Calorimetry direct

Studies on metal-pyrazole complexes in solution are few. The enthalpy and entropy of association of Co(II), Ni(II), Cu(II) and Zn(II) with pyrazole in aqueous solution have been determined by direct calorimetry (81MI40406). The nature of the nitrogen atom, pyridinic or pyrrolic, involved in the coordination with the metal cannot be determined from the available thermodynamic data. However, other experiments in solution (Section 4.04.1.3.3(i)) prove conclusively that only the N-2 atom has coordinating capabilities. 

The metabolic rate can be measured in several ways. When no external work is being performed, the metabolic rate equals the heat output of the body. This heat output can be measured by a process called direct calorimetry. In this process, the subject IS placed m an insulated chamber that is surrounded by a water jacket. Water flows through the jacket at constant input temperature. The heat from the subject s body warms the air of the chamber and is then removed by the water flowing through the jacketing. By measuring the difference between the inflow and outflow water temperatures and the volume of the water heated, it is possible to calculate the subject s heat output, and thus the metabolic rate, in calories. 

Direct calorimetry Energy expenditure can be measured from the heat lost by an individual, which is the same as that produced. All the energy used in the daily activities of the body is released as heat. For example, the mechanical energy expended walking to work, sprinting for the train or running a marathon is converted into heat. The method used for measuring heat production is known as direct calorimetry (Box 2.1). The individual lives in a... 

Figure 1. Methods of MCA Direct calorimetry by microorganism metabolism of samples for analysis stripping by microorganism binding of interfering compounds.

Non-invasive assessments of mitochondrial function in vivo typically reflect the techniques to monitor it in cells or isolated organelles. Direct calorimetry, organismal oxygen consumption, CO2 production and a host of other techniques all provide insight into mitochondrial capacity, albeit with confounding factors of movement and physical training of the subject. 

It is common to equate the strength of interaction of an acid and a base with the enthalpy of reaction. In some cases this enthalpy may be measured by direct calorimetry AH q for an adiabatic process at constant pressure. 

Heat capacity is best determined with a calorimeter incorporating an electric heater. The net energy input and the resultant temperature rise are both measured. Procedures and precautions for such direct calorimetry are discussed thoroughly by Sturtevant (1959). Differential scanning calorimetry is convenient to use for the determination of heat capacity (Watson et al. 1964). 

If AH 0 can be assumed constant over the temperature range of an experiment, a plot of In K vs 1/T provides a convenient estimate of AH 0 (or AH if In K is plotted). The slope of the line will be -AH0/R. Since AG0 can be calculated from K, the method also permits evaluation of AS0 using Eq. 6-15. However, unless great care is taken the method is of low accuracy23 and it is preferable to establish AH by direct calorimetry. Also, especially for proteins, the assumption that AH0 is constant over a significant temperature range may be erroneous. 

Direct calorimetry (heat production) represents a reliable method for the estimation of total benthic community metabolism, because it is a direct measurement of the energy flow through the system. Although the heat release from the activity of extracellular enzymes and from chemical oxidations are also included, the latter two components are thought to be of minor importance for total heat loss from sediments (Pamatmat, 1982). 

It appears, therefore, that the measurement of heat flow using direct calorimetry, is a suitable technique for biogeochemical studies in aquatic systems since under carefully controlled conditions a reproducible "fingerprint" (or power-time curve) is obtained. 

Jequier, E. (1975). Direct calorimetry. A new clinical approach for measuring thermoregulatory responses in man. Bibl. Radiol. 6,185-190. 

Information about this energy has been obtained from isotherm measurements over a temperature range (3, 7, 8, 9), by calorimetry 18, 19), and by differential thermal analysis (JJ). From the isotherms and by direct calorimetry, the isosteric heats, q t, may be found as functions of the amount of water sorbed. However, some disadvantages may be associated with each procedure. Such is the affinity between water and zeolites that to determine q t for small uptakes may require isotherm measurements at temperatures above 200°C. At these temperatures, lattice breakdown can take place by side reactions involving the water. 

Calculating Energy Expenditures Direct Calorimetry Metabolic Rate... 

The methods of indirect and direct calorimetry may not always result in the same values for energy expenditure. Indirect calorimetry is a measure of the heat produced by oxidative processes. Direct calorimetry measures the rate of dissipation of heat from the body. An increase in the rate of heat production, as with exercise, may not always result in an immediate, measurable increase in heat released by the body (from the skin). Instead, the increase in heat production may result in a rise in body temperature. That part of the energy requirement used to raise... 

The use of direct calorimetry is not a convenient technique, since it requires a specially constructed room and the confinement of human subjects for a day or longer in the room. The doubly labeled water technique offers a convenient alternative, providing that one has a machine to perform isotope ratio mass spectrometry. The doubly labeled water technique is used to measure the rate of total CO2 production in the body. This number alone is not sufficient to allow one to calculate the total energy expenditure. But the value for COj production (moles COi/day), along with the RQ, allows one to calculate the oxygen consumption using the following formula ... 

The energy expenditure of an animal or human may also be determined by the method of direct calorimetry. Direct calorimetry requires the use of an insulated room, chamber, or suit for the human or animal. The enclosure contains a water jacket. The water passes from one end of the jacket to the other, maintaining the room, chamber, or suit at a constant temperature. The temperature of the water leaving the jacket is used to calculate the energy expended by the subject. The principles behind the use of the chamber are identical to those behind the use of the bomb calorimeter. The major difference is that in bomb calorimetry combustion is catalyzed by a small spark. In addition, in the bomb calorimeter oxygen is present at a high pressure to facilitate combustion. With direct calorimetry, combustion is catalyzed by enzymes. This combustion proceeds more slowly than that catalyzed by a spark, and the temperature of the subject does not increase much over the normal resting body temperature with the various activities. 

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