 Then you can start. Yes, please. Yeah, it's good. Okay. Thanks for the introduction My name is Wingon Ouyang I'm a former postdoc in the group of Michael Wubak and now I came back to China Now I'm a PI in Wuhan University I'm honored to be able to talk here today to show a recent result for this Microscope mechanism of frictional aging This is the outline of my talk today Let me first introduce a brief background of frictional aging. So usually What what what do what do we mean frictional aging usually is defined in a kind of slide called slide experiments? So Imagine we have two subsist in contact and we slide the juicers into state-state Then we call some time and slide again Hold time and the experiments show that the start friction increases logarithmically with the whole time and this is called aging effect and and this effect exists at different length scales around Geophysical length scale to nano-length scale for this city car services and another feature of frictional aging is that there are transient dynamics of this friction prosthesis in doing this a whole slide hope slide experiment and To description describe the such dynamic effect people proposed this code We call it red state models and it is empirical models because it There's a they introduce a state variable which we don't know the physical meaning up to now And but it works it can describe the experimental observation where we're There are two main reasons that people Assume that can be the reason for the frictional aging the first one is that creepy fake basically when doing contacts the contact area increases with cold time and The other reason is that the formation of the artificial chemical box in 2011 this is a very excellent experimental work by Professor work copy and the professor Chiang Li and they in their nice experiment they exclude the first reason and They found that the second reason basically the formation of the facial cream pounds is the main origin of the frictional aging for city car contacts Which is also for the rocks rock surfaces and almost at the same time Professor Andrew Shaman and Professor Michael Park they proposed multi-contact model to describe such effects They they using this model with they forms kinetic simulations. They found that The chemical bond can induce friction with a non-monotonic temperature and velocity dependence Which agrees well with the experimental observations Recently there are more experimental result for this criminal agent. The first network is a Performed in the group of work copy and they the system is oxidized silicon tapes on silicon workers and they extend for the first time they extend to The whole time to wear short-term skills to many seconds and they observe transition from linear agent to local rhythmic agent and with the cable Kinetic Monte Carlo simulations. They found that to explain the linear agent area. It's essential to to introduce a distribution of Fund formation and its barrier basically it means that there are multi types of bonds at the state of a single type of funds and For a very similar system They also measure the normal load dependence personal agent and they found that at the different hold hands the Friction the friction drop increases almost linearly with the load Collaborate with Isabella. They did this kinetic Monte Carlo simulations as they have explained the chemical region of the Personal agent basically when there are distributions of the formation energy barrier The ageing effect will will happen will appear and with different distributions of the Energy barrier the behavior will be different and for this realistic MD energy barrier and the uniform energy barrier they both they found that the friction force Increase almost nearly with the load when the load is low enough, which is consistent with Experimental observations And this one was about this chemist simulation. This is a very popular tool and they can introduce the distribution of formation energy and also introduce the effect of Normal load and even the effect of the interaction between the same departments Now the next work is the the form in Group of Androsha my son and in collaboration with the roof areas They observe that also for silica silicon contacts the result that Personal agent is very sensitive to the temperature and the agent effect actually Decreases with the increase in temperature and actually they also observe two regions logarithmic region and Might be a plateau or linear region and some more cold time They also formed a nice MD simulations to explain the observations of of the experimental measurements they will For theoretical aspect we have a simulation and also a dissimulation There are they have given a nice women with the experiment, but they don't have analytical Expressions and usually they are very time-consuming. So our goal is to develop a theoretical framework for for chemical bonding use friction and frictional agent and we try to be give some analytical results This is our model. Basically, we have two surfaces and Here they have many types of bonds and the elasticity of the bond is represented by the sprint here And we introduce two rates K on for formation for bond formation and KO for bond rupture and both of them are similar small reactivated and we also introduced the Normal of dependence to the commercial energy and the normal distribution is basically we adopt the zero and here We also we can also introduce the uniform distribution as that in a chemistry relations to get an analytical result We found we found that only these two keep go in your money distribution Then with this assumption, we can calculate our friction force of the system as using this equation Here 5b is the probability density that the bond with the elevation x at 20 Then we can derive such Time evolution of 5b with the following equation and here Pb is the probability that the bond is at 20 We then will apply this approach to calculate as a force evolution in the slide for the slide experiment Firstly, we calculate we will apply this approach to calculate the friction and the state for both constant load and for first like load distribution in both cases, we can get analytical results and With this analytical result, we can fit the virus experimental result It's experimental result from Nikola Spencer and the panel B is from a copy and the panel C and D is from Andrew Shaman's So here we probe our analytical solution of the theoretical model allows us to improve the experimental data on timescales and then scales that are relevant to experimental conditions and Then we go for Study the frictional agent here the figure shows a typical process sliding cold sliding a process And here the force peaks is given by the logicals Which is determined by the number of connected bonds after the whole time and the data is the friction job that measured in the experiment and this can be expressed by this equation we can see that The time dependence of force is solely come from the number of bounded compounds so we're following well many folks analysis of this quantity and Since during the whole time the sliding loss is zero So the general formula can be reduced to choose this simple equation and we can get a simple solution for this Apparently, there's no 80 effect. It means that for single type of bonds. There's no agent So then we can include distribution for the activation by an edge barrier Here it should be noted that in principle, we should also include a distribution for the Robter energy barrier data EO but