General Principles of Operation

Thermal analysis refers to a variety of techniques in which a property of a sample is continuously measured as the sample is programmed through a predetermined temperature profile. Among the most common techniques are thermal gravimetric analysis (TA) and differential scanning calorimetry (DSC). 

In a DSC experiment the difference in energy input to a sample and a reference material is measured while the sample and reference are subjected to a controlled temperature program. DSC requires two cells equipped with thermocouples in addition to a programmable furnace, recorder, and gas controller. Automation is even more extensive than in TA due to the more complicated nature of the instrumentation and calculations. 

A thermal analysis curve is interpreted by relating the measured property versus temperature data to chemical and physical events occurring in the sample. It is frequently a qualitative or comparative technique. 

In DSC the measured energy differential corresponds to the heat content (enthalpy) or the specific heat of the sample. DSC is often used in conjunction with TA to determine if a reaction is endothermic, such as melting, vaporization and sublimation, or exothermic, such as oxidative degradation. It is also used to determine the glass transition temperature of polymers. Liquids and solids can be analyzed by both methods of thermal analysis. The sample size is usually limited to 10-20 mg. 

Thermal analysis can be used to characterize the physical and chemical properties of a system under conditions that simulate real world applications. It is not simply a sample composition technique. 

---

What is Reverse Osmosis and the general principle of operation ... 

We present here a summary of recent work with light-pulse interferometer based inertial sensors. We first outline the general principles of operation of light-pulse interferometers. This atomic interferometer (Borde et al., 1992 Borde et al., 1989) uses two-photon velocity selective Raman transitions (Kasevich et al., 1991), to manipulate atoms while keeping them in long-lived ground states. 

These include such instruments as opacity monitors, turbidimeters, colorimeters, refractometers and spectrophotometers. A selection of these is described—particularly where the instrument has a more general application as an on-line process analyser and/or to illustrate a general principle of operation. It is likely that development of fibre-optic techniques (Section 6.12.4) will extend the use of this type of sensor in the future(56). 

A typical layout of an EPR spectrometer is shown in Fig. 15.5. While the general principles of operation and detection are the same for different spectrometers, specific steps may vary. The readers are encouraged to consult the manual and vendor regarding each individual spectrometer. Examples used in discussions below are based on a Bruker EMX X-band spectrometer that is equipped with an ER-041X microwave bridge and a high-sensitivity cavity (ER-4119HS, Bruker Biospin, Inc.). 

Let us consider the general principles of operation of the LHASA program in finding a synthetic pathway to polycyclic system. The program can be aimed by the chemist along two modes of search. The first mode of operation implies that... 

The general principle of operation of the company is based on the responsibility of the importers/manufacturers/dealers to support the financial cost for collection, demanufacturing, sorting and recycling. This responsibility is covered by two french laws, the Decrees of 12 May 1999 (99/374) and 29 December 1999 (99/1171). 

In this paper general principles of operation will be briefly outlined for PEC cells, and most important systems surveyed. (For detailed presentation of the semiconductor photoelectrochemistry, see, e.g., [2], and for description of PEC cells at greater length, see [3].) In the last Section, some works on the semiconductor dispersions for purifying wastewaters from pollutants will be reviewed. 

The general principle of operation of valve-regulated lead—acid batteries can be summarized as follows ... 

In ISO standard,the size of sample, having length of 70 mm, width between 6 and 6.4 mm, and thickness between 1 and 5 mm differs from ASTM standard. The equipment, its general principle of operation, and results calculation are essentially similar to the description above for ASTM standard.A special method is developed to describe behavior of plasticized compounds.Plasticized PVC compositions are characteristic in respect to the appearance of curves of the logarithm of the stiffness in torsion as a function of temperature, which have form of reversed S. Three regions were identified in these curves ... 

The general principle of operation of the FTIR method is similar to the DOAS method, because they both measure and analyze over a broad region of the spectrum. The principal difference is that an FTIR spectrometer is used instead of a conventional dispersive monochromator. The benefits of using an FTIR in place of a monochromator can be summarized in terms of two types of advantage ... 

The general principle of operation of QCLs is depicted in Figure 4.19. Conventional semiconductor lasers (such as the diode lasers used CD-players and telecommunication applications and the lead-salt devices commonly used in the mid-lR) rely on electron-hole recombination across the doped... 

Fig. 1. General principle of operation for DTA and schematic of a DTA apparatus (4). The subscripts represent s-sample, r-reference, i-initial, f-final.

The reactions at the electrodes lead to the exchange of a lithium ion via the internal circuit (electrolyte, ionic solution) and an electron via the external electric circuit, as described by the following general principle of operation of a lithium-ion battery ... 

We are all familiar with the general principles of operation of an internal combustion reaction the combustion of fuel drives out the piston. It is possible to imagine engines that use reactions other than combustions, and we need to assess the work they can do. A chemical reaction takes place in a container of cross-sectional area 100 cm the container has a piston at one end. As a result of the reaction, the piston is pushed out through 10.0 cm against a constant external pressure of 100 kPa. Calculate the work done by the system. 

---