Phase transition dynamics

Besides the peaks of the local proton modes typical for hydrogen bond, a sharp peak at 28 meV was observed in KDP [34] and attracted much attention [34,38,39]. This peak exists in DKDP at somewhat higher frequency its intensity decreases in both crystals and its width decreases upon the transition from the FE to the PE phase, without any softening of its frequency [38]. Hence, it is concluded that this mode is connected with the phase transition dynamics, i.e., coupled to the polarization fluctuations. This mode is not the tunneling mode or any local mode of proton or deuteron, but rather some collective optical mode of the lattice that involves substantial proton or deuteron displacement. It has been suggested [38] that this mode corresponds to the mode that has a peak at about 200 cm (25 meV) in Raman scattering and infrared reflectivity spectra, and that it is coupled to the soft mode and usually... 

Sensitized for blue-green or red light, photoconductive polyimides and liquid crystal mixtures of cyanobiphenyls and azoxybenzene have been used in spatial light modulators [255-261]. Modulation procedure was achieved by means of the electrically controlled birefringence, optical activity, cholesteric-nematic phase transition, dynamic scattering and light scattering in polymer-dispersed liquid crystals. 

A property of NMR that has been used extensively to study the details of phase transition dynamics is the time required for the nuclei to establish an equilibrium population distribution among the energy levels, called spin-lattice relaxation and denoted by the characteristic time constant Ti. This relaxation time is also important to solid-state NMR in a practical sense, because once a spectrum is acquired one must wait until the nuclei have at least partially re-equilibrated before the spectrum can be acquired again, or fully re-equilibrated to obtain quantitatively correct intensity ratios. Most solid-state NMR spectra represent lOO s to lOOO s of co-added acquisitions to improve the signal-to-noise ratio. 

High-resolution in situ STM as well as phase transition dynamics of nucleobases on Au(lll) and other low-index electrode surfaces supported by infrared spectroscopy have been reviewed recently by Nichols and coworkers [142] and Wandlowski and coworkers [143]. We refer to these reviews for details and note instead another aspect of single-molecule dynamics of DNA-based molecules. The observed electronic conductivity of oligonucleotides of variable length and variable base composition has opened almost a Pandora s box of novel DNA-based electronic properties. These include particularly photochemical and interfacial electrochemical ET. We refer to other recent reviews [144, 145] for this, still far from settled, issue but note the following STM-based studies that illuminate the conductivity issue at the single-molecule level (Figure 2.4). 

While the molecular field tends to stabilize sublattices with symmetries [Fig. 10c, Eq. (24c)], the anisotropy contributions from the nonlinear Jahn-Teller coupling shift the sublattices towards the positions with tetragonal symmetry [Fig. 10a, Eq. (24b)]. Depending on the ratio of molecular field strength and anisotropy energy situations between the extremes (Fig. 10b) may be stabilized, as already discussed. If one approaches the phase transition, dynamic contributions become of... 

For example, see Onuki, A. Phase Transition Dynamics Cambridge University Press Cambridge, U.K., 2002. 

A. Onuki, Phase Transition Dynamics, Cambridge University Press, Cambridge,... 

Mochida, T, Funasako, Y, Inagaki, T, Li, M.J., Asahara, K. and Kuwahara, D., Crystal structures and phase-transition dynamics of cobaltocenium salts with... 

Temperatures of phase transitions Dynamic viscosity rj Kinematic viscosity v = rjIq Diamagnetic anisotropy Ax Thermal conductivity... 

One of the first study of lamellar-to-lamellar phase transition dynamics was performed on the lamellar phase formed by lipid extracts from E-coli membranes and on the membrane itself by TR-SAXS using a cell with a built-in Peltier element that allowed large T-jumps and rapid cooling of the cell. The time required to achieve the disorder-to-order transition was found to be 1-2 s for the lipid lamellar phases and the membrane. The transformation involved no induction period after the T-jump. Some results suggested that the time course of the transformation involved two relaxation times. 

Hokkaido University Laboratory for Phase Transition Dynamics of Ice Institute of Low Temperature Science... 

