Assessing the toxicity of a reconstituted water simulating streams influenced by mountaintop mining in central Appalachia

Freshwater ecosystems in Central Appalachia experience increased concentrations of manganese (Mn) and total dissolved solids from the runoff of surface mines and valley fills. Biological communities have been impacted by these surface mining operations and it has been suggested that the increase in total dissolved solids may contribute to these negative effects, but standard laboratory toxicity tests have not found increased concentrations of total dissolved solids to have such negative effects as seen in the field. The elevated total dissolved solids in mining influenced streams may only be toxic in conjunction with another toxicant that is presence in these systems such as manganese. This study’s primary goal was to determine the toxic effects of a simulated mine water representative of elevated ionic conditions in mining influenced streams of Central Appalachia on the fathead minnow (Pimephales promelas) and examine potential cumulative effects with manganese. Breeding colonies were exposed to different concentrations of the simulated mine water then toxicity tests were performed with manganese on the embryos and larvae. The adverse effects of the combination of toxicants were determined using traditional and non-traditional toxicity testing endpoints. This study found that fathead minnow larval growth was decreased in a concentration of 10 mg Mn/L in conjunction with a 50% dilution of the simulated mine water, but no effect was observed at higher simulated mine water concentrations most likely because of the increased water hardness that is known to reduce both sulfate and manganese toxicity. The concentration of sulfate in the simulated mine water was more toxic when combined with manganese in comparison to historic data for sulfate toxicity. These findings could be applied to mitigation and restoration efforts for streams affected by mountaintop mining operations in Central Appalachia

Crack Surveys of Low-Cracking High-Performance Concrete Bridge Decks in Kansas 2009-2010

The specifications for the construction of Low-Cracking High-Performance Concrete (LC-HPC) bridge decks are summarized and the survey procedure used for analysis of cracking performance of bridge decks is described. Thirteen LC-HPC decks and thirteen control decks were evaluated using the survey procedure. Crack densities were calculated and crack locations marked. LC-HPC bridge decks have significantly lower crack densities than do the control bridge decks. The majority of cracks develop in the transverse direction, directly above and parallel to the reinforcing steel. Longitudinal cracks often propagate from the abutments. The results suggest that crack densities will increase on the upper portions of superelevated decks due to increased settlement cracking caused by the use of high slump concrete and less than optimum curing when water is not directly supplied to the superelevated side of the deck. Overfinishing of concrete by means of a double-drum roller screed may increase cracking by increasing the amount of cement paste at the deck surface

Lightweight Aggregate as Internal Curing Agent to Limit Concrete Skrinkage

The effectiveness of prewetted, vacuum saturated (PVS) lightweight aggregate (LWA) as an internal curing agent to reduce concrete shrinkage is evaluated for curing periods of 7 and 14 days. Normalweight aggregate is replaced by LWA at volume replacement levels ranging from 8.9 to 13.8%. Some mixtures contain a partial replacement of portland cement with slag cement while maintaining the paste content at approximately 24.1% of concrete volume. Comparisons are made with mixtures containing low-absorption granite and high-absorption limestone normalweight coarse aggregates. At the replacement levels used in this study, PVS LWA results in a small reduction in concrete density, no appreciable effect on concrete compressive strength, and a substantial decrease in concrete shrinkage for drying periods up to 365 days. Increasing the curing period from 7 to 14 days reduces concrete shrinkage. Thirty and 60% volume replacements of portland cement by slag cement result in reduced shrinkage when used with a porous LWA or normalweight aggregate. After 30 and 365 days of drying, all mixtures with LWA exhibited less shrinkage than the mixtures with either low- or high-absorption normalweight aggregates

Lightweight Aggregate as Internal Curing Agent to Limit Concrete Shrinkage

The effectiveness of prewetted, vacuum-saturated (PVS) lightweight aggregate (LWA) as an internal curing agent to reduce concrete shrinkage is evaluated for curing periods of 7 and 14 days. Normalweight aggregate is replaced by LWA at volume replacement levels ranging from 8.9 to 13.8%. Some mixtures contain a partial replacement of portland cement with slag cement while maintaining the paste content at approximately 24.1% of concrete volume. Comparisons are made with mixtures containing low-absorption granite and high absorption limestone normalweight coarse aggregates. At the replacement levels used in this study, PVS LWA results in a small reduction in concrete density, no appreciable effect on concrete compressive strength, and a substantial decrease in concrete shrinkage for drying periods up to 365 days. Increasing the curing period from 7 to 14 days reduces concrete shrinkage. Thirty and 60% volume replacements of portland cement by slag cement result in reduced shrinkage when used with a porous LWA or normalweight aggregate. After 30 and 365 days of drying, all mixtures with LWA exhibited less shrinkage than the mixtures with either low- or high-absorption normalweight aggregates

Use of Innovative Concrete Mixes for Improved Constructability and Sustainability of Bridge Decks, 2010-2013

