1,866 research outputs found
Challenges of a feasible route towards sustainability in environmental protection
Anaerobic processes for treatment of low and high strength wastewaters and solid wastes constitute the core method in the natural biological mineralization (NBM) treatment concept. When adequately combined with the complementary NBM-systems and modern clean water saving practices in wastewater collection and transport, they represent a feasible route to sustainable environmental protection (EPsus), in essence even towards a more sustainable society. Despite the development and implementation of modern high rate Anaerobic Wastewater Treatment (AnWT-) systems and complementary innovative NBM-processes, the considerable progress made since the seventies in fundamental insights in microbiology, biochemistry and process technology, still numerous challenging improvements in the NBM-field can be realized. This contribution is mainly based on the insights attained from wide ranging literature evaluations and the results of experimental research conducted by numerous PhD students who participated in our group over the last four decades. An attempt is made here to identify major facets on which an improved insight can, and consequently should, be obtained in order to accomplish more optimal operation and design of various types of Anaerobic Degradation (AnDeg-) processes
Competition between shear banding and wall slip in wormlike micelles
The interplay between shear band (SB) formation and boundary conditions (BC)
is investigated in wormlike micellar systems (CPyCl--NaSal) using ultrasonic
velocimetry coupled to standard rheology in Couette geometry. Time-resolved
velocity profiles are recorded during transient strain-controlled experiments
in smooth and sand-blasted geometries. For stick BC standard SB is observed,
although depending on the degree of micellar entanglement temporal fluctuations
are reported in the highly sheared band. For slip BC wall slip occurs only for
shear rates larger than the start of the stress plateau. At low entanglement,
SB formation is shifted by a constant , while for more
entangled systems SB constantly "nucleate and melt." Micellar orientation
gradients at the walls may account for these original features.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
Self-diffusion of rod-like viruses in the nematic phase
We measure the self-diffusion of colloidal rod-like virus {\it fd} in an
isotropic and nematic phase. A low volume fraction of viruses are labelled with
a fluorescent dye and dissolved in a background of unlabelled rods. The
trajectories of individual rods are visualized using fluorescence microscopy
from which the diffusion constant is extracted. The diffusion parallel
() and perpendicular () to the nematic director is
measured. The ratio () increases monotonically with
increasing virus concentration. Crossing the isotropic-nematic phase boundary
results in increase of and decrease of when
compared to the diffusion in the isotropic phase ().Comment: 7 pages, 4 figures, to appear in Europhysics Letter
Interplay between a hydrodynamic instability and a phase transition: the Faraday instability in dispersions of rodlike colloids
Strong effects of the Faraday instability on suspensions of rodlike colloidal
particles are reported through measurements of the critical acceleration and of
the surface wave amplitude. We show that the transition to parametrically
excited surface waves displays discontinuous and hysteretic features. This
subcritical behaviour is attributed to the shear-thinning properties of our
colloidal suspensions thanks to a phenomenological model based on rheological
data under large amplitude oscillatory shear. Birefringence measurements
provide direct evidence that Faraday waves induce local nematic ordering of the
rodlike colloids. While local alignment simply follows the surface oscillations
for dilute, isotropic suspensions, permanent nematic patches are generated by
surface waves in samples close to the isotropic-to-nematic transition and above
the transition large domains align in the flow direction. This strong coupling
between the fluid microstructure and a hydrodynamic instability is confirmed by
numerical computations based on the microstructural response of rodlike viruses
in shear flow.Comment: 8 pages, 6 figure
Fast Diffusion of Long Guest Rods in a Lamellar Phase of Short Host Particles
We investigate the dynamic behavior of long guest rod-like particles immersed
in liquid crystalline phases formed by shorter host rods, tracking both guest
and host particles by fluorescence microscopy. Counter-intuitively, we evidence
that long rods diffuse faster than short rods forming the one-dimensional
ordered smectic-A phase. This results from the larger and non-commensurate size
of the guest particles as compared to the wavelength of the energy landscape
set by the lamellar stack of liquid slabs. The long guest particles are also
shown to be still mobile in the crystalline smectic-B phase, as they generate
their own voids in the adjacent layers.Comment: 5 pages, 4 figures, Accepted in Phys. Rev. Let
An outbreak of legionnaires' disease at a flower show: clinical findings and studies on host defense mechanisms
Dynamic Response of Block Copolymer Wormlike Micelles to Shear Flow
The linear and non-linear dynamic response to an oscillatory shear flow of
giant wormlike micelles consisting of Pb-Peo block copolymers is studied by
means of Fourier transform rheology. Experiments are performed in the vicinity
of the isotropic-nematic phase transition concentration, where the location of
isotropic-nematic phase transition lines is determined independently. Strong
shear-thinning behaviour is observed due to critical slowing down of
orientational diffusion as a result of the vicinity of the isotropic- nematic
spinodal. This severe shear-thinning behaviour is shown to result in gradient
shear banding. Time-resolved Small angle neutron scattering experiments are
used to obtain insight in the microscopic phenomena that underly the observed
rheological response. An equation of motion for the order-parameter tensor and
an expression of the stress tensor in terms of the order-parameter tensor are
used to interpret the experimental data, both in the linear and non-linear
regime. Scaling of the dynamic behaviour of the orientational order parameter
and the stress is found when critical slowing down due to the vicinity of the
isotropic-nematic spinodal is accounted for.Comment: Accepted by J. Phys.: Condens. Matter, CODEF II Special Issue. 20
pages, 9 figure
Crystallization Kinetics of Colloidal Spheres under Stationary Shear Flow
A systematic experimental study of dispersions of charged colloidal spheres
is presented on the effect of steady shear flow on nucleation and
crystal-growth rates. In addition, the non-equilibrium phase diagram as far as
the melting line is concerned is measured. Shear flow is found to strongly
affect induction times, crystal growth rates and the location of the melting
line. The main findings are that (i) the crystal growth rate for a given
concentration exhibits a maximum as a function of the shear rate, (ii) contrary
to the monotonous increase of the growth rate with increasing concentration in
the absence of flow, a maximum of the crystal growth rate as a function of
concentration is observed for sheared systems, and (iii) the induction time for
a given concentration exhibits a maximum as a function of the shear rate. These
findings will be partly explained on a qualitative level.Comment: 17 pages, 10 figures, accepted in Langmui
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