Journal of the Korea Society of Computer and Information
/
v.27
no.7
/
pp.35-48
/
2022
In this study, it propose a proof theory method for expressing and reasoning knowledge in a multiagent environment. Since this method determines logical results in a mechanical way, it has developed as a core field from early AI research. However, since the proposition cannot always be proved in any set of closed sentences, in order for the logical result to be determinable, the range of expression is limited to the sentence in the form of a clause. In addition, the resolution principle, a simple and strong reasoning rule applicable only to clause-type sentences, is applied. Also, since the proof theory can be expressed as a meta predicate, it can be extended to the metalogic of the proof theory. Metalogic can be superior in terms of practicality and efficiency based on improved expressive power over epistemic logic of model theory. To prove this, the semantic method of epistemic logic and the metalogic method of proof theory are applied to the Muddy Children problem, respectively. As a result, it prove that the method of expressing and reasoning knowledge and common knowledge using metalogic in a cooperative multiagent environment is more efficient.
Background: Long-term comparative data of phacoemulsification combined with endoscopic cyclophotocoagulation (phaco-ECP) versus phacoemulsification (phaco) alone in dogs are rare. Objectives: To investigate the effects of ECP on postoperative intraocular pressure (IOP) and complications after phaco in dogs with normal IOP. Methods: Medical records of IOP, conjunctival hyperemia, corneal edema, aqueous flare, posterior synechia, intraocular fibrin, and posterior capsule opacification (PCO) formation in 15 canine eyes that underwent phaco-ECP and 36 eyes that underwent phaco alone were evaluated retrospectively. ECP was applied when either the iridocorneal angle or the ciliary cleft was narrow or closed. Results: The IOP of the phaco-ECP group persisted within the normal range postoperatively. The phaco-ECP group had a shorter period of dorzolamide use than did the phaco group. PCO was formed earlier in the phaco-ECP group than in the phaco group. The phaco-ECP group showed more severe corneal edema than the phaco group at every follow-up visit. Posterior synechia was more severe in the phaco-ECP group than in the phaco group from two weeks until the last follow-up. Conclusions: Although ECP might cause more postoperative complications such as corneal edema and posterior synechia, it could effectively reduce the incidence of IOP increase after phaco in dogs with a high risk of postoperative glaucoma.
Jeeyoon Kim;Bommie Florence Seo;Junho Lee;Sung No Jung
Archives of Plastic Surgery
/
v.49
no.6
/
pp.760-763
/
2022
The dorsal metacarpal artery perforator flap is a flap that rises from the hand dorsum. Owing to its reliability and versatility, this flap is used as a workhorse for finger defect. However, to cover the radial-volar defect of the proximal interphalangeal joint (PIPJ) of the index finger, a longer flap is required than before. Here, we introduce the oblique extended reverse first dorsal metacarpal artery (FDMA) perforator flap to cover the radial-volar aspect defect of the index finger. A 45-year-old man got injured to the radial-volar defect of PIPJ of the left index finger caused by thermal press machine. The wound was 2 × 1 cm in size, and the joint and bone were exposed. We used FDMA perforator from anastomosis with palmar metacarpal artery at metacarpal neck. Since the defect was extended to the volar side, the flap was elevated by oblique extension to the fourth metacarpal base level. The fascia was included to the flap, and the flap was rotated counterclockwise. Finally, PIPJ was fully covered by the flap. Donor site was primarily closed. After 12 months of operation, the flap was stable without complication and limitation of range of motion. The oblique extended reverse FDMA perforator flap is a reliable method for covering the radial-volar defect of the PIPJ of the index finger. This flap, which also has an aesthetic advantage, will be a good choice for hand surgeons who want to cover the PIPJ defect of the index finger using a nonmicrosurgical option.
This study aimed to examine the effect of external pop-up satellite archival tags (PSATs) attachment and water temperature on the oxygen consumption rate (OCR) of the olive flounder (mean body weight 2281.7 g). The OCRs of fish were measured under conditions of three different water temperature conditions (15, 20, and 25℃) and two different tagging methods [non-tagging, control; bio-logger external attachment with a miniature PSAT (dummy mrPAT), BEA] using a closed flow-through respirometer. The OCRs of fish linearly increased with the increase in water temperature in both the control and BEA (P<0.001); however, the OCRs of BEA were approximately 1.8-1.9 times lower than those of the control at each water temperature (P<0.001). The Q10 values of the control and BEA were the highest in the water temperature range of 15 to 20℃, but sensitivity to water temperature changes was higher in BEA than in the control. The metabolic energy loss rate (MEL) of fish increased with increasing water temperature regardless of external tagging, but the MEL of the control was higher than that of BEA (P<0.001). These results demonstrate that OCR, thermal sensitivity, and energy expenditure are all affected in adult olive flounder with external PSAT attachment.
