Finite-size anisotropy in statistically uniform porous media

Anisotropy of the permeability tensor in statistically uniform porous media of sizes used in typical computer simulations is studied. Although such systems are assumed to be isotropic by default, we show that de facto their anisotropic permeability can give rise to significant changes of transport parameters such as permeability and tortuosity. The main parameter controlling the anisotropy is $a/L$, being the ratio of the obstacle to system size. Distribution of the angle $\alpha$ between the external force and the volumetric fluid stream is found to be approximately normal, and the standard deviation of $\alpha$ is found to decay with the system size as $(a/L)^{d/2}$, where $d$ is the space dimensionality. These properties can be used to estimate both anisotropy-related statistical errors in large-scale simulations and the size of the representative elementary volume.Comment: 7 pages, 9 figure

Usability evaluation of three admission and medical records subsystems integrated into nationwide hospital information systems: Heuristic evaluation

Introduction: Usability is one of the quality criteria for information systems and its weakness is one of the main barriers to the adoption of these systems. The purpose of this study was to evaluate the usability of admission and medical records module of three widely used hospital information systems (HISs). Methods: In this descriptive study the usability of admission and medical records module of three HISs (HIS1, HIS2, and HIS3) was evaluated using heuristic evaluation method. For each HIS, three expert users of the same system assessed the user interface independently, completed a usability evaluation checklist, and rated severity of each identified problem. The checklist was based on Nielsen's heuristics. For each HIS, three heuristics that have the highest and lowest problem rates and greatest severity of problems were categorized into three separate groups. The results were analyzed using descriptive statistics. Results: Although HIS1 and HIS2 were used in more hospitals than HIS3, the results showed that the usability problem rates of them were significantly higher than HIS3. The heuristics of "help and documentation", "flexibility and efficiency of use", and "visibility of system status" in the three HISs were categorized into the "highest rate of problems", "lowest rate of problems", and "highest severity of problems" groups, respectively. The heuristics of "diagnose and recover from errors", "error prevention", and "help and documentation" in HIS1 and HIS2 were categorized into the "highest rate of problems" group. Conclusions: The results of this study and previous studies show that the most common usability problems with HISs are related to heuristics of "help and documentation", "error prevention", and "help users recognize, diagnose and recover from errors." Also, the large number of hospitals using one HIS does not demonstrate its high usability to others. © 2018 Mehrdad Farzandipour, Ehsan Nabovati, Gholam-Hosein Zaeimi, Reza Khajouei