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Stalin R Abreu Alvarez
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NIKOLA TESLA MAN WHO CHANGED THE WORLD.WHO IS HE? Nikola Tesla was born on 10 July (O.S. 28 June) 1856 to Serbian parents in the village of Smiljan, Austrian Empire (modern-day Croatia).His father, Milutin Tesla, was a Serbian Orthodox priest.Tesla's mother, Đuka Tesla (née Mandić), whose father was also a Serbian Orthodox priest,had a talent for making home craft tools, mechanical appliances, and the ability to memorize Serbian epic poems. Đuka had never received a formal education. Nikola credited his eidetic memory and creative abilities to his mother's genetics and influence. Tesla's progenitors were from western Serbia, near Montenegro.Tesla gained experience in telephony and electrical engineering before emigrating to the United States in 1884 to work for Thomas Edison in New York City. He soon struck out on his own with financial backers, setting up laboratories and companies to develop a range of electrical devices. His patented AC induction motor and transformer were licensed by George Westinghouse, who also hired Tesla for a short time as a consultant. His work in the formative years of electric power development was also involved in the corporate struggle between making alternating current or direct current the power transmission standard, referred to as the war of currents. Tesla went on to pursue his ideas of wireless lighting and electricity distribution in his high-voltage, high-frequency power experiments in New York and Colorado Springs and made early (1893) pronouncements on the possibility of wireless communication with his devices. He tried to put these ideas to practical use in his ill-fated attempt at intercontinental wireless transmission; his unfinished Wardenclyffe Tower project. In his lab he also conducted a range of experiments with mechanical oscillator/generators, electrical discharge tubes, and early X-ray imaging. He even built a wireless controlled boat which may have been the first such device ever exhibited.
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What a thriller rallye weekend! Sébastien Ogier and Julien Ingrassia have shown their combative talent! Have a look at the results in Poland!

Was für ein spannendes Rallye Wochenende! Sébastien Ogier und Julien Ingrassia haben ihr kämpferisches Talent gezeigt. Schau dir die Ergebnisse aus Polen an!

#Volkswagen #RALLYTHEWORLD #WRC #RallyePoland
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5-Minute Healthy Strawberry Frozen Yogurt is made with just four ingredients, and there's no ice cream maker required!

RECIPE: http://www.justataste.com/2014/05/5-minute-healthy-strawberry-frozen-yogurt-recipe/

#recipe   #frozen   #froyo   #strawberry   #frozenyogurt   #dessert   #healthy   #easyrecipes  
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Meet Pepper: http://bbc.in/1njiEOO

It's a #robot that analyses gestures, expressions and voice tones - and can supposedly read human emotions.

Do you think, as the Japanese manufacturer claims, you'd fancy communicating with it, just as you'd talk to family or friends?
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Metro Santo Domingo L2
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Muy chulo
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Ecos PowerCube: electricidad, Wi-Fi y agua pura todo en uno.

Quiero uno. :)
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Germany got 50% of its electricity from solar on June 9th 2014. Between 1990 and 2012 they increased their solar capacity 16000 times. If all nations had the same installed capacity per capita, the world would have 50 times more solar power. :) They have only 64 sunny days a year, being a mostly cloudy country. Other big nations can generate 40 times more easily, i.e. 1000 GW. 

Solar and battery storage can replace coal-gas-nuclear-oil soon to power the whole planet and all electric transportation ► https://plus.google.com/110265788529286523789/posts/AbEg57jgHQF


1.3 million Earths fit into the Sun.  The Sun is huge.   The solar energy reaching the Earth is 5000 times the energy we use . Cost Of Solar Has Dropped 100 times since 1977, Bringing Solar Power To Grid Parity in many areas.  More than half the present global solar PV capacity was installed in the last 3 years. The age of renewables has begun, according to Citigroup ►  http://reneweconomy.com.au/2014/citigroup-says-the-age-of-renewables-has-begun-69852.  Morgan Stanley says the we are nearing the tipping point for going off-grid with solar/wind/green power, battery storage and electric cars ► http://reneweconomy.com.au/2014/say-investors-wake-solar-pro-sumers-24413

Solar power sells now at 5c/kwh - cheaper than 7c for natural gas and 10 cents for coal in many places as shown by this latest SunEdison contract for 150MW ► http://reneweconomy.com.au/2014/cheapest-solar-sunedison-sells-solar-pv-output-at-5ckwh-25296.
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A firmware update has made its way this evening from Palo Alto, Calif., to a Pebble smartwatch near you, and version 2.2 brings a couple of welcome improvements. First up is that you can now rearrange apps in the launcher. Just highlight it, then hold down the select button (that's the one in the...
A firmware update has made its way this evening from Palo Alto, Calif., to a Pebble smartwatch near you, and version 2.2 brings a couple of welcome improvements. First up is that you can now rearrange apps in the launcher. Just highlight it, then hold down the select button (that's the one in the middle on the right), then move the item up or down. It's especially useful because now...
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The Graphene Electro-Optic Modulator

(Those who wish to view this post in blog form can do so here: http://www.thephysicsmill.com/2014/05/25/graphene-electro-optic-modulator/)

Say we have a beam of light—maybe we made it with a laser. We’d like be able to change the intensity of the beam so that we can alternately brighten and dim it. Moreover, we’d like to be able to do so quickly. Physically blocking and unblocking the beam just isn’t fast enough. So what do we do?

