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Crustal shortening and thickening to c. 70-85 km in the Tibetan Plateau occurred both before and mainly after the c. 50 Ma India-Asia collision. Potassic-ultrapotassic shoshonitic and adakitic lavas erupted across the Qiangtang (c. 50-29 Ma) and Lhasa blocks (c. 30-10 Ma) indicate a hot mantle, thick crust and eclogitic root during that period. The progressive northward underthrusting of cold, Indian mantle lithosphere since collision shut off the source in the Lhasa block at c. 10 Ma. Late Miocene-Pleistocene shoshonitic volcanic rocks in northern Tibet require hot mantle. We review the major tectonic processes proposed for Tibet including 'rigid-block', continuum and crustal flow as well as the geological history of the major strikeslip faults. We examine controversies concerning the cumulative geological offsets and the discrepancies between geological, Quaternary and geodetic slip rates. Low present-day slip rates measured from global positioning system and InSAR along the Karakoram and Altyn Tagh Faults in addition to slow long-term geological rates can only account for limited eastward extrusion of Tibet since Mid-Miocene time. We conclude that despite being prominent geomorphological features sometimes with wide mylonite zones, the faults cut earlier formed metamorphic and igneous rocks and show limited offsets. Concentrated strain at the surface is dissipated deeper into wide ductile shear zones. [ABSTRACT FROM AUTHOR]

Discontinuous molecular dynamics simulation and thermodynamic perturbation theory have been used to study thermodynamic and transport properties for hydrocarbons and oxygenated compounds. The fundamental basis of the method relies on a stepwise characterization of the disperse interactions and Wertheim potentials for the hydrogen bonding. The study on the transferable step potential energies, which are used to correlate the physical properties, the vapor pressure and liquid density, from available experimental data in the literature for straight-chain alkanes is extended to straight-chain alkenes, alkynes, ethers, and alcohols. The transferable multistep potentials for the new training set of pseudo-atoms governed by two transferable square-well depths and diameters are introduced, being transferable for the selected model compounds in each family. Those transferable parameters are applied to a set of validation compounds, and the results are analyzed. Overall, the vapor pressures and liquid densities are correlated to within 5% error with reduced temperatures extending to 0.45 for n-alkanes, alkenes, alkynes, ethers, and alcohols while applying transferable characterizations of the individual pseudo-atoms' molecular interaction potentials.

The effect of hydrogen bonding on the phase behavior of binary polymer blends of poly(ethylene covinyl alcohol) (EVOH) with poly(n-butyl methacrylate) (PBMA) and poly(4-vinyl pyridine) (PVPy) was studied by Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR/ATR). The association model of Painter, Coleman, and co-workers was used to analyze the effect of hydrogen bonding on miscibility of polymer blends containing EVOH. The equilibrium constants of solvation of EVOH with PVPy are determined from the quantitative analysis of spectra at 60, 100, and 140 °C and compared with previous results available at room temperature. The equilibrium constants of solvation of EVOH with PBMA were similarly determined at 60, 100, and 140 °C. Results for these binary blends are of interest in understanding the roles of compatibilizers and predicting results for multicomponent blend. Because the pyridine nitrogen and the carbonyl oxygen absorb in different regions of the IR spectrum, this choice of components provides a useful combination for probing the role of hydrogen bonding.

The diffusion process of methane in a silicalite single-crystal membrane has been investigated using the Dual Control Volume-Grand Canonical Molecular Dynamics method. Simulations of full-membrane transport and the three individual contributions that comprise the overall process (entrance to the pores, intra-crystalline diffusion, and exit from the pores) show that the contribution of surface resistance to the overall transport resistance in zeolite membranes is larger and longer range than one might expect. A model is proposed on the basis of the additivity of these contributions. From the individual simulations of exit and entrance zones, it is shown that the adsorption and desorption resistances approach an asymptote with increasing crystal thickness. However, the asymptotic trend has not been observed in full membrane simulations within the thickness limit of this work, possibly because of the coupling between the entrance and exit effects. Since the surface resistance is limited to less than 1 μm and the single-crystal membrane comprises 100 μm, the surface resistance still represents a relatively small contribution to the overall resistance. Therefore, the diffusion process through the single-crystal membrane is dominated by the internal transport of the sorbate molecules along the principal (z-) axis of the crystal.

