Sehoon Kim

Address allocation is an essential part in maintaining a mobile ad hoc network (MANET) effectively, and several address allocation schemes have been proposed. In this paper, we present a set of analytical models to evaluate the efficiency of address allocation schemes. The derived models quantitatively characterize the efficiency of four popular address allocation schemes in terms of latency and communication overhead. Through the analysis, we achieve numerical results that show the impact of ne

E JECTORS have a wide variety of applications: thrust augmentation of jet engines, vacuuming systems, and thermocompressor of the desalination plant, to name a few [1–7]. Depending on the applications, different configurations of ejectors have been in use. Interestingly, however, most of the past works on ejectors reported central injection ejectors, where primary flow is injected along the centerline of the secondaryflow.When ejectors are used for pumping chemical lasers, central injection type

A N EJECTOR is a flow device in which the momentum of the primary flow is transferred to the secondary flow. The momentum transfer takes place as the primary flow is injected into the secondary flow that is stagnant or moving. Ejectors are classified as subsonic, transonic, and supersonic depending on the flow speed at the exit of the primary nozzle. Typically the flow channel of an ejector is axis symmetric. Depending on the configuration of the primary flow inlet, the ejectors are either a cen

The electronic structures and bonding configuration of histidine on Ge(100) have been investigated with various sample treatments using core-level photoemission spectroscopy (CLPES). Interpretation of the Ge 3d, C 1s, N 1s, and O 1s core level spectra being included in these systems revealed that both the imino nitrogen in the imidazole ring and the carboxyl group in the glycine moiety concurrently participate in the adsorption of histidine on a Ge(100) surface at 380 K. Moreover, we could clear

In a mobile ad hoc network (MANET), it has been addressed that packet losses due to collision are often misinterpreted as routing failures, and cause unnecessary overhead for routing maintenance. There have been several attempts to avoid the unnecessary overhead through reducing collision losses. They are effective in a static topology where most losses are due to collision. In a dynamic topology, however, packets are lost due to actual routing failures (induced by mobility) as well as due to co

Regarding to address allocation, a mobile ad hoc network (MANET) may suffer from the lack of address and network partition/merging due to mobility of nodes. In this paper, we propose a new address allocation protocol for dealing with those problems. The proposed protocol is developed based on disjoint address set distribution with binary splitting for scalability, and provides special treatments for resolving the lack of addresses. We also present an effective technique for handling network part

Determination of geometric design parameters of a second~throat type annual supersonic ejector is described Tested geometric parameters were primary nozzle area ratio, cross-sectional area of second-throat, L/D ratio of second-throat and primary flow Injection angle Varying these four geometric parameters, we build a test matrix made of 81 test conditions, and experimental apparatus was fabricated to accommodate them For each test condition, the stagnation pressure of primary flow and the static

From the geometric parameter study, an optimal ejector design procedure of pressure recovery system for chemical lasers was acquired. For given primary flow reservoir conditions, an up-scaled ejector was designed and manufactured. In the performance test, secondary mass flow rate of 100g/s air was entrained satisfying the design secondary pressure, 40~50torr. Performance validation of a supersonic ejector system along with an investigation of effects of supersonic diffuser ws conducted. Placemen

In an annular injection supersonic ejector, the supersonic primary flow is injected along the side wall, therefore a funnel-shaped shock wave is generated by the contraction angle of the mixing chamber. In the present study, we developed a simple funnel shock wave model using 2-D wedge and conical shock wave relations. In result, the secondary flow pressure can be predicted more accurately than using a simple 2-D wedge shock wave model. Through the same analysis, the compression ratio and the ad

A theoretical analysis is developed for an annular-injection-type supersonic ejector having a second-throat downstream the ejector under the assumption that the Fabri choking is placed in mixing chamber. Non mixing theory is applied to formulate secondary flow pressure in the region between inlet of the mixing chamber and Fabri choking. To describe the shock standing at the inlet of the mixing chamber, two dimensional oblique shock relations are used and it is assumed that the shock affects only

It is essential to operate chemical lasers with supersonic ejector system as the laser output power goes up. In this research, ejector design parameter study was carried out for optimal ejector design through understanding the ejector characteristics and design requirements for chemical lasers operating. Designed ejector was 3D annular type with 2nd-throat geometry and pressurized air was used for primary flow. Ejector design was carried out with two steps, quasi-1D gas dynamics was used for fir

A theoretical analysis of an annular injection supersonic ejector equipped with a second-throat was developed under the assumption that the secondary flow is choked aerodynamically by interaction with primary flow in the mixing chamber. The predicted secondary flow pressure agrees reasonably well with the measurements. Using the analysis, the compression ratio, the secondary flow Mach number, and the location of the choking point were presented in terms of entrainment ratio.

An axisymmetric supersonic ejector equipped with a converging-diverging diffuser was built and pressure at various locations along the ejector-diffuser system was recorded with emphasis on the supersonic starting of the secondary flow. In order to find the effects of the opening size of the secondary flow, a number of openings were used with a constant primary pressure. Supersonic starting was possible only for d/D, the ratio of the opening diameter and the diffuser throat diameter, less than 0.