• Korean Journal of Environment and Ecology
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• v.33 no.2
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• pp.202-215
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• 2019

This study was conducted to investigate the spawning preference of the Acheilognathinae fishes in relation to the shell size of host mussels after identifying the species of eggs and fries in the host mussel using our recently developed RFLP (Restriction Fragment Length Polymorphism) molecular marker at four sites [Hongcheon Naechoncheon (HN) and Deokchicheon (HD) from the North Han River basin and Jeongseon Goljicheon (JG) and Joyanggang (JJ) from the South Han River] in South Korea during May in each year between 2015 and 2018. The Acheilognathinae fish observed in the studied sites included one species (Acheilognathus signifer) in HN and JG, three species (Rhodeus uyekii, A. signifer, and Acheilognathus yamatsutae) in HD, and two species (A. signifer and Acheilognathus yamatsutae) in JJ, and we collected 982 host mussels (Unio douglasiae sinuolatus) that inhabited in all four sites. Using the RFLP molecular marker, we confirmed 46 eggs and fry of the Acheilognathinae fish (454 A. signifer, 43 Acheilognathus yamatsutae, and 149 Acheilognathus yamatsutae) in Unio douglasiae sinuolatus (N=163; 16.6%). We compare the average shell length, shell height, and shell width of mussels with [presence] eggs/fry and mussels without [absence] eggs/fry to examine the spawning preference according to the size of host mussels in each site. The results show that the shell length (1.98 mm), shell height (0.85 mm), and shell width (0.73 mm) of mussels with the eggs/fry were significantly larger (Mann-Whitney U test, P=0.002; difference=1.98 mm) than those of mussel without eggs/fry in HD where three species cohabitated. Although the shell length, shell height, and shell width of mussels with the eggs/fry were larger also in the other three sites, the difference was not statistically significant. In addition, we analyzed the mean number of spawned eggs and fry of each species and found $9.31{\pm}5.94$ R. uyekii, $2.86{\pm}2.45$ A.signifer, and $2.50{\pm}1.32$ A. yamatsutae. R. uyekii spawned 6.45-6.81 more eggs than A.signifer and A. yamatsutae on average per mussel, and it was statistically significant (Kruskal-Wallis test, P < 0.001). These findings indicate that the three species of Acheilognathinae fish tend to prefer larger mussels as their spawning hosts, and this tendency increases when the number of cohabitating bitterling fish species increases. Moreover, A.signifer and A. yamatsutae spawned a smaller number of eggs evenly in more host mussels while R. uyekii spawned many eggs on relatively fewer mussels. We found mussels (N=4) having the eggs/fry of two coexisting species, A. signifier and A. yamatsutae in HD and JJ where more than two bitterling fish species occurred. It suggests the interspecific competition taking place between the Acheilognathinae fishes for utilizing the same resource of mussels for spawning when two or more species cohabitate. This study is expected help to understand better the spawning patterns and reproductive ecology of the Acheilognathinae fishes, which will provide insightful information for advancing our understanding of their ecological relationships - mutualism or host-parasitism - with host mussels.

• Journal of Intelligence and Information Systems
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• v.25 no.1
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• pp.21-41
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• 2019

