877 research outputs found
Nesting Ecology of Sedge Wrens in Hall County, Nebraska
The status of the Sedge Wren (Cistothorus platensis) in Nebraska is not well known. Cink (1973) summarized summer records from 1867 to 1971 and described only a few nest records. One nest discovered on 28 August 1902 at Capitol Beach, Lancaster Co., was assumed empty, apparently because of the late date. Bedell (1987) recorded July and August sightings in south central Nebraska and raised the question of whether these birds were migrants or nesting.
Sedge Wrens are frequently polygynous (Crawford 1977, Burns 1982) and may exhibit two waves of nesting effort in some areas (Burns 1982). Nest initiation appears to fall into two periods depending on the latitude; one from early May to June in Michigan (Walkinshaw 1935), Minnesota (Burns 1982), North Dakota (stewart 1975), and Wisconsin (Manci and Rusch 1988), and the other beginning in late July through August in Kansas (Cink pers. comm., Williams 1981) and Arkansas (Meanley 1952) in addition to more northern latitudes as cited above. This may explain why Sedge Wrens are often not encountered during typical May and June breeding bird censuses, especially in southern and western portions of their nesting range (Robbins et al. 1986).
This paper compares nesting densities on a grazed versus an ungrazed area and describes the nesting phenology of Sedge Wrens during the 1988 nesting season in Hall Co
Hedonic Pricing of Chocolate Quality Characteristics: Is there A Difference for Fruit or Nut Chocolate?
Chocolate campaigns in the United States have focused on the production of premier quality and healthy blend chocolate bars. We expect that merchandising efforts will offer a higher price for fruit or nut blend chocolates. Using online retail data from Amazon, eBay, and Walmart, we applied the hedonic function to estimate retailers offer price for a blended bar. The findings show that online retailers have mixed offer prices for a blend or plain bar. The paper suggests that studies would learn much more from a data and analysis that control for quantity sold and time effects in the chocolate market
Robustness of a local Fermi Liquid against Ferromagnetism and Phase Separation
We study the properties of Fermi Liquids with the microscopic constraint of a
local self-energy. In this case the forward scattering sum-rule imposes strong
limitations on the Fermi-Liquid parameters, which rule out any Pomeranchek
instabilities. For both attractive and repulsive interactions, ferromagnetism
and phase separation are suppressed. Superconductivity is possible in an s-wave
channel only. We also study the approach to the metal-insulator transition, and
find a Wilson ratio approaching 2. This ratio and other properties of
Sr_{1-x}La_xTiO_3 are all consistent with the local Fermi Liquid scenario.Comment: 4 pages (twocolumn format), can compile with or without epsf.sty
latex style file -- Postscript files: fig1.ps and fig2.p
Vitexin as an active ingredient in passion flower with potential as an agent for nicotine cessation: Vitexin antagonism of the expression of nicotine locomotor sensitization in rats
Context: Nicotine, a bioactive component of tobacco, is highly addictive. Numerous therapies have been developed for smoking cessation, and all have met with limited success. Our laboratory has previously shown that an extract of Passiflora incarnata Linn. (Passifloraceae) antagonized the expression of nicotine locomotor sensitization in rats. Objective: This study examined the ability of vitexin, a flavonoid found in P. incarnata, to ameliorate the signs of nicotine sensitization in rats. Materials and methods: Male Wistar rats were administered 0.4 mg/kg nicotine or vehicle (n = 16–18 per group) once a day for four consecutive days. Nicotine administration produces sensitization of locomotor activity. On the fifth day, locomotor activity was monitored as rats from each treatment group were administered either 30 or 60 mg/kg vitexin or its vehicle (n = 4–6 per group) 30 min before a challenge dose of 0.4 mg/kg nicotine. Results: The challenge dose of nicotine resulted in locomotor activity in rats sensitized to nicotine for 4 days that was approximately twice that measured in rats treated with vehicle during the sensitization phase. Rats sensitized to nicotine and then treated with 60 mg/kg vitexin prior to the nicotine challenge exhibited a level of locomotor activity equivalent to the vehicle-treated controls. Discussion: Vitexin antagonized the expression of nicotine locomotor sensitization in rats as the whole extract did in the previous study. Conclusion: Vitexin should be examined in future studies to evaluate its potential for treating nicotine addiction in humans
