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Showing posts from October, 2014

Deep space network

I was discussing with a friend of mine about why early pictures of moon, say from the apollo missions, were so blurry. Well, astronomers don't enjoy the kind of speeds you and I do every day on our mobile phones, laptops and desktops. Most of us get impatient about low internet speeds, curse our service if the internet connection changes from 3G/H/H+to 2G. On the other hand, the data transmission rate from space craft back to earth is in the range of 100s of kbps. Deep space network, the title of this post, is a collection of radio antenna distributed all over the earth which are used to communicate with space craft and DSN NOW is a site which shows which antenna is communicating with which satellite, what the transmission rate is, what frequency they are transmitting at and so on. There are a lot more satellites than there are antenna so i guess data is pulled from the satellites based on demand or maybe periodically. As of now, MAVEN, the NASA mars mission is operating at a dat…

Astrophysical Masers

I thought I'd take care of my daily blog post business earlier today so, here's the 2 page report I made for a presentation as part of a course on Laser physics & Applications -
Astronomical Masers by Poruri Sai Rahul

PH5814 - Laser Physics & Applications

Masers are the microwave analogues of Lasers. So far, as part of the course, we’ve been looking at optical and IR lasers. Similar to optical lasers, masers can be produced by atomic/molecular species such as Ammonia, Hydrogen, Rubidium & Free electron masers and by solid state masers such as the Ruby maser & the Fe-sapphire maser. While lasers emit in the Thz regime, masers emit in the Ghz regime.

Coming to the astronomical significance of masers, Astronomers equipped with spectroscopes started observing very strong spectral lines from astronomical sources. These sources were extremely bright in the radio spectrum while their optical counterparts looked like young stars. This emission was also discrete and not a c…

Intrinsic spectral line widths and the uncertainty principle

Here's a question for you. According to the bohr model of the atom, the energy difference between two levels is quantized i.e it is an integer. Therefore, an absorption or emission quanta related to these two levels should have a unique energy/frequency value i.e in an intensity vs frequency profile, the emission or absorption line should be a perfect dirac delta function. But it is a known fact that spectral lines, em/abs, have a finite width. The profile is not a delta function but a lorentzian. How come?

The answer lies in the uncertainty principle. The uncertainty people, as most know it, is a relation between the uncertainty in position against the uncertainty in momentum of a species. It can also be written as the uncertainty in energy against the uncertainty in time of the species. As defined on Wiki, natural broadening occurs from the fact that excited species have a specific lifetime and the larger the uncertainty in this lifetime is, the smaller the uncertainty in energ…

Another last minute post

Nothing interesting today. Well, almost nothing. I have a couple of course presentations coming up, one as part of a course on laser physics and one for a course on atmospheric science. I intend to talk about "Astronomical Masers" for the laser physics course. If you don't know what astronomical masers are, they're microwave lasers that come from the stars. Literally. They were discovered in the second half of the 19th century and are mostly found near new stars or star-forming regions. And unlike conventional lasers, as is obvious, these are single pass i.e in a laser cavity, the laser light bounces back and forth between the mirrors on either sides multiple times before coming out, therefore multi-pass. There are a couple more interesting facts about them. I will not get into them now, I shall post a small report and a post next month, once i'm done with my presentation. Coming to the atmospheric science course, I intend to present on the exotic atmospheric co…

An obsession

I don't have anything new to add so i am going to write about an obsession of mine. Almost an year back, I was at IIST Trivandrum working with Prof. Anand Narayanan on Quasars. It was my first serious summer project on astronomy and i was having a fun time learning about quasars and working with python and sql query. I was asked to reproduce the results of the richards et al. 2001 paper but as I eventually learnt, it was getting harder and harder to find the original data set. So, instead of reproducing the results from the original data set, I intended to extend the results to a new data set - the data for quasars from the SDSS DR9. The original data set in question was put together using quasars from the SDSS DR3 and other surveys. As i reproduced the results for the new (much larger) data set, weird artifacts started popping up in the results. As i dug deeper, I found that these artifacts were grouped in red-shift space and in coordinate space. Further, when i looked at the sp…

A hiatus, if i can call it that!

