The combinatorial structure of beta negative binomial processes

We characterize the combinatorial structure of conditionally-i.i.d. sequences of negative binomial processes with a common beta process base measure. In Bayesian nonparametric applications, such processes have served as models for latent multisets of features underlying data. Analogously, random subsets arise from conditionally-i.i.d. sequences of Bernoulli processes with a common beta process base measure, in which case the combinatorial structure is described by the Indian buffet process. Our results give a count analogue of the Indian buffet process, which we call a negative binomial Indian buffet process. As an intermediate step toward this goal, we provide a construction for the beta negative binomial process that avoids a representation of the underlying beta process base measure. We describe the key Markov kernels needed to use a NB-IBP representation in a Markov Chain Monte Carlo algorithm targeting a posterior distribution.Comment: Published at http://dx.doi.org/10.3150/15-BEJ729 in the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm

Three New Empirical Tests of the Pollution Haven Hypothesis When Environmental Regulation is Endogenous

The validity of existing empirical tests of the Pollution Haven Hypothesis (PHH) is constantly under scrutiny due to two shortcomings. First, the issues of unobserved heterogeneity and measurement error in environmental regulation are typically ignored due to the lack of a credible, traditional instrumental variable. Second, while the recent literature has emphasized the importance of geographic spillovers in determining the location choice of foreign investment, such spatial eects have yet to be adequately incorporated into empirical tests of the PHH. As a result, the impact of environmental regulations on trade patterns and the location decisions of multinational enterprises remains unclear. In this paper, we circumvent the lack of a traditional instrument within a model incorporating geographic spillovers utilizing three novel identication strategies. Using state-level panel data on inbound U.S. FDI, relative abatement costs, and other determinants of FDI, we consistently nd (i) evidence of environmental regulation being endogenous, (ii) a negative impact of own environmental regulation on inbound FDI in pollution-intensive sectors, particularly when measured by employment, and (iii) larger eects of environmental regulation once endogeneity is addressed. Neighboring environmental regulation is not found to be an important determinant of FDI. Key Words: Foreign Direct Investment, Environmental Regulation, Spillovers, Instrumental Variables, Control Function, Heteroskedasticity

Denitrification by rhizobia: A possible factor contributing to nitrogen losses from soils

The intensive pastoral farming system on which New Zealand animal production is based is almost completely dependent upon the rhizobium-legurne symbiosis for the fixed nitrogen required for pasture production. The average annual fixation has been measured as 184 kg nitrogen/ha in developed lowland pastures Hoglund et cii., 1979 and about 13 kg nitrogen/ha in poorly developed bill country pastures (Grant and Lambert, 1979). From these figures it can be estimated that rhizobia in New Zealand pastures fix in excess of one million tonnes of nitrogen an nually. The current annual application of fertilizer nitrogen to pastures is about 12 500 tonnes (O'Connor, 1979)

A small evaluation suite for Ada compilers

After completing a small Ada pilot project (OCC simulator) for the Multi Satellite Operations Control Center (MSOCC) at Goddard last year, the use of Ada to develop OCCs was recommended. To help MSOCC transition toward Ada, a suite of about 100 evaluation programs was developed which can be used to assess Ada compilers. These programs compare the overall quality of the compilation system, compare the relative efficiencies of the compilers and the environments in which they work, and compare the size and execution speed of generated machine code. Another goal of the benchmark software was to provide MSOCC system developers with rough timing estimates for the purpose of predicting performance of future systems written in Ada

Astroenzymology – the environmental limits of enzyme activity

Using organisms from extreme terrestrial environments as models for extraterrestrial life may lead us to underestimate the range of environments that life may inhabit. An alternative approach is to inspect the range of conditions over which crucial biomolecules might function. Recent investigations of enzyme activity suggest that they have the potential to function over a wider range of environmental conditions than expected. Although the upper temperature limit for enzyme stability is unclear, some enzymes are active up to 130°C. The evidence is that the instability of enzymes is a functional requirement, rather then because of any restraint on achieving higher stability. There is no evidence that enzyme activity ceases at low temperatures; it declines in a predictable manner to the lowest temperature at which it has been possible to make measurements, -100°C. It has been generally accepted that dehydration stops enzyme activity but this acceptance may have arisen partly from the technical difficulty of assessing enzyme activity without a fluid medium for diffusion. Experiments using anhydrous organic solvents or gas phase substrates suggest activity occurs in enzymes at very low hydration

Merger Simulation: A Simplified Approach with New Applications

Merger simulation is growing in importance as a tool to evaluate the unilateral competitive effects of mergers. This paper offers a relatively non-technical description of the principles of merger simulation. In addition, it introduces PCAIDS, a new and highly flexible "calibrated-demand" merger simulation methodology that is based on a simplified version of AIDS. PCAIDS can be implemented using market shares and two price elasticities; scanner or transaction-level data are not required. The paper offers some applications of merger simulation with PCAIDS that include comparisons with other simulation models. It also shows how PCAIDS can be applied to the analysis of efficiencies, divestiture, and product repositioning/entry. Finally, the paper offers an analysis of the Merger Guidelines safeharbors. A detailed mathematical appendix is included.