Academic literature on the topic 'Conductance theories'
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Journal articles on the topic "Conductance theories"
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Mahdi, Loauy Abd Al-Azez, Wahid S. Mohammad, and Samir Akram Mahmood. "Exergy Analysis of a Domestic Refrigerator." Journal of Engineering 24, no. 9 (August 29, 2018): 1. http://dx.doi.org/10.31026/j.eng.2018.09.01.
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An energy and exergy thermodynamic analysis using EES program was done for a domestic refrigerator working with R-134a using vapor compression refrigeration cycle. The analysis deals with the system component, i.e. compressor, condenser, evaporator and the expansion device. The analysis depends on the entropy generation minimization approach to improve the refrigerator performance by exploring the optimum design points. These design points were derived from three different theories governing the entropy generation minimization using exergy analyzing method. These theories were first applied to find the optimum balance between the hot inner condenser area and the cold inner evaporator area of the refrigerator and between its hot and cold thermal conductances. Nine types of condensers were used according to its internal surface area and thermal conductance, in order to reach the minimum entropy generation in the refrigerator. The results showed that the compressor has the lowest exergy efficiency of 25%. The expansion device was the second component after the compressor with exergy efficiency of 92%, followed by the condenser with an efficiency of 93%. The evaporator was found to have an exergy efficiency of 98 %. The experimental tests were repeated for the nine condensers sizes with three different ambient temperatures 25℃, 30℃ and 35℃. The exergy analysis showed that the design of the refrigerator mainly depends on thermal conductance calculations rather than the surface inner area estimation.
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Anderegg, William R. L. "Quantifying seasonal and diurnal variation of stomatal behavior in a hydraulic-based stomatal optimization model." Journal of Plant Hydraulics 5 (December 22, 2018): e001. http://dx.doi.org/10.20870/jph.2018.e001.
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Plant responses to drought occur across many time-scales, with stomatal closure typically considered to be a critical short-term response. Recent theories of optimal stomatal conductance linked to plant hydraulic transport have shown promise, but it is not known if stomata update their hydraulic “shadow price” of water use (marginal increase in carbon cost with a marginal drop in water potential) over days, seasons, or in response to recent drought. Here, I estimate the hydraulic shadow price in five species – two semi-arid gymnosperms, one temperate and two tropical angiosperms – at daily timescales and in wet and dry periods. I tested whether the shadow prices varies predictably as a function of current and/or lagged drought conditions. Diurnal estimates of the hydraulic shadow price estimated from observed stomatal conductance, while variable, did not vary predictably with environmental variables. Seasonal variation in shadow price was observed in the gymnosperm species, but not the angiosperm species, and did not meaningfully influence prediction accuracy of stomatal conductance. The lack of systematic variation in shadow price and high predictive ability of stomatal conductance when using a single set of parameters further emphasizes the potential of hydraulic-based stomatal optimization theories.
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OVCHINNIKOV, A. A. "NON-RENORMALIZATION THEOREM IN CHERN-SIMONS THEORIES AND FRACTIONAL QUANTUM HALL EFFECT." Modern Physics Letters A 07, no. 07 (March 7, 1992): 611–17. http://dx.doi.org/10.1142/s0217732392000586.
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We prove the non-renormalization theorem resulting in the exact cancellation of Chern-Simons term (and superconductivity) in systems of both free and interacting anyons with the statistical parameter 1/N. The theorem is used to prove the quantization of transverse conductance in the proposed second-quantized fermionic description of fractional quantum Hall effect.
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Castro-Alvaredo, O. A., and A. Fring. "Rational sequences for the conductance in quantum wires from affine Toda field theories." Journal of Physics A: Mathematical and General 36, no. 26 (June 17, 2003): L425—L432. http://dx.doi.org/10.1088/0305-4470/36/26/101.
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Yevtushenko, Oleg M., and Vladimir I. Yudson. "Protection of edge transport in quantum spin Hall samples: spin-symmetry based general approach and examples." New Journal of Physics 24, no. 2 (February 1, 2022): 023040. http://dx.doi.org/10.1088/1367-2630/ac50e9.
