4,151 research outputs found
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Excess open solar magnetic flux from satellite data: 2. A survey of kinematic effects
We investigate the “flux excess” effect, whereby open solar flux estimates from spacecraft increase with increasing heliocentric distance. We analyze the kinematic effect on these open solar flux estimates of large-scale longitudinal structure in the solar wind flow, with particular emphasis on correcting estimates made using data from near-Earth satellites. We show that scatter, but no net bias, is introduced by the kinematic “bunching effect” on sampling and that this is true for both compression and rarefaction regions. The observed flux excesses, as a function of heliocentric distance, are shown to be consistent with open solar flux estimates from solar magnetograms made using the potential field source surface method and are well explained by the kinematic effect of solar wind speed variations on the frozen-in heliospheric field. Applying this kinematic correction to the Omni-2 interplanetary data set shows that the open solar flux at solar minimum fell from an annual mean of 3.82 × 1016 Wb in 1987 to close to half that value (1.98 × 1016 Wb) in 2007, making the fall in the minimum value over the last two solar cycles considerably faster than the rise inferred from geomagnetic activity observations over four solar cycles in the first half of the 20th century
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Excess open solar magnetic flux from satellite data: 1. Analysis of the third perihelion Ulysses pass
We use the third perihelion pass by the Ulysses spacecraft to illustrate and investigate the “flux excess” effect, whereby open solar flux estimates from spacecraft increase with increasing heliocentric distance. We analyze the potential effects of small-scale structure in the heliospheric field (giving fluctuations in the radial component on timescales smaller than 1 h) and kinematic time-of-flight effects of longitudinal structure in the solar wind flow. We show that the flux excess is explained by neither very small-scale structure (timescales 1 day) solar wind speed variations on the frozen-in heliospheric field. We show that averaging over an interval T (that is long enough to eliminate structure originating in the heliosphere yet small enough to avoid cancelling opposite polarity radial field that originates from genuine sector structure in the coronal source field) is only an approximately valid way of allowing for these effects and does not adequately explain or account for differences between the streamer belt and the polar coronal holes
Computed tomography head and facial bones review of a 2,700 year old Egyptian mummy
Computed tomography (CT) scanning techniques used in head and facial bones examination in the clinical environment can also be transferable to the imaging of post-mortem cases as a novel non-destructive and non-invasive investigation in forensic cases. We describe a study of the head and facial bones of a 2,700 year old Egyptian mummy. Cross-sectional investigation can lead to discovering unknown information of skeletal and soft tissue structures and anatomy to contribute to the knowledge of preserved mummified remains and the practice of palaeoradiology
Compton telescope with coded aperture mask: Imaging with the INTEGRAL/IBIS Compton mode
Compton telescopes provide a good sensitivity over a wide field of view in
the difficult energy range running from a few hundred keV to several MeV. Their
angular resolution is, however, poor and strongly energy dependent. We present
a novel experimental design associating a coded mask and a Compton detection
unit to overcome these pitfalls. It maintains the Compton performance while
improving the angular resolution by at least an order of magnitude in the field
of view subtended by the mask. This improvement is obtained only at the expense
of the efficiency that is reduced by a factor of two. In addition, the
background corrections benefit from the coded mask technique, i.e. a
simultaneous measurement of the source and background. This design is
implemented and tested using the IBIS telescope on board the INTEGRAL satellite
to construct images with a 12' resolution over a 29 degrees x 29 degrees field
of view in the energy range from 200 keV to a few MeV. The details of the
analysis method and the resulting telescope performance, particularly in terms
of sensitivity, are presented
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Comment on 'The effect of strong velocity shears on incoherent scatter spectra: a new interpretation of unusual high latitude spectra'
Optimal Anesthetic Regime for Motionless Three-Dimensional Image Acquisition During Longitudinal Studies of Adult Nonpigmented Zebrafish
With many live imaging techniques, it is crucial that a deep level of anesthesia is reached and maintained
throughout image acquisition without reducing zebrafish viability. This is particularly true for three-dimensional
tomographic imaging modalities. Currently, the most commonly used anesthetic in the zebrafish community, MS-
222 (tricaine methanesulfonate), does not allow this. We show, using a combination of both MS-222 and
isoflurane, that we can significantly improve the anesthetic regime required for motionless image acquisition of
live adult zebrafish. We have benchmarked this against the requirements of our novel quantitative imaging
platform, compressive sensing optical projection tomography. Using nonpigmented transgenic zebrafish, we show
that a combination of 175 ppm of both anesthetics improves the maintenance of deep anesthesia for prolonged
periods of time and it can be used repeatedly to enable longitudinal imaging. Importantly, it does not affect the
health or viability of the adult zebrafish. We also show that nonpigmented fish, with a mutated form of the gene
transparent, took significantly longer to reach deep anesthesia. The anesthetic regime presented in this study
should lead to significant improvements in accuracy and information achievable from imaging live adult zebrafish
and in its application to longitudinal studies
Geographic Variation in Health Care: The Role of Private Markets
health care, public sector, Medicare, insurance
The relationship between propagule pressure and establishment success in alien bird populations: a re-analysis of Moulton & Cropper (2019)
A recent analysis by Moulton & Cropper (2019) of a global dataset on alien bird population introductions claims to find no evidence that establishment success is a function of the size of the founding population. Here, we re-analyse Moulton & Cropper’s data and show that this conclusion is based on flawed statistical methods—their data in fact confirm a strong positive relationship between founding population size and establishment success. We also refute several non-statistical arguments against the likelihood of such an effect presented by Moulton & Cropper. We conclude that a core tenet of population biology—that small populations are more prone to extinction—applies to alien populations beyond their native geographic range limits as much as to native populations within them
Exact-Diagonalization Studies of Inelastic Light Scattering in Self-Assembled Quantum Dots
We report exact diagonalization studies of inelastic light scattering in
few-electron quantum dots under the strong confinement regime characteristic of
self-assembled dots. We apply the orthodox (second-order) theory for scattering
due to electronic excitations, leaving for the future the consideration of
higher-order effects in the formalism (phonons, for example), which seem
relevant in the theoretical description of available experiments. Our numerical
results stress the dominance of monopole peaks in Raman spectra and the
breakdown of selection rules in open-shell dots. The dependence of these
spectra on the number of electrons in the dot and the incident photon energy is
explicitly shown. Qualitative comparisons are made with recent experimental
results.Comment: 11 pages, 11 figure
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