Asymmetric synthesis of N-aryl aziridines

The reactions of a variety of N-arylhydroxamates as nitrogen transfer reagents to acryloyl derivatives of (−)-8-phenylmenthol, (−)-quinine and (−)-Oppolzer’s sultam acting as Michael acceptors was studied. Poor to modest diastereoselection was observed in the formation of aziridines. The absolute structure of one of the pure diastereomers secured from Oppolzer’s auxiliary was established by X-ray crystallography and hence the absolute configuration of the derived methyl-N-phenylaziridine-2-carboxylate could be assigned. Whilst only poor facial selectivity was observed for chiral hydroxamic acid prepared from dehydroabietic acid, moderate to good enantioselection of aziridines could be achieved with the chiral quaternary salts based on cinchona alkaloids, especially with that of cinchonine. A model is presented to explain the origin of enantioselection and a mechanism is proposed for the aziridination reaction.

Tailoring of structures and permeation properties of asymmetric nanocomposite cellulose acetatesilver membranes

Cellulose acetate (CA)-silver (Ag) nanocomposite asymmetric membranes were prepared via the wet-phase inversion method by dispersing polyvinylpirrolydone-protected Ag nanoparticles in the membrane casting solutions of different compositions. Silver nanoparticles were synthesized ex situ and added to the casting solution as a concentrated aqueous colloidal dispersion. The effects of the dispersion addition on the structure and on the selective permeation properties of the membranes were studied by comparing the nanocomposites with the silver-free materials. The casting solution composition played an important role in the adequate dispersion of the silver nanoparticles in the membrane. Incorporation of nanoscale silver and the final silver content resulted in structural changes leading to an increase in the hydraulic permeability and molecular weight cut-off of the nanocomposite membranes. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41796.

Influence of commercially available polyimide and formation conditions on the performance and structure of asymmetric polyimide organic solvent nanofiltration membranes

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para a obtenção do grau de Mestre em Engenharia Química e Bioquímica

Asymmetric taxation in a competition between nonprofit and for-profit firms

This paper considers a Cournot competition between a nonprofit firm and a for-profit firm in a homogeneous goods market, with uncertain demand. Given an asymmetric tax schedule, we compute explicitly the Bayesian-Nash equilibrium. Furthermore, we analize the effects of the tax rate and the degree of altruistic preference on market equilibrium outcomes.

Asymmetric dynamic price competition with uncertainty

We consider a dynamic setting-price duopoly model in which a dominant (leader) firm moves first and a subordinate (follower) firm moves second. We suppose that each firm has two different technologies, and uses one of them according to a certain probability distribution. The use of either one or the other technology affects the unitary production cost. We analyse the effect of the production costs uncertainty on the profits of the firms, for different values of the intercept demand parameters.

Asymmetric pulmonary edema after scorpion sting: a case report

A 12-year-old boy was referred with acute asymmetric pulmonary edema (APE) four-hour after scorpion sting to Emergency department. On admission, the main clinical manifestations were: dyspnea, tachypnea, and tachycardia. Chest x-ray revealed APE predominantly on the right hemithorax. The patient was treated with oxygen, intravenous frusemide and digoxin and discharged on the sixth hospital day in a good condition. This case report emphasizes the occurrence of asymmetric pulmonary edema after severe scorpion envenomation within few hours immediately after the sting.

Decline in prevalence and asymmetric distribution of human T cell lymphotropic virus 1 and 2 in blood donors, State of Minas Gerais, Brazil, 1993 to 2007

INTRODUCTION: Human T cell lymphotropic virus types 1 and 2 (HTLV-1/2) are endemic in Brazil and are screened for in transfusion services since 1993. This study evaluated the evolution of the prevalence of HTLV-1 and 2 in blood donors of the Hemominas Foundation from 1993 to 2007, and its geographical distribution in State of Minas Gerais, Brazil. METHODS: The Hemominas Foundation is a centralized blood center in Minas Gerais, Brazil. The sources of data were the Hemominas Foundation Technical Bulletin and files from the centralized serological laboratory. Donors were tested in the period using enzyme linked immuno sorbent assays (ELISA), followed by Western blot, when repeatedly reactive. The data were analyzed by EPIINFO 6.2 and TABWIN 3.5 softwares. RESULTS: The average seroprevalence in the period 1993-2007 was 0.1%. A steady decline occurred from 0.4% in 1993 to below 0.1% in 2002 and later, with a transient peak of 0.5% in 1994. HTLV reactivity distribution was asymmetrical in the state, with regions of higher prevalence, interspersed with low prevalence areas. Comparison of positive and negative donors verified that increasing age was proportional to virus positivity. Odds ratio for age ranged from 1.43 (30 to 39 years-old) to 3.09 (50 to 65 years-old). Women had a greater chance of being positive (OR-1.64), as previously described. CONCLUSIONS: Possible explanations for HTLV-1/2 prevalence decline are the exclusion of positive donors from the donor pool, an increase in repeat donors and ELISA test improvement, with reduction in the number of false positive results.

