Being a red blood cell

"Nanoparticles disguised as red blood cells could be used to deliver anti-cancer drugs directly to a tumour. So say researchers at the University of California at San Diego, whose new technique is unique in its approach to harnessing nanoparticles.

Drug delivery systems that mimic naturally occurring biological molecules seem to be the most efficient when it comes to delivering drugs to tumours. Such systems – usually based on nanoparticles – can also circulate in the body for extended periods of time without being rejected by the body's immune system."

Nanoparticles play at being red blood cells - physicsworld.com

Aircrafts make clouds rain

"For more than 50 years it has been known that aircraft can punch large holes or carve out canals inside clouds as they pass through them – but no-one had been able to explain exactly why this happens. Now researchers in the US have identified the cause by comparing satellite images of clouds with the results of computer modelling. They say that the phenomenon could lead to extra precipitation in the vicinity of major airports."

Aircraft punch holes in clouds and make it rain - physicsworld.com

A "Mobius" graphene

"In 1858, August Mobius dreamt up a shape with a single surface and only one edge. The Mobius strip has fascinated children and scientists alike since then.
How small can these shapes be? In December 2003, German chemists made a molecular Mobius strip out of a benzene-like ring modified with a belt-like carbon structure. Since then, various groups have produced increasingly bizarre Mobius-type molecules, including one that can switch back and forth from a Mobius to an ordinary strip when zapped with light.
Of course, the obvious choice of material with which to make Mobius molecules is graphene. But this particular trick has eluded chemists, an omission that clearly irks. Now Douglas Galvao from the Universidade Estadual de Campinas in Sao Paolo, Brazil, and buddies have decided to grip the bull by the horns and calculated the properties that Mobius carbon might have."New form of "Mobius" carbon predicted - Technology Review

New form of "Mobius" carbon predicted - Technology Review

Hot quarks break free

"Physicists in the US, India and China have calculated that quarks and gluons can break free from their confinement inside protons and neutrons at a temperature of around two trillion degrees Kelvin – the temperature of the universe a fraction of a second after the Big Bang. The researchers arrived at this figure by combining the results of supercomputer calculations and heavy-ion collision experiments. They say that it puts our knowledge of quark matter on a firmer footing."

Quarks break free at two trillion degrees - physicsworld.com

Wrinklons

"A new quasiparticle called the "wrinklon" could help explain why materials as diverse as graphene and household curtains wrinkle in much the same way – despite their very different length scales. The particle has been introduced by researchers in Belgium, France and the US as a result of measurements on a wide range of materials on length scales from micrometres to metres. While the work may not lead to more attractive curtains, wrinkles do turn out to affect the electronic properties of graphene and the analysis could therefore influence the development of graphene-based devices."
Introducing the 'wrinklon' - physicsworld.com

Voyager mission at the edge of the solar system

"Recent data from the spacecraft have shown a gentle decrease in the velocity of the solar wind at the heliopause – the outer boundary of the heliosheath – not the abrupt discontinuity predicted by current theories. Also, scientists looking at other data from both Voyager 1 and Voyager 2 have found that the magnetic field in the heliosheath is a tumultuous foam of magnetic bubbles, as compared to the graceful arcs of magnetic field lines they had expected."
More surprises for the Voyager mission at the edge of the solar system - physicsworld.com

Peer pressure keeps planets young...

"Two US astrophysicists claim they have answered an important question about how planets form: why don't young planets get pushed into their companion stars before they have a chance to grow? It turns out that a little company is enough to keep them there, say the researchers, who argue that multiple planets moving through a rocky disk can prevent one another from falling into the star."

Peer pressure keeps young planets growing - physicsworld.com

Domanda di teoria - entropia

Discutere l'entropia e la forma che essa assume nel caso del gas perfetto

Prima di parlare di entropia dobbiamo ricordare ciò che afferma Clausius

per un generico ciclo reversibile

Allora si ha che il lavoro L dipende dalla trasformazione, Q dipende dalla trasformazione (per esempio, abbiamo visto il calore scambiato a pressione o a volume costante). U ed S non dipendono dalla trasformazione. 

Calcoliamo la variazione di entropia per un gas perfetto:

dQ = dU+dL = dU+pdV

= ncvdT + nRT dV/V

dQ/T = ncv dT/T + nR dV/V

La variazione di Entropia 

Delta S = int_i^f  dQ/T

= ncv int_i^f  dT/T + nR int_i^f dV/V

= ncv ln (Tf/Ti) + nR ln (Vf/Vi) 

Ci possiamo chiedere come si può calcolare la variazione d'entropia nei processi irreversibili. L'entropia (come l'energia interna) dipende solo dallo stato del sistema. 

