Short Time Transient Behavior of SiGe-based Microrefrigerators

2009 ◽  
Vol 1166 ◽  
Author(s):  
Ezzahri Younes ◽  
James Christofferson ◽  
Kerry Maize ◽  
Ali Shakouri
Keyword(s):  
Time Constant ◽  
Joule Heating ◽  
Thermal Imaging ◽  
Heating Temperature ◽  
Transient Behavior ◽  
Experimental Results ◽  
Transient Temperature ◽  
Geometrical Parameters ◽  
Semiconductor Interface ◽  
Time Constants

AbstractWe use a Thermoreflectance Thermal Imaging technique to study the transient cooling of SiGe-based microrefrigerators. Thermal imaging with submicron spatial resolution, 0.1C temperature resolution and 100 nanosecond temporal resolution is achieved. Transient temperature profiles of SiGe-based superlattice microrefrigerator devices of different sizes are obtained. The dynamic behavior of these microrefrigerators, show an interplay between Peltier and Joule effects. On the top surface of the device, Peltier cooling appears first with a time constant of about 10-30 microseconds, then Joule heating in the device starts taking over with a time constant of about 100-150 microseconds. The experimental results agree very well with the theoretical predictions based on Thermal Quadrupoles Method. The difference in the two time constants can be explained considering the thermal resistance and capacitance of the thin film. In addition this shows that the Joule heating at the top metal/semiconductor interface does not dominate the microrefrigerator performance or else we would have obtained the same time constants for the Peltier and Joule effects. Experimental results show that under high current values, pulse-operation the microrefrigerator device can provide cooling for about 30 microseconds, even though steady state measurements show heating. Temperature distribution on the metal leads connected to the microrefrigerator’s cold junction show the interplay between Joule heating in the metal as well as heat conduction to the substrate. Modeling is used to study the effect of different physical and geometrical parameters of the device on its transient cooling. 3D geometry of heat and current flow in the device plays an important role. One of the goals is to maximize cooling over the shortest time scales.

Generalization and Analysis of the Lisberger-Sejnowski VOR Model

1995 ◽  
Vol 7 (4) ◽  
pp. 735-752 ◽  
Author(s):  
Ning Qian
Keyword(s):  
Steady State ◽  
Purkinje Cell ◽  
Time Constant ◽  
Transient Behavior ◽  
Point Of View ◽  
Additional Time ◽  
Time Constants ◽  
Generalized System ◽  
Special Cases ◽  
Physiological Tests

Lisberger and Sejnowski (1992) recently proposed a computational model for motor learning in the vestibular-ocular reflex (VOR) system. They showed that the steady-state gain of the system can be modified by changing the ratio of the two time constants along the feedforward and the feedback projections to the Purkinje cell unit in their model VOR network. Here we generalize their model by including two additional time constant variables and two synaptic weight variables, which were set to fixed values in their original model. We derive the stability conditions of the generalized system and thoroughly analyze its steady-state and transient behavior. It is found that the generalized system can display a continuum of behavior with the Lisberger-Sejnowski model and a static model proposed by Miles et al. (1980b) as special cases. Moreover, although mathematically the Lisberger-Sejnowski model requires two precise relationships among its parameters, the model is robust against small perturbations from the physiological point of view. Additional considerations on the gain of smooth pursuit eye movement, which is believed to share the positive feedback loop with the VOR network, suggest that the VOR network should operate in the parameter range favoring the behavior studied by Lisberger and Sejnowski. Under this condition, the steady-state gain of the VOR is found to depend on all four time constants in the network. The time constant of the Purkinje cell unit should be relatively small in order to achieve effective VOR learning through the modifications of the other time constants. Our analysis provides a thorough characterization of the system and could thus be useful for guiding further physiological tests of the model.

scholarly journals Application of Direct Resistance Heating in Hot Forging and Analysis of Processing Parameters based on Thermo-electro-mechanical Coupling FEM

