| 1. |
- Berger, Rolf, et al.
(författare)
-
Diffusion in Copper Sulphides : An experimental study of chalcocite, chalcopyrite and bornite
- 1996
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Diffusion measurements on three copper-containing sulphides have been performed by an electrochemical potentiometric method. -- The diffusion coefficient for chalcocite is in good agreement with values found previously, and a reasonable agreement is also found for chalcopyrite and bornite when our data are compared with values acquired at much higher temperatures with a different technique. The activation energies are remarkably similar for the three sulphides, considering that their relative errors are of a 10% magnitude, which indicates that the bonding strengths and the diffusion mechanisms are similar.
|
|
| 2. |
- Edvinsson, Tomas, et al.
(författare)
-
Cluster identification and percolation analysis using a recursive algorithm
- 1999
-
Ingår i: Molecular Simulation. - : Informa UK Limited. - 0892-7022 .- 1029-0435. ; 23:3, s. 169-190
-
Tidskriftsartikel (refereegranskat)abstract
- A recursive algorithm for sampling properties of physical clusters such as size distribution andpercolation is presented. The approach can be applied to any system with periodic boundaryconditions, given a spatial definition of a cluster. We also introduce some modifications in thealgorithm that increases the efficiency considerably if one is only interested in percolationanalysis. The algorithm is implemented in Fortran 90 and is compared with a number ofiterative algorithms. The recursive cluster identification algorithm is somewhat slower than theiterative methods at low volume fraction but is at least as fast at high densities. The percolationanalysis, however, is considerably faster using recursion, for all systems studied. We also notethat the CPU time using recursion is independent on the static allocation of arrays, whereas theiterative method strongly depends on the size of the initially allocated arrays.
|
|
| 3. |
- Feng, Xiaolong, 1961-
(författare)
-
Estimating molecular conformations by solid-state NMR spectroscopy
- 1998
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Our understanding of structure-function relationships in biological systems demands new and more sophisticated methods for examining molecular structure. This thesis presents an effort of methodology development for molecular structure determination by solid-state NMR spectroscopy and applications to biological systems.Rotational Resonance NMR is established as a major tool for extracting molecular structural information in solids. Some further aspects of the technique are explored. The technique is applied to obtain the binding conformation of an inhibitor, TMPIP, bound to gastric H+/K+-ATPase, an ab heterodimer with a molecular weight of over 150 kDa.A novel solid-state NMR method for the determination of the torsional angle of a 13C-labeled H-C-C-H moiety is developed. A detailed theoretical introduction of the method is presented. The technique has been applied to determine the H-C10-C11-H torsional angle of the retinylidene chromophore in bovine rhodopsin, a 41 kDa integral membrane protein, and its photo-intermediate metarhodopsin-I.A new solid-state NMR method is developed. It may be used to estimate the Ramachandran ( angle in a protein backbone chain. A detailed theory is presented. It is demonstrated on an isotopically labeled tripeptide.
|
|
| 4. |
- Krogh Andersen, A.M., et al.
(författare)
-
Structural Aspects of the Dehydration and Dehydroxylation of Layered γ-Titanium Phosphate, γ-Ti(PO4)(H2PO4)⋅2H2O.
