first of many citations to add

08_TEM.md

@@ -51,7 +51,7 @@ One example of the importance of aberrations and wavfunction modification is sho
 ```{figure} #app:tem_contrast
 :name: fig_tem_phase
 :placeholder: ./static/tem_contrast.png
-**TEM imaging of covid spike protein**: (left) In focus, (middle) defocued, and (right) Zernike phase plate TEM images. Structure from [citation for paper]
+**TEM imaging of covid spike protein **: (left) In focus, (middle) defocued, and (right) Zernike phase plate TEM images. [Covid structure](https://www.rcsb.org/structure/3jcl) from {cite}`walls2016cryo`
 ```
 
 For the same, dose the image contrast can be increased by modfying the wavefunctions through the introduction of aberrations. This is most often done with defocus, which is illustrated in the middle pannel. The resulting image has improved contrast, making it easier to visualize the covid spike protein. The middle pannel shows the defocused image, but the aberrations can often be corrected for later in post-processing. 

refs.bib

@@ -20775,3 +20775,14 @@ @article{wyrick_atom-by-atom_2018
   author = {Wyrick, Jonathan and Wang, Xiqiao and Namboodiri, Pradeep and Schmucker, Scott W. and Kashid, Ranjit V. and Silver, Richard M.},
   year = {2018},
 }
+
+@article{walls2016cryo,
+  title={Cryo-electron microscopy structure of a coronavirus spike glycoprotein trimer},
+  author={Walls, Alexandra C and Tortorici, M Alejandra and Bosch, Berend-Jan and Frenz, Brandon and Rottier, Peter JM and DiMaio, Frank and Rey, F{\'e}lix A and Veesler, David},
+  journal={Nature},
+  volume={531},
+  number={7592},
+  pages={114--117},
+  year={2016},
+  publisher={Nature Publishing Group UK London}
+}