Evaluating the Specification Errors of Asset Pricing Models

This paper examines the specification errors of several asset pricing models using the methodology of Hansen and Jagannathan (1997) and a common data set. The models are the CAPM, the Consumption CAPM, the Jagannathan and Wang (1996) conditional CAPM, the Campbell (1996) dynamic asset pricing model, the Cochrane (1996) production-based model, and the Fama-French (1993) three-factor and five-factor models. We use returns on the Fama-French twenty-five portfolios sorted by size and book-to-market ratio and the risk-free rate as our test assets. The sample is 1952 to 1997. We allow the parameters of the models' pricing kernels to fluctuate with the business cycle which we measure in two ways. One uses the Hodrick-Prescott (1997) filter applied to either industrial production for monthly models or real GNP for quarterly models. The second approach for quarterly models uses the consumption-wealth measure developed by Lettau and Ludvigson (1999). While we cannot reject correct pricing for Campbell's model, a stability test indicates that the parameters may not be stable. None of the models correctly prices returns that are scaled by the term premium.

Child Poverty Has Been Declining in Single-Mother Families, but the Gap Remains Large

Family structure (whether a child lives in a single parent or married family) is a strong predictor of childhood poverty. While childhood poverty has been on the decline, there is still a high rate of poverty among children in single-mother families, affecting the health of these children. This data slice describes the trends of childhood poverty among different family structures in the U.S

As Schools Close due to the Coronavirus, Mental Health Care for Children Must be Protected

This data slice highlights the expansive nation-wide school closings due to COVID-19 and encourages providers and government bodies to support the mental health needs of students across the country

Level search schemes for scalable information retrieval

Latent Semantic Indexing (LSI) has been demonstrated to outperform lexical matching in information retrieval. However, the enormous cost associated with the Singular Value Decomposition (SVD) of the large term-by-document matrix becomes a barrier for its application to scalable information retrieval. This thesis shows that information filtering using level search techniques can reduce the SVD computation cost for LSI. For each query, level search extracts a much smaller subset of the original term-by-document matrix with an average of 25% of the original non-zero entries. When LSI is applied to such subsets, the average precision only degrades by 5% due to level search filtering; however, for some document collections an increase in precision has been observed. Level search techniques are enhanced by a pruning scheme that deletes terms connected to only one document from the query-specific submatrix. An average 65% reduction in the number of non-zeros has been observed with a precision loss of 5% for most collections

Metal bioreduction by Shewanella alga in the presence of co-electron acceptors under non-growth and growth conditions

