Phase transitions in social networks

We study a model of network with clustering and desired node degree. The original purpose of the model was to describe optimal structures of scientific collaboration in the European Union. The model belongs to the family of exponential random graphs. We show by numerical simulations and analytical considerations how a very simple Hamiltonian can lead to surprisingly complicated and eventful phase diagram.Comment: 8 pages, 8 figure

Management Forecasts in Crowded Sectors

This paper documents a dual role for disclosure. In addition to the traditional role of alleviating information asymmetry, firms are motivated to disclose to attract investors’ limited resources and order flow away from other firms (Fishman and Hagerty, 1989). In periods when firms returns comove more with their sector's returns and thus face more competition for investors, they issue more guidance, especially capex guidance. The effect of firm-sector comovement ("sector crowdedness") on guidance increases with fiercer competition for investors. Guidance increases liquidity and price efficiency (measured as investment sensitivity to price), but the impact of guidance decreases in sector crowdedness, consistent with the proposition that more disclosure in the crowded sectors is investor-seeking rather than precision increasing. Although the impact of guidance on investment-price sensitivity is lower in more crowded sectors, the effect is still positive, suggesting that firms can improve price efficiency by issuing guidance to attract informed investors to the firm

Measuring Maximum Latewood Density By Image Analysis At The Cellular Level

A study was conducted to compare the precision of X-ray densitometry (XRD) and video image analysis (VIA) in measuring wood density of the last-formed latewood. The precision was determined by examining the convergence of the replicated measurements of maximum latewood density (MAXD). by XRD, and maximum percentage of cell-wall area (MAX%), by VIA. VIA was a more precise method for determining density of the last-formed tracheids than XRD. The linear relationship between MAXD and MAX% was significant at P < 0.01. The results indicate that MAX% can be used as an alternative to X-ray measurements of MAXD

Critical phenomena in exponential random graphs

The exponential family of random graphs is one of the most promising class of network models. Dependence between the random edges is defined through certain finite subgraphs, analogous to the use of potential energy to provide dependence between particle states in a grand canonical ensemble of statistical physics. By adjusting the specific values of these subgraph densities, one can analyze the influence of various local features on the global structure of the network. Loosely put, a phase transition occurs when a singularity arises in the limiting free energy density, as it is the generating function for the limiting expectations of all thermodynamic observables. We derive the full phase diagram for a large family of 3-parameter exponential random graph models with attraction and show that they all consist of a first order surface phase transition bordered by a second order critical curve.Comment: 14 pages, 8 figure

Spitzer Imaging and Spectral Mapping of the Oxygen-Rich Supernova Remnant G292.0+1.8

We present mid-infrared continuum and emission line images of the Galactic oxygen-rich supernova remnant (SNR) G292.0+1.8, acquired using the MIPS and IRS instruments on the Spitzer Space Telescope. The MIPS 24 micron and 70 micron images of G292.0+1.8 are dominated by continuum emission from a network of filaments encircling the SNR. The morphology of the SNR, as seen in the mid-infrared, resembles that seen in X-rays with the Chandra X-ray Observatory. Most of the mid-infrared emission in the MIPS images is produced by circumstellar dust heated in the non-radiative shocks around G292.0+1.8, confirming the results of earlier mid-IR observations with AKARI. In addition to emission from hot dust, we have also mapped atomic line emission between 14 micron and 36 micron using IRS spectral maps. The line emission is primarily associated with the bright oxygen-rich optical knots, but is also detected from fast-moving knots of ejecta. We confirm our earlier detection of 15-25 micron emission characteristic of magnesium silicate dust in spectra of the radiatively shocked ejecta. We do not detect silicon line emission from any of the radiatively shocked ejecta in the southeast of the SNR, possibly because that the reverse shock has not yet penetrated most of the Si-rich ejecta in that region. This may indicate that G292.0+1.8 is less evolved in the southeast than the rest of the SNR, and may be further evidence in favor of an asymmetric SN explosion as proposed in recent X-ray studies of G292.0+1.8.Comment: 16 pages, 1 table, 7 figures, accepted for publication in Ap