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Background/Aims: In vitro, prostaglandins(PGs) inhibit adenylate cyclase in the parietal cell, and thus inhibit acid secretion. In contrast, in the chief cell, PGs stimulate adenylate cyclase and cAMP generation, and thus stimulate pepsinogen secretion. The importance of PG-induced desensitization in pepsinogen secretion on cytoprotection is not known. The aim of this study was to determine whether in vivo exposure of the guinea pig to 16,16-dimethyl PGE? desensitized chief cells to subsequent stimulation; to determine whether desensitization in vivo was mediator-specific or -nonspecific; to evaulate whether desensitization was reversible; and finally to determine whether desensitization was mediated by decreases in cAMP generation. Methods: Guinea pigs were injected with l ? of 16,16-dimethyl PGE? or vehicle at 24, 4, 2, and 1 hour prior to sacrifice. Pepsinogen secretion was determined by hydrolysis of ^(125)I-hemoglobin in samples of supernatant. Intracellular concentration of cAMP was determined by radioimmunoassay. Results: In all of the 16,16-dimethyl PGE. Pretreated groups, their subsequent pepsinogen secretion stimulated by PGE? was significantly reduced compared with control(p$lt;0.01). In maximal desensitized group, PGE?, secretin, VIP, 8-BrcAMP, carbachol, and CCK-8 produced less secretion compared with control(p$lt;0.05). Desensitization of subsequent PGE?-stimulated pepsinogen secretion persisted 72 hours. Desensitization of subsequent carbachol-stimulated pepsinogen secretion persisted 24 hours but not 72 hours. Pretreatment with 16,16-dimetbyl PGE? did not alter cAMP generation in response to PGE? compared with control. Conclusions: 16,16-dimethyl PGE?-induced desensitization was generalized and nonmediator-specific. Desensitization lasted at least 24 hours for carbacholstimulated secretion and up to 3 days for PGE?-stimulated secretion. 16,16-dimethyl PGE?-induced desensitization might be mediated by a mechanism distal to generation of cAMP. Finally, prolonged in vivo desensitization involved different mechanisms from those of short-term in vitro desensitization.
The microstructure and stress corrosion cracking behaviors in 22Cr5Ni2Mo suplex stainless steel weldment have been investigated. The SCC has been examined in terms of relevant electrochemical parameters in boiling 40% MgCl₂solution. The austenite content of the weld metal had twice as much as that of the base metal due to the effect of additive elements Ni, N and reheat effect by the multipass welding. The steel had the threshold stress of 29.1 kg/㎟ and the critical cracking potencial(E_CC) of -410mV immune to the SCC, and possessed superior SCC resistance compared to the austennitic stainless steel. Above the E_cc the SCC of the weldment occurred at the base metal regardless of the welding method. Cracks were initiated and propagated transgranularly without retarding effect by the phase the austenite phase in high stress region.
본 연구의 목적은 광역 네트워크로 연결된 다수의 봇을 활용하여 단일처리 방식의 시간 지연의 문제점과 병렬처리 방식의 비용증가, 인력낭비에 대한 문제점을 해결할 수 있는 큐를 이용한 다중스레드 방식의 웹 크롤링을 연구한다. 본 연구는 큐를 이용한 다중스레드 방식의 시스템 구성을 바탕으로 독립된 시스템에서 실행하는 어플리케이션을 설계하고 분석한다. 큐를 이용하여 다중 스레드 방식의 웹 크롤러 설계를 제안한다. 또한, 웹 문서의 처리량을 수식에 따라 클라이언트와 스레드 별로 나누어 분석하고, 각각 효율성 비교를 통해 최적의 클라이언트의 개수와 스레드의 개수를 확인 할 수 있다. 제안하는 시스템의 설계 방식은 분산처리를 기반으로 각각의 독립된 환경에서의 클라이언트는 큐와 스레드를 이용하여 빠르고 신뢰성이 높은 웹 문서를 제공한다. 특정 사이트를 대상으로 하는 웹 크롤러 설계가 아닌 범용 웹 크롤러에 큐와 다중 스레드를 적용하여 다양한 웹 사이트를 빠르고 효율적으로 탐색 및 수집하는 시스템이 필요하다. The purpose of this study is to propose a multi-threaded web crawl using queues that can solve the problem of time delay of single processing method, cost increase of parallel processing method, and waste of manpower by utilizing multiple bots connected by wide area network Design and implement. This study designs and analyzes applications that run on independent systems based on multi-threaded system configuration using queues. We propose a multi-threaded web crawler design using queues. In addition, the throughput of web documents can be analyzed by dividing by client and thread according to the formula, and the efficiency and the number of optimal clients can be confirmed by checking efficiency of each thread. The proposed system is based on distributed processing. Clients in each independent environment provide fast and reliable web documents using queues and threads. There is a need for a system that quickly and efficiently navigates and collects various web sites by applying queues and multiple threads to a general purpose web crawler, rather than a web crawler design that targets a particular site.
