Affecting relaxation process

The spectroscopic behavior of a JT system is to a large extent governed by the quenching of electronic operators (Ham effect), which causes a shift of the absorption (or emission) bands and a modification of their shapes. Moreover the vibronic mixing of different electronic states can strongly affect relaxation processes, which also modify spectral band shapes. 

Studies on the mechanical properties of glassy polymer-solvent or, more generally, polymer-diluent mixtures have been primarily concerned with the deformation behavior at small strains which is governed by the viscoelastic properties of the material. From these studies it is well known that diluents significantly affect relaxation processes in glassy polymers, as clearly evidenced by phenomena such as plasticization and antiplasticization... 

In addition to the dipole-dipole relaxation processes, which depend on the strength and frequency of the fluctuating magnetic fields around the nuclei, there are other factors that affect nOe (a) the intrinsic nature of the nuclei I and S, (b) the internuclear distance (r,s) between them, and (c) the rate of tumbling of the relevant segment of the molecule in which the nuclei 1 and S are present (i.e., the effective molecular correlation time, Tf). 

If only single-quantum transitions (h, I2, S], and S ) were active as relaxation pathways, saturating S would not affect the intensity of I in other words, there will be no nOe at I due to S. This is fairly easy to understand with reference to Fig. 4.2. After saturation of S, the fMjpula-tion difference between levels 1 and 3 and that between levels 2 and 4 will be the same as at thermal equilibrium. At this point or relaxation processes act as the predominant relaxation pathways to restore somewhat the equilibrium population difference between levels 2 and 3 and between levels 1 and 4 leading to a negative or positive nOe respectively. 

For effective demulsification of a water-in-oil emulsion, both shear viscosity as well as dynamic tension gradient of the water-oil interface have to be lowered. The interfacial dilational modulus data indicate that the interfacial relaxation process occurs faster with an effective demulsifier. The electron spin resonance with labeled demulsifiers suggests that demulsifiers form clusters in the bulk oil. The unclustering and rearrangement of the demulsifier at the interface may affect the interfacial relaxation process. 

The dipole-dipole interactions of the fluorophore in the electronic excited state with the surrounding groups of atoms in the protein molecule or with solvent molecules give rise to considerable shifts of the fluorescence spectra during the relaxation process. These spectral shifts may be observed directly by time-resolved spectroscopic methods. They may be also studied by steady-state spectroscopic methods, but in this case additional data must be obtained by varying factors that affect the ratio between tf and xp. 

It has been postulated that 2-PAM exerts its cardiac action in rabbit atria through its alteration of calcium metabolism. The relaxation phase of skeletal muscle contraction seems to be directly affected by the sarcoplasmic reticulum because of its ability to sequester calcium actively.29,46 a similar role has been suggested for the sarcoplasmic reticulum in cardiac muscle. 6,83 The onset of muscle contraction takes place when calcium reaches a crit-cal concentration. This contraction is later reduced by the increased calcium-sequestering activity of the sarcoplasmic reticulum. Thus, 2-PAM can affect this process by decreasing the rate of calcium uptake by the sarcoplasmic reticulum, which results in increasing the time required to reduce the calcium concentration enough to allow relaxation to take place. This was demonstrated by the Increase in the relaxation phase. It was suggested that this... 

Other effects frequently encountered in inorganic systems that can severely affect line shape involve relaxation processes arising from interactions of nuclear quadrupole moments with electric field gradients. For quad-rupolar nuclei (I 1), the quadrupolar contribution to the spin-lattice relaxation time Ti is given approximately by... 

Therefore, data of Fig. 6 show the change of the reorientational-vibrational relaxation time of acetonitrile molecules confined in mesopores upon adsorption and desorption. Before the capillary condensation, the relaxation time is smaller than that of bulk liquid, whereas it is greater than that of the bulk liquid after condensation. The difference of molecular motion between precondensation and postcondensation states is not significant, but this work can show clearly the presence of such a difference. If vibrational and reorientational relaxation processes are dominated by molecular collisions, the molecular reorientation is more rapid before condensation and it becomes slower than that of the bulk liquid with the progress of the capillary condensation, which indicates the formation of a weakly organized molecular assembly structure in mesopores. Even the mesopore can affect the state of the condensates through a weak molecular potential. The organized state should be stable in mesopores, because the relaxation time is almost constant above the condensation PIP,. 

