fine sand, and medium sand, and air as fluid to conduct soil column ventilation tests.Pressure at both ends of the columns is measured under different ventilation flow rates during testing.The test results show that the aero conductivity, solved by Darcy's law, is not a constant.It is a variable, which increases first when air flow velocity is less than 0.258 7 cm/ s for sandy clay loam, 0.637 3 cm/s for fine sand and then decreases when air flow velocity is bigger than that with the increase of the ventilation flow rate when the medium is determined.By analyzing various factors that influence the flow resistance, the reasons for variation in aero conductivity are found as follows: first, the change of pore structure results in better ventilation; second, the relationship between pressure head loss and air flow velocity is nonlinear, and it is beyond the condition of the laminar flow domain to which Darcy's law can be applied, when the air flow rate increases to a certain value and the flow velocity is in the transition range to turbulent flow.
Fractional model for heat conduction in polar bear hairs
Directory of Open Access Journals (Sweden)
Wang Qing-Li
2012-01-01
Full Text Available Time-fractional differential equations can accurately describe heat conduction in fractal media, such as wool fibers, goose down and polar bear hair. The fractional complex transform is used to convert time-fractional heat conduction equations with the modified Riemann-Liouville derivative into ordinary differential equations, and exact solutions can be easily obtained. The solution process is straightforward and concise.
Thermal conductivity of granular porous media: A pore scale modeling approach
Directory of Open Access Journals (Sweden)
R. Askari
2015-09-01
Full Text Available Pore scale modeling method has been widely used in the petrophysical studies to estimate macroscopic properties (e.g. porosity, permeability, and electrical resistivity of porous media with respect to their micro structures. Although there is a sumptuous literature about the application of the method to study flow in porous media, there are fewer studies regarding its application to thermal conduction characterization, and the estimation of effective thermal conductivity, which is a salient parameter in many engineering surveys (e.g. geothermal resources and heavy oil recovery. By considering thermal contact resistance, we demonstrate the robustness of the method for predicting the effective thermal conductivity. According to our results obtained from Utah oil sand samples simulations, the simulation of thermal contact resistance is pivotal to grant reliable estimates of effective thermal conductivity. Our estimated effective thermal conductivities exhibit a better compatibility with the experimental data in companion with some famous experimental and analytical equations for the calculation of the effective thermal conductivity. In addition, we reconstruct a porous medium for an Alberta oil sand sample. By increasing roughness, we observe the effect of thermal contact resistance in the decrease of the effective thermal conductivity. However, the roughness effect becomes more noticeable when there is a higher thermal conductivity of solid to fluid ratio. Moreover, by considering the thermal resistance in porous media with different grains sizes, we find that the effective thermal conductivity augments with increased grain size. Our observation is in a reasonable accordance with experimental results. This demonstrates the usefulness of our modeling approach for further computational studies of heat transfer in porous media.
Azizollahi, Hamed; Aarabi, Ardalan; Wallois, Fabrice
2016-10-01
In this study, we investigated the impact of uncertainty in head tissue conductivities and inherent geometrical complexities including fontanels in neonates. Based on MR and CT coregistered images, we created a realistic neonatal head model consisting of scalp, skull, fontanels, cerebrospinal fluid (CSF), gray matter (GM), and white matter (WM). Using computer simulations, we investigated the effects of exclusion of CSF and fontanels, discrimination between GM and WM, and uncertainty in conductivity of neonatal head tissues on EEG forward modeling. We found that exclusion of CSF from the head model induced the strongest widespread effect on the EEG forward solution. Discrimination between GM and white matter also induced a strong widespread effect, but which was less intense than that of CSF exclusion. The results also showed that exclusion of the fontanels from the neonatal head model locally affected areas beneath the fontanels, but this effect was much less pronounced than those of exclusion of CSF and GM/WM discrimination. Changes in GM/WM conductivities by 25% with respect to reference values induced considerable effects in EEG forward solution, but this effect was more pronounced for GM conductivity. Similarly, changes in skull conductivity induced effects in the EEG forward modeling in areas covered by the cranial bones. The least intense effect on EEG was caused by changes in conductivity of the fontanels. Our findings clearly emphasize the impact of uncertainty in conductivity and deficiencies in head tissue compartments on modeling research and localization of brain electrical activity in neonates. Hum Brain Mapp 37:3604-3622, 2016. © 2016 Wiley Periodicals, Inc.
A SPICE model for a phase-change memory cell based on the analytical conductivity model
Yiqun, Wei; Xinnan, Lin; Yuchao, Jia; Xiaole, Cui; Jin, He; Xing, Zhang
2012-11-01
By way of periphery circuit design of the phase-change memory, it is necessary to present an accurate compact model of a phase-change memory cell for the circuit simulation. Compared with the present model, the model presented in this work includes an analytical conductivity model, which is deduced by means of the carrier transport theory instead of the fitting model based on the measurement. In addition, this model includes an analytical temperature model based on the 1D heat-transfer equation and the phase-transition dynamic model based on the JMA equation to simulate the phase-change process. The above models for phase-change memory are integrated by using Verilog-A language, and results show that this model is able to simulate the I-V characteristics and the programming characteristics accurately.
Tan, Cheng; Liang, Zhi-Shan
2016-03-01
In this paper, based on the fact that the inductors and capacitors are of fractional order in nature, the four-order mathematical model of the fractional order quadratic Boost converter in type I and type II discontinuous conduction mode (DCM) — DCM is established by using fractional calculus theory. Direct current (DC) analysis is conducted by using the DC equivalent model and the transfer functions are derived from the corresponding alternating current (AC) equivalent model. The DCM-DCM regions of type I and type II are obtained and the relations between the regions and the orders are found. The influence of the orders on the performance of the quadratic Boost converter in DCM-DCM is verified by numerical and circuit simulations. Simulation results demonstrate the correctness of the fractional order model and the efficiency of the proposed theoretical analysis.
Comparative study of electron conduction in azulene and naphthalene
Indian Academy of Sciences (India)
Sudipta Dutta; S Lakshmi; Swapan K Pati
2008-06-01
We have studied the feasibility of electron conduction in azulene molecule and compared with that in its isomer naphthalene. We have used non-equilibrium Green’s function formalism to measure the current in our systems as a response of the external electric field. Parallely we have performed the Gaussian calculations with electric field in the same bias window to observe the impact of external bias on the wave functions of the systems. We have found that the conduction of azulene is higher than that of naphthalene inspite of its intrinsic donor–acceptor property, which leads a system to more insulating state. Due to stabilization through charge transfer the azulene system can be fabricated as a very effective molecular wire. Our calculations show the possibility of huge device application of azulene in nano-scale instruments.
Energy Technology Data Exchange (ETDEWEB)
Huslage, J.; Buechi, F.N.; Scherer, G.G. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)
1999-08-01
Two perfluorosulfonic acid membranes, Nafion{sup R} 105 and Nafion{sup R} 115 with the same thickness but different equivalent weights (EW = 1000 g/eq. resp. 1100 g/eq.) were characterised by conductivity measurements at different water vapour activities in the temperature range of 25-70{sup o}C. The results demonstrate that a lower membrane equivalent weight opens the possibility to obtain the needed proton conductivity at lower water vapour activity. This is especially important for those fuel cell applications, in which the cell is operated without external humidification of the fuel gases. (author) 5 figs., 5 refs.
DEFF Research Database (Denmark)
Qin, Nan; Xu, Zhao
2008-01-01
in the discontinuous conducting mode (DCM). The new wind turbine model with the variable speed control of the PMSG based on duty cycle control of the boost converter has been developed in Matlab Simulink. Simulation studies show that DCM working mode of the boost converter provides more flexibility in controlling...
Model of electrical conductivity of skeletal muscle based on tissue structure
Gielen, F.L.H.; Cruts, H.E.P.; Alberts, B.A.; Boon, K.L.; Wallinga, W.; Boom, H.B.K.
1986-01-01
Recent experiments carried out in our laboratory with the four-electrode method showed that the electrical conductivity of skeletal muscle tissue depends on the frequency of the injected current and the distance between the current electrodes. A model is proposed in order to study these effects. The
Guidelines for Conducting Positivist Case Study Research in Information Systems
Directory of Open Access Journals (Sweden)
Graeme Shanks
2002-11-01
Full Text Available The case study research approach is widely used in a number of different ways within the information systems community. This paper focuses on positivist, deductive case study research in information systems. It provides clear definitions of important concepts in positivist case study research and illustrates these with an example research study. A critical analysis of the conduct and outcomes of two recently published positivist case studies is reported. One is a multiple case study that validated concepts in a framework for viewpoint development in requirements definition. The other is a single case study that examined the role of social enablers in enterprise resource planning systems implementation. A number of guidelines for successfully undertaking positivist case study research are identified including developing a clear understanding of key concepts and assumptions within the positivist paradigm; providing clear and unambiguous definitions of the units and interactions when using any theory; carefully defining the boundary of the theory used in the case study; using hypotheses rather than propositions in the empirical testing of theory; using fuzzy or probabilistic propositions in recognising that reality can never be perfectly known; selecting case studies carefully, particularly single case studies; and recognising that generalisation from positivist, single case studies is inherently different from generalisation from single experiments. When properly undertaken, positivist, deductive case study research is a valuable research approach for information systems researchers, particularly when used within pluralist research programs that use a number of different research approaches from different paradigms.
Evaluation of Regression and Neuro_Fuzzy Models in Estimating Saturated Hydraulic Conductivity
Directory of Open Access Journals (Sweden)
J. Behmanesh
2015-06-01
Full Text Available Study of soil hydraulic properties such as saturated and unsaturated hydraulic conductivity is required in the environmental investigations. Despite numerous research, measuring saturated hydraulic conductivity using by direct methods are still costly, time consuming and professional. Therefore estimating saturated hydraulic conductivity using rapid and low cost methods such as pedo-transfer functions with acceptable accuracy was developed. The purpose of this research was to compare and evaluate 11 pedo-transfer functions and Adaptive Neuro-Fuzzy Inference System (ANFIS to estimate saturated hydraulic conductivity of soil. In this direct, saturated hydraulic conductivity and physical properties in 40 points of Urmia were calculated. The soil excavated was used in the lab to determine its easily accessible parameters. The results showed that among existing models, Aimrun et al model had the best estimation for soil saturated hydraulic conductivity. For mentioned model, the Root Mean Square Error and Mean Absolute Error parameters were 0.174 and 0.028 m/day respectively. The results of the present research, emphasises the importance of effective porosity application as an important accessible parameter in accuracy of pedo-transfer functions. sand and silt percent, bulk density and soil particle density were selected to apply in 561 ANFIS models. In training phase of best ANFIS model, the R2 and RMSE were calculated 1 and 1.2×10-7 respectively. These amounts in the test phase were 0.98 and 0.0006 respectively. Comparison of regression and ANFIS models showed that the ANFIS model had better results than regression functions. Also Nuro-Fuzzy Inference System had capability to estimatae with high accuracy in various soil textures.
Otter, den Matthijs Willem
2000-01-01
Mixed conducting oxygen ion conductors can be applied as membranes for the separation of oxygen from air, as electrodes for both oxygen pumps and solid oxide fuel cells. In these applications, oxygen molecules dissociate on the surface of the material. The atomic oxygen species pick up two electrons
Mesophyll conductance and reaction-diffusion models for CO
Berghuijs, Herman N.C.; Yin, Xinyou; Tri Ho, Q.; Driever, Steven M.; Retta, Moges A.; Nicolaï, Bart M.; Struik, Paul C.
2016-01-01
One way to increase potential crop yield could be increasing mesophyll conductance g_{m}. This variable determines the difference between the CO_{2} partial pressure in the intercellular air spaces (C_{i}) and that near Rubisco (C_{c}). Various methods can determin
Universal conductivity in the boson Hubbard model in a magnetic field
Cha, Min-Chul; Girvin, S. M.
1993-01-01
The universal conductivity at the zero-temperature superconductor-insulator transition of the two-dimensional boson Hubbard model is studied for cases both with and without magnetic field by Monte Carlo simulations of the (2+1)-dimensional classical $XY$-model with disorder represented by random bonds correlated along the imaginary time dimension. The effect of magnetic field is characterized by the frustration $f$. From the scaling behavior of the stiffness, we determine the quantum dynamica...
Modeling of Proton-Conducting Solid Oxide Fuel Cells Fueled with Syngas
2014-01-01
Solid oxide fuel cells (SOFCs) with proton conducting electrolyte (H-SOFCs) are promising power sources for stationary applications. Compared with other types of fuel cells, one distinct feature of SOFC is their fuel flexibility. In this study, a 2D model is developed to investigate the transport and reaction in an H-SOFC fueled with syngas, which can be produced from conventional natural gas or renewable biomass. The model fully considers the fluid flow, mass transfer, heat transfer and r...
Study of conduction in vertical and lateral nanostructures
Kolagunta, Venkat Ramamurthi
It is predicted that Quantum devices would be used to develop future high-speed computers. The demonstration of quantum phenomenon in metal and semiconductor devices has been limited to temperatures of 4.2K or lower due to the minimum achievable feature sizes of conventional fabrication techniques. A vertical sidewall gating technique has been developed to study and demonstrate lateral confinement effects in quantum heterostructures. Room temperature pinch-off of the resonant peak in single well resonant devices with minimum widths in the sub-micron regime and an even gating in both positive and negative biasing regimes are presented. The first demonstration of pinch-off of multiple well resonant structures including observation of one-dimensional quantization and sub-band mixing at 77K is reported. A self-assembled structure of nanometer size single crystal metal metal clusters with organic linking between nearest neighbour clusters has been developed at Purdue with possible applications in future single electronic circuits. Activated temperature dependent conduction has been observed in these linked cluster networks (LCN) and is associated to the charging energy of a single charge (soliton) in the array. Changing the linking molecule between the clusters changes the conduction through the array and is associated to the conduction properties of the organic linking molecule. While room-temperature Coulomb blockade is not observed, means to achieve the same using the LCN structures are discussed.
Energy Technology Data Exchange (ETDEWEB)
Mesalhy, O.; Lafdi, K.; Elgafy, A.; Bowman, K. [Dayton University Research Inst., OH (United States)
2005-04-01
In this paper, the melting process inside an irregular geometry filled with high thermal conductivity porous matrix saturated with phase change material PCM is investigated numerically. The numerical model is resting on solving the volume averaged conservation equations for mass, momentum and energy with phase change (melting) in the porous medium. The convection motion of the liquid phase inside the porous matrix is solved considering the Darcy, Brinkman and Forchiemer effects. A local thermal non-equilibrium assumption is considered due to the large difference in thermal properties between the solid matrix and PCM by applying a two energy equation model. The numerical code shows good agreement for pure PCM melting with another published numerical work. Through this study it is found that the presence of the porous matrix has a great effect on the heat transfer and melting rate of the PCM energy storage. Decreasing the porosity of the matrix increases the melting rate, but it also damps the convection motion. It is also found that the best technique to enhance the response of the PCM storage is to use a solid matrix with high porosity and high thermal conductivity. (author)
Study of conduction aphasia by positron emission tomography
Energy Technology Data Exchange (ETDEWEB)
Shoji, Mikio; Harigawa, Yasuo; Kawarabayashi, Takeshi; Hirai, Shunsaku; Tamada, Junpei.
1988-04-01
We reported two cases of conduction aphasia with distinctive language disorder from early stage of stroke, as well as their cerebral blood flow and oxygen consumption investigated with PET. The case was a 72-year-old right handed man whose speech disturbance began acutely. On admission, neurological examination revealed hand pronation sign on the right and speech disturbance. Other neurological findings including cortical functions were normal. Brain CT scan showed low density area in the white matter of the left supramarginal gyrus. The diagnosis was cerebral infarction. The case 2 was a 64-year-old right handed man. He suffered right hemiparesis 2 months before. Neurological examination revealed mild right hemiparesis and speech disturbance. Other cortical functions were noncontributory. Brain CT scan showed old subcortical infarction of the left frontal lobe and new cerebral infarction. with supramarginal gyrus. The low density area of the supramarginal cortex extended into the subcortical white matter. The language performances in these two cases were similar. Two patients were definitely fluent, but the verbal output was contaminated by paraphasias which were predominantly literal. They performed poorly when attempting to repeat despite good comprehension. Thus, the primary characteristics of conduction aphasia were present. PET studies resulted as follows. 1) rCBF reduced 36 % in the supramarginal cortex, 50 % in the white matter. 2) rCMRO/sub 2/ reduced 37 % in the supramarginal cortex, 45 % in the white matter. 3) The CBF and the CMRO/sub 2/ images indicated that cerebral blood flow and oxygen consumption reduced in wider range of area than that shown by brain CT. These results indicated that not only the cortex but also the white matter were damaged in conduction aphasia and several methods including PET should be used to determine the locus of abnormality in conduction aphasia.
Directory of Open Access Journals (Sweden)
Lee Yueh-Chiang
2016-06-01
Full Text Available With the analysis of the industrial economic theory structure – conduct – performance model, the study investigates the existence of significant relationship among market structure, conduct and performance. Twelve Taiwan companies are studied during the study period from 2006 to 2012 which are analysed with fixed effect and random effect of panel data and ordinary least squares estimation. The empirical result backs the statement by “Structuralism” that market structure (market share, entry barrier and capital intensity directly affects firm conduct (R&D intensity and performance (ROA.
Modeling the Conductivity of a Subnanosecond Breakdown Gas Switch
Chen, Jinhui; Scott Tyo, J.; Jerald Buchenauer, C.
We present two different modeling methods for understanding subnanosecond breakdown processes in gas plasma switches. The first method uses a finite element time domain method in order to understand experimental measurements of the remote electromagnetic (EM) fields. This method only models the EM fields and is good for analysis, but lacks a predictive capability for the full nonlinear plasma system. The second modeling method uses a PIC code, and is fully self consistent. We make comparisons with experimental measurements and conclude that the PIC model may provide a good understanding of the subnanosecond breakdown phenomena.
Ionospheric conductance distribution and MHD wave structure: observation and model
Directory of Open Access Journals (Sweden)
F. Budnik
Full Text Available The ionosphere influences magnetohydrodynamic waves in the magnetosphere by damping because of Joule heating and by varying the wave structure itself. There are different eigenvalues and eigensolutions of the three dimensional toroidal wave equation if the height integrated Pedersen conductivity exceeds a critical value, namely the wave conductance of the magnetosphere. As a result a jump in frequency can be observed in ULF pulsation records. This effect mainly occurs in regions with gradients in the Pedersen conductances, as in the auroral oval or the dawn and dusk areas. A pulsation event recorded by the geostationary GOES-6 satellite is presented. We explain the observed change in frequency as a change in the wave structure while crossing the terminator. Furthermore, selected results of numerical simulations in a dipole magnetosphere with realistic ionospheric conditions are discussed. These are in good agreement with the observational data.
Key words. Ionosphere · (Ionosphere · magnetosphere interactions · Magnetospheric physics · Magnetosphere · ionosphere interactions · MHD waves and instabilities.
Kretschmer, Tina; Hickman, Matthew; Doerner, Rita; Emond, Alan; Lewis, Glyn; Macleod, John; Maughan, Barbara; Munafò, Marcus R; Heron, Jon
2014-07-01
Although conduct problems in childhood are stably associated with problem outcomes, not every child who presents with conduct problems is at risk. This study extends previous studies by testing whether childhood conduct problem trajectories are predictive of a wide range of other health and behavior problems in early adulthood using a general population sample. Based on 7,218 individuals from the Avon longitudinal study of parents and children, a three-step approach was used to model childhood conduct problem development and identify differences in early adult health and behavior problems. Childhood conduct problems were assessed on six occasions between age 4 and 13 and health and behavior outcomes were measured at age 18. Individuals who displayed early-onset persistent conduct problems throughout childhood were at greater risk for almost all forms of later problems. Individuals on the adolescent-onset conduct problem path consumed more tobacco and illegal drugs and engaged more often in risky sexual behavior than individuals without childhood conduct problems. Levels of health and behavior problems for individuals on the childhood-limited path were in between those for stable low and stable high trajectories. Childhood conduct problems are pervasive and substantially affect adjustment in early adulthood both in at-risk samples as shown in previous studies, but also in a general population sample. Knowing a child's developmental course can help to evaluate the risk for later maladjustment and be indicative of the need for early intervention.
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
It′s important that HTS tapes have lower thermal conductivity and higher transversal resistivity in order to reduce the heat leaks conducted along the tapes and AC losses in the high temperature superconducting system conduction-cooled by GM coolers. This paper presents an experimental investigation into the effects of pure Ag and AgAu alloys sheath materials on the properties of Bi(2223) multifilamentary tapes and the optimisation of conduction-cooled hybrid current leads made from copper and Bi(2223)/Ag or Bi(2223)/AgAu tapes. The thermal conductivity of the tapes were measured by cryogenic steady heat flux method and the resistance was measured by using standard DC four-probe method at low temperature. The results showed that the reduction of thermal conductivity by the addition of Au into the sheath material of Bi(2223) tapes was 650%, 750% and 850% lower than that of pure Ag sheathed Bi(2223) tapes and the increase of resistivity was 4.9, 10 and 19.4 times higher than that of pure Ag for the addition of 2.20%, 5.70% and 10.70%Au(atom ratio) respectively. And the study also attempts to optimise thermodynamically the conduction-cooled hybrid current lead by using a developed model, which took the irreversibility of commercial GM coolers, the contact resistance and thermal conductance into account. Predictions from the model showed that AgAu alloys were suitable candidate materials to replace Ag as sheath material of Bi(2223) tapes applied in HTS current leads. In addition, Bi(2223)/AgAu was a suitable material to be applied as the HTS section of hybrid current leads in conduction-cooled superconducting electric systems.
Chen, Yu-Yi; Juang, Jia-Yang
2016-07-01
The standard collinear four-point probe method is an indispensable tool and has been extensively used for characterizing conductive thin films with homogeneous and isotropic electrical properties. In this paper, we conduct three-dimensional (3D) finite element simulations on conductive multilayer films to study the relationship between the reading of the four-point probe and the conductivity of the individual layers. We find that a multilayer film may be modeled as a simple equivalent circuit with multiple resistances, connected in parallel for a wide range of resistivity and thickness ratios, as long as its total thickness is smaller than approximately half of the probe spacing. As a result, we may determine the resistivity of each layer sequentially by applying the four-point probe, with the original correction factor π/ln(2), after deposition of each layer.
Conductivity analysis of epoxy/carbon nanotubes composites by dipole relaxation and hopping models
Ramos, Airton; Pezzin, Sergio H.; Farias, Heric Denis; Becker, Daniela; Bello, Roger H.; Coelho, Luiz A. F.
2016-10-01
In this study it was used a numerical technique of successive approximations to estimate parameters of a conductivity model that includes the hopping process and the dipole relaxation for the purpose of describing the behavior of the conductivity measured on nanocomposites with carbon nanotubes in epoxy resin in the range of frequency of 100 Hz to 40 MHz. Two relaxation bands were detected, one with a response below 10 kHz and one above 10 MHz. For the first band, it was observed that the nanocomposites become more conductive, and its conductivity less temperature dependent, as the nanotube content increases. The second band is characterized by a large spread in relaxation time. The results show that the percolation threshold is below 0.15 vol% and that 'ac' hopping is the main transport process above 100 kHz, becoming dominant with respect to percolation at higher temperatures (>340 K).
Two-phase numerical model for thermal conductivity and convective heat transfer in nanofluids.
Kondaraju, Sasidhar; Lee, Joon Sang
2011-03-21
Due to the numerous applications of nanofluids, investigating and understanding of thermophysical properties of nanofluids has currently become one of the core issues. Although numerous theoretical and numerical models have been developed by previous researchers to understand the mechanism of enhanced heat transfer in nanofluids; to the best of our knowledge these models were limited to the study of either thermal conductivity or convective heat transfer of nanofluids. We have developed a numerical model which can estimate the enhancement in both the thermal conductivity and convective heat transfer in nanofluids. It also aids in understanding the mechanism of heat transfer enhancement. The study reveals that the nanoparticle dispersion in fluid medium and nanoparticle heat transport phenomenon are equally important in enhancement of thermal conductivity. However, the enhancement in convective heat transfer was caused mainly due to the nanoparticle heat transport mechanism. Ability of this model to be able to understand the mechanism of convective heat transfer enhancement distinguishes the model from rest of the available numerical models.
Directory of Open Access Journals (Sweden)
M. Banimahd Keivani
2010-01-01
Full Text Available Polyaniline (PAn was prepared chemically in the presence of bronsted acid from aqueous solutions. Polyaniline- nylon 6 composite (termed as PAn/Ny6 prepared via solvent casting method. The preparation conditions were optimized with regard to the mechanical properties of the polymer composite. It was found that the molar ratio of PAn to nylon have the greatest effect in determining the mechanical properties of polymer composite. Electrical conductivity was measured using standard method of four point probe. Spectrophotometric analysis (UV-Vis was used for investigation of the effect of thermal treatment on polyaniline and it’s composite.
Conducting Simulation Studies in the R Programming Environment.
Hallgren, Kevin A
2013-10-12
Simulation studies allow researchers to answer specific questions about data analysis, statistical power, and best-practices for obtaining accurate results in empirical research. Despite the benefits that simulation research can provide, many researchers are unfamiliar with available tools for conducting their own simulation studies. The use of simulation studies need not be restricted to researchers with advanced skills in statistics and computer programming, and such methods can be implemented by researchers with a variety of abilities and interests. The present paper provides an introduction to methods used for running simulation studies using the R statistical programming environment and is written for individuals with minimal experience running simulation studies or using R. The paper describes the rationale and benefits of using simulations and introduces R functions relevant for many simulation studies. Three examples illustrate different applications for simulation studies, including (a) the use of simulations to answer a novel question about statistical analysis, (b) the use of simulations to estimate statistical power, and (c) the use of simulations to obtain confidence intervals of parameter estimates through bootstrapping. Results and fully annotated syntax from these examples are provided.
Thermally stimulated discharge conductivity study of zinc oxide thermoelectrets
Indian Academy of Sciences (India)
Vijaya S Sangawar; Manisha C Golchha
2014-10-01
The present work deals with transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermally stimulated discharge current (TSDC) study of inorganic metal oxide (ZnO) nanoparticles and its thermoelectrets. The thermoelectrets were prepared by applying different electric polarizing field (P) at constant polarizing temperature (P), for constant polarization time (P). The TSDC study was carried out in the temperature region of 313–473 K. It was observed that the conductivity of ZnO samples increases with the increase in temperature and polarizing field. The dependence of TSDC data on polarizing agents, i.e. field and temperature shows Arrhenius type of behviour and is explained on the basis of variable range hopping mechanism.
Location and social context does matter when conducting consumer studies!
DEFF Research Database (Denmark)
Andersen, Barbara Vad; Kraggerud, Hilde; Bruun Brockhoff, Per
2015-01-01
an adequate level of research conducted in realistic eating contexts. In the aim to study how location and social context affected consumers’ feeling of food satisfaction and physical well-being a study was set up with, combined yoghurt with muesli products in two settings; a) in a sensory lab facility (n...... = 107), and b) a natural eating context (n = 132). In the natural eating context the consumer could bring the product along and eat it in a context where it felt natural. This further facilitated analysis of effect of eating location, social context and at which meal the product was consumed on feeling......, and food satisfaction, and one hour post intake of satisfaction. Overall the differences indicate that it takes more of a product to reduce appetite and increase food satisfaction in a natural context than it does in a lab context. Analysis of the natural eating context further showed an effect of social...
A Simple Model for the Non-Arrhenius Ionic Conductivity in Superionic Glasses
Indoh, Takaki; Aniya, Masaru; インドウ, タカキ; アニヤ, マサル; 犬童, 貴樹; 安仁屋, 勝
2010-01-01
Many superionic conducting glasses follow the Arrhenius type temperature dependence of ionic conductivity. However, in some superionic conductors it has been discovered that the conductivity deviate from the Arrhenius type behavior. In this paper, we present a simple model that describes the non-Arrhenius type ionic conductivity based on the Zwanzig model of diffusion. From the theory, the condition for the appearance of non-Arrhenius type ionic conductivity has been obtained.
A Model to Predict Thermal Conductivity of Irradiated U-Mo Dispersion Fuel
Energy Technology Data Exchange (ETDEWEB)
Burkes, Douglas; Huber, Tanja K.; Casella, Andrew M.
2016-05-01
The Office of Materials Management and Minimization Reactor Conversion Program continues to develop existing and new research and test reactor fuels to achieve maximum attainable uranium loadings to support the conversion of a number of the world’s remaining high-enriched uranium fueled reactors to low-enriched uranium fuel. The program is focused on assisting with the development and qualification of a fuel design that consists of a uranium-molybdenum (U-Mo) alloy dispersed in an aluminum matrix as one option for reactor conversion. Thermal conductivity is an important consideration in determining the operational temperature of the fuel and can be influenced by interaction layer formation between the dispersed phase and matrix and upon the concentration of the dispersed phase within the matrix. This paper extends the use of a simple model developed previously to study the influence of interaction layer formation as well as the size and volume fraction of fuel particles dispersed in the matrix, Si additions to the matrix, and Mo concentration in the fuel particles on the effective thermal conductivity of the U-Mo/Al composite during irradiation. The model has been compared to experimental measurements recently conducted on U-Mo/Al dispersion fuels at two different fission densities with acceptable agreement. Observations of the modeled results indicate that formation of an interaction layer and subsequent consumption of the matrix reveals a rather significant effect on effective thermal conductivity. The modeled interaction layer formation and subsequent consumption of the high thermal conductivity matrix was sensitive to the average dispersed fuel particle size, suggesting this parameter as one of the most effective in minimizing thermal conductivity degradation of the composite, while the influence of Si additions to the matrix in the model was highly dependent upon irradiation conditions.
A model to predict thermal conductivity of irradiated U-Mo dispersion fuel
Burkes, Douglas E.; Huber, Tanja K.; Casella, Andrew M.
2016-05-01
Numerous global programs are focused on the continued development of existing and new research and test reactor fuels to achieve maximum attainable uranium loadings to support the conversion of a number of the world's remaining high-enriched uranium fueled reactors to low-enriched uranium fuel. Some of these programs are focused on assisting with the development and qualification of a fuel design that consists of a uranium-molybdenum (U-Mo) alloy dispersed in an aluminum matrix as one option for reactor conversion. Thermal conductivity is an important consideration in determining the operational temperature of the fuel and can be influenced by interaction layer formation between the dispersed phase and matrix and upon the concentration of the dispersed phase within the matrix. This paper extends the use of a simple model developed previously to study the influence of interaction layer formation as well as the size and volume fraction of fuel particles dispersed in the matrix, Si additions to the matrix, and Mo concentration in the fuel particles on the effective thermal conductivity of the U-Mo/Al composite during irradiation. The model has been compared to experimental measurements recently conducted on U-Mo/Al dispersion fuels at two different fission densities with acceptable agreement. Observations of the modeled results indicate that formation of an interaction layer and subsequent consumption of the matrix reveals a rather significant effect on effective thermal conductivity. The modeled interaction layer formation and subsequent consumption of the high thermal conductivity matrix was sensitive to the average dispersed fuel particle size, suggesting this parameter as one of the most effective in minimizing thermal conductivity degradation of the composite, while the influence of Si additions to the matrix in the model was highly dependent upon irradiation conditions.
Decomposition model for phonon thermal conductivity of a monatomic lattice
Evteev, Alexander V.; Momenzadeh, Leila; Levchenko, Elena V.; Belova, Irina V.; Murch, Graeme E.
2014-12-01
An analytical treatment of decomposition of the phonon thermal conductivity of a crystal with a monatomic unit cell is developed on the basis of a two-stage decay of the heat current autocorrelation function observed in molecular dynamics simulations. It is demonstrated that the contributions from the acoustic short- and long-range phonon modes to the total phonon thermal conductivity can be presented in the form of simple kinetic formulas, consisting of products of the heat capacity and the average relaxation time of the considered phonon modes as well as the square of the average phonon velocity. On the basis of molecular dynamics calculations of the heat current autocorrelation function, this treatment allows for a self-consistent numerical evaluation of the aforementioned variables. In addition, the presented analysis allows, within the Debye approximation, for the identification of the temperature range where classical molecular dynamics simulations can be employed for the prediction of phonon thermal transport properties. As a case example, Cu is considered.
Conducting a multicentre and multinational qualitative study on patient transitions.
Johnson, Julie K; Barach, Paul; Vernooij-Dassen, Myrra
2012-12-01
A multicentre, multinational research study requires careful planning and coordination to accomplish the aims of the study and to ensure systematic and rigorous examination of all project methods and data collected. The aim of this paper is to describe the approach we used during the HANDOVER Project to develop a multicentre, multinational research project for studying transitions of patient care while creating a community of practice for the researchers. We highlight the process used to assure the quality of a multicentre qualitative study and to create a codebook for data analysis as examples of attending to the community of practice while conducting rigorous qualitative research. Essential elements for the success of this multinational, multilanguage research project included recruiting a strong research team, explicit planning for decision-making processes to be used throughout the project, acknowledging the differences among the study settings and planning the protocols to capitalise upon those differences. Although not commonly discussed in reports of large research projects, there is an underlying, concurrent stream of activities to develop a cohesive team that trusts and respects one another's skills and that engage independent researchers in a group process that contributes to achieving study goals. We discuss other lessons learned and offer recommendations for other teams planning multicentre research.
Conducting Simulation Studies in the R Programming Environment
Directory of Open Access Journals (Sweden)
Kevin A. Hallgren
2013-10-01
Full Text Available Simulation studies allow researchers to answer specific questions about data analysis, statistical power, and best-practices for obtainingaccurate results in empirical research. Despite the benefits that simulation research can provide, many researchers are unfamiliar with available tools for conducting their own simulation studies. The use of simulation studies need not be restricted toresearchers with advanced skills in statistics and computer programming, and such methods can be implemented by researchers with a variety of abilities and interests. The present paper provides an introduction to methods used for running simulationstudies using the R statistical programming environment and is written for individuals with minimal experience running simulation studies or using R. The paper describes the rationale and benefits of using simulations and introduces R functions relevant for many simulation studies. Three examples illustrate different applications for simulation studies, including (a the use of simulations to answer a novel question about statistical analysis, (b the use of simulations to estimate statistical power, and (c the use of simulations to obtain confidence intervals of parameter estimates throughbootstrapping. Results and fully annotated syntax from these examples are provided.
Power-Law Dynamics of Membrane Conductances Increase Spiking Diversity in a Hodgkin-Huxley Model.
Teka, Wondimu; Stockton, David; Santamaria, Fidel
2016-03-01
We studied the effects of non-Markovian power-law voltage dependent conductances on the generation of action potentials and spiking patterns in a Hodgkin-Huxley model. To implement slow-adapting power-law dynamics of the gating variables of the potassium, n, and sodium, m and h, conductances we used fractional derivatives of order η≤1. The fractional derivatives were used to solve the kinetic equations of each gate. We systematically classified the properties of each gate as a function of η. We then tested if the full model could generate action potentials with the different power-law behaving gates. Finally, we studied the patterns of action potential that emerged in each case. Our results show the model produces a wide range of action potential shapes and spiking patterns in response to constant current stimulation as a function of η. In comparison with the classical model, the action potential shapes for power-law behaving potassium conductance (n gate) showed a longer peak and shallow hyperpolarization; for power-law activation of the sodium conductance (m gate), the action potentials had a sharp rise time; and for power-law inactivation of the sodium conductance (h gate) the spikes had wider peak that for low values of η replicated pituitary- and cardiac-type action potentials. With all physiological parameters fixed a wide range of spiking patterns emerged as a function of the value of the constant input current and η, such as square wave bursting, mixed mode oscillations, and pseudo-plateau potentials. Our analyses show that the intrinsic memory trace of the fractional derivative provides a negative feedback mechanism between the voltage trace and the activity of the power-law behaving gate variable. As a consequence, power-law behaving conductances result in an increase in the number of spiking patterns a neuron can generate and, we propose, expand the computational capacity of the neuron.
Power-Law Dynamics of Membrane Conductances Increase Spiking Diversity in a Hodgkin-Huxley Model.
Directory of Open Access Journals (Sweden)
Wondimu Teka
2016-03-01
Full Text Available We studied the effects of non-Markovian power-law voltage dependent conductances on the generation of action potentials and spiking patterns in a Hodgkin-Huxley model. To implement slow-adapting power-law dynamics of the gating variables of the potassium, n, and sodium, m and h, conductances we used fractional derivatives of order η≤1. The fractional derivatives were used to solve the kinetic equations of each gate. We systematically classified the properties of each gate as a function of η. We then tested if the full model could generate action potentials with the different power-law behaving gates. Finally, we studied the patterns of action potential that emerged in each case. Our results show the model produces a wide range of action potential shapes and spiking patterns in response to constant current stimulation as a function of η. In comparison with the classical model, the action potential shapes for power-law behaving potassium conductance (n gate showed a longer peak and shallow hyperpolarization; for power-law activation of the sodium conductance (m gate, the action potentials had a sharp rise time; and for power-law inactivation of the sodium conductance (h gate the spikes had wider peak that for low values of η replicated pituitary- and cardiac-type action potentials. With all physiological parameters fixed a wide range of spiking patterns emerged as a function of the value of the constant input current and η, such as square wave bursting, mixed mode oscillations, and pseudo-plateau potentials. Our analyses show that the intrinsic memory trace of the fractional derivative provides a negative feedback mechanism between the voltage trace and the activity of the power-law behaving gate variable. As a consequence, power-law behaving conductances result in an increase in the number of spiking patterns a neuron can generate and, we propose, expand the computational capacity of the neuron.
Visual and dynamic conductivity studies of Laponite RTM hydrogels
Henry, Mark L.
