6,082 research outputs found
On Cournot-Nash equilibria with exogenous uncertainty
A large body of literature has accumulated which examines how the optimal solution of an agent maximizing the expectation of a real-valued function, depending on a random parameterp and the agent's behaviorx, reacts to perturbations in the first and second moments ofp. Here, by an approximation valid for small uncertainty, we allow many agents and consider their behavior in a Cournot-Nash equilibrium. We also allowp to depend on the behaviors of the participating agents. We apply the analysis to two models, one of a Cournot oligopoly, the other of a cooperative of individuals where there is uncertainty in the return to communal work
Quasi-periodic pulsations in solar and stellar flares: re-evaluating their nature in the context of power-law flare Fourier spectra
The nature of quasi-periodic pulsations in solar and stellar flares remains
debated. Recent work has shown that power-law-like Fourier power spectra, also
referred to as 'red' noise processes, are an intrinsic property of solar and
stellar flare signals, a property that many previous studies of this phenomenon
have not accounted for. Hence a re-evaluation of the existing interpretations
and assumptions regarding QPP is needed. Here we adopt a Bayesian method for
investigating this phenomenon, fully considering the Fourier power law
properties of flare signals. Using data from the PROBA2/LYRA, Fermi/GBM,
Nobeyama Radioheliograph and Yohkoh/HXT instruments, we study a selection of
flares from the literature identified as QPP events. Additionally we examine
optical data from a recent stellar flare that appears to exhibit oscillatory
properties. We find that, for all but one event tested, an explicit oscillation
is not required in order to explain the observations. Instead, the flare
signals are adequately described as a manifestation of a power law in the
Fourier power spectrum, rather than a direct signature of oscillating
components or structures. However, for the flare of 1998 May 8, strong evidence
for the existence of an explicit oscillation with P ~ 14-16 s is found in the
17 GHz radio data and the 13-23 keV Yohkoh HXT data. We conclude that, most
likely, many previously analysed events in the literature may be similarly
described in terms of power laws in the flare Fourier power spectrum, without
the need to invoke a narrowband, oscillatory component. As a result the
prevalence of oscillatory signatures in solar and stellar flares may be less
than previously believed. The physical mechanism behind the appearance of the
observed power laws is discussed.Comment: 11 pages, 7 figures, 1 table. Accepted for publication in The
Astrophysical Journa
Observable Effects of Dust Formation in Dynamic Atmospheres of M-type Mira Variables
The formation of dust with temperature-dependent non-grey opacity is
considered in a series of self-consistent model atmospheres at different phases
of an O-rich Mira variable of mass 1.2 . Photometric and
interferometric properties of these models are predicted under different
physical assumptions regarding the dust formation. The iron content of the
initial silicate that forms and the availability of grain nuclei are found to
be critical parameters that affect the observable properties. In particular,
parameters were found where dust would form at 2-3 times the average continuum
photospheric radius. This work provides a consistent physical explanation for
the larger apparent size of Mira variables at wavelengths shorter than 1 m
than that predicted by dust free fundamental-mode pulsation models.Comment: Accepted for MNRAS; 9 pages, 5 figure
Two Wide Planetary-mass Companions to Solar-type Stars in Upper Scorpius
At wide separations, planetary-mass and brown dwarf companions to solar-type stars occupy a curious region of
parameter space not obviously linked to binary star formation or solar system scale planet formation. These
companions provide insight into the extreme case of companion formation (either binary or planetary), and
due to their relative ease of observation when compared to close companions, they offer a useful template
for our expectations of more typical planets. We present the results from an adaptive optics imaging survey
for wide (~50–500 AU) companions to solar-type stars in Upper Scorpius. We report one new discovery of a
~14 M_J companion around GSC 06214−00210and confirm that the candidate planetary-mass companion 1RXS
J160929.1−210524 detected by Lafrenière et al. is in fact comoving with its primary star. In our survey, these
two detections correspond to ~4% of solar-type stars having companions in the 6–20 M_J mass and ~200–500 AU
separation range. This figure is higher than would be expected if brown dwarfs and planetary-mass companions
were drawn from an extrapolation of the binary mass function. Finally, we discuss implications for the formation
of these objects
The Angular Diameter and Fundamental Parameters of Sirius A
The Sydney University Stellar Interferometer (SUSI) has been used to make a
new determination of the angular diameter of Sirius A. The observations were
made at an effective wavelength of 694.1 nm and the new value for the
limb-darkened angular diameter is 6.048 +/- 0.040mas (+/-0.66%). This new
result is compared with previous measurements and is found to be in excellent
agreement with a conventionally calibrated measurement made with the European
Southern Observatory's Very Large Telescope Interferometer (VLTI) at 2.176
microns (but not with a second globally calibrated VLTI measurement). A
weighted mean of the SUSI and first VLTI results gives the limb-darkened
angular diameter of Sirius A as 6.041 +/- 0.017mas (+/-0.28%). Combination with
the Hipparcos parallax gives the radius equal to 1.713 +/- 0.009R_sun. The
bolometric flux has been determined from published photometry and
spectrophotometry and, combined with the angular diameter, yields the emergent
flux at the stellar surface equal to (5.32+/- 0.14)x10^8 Wm^-2 and the
effective temperature equal to 9845 +/- 64 K. The luminosity is 24.7 +/- 0.7
L_sun.Comment: Accepted for publication in PAS
Entanglement of arbitrary superpositions of modes within two-dimensional orbital angular momentum state spaces
We use spatial light modulators (SLMs) to measure correlations between arbitrary superpositions of orbital angular momentum (OAM) states generated by spontaneous parametric down-conversion. Our technique allows us to fully access a two-dimensional OAM subspace described by a Bloch sphere, within the higher-dimensional OAM Hilbert space. We quantify the entanglement through violations of a Bell-type inequality for pairs of modal superpositions that lie on equatorial, polar, and arbitrary great circles of the Bloch sphere. Our work shows that SLMs can be used to measure arbitrary spatial states with a fidelity sufficient for appropriate quantum information processing systems
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