Measurement of time

Quartz docks eventually replaced the mechanical docks around the middle of the 20th century. A quartz dock or watch makes use of the piezodectric property of quartz crystal A quartz crystal, when subjected to a mechanical pressure, creates an electric fidd. The inverse is also tme—that is to say, the shape of the crystal changes when it is subjected to an dectric fidd. These principles are used to design clocks that make the crystal vibrate and generate an electric signal of constant fisquency. 

As we stated in Chapter 6, the namral fi quenty of the cesium atom was adopted as the new standard unit of time. The unit of a second is now fiarmally defined as the duration of 9,192,631,770 periods of the radiation correspondii to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. 

The present, most widely used, method of regulating modem timepieces is a quartz crystal. A properly oriented quartz single crystal will expand and contract at a very precise frequency when subjected to an oscillating voltage produced by an inductive-capacitive (L-C) circuit oscillating at about the same frequency as the crystal. The crystal fine-tunes the oscillating frequency of the current [f = 2n LCf where L is the 

The phenomenon utilized in the quartz clock is called the piezoelectric effect. When a crystal is subjected to alternate compressive and tensile strains, oscillating (+, -) electric charges appear on opposing faces of the crystal. Similarly, when a crystal is subjected to oscillating charges, it undergoes expansion and contraction. 

A still more accurate timepiece is the atomic clock. In this case, regulation depends upon the frequency of molecular vibration. The maximum accuracy of a gaseous ammonia clock is about 1,000 times that of the best quartz clock. Thus, the best atomic clock has an accuracy of about3 ps/.  

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Kinematic viscosity NFT 60-100 ISO 3104 and 3105 ASTM D 445 and D 446 Measurement of time required to flow between 2 marks in a tube... 

The key to experimental gas-phase kinetics arises from the measurement of time, concentration, and temperature. Chemical kinetics is closely linked to time-dependent observation of concentration or amount of substance. Temperature is the most important single statistical parameter influencing the rates of chemical reactions (see chapter A3.4 for definitions and fiindamentals). 

The other necessary instrumental component for controlled-current coulometry is an accurate clock for measuring the electrolysis time, fe, and a switch for starting and stopping the electrolysis. Analog clocks can read time to the nearest +0.01 s, but the need to frequently stop and start the electrolysis near the end point leads to a net uncertainty of +0.1 s. Digital clocks provide a more accurate measurement of time, with errors of+1 ms being possible. The switch must control the flow of current and the clock, so that an accurate determination of the electrolysis time is possible. 

Results from measurements of time-dependent effects depend on the sample history and experimental conditions and should be considered approximate. For example, the state of an unsheared or undisturbed sample is a function of its previous shear history and the length of time since it underwent shear. The area of a thixotropic loop depends on the shear range covered, the rate of shear acceleration, and the length of time at the highest shear rate. However, measurements of time-dependent behavior can be usehil in evaluating and comparing a number of industrial products and in solving flow problems. 

Usually the experimental error in the measurement of time is negligible relative to the error in concentration, and the choice of plotting form may be determined by this factor. Another consideration is the extent of reaction that has been followed... 

Zeit-lose, /. colchicum. -mass, n. measure of time (Music) time, rhythm (Gram.) quantity. -massstab, m. time scale, -messer, m. chronometer, time piece, watch, clock, -messung, /. time measurement timing, -puukt, m. point of time, moment, zeitraubend, p.a, time-consuming. 

The yield of a gas-solid heterogeneous reaction depends not on the total time that molecules spend in the reactor but on the time that they spend on the catalyst surface. The contact time distribution provides a standardized measure of times spent in the absorbed state. A functional definition is provided by the following equation applicable to a first-order, heterogeneous reaction in an isothermal reactor ... 

Edwards RL, Chen JH, Wasseiburg GJ (1986) 238u.234y 230pjj 232jjj systematics and the precise measurement of time over the past 500,000 years. Earth Planet Sci Lett 81 175-192. 

Although some precautions must be observed in timing a reaction, the direct measurement of time seldom affects the accuracy of a rate determination. The time required for sampling, for... 

Put, L.W. and de Meijer, R.J., Measurements of Time-averaged Radon Daughter Concentrations with Passive Dosemeters. Sci. Total. Environ. 45 389-395 (1985). 

Measurement of time-resolved Ro(t) or R (0 under femtosecond-pulse irradiation. Evaluation with Monte Carlo simulation, /Vmethod, or numerical KM approximation. 

