904 research outputs found
Finding bridges in packings of colloidal spheres
We identify putative load-bearing structures (bridges) in experimental colloidal systems studied by confocal microscopy. Bridges are co-operative structures that have been used to explain stability and inhomogeneous force transmission in simulated granular packings with a range of densities. We show that bridges similar to those found in granular simulations are present in real experimental colloidal packings. We describe critically the bridge-finding procedure for real experimental data and propose a new criterion-Lowest Mean Squared Separation (LSQS)-for selecting optimum stabilisations
Engineering biocatalytic nanoreactors
Cellular compartmentalization enables enzymes to perform complex sequences of chemical transformations with high efficiency and exquisite enantio, regio and chemo-selectivity under mild conditions. Reproducing such performance of individual biocatalysts, as well as entire enzyme cascades at the bench and in industry offers tremendous opportunities for future developments of green and sustainable chemical processes. Native, protein-based nanocompartments from bacteria represent very robust carrier matrices for the assembly of artificial biocatalytic nanoreactors, yet suffer from ineffective permeability of metabolites and small molecules due to small pores in the protein shell and non-existence of exterior surface functionality. Addressing these shortfalls through protein engineering enables the creation of tailored carriers that have the potential to serve as highly versatile scaffold with excellent control over spatial organization of (bio)catalysts. Such immobilization benefits enzyme stability and catalyst recovery but also promises additional functional gains by substrate channeling between proximal active sites.
Please click Additional Files below to see the full abstract
Calculation of the heavy-hadron axial couplings g_1, g_2, and g_3 using lattice QCD
In a recent letter [Phys. Rev. Lett. 108, 172003 (2012), arXiv:1109.2480] we
have reported on a lattice QCD calculation of the heavy-hadron axial couplings
, , and . These quantities are low-energy constants of
heavy-hadron chiral perturbation theory (HHPT) and are related to the
, , and couplings.
In the following, we discuss important details of the calculation and give
further results. To determine the axial couplings, we explicitly match the
matrix elements of the axial current in QCD with the corresponding matrix
elements in HHPT. We construct the ratios of correlation functions used
to calculate the matrix elements in lattice QCD, and study the contributions
from excited states. We present the complete numerical results and discuss the
data analysis in depth. In particular, we demonstrate the convergence of
HHPT for the axial-current matrix elements at pion masses up to
about 400 MeV and show the impact of the nonanalytic loop contributions.
Finally, we present additional predictions for strong and radiative decay
widths of charm and bottom baryons.Comment: 42 pages, 20 figures, updated calculation of Xi_b^{*0} width using
mass measurement from CMS, published versio
Mean Field theory for a driven granular gas of frictional particles
We propose a mean field (MF) theory for a homogeneously driven granular gas
of inelastic particles with Coulomb friction. The model contains three
parameters, a normal restitution coefficient , a maximum tangential
restitution coefficient , and a Coulomb friction coefficient . The
parameters can be tuned to explore a wide range of physical situations. In
particular, the model contains the frequently used limit as a
special case. The MF theory is compared with the numerical simulations of a
randomly driven monolayer of spheres for a wide range of parameter values. If
the system is far away from the clustering instability (), we
obtain a good agreement between mean field and simulations for and
, but for much smaller values of the agreement is less good.
We discuss the reasons of this discrepancy and possible refinements of our
computational scheme.Comment: 6 pages, 3 figures (10 *.eps files), elsart style (macro included),
in Proceedings of the International Conference "Statistical Mechanics and
Strongly Correlated Systems", University of Rome "La Sapienza" (Italy), 27-29
September 199
Energy non-equipartition in systems of inelastic, rough spheres
We calculate and verify with simulations the ratio between the average
translational and rotational energies of systems with rough, inelastic
particles, either forced or freely cooling. The ratio shows non-equipartition
of energy. In stationary flows, this ratio depends mainly on the particle
roughness, but in nonstationary flows, such as freely cooling granular media,
it also depends strongly on the normal dissipation. The approach presented here
unifies and simplifies different results obtained by more elaborate kinetic
theories. We observe that the boundary induced energy flux plays an important
role.Comment: 4 pages latex, 4 embedded eps figures, accepted by Phys Rev
Recommended from our members
Vulnerability to fuel and transport poverty
This briefing highlights the groups of people that academic research has identified as vulnerable to experiencing fuel poverty and transport poverty. Fuel and transport poverty are distributed across the UK, although the groups affected in each place can vary and the characteristics can be different depending on the location and make up of households
Human and Animal Fecal Contamination of Community Water Sources, Stored Drinking Water and Hands in Rural India Measured with Validated Microbial Source Tracking Assays.
We examined pathways of exposure to fecal contamination of human and animal origin in 24 villages in Odisha, India. In a cross-sectional study during the monsoon season, fecal exposure via community water sources (N = 123) and in the home (N = 137) was assessed using human- and nonhuman-associated Bacteroidales microbial source tracking (MST) markers and fecal coliforms (FCs). Detection rates and marker concentrations were examined to pinpoint pathways of human fecal exposure in the public and domestic domains of disease transmission in study communities. Human fecal markers were detected much more frequently in the domestic domain (45% of households) than in public domain sources (8% of ponds; 4% of groundwater drinking sources). Animal fecal markers were widely detected in both domains (74% of ponds, 96% of households, 10% of groundwater drinking sources), indicating ubiquitous risks of exposure to animal feces and zoonotic pathogens. This study confirms an often suggested contamination link from hands to stored water in the home in developing countries separately for mothers' and children's hands and both human and animal fecal contamination. In contrast to MST markers, FCs provided a poor metric to assess risks of exposure to fecal contamination of human origin in this rural setting
- …