| 1. |
- Andersson, Egil, 1981-, et al.
(författare)
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Core-valence double photoionization of the CS2 molecule
- 2010
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 133:9, s. 94305-
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Tidskriftsartikel (refereegranskat)abstract
- Double photoionization spectra of the CS2 molecule have been recorded using the TOF-PEPECO technique in combination with synchrotron radiation at the photon energies h nu=220, 230, 240, 243, and 362.7 eV. The spectra were recorded in the S 2p and C 1s inner-shell ionization regions and reflect dicationic states formed out of one inner-shell vacancy and one vacancy in the valence region. MCSCF calculations were performed to model the energies of the dicationic states. The spectra associated with a S 2p vacancy are well structured and have been interpreted in some detail by comparison to conventional S 2p and valence photoelectron spectra. The lowest inner-shell-valence dicationic state is observed at the vertical double ionization energy 188.45 eV and is associated with a (2p(3/2))(-1)(2 pi(g))(-1) double vacancy. The spectrum connected to the C 1s vacancy shows a distinct line at 310.8 eV, accompanied by additional broad features at higher double ionization energies. This line is associated with a (C 1s)(-1)(2 pi(g))(-1) double vacancy. (C-) 2010 American Institute of Physics. [doi: 10.1063/1.3469812]
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| 2. |
- Brena, Barbara, et al.
(författare)
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Modeling near-edge fine structure x-ray spectra of the manganese catalytic site for water oxidation in photosystem II
- 2012
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 134:41, s. 17157-17167
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Tidskriftsartikel (refereegranskat)abstract
- The Mn 1s near-edge absorption fine structure (NEXAFS) has been computed by means of transition-state gradient-corrected density functional theory (DFT) on four Mn 4Ca clusters modeling the successive S 0 to S 3 steps of the oxygen-evolving complex (OEC) in photosystem II (PSII). The model clusters were obtained from a previous theoretical study where they were determined by energy minimization. They are composed of Mn(III) and Mn(IV) atoms, progressing from Mn(III) 3Mn(IV) for S 0 to Mn(III) 2Mn(IV) 2 for S 1 to Mn(III)Mn(IV) 3 for S 2 to Mn(IV) 4 for S 3, implying an Mn-centered oxidation during each step of the photosynthetic oxygen evolution. The DFT simulations of the Mn 1s absorption edge reproduce the experimentally measured curves quite well. By the half-height method, the theoretical IPEs are shifted by 0.93 eV for the S 0 → S 1 transition, by 1.43 eV for the S 1 → S 2 transition, and by 0.63 eV for the S 2 → S 3 transition. The inflection point energy (IPE) shifts depend strongly on the method used to determine them, and the most interesting result is that the present clusters reproduce the shift in the S 2 → S 3 transition obtained by both the half-height and second-derivative methods, thus giving strong support to the previously suggested structures and assignments.
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| 3. |
- Li, Xin, et al.
(författare)
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Glycine in aerosol water droplets : a critical assessment of Köhler theory by predicting surface tension from molecular dynamics simulations
- 2011
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 11:2, s. 519-527
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol particles in the atmosphere are important participants in the formation of cloud droplets and have significant impact on cloud albedo and global climate. According to the Kohler theory which describes the nucleation and the equilibrium growth of cloud droplets, the surface tension of an aerosol droplet is one of the most important factors that determine the critical supersaturation of droplet activation. In this paper, with specific interest to remote marine aerosol, we predict the surface tension of aerosol droplets by performing molecular dynamics simulations on two model systems, the pure water droplets and glycine in water droplets. The curvature dependence of the surface tension is interpolated by a quadratic polynomial over the nano-sized droplets and the limiting case of a planar interface, so that the so-called Aitken mode particles which are critical for droplet formation could be covered and the Kohler equation could be improved by incorporating surface tension corrections.
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| 4. |
- Li, Xin, et al.
(författare)
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Surface-Active cis-Pinonic Acid in Atmospheric Droplets : A Molecular Dynamics Study
- 2010
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Ingår i: The Journal of Physical Chemistry Letters. - Washington, USA : American Chemical Society (ACS). - 1948-7185. ; 1:4, s. 769-773
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Tidskriftsartikel (refereegranskat)abstract
- Water vapor in the atmosphere can condensate and form cloud droplets when there is a certain amount of humidity and a presence of cloud condensation nuclei, and organic solutes called surfactants can significantly lower the surface tension of water-one of the parameters determining cloud droplet population. We here present a molecular dynamics study of the behavior of cis-pinonic acid, a commonly found organic compound in cloud condensation nuclei, and its effect on the surface tension of water clusters. Specifically, the decrease in surface tension is found to depend on not only the concentration of the organic compound but also the droplet size due to the spontaneous assembly of the surfactant molecules on the droplet surface. This leads to the conclusion that the partitioning of the surfactant between the bulk and surface plays an important role in the behavior of atmospheric aerosol particles and thus in their availability for cloud formation.
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| 5. |
- Niskanen, Johannes, et al.