2018 ◽  
Vol 37 (6) ◽  
pp. 531-538
Author(s):  
Men Zhengxing ◽  
Wang Menghan ◽  
Ma Yaxin ◽  
Yue Taiwen ◽  
Liu Ruilin
Keyword(s):  
Contact Resistance ◽  
Heating Temperature ◽  
Hot Forging ◽  
Processing Parameters ◽  
Experimental Results ◽  
Transient Temperature ◽  
Resistance Heating ◽  
Forming Process ◽  
Mechanical Coupling ◽  
Forming Temperature

AbstractA series of experiments were designed in order to directly heat the billet of 42CrMo4 to the forming temperature in the dies prior to forming and continue to heat the billet during the forming process. Processing parameters during heating and forming were investigated by experimental method and thermo-electro-mechanical coupling FEM. The experimental results show that prior to forming the billet could be rapidly heated to forming temperature under relatively low initial contact pressure, and the heating temperature was proportional to the square of the current intensity. When the heating current remained constant, the heating temperature could not increase with heating time. During the forming process, the billet cooling rate slowed down and the forming time was extended due to the continuous resistance heating during forming. Finally, an incrementally coupled thermo-electro-mechanical model has been developed to analyze the hot-forging process by direct resistance heating. To obtain the transient temperature field prior to forming, a simple model of contact resistance was used in the thermal-electrical simulation, in which the electrical conductance of the contact resistance was proportional to the heating temperature. Contrasted the experimental results and the simulation results, it was found that they coincided well.

scholarly journals Individual motion perception parameters and motion sickness frequency sensitivity in fore-aft motion

2021 ◽  
Author(s):  
Tugrul Irmak ◽  
Ksander N. de Winkel ◽  
Daan M. Pool ◽  
Heinrich H. Bülthoff ◽  
Riender Happee
Keyword(s):  
Motion Sickness ◽  
Motion Perception ◽  
Time Constant ◽  
Storage Time ◽  
Velocity Storage ◽  
Strong Positive Correlation ◽  
Subjective Vertical ◽  
Time Constants ◽  
Frequency Sensitivity ◽  
Observer Model

AbstractPrevious literature suggests a relationship between individual characteristics of motion perception and the peak frequency of motion sickness sensitivity. Here, we used well-established paradigms to relate motion perception and motion sickness on an individual level. We recruited 23 participants to complete a two-part experiment. In the first part, we determined individual velocity storage time constants from perceived rotation in response to Earth Vertical Axis Rotation (EVAR) and subjective vertical time constants from perceived tilt in response to centrifugation. The cross-over frequency for resolution of the gravito-inertial ambiguity was derived from our data using the Multi Sensory Observer Model (MSOM). In the second part of the experiment, we determined individual motion sickness frequency responses. Participants were exposed to 30-minute sinusoidal fore-aft motions at frequencies of 0.15, 0.2, 0.3, 0.4 and 0.5 Hz, with a peak amplitude of 2 m/s2 in five separate sessions, approximately 1 week apart. Sickness responses were recorded using both the MIsery SCale (MISC) with 30 s intervals, and the Motion Sickness Assessment Questionnaire (MSAQ) at the end of the motion exposure. The average velocity storage and subjective vertical time constants were 17.2 s (STD = 6.8 s) and 9.2 s (STD = 7.17 s). The average cross-over frequency was 0.21 Hz (STD = 0.10 Hz). At the group level, there was no significant effect of frequency on motion sickness. However, considerable individual variability was observed in frequency sensitivities, with some participants being particularly sensitive to the lowest frequencies, whereas others were most sensitive to intermediate or higher frequencies. The frequency of peak sensitivity did not correlate with the velocity storage time constant (r = 0.32, p = 0.26) or the subjective vertical time constant (r = − 0.37, p = 0.29). Our prediction of a significant correlation between cross-over frequency and frequency sensitivity was not confirmed (r = 0.26, p = 0.44). However, we did observe a strong positive correlation between the subjective vertical time constant and general motion sickness sensitivity (r = 0.74, p = 0.0006). We conclude that frequency sensitivity is best considered a property unique to the individual. This has important consequences for existing models of motion sickness, which were fitted to group averaged sensitivities. The correlation between the subjective vertical time constant and motion sickness sensitivity supports the importance of verticality perception during exposure to translational sickness stimuli.

