Diverse Experimental Data Research Articles

Properties of a six-nucleon system in a multicluster dynamic model with antisymmetrization

A modification of the multicluster dynamic model with Pauli projection (MDMP) developed earlier for light nuclei is proposed. The modification consists in performing a total antisymmetrization of the MDMP wave functions over all nucleons using a technique worked out for this purpose. The formal and physical consequences of the antisymmetrization procedure, namely, the changes in the structure of the nuclear wave functions, the exchange effects in the electromagnetic and weak processes on six-nucleon (i.e. 6He and 6Li) nuclei, etc. are studied in detail. The exchange effects were shown to give the decisive contribution to the magnetic form factors at moderate and high momentum transfers. The general classification of the operators is carried out allowing one to determine before calculations the observables in which the exchange effects should be important and in which one can use the initial multicluster wave functions without their explicit antisymmetrization. The developed model (AMDMP) makes it possible to reproduce successfully a large array of diverse experimental data on six-nucleon nuclei. The problem of the 6Li quadrupole moment is also discussed.

Tertiary structure of ribosomal RNA

Abstract The secondary structures of ribosomal RNAs have been deduced by comparative sequence analysis. The same approach has also suggested some higher-order tertiary interactions. Some of these are now being tested by direct experiment, and it is clear that tertiary interactions play an important functional role in stabilizing protein-binding sites and folding the ribosomal RNAs into their functional forms. At the same time, diverse experimental data on the relative positioning of RNA segments and proteins within the ribosome are being incorporated into low-resolution models of the ribosome, which reveal a distinctive domain organization of the RNA.

Tertiary structure of ribosomal RNA

The secondary structures of ribosomal RNAs have been deduced by comparative sequence analysis. The same approach has also suggested some higher-order tertiary interactions. Some of these are now being tested by direct experiment, and it is clear that tertiary interactions play an important functional role in stabilizing protein-binding sites and folding the ribosomal RNAs into their functional forms. At the same time, diverse experimental data on the relative positioning of RNA segments and proteins within the ribosome are being incorporated into low-resolution models of the ribosome, which reveal a distinctive domain organization of the RNA.

Experimentally determined mineral-melt partition coefficients for Sc, Y and REE for olivine, orthopyroxene, pigeonite, magnetite and ilmenite

Our current lack of understanding of the partitioning behavior of Sc, Y and the REE (rare-earth elements) can be attributed directly to the lack of a sufficiently large or chemically diverse experimental data set. To address this problem, we conducted a series of experiments using several different natural composition lavas, doped with the elements of interest, as starting compositions. Microprobe analyses of orthopyroxene, pigeonite, olivine, magnetite, ilmenite and co-existing glasses in the experimental charges were used to calculate expressions that describe REE partitioning as a function of a variety of system parameters. Using expressions that represent mineral-melt reactions (versus element ratio distribution coefficients) it is possible to calculate terms that express low-Ca pyroxene-melt partitioning behavior and are independent of both pyroxene and melt composition. Compositional variations suggest that Sc substitution in olivine involves either a paired substitution with Al or, more commonly, with vacancies. The partitioning of Sc is dependent both on melt composition and temperature. Our experimentally determined olivine-melt REE Ds (partition coefficients) are similar to, but slightly higher than those reported by McKay (1986) and support their conclusions that olivines are strongly LREE depleted. Y and REE mineral/melt partition coefficients for magnetite range from 0.003 for La to 0.02 for Lu. Ilmenite partition coefficients range from 0.007 for La to 0.029 for Lu. These experimental values are two orders of magnitude lower than many of the published values determined by phenocryst/matrix separation techniques.

Evidence for two-pairing-phonon states in the odd-mass nucleus 143Nd

From the diverse and extensive experimental data on the low-lying structure of the 143 60Nd 83 nucleus, evidence is gathered for the existence of two-pairing-phonon configurations. Comparison of two-neutron pick-up data 145Nd(p,t) 143Nd and gamma-ray data from the reaction 140Ce(α,nγ) 143Nd with other experimental data allows one to identify the states at 3040 and 3071 keV as sharing the neutron-pairing vibration excitation ν(1, 1)ν f 7 2 and the state at 2035 keV as being the proton excitation 0 2 +ν f 7 2 . They are the only configurations of this type hitherto known in odd nuclei. The coupling between neutron- and proton-pairing vibrations and the coupling to other excitation modes are discussed.