Static hydration of a 3.0 wt. % of LaponiteRTM in deionized (DI) water was investigated at 30oC and 60oC using Electrochemical Impedance Spectrometry (EIS). The results show the transition of the low-density hydrogel to its pure electrostatic repulsion state or Wigner glass within 5 days with a significant reduction in preparation time and without the use of energetic agitation. This was accomplished in real time by placing the fine crystalline powder in a four-probe dynamic conductivity (DC) cell and gently adding DI water under a light vacuum of 17 torr below ambient pressure. Once the hydration began, impedance measurements were taken at regular intervals for several days, while a time-lapse camera recorded the dynamic changes within the DC cell. Combined with the four experimentally determined cell constants and a multi-point calibration curve, this study opens up new insight into the conductive properties of nanocomposite clays during static hydration.
Thermal conductivity and rectification study of restructured Graphene
Arora, Anuj
Electronics' miniaturization, has led to search for better thermal management techniques and discovery of important transport phenomenon. Thermal rectification, directionally preferential heat transport analogous to electrical diode, is one such technique, garnering tremendous interest. Its possibility has been explored through structural asymmetry, introducing a differential phonon density of states in hot and cold regions. As of now, mass and shape asymmetries have been studied, both experimentally and theoretically. However, strict requirements of material length being shorter than phonon mean free path and phonon coherence preservation at surface, makes connecting two materials with different temperature-dependent thermal conductivities, a more natural approach. To avoid resultant thermal boundary resistance and integration complexities, we achieve the affect in single material, by restructuring a region of Graphene by introducing defects. The asymmetry impedes ballistic phonon transport, modulating temperature dependence of thermal conductivity in the two regions. We perform deviational Monte Carlo simulations based on Energy-based formulation to microscopically investigate phonon transport, possibility and optimal conditions for thermal rectification. The proposed method uses phonon properties obtained from first principle, treat phonon-boundary scattering explicitly with properties drawn from Bose-Einstein Distribution.
Change over Time: Conducting Longitudinal Studies of Children's Cognitive Development.
Grammer, Jennie K; Coffman, Jennifer L; Ornstein, Peter A; Morrison, Frederick J
2013-10-01
Developmental scientists have argued that the implementation of longitudinal methods is necessary for obtaining an accurate picture of the nature and sources of developmental change (Magnusson & Cairns, 1996; Morrison & Ornstein, 1996; Magnusson & Stattin, 2006). Developmentalists studying cognition have been relatively slow to embrace longitudinal research, and thus few exemplar studies have tracked individual children's cognitive performance over time and even fewer have examined contexts that are associated with this growth. In this article we first outline some of the benefits of implementing longitudinal designs. Using illustrations from existing studies of children's basic cognitive development and of their school-based academic performance, we discuss when it may be appropriate to employ longitudinal (versus other) methods. We then outline methods for integrating longitudinal data into one's research portfolio, contrasting the leveraging of existing longitudinal data sets with the launching of new longitudinal studies in order to address specific questions concerning cognitive development. Finally, for those who are interested in conducting longitudinal investigations of their own, we provide practical on-the-ground guidelines for designing and carrying out such studies of cognitive development.
Study on Thermo-Conductive Plastic Finned Tube Radiators
Institute of Scientific and Technical Information of China (English)
无
1997-01-01
This paper discusses thermo-conductive plastic finned tube radiators used in water saving type power stations.First,the development of thermo-conductive plastics is introduced.Second,in order to determine the rational geometric dimensions of thermo-conductive plastic finned tubes,an objective function which takes the minimum volume of the consumed material for making finned tubes as an object is introduced.On the basis of the function,the economy comparison between thermo-conductive plastic finned tubes and metal finned tubes is conducted.
Study of the Kinetics of an S[subscript N]1 Reaction by Conductivity Measurement
Marzluff, Elaine M.; Crawford, Mary A.; Reynolds, Helen
2011-01-01
Substitution reactions, a central part of organic chemistry, provide a model system in physical chemistry to study reaction rates and mechanisms. Here, the use of inexpensive and readily available commercial conductivity probes coupled with computer data acquisition for the study of the temperature and solvent dependence of the solvolysis of…
Validation of a heat conduction model for finite domain, non-uniformly heated, laminate bodies
Desgrosseilliers, Louis; Kabbara, Moe; Groulx, Dominic; White, Mary Anne
2016-07-01
Infrared thermographic validation is shown for a closed-form analytical heat conduction model for non-uniformly heated, laminate bodies with an insulated domain boundary. Experiments were conducted by applying power to rectangular electric heaters and cooled by natural convection in air, but also apply to constant-temperature heat sources and forced convection. The model accurately represents two-dimensional laminate heat conduction behaviour giving rise to heat spreading using one-dimensional equations for the temperature distributions and heat transfer rates under steady-state and pseudo-steady-state conditions. Validation of the model with an insulated boundary (complementing previous studies with an infinite boundary) provides useful predictions of heat spreading performance and simplified temperature uniformity calculations (useful in log-mean temperature difference style heat exchanger calculations) for real laminate systems such as found in electronics heat sinks, multi-ply stovetop cookware and interface materials for supercooled salt hydrates. Computational determinations of implicit insulated boundary condition locations in measured data, required to assess model equation validation, were also demonstrated. Excellent goodness of fit was observed (both root-mean-square error and R 2 values), in all cases except when the uncertainty of low temperatures measured via infrared thermography hindered the statistical significance of the model fit. The experimental validation in all other cases supports use of the model equations in design calculations and heat exchange simulations.
Skin conductance fear conditioning impairments and aggression: a longitudinal study.
Gao, Yu; Tuvblad, Catherine; Schell, Anne; Baker, Laura; Raine, Adrian
2015-02-01
Autonomic fear conditioning deficits have been linked to child aggression and adult criminal behavior. However, it is unknown if fear conditioning deficits are specific to certain subtypes of aggression, and longitudinal research is rare. In the current study, reactive and proactive aggression were assessed in a sample of males and females when aged 10, 12, 15, and 18 years old. Skin conductance fear conditioning data were collected when they were 18 years old. Individuals who were persistently high on proactive aggression measures had significantly poorer conditioned responses at 18 years old when compared to others. This association was not found for reactive aggression. Consistent with prior literature, findings suggest that persistent antisocial individuals have unique neurobiological characteristics and that poor autonomic fear conditioning is associated with the presence of increased instrumental aggressive behavior.
Volkov, Alexey N.; Salaway, Richard N.; Zhigilei, Leonid V.
2013-09-01
The propensity of carbon nanotubes (CNTs) to self-organize into continuous networks of bundles has direct implications for thermal transport properties of CNT network materials and defines the importance of clear understanding of the mechanisms and scaling laws governing the heat transfer within the primary building blocks of the network structures—close-packed bundles of CNTs. A comprehensive study of the thermal conductivity of CNT bundles is performed with a combination of non-equilibrium molecular dynamics (MD) simulations of heat transfer between adjacent CNTs and the intrinsic conductivity of CNTs in a bundle with a theoretical analysis that reveals the connections between the structure and thermal transport properties of CNT bundles. The results of MD simulations of heat transfer in CNT bundles consisting of up to 7 CNTs suggest that, contrary to the widespread notion of strongly reduced conductivity of CNTs in bundles, van der Waals interactions between defect-free well-aligned CNTs in a bundle have negligible effect on the intrinsic conductivity of the CNTs. The simulations of inter-tube heat conduction performed for partially overlapping parallel CNTs indicate that the conductance through the overlap region is proportional to the length of the overlap for CNTs and CNT-CNT overlaps longer than several tens of nm. Based on the predictions of the MD simulations, a mesoscopic-level model is developed and applied for theoretical analysis and numerical modeling of heat transfer in bundles consisting of CNTs with infinitely large and finite intrinsic thermal conductivities. The general scaling laws predicting the quadratic dependence of the bundle conductivity on the length of individual CNTs in the case when the thermal transport is controlled by the inter-tube conductance and the independence of the CNT length in another limiting case when the intrinsic conductivity of CNTs plays the dominant role are derived. An application of the scaling laws to bundles of
Energy Technology Data Exchange (ETDEWEB)
Mendez, A. [Instituto de Fisica, Universidad Autonoma de Puebla, Apartado Postal J-48, Puebla 72570 (Mexico); Gopar, V. [Departamento de Fisica Teorica and Instituto de Biocomputacion y Fisica de Sistemas Complejos (BIFI), Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza (Spain); Varga, I. [Elmeleti Fizika Tanszek, Fizikai Intezet, Budapesti Mueszaki es Gazdasagtudomanyi Egyetem, 1521 Budapest (Hungary); Fachbereich Physik und Wissenschaftliches Zentrum fuer Materialwissenschaften, Philipps Universitaet Marburg, 35032 Marburg (Germany)
2009-12-15
We study numerically the conductance distribution function w(T) for the one-dimensional Anderson model with random long-range hopping described by the Power-law Banded Random Matrix model at criticality. We concentrate on the case of two single-channel leads attached to the system. We observe a smooth transition from localized to delocalized behavior in the conductance distribution by increasing b, the effective bandwidth of the model. Also, for b < 1 we show that w(ln T/T{sub typ}) is scale invariant, where T{sub typ} = exp left angle ln T right angle is the typical value of T. Moreover, we find that for T < T{sub typ}, w(ln T/T{sub typ}) shows a universal behavior proportional to (T/T{sub typ}){sup -1/2}. (Abstract Copyright [2009], Wiley Periodicals, Inc.)
Physical modeling of small shallow conductive 3-D targets with high-frequency electromagnetics
Energy Technology Data Exchange (ETDEWEB)
Birken, R.A.; Poulton, M.; Sterngerg, B.K.
1996-09-01
The goal of this study is to show that physical modeling can provide important support for three-dimensional (3D) interpretation of electromagnetic geophysical data for environmental problems. This is specially true when high-frequency electromagnetic methods are used, which are difficult to model with existing 3D forward modeling programs. Existing electromagnetic geophysical systems usually operate in the frequency range of a few hertz to several hundred hertz. For environmental problems, such as characterization of waste sites, systems with higher frequencies are desirable. This is because at lower frequencies, the depth of investigation is too deep for environmental characterizations. This leads to subsurface images, which don`t have enough resolution to map small shallow objects. Electromagnetic 3D modeling programs which solve the full wave equation are still not widely available, even though 3D modeling has improved remarkably during the last few years (Oristaglio and Spies, 1995). Since such a program was not available for this study, we used a specialized 3D program EM1DSH (Zhou, 1989). With this program, we can model layered-earth cases, taking dielectric effects into account over the whole frequency range of interest. Stewart et al. (1994) published ellipticity curves for similar system configurations and frequency ranges that indicate that dielectric effects can not be neglected for model calculations using frequencies above several 100 kHz. EM1DSH can also model thin conductive sheets in a two-layer earth but neglecting dielectric effects. Therefore we are only able to model and compare our field data with 3D forward modeling results for the lower frequencies. One way of bridging the gap between the interpretation needs and limitations of existing 3D forward modeling programs is to conduct physical modeling experiments. 6 refs., 2 figs.
Hettrick, D A; Battocletti, J; Ackmann, J; Warltier, D C
1999-01-01
Traditional methods for estimating the slope alpha and offset volume Vp for determining real-time chamber volume by the conductance catheter technique are not suited to measurements made in the aorta due to the relatively low resistivity of the aortic wall. We developed three distinct three-dimensional finite element models of the conductance catheter and surrounding tissues in order to predict alpha and Vp and to examine the nature of the electric field near the aortic wall. A heterogeneous isotropic model of the catheter, aorta and surrounding tissues accurately predicted the values of alpha and Vp. A homogeneous anisotropic model was developed to examine the effects of anisotropy of blood and the layers of the aortic wall on measured values of resistance, alpha and Vp. This model demonstrated that anisotropy of blood and aortic wall tissue can increase the values of both alpha and Vp. Finally, a three-dimensional homogeneous isotropic rectangular model allowed examination of the effects of catheter position. This model showed small effects of catheter position on measured resistance (9.7% increase) and larger effects on alpha (21.2% decrease) and Vp (41.9% increase). We conclude the following: the FEA models may lead to accurate estimate values of alpha and Vp in vivo. The unique anisotropic conductive properties of the layers of the aortic wall contribute to the high observed values of alpha and Vp in the aorta. Finally, catheter position has a proportionately greater effect on alpha and Vp than on measured resistance. The results of this study should assist in the determination of aortic mechanical properties using conductance catheter measurements of vessel dimension.
First-principles study of lattice thermal conductivity of Td-WTe2
Liu, Gang; Sun, Hong Yi; Zhou, Jian; Li, Qing Fang; Wan, Xian-Gang
2016-03-01
The structural and thermal properties of bulk Td-WTe2 have been studied by using first-principles calculations based on the simple Klemens model and an iterative self-consistent method. Both methods show that lattice thermal conductivity is anisotropic, with the highest value in the (001) plane, and lowest one along the c-axis at 300 K. The calculated average thermal conductivity of WTe2 is in agreement with the experimental measurement. The size dependent thermal conductivity shows that nanostructuring of WTe2 can possibly further decrease the lattice thermal conductivity, which can improve the thermoelectric efficiency. Such extremely low thermal conductivity, even much lower than WSe2, makes WTe2 having many potential applications in thermal insulation and thermoelectric materials.
CSIR Research Space (South Africa)
Grobler, Inus
2013-09-01
Full Text Available High density high switching frequency power converter conducted EMC had been analysed, modelling the noise source and noise path, while providing accurate conducted EMC noise limits comparable to accredited noise measurements up to 100 MHz...
Transient heat conduction in a pebble fuel applying fractional model
Energy Technology Data Exchange (ETDEWEB)
Gomez A, R.; Espinosa P, G. [Universidad Autonoma Metropolitana, Unidad Iztapalapa, Area de Ingenieria en Recursos Energeticos, Av. San Rafael Atlixco 186, Col. Vicentina, 09340 Mexico D. F. (Mexico)], e-mail: gepe@xanum.uam.mx
2009-10-15
In this paper we presents the equation of thermal diffusion of temporary-fractional order in the one-dimensional space in spherical coordinates, with the objective to analyze the heat transference between the fuel and coolant in a fuel element of a Pebble Bed Modular Reactor. The pebble fuel is the heterogeneous system made by microsphere constitutes by U O, pyrolytic carbon and silicon carbide mixed with graphite. To describe the heat transfer phenomena in the pebble fuel we applied a constitutive law fractional (Non-Fourier) in order to analyze the behaviour transient of the temperature distribution in the pebble fuel with anomalous thermal diffusion effects a numerical model is developed. (Author)
Two and Three-Phases Fractal Models Application in Soil Saturated Hydraulic Conductivity Estimation
Directory of Open Access Journals (Sweden)
ELNAZ Rezaei abajelu
2017-03-01
Full Text Available Introduction: Soil Hydraulic conductivity is considered as one of the most important hydraulic properties in water and solutionmovement in porous media. In recent years, variousmodels as pedo-transfer functions, fractal models and scaling technique are used to estimate the soil saturated hydraulic conductivity (Ks. Fractal models with two subset of two (solid and pore and three phases (solid, pore and soil fractal (PSF are used to estimate the fractal dimension of soil particles. The PSF represents a generalization of the solid and pore mass fractal models. The PSF characterizes both the solid and pore phases of the porous material. It also exhibits self-similarity to some degree, in the sense that where local structure seems to be similar to the whole structure.PSF models can estimate interface fractal dimension using soil pore size distribution data (PSD and soil moisture retention curve (SWRC. The main objective of this study was to evaluate different fractal models to estimate the Ksparameter. Materials and Methods: The Schaapetal data was used in this study. The complex consists of sixty soil samples. Soil texture, soil bulk density, soil saturated hydraulic conductivity and soil particle size distribution curve were measured by hydrometer method, undistributed soil sample, constant head method and wet sieve method, respectively for all soil samples.Soil water retention curve were determined by using pressure plates apparatus.The Ks parameter could be estimated by Ralws model as a function of fractal dimension by seven fractal models. Fractal models included Fuentes at al. (1996, Hunt and Gee (2002, Bird et al. (2000, Huang and Zhang (2005, Tyler and Wheatcraft (1990, Kutlu et al. (2008, Sepaskhah and Tafteh (2013.Therefore The Ks parameter can be estimated as a function of the DS (fractal dimension by seven fractal models (Table 2.Sensitivity analysis of Rawls model was assessed by making changes±10%, ±20% and±30%(in input parameters
A study on the thermal conductivity of compacted bentonites
Tang, Anh-Minh; Le, Trung Tinh; 10.1016/j.clay.2007.11.001
2008-01-01
Thermal conductivity of compacted bentonite is one of the most important properties in the design of high-level radioactive waste repositories where this material is proposed for use as a buffer. In the work described here, a thermal probe based on the hot wire method was used to measure the thermal conductivity of compacted bentonite specimens. The experimental results were analyzed to observe the effects of various factors (i.e. dry density, water content, hysteresis, degree of saturation and volumetric fraction of soil constituents) on the thermal conductivity. A linear correlation was proposed to predict the thermal conductivity of compacted bentonite based on experimentally observed relationship between the volumetric fraction of air and the thermal conductivity. The relevance of this correlation was finally analyzed together with others existing methods using experimental data on several compacted bentonites.
Krishna Jyothi, N.; Vijaya Kumar, K.; Sunita Sundari, G.; Narayana Murthy, P.
2016-03-01
Sodium ion conducting gel polymer electrolytes based on polyacrylonitrile (PAN) with ethylene carbonate and dimethyl formamide as plasticizing solvents are prepared by the solution cast technique. These electrolyte films are free standing, transparent and dimensionally stable. Na+ ions are derived from NaI. The structural properties of pure and complex formations have been examined by X-ray diffraction, Fourier transform infrared spectroscopic studies and differential scanning calorimetric studies. The variation of the conductivity with salt concentration ranging from 10 to 40 wt% is studied. The sample containing 30 wt% of NaI exhibits the highest conductivity of 2.35 × 10-4 S cm-1 at room temperature (303 K) and 1 × 10-3 S cm-1 at 373 K. The conductivity-temperature dependence of polymer electrolyte films obeys Arrhenius behavior with activation energy in the range of 0.25-0.46 eV. The transport numbers both electronic ( t e) and ionic ( t i) are evaluated using Wagner's polarization technique. It is revealed that the conducting species are predominantly due to ions. The ionic transport number of highest conducting film is found to be 0.991. Solid-state battery with configuration Na/(PAN + NaI)/(I2 + C + electrolyte) is developed using the highest conducting gel polymer electrolyte system and the discharge characteristics of the cell are evaluated over the load of 100 KΩ.
Drude Weight,Optical Conductivity of Two-Dimensional Hubbard Model at Half Filling
Institute of Scientific and Technical Information of China (English)
XU Lei; ZHANG Jun
2008-01-01
We study the Drude weight D and optical conductivity of the two-dimensional (2D) Hubbard model at half filling with staggered magnetic flux (SMF).When SMF being introduced,the hopping integrals are modulated by the magnetic flux.The optical sum rule,which is related to the mean kinetic energy of band electrons,is evaluated for this 2D Hubbard Hamiltonian.Our present result gives the dependence of the kinetic energy,D and the optical conductivity on SMF and U.At half filling D vanishes exponentially with system size.We also find in the frequency dependence of the optical conductivity,there is &function peak at ω≈2|m|U and the incoherent excitations begin to present themselves extended to a higher energy region.
Study of charge transport in highly conducting polymers based on a random resistor network
Energy Technology Data Exchange (ETDEWEB)
Zhou Liping [Department of Physics, Suzhou University, Suzhou 215006 (China)]. E-mail: lipichow@hotmail.com; Liu Bo [Department of Physics, Suzhou University, Suzhou 215006 (China); Department of Physics, Jiangsu Teachers University of Technology, Changzhou 213001 (China); Li Zhenya [CCAST (World Laboratory), P.O. Box 8730, Beijing 100080 (China) and Department of Physics, Suzhou University, Suzhou 215006 (China)]. E-mail: zyli@suda.edu.cn
2004-12-06
Based on a random resistor network (RRN), we study the unusual ac conductivity {sigma}({omega}) of highly conducting polymer such as PF{sub 6} doped polypyrrole. The system is modeled as a composite medium consisting of metallic regions randomly distributed in the amorphous parts. Within the metallic regions, the polymer chains are regularly and densely packed, outside which the poorly arranged chains form amorphous host. The metallic grains are connected by resonance quantum tunneling, which occurs through the strongly localized states in the amorphous media. {sigma}({omega}), calculated from this model, reproduces the main experimental features associated with the metal-insulator transition in these polymers.
Directory of Open Access Journals (Sweden)
Hyeon Seo
Full Text Available Subdural cortical stimulation (SuCS is an appealing method in the treatment of neurological disorders, and computational modeling studies of SuCS have been applied to determine the optimal design for electrotherapy. To achieve a better understanding of computational modeling on the stimulation effects of SuCS, the influence of anisotropic white matter conductivity on the activation of cortical neurons was investigated in a realistic head model. In this paper, we constructed pyramidal neuronal models (layers 3 and 5 that showed primary excitation of the corticospinal tract, and an anatomically realistic head model reflecting complex brain geometry. The anisotropic information was acquired from diffusion tensor magnetic resonance imaging (DT-MRI and then applied to the white matter at various ratios of anisotropic conductivity. First, we compared the isotropic and anisotropic models; compared to the isotropic model, the anisotropic model showed that neurons were activated in the deeper bank during cathodal stimulation and in the wider crown during anodal stimulation. Second, several popular anisotropic principles were adapted to investigate the effects of variations in anisotropic information. We observed that excitation thresholds varied with anisotropic principles, especially with anodal stimulation. Overall, incorporating anisotropic conductivity into the anatomically realistic head model is critical for accurate estimation of neuronal responses; however, caution should be used in the selection of anisotropic information.
A phase-field study on the oxidation behavior of Ni considering heat conduction
Institute of Scientific and Technical Information of China (English)
Chao Wang; Shigang Ai; Daining Fang
2016-01-01
Phase-field modeling approach has been used to study the oxidation behavior of pure Ni when considering heat conduction. In this calculation, the dependence of the coefficient of the Cahn–Hilliard equation Lc on the tem-perature T was considered. To this end, high-temperature oxidation experiments and phase-field modeling for pure Ni were performed in air under atmospheric pressure at 600, 700, and 800◦C. The oxidation rate was measured by ther-mogravimetry and Lc at these temperatures was determined via interactive algorithm. With the Lc−T relationship con-structed, oxidation behavior of Ni when considering heat conduction was investigated. The influence of temperature boundaries on the oxidation degree, oxide film thickness, and specific weight gain were discussed. The phase-field model-ing approach proposed in this study will give some highlights of the oxidation resistance analysis and cooling measures design of thermal protection materials.
Carbonyl mediated conductance through metal bound peptides: a computational study
Perrine, Trilisa M.; Dunietz, Barry D.
2007-10-01
Large increases in the conductance of peptides upon binding to metal ions have recently been reported experimentally. The mechanism of the conductance switching is examined computationally. It is suggested that oxidation of the metal ion occurs after binding to the peptide. This is caused by the bias potential placed across the metal-peptide complex. A combination of configurational changes, metal ion involvement and interactions between carbonyl group oxygen atoms and the gold leads are all shown to be necessary for the large improvement in the conductance seen experimentally. Differences in the molecular orbitals of the nickel and copper complexes are noted and serve to explain the variation of the improvement in conductance upon binding to either a nickel or copper ion.
'Schizoid' personality and antisocial conduct: a retrospective case not study.
Wolff, S; Cull, A
1986-08-01
A retrospective case not analysis for 30 boys diagnosed as having a 'schizoid' personality disorder (Asperger's syndrome) in childhood, and for 30 matched clinic attenders (with systematic follow-up data for 19 matched pairs), showed the incidence of antisocial conduct to be the same in the two groups. However, the 'schizoid' boys stole less often and had fewer alcohol problems. In this group antisocial conduct was less related to family disruption and social disadvantage, and more to an unusual fantasy life. Clinical descriptions of a series of 'schizoid' boys and girls with conspicuous antisocial conduct follow. They suggest that characteristic patterns of antisocial conduct in such children are persistent expressions of hostility and, especially in girls, pathological lying, for which environmental circumstances provide no explanation.
Directory of Open Access Journals (Sweden)
Asir Intisar Khan
2015-12-01
Full Text Available The thermal conductivity of graphene nanoribbons (GNRs has been investigated using equilibrium molecular dynamics (EMD simulation based on Green-Kubo (GK method to compare two interatomic potentials namely optimized Tersoff and 2nd generation Reactive Empirical Bond Order (REBO. Our comparative study includes the estimation of thermal conductivity as a function of temperature, length and width of GNR for both the potentials. The thermal conductivity of graphene nanoribbon decreases with the increase of temperature. Quantum correction has been introduced for thermal conductivity as a function of temperature to include quantum effect below Debye temperature. Our results show that for temperatures up to Debye temperature, thermal conductivity increases, attains its peak and then falls off monotonically. Thermal conductivity is found to decrease with the increasing length for optimized Tersoff potential. However, thermal conductivity has been reported to increase with length using 2nd generation REBO potential for the GNRs of same size. Thermal conductivity, for the specified range of width, demonstrates an increasing trend with the increase of width for both the concerned potentials. In comparison with 2nd generation REBO potential, optimized Tersoff potential demonstrates a better modeling of thermal conductivity as well as provides a more appropriate description of phonon thermal transport in graphene nanoribbon. Such comparative study would provide a good insight for the optimization of the thermal conductivity of graphene nanoribbons under diverse conditions.
Chiral magnetic conductivity in an interacting lattice model of parity-breaking Weyl semimetal
Buividovich, P. V.; Puhr, M.; Valgushev, S. N.
2015-11-01
We report on the mean-field study of the chiral magnetic effect (CME) in static magnetic fields within a simple model of parity-breaking Weyl semimetal given by the lattice Wilson-Dirac Hamiltonian with constant chiral chemical potential. We consider both the mean-field renormalization of the model parameters and nontrivial corrections to the CME originating from resummed ladder diagrams with arbitrary number of loops. We find that onsite repulsive interactions affect the chiral magnetic conductivity almost exclusively through the enhancement of the renormalized chiral chemical potential. Our results suggest that nontrivial corrections to the chiral magnetic conductivity due to interfermion interactions are not relevant in practice since they only become important when the CME response is strongly suppressed by the large gap in the energy spectrum.
Tseng, Yuan Heng; Shen, Wen Chao; Lin, Chrong Jung
2012-04-01
The intense development and study of resistive random access memory (RRAM) devices has opened a new era in semiconductor memory manufacturing. Resistive switching and carrier conduction inside RRAM films have become critical issues in recent years. Electron trapping/detrapping behavior is observed and investigated in the proposed contact resistive random access memory (CR-RAM) cell. Through the fitting of the space charge limiting current (SCLC) model, and analysis in terms of the random telegraph noise (RTN) model, the temperature-dependence of resistance levels and the high-temperature data retention behavior of the contact RRAM film are successfully and completely explained. Detail analyses of the electron capture and emission from the traps by forward and reverse read measurements provide further verifications for hopping conduction mechanism and current fluctuation discrepancies.
A Network Model for the Effective Thermal Conductivity of Rigid Fibrous Refractory Insulations
Marschall, Jochen; Cooper, D. M. (Technical Monitor)
1995-01-01
A procedure is described for computing the effective thermal conductivity of a rigid fibrous refractory insulation. The insulation is modeled as a 3-dimensional Cartesian network of thermal conductance. The values and volume distributions of the conductance are assigned to reflect the physical properties of the insulation, its constituent fibers, and any permeating gas. The effective thermal conductivity is computed by considering the simultaneous energy transport by solid conduction, gas conduction and radiation through a cubic volume of model insulation; thus the coupling between heat transfer modes is retained (within the simplifications inherent to the model), rather than suppressed by treating these heat transfer modes as independent. The model takes into account insulation composition, density and fiber anisotropy, as well as the geometric and material properties of the constituent fibers. A relatively good agreement, between calculated and experimentally derived thermal conductivity values, is obtained for a variety of rigid fibrous insulations.
Gao, Zhibin; Li, Nianbei; Li, Baowen
2016-02-01
The ding-a-ling model is a kind of half lattice and half hard-point-gas (HPG) model. The original ding-a-ling model proposed by Casati et al. does not conserve total momentum and has been found to exhibit normal heat conduction behavior. Recently, a modified ding-a-ling model which conserves total momentum has been studied and normal heat conduction has also been claimed. In this work, we propose a full-lattice ding-a-ling model without hard point collisions where total momentum is also conserved. We investigate the heat conduction and energy diffusion of this full-lattice ding-a-ling model with three different nonlinear inter-particle potential forms. For symmetrical potential lattices, the thermal conductivities diverges with lattice length and their energy diffusions are superdiffusive signaturing anomalous heat conduction. For asymmetrical potential lattices, although the thermal conductivity seems to converge as the length increases, the energy diffusion is definitely deviating from normal diffusion behavior indicating anomalous heat conduction as well. No normal heat conduction behavior can be found for the full-lattice ding-a-ling model.
Zhan, He-qing; Xia, Ling; Shou, Guo-fa; Zang, Yun-liang; Liu, Feng; Crozier, Stuart
2014-03-01
In this study, the effects of cardiac fibroblast proliferation on cardiac electric excitation conduction and mechanical contraction were investigated using a proposed integrated myocardial-fibroblastic electromechanical model. At the cellular level, models of the human ventricular myocyte and fibroblast were modified to incorporate a model of cardiac mechanical contraction and cooperativity mechanisms. Cellular electromechanical coupling was realized with a calcium buffer. At the tissue level, electrical excitation conduction was coupled to an elastic mechanics model in which the finite difference method (FDM) was used to solve electrical excitation equations, and the finite element method (FEM) was used to solve mechanics equations. The electromechanical properties of the proposed integrated model were investigated in one or two dimensions under normal and ischemic pathological conditions. Fibroblast proliferation slowed wave propagation, induced a conduction block, decreased strains in the fibroblast proliferous tissue, and increased dispersions in depolarization, repolarization, and action potential duration (APD). It also distorted the wave-front, leading to the initiation and maintenance of re-entry, and resulted in a sustained contraction in the proliferous areas. This study demonstrated the important role that fibroblast proliferation plays in modulating cardiac electromechanical behaviour and which should be considered in planning future heart-modeling studies.
Nerve conduction studies in upper extremities: skin temperature corrections.
Halar, E M; DeLisa, J A; Soine, T L
1983-09-01
The relationship of skin to near nerve (NN) temperature and to nerve conduction velocity (NCV) and distal latency (DL) was studied in 34 normal adult subjects before and after cooling both upper extremities. Median and ulnar motor and sensory NCV, DL, and NN temperature were determined at ambient temperature (mean X skin temp = 33 C) and after cooling, at approximately 26, 28, and 30 C of forearm skin temperature. Skin temperatures on the volar side of the forearm, wrist, palm, and fingers and NN temperature at the forearm, midpalm, and thenar or hypothenar eminence were compared with respective NCV and DL. Results showed a significant linear correlation between skin temperature and NN temperature at corresponding sites (r2 range, 0.4-0.84; p less than 0.005). Furthermore, both skin and NN temperatures correlated significantly with respective NCV and DL. Midline wrist skin temperature showed the best correlation to NCV and DL. Median motor and sensory NCV were altered 1.5 and 1.4m/sec/C degree and their DL 0.2 msec/C degree of wrist skin temperature change, respectively. Ulnar motor and sensory NCV were changed 2.1 and 1.6m/sec/C degree respectively, and 0.2 msec/C degree wrist temperature for motor and sensory DL. Average ambient skin temperature at the wrist (33 C) was used as a standard skin temperature in the temperature correction formula: NCV or DL(temp corrected) = CF(Tst degree - Tm degree) + obtained NCV or DL, where Tst = 33 C for wrist, Tm = the measured skin temperature, and CF = correction factor of tested nerve. Use of temperature correction formula for NCV and DL is suggested in patients with changed wrist skin temperature outside 29.6-36.4C temperature range.
Study of new conductive oxyfluorides based on bismuth, vanadium, zinc
Energy Technology Data Exchange (ETDEWEB)
Jacobsoone, V. [ENSCL, Villeneuve d' Ascq (France). Lab. de Cristallochimie et Physico-Chimie du Solide; Follet-Houttemane, C. [Lab. de Materiaux Avances Ceramiques (LAMAC), UVHC ISTV, Valenciennes (France)
2002-07-01
Syntheses in quartz crucibles realised in the Bi{sub 2}O{sub 3}-V{sub 2}O{sub 5}-ZnF{sub 2} diagram at 700 C have allowed to isolate a glass domain, named G, and a crystallized phase, named C, located near the Bi{sub 2}O{sub 3}-ZnF{sub 2} line. Structural determination by X-ray powder diffraction showed that the C phase is related to Bi{sub 2}MoO{sub 6}. Fluorine ions are mainly located in Bi{sub 2}O{sub 2}{sup 2+} sheets in order to form Bi{sub 2}F{sub 4}{sup 4+} layers, the other F{sup -} ions are located in the perovskite layers. However, the compounds formula in this part of the diagram leads to a ZnO excess in comparison with Bi{sub 2}MoO{sub 6} formula. Study achieved by Raman diffusion spectroscopy allowed to confirm the existence of a vitreous network within the perovskite layer in which the ZnO excess could be inserted. The vitreous compounds corresponding to G phase, recristallized into a isomorphous to C phase and evidenced by conductivity measurements, present glass-ceramic type properties. The glass ceramic {sigma} values are 50 times higher than vitreous compounds ({sigma} = 4.10{sup -4} Scm{sup -1} at 260 C for Bi{sub 0.65}Zn{sub 1.215}V{sub 0.135}O{sub 1.313}F{sub 2.43}). (orig.)
Li, G.; Lin, L.; Dong, Y.; An, D.; Li, Y.; Luo, W.; Yin, X.; Li, W.; Shao, J.; Zhou, Y.; Dai, J.; Chen, W.; Zhao, C.
2012-01-01
Estimating leaf stomatal conductance for CO2 diffusion (gsc) is pivotal for further estimation of crop transpiration as well as energy and mass balances between air and plant in greenhouses. In this study, we tested two models, i.e. the Jarvis model and a new version of BWB–Leuning model (BWB–Leunin
Conductivity Studies of the Plasticized-Poly(methylmethacrylate) Polymer Electrolytes
Institute of Scientific and Technical Information of China (English)
A.Ahmad; Z.Osman
2007-01-01
1 Results In this work,five systems of polymethylmethacrylate (PMMA)-based polymer electrolytes films have been prepared by the solution casting technique.The five systems are the (PMMA-EC) system,the (PMMA + PC) system,the (PMMA+LiCF3SO3) system,the ([PMMA+EC]+LiCF3SO3) system and the ([PMMA+PC]+LiCF3SO3) system.The conductivity for each system is characterized using impedance spectroscopy.The conductivity of the pure PMMA,the (PMMA+EC) system and the (PMMA+PC) system at room temperature is 2.37×10-9,3...
Burns, Clare L; Ward, Elizabeth C; Hill, Anne J; Phillips, Nick; Porter, Linda
2016-06-01
A small number of studies have examined the feasibility of conducting videofluoroscopic swallow studies (VFSS) via telepractice. While the results have confirmed this potential, the systems tested to date have either reported issues that impacted the ability to analyze/interpret the VFSS recordings in real time, or they were not designed to enable real-time interpretation. Further system design is needed to establish a telepractice model that enables the VFSS assessment to be both guided and interpreted live in real time. The aim of this study was to test the feasibility and reliability of using a telepractice system to enable live VFSS assessment. Twenty adult patients underwent a VFSS assessment directed by a telepractice SLP with competency in VFSS located in another room of the hospital. The telepractice clinician led the sessions using a C20 Cisco TelePresence System. This was linked in real time via a secure telehealth network (at 4 megabits per second (Mbit/s)) to a C60 Cisco TelePresence System located in a fluoroscopy suite, connected to the digital fluoroscopy system. Levels of agreement were calculated between the telepractice clinician and a face-to-face clinician who simultaneously rated the VFSS in real time. High levels of agreement for swallowing parameters (range = 75-100 %; k = -0.34 to 1.0) and management decisions (range = 70-100 %, k = 0.64-1.0) were found. A post-session questionnaire revealed clinicians agreed that the telepractice system enabled successful remote assessment of VFSS. The findings support the potential to conduct live VFSS assessment via a telepractice model.
The comparison of models for calculating heat conduction losses in laser cutting of metals
Galushkin, M. G.; Golubev, V. S.; Grishaev, R. V.; Khomenko, M. D.
2011-02-01
Numerical comparisons of some models for estimating the power losses due to heat conduction in process of gas-assisted laser cutting are presented in this paper. In spite of differences between these models their results match fairly well.
