Modelagem de ocorrência e densidade de juvenis de Callinectes sapidus (Decapoda, Portunidae) em dois estuários do Rio Grande do Sul, com dados zero-inflacionados

Dados de contagem de juvenis de siri-azul (Callinectes sapidus Rathbun, 1896) coletados em dois estuários do Rio Grande do Sul são objeto do presente estudo. Por se encontrarem zero-inflacionados, esses dados motivaram a formulação de modelos hierárquicos, que quantificam o efeito das covariáveis categóricas mês e local sobre a probabilidade de ocorrência e densidade dessas populações, levando em conta a detecção imperfeita. Foram também desenvolvidos modelos não-hierárquicos para comparação. Uma abordagem Bayesiana foi adotada para a estimação dos parâmetros dos modelos por simulação Monte Carlo com Cadeias de Markov (MCMC). A comparação entre modelos foi feita com o Critério de Informação da Deviância (DIC). Os modelos hierárquicos apresentaram ajustes melhores que os modelos convencionais, mitigaram o problema do excesso de zeros e permitiram analisar simultaneamente as probabilidades de ocorrência e a densidade de juvenis de siri-azul. No estuário da Lagoa dos Patos, a probabilidade de ocorrência de juvenis na Classe 2 aumenta com a distância da desembocadura, enquanto em Tramandaí os pontos intermediários apresentam as maiores probabilidades. Em ambos os estuários a ocorrência é mais provável nos meses de verão e de inverno. A densidade de juvenis da Classe 2 apresenta marcada variação em relação aos meses do ano sendo, em geral, maior no estuário de Tramandaí.

Real rank zero algebras have the corona factorization property

The purpose of this short note is to prove that a stable separable C*-algebra with real rank zero has the so-called corona factorization property, that is, all the full multiplier projections are properly in finite. Enroute to our result, we consider conditions under which a real rank zero C*-algebra admits an injection of the compact operators (a question already considered in [21]).

Debt and deficit fluctuations and the structure of bond markets

We analyse the implications of optimal taxation for the stochastic behaviour of debt. We show that when a government pursues an optimal fiscal policy under complete markets, the value of debt has the same or less persistence than other variables in the economy and it declines in response to shocks that cause the deficit to increase. By contrast, under incomplete markets debt shows more persistence than other variables and it increases in response to shocks that cause a higher deficit. Data for US government debt reveals diametrically opposite results from those of complete markets and is much more supportive of bond market incompleteness.

What Belongs Where? Variable Selection for Zero-Inflated Count Models with an Application to the Demand for Health Care

This paper develops stochastic search variable selection (SSVS) for zero-inflated count models which are commonly used in health economics. This allows for either model averaging or model selection in situations with many potential regressors. The proposed techniques are applied to a data set from Germany considering the demand for health care. A package for the free statistical software environment R is provided.

Forecasting US bond default ratings allowing for previous and initial state dependence in an ordered probit model

In this paper we investigate the ability of a number of different ordered probit models to predict ratings based on firm-specific data on business and financial risks. We investigate models based on momentum, drift and ageing and compare them against alternatives that take into account the initial rating of the firm and its previous actual rating. Using data on US bond issuing firms rated by Fitch over the years 2000 to 2007 we compare the performance of these models in predicting the rating in-sample and out-of-sample using root mean squared errors, Diebold-Mariano tests of forecast performance and contingency tables. We conclude that initial and previous states have a substantial influence on rating prediction.

The determinants of sovereign bond yield spreads in the EMU

We use a panel of euro area countries to assess the determinants of long-term sovereign bond yield spreads over the period 1999.01-2010.12. We find that, unlike the period preceding the global financial crisis, European government bond yield spreads are wellexplained by macro- and fiscal fundamentals over the crisis period. We also find that the menu of macro and fiscal risks priced by markets has been significantly enriched since March 2009, including the risk of the crisis’ transmission among EMU member states, international risk and liquidity risk. Finally, we find that sovereign credit ratings are statistically significant in explaining spreads, yet compared to macro- and fiscal fundamentals their role is limited.

The response of the external finance premium in Asian corporate bond markets to financial characteristics, financial constraints and two financial crises

Empirical investigation of the external finance premium has been conducted on the margin between internal finance and bank borrowing or equities but little attention has been given to corporate bonds, especially for the emerging Asian market. In this paper, we hypothesize that balance sheet indicators of creditworthiness could affect the external finance premium for bonds as they do for premia in other markets. Using bond-specific and firm-specific data for China, Hong Kong, Indonesia, Korea, Philippines, Singapore and Thailand during 1995-2009 we find that firms with better financial health face lower external finance premia in all countries. When we introduce firm-level heterogeneity, we show that financial variables appear to be both statistically and quantitatively more important for financially constrained firms. Finally, when we examine the effects of the 1997-98 Asian crisis and the 2007-09 global financial crisis, we find that the sensitivity of the premium is greater for constrained firms during the Asian crisis compared to other times.

