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The CNO Cycle Animation
The CNO Cycle Animation
Published: 2015/10/01
Channel: Tai Kirby
Astronomy Animation
Astronomy Animation
Published: 2011/04/22
Channel: overlookedx
CNO Cycle
CNO Cycle
Published: 2017/04/12
Channel: rebeccalovestea
CNO cycle
CNO cycle
Published: 2016/01/22
Channel: WikiAudio
Astronomy - The Sun (5.5 of 16) What is the Proton-Proton Chain?
Astronomy - The Sun (5.5 of 16) What is the Proton-Proton Chain?
Published: 2015/01/02
Channel: Michel van Biezen
Carbon Nitrogen Cycle | Nuclear Physics Animation
Carbon Nitrogen Cycle | Nuclear Physics Animation
Published: 2017/03/29
Channel: Physics4students
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ChuChu TV Police Chase Thief in Police Car to Save Huge Surprise Egg Toys Gifts – The Train Escape
Published: 2017/03/14
Channel: ChuChuTV Surprise Eggs Toys
Physics @ Amity - The CNO fusion cycle
Physics @ Amity - The CNO fusion cycle
Published: 2015/08/07
Channel: David Lee
carbon nitrogen cycle
carbon nitrogen cycle
Published: 2014/11/29
Channel: K.V.R Institute Of Physics
CNO cycle Meaning
CNO cycle Meaning
Published: 2015/04/25
Channel: ADictionary
CNO cycle
CNO cycle
Published: 2017/04/14
Channel: Victoria Benavides
Nuclear Fusion 500 Terawatt Laser at the National Ignition Facility
Nuclear Fusion 500 Terawatt Laser at the National Ignition Facility
Published: 2012/07/16
Channel: Muon Ray
proton proton chain reaction
proton proton chain reaction
Published: 2015/06/29
Channel: Scrivial
Nuclear Fission and Fusion
Nuclear Fission and Fusion
Published: 2015/09/10
Channel: SliderBase
Astronomy: Life Cycle of a Low Mass Star (13 of 17) 2nd Red Giant Branch: Stage 11
Astronomy: Life Cycle of a Low Mass Star (13 of 17) 2nd Red Giant Branch: Stage 11
Published: 2014/06/04
Channel: Michel van Biezen
Proton–proton chain reaction
Proton–proton chain reaction
Published: 2016/01/29
Channel: WikiAudio
Teach Astronomy - Carbon Cycle
Teach Astronomy - Carbon Cycle
Published: 2010/07/10
Channel: Teach Astronomy
Nitrogen Cycle ,Nitrogen Fixation   Oxygen Carbon Cycle xvid
Nitrogen Cycle ,Nitrogen Fixation Oxygen Carbon Cycle xvid
Published: 2015/09/20
Channel: GRADE VI SCIENCE CLASS
Nuclear fusion educational animations – for Science Photo Library
Nuclear fusion educational animations – for Science Photo Library
Published: 2016/07/01
Channel: equinoxgraphics
Nuclear Fusion Explained
Nuclear Fusion Explained
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Channel: The Science Asylum
CNO Rap feat. Vega
CNO Rap feat. Vega
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Channel: JINA-CEE
Fusion in Stars
Fusion in Stars
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Channel: William Koch
May 26th, 2017 - Carbon NITROGEN Oxygen Cycle - Star Stuff Week
May 26th, 2017 - Carbon NITROGEN Oxygen Cycle - Star Stuff Week
Published: 2017/05/27
Channel: Everyday Science
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Published: 2016/08/28
Channel: WikiWikiup
M14 Rifle: "U.S. Rifle 7.62mm  M14  Operation and Cycle of Function" 1960 US Army
M14 Rifle: "U.S. Rifle 7.62mm M14 Operation and Cycle of Function" 1960 US Army
Published: 2015/10/23
Channel: Jeff Quitney
Fusion TripleAlpha CNO cycle making Neutrons Carbon Catalyst OCT 10
Fusion TripleAlpha CNO cycle making Neutrons Carbon Catalyst OCT 10
Published: 2010/10/26
Channel: CosmicRay137
Fourteen Twentysix & EXM - After The Storm (CNO-cycle Remix)
Fourteen Twentysix & EXM - After The Storm (CNO-cycle Remix)
Published: 2011/09/08
Channel: FourteenTwentysix
Carbon-nitrogen-oxygen cycle Meaning
