Reversing a granular flow on a vibratory conveyor

Experimental results are presented on the transport properties of granular materials on a vibratory conveyor. For circular oscillations of the shaking trough a non-monotonous dependence of the transport velocity on the normalized acceleration is observed. Two maxima are separated by a regime, where the granular flow is much slower and, in a certain driving range, even reverses its direction. A similar behavior is found for a single solid body with a low coefficient of restitution, whereas an individual glass bead of 1 mm diameter is propagated in the same direction for all accelerations.Comment: 4 pages, 5 figures, submitted to Applied Physics Letter

Spontaneous Ratchet Effect in a Granular Gas

The spontaneous clustering of a vibrofluidized granular gas is employed to generate directed transport in two different compartmentalized systems: a "granular fountain" in which the transport takes the form of convection rolls, and a "granular ratchet" with a spontaneous particle current perpendicular to the direction of energy input. In both instances, transport is not due to any system-intrinsic anisotropy, but arises as a spontaneous collective symmetry breaking effect of many interacting granular particles. The experimental and numerical results are quantitatively accounted for within a flux model.Comment: 4 pages, 5 figures; Fig. 4 has been reduced in size and qualit

Relocating croplands could drastically reduce the environmental impacts of global food production

Agricultural production has replaced natural ecosystems across the planet, becoming a major driver of carbon emissions, biodiversity loss, and freshwater consumption. Here we combined global crop yield and environmental data in a ~1-million-dimensional mathematical optimisation framework to determine how optimising the spatial distribution of global croplands could reduce environmental impacts whilst maintaining current crop production levels. We estimate that relocating current croplands to optimal locations, whilst allowing ecosystems in then-abandoned areas to regenerate, could simultaneously decrease the current carbon, biodiversity, and irrigation water footprint of global crop production by 71%, 87%, and 100%, respectively, assuming high-input farming on newly established sites. The optimal global distribution of crops is largely similar for current and end-of-century climatic conditions across emission scenarios. Substantial impact reductions could already be achieved by relocating only a small proportion of worldwide crop production, relocating croplands only within national borders, and assuming less intensive farming systems. © 2022, The Author(s)R.M.B. and A.M. were supported by ERC Consolidator Grant 647797 “LocalAdaptation”. This work benefited from conversations with América P. Durán, Catherine Tayleur, Sharon E. Brooks, David Coomes, Paul F. Donald, and Fiona J. Sanderson during a separate research projec

Riemann solvers and undercompressive shocks of convex FPU chains

We consider FPU-type atomic chains with general convex potentials. The naive continuum limit in the hyperbolic space-time scaling is the p-system of mass and momentum conservation. We systematically compare Riemann solutions to the p-system with numerical solutions to discrete Riemann problems in FPU chains, and argue that the latter can be described by modified p-system Riemann solvers. We allow the flux to have a turning point, and observe a third type of elementary wave (conservative shocks) in the atomistic simulations. These waves are heteroclinic travelling waves and correspond to non-classical, undercompressive shocks of the p-system. We analyse such shocks for fluxes with one or more turning points. Depending on the convexity properties of the flux we propose FPU-Riemann solvers. Our numerical simulations confirm that Lax-shocks are replaced by so called dispersive shocks. For convex-concave flux we provide numerical evidence that convex FPU chains follow the p-system in generating conservative shocks that are supersonic. For concave-convex flux, however, the conservative shocks of the p-system are subsonic and do not appear in FPU-Riemann solutions

Actividad de glutation peroxidasa (GSH-Px) en sangre de bovinos a pastoreo de la IX Región, Chile y su relación con la concentración de selenio en el forraje

Con el objeto de determinar la actividad sanguínea de glutatión peroxidasa (GSH-Px; E.C. 1.11.1.9) en bovinos lecheros de la IX Región de la Araucanía (38º LS y 71º LO), Chile, y establecer su eventual asociación con el contenido de Se en el forraje, durante el otoño y la primavera de 1999 se tomaron muestras de forraje de las praderas y de sangre en grupos de vacas en inicio de lactancia y vaquillas en 12 predios lecheros. Se midió la concentración de Se en el forraje empleando la técnica de espectroscopía de plasma acoplado inductivamente con detector de masas (ICP-MS) y la actividad sanguínea de GSH-Px mediante una técnica cinética compuesta NADPH-dependiente. La concentración de Se del forraje fue 0.03±0.02 ppm, donde un 83% presentó valores deficitarios (0.05). Se encontró un 20% de los grupos analizados con valores deficitarios (0.05). Heifers showed a lower activity for GSH-Px than cows in both periods (p<0.05). Twenty percent of the animals showed a low activity of GSH-Px (below 60 U/g Hb), meaning a Se deficiency in the animals. There was a relation between the content of Se in forage and the blood activity of GSH-Px in heifers (r= 0.74; p<0.05). Accordingly, the content of Se in most of the forage produced in the dairy cattle area from the IXth Region, Chile is below the nutritional requirements for grazing dairy cattle and nutritional metabolic deficiencies of Se are present in dairy herds according to blood activity of GSH-Px. Heifers are mostly affecte

Fermi-Dirac statistics and the number theory

We relate the Fermi-Dirac statistics of an ideal Fermi gas in a harmonic trap to partitions of given integers into distinct parts, studied in number theory. Using methods of quantum statistical physics we derive analytic expressions for cumulants of the probability distribution of the number of different partitions.Comment: 7pages, 2 figures, epl.cls, revised versio

Multivalent display of minimal Clostridium difficile glycan epitopes mimics antigenic properties of larger glycans

Synthetic cell-surface glycans are promising vaccine candidates against Clostridium difficile. The complexity of large, highly antigenic and immunogenic glycans is a synthetic challenge. Less complex antigens providing similar immune responses are desirable for vaccine development. Based on molecular-level glycan-antibody interaction analyses, we here demonstrate that the C. difficile surface polysaccharide-I (PS-I) can be resembled by multivalent display of minimal disaccharide epitopes on a synthetic scaffold that does not participate in binding. We show that antibody avidity as a measure of antigenicity increases by about five orders of magnitude when disaccharides are compared with constructs containing five disaccharides. The synthetic, pentavalent vaccine candidate containing a peptide T-cell epitope elicits weak but highly specific antibody responses to larger PS-I glycans in mice. This study highlights the potential of multivalently displaying small oligosaccharides to achieve antigenicity characteristic of larger glycans. The approach may result in more cost-efficient carbohydrate vaccines with reduced synthetic effort