Effect of polycyclopentene on crystallization of isotactic polypropylene

The application of some polymers as nucleating agents for polypropylene has been examined. Among various polymeric nucleating agents, polycyclopentene was found to be a superior nucleating agent to typical organic nucleating agents. When polycyclopentene was added to polypropylene, the crystallization temperature and the degree of crystallinity of polypropylene increased. In addition, the crystallization rate and the number of spherulites increased whereas the size of spherulites decreased remarkably. As a result of polycyclopentene addition, the transparency of polypropylene film could be improved considerably. © 1994 John Wiley & Sons, Inc.     

A two-stage heuristic for single machine capacitated lot-sizing and scheduling with sequence-dependent setup costs

This paper considers a single machine capacitated lot-sizing and scheduling problem. The problem is to determine the lot sizes and the sequence of lots while satisfying the demand requirements and the machine capacity in each period of a planning horizon. In particular, we consider sequence-dependent setup costs that depend on the type of the lot just completed and on the lot to be processed. The setup state preservation, i.e., the setup state at the end of a period is carried over to the next period, is also considered. The objective is to minimize the sum of setup and inventory holding costs over the planning horizon. Due to the complexity of the problem, we suggest a two-stage heuristic in which an initial solution is obtained and then it is improved using a backward and forward improvement method that incorporates various priority rules to select the items to be moved. Computational tests were done on randomly generated test instances and the results show that the two-stage heuristic outperforms the best existing algorithm significantly. Also, the heuristics with better priority rule combinations were used to solve case instances and much improvement is reported over the conventional method as well as the best existing algorithm.     

Effect of deposition temperature on the structural and thermoelectric properties of bismuth telluride thin films grown by co-sputtering

Thermoelectric bismuth telluride thin films were prepared on SiO₂/Si substrates by radio-frequency (RF) magnetron sputtering. Co-sputtering method with Bi and Te targets was adopted to control films' composition. Bi_xTe_y thin films were elaborated at various deposition temperatures with fixed RF powers, which yielded the stoichiometric Bi₂Te₃ film deposition without intentional substrate heating. The effects of deposition temperature on surface morphology, crystallinity and electrical transport properties were investigated. Hexagonal crystallites were clearly visible at the surface of films deposited above 290 °C. Change of dominant phase from rhombohedral Bi₂Te₃ to hexagonal BiTe was confirmed with X-ray diffraction analyses. Seebeck coefficients of all samples have negative value, indicating the prepared Bi_xTe_y films are n-type conduction. Optimum of Seebeck coefficient and power factor were obtained at the deposition temperature of 225 °C (about − 55 μV/K and 3 × 10^− 4 W/K²·m, respectively). Deterioration of thermoelectric properties at higher temperature could be explained with Te deficiency and resultant BiTe phase evolution due to the evaporation of Te elements from the film surface.     

Enhanced soft-handoff scheme for real-time streaming services in intelligent transportation systems based on CDMA

Code division multiple access (CDMA)-based radio-on-fiber road-vehicle communication systems were proposed to support real-time streaming services in intelligent transportation systems (ITSs). Soft handoff should be provided for real-time streaming services because these services are required to guarantee real-time property and quality of service (QoS). However, soft handoff of real-time streaming services causes the shortage of resource in view of the system. In this paper, the double-adjustment soft-handoff (DASH) scheme is proposed to support seamless service regardless of the shortage of resource and maximize the resource efficiency when real-time streaming services are served in CDMA-based ITSs. The DASH scheme adjusts the data rate of a call when it starts and finishes soft handoff. The performance of the DASH scheme is evaluated by analytical and simulation methods. Performances are evaluated with respect to the blocking probability, the handoff failure probability, and the carried traffic. Numerical results show that the proposed scheme can give relative good maintenance of calls and good throughput.     

