95 research outputs found
Holographic storage of multiple coherence gratings in a Bose-Einstein condensate
We demonstrate superradiant conversion between a two-mode collective atomic
state and a single-mode light field in an elongated cloud of Bose-condensed
atoms. Two off-resonant write beams induce superradiant Raman scattering,
producing two independent coherence gratings with a different wave vector in
the cloud. By applying phase-matched read beams after a controllable delay, the
gratings can be selectively converted into the light field also in a
superradiant way. Due to the large cooperativity parameter and the small
velocity width of the condensate, a high conversion efficiency of % and
a long storage time of s were achieved.Comment: 5 pages, 4 figure
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é£ã®éå§ææãæ£ç¢ºã«å€å®ã§ããããšãå€æãããEcocement is a new type of hydraulic cement produced from incinerator ash. However. the incinerator ash contains large amounts of chloride, which, if not removed during the production process, is expected to accelerate the corrosion of steel bars when ecocement is used in reinforced concrete structures. The chlorides can be removed in the production process but at a high cost. Two types of ecocement have been produced, a high chloride type (type I) and a low chloride (type II). This paper investigates the corrosive behavior of steel bars embedded in the mortars containing both types of ecocement, cured under and exposed to wetting and drying cycles. Corrosion of the mild steel bars was monitored by halfcell potential, polarization resistance, and AC impedance measurements. The relative performance of the two types of ecocements with respect to the corrosive behavior of the embedded steel bars was discussed.From the results, the following conclusions could be drawn.(1) Steel bars embedded in mortars of high-chloride type ecocement is more susceptible to corrosion than that of low-chloride type one.(2) Carbonation accelerates corrosion of steel bars embedded in the mortars of both ecocements, although the effect is higher in high-chloride type than in low-chloride type.(3) Electrical measurement yields a good result in the monitoring of corrosion of steel bars embedded in cement mortars.(4) In both types of ecocement, the extent and severity of the corrsion of the embedded steel bars depend on the water to cement ratio, the higher the water to cement ratio, the greater the severity of corrosion.ç 究課é¡/é åçªå·:11650465, ç 究æé(幎床):1999-200
PCã³ã³ãã¡ã€ã³ãå·¥æ³ã«ããASRæå·éçã³ã³ã¯ãªãŒãæ©èã®è£åŒ·ã«é¢ããç 究
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šãªã³ã³ã¯ãªãŒããšåæ§ã§ããã(3)PCéŒæã§å·»ãç«ãŠãããšã«ãããã³ã³ã¯ãªãŒãã®åŒ·åºŠããã³éæ§ã倧ããæ¹åã§ãããããšã確èªããããã¢ãã«è©Šéšäœã®å±å€æŽé²è©Šéšã®çµæããã(1)ASRã®é²è¡ã¯æ¥å°ãééšãªã©ã®å±æçç°å¢ã®åœ±é¿ã倧ããåããããè¡šé¢è¢«èŠæã«ããå¡è£
ã®ASRæå¶å¹æã¯å°ããã(2)éŒæ¿å·»ãç«ãŠå·¥æ³ããã³PCéŒæå·»ãç«ãŠå·¥æ³ã«ããè£åŒ·ããè©Šéšäœã§ã¯é·æã«ããã£ãŠASRã«ããèšè¹ã®æå¶ããã³ã²ã³å²ãã®ææå¹æãèªããããã(3)éŒæ¿å·»ãç«ãŠå·¥æ³ã§ã¯æž©åºŠã«ãã圱é¿ã®ããè©Šéšäœã«çºçããæªã¿ã«ååæ¹åã®çžéãèŠããããããšã確èªããããäžèšã®ç 究ææãåããŠãå¹³æ8幎床ããã³å¹³æ9幎床ã«èœç»ææéè·¯ã®ASRæå·ã³ã³ã¯ãªãŒãæ©èã®PCéŒæå·»ãç«ãŠå·¥æ³ã«ããè£åŒ·å·¥äºãå®æœããããäž¡æ©èã§ã¯ãè£åŒ·åããASRã«ããæå·ã®ã¢ãã¿ãªã³ã°ãè¡ãªãããŠãããASRæå·æ©èã®èª¿æ»ãæœå·¥ããã³è£åŒ·èšèšã®èšé²ãä»é²ã®è³æãšããŠãŸãšããããŠãããA new strengthening method with prestressing steel wires, which is named the PC confined method, has been developed especially for ASR damaged RC piers. Reinforced concrete columns, 300 mm in diameter and 900 mm high, were prepared in order to examine the effects of the prestressing force around the concrete column on the confinement of the cracks of concrete due to alkali-silica reaction and on the improvement of load-carrying capacity and ductility of damaged concrete columns.From the experimental results, it was concluded that the prestressing force given around the concrete column could effectively confine the cracks due to ASR and decrease the expansion of concrete. Thus, it was found that both the strength and ductility of damaged RC column was much improved by PC confined method. Based on the results of the laboratory test, the PC confined method was successfully adopted in the strengthening for ASR damaged RC piers of the Toyokawa bridge and the Kumakigawa bridge in Noto peninsula in Ishikawa prefecture in 1997 and 1998, respectively. The measurements on changes with time in the stress and strain of concrete in the piers of the Toyokawa bridge after strengthening by PC confined method are now monitored.ç 究課é¡/é åçªå·:09650504, ç 究æé(幎床):1997-199
