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  • 1
    Language: English
    In: Water Research, 2010, Vol.44(4), pp.1246-1254
    Description: Dispersion describes the spreading of a tracer or contaminant in an aquifer. Detailed knowledge of dispersion is the key to successful risk assessment in case of groundwater pollution or groundwater protection. The dispersion of colloids on the pore scale is controlled by flow velocity, ionic strength, colloid size, colloid concentration, and colloid–matrix interactions. The objective of this study was to provide quantitative data and to assess the scale dependency of colloid dispersion on the pore scale. The positions of carboxylated polystyrene microspheres (1 μm, 0.5 μm) were recorded during transport experiments in silicon micromodels with three pore topologies. The positions were combined into particle trajectories revealing the flow path of individual colloids. More than thousand trajectories were evaluated for each experiment to obtain the dispersivity of the colloids for flow distances between 10 and 1000 μm. All experiments were run at high Peclet numbers. The pore scale dispersivity was on the order of 8–30% of the flow distance with pure water, dependent on the heterogeneity of the pore topology. The dispersivity was positively correlated with the ionic strength and inversely correlated with the colloid size and the flow velocity. A coating of the micromodel surface with humic acid also increased dispersivity. The quantitative data set presented here supports the theoretical framework for colloid transport and allows to parametrize colloid transport on the pore scale.
    Keywords: Colloid ; Transport ; Dispersivity ; Micromodel ; Particle Tracking ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 2
    Language: English
    In: The Science of the Total Environment, Dec 1, 2015, Vol.535, p.122(9)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.scitotenv.2014.12.026 Byline: Melanie Kuhn, Natalia P. Ivleva, Sondra Klitzke, Reinhard Niessner, Thomas Baumann Abstract: The widespread use of engineered inorganic nanoparticles (EINP) leads to a growing risk for an unintended release into the environment. Despite the good characterization of EINP in regard to their function scale and the application areas, there is still a gap of knowledge concerning their behaviour in the different environmental compartments. Due to their high surface to volume ratio, surface properties and existence or development of a coating are of high importance for their stability and transport behaviour. However, analytical methods to investigate organic coatings on nanoparticles in aqueous media are scarce. We used Raman microspectroscopy in combination with surface-enhanced Raman scattering (SERS) to investigate humic acid coatings on silver nanoparticles under environmentally relevant conditions and in real world samples. This setup is more challenging than previous mechanistic studies using SERS to characterize the humic acids in tailored settings where only one type of organic matter is present and the concentrations of the nanoparticles can be easily adjusted to the experimental needs. SERS offers the unique opportunity to work with little sample preparation directly with liquid samples, thus significantly reducing artefacts. SERS spectra of different natural organic matter brought into contact with silver nanoparticles indicate humic acid in close proximity to the nanoparticles. This coating was also present after several washing steps by centrifugation and resuspension in deionized water and after an increase in ionic strength. Article History: Received 15 October 2014; Revised 5 December 2014; Accepted 5 December 2014
    Keywords: Nanoparticles – Investigations ; Coatings – Investigations ; Humic Acids – Investigations
    ISSN: 0048-9697
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: Inorganic chemistry, 02 December 2013, Vol.52(23), pp.13509-20
    Description: Bridging P(^)N ligands bearing five-membered heterocyclic moieties such as tetrazoles, 1,2,4-triazoles, oxadiazoles, thiadiazoles, and oxazoles have been investigated regarding their complexation behavior with copper(I) iodide as metal salts. Different complex structures were found, depending either on the ligand itself or on the ligand-to-metal ratios used in the complexation reaction. Two different kinds of luminescent dinuclear complex structures and a kind of tetranuclear complex structure were revealed by X-ray single-crystal analyses and were further investigated for their photophysical properties. The emission maxima of these complexes are in the blue to yellow region of the visible spectrum for the dinuclear complexes and in the yellow to orange region for the tetranuclear complexes. Further investigations using density functional theory (DFT) show that the highest occupied molecular orbital (HOMO) is located mainly on the metal halide cores, while the lowest unoccupied molecular orbital (LUMO) resides mostly in the ligand sphere of the complexes. The emission properties were further examined in different environments such as neat powders, neat films, PMMA matrices, or dichloromethane solutions, revealing the high potential of these complexes for their application in organic light-emitting diodes. Especially complexes with 1,2,4-triazole moieties feature emission maxima in the blue region of the visible spectrum and quantum yields up to 95% together with short decay times of about 1-4 μs and are therefore promising candidates for blue-emitting materials in OLEDs.
