Clausius form of second law second law


As a general class of adhesives, the solvent-home polyurethanes are gradually being replaced by other adhesive types, such as waterborne polyurethane dispersions and curing hot melts. Increasing regulations regarding volatile organic compounds (VOC s) have restricted their use, and regulators are beginning to be levy fines. Chlorinated solvents, such as methylene chloride, were commonly used in solvent-home urethanes but now have nearly been eliminated. The most common solvents are the aromatics, such as toluene and xylene, as well as some esters, such as ethyl and butyl acetate, and various ketones. In some cases, acetone is used, since, as of this writing, acetone is considered to be a HAPS-free material and, therefore, excluded from the regulations associated with VOC s. Commonly, two or more solvents are employed for solvent-home urethanes. A low-boiling solvent is present to assure rapid flash-off of the majority of the solvent after the adhesive is applied. A second (higher-boiling) solvent has several functions. The higher-boiling solvent helps to control the crystallization kinetics of the soft segment (e.g., crystalline polyester) or phase out of the hard segment, in the case of TPU, thereby helping to extend the open time of the adhesive. Once crystallization of the soft segment or phase-out of the hard segment occurs, the bond can no longer be closed and the open time has expired. The second function is to keep viscosity of the urethane low. This helps the adhesive wet the substrate, by helping the urethane to penetrate the surface of the substrate to be bonded, thereby extending the interphase region and improving mechanical interlocking of the adhesive and the substrate. The commonly used terminology for this mechanical interlocking with the substrate is bite . Bite is a qualitative term, referring to the ability  [c.786]

This leads to what is called the Clausius form of the second law of thermodynamics. No processes are possible whose only result is the removal of energy from one reservoir and its absorption by another reservoir at a higher temperature. On the other hand, if energy flows from the hot reservoir to the cold reservoir with no other changes in the universe, then the same arguments can be used to show that the entropy increases, nr remains constant for reversible processes. Therefore, such energy flows, which arc vciy familiar, are in agreement with the laws of thermodynamics.  [c.1130]

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]

The human eye is known to contain two main types of light-sensitive cells rods and cones. These names come from the shape of the outer segment of the cell. The rods are by far the most numerous, outnumbering the cones by a factor of nearly 20, and operate as the main sensors at low illumination levels. Scotopic (rod) vision as shown in Figure 1 centers at about 510 nm and extends from 400—600 nm. Because there is only one type of rod, it lacks the abihty to discriminate colors and its electrical output varies as the integrated response over this wavelength range. Cones are the primary sensors of color vision, and there is strong evidence that there are three types, shown as p, y, and p. Over most of the visible range any single wavelength stimulates more than one receptor type. For example, the peak sensitivities of the p and y receptors, at 580 nm and 540 nm, respectively, are quite close together.  [c.466]

The amino acids are usually divided into three different classes defined hy the chemical nature of the side chain. The first class comprises those with strictly hydrophobic side chains Ala (A), Val (V), Leu (L), He (1), Phe (F), Pro (P), and Met (M). The four charged residues, Asp (D), Glu (E), Lys (K), and Arg (R), form the second class. The third class comprises those with polar side chains Ser (S), Thr (T), Cys (C), Asn (N), Gin (Q), His (H), Tyr (Y), and Trp (W). The amino acid glycine (G), which has only a hydrogen atom as a side chain and so is the simplest of the 20 amino acids, has special properties and is usually considered either to form a fourth class or to belong to the first class.  [c.5]

Esterification. Esters and polyesters comprise the second most important class of adipic acid derivatives, next to polyamides. The acid readily reacts with alcohols to form either the mono- or diester. Although the reaction usually is acid-catalyzed, conversion may be enhanced by removal of water as it is produced. The methyl ester is an industrially important material, because it is a distillable derivative which provides a means of separating or purifying acid mixtures. Recent modifications of adipic acid manufacturing processes have included methanol esterification of the dicarboxyUc acid by-product mixture. Thus glutaric acid [110-94-1] and succinic acid [110-15-6] can be recovered upon hydrolysis, or disposed of as the esters (28). Monomethyl adipate can be electrolyzed as the salt to give dimethyl sebacate [106-79-6] (Kolbe synthesis) (29), an important ten-carbon diacid. Diesters from moderately long-chain (8 or 10 carbon) alcohols are also an important group, finding use as plasticizers, eg, for PVC resins. Table 4 Hsts the boiling points of several representative adipate esters. Reactions with diols (especially ethylene glycol) give polyesters, also important as plasticizers in special apphcations. In another important use of adipate esters, low molecular weight polyesters terminated in hydroxyl groups react with polyisocyanates to give polyurethane resins. Polyurethanes consumed about 4% of adipic acid production in the United States in 1986 (30).  [c.239]

