Research Flow

Unzip, Untar and unrar (of different extension)

To unzip file with an extension .Z (e.g. foo.Z)

gzip -d foo.Z

This will create a file name foo on the folder.

tar xvjf foo.tar.bz2

(here j uncompresses *.bz2 file)

To extract *.tar.xz file use xf parameters in command

$ tar xf file.tar.xz

Some files are compressed with .tgz (for example parallel_studio_xe_2017_update5_cluster_edition_online.tgz which is available as a free student edition from Intel).

tar -xvzf fftw-3.1.1.tar.gz or tar -xvf fftw-3.1.1.tar.gz

We can use tar to extract a .tgz file.

tar -xvzf /path/to/yourfile.tgz

Here
x for extract
v for verbose
z for gnuzip
f for file (this 'f' should come last, just before the file name).

Similarly, for *.tar files,
tar -xvf fileName.tar

RAR Format

unrar e fileName.rar

This will extract all the files from .rar.

Relation between statistical adiabatic process and quantum adiabatic theorem

The adiabatic process which we learn in thermodynamics is the process where we decrease/increase the volume of the gases enclosed in a container, slowly so that the pressure remains constant throughout the process.

The quantum mechanical adiabatic theorem says: For a system with non-degenerate ground state, if the system is taken from the ground state to the next (only next excited state) energy level (i.e. excited state) very slowly (the time taken to go from one state to another in a smaller time than the characteristic time of the energy gap of the two energy-levels involved), then the system finally adapts ground state.

Here analogy is as follows (even though it doesn't make sense now)

Which remains constant: Pressure & Energy
Which is changed: Volume & State of the system
In what time : Both are slowly (in QM, it is exactly defined; In TD, not defined (?) clearly.

Adiabatic theorem plays an important role in the definition of topological phases of matter.

In approximate (but most successful) theory such as Density Functional theory, construction of the final state is obtained by slowly changing some parameters (for e.g., λ) and finally the ground state is obtained.

What are the connection among these?

Another similar idea (?) is the derivation of molecular forces by Feynman. What is the exact connection among these?

Topological Insulators

Recently, there is a widespread interest in the study of certain group of materials called "Topological Insulators" which may be considered as a subgroup of Quantum Materials.

First, what are topological materials?

Before coming to this question, we should know what is topology. I have been writing a separate post on Topology. Topology is a rich topic and consider spending a reasonable amount of time to get a clear picture of what really it is.

The 2016 Nobel prize has been awarded to David J. Thouless (University of Washington), F. Duncan M. Haldane (Princeton University) and J. Michael Kosterlitz (Brown University). The citation says that the prize is awarded "for theoretical discoveries of topological phase transitions and topological phases of matter".

To understand, let me give a rough idea. There are certain properties (eg. conductor on the surface only) which are protected in topological insulators. Here the word 'protected' means that the property won't vanish in any condition. You can do whatever modification you want i.e., you can change the sphere shaped material to any shape you want as for as you don't create edges/holes. If band structure is obtained for those different shapes, all other bands may change. But, surface states are protected and they will be always remain. When a hole is created in the material, these surface states will be destroyed. That is why, experts say that the property is "topologically protected".

These materials are interesting because of the technological applications and also many exotic phenomena they exhibit.

Majorana Fermion
Weyl semi-metal
Dirac Fermion
etc.

Following is a presentation by Prof. Charles Kane

Topological Band Theory I: Part 1 of 6.

Here is the part 2 of 6 videos:

Part 3 of 6:

Part 4 of 6:

Part 5 of 6:

Here is the final part of the presentation.

Spend as much time on understanding the materials presented in this video.

An introductory talk on the "Topological Insulators" from The Zurich Physics Colloquium given by Prof. Osterwalder Jürg would be useful.

(This page need additional improvement and update. Please visit this page later for a complete story. Comments are welcome. Thanks.)

Accessing Ubuntu Bash files from Windows 10

How to access the files in the Ubuntu Bash update from the Windows 10.

The obvious way is through C:/ folder.

Here is the steps for doing that.

First you need to change the "Hidden folder" default option.

