• Membrane Journal
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• v.8 no.3
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• pp.148-156
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• 1998

Diffusion dialysis is a membrane process driven by concentration difference using ion-exchange membranes and has been employed for many years for the acid recovery from acidic waste generated in steel, metal-refining and dectro-plating industries. Theoretically acid flux increases in propomon to the acid concentration difference. At acid concentrations higher than 3 N HCl, however, the acid flux had not increased linearly with the concentration difference. In this paper the effects of acid concentrations on diffusion dialysis for hydrochloric acid recovery and the acid transport mechanism in an anion exchange membrane were studied by membrane sorption tests and diffusion clialysis cell tests. The experimental results showed that the molecular diffusion was a major transport mechanism in a low acid concentration range and the proton leakage through an anion exchange membrane played an important role at higher acid concentrations. Also osmotic water transport and membrane dehydration retarded the transport of protons and caused the permeate flux to decrease.

• Journal of the Korea Society of Computer and Information
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• v.17 no.9
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• pp.91-101
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• 2012

Key exchange protocols are essential for building a secure communication channel over an insecure open network. In particular, password-based key exchange protocols are designed to work when user authentication is done via the use of passwords. But, passwords are easy for human beings to remember, but are low entropy and thus are subject to dictionary attacks. Recently, Zhao and Gu proposed a new server-aided protocol for password-based key exchange. Zhao and Gu's protocol was claimed to be provably secure in a formal adversarial model which captures the notion of leakage of ephemeral secret keys. In this paper, we mount a replay attack on Zhao and Gu's protocol and thereby show that unlike the claim of provable security, the protocol is not secure against leakage of ephemeral secret keys. Our result implies that Zhao and Gu's proof of security for the protocol is invalid.

• The KSFM Journal of Fluid Machinery
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• v.16 no.6
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• pp.19-25
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• 2013

The effect of tip gap height on heat/mass transfer characteristics on the floor of cavity squealer tip has been investigated in a turbine cascade for power generation by employing the naphthalene sublimation technique. The squealer rim height is chosen to be an optimal one of $h_{st}/c$ = 5.51% for the tip gap height-to-chord ratios of h/c = 1.0, 2.0, 3.0 and 4.0%. The results show that heat transfer on the cavity floor is strongly dependent upon the behavior of the cavity flow falling down onto the floor. For lower h/c, the floor heat transfer is influenced by the tip leakage flow falling down along the inner face of the suction-side squealer, whereas the floor heat transfer for higher h/c is augmented mainly due to the impingement of leakage flow on the floor near the leading edge. Compared to the plane tip surface heat transfer, the cavity floor heat transfer is less influenced by h/c. For h/c = 1.0%, the average thermal load is as low as a half of the plane tip surface one, and the difference in the thermal load between the two cases tends to decrease with increasing h/c.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.6 s.348
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• pp.18-22
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• 2006

The inspection of surface properties under n-octadecyltrichlorosilane treated $SiO_2$ film was carried out by current-voltage characteristic and the scanning electron microscope. The voltage at zero current in low electric field is the lowest at 0.3 % OTS treated $SiO_2$ film with hybrid type. $SiO_2$ films changed from inorganic to hybrid or organic properties according to the increase of OTS content. OTS treated $SiO_2$ films with hybrid properties decreased the leakage currents, and the grain size of pentacene deposited sample was also the most small at the hybrid properties. The perpendicular generation of pentacene molecular was related with the surface of insulators. The surface with hybrid properties decreased the grain size, but that with inorganic or organic properties increased the grain size.

• Journal of the Korean GEO-environmental Society
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• v.17 no.8
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• pp.29-37
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• 2016

In order to prevent leakage of contaminants in offshore landfill, vertical barrier should be installed. Vertical barrier should be installed at designed depth of seabed to prevent the horizontal transport of contaminant in the subsurface. In this study, the seepage and contaminant transport in the subsurface according to embedded depth of vertical barrier were analyzed by using 2-D finite element analysis program SEEP/W and 3-D finite difference analysis program Visual Modflow. Numerical modelling results show that seepage flux and contaminant transport in seabed was greatly reduced when vertical barrier was installed at certain depth of low permeable layer. Therefore, the determination of minimum embedded depth for preventing contaminant leakage is helpful to design the economical vertical barrier.

• Journal of Power Electronics
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• v.16 no.3
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• pp.1226-1235
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• 2016

For wearable health monitoring systems, a fundamental problem is the limited space for storing energy, which can be translated into a short operational life. In this paper, a highly efficient active voltage doubling rectifier with a wide input range for micro-piezoelectric energy harvesting systems is proposed. To obtain a higher output voltage, the Dickson charge pump topology is chosen in this design. By replacing the passive diodes with unbalanced-biased comparator-controlled active counterparts, the proposed rectifier minimizes the voltage losses along the conduction path and solves the reverse leakage problem caused by conventional comparator-controlled active diodes. To improve the rectifier input voltage sensitivity and decrease the minimum operational input voltage, two low power common-gate comparators are introduced in the proposed design. To keep the comparator from oscillating, a positive feedback loop formed by the capacitor C is added to it. Based on the SMIC 0.18-μm standard CMOS process, the proposed rectifier is simulated and implemented. The area of the whole chip is 0.91×0.97 mm², while the rectifier core occupies only 13% of this area. The measured results show that the proposed rectifier can operate properly with input amplitudes ranging from 0.2 to 1.0V and with frequencies ranging from 20 to 3000 Hz. The proposed rectifier can achieve a 92.5% power conversion efficiency (PCE) with input amplitudes equal to 0.6 V at 200 Hz. The voltage conversion efficiency (VCE) is around 93% for input amplitudes greater than 0.3 V and load resistances larger than 20kΩ.

