Introduction in Thermodynamics

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Introduction in Thermodynamics

LESSON 1AWhat is Thermodynamics?

The word thermodynamics was coined by William Thompson (Lord Kelvin) in 1749.It comes from the Greek words: therme (heat) and dynamis (power).The name heat-power is appropriate because thermodynamics developed from effortsto explain the conversion of heat into power by steam engines.

Timeline of the Early Developments of Thermodynamics

1712Newcomen invented an improved steam engine

1798Count Rumford began canon-boring experiments (dealing with the conversion

of work into heat)1840s

Mayer (1842), Joule (1847) and Helmholtz (1847) independently arrived at theconservation of energy principle

Carnot published "Reflections on the Motive Power of Fire"1824

Clausius formulated the Second Law of Thermodynamics1850

Reference : http://www.learnthermo.com/T1-tutorial/ch01/lesson-A/pg01.php

THERMODYNAMICS: the science of energy, specifically heat and work, and how the transfer of

energy effects the properties of materials

Thermodynamics is a physical sciencethat studies the effects on material bodies, and on

radiation in regions of space, oftransfer of heat and ofwork done on or by the bodies or

radiation. It interrelates macroscopicvariables, such as temperature,volume and pressure,

which describe physical properties of material bodies and radiation, which in this science are

called thermodynamic systems.

Historically, thermodynamics developed out of a desire to increase the efficiencyof early steam

engines, particularly through the work of French physicist Nicolas Lonard Sadi Carnot (1824)

who believed that the efficiency of heat engines was the key that could help France win

the Napoleonic Wars.[1]Scottish physicist Lord Kelvin was the first to formulate a concise

definition of thermodynamics in 1854:

Reference : http://en.wikipedia.org/wiki/Thermodynamics
http://www.learnthermo.com/T1-tutorial/ch01/lesson-A/pg01.phphttp://en.wikipedia.org/wiki/Physical_sciencehttp://en.wikipedia.org/wiki/Heat_transferhttp://en.wikipedia.org/wiki/Work_(thermodynamics)http://en.wikipedia.org/wiki/Macroscopichttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Volume_(thermodynamics)http://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Thermodynamic_systemhttp://en.wikipedia.org/wiki/Thermodynamic_efficiencyhttp://en.wikipedia.org/wiki/Steam_enginehttp://en.wikipedia.org/wiki/Steam_enginehttp://en.wikipedia.org/wiki/Nicolas_L%C3%A9onard_Sadi_Carnothttp://en.wikipedia.org/wiki/Napoleonic_Warshttp://en.wikipedia.org/wiki/Thermodynamics#cite_note-0http://en.wikipedia.org/wiki/Thermodynamics#cite_note-0http://en.wikipedia.org/wiki/William_Thomson,_1st_Baron_Kelvinhttp://en.wikipedia.org/wiki/Thermodynamicshttp://www.learnthermo.com/T1-tutorial/ch01/lesson-A/pg01.phphttp://en.wikipedia.org/wiki/Physical_sciencehttp://en.wikipedia.org/wiki/Heat_transferhttp://en.wikipedia.org/wiki/Work_(thermodynamics)http://en.wikipedia.org/wiki/Macroscopichttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Volume_(thermodynamics)http://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Thermodynamic_systemhttp://en.wikipedia.org/wiki/Thermodynamic_efficiencyhttp://en.wikipedia.org/wiki/Steam_enginehttp://en.wikipedia.org/wiki/Steam_enginehttp://en.wikipedia.org/wiki/Nicolas_L%C3%A9onard_Sadi_Carnothttp://en.wikipedia.org/wiki/Napoleonic_Warshttp://en.wikipedia.org/wiki/Thermodynamics#cite_note-0http://en.wikipedia.org/wiki/William_Thomson,_1st_Baron_Kelvinhttp://en.wikipedia.org/wiki/Thermodynamics


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LESSON 1BWhat are Dimensions ?

For example, consider water in the beaker shown here:Can be calculated or derived by multiplying or dividing fundamental dimensions.

Examples: area, velocity, density and volume

2. Derived Dimensions -Mass, Length, Time, Temperature, Moles and sometimes ForceFundamental dimensions can be directly measured or are independentlydefined.All other dimensions can be obtained from the fundamental dimensions.

1. Fundamental Dimensions - There are two types of dimensions.In science and engineering, numbers without units are notuseful (unless they happen to be dimensionless).

Mass

Density

has derived dimensions made up of a combination of fundamentaldimensions:is a fundamental dimension.

