32,698 research outputs found
Nonparametric detection using extreme-value theory
Nonparametric extreme value statistics for constant signal detection in additive nois
Critical properties of the double exchange ferromagnet Nd0.4Pb0.4MnO3
Results of a study of dc-magnetization M(T, H), performed on a Nd0.6Pb0.4MnO3
single crystal in the temperature range around T_C (Curie temperature) which
embraces the critical region | epsilon | = |T -T_C |/T_C <= 0.05 are reported.
The magnetic data analyzed in the critical region using the Kouvel-Fisher
method give the values for the T_C =156.47 +/- 0.06 K and the critical
exponents, beta = 0.374 +/- 0.006 (from the temperature dependence of
magnetization), and gamma = 1.329 +/- 0.003 (from the temperature dependence of
initial susceptibility). The critical isotherm M(T_C, H) gives delta = 4.547
+/- 0.1. Thus the scaling law gamma+beta=delta beta is fulfilled. The critical
exponents obey the single scaling-equation of state M(H, epsilon) = epsilon^b
f_+/- (H/epsilon^(beta + gamma)) where, f_+ for T > T_C and f_- for T< T_C. The
exponent values are very close to those expected for the universality class of
3D Heisenberg ferromagnets with short-range interactions.Comment: 19 pages, including 6 figure
Tunnel Spectroscopy of a Proximity Josephson Junction
We present tunnel spectroscopy experiments on the proximity effect in lateral
superconductor-normal metal-superconductor (SNS) Josephson junctions. Our weak
link is embedded into a superconducting (S) ring allowing phase biasing of the
Josephson junction by an external magnetic field. We explore the temperature
and phase dependence of both the induced mini-gap and the modification of the
density of states in the normal (N) metal. Our results agree with a model based
on the quasiclassical theory in the diffusive limit. The device presents an
advanced version of the superconducting quantum interference proximity
transistor (SQUIPT), now reaching flux sensitivities of 3 nA where
is the flux quantum.Comment: 5 pages, 4 figure
Tunneling Study of the Charge-Ordering Gap on the Surface of LaPrCaMnO Thin Films
Variable temperature scanning tunneling microscopy/spectroscopy studies on
(110) oriented epitaxial thin films of
LaPrCaMnO are reported in the temperature
range of 77 to 340 K. The films, grown on lattice matched NdGaO substrates,
show a hysteretic metal-insulator transition in resistivity at 170 K. The
topographic STM images show step-terrace morphology while the conductance
images display a nearly homogeneous surface. The normalized conductance spectra
at low temperatures (T150 K) show an energy gap of 0.5 eV while for
T180 K a gap of 0.16 eV is found from the activated behavior of the zero
bias conductance. The presence of energy gap and the absence of phase
separation on the surface over more than 2 m2 m area
contradicts the metallic behavior seen in resistivity measurements at low
temperatures. We discuss the measured energy gap in terms of the stabilization
of the insulating CO phase at the film surface.Comment: 5 pages, 5 figures To appear in Phys. Rev.
Inelastic Scattering in Metal-H2-Metal Junctions
We present first-principles calculations of the dI/dV characteristics of an
H2 molecule sandwiched between Au and Pt electrodes in the presence of
electron-phonon interactions. The conductance is found to decrease by a few
percentage at threshold voltages corresponding to the excitation energy of
longitudinal vibrations of the H2 molecule. In the case of Pt electrodes, the
transverse vibrations can mediate transport through otherwise non-transmitting
Pt -channels leading to an increase in the differential conductance even
though the hydrogen junction is characterized predominately by a single almost
fully open transport channel. In the case of Au, the transverse modes do not
affect the dI/dV because the Au d-states are too far below the Fermi level. A
simple explanation of the first-principles results is given using scattering
theory. Finally, we compare and discuss our results in relation to experimental
data.Comment: Accepted in Phys. Rev.