Posso calcolare la variazione di entropia (anche per i processi irreversibili) considerando una qualsiasi trasformazione reversibile tra gli stessi stati iniziale e finale  della trasformazione irreversibile, 

Consideriamo un'espansione libera di Joule. Un gas perfetto si trova in un contenitore isolato e occupa un volume Vi. Un setto divisore separa il gas da un'altra parte dove c'è il vuoto. Si toglie il setto e il gas espande in modo irreversibile in tutto il volume Vf. 

Per il Primo Principio:  Delta U = Q - L = 0, poiché Q=0 e L=0.

Il gas è perfetto Ti = Tf. Posso immaginare un'isoterma reversibile da i ad f. 

La variazione di Entropia 

Delta S = int_i^f  dQ/T 

= ncv ln (Tf/Ti) + nR ln (Vf/Vi) = nR ln (Vf/Vi) >0. 

Non 'cè variazione di energia interna ma c'è variazione di entropia.

L'entropia ci informa che qualcosa è successo al sistema, il volume è cambiato. 

Calore specifico dei gas perfetti

Il primo principio della termodinamica permette di capire perché, a parità di massa e di aumento di temperatura non è la stessa cosa scaldare un gas a volume costante a pressione costante. Infatti nel primo caso tutto il calore va ad incrementare l’energia interna del gas; nel secondo una parte del calore serve a far compiere al gas un lavoro esterno e perciò ne occorre di più.

Vogliamo mostrare che esiste una relazione tra l’energia interna e i calori specifici dei gas perfetti.

Sappiamo che il calore specifico di una sostanza è definito come:

Nel caso dei gas questa equazione è modificata riferendo il calore specifico non più all’unità di massa della sostanza ma a 1 mole di gas. Quindi:  

Quando un gas scambia calore, la quantità di calore scambiata è diversa a seconda del tipo di trasformazione termodinamica alla quale il gas è sottoposto; in particolare, risultano interessanti i due casi in cui lo scambio di calore avviene rispettivamente a pressione costante e a volume costante. Definiamo:

Per calcolare c_p e c_v per un gas perfetto  dobbiamo scrivere il primo principio della termodinamica che dice che  Q = DU+L, tenendo conto che l’energia interna di un gas monoatomico può essere scritta nel seguente modo: U=Ec=3/2n RT      e quindi:    ΔU = 3/2n RΔT

Uso questa espressione nel primo principio:  Q =3/2nR DT + L

Tenendo presente che quando V=cost si ha L = 0, si ricava: c_v=3/2 R

Tale relazione mostra che il calore specifico a volume costante di un gas perfetto non solo è indipendente dalla temperatura, ma è lo stesso per tutti i gas. Ricordiamo che il valore riportato vale per i gas monoatomici (He, Ne…) per i quali l’energia interna è solo energia cinetica traslazionale. Tenendo conto della cosiddetta relazione di Mayer c_p-c_v = R  si ricava che c_p = 5/2R. Infine otteniamo che:

DU = n c_v DT

Questa è l’espressione generalmente usata per il calcolo della variazione dell’energia interna di un gas perfetto. Allora possiamo scrivere per un gas perfetto il primo principio della termodinamica nella  forma: Q = n c_v DT + L

Se avessimo scelto un gas biatomico invece di uno monoatomico, essendo in questo caso:

avremmo ottenuto per il calore specifico a volume costante il valore c_v = 5/2R  e c_p = 7/2 R. 

Motore di Carnot

Vai al link per vedere l'animazione del funzionamento del motote
http://www.galileo.fr.it/marc/termologia_e_termodinamica/carnot/Carnot_Engine.htm
applet originale © .Wan Ching Hui

Cool microscope feels the heat

"Physicists in Germany have invented a new kind of microscope that uses a gas of extremely cold atoms to map the surface of nanoscale structures. The researchers say that their device is complimentary to atomic-force microscopes (AFMs) and that they ultimately hope to create a probe with precision that is limited only by fundamental quantum uncertainties."

Cool microscope feels the heat - physicsworld.com

Il birraio di Salford

James Prescott Joule FRS (1818 – 1889) was an English physicist and brewer, born in Salford, Lancashire. Joule studied the nature ofheat, and discovered its relationship to mechanical work (see energy). This led to the theory of conservation of energy, which led to the development of the first law of thermodynamics. The SI derived unit of energy, the joule, is named after him. He worked with Lord Kelvin to develop the absolute scale of temperature, made observations onmagnetostriction, and found the relationship between the current through a resistance and the heat dissipated, now called Joule's law.
http://en.wikipedia.org/wiki/James_Prescott_Joule

On the Relation between Heat and the Mechanical Power.

