List of my Publications

Monday, 31 October 2011

A wave power machine

http://en.wikipedia.org/wiki/Wave_power#Wave_energy_and_wave_energy_flux

"The Pelamis machine consists of a series of semi-submerged cylindrical sections linked by hinged joints. As waves pass along the length of the machine, the sections move relative to one another. The wave-induced motion of the sections is resisted by hydraulic cylinderswhich pump high pressure oil through hydraulic motors via smoothinghydraulic accumulators. The hydraulic motors drive electrical generators to produce electricity.[24] Pelamis Wave Power first tested and grid connected a Pelamis machine in 2004 at the European Marine Energy Center.[25] The first of a second generation of machines, the P2 started grid connected tests off Orkney in 2010, the machine is owned by E.ON.[26]."


Pelamis Wave Energy Converter on site at the European Marine Energy Test Centre (EMEC).
Author P123
Permission (Reusing this file)

Wave energy

"Wave energy is produced when electricity generators are placed on the surface of the ocean. The energy provided is most often used in desalination plants, power plants and water pumps. Energy output is determined by wave height, wave speed, wavelength, and water density. To date there are only a handful of experimental wave generator plants in operation around the world. The articles on this page explore the world of wave energy and its possible applications."
More http://www.alternative-energy-news.info/technology/hydro/wave-power/

Impact of wave energy conversion on marine environment

‘Underwater noise is a global environmental issue that has to be addressed if we are to take advantage of the huge potential of ocean energy,’ said EU commissioner for research, innovation and science Máire Geoghegan-Quinn.
Ireland has one of highest concentrations of wave energy in the world, presenting a significant opportunity to expand its renewable energy portfolio and develop new industry capabilities,’ said Prof Owen Lewis, chief executive officer of SEAI.

Read more:Project assesses impact of wave energy conversion noise | News | The Engineer

Thursday, 27 October 2011

Giant Waterworld Around Naked Eye Star 

Giant Waterworld Confirmed Around Naked Eye Star - Technology Review

"55 Cancri A is a Sun-like star some 40 light years away. It has an apparent magnitude of about 6 and so is visible to the naked eye in the constellation of Cancer.

This star is unusual in that it is just one of a handful that are known to have at least 5 planets. The innermost of these planets--55 Cancri e--was discovered in 2004 and has since had plenty of attention from astronomers. Various groups have observed the the changes in radial velocity that it causes its parent star. This tells them about that it orbits its star every 18 hours and that its mass is about 8 times Earth's or about half Neptune's."

"The innermost planet around 55 Cancri A is almost certainly an exotic waterworld with a radius about twice Earth's, say astronomers"

Tuesday, 18 October 2011

La transizione da liquido isotropo a smettico

La transizione da liquido isotropo a smettico

Amelia Carolina Sparavigna
Dipartimento di Fisica
Politecnico di Torino

Breve discussione della transizione di fase diretta dal liquido isotropo alla mesofase smettica, con osservazioni al microscopio polarizzatore.

I cristalli liquidi sono materiali composti di molecole di forma allungata, come bastoncini, oppure discoidale. Essi sono caratterizzati dalla presenza di mesofasi tra la fase liquida isotropa e quella cristallina. Tipiche mesofasi sono la fase nematica e quella smettica. La fase nematica ha i centri delle molecole che assumono posizioni arbitrarie, mentre gli assi delle molecole tendono a orientarsi nella stessa direzione. Nello smettico, le molecole si dispongono con i loro centri su piani definiti. Gli assi delle molecole hanno una direzione specifica rispetto al piano. Se la direzione è perpendicolare al piano, si dice che la fase è smettica A, se invece l’asse è inclinato, la fase è smettica B. La fase smettica è quindi più ordinata della nematica, ma più disordinata di un cristallo. Vi sono alcuni materiali termotropici in cui la fase nematica non c'è, ma si ha solo una fase smettica. Riscaldando o raffreddando il campione, si passa dalla fase smettica a quella liquido o viceversa, saltando la fase nematica.
Vediamo che cosa si può osservare col microscopo polarizzatore, quando si passa della fase liquida ordinaria, dove le molecole sono disordinate sia in posizione sia in orientamento, nella fase liquido-cristallina. La fase liquida ordinaria è detta “liquido isotropo”. Il cristallo liquido è preparato tra due vetrini e posto, all’interno di un termostato, sotto il microscopio, tra i due filtri polarizzatori. Lo spessore del materiale è di pochi micron. Il campione è riscaldato fino a raggiungere la fase liquida ordinaria. Questa fase, se vista al microscopio con i filtri polarizzatori incrociati, appare come un nero uniforme. L’isotropia ottica del materiale permette l’estinzione completa della luce. Se si raffredda il liquido ed esso passa nella fase nematica, si vedono comparire delle bolle colorate. Dove ci sono le bolle, il materiale è già nematico. Le bolle crescono fino a che tutto il materiale è nematico.

