Carbon-Enhanced Hyper-metal-poor Stars and the Stellar IMF at Low Metallicity

The two known ``hyper-metal-poor'' (HMP) stars, HE0107-5240 and HE1327-2326, have extremely high enhancements of the light elements C, N, and O relative to Fe and appear to represent a statistically significant excess population relative to the halo metallicity distribution extrapolated from [Fe/H] > -3. This study weighs the available evidence for and against three hypothetical origins for these stars: (1) that they formed from gas enriched by a primordial ``faint supernova'', (2) that they formed from gas enriched by core-collapse supernovae and C-rich gas ejected in rotation-driven winds from massive stars, and (3) that they formed as the low-mass secondaries in binary systems at Z ~ 10^{-5.5} Zsun and acquired their light-element enhancements from an intermediate-mass companion as it passed through an AGB phase. The observations interpreted here, especially the depletion of lithium seen in HE1327-2326, favor the binary mass-transfer hypothesis. If HE0107-5240 and HE1327-2326 formed in binary systems, the statistically significant absence of isolated and/or C-normal stars at similar [Fe/H] implies that low-mass stars could form at that metallicity, but that masses M ~< 1.4 Msun were disfavored in the IMF. This result is also explained if the abundance-derived top-heavy IMF for primordial stars persists to [Fe/H] ~ -5.5. This finding indicates that low-mass star formation was possible at extremely low metallicity, and that the typical stellar mass may have had a complex dependence on metallicity rather than a sharp transition driven solely by gas cooling.Comment: 11 pages emulateapj text including three figures, accepted for publication in ApJ v666 (Sept 2007). A companion paper to 0706.290

Flap Endonuclease Disengages Dna2 Helicase/Nuclease from Okazaki Fragment Flaps

Okazaki fragments contain an initiator RNA/DNA primer that must be removed before the fragments are joined. In eukaryotes, the primer region is raised into a flap by the strand displacement activity of DNA polymerase {delta}. The Dna2 helicase/nuclease and then flap endonuclease 1 (FEN1) are proposed to act sequentially in flap removal. Dna2 and FEN1 both employ a tracking mechanism to enter the flap 5' end and move toward the base for cleavage. In the current model, Dna2 must enter first, but FEN1 makes the final cut at the flap base, raising the issue of how FEN1 passes the Dna2. To address this, nuclease-inactive Dna2 was incubated with a DNA flap substrate and found to bind with high affinity. FEN1 was then added, and surprisingly, there was little inhibition of FEN1 cleavage activity. FEN1 was later shown, by gel shift analysis, to remove the wild type Dna2 from the flap. RNA can be cleaved by FEN1 but not by Dna2. Pre-bound wild type Dna2 was shown to bind an RNA flap but not inhibit subsequent FEN1 cleavage. These results indicate that there is a novel interaction between the two proteins in which FEN1 disengages the Dna2 tracking mechanism. This interaction is consistent with the idea that the two proteins have evolved a special ability to cooperate in Okazaki fragment processing

A Minimal SU(5) SuperGUT in Pure Gravity Mediation

The lack of evidence for low-scale supersymmetry suggests that the scale of supersymmetry breaking may be higher than originally anticipated. However, there remain many motivations for supersymmetry including gauge coupling unification and a stable dark matter candidate. Models like pure gravity mediation (PGM) evade LHC searches while still providing a good dark matter candidate and gauge coupling unification. Here, we study the effects of PGM if the input boundary conditions for soft supersymmetry breaking masses are pushed beyond the unification scale and higher dimensional operators are included. The added running beyond the unification scale opens up the parameter space by relaxing the constraints on $\tan\beta$. If higher dimensional operators involving the SU(5) adjoint Higgs are included, the mass of the heavy gauge bosons of SU(5) can be suppressed leading to proton decay, $p\to \pi^0 e^+$, that is within reach of future experiments. Higher dimensional operators involving the supersymmetry breaking field can generate additional contributions to the A- and B-terms of order $m_{3/2}$. The threshold effects involving these A- and B-terms significantly impact the masses of the gauginos and can lead to a bino LSP. In some regions of parameter space the bino can be degenerate with the wino or gluino and give an acceptable dark matter relic density.Comment: 37 pages, 27 figure

