Clausius form of second law first law


Second-order effects include experiments designed to clock chemical reactions, pioneered by Zewail and coworkers [25]. The experiments are shown schematically in figure Al.6.10. An initial 100-150 fs pulse moves population from the bound ground state to the dissociative first excited state in ICN. A second pulse, time delayed from the first then moves population from the first excited state to the second excited state, which is also dissociative. By noting the frequency of light absorbed from tlie second pulse, Zewail can estimate the distance between the two excited-state surfaces and thus infer the motion of the initially prepared wavepacket on the first excited state (figure Al.6.10 ).  [c.242]

In step (1) and step (2) there is an increase from one to two chain carriers . (For brevity, step (x) is used to refer to equation (A3.14.V) tliroughout.) Under typical experimental conditions close to the first and second explosion limits (see section A3.14.2.3). step (2) and step (3) are fast relative to the rate detemiining step (1).  [c.1094]

These can be started by adopting either a current limiting method or a definite time control method. In a current limiting method the closing of contactors at each step is governed by the current limiting relays which permit the accelerating contactor of each step to close when the motor current has fallen from its first peak value to the second pre-set lower value. The relays determine the closing time by sensing the motor data between each step and close only when the current has fallen to a predetermined value of the current relays. The closing sequence is automatic and adjusts against varying loads.  [c.83]

At least three types of problems contribute to air pollution problems on the regional scale. One is the carryover of urban oxidant problems to the regional scale. With the existence of major metropolitan areas in close proximity, the air from one metropolitan area, containing both secondary pollutants formed through reactions and primary pollutants, flows on to the adjacent metropolitan area. The pollutants from the second area are then added on top of the "background" from the first.  [c.37]

Each country adopts such and such a class as a function of its climatic conditions. France has chosen classes B, E, and F, respectively for the summer, winter, and cold wave periods. The first is from 1 May to 31 October, the second is from 1 November to 30 April, while the third has  [c.215]

Overvoltage effects may be divided roughly into three main classes with respect to causes. First, whenever current is flowing, there will be chemical change at the electrode and a corresponding local accumulation or depletion of material in the adjacent solution. This effect, known as concentration polarization, can be serious. Usually, however, it is possible to eliminate it by suitable stirring. Second, overvoltage arises from the Ohm s law potential drop when appreciable current is flowing. This effect is not very important when only small currents are involved and may be further minimized by the use of the circuit Ex - Eh with the electrode Eh in the form of a probe positioned close to E  [c.212]

A fiill quantum mechanical calculation based on these classical ideas is shown in fignre Al.6,28 and figure Al.6,29 [19], The dynamics of the two-electronic-state model was solved, starting in the lowest vibrational eigenstate of the ground electronic state, in the presence of a pair of femtosecond pulses that couple the states. Because the pulses were taken to be much shorter than a vibrational period, the effect of the pulses is to prepare a wavepacket on the excited/ground state which is almost an exact replica of the instantaneous wavefimction on the other surface. Thus, the first pulse prepares an initial wavepacket which is almost a perfect Gaussian, and which begins to evolve on the excited-state surface. The second pulse transfers the instantaneous wavepacket at the arrival time of the pulse back to the ground state, where it continues to evolve on the ground-state surface, given its position and momentum at the time of arrival from the excited state. For one choice of time delay the exit out of channel 1 is almost completely selective (fignre Al.h.lSk while for a second choice of time delay the exit out of channel 2 is almost completely selective (Al.6.29. Note the close correspondence with the classical model the wavepacket on the excited state is executing a Lissajous motion almost identical with that of the classical trajectory (the wavepacket is a nearly Gaussian wavepacket on a two-dimensional hannonic oscillator). On the groundstate, the wavepacket becomes spatially extended but its exit chaimel, as well as the partitioning of energy into translation and vibration (i.e. parallel and perpendicular to the exit direction) are seen to be in close agreement with the corresponding classical trajectory.  [c.271]

The exchange integrals K j contain terms such as (i,i + l g i+ l,i) + 25i i+[ i h i+i) [138]. The second term, representing the attractive interaction between two nuclei and the electronic overlap charge between them, is the dominant one and completely outweighs the first repulsive term. therefore has the same sign as the Coulomb integral Q. (For a similar derivation, see [139].) In Eq. (A.7), //ab.cl is the cross-term obtained by classic VB theory [140], in which only contributions from electron pairwise transposition permutations were considered. Bonding in these systems is due mainly to the exchange integrals Ki i+i between orbitals in the same cycle [138]. Pauling [140] showed that the most important contributions are due to neighboring orbitals, justifying the neglect of the smaller terms in Eq. (A.7).  [c.393]

