Improve citations

25 files changed, 151 insertions, 2 deletions

diff --git a/content/know/concept/bell-state/index.pdc b/content/know/concept/bell-state/index.pdc
index 5e147e2..9fe69d1 100644
--- a/content/know/concept/bell-state/index.pdc
+++ b/content/know/concept/bell-state/index.pdc
@@ -91,3 +91,9 @@ then $B$ instantly also collapses into $\ket{0}$, never $\ket{1}$,
 even if it was not measured.
 This was a specific example for $\ket*{\Phi^{+}}$,
 but analogous results can be found for the other Bell states.
+
+
+## References
+1.  J.B. Brask,
+    *Quantum information: lecture notes*,
+    2021, unpublished.
diff --git a/content/know/concept/calculus-of-variations/index.pdc b/content/know/concept/calculus-of-variations/index.pdc
index 576863c..a8861cb 100644
--- a/content/know/concept/calculus-of-variations/index.pdc
+++ b/content/know/concept/calculus-of-variations/index.pdc
@@ -338,3 +338,6 @@ And then the remaining $N - M$ equations can be solved in the normal unconstrain
 1.  G.B. Arfken, H.J. Weber,
     *Mathematical methods for physicists*, 6th edition, 2005,
     Elsevier.
+2.  O. Bang,
+    *Applied mathematics for physicists: lecture notes*, 2019,
+    unpublished.
diff --git a/content/know/concept/convolution-theorem/index.pdc b/content/know/concept/convolution-theorem/index.pdc
index 86543d8..9d1a666 100644
--- a/content/know/concept/convolution-theorem/index.pdc
+++ b/content/know/concept/convolution-theorem/index.pdc
@@ -98,3 +98,10 @@ $$\begin{aligned}
     &= \int_0^\infty \tilde{f}(s) g(t') \exp(- s t') \dd{t'}
     = \tilde{f}(s) \: \tilde{g}(s)
 \end{aligned}$$
+
+
+
+## References
+1.  O. Bang,
+    *Applied mathematics for physicists: lecture notes*, 2019,
+    unpublished.
diff --git a/content/know/concept/density-of-states/index.pdc b/content/know/concept/density-of-states/index.pdc
index 195ac2a..438a0d6 100644
--- a/content/know/concept/density-of-states/index.pdc
+++ b/content/know/concept/density-of-states/index.pdc
@@ -154,3 +154,6 @@ so a finite value can be chosen.
 1.  H. Gould, J. Tobochnik,
     *Statistical and thermal physics*, 2nd edition,
     Princeton.
+2.  B. Van Zeghbroeck,
+    [Principles of semiconductor devices](https://ecee.colorado.edu/~bart/book/book/chapter2/ch2_4.htm), 2011,
+    University of Colorado.
diff --git a/content/know/concept/diffie-hellman-key-exchange/index.pdc b/content/know/concept/diffie-hellman-key-exchange/index.pdc
index c0af364..7897e25 100644
--- a/content/know/concept/diffie-hellman-key-exchange/index.pdc
+++ b/content/know/concept/diffie-hellman-key-exchange/index.pdc
@@ -72,3 +72,10 @@ However, for quantum computers,
 it has already been *dis*proven!
