• Journal of the Korean Operations Research and Management Science Society
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• v.41 no.3
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• pp.75-96
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• 2016

This paper investigates the usefulness of drones in an urban delivery system. We define the vehicle and drone routing problem with time window (VDRPTW) and present a model that can describe a dual mode delivery system consisting of drones and vehicles in the metropolitan area. Drones are relatively free from traffic congestion but have limited flight range and capacity. Vehicles are not free from traffic congestion, and the complexity of urban road network reduces the efficiency of vehicles. Using drones and vehicles together can reduce inefficiency of the urban delivery system because of their complementary cooperation. In this paper, we assume that drones operate in a point-to-point manner between the depot and customers, and that customers in the need of fast delivery are willing to pay additional charges. For the experiment datasets, we use instances of Solomon (1987), which are well known in the Vehicle Routing Problem society. Moreover, to mirror the urban logistics demand trend, customers who want fast delivery are added to the Solomon's instances. We propose a hybrid evolutionary algorithm for solving VDRPTW. The experiment results provide different useful insights according to the geographical distributions of customers. In the instances where customers are randomly located and in instances where some customers are randomly located while others form some clusters, the dual mode delivery system displays lower total cost and higher customer satisfaction. In instances with clustered customers, the dual mode delivery system exhibits narrow competition for the total cost with the delivery system that uses only vehicles. In this case, using drones and vehicles together can reduce the level of dissatisfaction of customers who take their cargo over the time-window. From the view point of strategic flexibility, the dual mode delivery system appears to be more interesting. In meeting the objective of maximizing customer satisfaction, the use of drones and vehicles incurs less cost and requires fewer resources.

• Journal of KIISE:Software and Applications
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• v.32 no.8
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• pp.819-833
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• 2005

Code size reduction is ever becoming more important for compilers targeting embedded processors because these processors are often severely limited by storage constraints and thus the reduced code size can have a positively significant Impact on their performance. Various code size reduction techniques have different motivations and a variety of application contexts utilizing special hardware features of their target processors. In this work, we propose a novel technique that fully utilizes a set of hardware instructions, called the multiple load/store (MLS), that are specially featured for reducing code size by minimizing the number of memory operations in the code. To take advantage of this feature, many microprocessors support the MLS instructions, whereas no existing compilers fully exploit the potential benefit of these instructions but only use them for some limited cases. This is mainly because optimizing memory accesses with MLS instructions for general cases is an NP-hard problem that necessitates complex assignments of registers and memory off-sets for variables in a stack frame. Our technique uses a couple of heuristics to efficiently handle this problem in a polynomial time bound.

• Journal of Communications and Networks
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• v.8 no.1
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• pp.70-84
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• 2006

We propose a new distributed QoS routing scheme called pre-computation based selective probing (PCSP). The PCSP scheme is designed to provide an exact solution to the constrained optimization problem with moderate overhead, considering the practical environment where the state information available for the routing decision is not exact. It does not limit the number of probe messages, instead, employs a qualitative (or conditional) selective probing approach. It considers both the cost and QoS metrics of the least-cost and the best-QoS paths to calculate the end-to-end cost of the found feasible paths and find QoS-satisfying least-cost paths. It defines strict probing condition that excludes not only the non-feasible paths but also the non-optimal paths. It additionally pre-computes the QoS variation taking into account the impreciseness of the state information and applies two modified QoS-satisfying conditions to the selection rules. This strict probing condition and carefully designed probing approaches enable to strictly limit the set of neighbor nodes involved in the probing process, thereby reducing the message overhead without sacrificing the optimal properties. However, the PCSP scheme may suffer from high message overhead due to its conservative search process in the worst case. In order to bound such message overhead, we extend the PCSP algorithm by applying additional quantitative heuristics. Computer simulations reveal that the PCSP scheme reduces message overhead and possesses ideal success ratio with guaranteed optimal search. In addition, the quantitative extensions of the PCSP scheme turn out to bound the worst-case message overhead with slight performance degradation.

• Journal of The Korean Digital Architecture Interior Association
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• v.11 no.3
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• pp.53-59
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• 2011

In creative design, it is necessary to understand the characteristic of architectural design. In the world of design problem, a distinction can be made between those that are well-defined and those that are ill-defined. Well-defined problems are those for which the ends or goal, are already prescribed and apparent, their solution requires the provision of appropriate means. For ill-defined problems, on the other hand, both the ends and the means of solution are unknown at the outset of the problem solving exercise, at least in their entirety. Most of design problems is ill-defined, which is unknown at the beginning of the problem solving exercise. In order to solve the design problem, Designers take advantage of the search methods of problem space, such as global-search-methods(depth-first-methods, breath-first-methods), local-search-methods(generate and test, heuristics, hill-climbing, reasoning) and visual thinking, which is represented through sketching. Sketching is a real part of design reasoning and it does so through a special kind of visual imagery. Also in the design problem solving it have been an important means of problem exploration and solution generation. By sketching, they represent images held in the mind as well as makes graphic images which help generate mental images of entity that is being designed. The search methods of problem space and a visual thinking have been crucially considered in the architectural design. The purpose of this paper is to explore the property of design by means of the pre-existed-experiment data and literature research. The findings will help design the architectural design for more creative results.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.29 no.1
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• pp.413-421
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• 2005

Intra-block remarshalling is the task of rearranging into some target bays those containers which are scattered within around the block. If multiple transfer cranes installed in the block are all used together we may be able to complete the remarshalling task as early as possible. However, when multiple cranes are used simultaneously, there may occur significant delays if we do not carefully consider interferences between the cranes at the time of scheduling. Especially, delays caused by interferences occur more frequently in case of using non-crossing cranes. This paper presents an efficient heuristics method for assigning moves of containers to each crane and for determining an appropriate container moving order in a manner sensitive to the interferences. Simulation experiments have shown that the proposed method can effectively reduce delays in various environments.

