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Träfflista för sökning "AMNE:(NATURAL SCIENCES Physical Sciences) ;lar1:(hv)"

Sökning: AMNE:(NATURAL SCIENCES Physical Sciences) > Högskolan Väst

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1.
  • Jenkins, Samantha, 1967-, et al. (författare)
  • The role of hydrogen bonding in nanocolloidal amorphous silica particles in electrolyte solutions
  • 2009
  • Ingår i: Journal of colloid and interface science. - : Elsevier BV. - 1095-7103 .- 0021-9797.
  • Tidskriftsartikel (refereegranskat)abstract
    • Explicit solvent (water) molecular dynamics simulations were undertaken containing three pairs of amorphous silica nanoparticles, having diameters of 2.0nm, 2.4nm and 2.8nm, respectively. Mean forces acting between the silica nanoparticles were calculated in a background electrolyte, i.e., NaCl at four different concentrations. Dependence of the inter-particle potential of mean force on the center of mass separation, silicon to sodium ratio (Si:Na(+)), background electrolyte concentration, number of hydrogen bonds directly linking pairs of silica nanoparticles and the density of charged surface sites, are calculated. The pH was indirectly accounted for via the ratio of silicon to sodium used in the simulations. The close relationship between the variation of the number of hydrogen bonds between the pairs of silica nanoparticles and the inter-particle potential of mean force indicates that the degree of inter-particle hydrogen bonding quantifies, for a given size of nanoparticle, the degree of nanoparticle 'stickiness'. Simulations also show that the number of hydrogen bonds between the charged surface (O(-)) sites and the surrounding water molecules increases with increase in charged sites, in agreement with the interaction behavior of silica nanoparticles usually seen in experiments.
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5.
  • Eshagh, Mehdi, 1977-, et al. (författare)
  • Perturbations in orbital elements of a low earth orbiting satellite
  • 2007
  • Ingår i: Journal of the Earth and Space Physics. - : Institute of Geophysics, Tehran. - 1025-8647. ; 33:1, s. 1-12
  • Tidskriftsartikel (refereegranskat)abstract
    • The main point of this paper is to evaluate the perturbations in orbital elements of a low Earth orbiting satellite. The outcome of a numerical orbit integration process is the position and velocity vectors of satellite in an inertial coordinate system. The velocity and position vectors are converted into the corresponding orbital elements. Perturbations in a satellite motion affect the orbital elements in the sense of Keplerian motion. In this paper after introducing the perturbing forces acting on a satellite, the method of converting the position and velocity into the orbital elements is presented, and finally the perturbations in orbital elements of the low Earth orbiting satellite of CHAMP are evaluated. The numerical results show that, disregarding the geopotential perturbing forces, the air drag is the most predominant among other perturbing forces: rotational deformation, solar radiation, third body effect, solid Earth tide, ocean tide, and general relativity arranged by their magnitude respectively.
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6.
  • Jenkins, Samantha, 1967-, et al. (författare)
  • Molecular dynamics simulation of nanocolloidal amorphous silica particles : Part I.
  • 2007
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:22, s. 224711-
  • Tidskriftsartikel (refereegranskat)abstract
    • Explicit molecular dynamics simulations were applied to a pair of amorphous silica nanoparticles in aqueous solution, with diameter of 4.4 nm and with four different background electrolyte concentrations, to extract the mean force acting between the two silica nanoparticles. Dependences of the interparticle forces on the separation and the background electrolyte concentration were demonstrated. The nature of the interaction of the counterions with charged silica surface sites (deprotonated silanols) was investigated. A "patchy" double layer of adsorbed sodium counterions was observed. Dependences of the interparticle potential of mean force on the separation and the background electrolyte concentration were demonstrated. Direct evidence of the solvation forces is presented in terms of changes of the water ordering at the surfaces of the isolated and double nanoparticles. The nature of the interaction of the counterions with charged silica surface sites (deprotonated silanols) was investigated in terms of quantifying the effects of the number of water molecules separately inside each pair of nanoparticles by defining an impermeability measure. A direct correlation was found between the impermeability (related to the silica surface "hairiness") and the disruption of water ordering. Differences in the impermeability between the two nanoparticles are attributed to differences in the calculated electric dipole moment.
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7.
