• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2005.11a
• /
• pp.220-223
• /
• 2005

We studied the effect of composition, processing, and sintering temperature on the microwave properties of $Mg_{3-x}Co_x(VO_4)_2$ system which is applicable to LTCC. When $Mg_{3-x}Co_x(VO_4)_2$ was fabricated by solid-state reaction process and sintered at the temperature range of $800\sim910^{\circ}C$, it was found that the optimum composition of x was 2 at which microwave properties of 910$^{\circ}C$-sintered one were as follows: $Q\times f_0\sim55,200GHz$ and $\varepsilon_r\sim10$. When $(MgCo_2)(VO_4)_2$ was fabricated by sol-gel process and sintered at 800$^{\circ}C$, $Q\timesf_0$was 34,400GHz which is much high compared to those fabricated by solid-state reaction process at the same sintering temperature.

• The Korean Journal of Food & Health Convergence
• /
• v.8 no.1
• /
• pp.21-30
• /
• 2022

This study proposed a multiple regression equation for predicting VO2max of elderly men and women using functional performance variables required to conduct daily activities. The subjects of this study were 58 elderly men (72.4±5.9 yrs) and 117 elderly women (73.4±4.5 yrs) aged 65-90 who belong to the senior welfare center. The maximal graded exercise test using a cycle ergometer and functional performance representing muscle strength, endurance, static and dynamic flexibility, mobility, and agility were measured. For statistical processing, multiple regression analysis was performed, and the statistical significance level was α = .05. As a result, the VO2max estimation formula for the elderly was 0.419 (standing up and sitting down a chair) + 0.199 (leg endurance against wall) + 5.383, and R2=0.406. In addition, the VO2max estimation formula for elderly women is - 0.737 (standing up from a supine position) - 0.144 (waking around two cones in a figure 8) - 0.135 (%body fat) + 0.042 (one leg balance with eyes open) + 29.395, R2=0.367 was calculated. The conclusion is that if the maximal graded exercise test is not available, it is considered that VO2max of the elderly can be predicted properly by using the estimation formula calculated based on the functional performance variable.

• Journal of the Korean Chemical Society
• /
• v.29 no.6
• /
• pp.615-622
• /
• 1985

The chemical species formed by uranium and vanadium and their equilibria have been investigated in the various concentrations of oxalic and acetic acids by the ion exchange chromatography and UV-Vis spectrophotometry. Uranyl and vanadyl ions seem to be form the complex as $UO_2(C_2O_4)_2=$, $UO_2(C_2O_4)_3^{4-}$ and $VO_2(C_2O_4)-2^{3-}$ respectively in the concentration range of 0.005∼0.05M oxalic acid concentration. In the case of acetic acid the equilibria of $UO_2^{2+}+3Ac^-=UO_2(Ac)_3^-$ and $VO_2^++2Ac^-=VO_2(Ac)_2^-$ were existed individually according to the increase of acetic acid concentration.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.8 no.1
• /
• pp.71-76
• /
• 2013

In this paper, end-to-end performances for some VoIP traffics are measured and analyzed over MANET(Mobile Ad-hoc Networks) with packet aggregation transmission under blackhole attacks. A VoIP simulator based on NS-2 is used for performance measure. In the simulation, MOS, call connection ratio, network delay and packet loss rate are measured for end-to-end transmission performance. With analysis of measured data, characteristics of each traffics for performance parameters of packet aggregation transmission is showed on MANET under blackhole attack, As a results of this paper, some considerations be required for packet aggregation transmission are suggested to implement VoIP services on MANET under blackhole attacks.

• Elastomers and Composites
• /
• v.51 no.3
• /
• pp.240-249
• /
• 2016

$BiVO_4$ nanomaterial was synthesized from bismuth (III) nitrate pentahydrate [$Bi(NO_3)_3{\cdot}5H_2O$] and ammonium vanadate (V) [$NH_4VO_3$]. The $BiVO_4$-graphene nanocomposite was fabricated by calcining the $BiVO_4$ nanomaterial and graphene under an oxygen-free atmosphere at $700^{\circ}C$. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize structural and morphological properties of samples. The catalytic activity of the $BiVO_4$-graphene nanocomposite was studied for the reduction of 4-nitrophenol, 3-nitrophenol and 2-nitrophenol by sodium borohydride [$NaBH_4$]. The photocatalytic activity of the $BiVO_4$-graphene nanocomposite was demonstrated by the degradation of organic dyes like BG, MB, MO and RhB under irradiation at 365 nm. The catalytic and photocatalytic activity were studied by UV-vis spectrophotometry.