The Value of Deregulating Over-The-Counter Options

Hedgers located far from organized commodity exchanges suffer the mismatch between their local prices and exchange prices. Futures and options traded on the exchange may still be valuable to distant hedgers but only to the extent that basis risk is small. Forward contracting allows hedgers to manage risk using a local delivery price, but the CFTC has long banned the sale off-exchange options, limiting the opportunities available to hedgers. Recently, Agricultural Trade Options (ATOs) have been introduced as over-the-counter option products designed specifically for hedgers. To date, ATOs have found little interest from potential sellers, but the potential demand for these options may be substantial. This paper describes and quantifies the demand for corn ATOs by dairy farms in Southeastern Pennsylvania and estimates the value these farms might place on options contracts offered locally.Marketing,

Autocracy, democracy, bureaucracy, or monopoly: can you judge a government by its size?

We develop a simple theoretical framework to examine on an integrated basis how the form of government affects its power and size. The analytical framework abstracts from distortions that arise from the means ofgovernment finance and separates government power into two dimensions-pure coercive power and pure monopoly power. A government can exert its coercive power to shift the demand for its services outward and/or its monopoly power to restrict the output along a given demand curve to earn rents. Among the implications drawn from the analysis are that government officials have an incentive to provide a non-optimal combination of taxes and services, and that neither size nor rents alone are reliable indicators of the extent to which government fails to achieve optimality in its provision of services.Finance ; Power resources

Dynamic removal of replication protein A by Dna2 facilitates primer cleavage during Okazaki fragment processing in Saccharomyces cerevisiae

Eukaryotic Okazaki fragments are initiated by an RNA/DNA primer, which is removed before the fragments are joined. Polymerase d displaces the primer into a flap for processing. Dna2 nuclease/helicase and flap endonuclease 1 (FEN1) are proposed to cleave the flap. The single-stranded DNA binding protein, replication protein A (RPA), governs cleavage activity. Flap-bound RPA inhibits FEN1. This necessitates cleavage by Dna2, which is stimulated by RPA. FEN1 then cuts the remaining RPA-free flap to create a nick for ligation. Cleavage by Dna2 requires that it enter the 5'-end and track down the flap. Since Dna2 cleaves the RPA-bound flap, we investigated the mechanism by which Dna2 accesses the protein-coated flap for cleavage. Using a nuclease-defective Dna2 mutant, we showed that just binding of Dna2 dissociates the flap-bound RPA. Facile dissociation is specific to substrates with a genuine flap, and will not occur with an RPA-coated single strand. We also compared the cleavage patterns of Dna2 with and without RPA to better define RPA stimulation of Dna2. Stimulation derived from removal of DNA folding in the flap. Apparently, coordinated with its dissociation, RPA relinquishes the flap to Dna2 for tracking in a way that does not allow flap structure to reform. We also found that RPA strand melting activity promotes excessive flap elongation, but it is suppressed by Dna2-promoted RPA dissociation. Overall, results indicate that Dna2 and RPA coordinate their functions for efficient flap cleavage and preparation for FEN1

Sulfur amino acid requirements of broilers from two to five weeks of age

Phase-feeding (PF) in broiler chickens has been researched as a way to reduce feed costs without reducing growth performance and yield. Predicted amino acid requirements for PF are generated using linear regression equations derived from best estimates of lysine (Lys), sulfur amino acid (SAA), and threonine (Thr) requirements. During the late starter and early grower periods, predicted requirements for the SAA methionine (Met) and cysteine (Cys) are higher than levels recommended by the National Research Council (NRC), and previous research suggests that SAA may be lowered during the grower period without sacrificing growth performance or yield. The objective of this study was to estimate Met and Cys requirements for broilers from 2 to 5 weeks of age. In Experiment 1, a Met-deficient corn-peanut meal diet was formulated to contain excess Cys, so that supplemental Met was not utilized for Cys synthesis. The basal diet for Experiment 2 met the Met requirement but was deficient in Cys. Graded levels of Met (0, 0.045, 0.09, 0.135, and 0.225%) and Cys (0, 0.035, 0.070, 0.105, 0.140, 0.175%) were added in Experiments 1 and 2, respectively, and diets were fed to five replicates of five broilers per pen. Broken-line analysis was used to estimate SAA requirements. The digestible Met and Cys requirements from 2 to 5 weeks of age were 0.33% and 0.31%, respectively. Requirement estimates were lower than those predicted by PF or recommended by NRC, indicating that lower SAA levels may be utilized in a PF progra