6,155 research outputs found
Drought Injuries to Evergreen Trees in Windbreaks in Iowa
As in all the Plains states, in Iowa the first windbreaks were of the quicker growing species of trees. Cottonwoods, boxelders, willows and silver maples were heavy favorites several decades ago when farm homes began to dot the prairies, but after a few years when these trees began to lose what little ability they did have in wind protection, the Iowa farmers considered trees o£ more lasting qualities and more ability to check and effectively block the bitter winds of winter
The infrared morphology of galactic centers
Initial results are presented of a program to map the centers of galaxies in the mid-infrared using the NASA-MSFC 20 pixel bolometer array. Maps at 10.8 micrometer of the galaxies NGC 5236 (M82), NGC 1808, NGC 4536, and NGC 4527 reveal complex emitting regions ranging in size from 500 pc to 2 kpc. The infrared spatial distributions generally resemble those in the visible and radio. In all cases a large fraction of the IRAS 12 micrometer flux originates in spatial structures prominent in the maps
Wide-angle elastic scattering and color randomization
Baryon-baryon elastic scattering is considered in the independent scattering
(Landshoff) mechanism. It is suggested that for scattering at moderate
energies, direct and interchange quark channels contribute with equal color
coefficients because the quark color is randomized by soft gluon exchange
during the hadronization stage. With this assumption, it is shown that the
ratio of cross sections at CM angle
decreases from a high energy value of R_{\pbar p / pp} \approx 1/2.7, down to
R_{\pbar p / pp} \approx 1/28, compatible with experimental data at moderate
energies. This sizable fall in the ratio seems to be characteristic of the
Landshoff mechanism, in which changes at the quark level have a strong effect
precisely because the hadronic process occurs via multiple quark scatterings.
The effect of color randomization on the angular distribution of proton-proton
elastic scattering and the cross section ratio is also discussed.Comment: 18 pages, latex2e, 4 uuencoded figures, include
Environmental, developmental, and genetic factors controlling root system architecture
A better understanding of the development and architecture of roots is essential to develop strategies to increase crop yield and optimize agricultural land use. Roots control nutrient and water uptake, provide anchoring and mechanical support and can serve as important storage organs. Root growth and development is under tight genetic control and modulated by developmental cues including plant hormones and the environment. This review focuses on root architecture and its diversity and the role of environment, nutrient, and water as well as plant hormones and their interactions in shaping root architecture
Radiocarbon dates from the Oxford AMS system: archaeometry datelist 35
This is the 35th list of AMS radiocarbon determinations measured at the Oxford Radiocarbon Accelerator Unit (ORAU). Amongst some of the sites included here are the latest series of determinations from the key sites of Abydos, El Mirón, Ban Chiang, Grotte de Pigeons (Taforalt), Alepotrypa and Oberkassel, as well as others dating to the Palaeolithic, Mesolithic and later periods. Comments on the significance of the results are provided by the submitters of the material
Constraints on T-Odd, P-Even Interactions from Electric Dipole Moments
We construct the relationship between nonrenormalizable,effective,
time-reversal violating (TV) parity-conserving (PC) interactions of quarks and
gauge bosons and various low-energy TVPC and TV parity-violating (PV)
observables. Using effective field theory methods, we delineate the scenarious
under which experimental limits on permanent electric dipole moments (EDM's) of
the electron, neutron, and neutral atoms as well as limits on TVPC observables
provide the most stringent bounds on new TVPC interactions. Under scenarios in
which parity invariance is restored at short distances, the one-loop EDM of
elementary fermions generate the most severe constraints. The limits derived
from the atomic EDM of Hg are considerably weaker. When parity symmetry
remains broken at short distances, direct TVPC search limits provide the least
ambiguous bounds. The direct limits follow from TVPC interactions between two
quarks.Comment: 43 pages, 9 figure
Schiff Theorem and the Electric Dipole Moments of Hydrogen-Like Atoms
The Schiff theorem is revisited in this work and the residual - and
-odd electron--nucleus interaction, after the shielding takes effect, is
completely specified. An application is made to the electric dipole moments of
hydrogen-like atoms, whose qualitative features and systematics have important
implication for realistic paramagnetic atoms.Comment: 3 pages. Contribution to PANIC05, Particles and Nuclei International
Conference, Santa Fe, New Mexico, Oct. 24-28, 200
The SXI telescope on board EXIST: scientific performances
The SXI telescope is one of the three instruments on board EXIST, a
multiwavelength observatory in charge of performing a global survey of the sky
in hard X-rays searching for Supermassive Black Holes. One of the primary
objectives of EXIST is also to study with unprecedented sensitivity the most
unknown high energy sources in the Universe, like high redshift GRBs, which
will be pointed promptly by the Spacecraft by autonomous trigger based on hard
X-ray localization on board. The recent addition of a soft X-ray telescope to
the EXIST payload complement, with an effective area of ~950 cm2 in the energy
band 0.2-3 keV and extended response up to 10 keV will allow to make broadband
studies from 0.1 to 600 keV. In particular, investigations of the spectra
components and states of AGNs and monitoring of variability of sources, study
of the prompt and afterglow emission of GRBs since the early phases, which will
help to constrain the emission models and finally, help the identification of
sources in the EXIST hard X-ray survey and the characterization of the
transient events detected. SXI will also perform surveys: a scanning survey
with sky coverage of about 2pi and limiting flux of 5x10^{-14}cgs plus other
serendipitous. We give an overview of the SXI scientific performance and also
describe the status of its design emphasizing how it has been derived by the
scientific requirements.Comment: 9 pages, 6 figures, to be published in Proc. of SPIE, vol 7435-11,
200
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