461 research outputs found
Scotland, Catalonia and the “right” to self-determination: a comment suggested by Kathryn Crameri’s “Do Catalans Have the Right to Decide?
No abstract available
Responsivity mapping techniques for the non-positional CCD: the swept charge device CCD236
The e2v CCD236 is a swept charge device (SCD) designed as a soft X-ray detector for spectroscopy in the range 0.8 keV to 10 keV [1]. It benefits from improvements in design over the previous generation of SCD (the e2v CCD54) [2] to allow for increased detector area, a reduction in split X-ray events and improvements to radiation hardness [3]. To enable the suppression of surface dark current the device is clocked continuously, therefore there is no positional information making responsivity variations difficult to measure. This paper describes investigated techniques to achieve a responsivity map across the device using masking and XRF, and spot illumination from an organic light-emitting diode (OLED). The results of this technique should allow a deeper understanding of the device sensitivity and allow better data interpretation in SCD applications
Measurement of the electric dipole moments for transitions to rubidium Rydberg states via Autler-Townes splitting
We present the direct measurements of electric-dipole moments for
transitions with for Rubidium atoms. The
measurements were performed in an ultracold sample via observation of the
Autler-Townes splitting in a three-level ladder scheme, commonly used for
2-photon excitation of Rydberg states. To the best of our knowledge, this is
the first systematic measurement of the electric dipole moments for transitions
from low excited states of rubidium to Rydberg states. Due to its simplicity
and versatility, this method can be easily extended to other transitions and
other atomic species with little constraints. Good agreement of the
experimental results with theory proves the reliability of the measurement
method.Comment: 12 pages, 6 figures; figure 6 replaced with correct versio
The Social Power of Algorithms
This article explores the questions associated with what might be thought of as the social power of algorithms. The article, which introduces a special issue on the same topic, begins by reflecting on how we might approach algorithms from a social scientific perspective. The article is then split into two sections. The first deals with the issues that might be associated with an analysis of the power of the algorithms themselves. This section outlines a series of issues associated with the functionality of the algorithms and how these functions are powerfully deployed within social world. The second section then focuses upon the notion of the algorithm. In this section, the article argues that we need to look beyond the algorithms themselves, as a technical and material presence, to explore how the notion or concept of the algorithm is also an important feature of their potential power. In this section, it is suggested that we look at the way that notions of the algorithm are evoked as a part of broader rationalities and ways of seeing the world. Exploring the notion of the algorithm may enable us to see how algorithms also play a part in social ordering processes, both in terms of how the algorithm is used to promote certain visions of calculative objectivity and also in relation to the wider governmentalities that this concept might be used to open up
Photofission of heavy nuclei at energies up to 4 GeV
Total photofission cross sections for 238U, 235U, 233U, 237Np, 232Th, and
natPb have been measured simultaneously, using tagged photons in the energy
range Egamma=0.17-3.84 GeV. This was the first experiment performed using the
Photon Tagging Facility in Hall B at Jefferson Lab. Our results show that the
photofission cross section for 238U relative to that for 237Np is about 80%,
implying the presence of important processes that compete with fission. We also
observe that the relative photofission cross sections do not depend strongly on
the incident photon energy over this entire energy range. If we assume that for
237Np the photofission probability is equal to unity, we observe a significant
shadowing effect starting below 1.5 GeV.Comment: 4 pages of RevTex, 6 postscript figures, Submitted to Phys. Rev. Let
Proton polarizability effect in the Lamb shift of the hydrogen atom
The proton polarizability correction to the Lamb shift of electronic and
muonic hydrogen is calculated on the basis of isobar model and experimental
data on the structure functions of deep inelastic lepton-nucleon scattering.
The contributions of the Born terms, vector-meson exchanges and nucleon
resonances are taken into account in the construction of the photoabsorption
cross sections for transversely and longitudinally polarized virtual photons
sigma_{T,L}.Comment: 11 pages, 3 figure
Pion production in deeply virtual Compton scattering
Using a soft pion theorem based on chiral symmetry and a
resonance model we propose an estimate for the production cross section of low
energy pions in the deeply virtual Compton scattering (DVCS) process. In
particular, we express the processes in terms of
generalized parton distributions. We provide estimates of the contamination of
the DVCS observables due to this associated pion
production processes when the experimental data are not fully exclusive, for a
set of kinematical conditions representative of present or planned experiments
at JLab, HERMES and COMPASS.Comment: 50 pages, 22 figure
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