Microkinetic analysis of diverse experimental data for ethylene hydrogenation on platinum

Kinetic analysis employing a mechanism that captures the essential surface chemistry of the reaction allows quantitative interpretation of diverse experimental data. This approach is used with a Horiuti-Polanyi mechanism, modified by hydrogen activation steps, to describe the surface chemistry for ethylene hydrogenation over platinum catalysts. In this investigation, kinetic analysis provides a quantitative means of comparing, contrasting, and consolidating results from steady-state kinetic studies, deuterium tracing measurements, vibrational spectroscopy, and temperature programmed desorption

The relationship between the ferroelectric phase transition nearT0= 235 K in YBa2Cu3O7-xand High-Tcsuperconductivity: Comparison with the polaron theory of pardee and mahan

Abstract A variety of data summarized in this special issue imply that diverse experimental data, including specific heat, dielectric permittivity, and Raman sectra, can be interpreted as evidence for a structural phase transition near 235 K, probably from mmm to mm2 space group symmetry. In the present paper we emphasize the Raman results of Zhang et al. and of Rebane et al. (Sol. St. Commun. 65, 487, 1535 (1988)) and attempt to relate them to the high-temperature superconductivity changes near T = 235 K reported by Bhargava et al. (Phys. Rev. Lett, 59, 1468 (1987)) as well as other phenomena near T c. The phenomena at T c and To bear a strong resemblance to those of sequential phase transitions in the polaron theory of Pardee and Mahan (J. Sol. St. Chem. 15, 310 (1975))

Muscarinic Receptor Subtypes

In 1914, Sir Henry Dale provided the basis for the classical and comfortable definition of muscarinic and nicotinic acetylcholine receptors: Muscarinic receptors are selectively activated by muscarine and blocked by atropine; nicotinic receptors are activated by nicotine and blocked by curare. This definition lasted over 60 years, despite isolated reports that the picture might not be so simple. We now know, as the result of molecular biological studies, that there are multiple variants of both muscarinic and nicotinic receptors . These receptors are members of two quite separate gene superfamilies and only share the property of being activated by the same ligand, acetylcholine. The aim of this review is to discuss the structure, function, and binding properties of the different muscarinic receptor species, attempting where possible to coordinate the diverse experimental data into a uniform picture. For a more comprehensive review on muscarinic receptors, readers are di­ rected to a recent book by Brown (l).

Flame curvature and preferential diffusion in the burning intensity of bunsen flames

Flame temperature distributions over axisymmetric and two-dimensional Bunsen flames have been experimentally measured for methane, ethylene, and propane mixtures with air, and interpreted on the basis of preferential diffusion and aerodynamic stretching induced by flame curvature. Results substantite the validity of the non-unity Lewis number interpretation of stretched flame phenomena, verify the theoretical prediction that deviations of the flame temperature from the adiabatic flame temperature can occur only in the simultaneous presence of stretch and preferential diffusion, and demonstrate that such a deviation can be correlated by a nondimensional stretch factor for extensive experimental data obtained with various concentrations, flow velocities, and nozzle diameters. Identification of such a correlation strongly suggests the possibility of synthesizing the diverse experimental data on stretched flames in accordance with the generalized expression derived theoretically.

Modeling the dopaminergic nerve terminal

A method is described for developing and evaluating models of neurochemical processes. Computer simulation and simplex optimization are used to examine a model of the dopaminergic nerve terminal of the rat striatum. In the model, synthesis, storage, release, uptake, and metabolism are described by a set of non-linear differential equations. Parameters of the model are optimized with respect to diverse experimental data. These data include steady state passage of radioactivity, decline in total dopamine after synthesis inhibition, and change in extracellular dopamine concentration during electrical stimulation.

Thermodynamic modeling of the Hg-Cd-Te and Hg-Zn-Te systems

The basic thermodynamic equations governing the equilibrium between (A1-uBu)2-yTey(s) with y near unity and its liquid and vapor phases are summarized. These are used along with an associated solution model for the liquid with species, Hg, Cd, Te, HgTe, and CdTe, to obtain quantitatively good fits to the diverse experimental data. The less extensive data for the Hg-Zn-Te system are also fit and based upon the parameters established, some properties are calculated for which there are no experimental data at present.

Derivation of Internally-Consistent Thermodynamic Data by the Technique of Mathematical Programming: a Review with Application the System MgO-SiO2-H2O

The problem of deriving an optimal set of thermodynamic properties of minerals from a diverse experimental data base is reviewed and a preferred methodology proposed. Mathematical pro-gramming(MAP) methods extend the linear programming (LIP) approach first presented by Gordon (1973), and make it possible to account for the type of information conveyed, and the uncertainties attending both phase equilibrium data and direct measurements of phase properties. For phase equilibrium data which are (in most cases) characterized by non-normal error distributions across experimental brackets, the midpoint of a bracket is no more probable than other points, and the data are best treated by considering the inequality in the change in Gibbs free energy of reaction at each half-bracket. Direct measurements of phase properties can be assumed to have approximately normal error distributions, and the MAP technique optimizes agreement with these values by using the principles of least squares in the definition of an objective function. The structure of this problem, treatment of uncertainties in various types of experimental data, and method of optimizing final solutions are discussed in some detail. The method is applied to experimental data in the MgO-SiO2-H2O system, where inconsistencies among the data are resolved and an optimal set of thermodynamic properties is presented. The derived standard state entropies and volumes agree with all direct measurements (within their uncertainties), as do enthalpies of formation from the elements except for those of talc (+16 kJ mol−1), anthophyllite (+ 14 kJ mol−1), and brucite (−1 kJ mol−1). Stable phase relations in the system have the topology predicted by Greenwood (1963, 1971), with quartz- and forsterite-absent invariant points at 683 °C-6-4 kb and 797 °C-12 kb respectively, repeating at 552 °C-120 b and 550 °C-55 b. The thermodynamic analysis indicates little remaining flexibility in the phase relations, which, when combined with suitable activity models for solid solution, should allow for accurate determination of the conditions of metamorphism of ultramafic rocks.

