18,825 research outputs found
Comparison of different methods for estimating snowcover in forested, mountainous basins using LANDSAT (ERTS) images
Snow-covered areas on LANDSAT (ERTS) images of the Santiam River basin, Oregon, and other basins in Washington were measured using several operators and methods. Seven methods were used: (1) Snowline tracing followed by measurement with planimeter, (2) mean snowline altitudes determined from many locations, (3) estimates in 2.5 x 2.5 km boxes of snow-covered area with reference to snow-free images, (4) single radiance-threshold level for entire basin, (5) radiance-threshold setting locally edited by reference to altitude contours and other images, (6) two-band color-sensitive extraction locally edited as in (5), and (7) digital (spectral) pattern recognition techniques. The seven methods are compared in regard to speed of measurement, precision, the ability to recognize snow in deep shadow or in trees, relative cost, and whether useful supplemental data are produced
Overcoming the false-minima problem in direct methods: Structure determination of the packaging enzyme P4 from bacteriophage φ13
The problems encountered during the phasing and structure determination of the packaging enzyme P4 from bacteriophage φ13 using the anomalous signal from selenium in a single-wavelength anomalous dispersion experiment (SAD) are described. The oligomeric state of P4 in the virus is a hexamer (with sixfold rotational symmetry) and it crystallizes in space group C2, with four hexamers in the crystallographic asymmetric unit. Current state-of-the-art ab initio phasing software yielded solutions consisting of 96 atoms arranged as sixfold symmetric clusters of Se atoms. However, although these solutions showed high correlation coefficients indicative that the substructure had been solved, the resulting phases produced uninterpretable electron-density maps. Only after further analysis were correct solutions found (also of 96 atoms), leading to the eventual identification of the positions of 120 Se atoms. Here, it is demonstrated how the difficulties in finding a correct phase solution arise from an intricate false-minima problem. © 2005 International Union of Crystallography - all rights reserved
Research on the design of adaptive control systems, volume 1 Final report
Adaptive control systems - combined optimization and adaptive control, analysis-synthesis and passive adaptive systems, learning systems, and measurement adaptive system
Hydrogen reliquifier Quarterly report, 27 Sept. - 26 Dec. 1967
Computer analyzed hydrogen reliquefier cycles for selection of optimal cycle, rates, and heat exchanger
The in-medium isovector pi N amplitude from low energy pion scattering
Differential cross sections for elastic scattering of 21.5 MeV positive and
negative pions by Si, Ca, Ni and Zr have been measured as part of a study of
the pion-nucleus potential across threshold. The `anomalous' repulsion in the
s-wave term was observed, as is the case with pionic atoms. The extra repulsion
can be accounted for by a chiral-motivated model where the pion decay constant
is modified in the medium. Unlike in pionic atoms, the anomaly cannot be
removed by merely introducing an empirical on-shell energy dependence.Comment: 9 pages, 2 figures. Minor changes, to appear in PR
Detoxification in rehabilitation in England: effective continuity of care or unhappy bedfellows?
There is evidence that residential detoxification alone does not provide satisfactory treatment outcomes and that outcomes are significantly enhanced when clients completing residential detoxification attend rehabilitation services (Gossop, Marsden, Stewart, & Rolfe, 1999; Ghodse, Reynolds, Baldacchino, et al., 2002). One way of increasing the likelihood of this continuity of treatment is by providing detoxification and rehabilitation within the same treatment facility to prevent drop-out, while the client awaits a rehabilitation bed or in the transition process. However, there is little research evidence available on the facilities that offer both medical detoxification and residential rehabilitation. The current study compares self-reported treatment provision in 87 residential rehabilitation services in England, 34 of whom (39.1%) reported that they offered detoxification services within their treatment programmes. Although there were no differences in self-reported treatment philosophies, residential rehabilitation services that offered detoxification were typically of shorter duration overall, had significantly more beds and reported offering more group work than residential rehabilitation services that did not offer detoxification. Outcomes were also different, with twice as many clients discharged on disciplinary grounds from residential rehabilitation services without detoxification facilities. The paper questions the UK classification of residential drug treatment services as either detoxification or rehabilitation and suggests the need for greater research focus on the aims, processes and outcomes of this group of treatment providers
First principles study of local electronic and magnetic properties in pure and electron-doped NdCuO
The local electronic structure of Nd2CuO4 is determined from ab-initio
cluster calculations in the framework of density functional theory.
Spin-polarized calculations with different multiplicities enable a detailed
study of the charge and spin density distributions, using clusters that
comprise up to 13 copper atoms in the CuO2plane. Electron doping is simulated
by two different approaches and the resulting changes in the local charge
distribution are studied in detail and compared to the corresponding changes in
hole doped La2CuO4. The electric field gradient (EFG) at the copper nucleus is
investigated in detail and good agreement is found with experimental values. In
particular the drastic reduction of the main component of the EFG in the
electron-doped material with respect to LaCuO4 is explained by a reduction of
the occupancy of the 3d3z^2-r^2 atomic orbital. Furthermore, the chemical
shieldings at the copper nucleus are determined and are compared to results
obtained from NMR measurements. The magnetic hyperfine coupling constants are
determined from the spin density distribution
Single-qubit-gate error below 10^-4 in a trapped ion
With a 9Be+ trapped-ion hyperfine-states qubit, we demonstrate an error
probability per randomized single-qubit gate of 2.0(2) x 10^-5, below the
threshold estimate of 10^-4 commonly considered sufficient for fault-tolerant
quantum computing. The 9Be+ ion is trapped above a microfabricated
surface-electrode ion trap and is manipulated with microwaves applied to a trap
electrode. The achievement of low single-qubit-gate errors is an essential step
toward the construction of a scalable quantum computer.Comment: 5 pages, 3 figures, 1 table; changed to match published versio
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