Elson, Edward
2009-01-01
A theory of control of cellular proliferation and differentiation in the early development of metazoan systems, postulating a system of electrical controls "parallel" to the processes of molecular biochemistry, is presented. It is argued that the processes of molecular biochemistry alone cannot explain how a developing organism defies a stochastic universe. The demonstration of current flow (charge transfer) along the long axis of DNA through the base-pairs (the "pi-way) in vitro raises the question of whether nature may employ such current flows for biological purposes. Such currents might be too small to be accessible to direct measurement in vivo but conduction has been measured in vitro, and the methods might well be extended to living systems. This has not been done because there is no reasonable model which could stimulate experimentation. We suggest several related, but detachable or independent, models for the biological utility of charge transfer, whose scope admittedly outruns current concepts of thinking about organization, growth, and development in eukaryotic, metazoan systems. The ideas are related to explanations proposed to explain the effects demonstrated on tumors and normal tissues described in Article I (this issue). Microscopic and mesoscopic potential fields and currents are well known at sub-cellular, cellular, and organ systems levels. Not only are such phenomena associated with internal cellular membranes in bioenergetics and information flow, but remarkable long-range fields over tissue interfaces and organs appear to play a role in embryonic development (Nuccitelli, 1992 ). The origin of the fields remains unclear and is the subject of active investigation. We are proposing that similar processes could play a vital role at a "sub-microscopic level," at the level of the chromosomes themselves, and could play a role in organizing and directing fundamental processes of growth and development, in parallel with the more discernible fields and
Discrete Element Modeling Results of Proppant Rearrangement in the Cooke Conductivity Cell
Energy Technology Data Exchange (ETDEWEB)
Earl Mattson; Hai Huang; Michael Conway; Lisa O' Connell
2014-02-01
The study of propped fracture conductivity began in earnest with the development of the Cooke cell which later became part of the initial API standard. Subsequent developments included a patented multicell design to conduct 4 tests in a press at the same time. Other modifications have been used by various investigators. Recent studies by the Stim-Lab proppant consortium have indicated that the flow field across a Cooke proppant conductivity testing cell may not be uniform as initially believed which resulted is significantly different conductivity results. Post test analysis of low temperature metal alloy injections at the termination of proppant testing prior to the release of the applied stress suggest that higher flow is to be expected along the sides and top of the proppant pack than compared to the middle of the pack. To evaluate these experimental findings, a physics-based two-dimensional (2-D) discrete element model (DEM) was developed and applied to simulate proppant rearrangement during stress loading in the Cooke conductivity cell and the resulting porosity field. Analysis of these simulations are critical to understanding the impact of modification to the testing cell as well as understanding key proppant conductivity issues such as how these effects are manifested in proppant concentration testing results. The 2-D DEM model was constructed to represent a realistic cross section of the Cooke cell with a distribution of four material properties, three that represented the Cooke cell (steel, sandstone,square rings), and one representing the proppant. In principle, Cooke cell materials can be approximated as assemblies of independent discrete elements (particles) of various sizes and material properties that interact via cohesive interactions, repulsive forces, and frictional forces. The macroscopic behavior can then be modeled as the collective behavior of many interacting discrete elements. This DEM model is particularly suitable for modeling proppant
Thermal conductivity of local moment models with strong spin-orbit coupling
Stamokostas, Georgios L.; Lapas, Panteleimon E.; Fiete, Gregory A.
2017-02-01
We study the magnetic and lattice contributions to the thermal conductivity of electrically insulating strongly spin-orbit coupled magnetically ordered phases on a two-dimensional honeycomb lattice using the Kitaev-Heisenberg model. Depending on model parameters, such as the relative strength of the spin-orbit induced anisotropic coupling, a number of magnetically ordered phases are possible. In this work, we study two distinct regimes of thermal transport depending on whether the characteristic energy of the phonons or the magnons dominates, and focus on two different relaxation mechanisms, boundary scattering and magnon-phonon scattering. For spatially anisotropic magnetic phases, the thermal conductivity tensor can be highly anisotropic when the magnetic energy scale dominates, since the magnetic degrees of freedom dominate the thermal transport for temperatures well below the magnetic transition temperature. In the opposite limit in which the phonon energy scale dominates, the thermal conductivity will be nearly isotropic, reflecting the isotropic (at low temperatures) phonon dispersion assumed for the honeycomb lattice. We further discuss the extent to which thermal transport properties are influenced by strong spin-orbit induced anisotropic coupling in the local moment regime of insulating magnetic phases. The developed methodology can be applied to any 2D magnon-phonon system, and more importantly to systems where an analytical Bogoliubov transformation cannot be found and magnon bands are not necessarily isotropic.
Kahouli, Abdelkader; Sylvestre, Alain; Jomni, Fethi; Yangui, Béchir; Legrand, Julien
2012-01-26
The electrical conduction mechanisms of semicrystalline thermoplastic parylene C (-H(2)C-C(6)H(3)Cl-CH(2)-)(n) thin films were studied in large temperature and frequency regions. The alternative current (AC) electrical conduction in parylene C is governed by two processes which can be ascribed to a hopping transport mechanism: correlated barrier hopping (CBH) model at low [77-155 K] and high [473-533 K] temperature and the small polaron tunneling mechanism (SPTM) from 193 to 413 K within the framework of the universal law of dielectric response. The conduction mechanism is explained with the help of Elliot's theory, and the Elliot's parameters are determined. From frequency- and temperature-conductivity characteristics, the activation energy is found to be 1.27 eV for direct current (DC) conduction interpreted in terms of ionic conduction mechanism. The power law dependence of AC conductivity is interpreted in terms of electron hopping with a density N(E(F)) (~10(18) eV cm(-3)) over a 0.023-0.03 eV high barrier across a distance of 1.46-1.54 Å.
Conduction mechanism studies on electron transfer of disordered system
Institute of Scientific and Technical Information of China (English)
徐慧; 宋祎璞; 李新梅
2002-01-01
Using the negative eigenvalue theory and the infinite order perturbation theory, a new method was developed to solve the eigenvectors of disordered systems. The result shows that eigenvectors change from the extended state to the localized state with the increase of the site points and the disordered degree of the system. When electric field is exerted, the electrons transfer from one localized state to another one. The conductivity is induced by the electron transfer. The authors derive the formula of electron conductivity and find the electron hops between localized states whose energies are close to each other, whereas localized positions differ from each other greatly. At low temperature the disordered system has the character of the negative differential dependence of resistivity and temperature.
Energy Technology Data Exchange (ETDEWEB)
Stigsson, Martin
2009-12-15
The objectives of this report is to investigate the frequency of fractures assumed to be water conductive, i.e. open or partly open and directly or indirectly connected to a source. Also the distribution of total transmissivity in 100 m and 20 m horizontal sections and 8 m vertical sections is calculated. The report is only intended to serve as input to the SER, Site Engineering Report, at Laxemar and Forsmark. The input data for the analyses is taken, as is, from the Discrete Fracture Network sections in published reports. No evaluation that the model parameters are appropriate for the task or sensitivity analysis is performed. The tunnels and deposition holes are modelled as scanlines which is a very coarse approximation, but it may give some rough estimation of the frequency of the water bearing features, especially for the larger ones, and the total transmissivity in a section
Ionic conductivity studies of gel polyelectrolyte based on ionic liquid
Energy Technology Data Exchange (ETDEWEB)
Cha, E.H. [The Faculty of Liberal Arts (Chemistry), Hoseo University, Asan Choongnam 336-795 (Korea); Lim, S.A. [Functional Proteomics Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea); Park, J.H. [Department of Herbal Medicine, Hoseo University, Asan Choongnam 336-795 (Korea); Kim, D.W. [Department of Chemical Technology, Han Bat National University, Daejon 305-719 (Korea); Macfarlane, D.R. [School of Chemistry, Monash University, Clayton, Vic. 3800 (Australia)
2008-04-01
Novel lithium polyelectrolyte-ionic liquids have been prepared and characterized of their properties. Poly(lithium 2-acrylamido-2-methyl propanesulfonate) (PAMPSLi) and its copolymer with N-vinyl formamide (VF) also has been prepared as a copolymer. 1-Ethyl-3-methylimidazolium tricyanomethanide (emImTCM) and N,N-dimethyl-N-propyl-N-butyl ammonium tricyanomethanide (N{sub 1134}TCM) which are chosen because of the same with the anion of ionic liquid were prepared. The ionic conductivity of copolymer system (PAMPSLi/PVF/emImTCM: 5.43 x 10{sup -3} S cm{sup -1} at 25 C) exhibits about over four times higher than that of homopolymer system (PAMPSLi/emImTCM: 1.28 x 10{sup -3} S cm{sup -1} at 25 C). Introduction of vinyl formamide into the copolymer type can increase the dissociation of the lithium cations from the polymer backbone. The ionic conductivity of copolymer with emImTCM (PAMPSLi/PVF/emImTCM) exhibits the higher conductivity than that of PAMPSLi/PVF/N{sub 1134}TCM (2.48 x 10{sup -3} S cm{sup -1}). Because of using the polymerizable anion it is seen to maintain high flexibility of imidazolium cation effectively to exhibit the higher conductivity. And also the viscosity of emImTCM (19.56 cP) is lower than that of N{sub 1134}TCM (28.61 cP). Low viscosity leads to a fast rate of diffusion of redox species. (author)
Modelling the Complex Conductivity of Charged Porous Media using The Grain Polarization Model
Leroy, P.; Revil, A.; Jougnot, D.; Li, S.
2015-12-01
The low-frequency complex conductivity response of charged porous media reflects a combination of three polarization processes occuring at different frequency ranges. One polarization process corresponds to the membrane polarization phenomenon, which is the polarization mechanism associated with the back-diffusion of salt ions through different pore spaces of the porous material (ions-selective zones and zones with no selectivity). This polarization process generally occurs at the lowest frequency range, typically in the frequency range [mHz Hz] because it involves polarization mechanism occurring over different pore spaces (the relaxation frequency is inversely proportional to the length of the polarization process). Another polarization process corresponds to the electrochemical polarization of the electrical double layer coating the surface of the grains. In the grain polarization model, the diffuse layer is assumed to not polarize because it is assumed to form a continuum in the porous medium. The compact Stern layer is assumed to polarize because the Stern layer is assumed to be discontinuous over multiple grains. The electrochemical polarization of the Stern layer typically occurs in the frequency range [Hz kHz]. The last polarization process corresponds to the Maxwell-Wagner polarization mechanism, which is caused by the formation of field-induced free charge distributions near the interface between the phases of the medium. In this presentation, the grain polarization model based on the O'Konski, Schwarz, Schurr and Sen theories and developed later by Revil and co-workers is showed. This spectral induced polarization model was successfully applied to describe the complex conductivity responses of glass beads, sands, clays, clay-sand mixtures and other minerals. The limits of this model and future developments will also be presented.
Compilation of 3D global conductivity model of the Earth for space weather applications
Alekseev, Dmitry; Kuvshinov, Alexey; Palshin, Nikolay
2015-07-01
We have compiled a global three-dimensional (3D) conductivity model of the Earth with an ultimate goal to be used for realistic simulation of geomagnetically induced currents (GIC), posing a potential threat to man-made electric systems. Bearing in mind the intrinsic frequency range of the most intense disturbances (magnetospheric substorms) with typical periods ranging from a few minutes to a few hours, the compiled 3D model represents the structure in depth range of 0-100 km, including seawater, sediments, earth crust, and partly the lithosphere/asthenosphere. More explicitly, the model consists of a series of spherical layers, whose vertical and lateral boundaries are established based on available data. To compile a model, global maps of bathymetry, sediment thickness, and upper and lower crust thicknesses as well as lithosphere thickness are utilized. All maps are re-interpolated on a common grid of 0.25×0.25 degree lateral spacing. Once the geometry of different structures is specified, each element of the structure is assigned either a certain conductivity value or conductivity versus depth distribution, according to available laboratory data and conversion laws. A numerical formalism developed for compilation of the model, allows for its further refinement by incorporation of regional 3D conductivity distributions inferred from the real electromagnetic data. So far we included into our model four regional conductivity models, available from recent publications, namely, surface conductance model of Russia, and 3D conductivity models of Fennoscandia, Australia, and northwest of the United States.
Reporting guidelines for modelling studies
Directory of Open Access Journals (Sweden)
Bennett Carol
2012-11-01
Full Text Available Abstract Background Modelling studies are used widely to help inform decisions about health care and policy and their use is increasing. However, in order for modelling to gain strength as a tool for health policy, it is critical that key model factors are transparent so that users of models can have a clear understanding of the model and its limitations.Reporting guidelines are evidence-based tools that specify minimum criteria for authors to report their research such that readers can both critically appraise and interpret study findings. This study was conducted to determine whether there is an unmet need for population modelling reporting guidelines. Methods We conducted a review of the literature to identify: 1 guidance for reporting population modelling studies; and, 2 evidence on the quality of reporting of population modelling studies. Guidance for reporting was analysed using a thematic approach and the data was summarised as frequencies. Evidence on the quality of reporting was reviewed and summarized descriptively. Results There were no guidelines that specifically addressed the reporting of population modelling studies. We identified a number of reporting guidelines for economic evaluation studies, some of which had sections that were relevant population modelling studies. Amongst seven relevant records, we identified 69 quality criteria that have distinct reporting characteristics. We identified two papers that addressed reporting practices of modelling studies. Overall, with the exception of describing the data used for calibration, there was little consistency in reporting. Conclusions While numerous guidelines exist for developing and evaluating health technology assessment and economic evaluation models, which by extension could be applicable to population modelling studies, there is variation in their comprehensiveness and in the consistency of reporting these methods. Population modelling studies may be an area which would
Models for Unsaturated Hydraulic Conductivity Based on Truncated Lognormal Pore-size Distributions
Malama, Bwalya
2013-01-01
We develop a closed-form three-parameter model for unsaturated hydraulic conductivity associated with a three-parameter lognormal model of moisture retention, which is based on lognormal grainsize distribution. The derivation of the model is made possible by a slight modification to the theory of Mualem. We extend the three-parameter lognormal distribution to a four-parameter model that also truncates the pore size distribution at a minimum pore radius. We then develop the corresponding four-parameter model for moisture retention and the associated closed-form expression for unsaturated hydraulic conductivity. The four-parameter model is fitted to experimental data, similar to the models of Kosugi and van Genuchten. The proposed four-parameter model retains the physical basis of Kosugi's model, while improving fit to observed data especially when simultaneously fitting pressure-saturation and pressure-conductivity data.
Decoherence-induced conductivity in the one-dimensional Anderson model
Energy Technology Data Exchange (ETDEWEB)
Stegmann, Thomas; Wolf, Dietrich E. [Department of Physics, University of Duisburg-Essen and CENIDE, 47048 Duisburg (Germany); Ujsághy, Orsolya [Department of Theoretical Physics, Budapest University of Technology and Economics, Budafoki út 8., H-1521 Budapest (Hungary)
2014-08-20
We study the effect of decoherence on the electron transport in the one-dimensional Anderson model by means of a statistical model [1, 2, 3, 4, 5]. In this model decoherence bonds are randomly distributed within the system, at which the electron phase is randomized completely. Afterwards, the transport quantity of interest (e.g. resistance or conductance) is ensemble averaged over the decoherence configurations. Averaging the resistance of the sample, the calculation can be performed analytically. In the thermodynamic limit, we find a decoherence-driven transition from the quantum-coherent localized regime to the Ohmic regime at a critical decoherence density, which is determined by the second-order generalized Lyapunov exponent (GLE) [4].
Energy Technology Data Exchange (ETDEWEB)
Flukiger, F
2005-10-15
This work is motivated by tightness technological problems associated with metallic gasket. The objective is a better understanding of leakage mechanisms, through the development of new computational tools. In this study, the aperture field between two rough surfaces in contact is described by a short correlated isotropic random Gaussian process. The system is studied as a set of independent elementary surfaces. Joint conductances are evaluated from a statistical study on those elementary surfaces. A computational code is developed using a network approach based on lubrication theory estimation of local conductances. The global conductance computation becomes analogous to an electrical problem for which the resistances are distributed on a random network. The network is built from the identification of the aperture field critical points. Maxima are linked through saddle points. Bond conductances are estimated at the aperture field saddle points. First, a purely plastic model of deformations is considered. Near percolation threshold the conductances display a power behaviour. Far from percolation threshold, numerical results are favourably compared with an effective medium approximation. Secondly, we study the impact of elastic deformations. A computational code based on Boussinesq approximation is coupled to the network approach. The results indicate a significant impact of elastic deformations on conductances. Finally, the network approach is adapted to simulate quasi-static drainage thanks to a classical invasion percolation algorithm. A good comparison between previous experiments and numerical predictions is obtained. (author)
Cross-correlations in high-conductance states of a model cortical network
DEFF Research Database (Denmark)
Hertz, John
2010-01-01
(dansk abstrakt findes ikke) Neuronal firing correlations are studied using simulations of a simple network model for a cortical column in a high-conductance state with dynamically balanced excitation and inhibition. Although correlations between individual pairs of neurons exhibit considerable...... heterogeneity, population averages show systematic behavior. When the network is in a stationary state, the average correlations are generically small: correlation coefficients are of order 1/N, where N is the number of neurons in the network. However, when the input to the network varies strongly in time, much...... larger values are found. In this situation, the network is out of balance, and the synaptic conductance is low, at times when the strongest firing occurs. However, examination of the correlation functions of synaptic currents reveals that after these bursts, balance is restored within a few ms...
Energy Technology Data Exchange (ETDEWEB)
Strub, P. [Pierre Strub, freischaffender Berater, Binningen (Switzerland); Ziegler, Ch. [Inter Act, Basel (Switzerland)
2009-02-15
This final report deals with the results of a feasibility study concerning the development of a Code of Conduct for wind-power projects. The aim is to strengthen the acceptance of wind-power by the general public. The necessity of new, voluntary market instruments is discussed. The urgency of development in this area is quoted as being high, and the authors consider the feasibility of the definition of a code of conduct as being proven. The code of conduct can, according to the authors, be of use at various levels but primarily in project development. Further free-enterprise instruments are also suggested that should help support socially compatible and successful market development. It is noted that the predominant portion of those questioned are prepared to co-operate in further work on the subject
A Model of Thermal Conductivity for Planetary Soils: 1. Theory for Unconsolidated Soils
Piqueux, S.; Christensen, P. R.
2009-01-01
We present a model of heat conduction for mono-sized spherical particulate media under stagnant gases based on the kinetic theory of gases, numerical modeling of Fourier s law of heat conduction, theoretical constraints on the gas thermal conductivity at various Knudsen regimes, and laboratory measurements. Incorporating the effect of the temperature allows for the derivation of the pore-filling gas conductivity and bulk thermal conductivity of samples using additional parameters (pressure, gas composition, grain size, and porosity). The radiative and solid-to-solid conductivities are also accounted for. Our thermal model reproduces the well-established bulk thermal conductivity dependency of a sample with the grain size and pressure and also confirms laboratory measurements finding that higher porosities generally lead to lower conductivities. It predicts the existence of the plateau conductivity at high pressure, where the bulk conductivity does not depend on the grain size. The good agreement between the model predictions and published laboratory measurements under a variety of pressures, temperatures, gas compositions, and grain sizes provides additional confidence in our results. On Venus, Earth, and Titan, the pressure and temperature combinations are too high to observe a soil thermal conductivity dependency on the grain size, but each planet has a unique thermal inertia due to their different surface temperatures. On Mars, the temperature and pressure combination is ideal to observe the soil thermal conductivity dependency on the average grain size. Thermal conductivity models that do not take the temperature and the pore-filling gas composition into account may yield significant errors.
Structural and AC conductivity study of CdTe nanomaterials
Das, Sayantani; Banerjee, Sourish; Sinha, T. P.
2016-04-01
Cadmium telluride (CdTe) nanomaterials have been synthesized by soft chemical route using mercapto ethanol as a capping agent. Crystallization temperature of the sample is investigated using differential scanning calorimeter. X-ray diffraction and transmission electron microscope measurements show that the prepared sample belongs to cubic structure with the average particle size of 20 nm. Impedance spectroscopy is applied to investigate the dielectric relaxation of the sample in a temperature range from 313 to 593 K and in a frequency range from 42 Hz to 1.1 MHz. The complex impedance plane plot has been analyzed by an equivalent circuit consisting of two serially connected R-CPE units, each containing a resistance (R) and a constant phase element (CPE). Dielectric relaxation peaks are observed in the imaginary parts of the spectra. The frequency dependence of real and imaginary parts of dielectric permittivity is analyzed using modified Cole-Cole equation. The temperature dependence relaxation time is found to obey the Arrhenius law having activation energy ~0.704 eV. The frequency dependent conductivity spectra are found to follow the power law. The frequency dependence ac conductivity is analyzed by power law.
Factors influencing childhood conduct disorders: Study of 43 cases
Directory of Open Access Journals (Sweden)
Jalili B
2000-08-01
Full Text Available Conduct disorders are a group of behavior disorders in which the basic rights of others or major age appropriate social norms or rules are violated. To evaluate the factors influencing childhood conduct disorders, we reviewed records of 43 cases (84% boys, mean age 11 years referred to Shahid Esmaili psychiatric hospital, Tehran. All patients fulfilled diagnostic criteria of DSMIV. 15 variables were included; Age and sex and step of patient among sibling, parental educational level, social class of the family, medical and psychiatric history of entire family members and the kind of therapy. The most frequent complaints were aggressiveness, stealing and lying. The dominant age group was 10-14 years. The most frequent family members were 5. Most of the children were 2nd child of the family. The most often educational level of the parents were illiteracy followed by primary school educated. Most of the patients were of low to intermediate socioeconomic classes. The most effective therapy was behavior modification along with appropriate medications.
Experimental and simulation studies on laser conduction welding of AA5083 aluminium alloys
Tobar, M. J.; Lamas, M. I.; Yáñez, A.; Sánchez-Amaya, J. M.; Boukha, Z.; Botana, F. J.
In this paper, a three-dimensional numerical model was developed to study laser welding in an aluminium alloy (AA5083). The CFD model was used to solve the governing equations of conservation of mass, momentum and energy, so as to obtain the morphology, velocity field and temperature field of the melted zone in steady state. The predicted dimensions of the weld pool agreed well with experimental results obtained on laser conduction welding with a (CW) high power diode laser. The study allowed to determine the effect of different surface treatment (sandblasting, black painting) on the laser absorptivity of the alloy and analyze the heat transfer mechanism within the weld pool.
NAFTA Guidance Document for Conducting Terrestrial Field Dissipation Studies
Harmonized guidance for TFD studies that demonstrate transformation, transport and fate of pesticides under representative actual use conditions. Field studies substantiate physicochemical, mobility and biotransformation data from laboratory studies.
Guidelines for Conducting Positivist Case Study Research in Information Systems
National Research Council Canada - National Science Library
Graeme Shanks
2002-01-01
.... This paper focuses on positivist, deductive case study research in information systems. It provides clear definitions of important concepts in positivist case study research and illustrates these with an example research study...
Energy Technology Data Exchange (ETDEWEB)
Barton, R.L.; Keith, J.M.; King, J.A. [Michigan Technological Univ., Houghton, MI (United States). Dept. of Chemical Engineering
2008-08-15
This study modelled the electrical conductivity of a single filler composite system using a general effective media (GEM) equation. The aim of the study was to investigate the use of synthetic graphite and carbon fiber in liquid crystal polymers for fuel cell bipolar plate applications. The polymer consisted of 73 mole per cent hydroxybenzoic acid and 27 mole per cent hydroxynaphthoic acid. Composites of various concentrations of single and multiple filler combinations were tested. A volumetric in-plane electrical conductivity test was conducted on all samples in order to measure voltage drop. A through-plane conductivity test was conducted to measure resistivity. The GEM equation was then used to model the conductivity data obtained during the tests. Results of the study showed that at 45 vol per cent, the electrical conductivity of the multiple filler composite was comparable to data obtained from single filler electrical conductivities. The electrical conductivity of the multiple filler composite at 60 per cent graphite and 10 per cent carbon fiber was comparable to the single filler carbon fiber composite, but lower than the single filler synthetic graphite composite. Results also showed that the GEM equation provided excellent agreement with results obtained during the experiments. It was concluded that the percolation threshold of the multiple filler composite was almost identical to the single carbon fiber filler, but lower than the single synthetic graphite composite. 35 refs., 3 tabs., 2 figs.
Multi-ion conduction bands in a simple model of calcium ion channels
Kaufman, I; Tindjong, R; McClintock, P V E; Eisenberg, R S
2012-01-01
We report self-consistent Brownian dynamics simulations of a simple electrostatic model of the selectivity filters (SF) of calcium ion channels. They reveal regular structure in the conductance and selectivity as functions of the fixed negative charge Qf at the SF. This structure comprises distinct regions of high conductance (conduction bands) M0, M1, M2 separated by regions of zero-conductance (stop-bands). Two of these conduction bands, M1 and M2, demonstrate high calcium selectivity and prominent anomalous mole fraction effects and can be identified with the L-type and RyR calcium channels.
Directory of Open Access Journals (Sweden)
Rafael Vargas-Bernal
2013-01-01
Full Text Available The design of nanometric electronic devices requires novel materials for improving their electrical performance from stages of design until their fabrication. Until now, several DC electrical conductivity models for composite materials have been proposed. However, these models must be valued to identify main design parameters that more efficiently control the electrical properties of the materials to be developed. In this paper, four different models used for modeling DC electrical conductivity of carbon nanotube-polymer composites are studied with the aim of obtaining a complete list of design parameters that allow guarantying to the designer an increase in electrical properties of the composite by means of carbon nanotubes.
Design study of a normal conducting helical snake for AGS
Takano, Junpei; Okamura, Masahiro; Roser, Thomas; MacKay, William W; Luccio, Alfredo U; Takano, Koji
2004-01-01
A new normal conducting snake magnet is being fabricated for the Alternate Gradient Synchrotron (AGS) at Brookhaven National Laboratory (BNL). In the Relativistic Heavy Ion Collider (RHIC) project, a superconducting type helical dipole magnets had been developed and it performed successfully in high-energy polarized proton acceleration. The new AGS helical snake has the same basic magnetic structure but is more complicated. To achieve no beam shift and no beam deflection in one magnetic device, helical pitches and rotating angles were carefully calculated. Compared to a superconducting magnet, a normal warm magnet must have a large cross- sectional area of conductors which make it difficult to design a magnet with large helical pitch. We developed a modified window frame structure to accommodate the large number of conductors. Its three dimensional magnetic field was simulated by using OPERA3D/TOSCA. 3 Refs.
Iden, Sascha C.; Peters, Andre; Durner, Wolfgang
2015-11-01
The prediction of unsaturated hydraulic conductivity from the soil water retention curve by pore-bundle models is a cost-effective and widely applied technique. One problem for conductivity predictions from retention functions with continuous derivatives, i.e. continuous water capacity functions, is that the hydraulic conductivity curve exhibits a sharp drop close to water saturation if the pore-size distribution is wide. So far this artifact has been ignored or removed by introducing an explicit air-entry value into the capillary saturation function. However, this correction leads to a retention function which is not continuously differentiable. We present a new parameterization of the hydraulic properties which uses the original saturation function (e.g. of van Genuchten) and introduces a maximum pore radius only in the pore-bundle model. In contrast to models using an explicit air entry, the resulting conductivity function is smooth and increases monotonically close to saturation. The model concept can easily be applied to any combination of retention curve and pore-bundle model. We derive closed-form expressions for the unimodal and multimodal van Genuchten-Mualem models and apply the model concept to curve fitting and inverse modeling of a transient outflow experiment. Since the new model retains the smoothness and continuous differentiability of the retention model and eliminates the sharp drop in conductivity close to saturation, the resulting hydraulic functions are physically more reasonable and ideal for numerical simulations with the Richards equation or multiphase flow models.
Study on delayed cracking of conductive notch under electric field in PZT-5H ferroelectric ceramics
Institute of Scientific and Technical Information of China (English)
QIAO Guangli; SU Yanjing; QIAO Lijie; CHU Wuyang
2006-01-01
Electric-field-induced delay cracking of conducting notch in PZT-5H ferroelectric ceramics has been studied using a compact specimen with a notch filled in conductive silver paste. The critical electric field that induces instant failure of the PZT-5H specimen is shown to be EF = 14.7(3.2 kV/cm. When an electric field lower than EF, but higher than EDF = 9.9 kV/cm was applied, a micro-crack formed at the conductive notch tip instantly, propagating slowly until the specimen failure. When the electric field was lower than EDF, the micro-crack propagated a short distance, and then stopped. When the electric field was lower than EK＝4.9 kV/cm, no cracks formed at the conductive notch tip instantly, however, a delay micro-crack would form and propagate. When the electric field was lower than EDK=2.4 kV/cm, no cracks formed and delay propagation occurred. A model for electric charge emission and concentration at a conductive notch is proposed to explain the delay cracking of conducting notch.
Use of artificial neural networks for electrical conductivity modeling in Asi River
Ghorbani, Mohammad Ali; Aalami, Mohammad Taghi; Naghipour, Leila
2017-07-01
This study aims to model monthly electrical conductivity (EC) values in the Asi River using artificial neural networks (ANNs) to evaluate water quality conditions using pH, temperature, water discharge, sodium, sum of calcium and magnesium concentrations. The results are compared using multiple linear regression (MLR). Recorded data are available at a gauging site in Antakya, Turkey, for the period from 1984 to 2008. Comparing the modeled values by ANNs with the experimental data indicates that neural network model with seven neurons in hidden layer provides accurate results ( R 2 = 0.968, RMSE = 46.927 µS/cm, MAE = 32.462 µS/cm and MRSE = 0.0029 for the training data and R 2 = 0.965, RMSE = 50.810 µS/cm, MAE = 37.495 µS/cm and MRSE = 0.0024 for the testing data). The Garson method of the connection weights of the network was used to study the relative % contribution of each of the input variables. It was found that the sum of calcium and magnesium concentration and temperature had the most effect on the predicted EC. The results indicate that two proposed models were able to approximate the EC parameter reasonably well; however, the ANN was found to perform better than the MLR model.
Use of artificial neural networks for electrical conductivity modeling in Asi River
Ghorbani, Mohammad Ali; Aalami, Mohammad Taghi; Naghipour, Leila
2015-10-01
This study aims to model monthly electrical conductivity (EC) values in the Asi River using artificial neural networks (ANNs) to evaluate water quality conditions using pH, temperature, water discharge, sodium, sum of calcium and magnesium concentrations. The results are compared using multiple linear regression (MLR). Recorded data are available at a gauging site in Antakya, Turkey, for the period from 1984 to 2008. Comparing the modeled values by ANNs with the experimental data indicates that neural network model with seven neurons in hidden layer provides accurate results (R 2 = 0.968, RMSE = 46.927 µS/cm, MAE = 32.462 µS/cm and MRSE = 0.0029 for the training data and R 2 = 0.965, RMSE = 50.810 µS/cm, MAE = 37.495 µS/cm and MRSE = 0.0024 for the testing data). The Garson method of the connection weights of the network was used to study the relative % contribution of each of the input variables. It was found that the sum of calcium and magnesium concentration and temperature had the most effect on the predicted EC. The results indicate that two proposed models were able to approximate the EC parameter reasonably well; however, the ANN was found to perform better than the MLR model.
Shen, Xueqin; Yan, Hui; Yan, Weili; Guo, Lei
2007-01-01
In this paper, we introduce multidimensional support vector regression (MSVR) with iterative re-weight least square (IRWLS) based procedure to estimating the regional conductivity in 2D disc head model. The results show that the method is capable of determining for the regional location of the disturbed conductivity in the 2D disc head model with single tissue and estimating for the tissue conductivities in the 2D disc head model with four kinds of tissue. The estimation errors are all within a few percent.
DPL Model Analysis of Non-Fourier Heat Conduction Restricted by Continuous Boundary Interface
Institute of Scientific and Technical Information of China (English)
Jiang Fangming; Liu Dengying
2001-01-01
Dual-phase lag (DPL) model is used to describe the non-Fourier heat conduction in a finite medium where the boundary at x=-0 is heated by a rectangular pulsed energy source and the other boundary is tightly contacted with another medium and satisfies the continuous boundary condition. Numerical solution of this kind of. non-Fourier heat conduction is presented in this paper. The results are compared with those predicted by the hyperbolic heat conduction (HHC) equation.
A Fractal Model for the Effective Thermal Conductivity of Granular Flow with Non-uniform Particles
Institute of Scientific and Technical Information of China (English)
ZHANG Duan-Ming; LEI Ya-Jie; YU Bo-Ming; ZHANG Mei-Jun; HUANG Ming-Tao; LI Zhi-Hua; GUAN Li
2002-01-01
The equipartition of energy applied in binary mixture of granular flow is extended to granular flow withnon-uniform particles. Based on the fractal characteristic of granular flow with non-uniform particles as well as energyequipartition, a fractal velocity distribution function and a fractal model of effective thermal conductivity are derived.Thermal conduction resulted from motions of particles in the granular flow, as well as the effect of fractal dimension oneffective thermal conductivity, is discussed.
Modeling of Proton-Conducting Solid Oxide Fuel Cells Fueled with Syngas
Directory of Open Access Journals (Sweden)
Meng Ni
2014-07-01
Full Text Available Solid oxide fuel cells (SOFCs with proton conducting electrolyte (H-SOFCs are promising power sources for stationary applications. Compared with other types of fuel cells, one distinct feature of SOFC is their fuel flexibility. In this study, a 2D model is developed to investigate the transport and reaction in an H-SOFC fueled with syngas, which can be produced from conventional natural gas or renewable biomass. The model fully considers the fluid flow, mass transfer, heat transfer and reactions in the H-SOFC. Parametric studies are conducted to examine the physical and chemical processes in H-SOFC with a focus on how the operating parameters affect the H-SOFC performance. It is found that the presence of CO dilutes the concentration of H2, thus decreasing the H-SOFC performance. With typical syngas fuel, adding H2O cannot enhance the performance of the H-SOFC, although water gas shift reaction can facilitate H2 production.
A simple model for conduction band states of nitride-based double heteroestructures
Energy Technology Data Exchange (ETDEWEB)
Gaggero-Sager, L M; Mora-Ramos, M E, E-mail: lgaggero@uaem.m [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, CP 62209, Cuernavaca, Morelos (Mexico)
2009-05-01
In this work we propose an analytical expression for the approximate modeling of the potential energy function describing conduction band bending in III-V nitride quantum wells. It is an alternative approach to the self-consistent Poisson-Schoedinger calculation. The model considers the influence of the many electron system and the built-in electric field inside the well. Hartree and exchange contributions are included along the lines of a local-density Thomas-Fermi-based theory. The effects due to the modulated doping in the barriers is also considered. We report the calculation of the energy spectrum as a function of several input parameters: alloy composition in the barriers, barrier doping concentration, and quantum well width. Our results could be of usefulness in the study of optoelectronic properties in this kind of systems.
Thermal Conductivity in Suspension Sprayed Thermal Barrier Coatings: Modeling and Experiments
Ganvir, Ashish; Kumara, Chamara; Gupta, Mohit; Nylen, Per
2016-12-01
Axial suspension plasma spraying (ASPS) can generate microstructures with higher porosity and pores in the size range from submicron to nanometer. ASPS thermal barrier coatings (TBC) have already shown a great potential to produce low thermal conductivity coatings for gas turbine applications. It is important to understand the fundamental relationships between microstructural defects in ASPS coatings such as crystallite boundaries, porosity etc. and thermal conductivity. Object-oriented finite element (OOF) analysis has been shown as an effective tool for evaluating thermal conductivity of conventional TBCs as this method is capable of incorporating the inherent microstructure in the model. The objective of this work was to analyze the thermal conductivity of ASPS TBCs using experimental techniques and also to evaluate a procedure where OOF can be used to predict and analyze the thermal conductivity for these coatings. Verification of the model was done by comparing modeling results with the experimental thermal conductivity. The results showed that the varied scaled porosity has a significant influence on the thermal conductivity. Smaller crystallites and higher overall porosity content resulted in lower thermal conductivity. It was shown that OOF could be a powerful tool to predict and rank thermal conductivity of ASPS TBCs.
Thermal Conductivity in Suspension Sprayed Thermal Barrier Coatings: Modeling and Experiments
Ganvir, Ashish; Kumara, Chamara; Gupta, Mohit; Nylen, Per
2017-01-01
Axial suspension plasma spraying (ASPS) can generate microstructures with higher porosity and pores in the size range from submicron to nanometer. ASPS thermal barrier coatings (TBC) have already shown a great potential to produce low thermal conductivity coatings for gas turbine applications. It is important to understand the fundamental relationships between microstructural defects in ASPS coatings such as crystallite boundaries, porosity etc. and thermal conductivity. Object-oriented finite element (OOF) analysis has been shown as an effective tool for evaluating thermal conductivity of conventional TBCs as this method is capable of incorporating the inherent microstructure in the model. The objective of this work was to analyze the thermal conductivity of ASPS TBCs using experimental techniques and also to evaluate a procedure where OOF can be used to predict and analyze the thermal conductivity for these coatings. Verification of the model was done by comparing modeling results with the experimental thermal conductivity. The results showed that the varied scaled porosity has a significant influence on the thermal conductivity. Smaller crystallites and higher overall porosity content resulted in lower thermal conductivity. It was shown that OOF could be a powerful tool to predict and rank thermal conductivity of ASPS TBCs.
Conducting event studies on a small stock exchange
DEFF Research Database (Denmark)
Bartholdy, Jan; Olson, Dennis; Peare, Paula
This paper analyses whether it is possible to perform an event study on a small stock exchange with thinly trade stocks. The main conclusion is that event studies can be performed provided that certain adjustments are made. First, a minimum of 25 events appears necessary to obtain acceptable size...
Comparative study of atrial fibrillation and AV conduction in mammals
Meijler, F.L.; Tweel, I. van der
1987-01-01
Atrial fibrillation is one ofthe most common cardiac arrhythmias in humans. It a1so occurs quite frequent1y in dogs and horses. Comparative study of this arrhythmia may contribute to better understanding of the pathophysiologica1 mechanisms involved. In this study, we present a quantitative analysis
Characterization and dynamic charge dependent modeling of conducting polymer trilayer bending
Farajollahi, Meisam; Sassani, Farrokh; Naserifar, Naser; Fannir, Adelyne; Plesse, Cédric; Nguyen, Giao T. M.; Vidal, Frédéric; Madden, John D. W.
2016-11-01
Trilayer bending actuators are charge driven devices that have the ability to function in air and provide large mechanical amplification. The electronic and mechanical properties of these actuators are known to be functions of their charge state making prediction of their responses more difficult when they operate over their full range of deformation. In this work, a combination of state space representation and a two-dimensional RC transmission line model are used to implement a nonlinear time variant model for conducting polymer-based trilayer actuators. Electrical conductivity and Young’s modulus of electromechanically active PEDOT conducting polymer containing films as a function of applied voltage were measured and incorporated into the model. A 16% drop in Young’s modulus and 24 times increase in conductivity are observed by oxidizing the PEDOT. A closed form formulation for radius of curvature of trilayer actuators considering asymmetric and location dependent Young’s modulus and conductivity in the conducting polymer layers is derived and implemented in the model. The nonlinear model shows the capability to predict the radius of curvature as a function of time and position with reasonable consistency (within 4%). The formulation is useful for general trilayer configurations to calculate the radius of curvature as a function of time. The proposed electrochemical modeling approach may also be useful for modeling energy storage devices.
