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 Riemannian Geometry (PDF)
from above that (TM,M, pi) together with the maximal bundle atlas B̂ defined by B is a differen- tiable vector bundle. Definition 4.8. Let M be a differentiable manifold, then a section X : M → TM of the tangent bundle is called a vector field. The set of smooth vector fields X : M →...
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from above that (TM,M, pi) together with the maximal bundle atlas B̂ defined by B is a differen- tiable vector bundle. Definition 4.8. Let M be a differentiable manifold, then a section X : M → TM of the tangent bundle is called a vector field. The set of smooth vector fields X : M → TM is denoted by C∞(TM). Example 4.9. We have seen earlier that the 3-sphere S3 in H ∼= C2 carries a group structure · given by (z, w) · (α, β) = (zα− wβ̄, zβ + wᾱ). This makes (S3, ·) into a Lie group with neutral element e = (1
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www.matematik.lu.se/matematiklu/personal/sigma/Riemann.pdf#page=18
16 2. DIFFERENTIABLE MANIFOLDS Example 2.25. The result of Proposition 2.24 can be used to show that the following maps are all smooth. (i) φ1 : S 2 ⊂ R3 → <span class="highlight">S3</span> ⊂ R4, φ1 : (x, y, z) 7→ (x, y, z, 0), (ii) φ2 : S 3 ⊂ C2 → S2 ⊂ C×R, φ2 : (z1, z2) 7→ (2z1z̄2, |z1|2−|z2|2), (iii) φ3 : R1 → S1 ⊂ C, φ3 : t 7→ eit, (iv) φ4 : Rm+1 \ {0} → Sm, φ4 : x 7→ x/|x|, (v) φ5 : Rm+1 \ {0} → RPm, φ5 : x 7→ [x], (vi) φ6 : S m → RPm, φ6 : x 7→ [x]. In differential geometry we are especially interested in differentiable manifolds
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www.matematik.lu.se/matematiklu/personal/sigma/Riemann.pdf#page=19
→ p · q̄ and a real valued norm given by |p|2 = p · p̄. Then the 3-dimensional unit sphere <span class="highlight">S3</span> in H ∼= R4 with the restricted multiplication forms a compact Lie subgroup (<span class="highlight">S3</span>, ·) of (H∗, ·). They are both non-abelian. We shall now introduce some of the classical real and complex matrix Lie groups. As a reference on this topic we recommend the wonderful book: A. W. Knapp, Lie Groups Beyond an Introduction, Birkhäuser (2002). Example 2.31. Let Nil3 be the subset of R3×3 given by Nil3 = { 1 x z0 1 y 0 0 1
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www.matematik.lu.se/matematiklu/personal/sigma/Riemann.pdf#page=22
R3 and the Riemann sphere Ĉ are diffeomorphic. Exercise 2.8. Find a proof of Proposition 2.24. Exercise 2.9. Let the spheres S1, <span class="highlight">S3</span> and the Lie groups SO(n), O(n), SU(n), U(n) be equipped with their standard differentiable structures introduced above. Use Proposition 2.24 to prove the fol- lowing diffeomorphisms S1 ∼= SO(2), <span class="highlight">S3</span> ∼= SU(2), SO(n)×O(1) ∼= O(n), SU(n)×U(1) ∼= U(n). Exercise 2.10. Find a proof of Corollary 2.28. Exercise 2.11. Let (G, ∗) and (H, ·) be two Lie groups. Prove that the product
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www.matematik.lu.se/matematiklu/personal/sigma/Riemann.pdf#page=32
embedding if and only if k = ±1. Example 3.23. Let q ∈ <span class="highlight">S3</span> be a quaternion of unit length and φq : S 1 → <span class="highlight">S3</span> be the map defined by φq : z 7→ qz. For w ∈ S1 let γw : R → S1 be the curve given by γw(t) = weit. Then γw(0) = w, γ̇w(0) = iw and φq(γw(t)) = qwe it. By differentiating we yield dφq(γ̇w(0)) = d dt (φq(γw(t)))|t=0 = d dt (qweit)|t=0 = qiw. Then |dφq(γ̇w(0))| = |qwi| = |q||w| = 1 6= 0 implies that the differen- tial dφq is injective. It is easily checked that the immersion φq is an embedding. In the next
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www.matematik.lu.se/matematiklu/personal/sigma/Riemann.pdf#page=36
ψk : z 7→ zk. For which k ∈ N0 are φk, ψk immersions, submersions or embeddings. Exercise 3.7. Prove that the map φ : Rm → Cm given by φ : (x1, . . . , xm) 7→ (eix1 , . . . , eixm) is a parametrization of the m-dimensional torus Tm in Cm. Exercise 3.8. Find a proof for Theorem 3.26. Exercise 3.9. Prove that the Hopf-map φ : <span class="highlight">S3</span> → S2 with φ : (x, y) 7→ (2xȳ, |x|2 − |y|2) is a submersion.