On the Existence of an Equivalent Relation between Heat and the ordinary Forms of Mechanical Power.

By James P. Joule, Esq.

[In the letter to the Editors of the 'Philosophical Magazine.']
series 3, vol. xxvii, p. 205Gentlemen,
The principal part of this letter was brought under the notice of the British association at its last meeting at Cambridge. I have hitherto hesitated to give it further publication, not because I was in any degree doubtful of the conclusions at which I had arrived, but because I intended to make a slight alteration in the apparatus calculated to give still greater precision to the experiments. Being unable, however, just at present to spare time necessary to fulfil this design, and being at the same time most anxious to convince the scientific world of the truth of the positions I have maintained, I hope you will do me the favour of publishing this letter in your excellent Magazine.
The apparatus exhibited before the Association consisted of a brass paddle-wheel working horizontally in a can of water. Motion could be communicated to this paddle by means of weights, pulleys, &c., exactly in the matter described in a previous paper.*
The paddle moved with great resistence in the can of water, so that the weights (each of four pounds) descended at the slow rate of about one foot per second. The height of the pulleys from the ground was twelve yards, and consequently, when the weights had descended through that distance, they had to be wound up again in order to renew the motion of the paddle. After this operation had been repeated sixteen times, the increase of the temperature of the water was ascertained by means of a very sensible and accurate thermometer.
A series of nine experiments was performed in the above manner, and nine experiments were made in order to eliminate the cooling or heating effects of the atmosphere. After reducing the result to the capacity for heat of a pound of water, it appeared that for each degree of heat evolved by the friction of water a mechanical power equal to that which can raise a weight of 890 lb. to the height of one foot had been expended.
The equivalents I have already obtained are; -- 1st, 823 lb., derived from magneto-electrical experiments (Phil. Mag. ser. 3 vol. xxiii. pp. 263, 347); 2nd, 795 lb., deduced from the cold produced by the rarefaction of air (Ibid. May 1845, p. 369); and 3rd, 774 lb. from experiments (hitherto unpublished) on the motion of water through narrow tubes. This last class of experiments being similar to that with the paddle wheel, we may take the mean of 774 and 890, or 832 lb., as the equivalent derived from the friction of water. In such delicate experiments, where one hardly ever collects more than one another than that above exhibited could hardly have been expected. I may therefore conclude that the existence of an equivalent relation between heat and the ordinary froms of mechanical power is proved; and assume 817 lb., the mean of the results of three distinct classes of experiments, as the equivalent, until more accurate experiments shall have been made.
Any of your readers who are so fortunate as to reside amid the romantic scenery of Wales or Scotland could, I doubt not, confirm my experiments by trying the temperature of the water at the top and at the bottom of a cascade. If my views be correct, a fall of 817 feet will course generate one degree of heat, and the temperature of the river Niagra will be raised about one fifth of a degree by its fall of 160 feet.
Admitting the correctness of the equivalent I have named, it is obvious that the vis viva of the particles of a pound water at (say) 51° is equal to the vis viva possessed by a pound of water at 50° plus the vis viva which would be acquired by a weight of 817 lb. after falling through the perpendicular height of one foot.
Assuming that the expansion of elastic fluids on the removal of pressure is owing to the centrifugal force of revolving atmospheres of electricity, we can easily estimate the absoute quantity of heat in matter. For in an elastic fluid the pressure will be proportional to the square of the velocity of the revolving atmosphere, and the vis viva of the atmospheres will also be proportional to the square of their velocity; consequently the pressure of elastic fluids at the temperatures 32° and 33° is 480 : 481; consequently the zero of temperature must be 480° below the freezing-point of water.
We see then what an enormous quantity of vis viva exists in matter. A single pound of water at 60° must possess 480° + 28° = 508° of heat; in other words, it must possess a vis viva equal to that acquired bt a weight of 415036 lb. after falling through the perpendicular height of one foot. The velocity with which the atmosphere of electricity must revolve in order to present this enormous amount of vis viva must of course be prodigious, and equal probably to the velocity of light in the planetary space, or to that of an electric discharge as determined by the experiments of Wheatstone.
* Phil. Mag. ser. 3, vol. xxiii, p. 436. The paddle-wheel used by Rennie in his experiments on the friction of water (Phil. Trans. 1831, plate xi, fig, 1) was somewhat similar to mine. I have employed, however, a greater number of "floats," and also a corresponding number of stationary floats, in order to prevent the rotatory motion of the can.
I remain, Gentlemen,
Yours Respectfully,
James P Joule.

Dal sito


http://www.chemteam.info/Chem-History/Joule-Heat-1845.html