Computational modeling of elastic constants as a function of temperature and composition in Zr–Nb alloys

We used CALPHAD-type model to describe single crystal elastic constants of bcc solution phases in Zr–Nb system. The model parameters were evaluated by utilizing least square algorithm based on available experimental and first-principles data. The composition-polycrystalline elastic properties profiles of the Zr–Nb alloys of full composition were predicted and are in agreement with experimental data. The critical temperature corresponding to the dynamical stabilization of bcc pure Zr can be estimated to 600 K and the critical composition corresponding to the dynamical stabilization of bcc Zr–Nb alloys at room temperature is about 4 at% Nb. The current calculations present an effective strategy to design biomedical alloys using a computational method.     

The design and implementation of an individual-based predator–prey model for a distributed computing environment

A distributed implementation of the Spatially-Explicit Individual-Based Simulation Model of Florida Panther and White-Tailed Deer in the Everglades and Big Cypress Landscapes (SIMPDEL) model is presented. SIMPDEL models the impact of different water management strategies in the South Florida region on the white-tailed deer and the Florida panther populations. SIMPDEL models the interaction of the four interrelated components – vegetation, hydrology, white-tailed deer and Florida panther, over a time span up to several decades. Very similar outputs of bioenergetic and survival statistics were obtained from the serial and distributed models. A performance evaluation of the two models revealed moderate speed improvements for the distributed model (referred to as DSIMPDEL). The 4-processor configuration attained a speed improvement of 3.83 with small deer populations on an ATM-based network of SUN Ultra 2 workstations over the serial model executing on a single SUN Ultra 2 workstation.     

A priori and a posteriori error analysis of an augmented mixed-FEM for the Navier–Stokes–Brinkman problem

We introduce and analyze an augmented mixed finite element method for the Navier–Stokes–Brinkman problem with nonsolenoidal velocity. We employ a technique previously applied to the stationary Navier–Stokes equation, which consists of the introduction of a modified pseudostress tensor relating the gradient of the velocity and the pressure with the convective term, and propose an augmented pseudostress–velocity formulation for the model problem. The resulting augmented scheme is then written equivalently as a fixed point equation, so that the well-known Banach fixed point theorem, combined with the Lax–Milgram lemma, are applied to prove the unique solvability of the continuous and discrete systems. We point out that no discrete inf–sup conditions are required for the solvability analysis, and hence, in particular for the Galerkin scheme, arbitrary finite element subspaces of the respective continuous spaces can be utilized. For instance, given an integer $k\ge 0$, the Raviart–Thomas spaces of order $k$ and continuous piecewise polynomials of degree $\le k+1$ constitute feasible choices of discrete spaces for the pseudostress and the velocity, respectively, yielding optimal convergence. We also emphasize that, since the Dirichlet boundary condition becomes a natural condition, the analysis for both the continuous an discrete problems can be derived without introducing any lifting of the velocity boundary datum. In addition, we derive a reliable and efficient residual-based a posteriori error estimator for the augmented mixed method. The proof of reliability makes use of a global inf–sup condition, a Helmholtz decomposition, and local approximation properties of the Clément interpolant and Raviart–Thomas operator. On the other hand, inverse inequalities, the localization technique based on element-bubble and edge-bubble functions, approximation properties of the $L^2$-orthogonal projector, and known results from previous works, are the main tools for proving the efficiency of the estimator. Finally, some numerical results illustrating the performance of the augmented mixed method, confirming the theoretical rate of convergence and properties of the estimator, and showing the behavior of the associated adaptive algorithms, are reported.     

Message classification as a basis for studying command and control communications—an evaluation of machine learning approaches

In military command and control, success relies on being able to perform key functions such as communicating intent. Most staff functions are carried out using standard means of text communication. Exactly how members of staff perform their duties, who they communicate with and how, and how they could perform better, is an area of active research. In command and control research, there is not yet a single model which explains all actions undertaken by members of staff well enough to prescribe a set of procedures for how to perform functions in command and control. In this context, we have studied whether automated classification approaches can be applied to textual communication to assist researchers who study command teams and analyze their actions. Specifically, we report the results from evaluating machine leaning with respect to two metrics of classification performance: (1) the precision of finding a known transition between two activities in a work process, and (2) the precision of classifying messages similarly to human researchers that search for critical episodes in a workflow. The results indicate that classification based on text only provides higher precision results with respect to both metrics when compared to other machine learning approaches, and that the precision of classifying messages using text-based classification in already classified datasets was approximately 50%. We present the implications that these results have for the design of support systems based on machine learning, and outline how to practically use text classification for analyzing team communications by demonstrating a specific prototype support tool for workflow analysis.     

Is cheating a human function? The roles of presence,state hostility,and enjoyment in an unfair video game

In sports and board games, when an opponent cheats, the other players typically greet it with disdain, anger, and disengagement. However, work has yet to fully address the role of the computer cheating in video games. In this study, participants played either a cheating or a non-cheating version of a modified open-source tower-defense game. Results indicate that when a computer competitor cheats, players perceive the opponent as being more human. Cheating also increases player aggravation and presence, but does not affect enjoyment of the experience. Additionally, players that firmly believed that their opponent was controlled by the computer exhibited significantly less state hostility compared to players that were less certain of the nature of their competitor. Game designers can integrate subtle levels of cheating into computer opponents without any real negative responses from the players. The results indicate that minor levels of cheating might also increase player engagement with video games.     

A numerical model on pulsatile flow of magnetic nanoparticles as drug carrier suspended in Herschel–Bulkley fluid through an arterial stenosis under external magnetic field and body force

ABSTRACT

A theoretical model for blood flow through an artery with stenosis carrying magnetic particles in the presence of magnetic field and periodic body acceleration is analysed. In the present study, blood is assumed to be Herschel–Bulkley fluid carrying iron oxide nanoparticles. The governing equations are highly non-linear and were solved numerically. The effects of model parameters are investigated and the results are represented graphically. The shear stress at the arterial wall and resistive impedance increases with enhancing values of stenotic height, yield stress, flow behaviour index, consistency index, pulsatile Reynolds number, amplitude of body acceleration, particle concentration and particle mass parameters. In order to treat the circulation disorders, control of the parameters involved in blood flow is necessary. The present model is useful in normalizing the parameter values and hence it can be applied in the field of medicine. The study has significant applications in drug delivery for treating cancer.     

Modeling and simulating the stick–slip motion of the μWalker,a MEMS-based device for μSPAM

In this paper, the accent is on modeling the stick–slip phenomenon of micro devices, where a case shall be presented from the field of scanning probe microactuators. The case is about the μWalker, an electrostatic stepper motor which can deliver forces up to 1.7 mN and has ranges up to 140 μm. For the sake of a reliable operation, it is very important to control the stick–slip effects at the sliding surfaces. In order to introduce the stick–slip effect, a basic model of a mass, spring and sliding surface is presented, accompanied by simulation results. The total model of the device is then shown, again stressing the stick–slip phenomenon at the two sliding surfaces. Simulations from the model presented fit the measurements and can also predict step sizes as a function of varying inputs. Using a model for predictions is very attractive when looking for a way to decrease development cost and time.

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