Reversal temperature

The SPATE technique is based on measurement of the thermoelastic effect. Within the elastic range, a body subjected to tensile or compressive stresses experiences a reversible conversion between mechanical and thermal energy. Provided adiabatic conditions are maintained, the relationship between the reversible temperature change and the corresponding change in the sum of the principal stresses is linear and indipendent of the load frequency. 

Another interesting chiral chain end effect is exhibited by the helical polymer block co-polymer, poly(l,l-dimethyl-2,2-di-/z-hexylsilylene)- -poly(triphenylmethyl methacrylate), reported by Sanji and Sakurai (see Scheme 7) and prepared by the anionic polymerization of a masked disilene.333 The helical poly(triphenylmethyl methacrylate) block (PTrMA) is reported to induce a PSS of the same sign in the poly(di- -propylsilylene) block in THF below — 20 °C, and also in the solid state, by helicity transfer, as evidenced by the positive Cotton effect at 340 nm, coincident with a fairly narrow polysilane backbone UV absorption characteristic of an all-transoid-conformation. This phenomenon was termed helical programming. Above 20°C, the polysilane block loses its optical activity and the UV absorption shifts to 310 nm in a reversible, temperature-dependent effect, due to the disordering of the chain, as shown in Figure 45. 

Reversible temperature-dependent partitioning of PFC-tagged molecules between a PFC phase and an organic solvent is the basis for fluorous synthesis, catalysis, and separation technologies [13,14]. These technologies are now being extensively applied to biologically important molecules. 

On pp 289-310 (Ref 21), A.G. Gaydon, Shock-Tube Studies of Processes of Electronic Excitation in Gases reported that the spectrum-line reversal temperature in shock-heated gases can be used to obtain information about efficiencies and processes of electronic excitation of metal atoms at high temperatures. For excitation by molecules, the electronic excitation temperature tends to follow the effective vibrational temperature of the molecules, and reversal temperatures may be low near the shock front if. the vibrational relaxation time is appreciable. Although excitation of metal atoms by cold inert gases has a very small effective cross-section, it is shown that at 2500°K the cross-sections of excitation of Cr or Na by Ar or Ne are around 1/20 of the gas-kinetic cross-sections... 

Reversal-temperature measurements of the Na and Cr lines in simple molecular gases, shock-heated to 2000-3000°K and to 0,2-2 atmospheres agree excellently with temperatures calculated from the measured shock velocity. Thus in these cases, collision processes are rapid enough to maintain effective equilibrium between ground and excited state populations despite radiatio n losses. In some shock tube work, however, the reversal temperature is initially above the equilibrium value, probably owing to delay in dissociation of the molecules, so that the temperature in translation and in internal degrees of freedom of the molecules is initially too high... 

Magnesium anthracene Ci4HioMg(THF)3 (118) can be prepared in high yield from the reaction of metallic magnesium and anthracene in THE (equation 12) . Kinetic measurements showed that a reversible temperature-dependent equilibrium exists between anthracene, magnesium and 118, the latter being favored at lower temperatures. This equilibrium opened a way to the preparation of elemental magnesium in a finely dispersed. 

The two methyl groups in the olefin-copper(I) complex 26 are crucial for asymmetric induction. The 150° dihedral angle between the a- and /3-protons of the magnesium enolate 27 provides valuable information to determine the stereochemical effects on the a center. The two magnesium enolates 27 and 28 are reversibly temperature-dependent. Enolate 27 is the major component at 253 K, while enolate 28 becomes the major component at 293 K. Therefore, temperature lower than ca 256 K is required to obtain high stereoselectivity. 

Environmental Protection. During the reduction of barite and the calcination of Sachtolith and lithopone, sulfur dioxide is liberated. This is removed from the waste gas in a purification stage which is based on the reversible, temperature-dependent solubility of sulfur dioxide in poly glycol. The absorbed sulfur dioxide can be recovered as a liquid product or as a raw material for sulfuric acid. Any soluble barium in the residue from the dissolution of the fused BaS is removed by treatment with... 

After about 40 hours the reaction is complete, and the tube is placed immediately in a reverse temperature gradient of 200°C./ room temperature in order to separate the more volatile species from the desired product. The preparation of tungsten(V) trichloride oxide, first reported by Fowles and Frost,4,s is very dependent on the amount of excess tungsten(VI) chloride and the temperature gradient used. Employing the above conditions, 15.2 g. of tungsten(V) trichloride oxide (83% yield) was obtained. 

In order to design and facilitate a reversibly temperature-responsive micelle fora drug delivery system, Chung et al. (1997, 1999) and Cammas et al. (1997) conducted extensive research on the... 

Temperature Measurements. Sodium line reversal temperature profile measurements were made on the flame series with varying additions of H2S. Results for H2/O2/N2 (3/1/4,5,6) are shown in Figure 3. The increase in temperature with distance above the burner is due to the slow recombination of the radicals H and OH. In the stoichiometric flames the temperature reaches a plateau in a few centimeters above the burner. In the richer flames the temperature gradient is steeper indicating a larger departure of the radical concentration from equilibrium values. The equilibrium temperatures decrease with H2S addition. However, the presence of sulfur compounds enhances radical recombination (6,11) producing almost equivalent temperature profiles, independent of H2S addition. 

Figure 3. Sodium line reversal temperature profiles above the burner surface in...

The reversible (temperature-modulated) equilibrium between the CT complex and the ET products is shown in Figure 10. This process can be designated as ... 

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