Ever since I was young it seemed like the pinnacle of common sense that if a very, very small component was required it would be foolish to try and break down bigger things to get it. Building what was required atom by atom was the way I thought it should be done. One of the ways scientists attempt to construct items from the ground up is by using optical tweezers. These tweezers are lasers that can exert a force based on the difference in refractive index between a particle and its surroundings in order to trap the molecule and so move it where required. Generally the ability to not just create but manipulate materials on this scale can do incredible things such as having a substance with a specifically changing conductivity across its surface or artificially create chemical functional groups.
Stars are well known to have magnetic fields surrounding them like many planets do. These magnetic fields are generated due to the movement of the plasma, which is of course charged, inside the star. It is through a series of convection currents that the dynamic action of the plasma keeps going and so the magnetic field remains. As magnetic fields themselves exert forces on plasma this creates a very interesting effect where without a density change the internal pressure of the star can change. This is one of the aspects that makes the modelling of stars as perfect gasses a foolish task. Although it was believed for some time that the swirling plasma must cause the magnetic fields recent observations have shown that even the calmer, static regions of the Sun maintain a magnetic field over them.
There has been quite a bit of excitement in the public science sphere this week with NASA announcing the discovery of a series of exoplanets on Wednesday. The letter, sent to Nature, contains many of the more technical details that have been absent in many reports of the event. The star that these exoplanets have been found around is called TRAPPIST-1 and is very small even by the Sun’s standards being only 0.08 solar masses, about 1.6×1029 kg putting it in the dwarf star. This star is only 12 parsecs away, which is quite close astronomically speaking, but the real marvel comes from its satellites. Of the eight known planets that orbit this star seven are very similar to the Earth. Five of the planets have masses within 0.6 to 1.4 of the Earth’s mass with the final two being 0.41 Terra masses and an incalculable value. The surface temperatures of these planets are also very similar to the Earth’s 287 K with one planet actually being estimated at 288 K, an astonishing similarity. The other temperatures range range from 168 K (quite nippy) to 400 K (sweltering), although as these are just average calculated temperatures it is very possible liquid water could exist on all seven Earth like planets. The thing that should probably be noted is that these results are based on a preliminary glance over the system. Although the temperatures are believed to be accurate the masses have a percentage uncertainty averaging at 63.4% (I calculated it) which is really terrible. The letter itself talks about how predictive analysis can’t be performed because of this uncertainty. Overall it is quite clear why people can get very excited about discoveries like this. Apart from the massive galactic coincidence the idea that somewhere among the stars there is a place just like this is quite appealing.
Until tomorrow, goodnight.
I have talked about polaritons before but to cut it short a polariton is a quasiparticle that is formed from the fusion of a photon with an excitation in a material e.g a phonon polariton is, unsurprisingly, a photon and a crystal phonon. The ones that will be focused on today are exciton polaritons. An exciton is another quasiparticle that is in fact an electron and a positive hole in a lattice that are attracted to each other but because of the structure of material they can’t combine and are in fact in a slightly less energetic state from existing as a pair. When put together the exciton polariton has aspects of both the electron and the photon. The exciton’s mass is dropped by the photon 1000 times (technically due to the quantum nature it is only an effective mass estimation but still it is a lot lower than an electron) meanwhile the photon acts like it is trapped in an effective optical micro cavity. Together the exciton polariton becomes a boson and, unlike light normally, can form a Bose-Einstein condensate. Despite all the amazing observations these quasi particles have provided in material science they have yet to be observed in a organic systems.
Optical fibres were a brilliant piece of engineering combined with a bit of physics knowledge. When light is travelling in a block and reaches the surface, it will normally refract out into the air. But if the angle of incidence is large enough total internal reflection occurs where all of the light is reflected back into the material and so none is lost. Optical fibres work by constantly bouncing the light using total internal reflection as shown in the diagram below:
Studying physics means that you get a good grasp of basic chemistry as well. Although there are many complicated exceptions that chemists specialise in and I would never claim to even begin to understand a fraction of all chemical knowledge there is something reassuring about physical chemistry; the way it can all be explained with interacting forces and electron movement and how inorganic chemistry follows the basic rule that everything must end in a lower energy state. When it comes to organic chemistry it begins to pass out of my understanding and by the time biochemistry is reached I am completely lost. It seems to me almost impossible to create the link between chemicals reacting and massive molecules with different reactions at different points along its chain with the ability to coil and move with the help of other molecules.
As time goes on the progress of solar technology continues likewise. One of the developments that is taking a considerable proportion of research effort is that of organic solar cells and organic photovoltaics in general. The efficiencies of these cells have recently surpassed 10% which, despite seeming low, is a very credible achievement considering the difficulties involved in forcing light to do work. Almost all of these solar cells work on a principle called the bulk heterojunction structure. What this means is that two semiconductor layers, with different band gaps, are placed next to each other. Photons then have the ability to transfer electrons from one layer to the other through excitation and when these electrons recombine with holes in the other semiconductor layer a charge flow occurs.