Increasing United States Investment in Foreign Securities: An Evaluation of SEC Rule 144A

The dimension of a poset $P$ is the minimum number of total orders whose intersection is $P$. We prove that the dimension of every poset whose comparability graph has maximum degree $\Delta$ is at most $\Delta \log ^{1+o(1)} \Delta$. This result improves on a 30-year old bound of Füredi and Kahn and is within a $\log ^{o(1)}\Delta$ factor of optimal. We prove this result via the notion of boxicity. The boxicity of a graph $G$ is the minimum integer $d$ such that $G$ is the intersection graph of $d$-dimensional axis-aligned boxes. We prove that every graph with maximum degree $\Delta$ has boxicity at most $\Delta \log ^{1+o(1)} \Delta$, which is also within a $\log ^{o(1)}\Delta$ factor of optimal. We also show that the maximum boxicity of graphs with Euler genus $g$ is $\Theta (\sqrt {g \log g})$, which solves an open problem of Esperet and Joret and is tight up to a constant factor

Characterization of Freshwater Natural Dissolved Organic Matter (DOM): Mechanistic Explanations for Protective Effects Against Metaltoxicity and Direct Effects on Organisms

Dissolved organic matter (DOM) exerts direct and indirect influences on aquatic organisms. In order to better understand how DOM causes these effects, potentiometric titration was carried out for a wide range of autochthonous and terrigenous freshwater DOM isolates. The isolates were previously characterized by absorbance and fluorescence spectroscopy. Proton binding constants (pKa) were grouped into three classes:acidic (pKa ≤ 5), intermediate (5 \u3c pKa ≤ 8.5) and basic (pKa \u3e 8.5). Generally, the proton site densities (LT) showed maximum peaks at the acidic and basic ends around pKa values of 3.5 and 10, respectively. More variably positioned peaks occurred in the intermediate pKa range. The acid–base titrations revealed the dominance of carboxylic and phenolic ligands with a trend for more autochthonous sources to have higher total LT. A summary parameter, referred to as the Proton Binding Index (PBI), was introduced to summarize chemical reactivity of DOMs based on the data of pKa and LT. Then, the already published spectroscopic data were explored and the specific absorbance coefficient at 340 nm (i.e. SAC340), an index of DOM aromaticity,was found to exhibit a strong correlation with PBI. Thus, the tendencies observed in the literature that darker organic matter is more protective against metal toxicity and more effective in altering physiological processes in aquatic organisms can now be rationalized on a basis of chemical reactivity to protons

The Influence of Dissolved Organic Matter (DOM) on Sodium Regulation and Nitrogenous Waste Excretion in the Zebrafish (Danio rerio)

Dissolved organic matter (DOM) is both ubiquitous and diverse in composition in natural waters, but its effects on the branchial physiology of aquatic organisms have received little attention relative to other variables (e.g. pH, hardness, salinity, alkalinity). Here, we investigated the effects of four chemically distinct DOM isolates (three natural, one commercial, ranging from autochthonous to highly allochthonous, all at ∼6 mg C l−1) on the physiology of gill ionoregulation and nitrogenous waste excretion in zebrafish acclimated to either circumneutral (7.0–8.0) or acidic pH (5.0). Overall, lower pH tended to increase net branchial ammonia excretion, net K+ loss and [3H]PEG-4000 clearance rates (indicators of transcellular and paracellular permeability, respectively). However, unidirectional Na+ efflux, urea excretion and drinking rates were unaffected. DOM sources tended to stimulate unidirectional Na+ influx rate and exerted subtle effects on the concentration-dependent kinetics of Na+ uptake, increasing maximum transport capacity. All DOM sources reduced passive Na+ efflux rates regardless of pH, but exerted negligible effects on nitrogenous waste excretion, drinking rate, net K+ loss or [3H]PEG4000 clearance, so the mechanism of Na+ loss reduction remains unclear. Overall, these actions appear beneficial to ionoregulatory homeostasis in zebrafish, and some may be related to physicochemical properties of the DOM sources. They are very different from those seen in a recent parallel study on Daphnia magna using the same DOM isolates, indicating that DOM actions may be both species and DOM specific

Forming the Dusty Ring in HR 4796A

We describe planetesimal accretion calculations for the dusty ring observed in the nearby A0 star HR 4796A. Models with initial masses of 10-20 times the minimum mass solar nebula produce a ring of width 7-15 AU and height 0.3-0.6 AU at 70 AU in roughly 10 Myr. The ring has a radial optical depth of 1. These results agree with limits derived from infrared images and from the excess infrared luminosity.Comment: 6 pages, including 2 figures and 1 table; ApJ Letters, in pres

Experimental determination of the hydrothermal solubility of ReS(2 )and the Re–ReO(2 )buffer assemblage and transport of rhenium under supercritical conditions

To understand the aqueous species important for transport of rhenium under supercritical conditions, we conducted a series of solubility experiments on the Re–ReO(2 )buffer assemblage and ReS(2). In these experiments, pH was buffered by the K–feldspar–muscovite–quartz assemblage; [Image: see text] in sulfur-free systems was buffered by the Re–ReO(2 )assemblage; and [Image: see text] and [Image: see text] in sulfur-containing systems were buffered by the magnetite–pyrite–pyrrhotite assemblage. Our experimental studies indicate that the species ReCl(4)(0 )is dominant at 400°C in slightly acidic to near-neutral, and chloride-rich (total chloride concentrations ranging from 0.5 to 1.0 M) environments, and ReCl(3)(+ )may predominate at 500°C in a solution with total chloride concentrations ranging from 0.5 to 1.5 M. The results also demonstrate that the solubility of ReS(2 )is about two orders of magnitude less than that of ReO(2). This finding not only suggests that ReS(2 )(or a ReS(2 )component in molybdenite) is the solubility-controlling phase in sulfur-containing, reducing environments but also implies that a mixing process involving an oxidized, rhenium-containing solution and a solution with reduced sulfur is one of the most effective mechanisms for deposition of rhenium. In analogy with Re, TcS(2 )may be the stable Tc-bearing phase in deep geological repositories of radioactive wastes