Reference:http://www.learnthermo.com/T1-tutorial/ch01/lesson-B/pg01.php
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LESSON 1C

Three Key Terms For The Study of Thermodynamics

1. In Lesson 1A, we learned a little bit about the history and nature of thermodynamics.

2. In Lesson 1B, we learned the importance of dimensions and units and how to use themto help us solve problems.

3. Now, we need to learn the meaning of some key terms that we will use throughout thiscourse. That is the goal of this lesson.

4. In this lesson, we will study the terms system, state and property.5. You are probably already familiar with these terms, but they have very specific meanings

when they are applied to thermodynamics.6. Because these three terms form the basis for this entire course, it is very important to

understand them very well before we move on.

Reference: http://www.learnthermo.com/T1-tutorial/ch01/lesson-C/pg01.php

What is a Process ?

In the previous lesson, we defined a state as the condition ofa substance or system that is determined by its properties.

We also learned that when the value of a property of the system changes, the

system is in a different state. This is called aprocess

.Reference : http://www.learnthermo.com/T1-tutorial/ch01/lesson-D/pg01.php
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LESSON1DVolume

Pressure, volume, and temperature are the three most important properties in classicalthermodynamics because they are the easiest properties to measure.

Volume

The space occupied by the system.An important extensive property of a system.Units: SI = m3, AE = ft3

Molar Volume

The volume of the system per mole of molecules within the system. (Intensive)

Density

- The volume of the system per unit of mass within the system. (Intensive)

Specific Volume

-The mass per unit volume of the system.


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What is Pressure ?Pressure

Force per unit area exerted by a fluid(gas or liquid) on a solid surface.

Pressure force acts in all directions and is due to thesum of all the random collisions of fluid moleculeswith the solid surface.

The pressure force always acts on a surface in adirection perpendicular or normal to the surface.

SI Units:Pascal (Pa) 1 kPa = 1000 Pa1 Pa = 1 N/m2 1 bar = 100 kPa 1 MPa = 106 Pa1 atm = 101.325 kPa

AE Units:lbf /in2 (psia or psig)1 psi = 6.895 kPa 1 atm = 14.696 psia

Rference : http://www.learnthermo.com/T1-tutorial/ch01/lesson-E/pg02.php
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Types of Pressure: DefinitionsPressure

- Force per unit area exerted by a fluid(gas or liquid) on a solid surface.

Absolute Pressure

- Pressure measured relative to an absolute vacuum(absolute zero pressure).

Gage Pressure

- Pressure greater than atmospheric pressure that are measuredrelative to atmospheric pressure. Gage pressure is

the difference between the absolute pressure andatmospheric pressure : Pgage = Pabs - Patm

Vacuum Pressure

- Pressure less than atmospheric pressure that are measuredrelative to atmospheric pressure. Vacuum pressure equalsatmospheric pressure minus the absolute pressure: Pvac = Patm

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The Barometer EquationWhere is the pressure greater, at the surface ofthe water, 1, or at the bottom of the tank, 2 ?P2 > P1because atmospheric pressure plusthe weightof all of the water in the tank is pushing downon the fluid at the bottom of the tank.If we assume the fluid in the tank is atequlibrium, then the forces acting on it must bebalanced.

Pressure forces at the bottom and top of the water act in opposite directionsand the weight of the water acts in the downward direction:

The Barometer Equation

Ch1, Lesson E, Page 4 - The Barometer Equation

Lets start by looking at the open tank of water, shown here.

Where do you think the pressure is greater, at the surface of the water or at the bottom of theliquid in the tank ?

Ill bet you know that P2 is greater than P1.

Basically, at the bottom of the tank you have the weight of all of the atmosphere pushing downPLUS all the weight of all the water in the tank pushing down.

As a result the pressure is greater at the bottom of the tank.

Now, lets see if we can quantify the difference between P1 and P2.

If the water in the tank is at equilibrium, then all the forces acting on it must be balanced.

In particular, the force acting upwards on the water due to the pressure at the bottom of the tankmust be equal to the force due to atmospheric pressure acting downward on the surface of the

water PLUS the weight of the water itself. This is exactly what the first equation says.

The forces due to pressure are just the pressure multiplied by the area over which the pressureacts.

You may be worried about some horizontal component of the pressure force due to waves on thesurface of the water, but we are only interested in the vertical component of the pressure force inthis case.

I used Newton 1st law to express the weight of the water.


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In the 2nd equation, I show how we can express the mass of the water in terms of its density, thecross-sectional area of the tank and the depth of the water, h.

When we plug this expression for the mass back into our force balance, an interesting thinghappens.

The cross-sectional area cancels out.

This makes sense though.