 In this case, another method must be used,
 for example the [BB84 protocol](/know/concept/bb84-protocol/).
+
+
+
+## References
+1.  J.B. Brask,
+    *Quantum information: lecture notes*,
+    2021, unpublished.
diff --git a/content/know/concept/dirac-delta-function/index.pdc b/content/know/concept/dirac-delta-function/index.pdc
index 97704d7..76b6e97 100644
--- a/content/know/concept/dirac-delta-function/index.pdc
+++ b/content/know/concept/dirac-delta-function/index.pdc
@@ -109,3 +109,10 @@ $$\begin{aligned}
         \int f(\xi) \: \dv[n]{\delta(x - \xi)}{x} \dd{\xi} = \dv[n]{f(x)}{x}
     }
 \end{aligned}$$
+
+
+
+## References
+1.  O. Bang,
+    *Applied mathematics for physicists: lecture notes*, 2019,
+    unpublished.
diff --git a/content/know/concept/dirac-notation/index.pdc b/content/know/concept/dirac-notation/index.pdc
index 999c90c..176f769 100644
--- a/content/know/concept/dirac-notation/index.pdc
+++ b/content/know/concept/dirac-notation/index.pdc
@@ -127,3 +127,10 @@ $$\begin{aligned}
     \\
     &= \braket{u}{f} \braket{g}{w}
 \end{aligned}$$
+
+
+
+## References
+1.  R. Shankar,
+    *Principles of quantum mechanics*, 2nd edition,
+    Springer.
diff --git a/content/know/concept/dispersive-broadening/index.pdc b/content/know/concept/dispersive-broadening/index.pdc
index f053eb6..cae856d 100644
--- a/content/know/concept/dispersive-broadening/index.pdc
+++ b/content/know/concept/dispersive-broadening/index.pdc
@@ -93,3 +93,10 @@ Of great importance is the sign of $\beta_2$:
 in the **anomalous dispersion regime** ($\beta_2 < 0$),
 lower frequencies travel more slowly than higher ones,
 and vice versa in the **normal dispersion regime** ($\beta_2 > 0$).
+
+
+
+## References
+1.  O. Bang,
+    *Numerical methods in photonics: lecture notes*, 2019,
+    unpublished.
diff --git a/content/know/concept/fourier-transform/index.pdc b/content/know/concept/fourier-transform/index.pdc
index 96653f5..3be47ff 100644
--- a/content/know/concept/fourier-transform/index.pdc
+++ b/content/know/concept/fourier-transform/index.pdc
@@ -116,3 +116,10 @@ $$\begin{aligned}
         = \hat{\mathcal{F}}\{ (i s x)^n f(x) \}
     }
 \end{aligned}$$
+
+
+
+## References
+1.  O. Bang,
+    *Applied mathematics for physicists: lecture notes*, 2019,
+    unpublished.
diff --git a/content/know/concept/gram-schmidt-method/index.pdc b/content/know/concept/gram-schmidt-method/index.pdc
index 0b02eee..97362e0 100644
--- a/content/know/concept/gram-schmidt-method/index.pdc
+++ b/content/know/concept/gram-schmidt-method/index.pdc
@@ -46,3 +46,10 @@ turns them into an orthonormal set $\ket*{n_1}, \ket*{n_2}, ...$ as follows:
 4.  Loop back to step 2, taking the next vector $\ket*{V_{j+1}}$.
 
