Drops direct evidence

Very direct evidence for the existence of bound spin polarons is provided by the work of Torrance et al (1972) on the metal-insulator transition in Eu-rich EuO At low temperatures, when the moments on the Eu ions are ferromagnetically aligned, the electrons in the oxygen vacancies cannot form spin polarons and are present in sufficient concentration to give metallic conduction. Above the Curie temperature the conductivity drops by a factor of order 10 , because the electrons now polarize the surrounding moments, forming spin polarons with higher effective mass. 

Special care has to be taken, however, that the quinoline titer truly represents the minimum amount of catalyst poison. In most cases this type of base is adsorbed by inactive as well as active sites. Demonstration of indiscriminate adsorption is furnished by the titration results of Roman-ovskii et al. (52). These authors (Fig. 13) showed that introduction of a given dose of quinoline at 430°C in a stream of carrier gas caused the activity of Y-zeolite catalyst (as measured by cumene conversion) to drop with time, reach a minimum value, then slowly rise as quinoline was desorbed. The decrease in catalytic activity with time is direct evidence for the redistribution of initially adsorbed quinoline from inactive to active centers. We have observed similar behavior in carrying out catalytic titrations of amorphous and crystalline aluminosilicates with pyridine, quinoline, and lutidine isomers. In most cases, we found that the poisoning effectiveness of a given amine can be increased either by lengthening the time interval between pulse additions or by raising the sample temperature for a few minutes after each pulse addition. 

In contrast to what is known about a-Si, much less is understood about polyamorphism in Ge. The authors of most early experiments reported no direct evidence of LDA-HDA transition in Ge [260-262, 270, 271]. Shimomura et al. [260] observed a stepwise drop of the electronic resistance (at 6 and lOGPa) after compression of an -Ge him. This decrease, however, may have resulted from (partial) recrystallization to a metallic high-pressure polymorph under pressure. Tanaka [270] measured X-ray diffraction patterns and optical absorption spectra of -Ge at pressures up to lOGPa. In this experiment, the sample was indeed partly transformed to the (3-tin crystalline phase ( 25% in volume) at 6 GPa. Imai et al. [262] also observed an amorphous to [3-tin crystal transition. Freund et al. [271], in contrast, have observed no sign of crystallization or transition to an HDA form after compression up to 9 GPa. 

In this paper we present three techniques for the study of thin middle phase films adsorbed on emulsion droplets. Film thicknesses have been measured by small angle X-ray scattering, contact angles of adjacent droplets have been measured in flocculated emulsions, and much direct evidence for such films has been observed visually in the spinning drop interfacial tensiometer. 

With respect to understanding the nature of models it should be noted that the phenomenon of melting of itself is not direct evidence for the existence of particles. The model can be presented as a useful way of thinking. As noted in Chapter 1, everyday discourse often uses particle to describe small yet visible pieces of material and it is important to emphasise the special scientific meaning within the particle theory. A small drop of water (0.05 cm ) contains the order of 1.7x 10 water particles (molecules). Employing terms such as grains , pieces , bits ,... 

After dropping for several years, the number of TV set fires in Europe has stopped decreasing, and in countries such as the UK, Sweden and the Netherlands where detailed statistics are kept there is direct evidence that the figures are rising. 

Joshi et al. [133] present entry, spreading, and bridging coefficients for this system, which are clearly non-equilibrium initial values (which violate Equations 3.11, 3.12, and 4.31, respectively). Direct evidence of coalescence of bubbles by bridging drops of gel phase is also presented. However, it would seem that this happens only if air-water surfaces are at nonequilibrium surface tensions, which in turn could imply negative values of the bridging coefficient under equilibrium conditions. Interestingly, Joshi et al. [133] also show that the antifoam effect diminishes markedly as the temperature is increased well above the cloud point. This effect is attributed to decreases in the bulk phase viscosity of the gel phase, rendering drops more readily deformable and more readily ejected from foam films before rupture of the relevant pseudoemulsion films. 

Antifoam effects are usually attributed to undissolved materials. In general, much of the evidence concerning the supposed adverse effect of solubilized oils on the foamabUity of aqueous micellar surfactant solutions may simply concern the presence of undissolved oil drops. Evidence that solubilized alkanes adversely affect the stability of foams of certain aqueous micellar solutions [15, 21] is, however, difficult to simply dismiss in this manner. These observations have been attributed to the effect of the solubilizate on the repulsion forces between micelles. In turn, this is supposed to reduce stratification and therefore foam film stability. Direct evidence of this supposed reduced stability, using, for example, a suitable film balance method, is lacking. 

GPa with magnetic fields up to 0.7 T, parallel to the excitation current direction. The resistivity drop is suppressed by magnetic field and disappears above 0.7 T. This is a further direct evidence of the superconducting transition in CePtSi2. Field dependence of Tc is displayed in the inset (A) of Figure 116. The upper critical field Hcz is foimd to be 0.7 T at... 

The role of IR drop in crevice initiation is not clear. Different authors [58,60,61] observed crevice initiation on stainless steels at a very low IR drop level. It is clear that initiation processes can be separated into two classes (a) those that operate at relatively high potentials (pitting in the crevice gap), which cannot be enhanced by laige ohmic drops, and (b) those that occur at low potential (general passivity breakdown), which are favored by large IR drops. However, on stainless steels and nickel-base alloys, there is at present no direct evidence to support the last t5q)e of process, mainly because high free surface potential always enhances crevice initiation of passive alloys. 

Direct evidence of silicon balls and drops to some extent proves this concept. Prom Prof. 0ye s viewpoint, the mechanism opens the way for the transport of electrolyte through permeable pores due to the capillary forces [181]. 

A three-necked round-bottom flask is fitted with a dropping funnel, a thermometer, and a magnetic stirrer and is heated in a water bath to 30°. Tetralin (1.32 g, 0.01 mole) and 50 ml of 3.5 Anitric acid solution are placed in the flask and brought to temperature. Ceric ammonium nitrate (21.9 g, 0.04 mole) is dissolved in 100 ml of 3.5 N nitric acid, and the solution is added dropwise to the reaction mixture at a rate such that the temperature does not rise and only a pale yellow color is evident in the reaction mixture. At the completion of the reaction (1 to 2 hours), the mixture should be colorless. The solution is cooled to room temperature, diluted with an equal volume of water, and extracted twice with ether. The ether solution is dried with anhydrous sodium sulfate, filtered, and the ether is evaporated. The residue may be distilled to yield a-tetralone (bp 113-11676 mm or 170749 mm) or may be converted directly to the oxime, which is recrystallized from methanol, mp 88-89°. 

---