Thanks to the rapid development of information technologies, the data available on Internet have grown rapidly. In this era of big data, many studies have attempted to offer insights and express the effects of data analysis. In the tourism and hospitality industry, many firms and studies in the era of big data have paid attention to online reviews on social media because of their large influence over customers. As tourism is an information-intensive industry, the effect of these information networks on social media platforms is more remarkable compared to any other types of media. However, there are some limitations to the improvements in service quality that can be made based on opinions on social media platforms. Users on social media platforms represent their opinions as text, images, and so on. Raw data sets from these reviews are unstructured. Moreover, these data sets are too big to extract new information and hidden knowledge by human competences. To use them for business intelligence and analytics applications, proper big data techniques like Natural Language Processing and data mining techniques are needed. This study suggests an analytical approach to directly yield insights from these reviews to improve the service quality of hotels. Our proposed approach consists of topic mining to extract topics contained in the reviews and the decision tree modeling to explain the relationship between topics and ratings. Topic mining refers to a method for finding a group of words from a collection of documents that represents a document. Among several topic mining methods, we adopted the Latent Dirichlet Allocation algorithm, which is considered as the most universal algorithm. However, LDA is not enough to find insights that can improve service quality because it cannot find the relationship between topics and ratings. To overcome this limitation, we also use the Classification and Regression Tree method, which is a kind of decision tree technique. Through the CART method, we can find what topics are related to positive or negative ratings of a hotel and visualize the results. Therefore, this study aims to investigate the representation of an analytical approach for the improvement of hotel service quality from unstructured review data sets. Through experiments for four hotels in Hong Kong, we can find the strengths and weaknesses of services for each hotel and suggest improvements to aid in customer satisfaction. Especially from positive reviews, we find what these hotels should maintain for service quality. For example, compared with the other hotels, a hotel has a good location and room condition which are extracted from positive reviews for it. In contrast, we also find what they should modify in their services from negative reviews. For example, a hotel should improve room condition related to soundproof. These results mean that our approach is useful in finding some insights for the service quality of hotels. That is, from the enormous size of review data, our approach can provide practical suggestions for hotel managers to improve their service quality. In the past, studies for improving service quality relied on surveys or interviews of customers. However, these methods are often costly and time consuming and the results may be biased by biased sampling or untrustworthy answers. The proposed approach directly obtains honest feedback from customers' online reviews and draws some insights through a type of big data analysis. So it will be a more useful tool to overcome the limitations of surveys or interviews. Moreover, our approach easily obtains the service quality information of other hotels or services in the tourism industry because it needs only open online reviews and ratings as input data. Furthermore, the performance of our approach will be better if other structured and unstructured data sources are added.

• Tuberculosis and Respiratory Diseases
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• v.64 no.6
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• pp.433-438
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• 2008

Background: Measurement of the maximum oxygen uptake in patients with chronic obstructive pulmonary disease (COPD) has been used to determine the intensity of exercise and to estimate the patient's response to treatment during pulmonary rehabilitation. However, cardiopulmonary exercise testing is not widely available in Korea. The 6-minute walk test (6MWT) is a simple method of measuring the exercise capacity of a patient. It also provides high reliability data and it reflects the fluctuation in one' s exercise capacity relatively well with using the standardized protocol. The prime objective of the present study is to develop a regression equation for estimating the peak oxygen uptake ($VO_2$) for men with moderate to very severe COPD from the results of a 6MWT. Methods: A total of 33 male patients with moderate to very severe COPD agreed to participate in this study. Pulmonary function testing, cardiopulmonary exercise testing and a 6MWT were performed on their first visits. The index of work ($6M_{work}$, 6-minute walk distance [6MWD]${\times}$body weight) was calculated for each patient. Those variables that were closely related to the peak $VO_2$ were identified through correlation analysis. With including such variables, the equation to predict the peak $VO_2$ was generated by the multiple linear regression method. Results: The peak $VO_2$ averaged $1,015{\pm}392ml/min$, and the mean 6MWD was $516{\pm}195$ meters. The $6M_{work}$ (r=.597) was better correlated to the peak $VO_2$ than the 6MWD (r=.415). The other variables highly correlated with the peak $VO_2$ were the $FEV_1$ (r=.742), DLco (r=.734) and FVC (r=.679). The derived prediction equation was $VO_2$ (ml/min)=($274.306{\times}FEV_1$)+($36.242{\times}DLco$)+($0.007{\times}6M_{work}$)-84.867. Conclusion: Under the circumstances when measurement of the peak $VO_2$ is not possible, we consider the 6MWT to be a simple alternative to measuring the peak $VO_2$. Of course, it is necessary to perform a trial on much larger scale to validate our prediction equation.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.7 no.1
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• pp.5-28
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• 2001

