Water dynamics

The scatter plots shown in Fig. 12 are a very intuitive approach to investigate the mobility parallel to the surface. These plots show that the water molecules next to the (weakly corrugated) mercury surface are obviously more mobile than the molecules on the (strongly corrugated) Pt(lOO) surface, and that the molecules in the second layers are more mobile than the ones in the adsorbed layers. 

Sonnenschein and Heinzinger [163] and later Wallqvist [141] calculated residence times for water in various layers. While the residence times of water near non-metallic surfaces are typically of the order of ten to hundred picoseconds, the values near uncharged metal surfaces are of the order of several hundred picoseconds [167]. 

The reorientational dynamics of water molecules has been analyzed by calculating the relaxation times of the molecular dipole vector relative to the laboratory fixed 

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Goldanskii V I and Krupyanskii Y F 1989 Protein and protein-bound water dynamics studied by Rayleigh scattering of Mdssbauer radiation (RSMR) Q. Rev. Biophys. 22 39-92... 

Fig. 2. Power spectrum of water dynamics with frequency in units of fs...

We finish this section by comparing our results with NMR and incoherent neutron scattering experiments on water dynamics. Self-diffusion constants on the millisecond time scale have been measured by NMR with the pulsed field gradient spin echo (PFGSE) method. Applying this technique to oriented egg phosphatidylcholine bilayers, Wassail [68] demonstrated that the water motion was highly anisotropic, with diffusion in the plane of the bilayers hundreds of times greater than out of the plane. The anisotropy of... 

In addition, water motion has been investigated in reverse micelles formed with the nonionic surfactants Triton X-100 and Brij-30 by Pant and Levinger [41]. As in the AOT reverse micelles, the water motion is substantially reduced in the nonionic reverse micelles as compared to bulk water dynamics with three solvation components observed. These three relaxation times are attributed to bulklike water, bound water, and strongly bound water motion. Interestingly, the overall solvation dynamics of water inside Triton X-100 reverse micelles is slower than the dynamics inside the Brij-30 or AOT reverse micelles, while the water motion inside the Brij-30 reverse micelles is relatively faster than AOT reverse micelles. This work also investigated the solvation dynamics of liquid tri(ethylene glycol) monoethyl ether (TGE) with different concentrations of water. Three relaxation time scales were also observed with subpicosecond, picosecond, and subnanosecond time constants. These time components were attributed to the damped solvent motion, seg-... 

Payer80 states that the UNSAT-H model was developed to assess the water dynamics of arid sites and, in particular, estimate recharge fluxes for scenarios pertinent to waste disposal facilities. It addresses soil-water infiltration, redistribution, evaporation, plant transpiration, deep drainage, and soil heat flow as one-dimensional processes. The UNSAT-H model simulates water flow using the Richards equation, water vapor diffusion using Fick s law, and sensible heat flow using the Fourier equation. 

H Levine, L Slade. Water as a plasticizer Physico-chemical aspects of low moisture polymeric systems Water Science Reviews 3 Water Dynamics, F Franks, editor. Cambridge Cambridge University Press 79-185, 1988. 

The oil-water dynamic interfacial tensions are measured by the pulsed drop (4) technique. The experimental equipment consists of a syringe pump to pump oil, with the demulsifier dissolved in it, through a capillary tip in a thermostated glass cell containing brine or water. The interfacial tension is calculated by measuring the pressure inside a small oil drop formed at the tip of the capillary. In this technique, the syringe pump is stopped at the maximum bubble pressure and the oil-water interface is allowed to expand rapidly till the oil comes out to form a small drop at the capillary tip. Because of the sudden expansion, the interface is initially at a nonequilibrium state. As it approaches equilibrium, the pressure, AP(t), inside the drop decays. The excess pressure is continuously measured by a sensitive pressure transducer. The dynamic tension at time t, is calculated from the Young-Laplace equation... 

The importance of rapid relaxation in demulsification effectiveness can be seen with the crude oil-water dynamic tension results with P2 (Figure 3) and 0P1 (Figure 4). As can be seen, it takes only about 60 seconds for the interface to reach its equilibrium state with the effective demulsifier P2, whereas with less effective demulsifier 0P1, the equilibrium is reached only after 800 seconds. 

Ben Othman D, Luck JM, Toumoud MG (1997) Geochemistry and water dynamics application to short time-scale flood phenomena in a small Mediterranean catchment. I- Alkalis, alkali-earths and Sr isotopes. Chem Geol 140 9-28... 

The site http //www.nyu.edu/pages/mathmol/modules/water/info water.html hosts a nice discussion of water, including two short video clips (1) the quantum-mechanically computed movement of two water molecules united by means of a single hydrogen bond, at http //www.nyu.edu/pages/mathmol/modules/water/dimer.mpg-, (2) a short film of several hundred water molecules dancing within a cube at http //www. nyu. edu/pages/mathmol/modules/water/water dynamics.mpg. 

