3,827 research outputs found
Spatial clustering of interacting bugs: Levy flights versus Gaussian jumps
A biological competition model where the individuals of the same species
perform a two-dimensional Markovian continuous-time random walk and undergo
reproduction and death is studied. The competition is introduced through the
assumption that the reproduction rate depends on the crowding in the
neighborhood. The spatial dynamics corresponds either to normal diffusion
characterized by Gaussian jumps or to superdiffusion characterized by L\'evy
flights. It is observed that in both cases periodic patterns occur for
appropriate parameters of the model, indicating that the general macroscopic
collective behavior of the system is more strongly influenced by the
competition for the resources than by the type of spatial dynamics. However,
some differences arise that are discussed.Comment: This version incorporates in the text the correction published as an
Erratum in Europhysics Letters (EPL) 95, 69902 (2011) [doi:
10.1209/0295-5075/95/69902
One-dimensional relativistic dissipative system with constant force and its quantization
For a relativistic particle under a constant force and a linear velocity
dissipation force, a constant of motion is found. Problems are shown for
getting the Hamiltoninan of this system. Thus, the quantization of this system
is carried out through the constant of motion and using the quantization of the
velocity variable. The dissipative relativistic quantum bouncer is outlined
within this quantization approach.Comment: 11 pages, no figure
Balances de elementos en un agroecosistema de caña de azúcar: I. Balance de nitrógeno
In a tropical mollisol cropped with sugar cane the annual nitrogen balance was quantified taken into account the main i) inputs, ii) outputs and iii) transference of the element (N-NO3 + N-NH4) in the plant and soil subsystems. Precipitation input corresponded to 26.3 kg N.h–1.yr-1 mainly as N-NH4. After the rain water passes the sugar cane canopy there was a retention of N in the N-NH4 form, whereas N-NO3 was leached from the canopy. Outputs through leaching reached 5.3 kg N. ha-1.yr–1 mainly as N-NO3. An important part of total soil N is fixed to the 2:1 type clay particles (montmorillonitic), abundant in the studied mollisol. It is hypothesised that this fixed N could act as a soil N reserve. Net mineralization of the organic-N reached a high value (343 kg N.ha-1.yr–1) in accordance with the intense nitrification process occurring in the soil as a consequence of the convenient C/N ratio and urea fertilisation. Major N losses in the agrosystem correspond to cropping export and removal of ashes after fire. Yearly 98% of N accumulated in the aerial biomass is lost through those ways. In general the annual nitrogen budget is driven off through input by fertilisation and output through stem cropping and N volatilisation by fire
Balances de elementos en un agroecosistema de caña de azúcar: II. Balance de Fósforo
The paper considers the application of the studies of nutrient cycling on the determination of phosphorus requirements in sugarcane plantations. The work was performed in a 4.5 ha experimental plot located in the valley of Yaracuy river in central, Venezuela. The plot was planted with the varieties Puerto Rico (PR) 1028 and Venezuela (V) 58-4. The principal flows of phosphorus, as well the quantities of this element in the soil-plant components were measured throughout the growing cycle of the crop (second ratoon). The inputs through precipitation (wet and dry) were high, that was associated with the intense agricultural (prescribed burning of sugarcane plantation) and industrial activities occurring in the area. The annual balance for both varieties was negative (-17 and - 23.3 kg.ha-1 for V 58-4 and PR 1028, respectively). The negative budget is mainly due to the important amounts of P that are exported with the cane stems. The losses must be compensated though fertilisation, nonetheless, preliminary results indicated no response to P dressing, suggesting that in the studied mollisol the internal processes e.g. Po mineralization and P solubilization, efficiently operate generating important available P levels. It was also found that the burning of the sugar cane plantation plays an important role in the recycling of phosphorus, since 25-30% of the P requirements of the varieties are reincorporated into the soil from the ashes
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