Pulse-type system

Pulse-type systems. The output consists of voltage pulses, one pulse per particle detected. 

A basic pulse-type system consists of the instruments shown in Fig. 1.2. The function of each component is discussed in later sections of this chapter. 

A current-type system (e.g., an electrometer or a rate meter) is simpler than the pulse-type system. Such systems are discussed in Chap. 5. The remainder of this chapter concerns only pulse-type counting systems. 

Transmission by Positive Pulses. This system is used by Inteq/Teleco. It is placed in a nonmagnetic drill collar containing sensors of the flux-gate type... 

Fig. 2 Two types of dissolution-controlled, pulsed delivery systems (A) single bead-type device with alternating drug and rate-controlling layers (B) beads containing drug with differing thickness of dissolving coats.

The main components of the GM-type PTR are shown in Fig. 5.21(b). From the left to the right, the pulse tube system consists of a compressor (CP), a room temperature heat exchanger or an after-cooler (E,), a rotary valve (RV), a regenerator (RG), a low-temperature heat exchanger (Ej), a pulse tube (PT), another room temperature heat exchanger (E3), two orifices (C and 02) and a buffer volume (BF). 

The matrices in equation (35) for a system of n spins of 1/2 have dimensions of 22n. This means that, for example, a four-spin system must be considered within a space of 256 dimensions. If we deal with the motion of a spin system in a static magnetic field (as in pulse-type experiments), significant simplifications are possible owing to the rules of commutation. Namely, if the Hermitian operators A and 6 commute in Hilbert space, then all the corresponding superoperators AL, AR, AD, BL, BR, and BD in Liouville space also commute. The proof of this is given in reference (12). In Hilbert space, the following commutation takes place ... 

The spin density matrix Pj(t) which describes the properties of any spin system of a molecule A, is defined as follows. We assume that the density matrices Pj(0), j = 1, 2,..., S, which describe the individual components of the dynamic equilibrium at any arbitrary time zero, are known explicitly, and that at any time t such that t > t > 0 the pj(t ) matrices are already defined. Our reasoning is applied to a pulse-type NMR experiment, and we therefore construct the equation of motion in a static magnetic field. The p,(t) matrix is the weighted average over the states involved, according to equation (5). The state of a molecule A, formed at the moment t and persisting as such until t, is given by the solution of equation (35) with the super-Hamiltonian H° ... 

For a pulse-type NMR experiment, the assumption has a straightforward interpretation, since the pulse applied at the moment zero breaks down the dynamic history of the spin system involved. The reasoning presented here, which leads to the equation of motion in the form of equation (72), bears some resemblance to Kaplan and Fraenkel s approach to the quantum-mechanical description of continuous-wave NMR. (39) The crucial point in our treatment is the introduction of the probabilities izUa which are expressed in terms of pseudo-first-order rate constants. This makes possible a definition of the mean density matrix pf of a molecule at the moment of its creation, even for complicated multi-reaction systems. The definition of the pf matrix makes unnecessary the distinction between intra- and inter-molecular spin exchange which has so far been employed in the literature. 

In a pulse-type NMR experiment the density matrix p(t) of a nonexchanging system approaches the thermal equilibrium p which is described satisfactorily by equation (16). The same matrices p0 approximate, with good accuracy, the time-independent solution of the system of differential equations (72). This can be inferred from equation (99) which is derived from equations (95a) and (95b) ... 

It follows that, in a pulse-type experiment on an exchanging spin system, the initial conditions from equation (47) can be rewritten as ... 

Starting in the late 1980s, picosecond and sub-picosecond electron pulses have been available for the experiments through implementation of the magnetic compression technique. A typical chicane -type system used at the Nuclear Professional School, University of Tokyo is presented in Fig. 2 An electron pulse with a duration of seven picoseconds is generated by an S-band linac and compressed down to less than two picoseconds by the chicane. 

Large-scale applications might also be possible as indicated by Bishop et al. [16] using a honeycomb dead-end type microfiltration membrane structure with a relatively large surface eirea to volume ratio of 155 ft /ft. Particulates are filtered from air streams and the filter cake can be easily removed by gas back-pulsing. The system can be loaded with catalysts and is said to be suitable for NO reductions and VOC (volatile organic compounds) oxidation with efficiencies of >95% and >99% respectively. 