Co-Movement, Spillovers and Excess Returns in Global Bond Markets

This paper investigates global term structure dynamics using a Bayesian hierarchical factor model augmented with macroeconomic fundamentals. More than half of the variation in bond yields of seven advanced economies is due to global co-movement, which is mainly attributed to shocks to non-fundamentals. Global fundamentals, especially global inflation, affect yields through a ‘policy channel’ and a ‘risk compensation channel’, but the effects through two channels are offset. This evidence explains the unsatisfactory performance of fundamentals-driven term structure models. Our approach delineates asymmetric spillovers in global bond markets connected to diverging monetary policies. The proposed model is robust as identified factors has significant explanatory power of excess returns. The finding that global inflation uncertainty is useful in explaining realized excess returns does not rule out regime changing as a source of non-fundamental fluctuations.

Quantiles of the Realized Stock-Bond Correlation

Abstract: We scrutinize the realized stock-bond correlation based upon high frequency returns. We use quantile regressions to pin down the systematic variation of the extreme tails over their economic determinants. The correlation dependence behaves differently when the correlation is large negative and large positive. The important explanatory variables at the extreme low quantile are the short rate, the yield spread, and the volatility index. At the extreme high quantile the bond market liquidity is also important. The empirical fi…ndings are only partially robust to using less precise measures of the stock-bond correlation. The results are not caused by the recent …financial crisis. Keywords: Extreme returns; Financial crisis; Realized stock-bond correlation; Quantile regressions; VIX. JEL Classifi…cations: C22; G01; G11; G12

Smooth Transition Patterns in the Realized Stock- Bond Correlation

Abstract: We analyze the realized stock-bond correlation. Gradual transitions between negative and positive stock-bond correlation is accommodated by the smooth transition regression (STR) model. The changes in regime are de…ned by economic and …financial transition variables. Both in sample and out-of- sample results document that STR models with multiple transition variables outperform STR models with a single transition variable. The most important transition variables are the short rate, the yield spread, and the VIX volatility index. Keywords: realized correlation; smooth transition regressions; stock-bond correlation; VIX index JEL Classifi…cations: C22; G11; G12; G17

The nature of the Cr-C bond: direct estimation of aromaticity in Fischer carbenes

Report for the scientific sojourn at the the Philipps-Universität Marburg, Germany, from september to december 2007. For the first, we employed the Energy-Decomposition Analysis (EDA) to investigate aromaticity on Fischer carbenes as it is related through all the reaction mechanisms studied in my PhD thesis. This powerful tool, compared with other well-known aromaticity indices in the literature like NICS, is useful not only for quantitative results but also to measure the degree of conjugation or hyperconjugation in molecules. Our results showed for the annelated benzenoid systems studied here, that electron density is more concentrated on the outer rings than in the central one. The strain-induced bond localization plays a major role as a driven force to keep the more substituted ring as the less aromatic. The discussion presented in this work was contrasted at different levels of theory to calibrate the method and ensure the consistency of our results. We think these conclusions can also be extended to arene chemistry for explaining aromaticity and regioselectivity reactions found in those systems.In the second work, we have employed the Turbomole program package and density-functionals of the best performance in the state of art, to explore reaction mechanisms in the noble gas chemistry. Particularly, we were interested in compounds of the form H--Ng--Ng--F (where Ng (Noble Gas) = Ar, Kr and Xe) and we investigated the relative stability of these species. Our quantum chemical calculations predict that the dixenon compound HXeXeF has an activation barrier for decomposition of 11 kcal/mol which should be large enough to identify the molecule in a low-temperature matrix. The other noble gases present lower activation barriers and therefore are more labile and difficult to be observable systems experimentally.

Fase Zero de qualsevol projecte informàtic : l'acció comercial

El propòsit d'aquest TFC és presentar una metodologia lleugera per a aplicar en aquesta anomenada

A tale of two logits, compositional data analysis and zero observations

The application of compositional data analysis through log ratio trans-formations corresponds to a multinomial logit model for the shares themselves.This model is characterized by the property of Independence of Irrelevant Alter-natives (IIA). IIA states that the odds ratio in this case the ratio of shares is invariant to the addition or deletion of outcomes to the problem. It is exactlythis invariance of the ratio that underlies the commonly used zero replacementprocedure in compositional data analysis. In this paper we investigate using thenested logit model that does not embody IIA and an associated zero replacementprocedure and compare its performance with that of the more usual approach ofusing the multinomial logit model. Our comparisons exploit a data set that com-bines voting data by electoral division with corresponding census data for eachdivision for the 2001 Federal election in Australia

Electrochemically promoted carbon-halide bond cleavage in 4-nitrobenzyl halides

This manuscript reports the study of the carbon-halide bond cleavage in 4-nitrobenzyl halides, taking special attention to the iodide and fluoride derivatives. The electrochemical reduction mechanism has been disclosed for both compounds by terms of cyclic voltammetry and controlled potential electrolysis. In the case of 4-nitrobenzyl iodide, a first one electron irreversible wave leads to the corresponding 4-nitrobenzyl radical and iodide. However, in the case of 4-nitrobenzyl fluoride, a first one-electron reversible wave appears at –1.02 vs. SCE followed by one electron irreversible wave. In this second electron transfer process, the cleavage of the C-F bond is taking place, so the bond cleavage reaction occurs at the dianion level. To disclose and understand the electrochemical reduction mechanisms that allows to obtain important thermodynamic and kinetic data that would help in the understanding of C-X bond cleavage. This type of bond dissociation reactions are involved in the metabolism pathways of the human body.