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When users control the algorithms: Values expressed in practices on the twitter platform
Recent interest in ethical AI has brought a slew of values, including fairness, into conversations about technology design. Research in the area of algorithmic fairness tends to be rooted in questions of distribution that can be subject to precise formalism and technical implementation. We seek to expand this conversation to include the experiences of people subject to algorithmic classification and decision-making. By examining tweets about the “Twitter algorithm” we consider the wide range of concerns and desires Twitter users express. We find a concern with fairness (narrowly construed) is present, particularly in the ways users complain that the platform enacts a political bias against conservatives. However, we find another important category of concern, evident in attempts to exert control over the algorithm. Twitter users who seek control do so for a variety of reasons, many well justified. We argue for the need for better and clearer definitions of what constitutes legitimate and illegitimate control over algorithmic processes and to consider support for users who wish to enact their own collective choices
Partially suppressed long-range order in the Bose-Einstein condensation of polaritons
We adopt a kinetic theory of polariton non-equilibrium Bose-Einstein
condensation, to describe the formation of off-diagonal long-range order. The
theory accounts properly for the dominant role of quantum fluctuations in the
condensate. In realistic situations with optical excitation at high energy, it
predicts a significant depletion of the condensate caused by long-wavelength
fluctuations. As a consequence, the one-body density matrix in space displays a
partially suppressed long-range order and a pronounced dependence on the finite
size of the system
Dynamic response of strongly correlated Fermi gases in the quantum virial expansion
By developing a quantum virial expansion theory, we quantitatively calculate
the dynamic density response function of a trapped strongly interacting Fermi
gas at high temperatures near unitarity. A clear transition from atomic to
molecular responses is identified in the spectra when crossing from the BCS to
BEC regimes, in qualitative agreement with recent Bragg spectroscopy
observations. Our virial expansion method provides a promising way to solve the
challenging strong-coupling problems and is applicable to other dynamical
properties of strongly correlated Fermi gases.Comment: 5 pages, 4 figures; published version in Phys. Rev. A. The quantum
virial expansion of single-particle spectral function is discussed in
arXiv:1003.1538 (Phys. Rev. Lett. 104, 240407 (2010)
Single-particle and collective excitations in a charged Bose gas at finite temperature
The main focus of this work is on the predictions made by the dielectric
formalism in regard to the relationship between single-particle and collective
excitation spectra in a gas of point-like charged bosons at finite temperature
below the critical region of Bose-Einstein condensation. Illustrative
numerical results at weak coupling () are presented within the Random
Phase Approximation. We show that within this approach the single-particle
spectrum forms a continuum extending from the transverse to the longitudinal
plasma mode frequency and leading to a double-peak structure as increases,
whereas the density fluctuation spectrum consists of a single broadening peak.
We also discuss the momentum distribution and the superfluidity of the gas.Comment: 15 pages, 5 figure
Astrometric orbits of SB9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to derive
astrometric orbital elements for spectroscopic binaries from the newly released
Ninth Catalogue of Spectroscopic Binary Orbits (SB9). Among the 1374 binaries
from SB9 which have an HIP entry, 282 have detectable orbital astrometric
motion (at the 5% significance level). Among those, only 70 have astrometric
orbital elements that are reliably determined (according to specific
statistical tests discussed in the paper), and for the first time for 20
systems, representing a 10% increase relative to the 235 DMSA/O systems already
present in the Hipparcos Double and Multiple Systems Annex.
The detection of the astrometric orbital motion when the Hipparcos IAD are
supplemented by the spectroscopic orbital elements is close to 100% for
binaries with only one visible component, provided that the period is in the 50
- 1000 d range and the parallax is larger than 5 mas. This result is an
interesting testbed to guide the choice of algorithms and statistical tests to
be used in the search for astrometric binaries during the forthcoming ESA Gaia
mission.
Finally, orbital inclinations provided by the present analysis have been used
to derive several astrophysical quantities. For instance, 29 among the 70
systems with reliable astrometric orbital elements involve main sequence stars
for which the companion mass could be derived. Some interesting conclusions may
be drawn from this new set of stellar masses, like the enigmatic nature of the
companion to the Hyades F dwarf HIP 20935. This system has a mass ratio of 0.98
but the companion remains elusive.Comment: Astronomy & Astrophysics, in press (16 pages, 12 figures); also
available at http://www.astro.ulb.ac.be/Html/ps.html#Astrometr
S-band antenna phased array communications system
The development of an S-band antenna phased array for spacecraft to spacecraft communication is discussed. The system requirements, antenna array subsystem design, and hardware implementation are examined. It is stated that the phased array approach offers the greatest simplicity and lowest cost. The objectives of the development contract are defined as: (1) design of a medium gain active phased array S-band communications antenna, (2) development and test of a model of a seven element planar array of radiating elements mounted in the appropriate cavity matrix, and (3) development and test of a breadboard transmit/receive microelectronics module
Research and development in cds photovoltaic film cells third quarterly report, nov. 19, 1964 - feb. 19, 1965
Cadmium sulfide photovoltaic film cell
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