- 1998
-
Ingår i: Inorganic chemistry. - : American Chemical Society. - 1520-510X .- 0020-1669. ; 37:17, s. 4313-4320
-
Tidskriftsartikel (refereegranskat)abstract
- The thermal transformations of γ-titanium phosphate, γ-Ti(PO4)(H2PO4)·2H2O, have been studied using thermogravimetric analysis, differential scanning calorimetry, X-ray powder diffraction, and temperature-resolved in-situ powder diffraction. The transformation sequence goes from γ-Ti(PO4)(H2PO4)·2H2O over a new partially dehydrated form γ‘-Ti(PO4)(H2PO4)·(2−x)H2O (x 1) to the anhydrous form β-Ti(PO4)(H2PO4) and then through a two-step condensation process where layered titanium pyrophosphate, Ti(PO4)(H2P2O7)0.5, is formed first and finally cubic titanium pyrophosphate TiP2O7. The dehydration of γ-Ti(PO4)(H2PO4)·2H2O and the dehydroxylation/condensation process from β-Ti(PO4)(H2PO4) to layered titanium pyrophosphate,Ti(PO4)(H2P2O7)0.5, was followed in-situ. A new partially dehydrated phase, γ‘-Ti(PO4)(H2PO4)·(2−x)H2O (x 1), which forms at approximately 50 °C has been detected and characterized. The unit cell is monoclinic with the lattice parameters a = 23.670(1) Å, b = 6.264(1) Å, c = 5.036(1) Å, β = 102.41(1)°, and Z = 4. Layered titanium pyrophosphate, Ti(PO4)(H2P2O7)0.5, which forms at 375 °C has been characterized. The unit cell is monoclinic with lattice parameters a = 16.271(3) Å, b = 6.319(1) Å, c = 5.122(1) Å, β = 90.59(2)°, and Z = 4.
|
|
| 5. |
- Bauschlicher, C.W., et al.
(författare)
-
A further study of the products of scandium and dioxygen reactions
- 1999
-
Ingår i: Journal of Physical Chemistry A. - 1089-5639 .- 1520-5215. ; 103:28, s. 5463-5467
-
Tidskriftsartikel (refereegranskat)abstract
- The products of the reaction of Sc and dioxygen have been reinvestigated. By adding the electron-trapping molecule CCl4 additional information about the IR spectra has been obtained, as well as the observation of new bands. New ab initio calculations are also performed on possible products of the Sc plus O-2 reaction. The previously observed band at 722.5 cm(-1) is assigned as the b(2) mode of ScO2-. Bands arising from ScO+, Sc(O-2)(+), and(O-2)ScO are also assigned. We are still unable to assign any bands to OScO. The problems associated with the computational study of ScO2 are discussed.
|
|
| 6. |
- Snis, Anders, et al.
(författare)
-
Characterizations of (NO)(3)- and N3O2- molecular anions
- 1999
-
Ingår i: Chemical Physics Letters. - 0009-2614. ; 305:3-4, s. 285-292
-
Tidskriftsartikel (refereegranskat)abstract
- Isomers of (NO)3− are characterized by means of B3LYP density functional theory and the wavefunction-based CASPT2 method. Stabilities, vertical electron detachment energies (VDEs), vertical electron excitation energies (VEEs), and vibration frequencies are determined. Experimental isotope shifts in the IR spectrum of (NO)3− and theory were previously employed to determine the structure of an N–N–N connected anion. Further support for this assignment is obtained in the present study by comparing experimental and theoretical VDEs and VEEs. A parallel analysis of a w-shaped N3O2− molecular anion along the above lines is performed for reference, as a comprehensive understanding of the two systems is sought.
|
|
| 7. |
- Snis, Anders, et al.
(författare)
-
N2O2, N2O2- and N2O22-: structures, energetics and N-N bonding
- 1997
-
Ingår i: Chemical Physics. - 0301-0104. ; 221:1-2, s. 1-10
-
Tidskriftsartikel (refereegranskat)abstract
- The density functional theory and the ab initio quantum chemistry methods, Becke3LYP and CASPT2, have been employed to determine structures and energetics of neutral and anionic N2O2 species. When going from a neutral NO dimer to an anionic species the N---N bond lengths decrease drastically and the corresponding N---N frequencies increase. The relative stabilities of the different N2O2− isomers suggest an ONNO structure in a Trans configuration to be the most stable mono valent anion. The formation energies of 1.4–1.7 eV relative to the NO + NO− asymptote are in agreement with experiments. Excitation energies are determined and specific formation channels for three N2O2− isomers are discussed. The hyponitrite ion, N2O22−, is also studied. Its total energy is 2.7–2.8 eV above the total energy of two NO−. In order to connect to an experimental study of NO adsorption on MgO the ability of two NO molecules to form a complex with Mg and Mg+ is investigated.
