Temperature Feedback Loop Research Articles

Control Software Design for a Multisensing Multicellular Microscale Gas Chromatography System.

Microscale gas chromatography (μGC) systems are miniaturized instruments that typically incorporate one or several microfabricated fluidic elements; such systems are generally well suited for the automated sampling and analysis of gas-phase chemicals. Advanced μGC systems may incorporate more than 15 elements and operate these elements in different coordinated sequences to execute complex operations. In particular, the control software must manage the sampling and analysis operations of the μGC system in a time-sensitive manner; while operating multiple control loops, it must also manage error conditions, data acquisition, and user interactions when necessary. To address these challenges, this work describes the investigation of multithreaded control software and its evaluation with a representative μGC system. The μGC system is based on a progressive cellular architecture that uses multiple μGC cells to efficiently broaden the range of chemical analytes, with each cell incorporating multiple detectors. Implemented in Python language version 3.7.3 and executed by an embedded single-board computer, the control software enables the concurrent control of heaters, pumps, and valves while also gathering data from thermistors, pressure sensors, capacitive detectors, and photoionization detectors. A graphical user interface (UI) that operates on a laptop provides visualization of control parameters in real time. In experimental evaluations, the control software provided successful operation and readout for all the components, including eight sets of thermistors and heaters that form temperature feedback loops, two sets of pressure sensors and tunable gas pumps that form pressure head feedback loops, six capacitive detectors, three photoionization detectors, six valves, and an additional fixed-flow gas pump. A typical run analyzing 18 chemicals is presented. Although the operating system does not guarantee real-time operation, the relative standard deviations of the control loop timings were <0.5%. The control software successfully supported >1000 μGC runs that analyzed various chemical mixtures.

Positive temperature feedback loop in the catalytic cycle of heterogeneous catalysis

The mechanism of heterogeneous catalysis taking into account the influence of temperature is briefly considered in the development of the concept "electron as a catalyst". Here the catalytic cycle includes the heat transfer and electron generation besides the mass transfer. The mechanism of temperature influence in heterogeneous catalysis is realised through the generation of electrons in a positive feedback loop. This mechanism involves the Edison and Seebeck thermoelectronic effects. The catalytic cycle of heterogeneous catalysis is supplemented with a thermoelectronic stage. The thermoelectronic stage of catalysis involves heat transfer and electron generation. Energy transfer to the active centre of the catalyst is an integral part of the catalytic cycle. Energy transfer is considered as a positive temperature feedback loop. The generation of electrons in the positive feedback loop and their transfer to the reactants leads to an increase in reactivity of the reactants. The positive temperature feedback loop leads to an exponential (sigmoidal) dependence of the reaction rate.

Soft multi-modal thermoelectric skin for dual functionality of underwater energy harvesting and thermoregulation

Sustaining a long-term but viable power source for underwater electronics has been an engineering conundrum due to a lack of feasible physical mechanisms to harvest energy in the underwater environment. In this regard, thermoelectricity, which converts heat into electricity, can suggest a potent solution, since the ocean and other water bodies maintain the constant water temperature and therefore serve as a permanent thermal differential. In addition to energy harvesting, the same thermoelectric device can be also utilized to both heat and cool, thereby providing an effective means of controlling the temperature of the arbitrary subject in the underwater environment. In this light, we present a soft and stretchable multi-modal thermoelectric skin (TES) that can both (i) generate electricity across the temperature differential between the ocean water and the human body and (ii) thermoregulate the body temperature in the underwater environment. The soft and elastic nature of TES enables an intimate and thorough contact with the deformable and irregular surfaces of the human skin, therefore maximizing the heat conduction at the human-device interface that the rigid or flexible thermoelectric devices can not fully attain. To the authors’ best knowledge, TES produces the highest electrical power density when compared to the stretchable thermoelectric devices reported so far, mainly owing to its optimum design factors. Along with the outstanding device performance, the underwater environment further boosts the thermoelectric efficiency of TES both in energy harvesting and thermoregulatory perspectives due to the much more favorable thermal properties of water than those of air. Furthermore, to verify the practical usage of TES and demonstrate its high wearability, we incorporated multiple TES units into the neoprene dry-suit. The TES units can self-power multiple embedded sensors that wirelessly monitor the physiological condition and further provide the spatial information of the tactical diver, such that the TES units and embedded system can function as a wearable underwater rescue platform. Lastly, the temperature feedback loop algorithm embedded in the thermoregulatory system allows the TES units to constantly regulate the temperature of the human body and thus prevent underwater hypo-/hyperthermia.

