111 research outputs found
Probing a critical length scale at the glass transition
We give evidence of a clear structural signature of the glass transition, in
terms of a static correlation length with the same dependence on the system
size which is typical of critical phenomena. Our approach is to introduce an
external, static perturbation to extract the structural information from the
system's response. In particular, we consider the transformation behavior of
the local minima of the underlying potential energy landscape (inherent
structures), under a static deformation. The finite-size scaling analysis of
our numerical results indicate that the correlation length diverges at a
temperature , below the temperatures here the system can be equilibrated.
Our numerical results are consistent with random first order theory, which
predicts such a divergence with a critical exponent at the Kauzmann
temperature, where the extrapolated configurational entropy vanishes.Comment: 5 pages, 5 figures, to appear in Phys. Rev. Lett. 2010
Beyond icosahedral symmetry in packings of proteins in spherical shells
The formation of quasi-spherical cages from protein building blocks is a
remarkable self-assembly process in many natural systems, where a small number
of elementary building blocks are assembled to build a highly symmetric
icosahedral cage. In turn, this has inspired synthetic biologists to design de
novo protein cages. We use simple models, on multiple scales, to investigate
the self-assembly of a spherical cage, focusing on the regularity of the
packing of protein-like objects on the surface. Using building blocks, which
are able to pack with icosahedral symmetry, we examine how stable these highly
symmetric structures are to perturbations that may arise from the interplay
between flexibility of the interacting blocks and entropic effects. We find
that, in the presence of those perturbations, icosahedral packing is not the
most stable arrangement for a wide range of parameters; rather disordered
structures are found to be the most stable. Our results suggest that (i) many
designed, or even natural, protein cages may not be regular in the presence of
those perturbations, and (ii) that optimizing those flexibilities can be a
possible design strategy to obtain regular synthetic cages with full control
over their surface properties.Comment: 8 pages, 5 figure
Transcranial direct current stimulation over the tongue motor cortex reduces appetite in healthy humans
Obesity is avmajor concern in many societies for its impact on individual health and societal costs. Therapeutic options however are still limited with respect to efficacy and applicability. Food impulsivity and hyperphagia play a key role in obesity and are associated with alterations of the activity of several brain structures of the reward system. Here, we tested whether downregulation of the tongue muscle representing area of the primary motor cortex (tnM1) via transcranial direct current stimulation (tDCS) e a plasticity-inducing noninvasive brain stimulation tool - reduces hunger in healthy humans
The accumulation of particles in ureteric stents is mediated by flow dynamics: Full-scale computational and experimental modeling of the occluded and unoccluded ureter
Ureteric stents are clinically deployed to restore urinary drainage in the presence of ureteric occlusions. They consist of a hollow tube with multiple side-holes that enhance urinary drainage. The stent surface is often subject to encrustation (induced by crystals-forming bacteria such as Proteus mirabilis) or particle accumulation, which may compromise stent's drainage performance. Limited research has, however, been conducted to evaluate the relationship between flow dynamics and accumulation of crystals in stents. Here, we employed a full-scale architecture of the urinary system to computationally investigate the flow performance of a ureteric stent and experimentally determine the level of particle accumulation over the stent surface. Particular attention was given to side-holes, as they play a pivotal role in enhancing urinary drainage. Results demonstrated that there exists an inverse correlation between wall shear stress (WSS) and crystal accumulation at side-holes. Specifically, side-holes with greater WSS levels were those characterized by inter-compartmental fluid exchange between the stent and ureter. These "active " side-holes were located either nearby ureteric obstructions or at regions characterized by a physiological constriction of the ureter. Results also revealed that the majority of side-holes (> 60%) suffer from low WSS levels and are, thus, prone to crystals accumulation. Moreover, side-holes located toward the proximal region of the ureter presented lower WSS levels compared to more distal ones, thus suffering from greater particle accumulation. Overall, findings corroborate the role of WSS in modulating the localization and extent of particle accumulation in ureteric stents. (C) 2022 Author(s)
- …