Figure 1.2 A basic pulse-type detection system.

External signals may be picked up by the apparatus and be recorded. Sparks, radio signals, welding machines, etc., produce signals that may be recorded by a pulse-type counting system. 

This chapter discusses the factors that should be taken into account in performing relative and absolute measurements. Assume that there is a source of peuTicles placed a certain distance away from a detector (Fig. 8.1) and that the deteetor is connected to a pulse-type coimting system. The source may be located outside the detector as shown in Fig. 8.1, or it may be inside the detector (e.g., liquid-scintillation counting and intemal-gas counting), and may be isotropic (e.g., particles emitted with equal probability in all directions) or anisotropic (e.g., parallel beam of particles). Both cases will be examined. Let... 

Figure 8.1 A point isotropic source counted by a pulse-type counting system.

The rectifier (1) may be of the 6 or 12-pnlse type. The choice mainly depends npon the tolerance that is available for the harmonics, which will be injected into the upstream power system. The rectifier will be designed to provide a sonrce of variable voltage to the DC link. The 12-pulse type will usually be necessary for the highly rated motors within their voltage level. Inside the rectifier compartment will be a set of voltage transformers (9) which will be nsed to derive a set of firing pulses (10) for the rectifier elements. These pnlses will be in synchronism with the power supply. 

Static inverters are used to convert DC voltage into AC voltage. The simplest forms of inverters prodnce an output waveform that is rectangular, as a result of the simple switching process described in snb-section 15.4.1. A rectangular waveform can be used to feed some types of AC equipment e.g. incandescent lamps, domestic equipment such as kitchen mixers and kettles. Equipment that contains electronic devices may not function properly if their supply waveform is non-sinusoidal. Their timing circuits and pulse generating systems may be disturbed by the shape of the waveform or its derivative. 

The practical counting efficiency e represents the probability that any particular photon or particle of radiation emitted by the sample source will be recorded by the detector. As explained in Section 8.2, its value may depend on many factors, including the detector, the type and energy of the radiation, the composition of the source, and the geometry of the source-detector configuration. It includes the loss factor in the pulse analysis system and attenuation and scattering fractions associated with the sample-detector system. All of these factors are discussed further in Section 8.2. 

Phase-dependent coherence and interference can be induced in a multi-level atomic system coupled by multiple laser fields. Two simple examples are presented here, a three-level A-type system coupled by four laser fields and a four-level double A-type system coupled also by four laser fields. The four laser fields induce the coherent nonlinear optical processes and open multiple transitions channels. The quantum interference among the multiple channels depends on the relative phase difference of the laser fields. Simple experiments show that constructive or destructive interference associated with multiple two-photon Raman channels in the two coherently coupled systems can be controlled by the relative phase of the laser fields. Rich spectral features exhibiting multiple transparency windows and absorption peaks are observed. The multicolor EIT-type system may be useful for a variety of application in coherent nonlinear optics and quantum optics such as manipulation of group velocities of multicolor, multiple light pulses, for optical switching at ultra-low light intensities, for precision spectroscopic measurements, and for phase control of the quantum state manipulation and quantum memory. 

Figure 7.29 shows the design of a spray-pulse type catalytic reactor system for isooctane developed by Biniwale etal.[93]. The main plasmatron reactor was a vertical cylinder carrying an atomiser at the top, which was supplied with liquid feed at a pressure of 120 bar. Air was introduced through separate inlets positioned at the top of the reactor. The catalyst was positioned at the reactor bottom, coated onto an alumina mesh and heated by a tungsten wire coil. 

Figure 7.29 Spray-pulse type catalytic reactor system [93],...

The theory of sonic-electronic level measurement is fundamentally based on a sound wave emission source from a transmitter, and a reflection of the sonic wave pulse to a receiver. Measurement of the transit time of this sound pulse and its correlation with electrical impulses provide a means for liquid level detection. Two basic designs operating on this principle use the vapor phase and the liquid phase methods. As most of the attention is currently devoted to the latter type system, this discussion deals exclusively with ultrasonic gaging over a liquid path. 

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