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]

Rotary Impeller Vane and Gear Meters. One group of positive-displacement meters depends on shaped impellers or gears to form the measuring chambers. Figure 4 illustrates a two-lobed rotary meter of the type used to measure gas flow. The impellers are designed to maintain a continuous seal during rotation. Close tolerances and the use of precision bearings permit these meters to have minimal leakage while keeping overall pressure loss low. Rotating-vane meters are somewhat similar in design but include a timed gate to isolate the inlet and outlet ports. Figure 5 shows one cycle of a rotating-vane gas meter. The pressure of the entering gas rotates the vane assembly counterclockwise and, through timing gears, rotates the gate. In successive positions, the annular segment of gas is isolated by vanes 1 and 2, rotated through the housing, and discharged by the action of the gate.  [c.58]

A number of distinct processes undedie the several receptor regulatory events and these may be distinguished in part by the time scale on which they occur. Cells frequendy exhibit several desensitization events. Rapid desensitization processes frequentiy occur with ion channels of both the ligand-gated and voltage-gated families. On this time scale, channels may open and subsequendy close in the maintained presence of the dmg or stimulus in seconds or less (74). Such a process is usually rapidly reversible and involves the formation of a closed channel state. For G-protein coupled receptors, and particulady for the P-adrenergic receptor, the desensitization process has been shown to involve several stages. Both protein kinase A (PKA), activated through cAMP, and P-adrenergic receptor kinase (bARK) are involved, and the receptor phosphorylation, at different sites, uncouples the receptor and G-protein (90,91). At low agonist concentrations, phosphorylation is principally through the PKA pathway at high agonist concentrations, both the PKA and bARK pathways are involved. Continued occupancy by agonist leads to a second phase of desensitization in which the receptor is sequestered or transiendy and reversibly internalized in vesicular form (Fig. 17). Further occupancy leads to down-regulation proper in which the receptors are internalized and reprocessed through the lysosomal machinery. Similar events, but differing in detail, seem likely to occur for some other receptors.  [c.282]

In electroplating, the reactions at the cathode can be very complex. One example is the electroplating of chromium, which has an electronegativity close to that of hydrogen. There are three distinct cathodic reactions. Eirst, when the potential is low, chromic acid is reduced from its hexavalent state to a trivalent state. Second, as the potential is made higher, hydrogen gas is formed. Third, at higher potentials, the hexavalent chromium is reduced to the metallic state through several intermediate species. At the anode, two oxidation reactions take place. One is the decomposition of water to give oxygen the other is oxidation of the trivalent chromium ion to the hexavalent ion. Chromium plating takes place with the addition of a sulfate anion as a catalyst for the reduction of the hexavalent chromium ion. Using only the sulfate ion, the current efficiency is only about 12% and the rest goes into generating hydrogen and trivalent chromium, which is oxidized at the anode. If a mixture of sulfates and fluorides are used, the chromium deposition efficiency can be as high as 25%.  [c.527]

That halide ligands should cause spin-pairing may in itself seem surprising, but this is not all. The regular, octahedral complexes of Os have magnetic moments at room temperature in the region of 1,48 BM and these decrease rapidly as the temperature is reduced. Even the moments of similar complexes of Ru (which at around 2,9 BM are close to the spin-only moment expected solely from the angular momentum of 2 unpaired electrons) fall sharply with temperature. In the first place, low-spin configurations are much more common for the second- and third-row than for first-row transition elements and this is due to (a) the higher nuclear charges of the heavier elements which exert stronger attractions on the ligands so that a given set of ligands produces a greater splitting of the metal d orbitals, and (b) the larger sizes of 4d and 5d orbitals compared to 3d orbitals, with the result that interelectronic repulsions, which tend to oppose spin-pairing, are lower in the former cases. These factors explain why the halide complexes of Os and Ru are low-spin but what of the temperature dependence and their magnetic behaviour This arises from the effect of spin-orbit coupling which can be summarized in a plot of jXc versus kJ X (Fig, A). A is the spin-orbit coupling constant for a particular ion and is indicative of the strength of the coupling between the angular momentum vectors associated with S and L, and also of the magnitude of the splitting of the ground term of the ion ( T, in the case of low-spin d ). When A is of comparable magnitude to kT, fXe 3,6 BM. which is the spin-only moment (2,83 BM) plus a contribution from the orbital angular momentum. Thus, Cr (A = —115 cm ) and Mn (A = —178 cm ) at room temperature (kT 200 cm ), lie on the flat portion of the curve and so have magnetic moments of about 3,6 BM which only begin to fall at appreciably lower temperatures. On the other hand, Ru (A = -700 cm ) and Os (A -2000 cm ) have moments which at room temperature are already on the steep portion of the curve and so are extremely dependent on temperature. In each case, as the temperature approaches 0 K so also 0. corresponding to a coupling of L and S vectors in opposition and their associated magnetic moments therefore cancelling each other.  [c.1087]