D. J. S. Birch, A. S. Holmes, J. R. Gilchrist, R. E. Imhof, S. M. A1 Alawi and B. Nadolski, A multiplexed single-photon instrument for routine measurement of time-resolved fluorescence anisotropy, J. Phys. E Sci. Instrum. 20, 471-473 (1987). 

A better description of the design matrix would involve not only the concentration of sodium ion (x mM), but also the time at which each experiment was carried out (xj, min). If we begin our measurement of time with the first experiment, then the design matrix for the previous set of experiments would be... 

When peak-width at the basehne is used, the overall shape of the peak is insignificant and the simple measurement of time characterizes the analytical signals. Originally, two FIA approaches were introduced— the American AMFIA System which attempted to provide an automated system using HPLC instrumentation, and a manual unit which was developed by Ruzicka and Hansen [40]. A novel development of FIA has recently been... 

A measure of time to reduce the amount of agent by one-half... 

We should be clearly aware of the distinction between these two measures of time, t and r. They are defined as follows ... 

A specific example of applications in the second category is the dating of rocks. Age determination is an inverse problem of radioactive decay, which is a first-order reaction (described later). Because radioactive decay follows a specific law relating concentration and time, and the decay rate is independent of temperature and pressure, the extent of decay is a measure of time passed since the radioactive element is entrapped in a crystal, hence its age. In addition to the age, the initial conditions (such as initial isotopic ratios) may also be inferred, which is another example of inverse problems. 

As described in the previous section, the femtosecond fluorescence up-conversion microscope enabled us to visualize microscopic samples based on position-depen-dent ultrafast fluorescence dynamics. However, in the imaging measurements using the fluorescence up-conversion microscope, XY scanning was necessary as when using FLIM systems. To achieve non-scanning measurements of time-resolved fluorescence images, we developed another time-resolved fluorescence microscope. 

Many Earthly cultures have devised interesting words for long periods of time. For example, one of the longest measures of time is the kalpa in Hindu chronology, equivalent to 4,320 million years. The kalpa is divided into 14 periods, and the universe is recreated at the end of each of these periods. We are currently in the seventh of these 14 periods of the present kalpa. 

C. Measurement of times to ignition of explosive exposed to hot flames. 

The first two quantities calculated from S(t, y) depended on measurements of times the second two depend on measurements of amplitudes. From the amplitude of the reflection from the top surface of the cell the impedance, and hence the density, can be found using eqns (8.58) and (8.59). The impedance is plotted in Fig. 9.4(c). Finally, knowing the thickness and the impedance of the cell, the attenuation can be deduced from the amplitude of the echo from the interface between the cell and the substrate the weaker this echo, the greater the attenuation. The attenuation calculated from (8.60), neglecting frequency dependence, is plotted in Fig. 9.4(d). It is also possible to calculate the frequency dependence of the attenuation using (8.70) (Daft et al. 1989). 

Evans, M., et al, The Practical Application of the Praton Diffusion Sampler for the Measurement of Time-Weighted Average Exposure to Volatile Organic Substances in Air,... 

Errors in sampling (sample volume determination) are due to erroneous measurement of time or flow rate. Time can be measured so accurately that flow rate errors make up the majority of the 10% variation attributed to the average sampling pump. 

If the quantity 0 is used to represent any measure of time duration of the wave, e.g., the time constant of an exponential decay, it is evident that 0/ao can be a function only of the ratio a0/r. Another important property of such a wave is the impulse associated with it, which measures the momentum imparted to the water by its passage. For unit area of the wave front the impulse I is given by... 

Cell kinetics is defined as the measurement of time parameters m biological systems. Traditionally, this has involved the use of radioactive precursors of DNA, such as tritiated thymidine (3HTdR), and autoradiography to detect their incorporation into DNA. This technique has provided detailed knowledge of cell kinetics in both in vitro and in vivo experimental systems. The technique, however, is time consuming and arduous and is not readily applicable to human tumor research because of ethical problems involved in incorporation of a radioisotope into DNA. 

The pulses produced by this action proceed thru mixer circuits to an oscillograph where they are displayed on a cathode-ray oscilloscope screen along with time calibration markers. This display is photographed and detonation rates are computed from expl increment lengths, and measurements of time displacements are read on a film reader... 

If multiple procedures are performed, a qualitative measure of time dependence can be gained. This is achieved by linking two ramps in an up-and-down sequence and examining the area of hysteresis. A second option is to connect three segments as an up ramp, a peak hold step, and a down ramp sequence this option has the effect of altering the area of hysteresis because the sample is broken down more effectively before the down step. 

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