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Sökning: LAR1:gu > Tidskriftsartikel > Chalmers tekniska högskola > (2005-2009)

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1.
  • Abbas, Zareen, 1962, et al. (författare)
  • From restricted towards realistic models of salt solutions: Corrected Debye–Hückel theory and Monte Carlo simulations
  • 2007
  • Ingår i: Journal of Mathematical Fluid Mechanics. - : Elsevier BV. - 1422-6952 .- 1422-6928 .- 0378-3812. ; 260:2, s. 233-247
  • Tidskriftsartikel (refereegranskat)abstract
    • The properties of bulk salt solutions over wide concentration ranges are explored by a combination of simple physical theory and Monte Carlo (MC) simulations. The corrected Debye–Hückel (CDH) theory which incorporates ion size effects in a linear response approximation is extended to yield free energy and other thermodynamic properties by integration of the chemical potential over concentration. Charging integration which is usually used to obtain an electrostatic contribution of total free energy of electrolytes is avoided in this new direct approach. MC simulations are performed with a modified Widom particle insertion method, which also provides directly the ionic activity coefficients. The validity of the CDH theory is tested by comparison with the MC simulation data for 1:1, 2:1, 2:2 and 3:1 restricted primitive model (RPM) electrolytes over a wide concentration range and at various ion sizes. Mean ionic activity and osmotic coefficients calculated by the CDH theory in RPM approximation of electrolyte are fitted to experimental data by adjusting only a mean ionic diameter. Good fits up to 1 molal (m) concentration are obtained for a large number of salt solutions. MC simulations data for unrestricted primitive model (UPM) of 1:1 and 2:1 electrolytes are also fitted to the experimental data by varying the cation radius while keeping the anion radius fixed at a crystallographic value. The success of this approach is found to be salt specific. For example good fits up to 2 and 3.5 m concentrations were obtained for LiCl and LiBr, respectively. However in the case of less dissociated salts such as NaCl and KI the experimental data could only be fitted up to one molal concentration. Possibility of extending the applicability range of the CDH theory to concentrations >2 m is explored by including a concentration dependent dielectric constant as measured in experiments. Mean ionic activity coefficients for a number of salts could successfully be fitted up to 3 m concentration by adjusting only a mean ionic diameter. Difficulties encountered in simultaneously fitting the mean ionic activity and osmotic coefficients at salt concentrations >2 m are discussed.
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2.
  • Abbas, Zareen, 1962, et al. (författare)
  • Monte Carlo Simulations of Salt Solutions: Exploring the Validity of Primitive Models
  • 2009
  • Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 113:17, s. 5905-5916
  • Tidskriftsartikel (refereegranskat)abstract
    • An extensive series of Monte Carlo (MC) simulations were performed in order to explore the validity of simple primitive models of electrolyte solutions and in particular the effect of ion size asymmetry on the bulk thermodynamic properties of real salt solutions. Ionic activity and osmotic coefficients were calculated for 1:1, 2:1, and 3:1 electrolytes by using the unrestricted primitive model (UPM); i.e., ions are considered as charged hard spheres of different sizes dissolved in a dielectric continuum. Mean ionic activity and osmotic coefficients calculated by the MC simulations were fitted simultaneously to the experimental data by adjusting only the cation radius while keeping the anion radius fixed at its crystallographic value. Ionic radii were further optimized by systematically varying the cation and anion radii at a fixed sum of ionic radii. The success of this approach is found to be highly salt specific. For example, experimental data (mean ionic activity and osmotic coefficients) of salts which are usually considered as dissociated such as HCl, HBr, LiCl, LiBr, LiClO4, and KOH were successfully fitted up to 1.9, 2.5, 1.9, 3, 2.5, and 4.5 M concentrations, respectively. In the case of partially dissociated salts such as NaCl, the successful fits were only obtained in a more restricted concentration range. Consistent sets of the best fitted cation radii were obtained for acids, alkali, and alkaline earth halides. A list of recommended ionic radii is also provided. The reliability of the optimized ionic radii was further tested in simulations of the osmotic coefficients of LiCl−NaCl−KCl salt mixtures. A very good agreement between the simulated and experimental data was obtained up to ionic strength of 4.5 M.
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3.