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çå³ãå®æãããšãšãã«,ãé·çæ©ãã§äœ¿çšããã³ã³ã¯ãªãŒãåã³PCéŒç·(çŽåŸ3mmã®ãã¢ãç·)ã®å質ããæ³°å¹³æ©ããšæ¯èŒæ€èšãã.ãã®åŸ,\u27å¹³æ13幎10æã«(æ ª)ããŒãšã¹äžå°Ÿå·¥å Ž(çŸ(æ ª)ããŒãšã¹äžè±)ã«ãŠ,PCæ¡æ¬äœåã³åææ¡ã®æ²ãåã³ããæèŒè·è©Šéšãå
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¬åã«ç§»èšããã.ãŸã,ãæ³°å¹³æ©ã,ãé·çæ©ãã«é¢ãã調æ»è³æãæŽçã,æŽå²ç䟡å€ã®é«ãäž¡æ©æ¢ã®èšé²ãååãšããŠãŸãšãããšãšãã«,å¹³æ14幎11æã«ç¹å¥è¬æŒäŒãã³ã³ã¯ãªãŒãã¯æ¬åœã«äžå€«ã§é·æã¡ãããäž»å¬ã,ãæ³°å¹³æ©ã,ãé·çæ©ãã®èª¿æ»çµæãå€ãã®åæšé¢ä¿è
ã«å ±åãã.ããã«,解äœèª¿æ»ã®èšé²ã2æ¬ã®ãããª(é沢倧åŠå·¥åŠéšç·šé,(æ ª)ããŒãšã¹äžè±ç·šé)ã«ãŸãšãã.The Chousei bridge and the Taihei bridge are the first prestressed concrete bridges (PC) in Japan, which were constructed in 1953 and 1954 across the Misogi river in Nanao city in Ishikawa Prefecture. After symbolizing the birth of PC bridge in Japan for 50 years, the bridge was earmarked for relocation as part of an urban development project. They were dismantled in August 2000 and in September 2001. Following its removal, some of the girders were subjected to examination and load testing to determine both the physical and chemical properties of old concrete and the load-bearing capacity of old bridge. The water to cement ratio of the concrete was found to be as low as 33 % and it texture was also very dense. This proves that the concrete mixed for bridge is very durable, which results in no carbonation of concrete and little corrosion of stee bars and PC wires in concrete. The bending and shearing load capacity of girders of the gbridge was also found to be satisfactory for the requirements of specifications of road bridges. After the test, the Chousei bridge was relocated to the memorial park on the outskirts of Nanao city.ç 究課é¡/é åçªå·:13650503, ç 究æé(幎床):2001-2002åºå
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åãããããšãå€æãã.(4)ASRå£åæ©èã®è£åŒ·ããã³ã¢ãã¿ãªã³ã°ã®æè¡éçº---ASRå£åæ©èã§ã¯,éçç Žæãçºçããææ¢ãéŒè£œæ¯ä¿å·¥ã§ä»®åãããåŸã«,ææ¿ããããšã«æ±ºãã.ASRå£åæ©èã®è£åŒ·æè¡ã¯æªç¢ºç«ã§ããã®ã§,ã¢ãã¿ãªã³ã°ãåæã«å®æœã,ãã®èšæž¬çµæãä»åŸã®è£åŒ·èšèšã«åæ ããã.çŸåšã,èœç»ææéè·¯ã§ã¯ææ¿ããå®æœããæ©èãè£åŒ·ããããŒãã³ã°,äŸçšäžã®ãã³ãã«ãªã©ã§èªåèšæž¬ã«ããã¢ãã¿ãªã³ã°ãå®æœããŠãã.Research results obtained in this study are summarized as follows ;(1)Investigation on fracture of steel bars in ASR-affected structuresResearch works revealed that the embrittle fracture of steel bars at the bending corner of stirrup or bent-up steel bars, due to excessive expansion of concrete due to ASR, occurred in the pillow beam or footing of piers and the abutment in bridges located in Ishikawa Prefecture, leading to the significant loss of structural integrity of concrete elements.(2)Mechanisms of fracture of steel bar due to ASRIn the pillow beam or foundation of bridge pier, a lot of stirrup steel bars fractured at the bending corners, without any elongation of steel bar. The fracture surface of steel bar seemed to be very flat and smooth, which indicated the typical embrittlement fracture of steel bar. Whether or not the fracture of steel bars may be associated with the stress corrosion cracking and/or the hydrogen embrittlement fracture was discussed.(3)Asset management for ASR-deteriorated bridgesFor all bridge piers located in Ishikawa prefecture, which is considered to be the most serious ASR case in Japan, the degree of deterioration of bridge pier due to ASR was investigated by the visual inspection of cracking. Corresponding to the classification of ASR deterioration level of each bridge pier, the repair/strengthening method and maintenance procedure were proposed.(4)Strengthening and monitoring of ASR-deteriorated bridge piersIn the case study of the pillow beam of Kashima Bridge and the foundation of Tokuda No.2 Bridge in Ishikawa Prefecture, the degree of deterioration of bridge pier due to ASR was also investigated by the non-destructive inspection. Based on the classification of ASR deterioration level of each element, the most appropriate strengthening methods were adopted for them. In the maintenance of these bridges, the monitoring using crack sensors was successfully applied in order to ensure the daily safety of these bridges.ç 究課é¡/é åçªå·:16360218, ç 究æé(幎床):2004-200
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