DEFF Research Database (Denmark)
Zhu, Huayang; Ricote, Sandrine; Coors, W. Grover;
2014-01-01
A model-based approach is used to interpret equilibrium and transient conductivity measurements for 10% gadolinium-doped ceria: Ce0.9Gd0.1O1.95 − δ (GDC10). The measurements were carried out by AC impedance spectroscopy on slender extruded GDC10 rods. Although equilibrium conductivity measurements...
A fractal model for the effective thermal conductivity of nanoparticle suspensions
Institute of Scientific and Technical Information of China (English)
WANG Buxuan; ZHOU Leping; PENG Xiaofeng
2004-01-01
Extending the effective medium approximation with the fractal theory for describing nanoparticle clusters and their radius distribution, a predictive model is proposed for the effective thermal conductivity of nanoparticle suspension, combined with the consideration of size effect and surface adsorption effect of nanoparticles.The predicted effective thermal conductivity of nanoparticle suspension is consistent with experimental data in the dilute limit.
Electron and Ion Conductivity Calculations using the Model of Lee and More
Energy Technology Data Exchange (ETDEWEB)
Hayes, John C. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2016-09-30
The following notes describe the ARES implementation of the inverse of the electron conduction coefficient, using the model of Lee and More, Physics of Fluids 27, page 1273, 1984. An addendum describing the modifications for analogous ion conduction coeffiecient appears at the bottom.
Azuchi, Fumika; Kinose, Yoshiyuki; Matsumura, Tomoe; Kanomata, Tomoaki; Uehara, Yui; Kobayashi, Ayumi; Yamaguchi, Masahiro; Izuta, Takeshi
2014-01-01
A multiplicative stomatal conductance model was constructed to estimate stomatal O3 uptake of Fagus crenata exposed to O3 under different N loads to the soil. Our stomatal conductance model included environmental functions such as the stomatal responses of F. crenata to diurnal changes, chronic O3 stress (AOT0), acute O3 stress (O3 concentration), and nitrogen load to soil. The model could explain 62% of the variability in stomatal conductance. We suggest therefore that stomatal closure induced by O3 and N load-induced soil acidification must be taken into account in developing a stomatal conductance model for estimating stomatal O3 uptake for future risk assessment of O3 impact on Japanese forest tree species such as F. crenata.
The Lattice and Thermal Radiation Conductivity of Thermal Barrier Coatings: Models and Experiments
Zhu, Dongming; Spuckler, Charles M.
2010-01-01
The lattice and radiation conductivity of ZrO2-Y2O3 thermal barrier coatings was evaluated using a laser heat flux approach. A diffusion model has been established to correlate the coating apparent thermal conductivity to the lattice and radiation conductivity. The radiation conductivity component can be expressed as a function of temperature, coating material scattering, and absorption properties. High temperature scattering and absorption of the coating systems can be also derived based on the testing results using the modeling approach. A comparison has been made for the gray and nongray coating models in the plasma-sprayed thermal barrier coatings. The model prediction is found to have a good agreement with experimental observations.
DEFF Research Database (Denmark)
Kuvshinov, A.; Sabaka, T.; Olsen, Nils
2006-01-01
satellite data that contain contributions from the core and lithosphere, from the rnagnetosphere and ionosphere (and their Earth-induced counterparts), as well as payload noise has been investigated. The model Studies have shown that C-responses obtained oil a regular grid might be used to map regional deep......An approach is presented to detect deep-seated regional conductivity anomalies by analysis of magnetic observations taken by low-Earth-orbiting satellites. The approach deals with recovery of C-responses on a regular grid and starts with a determination of time series of external and internal....... For validation of the approach, 3 years of realistic synthetic data at Simulated orbits of the forthcoming Swarm constellation of 3 satellites have been used. To obtain the synthetic data for a given 3-D conductivity Earth's model a time-domain scheme has been applied which relies oil a Fourier transformation...
Methodological Considerations in Conducting an Olfactory fMRI Study
Directory of Open Access Journals (Sweden)
Faezeh Vedaei
2013-01-01
Full Text Available The sense of smell is a complex chemosensory processing in human and animals that allows them to connect with the environment as one of their chief sensory systems. In the field of functional brain imaging, many studies have focused on locating brain regions that are involved during olfactory processing. Despite wealth of literature about brain network in different olfactory tasks, there is a paucity of data regarding task design. Moreover, considering importance of olfactory tasks for patients with variety of neurological diseases, special contemplations should be addressed for patients. In this article, we review current olfaction tasks for behavioral studies and functional neuroimaging assessments, as well as technical principles regarding utilization of these tasks in functional magnetic resonance imaging studies.
A Fractal Model for the Transverse Thermal Dispersion Conductivity in Porous Media
Institute of Scientific and Technical Information of China (English)
郁伯铭; 李建华
2004-01-01
A quasi-analytical model, i.e. the fractal model, for the transverse thermal dispersion conductivity in porous media is presented based on the fractal characteristics of tortuous flow paths/streamlines in porous media. The fractal dimension of tortuous flow paths, the spatial deviation velocity and the transverse thermal dispersion conductivity are derived. The proposed model is expressed as functions of the fractal dimension of tortuous flow paths/streamlines, Peclet number, porosity and structural parameters. The present results are compared with those from the existing correlation, and good agreement is found between the present model predictions and those from the existing correlation.
Energy Technology Data Exchange (ETDEWEB)
Amine Fersi, M., E-mail: fersi_amine@yahoo.fr; Chaabane, I.; Gargouri, M.
2014-07-01
The Bis (4-acetylanilinium) tetrachloridozincate [C{sub 8}H{sub 10}NO]{sub 2}[ZnCl{sub 4}] compound was obtained by slow evaporation at room temperature and characterized by XRD. It is crystallized in an orthorhombic system (Cmca space group). The material was characterized by impedance spectroscopy technique measured in the 209 Hz–5 MHz frequency range from 423 to 498 K. Besides, the Cole–Cole (Z″ versus Z′) plots were well fitted to an equivalent circuit built up by a parallel combination of resistance (R), fractal capacitance (CPE) and capacitance (C). Furthermore, the AC conductivity was investigated as a function of temperature and frequency in the same range. The experimental results indicated that AC conductivity (σ{sub ac}) was proportional to Aω{sup S1}+Bω{sup S2}(0model. An agreement between the experimental and theoretical results suggests that the AC conductivity behavior of [C{sub 8}H{sub 10}NO]{sub 2}[ZnCl{sub 4}] can be explained by CBH model. The contribution of single polaron hopping to AC conductivity in a present alloy was also studied.
Computer Simulation Study of Thermal Conduction in 1D Chains of Anharmonic Oscillators
Institute of Scientific and Technical Information of China (English)
Tejal N.Shah; P.N.Gajjar
2013-01-01
In this work thermal conduction in one-dimensional (1D) chains of anharmonic oscillators are studied using computer simulation.The temperature profile,heat flux and thermal conductivity are investigated for chain length N =100,200,400,800 and 1600.In the computer simulation anharmonicity is introduced due to Fermi-Pasta-Ulam-β (FPU-β) model For substrate interaction,an onsite potential due to Frenkel-Kontorova (FK) model has been used.Numerical simulations demonstrate that temperature gradient scales behave as N-1 linearly with the relation J =0.1765/N.For the thermal conductivity K,KN to N obey the linear relation of the type KN =0.8805N.It is shown that thermal transport is dependent on phonon-phonon interaction as well as phonon-lattice interaction.The thermal conductivity increaseslinearly with increase inanharmonicity and predicts relation κ =0.133 + 0.804β.It is also concluded that for higher value of the strength of the onsite potential system tends to a thermal insulator.
Field emission study of MWCNT/conducting polymer nanocomposite
Energy Technology Data Exchange (ETDEWEB)
Alvi, M.A., E-mail: maalvee@yahoo.co.in [Department of Physics, King Abdulaziz University, Jeddah-21589 (Saudi Arabia); Al-Ghamdi, A.A. [Department of Physics, King Abdulaziz University, Jeddah-21589 (Saudi Arabia); Husain, M. [Department of Physics, Jamia Millia Islamia, New Delhi-110025 (India)
2014-12-01
MWCNTs/Polypyrrole nanocomposites were synthesized by solution mixing method. These synthesized nanocomposites were studied carefully by Raman Spectroscopy and Scanning Electron Microscopy measurements. The field emission study of MWCNTs/Polypyrrole nanocomposites were performed in diode arrangement under vacuum of the order of 10{sup −5} Torr. The emission current under exploration depends on applied voltage. The prepared nanocomposites depict low turn-on field at 1.4 V/μm that reaches to a maximum emission current density 0.020 mA/cm{sup 2} at 2.4 V/µm, which is calculated from the graph of current density (J) against the applied electric field (E) and from Fowler–Nordheim (F–N) plot.
Thermal conductivity studies of CdZnTe with varying Te excess
Jackson, Maxx; Bennett, Brittany; Giltnane, Dustin; Babalola, Stephen; Ohmes, Martin F.; Stowe, A. C.
2016-09-01
Cadmium Zine Telluride (CZT) has been extensively studied as a room temperature semiconductor gamma radiation detector. CZT continues to show promise as a bulk and pixelated gamma spectrometer with less than one percent energy resolution; however the fabrication costs are high. Improved yields of high quality, large CZT spectroscopy grade crystals must be achieved. CZT is grown by the Traveling Heater Method (THM) with a Te overpressure to account for vaporization losses. This procedure creates Te rich zones. During growth, boules will often cleave limiting the number of harvestable crystals. As a result, crystal growth parameter optimization was evaluated by modeling the heat flow within the system. Interestingly, Cadmium Telluride (CdTe) is used as a thermal conductivity surrogate in the absence of a thorough study of the CZT thermal properties. The current study has measured the thermal conductivity of CZT pressed powders with varying Te concentrations from 50-100% over 25-800°C to understand the variation in this parameter from CdTe. Cd0.9Zn0.1Te1.0 is the base CZT (designated 50%). CZT exhibits a thermal conductivity of nearly 1 W/mK, an order of magnitude greater than CdTe. Further, the thermal conductivity decreased with increasing Te concentration.
Model technical and tactical training karate «game» manner of conducting a duel
Directory of Open Access Journals (Sweden)
Natalya Boychenko
2015-04-01
Full Text Available Purpose: optimization of technical and tactical training karate «gaming» the manner of conducting a duel. Material and Methods: analysis and compilation of scientific and methodological literature, interviews with coaches for shock combat sports, video analysis techniques, teacher observations. Results: the model of technical and tactical training karate «game» manner of conducting a duel. Selection was done complexes jobs matching techniques to improve athletes 'game' in the manner of conducting a duel «Kyokushin» karate. Conclusion: the model of technical and tactical training fighters "game" manner of conducting a duel, which reveals the particular combination technique karate style «Kyokushin». Selection was done complexes jobs matching techniques to improve athletes 'game' in the manner of conducting a duel «Kyokushin» karate, aimed at improving the combinations with the action on the response of the enemy.
Network model for thermal conductivities of unidirectional fiber-reinforced composites
Wang, Yang; Peng, Chaoyi; Zhang, Weihua
2014-12-01
An empirical network model has been developed to predict the in-plane thermal conductivities along arbitrary directions for unidirectional fiber-reinforced composites lamina. Measurements of thermal conductivities along different orientations were carried out. Good agreement was observed between values predicted by the network model and the experimental data; compared with the established analytical models, the newly proposed network model could give values with higher precision. Therefore, this network model is helpful to get a wider and more comprehensive understanding of heat transmission characteristics of fiber-reinforced composites and can be utilized as guidance to design and fabricate laminated composites with specific directional or specific locational thermal conductivities for structures that simultaneously perform mechanical and thermal functions, i.e. multifunctional structures (MFS).
RELAP5-3D multidimensional heat conduction enclosure model for RBMK reactor application
Energy Technology Data Exchange (ETDEWEB)
Paik, S.
1999-10-01
A heat conduction enclosure model is conceived and implemented by RELAP5-3D between heat structures. The suggested model uses a lumped parameter model that is generally applicable to multidimensional calculational domain. This new model is applied to calculation of RBMK reactor core graphite blocks and is compared to the commercially available Fluid Dynamics Analysis Package (FIDAP) finite element code. Reasonably good agreement between the results of RELAP5-3D and FIDAP is obtained. The new heat conduction enclosure model gives RELAP5-3D a general multidimensional heat conduction capability. It also provides new routes for temperature cooloff of the RBMK graphite blocks from the ruptured channel to the surrounding ones. This ability to predict graphite temperature cooloff is very important during accidents or for transient simulation, especially concerning long-term coolability of the RBMK reactor core.
ELECTROCHEMICAL STUDIES ON CONDUCTING COMPOSITE FILMS FROM POLYURETHANE AND POLYPYRROLE
Institute of Scientific and Technical Information of China (English)
BI Xiantong; PEI Qibing; LI Yongfang
1988-01-01
A study on the electrooxidative polymerization of pyrrole onto polyurethane-coated platinum electrodes and the electrochemical properties of the composite polyurethane/polypyrrole films (PU/PPy) as-prepared is presented. It is found that polypyrrole grows layer by layer from the polyurethane/platinum interface through the polyurethane matrix, and ca. 20 wt.% of polypyrrole will fill up the matrix. Cyclic voltammograms show that the composite films are porous, and the reduction-reoxidation (redox) rate of the composite films is limited by the diffusion ofcounteranions through the films. Larger anion size leads to slower diffusion process.The composite films can also act as modified electrodes.
Breakdown of the resistor-network model for steady-state hopping conduction
Energy Technology Data Exchange (ETDEWEB)
Emin, D. [Sandia National Labs., Albuquerque, NM (United States); Kuper, C.G. [Technion-Israel Inst. of Tech., Haifa (Israel). Dept. of Physics
1996-05-01
General master equations are used to study steady-state hopping transport in a disordered solid. We express a site`s occupancy in terms of its quasi-electrochemical potential (QECP); currents flow between sites whose QECP`s differ. Coupled nonlinear circuit equations for the QECP`s result from the steady-state condition and the boundary condition that the total QECP drop is the applied emf. When the site-to-site QECP differences are much smaller than the thermal energy, K{sub B}t, the effect of current flow on site occupancies is ignorable. These equations then reduce to those of a resistance network. However, the resistor-network model fails: (a) at low temperatures, (b) with increasing disorder, and (c) with increasing emf. We therefore study hopping conduction beyond this approximation. Exact examples show the importance of current-induced charge redistribution in non-ohmic steady-state flow.
Resistors Network Model of Bcc Cell for Investigating Thermal Conductivity of Nanofluids
Masturi, Masturi; Sustini, Euis; Khairurrijal, Khairurrijal; Abdullah, Mikrajuddin
2011-12-01
A model was developed to investigate thermal conductivity of nanofluids. It was based on resistors circuit network in bcc cell as alternative form of simple cubic cell has been successfully developed. The present model has involved the Brownian motion of nanoparticles in the fluid with an assumption that the nanoparticles are in low volume fraction so the diameter size of nanoparticle can be neglected in comparison to particles distance. Generally, this model was very fit to experimental results has been obtained from some authors. As an example, for alumina-water nanofluid, that is alumina (Al2O3) dispersed in water, it was found that the enhancement of its thermal conductivity calculated using this model was in good agreement with experimental results that it tended to increase as nanoparticle fraction increases. As in alumina-water, the agreement was also shown in titania (TiO2)-water and cuprum oxide (CuO)-water. This model also showed the dependence of thermal conductivity enhancement to diameter size of nanoparticle and temperature of the nanofluid. In relation to diameter size, thermal conductivity enhancement decreases as diameter size increases. Otherwise, thermal conductivity enhancement increases as temperature increases. However, even though this model was very close to experimental results, the problem of this model was in dimensionless constant that varied for different nanofluids.
Modeling the evolution of complex conductivity during calcite precipitation on glass beads
Leroy, Philippe; Li, Shuai; Jougnot, Damien; Revil, André; Wu, Yuxin
2017-01-01
SUMMARYWhen pH and alkalinity increase, calcite frequently precipitates and hence modifies the petrophysical properties of porous media. The complex conductivity method can be used to directly monitor calcite precipitation in porous media because it is sensitive to the evolution of the mineralogy, pore structure and its connectivity. We have developed a mechanistic grain polarization model considering the electrochemical polarization of the Stern and diffuse layer surrounding calcite particles. Our complex conductivity model depends on the surface charge density of the Stern layer and on the electrical potential at the onset of the diffuse layer, which are computed using a basic Stern model of the calcite/water interface. The complex conductivity measurements of Wu et al. (2010) on a column packed with glass beads where calcite precipitation occurs are reproduced by our surface complexation and complex conductivity models. The evolution of the size and shape of calcite particles during the calcite precipitation experiment is estimated by our complex conductivity model. At the early stage of the calcite precipitation experiment, modeled particles sizes increase and calcite particles flatten with time because calcite crystals nucleate at the surface of glass beads and grow into larger calcite grains around glass beads. At the later stage of the calcite precipitation experiment, modeled sizes and cementation exponents of calcite particles decrease with time because large calcite grains aggregate over multiple glass beads, a percolation threshold is achieved, and small and discrete calcite crystals polarize.
[Modeling and analysis of volume conduction based on field-circuit coupling].
Tang, Zhide; Liu, Hailong; Xie, Xiaohui; Chen, Xiufa; Hou, Deming
2012-08-01
Numerical simulations of volume conduction can be used to analyze the process of energy transfer and explore the effects of some physical factors on energy transfer efficiency. We analyzed the 3D quasi-static electric field by the finite element method, and developed A 3D coupled field-circuit model of volume conduction basing on the coupling between the circuit and the electric field. The model includes a circuit simulation of the volume conduction to provide direct theoretical guidance for energy transfer optimization design. A field-circuit coupling model with circular cylinder electrodes was established on the platform of the software FEM3.5. Based on this, the effects of electrode cross section area, electrode distance and circuit parameters on the performance of volume conduction system were obtained, which provided a basis for optimized design of energy transfer efficiency.
Linear Regression Model of the Ash Mass Fraction and Electrical Conductivity for Slovenian Honey
Directory of Open Access Journals (Sweden)
Mojca Jamnik
2008-01-01
Full Text Available Mass fraction of ash is a quality criterion for determining the botanical origin of honey. At present, this parameter is generally being replaced by the measurement of electrical conductivity (κ. The value κ depends on the ash and acid content of honey; the higher their content, the higher the resulting conductivity. A linear regression model for the relationship between ash and electrical conductivity has been established for Slovenian honey by analysing 290 samples of Slovenian honey (including acacia, lime, chestnut, spruce, fir, multifloral and mixed forest honeydew honey. The obtained model differs from the one proposed by the International Honey Commission (IHC in the slope, but not in the section part of the relation formula. Therefore, the Slovenian model is recommended when calculating the ash mass fraction from the results of electrical conductivity in samples of Slovenian honey.
Sivanesan, Umaseh; Izmaylov, Artur F
2016-01-01
Most of the textbooks explaining electric conductivity in the context of quantum mechanics provide either incomplete or semi-classical explanations that are not connected with the elementary concepts of quantum mechanics. We illustrate the conduction phenomena using the simplest model system in quantum dynamics, a particle in a box (PIB). To induce the particle dynamics, a linear potential tilting the bottom of the box is introduced, which is equivalent to imposing a constant electric field for a charged particle. Although the PIB model represents a closed system that cannot have a flow of electrons through the system, we consider the oscillatory dynamics of the particle probability density as the analogue of the electric current. Relating the amplitude and other parameters of the particle oscillatory dynamics with the gap between the ground and excited states of the PIB model allows us to demonstrate one of the most basic dependencies of electric conductivity on the valence-conduction band gap of the materia...
INTERACTION MODELS FOR EFFECTIVE THERMAL AND ELECTRIC CONDUCTIVITIES OF CARBON NANOTUBE COMPOSITES
Institute of Scientific and Technical Information of China (English)
Fei Deng; Quanshui Zheng
2009-01-01
The present article provides supplementary information of previous works of ana-lytic models for predicting conductivity enhancements of carbon nanotube composites. The mod-els, though fairly simple, are able to take account of the effects of conductivity anisotropy, non-straightness, and aspect ratio of the CNT additives on the conductivity enhancement of the com-posite and to give predictions agreeing well with existing experimental data. The omitted detailed derivation of this model is demonstrated in the present article with a more systematical analysis, which may help with further development in this direction. Furthermore, the effects of various orientation distributions of CNTs are reported here for the first time. The information may be useful in design or fabrication technology of CNT composites for better or specified conductivities.
A Model of Thermal Conductivity for Planetary Soils. 2; Theory for Cemented Soils
Piqueux, S.; Christensen, P. R.
2009-01-01
A numerical model of heat conduction through particulate media made of spherical grains cemented by various bonding agents is presented. The pore-filling gas conductivity, volume fraction, and thermal conductivity of the cementing phase are tunable parameters. Cement fractions thermal conductivity. A significant conductivity increase (factor 3-8) is observed for bond fractions of 0.01 to 1% in volume. In the 1 to 15% bond fraction domain, the conductivity increases continuously but less intensely (25-100% conductivity increase compared to a 1% bond system). Beyond 15% of cements, the conductivity increases vigorously and the bulk conductivity rapidly approaches that of bedrock. The composition of the cements (i.e. conductivity) has little influence on the bulk thermal inertia of the soil, especially if the volume of bond thermal inertia (200-600 J s(0.5)/sq m/K) has long been hypothesized to be associated with a duricrust. The fraction of cement required to fit the thermal data is less than approx.1-5% by volume. This small amount of material is consistent with orbital observations, confirming that soil cementation is an important factor controlling the thermal inertia of the Martian surface
Theoretical and experimental study of the thermal conductivity of nanoporous media
Institute of Scientific and Technical Information of China (English)
JIANG PeiXue; XIANG Heng; XU RuiNa
2012-01-01
The nanoparticle thermal conductivity and nanoscale thermal contact resistance were investigated by molecular dynamics (MD) simulations to further understand nanoscale porous media thermal conductivity.Macroscale porous media thermal conductivity models were then revised for nanoporous media.The effective thermal conductivities of two packed beds with nanoscale nickel particles and a packed bed with microscale nickel particles were then measured using the Hot Disk.The measured results show that the nano/microscale porous media thermal conductivities were much less than the thermal conductivities of the solid particles.Comparison of the measured and calculated results shows that the revised combined parallel-series model and the revised Hsu-Cheng model can accurately predict the effective thermal conductivities of micro-and nanoparticle packed beds.
Vijay, Venugopalan; Rao, Arun D.; Narayan, K. S.
2011-04-01
We report the changes in the surface electrical resistance, R, of conducting polymer, Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) films coated on appropriate flexible substrates in stretched conditions. These studies are important in the context of flexible organic electronic applications. In situ conductivity measurements on pristine PEDOT:PSS thin films on elastomeric substrates upon stretching reveal a minima in R as a function of strain, x, prior to the expected increase at higher strain levels. The studies emphasize (i) role of substrates, (ii) stress-induced anisotropic features, and temperature dependence of R (iii) in comparison of R(x) in polymer films to that of conventional metal films. The stress induced changes is modeled in terms of effective medium approximation.
Energy Technology Data Exchange (ETDEWEB)
Thielen, Joerg
2011-07-27
In view of both, energy density and energy drain, rechargeable lithium ion batteries outperform other present accumulator systems. However, despite great efforts over the last decades, the ideal electrolyte in terms of key characteristics such as capacity, cycle life, and most important reliable safety, has not yet been identified. Steps ahead in lithium ion battery technology require a fundamental understanding of lithium ion transport, salt association, and ion solvation within the electrolyte. Indeed, well defined model compounds allow for systematic studies of molecular ion transport. Thus, in the present work, based on the concept of immobilizing ion solvents, three main series with a cyclotriphosphazene (CTP), hexaphenylbenzene (HBP), and tetramethylcyclotetrasiloxane (TMS) scaffold were prepared. Lithium ion solvents, among others ethylene carbonate (EC), which has proven to fulfill together with propylene carbonate safety and market concerns in commercial lithium ion batteries, were attached to the different cores via alkyl spacers of variable length. All model compounds were fully characterized, pure and thermally stable up to at least 235 C, covering the requested broad range of glass transition temperatures from -78.1 C up to +6.2 C. While the CTP models tend to rearrange at elevated temperatures over time, which questions the general stability of alkoxide related (poly)phosphazenes, both, the HPB and CTP based models show no evidence of core stacking. In particular the CTP derivatives represent good solvents for various lithium salts, exhibiting no significant differences in the ionic conductivity {sigma}{sub dc} and thus indicating comparable salt dissociation and rather independent motion of cations and ions. In general, temperature-dependent bulk ionic conductivities investigated via impedance spectroscopy follow a William-Landel-Ferry (WLF) type behavior. Modifications of the alkyl spacer length were shown to influence ionic conductivities only in
Energy Technology Data Exchange (ETDEWEB)
Folsom, Charles [Utah State Univ., Logan, UT (United States). Mechanical and Aerospace Engineering Dept.; Xing, Changhu [Utah State Univ., Logan, UT (United States). Mechanical and Aerospace Engineering Dept.; Jensen, Colby [Utah State Univ., Logan, UT (United States). Mechanical and Aerospace Engineering Dept.; Ban, Heng [Utah State Univ., Logan, UT (United States). Mechanical and Aerospace Engineering Dept.; Marshall, Douglas W. [Idaho National Lab. (INL), Idaho Falls, ID (United States)
2015-03-01
Accurate modeling capability of thermal conductivity of tristructural-isotropic (TRISO) fuel compacts is important to fuel performance modeling and safety of Generation IV reactors. To date, the effective thermal conductivity (ETC) of tristructural-isotropic (TRISO) fuel compacts has not been measured directly. The composite fuel is a complicated structure comprised of layered particles in a graphite matrix. In this work, finite element modeling is used to validate an analytic ETC model for application to the composite fuel material for particle-volume fractions up to 40%. The effect of each individual layer of a TRISO particle is analyzed showing that the overall ETC of the compact is most sensitive to the outer layer constituent. In conjunction with the modeling results, the thermal conductivity of matrix-graphite compacts and the ETC of surrogate TRISO fuel compacts have been successfully measured using a previously developed measurement system. The ETC of the surrogate fuel compacts varies between 50 and 30 W m^{-1} K^{-1} over a temperature range of 50-600°C. As a result of the numerical modeling and experimental measurements of the fuel compacts, a new model and approach for analyzing the effect of compact constituent materials on ETC is proposed that can estimate the fuel compact ETC with approximately 15-20% more accuracy than the old method. Using the ETC model with measured thermal conductivity of the graphite matrix-only material indicate that, in the composite form, the matrix material has a much greater thermal conductivity, which is attributed to the high anisotropy of graphite thermal conductivity. Therefore, simpler measurements of individual TRISO compact constituents combined with an analytic ETC model, will not provide accurate predictions of overall ETC of the compacts emphasizing the need for measurements of composite, surrogate compacts.
Iden, Sascha; Peters, Andre; Durner, Wolfgang
2017-04-01
Soil hydraulic properties are required to solve the Richards equation, the most widely applied model for variably-saturated flow. While the experimental determination of the water retention curve does not pose significant challenges, the measurement of unsaturated hydraulic conductivity is time consuming and costly. The prediction of the unsaturated hydraulic conductivity curve from the soil water retention curve by pore-bundle models is a cost-effective and widely applied technique. A well-known problem of conductivity prediction for retention functions with wide pore-size distributions is the sharp drop in conductivity close to water saturation. This problematic behavior is well known for the van Genuchten model if the shape parameter n assumes values smaller than about 1.3. So far, the workaround for this artefact has been to introduce an explicit air-entry value into the capillary saturation function. However, this correction leads to a retention function which is not continuously differentiable and thus a discontinuous water capacity function. We present an improved parametrization of the hydraulic properties which uses the original capillary saturation function and introduces a maximum pore radius only in the pore-bundle model. Closed-form equations for the hydraulic conductivity function were derived for the unimodal and multimodal retention functions of van Genuchten and have been tested by sensitivity analysis and applied in curve fitting and inverse modeling of multistep outflow experiments. The resulting hydraulic conductivity function is smooth, increases monotonically close to saturation, and eliminates the sharp drop in conductivity close to saturation. Furthermore, the new model retains the smoothness and continuous differentiability of the water retention curve. We conclude that the resulting soil hydraulic functions are physically more reasonable than the ones predicted by previous approaches, and are thus ideally suited for numerical simulations
Electric Conduction in Semiconductors: A Pedagogical Model Based on the Monte Carlo Method
Capizzo, M. C.; Sperandeo-Mineo, R. M.; Zarcone, M.
2008-01-01
We present a pedagogic approach aimed at modelling electric conduction in semiconductors in order to describe and explain some macroscopic properties, such as the characteristic behaviour of resistance as a function of temperature. A simple model of the band structure is adopted for the generation of electron-hole pairs as well as for the carrier…
Addressing Conduct Disorder in Elementary School Children: An Application of the ASCA National Model
Demanchick, Stephen P.; Rangan, Malathi; Douthit, Kathryn
2006-01-01
The range of management strategies for school counselors dealing with conduct disorder in elementary school children can be expanded through an integration of several of the principles of the ASCA National Model[R]. This paper discusses ways the counselor can use the model to assist struggling children, teachers, administrators, and families as…
Johnson, Colena A; Winkelmann, Christopher T; Wise, L David
2014-09-01
Preclinical imaging technologies are increasingly being applied to developmental toxicology studies in drug development to determine potential compound toxicity. Although most of these studies are conducted in a non-regulatory setting, there is interest in performing these imaging studies under applicable regulations, for example Good Laboratory Practices (GLP), to support regulatory decisions concerning drug safety. This manuscript will describe regulations and processes to consider when bringing an imaging technology into GLP compliance.
Comparison among Models to Estimate the Shielding Effectiveness Applied to Conductive Textiles
Directory of Open Access Journals (Sweden)
Alberto Lopez
2013-01-01
Full Text Available The purpose of this paper is to present a comparison among two models and its measurement to calculate the shielding effectiveness of electromagnetic barriers, applying it to conductive textiles. Each one, models a conductive textile as either a (1 wire mesh screen or (2 compact material. Therefore, the objective is to perform an analysis of the models in order to determine which one is a better approximation for electromagnetic shielding fabrics. In order to provide results for the comparison, the shielding effectiveness of the sample has been measured by means of the standard ASTM D4935-99.
Cuk, S.; Middlebrook, R. D.
1977-01-01
A method for modelling switching converters in the discontinuous conduction mode is developed, whose starting point is the unified state-space representation, and whose end result is a complete linear circuit model which correctly represents all essential features, namely, the input, output, and transfer properties (static dc as well as dynamic ac small signal). While the method is generally applicable to any switching converter operating in the discontinuous conduction mode, it is extensively illustrated for the three common power stages (buck, boost, and buck-boost). The results for these converters are then easily tabulated owing to the fixed equivalent circuit topology of their canonical circuit model.
Kelley, Chris S; Naughton, James; Benson, Emma; Bradley, Ruth C; Lazarov, Vlado K; Thompson, Sarah M; Matthew, Jim A D
2014-01-22
A model of the magnetorefractive effect is developed for metallic oxides which allows the MRE to be used to study the magnetic dependence of their transport and phononic properties. This model is successfully applied to Fe3O4 and compared to experiments on a series of magnetite thin films of varying thickness (10, 18, 37, 64 and 110 nm) deposited on MgO(111) substrates. Reflection spectra were modelled as a function of film thickness, calculated from the Fresnel equations using an Fe3O4 dielectric function consisting of Drude, hopping, phononic and d-s transition conductivity processes. The reflectivity spectra of the different thickness films are reasonably reproduced by the model and reveal that the Fe3O4 18.5 μm phonon peak is shifted to a shorter wavelength in the thin films, approaching the bulk value for t > 110 nm. The MRE spectra are modelled by introducing a magnetic field dependence to the hopping and phononic terms, where previous models have considered the magnetic dependence to be on the Drude term only. In addition, the position of the Fe3O4 18.5 μm phonon peak was also found to shift in energy in the applied magnetic field by 0.05 μm. These results demonstrate the potential for using the MRE technique for probing the underlying magnetoelectronic properties of thin film oxides in a quick and non-destructive way.
Energy Technology Data Exchange (ETDEWEB)
Pike, J. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Reboul, S. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
2015-06-01
SRS High Level Waste Tank Farm personnel rely on conductivity probes for detection of incipient overflow conditions in waste tanks. Minimal information is available concerning the sensitivity that must be achieved such that that liquid detection is assured. Overly sensitive electronics results in numerous nuisance alarms for these safety-related instruments. In order to determine the minimum sensitivity required of the probe, Tank Farm Engineering personnel need adequate conductivity data to improve the existing designs. Little or no measurements of liquid waste conductivity exist; however, the liquid phase of the waste consists of inorganic electrolytes for which the conductivity may be calculated. Savannah River Remediation (SRR) Tank Farm Facility Engineering requested SRNL to determine the conductivity of the supernate resident in SRS waste Tank 40 experimentally as well as computationally. In addition, SRNL was requested to develop a correlation, if possible, that would be generally applicable to liquid waste resident in SRS waste tanks. A waste sample from Tank 40 was analyzed for composition and electrical conductivity as shown in Table 4-6, Table 4-7, and Table 4-9. The conductivity for undiluted Tank 40 sample was 0.087 S/cm. The accuracy of OLI Analyzer™ was determined using available literature data. Overall, 95% of computed estimates of electrical conductivity are within ±15% of literature values for component concentrations from 0 to 15 M and temperatures from 0 to 125 °C. Though the computational results are generally in good agreement with the measured data, a small portion of literature data deviates as much as ±76%. A simplified model was created that can be used readily to estimate electrical conductivity of waste solution in computer spreadsheets. The variability of this simplified approach deviates up to 140% from measured values. Generally, this model can be applied to estimate the conductivity within a factor of two. The comparison of the
Electrical conductance in a single wall carbon nanotube (SWCNT: tight binding model
Directory of Open Access Journals (Sweden)
T Mardaani
2010-03-01
Full Text Available In this study, we derive analytically Green’s function (GF formalism to calculate the electrical conductance for an armchair SWCNT in the ballistic regime. We obtain an exact analytical formula for the conductance of the SWCNT, in the tight-binding approach and assuming nearest-neighbor interaction by recursion process in the GF formalism. We show that in the presence of uniform external potential, the number of conductance channels and resonance energy range of the system decrease.
Brannon, Sean
2014-01-01
Magnetic reconnection in the corona results in contracting flare loops, releasing energy into plasma heating and shocks. The hydrodynamic shocks so produced drive thermal conduction fronts (TCFs) which transport energy into the chromosphere and drive upflows (evaporation) and downflows (condensation) in the cooler, denser footpoint plasma. Observations have revealed that certain properties of the transition point between evaporation and condensation (the "flow reversal point" or FRP), such as temperature and velocity-temperature derivative at the FRP, vary between different flares. These properties may provide a diagnostic tool to determine parameters of the coronal energy release mechanism and the loop atmosphere. In this study, we develop a 1-D hydrodynamical flare loop model with a simplified three-region atmosphere (chromosphere/transition region/corona), with TCFs initiated by shocks introduced in the corona. We investigate the effect of two different flare loop parameters (post-shock temperature and tra...
Directory of Open Access Journals (Sweden)
Dr. N. Mukhopadhyay
2015-05-01
Full Text Available In this project work a mathematical heat conduction model of a cold storage (with the help of computer program; and multiple regression analysis has been proposed which can be used for further development of cold storages in the upcoming future. In cold storage refrigeration system brings down the temperature initially during start up but thermal insulation maintains the temperature later on continuously. In this view, the simple methodology is presented to calculate heat transfer by analytical method also attempt has been made to minimize the energy consumption by replacing 150 mm Expanded polystyrene (EPS by 100 mm Poly Urethane foam (PUF insulation. The methodology is validated against actual data obtained from Penguin cold storage situated in Pune, India. Insulation thickness of the side walls (TW, area of the wall (AW, and insulation thickness of the roof (TR have been chosen as predictor variables of the study.
A test of an optimal stomatal conductance scheme within the CABLE land surface model
De Kauwe, M. G.; Kala, J.; Lin, Y.-S.; Pitman, A. J.; Medlyn, B. E.; Duursma, R. A.; Abramowitz, G.; Wang, Y.-P.; Miralles, D. G.
2015-02-01
Stomatal conductance (gs) affects the fluxes of carbon, energy and water between the vegetated land surface and the atmosphere. We test an implementation of an optimal stomatal conductance model within the Community Atmosphere Biosphere Land Exchange (CABLE) land surface model (LSM). In common with many LSMs, CABLE does not differentiate between gs model parameters in relation to plant functional type (PFT), but instead only in relation to photosynthetic pathway. We constrained the key model parameter "g1", which represents plant water use strategy, by PFT, based on a global synthesis of stomatal behaviour. As proof of concept, we also demonstrate that the g1 parameter can be estimated using two long-term average (1960-1990) bioclimatic variables: (i) temperature and (ii) an indirect estimate of annual plant water availability. The new stomatal model, in conjunction with PFT parameterisations, resulted in a large reduction in annual fluxes of transpiration (~ 30% compared to the standard CABLE simulations) across evergreen needleleaf, tundra and C4 grass regions. Differences in other regions of the globe were typically small. Model performance against upscaled data products was not degraded, but did not noticeably reduce existing model-data biases. We identified assumptions relating to the coupling of the vegetation to the atmosphere and the parameterisation of the minimum stomatal conductance as areas requiring further investigation in both CABLE and potentially other LSMs. We conclude that optimisation theory can yield a simple and tractable approach to predicting stomatal conductance in LSMs.
