Coincidences

Apolar stationary phases having no dipolar moments, that is their center of gravities of their positive and negative electric charges coincide. With this type of compound, the components elute as a function of their increasing boiiing points. The time difference between the moment of injection and the moment the component leaves the column is called the retention time. 

When the two components are mixed together (say in a mixture of 10% ethane, 90% n-heptane) the bubble point curve and the dew point curve no longer coincide, and a two-phase envelope appears. Within this two-phase region, a mixture of liquid and gas exist, with both components being present in each phase in proportions dictated by the exact temperature and pressure, i.e. the composition of the liquid and gas phases within the two-phase envelope are not constant. The mixture has its own critical point C g. 

The point t, on the abscissa denotes the end of the active stage of the impact, or time of the indenter intrusion The break of the contact of indenter with material tested is designated by Xk Analyzing the curves V(t), a(t) and F(t), it is seen that the maximum of the contact force does not coincide in time with the moment of achievement of the maximum intrusion and zero... 

As it is shown in Fig.3 coincidence of curves is rather good. A calculated curve shows a clearly defined defect in on internal coating of a kiln. 

Use now this equation to describe liquid film flow in conical capillary. Let us pass to spherical coordinate system with the origin coinciding with conical channel s top (fig. 3). It means that instead of longitudinal coordinate z we shall use radial one r. Using (6) we can derive the total flow rate Q, multiplying specific flow rate by the length of cross section ... 

First, the plane n(x,y) coincides with the diffuser mean plane of G, IT (x ,y ). When G is translated a distance x and rotated an angle Aa respect to the y axis of Il (x ,y ), we ob-a null movement of the speckle pattern on a circumference of center C and radius R ... 

Structural noise is sometimes called a "correlated" one because signals reflected by structural heterogeneities and forming structural noise, repeat the form of the initial pulse, have the same spectral composition. Energy spectrum of the structural noise to an approximation of constant coincides with energy spectrum of the signal ... 

It can easily be shown that an experimentally generated curve coincides with the synthetically generated DGS curve having applicable corrections (transfer loss and sound attenuation) with acceptable tolerances. However, our intention is not to replace the reference block method by the DGS method. In practical application you may encounter many cases, where only the reference block method can be applied, e.g. ... 

In pulse version of MIA method the probes excite in tested object (TO) free attenuating pulses. Their carrier frequencies coincide with natural frequencies of transmitting probe vibrator loaded to the mechanical impedance Zg = / (Z -tZ,), where Z is elastic... 

To increase the sensitivity, direction of amplitude variation of probe output signal in defective area must coincide with the one after CCF processing. If the defect decreases the probe signal (single contact probe) A((/should be set Ai// = 0, in the opposite case (twin contact probe) it should be set Aif/= n. So the instrument should be supplied with a device to adjust A((/ and to sustain it constant. 

Comparative evaluation of international and national requirements both in the part of the volume and frequence of calibration procedures and examination of devices for ultrasonic and radiographic testing was accomplished. This review showed that procedures specified in national documents on testing and documents of EAL coincide very much. 

The quantity 1 /k is thus the distance at which the potential has reached the 1 je fraction of its value at the surface and coincides with the center of action of the space charge. The plane at a = l//c is therefore taken as the effective thickness of the diffuse double layer. As an example, 1/x = 30 A in the case of 0.01 M uni-univalent electrolyte at 25°C. 

In classical mechanics, it is certainly possible for a system subject to dissipative forces such as friction to come to rest. For example, a marble rolling in a parabola lined with sandpaper will eventually lose its kinetic energy and come to rest at the bottom. Rather remarkably, making a measurement of E that coincides with... 

The FCC structure is illustrated in figure Al.3.2. Metallic elements such as calcium, nickel, and copper fonu in the FCC structure, as well as some of the inert gases. The conventional unit cell of the FCC structure is cubic with the lengdi of the edge given by the lattice parameter, a. There are four atoms in the conventional cell. In the primitive unit cell, there is only one atom. This atom coincides with the lattice pomts. The lattice vectors for the primitive cell are given by... 

Below T, liquid and vapour coexist and their densities approach each other along the coexistence curve in the T-Vplane until they coincide at the critical temperature T. The coexisting densities in the critical region are related to T-T by the power law... 

Electron-impact energy-loss spectroscopy (EELS) differs from other electron spectroscopies in that it is possible to observe transitions to states below the first ionization edge electronic transitions to excited states of the neutral, vibrational and even rotational transitions can be observed. This is a consequence of the detected electrons not originating in the sample. Conversely, there is a problem when electron impact induces an ionizing transition. For each such event there are two outgoing electrons. To precisely account for the energy deposited in the target, the two electrons must be measured in coincidence. 

Figure Bl.6.12 Ionization-energy spectrum of carbonyl sulphide obtained by dipole (e, 2e) spectroscopy [18], The incident-electron energy was 3.5 keV, the scattered incident electron was detected in the forward direction and the ejected (ionized) electron detected in coincidence at 54.7° (angular anisotropies cancel at this magic angle ). The energy of the two outgoing electrons was scaimed keeping the net energy loss fixed at 40 eV so that the spectrum is essentially identical to the 40 eV photoabsorption spectrum. Peaks are identified with ionization of valence electrons from the indicated molecular orbitals.

Time-of-flight mass spectrometers have been used as detectors in a wider variety of experiments tlian any other mass spectrometer. This is especially true of spectroscopic applications, many of which are discussed in this encyclopedia. Unlike the other instruments described in this chapter, the TOP mass spectrometer is usually used for one purpose, to acquire the mass spectrum of a compound. They caimot generally be used for the kinds of ion-molecule chemistry discussed in this chapter, or structural characterization experiments such as collision-induced dissociation. Plowever, they are easily used as detectors for spectroscopic applications such as multi-photoionization (for the spectroscopy of molecular excited states) [38], zero kinetic energy electron spectroscopy [39] (ZEKE, for the precise measurement of ionization energies) and comcidence measurements (such as photoelectron-photoion coincidence spectroscopy [40] for the measurement of ion fragmentation breakdown diagrams). 

Coincidence experiments explicitly require knowledge of the time correlation between two events. Consider the example of electron impact ionization of an atom, figure Bl.10.7. A single incident electron strikes a target atom or molecule and ejects an electron from it. The incident electron is deflected by the collision and is identified as the scattered electron. Since the scattered and ejected electrons arise from the same event, there is a time correlation... 

Figure Bl.10.7. Electron impact ionization coincidence experiment. The experiment consists of a source of incident electrons, a target gas sample and two electron detectors, one for the scattered electron, the other for the ejected electron. The detectors are coimected tlirough preamplifiers to the inputs (start and stop) of a time-to-amplitiide converter (TAC). The output of the TAC goes to a pulse-height-analyser (PHA) and then to a nuiltichaimel analyser (MCA) or computer.

Comcidence experiments have been connnon in nuclear physics since the 1930s.The widely used coincidence circuit of Rossi [9] allowed experimenters to detennine, within tire resolution time of the electronics of the day, whether two events were coincident in time. The early circuits were capable of submicrosecond resolution, but lacked the flexibility of today s equipment. The most important distinction between modem comcidence methods and those of the earlier days is the availability of semiconductor memories that allow one to now record precisely the time relations between all particles detected in an experiment. We shall see the importance of tliis in the evaluation of the statistical uncertainty of the results. 

When a time window twice the duration of the delay time is used, perfect coincidence is at the centre of the time window and it is possible to make an accurate assessment of the background by considering the region to either side of the perfect coincidence region. An example of a time spectrum is shown m figure Bl.10.8. 

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