Carbon-nitrogen-oxygen cycle Meaning
Published: 2015/04/25
Channel: ADictionary
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CNO Cycle Yttria Poem Standard Model Alpha Fish Intro end 4
Published: 2009/08/27
Channel: CosmicRay137
Hans Bethe - Work on the carbon/nitrogen cycle of massive stars (73/158)
Hans Bethe - Work on the carbon/nitrogen cycle of massive stars (73/158)
Published: 2017/06/27
Channel: Web of Stories - Life Stories of Remarkable People
Proton Proton Cycle | Nuclear Physics | Animated Lessons
Proton Proton Cycle | Nuclear Physics | Animated Lessons
Published: 2017/03/28
Channel: Physics4students
CN Cycle 2015 Thank you!
CN Cycle 2015 Thank you!
Published: 2015/05/04
Channel: CHEOvideos
Lecture 9a (Energy Creation in the Core)
Lecture 9a (Energy Creation in the Core)
Published: 2013/04/26
Channel: Viken Kiledjian
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CNO 2015 - leg 3 - Cadet - Male. 500m sprint final
Published: 2015/06/08
Channel: rbaietta
The Carbon and Nitrogen Cycles
The Carbon and Nitrogen Cycles
Published: 2016/09/21
Channel: Boden Puetz
Complete Nitrogen Cycle Photostory
Complete Nitrogen Cycle Photostory
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Channel: Heather Anderson
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Main sequence - Video Learning - WizScience.com
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Channel: Wiz Science™
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Carbon & Nitrogen Cycle
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Channel: Marian Scott
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Science With Méls: Stellar Evolution
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Nuclear Fusion and Proton-Proton Cycle
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Channel: AK LECTURES
The Value of Practice Reflection
The Value of Practice Reflection
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Channel: College of Nurses of Ontario CNO
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IDC Self Synchronization Live: CNO's Rapid Innovation Cell (CRIC)
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Channel: IWC Self Synchronization
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Nucleosynthesis Process (Philippines)
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WARNING SUN CORE: SOLAR "EXPLOSION" OF LIGHT IS COMING - 07/19/2017
WARNING SUN CORE: SOLAR "EXPLOSION" OF LIGHT IS COMING - 07/19/2017
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Channel: Zion Zeus
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WWR: CNO’s releases navigation plan, new career paths for SWOs and Feds Feed Families kickoff
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Channel: U.S. Navy
QG 76   Stellar Mechanics
QG 76 Stellar Mechanics
Published: 2012/10/01
Channel: KELVIN ABRAHAM
Introduction to Practice Reflection and Guided Reflection
Introduction to Practice Reflection and Guided Reflection
Published: 2014/11/04
Channel: College of Nurses of Ontario CNO
The Cosmic Classroom - Proton Proton Chain
The Cosmic Classroom - Proton Proton Chain
Published: 2009/10/10
Channel: Vera Margoniner
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Nuclear fusion in the sun
Published: 2017/05/03
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Microscopic Model for Proton Emission_Nuclear Physics Meet 2015
Microscopic Model for Proton Emission_Nuclear Physics Meet 2015
Published: 2015/07/06
Channel: Dr Sushil Kumar Guruji
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WIKIPEDIA ARTICLE

