Sailing the Deep Blue Sea of Decaying Burgers Turbulence

We study Lagrangian trajectories and scalar transport statistics in decaying Burgers turbulence. We choose velocity fields, solutions of the inviscid Burgers equation, whose probability distributions are specified by Kida's statistics. They are time-correlated, not time-reversal invariant and not Gaussian. We discuss in some details the effect of shocks on trajectories and transport equations. We derive the inviscid limit of these equations using a formalism of operators localized on shocks. We compute the probability distribution functions of the trajectories although they do not define Markov processes. As physically expected, these trajectories are statistically well-defined but collapse with probability one at infinite time. We point out that the advected scalars enjoy inverse energy cascades. We also make a few comments on the connection between our computations and persistence problems.Comment: 18 pages, one figure in eps format, Latex, published versio

Computer assisted mathematical programming

A Computer Assisted Mathematical Programming (Modelling) System (CAMPS) is described in this paper. The system uses program generator techniques for model creation and contrasts with earlier approaches which use a special purpose language to construct models. Thus no programming skill is required to formulate a model. In designing the system we have first analysed the salient components of the mathematical programming activity. A mathematical programming model is usually constructed by progressive definition of dimensions, data tables, model variables, model constraints and the matrix coefficients which connect the last two entities. Computer assistance is provided to structure the data and the resulting model in the above sequence. In addition to this novel feature and the automatic documentation facility, the system is in line with recent developments, and incorporates a friendly and flexible user interface

Effective Tax Rates in Transition

The paper addresses the question of effective tax rates for Russian economic sectors in transition. It presents a detailed account of fiscal environment for 1995 and compares statutory obligations with reported tax liabilities. The paper finds that taxation did not contribute to recession, as some observors believed at the time. It extends research by questioning the role that inflation played distorting revenue structure. When the costs of intermediate inputs are adjusted for inflation, many sectors have negative residual revenue, which is indicative of recession. Yet, modeling tax changes to correct the situation does not produce positive results, for the tax share in the cost structure of many sectors is small and cannot compensate for inflationhttp://deepblue.lib.umich.edu/bitstream/2027.42/39762/3/wp378.pd

Efficient Iterative Programs with Distributed Data Collections

Big data programming frameworks have become increasingly important for the development of applications for which performance and scalability are critical. In those complex frameworks, optimizing code by hand is hard and time-consuming, making automated optimization particularly necessary. In order to automate optimization, a prerequisite is to find suitable abstractions to represent programs; for instance, algebras based on monads or monoids to represent distributed data collections. Currently, however, such algebras do not represent recursive programs in a way which allows for analyzing or rewriting them. In this paper, we extend a monoid algebra with a fixpoint operator for representing recursion as a first class citizen and show how it enables new optimizations. Experiments with the Spark platform illustrate performance gains brought by these systematic optimizations.Comment: 36 page

Effective Tax Rates in Transition

The paper addresses the question of effective tax rates for Russian economic sectors in transition. It presents a detailed account of fiscal environment for 1995 and compares statutory obligations with reported tax liabilities. The paper finds that taxation did not contribute to recession, as some observors believed at the time. It extends research by questioning the role that inflation played distorting revenue structure. When the costs of intermediate inputs are adjusted for inflation, many sectors have negative residual revenue, which is indicative of recession. Yet, modeling tax changes to correct the situation does not produce positive results, for the tax share in the cost structure of many sectors is small and cannot compensate for inflationTaxation in transition, Russian fiscal system

Role-playing games as a mean to validate agent-based models : an application to stakeholder-driven urban freight transport policymaking

Agent-based models (ABMs) are widely used to replicate transport environments accounting for interaction among stakeholders. Validation of ABMs implies assessing the extent to which the model, from assumptions to results, is capable of approximating reality. To this end, different methods have been proposed, but yet no widely accepted procedure has emerged. This paper addresses this problem and suggests using a procedure based on role-playing games (RPGs). A first application is described with the intent of providing a preliminary contribution to validate an ABM trying to mimic stakeholders’ interaction in a multi-level decisionmaking process in the context of urban freight transport policy-making. The aim is twofold: (1) understand if the structure of the model and the opinion dynamics envisioned are consistent with a real negotiation process, (2) verify if the results derived from the ABM effort are in line with those derived from a real-life experiment. Results of the first preliminary experiment show that the model seems capable of reproducing real-world processes and confirm that well-thought-out RPGs can contribute to validating ABMs. Keywords: city logistics, stakeholder engagement, participatory simulation, model validation, discrete choice modelspublishedVersio