Kim, Dong-Kwan;Ji, Won Hyun;Kim, Duk-Min;Park, Hyun-Sung;Oh, Youn Soo
Economic and Environmental Geology
/
v.51
no.5
/
pp.401-407
/
2018
For the treatment of heavy metals in the mine drainage from the closed mine area, various methods such as passive, active and semi-active treatments are considered. Among contaminated elements in the mine drainage, Mn is one of the difficult elements for the treatment because it needs high pH over 9.0 for its concentration to be reduced. In this study, the efficiency of various slag complex reactors (slag (S), slag+limestone (SL) and slag+Mn coated gravel (SG)) on Mn removal in the presence of Fe, which is a competitive element with Mn, was evaluated to investigate effective methods for the treatment of Mn in mine drainage. As a result of experiments on Mn removal without Fe during 358 days, using influent with $30{\sim}50Mn{\cdot}mg/L$ and pH 6.7 on the average, S reactor showed continuously high Mn removal efficiency with the average of 99.9% with pH 8.9~11.4. Using the same reactors, Mn removal experiments with Fe during 237 days were conducted with the influent with $40{\sim}60Mn{\cdot}mg/L$. The pH range of effluent reached to 6.1~10.0, which is slightly lower than that of effluent without Fe. S reactor showed the highest range of pH with 7.1~9.9, followed by S+L and S+G reactor. However, the efficiency of Mn removal showed S+L>S>S+G with the range of 94~100%, 68~100% and 68~100%, respectively in spite of relatively low pH range. S+L reactor showed the most resistance on Fe input, which means other mechanisms such as $MnCO_3$ formation by the carbonate prouced from the limestone or autocatalysis reaction of Mn contributed to Mn removal rather than pH related mechanisms. The evidence of reactions between carbonates and Mn, rhodochrosite ($MnCO_3$), was found from the X-ray diffraction analysis of precipitates sample from S+L reactor. From this study, the most effective reactors on Mn removal in the presence of Fe was S+L reactor. The results are expected to be applied for the Mn containing mine water treatment in the presence of Fe within the relatively low range of pH.
Purpose: Problematic late sequelae are common following a calcaneal fracture regardless of the initial treatment. We retrospectively evaluated the painful conditions and reviewed the results of the operative treatment in patients with previously treated calcaneal fractures. Materials and Methods: Between October 1996 and September 2001, forty-three patients who underwent subsequent surgical treatment for late sequelae of calcaneal fracture were reviewed. The initial treatment consisted of only immobilization in a cast in 7 patients, closed reduction with pin fixation (Essex-Lopresti technique) in 22 and open reduction and internal fixation in 14. Painful conditions in the hind foot included subtalar arthritis in 31 patients, calcaneofibular impingement in 13, peroneal tendinitis in 6, displaced posterior bony fragment in 3, sural neuritis in 2, subtalar and midtarsal arthritis in 1 and displaced plantar bony fragment in 1. The surgical procedures for the late complications were performed at a mean of 19 months (range, 6 to 35 months) after the injury and consisted of lateral wall ostectomy and in situ subtalar fusion in 28 patients, only lateral wall ostectomy in 5 patients, lateral wall ostectomy and subtalar distraction arthrodesis in 3, removal of displaced posterior bony fragment in 3, sural nerve transposition in the peroneus brevis in 2, triple arthrodesis in 1 and removal of displaced plantar bony fragment in 1. Mean postoperative follow up period was 57 months (range, 33 to 82 months). The results of treatment were evaluated on the basis of pain, improvement in the ability to perform activities of daily living, to return to work or to a pre-injury level of activity. Results: Pain was partially relieved in 38 patients (88%), but not relieved in 5. Function improved in 34 patients (79%), and 32 (74%) returned to work or to a pre-injury level of activity. There was a trend that the longer the interval between the injury and the operation, the longer the subsequent interval until the patient returned to full activities or work. Conclusion: Meticulous physical examination and intensive prompt treatment for remaining pain after initial treatment of calcaneal fractures are recommended for patient's satisfaction and returning to work.
