Variety Of Modeling Assumptions Research Articles

Statistical Catch‐Free Age‐Structured Assessment to Estimate Year‐Class Strength for Inland Recreational Fisheries: A Largemouth Bass Example

AbstractStatistical catch‐at‐age analysis (SCAA) is commonly used to estimate recruitment and mortality for large‐scale, economically important fish stocks, but fishery‐dependent catch‐at‐age data are often unavailable for smaller‐scale inland fisheries, thus limiting the use of SCAA. In these systems, a catch‐free approach to age‐structure modeling may be useful for estimating recruitment and mortality rates solely from a time series of survey age composition and catch rate data by estimating recruitment as a relative index of year‐class strength (Rt). Here, we demonstrate a statistical catch‐free age‐structured assessment (SCFASA) model for small‐scale inland fish stocks as an alternative to traditional catch curve approaches by using Largemouth Bass Micropterus salmoides as an example. We fitted the SCFASA to fishery‐independent survey age composition and catch‐per‐effort data from Largemouth Bass stocks in three Alabama reservoirs to estimate Rt, annual fishing mortality rates, and age‐specific electrofishing survey vulnerability; we compared Rt to catch curve residual estimates and performed a sensitivity analysis under a variety of model assumptions. Model estimates of Rt and temporal trends in fishing mortality were robust to changes in assumptions about the effective sample size of multinomial age samples, natural mortality rate, and temporal variability in fishing mortality. However, the magnitude of instantaneous fishing mortality rates at two of the three reservoirs was somewhat higher than empirical estimates for similar stocks and was sensitive to model assumptions. Our application of the SCFASA to survey data sets routinely collected by management agencies for Largemouth Bass potentially provides a comprehensive approach to estimating Rt, mortality, and sampling vulnerability for these stocks without increasing sampling effort. Future investigations of SCFASA's utility for small‐scale inland stocks should address the potential for bias in the magnitude of fishing mortality estimates due to incorrectly specified vulnerability schedules.Received October 5, 2015; accepted September 19, 2016 Published online December 21, 2016

Copyright piracy as prey–predator behavior

The economic analysis of the piracy of copyright products has used a variety of modeling assumptions, the majority of which use typical industrial organization settings. The results of such models are manyfold, but in general they are ambiguous as to the optimal protection strategy, and the effects of protection on the welfare of copyright holders, and on the existence of piracy. Concretely, little has been said about which types of protection mechanisms are most adequate for controlling piracy. In the present paper, we propose a new theoretical framework by drawing an analogy between copyright piracy and prey–predator behavior. This analogy gives us a new perspective to approach copyright issues and it provides the economic theory of copyright piracy with a new set of mathematical models. We consider a very simple model that can be used to show that publicly instigated and financed policies designed to deter piracy can have the effect of increasing the amount of piracy, while privately financed strategies (e.g. DRM) will always decrease piracy.

Manufacturing delivery performance for supply chain management

This paper considers single-stage make-to-order production systems. We focus on (1) modeling the appropriate expected costs under a variety of modeling assumptions and (2) characterizing the optimal policies. Our approach to solving the problem is to derive the distribution of actual completion times of the process for individual orders and to compare it to the corresponding quoted due dates in order to obtain the expected total costs. We then show the convexity of the objective cost function for determining the decision variable(s), the planned customer order leadtime.

Quoting Customer Lead Times

We consider the problem of quoting customer lead times in a manufacturing environment under a variety of modeling assumptions. First, we examine the case where capacity is infinite. For this case, we derive a closed-form expression for the optimal lead time quote. Second, we consider the case where capacity is finite and the firm processes jobs in first-come-first-served (FCFS) order. We prove the optimality of different forms of control limit policies for the situations where the lead time is dictated by the market and where firms are able to compete on the basis of lead time. Finally, we consider the case where the firm may choose to schedule jobs in other than FCFS order and give conditions under which the optimal due-date-quoting/order-scheduling policy will process jobs in earliest due date (EDD) order.

Impurity profiles at the JET divertor targets compared with the DIVIMP code

In this paper we describe the simulation of edge diagnostics in JET using the DIVIMP (divertor impurity) Monte Carlo code. We concentrate on two ohmic pulses and show how the results are influenced by a variety of modeling assumptions. Our results show that a wall source must be included to explain the diagnostic signals. The wall source is shown to be a significant source of impurity in the discharges studied and more generally.

The Relationship Between Distribution and Market Share

This paper develops an aggregate-level model of distribution and market share for frequently purchased, branded consumer goods that is founded in the concepts of “push” and “pull.” The model makes a key distinction between uncompromised and compromised demand as sources of market share. Uncompromised demand is demand that is satisfied when the preferred brand is found; compromised demand results from brands that lack broad distribution and whose potential customers are willing to compromise and purchase another brand when the preferred brand is not present. Trade behavior is also addressed by analyzing the effects of consumer demand “feedback” on the trade's decision to stock and merchandise the brand. Compromised demand and feedback effects may be critical, and often overlooked, determinants of market share. Under a variety of model assumptions, analytical results are consistent with longitudinal and cross-sectional evidence that market share is a convex function of distribution, increasing at an increasing rate up to 100 percent distribution. In addition to these insights, we believe that the model has promise for future normative work on balancing push and pull marketing effects.

Concurrency control performance modeling: alternatives and implications

A number of recent studies have examined the performance of concurrency control algorithms for database management systems. The results reported to date, rather than being definitive, have tended to be contradictory. In this paper, rather than presenting “yet another algorithm performance study,” we critically investigate the assumptions made in the models used in past studies and their implications. We employ a fairly complete model of a database environment for studying the relative performance of three different approaches to the concurrency control problem under a variety of modeling assumptions. The three approaches studied represent different extremes in how transaction conflicts are dealt with, and the assumptions addressed pertain to the nature of the database system's resources, how transaction restarts are modeled, and the amount of information available to the concurrency control algorithm about transactions' reference strings. We show that differences in the underlying assumptions explain the seemingly contradictory performance results. We also address the question of how realistic the various assumptions are for actual database systems.