Local Magnetic and Electronic Structure of the Surface Region of Postsynthesis Oxidized Iron Oxide Nanoparticles for Magnetic Resonance Imaging

Iron oxide nanoparticles FeOx NP are applied in medicine as contrast agents in magnetic resonance imaging MRI where they reduce the spin amp; 8722;spin relaxation time T2 time of absorbing tissue. Hence, control of their magnetic properties is essential for these applications. Magnetic properties strongly depend on the particle size and shape as well as the surface functionalization of the iron oxide nanoparticles. Especially, structural and magnetic disorder in the region close to the surface 1 amp; 8722;2 nm lead usually to a reduced magnetization compared to the corresponding bulk material. Therefore, X ray magnetic circular dichroism XMCD in the total electron yield TEY mode is used to investigate local magnetic and electronic properties of the surface region of monodisperse, spherical FeOx NPs Fe3O4 amp; 947; Fe2O3 before and after the postsynthetic treatment in oxygen rich environment. Charge transfer multiplet calculations of the XMCD spectra are performed to analyze the contributions of Fe2 and Fe3 at different lattice sites, i.e., either in octahedral or tetrahedral environment. The analysis of the XMCD data reveals that both, the magnetization of the nanoparticle surface region as well as their maghemite to magnetite ratio, are strongly increased after tempering in an oxidative environment, which likely causes rearrangement of their crystalline order. The magnitude and the kinetics of these variables depend strongly on the particle size. In addition, after thermal annealing a reduced spin canting is extrapolated from the lower magnetic coercivity, which confirms that a structural rearrangement takes plac

Low-level exposure of MRSA to octenidine dihydrochloride does not select for resistance

No abstract available

Optical and Geometric Properties of Free Silica Nanoparticles Studied by Small Angle X Ray Scattering

Abstract Elastic small-angle X-ray scattering (SAXS) of free silica (SiO2) nanoparticles is reported (d = 100–180 nm). The particles were prepared by a modified Stöber synthesis in narrow size distributions with controlled surface roughness and functionalization. Angle-resolved small-angle X-ray scattering patterns are shown to be sensitive to these changes in particle properties. It is reported that there is an exponential decrease in scattered X-ray intensity towards larger scattering angles as well as distinct oscillations, which is fully explained by Mie theory. Small-angle X-ray scattering of mesoporous nanoparticles with rough surfaces is compared to that of microporous nanoparticles with smooth surfaces, revealing distinct differences that are rationalized by diffuse scattering from nanoparticle pores in addition to the dominating contribution of Mie scattering. Furthermore, results from small-angle X-ray scattering experiments on functionalized silica nanoparticles are presented, where the incorporation of the dye fluorescein isothiocyanate is found to cause changes in the optical properties of the nanoparticles, as compared to non-functionalized samples. Small, but distinct deviations in particle size derived from electron microscopy and from small-angle X-ray scattering are observed. These are rationalized by particle shrinking occurring in electron microscopy as well as slight changes in optical properties of the nanoparticle samples.</jats:p

Surface Properties and Porosity of Silica Particles Studied by Wide Angle Soft X ray Scattering

Wide-angle soft X-ray scattering on free silica particles of different porosity prepared in a beam is reported. The explored q region is mostly dominated by features due to surface roughness and bulk porosity. A comprehensive experimental and theoretical analysis of silica particles of different porosity is presented for various incident photon energies. A correlation analysis, based on the theory of Porod, is used to test the validity of exact Mie theory in different pore density limits. The ability of the discrete dipole scattering model (DDSCAT) to resolve local effects, caused by various pore distributions, is discussed. Characteristic differences between the soft X-ray scattering patterns of the particle samples of different surface properties and porosity are detected. For all mentioned cases, it was confirmed that the effective radius concept of the Guinier model can be successfully extended to Mie theory and DDSCAT in describing the additive contributions of the primary particles, including a thin inhomogeneous solvent-rich surface shell and empty bulk pores. Close agreement, within ±15%, between the calculated and observed pore sizes and porosity values is reached. The influence of pores is alternatively described either in terms of secondary Mie scattering, which is modulated by the local internal electrical field within the particles, or by an independent Mie scattering process induced by the incident field on isolated pores. It is found that for the typical pore/particle size ratios the latter approach presents the best choice

'Meteor'-Reise Nr. 71 (Juni-August 1985). Norwegen-Groenlandsee. Untersuchung der Verteilung kuenstlicher Radionuklide Datenbericht

SIGLEAvailable from TIB Hannover: RR 6782(12) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Chemische Desinfektion in Gesundheitseinrichtungen: Kritische Aspekte für die Entwicklung einer globalen Strategie

Chemical disinfection is an indispensable means of preventing infection. This holds true for healthcare settings, but also for all other settings where transmission of pathogens poses a potential health risk to humans and/or animals. Research on how to ensure effectiveness of disinfectants and the process of disinfection, as well as on when, how and where to implement disinfection precautions is an ongoing challenge requiring an interdisciplinary team effort. The valuable resources of active substances used for disinfection must be used wisely and their interaction with the target organisms and the environment should be evaluated and monitored closely, if we are to reliable reap the benefits of disinfection in future generations. In view of the global threat of communicable diseases and emerging and re-emerging pathogens and multidrug-resistant pathogens, the relevance of chemical disinfection is continually increasing. Although this consensus paper pinpoints crucial aspects for strategies of chemical disinfection in terms of the properties of disinfectant agents and disinfection practices in a particularly vulnerable group and setting, i.e., patients in healthcare settings, it takes a comprehensive, holistic approach to do justice to the complexity of the topic of disinfection.Die chemische Desinfektion ist ein unverzichtbares Mittel zur Infektionsprävention. Dies gilt für das Gesundheitswesen, aber auch für alle anderen Bereiche, in denen die Übertragung von Krankheitserregern ein potenzielles Gesundheitsrisiko für Mensch und/oder Tier darstellt. Zu erforschen, wie die Wirksamkeit von Desinfektionsmitteln und des Desinfektionsprozesses sichergestellt werden kann und wann, wie und wo Desinfektionsmaßnahmen durchzuführen sind, ist eine ständige Herausforderung, die eine interdisziplinäre Teamarbeit erfordert. Die wertvollen Ressourcen der für die Desinfektion verwendeten Wirkstoffe müssen klug genutzt werden und ihre Wechselwirkung mit den Zielorganismen und der Umwelt sollte genau bewertet und überwacht werden, wenn wir die Vorteile der Desinfektion in zukünftigen Generationen zuverlässig nutzen wollen. Angesichts der globalen Bedrohung durch übertragbare Krankheiten sowie durch neu- und wiederauftretende Krankheitserreger und multiresistente Erreger nimmt die Bedeutung der chemischen Desinfektion ständig zu. Dieses Konsensuspapier befasst sich vor allem mit den entscheidenden Aspekten für Strategien der chemischen Desinfektion im Hinblick auf die Eigenschaften von Desinfektionsmitteln und Desinfektionspraktiken in einer besonders gefährdeten Gruppe und Umgebung, nämlich bei Patienten in Einrichtungen des Gesundheitswesens, jedoch verfolgt es dabei auch einen umfassenden, ganzheitlichen Ansatz, um der Komplexität des Themas Desinfektion gerecht zu werden