• Macromolecular Research
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• v.17 no.7
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• pp.528-532
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• 2009

The size and shape of free volume (FV) holes available in membrane materials control the rate of gas diffusion and its permeability. Based on this principle, a segmented, thermo-sensitive polyurethane (TSPU) membrane with functional gate, i.e., the ability to sense and respond to external thermo-stimuli, was synthesized. This smart membrane exhibited close-open characteristics to the size of the FV hole and water vapor permeation and thus can be used as smart food packaging materials. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), positron annihilation lifetimes (PAL) and water vapor permeability (WVP) were used to evaluate how the morphological structure of TSPU and the temperature influence the FV holes size. In DSC and DMA studies, TSPU with a crystalline transition reversible phase showed an obvious phase-separated structure and a phase transition temperature at $53^{\circ}C$ (defined as the switch temperature and used as a functional gate). Moreover, the switch temperature ($T_s$) and the thermal-sensitivity of TSPU remained available after two or three thermal cyclic processes. The PAL study indicated that the FV hole size of TSPU is closely related to the $T_s$. When the temperature varied cyclically from $T_s-10{\circ}C$ to $T_s+10^{\circ}C$, the average radius (R) of the FV holes of the TSPU membrane also shifted cyclically from 0.23 to 0.467 nm, exhibiting an "open-close" feature. As a result, the WVP of the TSPU membrane also shifted cyclically from 4.30 to $8.58\;kg/m^2{\cdot}d$, which produced an "increase-decrease" response to the thermo-stimuli. This phase transition accompanying significant changes in the FV hole size and WVP can be used to develop "smart materials" with functional gates and controllable water vapor permeation, which support the possible applications of TSPU for food packaging.

• Polymer(Korea)
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• v.34 no.4
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• pp.326-332
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• 2010

Nanocomposite films were prepared by blending poly(amic acid)(PAA), poly(o-hydroxyamide)( PHA) and organically modified montmorillonite (OMMT) that has a layered structure. XRD, SEM and TEM were used to study the morphology of PAA/PHA nanocomposites, and DMA, TGA, UTM, LOI and PCFC techniques were used to characterize the mechanical and thermal properties, and flame retardancy of the nanocomposites. TEM images revealed that OMMT layers were well dispersed in the PAA/PHA matrix and showed exfoliation and intercalation behavior. The addition of 3 wt% OMMT to the PAA/PHA blend increased the initial modulus of PAA/ PHA blend to 3.68 GPa that was ca. 48% higher than that of the control PAA/PHA blend. Above 4 wt%, however, both the initial modulus and the tensile strength were found to decrease, which might be due to the aggregation of OMMT in PAA/PHA matrix. When the OMMT content was below 3 wt%, the thermal stability and flame retardancy of the PAA/PHA nanocomposites increased with increasing OMMT content.

• Journal of information and communication convergence engineering
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• v.15 no.1
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• pp.37-42
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• 2017

The constrained application protocol (CoAP) can be used for remotely controlling various sensor devices in Internet of Things (IoT) networks. In CoAP, to support the handover of a mobile sensor device, service discovery and message transmission needs to be repeated, although doing so would increase the handover delay significantly. To address this limitation of CoAP, a centralized CoAP scheme has been proposed. However, it tends to result in performance degradation for an inter-domain handover case. In this letter, we propose a distributed CoAP handover scheme to support the inter-domain handover. In the proposed scheme, a distributed mobility agent (DMA) is used for managing the location of mobile sensors in a domain and performing handover control operations with its neighboring DMAs in a distributed manner. A performance comparison reveals that the proposed scheme offers a performance improvement of up to 29.5% in terms of the handover delay.

• Journal of the Semiconductor & Display Technology
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• v.1 no.1
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• pp.35-40
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• 2002

Understanding of charging properties of a small particle is necessary to control the particle contamination and to improve productivity of the electronic device in the plasma aided semiconductor manufacturing processes. In this study, the effects of both magnetic field and particle size on the charging properties are experimentally investigated in collisional dusty plasmas. The experiments carried out in the system consisted of a monodisperse particle generation system, a DC magnetized plasma generation system and a charge measurement system. The plasma chamber is made of cross-shape Pyrex surrounded by magnetic bucket (composed of 12 permanent magnetic bar) to confine the plasma. DC magnetic field up to 250G are applied to the plasma zone by external magnetic coil. Previous work shows the charging effect clearly increase with increasing the size of the particle and plasma density, as it was expected.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.9A
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• pp.729-736
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• 2005

