4,744 research outputs found
Non-properly Embedded Minimal Planes in Hyperbolic 3-Space
In this paper, we show that there are non-properly embedded minimal surfaces
with finite topology in a simply connected Riemannian 3-manifold with
nonpositive curvature. We show this result by constructing a non-properly
embedded minimal plane in hyperbolic 3-space. Hence, this gives a
counterexample to Calabi-Yau conjecture for embedded minimal surfaces in the
negative curvature case
Stochastic resonance in a suspension of magnetic dipoles under shear flow
We show that a magnetic dipole in a shear flow under the action of an
oscillating magnetic field displays stochastic resonance in the linear response
regime. To this end, we compute the classical quantifiers of stochastic
resonance, i.e. the signal to noise ratio, the escape time distribution, and
the mean first passage time. We also discuss limitations and role of the linear
response theory in its applications to the theory of stochastic resonance.Comment: 17 pages, 5 figures, approved for publication in PR
Periodic Modulation Induced Increase of Reaction Rates in Autocatalytic Systems
We propose a new mechanism to increase the reactions ratesin multistable
autocatalytic systems. The mechanism is based upon the possibility for the
enhancement of the response of the system due to the cooperative behavior
between the noise and an external periodic modulation. In order to illustrate
this feature we compute the reaction velocities for the particular case of the
Sel'Kov model, showing that they increase significantly when the periodic
modulation is introduced. This behavior originates from the existence of a
minimum in the mean first passage time, one of the signatures of stochastic
resonance.Comment: Submitted to J. Chem. Phy
Cosmic ray anisotropies at high energies
The directional anisotropies of the energetic cosmic ray gas due to the relative motion between the observers frame and the one where the relativistic gas can be assumed isotropic is analyzed. The radiation fluxes formula in the former frame must follow as the Lorentz invariance of dp/E, where p, E are the 4-vector momentum-energy components; dp is the 3-volume element in the momentum space. The anisotropic flux shows in such a case an amplitude, in a rotating earth, smaller than the experimental measurements from say, EAS-arrays for primary particle energies larger than 1.E(14) eV. Further, it is shown that two consecutive Lorentz transformations among three inertial frames exhibit the violation of dp/E invariance between the first and the third systems of reference, due to the Wigner rotation. A discussion of this result in the context of the experimental anisotropic fluxes and its current interpretation is given
Integration of production and financial models to analyse the financial impact of livestock diseases: a case study of Schmallenberg virus disease on British and French dairy farms
AIMS AND OBJECTIVES: The aim of the study was to investigate and compare the financial impact of Schmallenberg disease for different dairy production types in the United Kingdom and France. MATERIALS AND METHODS: Integrated production and financial models for dairy cattle were developed and applied to Schmallenberg virus (SBV) disease in a British and French context. The five main production systems that prevail in these two countries were considered. Their respective gross margins measuring the holding's profitability were calculated based on public benchmarking, literature and expert opinion data. A partial budget analysis was performed within each production model to estimate the impact of SBV in the systems modelled. Two disease scenarios were simulated: low impact and high impact. RESULTS: The model gross margin obtained per cow space and year ranged from £1014 to £1484 for the UK and from £1037 to £1890 for France depending on the production system considered. In the UK, the net SBV disease costs in £/cow space/year for an average dairy farm with 100 milking spaces were estimated between £16.3 and £51.4 in the high-impact scenario and between £8.2 and £25.9 in the low-impact scenario. For France, the net SBV disease costs in £/cow space/year ranged from £19.6 to £48.6 in the high-impact scenario and £9.7 to £22.8 in the low-impact scenario, respectively. CONCLUSION: The study illustrates how the combination of production and financial models allows assessing disease impact taking into account differing management and husbandry practices and associated price structures in the dairy sector. It supports decision-making of farmers and veterinarians who are considering disease control measures as it provides an approach to estimate baseline disease impact in common dairy production systems in the UK and France
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