Development of a calorimetric sensor for medical application

A calorimetric sensor has been developed for local and direct measurement of calorific dissipations in different parts of the human body. The constructed prototype has a detection surface of 36 cm². The calibration of the sensor is based on a semi-empirical model that permits to simulate the operation of the device, making easier an operational functioning method. The device is modeled as a system with two inputs and two outputs. The inputs are the calorific power (W) that is intended to be measured and the power (W _pid) that dissipates a resistance, keeping constant the thermostat temperature through the use of a PID controller. The outputs are the thermostat temperature (T _pid) and the calorimetric signal (y) that provides the thermopile that is in contact with the body.     

Development of a calorimetric sensor for medical application

A calorimetric sensor has been developed to measure the calorific dissipation through a determined area of the human body surface. An experimental laboratory prototype with a capturing surface of 36 cm² has been built, and a functioning model suggesting an operational method that allows to determine the calorific power going through the sensor has been proposed.     

Novel Thermal Flow Sensors Based on a Wheatstone Bridge Read-out

A novel thermal flow sensor transduction method is presented combining advantages of the calorimetric and the hot-film transduction principle. Four thin-film germanium thermistors are embedded in the silicon-nitride membrane acting as heat sources and as temperature sensors simultaneously. These devices operate in a Wheatstone bridge. The voltage across the bridge as well as the total dissipated power serves as output quantities. Two sensor configurations with different arrangement of the membrane thermistors were examined experimentally. Moreover, we investigated the influence of different layouts on the rise time, the sensitivity, and the usable flow range by means of two-dimensional finite element simulations.     

A new approach for isothermal calorimetric technique

Using flexible heat flux sensors mounted on the lateral and bottom of outside reactor wall, a new approach is developed for isothermal calorimetric technique to overcome the disadvantages of heat flow calorimetric methods. Although the proposed system needs a calibration procedure before or after the reaction completion to evaluate the lateral heat transfer area, the measurement is versatile and totally independent of the reaction media, jacket fluid, and the variations of heat transfer coefficient. Knowledge of the variations of the heat transfer coefficient is essential for the effective control and scale up of a reactor and can be inferred by the new method during the reaction. The stirrer power and the heat loss can be determined easily as well. No pre-calibration is needed for the sensors and no heating element is applied inside the reactor for temperature control. Experiments are carried out to validate the performance of the new proposed technique. With the help of a heater, the heat generated in the reactor is measured at various levels of power input. The predicted heater power inputs are in good agreement with the corresponding heat inputs. The relative detection limit in the range of 0.8–1 W L⁻¹ is expected for this technique. Using the hydrolysis of acetic anhydride, the heat of reaction at 25°C is determined, which is within the range reported in the literatures. The capability of the system to deal with the variations in the overall heat transfer coefficient is also demonstrated using a simulated reaction.     

Calorimetric measurements of microtubule assembly in vitro

The assembly of microtubules in extracts of mammalian brain tissue has been characterized by electron microscopy and the course of the temperature-induced polymerization of the heterodimers of α-tubulin and β-tubulin has been followed by the help of an adiabatic scanning calorimeter. Tubulin was purified by the reversible, temperature-dependent assembly procedure and was analyzed by gel electrophoresis. In a typical calorimetric experiment 1 ml of a protein solution (7.5 mg ml^?1) was placed into the sample cell while the same amount of this solution containing 5 mM Ca²⁺ to prevent tubulin aggregation, was placed into the reference cell. After cooling the cells to 0°C, the solutions were heated at a rate of 1 deg min^?1 and the excess energy to keep the temperature difference of both cells close to zero was recorded as a function of temperature. The peak due to compensation of the heat of polymerization starts to rise at 20°C and declines to the base line at 32°C. The area of the peak can be calibrated in energy units by the help of an electric calibration signal. The heat of polymerization per mole of the heterodimers calculated from the experiments is 8.3 kcal. The entropy change due to this process is 27.8 e.u. The van't Hoff enthalpy calculated from the calorimetric curve is 212 kcal mole^?1 tubulin. The heat of denaturation of tubulin was determined to be 180 kcal mole^?1. The polymerization reaction was shown to be reversible whereas the denaturation is an irreversible process.     