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]

From the beginning of his studies Clausius s interest was mathematical physics. He exhibited keen mathematical thinking, although he was not particularly communicative. His textbooks were popular. The works of Julius Mayer, Janies Joule, and Hermann Helmholtz were the basis of the knowledge of heat nature in the 1840s and the starting point for Clausius s research. In 1850 Clausius gave a lecture in Berlin in which he formulated the basis for heat theoiy. He stressed that heat is not a substance, but consists of a motion of the least parts of bodies. Furthermore he noted that heat is not conserved. Clausius formulated the equivalence between heat and work and the first law of thermodynamics as follows mechanical work may be transformed into heat, and conversely heat into work, the magnitude of the one being always proportional to that of the other. During the next fifteen years Clausius concentrated his research on thermodynamics. He gave several formulations of the second law and finally defined and named the concept of entropy. He started his theoretical investigations with the consideration of the idealized process of the so-called Carnot cycle on the basis of the ideal gas. For this purpose, one assumes that the gas is enclosed in an expansible wrap through which no heat exchange is possible. The Carnot cycle consists of four steps  [c.237]

Fleat as energy is somehow an energy unlike all the rest. Defining how takes a second law, a law so special that Clausius and Thomson found two opposite ways of framing it. To Clausius the issue was the age-old one of perpetual motion. With two Carnot engines coupled in opposition, the rule forbidding perpetual motion translated into a rule about heat. Flis second law of thermodynamics was that heat cannot flow without work uphill from a cold body to a hot body. Refrigerators need power to stay cold. Thomson s guide was Joseph Fourier s great treatise on heat Theorie analydque de la chaleur (1827), and the fact that unequally heated bodies, left to themselves, come always to equilibrium. IIis version was that work has to be expended to maintain bodies above the temperature of their surroundings. Animals need food to stay warm.  [c.1032]

A minimum boiling azeotrope exhibits a constant composition as shown by its crossing of the x = y, 45° line in Figure 8-8, which boils at a lower temperature than either of its pure components. This class of azeotrope results from positive deviations from Raoult s Law. Likewise, the maximum (Figure 8-9) boiling azeotrope represents negative deviations from Raoult s Law and exhibits a constant boiling point greater than either pure component. At the point where the equilibrium curve crosses x = y, 45° line, the composition is constant and cannot be further purified by normal distillation. Both the minimum and maximum azeotropes can be modified by changing the system pressure and/or addition of a third component, which should form a minimum boiling azeotrope with one of the original pair. To be effective the new azeotrope should boil well below or above the original azeotrope. By this technique one of the original components can often be recovered as a pure product, while still obtaining the second azeotrope for separate purification.  [c.12]

Calcium chloride (CaCL) is similar to NaCl. It is the second lowest-cost brine, with a somewhat lower freezing point (used for temperatures as low as —37°C). Highly corrosive and not appropriate for direct contac t with food. Heat transfer coefficients are rapidly reduced at temperatures below —20°C. The presence of magnesium salts in either sodium or calcium chloride is undesirable because they tend to form sludge. Air and carbon dioxide are contaminants and excessive aeration of the brine should be prevented by use of close systems. Oxygen, required for corrosion, normally comes from the atmosphere and dissolves in the brine solution. Dilute brines dissolve oxygen more readily and are generally more corrosive than concentratedbriues. It is beheved that even a closed brine system will not prevent the infiltration of oxygen.  [c.1124]

