A model for J/ψJ/\psi - kaon cross section

We calculate the cross section for the dissociation of $J/\psi$ by kaons within the framework of a meson exchange model. We find that, depending on the values of the coupling constants used, the cross section can vary from 5 mb to 30 mb at $\sqrt{s}\sim5$ GeV.Comment: 4 pages, 3 eps figure

Dynamic analysis of the train-bridge interaction: an accurate and efficient numerical method

The dynamic behavior of railway bridges carrying high-speed trains can be analyzed with or without the consideration of the vehicle's own structure. However, due to the amount of kinetic energy carried at high speeds, the train may interact significantly with the bridge, especially when resonance occurs. Equally important is the riding comfort and the stability of the track and train cars, which are usually the most critical limit states in the design of this type of structures. With the aim of studying this problem a computer code was developed, being the interaction between the bridge and the train implemented by means of contact conditions between each train wheel (nodal point) and the structure (point inside a finite element). The treatment of the interaction between a train wheel and a point on the surface of a finite element is directly and efficiently implemented by means of an extended stiffness matrix, which includes stiffness, flexibility and additional terms that stem from the compatibility equations between the displacements of the vehicle and the bridge. This methodology was applied to the study of the dynamic behavior of a bowstring arch bridge and proved to be very accurate and efficien

Development of an efficient finite element model for the dynamic analysis of the train-bridge interaction

The design of high-speed railway bridges comprises a set of demands, from safety and serviceability aspects, to new types of equipment and construction solutions. In order to perform an accurate and realistic evaluation of the corresponding dynamic behavior, adequate analysis tools that take into account the complexity of the train-bridge system are required. These computational tools must be based on efficient algorithms to allow for the completion of detailed dynamic analyses in a reasonable amount of time. The classical methods of analysis may be unsatisfactory in the evaluation of the dynamic effects of the train-bridge system and fully assessment of the structural safety, track safety and passenger comfort. A direct and versatile technique for the simulation of the train-bridge interaction was implemented in the FEMIX code, which is a general purpose finite element computer program. The presented case study is an application of the proposed formulation, which proved to be very accurate and efficient

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.

A nonlinear vehicle-structure interaction methodology with wheel-rail detachment and reattachment

. A vehicle-structure interaction methodology with a nonlinear contact formulation based on contact and target elements has been developed. To solve the dynamic equations of motion, an incremental formulation has been used due to the nonlinear nature of the contact mechanics, while a procedure based on the Lagrange multiplier method imposes the contact constraint equations when contact occurs. The system of nonlinear equations is solved by an efficient block factorization solver that reorders the system matrix and isolates the nonlinear terms that belong to the contact elements or to other nonlinear elements that may be incorporated in the model. Such procedure avoids multiple unnecessary factorizations of the linear terms during each Newton iteration, making the formulation efficient and computationally attractive. A numerical example has been carried out to validate the accuracy and efficiency of the present methodology. The obtained results have shown a good agreement with the results obtained with the commercial finite element software ANSY

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