  • Abbas, Zareen, 1962, et al. (författare)
  • Size-Dependent Surface Charging of Nanoparticles
  • 2008
  • Ingår i: J of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:15, s. 5715-5723
  • Tidskriftsartikel (refereegranskat)abstract
    • Experimental interest in the possible curvature dependence of particle charging in electrolyte solutions is subjected to theoretical analysis. The corrected Debye-Hückel theory of surface complexation (CDH-SC) and Monte Carlo (MC) simulation are applied to investigate the dependence of surface charging of metal oxide nanoparticles on their size. Surface charge density versus pH curves for spherical metal oxide nanoparticles in the size range of 1-100 nm are calculated at various concentrations of a background electrolyte. The surface charge density of a nanoparticle is found to be highly size-dependent. As the particle diameter drops to below 10 nm there is considerable increase in the surface charge density as compared with the limiting values seen for particles larger than 20 nm. This increase in the surface charge density is due to the enhanced screening efficiency of the electrolyte solution around small nanoparticles, which is most prominent for particles of diameters less than 5 nm. For example, the surface charge densities calculated for 2 nm particles at 0.1 M concentration are very close to the values obtained for 100 nm particles at 1 M concentration. These predictions of the dependence of surface charge density on particle size by the CDH-SC theory are in very good agreement with the corresponding results obtained by the MC simulations. A shift in the pH value of the point of zero charge toward higher pH values is also seen with a decreasing particle size.
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4.
  • Abel, Andreas, 1974, et al. (författare)
  • Normalization by Evaluation for Martin-Löf Type Theory with Equality Judgements
  • 2007
  • Ingår i: Proceedings of 22nd IEEE Annual Symposium on Logic in ComputerScience, Wroclaw, Poland, July 2007.. - : IEEE. - 1043-6871. - 0769529089 ; , s. 3-12
  • Tidskriftsartikel (refereegranskat)abstract
    • The decidability of equality is proved for Martin-Löf type theory with a universe a la Russell and typed beta-eta-equality judgements. A corollary of this result is that the constructor for dependent function types is injective, a property which is crucial for establishing the correctness of the type-checking algorithm. The decision procedure uses normalization by evaluation, an algorithm which first interprets terms in a domain with untyped semantic elements and then extracts normal forms. The correctness of this algorithm is established using a PER-model and a logical relation between syntax and semantics.
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5.
  • Abel, Andreas, 1974, et al. (författare)
  • Untyped algorithmic equality for Martin-Löf's logical framework with surjective pairs
  • 2007
  • Ingår i: Fundamenta Informaticae. - 0169-2968. ; 77:4, s. 345-395
  • Tidskriftsartikel (refereegranskat)abstract
    • Martin-Löf's Logical Framework is extended by strong Sigma-types and presented via judgmental equality with rules for extensionality and surjective pairing. Soundness of the framework rules is proven via a generic PER model on untyped terms. An algorithmic version of the framework is given through an untyped beta eta-equality test and a bidirectional type checking algorithm. Completeness is proven by instantiating the PER model with eta-equality on beta-normal forms, which is shown equivalent to the algorithmic equality.
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6.
  • Abel, Frida, 1974, et al. (författare)
  • Imbalance of the mitochondrial pro- and anti-apoptotic mediators in neuroblastoma tumours with unfavourable biology.
  • 2005
  • Ingår i: European journal of cancer (Oxford, England : 1990). - : Elsevier BV. - 0959-8049. ; 41:4, s. 635-46
  • Tidskriftsartikel (refereegranskat)abstract
    • It has been proposed that a lack of apoptosis plays an important role in neuroblastoma (NB) progression. We therefore screened cDNA array filters, including 198 apoptotic genes, in order to identify mRNA transcripts that are differentially expressed in tumours with unfavourable versus favourable biology. Twenty-one genes were analysed further using real-time reverse-transcriptase-polymerase chain reaction (RT-PCR). Significantly lower levels of DNCL1 (PIN; P(c)(corrected) = 0.0054) and NTRK1 (TrkA; P(c) = 0.039) were found in NB tumours with unfavourable biology. In addition, BID, BCL2, APAF1, CASP2, CASP3 and CASP9 were found to be preferentially expressed in tumours with favourable biology, whereas CDKN1A (p21), IL2RA, and MCL1, were found to be preferentially expressed in NB tumours with unfavourable biology. In conclusion, mRNA levels of transcripts encoding pro-apoptotic mediators of the mitochondrial apoptotic pathway were found to be expressed to a lower extent in tumours with unfavourable biology. Our data also suggest that the mitochondrial pathway is suppressed in advanced stages of NB tumours, due to an imbalance between anti-apoptotic and pro-apoptotic mediators which is a finding that may have therapeutic significance.
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7.
