| publications-4381 |
article |
1971 |
Tarjan, Robert E. and Tarjan, Robert E. |
Depth-first search and linear graph algorithms |
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10.1109/swat.1971.10 |
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The value of depth-first search or "backtracking" as a technique for solving graph problems is illustrated by two examples. An algorithm for finding the biconnected components of an undirected graph and an improved version of an algorithm for finding the strongly connected components of a directed graph are presented. The space and time requirements of both algorithms are bounded by k1V + k2E + k3 for some constants k1, k2, and k3, where V is the number of vertices and E is the number of edges of the graph being examined. |
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| publications-4382 |
article |
1979 |
Shamir, Uri and Shamir, Uri and Howard, Charles D. D. and Howard, Charles D. D. |
An Analytic Approach to Scheduling Pipe Replacement |
Journal American Water Works Association |
10.1002/j.1551-8833.1979.tb04345.x |
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Water main breaks are a problem of concern to many water supply agencies. Breaks cause disruption in service, pose a potential danger when they reduce temporarily fire fighting capabilities, may cause damage to other services and to property, and incur substantial repair costs. Breaks may also cause a disruption in the normal work schedule and create an atmosphere of public concern that pressures the water supply agency. When a pipe breaks, the leak has to be located, the pipe exposed, and the leak fixed or a section replaced. When a length of pipe shows an increasing susceptibility to breaks, consideration should be given to replacing it entirely with a new pipe. The reasons for breaks are many and can be classi fied in several categories: 1. The quality and age of the pipe itself, including connectors and other equipment 2. The type of environment in which the pipe is laid e.g., the corrosivity of the soil, frost and heaving, external loads 3. The quality of the workmanship used,in laying the pipe 4. The service conditions, such as pressure and water hammer. An analysis of break data may help pinpoint the main reasons for breaks in a certain area of the network or in a specific pipe. Changes in pipeline design and construction policies may then be issued. This, how ever, does not solve the problem of a pipeline that is in service and exhibits a history of many breaks. There are essentially two ways of dealing with such a situa tion: to either repair or to replace the pipe. A rational decision to replace or not to replace a pipe at a particular time must be based on a comparison of the two alternatives: whether to replace the pipe, incurring the replacement cost and whatever future costs are associated with the new line, or to retain the existing length of pipe, at least for the time being, saving the replacement cost but incurring possible future costs of repair, disruption of service, and damages. The analysis required for such a decision must include a projection |
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| publications-4383 |
article |
1981 |
LatanΓ©, Bibb and LatanΓ©, Bibb |
The psychology of social impact. |
American Psychologist |
10.1037/0003-066x.36.4.343 |
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The author proposes a theory of social im- pact specifying the effect of other persons on an in- dividual. According to the theory, when other people are the source of impact and the individual is the target, impact should be a multiplicative function of the strength, immediacy, and number of other people. Fur- thermore, impact should take the form of a power func- tion, with the marginal effect of the Nth other person being less than that of the (N β€” l)th. Finally, when other people stand with the individual as the target of forces from outside the group, impact should be divided such that the resultant is an inverse power function of the strength, immediacy, and number of persons stand- ing together. The author reviews relevant evidence from research on conformity and imitation, stage fright and embarrassment, news interest, bystander interven- tion, tipping, inquiring for Christ, productivity in groups, and crowding in rats. He also discusses the unresolved issues and desirable characteristics of the theory. |
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| publications-4384 |
article |
1986 |
Walski, Thomas M. and Walski, Thomas M. and Walski, Thomas M. and Walski, Thomas M. |
Case Study: Pipe Network Model Calibration Issues |
Journal of Water Resources Planning and Management |
10.1061/(asce)0733-9496(1986)112:2(238) |
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This paper illustrates that it is possible to calibrate accurately a mathematical model of a complicated water distribution system (271 nodes, 307 pipes, 9 pressure reducing valves) if adequate and accurate data are collected. It is essential that the model be calibrated for a range of water use rates and patterns as otherwise it is possible for the model to appear to be calibrated even though it contains significant errors. For example, in this system it was possible to make the model appear calibrated for Cβ€factors that varied by a factor of 3 provided that sufficient errors were made on other input parameters. The key to collecting adequate data is that the head at boundary nodes (pumps, tanks, pressure reducing valves) be known when pressure readings are made in the system. |
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| publications-4385 |
article |
1988 |
Clark, Robert M. and Clark, Robert M. and Grayman, Walter M. and Grayman, Walter M. and Males, Richard M. and Males, Richard M. |
Contaminant Propagation in Distribution Systems |
Journal of Environmental Engineering |
10.1061/(asce)0733-9372(1988)114:4(929) |
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The Safe Drinking Water Act (SDWA) of 1974 requires that the U.S. Environmental Protection Agency (EPA) establish maximum contaminant levels (MCLs) for each contaminant which may have an adverse effect on the health of persons. The SDWA clearly specifies that these MCLs shall be met at the consumers tap. Nevertheless most regulatory concern has been focused on water as it leaves the treatment plant before entering the distribution system. There is, however, growing interest in determining the factors that cause water quality variations in drinking water distribution systems. In order to study this effect, the Drinking Water Research Division of EPA initiated a cooperative agreement with the North Penn Water Authority. This cooperative agreement has resulted in a series of field monitoring and systems modeling studies that lend insight into the movement of contaminants in distribution systems. Previous research has resulted in development of a steady-state model, a quasi-steady-state model and dynamic model that have provided useful approaches to modeling the general propagation of contaminants in distribution systems. In this paper, results from the steady-state model are utilized to examine the actual pathways of water flow and the time of passage and percentage of water that flows from a given source to a given node in a distribution system. The contaminant propagation technique developed from this extension of the steady-state model provides a useful technique for analyzing many of the factors that affect water quality in a distribution system. A major finding of this research study is the importance of adequate hydraulic modeling of the systems being studied and the importance of field studies in verifying systems performance. The approach suggested in this research will provide useful insight into the water quality variations that may impact consumers at the tap and the development of time and spatially sensitive monitoring strategies. |