Thermally-Compensated Magnetic Core Loss Model for Time-Domain Simulations of Electrical Circuits

This article introduces a thermally-compensated magnetic hysteresis model, capable of accurately determining core losses of ferrite materials while accounting for core temperature variations. The employed model is based on permeance-capacitance analogy and it captures the frequency-independent hysteresis effect with the help of the Preisach model. For validation purposes, a 100 kW, 10 kHz realized medium frequency transformer prototype is selected and modeled as a part of a full-bridge LLC resonant converter in a time-domain simulation environment. Conducted simulations show the ability of the thermally-compensated magnetic hysteresis model to impact the generated core losses for core temperatures of up to 120 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> C. Finally, a temperature-feedback loop within the transformer is successfully closed inside of a system-level simulation, allowing for a more precise determination of the core and winding steady-state temperatures.

A Fast Leakage-Aware Green’s-Function-Based Thermal Simulator for 3-D Chips

In this article, we propose a fast thermal modeling tool, 3DSim , using a Green’s-function-based approach. Green’s-function-based approaches have been shown to be faster than the traditional finite-difference-based techniques. Our proposed tool can model steady-state and transient thermal profiles for both 2-D and 3-D chips, which may contain multiple active layers and fluid-carrying microchannels for heat removal. The unique advantage of our tool is that it models leakage power analytically using a piecewise-linear leakage model, thereby eliminating the need to iterate multiple times through the leakage–temperature feedback loop. We use several algebraic techniques and transforms to compute the thermal profile analytically and thereby speedup the process of calculation. To the best of our knowledge, transform-based approaches have not been used before to model the temperature in 3-D chips with microchannels. Our approach provides a $150\times $ speedup over state-of-the-art thermal simulators, with an error limited to 5%.

Evaluating the temperature dependence of heat-transfer based detection: A case study with caffeine and Molecularly Imprinted Polymers as synthetic receptors

Molecularly Imprinted Polymers (MIPs) are synthesized for the selective detection of caffeine. The polymerization process, monomer and crosslinker monomer composition are varied to determine the optimal synthesis procedure via batch rebinding experiments evaluated with optical detection. The selectivity is tested by comparing the response of caffeine to compounds with similar chemical structures (theophylline and theobromine) and dopamine, another neurotransmitter. Subsequently, the MIP polymer particles are integrated into bulk modified MIP screen-printed electrodes (MIP-modified SPEs). The sensors are used to measure caffeine content in various samples employing the Heat-Transfer Method (HTM), a low-cost and simple thermal detection method that is based on differences in thermal resistance at the solid-liquid interface. At first, the noise is minimized by adjusting the settings of temperature feedback loop. Second, the response of the MIP-modified SPE is studied at various temperatures ranging from 37 to 50 and 85 °C. The binding to MIP-modified SPEs has never been studied at elevated temperatures since most biomolecules are not stable at those temperatures. Using caffeine as proof-of-concept, it is demonstrated that at 85 °C the detection limit is significantly enhanced due to higher signal to noise ratios and enhanced diffusion of the biomolecule. Thermal wave transport analysis (TWTA) is also optimized at 85 °C producing a limit of detection of ∼1 nM. Next, MIP-modified SPEs are used to measure the caffeine concentration in complex samples including caffeinated beverages, spiked tap water and waste water samples.The use of MIP-modified SPEs combined with thermal detection provides sensors that can be used for fast and low-cost detection performed on-site, which holds great potential for the determination of contaminants in environmental samples. The platform is generic and by adapting the MIP layer, we can expand to this a range of relevant targets.

