91 research outputs found
Turing instabilities in a mathematical model for signaling networks
GTPase molecules are important regulators in cells that continuously run
through an activation/deactivation and membrane-attachment/membrane-detachment
cycle. Activated GTPase is able to localize in parts of the membranes and to
induce cell polarity. As feedback loops contribute to the GTPase cycle and as
the coupling between membrane-bound and cytoplasmic processes introduces
different diffusion coefficients a Turing mechanism is a natural candidate for
this symmetry breaking. We formulate a mathematical model that couples a
reaction-diffusion system in the inner volume to a reaction-diffusion system on
the membrane via a flux condition and an attachment/detachment law at the
membrane. We present a reduction to a simpler non-local reaction-diffusion
model and perform a stability analysis and numerical simulations for this
reduction. Our model in principle does support Turing instabilities but only if
the lateral diffusion of inactivated GTPase is much faster than the diffusion
of activated GTPase.Comment: 23 pages, 5 figures; The final publication is available at
http://www.springerlink.com http://dx.doi.org/10.1007/s00285-011-0495-
Pathogen- and Host-Directed Antileishmanial Effects Mediated by Polyhexanide (PHMB)
BACKGROUND:Cutaneous leishmaniasis (CL) is a neglected tropical disease caused by protozoan parasites of the genus Leishmania. CL causes enormous suffering in many countries worldwide. There is no licensed vaccine against CL, and the chemotherapy options show limited efficacy and high toxicity. Localization of the parasites inside host cells is a barrier to most standard chemo- and immune-based interventions. Hence, novel drugs, which are safe, effective and readily accessible to third-world countries and/or drug delivery technologies for effective CL treatments are desperately needed. METHODOLOGY/PRINCIPAL FINDINGS:Here we evaluated the antileishmanial properties and delivery potential of polyhexamethylene biguanide (PHMB; polyhexanide), a widely used antimicrobial and wound antiseptic, in the Leishmania model. PHMB showed an inherent antileishmanial activity at submicromolar concentrations. Our data revealed that PHMB kills Leishmania major (L. major) via a dual mechanism involving disruption of membrane integrity and selective chromosome condensation and damage. PHMB's DNA binding and host cell entry properties were further exploited to improve the delivery and immunomodulatory activities of unmethylated cytosine-phosphate-guanine oligodeoxynucleotides (CpG ODN). PHMB spontaneously bound CpG ODN, forming stable nanopolyplexes that enhanced uptake of CpG ODN, potentiated antimicrobial killing and reduced host cell toxicity of PHMB. CONCLUSIONS:Given its low cost and long history of safe topical use, PHMB holds promise as a drug for CL therapy and delivery vehicle for nucleic acid immunomodulators
Orthogonality conditions and asymptotic stability in the Stefan problem with surface tension
We prove nonlinear asymptotic stability of steady spheres in the two-phase
Stefan problem with surface tension. Our method relies on the introduction of
appropriate orthogonality conditions in conjunction with a high-order energy
method.Comment: 25 pages, important references added, two remarks added, typos
correcte
Laboratory intercomparison of solar absorptance and thermal emittance measurements at room temperature
Solar thermal absorber coatings play an important role in the opto-thermal efficiency of receivers in Concentrated Solar Power (CSP). Two standard figures of merit are the solar absorptance αsol and thermal emittance εth, derived from spectral directional hemispherical reflectance measurements at room temperature. These two figures of merit allow comparing coating formulations in terms of performance and durability.
In this study, a black coating and a solar selective coating are optically characterized by different laboratories to compare spectral datasets, solar absorptance αsol and thermal emittance εth calculations. The comparison includes various benchtop spectrophotometers operating in the UV-VIS-NIR and Infrared spectral ranges as well as three commercial portable reflectometers/emissometers.
A good agreement is found between the nine parties participating in this intercomparison campaign. The black coating αsol value is 96.6 ± 0.2%, while the solar selective coating αsol value is 94.5 ± 0.4%. For the thermal emittance, spectral data is concatenated and integrated from 0.3 to 16 μm. The black coating εth value calculated at 650 °C is 80.8 ± 3.8%, while the solar selective coating εth value calculated at 650 °C is 25.0 ± 0.5%
Qualitative behavior of solutions for thermodynamically consistent Stefan problems with surface tension
The qualitative behavior of a thermodynamically consistent two-phase Stefan
problem with surface tension and with or without kinetic undercooling is
studied. It is shown that these problems generate local semiflows in
well-defined state manifolds. If a solution does not exhibit singularities in a
sense made precise below, it is proved that it exists globally in time and its
orbit is relatively compact. In addition, stability and instability of
equilibria is studied. In particular, it is shown that multiple spheres of the
same radius are unstable, reminiscent of the onset of Ostwald ripening.Comment: 56 pages. Expanded introduction, added references. This revised
version is published in Arch. Ration. Mech. Anal. (207) (2013), 611-66
- …