A methodology is presented for applying the Elliott−Suresh−Donohue (ESD) equation of state to polymer solutions based on knowledge of the polymer's molecular structure. Group contributions to the ESD shape parameter are presented for 88 functional groups to complement the existing group contribution methods for the solubility parameter and molar volume. Hydrogen-bonding contributions are treated explicitly through Wertheim's theory. The resulting extension provides a framework for solutions that may include any combination of small molecules, polymers, or intermediate compounds such as waxes and asphaltenes. As a demonstration, 20 polymer solutions are studied involving liquid and supercritical solvents exhibiting a range of phase behaviors. The polymers treated are polyethylene, polystyrene, polyisobutylene, poly(ethylene oxide), poly(propylene oxide), poly(vinyl acetate), poly(vinyl chloride), and poly(vinyl alcohol). Solvent partial pressures are generally correlated to high accuracy, but the accuracy for lower and upper critical solution behavior is only qualitative.

We report vapor−liquid equilibrium data for the system dimethyl ether (DME) + 2-propanol at 323.45, 348.45, and 373.45 K and for the system dimethyl ether + 2-propanol + water at 323.25, 348.05, and 373.15 K. The experimental data are correlated using the Peng−Robinson equation of state and the Elliott−Suresh−Donohue equation of state. We explore the properties of dimethyl ether in the ternary system as a near-critical or supercritical solvent or cosolvent. The data for the dimethyl ether solutions are compared to literature data for ternary systems containing propylene or propane + 2-propanol + water. Dimethyl ether exhibits relatively higher solubility in the aqueous phase, leading to enhanced volatility of water at relatively low pressures compared to the case for propane. On the other hand, dimethyl ether also becomes completely soluble in the aqueous solution at relatively low pressures, precluding two-phase mass transfer under certain conditions.

The first part of this paper is a review of experimental methods and the high-pressure phase behavior of dimethyl ether systems for which data have been published between 1932 and 1999. For the systems investigated, the references, temperatures, pressures, cell volumes, and experimental procedures are reported. The second part of this paper is high-pressure vapor−liquid equilibrium (VLE) data for the systems dimethyl ether (DME) + ethanol at (332.95, 353.25, and 373.15) K and dimethyl ether + ethanol + water at (333.55, 353.55, and 373.65) K. The experimental data are correlated using the Elliott−Suresh−Donohue (ESD-EOS) and Peng Robinson (PR-EOS) equations of state.

High-pressure vapor−liquid equilibrium (VLE) data for the systems CO2 + methanol at 313.05 K, CO2 + ethanol at 323.55, 325.15, and 333.35 K, R-22 (chlorodifluoromethane) + ethanol at 343.25, 361.45, and 382.45 K, and R-22 + ethanol + water at 351.55, 362.65, and 371.85 K are obtained using a circulation-type VLE apparatus. The apparatus is tested with measurements of the CO2 + methanol and CO2 + ethanol systems. The experimental data are correlated using the Peng−Robinson and Elliott−Suresh−Donohue equations of state.

1. The whole‐cell patch‐clamp technique has been used to investigate the actions of n‐butanol, n‐pentanol, n‐hexanol and n‐octanol on the sodium current of cells isolated from the dorsal root ganglia (DRGs) of neonatal rats and maintained in short‐term tissue culture. 2. The influence of n‐alkanols on the level of steady‐state inactivation of the sodium current was investigated by a standard two‐pulse protocol. All alkanols increased the level of resting inactivation and this was manifested as a hyperpolarizing shift of the relationship between the steady‐state inactivation parameter (h infinity) and membrane potential. The mid‐point of the h infinity curve was moved by up to ‐30 mV. 3. The relationship between the shift in the mid‐point of the inactivation curve (delta Vh) and aqueous n‐alkanol concentration has been derived for each n‐alkanol. These are complex in shape and do not appear consistent with a hypothesis that the increase in inactivation results from 1:1 binding of an alkanol molecule to a single site on the channel protein. 4. The aqueous concentrations used ranged from 70 mM‐n‐butanol to 0.05 mM‐n‐octanol. However, equal fractional saturations of n‐alkanols produced approximately equal shifts in the h infinity curve, particularly in the range 0.01‐0.07 saturated. This implies a hydrophobic site of action, with a standard free energy per methylene group for adsorption to the site from the aqueous phase of ca ‐3.2 kJ/mol. 5. The increase in resting inactivation was not the sole means by which n‐alkanols reduced the sodium current. The current was still reduced in cells pre‐pulsed to sufficiently negative potentials to remove steady‐state inactivation even in the presence of alkanols. The concentration required to reduce the current by 50% (ED50) has been interpolated for each n‐alkanol. From these data it was estimated that the standard free energy per methylene group for adsorption to the site of action was ca ‐3.1 kJ/mol, similar to that calculated for the effect on inactivation. The concentration dependence of this residual block indicated the involvement of more than one n‐alkanol molecule. 6. The n‐alkanols increase the level of inactivation of rat DRG cell sodium channels at potentials around the resting membrane potential and this effect contributes to their local anaesthetic action.(ABSTRACT TRUNCATED AT 400 WORDS)