Bridge deck crack surveys were performed on twelve bridges on US-59 south of Lawrence, KS to determine the effects of mixture proportions, concrete properties, deck type, and girder type on the crack density of reinforced concrete bridge decks. Of the twelve decks surveyed, eight are supported by prestressed concrete girders and four are supported by steel girders. Four of the decks supported by prestressed girders are cast on partial-depth precast deck panels, two are monolithic with synthetic fibers, and two have overlays. Of the four decks supported by steel girders, two have silica fume overlays (SFO) and two are monolithic. One of two decks with a silica fume overlay contains synthetic fibers in the overlay. Following the surveys, crack maps were plotted and analyzed and cracking trends were observed. The results for the US-59 bridge decks are compared with crack densities obtained in a study of low-cracking high-performance concrete (LC-HPC) bridge decks. The monolithic concrete bridge decks supported by prestressed concrete girders within this study exhibit less cracking than decks supported by steel girders. At an age of approximately three and a half years, the US-59 monolithic decks supported by prestressed girders with deck panels are not displaying significant cracking; most of the cracks are short transverse cracks aligned with the joints between the deck panels. The US-59 decks supported by prestressed girders with overlays exhibit significantly more cracking than the decks on prestressed girders without overlays. Bridge decks supported by steel girders without overlays have slightly higher crack densities than the decks with overlays. No benefits of using fibers in either the overlay or deck have been observed in this study, the sample size, however, is small. An increase in crack density was observed with an increase in average concrete slump for decks supported by both prestressed and steel girders. Decks with deck panels supported by prestressed girders exhibited an increased crack density with an increase in paste content

New evidence on housing wealth and consumption channels

This paper provides new evidence on the effect of housing wealth on consumption by focusing on the impact of home-equity extraction. We develop a household consumption decision model to illustrate the differential effect of home-equity extraction, relative to net home equity, on consumption. The home-equity extraction channel is also shown to vary with household-level borrowing constraints. Based on U.S. household survey data and an instrumental-variables approach, our empirical results validate model predictions. We find that the marginal propensity to consume is two times higher for the home-equity extraction channel relative to the conventional housing wealth effect. The consumption effect of home-equity extraction is more than 2.5 times greater for liquidity-constrained households than for unconstrained households. These results are even more pronounced in the case of durable goods consumption for constrained borrowers

Should UI Eligibility Be Expanded to Low-Earning Workers? Evidence on Employment, Transfer Receipt, and Income from Administrative Data

Recent efforts to expand unemployment insurance (UI) eligibility are expected to increase low-earning workers’ access to UI. Although the expansion’s aim is to smooth the income and consumption of previously ineligible workers, it is possible that UI benefits simply displace other sources of income. Standard economic models predict that UI delays reemployment, thereby reducing wage income. Additionally, low-earning workers are often eligible for benefits from means-tested programs, which may decrease with UI benefits. In this paper, we estimate the impact of UI eligibility on employment, means-tested program participation, and income after job loss using a unique individual-level administrative data set from the state of Michigan. To identify a causal effect, we implement a fuzzy regression discontinuity design around the minimum earnings threshold for UI eligibility. Our main finding is that while UI eligibility increases jobless durations by up to 25 percent and temporarily lowers receipt of cash assistance (TANF) by 63 percent, the net impact on total income is still positive and large. In the quarter immediately following job loss, UI-eligible workers have 46-61 percent higher incomes than ineligibles

Theory and Applications of Non-Relativistic and Relativistic Turbulent Reconnection

Realistic astrophysical environments are turbulent due to the extremely high Reynolds numbers. Therefore, the theories of reconnection intended for describing astrophysical reconnection should not ignore the effects of turbulence on magnetic reconnection. Turbulence is known to change the nature of many physical processes dramatically and in this review we claim that magnetic reconnection is not an exception. We stress that not only astrophysical turbulence is ubiquitous, but also magnetic reconnection itself induces turbulence. Thus turbulence must be accounted for in any realistic astrophysical reconnection setup. We argue that due to the similarities of MHD turbulence in relativistic and non-relativistic cases the theory of magnetic reconnection developed for the non-relativistic case can be extended to the relativistic case and we provide numerical simulations that support this conjecture. We also provide quantitative comparisons of the theoretical predictions and results of numerical experiments, including the situations when turbulent reconnection is self-driven, i.e. the turbulence in the system is generated by the reconnection process itself. We show how turbulent reconnection entails the violation of magnetic flux freezing, the conclusion that has really far reaching consequences for many realistically turbulent astrophysical environments. In addition, we consider observational testing of turbulent reconnection as well as numerous implications of the theory. The former includes the Sun and solar wind reconnection, while the latter include the process of reconnection diffusion induced by turbulent reconnection, the acceleration of energetic particles, bursts of turbulent reconnection related to black hole sources as well as gamma ray bursts. Finally, we explain why turbulent reconnection cannot be explained by turbulent resistivity or derived through the mean field approach.Comment: 66 pages, 24 figures, a chapter of the book "Magnetic Reconnection - Concepts and Applications", editors W. Gonzalez, E. N. Parke

Benefits and risks of antiretroviral therapy for perinatal HIV prevention.

CAPRISA, 2016.Abstract available in pdf