94 research outputs found
Natural tracers in recent groundwaters from different Alpine aquifers
Groundwater with underground residence times between days and a few years have been investigated over more than 20 years from 487 remote sites located in different aquifer types in the Alpine belt. Analysis of the data reveals that groundwaters evolved in crystalline, evaporite, carbonate, molasse, and flysch aquifers can be clearly distinguished based on their major and trace element composition and degree of mineralisation. A further subdivision can be made even within one aquifer type based on the trace element compositions, which are characteristic for the lithologic environment. Major and trace element concentrations can be quantitatively described by interaction of the groundwater with the aquifer-specific mineralogy along the flow path. Because all investigated sites show minimal anthropogenic influences, the observed concentration ranges represent the natural background concentrations and can thus serve as a "geo-referenceâ for recent groundwaters from these five aquifer types. This "geo-referenceâ is particularly useful for the identification of groundwater contamination. It further shows that drinking water standards can be grossly exceeded for critical elements by purely natural processe
Evidence for TiON sputtered surfaces showing accelerated antibacterial activity under simulated solar irradiation
New evidence is reported for TiON sputtered polyester surfaces activated by sunlight irradiation leading to the accelerated bacterial inactivation in the minute range. The absorption in Kubelka-Munk units of the TiON film was observed to be directly proportional to the time of Escherichia coil inactivation as detected by diffuse reflection spectroscopy (DRS). TiON layers were characterized by electron microscopy and by high angle angular dark field (HAADF) showing the continuous coverage of the polyester fibers by the TiON film. Ti4+/Ti3+ redox catalysis was detected on the TiON surface by the XPS shifts during the bacteria inactivation process. Production of HO radicals on TiON polyester as a function of sunlight irradiation was determined following the fluorescence of 2-hydroxyterephthalic acid. Release of Na and K-ions was determined by ICP-MS and provides the evidence that cell wall damage is a preceding step leading the bacterial inactivation. A stable performance of the TiON films was observed during repetitive bacterial inactivation. (C) 2013 Elsevier Ltd. All rights reserved
Easily-prepared dinickel phosphide (Ni2P) nanoparticles as an efficient and robust electrocatalyst for hydrogen evolution
Polydispersed dinickel phosphide (Ni2P) nanoparticles were synthesized by a simple and scalable solid-state reaction. These nanoparticles are an excellent and robust catalyst for the electrochemical hydrogen evolution reaction, operating in both acidic and basic solutions
Parallel flow in Hele-Shaw cells with ferrofluids
Parallel flow in a Hele-Shaw cell occurs when two immiscible liquids flow
with relative velocity parallel to the interface between them. The interface is
unstable due to a Kelvin-Helmholtz type of instability in which fluid flow
couples with inertial effects to cause an initial small perturbation to grow.
Large amplitude disturbances form stable solitons. We consider the effects of
applied magnetic fields when one of the two fluids is a ferrofluid. The
dispersion relation governing mode growth is modified so that the magnetic
field can destabilize the interface even in the absence of inertial effects.
However, the magnetic field does not affect the speed of wave propagation for a
given wavenumber. We note that the magnetic field creates an effective
interaction between the solitons.Comment: 12 pages, Revtex, 2 figures, revised version (minor changes
Gravity-driven instability in a spherical Hele-Shaw cell
A pair of concentric spheres separated by a small gap form a spherical
Hele-Shaw cell. In this cell an interfacial instability arises when two
immiscible fluids flow. We derive the equation of motion for the interface
perturbation amplitudes, including both pressure and gravity drivings, using a
mode coupling approach. Linear stability analysis shows that mode growth rates
depend upon interface perimeter and gravitational force. Mode coupling analysis
reveals the formation of fingering structures presenting a tendency toward
finger tip-sharpening.Comment: 13 pages, 4 ps figures, RevTex, to appear in Physical Review
Mode-coupling approach to non-Newtonian Hele-Shaw flow
The Saffman-Taylor viscous fingering problem is investigated for the
displacement of a non-Newtonian fluid by a Newtonian one in a radial Hele-Shaw
cell. We execute a mode-coupling approach to the problem and examine the
morphology of the fluid-fluid interface in the weak shear limit. A differential
equation describing the early nonlinear evolution of the interface modes is
derived in detail. Owing to vorticity arising from our modified Darcy's law, we
introduce a vector potential for the velocity in contrast to the conventional
scalar potential. Our analytical results address how mode-coupling dynamics
relates to tip-splitting and side branching in both shear thinning and shear
thickening cases. The development of non-Newtonian interfacial patterns in
rectangular Hele-Shaw cells is also analyzed.Comment: 14 pages, 5 ps figures, Revtex4, accepted for publication in Phys.
