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76 Cards in this Set
- Front
- Back
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Newton's solution to avoiding a collapse in the universe
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the universe in infinitely large and there is no center mass. therefore, objects are pulling in all directions and the force of gravity is the same in all directions. the net force is zero.
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If objects move around and are expected to clump together, how did Newton explain this?
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1) stars are too from each other and the force is small.
2) God constantly acts to prevent gravitational collapse. |
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What is the problem with resorting to God for an explanation?
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A scientist stops searching for a scientific answer
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What is the Clockwork Universe Proposal?
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The universe has operated mechanically since it was originally set in motion.
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Why is the night sky not dark?
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It is neither infinitely old or infinitely large. This is explained by the dark sky paradox. If the opposite were the case, we would see a star in every direction and the night sky would be bright.
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What is the Copernican cosmological principal?
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There is no special place in the universe. The universe should appear the same to an observer from any point inside the universe as another observer (relative appearance will not be exactly the same).
the universe is uniform and isotropic |
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How do we measure distances to nearby stars?
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If the brightness and apparent anglular sizes(how much of the field of vision is taken up) of galaxies are known, the distances can be measured. To determine the distance to nearby stars, you can use parallax which is the inversely proportional to the distance.
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The distances of stars are measured in what units?
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parcseconds: the distance of a hypothetical star with a parallaz of 1 arcsecond.
1pc=206000AU=3.26 lt-yr 1pc |
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Parallax is measured in what unit?
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Arcsecond
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How do we measure distant stars?
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Astronomers were able to derive the lumiosities of stars once the parallax's were determined. For stars that are too distant, we can measure the luminosity from the absorption line spectrum.
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What is a Cepheid Variable?
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A star that pulsates and whose brightness changes with a very regular period. Their period is proportional to their luminosity.
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What is the problem with dust?
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dust in galaxies block the light and cause stars to appear fainter and redder (especially for distant stars)
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What is a standard candle?
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a star whose luminosity is well established.
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What is temperature?
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the measure of thermal energy which is also known as kinetic energy.
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Explain conservation of energy in terms of potential, kinetic, and thermal energy.
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Energy that is lost from a system is converted into thermal energy. The initial potential energy will be equal to the thermal energy in the after an object moves.
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What does the light of a hot,transparent gas appear like?
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it appears in very narrow bands of wavelengths called spectral lines.
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What is thermal energy?
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the average kinetic energy in a system
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What did Bohr discover about energy in electrons?
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Light is found in packets or photons of energy. therefore, energy of light is quantized. energy bound to an electron can only have certain discrete energies which are negative.
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What happens when light jumps from one energy level to another?
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When an electron jumps to a higher energy level, the photon disappears because its' energy is used up. When it jumps down, light is emitted in the form of a photon with energy equal to the diff. between the energies of the 2 states.
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excited state vs. ground state
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ground state is the lowest energy and the higher bound states are excited states
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3 ways that an electron can achieve an excited state
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1) it previously absorbed a photon
2) in a collision with another atom 3) the electron was previously free and was captured by an electron |
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What type of spectrum does a opaque object have?
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a continuous spectrum, that of a blackbody. the visible color of an opaque object depends on its temperature.
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What type of spectrum does a hot, transparent gas have?
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a hot, transparent gas has an emission line (or bright line) spectrum. The brightness of each line depends on the relative number of the various elements as well as the temperature
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What type of spectrum does a hot, opaque object have?
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an absorption line spectrum. this is the spectra of most stars.
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What is the uncertainty principle?
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there is a limit to the precision in the measurements that can be made of basic physical quantities on tiny scales. The symbol delta means "uncertainty in." The position and velocity of individual particles cannot be measured at the same time.
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Why can't position and velocity of particles be measured at the same time?
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1) If they could both be measured, this would mean that the future position and velocity of particles could be measured. But the wave function only provides probabilities
2) This measurement would require an interaction with the particle which would change the physical state. A detector could be used but it would interfere. |
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What is the doppler effect on a spectral line when the motion is away from the observer?
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wavelength is shifted to longer values: red shift
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What is the doppler effect on a spectral line when the motion is towards the observer?
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blue shift: wavelength is shifted to shorter values
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What are nanometers?
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the size of things in the atom
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What did DeBroliger conclude about particles?
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if a light can act both as a particle and a wave, maybe the same thing is true for an electron....it is a particle-wave. The same thing for light holds true for particle.
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what is the solution to shrodinger's "free" particle case?
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when no bining forces are present, a free particle is a wave packet, a wave whose amplitude decreases away from the central point. when a wave does not have binding forces, it spreads out.
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What does the wave function represent?
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the wave function provides information on a particle's location. It provides the probability of finding a particle in a particular place.
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If you don't try to make an observation of a particle, then
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the particle is assumed to be everywhere else.
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What happens when an electron changes energy levels?
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it corresponds to a photon being emitted or absorbed.
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is the wave function an accurate measurement?
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it leaves out some information such as whether the spin of the particle is clockwise or counterclockwise.
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When does a wave packet spread out and when does it scrunch up?
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a wave packet scrunched up (or collapses to the size of the uncertainty in the measurement when it is located and spreads out when there is no measurement being made.
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What does the act of detection do to a particle-wave?
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the act of detection changes the property of the particle. The particles act more like waves when they hit the screen.
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What does John Bell mean by hybrid state?
