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MicroscopyEducation


eliminates the need to spend time “cleaning” the images. In addition, cutting along a side of the rectangular cheese block ensures that each cross section/slice has the same area, removing the need to manually delete out-of-focus portions of the image. Images in Figure 4c show a 3D reconstruction of the cheese block achieved using the same code as the cabbage reconstruction. In addition to reconstructing the full geometry, simple binarization and color inversion can be used to extract the shape of the holes ( Figure 4d ). Based on the reconstruction of the 3D distri- bution of the holes, the Swiss cheese that was used had a hole density of ~0.0023 holes per cm 3 (~18 holes per 800 cm 3 ).


Figure 3 : (a) Macroscale “destructive tomography” setup: red cabbage and mandolin slicer; (b) example color and binarized cross sections of the red cabbage; (c) and (d) 3D reconstruction of the red cabbage. (c) shows “cut-aways” along the z -axis, and (d) shows a z -axis and x -axis square cut-away.


and reassembled prior to giving the “sample” to students. We found that a large block of Swiss cheese is ideal for this purpose. T e images in Figures 4 a and 4 b show an individual slice of the cheese and the 8 cm × 10 cm × 10 cm block of the cheese aſt er slicing and “reassembling,” respectively. Putting each slice of cheese in the same corner of the sheet of paper placed under a camera on a tripod ensures that all images are well aligned. Furthermore, the white background within the holes


2017 September • www.microscopy-today.com


Results: Destructive Tomography Activity in Middle School Demonstration program . In the Spring of 2017 undergraduate student interns from ASU’s Science Is Fun educational outreach group, which is a part of the LeRoy Eyring Center for Solid State Science [ 7 ], implemented the destructive tomography instructional activity at Madison Park Middle School in Phoenix, Arizona. In this activity, three classroom rotations of about thirty 7th grade students each were introduced to the basic concepts of wavelength, imaging resolution, electron microscopy, focused ion beam, and 3D image reconstruction through an engaging 45-minute demonstration that included destructive tomography of red potatoes. T e primary goals of this activity were to introduce students to the tools scientists use in a microscopy lab and to provide examples of how these tools are used. T e theoretical framework of this instructional activity was based on the educational philosophy of constructivism, in which learning is derived from experience and assessment [ 23 ]. Demonstrations in the activity were therefore designed to emphasize student engagement (touching, experimenting) and exploration through questioning rather than repetition of presented facts.


Image resolution . T e presentation was structured as a brief introduction to background concepts (5 min), followed by a series of discussion questions with multiple short demonstrations (15 min), leading to the primary activity (15 minutes), and a concluding discussion with questions (10 minutes). Aſt er the brief discussion and few short activities on the electromagnetic spectrum and image resolution, students were asked, “What do we use to see things that are smaller than the wavelength of our visible light source?” We observed that, using a diagram of the electromagnetic


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