Optimization of Production, Maintenance, Design and Reliability for Multipurpose Process Plants: an Analysis and Revision of Models

The successful design of multipurpose process plants, which are characterized by their flexibility, is accomplished by maximizing the availability of process units and therefore, the profitability of the process. Maximum availability is achieved through the optimization of the design and production scheduling of a process under constraints relating to equipment maintenance and failure. Mathematical models that incorporate the production scheduling, maintenance scheduling, process design and initial reliability aspects of a process can be optimized in order to maximize availability. These mathematical models are solved through the use of computers. Mathematical process models, presented in the literature and containing the aforementioned components, were replicated and analyzed in this research; the simplest was replicated first and additional complexity was added thereafter. The last model replicated from the literature, the one containing the initial reliability component, is revised and improved. Specifically, the mathematics of the model are altered and simplified. Analysis reveals that as the models became more complex the harder it was to replicate the results provided in the literature. However, the revisionist model significantly improved upon the literature initial reliability model; it was solved faster and with greater accuracy. At the beginning of this report, a review of the mathematical and theoretical framework for this type of process optimization research is provided. The models of the multipurpose process plants are formulated as mixed-integer linear programming (MILP) problems in the General Algebraic Modeling System and solved using the XPRESS and CPLEX solvers

Precision Automatic Tracking Using a CW Laser

This paper describes the design and performance of a precision CW laser tracker. When tracking low acceleration targets such as satellites and airplanes, this tracker has an accuracy of approximately 25 microradians rms. The accuracy under these conditions is set by the static friction, the background noise present in the equivalent noise bandwidth of the tracker and the scintillation of the atmosphere. When tracking high acceleration targets such as rockets, the tracker has a tracking error which is essentially proportional to the relative angular acceleration. If the rocket acceleration and the tracker-target geometry are such as to cause a relative angular acceleration of 0.6 radians/second , the tracking angular error peaks to 0.3 mr at the instant of launch settling to 0.1 mr within 0.1 second thereafter and remaining at the level during the rest of the propulsion period after which it reduces further to 25 microradians during the coasting phase. Thus, the tracking accuracy against low acceleration targets is comparable to the accuracy of a star tracker. However, the laser tracker has the added capability of measuring range to the target. This accuracy particularly at low altitudes exceeds that which can be provided by a high performance radar. Interest in high precision tracking, of course, results from the instrumentation tracking requirements that arise at the missile ranges and other test stations. High precision tracking is also a necessary part of long-range optical communications which can be efficiently accomplished only by using very narrow beams. The advantage of optical tracking over radar tracking is that it is not affected by undesired reflections from surrounding objects, and the accuracy is somewhat less affected by variations in the index of refraction of the atmosphere. Laser tracking, as contrasted to passive optical tracking, has the advantage of discriminating against other optical sources and also has the capability of simultaneously measuring range

Nonaxisymmetric, multi-region relaxed magnetohydrodynamic equilibrium solutions

We describe a magnetohydrodynamic (MHD) constrained energy functional for equilibrium calculations that combines the topological constraints of ideal MHD with elements of Taylor relaxation. Extremizing states allow for partially chaotic magnetic fields and non-trivial pressure profiles supported by a discrete set of ideal interfaces with irrational rotational transforms. Numerical solutions are computed using the Stepped Pressure Equilibrium Code, SPEC, and benchmarks and convergence calculations are presented.Comment: Submitted to Plasma Physics and Controlled Fusion for publication with a cluster of papers associated with workshop: Stability and Nonlinear Dynamics of Plasmas, October 31, 2009 Atlanta, GA on occasion of 65th birthday of R.L. Dewar. V2 is revised for referee

Hamilton--Jacobi theory for continuation of magnetic field across a toroidal surface supporting a plasma pressure discontinuity

The vanishing of the divergence of the total stress tensor (magnetic plus kinetic) in a neighborhood of an equilibrium plasma containing a toroidal surface of discontinuity gives boundary and jump conditions that strongly constrain allowable continuations of the magnetic field across the surface. The boundary conditions allow the magnetic fields on either side of the discontinuity surface to be described by surface magnetic potentials, reducing the continuation problem to that of solving a Hamilton--Jacobi equation. The characteristics of this equation obey Hamiltonian equations of motion, and a necessary condition for the existence of a continued field across a general toroidal surface is that there exist invariant tori in the phase space of this Hamiltonian system. It is argued from the Birkhoff theorem that existence of such an invariant torus is also, in general, sufficient for continuation to be possible. An important corollary is that the rotational transform of the continued field on a surface of discontinuity must, generically, be irrational.Comment: Prepared for submission to Phys. Letts.

Mission Operations Planning with Preferences: An Empirical Study

This paper presents an empirical study of some nonexhaustive approaches to optimizing preferences within the context of constraint-based, mixed-initiative planning for mission operations. This work is motivated by the experience of deploying and operating the MAPGEN (Mixed-initiative Activity Plan GENerator) system for the Mars Exploration Rover Mission. Responsiveness to the user is one of the important requirements for MAPGEN, hence, the additional computation time needed to optimize preferences must be kept within reasonabble bounds. This was the primary motivation for studying non-exhaustive optimization approaches. The specific goals of rhe empirical study are to assess the impact on solution quality of two greedy heuristics used in MAPGEN and to assess the improvement gained by applying a linear programming optimization technique to the final solution

Diffusion and Impacts of E-Commerce in the United States of America: Results from an Industry Survey

