Benvenuti in queste pagine dedicate a scienza ed arte. Amelia Carolina Sparavigna

Friday, December 31, 2010

Where is Voyager 1?

"NASA Probe Sees Solar Wind Decline. The 33-year odyssey of NASA's Voyager 1 spacecraft has reached a distant point at the edge of our solar system where there is no outward motion of solar wind."

7 Exoplanets (Amazing video)

"Hundreds of planets around other stars have been discovered recently, but many centuries may pass before human eyes actually see them up close. Interpreting current data, Hugo award-winning artist Ron Miller takes us to seven of the most fascinating of these worlds."
"And while we are not quite ready for something like Star Trek’s United Federation of Planets, the almost daily discovery of new planets has brought the number of known worlds to well over 450."

T-Rex bad reputation got worse

It seems that the largest land predators, which ever stalked the earth, were cannibals. As reported among news in Telegraph UK (15 Oct 2010), the reserchers noticed bite marks on the bones of the dinosaurs. Comparing the marks, the scientists realised that a T-Rex was the only animal large enough to have caused them.

T-Rex, Museo Scienze

Thera and the biblical plagues

Thera, a volcano in the Mediterranean sea, produced with its explosion  around 3,500 year ago, one of the biggest cataclysms in the human history. The remains of  Thera are the Mediterranean islands of Santorini,  north of Crete.  As we can read from an article of Telegraph, the volcanic ash of eruption could have clashed with thunderstorms above Egypt, producing severe  hail storms (one of the biblical plagues).
According to Prof.Trevisanato, a Canadian biologist, another plague, the locusts, could be explained by the volcanic fall out from the ash. The ash fall out caused weather anomalies, which produced higher precipitations and humidity, fostering the presence of the locusts. The volcanic ash could also have caused the plague of darkness. In fact, pumice stones have been found during excavations of Egyptian ruins despite there not being any volcanoes in Egypt.
Very interesting article.

Thursday, December 30, 2010

Powering the space missions

Deep-space missions are powered by a RTG system. A radioisotope thermoelectric generator (RTG, RITEG) is a generator that obtains its power from radioactive decay. The heat released by the decay of a  radioactive material is converted into electricity by the Seebeck effect using an array of thermocouples (see "how did Georg do it?").
RTGs are systems quite suitable as power sources for satellites and space probes and also for remote facilities where the use of solar cells is not feasible (for instance, lighthouses built by the former Soviet Union inside the Arctic Circle). RTGs are able to give few hundred watts for very long periods. The problem is to guarentee a safe use of radioisotopes.

Where is Cassini spacecraft?

Cassini–Huygens is a robotic spacecraft currently studying the planet Saturn and its  satellites. The launched spacecraft consisted of two elements: the Cassini orbiter, named for the astronomer Giovanni Domenico Cassini, and the Huygens probe, named for the astronomer, mathematician and physicist Christiaan Huygens. Cassini-Huygens  was launched on October 15, 1997, and it entered into orbit around Saturn on July 1, 2004. On December 25, 2004, the Huygens probe was separated from the orbiter and  reached Saturn's moon Titan on January 14, 2005. It descended into the atmosphere of the moon, sending information back to the Earth. This was the first landing ever accomplished in the outer solar system. The mission will continue until 2017. 
On November 2, Cassini was triggered into a standby mode, after a bit flip caused it to miss an important instruction. Cassini was reactivated as scheduled on November 24 and has returned to perfect working order, in time for two scheduled close fly-bys with Enceladus.
What is powering Cassini?

Bacteria in Titanic rusticles

"A new bacterium isolated from the Titanic wreck is accelerating the wreck's disintegration into a pile of dust."
These are bacteria potentially dangerous to underwater metal structures.  Shipwrecks disapper but also offshore oil and gas pipelines. The articecle tells that the newly discovered species could also have positive applications for industry for instance in the recycling of iron structures in deep ocean.

Night at the Museum - 4 - Egypt

Wood and faience objects at the Egyptian Museum

Torino, Palazzo Madama

Striges (Owls)

Strix (pl. striges or strixes) was the Ancient Roman and Greek word for owl. The name is Greek in origin. From it, the name of the genus Strix was derived.

Wednesday, December 29, 2010

Treasure Island

A seafarer...
"This is a handy cove," says he at length; "and a pleasant sittyated grog-shop. Much company, mate?" My father told him no, very little company, the more was the pity.
"Well, then," said he, "this is the berth for me. Here you, matey," he cried to the man who trundled the barrow; "bring up alongside and help up my chest. I'll stay here a bit," he continued. "I'm a plain man; rum and bacon and eggs is what I want, and that head up there for to watch ships off. What you mought call me? You mought call me captain. Oh, I see what you're at-- there"; and he threw down three or four gold pieces on the threshold. "You can tell me when I've worked through that," says he, looking as fierce as a commander.


