1,208 research outputs found
Capillary focusing close to a topographic step: Shape and instability of confined liquid filaments
Step-emulsification is a microfluidic technique for droplet generation which
relies on the abrupt decrease of confinement of a liquid filament surrounded by
a continuous phase. A striking feature of this geometry is the transition
between two distinct droplet breakup regimes, the "step-regime" and
"jet-regime", at a critical capillary number. In the step-regime, small and
monodisperse droplets break off from the filament directly at a topographic
step, while in the jet-regime a jet protrudes into the larger channel region
and large plug-like droplets are produced. We characterize the breakup behavior
as a function of the filament geometry and the capillary number and present
experimental results on the shape and evolution of the filament for a wide
range of capillary numbers in the jet-regime. We compare the experimental
results with numerical simulations. Assumptions based on the smallness of the
depth of the microfluidic channel allow to reduce the governing equations to
the Hele-Shaw problem with surface tension. The full nonlinear equations are
then solved numerically using a volume-of-fluid based algorithm. The
computational framework also captures the transition between both regimes,
offering a deeper understanding of the underlying breakup mechanism
Energy dissipation in sheared wet granular assemblies
Energy dissipation in sheared dry and wet granulates is considered in the presence of an externally applied confining pressure. Discrete element simulations reveal that for sufficiently small confining pressures, the energy dissipation is dominated by the effects related to the presence of cohesive forces between the particles. The residual resistance against shear can be quantitatively explained by a combination of two effects arising in a wet granulate: (i) enhanced friction at particle contacts in the presence of attractive capillary forces and (ii) energy dissipation due to the rupture and reformation of liquid bridges. Coulomb friction at grain contacts gives rise to an energy dissipation which grows linearly with increasing confining pressure for both dry and wet granulates. Because of a lower Coulomb friction coefficient in the case of wet grains, as the confining pressure increases the energy dissipation for dry systems is faster than for wet ones
Generic morphologies of viscoelastic dewetting fronts
A simple model is put forward which accounts for the occurrence of certain
generic dewetting morphologies in thin liquid coatings. It demonstrates that by
taking into account the elastic properties of the coating, a morphological
phase diagram may be derived which describes the observed structures of
dewetting fronts. It is demonstrated that dewetting morphologies may also serve
to determine nanoscale rheological properties of liquids.Comment: 4 pages, 2 figure
Transcripts with in silico predicted RNA structure are enriched everywhere in the mouse brain
BACKGROUND: Post-transcriptional control of gene expression is mostly conducted by specific elements in untranslated regions (UTRs) of mRNAs, in collaboration with specific binding proteins and RNAs. In several well characterized cases, these RNA elements are known to form stable secondary structures. RNA secondary structures also may have major functional implications for long noncoding RNAs (lncRNAs). Recent transcriptional data has indicated the importance of lncRNAs in brain development and function. However, no methodical efforts to investigate this have been undertaken. Here, we aim to systematically analyze the potential for RNA structure in brain-expressed transcripts. RESULTS: By comprehensive spatial expression analysis of the adult mouse in situ hybridization data of the Allen Mouse Brain Atlas, we show that transcripts (coding as well as non-coding) associated with in silico predicted structured probes are highly and significantly enriched in almost all analyzed brain regions. Functional implications of these RNA structures and their role in the brain are discussed in detail along with specific examples. We observe that mRNAs with a structure prediction in their UTRs are enriched for binding, transport and localization gene ontology categories. In addition, after manual examination we observe agreement between RNA binding protein interaction sites near the 3ā UTR structures and correlated expression patterns. CONCLUSIONS: Our results show a potential use for RNA structures in expressed coding as well as noncoding transcripts in the adult mouse brain, and describe the role of structured RNAs in the context of intracellular signaling pathways and regulatory networks. Based on this data we hypothesize that RNA structure is widely involved in transcriptional and translational regulatory mechanisms in the brain and ultimately plays a role in brain function
Thin film evolution equations from (evaporating) dewetting liquid layers to epitaxial growth
In the present contribution we review basic mathematical results for three
physical systems involving self-organising solid or liquid films at solid
surfaces. The films may undergo a structuring process by dewetting,
evaporation/condensation or epitaxial growth, respectively. We highlight
similarities and differences of the three systems based on the observation that
in certain limits all of them may be described using models of similar form,
i.e., time evolution equations for the film thickness profile. Those equations
represent gradient dynamics characterized by mobility functions and an
underlying energy functional.
