50 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
1-(2-Oxo-3,4-dihydro-2H-1,3-benzoxazin-4-yl)urea monohydrate
The organic molecule in the title hydrate, C9H9N3O3·H2O, was obtained by the condenstation of salicylic aldehyde with urea in acetonitrile. The oxazine ring adopts a slightly distorted sofa conformation, with the N atom deviating from the plane passing through the other atoms of the ring by 0.267 (2) Å. The crystal structure displays intermolecular N—H⋯O and O—H⋯O hydrogen bonding
Phenomenology of a-axis and b-axis charge dynamics from microwave spectroscopy of highly ordered YBa2Cu3O6.50 and YBa2Cu3O6.993
Extensive measurements of the microwave conductivity of highly pure and
oxygen-ordered \YBCO single crystals have been performed as a means of
exploring the intrinsic charge dynamics of a d-wave superconductor. Broadband
and fixed-frequency microwave apparatus together provide a very clear picture
of the electrodynamics of the superconducting condensate and its thermally
excited nodal quasiparticles. The measurements reveal the existence of very
long-lived excitations deep in the superconducting state, as evidenced by sharp
cusp-like conductivity spectra with widths that fall well within our
experimental bandwidth. We present a phenomenological model of the microwave
conductivity that captures the physics of energy-dependent quasiparticle
dynamics in a d-wave superconductor which, in turn, allows us to examine the
scattering rate and oscillator strength of the thermally excited quasiparticles
as functions of temperature. Our results are in close agreement with the
Ferrell-Glover-Tinkham sum rule, giving confidence in both our experiments and
the phenomenological model. Separate experiments for currents along the and directions of detwinned crystals allow us to isolate the role
of the CuO chain layers in \YBCO, and a model is presented that incorporates
both one-dimensional conduction from the chain electrons and two-dimensional
transport associated with the \cuplane plane layers.Comment: 17 pages, 13 figure
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
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
Absolute values of the London penetration depth in YBa2Cu3O6+y measured by zero field ESR spectroscopy on Gd doped single crystals
Zero-field electron spin resonance (ESR) of dilute Gd ions substituted for Y
in the cuprate superconductor YBaCuO is used as a novel
technique for measuring the absolute value of the low temperature magnetic
penetration depth . The Gd ESR spectrum of samples with
substitution was obtained with a broadband microwave technique
that measures power absorption bolometrically from 0.5 GHz to 21 GHz. This ESR
spectrum is determined by the crystal field that lifts the level degeneracy of
the spin 7/2 Gd ion and details of this spectrum provide information
concerning oxygen ordering in the samples. The magnetic penetration depth is
obtained by relating the number of Gd ions exposed to the microwave magnetic
field to the frequency-integrated intensity of the observed ESR transitions.
This technique has allowed us to determine precise values of for
screening currents flowing in the three crystallographic orientations (, and ) in samples of GdYBaCuO of three different oxygen contents ( K), ( K) and
( K). The in-plane values are found to depart substantially from the
widely reported relation .Comment: 14 pages, 12 figures; version to appear in PR
Rapid Plant Identification Using Species- and Group-Specific Primers Targeting Chloroplast DNA
Plant identification is challenging when no morphologically assignable parts are available. There is a lack of broadly applicable methods for identifying plants in this situation, for example when roots grow in mixture and for decayed or semi-digested plant material. These difficulties have also impeded the progress made in ecological disciplines such as soil- and trophic ecology. Here, a PCR-based approach is presented which allows identifying a variety of plant taxa commonly occurring in Central European agricultural land. Based on the trnT-F cpDNA region, PCR assays were developed to identify two plant families (Poaceae and Apiaceae), the genera Trifolium and Plantago, and nine plant species: Achillea millefolium, Fagopyrum esculentum, Lolium perenne, Lupinus angustifolius, Phaseolus coccineus, Sinapis alba, Taraxacum officinale, Triticum aestivum, and Zea mays. These assays allowed identification of plants based on size-specific amplicons ranging from 116 bp to 381 bp. Their specificity and sensitivity was consistently high, enabling the detection of small amounts of plant DNA, for example, in decaying plant material and in the intestine or faeces of herbivores. To increase the efficacy of identifying plant species from large number of samples, specific primers were combined in multiplex PCRs, allowing screening for multiple species within a single reaction. The molecular assays outlined here will be applicable manifold, such as for root- and leaf litter identification, botanical trace evidence, and the analysis of herbivory