The phase diagram of Hamiltonian (Eq. (25)) has the following features (ojo = 4 and Jq = 1 where chosen, as in the simulation). In the high temperature limit, the system is paramagnetic for all densities and the (temperature independent) hard disc freezing transition can be found. The estimates for the freezing density (p = 0.847) and the fractional density change during freezing (p = 0.066) are close to the estimates for the same quantities in computer simulations (p = 0.878, rj = 0.0499) and previous theoretical studies (p = 0.858, rj = 0.0723) of the two-dimensional hard disc system, both known from the literature [298]. As the temperature is reduced below T = 5.9, the system undergoes a second-order transition from a paramagnetic fluid phase at low densities to a ferromagnetic fluid at high densities and a first-order transition from a ferromagnetic fluid to a ferromagnetic triangular solid. As expected, the freezing density decreases with decreasing temperature due to the greater stability of the solid phase arising from the magnetic interaction. The DFT prediction for the location of the fluid-solid transition was confirmed by an analysis of the bond orientation order parameter of Monte Carlo data [299]. Also, the average magnetization of the solid wq is observed to be higher than that of the fluid. At temperatures below the tricritical point = 1-25, one gets a first-order transition from a paramagnetic gas to a ferromagnetic fluid in addition to the liquid-solid transition. The liquid phase is stable only for temperatures above a first triple temperature = 0.55, whereas for temperatures below and above = 0.07, a paramagnetic gas is in coexistence with a ferromagnetic triangular solid. The square lattice solid, observed in the Monte Carlo simulations [297] at T = 0.16 0.01, starts appearing at temperatures below T = 0.09, and for a range of temperatures Typ, < T < 0.09 there exists a re-entrant transition with the triangular solid appearing for low and high densities separated by a narrow region of square solid stability centered around p = 1.0. Upon lowering temperatures below the paramagnetic gas -ferromagnetic square solid-ferromagnetic triangular solid triple point (TjpJ, a gas phase is in coexistence with a square solid, followed by a square solid-triangular solid structural transition at higher densities.  [c.101]

Consider for example a molecule having 10 torsional angles, which may have 100 000 possible conformations. The species in an initial population of say 100 different conformations is characterized by their fitness, e.g. a low energy is equivalent to a good structure. These 100 structures are allowed to produce offspring with a probability depending on their fitness, i.e. low energy structures are more likely to contribute to the next generation than high energy conformations. Two child conformations can be generated by taking the first n torsional angles from one of the parents and tire remaining 10 — from the other ( single-point crossover ), with the second child being the complementary. A small amount of mutation is usually allowed in the process, i.e. angles are randomly changed to produce conformations outside the range contained in the current population. Having generated say 100 such children, their (minimized) energies are determined, and a suitable portion of the best parent and children structures are carried over to the next generation. The population is then allowed to evolve for perhaps a few hundred generations. There are several variations on the GA method varying the size of the population, tire mutation rate, the breading selection, the ratio of children to parent surviving to the next generation, single- or multi-point crossover, etc. Genetic algorithms have become popular in recent years as they are easy to implement and have proved to be robust for locating a point in parameter space close to the global minimum. Owing to the coding of the parameters into genes, the sampling is pointwise, and the final structures should therefore be refined using a standard gradient optimization.  [c.342]

They form a monolayer that is rich in defects, but no second monolayer is observed. The interpretation of these results is not straightforward from a chemical point of view both the electrodeposition of low-valent Ge Iy species and the formation of Au-Ge or even Au Ge h compounds are possible. A similar result is obtained if the electrodeposition is performed from GeGl4. There, 250 20 pm high islands are also observed on the electrode surface. They can be oxidized reversibly and disappear completely from the surface. With Gel4 the oxidation is more complicated, because the electrode potential for the gold step oxidation is too close to that of the island electrodissolution, so that the two processes can hardly be distinguished. The gold step oxidation already occurs at -i-lO mV vs. the former open circuit potential, at h-485 mV the oxidation of iodide to iodine starts.  [c.314]


See pages that mention the term Clausius form of second law second law : [c.1131]    [c.555]    [c.130]    [c.397]    [c.841]    [c.1094]    [c.114]    [c.327]    [c.296]    [c.295]   
Macmillan encyclopedia of energy Volumes 1,2,3 (2001) -- [ c.1127 , c.1128 , c.1129 , c.1130 , c.1131 ]