Objectives: The objective of this study was to investigate analysis of bone mineral density according to Women with low back pain women. Methods: The data were collected from women who visited Physical Examination Center of a Catholic university hospital located in Daegu. Questionnaires were completed by 50 women during the period from July 20, 2000 to January 12, 2001. The sample was divided into three groups(the normal group of 16 cases and the osteopenia group of 12cases and the osteoporosis group of 22 cases). Bone mineral density(BMD) of lumbar spine was measured using energy absorptiometry. Results: The bone mineral density of the lumbar spine decreased with aging. The bone mineral density of the lumbar spine decreased with the serum Calcium and Phosphorus and Alkaline phosphatase increased. The mean bone mineral density of the lumbar spine of healthy women in age(50~59) was 0.87g/$cm^2$, the lumbar spine of women with low back pain in age(50~59) was 0.77g/$cm^2$. In the multiple regression of risk factors to bone mineral density(BMD) of lumbar spine were correlated with age, marriage existence, exercise time, the loving food of taste, calcium, bone mineral density standard T scores(p<0.05). The experience for LBP increased as weight increased(Odds ratio=999.000). The experience for LBP increased as number of Exercise decreased(Odds ratio=999.000). The experience for LBP increased as menopause existence increased(Odds ratio=999.000). The experience for LBP increased as serum Calcium and Phosphorus increased (Odds ratio=999.000). however all four variables had significant no relationship. The correlation in variables in relation to low back pain and bone mineral density, age showed contra-correlation with low back pain existence, Alkaline phosphatase(p<0.01). Weight showed contra-correlation with body mass index(BMI)(p<0.01). Exercise time showed correlation with number of exercise(p<0.01). The loving food of taste showed contra-correlation with Alkaline phosphatase(p<0.05). Bone mineral density showed correlation with menopause existence(p<0.05). Conclusions: Results from this study indicated that a statistically significant association between bone mineral density of the lumbar spin and age, marriage existence, exercise time, the loving food of taste, calcium, bone mineral density standard T scores. In logistic regression test, there were no related variables. The combination of bone mineral density measurement and assessment of the bone turnover rate by measuring biochemical would be helpful for the treatment of patients with risks of osteoporosis. The more precise study for risk factors to osteoporosis is essential.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.2 no.2
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• pp.139-146
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• 1999

Purpose: The aim of this study was to evaluate the clinical significance of 24 hour pH monitoring in the pediatric patients with recurrent vomiting or regurgitation. Methods: We performed 24 hour pH monitoring on 87 pediatric patients with recurrent vomiting or regurgitation using GastrograpH with glass electrode. The pathologic GER was determined by the reflux index (RI). RIs>10% were considered positive in patients <1 year of age, whereas RIs of >5% were positive in other age groups. We evaluated the mean and standard deviation of the reflux parameters between physiologic and pathologic GER groups, and also compared the reflux indices of each group with respect to time zones of the day. Results: Pathologic GER was found in 32 of 87 patients (36.8%), and the age incidence included 32.5% in infants <6 months old, 13.3% in infants aged 6 months-1 year old, 61.5% in children aged 1~2 years old, 14.3% in children aged 2~3 years old and 66.7% in children >3 years old. In physiologic GER patients, the RI was $3.7{\pm}2.9%$ for the patients <1 year old (group A), and $1.8{\pm}1.5%$ for those ${\geq}1$ year old (group B) which was statistically significant between the 2 age groups (p=0.02). The number of long refluxes more than 5 minutes was significantly increased (p=0.03) in group A ($1.7{\pm}1.9$) than in group B ($0.8{\pm}1.0$). The duration of the longest reflux was significantly longer (p=0.007) in group A ($604{\pm}551$ sec) than in group B ($275{\pm}296$ sec). In pathologic GER patients, the RI was $17.7{\pm}11.6%$ for the patients <1 year old and $7.8{\pm}2.9$ for those ${\geq}1$ year old. The number of long refluxes of more than 5 minutes were $8.9{\pm}4.6$ and $3.2{\pm}1.8$, and the duration of the longest reflux were $1955{\pm}2190$ sec and $1093{\pm}706$ sec for each age group. In both physiologic and pathologic GER patients, there was no significant difference of RI among the time zones of the day. Conclusion: Pathologic GER was found in 36.8% of patients. There was significant difference of RI between those <1 year old and those ${\geq}1$ year old in physiologic GER patients. There was no significant difference of RI among the time zones of the day in both pathologic and physiologic groups. In our study, the frequency of pathplogic GER was too much higher in age group of 1~2 years old (61.5%) than in group of 6 months-1 year old (13.3%), which means that further study is needed to determine the pathologic criteria of RI (Vandenplas criteria is >5%) in the age group of 1~2 years old.