The solution is to make an electric switch so we can change how the light behaves via electrical signals. This is an electro-optic modulator (EOM). Two weeks ago (see: http://www.thephysicsmill.com/2014/05/12/graphene-story-wonder-material/), I introduced graphene to you all. And last week (see: http://www.thephysicsmill.com/2014/05/17/graphene-brush-wonder-material/), I described some of the work I did on graphene as an undergraduate student in the Schibli lab [1]. This time, I’ll explain the ultimate product of that research: a graphene-based electro-optic modulato like the one shown in figure 1. I want to emphasize that I didn’t build this device and I take no credit for its design. I did, however, do some experiments that helped prove that such a device was possible. I’ll talk about all of that today.

(Important side note: one can also make an acousto-optic modulator, which uses sound to change how light behaves.)

The Strange Dance of Light and Matter

Before I can tell you how a graphene EOM works, I need to briefly discuss how a material absorbs light. I’ve given fairly detailed explanations of absorption in the past[2,3,4,5,6]. But today I want to focus on other things, so I’ll only be presenting a very rough, inaccurate picture of what goes on. Take it with a grain of salt.

We know from James Clerk Maxwell that light is a wave made of electric and magnetic fields. These fields feed into each other and wiggle back and forth, as shown in figure 2.

Electrons carry negative charge and are thus affected by electromagnetism. So when light passes through a material, its wiggling pushes the electrons around, accelerating them. But when an electron is accelerated, it leeches energy out of the light. This is absorption.

(Things are much more complicated than this, of course. In insulators, this wiggling causes all sorts of other things to happen to the light. It can bend, slow down, or change direction. We call this refraction, which I’ve written about before here: http://www.thephysicsmill.com/2013/02/17/refraction-how-we-see-through-the-looking-glass/. In a conductor, the light will probably be reflected.  Also, absorption is actually a quantum-mechanical effect. See: http://www.thephysicsmill.com/2013/11/17/things-work-lasers/)

The Obstacles

To absorb the light, our electrons must be free to wiggle around. But many electrons are not free to wiggle in this way. The material might be too crowded, so that an electron that “wanted” to move would be trapped by all the other electrons in its way. Or an electron might be too tightly bound to the atomic nucleus to be able to wobble. This means that, if we can figure out how to control how mobile electrons are in a material, we can control how absorptive it is!

Chemical Doping

Now let’s talk about graphene. In its natural state, graphene has many electrons that are free to wobble (and thus absorb light). However, let’s say we pour some nitric acid [7] on our graphene. Acid eats things because each acid molecule breaks into two pieces: a negatively charged anion and a single hungry proton (a positive hydrogen ion) that wants to chemically react with anything it can find.

Graphene is too tough for the acid to eat, but the proton still has an effect. It lands on the surface of the graphene, attracts one of the electrons within the graphene, and bonds to it. The electron stays within the graphene, but becomes immobilized so that it can’t wiggle around anymore, as shown in figure 3. One less electron to wiggle means one less electron to absorb any light that passes through the graphene, so this causes the whole graphene piece to become less absorptive. This process is called p-doping because we place a positive charge on the surface of the graphene.

If we had used a base instead of an acid, we could have played the same game. The base’s negatively charged ion would have latched onto the graphene and bonded with one of its protons, which would free up an electron. If the graphene had already been p-doped, this might make the graphene more absorptive. If the graphene started in its natural state, the newly freed electron might crowd out its peers and make the material less absorptive. This process is called n-doping because we place a negative charge on the surface of the graphene.

(I’m glossing over a lot. The real story of doping involves the band structure of a material. I wrote about that here: http://www.thephysicsmill.com/2013/02/03/im-with-the-valence-band-band-structure-and-the-science-of-conduction/)

So if we shine light through a graphene sheet, we can control how much of the light it absorbs by adding protons (p-doping) or removing them (n-doping).

Electrostatic Doping

Now remember, we’re trying to make an electro-optic modulator: a device that lets us quickly control how much light passes through it depending on an electrical signal. For our purposes, adding acids and bases is much too slow. We need a new trick. Is there any way we can mimic chemical doping?

As it turns out, there is! Say we place a sheet of graphene on top of some glass and sandwich our glass between two metal places, as shown in figure 4. If we apply a voltage across the plates, we can create an electric field that pushes the protons within the glass towards the graphene. These protons will act just like the protons from our acid; our glass-bound protons bond with electrons in the graphene, immobilizing them! This process is called electrostatic doping, and it’s exciting because we can turn its effects on and off as fast as we can turn the voltage on and off.