Two basic steps of mathematical analysis are used to compare the different
system. First, we discuss the linear stability of homogeneous steady states,
i.e., flat films; and second the systematics of non-trivial steady states,
i.e., drop/hole states for dewetting films and quantum dot states in epitaxial
growth, respectively. Our aim is to illustrate that the underlying solution
structure might be very complex as in the case of epitaxial growth but can be
better understood when comparing to the much simpler results for the dewetting
liquid film. We furthermore show that the numerical continuation techniques
employed can shed some light on this structure in a more convenient way than
time-stepping methods.
Finally we discuss that the usage of the employed general formulation does
not only relate seemingly not related physical systems mathematically, but does
as well allow to discuss model extensions in a more unified way
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Solar spectral conversion for improving the photosynthetic activity in algae reactors
Sustainable biomass production is expected to be one of the major supporting pillars for future energy supply, as well as for renewable material provision. Algal beds represent an exciting resource for biomass/biofuel, fine chemicals and CO2 storage. Similar to other solar energy harvesting techniques, the efficiency of algal photosynthesis depends on the spectral overlap between solar irradiation and chloroplast absorption. Here we demonstrate that spectral conversion can be employed to significantly improve biomass growth and oxygen production rate in closed-cycle algae reactors. For this purpose, we adapt a photoluminescent phosphor of the type Ca 0.59Sr0.40Eu0.01S, which enables efficient conversion of the green part of the incoming spectrum into red light to better match the Qy peak of chlorophyll b. Integration of a Ca 0.59Sr0.40Eu0.01S backlight converter into a flat panel algae reactor filled with Haematococcus pluvialis as a model species results in significantly increased photosynthetic activity and algae reproduction rate
Mapping QGP properties in Pb--Pb and Xe--Xe collisions at the LHC
A phenomenological analysis of the experimental measurements of transverse
momentum spectra of identified charged hadrons and strange hyperons in \PbPb
and \XeXe collisions at the LHC is presented. The analysis is based on the
relativistic fluid dynamics description implemented in the numerically
efficient \fluidum approach. Building on our previous work, we separate in our
treatment the chemical and kinetic freeze-out, and incorporate the partial
chemical equilibrium to describe the late stages of the collision evolution.
This analysis makes use of Bayesian inference to determine key parameters of
the QGP evolution and its properties including the shear and bulk viscosity to
entropy ratios, the initialisation time, the initial entropy density, and the
freeze-out temperatures. The physics parameters and their posterior
probabilities are extracted using a global search in multidimensional space
with modern machine learning tools, such as ensembles of neural networks. We
employ our newly developed fast framework to assess systematic uncertainties in
the extracted model parameters by systematically varying key components of our
analysis.Comment: 17 pages, 7 figure
Origin of the highest energy cosmic rays observed
Introducing a simple Galactic wind model patterned after the solar wind we
show that back-tracing the orbits of the highest energy cosmic events suggests
that they may all come from the Virgo cluster, and so probably from the active
radio galaxy M87. This confirms a long standing expectation. Those powerful
radio galaxies that have their relativistic jets stuck in the interstellar
medium of the host galaxy, such as 3C147, will then enable us to derive limits
on the production of any new kind of particle, expected in some extensions of
the standard model in particle physics. New data from HIRES will be crucial in
testing the model proposed here.Comment: At TAUP99, the 6th international workshop on topics in Astroparticle
Physics and Underground Physics, College de France, Eds. J. Dumarchez, M.
Froissart, D. Vignaud, (Sep 1999
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