• Applied Biological Chemistry
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• v.4
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• pp.1-9
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• 1963

For the studies on the Chemical compositions of Sweet potatoes grown in Korean soil, Suwon No. 118 and Suwon No. 147 were applied as the samples during growing period, and 15 varieties of swee tpotatoes as the samples or comparisons among them. As the results of the studies followings were obtained. Changes of the chemical compositions of root tuber during growing period. 1. Total weights of root tubers and mean weight per root tuber were increased gradually as grew with the values of Suwon No. 147 is higher than that of Suwon No. 18 except the weight of Suwon No. 147 on September 9. 2. The moisture content of the roots were fairy uniform. 3. While the starch contents and crude starch yield in the root tuber were gradually increased with almost parallel as grew except the values of Suwon No. 147 on September 7. were markedly higher. 4. The total weight of the Sweet potatoes per Dan-Bo (about 0.25 acre) showed increased values with Suwon No. 147 is higher than Suwon No. 118 except the unexpected lower weight of Suwon No. 147 on September 9. and the crude starch yield of Suwon No. 147 per Dan-Bo also showed higher values than that of Suwon No. 18 with almost parallel increase of them as they grew. 5. Reducing sugar contents of them showed gradual decreases at earlier stages then increases at latter stages as grew, and total sugar and sucrose of them also showed gradual increases except extremly higher contents of Suwon No. 147 and lower values of Suwon No. 118 on September 9. 6. Total protein and soluble protein contents of them showed that initial and last stages of the growth are in higher values but middle stages are fairy low values with a little changes of difference between total protein, and soluble protein. The comparisons among those varieties. 7. The moisture contents of root tuber varies from 63% to 72% among them. 8. The starch contents of Suwon No. 18 (23.9%) is highest value among them, Ko-Ke No. 14 and Won-Ki successively lower and Dae-Nong No. 45 is the lowest one. Crude starch yield (%) of Ko-Ke No. 14 and Won-Ki successively lower and Dae-Nong No.45 is the lowest one. Crude starch yield (%) of Ko-Ke No. 147 is highest value, Suwon No. 118, Won-Ki are successively lower and Do-Ip is the lowest one. 9. Won-Ki is highest value in reducing sugar content, and Do-Ip No. 2 is lowest one in it. The sucrose content of Chil-Bok is highest and Won-Ki is lowest among them. Soluble total sugar content of Yu-Sim is in highest and Chun-Mi is in lowest value. 10. Total protein content showed that Suwon No. 147 is in highest value and Yu-Sim is in lowest one. On the other hand, soluble protein contents showed that Chil-Bok is in highest value and Yu-Sim is in lowest one.

• Applied Biological Chemistry
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• v.18 no.3
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• pp.145-166
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• 1975

The calcium balance study was carried out to determine the availability of calcium in different sources for chicks and laying hens. The sources of calcium were calcium carbonate (CC), dicalcium phosphate-dihydrate (DCPH), and dicalcium phosphate-anhydride (DCPA) for chicks and calcium carbonate (CC) and oyster shell (OS) for laying hens. The radioisotope dilution method was employed to measure the endogenous excreta calcium during the period of balance study following preliminary feeding. A. Experimental results with chicks: No significant difference was found among feed consumption of chicks fed diets containing different sources of calcium. Body weight gain of chicks was dependent upon the source of calcium. The gain decreased in the order of DCPH, DCPA and CC (P<0.01). The feed conversion efficiency in chicks fed DCPH was better than those in chicks fed CC or DCPA. The average tibia ash contents for chicks fed different sources of calcium were similar. The DCPH was superior to CC or DCPA regarding the calcium content in tibia ash. There were no significant differences among the average calcium contents in plasma trichloracetic acid filtrate in chicks irrespective of calcium sources. The mean apparent retention of calcium by chicks fed DCPH, CC and DCPA were 65.9, 64.0 and 59.9% respectively. The calcium to phosphorus ratios in tibia ash and plasma trichloracetic acid filtrate for chicks fed different sources of calcium were similar. The chicks fed DCPH showed the partition of endogenous excreta calcium in total excreta calcium as 35.6% which was higher than 31.0 or 31.4% for chicks fed CC or DCPA. The endogenous excreta calcium per day per chick in group fed DCPH, DCPA or CC were 17.2, 16.1 and 14.6mg respectively. The true retained calcium per day per chick in group fed DCPH were 109.9 mg which was higher than those observed with CC or DCPA group (P<0.01). The true retention of calcium by the birds fed diets containing DCPH, CC or DCPA were 78.1, 75.1 or 72.6% respectively. B. Experimental results with laying hens: The feed consumption, egg production and feed converion efficiency of laying hens fed diets containing different sources of calcium were similar. Calcium concentration in plasma trichloracetic acid filtrate in laying birds fed CC was equivalent to the value obtained by feeding OS. The apparent calcium retention by laying birds fed CC was 61.6% and it was significantly more than that of hens fed OS of 51.6% (P<0.05). The partition of endogenous excreta calcium in total excreta calcium of laying hens fed CC was 23.5% and this was higher than that of birds fed OS of 15.6%. The laying hens fed CC showed 310 mg of endogenous excreta calcium per day per bird while birds fed OS showed 261mg. The true retention of calcium by layers fed CC was 70.7% against 59.2% for birds fed OS (P<0.05).