scholarly journals Thermal Analysis of Stomatal Response under Salinity and High Light

2021 ◽  
Vol 22 (9) ◽  
pp. 4663
Author(s):  
Aleksandra Orzechowska ◽  
Martin Trtílek ◽  
Krzysztof Michał Tokarz ◽  
Renata Szymańska ◽  
Ewa Niewiadomska ◽  
...  
Keyword(s):  
Thermal Imaging ◽  
Initial Response ◽  
Co2 Assimilation ◽  
High Light ◽  
Stomatal Aperture ◽  
Imaging Method ◽  
Stomatal Response ◽  
Time Constants ◽  
Net Co2 Assimilation ◽  
Temporary Response

A non-destructive thermal imaging method was used to study the stomatal response of salt-treated Arabidopsis thaliana plants to excessive light. The plants were exposed to different levels of salt concentrations (0, 75, 150, and 220 mM NaCl). Time-dependent thermograms showed the changes in the temperature distribution over the lamina and provided new insights into the acute light-induced temporary response of Arabidopsis under short-term salinity. The initial response of plants, which was associated with stomatal aperture, revealed an exponential growth in temperature kinetics. Using a single-exponential function, we estimated the time constants of thermal courses of plants exposed to acute high light. The saline-induced impairment in stomatal movement caused the reduced stomatal conductance and transpiration rate. Limited transpiration of NaCl-treated plants resulted in an increased rosette temperature and decreased thermal time constants as compared to the controls. The net CO2 assimilation rate decreased for plants exposed to 220 mM NaCl; in the case of 75 mM NaCl treatment, an increase was observed. A significant decline in the maximal quantum yield of photosystem II under excessive light was noticeable for the control and NaCl-treated plants. This study provides evidence that thermal imaging as a highly sensitive technique may be useful for analyzing the stomatal aperture and movement under dynamic environmental conditions.

Why is the perceptual octave stretched? An account based on mismatched time constants within the auditory brainstem

2021 ◽  
Author(s):  
Alain de Cheveigné
Keyword(s):  
Time Constant ◽  
Auditory Brainstem ◽  
The Other ◽  
Inhibitory Synapses ◽  
Coincidence Counting ◽  
Time Constants ◽  
Direct Pathway ◽  
Lower Tone ◽  
Excitatory And Inhibitory Synapses

This paper suggests an explanation for listener’s greater tolerance to positive than negative mistuning of the higher tone within an octave pair. It hypothesizes a neu- ral circuit tuned to cancel the lower tone, that also cancels the higher tone if that tone is in tune. Imperfect cancellation is the cue to mistuning of the octave. The circuit involves two pathways, one delayed with respect to the other, that feed a coincidence-counting neuron via excitatory and inhibitory synapses. A mismatch between the time constants of these two synapses results in an asymmetry in sen- sitivity to mismatch. Specifically, if the time constant of the delayed pathway is greater than that of the direct pathway, there is a greater tolerance to positive than to negative mistuning, which can lead to a perceptual“stretch” of the octave. The model is applicable to both harmonic and – with qualification – melodic oc- taves. The paper describes the model and reviews the evidence from auditory psychophysics and physiology in favor – or against – it.

Rewetting Analysis of Hot Moving Surface by Round Water Jet Impingement

2018 ◽  
Author(s):  
Avadhesh Kumar Sharma ◽  
Mayank Modak ◽  
Santosh K. Sahu
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Thermal Imaging ◽  
Transient Temperature ◽  
Axial Distance ◽  
Initial Surface ◽  
Moving Plate ◽  
Thermal Imaging Camera ◽  
Plate Velocity ◽  
Imaging Camera