Efficiency estimation of toxicity free resistance cable experiments were conducts to understand toxicity free fire ersistance polyolefin insulation material and smoke density characteristic and combustion gas corrosion analysis. A main cause of fire-growth and generating toxic gas when it burns, should be dealt with great care in life safety design. Similar patterned fire incidents such as, Inchon Live-Hof Pub Restaurant as, Sea-land Children Resort have proven that serious loss of lives were caused by hazardous gas generated fire resistance cable materials. In this paper, Referenced documents were ASTM E662 standard test method for specific Ds genalated by solid materials. The furnace control system shall maintain the required irradiance level under steady-state condition with the chamber door closed of 2.5$\pm40.04〔w/$\textrm{cm}^2$〕for 20 min. According to the results of the smoke density analysis of NFR-8 and FR-PVC the highest decomposition flaming smoke density range of NFR-8 and FR-PVC were 25.2 to 37.5 and 51.1 respectively. Nonflaming smoke density range of NFR-8 and FR-PVC were 100.4 to 112.2 and 126.5 to 398.8. Also, the fire gases was occurred carbon monoxide and decomposition than in polyolefin due to incomplete combustion of PVC which has high content of carbon in chemical compound.
Atrial septal defect is one of the most frequently encountered congenital heart disease. Up to December 31, 1976, 1682 cardiac patients received cardiac catheterization in the cardiac department of Yonsei university medical college. Out of the 1682 cardiac patients 723 cases had congenital heart disease and only 116 cases had congetial atrial septal defect. This amounted to 16.04% of all those with congenital heart disease. 58 cases of congenital atrial septal defect operated in the chest surgery department were presented. Of these 58 cases of atrial septal defect, 27 cases were male and 31 cases were female. Their ages ranged from 5 years to 54 years. The systolic pressure of the main pulmonary artery of 40 out of the 58 cases of atrial septal defect was below 40% of that of the systemic blood pressure: in 6 cases, the range of the systolic pressure of the main pulmonary artery was 50-90mmHg; in 12 cases, the range of the systolic pressure of the main pulmonary artery was 40-50mmHg. Average age of these was 30. 1 years. This study tends to show that Korean patients with atrial septal defect even though younger have a slight higher systolic pressure of the main pulmonary artery than Western patients have. The pulmonary blood is 1.5-2.5 times of systemic blood flow in 52 cases out of 58 cases of atrial septal defect.In only one of the 58 cases of atrial septal defect, the Rp was found to be as high as 45% of Rs. All other cases were below this level.51 cases had ostium secundum defect, 4 out of these cases had ostium secundum defect combined with mitral incompetence and 6 out of them had double ostium secundum defect. The remaining 7 cases had ostium primum defect. Their atrial defects were repaired under direct vision utilizing extracorporeal circulation, by hemodilution technic combined with moderate hypothermia. 44 cases [2nd atrial septal defect] were repaired by direct sutures while 14 cases, including the 7 cases ostium primum defects needed patches [1 pericardium and 13 teflon patch]. In 4 cases there were single defects while showed two defects. However the associated septal defect was so small that it could be closed by direct sutures. The size of the defect ranged between 6.0cm2and 10.0cm2 in 19 cases[33.7%]: the smallest being 0. 5cm2 and the largest 24cm2. The surgical mortality was 2 cases [3.4%]. These one case with ostium primum defect, could not be resuscitated on operation table. The cause of death in this case was myocardial failure and MI. The other, a case of ostium primum defect had a second operation on the first operative day due to massive bleeding from LV vent-line insertion site.The patient died on 26th post-operative day due to sepsis.