As you would've noticed, I didn't write anything yesterday and I wont be writing anything today either. In fact, you will only be hearing from me again on monday. My schedule is screwed up to squeeze this into it. Rather, I've screwed up my schedule to such an extent that i forget about writing. I could've written in advance and set blogger to post the blog posts every day but well, that'd kinda be cheating. Well then, until Monday...

Computational physics

Specifically, a course on computational physics which I am taking this semester. Sorry if you were expecting something different or something broader! Either way, given that I have a course viva tomorrow for which I need to clean up my codes and get together my results, I thought that I'd talk about it today. As part of the course so far, we've simulated classical (say rutherford scattering) and quantum scattering, learnt the verlet and velocity verlet algorithms to simulate molecular dynamics, learnt the metropolis-hastings sampling method to implement markov chain monte carlo techniques to simulate said molecular systems. Coming to an end, we're learning the entropic sampling method to implement monte carlo and using said method to measure the free energy of systems. And eventually, we will be taught parallel programming as well but as I've written before, it's pretty easy to do parallel processing in python so I implemented a rudimentary version. You can check …

I cant stop reading!!!

Over the course of the weekend, I've been reading a lot! A lot more than i have over the last month! I finished a book that i bought a month ago and I've read length articles on the GM recalls, on the ranbaxy drug fraud, an article explaining how glow sticks work, an article explaining how airplanes actually fly and a beautiful piece on living off the grid. I've reduced this habit of mine, of checking hacker news every two hours checking for new articles but it still persists, mostly on the weekends when i need to manage my own schedule. I am fascinated by all of the problems in this world and how people come up with ingenious solutions to such problems. Maybe I should address the problems in my life before reading about how others addressed their problems. I guess i'm procrastinating :d Either way, I intend to stick to books, preferably non-fiction because there's so much to know about this world before knowing about fictitious ones :P And i intend to only read t…

Caught by surprise!

My intentions to write everyday, no matter how small or inconsequential my piece of writing is, is being put on test! :D Having slept late, i woke up just in time to catch lunch and have been reading the book "Flash Boys" by Micheal Lewis for most of the day, in a cafe after lunch, in a friend's office all evening and now, post dinner. Having reached the epilogue, it's an interesting read. I had read an article, an excerpt from the book to be specific, about high frequency trading and how RBC alumni started a new stock exchange called IEX, about high frequency trading and the post-crash wall street in general. I took a break from reading 'Emperor of all Maladies', it was physically and mentally exhausting. I've finished this book in under two days and I've been reading the former for over a week now, in stints lasting 3 hours at the most. I couldnt't hold the book up or keep up with the amount of information that the book was throwing at me. Eith…

the multiprocessing library in python

As part of a course on computational methods, I am simulating molecular dynamics using the velocity verlet algorithm. Simply put, given an initial distribution of particle position & momenta and an interaction potential, we can use the momenta to update the position and the forces, derived from the potential, to update the momenta. Depending on which is updated first, the position or the momentum, we call them the verlet or the velocity verlet. One of the major hurdles here, given a large system size is to measure forces on all particles, the x and y components, simultaneously. Note that one cannot measure the force for a particle, update it's position and momentum and then move to the next particle! That's wrongedy wrong wrong! One needs to measure the forces on each particle given the current positions/configuration and then update the momentum, followed by an update to the positions. And then the cycle repeats. Like i was saying, one of the time-taking things is to mea…

Fusion reactors and magnetic bottles

Roughly an year ago, I wrote about magnetic bottles, a way to confine plasma using magnetic fields. Basically, the construction is such that the farther from the center we go, the stronger the magnetic field is and the harder it will pull you back. So if a plasma is generated within the confines of this magnetic field, it will stay confined! And today, I was reading about Lockheed Matrin developing a new kind of fusion reactor based on this exact theory. Science! :D

PS - this is turning to be harder than expected. I promised to write a blog every day but my tendency to be laze around for a day or two of a week doesn't let me do justice to this commitment. I need to be more serious about this. BTW, I got inspired by looking at the daily research journal of a Dr. David Hogg.

