Return to Traffic of Full Depth Reclamation Pavements

Full-Depth Reclamation (FDR) is a cost-effective rehabilitation treatment for deteriorated pavements. However, when using asphalt emulsion based rehabilitation techniques one of the most challenging aspects of FDR is determining when traffic can be returned to the rehabilitated pavement surface. Since asphalt emulsion mixtures need ample time for curing, they cannot be sealed with a surface layer until the water has evaporated from the rehabilitated layer. It is often not possible to keep the road closed until all of the water has evaporated and the surface layer is placed, therefore, at some point the traffic needs to be returned to the rehabilitated surface. Determining when this point occurs, however, is still unclear. A laboratory raveling test run on Superpave Gyratory Compactor prepared samples simulates the raveling that can occur on the newly recycled pavement, and will be used in conjunction with inexpensive, simple tests that can be used in the field by agencies and contractors to determine if traffic can be released without causing damage to the rehabilitated pavement surface. Three mix designs were analyzed and used in conjunction to produce the emulsion and foam samples used in the testing. An optimum emulsion content was found and used to produce all of the samples. Based on a review of literature and an evaluation of practicality, four tests are recommended to be modeled for field use: British Pendulum Tester, Dynamic Friction Tester, a field-scale cohesiometer, and a rebound tester. The in-house testers were put through numerous tests on asphalt emulsion and asphalt foam samples. It was decided that of all of the testers, the one that showed the most potential was the Sweep Tester. Alterations to improve the devices were stated after all of the testing was completed

Photoionization of High Altitude Gas in a Supernova-Driven Turbulent Interstellar Medium

We investigate models for the photoionization of the widespread diffuse ionized gas in galaxies. In particular we address the long standing question of the penetration of Lyman continuum photons from sources close to the galactic midplane to large heights in the galactic halo. We find that recent hydrodynamical simulations of a supernova-driven interstellar medium have low density paths and voids that allow for ionizing photons from midplane OB stars to reach and ionize gas many kiloparsecs above the midplane. We find ionizing fluxes throughout our simulation grids are larger than predicted by one dimensional slab models, thus allowing for photoionization by O stars of low altitude neutral clouds in the Galaxy that are also detected in Halpha. In previous studies of such clouds the photoionization scenario had been rejected and the Halpha had been attributed to enhanced cosmic ray ionization or scattered light from midplane H II regions. We do find that the emission measure distributions in our simulations are wider than those derived from Halpha observations in the Milky Way. In addition, the horizontally averaged height dependence of the gas density in the hydrodynamical models is lower than inferred in the Galaxy. These discrepancies are likely due to the absence of magnetic fields in the hydrodynamic simulations and we discuss how magnetohydrodynamic effects may reconcile models and observations. Nevertheless, we anticipate that the inclusion of magnetic fields in the dynamical simulations will not alter our primary finding that midplane OB stars are capable of producing high altitude diffuse ionized gas in a realistic three-dimensional interstellar medium.Comment: ApJ accepted. 17 pages, 7 figure

Magnetized gas in the smith high velocity cloud

We report the first detection of magnetic fields associated with the Smith High Velocity Cloud. We use a catalog of Faraday rotation measures toward extragalactic radio sources behind the Smith Cloud, new H I observations from the Robert C. Byrd Green Bank Telescope, and a spectroscopic map of Hα from the Wisconsin H-Alpha Mapper Northern Sky Survey. There are enhancements in rotation measure (RM) of =100 rad m-2 which are generally well correlated with decelerated Hα emission. We estimate a lower limit on the line-of-sight component of the field of =8 μG along a decelerated filament; this is a lower limit due to our assumptions about the geometry. No RM excess is evident in sightlines dominated by H I or Hα at the velocity of the Smith Cloud. The smooth Hα morphology of the emission at the Smith Cloud velocity suggests photoionization by the Galactic ionizing radiation field as the dominant ionization mechanism, while the filamentary morphology and high (=1 Rayleigh) Hα intensity of the lower-velocity magnetized ionized gas suggests an ionization process associated with shocks due to interaction with the Galactic interstellar medium. The presence of the magnetic field may contribute to the survival of high velocity clouds like the Smith Cloud as they move from the Galactic halo to the disk. We expect these data to provide a test for magnetohydrodynamic simulations of infalling gas

Warm Ionized Medium throughout the Sagittarius–Carina Arm

Wisconsin H-Alpha Mapper (WHAM) observations of H-Alpha and [S II]$\lambda6716$ emission are used to trace the vertical distribution and physical conditions of the warm ionized medium (WIM) along the Sagittarius-Carina arm. CO emission, tracing cold molecular gas in the plane of the Galaxy, is used as a guide to isolate H-Alpha and [S II] emission along individual spiral arms. Exponential scale heights of electron density squared (or emission measure) are determined using H-Alpha emission above (below) the midplane to be $330 \pm 80$ pc ( $550 \pm 230$ pc) along the near Sagittarius arm, $300 \pm 100$ pc ($250 \pm 30$ pc) along the near Carina arm, and $>1000$ pc along the far Carina arm. The emission measure scale height tends to increase as a function of Galactocentric radius along the Sagittarius-Carina arm for $R_G > 8$ kpc. Physical conditions of the ionized gas are analyzed using the [S II]/H-Alpha line ratio, which more closely traces H-Alpha Intensity than height above the plane, z, suggesting a stronger relationship with the in-situ electron density. We interpret this result as further evidence for the majority of the observed diffuse emission originating from in-situ ionized gas as opposed to scattered light from classical H II regions in the plane.Comment: 18 pages, 19 figures, 2 tables, accepted for publication in Ap

The Turbulent Warm Ionized Medium: Emission Measure Distribution and MHD Simulations

We present an analysis of the distribution of H-alpha emission measures for the warm ionized medium (WIM) of the Galaxy using data from the Wisconsin H-Alpha Mapper (WHAM) Northern Sky Survey. Our sample is restricted to Galactic latitudes |b| > 10. We removed sightlines intersecting nineteen high-latititude classical H II regions, leaving only sightlines that sample the diffuse WIM. The distribution of EM sin |b| for the full sample is poorly characterized by a single normal distribution, but is extraordinarily well fit by a lognormal distribution, with = 0.146 +/- 0.001 and standard deviation 0.190 +/- 0.001. drops from 0.260 +/- 0.002 at Galactic latitude 10<|b|<30 to 0.038 +/- 0.002 at Galactic latitude 60<|b|<90. The distribution may widen slightly at low Galactic latitude. We compare the observed EM distribution function to the predictions of three-dimensional magnetohydrodynamic simulations of isothermal turbulence within a non-stratified interstellar medium. We find that the distribution of EM sin |b| is well described by models of mildy supersonic turbulence with a sonic Mach number of ~1.4-2.4. The distribution is weakly sensitive to the magnetic field strength. The model also successfully predicts the distribution of dispersion measures of pulsars and H-alpha line profiles. In the best fitting model, the turbulent WIM occupies a vertical path length of 400-500 pc within the 1.0-1.8 kpc scale height of the layer. The WIM gas has a lognormal distribution of densities with a most probable electron density n_{pk} = 0.03 cm^{-3}. We also discuss the implications of these results for interpreting the filling factor, the power requirement, and the magnetic field of the WIM.Comment: 16 pages, 13 figures, ApJ in press. Replacement reflects version accepted for publicatio