In this paper, we introduce a new approach for the design of uplink sub-channel allocation and power control in the High-speed Portable Internet system that is based on OmMAnDD scheme. In OFDMA system, because the number of allocated sub-channel in mobile station varies from one to the whole sub-channel as in base station while mobile station's transmit power is lower than that of base station, full loading range(FLR) constraint occurs where whole sub-channel can be used and the conventional open-loop power control scheme can not be used beyond FLR. We propose a new scheme that limits the maximum sub-channel allocation number and uses power concentration gain(PCG) depending on location of mobile station, which is based on ranging in OfDMA system. Simulation results show that the proposed scheme extends the uplink coverage to the entire cell service coverage area, provides solutions for optimum utilization of radio resource and enables open-loop power control beyond FLR without extra hardware complexity.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1254-1260
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• 2009

CDMA tele-Controller system is designed with a low power consumption 8 bit microcontroller, ATmega 2560. ATmega 2560 microcontroller consists of 4 UART (Universal asynchronous receiver/transmitter) ports, 4 kbytes EEPROM, 256 kbytes flash memory, 4 kbytes SRAM. 4 URAT is used for CDMA modem, communication for GPS module, EEPROM is used for saving a configuration for program running, a flash memory of 256 kbytes is used for storing a F/W(Firm Ware), and SRAM is used for stack, storing memory of global variables while program running. We have tested the communication distance between the coast station and sea by the fabricated control board using 800 MHz CDMA modem and GPS module, which is building for the navigational aid management system by remote control. As a results, the receiving signal strength is above -80 dBm, and then the characteristics of the control board implemented more than 10 km in the distance of the communication.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.11 no.2
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• pp.137-145
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• 1986

The contention resolution algorithm with the limited packet delay time as well stable distribution as the packet delay time is proposed and implementes for improving the mean packet delay time in the network employing CSMA/CD as the access method. The implementation of node controller is based on IEEE 802.2 standard logical link control(LLC) and IEEE 802.3 standard medium access control(MAC). Some portion of IEEE 802.3 Standard MAC, and the Binary Exponential Back-off(BEB) algorithm is replaced by the proposed algorithm. From the view of normalized mean packet transmission delay time, the controller implemented here can be applicable to the office-automation system, and the factory-and laboratory-automation environment where the limited time criterion is very significant.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.6
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• pp.39-46
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• 2003

In this papers, We studied system requirement specification, hardware design and implementation, protective algorithm and software design method to implement digital protective relay which has high trust and high function of protection as well as control and metering for power transformers. Protective relay for transformer is implemented on real time using DSP, which is the specific processor for digital signal processing, as a result, it is completed by the wide improvement of arithmetic capability of protective relay. Reliability is proved testing operating value and operating time, reset value and reset time of an relaying element using protective relay tester made in NF Corporation of Japan.

• Journal of the Microelectronics and Packaging Society
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• v.20 no.2
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• pp.33-38
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• 2013

In this study, both a finite element analysis and an experimental analysis are executed to investigate the mechanical characteristics of dielectric material effects on warpage. Also, viscoelastic material properties are measured by DMA and are considered in warpage simulation. A finite element analysis is done by using both thermal elastic analysis and a thermo-viscoelastic analysis to predict the nonlinear effects. For experimental study, specimens warpage of non-symmetric structure with body size of $22.5{\times}22.5$ mm, $37.5{\times}37.5$ mm and $42.5{\times}42.5$ mm are measured under the reflow temperature condition. From the analysis results, experimental warpage is not similar to FEA results using thermal elastic analysis but similar to FEA results using thermo-viscoelastic analysis. Also, its effect on substrate warpage is increased as core thickness is decreased and body size is getting larger. These FEA and the experimental results show that the nonlinear characteristics of dielectric material play an important role on substrate warpage. Therefore, it is strongly recommended that non-linear behavior characteristics of a dielectric material should be considered to control warpage of FCBGA substrate under conditions of geometry, structure and manufacturing process and so on.

• Journal of Technologic Dentistry
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• v.35 no.4
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• pp.287-293
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• 2013

Purpose: This study is to provide basic data of the dental acrylic denture base resin in the mechanical property difference investigation according to the monomer composition weight ratio of the acrylic denture base resin. Methods: The monomer composition of the acrylic denture base resin and weight ratio makes the different specimen. It measured the mechanical property with the specimens through Hardness Test, Tensile Test, Flexural Test, Flexural Modulus, FT-IR Test. Results: The control group Vertex was 18.4 Hv and the experimental group MED was 14.46~19.07Hv in the hardness test. Vertex was 364N, MED-3 was lowest in the tensile strength test and the Head of a family cursor declination was big. The result declination of the experimental specimens showed. Vertex and MED-2 was the highestest in the flexural test and after coming MED-6, MED-5, MED-1, MED-3, MED-4. Vertex and MED-2, as to a spectrum for $500{\sim}1800cm^{-1}$ peak can show the excellent degree of polymerization in the FT-IR Test. Conclusion: The ideal weight ratio of the monomer of the acrylic denture base resin of which the mechanical property is the highestest was MMA 100g, EDGMA 5g, DMA 0.2g, of MED-2.