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www.matematik.lu.se/matematiklu/personal/sigma/Riemann.pdf#page=41
from above that (TM,M, pi) together with the maximal bundle atlas B̂ defined by B is a differen- tiable vector bundle. Definition 4.8. Let M be a differentiable manifold, then a section X : M → TM of the tangent bundle is called a vector field. The set of smooth vector fields X : M → TM is denoted by C∞(TM). Example 4.9. We have seen earlier that the 3-sphere <span class="highlight">S3</span> in H ∼= C2 carries a group structure · given by (z, w) · (α, β) = (zα− wβ̄, zβ + wᾱ). This makes (<span class="highlight">S3</span>, ·) into a Lie group with neutral element e = (1
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www.matematik.lu.se/matematiklu/personal/sigma/Riemann.pdf#page=83
(− � , � )→ O(n) is a geodesic if and only if γt · γ̈ = γ̈t · γ. Exercise 7.3. Find a proof for Proposition 7.23. Exercise 7.4. Find a proof for Corollary 7.24. Exercise 7.5. For the real parameter θ ∈ (0, pi/2) define the 2- dimensional torus T 2θ by T 2θ = {(cos θeiα, sin θeiβ) ∈ <span class="highlight">S3</span>| α, β ∈ R}. Determine for which θ ∈ (0, pi/2) the torus T 2θ is a minimal submanifold of the 3-dimensional sphere <span class="highlight">S3</span> = {(z1, z2) ∈ C2| |z1|2 + |z2|2 = 1}. Exercise 7.6. Find a proof for Corollary 7.27. Exercise 7.7. Determine the totally
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www.matematik.lu.se/matematiklu/personal/sigma/Riemann.pdf#page=95
zkw̄k and let Tm = {z ∈ Cm| |z1| = ... = |zm| = 1} be the m-dimensional torus in Cm with the induced metric. Find an isometric immersion φ : Rm → Tm, determine all geodesics on Tm and prove that the torus is flat. Exercise 8.6. Find a proof for Proposition 8.17. Exercise 8.7. Let the Lie group <span class="highlight">S3</span> ∼= SU(2) be equipped with the metric g(Z,W ) = 1 2 Re(trace(Z̄tW )). (i) Find an orthonormal basis for TeSU(2). (ii) Prove that (SU(2), g) has constant sectional curvature +1. Exercise 8.8. Let Sm be the unit sphere in
Logic and Circuits
are TWO complete circles. S1 and S3 will light the bulb. S2 and S3 will light the bulb. Logically this circuit is You can arrange any patterns you wish your students to investigate. You can assign a logical sentence and ask the students to arrange the circuits, or you can show a...
PAL Bibliography: Elizabeth Stoddard
E-Mail Source: Legacy Primary Works The Morgensons, 1862 (novel); Two Men, 1865 (novel); Temple House, 1867 (novel); Lolly Dinks' Doings, 1874 (children's tales); Poems, 1895. Wrote a bi-monthly column for Daily Alta California, a San Francisco newspaper, 1854-1858. Temple House; a novel. Ph...
PAL Bibliography: Bret Harte
Californian, 1864 67. San Francisco, J. Howell, 1927. PS1821 .H6 San Francisco (from the sea) by Bret Harte. San Francisco, Calif. : The Kennedy Ten Bosch Co., 1927. Case PS1829 .S3 Tales of the gold rush, by Bret Harte, illus. by Fletcher Martin, with an introd. by Oscar Lewis.NY: Herita...
PAL Bibliography: Archibald Macleish
& other poems. Boston: Houghton Mifflin, 1968. PS3525 A27 W5 A continuing journey. Boston: Houghton Mifflin, 1968 1967. PS3525.A27 C69 Scratch. Suggested by Stephen Vincent Benet's short story "The devil and Daniel Webster." Boston: Houghton Mifflin, 1971. PS3525 A27 S3 Th...
PAL Bibliography: Josephine Miles
Classic essays in English. Boston, Little, Brown, 1965. PR1363 .M53 Saving the bay. San Francisco: Open Space, 1967. PS3525.I4835 S3 Kinds of affection. Middletown, Conn.: Wesleyan UP, 1967. PS3525 .I4835 K5 Fields of learning. Berkeley: Oyez, 1968. PS3525.I4835 F5 To all appearances;...
PAL Bibliography: James Wright
1977; This Journey, 1982; Above the River: The Complete Poems, 1992. Saint Judas. Middletown, Conn: Wesleyan UP, 1959. PS3545.R58 S3 The branch will not break; poems. Middletown, Conn: Wesleyan UP, 1963. PS3545 .R58 B7 Shall we gather at the river; poems by James Wright. Middletown, Conn...
Fran�ois Edouard Anatole Lucas
also devised methods of testing primality, essentially those used today. In 1876 he used his methods to prove that the Mersenne number 2127 - 1 is prime. This remains the largest prime number discovered without the aid of a computer. The Lucas test for primes was refined by Lehmer in 1930. It work...
PAL Bibliography: Randall Jarrell
November 4, 2011 E-Mail Source: R. Jarrell © g. Paul Bishop 1956 Primary Works Poetry and the age. NY: Knopf, 1953. PN1271 .J3 A sad heart at the supermarket; essays & fables. NY: Atheneum, 1962. PS3519.A86 S3 The bat-poet. Pictures by Maurice Sendak. NY: Macmillan, 1964. PS...
PAL Bibliography: James Merrill
Nights and days; poems. NY: Atheneum, 1966. PS3525.E6645 N5 The fire screen; poems. NY: Atheneum, 1969. PS3525.E6645 F47 Braving the elements. London: Chatto and Windus [with] The Hogarth P, 1973, 1972. PS3525.E6645 B7 Divine comedies: poems. NY: Atheneum, 1976. PS3525 E6645 D5 Mirabell, boo...
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