| 1. |
- Persson, Per-Axel, et al.
(författare)
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Enhanced thermal dissociation of optically excited C60 chains.
- 2000
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Ingår i: Europhysics letters. - : EDP Sciences. - 0295-5075 .- 1286-4854. ; 49:5, s. 631-636
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Tidskriftsartikel (refereegranskat)abstract
- The thermal dissociation of C60 polymers has been studied using Raman scattering. The measured dissociation rate depends on the intensity of the 1064 nm NIR excitation, showing that i) the band gap is smaller than 1.17 eV and ii) a radiation-enhanced thermal breakdown path exists in addition to the "normal'' thermal breakdown mechanism. Quantum chemical calculations show that the energy barrier Ea for thermal breakdown is about 40% lower in the first (optically) excited state than in the ground state. This agrees well with the ratio between our radiation-enhanced value $E_{a} = (1.1 \pm 0.02)\,eV$ and values near 1.9 eV measured by purely thermal methods.
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| 2. |
- Sundqvist, Bertil, et al.
(författare)
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Structure and stability of pressure polymerized C60
- 2000
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Ingår i: Molecular Materials: Molecular Crystals and Liquid Crystals Section C, vol. 13. - : Overseas Publishers Association N.V.. ; 13:1-4, s. 117-122
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Konferensbidrag (refereegranskat)abstract
- We discuss the bond energy of the orthorhombic C60 polymer and the structure of the two-dimensional C60 polymers. For the orthorhombic polymer, measurements of the dissociation energy by different methods give results that differ by a factor of two. We show that optical excitations lead to a temporary weakening of the intermolecular bonds and optical measurements thus show a low apparent bond energy. We have also polymerized a single crystal of C60 into two-dimensional phases. X-ray diffraction studies of this crystal have enabled us to determine the stacking sequences of both the tetragonal and the rhombohedral structures.
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| 3. |
- Benkestock, Kurt, et al.
(författare)
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Influence of droplet size, capillary-cone distance and selected instrumental parameters for the analysis of noncovalent protein-ligand complexes by nano-electrospray ionization mass spectrometry
- 2004
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Ingår i: Journal of Mass Spectrometry. - : Wiley. - 1076-5174 .- 1096-9888. ; 39:9, s. 1059-1067
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested in the literature that nano-electrospray ionization (nano-ESI) mass spectrometry better reflects the equilibrium between complex and free protein in solution than pneumatically assisted electrospray ionization (ESI) in noncovalent interaction studies. However, no systematic studies of the effects of ionization conditions have been performed to support this statement. In the present work, different instrumental and sample-derived parameters affecting the stability of noncovalent complexes during analysis by nano-ESI were investigated. In general, increased values of parameters such as drying gas flow-rate, ion-source temperature, capillary tip voltage and buffer concentration lead to a dissociation of ribonuclease A (RNAse)-cytidine 2'-monophosphate (CMP) and cytidine 5'-triphosphate (CTP) complexes. The size of the electrosprayed droplets was shown to be an important issue. Increasing the capillary to cone distance yielded an increased complex to free protein ratio when a hydrophilic ligand was present and the reverse effect was obtained with a hydrophobic ligand. Important in this regard is the degree of sampling of ions originating from late-generation residue droplets, that is, ions present in the droplet bulk. Sampling of these ions increases with longer capillary-cone distance (flight time). Furthermore, when the sample flow-rate was increased by increasing the capillary internal tip i.d. from 4 to 30 mum, a decreased complex to free protein ratio for the RNAse-CTP system was observed. This behavior was consistent with the change in surface to volume ratio for flow-rates between 2 and 100 nl min(-1). Finally, polarity switching between positive and negative ion modes gave a higher complex to free protein ratio when the ligand and the protein had the same polarity.
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| 4. |
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| 5. |
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| 6. |
- Brandén, Henrik, et al.
(författare)
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Discrete Fundamental Solution Preconditioning for Hyperbolic Systems of PDE
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We present a new preconditioner for the iterative solution of linear systems of equations arising from discretizations of systems of first order partial differential equations (PDEs) on structured grids. Such systems occur in many important applications, including compressible fluid flow and electormagnetic wave propagation. The preconditioner is a truncated convolution operator, with a kernel that is a fundamental solution of a difference operator closely related to the original discretization.Analysis of a relevant scalar model problem in two spatial dimensions shows that grid independent convergence is obtained using a simple one-stage iterative method. As an example of a more involved problem, we consider the steady state solution of the non-linear Euler equations in a two dimensional, non-axisymmetric duct. We present results from numerical experiments, verifying that the preconditioning technique again achieves grid independent convergence, both for an upwind discretization and for a centered second order discretization with fourth order artificial viscosity.
