• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.7
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• pp.2027-2046
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• 2024

Reconfigurable Intelligent Surface (RIS) is an innovative technique to precisely control the phase of incident signals with the help of low-cost passive reflective elements. It shows excellent potential in the sixth generation of mobile communication systems, which not only extends wireless coverage but also boosts channel capacity. Considering that multipath propagation and a high number of antennas are involved in RIS in assisted mega multiple-input multiple-output (MIMO) systems, it suffers from severe channel fading and multipath effects, which in turn lead to signal instability and degradation of transmission performance. To overcome this obstacle, this essay suggests an improved gradient optimization algorithm to dynamically and optimally adjust the phase of the reflective elements to counteract channel fading and multipath effects as a strategy. In order to overcome the optimization problem of falling into local minima, this paper proposes an adaptive learning rate algorithm based on Adagrad improvement, which searches for the global optimal solution more efficiently and improves the robustness of the optimization algorithm. The suggested technique helps to enhance the estimate of channel efficiency of RIS-assisted large MIMO systems, according to simulation results.

• Journal of Electrochemical Science and Technology
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• v.8 no.1
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• pp.15-24
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• 2017

A comparative study was performed on the passivating abilities of surface films generated on lithium titanate (LTO; $Li_4Ti_5O_{12}$) electrodes during pre-cycling at two different rates. The surface film deposited at a faster pre-cycling rate (i.e., 0.5 C) is irregularly shaped and unevenly covers the LTO electrode. Owing to the incomplete coverage of the protective film, this LTO electrode exhibits poor passivating ability. Additional electrolyte decomposition and concomitant film deposition occur during subsequent charge/discharge cycles. As a result of the thick surface film, severe cell polarization occurs and eventually causes cell failure. However, pre-cycling the Li/LTO cell at a slower rate (0.1 C) improves cell polarization and capacity retention; this occurs because the surface film uniformly covers the LTO electrode and provides strong passivation. Accordingly, there is no significant film deposition during subsequent charge/discharge cycling. Additionally, self-discharge is reduced during high-temperature storage.

• Corrosion Science and Technology
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• v.4 no.6
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• pp.231-235
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• 2005

The inhibitive effect of extracts of tamarind seeds and jackfruit seeds, curry leaves and henna leaves on corrosion of mild steel in 1M HCl solution have been studied by weight loss, potentiodynamic polarization and impedance measurements. Results obtained from the electrochemical techniques were in good agreement with weight loss results. From the weight loss data, the values of surface coverage ($\Theta$) and corrosion rate were calculated. The inhibition efficiency (IE) increased with increasing inhibitor concentration in 1M HCl solution. In all the cases the adsorption of the natural product extracts on the mild steel surface from 1M HCl follows the Langmuir adsorption isotherm relationship. Potentiodynamic polarization studies reveal the fact that all the four natural product extracts act as mixed type inhibitors. The decrease in the inhibition efficiency follows the order: Extracts of jackfruit seed>henna leaves>curry leaves>tamarind seed.

• Bulletin of the Korean Chemical Society
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• v.33 no.1
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• pp.248-254
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• 2012

During the monolayer assembly of zeolite microcrystals using sonication with stacking (SS) method, the factors that govern the degree of close packing (DCP) between the microcrystals, the rate of attachment (rA) of microcrystals onto the substrate, the degree of coverage (DOC), and the binding strength (BS) between each crystal and the substrate were investigated for each mode of binding linkage (MBL). The tested MBLs were covalent linkage (CL), ionic linkage (IL), and polyelectrolyte-mediated ionic linkage (p-IL). Unlike the monolayers of zeolite crystals assembled on glass with a covalent linkage, the strong BS, very high DOC, and very high DCP do not decrease during monolayer assembly on glass through ionic linkages. This results indicate that the surface migration of crystals undergo linkage-nondestructively when crystals were attached to the substrates through ionic linkages.

• Korean Journal of Materials Research
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• v.16 no.4
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• pp.213-217
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• 2006

In this study, atomic layer etching of Si has been carried out using $Cl_2$ adsorption followed by the irradiation Ar neutral beam of low energy. In this experiment, the etch rate of Si was dependent on the $Cl_2$ pressure(the surface coverage of chlorine) and the irradiation time of Ar neutral beam(the flux density of Ar neural beam). And the etch rate of Si(100) and Si(111) were saturated exactly at one monolayer per cycle with $1.36{\AA}/cycle\;and\;1.57{\AA}/cycle$, respectively.