  
Transizione da liquido isotropo, che appare nero nella foto, a nematico, che è colorato. Il cristallo liquido è il 12OBAC (alkyloxybenzoic acid).

Il nematico è otticamente anisotropo. Il materiale modifica la luce che polarizzata dal primo filtro del microscopio. Il secondo non riesce più a estinguere tutta la luce. Il materiale appare colorato per via di fenomeni d’interferenza. Cosa si vede quando si passa del liquido isotropo allo smettico? Dato che ci sono diverse fasi smettiche, quello che si vede dipende dalla fase.

Smettico A
Utilizziamo un oxadiazolo, che ha la transizione diretta dalla fase isotropa a quella smettica. Il materiale ha una fase smettica di tipo A. Al microscopio polarizzatore, questo materiale mostra una  fase caratterizzata da domini a ventaglio (in letteratura si trovano definiti come “fan” oppure  “focal-conic”).


Domini “focal-conic” nella fase smettica.

Aumentando la temperatura, portiamo il campione nella fase liquida isotropa. Il campione diventa nero. Cominciamo a raffreddare lentamente il campione per portarlo nella fase smettica. Nel campo visivo del microscopio appaiono i “batonnets”, che cominciamo a crescere nella fase isotropa.


Batonnets della fase smettica che crescono nella fase isotropa (a sinistra). I domini crescono e si uniscono a formare la tessitura focal-conic.

Questi domini crescono e si uniscono insieme fino a formare la tessitura, ossia l’insieme dei domini osservati al microscopio polarizzatore, della fase smettica. I domini sono in questo caso focal-conic.  

Smettico C
La tessitura vista sopra non è l’unica mostrata dalla fase smettica. Prendiamo un altro materiale, anche lui avente la transizione diretta liquido isotropo - smettico.  Il materiale utilizzato è il 16OBAC della famiglia degli acidi ossibenzoici alchilici (alkyloxybenzoic). Il materiale è cristallino fino a 90 °C e poi passa nella fase smettica C.


A sinistra la fase cristallina del  16OBAC; a destra la fase smettica  osservata in riscaldamento dalla fase cristallina.

Alla temperatura di 131 °C diventa un liquido isotropo, non ha quindi fase nematica. Questo è dovuto al fatto che le molecole sono così lunghe da mantenere l'ordine smettico fino ad alta temperatura, vincendo la tendenza al disordine dovuta all'agitazione termica. In raffreddamento, la fase smettica compare dalla fase isotropa: si osservano delle strutture ramificate che compaiono nel campo nero della cella vista tra polarizzatori incrociati.


Ecco come cresca la fase smettica nella fase isotropa.


La crescita della fase smettica  dalla fase isotopa vista ad un ingrandimento maggiore.


La sequenza mostra l'evoluzione della struttura ramificata, quando si abbassa la temperatura (0.5 gradi al minuto).


E’ interessante notare che la fase smettica che si forma in raffreddamento ha una tessitura differente da quella che si osserva in riscaldamento. La tessitura è di tipo schlieren: poiché la fase è smettica, ci sono solo difetti con carica 1. Possiamo quindi distinguerla dalla fase nematica, che è simile, perché questa ha anche i difetti 1/2.


Fase smettica del 16OBAC che si forma in raffreddamento. La tessitura è di tipo schiere, con i soli difetti con carica 1.


Discussione
Il processo di crescita delle mesofasi dalla fase isotropa è un problema interessante e forse poco studiato ancora [1]. Questo processo ha due fasi, quella di nucleazione e quella di accrescimento. Esse sono state ben studiate per i processi di cristallizzazione dal liquido isotropo. Nella fase di nucleazione succede che, all'interno del liquido si creano dei punti in cui la concentrazione locale è maggiore. Questi punti sono chiamati cluster. Crescendo, si creano dei nuclei che rispecchiano fedelmente l'ordine del cristallo. Sono piccoli cristallini di dimensioni microscopiche.
Anche le mesofasi hanno i loro nuclei. Per quanto riguarda i nematici, di solito si osservano delle piccolissime gocce circolari, che si formano nel liquido isotropo e che poi si uniscono a formare la fase nematica. Anche se il nematico è anisotropo come orientazione, è disordinato come posizione. Immaginiamo le molecole del nematico come dei bastoncini. Quando esse sono nella fase liquida isotropa, i loro centri sono disordinati, come anche le loro direzioni. Al decrescere della temperatura, quando il materiale arriva alla transizione di fase, le molecole possono girare i loro assi lunghi senza doversi spostare. Questo può avvenire nello stesso modo in tutte le direzioni dello spazio. Il nucleo di nematico cresce nel liquido isotropo con una simmetria sferica.
Nello smettico invece, l’ordine locale è molto diverso. Ci sono dei piani microscopici, su cui si devono sistemare i centri delle molecole. Le molecole devono orientarsi ma anche spostare i loro centri per formare i piani. I clusters iniziali possiedono quindi una direzione privilegiata, quella perpendicolare ai piano dello smettico. Ecco quindi che possono comparire i nuclei come batonnets.
E’ molto interessante la crescita dello smettico C, che appare come una struttura ramificata. Sicuramente sono necessari ulteriori studi per determinare meglio le caratteristiche dei nuclei.