Basically all factors are important which display an effect on the solubility of the macromolecule and its flexibility, i.e., the capacity for deformation of the polymer backbone. According to Brostow s theory, there are two effects of central importance for practical application degradation and relaxation. Every type of energy transferred to a polymer chain in solution does so via one of these two processes. Thus, all parameters which directly affect these processes are of corresponding significance. 

Of the diluents known to affect the dynamic relaxation behavior of polymers in the glassy state, water has so far received the greatest attention. Many polymers, which in the dry state are lacking any secondary relaxation process at temperatures from 77 to 273 K, e.g. poly(methyl methacrylate)135, polymethacrylamide136, cellulose and its derivatives137, collagen138, polysulfones139, poly(2,6-dimethylphenylene oxide)139, and others,... 

The temperature position of the secondary fi relaxation (about 290 K 1 Hz), generally attributed to partial rotations of the side chains COOR, is only slightly affected by the polarity and volume of the substituent R but decreases markedly (by 120 K) on removal of the a-methyl group on the main chain. The experimental data obtained contradict the assumption that there is a certain relationship between this temperature and the glass transition temperature. Nevertheless, we can infer that the pertinent molecular mechanism in polymethacrylates differs from that in polyacrylates, probably due to the different participation of the main chains. The values of the individual contributions to the activation energy were estimated by employing a procedure similar to that used in the y relaxation process, and their sum was found to agree approximately with the experimental values. 

The application of stress relaxation is shown in Figure 3. The relaxation modulus (G) is determined after a step strain as a function of time. A step strain is applied to the sample causing a stress. The modulus is measured as the stress relaxes. The stress relaxation modulus shows how molecular weight affects the relaxation process as a function of time as depicted in Figure 4. 

It is worth noting that an amount of DMT as small as 2 wt % affects the temperature and the amplitude of the fJ> peak. Saturation seems to be approached from 10 to20% of additive. It can Ire seen that the additive suppresses the high-temperature side of the /> peak considerably more than the low-temperature side. This would appear to support the statement that the (J> peak consists of more than one relaxation process, as evidenced by NMR studies and that the antiplasticiser has suppressed the relaxation processes that occur on the high-temperature side of the /> peak. 

Carbon-13 relaxation measurements have been covered in a number of texts (3, 23—25) and reviews. (26—30) For steroids it is clearly established that 13C relaxation is almost entirely due to interactions (dipole-dipole) with attached or nearby protons. (31-33) The relaxation process is kinetically first-order, characterized by a rate constant Tf1. For steroids, at useful concentrations, 13C T, values range from 0-02 to 5 s. Since Tt is markedly affected by molecular tumbling, it is necessary carefully to control and state solvents, concentrations, and temperatures in acquiring and reporting Tx values. Given all of these variables, Tx reproducibilities are usually found to be around 10%, while reports from different laboratories not infrequently differ by 20%. 

Unpaired electronic density can be delocalized onto the various nuclei of the complex via through-bond scalar hyperfine interactions involving occupied orbitals containing s-character (direct interaction or polarization according to the Fermi mechanism, Wertz and Bolton (1986)). Random electron relaxation thus produces a flip-flop mechanism which affects the nuclear spin and increases nuclear relaxation processes (Bertini and Luchinat, 1996). Since these interactions are isotropic, they do not depend on molecular tumbling and re is the only relevant correlation time for non-exchanging semi-rigid complexes. Moreover, only electronic spin can be delocalized via hyperfine interactions (no orbital contribution) and the contact re-... 

Because Dcr is proportional to the content of Ag nanocrystals and Ai/2 is in inverse proportion to their mean size d [77, 78], one may conclude that the state and amount of Ag nanocrystals were not affected by the cryopolymerization. Sharp growth of DCI at heating of obtained metal-polymer films specifies that the main part of Ag at 77 K is in a form of small noncrystalline Ag clusters, which aggregate with formation of nanocrystals under action of thermal relaxation processes in polymer matrix. According to data in work [79], in UV vis spectra of PPX films on a background of the PPX absorption only absorption bands of Ag with n> 15 could be observed in open range of PPX spectrum at X >320 nm. Because in this spectral range... 

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