Impinging jets are commonly utilized in the run-out table (ROT) cooling in the hot rolling process in steel manufacturing industries. The phenomenon of rapid cooling of a sufficiently hot surface is termed as the quenching. The present paper reports the rewetting behavior of 0.15 mm thick hot moving stainless steel foil (SS-304) by circular impinging jet from bottom side through experimental investigation. The transient temperature of the hot foil is recorded by using thermal imaging camera (A655sc, FLIR system). Tests are performed for a varied range of Reynolds number (Re = 2500–10000), nozzle to plate distance (z/d = 6), moving plate velocity (0–40 mm/s) and initial surface temperature 500±10 °C. Transient temperature obtained from thermal imaging camera is used to evaluate rewetting time and rewetting velocity. Based on the experimental investigation correlation has been proposed to predict non-dimensional rewetting velocity as a function of various parameters, namely, Reynolds number, non-dimensional axial distance and moving plate velocity.

scholarly journals Voltage-gated transient currents in bovine adrenal fasciculata cells. I. T-type Ca2+ current.

1993 ◽  
Vol 102 (2) ◽  
pp. 217-237 ◽  
Author(s):  
B Mlinar ◽  
B A Biagi ◽  
J J Enyeart
Keyword(s):  
Time Constant ◽  
Low Voltage ◽  
Zona Fasciculata ◽  
Patch Clamp Technique ◽  
Time Constants ◽  
Voltage Gated ◽  
Wide Range ◽  
Boltzmann Function ◽  
Voltage Dependent ◽  
Ca2 Channels

The whole cell version of the patch clamp technique was used to identify and characterize voltage-gated Ca2+ channels in enzymatically dissociated bovine adrenal zona fasciculata (AZF) cells. The great majority of cells (84 of 86) expressed only low voltage-activated, rapidly inactivating Ca2+ current with properties of T-type Ca2+ current described in other cells. Voltage-dependent activation of this current was fit by a Boltzmann function raised to an integer power of 4 with a midpoint at -17 mV. Independent estimates of the single channel gating charge obtained from the activation curve and using the "limiting logarithmic potential sensitivity" were 8.1 and 6.8 elementary charges, respectively. Inactivation was a steep function of voltage with a v1/2 of -49.9 mV and a slope factor K of 3.73 mV. The expression of a single Ca2+ channel subtype by AZF cells allowed the voltage-dependent gating and kinetic properties of T current to be studied over a wide range of potentials. Analysis of the gating kinetics of this Ca2+ current indicate that T channel activation, inactivation, deactivation (closing), and reactivation (recovery from inactivation) each include voltage-independent transitions that become rate limiting at extreme voltages. Ca2+ current activated with voltage-dependent sigmoidal kinetics that were described by an m4 model. The activation time constant varied exponentially at test potentials between -30 and +10 mV, approaching a voltage-independent minimum of 1.6 ms. The inactivation time constant (tau i) also decreased exponentially to a minimum of 18.3 ms at potentials positive to 0 mV. T channel closing (deactivation) was faster at more negative voltages; the deactivation time constant (tau d) decreased from 8.14 +/- 0.7 to 0.48 +/- 0.1 ms at potentials between -40 and -150 mV. T channels inactivated by depolarization returned to the closed state along pathways that included two voltage-dependent time constants. tau rec-s ranged from 8.11 to 4.80 s when the recovery potential was varied from -50 to -90 mV, while tau rec-f decreased from 1.01 to 0.372 s. At potentials negative to -70 mV, both time constants approached minimum values. The low voltage-activated Ca2+ current in AZF cells was blocked by the T channel selective antagonist Ni2+ with an IC50 of 20 microM. At similar concentrations, Ni2+ also blocked cortisol secretion stimulated by adrenocorticotropic hormone. Our results indicate that bovine AZF cells are distinctive among secretory cells in expressing primarily or exclusively T-type Ca2+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)

Generation of reduced dynamic thermal models of electronic systems from time constant spectra of transient temperature responses

