• Journal of Communications and Networks
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• v.15 no.6
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• pp.606-613
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• 2013

This paper proposes a complete solution of a contention-based medium access control in wireless local networks to provide station level quality of service guarantees in both downstream and upstream directions. The solution, based on the mature distributed coordination function protocol, includes a new fixed contention window backoff scheme, a tuning procedure to derive the optimal parameters, a super mode to mitigate the downstream bottleneck at the access point, and a simple admission control algorithm. The proposed system guarantees that the probability of the delay bound violation is below a predefined threshold. In addition, high channel utilization can be achieved at the same time. The numerical results show that the system has advantages over the traditional binary exponential backoff scheme, including efficiency and easy configuration.

• Journal of the Korean Mathematical Society
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• v.58 no.5
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• pp.1227-1237
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• 2021

This paper is concerned with a reaction-diffusion logistic model. In [17], Lou observed that a heterogeneous environment with diffusion makes the total biomass greater than the total carrying capacity. Regarding the ratio of biomass to carrying capacity, Ni [10] raised a conjecture that the ratio has a upper bound depending only on the spatial dimension. For the one-dimensional case, Bai, He, and Li [1] proved that the optimal upper bound is 3. Recently, Inoue and Kuto [13] showed that the supremum of the ratio is infinity when the domain is a multi-dimensional ball. In this paper, we generalized the result of [13] to an arbitrary smooth bounded domain in ℝⁿ, n ≥ 2. We use the sub-solution and super-solution method. The idea of the proof is essentially the same as the proof of [13] but we have improved the construction of sub-solutions. This is the complete answer to the conjecture of Ni.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.4
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• pp.281-288
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• 1996

This study has been investigated the influence of solid solution treatment on the microstructure of Mg-6Al-xZn(x=0,1,2) alloys fabricated by squeeze casting process. The products having clean surface and fine microstructure are fabricated by adopting the liquid metal forging method. The microstructures of as-fabricated state show ${\beta}(Mg_{17}Al_{12})$ precipitates between the dendrite boundaries. It is found that the hardness of the alloys is increased with increasing amount of zinc due to the solid solution hardening effect of zinc. In the changes of microstructure upon solid solution treatment time at $405^{\circ}C$, ${\beta}$ phases are dissolved in ${\alpha}$ matrix up to 1hr and the microstructure are coarsened rapidly after 2hrs. The microhardness are decreased rapidly until 1hr of solution treatment time and then stabilized. From the above results, it is concluded that the optimum solid solution treatment condition for Mg-6Al-xZn alloys is at $405^{\circ}C$ for 1hr. The solution treatment time is greatly reduced comparing to conventional casting(at $385{\sim}418^{\circ}C$ for 10~14hrs) due to the formation of the super-saturated solid solution by liquid metal forging.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.11B
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• pp.1373-1382
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• 2011

Zigbee is communication technology most ideal because Zigbee support low power communication and wide expansion in wireless home network. However, Zigbee is not popular, because of Zigbee always has Hidden Node Problem and Transit Delay Problem. We propose new Beacon Frame structure to solve the two problem in Zigbee. New Beacon Frame structure reduces a Super Frame Duration and add a same space of a Control Frame Duration. We expect to solved method of Hidden Node Problem that exchange terminal information to using RTS/CTS. Also, We expect to solved method of Transit Delay Problem that put Beacon between Control Frame Duration and Super Frame Duration for synchronization. We confirm new Beacon Frame to solved two problem in OPNET simulation at Zigbee QoS Parameters. We measure Delay(sec) for solution degree of Transit Delay Problem, and measure Throughput(bits/sec) and Load (bits/sec) for solution degree of Hidden Node Problem.

• Archives of Plastic Surgery
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• v.43 no.5
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• pp.395-401
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• 2016

Background Some of the relatively newer, more efficacious, and potent topical wound dressing solutions include tetrachlorodecaoxide and super-oxidised solution. This study compares the efficacy and safety of these two drugs. Methods This is a block-randomised, double blind, parallel-arm, post-marketing study. One hundred fifty patients with ulcers (75 blocks uniform for sex, ulcer aetiology, diabetes mellitus, and wound area score) were randomised into the two treatment arms. Patients were observed for eight weeks with weekly assessments. One hundred and twenty patients completed the study. Wound healing was objectively assessed by measurement of wound area, scoring of wound exudation and tissue type, and using the pressure ulcer scale of healing Tool (validated for multiple wound aetiologies). Subjective improvement in pain was noted using a visual analogue scale. Both groups were compared using Mann-Whitney U test on all indicators. Results Difference in change in wound tissue type in the two groups was significant (${\alpha}$=0.05) by intention-to-treat (ITT) and per-protocol (PP) analysis at the end of week two (ITT and PP, P<0.001) and week four (ITT, P=0.010; PP, P=0.009). P-values for other comparisons were not significant (P>0.05). No study-related adverse events were observed. Conclusions Both drugs are efficacious. Tetrachlorodecaoxide yields healthy granulation tissue earlier. Both drugs appear to be safe for application.

