[[EricNanoJapan (Open)]]
**June 8 [#l4a9dac5]
This morning Nugraha-san came and we talked a little bit about the reciproical lattice. We then attacked the problem of the differential equation given by a Gaussian force. After working for a while we did not find a satisfying solution, and it's possible that for this equation a simple solution doesn't exists. If we had more boundary conditions it's possible that the solution would be simpler.
We then talked a little bit about Fortran and Nugraha-san showed me a website from Boston University that had a lot of good Frotran tutorials.
In the afternoon Tapsanit-san came in and we constructed the Brillioun zone of both the square lattice and of graphene. We obtained the symmetry points (Gamma, M, K and K') in the Brillioun zone. We compared the area of the Brillioun zone with that of the square lattice.
Finally, we looked at the Fortran task given by Hasdeo-san and we created a program that gives a cascading array of integers, as desired. Tapsanit-san printed out some pages on optical processes that I can read this weekend if I have time.
To Do:
-Complete the fortran programming assignments given by Hasdeo-san.
-Solve the diffeq for a parabolic force, and then consider the Gaussian case
-Learn LaTeX
-Solve the problems given by Ominato-san
-If I have time, work through the BU Fortran tutorial
-If I have time, read the pages given by Tapsanit-san
**June 7 [#rep20120607]
In the morning Tatsumi-san and Ominato-san explained to me the reciprocal lattice of graphene. First we derived the unit cell of graphene. We derived the reciprocal lattice and found then found the Brillouin zone of graphene, which is also a hexagon but rotated by 90 degrees.
To somewhat review what Tapsanit-san taught me yesterday we then talked about the wavevector (k) in the reciprocal lattice, and frequency as a function of k. We showed that this satisfied Bloch's theorem and described the periodic boundary conditions. Then, we talked about the acoustic mode vs the optical mode. We showed that the number of modes will increase if we increase the number of atoms in a unit cell. In the problem where two different types of masses are connected with identical springs, the lower valued function is the 'acoustic mode', where all the atoms vibrate in the same direction at the same value of time. The higher valued function is the optical mode, where some of the atoms are pushed towards each other while other atoms are pushed away from each other.
At 10:30 I accompanied Hasdeo-san to Japanese class where I learned the ta form of verbs. For instance: "Kyoto e itta koto ga arimaska?" = "Have you ever been to Kyoto?". Iie, arimasen. Watashi wa Kyoto ni ikitai.
In the afternoon I went to the group meeting where Simon-san presented his animations and some differential equations. His POV-Ray animations were very cool and also really helped to illustrate the acoustic vs. optical vibrational modes. Tomorrow we made plans to discuss some of the differential equations he had been working with, because I need to know them as well.
Later in the afternoon, Ominato-san and Tatsumi-san returned to teach me more physics. Ominato-san had written a long sequence of very good problems some of which we worked through. We defined the Drude Model of electron conduction, and wrote the equation of electron motion including a frictional term:
\[ m\frac{dv}{dt}=e(E+\frac{1}{c}v X H)-(\frac{m}{T})v \]
We derived v(t) when H=0, and then for the steady state solution (dv/dt=0)
We then Derived $\sigma$ (the conductivity) based on the relation:
\[ j=nev= \sigma E \]
Next, we derived v(t) for a more general case and put into matrix form the equation:
\[ j= \sigma E \]
Ominato-san explained the classical Hall effect and we breifly talked about special relativity. The energy of a particle with mass is given by
E=+/- sqrt((cp)^2+(mc^2)^2) were E is a parabolic function of p. However in graphene electron behave as if they have no mass and E=+/- cp.
To Do:
-Finish the problems given by Ominato-san, and rewrite good solutions for the problems we went over this afternoon.
-Consider the differential equation given by Saito-sensei, study his email and study the equation in more detail.
-Finish the graphs for Nugraha-san.
-Finish the graphs for Hasdeo-san and the cascading number Fortran program.
I learned a tremendous amount of theory today. My understanding of the lattice has made good progress over the last several days.
** June 6 [#rep20120606]
- Tapsanit-san explained the Brillouin zone of a 1D lattice, as well as 2D and 3D square lattices. We discussed what k (the wave vector) is and constructed the reciprocal lattice. We then talked about how Bloch's wavefunction has periodic boundary conditions. We have a finite number of k, equal to N, the number of atoms. On Friday we will construct the Brillouin zone of graphene. Later in the morning I fixed the format of the equations I'd posted on PukiWiki and finished the graph of the different modes of phonon frequency as a function of k. I did this graph on SciDAVis and am not entirely happy with the axis format, so I should do it on Xmgrace too.
In the afternoon Hasdeo-san explained further about Fortran programming language. After working through a program he made he gave me several assignments to do. Hasdeo-san also helped me learn to navigate the directories of command prompt.
To Do:
1. Get a correctly formatted w(k) graph to Nugraha-san AND learn about/explain which is the optical mode and which is the acoustic mode.
2. Solve Saito-sensei's differential equation by learning about Fourier transforms.
3. Solve Hasdeo-san's problems:
- plot the cascading list of integers
- graph two fxns (different parabolas) using Fortran
- output fxn data in column form
** June 5 [#rep20120605]
- Nugraha-san explained the problem of an infitie 1D series of masses connected by springs. We solved for the value of w^2, although there was a small error in my calculation. In excel we graphed the value of w^2 as a function of k, the wavevector. In the afternoon we graphed the (incorrect) data generated in excel into an xmgrace graph. Nugraha-san also explained how to use the simpler SciDAVis software.
Also, Florian-san showed me how to use the POV-Ray software. We installed it on the desktop machine and I worked through the basic tutorial.
- The homework is: by friday complete a graph of w(k) for the 1D phonon problem, determine the max/min for each branch, and interpret this physically. Which branch is optical and which is acoustic?
Also, solve the diff eq for a Gaussian.
If I have time consider the infinite 1D series of spring mass problems, but in the case that all masses are the same, but the spring constants are different.
** June 4 [#rep20120604]
- Sato-sensei showed me around the campus and installed Xming on the desktop.
- Hasedo-sensei introduced me to Fortran language and we wrote a very simple program.
- Solved the differential equation for f(t)=(bt)/a=x''+w^2x
Solution is: f(t)=(b/(aw^2))(t-(1/w)sin(wt))
Could look into the eqn and new initial conditions for t>a
to do:
- Solve the same diff eq for f(t)=Ae^(-t^2/a^2)
- Clean up the solution for the reciprocal lattice from last week
![[PukiWiki]](image/c60.png "[PukiWiki]")
