Speed The rate at which

The wavelength and frequency of a wave are related through its speed—the rate at which a particular wave crest moves through the medium. In Figure 4.1, the crest at the left end of the horizontal black arrow will move forward exactly one wavelength in one cycle of the wave. By definition, the time required for the crest to... 

Enzymes are proteins that act as catalysts, speeding the rate at which biochemical reactions proceed but not altering the direction or nature of the reactions. The presence or absence of these important substances affects the biochemical conditions, which then influence the other physiologic processes in the body. Enzyme deficiencies are often inherited as autosomal recessive conditions and may be passed from parent to child. Clearly, when students begin to understand the role of the enzyme and the chemical reaction that it governs, they begin to nnderstand the intricacies of the human biological processes. 

Fourthly, avoid the use of very high cavity temperatures. These are not generally necessary to obtain short cure times, and certainly speed the rates at which residues are deposited. For natural rubber aim at a cavity temperature of 165 °C. For synthetic rubbers with low levels of unsaturation such as ethylene-propylene diene terpolymer this will need to be increased to 180 °C. The cavity temperature is usually 10 °C to 15 °C below the set point of the platens. 

At equilibrium, the net current is equal to zero. However, this does not mean that both the forward reaction and the backward reaction stop. Actually, both reactions proceed in opposite directions but with the same speed. The rate at which they proceed at equilibrium is called the exchange current density, [1]. 

In the simplest form the vertical plates are supplied with a voltage which is a linear function of time, and, in the absence of a signal on the horizontal plates, the beam will move horizontally from left to right across the screen. The speed of movement is controlled by the rate at which... 

This observation is now known as Graham s law of effusion. The rate of effusion is proportional to the average speed of the molecules in the gas because the average speed of the molecules determines the rate at which they approach the hole. Therefore, we can conclude that... 

A catalyst is a substance that increases the rate of a chemical reaction without being consumed itself. We shall see a lot more of catalysts later, when we consider reaction rates in Chapter 13. However, it is important to be aware at this stage that a catalyst has no effect on the equilibrium composition of a reaction mixture. A catalyst can speed up the rate at which a reaction reaches equilibrium, but it does not affect the composition at equilibrium. It acts by providing a faster route to the same destination. 

As the wetting front advances at speed U, the solid undergoes a strain cycle at a variety of frequencies, /, the local frequency depending on the distance of the element of solid from the contact line at the moment under consideration. The solid the furthest from the contact line, yet still perturbed by the presence of the three-phase line, is at a distance of ca. to and thus feels a strain cycle at frequency [//to. At the other extreme, near the lower cutoff at x = 8, the frequency is ca. [7/8. The latter frequency will be dominant, since it is in the direct vicinity of the three-phase line that the solid is strained the most. As a consequence, and using Eq. (10), we can define the rate at which work is being done as ... 

Quantitative Analysis. The efficiency of the detector is such that almost 100% of the X-rays entering it will produce a pulse, but the pulse processing speed limits the rate at which X-rays can be counted. If the count rate is less than a few thousand counts per second, then most of the incoming pulses are processed, but as the count rate rises an increasing fraction of the pulses are rejected. The live time during an analysis when the detector was counting is thus less than the elapsed time, and the EDS system records both times in order that the true count rate may be measured. 

In the molten state polymers are viscoelastic that is they exhibit properties that are a combination of viscous and elastic components. The viscoelastic properties of molten polymers are non-Newtonian, i.e., their measured properties change as a function of the rate at which they are probed. (We discussed the non-Newtonian behavior of molten polymers in Chapter 6.) Thus, if we wait long enough, a lump of molten polyethylene will spread out under its own weight, i.e., it behaves as a viscous liquid under conditions of slow flow. However, if we take the same lump of molten polymer and throw it against a solid surface it will bounce, i.e., it behaves as an elastic solid under conditions of high speed deformation. As a molten polymer cools, the thermal agitation of its molecules decreases, which reduces its free volume. The net result is an increase in its viscosity, while the elastic component of its behavior becomes more prominent. At some temperature it ceases to behave primarily as a viscous liquid and takes on the properties of a rubbery amorphous solid. There is no well defined demarcation between a polymer in its molten and rubbery amorphous states. 

In many applications, we exert forces on polymer products for extended periods of time. In such cases it is important that they do not deform beyond acceptable limits. We address this concern through creep testing, which may take days, weeks, or even months to perform. We can also change the rate at which we perform certain tests. Thus we might test the polymer resin to be used in a crash helmet at high speed to mimic an impact. In contrast, the film used in a plastic bag would be better tested at slower speeds, which are more representative of what it would experience during use. 

We control fiber properties by changing the relative speeds of different stages of the process. Orientation is increased and fiber thickness decreased by increasing the final take-up speed relative to the rate at which the molten polymer strands leave the spinneret. To produce high modulus fibers we generally adopt conditions that maximize orientation. Fiber diameters... 

Photothermal decomposition of palladium acetate by scanned cw Ar+ laser irradiation produces metal features that exhibit pronounced periodic structure as a function of laser power, scan speed, substrate and beam diameter, as shown in Figures 3 and 4. The periodic structure is a function of the rate at which the film is heated by absorption of the incident laser radiation coupled with the rate at which the heat of the decomposition reaction is liberated. This coupling generates a reaction front that outruns the scanning laser until quenched by thermal losses, the process to be repeated when the laser catches up and reaches unreacted material. Clearly, such a thermal process is also affected by the thermal conductivity of the substrate, the optical absorption of the substrate in those cases where the overlying film is not fully absorbing,... 

The reaction mixture is heated to speed up the rate at which equilibrium is reached, not to shift the equilibrium toward more product. Heating actually decreases the amount of product present at equilibrium since the reaction is exothermic (AH is negative). 

As expected, an increase of the light intensity leads to both sharper temperature profiles and higher values of the maximum temperature. A linear relationship was found to exist between the rate at which the temperature rises and the rate of polymerization (Rp)max (Figure 9, curve a). Therefore, the speed of the... 

---