7,554 research outputs found
A target for production of radioxenons
A liquid cesium target has been developed which allows the production and separate identification of the neutron deficient isotopes of xenon. The present report describes irradiations utilizing 34 to 41 MeV protons to produce millicurie quantities of Xe-127 and Xe-129m. At higher energies, however, the target could be used without modification to produce xenon isotopes as light as 119
Supersensitive measurement of angular displacements using entangled photons
We show that the use of entangled photons having non-zero orbital angular
momentum (OAM) increases the resolution and sensitivity of angular-displacement
measurements performed using an interferometer. By employing a 44
matrix formulation to study the propagation of entangled OAM modes, we analyze
measurement schemes for two and four entangled photons and obtain explicit
expressions for the resolution and sensitivity in these schemes. We find that
the resolution of angular-displacement measurements scales as while the
angular sensitivity increases as , where is the number of
entangled photons and the magnitude of the orbital-angular-momentum mode
index. These results are an improvement over what could be obtained with
non-entangled photons carrying an orbital angular momentum of per
photonComment: 6 pages, 3 figure
Constraints on nuclear matter parameters of an Effective Chiral Model
Within an effective non-linear chiral model, we evaluate nuclear matter
parameters exploiting the uncertainties in the nuclear saturation properties.
The model is sternly constrained with minimal free parameters, which display
the interlink between nuclear incompressibility (), the nucleon effective
mass (), the pion decay constant () and the meson
mass (). The best fit among the various parameter set is then
extracted and employed to study the resulting Equation of state (EOS). Further,
we also discuss the consequences of imposing constraints on nuclear EOS from
Heavy-Ion collision and other phenomenological model predictions.Comment: 10 pages, 8 figure
Optimal Placement of Conservation Practices Using Genetic Algorithm with SWAT
The effectiveness of conservation practices depends on their placement on the fields within the watershed. Cost-effective placement of these practices for maximum water quality benefits on each field requires comparing a very large number of possible land-use scenarios. To address this problem, we combine the tools of evolutionary algorithm with the Soil and Water Assessment Tool (SWAT) model and cost data to develop a trade-off frontier of least cost of achieving nutrient reductions and the corresponding locations of conservation practices. This approach was applied to the Raccoon River Watershed, which drains about 9,400 km2 of an intensive agriculture region in west-central Iowa. Applying genetic algorithm to the calibrated SWAT modeling setup produced multitudes of optimal solutions of achieving nutrient reductions in relation to the total cost of placing these practices. For example, a 30% reduction in nitrate (and a corresponding 53% reduction in phosphorus) at the watershed outlet can be achieved with a cost of $80 million per year. This solution frontier allows policymakers and stakeholders to explicitly see the trade-offs between cost and nutrient reductions
An Upper Limit on the Reflected Light from the Planet Orbiting the Star tau Bootis
The planet orbiting tau Boo at a separation of 0.046 AU could produce a
reflected light flux as bright as 1e-4 relative to that of the star. A spectrum
of the system will contain a reflected light component which varies in
amplitude and Doppler-shift as the planet orbits the star. Assuming the
secondary spectrum is primarily the reflected stellar spectrum, we can limit
the relative reflected light flux to be less than 5e-5. This implies an upper
limit of 0.3 for the planetary geometric albedo near 480 nm, assuming a
planetary radius of 1.2 R_Jup. This albedo is significantly less than that of
any of the giant planets of the solar system, and is not consistent with
certain published theoretical predictions.Comment: 5 pages, 1 figure, accepted by ApJ Letter
Towards a Mg lattice clock: Observation of the transition and determination of the magic wavelength
We optically excite the electronic state in Mg atoms,
laser-cooled and trapped in a magic-wavelength lattice. An applied magnetic
field enhances the coupling of the light to the otherwise strictly forbidden
transition. We determine the magic wavelength, the quadratic magnetic Zeeman
shift and the transition frequency to be 468.463(207)nm,
-206.6(2.0)MHz/T and 655 058 646 691(101)kHz, respectively. These
are compared with theoretical predictions and results from complementary
experiments. We also developed a high-precision relativistic structure model
for magnesium, give an improved theoretical value for the blackbody radiation
shift and discuss a clock based on bosonic magnesium.Comment: 5 pages, 3 figure
The Discovery of Cepheids and a New Distance to NGC 2841 Using the Hubble Space Telescope
We report on the discovery of Cepheids in the spiral galaxy NGC 2841, based
on observations made with the Wide Field and Planetary Camera 2 on board the
Hubble Space Telescope. NGC 2841 was observed over 12 epochs using the F555W
filter, and over 5 epochs using the F814W filter. Photometry was performed
using the DAOPHOT/ALLFRAME package.
We discovered a total of 29 variables, including 18 high-quality Cepheids
with periods ranging from 15 to 40 days. Period-luminosity relations in the V
and I bands, based on the high-quality Cepheids, yield an extinction-corrected
distance modulus of 30.74 +/- 0.23 mag, which corresponds to a distance of 14.1
+/- 1.5 Mpc. Our distance is based on an assumed LMC distance modulus of 18.50
+/- 0.10 mag (D = 50+/- 2.5 kpc) and a metallicity dependence of the Cepheid
P-L relation of gamma (VI) = -0.2 +/- 0.2 mag/dex.Comment: 31 preprint pages including 10 figures. Accepted for publication in
ApJ. High-resolution version available from
http://cfa-www.harvard.edu/~lmacri/n2841.p
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