Development of a novel flexible polymer-based biosensor platform for the thermal detection of noradrenaline in aqueous solutions

Molecularly Imprinted Polymers (MIPs) are synthesized for the neurotransmitter noradrenaline with the optimal composition and binding conditions being determined via optical batch rebinding experiments. Next, the obtained MIP polymer particles are mixed within screen-printed inks to produce mass-producible bulk modified MIPs screen-printed electrodes (MIP-SPEs). In this contribution, the supporting surface which the MIP-SPEs are screen-printed upon are explored to deviate from conventional polyester, to polyvinylchloride, tracing paper and household-printing paper. The performance of the MIP-SPEs are measured using the Heat-Transfer Method (HTM), a straightforward and low-cost detection technique based on thermal resistance. At first, the noise on the signal is minimized by adjusting the settings of the temperature feedback loop. Second, the response of the MIP-SPEs to noradrenaline is measured and compared for the different substrate materials. Sensors printed onto paper are considered in further experiments as their response to noradrenaline is the highest and advantageous material properties, including sustainability and flexibility of the material. Subsequently, dose-response curves are determined by simultaneously measuring HTM and Thermal Wave Transport Analysis (TWTA). The latter is a new thermal detection method that relies on the use of thermal waves and has the advantage of a short measurement time (2min). With these thermal methods, it is possible to specifically detect noradrenaline in aqueous solutions and quantify it at relevant concentrations. In summary, by combining synthetic receptors with thermal measurement techniques it is possible to develop a portable sensor platform that is capable of low-cost and straightforward detection of biomolecules. Through exploring novel SPE substrates, a system is designed that is flexible and holds potential for the use in commercial biomedical devices and complex sensor architectures.

Fast and Reliable Primary Frequency Reserves From Refrigerators With Decentralized Stochastic Control

Due to increasing shares of renewable energy sources, more frequency reserves are required to maintain power system stability. In this paper, we present a decentralized control scheme that allows a large aggregation of refrigerators to provide Primary Frequency Control (PFC) reserves to the grid based on local frequency measurements and without communication. The control is based on stochastic switching of refrigerators depending on the frequency deviation. We develop methods to account for typical lockout constraints of compressors and increased power consumption during the startup phase. In addition, we propose a procedure to dynamically reset the thermostat temperature limits in order to provide reliable PFC reserves, as well as a corrective temperature feedback loop to build robustness to biased frequency deviations. Furthermore, we introduce an additional randomization layer in the controller to account for thermostat resolution limitations, and finally, we modify the control design to account for refrigerator door openings. Extensive simulations with actual frequency signal data and with different aggregation sizes, load characteristics, and control parameters, demonstrate that the proposed controller outperforms a relevant state-of-the-art controller.

Isolating the Temperature Feedback Loop and Its Effects on Surface Temperature

Abstract Climate feedback processes are known to substantially amplify the surface warming response to an increase of greenhouse gases. When the forcing and feedbacks modify the temperature response they trigger temperature feedback loops that amplify the direct temperature changes due to the forcing and nontemperature feedbacks through the thermal–radiative coupling between the atmosphere and surface. This study introduces a new feedback-response analysis method that can isolate and quantify the effects of the temperature feedback loops of individual processes on surface temperature from their corresponding direct surface temperature responses. The authors analyze a 1% yr−1 increase of CO2 simulation of the NCAR CCSM4 at the time of CO2 doubling to illustrate the new method. The Planck sensitivity parameter, which indicates colder regions experience stronger surface temperature responses given the same change in surface energy flux, is the inherent factor that leads to polar warming amplification (PWA). This effect explains the PWA in the Antarctic, while the direct temperature response to the albedo and cloud feedbacks further explains the greater PWA of the Arctic. Temperature feedback loops, particularly the one associated with the albedo feedback, further amplify the Arctic surface warming relative to the tropics. In the tropics, temperature feedback loops associated with the CO2 forcing and water vapor feedback cause most of the surface warming. Overall, the temperature feedback is responsible for most of the surface warming globally, accounting for nearly 76% of the global-mean surface warming. This is 3 times larger than the next largest warming contribution, indicating that the temperature feedback loop is the preeminent contributor to the surface warming.

