• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.57-58
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• 2015

In this study, we present geometrical and kinematical analysis of Moreton wave observed in 2012 June 3rd and July 6th, recorded in H-${\alpha}$ images of Global Oscillation Network Group (GONG) archive. These large-scale waves exhibit different features compared to each other. The observed wave of June 3rd has angular span of about $70^{\circ}$ with a diffuse wave front associated to NOAA active region 11496. It was found that the propagating speed of the wave at 17:53 UT is about $931{\pm}80km/s$. The broadness nature of this Moreton wave can be interpreted as the vertical extension of the wave over the chromosphere. On the other hand, the wave of July 6th associated with X1.1 class are that occurred at 23:01 UT in AR NOAA11515. From the kinematical analysis, the wave propagated with the initial velocity of about $994{\pm}70km/s$ which is in agreement with the speed of coronal shock derived from type II radio burst, v ~ 1100 km/s. These two identified waves add the inventory of the large-scale waves observed in 24th Solar Cycle.

• Journal of The Korean Astronomical Society
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• v.35 no.3
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• pp.151-157
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• 2002

From the data of solar wind observation by ACE spacecraft orbiting the Earth-Sun Lagrangian point, we selected 48 forward interplanetary shocks(IPSs) occurred in 2000, maximum solar activity period. Examining the profiles of solar wind parameters, the IPSs are classified by their shock drivers. The significant shock drivers are the interplanetary coronal mass ejection(ICME) and the high speed stream(HSS). The IPSs driven by the ICMEs are classified into shocks driven by magnetic clouds and by ejectas based on the existence of magnetic flux rope structure and magnetic field strength. Some IPSs could be formed as the blast wave by the smaller energy and shorter duration of shock drivers such as type II radio burst. Out of selected 48 forward IPSs, $56.2\%$ of the IPSs are driven by ICME, $16.7\%$ by HSS, and $16.7\%$ of the shocks are classified into blast-wave type shocks. However, the shock drivers of remaining $10\%$ of the IPSs are unidentified. The classification of the IPSs by their driver is a first step toward investigating the critical magnitudes of the IPS drivers commencing the magnetic storms in each class.

• Journal of Korean Society for Atmospheric Environment
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• v.29 no.5
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• pp.656-667
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• 2013

The non-exhaust coarse, fine, and ultrafine particles were characterized by on-road driving measurements using a mobile sampling system. The on-road driving measurements under constant speed driving revealed that mass concentrations of roadway particles (RWPs) were distributed mainly in a size range of 2~3 ${\mu}m$ and slightly increased with increasing vehicle speed. Under braking conditions, the mode diameters of the particles were generally similar with those obtained under constant speed conditions. However, the PM concentrations emitted during braking condition were significantly higher than those produced under normal driving conditions. Higher number concentrations of ultrafine particles smaller than 70 nm were observed during braking conditions, and the number concentration of particles sampled 90 mm above the pavement was 6 times higher than that obtained 40 mm above the pavement. Under cornering conditions, the number concentrations of RWPs sampled 40 mm above the pavement surface were higher than those sampled 90 mm above the pavement. This might be explained that a nucleation burst of a lot of vapor evaporated from the interaction between the tire and the road pavement under braking conditions continuously occurred by cooling during the transport to the sampling height 90 mm, while, for the case of cornering situations, the ultrafine particle formation was completed before the transport to the sampling height of 40 mm.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.101-104
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• 2000

Nowadays, the issue of congestion control in high-speed communication networks becomes critical in view of the bandwidth-delay products for efficient data flow. In particular, the fact that the congestion is often accompanied by the data flow from the high-speed link to low-speed link is important with respect to the stability of closed-loop congestion control. The Virtual-Connection Network (VCN) in Gigabit Ethernet networks is a packet-switching based network capable of implementing cell- based connection, link-by-link flow-controlled connection, and single- or multi-destination virtual connections. VCN described herein differ from the virtual channel in ATM literature in that VCN have link-by-link flow control and can be of multi-destination. VCNs support both connection-oriented and connectionless data link layer traffic. Therefore, the worst collision scenario in Ethernet CSMA/CD with virtual collision brings about end-to-end delay. Gigabit Ethernet networks based on CSMA/CD results in non-deterministic behavior because its media access rules are based on random probability. Hence, it is difficult to obtain any sound mathematical formulation for congestion control without employing random processes or fluid-flow models. In this paper, an analytical method for the design of a congestion control scheme is proposed based on Smith＇s principle to overcome instability accompanied with the increase of end-to-end delays as well as to avoid cell losses. To this end, mathematical analysis is provided such that the proposed control scheme guarantees the performance improvement with respect to bandwidth and latency for selected network links with different propagation delays. In addition, guaranteed bandwidth is to be implemented by allowing individual stations to burst several frames at a time without intervening round-trip idle time.