Rev.
Radial fingering in a Hele-Shaw cell: a weakly nonlinear analysis
The Saffman-Taylor viscous fingering instability occurs when a less viscous
fluid displaces a more viscous one between narrowly spaced parallel plates in a
Hele-Shaw cell. Experiments in radial flow geometry form fan-like patterns, in
which fingers of different lengths compete, spread and split. Our weakly
nonlinear analysis of the instability predicts these phenomena, which are
beyond the scope of linear stability theory. Finger competition arises through
enhanced growth of sub-harmonic perturbations, while spreading and splitting
occur through the growth of harmonic modes. Nonlinear mode-coupling enhances
the growth of these perturbations with appropriate relative phases, as we
demonstrate through a symmetry analysis of the mode coupling equations. We
contrast mode coupling in radial flow with rectangular flow geometry.Comment: 36 pages, 5 figures, Latex, added references, to appear in Physica D
(1998
The Saffman-Taylor problem on a sphere
The Saffman-Taylor problem addresses the morphological instability of an
interface separating two immiscible, viscous fluids when they move in a narrow
gap between two flat parallel plates (Hele-Shaw cell). In this work, we extend
the classic Saffman-Taylor situation, by considering the flow between two
curved, closely spaced, concentric spheres (spherical Hele-Shaw cell). We
derive the mode-coupling differential equation for the interface perturbation
amplitudes and study both linear and nonlinear flow regimes. The effect of the
spherical cell (positive) spatial curvature on the shape of the interfacial
patterns is investigated. We show that stability properties of the fluid-fluid
interface are sensitive to the curvature of the surface. In particular, it is
found that positive spatial curvature inhibits finger tip-splitting. Hele-Shaw
flow on weakly negative, curved surfaces is briefly discussed.Comment: 26 pages, 4 figures, RevTex, accepted for publication in Phys. Rev.
Modulation of Localized States in Electroconvection
We report on the effects of temporal modulation of the driving force on a
particular class of localized states, known as worms, that have been observed
in electroconvection in nematic liquid crystals. The worms consist of the
superposition of traveling waves and have been observed to have unique, small
widths, but to vary in length. The transition from the pure conduction state to
worms occurs via a backward bifurcation. A possible explanation of the
formation of the worms has been given in terms of coupled amplitude equations.
Because the worms consist of the superposition of traveling waves, temporal
modulation of the control parameter is a useful probe of the dynamics of the
system. We observe that temporal modulation increases the average length of the
worms and stabilizes worms below the transition point in the absence of
modulation.Comment: 4 pages, 4 figure
Genetic variants of the alpha-synuclein gene SNCA are associated with multiple system atrophy.
Multiple system atrophy (MSA) is a progressive neurodegenerative disorder characterized by parkinsonism, cerebellar ataxia and autonomic dysfunction. Pathogenic mechanisms remain obscure but the neuropathological hallmark is the presence of alpha-synuclein-immunoreactive glial cytoplasmic inclusions. Genetic variants of the alpha-synuclein gene, SNCA, are thus strong candidates for genetic association with MSA. One follow-up to a genome-wide association of Parkinson's disease has identified association of a SNP in SNCA with MSA
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