Anaerobic microbial reduction of soluble hexavalent uranium (U (VI)) has been reported for iron and sulfur reducing bacteria. A facultative anaerobic iron reducer, Shewanella alga is considered one of the most promising strains for uranium biotreatment because it is easy to grow and can effectively reduce U (VI). The purpose of this research is to further evaluate the potential of this organism in uranium waste biotreatment. The research goals include investigating possible growth of S. alga using U (VI) as the sole electron acceptor and exploring the impact of iron on uranium reduction under both non-growth and growth conditions. Metal reduction and microbial growth kinetics were also studied and the kinetic coefficients determined to predict the performance of S. alga for metal reduction. All batch tests were conducted in duplicate using 100 mL serum bottles. The seed S. alga culture was grown in an anaerobic medium containing ferric citrate as the electron acceptor. U (VI) and/or Fe (III) were introduced into test solutions as terminal electron acceptors. Each test solution contained 2.5 g/L of sodium bicarbonate (pH buffer) and 2mL/L of 60% w/w lactate syrup (equivalent to 20 mM lactate) as the electron donor. For growth coupled studies, a chemically defined medium which included nutrients essential for microbial growth was used. The initial Fe (III) and/or U (VI) concentrations used were ten times higher than those used in non-growth studies in order to support measurable cell mass. All experiments were conducted at constant pH (8.4) and temperature (35°C). The Monod model was used to quantify the kinetic data for Fe (III) and U (VI) reduction under non-growth conditions. Results show that the maximum specific reduction rate for Fe (III) was ~5.13 /hr, more than ten times higher than that for U (VI) ( ~0.39 /hr). The half-saturation constant for Fe (III) was ~36.8 mg/L, two times lower than that for U (VI) ( ~ 74.04 mg/L). This suggests that S. alga has a higher reduction capability and a higher enzymatic affinity for Fe (III) than U (VI) when lactate serves as the electron donor. When both metals were present in test solutions under non-growth conditions, S. alga preferentially reduced Fe (III). This was most likely because Fe (III) reduction does not require as low a redox potential as U (VI) and was therefore more thermodynamically favorable. Subsequent U (VI) reduction after significant Fe (ill) reduction appeared to be impeded by poising the electron potential caused by the [Fe (II)/Fe (III)] redox couple. At low initial Fe (III) concentrations, U (VI) reduction occurred slowly after Fe (III) reduction, suggesting a weak Eh buffering effect. At high initial Fe (III) concentrations, no U (VI) reduction was measured during the experimental duration. It\u27s believed that, high initial Fe (III) levels produced high [Fe (Il)/Fe (III)] ratios which result in strong Eh buffering. Such buffering may poison the system by keeping the Eh value higher than that required for U (VI) reduction. The presence of U (VI) had no impact on Fe (III) reduction kinetics. Tests also showed that Fe (II) initially added had a negative impact on U (VI) reduction. Growth of S. alga using U (VI) as the sole terminal electron acceptor was demonstrated under batch conditions. Unlike D. desulfuricans, S. alga grew in a minimum salt medium with lactate as the electron donor/carbon source and U (VI) as the electron acceptor. The rate of microbial growth was four times higher than that previously reported for another iron reducer, Geobacter metalireducens. The maximum specific growth rate was estimated to be 0.0215 /hr for U (VI) reduction, and 0.139 /hr for Fe (III) reduction. Growth-coupled reduction was more complicated because active microbial activities, such as oxidative phosphorylation and cellular synthesis/division, were involved (Bailey and Ollis, 1986). The individual reduction rate of either metal was slower when both metals were present in the medium compared to the rate when one of them was absent. The impact of one metal on the initial reduction rate of the other was both concentration dependent. A combination of initial concentrations of 10 mM Fe (III) and 5 mM U (VI) impeded 90% of the reduction of both metals. Unlike non-growth results, reduction of U (VI) occurred during iron reduction when coupled with microbial growth. In addition, the presence of U (VI) inhibited iron reduction. The reasons are believed associated with growth mechanisms. Similar to G. metalireducens and Shewanella putrefaciens, S. alga grew when U (VI) served as the sole electron acceptor when lactate was the electron donor. But unlike D. desulfuricans, which utilized two different enzyme systems for sulfate and uranium reduction, the reduction of U (VI) and Fe (III) by S. alga seemed to share the same active enzyme. Under non-growth conditions, the presence of Fe (III) delayed U (VI) reduction. The Fe (Il)/Fe (III) redox couple subsequently inhibited U (VI) reduction by keeping the electron potential of the medium higher than that required for the reaction to occur. While under growth conditions, the reduction of U (VI) and Fe (III) occurred simultaneously. However, reduction was slower and incomplete for each metal compared to that when one of them was absent. The significance of growth using U (VI) as the sole electron acceptor by S. alga is important. Combined with other advantages of this bacterium, such as the high tolerance to oxygen, the high uranium reduction rate, and no sulfide co-precipitation problems, a continuous flow treatment process using this organism appears promising for selective reduction of U (VI) at a high rate. Regarding results in the presence of both electron acceptors, predictions could be made on iron containing uranium wastewater treatment. A delay in uranium reduction is expected if S. alga cell suspensions are used. The duration of the delay is Fe (ill) concentration dependent. Above certain iron concentrations, the iron redox couple could possibly poise the system such that U (VI) reduction could never occur. However, U (VI) reduction will occur slowly, although incompletely, when cells are placed in a growth medium. It\u27s suggested that for a uranium waste containing high levels of sulfate and low levels of iron (less than 0.2 mM), S. alga, rather than D. desulfuricans should be utilized