A test of an optimal stomatal conductance scheme within the CABLE Land Surface Model
Directory of Open Access Journals (Sweden)
M. G. De Kauwe
2014-10-01
Full Text Available Stomatal conductance (gs affects the fluxes of carbon, energy and water between the vegetated land surface and the atmosphere. We test an implementation of an optimal stomatal conductance model within the Community Atmosphere Biosphere Land Exchange (CABLE land surface model (LSM. In common with many LSMs, CABLE does not differentiate between gs model parameters in relation to plant functional type (PFT, but instead only in relation to photosynthetic pathway. We therefore constrained the key model parameter "g1" which represents a plants water use strategy by PFT based on a global synthesis of stomatal behaviour. As proof of concept, we also demonstrate that the g1 parameter can be estimated using two long-term average (1960–1990 bioclimatic variables: (i temperature and (ii an indirect estimate of annual plant water availability. The new stomatal models in conjunction with PFT parameterisations resulted in a large reduction in annual fluxes of transpiration (~ 30% compared to the standard CABLE simulations across evergreen needleleaf, tundra and C4 grass regions. Differences in other regions of the globe were typically small. Model performance when compared to upscaled data products was not degraded, though the new stomatal conductance scheme did not noticeably change existing model-data biases. We conclude that optimisation theory can yield a simple and tractable approach to predicting stomatal conductance in LSMs.
Kumar, Prashant; Topin, Frédéric
2017-08-01
It is often desirable to predict the effective thermal conductivity (ETC) of a homogenous material like open-cell foams based on its composition, particularly when variations in composition are expected. A combination of five fundamental simplified thermal conductivity bounds and models (series, parallel, Hashin-Shtrikman, effective medium theory, and reciprocity models) is proposed to predict ETC of open-cell foams. Usually, these models use a parameter as the weighted mean to account the proportion of each bound arranged in arithmetic and geometric schemes. Based on ETC data obtained on numerous virtual Kelvin-like foam samples, the dependence of this parameter has been deduced as a function of morphology and phase thermal conductivity ratio. Various effective thermal conductivity correlations are derived based on material properties and foam structure. This is valid for open-cell foams filled with any arbitrary working fluid over a solid conductivity of materials range (λs /λf = 10-30,000) and over a wide range of porosity (0.60 < ɛo < 0.95). Arrangement of series and parallel models together using the simplest models for both, arithmetic and geometric schemes, is found to predict excellent results among all the generic combinations.
Kumar, Prashant; Topin, Frédéric
2017-02-01
It is often desirable to predict the effective thermal conductivity (ETC) of a homogenous material like open-cell foams based on its composition, particularly when variations in composition are expected. A combination of five fundamental simplified thermal conductivity bounds and models (series, parallel, Hashin-Shtrikman, effective medium theory, and reciprocity models) is proposed to predict ETC of open-cell foams. Usually, these models use a parameter as the weighted mean to account the proportion of each bound arranged in arithmetic and geometric schemes. Based on ETC data obtained on numerous virtual Kelvin-like foam samples, the dependence of this parameter has been deduced as a function of morphology and phase thermal conductivity ratio. Various effective thermal conductivity correlations are derived based on material properties and foam structure. This is valid for open-cell foams filled with any arbitrary working fluid over a solid conductivity of materials range (λs /λf = 10-30,000) and over a wide range of porosity (0.60 < &epsilono < 0.95). Arrangement of series and parallel models together using the simplest models for both, arithmetic and geometric schemes, is found to predict excellent results among all the generic combinations.
Rabbi, Fazle
Dense mixed ionic-electronic conducting (MIEC) membranes consisting of ionic conductive perovskite-type and/or fluorite-type oxides and high electronic conductive spinel type oxides, at elevated temperature can play a useful role in a number of energy conversion related systems including the solid oxide fuel cell (SOFC), oxygen separation and permeation membranes, partial oxidization membrane reactors for natural gas processing, high temperature electrolysis cells, and others. This study will investigate the impact of different heterogeneous characteristics of dual phase ionic and electronic conductive oxygen separation membranes on their transport mechanisms, in an attempt to develop a foundation for the rational design of such membranes. The dielectric behavior of a material can be an indicator for MIEC performance and can be incorporated into computational models of MIEC membranes in order to optimize the composition, microstructure, and ultimately predict long term membrane performance. The dielectric behavior of the MIECs can also be an indicator of the transport mechanisms and the parameters they are dependent upon. For this study we chose a dual phase MIEC oxygen separation membrane consisting of an ionic conducting phase: gadolinium doped ceria-Ce0.8 Gd0.2O2 (GDC) and an electronic conductive phase: cobalt ferrite-CoFe2O4 (CFO). The membranes were fabricated from mixtures of Nano-powder of each of the phases for different volume percentages, sintered with various temperatures and sintering time to form systematic micro-structural variations, and characterized by structural analysis (XRD), and micro-structural analysis (SEM-EDS). Performance of the membranes was tested for variable partial pressures of oxygen across the membrane at temperatures from 850°C-1060°C using a Gas Chromatography (GC) system. Permeated oxygen did not directly correlate with change in percent mixture. An intermediate mixture 60%GDC-40%CFO had the highest flux compared to the 50%GDC
Global High-Latitude Conductivity Modeling: New Data and Improved Methods
McGranaghan, R. M.; Knipp, D. J.; Matsuo, T.; Godinez, H. C.
2014-12-01
The ionospheric conductivity distribution is essential for understanding the coupling in the magnetosphere-ionosphere-thermosphere (MIT) system. Hall conductivities, which regulate ionospheric current flow in the direction perpendicular to both the background magnetic field and the electric field, exert control over magnetospheric configuration, including transport within the plasmasphere and reconnection in the magnetotail [Lotko et al., 2014]. Pedersen conductivities control electric field variability and, in turn, determine the distribution and intensity of Joule heating, a prominent source of upper atmospheric temperature and neutral density enhancement. Contemporary conductivity modeling techniques rely on limiting assumptions and are 2-dimensional by design. Typically these models assume Maxwellian incoming particle energy distributions and simplistic current closure paths within an ionospheric 'shell' located at 110 km. We have developed a method to: 1) eliminate these assumptions and 2) allow 3-dimensional conductivity analysis using particle energy spectra provided by Defense Meteorological Satellite Program (DMSP) satellites. A sequential non-linear procedure then regresses the conductivities derived from DMSP data on the same basis functions used in the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure to obtain a realistic form of the covariance model, with the goal to integrate 3-dimensional conductivity analysis into the AMIE procedure. This addresses one of the primary sources of uncertainty within AMIE, and will ultimately allow more accurate characterization of high-latitude ionospheric electrodynamics. We present 3-dimensional conductivity distributions derived from satellite observations and global maps of these conductivities for the year 2010. References:Lotko, W., et al. (2014), Ionospheric control of magnetotail reconnection, Science, 345(6193), 184-187, doi:10.1126/science.1252907.
Early diagnosis of Carpal Tunnel Syndrome (CTS) in Indian patients by nerve conduction studies
2010-01-01
The present study was carried out for early confirmation of clinically diagnosed patients of Carpal Tunnel Syndrome (CTS) by electro-diagnostic tests which included motor conduction, sensory conduction studies and F-wave studies. The aim of the study was early confirmation of clinically suspected patients of CTS by motor and sensory conduction studies of median and ulnar nerves. Eighty subjects of age group 30-50 years (40 clinically suspected patients of CTS, 40 as control group) were studie...
Optimizing the transverse thermal conductivity of 2D-SiCf/SiC composites, I. Modeling
Energy Technology Data Exchange (ETDEWEB)
Youngblood, Gerald E.; Senor, David J.; Jones, Russell H.
2002-12-31
For potential fusion applications, considerable fabrication efforts have been directed to obtaining transverse thermal conductivity (Keff) values in excess of 30 W/mK (unirradiated) in the 800-1000°C temperature range for 2D-SiCf/SiC composites. To gain insight into the factors affecting Keff, at PNNL we have tested three different analytic models for predicting Keff in terms of constituent (fiber, matrix and interphase) properties. The tested models were: the Hasselman-Johnson (H-J) “2-Cylinder” model, which examines the effects of fiber-matrix (f/m) thermal barriers; the Markworth “3-Cylinder” model, which specifically examines the effects of interphase thickness and thermal conductivity; and a newly-developed Anisotropic “3-Square” model, which examines the potential effect of introducing a fiber coating with anisotropic properties to enhance (or diminish) f/m thermal coupling. The first two models are effective medium models, while the third model is a simple combination of parallel and series conductances. Model predictions suggest specific designs and/or development efforts directed to optimize the overall thermal transport performance of 2D-SiCf/SiC.
Dual conical conducting filament model in resistance switching TiO2 thin films.
Kim, Kyung Min; Park, Tae Hyung; Hwang, Cheol Seong
2015-01-19
The resetting behaviors of Pt/TiO2/Pt resistive switching (RS) cell in unipolar RS operations were studied in detail through an experiment and by modeling. The experiment showed that the apparently highly arbitrary resetting current-voltage (I-V) curves could be grouped into three types: normal, delayed, and abnormal behaviors. A dual conical conducting filament (CF) model was conceived, and their electrothermal behaviors were analytically described from the heat-balance and charge-transport equations. The almost spontaneous resetting behavior of the normal reset could be easily understood from the mutually constructive interference effect between the Joule heating and temperature-dependent resistance effect along the CF. The delayed reset could be explained by the time-dependent increase in the reset voltage during the rest process, which was most probably induced in the more conical-shaped CF. The abnormal reset could be understood from the temporal transfer of oxygen ions near the kink positions of the two different-diameter portions of the more cylindrical CFs, which temporally decreases the overall resistance immediately prior for the actual reset to occur. The accuracy of the dual conical CF model was further confirmed by adopting a more thorough electrothermal simulation package, COMSOL.
41 CFR 101-5.104-6 - Conduct of feasibility studies.
2010-07-01
... FEDERAL BUILDINGS AND COMPLEXES 5.1-General § 101-5.104-6 Conduct of feasibility studies. An initial... and detailed procedures to be followed in the conduct of each feasibility study. Arrangements will be... 41 Public Contracts and Property Management 2 2010-07-01 2010-07-01 true Conduct of...
Kretschmer, Tina; Hickman, Matthew; Doerner, Rita; Emond, Alan; Lewis, Glyn; Macleod, John; Maughan, Barbara; Munafo, Marcus R.; Heron, Jon
Although conduct problems in childhood are stably associated with problem outcomes, not every child who presents with conduct problems is at risk. This study extends previous studies by testing whether childhood conduct problem trajectories are predictive of a wide range of other health and behavior
Thermal conduction study of warm dense aluminum by proton differential heating
Ping, Y.; Kemp, G.; McKelvey, A.; Fernandez-Panella, A.; Shepherd, R.; Collins, G.; Sio, H.; King, J.; Freeman, R.; Hua, R.; McGuffey, C.; Kim, J.; Beg, F.
2016-10-01
A differential heating platform has been developed for thermal conduction study (Ping et al. PoP 2015), where a temperature gradient is induced and subsequent heat flow is probed by time-resolved diagnostics. An experiment using proton differential heating has been carried out at Titan laser for Au/Al targets. Two single-shot time-resolved diagnostics are employed, SOP (streaked optical pyrometry) for surface temperature and FDI (Fourier Domain Interferometry) for surface expansion. Hydrodynamic simulations show that after 15ps, absorption in underdense plasma needs to be taken into account to correctly interpret SOP data. Comparison between simulations with different thermal conductivity models and a set of data with varying target thickness will be presented. This work was performed under DOE contract DE-AC52-07NA27344 with support from OFES Early Career program and LLNL LDRD program.
Random free energy barrier hopping model for ac conduction in chalcogenide glasses
Murti, Ram; Tripathi, S. K.; Goyal, Navdeep; Prakash, Satya
2016-03-01
The random free energy barrier hopping model is proposed to explain the ac conductivity (σac) of chalcogenide glasses. The Coulomb correlation is consistently accounted for in the polarizability and defect distribution functions and the relaxation time is augmented to include the overlapping of hopping particle wave functions. It is observed that ac and dc conduction in chalcogenides are due to same mechanism and Meyer-Neldel (MN) rule is the consequence of temperature dependence of hopping barriers. The exponential parameter s is calculated and it is found that s is subjected to sample preparation and measurement conditions and its value can be less than or greater than one. The calculated results for a - Se, As2S3, As2Se3 and As2Te3 are found in close agreement with the experimental data. The bipolaron and single polaron hopping contributions dominates at lower and higher temperatures respectively and in addition to high energy optical phonons, low energy optical and high energy acoustic phonons also contribute to the hopping process. The variations of hopping distance with temperature is also studied. The estimated defect number density and static barrier heights are compared with other existing calculations.
Conduction in quasiperiodic and quasirandom lattices: Fibonacci, Riemann, and Anderson models
Varma, V. K.; Pilati, S.; Kravtsov, V. E.
2016-12-01
We study the ground state conduction properties of noninteracting electrons in aperiodic but nonrandom one-dimensional models with chiral symmetry and make comparisons against Anderson models with nondeterministic disorder. The first model we consider is the Fibonacci lattice, which is a paradigmatic model of quasicrystals; the second is the Riemann lattice, which we define inspired by Dyson's proposal on the possible connection between the Riemann hypothesis and a suitably defined quasicrystal. Our analysis is based on Kohn's many-particle localization tensor defined within the modern theory of the insulating state. In the Fibonacci quasicrystal, where all single-particle eigenstates are critical (i.e., intermediate between ergodic and localized), the noninteracting electron gas is found to be an insulator, due to spectral gaps, at various specific fillings ρ , including the values ρ =1 /gn , where g is the golden ratio and n is any integer; however away from these spectral anomalies, the system is found to be a conductor, including the half-filled case. In the Riemann lattice metallic behavior is found at half filling as well; however, in contrast to the Fibonacci quasicrystal, the Riemann lattice is generically an insulator due to single-particle eigenstate localization, likely at all other fillings. Its behavior turns out to be alike that of the off-diagonal Anderson model, albeit with different system-size scaling of the band-center anomalies. The advantages of analyzing the Kohn's localization tensor instead of other measures of localization familiar from the theory of Anderson insulators (such as the participation ratio or the Lyapunov exponent) are highlighted.
Johnston, Barbara M
2013-07-01
When using the bidomain model to model the electrical activity of the heart, there are potentially six cardiac conductivity values involved: conductivity values in directions along and normal to the cardiac fibres with a sheet, as well as a conductivity value in the normal direction between the sheets, and these occur for both the extracellular and intracellular domains in the model. To date it has been common to assume that the two normal direction conductivity values are the same. However, recent work has demonstrated that six cardiac conductivity values, rather than four, are necessary for accurate modelling, which can then facilitate understanding of cardiovascular disease. To design a method to determine these conductivities, it is also necessary to design a suitable multi-electrode array, which can be used, in conjunction with an inversion technique, to retrieve conductivity values from measurements of potential made on the array. This work uses the results of a study, into the sensitivity of the measuring potentials to variability in the input conductivities, to facilitate the design of an array that could be used to retrieve six cardiac conductivity values, as well as fibre rotation angle. It is found that if an electrode in the array has a much lower value of potential than the other electrodes, then it tends to be much more sensitive to the input conductivities than the other electrodes. It also appears that inclusion of this type of electrode in the set of measuring electrodes is essential for accurately retrieving conductivity values. This technique is used to identify electrodes to be included in the array and using the final design it is demonstrated, using synthetic values of potential, that the six cardiac conductivity values, and the fibre rotation angle, can be retrieved very accurately.
Multi-channel conduction in redox-based resistive switch modelled using quantum point contact theory
Energy Technology Data Exchange (ETDEWEB)
Miranda, E., E-mail: enrique.miranda@uab.cat; Suñé, J. [Departament d' Enginyeria Electrònica, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallés, Barcelona (Spain); Mehonic, A.; Kenyon, A. J. [Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE (United Kingdom)
2013-11-25
A simple analytic model for the electron transport through filamentary-type structures in Si-rich silica (SiO{sub x})-based resistive switches is proposed. The model is based on a mesoscopic description and is able to account for the linear and nonlinear components of conductance that arise from both fully and partially formed conductive channels spanning the dielectric film. Channels are represented by arrays of identical scatterers whose number and quantum transmission properties determine the current magnitude in the low and high resistance states. We show that the proposed model not only reproduces the experimental current-voltage (I-V) characteristics but also the normalized differential conductance (dln(I)/dln(V)-V) curves of devices under test.
Energy Technology Data Exchange (ETDEWEB)
Caillon-Caravanier, M.
2002-12-01
With the development of new electronic technologies, the research on gel electrolytes basic properties has been widely increased. The use of these materials, produced under thin plastic films, improves the stored energy - battery volume ratio. The ionic gel conductivity, liquid-type, is ensured by the ion migration in the liquid electrolyte incorporated to the polymer network. Thus a preliminary study of liquid phases to be incorporated has been done before the gel investigation. In order to optimize the conductive properties of liquid electrolytes, a simplified model of ionic conductivity has been established. It is based on the ion pair dissociation equilibrium. The ionic mobility is supposed to be inversely proportional to the macroscopic medium viscosity. The liquid electrolytes are then incorporated in the polymer network, based on di-acrylate monomers (DAC) or fluorinated copolymer (PVdF-HFP/SiO{sub 2}). The conductivity loss of the liquid encapsulated phases, more pronounced in the DAC case, is attributed to ion-polymer network interactions, which lead to a decrease of both the concentration and the mobility of free ions in the system. In the case of gel electrolytes DAC based, these interactions are quantified from an ionic transport model, which relies on the hypothesis of a 3D quasi-cubic reticulation. This hypothesis also allows anticipating the network maximal ability to contain the liquid phase. For gel electrolytes PVdF-HFP/SiO{sub 2} based, the kinetic study of the liquid phase absorption has allowed us to optimize the elaboration conditions. The ion-ion, ion-solvent and ion-polymer interactions have. been qualitatively and quantitatively studied by the mean of Raman spectroscopy. The performance of elaborated gel electrolytes is also estimated in cyclability terms towards commercial electrodes for lithium batteries. So the gel behavior has been studied with half-batteries associating a metal lithium electrode to a carbon anode or a lithiated cobalt
Lessons learnt from the first controlled human malaria infection study conducted in Nairobi, Kenya.
Hodgson, Susanne H; Juma, Elizabeth; Salim, Amina; Magiri, Charles; Njenga, Daniel; Molyneux, Sassy; Njuguna, Patricia; Awuondo, Ken; Lowe, Brett; Billingsley, Peter F; Cole, Andrew O; Ogwang, Caroline; Osier, Faith; Chilengi, Roma; Hoffman, Stephen L; Draper, Simon J; Ogutu, Bernhards; Marsh, Kevin
2015-04-28
Controlled human malaria infection (CHMI) studies, in which healthy volunteers are infected with Plasmodium falciparum to assess the efficacy of novel malaria vaccines and drugs, have become a vital tool to accelerate vaccine and drug development. CHMI studies provide a cost-effective and expeditious way to circumvent the use of large-scale field efficacy studies to deselect intervention candidates. However, to date few modern CHMI studies have been performed in malaria-endemic countries. An open-label, randomized pilot CHMI study was conducted using aseptic, purified, cryopreserved, infectious P. falciparum sporozoites (SPZ) (Sanaria® PfSPZ Challenge) administered intramuscularly (IM) to healthy Kenyan adults (n = 28) with varying degrees of prior exposure to P. falciparum. The purpose of the study was to establish the PfSPZ Challenge CHMI model in a Kenyan setting with the aim of increasing the international capacity for efficacy testing of malaria vaccines and drugs, and allowing earlier assessment of efficacy in a population for which interventions are being developed. This was part of the EDCTP-funded capacity development of the CHMI platform in Africa. This paper discusses in detail lessons learnt from conducting the first CHMI study in Kenya. Issues pertinent to the African setting, including community sensitization, consent and recruitment are considered. Detailed reasoning regarding the study design (for example, dose and route of administration of PfSPZ Challenge, criteria for grouping volunteers according to prior exposure to malaria and duration of follow-up post CHMI) are given and changes other centres may want to consider for future studies are suggested. Performing CHMI studies in an African setting presents unique but surmountable challenges and offers great opportunity for acceleration of malaria vaccine and drug development. The reflections in this paper aim to aid other centres and partners intending to use the CHMI model in Africa.
Martin, Neilson C.; Levy, Florence; Pieka, Jan; Hay, David A.
2006-01-01
Attention Deficit Hyperactivity Disorder (ADHD) commonly co-occurs with Oppositional Defiant Disorder, Conduct Disorder and Reading Disability. Twin studies are an important approach to understanding and modelling potential causes of such comorbidity. Univariate and bivariate genetic models were fitted to maternal report data from 2040 families of…
Practical modeling of acoustic losses in air due to heat conduction and viscosity
DEFF Research Database (Denmark)
Christensen, René; Juhl, Peter Møller; Cutanda Henríquez, Vicente
2008-01-01
Accurate acoustics models of small devices with cavities and narrow slits and ducts should include the socalled boundary layer attenuation caused by thermal conduction and viscosity. The purpose of this paper is to present and compare different methods for including these loss mechanisms in analy......Accurate acoustics models of small devices with cavities and narrow slits and ducts should include the socalled boundary layer attenuation caused by thermal conduction and viscosity. The purpose of this paper is to present and compare different methods for including these loss mechanisms...
43 CFR 404.47 - How will a feasibility study be conducted under this program?
2010-10-01
... 43 Public Lands: Interior 1 2010-10-01 2010-10-01 false How will a feasibility study be conducted... Studies § 404.47 How will a feasibility study be conducted under this program? Feasibility studies will be... feasibility study, including the Principles and Guidelines (incorporated by reference at § 404.4). You...
Xia, Hong; Luo, Zhendong
2017-01-01
In this study, we devote ourselves to establishing a stabilized mixed finite element (MFE) reduced-order extrapolation (SMFEROE) model holding seldom unknowns for the two-dimensional (2D) unsteady conduction-convection problem via the proper orthogonal decomposition (POD) technique, analyzing the existence and uniqueness and the stability as well as the convergence of the SMFEROE solutions and validating the correctness and dependability of the SMFEROE model by means of numerical simulations.
Liu, Hong; Akhtar, Zoheb; Li, Peiwen; Wang, Kai
2014-01-01
A proton-conductive solid oxide fuel cell (H-SOFC) has the advantage of operating at higher temperatures than a PEM fuel cell, but at lower temperatures than a SOFC. This study proposes a mathematical model for an H-SOFC in order to simulate the performance and optimize the flow channel designs. The model analyzes the average mass transfer and species’ concentrations in flow channels, which allows the determination of an average concentration polarization in anode and cathode gas channels, th...
Hong Liu; Zoheb Akhtar; Peiwen Li; Kai Wang
2014-01-01
A proton-conductive solid oxide fuel cell (H-SOFC) has the advantage of operating at higher temperatures than a PEM fuel cell, but at lower temperatures than a SOFC. This study proposes a mathematical model for an H-SOFC in order to simulate the performance and optimize the flow channel designs. The model analyzes the average mass transfer and species’ concentrations in flow channels, which allows the determination of an average concentration polarization in anode and cathode gas channels, t...
Auditory brain stem responses of premature infants to bone-conducted stimuli: a feasibility study.
Hooks, R G; Weber, B A
1984-01-01
The feasibility of bone conduction auditory brain stem response (ABR) audiometry in intensive care nursery neonates was investigated. Forty premature infants were tested with both air- and bone-conducted stimuli. Bone-conducted stimuli resulted in more identifiable ABRs and a greater number of subjects passing the hearing screening. The findings of this study suggest that bone conduction ABR audiometry is a feasible technique with premature infants. Due to the lower frequency composition of the bone-conducted click, it may be more effective than an air-conducted click when the immature cochlea is being evaluated.
A Model of Thermal Conductivity for Planetary Soils. 2; Theory for Cemented Soils
Piqueux, S.; Christensen, P. R.
2009-01-01
A numerical model of heat conduction through particulate media made of spherical grains cemented by various bonding agents is presented. The pore-filling gas conductivity, volume fraction, and thermal conductivity of the cementing phase are tunable parameters. Cement fractions conductivity. A significant conductivity increase (factor 3-8) is observed for bond fractions of 0.01 to 1% in volume. In the 1 to 15% bond fraction domain, the conductivity increases continuously but less intensely (25-100% conductivity increase compared to a 1% bond system). Beyond 15% of cements, the conductivity increases vigorously and the bulk conductivity rapidly approaches that of bedrock. The composition of the cements (i.e. conductivity) has little influence on the bulk thermal inertia of the soil, especially if the volume of bond <10%. These results indicate that temperature measurements are sufficient to detect cemented soils and quantify the amount of cementing phase, but the mineralogical nature of the bonds and the typical grain size are unlikely to be determined from orbit. On Mars, a widespread surface unit characterized by a medium albedo (0.19-0.26) and medium/high thermal inertia (200-600 J s(0.5)/sq m/K) has long been hypothesized to be associated with a duricrust. The fraction of cement required to fit the thermal data is less than approx.1-5% by volume. This small amount of material is consistent with orbital observations, confirming that soil cementation is an important factor controlling the thermal inertia of the Martian surface
Modeling of heat evolution in silicate building materials with electrically conductive admixtures
Fiala, Lukáš; Maděra, Jiří; Vejmelková, Eva; Černý, Robert
2016-12-01
Silicate building materials are electrically non-conductive, in general. However, a sufficient amount of electrically conductive admixtures can significantly increase their electrical conductivity. Consequently, new practical applications of such materials are available. Materials with enhanced electrical properties can be used as self-sensing sensors monitoring evolution of cracks, electromagnetic shields or cores of deicing systems. This paper deals with the modeling of heat evolution in silicate building materials by the action of passing electric current. Due to the conducting paths formed in the material's matrix by adding a sufficient amount of electrically conductive admixture and applying electric voltage on the installed electrodes, electric current is passing through the material. Thanks to the electric current, Joule heat is successively evolved. As it is crucial to evaluate theoretically the amount of evolved heat in order to assess the effectiveness of such a system, a model describing the Joule heat evolution is proposed and a modeling example based on finite-element method is introduced.
High-frequency magneto-conductivity studies of low-dimensional organic conductors
Energy Technology Data Exchange (ETDEWEB)
Schrama, J.M
2000-07-01
In this thesis I present experimental studies of the millimetre-wave magneto-conductivity of the organic charge-transfer salts {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2}, {alpha}-(BEDT-TTF){sub 2}KHg(SCN){sub 4} and (TMTSF){sub 2}ClO{sub 4}. A rotating resonant cavity insert was developed to investigate the angle dependence of resonances in the magneto-conductivity. The technique revealed a new kind of magnetic resonance, the Fermi-surface traversal resonance (FTR), which is described by a semiclassical model. The FTRs give information about the topology of the quasi-one-dimensional (Q1D) Fermi-surface sections. The Q1D Fermi-surface sections play an important role in forming the ground states in organic conductors giving rise, for example, to nesting associated with a density-wave. Chapter 1 gives a brief historical overview of the development of organic conductors and provides basic information about crystal structures and Fermi surfaces of BEDT-TTF based systems. Chapter 2 introduces the reader to basic solid state physics used later in the thesis. In Chapter 3 I discuss the operation of the experimental techniques and apparatus, including millimetre-wave techniques. In addition, Chapter 3 contains a description of the design of the FTR rotating cavity insert which is unique of its kind. In Chapter 4 a model of oscillating real-space velocity vectors is presented. The model is used to explain the origin of the FTRs observed in the high-frequency magneto- conductivity data. In Chapter 5 I report two studies of the angle dependence of FTRs in the high-frequency magneto-conductivity. The FTRs in {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2} and {alpha}-(BEDT- TTF){sub 2}KHg(SCN){sub 4} show two previously unknown corrugations in the Q1D Fermi-surface sections of the two materials. The FTRs in {alpha}-(BEDT-TTF){sub 2}KHg(SCN){sub 4} are investigated both in the density-wave state and near its collapse into a high-temperature, high-field state. In Chapter 6 a study of the
Tamma, Kumar K.; Railkar, Sudhir B.
1988-01-01
The present paper describes the applicability of hybrid transfinite element modeling/analysis formulations for nonlinear heat conduction problems involving phase change. The methodology is based on application of transform approaches and classical Galerkin schemes with finite element formulations to maintain the modeling versatility and numerical features for computational analysis. In addition, in conjunction with the above, the effects due to latent heat are modeled using enthalpy formulations to enable a physically realistic approximation to be dealt computationally for materials exhibiting phase change within a narrow band of temperatures. Pertinent details of the approach and computational scheme adapted are described in technical detail. Numerical test cases of comparative nature are presented to demonstrate the applicability of the proposed formulations for numerical modeling/analysis of nonlinear heat conduction problems involving phase change.
Kubo-Greenwood approach to conductivity in dense plasmas with average atom models
Starrett, C E
2016-01-01
A new formulation of the Kubo-Greenwood conductivity for average atom models is given. The new formulation improves upon previous by explicitly including the ionic-structure factor. Calculations based on this new expression lead to much improved agreement with ab initio results for DC conductivity of warm dense hydrogen and beryllium, and for thermal conductivity of hydrogen. We also give and test a slightly modified Ziman-Evans formula for the resistivity that includes a non-free electron density of states, thus removing an ambiguity in the original Ziman-Evans formula. Again results based on this expression are in good agreement with ab initio simulations for warm dense beryllium and hydrogen. However, for both these expressions, calculations of the electrical conductivity of warm dense aluminum lead to poor agreement at low temperatures compared to ab initio simulations.
Space-charge-controlled field emission model of current conduction through Al2O3 films
Hiraiwa, Atsushi; Matsumura, Daisuke; Kawarada, Hiroshi
2016-02-01
This study proposes a model for current conduction in metal-insulator-semiconductor (MIS) capacitors, assuming the presence of two sheets of charge in the insulator, and derives analytical formulae of field emission (FE) currents under both negative and positive bias. Since it is affected by the space charge in the insulator, this particular FE differs from the conventional FE and is accordingly named the space-charge-controlled (SCC) FE. The gate insulator of this study was a stack of atomic-layer-deposition Al2O3 and underlying chemical SiO2 formed on Si substrates. The current-voltage (I-V) characteristics simulated using the SCC-FE formulae quantitatively reproduced the experimental results obtained by measuring Au- and Al-gated Al2O3/SiO2 MIS capacitors under both biases. The two sheets of charge in the Al2O3 films were estimated to be positive and located at a depth of greater than 4 nm from the Al2O3/SiO2 interface and less than 2 nm from the gate. The density of the former is approximately 1 × 1013 cm-2 in units of electronic charge, regardless of the type of capacitor. The latter forms a sheet of dipoles together with image charges in the gate and hence causes potential jumps of 0.4 V and 1.1 V in the Au- and Al-gated capacitors, respectively. Within a margin of error, this sheet of dipoles is ideally located at the gate/Al2O3 interface and effectively reduces the work function of the gate by the magnitude of the potential jumps mentioned above. These facts indicate that the currents in the Al2O3/SiO2 MIS capacitors are enhanced as compared to those in ideal capacitors and that the currents in the Al-gated capacitors under negative bias (electron emission from the gate) are more markedly enhanced than those in the Au-gated capacitors. The larger number of gate-side dipoles in the Al-gated capacitors is possibly caused by the reaction between the Al and Al2O3, and therefore gate materials that do not react with underlying gate insulators should be chosen
Brannon, Sean; Longcope, D.
2013-07-01
Magnetic reconnection in the corona results in contracting flare loops, releasing energy into plasma heating and shocks. These hydrodynamic shocks drive thermal conduction fronts (TCFs), which deposit energy into the chromosphere, driving upflows (evaporation) and downflows (condensation) across a range of temperatures. Observations have revealed that the transition between evaporation and condensation, the "velocity reversal point" (VRP), occurs at a characteristic temperature and with a characteristic slope, which vary between different flares. In this study, we develop a 1-D hydrodynamical flare loop model with a simplified three-region atmosphere (chromosphere / transition region (TR) / corona), with TCFs initiated by piston shocks introduced in the corona. We investigate the effect of three different flare loop parameters (post-shock temperature, TR temperature ratio, and TR thickness) on the temperature and slope of the VRP. We find that both of the evaporation characteristics have power-law relationships to the varied flare parameters, and we report the scaling exponents for our model. Finally, we develop a method to determine the best-fit post-shock temperature and TR temperature ratio based on the observed quantities, and discuss the results for two sets of published data.
Bui, Khoa; Papavassiliou, Dimitrios
2012-02-01
The effective thermal conductivity (Keff) of carbon nanotube (CNT) composites is affected by the thermal boundary resistance (TBR) and by the dispersion pattern and geometry of the CNTs. We have previously modeled CNTs as straight cylinders and found that the TBR between CNTs (TBRCNT-CNT) can suppress Keff at high volume fractions of CNTs [1]. Effective medium theory results assume that the CNTs are in a perfect dispersion state and exclude the TBRCNT-CNT [2]. In this work, we report on the development of an algorithm for generating CNTs with worm-like geometry in 3D, and with different persistence lengths. These worm-like CNTs are then randomly placed in a periodic box representing a realistic state, since the persistence length of a CNT can be obtained from microscopic images. The use of these CNT geometries in conjunction with off-lattice Monte Carlo simulations [1] in order to study the effective thermal properties of nanocomposites will be discussed, as well as the effects of the persistence length on Keff and comparisons to straight cylinder models. References [1] K. Bui, B.P. Grady, D.V. Papavassiliou, Chem. Phys. Let., 508(4-6), 248-251, 2011 [2] C.W. Nan, G. Liu, Y. Lin, M. Li, App. Phys. Let., 85(16), 3549-3551, 2006
Degueldre, C.; Arima, T.; Lee, Y. W.
2003-06-01
An inert matrix fuel material based on yttria-stabilized cubic zirconia: Er xY yPu zZr 1- x- y- zO 2-( x + y)/2 ( x+ y=0.15, z: [0.05-0.15]) was proposed for burning excess plutonium in light water reactors. The studied inert matrix fuel is made of cubic stabilized zirconia. The limited number of experimental thermal conductivity data justifies this formal and intensive study. Approaches derived from Klemens theory were revisited and the derived conductivity model applied for zirconia, accounting the effects of phononic scattering centers. The hyperbolic thermal conductivity trend with temperature known for pure zirconia, is reduced by isotopes, impurities, dopants and oxygen vacancies, which act as scattering centers and contribute to conductivity reduction to a flat plot with temperature for stabilized zirconia. It is experimentally observed that the thermal conductivity derived from laser flash measurements for Er xY yM zZr 1- x- y- zO 2-( x + y)/2 (with M=Ce or Pu, z=0 or ˜0.1 and x+ y=0.15) is rather constant as a function of temperature in the range 300-1000 K. The thermal conductivity was observed to depend on the concentration of dopants such as YO 1.5 and/or ErO 1.5, CeO 2 (analogous of PuO 2) or PuO 2. The bulk material conductivity of Er 0.05Y 0.10Pu 0.10Zr 0.75O 1.925 is about 2 W m -1 K -1. In this study, the thermal conductivity data of both monoclinic and stabilized cubic zirconia based IMF are tested with the model approach in order to understand the experimental data in a semi-quantitative way.
Effective Thermal Conductivity For Drift-Scale Models Used In TSPA-SR
Energy Technology Data Exchange (ETDEWEB)
N.D. Francis
2001-01-25
The objective of this calculation is to develop a time dependent in-drift effective thermal conductivity parameter that will approximate heat conduction, thermal radiation, and natural convection heat transfer using a single mode of heat transfer (heat conduction). In order to reduce the physical and numerical complexity of the heat transfer processes that occur (and must be modeled) as a result of the emplacement of heat generating wastes, a single parameter will be developed that approximates all forms of heat transfer from the waste package surface to the drift wall (or from one surface exchanging heat with another). Subsequently, with this single parameter, one heat transfer mechanism (e.g., conduction heat transfer) can be used in the models. The resulting parameter is to be used as input in the drift-scale process-level models applied in total system performance assessments for the site recommendation (TSPA-SR). The format of this parameter will be a time-dependent table for direct input into the thermal-hydrologic (TH) and the thermal-hydrologic-chemical (THC) models.
Development of a LSSVM-GC model for estimating the electrical conductivity of ionic liquids
DEFF Research Database (Denmark)
Gharagheizi, Farhad; Ilani-Kashkouli, Poorandokht; Sattari, Mehdi
2014-01-01
In this communication, an extensive set of 1077 experimental electrical conductivity data for 54 ionic liquids (ILs) was collected from 21 different literature sources. Using this dataset, a reliable least square support vector machine-group contribution (LSSVM-GC) model has been developed, which...
Research on modeling and conduction disturbance simulation of secondary power system in a device
Ding, Xu; Yu, Zhi-Yong; Jin, Rui
2017-06-01
To find electromagnetic interference (EMI) and other problems in the secondary power supply system design quickly and effectively, simulations are carried out under the Saber simulation software platform. The DC/DC converter model with complete performance and electromagnetic characteristics is established by combining parametric modeling with Mast language. By using the method of macro modeling, the hall current sensor and power supply filter model are established respectively based on the function, schematic diagram of the components. Also the simulation of the component model and the whole secondary power supply system are carried out. The simulation results show that the proposed model satisfies the functional requirements of the system and has high accuracy. At the same time, due to the ripple characteristics in the DC/DC converter modeling, it can be used as a conducted interference model to simulate the power bus conducted emission CE102 project under the condition that the simulated load is full, which provides a useful reference for the electromagnetic interference suppression of the system.
Henke, Stephan; Trieloff, Mario
2016-01-01
The construction of models for the internal constitution and the temporal evolution of large planetesimals, the parent bodies of chondrites, requires information on the heat conductivity of the complex mixture of minerals and iron metal found in chondrites. It is attempted to evaluate the heat conductivity of a multi-component mineral mixture and granular medium from the heat conductivities of its mixture components. Random mixtures of solids with chondritic composition and packings of spheres are numerically generated. The heat conduction equation is solved in high spatial resolution for a test cube filled with such matter. From the heat flux through the cube the heat conductivity of the mixture is derived. The model results for porous material are consistent with data for compacted sandstone, but are at odds with measurements for H and L chondrites. The discrepancy is traced back to shock modification of the currently available meteoritic material by impacts on the parent body over the last 4.5 Ga. This cau...
