• Journal of KIISE:Information Networking
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• v.31 no.4
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• pp.414-428
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• 2004

Many portable devices are coming to be commercially successful and provide useful services to mobile users. Mobile devices may request a variety of data types, including text and multimedia data, thanks to the rich content of the Internet. Different types of data and/or different classes of users may need to be treated with different qualities of service. The implementation of service differentiation in wireless networks is very difficult because of device mobility and wireless channel contention when the backoff algorithm is used to resolve contention. Modification of the t)mary exponential backoff algorithm is one possibility to allow the design of several classes of data traffic flows. We present a study of modifications to the backoff algorithm to support three classes of flows: sold, silver, and bronze. For example, the gold c]ass flows are the highest priority and should satisfy their required target bandwidth, whereas the silver class flows should receive reasonably high bandwidth compared to the bronze class flows. The mixture of the two different transport protocols, UDP and TCP, in ad hoc networks raises significant challenges when defining backoff algorithm modifications. Due to the different characteristics of UDP and TCP, different backoff algorithm modifications are applied to each class of packets from the two transport protocols. Nevertheless, we show by means of simulation that our approach of backoff algorithm modification clearly differentiates service between different flows of classes regardless of the type of transport protocol.

• Journal of Distribution Research
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• v.10 no.1
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• pp.33-57
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• 2005

After 1990's, many multi-level marketing companies lave been introduced in Korea. These MLM companies operate their stores as same way as general retailing stores. The major characteristics of these MLM companys' store is that their main customers are distributors who sell the purchased merchandise to another customers. Many studies about merchandise display in general retailing stores were reported. But, there was less research about merchandise display in these special type stores such as MLM companys' stores. This paper investigates the effects of merchandise display on distributor's merchandise selection in channel flow of multi-level marketing company. For this purpose, we formulated four hypotheses about display variance in quantity, height, location, and related merchandise to analyze the effect of merchandise display methods in MLM companys' stores. The experiment had been proceeded in three stores in a MLM company for 6 weeks and the sales data were collected by POS. The methods to analyze the data were used ANOVA and T-test. Findings of this study are as follows; First, there was no effect to store sale by the interaction effect between merchandise display method and scale of store. Second, scale of store affected considerably the volume of sales of each store according to main effect analysis. Third, display variance in quantity, height, and location did not affect store sale. In the related merchandise display, however, sale in all store was increased. Fourth, in additional analysis considering merchandise display only, display variance in both height and location affected their sale in large scale store. Based on the above results, we may predict merchandise display can affect sale in MLM companys' store as well as general retailing stores. Therefore if MLM company has large scale store, it should consider merchandise display methods in its stores.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.1-11
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• 2016

The effect of the migration of nanoparticles near the wall of a channel on the convective heat transfer in a laminar flow of $SiO_2$ nanoparticle suspensions (nanofluids) under constant wall heat flux boundary conditions was numerically and experimentally investigated in this study. The dynamic thermal conductivity of the aqueous $SiO_2$ nanofluids was measured using T-type thermocouples attached to the outer surface of a stainless steel circular tube (with a length of 1 m and diameter of 1.75 mm). The nanofluids used in this study were synthesized by dispersing $SiO_2$ spherical nanoparticles with a diameter of 24 nm in de-ionized water (DIW). The enhancement of the thermal conductivity of the nanofluids (e.g., an increase of up to 7.9 %) was demonstrated by comparing the temperature profiles in the flow of the nanofluids with that in the flow of the basefluids (i.e., DIW). However, this trend was not demonstrated in the computational analysis, because the numerical models were based on continuum assumptions and flow features involving nanoparticles in a stable colloidal solution. Thus, to explore the non-continuum effects, such as the modification of the morphology caused by nanoparticle-wall interactions on the heat exchanging surfaces (e.g., the isolated and dispersed precipitation of the nanoparticles), additional experiments were performed using DIW right after the measurements using the nanofluids.

