| 3751. |
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| 3752. |
- Shchukarev, Andrey, et al.
(författare)
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XPS study of living tree : Per Persson
- 2002
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Ingår i: Surface and Interface Analysis. - : Wiley. - 0142-2421 .- 1096-9918. ; 34:1, s. 284-8
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Tidskriftsartikel (refereegranskat)abstract
- X-ray photoelectron spectroscopy (XPS) was used to study the distribution of elements and main wood components (cellulose and lignin) within the wood and at the bark/wood interface of a living hybrid aspen stem. The hybrid aspen was grown upright in a greenhouse and then tilted at 45° to induce tension wood formation and upright bending of the stem. The wood between the pith and the bark on the upper side of the tilted stem was analysed. Changes in the middle lamella/S1 layer chemical composition, which corresponded to the transition from normal wood produced during upright stem growth to tension wood produced upon stem tilting, were observed. Such changes were related to the lower lignin and higher cellulose/hemicellulose contents in the tension wood. A non-uniform radial distribution of nitrogen (amino acids, proteins) within the stem was also noted. At the bark/wood interface the presence of inorganic elements (Ca, K and P) and a significant increase in nitrogen were found. The opposite wood side of the tree was enriched in lignin and fatty acids. It was shown that application of XPS imaging to a very rough surface of wood split allows the inhomogeneous lateral lignin distribution to be visualized. Copyright © 2002 John Wiley & Sons, Ltd.
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| 3753. |
- Shchukarev, Andrey, et al.
(författare)
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XPS study of the silica–water interface
- 2004
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 137-140, s. 171-6
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Tidskriftsartikel (refereegranskat)abstract
- XPS was applied to study the silica–water interface formed in NaCl solution at variable pH (2–9) and ionic strength (10–600 mM).To prevent alteration of the interface, the wet silica pastes were precooled with liquid nitrogen. After measurements under liquid nitrogen, XPS spectra were collected the next day at room temperature to follow changes at the silica surface caused by water loss.XPS data show that, at low ionic strength (<20 mM), Cl− ions could not be detected at the surface even at the lowest pH. Changes of the Na/Si atomic ratio with pH are in close agreement with the adsorption curve of OH− ions. At higher ionic strength (>100 mM), the silica surface’s point of zero charge can be determined from the Na/Cl atomic ratio. At pH 9 the amount of “free” Na+ at the surface is independent of NaCl concentration reflecting the formation of SiO---Na bonds, confirmed by O 1s spectra.Removing water from the sample surface allows determination of a “built-in” potential at the interface. Si 2p and O 1s spectra of the matrix shift to lower BE values whereas Na 1s and Cl 2p lines of the counter-ions shift to higher BE. At higher ionic strength and pH<2, shifts of Si 2p and O 1s spectra change sign, reflecting the formation of positively charged silica surfaces. The absolute value of the photoelectron line shifts for the matrix elements does not exceed 0.25 eV at any pH, whereas the shifts for counter-ions can reach 0.6 eV. The shifts decrease with increasing ionic strength, implying the formation of a more compact interface.
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| 3754. |
- Sheals, Julia, et al.
(författare)
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Adsorption of Glyphosate on Goethite: Molecular Characterization of Surface Complexes
- 2002
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 36:14, s. 3090-5
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Tidskriftsartikel (refereegranskat)abstract
- As a component of herbicides, the fate of glyphosate (PMG) in the environment is of significant interest. The nature of PMG adsorption on mineral surfaces plays a significant role in the degradation of PMG. The adsorption of PMG on goethite (-FeOOH) has been studied as a function of pH and PMG concentration. Adsorption was investigated with batch experiments, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS). The N 1s line in XPS spectra showed deprotonation of the amine group of PMG (NH2+) with increasing pH. IR analyses showed no evidence for the interaction of PMG's carboxylate group with the goethite surface, while the phosphonate group formed inner-sphere complexes. There is evidence for intramolecular hydrogen bonding between NH2+ and both the carboxylate and the phosphonate groups at low pH. Intramolecular hydrogen bonding is lost when the amine group is deprotonated, and the trend in intramolecular hydrogen bonding between NH2+ and phosphonate shows that PMG adsorbs via predominantly monodentate complexation. A minor quantity of bidentate complexes is thought to form both at near-neutral pH and when the surface concentration of PMG is low. While the phosphonate group of PMG binds directly, the carboxylate group remains relatively "free" from complexation with goethite, leaving it subject to degradation and/or complexation with metal ions present in the environment.