A Collection of Studies Conducted in Education about "Global Warming" Problem
Bozdogan, Aykut Emre
2011-01-01
The studies global warming problem conducted in education discipline in the world and in Turkey were analysed for this study. The literature was reviewed extensively especially through the articles in the indexed journals of Ebsco Host, Science Direct, Taylor and Francis and Web of Science databases and this study was conducted according to the…
Liu, L; Patey, G N
2014-11-14
The conduction rate of water through (8,8) and (9,9) carbon nanotubes at 300 K and a pressure difference of 220 MPa is investigated using molecular dynamics simulations. The TIP3P, SPC/E, and TIP4P/2005 water models are considered. The pressure-driven flow rate is found to be strongly model dependent for both nanotubes. The fastest model (TIP3P) has a flow rate that is approximately five times faster than the slowest (TIP4P/2005). It is shown that the flow rate is significantly influenced by the structure taken on by the water molecules confined in the nanotube channels. The slower models, TIP4P/2005 and SPC/E, tend to favor stacked ring arrangements, with the molecules of a ring moving together through the nanotube, in what we term a "cluster-by-cluster" conduction mode. Confined TIP3P water has a much weaker tendency to form ring structures, and those that do form are fragile and break apart under flow conditions. This creates a much faster "diffusive" conduction mode where the water molecules mainly move through the tube as individual particles, rather than as components of a larger cluster. Our results demonstrate that water models developed to describe the properties of bulk water can behave very differently in confined situations.
Plate Fin Heat Exchanger Model with Axial Conduction and Variable Properties
Hansen, B J; Klebaner, A; 10.1063/1.4706971
2012-01-01
Future superconducting radio frequency (SRF) cavities, as part of Project X at Fermilab, will be cooled to superfluid helium temperatures by a cryogenic distribution system supplying cold supercritical helium. To reduce vapor fraction during the final Joule-Thomson (J-T) expansion into the superfluid helium cooling bath, counter-flow, plate-fin heat exchangers will be utilized. Due to their compact size and ease of fabrication, plate-fin heat exchangers are an effective option. However, the design of compact and high-effectiveness cryogenic heat exchangers operating at liquid helium temperatures requires consideration of axial heat conduction along the direction of flow, in addition to variable fluid properties. Here we present a numerical model that includes the effects of axial conduction and variable properties for a plate fin heat exchanger. The model is used to guide design decisions on heat exchanger material choice and geometry. In addition, the J-T expansion process is modeled with the heat exchanger ...
A Novel Equivalent Agglomeration Model for Heat Conduction Enhancement in Nanofluids
Sui, Jize; Zheng, Liancun; Zhang, Xinxin; Chen, Ying; Cheng, Zhengdong
2016-01-01
We propose a multilevel equivalent agglomeration (MEA) model in which all particles in an irregular cluster are treated as a new particle with equivalent volume, the liquid molecules wrapping the cluster and in the gaps are considered to assemble on the surface of new particle as mixing nanolayer (MNL), the thermal conductivity in MNL is assumed to satisfy exponential distribution. Theoretical predictions for thermal conductivity enhancement are highly in agreement with the classical experimental data. Also, we first try to employ TEM information quantitatively to offer probable reference agglomeration ratio (not necessary a very precise value) to just test rational estimations range by present model. The comparison results indicate the satisfactory priori agglomeration ratio estimations range from renovated model. PMID:26777389
On The Construction of Models for Electrical Conduction in Biological Tissues
Gómez-Aguilar, F.; Bernal-Alvarado, J.; Cordova-Fraga, T.; Rosales-García, J.; Guía-Calderón, M.
2010-12-01
Applying RC circuit theory, a theoretical representation for the electrical conduction in a biological multilayer system was developed. In particular an equivalent circuit for the epidermis, dermis and the subcutaneous tissue was constructed. This model includes an equivalent circuit, inside the dermis, in order to model a small formation like tumor. This work shows the feasibility to apply superficial electrodes to detect subcutaneous abnormalities. The behavior of the model is shown in the form of a frequency response chart. The Bode and Nyquist plots are also obtained. This theoretical frame is proposed to be a general treatment to describe the bioelectrical transport in a three layer bioelectrical system.
Energy Technology Data Exchange (ETDEWEB)
Abiddin, Jamal Farghali Bin Zainal [Faculty of Applied Sciences, Universiti Teknologi MARA, 40450 Shah Alam, Selangor D.E. (Malaysia); Ahmad, Azizah Hanom [Faculty of Applied Sciences, Universiti Teknologi MARA, 40450 Shah Alam, Selangor D.E. (Malaysia); Institute of Science, Universiti Teknologi MARA, 40450 Shah Alam, Selangor D.E. (Malaysia)
2015-08-28
Sodium ion (Na{sup +}) based solid polymer electrolyte (SPE) has been prepared using solution cast technique with distilled water as solvent and Methylcellulose (MC) as a polymer host. Methylcellulose polymer was chosen as the polymer host due to the abundance of lone pair electrons in the carbonyl and C-O-C constituents, which in turn provide multiple hopping sites for the Na{sup +} conducting ions. Variable compositions of sodium iodide (NaI) salt were prepared to investigate the optimum MC-NaI weight ratio. Results from Electrical Impedance Spectroscopy (EIS) technique show that pure methylcellulose has a low conductivity of 3.61 × 10{sup −11} S/cm.The conductivity increases as NaI content increases up to optimum NaIcomposition of 40 wt%, which yields an average conductivity of 2.70 × 10{sup −5} S/cm.
Molecular dynamics study on thermal conductivity of na-noscale thin films
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
A simple and effective model of heat conduction across thin films is set up and molecular dynamics simulations are implemented to explore the thermal conductivity of nanoscale thin dielectric films in the direction perpendicular to the film plane. Solid argon is selected as the model system due to its reliable experimental data and potential function. Size effects of the thermal conductivity across thin films are found by computer simulations: in a film thickness range of 2-10 nm, the conductivity values are remarkably lower than the corresponding bulk experimental data and increase as the thickness increases. The consistency between the approximate solution of the phonon Boltzmann transport equation and the simulation results ascribes the thermal conductivity size effect to the phonon scattering at film boundaries.
Practical Issues of Conducting a Q Methodology Study: Lessons Learned From a Cross-cultural Study.
Stone, Teresa Elizabeth; Maguire, Jane; Kang, Sook Jung; Cha, Chiyoung
2016-12-06
This article advances nursing research by presenting the methodological challenges experienced in conducting a multination Q-methodology study. This article critically analyzes the relevance of the methodology for cross-cultural and nursing research and the challenges that led to specific responses by the investigators. The use of focus groups with key stakeholders supplemented the Q-analysis results. The authors discuss practical issues and shared innovative approaches and provide best-practice suggestions on the use of this flexible methodology. Q methodology has the versatility to explore complexities of contemporary nursing practice and cross-cultural health research.
Mulhearn, Tyler J; Watts, Logan L; Todd, E Michelle; Medeiros, Kelsey E; Connelly, Shane; Mumford, Michael D
2017-01-01
Although recent evidence suggests ethics education can be effective, the nature of specific training programs, and their effectiveness, varies considerably. Building on a recent path modeling effort, the present study developed and validated a predictive modeling tool for responsible conduct of research education. The predictive modeling tool allows users to enter ratings in relation to a given ethics training program and receive instantaneous evaluative information for course refinement. Validation work suggests the tool's predicted outcomes correlate strongly (r = 0.46) with objective course outcomes. Implications for training program development and refinement are discussed.
Energy Technology Data Exchange (ETDEWEB)
Leu, W.; Greber, E. [Geoform, Geologische Beratungen und Studien AG, Winterthur (Switzerland); Hopkirk, R.J. [Polydynamics Engineering, Maennedorf (Switzerland); Keller, B. [Mengis und Lorenz AG, Luzern (Switzerland); Rybach, L. [ETH Hoenggerberg, Zuerich (Switzerland). Inst. fuer Geophysik und Radiometrie
1997-12-01
Detailed knowledge of the geothermal properties (thermal conductivity and specific heat capacity) of the undergorund becomes more and more important with increasing exploitation of geothermal resources by deep vertical borehole heat exchangers or by seasonal storage installations. For this pilot study all existing thermal conductivity data of the Swiss Molasse were compiled and supplemented with new laboratory measurements on core and cutting samples from deep wells (2.5 to 3.0 W/mK). In a second step top-to-bottom thermal conductivity profiles were calculated from geophysical well logs. These profiles show a clear dependence on lithology and variations in thermal conductivity of up to 1 W/mK over 50-200 m thick intervals. In clay-rich lithofacies thermal conductivity is only slightly dependent on the sedimentary architecture, whereas, in sandy facies obvious distinctions are possible. The modelling of a theoretical 750 m long vertical borehole heat exchanger shows that the potential quality of extractable heat increases or decreases by up to 20% by varying the thermal conductivity with only {+-}0.5 W/mK. (orig.) [Deutsch] Fuer die Nutzung geothermischer Ressourcen mit tiefen Erdwaermesonden und saisonalen Speicheranlagen werden detaillierte Kenntnisse der geothermischen Eigenschaften (Waermeleitfaehigkeit und Waemekapazitaet) des Untergrundes zunehmend wichtig. Im Rahmen dieser Pilotstudie wurden saemtliche verfuegbaren Waermeleitfaehigkeits-Daten von Schweizer Molassegesteinen kompiliert und mit Neumessungen an Kern- und Cuttingsmaterial von Tiefbohrungen ergaenzt (2.5 bis 3.0 W/mK). In einem zweiten Schritt wurden Waermeleitfaehigkeits-Profile mit geophysikalischen Bohr-Logs berechnet. Diese Profile zeigen eine deutliche Abhaengigkeit von der Lithologie mit einer Variation der Waermeleitfaehigkeit von bis zu 1 W/mK ueber 50-200 m maechtige Intervalle. In den tonigen Lithologien kann nur eine schwache Abhaengigkeit der Waermeleitfaehigkeit von der sedimentaeren
Fullea, J.; Muller, M.R.; Jones, A. G.
2011-01-01
The electrical conductivity of mantle minerals is highly sensitive to parameters that characterize the structure and state of the lithosphere and sublithospheric mantle, and mapping its lateral and vertical variations gives insights into formation and deformation processes. We review state-of-the-art conductivity models based on laboratory studies for the most relevant upper mantle minerals and define a bulk conductivity model for the upper mantle that accounts for temperature, pressure, and ...
Optical conductivity and resistivity in the two-band Emery model
Minh-Tien, Tran
1994-01-01
The temperature- and frequency-dependent conductivity due to the scattering of oxygen holes by antiferromagnetic spin fluctuations of the copper spins in the two-band Emergy model is calculated. Using the dynamic spin susceptibility obtained in the mean-field Schwinger boson approach, the resistivity obeys a near linear temperature dependence at high temperatures, whereas at low temperatures a quadratic behaviour holds. At the same time, the optical conductivity contains the Drude peak around zero frequency, whereas the scattering rate of quasiparticle appears to be proportional to frequency. Our results are essentially in agreement with experiments, at least qualitatively, and support the conclusion that the normal-state basal-plane resistivity and optical conductivity of high- Tc superconductors may be explained by two-dimensional spin-fluctuation scattering in the Fermi-liquid picture.
Rumor Propagation Model: An Equilibrium Study
Directory of Open Access Journals (Sweden)
José Roberto C. Piqueira
2010-01-01
information is analogous phenomena. Here, in an analogy with the SIR (Susceptible-Infected-Removed epidemiological model, the ISS (Ignorant-Spreader-Stifler rumor spreading model is studied. By using concepts from the Dynamical Systems Theory, stability of equilibrium points is established, according to propagation parameters and initial conditions. Some numerical experiments are conducted in order to validate the model.
DEFF Research Database (Denmark)
Jakobsen, Ida Skytte; Fergusson, David; Horwood, John L.
2012-01-01
This study used dato from a 30-year longitudinal study to esamine the associations between early conduct problems, school achievement and later crime. The analysis showed that, even following extensive adjustment for confounding, both early conduct problems and later educational achievement made...
Mathematical model for solar drying of potato cylinders with thermal conductivity radially modulated
Trujillo Arredondo, Mariana
2014-05-01
A mathematical model for drying potato cylinders using solar radiation is proposed and solved analytically. The model incorporates the energy balance for the heat capacity of the potato, the radiation heat transfer from the potato toward the drying chamber and the solar radiation absorbed by the potato during the drying process. Potato cylinders are assumed to exhibit a thermal conductivity which is radially modulated. The method of the Laplace transform, with integral Bromwich and residue theorem will be applied and the analytic solutions for the temperature profiles in the potato cylinder will be derived in the form of an infinite series of Bessel functions, when the thermal conductivity is constant; and in the form of an infinite series of Heun functions, when the thermal conductivity has a linear radial modulation. All computations are performed using computer algebra, specifically Maple. It is expected that the analytical results obtained will be useful in food engineering and industry. Our results suggest some lines for future investigations such as the adoption of more general forms of radial modulation for the thermal conductivity of potato cylinders; and possible applications of other computer algebra software such as Maxima and Mathematica.
Directory of Open Access Journals (Sweden)
Roberta Porretta
2016-07-01
Full Text Available A mathematical model of water diffusion in the vadose zone has been implemented for different types of soil textures in order to determine the soil water content (SWC profiles in dependence of depth and time. From these profiles, obtained for different soils, we derived the characteristic electrical parameters, such as relative permittivity (epsilonr and electrical conductivity (sigma, and their variation in time, employing empirical relations available in the scientific literature. The simulation through mathematical models has been performed taking into account different types of soils characterized by the percentage composition of sand, clay and silt in the textural triangle, which provides some physical and chemical properties that affect the water retention in the soil. The resulting simulated profiles of SWC and consequently permittivity and conductivity profiles, span over a certain range of values suggesting the best techniques and the limits in geophysical investigation. Moreover this a-prior knowledge helps in the elaboration and interpretation of permittivity and conductivity data obtained by the measurements. Permittivity and conductivity profiles are particularly useful in some environmental applications when the soil textures are (or supposed to be known as in the typical case of landfill leachate dispersion. Since the soil textures beneath or nearby a disposal waste are characterized by a SWC, the values of (epsilonr and (sigma at various depth can be directly inferred.
Stephenson, Robert S; Atkinson, Andrew; Kottas, Petros; Perde, Filip; Jafarzadeh, Fatemeh; Bateman, Mike; Iaizzo, Paul A; Zhao, Jichao; Zhang, Henggui; Anderson, Robert H; Jarvis, Jonathan C; Dobrzynski, Halina
2017-08-03
Cardiac arrhythmias and conduction disturbances are accompanied by structural remodelling of the specialised cardiomyocytes known collectively as the cardiac conduction system. Here, using contrast enhanced micro-computed tomography, we present, in attitudinally appropriate fashion, the first 3-dimensional representations of the cardiac conduction system within the intact human heart. We show that cardiomyocyte orientation can be extracted from these datasets at spatial resolutions approaching the single cell. These data show that commonly accepted anatomical representations are oversimplified. We have incorporated the high-resolution anatomical data into mathematical simulations of cardiac electrical depolarisation. The data presented should have multidisciplinary impact. Since the rate of depolarisation is dictated by cardiac microstructure, and the precise orientation of the cardiomyocytes, our data should improve the fidelity of mathematical models. By showing the precise 3-dimensional relationships between the cardiac conduction system and surrounding structures, we provide new insights relevant to valvar replacement surgery and ablation therapies. We also offer a practical method for investigation of remodelling in disease, and thus, virtual pathology and archiving. Such data presented as 3D images or 3D printed models, will inform discussions between medical teams and their patients, and aid the education of medical and surgical trainees.
Comparison of Measured and Modelled Hydraulic Conductivities of Fractured Sandstone Cores
Baraka-Lokmane, S.; Liedl, R.; Teutsch, G.
- A new method for characterising the detailed fracture geometry in sandstone cores is presented. This method is based on the impregnation of samples with coloured resin, without significant disturbance of the fractures. The fractures are made clearly visible by the resin, thus allowing the fracture geometry to be examined digitally. In order to model the bulk hydraulic conductivity, the samples are sectioned serially perpendicular to the flow direction. The hydraulic conductivity of individual sections is estimated by summing the contribution of the matrix and each fracture from the digital data. Finally, the hydraulic conductivity of the bulk sample is estimated by a harmonic average in series along the flow path. Results of this geometrical method are compared with actual physical conductivity values measured from fluid experiments carried out prior to sectioning. The predicted conductivity from the fracture geometry parameters (e.g., fracture aperture, fracture width, fracture length and fracture relative roughness all measured using an optical method) is in good agreement with the independent physical measurements, thereby validating the approach.
Occupational exposure to pesticides and nerve conduction studies among Korean farmers.
Park, Su Kyeong; Kong, Kyoung Ae; Cha, Eun Shil; Lee, Young Joo; Lee, Gyu Taek; Lee, Won Jin
2012-01-01
This study aimed to determine whether occupational exposure to pesticides was associated with decreased nerve conduction studies among farmers. On 2 separate occasions, the authors performed a cross-sectional study of a group of 31 male farmers who periodically applied pesticides. The study included questionnaire interviews and nerve conduction studies on the median, ulnar, posterior tibial, peroneal, and sural nerves. Although all mean values remained within laboratory normal limits, significant differences between the first and second tests were found in sensory conduction velocities on the median and sural nerves, and motor conduction velocities on the posterior tibial nerve. Lifetime days of pesticide application was negatively associated with nerve conduction velocities at most nerves after adjusting for potential confounders. These findings may reflect a link between occupational pesticide exposure and peripheral neurophysiologic abnormality that deserves further evaluation.
Jatnieks, J.; Popovs, K.; Klints, I.; Timuhins, A.; Kalvans, A.; Delina, A.; Saks, T.
2012-04-01
The cover of Quaternary sediments especially in formerly glaciated territories usually is the most complex part of the sedimentary sequences. In regional hydro-geological models it is often assumed as a single layer with uniform or calibrated properties (Valner 2003). However, the properties and structure of Quaternary sediments control the groundwater recharge: it can either direct the groundwater flow horizontally towards discharge in topographic lows or vertically, recharging groundwater in the bedrock. This work aims to present calibration results and detail our experience while integrating a scalable generalization of hydraulic conductivity for Quaternary strata in the regional groundwater modelling system for the Baltic artesian basin - MOSYS V1. We also present a method for solving boundary transitions between spatial clusters of lithologically similar structure. In this study the main unit of generalization is the spatial cluster. Clusters are obtained from distance calculations combining the Normalized Compression Distance (NCD) metric, calculated by the CompLearn parameter-free machine learning toolkit, with normalized Euclidean distance measures for coordinates of the borehole log data. A hierarchical clustering solution is used for obtaining cluster membership identifier for each borehole. Using boreholes as generator points for Voronoi tessellation and dissolving resulting polygons according to their cluster membership attribute, allows us to obtain spatial regions representing a certain degree of similarity in lithological structure. This degree of similarity and the spatial heterogeneity of the cluster polygons can be varied by different flattening of the hierarchical cluster model into variable number of clusters. This provides a scalable generalization solution which can be adapted according to model calibration performance. Using the dissimilarity matrix of the NCD metric, a borehole most similar to all the others from the lithological structure
Lattice Thermal Conductivity of Superlattices from an Adiabatic Bond Charge Model
Ward, Alistair; Broido, David
2007-03-01
The adiabatic bond charge model (ABCM) has successfully rendered phonon dispersions of a host of bulk semiconductors [1,2] and has also been used to calculate the phonon dispersions in quantum well superlattices [3]. We have developed an ABCM for superlattices and combined it with a symmetry-based representation of the anharmonic interatomic forces to calculate the lattice thermal conductivity of short-period superlattices, using an iterative solution to the Boltzmann-Peierls equation [4]. We compare our ABCM results with those obtained from some commonly used models for the interatomic forces in semiconductors to assess the importance of accurate descriptions of the phonon dispersions in thermal conductivity calculations. [1] W. Weber, Physical Review B 15, 4789 (1977). [2] K. C. Rustagi and W. Weber, Solid State Communications 18, 673 (1976). [3] S. K. Yip and Y. C. Chang, Physical Review B 30 7037 (1984). [4] D. A. Broido, A. Ward, and N. Mingo, Physical Review B 72, 014308 (2005).
Modeling of the optical properties of a two-dimensional system of small conductive particles.
Kondikov, A. A.; Tonkaev, P. A.; Chaldyshev, V. V.; Vartanyan, T. A.
2016-08-01
Software was developed for quick numerical calculations and graphic display of the absorption, reflection and transmittance spectra of two-dimensional systems of small conductive particles. It allowed us to make instant comparison of calculation results and experimental data. A lattice model was used to simulate nearly distributed particles, and the coherent-potential approximation was applied to obtain a solution to the problem of interacting particles. The Delphi programming environment was used.
From non-degenerate conducting polymers to dense matter in the massive Gross-Neveu model
Thies, M; Thies, Michael; Urlichs, Konrad
2005-01-01
Using results from the theory of non-degenerate conducting polymers like cis-polyacetylene, we generalize our previous work on baryonic matter in the massless Gross-Neveu model to finite bare fermion mass. In the large N limit, the exact ground state is constructed analytically, in close analogy to the bipolaron lattice in polymers. These findings are contrasted to the standard scenario with a first order phase transition as a function of density.
Borojeni, Azadeh A T; Noga, Michelle L; Martin, Andrew R; Finlay, Warren H
2015-07-16
This work describes in vitro measurement of the total pressure loss at varying flow rate through anatomically realistic conducting airway replicas of 10 children, 4 to 8 years old, and 5 adults. Experimental results were compared with analytical predictions made using published airway resistance models. For the adult replicas, the model proposed by van Ertbruggen et al. (2005. J. Appl. Physiol. 98, 970-980) most accurately predicted central conducting airway resistance for inspiratory flow rates ranging from 15 to 90 L/min. Models proposed by Pedley et al. (1970. J. Respir. Physiol. 9, 371-386) and by Katz et al. (2011. J. Biomech. 44, 1137-1143) also provided reasonable estimates, but with a tendency to over predict measured pressure loss for both models. For child replicas, the Pedley and Katz models both provided good estimation of measured pressure loss at flow rates representative of resting tidal breathing, but under predicted measured values at high inspiratory flow rate (60 L/min). The van Ertbruggen model, developed based on flow simulations performed in an adult airway model, tended to under predict measured pressure loss through the child replicas across the range of flow rates studied (2 to 60 L/min). These results are intended to provide guidance for selection of analytical pressure loss models for use in predicting airway resistance and ventilation distribution in adults and children. Copyright © 2015 Elsevier Ltd. All rights reserved.
Development of a Field-Aligned Integrated Conductivity Model Using the SAMI2 Open Source Code
Hildebrandt, Kyle; Gearheart, Michael; West, Keith
2003-03-01
The SAMI2 open source code is a middle and low latitude ionspheric model developed by the Naval Research Lab for the dual purposes of research and education. At the time of this writing the source code has no component for the integrated magnetic field-aligned conductivity. The dependence of human activities on conditions in the space environment, such as communications, has grown and will continue to do so. With this growth comes higher financial stakes, as changes in the space environment have greater economic impact. In order to minimize the adverse effects of these changes, predictive models are being developed. Among the geophysical parameters that affect communications is the conductivity in the ionosphere. As part of the commitment of Texas A & M Univeristy-Commerce to build a strong undergraduate research program, a team consisting of two students and a faculty mentor are developing a model of the integrated field-aligned conductivity using the SAMI2 code. The current status of the research and preliminary results are presented as well as a summary of future work.
Energy Technology Data Exchange (ETDEWEB)
Moscicki, J. K.; Sokolowska, D.; Dziob, D.; Nowak, J. [Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krakow (Poland); Kwiatkowski, L. [Department of Econometrics and Operations Research, Cracow University of Economics, Rakowicka 27, 31-510 Krakow (Poland)
2014-02-15
A simplified data analysis protocol, for dielectric spectroscopy use to study conductivity percolation in dehydrating granular media is discussed. To enhance visibility of the protonic conductivity contribution to the dielectric loss spectrum, detrimental effects of either low-frequency dielectric relaxation or electrode polarization are removed. Use of the directly measurable monofrequency dielectric loss factor rather than estimated DC conductivity to parameterize the percolation transition substantially reduces the analysis work and time.
Moscicki, J K; Sokolowska, D; Kwiatkowski, L; Dziob, D; Nowak, J
2014-02-01
A simplified data analysis protocol, for dielectric spectroscopy use to study conductivity percolation in dehydrating granular media is discussed. To enhance visibility of the protonic conductivity contribution to the dielectric loss spectrum, detrimental effects of either low-frequency dielectric relaxation or electrode polarization are removed. Use of the directly measurable monofrequency dielectric loss factor rather than estimated DC conductivity to parameterize the percolation transition substantially reduces the analysis work and time.
Directory of Open Access Journals (Sweden)
J. Raffiea Baseri
2012-01-01
Full Text Available This study analyses the feasibility of removing Direct Blue 71 from aqueous solution by different adsorbents such as activated carbon (TPAC and Poly pyrrole polymer composite (PPC prepared from Thevetia Peruviana. Batch mode adsorption was performed to investigate the adsorption capacities of these adsorbents by varying initial dye concentration, temperature, agitation time and pH. The performance of TPAC was compared with PPC. Among the adsorbents, PPC had more adsorption capacity (88.24% than TPAC (58.82% at an initial concentration of 50 mg/L and at 30°C. The experimental data best fitted with pseudo second order kinetic model. The adsorption data fitted well for Langmuir adsorption isotherm. Thermodynamic parameters for the adsorbents were also evaluated. The carbon embedded in conducting polymers matrix show better adsorptive properties than activated carbon.
Study of ac hopping conductivity on one-dimensional nanometre systems
Institute of Scientific and Technical Information of China (English)
徐慧; 宋祎璞
2002-01-01
In this paper, we establish a one-dimensional random nanocrystalline chain model, we derive a new formula of ac electron-phonon-field conductance for electron tunnelling transfer in one-dimensional nanometre systems. By calculating the ac conductivity, the relationship between the electric field, temperature and conductivity is analysed, and the effect of crystalline grain size and distortion of interfacial atoms on the ac conductance is discussed. A characteristic of negative differential dependence of resistance and temperature in the low-temperature region for a nanometre system is found. The ac conductivity increases linearly with rising frequency of the electric field, and it tends to increase as the crystalline grain size increases and to decrease as the distorted degree of interfacial atoms increases.
Nikolić, Dalibor; Milošević, Žarko; Saveljić, Igor; Filipović, Nenad
2015-12-01
Vibration of the skull causes a hearing sensation. We call it Bone Conduction (BC) sound. There are several investigations about transmission properties of bone conducted sound. The aim of this study was to develop a software tool for easy generation of the finite element (FE) model of the human head with different materials based on human head anatomy and to calculate sound conduction through the head. Developed software tool generates a model in a few steps. The first step is to do segmentation of CT medical images (DICOM) and to generate a surface mesh files (STL). Each STL file presents a different layer of human head with different material properties (brain, CSF, different layers of the skull bone, skin, etc.). The next steps are to make tetrahedral mesh from obtained STL files, to define FE model boundary conditions and to solve FE equations. This tool uses PAK solver, which is the open source software implemented in SIFEM FP7 project, for calculations of the head vibration. Purpose of this tool is to show impact of the bone conduction sound of the head on the hearing system and to estimate matching of obtained results with experimental measurements.
Plate Fin Heat Exchanger Model with Axial Conduction and Variable Properties
Energy Technology Data Exchange (ETDEWEB)
Hansen, B.J.; White, M.J.; Klebaner, A.; /Fermilab
2011-06-10
Future superconducting radio frequency (SRF) cavities, as part of Project X at Fermilab, will be cooled to superfluid helium temperatures by a cryogenic distribution system supplying cold supercritical helium. To reduce vapor fraction during the final Joule-Thomson (J-T) expansion into the superfluid helium cooling bath, counter-flow, plate-fin heat exchangers will be utilized. Due to their compact size and ease of fabrication, plate-fin heat exchangers are an effective option. However, the design of compact and high-effectiveness cryogenic heat exchangers operating at liquid helium temperatures requires consideration of axial heat conduction along the direction of flow, in addition to variable fluid properties. Here we present a numerical model that includes the effects of axial conduction and variable properties for a plate fin heat exchanger. The model is used to guide design decisions on heat exchanger material choice and geometry. In addition, the J-T expansion process is modeled with the heat exchanger to analyze the effect of heat load and cryogenic supply parameters. A numerical model that includes the effects of axial conduction and variable properties for a plate fin heat exchanger was developed and the effect of various design parameters on overall heat exchanger size was investigated. It was found that highly conductive metals should be avoided in the design of compact JT heat exchangers. For the geometry considered, the optimal conductivity is around 3.5 W/m-K and can range from 0.3-10 W/m-K without a large loss in performance. The model was implemented with an isenthalpic expansion process. Increasing the cold side inlet temperature from 2K to 2.2 K decreased the liquid fraction from 0.856 to 0.839 which corresponds to a 0.12 g/s increase in supercritical helium supply needed to maintain liquid level in the cooling bath. Lastly, it was found that the effectiveness increased when the heat load was below the design value. Therefore, the heat exchanger
Romano, Vittorio; Naddeo, Carlo; Guadagno, Liberata; Vertuccio, Luigi
2014-05-01
Aim of this work is to study the effect clay on the thermal conductivity of epoxy resin filled with CNTs. Experiments and theoretical predictions show that the presence of hydrotalcite clay in a mesh of carbon nanotubes gives rise to aggregates and twisted bundles, resulting in a lower carbon nanotubes length and a lower thermal conductivity of epoxy nanocomposites.
Oxidation of clean silicon surfaces studied by four-point probe surface conductance measurements
DEFF Research Database (Denmark)
Petersen, Christian Leth; Grey, Francois; Aono, M.
1997-01-01
We have investigated how the conductance of Si(100)-(2 x 1) and Si(111)-(7 x 7) surfaces change during exposure to molecular oxygen. A monotonic decrease in conductance is seen as the (100) surfaces oxidizes. In contract to a prior study, we propose that this change is caused by a decrease in sur...
Conductance of Alkanedithiol Single-Molecule Junctions: A Molecular Dynamics Study
DEFF Research Database (Denmark)
Paulsson, Magnus; Krag, Casper; Frederiksen, Thomas;
2009-01-01
We study formation and conductance of alkanedithiol junctions using density functional based molecular dynamics. The formation involves straightening of the molecule, migration of thiol end-groups, and pulling out Au atoms. Plateaus are found in the low-bias conductance traces which decrease by 1...
First-Year Students' Expectations of Conduct and Consequence: A Case Study
Crance Gutmann, Gina-Lyn
2008-01-01
Research on first-year students' expectations about college has explored areas of academic and social expectations, but not first-year college students' expectations about judicial conduct and consequence. The purpose of this study was to empirically explore two questions: what are first year students' expectations about campus conduct and…
Indian Academy of Sciences (India)
Jagjiwanram; Ramvir Singh
2004-08-01
A theoretical model has been developed for real two-phase system assuming linear flow of heat flux lines having ellipsoidal particles arranged in a three-dimensional cubic array. The arrangement has been divided into unit cells, each of which contains an ellipsoid. The resistor model has been applied to determine the effective thermal conductivity (ETC) of the unit cell. To take account of random packing of the phases, non-uniform shape of the particles and non-linear flow of heat flux lines in real systems, incorporating an empirical correction factor in place of physical porosity modifies an expression for ETC. An effort is made to correlate it in terms of the ratio of thermal conductivities of the constituents and the physical porosity. Theoretical expression so obtained has been tested on a large number of samples cited in the literature and found that the values predicted are quite close to the experimental results. Comparison of our model with different models cited in the literature has also been made.
Energy Technology Data Exchange (ETDEWEB)
Dhuley, R. C. [Fermilab; Hollister, M. I. [Fermilab; Ruschman, M. K. [Fermilab; Martin, L. D. [Fermilab; Schmitt, R. L. [Fermilab; Tatkowski, Tatkowski,G.L. [Fermilab; Bauer, D. a. [Fermilab; Lukens, P. T. [Fermilab
2017-09-13
The detectors of the Super Cryogenic Dark Matter Search experiment at SNOLAB (SuperCDMS SNOLAB) will operate in a seven-layered cryostat with thermal stages between room temperature and the base temperature of 15 mK. The inner three layers of the cryostat, which are to be nominally maintained at 1 K, 250 mK, and 15 mK, will be cooled by a dilution refrigerator via conduction through long copper stems. Bolted and mechanically pressed contacts, at and cylindrical, as well as exible straps are the essential stem components that will facilitate assembly/dismantling of the cryostat. These will also allow for thermal contractions/movements during cooldown of the sub-Kelvin system. To ensure that these components and their contacts meet their design thermal conductance, prototypes were fabricated and cryogenically tested. The present paper gives an overview of the SuperCDMS SNOLAB sub-Kelvin architecture and its conductance requirements. Results from the conductance measurements tests and from sub-Kelvin thermal modeling are discussed.
Radionuclides in fruit systems: Model-model intercomparison study
Energy Technology Data Exchange (ETDEWEB)
Linkov, I. [Cambridge Environmental, 58 Charles Street, Cambridge, MA 02141 (United States)]. E-mail: linkov@cambridgeenvironmental.com; Carini, F. [Universita Cattolica del Sacro Cuore, Faculty of Agricultural Sciences, Institute of Agricultural and Environmental Chemistry, Via Emilia Parmense, 84, I-29100 Piacenza (Italy); Collins, C. [T.H. Huxley School of Environment, Earth Sciences and Engineering (United Kingdom); Eged, K. [Department of Radiochemistry, University of Veszprem, P.O. Box 158 H-8201, H-8200 Veszprem (Hungary); Mitchell, N.G. [Mouchel Consulting Ltd., West Hall, Parvis Road, West Byfleet, Surrey, KT14 6EZ (United Kingdom); Mourlon, C. [Institute of Protection and Nuclear Safety (IPSN)/Division of Environmental Protection (DPRE), Laboratory of Environmental Modelling - LMODE, CE/Cadarache, 13 108 St Paul-lez-Durance Cedex (France); Ould-Dada, Z. [Food Standards Agency, Radiological Protection and Research Management Division, Aviation House, 125 Kingsway, Room 715B, London WC2B 6NH (United Kingdom); Robles, B. [CIEMAT, Dept. de Impacto Ambiental (DIAE), Edif. 3A, Avenida Complutense 22, E-28040 Madrid (Spain); Sweeck, L. [SCK.CEN, Boeretang 200, 2400 Mol (Belgium); Venter, A. [Enviros Consulting Ltd., Telegraphic House, Waterfront Quay, Salford Quays, Greater Manchester, M50 3XW (United Kingdom)
2006-07-01
Modeling is widely used to predict radionuclide distribution following accidental radionuclide releases. Modeling is crucial in emergency response planning and risk communication, and understanding model uncertainty is important not only in conducting analysis consistent with current regulatory guidance, but also in gaining stakeholder and decision-maker trust in the process and confidence in the results. However, while methods for dealing with parameter uncertainty are fairly well developed, an adequate representation of uncertainties associated with models remains rare. This paper addresses uncertainty about a model's structure (i.e., the relevance of simplifying assumptions and mathematical equations) that is seldom addressed in practical applications of environmental modeling. The use of several alternative models to derive a range of model outputs or risks is probably the only available technique to assess consistency in model prediction. Since each independent model requires significant resources for development and calibration, multiple models are not generally applied to the same problem. This study uses results from one such model intercomparison conducted by the Fruits Working Group, which was created under the International Atomic Energy Agency (IAEA) BIOMASS (BIOsphere Modelling and ASSessment) Program. Model-model intercomparisons presented in this study were conducted by the working group for two different scenarios (acute or continuous deposition), one radionuclide ({sup 137}Cs), and three fruit-bearing crops (strawberries, apples, and blackcurrants). The differences between models were as great as five orders of magnitude for short-term predictions following acute radionuclide deposition. For long-term predictions and for the continuous deposition scenario, the differences between models were about two orders of magnitude. The difference between strawberry, apple, and blackcurrant contamination predicted by one model is far less than the
Radionuclides in fruit systems. Model-model intercomparison study
Energy Technology Data Exchange (ETDEWEB)
Linkov, I. [Cambridge Environmental, 58 Charles Street, Cambridge, MA 02141 (United States); Carini, F. [Universita Cattolica del Sacro Cuore, Faculty of Agricultural Sciences, Institute of Agricultural and Environmental Chemistry, Via Emilia Parmense, 84, I-29100 Piacenza (Italy); Collins, C. [T.H. Huxley School of Environment, Earth Sciences and Engineering (United Kingdom); Eged, K. [Department of Radiochemistry, University of Veszprem, P.O. Box 158 H-8201, H-8200 Veszprem (Hungary); Mitchell, N.G. [Mouchel Consulting Ltd., West Hall, Parvis Road, West Byfleet, Surrey, KT14 6EZ (United Kingdom); Mourlon, C. [Institute of Protection and Nuclear Safety IPSN, Division of Environmental Protection (DPRE), Laboratory of Environmental Modelling LMODE, CE/Cadarache, 13 108 St Paul-lez-Durance (France); Ould-Dada, Z. [Food Standards Agency, Radiological Protection and Research Management Division, Aviation House, 125 Kingsway, Room 715B, London WC2B 6NH (United Kingdom); Robles, B. [CIEMAT, Dept. de Impacto Ambiental (DIAE), Edif. 3A, Avenida Complutense 22, E-28040 Madrid (Spain); Sweeck, L. [SCK-CEN, Boeretang 200, 2400 Mol (Belgium); Venter, A. [Enviros Consulting Ltd., Telegraphic House, Waterfront Quay, Salford Quays, Greater Manchester, M50 3XW (United Kingdom)
2006-07-01
Modeling is widely used to predict radionuclide distribution following accidental radionuclide releases. Modeling is crucial in emergency response planning and risk communication, and understanding model uncertainty is important not only in conducting analysis consistent with current regulatory guidance, but also in gaining stakeholder and decision-maker trust in the process and confidence in the results. However, while methods for dealing with parameter uncertainty are fairly well developed, an adequate representation of uncertainties associated with models remains rare. This paper addresses uncertainty about a model's structure (i.e., the relevance of simplifying assumptions and mathematical equations) that is seldom addressed in practical applications of environmental modeling. The use of several alternative models to derive a range of model outputs or risks is probably the only available technique to assess consistency in model prediction. Since each independent model requires significant resources for development and calibration, multiple models are not generally applied to the same problem. This study uses results from one such model intercomparison conducted by the Fruits Working Group, which was created under the International Atomic Energy Agency (IAEA) BIOMASS (BIOsphere Modelling and ASSessment) Program. Model-model intercomparisons presented in this study were conducted by the working group for two different scenarios (acute or continuous deposition), one radionuclide ({sup 137}Cs), and three fruit-bearing crops (strawberries, apples, and blackcurrants). The differences between models were as great as five orders of magnitude for short-term predictions following acute radionuclide deposition. For long-term predictions and for the continuous deposition scenario, the differences between models were about two orders of magnitude. The difference between strawberry, apple, and blackcurrant contamination predicted by one model is far less than the
Gheribi, Aïmen E.; Poncsák, Sándor; Guérard, Sébastien; Bilodeau, Jean-François; Kiss, László; Chartrand, Patrice
2017-03-01
During aluminium electrolysis, a ledge of frozen electrolytes is generally formed, attached to the sides of the cells. This ledge acts as a protective layer, preventing erosion and chemical attacks of both the electrolyte melt and the liquid aluminium on the side wall materials. The control of the sideledge thickness is thus essential in ensuring a reasonable lifetime for the cells. The key property for modelling and predicting the sideledge thickness as a function of temperature and electrolyte composition is the thermal conductivity. Unfortunately, almost no data is available on the thermal conductivity of the sideledge. The aim of this work is to alleviate this lack of data. For seven different samples of sideledge microstructures, recovered from post-mortem industrial electrolysis cells, the thermal diffusivity, the density, and the phase compositions were measured in the temperature range of 423 K to 873 K. The thermal diffusivity was measured with a laser flash technique and the average phase compositions by X-ray diffraction analysis. The thermal conductivity of the sideledge is deduced from the present experimental thermal diffusivity and density, and the thermodynamically assessed heat capacity. In addition to the present experimental work, a theoretical model for the prediction of the effective thermal transport properties of the sideledge microstructure is also proposed. The proposed model considers an equivalent microstructure and depends on phase fractions, porosity, and temperature. The strength of the model lies in the fact that only a few key physical properties are required for its parametrization and they can be predicted with a good accuracy via first principles calculations. It is shown that the theoretical predictions are in a good agreement with the present experimental measurements.