• Applied Chemistry for Engineering
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• v.25 no.6
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• pp.598-601
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• 2014

The effects of process parameters for the formation of polypropylene film such as the polypropylene concentration in the solution, drying temperature for coating film, and variation of nano-silica content on the surface structure and property of polypropylene film have been studied. A super-hydrophobic polypropylene film with a maximum contact angle of $154^{\circ}$ was obtained at the condition of a polypropylene concentration of 30 mg/mL, a drying temperature of $30^{\circ}C$, a drying pressure of 93 mtorr for 90 min. The increase of a drying temperature reduced the contact angle by enhancing the surface smoothness of the film. The increase of nano-silica content in the composite film composed of polypropylene and silica changed the surface shape from microporous to microglobular, which led to increasing the contact angle and showed the super-hydrophobic surface property.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.5
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• pp.243-250
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• 2011

When alloys are vacuum-deposited on cooled substrates, super-rapidly cooled alloy films in the unequilibrium state can be obtained. As an application of this method, Ag-Cu, Ag-Ni and Ag-C alloys were successfully produced, and their mechanical properties with tempering temperature were investigated. The following results were obtained : (1) In case of Ag-Cu alloys, the solid solution was hardened by tempering at $150^{\circ}C$. The hardening is considered to occur when the solid solution begins to decompose into ${\alpha}$ and ${\beta}$ phases. The Knoop hardness number of a 40 at.%Ag-Cu alloy film deposited on a cooled glass substrate was 390 $kg/mm^2$. The as-deposited films were generally very hard but fractured under stresses below their elastic limits. (2) In case of Ag-Ni and Ag-C alloys, after the tempering of 4 at.%Ni-Ag alloy at $400^{\circ}C$ and of 1 and 2 at.%C-Ag alloys at $200^{\circ}C$, they were hardened by the precipitation of fine nickel and carbon particles. The linear relationship between proof stress vs. $(grain\;diameter)^{-l/2}$ for bulk silver polycrystals can be applied to vacuum-deposited films up to about 0.1 ${\mu}m$ grain diameter, but the proof stress of ultra-fine grained silver with grain diameters of less than 0.1 ${\mu}m$ was smaller than the value expected from the Petch's relation.

• Korean Journal of Materials Research
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• v.23 no.10
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• pp.550-554
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• 2013

As continued scaling becomes increasingly difficult, 3D integration has emerged as a viable solution to achieve higher bandwidths and good power efficiency. 3D integration can be defined as a technology involving the stacking of multiple processed wafers containing integrated circuits on top of each other with vertical interconnects between the wafers. This type of 3D structure can improve performance levels, enable the integration of devices with incompatible process flows, and reduce form factors. Through silicon vias (TSVs), which directly connect stacked structures die-to-die, are an enabling technology for future 3D integrated systems. TSVs filled with copper using an electro-plating method are investigated in this study. DC and pulses are used as a current source for the electro-plating process as a means of via filling. A TiN barrier and Ru seed layers are deposited by plasma-enhanced atomic layer deposition (PEALD) with thicknesses of 10 and 30 nm, respectively. All samples electroplated by the DC current showed defects, even with additives. However, the samples electroplated by the pulse current showed defect-free super-filled via structures. The optimized condition for defect-free bottom-up super-filling was established by adjusting the additive concentrations in the basic plating solution of copper sulfate. The optimized concentrations of JGB and SPS were found to be 10 and 20 ppm, respectively.

• Journal of Welding and Joining
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• v.32 no.4
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• pp.26-33
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• 2014

The metallurgical and mechanical characteristics, toughness and corrosion resistance of dissimilar welds between super duplex stainless steel UNS S32750 and carbon steel ASTM A516Gr.70 have been evaluated. Three heat inputs of 21.12, 24.00, 26.88kJ/cm were employed to make joints of dissimilar metals with flux cored arc welding(FCAW). Based on microstructural examination, vermicular ferrite was formed in the first layer of weld at low heat input(21.12kJ/cm) and $Cr_{eq}/Ni_{eq}$ of 1.61 while acicular ferrite was formed in last layer of weld at high heat input(26.88kJ/cm) and $Cr_{eq}/Ni_{eq}$ of 1.72. Ferrite percentage in dissimilar welds was lowest in the first layer of weld regardless of heat inputs and it gradually increased in the second and third layers of weld. Heat affected zone showed higher hardness than the weld metal although reheated zone showed lower hardness than weld metal due to the formation of secondary austenite. Tensile strengths of dissimilar welds increased with heat input and there was 100MPa difference. The corrosion test by ferric chloride solution showed that carbon steel had poor corrosion resistance and pitting corrosion occurred in the first layer(root pass) of weld due to the presence of reheated zone where secondary austenite was formed. The salt spray test of carbon steel showed that the surface only corroded but the amount of weight loss was extremely low.

• Journal of Distribution Research
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• v.15 no.5
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• pp.1-18
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• 2010

Recent rapid growth of Super-Supermarket(SSM) may be the last process of penetration of big retailers' into the grocery market where small supermarkets have dominated for the past several decades. Anti-SSM movement led by small supermarket owners is mainly due to the fear of shaky viability. The authors believe that the ultimate solution should be strengthening the competitiveness of small retailers. This study concludes that satisfying customers will make small retailers more sustainable. The study suggests the improvement of merchandising and customer services. In particular, the study performed an ideation survey for developing services suitable for supermarket customers. The study suggests service alternatives optimal for small retailers through confirmation survey of 300 consumers.