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Abstract Understanding possible mechanisms, which can lead to suppression of helical edge transport in quantum spin Hall (QSH) systems, attracted huge attention right after the first experiments revealing the fragility of the ballistic conductance. Despite the very intensive research and the abundance of theoretical models, the fully consistent explanation of the experimental results is still lacking. We systematize various theories of helical transport with the help of the spin conservation analysis which allows one to single out setups with the ballistic conductance being robustly protected regardless of the electron backscattering. First, we briefly review different theories of edge transport in the QSH samples with and without the spin axial symmetry of the electrons including those theoretical predictions which are not consistent with the spin conservation analysis and, thus, call for a deeper study. Next, we illustrate the general approach by a detailed study of representative examples. One of them addresses the helical edge coupled to an array of Heisenberg-interacting magnetic impurities (MIs) and demonstrates that the conductance remains ballistic even if the time-reversal symmetry on the edge is (locally) broken but the total spin is conserved. Another example focuses on the effects of the space-fluctuating spin–orbit interaction on the QSH edge. It reveals weakness of the protection in several cases, including, e.g. the presence of either the U(1)-symmetric, though not fully isotropic, MIs or generic electron–electron interactions.
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Lambert, M. A., and L. S. Fletcher. "Thermal Contact Conductance of Non-Flat, Rough, Metallic Coated Metals." Journal of Heat Transfer 124, no. 3 (May 10, 2002): 405–12. http://dx.doi.org/10.1115/1.1464565.
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Thermal contact conductance is an important consideration in such applications as nuclear reactor cooling, electronics packaging, spacecraft thermal control, and gas turbine and internal combustion engine cooling. In many instances, the highest possible thermal contact conductance is desired. For this reason, soft, high conductivity, metallic coatings are sometimes applied to contacting surfaces (often metallic) to increase thermal contact conductance. O’Callaghan et al. (1981) as well as Antonetti and Yovanovich (1985, 1988) developed theoretical models for thermal contact conductance of metallic coated metals, both of which have proven accurate for flat, rough surfaces. However, these theories often substantially overpredict the conductance of non-flat, rough, metallic coated metals. In the present investigation, a semi-empirical model for flat and non-flat, rough, uncoated metals, previously developed by Lambert and Fletcher (1996), is employed in predicting the conductance of flat and non-flat, rough, metallic coated metals. The models of Antonetti and Yovanovich (1985, 1988) and Lambert and Fletcher (1996) are compared to experimental data from a number of investigations in the literature. This entailed analyzing the results for a number of metallic coating/substrate combinations on surfaces with widely varying flatness and roughness. Both models agree well with experimental results for flat, rough, metallic coated metals. However, the semi-empirical model by Lambert and Fletcher (1996) is more conservative than the theoretical model by Antonetti and Yovanovich (1985, 1988) when compared to the majority of experimental results for non-flat, rough, metallic coated metals.
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Wojtczak, Lech, and Mariusz R. Więckowski. "From mitochondrial large amplitude swelling to the permeability transition – a short historic overview." Postępy Biochemii 62, no. 3 (November 18, 2016): 298–302. http://dx.doi.org/10.18388/pb.2016_29.
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An outline of studies on the mitochondrial large conductance permeability pore is presented starting from the early observations in the 1950s on the large amplitude mitochondrial swelling, through the concept of the permeability transition and various theories on the structure of the related permeability transition pore, up to its present identification as a part of mitochondrial (F1 FO) ATPase/ATP synthase.
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Mazzone, A. M. "The conductance of SnO2 small nanowires: A study based on density functional and scattering theories." Solid State Communications 143, no. 10 (September 2007): 481–86. http://dx.doi.org/10.1016/j.ssc.2007.06.023.
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Gao, Jun Li, Yan Hong Que, Dong Ying Feng, and Wei Chen. "Research of the Model and MPPT Algorithm of Solar Cells." Advanced Materials Research 724-725 (August 2013): 67–73. http://dx.doi.org/10.4028/www.scientific.net/amr.724-725.67.
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According to the mathematic model of solar cells, builds its general simulation model based on the S-function designed under the Matlab/Simulink environment. Presents the incremental conductance algorithm based on the optimal gradient to simulate and verify the theories about the maximum power point tracking (MPPT) of photovoltaic power generation. Give the in-depth contrast analysis on the power, output voltage characteristics of photovoltaic power generation, which lays a solid foundation for engineering practice.