When you dive into a pool, the pressure depends on how deep the pools is, but it doesnt dependon the surface area of the pool, now does it ?

After a slight rearrangement we obtain the Barometer Equation.

This equation tells us how pressure varies with depth in a gravitational field.

It may be interesting to note that this equation is slightly easier to apply in the AE System than inthe SI System.

Why you may ask ? Because in the AE System, g over gc = 1 lbf / lbm. Cool.

Now, lets see what we can do with this equation.

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The Basic Manometer

A simple device tomodest pressure

differences is themanometer.

If P4 = 1 atm, then what is thepressureof the gas inside the tank ?

If the tank contains a gas and gas


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The Differential Manometer

A differential manometer measures thepressure difference between two points, in

this case P1 - P5.

Given h, m and w, determine P1 - P5.

What do we know ?

Apply the Barometer Equation to determine P2relative to P1 and P3 relativeto P5.

The Differential Manometer Equation

Cancel and then group terms to get:


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Other Types of Pressure Measurement Devices

Pressure Measurement Devices:Bourdon Tube Pressure Gauge(C-type)Pressure Transducers

P = 1 atm P = 9.5 atm

As the pressure inside the Bourdon tube increases, the tube deflects and thisaction, through a linkage and a pinion gear, rotates the needle on the gauge.

Ch1, Lesson E, Page 7 - Other Types of Pressure Measurement Devices

Common pressure measurement devices include the Bourdon Gauge and the pressuretransducer.

Pressure gauges are common in existing industrial plants, but pressure transducers are morecommon in laboratories and are becoming more common in new industrial plants.

Two C-type Bourdon Gauges are shown here.

At atmospheric pressure the curled tube inside the gauge is undeflected or relaxed and the gaugereads a GAUGE pressure of ZERO.

At higher pressures, the Bourdon tube begins to uncoil.

This action is translated into a rotation of the gauge needle by a series of gears.

This gauge reads 8.5 atm GAUGE because the pressure within the tank is 8.5 atm aboveatmospheric pressure.


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There are many different types of Bourdon Gauges. The C-type is just the easiest to sketch !

They all work in a very similar manner.

Pressure transducers are entirely different.

Usually, pressure transducers work by measuring the deflection of a diaphragm placed betweentwo regions at different pressures.

When the transducer is built to read absolute pressure, one side of the diaphragm is exposed

only to a vacuum. Transducers designed to read gauge pressure have one side open to the atmosphere.

In either case, the deflection of the diaphragm is generally measured using strain gauges.

Pressure transducers are small, inexpensive and rugged.

In addition, because they produce an electrical signal, it is very easy to digitize the signal andrecord the pressure.

That explains why they have become so popular.

Now, lets wrap us this lesson with a look at temperature and temperature measuring devices.

What is Temperature?

Temperature is a physical propertyof matter that quantitatively expresses the common notions

ofhot and cold. Objects of low temperature are cold, while various degrees of higher

temperatures are referred to as warm or hot.

Quantitatively, temperature is measured with thermometers, which may be calibrated to a

variety oftemperature scales.

Thermal vibration of a segment ofproteinalpha helix. The amplitude of the vibrations increases with temperature.

Temperature plays an important role in all fields of natural science,

including physics,geology, chemistry, atmospheric sciencesand biology.

In a microscopic explanation, the temperature of a body varies with the speed of the

fundamental particles that it contains, raised to the second power. Therefore, temperature is tied

directly to the mean kinetic energyof particles moving relative to the center of mass

coordinates for that object.

We think of temperature

as the numerical measurement of "hotness" or "coldness".
http://en.wikipedia.org/wiki/Physical_propertyhttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Coldhttp://en.wikipedia.org/wiki/Thermometershttp://en.wikipedia.org/wiki/Calibrationhttp://en.wikipedia.org/wiki/Temperature_conversion_formulashttp://en.wikipedia.org/wiki/Temperature_conversion_formulashttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Alpha_helixhttp://en.wikipedia.org/wiki/Physicshttp://en.wikipedia.org/wiki/Physicshttp://en.wikipedia.org/wiki/Geologyhttp://en.wikipedia.org/wiki/Chemistryhttp://en.wikipedia.org/wiki/Atmospheric_scienceshttp://en.wikipedia.org/wiki/Biologyhttp://en.wikipedia.org/wiki/Kinetic_energyhttp://en.wikipedia.org/wiki/Center_of_mass_coordinateshttp://en.wikipedia.org/wiki/Center_of_mass_coordinateshttp://en.wikipedia.org/wiki/Physical_propertyhttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Coldhttp://en.wikipedia.org/wiki/Thermometershttp://en.wikipedia.org/wiki/Calibrationhttp://en.wikipedia.org/wiki/Temperature_conversion_formulashttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Alpha_helixhttp://en.wikipedia.org/wiki/Physicshttp://en.wikipedia.org/wiki/Geologyhttp://en.wikipedia.org/wiki/Chemistryhttp://en.wikipedia.org/wiki/Atmospheric_scienceshttp://en.wikipedia.org/wiki/Biologyhttp://en.wikipedia.org/wiki/Kinetic_energyhttp://en.wikipedia.org/wiki/Center_of_mass_coordinateshttp://en.wikipedia.org/wiki/Center_of_mass_coordinates