• Korea Trade Review
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• v.48 no.3
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• pp.43-68
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• 2023

In this study, in relation to "Chapter 3 Support for Priority Purchase of Technology Development Products" of the 「Market Channel Support Act」, this study investigated the positive growth impact of technology development products subject to preferential purchase on small and medium sized enterprises. The data used for empirical verification is for 371 companies that obtained certification for technology development products subject to preferential purchase in 2016 and Data from SMEs were collected from 2017 to 2021, Sales, operating profit, and net profit was identified, and empirical verification. And conducted through statistical analysis to determine whether it had a positive effect on the growth factors of SMEs. In addition, data from 225 technology development product certification companies were collected, and empirical testing was conducted through t-test analysis on the change in growth factors before and after acquiring certification. As a result of statistical analysis, it was found that the total assets, certified sales, operating profit, and net profit, which are the growth factors of a company, are all positively affected according to the type of technology development product certification. However, in the case of authentication types, some authentications showed significant negative results. In addition, significant results were derived that after acquiring certification had a positive effect on growth factors than before acquiring certification. Consistent with this conclusion, I think that it is effective for technology development-based SMEs to enter the public procurement market and utilize the technology development product priority purchase policy for market exploitation and corporate growth. And the government should strengthen the market support policy to create demand so that SMEs can enter the procurement market and actively utilize the preferential purchase system, and come up with an improvement plan so that public institutions can actively utilize the preferential purchase system.

• 한국균학회소식:학술대회논문집
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• 2016.05a
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• pp.19-20
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• 2016

