207 research outputs found
Puckering Free Energy of Pyranoses: an NMR and Metadynamics--Umbrella Sampling Investigation
We present the results of a combined metadynamics--umbrella sampling
investigation of the puckered conformers of pyranoses described using the
gromos 45a4 force field. The free energy landscape of Cremer--Pople puckering
coordinates has been calculated for the whole series of alpha and beta
aldohexoses, showing that the current force field parameters fail in
reproducing proper puckering free energy differences between chair conformers.
We suggest a modification to the gromos 45a4 parameter set which improves
considerably the agreement of simulation results with theoretical and
experimental estimates of puckering free energies. We also report on the
experimental measurement of altrose conformers populations by means of NMR
spectroscopy, which show good agreement with the predictions of current
theoretical models
A two-species continuum model for aeolian sand transport
Starting from the physics on the grain scale, we develop a simple continuum
description of aeolian sand transport. Beyond popular mean-field models, but
without sacrificing their computational efficiency, it accounts for both
dominant grain populations, hopping (or "saltating") and creeping (or
"reptating") grains. The predicted stationary sand transport rate is in
excellent agreement with wind tunnel experiments simulating wind conditions
ranging from the onset of saltation to storms. Our closed set of equations thus
provides an analytically tractable, numerically precise, and computationally
efficient starting point for applications addressing a wealth of phenomena from
dune formation to dust emission.Comment: 23 pages, 9 figure
Animal movements in the Kenya Rift and evidence for the earliest ambush hunting by hominins
Animal movements in the Kenya Rift Valley today are influenced by a combination of topography and trace nutrient distribution. These patterns would have been the same in the past when hominins inhabited the area. We use this approach to create a landscape reconstruction of Olorgesailie, a key site in the East African Rift with abundant evidence of large-mammal butchery between ~1.2 and ~0.5 Ma BP. The site location in relation to limited animal routes through the area show that hominins were aware of animal movements and used the location for ambush hunting during the Lower to Middle Pleistocene. These features explain the importance of Olorgesailie as a preferred location of repeated hominin activity through multiple changes in climate and local environmental conditions, and provide insights into the cognitive and hunting abilities of Homo erectus while indicating that their activities at the site were aimed at hunting, rather than scavenging
Nanoscale temperature measurements using non-equilibrium Brownian dynamics of a levitated nanosphere
Einstein realised that the fluctuations of a Brownian particle can be used to
ascertain properties of its environment. A large number of experiments have
since exploited the Brownian motion of colloidal particles for studies of
dissipative processes, providing insight into soft matter physics, and leading
to applications from energy harvesting to medical imaging. Here we use
optically levitated nanospheres that are heated to investigate the
non-equilibrium properties of the gas surrounding them. Analysing the sphere's
Brownian motion allows us to determine the temperature of the centre-of-mass
motion of the sphere, its surface temperature and the heated gas temperature in
two spatial dimensions. We observe asymmetric heating of the sphere and gas,
with temperatures reaching the melting point of the material. This method
offers new opportunities for accurate temperature measurements with spatial
resolution on the nanoscale, and a new means for testing non-equilibrium
thermodynamicsComment: 5 pages, 4 figures, supplementary material available upon reques
Gut microbiota and its diet-related activity in children with intestinal failure receiving long-term parenteral nutrition
Background This study characterized gut microbiota and its diet-related activity in children with intestinal failure (IF) receiving parenteral nutrition (PN) compared with those of healthy controls (HC) and in relation to disease characteristics. Methods The fecal microbiota and short-chain fatty acids (SCFAs) were measured in 15 IF patients (n = 68) and 25 HC (n = 25). Results Patients with IF had a lower bacterial load (P = .003), diversity (P < .001), evenness (P < .001) and richness (P = 0.006) than HC. Patients with surgical IF had lower diversity (P < .039) than those with functional IF. Propionic acid and butyric acid (p < .001) were lower and d-lactate and l-lactate were higher (p < 0.001) in IF patients than in HC. The energy supplied by PN (%PN) was negatively associated with microbiota diversity and SCFA profile. IF patients had more Escherichia-Shigella (P = .006), Cronobacter (P = .001), and Staphylococcus (Operational Taxonomic Unit 14, P < .001) and less Faecalibacterium (P < 0.001) and Ruminococcus 1 and 2 (P < .001). Duration of PN (P = .005), %PN (P = .005), and fiber intake (P = .011) were predictive of microbiota structure. Higher intake of enteral nutrition was associated with microbiota structure and function closer to those of HC. Conclusions Microbiota composition and its diet-related function are altered in IF, with depletion of beneficial SCFAs and species and supraphysiological increase of potentially harmful pathobionts. The influence of this compositional and functional microbial dysbiosis on patients' outcomes and management warrants further exploration.Transplantation and immunomodulatio
Methicillin-Resistant Staphylococcus aureus, Samoa, 2007â2008
TOC Summary: A wide range of MRSA genotypes cause wound infections
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