Atrial septal defect is one of the most frequently encountered congenital heart disease. Up to December 31, 1976, 1682 cardiac patients received cardiac catheterization in the cardiac department of Yonsei university medical college. Out of the 1682 cardiac patients 723 cases had congenital heart disease and only 116 cases had congetial atrial septal defect. This amounted to 16.04% of all those with congenital heart disease. 58 cases of congenital atrial septal defect operated in the chest surgery department were presented. Of these 58 cases of atrial septal defect, 27 cases were male and 31 cases were female. Their ages ranged from 5 years to 54 years. The systolic pressure of the main pulmonary artery of 40 out of the 58 cases of atrial septal defect was below 40% of that of the systemic blood pressure: in 6 cases, the range of the systolic pressure of the main pulmonary artery was 50-90mmHg; in 12 cases, the range of the systolic pressure of the main pulmonary artery was 40-50mmHg. Average age of these was 30. 1 years. This study tends to show that Korean patients with atrial septal defect even though younger have a slight higher systolic pressure of the main pulmonary artery than Western patients have. The pulmonary blood is 1.5-2.5 times of systemic blood flow in 52 cases out of 58 cases of atrial septal defect.In only one of the 58 cases of atrial septal defect, the Rp was found to be as high as 45% of Rs. All other cases were below this level.51 cases had ostium secundum defect, 4 out of these cases had ostium secundum defect combined with mitral incompetence and 6 out of them had double ostium secundum defect. The remaining 7 cases had ostium primum defect. Their atrial defects were repaired under direct vision utilizing extracorporeal circulation, by hemodilution technic combined with moderate hypothermia. 44 cases [2nd atrial septal defect] were repaired by direct sutures while 14 cases, including the 7 cases ostium primum defects needed patches [1 pericardium and 13 teflon patch]. In 4 cases there were single defects while showed two defects. However the associated septal defect was so small that it could be closed by direct sutures. The size of the defect ranged between 6.0cm2and 10.0cm2 in 19 cases[33.7%]: the smallest being 0. 5cm2 and the largest 24cm2. The surgical mortality was 2 cases [3.4%]. These one case with ostium primum defect, could not be resuscitated on operation table. The cause of death in this case was myocardial failure and MI. The other, a case of ostium primum defect had a second operation on the first operative day due to massive bleeding from LV vent-line insertion site.The patient died on 26th post-operative day due to sepsis.
Through the low-temperature(60-150${\circ}C$) hydrothermal treatment of perlite with the alkaline solution at various NaOH concentrations, the mode of volcanic glass alteration and resultant zeolite formation were investigated in a closed system. At a temperature of 80${\circ}C$ and alkalinities of pH range 8 to 12, corresponding to the natural environments of diagenetic zeolite formation, only weak dissolution of perlitic glass occurs without zeolite formation despite the residence time of 100 days. Activities of Si and Al increase progressively, as a consequence of increasing pH, whereas activity ratios of Si/Al decrease. Zeolites were synthesized from perlite in the alkaline solution at above 0.1M NaOH concentrations. Below the temperature of 100${\circ}C$ Na-P was mainly formed, whereas analcime was the dominant zeolite at the temperature range of 100-150${\circ}C$. During Na-P synthesis chabazite and Na-X were also formed as by-products in case of lower proportion of solution/sample(<10ml/g) and higher NaOH concentraion (>3M), respectively. The alteration modes of perlite in the zeolite synthesis reflect that the formation of synthetic zeolites occurs as an incongruent dissolution likely with the diagenetic formation of natural zeolites from volcanic glass. Considering much difference in reaction kinetics between natural and synthetic systems, however, the evaluated synthetic conditions in these experiments were not directly applicable to the natural diagenetic system.
본 웹사이트에 게시된 이메일 주소가 전자우편 수집 프로그램이나
그 밖의 기술적 장치를 이용하여 무단으로 수집되는 것을 거부하며,
이를 위반시 정보통신망법에 의해 형사 처벌됨을 유념하시기 바랍니다.
[게시일 2004년 10월 1일]
이용약관
제 1 장 총칙
제 1 조 (목적)
이 이용약관은 KoreaScience 홈페이지(이하 “당 사이트”)에서 제공하는 인터넷 서비스(이하 '서비스')의 가입조건 및 이용에 관한 제반 사항과 기타 필요한 사항을 구체적으로 규정함을 목적으로 합니다.
제 2 조 (용어의 정의)
① "이용자"라 함은 당 사이트에 접속하여 이 약관에 따라 당 사이트가 제공하는 서비스를 받는 회원 및 비회원을
말합니다.
② "회원"이라 함은 서비스를 이용하기 위하여 당 사이트에 개인정보를 제공하여 아이디(ID)와 비밀번호를 부여
받은 자를 말합니다.
