372 research outputs found
Teaching Business Models Through Student Consulting Projects
This article aims to contribute to the literature on business models teaching practices by presenting how the implementation of consulting missions with entrepreneurs in the integration phase can be an effective pedagogical approach for learning business models with bachelor students
Structure factor of polymers interacting via a short range repulsive potential: application to hairy wormlike micelles
We use the Random Phase Approximation (RPA) to compute the structure factor,
S(q), of a solution of chains interacting through a soft and short range
repulsive potential V. Above a threshold polymer concentration, whose magnitude
is essentially controlled by the range of the potential, S(q) exhibits a peak
whose position depends on the concentration. We take advantage of the close
analogy between polymers and wormlike micelles and apply our model, using a
Gaussian function for V, to quantitatively analyze experimental small angle
neutron scattering profiles of semi-dilute solutions of hairy wormlike
micelles. These samples, which consist in surfactant self-assembled flexible
cylinders decorated by amphiphilic copolymer, provide indeed an appropriate
experimental model system to study the structure of sterically interacting
polymer solutions
Role of cilia activity and surrounding viscous fluid on properties of metachronal waves
Large groups of active cilia collectively beat in a fluid medium as
metachronal waves, essential for some microorganisms motility and for flow
generation in mucociliary clearance. Several models can predict the emergence
of metachronal waves, but what controls the properties of metachronal waves is
still unclear. Here, we investigate numerically a simple model for cilia in the
presence of noise on regular lattices in one- and two-dimensions. We
characterize the wave using spatial correlation and the frequency of collective
beating. Our results clearly show that the viscosity of the fluid medium does
not affect the wavelength; the activity of the cilia does. These numerical
results are supported by a dimensional analysis, which is expected to be robust
against the model for active force generation, unless surrounding fluid
influences the cilia activity. Interestingly, enhancement of cilia activity
increases the wavelength and decreases the beating frequency, keeping the wave
velocity almost unchanged. These results might have significance in
understanding paramecium locomotion and mucociliary clearance diseases.Comment: 6 pages, 5 figure
Fragility and Mechanosensing in a Thermalized Cytoskeleton Model with Forced Protein Unfolding
We describe a model of cytoskeletal mechanics based on the force-induced conformational change of protein cross-links in a stressed polymer network. Slow deformation of simulated networks containing cross-links that undergo repeated, serial domain unfolding leads to an unusual state — with many cross-links accumulating near the critical force for further unfolding. This state is robust to thermalization and does not occur in similar protein unbinding based simulations. Moreover, we note that the unusual configuration of near-critical protein cross-links in the fragile state provides a physical mechanism for the chemical transduction of cell-level mechanical strain and extra-cellular matrix stiffness
Vegetable oil hybrid films cross-linked at the air-water interface: formation kinetics and physical characterization
Vegetable oil based hybrid films were developed thanks to a novel solvent-
and heating- free method at the air-water interface using silylated castor oil
cross-linked via a sol-gel reaction. To understand the mechanism of the hybrid
film formation, the reaction kinetics was studied in detail by using
complementary techniques: rheology, thermogravimetric analysis, and infrared
spectroscopy. The mechanical properties of the final films were investigated by
nano-indentation, whereas their structure was studied using a combination of
wide-angle X-ray scattering, electron diffraction, and atomic force microscopy.
We found that solid and transparent films form in 24 hours and, by changing the
silica precursor to castor oil ratio, their mechanical properties are tunable
in the MPa-range by about a factor of twenty. In addition to that, a possible
optimization of the cross-linking reaction with different catalysts was
explored and finally, cytotoxicity tests were performed on fibroblasts proving
the absence of film toxicity. The results of this work pave the way to a
straightforward synthesis of castor-oil films with tunable mechanical
properties: hybrid films cross-linked at the air-water interface combine an
easy and cheap spreading protocol with the features of their thermal history
optimized for possible future micro/nano drug loading, thus representing
excellent candidates for the replacement of non-environment friendly
petroleum-based materials
Anharmonic vs. relaxational sound damping in glasses: I. Brillouin scattering from densified silica
This series discusses the origin of sound damping and dispersion in glasses.
In particular, we address the relative importance of anharmonicity versus
thermally activated relaxation. In this first article, Brillouin-scattering
measurements of permanently densified silica glass are presented. It is found
that in this case the results are compatible with a model in which damping and
dispersion are only produced by the anharmonic coupling of the sound waves with
thermally excited modes. The thermal relaxation time and the unrelaxed velocity
are estimated.Comment: 9 pages with 7 figures, added reference
Curling dynamics of naturally curved ribbons: from high to low Reynolds numbers
Curling deformation of thin elastic sheets appears in numerous structures in nature, such as membranes of red blood cells, epithelial tissues or green algae colonies to cite just a few examples. However, despite its ubiquity, the dynamics of curling propagation in a naturally curved material remains still poorly investigated. Here, we present a coupled experimental and theoretical study of the dynamical curling deformation of naturally curved ribbons. Using thermoplastic and metallic ribbons molded on cylinders of different radii, we tune separately the natural curvature and the geometry to study curling dynamics in air, water and in viscous oils, thus spanning a wide range of Reynolds numbers. Our theoretical and experimental approaches separate the role of elasticity, gravity and hydrodynamic dissipation from inertia and emphasize the fundamental differences between the curling of a naturally curved ribbon and a rod described by the classical Elastica. Ribbons are indeed an intermediate class of objects between rods, which can be totally described by one-dimensional deformations, and sheets. Since Lord Rayleigh, it is known that a thin sheet can easily be bent but not stretched. As a result, large deformations in thin sheets usually lead to the localization of deformations into small peaks and ridges as observed by crumpling a simple piece of paper. These elastic defects induce critical buckling situations studied in detail statically in the literature, while experimental and theoretical studies on their dynamics are scarce. Our work shows evidence for the propagation of such a single instability front, selected by a local buckling mechanism. Finally, we show that depending on gravity, and both the Reynolds and the Cauchy numbers, the curling speed and shape are modified by the large scale drag and the local lubrication forces, shedding a new light on microscopic experiences where curling is observed
The Adipose Renin-Angiotensin System Modulates Systemic Markers of Insulin Sensitivity and Activates the Intrarenal Renin-Angiotensin System
Background. The adipose tissue renin-angiotensin system (RAS) contributes to regulation of fat mass and may also impact systemic functions such as blood pressure and metabolism. Methods and results. A panel of mouse models including mice lacking angiotensinogen, Agt (Agt-KO), mice expressing Agt solely in adipose tissue (aP2-Agt/Agt-KO), and mice overexpressing Agt in adipose tissue (aP2-Agt) was studied. Total body weight, epididymal fat pad weight, and circulating levels of leptin, insulin, and resistin were significantly decreased in Agt-KO mice, while plasma adiponectin levels were increased. aP2-Agt mice exhibited increased adiposity and plasma leptin and insulin levels compared to wild type (WT) controls. Angiotensinogen and type I Ang II receptor protein levels were also elevated in kidney of aP2-Agt mice. Conclusion. These findings demonstrate that alterations in adipose RAS activity significantly impact both local and systemic physiology in a way that may contribute to the detrimental health effects of obesity
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