Treating intrasurgical complications of corneal refractive operation with customized ablation. A clinical case

Purpose: to evaluate the prospects of customized Finalfit based ablation for optical rehabilitation of a patient with corneal surface errors caused by intrasurgical microtome-induced damage of a corneal flap during a LASIK excimer laser correction of vision.Material and methods. In Helmholtz Center, a patient with such damage was given a phototherapeutic keratectomy (PTK) combined with topographyguided photorefractive keratectomy.Results. In two months after the surgery, the patient’s uncorrected visual acuity rose from 0.15 to 1.0; the spherical component of refraction changed from -3.5 to +1.0 D, the cylindrical component of refraction fell from 1.75 to 0.25 D. Aberrometry demonstrated a decrease of RMS from 2.19 to 0.61 D, Total HOAs from 2.281 to 0.829; Tilt from 0.406 to 0.313; HOA from 1.152 to 0.247, Coma from 0.298 to 0.124, Trefoil from 1.088 to 0.094, SA from 0,127 to 0,021.Conclusion. The clinical case demonstrates the expediency and efficiency of corneal remodeling for the rehabilitation of induced errors of the corneal surface by excimer laser correction of vision based on PTK (Flex scan) + FinalFit after corneal refractive surgery.

A New Method for Precision Measurement of Wall-Thickness of Thin-Walled Spherical Shell Parts

Thin-walled parts are widely used in shock wave and detonation physics experiments, which require high surface accuracy and equal thickness. In order to obtain the wall thickness of thin-walled spherical shell parts accurately, a new measurement method is proposed. The trajectories, including meridian and concentric trajectories, are employed to measure the thickness of thin-walled spherical shell parts. The measurement data of the inner and outer surfaces are unified in the same coordinate system, and the thickness is obtained based on a reconstruction model. The meridian and concentric circles’ trajectories are used for measuring a spherical shell with an outer diameter of Φ210.6 mm and an inner diameter of Φ206.4 mm. Without the data in the top area, the surface errors of the outer and inner surfaces are about 5 μm and 6 μm, respectively, and the wall-thickness error is about 8 μm with the meridian trajectory.

Surface Features of Code-switching in ‘The Nigerian Online Community’ Page on Facebook

Existing studies on code-switching have mainly been carried out among English/Chinese bilinguals. Studies on English/Yoruba/Pidgin English bilinguals with emphasis on code-mixing and code-switching on the Internet have been grossly insufficient. Therefore, this study reveals the surface features of code-switching among Yoruba/English/Pidgin English bilinguals in the Nigerian Online Community on Facebook. For theoretical framework, we relied on insights from Halliday’s (1994) functional theory of language. Five types of surface features were identified: simplified lexicon and sentences, non-adherence to the use of tones/diacritics, inconsistencies of spellings and words, unnecessary lengthening of letters, and tolerance of surface errors. The study has revealed the distinctive features of code-switching in the Nigerian Online Community page on Facebook. These linguistic features have thrown more light on the characteristics of the language use on the Facebook forum and how the posters use the codes in their speech repertoire to achieve this

Accuracy of intraoral scan images in full arch with orthodontic brackets: a retrospective in vivo study

Objectives The purpose of this retrospective study was to evaluate the accuracy of intraoral scan (IOS) images in the maxillary and mandibular arches with orthodontic brackets. Material and methods From digital impressions of 140 patients who underwent orthodontic treatment, consecutive IOS images were selected based on standardized inclusion criteria: Two pre-orthodontic IOS images (IOS1 and IOS2) of permanent dentition with fully erupted second molars and IOS images obtained immediately after orthodontic bracket bonding (IOSb). Superimpositions were performed to evaluate the reproducibility of repeated IOS images. Accuracy of IOSb images was analyzed by comparing the average surface errors between IOS1c and IOS2c images, which were IOS images cut based on the same region of the interest as between IOS1 and IOSb images. Results A total of 84 IOS images was analyzed. The average surface errors between IOS1 and IOS2 images were 57 ± 8 μm and 59 ± 14 μm in the maxillary and mandibular arch, respectively, and their reliability was almost perfect. The average errors between IOSb and IOS1c images exhibited an increase, which measured 97 ± 28 μm in the maxillary arch and 95 ± 29 μm in the mandibular arch. These surface deviations between IOSb and IOS1c images were significantly larger in each region as well as entire dentition (P < 0.001) compared to those between IOS1c and IOS2c images. Conclusions The average surface errors of the scans with brackets showed increased values compared with those without brackets. This suggests that orthodontic brackets could affect the trueness of intraoral scan images. Clinical relevance It is necessary for clinicians to consider the effect of brackets on digital impression when using IOS images in orthodontic patients.

