Conditioning film and environmental effects on the adherence of Candida spp. to silicone and poly(vinylchloride) biomaterials.

The reported incidence of colonization of oropharyngeal medical devices with Candida spp. has increased in recent years, although few studies that have systematically examined the adherence of yeast cells to such biomaterials, the primary step in the process of colonization. This study, therefore, examined the effects of oropharyngeal atmospheric conditions (5% v/v carbon dioxide) and the presence of a salivary conditioning film on both the surface properties and adherence of Candida albicans, Candida krusei and Candida tropicalis to PVC and silicone. Furthermore, the effects of the salivary conditioning film on the surface properties of these biomaterials are reported. Growth of the three Candida spp. in an atmosphere containing 5% v/v CO2 significantly increased their cell surface hydrophobicity and reduced the zeta potential of C. albicans and C. krusei yet increased the zeta potential of C. tropicalis (p < 0.05). Furthermore, growth in 5% v/v CO2 decreased the adherence of C. tropicalis and C. albicans to both PVC and silicone, however, increased adherence of C. krusei (p < 0.05). Pre-treatment of the microorganisms with pooled human saliva significantly decreased their cell surface hydrophobicity and increased their adherence to either biomaterial in comparison to yeast cells that had been pre-treated with PBS (p < 0.05). Saliva treatment of the microorganisms had no consistent effect on microbial zeta potential. Interestingly, adherence of the three, saliva-treated Candida spp. to saliva-treated silicone and PVC was significantly lower than whenever the microorganisms and biomaterials had been treated with PBS (p < 0.05). Treatment of silicone and PVC with saliva significantly altered the surface properties, notably reducing both the advancing and receding contact angles and, additionally, the microrugosity. These effects may contribute to the decreased adherence of saliva-treated microorganisms to these biomaterials. In conclusion, this study has demonstrated the effects of physiological conditions within the oral cavity on the adherence of selected Candida spp. to biomaterials employed as oropharyngeal medical devices. In particular, this study has ominously shown that these materials act as substrates for yeast colonization, highlighting the need for advancements in biomaterial design. Furthermore, it is important that physiological conditions should be employed whenever biocompatibility of oropharyngeal biomaterials is under investigation. © 2001 Kluwer Academic Publishers.

The near-edge structure in energy-loss spectroscopy: many-electron and magnetic effects in transition metal nitrides and carbides

We investigate the ability of the local density approximation (LDA) in density functional theory to predict the near-edge structure in electron energy-loss spectroscopy in the dipole approximation. We include screening of the core hole within the LDA using Slater's transition state theory. We find that anion K-edge threshold energies are systematically overestimated by 4.22 +/- 0.44 eV in twelve transition metal carbides and nitrides in the rock-salt (B1) structure. When we apply this 'universal' many-electron correction to energy-loss spectra calculated within the transition state approximation to LDA, we find quantitative agreement with experiment to within one or two eV for TiC, TiN and VN. We compare our calculations to a simpler approach using a projected Mulliken density which honours the dipole selection rule, in place of the dipole matrix element itself. We find remarkably close agreement between these two approaches. Finally, we show an anomaly in the near-edge structure in CrN to be due to magnetic structure. In particular, we find that the N K edge in fact probes the magnetic moments and alignments of ther sublattice.

Pension structural reforms, re-reforms and their effects on social welfare: The case of Chile

This article fi rst summarizes the structural reforms of pensions (total or partial privatization) in Latin America and Central and Eastern Europe, identifying their advantages and disadvantages, and does the same with the international process of re-reforms of pensions with a greater role of the state. Second, chooses Chile as a case study, as a world pioneer in both types of reforms; describes their characteristics and effects on social welfare of the structural reform of 1981 and the re-reform of 2008. Such effects are evaluated based on ten basic principles of social security from the International Labour Offi ce (ILO): 1) social dialogue to approve the reforms, 2) universal coverage of the population, 3) equal treatment of insured persons, 4) social solidarity, 5) gender equity, 6) suffi ciency of benefi ts, 7) effi ciency and reasonable administrative cost, 8) social participation in the management of the system, 9) role of the state and supervision, and 10) fi nancial sustainability. Third, it summarizes the advantages and disadvantages-challenges of the re-reform and informs on the current debate for further reforms.