Sesquiterpenoids are defined as $C_{15}$ compounds derived from farnesyl pyrophosphate (FPP), and their complex structures are found in the tissue of many diverse plants (Degenhardt et al. 2009). FPP's long chain length and additional double bond enables its conversion to a huge range of mono-, di-, and tri-cyclic structures. A number of cyclic sesquiterpenes with alcohol, aldehyde, and ketone derivatives have key biological and medicinal properties (Fraga 1999). Fungi, such as the wood-rotting Polyporus brumalis, are excellent sources of pharmaceutically interesting natural products such as sesquiterpenoids. In this study, we investigated the biosynthesis of P. brumalis sesquiterpenoids on modified medium. Fungal suspensions of 11 white rot species were inoculated in modified medium containing $C_6H_{12}O_6$, $C_4H_{12}N_2O_6$, $KH_2PO_4$, $MgSO_4$, and $CaCl_2$ for 20 days. Cultivation was stopped by solvent extraction via separation of the mycelium. The metabolites were identified as follows: propionic acid (1), mevalonic acid lactone (2), ${\beta}$-eudesmane (3), and ${\beta}$-eudesmol (4), respectively (Figure 1). The main peaks of ${\beta}$-eudesmane and ${\beta}$-eudesmol, which were indicative of sesquiterpene structures, were consistently detected for 5, 7, 12, and 15 days These results demonstrated the existence of terpene metabolism in the mycelium of P. brumalis. Polyporus spp. are known to generate flavor components such as methyl 2,4-dihydroxy-3,6-dimethyl benzoate; 2-hydroxy-4-methoxy-6-methyl benzoic acid; 3-hydroxy-5-methyl phenol; and 3-methoxy-2,5-dimethyl phenol in submerged cultures (Hoffmann and Esser 1978). Drimanes of sesquiterpenes were reported as metabolites from P. arcularius and shown to exhibit antimicrobial activity against Gram-positive bacteria such as Staphylococcus aureus (Fleck et al. 1996). The main metabolites of P. brumalis, ${\beta}$-Eudesmol and ${\beta}$-eudesmane, were categorized as eudesmane-type sesquiterpene structures. The eudesmane skeleton could be biosynthesized from FPP-derived IPP, and approximately 1,000 structures have been identified in plants as essential oils. The biosynthesis of eudesmol from P. brumalis may thus be an important tool for the production of useful natural compounds as presumed from its identified potent bioactivity in plants. Essential oils comprising eudesmane-type sesquiterpenoids have been previously and extensively researched (Wu et al. 2006). ${\beta}$-Eudesmol is a well-known and important eudesmane alcohol with an anticholinergic effect in the vascular endothelium (Tsuneki et al. 2005). Additionally, recent studies demonstrated that ${\beta}$-eudesmol acts as a channel blocker for nicotinic acetylcholine receptors at the neuromuscular junction, and it can inhibit angiogenesis in vitro and in vivo by blocking the mitogen-activated protein kinase (MAPK) signaling pathway (Seo et al. 2011). Variation of nutrients was conducted to determine an optimum condition for the biosynthesis of sesquiterpenes by P. brumalis. Genes encoding terpene synthases, which are crucial to the terpene synthesis pathway, generally respond to environmental factors such as pH, temperature, and available nutrients (Hoffmeister and Keller 2007, Yu and Keller 2005). Calvo et al. described the effect of major nutrients, carbon and nitrogen, on the synthesis of secondary metabolites (Calvo et al. 2002). P. brumalis did not prefer to synthesize sesquiterpenes under all growth conditions. Results of differences in metabolites observed in P. brumalis grown in PDB and modified medium highlighted the potential effect inorganic sources such as $C_4H_{12}N_2O_6$, $KH_2PO_4$, $MgSO_4$, and $CaCl_2$ on sesquiterpene synthesis. ${\beta}$-eudesmol was apparent during cultivation except for when P. brumalis was grown on $MgSO_4$-free medium. These results demonstrated that $MgSO_4$ can specifically control the biosynthesis of ${\beta}$-eudesmol. Magnesium has been reported as a cofactor that binds to sesquiterpene synthase (Agger et al. 2008). Specifically, the $Mg^{2+}$ ions bind to two conserved metal-binding motifs. These metal ions complex to the substrate pyrophosphate, thereby promoting the ionization of the leaving groups of FPP and resulting in the generation of a highly reactive allylic cation. Effect of magnesium source on the sesquiterpene biosynthesis was also identified via analysis of the concentration of total carbohydrates. Our current study offered further insight that fungal sesquiterpene biosynthesis can be controlled by nutrients. To profile the metabolites of P. brumalis, the cultures were extracted based on the growth curve. Despite metabolites produced during mycelia growth, there was difficulty in detecting significant changes in metabolite production, especially those at low concentrations. These compounds may be of interest in understanding their synthetic mechanisms in P. brumalis. The synthesis of terpene compounds began during the growth phase at day 9. Sesquiterpene synthesis occurred after growth was complete. At day 9, drimenol, farnesol, and mevalonic lactone (or mevalonic acid lactone) were identified. Mevalonic acid lactone is the precursor of the mevalonic pathway, and particularly, it is a precursor for a number of biologically important lipids, including cholesterol hormones (Buckley et al. 2002). Farnesol is the precursor of sesquiterpenoids. Drimenol compounds, bi-cyclic-sesquiterpene alcohols, can be synthesized from trans-trans farnesol via cyclization and rearrangement (Polovinka et al. 1994). They have also been identified in the basidiomycota Lentinus lepideus as secondary metabolites. After 12 days in the growth phase, ${\beta}$-elemene caryophyllene, ${\delta}$-cadiene, and eudesmane were detected with ${\beta}$-eudesmol. The data showed the synthesis of sesquiterpene hydrocarbons with bi-cyclic structures. These compounds can be synthesized from FPP by cyclization. Cyclic terpenoids are synthesized through the formation of a carbon skeleton from linear precursors by terpene cyclase, which is followed by chemical modification by oxidation, reduction, methylation, etc. Sesquiterpene cyclase is a key branch-point enzyme that catalyzes the complex intermolecular cyclization of the linear prenyl diphosphate into cyclic hydrocarbons (Toyomasu et al. 2007). After 20 days in stationary phase, the oxygenated structures eudesmol, elemol, and caryophyllene oxide were detected. Thus, after growth, sesquiterpenes were identified. Per these results, we showed that terpene metabolism in wood-rotting fungi occurs in the stationary phase. We also showed that such metabolism can be controlled by magnesium supplementation in the growth medium. In conclusion, we identified P. brumalis as a wood-rotting fungus that can produce sesquiterpenes. To mechanistically understand eudesmane-type sesquiterpene biosynthesis in P. brumalis, further research into the genes regulating the dynamics of such biosynthesis is warranted.