(författare)
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Experimental and theoretical study of core-valence double photoionization of OCS
- 2010
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 82:4, s. 043436-
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Tidskriftsartikel (refereegranskat)abstract
- O 1s, C 1s, and S 2p core-valence double ionization electron spectra of the OCS molecule have been obtained experimentally by a time-of-flight photoelectron-photoelectron coincidence spectroscopy technique. In order to analyze and assign the spectral features observed, we present a protocol for computing core-valence ionization energies of such systems. The protocol is based on a restricted active space multiconfigurational self-consistent field (MCSCF) methodology with a freeze-relax procedure to guarantee a correct core-valence state root index without variational collapse. Corrections for extended dynamical correlation and core-core correlation, respectively, are made by multiconfigurational perturbation theory and by uncontracted basis set Moller-Plesset theory. Envisioning applications to larger molecules, a spin-restricted open-shell density functional method is also applied for the lowest core-valence energies. Furthermore, cross sections through a scheme for computing multiatom Auger transitions generating core-valence holes are presented. We find that the procedure outlined is capable of deriving the energy onset of core-valence ionization within a fraction of an eV and that assignments can be made of the most salient spectral features.
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| 6. |
- Ning, Zhijun, et al.
(författare)
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Role of surface ligands in optical properties of colloidal CdSe/CdS quantum dots.
- 2011
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Ingår i: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 13:13, s. 5848-54
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Tidskriftsartikel (refereegranskat)abstract
- In order to study the role of surface ligands in determining optical properties of colloidal quantum dots (QDs), we have selectively fabricated and studied CdSe/CdS core-shell QDs with strongly confined electron and hole states attached with commonly used surface ligands. Optical properties, viz. absorption and fluorescence of these QDs, are characterized from which salient changes have been observed for different ligand substitutions which, through theoretical analysis, can be associated with electronic structure properties of the QD-ligand composite systems, in particular localization of wave functions of electrons and holes in the QDs and the band matching of the HOMO-LUMO gap of the ligands. The findings can be utilized to facilitate the understanding and optimization of properties of QD biomarkers with functionalizing surface ligands for targeting cellular objects.
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| 7. |
- Murugan, N. Arul, et al.
(författare)
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Promising two-photon probes for in vivo detection of beta amyloid deposits
- 2014
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 50:79, s. 11694-11697
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Tidskriftsartikel (refereegranskat)abstract
- Based on electronic structure calculations we propose that particular small-sized organic molecules - donor-acceptor substituted phenyl polymethines - can be used as two-photon diagnostic probes for non-invasive imaging of amyloid oligomers and fibrils, which are often referred to as the "early signatures'' of Alzheimer's disease.
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| 8. |
- Qin, Hai-Yan, et al.
(författare)
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Observation of Bunched Blinking from Individual CdSe/CdS and CdSe/ZnS Colloidal Quantum Dots
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:23, s. 12786-12790
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Tidskriftsartikel (refereegranskat)abstract
- Blinking and time correlation between fluorescences of neighboring negatively charged CdSe/CdS and CdSe/ZnS colloidal quantum dots have been studied experimentally. A tendency of synchronous blinking, that is, a bunching effect, is clearly observed from two neighboring QDs with a spatial separation up to 1.1 mu m. We believe that our observations will help to better understand the mechanisms for the blinking.
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| 9. |
- Nakasujja, N., et al.
(författare)
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Cognitive Dysfunction among HIV Positive and HIV Negative Patients with Psychosis in Uganda
- 2012
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Ingår i: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 7:9
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Tidskriftsartikel (refereegranskat)abstract
- Background: Cognitive impairment is an established phenomenon in HIV infected individuals and patients that have psychosis. However there is need to establish the severity of the impairment if patients are co morbid with both conditions. Aim: To compare cognitive function among HIV positive individuals and HIV negative individuals with psychosis. Methods: We recruited patients with psychosis at two national referral hospitals. A standardized demographics questionnaire and psychiatric, physical, and laboratory assessments were conducted. Types of psychosis were diagnosed using the Mini International Neuropsychiatric Inventory-PLUS while cognitive functioning was determined using the Mini mental state examination (MMSE) and a neuropsychological test battery. Follow-up assessments on cognitive function and severity of psychiatric illness were performed at 3 and 6 months. Pairwise comparison and multivariable logistic regression analysis were used to determine the differences between the HIV positive and HIV negative individuals. Results: There were 156 HIV positive and 322 HIV negative participants. The mean age was 33 years for the HIV positive group and 29 years for the HIV negative group (p<0.001). The HIV positive individuals were almost three times (OR = 2.62 CI 95% 1.69-4.06) more likely to be cognitively impaired on the MMSE as well as the following cognitive tests:- WHO-UCLA Auditory Verbal Learning Test (OR 1.79, 95% CI 1.09-2.92), Verbal Fluency (OR 3.42, 95% CI 2.24-5.24), Color Trails 1 (OR 2.03, 95% CI 1.29-3.02) and Color Trails 2 (OR 3.50 95% 2.00-6.10) all p = 0.01. There was improvement in cognitive function at follow up; however the impairment remained higher for the HIV positive group (p<0.001). Conclusion: Cognitive impairment in psychosis was worsened by HIV infection. Care plans to minimize the effect of this impairment should be structured for the management of individuals with HIV and psychosis.
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| 10. |
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