125 research outputs found

    Have I Met You Before? Using Cross-Media Relations to Reduce SPIT

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    Most legitimate calls are from persons or organizations with strong social ties such as friends. Some legitimate calls, however, are from those with weak social ties such as a restaurant the callee booked a table on-line. Since a callee's contact list usually contains only the addresses of persons or organizations with strong social ties, filtering out unsolicited calls using the contact list is prone to false positives. To reduce these false positives, we first analyzed call logs and identified that legitimate calls are initiated from persons or organizations with weak social ties through transactions over the web or email exchanges. This paper proposes two approaches to label incoming calls by using cross-media relations to previous contact mechanisms which initiate the calls. One approach is that potential callers offer the callee their contact addresses which might be used in future correspondence. Another is that a callee provides potential callers with weakly-secret information that the callers should use in future correspondence in order to identify them as someone the callee has contacted before through other means. Depending on previous contact mechanisms, the callers use either customized contact addresses or message identifiers. The latter approach enables a callee to label incoming calls even without caller identifiers. Reducing false positives during filtering using our proposed approaches will contribute to the reduction in SPIT (SPam over Internet Telephony)

    One Server Per City: Using TCP for Very Large SIP Servers

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    The transport protocol for SIP can be chosen based on the requirements of services and network conditions. How does the choice of TCP affect the scalability and performance compared to UDP? We experimentally analyze the impact of using TCP as a transport protocol for a SIP server. We first investigate scalability of a TCP echo server, then compare performance of a SIP server for three TCP connection lifetimes: transaction, dialog, and persistent. Our results show that a Linux machine can establish 450,000+ TCP connections and maintaining connections does not affect the transaction response time. Additionally, the transaction response times using the three TCP connection lifetimes and UDP show no significant difference at 2,500 registration requests/second and at 500 call requests/second. However, sustainable request rate is lower for TCP than for UDP, since using TCP requires more message processing. More message processing causes longer delays at the thread queue for the server implementing a thread-pool model. Finally, we suggest how to reduce the impact of TCP for a scalable SIP server especially under overload control. This is applicable to other servers with very large connection counts

    関節リウマチ患者における骨強度評価および身体機能に関する研究

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    学位の種別: 課程博士審査委員会委員 : (主査)東京大学教授 芳賀 信彦, 東京大学講師 浅野 善英, 東京大学特任准教授 吉村 典子, 東京大学特任准教授 神田 浩子, 東京大学准教授 小川 純人University of Tokyo(東京大学

    BMP-2/beta-TCP Local Delivery for Bone Regeneration in MRONJ-Like Mouse Model

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    Medication-related osteonecrosis of the jaw (MRONJ) is a severe pathological condition associated mainly with the long-term administration of bone resorption inhibitors, which are known to induce suppression of osteoclast activity and bone remodeling. Bone Morphogenetic Protein (BMP)-2 is known to be a strong inducer of bone remodeling, by directly regulating osteoblast differentiation and osteoclast activity. This study aimed to evaluate the effects of BMP-2 adsorbed onto beta-tricalcium phosphate (beta-TCP), which is an osteoinductive bioceramic material and allows space retention, on the prevention and treatment of MRONJ in mice. Tooth extraction was performed after 3 weeks of zoledronate (ZA) and cyclophosphamide (CY) administration. For prevention studies, BMP-2/beta-TCP was transplanted immediately after tooth extraction, and the mice were administered ZA and CY for an additional 4 weeks. The results showed that while the tooth extraction socket was mainly filled with a sparse tissue in the control group, bone formation was observed at the apex of the tooth extraction socket and was filled with a dense connective tissue rich in cellular components in the BMP-2/beta-TCP transplanted group. For treatment studies, BMP-2/beta-TCP was transplanted 2 weeks after tooth extraction, and bone formation was followed up for the subsequent 4 weeks under ZA and CY suspension. The results showed that although the tooth extraction socket was mainly filled with soft tissue in the control group, transplantation of BMP-2/beta-TCP could significantly accelerate bone formation, as shown by immunohistochemical analysis for osteopontin, and reduce the bone necrosis in tooth extraction sockets. These data suggest that the combination of BMP-2/beta-TCP could become a suitable therapy for the management of MRONJ

    Assessment of Demineralization Inhibition Effects of Dentin Desensitizers Using Swept-Source Optical Coherence Tomography

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    The purpose of this study was to evaluate the mechanism of action and the inhibiting effects of two types of desensitizers against dentin demineralization using pre-demineralized hypersensitivity tooth model in vitro. In this study, we confirmed that a hypersensitivity tooth model from our preliminary experiment could be prepared by immersing dentin discs in an acetic acid-based solution with pH 5.0 for three days. Dentin discs with three days of demineralization were prepared and applied by one of the desensitizers containing calcium fluoro-alumino-silicate glass (Nanoseal, NS) or fluoro-zinc-silicate glass (Caredyne Shield, CS), followed by an additional three days of demineralization. Dentin discs for three days of demineralization (de3) and six days of demineralization (de6) without the desensitizers were also prepared. The dentin discs after the experimental protocol were scanned using swept-source optical coherence tomography (SS-OCT) to image the cross-sectional (2D) view of the samples and evaluate the SS-OCT signal. The signal intensity profiles of SS-OCT from the region of interest of 300, 500, and 700 mu m in depth were obtained to calculate the integrated signal intensity and signal attenuation coefficient. The morphological differences and remaining chemical elements of the dentin discs were also analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. SS-OCT images of CS and NS groups showed no obvious differences between the groups. However, SS-OCT signal profiles for both the CS and NS groups showed smaller attenuation coefficients and larger integrated signal intensities than those of the de6 group. Reactional deposits of the desensitizers even after the additional three days of demineralization were observed on the dentin surface in NS group, whereas remnants containing Zn were detected within the dentinal tubules in CS group. Consequently, both CS and NS groups showed inhibition effects against the additional three days of demineralization in this study. Our findings demonstrate that SS-OCT signal analysis can be used to monitor the dentin demineralization and inhibition effects of desensitizers against dentin demineralization in vitro
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