Open File Explorer
Select File --> Change folder and search options
Click on View tab, and select Show hidden files, folders, and drives (if already selected, leave as it is)
Click OK

Now, the hidden folders also will be visible. Remaining steps are

Click on the folder directory address box, copy and paste: %localappdata%\lxss and Enter
Now you will be in Bash directory: C:\Users\{username}\AppData\Local\lxss
Now you can access files in home folder and subfolders.

You can create a Shortcut to this folder (right click on home folder and select create shortcut) and paste the short cut in Desktop or convenient location quick access.

Windows PC Network disconnects after some time

Just chose "Never" in sleep mode.

This may solve the problem.

Notes on Relativity

Relativity theory (both special and general theories together) is considered to be one of the greatest intellectual marvels ever discovered by human. So to me no surprise why it is very hard to "really" understand and comprehend "Relativity theory". While special theory of relativity deals with the objects there are moving at constant speed (i.e., inertial motion only), general theory of relativity explores the difficult accelerating motions.

So, if you take long time to understand relativity theory, no worries. Just take a challenge and try to understand a little further.

OK. Before going to "What is" question, let us answer the question "Why".

When relativity is becomes important?

"Special relativity applies to situations where objects are moving very quickly, at speeds near the speed of light. Generally, one should account for relativistic effects when speeds are higher than 1/10th of the speed of light".

In graphene, relativistic effects are important because, the speed of electrons in graphene is of the order of c/300 (for reference see here)

Here is a list of questions you need Relativity to understand.

References

Special Relativity (see link: http://physics.bu.edu/py106/notes/Relativity.html)
Graphene: The running of the constants (http://www.nature.com/nphys/journal/v7/n9/full/nphys2066.html?message-global=remove)

Some other reading materials

What is the experimental basis of Special Relativity?

History of relativity (for Wikipedia)

Feynman's lectures on Special theory of relativity

Using Mendeley in a new PC

If you are using a PC for storing all the journal papers and now you want to change the PC, no worries. Follow these steps.

Synchronize your files with the web.
Install Mendeley in new PC.
If you install and login, all of your papers will be downloaded in a single file or based on year (or whatever your settings is)
Copy the folder in which all of your files are stored and past in the new system where you want it
Again, upload from the new folder.
Now, go to the C:/Users/../Mendeley cut the folder and paste somewhere else (keep the file in case something goes wrong, you can again replace the file)
Now, if you open your file from Mendeley (using open the folder location), it will be linked to the desired folder.

Hope it helps. Comment if something is unclear.

How to do research Series (1/100)

Four golden lessons

by Prof. Steven Weinberg, Nobel Laureate in Physics (from Nature article)

Rule #1:

"I managed to get a quick PhD — though when I got it I knew almost nothing about physics. But I did learn one big thing: that no one knows everything, and you don't have to."

Rule #2:

"When I was teaching at the Massachusetts Institute of Technology in the late 1960s, a student told me that he wanted to go into general relativity rather than the area I was working on, elementary particle physics, because the principles of the former were well known, while the latter seemed like a mess to him. It struck me that he had just given a perfectly good reason for doing the opposite."

"My advice is to go for the messes — that's where the action is."

Rule #3:

It is to forgive yourself for wasting time. As you will never be sure which are the right problems to work on, most of the time that you spend in the laboratory or at your desk will be wasted. If you want to be creative, then you will have to get used to spending most of your time not being creative, to being becalmed on the ocean of scientific knowledge.

Rule #4:

Finally, learn something about the history of science, or at a minimum the history of your own branch of science. You can get great satisfaction by recognizing that your work in science is a part of history.

Reference:

Things to do when you leave your PC Series - Part 1

Now a days, it is normal to upgrade to a new PC. In older PC, we may use a lot of things such as synchronizing browsers, installing Dropbox etc.

Before abandon old systems, these things have to be given much importance. The update link to such systems should be removed (especially for Dropbox etc).

Need to uninstall important personal packages. If some one is interested in a package, let them install the package again.

If you are using Mendeley, click here to read related to Medeley desktop.

(will be updated soon...)

Etymology of Scientific Words

convex

ˈkɒnvɛks/

adjective

Origin

late 16th century: from Latin convexus ‘vaulted, arched’.

concave

ˈkɒnkeɪv/