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Chung, Tien Tung, Chih Kang Lu, and Yi Ting Tu. "Design, Manufacturing and Pump-down Curve Simulation of High Vacuum Systems." Applied Mechanics and Materials 220-223 (November 2012): 575–79. http://dx.doi.org/10.4028/www.scientific.net/amm.220-223.575.
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This paper presents a vacuum system design for extreme ultraviolet lithography (EUV) and studies the prediction of pump-down curves for vacuum chambers. Related basic theories include gas laws, conductance for several kinds of flow regimes, equivalent length for pipes, outgassing, diffusion, and permeation etc. The simulation program consists of a MFC module and a MATLAB module. The MFC module is used to input necessary parameters, including start and target pressure for pumping, volume and inner surface area of vacuum chambers, configuration of pumping lines, performance of vacuum pumps, and gas loads. The MATLAB module deals with the pump-down curve calculation based on related theories. The governing equation of the conservation of mass in a pumped vacuum chamber is derived from extended Temkin isotherm. The pump-down curve of vacuum chamber is predicted by four steps, including calculation of equivalent length for pipes, conductance of pipes, and effective pumping speed of pumps, and pump-down time. An empty vacuum chamber is used to test the developed program. The pump-down curve reaches 6.5E-8 torr with 42 hours pump-down time in experiment measurement, and the simulated curve reaches 5.79E-8 torr at the same time point. The developed program can predict pump-down curve with a good accuracy in the range from low vacuum pressure to high vacuum pressure.
Dissertations / Theses on the topic "Conductance theories"
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Hoyles, Matthew, and Matthew Hoyles@anu edu au. "Computer Simulation of Biological Ion Channels." The Australian National University. Theoretical Physics, 2000. http://thesis.anu.edu.au./public/adt-ANU20010702.135814.
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This thesis describes a project in which algorithms are developed for the rapid and accurate solution of Poisson's equation in the presence of a dielectric boundary and multiple point charges. These algorithms are then used to perform Brownian dynamics simulations on realistic models of biological ion channels. An iterative method of solution, in which the dielectric boundary is tiled with variable sized surface charge sectors, provides the flexibility to deal with arbitrarily shaped boundaries, but is too slow to perform Brownian dynamics. An analytical solution is derived, which is faster and more accurate, but only works for a toroidal boundary. Finally, a method is developed of pre-calculating solutions to Poisson's equation and storing them in tables. The solution for a particular configuration of ions in the channel can then be assembled by interpolation from the tables and application of the principle of superposition. This algorithm combines the flexibility of the iterative method with greater speed even than the analytical method, and is fast enough that channel conductance can be predicted. The results of simulations for a model single-ion channel, based on the acetylcholine receptor channel, show that the narrow pore through the low dielectric strength medium of the protein creates an energy barrier which restricts the permeation of ions. They further show that this barrier can be removed by dipoles in the neck of the channel, but that the barrier is not removed by shielding by counter-ions. The results of simulations for a model multi-ion channel, based on a bacterial potassium channel, show that the model channel has conductance characteristics similar to those of real potassium channels. Ions appear to move through the model multi-ion channel via rapid transitions between a series of semi-stable states. This observation suggests a possible physical basis for the reaction rate theory of channel conductance, and opens up an avenue for future research.
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Eisel, Thomas. "Cooling of electrically insulated high voltage electrodes down to 30 mK." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-77442.
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The Antimatter Experiment: Gravity, Interferometry, Spectroscopy (AEGIS) at the European Organization for Nuclear Research (CERN) is an experiment investigating the influence of earth’s gravitational force upon antimatter. To perform precise measurements the antimatter needs to be cooled to a temperature of 100 mK. This will be done in a Penning trap, formed by several electrodes, which are charged with several kV and have to be individually electrically insulated. The trap is thermally linked to a mixing chamber of a 3He-4He dilution refrigerator.
