Alternative Approaches to Incorporating the Opportunity Cost of Time in Recreation Demand Models

The importance of accounting for a respondent’s travel time in recreation demand models is well established. In practice, most analysts use a fixed fraction of the respondent’s wage rate to value travel time. However, other approaches have been suggested in the literature. In this paper revealed and stated preference data on Iowa wetland usage is used to explore various specifications of travel time. It is shown that the choice of a particular specification has a direct impact on welfare estimates as well as the consistency between revealed and stated preference data.

tRNA splicing

Introns interrupt the continuity of many eukaryal genes, and therefore their removal by splicing is a crucial step in gene expression. Interestingly, even within Eukarya there are at least four splicing mechanisms. mRNA splicing in the nucleus takes place in two phosphotransfer reactions on a complex and dynamic machine, the spliceosome. This reaction is related in mechanism to the two self-splicing mechanisms for Group 1 and Group 2 introns. In fact the Group 2 introns are spliced by an identical mechanism to mRNA splicing, although there is no general requirement for either proteins or co-factors. Thus it seems likely that the Group 2 and nuclear mRNA splicing reactions have diverged from a common ancestor. tRNA genes are also interrupted by introns, but here the splicing mechanism is quite different because it is catalyzed by three enzymes, all proteins and with an intrinsic requirement for ATP hydrolysis. tRNA splicing occurs in all three major lines of descent, the Bacteria, the Archaea, and the Eukarya. In bacteria the introns are self-splicing (1-3). Until recently it was thought that the mechanisms of tRNA splicing in Eukarya and Archaea were unrelated as well. In the past year, however, it has been found that the first enzyme in the tRNA splicing pathway, the tRNA endonuclease, has been conserved in evolution since the divergence of the Eukarya and the Archaea. Surprising insights have been obtained by comparison of the structures and mechanisms of tRNA endonuclease from these two divergent lines

Spectroscopy of Four Cataclysmic Variables with Periods above 7 Hours

We present spectroscopy of four cataclysmic variables. Using radial velocity measurements, we find orbital periods for the first time. The stars and their periods are GY Hya, 0.347230(9) d; SDSS J204448-045929, 1.68(1) d; V392 Hya, 0.324952(5) d; and RX J1951.7+3716, 0.492(1) d. We also detect the spectra of the secondary stars, estimate their spectral types, and derive distances based on surface brightness and Roche lobe constraints.Comment: 22 pages, 3 figures, 5 tables, to be published in December 2006 PAS

Kinetic Mixing and the Supersymmetric Gauge Hierarchy

The most general Lagrangian for a model with two U(1) gauge symmetries contains a renormalizable operator which mixes their gauge kinetic terms. Such kinetic mixing can be generated at arbitrarily high scales but will not be suppressed by large masses. In models whose supersymmetry (SUSY)-breaking hidden sectors contain U(1) gauge factors, we show that such terms will generically arise and communicate SUSY-breaking to the visible sector through mixing with hypercharge. In the context of the usual supergravity- or gauge-mediated communication scenarios with D-terms of order the fundamental scale of SUSY-breaking, this effect can destabilize the gauge hierarchy. Even in models for which kinetic mixing is suppressed or the D-terms are arranged to be small, this effect is a potentially large correction to the soft scalar masses and therefore introduces a new measurable low-energy parameter. We calculate the size of kinetic mixing both in field theory and in string theory, and argue that appreciable kinetic mixing is a generic feature of string models. We conclude that the possibility of kinetic mixing effects cannot be ignored in model-building and in phenomenological studies of the low-energy SUSY spectra.Comment: 16 pages, LaTeX, 1 figure. Revised to match published versio

Testing for the Internal Consistency of Choice Experiments Using Explicit Rankings of Quality Attributes

Choice experiments (CEs) are an increasingly important tool in the environmental valuation literature because of their ability to deal with multifaceted environmental issues and their basis in random utility theory. One particularly useful aspect of the CE method is that it allows researchers to estimate marginal rates of substitution between an environmental resource’s various attributes. These marginal rates of substitution provide an implicit ranking of the attributes, which can be compared with other ranking mechanisms. In this paper we describe a method for testing for the internal consistency of choice experiments by comparing the implicit attribute ranking generated by a CE with that generated by an explicit attribute-ranking exercise. The analysis uses data gathered through a unique survey in which respondents completed both a CE exercise and an attribute-ranking exercise indicating their preferences over pollution abatement and water quality improvement strategies for a freshwater lake in north-central Iowa. Comparisons are made on a sample-wide basis as well as an individual basis.Environmental valuation, choice experiments, internal consistency

Exploring Respondent’s Perception of Bid Precision in Non-Market Valuation

Bid design is an important component of the nonmarket valuation process. To date, no research has been done on the possible effects of using round dollar amounts. It seems reasonable to believe that respondents may respond to round dollar amounts differently than they would respond to bids that include both dollar and cent amounts. One possibility is that the respondent may infer that the dollar/cent bids are more precise estimates of the true cost than the round dollar amount, and therefore put more thought into their response to survey questions. In order to explore this idea, we test whether the use of a precise versus imprecise bid design influences respondent’s willingness to pay. In particular, our sample of survey recipients was stratified into two groups based on whether they were presented with imprecise or precise bids (round dollar bids or dollar/cent bids). Precise bids were generated by adding or subtracting a randomly-drawn number of cents (between -200 and +200 cents) to each of the imprecise bid levels. We explore this issue in the context of a valuation project concerned with The Battle of Lexington State Historic Site in Lexington, MO.

Prediction, Retrodiction, and The Amount of Information Stored in the Present

We introduce an ambidextrous view of stochastic dynamical systems, comparing their forward-time and reverse-time representations and then integrating them into a single time-symmetric representation. The perspective is useful theoretically, computationally, and conceptually. Mathematically, we prove that the excess entropy--a familiar measure of organization in complex systems--is the mutual information not only between the past and future, but also between the predictive and retrodictive causal states. Practically, we exploit the connection between prediction and retrodiction to directly calculate the excess entropy. Conceptually, these lead one to discover new system invariants for stochastic dynamical systems: crypticity (information accessibility) and causal irreversibility. Ultimately, we introduce a time-symmetric representation that unifies all these quantities, compressing the two directional representations into one. The resulting compression offers a new conception of the amount of information stored in the present.Comment: 17 pages, 7 figures, 1 table; http://users.cse.ucdavis.edu/~cmg/compmech/pubs/pratisp.ht