The values due to the two separate calculations are of the same quality we usually get from (pure) two-state calculations, that is, veiy close to 1.0 but two comments have to be made in this respect (1) The quality of the numbers are different in the two calculations The reason might be connected with the fact that in the second case the circle surrounds an area about three times larger than in the first case. This fact seems to indicate that the deviations are due noise caused by CIs belonging to neighbor states [e.g., the (1,2) and the (4,5) CIs]. (2) We would like to remind the reader that the diagonal element in case of the two-state system was only (—)0.39 [73] [instead of (—)1.0] so that incorporating the third state led, indeed, to a significant improvement.  [c.711]

The energy functions used in molecular modelling are rarely quadratic and so the Taylor series expansion. Equation (5.3), can only be considered an approximation. There are two important consequences of this. The first consequence is that the performance of a given minimisation method will not be as good for a molecular mechanics or quantum mechanics energy surface as it is for a pure quadratic function. As we shall see, a second derivative method such as the Newton-Raphson algorithm can locate the minimum in a single step for a purely quadratic function, but several iterations are usually required for a typical molecular modelling energy function. The second consequence is that, far from the minimum, the harmonic approximation is a poor one and some of the less robust methods will fail, even though they may work very well close to a minimum, where the harmonic approximation is more valid. For this reason it is important to choose the minimisation  [c.279]

The second flocculation mechanism is lefeiied to as the charge patch oi electrostatic mechanism (32). A highly cationic polymer is adsorbed on a negative particle surface in a flat conformation. That is to say most of the charged groups are close to the surface of the particle, as illustrated in Figure 3. This promotes flocculation by first reducing the overall negative charge on the particle thus reducing interparticle repulsion. This effect is called charge neutralization and is associated with reduced electrophoretic mobiUty. In addition, the areas of polymer adsorption can actually have a net positive charge because of the high charge density of the polymer. The positive regions are also attracted to negative regions on other particles, which is called heterocoagulation. Polymeric inorganic materials may also adsorb on surfaces and cause flocculation by a similar mechanism. A third mechanism is called bridging. Some individual segments of a very high molecular weight polymer, usually a high molecular weight anionic polyacrylamide, adsorb on a surface. As shown in Figure 4a, large segments of the polymer extend into the Hquid phase where other segments are adsorbed on other particles, effectively linking the particles together with polymer bridges. In contrast to the first two mechanisms, bridging is strongly affected by molecular weight and the ionic content of the solution. Only large molecules (33) can bridge between particles. Low molecular weight anionic polymers actually act as dispersants in the same systems. The partial adsorption of the anionic polymer on a negatively charged particle is promoted by the presence of divalent and trivalent ions (34). The charge density of the polymer is also critical. As the negative charge on the polymer increases, the mutual repulsion of negatively charged groups along the chain causes the molecule to have a more extended conformation in solution that favors bridging. The higher charge, however, works against adsorption on negatively charged particles. Increasing the ionic strength of the medium promotes adsorption however, the ions shield the negatively charged groups along the chain, which favors a less extended conformation. For this reason, for each combination of aqueous and soHd phases there is an optimal charge (35). This effect was first reported in 1954 (36). This principle is well illustrated in the Bayer process, where the residue from bauxite leaching is alternately flocculated and repulped in solutions with decreasing ionic content. As the ionic content goes down, the optimal charge, in terms of settling rate, of the anionic polymer used as a flocculant decreases (37).  [c.34]

Alternative fuels fall into two general categories. The first class consists of fuels that are made from sources other than cmde oil but that have properties the same as or similar to conventional motor fuels. In this category are fuels made from coal and shale (see Fuels, synthetic). In the second category are fuels that are different from gasoline and diesel fuel and which require redesigned or modified engines. These include methanol (see Alcohol fuels), compressed natural gas (CNG), and Hquefted petroleum gas (LPG).  [c.194]