③ "회원 아이디(ID)"라 함은 회원의 식별 및 서비스 이용을 위하여 자신이 선정한 문자 및 숫자의 조합을
말합니다.
④ "비밀번호(패스워드)"라 함은 회원이 자신의 비밀보호를 위하여 선정한 문자 및 숫자의 조합을 말합니다.
제 3 조 (이용약관의 효력 및 변경)
① 이 약관은 당 사이트에 게시하거나 기타의 방법으로 회원에게 공지함으로써 효력이 발생합니다.
② 당 사이트는 이 약관을 개정할 경우에 적용일자 및 개정사유를 명시하여 현행 약관과 함께 당 사이트의
초기화면에 그 적용일자 7일 이전부터 적용일자 전일까지 공지합니다. 다만, 회원에게 불리하게 약관내용을
변경하는 경우에는 최소한 30일 이상의 사전 유예기간을 두고 공지합니다. 이 경우 당 사이트는 개정 전
내용과 개정 후 내용을 명확하게 비교하여 이용자가 알기 쉽도록 표시합니다.
제 4 조(약관 외 준칙)
① 이 약관은 당 사이트가 제공하는 서비스에 관한 이용안내와 함께 적용됩니다.
② 이 약관에 명시되지 아니한 사항은 관계법령의 규정이 적용됩니다.
제 2 장 이용계약의 체결
제 5 조 (이용계약의 성립 등)
① 이용계약은 이용고객이 당 사이트가 정한 약관에 「동의합니다」를 선택하고, 당 사이트가 정한
온라인신청양식을 작성하여 서비스 이용을 신청한 후, 당 사이트가 이를 승낙함으로써 성립합니다.
② 제1항의 승낙은 당 사이트가 제공하는 과학기술정보검색, 맞춤정보, 서지정보 등 다른 서비스의 이용승낙을
포함합니다.
제 6 조 (회원가입)
서비스를 이용하고자 하는 고객은 당 사이트에서 정한 회원가입양식에 개인정보를 기재하여 가입을 하여야 합니다.
제 7 조 (개인정보의 보호 및 사용)
당 사이트는 관계법령이 정하는 바에 따라 회원 등록정보를 포함한 회원의 개인정보를 보호하기 위해 노력합니다. 회원 개인정보의 보호 및 사용에 대해서는 관련법령 및 당 사이트의 개인정보 보호정책이 적용됩니다.
제 8 조 (이용 신청의 승낙과 제한)
① 당 사이트는 제6조의 규정에 의한 이용신청고객에 대하여 서비스 이용을 승낙합니다.
② 당 사이트는 아래사항에 해당하는 경우에 대해서 승낙하지 아니 합니다.
- 이용계약 신청서의 내용을 허위로 기재한 경우
- 기타 규정한 제반사항을 위반하며 신청하는 경우
제 9 조 (회원 ID 부여 및 변경 등)
① 당 사이트는 이용고객에 대하여 약관에 정하는 바에 따라 자신이 선정한 회원 ID를 부여합니다.
② 회원 ID는 원칙적으로 변경이 불가하며 부득이한 사유로 인하여 변경 하고자 하는 경우에는 해당 ID를
해지하고 재가입해야 합니다.
③ 기타 회원 개인정보 관리 및 변경 등에 관한 사항은 서비스별 안내에 정하는 바에 의합니다.
제 3 장 계약 당사자의 의무
제 10 조 (KISTI의 의무)
① 당 사이트는 이용고객이 희망한 서비스 제공 개시일에 특별한 사정이 없는 한 서비스를 이용할 수 있도록
하여야 합니다.
② 당 사이트는 개인정보 보호를 위해 보안시스템을 구축하며 개인정보 보호정책을 공시하고 준수합니다.
③ 당 사이트는 회원으로부터 제기되는 의견이나 불만이 정당하다고 객관적으로 인정될 경우에는 적절한 절차를
거쳐 즉시 처리하여야 합니다. 다만, 즉시 처리가 곤란한 경우는 회원에게 그 사유와 처리일정을 통보하여야
합니다.
제 11 조 (회원의 의무)
① 이용자는 회원가입 신청 또는 회원정보 변경 시 실명으로 모든 사항을 사실에 근거하여 작성하여야 하며,
허위 또는 타인의 정보를 등록할 경우 일체의 권리를 주장할 수 없습니다.
