• International Journal of Internet, Broadcasting and Communication
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• 제13권4호
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• pp.1-10
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• 2021

The purpose of the study is to contribute to the positive development of blockchain technology by providing data to examine security vulnerabilities and threats to blockchain-based services and review countermeasures. The findings of this study are as follows. Threats to the security of blockchain-based services can be classified into application security threats, smart contract security threats, and network (P2P) security threats. First, application security threats include wallet theft (e-wallet stealing), double spending (double payment attack), and cryptojacking (mining malware infection). Second, smart contract security threats are divided into reentrancy attacks, replay attacks, and balance increasing attacks. Third, network (P2P) security threats are divided into the 51% control attack, Sybil attack, balance attack, eclipse attack (spread false information attack), selfish mining (selfish mining monopoly), block withholding attack, DDoS attack (distributed service denial attack) and DNS/BGP hijacks. Through this study, it is possible to discuss the future plans of the blockchain technology-based ecosystem through understanding the functional characteristics of transparency or some privacy that can be obtained within the blockchain. It also supports effective coping with various security threats.

• Journal of Communications and Networks
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• 제8권2호
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• pp.241-252
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• 2006

Traditional service-level agreements (SLAs), defined by average delay or packet loss, often camouflage the instantaneous performance perceived by end-users. We define a set of metrics for service availability to quantify the performance of Internet protocol (IP) backbone networks and capture the impact of routing dynamics on packet forwarding. Given a network topology and its link weights, we propose a novel technique to compute the associated service availability by taking into account transient routing dynamics and operational conditions, such as border gateway protocol (BGP) table size and traffic distributions. Even though there are numerous models for characterizing topologies, none of them provide insights on the expected performance perceived by end customers. Our simulations show that the amount of service disruption experienced by similar networks (i.e., with similar intrinsic properties such as average out-degree or network diameter) could be significantly different, making it imperative to use new metrics for characterizing networks. In the second part of the paper, we derive goodness factors based on service availability viewed from three perspectives: Ingress node (from one node to many destinations), link (traffic traversing a link), and network-wide (across all source-destination pairs). We show how goodness factors can be used in various applications and describe our numerical results.

• 대한핵의학회지
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• 제24권2호
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• pp.222-228
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• 1990

The development of histomorphometric and histodynamic investigations has permitted the description of a specific and complex osteopathy in hyperthyroidism. The increased bone turnover rate in hyperthyroid patients may be accompanied by a considerable bone loss. These features are associated with both inclosed osteoclastic bone resorption and increased osteoblastric bone formation, with an accelerated calcification rate. Conventional biochemical markers of bone metabolism, i.e. serum calcium and alkaline phosphatase and urinary hydroxyproline and calcium are normal in most patients with hyperthyroidism. However, the correlation between serum BGP and serum concentration of thyroid hormon suggests that serum BGP may be a sensitive marker of increased bone formation due to the hypersecretion of thyroid hormones. Any increase in bone turnover, whether focal or diffuse, will result in an increase in $^{99m}Tc-methylenediphosphonate$ uptake (MDP). The measurement of this uptake in hyperthyroid patients by bone provides a sensitive and objective means of quantifying skeletal metabolism. Using a standard shadow-shield whole-body monitor and radioimmunoassay kit, we have measured whole-body retention of $^{99m}Tc-MDP$ up to 24hr and concentration of serum Osteocalcin in 20 patients with hyperthyroidism and in 42 normals. The results were as follows; 1) The average of serum Osteocalcin level in 42 patients with normals was $9.90{\pm}4.87(ng/ml)$ and in 20 patients with hyperthyroidism was $19.54{\pm}5.7(ng/ml)$. Both the averages of serum Osteocalcin and 24hr $^{99m}Tc-MDP$ uptakes in hyperthyroid patients were higher than those in normals. 2) $^{99m}Tc-MDP$ uptakes in skeletal system increased in proportion to normal ageing after 40 yrs old in 42 patients with normals. The average of $^{99m}Tc-MDP$ uptakes in hyperthyroid patients were higher than those in normals without related ageing. 3) A significant relationships between the $^{99m}Tc-MDP$ uptakes and serum Osteocalcin level were peformed (r=0.55, $y=17.58+6.7\times$). From the above results we concluded that the measurement of serum Osteocalcin and 24hr $^{99m}Tc-MDP$ uptakes can be used for evaluation of bone turnover as a specific marker in hyperthyroid patients.

• Journal of Microbiology and Biotechnology
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• 제22권3호
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• pp.343-351
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• 2012

In this paper, the kinetics of a cloned special glucosidase, named ginsenosidase type III hydrolyzing 3-O-glucoside of multi-protopanaxadiol (PPD)-type ginsenosides, were investigated. The gene (bgpA) encoding this enzyme was cloned from a Terrabacter ginsenosidimutans strain and then expressed in E. coli cells. Ginsenosidase type III was able to hydrolyze 3-O-glucoside of multi-PPD-type ginsenosides. For instance, it was able to hydrolyze the 3-O-${\beta}$-D-(1${\rightarrow}$2)-glucopyranosyl of Rb1 to gypenoside XVII, and then to further hydrolyze the 3-O-${\beta}$-D-glucopyranosyl of gypenoside XVII to gypenoside LXXV. Similarly, the enzyme could hydrolyze the glucopyranosyls linked to the 3-O-position of Rb2, Rc, Rd, Rb3, and Rg3. With a larger enzyme reaction $K_m$ value, there was a slower enzyme reaction speed; and the larger the enzyme reaction $V_{max}$ value, the faster the enzyme reaction speed was. The $K_m$ values from small to large were 3.85 mM for Rc, 4.08 mM for Rb1, 8.85 mM for Rb3, 9.09 mM for Rb2, 9.70 mM for Rg3(S), 11.4 mM for Rd and 12.9 mM for F2; and $V_{max}$ value from large to small was 23.2 mM/h for Rc, 16.6 mM/h for Rb1, 14.6 mM/h for Rb3, 14.3 mM/h for Rb2, 1.81mM/h for Rg3(S), 1.40 mM/h for Rd, and 0.41 mM/h for F2. According to the $V_{max}$ and $K_m$ values of the ginsenosidase type III, the hydrolysis speed of these substrates by the enzyme was Rc>Rb1>Rb3>Rb2>Rg3(S)>Rd>F2 in order.