Instantaneous detection

In order to clarify the photolytic behavior of thietanones, Langendries et al. monitored their reactions directly by IR spectroscopy in a cryostat. With the appearance of their specific IR absorption bands the sulfenes could be instantaneously detected and a cycloreversion mechanism postulated (Eq, 57). The sulfene bands could not be observed, however, when light with wavelengths below 220 nm was used for the irradiation. 

To meet this critical challenge, new technologies for detection and identification of threat agents should be developed. The availability of detectors that are small, ragged, and low cost would allow om detection capability to be dispersed widely at home and abroad. The objective must be instantaneous detection and rapid identification, both with near 100 percent reliability, because erroneous... 

A new inexpensive diagnostic biosensor test for the first time allowed instantaneous detection of the toxic strain of E. coli (E. coli strain 0157 H7), the bacteria responsible for several recent food-poisoning outbreaks. 

Tanner SD, Davidson WR, Fulford JE. 1983. The instantaneous detection of explosives by tandem mass spectrometry. In Proceedings of the International Symposium on the Analysis and Detection of Explosives, FBI Academy, Quantico, VA, March 29-31, 1983. Washington, DC U.S. Department of Justice, Federal Bureau of Investigation, 409-417. 

In one application, the TRC/TRC cascade control was used with four thermocouples installed, in parallel, in the convection section of the heater which was installed in thermowells. The thermowells were inserted in the heater wall between the tubes. Because the thermocouples receive the same heat as the convection section tubes, an instantaneous detection of furnace temperature was made. 

Laser-induced fluorescence (LIF) is a nonintrusive visualization technique that can instantaneously detect the fluorescence of fluorescent molecules to show their concentration, density, temperature, velocity, and even pressure. It is an important detection method in microfluidics and nanofluidics to indicate the characteristics of fluid. 

Acmally, the florescence induced by laser is an instantaneous detection (the decay of the excited state is about 10 ns) [4]. It also could be performed to access the velocity of molecules, particles, as well as cells. Additionally, LIF reflects the distribution of individual vibration and rotational states it could in principle be used for the temperature measurement, too. 

To overcome the disadvantages of these previously described systems, the HELM tracker system allows continuous measurement of the current flow in every cathode in an electrolytic tankhouse. The system allows for instantaneous detection of the magnitude and specific location of electrode current distribution anomalies such as short circuits and poor contacts, which is displayed to the operators through the systems HMI. The system requires no electrical or physical contact with the cathodes, and can be easily retrofitted into an existing plant, without interfering with the operation. 

The method implies injection of a mixture of 3 radioactive tracers each being distributed into one of the 3 phases. The tracers must show such differences in the emitting y-radiation energy spectra that they can be simultaneously detected by on line y-spectrometry. Candidate tracers are Br-82 as bromobenzene for oil, Na-24 or La-140 for water, and Kr-85 for gas. The tracers are injected simultaneously at a constant rate into the flow in the pressurised pipe, and the concentration is detected as series of instantaneous measurements taken downstream as illustrated in figure 2. 

O, a large current is detected, which decays steadily with time. The change in potential from will initiate the very rapid reduction of all the oxidized species at the electrode surface and consequently of all the electroactive species diffrising to the surface. It is effectively an instruction to the electrode to instantaneously change the concentration of O at its surface from the bulk value to zero. The chemical change will lead to concentration gradients, which will decrease with time, ultimately to zero, as the diffrision-layer thickness increases. At time t = 0, on the other hand, dc-Jdx) r. will tend to infinity. The linearity of a plot of i versus r... 

There are two common occasions when instantaneous measurement of a range of m/z values is preferable. First, with ionization sources such as those using laser desorption or radionuclides, a pulse of ions is produced in a very short interval of time, often of the order of a few nanoseconds. If the mass spectrometer takes 1 sec to attempt to scan the range of ions produced, then clearly there will be no ions left by the time the scan has completed more than a few microseconds (ion traps excluded). The array collector overcomes this difficulty by detecting the ions produced all at the same instant... 

A multipoint ion collector (also called the detector) consists of a large number of miniature electron multiplier elements assembled, or constructed, side by side over a plane. A multipoint collector can be an array, which detects a dispersed beam of ions simultaneously over a range of m/z values and is frequently used with a sector-type mass spectrometer. Alternatively, a microchannel plate collector detects all ions of one m/z value. When combined with a TOP analyzer, the microchannel plate affords an almost instantaneous mass spectrum. Because of their construction and operation, microchannel plate detectors are cheaper to fit and maintain. Multipoint detectors are particularly useful for situations in which ionization occurs within a very short space of time, as with some ionization sources, or in which only trace quantities of any substance are available. For such fleeting availability of ions, only multipoint collectors can measure a whole spectrum or part of a spectrum satisfactorily in the short time available. 

In a beam of ions separated in time according to m/z value, the total time taken for ions of different m/z values to arrive at a microchannel plate is so short (about 30 psec) that the spectrum appears to have been obtained instantaneously. Thus, for practical purposes, the array and microchannel plate collectors produce an instantaneous mass spectrum, even though the first detects a spatially dispersed set of m/z values and the second detects a temporally dispersed set. 

A final type of measurement is the detection of localized corrosion, such as pitting or crevice attack. Several corrosion-measuring probes can be used to detec t localized corrosion. Some can detect locahzed corrosion instantaneously and others only its result. These types of corrosion may contribute little to the actual mass loss, but can be devastating to equipment and piping. Detec tion and measurement of localized corrosion is one of the areas with the greatest potential for the use of some of the newest electrochemicaUy Based corrosion monitoring probes. 

Such relays are normally instantaneous, highly sensitive and operate at low spill cuiTents. Since they detect the residual current of the system, the current may contain third-harmonic components (Section 23.6) and operate the highly sensitive relay in a healthy condition. To avoid operation of the relay under such conditions, it is a normal practice to supply the relay coil with a tuned filter, i.e. a series L-C circuit to filter out the third-harmonic components. The capacitance of the filter circuit may also tame a steep rising TRV (Section 17.10.3) during a momentary transient condition and protect the relay. 

Electronic Flow Calibrators These units are high accuracy electronic bubble flowmeters that provide instantaneous air flow readings and a cumulative averaging of multiple samples. These calibrators measure the flow rate of gases and report volume per unit of time. The timer is capable of detecting a soap film at 80... 

A practical method of predicting the molecular behavior within the flow system involves the RTD. A common experiment to test nonuniformities is the stimulus response experiment. A typical stimulus is a step-change in the concentration of some tracer material. The step-response is an instantaneous jump of a concentration to some new value, which is then maintained for an indefinite period. The tracer should be detectable and must not change or decompose as it passes through the mixer. Studies have shown that the flow characteristics of static mixers approach those of an ideal plug flow system. Figures 8-41 and 8-42, respectively, indicate the exit residence time distributions of the Kenics static mixer in comparison with other flow systems. 

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