49 research outputs found
Perch-type Characteristics of Overwintering Red-tailed Hawks (Buteo jamaicensis) and American Kestrels (Falco sparverius)
Red-tailed Hawks (Buteo jamaicensis) and American Kestrels (Falco sparverius) are primarily sitand-wait predators that rely on perches to forage most efficiently. Overwintering Red-tailed Hawks and American Kestrels use available perches (e.g., utility poles and wires, trees, fences, gates, etc.) to hunt for prey items in agricultural fields in northeast Arkansas. Observations were made from December 2011-March 2012 and November 2012-March 2013 in three representative cover-types (short rice stubble, soybean stubble, and fallow areas including roadsides) to determine which perch-types were used by Red-tailed Hawks and American Kestrels. Utility pole crossbeams at an average height of 6.3 m were the main perchtypes used by Red-tailed Hawks, demonstrating the use of man-made structures’. These perches were generally in or near fallow areas or short rice stubble fields. Conversely, American Kestrels usually perched on wires at an average height of 4.9 m, over fallow roadsides’. Fallow areas had high prey density and vegetation cover. Niche separation via differential use of perches may be one factor that allows these raptors to avoid inter-specific competition
Bolometric technique for high-resolution broadband microwave spectroscopy of ultra-low-loss samples
A novel low temperature bolometric method has been devised and implemented
for high-precision measurements of the microwave surface resistance of small
single-crystal platelet samples having very low absorption, as a continuous
function of frequency. The key to the success of this non-resonant method is
the in-situ use of a normal metal reference sample that calibrates the absolute
rf field strength. The sample temperature can be controlled independently of
the 1.2 K liquid helium bath, allowing for measurements of the temperature
evolution of the absorption. However, the instrument's sensitivity decreases at
higher temperatures, placing a limit on the useful temperature range. Using
this method, the minimum detectable power at 1.3 K is 1.5 pW, corresponding to
a surface resistance sensitivity of 1 for a typical 1
mm1 mm platelet sample.Comment: 13 pages, 12 figures, submitted to Review of Scientific Instrument
Stability of nodal quasiparticles in underdoped YBa2Cu3O6+y probed by penetration depth and microwave spectroscopy
High resolution measurements of superfluid density and broadband
quasiparticle conductivity have been used to probe the low energy excitation
spectrum of nodal quasiparticles in underdoped YBCO. Penetration depth is
measured to temperatures as low as 0.05 K. Microwave conductivity is measured
from 0.1 to 20 GHz and is a direct probe of zero-energy quasiparticles. The
data are compared with predictions for a number of theoretical scenarios that
compete with or otherwise modify pure d-wave superconductivity, in particular
commensurate and incommensurate spin and charge density waves; d + i s and d +
i d superconductivity; circulating current phases; and the BCS--BEC crossover.
We conclude that the data are consistent with a pure d-wave state in the
presence of a small amount of strong scattering disorder, and are able to rule
out most candidate competing states either completely, or to a level set by the
energy scale of the disorder, ~ 4 K. Commensurate spin and charge density
orders, however, are not expected to alter the nodal spectrum and therefore
cannot be excluded