08:00:42 From Alex Klotz to Everyone:
	good morning everyone
08:01:02 From Abdou-Rachid Thiam to Everyone:
	Hi everyone
08:03:29 From Rana Ashkar to Everyone:
	This might be a good point to remind everyone that all are supposed to abide by the workshop code of conduct.
08:03:47 From Markus Deserno to Everyone:
	Absolutely!
08:05:29 From Alex Klotz to Everyone:
	Relevant to today's talk 
	
	https://pbs.twimg.com/media/E1hWVMeXIAEcr_Y?format=png&name=medium
08:06:03 From Rumiana Dimova to Everyone:
	Link to Google drive: https://drive.google.com/drive/u/1/folders/1WEmN3j5Ma_zNfDLe58xFnP4Q0D5Z_nuZ
08:07:26 From Anand Srivastava to Everyone:
	Thanks for the decision to record the discussions. Regards
08:12:48 From Robin Selinger to Everyone:
	The nonlinear term in the Green-Lagrange strain is important for rotation invariance. Without it, a simple rotation of the sample produces a nonzero strain even though the sample is not in any way deformed.
08:12:48 From Alex Klotz to Everyone:
	Maybe overly basic but how are you determining "flatness" on a globally curved sheet? Is it the GR sense of local flatness? In that case, how do you decide if a flexion is a local fluctuation or part of the global curvature?
08:13:28 From Alex Klotz to Everyone:
	particularly with regards to open surfaces
08:15:13 From Suraj Shankar to Everyone:
	@Robin: you are correct, and one way to see it is that by retaining the flexural modes in the nonlinear strain tensor, you do maintain rotational invariance at least in a (quasi-)linearized form
08:15:44 From Suraj Shankar to Everyone:
	and this is more important, as David mentioned, than the u^2 term.
08:16:38 From Robin Selinger to Everyone:
	Thanks @suraj .
08:18:44 From Rana Ashkar to Everyone:
	Just a quick question: is the discussion here going to be only based on the Slack questions? Or will there be chance to ask questions here?
08:18:53 From Richard Pastor to Everyone:
	"muted" is better than "cancelled"
08:19:16 From Andrej Kosmrlj to Everyone:
	Slack questions will only be used at the beginning
08:19:25 From Andrej Kosmrlj to Everyone:
	We will open the floor for other questions
08:19:32 From Markus Deserno to Everyone:
	Rana, maybe Alex starts off with slack, but you can definitely raise your hand and bring up a question on your own!
08:25:54 From Robin Selinger to Everyone:
	It would be helpful if you could put the list of references in a common location in the slack or on google docs. That would be a lot easier than searching the chats.
08:25:59 From Andrej Kosmrlj to Everyone:
	Here is the paper related to the phase behavior of viral capsids at finite temperatures
08:26:00 From Andrej Kosmrlj to Everyone:
	https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.124.158101
08:26:32 From Alex Klotz to Everyone:
	There's a virus whose capsid is made of catenated protein rings, would be interesting to see how it compares
08:26:59 From Markus Deserno to Everyone:
	Yes, Google Doc would probably be even better! We shall think about some format that would help everyone place relevant literature at a point where everyone can easily find it. (Not guaranteeing that we figure it out, though.)
08:27:48 From Padmini Rangamani to Everyone:
	I think a slack channel that is dedicated to references might be the simplest rather than managing a google doc
08:28:02 From Padmini Rangamani to Everyone:
	And that can separate the conversations from references.
08:28:31 From Edward Lyman to Everyone:
	I was thinking the same re a slack channel for refs…maybe like a biblio with brief annotations.
08:29:07 From Padmini Rangamani to Everyone:
	I’ve created a channel called references to share.
08:29:15 From Edward Lyman to Everyone:
	Then I can just cut and paste and add some text and turn it into a review article ;0)
08:29:31 From Markus Deserno to Everyone:
	LOL
08:29:38 From Markus Deserno to Everyone:
	Thank you, Padmini!
08:30:00 From Markus Deserno to Everyone:
	(LOL —> Ed.   Thank you —> Padmini)
08:30:04 From Andrej Kosmrlj to Everyone:
	Padmini, can you rename the channels to start with films21?
08:30:05 From Daniel Matoz to Everyone:
	I think that google sheets is better
08:30:22 From Daniel Matoz to Everyone:
	one can add a short description
08:30:26 From Daniel Matoz to Everyone:
	and a tag
08:30:42 From Markus Deserno to Everyone:
	I suggest we’ll just try what works.