As discussed earlier, the usefulness of the food polymer science approach to the study of water dynamics in foods has been widely demonstrated by numerous researchers studying both model and real food systems. Along with the success of the approach, there still exist a number of areas of concern that need to be mentioned. 

Hills, B.P. and Manning, C.E. 1998. NMR oxygen-17 studies of water dynamics in heterogeneous gel and particulate systems. J. Mol. Liquids 75, 61-76. 

Warrick AW. Soil Water Dynamics. New York Oxford University Press 2003. 

Buchsteiner A, Lerf A, Piepe Jr. Water dynamics in graphite oxide investigated with neutron scattering, . Phys. Chem. B 2006,110, 22328-22338. 

It is assumed that erosion is the main cause of soil degradation around the world (Oldeman, 1994). The effeets of soil erosion occur on eroded fields (on-site effeets) and downstream (off-site effects). On-site effects include the loss of fertile topsoil and ehanges soil water dynamics, nutrient status, soil organic... 

Schreier H, Shah PB (1996) Water dynamics and population pressure in the Nepalese Himalayas. Geo J 40(l-2) 45-51... 

Fig. 7. Hydration of DNA, and with a drug recognized in the minor groove. Time scales are indicated for bulk water, dynamically ordered water, configurational changes and structured water...

In this contribution we present a study of ultrafast dynamics in liquid water employing heterodyne-detected TG and EPS techniques. Heterodyne detection allows us to separate the genuine photon echo signal that contains information on water dynamics, from thermal effects. The analysis of the experimental EPS data that includes thermal effects yields a 700-fs... 

The developed model was applied to the EPS experiment (Fig.lb) to extract information on the water dynamics. Similar to the previous report [17], the EPS function decreases rapidly at a time scale of -0.5 ps, then raises again at -2 ps, and finally falls off to zero. The EPS functions acquired while keeping the delays tn (empty circles) and t23 (solid circles) fixed [20], are shifted along the vertical axis which is a consequence of the relatively short excited-state lifetime (700 fs). The peak in the EPS function around -2 ps is explained in the framework of our model as arising from interference between the chromophore and solvent responses. The delicate balance between phases of genuinely nonlinear and thermal contributions as the delay t12 between the two excitation pulses is increased, leads to the enhancement of the integrated signal that is measured in the EPS experiment. 

Our experiments and numerical simulations have proven that interference between chromophore and solvent responses greatly obscures the experimental observables in IR spectroscopy on water at waiting times >0.5 ps. However, the water dynamics can still be obtained if the thermal effects are carefully characterized and self-consistently included in the model. This results in the longest time scale for the frequency correlation function of 700 fs. 

This bimodal dynamics of hydration water is intriguing. A model based on dynamic equilibrium between quasi-bound and free water molecules on the surface of biomolecules (or self-assembly) predicts that the orientational relaxation at a macromolecular surface should indeed be biexponential, with a fast time component (few ps) nearly equal to that of the free water while the long time component is equal to the inverse of the rate of bound to free transition [4], In order to gain an in depth understanding of hydration dynamics, we have carried out detailed atomistic molecular dynamics (MD) simulation studies of water dynamics at the surface of an anionic micelle of cesium perfluorooctanoate (CsPFO), a cationic micelle of cetyl trimethy-lainmonium bromide (CTAB), and also at the surface of a small protein (enterotoxin) using classical, non-polarizable force fields. In particular we have studied the hydrogen bond lifetime dynamics, rotational and dielectric relaxation, translational diffusion and vibrational dynamics of the surface water molecules. In this article we discuss the water dynamics at the surface of CsPFO and of enterotoxin. 

WATER DYNAMICS AT THE SURFACE OF A SMALL PROTEIN, ENTEROTOXIN... 

To a good first approximation, the Great Lakes fit a model involving the equilibrium of calcite, dolomite, apatite, kao-Unite, gibbsite, Na- and K-feldspars at 5°C., 1 atm. total pressure with air of PCo2 = 3.5 X 10" atm. and water. Dynamic models, considering carbon dioxide pressure and temperature as variables (but gross concentrations fixed), show that cold waters contain excess carbon dioxide and are unsaturated with respect to calcite, dolomite, and apatite, whereas warm waters are nearly at equilibrium with the atmosphere but somewhat supersaturated with respect to calcite, dolomite, and apatite. 

MWD Model for the Water Dynamics of the Arctic Basin (Riedlinger and Preller, 1991). 

The circulation of water in the Arctic Basin is a complex system of cycles and currents with different scales. Block HB simulates the dynamics of Arctic Basin water by the system of sub-blocks presented in Figure 6.2. The water dynamics in 2 is presented by flows between compartments Eijk. The directions of water exchanges are represented on every level zk = z0 + (k — 1 )A k according to Aota et al. (1992) in conformity with the current maps assigned as SSMAE input. The external boundary of 2 is determined by the coastline, the sea bottom, the Bering Strait, the southern boundary of the Norwegian Sea, and the water-atmosphere interface. 

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