Queste sono le parole con cui si presenta il vecchio lupo di mare alla locanda dell'Ammiraglo Benbow.
Isola del Tesoro, R.L. Stevenson

Paleolithic Crete

A research team led by Thomas Strasser and Eleni Panagopoulou announced the discovery of stone tools at two sites on the island of Crete that are between 130,000 and 700,000 years old. The tools resemble those made by Homo heidelbergensis and Homo erectus, showing that our human ancestors boated across at least 40 miles of open sea to reach the island. This is the earliest  evidence of seafaring.
Cenabis bene, mi Fabulle, apud me paucis, si tibi di favent, diebus, si tecum attuleris bonam atque magnam cenam, non sine candida puella et vino et sale et omnibus cachinnis.
Haec si, inquam, attuleris, venuste noster, cenabis bene; nam tui Catulli plenus sacculus est aranearum. Sed contra accipies meros amores, seu quid suavius elegantiusve est: nam unguentum dabo, quod meae puellae donarunt Veneres Cupidinesque; quod tu cum olfacies, deos rogabis totum ut te faciant, Fabulle, nasum.
Gaius Valerius Catullus

Revisiting the construction of pyramids

"The Kufu pyramid, with a volume of 2,7 millions of meter cubes, was completed over a period of 20 to 30 years. From this one can estimate a daily rhythm of 300 to 400 blocks, each having an average volume of 1 meter cube. This means one block put at the right place every 2 minutes.  To achieve this goal,  1 meter square of block face would have to be hewn every 20 seconds! What a performance, with tools made of stone or with soft copper ..."  As we can read in the Europhysics News Vol. 40, No. 1, 2009, pp. 27-31, Revisiting the construction of the Egyptian pyramids, Guy Demortier,  www.europhysicsnews.org/epn20091p27.pdf ...
"In 1978,  the French chemist Joseph Davidovits rejected the generally accepted technique of carving and hoisting stones. He proposed that the building method involved the moulding on site: blocks were made of a kind of concrete whose basic binding compound was natron: a sodium carbonate extracted very close to the site of Giza.  The binder was obtained by some chemical reaction leading to a geopolymer (a name given by Davidovits). It is a poly-sialate containing an alkaline nucleus: sodium from natron.  Natron, lime and water form caustic soda,  which reacts with aluminous limestone to yield the basic geopolymer.  X-ray fluorescence and X-ray diffraction have shown that the blocks consist of limestone (85 to 92%) associated with a binder.  Additional analyses were performed by PIXE (Particle-Induced X-ray Emission), PIGE (Particle-Induced gamma-ray Emission) and by NMR-Spectroscopy for structural characterization in laboratories of Namur and Lecce. One of the pyramid’s samples appeared  to be made of  a central compact structure embedded in a material of different composition. The central part is identified as natural limestone but the outer part contains a large amount of F,  Na,  Mg,  Al,  Si."

The owls of Harry Potter

Hedwig is the snowy Harry Potter's owl. At the following link, a precious discussion on the owls playing in the books and movies, by Laura L. Erickson, The Owls Of Harry Potter:


Owls - rapaci notturni d'Europa

Mediante fotografie e testi, 32 pannelli descrivono la sistematica, la classificazione, la biologia, l’etologia e la conservazione degli Strigiformi. Un’attenzione particolare è rivolta alle specie viventi nel continente europeo: dal gufo delle nevi al barbagianni, dalla civetta capogrosso all’assiolo. I pannelli sono affiancati da numerosi reperti di animali tassidermizzati provenienti dalle collezioni scientifiche del Museo.
Exhibition, Museo Regionale di Scienze Naturali, Torino

Human, All Too Human - 3 - Denisova

The Denisova hominin is the name given to the remains of a member of the genus Homo that may be a previously unknown species. The discover is based on the analysis of mitochondrial DNA, obtained from a bone of a juvenile that lived about 41,000 years ago. The find happened in  the Denisova Cave (Altai Krai, Russia), a region also inhabited at about the same time by Neanderthals and modern humans. From

El sacrificio de los bosques

"La construcción de las cinco centrales hidroeléctricas contempladas en el pacto energético entre Brasil y Perú no sólo demandará una inversión millonaria sino que también implicará un gran daño ambiental. Casi 1,5 millones de hectáreas de bosques desaparecerían en 20 años, según un cálculo independiente."

The Red-Headed League

"Set in 1890, a business-man named Jabez Wilson, a man with red hair, comes to consult Holmes. He tells them that his young assistant, Vincent Spaulding, some weeks ago had shown him, and urged him to respond, to a newspaper want-ad offering work to only red-headed male applicants. The next morning, Wilson had waited in a long line of fellow red-headed men, was interviewed and was the only applicant hired, because none of the other applicants had hair to match Wilson's red locks. Wilson, whose business mainly operates in evenings, was well-paid, receiving four pounds a week for several weeks; the work was obviously useless clerical work in a bare office. Finally one morning, a sign on the locked office door inexplicably announced that "THE RED-HEADED LEAGUE IS DISSOLVED."" from Wiki
"Sherlock Holmes and I surveyed this curt announcement and the rueful face behind it, until the comical side of the affair so completely overtopped every other consideration that we both burst out into a roar of laughter.
"I cannot see that there is anything very funny,” cried our client, flushing up to the roots of his flaming head. “If you can do nothing better than laugh at me, I can go elsewhere.”
"No, no,” cried Holmes, shoving him back into the chair from which he had half risen. “I really wouldn’t miss your case for the world. It is most refreshingly unusual. But there is, if you will excuse my saying so, something just a little funny about it. Pray what steps did you take when you found the card upon the door?” 