Inhibition of gas hydrates by methanol

AbstractA molecular‐thermodynamic correlation has been developed for calculating the inhibition effect of methanol on the formation of hydrates in moist gas mixtures. Six phases are potentially present in these mixtures: gas, aqueous liquid, hydrocarbon liquid, ice, and hydrate structures I and II. For a given temperature and system composition, the molecular‐thermodynamic method described here allows computation of the hydrate‐point pressure as well as relative amounts and compositions of all coexisting phases. Good agreement is obtained when calculated results are compared with diverse experimental data reported in the literature. The correlation given here may be useful for computeraided design for gas processing and transportation.

Interactive system for preliminary processing of diverse experimental data

Interactive system for preliminary processing of diverse experimental data

Nonlinear dynamics in expanding plasmas

The expansion of a plasma occupying initially a half-space is investigated numerically and, by means of a novel description of the ion fluid, also analytically. A simple wave structure is found in the collisionless approximation. Stabilized by dissipation, the associated ion bunching gives rise to a fast ion component, similar to the ion blow-off in laser fusion. Three non-stationary regimes of this strongest nonlinear and inhomogeneous dynamical system are distinguished and discussed. For large t the ion front propagates with a speed proportional to (t−t 1) 1 2 where t 1 is a reference time. A simple picture emerges, explaining the diverse experimental data.

Possibility of ferroelastic domains in orientational glass state in (KBr)1-x(KCN)x.

Based on diverse experimental data on (KBr${)}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$(KCN${)}_{\mathrm{x}}$ mixed crystals, we propose a model in which quadrupole moments of CN molecules freeze in small ferroelastic domains with random orientations, while dipole moments remain free to flip. This model leads to an interesting phase diagram with two different orientational glass phases.

Improved corresponding states principle for the noble gases

Abstract This paper contains the background for a complete synthesis of all the properties-equilibrium as well as transport—of the five noble gases and of the 26 mixtures that can be formed with them. The synthesis is valid for the zero-density limit only, but covers the temperature range from absolute zero to the onset of ionization. The synthesis is based on a thorough revision of the two-parameter extended law of corresponding states of Kestin, Ro and Wakeham. The paper recalls the basis for the original corresponding-states principle, identifies the places at which experiment and the theory of statistical mechanics suggest deviations, and proceeds to remove them to a point where almost perfect agreement between calculation and a very large body of diverse experimental data is achieved, in the sense that deviations of experimental data from calculation are of the same order as the uncertainty in the best contemporary measurements. The basis of the revised corresponding-states principle is a set of five parameters which characterize each pair-interaction together with a fully consistent and asymptotically correct set of universal collision integrals and functionals that appear in the rigorous theory. These are reinforced with selected quantum-mechanical calculations applied in regions where they are significant.

Optimization of binary thermodynamic and phase diagram data

An optimization technique based upon least squares regression is presented to permit the simultaneous analysis of diverse experimental binary thermodynamic and phase diagram data. Coefficients of polynomial expansions for the enthalpy and excess entropy of binary solutions are obtained which can subsequently be used to calculate the thermodynamic properties or the phase diagram. In an interactive computer-assisted analysis employing this technique, one can critically analyze a large number of diverse data in a binary system rapidly, in a manner which is fully self-consistent thermodynamically. Examples of applications to the Bi-Zn, Cd-Pb, PbCl2-KCl, LiCl-FeCl2, and Au-Ni binary systems are given.

Seabed characterization from broad-band acoustic echosounding with scattering models

Acoustic echoes obtained during high-resolution shallow marine seismic surveys contain information about the statistical nature of the sedimentary bottom and its spatial variability. Use of a broad-band seismic source and an appropriately chosen data acquisition window makes the acoustic responses particularly amenable to quantitive analysis. The work reported utilizes experimental frequency-domain spatial coherence functions of along-track acoustic echoes as empirical metrics of bottom character, and by virtue of their correlation with known sediment types, as objective bases for remote sediment classification. Theoretical relationships between parameters describing sediment surface topographies and echo coherence are derived for the case of dominant water-sediment interface acoustic scattering. The diverse experimental data base was acquired from the Grand Banks of Newfoundland using a 1- to 10-kHz Huntec DTS system. Bottom photographs, cores, and grab samples combined with expert geological synthesis provide qualitative and quantitative control.

Interaction potential of nonpolar polyatomic molecules

The extension of the (12-7)-pair potential model to nonpolar polyatomic molecules is proposed. It is demonstrated that this model consistently fits diverse experimental data.