A situation that arises from the intramolecular dynamics of A and completely distinct from apparent non-RRKM behaviour is intrinsic non-RRKM behaviour [9], By this, it is meant that A has a non-random P(t) even if the internal vibrational states of A are prepared randomly. This situation arises when transitions between individual molecular vibrational/rotational states are slower than transitions leading to products. As a result, the vibrational states do not have equal dissociation probabilities. In tenns of classical phase space dynamics, slow transitions between the states occur when the reactant phase space is metrically decomposable [13,14] on the timescale of the imimolecular reaction and there is at least one bottleneck [9] in the molecular phase space other than the one defining the transition state. An intrinsic non-RRKM molecule decays non-exponentially with a time-dependent unimolecular rate constant or exponentially with a rate constant different from that of RRKM theory. 

Ddnweg B 1996 Simulation of phase transitions critical phenomena Monte Carlo and Molecular Dynamics of Condensed Matter Systems vol 49, ed K Binder and G Ciccotti (Bologna Italian Physical Society) pp 215-54... 

Frenkel D 1986 Free-energy computation and first-order phase transitions Moiecuiar Dynamics Simuiation of Statisticai Mechanicai Systems ed G Ciccotti and W G Hoover (Amsterdam North-Holland) pp 151-88... 

Prenkel, D. Pree energy computation and first order phase transitions. In Molecular Dynamic Simulation of Statistical Mechanical Systems, Enrico Fermi Summer School, Varenna 1985, G. Ciccotti and W. Hoover, eds. North Holland, Amsterdam (1986) 43-65. 

Just as one may wish to specify the temperature in a molecular dynamics simulation, so may be desired to maintain the system at a constant pressure. This enables the behavior of the system to be explored as a function of the pressure, enabling one to study phenomer such as the onset of pressure-induced phase transitions. Many experimental measuremen are made under conditions of constant temperature and pressure, and so simulations in tl isothermal-isobaric ensemble are most directly relevant to experimental data. Certai structural rearrangements may be achieved more easily in an isobaric simulation than i a simulation at constant volume. Constant pressure conditions may also be importai when the number of particles in the system changes (as in some of the test particle methoc for calculating free energies and chemical potentials see Section 8.9). 

For the analysis heat and mass transfer in concrete samples at high temperatures, the numerical model has been developed. It describes concrete, as a porous multiphase system which at local level is in thermodynamic balance with body interstice, filled by liquid water and gas phase. The model allows researching the dynamic characteristics of diffusion in view of concrete matrix phase transitions, which was usually described by means of experiments. 

Shock-Induced Dynamic Yielding and Phase Transitions... 

Surface SHG [4.307] produces frequency-doubled radiation from a single pulsed laser beam. Intensity, polarization dependence, and rotational anisotropy of the SHG provide information about the surface concentration and orientation of adsorbed molecules and on the symmetry of surface structures. SHG has been successfully used for analysis of adsorption kinetics and ordering effects at surfaces and interfaces, reconstruction of solid surfaces and other surface phase transitions, and potential-induced phenomena at electrode surfaces. For example, orientation measurements were used to probe the intermolecular structure at air-methanol, air-water, and alkane-water interfaces and within mono- and multilayer molecular films. Time-resolved investigations have revealed the orientational dynamics at liquid-liquid, liquid-solid, liquid-air, and air-solid interfaces [4.307]. 

P. A. Thompson, G. S. Grest, M. O. Robbins. Phase transitions and universal dynamics in confined fihns. Phys Rev Lett (55 3448-3451, 1992. 

Phase transitions in two-dimensional layers often have very interesting and surprising features. The phase diagram of the multicomponent Widom-Rowhnson model with purely repulsive interactions contains a nontrivial phase where only one of the sublattices is preferentially occupied. Fluids and molecules adsorbed on substrate surfaces often have phase transitions at low temperatures where quantum effects have to be considered. Examples are molecular layers of H2, D2, N2 and CO molecules on graphite substrates. We review the path integral Monte Carlo (PIMC) approach to such phenomena, clarify certain experimentally observed anomalies in H2 and D2 layers, and give predictions for the order of the N2 herringbone transition. Dynamical quantum phenomena in fluids are analyzed via PIMC as well. Comparisons with the results of approximate analytical theories demonstrate the importance of the PIMC approach to phase transitions where quantum effects play a role. 

In order to analyze the quantum dynamics of a two-dimensional fiuid undergoing a phase transition, it turns out to be essential to go beyond MF approximation and to apply methods such as those presented here. 

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