• Journal of Chest Surgery
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• v.42 no.4
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• pp.480-486
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• 2009

Background: The Fogarty thromboembolectomy catheter technique was devised to extract distal arterial emboli and it represents a milestone for the treatment of patients with acute arterial occlusion since the 1960s. The major causes of arterial occlusion have changed from emboli of a heart origin to atherosclerosis over the past 30 years. Accordingly, questions have been raised about the effectiveness of simple Fogarty thromboembolectomy. Material and Method: During the period from March 1990 through August 2008, 156 patients who requiring Fogarty thromboembolectomy were analyzed. The patients were divided into two groups: those with simple Fogarty thromboembolectomy (Group 1, 79 patients) and those with additional vascular bypass graft surgery (Group 2, 77 patients). The duration of symptoms, the cause of thrombi, admission via the emergency room, a history of acupuncture or misdiagnosis, combined diseases, the anatomic occlusion site and the cause of death were analyzed using T-tests, cross tab tests, Chi square tests and Kaplan-Meier tests, respectively. Result: The mean age was 64$\pm$10 years in the 2 groups. The duration of symptoms (pain) in Group 1 vs Group 2 was 12$\pm$4 days vs 71$\pm$14 days (p=0.001). 50 (63%) patients in Group 1 were admitted via the emergency room vs 18 (23%) patients in Group 2 (p=0.005). Misdiagnosis and the treatment for herniated intervertebral disc or acupuncture were given to, 20 (25%) patients in Group 1 vs 30 (39%) patients in Group 2. Anticoagulation treatment before admission was performed in 22 (28%) patients in Group 1 vs 11 (14%) patients in Group 2. The causes of thrombi were heart disease in, 24 (30%) patients in Group 1 vs 6 (8%) patients in Group 2 (p=0.001), atherosclerosis in 46 (58%) patients in Group 1 vs 67 (87%) patients in Group 2 (p=0.001) and trauma in 9 (11%) patients in Group 1 vs 6 (8%) patients in Group 2. The combined diseases were cerebrovascular accident, hypertension and diabetes mellitus in 22 $\sim$ 37% of the total patients. The occlusion sites were mainly in the iliac and femoral arteries. Endarterectomy was performed in 7 (9%) patients in Group 1 vs 18 (23%) patients in Group 2 (p=0.012). Treatment was successful in 27 (34%) patients in Group 1 and in 40 (52%) patients in Group 2 (p=0.019). Reocclusion occurred in 37(47%) patients in Group 1 vs 20 (26%) patients in Group 2 (p=0.000), Amputation was done in 4 (5%) patients in Group 1 vs 12 (16%) patients in Group 2 (p=0.012) and death occurred in 10 (13%) patients (Group 1) vs 3(4%) patients (Group 2) (p=0.044). Conclusion: The recent past has shown a decline in the effectiveness of simple Fogarty thromboembolectomy with a changing pattern of acute arterial occlusion from a rheumatic heart origin to atherosclerosis. Additional bypass procedures play a role for the treatment of arterial occlusion instead of always performing simple Fogarty thromboembolectomy.

