2,751 research outputs found
Effect of aspect ratio on transverse diffusive broadening: A lattice Boltzmann study
We study scaling laws characterizing the inter-diffusive zone between two
miscible fluids flowing side by side in a Y-shape laminar micromixer using the
lattice Boltzmann method. The lattice Boltzmann method solves the coupled 3D
hydrodynamics and mass transfer equations and incorporates intrinsic features
of 3D flows related to this problem. We observe the different power law regimes
occurring at the center of the channel and close to the top/bottom wall. The
extent of the inter-diffusive zone scales as square root of the axial distance
at the center of the channel. At the top/bottom wall, we find an exponent 1/3
at early stages of mixing as observed in the experiments of Ismagilov and
coworkers [Appl. Phys. Lett. 76, 2376 (2000)]. At a larger distance from the
entrance, the scaling exponent close to the walls changes to 1/2 [J.-B. Salmon
et al J. Appl. Phys. 101, 074902 (2007)]. Here, we focus on the effect of
finite aspect ratio on diffusive broadening. Interestingly, we find the same
scaling laws regardless of the channel's aspect ratio. However,the point at
which the exponent 1/3 characterizing the broadening at the top/bottom wall
reverts to the normal diffusive behavior downstream strongly depends on the
aspect ratio. We propose an interpretation of this observation in terms of
shear rate at the side walls. A criterion for the range of aspect ratios with
non-negligible effect on diffusive broadening is also provided.Comment: 19 pages, 7 figure
How specific is synchronous neuronal firing? : Poster presentation
Background Synchronous neuronal firing has been discussed as a potential neuronal code. For testing first, if synchronous firing exists, second if it is modulated by the behaviour, and third if it is not by chance, a large set of tools has been developed. However, to test whether synchronous neuronal firing is really involved in information processing one needs a direct comparison of the amount of synchronous firing for different factors like experimental or behavioural conditions. To this end we present an extended version of a previously published method NeuroXidence [1], which tests, based on a bi- and multivariate test design, whether the amount of synchronous firing above the chance level is different for different factors
Shear stress in lattice Boltzmann simulations
A thorough study of shear stress within the lattice Boltzmann method is
provided. Via standard multiscale Chapman-Enskog expansion we investigate the
dependence of the error in shear stress on grid resolution showing that the
shear stress obtained by the lattice Boltzmann method is second order accurate.
This convergence, however, is usually spoiled by the boundary conditions. It is
also investigated which value of the relaxation parameter minimizes the error.
Furthermore, for simulations using velocity boundary conditions, an artificial
mass increase is often observed. This is a consequence of the compressibility
of the lattice Boltzmann fluid. We investigate this issue and derive an
analytic expression for the time-dependence of the fluid density in terms of
the Reynolds number, Mach number and a geometric factor for the case of a
Poiseuille flow through a rectangular channel in three dimensions. Comparison
of the analytic expression with results of lattice Boltzmann simulations shows
excellent agreement.Comment: 15 pages, 4 figures, 2 table
Microchemistry-dependent simulation of yield stress and flow stress in non-heat treatable Al sheet alloys
Site-selective protein modification via disulfide rebridging for fast tetrazine/trans-cyclooctene bioconjugation
An inverse electron demand DielsâAlder reaction between tetrazine and trans-cyclooctene (TCO) holds great promise for protein modification and manipulation. Herein, we report the design and synthesis of a tetrazine-based disulfide rebridging reagent, which allows the site-selective installation of a tetrazine group into disulfide-containing peptides and proteins such as the hormone somatostatin (SST) and the antigen binding fragment (Fab) of human immunoglobulin G (IgG). The fast and efficient conjugation of the tetrazine modified proteins with three different TCO-containing substrates to form a set of bioconjugates in a site-selective manner was successfully demonstrated for the first time. Homogeneous, well-defined bioconjugates were obtained underlining the great potential of our method for fast bioconjugation in emerging protein therapeutics. The formed bioconjugates were stable against glutathione and in serum, and they maintained their secondary structure. With this work, we broaden the scope of tetrazine chemistry for site-selective protein modification to prepare well-defined SST and Fab conjugates with preserved structures and good stability under biologically relevant conditions
Experimental investigation of the deformation behavior of aluminium-bicrystals
This Max-Planck project report discusses the deformation behaviour of an aluminium-bicrystal with a symmetrical tilt boundary and an initial misorientation of 8.7 Degrees. The specimen was compressed in a channel die to 30% engineering thickness reduction at room temperature. Afterwards the crystal orientations were determined by electron backscatter diffraction (EBSD) and the plastic strain distribution was measured by photogrametry. It was found that the two abutting crystals close to the grain boundary rotate towards each other, whereas the grain interiors increase their mutual misorientation during plastic loading
Modeling of orographic precipitation events in South America to couple hydrological and atmospheric models; part 1: The simulation of rain with the Mesoscale Model GESIMA
Globalmodelle sind aufgrund ihres groben Gitters (60 x 60 km) nur unzureichend in der Lage kleinskalige Prozesse (orographische NiederschlagsverstÀrkung) in der AtmosphÀre aufzulösen. Mit Mesoskalenmodellen z.B. dem GESIMA (5 x 5 km) können deshalb die
physikalische Grundlagen der AtmosphĂ€re (Wolken- und Niederschlagsbildung) besser studiert und eine Kopplung mit hydrologischen Abflussmodellen erprobt werden. ZukĂŒnftig sieht dieses Projekt genau das vor, wobei der erste Teil, die Arbeit mit dem meteorologische Modell hier vorgestellt werden soll. Starkniederschlagserreignisse sind vielerorts auf der Welt mit charakteristischen Wetterlagen verbunden, die quasi ĂŒber Tage unverĂ€ndert ergiebigen Regen produzieren. Initialisiert mit den lokalen Vertikalprofilen aus Radiosondendaten, produzieren das prognostische
Mesoskalenmodell GESIMA und das diagnostische Niederschlagsberechungsverfahren (MAXRR) maximale Regenmengen vergleichbarer GröĂenordnung.Global models are insufficient to solve small scale atmospheric processes (e.g. orographic precipitation) due to their gross resolution (60 x 60 km). With mesoscale models e.g. the GESIMA (5 x 5 km), the physical fundamentals of the atmosphere (formation of precipitation
and clouds) can better be studied and a coupling with hydrological models be tested through. This project plans exactly, as a first step, the work with the cited meteorological model. Heavy rainfall events are connected with characteristic weather conditions in many places in the world which produce invariably rain quasi over days. Initialized with the local vertical profiles from radiosonde data, the prediction model GESIMA and the diagnostic model MAXRR produced rain quantities of comparable order of magnitude
Viscous coalescence of droplets: a Lattice Boltzmann study
The coalescence of two resting liquid droplets in a saturated vapor phase is
investigated by Lattice Boltzmann simulations in two and three dimensions. We
find that, in the viscous regime, the bridge radius obeys a t^{1/2}-scaling law
in time with the characteristic time scale given by the viscous time. Our
results differ significantly from the predictions of existing analytical
theories of viscous coalescence as well as from experimental observations.
While the underlying reason for these deviations is presently unknown, a simple
scaling argument is given that describes our results well.Comment: 12 pages, 10 figures; as published in Phys. Fluid
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