Two link designs are examined, the Rod design and the Sandwich design. The Rod design electrically connects a single electrode with a heat exchanger, immersed in the helium of the mixing chamber, by a copper pin. An alumina ring and the helium electrically insulate the Rod design. The Sandwich uses an electrically insulating sapphire plate sandwiched between the electrode and the mixing chamber. Indium layers on the sapphire plate are applied to improve the thermal contact. Four differently prepared test Sandwiches are investigated. They differ in the sapphire surface roughness and in the application method of the indium layers.
Measurements with static and sinusoidal heat loads are performed to uncover the behavior of the thermal boundary resistances. The thermal total resistance of the best Sandwich shows a temperature dependency of T-2,64 and is significantly lower, with roughly 30 cm2K4/W at 50 mK, than experimental data found in the literature. The estimated thermal boundary resistance between indium and sapphire agrees very well with the value of the acoustic mismatch theory at low temperatures.
In both designs, homemade heat exchangers are integrated to transfer the heat to the cold helium. These heat exchangers are based on sintered structures to increase the heat transferring surface and to overcome the significant influence of the thermal resistance (Kapitza resistance). The heat exchangers are optimized concerning the adherence of the sinter to the substrate and its sinter height, e.g. its thermal penetration length.
Ruthenium oxide metallic resistors (RuO2) are used as temperature sensors for the investigations. They consist of various materials, which affect the reproducibility. The sensor conditioning and the resulting good reproducibility is discussed as well.
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"Critical and crossover behaviours in linear and nonlinear conductance networks near percolation =: 線性與非線性電導網絡之臨界及交疊特性." Chinese University of Hong Kong, 1995. http://library.cuhk.edu.hk/record=b5888449.
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by Hon-chor Lee.Thesis (M.Phil.)--Chinese University of Hong Kong, 1995.
Includes bibliographical references (leaf 56).
by Hon-chor Lee.
Introduction --- p.1
Series expansion for the conductivity of a linear random resistor network
Chapter 1. --- Introduction --- p.4
Chapter 2. --- Comparison of the EMA with symbolic simulations in 2D --- p.5
Chapter 3. --- Comparison of the EMA with Bergman and Kantor's findings --- p.6
Chapter 4. --- Conclusion --- p.7
Current moments of linear random resistor network
Chapter 1. --- Introduction --- p.10
Chapter 2. --- Review of the definition of current moment --- p.10
Chapter 3. --- Tremblay et. al.'s findings and symbolic simulation of current moments --- p.11
Chapter 4. --- Conclusion --- p.13
Effective medium theory for strongly nonlinear composites: comparison with numerical simulations
Chapter 1. --- Introduction --- p.15
Chapter 2. --- Variational principles --- p.16
Chapter 3. --- Formalism of EMA --- p.17
Chapter 4. --- Comparison with numerical simulations --- p.19
Chapter 5. --- Discussion --- p.21
Percolative conduction in two-component strongly nonlinear composites
Chapter 1. --- Introduction --- p.25
Chapter 2. --- Spherical inclusions --- p.25
Chapter 3. --- Effective medium approximation in the vicinity of the percolation threshold --- p.27
Chapter 4. --- Acknowledgment --- p.29
Percolation Effects in Two Component Strongly Nonlinear Composites: Universal Scaling Behaviours
Chapter 1. --- Introduction --- p.31
Chapter 2. --- General Scaling Relations for Two-Component Composites --- p.33
Chapter 3. --- Estimate of Critical Exponents --- p.35
Chapter 4. --- Numerical Simulations --- p.38
Chapter 5. --- Discussions and Conclusions --- p.40
Chapter 6. --- Acknowledgment --- p.40
Improved effective medium theory for strongly nonlinear composites
Chapter 1. --- Introduction --- p.46
Chapter 2. --- Formalism of Improved EMA --- p.47
Chapter 3. --- Comparisons with numerical simulations and HS bound --- p.50
Chapter 4. --- Discussions --- p.51
Conclusion --- p.54
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Hoyles, Matthew. "Computer Simulation of Biological Ion Channels." Phd thesis, 1999. http://hdl.handle.net/1885/47286.
