List of my Publications

Friday, 29 June 2012

Piccole oscillazioni...

"Researchers Terry Hunt and Carl Lipo test a new theory that suggests how ancient Easter Islanders may have used ropes to “walk” the moai to their platforms. Mystery of Easter Island, a new NOVA-National Geographic special, airs Wednesday,"
http://ngm.nationalgeographic.com/2012/07/easter-island/walking-statue-video

Friday, 22 June 2012

Alan Turing

Google celebrates the 100th birthday of a computer genius, Alan Mathison Turing (23 June 1912 - 7 June 1954) with a doodle. He is the founder of computer science. He broke the german Enigma-ciphered code.

http://timesofindia.indiatimes.com/tech/news/internet/Alan-Mathison-Turings-100th-birthday-Google-pays-tribute-with-a-doodle/articleshow/14353203.cms

Thursday, 21 June 2012

Silicene

Silicene pops out of the plane - physicsworld.com
"Researchers in Japan say that they have made 2D honeycomb crystals of silicon that resemble the carbon-based material graphene. This is the second potential sighting of the material dubbed "silicene"; the other was reported in April by an independent group in Europe. The Japanese research suggests it may be relatively easy to alter the structure of silicene by changing the substrate on which it is grown – which could allow different versions of silicene to be produced with a range of useful electronic properties. However, not all scientists agree that this latest material is actually silicene."

Tuesday, 12 June 2012

Ancient Rainfall, Carved in Stone

"Stalactites grow from cave ceilings not as dull cones but often sporting elegant corrugations. In Physical Review Letters, two Italian researchers now explain these mysterious, wavy patterns using standard fluid mechanics. Their theory shows that the horizontal ripples form because spatially periodic patterns arise in the rate of mineral deposits from the water flowing down the stalactite. Starting from this model, climate scientists might in the future use stalactite surface structure to reconstruct variations in precipitation patterns over tens of thousands of years."
Ancient Rainfall, Carved in Stone

Friday, 1 June 2012

Tabella termodinamica

Libro sul calore

L'autore, Giovanni Tonzig, mette a disposizione alcuni capitoli pdf del suo libro.
http://www.giovannitonzig.it/loadpage.php?page=fisica_calore


Le pagine sotto elencate sono disponibili in formato PDF.
Domanda trovata in rete: qualcuno sa spiegarmi per bene come si calcola l'entropia in una trasformazione adiabatica irreversibile???


Bisogna capire cosa significa "entropia in una trasformazione", adiabatica o meno. Agli stati di equilibrio possibili di un sistema termodinamico è associata una funzione (detta appunto "di stato") S, chiamata entropia, che tra le altre caratteristiche ha quella di soddisfare le relazionI:

(1) S(B) – S(A) = ∫ (δQ)/T se l'integrale è effettuato lungo una qualsiasi trasformazione reversibile da A a B;

(2) S(B) – S(A) > ∫ (δQ)/T se l'integrale è effettuato lungo una qualsiasi trasformazione irreversibile da A a B.

In particolare, se A e B sono collegabili da una trasformazione adiabatica reversibile allora S(B) – S(A) = 0, cioè non si ha variazione di entropia. Se tu hai due stati A, B e vuoi calcolare esattamente S(B) – S(A), dovrai cercare una trasformazione reversibile (quindi diversa da ogni trasformazione irreversibile di qualunque tipo che abbia portato il sistema da A a B), e calcolare poi ∫ (δQ)/T lungo questa trasformazione reversibile.
Se poi il sistema è formato da un gas perfetto, tutto si semplifica! In questo caso, sempre e comunque,

ΔS = S2 – S1 = n[Cv·ln(T2/T1) + R·ln(V2/V1)] 

e quindi basta conoscere i valori delle variabili di stato iniziali e finali (p1,V1,T1), (p2,V2,T2).





Esercizio dal documento
Sappiamo che una trasformazione adiabatica reversibile è una isoentropica. Prendiamo uno stato iniziale i ed uno stato finale f di un gas perfetto su un'adiabatica.reversibile: Delta S = S_f - S_i = 0.
Dimostrate che Delta S è zero usando  l'espressione della variazione dell'entropia per un gas perfetto.
Vedi anche:
http://physics-sparavigna.blogspot.it/2011/06/domanda-di-teoria-50.html

Transit of Mercury

Very beautiful image at http://apod.nasa.gov/apod/ap120527.html Image Credit: SOHO - EIT Consortium, NASA "The diminutive disk of Mercury, the solar system's innermost planet, spent about five hours crossing in front of the enormous solar disk in 2003 ... the horizon was certainly no problemfor the sun-staring SOHO spacecraft. Seen as a dark spot, Mercury progresses from left to right (top panel to bottom) in these four images from SOHO's extreme ultraviolet camera. The panels' false-colors correspond to different wavelengths in the extreme ultraviolet which highlight regions above the Sun's visible surface."

Here the image from NASA after processing with IRIS


Transit of Venus

"The next transit of Venus, where Venus appears as a dark spot in front of the Sun, will begin at 22:09 UTC on 5 June 2012, and will finish at 04:49 UTC on 6 June.[1] Depending on the position of the observer, the exact times can vary by up to ±7 minutes. Transits of Venus occur in pairs that are eight years apart: the previous transit was in June 2004, and the next pair of transits will occur in December 2117 and December 2125." from Wikipedia

Aristarchus proposed to measure the distance to the Sun using parallax. This approach based on the geometric principles of parallax last for two thousands of years, until Edmond Halley in 1716 proposed to observe the transit of Venus. The use of Venus transits gave an estimate of 1.53×10^13 cm, 2.6% above the currently accepted value, that of l.49 × 10^13 cm. More recently, in 1910, the parallax was measured using the asteroid Eros that passed much closer to Earth than Venus. A transit of Venus happens when this planet passes directly between the Sun and Earth, appearing as a small black disk moving across the Sun bright disk. The duration of such transits is usually measured in hours.
Read  more "Two amateur astronomers at Berkeley", at http://arxiv.org/abs/1202.0950