3,948 research outputs found
Theoretical He I Emissivities in the Case B Approximation
We calculate the He I case B recombination cascade spectrum using improved
radiative and collisional data. We present new emissivities over a range of
electron temperatures and densities. The differences between our results and
the current standard are large enough to have a significant effect not only on
the interpretation of observed spectra of a wide variety of objects but also on
determinations of the primordial helium abundance.Comment: Accepted to ApJ
Neutron Radiation Damage In Silicon Transistors
In the investigation of base and collector current as a function of the emitter-to-base voltage, previous studies have shown that neutron-induced base current has components originating in the emitter space charge region as well as the neutral base region. This study shows that while the low injection level neutron-induced base current is dominated by the space charge component, the high injection behavior appears to be controlled by recombination in the neutral base region. Additional experiments performed in special tetrode transistors and van der Pauw-type samples indicate that changes in collector current are dominated by recombination in the neutral base, while changes in base doping and mobility have only a secondary effect. These conclusions are reached from experiments on transistors with a ring emitter, on tetrode-type test transistors, and on special Hall-effect devices, and by a detailed analysis of the emission crowding characteristics of a ring-dot geometry device. Copyright © 1968 by The Institute of Electrical and Electronics Engineers, Inc
Zacht ligbed favoriet bij vleesstieren
Een volledig roostervloer zonder zacht ligbed is uit oogpunt van welzijn ongewenst. Vleesstieren gaan hier vaker op een abnormale manier staan en liggen dan in een hok met meer ruimte en een zacht ligbed van stro of rubber. Zo'n zacht ligbed bevordertduidelijk het welzijn
Flow in a Commercial Steel Pipe
Fully-developed turbulent flow in a commercial steel pipe is studied using single component hot-wire probes in both oneand two-point experiments. The streamwise turbulence component was measured over a Reynolds number range from 7.6Ă— 104 to 8.3Ă—106, covering the smooth to fully rough regimes. The experiments were conducted in the Princeton/ONR Superpipe facility that uses compressed air at pressures up to 200 atm as the working fluid. For Reynolds numbers less than about 8 Ă—105 the surface was hydraulically-smooth, and the results agreed closely with the smooth-wall turbulence intensity and spectral data obtained by Morrison et al. [10] and Zhao & Smits [14]. An assessment was performed of probe resolution and results indicate that the turbulence statistics of the large-scale motions were unaffected by the sensing wire length even at high Reynolds numbers. Transitionally-rough and fully-rough data showed deviation from the smooth-wall data as roughness effects became more prominent. In particular, the outer peak in the turbulence intensity observed at high Reynolds numbers in smooth pipe flow decreased in magnitude or stayed constant for transitionally rough and fully rough flow. The two-point azimuthal correlations were found to be consistent with the presence of very large scale coherent regions of low-wavenumber, low-momentum fluid observed in previous studies of wall-bounded flows. The correlations indicated that the azimuthal scale of these regions is Reynolds number independent
Supra-oscillatory critical temperature dependence of Nb-Ho bilayers
We investigate the critical temperature Tc of a thin s-wave superconductor
(Nb) proximity coupled to a helical rare earth ferromagnet (Ho). As a function
of the Ho layer thickness, we observe multiple oscillations of Tc superimposed
on a slow decay, that we attribute to the influence of the Ho on the Nb
proximity effect. Because of Ho inhomogeneous magnetization, singlet and
triplet pair correlations are present in the bilayers. We take both into
consideration when solving the self consistent Bogoliubov-de Gennes equations,
and we observe a reasonable agreement. We also observe non-trivial transitions
into the superconducting state, the zero resistance state being attained after
two successive transitions which appear to be associated with the magnetic
structure of Ho.Comment: Main article: 5 pages, 4 figures; Supplementary materials: 4 pages, 5
figure
Meer oppervlak geeft betere groei bij vleesstieren
Hoeveel ruimte hebben de stieren uit welzijnsoogpunt nodig en leidt dat tot betere prestaties? En geeft een zacht ligbed een verbetering van het welzijn
Size of the Vela Pulsar's Radio Emission Region: 500 km
We use interstellar scattering of the Vela pulsar to determine the size of
its emission region. From interferometric phase variations on short baselines,
we find that radio-wave scattering broadens the source by 3.4+/-0.3
milliarcseconds along the major axis at position angle 81+/-3 degrees. The
ratio of minor axis to major axis is 0.51+/-0.03. Comparison of angular and
temporal broadening indicates that the scattering material lies in the Vela-X
supernova remnant surrounding the pulsar. From the modulation of the pulsar's
scintillation on very short baselines, we infer a size of 500 km for the
pulsar's emission region. We suggest that radio-wave refraction within the
pulsar's magnetosphere may plausibly explain this size.Comment: 14 pages, includes 2 figures. Also available at:
http://charm.physics.ucsb.edu:80/people/cgwinn/cgwinn_group/cgwinn_group.htm
Model-based asymptotically optimal dispersion measure correction for pulsar timing
In order to reach the sensitivity required to detect gravitational waves,
pulsar timing array experiments need to mitigate as much noise as possible in
timing data. A dominant amount of noise is likely due to variations in the
dispersion measure. To correct for such variations, we develop a statistical
method inspired by the maximum likelihood estimator and optimal filtering. Our
method consists of two major steps. First, the spectral index and amplitude of
dispersion measure variations are measured via a time-domain spectral analysis.
Second, the linear optimal filter is constructed based on the model parameters
found in the first step, and is used to extract the dispersion measure
variation waveforms. Compared to current existing methods, this method has
better time resolution for the study of short timescale dispersion variations,
and generally produces smaller errors in waveform estimations. This method can
process irregularly sampled data without any interpolation because of its
time-domain nature. Furthermore, it offers the possibility to interpolate or
extrapolate the waveform estimation to regions where no data is available.
Examples using simulated data sets are included for demonstration.Comment: 15 pages, 15 figures, submitted 15th Sept. 2013, accepted 2nd April
2014 by MNRAS. MNRAS, 201
A new integrative assessment indicator for damage caused by major pests and diseases in the vineyard
An original and integrative evaluation indicator has been developed to quantify the cumulated damage from major pests and diseases affecting grape bunches: downy mildew, powdery mildew, gray mould and tortricid moths. It made it possible to estimate the associated crop losses and to relate them to the plant protection strategy in different modes of production (organic farming, in-transition, conventional). Thus, overall plant losses were higher in 2012 than in 2011. The in-transition growers’ strategy, with reduced copper doses but increased numbers of sprays, led to a 20% increase in average severity on bunches (essentially due to Downy mildew). The more pragmatic approach of experienced organic growers and conventional ones (higher doses and fewer sprays) reduced the yield losses. The proposed indicator is used for two purposes, i) evaluating the quantitative losses due to pest attacks and ii) differentiating them from other non-pest ones. A more detailed analysis including the impact on performance will be achieved and published soon
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