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Contains reports on three research projects.U. S. Air Force Electronics Systems Division) under Contract AF 19(628)-2487Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 36-039-AMC-03200(E)National Science Foundation (Grant GP-2495)National Institutes of Health (Grant MH-04737-05)National Aeronautics and Space Administration (Grant NsG-496
Acoustic attenuation probe for fermion superfluidity in ultracold atom gases
Dilute gas Bose-Einstein condensates (BEC's), currently used to cool
fermionic atoms in atom traps, can also probe the superfluidity of these
fermions. The damping rate of BEC-acoustic excitations (phonon modes), measured
in the middle of the trap as a function of the phonon momentum, yields an
unambiguous signature of BCS-like superfluidity, provides a measurement of the
superfluid gap parameter and gives an estimate of the size of the Cooper-pairs
in the BEC-BCS crossover regime. We also predict kinks in the momentum
dependence of the damping rate which can reveal detailed information about the
fermion quasi-particle dispersion relation.Comment: 4 pages, 2 figures. Revised versio
The Sun Remains Relatively Refractory Depleted: Elemental Abundances for 17,412 Gaia RVS Solar Analogs and 50 Planet Hosts
The elemental abundances of stars, particularly the refractory elements
(e.g., Fe, Si, Mg), play an important role in connecting stars to their
planets. Most Sun-like stars do not have refractory abundance measurements
since obtaining a large sample of high-resolution spectra is difficult with
oversubscribed observing resources. In this work we infer abundances for C, N,
O, Na, Mn, Cr, Si, Fe, Ni, Mg, V, Ca, Ti, Al, and Y for solar analogs with Gaia
RVS spectra (R=11,200) using the Cannon, a data-driven method. We train a
linear model on a reference set of 34 stars observed by Gaia RVS with precise
abundances measured from previous high resolution spectroscopic efforts (R >
30,000--110,000). We then apply this model to several thousand Gaia RVS solar
analogs. This yields abundances with average upper limit precisions of
0.04--0.1 dex for 17,412 stars, 50 of which are identified planet (candidate)
hosts. We subsequently test the relative refractory depletion of these stars
with increasing element condensation temperature compared to the Sun. The Sun
remains refractory depleted compared to other Sun-like stars regardless of our
current knowledge of the planets they host. This is inconsistent with theories
of various types of planets locking up or sequestering refractories.
Furthermore, we find no significant abundance differences between identified
close-in giant planet hosts, giant planet hosts, and terrestrial/small planet
hosts and the rest of the sample within our precision limits. This work
demonstrates the utility of data-driven learning for future exoplanet
composition and demographics studies.Comment: 24 pages, 10 figures, 4 tables, 1 appendix. Accepted in ApJ. Tables 1
and 2 available upon reques
Acoustic attenuation rate in the Fermi-Bose model with a finite-range fermion-fermion interaction
We study the acoustic attenuation rate in the Fermi-Bose model describing a
mixtures of bosonic and fermionic atom gases. We demonstrate the dramatic
change of the acoustic attenuation rate as the fermionic component is evolved
through the BEC-BCS crossover, in the context of a mean-field model applied to
a finite-range fermion-fermion interaction at zero temperature, such as
discussed previously by M.M. Parish et al. [Phys. Rev. B 71, 064513 (2005)] and
B. Mihaila et al. [Phys. Rev. Lett. 95, 090402 (2005)]. The shape of the
acoustic attenuation rate as a function of the boson energy represents a
signature for superfluidity in the fermionic component
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