The reactor effluent, containing 1—2% hydrazine, ammonia, sodium chloride, and water, is preheated and sent to the ammonia recovery system, which consists of two columns. In the first column, ammonia goes overhead under pressure and recycles to the anhydrous ammonia storage tank. In the second column, some water and final traces of ammonia are removed overhead. The bottoms from this column, consisting of water, sodium chloride, and hydrazine, are sent to an evaporating crystallizer where sodium chloride (and the slight excess of sodium hydroxide) is removed from the system as a soHd. Vapors from the crystallizer flow to the hydrate column where water is removed overhead. The bottom stream from this column is close to the hydrazine—water azeotrope composition. Standard materials of constmction may be used for handling chlorine, caustic, and sodium hypochlorite. For all surfaces in contact with hydrazine, however, the preferred material of constmction is 304 L stainless steel.  [c.282]

Films grown in Hg (72,73) are usually stmctured to make heterojunction photodiode arrays. The first or base layer is narrower band gap HgCdTe, grown on CdZnTe substrates, doped with indium for excess electrons (n-ty- e) in the 3 x 10 /cm range and is 10-p.m thick. The second or cap layer is wider band gap HgCdTe, doped with arsenic for excess holes (p-type) in the 5 x 10 /cm range and is 4-p.m thick. The composite HgCdTe film is photohthographicaHy etched part way into the base layer to form an array of mesas, each one being a photodiode detector element. The p—n junction is close to or coincident with the metallurgical heterojunction. For infrared detection in the 8—12 p.m atmospheric spectral window the base layer CdTe content is ca 20% and the cap layer CdTe content is ca 30%.  [c.434]

A unique design is employed in the Clairton refinery of the Aristech Chemical Corporation (formerly United States Steel Corporation), where a sequence of fractionation stages is operated at increasing temperature (14). Each stage consists of a hehcal-coil heater, a vacuum flash dmm, and a vacuum fractionating column. Dehydration and the removal of light oil are carried out at atmospheric pressure. The topped tar is pumped to the first stage which yields a phenoHc oil overhead. The bottoms pass to the second stage which yields a close cut naphthalene oil as the overhead product. The third stage separates residual oils from the pitch, and in the fourth the residual oils are separated into fractions required for various grades of creosote.  [c.336]

If, on the other hand, stride = 2, then the system memory may limit the speed of the calculation. During the first clock cycle, a request is sent to bank 1 for X(l). During the second clock cycle, a request is sent to bank 3 for X(3). During the 8th clock cycle, a request is sent to bank 15 for X(15). On the 9th clock cycle, when X(17) should be fetched from memory bank 1, that memory bank is still processing the previous request, because X(l) initiated during the first clock cycle. The system must wait until that request is completed before initiating a new request to memory bank 1. This access pattern uses only half the elements of X More importantly, it uses only half the memory banks available. Consequently, effective memory bandwidth is halved. The most pathological case comes with stride = 16, when all references come from a single memory bank effective memory bandwidth is one-sixteenth theoretical maximum.  [c.89]

This large class of dyes with a wide variety of colors shows absorptions that cover the ultraviolet to the infrared region and, as a group, cover a wider span of the spectrum than those of any other dye class. The cyanine dyes are also among the oldest known class of synthetic dyes the first dye was discovered in 1856 (1). The name cyanine (from the Greek kyanos) was attributed to its beautiful blue color however, the dye was extremely fugitive to light and of no practical use at the time for ordinary (fabric) dyeing purposes. The great usefiilness of cyanines was discovered later in photography, and they include the most powerful photographic sensitizing dyes known (2—4) (see Color photography). There are several important reasons for the cyanines prominence as sensitizers first, they have high light absorption per molecule coupled in many cases with a single absorption band in the visible or infrared spectral region, which gives very color-selective absorption of light second, they have a tendency to form dye aggregates that have even narrower, more color-selective absorptions than the monomeric dyes themselves and third, they have high chemical and photochemical reactivity for dyes adsorbed to silver haUdes, which leads to efficient participation in photographic sensitization processes (see Dyes, sensitizing).  [c.389]

BTighteners are used to obtain bright deposits direcdy from the bath (117). The additives currentiy used fall into two classes, which have vatiously been labeled primary and secondary, first class and second class, and carrier and brightener. The last is more commonly used in plating plants.  [c.162]