• The KIPS Transactions:PartC
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• v.11C no.5
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• pp.677-682
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• 2004

In the present paper routing and wavelength assignment (RWA) in optical WDM networks is considered. Previous techniques based on the combination of integer linear programming and graph coloring are complex and require extensive use of heuristics. Such methods are mostly slow and sometimes impossible to get results due to infeasibility. An alternative approach applied to RWA employs on the greedy algorithm for obtaining the maximum edge disjoint paths. Even though this approach is fast, it produces a solution for any connection request, which is very far from the optimal utilization of wavelengths. We propose a novel algorithm, which is based on the maximum flow technique to obtain the maximum quantity of edge, disjoint paths. Here we compare the offered method with previous maximum edge disjoint paths algorithms ap plied to the RWA.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.5C
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• pp.519-533
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• 2006

The number of channels specified in IEEE 802.15.4 Low-Rate Wireless Personal Area Networks(LRWPANs) is too few to operate many applications of WPANs in the same area. To overcome this limit, we introduce Virtual Channel, a novel concept to increase the number of available channels when various WPAN applications coexist. Basically, a virtual channel is a newly-created channel via superframe scheduling within the inactive period of a logical channel preoccupied by other WPANs. To maximize the coexistence capability of WPANs using virtual channels, we propose Least Collision superframe scheduler(LC-scheduler), its less complex heuristics both for a given single channel, and Virtual Channel Selector(VCS) to efficiently manage multiple available logical channels. In addition, a simple but practical synchronization method is developed to compensate different time drifts among coexisting WPANs. The simulation results demonstrate that a remarkable improvement on the coexistence capability of the 802.15.4 can be achieved through the proposed schemes.

• Journal of the Korean Institute of Intelligent Systems
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• v.16 no.1
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• pp.1-7
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• 2006

In this paper, adaptive Facial Emotional Recognition system based on Gabor Wavelet Neural Network, considering six feature Points in face image to extract specific features of facial expression, is proposed. Levenberg-Marquardt-based training methodology is used to formulate initial network, including feature extraction stage. Therefore, heuristics in determining feature extraction process can be excluded. Moreover, to make an adaptive network for new user, Q-learning which has enhanced reward function and unsupervised fuzzy neural network model are used. Q-learning enables the system to ge optimal Gabor filters' sets which are capable of obtaining separable features, and Fuzzy Neural Network enables it to adapt to the user's change. Therefore, proposed system has a good on-line adaptation capability, meaning that it can trace the change of user's face continuously.

• Journal of Institute of Control, Robotics and Systems
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• v.3 no.5
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• pp.542-554
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• 1997

In this paper, we present a resource conscious approach to designing distributed real-time systems as an extension of our original approach [8][9] which was limited to single processor systems. Starting from a given task graph and a set of end-to-end constraints, we automatically generate task attributes (e.g., periods and deadlines) such that (i) the task set is schedulable, and (ii) the end-to-end timing constraints are satisfied. The method works by first transforming the end-to-end timing constraints into a set of intermediate constraints on task attributes, and then solving the intermediate constraints. The complexity of constraint solving is tackled by reducing the problem into relatively tractable parts, and then solving each sub-problem using heuristics to enhance schedulability. In this paper, we build on our single processor solution and show how it can be extended for distributed systems. The extension to distributed systems reveals many interesting sub-problems, solutions to which are presented in this paper. The main challenges arise from end-to-end propagation delay constraints, and therefore this paper focuses on our solutions for such constraints. We begin with extending our communication scheme to provide tight delay bounds across a network, while hiding the low-level details of network communication. We also develop an algorithm to decompose end-to-end bounds into local bounds on each processor of making extensive use of relative load on each processor. This results in significant decoupling of constraints on each processor, without losing its capability to find a schedulable solution. Finally, we show, how each of these parts fit into our overall methodology, using our previous results for single processor systems.

• Journal of Korea Spatial Information System Society
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• v.9 no.2
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• pp.25-34
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• 2007

Existing approaches that select an order for the join of three or more data streams have always used the simple heuristics. For their disadvantage - only one factor is considered and that is join selectivity or arrival rate, these methods lead to poor performance and inefficiency In some applications. The graph-based sliding window multi -join algorithm with optimal join sequence is proposed in this paper. In this method, sliding window join graph is set up primarily, in which a vertex represents a join operator and an edge indicates the join relationship among sliding windows, also the vertex weight and the edge weight represent the cost of join and the reciprocity of join operators respectively. Then the optimal join order can be found in the graph by using improved MVP algorithm. The final result can be produced by executing the join plan with the nested loop join procedure, The advantages of our algorithm are proved by the performance comparison with existing join algorithms.