| 1. |
- Black, John H, 1949
(författare)
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Chemistry and cosmology
- 2006
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 133, s. 27-32
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Tidskriftsartikel (refereegranskat)abstract
- The simplest elements, hydrogen and helium, offer a remarkably rich chemistry, which has controlled crucial features of the early evolution of the universe. Theoretical models of the origin of structure (stars, galaxies, clusters of galaxies, etc.) now incorporate this chemistry in some detail. In addition to the origin of structure, cosmologists are concerned with observational tests of competing world models. Primordial chemistry may give rise to some of the earliest departures from thermodynamic equilibrium in the universe. These effects may be observable as broad-band spectroscopic distortions of the cosmic background radiation, which otherwise exhibits a nearly perfect blackbody spectrum. The chemical history of the expanding universe is followed through a detailed calculation of the evolution of the abundances of H, H+, H, H2, H+2, H+3, and other minor species. It is shown that continuous absorption by the small concentration of H can produce a distortion in the cosmic background spectrum with a maximum at a frequency near /c = 9 cm1 (wavelength 1.1 mm). The predicted effect lies only a factor of 5 below current limits. Its detection would provide an important test of our understanding of the recombination epoch of the universe.
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| 2. |
- Buckle, J. V., et al.
(författare)
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Observations of chemical differentiation in clumpy molecular clouds
- 2006
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 133, s. 63 - 82
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Tidskriftsartikel (refereegranskat)abstract
- We have extensively mapped a sample of dense molecular clouds (L1512, TMC-1C, L1262, Per7, L1389, L1251E) in lines of HC 3 N, CH 3 OH, SO and C 18 O. We demonstrate that a high degree of chemical differentiation is present in all of the observed clouds. We analyse the molecular maps for each cloud, demonstrating a systematic chemical differentiation across the sample, which we relate to the evolutionary state of the cloud. We relate our observations to the cloud physical, kinematical and evolutionary properties, and also compare them to the predictions of simple chemical models. The implications of this work for understanding the origin of the clumpy structures and chemical differentiation observed in dense clouds are discussed. © The Royal Society of Chemistry 2006.
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| 3. |
- Geppert, W.D., et al.
(författare)
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Dissociative recombination of protonated methanol
- 2006
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Ingår i: Faraday discussions. - Cambridge : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 133, s. 177-190
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Tidskriftsartikel (refereegranskat)abstract
- The branching ratios of the different reaction pathways and the overall rate coefficients of the dissociative recombination reactions of CH3OH2+ and CD3OD2+ have been measured at the CRYRING storage ring located in Stockholm, Sweden. Analysis of the data yielded the result that formation of methanol or deuterated methanol accounted for only 3 and 6% of the total rate in CH3OH2+ and CD3OD2+, respectively. Dissociative recombination of both isotopomeres mainly involves fragmentation of the C - O bond, the major process being the three-body break-up forming CH3, OH and H (CD3, OD and D). The overall cross sections are best fitted by sigma = 1.2 +/- 0.1 x 10(-15) E-1.15 +/- 0.02 cm(2) and sigma = 9.6 +/- 0.9 x 10(-16) E-1.20 +/- 0.02 cm(2) for CH3OH2+ and CD3OD2+, respectively. From these values thermal reaction rate coefficients of k(T) = 8.9 +/- 0.9 x 10(-7) (T/300) (- 0.59 +/- 0.02) cm(3) s(-1) (CH3OH2+) and k( T) = 9.1 +/- 0.9 x 10(-7) (T/ 300) (- 0.63 +/- 0.02) cm(3) s(-1)(CD3OD2+) can be calculated. A non-negligible formation of interstellar methanol by the previously proposed mechanism via radiative association of CH3+ and H2O and subsequent dissociative recombination of the resulting CH3OH2+ ion to yield methanol and hydrogen atoms is therefore very unlikely.
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| 4. |
- Gotter, M, et al.