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| 3755. |
- Sheals, Julia, et al.
(författare)
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Coadsorption of Cu(II) and glyphosate at the water–goethite (α-FeOOH) interface: molecular structures from FTIR and EXAFS measurements
- 2003
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Ingår i: Journal of Colloid and Interface Science. ; 262:1, s. 38-47
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Tidskriftsartikel (refereegranskat)abstract
- The coadsorption of Cu(II) and glyphosate (N-(phosphonomethyl)glycine, abbreviated to PMG) at the water–goethite interface was studied by means of batch adsorption experiments, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and extended X-ray absorption fine structure (EXAFS) spectroscopy. The system was investigated over the pH range 3–9 and at total concentrations of 0.9 μmol and 2.2 μmol Cu(II) and PMG per m2 of goethite. The collective quantitative and spectroscopic results show that Cu(II) and PMG directly interact at the water–goethite interface to form ternary surface complexes. Two predominating complexes have been identified. At pH 4 the IR and CuK-edge EXAFS data indicate a molecular structure where the phosphonate group of PMG bonds monodentately to the surface in an inner sphere mode, while carboxylate and amine groups coordinate to Cu(II) to form a 5-membered chelate ring. Hence, at pH 4, Cu(II) and PMG form a ternary surface complex on goethite with the general structure goethite–PMG–Cu(II). At the highest pH investigated (pH 9), the carboxylate group is still coordinated to Cu(II) but the phosphonate group is present in a relatively free, noncoordinated and/or disordered state. Although the spectroscopic data are not conclusive they indicate the formation of ternary surface complexes with the molecular architecture goethite–Cu(II)–PMG at high pH.
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| 3756. |
- Sheals, Julia, et al.
(författare)
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IR and EXAFS Spectroscopic Studies of Glyphosate Protonation and Copper(II) Complexes of Glyphosate in Aqueous Solution
- 2001
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 40:17, s. 4302-9
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Tidskriftsartikel (refereegranskat)abstract
- The varying degrees of protonation of N-(phosphonomethyl)glycine (PMG, glyphosate) were investigated with infrared (IR) spectroscopy and ab initio frequency calculations. The zwitterionic nature of PMG in solution was confirmed, and intramolecular hydrogen bonding was identified. Successive protonation of the PMG molecule follows the order amine, phosphonate, carboxylate. Intramolecular hydrogen bonding is indicated to exist at all stages of protonation: between both RCO2- and RNH2+ and RPO32- and RNH2+ in HL2- (where L represents the ligand PMG); between RCO2- and RNH2+ in H2L-; predominantly between RPO32- and RNH2+ in H3L. There are strong indications that the zwitterion is intact throughout the pH range investigated. Results from IR and extended X-ray absorption fine structure (EXAFS) spectroscopies provide new evidence for structures of N-(phosphonomethyl)glycinecopper(II) complexes. The structures of 1:1 complexes, CuL- and CuHL, are essentially the same, differing only in protonation of the phosphonate group. Copper(II) lies at the center of a Jahn-Teller distorted octahedron with all three donor groups (amine, carboxylate, phosphonate) of PMG chelating with copper(II) to form two five-membered chelate rings oriented in the equatorial plane. EXAFS indicates that oxygen (most likely a water molecule) is a fourth ligand, which would thus occupy the fourth corner in the equatorial plane of the elongated octahedron. CuL24- most probably forms an isomeric mixture in solution, and there are indications that this mixture is dominated by complexes where two PMG ligands are bound to copper(II) via equatorial and axial positions, with both phosphonate and carboxylate donor groups responsible for chelation at axial positions.
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| 3757. |
- Shelankov, Andrei, 1946-, et al.
(författare)
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Charge transfer counting statistics revisited
- 2003
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 63:4, s. 485-491
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Tidskriftsartikel (refereegranskat)abstract
- Charge transfer statistics of quantum particles is obtained by analysing the time evolution of the many-body wave function. Exploiting properly chosen gauge transformations, we construct the probabilities for transfers of a discrete number of particles. Generally, the derived formula for counting statistics differs from the one previously obtained by Levitov et al. (J. Math. Phys., 37 (1996) 4845). The two formulae agree only if the initial state is prohibited from being a superposition of different charge states. Their difference is illustrated for cases of a single particle and a tunnel junction, and the role of charge coherence is demonstrated
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| 3758. |
- Shelankov, Andrei, et al.