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Overview of the CNO-I Cycle
Carbon-Nitrogen-Oxygen Cycle-1

The CNO cycle (for carbonnitrogenoxygen) is one of the two known sets of fusion reactions by which stars convert hydrogen to helium, the other being the proton–proton chain reaction. Unlike the latter, the CNO cycle is a catalytic cycle. It is dominant in stars that are more than 1.3 times as massive as the Sun.[1]

In the CNO cycle, four protons fuse, using carbon, nitrogen and oxygen isotopes as catalysts, to produce one alpha particle, two positrons and two electron neutrinos. Although there are various paths and catalysts involved in the CNO cycles, all these cycles have the same net result:

4 1
1
H
 +  2 
e
 →  4
2
He
 +  2 
e+
 +  2 
e
 +  2 
ν
e
 +  3 
γ
 +  24.7 MeV  →  4
2
He
 +  2 
ν
e
 +  3 
γ
 +  26.7 MeV

The positrons will almost instantly annihilate with electrons, releasing energy in the form of gamma rays. The neutrinos escape from the star carrying away some energy. One nucleus goes to become carbon, nitrogen, and oxygen isotopes through a number of transformations in an endless loop.

Theoretical models suggest that the CNO cycle is the dominant source of energy in stars whose mass is greater than about 1.3 times that of the Sun.[1] The proton–proton chain is more prominent in stars the mass of the Sun or less. This difference stems from temperature dependency differences between the two reactions; pp-chain reaction starts at temperatures around 4×106 K[2] (4 megakelvins), making it the dominant energy source in smaller stars. A self-maintaining CNO chain starts at approximately 15×106 K, but its energy output rises much more rapidly with increasing temperatures.[1] At approximately 17×106 K, the CNO cycle starts becoming the dominant source of energy.[3] The Sun has a core temperature of around 15.7×106 K, and only 1.7% of 4
He
nuclei produced in the Sun is born in the CNO cycle. The CNO-I process was independently proposed by Carl von Weizsäcker[4] and Hans Bethe[5] in 1938 and 1939, respectively.

Cold CNO cycles[edit]

Under typical conditions found in stars, catalytic hydrogen burning by the CNO cycles is limited by proton captures. Specifically, the timescale for beta decay of the radioactive nuclei produced is faster than the timescale for fusion. Because of the long timescales involved, the cold CNO cycles convert hydrogen to helium slowly, allowing them to power stars in quiescent equilibrium for many years.

CNO-I[edit]

The first proposed catalytic cycle for the conversion of hydrogen into helium was initially called the carbon–nitrogen cycle (CN cycle), also honorarily referred to as the Bethe–Weizsäcker cycle, because it does not involve a stable isotope of oxygen. Bethe's original calculations suggested the CN-cycle was the Sun's primary source of energy, owing to the belief at the time that the Sun's composition was 10% nitrogen;[5] the solar abundance of nitrogen is now known to be less than half a percent. This cycle is now recognized as the first part of the larger CNO nuclear burning network. The main reactions of the CNO-I cycle are 12
6
C
13
7
N
13
6
C
14
7
N
15
8
O
15
7
N
12
6
C
:[6]

12
6
C
 
1
1
H
 
→  13
7
N
 

γ
 
    1.95 MeV
13
7
N
 
    →  13
6
C
 

e+
 

ν
e
 
1.20 MeV (half-life of 9.965 minutes[7])
13
6
C
 
1
1
H
 
→  14
7
N
 

γ
 
    7.54 MeV
14
7
N
 
1
1
H
 
→  15
8
O
 

γ
 
    7.35 MeV
15
8
O
 
    →  15
7
N
 

e+
 

ν
e
 
1.73 MeV (half-life of 122.24 seconds[7])
15
7
N
 
1
1
H
 
→  12
6
C
 
4
2
He
 
    4.96 MeV

where the carbon-12 nucleus used in the first reaction is regenerated in the last reaction. After the two positrons emitted annihilate with two ambient electrons producing an additional 2.04 MeV, the total energy released in one cycle is 26.73 MeV; it should be noted that in some texts, authors are erroneously including the positron annihilation energy in with the beta-decay Q-value and then neglecting the equal amount of energy released by annihilation, leading to possible confusion. All values are calculated with reference to the Atomic Mass Evaluation 2003.[8]

The limiting (slowest) reaction in the CNO-I cycle is the proton capture on 14
7
N
. In 2006 it was experimentally measured down to stellar energies, revising the calculated age of globular clusters by around 1 billion years.[9]

The neutrinos emitted in beta decay will have a spectrum of energy ranges, because although momentum is conserved, the momentum can be shared in any way between the positron and neutrino, with either emitted at rest and the other taking away the full energy, or anything in between, so long as all the energy from the Q-value is used. All momentum which get the electron and the neutrino together is not great enough to cause a significant recoil of the much heavier daughter nucleus and hence, its contribution to kinetic energy of the products, for the precision of values given here, can be neglected. Thus the neutrino emitted during the decay of nitrogen-13 can have an energy from zero up to 1.20 MeV, and the neutrino emitted during the decay of oxygen-15 can have an energy from zero up to 1.73 MeV. On average, about 1.7 MeV of the total energy output is taken away by neutrinos for each loop of the cycle, leaving about 25 MeV available for producing luminosity.[10]

CNO-II[edit]

In a minor branch of the above reaction, that occurs in the Sun's core 0.04% of the time, the final reaction involving 15
7
N
shown above does not produce carbon-12 and an alpha particle, but instead produces oxygen-16 and a photon and continues 15
7
N
16
8
O
17
9
F
17
8
O
14
7
N
15
8
O
15
7
N
:

15
7
N
 
1
1
H
 
→  16
8
O
 

γ
 
    12.13 MeV
16
8
O
 
1
1
H
 
→  17
9
F
 

γ
 
    0.60 MeV
17
9
F
 
    →  17
8
O
 

e+
 

ν
e
 
2.76 MeV (half-life of 64.49 seconds)
17
8
O
 
1
1
H
 
→  14
7
N
 
4
2
He
 
    1.19 MeV
14
7
N
 
1
1
H
 
→  15
8
O
 

γ
 
    7.35 MeV
15
8
O
 
    →  15
7
N
 

e+
 

ν
e
 
2.75 MeV (half-life of 122.24 seconds)

Like the carbon, nitrogen, and oxygen involved in the main branch, the fluorine produced in the minor branch is merely an intermediate product and at steady state, does not accumulate in the star.

