2,101 research outputs found
Instability and `Sausage-String' Appearance in Blood Vessels during High Blood Pressure
A new Rayleigh-type instability is proposed to explain the `sausage-string'
pattern of alternating constrictions and dilatations formed in blood vessels
under influence of a vasoconstricting agent. Our theory involves the nonlinear
elasticity characteristics of the vessel wall, and provides predictions for the
conditions under which the cylindrical form of a blood vessel becomes unstable.Comment: 4 pages, 4 figures submitted to Physical Review Letter
Cooling dynamics of a dilute gas of inelastic rods: a many particle simulation
We present results of simulations for a dilute gas of inelastically colliding
particles. Collisions are modelled as a stochastic process, which on average
decreases the translational energy (cooling), but allows for fluctuations in
the transfer of energy to internal vibrations. We show that these fluctuations
are strong enough to suppress inelastic collapse. This allows us to study large
systems for long times in the truely inelastic regime. During the cooling stage
we observe complex cluster dynamics, as large clusters of particles form,
collide and merge or dissolve. Typical clusters are found to survive long
enough to establish local equilibrium within a cluster, but not among different
clusters. We extend the model to include net dissipation of energy by damping
of the internal vibrations. Inelatic collapse is avoided also in this case but
in contrast to the conservative system the translational energy decays
according to the mean field scaling law, E(t)\propto t^{-2}, for asymptotically
long times.Comment: 10 pages, 12 figures, Latex; extended discussion, accepted for
publication in Phys. Rev.
Collision of One-Dimensional Nonlinear Chains
We investigate one-dimensional collisions of unharmonic chains and a rigid
wall. We find that the coefficient of restitution (COR) is strongly dependent
on the velocity of colliding chains and has a minimum value at a certain
velocity. The relationship between COR and collision velocity is derived for
low-velocity collisions using perturbation methods. We found that the velocity
dependence is characterized by the exponent of the lowest unharmonic term of
interparticle potential energy
Field water dynamics in integrated systems in the Brazilian.
Agroforestry systems were established as a viable option for Brazilian farmers in recent decades. Shading is expected to affect the system?s microclimate and thus it is likely to alter water fluxes to the atmosphere via evapotranspiration. In this study we measured the evapotranspiration (ET) with micro-lysimeters in four different treatments as a proxy for different land use systems at EMBRAPA Beef Cattle, the Brazilian Agricultural Research Corporation, located in Campo Grande-MS, Brasil. The four treatments are: Integrated systems with rows of Eucalypt (Eucalyptus urograndis) trees (ICLF), integrated systems without Eucalypt trees (ICL), continuous pasture (CP) and native Cerrado (Savannah) vegetation. In the ICLF and ICL plots Bracchiaria brizantha was planted and in the CP plots Brachiaria decumbens. To measure the evapotranspiration lysimeters (diameter of 10 cm and a depth of 20 cm) were inserted into the ground and weighed daily during a period of 8 weeks. Within the ICLF systems, measurements were conducted in three different distances to the tree rows. In the treatments without trees the lysimeters were distributed randomly. Results were linked to data from the microclimate, i.e. wind speed, air humidity, and global radiation
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Residential solar-photovoltaic power systems: the need for battery storage
Benefits of battery storage used in conjunction with residential solar photovoltaic (PV) power systems were evaluated for a representative set of utility service areas. The PV systems were assumed capable of exporting excess power to the utility grid, and the batteries sited at the substation level were operated as a form of load-leveling utility storage. A cost-allocation model, SIMSTOR, was employed to determine utility fuel and capital cost savings resulting from the addition of batteries as a function of PV system penetration level. These benefits were compared with the savings of batteries used alone without introduction of the PV systems. Battery storage capacities and discharge rates were varied to determine the battery configurations that maximize net utility savings as a function of battery costs. Installed (rated) PV device capacities up to 20 percent of the generation peak load in each service area were considered. Findings indicate that batteries and PV systems are complementary rather than competing technologies, when attached to the electric supply grid. The utility benefits of the PV systems are primarily fuel savings, while those of the battery are primarily due to savings in utility capacity. The economic rationale for batteries does not change significantly as the penetration level for the PV systems increases. In some of the service areas, the addition of the PV systems tended to sharpen rather than flatten the peaks in the utility's load curves, with the magnitude of the effect becoming more pronounced at the higher PV system penetration levels. As a result of these load shape changes, batteries with higher discharge rates and larger storage capacities were favored
Amide neighbouring-group effects in peptides: phenylalanine as relay amino acid in long-distance electron transfer
In nature, proteins serve as media for long‐distance electron transfer (ET) to carry out redox reactions in distant compartments. This ET occurs either by a single‐step superexchange or through a multi‐step charge hopping process, which uses side chains of amino acids as stepping stones. In this study we demonstrate that Phe can act as a relay amino acid for long‐distance electron hole transfer through peptides. The considerably increased susceptibility of the aromatic ring to oxidation is caused by the lone pairs of neighbouring amide carbonyl groups, which stabilise the Phe radical cation. This neighbouring‐amide‐group effect helps improve understanding of the mechanism of extracellular electron transfer through conductive protein filaments (pili) of anaerobic bacteria during mineral respiration
Diffraction in low-energy electron scattering from DNA: bridging gas phase and solid state theory
Using high-quality gas phase electron scattering calculations and multiple
scattering theory, we attempt to gain insights on the radiation damage to DNA
induced by secondary low-energy electrons in the condensed phase, and to bridge
the existing gap with the gas phase theory and experiments. The origin of
different resonant features (arising from single molecules or diffraction) is
discussed and the calculations are compared to existing experiments in thin
films.Comment: 40 pages preprint, 12 figures, submitted to J. Chem. Phy
Towards a Proof Theory of G\"odel Modal Logics
Analytic proof calculi are introduced for box and diamond fragments of basic
modal fuzzy logics that combine the Kripke semantics of modal logic K with the
many-valued semantics of G\"odel logic. The calculi are used to establish
completeness and complexity results for these fragments
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