Riferimenti

[1] I DierkingC Russell, Universal scaling laws for the anisotropic growth of SmA liquid crystal bâtonnets, Physica B: Condensed Matter, Volume 325, January 2003, Pages 281-286.

Friday, 14 October 2011

Mesophases transitions


An interesting transition is the texture transition inside the nematic phase. We observe in some liquid crystalline compounds a transition from a low-temperature nematic texture which looks like a texture of a smectic phase to a high temperature nematic Schlieren texture. Compounds that have the texture transition are the alkyloxybenzoic acids. Here, you can see a movie of the texture transtion inside the nematic phase of 6OBAC. The sample is heated from the crystal phase. We can see the smectic pahse and then the two following nematic subphases. Click on the image to see the movie.


More details  in my papers:
Texture transitions in binary mixtures of 6OBAC
with compounds of its homologous series
A. Sparavigna;  A. Mello; B. Montrucchio 

Phase Transitions: A Multinational Journal, 1029-0338
Volume 80, Issue 3, 2007, Pages 191 – 201
Abstract 
Texture transitions in the liquid crystalline 
alkyloxybenzoic acid 6OBAC
A. Sparavigna;  A. Mello; B. Montrucchio 
Phase Transitions: A Multinational Journal, 1029-0338
Volume 79Issue 4, 2006, Pages 293 – 303
Abstract 

A new image processing method for enhancing
the detection sensitivity of smooth transitions in liquid crystals

Liquid Crystals, 1366-5855, Volume 24Issue 6, 2001, Pages 841 – 852
Abstract 

novel order transition inside the nematic phase of 
trans -4-hexylcyclohexane-1-carboxylic acid discovered by image processing
Liquid Crystals, 1366-5855, Volume 25Issue 5, 2001, Pages 613 – 620
Abstract 


In the following, three movies show a transition on cooling from the nematic to the smectic phase of an oxadiazole compound. We see a transition from the nemtic to a smectic phase with toric domains.
Clink on images to launch the movies.

  

For more detailsthese are my articles:

Growth of toric domains in mesophases of oxadiazoles
A. Sparavigna;  A. Mello; B. Montrucchio 
Phase Transitions: A Multinational Journal
1029-0338, Volume 81Issue 5, 2008, Pages 471 – 477
Abstract 

Fan-shaped, toric and spherulitic textures of mesomorphic oxadiazoles
A. Sparavigna;  A. Mello; B. Montrucchio 
Phase Transitions: A Multinational Journal
1029-0338, Volume 80Issue 9, 2007, Pages 987 – 998
Abstract 