② 당 사이트가 관계법령 및 개인정보 보호정책에 의거하여 그 책임을 지는 경우를 제외하고 회원에게 부여된
ID의 비밀번호 관리소홀, 부정사용에 의하여 발생하는 모든 결과에 대한 책임은 회원에게 있습니다.
③ 회원은 당 사이트 및 제 3자의 지적 재산권을 침해해서는 안 됩니다.
제 4 장 서비스의 이용
제 12 조 (서비스 이용 시간)
① 서비스 이용은 당 사이트의 업무상 또는 기술상 특별한 지장이 없는 한 연중무휴, 1일 24시간 운영을
원칙으로 합니다. 단, 당 사이트는 시스템 정기점검, 증설 및 교체를 위해 당 사이트가 정한 날이나 시간에
서비스를 일시 중단할 수 있으며, 예정되어 있는 작업으로 인한 서비스 일시중단은 당 사이트 홈페이지를
통해 사전에 공지합니다.
② 당 사이트는 서비스를 특정범위로 분할하여 각 범위별로 이용가능시간을 별도로 지정할 수 있습니다. 다만
이 경우 그 내용을 공지합니다.
제 13 조 (홈페이지 저작권)
① NDSL에서 제공하는 모든 저작물의 저작권은 원저작자에게 있으며, KISTI는 복제/배포/전송권을 확보하고
있습니다.
② NDSL에서 제공하는 콘텐츠를 상업적 및 기타 영리목적으로 복제/배포/전송할 경우 사전에 KISTI의 허락을
받아야 합니다.
③ NDSL에서 제공하는 콘텐츠를 보도, 비평, 교육, 연구 등을 위하여 정당한 범위 안에서 공정한 관행에
합치되게 인용할 수 있습니다.
④ NDSL에서 제공하는 콘텐츠를 무단 복제, 전송, 배포 기타 저작권법에 위반되는 방법으로 이용할 경우
저작권법 제136조에 따라 5년 이하의 징역 또는 5천만 원 이하의 벌금에 처해질 수 있습니다.
제 14 조 (유료서비스)
① 당 사이트 및 협력기관이 정한 유료서비스(원문복사 등)는 별도로 정해진 바에 따르며, 변경사항은 시행 전에
당 사이트 홈페이지를 통하여 회원에게 공지합니다.
② 유료서비스를 이용하려는 회원은 정해진 요금체계에 따라 요금을 납부해야 합니다.
제 5 장 계약 해지 및 이용 제한
제 15 조 (계약 해지)
회원이 이용계약을 해지하고자 하는 때에는 [가입해지] 메뉴를 이용해 직접 해지해야 합니다.
제 16 조 (서비스 이용제한)
① 당 사이트는 회원이 서비스 이용내용에 있어서 본 약관 제 11조 내용을 위반하거나, 다음 각 호에 해당하는
경우 서비스 이용을 제한할 수 있습니다.
- 2년 이상 서비스를 이용한 적이 없는 경우
- 기타 정상적인 서비스 운영에 방해가 될 경우
② 상기 이용제한 규정에 따라 서비스를 이용하는 회원에게 서비스 이용에 대하여 별도 공지 없이 서비스 이용의
일시정지, 이용계약 해지 할 수 있습니다.
제 17 조 (전자우편주소 수집 금지)
회원은 전자우편주소 추출기 등을 이용하여 전자우편주소를 수집 또는 제3자에게 제공할 수 없습니다.
제 6 장 손해배상 및 기타사항
제 18 조 (손해배상)
당 사이트는 무료로 제공되는 서비스와 관련하여 회원에게 어떠한 손해가 발생하더라도 당 사이트가 고의 또는 과실로 인한 손해발생을 제외하고는 이에 대하여 책임을 부담하지 아니합니다.
제 19 조 (관할 법원)
서비스 이용으로 발생한 분쟁에 대해 소송이 제기되는 경우 민사 소송법상의 관할 법원에 제기합니다.
[부 칙]
1. (시행일) 이 약관은 2016년 9월 5일부터 적용되며, 종전 약관은 본 약관으로 대체되며, 개정된 약관의 적용일 이전 가입자도 개정된 약관의 적용을 받습니다.