Electric compensation

In balances which give two TG-curves with different sensitivity, an electrical compensation device switches automatically the expanded curve to the next passage in the chart strip (see Fig. 7 with the two recorded TG-curves). 

In summary, while some of the above polymers can form polar crystals, their three-dimensional arrangement in macroscopic specimens results in internal electrical compensation. To overcome this, such specimens must be externally polarized [55]. 

The calorimetric technique used in the titration experiment illustrated in Figure 9 allows short time intervals between the injections due to a comparatively low time constant for the instrument in combination with the electrical compensation technique. Rather, slow heat conduction microcalorimeters can be used in fast titration experiments if a dynamic correction, based on the Tian equation (equation (17)), is employed (Bastos et al., 1991 Backman et al., 1994). 

The initiation of an electrogenic process causes an adjustment of the passive ionic fluxes across the membrane. In particular, the net charge actively brought in is soon electrically compensated by appropriate passive movements of that ion and other ions into or out of the cell. The actual electrical potential difference across the membrane then results from the diffusion potential caused by these new passive fluxes plus a steady-state contribution from the electrogenic process involving the active transport of various charged species. We can represent the electrical potential difference generated by the active transport of species/, atj, by... 

At the rest potential this reaction is electrically compensated for by the anodic oxidation of GaP (reaction (13 )), so that the overall reaction can be written as ... 

In the /i"-alumina structure, the phase is stabilized at high temperatures by small amounts of monovalent (e.g., Li20) or divalent (e.g., MgO, ZnO, NiO) oxidesIn these stabilized structures, the cation dopant substitutes directly for trivalent aluminum ions in the spinel block (i.e., LiXi, MgAi) and is electrically compensated by additional sodium ions (Nai) in the conduction plane. 

The electrical and optical activity of acceptors as a function of their charge state and of the electrical compensation of the semiconductor can be derived in the same way as what has been described for donors. Also, in all semiconductors and insulators, many of the spectroscopic properties of the hydrogen-like acceptors are determined by the energy structure of the VB maximum, located at k = 0. There is no strict equivalent of the Fano resonances observed for donors in crystals with several equivalent CB minima in k space, but discrete... 

In contrast to direct EMF-readout systems, electrical compensation can be used [36], The ice bath is replaced by an electrical circuit that has a temperature-sensitive resistor. The circuit is preset to compensate for variation in the reference junction temperature. 

Where accuracy of measurement is not vital, commercially available electrical compensators (which assume the outputs of the thermocouples used will match the standard function within the tolerances stated in Table 16.9) are sufficient for direct readout of temperatures. With proper selection, accuracy of at least 2.2°C (or 0.75 percent of readings) for standard wires and 1.1°C (or 0.4 percent of readings) for wires of special tolerance can be achieved without calibration (Table 16.9). However, the precision or reproducibility of a single thermocouple is usually much better than these limits. 

Several methods are commonly used to compensate for these errors. One is electrical compensation [59]. However, this method cannot be used at very high temperatures, where the thermocouple may already be near its melting point. Any additional heating caused by the electrical heating may cause the thermocouple to fail. As examples, Buhr, Haupt, and Kremer [60] and Kremer, Buhr, and Haupt [61] used electrical compensation for radiation and conduction heat losses. 

The results for (M-I) compensated a-Si H films containing both phosphorus and boron (Beyer eta/., 198 la) are shown in Fig. 7. Also included are data of Street et al. (1981). For this series of films the phosphorus doping level has been kept at 1000 ppm and the boron concentration varies. Both type conduction within a factor of 2 near the point of nominal compensation. 

These authors were aware of the difficulty of establishing a comprehensive classification of calorimeters In every classification there are certain calorimeters which do not clearly belong to a particular category.The Calvet calorimeter, for instance, can be used eidier isothermally with electric compensation... or in an isoperibol manner involving the measurement of a local temperature difference. Moreover, a number of existing calorimeters remain outside our classification. One example is a calorimeter involving a compensation of the thermal effect other than by thermoelectric means or by phase transition. But such devices can be easily included in our classification by analogy. ... 

The electrical properties of NiO, doped with monovalent ions (Li+) and trivalent ions (Ga +, Cr +) have been studied quite extensively. The study of Cr-doped NiO is of particular interest for understanding the oxidation behavior of Ni—Cr alloys. When trivalent Cr ions are introduced into a NiO crystal, the electrical compensation could occur by formation of doubly ionized nickel vacancies, according to... 

Thus also an unbalancing of the original electrical compensation characteristic of the isoelectric state, will be the result, which will increase in the order 1—2y 1—3, 1—4. Of course this unbalancing will in itself diminish the efficiency of the mutual... 

Tian A (1933) Researches on Calorimetry. Generalization of the Method of Electrical Compensation. Microcalorimetry. J Chim Phys 30 665-708 and Calvet E (1948) Compensated Differential Microcalorimeter. Compt rend 226 1702-1704. 

As we were not able to observe K or Mg " channels in thylakoid membranes exposed to solutions containing 5 mM MgCl and up to 200 mM KCl, it is anion flow through the Cl channel we describe Jiere, that would allow a rapid, voltage-dependent electric compensation of the light-driven net proton uptake into the thylakoid lumen [Fig. 6]. 

The A sites in an ABO3 type perovskite structure are all filled with Pb and La, but the B sites are not necessarily filled with Zr and Ti, and the PLZT material as a whole is electrically compensated by the presence of vacancies. Accordingly, for a composition with 4at% La, a single vacancy exists at the B sites. 

This disadvantage does not apply to an isothermal device based on electrical compensation. Nevertheless, calorimeters of the latter type operate only in a quasi-isothermal mode, since electronic control systems depend for their response upon small deviations from an established set point, and a certain amount of time is required for changing the prevailing temperature. The use of modem circuits and components ensures that errors from this source will be negligible, however. Electrical compensation makes it possible to follow both endothermic and exothermic processes. In both cases the compensation power is readily measured and recorded or processed further with a computer. Isothermal calorimeters are used quite generally for determining heats of mixing and solution. Commercial devices are available that al.so support the precise work required for multiphase thermo-... 

These concentrations are moreover linked by the electroneutrality equation which expresses the local electric compensation. In the case of a pure material it can be written ... 

It is noteworthy that any exact measurement of heat consists essentially of the measurement of electric energy or is traceable to electric energy determinations because the latter form of energy is easy to release, can be measured with great accuracy, and is directly connected to the base unit of the SI (Systeme international d unites) for the electric current, the ampere. Accordingly, all calorimeters are calibrated either directly by the use of electricity or by means of precisely known heats of reaction or transition, which in turn are measured in electrically calibrated or electrically compensated calorimeters. 

Differential temperature or electrical compensation power as a function of time Evaluation result ... 

The term isothermal refers to equilibrium thermodynamics, where it means constant temperature. Strictly speaking, the temperature of isothermal calorimeters must be kept constant in every part and every moment. But in such a case, no heat transport would occur because heat can only flow when a temperature difference exists (see Chapters 4 and 5). In other words, at least the sample temperature must be more or less different from the calorimeter temperature, and therefore it is more correct to call this type of calorimeter quasi-isothermal rather than isothermal. Furthermore, the heat produced during a reaction in such a calorimeter must be compensated for immediately in one way or the other otherwise, it would change the temperature of the calorimeter. There are two possibilities to compensate for the heat produced by the sample by a phase transition or by electrical compensation. In the first case, the amount of heat produced by the sample is proportional to the amount of substance transformed in the second case, the heat flow rate from the sample is proportional to the electric compensation power. 

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