nedelja, 07. december 2014

Magnetni monopol

Učenje, da je mogoče magnet razpoloviti in nastaneta dva magneta, en s severnim in drug z južnim polom, je seveda napačno. Kakorkoli se trudite razpoloviti magnet, vedno nastaneta dva, ki imata oba severni in južni pol. To izhaja iz lastnosti magnetnega polja, ki ga oblikujejo lastnosti kroženja in vrtenja elektronov okoli lastne osi v atomih. Je pa mogoče v materialih doseči način, da se elektroni obnašajo tako, kot da bi imeli opravka z magnetnimi monopoli.

Več:

Artificial magnetic monopoles discovered


When a magnet is divided, a new magnet with north and south poles is always created. However, a monopole, i.e. a north pole without a south pole or a south pole without a north pole has not yet been discovered. In the current edition of the journal Science, researchers from Cologne, Munich and Dresden describe the discovery of new type of artificial monopole in a solid, i.e. particles, which have similar characteristics to monopoles, but which only exist within materials.
Over the last few years, materials in which magnetic whirls, so-called skyrmions, are formed, have been examined intensively. These whirls influence the movements of the electrons in exactly the same manner as magnetic fields. For this reason, artificial magnet fields are used to describe these whirls as well as their influence on the electrons.
Even if these are not "real" magnetic fields, it is possible to measure them experimentally in the same manner as normal magnet fields as they deflect electrons.
The researchers asked questions as to the consequences of attempting to destroy the magnetic whirls. To do this, the group working under the direction of Prof. Eng from the Technischen Universität Dresden observed magnetic whirls with a magnetic force microscope: a tiny magnetic tip samples the surface of the magnets and measures the direction of the magnetization thus making the ca. 50 nanometer sized whirl visible. They were able to observe on the surface that the magnetic whirls apparently coalesce when the skyrmion phase is destroyed.
What happens, however, within the materials? Measurements taken by the group working under the direction of Prof. Pfleiderer in Munich using neutron scattering suggest that similar processes occur there, but individual whirls were not observed in this manner. For this reason, Stefan Buhrandt and Christoph Schütte working in Prof. Rosch's group at the University of Cologne conducted computer simulations. These showed that the whirls neighbouring the merging process observed on the surface in the experiment also occur within the materials.
Due to the fact that every whirl carries an artificial magnetic field, their creation or destruction occurs at the point of merging. "This means that an artificial magnetic monopole has to sit on this point," describes Prof. Rosch, "whenever two magnetic whirls merge in the experiment, an artificial magnetic monopole has flown through surface."
Magnetic monopoles have been searched for in vain in the area of particle physics for a long time. In 1931, Paul Dirac postulated the existence of a fundamental particle to explain why electrons and protons carry electrical charges of the same size. This is surprising because the elements of the protons and electrons are completely different fundamental particles. Dirac, however, argued that the existence of a single magnetic monopole would be enough to explain that the charges of all fundamental particles have to be quantized, i.e. exactly an integer multiple of an elementary charge. The newly discovered artificial monopoles fulfil exactly this quantization requirement. "It is fascinating that something as fundamental as a magnetic monopole can be realized in a piece of material," describes Stefan Buhrandt. Despite this, artificial monopoles cannot solve Dirac's problem: only electrons in solid state, but not protons, feel the artificial magnet fields.

Konoplja za energijsko učinkovito baterijo


HempGrafen (čisti ogljik zložen v zelo tanko (atomsko) plast)  je v zadnjih letih požel veliko zanimanja kot material za bodoče aplikacije v elektroniki, medicini, itd. Iz enostavne enačbe za kapacitivnost  preprostega ploščnega kondenzatorja C=er*e0*A/d, kjer je A površina plošče, d razdalja med ploščama in er relativna dielektričnost, lahko hitro ugotovimo, da je za zvečanje kapacitivnosti potrebno imeti čim večjo površino plošč in čim manjšo razdaljo med ploščama. In seveda dober vmesni material, ki se ob vnosu v električno polje močno polarizira, kar opišemo z relativno dielektričnostjo. No, grafen ima veliko površino na težo, kar 2630 m2/g, kar teoretično omogoča kapacitivnosti velikosti 550 F/g.  


