Communication Optimization for Multiphase Flow Solver in the Library of OpenFOAM

Multiphase flow solvers are widely-used applications in OpenFOAM, whose scalability suffers from the costly communication overhead. Therefore, we establish communication-optimized multiphase flow solvers in OpenFOAM. In this paper, we first deliver a scalability bottleneck test on the typical multiphase flow case damBreak and reveal that the Message Passing Interface (MPI) communication in a Multidimensional Universal Limiter for Explicit Solution (MULES) and a Preconditioned Conjugate Gradient (PCG) algorithm is the short slab of multiphase flow solvers. Furthermore, an analysis of the communication behavior is carried out. We find that the redundant communication in MULES and the global synchronization in PCG are the performance limiting factors. Based on the analysis, we propose our communication optimization algorithm. For MULES, we remove the redundant communication and obtain optMULES. For PCG, we import several intermediate variables and rearrange PCG to reduce the global communication. We also overlap the computation of matrix-vector multiply and vector update with the non-blocking computation. The resulting algorithms are respectively referred to as OFPiPePCG and OFRePiPePCG. Extensive experiments show that our proposed method could dramatically increase the parallel scalability and solving speed of multiphase flow solvers in OpenFOAM approximately without the loss of accuracy.

Nonpoint source pollution: experiments on the average Pigouvian tax under costly communication

The ‘average Pigouvian tax’ (APT) was proposed to reduce the financial burden imposed by the standard ambient tax. This instrument consists of a standard ambient tax divided by the number of firms and it requires polluters to cooperate in order to achieve the social optimum. To enable polluters to cooperate, communication is allowed in most of the experimental treatments. We introduce different types of communication: cheap talk, exogenous costly communication and endogenous costly communication. Our experiment confirms that under cheap talk, the APT promotes a reduction in polluters’ emissions. In contrast, under costly communication, the APT reduces group emissions to a lesser extent.

An Empirical Investigation of Internet Users' Perceptions towards National and International e-Shops

Nowadays, the broad Internet utilization and the advancement of Information and Communication Technologies (ICT) have greatly changed the way goods and services are bought and sold. As a consequence, even more online users prefer not only to shop online, but also purchase abroad taking advantage of Internet's limitless feature. Thus, technology's success has stimulated the process of cross-border e-shopping, allowing fast, less costly communication, as well as access to a wider variety of goods and services. The purpose of this consumer-oriented approach paper is to examine the perceptions of Greek Internet users concerning e-shops. In specific, it aims to reveal if there are differences on users' perceptions regarding Greek versus international e-shops, as even more individuals visit non-domestic online stores for their e-purchases. Hence, it provides tangible results to an under-explored area of online shopping and shed light on the difficulty of understanding important aspects of e-shopping behavior; presenting vital implications to both academia and practitioners.