What Is Urban Environmental Stewardship? Constructing a Practitioner-Derived Framework
Agencies and organizations deploy various strategies in response to environmental challenges, including the formulation of policy, programs, and regulations. Citizen-based environmental stewardship is increasingly seen as an innovative and important approach to improving and conserving landscape health. A new research focus on the stewardship of urban natural resources is being launched by the U.S. Forest Service in the Pacific Northwest region. Early scoping efforts are addressing various scales of human systems ranging from individuals to organizations to the entire positive âfootprintâ of stewardship on the land. This report addresses a fundamental needâto understand and describe civic environmental stewardship in urban settings. Stewardship has been described and defined in diverse ways within a variety of contexts, including the philosophical literature of environmentalism, agency program descriptions, and outreach by sponsoring organizations. Constructing a framework to convey the layered meanings of stewardship will help to focus and guide future research. A cognitive mapping technique was used to elicit responses to the question âWhat is environmental stewardship?â Semistructured interviews were conducted with representatives of nine Seattle environmental organizations, a group of practitioners who collectively represent over 100 years of experience in the field. Program planners and managers have particularly direct experiences of stewardship. Cognitive mapping enables participants to explore, then display, their particular knowledge and perceptions about an idea or activity. Analysis generated thematic, structural representations of shared concepts. Results show that the practitioners have multilayered perceptions of stewardship, from environmental improvement to community building, and from actions to outcomes. The resulting conceptual framework demonstrates the full extent of stewardship activity and meaning, which can aid stewardship sponsors to improve stewardship programs, leading to better experiences for participants and higher quality outcomes for projects and environments
A catalogue of the Chandra Deep Field South with multi-colour classification and photometric redshifts from COMBO-17
We present the COMBO-17 object catalogue of the Chandra Deep Field South for
public use, covering a field which is 31.5' x 30' in size. This catalogue lists
astrometry, photometry in 17 passbands from 350 to 930 nm, and ground-based
morphological data for 63,501 objects. The catalogue also contains multi-colour
classification into the categories 'Star', 'Galaxy' and 'Quasar' as well as
photometric redshifts. We include restframe luminosities in Johnson, SDSS and
Bessell passbands and estimated errors. The redshifts are most reliable at
R<24, where the sample contains approximately 100 quasars, 1000 stars and 10000
galaxies. We use nearly 1000 spectroscopically identified objects in
conjunction with detailed simulations to characterize the performance of
COMBO-17. We show that the selection of quasars, more generally type-1 AGN, is
nearly complete and minimally contaminated at z=[0.5,5] for luminosities above
M_B=-21.7. Their photometric redshifts are accurate to roughly 5000 km/sec.
Galaxy redshifts are accurate to 1% in dz/(1+z) at R<21. They degrade in
quality for progressively fainter galaxies, reaching accuracies of 2% for
galaxies with R~222 and of 10% for galaxies with R>24. The selection of stars
is complete to R~23, and deeper for M stars. We also present an updated
discussion of our classification technique with maps of survey completeness,
and discuss possible failures of the statistical classification in the faint
regime at R>24.Comment: submitted to Astronomy & Astrophysics, public data set available at
http://www.mpia.de/COMBO/combo_index.htm
Dilepton Production in Nucleon-Nucleon Reactions With and Without Hadronic Inelasticities
We calculate elementary proton-proton and neutron-proton bremsstrahlung and
their contribution to the invariant mass distribution. At 4.9 GeV, the
proton-proton contribution is larger than neutron-proton, but it is small
compared to recent data. We then make a first calculation of bremsstrahlung in
nucleon-nucleon reactions with multi-hadron final states. Again at 4.9 GeV, the
many-body bremsstrahlung is larger than simple nucleon-nucleon bremsstrahlung
by more than an order of magnitude in the low-mass region. When the
bremsstrahlung contributions are summed with Dalitz decay of the ,
radiative decay of the and from two-pion annihilation, the result
matches recent high statistics proton-proton data from the Dilepton
Spectrometer collaboration.Comment: 1+17 pages plus 11 PostScript figures uuencoded and appended,
McGill/93-9, TPI-MINN-93/18-
- âŠ