CNO-III[edit]

This subdominant branch is significant only for massive stars. The reactions are started when one of the reactions in CNO-II results in fluorine-18 and gamma instead of nitrogen-14 and alpha, and continues 17
8
O
18
9
F
18
8
O
15
7
N
16
8
O
17
9
F
17
8
O
:

17
8
O
 
1
1
H
 
→  18
9
F
 

γ
 
    5.61 MeV
18
9
F
 
    →  18
8
O
 

e+
 

ν
e
 
1.656 MeV (half-life of 109.771 minutes)
18
8
O
 
1
1
H
 
→  15
7
N
 
4
2
He
 
    3.98 MeV
15
7
N
 
1
1
H
 
→  16
8
O
 

γ
 
    12.13 MeV
16
8
O
 
1
1
H
 
→  17
9
F
 

γ
 
    0.60 MeV
17
9
F
 
    →  17
8
O
 

e+
 

ν
e
 
2.76 MeV (half-life of 64.49 seconds)

CNO-IV[edit]

A proton reacts with a nucleus causing release of an alpha particle.

Like the CNO-III, this branch is also only significant in massive stars. The reactions are started when one of the reactions in CNO-III results in fluorine-19 and gamma instead of nitrogen-15 and alpha, and continues 19
9
F
16
8
O
17
9
F
17
8
O
18
9
F
18
8
O
19
9
F
:

19
9
F
 
1
1
H
 
→  16
8
O
 
4
2
He
 
    8.114 MeV
16
8
O
 
1
1
H
 
→  17
9
F
 

γ
 
    0.60 MeV
17
9
F
 
    →  17
8
O
 

e+
 

ν
e
 
2.76 MeV (half-life of 64.49 seconds)
17
8
O
 
1
1
H
 
→  18
9
F
 

γ
 
    5.61 MeV
18
9
F
 
    →  18
8
O
 

e+
 

ν
e
 
1.656 MeV (half-life of 109.771 minutes)
18
8
O
 
1
1
H
 
→  19
9
F
 

γ
 
    7.994 MeV

Hot CNO cycles[edit]

Under conditions of higher temperature and pressure, such as those found in novae and x-ray bursts, the rate of proton captures exceeds the rate of beta-decay, pushing the burning to the proton drip line. The essential idea is that a radioactive species will capture a proton before it can beta decay, opening new nuclear burning pathways that are otherwise inaccessible. Because of the higher temperatures involved, these catalytic cycles are typically referred to as the hot CNO cycles; because the timescales are limited by beta decays instead of proton captures, they are also called the beta-limited CNO cycles.[clarification needed]

HCNO-I[edit]

The difference between the CNO-I cycle and the HCNO-I cycle is that 13
7
N
captures a proton instead of decaying, leading to the total sequence 12
6
C
13
7
N
14
8
O
14
7
N
15
8
O
15
7
N
12
6
C
:

12
6
C
 
1
1
H
 
→  13
7
N
 

γ
 
    1.95 MeV
13
7
N
 
1
1
H
 
→  14
8
O
 

γ
 
    4.63 MeV
14
8
O
 
    →  14
7
N
 

e+
 

ν
e
 
5.14 MeV (half-life of 70.641 seconds)
14
7
N
 
1
1
H
 
→  15
8
O
 

γ
 
    7.35 MeV
15
8
O
 
    →  15
7
N
 

e+
 

ν
e
 
2.75 MeV (half-life of 122.24 seconds)
15
7
N
 
1
1
H
 
→  12
6
C
 
4
2
He
 
    4.96 MeV

HCNO-II[edit]

The notable difference between the CNO-II cycle and the HCNO-II cycle is that 17
9
F
captures a proton instead of decaying, and neon is produced in a subsequent reaction on 18
9
F
, leading to the total sequence 15
7
N
16
8
O
17
9
F
18
10
Ne
18
9
F
15
8
O
15
7
N
:

15
7
N
 
1
1
H
 
→  16
8
O
 

γ
 
    12.13 MeV
16
8
O
 
1
1
H
 
→  17
9
F
 

γ
 
    0.60 MeV
17
9
F
 
1
1
H
 
→  18
10
Ne
 

γ
 
    3.92 MeV
18
10
Ne
 
    →  18
9
F
 

e+
 

ν
e
 
4.44 MeV (half-life of 1.672 seconds)
18
9
F
 
1
1
H
 
→  15
8
O
 
4
2
He
 
    2.88 MeV
15
8
O
 
    →  15
7
N
 

e+
 

ν
e
 
2.75 MeV (half-life of 122.24 seconds)

HCNO-III[edit]

An alternative to the HCNO-II cycle is that 18
9
F
captures a proton moving towards higher mass and using the same helium production mechanism as the CNO-IV cycle as 18
9
F
19
10
Ne
19
9
F
16
8
O
17
9
F
18
10
Ne
18
9
F
:

18
9
F
 
1
1
H
 
→  19
10
Ne
 

γ
 
    6.41 MeV
19
10
Ne
 
    →  19
9
F
 

e+
 

ν
e
 
3.32 MeV (half-life of 17.22 seconds)
19
9
F
 
1
1
H
 
→  16
8
O
 
4
2
He
 
    8.11 MeV
16
8
O
 
1
1
H
 
→  17
9
F
 

γ
 
    0.60 MeV
17
9
F
 
1
1
H
 
→  18
10
Ne
 

γ
 
    3.92 MeV
18
10
Ne
 
    →  18
9
F
 

e+
 

ν
e
 
4.44 MeV (half-life of 1.672 seconds)

Use in astronomy[edit]

While the total number of "catalytic" nuclei are conserved in the cycle, in stellar evolution the relative proportions of the nuclei are altered. When the cycle is run to equilibrium, the ratio of the carbon-12/carbon-13 nuclei is driven to 3.5, and nitrogen-14 becomes the most numerous nucleus, regardless of initial composition. During a star's evolution, convective mixing episodes moves material, within which the CNO cycle has operated, from the star's interior to the surface, altering the observed composition of the star. Red giant stars are observed to have lower carbon-12/carbon-13 and carbon-12/nitrogen-14 ratios than do main sequence stars, which is considered to be convincing evidence for the operation of the CNO cycle.[citation needed]

See also[edit]

References[edit]

  1. ^ a b c Salaris, Maurizio; Cassisi, Santi (2005), Evolution of stars and stellar populations, John Wiley and Sons, pp. 119–121, ISBN 0-470-09220-3 
  2. ^ Reid, I. Neill; Suzanne L., Hawley (2005), New light on dark stars: red dwarfs, low-mass stars, brown dwarfs, Springer-Praxis books in astrophysics and astronomy (2nd ed.), Springer, p. 108, ISBN 3-540-25124-3 
  3. ^ Schuler, S. C.; King, J. R.; The, L.-S. (2009). "Stellar Nucleosynthesis in the Hyades Open Cluster". The Astrophysical Journal. 701 (1): 837–849. Bibcode:2009ApJ...701..837S. arXiv:0906.4812Freely accessible. doi:10.1088/0004-637X/701/1/837. 
  4. ^ von Weizsäcker, C. F. (1938). "Über Elementumwandlungen in Innern der Sterne II". Physikalische Zeitschrift. 39: 633–46. 
  5. ^ a b Bethe, H. A. (1939). "Energy Production in Stars". Physical Review. 55 (5): 434–56. Bibcode:1939PhRv...55..434B. doi:10.1103/PhysRev.55.434. 
  6. ^ Krane, K. S. (1988). Introductory Nuclear Physics. John Wiley & Sons. p. 537. ISBN 0-471-80553-X. 
  7. ^ a b Principles and Perspectives in Cosmochemistry, Springer, 2010, ISBN 9783642103681, page 233
  8. ^ Wapstra, Aaldert; Audi, Georges (18 November 2003). "The 2003 Atomic Mass Evaluation". Atomic Mass Data Center. Retrieved 25 October 2011. 
  9. ^ LUNA Collaboration; Lemut, A.; Bemmerer, D.; Confortola, F.; Bonetti, R.; Broggini, C.; Corvisiero, P.; Costantini, H.; Cruz, J.; Formicola, A.; Fülöp, Zs.; Gervino, G.; et al. (2006). "First measurement of the 14N(p,gamma)15O cross section down to 70 keV". Physics Letters B. 634: 483–487. Bibcode:2006PhLB..634..483L. arXiv:nucl-ex/0602012Freely accessible. doi:10.1016/j.physletb.2006.02.021. 
  10. ^ Scheffler, Helmut; Elsässer, Hans (1990). Die Physik der Sterne und der Sonne. Bibliographisches Institut (Mannheim, Wien, Zürich). ISBN 3-411-14172-7. 

Further reading[edit]

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