As one might expect, tire first tenn that contributes to the expectation value of A is simply its value at t = 0, while the second tenn exhibits an oscillatory time dependence. If the superposition initially includes large contributions from states of widely varying energy, then the oscillations in (A) will be rapid. If the states that are strongly mixed have similar energies, then the timescale for oscillation in the properties will be slower. However, there is one special class of system properties A that exlribit no time dependence whatsoever. If (and only if) every one of the states is an eigenfiinction of A, then the property of orthogonality can be used to show that every contribution to the second tenn vanishes. An obvious example is the Hamiltonian operator itself it turns out that the expectation value for the energy of a system subjected to forces that do not vary with time is a constant. Are there other operators that share the same set of eigenfimetions with //, and if so, how can they be recognized It can be shown that any two operators which satisfy the property  [c.14]

Consider die following intuitive scheme, in which the timing between a pair of pulses is used to control the identity of products [ ]. The scheme is based on the close correspondence between the centre of a wavepacket in time and that of a classical trajectory (Elirenfest s theorem). The first pulse produces an excited electronic state wavepacket. The time delay between the pulses controls the time that the wavepacket evolves on the excited electronic state. The second pulse stimulates emission. By the Franck-Condon principle, the second step prepares a wavepacket on the ground electronic state with the same position and momentum, instantaneously, as the excited-state wavepacket. By controlling the position and momentum of the wavepacket produced on the ground state through the second step, one can gain some measure of control over product fonnation on the ground state. This pump-dump scheme is illustrated classically in figure Al.6.27. The trajectory originates at the ground-state surface minimum (the equilibrium geometry). At t = 0 it is promoted to the excited-state potential surface (a two-dimensional hamionic oscillator in this model) where it originates at the Condon point, that is, vertically above the ground-state minimum. Since this position is displaced from equilibrium on the excited state, the trajectory begins to evolve, executing a two-dimensional Lissajous motion. After some time delay, the trajectory is brought down vertically to the ground state (keeping both the instantaneous position and momentum it had on the excited state) and allowed to continue to evolve on the ground-state, figure Al.6.27 shows that for one choice of time delay it will exit mto chaimel 1, for a second choice of time delay it will exit into channel 2. Note how the position and momentum of the trajectory on the ground state, innnediately after it comes down from the excited state, are both consistent with the values it had when it left the excited state, and at the same time are ideally suited for exiting out their respective chaimels.  [c.270]

Figure B3.6.3. Sketch of the coarse-grained description of a binary blend in contact with a wall, (a) Composition profile at the wall, (b) Effective interaction g(l) between the interface and the wall. The different potentials correspond to complete wettmg, a first-order wetting transition and the non-wet state (from above to below). In case of a second-order transition there is no double-well structure close to the transition, but g(l) exhibits a single minimum which moves to larger distances as the wetting transition temperature is approached from below, (c) Temperature dependence of the thickness / of the enriclnnent layer at the wall. The jump of the layer thickness indicates a first-order wetting transition. In the case of a conthuious transition the layer thickness would diverge continuously upon approaching from below. Figure B3.6.3. Sketch of the coarse-grained description of a binary blend in contact with a wall, (a) Composition profile at the wall, (b) Effective interaction g(l) between the interface and the wall. The different potentials correspond to complete wettmg, a first-order wetting transition and the non-wet state (from above to below). In case of a second-order transition there is no double-well structure close to the transition, but g(l) exhibits a single minimum which moves to larger distances as the wetting transition temperature is approached from below, (c) Temperature dependence of the thickness / of the enriclnnent layer at the wall. The jump of the layer thickness indicates a first-order wetting transition. In the case of a conthuious transition the layer thickness would diverge continuously upon approaching from below.
From this theorem it follows that, close to the point of intersection and slightly away from it, the corresponding adiabatic or BO electronic wave functions will be given (to a good approximation) by a superposition of the two degenerate states, with coefficients that are functions of the nuclear coordinates. (For a formal proof of this statement, one has to assume, as is done in [158], that the state is continuous function of the nuclear coordinates.) Moreover, the coefficients of the two states have to differ from each other, otherwise they can be made to disappear from the normalized electronic state. Necessarily, there is also a second superposition state, with coefficients such that it is orthogonal to the first at all points in the configuration space. (If more than two states happen to be codegenerate at a point, then the adiabatic states are mutually orthogonal superpositions of all these states, again with coefficients that are functions of the nuclear coordinates.)  [c.106]