    Keywords: Copper Compounds -- Structure ; Copper Compounds -- Electric Properties ; Luminescence -- Analysis ; Phosphorus Compounds -- Structure ; Phosphorus Compounds -- Electric Properties ; Nitrogen (Chemical element) -- Structure ; Nitrogen (Chemical element) -- Electric Properties;
    ISSN: 00201669
    E-ISSN: 1520-510X
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  • 4
    In: Chemical Communications, 2013, Vol.49(58), pp.6501-6503
    Description: Strongly luminescent, neutral copper( i ) complexes bearing 5-(2-pyridyl)tetrazolate and various phosphine ligands were synthesized. While the cationic copper( i ) precursors 1b4b do not exceed photoluminescence quantum yields (PLQY) of 446%, the neutral complexes 1a4a show PLQYs of up to 89%.
    Keywords: Coordination Complexes -- Chemistry ; Copper -- Chemistry ; Phosphines -- Chemistry ; Tetrazoles -- Chemistry;
    ISSN: 1359-7345
    E-ISSN: 1364-548X
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  • 5
    Language: English
    In: The Science of the Total Environment, Dec 1, 2015, Vol.535, p.1(2)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.scitotenv.2015.06.006 Byline: Gabriele E. Schaumann, Thomas Baumann, Friederike Lang, George Metreveli, Hans-Jorg Vogel
    Keywords: Soils
    ISSN: 0048-9697
    Source: Cengage Learning, Inc.
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  • 6
    Language: English
    In: Langmuir : the ACS journal of surfaces and colloids, 05 March 2013, Vol.29(9), pp.3034-44
    Description: Polymorphism is often linked to the choice of processing solvents. Packing effects or the preference of one certain conformer as possible causes of this phenomenon are strongly dependent on solvents and especially on their polarity. Even in amorphous solids, the microstructure can be controlled by the choice of solvents. Polymorphs or amorphous solids featuring different packing densities can exhibit different properties in terms of stability or optical effects. The influence of these effects on a binuclear, strongly luminescent copper(I) complex was investigated. Many possible applications for luminescent, amorphous coordination compounds, such as organic light-emitting diodes, sensors, and organic lasers, rely on photophysical properties like quantum efficiency to be repeatable. The effect of processing solvents in this context is often underestimated, but very relevant for utilization in device manufacturing and should therefore be understood more deeply. In this work, theoretical derivations, DFT calculations, X-ray-diffraction, photoluminescence spectroscopy, and the time-dependent single-photon-counting-technique (TDSPC) were used to understand this phenomenon more deeply. The influence of five different solvents on Cu2I2(MePyrPHOS)3 was probed. This resulted in a modulation of the photoluminescence quantum yield ϕ between 0.5 and 0.9 in amorphous solid state. A new polymorph of the material with slightly reduced values for ϕ has been identified. The reduced efficiency could be correlated with a higher porosity and a reduced packing density. Dense packing reduces nonradiative decay by geometrical fixation and thus increases the quantum efficiency. The existence of similar effects on aluminum and iridium compounds has been confirmed by application of different processing solvents on Alq3 and Ir(ppy)3. These results show that a tuning of the efficiency of a emissive metal complexes by choosing a proper processing solvent is possible. If highly efficient materials for practical applications are desired, an evaluation of multiple solvents has to be considered.
    ISSN: 07437463
    E-ISSN: 1520-5827
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  • 7
    Language: English
    In: Chemistry – A European Journal, 26 May 2014, Vol.20(22), pp.6578-6590
    Description: Easy come, easy go: the great structural diversity of Cu complexes is an ambivalent trait. Apart from the well‐known catalytic properties of Cu, a great number of potent luminescent complexes have been found in the last ten years featuring a plethora of structural motifs. The downside of this variety is the undesired formation of other species upon processing. In here, strategies to avoid this behavior are presented: Only one favorable structural unit often exists for multinuclear Cu complexes with bridging ligands. In addition, these complexes exhibit favorable photophysical properties due to cooperative effects of the metal halide core. Furthermore, we demonstrate the broad range of applications of emitting Cu compounds. : The great structural diversity of Cu complexes is an ambivalent trait. Apart from the well‐known catalytic properties of Cu, a great number of potent luminescent complexes (see figure) have been found in the last ten years featuring a plethora of structural motifs. The downside of this variety is the undesired formation of other species upon processing. Strategies to avoid this behavior are presented.
