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$/\Phi_0$ where $\Phi_0$ is the flux quantum.Comment: 5 pages, 4 figure

Tunneling Study of the Charge-Ordering Gap on the Surface of La0.350_{0.350}Pr0.275_{0.275}Ca0.375_{0.375}MnO3_3 Thin Films

Variable temperature scanning tunneling microscopy/spectroscopy studies on (110) oriented epitaxial thin films of La$_{0.350}$Pr$_{0.275}$Ca$_{0.375}$MnO$_3$ are reported in the temperature range of 77 to 340 K. The films, grown on lattice matched NdGaO$_3$ 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 (T$<$150 K) show an energy gap of 0.5 eV while for T$\geq$180 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 $\mu$m$\times$2 $\mu$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 $d$-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 “footprint” of stewardship on the land. This report addresses a fundamental need—to 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 “What is environmental stewardship?” 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 $e^+e^-$ 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 $\eta$, radiative decay of the $\Delta$ 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-