10,401 research outputs found
Blackland Prairies of Southwestern Arkansas
The Blackland Prairie community type has been described in Texas; related communities exist in Alabama and Mississippi. The Arkansas variant of the community has not been described in detail. Since the Arkansas Natural Heritage Commission began a systematic inventory of the community in 1985, more than 36 remnants have been identified that retain substantial natural character. However, all show some degree of disturbance. Based on aerial photo interpretation, aerial inspection, and ground study, an initial description of the community is presented, including original distribution, soil, vegetation and relationship to similar communities of Texas, Mississippi, and Alabama
A Seat at the Table: Including the Poor in Decisions for Development and Environment
Presents case studies of the access to information, public participation, and justice for the poor in environmental decision-making processes and barriers, including issues of literacy, costs, risk, and cultural context. Makes policy recommendations
Propagation and deposition of stony debris flows at channel confluences
The fluid dynamics of stony debris flows generated in two small tributaries adjacent to each
other and flowing into a main receiving channel was analyzed experimentally at a laboratory scale. The
analysis on the propagation along the tributaries and deposition in the main channel provide information
about sediment-water mobility, dangerous damming, and potential hazard. Debris flows were generated by
releasing a preset water discharge over an erodible layer of saturated gravels material. As a consequence,
the debris flow sediment concentration varied accordingly to the entrainment rate which, in turn, was
strongly controlled by the tributary slope. The data collected by acoustic level sensors, pore fluid pressure
transducers, and a load cell were used to characterize the evolution of bulk density and solid concentration
of the sediment-water mixture. These two parameters were relevant to assess the stony debris flow mobility
which contributes to determine the shape of sediment deposits in the main channel. The detailed bed
topography surveys carried out in the main channel at the end of each experiment provided information on
the morphology of these deposits and on the interplay of adjacent confluences. The influences of conflu-
ence angle, tributary slopes, and triggering conditions have been investigated, for a total of 18 different
configurations. Within the investigated range of parameters, the slope angle was the parameter that mainly
influences the stony debris flow mobility while, for adjacent confluences, the degree of obstruction within
the receiving channel was strongly influenced by the triggering scenario
A new low profile antenna with improved performance for satellite on-the-move communications
A novel design solution for a low-profile fullduplex Satellite-On-The-Move Communications hybrid
scanned phased array antenna for low elevation angle
coverage (down to 10°) is described. The antenna is
operated at Ku-Band. The unique louvered array element
geometry in combination with a spatial filter/ âray
bendingâ lens facilitates the shaping of the element
pattern to increase gain at low elevation angles.
Preliminary modelling results using simple ray-tracing
and 3D E simulation indicate that the desired low angle
coverage can be achieved
A low profile radiating element with nearly hemispheric coverage for satellite communications on-the-move hybrid array antenna
A novel design solution of a dual-linearly polarised Ku-band low-profile radiating element for low elevation angle coverage (down to 10° above horizon) is presented. Such an element is suitable for full-duplex Satellite Communications On-The-Move (SCOTM) hybrid scanned phased array antenna applications. Standard designed radiating elements for array applications with low profile physical structure suffer poor low elevation angle coverage as the element pattern reduces by sine of the elevation angle. The element design demonstrated in this paper features unique louvered array element geometry incorporating a spatial âray bendingâ lens facilitates the shaping of the element pattern to increase gain at low elevation angles. Preliminary modelling results using ray tracing analysis shows that the desired low angle coverage can be achieved. Currently in progress full 3D electromagnetic simulations which include the interaction between the basic radiator and the spatial lens indicates that using an ideal tilted element with novel louvered reflector in addition with proposed lens, low angular coverage can potentially be realised in a low profile structure
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