• Journal of Soil and Groundwater Environment
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• v.18 no.6
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• pp.48-55
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• 2013

This study aimed at characterizing unsaturated zone at the source zone area contaminated by DNAPL and investigating feasibility of soil vapor extraction (SVE). Five boreholes with three multi-level screens at the depth of 3.0~4.5 m, 5.5~7.0 m, and 8.0~12.0 m were installed at the source zone. Pneumatic tests were performed to determine the permeability of porous medium. Permeability was estimated to be 81.6 to 203.7 darcy, depending on the applied solutions, which was contradicted by grain size analysis of cored soil samples leading to 3.51 darcy. This is due to air flow through gravel pack during the early stage of pneumatic test. Pressure-drawdown curve in the late stage also well showed the leaky aquifer type, indicating air leakage to the ground. Air flow tests were also carried out to investigate air flow connectivity between multi-level wells, indicating that the horizontal air flow was well developed between the lower screens of the wells, not between the upper and middle screens due to the leakage to the surface. For the SVE test, there was no noticeable variation in TCE vapor concentration between three different test runs: 1. 8 hours daily for 5 days, 2. 24 hours together with air blowing at another well (BH1), 3. five consecutive days. Even for five-day consecutive test, total amount of removed TCE was estimated only to be as low as 46.5 g.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.5 s.248
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• pp.446-456
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• 2006

The effect of relative position of the stationary turbine blade for the fixed vane has been investigated on blade tip and shroud heat transfer. The local mass transfer coefficients were measured on the tip and shroud fur the blade fixed at six different positions within a pitch. A low speed stationary annular cascade with a single turbine stage was used. The chord length of the tested blade is 150 mm and the mean tip clearance of the blade having flat tip is 2.5% of the blade chord. A naphthalene sublimation technique was used for the detailed mass transfer measurements on the tip and the shroud. The inlet flow Reynolds number based on chord length and incoming flow velocity is fixed to $1.5{\times}10^5$. The results show that the incoming flow condition and heat transfer characteristics significantly change when the relative position of the blade changes. On the tip, the size of high heat/mass transfer region along the pressure side varies in the axial direction and the difference of heat transfer coefficient is up to 40% in the upstream region of the tip because the position of flow reattachment changes. On shroud, the effect of tip leakage vortex on the shroud as well as tip gap entering flow changes as the blade position changes. Thus, significantly different heat transfer patterns are observed with various blade positions and the periodic variation of heat transfer is expected with the blade rotation.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.5
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• pp.55-62
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• 2019

In this paper, we consider K-user multiple-input multiple-output (MIMO) interference channel and present a transceiver design for simultaneous wireless information and power transfer (SWIPT) systems. In addition, we consider a SWIPT system where an information decoding receiver and an energy harvesting receiver are co-located at the same receiver. In the proposed scheme, signal-to-leakage plus noise ratio (SLNR) is used as a cost function and a transceiver is designed to satisfy the threshold of the harvested energy. More specifically, transmitter precoding vector, receiver filter vector, and power spitting factor are simultaneously designed to maximize SLNR with a constraint on the harvested energy. Through computer simulation, we compare the signal-to-interference plus noise ratio (SINR) performance of the proposed and conventional schemes. When a special condition among the number of transmit antennas, receive antennas, and users is satisfied, the proposed scheme showed better SINR performance than the conventional scheme at low signal-to-noise ratio (SNR) range. Also, when the condition is not satisfied, the proposed scheme showed better performance than the conventional scheme at all SNR range.

• Korean Journal of Materials Research
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• v.29 no.8
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• pp.463-468
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• 2019

The electrical and interfacial properties of $HfO_2/Al_2O_3$ and $Al_2O_3/HfO_2$ dielectrics on AlN/p-Ge interface prepared by thermal atomic layer deposition are investigated by capacitance-voltage(C-V) and current-voltage(I-V) measurements. In the C-V measurements, humps related to mid-gap states are observed when the ac frequency is below 100 kHz, revealing lower mid-gap states for the $HfO_2/Al_2O_3$ sample. Higher frequency dispersion in the inversion region is observed for the $Al_2O_3/HfO_2$ sample, indicating the presence of slow interface states A higher interface trap density calculated from the high-low frequency method is observed for the $Al_2O_3/HfO_2$ sample. The parallel conductance method, applied to the accumulation region, shows border traps at 0.3~0.32 eV for the $Al_2O_3/HfO_2$ sample, which are not observed for the $Al_2O_3/HfO_2$ sample. I-V measurements show a reduction of leakage current of about three orders of magnitude for the $HfO_2/Al_2O_3$ sample. Using the Fowler-Nordheim emission, the barrier height is calculated and found to be about 1.08 eV for the $HfO_2/Al_2O_3$ sample. Based on these results, it is suggested that $HfO_2/Al_2O_3$ is a better dielectric stack than $Al_2O_3/HfO_2$ on AlN/p-Ge interface.