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This thesis describes a project in which algorithms are developed for the rapid and accurate solution of Poisson's equation in the presence of a dielectric boundary and multiple point charges. These algorithms are then used to perform Brownian dynamics simulations on realistic models of biological ion channels. An iterative method of solution, in which the dielectric boundary is tiled with variable sized surface charge sectors, provides the flexibility to deal with arbitrarily shaped boundaries, but is too slow to perform Brownian dynamics. An analytical solution is derived, which is faster and more accurate, but only works for a toroidal boundary. Finally, a method is developed of pre-calculating solutions to Poisson's equation and storing them in tables. The solution for a particular configuration of ions in the channel can then be assembled by interpolation from the tables and application of the principle of superposition. This algorithm combines the flexibility of the iterative method with greater speed even than the analytical method, and is fast enough that channel conductance can be predicted. The results of simulations for a model single-ion channel, based on the acetylcholine receptor channel, show that the narrow pore through the low dielectric strength medium of the protein creates an energy barrier which restricts the permeation of ions. They further show that this barrier can be removed by dipoles in the neck of the channel, but that the barrier is not removed by shielding by counter-ions. The results of simulations for a model multi-ion channel, based on a bacterial potassium channel, show that the model channel has conductance characteristics similar to those of real potassium channels. Ions appear to move through the model multi-ion channel via rapid transitions between a series of semi-stable states. This observation suggests a possible physical basis for the reaction rate theory of channel conductance, and opens up an avenue for future research.
Book chapters on the topic "Conductance theories"
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Lee, Patrick A. "Universal Conductance Fluctuations in Disordered Metals." In Condensed Matter Theories, 265–66. Boston, MA: Springer US, 1987. http://dx.doi.org/10.1007/978-1-4613-0917-8_29.
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Chen, C. Julian. "Overview." In Introduction to Scanning Tunneling Microscopy, 1–40. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198856559.003.0001.
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This chapter presents the basic designs and working principles of STM and AFM, as well as an elementary theory of tunneling and the imaging mechanism of atomic resolution. Three elementary theories of tunneling are presented: the one-dimensional Schrödinger’s equation in vacuum, the semi-classical approximation, and the Landauer formalism. The relation between the decay constant and the work function, and a general expression of tunneling conductance versus tip-sample distance are derived. A brief summary of experimental facts on the mechanism of atomic resolution STM and AFM is presented, which leads to a picture of interplay between the atomic states of the tip and the sample, as well as the role of partial covalent bonds formed between those electronic states. Four illustrative applications are presented, including imaging self-assembed molecules on solid-liquid interfaces, electrochemical STM, catalysis research, and atom manipulation.
Conference papers on the topic "Conductance theories"
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Castro-Alvaredo, Olalla A., and Andreas Fring. "Conductance from Non-perturbative Methods II." In Workshop on Integrable Theories, Solitons and Duality. Trieste, Italy: Sissa Medialab, 2002. http://dx.doi.org/10.22323/1.008.0010.
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Fring, Andreas, and Olalla A. Castro-Alvaredo. "Conductance from Non-perturbative Methods I." In Workshop on Integrable Theories, Solitons and Duality. Trieste, Italy: Sissa Medialab, 2002. http://dx.doi.org/10.22323/1.008.0015.
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Sefriti, Bouchra, and Ismail Boumhidi. "Neural network Incremental conductance MPPT algorithm for photovoltaic water pumping system." In 2015 10th International Conference on Intelligent Systems: Theories and Applications (SITA). IEEE, 2015. http://dx.doi.org/10.1109/sita.2015.7358383.
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Yovanovich, Milan Michael. "RECENT DEVELOPMENTS IN THERMAL CONTACT, GAP AND JOINT CONDUCTANCE THEORIES AND EXPERIMENT." In International Heat Transfer Conference 8. Connecticut: Begellhouse, 1986. http://dx.doi.org/10.1615/ihtc8.2260.
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Phelan, Patrick E., and Meng Zhang. "The Thermal Conductance of Indium-Filled Contacts at Cryogenic Temperatures." In ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-61971.
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Indium foil is often used to increase the thermal contact conductance hc of junctions at cryogenic temperatures, yet relatively few experimental data on hc at subambient temperatures are available. Here, experimental measurements of hc at a copper/copper junction containing a 25.4-μm-thick indium foil are reported. The average sample temperature ranged from 40 to 180 K, and the contact pressures ranged from 0.2 to 20 MPa. Although it was originally anticipated that increasing the contact pressure would lead to increasing hc, the observed hc showed little or no dependence on contact pressure. This was attributed to the severe nonflatness of the copper surfaces. Comparison between the measured hc, and that calculated from existing “flat” and “nonflat” theories indicated better agreement with the “nonflat” model, although the model still predicted that hc should depend on pressure.