2011 ◽  
Vol 51 (8) ◽  
pp. 1351-1355 ◽  
Author(s):  
Marcin Janicki ◽  
Jedrzej Banaszczyk ◽  
Bjorn Vermeersch ◽  
Gilbert De Mey ◽  
Andrzej Napieralski
Keyword(s):  
Time Constant ◽  
Transient Temperature ◽  
Electronic Systems ◽  
Thermal Models ◽  
Temperature Responses ◽  
Reduced Dynamic

Identification of Time-Varying Time Constants of Thermocouple Sensors and Its Application to Temperature Measurement

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Kenneth Kar ◽  
Akshya K. Swain ◽  
Robert Raine
Keyword(s):  
Kalman Filter ◽  
Least Squares ◽  
Time Constant ◽  
Identification Problem ◽  
Basis Functions ◽  
New Technique ◽  
Ratio Test ◽  
Time Varying ◽  
Time Constants ◽  
Orthogonal Least Squares

The present study addresses the problem of estimating time-varying time constants associated with thermocouple sensors by a set of basis functions. By expanding each time-varying time constant onto a finite set of basis sequences, the time-varying identification problem reduces to a parameter estimation problem of a time-invariant system. The proposed algorithm, to be called as orthogonal least-squares with basis function expansion algorithm, combines the orthogonal least-squares algorithm with an error reduction ratio test to include significant basis functions into the model, which results in a parsimonious model structure. The performance of the method was compared with a linear Kalman filter. Simulations on engine data have demonstrated that the proposed method performs satisfactorily and is better than the Kalman filter. The new technique has been applied in a Stirling cycle compressor. The sinusoidal variations in time constant are tracked properly using the new technique, but the linear Kalman filter fails to do so. Both model validation and thermodynamic laws confirm that the new technique gives unbiased estimates and that the assumed thermocouple model is adequate.

Voltage Dependence of the Glycine Receptor–Channel Kinetics in the Zebrafish Hindbrain

1999 ◽  
Vol 82 (5) ◽  
pp. 2120-2129 ◽  
Author(s):  
Pascal Legendre
Keyword(s):  
Time Constant ◽  
Rise Time ◽  
Time Course ◽  
Voltage Dependence ◽  
Good Description ◽  
Glycine Receptor ◽  
Relative Amplitude ◽  
Time Constants ◽  
Low Concentration ◽  
Voltage Dependent

Electrophysiological recordings of outside-out patches to fast-flow applications of glycine were made on patches derived from the Mauthner cells of the 50-h-old zebrafish larva. As for glycinergic miniature inhibitory postsynaptic currents (mIPSCs), depolarizing the patch produced a broadening of the transient outside-out current evoked by short applications (1 ms) of a saturating concentration of glycine (3 mM). When the outside-out patch was depolarized from −50 to +20 mV, the peak current varied linearly with voltage. A 1-ms application of 3 mM glycine evoked currents that activated rapidly and deactivated biexponentially with time constants of ≈5 and ≈30 ms (holding potential of −50 mV). These two decay time constants were increased by depolarization. The fast deactivation time constant increased e-fold per 95 mV. The relative amplitude of the two decay components did not significantly vary with voltage. The fast component represented 64.2 ± 2.8% of the total current at −50 mV and 54.1 ± 10% at +20 mV. The 20–80% rise time of these responses did not show any voltage dependence, suggesting that the opening rate constant is insensitive to voltage. The 20–80% rise time was 0.2 ms at −70 mV and 0.22 ms at +20 mV. Responses evoked by 100–200 ms application of a low concentration of glycine (0.1 mM) had a biphasic rising phase reflecting the complex gating behavior of the glycine receptor. The time constant of these two components and their relative amplitude did not change with voltage, suggesting that modal shifts in the glycine-activated channel gating mode are not sensitive to the membrane potential. Using a Markov model to simulate glycine receptor gating behavior, we were able to mimic the voltage-dependent change in the deactivation time course of the responses evoked by 1-ms application of 3 mM glycine. This kinetics model incorporates voltage-dependent closing rate constants. It provides a good description of the time course of the onset of responses evoked by the application of a low concentration of glycine at all membrane potentials tested.

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