875 research outputs found
Positive Changes in Regional Vegetation Cover in Patagonia Shown by MARAS Monitoring System
MARAS (Environmental monitoring of arid and semiarid lands) is a vegetation and soil monitoring system in Patagonia, a 700.000 km2 area in southern South America. Installed between 2008-2015 within INTA-Argentina and INIA-Chile national agricultural research institutes, it includes photographs, 500-point intercepts, 50-m canfield lines to detect patches, 10 land function observations and 0-10 cm soil samples in 458 ground sites. Data is centralized and freely accessible https://maras.inta.gob.ar. We analysed changes based in the first 255 reassessments made at 5-year intervals. At a regional scale significant changes (P \u3c 0.05 paired T test) were detected for: perennial vegetation cover, that was originally 42% and increased +3.1%. Plant species richness of 13.7 species/monitor increased +0.7, bare soil of 35% decreased -7.9%. Length of bare soil interpatches was 157 cm and decreased -42 cm. Land function indexes of Stability 46.2%, Infiltration 45.1% and Recycling 31.0% showed small non-significant changes (-1.3, +0.7 and +1.42 respectively). Significant changes in soils under vegetated patches were: conductivity 0.59 dS/m increased +0.49, and pH 7.3 +0.33. Organic matter was 2.0% and increased 0.35%, and sand was 73% and increased 3%. Finer soil particles decreased non-significantly. Bare soil interpatches had 1.4% organic matter and also increased 0.33%, and clay, that initially was 9.3% reduced -2.3%. The long-term ground sites provide a means to monitor slow changes in these rangelands in relation to global climatic change and regional grazing patterns. Patagonia has currently the lowest domestic stocking rates of the last century and vegetation seems to be slowly growing in perennial cover, with significant reductions in exposed bare soil, increase in biodiversity and soil organic carbon
Identical transacting factor requirement for knirps and knirps-related Gene expression in the anterior but not in the posterior region of the Drosophila embryo.
Microscopic Analysis of the Non-Dissipative Force on a Line Vortex in a Superconductor: Berry's Phase, Momentum Flows and the Magnus Force
A microscopic analysis of the non-dissipative force acting on
a line vortex in a type-II superconductor at is given. We first examine
the Berry phase induced in the true superconducting ground state by movement of
the vortex and show how this induces a Wess-Zumino term in the hydrodynamic
action of the superconducting condensate. Appropriate variation of
gives and variation of the Wess-Zumino term is seen to
contribute the Magnus (lift) force of classical hydrodynamics to . This first calculation confirms and strengthens earlier work by Ao and
Thouless which was based on an ansatz for the many-body ground state. We also
determine through a microscopic derivation of the continuity
equation for the condensate linear momentum. This equation yields the
acceleration equation for the superflow and shows that the vortex acts as a
sink for the condensate linear momentum. The rate at which momentum is lost to
the vortex determines and the result obtained agrees with the
Berry phase calculation. The Magnus force contribution to is
seen to be a consequence of the vortex topology. Preliminary remarks are made
regarding finite temperature extensions, with emphasis on its relevance to the
sign anomaly occurring in Hall effect experiments done in the flux flow regime.Comment: 40 pages, RevTex, UBCTP-94-00
Comment on "Transverse Force on a Quantized Vortex in a Superfluid"
The result of Thouless, Ao and Niu (TAN), that the mutual friction parameter
, contradicts to the experiments made in rotating 3He-B by
Manchester group. The Manchester group observed that at low
temperature and approaches 1 at high temperature. The reason of the
contradiction is that TAN did not take into account the Iordanskii force on the
vortex and the spectral flow force, which comes from the anomaly related to the
low-energy bound states of fermions in cores of quantized vortices. The
Iordanskii force is responsible for the negative at low
temperature, while due to the spectral flow approaches 1 at high
temperature. Relation of the spectral flow anomaly with the paradoxes of the
linear and angular momenta in gapless superfluids is discussed.Comment: revtex, 2 pages, submitted to Physical Review Letters as "Comment" to
the paper D.J. Thouless, P. Ao and Q. Niu, Phys. Rev. Lett. 76, 3758 (1996
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