Magnetic properties of the α -T3 model: Magneto-optical conductivity and the Hofstadter butterfly
Illes, E.; Nicol, E. J.
2016-09-01
The α -T3 model interpolates between the pseudospin S =1 /2 honeycomb lattice of graphene and the pseudospin S =1 dice lattice via parameter α . We present calculations of the magnetic properties of this hybrid pseudospin model, namely the absorptive magneto-optical conductivity and the Hofstadter butterfly spectra. In the magneto-optics curves, signatures of the hybrid system include a doublet structure present in the peaks, resulting from differing Landau level energies in the K and K' valleys. In the Hofstadter spectra, we detail the evolution of the Hofstadter butterfly as it changes its periodicity by a factor of three as we vary between the two limiting cases of the α -T3 model.
Electronic conductance model in constricted MoS{sub 2} with nanopores
Energy Technology Data Exchange (ETDEWEB)
Sarathy, Aditya [Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Illinois 61801 (United States); Department of Electrical and Computer Engineering, University of Illinois, Urbana, Illinois 61801 (United States); Leburton, Jean-Pierre, E-mail: jleburto@illinois.edu [Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Illinois 61801 (United States); Department of Electrical and Computer Engineering, University of Illinois, Urbana, Illinois 61801 (United States); Department of Physics, University of Illinois, Urbana, Illinois 61801 (United States)
2016-02-01
We describe a self-consistent model for electronic transport in a molybdenum di-sulphide (MoS{sub 2}) layer containing a nanopore in a constricted geometry. Our approach is based on a semi-classical thermionic Poisson-Boltzmann technique using a two-valley model within the effective mass approximation to investigate perturbations caused by the nanopore on the electronic current. In particular, we show that the effect of the nanopore on the conductance is reduced as the nanopore is moved from the center to the layer edges. Our model is applied to the detection of DNA translocating through the nanopore, which reveals current features similar to those as predicted in nanopore graphene layers.
Directory of Open Access Journals (Sweden)
Hong Liu
2014-01-01
Full Text Available A proton-conductive solid oxide fuel cell (H-SOFC has the advantage of operating at higher temperatures than a PEM fuel cell, but at lower temperatures than a SOFC. This study proposes a mathematical model for an H-SOFC in order to simulate the performance and optimize the flow channel designs. The model analyzes the average mass transfer and species’ concentrations in flow channels, which allows the determination of an average concentration polarization in anode and cathode gas channels, the proton conductivity of electrolyte membranes, as well as the activation polarization. An electrical circuit for the current and proton conduction is applied to analyze the ohmic losses from an anode current collector to a cathode current collector. The model uses relatively less amount of computational time to find the V-I curve of the fuel cell, and thus it can be applied to compute a large amount of cases with different flow channel dimensions and operating parameters for optimization. The modeling simulation results agreed satisfactorily with the experimental results from literature. Simulation results showed that a relatively small total width of flow channel and rib, together with a small ratio of the rib’s width versus the total width, are preferable for obtaining high power densities and thus high efficiency.
Experimental and numerical study on thermal conductivity of partially saturated unconsolidated sands
Lee, Youngmin; Keehm, Youngseuk; Kim, Seong-Kyun; Shin, Sang Ho
2016-04-01
A class of problems in heat flow applications requires an understanding of how water saturation affects thermal conductivity in the shallow subsurface. We conducted a series of experiments using a sand box to evaluate thermal conductivity (TC) of partially saturated unconsolidated sands under varying water saturation (Sw). We first saturated sands fully with water and varied water saturation by drainage through the bottom of the sand box. Five water-content sensors were integrated vertically into the sand box to monitor water saturation changes and a needle probe was embedded to measure thermal conductivity of partially saturated sands. The experimental result showed that thermal conductivity decreases from 2.5 W/mK for fully saturated sands to 0.7 W/mK when water saturation is 5%. We found that the decreasing trend is quite non-linear: highly sensitive at very high and low water saturations. However, the boundary effects on the top and the bottom of the sand box seemed to be responsible for this high nonlinearity. We also found that the determination of water saturation is quite important: the saturation by averaging values from all five sensors and that from the sensor at the center position, showed quite different trends in the TC-Sw domain. In parallel, we conducted a pore-scale numerical modeling, which consists of the steady-state two-phase Lattice-Boltzmann simulator and FEM thermal conduction simulator on digital pore geometry of sand aggregation. The simulation results showed a monotonous decreasing trend, and are reasonably well matched with experimental data when using average water saturations. We concluded that thermal conductivity would decrease smoothly as water saturation decreases if we can exclude boundary effects. However, in dynamic conditions, i.e. imbibition or drainage, the thermal conductivity might show hysteresis, which can be investigated with pore-scale numerical modeling with unsteady-state two-phase flow simulators in our future work.
Numerical modeling of the conduction and radiation heating in precision glass moulding
DEFF Research Database (Denmark)
Sarhadi, Ali; Hattel, Jesper Henri; Hansen, Hans Nørgaard
2012-01-01
and the temperature uniformity in the glass wafer are evaluated for both heating mechanisms. Subsequently, the approximate radiation heat loss from the glass wafer during cooling is calculated using both numerical and analytical methods and the temperature change in the glass wafer versus time is obtained...... wafer, heating can be performed by either conduction or radiation. The numerical simulation of these two heating mechanisms in the wafer based glass moulding process is the topic of the present paper. First, the transient heating of the glass wafer is simulated by the FEM software ABAQUS. Temperature...... dependent material data of the glass wafer are taken into account in the simulation to have a more realistic model of the material. Heating curves depicting temperature as a function of time inside the glass wafer are predicted for both radiation and conduction heating and based on that the heating time...
High-conductance states in a mean-field cortical network model
DEFF Research Database (Denmark)
Lerchner, Alexander; Ahmadi, Mandana; Hertz, John
2004-01-01
cortical network model with random connectivity and conductance-based synapses. We employ mean-field theory with correctly colored noise to describe temporal correlations in the neuronal activity. Our results illuminate the connection between two independent experimental findings: high-conductance states......Measured responses from visual cortical neurons show that spike times tend to be correlated rather than exactly Poisson distributed. Fano factors vary and are usually greater than 1, indicating a tendency toward spikes being clustered. We show that this behavior emerges naturally in a balanced...... of cortical neurons in their natural environment, and variable non-Poissonian spike statistics with Fano factors greater than 1. (C) 2004 Elsevier B.V. All rights reserved....
Explicitly Solvable Model of the Charge Carriers' Phenomena in Isotropic Conducting Crystals
Budzak, Yaroslav S.; Wacławski, Tadeusz
2017-01-01
In this paper, a theoretical analysis of the kinetic properties of the isotropic conducting crystals is presented. The general formulas for these kinetic properties are expressed in terms of the Fermi integrals. These integrals were obtained using methods of statistical ensembles with varying number of particles and the Gibbs's grand canonical distribution. The determination of the scattering function and the exploration of its relation with the mobility of the current carriers inside these crystals have been made. Together with the results of theoretical analysis of the scattering function and its relation with the current carriers' mobility, these formulas constitute the mathematical model of the charge carriers' transport phenomena in conducting crystals (where a non-parabolic energy spectrum is described by Kane's formula) and provide algorithms for the calculation of these properties.
Cardiac conduction system anomalies and sudden cardiac death: insights from murine models
Directory of Open Access Journals (Sweden)
Amelia Eva Aranega
2012-06-01
Full Text Available The cardiac conduction system (CCS is a series of specialized tissues in the heart responsible for the initiation and co-ordination of the heartbeat. Alterations in the CCS, especially the His-Purkinje system, have been identified as an important player in the generation of lethal arrhythmias. Unstable arrhythmias secondary to channelopathies highly increase the risk of sudden cardiac death (SCD. Sudden cardiac death is a major contributor to mortality in industrialized nations, and most cases of SCD in the young are related to inherited ion channel diseases. In this review we examine how murine transgenic models have contributed to understanding that a broad variety of cardiac arrhythmias involve the cardiac specialized conduction system and may lead to sudden cardiac death.
Toward Multi-scale Modeling and simulation of conduction in heterogeneous materials
Energy Technology Data Exchange (ETDEWEB)
Lechman, Jeremy B. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Battaile, Corbett Chandler. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Bolintineanu, Dan [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Cooper, Marcia A. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Erikson, William W. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Foiles, Stephen M. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Kay, Jeffrey J [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Phinney, Leslie M. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Piekos, Edward S. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Specht, Paul Elliott [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Wixom, Ryan R. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Yarrington, Cole [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
2015-01-01
This report summarizes a project in which the authors sought to develop and deploy: (i) experimental techniques to elucidate the complex, multiscale nature of thermal transport in particle-based materials; and (ii) modeling approaches to address current challenges in predicting performance variability of materials (e.g., identifying and characterizing physical- chemical processes and their couplings across multiple length and time scales, modeling information transfer between scales, and statically and dynamically resolving material structure and its evolution during manufacturing and device performance). Experimentally, several capabilities were successfully advanced. As discussed in Chapter 2 a flash diffusivity capability for measuring homogeneous thermal conductivity of pyrotechnic powders (and beyond) was advanced; leading to enhanced characterization of pyrotechnic materials and properties impacting component development. Chapter 4 describes success for the first time, although preliminary, in resolving thermal fields at speeds and spatial scales relevant to energetic components. Chapter 7 summarizes the first ever (as far as the authors know) application of TDTR to actual pyrotechnic materials. This is the first attempt to actually characterize these materials at the interfacial scale. On the modeling side, new capabilities in image processing of experimental microstructures and direct numerical simulation on complicated structures were advanced (see Chapters 3 and 5). In addition, modeling work described in Chapter 8 led to improved prediction of interface thermal conductance from first principles calculations. Toward the second point, for a model system of packed particles, significant headway was made in implementing numerical algorithms and collecting data to justify the approach in terms of highlighting the phenomena at play and pointing the way forward in developing and informing the kind of modeling approach originally envisioned (see Chapter 6). In
Toward Multi-scale Modeling and simulation of conduction in heterogeneous materials.
Energy Technology Data Exchange (ETDEWEB)
Lechman, Jeremy B.; Battaile, Corbett Chandler.; Bolintineanu, Dan; Cooper, Marcia A.; Erikson, William W.; Foiles, Stephen M.; Kay, Jeffrey J [Sandia National Laboratories, Livermore, CA; Phinney, Leslie M.; Piekos, Edward S.; Specht, Paul Elliott; Wixom, Ryan R.; Yarrington, Cole
2015-01-01
This report summarizes a project in which the authors sought to develop and deploy: (i) experimental techniques to elucidate the complex, multiscale nature of thermal transport in particle-based materials; and (ii) modeling approaches to address current challenges in predicting performace variability of materials (e.g., identifying and characterizing physical- chemical processes and their couplings across multiple length and time scales, modeling infor- mation transfer between scales, and statically and dynamically resolving material structure and its evolution during manufacturing and device performance). Experimentally, several capabilities were sucessfully advanced. As discussed in Chapter 2 a flash diffusivity capabil- ity for measuring homogeneous thermal conductivity of pyrotechnic powders (and beyond) was advanced; leading to enhanced characterization of pyrotechnic materials and properties impacting component development. Chapter 4 describes sucess for the first time, although preliminary, in resolving thermal fields at speeds and spatial scales relevant to energetic components. Chapter 7 summarizes the first ever (as far as the authors know) application of TDTR to actual pyrotechnic materials. This is the first attempt to actually characterize these materials at the interfacial scale. On the modeling side, new capabilities in image processing of experimental microstructures and direct numerical simulation on complicated structures were advanced (see Chapters 3 and 5). In addition, modeling work described in Chapter 8 led to improved prediction of interface thermal conductance from first principles calculations. Toward the second point, for a model system of packed particles, significant headway was made in implementing numerical algorithms and collecting data to justify the approach in terms of highlighting the phenomena at play and pointing the way forward in de- veloping and informing the kind of modeling approach oringinally envisioned (see Chapter 6
Study of thermal conductivity of nanofluids for the application of heat transfer fluids
Energy Technology Data Exchange (ETDEWEB)
Yoo, Dae-Hwang [Research Center for Dielectric and Advanced Matter Physics, Pusan National University, Busan 609-735 (Korea); Hong, K.S. [Busan Center, Korea Basic Science Institute, Busan 609-735 (Korea); Yang, Ho-Soon [Department of Physics, Pusan National University, Busan 609-735 (Korea)
2007-04-01
TiO{sub 2}, Al{sub 2}O{sub 3}, Fe, and WO{sub 3} nanofluids are prepared in a two-step procedure by dispersing nanoparticles in a basefluid. Since nanoparticles form clusters in fluids, a cell disrupter generating high power pulses is used for improving the dispersion of nanoparticles. The transient hot wire method is used for the measurement of thermal conductivity. The thermal conductivities of TiO{sub 2}, Al{sub 2}O{sub 3}, Fe, and WO{sub 3} nanofluids are studied and compared with each other. Nanofluids show a large enhancement of thermal conductivity compared with their basefluids, which exceeds the theoretical expectation of two-component mixture system. We compare thermal conductivities of various nanofluids and discuss the important factors in determining thermal conductivity in this study. (author)
Electrical conductivity studies on CuBr containing Al2O3 particles
Dubec, P. M.; Wagner, J. B., Jr.
1984-01-01
The conductivity of CuBr was studied and the role of a second phase, Al2O3, dispersed in CuBr was tested. CuBr melts at 493 C and exhibits three phases in the solid state. CuBr is a good ionic conductor with a transport number for copper ions of virtually unity with weighed proportions of the appropriate chemicals used. The CuBr materials were heated above melting point of CuBr, and the samples were sandwiched between copper electrodes. The ac conductivity, was determined at 1 kHz between 25 and 440 C depending on the sample. It was shown that at low temperatures, the conductivity for CuBr (Al2O3) increased by as much as 100, whereas in the beta phase the conductivity of CuBr containing Al2O3 decreased. The electrical conductivity studies are in agreement with earlier data.
Sysun, V. I.; Bute, I. V.; Boriskov, P. P.
2016-09-01
The transition process from the low resistance state into the high resistance state in a Pt/NiO/Pt memory switching structure has been studied by numerical modeling. Detailed analysis shows, that thermally induced diffusion oxidation by nickel vacancies is the key factor for distortion of the channel metallic conductivity. Spatial dynamics of the process of oxidation defines channel narrowing mainly in its central part, and also sets the critical current through the structure sufficient for final rupture of the channel and the transition to high resistance state. The increase in critical current above the limit even by 10% reduces the switching time by an order of magnitude, which is in agreement with experiments. The developed radial diffusion model of conductive channel (or filaments) oxidation may be suitable for the analysis of switching effect a number of other ReRAM oxide structures.
Ahmed, Muneeb; Liu, Zhengjun; Humphries, Stanley; Goldberg, S Nahum
2008-11-01
To use an established computer simulation model of radiofrequency (RF) ablation to characterize the combined effects of varying perfusion, and electrical and thermal conductivity on RF heating. Two-compartment computer simulation of RF heating using 2-D and 3-D finite element analysis (ETherm) was performed in three phases (n = 88 matrices, 144 data points each). In each phase, RF application was systematically modeled on a clinically relevant template of application parameters (i.e., varying tumor and surrounding tissue perfusion: 0-5 kg/m(3)-s) for internally cooled 3 cm single and 2.5 cm cluster electrodes for tumor diameters ranging from 2-5 cm, and RF application times (6-20 min). In the first phase, outer thermal conductivity was changed to reflect three common clinical scenarios: soft tissue, fat, and ascites (0.5, 0.23, and 0.7 W/m- degrees C, respectively). In the second phase, electrical conductivity was changed to reflect different tumor electrical conductivities (0.5 and 4.0 S/m, representing soft tissue and adjuvant saline injection, respectively) and background electrical conductivity representing soft tissue, lung, and kidney (0.5, 0.1, and 3.3 S/m, respectively). In the third phase, the best and worst combinations of electrical and thermal conductivity characteristics were modeled in combination. Tissue heating patterns and the time required to heat the entire tumor +/-a 5 mm margin to >50 degrees C were assessed. Increasing background tissue thermal conductivity increases the time required to achieve a 50 degrees C isotherm for all tumor sizes and electrode types, but enabled ablation of a given tumor size at higher tissue perfusions. An inner thermal conductivity equivalent to soft tissue (0.5 W/m- degrees C) surrounded by fat (0.23 W/m- degrees C) permitted the greatest degree of tumor heating in the shortest time, while soft tissue surrounded by ascites (0.7 W/m- degrees C) took longer to achieve the 50 degrees C isotherm, and complete ablation
Directory of Open Access Journals (Sweden)
Risheng Ding
Full Text Available The dual-source Shuttleworth-Wallace model has been widely used to estimate and partition crop evapotranspiration (λET. Canopy stomatal conductance (Gsc, an essential parameter of the model, is often calculated by scaling up leaf stomatal conductance, considering the canopy as one single leaf in a so-called "big-leaf" model. However, Gsc can be overestimated or underestimated depending on leaf area index level in the big-leaf model, due to a non-linear stomatal response to light. A dual-leaf model, scaling up Gsc from leaf to canopy, was developed in this study. The non-linear stomata-light relationship was incorporated by dividing the canopy into sunlit and shaded fractions and calculating each fraction separately according to absorbed irradiances. The model includes: (1 the absorbed irradiance, determined by separately integrating the sunlit and shaded leaves with consideration of both beam and diffuse radiation; (2 leaf area for the sunlit and shaded fractions; and (3 a leaf conductance model that accounts for the response of stomata to PAR, vapor pressure deficit and available soil water. In contrast to the significant errors of Gsc in the big-leaf model, the predicted Gsc using the dual-leaf model had a high degree of data-model agreement; the slope of the linear regression between daytime predictions and measurements was 1.01 (R2 = 0.98, with RMSE of 0.6120 mm s-1 for four clear-sky days in different growth stages. The estimates of half-hourly λET using the dual-source dual-leaf model (DSDL agreed well with measurements and the error was within 5% during two growing seasons of maize with differing hydrometeorological and management strategies. Moreover, the estimates of soil evaporation using the DSDL model closely matched actual measurements. Our results indicate that the DSDL model can produce more accurate estimation of Gsc and λET, compared to the big-leaf model, and thus is an effective alternative approach for estimating and
Energy Technology Data Exchange (ETDEWEB)
Kukkonen, I.; Suppala, I. [Geological Survey of Finland, Espoo (Finland)
1999-01-01
In situ measurements of thermal conductivity and diffusivity of bedrock were investigated with the aid of a literature survey and theoretical simulations of a measurement system. According to the surveyed literature, in situ methods can be divided into `active` drill hole methods, and `passive` indirect methods utilizing other drill hole measurements together with cutting samples and petrophysical relationships. The most common active drill hole method is a cylindrical heat producing probe whose temperature is registered as a function of time. The temperature response can be calculated and interpreted with the aid of analytical solutions of the cylindrical heat conduction equation, particularly the solution for an infinite perfectly conducting cylindrical probe in a homogeneous medium, and the solution for a line source of heat in a medium. Using both forward and inverse modellings, a theoretical measurement system was analysed with an aim at finding the basic parameters for construction of a practical measurement system. The results indicate that thermal conductivity can be relatively well estimated with borehole measurements, whereas thermal diffusivity is much more sensitive to various disturbing factors, such as thermal contact resistance and variations in probe parameters. In addition, the three-dimensional conduction effects were investigated to find out the magnitude of axial `leak` of heat in long-duration experiments. The radius of influence of a drill hole measurement is mainly dependent on the duration of the experiment. Assuming typical conductivity and diffusivity values of crystalline rocks, the measurement yields information within less than a metre from the drill hole, when the experiment lasts about 24 hours. We propose the following factors to be taken as basic parameters in the construction of a practical measurement system: the probe length 1.5-2 m, heating power 5-20 Wm{sup -1}, temperature recording with 5-7 sensors placed along the probe, and
Whitley, Rhys; Medlyn, Belinda; Zeppel, Melanie; Macinnis-Ng, Catriona; Eamus, Derek
2009-06-01
SUMMARYThe responses of canopy conductance to variation in solar radiation, vapour pressure deficit and soil moisture have been extensively modelled using a Jarvis-Stewart (JS) model. Modelled canopy conductance has then often been used to predict transpiration using the Penman-Monteith (PM) model. We previously suggested an alternative approach in which the JS model is modified to directly estimate transpiration rather than canopy conductance. In the present study we used this alternative approach to model tree water fluxes from an Australian native forest over an annual cycle. For comparative purposes we also modelled canopy conductance and estimated transpiration via the PM model. Finally we applied an artificial neural network as a statistical benchmark to compare the performance of both models. Both the PM and modified JS models were parameterised using solar radiation, vapour pressure deficit and soil moisture as inputs with results that compare well with previous studies. Both models performed comparably well during the summer period. However, during winter the PM model was found to fail during periods of high rates of transpiration. In contrast, the modified JS model was able to replicate observed sapflow measurements throughout the year although it too tended to underestimate rates of transpiration in winter under conditions of high rates of transpiration. Both approaches to modelling transpiration gave good agreement with hourly, daily and total sums of sapflow measurements with the modified JS and PM models explaining 87% and 86% of the variance, respectively. We conclude that these three approaches have merit at different time-scales.
LENUS (Irish Health Repository)
Neligan, A
2010-01-01
Entrapment neuropathies, particularly those affecting upper limbs, are common reasons for referral for nerve conduction studies (NCS). However, concordance between clinical findings and NCS findings, especially in patients being considered for intervention including decompressive surgery, has not been assessed.
Thermal design studies in superconducting rf cavities: Phonon peak and Kapitza conductance
Directory of Open Access Journals (Sweden)
A. Aizaz
2010-09-01
Full Text Available Thermal design studies of superconducting radio frequency (SRF cavities involve two thermal parameters, namely the temperature dependent thermal conductivity of Nb at low temperatures and the heat transfer coefficient at the Nb-He II interface, commonly known as the Kapitza conductance. During the fabrication process of the SRF cavities, Nb sheet is plastically deformed through a deep drawing process to obtain the desired shape. The effect of plastic deformation on low temperature thermal conductivity as well as Kapitza conductance has been studied experimentally. Strain induced during the plastic deformation process reduces the thermal conductivity in its phonon transmission regime (disappearance of phonon peak by 80%, which may explain the performance limitations of the defect-free SRF cavities during their high field operations. Low temperature annealing of the deformed Nb sample could not recover the phonon peak. However, moderate temperature annealing during the titanification process recovered the phonon peak in the thermal conductivity curve. Kapitza conductance measurements for the Nb-He II interface for various surface topologies have also been carried out before and after the annealing. These measurements reveal consistently increased Kapitza conductance after the annealing process was carried out in the two temperature regimes.
Studies on conductivity and dielectric properties of polyaniline–zinc sulphide composites
Indian Academy of Sciences (India)
H C Pant; M K Patra; S C Negi; A Bhatia; S R Vadera; N Kumar
2006-08-01
In the present paper, we report electrical conductivity and dielectric studies on the composites of conducting polyaniline (PANI) with crystalline semiconducting ZnS powder, wherein PANI has been taken as inclusion and ZnS crystallites as the host matrix. From the studies, it has been observed that the value of room temperature d.c. conductivity of the composites with volume fraction of PANI > 0.65 shows an unusual behaviour wherein, conductivity values of the composites exceed that of PANI itself with maximum value as high as 6 times that of PANI at the volume fraction of 0.85. A similar trend has also been observed for the real and imaginary parts of complex dielectric constant values of the composites. This unusual behaviour in the d.c. conductivity and dielectric properties has been attributed to the enhancement in the degree of crystallinity of PANI as a consequence of its interfacial interaction with ZnS matrix. The results of optical microscopy show coating of PANI all around the ZnS particles. The temperature dependent conductivity studies suggest the quasi one-dimensional VRH conduction in PANI as well as its composites with ZnS. FTIR and XRD studies have also been reported.
Pusateri, Elise Noel
abruptly. The objective of the PhD research is to mitigate this effect by integrating a conduction electron model into CHAP-LA which can calculate the conduction current based on a non-equilibrium electron distribution. We propose to use an electron swarm model to monitor the time evolution of conduction electrons in the EMP environment which is characterized by electric field and pressure. Swarm theory uses various collision frequencies and reaction rates to study how the electron distribution and the resultant transport coefficients change with time, ultimately reaching an equilibrium distribution. Validation of the swarm model we develop is a necessary step for completion of the thesis work. After validation, the swarm model is integrated in the air chemistry model CHAP-LA employs for conduction electron simulations. We test high altitude EMP simulations with the swarm model option in the air chemistry model to show improvements in the computational capability of CHAP-LA. A swarm model has been developed that is based on a previous swarm model developed by Higgins, Longmire and O'Dell 1973, hereinafter HLO. The code used for the swarm model calculation solves a system of coupled differential equations for electric field, electron temperature, electron number density, and drift velocity. Important swarm parameters, including the momentum transfer collision frequency, energy transfer collision frequency, and ionization rate, are recalculated and compared to the previously reported empirical results given by HLO. These swarm parameters are found using BOLSIG+, a two term Boltzmann solver developed by Hagelaar and Pitchford 2005. BOLSIG+ utilizes updated electron scattering cross sections that are defined over an expanded energy range found in the atomic and molecular cross section database published by Phelps in the Phelps Database 2014 on the LXcat website created by Pancheshnyi et al. 2012. The swarm model is also updated from the original HLO model by including
Colbert, Keegan; Naraghi, Mohammad; Boyd, James G.
2017-02-01
This paper presents a model and computational method to predict the steady-state performance of thermal flexure microactuators at high input powers and various levels of partial vacuum. The model accounts for nonlinear temperature dependence of material properties, heat loss due to radiation, and intra-device heat transfer by conduction across an air gap. The model is validated by comparing the model predictions with the experimentally measured voltage, current, and displacement at standard conditions, prior to adjusting for partial vacuum. In order to understand the effect of nonlinearities on model reliability, the predictions of six additional hypothetical models are considered where (1) intra-device heat transfer is neglected, (2) radiation is neglected, (3) the thermal conductivity of silicon is assumed to be temperature-independent, (4) the thermal conductivity of air is assumed to be temperature-independent, (5) the electrical resistivity of silicon is assumed to be linear in temperature, and (6) the thermal expansion coefficient of silicon is assumed to be temperature-independent. All factors except radiation were shown to have a significant influence on the device performance especially at high input powers. The experimentally validated full model is then employed to predict the effect of reduced air pressure on the displacement and heat transfer properties of the actuator. This aspect of the study targets applications of thermal actuators in controlled environments such as space applications, actuators used for in situ micropositioning and tensile testing inside electron microscopy chambers, or actuators incorporated into the design of MEMS resonators. It was demonstrated that the maximum actuator displacement is not a linear function of reduced pressure and that it reaches a maximum at a certain partial vacuum level.
Feasibility study of injection mouldable conductive plastic for the hearing aid applications
DEFF Research Database (Denmark)
Merca, Timea D.den; Lindberg, Torbjörn; Islam, Aminul
2016-01-01
Electrically conductive polymers can combine the advantage of plastic processing with the unique electrical properties which are usually found in metals. This article presents a feasibility study of an electrically conductive plastic for hearing aid antennas. Focus will be placed to critically...... analyse the electrical properties of the potential conductive plastic in a two component injection moulding process chain. The purpose of this experimental study is to mimic the real scenario in a hearing aid device and conclude the antenna’s efficiency based on the results obtained with OTA (over the air...
Kubo-equivalent closed-form graphene conductivity models (Conference Presentation)
Kudyshev, Zhaxylyk A.; Prokopeva, Ludmila J.; Kildishev, Alexander V.
2016-09-01
The optical response of graphene is described by its surface conductivity - a multivariate function of frequency, temperature, chemical potential, and scattering rate. A Kubo formula that accounts for both interband and intraband transitions with two Fermi-Dirac-like integrals is conventionally used to model graphene. The first (intraband) integral can be reduced analytically to a Drude term. The second (intraband) term requires computationally expensive numerical integration over the infinite range of energies, and thus it is usually either neglected or substituted with a simpler approximation (typically valid within a limited range of parameters). Additional challenge is an integral-free time-domain (TD) formulation that would allow efficient coupling of the interband conductivity term to TD electromagnetic solvers. We propose Kubo-equivalent models of graphene surface conductivity that offer closed-form computationally efficient representations in time and frequency domains. We show that in time domain Kubo's formula reduces to a combination of rational, trigonometric, hyperbolic, and exponential functions. In frequency domain the integral term is equivalent to an expression with digamma and incomplete gamma functions. The accuracy and improved performance of our integral-free formulations versus the direct integration of Kubo's formula is critically analyzed. The result provides efficient broadband multivariate coupling of graphene dispersion to time-domain and frequency-domain solvers. To reinforce theory with practical examples, we use obtained closed-form frequency-domain model to retrieve the optical properties of graphene samples from variable angle spectroscopic ellipsometry (VASE) measurements. . We present ellipsometry fitting cases that are built on an in-the-cloud tool freely available online (https://nanohub.org/resources/photonicvasefit).
Study of thermal conductivity enhancement of aqueous suspensions containing silver nanoparticles
Iyahraja, S.; Rajadurai, J. Selwin
2015-05-01
Nanofluids are prepared by dispersing polyvinylpyrrolidone coated silver nanoparticles in distilled water. The thermal conductivity of nanofluids is measured by KD2 Pro thermal analyzer which is based on transient hot wire method. The influence of size and concentration of nanoparticles, surfactant and temperature of suspensions on the enhancement of the thermal conductivity is analyzed. The experimental results show that the thermal conductivity of nanofluids increases with the decrease in the size and increase in the concentration of the nanoparticles. Even with low volume fraction of 0.1 % and 20 nm size of silver nanoparticles, a high thermal conductivity enhancement of 54 % has been achieved. The surfactant and the temperature have a significant effect on the thermal conductivity enhancement of the nanofluids. The increase in temperature of the nanofluid from 30oC to 60oC increases its thermal conductivity up to 69 % whereas the addition of surfactant lessens the thermal conductivity enhancement to 34.2% with polyvinylpyrrolidone and 31.5 % with sodium dodecyl sulfate. The experimental results are compared with the existing theoretical models.
Study of thermal conductivity enhancement of aqueous suspensions containing silver nanoparticles
Directory of Open Access Journals (Sweden)
S. Iyahraja
2015-05-01
Full Text Available Nanofluids are prepared by dispersing polyvinylpyrrolidone coated silver nanoparticles in distilled water. The thermal conductivity of nanofluids is measured by KD2 Pro thermal analyzer which is based on transient hot wire method. The influence of size and concentration of nanoparticles, surfactant and temperature of suspensions on the enhancement of the thermal conductivity is analyzed. The experimental results show that the thermal conductivity of nanofluids increases with the decrease in the size and increase in the concentration of the nanoparticles. Even with low volume fraction of 0.1 % and 20 nm size of silver nanoparticles, a high thermal conductivity enhancement of 54 % has been achieved. The surfactant and the temperature have a significant effect on the thermal conductivity enhancement of the nanofluids. The increase in temperature of the nanofluid from 30oC to 60oC increases its thermal conductivity up to 69 % whereas the addition of surfactant lessens the thermal conductivity enhancement to 34.2% with polyvinylpyrrolidone and 31.5 % with sodium dodecyl sulfate. The experimental results are compared with the existing theoretical models.
Farrokhpanah, Amirsaman; Mostaghimi, Javad
2016-01-01
When modelling phase change, the latent heat released (absorbed) during solidification (melting) must be included in the heat transfer equation. In this paper, different SPH methods for the implementation of latent heat, in the context of transient heat conduction, are derived and tested. First, SPH discretizations of two finite element methods are presented, but these prove to be computationally expensive. Then, by starting from a simple approximation and enhancing accuracy using different numerical treatments, a new SPH method is introduced, that is fast and easy to implement. An evaluation of this new method on various analytical and numerical results confirms its accuracy and robustness.
On Thermodynamics Problems in the Single-Phase-Lagging Heat Conduction Model
Directory of Open Access Journals (Sweden)
Shu-Nan Li
2016-11-01
Full Text Available Thermodynamics problems for the single-phase-lagging (SPL model have not been much studied. In this paper, the violation of the second law of thermodynamics by the SPL model is studied from two perspectives, which are the negative entropy production rate and breaking equilibrium spontaneously. The methods for the SPL model to avoid the negative entropy production rate are proposed, which are extended irreversible thermodynamics and the thermal relaxation time. Modifying the entropy production rate positive or zero is not enough to avoid the violation of the second law of thermodynamics for the SPL model, because the SPL model could cause breaking equilibrium spontaneously in some special circumstances. As comparison, it is shown that Fourier’s law and the CV model cannot break equilibrium spontaneously by analyzing mathematical energy integral.
A Study on Electrically Conducting Magnesia—carbon Bricks for DC EAF
Institute of Scientific and Technical Information of China (English)
TONGXiaojun; YANLiyi; 等
1998-01-01
This paper gives a brief introduction to a kind of special refractories for DC EAF-electrically conducting magnesia-carbon bricks.The application of the conductive magnesia-carbon brick as a hearth electrode is a trend of development in DC arc furnace hearth bootom because of its features of anti corrosion and easy repatching,This is a proven process already available abroad.After a study of teh effect of different amount of graphite added and pretreating temperatures on the eletric-conductivity of magnesia-carbon bricks it has been found that for a balance between electric and thermal conductivities,the proper amount of graphite to be added should be 8%-14% and the pretreatment at temperature of 1300-1500℃ will result in the formation inside the magnesia-carbon bricks of a continuous three-dimensional network of graphite and semi-coke,thus making the brick conductive.
A study on nanocomposites made of a conducting polymer and metallic nanoparticles
Energy Technology Data Exchange (ETDEWEB)
Mohammed Ahmed Khalil, Rania [Nanochemistry and Nanoengineering, Institute for Materials Science, Faculty of Engineering, Christian-Albrechts-University of Kiel (Germany); Multicomponent Materials, Institute for Materials Science, Faculty of Engineering, Christian-Albrechts-University of Kiel (Germany); Abdelaziz Mahmoud Abdelaziz, Ramzy [Nanochemistry and Nanoengineering, Institute for Materials Science, Faculty of Engineering, Christian-Albrechts-University of Kiel (Germany); Strunkus, Thomas; Faupel, Franz [Multicomponent Materials, Institute for Materials Science, Faculty of Engineering, Christian-Albrechts-University of Kiel (Germany); Elbahri, Mady [Nanochemistry and Nanoengineering, Institute for Materials Science, Faculty of Engineering, Christian-Albrechts-University of Kiel (Germany); Helmholtz-Zentrum Geesthacht GmbH, Institute of Polymer Research, Nanochemistry and Nanoengineering (Germany)
2011-07-01
Conducting polymers offer a unique combination of properties that makes them attractive materials for many electronic applications. PEDOT:PSS is one of the most successful conductive materials which is considered to be highly stable and resisting degradation under typical ambient conditions. In this study, we have prepared two sets of conducting polymer nano-composites. The first set is composed of PEDOT:PSS doped with different aspect ratios of gold nanorod and the other one is PEDOT:PSS doped with different sizes of gold nanosphere. The chemical reduction method was used for preparing the nano-particles. Indeed, gold nanorods and nanosphere which exhibit tunable absorption as a function of their size and aspect ratio, respectively, have tuned the absorption coefficient for PEDOT: PSS. The nature of the dopant as well as the degree of doping has played a significant role in the improvement of the electrical conductivity of conducting polymer.
