Group items tagged

Leo on BBC news

the currently official website of IRENA - the new international renewable energy agency just created in Bonn

New trend in power policies?

of interest? -LS

See, I told you smashing things around in the solar system is useful!

Agree, but they knew from before..... see last post

Anyone out there still doing propulsion stuff? Two more papers just waiting to get busted... http://arxiv.org/abs/0908.1429v1 http://arxiv.org/abs/0908.1803

One reply to Pacome, though the discussion exceeds by far the relevance of the topic already. Baryonic DM is strictly limited by cosomology, if one believes in these models, of course. Anyway, even though most DM is cold, we are constantly bombarded by some DM particles that come together with cosmic radiation, solar wind etc. etc. If DM easily interacted with normal matter, we would have found it long ago. In the paper they consider DM as neutralinos, which are neither baryonic nor strongly or electromagnetically interacting.

well then I agree, how the fu.. they want to collect them !!!

what to think about that? spoiling important ressources, smart idea?, and is it really cheap?

Duncan: of interest to have a closer look at it?

In a surprise announcement earlier today (July 13), the European Southern Observatory said that monster black holes - those giants of millions or billions of solar masses, thought to lurk at the hearts of most galaxies - have a mechanism to become active other than galaxy collisions.

"A new study combining data from ESO's Very Large Telescope and ESA's XMM-Newton X-ray space observatory has turned up a surprise. Most of the huge black holes in the centers of galaxies in the past 11 billion years were not turned on by mergers between galaxies, as had been previously thought." and "The process that activates a sleeping black hole - turning its galaxy from quiet to active - has been a mystery in astronomy. What triggers the violent outbursts at a galaxy's center, which then becomes an active galactic nucleus? Up to now, many astronomers thought that most of these active nuclei were turned on when two galaxies merged, or when they passed close to each other and the disrupted material became fuel for the central black hole. Results of the new study indicate this idea may be wrong for many active galaxies." very interesting indeed

Theoretized 80 years ago was Breit-Wheeler pair production in which two photons result in an electron-positron pair (via a virtual electron). It is a relatively simple Feynmann diagram, but the problem is/was how to produce in practice a high energy photon-photon collider... The collider experiment that the scientists have proposed involves two key steps. First, the scientists would use an extremely powerful high-intensity laser to speed up electrons to just below the speed of light. They would then fire these electrons into a slab of gold to create a beam of photons a billion times more energetic than visible light. The next stage of the experiment involves a tiny gold can called a hohlraum (German for 'empty room'). Scientists would fire a high-energy laser at the inner surface of this gold can, to create a thermal radiation field, generating light similar to the light emitted by stars. They would then direct the photon beam from the first stage of the experiment through the centre of the can, causing the photons from the two sources to collide and form electrons and positrons. It would then be possible to detect the formation of the electrons and positrons when they exited the can. Now this is a good experiment... :)

True, but isnt it E2=(pc)^2 + (m0c^2)^2 such that for photons E\propto{pc} and for mass E\propto{mc^2}. I agree it will take a lot of energy, but this assumes that that wont be the problem at least. The question therefore is whether the mass flow of the photon rocket (fuel consumed to create photons, eg fission/fusion) is higher/lower than the mass flow for e-p creation. You are probably right that the low e-p cross-section will favour direct use of photons to create low thrust for long periods of time, but with significant power available the ISP might be higher for e-p pair creation.

In essence the equation tells you that for photons with zero rest mass m0 all the energy will be converted to momentum of the particles. If you want to accelerate e-p then you first spend part of the energy on creating them (~511 keV each) and you can only use the remaining energy to accelerate them. In this case the equation gives you a lower particle momentum which leads to lower thrust (even when assuming 100% acceleration efficiency). ISP is a tricky concept in this case because there are different definitions which clash in the relativistic context (due to the concept of mass flow). R. Tinder gets to a I_SP = c (speed of light) for a photon rocket (using the relativistic mass of the photons) which is the maximum possible relativistic I_SP: http://goo.gl/Zz5gyC .

A new mechanism was discovered on how H2 and N2 participate in the radiation budget. This may help to resolve the "faint young sun paradox", a hypothesis according to which during the earlier age of the solar system when sun radiation had lower intensity than now, the earth was warmer. Extended, it could reassess the past habitability of Mars.

A new, sponge-like material developed engineers at MIT can convert water to steam using just 1% of the sunlight required by conventional steam-producing solar generators.

The UK-led Beagle 2 Mars lander, thought lost on the red planet since 2003, has been found partially deployed on the Martian surface. New images show that it successfully touched down on the planet's surface in 2003 but failed to deploy all four of its solar panels, thereby allowing no communication with scientists on Earth.

Two apps - the Distributed Electronic Cosmic-ray Observatory (DECO) and Cosmic Rays Found in Smartphones (CRAYFIS) - transform smartphones into miniature cosmic-ray detectors. They use the CMOS chips inside phones' onboard cameras to detect the secondary particles produced when cosmic rays - energetic, charged subatomic particles arriving from beyond the solar system - collide with air molecules in the Earth's atmosphere

The first complete theory of how plasmons produce "hot carriers" has been developed by researchers in the US. The new model could help make this process of producing carriers more efficient, which would be good news for enhancing solar-energy conversion in photovoltaic devices.

I did not read the paper but what is further down written in the article, does not give much hope that this actually gives much more insight than what we had nor that it could be used in any way to improve current PV cells soon: e.g. "To fully exploit these carriers for such applications, researchers need to understand the physical processes behind plasmon-induced hot-carrier generation. Nordlander's team has now developed a simple model that describes how plasmons produce hot carriers in spherical silver nanoparticles and nanoshells. The model describes the conduction electrons in the metal as free particles and then analyses how plasmons excite hot carriers using Fermi's golden rule - a way to calculate how a quantum system transitions from one state into another following a perturbation. The model allows the researchers to calculate how many hot carriers are produced as a function of the light frequency used to excite the metal, as well as the rate at which they are produced. The spectral profile obtained is, to all intents and purposes, the "plasmonic spectrum" of the material. Particle size and hot-carrier lifetimes "Our analyses reveal that particle size and hot-carrier lifetimes are central for determining both the production rate and the energies of the hot carriers," says Nordlander. "Larger particles and shorter lifetimes produce more carriers with lower energies and smaller particles produce fewer carriers, but with higher energies."

NASA Releases Tool Enabling Citizen Scientists to Examine Asteroid Vesta Vesta Trek is a free, web-based application that provides detailed visualizations of Vesta, one of the largest asteroids in our solar system. NASA's Dawn spacecraft studied Vesta from July 2011 to September 2012. Data gathered from multiple instruments aboard Dawn have been compiled into Vesta Trek's user-friendly set of tools, enabling citizen scientists and students to study the asteroid's features. The application includes: -- Interactive maps with the ability to overlay a growing range of data sets including topography, mineralogy, abundance of elements and geology, as well as analysis tools for measuring the diameters, heights and depths of surface features and more. -- 3-D printer-exportable topography so users can print physical models of Vesta's surface. -- Standard keyboard gaming controls to manoever a first-person visualization of "flying" across the surface of the asteroid. "There's nothing like seeing something with your own eyes, but these types of detailed data-visualizations are the next best thing," said Kristen Erickson, Director, Science Engagement and Partnerships at NASA Headquarters in Washington DC.

Astronomers have observed up to three newborn planets evolving from a disk of gas and dust particles circling a distant Sun-like star. While 1,900 planets have been discovered outside our solar system, these are the first to be seen that are still forming.