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De Bellis, Lisa, and Patrick E. Phelan. "Measurement and Prediction of the Contact Conductance Across Epoxied Copper Contacts at Cryogenic Temperatures." In ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1386.
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Abstract Literature has demonstrated that the investigation of the contact conductance (hc) across epoxied joints at cryogenic temperatures is important to the microelectronic, satellite and other space industries. The accurate theoretical prediction of the hc arising across a metal-epoxy interface is still being researched. Several researchers have shown that the acoustic mismatch and other theories do not agree well with experimental data. This paper presents the results of an experimental and theoretical investigation of the hc across copper/epoxy/copper contacts. From the hc data, it was possible to extract the thermal conductivity (k) of the epoxy and the thermal boundary resistance (Rb) between the epoxy and copper. The Rb extracted from the experimental data was compared to model predictions made by the Acoustic Mismatch Model (AMM) and the Scattering Mediated Acoustic Mismatch Model (SMAMM). In the case of the AMM, the predictions underestimated the experimental values significantly. This finding is consistent with many investigations to date. The SMAMM was able to predict the experimental data very well when using an extremely small scattering time of 5×10−18 s.
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Broido, D. A., Natalio Mingo, and Derek Stewart. "Phonon Thermal Transport in Bulk and Nanostructured Materials From First Principles." In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-67049.
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Current theories of phonon thermal transport in nanomaterials are often based on highly parametrized approximations or on purely classical molecular dynamics calculations. We present a rigorous theoretical approach to accurately describe phonon thermal transport in bulk and nanostructured materials. This technique is based on Boltzmann and non-equilibrium Green’s function calculations of thermal transport, and employs ab-initio calculations of harmonic and anharmonic interatomic force constants using density functional perturbation theory. The approach has been applied to bulk semiconductors, where excellent agreement is obtained between the calculated and measured intrinsic lattice thermal conductivities of silicon and germanium without any adjustable parameters. In addition, ab initio calculations of phonon thermal conductance in carbon nanotubes with isolated Stone-Wales and substitutional defects are presented and discussed.
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Kogut, Lior. "Electrical Performance of Degraded MEMS Ohmic Switches." In World Tribology Congress III. ASMEDC, 2005. http://dx.doi.org/10.1115/wtc2005-63169.
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Electrical performance of degraded MEMS metallic switches (ohmic contacts) is studied analytically in this paper. The degradation mechanism is based on gradual growth of an insulating film at the contact interface and the characteristics of the insulating film are assumed to be known without considering details regarding the physical and chemical origins of the growth mechanisms. The present study relies on recently developed theories for electrical contact resistance (ECR) of clean and fully-contaminated (i.e., the entire contact area is coated with an insulating film) rough surfaces thus, bridging the gap between these two extreme cases. A relationship is obtained between the degraded ECR and the metallic conductance area. The effect of tunneling currents on the performance of partially-contaminated surfaces is found to be negligible due to the considerable current flow across the metallic asperity contacts.
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Stevens, Robert J., Pamela M. Norris, and Arthur W. Lichtenberger. "Experimental Determination of the Relationship Between Thermal Boundary Resistance and Non-Abrupt Interfaces and Electron-Phonon Coupling." In ASME 2004 Heat Transfer/Fluids Engineering Summer Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/ht-fed2004-56556.
