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Abstract  

It is claimed, though not without dispute, that genetically engineered mammalian cells grow more slowly than their progenitor cells because the recombinant gene system causes a metabolic burden. This was found to be the case for CHO cells transfected with expression vectors forcytochrome b5. The slower growth was associated with lower metabolic activity measured by heat flux and mitochondrial activity (rhodamine 123 fluorescence). The calorimetric-respirometric ratio was similar for all cell types, implying that the greater fluxes of glucose and glutamine in the recombinant cells was channelled to biosynthesis. This demand probably restricted the supply of pyruvate to the mitochondria in these cells.

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heat flux meter method 1 The heat flux meter (ASTM C518, ISO8301) uses homogeneous samples with good planarity. The procedure is based on multi thicknesses of the specimen. Thermal contact (or contact resistivity) may cause huge errors of

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Abstract  

A numerical program has been written to treat a heat-flux DSC. The model operates in two modes. In the first,experimental data is used as input and the enthalpy is calculated as a function of the sample temperature rather than the sample thermocouple temperature. This allows accurate enthalpies and transition temperatures to be obtained without smearing. In the second mode, enthalpy is used as an input and the responses of the calorimeter are calculated. Using this mode it is possible to investigate the effects of sample size, heating rate and alloy composition. Non-equilibrium effects and difficulty in nucleation can also be included.

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In an attempt to explain how the calibration factor of a heat flux DSC cell depends both on the standard utilized and on the experimental variables, a study has been undertaken of the entire DSC trace.

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A general mathematical treatment for heat-flux differential scanning calorimetry is given. It combines equations derived for heat transfer in the calorimeter cell with an approach to the solidification of metal or alloy carried out in this type of instrument. The differences are discussed between temperature evolution, kinetics of latent heat and undercooling evolution within the sample, and temperature evolution, recorded signal and measured undercooling at the monitoring station.

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Abstract  

The specific heat capacities of some triglycerides commonly found in palm oil were determined with a heat-flux differential scanning calorimeter. The specific heat capacity measurements were made under the optimum operating conditions determined earlier: scan rate 17 deg·min−1, sample mass 21 mg and purge gas (nitrogen) flow rate 50 ml/min. Pure triglycerides (four simple and four mixed) were used in the experiments. The four simple triglycerides were trilaurin, trimyristin, tripalmitin and tristearin, and the mixed triglycerides were 1,2-dimyristoyl-3-oleoyl, 1,2-dimyristoyl-3-palmitoyl, 1,2-dipalmitoyl-3-oleoyl and 1,2-dioleoyl-3-palmitoyl. The results of this study are compared with literature values and also with values obtained by using estimation methods. The experimental specific heat capacities are within ±1% precision with a 95% confidence level.

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Abstract  

A new method to measure heat flux and thermal expansion simultaneously with a temperature resolution of milli-Kelvin is presented to observe the multistage transitions. At least six thermal anomalies are observed between 402 and 403 K in BaTiO3 simultaneously in heat flux and thermal expansion in the cooling process. The correspondence of the anomalies observed in the two physical properties is excellent.

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Abstract  

The temperature calibration of a TA Instruments 3200-2920 DSC has been performed on cooling using the isotropic → nematic, isotropic → cholesteric and other liquid crystal → liquid crystal transitions of thermally stable, high purity liquid crystals. The thermal stability of these liquid crystals has been verified by measuring the temperature of the mentioned transitions during cyclic heating and cooling experiments. Correspondence has been established between the real and indicated temperature during cooling for all combinations of heating and cooling rates of practical interest: correction values were determined to the indicated temperature in order to obtain the real temperature on cooling. These correction values were calculated as the average from the temperatures of four or five different liquid crystal transitions for each heating-cooling rate combination. The accuracy of the temperature calibration on cooling is ca. 0.2‡C for heating and cooling rates up to 20‡C min−1.

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Abstract  

After a formal explanation of Mayer's enthalpy balance method as applied to biological reaction rates, the history of its application is traced from Rubner's dog to accounting for the energy of muscle contraction. The introduction of microcalorimetry allowed the method generally to be used for cells in vitro and now particular emphasis can be paid to the growth of cells for the production of therapeutically-important heterologous proteins. In these systems, enthalpy balance studies contribute to defining catabolic processes, designing media, understanding the mechanisms of growth and controlling cultures using heat flux as an on-line sensor of metabolic activity.

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Abstract  

The determination of heat capacity data with sawtooth-type, temperature-modulated differential scanning calorimetry is analyzed using the Mettler-Toledo 820 ADSC™temperature-modulated differential scanning calorimeter (TMDSC). Heat capacities were calculated via the amplitudes of the first and higher harmonics of the Fourier series of the heat flow and heating rates. At modulation periods lower than about 150 s, the heat capacity deviates increasingly to smaller values and requires a calibration as function of frequency. An earlier derived correction function which was applied to the sample temperature-controlled power compensation calorimeter enables an empirical correction down to modulation periods of about 20 s. The correction function is determined by analysis of the higher harmonics of the Fourier transform from a single measurement of sufficient long modulation period. The correction function reveals that the time constant of the instrument is about 5 s rad−1 when a standard aluminum pan is used. The influence of pan type and sample mass on the time constant is determined, the correction for the asymmetry of the system is described, and the effect of smoothing of the modulated heat flow rate data is discussed.

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