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you

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we have ignition and liftoff of Columbia

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on an ambitious tims a international

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research flight the critical fluid bite

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scattering experiment isn't exciting

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part of the second United States

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microgravity payload that will fly

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aboard the space shuttle Columbia this

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precise experiment will challenge the

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universal understanding of some physical

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phenomena the experiment is named Zeno

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in honor of an ancient Greek philosopher

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Zeno evelia who first pondered the

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concept of infinity Zeno's most famous

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paradox of infinity demonstrates that an

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infinite number of successively smaller

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steps can be squeezed into the distance

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between two points Zeno's paradox is

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analogous to the modern-day Zeno

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experiment where a series of minut steps

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are made toward the critical temperature

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of a fluid the critical temperature of a

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fluid is the highest temperature at

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which it's liquid and vapor phases can

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coexist at low temperatures both the

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liquid and its vapor can be observed and

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exhibit on earth a visible meniscus or

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boundary at temperatures above the

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critical temperature only a single phase

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exists the Zeno experiment will begin in

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this supercritical single phase region

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and will progress toward the critical

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point to study fluid properties as the

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fluid prepares to separate into two

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phases this is an example of a second

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order phase transition other examples of

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second order phase transitions include

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normal conductors superconductor

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transitions and magnetic transitions at

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the Curie point at the critical

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temperatures of these second order phase

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transitions the materials fluctuate

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between different states it's these

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fluctuations that scientists want to

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study much progress has been made in

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theory and measurement of these phase

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transitions but the Earth's gravity

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makes it impossible to do a careful

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study of the secondary liquid vapor

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phase change at the critical

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temperature fortunately the space

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environment now permits a new generation

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of experiments to test the best theories

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currently available zeno principal

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investigator Robert gammon explains why

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the gaseous elements xenon was chosen

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for this experiment we believe that

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xenon is an ideal fluid for studying the

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liquid vapor critical point it's

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available in very high purity it's a

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simple monatomic spherical atomic fluid

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and it has a convenient critical

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temperature it's better than all the

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other systems we could think of for very

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precise studies close to the critical

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point because it's not limited by purity

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and not limited by crystal perfection

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the xeno experiment is being done in the

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microgravity environment of space

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because on earth as you near the

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critical temperature the Earth's gravity

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causes the fluid to stratify or form

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layers this distorts the sample but the

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microgravity environment of space

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permits a very close approach to the

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critical temperature before the

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stratification begins during this

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experiment careful control of the sample

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density and thermal environment enables

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precise measurement to be made within a

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few millions of a degree of the critical

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temperature 100 to 1,000 times closer

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than is possible on earth we might

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compare the experiment to climbing a

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mountain the goal is to analyze the area

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closest to the peak the critical point

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to do that the climber makes minut moves

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toward that point as the climber gets

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closer some unusual things happen it's

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fascinating xenon near the critical

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point is a billion times softer than

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water the system doesn't know whether it

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wants to be a liquid or a vapor and it

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readily goes back and forth between the

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two and has nearly an infinite heat

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capacity in the process of this sloshing

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back and forth it turns milky white it's

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in this state that important

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measurements will be made as the

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temperature of the fluid sample and the

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xeno experiment approaches the critical

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temperature density fluctuations

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increase dramatically a laser serves as

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a

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the science requirements for the

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experiment and developed the flight

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instrument the instrument was fabricated

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and tested by Ball Aerospace the heart

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of the experiment is a high pressure

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sample sale located in the thermostat

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the this sample is eliminated by a laser

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which is brought around through the

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apparatus with mirrors and a beam

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splitter and in along the axis from

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either end the sample is located close

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to the center of this thermostat and

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scatters light to this photo multiplier

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at a small angle or through a bending

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mirror to a second photo multiplier so

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that we can see two angles at once the

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other principle detectors in the

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experiment are photo diodes which sample

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the light behind this partially

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transmitting mirror and there's one at

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the other end as well the Zeno

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instrument will fly aboard the space

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shuttle Columbia as part of the second

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United States microgravity payload this

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series of payloads has been sponsored by

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the NASA office of life and microgravity

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Sciences and applications these payloads

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include some of the most challenging

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experiments to be conducted in space

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during this decade Zeno will provide

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data that is not observable on earth

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theories will be challenged and

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experience will be expanded improved

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understanding of second-order

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transitions will help in here