Performance Analysis on Coexistence of EDCA and Legacy DCF Stations in IEEE 802.11 Wireless LANs

The distributed coordination function (DCF) scheme of IEEE 802.11 MAC protocol does not support any concepts of quality of service (QoS) but the enhanced distributed channel access (EDCA) scheme in IEEE 802.11e standard provides QoS according to access categories using different access parameters. However, the legacy DCF stations may be used together with EDCA stations. In this letter, we investigate and analyze the performance discrimination when EDCA and DCF stations operate simultaneously     

Performance evaluation of soft handoff for multimedia services in intelligent transportation systems based on CDMA

To support multimedia services in intelligent transportation systems (ITS), CDMA based radio-on-fiber road-vehicle communication systems were proposed. Soft handoff should be provided for multimedia services because these services are required to guarantee real-time property and quality of service (QoS). The performance evaluation of soft handoff is important in view of system management such as determination of optimal resource allocation, cell configuration, and admission strategy. But, the performance evaluation of soft handoff when multimedia services are serviced has not been previously researched, even though there have been some previous works for voice-call service. In this paper, we develop a new analytical model of soft handoff when multimedia services are served in CDMA based ITS. We evaluate the performance of soft handoff scheme by analytical and simulational method. Blocking probability, handoff failure probability and carried traffic are obtained.     

Disassembly leveling and lot sizing for multiple product types: a basic model and its extension

We consider two interrelated problems that occurred in disassembly systems: disassembly leveling and lot sizing. Disassembly leveling, one of disassembly process planning decisions, is to determine disassembly structures that specify parts and/or subassemblies to be obtained from disassembling used/end-of-life products, and disassembly lot sizing is the problem of determining the amounts of disassembly operations required to satisfy the demands of their parts and/or subassemblies. Unlike the existing studies, this study considers the two problems at the same time for the objective of minimizing the sum of disassembly setup and operation costs. In particular, we consider a generalized version in which disassembly levels may be different even for products of the same type. Two types of the problem are considered in this study. The first one is the basic problem without parts commonality, i.e., products do not share their parts or subassemblies, for which a polynomial time optimal algorithm is suggested after developing a mathematical programming model. The second one is an extended problem with parts commonality. After developing another mathematical programming model for the extension, we prove that it is NP hard. Then, a heuristic algorithm is suggested together with its computational results.     

Exposure assessment of caffeine in children’s snacks in Korea

This study was conducted to develop an appropriate management strategy for the safe consumption of children’s snacks. In this study, a caffeine content analysis was performed on children’s snacks which were distributed at stores located near to schools. A total of 213 samples (63 chocolates, 40 ice cakes, 19 canned instant coffees, and 91 beverages) were analyzed for caffeine content. The caffeine content of chocolates, ice cakes, canned instant coffees, and beverages was 94.30, 35.03, 391.78, and 68.32 mg/kg, respectively. The results of the exposure assessment for caffeine were expressed as estimated daily intake (EDI) compared to the acceptable daily intake (ADI). The EDI/ADI ratio of the high risk group (95^th percentile) for caffeine intake was 7.63–27.13 %. The results of this study indicate that the EDI of caffeine from snacks sold at stores located near to schools is much lower than the ADI in general. Consequently, children’s snacks are thought to be safe for consumption.     

Ground effects for VHF/HF antennas on helicopter airframes

In this paper, the finite element method (FEM) is used to predict the space and surface wave radiation patterns of VHF/HF antennas mounted on a helicopter in the presence of a lossy ground. The equivalent sources of the radiation system are obtained by solving an FEM problem in conjunction with an absorbing boundary condition (ABC) or an impedance boundary condition (IBC). From the equivalent sources, the total radiated field is calculated using the equivalence principle and superposition; the original problem is converted into a set of properly combined Hertzian dipoles referred to as the Sommerfeld problem. Instead of evaluating the Sommerfeld integral rigorously, Norton's approximation is used to improve the overall computational efficiency. The validation of this method is accomplished in two steps: first, the FEM is compared with the finite-difference time-domain method (FDTD) in the absence of a lossy ground; second, the Hertzian dipole problem is solved in the presence of a lossy ground and the results are compared with analytic solutions. Finally, this technique is extended to analyze an antenna on a helicopter above a lossy ground