Group items tagged

See Also: Matter & Energy Nanotechnology Optics Physics Materials Science Graphene Organic Chemistry Reference White gold Electromagnetic radiation Nanomedicine Nanoparticle Any use for the smell project? "We have demonstrated resonant antenna-enhanced single-particle hydrogen sensing in the visible region and presented a fabrication approach to the positioning of a single palladium nanoparticle in the nanofocus of a gold nanoantenna,"

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 .

Looks like good business. Tobias?

this is a gold mine :D Portugal, a bankrupt country in crisis where the Most Searched How to... is "Como emagrecer" (how to lose weight?). Netherlands, where the Most Searched How to... is "Hoe overleef ik" (how do I survive?) UK where the most Trending What is... is "What is love?" and Italians... please explain how come the top Trending How to... are 1. Come fare Sesso 2. Come fare un Clistere !?!? Respect for Austria though, where the top trending What is... are: 1. Was ist ACTA 2. Was ist SOPA any other interesting finds?

From Ghana "What is...?": What is a Constitution What is Government [edit] Some top Science searches in the US: Hemorrhoid, Pregnancy Syndroms. Any potential for Ariadna? [edit] ... and finally, for the sake of my shield, top search from Poland in the Music category

[spam] Obama expressed his disappointment recently when rapper Kanye West stormed the stage at the MTV Video Music Awards to protest singer Taylor Swift's win of the "Best Female Video" trophy. Soon after, Obama himself was Swifted by critics who felt he was undeserving of his Nobel Prize win. It is obviously connected to the study of the Journal of Wine Economics that wine gold awards are given randomly http://www.wine-economics.org/journal/content/Volume4/number1/Full%20Texts/1_wine%20economics_vol%204_1_Robert%20Hodgson.pdf which also raised some controversy

Physicists have simulated two universes colliding inside a metamaterial--  Now, this is cool (if it is true...)

Hm, they use more or less everything I don't especially like. They are nonmagnetic, so the relation materialGR is already rather weak. Usually, experimentalists prefer nonmagnetic media, since they are cheaper and broadband. At least the broadband is no argument here, since the frequency defines the "mass", which I find a rather strange point of view. And finally, they use strong anisotropy as a model of "time", which is rather problematic. Of course, the spatial direction with eps<0 appears in the wave equation with the same sign as time. But this does not mean that it behaves like time. But to teach material physicists that time is more than just a different sign in the wave equation seems to be as hopeless as to teach them that a black hole is more than something that absorbs all light... SIGHHH

Luzi I miss you ...

We made it to Slashdot's frontpage !!! :)

Congratulations, gentlemen!

Our achievement is reported on the italian government web pages .....

Grande fratello is watching...

Again some plasmonic metamaterial...

Sounds good!

well of course money is trust, and even more loans and credit and even more stock and bond markets. It all represents trust and expectations. However since the first banks 500 years ago and the first loans etc. etc., and as well the fact that bonds and currencies bring down whole countries (Greece lately), and are mainly controlled by large financial centres and (central) banks, banks have always been on the winning side no matter what and that isn't going to change easily. So if you are talking about these new currencies it would be a new era, not just a new currency. So should Greece convert its debt to bitcoins ;P ?

well, from 1936 to 1993 the central bank of france was owned by the state and was supposed to serve the general interest...

A good example of "Can we use it for space.com"... For shielding of course !

We're all here about inventiveness and creativity, so here you go... Story of a guy who's life's motto has been "Gold lies on the streets and you just need to dig it up with ideas. Ideas are like the shovel" Add to it Monte Carlo, Marlene Dietrich and, say, King Farouk and you get quite an amazing story... And most of all, after reading this you'll know the value of knowing how to ski.

nice story indeed ...

First peer review study about he criticality of rare-earth metals. It can be read "They found that supply limits for many metals critical in the emerging electronics sector (including gallium and selenium) are the result of supply risks. The environmental implications of mining and processing present the greatest challenges with platinum-group metals, gold, and mercury. For steel alloying elements (including chromium and niobium) and elements used in high-temperature alloys (tungsten and molybdenum), the greatest vulnerabilities are associated with supply restrictions" Questions about estimation apart, this can be a valuable market for asteroid mining.. (ot just more market for Infinium-like companies http://www.technologyreview.com/news/527526/a-cleaner-cheaper-way-to-make-metals/).

Research in active-matter systems is a growing field in biology. It consists in using theoretical statistical physics in living systems such as molecule colonies to deduce macroscopic properties. The aim and hope is to understand how cells divide, take shape and move on these systems. Being a crossing field between physics and biology "The pot of gold is at the interface but you have to push both fields to their limits." one can read

Maybe we should discuss about this active matter one of these days? "These are the hallmarks of systems that physicists call active matter, which have become a major subject of research in the past few years. Examples abound in the natural world - among them the leaderless but coherent flocking of birds and the flowing, structure-forming cytoskeletons of cells. They are increasingly being made in the laboratory: investigators have synthesized active matter using both biological building blocks such as microtubules, and synthetic components including micrometre-scale, light-sensitive plastic 'swimmers' that form structures when someone turns on a lamp. Production of peer-reviewed papers with 'active matter' in the title or abstract has increased from less than 10 per year a decade ago to almost 70 last year, and several international workshops have been held on the topic in the past year."