 If you are unfamiliar with this notation, take a look at [Dirac notation](/know/concept/dirac-notation/).
+
+
+
+## References
+1.  R. Shankar,
+    *Principles of quantum mechanics*, 2nd edition,
+    Springer.
diff --git a/content/know/concept/impulse-response/index.pdc b/content/know/concept/impulse-response/index.pdc
index 012a2c3..b055fe7 100644
--- a/content/know/concept/impulse-response/index.pdc
+++ b/content/know/concept/impulse-response/index.pdc
@@ -62,3 +62,10 @@ $$\begin{aligned}
 \end{aligned}$$
 
 *__Q.E.D.__*
+
+
+
+## References
+1.  O. Bang,
+    *Applied mathematics for physicists: lecture notes*, 2019,
+    unpublished.
diff --git a/content/know/concept/kramers-kronig-relations/index.pdc b/content/know/concept/kramers-kronig-relations/index.pdc
index 1d29f96..9b67d60 100644
--- a/content/know/concept/kramers-kronig-relations/index.pdc
+++ b/content/know/concept/kramers-kronig-relations/index.pdc
@@ -132,3 +132,10 @@ $$\begin{aligned}
 \end{aligned}$$
 
 To reiterate: this version is only valid if $\chi(t)$ is real in the time domain.
+
+
+
+## References
+1.  M. Wubs,
+    *Optical properties of solids: Kramers-Kronig relations*, 2013,
+    unpublished.
diff --git a/content/know/concept/lagrange-multiplier/index.pdc b/content/know/concept/lagrange-multiplier/index.pdc
index fc1319e..7476dca 100644
--- a/content/know/concept/lagrange-multiplier/index.pdc
+++ b/content/know/concept/lagrange-multiplier/index.pdc
@@ -122,3 +122,6 @@ $$\begin{aligned}
 1.  G.B. Arfken, H.J. Weber,
     *Mathematical methods for physicists*, 6th edition, 2005,
     Elsevier.
+2.  O. Bang,
+    *Applied mathematics for physicists: lecture notes*, 2019,
+    unpublished.
diff --git a/content/know/concept/legendre-transform/index.pdc b/content/know/concept/legendre-transform/index.pdc
index 8a0d3e3..290a89a 100644
--- a/content/know/concept/legendre-transform/index.pdc
+++ b/content/know/concept/legendre-transform/index.pdc
@@ -87,3 +87,10 @@ $$\begin{aligned}
 Legendre transformation is important in physics,
 since it connects Lagrangian and Hamiltonian mechanics to each other.
 It is also used to convert between thermodynamic potentials.
+
+
+
+## References
+1.  H. Gould, J. Tobochnik,
+    *Statistical and thermal physics*, 2nd edition,
+    Princeton.
diff --git a/content/know/concept/modulational-instability/index.pdc b/content/know/concept/modulational-instability/index.pdc
index 26d2552..6856941 100644
--- a/content/know/concept/modulational-instability/index.pdc
+++ b/content/know/concept/modulational-instability/index.pdc
@@ -197,3 +197,12 @@ In that case, amplification occurs at the strongest peak of the Raman gain $\til
 even when the parent pulse is in the NDR.
 This is an example of stimulated Raman scattering (SRS).
 
+
+
+## References
+1.  O. Bang,
+    *Numerical methods in photonics: lecture notes*, 2019,
+    unpublished.
+2.  O. Bang,
+    *Nonlinear mathematical physics: lecture notes*, 2020,
+    unpublished.
diff --git a/content/know/concept/parsevals-theorem/index.pdc b/content/know/concept/parsevals-theorem/index.pdc
index ae34bda..824afa6 100644
--- a/content/know/concept/parsevals-theorem/index.pdc
+++ b/content/know/concept/parsevals-theorem/index.pdc
@@ -73,3 +73,10 @@ $$\begin{aligned}
     &= \frac{2 \pi A^2}{|s|} \int_{-\infty}^\infty f^*(x) \: g(x) \dd{x}
     = \frac{2 \pi A^2}{|s|} \braket{f}{g}
 \end{aligned}$$
+
+
+
+## References
+1.  O. Bang,
+    *Applied mathematics for physicists: lecture notes*, 2019,
+    unpublished.
diff --git a/content/know/concept/partial-fraction-decomposition/index.pdc b/content/know/concept/partial-fraction-decomposition/index.pdc
index 1f4207f..7a3847b 100644
--- a/content/know/concept/partial-fraction-decomposition/index.pdc
+++ b/content/know/concept/partial-fraction-decomposition/index.pdc
@@ -58,3 +58,10 @@ $$\begin{aligned}
 