• Korean Journal of Head & Neck Oncology
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• v.4 no.1
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• pp.21-28
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• 1988

Skin replacement in large cheek defects after excision of benign or malignant tumor on the face is a challenging task. The physical characteristics of cheek skin are matched best by adjacent skin. Various methods of reconstructing of the facial surface such as forehead flap, distant flap, or a full thickness or split thickness skin graft have replaced adjacent tissue for coverage in many cases. We have reviewed ten cases of aesthetic reconstruction of the face after resection of the facial skin tumor within the last 5 years. The first group of 3 patients were reconstructed with split thickness skin graft from the scalp or lower abdomen. The second group of patients were reconstructed with cheek flap. The third group of 3 patients were reconstructed with cervicofacial flap. The last 2 patients were reconstructed with nasolabial flap & island falp respectively. The advantages from our experience with various method of coverage are its hidden donor area & good color match with the facial skin & increased success rate.

• Journal of Korea Water Resources Association
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• v.36 no.3 s.134
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• pp.455-464
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• 2003

In this paper, the experiments with installing a rainfall storage tank in the sub-surface were conducted and the reduction rates of the total runoff volume were investigated. The analysis were conducted based upon the variations of the rainfall intensity, surface coverage and surface slope. The reduction rate of the runoff volume was varied from 42.3% to 52.9% with the soil in the bank of the Seung Gi stream. In the experiments, the rainfall intensities were varied from 40mm/hr to 100mm/hr and the results indicate that the direct runoff reduction can be obtained with the installation of the rainfall storage tank in the sub-surface. The variation of the stored volume in the tank is very large in the mild slope but very small in the steep slope with over 3% slope. With this results, the reduction of the direct runoff volume for the longtime flood is expected with the installation of the rainfall storage tank in the region haying the steep slope such as the mountain area.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.11
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• pp.848-853
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• 2010

We have grown GaN nanowires by the low pressure MOCVD method on Ni deposited oxidized Si surface and have established optimum conditions by observing surface microstructure and its photoluminescence. Optimum growth temperature of $880^{\circ}C$, growth time of 30 min, TMG source flow rate of 10 sccm have resulted in dense nanowires on the surface, however further increase of growth time or TMG flow rate has not increased the length of nanowire but has formed nanocrystals. On the contrary, the increase of ammonia flow has increased the length of nanowires and the coverage of nanowire over the surface. The shape of nanowire is needle-like with a Ni droplet at its tip; the length is tens of micron with more than 40 nm in diameter. Low temperature photoluminescence obtained from the sample at optimum growth condition has revealed several peaks related to exciton decay near band-edge, but does not show any characteristic originated from one dimensional quantum confinement. Strong and broad luminescence at 2.2 eV is observed from dense nanowire samples and this suggests that the broad band is related to e-h recombination at the surface state in a nanowire. The current result is implemented to the nanowire device fabrication by nanowire bridging between micro-patterned neighboring Ni catalysis islands.

• Journal of the Korean Electrochemical Society
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• v.2 no.2
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• pp.70-74
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• 1999

The electrode kinetic parameters at the Pd/0.5 M LiOH electrolyte interface have been qualitatively studied using the phase-shift method. The phase shift $(\phi)$ depends on both the cathode potential (E>0) and frequency (f), and $\theta$ is inversely proportional to the fractional surface coverage $\theta$. At an intermediate frequency (10 Hz), the phase-shift profile $(\phi\;vs.\;E)$ can be related to the fractional surface coverage $(\theta\;vs.\;E)$. The phase-shift method can be used to estimate or plot the Frumkin adsorption isotherm. The rate (r) of change of the free energy of adsorption with $({\theta})$ is 22.3 kJ/mol. The equilibrium constant (K) for adsorption and the standard free energy $({\Delta}G_{\theta})$ of the adsorbed hydrogen atom $(H_{ads})$ are $3.7\times10^{-3}{\Delta}G_{\theta}>-8.4kJ/mol$, respectively. For 1$0.38>\theta>0$, the energy liberation or the exothermic reaction for hydrogen adsorption at the Pd cathode can be occurred. The electrode kinetic parameters $(r,\;K,\;{\Delta}G_{\theta}$ depend on the fractional surface coverage $({\theta})$ or the phase shift $(\phi)$.

• Korean Journal of Plant Resources
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• v.33 no.1
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• pp.15-23
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• 2020

There is high vulnerability of soil loss in sloping and highland used for agricultural production due to the low surface covering in summer rainy season. This study evaluated the surface-covering rate of landscape crop in reducing soil loss in the highland. The experiment was conducted in a 55% sloped lysimeter with three treatments of planting density using Korean native chrysanthemum, and investigated the soil coverage rate, run-off water, and soil erosion. The three treatments according to the degree of soil covering are bare soil as the control treatment TC, coverage rate of 43-59% for treatment T1, and, coverage rate of 63-81% for treatment T1, and T2. During the cultivation period, the average reduction of run-off water was 71% for treatment T1 and 76% for treatment T2, which are better, compared with the control. The reduction in eroded soil was 84% in treatment T1 and 98% for treatment T2, which is also better than the control treatment. Therefore, it is possible to alleviate the soil loss in sloping lands by planting chrysanthemum, which is superior among the perennial plant species and considered as a crop with economic value.