(författare)
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Quasiclassical theory of superconductivity : A multiple-interface geometry
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:10, s. 7077-7100
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Tidskriftsartikel (refereegranskat)abstract
- A method is suggested that allows one to study multiple coherent reflection/transmissions by partially transparent interfaces (e.g., in multilayer mesoscopic structures or grain boundaries in high T-c's), in the framework of the quasiclassical theory of superconductivity. It is argued that in the presence of interfaces, a straight-line trajectory transforms to a simple connected one-dimensional tree (graph) with knots, i.e., the points where the interface scattering events occur and pieces of the trajectories are coupled. For the two-component trajectory "wave function" which factorizes the Gor'kov matrix Green's function, a linear boundary condition on the knot is formulated for an arbitrary interface, specular or diffusive (in the many channel model). From the new boundary condition, we derive (i) the excitation scattering amplitude for the multichannel Andreev/ordinary reflection/transmission processes; (ii) the boundary conditions for the Riccati equation; (iii) the transfer matrix which couples the trajectory Green's function before and after the interface scattering. To show the usage of the method, the cases of a him separated from a hulk superconductor by a partially transparent interface, and a SIS' sandwich with finite thickness layers, are considered. The electric current response to the vector potential (the superfluid density rho(s)) with the pi phase difference in S and S' is calculated for the sandwich. It is shown that the model is very sensitive to imperfection of the SS' interface: the low temperature response being paramagnetic (rho(s) < 0) in the ideal system case, changes its sign and becomes diamagnetic (rho(s) > 0) when the probability of reflection is as low as a few percent.
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| 3759. |
- Shibre, T, et al.
(författare)
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An evaluation of two screening methods to identify cases with schizophrenia and affective disorders in a community survey in rural Ethiopia
- 2002
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Ingår i: International Journal of Social Psychiatry. - : Sage Publications. - 0020-7640 .- 1741-2854. ; 48:3, s. 200-208
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Tidskriftsartikel (refereegranskat)abstract
- Background: Detecting cases with psychiatric disorders in the general population is costly and it is not clear which is the method of choice for community surveys in low-income countries. Aim: To compare the performance of a standardized diagnostic layman interview instrument-the Composite International Diagnostic Interview (CIDI 2.1) versus the Key Informant method in identifying cases with schizophrenia and major affective disorders in a community survey. Method: Both screening methods were tested against an expert interview the Schedule for Clinical Assessment in Neuropsychiatry (SCAN 2.1) in a rural district in Ethiopia with 25,632 inhabitants. Result: CIDI identified 524 and key informants 192 individuals as probable cases who were invited for a further SCAN interview. Seventy-two individuals were identified by both methods. Of those identified as probable cases by either method, a total of 481 volunteered the SCAN interviews. The Key Informant method alone detected more cases of schizophrenia, 59 vs. 29 for CIDI, whereas CIDI alone detected more cases of affective disorders, 45 vs. 30. Key informants performed better in detecting chronic cases. Conclusion: For community surveys, which aim at identifying cases with major mental disorders in low-income countries like Ethiopia, the combined use of both CIDI and the Key Informant method is recommended.
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| 3760. |
- Shibre, Teshome, et al.
(författare)
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Neurological soft signs (NSS) in 200 treatment-naïve cases with schizophrenia : a community-based study in a rural setting.
- 2002
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Ingår i: Nordic Journal of Psychiatry. - : Informa UK Limited. - 0803-9488 .- 1502-4725. ; 56:6, s. 425-31
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Tidskriftsartikel (refereegranskat)abstract
- Several studies have reported neurological soft signs (NSS) to be common in individuals with schizophrenia. The majority of these studies are based on clinical samples exposed to neuroleptic treatment. The present study reports on 200 treatment-naïve and community-identified cases of schizophrenia and 78 healthy individuals from the same area, evaluated using the Neurological Evaluation Scale (NES). The median NES score was 5.0 for cases of schizophrenia and 1.5 for healthy subjects. The impairment rate of NSS in cases with schizophrenia was 65.0% against 50.0% in healthy subjects, and the difference was statistically significant (chi2 = 5.30; df = 1; P < 0.021). NSS abnormality is as common in treatment-naïve cases as reported in many studies in those on neuroleptic medication. There was no significant relation between the NSS impairment and duration of illness, remission status, positive symptoms, negative symptoms and disorganized symptoms.
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