Fun with physics models

Since i discovered IPywidgets, I've been trying to create interactive plots for simple and common physics topics. For example, here is a model of how the sum of two waves of different frequencies looks like. Here is another model showing how adding sine waves of odd multiples of a frequency will result in a square wave. Here is a model of how the blackbody spectrum will look like at different temperatures. The models were created using the IPywidgets library, on IPython. I am maintaining a github repository which i shall update with more models. Models showing the far field diffraction pattern of a square, rectangular slit and the circular diffraction patterns of two bodies close by are also on said repository.

IPython FTW \m/

Yes! That title is very much justified! IPython keeps surprising me with ways to make my life easy, to understand python better and to code in ease with emphasis on the IPython-Notebook(ipynb). To quote "The IPython Notebook is a web-based interactive computational environment where you can combine code execution, text, mathematics, plots and rich media into a single document." I've just begun exploiting each of those features. For starters, plots can be embedded into the ipynb files ("%matplotlib inline"), making it easier to show the results of various segments of code. You can define a raw text/markdown cell where you can add comments to the code or explain what's going on at various parts. You can convert said ipynb files (ipython nbconvert) into html files ( --to html) or python ( --to python) files so you can show the results online and run the files without the need for a ipy interpreter. And I found ipywidgets, which helps interact with plots and un…

Space laser

A while back, I was thinking of a space laser. No, not one which looks down at the earth but one that looks up at the heavens. So you don't need to worry. You don't. Really. Don't!

Anyway, the point was to build a microwave laser satellite with the ability to shoot high powered laser beams at nearby planets, comets, asteroids or meteors. No, it won't be strong enough to blow up potentially life-threatening asteroids hurtling towards earth (sorry) but it is supposed to be strong enough to burn/ionize/vaporize a part of the surface. The whole point of the laser was to study the composition of these objects. Currently, studying the albedo of an object is the one way to understand it's composition (surface and atmospheric). Albedo is the amount of light reflected off the surface+atmosphere of an object. This gives us a good idea of the object's composition. And i thought that it might be better if we vaporize bits of the surface so we can study it better.

But i fo…

Binge watching

I spent most of my morning binge watching a new TV show, Brooklyn 99, based on the lives of the police in the 99th precinct, brooklyn. It's funny at times but overall, it's not boring. This is not new for me, binge watching i mean. I have binge watched the tv show Scandal last summer. Tt wasn't even a good show to start with but i could never get myself to stop watching it. The acting wasn't any good, it wasn't funny. Overall, it wasn't grippy. But i still didn't stop without finishing all of it. I was wondering today why i binge watch. I know that this is a common thing, i am not the only one. I mean heck, Wired releases a weekly binge watching  guide! Is there a reason people binge watch tv shows or movies, even if they're not really good? Is it in a kind of obsession? Should it be added to the 7 cardinal sins?! :D Just saying...

Photonic band gap materials as astronomical filters

Photonic band gaps are created when materials (at least 2) of different refractive index are stacked on top of one another. If the thickness of these alternating layers is exactly right, these materials act like optical band passes i.e allowing only a certain portion of the optical/electromagnetic spectrum to pass through them. I was taught this last year as part of a course on Optics & Photonics. And now, almost an year from when i was taught this, i realize how they can be applied in astronomy.

Astronomical filters, such as the Johnson UBVRI or the SDSS ugriz, are lenses which act like band passes. The band structures of UBVRI and the ugriz are shown.

source : http://www.vikdhillon.staff.shef.ac.uk/ultracam/filters.gif
Coming back, the idea is to look for a photonic band gap material which can be used as an astronomical filter. But before that, i needed to know what the actual composition of filters are! And this was harder than i thought. Google and wikipedia were of no help a…