This case is particularly interesting for two reasons. First, time-periodic potentials such that arise from external periodic forces, frequently give rise to cyclically varying states. (According to the authors of [253] The universal existence of the cyclic evolution is guaranteed for any quantum system. ) The second reason is that the Fourier expansion of the cyclic state spares us the consideration of the convergence of the infinite-range integrals in Eqs. (9) and (10) instead, we need to consider the convergence of the (discrete) coefficients of the expansion. In this section, we show that in a broad class of cyclic functions one-half of the complex t plane is either free of amplitude zeros, or has zeros whose contributions can be approximately neglected. As already noted, in such cases, the reciprocal relations connect observable phases and moduli (exacdy or approximately). The essential step is that a function [c.120]

A porous medium may be modelled in two basically dissimilar ways for the purpose of predicting flux relations. In the first, attention is focussed on the pore network through which the gaseous fluxes pass, while in the second, attention is focussed on the obstacles to gaseous motion presented by the solid matrix. The earliest of all models, due to Maxwell [16], and its modern development as the dusty gas model, is the sole representative of the second type. Other treatments are all of the first type and include the early discussion of diffusional limitations in porous catalysts by Thiele [46], the raacropore-micropore model of Wakao and Smith [32], the model of Johnson and Stewart [47], Foster and Butt s [48] model based on convergent and divergent parallel pore arrays, and Feng and Stewart s [49] class of models developed from the earlier work of Johnson and Stewart- The Feng and Stewart models, In particular, are rather comprehensive in scope, and today it is probably reasonable to regard these and the dusty gas model as the principal contenders for serious attention-  [c.63]

Now in the present case i/a 1, so it follows from equation (A.1.7) that G/a 1, provided f differs significantly from zero. Thus che first term on the right hand side of (A.L.8) is a close approximation to the familiar Poisoiille flux. The second term, on the other hand, represents thermal transpiration. In particular, setting N 0, we find  [c.181]

The rate at which bubbles of gas enter the nitrometer is now determined solely by the rate at which the heating is carried out it should be controlled so as never to exceed one bubble of gas per second. The oxidised copper spiral is carefully heated to redness by very slowly moving the burner along it, and the heating of the powder copper oxide, containing the washings from the mixing tube, is then started. Up to this point, any gas that enters the nitrometer will be carbon dioxide, and even while heating the initial portion of copper oxide, the amount of nitrogeneous material contained in it is so small that very little nitrogen will be evolved. As the burner approaches the first chalk mark, however, extra care is required as very nearly all the sample is contained in this small section of tube filling, and overheating will cause rapid combustion with a consequent rapid stream of gas bubbles in the nitrometer. The great danger here is that these bubbles contain ing both nitrogen and carbon dioxide may rise rapidly through the potash and a considerable proportion of the constituent carbon dioxide will then never be absorbed by the alkali, thus leading to high results. Nearly all the errors made in nitrogen determinations arise from this source and the importance of a slow, regular evolution of gas controlled by careful combustion, cannot be overstressed. As soon as there is any sign of too rapid an evolution of gas the burner should immediately be moved 5 cm. back along the tube rapidity of this movement is particularly important as there is usually a time lag between any overheating and the emergence of the offending bubbles in the nitrometer. Heating is continued until the burner arrives at the furnace mouth. The burner may then be extinguished.  [c.490]

My initial excursion into writing was in Hungary, where my university lectures on theoretical organic chemistry (really physical organic chemistry) were published in two volumes in 1955. A substantially revised German version of the first volume, written in 1956, was published in Berlin in 1960 (the second volume, however, was never realized due to circumstances). With few exceptions (as indicated) all my subsequent books were published by my publisher Wiley-Interscience in New York, with whom I still have a most rewarding, close relationship. It started in the early 1960s when I met Eric Proskauer, who at the time was running Interscience Publisher, and Ed Immergut, who was his editor. Later, Interscience was bought out by John Wiley and we continued our relationship, with Ted Hoffman becoming my longtime editor and friend with whom it was always a pleasure to work. Barbara Goldman and now Darla Henderson took over to continue a rewarding relationship. I also consulted for Wiley for many years concerning their organic chemistry publishing program and was able from time to time to suggest new authors and projects. I remember, for example, the start of Saul Patai s project. The Chemistry of Functional Groups, which later, with the involvement of Zvi Rappoport, developed into a truly monumental series. To keep the volumes from becoming obsolete, at one point I suggested adding supplemental volumes to upgrade the discussed topics. These turned out to be very useful.  [c.236]