Fast convolution-based performance estimation method for diffraction-limited source with imperfect X-ray optics

Although optical element error analysis is always an important part of beamline design for highly coherent synchrotron radiation or free-electron laser sources, the usual wave optics simulation can be very time-consuming, which limits its application at the early stage of the beamline design. In this work, a new theoretical approach has been proposed for quick evaluations of the optical performance degradation due to optical element error. In this way, time-consuming detailed simulations can be applied only when truly necessary. This approach treats the imperfections as perturbations that convolve with the ideal performance. For simplicity, but not by necessity, the Gaussian Schell-model has been used to show the application of this theoretical approach. The influences of the finite aperture size and height error of a focusing mirror are analysed using the proposed theory. The physical explanation of the performance degradation acquired from the presented approach helps to give a better definition of the critical range of error spatial frequencies that most affect the performance of a mirror. An example comparing two mirror surface errors with identical power spectral density functions is given. These two types of mirror surface errors result in very different intensity profiles. The approach presented in this work could help beamline designers specify the error tolerances on general optical elements more accurately.

Minimizing Flute Engagement to Adjust Tool Orientation for Reducing Surface Errors in Five-Axis Ball End Milling Operations

Surface errors due to force-induced tool and workpiece deflections are one of the major errors in multi-axis machining of parts especially with thin-walled structures. Dominant approaches to reduce these surface errors are re-machining the part, feed scheduling, and tool path modification. These methods are time consuming and computationally costly, and they rely on experimental data which is used in cutting force and deflection predictions. The present paper introduces a pure geometrical approach to reduce surface errors drastically by minimizing the engagement lengths of flutes’ cutting edges when a point on the flute’s cutting edge is in contact with the design surface. The total engagement length of the flutes’ cutting edges when one of them generates a contact point on the workpiece surface is formulated and considered as the minimization objective function of an optimization problem. Tilt and lead angles, which define the tool orientation, are the design variables of the optimization problem subjected to constraints based on the geometrical requirements of the ball end milling process. The optimization problem uses the nominal tool path to generate an optimal tool path with adjusted tool orientations. The presented method is computationally inexpensive and does not need any experimentally calibrated coefficients to predict cutting forces because of the pure geometrical nature of the approach. The method is experimentally validated through five-axis ball end milling experiments in which more than 90% surface error reduction is achieved.

Looking in the Mirror: Self-Assessment in EFL Writing

Self-assessment helps students take greater control of the learning process and develop critical analytical skills to improve future performances. This project tracks 28 second-year writing students at a university in Japan. Over a 15-week term, the students wrote three papers on a variety of topics that required research and argumentation. Student writers conducted self-assessment on the final drafts of a three-draft process through the use of a rubric worksheet that was also used in peer review and teacher assessment. The assessments were then analyzed by this researcher to identify and interpret any patterns as evidence of students’ progress in evaluation and gain insight into students’ priorities in evaluation. The results indicated that students prioritize the content of their writing for the majority of the feedback they gave themselves. The inference made here is that students are developing assessment skills as they focused on more substantial issues with their writing as opposed to focusing mainly on surface errors (such as spelling and grammar). 自己診断(セルフアセスメント)を用いることにより、学習者は自己の学習過程を管理しやすくなり、また今後の成長を促す批判的分析能力を伸ばすことに役立つ。本論文では日本の大学における28人の2年生を調査対象とした。15週間の間にリサーチ・討論が必要な様々なテーマにつきそれぞれの学生が3つのレポートを書き、相互診断・教師の評価時にも使用できるチェックシートを用い、3回の草稿中、最終草稿について自己診断を実施。その後、この自己診断内容は、学生の評価能力向上を証明するパターンとして認識もしくは解釈できるか分析され、また学生が評価の際に何に主眼をおくかを見極めることに使用された。結果として、学生が自身に与えるフィードバックの大部分が文章の内容を優先していることが示された。学生達はスペルや文法などという表面上のミスに重点を置くよりも、実質的な議題に重点を置くため、彼らの評価能力が向上したことを推論する。