Patterens of Urbanization in a Midwestern Community: Bloomington, Illinois, 1850-1870

American development in the 19th century is a generally considered as the westward-moving agricultural frontier of an ever-diminishing frontier. However, the movement westward was accompanied by the growth of towns and cities

EVALUATION OF FRACTURE TOUGHNESS FROM INSTRUMENTED CHARPY IMPACT TESTS FOR A REACTOR PRESSURE VESSEL STEEL

ABSTRACT The monitoring of neutron induced embrittlement of nuclear power plants is provided using Charpy impact test in the surveillance program. However structural integrity assessments require the fracture toughness. Some empirical formulas have been developed but no direct relationship was found. The aim of our study is to determine the fracture toughness of a Reactor Pressure Vessel steel from instrumented Charpy impact test using local approach to fracture. This nonempirical method has been applied in the brittle domain as well as in the ductile to brittle transition for an A508 C1.3 steel. In the brittle domain, fracture occurs by cleavage and can be modeled with the Beremin model. Fracture toughness has been successfully determined from Charpy impact tests results and the influence of several parameters (mesh design, Beremin model with one or two parameters, number of Charpy impact tests results) on the results was considered. In the ductile to brittle transition, cleavage fracture is preceded by ductile crack growth. Ductile tearing has been accounted for in the simulations with the Rousselier model whereas cleavage fracture is still described with the Beremin model. The determination of fracture toughness from Charpy impact tests gave encouraging results but finite element simulations have to be refined in order to improve predictions

Low-latitude ionospheric turbulence observed by Aureol-3 satellite

Using PSD (Power Spectral Density) data on electron density and electric field variations observed on board Aureol-3 satellite at low-to-mid-latitude ionosphere we analyze a scale distribution of the ionospheric turbulence in a form <i>k<sup>-α</sup></i>, where <i>k</i> is the wave number and α is the spectral index. At first, high-resolution data in the near-equator region for several orbits have been processed. In this case the frequency range is from 6Hz to 100Hz (corresponding spatial scales from 80m to 1.3km), each power spectrum obeys a single power law fairly well, and the mean spectral indices are rather stable with α<sub><i>N</i></sub>=2.2±0.3 and α<sub><i>E</i></sub>=1.8±0.2, for the density and electric field, respectively. Then we produce a statistical study of 96 electric field bursts in the frequency range 10-100Hz from low-time resolution data (filter bank envelope). These bursts concentrate on the side of the Equatorial Anomaly crest (geomagnetic latitude 30-40°). Spectral indices of the bursts vary in the interval α<sub><i>E</i></sub>=2.0-2.5 but are fairly stable in seasons and local times. The electric field power of the burst has rather a large variability but has a relative increase in mean values for the summer and winter, as well as the daytime. The effect of major seismic activities toward the ionospheric turbulence is not conclusive either for the refractive index or for the electric field power. However, the mean value for the electric field power of bursts during seismic periods is larger than that for non seismic periods, and the statistical difference of the mean values is rather significant

Lattice thermal conductivity of disordered NiPd and NiPt alloys

Numerical calculations of lattice thermal conductivity are reported for the binary alloys NiPd and NiPt. The present work is a continuation of an earlier paper by us [PRB, 72, 214207 (2005)]which had developed a theoretical framework for the calculation of configuration-averaged lattice thermal conductivity and thermal diffusivity in disordered alloys. The formulation was based on the augmented space theorem combined with a scattering diagram technique. In this paper we shall show dependence of the lattice thermal conductivity on a series of variables like phonon frequency, temperature and alloy composition. The temperature dependence of $\kappa(T)$ and its realtion to the measured thermal conductivity is discussed. The concentration dependence of $\kappa$ appears to justify the notion of a minimum thermal conductivity as discussed by Kittel, Slack and others. We also study the frequency and composition dependence of the thermal diffusivity averaged over modes. A numerical estimate of this quantity gives an idea about the location of mobility edge and the fraction of states in the frequency spectrum which is delocalized.Comment: 23 pages, 18 figure

Simulations of ionospheric turbulence produced by HF heating near the upper hybrid layer

Heating of the ionosphere by high-frequency (HF), ordinary (O) mode electromagnetic waves can excite magnetic field aligned density striations (FAS), associated with upper and lower hybrid turbulence and electron heating. We have used Vlasov simulations in one spatial and two velocity dimensions to study the induced turbulence in the presence of striations when the O-mode pump is mode converted to large amplitude upper hybrid oscillations trapped in a striation. Parametric processes give rise to upper and lower hybrid turbulence, as well as to large amplitude, short wavelength electron Bernstein waves. The latter excite stochastic electron heating when their amplitudes exceed a threshold for stochasticity, leading to a rapid increase of the electron temperature by several thousands of Kelvin. The results have relevance for high latitude heating experiments

Influence of dynamic strain ageing on ductile fracture of a C-Mn steel

International audienceDuctile fracture of a C-Mn steel was characterised by tensile tests performed in a largetemperature range (from 20 to 350°C) on round notched specimens. The experimentalresults revealed a sharp drop of fracture strain around 250°C. This corresponds to thedomain of dynamic strain ageing (DSA) occurrence. The Portevin-Le Chatelier (PLC) effect,which is the most classical effect of DSA, was modelled on round notched specimens with amechanical behaviour model including the strain ageing effect. Local approach to fracturewas applied to predict the ductile fracture using the Rice and Tracey criterion. Thepredictions are rather close to the experimental results for the low and high temperatures. Inthe DSA domain, the approach predicts a decrease of the fracture strain but with a lowermagnitude than the experimental one. Therefore, DSA has an effect on mechanical behaviour but also on fracture mechanisms. Consequently, the fracture criterion has to bemodified in the presence of DSA

Satellite observations of banded VLF emissions in conjunction with energy‐banded ions during very large geomagnetic storms

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95489/1/jgra22114.pd