(författare)
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Fusion and fission of fluid amphiphilic bilayers
- 2005
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1364-5498. ; 129, s. 327-338
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Tidskriftsartikel (refereegranskat)abstract
- The system water-oil (n-decane)-nonionic surfactant (C12E5) forms bilayer phases in a large concentration region, but, for a given oil-to-surfactant ratio, only in a narrow temperature range. In addition to the anisotropic lamellar phase (L-alpha) there is also, at slightly higher temperature, a sponge or L-3-phase where the bilayers build up an isotropic structure extending macroscopically in three dimensions. In this phase the bilayer mid-surface has a mean curvature close to zero and a negative Euler characteristic. In this paper we study how the bilayers in the lamellar and the sponge phase respond dynamically to sudden temperature changes. The monolayer spontaneous curvature depends sensitively on temperature and a change of temperature thus provides a driving force for a change in bilayer topology. The equilibration therefore involves kinetic steps of fusion/fission of bilayers. Such dynamic processes have previously been monitored by temperature jump experiments using light scattering in the sponge phase. These experiments revealed an extraordinarily strong dependence of the relaxation time on the bilayer volume fraction phi. At phi<0.1 the relaxation times are so slow that experiments using deuterium nuclear magnetic resonance (H-2-NMR) appear feasible. We here report on the first experiments concerned with the dynamics of the macroscopic phase transition sponge-lamellae by H-2-NMR. We find that the sponge-to-lamellae transition occurs through a nucleation process followed by domain growth involving bilayer fission at domain boundaries. In contrast, the lamellae-to-sponge transformation apparently occurs through a succession of uncorrelated bilayer fusion events.
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| 5. |
- Ikkala, O., et al.
(författare)
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Solid state nanofibers based on self-assemblies : From cleaving from self-assemblies to multilevel hierarchical constructs
- 2009
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Ingår i: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 143, s. 95-107
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Tidskriftsartikel (refereegranskat)abstract
- Self-assemblies and their hierarchies are useful to construct soft materials with structures at different length scales and to tune the materials properties for various functions. Here we address routes for solid nanofibers based on different forms of self-assemblies. On the other hand, we discuss rational "bottom-up" routes for multi-level hierarchical self-assembled constructs, with the aim of learning more about design principles for competing interactions and packing frustrations. Here we use the triblock copolypeptide poly(l-lysine)-b-poly(γ-benzyl-l-glutamate)-b-poly(l-lysine) complexed with 2′-deoxyguanosine 5′-monophosphate. Supramolecular disks (G-quartets) stabilized by metal cations are formed and their columnar assembly leads to a packing frustration with the cylindrical packing of helical poly(γ-benzyl-l-glutamate), which we suggest is important in controlling the lateral dimensions of the nanofibers. We foresee routes for functionalities by selecting different metal cations within the G-quartets. On the other hand, we discuss nanofibers that are cleaved from bulk self-assemblies in a "top-down" manner. After a short introduction based on cleaving nanofibers from diblock copolymeric self-assemblies, we focus on native cellulose nanofibers, as cleaved from plant cell wall fibers, which are expected to have feasible mechanical properties and to be templates for functional nanomaterials. Long nanofibers with 5-20 nm lateral dimensions can be cleaved within an aqueous medium to allow hydrogels and water can be removed to allow highly porous, lightweight, and flexible aerogels. We further describe inorganic/organic hybrids as prepared by chemical vapour deposition and atomic layer deposition of the different nanofibers. We foresee functional materials by selecting inorganic coatings. Finally we briefly discuss how the organic template can be removed e.g., by thermal treatments to allow completely inorganic hollow nanofibrillar structures.
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| 6. |
- Larsson, Sven, 1941
(författare)
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Electronic and vibrational structure of one-dimensional conductors and superconductors
- 2006
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Ingår i: Faraday Discussions. - 1359-6640 .- 1364-5498. ; 131, s. 69-77
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Tidskriftsartikel (refereegranskat)abstract
- An attempt is made to treat molecular wires by quantum chemical methods. What is the electronic difference between systems (molecules, stacks of molecules, or polymers) that are conducting and almost identical systems that are insulating? At 50% band filling a one-dimensional crystal undergoes a Peierls transition and becomes an insulator (without doping). In the case of 75% band filling, on the other hand, two phases are possible: charge density wave (CDW) and spin-density wave (SDW). The transition between these two insulating phases should be connected to a high conductivity. If CDW and SDW are energetically possible at zero T, vibrational coupling leads to stabilization of a superconducting (SC) ground state and the formation of an energy gap. This hypothesis is exemplified on (SN)(x) and (TMTSF)(2)X (X = ClO4, PF6).
