Thursday 28 July 2011

Spinons

"An international group of researchers has measured, for the first time, the phenomenon of spin–charge separation in bulk in a solid. They also found that the material violates the empirical Wiedemann–Franz law that has held true for more than 150 years."
Spinons take the heat - physicsworld.com
In fact, it is well kwown that the Wiedermann-Franz law is an approximation.

Thursday 21 July 2011

Artificial leaves make fuel


"Two teams of researchers in the US have taken important steps towards the creation of commercially viable "artificial leaf" – a hypothetical device that can turn sunlight into electrical energy or fuel by mimicking some aspects of photosynthesis.
Earlier this year, the chemist Daniel Nocera at the Massachusetts Institute of Technology (MIT) announced artificial-leaf prototypes at the annual meeting of the American Chemical Society in California. Now, working with two different teams of researchers, he has published two papers on different devices that represent progress towards effective and commercially viable versions of the artificial leaf."
Artificial leaves make fuel from sunlight - physicsworld.com

Shoemaker (formerly Teague) Impact Structure

"The Shoemaker (formerly Teague) Impact Structure—located in Western Australia in a drainage basin south of the Waldburg Range—presents an other-worldly appearance in this astronaut photograph. The Shoemaker impact site is approximately 30 kilometers (19 miles) in diameter and clearly defined by concentric ring structures formed in sedimentary rocks (brown to dark brown, image center). The rocks were deformed by the impact event approximately 1.63 billion years ago (as reported by the Earth Impact Database). Other age-dating analyses of granitic rocks at the core of the structure call this age into question (Pirajno et al. 2003)."
http://eol.jsc.nasa.gov/EarthObservatory/Shoemaker_Impact_Structure.htm
"Beginning with the Mercury missions in the early 1960s, astronauts have taken photographs of the Earth. Our database tracks the locations, supporting data, and digital images for these photographs. We process images coming down from the International Space Station on a daily basis and add them to the 1,101,059 views of the Earth already made accessible on our website."

Monday 18 July 2011

Biofuel for flights

"Lufthansa, Europe's second-largest airline, became the first carrier in the world to offer regular scheduled flights running on biofuel, with four daily round trips between Hamburg and Frankfurt.
The airline will use a biofuel blend using 50 per cent so- called hydrotreated renewable jet fuel, Lufthansa said. The fuel is made from feedstocks including inedible plants and wood chips. Lufthansa will fly an Airbus A321 on the services." Read more
http://www.smh.com.au/travel/travel-news/lufthansa-begins-worlds-first-regular-biofuel-flights-20110718-1hks1.html

La portata

Testo e immagini adattate da 
Halliday Resnick Walker
Fondamenti di Fisica

Millikan's experiment

Testo e immagine adattati da
Halliday - Resnick - Crane
Fisica II

Dipolo

Un dipolo elettrico è un sistema composto da due cariche elettriche uguali e opposte di segno. È uno dei più semplici sistemi di cariche che si possano studiare e rappresenta inoltre l'approssimazione basilare del campo generato da un insieme di cariche globalmente neutro tramite lo sviluppo in multipoli di quest'ultimo.



Immagini adattate dal libro
Halliday, Resnick, Krane, Fisica 2







n.14 - Esercizio - elettrostatica

Sunday 17 July 2011

Volcanoes under Antarctic waters

"Scientists from British Antarctic Survey (BAS) have discovered previously unknown volcanoes in the ocean waters around the remote South Sandwich Islands. Using ship-borne sea-floor mapping technology during research cruises onboard the RRS James Clark Ross, the scientists found 12 volcanoes beneath the sea surface — some up to 3km high. They found 5km diameter craters left by collapsing volcanoes and 7 active volcanoes visible above the sea as a chain of islands."
More http://www.antarctica.ac.uk/press/press_releases/press_release.php?id=1541

Thursday 14 July 2011

An acoustic superlens from a few cans of cola

""Acoustic metamaterial" may sound exotic, but researchers in France have managed to assemble one from a few multipacks of cola cans. Arranged in a grid, the drinks cans act as a superlens for sound, focusing acoustic waves into much smaller regions than their metre-long wavelengths typically allow. The cans act as resonators, directing the volume of the sound to peak in a space just a few centimetres wide, and this heightened precision could improve acoustic-actuator systems."
How to make a superlens from a few cans of cola - physicsworld.com

Wednesday 13 July 2011

n.13 - due piani carichi

Two infinite sheets of  electric charges with uniform densities intersect at right angles. The plane of the figure is perpendicular to the planes. Let us suppose that changes cannot move.
a) Find the magnitude and direction  of the electric field everywhere and sketch the lines of the field, in the case that a sheet has positive density (+sigma) and the other an equal but negative density (-sigma).
b) find the magnitude and direction of the electric  field everywhere and sketch the lines of the field, in the case that the two sheets have the same densitity with the same positive sign, + sigma.
c) Find the difference of potential V(A)-V(B), between the point A and B placed at a distance d on a line in the plane of the figure at 45° with respect to the charged planes.




n.12 - una piccola sfera




n.11 - tre piani

n.10 - due piani

n.9 - tre cariche puntiformi

n.8

Monday 11 July 2011

DNA transistor

"Passivated nanopores withstand extreme voltages.
Solid-state nanopores are a core element of next-generation single molecule tools in the field of nanobiotechnology, most prominently in the area of DNA-sequencing technology. Researchers at the IBM T. J. Watson Research Center have recently introduced a nanopore-based DNA sequencing platform, which they call a DNA transistor. Thin-film electrodes are integrated into the nanopore device for electrically interacting with translocating DNA. They have now shown that TiN electrodes inside a nanopore can be passivated and completely shielded against electrochemical deterioration even when extreme voltages are applied."

electrochemical impedance spectroscopy

"Functionalized electrochemical impedance spectroscopy device targets personalized medicine.
Rapid, sensitive, accurate, miniaturized and inexpensive biosensors are highly desirable for assisting clinical medical diagnosis. Researchers based at National Chiao Tung University, Taiwan, have developed such a portable bio-sensing platform to detect intermolecular interactions using nanogold-enhanced electrochemical impedance spectroscopy (EIS)."