08:31:38 From Padmini Rangamani to Everyone:
	I can offer to create a Paperpile shared folder once we have the reference list for each week if there is interest.
08:32:58 From Markus Deserno to Everyone:
	I’m not sure what “paper pile” is. But we already have a Google Drive?
08:33:23 From Daniel Matoz to Everyone:
	yes we have, I cant find the link :P
08:34:00 From Padmini Rangamani to Everyone:
	@Markus, Paperpile is a reference manager software. It works with google drive etc. But for now, I’ll stick with the slack channel (easier for me to find references)
08:34:40 From Edward Lyman to Everyone:
	and likely there are defects entailed when the bilayer collapses
08:34:40 From Markus Deserno to Everyone:
	I can offer to start a Google Doc with some sort of structure where people can add links to paper and a once-sentence description, and maybe a few keywords, what this is all about, so that it becomes easy to find.
08:35:09 From Rumiana Dimova to Everyone:
	Great idea Markus!
08:36:03 From Daniel Matoz to Everyone:
	Perfect @Markus, thanks!
08:37:03 From Rumiana Dimova to Everyone:
	@Markus: Maybe also point out by which talk the question was generated
08:39:19 From Cecilia Leal to Everyone:
	I don’t know if this is relevant. But a polymersome (made with block copolymers)  have considerably smaller stretch moduli (and higher bending moduli) than liposomes/GUVs made of lipids.
08:46:53 From Richard Pastor to Everyone:
	peptides can aggregate and thin the membrane
08:47:23 From Rumiana Dimova to Everyone:
	@Cecilia: Please note that elastic (and rheological) properties of polymersomes vary drastically depending on molecular weight
08:47:47 From Rana Ashkar to Everyone:
	That's an excellent point, Richard. But we ran structural measurements as well and we did not see much of a difference in the membrane thickness.
08:47:50 From Hammad Faizi to Everyone:
	@Celilia leal it is not entirely true that polymersomes have small bending rigidity and viscosities. I have measured bending rigidity and viscosity of Pbd-peo (13:11) which is smaller than DOPC lipid vesicles.
08:49:52 From Hammad Faizi to Everyone:
	https://arxiv.org/pdf/2103.02106.pdf. Here is the link to the data.
08:51:22 From Alex Klotz to Everyone:
	Brandon Sanderson's Kosmrlj
08:51:27 From Cecilia Leal to Everyone:
	@Rumiana: yes, very true. @Hammad interesting! I always thought it was the case compared to DPPC not DOPC. Did you measure stretching too?
08:51:37 From Alex Klotz to Everyone:
	hopefully nonzero people get that joke ^
08:53:24 From Andrej Kosmrlj to Everyone:
	Our PRE paper with David Nelson
08:53:24 From Andrej Kosmrlj to Everyone:
	https://journals.aps.org/pre/abstract/10.1103/PhysRevE.89.022126
08:53:47 From Andrej Kosmrlj to Everyone:
	Review paper by Le Doussal and Radzihovsky
08:53:48 From Andrej Kosmrlj to Everyone:
	https://www.sciencedirect.com/science/article/pii/S0003491617302531
08:54:16 From Hammad Faizi to Everyone:
	@Cecilia For stretching modulus, they have a constant value around 100 mN/m which is measured by my neighboring lab from Prof Neha Kamat at Northwestern.
08:57:13 From Markus Deserno to Everyone:
	Folks, here’s an alternative option for collecting papers—a Google Doc on the site where you can add references with keywords and a link. Try to get inspired by the two examples I already added:
	https://docs.google.com/document/d/1WPPue10ovxwfhmUkQTdoUCA6lfsZIXrvbeTxBrs4xk8/edit?usp=sharing
08:57:52 From Cecilia Leal to Everyone:
	Thanks @Hammad. We are neighbors a bit too (I’m at UIUC). Neha’s measurements of 100mN/m you refer to is to DOPC vesicles or PBD-PEO?