The Effect of Organic Ligands on the Sorption of Neodymium, Gadolinium and Uranium onto Nontronite and Goethite

The sorption of the rare earth elements (REE) Nd(III) and Gd(III) onto goethite in the presence of Suwannee River fulvic acid in 0.1 m NaCl solutions at 25 ºC was investigated quantitatively. The experiments involved batch titrations whereby the concentrations of REE and/or fulvic acid remaining in solution were determined as a function of pH. In the absence of fulvic acid, removal of REE from solution is enhanced in the presence of goethite over the pH range from 6 to 8, compared to the unary system (REE only) in which precipitation of an amorphous hydroxide occurred at pH greater than or equal to 8. In the absence of REE, removal of fulvic acid from solution is enhanced in the presence of goethite in the pH range from 2 to 8 at least 9, compared to a unary (fulvic acid only) system. The presence of fulvic acid at concentrations from 10 to 50 ppm enhanced REE sorption onto goethite slightly at pH less than 7, but had no discernable effect at higher pH values. Fulvic acid at a concentration of 100 ppm exhibited a greater enhancement of REE sorption at pH 7. Experiments investigating the effect of sorption of REE onto goethite by citrate were also performed. However, these studies were not completed owing to experimental difficulties. The results obtained in this study represent an important contribution to the ultimate goal of predicting the mobility of trivalent REE (and analogous trivalent actinides) in the presence of natural organic matter and goethite

Characterization of Freshwater Natural Dissolved Organic Matter (DOM): Mechanistic Explanations for Protective Effects Against Metaltoxicity and Direct Effects on Organisms

Dissolved organic matter (DOM) exerts direct and indirect influences on aquatic organisms. In order to better understand how DOM causes these effects, potentiometric titration was carried out for a wide range of autochthonous and terrigenous freshwater DOM isolates. The isolates were previously characterized by absorbance and fluorescence spectroscopy. Proton binding constants (pKa) were grouped into three classes:acidic (pKa ≤ 5), intermediate (5 \u3c pKa ≤ 8.5) and basic (pKa \u3e 8.5). Generally, the proton site densities (LT) showed maximum peaks at the acidic and basic ends around pKa values of 3.5 and 10, respectively. More variably positioned peaks occurred in the intermediate pKa range. The acid–base titrations revealed the dominance of carboxylic and phenolic ligands with a trend for more autochthonous sources to have higher total LT. A summary parameter, referred to as the Proton Binding Index (PBI), was introduced to summarize chemical reactivity of DOMs based on the data of pKa and LT. Then, the already published spectroscopic data were explored and the specific absorbance coefficient at 340 nm (i.e. SAC340), an index of DOM aromaticity,was found to exhibit a strong correlation with PBI. Thus, the tendencies observed in the literature that darker organic matter is more protective against metal toxicity and more effective in altering physiological processes in aquatic organisms can now be rationalized on a basis of chemical reactivity to protons

The Influence of Dissolved Organic Matter (DOM) on Sodium Regulation and Nitrogenous Waste Excretion in the Zebrafish (Danio rerio)

Dissolved organic matter (DOM) is both ubiquitous and diverse in composition in natural waters, but its effects on the branchial physiology of aquatic organisms have received little attention relative to other variables (e.g. pH, hardness, salinity, alkalinity). Here, we investigated the effects of four chemically distinct DOM isolates (three natural, one commercial, ranging from autochthonous to highly allochthonous, all at ∼6 mg C l−1) on the physiology of gill ionoregulation and nitrogenous waste excretion in zebrafish acclimated to either circumneutral (7.0–8.0) or acidic pH (5.0). Overall, lower pH tended to increase net branchial ammonia excretion, net K+ loss and [3H]PEG-4000 clearance rates (indicators of transcellular and paracellular permeability, respectively). However, unidirectional Na+ efflux, urea excretion and drinking rates were unaffected. DOM sources tended to stimulate unidirectional Na+ influx rate and exerted subtle effects on the concentration-dependent kinetics of Na+ uptake, increasing maximum transport capacity. All DOM sources reduced passive Na+ efflux rates regardless of pH, but exerted negligible effects on nitrogenous waste excretion, drinking rate, net K+ loss or [3H]PEG4000 clearance, so the mechanism of Na+ loss reduction remains unclear. Overall, these actions appear beneficial to ionoregulatory homeostasis in zebrafish, and some may be related to physicochemical properties of the DOM sources. They are very different from those seen in a recent parallel study on Daphnia magna using the same DOM isolates, indicating that DOM actions may be both species and DOM specific

The Effects of Different Types of Internal Controls on Self-Control

One reason companies implement internal controls is to reduce the likelihood of unethical behavior. Yet, ego depletion theory suggests that some controls may cause reductions in employees’ self-control, which could undermine the ability of controls to reduce unethical behavior. We examine whether various types of controls impact self-control and ethical judgments. Our results show that contrary to the ego depletion hypothesis, we find no significant relation between self-control and internal controls. Furthermore, we find that controls have no effect on ethical judgments or ethical ideology. Thus, our results suggest that internal controls do not differentially impact self-control and ethical decision-making