Testing for unobserved heterogeneity in exponential and Weibull duration models

We examine the use of the likelihood ratio (LR) statistic to test for unobserved heterogeneity in duration models, based on mixtures of exponential or Weibull distributions. We consider both the uncensored and censored duration cases. The asymptotic null distribution of the LR test statistic is not the standard chi-square, as the standard regularity conditions do not hold. Instead, there is a nuisance parameter identified only under the alternative, and a null parameter value on the boundary of the parameter space, as in Cho and White (2007a). We accommodate these and provide methods delivering consistent asymptotic critical values. We conduct a number of Monte Carlo simulations, comparing the level and power of the LR test statistic to an information matrix (IM) test due to Chesher (1984) and Lagrange multiplier (LM) tests of Kiefer (1985) and Sharma (1987). Our simulations show that the LR test statistic generally outperforms the IM and LM tests. We also revisit the work of van den Berg and Ridder (1998) on unemployment durations and of Ghysels et al. (2004) on interarrival times between stock trades, and, as it turns out, affirm their original informal inferences.     

A Ricardian Analysis of the Distribution of Climate Change Impacts on Agriculture across Agro-Ecological Zones in Africa

This paper examines the distribution of climate change impacts across the sixteen Agro-Ecological Zones (AEZs) of Africa. We combine net revenue from livestock and crops and regress total net revenue on a set of climate, soil, and socio-economic variables with and without country fixed effects. Although African crop net revenue is very sensitive to climate change, combined livestock and crop net revenue is more climate resilient. With the hot and dry CCC climate scenario, average damage estimates reach 27% by 2100, but with the mild and wet PCM scenario, African farmers will benefit. The analysis of AEZs implies that the effects of climate change will be quite different across Africa. For example, currently productive areas such as dry/moist savannah are more vulnerable to climate change while currently less productive agricultural zones such as humid forest or sub-humid AEZs become more productive in the future. S. Niggol Seo is the Consultant to the World Bank.     

Consistent Planning Under Uncertain Lifetime

This paper considers the problem of intertemporal planning when changing tastes result in inconsistent plans. This problem has been considered in the literature under the assumption of a lifetime certainty. Some of the solutions proposed in the literature exhibit certain undesirable properties such as incoherence and lack of Pareto-optimality. This paper proposes a procedure for solving the intertemporal dilemma when lifetime is uncertain. The proposed solution is coherent and Pareto-optimal, and is, in fact, valid for the case of certain as well as uncertain lifetime. [020]     

Testing for two-regime threshold cointegration in vector error-correction models

This paper examines a two-regime vector error-correction model with a single cointegrating vector and a threshold effect in the error-correction term. We propose a relatively simple algorithm to obtain maximum likelihood estimation of the complete threshold cointegration model for the bivariate case. We propose a SupLM test for the presence of a threshold. We derive the null asymptotic distribution, show how to simulate asymptotic critical values, and present a bootstrap approximation. We investigate the performance of the test using Monte Carlo simulation, and find that the test works quite well. Applying our methods to the term structure model of interest rates, we find strong evidence for a threshold effect.     

Maximal surplus from the pivotal mechanism: a closed form solution

The paper derives a closed form solution for the maximal surplus generated by the pivotal mechanism in the case of a binary public good. The formula may be used to compare the pivotal mechanism to other mechanisms. An illustration is provided to demonstrate how such a comparison may be made. Received: 30 April 1997 / Accepted: 16 June 1998     

Treatment of non-biodegradable cutting oil wastewater by ultrasonication-Fenton oxidation process.

To treat cutting oil wastewater produced in metal surface treatment industry, Ultrasonication (US)-Fenton process, which is one of the advanced oxidation processes, was used. The optimum conditions to treat non-biodegradable pollutants using the US-Fenton process were that the application rates of H2O2 and FeSO4 were 10% and 3 g/L, respectively, the value of pH was 3, and the ultrasonication time was 30 min. It identified non-degradable pollutants such as ethylene diamine tetraacetic acid (EDTA) and Triethanolamine (TEA) in the cutting oil wastewater. TLC analysis of two compounds of treated water by the coagulation process was similar to that of raw water. However, TLC analysis of two compounds of US-Fenton process was different from that of raw water, meaning that US-Fenton process decomposed the EDTA and TEA. To study the possibility of application with the US-Fenton process to pilot plant, the pollutants treatment efficiency of three different methods, such as US-Fenton process, activated sludge process and coagulation process, in continuous experiments were compared. The removal rate of pollutants by the US-Fenton process according to the effluent time was higher than any other processes. The removal rates of COD, SS, T-N and T-P by US-Fenton process were 98, 93, 75 and 95%, respectively.     

Characterisation of heavy metal tolerance and biosorption capacity of bacterium strain CPB4 (Bacillus spp.).

A heavy metal resistant bacterium Bacillus spp. strain CPB4 was isolated from heavy metal contaminated soil in Korea and further characterised. The CPB4 strain showed a high capacity for uptake of heavy metal Pb (Pb > Cd > Cu > Ni > Co > Mn > Cr > Zn) both in single and in mixed heavy metal solution. Optimal conditions for heavy metal uptakes of CPB4 strain were 20-40 degrees C culture temperature, 5-7 pH and 24 h pre-culture times. TEM showed that large amounts of the electron-dense granules (heavy metal complexes) were found mainly on the cell wall and cell membrane. Furthermore, more than 90% of adsorbed heavy metals were distributed both in cell wall and in cell membrane fractions. The amount of heavy metal uptake was remarkably decreased by reducing the crude protein contents when cells were treated by alkali solutions. Therefore, this study showed one of the possible examples for useful bioremediation.     

River Stage Forecasting Using Wavelet Packet Decomposition and Machine Learning Models

Water Resources Management - This study develops and applies three hybrid models, including wavelet packet-artificial neural network (WPANN), wavelet packet-adaptive neuro-fuzzy inference system...     

Effective Luxury-Brand Advertising: The ES–IF Matching (Entity–Symbolic Versus Incremental–Functional) Model

This study draws on the psychological tenets of implicit self-theories, which differentiate between individuals with entity versus incremental orientations, to deepen our understanding about how consumers evaluate luxury-brand advertising appeals. Our findings show that entity theorist consumers are more attracted to the symbolic value appeals of luxury brands, whereas incremental theorists are more attracted to functional value appeals. Furthermore, we show how consumers' implicit self-theories can be purposively primed by managers with the textual elements of a luxury-brand advertising message to increase its effectiveness, which provides useful implications for designing and executing effective luxury advertising.