• Journal of Astronomy and Space Sciences
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• v.24 no.3
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• pp.219-226
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• 2007

Among the interplanetary shock (IP shock)s observed by ACE spacecraft at 1AU during 1997 to 2000, we have selected 31 IP shocks which had triggered the interplanetary type II radio bursts detected by the WIND spacecraft while those shocks were leaving the Sun. We compared the observed IP shock propagation speeds and the IP shock transit speeds estimated by time difference between the interplanetary type II radio burst detection and the IP shock observation. Then, we found that the mean acceleration of the IP shocks between the Sun and the Earth is about $-1.02m/sec^2$, which means the deceleration contrary to the positive acceleration predicted by Parker solar wind model. It is also verified that the acceleration of the IP shock does not show any linear correlation with the shock propagation speed and the Mach number of the IP shock.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.1
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• pp.53-58
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• 2017

UFMC is known as the one among novel multi-carrier modulation techniques which are designed for replacing OFDM for 5G wireless communication systems. It is the generalized model of OFDM and FBMC, which combines the advantages of OFDM and FBMC and avoids their weak points. UFMC is more robust in synchronization condition like Time-frequency misalignment compared to CP-OFDM. Moreover UFMC is more proper to burst uplink transmission like M2M 5G Communications. In this paper we analyze the BER performance in various channels and speeds. The simulation result shows that the BER performance is lowered when mobile devices are moving fast and the BER performance is so sensitive for the good channel environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.6
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• pp.1490-1500
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• 1996

One of the important issues for multimedia communications over ATM netowrks is efficient use of net-work resources since transmitting video at low cost requires high utilization of channel bandwidth. In this paper, we propose an effective bandwidth estimation scheme for MPEG sources in ATM networks. It has been known difficult to allocate effective transmission bandwidth to MPEG sources due to its bursty charactersitics. The MPEG traffic stream can bemodeled using five traffic parameters:service rate, burst load ratio, interburst load ratio, burst period, and interburst period. Using these parameters, a transmission bandwidth for each source can be estimated, and the estimated bandwidth is applied synchronously to reduce the queue size in a buffer. For a simple network modelof a high speed link that multiplexes a number of virtual-circuit connections, simulations on adaptive bandwidth allocation were performed, and the results show that the queueing delay is significantly reduced, when compared to a fixed bandwidth allocation.

• Geomechanics and Engineering
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• v.30 no.4
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• pp.345-352
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• 2022

When rock burst occurs, the damaged coal, rock and other fragments can be ejected to the roadway at a speed of up to 10 m/s. It is extremely harmful to personnel and mining equipment, and seriously affects the mining activities. In order to study the energy evolution characteristics, especially kinetic energy, in the process of rock mass failure, this paper first analyzes the energy changes of the rock in different stages under uniaxial compression. The formula of the kinetic energy of rock sample considering the energy from the indenter of the testing machine is obtained. Then, the uniaxial compression tests with different stiffness ratios of the indenter and rock sample are simulated by numerical simulation. The kinetic energy U_d, elastic strain energy U_e, friction energy U_f, total input energy U and surface energy U_θ of crack cracking are analyzed. The results show that: The stiffness ratio has influence on the peak strength, peak strain, U_d, U_e, U_θ, U_f and U of rock samples. The variation trends of strength, strain and energy with stiffness are different. And when the stiffness ratio increases to a certain value, if the stiffness of the indenter continues to increase, it will have no longer effect on the rock sample.

• KIEE International Transactions on Electrophysics and Applications
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• v.4C no.4
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• pp.155-159
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• 2004

This work reports the theoretical and experimental investigations of capillary bust valves to regulate liquid flow in microchannels. The theoretical analysis uses the Young-Laplace equation and geometrical considerations to predict the pressure at the edge of the valve opening. Numerical simulations are employed to calculate the meniscus shape evolution while the interface is pinned at the valve edge. Microchannels and valves are fabricated using soft lithography. A wafer-rotating system, which can adjust the driving pressure by rotational speed, induces a liquid flow. Experimentally measured valve-bursting pressure agrees with theoretical predictions.

• The Transactions of the Korea Information Processing Society
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• v.6 no.11
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• pp.3116-3123
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• 1999

Current disk systems are generally designed to reduce read traffic more effectively. Hence, write traffic of the I/O workload could potentially become a bottleneck of the disk system performance. In order to overcome this problem without much cost, this paper presents using outermost-zone track of multi-zoned recording disk as a secondary disk cache. The proposed disk cache improves the disk system performance by following exploitations: speed difference between block transfer and track transfer, difference in transfer rate between outermost-zone tracks and inner tracks, reduction in the seek time caused by decreasing the number of disk cache tracks, and idle period during burst accesses. In addition, it does not waste the disk space because it allocates the caching space by the cylinder unit. The simulation results show that the proposed system improves 2.54∼3.11 times better in terms of average response time for write operations than existing disk systems..