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| 7. |
- Qvist, Johan, et al.
(författare)
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Time scales of water dynamics at biological interfaces: peptides, proteins and cells
- 2009
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1364-5498. ; 141:1, s. 131-144
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Tidskriftsartikel (refereegranskat)abstract
- Water 2H and 17O spin relaxation is used to study water dynamics in the hydration layers of two small peptides, two globular proteins and in living cells of two microorganisms. The dynamical heterogeneity of hydration water is characterized by performing relaxation measurements over a wide temperature range, extending deeply into the supercooled regime, or by covering a wide frequency range. Protein hydration layers can be described by a power-law distribution of rotational correlation times with an exponent close to 2. This distribution comprises a small fraction of protein-specific hydration sites, where water rotation is strongly retarded, and a dominant fraction of generic hydration sites, where water rotation is as fast as in the hydration shells of small peptides. The generic dynamic perturbation factor is less than 2 at room temperature and exhibits a maximum near 260 K. The dynamic perturbation is induced by H-bond constraints that interfere with the cooperative mechanism that facilitates rotation in bulk water. Because these constraints are temperature-independent, hydration water does not follow the super-Arrhenius temperature dependence of bulk water. Water in living cells behaves as expected from studies of simpler model systems, the only difference being a larger fraction of secluded (strongly perturbed) hydration sites associated with the supramolecular organization in the cell. Intracellular water that is not in direct contact with biopolymers has essentially the same dynamics as bulk water. There is no significant difference in cell water dynamics between mesophilic and halophilic organisms, despite the high K+ and Na+ concentrations in the latter.
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| 8. |
- Savini, G., et al.
(författare)
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Core structures and kink migrations of partial dislocations in 4H-SiC
- 2007
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Ingår i: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 134, s. 353-367
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Tidskriftsartikel (refereegranskat)abstract
- First-principles calculations are used to investigate the Shockley partial dislocations in 4H-SiC. We show that both dislocations can sustain the asymmetric and symmetric reconstructions along the dislocation line. The latter reconstructions are always electrically active. In particular, the Si(g) 30 degrees partials can explain the optical activation energy for the dislocation glide at similar to 2.4 eV above the VB, the narrow peak at 2.87 eV and the broadband at similar to 1.8 eV found in photoluminescence spectra. Further, we propose a new model to explain the stability of the symmetric reconstructions and the enhancement of the dislocation velocity in SiC.
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| 9. |
- Seidel, Y.E., et al.
(författare)
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Mesoscopic mass transport effects in electrocatalytic processes
- 2008
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 140, s. 167-184
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Tidskriftsartikel (refereegranskat)abstract
- The role of mesoscopic mass transport and re-adsorption effects in electrocatalytic reactions was investigated using the oxygen reduction reaction (ORR) as an example. The electrochemical measurements were performed on structurally well-defined nanostructured model electrodes under controlled transport conditions in a thin-layer flow cell. The electrodes consist of arrays of Pt ultra-microelectrodes (nanodisks) of defined size (diameter similar to 100 nm) separated on a planar glassy carbon (GC) substrate, which were fabricated employing hole-mask colloidal lithography (HCL). The measurements reveal a distinct variation in the ORR selectivity with Pt nanodisk density and with increasing electrolyte flow, showing a pronounced increase of the H2O2 yield, by up to 65%, when increasing the flow rate from 1 to 30 mu L s(-1). These results are compared with previous findings and discussed in terms of a reaction model proposed recently (A. Schneider et al., Phys. Chem. Chem. Phys., 2008, 10, 1931), which includes (i) direct reduction to H2O on the Pt surface and (ii) additional H2O2 formation and desorption on both Pt and carbon surfaces and subsequent partial re-adsorption and further reduction of the H2O2 molecules on the Pt surface. The potential of model studies on structurally defined catalyst surfaces and under well-defined mass transport conditions in combination with simulations for the description of electrocatalytic reactions is discussed.
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