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| publications-4386 |
article |
1992 |
Pudar, Ranko S. and Pudar, Ranko S. and Liggett, James A. and Liggett, James A. |
LEAKS IN PIPE NETWORKS |
Journal of Hydraulic Engineering |
10.1061/(asce)0733-9429(1992)118:7(1031) |
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Leak detection in waterβ€distribution systems can be accomplished by solving an inverse problem using measurements of pressure and/or flow. The problem is formulated with equivalent orifice areas of possible leaks as the unknowns. Minimization of the difference between measured and calculated heads produces a solution for the areas. The quality of the result depends on number and location of the measurements. A sensitivity matrix is key to deciding where to make measurements. Both location and magnitude of leaks are sensitive to the quantity and quality of pressure measurements and to how well the pipe friction parameters are known. The overdetermined problem (more measurements than suspected leaks) gives the best results, but some information can be derived from the underdetermined problem. The variance of leak areas, based on the quality of system characteristics and pressure data, indicates the likely accuracy of the results. The method will not substitute for more traditional leak surveys but can serve... |
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| publications-4387 |
article |
1998 |
Parunak, H. Van Dyke and Parunak, H. Van Dyke and Parunak, H. Van Dyke and Parunak, H. Van Dyke and Savit, Robert and Savit, Robert and Riolo, Rick L. and Riolo, Rick L. |
Agent-Based Modeling vs. Equation-Based Modeling: A Case Study and Users' Guide |
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10.1007/10692956_2 |
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In many domains, agent-based system modeling competes with equation-based approaches that identify system variables and evaluate or integrate sets of equations relating these variables. The distinction has been of great interest in a project that applies agent-based modeling to industrial supply networks, since virtually all computer-based modeling of such networks up to this point has used system dynamics, an approach based on ordinary differential equations (ODE’s). This paper summarizes the domain of supply networks and illustrates how they can be modeled both with agents and with equations. It summarizes the similarities and differences of these two classes of models, and develops criteria for selecting one or the other approach. |
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| publications-4388 |
article |
1998 |
Clark, Robert M. |
CHLORINE DEMAND AND TTHM FORMATION KINETICS: A SECOND-ORDER MODEL |
Journal of Environmental Engineering |
10.1061/(asce)0733-9372(1998)124:1(16) |
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Much effort has been expended in attempting to develop mathematical models for chlorine demand in water and wastewater. Most of these efforts have centered around the use of first-order functions or modifications of first-order functions. Recently there has also been interest in characterizing the formation of total trihalomethanes. These efforts have taken on new meaning because of the importance of maintaining chlorine residuals for microbial protection and concerns over the formation of trihalomethanes in drinking water distribution systems. This paper applies second-order kinetics to describe both of these relationships, using data collected from a recent collaborative study between the EPA and the American Water Works Association Research Foundation. It demonstrates that TTHM formation can be characterized as a function of chlorine demand. |
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| publications-4389 |
article |
1999 |
Epstein, Joshua M. and Epstein, Joshua M. |
Agent-based computational models and generative social science |
Complexity |
10.1002/(sici)1099-0526(199905/06)4:5<41::aid-cplx9>3.0.co;2-f |
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This article argues that the agent-based computational model permits a distinctive approach to social science for which the term β€_x009c_generativeβ€_x009d_ is suitable. In defending this terminology, features distinguishing the approach from both β€_x009c_inductiveβ€_x009d_ and β€_x009c_deductiveβ€_x009d_ science are given. Then, the following specific contributions to social science are discussed: The agent-based computational model is a new tool for empirical research. It offers a natural environment for the study of connectionist phenomena in social science. Agent-based modeling provides a powerful way to address certain enduringβ€”and especially interdisciplinaryβ€”questions. It allows one to subject certain core theoriesβ€”such as neoclassical microeconomicsβ€”to important types of stress (e.g., the effect of evolving preferences). It permits one to study how rules of individual behavior give riseβ€”or β€_x009c_map upβ€_x009d_β€”to macroscopic regularities and organizations. In turn, one can employ laboratory behavioral research findings to select among competing agent-based (β€_x009c_bottom upβ€_x009d_) models. The agent-based approach may well have the important effect of decoupling individual rationality from macroscopic equilibrium and of separating decision science from social science more generally. Agent-based modeling offers powerful new forms of hybrid theoretical-computational work; these are particularly relevant to the study of non-equilibrium systems. The agentbased approach invites the interpretation of society as a distributed computational device, and in turn the interpretation of social dynamics as a type of computation. This interpretation raises important foundational issues in social scienceβ€”some related to intractability, and some to undecidability proper. Finally, since β€_x009c_emergenceβ€_x009d_ figures prominently in this literature, I take up the connection between agent-based modeling and classical emergentism, criticizing the latter and arguing that the two are incompatible. ! 1999 John Wiley & Sons, Inc. |
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| publications-4390 |
article |
2000 |
Powell, Jennifer and Powell, James C. and Hallam, Nicholas B. and Hallam, Nicholas B. and West, John R. and West, John R. and Forster, C.F. and Forster, C.F. and Simms, John and Simms, John |
Factors which control bulk chlorine decay rates |
Water Research |
10.1016/s0043-1354(99)00097-4 |
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