The general and specific effects of educational programmes aimed at promoting awareness of and respect for diversity among young children

This article reports the findings of a mixed-method evaluation of a pilot educational programme undertaken with 6-7 year olds in a sample of primary schools in England with the aim of increasing their awareness of and respect for diversity through theatre, workshops and related teacher-led classroom activities. The qualitative feedback from the teachers involved was extremely positive and encouraging and an analysis of the actual impact of the pilot programme on the children’s attitudes and awareness, using an experimental design, demonstrated some positive effects. In particular, the programme was found to increase the children’s general awareness of diversity and their ability to recognise instances of exclusion. While not a planned objective of the pilot programme, the evaluation also examined whether it had any effects on the children’s attitudes to specific differences, in this particular case racial differences. Interestingly, however, no evidence was found of any change in the children’s racial attitudes. With this in mind the article suggests that there is a need to distinguish between the general and specific effects of such educational programmes. The article considers the implications of this for future work in the area and also stresses the need to undertake more thorough and rigorous evaluations of such initiatives.

Ferroelectricity and isotope effects in hydrogen-bonded KDP crystals

Based on an accurate first principles description of the energetics in H-bonded potassium-dihydrogen-phosphate crystals, we conduct a first study of nuclear quantum effects and of the changes brought about by deuteration. Tunneling is allowed only for clusters involving correlated protons and heavy ion displacements, the main effect of deuteration being a depletion of the proton probability density at the O-H-O bridge center, which in turn weakens its proton-mediated covalent bonding. The ensuing lattice expansion couples self-consistently with the proton off-centering, thus explaining both the giant isotope effect and its close connection with geometrical effects.

First-principles study of ferroelectricity and isotope effects in H-bonded KH2PO4 crystals

By means of extensive first-principles calculations we studied the ferroelectric phase transition and the associated isotope effect in KH2PO4 (KDP). Our calculations revealed that the spontaneous polarization of the ferroelectric phase is due to electronic charge redistributions and ionic displacements which are a consequence of proton ordering, and not vice versa. The experimentally observed double-peaked proton distribution in the paraelectric phase cannot be explained by a dynamics of only protons. This requires, instead, collective displacements within clusters that include also the heavier ions. These tunneling clusters can explain the recent evidence of tunneling obtained from Compton scattering measurements. The sole effect of mass change upon deuteration is not sufficient to explain the huge isotope effect. Instead, we find that structural modifications deeply connected with the chemistry of the H bonds produce a feedback effect on tunneling that strongly enhances the phenomenon. The resulting influence of the geometric changes on the isotope effect agrees with experimental data from neutron scattering. Calculations under pressure allowed us to analyze the issue of universality in the disappearance of ferroelectricity upon compression. Compressing DKDP so that the distance between the two peaks in the deuteron distribution is the same as for protons in KDP, corresponds to a modification of the underlying double-well potential, which becomes 23 meV shallower. This energy difference is what is required to modify the O-O distance in such a way as to have the same distribution for protons and deuterons. At the high pressures required experimentally, the above feedback mechanism is crucial to explain the magnitude of the geometrical effect.

Concertedness and solvent effects in multiple proton transfer reactions: The formic acid dimer in solution

The issue of multiple proton transfer (PT) reactions in solution is addressed by performing molecular dynamics simulations for a formic acid dimer embedded in a water cluster. The reactant species is treated quantum mechanically, within a density functional approach, while the solvent is represented by a classical model. By constraining different distances within the dimer we analyze the PT process in a variety of situations representative of more complex environments. Free energy profiles are presented, and analyzed in terms of typical solvated configurations extracted from the simulations. A decrease in the PT barrier height upon solvation is rationalized in terms of a transition state which is more polarized than the stable states. The dynamics of the double PT process is studied in a low-barrier case and correlated with solvent polarization fluctuations. Cooperative effects in the motion of the two protons are observed in two different situations: when the solvent polarization does not favor the transfer of one of the two protons and when the motion of the two protons is not synchronized. This body of observations is correlated with local structural and dynamical properties of the solvent in the vicinity of the reactant. (C) 2000 American Institute of Physics. [S0021-9606(00)51121-0].

Compton profiles of Si: Pseudopotential calculation and reconstruction effects

Using an ab initio pseudopotential calculation, we compute Compton profiles of silicon along the (100), (110), and (111) directions, and then reconstruct the pseudo-wave-functions to regain the oscillatory behavior of the all-electron valence wave functions near the atomic cores. We study the effect that this reconstruction has on the Compton profiles and their anisotropies. We find a decrease in the magnitude of the profiles at small wave vectors and in their anisotropies. These changes bring the theoretical predictions closer to experimental results.

Glory and thresholds effects in H+D-2 reactive angular scattering

We analyse H + D-2 reactive angular scattering using the S- matrix elements obtained by Aoiz et al. and Althorpe et al. Enhancement of small angle scattering in the v' = 3