From morning everyone my name is a kill
and I working in barbarian to a lab

at Duke University today I would like to
present fairly in the over results on.

The ground in a lot of materials.

So first of all I want to explain
why you're doing the experiment

that I'm going to show you there is these
are all fairly old problem of crackling

noise that we have very different kinds of
system that the kind of behave similarly

if for instance if we want
to magnetize for a magnet

it doesn't magnetised continuously
rather than that if magnetizes in.

Erratic discrete jumps and
it also all we can see that also in crack

propagation happens in the rats of germs
or what's happening in error squeaks so

tectonic plates to not move continuously
the rather moving or at Giles.

And interesting properties of those.

Signals is that those are kind
of of a scale even Mary and

he means that if we
take it this signal and

zoom in a part in this case properly we
see a statistically some a statistical

measures are the same as the whole
signal that results in poverty

low distribution of events and that's
one of the results that we can see that

each of those events contribute to some
amount of energy in the system and

we can calculate that energy and
those events actually have a very

wide range of distributions and
are usually poverty loss.

So in the case of earthquakes or
specifically it is believed.

It's caused by tectonic plates that
shearing on each other and there is a fine

granular media between those tectonic
plates and basically dad granule are.

Media it's part of the police response of
all for what's happening in earthquakes so

to understand the dynamics
of that shared granular

materials between tectonic plates we
came up with an experimental setup so

our experimental set up looks like
something like this we have a slide there

that sits on through the granular system
this slide there is connected with

a spring to a gauge that moves
with a constant speed C.

and we are measuring the force
on the spring we also use for

two or less the particles that when they
are on the wrists wrists and they are in

between two cross polarizers we can see
actually particles are under a stress so

we record the system
are here we cameras and

we can basically see the surface
propagation inside the ground like me.

So this is an experiment that I'm showing
this is the global force signal and

this is what we see with cameras one need
polarizer one with Al Fuller is that

we can see the flow of particles so each
of these events that you see there is of.

Those are called avalanches arm and

the you're going to see a rather
big challenge right there.

That's how the system basically evolves.

So what's happening here this
is roughly what's happening in

our system is that this is the basically
the phase they are on the diagram of

granular media's function of shearers
stress and packing Fraction We can go to

the jammed regimes of granular materials
that is kind of solid like by increasing

packing fraction or by shearing the system
here we are shearing the system so

we get to a bridging those called
shear bridging here and if the passer

Trish all that is called yielding
Trish will be go to unjam bridge and

so you becomes a fluid like and
the granular material can flow and

when it flows of you have those
relaxations and when we have relayed

station it goes back to the shear
exam regime and it happens again and

again and each of those jumps
basically is called an avalanche and

you're interested in those avalanches and
how they behave why the behave and.

What are the surface
called properties of that.

So as I mentioned to you we have two
different measures of calculating

these al inches one is looking at
the granular media on the surface

fluctuations one is the global measure
looking at this force and interesting.

To give us who the friend
behavior of system

this force basically tells you how
fast this light there is moving and

that is called hold to the flows of
particles so this is a measure of

how particles are flowing and
when we look at this wrist it's basically

this Tristen at Ford and that these are
peers and construct a they again that's.

A measure of how basically.

Stress fluctuations are happening and
if you look at basically.

Distributed.

Even seen those measures we received
two different universality classes

that this is more like
I mean feel teary and

this is not more like what's happening
in earthquakes and within the world

we have a point there why people don't
see me and feel teary in earthquakes but

they don't want to get into that problem
now the thing that I want to focus

now is that what's happening as
we change all these power meters

that we have in the system we have several
control parameters that we can change for

instance we can change the loading of
speed how fast you're moving the slider or

we can change the system size
arm pressure on the system and

your interests that how avalanches
basically behave as if you're changing

these parameters interesting
seems that the speed is

more the more relevant one as we
increase the speed the distribution of

events from a broader range goes to
a very narrow range of becomes galaxy and

from a POV of law and we wanted to
understand why this is happening.

There has been some in the American
simulations on that on a deterministic

system and it gives you OK as you increase
the speed you basically are changing

into a different regime so
we wanted to assert it.

So let me show you some signals so
this is for very very low loading of speed

as being create the speed we see that
basically the systems behavior changes

a lot so kill eagerly we see
year bifurcation going from.

Erratic fractal shape
behavior to be Hevia this is.

More obvious as we look at the poverty
spectrum of these four signal so

for lower speeds we see something that
is like a brownie in the noise and

as we go to higher speeds
we see the peak coming of.

Shows basically we are getting into a
periodic routine we have a characteristic

frequency the system oscillates with.

We can use.

The number of decades and
also the properties of that maximum and

we can come up with a dynamic called
phase of this system so it basically

tells of as we change loading a speed and
the stiffness how the system evolves from

crackling routine to periodic critique
I don't want to go into the details but

the point here is that increasing
the speed we get into per yard and as B.

increases stiffness it's getting harder
and harder to get into the periodic reach.

So you might argue OK it's not that
interesting it's might be that.

When we are going we are running into
the highest speed basically the slide

their fields mean field friction force and

that's a constant friction force and
read that you can get this city.

So we can write.

Such an equation we mean
field of friction force and

with some algebra we can show that
that's basically impossible to get such

a behavior you get you most of the time
we divergence it diverges if you have

such a behavior the other point is our
frequency the frequency that the system

oscillates if that is true should
be only function of Kerry and M.

but here we see that the frequency
basically depends on the loading It's so

as we increase the loading of
speed the frequency increases and

it seems that it increases in.

A logo to make way that is kind of
a sign of Homer clinic bifurcation.

By freakish and just to say roughly it's
basically when you have a saddle point

a center point in your face there ground
that they are colliding with the shuttle.

Calculation again and
you can see basically that gives you.

Dependence Aadhaar solution
dependence that is looking at it.

So the question now is that what is
happening down there in granular materials

that we see this period this city is these
per year this is the cause or induced

by the freak show for studies provided
by granular media or something else and

we are recording granular media so we can
we can basically look into the granular

media see how the force network
is fluctuating inside ground.

So here I have basically
I have the forest and

also image intensity the forces in blue
image intensities in green and you see for

lower speeds the fours and
image intensity all correlated

as we go to higher speeds we see the force
of slits but the image intensity

basically shows you the fluctuations
of forces still fluctuating very fast

that means that the friction force is
basically almost the same thing but

there is some other phenomena that
it's happening that raising this.

City and we can also look at the poverty
spectrum of that if you look at

the poverty spectrum of force as I showed
you we see that peak but the poverty

spectrum of the image intensity basically
we don't see a clear peak so the.

Basically tells us that the underlying.

Frictional force is not
what is inducing for.

The city and you can basically if you want
more details you can go over our paper

with that because I don't have that
much time I just leave my conclusion and

I'll take questions.