|
|
| 8. |
|
|
| 9. |
- Bagger-Jörgensen, Håkan
(författare)
-
Polymer effects on microemulsions and lamellar phases
- 1997
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main part of this thesis deals with the effects of adsorbing and non-adsorbing polymers when mixed with microemulsion droplets and bilayers in a lamellar phase. The phase behaviour, microstructure and interactions in a nonionic surfactant/ water/ oil-system, comprising penta ethylene oxide dodecyl ether (C12E5) and decane, was investigated. The microemulsion phase was studied by small angle neutron scattering (SANS), and was shown to contain spherical oil-swollen micelles with a radius =80Å, having a low size polydispersity. The interactions between the micelles basically resemble that between hard spheres, as was shown by osmometry. The surfactant film was made weakly charged by incorporating an ionic surfactant, and the impact on phase behaviour and interactions was studied. The introduction of electrostatics affected both droplet stability and interactions, which are well described by the Poisson-Boltzmann equation. The main part of the experimental work concerns the addition of polymer and polyelectrolyte to the surfactant/water/oil system. Two types of polymers were used, poly ethylene oxide (PEO) and poly sodium acrylate (PA), and their hydrophobically modified analogues, HM-PEO and HMPA, onto which hydrophobic octadecyl chains had been anchored. While PEO and PA are non-adsorbing with respect to the surfactant film, HM-PEO and HMPA are adsorbing. Polymeric additives in most cases changed the phase behaviour. Moreover, in the case of HM-PEO and HMPA also the droplet interactions and self-diffusion were influenced, as was evidenced by SANS, NMR self-diffusion and rheology measurements. The lamellar (La) phase was studied with small angle X-ray scattering (SAXS). HM-PEO and HMPA dissolve in the La phase and lower the swelling capacity. PA and PEO are not soluble in the La phase. This polymer-incompatibility was used in an osmotic stress study of the La phase, the results of which gave support for the concentration dependence of the Helfrich undulation force and providing a value for the bilayer bending modulus.
|
|
| 10. |
- Bergman, Dan, 1970-
(författare)
-
Computer simulation of topological and spatial structure in water and aqueous solutions
- 1999
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis concerns molecular-dynamics and expanded-ensemble simulation of topological and spatial structure in water and aqueous solutions.First, methods for analysis of molecular pair configurations using angularly resolved density distributions were considered. It was shown that these distributions expose major features of liquid structure and that they can be used to define the hydrogen bond. Second, a method was developed for analysis of hydrogen-bond network topology. It characterizes networks in terms of the local bond patterns surrounding the water molecules and in terms of loops and chains of directed bonds.The methods developed have been applied to pure water, to water--acetonitrile mixtures and to charged Lennard-Jones spheres dissolved in water. Solvation structures in aqueous solutions of methylamine and tert-butyl alcohol have also been considered. The main results are: (a) In pure water, there is proton ordering around short loops, but not along chains. (b) The hydrogen-bond network in water--acetonitrile mixtures with acetonitrile mole fractions x=0.1, 0.5 and 0.9 have been characterized. As x increases from 0.1 to 0.9, the network is depleted of crosslinks, the proton ordering along chains increases and the most probable loop length decreases. For x=0.5 and 0.9 large water clusters form. (c) The hydration structures surrounding charged Lennard-Jones solutes corresponding to extrema in the solvation entropy have been characterized. Of the two solutes corresponding to the maxima, one acts as a double proton-donor and the other as a double proton-acceptor. The solute corresponding to the minimum enhances the water--water correlations. Further, the orientational and the radial parts of the two-body solute--water entropy have been calculated. The orientational part has a single maximum, whereas the radial part maintains the bimodal form of the full solvation entropy.
|
|
