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5.
  • 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: Fluid Phase Equilibria. - 1422-6928. ; 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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6.
  • Abdelkader, Amal F., 1969-, et al. (författare)
  • High salt stress in wheat leaves causes retardation of chlorophyll accumulation due to a limited rate of protochlorophyllide formation
  • 2007
  • Ingår i: Physiologia Plantarum. - 0031-9317. ; 130:1, s. 157-166
  • Tidskriftsartikel (refereegranskat)abstract
    • When exposed to salt stress, leaves from dark-grown wheat seedlings (Triticum aestivum, cv. Giza 168) showed reduced accumulation of chlorophyll during irradiation. To elucidate the mechanism behind salt-influenced reduction of chlorophyll biosynthesis, we have investigated the effect of salt stress on the spectral forms of Pchlide, the phototransformation of Pchlide to Chlide, the Shibata shift, the regeneration of Pchlide and the accumulation of Pchlide from 5-aminolevulinic acid (ALA). We found that the phototransformation of Pchlide to Chlide was not affected by salt stress. The blue shift (Shibata shift) of newly formed Chlide was delayed both after flash irradiation and in continuous light. The reformation of Pchlide in darkness after a flash irradiation or after a period of 3-h irradiation was retarded in the salt-treated leaves. However, after a 20-h dark period, Pchlide was reformed even in salt-treated leaves but the formation of short-wavelength Pchlide was suppressed. Compared to controls, salt treatment also reduced the amount of Pchlide accumulated in leaves floated on ALA. The increase in the low temperature fluorescence emission spectrum at 735 nm, which occurred gradually during several hours of irradiation with continuous light in control leaves, was completely suppressed in salt-treated leaves. It is concluded that salt stress inhibits chlorophyll accumulation partly by reducing the rate of porphyrin formation but, as discussed, also by a possible reduction in the formation of chlorophyll-binding proteins.
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  • Abdelkader, Amal F., 1969-, et al. (författare)
  • High salt stress induces swollen prothylakoids in dark-grown wheat and alters both prolamellar body transformation and reformation after irradiation
  • 2007
  • Ingår i: Journal of Experimental Botany. - 0022-0957. ; 58:10, s. 2553-2564
  • Tidskriftsartikel (refereegranskat)abstract
    • High salinity causes ion imbalance and osmotic stress in plants. Leaf sections from 8-d-old dark-grown wheat (Triticum aestivum cv. Giza 168) were exposed to high salt stress (600 mM) and the native arrangements of plastid pigments together with the ultrastructure of the plastids were studied using low-temperature fluorescence spectroscopy and transmission electron microscopy. Although plastids from salt-treated leaves had highly swollen prothylakoids (PTs) the prolamellar bodies (PLBs) were regular. Accordingly, a slight intensity decrease of the short-wavelength protochlorophyllide (Pchlide) form was observed, but no change was found in the long-wavelength Pchlide form emitting at 656 nm. After irradiation, newly formed swollen thylakoids showed traversing stromal strands. The PLB dispersal was partly inhibited and remnants of the PLBs formed an electron-dense structure, which remained after prolonged (8 h) irradiation. The difference in fluorescence emission maximum of the main chlorophyll form in salt-stressed leaves (681 nm) and in control leaves (683 nm) indicated a restrained formation of the photosynthetic apparatus. Overall chlorophyll accumulation during prolonged irradiation was inhibited. Salt-stressed leaves returned to darkness after 3 h of irradiation had, compared with the control, a reduced amount of Pchlide and reduced reformation of regular net-like PLBs. Instead, the size of the electron-dense structures increased. This study reports, for the first time, the salt-induced swelling of PTs and reveals traversing stromal strands in newly formed thylakoids. Although the PLBs were intact and the Pchlide fluorescence emission spectra appeared normal after salt stress in darkness, plastid development to chloroplasts was highly restricted during irradiation.
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  • Abdulle, Sahra, 1970-, et al. (författare)
  • CSF neurofilament protein (NFL) - a marker of active HIV-related neurodegeneration.
  • 2007
  • Ingår i: Journal of neurology. - 0340-5354. ; 254:8, s. 1026-32
  • Tidskriftsartikel (refereegranskat)abstract
    • BACKGROUND AND METHODS : The light subunit of the neurofilament protein (NFL), a major structural component of myelinated axons, is a sensitive indicator of axonal injury in the central nervous system (CNS) in a variety of neurodegenerative disorders. Cerebrospinal fluid (CSF) NFL concentrations were measured by ELISA (normal < 250 ng/l) in archived samples from 210 HIV-infected patients not taking antiretroviral treatment: 55 with AIDS dementia complex (ADC), 44 with various CNS opportunistic infections/tumours (CNS OIs), 95 without neurological symptoms or signs, and 16 with primary HIV infection (PHI). The effect of highly active antiretroviral treatment (HAART) was studied by repeated CSF sampling in four of the ADC patients initiating treatment. RESULTS : CSF NFL concentrations were significantly higher in patients with ADC (median 2590 ng/l, IQR 780-7360) and CNS OIs (2315 ng/l, 985-7390 ng/l) than in neuroasymptomatic patients (<250 ng/l, <250-300) or PHI (<250 ng/l, <250-280), p < 0.001. Among patients with ADC, those with more severe disease (stage 2-4) had higher levels than those with milder disease (stage 0.5-1), p < 0.01. CSF NFL declined during HAART to the limit of detection in parallel with virological response and neurological improvement in ADC.CSF NFL concentrations were higher in neuroasymptomatic patients with lower CD4-cell strata than higher, p < 0.001. This increase was less marked than in the ADC patients and noted in 26/58 neuroasymptomatic patients with CD4 counts <200/mul compared to 1/37 with CD4-cells >/=200/mul. CONCLUSIONS : The findings of this study support the value of CSF NFL as a useful marker of ongoing CNS damage in HIV infection. Markedly elevated CSF NFL concentrations in patients without CNS OIs are associated with ADC, follow the grade of severity, and decrease after initiation of effective antiretroviral treatment. Nearly all previously suggested CSF markers of ADC relate to immune activation or HIV viral load that do not directly indicate brain injury. By contrast NFL is a sensitive marker of such injury, and should prove useful in evaluating the presence and activity of ongoing CNS injury in HIV infection.
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10.
  • 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..
  • 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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