The actions of members of the homologous series of alkyl cations CH3 (CH2)n‐1 N+ (CH3)3 (Cn TMA) on the sodium current in giant axons of Loligo forbesi have been investigated. The substances tested correspond to n = 6, 8, 10, 12, 14 and 16. These cations only produced significant sodium current suppression when applied inside the axon. Actions on first‐pulse sodium currents and use‐dependent effects were separately studied. The shorter members of the series (C6TMA and C8TMA) produced suppression of first‐pulse sodium currents without causing significant use dependence. The first‐pulse suppression arose partly from a positive shift along the voltage axis of the steady‐state activation parameter (m infinity) and partly from a reduction in the maximum sodium conductance (gNa). C12TMA and C14TMA produced little first‐pulse suppression but caused clear use dependence. C10TMA showed intermediate properties while C16TMA was inactive. The use‐dependent actions have been quantitatively investigated using a double‐pulse protocol. The results are consistent with a model in which the cations enter a blocking site on the ion‐channel via the intra‐axonal aqueous phase. The cations appear able to bind to inactivated sodium channels at significant rates. The possible molecular locations of the sites responsible for m infinity shifts and use dependence are discussed. It is argued that the existence of two separate sites may help to explain certain distinctions between the actions of neutral general anaesthetics and clinical local anaesthetics on the sodium channel.

The effects of octyltrimethylammonium ions (OTMA+), octyl sulphate ions (OS‐) and octanoic acid (OA) on the sodium current of the voltage‐clamped squid giant axon have been investigated using intracellular and extracellular application of the test substances. OTMA+ applied externally at concentrations of 0.8‐5.0 mM produces a small reversible increase in the peak inward sodium current in both intact and CsF‐perfused axons. Intracellular application of OTMA+ at 0.8 mM to CsF‐perfused axons causes a reversible 50% suppression of peak inward sodium current. The inhibition of peak inward current by internal OTMA+ arises largely from a shift of the steady‐state activation parameter (m infinity) in the depolarizing direction along the voltage axis. There is little use dependence of the current suppression by OTMA+ OA applied either internally or externally is more effective at suppressing peak inward sodium current at pH 6.0 than at pH 7.4. At pH 6.0 external application of 5 mM‐OA to perfused axons causes approximately 60% suppression. This is associated with a depolarizing shift of m infinity of about 13 mV and a hyperpolarizing shift of the steady‐state inactivation (h infinity) curve of about 4 mV. The effects of internal and external OA are broadly similar except that the h infinity shift is not seen with internal application. OS‐ at concentrations above 2.0 mM produces complete irreversible loss of sodium current. At 2.0 mM, OS‐ produces 10% current suppression and a small depolarizing shift of the m infinity curve. Internal and external applications of OS‐ differ little except that external OS‐ causes a 25% increase in the time constant of activation (tau m). The possible origins of these effects are discussed. It is proposed that the shift of m infinity caused by internal OTMA+ is due to a diminution of the lipid dipole potential at the internal surface of the membrane caused by OTMA+ adsorption. This effect could also account for the m infinity shift caused by OA. The results showing that OA produces shifts of opposite sign in the voltage dependence of m infinity and h infinity are discussed with respect to their implications for models of sodium channel gating.

The effects of methyl butyl ketone, methyl heptyl ketone and methyl pentanoate on the sodium current of the squid giant axon have been examined. The peak inward current in intact axons was reduced reversibly by each substance. Sodium currents were recorded in intracellularly perfused axons before and during exposure to the test substances and the records were fitted with equations similar to those proposed by Hodgkin & Huxley (1952). Shifts in the voltage dependence of the steady‐state activation and inactivation parameters (m infinity and h infinity), reductions in the peak heights of the activation and inactivation time constants (tau m and tau h) and changes in the maximum sodium conductance (gNa) caused by these substances have been tabulated and compared with the effects of methyl octanoate (Haydon & Urban, 1983b). Each compound shifted the voltage dependence of the steady‐state inactivation parameter in the hyperpolarizing direction and that of the steady‐state activation parameter in the depolarizing direction. The shifts produced by the ketones are compared with those produced by methyl pentanoate and by methyl octanoate. The possible role of an interaction between the carbonyl oxygen of the test substance and the sodium channel protein in producing the h infinity shift is discussed. The peak time constants are reduced and the voltage dependences of tau m and tau h are shifted in a direction commensurate with the shifts in steady‐state properties. The maximum sodium conductance is not much affected either by the ketones or by methyl pentanoate. Large reductions in peak inward current coupled with little effect on gNa have been reported for the n‐alkanols and other surface‐active compounds (Haydon & Urban, 1983b). This lack of a large effect on gNa indicates that whatever direct interaction does take place between the test substance and the channel protein, it does not result in a blockage of the channel.