Drag the light

"By slowing a beam of light down to the speed of sound, UK researchers have dragged photons by an unprecedented 5°, proving a longstanding theory of physics and opening up potential applications in quantum data storage."
Scientists drag light by 5° by slowing to the speed of sound | News | The Engineer

Thursday 7 July 2011

Pendolo cicloidale

Il pendolo cicloidale è un tipo di moto periodico ideato da Christiaan Huygens intorno al 1659 con una peculiare proprietà: le sue oscillazioni sono isocrone indipendentemente dalla loro ampiezza. Si è visto infatti che questo vale nel caso del pendolo semplice solo per ampiezze abbastanza piccole. Huygens dimostrò invece che un punto materiale che oscilla seguendo una traiettoria cicloidale sotto l'azione della gravità ha un periodo costante che dipende unicamente dalle dimensioni della cicloide.
more  http://it.wikipedia.org/wiki/Pendolo#Pendolo_cicloidale

Friday 1 July 2011

A far quasar

"A team of European astronomers, including UK astronomers, have discovered a bright quasar that has been beaming light since the Universe was a mere 770 million years old.
The brilliant beacon, named ULAS J1120+0641, is powered by a black hole with a mass two billion times that of the Sun. Located at a redshift – a term relating to astronomical distances – of 7.1, its light has taken 12.9 billion years to reach us. The next most distant quasar is seen at 870 million years after the big bang, or a redshift of 6.4, although gamma ray bursts have been detected at greater distances of 8.6 and 8.2 redshifts."
Most distant quasar shines brightly

Treni

Due treni partono da due stazioni distanti 20 km dirigendosi uno verso l’altro alle rispettive velocità costanti di v1  = 50 km/h  e v2  = 100 km /h. Dopo quanto tempo si incontrano ?

I due treni si incontrano quando sono nello stesso punto allo stesso istante. Oppure quando lo spazio x1 percorso dal primo più lo spazio x2 percorso dal secondo, sommati, danno la distanza totale che separa le due stazioni.

In formule, per il moto uniforme: x1 = v1 t,   x2 = v2 t

All’istante dell’incontro: x1  + x2 = v1 t + v2 t = 20 km

v1 =  50 km/h =   13,89 m/s
v2 = 100 km/h =   27,778 m/s
20 000 m = (13,89m/s) t + (27,778 m/s) t
t = 20 000 / 41,67 s = 480 s

v^2

Un automobilista sta guidando a una velocità costante di 80 km/h quando vede un ostacolo sulla strada a 50 m. I freni gli consentono di sviluppare una decelerazione  a = - 6 m/s^2. Riuscirà il guidatore a fermarsi prima dell'ostacolo?  (s^2 significa s al quadrato)

Il moto é rettilineo uniformemente decelerato, ossia con accelerazione costante negativa. Diciamo S lo spazio di frenata, conosciamo accelerazione, velocità iniziale e velocità finale, che deve essere zero. Utilizziamo l'equazione:

vfin^2 = viniz^2 + 2aS

Trasformiamo la velocità in m/s: viniz = 80 km/h = 22,222 m/s.

L’equazione precedente diventa: 0 = (22,222 m/s)^2 + 2⋅(-6 m/s^2)⋅S

Quindi: S = 41,2 m

L'ostacolo è a 50 metri e quindi l'automobilista si ferma prima.

Cinematica con dinamica

Un oggetto viene lanciato su una rampa inclinata di 45° con una velocità iniziale di 30 m/s. Dopo quanto tempo si ferma ? A che altezza dal suolo arriva?


Sia O l'origine. Il riferimento sia paralleo al piano inclinato verso l'alto. La direzione di moto è  positiva quando è erso l’alto. La velocità iniziale risulta positiva e l’accelerazione di gravità (diretta verso il basso)
negativa.  Valuatiamo la componente dell’accelerazione lungo la direzione di moto, che risulta essere: a = -g sen α = - 6,94 m/s (con g indico il modulo dell'acc. di gravità, pari a 9.8m/s^2).
Per calcolare il tempo che occorre all’oggetto per fermarsi devo ricordarmi che la velocità finale, in
questo caso, é nulla, e poi usare la definizione di accelerazione:

a = (vfin - v iniz)/ t

Nel nostro caso: -g sen α = - 6,94  m/s^2= (vfin - v iniz)/ t= (0 -  30 m/s) / t

Quindi:

t = 4,32 s

Per calcolare lo spazio S percorso sulla rampa, ho a disposizione due espressioni:

S = 1/2 a t^2 + viniz t

Si ottiene:

S = 1/2 (- 6,94) (4,32)^2 + 30 ⋅ 4,32 =  64,8 m

La quota H raggiunta sul livello del suolo la si ricava come:

H = S sen α = 64,8 m ⋅ sen 45° = 45,8 m

Asta

Esercizio sulla Statica dei Corpi Rigidi,  Prof. T.Papa.