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From our senses, we assign the "hotter" cup with ahigher temperature.

Ch1, Lesson E, Page 8 - What is Temperature?

The concept of temperature seems to be pretty straightforward as well.

We all know hot and cold when we tough it, right ?

But our senses can deceive us.

When we perceive an object to be hot, what our senses are really telling us is that the rate of heattransfer into our skin from the object is high. That doesnt always indicate that an object is hot.

Well clear up this little mystery in chapter 4.

For now, we need to think about how we can QUANTIFY hotness or temperature.

Flip the page to see how.


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The Zeroth Law of Thermodynamics

Zeroth Law of Thermodynamics

states that if two objects are in thermal equilibrium with a third object thenthey are equilibrium with each other. This law may seem obvious but it veryimportant because it allows the temperature of an object to be determined bycalibrating it with an object of known temperature.LiquidThermometer

Thermometers

are common temperature measuring devices that are based on the zerothlaw of thermodynamics.

Thermocouples

are are electrical devices in which two different metals are bonded. A smallelectrical potential, called a junction potential, is created by the junctionbetween the two metals. The juntion potential increases with increasingtemperature.


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Both thermometers and thermocouples must be calibrated using substancesat known temperatures, like the normal boiling point and melting point ofwater.

Reference: http://www.learnthermo.com/T1-tutorial/ch01/lesson-E/pg09.php


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Temperature Scales in the SI & AE SystemsTemperature Scales Used in the SI System:1. The Celsius temperature scale uses degrees Celsius (oC).

Defined such that:0oC corresponds to the freezing point of water100oC corresponds to the boiling point of water.

2. The Kelvin temperature scale is an absolute or thermodynamic scale inwhich temperature is measure in Kelvins (K). 1 K = 1oC.

Conversion Factors

T(K) = T(oC) + 273.15

T(R) = T(oF) + 459.67

T(R) = 1.8 T(K)T(oF) = 1.8 T(oC) + 32

Temperature Scales Used in the AE System:

1. The Fahrenheit temperature scale uses degrees Fahrenheit (oF). Definedsuch that:

32oF corresponds to the freezing point of water

212oF corresponds to the boiling point of water.

2. The Rankine temperature scale is an absolute or thermodynamic scale inwhich temperature is measure in degrees Rankine (oR). 1oR = 1oF.

The Ideal Gas Thermometer


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A bulb containg a very small amount of an ideal gas is allowed to cometo thermal equilibrium with the system, in this case, a bath of water. The right leg of the manometer is raised or lowered to keep the level ofthe manometer fluid in the left leg constant. We do this to keep the volumethat the ideal gas occupies constant. Use the manometer reading, h, to calculate the pressure of the gas. Ideal Gas "Law": P V = n R T One equation, but three unknowns: V, n, & T

Two problems:

1. The gas thermometer must be calibrated2. No real gas is actually an ideal gas except at zero pressure !

Flip the page to see how these problems can be resolved to make our gas

thermometer more accurate.

Gas Thermometer:

Ch1, Lesson E, Page 11 - The Ideal Gas Thermometer

A gas thermometer consists of a small bulb that contains the gas and is connected by a smalltube to a manometer.

The density of the manometer fluid must be much greater than the density of the gas if the deviceis going to work well.

As the gas comes to thermal equilibrium with some warm water, it expands and pushes themanometer fluid up into the right leg of the manometer, as shown here.

The trick is that you can MOVE the right manometer leg up and down.


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You must raise or lower the right leg to adjust the level of the manometer fluid in the left leg backto its original level.

You do this in order to keep the volume that the gas occupies CONSTANT.

You use the manometer reading, h, to calculate the pressure of the gas.

You are probably familiar with the Ideal Gas Law, but if not, dont worry. Well lear a lot moreabout it in the next chapter.

We have a problem though. We know P and R, but the volume, temperature and number ofmoles of gas are unknown and we only have ONE equation.