Development of a special molecular dynamics algorithm (discontinuous molecular dynamics with bonding) was previously reported for simulating molecules via potentials with small square-well potential bonding sites that mimic hydrogen bonding. The present study extends this approach to fluids composed of two new molecular models and focuses especially on the kinetics of bond associations and dissociations in addition to the equilibrium effects. The first molecular model comprises two repulsive sites and three bonding sites (simulated methanol). The second molecular model comprises five repulsive sites where bonding sites are placed at the end and the middle of the chain (a simulated 5-mer diamine). Equilibrium properties focus on the fractions of bonding sites that remain unbonded after extended equilibration. At moderate to high packing fractions, the equilibrium fraction of unbonded acceptors for the middle site of the 5-mer is roughly equal to that of the end site. The fluid structures around end sites and middle sites are analyzed in order to suggest how the equilibrium effects may be analytically predicted. The rates of bond association and dissociation are studied for each type of bonding site as a function of temperature, molecular packing fraction, position along the chain, and bonding energy. The kinetic data more strongly suggest the presence of a mild screening effect by showing a shift in the rate constant. At all densities, the bonding in the 5-mer is higher than expected, indicating a stabilization effect that was not previously anticipated. These data point the way toward a fundamental theory of the kinetics of hydrogen bonding.

A simplification of Wertheim's theory is described by which the extents of association of all species may be efficiently determined by solution of a single nonlinear equation rather than a nonlinear system of equations. This simplification should facilitate the implementation of Wertheim's theory into chemical engineering process simulators for equations of state like the statistical associating fluid theory and the simple equation of state for associating mixtures of Elliott et al. (Ind. Eng. Chem. Res. 1990, 29, 1476). The computation speed for an associative equation of state is about 2−3 times slower than that for the Soave equation when this simplification is applied, regardless of the number of components.

Single pass conversions in conventional vapor phase methanol synthesis are low, necessitating recycle of large quantities of unconverted reactants. In the Solvent Methanol Process (SMP), the use of an inert and highly selective solvent in the synthesis loop enables the removal of methanol as soon as it is formed and helps overcome equilibrium limitations that exist in the vapor phase process. An industrial scale, packed bed, adiabatic reactor with cocurrent upflow of synthesis gas and solvent has been simulated for the SMP. The simulation shows that very high single pass conversions of CO and H2 are attainable such that recycle can be eliminated. Reaction rates are however lower than vapor phase rates due to pore diffusion limitations.

The relation of preferred temperature to acclimation temperature of 29 rainbow trout 15 months old was examined during summer. Fish were acclimated to 5, 10, 15, 20, and 25 C, respectively, and tested individually in an electrically controlled shuttlebox device. Body temperatures monitored by a radiothermometer ingested by the fish closely approximated occupied temperatures to within 0.2 C. No significant differences were found in preferred temperature over the acclimation range studied. The calculated final preferendum was 11.3 C. Fish regulated environmental and body temperature with the same precision as they selected temperature in a spatial gradient.

Abstract:  n-Alkyl sulphate anions have been shown to reversibly affect the functioning of voltage-gated ion channels in a variety of preparations. They are suggested to exert their effects by increasing the magnitude of the negative surface potential at the external face of the membrane. Here we report the effects of n-octyl sulphate (OS–) and n-dodecyl sulphate (DDS–) on RCK1 (Kv1.1), RCK4 (Kv1.4) and Shaker B potassium channels exogenously expressed in Xenopus oocytes. Both OS–and DDS–produced a hyperpolarising shift in the activation voltage dependence of all three channels, consistent with an increased negative external surface potential. Similar kinetic changes were also observed, the kinetics of both activation and inactivation being accelerated in the presence of OS–and DDS–. However, we also found that while 10 mM OS–and 50 μM DDS–significantly increased the maximum conductance of RCK1 and Shaker B channels, 5 mM OS–and 15 μM DDS–produced a large decrease in RCK4 conductance; the possible involvement of RCK4 residue K533 in this effect is discussed. Our data indicate that n-alkyl sulphate anions can perturb ion channel function in a variety of ways and that their effects are complex and channel specific.