Gravitational waves are predicted by the Einstein's theory of General Relativity. The direct detection of gravitational waves is one of the most challenging tasks in modern science and engineering due to the 'weak' nature of gravity. Recent development of the laser interferometer technology, however, makes it possible to build a detector on Earth that is sensitive up to 100-1000 Mpc for strong sources. It implies an expected detection rate of neutron star mergers, which are one of the most important targets for ground-based detectors, ranges between a few to a few hundred per year. Therefore, we expect that the gravitational-wave observation will be routine within several years. Strongest gravitational-wave sources include tight binaries composed of compact objects, supernova explosions, gamma-ray bursts, mergers of supermassive black holes, etc. Together with the electromagnetic waves, the gravitational wave observation will allow us to explore the most exotic nature of astrophysical objects as well as the very early evolution of the universe. This review provides a comprehensive overview of the theory of gravitational waves, principles of detections, gravitational-wave detectors, astrophysical sources of gravitational waves, and future prospects.

Central commissary school foodservice operations' practices and their dietitians' job duties were assessed and compared with those of their counterpart of conventional school foodservice operations to find out strategies for early settlement and better management for commissary system. Survey qestionnaires consisted of general background, employees' work schedule and dietitians' job duties. 12 commissary schools(out of 22 existing in Korea) and 77 conventional schools from Kyungkido were participated in the survey. The results of this study can be summarized as follows: 1. Central commissary school foodservice was presently utilized at 5 schools from islands type, 11 schools from rural type, and 6 schools from urban type, consisting total of 22 commissary schools, and 52 satellite schools. 2. Dietitians were evenly employed with their experiences, 55.5% were those with less than 2 years of experience, 44.6% were those with more than 2 years of experience. 3. Commissary schools employed more full-time empolyees(1.8±0.7) than conventional schools(0.3±0.5), however as far as the production capacity was concerned, only the part-time employees played significant roles(p〈.01). Regardless of the number of students, an absolute number of full-time employees were employed, and their duties were not carried out efficiently. The part-time employees of commissary schools performed more loaded work compared to their counterparts in conventional schools. 4. Out of the dietitians' foodservice duties, 'basic food service production(3.9±0.7)' were carried out adequately, whereas 'nutrition education and advertisement(2.5±0.6)' and 'administrative affairs and information related duties(2.8±0.9)' were not. In order to enhance their working capacity, systematic organizational reforms are imminent. 5. Survey results also showed that dietitians performed less duties at satellite school than at the central commissary. This indicates more systematic foodservice management practices are urgently needed.