The rate at which bubbles of gas enter the nitrometer is now determined solely by the rate at which the heating is carried out it should be controlled so as never to exceed one bubble of gas per second. The Oxidised copper spiral is carefully heated to redness by very slowly moving the burner along it, and the heating of the powder copper oxide, containing the washings from the mixing tube, is then started. Up to this point, any gas that enters the nitrometer will be carbon dioxide, and even while heating the initial portion of copper oxide, the amount of nitrogeneous material contained in it is so small that very little nitrogen will be evolved. As the burner approaches the first chalk mark, however, extra care is required as very nearly all the sample is contained in this small section of tube filling, and overheating will cause rapid combustion with a consequent rapid stream of gas bubbles in the nitrometer. The great danger here is that these bubbles containing both nitrogen and carbon dioxide may rise rapidly through the potash and a considerable proportion of the constituent carbon dioxide will then never be absorbed by the alkali, thus leading to high results. Nearly all the errors made in nitrogen determinations arise from this source and the importance of a slow, regular evolution of gas controlled by careful combustion, cannot be overstressed. As soon as there is any sign of too rapid an evolution of gas the burner should immediately be moved 5 cm. back along the tube rapidity of this movement is particularly important as there is usually a time lag between any overheating and the emergence of the offending bubbles in the nitrometer. Heating is continued until the burner arrives at the furnace mouth. The burner may then be extinguished.  [c.490]

The removal of particles that would block the spinneret holes occurs in several stages. The traditional plate-and-frame first-filters dressed with disposable multilayers chosen from woven cotton, cotton wadding, or wood pulp have now been replaced by durable nylon needlefelts that can be cleaned by automatic backwashing (17). Second filtration, usually after deaeration, is also changing to fully automatic systems with sintered steel elements that do not need manual cleaning. Third-stage filtration, close to the spinning machines, is used to provide a final polishing of viscose quaUty, but is only justifiable for the premium quaUty fibers. AH processes nevertheless use small filters in each spinneret to catch any particulate matter which may have eluded, or been formed after, the main filter systems.  [c.347]

Ra.tlo Sc Ig-. The ratio scale has name, order, distance, and a meaningful origin. A zero value on the scale means the absence of any of the property, eg, zero Kelvin means the absence of motion and gives meaning to the gas law, PV = nRT, whereas zero Celsius is arbitrary and meaningless in terms of the gas law. The mathematical form of Stevens law has been used to argue that a ratio scale could be developed to measure flavor intensity (14). The magnitude estimation method yields a ratio scale when the data foHow certain rules. In this method a paneHst is instmcted to associate the flavor intensity of a second flavor with a number, Y, that is perceived to be a multiple of the flavor intensity, X, of the first sample. If the ratio of X to Y is always the same no matter what the value of X given for the first sample, then the paneHst is estimating the flavor intensity on a ratio scale. However, if the difference between X and Y is constant for different values for X the flavor is being estimated on an interval scale. Zero on a ratio scale means the absence of the perception being measured and this is a controversial conclusion for some psychologists (25). Nevertheless, magnitude estimation is frequently used and often defended as an appropriate scaling method for sensory data (24). There has been considerable discussion (26—29) of the many psychological scales used to quantitate sensory perceptions, motivated by the desire to devise analytical methods that are consistent with the demands of Weber s and Stevens laws and appropriate for the use of parametric statistical methods. Although the method of magnitude estimation has some theoretical appeal, data produced with nine-point interval and graphical line marking scales are much easier to obtain and are statisticaHy similar. An important consideration is that interval data should be used in models without a fixed intercept or defined origin whereas ratio scaled data requires the inclusion of a zero intercept in most models (29).  [c.2]

Expa.ndedFilm. Expanded-film membranes are made from crystalline polymers by an orientation and stretching process. In the first step of the process, a highly oriented film is produced by extruding the polymer at close to its melting point coupled with a very rapid drawdown (9,10). After cooling, the film is stretched a second time, up to 300%, at right angles to the original orientation of the polymer crystallites. This second elongation deforms the crystalline stmcture of the film and produces slit-like voids 20 to 250 nm wide between crystallites. The process is illustrated ia Figure 5. This type of membrane was first developed by Hoechst-Celanese and is sold under the trade name Celgard a number of companies make similar products. The membranes made by W. L. Gore, sold under the trade name Gore-Tex, are made by this type of process (11).  [c.63]