Calibrated Heat Flow Model for Determining the Heat Conduction Losses in Laser Cutting of CFRP
Mucha, P.; Weber, R.; Speker, N.; Berger, P.; Sommer, B.; Graf, T.
Laser machining has great potential regarding automation in fabrication of CFRP (carbon-fiber-reinforced plastics) parts, due to the nearly force and tool-wear free processing at high process speeds. The high vaporization temperatures and the large heat conductivity of the carbon fibers lead to a large heat transport into the sample. This causes the formation of a heat-affected zone and a decrease of the process speed. In the present paper,an analytical heat flow model was adapted in order to understand and investigate the heat conduction losses. Thermal sensors were embedded in samples at different distances from the kerf to fit the calculated to the measured temperatures. Heat conduction losses of up to 30% of the laser power were determined. Furthermore, the energy not absorbed by the sample, the energy for sublimating the composite material in the kerf, the energy for the formation of the HAZ, and the residual heat in the sample are compared in an energy balance.
Indian Academy of Sciences (India)
G Saibaba; D Srikanth; A Ramachandra Reddy
2004-02-01
Poly(ethylene oxide)–LiX complexes and poly[bis(methoxy ethoxy ethoxide) phosphazene]–LiX complexes of polymer thin films were prepared. Conductivity measurements were carried out and the values were found to lie between 10-8 and 1.7 × 10-5 (S/cm). MEEP : LiX salts showed higher conductivity than PEO–LiX salts despite lower dimensional stability. For enhancing stability and conductivity, MEEP–PEO : (LiX) systems were prepared and conductivity measurements carried out. Further the MEEP/PEO : (LiX) was doped with Al2O3 and TiO2 nanocomposite ceramic fillers and the conductivity was studied. The conductivity vs temperature plots showed the enhancement of conductivity with TiO2 added nanocomposite ceramic fillers. The enhanced conductivity is explained on the basis of the effect of local structural modification-promoting localized amorphous region-for enhancement of the Li+ ion transport.
Pathophysiological power of improper tonic GABAA conductances in mature and immature models
Directory of Open Access Journals (Sweden)
Kiyoshi eEgawa
2013-10-01
Full Text Available High-affinity extrasynaptic gamma-aminobutyric acid A (GABAA receptors are tonically activated by low and consistent levels of ambient GABA, mediating chronic inhibition against neuronal excitability (tonic inhibition and the modulation of neural development. Synaptic (phasic inhibition is spatially and temporally precise compared with tonic inhibition, which provides blunt yet strong integral inhibitory force by shunting electrical signaling. Although effects of acute modification of tonic inhibition are known, its pathophysiological significance remains unclear because homeostatic regulation of neuronal excitability can compensate for long-term deficit of extrasynaptic GABAA receptor activation. Nevertheless, tonic inhibition is of great interest for its pathophysiological involvement in central nervous system (CNS diseases and thus as a therapeutic target. Together with the development of experimental models for various pathological states, recent evidence demonstrates such pathological involvements of tonic inhibition in neuronal dysfunction. This review focuses on the recent progress of tonic activation of GABAA conductance on the development and pathology of the CNS. Findings indicate that neuronal function in various brain regions are exacerbated with a gain or loss of function of tonic inhibition by GABA spillover. Disturbance of tonic GABAA conductance mediated by non-synaptic ambient GABA may result in brain mal-development. Therefore, various pathological states (epilepsy, motor dysfunctions, psychiatric disorders, and neurodevelopmental disorders may be partly attributable to abnormal tonic GABAA conductances. Thus, the tone of tonic conductance and level of ambient GABA may be precisely tuned to maintain the regular function and development of the CNS. Therefore, receptor expression and factors for regulating the ambient GABA concentration are highlighted to gain a deeper understanding of pathology and therapeutic strategy for CNS
Sun, Jindong; Feng, Zhaozhong; Leakey, Andrew D B; Zhu, Xinguang; Bernacchi, Carl J; Ort, Donald R
2014-09-01
The responses of CO2 assimilation to [CO2] (A/Ci) were investigated at two developmental stages (R5 and R6) and in several soybean cultivars grown under two levels of CO2, the ambient level of 370 μbar versus the elevated level of 550 μbar. The A/Ci data were analyzed and compared by either the combined iterations or the separated iterations of the Rubisco-limited photosynthesis (Ac) and/or the RuBP-limited photosynthesis (Aj) using various curve-fitting methods: the linear 2-segment model; the non-rectangular hyperbola model; the rectangular hyperbola model; the constant rate of electron transport (J) method and the variable J method. Inconsistency was found among the various methods for the estimation of the maximum rate of carboxylation (Vcmax), the mitochondrial respiration rate in the light (Rd) and mesophyll conductance (gm). The analysis showed that the inconsistency was due to inconsistent estimates of gm values that decreased with an instantaneous increase in [CO2], and varied with the transition Ci cut-off between Rubisco-limited photosynthesis and RuBP-regeneration-limited photosynthesis, and due to over-parameters for non-linear curve-fitting with gm included. We proposed an alternate solution to A/Ci curve-fitting for estimates of Vcmax, Rd, Jmax and gm with the various A/Ci curve-fitting methods. The study indicated that down-regulation of photosynthetic capacity by elevated [CO2] and leaf aging was due to partially the decrease in the maximum rates of carboxylation and partially the decrease in gm. Mesophyll conductance lowered photosynthetic capacity by 18% on average for the case of soybean plants.
Ionic conductivity in a quantum lattice gas model with three-particle interactions
Barry, J. H.; Muttalib, K. A.; Tanaka, T.
2012-12-01
A system of mesoscopic ions with dominant three-particle interactions is modeled by a quantum lattice liquid on the planar kagomé lattice. The two-parameter Hamiltonian contains localized attractive triplet interactions as potential energy and nearest neighbor hopping-type terms as kinetic energy. The dynamic ionic conductivity σ(ω) is theoretically investigated for ‘weak hopping’ via a quantum many-body perturbation expansion of the thermal (Matsubara) Green function (current-current correlation). A simple analytic continuation and mapping of the thermal Green function provide the temporal Fourier transform of the physical retarded Green function in the Kubo formula. Substituting pertinent exact solutions for static multi-particle correlations known from previous work, Arrhenius relations are revealed in zeroth-order approximation for the dc ionic conductivity σdc along special trajectories in density-temperature space. The Arrhenius plots directly yield static activation energies along the latter loci. Experimental possibilities relating to σdc are discussed in the presence of equilibrium aggregation. This article is part of ‘Lattice models and integrability’, a special issue of Journal of Physics A: Mathematical and Theoretical in honour of F Y Wu's 80th birthday.
Fuel rod model based on Non-Fourier heat conduction equation
Energy Technology Data Exchange (ETDEWEB)
Espinosa-Paredes, G. [Area de Ingenieria en Recursos Energeticos, Universidad Autonoma Metropolitana-Iztapalapa, Av. San Rafael Atlixco 186, Col. Vicentina, Mexico DF., CP 09340 (Mexico)], E-mail: gepe@xanum.uam.mx; Espinosa-Martinez, E-G. [Retorno Quebec 6, Col. Burgos de Cuernavaca 62580, Temixco, Mor. (Mexico)
2009-05-15
In this paper we explore the applicability of a fuel rod mathematical model based on Non-Fourier transient heat conduction as constitutive law for the Light Water Reactors transient analysis (LWRs). In the classical theory of diffusion, Fourier law of heat conduction is used to describe the relation between the heat flux vector and the temperature gradient assuming that the heat propagation speeds are infinite. The motivation for this research was to eliminate the paradox of an infinite thermal wave speed. The time-dependent heat sources were considered in the fuel rod heat transfer model. The close of the Main Steam Isolated Valves (MSIV) transient in a Boiling Water Reactor (BWR) was analyzed by different relaxation times. The results show that for long-times the heat fluxes on the clad surface under Non-Fourier approach can be important, while for short-times and from the engineering point of view the changes are very small. Some results from transient calculations are examined.
Phase change heat transfer during cryosurgery of lung cancer using hyperbolic heat conduction model.
Kumar, Ajay; Kumar, Sushil; Katiyar, V K; Telles, Shirley
2017-05-01
The paper reports a numerical study of phase change heat transfer process in lung cancer undergoing cryosurgery. A two dimensional hyperbolic bio-heat model with non-ideal property of tissue, blood perfusion and metabolism is used to analyze the problem. The governing equations are solved by finite difference method based on enthalpy formulation. Effects of relaxation time of heat flux in hyperbolic model on freezing process have been examined. A comparative investigation of two different models (hyperbolic and parabolic bio-heat models) is also presented. Copyright © 2017 Elsevier Ltd. All rights reserved.
Wheeler, John J.; Mayton, Michael R.; Carter, Stacy L.; Chitiyo, Morgan; Menendez, Anthony L.; Huang, Ann
2009-01-01
The purpose of this study was to assess the degree to which behavioral intervention studies conducted with persons with mental retardation operationally defined the independent variables and evaluated and reported measures of treatment integrity. The study expands the previous work in this area reported by Gresham, Gansle, and Noell (1993) and…
A developmental study of bone conduction auditory brain stem response in infants.
Yang, E Y; Rupert, A L; Moushegian, G
1987-08-01
Two studies, vibrator placement and masking, were performed to evaluate the developmental aspect of bone conduction auditory brain stem response (ABR) in human infants. Subject groups included newborns, 1-yr-olds, and adults. In the vibrator studies, ABRs were obtained from placements of the bone conduction vibrator on the frontal, occipital, and temporal bones. Results showed that temporal placements in neonates and 1-yr-olds produce significantly shorter wave V latencies of ABR than frontal or occipital placements. In adults, differences of wave V latencies from various vibrator placements were comparatively small. In the masking studies, ABRs were acquired from vibrator placements at the temporal bone in the presence of ipsilateral air conducted masking noise from the experimental groups. Results showed that interaural attenuations of bone conduction click stimuli are the largest in neonates, somewhat smaller from 1-yr-olds, and the smallest in adults. The findings of this research strongly suggest that temporal placements for bone conduction ABR should be used, in some instances, when testing infants and 1-yr-olds. The results of this study support the proposition that bone conduction ABR is a feasible and reliable diagnostic tool in testing infants.
A study of the electronic conductance in converting a polyacetylene into polystyrene oligomer
Directory of Open Access Journals (Sweden)
H Rabani
2014-11-01
Full Text Available In this paper, the electronic conductance of a polyacetylene polymer embedded between two simple chains is studied by using transfer matrix method within the tight-binding and first neighbor approach. Also, by adding benzene molecules to polyacetylene we obtain the system conductance in its conversion to polystyrene polymer. The results show that as the number of benzene molecules in the middle of center system increases the conductance in the tunneling area of polyacetylene improves and this area comes close to the resonance area. In contrast, a part of resonance area tends to transform into polystyrene tunneling zone.
Institute of Scientific and Technical Information of China (English)
M.F.Z.Abdul; Kadir; A.K.Arof
2007-01-01
1 Results The effect of ammonium nitrate (NH4NO3) content in 40 wt.% PEO and 60 wt.% chitosan blend has been analyzed in this study.The sample containing 40 wt.% NH4NO3 exhibited the highest room temperature conductivity.In order to ascertain that water does not influence the conductivity,the samples were dried in a dessicator and the conductivity determined daily until it shows a constant value.Results are as shown in Fig.1.Samples containing other salt concentrations were also kept in the dessicator f...
Study of the Pyrrol/Diphenylamine Copolymer by FT-IR spectroscopy and conductivity
Directory of Open Access Journals (Sweden)
Carlos Alberto Perez
2004-01-01
Full Text Available The main goal of this study was to analyze the physical properties of the copolymer formed by the electrochemical deposition of the polydiphenylamine (PDPA on polypyrrole (Ppy and Ppy on PDPA, in different conditions, through the characterization of the materials formed by the resonant Raman, FT-IR and conductivity techniques. The interactions among the species which are present in the new copolymer structure and the changes in electronic conductivity, were verified. The copolymer was also synthesized electrochemically in the presence of iodide species and the material was characterized by FT-IR spectroscopy and conductivity. The role of the dopant was studied in the process of charge transfer between the copolymer-dopant, acting in the stabilization of the species in the polymer backbone and the increase of the electronic conductivity.
Early diagnosis of Carpal Tunnel Syndrome (CTS in Indian patients by nerve conduction studies
Directory of Open Access Journals (Sweden)
Dr. Geetanjali Sharma MD
2010-07-01
Full Text Available The present study was carried out for early confirmation of clinically diagnosed patients of Carpal Tunnel Syndrome (CTS by electro-diagnostic tests which included motor conduction, sensory conduction studies and F-wave studies. The aim of the study was early confirmation of clinically suspected patients of CTS by motor and sensory conduction studies of median and ulnar nerves. Eighty subjects of age group 30-50 years (40 clinically suspected patients of CTS, 40 as control group were studied. Motor and Sensory conduction velocities, distal motor and sensory latencies and F wave latencies of median and ulnar nerves were performed using RMS EMG EP Mark –II. Statistically significant (P < 0.001 slowing of motor conduction velocities for both nerves was seen in the CTS group as compared to control group. Decrease in sensory conduction velocity was more pronounced in CTS group as compared to Control group. Statistically significant (P < 0.001 increase in distal motor and sensory latencies was also observed for both median and ulnar nerves in the CTS group as compared to Control group, with more increase in distal motor latency than sensory latency. Increase in F wave latencies of both nerves was seen in the CTS group. Electrophysiological studies confirmed the early diagnosis of CTS with a high degree of sensitivity. Present results confirm selective slowing of sensory & motor conduction within wrist to palm segment in patients of CTS which is attributable to compression by the transverse carpal ligament or to a disease process of the terminal segment.
Coarse-grained model of water diffusion and proton conductivity in hydrated polyelectrolyte membrane
Lee, Ming-Tsung; Vishnyakov, Aleksey; Neimark, Alexander V.
2016-01-01
Using dissipative particle dynamics (DPD), we simulate nanoscale segregation, water diffusion, and proton conductivity in hydrated sulfonated polystyrene (sPS). We employ a novel model [Lee et al. J. Chem. Theory Comput. 11(9), 4395-4403 (2015)] that incorporates protonation/deprotonation equilibria into DPD simulations. The polymer and water are modeled by coarse-grained beads interacting via short-range soft repulsion and smeared charge electrostatic potentials. The proton is introduced as a separate charged bead that forms dissociable Morse bonds with the base beads representing water and sulfonate anions. Morse bond formation and breakup artificially mimics the Grotthuss mechanism of proton hopping between the bases. The DPD model is parameterized by matching the proton mobility in bulk water, dissociation constant of benzenesulfonic acid, and liquid-liquid equilibrium of water-ethylbenzene solutions. The DPD simulations semi-quantitatively predict nanoscale segregation in the hydrated sPS into hydrophobic and hydrophilic subphases, water self-diffusion, and proton mobility. As the hydration level increases, the hydrophilic subphase exhibits a percolation transition from isolated water clusters to a 3D network. The analysis of hydrophilic subphase connectivity and water diffusion demonstrates the importance of the dynamic percolation effect of formation and breakup of temporary junctions between water clusters. The proposed DPD model qualitatively predicts the ratio of proton to water self-diffusion and its dependence on the hydration level that is in reasonable agreement with experiments.
Advances on the time differential three-phase-lag heat conduction model and major open issues
D'Apice, Ciro; Zampoli, Vittorio
2017-07-01
The main purpose of this short contribution is to summarize the recent achievements concerning the so-called time differential three-phase-lag heat conduction model, contextually focusing attention on some of the numerous open problems associated with such an attractive theory. After having briefly recalled the origin of the model at issue, the restrictions upon the delay times and the constitutive tensors able to make it thermodynamically consistent are recalled. Under these hypotheses, the investigation of the well-posedness issue has already provided important results in terms of uniqueness and continuous dependence of the solutions (even related to the thermoelastic case), as well as in terms of existence of a domain of influence of the assigned data in connection with the thermoelastic model. Finally, some of the main problems currently object of investigation are recalled, including the very challenging issues about the different possible choices of Taylor series expansion orders for the constitutive equation, the interaction of the model with energy processes that take place on the nanoscale, with multi-porous materials and with biological systems.
Cystic Fibrosis Transmembrane Conductance Regulator (CFTR): CLOSED AND OPEN STATE CHANNEL MODELS.
Corradi, Valentina; Vergani, Paola; Tieleman, D Peter
2015-09-18
The cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ATP-binding cassette (ABC) transporter superfamily. CFTR controls the flow of anions through the apical membrane of epithelia. Dysfunctional CFTR causes the common lethal genetic disease cystic fibrosis. Transitions between open and closed states of CFTR are regulated by ATP binding and hydrolysis on the cytosolic nucleotide binding domains, which are coupled with the transmembrane (TM) domains forming the pathway for anion permeation. Lack of structural data hampers a global understanding of CFTR and thus the development of "rational" approaches directly targeting defective CFTR. In this work, we explored possible conformational states of the CFTR gating cycle by means of homology modeling. As templates, we used structures of homologous ABC transporters, namely TM(287-288), ABC-B10, McjD, and Sav1866. In the light of published experimental results, structural analysis of the transmembrane cavity suggests that the TM(287-288)-based CFTR model could correspond to a commonly occupied closed state, whereas the McjD-based model could represent an open state. The models capture the important role played by Phe-337 as a filter/gating residue and provide structural information on the conformational transition from closed to open channel.
Coarse-grained model of water diffusion and proton conductivity in hydrated polyelectrolyte membrane
Energy Technology Data Exchange (ETDEWEB)
Lee, Ming-Tsung; Vishnyakov, Aleksey; Neimark, Alexander V., E-mail: aneimark@rutgers.edu [Department of Chemical and Biochemical Engineering, Rutgers, The State University of New Jersey, 98 Brett Road, Piscataway, New Jersey 08854-8058 (United States)
2016-01-07
Using dissipative particle dynamics (DPD), we simulate nanoscale segregation, water diffusion, and proton conductivity in hydrated sulfonated polystyrene (sPS). We employ a novel model [Lee et al. J. Chem. Theory Comput. 11(9), 4395-4403 (2015)] that incorporates protonation/deprotonation equilibria into DPD simulations. The polymer and water are modeled by coarse-grained beads interacting via short-range soft repulsion and smeared charge electrostatic potentials. The proton is introduced as a separate charged bead that forms dissociable Morse bonds with the base beads representing water and sulfonate anions. Morse bond formation and breakup artificially mimics the Grotthuss mechanism of proton hopping between the bases. The DPD model is parameterized by matching the proton mobility in bulk water, dissociation constant of benzenesulfonic acid, and liquid-liquid equilibrium of water-ethylbenzene solutions. The DPD simulations semi-quantitatively predict nanoscale segregation in the hydrated sPS into hydrophobic and hydrophilic subphases, water self-diffusion, and proton mobility. As the hydration level increases, the hydrophilic subphase exhibits a percolation transition from isolated water clusters to a 3D network. The analysis of hydrophilic subphase connectivity and water diffusion demonstrates the importance of the dynamic percolation effect of formation and breakup of temporary junctions between water clusters. The proposed DPD model qualitatively predicts the ratio of proton to water self-diffusion and its dependence on the hydration level that is in reasonable agreement with experiments.
Lahey, Benjamin B.; Applegate, Brooks; Chronis, Andrea M.; Jones, Heather A.; Williams, Stephanie Hall; Loney, Jan; Waldman, Irwin D.
2008-01-01
Lahey and Waldman proposed a developmental propensity model in which three dimensions of children's emotional dispositions are hypothesized to transact with the environment to influence risk for conduct disorder, heterogeneity in conduct disorder, and comorbidity with other disorders. To prepare for future tests of this model, a new measure of…
First Principles Modeling of Phonon Heat Conduction in Nanoscale Crystalline Structures
Energy Technology Data Exchange (ETDEWEB)
Sandip Mazumder; Ju Li
2010-06-30
The inability to remove heat efficiently is currently one of the stumbling blocks toward further miniaturization and advancement of electronic, optoelectronic, and micro-electro-mechanical devices. In order to formulate better heat removal strategies and designs, it is first necessary to understand the fundamental mechanisms of heat transport in semiconductor thin films. Modeling techniques, based on first principles, can play the crucial role of filling gaps in our understanding by revealing information that experiments are incapable of. Heat conduction in crystalline semiconductor films occurs by lattice vibrations that result in the propagation of quanta of energy called phonons. If the mean free path of the traveling phonons is larger than the film thickness, thermodynamic equilibrium ceases to exist, and thus, the Fourier law of heat conduction is invalid. In this scenario, bulk thermal conductivity values, which are experimentally determined by inversion of the Fourier law itself, cannot be used for analysis. The Boltzmann Transport Equation (BTE) is a powerful tool to treat non-equilibrium heat transport in thin films. The BTE describes the evolution of the number density (or energy) distribution for phonons as a result of transport (or drift) and inter-phonon collisions. Drift causes the phonon energy distribution to deviate from equilibrium, while collisions tend to restore equilibrium. Prior to solution of the BTE, it is necessary to compute the lifetimes (or scattering rates) for phonons of all wave-vector and polarization. The lifetime of a phonon is the net result of its collisions with other phonons, which in turn is governed by the conservation of energy and momentum during the underlying collision processes. This research project contributed to the state-of-the-art in two ways: (1) by developing and demonstrating a calibration-free simple methodology to compute intrinsic phonon scattering (Normal and Umklapp processes) time scales with the inclusion
Nerve conduction in relation to vibration exposure - a non-positive cohort study
Directory of Open Access Journals (Sweden)
Nilsson Tohr
2010-07-01
Full Text Available Abstract Background Peripheral neuropathy is one of the principal clinical disorders in workers with hand-arm vibration syndrome. Electrophysiological studies aimed at defining the nature of the injury have provided conflicting results. One reason for this lack of consistency might be the sparsity of published longitudinal etiological studies with both good assessment of exposure and a well-defined measure of disease. Against this background we measured conduction velocities in the hand after having assessed vibration exposure over 21 years in a cohort of manual workers. Methods The study group consisted of 155 male office and manual workers at an engineering plant that manufactured pulp and paper machinery. The study has a longitudinal design regarding exposure assessment and a cross-sectional design regarding the outcome of nerve conduction. Hand-arm vibration dose was calculated as the product of self-reported occupational exposure, collected by questionnaire and interviews, and the measured or estimated hand-arm vibration exposure in 1987, 1992, 1997, 2002, and 2008. Distal motor latencies in median and ulnar nerves and sensory nerve conduction over the carpal tunnel and the finger-palm segments in the median nerve were measured in 2008. Before the nerve conduction measurement, the subjects were systemically warmed by a bicycle ergometer test. Results There were no differences in distal latencies between subjects exposed to hand-arm vibration and unexposed subjects, neither in the sensory conduction latencies of the median nerve, nor in the motor conduction latencies of the median and ulnar nerves. Seven subjects (9% in the exposed group and three subjects (12% in the unexposed group had both pathological sensory nerve conduction at the wrist and symptoms suggestive of carpal tunnel syndrome. Conclusion Nerve conduction measurements of peripheral hand nerves revealed no exposure-response association between hand-arm vibration exposure and
Energy Technology Data Exchange (ETDEWEB)
Gorbunov, V.A.; Frolov, V.V.; Kolesnikov, Yu.B.; Kolokolov, V.Ye.; Polyakov, N.N.
1984-01-01
The design of a mock up of a centrifugal conduction magnetohydrodynamic (MGD) pump is described. The dependences of the pressure developed by the pump in a locked mode on the magnetic induction and the operational current are cited, along with the flow rate and pressure characteristics of the pump. The dependences of the characteristics of the pump on the dimensions of the operational zone and the conductivity of the facial walls are experimentally studied.
Modelling electrical conductivity of groundwater using an adaptive neuro-fuzzy inference system
B. Tutmez (Bulent); Z. Hatipoglu (Z.); U. Kaymak (Uzay)
2006-01-01
textabstractElectrical conductivity is an important indicator for water quality assessment. Since the composition of mineral salts affects the electrical conductivity of groundwater, it is important to understand the relationships between mineral salt composition and electrical conductivity. In this
Model building in AdS/CMT: DC Conductivity and Hall angle
Pal, Shesansu Sekhar
2010-01-01
Using the bottom-up approach in a holographic setting, we attempt to study both the transport and thermodynamic properties of a generic system in $3+1$ dimensional bulk spacetime. We show the exact $1/T$ and $T^2$ dependence of conductivity and Hall angle, as seen experimentally in most copper-oxide systems, which are believed to be close to quantum critical point. Generically, the study of transport properties, using the probe brane approach, at low temperature suggests us to consider only metrics with two exponents. More precisely, the spatial part of the metric components should not be same i.e., $g_{xx}\
Lima, L. S.
2017-01-01
We use the SU(3) Schwinger boson formalism to study the spin transport in the three-dimensional S=1 Heisenberg ferromagnet in the cubic lattice with an easy plane crystal field, considering first-, second- and third-neighbor interactions. We have got one single peak for the spin conductivity for this system at ω =ωk and a variation of the height of the peak with the parameters Dc and η, and hence an influence of the quantum phase transition, between the disordered paramagnetic phase and the ordered ones, on the spin conductivity of this system. We have considered the exchange interaction J1 as ferromagnetic and the interactions J2 and J3 as antiferromagnetic.
Wang, H. L.; Wu, T. H.; Guo, F. Z.
1994-02-01
The influence of Kapitza thermal resistance of the composite material at superfluid helium temperatures is studied from the point of view of the heat transfer theory of cryogenics. A numerical model is developed for calculating the effective thermal conductivity coefficient of Cu-epoxide resin with the wires arranged in a square or crosswise. Experimental investigations have also been made at superfluid helium temperatures. The effective thermal conductivity coefficient of this kind of composite material measured by experiment is λ e=0.5929W/m·K.
Modeling the sensing characteristics of chemi-resistive thin film semi-conducting gas sensors.
Ghosh, Abhishek; Majumder, S B
2017-08-30
For chemi-resistive thin film gas sensors a generic theoretical model is proposed to predict the variation of sensor response with the operating temperature and thickness of the sensing film. A diffusion equation is formulated assuming that inflammable target gases move through the sensing film by Knudsen diffusion and react with the adsorbed oxygen following first-order kinetics. We have assumed a realistic non-linear variation between the conductance and test gas concentration and derived a general expression relating the sensor response to the operating temperature and thickness of the film. Assuming Langmuir adsorption kinetics, we have theoretically predicted the response and recovery transients during gas sensing using thin film sensing elements. It is predicted that for irreversible type sensing, the response time is reduced with an increase in test gas concentration, whereas for reversible sensing, the response time is independent of test gas concentration. For zinc oxide thin film sensors, an excellent match is obtained between the model prediction and experimental data for their thickness (122 nm to 380 nm) and temperature variation (200 °C to 325 °C) in 500 ppm carbon monoxide (CO) sensing. The maximum CO response% (∼53%) was achieved in 320 nm thick ZnO films. The conductance transients for response and recovery for CO sensing closely follow Langmuir adsorption kinetics and as predicted theoretically, indeed for irreversible sensing, the response time reduces from 350 s to 220 s with an increase in test gas concentration from 20 to 550 ppm. In the case of reversible sensing we found that the response time is ∼55 s irrespective of the CO gas concentration in the range of 5-500 ppm. The models developed in the present work are quite generic in nature and we have discussed their applicability to a wide variety of sensing materials with various types of surface morphologies.
Matthes, L.; Küfner, S.; Furthmüller, J.; Bechstedt, F.
2016-03-01
Ab initio relativistic band structure calculations are performed for the frequency-dependent spin Hall conductivity of two-dimensional atomically thin crystals and one-dimensional nanoribbons. We study the influence of topology, quantization, and topological edge states. As model systems fully halogenated germanene, GeI, and its zigzag nanoribbons are investigated. GeI represents a topological insulator (TI). For comparison, also the TI germanene and the trivial insulator hydrogenated germanene are studied. For the TIs we demonstrate the quantization of the static spin Hall conductivity. It is hardly influenced by temperature and Fermi level shift. Its frequency dependence is governed by the band-structure details. Topological edge states influence the conductivity mainly for vanishing frequencies.
Electrical conductivity studies of nanocrystalline lanthanum silicate synthesized by sol-gel route
Energy Technology Data Exchange (ETDEWEB)
Nallamuthu, N.; Prakash, I. [Department of Physics, Pondicherry University, Puducherry 605 014 (India); Satyanarayana, N., E-mail: nallanis2000@yahoo.com [Department of Physics, Pondicherry University, Puducherry 605 014 (India); Venkateswarlu, M. [R and D, Amara Raja Batteries Ltd., Tirupati 517520, AP (India)
2011-01-28
Research highlights: > Nanocrystalline La{sub 10}Si{sub 6}O{sub 27} material was synthesized by sol-gel method. > TG/DTA curves predicted the thermal behavior of the material. > FTIR spectra confirmed the formation of SiO{sub 4} and La-O network in the La{sub 10}Si{sub 6}O{sub 27}. > XRD patterns confirmed the formation of pure crystalline La{sub 10}Si{sub 6}O{sub 27} phase. > The grain interior and the grain boundary conductivities are evaluated. - Abstract: Nanocrystalline apatite type structured lanthanum silicate (La{sub 10}Si{sub 6}O{sub 27}) sample was synthesized by sol-gel process. Thermal behavior of the dried gel of lanthanum silicate sample was studied using TG/DTA. The structural coordination of the dried gel of lanthanum silicate, calcined at various temperatures, was identified from the observed FTIR spectral results. The observed XRD patterns of the calcined dried gel were compared with the ICDD data and confirmed the formation of crystalline lanthanum silicate phase. The average crystalline size of La{sub 10}Si{sub 6}O{sub 27} was calculated using the Scherrer formula and it is found to be {approx}80 nm. The observed SEM images of the lanthanum silicate indicate the formation of the spherical particles and the existence of O, Si and La in the lanthanum silicate are confirmed from the SEM-EDX spectrum. The grain and grain boundary conductivities are evaluated by analyzing the measured impedance data, using winfit software, obtained at different temperatures, of La{sub 10}Si{sub 6}O{sub 27} sample. Also, the observed grain and grain boundary conductivity behaviors of the La{sub 10}Si{sub 6}O{sub 27} sample are analysed using brick layer model. The electrical permittivity and electrical modulus were calculated from the measured impedance data and were analyzed by fitting through the Havriliak and Negami function to describe the dielectric relaxation behavior of the nanocrystalline lanthanum silicate.
Jackisch, Conrad; Demand, Dominic; Allroggen, Niklas; Loritz, Ralf; Zehe, Erwin
2017-04-01
In order to discuss hypothesis testing in hydrology, the question of the solid foundation of such tests has to be answered. But how certain are we about our measurements of the components of the water balance and the states and dynamics of the complex systems? What implicit assumptions or bias are already embedded in our perception of the processes? How can we find light in the darkness of heterogeneity? We will contribute examples from experimental findings, modelling approaches and landscape analysis to the discussion. Example soil moisture and the soil continuum: The definition of soil moisture as fraction of water in the porous medium assumes locally well-mixed conditions. Moreover, a unique relation of soil water retention presumes instant local thermodynamic equilibrium in the pore water arrangement. We will show findings from soil moisture responses to precipitation events, from irrigation experiments, and from a model study of initial infiltration velocities. The results highlight, that the implicit assumption relating soil moisture state dynamics with actual soil water flow is biased towards the slow end of the actual velocity distribution and rather blind for preferential flow acting in a very small proportion of the pore space. Moreover, we highlight the assumption of a well-defined continuum during the extrapolation of point-scale measurements and why spatially and temporally continuous observation techniques of soil water states are essential for advancing our understanding and development of subsurface process theories. Example hydraulic conductivity: Hydraulic conductivity lies at the heart of hydrological research and modelling. Its values can range across several orders of magnitude at a single site alone. Yet, we often consider it a crisp, effective parameter. We have conducted measurements of soil hydraulic conductivity in the lab and in the field. Moreover, we assessed infiltration capacity and conducted plot-scale irrigation experiments to
Energy Technology Data Exchange (ETDEWEB)
Lee, S.
2011-08-30
The Saltstone facility has a grout hopper tank to provide agitator stirring of the Saltstone feed materials. The tank has about 300 gallon capacity to provide a larger working volume for the grout slurry to be held in case of a process upset, and it is equipped with a mechanical agitator, which is intended to keep the grout in motion and agitated so that it won't start to set up. The dry feeds and the salt solution are already mixed in the mixer prior to being transferred to the hopper tank. The hopper modeling study through this work will focus on fluid stirring and agitation, instead of traditional mixing in the literature, in order to keep the tank contents in motion during their residence time so that they will not be upset or solidified prior to transferring the grout to the Saltstone disposal facility. The primary objective of the work is to evaluate the flow performance for mechanical agitators to prevent vortex pull-through for an adequate stirring of the feed materials and to estimate an agitator speed which provides acceptable flow performance with a 45{sup o} pitched four-blade agitator. In addition, the power consumption required for the agitator operation was estimated. The modeling calculations were performed by taking two steps of the Computational Fluid Dynamics (CFD) modeling approach. As a first step, a simple single-stage agitator model with 45{sup o} pitched propeller blades was developed for the initial scoping analysis of the flow pattern behaviors for a range of different operating conditions. Based on the initial phase-1 results, the phase-2 model with a two-stage agitator was developed for the final performance evaluations. A series of sensitivity calculations for different designs of agitators and operating conditions have been performed to investigate the impact of key parameters on the grout hydraulic performance in a 300-gallon hopper tank. For the analysis, viscous shear was modeled by using the Bingham plastic approximation
Energy Technology Data Exchange (ETDEWEB)
Lee, S.
2011-08-30
The Saltstone facility has a grout hopper tank to provide agitator stirring of the Saltstone feed materials. The tank has about 300 gallon capacity to provide a larger working volume for the grout slurry to be held in case of a process upset, and it is equipped with a mechanical agitator, which is intended to keep the grout in motion and agitated so that it won't start to set up. The dry feeds and the salt solution are already mixed in the mixer prior to being transferred to the hopper tank. The hopper modeling study through this work will focus on fluid stirring and agitation, instead of traditional mixing in the literature, in order to keep the tank contents in motion during their residence time so that they will not be upset or solidified prior to transferring the grout to the Saltstone disposal facility. The primary objective of the work is to evaluate the flow performance for mechanical agitators to prevent vortex pull-through for an adequate stirring of the feed materials and to estimate an agitator speed which provides acceptable flow performance with a 45{sup o} pitched four-blade agitator. In addition, the power consumption required for the agitator operation was estimated. The modeling calculations were performed by taking two steps of the Computational Fluid Dynamics (CFD) modeling approach. As a first step, a simple single-stage agitator model with 45{sup o} pitched propeller blades was developed for the initial scoping analysis of the flow pattern behaviors for a range of different operating conditions. Based on the initial phase-1 results, the phase-2 model with a two-stage agitator was developed for the final performance evaluations. A series of sensitivity calculations for different designs of agitators and operating conditions have been performed to investigate the impact of key parameters on the grout hydraulic performance in a 300-gallon hopper tank. For the analysis, viscous shear was modeled by using the Bingham plastic approximation
Formal feasibility studies in palliative care: why they are important and how to conduct them.
Hagen, Neil A; Biondo, Patricia D; Brasher, Penny M A; Stiles, Carla R
2011-08-01
The concept of clinical trial feasibility is of great interest to the community of palliative care researchers, clinicians, and granting agencies. Significant allocation of resources is required in the form of funding, time, intellect, and motivation to carry out clinical research, and understandably, clinical investigators, institutions, and granting agencies are disappointed when funded trials are unsuccessfully conducted. We argue that for many trials conducted in palliative care, the feasibility of conducting the proposed trial should be formally explored before implementation. There is substantial information available within the literature on the topic of study feasibility but no singular guide on how one can pragmatically apply this advice in the palliative care setting. We suggest that a Formal Feasibility Study for palliative care trials should be commonly conducted before development of a larger pivotal trial, to prospectively identify barriers to research, develop strategies to address these barriers, and predict whether the larger study is feasible. If a Formal Feasibility Study is not required, elements of feasibility can be specifically tested before launching clinical trials. The purpose of this article is to offer a draft framework for the design and conduct of a Formal Feasibility Study that, if implemented, could concretely support successful completion of high-quality research in a timely fashion. Additionally, we hope to foster dialogue within the palliative care research community regarding the relevance of establishing feasibility before initiation of definitive trials in the palliative care population.
Pandey, Hari Datt; Leitner, David M.
2017-08-01
Thermalization in molecular junctions and the extent to which it mediates thermal transport through the junction are explored and illustrated with computational modeling of polyethylene glycol (PEG) oligomer junctions. We calculate rates of thermalization in the PEG oligomers from 100 K to 600 K and thermal conduction through PEG oligomer interfaces between gold and other materials, including water, motivated in part by photothermal applications of gold nanoparticles capped by PEG oligomers in aqueous and cellular environments. Variation of thermalization rates over a range of oligomer lengths and temperatures reveals striking effects of thermalization on thermal conduction through the junction. The calculated thermalization rates help clarify the scope of applicability of approaches that can be used to predict thermal conduction, e.g., where Fourier's law breaks down and where a Landauer approach is suitable. The rates and nature of vibrational energy transport computed for PEG oligomers are compared with available experimental results.