336 research outputs found
High-resolution antenna near-field imaging and sub-THz measurements with a small atomic vapor-cell sensing element
Atomic sensing and measurement of millimeter-wave (mmW) and THz electric
fields using quantum-optical EIT spectroscopy of Rydberg states in atomic
vapors has garnered significant interest in recent years towards the
development of atomic electric-field standards and sensor technologies. Here we
describe recent work employing small atomic vapor cell sensing elements for
near-field imaging of the radiation pattern of a K-band horn antenna at
13.49 GHz. We image fields at a spatial resolution of and measure
over a 72 to 240 V/m field range using off-resonance AC-Stark shifts of a
Rydberg resonance. The same atomic sensing element is used to measure sub-THz
electric fields at 255 GHz, an increase in mmW-frequency by more than one order
of magnitude. The sub-THz field is measured over a continuous 100 MHz
frequency band using a near-resonant mmW atomic transition
Measurement of Radio-Frequency Radiation Pressure
We perform measurements of the radiation pressure of a radio-frequency (RF)
electromagnetic field which may lead to a new SI-traceable power calibration.
There are several groups around the world investigating methods to perform more
direct SI traceable measurement of RF power (where RF is defined to range from
100s of MHz to THz). A measurement of radiation pressure offers the possibility
for a power measure traceable to the kilogram and to Planck's constant through
the redefined SI. Towards this goal, we demonstrate the ability to measure the
radiation pressure/force carried in a field at 15~GHz.Comment: 2 pages 4 figure
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Edge and Surface Shape effects on Conductor Loss Associated with Planar Circuits
Agroindustrialization through institutional innovation
Some small-holders are able to generate reliable and substantial income flows through small-scale dairy production for the local market; for others, a set of unique transactions costs hinders participation. Cooperative selling institutions are potential catalysts for mitigating these costs, stimulating entry into the market, and precipitating growth in rural communities. Trends in cooperative organization in East-African dairy are evaluated. Empirical work focuses on alternative techniques for effecting participation among a representative sample of peri-urban milk producers in the Ethiopian highlands. The techniques considered are a modern production practice (cross-bred cow use), a traditional production practice (indigenous-cow use), three intellectual-capital-forming variables (experience, education, extension), and the provision of infrastructure (as measured by time to transport milk to market). A Tobit analysis of marketable surplus generates precise estimates of non-participants' ‘distances' to market and their reservation levels of the covariates—measures of the inputs necessary to sustain and enhance the market. Policy implications focus on the availability of cross-bred stock and the level of market infrastructure, both of which have marked effects on participation, the velocity of transactions in the local community and, inevitably, the social returns to agroindustrialization.Dairy farming Ethiopia. ,Collective farms Ethiopia. ,
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Linking mesoscale landscape heterogeneity and biodiversity: gardens and tree cover significantly modify flower-visiting beetle communities
Context
Maintaining biodiversity in multifunction landscapes is a significant challenge. Planning for the impacts of change requires knowledge of how species respond to landscape heterogeneity. Some insect groups are known to respond to heterogeneity at the mesoscale, defined here as hundreds of metres. However, for many taxa these effects are poorly known.
Objectives
To identify key elements of mesoscale landscape heterogeneity influencing community composition in flower-visiting beetles, and whether landscape explains any variation in beetle communities beyond that driven by immediate habitat cover.
Methods
Flower-visiting beetles were sampled from 36 transects, laid out using a 6 km2 grid located in southern Britain. Landscape heterogeneity was measured for 30 and 200 m buffers around the transects and the relative response of beetle communities to each assessed using ordination analyses followed by variation partitioning.
Results
The composition of immediately adjacent habitat (30 m) and mesoscale landscape heterogeneity (200 m) explained unique portions of the variation in flower-visiting beetle communities. A number of species, including those affiliated with deadwood habitats, were positively linked to tree cover in the surrounding mesoscale landscape. Gardens covered a smaller area than trees but modified beetle communities to the same extent.
Conclusions
The local abundance of some flower-visiting beetles is modified by the composition of the surrounding landscape. Results highlight the importance of tree cover for maintaining insect biodiversity in agricultural landscapes, while suggesting that gardens associated with small urban areas may have a disproportionate influence on biodiversity
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