5 research outputs found
Modelling Tachyon Cosmology with Non-Minimal Derivative Coupling to Gravity
We study a tachyon model with non-minimal derivative coupling to gravity in
the Friedmann-Robertson-Walker flat cosmology. We propose the special
re-definition of the tachyon field which allows us to represent tachyon field
equation formally coinciding with its usual form but with re-defined Hubble
parameter. Two first integrals for the model equations are obtained that can
essentially simplify both further analysis and analytical solving for the
model. These integrals become the trivial identities in the case of minimal
coupling. The effective energy density and pressure of the tachyon field are
obtained, and the necessary condition of the possibility for this model to
expand with acceleration is derived.Comment: 7 page
Widespread Climate Change in the Himalayas and Associated Changes in Local Ecosystems
Background: Climate change in the Himalayas, a biodiversity hotspot, home of many sacred landscapes, and the source of eight largest rivers of Asia, is likely to impact the well-being of 20% of humanity. However, despite the extraordinary environmental, cultural, and socio-economic importance of the Himalayas, and despite their rapidly increasing ecological degradation, not much is known about actual changes in the two most critical climatic variables: temperature and rainfall. Nor do we know how changes in these parameters might impact the ecosystems including vegetation phenology. Methodology/Principal Findings: By analyzing temperature and rainfall data, and NDVI (Normalized Difference Vegetation Index) values from remotely sensed imagery, we report significant changes in temperature, rainfall, and vegetation phenology across the Himalayas between 1982 and 2006. The average annual mean temperature during the 25 year period has increased by 1.5C with an average increase of 0.06C yr. The average annual precipitation has increased by 163 mm or 6.52 mmyr. Since changes in temperature and precipitation are immediately manifested as changes in phenology of local ecosystems, we examined phenological changes in all major ecoregions. The average start of the growing season (SOS) seems to have advanced by 4.7 days or 0.19 days yr and the length of growing season (LOS) appears to have advanced by 4.7 days or 0.19 days yr, but there has been no change in the end of the growing season (EOS). There is considerable spatial and seasonal variation in changes in climate and phenological parameters. Conclusions/Significance: This is the first time that large scale climatic and phenological changes at the landscape level have been documented for the Himalayas. The rate of warming in the Himalayas is greater than the global average, confirming that the Himalayas are among the regions most vulnerable to climate change