Amelia Carolina Sparavigna

Saturday, 8 October 2011

Of the Education of an Engineer

"Architecture is a science arising out of many other sciences, and adorned with much and varied learning; by the help of which a judgment is formed of those works which are the result of other arts. Practice and theory  are its parents. Practice is the frequent and continued contemplation of the mode of executing any given work, or of the mere operation of the hands, for the conversion of the material in the best and readiest way. Theory is the result of that reasoning which demonstrates and explains that the material wrought has been so converted as to answer the end proposed. Wherefore the mere practical architect is not able to assign sufficient reasons for the forms he adopts ; and the theoretic architect also fails, grasping the shadow instead of the substance. He who is theoretic as well as practical, is therefore doubly armed; able not only to prove the propriety of his design, but equally so to carry it into execution.
In architecture, as in other arts, two considerations must  be constantly kept in view; namely, the intention, and the matter used to express that intention: but the intention is founded on a conviction that the matter wrought will fully suit the purpose; he, therefore, who is not familiar with both branches of the art, has no pretension to the title of architect. An architect should be ingenious, and apt in the acquisition of knowledge. Deficient in either of these qualities, he cannot be a perfect master.
He should be a good writer, a skillful draftsman, versed in geometry and optics, expert at figures, acquainted with history, informed on the principles of natural and moral philosophy, somewhat of a musician, not ignorant of the sciences both of law and physics, nor of the motions, laws, and relations to each other, of the heavenly bodies. By means of the first named acquirement, he is to commit to writing his observations and experience, in order to assist his memory. Drawing is employed in representing the forms of his designs. Geometry affords much aid to the architect: to it he owes the use of the right line and circle, the level and the square; whereby his delineations of buildings on plane surfaces are greatly facilitated. The science of optics enables him to introduce with judgment the requisite quantity of light, according to the aspect. Arithmetic estimates the cost, and aids in the measurement of the works; this, assisted by the laws of geometry, determines those abstruse questions, wherein the different proportions of some parts to others are involved. Unless acquainted with history, he will be unable to account for the use of many ornaments which he may have occasion to introduce. ...
Many other matters of history have a connexion with architecture, and prove the necessity of its professors being well versed in it. Moral philosophy will teach the architect  to be above meanness in his dealings, and to avoid arrogance: it will make him just, compliant and faithful to his employer ; and what is of the highest importance, it will prevent avarice gaining an ascendancy over him: for he should not be occupied with the thoughts of filling his coffers, nor with the desire of grasping every thing in the shape of gain, but, by the gravity of his manners, and a good character, should be careful to preserve his dignity. In these respects we see the importance of moral philosophy; for such are her precepts. That branch of philosophy which the Greeks call phusiologia, or the doctrine of physics, is necessary to him in the solution of various problems; as for instance, in the conduct of water, whose natural force, in its meandering and expansion over flat countries, is often such as to require restraints, which none know how to apply, but those who are acquainted with the laws of nature: nor, indeed, unless grounded in the first principles of physics, can he study with profit the works of Ctesibius, Archimedes, and many other authors who have written on the subject.
Music assists him in the use of harmonic and mathematical proportion. It is, moreover, absolutely necessary in adjusting the force of the balistae, catapultae, and scorpions...
Astronomy instructs him in the points of the heavens, the laws of the celestial bodies, the equinoxes, solstices, and courses of the stars; all of which should be well understood, in the construction and proportions of clocks. Since, therefore, this art is founded upon and adorned with so many different sciences, I am of opinion that those who have not, from their early youth, gradually climbed up to the summit, cannot, without presumption, call themselves masters of it. Perhaps, to the uninformed, it may appear unaccountable that a man should be able to retain in his memory such a variety of learning ; but the close alliance with each other, of the different branches of science, will explain the difficulty. For as a body is composed of various concordant members, so does the whole circle of learning consist in one harmonious system. Wherefore those, who from an early age are initiated in the different branches of learning, have a facility in acquiring some knowledge of all, from their common connexion with each other...
For in such a variety of matters, it cannot be supposed that the same person can arrive at excellence in each, since to be aware of their several niceties and  bearings, cannot fall within his power. We see how few of those who profess a particular art arrive at perfection in it, so as to distinguish themselves: hence, if but few of those practising an individual art, obtain lasting fame, how should the architect, who is required to have a knowledge of so many, be deficient in none of them, and even excel those who have professed any one
exclusively. ...
I beseech you, O Caesar, and those who read this my work, to pardon and overlook grammatical errors; for I write neither as an accomplished philosopher, an eloquent rhetorician, nor an expert grammarian, but as an architect: in respect, however, of my art and its principles, I will lay down rules which may serve as an authority to those who build, as well as to those who are already somewhat acquainted with the science."

From "The Architecture", by Marcus Vitruvius Pollio

Friday, 7 October 2011

Solid angle

A Lecture on Solid Angle, by Ben Kravitz
http://www.stanford.edu/~bkravitz/research/solidangle.pdf
"In order to talk about solid angles, we fi rst need to talk about projections. There are lots of diff erent kinds of projections, some of which you already know. We should begin with a very simple defi nition of what a projection is, and then we'll get more complex as we go along. A projection is the transformation of points and lines in one plane onto another plane by connecting corresponding points on the two planes with parallel lines".

Wednesday, 5 October 2011

Theory and practice

From the post
Teaching: Theory or practice? by Marcus Wilson Aug 07

"What’s clear is that many teachers take the view that theory is the opposite of practice. Since, in teaching, it is clearly the practice that matters (since it’s what the students experience) this leads to the conclusion that theory is irrelevant and there is no benefit in engaging with it. ... The fallacy is the implicit assumption that theory and practice are unconnected. (I mean, you don’t have experimental physicists and theoretical physicists working in complete isolation from each other, so why expect that with teaching?) What you believe about student learning will influence the way you teach, whether you formally acknowledge it or not. That’s become clear for me as I think about my teaching practice. I have my own ‘beliefs’, or my own models, call them ‘theories’, of how students learn, and these influence how I teach."

Read the post at
http://sciblogs.co.nz/physics-stop/2011/08/07/teaching-theory-or-practice/