    Keywords: Copper ; Oleds ; Phosphines ; Photoluminescence ; Singlet Harvesting
    ISSN: 0947-6539
    E-ISSN: 1521-3765
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  • 8
    Language: English
    In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2005, Vol.265(1), pp.2-10
    Description: The effects of heterogeneous grain packing on colloid transport were evaluated in flow-through columns using magnetic resonance imaging (MRI). Two columns were packed, each with a core of fine-grained silica gel surrounded by a shell of coarse-grained silica gel. In column 1, 600–850 μm silica gel was surrounded by 850–1000 μm silica gel. In column 2, 250–600 μm silica gel was surrounded by 850–1000 μm silica gel. Both columns were continuously purged with water and colloids were introduced as pulses. MRI images of column 1 showed that colloid transport in the core and shell was not distinguishable. However, colloid transport was slightly faster along the bottom of the column. -weighted images showed that small variations in the packing density of silica gel caused this effect. MRI images of column 2 showed that colloid transport in the core was much slower than colloid transport in the shell. Colloid exchange between the shell and the core was also observed. Colloid transport velocities and collision efficiencies were calculated from the images. In agreement with the visualization, velocities for column 1 increased from the top to bottom of the column and velocities for column 2 were greater in the shell than in the core. Collision efficiencies were calculated, but trends were not apparent because of the difficulty of applying filtration theory to heterogeneous media. Velocities from images were compared to those from conventional experiments where colloid concentrations were measured at the column effluent. While often comparable, results from the latter mask many of the complexities that control the overall rate of colloid transport. Since these complexities can give rise to very different transport behavior, it is critical to understand their effects in real systems. Hence, MRI is a technique that has the power to elucidate many of the small-scale processes that affect the behavior of colloids in the field.
    Keywords: Colloid Transport ; Magnetic Resonance Imaging ; Attachment ; Engineering ; Chemistry
    ISSN: 0927-7757
    E-ISSN: 1873-4359
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  • 9
    Language: English
    In: Neuroscience Letters, 2011, Vol.493(3), pp.92-96
    Description: ► Different profiles of activity-dependent slowing of C fibres have been identified. ► Each profile correlates with a functional modality. ► The function of fibres with the least activity-dependent has not been yet identified. ► We describe one such a profile corresponding to a low threshold, tactile C fibre. It has been previously shown that unmyelinated afferent fibres in human skin are differentiated not only by their receptor characteristics, but also by their profiles of activity-dependent slowing. One type of profile, described originally as ‘type 3’, is different from that of nociceptors (type 1), cold afferents (type 2) and sympathetic efferents (type 4), in that these fibres display a minimal activity-dependent slowing (∼1% at 2 Hz). However, their function remains to be determined. Here we describe one unit with a typical ‘type 3’ activity-dependent slowing profile recorded from an undamaged fascicle of the superficial peroneal nerve of a patient. Its conduction velocity was 1.8 m s and it slowed by 1.3% during the 2 Hz tetanus. This unit had a mechanical receptive field in the hairy skin and responded readily to weak mechanical stimuli, and not to cold. This suggests that the low threshold unmyelinated mechanoreceptors recently described in human hairy skin are probably endowed with a ‘type 3’ activity-dependent profile.
    Keywords: Unmyelinated Fibres ; Microneurography ; Low Threshold Mechanoreceptors ; Medicine ; Anatomy & Physiology
    ISSN: 0304-3940
    E-ISSN: 1872-7972
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  • 10
    Article
    Article
    Language: German
    In: Praxis, 04 September 2013, Vol.102(18), pp.1129-35
    Description: Jugendliche sind eine medizinisch unterversorgte Altersgruppe. Sind befinden sich in der Transition vom Kinderarzt weg zum Hausarzt. Sie sind häufig vom Ersten nicht ganz gelöst, geschweige bei Letzterem angekommen. In diesem Artikel wird eine sehr kurze Zusammenfassung alterstypischer Probleme und Fragestellungen mit den praktischen Erfahrungen, speziell der den Jugendlichen entgegenkommenden «Walk-in Praxis» ergänzt.
    Keywords: Motivation ; Adolescent Health Services -- Statistics & Numerical Data ; Ambulatory Care Facilities -- Statistics & Numerical Data ; Referral and Consultation -- Statistics & Numerical Data ; Transition to Adult Care -- Statistics & Numerical Data
    ISSN: 1661-8157
    E-ISSN: 16618165
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