Calorimetry under Stress A Preliminary Study in Single Crystalline Cu-Zn-Al Shape Memory Alloys

A non-differential calorimetric analyzer was developed for an INSTRON 1123 machine (a stress-strain-temperature analyzer) with a temperature chamber INSTRON 1110. The study was performed using the Joule effect and pseudoelastic martensitic transformations in single crystals of Cu-Zn-Al alloys. The analysis of the system establishes that: the sensitivity of calorimetric measurements after a filter of two poles and two zeros is 166 mV W^-1 (at 297 K), the noise is near 1.5 μV and the drift is close to 30 μV in 6 h. The reproducibility of the sensitivity working with one sample is better than ±0.3%, and the change to a new sample keeps the value below ±0.5%. The uncertainty in reproducibility in the martensitic transformation (including repositioning) does not overcome ±1.6%. The used calorimetric sensors limit the temperature to 373 K. The furnace control originated fluctuations on the base line (near ±20 μV), which by means of an auxiliary signal processing were reduced to 50% (less than ±10 μV). This revised version was published online in July 2006 with corrections to the Cover Date.     

Calorimetric titration experiment modelled by equilibrium of 2:1 and 1:1 complexes

The analysis of the calorimetric continuous titration experiment is presented. The proposed method is basing on the collection of larger number of experimental data points than could be obtained from the classical isothermal titration calorimetry experiment. After the deconvolution procedure resulting in the correction for the calorimeter time response the pure power effect signal could be obtained. The collected data enable the detailed analysis of the closely populated 2:1 and 1:1 weak complexes.     

Application of a simple calorimetric data analysis on the binding study of calcium ions by human growth hormone

A simple graphical linear method was introduced for isothermal titration calorimetric data analysis in the protein-ligand interaction. The number of binding sites, the dissociation binding constant and the molar enthalpy of binding site can be obtained by using this new isothermal titration calorimetric data analysis method. The method was applied to the study of the interaction of human growth hormone (hGH) with divalent calcium ion at 27°C in NaCl solution, 50 mM. hGH has a set of three identical and independent binding sites for Ca ²⁺ . The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 52 μMand -17.4, respectively. Results obtained by this new calorimetric data analysis are in good agreement with results obtained using our previous method.     

Filler effects on the thermomechanical response of stretched rubbers

This paper deals with the calorimetric analysis of deformation processes in filled styrene-butadiene rubbers. More especially, the study focuses on the effects of the addition of carbon black fillers on the calorimetric response of “demullinized” SBR. Temperature variations are measured by infrared thermography during cyclic uniaxial tensile tests at ambient temperature. Heat sources¹ produced or absorbed by the material due to deformation processes are deduced from temperature fields by using the heat diffusion equation. First, the results show that no mechanical (intrinsic) dissipation is detected for weakly filled SBR, meaning that the heat produced and absorbed over one mechanical cycle is the same whatever the stretch ratio reached. Second, the mechanical dissipation in highly filled SBR is significant. The quantitative analysis carried out highlights the fact that it increases quasi-linearly with the stretch ratio. Finally, a simplified framework is proposed to discuss the identification of the heat sources, in particular the mechanical dissipation.     

Features of the Current Sustainment in a Low-Current Discharge in Airflow

The paper relates to the investigations of a low-current discharge in a vortex airflow with the electrode configuration corresponding to classical coaxial plasmatron. The gas flow rate is varied from 0.1 to 0.3 g/s at an inner diameter of the plasmatron nozzle of 5 mm. The discharge is powered by dc voltage via a ballast resistor. Typical averaged current is changed from 0.06 to 0.15 A so that a maximum averaged power dissipated in the discharge amounts to 160 W. In these conditions, a luminous gas region at the plasmatron exit, which in most publications is associated with a plasma jet, is observed. The method for the jet diagnostics based on a usage of the additional electrodes at the plasmatron exit has been proposed. The main idea of the experiments is the elucidation of the problem whether the jet actually represents the plasma area or we have to apply the term “plasma” with care. In particular, in the case under discussion the main charged particles in the jet are electrons that are emitted from a plasma column located in the plasmatron nozzle. The model that describes the formation of electron flow in the jet has been proposed. Typical electron density in the jet estimated with a usage of the model is at a level of 10⁹ cm^?3.