• International Journal of Computer Science & Network Security
• /
• v.22 no.2
• /
• pp.175-184
• /
• 2022

Voice over Internet Protocol (VoIP) has grown in popularity as a low-cost, flexible alternative to the classic public switched telephone network (PSTN) that offers advanced digital features. However, additional security vulnerabilities are introduced by the VoIP system's flexibility and the convergence of voice and data networks. These additional challenges add to the normal security challenges that a VoIP system's underlying IP data network infrastructure confront. As a result, the VoIP network adds to the complexity of the security assurance task faced by businesses that use this technology. It's time to start documenting the many security risks that a VoIP infrastructure can face, as well as analyzing the difficulties and solutions that could help guide future efforts in research & development. We discuss and investigate the challenges and requirements of VoIP security in this research. Following a thorough examination of security challenges, we concentrate on VoIP system threats, which are critical for present and future VoIP deployments. Then, towards the end of this paper, some future study directions are suggested. This article intends to guide future scholars and provide them with useful guidance.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.385-385
• /
• 2012

Understanding the thermodynamics and structural transformation during the Metal-Insulator Transition (MIT) is critical to better understand the underlying physical origin of phase transition in the vanadiumdioxide ($VO_2$). Here, through the temperature-dependent in-situ high resolutiontransmission electron microscopy (HR-TEM), and systematic electrical transport study, we have shown that the tunable MIT transition of $VO_2$ nanowires is strongly affected by interplay between strain and domain nucleation by ion beam irradiation. Surprsingly, we have also observed that the $VO_2$ rutile (R) metallic phase could form directly in a strain-induced metastable monoclinic (M2) phase. These insights open the door toward more systematic approaches to synthesis for $VO_2$ nanostructures in desired phase and to use for applications including ultrafast optical switching, smart window, metamaterial, resistance RAM and synapse devices.

• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.2007-2010
• /
• 2008

Vanadium pentoxide ($V_2O_5$) powder was prepared and mixed with Molybdenum Oxides ($MoM_3$) to form Mo-doped and -undoped $VO_2$ films by a sol-gel method on graphite conductive substrates. X-Ray diffraction (XRD) and scanning electron microscopy (SEM) was used to investigate the chemical compositions and microstructures of the Mo-doped and -undoped $VO_2$ films. The variation of electrical resistance was measured as a function of temperature and stoichiometric composition between vanadium and molybdenum. In this study, it was found that Mo-doped and -undoped $VO_2$ shows the typical negative temperature coefficient (NTC) behavior. As the amount of the molybdenum increases, the electrical resistance of Modoped $VO_2$ film gets reduced under the transition temperature and a linear decrease in the transition temperature is observed. From these experimental results, we can conclude that the electrical resistance behavior with temperature change of $VO_2$ films can be utilized as a self-heating source with the electrical current flowing through the graphite substrate.

• Journal of the Korean institute of surface engineering
• /
• v.50 no.3
• /
• pp.141-146
• /
• 2017

We investigated configuration of metallic and insulating domains in $VO_2$ thin films, while spanning metal-insulator phase transition. Kelvin probe force microscopy, of which spatial resolution is less than 100 nm, enables us to measure local work function (WF) at the sample surface. The WF of $VO_2$ thin films decreased (increased) as increasing (decreasing) the sample temperature, during the phase transition. The higher and lower WF regions corresponded to the insulating and metallic domains, respectively. The metallic fraction, estimated from the WF maps, well explained the temperature-dependent resistivity based on the percolation model. The WF mapping also showed us how the structural defects affected the phase transition behaviors.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.196.1-196.1
• /
• 2014

VO2 exhibits metal-insulator transition (MIT), of which critical temperature (TC) is about 340 K. There have been many reports that MIT can be induced by UV light as well as heat. Clear mechanism regarding such photo-induced MIT has not been clarified. We have compared the MIT behaviors of VO2 thin film during heating-cooling cycles with and without light. We tried several light sources with different wavelengths (red, blue, and UV). Tc and hysteresis width of the resistance change were influenced by the illumination of the samples. We performed Kelvin probe force microscopy (KPFM) studies, which can reveal the evolution of the local sample work function. In this presentation, we will discuss possible physical origins for the photo-induced effects on the MIT behaviors of the VO2 samples.