We have some other issues as well.

We know that thermometers generally need to be calibrated and the gas thermometer is noexception.

The other problem is that there is NO SUCH THING as an ideal gas except at ZERO pressure !

Why do we bother dealing with all these problems ? Because the gas thermometer is a veryprecise instrument when it is built and used properly.

Calibrating an Ideal Gas Thermometer

Measure the pressure in the gas thermometer when it has equilibratedwith a system at a well known reference temperature, such as the triplepoint of water, Tref = 0.01oC.

Measure the pressure in the gas thermometer when it has equilibratedwith your system at the unknown temperature, Tunk.

If you repeat this experiment withdifferent masses of gas in the bulb


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and extrapolate back to zero pressure, you will find that the interceptis absolute zero or-273.15 oC.Therefore, the ideal gas temperature scale is identical to the Kelvin scale aslong as the gas in the bulb does not condense or dissociate.If you use a different gas in the bulb, you will get a different slope, but theintercept will still be -273.15 oC.

Ch1, Lesson E, Page 12 - Calibrating an Ideal Gas Thermometer

Calibrating a gas thermometer is similar to calibrating any other type of thermometer.

You must let the gas bulb equilibrate thermally with a system at a very well known referencetemperature, such as the triple point of water.

Next, you use the manometer to measure the pressure. Ill call this pressure Pref.

Then, you let the gas bulb equilibrate with the unknown system and then measure the pressure.Ill call this pressure Punk.

If you write the Ideal Gas Law for each of these two systems and take the ratio of the two

equations, as shown here, some good things happen. V, n and R all cancel. Two of our unknown variable have cancelled. Cool !

Now, all we need to do is solve for Tunk. The result appears in the yellow box.

This equation looks simple enough, right ? Sure, but dont forget that these temperatures mustbe ABSOLUTE ! So, use Kelvin or Rankine.

Now, lets think about this thermometer for a moment.

What would happen if we had put LESS gas in the bulb but we adjusted the gas volume to thesame point ?

Well, ALL of the pressures that we measure would be lower.

Consider the three curves for different masses of gas in the bulb shown in the diagram: A, B andC.

The interesting part is that all of the lines converge at zero pressure to a temperature of 273.15oC or 0 K !

What does this mean ? It means that, as long as the gas in the bulb doesnt condense or dissociate (at very high

temperatures), the ideal gas thermometer is a thermodynamic temperature scale that exactlycoincides with the Kelvin or Rankine scales !

This is very cool, but has this little thought experiment given you any ideas about how to handlethe problem that real gases are not ideal gases ?

What happens as we put less and less gas in the thermometer bulb ?

Flip the page and lets see.

High Precision Gas Thermometry

Extrapolating Gas Thermometry to Zero Pressure

Use the gas thermometer to estimate Punk/Pref using the methoddescribed on the previous page.


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Repeat the procedure with a smaller and smaller mass of gas in thebulb. Note that the volume occupied by the gas must be same in all trials.

Plot Punk/Pref as a function ofPref, as shown here.

Extrapolate back to determine Punk/Pref when Prefis zero.

Since all gases are ideal at zero pressure, this extrapolated valueofPunk/Pref is our most precise value.

Use the extrapolated value ofPunk/Pref in the boxed equation, above, todetermine our most precise value ofTunk.

Ch1, Lesson E, Page 13 - High Precision Gas Thermometry

At zero pressure all gases are ideal gases.

So we need to extrapolate the results from our gas thermometer back to the point where thepressure is zero.

On the last page, we discussed how to measure Punk and Pref.

Here we take the ratio or Punk to Pref.

Then, we repeat the experiment and measure Punk / Pref with LESS gas in the thermometerbulb.

We repeat this several times and construct a plot of Punk / Pref as a function of Pref, like the oneshown here.

If we extrapolate back to Pref = zero, we obtain the value of Punk / Pref that we would measure ifthe pressure in the bulb were zero.

In other words, we get the value of Punk / Pref that we would get if the gas in the bulb were reallyan ideal gas !

This is very cool because we can take this very precise value of Punk / Pref and plug it back intothe boxed equation from the previous page and get a very precise value for the unknowntemperature, Tunk.


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This extrapolation back to the ideal gas state of zero pressure is why this technique is often calledideal gas thermometry.

That concludes our discussion of pressure, volume and temperature.

Now, take a look at a couple of example problems. Then, read the lesson summary and try thequiz for this lesson.

Reference : http://www.learnthermo.com/T1-tutorial/ch01/lesson-E/pg13.php

Introduction in Thermodynamics

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