     

Losses evaluation in converters using the calorimetric technique

In this paper, a measurement technique of losses in the switching cell, based on calorimetric technique is presented. A special calorimeter was designed to be able to access the heat generated by an operating converter. Power component losses are studied according to the cyclic ratio and to operating frequency and an extraction method of the different terms of these losses, using calorimetric measurements, is presented. An accurate expression of the switching losses in the power semiconductors devices is proposed.     

A differential scanning calorimetric study on the irreversible thermal unfolding of concanavalin A

A differential scanning calorimetry study on the thermal denaturation of concanavalin A at pH 5.2 where it exists in the dimeric form was carried out. The calorimetric transitions were observed to be irreversible and the transition temperature of the protein increased with increasing scan rate, indicating that the thermal denaturation process is under kinetic control. The thermal unfolding, and its scan rate dependence could be explained according to the kinetic scheme with k as first-order kinetic constant whose change with temperature is given by the Arrhenius equation. Using this model, rate constant as a function of temperature and activation energy of the process have been calculated. The average activation energy of the kinetic process using different approaches is 129±10 kJ mol⁻¹. The differential scanning calorimetric results on transition temperatures and calorimetric enthalpies supported by intrinsic fluorescence indicate that the irreversibility in the calorimetric transitions of concanavalin A includes a combination of post-transition aggregation, chain separation and loss of cofactor.     

Solving the spin-boson model of strong dissipation with flexible random-deterministic scheme

The zero-temperature dynamics of the spin-boson model with strong dissipation has been a challenging problem for more than 20 years. To solve this and quantum dynamics of dissipative systems at large, we recently proposed a mixed random-deterministic method. This scheme has been successfully used to simulate the time evolution of the spin-boson model at zero temperature for weak to moderate dissipation. For a better numerical performance, the approach is further modified so that it is flexible to convert a certain part of the random treatment to a deterministic one a la hierarchical equations. Applying the new method to the strong dissipated spin-boson model at zero temperature, we observe that the population in the localized state obeys a simple decay dynamics and the time scale is proportional to the reciprocal of the cutoff frequency.     

Calorimetric investigations of association equilibria: the pyridine-iodine complex in cyclohexane and in carbon tetrachloride

The results of two independent calorimetric investigations of the pyridine- iodine complex are reported. “Best” values are reported as K_m = 128 1/mol and ΔH° = -8.4 kcal mol^?1 for the formation of the complex in cyclohexane at 25°C, and K_m = 104 and ΔH° = -7.9 kcal mol^?1 in carbon tetrachloride. Evidence is presented to support the contention that association constants for weak complexes determined by calorimetric methods can be as reliable as those determined by spectrometric methods, and that values of ΔH° determined by the calorimetric method are much more reliable than those derived from the temperature dependence of equilibrium constants.     

Differential scanning calorimetric measurement of cartilage destruction caused by Gram-negative septic arthritis

The treatment of the bacterial arthritis of the joints is still a great challenge for orthopedic surgeons and rheumatologists. Aerobic Gram-negative bacteria are involved only in 20–25 % of cases. The inadequate therapy can cause cartilage destruction and can result in severe osteoarthritis of the affected joint. The aim of this study was to demonstrate and follow the destruction of the joints’ hyaline cartilage by calorimetric method. We induced experimental septic arthritis in knee joints of seven New Zealand rabbits by a single inoculation of Escherichia coli ATCC 25922 culture (0.5 mL cc. 10⁸ ± 5 % c.f.u.). The duration of this experiment was 7 days from the first to the last injection. After euthanizing the first subject, all other animals were given an overdose of anesthetics and samples were isolated from the cartilage of the femurs by surgical intervention for calorimetric measurements. The DSC scans clearly demonstrated the development of infective structural destruction in the cartilage from the first to the tenth day of incubation. In case of healthy control the melting temperatures (T _m) were: 57 and 63.1 °C and the total calorimetric enthalpy change (ΔH) was 0.37 J g^?1. After the third day, the enthalpy increased extremely (3.67 J g^?1), the two transition temperatures shifted toward lower temperature: 47.7 and 62.3 °C. At the fifth day, the effect of infection is culminated with T _m = 62.2 °C and a further elevation in ΔH (3.75 J g^?1). These results can indicate a dramatic change of the structure of rabbit cartilage between the third and fifth days. Therefore, the time elapsed seems to be critical and possesses clinical relevance, since by the sixth day, ΔH decreased to 2.6 J g^?1 with a practically unchanged melting temperature. Between the sixth and tenth days, significantly increased melting temperatures (64.9 °C) were observed with decreased (3.38 J g^?1) calorimetric enthalpy. In conclusion, calorimetric measurements have been proven to be a reliable method in the measurement of cartilage destruction, caused by Gram-negative septic arthritis.     