  • Abrahamsson, Erik, 1974, et al. (författare)
  • A new reaction path for the C + NO reaction: dynamics on the 4A'' potential-energy surface.
  • 2008
  • Ingår i: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 10:30, s. 4400-9
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a new reaction path without significant barriers for the C + NO reaction, forming ground state N((4)S) and CO. Electronic structure (CASPT2) calculations have been performed for the two lowest (4)A'' states of the CNO system. The lowest of these states shows no significant barriers against reaction in the C + NO or O + CN channels. This surface has been fitted to an analytical function using a many-body expansion. Using this surface, and the previously published (2)A' and (2)A'' surfaces [Andersson et al., Phys. Chem. Chem. Phys., 2000, 2, 613; Andersson et al., Chem. Phys., 2000, 259, 99], we have performed quasiclassical trajectory (QCT) calculations, obtaining rate coefficients for the C((3)P) + NO(X(2)Pi) --> CO(X(1)Sigma(+)) + N((4)S,(2)D) and C((3)P) + NO(X(2)Pi) --> O((3)P) + CN(X(2)Sigma(+)) reactions. We have also simulated the crossed molecular beam experiments of Naulin et al. [Chem. Phys., 1991, 153, 519] The inclusion of the (4)A'' surface in the QCT calculations gives excellent agreement with experiments. This is the first time an adiabatic pathway from C((3)P) + NO(X(2)Pi) to CO(X(1)Sigma(+))+N((4)S) has been reported.
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8.
  • Abrahamsson, Erik, 1974, et al. (författare)
  • Classical and quantum dynamics of the O+CN reaction
  • 2006
  • Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 324:2-3, s. 507-514
  • Tidskriftsartikel (refereegranskat)abstract
    • Electronic structure (CASPT2) calculations have been performed for the (2)Pi and (4)Sigma(-) states of the NCO system. To create the potential energy surfaces, the generalized discrete variable representation (GDVR) method has been used. Wave packet calculations have been performed for the collinear O + CN reaction on both surfaces. These are the first reported quantum dynamics calculations on this reaction. State-to-state reaction probabilities are presented. On the (2)Pi surface, which has an almost 6 eV deep well, we obtain structure in the reaction probabilities at low kinetic energies but at higher energies they are smooth. The (4)Sigma(-) surface is highly exoergic and vibrationally non-adiabatic dynamics is observed. The (4)Sigma(-) surface has an early barrier and as a result we find that translational energy more efficiently promotes the reaction than vibrational energy does. The wave packet results are compared with QCT results. Generally the agreement is good as would be expected but some notable differences are found, particularly for reaction out of the vibrational ground state. (c) 2005 Elsevier B.V. All rights reserved.
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9.
  • Abrahamsson, Erik, 1974, et al. (författare)
  • Dynamics of the O + CN Reaction and N + CO Scattering on Two Coupled Surfaces
  • 2009
  • Ingår i: J. Phys. Chem. A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 113:52, s. 14824-14830
  • Tidskriftsartikel (refereegranskat)abstract
    • Spin−orbit coupling between the two collinear 2Π and 4Σ− potential energy surfaces for the NCO system are calculated using the RASSI method with CASSCF wave functions as basis set. The GDVR method has been used to interpolate a spin−orbit coupling surface. Wave packet and quasi-classical trajectory surface hopping calculations have been performed and compared for both the O(3P) + CN(X2Σ+) → N(4S) + CO(X1Σ+) reaction and for electronically inelastic scattering in the N + CO channels. The O + CN nonadiabatic reaction probabilities are small. The wavepacket study gives a resonance structure. Also for the N + CO electronically inelastic scattering the wave packet calculations give a distinct resonance structure with peak transition probabilities up to around 10%, which is somewhat lower than the trajectory surface hopping results.
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10.
  • Abramowicz, Marek A, 1945, et al. (författare)
  • No Observational Constraints from Hypothetical Collisions of Hypothetical Dark Halo Primordial Black Holes with Galactic Objects
  • 2009
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 705:1, s. 659-669
  • Tidskriftsartikel (refereegranskat)abstract
    • It was suggested by several authors that hypothetical primordial black holes (PBHs) may contribute to the dark matter (DM) in our Galaxy. There are strong constraints based on the Hawking evaporation that practically exclude PBHs with masses m pbh ~ 1015to1016 g and smaller as significant contributors to the Galactic DM. Similarly, PBHs with masses greater than about 1026 g are practically excluded by the gravitational lensing observation. The mass range between 1016 g
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