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When a particle is not observed, it is simultaneously in all possible states at all times.
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Quantum mechanics is holistic. what does this mean?
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Things cannot be divided up.
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Who devised the cat thought experiment? (3/5) Explain.
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Shrodinger devised it to explain the absurdity of the hybrid state.
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Solutions to the Cat Thought Experiment.
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1) Decoherence: the environment acts with the atom to create a definite state. (the environment is essentially the observer)
2) God continuously acts as the observer who collapses wave functions. 3) Many World's hypothesis: all possibilities actually happen |
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What did Ernest Rutherford discover?
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He discovered where the positive charge was in the atom (in the nucleus). He cut a slit and then put a thin gold foil in front. Targeted atoms at foil to see result. Scattering in diff. directions (nucleus is a little tiny thing). Atoms are mostly empty space.
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What did JJ Thompson discover?
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The electron. That there are negatively charged particles found in the atom.
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What is the smallest nucleus?
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The nucleus of hydrogen.
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What is an isotope?
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Things that have the same chemical properties (same element) but have slightly different masses than the most common form of that atom. Different masses of neutron.
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Nucleons
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Equal to the atomic weight. protons plus neutrons.
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What does a neutron decay into?
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If you take a neutron out of a neutron it decays into a proton, an electron, and third particle (neutrino) to preserve momentum. half life of 15 minutes.
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what is a neutrino?
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an electrically neutral particle lighter than an electron.
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What are the 4 fundamental forces in nature?
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1) Gravity (negligible on small scales: macroscopic force)
2) Electromagnatism (important on both scales) 3) Strong Nuclear Force (important on small sales) 4) Weak Interaction (small scales) |
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What was Einstein's theory about energy?
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energy and mass are really the same thing. energy can be changed into mass and vice versa.
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What does E=MC2 represent?
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The lowest energy that is particle can have. You need at least this much energy to create a particle.
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What is antimatter?
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a particle with the mass and opposite electric charge of a charged particle.
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What is a positron?
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The antimatter of an electon.
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What is an antiproton?
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the antimatter of a proton.
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What is an anti-neutron?
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The antimatter of a neutron.
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What happens when matter and antimatter collide.
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when a particle and an antiparticle collide, they annihilate or they leave the universe. But they leave behind mass-energy.
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what happens when an electron and a positron collide?
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they produce 2 photons and gamma rays form (explosion).
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what happens when photons collide?
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they produce an electron and positron pair.
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What is the advantage of using an anti matter/matter pair to propel a spacecraft? disadvantages?
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very efficient (small material for a lot of energy)
gamma rays are dangerous. need to isolate anti-matter (or keep it away from space shuttle |
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What are the 3 fundamental indivisible particles?
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1) Lepton
2) Quarts 3) Bosons |
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What indivisible particle is a proton made out of? an anti-proton?
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Proton: 1 down + 2 up quarks,
anti-proton: 1 anti-down + 2 anti-up quarks |
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What indivisible particle is a neutron made out of? a anti- neutron?
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neutron: 1 up + 2 down quarks
anti-neutron: 1 anti-up + 2 anti-down |
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what is a boson?
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include photon, gluon, w-boson, z-boson. they are the ones that cause the forces and make things less confusing. do not obey the pauli exclusion principle.
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what causes forces?
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the exchange of virtual bosons. solves Newton's issue of action at a distance. force is very strong over a short range which is what causes the forces to stick together. acts like a rubber band: the farther it is stretched, the rubber band will break. when you get beyond the range, the force gets very weak. gluons hold quarks together and neutrons help with force without causing repulsion.
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what is a virtual photon?
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a photon that is exchanged between forces that is never observed.
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What is the Higgs Boson?
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supposed to answer the question about where mass comes from. mass is a creates resistance to acceleration. the boson creates a field in space where the particles interact with the field. That is what gives it mass. the mass corresponds to the type of particle it is.
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what is a vacuum?
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a region in space where there is no matter but that is a lie because there are a lot virtual photons that are not observed such as particle and antiparticle pairs. no matter that we can easily measure but there are quantum fluctuations (things popping in and out of existence all the time).
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how do we know that particle antiparticle pair exist if they only exist shortly and we do not observe them?
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casmere came up with an answer. experiment takes advantage of the wave nature of particles.
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explain quantum fluctuation
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A particle and antiparticle pair can pop into and out of existence for very short period of time using borrowed energy. the time is shorter for higher mass particles.
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explain the casimir effect
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two metal plates are placed extremely close to one another. this causes the exclusion of virtual particles with wavelengths smaller than the distance between the plates. Without waves flowing through the plates, the pressure is lower and the plates ate forced together by the wavelengths on the outside. Therefore, virtual particles exist throughout space.
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what is nuclear fission?
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the splitting of one nuclei into 2 smaller nuclei either as a spontaneous process or as a result of being struck by some other particle. nuclei can also combine in this process. important when dealing with the energy of stars.
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What happens when a proton or neutron jumps down to a lower energy level?
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a gamma ray is emitted
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what is the result of extra neutrons
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they create extra support for an unstable nucleus because they do not cause repulsion.
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what is radioactivity
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the general term for the emission of particles by a nucleus as it drops to a lower energy state.
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what is alpha decay?
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the original nucleus becomes lighter by also producing the nucleus of a helium atom.
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what is a nucleon?
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a proton plus a neutron
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