The paper provides baseline conditions of U.S. e-commerce in the post-dot.com era. The article examines the key factors that act as determinants of e-commerce diffusion. It is based on qualitative analysis of U.S. industry survey data, matched to a similar data and analyses from other countries. It presents data taken from one of the most comprehensive sample surveys of U.S. firm activity in e-commerce. The paper analyzes differences among three industry sectors, and between small/medium and large firms using both qualitative interpretations and direct observations from the survey data, as well as use of structural equation modeling of e-commerce diffusion and impacts. Some differences in e-commerce orientation and experience were found across the three industry sectors studied in the survey. These differences are related largely to the nature of the tasks done in the respective industries, and to prior industry-level investment and learning related to e-commerce. There were also differences found in e-commerce attitudes and experience between small/medium sized enterprises (SMEs) and large establishments. Only modest differences were found between U.S. and non-U.S. establishments. Quantitative analysis revealed significant regression relationships with their level of statistical significance. Results show that e-commerce adoption is path dependent (i.e., establishments follow earlier investment patterns), and that each industry\u27s market and institutional context play a significant role in adoption

Globalization and E-Commerce VII: Environment and Policy in the U.S.

The United States is a global leader in both Business-to-Customer (B2C) and Business-to-Business (B2B) electronic commerce. This leadership comes in part from the historical US strengths in information technology, telecommunications, financial services, and transportation - all of which are essential enabling components of e-commerce. The size and strength of the US economy, the wealth of its consumer base, and the relatively open access to venture capital creates an attractive environment for e-commerce investment. Official US Government policy toward e-commerce is to let the private sector take the lead, with government helping to make the business climate right for innovation and investment. Prior US Government investments in essential e-commerce infrastructure for military purposes (e.g., digital computing, the Internet) and for civilian purposes (e.g., interstate highways, air transport) played an important role in the US lead in e-commerce. US Government policies favoring widespread economic liberalization since the 1970\u27s in areas such as financial services, transportation, and telecommunications helped enable and stimulate private sector investment and innovation in e-commerce. The collapse of the dot.com era in the late 1990\u27s hit key sectors of e-commerce hard, suggesting that some of the more dramatic and positive predictions of e-commerce growth and impact will either be delayed substantially or will not come to pass. The strength of surviving e-commerce companies (e.g., Amazon and eBay), as well as the relative stability of the technology sector (e.g., Cisco Systems, Dell, Intel, IBM) and the continued investment of large industry sectors (e.g., autos, finance) suggest that e-commerce is still growing and is here to stay. Consumers are intrigued by B2C e-commerce, and many have used such services, but serious concerns related to privacy and transaction security remain obstacles to universal adoption of B2C e-commerce

Zooplankton recovery from a whole-lake disturbance: Examining roles of abiotic factors, biotic interactions, and traits

Community assembly following disturbance is a key process in determining the composition and function of the future community. However, replicated studies of community assembly at whole-ecosystem scales are rare. Here, we describe a series of whole-lake experiments, in which the recovery of zooplankton communities was tracked following an ecosystem-scale disturbance, that is, application of the piscicide, rotenone. Using a before-after-control-impact design, 14 lakes in eastern Washington were studied: Seven lakes were treated with rotenone, while seven lakes acted as reference systems. Each lake was monitored up to 6 months before and 1–2 years after the rotenone treatments. Zooplankton samples and environmental measurements were collected approximately monthly from each lake. Community responses following disturbance were assessed using metrics of abundance, diversity, and community composition, as well as taxonomic group abundance. Zooplankton recovery was also assessed using species traits related to habitat, feeding mode, trophic level, body size, and life history. In addition to patterns of recovery, potential mechanisms were explored relating to abiotic conditions, biotic interactions, and traits. There were steep declines in the abundance (average across years: 99%) and diversity (average across years: 75%) of the zooplankton community following rotenone treatment. Although abundance had recovered by the second year of the study, community diversity had not fully recovered after 2 years. Communities from rotenone lakes appeared to be compositionally recovered within about 8 months following disturbance. Cyclopoid copepods were typically the first group to recover and remained dominant for a few months, whereas cladocerans recovered more slowly, typically within ~6–7 months following rotenone. Calanoid copepods were not fully recovered 2 years after rotenone treatment. Traits related to body size and feeding mode were associated with the zooplankton communities following rotenone treatment. We failed to observe significant spatial synchrony in recovery patterns of zooplankton across lakes, though we did observe significant synchrony of zooplankton taxonomic groups within lakes. These findings suggest that traits related to ecological function, and to a lesser extent, biotic, and abiotic factors, as well as characteristics of the disturbance itself, may be important in helping to understand recovery processes

Computation of multi-region relaxed magnetohydrodynamic equilibria

We describe the construction of stepped-pressure equilibria as extrema of a multi-region, relaxed magnetohydrodynamic (MHD) energy functional that combines elements of ideal MHD and Taylor relaxation, and which we call MRXMHD. The model is compatible with Hamiltonian chaos theory and allows the three-dimensional MHD equilibrium problem to be formulated in a well-posed manner suitable for computation. The energy-functional is discretized using a mixed finite-element, Fourier representation for the magnetic vector potential and the equilibrium geometry; and numerical solutions are constructed using the stepped-pressure equilibrium code, SPEC. Convergence studies with respect to radial and Fourier resolution are presented.The authors gratefully acknowledge support of the U.S. Department of Energy and the Australian Research Council, through Grants DP0452728, FT0991899, and DP110102881