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45 results

Page 1 of 3

  • The pH of aqueous bentonite suspensions

  • Stephan Kaufhold, Reiner Dohrmann, Dietrich Koch, Georg Houben
  • Journal:
    Clays and Clay Minerals / Volume 56 / Issue 3 / June 2008
    Published online by Cambridge University Press:
    01 January 2024, pp. 338-343
    • Article
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  • The pH of aqueous bentonite suspensions is known to be influenced by carbonates present even in minor amounts. On the other hand, at high solid:liquid ratios (at standard pH measurement conditions: 2% w/w suspension), the type of exchangeable cation in the smectite is also known to determine pH (particularly Na+ or Ca2+). By cation-exchange tests we proved that exchanging the Ca2+ for Na+ results in an increase in the pH. However, this increase in pH was only found if excess salts were removed from the system (by washing or dialysis, respectively). The effect of the type of exchangeable cation can, at least partially, be explained by hydrolysis of Ca2+. On the other hand, a pronounced alkalinity of Na bentonites is observed which can, at least partially, be attributed to the hydrolysis of montmorillonite (Na+ is exchanged for H+ of water). The increase in the volume of the Stern layer, caused by increasing the degree of delamination, is also suggested to play a role. H+ and Na+ are concentrated in the Stern layer. Hence, increasing the Stern layer volume decreases the amount of H+ and Na+ in solution and thus increases pH. Unfortunately, both processes, montmorillonite hydrolysis and delamination, depend on the ionic strength. Distinguishing the processes quantitatively, therefore, is an analytical challenge, and impossible based on the data presented here.

    To model the pore-water chemistry of clays and clay stones, all of the above-mentioned processes have to be considered. It is possible that other reactions, not identified in the present work, contribute toward the pH values of aqueous bentonite suspensions.

  • Development and evaluation of a case group concept for inpatients with mental disorders in Germany: Using self-report and expert-rated instruments

  • Sylke Andreas, Jörg Dirmaier, Timo Harfst, Stephan Kawski, Uwe Koch, Holger Schulz
  • Journal:
    European Psychiatry / Volume 24 / Issue 2 / March 2009
    Published online by Cambridge University Press:
    16 April 2020, pp. 105-111

  • The aim of this study was to evaluate a case-mix system to classify inpatients with mental disorders in Germany by means of self-report and expert-rated instruments. The use of case-mix systems enhances the transparency of performance and cost structure and can thus improve the quality of mental health care. We analysed a consecutive sample of 1677 inpatients with mental disorders from 11 hospitals using regression tree analysis. The model assigns patients to 17 groups, accounting for 17% of the variance for duration of stay. Patients with eating disorders had a longer duration of stay than patients with anxiety disorder, duration of mental illness of less than 3–5 years, lower levels of interpersonal problems and higher occupational position. The results showed that besides diagnosis, variables such as duration of illness and interpersonal problems are important for classifying inpatients with mental disorders. The results of the study should be critically reviewed regarding the empirical results of other studies and the appropriateness of case group concepts for inpatients with mental disorders.

  • A systematic review of economic evaluation in fecal microbiota transplantation

  • Thomas Stalder, Nathalie Kapel, Sophie Diaz, Frédéric Grenouillet, Stéphane Koch, Samuel Limat, Franck Daval, Lucine Vuitton, Virginie Nerich
  • Journal:
    Infection Control & Hospital Epidemiology / Volume 41 / Issue 4 / April 2020
    Published online by Cambridge University Press:
    24 January 2020, pp. 458-466
    Print publication:
    April 2020
  • Background:

    Fecal microbiota transplantation (FMT) is an effective therapy in recurrent Clostridium difficile infection (rCDI). It is only recommended for this indication by European and American guidelines. Other indications of FMT are being studied, such as inflammatory bowel disease (IBD), and they have shown promising results.

    Objectives:

    To identify and review published FMT-related economic evaluations (EEs) to assess their quality and the economic impact of FMT in the treatment of these diseases.

