198 research outputs found
Differences between tree species in hydraulic press calibration of leaf water potential are correlated with specific leaf area
. To determine the usefulness of the J-14 Hydraulic Press (Campbell Scientific, Inc., Logan, Utah, U.S.A.) in estimating leaf water potential, we calibrated the J-14 Press against a Scholander-type pressure chamber for leaves of various tree species. The species tested were: Acer saccharum, Acer negundo, Acer rubrum. Populus tremuloides, Populus grandidentata, Quercus rubra , and Brassaia actinophylla (Schefflera). The regression calibrations were linear with standard errors about the regression less than 0.1 MPa. The regression equations for the four genera were significantly different, with the y- intercept increasing and the slope decreasing in order of decreasing specific leaf area (SLA). There were no significant differences between species of the calibration lines within the genera Acer and Populus. These data may indicate that leaves with lower SLA resist mechanical compression by the hydraulic press, causing the J-14 Press to be less sensitive to differences of leaf water potential. Therefore the J-14 Press is only a relative measure of leaf water status and does not measure leaf water potential.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73416/1/1365-3040.ep11591871.pd
The role of occupied d states in the relaxation of hot electrons in Au
We present first-principles calculations of electron-electron scattering
rates of low-energy electrons in Au. Our full band-structure calculations
indicate that a major contribution from occupied d states participating in the
screening of electron-electron interactions yields lifetimes of electrons in Au
with energies of above the Fermi level that are larger than
those of electrons in a free-electron gas by a factor of . This
prediction is in agreement with a recent experimental study of ultrafast
electron dynamics in Au(111) films (J. Cao {\it et al}, Phys. Rev. B {\bf 58},
10948 (1998)), where electron transport has been shown to play a minor role in
the measured lifetimes of hot electrons in this material.Comment: 4 pages, 2 figures, to appear in Phys. Rev.
New exact solution of Dirac-Coulomb equation with exact boundary condition
It usually writes the boundary condition of the wave equation in the Coulomb
field as a rough form without considering the size of the atomic nucleus. The
rough expression brings on that the solutions of the Klein-Gordon equation and
the Dirac equation with the Coulomb potential are divergent at the origin of
the coordinates, also the virtual energies, when the nuclear charges number Z >
137, meaning the original solutions do not satisfy the conditions for
determining solution. Any divergences of the wave functions also imply that the
probability density of the meson or the electron would rapidly increase when
they are closing to the atomic nucleus. What it predicts is not a truth that
the atom in ground state would rapidly collapse to the neutron-like. We
consider that the atomic nucleus has definite radius and write the exact
boundary condition for the hydrogen and hydrogen-like atom, then newly solve
the radial Dirac-Coulomb equation and obtain a new exact solution without any
mathematical and physical difficulties. Unexpectedly, the K value constructed
by Dirac is naturally written in the barrier width or the equivalent radius of
the atomic nucleus in solving the Dirac equation with the exact boundary
condition, and it is independent of the quantum energy. Without any divergent
wave function and the virtual energies, we obtain a new formula of the energy
levels that is different from the Dirac formula of the energy levels in the
Coulomb field.Comment: 12 pages,no figure
Half-metallicity and Slater-Pauling behavior in the ferromagnetic Heusler alloys
Introductory chapter for the book "Halfmetallic Alloys - Fundamentals and
Applications" to be published in the series Springer Lecture Notes on Physics,
P. H. Dederichs and I. Galanakis (eds). It contains a review of the theoretical
work on the half-metallic Heusler alloys.Comment: Introductory chapter for the book "Halfmetallic Alloys - Fundamentals
and Applications" to be published in the series Springer Lecture Notes on
Physics, P. H. Dederichs and I. Galanakis (eds
Observation of exclusive DVCS in polarized electron beam asymmetry measurements
We report the first results of the beam spin asymmetry measured in the
reaction e + p -> e + p + gamma at a beam energy of 4.25 GeV. A large asymmetry
with a sin(phi) modulation is observed, as predicted for the interference term
of Deeply Virtual Compton Scattering and the Bethe-Heitler process. The
amplitude of this modulation is alpha = 0.202 +/- 0.028. In leading-order and
leading-twist pQCD, the alpha is directly proportional to the imaginary part of
the DVCS amplitude.Comment: 6 pages, 5 figure
A resposta do milho irrigado ao espaçamento entrelinhas depende do híbrido e da densidade de plantas
Animating tree colonization and growth
In the early twentieth century the woodland at Heald Brow, north-west England, was largely a tree-less pasture, but changing land management practices lead to natural tree colonization and the development of a mixed deciduous woodland with ash (Fraxinus excelsior), oak (Quercus robur), yew (Taxus baccata) and small-leaved Lime (Tilia cordata) the main components. The research focused on T. cordata due to its rarity and conservation value, and aimed to investigate the timing of its appearance, rates of reproduction by layering and the effects of competition on its longer-term survival. A small, 0.32 ha area of woodland was mapped using standard field-based survey methods and increment cores were taken to provide minimum age estimates for living stems of all species present. The spatial and temporal data generated led to the development of a new micro-GIS animation method, using ArcGIS software, that visually highlighted secondary woodland establishment and development, and gave novel insights into the competitive interactions that governed the development. Results showed T. cordata colonization in the 1940s and layering developing in the 1960s. The later appearance and rapid establishment of T. baccata with its light-excluding canopy produced high competition scores and undoubtedly restricted further development of the main T. cordata canopy aided by F. excelsior at the periphery. This animation method and associated GIS analyses have potential application in both dendrochronological, wider ecological research and in conservation management
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