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on most days we get a chance to see the

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international space station crew members

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working on science experiments

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sometimes we get to see the experiments

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themselves as they do their thing

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recently the international space station

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program science office posted a video

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clip on the real nasa youtube channel

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from a combustion experiment that's

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underway and that clip has caught an

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awful lot of attention

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that's from the flame extinguishment

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experiment 2 or flex 2.

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earlier this week i spoke with dr tom

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avedisian of cornell university who is

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the flex 2 co-investigator who requested

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that particular test burn

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to find out what it is we're seeing here

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and what scientists are trying to learn

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from burning things in space

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well our overarching objectives are to

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obtain information about how liquid

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fuels burn so we can design ultimately

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more efficient combustion engines used

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in transportation systems on earth

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the the problem with that is that real

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liquid fuels like gasoline diesel and

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jet fuel are so complex

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that it's really a hopeless task to

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develop models for how they burn as they

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contain hundreds of miscible

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constituents with a wide range of

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boiling points propensities to form soot

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during combustion

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and heats of vaporization soot is the

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black carbonaceous material we sometimes

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see

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spew out the dispute out of the exhaust

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line of diesel trucks which is

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responsible for a whole host of health

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risks

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where we are addressing this problem our

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approach by studying the combustion

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dynamics of fuel blends comprised of a

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much smaller number of constituents say

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for example two or three ideally

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with the hope that they will replicate

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certain combustion targets of the real

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fuel

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we would then develop the understanding

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of that simpler blend which we call a

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surrogate and use the combustion

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properties of the surrogate to assess

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the performance of the real fuel

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now in fact you're doing the these uh

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experiments in space by burning just

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single droplets of fuel right tell me

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why that why you do it that way

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well that that's that's correct our our

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strategy has been developed the

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combustion properties for evaluating a

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surrogate by using the simplest possible

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configuration of burning for a liquid

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fuel namely a droplet burning under

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conditions that promote spherically

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symmetric gas transport this kind of

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combustion symmetry is currently the

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only one for a liquid fuel that can be

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modeled using detailed

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simulation or first principles approach

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where no sub models or adjustable

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constants are required

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this is precisely what is needed to

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evaluate the efficacy of a surrogate to

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perform like a real fuel it is intended

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to replicate and in space you get to do

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these experiments inside an apparatus

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called the multi-use droplet combustion

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apparatus that allows you to control

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variables right that is correct the mdca

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as its

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shorthand notation has the capability to

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control the droplet size which is a very

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important parameter that influences soot

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formation and radiative losses

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as well as the ambient oxygen and inner

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gas concentration

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and pressure up to about three

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atmospheres

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currently we do experiments my component

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of the flex project is essentially at

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room temperature air

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obviously the facility includes storage

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chambers for a range of fuels with the

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ones we are investigating being

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representative of components of real

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transportation fuels

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now we mentioned earlier that there's a

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a video on youtube that shows kind of a

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remarkable burn and i'd like to play

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that again and have you described for me

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what it is that we see in this video

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okay

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um it's a very delicate operation

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there's a zooming out and you'll see

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very quickly the the activation and the

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ignition event

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the droplet looks motionless but

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actually it is moving a little bit

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and you'll see in the lower left-hand

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corner the flame disappearing and then

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reappearing

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and we believe that this is the result

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of movement of the droplet such that

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when the droplet is moving fresh oxygen

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is drawn into the combustion zone but it

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also depletes the oxygen on the back

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side of the droplet which causes

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extinction but that movement of the

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droplet allows the flame to close on the

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backside the continued movement it opens

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up again and you can execute multiple

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cycles of this what appears like a

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jellyfish type of motion

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i mean we don't really know

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the the detailed mechanism for this this

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is purely speculation on our part but

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this is what we think is happening

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but as you explained earlier one of the

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things that you're looking at is what

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happens to the soot during these burns

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and you really can't see that in that

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video but you provided us with another

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uh video clip

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from a black and white camera in the

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mdca i want to show that because it also

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has some pretty remarkable movement in

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there and get you to describe what we're

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seeing

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well this video is of a toluene fuel

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toluene is a constituent of uh gasoline

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here you see as soon as the ignition

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process occurs soot explodes into view

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and as you noted this is a backlit image

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so we see the dropper that's the black

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ball that's kind of very slowly drifting

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and the soot particles are almost in the

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state of left um

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animated levitation around the droplet

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the flame is actually extinguished but

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you can't see it here

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um the droplet is drifting but the soot

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particles remain somewhat in place that

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is a remarkable illustration of the

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formation of soot under the spherically

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symmetric condition it's remarkable even

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for for the layman to look at that and

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and to have just a beginning of an

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understanding of what we're seeing there

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can you explain to us

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how you imagine the results what you're

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getting in these burns how they can be

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applicable

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for in future uses

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well as i as i remarked earlier we have

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been using the multi-user droplet

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combustion apparatus on on the space

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station to study how surrogates for real

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liquid transportation fuels burn when

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subjected to the idealized environment

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of

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no convection and no relative droplet

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gas velocity that's going to create

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spherical drop of flames

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we feel there are few configurations

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better suited to get this type of

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understanding i would also note

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or like to note that with the new

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generation of fuels emerging that will

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be derived from a wide range of biofeed

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stocks like algae camelina soybean and

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so forth the mdca

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with the spherically symmetric burning

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process it can promote is i think well

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positioned to reveal the influence of

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fuel composition and droplet size

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effects on ignition combustion kinetic

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measurement

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combustion kinetic mechanisms and so

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forth that control burning developing

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surrogates for these biofuels

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is essential to access this information

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and and armed with it

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uh the combustion chemistry for these

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simpler brands uh other characteristics

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of biofuels uh can be obtained uh that

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should ultimately uh allow us to predict

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their performance in combustion engines

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for this new generation of fuels

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be very interesting to keep track of

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this as it goes forward and see how it

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works i appreciate you taking the time

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to explain it to us thank you very much

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dr tom avedisian of cornell university

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is a co-investigator of the flex 2