8,656 research outputs found
The application of time-series MODIS NDVI profiles for the acquisition of crop information across Afghanistan
We investigated and developed a prototype crop information system integrating 250 m Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI) data with other available remotely sensed imagery, field data, and knowledge as part of a wider project monitoring opium and cereal crops. NDVI profiles exhibited large geographical variations in timing, height, shape, and number of peaks, with characteristics determined by underlying crop mixes, growth cycles, and agricultural practices. MODIS pixels were typically bigger than the field sizes, but profiles were indicators of crop phenology as the growth stages of the main first-cycle crops (opium poppy and cereals) were in phase. Profiles were used to investigate crop rotations, areas of newly exploited agriculture, localized variation in land management, and environmental factors such as water availability and disease. Near-real-time tracking of the current years’ profile provided forecasts of crop growth stages, early warning of drought, and mapping of affected areas. Derived data products and bulletins provided timely crop information to the UK Government and other international stakeholders to assist the development of counter-narcotic policy, plan activity, and measure progress. Results show the potential for transferring these techniques to other agricultural systems
Survey and monitoring of opium poppy and wheat in Afghanistan: 2003-2009
An integrated application of remote-sensing technology was devised and applied in Afghanistan during 2003–2009 providing critical information on cereal and poppy cultivation and poppy eradication. The results influenced UK and international policy and counter-narcotics actions in Afghanistan
Application of digital particle image velocimetry to insect aerodynamics: measurement of the leading-edge vortex and near wake of a Hawkmoth.
Some insects use leading-edge vortices to generate high lift forces, as has been inferred from qualitative smoke visualisations of the flow around their wings. Here we present the first Digital Particle Image Velocimetry (DPIV) data and quantitative analysis of an insect’s leading-edge vortex and near wake at two flight speeds. This allows us to describe objectively 2D slices through the flow field of a tethered Tobacco Hawkmoth (Manduca sexta). The near-field vortex wake appears to braodly resemble elliptical vortex loops. The presence of a leading-edge vortex towards the end of the downstroke is found to coincide with peak upward force production measured by a six-component force–moment balance. The topology of Manduca’s leading-edge vortex differs from that previously described because late in the downstroke, the structure extends continuously from wingtip across the thorax to the other wingtip
Comparison of Millimeter-wave and X-Ray Emission in Seyfert Galaxies
We compare the emission at multiple wavelengths of an extended Seyfert galaxy
sample, including both types of Seyfert nuclei. We use the Caltech
Submillimeter Observatory to observe the CO J = 2-1 transition line in a sample
of 45 Seyfert galaxies and detect 35 of them. The galaxies are selected by
their joint soft X-ray (0.1-2.4 keV) and far-infrared ({\lambda} = 60-100
{\mu}m) emission from the ROSAT/IRAS sample. Since the CO line widths (W CO)
reflect the orbital motion in the gravitational potential of the host galaxy,
we study how the kinematics are affected by the central massive black hole
(BH), using the X-ray luminosity. A significant correlation is found between
the CO line width and hard (0.3-8 keV from Chandra and XMM-Newton) X-ray
luminosity for both types of Seyfert nuclei. Assuming an Eddington accretion to
estimate the BH mass (M BH) from the X-ray luminosity, the W CO-L X relation
establishes a direct connection between the kinematics of the molecular gas of
the host galaxy and the nuclear activity, and corroborates the previous studies
that show that the CO is a good surrogate for the bulge mass. We also find a
tight correlation between the (soft and hard) X-ray and the CO luminosities for
both Seyfert types. These results indicate a direct relation between the
molecular gas (i.e., star formation activity) of the host galaxy and the
nuclear activity. To establish a clear causal connection between molecular gas
and the fueling of nuclear activity, high-resolution maps (<100 pc) of the CO
emission of our sample will be required and provided in a forthcoming Atacama
Large Millimeter Array observation
Exclusion of actin microfilaments from the cell-cell contact zone in HTLV-1 infected T-lymphocyte during the establishment of a functional virological synapse
- …