This study was aimed to clarify the histopathological changes in the experimental animal model subjcted to rigid fixation performed across the frontonasal sutrue in growing rabbits. Sixteen rabbits aged 6 weeks used. In experimental group(n=12), rigid fixation with miniplates and screws was performed across the frontonasal suture. Control group(n=4) was those with periosteal elevation only. Experimental animals were sacrificed on the 2nd, 4th, 8th, and 12th week after operation, and frontonasal suture area was excised for light microscopic and scanning electron microscopic examination. The results obtained were as follows : 1. In control groups, collagen fiber bundles ran in the midportion of bone sutrue and cambial layers were seen at bone surface. Sutural surfaces are beveled and external and internal bony projected portions were observed. 2. In experimental groups, distance of bone suture was decreased by new bone formation on the 2nd week, while increased by bone resorption at the miniplate applied area and bone formation in the adjacent bone on the 4th week. 3. In experimental groups, the original bone surface was almost resorbed and new bone formation was found on the 8th week. Regulary-run collagen fibers, smooth and dense bone surfaces were similar to the bone patterns of control groups on the 12th week. Above results suggest that bone formation is restricted where the miniplate is applied, while compensatory growth is appeared in the adjacent bont. It is considered that rigid fixation with miniplates and acrews results in a little disturbance of sutural growth of the craniofacial bone in infancy and children when applied for short duration.
정보통신기술의 발전에 따라 DDoS와 DRDoS은 지속적으로 보안상 이슈가 되고, 고도화된 기법으로 점차 발전하 고 있다. 최근에는 정상 서버의 프로토콜을 이용하여 반사 서버로 악용하는 DRDoS 기법으로 IT 기업들을 위협하고 있 다. 반사 트래픽은 정상적인 서버에서 발생되는 트래픽으로 보안장비에서 판별하기가 어렵고 실제 사례에서도 최대 Tbps 까지 증폭되었다. 본 논문에서는 DRDoS 공격에서 사용되는 DNS증폭과 Memcached증폭을 비교 분석한 뒤 공격의 효 과를 감소시킬 수 있는 대응방안을 제안한다. 반사 트래픽으로 사용되는 프로토콜은 TCP와 UDP, 그리고 NTP, DNS, Memcached등이 존재한다. 반사 트래픽으로 이용되는 프로토콜 중에서 반사 트래픽의 응답크기가 높은 DNS 프로토콜 과 Memcached 프로토콜을 비교분석결과, Memcached 프로토콜은 DNS 프로토콜보다 ±21% 증폭된다. 대응방안은 Memcached 프로토콜의 메모리 초기화 명령어를 사용하여 공격의 효과를 감소시킬 수 있다. 향후 연구에서는 보안에 취약한 다양한 서버들을 보안 네트워크를 통해 공유하여 원천적 차단효과를 전망할 수 있다. With the development of information and communication technology, DDoS and DRDoS continue to become security issues, and gradually develop into advanced techniques. Recently, IT companies have been threatened with DRDoS technology, which uses protocols from normal servers to exploit as reflective servers. Reflective traffic is traffic from normal servers, making it difficult to distinguish from security equipment and amplified to a maximum of Tbps in real-life cases. In this paper, after comparing and analyzing the DNS amplification and Memcached amplification used in DRDoS attacks, a countermeasure that can reduce the effectiveness of the attack is proposed. Protocols used as reflective traffic include TCP and UDP, and NTP, DNS, and Memcached. Comparing and analyzing DNS protocols and Memcached protocols with higher response sizes of reflective traffic among the protocols used as reflective traffic, Memcached protocols amplify ±21% more than DNS protocols. The countermeasure can reduce the effectiveness of an attack by using the Memcached Protocol's memory initialization command. In future studies, various security-prone servers can be shared over security networks to predict the fundamental blocking effect.