08:57:56 From Andrej Kosmrlj to Everyone:
	Paper from Alex Levine on viscoelastic shells
08:57:56 From Andrej Kosmrlj to Everyone:
	https://journals.aps.org/pre/abstract/10.1103/PhysRevE.77.031921
08:58:14 From Hammad Faizi to Everyone:
	PBD-PEO
08:59:06 From Padmini Rangamani to Everyone:
	At the larger length scales — https://link.springer.com/article/10.1007/s10237-012-0447-y
08:59:23 From Padmini Rangamani to Everyone:
	https://journals.aps.org/pre/abstract/10.1103/PhysRevE.86.011932
09:00:33 From Grace Zhang to Everyone:
	Alex Levine and Jonathan Kerne’s paper on localization of flexural phonons: https://journals.aps.org/pre/abstract/10.1103/PhysRevE.103.053002
09:00:53 From Markus Deserno to Everyone:
	“polymer brush formula” (by Evans and Rawicz): kappa = km d^2 / 24
09:01:43 From Rana Ashkar to Everyone:
	We are in the process of reassessing our data based on the new model from Petia
09:05:02 From Peter Tieleman to Everyone:
	Diffusion of protons, not water ?
09:05:54 From Peter Tieleman to Everyone:
	Proton diffusion is faster than expected for a charge and might use a water wire.
09:06:45 From Markus Deserno to Everyone:
	Also known as the “Grotthuss mechanism”: https://en.wikipedia.org/wiki/Grotthuss_mechanism
09:19:09 From Rana Ashkar to Everyone:
	Ed, are the scales that you probe with simulations smaller than those probed by NSE? My understanding is that they are comparable.
09:19:40 From Edward Lyman to Everyone:
	Y but NSE is like, complicated :0)
09:19:53 From Edward Lyman to Everyone:
	But yes, that is our best experimental match
09:19:56 From Rana Ashkar to Everyone:
	LOL. Fair enough :)
09:24:58 From Anand Srivastava to Everyone:
	Nice response Ed.
09:25:14 From Rumiana Dimova to Everyone:
	@Ed please note that diffusivity is not trivially related to fluidity
09:27:37 From Edward Lyman to Everyone:
	Yes of course. It gets even worse when you read the membrane biophysics literature and look at how “fluidity” is used.
09:29:13 From Edward Lyman to Everyone:
	let alone cell biology!
09:33:35 From Markus Deserno to Everyone:
	I might need a refresher on the difference between diffusivity and fluidity. Is it just the difference between diffusion and (2d) viscosity? Sorry of this is a dumb question. 😬
09:34:06 From Alex Klotz to Everyone:
	put on the spot
09:34:17 From Markus Deserno to Everyone:
	LOL
09:34:24 From Peter Tieleman to Everyone:
	I think fluidity is more of a cell biology concept loosely related to how gooey biologists think a membrane is
09:34:25 From AURELIA HONERKAMP-SMITH to Everyone:
	I always read “fluidity” as “1/viscosity”
09:34:36 From AURELIA HONERKAMP-SMITH to Everyone:
	but that may not be how people are using it
09:34:46 From Hammad Faizi to Everyone:
	@Markus I think the same way
09:35:18 From Markus Deserno to Everyone:
	Aurelia: “I always read ‘fluidity’ as ‘1/viscosity’” I really like that!
09:36:51 From James Fitzgerald to Everyone:
	In my experience “fluidity” is some sort of “inverse viscosity” or “diffusivity” or really anything along those lines… I always read it as something not particularly well defined, more quantitative than qualitative
09:37:06 From James Fitzgerald to Everyone:
	my *limited* experience ha
09:37:18 From Riccardo Capovilla to Everyone:
	Good question. Think of ice cream or worse glass
09:37:36 From AURELIA HONERKAMP-SMITH to Everyone:
	yes “not well defined” springs to mind when I see “fluidity” as well…
09:38:10 From Edward Lyman to Everyone:
	I hope Itay Budin isn’t here, he might unfriend me for starting this discussion.
09:38:55 From Peter Tieleman to Everyone:
	First day and you’ll already be unfriended by NSE types and Itay
09:39:05 From Markus Deserno to Everyone:
	Some sacrifices need to me made 🤷🏼‍♂️
09:39:19 From Alex Klotz to Everyone:
	everyone is friends in the world of elastic sheets
09:40:27 From Rumiana Dimova to Everyone:
	@Markus: Diffusion measurements are so dependent of the probe you use and how this probe interacts with its immediate environment and it is thus difficult to check trends. Hammad measured viscosity and plotted them against diffusion coefficients (of the same probe) in membranes of the same compositions and does not really see the viscosity~1/diff_coef dependence. You can check the supplement of https://arxiv.org/pdf/2103.02106.pdf (soon to be updated)
09:42:55 From Markus Deserno to Everyone:
	That reminds me of old work by our chair, Alex, on 2-point rheometry—aiming to decouple the local effect of the probe from the bulk behavior of the phase by looking at correlations. I wonder whether we can also do this with probes in membranes.