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Understanding thermal boundary resistance (TBR) is becoming increasingly important for the thermal management of micro and optoelectronic devices. The current understanding of room temperature TBR is often not adequate for the thermal design of tomorrow’s complex micro and nano devices. Theories have been developed to explain the resistance to energy transport by phonons across interfaces. The acoustic mismatch model (AMM) [1, 2], which has had success at explaining low temperature TBR, does not account for the high frequency phonons and imperfect interfaces of real devices at room temperature. The diffuse mismatch model (DMM) was developed to account for real surfaces with higher energy phonons [3, 4]. DMM assumes that all phonons incident on the interface from both sides are elastically scattered and then emitted to either side of the interface. The probability that a phonon is emitted to a particular side is proportional to the phonon density of states of the two interface materials. Inherent to the DMM is that the transport is independent of the interface structure itself and is only dependent on the properties of the two materials. Recent works have shown that the DMM does not adequately capture all the energy transport mechanisms at the interface [5, 6]. In particular, the DMM under-predicts transport across interfaces between non Debye-like materials, such at Pb and diamond, by approximately an order of magnitude. The DMM also tends to over-predict transport for interfaces made with materials of similar acoustic properties, Debye-like materials. There have been several explanations and models developed to explain the discrepancies between the mismatch models and experimental data. Some of these models are based on modification of the AMM and DMM [7–9]. Other works have utilized lattice-dynamical modeling to calculate phonon transmission coefficients and thermal boundary conductivities for abrupt and disordered interfaces [3, 6, 10–13]. Recent efforts to better understand room temperature TBR have utilized molecular dynamics simulations to account for more realistic anharmonic materials and inelastic scattering [14–18]. Models have also been developed to account for electron-phonon scattering and its effect on the thermal boundary conductance for interfaces with one metal side [19–22]. Although there have been numerous thermal boundary resistance theoretical developments since the introduction of the AMM, there still is not an unifying theory that has been well validated for high temperature solid-solid interfaces. Most of the models attempt to explain some of the experimental outliers, such as Pb/diamond and TiN/MgO interfaces [6, 23], but have not been fully tested for a range of experimental data. Part of the problem lies in the fact that very little reliable data is available, especially data that is systematically taken to validate a particular model. To this end, preliminary measurements of TBR are being made on a series of metal on non-metal substrate interfaces using a non-destructive optical technique, transient thermal reflectance (TTR) described in Stevens et al. [5]. Initial testing examines the impact of different substrate preparation and deposition conditions on TBR for Debye-like interfaces for which TBR should be small for clean and abrupt interfaces. Variables considered include sputter etching power and duration, electron beam source clean, and substrate temperature control. The impact of alloying and non-abrupt interfaces on the TBR is examined by fabricating interfaces of both Debye-like and non Debye-like interfaces followed by systematically measuring TBR and altering the interfaces by annealing the samples to increase the diffusion depths at the interfaces. Inelastic electron scattering at the interface has been proposed by Hubermann et al. and Sergeev to decrease TBR at interfaces [19–21]. Two sets of samples are prepared to examine the electron-phonon connection to improved thermal boundary conductance. The first consists of thin Pt and Ag films on Si and sapphire substrates. Pt and Ag electron-phonon coupling factors are 60 and 3.1×1016 W/m3K respectively. Both Pt and Ag have similar Debye temperatures, so electron scattering rates can be examined without much change in acoustic effects. The second electron scattering sample series consist of multiple interfaces fabricated with Ni, Ge, and Si to separate the phonon and electron portions of thermal transport. The experimental data is compared to several of the proposed theories.
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Ciavarella, M., and J. R. Barber. "Elastic Contact Stiffness and Contact Resistance for Fractal Profiles." In ASME/STLE 2004 International Joint Tribology Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/trib2004-64357.
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A recent theorem due to Barber shows an analogy between conductance and incremental stiffness of a contact, implying bounds on conductance based on peak-to-peak roughness. This shows that even a fractal roughness, with bounded amplitude, has a finite conductance. The analogy also permits a simple interpretation of classical results of rough contact models based on independent asperities such as Greenwood-Williamson and developments. For example, in the GW model with exponential distribution of asperity heights, the conductance is found simply proportional to load, and inversely proportional to a roughness amplitude parameter which does not depend greatly on resolution, contrary to parameters of slopes and curvatures. However, for the Gaussian distribution or for more refined models also considering varying curvature of asperities (such as Bush Gibson and Thomas), there is dependence on sampling interval and the conductance grows unbounded. An alternative choice of asperity definition (Aramaki-Majumdar-Bhushan) is suggested, which builds on the geometrical intersection of the rough surface, with the consequence of a finite contact area, and converging load-separation and load-conductance relationship. A discussion follows, also based on numerical results.