5,142 research outputs found
Comparison of cattail (Typha sp.) occurrence on a photo-interpreted map versus a satellite data map
A comparison between a 1985 photo-interpreted vegetation map
and a vegetation map made from classified 1987 satellite data of
the Loxahatchee National Wildlife Refuge showed that 81% of
samples taken in areas occupied by cattail (Typha sp.) on the
photo-interpreted map corresponded with cattail on the satellite
data map.(5 page document
Orbital operations study. Appendix B: Operational procedures
Operational procedures for each alternate approach for each interfacing activity of the orbital operations study are presented. The applicability of the procedures to interfacing element pairs is identified
Shadowing Ministers: Monitoring Partners in Coalition Governments
In this article the authors study delegation problems within multiparty coalition
governments. They argue that coalition parties can use the committee system to
“shadow” the ministers of their partners; that is, they can appoint committee
chairs from other governing parties, who will then be well placed to monitor
and/or check the actions of the corresponding ministers. The authors
analyze which ministers should be shadowed if governing parties seek to
minimize the aggregate policy losses they suffer as the result of ministers pursuing
their own parties’ interests rather than the coalition’s. Based on data
from 19 mostly European parliamentary democracies, the authors find that the
greater the policy disagreement between a minister’s party and its partners,
the more likely the minister is to be shadowed
Doubly heavy quark baryon spectroscopy and semileptonic decay
Working in the framework of a nonrelativistic quark model we evaluate the
spectra and semileptonic decay widths for the ground state of doubly heavy
and baryons. We solve the three-body problem using a variational
ansatz made possible by the constraints imposed by heavy quark spin symmetry.
In order to check the dependence of our resultson the inter-quark interaction
we have used five different quarkquark potentials which include Coulomb and
hyperfine terms coming fromone-gluon exchange, plus a confining term. Our
results for the spectra are in good agreement with a previous calculation done
using a Faddeev approach. For the semileptonic decay our results for the total
decay widths are in a good agreement with the ones obtained within a
relativistic quark model in the quark-diquark approximation.Comment: Talk given at the IVth International Conference on Quarks an Nuclear
Physics (QNP06), Madrid, June 5th-10th 200
Enhanced Charge Photogeneration Promoted by Crystallinity in Small-Molecule Donor-Acceptor Bulk Heterojunctions
We examined sub-nanosecond time-scale charge carrier dynamics in crystalline films of a functionalized anthradithiophene (ADT) donor (D) with three different acceptor (A) molecules. A four-fold enhancement in ultrafast charge carrier separation efficiency was observed in D/A blends with a fullerene acceptor added at 7–10 wt. % concentrations, whereas a gradual decrease in peak photocurrent amplitude with acceptor concentration was observed with functionalized pentacene and indenofluorene acceptors. The results were directly correlated with the ADT-tri(ethylsilyl)ethynyl-F donor crystallinity. In the best-performing blends, the presence of crystalline acceptor domains was also established
Chiral Multiplets of Heavy-Light Mesons
The recent discovery of a narrow resonance in D_s+pi^0 by the BABAR
collaboration is consistent with the interpretation of a heavy J^P(0+,1+) spin
multiplet. This system is the parity partner of the groundstate (0-,1-)
multiplet, which we argue is required in the implementation of SU(3)_L x
SU(3)_R chiral symmetry in heavy-light meson systems. The (0+,1+)->(0-,1-)+pi
transition couplings satisfy a Goldberger-Treiman relation, g_pi =
Delta(M)/f_pi, where Delta(M) is the mass gap. The BABAR resonance fits the 0+
state, with a kinematically blocked principal decay mode to D+K. The allowed
D_s+pi, D_s+2pi and electromagnetic transitions are computed from the full
chiral theory and found to be suppressed, consistent with the narrowness of the
state. This state establishes the chiral mass difference for all such
heavy-quark chiral multiplets, and precise predictions exist for the analogous
B_s and strange doubly-heavy baryon states.Comment: 10 pages; minor editorial revisions; recomputed M1 transitio
Ozone Depletion from Nearby Supernovae
Estimates made in the 1970's indicated that a supernova occurring within tens
of parsecs of Earth could have significant effects on the ozone layer. Since
that time, improved tools for detailed modeling of atmospheric chemistry have
been developed to calculate ozone depletion, and advances have been made in
theoretical modeling of supernovae and of the resultant gamma-ray spectra. In
addition, one now has better knowledge of the occurrence rate of supernovae in
the galaxy, and of the spatial distribution of progenitors to core-collapse
supernovae. We report here the results of two-dimensional atmospheric model
calculations that take as input the spectral energy distribution of a
supernova, adopting various distances from Earth and various latitude impact
angles. In separate simulations we calculate the ozone depletion due to both
gamma-rays and cosmic rays. We find that for the combined ozone depletion
roughly to double the ``biologically active'' UV flux received at the surface
of the Earth, the supernova must occur at <8 pc. Based on the latest data, the
time-averaged galactic rate of core-collapse supernovae occurring within 8 pc
is ~1.5/Gyr. In comparing our calculated ozone depletions with those of
previous studies, we find them to be significantly less severe than found by
Ruderman (1974), and consistent with Whitten et al. (1976). In summary, given
the amplitude of the effect, the rate of nearby supernovae, and the ~Gyr time
scale for multicellular organisms on Earth, this particular pathway for mass
extinctions may be less important than previously thought.Comment: 24 pages, 4 Postscript figures, to appear in The Astrophysical
Journal, 2003 March 10, vol. 58
Spin-dependent electrical transport in ion-beam sputter deposited Fe-Cr multilayers
The temperature dependence of the electrical resistivity and
magnetoresistance of Xe-ion beam sputtered Fe-Cr multilayers has been
investigated. The electrical resistivity between 5 and 300 K in the fully
ferromagnetic state, obtained by applying a field beyond the saturation field
(H_sat) necessary for the antiferromagnetic(AF)-ferromagnetic(FM) field-induced
transition, shows evidence of spin-disorder resistivity as in crystalline Fe
and an s-d scattering contribution (as in 3d metals and alloys). The sublattice
magnetization m(T) in these multilayers has been calculated in terms of the
planar and interlayer exchange energies. The additional spin-dependent
scattering \Delta \rho (T) = \rho(T,H=0)_AF - \rho(T,H=H_sat)_FM in the AF
state over a wide range of temperature is found to be proportional to the
sublattice magnetization, both \Delta \rho(T) and m(T) reducing along with the
antiferromagnetic fraction. At intermediate fields, the spin-dependent part of
the electrical resistivity (\rho_s (T)) fits well to the power law \rho_s (T) =
b - cT^\alpha where c is a constant and b and \alpha are functions of H. At low
fields \alpha \approx 2 and the intercept b decreases with H much the same way
as the decrease of \Delta \rho (T) with T. A phase diagram (T vs. H_sat) is
obtained for the field- induced AF to FM transition. Comparisons are made
between the present investigation and similar studies using dc magnetron
sputtered and molecular beam epitaxy (MBE) grown Fe-Cr multilayers.Comment: 8 pages, 10 figures, to appear in Phys. Rev.
- …