3,448 research outputs found

    Impact of incisions of cataract surgery on patients with corneal astigmatism

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    AIM: To research the impact of different 3.2mm incisions of cataract surgery on patients whose corneal astigmatism was within 25 degrees by Orbscan. METHODS: We collected 40 cases of cataract patients whose corneal astigmatism was within 25 degrees detected by Orbscan and randomly divided them into groups A, B. Detected by Orbscan, 20 patients(20 eyes)in group A was conducted with 3.2mm corneal astigmatism axial incision and 20 patients(20 eyes)in group B was conducted with 3.2mm corneal incision on 90 degrees of the axis. All cataract operations were implemented by the same physician. We observed the postoperative changes of corneal astigmatism between two groups. RESULTS: The comparisons of Polar K on each time preoperative and postoperative point were significant differences within each group. But the comparisons of Polar K on each time preoperative and postoperative point were not statistically significant between two groups. After 3 months, two kinds of incisions would both increase about 0.3D Polar K in the cornea. CONCLUSION: 3.2mm corneal incision may cause Polar K 0.3D in corneal astigmatism

    A feedback-driven bubble G24.136+00.436: a possible site of triggered star formation

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    We present a multi-wavelength study of the IR bubble G24.136+00.436. The J=1-0 observations of 12^{12}CO, 13^{13}CO and C18^{18}O were carried out with the Purple Mountain Observatory 13.7 m telescope. Molecular gas with a velocity of 94.8 km s1^{-1} is found prominently in the southeast of the bubble, shaping as a shell with a total mass of 2×104\sim2\times10^{4} MM_{\odot}. It is likely assembled during the expansion of the bubble. The expanding shell consists of six dense cores. Their dense (a few of 10310^{3} cm3^{-3}) and massive (a few of 10310^{3} MM_{\odot}) characteristics coupled with the broad linewidths (>> 2.5 km s1^{-1}) suggest they are promising sites of forming high-mass stars or clusters. This could be further consolidated by the detection of compact HII regions in Cores A and E. We tentatively identified and classified 63 candidate YSOs based on the \emph{Spitzer} and UKIDSS data. They are found to be dominantly distributed in regions with strong emission of molecular gas, indicative of active star formation especially in the shell. The HII region inside the bubble is mainly ionized by a \simO8V star(s), of the dynamical age \sim1.6 Myr. The enhanced number of candidate YSOs and secondary star formation in the shell as well as time scales involved, indicate a possible scenario of triggering star formation, signified by the "collect and collapse" process.Comment: 13 pages, 10 figures, 4 tables, accepted by Ap

    A multi-wavelength observation and investigation of six infrared dark clouds

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    Context. Infrared dark clouds (IRDCs) are ubiquitous in the Milky Way, yet they play a crucial role in breeding newly-formed stars. Aims. With the aim of further understanding the dynamics, chemistry, and evolution of IRDCs, we carried out multi-wavelength observations on a small sample. Methods. We performed new observations with the IRAM 30 m and CSO 10.4 m telescopes, with tracers HCO+{\rm HCO^+}, HCN, N2H+{\rm N_2H^+}, C18O{\rm C^{18}O}, DCO+^+, SiO, and DCN toward six IRDCs G031.97+00.07, G033.69-00.01, G034.43+00.24, G035.39-00.33, G038.95-00.47, and G053.11+00.05. Results. We investigated 44 cores including 37 cores reported in previous work and seven newly-identified cores. Toward the dense cores, we detected 6 DCO+^+, and 5 DCN lines. Using pixel-by-pixel spectral energy distribution (SED) fits of the Herschel\textit{Herschel} 70 to 500 μ\mum, we obtained dust temperature and column density distributions of the IRDCs. We found that N2H+{\rm N_2H^+} emission has a strong correlation with the dust temperature and column density distributions, while C18O{\rm C^{18}O} showed the weakest correlation. It is suggested that N2H+{\rm N_2H^+} is indeed a good tracer in very dense conditions, but C18O{\rm C^{18}O} is an unreliable one, as it has a relatively low critical density and is vulnerable to freezing-out onto the surface of cold dust grains. The dynamics within IRDCs are active, with infall, outflow, and collapse; the spectra are abundant especially in deuterium species. Conclusions. We observe many blueshifted and redshifted profiles, respectively, with HCO+{\rm HCO^+} and C18O{\rm C^{18}O} toward the same core. This case can be well explained by model "envelope expansion with core collapse (EECC)".Comment: 24 pages, 11 figures, 4 tables. To be published in A&A. The resolutions of the pictures are cut dow