149 research outputs found
Partial constraint singularities in elastic rods
We present a unified classical treatment of partially constrained elastic
rods. Partial constraints often entail singularities in both shapes and
reactions. Our approach encompasses both sleeve and adhesion problems, and
provides simple and unambiguous derivations of counterintuitive results in the
literature. Relationships between reaction forces and moments, geometry, and
adhesion energies follow from the balance of energy during quasistatic motion.
We also relate our approach to the balance of material momentum and the concept
of a driving traction. The theory is generalizable and can be applied to a wide
array of contact, adhesion, gripping, and locomotion problems.Comment: edited tex
Sessile droplet with negative line tension
Abstract: We study the local stability of a sessile droplet with
non-vanishing line tension along the contact line, where three phases are in
equilibrium. We confirm Widom\u27s results (B. Widom, Line tension and the shape
of a sessile drop. J. Chem. Phys. 99 (1995), 2803-2806.) on the local stability
of a droplet with positive line tension in a larger class of perturbations.
When the line tension is negative, although equilibria would be unstable
against modes that make the contact line wigglier and wigglier, the length over
which the oscillations of destabilizing modes are effective can become too
short compared ti the natural cut-off length given by the ratio between the
line and the surface tensions of the droplet. Thus, provided that the line
tension strength is not too large, conditionally stable equilibria exist, even
when the line tension is negative
Bulk and surface biaxiality in nematic liquid crystals
Nematic liquid crystals possess three different phases: isotropic, uniaxial,
and biaxial. The ground state of most nematics is either isotropic or uniaxial,
depending on the external temperature. Nevertheless, biaxial domains have been
frequently identified, especially close to defects or external surfaces. In
this paper we show that any spatially-varying director pattern may be a source
of biaxiality. We prove that biaxiality arises naturally whenever the symmetric
tensor \Sb=(\grad \nn)(\grad \nn)^T possesses two distinct nonzero
eigenvalues. The eigenvalue difference may be used as a measure of the expected
biaxiality. Furthermore, the corresponding eigenvectors indicate the directions
in which the order tensor \QQ is induced to break the uniaxial symmetry about
the director \nn. We apply our general considerations to some examples. In
particular we show that, when we enforce homeotropic anchoring on a curved
surface, the order tensor become biaxial along the principal directions of the
surface. The effect is triggered by the difference in surface principal
curvatures
Pantothenamides Are Potent, On-Target Inhibitors of Plasmodium falciparum Growth When Serum Pantetheinase Is Inactivated
Growth of the virulent human malaria parasite Plasmodium falciparum is dependent on an extracellular supply of pantothenate (vitamin B(5)) and is susceptible to inhibition by pantothenate analogues that hinder pantothenate utilization. In this study, on the hunt for pantothenate analogues with increased potency relative to those reported previously, we screened a series of pantothenamides (amide analogues of pantothenate) against P. falciparum and show for the first time that analogues of this type possess antiplasmodial activity. Although the active pantothenamides in this series exhibit only modest potency under standard in vitro culture conditions, we show that the potency of pantothenamides is selectively enhanced when the parasite culture medium is pre-incubated at 37°C for a prolonged period. We present evidence that this finding is linked to the presence in Albumax II (a serum-substitute routinely used for in vitro cultivation of P. falciparum) of pantetheinase activity: the activity of an enzyme that hydrolyzes the pantothenate metabolite pantetheine, for which pantothenamides also serve as substrates. Pantetheinase activity, and thereby pantothenamide degradation, is reduced following incubation of Albumax II-containing culture medium for a prolonged period at 37°C, revealing the true, sub-micromolar potency of pantothenamides. Importantly we show that the potent antiplasmodial effect of pantothenamides is attenuated with pantothenate, consistent with the compounds inhibiting parasite proliferation specifically by inhibiting pantothenate and/or CoA utilization. Additionally, we show that the pantothenamides interact with P. falciparum pantothenate kinase, the first enzyme involved in converting pantothenate to coenzyme A. This is the first demonstration of on-target antiplasmodial pantothenate analogues with sub-micromolar potency, and highlights the potential of pantetheinase-resistant pantothenamides as antimalarial agents.Aspects of this work were supported by grants from the South African Malaria Initiative (SAMI) to ES and KJS and the American Lebanese Syrian Associated Charities (ALSAC), St. Jude Children’s Research Hospital, to REL. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Thermodynamical Consistent Modeling and Analysis of Nematic Liquid Crystal Flows
The general Ericksen-Leslie system for the flow of nematic liquid crystals is
reconsidered in the non-isothermal case aiming for thermodynamically consistent
models. The non-isothermal model is then investigated analytically. A fairly
complete dynamic theory is developed by analyzing these systems as quasilinear
parabolic evolution equations in an -setting. First, the existence of
a unique, local strong solution is proved. It is then shown that this solution
extends to a global strong solution provided the initial data are close to an
equilibrium or the solution is eventually bounded in the natural norm of the
underlying state space. In these cases, the solution converges exponentially to
an equilibrium in the natural state manifold
Parity Breaking in Nematic Tactoids
We theoretically investigate under what conditions the director field in a
spindle-shaped nematic droplet or tactoid obtains a twisted, parity-broken
structure. By minimizing the sum of the bulk elastic and surface energies, we
show that a twisted director field is stable if the twist and bend elastic
constants are small enough compared to the splay elastic constant, but only if
the droplet volume is larger than some minimum value. We furthermore show that
the transition from an untwisted to a twisted director-field structure is a
sharp function of the various control parameters. We predict that suspensions
of rigid, rod-like particles cannot support droplets with a parity broken
structure, whereas they could possibly occur in those of semi-flexible,
worm-like particles.Comment: 20 pages, 9 figures, submitted to Journal of Physics: Condensed
Matte
ESDN inhibits melanoma progression by blocking E-selectin expression in endothelial cells via STAT3
An interactive crosstalk between tumor and stroma cells is essential for metastatic melanoma progression. We evidenced that ESDN/DCBLD2/CLCP1 plays a crucial role in endothelial cells during the spread of melanoma. Precisely, increased extravasation and metastasis formation were revealed in ESDN-null mice injected with melanoma cells, even if the primary tumor growth, vessel permeability, and angiogenesis were not enhanced. Interestingly, improved adhesion of melanoma cells to ESDN-depleted endothelial cells was observed, due to the presence of higher levels of E-selectin transcripts/proteins in ESDN-defective cells. In accordance with these results, anticorrelation was observed between ESDN and E-selectin in human endothelial cells. Most importantly, our data revealed that cimetidine, an E-selectin inhibitor, was able to block cell adhesion, extravasation, and metastasis formation in ESDN-null mice, underlying a major role of ESDN in E-selectin transcription upregulation, which according to our data, may presumably be linked to STAT3. Based on our results, we propose a protective role for ESDN during the spread of melanoma and reveal its therapeutic potential
Global Weak Solutions to a General Liquid Crystals System
We prove the global existence of finite energy weak solutions to the general
liquid crystals system. The problem is studied in bounded domain of with
Dirichlet boundary conditions and the whole space
Access to administrative documents and to public sector information in Italy
Law No. 241 of 1990 on administrative procedure (Italian APA) established general rules on the right of access to administrative documents for the first time in the Italian legal system, which partly reproduced rules defined in sectorial legislations. From such very restrictive regime of access to administrative documents\u2014lately accompanied by a rather demagogical obligation imposed on public administrations to disclose a set of information in the context of the so-called open data policies\u2014Italy has recently moved forth to public access to data and documents held by public administrations
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