Design of piezoelectric transformer-based DC/DC converter to improve power by using heat transfer equipment

In this paper, we propose a new design of a piezoelectric transformer (PT) for low-profile DC/DC converter appli- cations, which increases the output power by using heat transfer equipment. We examined several parameters, which allow us to produce a piezoelectric transformer with optimal efficiency. Instead of looking at the typically optimal loading condition of the PT, we consider the influence of the temperature rise on losses. When the vibration velocity is too large, the piezoelectric transformer generates heat unstably until it cracks. By maintaining the vibration mode and limiting the heat produced by the PT, this design can enhance the power capacities of the PT and thus increase the output power of the DC/DC converter. A finite element analysis (FEA) approach with COMSOL Multiphysics was made to predict PT's working temperature. A theoretical- phenomenological model was also developed to explain the relationship between the equivalent losses resistances and the input voltage at different temperatures. It will be shown that the vibration velocity as well as the heat generation increases the losses. A large vibration velocity and generated heat may cause the temperature feedback loop to enter into an unstable state. We began by modeling a piezoelectric transformer in a DC/DC converter configuration in order to determine the design constraints and variables such as the maximum mechanical current, the temperature distribution, the PT geometrical configuration and the energy balance. In our design, the PT power capacity increases 3 times (i.e. from 4.54 W to 13.29 W) at specific temperature and the effects of the different cooling methods of the system were verified. The study comprises of a theoretical part and experimental proof-of-concept demonstration of the proposed design method.

Endoluminal MR‐guided ultrasonic applicator embedding cylindrical phased‐array transducers and opposed‐solenoid detection coil

MR-guided high-intensity contact ultrasound (HICU) was suggested as an alternative therapy for esophageal and rectal cancer. To offer high-quality MR guidance, two prototypes of receive-only opposed-solenoid coil were integrated with 64-element cylindrical phased-array ultrasound transducers (rectal/esophageal). The design of integrated coils took into account the transducer geometry (360° acoustic window within endoluminal space). The rectal coil was sealed on a plastic support and placed reversibly on the transducer head. The esophageal coil was fully embedded within the transducer head, resulting in one indivisible device. Comparison of integrated versus external coils was performed on a clinical 1.5T scanner. The integrated coils showed higher sensitivity compared with the standard extracorporeal coil with factors of up to 7.5 (rectal applicator) and 3.3 (esophageal applicator). High-resolution MR images for both anatomy (voxel 0.4 × 0.4 × 5 mm(3)) and thermometry (voxel 0.75 × 0.75 × 8 mm(3), 2 s/image) were acquired in vivo with the rectal endoscopic device. The temperature feedback loop accurately controlled multiple control points over the region of interest. This study showed significant improvement of MR data quality using endoluminal integrated coils versus standard external coil. Inframillimeter spatial resolution and accurate feedback control of MR-guided HICU thermotherapy were achieved.

Multiple Probe Radiofrequency Ablation: Pilot Study in an Animal Model

Radiofrequency ablation (RFA) is becoming increasingly popular for the minimally invasive treatment of benign and malignant tumors. Currently available systems are limited to the use of a single probe because of electrical interactions between probes. The purpose of this study was to test a new prototype multiple probe generator with a built-in switching mechanism to determine if multiple zones of necrosis could be formed simultaneously without a significant penalty in terms of lesion size and procedure time. A dual probe generator was created by modifying a commercially available system into an alternating monopolar system with an external electronic switch controlled by a temperature feedback loop. A total of 20 radiofrequency (RF) lesions (conventional single probe, n = 10; switched dual probe, n = 10) were created in the livers of six adult pigs (temperature, 100 degrees C; 10-minute ablation). Lesions were excised and examined for volume, minimum diameter, and maximum diameter. The time to target temperature was slightly greater for dual (3.5 minutes) versus single ablations (2.7 minutes). However, this resulted in only a 48 second (6.5%) longer total ablation time. There was no significant difference between conventional single and dual lesions for lesion volume (13.6 +/- 9.3 cm(3) versus 13.7 +/- 7.0 cm(3); P >.05), minimum diameter (1.63 +/- 0.56 cm(3) versus 1.61 +/- 0.53; P >.05) or maximum diameter (3.3 +/- 0.84 versus 3.4 +/- 0.55, P >.05). A multiple probe RFA system that can simultaneously ablate multiple areas in the liver is feasible. If multiple probe units become clinically available, large or irregularly shaped lesions could be treated more effectively than with conventional single probe units, and multiple tumors could be ablated simultaneously, thus potentially decreasing procedure time and anesthetic complications.

