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1.
Muonic hydrogen isotopes (μ p, μ d, and μt) are simple quantum mechanical systems ideally suited for studies of numerous fundamental phenomena in electroweak and strong interactions as well as in applied areas such as muon chemistry or muon catalyzed fusion. Emission of muonic hydrogen isotopes into vacuum helps to overcome the limitations which are normally imposed on conventional investigations with gaseous and liquid targets. A proof of principle experiment for this new technique was performed at TRIUMF last year. Negative muons with 30 MeV/c momentum were stopped in a thin film of solid hydrogen and produced very low energy μd in vacuum. The distribution center of the normal velocity components of emitted μd atoms was measured to be ∼1 cm/μs. The yield of μd in vacuum is an increasing function of H2 film thickness δ up to a value of δ≥1 mm.  相似文献   
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A theoretical study of ion hydration using the statistical thermodynamic supermolecule-continuum method is described. The cell and shell methods are used for configurational averaging. Enthalpies, free energies and entropies are calculated for Li+, Na+, K+, F and Cl each four coordinated with water. The results are in reasonable accord with experiment. A comparison of the site method, cell method and shell method results is presented. The supermolecule-continuum approach to solvent effects seems to be capable of accommodating essential features for the calculation of solvation energy and solvent effects on structure and properties.  相似文献   
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Monte Carlo computer simulations were performed on dilute aqueous solutions of the dimethylphosphate anion and the sodium dimethylphosphate ion pair, with the two phosphodiester torsional angles in the gauche–gauche, gauche–trans, and trans–trans conformations. The structural and energetic aspects of the aqueous hydration of each molecule were analyzed in terms of quasi component distribution functions based on the proximity criterion and partitioned into ionic, hydrophilic, and hydrophobic contributions to facilitate an understanding of the hydration pattern and conformational trends in these multifunctional solutes. Special attention was also paid to methodological issues affecting hydration, such as statistical uncertainty in the determined hydration indices, choice of partial atomic charges for the solute atoms, and solute–water interaction potentials adopted in the simulations. The results showed that gauche–trans and gauche–gauche forms are equally favorable for the dimethylphosphate anion with the trans extended form destabilized by hydration. The sodium dimethylphosphate ion pair hydration energetically favors the trans–trans conformation.  相似文献   
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The thermal initiation of the polymerization of styrene has been studied at temperatures from 60–140°C using DPPH as a free radical scavenger. Rates of free radical formation, measured by the decrease in absorbance at 525 nm, are about seven times greater than those obtained from inhibition period measurements. The difference is probably due to the much greater reactivity of trinitrobenzene derivatives towards diradicals from styrene than towards styryl monoradicals. This view is supported by the different behaviour of the AIBN initiated polymerization of styrene in the presence of DPPH. The thermal initiation process has a low efficiency of initiation and the activation energy is 121 kJ/mole. The results strongly support the diradical mechanism for the thermal initiation of styrene polymerization.  相似文献   
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An analytical potential function for the pairwise interaction of methane and water is reported. The function is representative of 225 ab initio quantum-mechanical calculations of the intermolecular interaction using 6–31G self-consistent-field molecular-orbital theory. The statistical parameters of the curve fitting are given and isoenergy contour maps of the interaction energy are presented and discussed.  相似文献   
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In recent TRIUMF experiments, a μ- beam is stopped in a solid hydrogen film with a small fraction of T2. The Ramsauer-Townsend (RT) mechanism allows μt to escape into vacuum with a few eV of energy. To study the emission process, an imaging system was used to determine the position of muon decays. Experimental histograms are in good agreement with a Monte Carlo simulation. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
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An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations.  相似文献   
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