Improved high-performance shock tube

Mylar diaphragms in shock tubes are a major improvement over steel diaphragms. Other improvements include: better electrode design; improved flow by opening the throat and removing all constrictions; and improved driver geometry by optimizing volume and shape

Spectra of large diluted but bushy random graphs

We compute an asymptotic expansion in $1/c$ of the limit in $n$ of the empirical spectral measure of the adjacency matrix of an Erd\H{o}s-R\'enyi random graph with $n$ vertices and parameter $c/n$. We present two different methods, one of which is valid for the more general setting of locally tree-like graphs. The second order in the expansion gives some information about the edge.Comment: 24 pages, 5 figure

The two uniform infinite quadrangulations of the plane have the same law

We prove that the uniform infinite random quadrangulations defined respectively by Chassaing-Durhuus and Krikun have the same distribution.Comment: English version of arXiv:0805.4687, with various improvement

One School: Using Teach-Throughs to Ensure Consistency

Presented as a Poster Presentation at 2020 IUSM Education Day

A program for computing shock-tube gas dynamic properties

Computer program calculates thermodynamic properties from basic spectroscopic data. Program capacity is a mixture of 100 different species composed of ten different elements. The output is a complete thermodynamic and chemical description of the gas

Weak lensing study of Abell 2029

Abell 2029 is one of the most studied clusters due to its proximity (z=0.07), its strong X-ray brightness and its giant cD galaxy which is one of the biggest stellar aggregates we know. We present here the first weak lensing mass reconstruction of this cluster made from a deep I-band image of 28.5'x28.5' centered on the cluster cD galaxy. This preliminary result allows us already to show the shape similarities between the cD galaxy and the cluster itself, suggesting that they form actually a single structure. We find a lower estimate of the total mass of 1.8 10^14 h^-1 solar masses within a radius of 0.3 h^-1 Mpc. We finally compute the mass-to-cD-light ratio and its evolution as a function of scale.Comment: 5 pages, to appear in the proceedings of "Matter and Energy in Clusters of Galaxies", ASP Conference Serie

The Small-Scale Environment of Quasars

Where do quasars reside? Are quasars located in environments similar to those of typical L* galaxies, and, if not, how do they differ? An answer to this question will help shed light on the triggering process of quasar activity. We use the Sloan Digital Sky Survey to study the environment of quasars and compare it directly with the environment of galaxies. We find that quasars (M_i < -22, z < 0.4) are located in higher local overdensity regions than are typical L* galaxies. The enhanced environment around quasars is a local phenomenon; the overdensity relative to that around L* galaxies is strongest within 100 kpc of the quasars. In this region, the overdensity is a factor of 1.4 larger than around L* galaxies. The overdensity declines monotonically with scale to nearly unity at ~1 Mpc, where quasars inhabit environments comparable to those of L* galaxies. The small-scale density enhancement depends on quasar luminosity, but only at the brightest end: the most luminous quasars reside in higher local overdensity regions than do fainter quasars. The mean overdensity around the brightest quasars (M_i < -23.3) is nearly three times larger than around L* galaxies while the density around dimmer quasars (M_i = -22.0 to -23.3) is ~1.4 times that of L* galaxies. By ~0.5 Mpc, the dependence on quasar luminosity is no longer significant. The overdensity on all scales is independent of redshift to z = 0.4. The results suggest a picture in which quasars typically reside in L* galaxies, but have a local excess of neighbors within ~0.1 - 0.5 Mpc; this local density excess likely contributes to the triggering of quasar activity through mergers and other interactions.Comment: Accepted by ApJ; 7 pages, 5 figure

870 micron Imaging of a Transitional Disk in Upper Scorpius: Holdover from the Era of Giant Planet Formation?

We present 880 micron images of the transition disk around the star [PZ99] J160421.7-213028, a solar-mass star in the nearby Upper Scorpius association. With a resolution down to 0.34 arcsec, we resolve the inner hole in this disk, and via model fitting to the visibilities and spectral energy distribution we determine both the structure of the outer region and the presence of sparse dust within the cavity. The disk contains about 0.1 Jupiter masses of mm-emitting grains, with an inner disk edge of about 70 AU. The inner cavity contains a small amount of dust with a depleted surface density in a region extending from about 20-70 AU. Taking into account prior observations indicating little to no stellar accretion, the lack of a binary companion, and the presence of dust near 0.1 AU, we determine that the most likely mechanism for the formation of this inner hole is the presence of one or more giant planets.Comment: 12 pages, 7 figures. To appear in the Astrophysical Journa

Shock-tube thermochemistry tables for high- temperature gases, 90% carbon dioxide and 10% nitrogen, volume 2

Shock tube tabulated computer equilibrium thermodynamic properties for carbon dioxide and nitrogen mixtur

A transitory regime : water supply in Conakry, Guinea

Both consumers and the government benefited from reform of the water system in Conakry, Guinea, whose deterioration since independence had become critical by the mid-1980s. Less than 40 percent of Conakry's population had access to piped water - low even by regional standards - and service was intermittent, at best, for the few who had connections. The public agency in charge of the sector was inefficient, overstaffed, and virtually insolvent. In several ways, the reform introduced to the sector in 1989 under a World Bank-led project was remarkable. It showed that even in a weak institutional environment, where contracts are hard to enforce and political interference is common, private sector participation can improve sector performance. The authors discuss the mechanismsthat made progress possible and identify factors that inhibit the positive effects of reform. Water has become very expensive, the number of connections has increased very slowly, and conflicts have developed between SEEG (the private operator) and SONEG (the state agency). Among the underlying problems: a) The lack of strong, stable institutions. b) The lack of an independent agency capable of restraining arbitrary government action, regulating the private operator, and enforcing contractual arrangements. c) The lack of adequate conflict resolution mechanisms for contract disputes. d) Weak administrative capacity.Environmental Economics&Policies,Water and Industry,Water Conservation,Decentralization,Water Supply and Systems,Town Water Supply and Sanitation,Water and Industry,Water Supply and Sanitation Governance and Institutions,Environmental Economics&Policies,Water Conservation