9,897 research outputs found

    Modeling and Simulation of Thermo-Fluid-Electrochemical Ion Flow in Biological Channels

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    In this article we address the study of ion charge transport in the biological channels separating the intra and extracellular regions of a cell. The focus of the investigation is devoted to including thermal driving forces in the well-known velocity-extended Poisson-Nernst-Planck (vPNP) electrodiffusion model. Two extensions of the vPNP system are proposed: the velocity-extended Thermo-Hydrodynamic model (vTHD) and the velocity-extended Electro-Thermal model (vET). Both formulations are based on the principles of conservation of mass, momentum and energy, and collapse into the vPNP model under thermodynamical equilibrium conditions. Upon introducing a suitable one-dimensional geometrical representation of the channel, we discuss appropriate boundary conditions that depend only on effectively accessible measurable quantities. Then, we describe the novel models, the solution map used to iteratively solve them, and the mixed-hybrid flux-conservative stabilized finite element scheme used to discretize the linearized equations. Finally, we successfully apply our computational algorithms to the simulation of two different realistic biological channels: 1) the Gramicidin-A channel considered in~\cite{JeromeBPJ}; and 2) the bipolar nanofluidic diode considered in~\cite{Siwy7}

    Terahertz thermometry: combining hyperspectral imaging and temperature mapping at terahertz frequencies

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    The accurate and non-invasive determination of multiple physical parameters, with well-defined spatial resolution, is crucial for applications in manufacturing, chemistry, medicine and biology. Specifically, the ability to simultaneously measure both temperature and spectral signatures is still experimentally unavailable. To this end, we propose a mapping technique for biological systems, which exploits a linear correlation between terahertz wave reflectivity and temperature, and allows to spatially and spectrally resolve thermal distributions. This method is applied to a model biological system in two relevant cases where in one example, nanoplasmonic-induced photothermal effects are imaged gaining new insights into collective heating phenomena. In the second example, we demonstrate a joint thermal-hyperspectral imaging approach to chemically map the presence of a model drug formulation and simultaneously investigate its thermal stability in our biological system. This concept can be easily extended and widely applied to all materials that demonstrate a measurable change in their dielectric properties

    Transient electrothermal simulation of power semiconductor devices

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    In this paper, a new thermal model based on the Fourier series solution of heat conduction equation has been introduced in detail. 1-D and 2-D Fourier series thermal models have been programmed in MATLAB/Simulink. Compared with the traditional finite-difference thermal model and equivalent RC thermal network, the new thermal model can provide high simulation speed with high accuracy, which has been proved to be more favorable in dynamic thermal characterization on power semiconductor switches. The complete electrothermal simulation models of insulated gate bipolar transistor (IGBT) and power diodes under inductive load switching condition have been successfully implemented in MATLAB/Simulink. The experimental results on IGBT and power diodes with clamped inductive load switching tests have verified the new electrothermal simulation model. The advantage of Fourier series thermal model over widely used equivalent RC thermal network in dynamic thermal characterization has also been validated by the measured junction temperature

    NASA SBIR abstracts of 1991 phase 1 projects

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    The objectives of 301 projects placed under contract by the Small Business Innovation Research (SBIR) program of the National Aeronautics and Space Administration (NASA) are described. These projects were selected competitively from among proposals submitted to NASA in response to the 1991 SBIR Program Solicitation. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 301, in order of its appearance in the body of the report. Appendixes to provide additional information about the SBIR program and permit cross-reference of the 1991 Phase 1 projects by company name, location by state, principal investigator, NASA Field Center responsible for management of each project, and NASA contract number are included

    Electro-Thermal Model for Multi-Anode Schottky Diode Multipliers

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    We present a self-consistent electro-thermal model for multi-anode Schottky diode multiplier circuits. The thermal model is developed for an -anode multiplier via a thermal resistance matrix approach. The nonlinear temperature responses of the material are taken into consideration by using a linear temperature dependent approximation for the thermal resistance. The electrothermal model is capable of predicting the hot spot temperature, providing useful information for circuit reliability study as well as high power circuit design and optimization. Examples of the circuit analysis incorporating the electro-thermal model for a substrateless- and a membrane-based multiplier circuits, operating up to 200 GHz, are demonstrated. Compared to simulations without thermal model, the simulations with electro-thermal model agree better with the measurement results. For the substrateless multiplier, the error between the simulated and measured peak output power is reduced from ~13% to ~4% by including the thermal effect

    Laser driven variable dot size thermal wax transfer printing

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    A digital image hardcopy device has been designed using a laser exposure mechanism, a pigmented wax /resin donor ink sheet, and an opaque receiver sheet. The writing system relies on image-wise thermal mass transfer of molten ink to the receiver in order to produce high resolution output. With the receiver media and a specially designed donor ribbon being held to a platen through vacuum pressure, a pulsed solid-state diode pumped near IR NdrYAG laser provides the energy necessary to complete the thermal transfer process. By varying pulse width, dot size variation is possible. A mathematical model was developed to explain the physics of the imaging process and aid further experimentation. In order to maximize photothermal conversion and transfer efficiency while maintaining environmental friendliness, a water/ alcohol based multi-layer donor ribbon was designed. Digital image analysis techniques and processing algorithms were developed specifically to provide a reliable quantification scheme for all variables. A randomized four factor central composite design provided a statistically robust means by which to map measured image quality. Response surface methods of factorial experimental design afforded a means to model the ribbon design space. Utilization of the Downhill Simplex Method (Nelder and Mead, 1965) yielded the optimum point on the estimated image quality response surface. The optimum point represented the final donor ribbon composition. It is primarily the continuously variable dot size capability and high thermal efficiency of the developed system that sets this research apart from other published works related to laser driven thermal transfer

    Temperature-dependent Characterization of Power Amplifiers Using an Efficient Electrothermal Analysis Technique

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    In this paper, we propose an efficient methodology for the electrothermal characterization of power amplifier (PA) integrated circuits. The proposed electrothermal analysis method predicts the effect of temperature variations on the key performances of PAs, such as gain and linearity, under realistic dynamic operating conditions. A comprehensive technique for identifying an equivalent compact thermal model, using data from 3-D finite element method thermal simulation and nonlinear curve fitting algorithms, is described. Two efficient methods for electrothermal analysis applying the developed compact thermal model are reported. The validity of the methods is evaluated using commercially available electrothermal computer-aided design (CAD) tools and through extensive pulsed RF signal measurements of a PA device under test. The measurement results confirm the validity of the proposed electrothermal analysis methods. The proposed methods show significantly faster simulation speed comparing to available CAD tools for electrothermal analysis. Moreover, the results reveal the importance of electrothermal characterization in the prediction of the temperature-aware PA dynamic operation
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