NUMERICAL MODELLING OF GENERATION AND TRANSPORT OF GAS AND HEAT IN SANITARY LANDFILLS III. SENSITIVITY ANALYSIS

A mathematical model for the generation and transport of gas and heat in a sanitary landfill is developed based on earlier work on the Mountain View Controlled Landfill Project (MVCLP) in California. The present model incorporates biokinetic model equations describing the dynamics of the microbial landfill ecosystem into a multi-layer, time-dependent gas and heat transport and generation models. It is based on the fundamental principles governing the physical, chemical, and microbiological processes in a porous media context such as a sanitary landfill. The model includes biochemical and temperature feedback loops to simulate the effects of their corresponding parameters on microbiological processes. The resulting integrated biokinetic, gas, and heat generation and transport model was used to simulate field data from the MVCLP and to assess the sensitivity of model results to biological parameters. The model can be used to predict the rate and total production of methane in a landfill.

Numerical Modelling of Generation and Transport of Gas and Heat in Sanitary Landfills Iii. Sensitivity Analysis

A mathematical model for the generation and transport of gas and heat in a sanitary landfill is developed based on earlier work on the Mountain View Controlled Landfill Project (MVCLP) in California. The present model incorporates biokinetic model equations describing the dynamics of the microbial landfill ecosystem into a multilayer, time-dependent gas and heat transport and generation models. It is based on the fundamental principles governing the physical, chemical, and microbiological processes in a porous media context such as a sanitary landfill. The model includes biochemical and temperature feedback loops to simulate the effects of their corresponding parameters on microbiological processes. The resulting integrated biokinetic, gas, and heat generation and transport model was used to simulate field data from the MVCLP and to assess the sensitivity of model results to biological parameters. The model can be used to predict the rate and total production of methane in a landfill. © 1997 ISWA

Numerical Modelling of Generation and Transport of Gas and Heat in Sanitary Landfills Ii. Model Application

A mathematical model for the generation and transport of gas and heat in a sanitary landfill was developed based on earlier work on the Mountain View Controlled Landfill Project (MVCLP) in California, U.S.A. The present model incorporates biokinetic model equations describing the dynamics of the microbial landfill ecosystem into multi-layer, time-dependent transport and generation of gas and heat models. It is based on the fundamental principles governing the physical, chemical and microbiological processes in a porous media context such as a sanitary landfill. The model includes biochemical and temperature feedback loops to simulate the effects of their corresponding parameters on microbiological processes. The resulting integrated biokinetic, gas and heat generation and transport model was used to simulate field data from the MVCLP and to assess the sensitivity of model results to biological parameters. The model can be used to predict the rate and total production of methane in a landfill. The present work is pressented in a series of three papers: (I) model formulation; (II) model application; and (III) sensitivity analysis*.

Numerical Modelling of Generation and Transport of Gas and Heat in Landfills I. Model Formulation

A mathematical model for the generation and transport of gas and heat in a sanitary landfill was developed based on earlier work on the Mountain View Controlled Landfill Project (MVCLP) in California, U.S.A. The present model incorporates biokinetic model equations describing the dynamics of the microbial landfill ecosystem into multi-layer, time-dependent transport and generation of gas and heat models. It is based on the fundamental principles governing the physical, chemical and microbiological processes in a porous media context such as a sanitary landfill. The model includes biochemical and temperature feedback loops to simulate the effects of their corresponding parameters on microbiological processes. The resulting integrated biokinetic, gas and heat generation and transport model was used to simulate field data from the MVCLP and to assess the sensitivity of model results to biological parameters. The model can be used to predict the rate and total production of methane in a landfill. The present work is presented in a series of three papers: (I) model formulation; (II) model application; and (III) sensitivity analysis*.

Simulation of automatic temperature control in tissue hyperthermia calculations

Calculations of transient tissue temperature distributions are enhanced by the use of an algorithm to simulate automatic temperature regulation by negative feedback. This feature is quite useful in treatment planning, enabling the physicist to predict the effects on the treatment of variations in temperature regulation system parameters, such as temperature sensor placement and feedback loop gain.