Katrin Rohlf

A comparative analysis of learning curves: Implications for new technology implementation management

New technology implementation projects are notoriously over time and budget resulting in significant financial and strategic organizational consequences. Some argue that inadequate planning and management, misspecification of requirements, team capabilities and learning contribute to cost and schedule over runs. In this paper we examine how learning curve theory could inform better management of new technology implementation projects. Our research makes four important contributions: (1) It presents a comparative analysis of learning curves and proposes how they can be used to help ERP implementation planning and management. (2) Based on empirical data from four ERP implementation projects, it provides illustrations of how managers can apply the curves in different project situations. (3) It provides a theoretical basis for empirical studies of learning and ERP (and other IT) implementations in different organizational settings. (4) It provides empirical justification for the development of learning curve theory in IT implementation.

Reactive multiparticle collision dynamics

Abstract A mesoscopic dynamics method for the simulation of spatially distributed chemically reacting systems under equilibrium and nonequilibrium conditions is described. Non-reactive collisions are modeled by multiparticle collision dynamics that conserves mass, momentum and energy. Reactive collisions are described by birth–death stochastic processes. The dynamics is governed by a Markov chain in the full phase space of the system, which reduces to mass action rate laws in the mean field limit. Simulations on the Selkov model are carried out to illustrate the simulation method.

The role of the Womersley number in pulsatile blood flow: a theoretical study of the Casson model

The purpose of this Note is to clarify the meaning of the Womersley number alpha in pulsatile blood flow in small vessels. In particular. we explain why the use of alpha as aperturbation parameter to obtain approximate solutions of the Casson model (frequently used in the literature) is not appropriate. Using the techniques of dimensional analysis and scaling, we show that alpha is the product of the Reynolds and Strouhal numbers. Since the latter is very small for physiological flows, the result is that alpha < 1 even at relatively high values of the Reynolds number (i.e., for non-negligible inertia) and we validate our perturbation theory results by comparison with a numerical integration of the full model. Although this analysis is based on the Casson model, our method has general validity and may be applied to other models which describe more accurately the rheological properties of blood.

Spiral wave dynamics in excitable media with spherical geometries

We describe the spatial and temporal organization of spiral and scroll waves in spherical shells of different sizes and solid spheres. We present simulation results for the evolution of the dynamics and clustering of spiral waves as a function of the excitability of the medium. The excitability, topology, and size of the domain places restrictions on how single and multiarmed spiral waves are organized in space. The results in spherical geometries are compared with those in planar two-dimensional media. These studies are relevant to the dynamics of spiral waves in a variety of media including the heart, and chemical reactions on spherical surfaces.

Steady flow through a constricted cylinder by multiparticle collision dynamics

The flow characterization of blood through healthy and diseased flow geometries is of interest to researchers and clinicians alike, as it may allow for early detection, and monitoring, of cardiovascular disease. In this paper, we use a numerically efficient particle-based flow model called multiparticle collision dynamics (MPC for short) to study the effect of compressibility and slip of flow of a Newtonian fluid through a cylinder with a local constriction. We use a cumulative averaging method to compare our MPC results to the finite-element solution of the incompressible no-slip Navier-Stokes equations in the same geometry. We concentrate on low Reynolds number flows [

Reactive multi-particle collision dynamics with reactive boundary conditions

Re \in (4,30)

Impulsive control of a Lotka-Volterra system

] and quantify important differences observed between the MPC results and the Navier-Stokes solution in constricted geometries. In particular, our results show that upstream recirculating zones can form with the inclusion of slip and compressibility, which are not observed in the flow of an incompressible Newtonian fluid using the no-slip assumption, but have been observed experimentally for blood. Important flow features are also presented that could be used as indicators to observe compressibility and slip in experimental data where near-wall data may be difficult to obtain. Finally, we found that the cumulative averaging method used is ideal for steady particle-based flow methods, as macroscopic no-slip is readily obtained using the MPC bounce-back rule. Generally, a small spurious slip is seen using other averaging methods such as weighted spatial averages or averages over several runs, and the bounce-back rule has to be modified so as to achieve macroscopic no-slip. No modifications of the bounce-back rule were required for our simulations.

Learning and performance in ERP implementation projects: A learning-curve model for analyzing and managing consulting costs

An efficient yet accurate simulation method for modeling diffusion-influenced reaction networks is presented. The method extends existing reactive multiparticle collision dynamics by incorporating species-dependent diffusion coefficients, and developing theoretical expressions for the reactant-dependent diffusion control. This off-lattice particle-based mesoscopic simulation tool is particularly suited for problems in which detailed descriptions of particle trajectories and local reactions are required. Numerical simulations of an intracellular signaling pathway for bacterial chemotaxis are carried out to validate our approach, and to demonstrate its efficiency.