    Data sources:

    The systematic literature research was conducted in both PubMed and Cochrane to identify EEs published before July 1, 2019.

    Study eligibility criteria:

    Articles were included if they concerned FMT (whatever the disease and its line of treatment), if they reported full or partial EEs, and if they were written in English. Articles were excluded if they did not concern FMT; if they did not report an EE; or if they were a systematic review, editorial, comment, letter to the editor, practice point, or poster.

    Methods:

    A measurement tool, AMSTAR, was used to optimize the quality of this systematic review. Based on the CHEERS checklist, data were identified and extracted from articles. The quality of each EE was assessed using the Drummond checklist.

    Results:

    Overall, 9 EEs were included: all EEs were full evaluations and 8 were cost-utility analyses (CUAs). All EEs had a Drummond score ≥ 7, which indicated high quality. All CUAs related to rCDI and IBD concluded that FMT was cost-effective compared with other reference treatments, at a threshold ≤$50,000/QALY. One EE about initial CDI showed that FMT was dominated by metronidazole.

    Conclusions:

    Despite a limited number of EEs, FMT seems to be a promising and cost-effective treatment for rCDI. More EE studies on other diseases like IBD are necessary to address FMT efficiency for new indications. Therefore, our systematic review provides a framework for healthcare decision making.

  • Magnetic field morphologies at mpc scale

  • Ya-Wen Tang, Patrick M. Koch, Paul T. P. Ho, Stephane Guilloteau, Anne Dutrey
  • Journal:
    Proceedings of the International Astronomical Union / Volume 10 / Issue H16 / August 2012
    Published online by Cambridge University Press:
    05 March 2015, p. 392
    Print publication:
    August 2012
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  • We report our new results of the magnetic field (B) morphologies toward W51 North, traced with the linear polarization of the dust continuum at wavelengths of 870 μm. The B morphologies are resolved with an angular resolution of typically 1” using the Submillimeter Array (SMA). Dense structures with a number density 105 to 107 cm−3 are traced. In comparison, the B morphologies of sources at different evolutionary stages, from the collapsing core in W51 e2 (Tang et al. 2009a) and part of Orion BN/KL (Tang et al. 2010) to the ultra-compact HII region G5.89-0.39 (Tang et al. 2009b) clearly exhibit different morphologies, likely suggesting different roles of the B fields at different stages.

  • Assessment of cavopulmonary connections by advanced imaging: value of flat-detector computed tomography

  • Martin Glöckler, Andreas Koch, Julia Halbfaß, Verena Greim, Andrè Rüffer, Robert Cesnjevar, Stephan Achenbach, Sven Dittrich
  • Journal:
    Cardiology in the Young / Volume 23 / Issue 1 / February 2013
    Published online by Cambridge University Press:
    08 March 2012, pp. 18-26
  • Objectives

    To investigate the impact of flat-detector computed tomography on the clinical assessment of patients with cavopulmonary connections, and to evaluate the obtained diagnostic accuracy and supplementary information, as well as the value of overlaid three-dimensional reconstructions on fluoroscopic images during catheter-based interventions.

    Methods

    We analysed 31 consecutive patients retrospectively in whom flat-detector computed tomography was used to visualise the cavopulmonary connection. We investigated patients with cavopulmonary connections either early post-operatively (first group), before converting to a total cavopulmonary connection (second group), and patients with failing total cavopulmonary connection (third group). Flat-detector computed tomography based on a single rotational angiography was used to create a three-dimensional vascular model. The clinical value of flat-detector computed tomography was evaluated using standard categories of diagnostic utility. Used contrast volume and radiation exposure were quantified.

    Results

    Within 18 months, flat-detector computed tomography was performed in 31 cases with cavopulmonary connections. The median age was 1.9 years (range 0.3–43 years). In the first group, we found anomalies in 4 out of 8 cases, which led to therapeutic or prophylactic procedures; in the second and third groups, we performed interventions in 14 out of 23 cases. The overall clinical value was always rated superior to conventional biplane angiography. The median dose area product was 91.8 microgray square metres (range 33.0–679.3 microgray square metres). The required contrast medium was 2.08 millilitres per kilogram (range 0.66–4.7 millilitres per kilogram).

