The non-Gaussianity of the cosmic shear likelihood - or: How odd is the Chandra Deep Field South?

(abridged) We study the validity of the approximation of a Gaussian cosmic shear likelihood. We estimate the true likelihood for a fiducial cosmological model from a large set of ray-tracing simulations and investigate the impact of non-Gaussianity on cosmological parameter estimation. We investigate how odd the recently reported very low value of $\sigma_8$ really is as derived from the \textit{Chandra} Deep Field South (CDFS) using cosmic shear by taking the non-Gaussianity of the likelihood into account as well as the possibility of biases coming from the way the CDFS was selected. We find that the cosmic shear likelihood is significantly non-Gaussian. This leads to both a shift of the maximum of the posterior distribution and a significantly smaller credible region compared to the Gaussian case. We re-analyse the CDFS cosmic shear data using the non-Gaussian likelihood. Assuming that the CDFS is a random pointing, we find $\sigma_8=0.68_{-0.16}^{+0.09}$ for fixed $\Omega_{\rm m}=0.25$. In a WMAP5-like cosmology, a value equal to or lower than this would be expected in $\approx 5$ of the times. Taking biases into account arising from the way the CDFS was selected, which we model as being dependent on the number of haloes in the CDFS, we obtain $\sigma_8 = 0.71^{+0.10}_{-0.15}$. Combining the CDFS data with the parameter constraints from WMAP5 yields $\Omega_{\rm m} = 0.26^{+0.03}_{-0.02}$ and $\sigma_8 = 0.79^{+0.04}_{-0.03}$ for a flat universe.Comment: 18 pages, 16 figures, accepted for publication in A&A; New Bayesian treatment of field selection bia

An effective Hamiltonian for phase fluctuations on a lattice: an extended XY model

We derive an effective Hamiltonian for phase fluctuations in an s-wave superconductor starting from the attractive Hubbard model on a square lattice. In contrast to the common assumption, we find that the effective Hamiltonian is not the usual XY model but is of an extended XY type. This extended feature is robust and leads to essential corrections in understanding phase fluctuations on a lattice. The effective coupling in the Hamiltonian varies significantly with temperature.Comment: 2 figure

On the use of the Fourier Transform to determine the projected rotational velocity of line-profile variable B stars

The Fourier Transform method is a popular tool to derive the rotational velocities of stars from their spectral line profiles. However, its domain of validity does not include line-profile variables with time-dependent profiles. We investigate the performance of the method for such cases, by interpreting the line-profile variations of spotted B stars, and of pulsating B tars, as if their spectral lines were caused by uniform surface rotation along with macroturbulence. We perform time-series analysis and harmonic least-squares fitting of various line diagnostics and of the outcome of several implementations of the Fourier Transform method. We find that the projected rotational velocities derived from the Fourier Transform vary appreciably during the pulsation cycle whenever the pulsational and rotational velocity fields are of similar magnitude. The macroturbulent velocities derived while ignoring the pulsations can vary with tens of km/s during the pulsation cycle. The temporal behaviour of the deduced rotational and macroturbulent velocities are in antiphase with each other. The rotational velocity is in phase with the second moment of the line profiles. The application of the Fourier method to stars with considerable pulsational line broadening may lead to an appreciable spread in the values of the rotation velocity, and, by implication, of the deduced value of the macroturbulence. These two quantities should therefore not be derived from single snapshot spectra if the aim is to use them as a solid diagnostic for the evaluation of stellar evolution models of slow to moderate rotators.Comment: 13 pages, 9 figures, accepted for publication in Astronomy & Astrophysic

Improving LMOF luminescence quantum yield through guest-mediated rigidification

Rotation of a specific pyridyl ring in LMOF-236 is locked by loading guest molecules into the MOF's pore, improving quantum yield by nearly 400%–an example of a generalizable strategy for maximizing quantum yield via guest-packing rigidification

The media and advertising : a table of two-sided markets

Media industries are important drivers of popular culture. A large fraction of leisure time is devoted to radio, magazines, newspapers, the Internet, and television (the illustrative example henceforth). Most advertising expenditures are incurred for these media. They are also mainly supported by advertising revenue. Early work stressed possible market failures in program dupplication and catering to the Lowest Common Denominator, indicating lack of cultual diversisty and quality. The business model for most media industries is underscored by advertisers’ demand to reach prospectie customers. This business model has important impllications for performance in the market since viewer sovereignty is indirect. Viewers are attracted by programming, though they dislike the ads it carries, and advertisers want viewers as potential consumers. The two sides are coordinated by broadcasters (or “platforms”) that choose ad levels and program types, and advertising finances the programming. Competition for viewers of the demographics most desired by advertisers implies that programming choices will be biased towards the tastes of those with such demographics. The ability to use subscription pricing may help improve performance by catering to the tastes of those otherwise under-represented, though higher full prices tend to favor broadcasters at the expense of viewers and advertisers. If advertising demand is weak, program equilibrium porgram selection may be too extreme as broadcasters strive to avoid ruinous subscription price competition, but strong advertising demand may lead to strong competition for viewers and hence minimum differentiation (“la pensée unique”). Markets (such as newspapers) with a high proportion of ad-lovers may be served only by monopoly due to a circulation spiral : advertisers want to place ads in the paper with most readers, but readers want to buy the paper with more ads.Advertising finance; two-sided markets; platform competition