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Unit 3.7 - Glide Planes and Wallpaper Groups 

Frank Hoffmann
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Unit 3.7 of our course The Fascination of Crystals and Symmetry
Additonal resources at: crystalsymmetr...
In this unit we want to look at glide planes, one of the hree symmetry elements, which have a translational component. In the plane, i.e. in 2D objects these kind of symmetry elements are caled glide lines.
Furthermore, we will explore the 5 Bravais lattices of the plane and the 17 plane symmetry groups, which describe the symmetry of 2D pattern completely.
If you prefer books instead of videos have a look at:
www.amazon.com...

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18 сен 2024

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Комментарии : 28   
@julietten5614
@julietten5614 6 лет назад
You are a legend. Thank you for the very clear explanations.
@honestlordcommissarbrighte7921
@honestlordcommissarbrighte7921 4 года назад
Bless you sir, you just summarized my problem in minutes what two one hour and thirty minute lectures tried to do and failed miserably.
@narminsalimova7334
@narminsalimova7334 5 лет назад
Just amazing! Can't be clearer explanation!
@bina5580
@bina5580 5 лет назад
I am obsessed with your lectures !
@deathslayer1411
@deathslayer1411 5 лет назад
Where is the glide plane on the p2mg image at the end? Could you explain that image in more detail please?
@FrankHoffmann1000
@FrankHoffmann1000 5 лет назад
Have a look at the following image: crystalsymmetry.wordpress.com/fig_4-18/
@suvarnnacokepaishatsa8195
@suvarnnacokepaishatsa8195 5 лет назад
Thank you very much! Your materials can be understood easily.
@FrankHoffmann1000
@FrankHoffmann1000 5 лет назад
Thank you very much - you are very welcome!
@abbes635
@abbes635 4 года назад
you are amazing, im graduating this year because of you thankyou❤️
@FrankHoffmann1000
@FrankHoffmann1000 4 года назад
Thank you very much for your kind words. Glad that you find these videos helpful.
@tengocaries
@tengocaries 3 года назад
Thank you so much, you are an amazing teacher! :)
@kamalgurnani924
@kamalgurnani924 5 лет назад
Could you please explain how do we decide 'p' or 'c' in the p2mg image shown at the end of the video? Thanks for such a clear presentation.
@FrankHoffmann1000
@FrankHoffmann1000 5 лет назад
Look for the smallest possible unit cell - is this cell already rectangular (angle of 90°)? Then take 'p'! And then the cell should consists of exactly one motif. In a c-centered cell, there were already two motifs in the cell. You would only choose 'c', if the primitive cell had an angle ≠ 90°.
@gracesolante7357
@gracesolante7357 4 года назад
Thank you for this. Where can i find the notation names for all those 17 patterns?
@FrankHoffmann1000
@FrankHoffmann1000 4 года назад
en.wikipedia.org/wiki/List_of_planar_symmetry_groups
@azrulazwan6101
@azrulazwan6101 5 лет назад
tq for the video
@Brucebod
@Brucebod 2 года назад
Thank you.
@wiwiwi6446
@wiwiwi6446 Год назад
Hi! question, in minute 7:05 tiy say 5 bravais lattices and 17 plane groups. Shouldn't it be 7 and 14?
@FrankHoffmann1000
@FrankHoffmann1000 Год назад
No - you're probably thinking of the number of crystal systems (7) and Bravais lattices (14) in 3D space. The number of space groups is then 230. But here we discuss the symmetry of the plane, i.e. we are in 2D. There are 4 crystal systems, 5 Bravais lattices and 17 plane groups.
@wiwiwi6446
@wiwiwi6446 Год назад
@@FrankHoffmann1000 Oh right! Sorry I mixed stuff up. THnak you for answering!!
@meetatrivedi7332
@meetatrivedi7332 5 лет назад
Thanks for the lectures, can you please explain Fmmm too?
@FrankHoffmann1000
@FrankHoffmann1000 5 лет назад
Fmmm is not a plane group but a space group - please refer to the units of chapter 4
@asailingstone
@asailingstone 5 лет назад
where can I find all lecture videos?
@FrankHoffmann1000
@FrankHoffmann1000 5 лет назад
ru-vid.com/show-UCts9FTFNInqTMvcFpdyap7wvideos?disable_polymer=1
@beyelear9665
@beyelear9665 2 года назад
Dear Sir, Thank you for your great work! I have a question: for the notation say "P3m1", it has a mirror plane perpendicular to the x-axis, but no mirror/glide plane to the y-axis, but how should we define the x and y axis? I'm comparing P3m1 and P31m, they both have the same type of primitive cell with edges 120/60 degrees to each other, I tried to make two neighboring edges of the cell as x-axis and y-axis, but find it hard to explain the mirror plane perpendicular to axis then.
@FrankHoffmann1000
@FrankHoffmann1000 2 года назад
For these complicated cases it is always advisable to have a look at the International Tables for Crystallography. First of all, it might be allowed to correct your first statement. In the trigonal crystal system the x and y axis are identical / symmetry equivalent. This means that in the space group P3m1 you have mirrors perpendicular to the x _and_ the y axis. For this reason you are free to define any of the two axes as x or y. The more difficult case is indeed the other space group P31m, whoch can be described as a variant of the space group P3m1 with a different setting (actually the coordinate sytem is rotated by 30° with respect to P3m1). Here the two mirror planes are perpendicular to the direction [210] and [120], directions that are not perpendicular to the x or y axis, indeed. For a sketch of the somewhat simplified (leaving out the glides) symmetry element diagrams see: crystalsymmetry.files.wordpress.com/2022/02/p3m1_vs_p31m.pdf
@beyelear9665
@beyelear9665 2 года назад
@@FrankHoffmann1000 Thank you very much! So the only difference is how the two mirror planes are placed.
@FrankHoffmann1000
@FrankHoffmann1000 2 года назад
@@beyelear9665 Exactly!
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