Modelling and Simulation of a River-Crossing Operation via Discrete Event Simulation with Engineering Details

From a military standpoint, a river is an area that should be avoided in a potential engagement because of lack of cover and the necessity of dividing the unit while crossing. Thus, a key point of a river-crossing operation is speed. Many efforts have been made to enable faster river crossing by improvement of tactics, techniques, and procedures (TTP). However, improvements in TTP are evaluated by modelling and simulation much less frequently than are the toe-to-toe engagements between two opposing forces, and to our knowledge, this is the first simulation model of brigade-level river crossing with engineering details. This study presents a simulation model of the river-crossing operation, applies real world parameters, and evaluates which tactics are preferable in a particular operational environments. This analysis has led to new operational methods of river crossing that have been suggested by experienced subject-matter experts. For instance, the current Republic of Korea Army Field Manual dictates to rotate river-crossing rafts in all situations, but our experiment suggests that no rotation is preferable when the width of river is less than 400 m based on the statistical analyses, which includes the regression-based meta-modelling and the ANOVA, of our simulation model that embodies the engineering details of river-crossing equipment.Defence Science Journal, Vol. 65, No. 2, March 2015, pp.135-143, DOI:http://dx.doi.org/10.14429/dsj.65.814

Effect of pre-stroke statin use on stroke severity and early functional recovery: a retrospective cohort study

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.Abstract Background Experimental studies suggest that pre-stroke statin treatment has a dual effect of neuroprotection during ischemia and neurorestoration after ischemic injury. The aim of this study was to evaluate the effect of pre-stroke statin use on initial stroke severity and early clinical outcome. Methods We used a prospective database enrolling patients with acute ischemic stroke from 12 hospitals in Korea between April 2008 and January 2012. Primary endpoint was the initial stroke severity as measured by the National Institutes of Health Stroke Scale (NIHSS) score. Secondary endpoints were good outcome (modified Rankin Scale [mRS], 0–2) and overall mRS distribution at discharge. Multivariable regression model and propensity score (PS) matching were used for statistical analyses. Results Among the 8340 patients included in this study, 964 patients (11.6 %) were pre-stroke statin users. The initial NIHSS score (mean [95 % CI]) was lower among pre-stroke statin users vs. non-users in multivariable analysis (5.7 [5.2–6.3] versus 6.4 [5.9–6.9], p = 0.002) and PS analysis (5.2 [4.7–5.7] versus 5.7 [5.4–6.0], p = 0.043). Pre-stroke statin use was associated with increased achievement of mRS 0–2 outcome (multivariable analysis: OR [95 % CI], 1.55 [1.25–1.92], p < 0.001; PS matching: OR [95 % CI], 1.47 [1.16-1.88]; p = 0.002) and favorable shift on the overall mRS distribution (multivariable analysis: OR [95 % CI], 1.29 [1.12-1.51], p = 0.001; PS matching: OR [95 % CI], 1.31 [1.11-1.54]; p = 0.001). Conclusions Pre-stroke statin use was independently associated with lesser stroke severity at presentation and better early functional recovery in patients with acute ischemic stroke

Machine capacity allocation strategies for scheduling a large multi-chip assembly line

A multi-chip package (MCP) consists of several chip modules in a single package. We consider a scheduling problem for assembling MCPs. In order to assemble an MCP, a lot should repeat assembly process stages such as die attach and wire bonding as many as the number of chips to be assembled. The two key process stages have many parallel machines of various types. A machine processes different types of MCP lots with significant setup times. We therefore should reduce the number of setups effectively while not sacrificing the on-time delivery performance significantly. We propose a scheduling strategy that first allocates the machine capacity of many parallel machines to product groups and lots depending on their production progresses appropriately and then applies known dispatching rules. We report experimental performances of the proposed methods. [Received: 21 June 2009; Revised: 03 December 2009; Accepted: 01 February 2010]multi-chip packages; MCP; machine capacity allocation; unrelated parallel machines; on-time delivery; OTD; setups; parallel machine scheduling; multi-chip assembly lines.

MINIMIZING TOTAL TARDINESS ON PARALLEL MACHINES SUBJECT TO FLEXBLE MAINTENANCE

We consider a scheduling problem on parallel machines for the objective of minimizing total tardiness. Each of the machines needs preventive maintenance tasks that should be started within a given cumulative working time limit after the previous maintenance. The starting time of a maintenance task is not fixed but flexible; that is, a maintenance task can be started at any time unless the cumulative working time after the end of the previous maintenance exceeds the given limit. We develop dominance properties and lower bounds for the problem, and present a branch and bound algorithm using these. Computational tests on 3600 randomly-generated instances are performed to evaluate the branch and bound algorithm, and the results show that the algorithm finds optimal solutions for problems with up to 20 jobs

A three-level supply chain network design model with risk-pooling and lead times

This paper considers a single-sourcing network design problem for a three-level supply chain consisting of suppliers, distribution centers (DC's) and retailers, where risk-pooling strategy and DC-to-supplier dependent lead times are considered. The objective is to determine the number and locations of suppliers and DC's, the assignment of each location-fixed DC to a supplier and that of each retailer to a DC, which minimizes the system-wide location, transportation, and inventory costs. The problem is formulated as a nonlinear integer programming model, for which a two-phase heuristic solution algorithm is derived based on the Lagrangian relaxation approach. Numerical experiments show that the proposed heuristic is effective and also efficient.Location-inventory model Risk-pooling Lead time Lagrangian relaxation Supply chain management