  • Jenkins, Samantha, 1967-, et al. (författare)
  • Molecular dynamics simulation of nanocolloidal amorphous silica particles: Part III
  • 2009
  • Ingår i: The Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 130
  • Tidskriftsartikel (refereegranskat)abstract
    • Explicit-solvent molecular dynamics simulations were applied to four pairs of amorphous silica nanoparticles, two pairs having a diameter of 2.0 nm and two pairs with diameter 3.2 nm. The silica nanoparticles were immersed in a background electrolyte consisting of Ca2+ and Cl− ions and water and mean forces acting between the pair of silica nanoparticles were extracted at four different background electrolyte concentrations. The pH was indirectly accounted for via the ratio of silicon to sodium used in the simulations. Dependence of the interparticle potential of mean force on the center-of-mass separation and the silicon to sodium ratio (5:1 and 20:1) is demonstrated. A Si:Na+ ratio of 5:1 gave more repulsive interparticle potentials and lower numbers of internanoparticle or “bridging” hydrogen bonds. Conversely a Si:Na+ ratio of 20:1 yielded more attractive potentials and higher numbers of bridging hydrogen bonds. The nature of the interaction of the counterions with charged silica surface sites (deprotonated silanols) was also investigated. The effect of the sodium double layer on water ordering was observed. The number of water molecules trapped inside the nanoparticles was investigated, and at the highest background ionic concentrations were found to consistently behave in accordance with there being an osmotic pressure. This study highlights the effect of divalent (Ca2+) background ions on the interparticle potentials compared with previous work using monovalent (Na+) background ions. Mechanisms of coagulation and the stability of silica nanocolloids found from this work appear to be in agreement with findings from experiments described in the literature.
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8.
  • Jenkins, Samantha, 1967-, et al. (författare)
  • Molecular dynamics simulations of nanocolloidal amorphous silica particles: Part II
  • 2008
  • Ingår i: The Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:16
  • Tidskriftsartikel (refereegranskat)abstract
    • Explicit molecular dynamics simulations were applied to a pair of amorphous silica nanoparticles with diameter of 3.2 nm immersed in a background electrolyte. Mean forces acting between the pair of silica nanoparticles were extracted at four different background electrolyte concentrations. The dependence of the interparticle potential of mean force on the separation and the silicon to sodium ratio, as well as on the background electrolyte concentration, are demonstrated. The pH was indirectly accounted for via the ratio of silicon to sodium used in the simulations. The nature of the interaction of the counterions with charged silica surface sites (deprotonated silanols) was also investigated. The effect of the sodium double layer on the water ordering was investigated for three Si:Na+ ratios. The number of water molecules trapped inside the nanoparticles was investigated as the Si:Na+ ratio was varied. Differences in this number between the two nanoparticles in the simulations are attributed to differences in the calculated electric dipole moment. The implications of the form of the potentials for aggregation are also discussed.
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9.
  • Frost, Robert J. W., et al. (författare)
  • Preliminary results from a study of luminescent materials : For application in the beam imaging system at the ESS
  • 2023
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier. - 0168-583X .- 1872-9584. ; 540, s. 227-233
  • Tidskriftsartikel (refereegranskat)abstract
    • As part of the development of the beam imaging system at the European Spallation Source, luminescent screens have been fabricated by the flame spraying of scintillating materials onto stainless steel backings. A total of seven screens were produced, three of chromia alumina (Al2O3:Cr), two of YAG (Y3Al5O12:Ce) and two of a 50/50 mix of these. The properties of these screens under proton irradiation were evaluated using a2.55 MeV proton beam at currents of up to 10 μA. Irradiation times were up to 25 h per sample, during which luminescence-, spectrographic-, thermal- and current-data was sampled at a rate of 1 Hz. Preliminary results of these measurements are reported here; with a quantitative analysis presented for one of the chromia alumina screens and a qualitative comparison of all three material types. The luminescent yield for chromia alumina was determined to be around 2000 photons/MeV for a virgin screen, and was found to drop to 1.5% after 167 mC of proton irradiation. A recovery of the luminescence of chromia alumina to >60% was observed after beam current was reduced for an 8 h period. Observations indicate that the YAG and mixed composition screens retain higher luminescence than the chromia alumina even at temperatures of over 200 ◦C. It is indicated that the luminescence from YAG feeds the R-lines of chromia alumina in the mixed composition screens. 
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10.
  • Jenkins, Samantha, 1967-, et al. (författare)
  • The chemical character of very high pressure ice phases.
  • 2006
  • Ingår i: Proceedings of the 11th International Conference on the Physics and Chemistry of Ice. - Cambridge : RSC publishing. - 9780854043507 ; , s. 265-273
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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