A Simple and Enriched Closed-Form Formula for Cell Residence Time in 5G Heterogeneous Networks

Wireless Personal Communications - Libraries may become a liability for users security. Existing studies show that libraries can be exploited to propagate malware. Hackers utilize fake or modified...     

Heuristics for assembly operation scheduling problem in flexible assembly systems

In this paper we address the problem of scheduling n assembly operations with in-tree constraints on m unrelated parallel workstations in flexible assembly systems, which we call the assembly operation scheduling problem (AOSP). No preemption of assembly operations is allowed and the primary objective is to minimize the maximum completion time. This problem is equivalent to R|tree|C_max. For this notorious NP-hard problem, four heuristic algorithms including decomposition (DECOMP), earliest completion time (ECT), shortest processing time (SPT), and earliest starting time(EST) heuristic are proposed and their performances are comparatively investigated. DECOMP uses a decomposition technique to practically solve this problem. The assembly operation tree is decomposed and then AOSP is reduced to a set of subproblems of R||C_max and R,r_j|r_i|C_max. Two efficient heuristics were proposed for the reduced subproblems. The other three heuristics basically use the machine selection rules to determine the machine for processing the current operation. Of these heuristics, DECOMP showed the best performance in terms of quality of schedule. Computational results show that all the proposed algorithms except the EST heuristic perform quite well in terms of both quality of solution and computation time.     

Numerical simulation and prediction of polymer flammability in non-standard conditions

Fire safety of plastics is commonly characterized in terms of Oxygen Index (OI), or the limit oxygen concentration in oxidizing atmosphere that supports combustion. OI is determined in normal conditions (atmospheric pressure, room temperature, etc.) according to the procedure prescribing the ambient conditions, number of samples, their dimensions. However, polymer materials and products where they are used meet the variety of ambient conditions; low and high temperatures, pressures, flow velocities, accelerations, and etc. The methods of prediction of polymer flammability and OI in the wide range of operating conditions have not been available until now. In this study, a mathematical model is worked out and the theory of limits of polymer combustion is developed to predict OI and other critical values in non-standard conditions; pressure 0.1–100 atm; initial temperature of polymer 250–550 K; gravity force acceleration 0.1–50 g; velocity of oxidizing O₂/N₂ stream 0–50 m/sec; different thickness of polymer layers covering the cold base and their simultaneous action. The model involves two-dimensional numerical simulation of the diffusion combustion of a polymer in the presence of heat losses. The main factor to be taken into account is the decrease of flame temperature due to the cooling effect of different agents. Therefore, the extinction criterion and OI are expressed in terms of the relationship between Damköhler and Peclet numbers. Two critical conditions, observed earlier in the experiments on polymer extinction limits, are explained. The predictions of the model were tested for PMMA and were found to be in good agreement with experimental data available.     

Modeling investment priorities for national road improvements: A case study of Korea

The paper addresses specific problems associated with formulating investment priorities for national road improvements in Korea. More specifically, the objectives of the paper are (1) to present a model for formulating investment priorities for road improvements that may be useful to developing countries, (2) to test the model with simplified data for deriving investment priorities for Korea's road improvements, and (3) to learn lessons that can be applicable to other developing countries with particular respect to recommending investment priorities for road improvements. The study results are useful for planners, in developing countries, and also for evaluation analysts in funding institutions who are confronted with evaluating investment priorities for deteriorating road conditions.     

Low digestion property of amylosucrase-modified waxy adlay starch

Structural and digestion properties of amylosucrase-modified waxy adlay starch were investigated. The unique reaction of amylosucrase caused a decrease and an increase in the proportion of short chains and long chains, respectively, via attachment of glucosyl units to the non-reducing ends of branch chains. The in vitro digestion profile of amylosucrase-modified starch revealed that elongated branch chains were the main reason for high contents of slowly digestible and resistant starches due to formation of a more perfect crystalline structure via easy association between elongated branch chains. The glucose response in mice after consumption of amylosucrase-modified starch was similar to the response for commercial resistant starch with a gradual increase followed by a gradual decrease in blood glucose concentrations over a prolonged time. Both in vitro and in vivo tests were used to verify increased resistance to digestive enzymes caused by amylosucrase modification.     

Controllability for Semilinear Retarded Control Systems in Hilbert Spaces

This paper deals with well-posedness and L ²-regularity properties for a class of semilinear retarded functional differential equations. A relation between the reachable set of a semilinear system and that of the corresponding linear system is proved. We also show that the Lipschitz continuity and the uniform boundedness of the nonlinear term can be considerably weakened. Finally, a simple example is given, to which our main result can be applied. This work was supported by the Brain Korea 21 Project in 2006.