Investigation of catalytic activities by differential thermal analysis

A calorimetric method is proposed to evaluate the catalytic activity of a solid catalyst with respect to the exothermic oxidation of Volatile Organic Compounds (VOC).This method employs a differential thermal analyzer in which an inert reference and a catalytically active sample are both fluxed at a constant rate with a reactive gaseous mixture composed of an inert gas (N₂ 90% vol.), oxygen and VOC, the last typically 900 to 5000 ppm. While the temperature is varied according to a predefined cycle, the output signal due to the exothermic reaction on the catalyst is continuously recorded. The design of the test chamber, the amount of catalyst, the shape of the holders and finally the flow rate and composition of the gaseous mixture should be carefully selected in order to achieve reproducible results.     

New approach for sensitive photothermal detection of C60 and C70 fullerenes on micro-thin-layer chromatographic plates

In this paper the pulse thermovision (photothermal) detection and quantification methods of C60 and C70 fullerenes are presented. Quantification results are compared with optical and fluorescence measurements. Target components were separated under isothermal conditions (30 °C) on micro-TLC plates (RP18WF₂₅₄S) using n-hexane as the mobile phase. The principle of described analytical protocol is based on sensitive measurement of the temperature contrast generated within TLC stationary phase and fullerenes spots after white light pulse excitation. It has been demonstrated that observed temperature contrast is mainly driven by the optical properties of fullerenes (UV–vis absorption spectra). Contrary to the commonly applied optical reflection or transmission techniques the proposed thermovision method involves dissipated light. The results of presented experimental work have revealed that both types of quantitative measurements provide similar outcome despite the key differences in the signal origin. However, it has been found that thermovision method was characterized by smaller value of LOD, particularly for C60 molecule. We demonstrated that application of correlation technique to post-acquisition analysis of the sequence of temperature contrast images significantly increase detection limits of fullerenes, even in comparison to fluorescence quenching detection mode. Moreover, the thermal contrast images and particularly, computed correlation image, allow detection of stationary phase layer nonuniformities, including changes in the adsorbent thickness and thermal conductivity. Therefore, invented pulsed thermovision methodology can be additionally used for fast quality screening of home made and commercially available TLC plates.     

Signal processing and uncertainty in an isothermal titration calorimeter

In this paper, it is made a study of the accuracy of an isothermal titration calorimeter in the operating mode of ‘continuous injection’. The experimental equipment has been a TAM2277-201/2250 by Thermometric AB and the liquid mixtures used in the calibration have been the mixture cyclohexane+benzene and the mixture water+ethanol. The calibration contemplates different effects that affect the uncertainty in the determination of the sensitivity, the effect of the liquid injection, the treatment of the calorimetric signal, the variation of the experimental baseline and the different noises included in the calorimetric signal.     

Thermodynamic study on molecular association of some organic dyestuffs in aqueous solution

The temperature effects on the absorption spectra of acridine orange and methylene blue in aqueous solution at various concentrations have been observed, and it was found that the increase in temperature has an effect on the spectra similar to that of the dilution. The heats of dimerization of the dyestuffs in aqueous solution have been measured directly by the calorimetric titration method, and ΔH_d for acridine orange and methylene blue were found to be ?49.6 and ?83.3 kJ mol^?1, respectively. The entropy of dimerization values were also calculated to be ΔS_d = ?54.9 and ?211.6 J K^?1 mol^?1 for acridine orange and methylene blue, respectively. It has been concluded that the stacking interactions are primarily responsible for the self-association of the dye molecules.