Asymmetric demand information in uniform and discriminatory call auctions: an experimental analysis motivated by electricity markets

We study the outcomes of experimental multi-unit uniform and discriminatory auctions with demand uncertainty. Our study is motivated by the ongoing debate about market design in the electricity industry. Our main aim is to compare the effect of asymmetric demand-information between sellers on the performance of the two auction institutions. In our baseline conditions all sellers have the same information, whereas in our treatment conditions some sellers have better information than others. In both information conditions we find that average transaction prices and price volatility are not significantly different under the two auction institutions. However, when there is asymmetric information among sellers the discriminatory auction is significantly less efficient. These results are not in line with the typical arguments made in favor of discriminatory pricing in electricity industries; namely, lower consumer prices and less price volatility. Moreover, our results provide some indication that discriminatory auctions reduce technical efficiency relative to uniform auctions.

General equilibrium with asymmetric information: a dual approach

We study markets where the characteristics or decisions of certain agents are relevant but not known to their trading partners. Assuming exclusive transactions, the environment is described as a continuum economy with indivisible commodities. We characterize incentive efficient allocations as solutions to linear programming problems and appeal to duality theory to demonstrate the generic existence of external effects in these markets. Because under certain conditions such effects may generate non-convexities, randomization emerges as a theoretic possibility. In characterizing market equilibria we show that, consistently with the personalized nature of transactions, prices are generally non-linear in the underlying consumption. On the other hand, external effects may have critical implications for market efficiency. With adverse selection, in fact, cross-subsidization across agents with different private information may be necessary for optimality, and so, the market need not even achieve an incentive efficient allocation. In contrast, for the case of a single commodity, we find that when informational asymmetries arise after the trading period (e.g. moral hazard; ex post hidden types) external effects are fully internalized at a market equilibrium.

Endogenous capacity utilization and the asymmetric effects of monetary policy

This paper investigates the role of variable capacity utilization as a source of asymmetries in the relationship between monetary policy and economic activity within a dynamic stochastic general equilibrium framework. The source of the asymmetry is directly linked to the bottlenecks and stock-outs that emerge from the existence of capacity constraints in the real side of the economy. Money has real effects due to the presence of rigidities in households' portfolio decisions in the form of a Luces-Fuerst 'limited participation' constraint. The model features variable capacity utilization rates across firms due to demand uncertainty. A monopolistic competitive structure provides additional effects through optimal mark-up changes. The overall message of this paper for monetary policy is that the same actions may have different effects depending on the capacity utilization rate of the economy.

Leadership and overcoming coordination failure with asymmetric costs

We study how the heterogeneity of agents affects the extent to which changes in financial incentives can pull a group out of a situation of coordination failure. We focus on the connections between cost asymmetries and leadership. Experimental subjects interact in groups of four in a series of weak-link games. The treatment variable is the distribution of high and low effort cost across subjects. We present data for one, two and three low-cost subjects as well as control sessions with symmetric costs. The overall pattern of coordination improvement is common across treatments. Early coordination improvements depend on the distribution of high and low effort costs across subjects, but these differences disappear with time. We find that initial leadership in overcoming coordination failure is not driven by low-cost subjects but by subjects with the most frequent cost. This conformity effect can be due to a kind of group identity or to the cognitive simplicity of acting with identical others.

Internship report: improving asymmetric term extraction from bilingual text

Estudi elaborat a partir d’una estada a Xerox Research Centre Europe a Grenoble, França,entre juny i desembre del 2006. El projecte tradueïx termes tècnics anglesos a noruec. És asimètric perquè no tenim recursos lingüístics per a la llengua noruega, però solament per a l'anglès. S’ha desenvolupat i posat en pràctica mètodes que comprovaven contigüitat ("local reordering" i permutació selectiva) per a millorar el funcionament d’una eina anterior. Contigüitat és quan una paraula es traduïx en paraules múltiples, aquestes paraules han de ser adjacents en l'oració. A més, s’ha construït una taula de les operacions de recerca per als termes tècnics i s’ha integrat aquesta taula en un programa de demostració.

Technical Appendix-3-Regime asymmetric STAR modeling and exchange rate reversion

The breakdown of the Bretton Woods system and the adoption of generalized oating exchange rates ushered in a new era of exchange rate volatility and uncer- tainty. This increased volatility lead economists to search for economic models able to describe observed exchange rate behavior. The present is a technical Appendix to Cerrato et al. (2009) and presents detailed simulations of the proposed methodology and additional empirical results.

Modeling Dependence Structure and Forecasting Market Risk with Dynamic Asymmetric Copula

We investigate the dynamic and asymmetric dependence structure between equity portfolios from the US and UK. We demonstrate the statistical significance of dynamic asymmetric copula models in modelling and forecasting market risk. First, we construct “high-minus-low" equity portfolios sorted on beta, coskewness, and cokurtosis. We find substantial evidence of dynamic and asymmetric dependence between characteristic-sorted portfolios. Second, we consider a dynamic asymmetric copula model by combining the generalized hyperbolic skewed t copula with the generalized autoregressive score (GAS) model to capture both the multivariate non-normality and the dynamic and asymmetric dependence between equity portfolios. We demonstrate its usefulness by evaluating the forecasting performance of Value-at-Risk and Expected Shortfall for the high-minus-low portfolios. From back-testing, e find consistent and robust evidence that our dynamic asymmetric copula model provides the most accurate forecasts, indicating the importance of incorporating the dynamic and asymmetric dependence structure in risk management.