Single displacement reaction: Difference between revisions

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{{for|preliminary discussion|Cartan connection applications}}
In [[Riemannian geometry]], we can introduce a [[coordinate system]] over the [[Riemannian manifold]] (at least, over a [[Chart (topology)|chart]]), giving ''n'' coordinates
 
:<math>x_{i}\;\text{,}\qquad i = 1, \dots, n</math>
 
for an n-dimensional manifold. Locally, at least, this gives a basis for the 1-forms, dx<sup>i</sup> where d is the [[exterior derivative]]. The [[dual basis]] for the [[tangent space]] T is '''e'''<sub>i</sub>.
 
Now, let's choose an [[orthonormal basis]] for the [[fiber bundle|fibers]] of T. The rest is index manipulation.
 
==Example==
 
Take a [[3-sphere]] with the [[radius]] ''R'' and give it [[polar coordinate]]s &alpha;, &theta;, &phi;.
 
:e('''e'''<sub>&alpha;</sub>)/R,
:e('''e'''<sub>&theta;</sub>)/R sin(&alpha;) and
:e('''e'''<sub>&phi;</sub>)/R sin(&alpha;) sin(&theta;)
 
form an orthonormal basis of T.
 
Call these '''e'''<sub>1</sub>, '''e'''<sub>2</sub> and '''e'''<sub>3</sub>. Given the metric &eta;, we can ignore the [[Covariance|covariant]] and [[contravariant]] distinction for T.
 
Then, the dreibein (triad),
 
:<math>e_1 = R\, d\alpha</math>
:<math>e_2 = R\, \sin{(\alpha)} d\theta</math>
:<math>e_3 = R\, \sin{(\alpha)} \sin{(\theta)} d\phi</math>.
 
So,
 
:<math>de_1=0</math>
:<math>de_2=R \cos{(\alpha)} d\alpha \wedge d\theta</math>
:<math>de_3=R (\cos{(\alpha)} \sin{(\theta)} d\alpha \wedge d\phi + \sin{(\alpha)} \cos{(\theta)} d\theta \wedge d\phi)</math>.
 
from the relation
 
:<math>d_\mathbf{A} e = de + A \wedge e = 0</math>,
 
we get
 
:<math>A_{12} = -\cos{(\alpha)} \, d\theta</math>
:<math>A_{13} = -\cos{(\alpha)} \, \sin{(\theta)} d\phi</math>
:<math>A_{23} = -\cos{(\theta)} \, d\phi</math>.
 
(d<sub>'''A'''</sub>&eta;=0 tells us A is antisymmetric)
 
So, <math>\mathbf{F} = d\mathbf{A} + \mathbf{A} \wedge \mathbf{A}</math>,
 
:<math>F_{12}=\sin{(\alpha)} d\alpha\wedge d\theta</math>
:<math>F_{13}=\sin{(\alpha)} \sin{(\theta)} d\alpha\wedge d\phi</math>
:<math>F_{23}=\sin^2{(\alpha)} \sin{(\theta)} d\theta\wedge d\phi</math>
 
{{tensors}}
{{differential-geometry-stub}}
 
[[Category:Differential geometry]]
[[Category:Mathematical notation]]

Revision as of 19:42, 10 January 2014

28 year-old Painting Investments Worker Truman from Regina, usually spends time with pastimes for instance interior design, property developers in new launch ec Singapore and writing. Last month just traveled to City of the Renaissance. In Riemannian geometry, we can introduce a coordinate system over the Riemannian manifold (at least, over a chart), giving n coordinates

xi,i=1,,n

for an n-dimensional manifold. Locally, at least, this gives a basis for the 1-forms, dxi where d is the exterior derivative. The dual basis for the tangent space T is ei.

Now, let's choose an orthonormal basis for the fibers of T. The rest is index manipulation.

Example

Take a 3-sphere with the radius R and give it polar coordinates α, θ, φ.

e(eα)/R,
e(eθ)/R sin(α) and
e(eφ)/R sin(α) sin(θ)

form an orthonormal basis of T.

Call these e1, e2 and e3. Given the metric η, we can ignore the covariant and contravariant distinction for T.

Then, the dreibein (triad),

e1=Rdα
e2=Rsin(α)dθ
e3=Rsin(α)sin(θ)dϕ.

So,

de1=0
de2=Rcos(α)dαdθ
de3=R(cos(α)sin(θ)dαdϕ+sin(α)cos(θ)dθdϕ).

from the relation

dAe=de+Ae=0,

we get

A12=cos(α)dθ
A13=cos(α)sin(θ)dϕ
A23=cos(θ)dϕ.

(dAη=0 tells us A is antisymmetric)

So, F=dA+AA,

F12=sin(α)dαdθ
F13=sin(α)sin(θ)dαdϕ
F23=sin2(α)sin(θ)dθdϕ

Template:Tensors Template:Differential-geometry-stub