• Radiation Oncology Journal
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• v.21 no.4
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• pp.299-305
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• 2003

Purpose: In order to develop the national guide-lines for the standardization of radiotherapy we are planning to establish a web-based, on-line data-base system for laryngeal cancer. As a first step this study was performed to accumulate the basic clinical information of laryngeal cancer and to determine the items needed for the data-base system. Materials and Methods: We analyzed the clinical data on patients who were treated under the diagnosis of laryngeal cancer from January 1998 through December 1999 In the South-west area of Korea. Eligiblity criteria of the patients are as follows: 18 years or older, currently diagnosed with primary epithelial carcinoma of larynx, and no history of previous treatments for another cancers and the other laryngeal diseases. The items were developed and filled out by radiation oncologlst who are members of forean Southwest Radiation Oncology Group. SPSS vl0.0 software was used for statistical analysis. Results: Data of forty-five patients were collected. Age distribution of patients ranged from 28 to 88 years(median, 61). Laryngeal cancer occurred predominantly In males (10 : 1 sex ratio). Twenty-eight patients (62$\%$) had primary cancers in the glottis and 17 (38$\%$) in the supraglottis. Most of them were diagnosed pathologically as squamous cell carcinoma (44/45, 98$\%$). Twenty-four of 28 glottic cancer patients (86$\%$) had AJCC (American Joint Committee on Cancer) stage I/II, but 50$\%$ (8/16) had In supraglottic cancer patients (p=0.02). Most patients(89$\%$) had the symptom of hoarseness. indirect laryngoscopy was done in all patients and direct laryngoscopy was peformed in 43 (98$\%$) patients. Twenty-one of 28 (75$\%$) glottic cancer cases and 6 of 17 (35$\%$) supraglottic cancer cases were treated with radiation alone, respectively. The combined treatment of surgery and radiation was used in 5 (18$\%$) glottic and 8 (47$\%$) supraglottic patients. Chemotherapy and radiation was used in 2 (7$\%$) glottic and 3 (18$\%$) supraglottic patients. There was no statistically significant difference in the use of combined modality treatments between glottic and supraglottic cancers (p=0.20). In all patients, 6 MV X-ray was used with conventional fractionation. The iraction size was 2 Gy In 80$\%$ of glottic cancer patients compared with 1.8 Gy in 59$\%$ of the patients with supraglottic cancers. The mean total dose delivered to primary lesions were 65.98 ey and 70.15 Gy in glottic and supraglottic patients treated, respectively, with radiation alone. Based on the collected data, 12 modules with 90 items were developed or the study of the patterns of care In laryngeal cancer. Conclusion: The study Items for laryngeal cancer were developed. In the near future, a web system will be established based on the Items Investigated, and then a nation-wide analysis on laryngeal cancer will be processed for the standardization and optimization of radlotherapy.

• The Korean Journal of Air & Space Law and Policy
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• v.29 no.2
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• pp.109-134
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• 2014

Regulation (EC) No 261/2004 of the European Parliament and of the Council of 11 February 2004 establishing common rules on compensation of assistance to passengers in the event of denied boarding and of cancellation or long delay of flights (Regulation No 261/2004) provides extra protection to air passengers in circumstances of denied boarding, cancellation and long-delay. The Regulation intends to provide a high level of protection to air passengers by imposing obligations on air carriers and, at the same time, offering extensive rights to air passengers. If denied boarding, cancellation and long-delay are caused by reasons other than extraordinary circumstances, passengers are entitled for compensation under Article 7 of Regulation No 261/2004. In Wallentin-Hermann v Alitalia-Linee Aeree Italiane SpA(Case C-549/07, [2008] ECR I-11061), the Court did, however, emphasize that this does not mean that it is never possible for technical problems to constitute extraordinary circumstances. It cited specific examples of where: an aircraft manufacturer or competent authority revealed that there was a hidden manufacturing defect on an aircraft which impacts on safety; or damage was caused to an aircraft as a result of an act of sabotage or terrorism. Such events are not inherent in the normal exercise of the activity of the air carrier concerned and is beyond the actual control of that carrier on account of its nature or origin. One further point arising out of the court's decision is worth mentioning. It is not just necessary to satisfy the extraordinary circumstances test for the airline to be excused from paying compensation. It must also show that the circumstances could not have been avoided even if all reasonable measures had been taken. It is clear from the language of the Court's decision that this is a tough test to meet: the airline will have to establish that, even if it had deployed all its resources in terms of staff or equipment and the financial means at its disposal, it would clearly not have been able - unless it had made intolerable sacrifices in the light of the capacities of its undertaking at the relevant time - to prevent the extraordinary circumstances with which it was confronted from leading to the cancellation of the flight.