09:44:32 From Alfredo Sciortino to Everyone:
	I think David Weitz did a similar thing with cytoskeletal network recently - 2 points rheology I mean.
09:44:38 From Buddhapriya Chakrabarti to Everyone:
	I was under the impression that Gompper et al. has worked on this problem but I might be wrong.
09:44:43 From Brian Camley to Everyone:
	@Markus - yes. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.97.176001 - and followups
09:44:51 From Alfredo Sciortino to Everyone:
	But is the fluidity/viscosity/diffusion problem an experimental one or a fundamental one…?
09:45:25 From Rumiana Dimova to Everyone:
	Of course in theory this all fits. Now look at experiments :-)
09:46:33 From Alfredo Sciortino to Everyone:
	experiments are so hard though :D and I speak as an experiment person.
09:46:47 From Alfredo Sciortino to Everyone:
	but what about FRAP on flat membranes for example.. that would sort of work..?
09:46:48 From Alex Klotz to Everyone:
	it's true
09:47:03 From Alex Klotz to Everyone:
	if anyone wants to chat, I do experiment with elastic membranes
09:47:25 From Hammad Faizi to Everyone:
	@alfredo FRAP is probe dependent
09:48:04 From Alfredo Sciortino to Everyone:
	touchee ): that is also right
09:51:21 From Buddhapriya Chakrabarti to Everyone:
	Is this chat being saved somewhere?
09:51:30 From Edward Lyman to Everyone:
	I’ll ask my question here, since it is for the group: Do the experimental folks fell that we have a good handle on the bending modulus of a cholesterol rich, liquid ordered phase? What is it?
09:51:39 From Andrej Kosmrlj to Everyone:
	Chat will be saved and posted on Slack and Google Drive
09:51:39 From Edward Lyman to Everyone:
	Fell = feel
09:51:47 From Buddhapriya Chakrabarti to Everyone:
	Thanks Andrej
09:51:55 From Markus Deserno to Everyone:
	Yes, we aim to save and publish the chat. But you should also be able to save it yourself.
09:52:09 From Rana Ashkar to Everyone:
	Rich, can you please share the link to this paper? Thanks!
09:52:13 From Markus Deserno to Everyone:
	Andrej’s always faster 🤷🏼‍♂️
09:52:14 From Buddhapriya Chakrabarti to Everyone:
	Yes @MarkusDeserno
09:53:22 From Peter Tieleman to Everyone:
	Already in this paper: https://science.sciencemag.org/content/262/5131/223.abstract
09:53:41 From Peter Tieleman to Everyone:
	One of the very first membrane simulations, already on viscosity
09:53:45 From Rumiana Dimova to Everyone:
	@Ed: Tobias Baumgart (for example) has measured liquid-ordered membranes and gets values like 80kBT but this number will depend on the specific composition
09:54:30 From Alex Klotz to Everyone:
	Do you have a sense of how many kT it takes to "taco" a flat elastic membrane?
09:54:33 From Peter Tieleman to Everyone:
	(Maybe we can blame him for introducing membrane fluidity)
09:54:57 From Markus Deserno to Everyone:
	Let me share one more time a Google Doc for references: https://docs.google.com/document/d/1WPPue10ovxwfhmUkQTdoUCA6lfsZIXrvbeTxBrs4xk8/edit?usp=sharing
09:59:09 From Buddhapriya Chakrabarti to Everyone:
	Thanks @MarcusDeserno
09:59:13 From david nelson to Everyone:
	Here is a paper on boundary conditions:
09:59:16 From Alex Klotz to Everyone:
	thermalized elastic membrane group!
09:59:23 From david nelson to Everyone:
	Shankar, Suraj, and David R. Nelson. "Thermalized buckling of isotropically compressed thin sheets." arXiv preprint arXiv:2103.07455 (2021).
09:59:33 From Alex Klotz to Everyone:
	thanks all
09:59:41 From Markus Deserno to Everyone:
	gather.town link, if anyone wants to go there: https://gather.town/i/qJlb1M2p
09:59:42 From Sarah Keller to Everyone:
	Thank you!
09:59:54 From Vikram Jadhao to Everyone:
	Thank you, all!
10:00:03 From Michael Dimitriyev to Everyone:
	Thanks!
10:00:08 From Anand Srivastava to Everyone:
	Thanks you all
10:00:18 From Thomas Shaw to Everyone:
	Thank you!
10:00:30 From James Fitzgerald to Everyone:
	save chat!