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| 7. |
- Brandén, Henrik, et al.
(författare)
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Preconditioners Based on Fundamental Solutions
- 2000
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We consider a new convergence acceleration technique for the iterative solution of linear systems of equations that arise when discretizing partial differential equations. The method is applied to finite difference discretizations, but the ideas and the basic theory apply to other discretizations too. If $E$ is a fundamental solution of a differential operator $P$, we have \mbox$E\ast(Pu)=u$. Inspired by this, we choose the preconditioner to be a discretization of the approximative inverse $K$, given by \[ (Ku)(x)=\int_ØmegaE(x-y)u(y)dy, \qquad x\inØmega\subset\mathdsR^d, \] where Ω is the domain of interest. The operator $K$ is only an approximation of $P^-1$ since we do not integrate over all of $\mathdsR^d$ as for the convolution, and since we impose boundary conditions. Two main advantages of this method are that we can perform analysis before we discretize the operators, and that there is a fast way of applying the preconditioner using FFT. We present analysis showing that if $P$ is a first order differential operator, $KP$ is bounded. The analysis also describes how $K$ differs from $P^-1$. Implementation aspects are considered, and numerical results show grid independent convergence for first order partial differential equations. For the second order convection-diffusion equation convergence is no longer grid independent, a result that is consistent with our theory. However, if the grid is chosen to give a fixed number of grid points within boundary layers, the number of iterations is independent of the physical viscosity parameter.
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| 8. |
- Cedergren, Jan, et al.
(författare)
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Inducible nitric oxide synthase (NOS II) is constitutive in human neutrophils
- 2003
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Ingår i: APMIS. - : Wiley. - 0903-4641 .- 1600-0463. ; 111:10, s. 963-968
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Tidskriftsartikel (refereegranskat)abstract
- The objective was to study the expression of inducible nitric oxide synthase (NOS II) in and NO production by human blood neutrophils and in in vivo exudated neutrophils. Cellular expression of NOS II was evaluated by flow cytometry in whole blood, in isolated blood neutrophils, and in neutrophils obtained by exudation in vivo into skin chambers. Neutrophil NOS II was also demonstrated by Western blotting. Uptake of 3H-labelled L-arginine was studied in vitro and NOS activity measured in a whole cell assay by the conversion of 3H-arginine to 3H-citrulline. In contrast to unseparated blood cells, NOS II was demonstrable both in isolated blood neutrophils and exudated cells. The failure to detect NOS II by flow cytometry in whole blood cells thus proved to be due to the quenching effect of hemoglobin. Western blotting revealed a 130 kD band corresponding to NOS II in isolated blood neutrophils, but detection was dependent on diisopropylfluorophosphate for proteinase inhibition. L-arginine was taken up by neutrophils, but enzymatic activity could not be demonstrated. We conclude that human neutrophils constitutively express NOS II, but that its demonstration by FITC-labelling is inhibited by hemoglobin-mediated quenching in whole blood samples.
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| 9. |
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| 10. |
- McRae, Edward, et al.
(författare)
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Raman light scattering and c-axis resistivity evidence for a pressure-induced stage transformation in PdAl2Cl8 intercalated graphite.
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 62:20, s. 13757-13766
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Tidskriftsartikel (refereegranskat)abstract
- We have examined several samples of first- to third-stage PdAl2Cl8-intercalated graphite under hydrostatic pressures up to 1 GPa. In stage-1 highly oriented pyrolytic graphite–(HOPG) and single-crystal-graphite-based materials, the c-axis resistivity decreases sharply above a few kilobars; pressure release induces a reversible return to the initial value only in the case of the latter sample. Raman spectra taken in situ under pressure on a HOPG-based material show similarly irreversible effects. Analysis of the spectra taken on higher-stage samples leads to the conclusion that hydrostatic pressure beyond a few kilobars increases the density of the intercalate within the graphitic galleries, transforming the initial sample to a higher-stage material. Since there is no loss of intercalate, the overall intercalate-to-host charge transfer remains constant so that the Raman frequency is approximately the same for both first- and second-stage products. This is an unusual situation in which there is thus an apparent lack of Raman signature in spite of the stage change.
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