according to a game simulation for city complex The net the distribution for data EO is much narrower than that for data young So here we treat it at a constant Here we can see the two typical Distribution uniform and the gamma distribution and we can get analytical result You see here is still very complicated because it contains a series of special functions. So we need a Sympathetic analysis to simplify it at short-term scales. We could a worse between the number of contacts and Cold time it's a you see the number of contacts and be is grows nearly with time and Also proportional to the maximum rate of contact formation and the laplace transform opposite of the distribution And here the body of time is also determined by the maximum rate of contact formation Well, for long the times is divided into two regions For intermediate time scale is the scales like logarithmic or miss like It's in behavior and for even longer time then it becomes saturated becomes a constant for both uniform and the gamma distributions Then we have also include the normal load distribution to choose the energy activation barrier Even and also a combination of this load distribution and the uniform and the gamma distribution For the general case, we don't have an analytical expression for At the very short and long-term scales we can go to very simple Sympathetic behavior of the number of contacts that function with normal load As you can see here when the normal load is very low actually I've told it's the This is a this our normal load and this is a gene force when normal load is much smaller than the addition force then the At low load region the number of contacts will scale linearly with normal load with this consistent with experiment data So here is a more detailed comparison with the experiments. You see here. We can see panel A The black circles is extracted from the paper by work copy and the red line. It's the exact formula with fittings and then You see the green blue and black dash lines are the Sympathetic formula at the corresponding agent regions For both uniform and gamma distribution with the very good fitting Here we have five fitting parameters and each parameters We are using a Basically we use a physical the regions of the parameter is in the physical regions consistent with the chemical reactions And to avoid overfitting we apply the same model to Where a similar system did given by the same group and Here's a major. There's a normal load dependence friction agent and you see here for both pure normal load and combination for normal load and uniform or gamma distribution they give a Very good agreement and especially here we can see that the friction force is the increase in DNA with normal load at the lower load region So here we also calculate the temperature dependence of aging as for uniform distribution distribution as we can see here as the temperature increases the Aging accelerates basically it happens earlier you see here and The basically shifting the locomotive time depends to show time scales and at the same time the aging slow The locomotive aging decreases with the increase in temperature. This is consistent with the experimental observation and androchromycin and here we also observe if we calculate the friction force as a function for temperature Observe a non-monotonic carrier because there's a two competing Processes for both bond formation and the bond rupture and here we also calculate Tragical relation between average genetic friction and the functional aging as we all know that in the typical Experiment this one a steep deep sliding on surface usually they have Steak-steep events and actually you if they are chemical bonds actually The sliding velocity of TV zero Aching my hyper act as expected by the case relations So here we provide a nanonit and a little Explanation between this aging induced average in it friction and Concluding that we found that the average friction Decreases with increasing sliding velocity and this is each to understand because when we increase in the sliding velocity The average is ticked on is reduced So basically this is our main conclusions We developed an analytical model for description of regional aging that mediated by dynamic formation and the rupture of Microscopic in the patient contacts and the model predicts three different aging regions linear rhythmic and level of saturation and This is consistent with the experimental observations and a second the predicted Dependencies of frictional aging and the normal load and also on temperature I include agreement with experimental observations and the result of KMC simulations We think our work of promising opportunities for understanding the Metroscopic mechanism of frictional aging That's all. Thank you talk and Yeah, if they are question, please Your hand or if it's on zoom Thank you, and thank you for the attention to our work and other groups that have been working on this and I wanted to ask how could you just say a little more about how you handled looking at the load dependence? So increasing load will increase the contact area so you can get more bonds forming Just more sites and contact, but also it increases the pressure and that pressure can maybe Accelerate bond formation, but it could also inhibit bond breaking and I believe you've got both going on So, yeah, how did you handle the physics of the effective load? Okay, thank you. Thanks for the question Here, yeah, you're right when when we increase in the normal load actually here You see, this is the way how we Yeah, this is the way how we include in the normal load effect here actually when we increase in the pressure For much energy will be reduced. So it's more easier for the bond to bond formation and Actually here So here actually here we also We consider this effect when we basically the effect of normal load are also in the rupture energy barrier It will influence the quantity of the production force But the general behavior is that keeps here. This we checked, yeah Thank you. So you did not So there you have bond breaking is accelerated by stress But you you didn't you do not have bond sorry bond forming is accelerated by stress But you did not put bond breaking being inhibited by stress. Is that right? Here, yeah, here we didn't but we checked actually You know work in the supplementary way we check this we also include in this effect on the bond formation and Basically, maybe you can show So I didn't Comment it's an interesting question because you know pressure will increase You know, it should make bond formation easier. It makes bond breaking harder But it also will increase friction and with more friction as you slide that should help bond breaking So it's it does a sort of to the compression is prevent So here we also include the effect of No, no, no on the rupture force you see here for when for Here basically for we be is basically for for the for for your Yes, basically when when it's equal to zero basically is the case what I showed yesterday in the presentation when it's when it's possible is it's just It's all will basically when it's possible is reduce the energy barrier for rupture with negative Then it will increase the energy for rupture that you see here. This is the trend the change Yeah, so the general behavior is it's similar But as you're saying it if we assume in that the pressure will increase the rupture energy barrier Then the friction force will increase. It's the the curve will globally shift up Can you open the chat and look for the question