Monofilament. Standard and medium viscosity nylons are used. Close control of diameter is important and a gear pump is used before the die (after filtering through a fine filter pack) to minimi2e pressure variations. The die hole diameter is normally 1.5—2 times the diameter of the undrawn filament. The filaments are drawn through a quench tank at approximately 40°C, after which they are separated by a comb-type guide and passed through two sets of Godet roUs (pull roUs) separated by an electrically heated chamber. The second set of roUs operates at four or five times the speed of the first set. This drawing process enhances the properties by orienting the chains. The drawn filament then needs to be set in the oriented form by being drawn through a heated conditioning chamber by a third set of roUs operating at a similar speed as the second set. The filaments are then wound onto separate bobbins.  [c.274]

Polymer Cha.in Interactions. If the surface of each particle is covered with links to polymer chains, whose segments are soluble in the surrounding Hquid, then particles will be hindered from coming close together. The chains extend out a distance, 5. In this context the Hquid is referred to as the solvent. There are two phenomena involved (/) mixing energy, based on the enthalpy change due to increased segment—segment interaction and decreased segment—solvent interaction as the solvent is squee2ed out of the region between the particles, and (2) elastic energy, based on the entropy change as the number of possible chain configurations becomes restricted when the particle surfaces come closer together (19). Unlike the polari2abiHty and electrostatic interactions which extend out to large distances, the steric repulsive interactions act only when s < 26. As a first approximation the joint effect of these two contributions to the interparticle potential is a single term  [c.545]

Va.lvula.r Disea.se, Valve problems severely limit the efficiency of the heart s pumping action bringing forth definitive symptoms. There are two types of conditions, both of which may be present in the same valve. The first is narrowing, or stenosis, of the valve. The second condition is inabiUty of the valve to close completely. Narrowing of the mitral valve, for example, can result in less blood flowing into the left ventricle and subsequentiy less blood being pumped into the body. If the same valve does not close completely, blood may also back up or regurgitate into the left atrium when the ventricle contracts, preventing even more blood from propedy dowing. The backward pressure which results can cause a reduction in the efficiency of the lungs.  [c.180]

Compounds having relatively specific cerebral stimulant properties are classified as psychostimulants or psychoanaleptics. Caffeiae [58-08-2] (16), a mild psychostimulant, has been called the most widely used psychoactive substance on earth (16,17). Caffeiae, theophylline [58-55-9] (17), and theobromine [83-67-0] (18) are three closely related alkaloids known as methylxanthines that occur ia plants widely distributed throughout the wodd. The first two have CNS stimulant properties the last is virtually iaactive as a stimulant. The basis for the popularity of caffeine-containing beverages is their abiUty to elevate mood, decrease fatigue, and iacrease capacity for work. It is estimated that at least half the population of the wodd consumes tea on a regular basis ia the United States, coffee is the most important source of caffeiae, and cola-davored drinks seem a close second. The word caffeiae is used exclusively hereia evea though some of the effects of caffeiaated beverages may result from the theophylline coateat. Average caffeiae coateats per cup of brewed coffee (qv), iastant coffee, tea (qv) (bagged), and cola beverages (12 oz (340 g)) are 110, 66, 46, and 47 mg, respectively (18) (see Carbonated beverages).  [c.463]

Whereas the effect of the pH of the processing solution on coupling is most often considered in the context of the coupler, the stmcture of which can be varied, pH can also affect the activity of the oxidized developer (43,56). In general, oxidized developers fall into three categories. The first, like CD-2, have a constant charge, either cationic or zwitterionic, at normal processing pH values and coupling rates are Httie affected by pH changes. The second class exists in cationic or neutral forms as a function of pH. For example, the oxidized form of the commercially important CD-4 reacts reversibly with hydroxide ion to form a neutral pseudo-base, which is unreactive toward coupling (41). Finally, the quinonedimine derived from developers like CD-3 can exist in cationic and zwitterionic forms as a function of pH. Both forms can react with ionized coupler, but at different rates.  [c.475]


See pages that mention the term Clausius form of second law first law : [c.1047]    [c.396]    [c.1243]    [c.319]    [c.87]    [c.170]    [c.1094]    [c.1265]    [c.657]    [c.47]    [c.317]    [c.399]    [c.159]    [c.1616]   
Macmillan encyclopedia of energy Volumes 1,2,3 (2001) -- [ c.1126 ]