Kot kaže, pa je mogoče nekaj podobnega ali celo boljše doseči iz lubja marihuane. Kdo bi si mislil? Za to ne potrebujete niti tiste, ki vsebuje THC. Zato se kondenzatorsko marihuano lahko goji kot industrijsko rastlino. Če prav razumem, so v ta namen stebla izpostavili visoki temmperaturi in potem še dodatni toplotni obdelavi in dosegli razkroj stebla in ob tem zelo tanke plasti ogljika, ki so bile precej podobne plastem grafena. Ta material so uporabili za izdelavo elektrod v kondenzatorju in dobili odlične rezultate z gostoto energije 12 W/kg. 
Začnimo torej gojiti konopljo - za dobre kondezatorje. 

Zaključna misel: včasih ima tisto, kar navidezno deluje kot popolni odpadek, s katerim si ne moremo nič pomagati in ne vemo, kako bi se ga znebili, največjo vrednost !?


Več: 


Abstract ImageIz abstrakta članka:
We created unique interconnected partially graphitic carbon nanosheets (10–30 nm in thickness) with high specific surface area (up to 2287 m2 g–1), significant volume fraction of mesoporosity (up to 58%), and good electrical conductivity (211–226 S m–1) from hemp bast fiber. The nanosheets are ideally suited for low (down to 0 °C) through high (100 °C) temperature ionic-liquid-based supercapacitor applications: At 0 °C and a current density of 10 A g–1, the electrode maintains a remarkable capacitance of 106 F g–1. At 20, 60, and 100 °C and an extreme current density of 100 A g–1, there is excellent capacitance retention (72–92%) with the specific capacitances being 113, 144, and 142 F g–1, respectively. These characteristics favorably place the materials on a Ragone chart providing among the best power–energy characteristics (on an active mass normalized basis) ever reported for an electrochemical capacitor: At a very high power density of 20 kW kg–1 and 20, 60, and 100 °C, the energy densities are 19, 34, and 40 Wh kg–1, respectively. Moreover the assembled supercapacitor device yields a maximum energy density of 12 Wh kg–1, which is higher than that of commercially available supercapacitors. By taking advantage of the complex multilayered structure of a hemp bast fiber precursor, such exquisite carbons were able to be achieved by simple hydrothermal carbonization combined with activation. This novel precursor-synthesis route presents a great potential for facile large-scale production of high-performance carbons for a variety of diverse applications including energy storage.

sreda, 03. december 2014



Zajemanje vibracijske energije s pomočjo razlike v izstopnih energijah materialov 

tudi s tem se bom nekoč ukvarjal :) Samo enega dobrega študenta rabim, pa gremo v akcijo... 
... zaenkrat pa so nas prehiteli Finci, ki so za zajemanje vibracijske energije uporabili razliko izstopnih del dveh materialov. Zanimiv članek, poln osnov elektrotehnike. Ko želimo dva različna materiala združiti želita preiti v termodinamično ravnovesje tako, da se izenačita fermijeva nivoja obeh materialov. Pri tem pride do potencialne razlike,  ta pa se odraža v spremembi koncentracije električnih nabojev na površini materialov. Časovna sprememba naboja pa ni nič drugega kot električni tok. Če torej dva materiala z različnimi izstopnimi deli gibljemo tako, da se približujeta in oddaljujeta, dobimo električni tok, ki ga je potrebno le še ustrezno usmeriti in shraniti. ....



Preberite več o tem v:
http://www.vtt.fi/news/2014/30102014_VTTlta_uusi_menetelma_sahkon_tuottamiseen.jsp?lang=en
http://www.nature.com/srep/2014/141028/srep06799/full/srep06799.html