    Conclusion

    Flat-detector computed tomography improves the diagnostic accuracy in cavopulmonary connections and provides additional diagnostic information, which may lead to therapeutic or prophylactic procedures. Overlaid three-dimensional images on fluoroscopy facilitate and provide security for interventions.

  • 7 - Hamiltonian formulation of classical electrodynamics

  • Mackillo Kira, Philipps-Universität Marburg, Germany, Stephan W. Koch, Philipps-Universität Marburg, Germany
  • Book:
    Semiconductor Quantum Optics
    Published online:
    05 January 2012
    Print publication:
    17 November 2011, pp 121-140

  • Summary

    At the conceptual level, the quantization procedure replaces the pure particle description of classical mechanics by a particle-wave treatment satisfying the requirements of the fundamental wave–particle dualism. Technically, one can always start from a generalized wave equation and use it as a basis to discuss wave-front propagation in the form of rays following classical particle trajectories, see Sections 2.2.1 and 3.1. Consequently, any wave theory inherently contains that aspect of the wave–particle dualism.

    Especially, Maxwell's equations of electrodynamic theory include both wave and particle aspects of electromagnetic fields. Hence, it could be that there are no additional “quantum,” i.e., wave–particle dualistic aspects. However, as we discuss in this chapter, Maxwell's equations can be expressed in the framework of Hamilton's formulation of particle mechanics. This then suggests that in addition to the approximate ray-like behavior, electromagnetic fields do have a supplementary level of particle-like properties.

    Due to the fundamental axiom of wave–particle dualism, the additional particle-like aspects of electromagnetic fields must then also have a wave counterpart that can be axiomatically introduced via the canonical quantization scheme described in Section 3.2.3. Since the spatial dependency in Maxwell's equation contains wave–particle dualism already at the classical level, it is clear that the new level of quantization cannot be a simple real-space feature but has to involve some other space describing the structure of the electromagnetic fields. In fact, this quantization yields several very concrete implications such as quantization of the light energy, elementary fluctuations in the light-field amplitude and intensity, and more.

  • 24 - General aspects of semiconductor optics

  • Mackillo Kira, Philipps-Universität Marburg, Germany, Stephan W. Koch, Philipps-Universität Marburg, Germany
  • Book:
    Semiconductor Quantum Optics
    Published online:
    05 January 2012
    Print publication:
    17 November 2011, pp 480-498

  • Summary

    The optically generated excitations in semiconductors constitute a genuine many-body system. To describe its quantum-optical features, we have to expand significantly the theoretical models used so far. However, the important insights of Chapters 16–23 are already presented in a form in which most of them can directly be used and generalized to analyze central properties of the optical excitations in solids. As for atoms, the optical transitions in semiconductors are induced via dipole interaction between photons and electrons. We can thus efficiently construct a systematic quantum-optical theory for semiconductors by following the cluster-expansion approach.

    One of the main differences from atoms is that the electronic excitations in semiconductors form a strongly interacting many-body system. Thus, we must systematically treat the arising Coulomb-induced hierarchy problem together with the quantum-optical one. Moreover, the coupling of electrons to lattice vibrations, i.e., the phonons, produces yet another hierarchy problem. In addition, in solid-state spectroscopy one often uses multimode light fields such that one cannot rely on the single-mode simplifications to study semiconductor quantum optics.

    As shown in Chapter 15, the Coulomb-, phonon-, and photon-induced hierarchy problems have formally an identical structure. Thus, we start the analysis by investigating how semiconductor quantum optics emerges from the dynamics of correlated clusters. We first focus on the basic properties of the optical transitions in the classical regime. This means investigating the fundamental optical phenomena resulting from the singlets. The full singlet–doublet approach is presented in Chapters 28–30.

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