 And then, using the linear independence of $x^0, x^1, x^2, ...$, solving
 a system of $m$ equations to find all $c_{1,1}, ..., c_{1,m}$.
+
+
+
+## References
+1.  O. Bang,
+    *Applied mathematics for physicists: lecture notes*, 2019,
+    unpublished.
diff --git a/content/know/concept/probability-current/index.pdc b/content/know/concept/probability-current/index.pdc
index c67956a..37cad52 100644
--- a/content/know/concept/probability-current/index.pdc
+++ b/content/know/concept/probability-current/index.pdc
@@ -96,3 +96,10 @@ $$\begin{aligned}
         = \mathrm{Re} \Big\{ \psi^* \frac{\hat{p} - q \vec{A}}{m} \psi \Big\}
     }
 \end{aligned}$$
+
+
+
+## References
+1.  L.E. Ballentine,
+    *Quantum mechanics: a modern development*, 2nd edition,
+    World Scientific.
diff --git a/content/know/concept/rayleigh-plateau-instability/index.pdc b/content/know/concept/rayleigh-plateau-instability/index.pdc
index df3d6ab..59407d6 100644
--- a/content/know/concept/rayleigh-plateau-instability/index.pdc
+++ b/content/know/concept/rayleigh-plateau-instability/index.pdc
@@ -284,6 +284,6 @@ In other words, the liquid column is stable in this case.
 1.  B. Lautrup,
     *Physics of continuous matter: exotic and everyday phenomena in the macroscopic world*, 2nd edition,
     CRC Press.
-2.  T. Bohr, A. Anderson,
+2.  T. Bohr, A. Andersen,
     *The Rayleigh-Plateau instability of a liquid column*, 2020,
     unpublished.
diff --git a/content/know/concept/schwartz-distribution/index.pdc b/content/know/concept/schwartz-distribution/index.pdc
index 2d9f9df..bf13f13 100644
--- a/content/know/concept/schwartz-distribution/index.pdc
+++ b/content/know/concept/schwartz-distribution/index.pdc
@@ -117,3 +117,10 @@ $$\begin{aligned}
         = \braket*{f}{\tilde{\phi}}
     }
 \end{aligned}$$
+
+
+
+## References
+1.  K.W. Jacobsen,
+    *Note on generalized functions (distributions)*, 2020,
+    unpublished.
diff --git a/content/know/concept/self-phase-modulation/index.pdc b/content/know/concept/self-phase-modulation/index.pdc
index 1ec3fdd..47775b2 100644
--- a/content/know/concept/self-phase-modulation/index.pdc
+++ b/content/know/concept/self-phase-modulation/index.pdc
@@ -95,3 +95,10 @@ and [dispersion](/know/concept/dispersive-broadening/)
 leads to many interesting effects,
 such as [modulational instability](/know/concept/modulational-instability/)
 and [optical wave breaking](/know/concept/optical-wave-breaking/).
+
+
+
+## References
+1.  O. Bang,
+    *Numerical methods in photonics: lecture notes*, 2019,
+    unpublished.
diff --git a/content/know/concept/self-steepening/index.pdc b/content/know/concept/self-steepening/index.pdc
index 97999b7..256bafb 100644
--- a/content/know/concept/self-steepening/index.pdc
+++ b/content/know/concept/self-steepening/index.pdc
@@ -143,4 +143,4 @@ $$\begin{aligned}
 
 
 ## References
-1. B.R. Suydam, [Self-steepening of optical pulses](https://doi.org/10.1007/0-387-25097-2_6), 2006, Springer Media.
+1. B.R. Suydam, [Self-steepening of optical pulses](https://doi.org/10.1007/0-387-25097-2_6), 2006, Springer.
diff --git a/content/know/concept/sturm-liouville-theory/index.pdc b/content/know/concept/sturm-liouville-theory/index.pdc
index 7ccd625..66a4a82 100644
--- a/content/know/concept/sturm-liouville-theory/index.pdc
+++ b/content/know/concept/sturm-liouville-theory/index.pdc
@@ -344,3 +344,9 @@ $$\begin{aligned}
     }
 \end{aligned}$$
 
+
+
+## References
+1.  O. Bang,
+    *Applied mathematics for physicists: lecture notes*, 2019,
+    unpublished.
diff --git a/content/know/concept/toffoli-gate/index.pdc b/content/know/concept/toffoli-gate/index.pdc
index da5f2a5..f3ab0ba 100644
--- a/content/know/concept/toffoli-gate/index.pdc
+++ b/content/know/concept/toffoli-gate/index.pdc
@@ -91,3 +91,10 @@ $$\begin{aligned}
     &= c_{000} \ket{000} + c_{001} \ket{001} + c_{010} \ket{010} + c_{011} \ket{011} \\
     &\quad\,\, c_{100} \ket{100} + c_{101} \ket{101} + c_{111} \ket{110} + c_{110} \ket{111}
 \end{aligned}$$
+
+
+
+## References
+1.  J.S. Neergaard-Nielsen,
+    *Quantum information: lectures notes*,
+    2021, unpublished.
diff --git a/content/know/concept/wetting/index.pdc b/content/know/concept/wetting/index.pdc
index 2cb7c08..a3e7c1a 100644
--- a/content/know/concept/wetting/index.pdc
+++ b/content/know/concept/wetting/index.pdc
@@ -124,3 +124,10 @@ for example, if one is air, we recover the previous case for rough surfaces.
 Cassie's law can also easily be generalized to three or more materials,
 and to include Wenzel-style roughness ratios $r_1$, $r_2$, etc.
 
+
+
+## References
+1.  T. Bohr,
+    *Continuum physics: lecture notes*, 2021,
+    unpublished.
+