Electro-Optic Modulator

Now this is an effect fast enough to make an electro-optic modulator. In the Schilbi Lab, where I worked as an undergraduate student, Professor Thomas Schibli and his students Chien-Chung Lee and Seiya Suzuki placed a piece of tantalum oxide [8]—which has nicer properties than glass—on top of an aluminum mirror. On top of that, they put a sheet of graphene. And on top of that, they placed a ring of aluminum, as shown in figure 5. (The shape was a ring so that light could pass through the center.) When they applied a voltage between the ring of aluminum and the mirror, they were able to electrostatically dope the graphene and change how much light it absorbed.

It worked beautifully! Figure six shows one of the devices actually made in the lab. On the left is an optical photograph of the device through a microscope. On the right is a two-dimensional color-plot of the “modulation depth,” which is a measure of how much the graphene’s absorption changes over time. The brighter the color, the bigger the modulation depth in that spot.

My Part in All of This

I take no credit for the idea of using graphene for an electro-optic modulator—that was all Professor Schibli. I also take no credit for tackling the engineering challenges of designing and building one—that was all Chien-Chung Lee and Seiya Suzuki. What I did was help prove this device could work before they started building it. I grew graphene samples and then Chien-Chung doped them with acid and measured their absorption. While the samples were still doped, I measured their Raman spectra (see: http://www.thephysicsmill.com/2014/03/23/sky-blue-lord-rayleigh-sir-raman-scattering/) to prove that the acid was having the expected doping effect. Afterwards, I looked at the Raman spectra again to look for signs of acid damage.

I did have the privilege, however, of seeing a working device. The team managed to get one functional while I was writing my undergraduate honors thesis on what I’d done. Pretty neat, huh?

Further Reading

1. This is part three of a three-part series on graphene. In the first part, I introduced graphene: http://www.thephysicsmill.com/2014/05/12/graphene-story-wonder-material/
2. In the second part of the series, I discussed some of my personal experiences with graphene: http://www.thephysicsmill.com/2014/05/17/graphene-brush-wonder-material/
3. I glossed over many, many details here. The true story of how doping works is rooted in the band structure of a material. I talk about that here: http://www.thephysicsmill.com/2013/02/03/im-with-the-valence-band-band-structure-and-the-science-of-conduction/
4. I also glossed over important aspects of how light and matter interact. I’ve covered these in several articles, but a good place to start is my article on refraction: http://www.thephysicsmill.com/2013/02/17/refraction-how-we-see-through-the-looking-glass/
5. The quantum mechanics of absorption is first detailed in my article on the Bohr model of the atom: http://www.thephysicsmill.com/2012/12/24/unreal-truths-the-bohr-model-of-the-atom/
6. I also talk about the interaction of light and matter in my article on lasers, my article on mode-locking, and my articles on scattering, which you can find below:
http://www.thephysicsmill.com/2013/11/17/things-work-lasers/
http://www.thephysicsmill.com/2014/04/27/mode-locked-lasers-beating-pulse-metrology/
http://www.thephysicsmill.com/2014/03/23/sky-blue-lord-rayleigh-sir-raman-scattering/
http://www.thephysicsmill.com/2014/03/30/a-quantum-of-scattering/
7. If you’re very brave, you can look at my honors thesis, which explains all of this in extreme detail: http://www.thephysicsmill.com/blog/wp-content/uploads/jm_thesis_draft_3.pdfhttp://
8.  I am a co-author on a paper detailing the proof-of-concept work. Sadly, it’s behind a paywall, but you can get it here if you have a journal subscription: http://link.springer.com/article/10.1007/s00340-012-5095-5
*9.*The Schibli group also published a paper on the modulator. It’s behind a paywall too, but if you have a journal subscription, you can find it here: http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-20-5-5264

References
[1]  http://spot.colorado.edu/~trs/index.shtml
[2] http://www.thephysicsmill.com/2013/02/03/im-with-the-valence-band-band-structure-and-the-science-of-conduction/
[3] http://www.thephysicsmill.com/2014/03/23/sky-blue-lord-rayleigh-sir-raman-scattering/
[4] http://www.thephysicsmill.com/2014/03/30/a-quantum-of-scattering/
[5] http://www.thephysicsmill.com/2013/11/17/things-work-lasers/
[6] http://www.thephysicsmill.com/2014/04/27/mode-locked-lasers-beating-pulse-metrology/
[7] https://en.wikipedia.org/wiki/Nitric_acid
[8] https://en.wikipedia.org/wiki/Tantalum_oxide

#physics   #ScienceSunday   #ScienceEveryDay   #optics   #condensedmatter   #lasers   #quantummechanics  
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electric fan motor & gears.... keep cool

#howstuffworks   #electric   #acmotor   #dcmotor  
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