More http://ignisart.com/camdenhouse/ or http://etext.virginia.edu/

Red-headed Neanderthals

Probably this fact is already well-known...
BBC reported that a research team  extracted DNA from the remains of two Neanderthals and retrieved part of a gene called MC1R. In modern people, a mutation in this gene causes red hair. Until this discovery, no one knew what hair colour our extinct relatives had: by analysing a version of the gene in Neanderthals, the scientists found that they were flame-haired.

Human, All Too Human - 2 - DNA

Researchers compared the Neanderthal DNA to the DNA of three modern people (French, Han Chinese, Polynesian). The team found that all three had inherited between 1 and 4 percent of their DNA from Neanderthals. They also compared the Neanderthal sequence to two African individuals (Yoruba, San) and found no indication that they had inherited genes from Neanderthals, who evolved outside Africa. The research supports the idea that Neanderthals interbred with Homo sapiens between 100,000 and 80,000 years ago as our anatomically modern ancestors left Africa and spread across the globe, as we can read from http://www.archaeology.org/1101/topten/germany.html
See also http://stretchingtheboundaries.blogspot.com/2010/12/human-all-too-human.html

Graphene Transistors

Technological Review reports that IBM has created graphene transistors, quite faster that silicon ones. The prototype devices are made from atom-thick sheets of carbon and operate at 100 gigahertz, meaning that they switching on and off 100 billion times each second. As a consequence they are about 10 times as fast as the speediest transistors.

Aral Sea

"The expanse of water, like several others across the globe, has been reduced to worryingly sparse levels.In April the situation at the Aral Sea was described as 'one of the planet's worst environmental disasters' by UN Secretary General Ban Ki-Moon." From

This image is in the public domain because it was created by NASA. NASA copyright policy states that "NASA material is not protected by copyright unless noted".NASA, derivative work by Zafiroblue05 at en.wikipedia

Torino, L'Arsenale

Tuesday, December 28, 2010

Torino, Mascherone sulla cancellata di Palazzo Reale

Torino, Vittorio Emanuele I, Palazzo Madama

Isis and Harpocrates

In late Greek mythology as developed in Ptolemaic Alexandria, Harpocrates is the god of silence, adapted from the Egyptian child god Horus. To the ancient Egyptians, Horus represented the new-born Sun, rising each day at dawn. When the Greeks conquered Egypt under Alexander the Great, they transformed the Egyptian Horus into their Hellenistic god known as Harpocrates, a rendering from Egyptian Har-pa-khered or Heru-pa-khered (meaning "Har, the Child"). Horus was conceived by Isis, the mother goddess, from Osiris, the original god-king of Egypt, who had been murdered by his brother Set.  Among the Egyptians the full-grown Horus was considered the victorious god of the Sun who each day overcomes darkness. In this way Harpocrates, the child Horus, personifies the newborn sun each day, the first strength of the winter sun, and also the image of early vegetation. Egyptian statues represent the child Horus, pictured as a naked boy with his finger on his mouth, a realization of the hieroglyph for "child" , or with the mother Isis.
From Wiki

Isis and the child Harpocrates - Museo Egizio


The king and the god Amun. This sculpture represents the king's allegiance to the Theban god Amun. The sides of the throne are decorated with hieroglyphs forthe unification of Upper and Lower Egypt. Limestone, Dinasty XVIII,reign of Horemheb (1319-1292 BC), Temple of Amun, Thebes.


"Hathor was an Ancient Egyptian goddess who personified the principles of love, beauty, music, motherhood and joy. She was one of the most important and popular deities throughout the history of Ancient Egypt. Hathor was worshipped  ... as "Mistress of the West" welcoming the dead into the next life. In other roles she was a goddess of music, dance, foreign lands and fertility who helped women in childbirth, as well as the patron goddess of miners. The cult of Hathor predates the historical period and the roots of devotion to her are, therefore, difficult to trace, though it may be a development of predynastic cults who venerated the fertility, and nature in general, represented by cows.
Hathor is commonly depicted as a cow goddess with head horns in which is set a sun disk with Uraeus."
Source: Wiki

Museo Egizio, Torino

W H Hodgson - The Haunted Jarvee

"Dinner over, Carnacki as usual passed round his smokes, snuggled himself down luxuriously in his favourite armchair and went straight to the story we knew he had invited us to hear.
'I've been on a trip in one of the real old-time sailing ships,' he said without any preliminary remarks. 'The Jarvee, owned by my old friend Captain Thompson. I went on the voyage primarily for my health, but I picked on the old Jarvee because Captain Thompson had often told me there was something queer about her. I used to ask him up here whenever he came ashore and try to get him to tell me more about it, you know; but the funny thing was he never could tell me anything definite concerning her queerness. He seemed always to know but when it came to putting his knowledge into words it was as if he found that the reality melted out of it. ....
Then on the eighteenth day something truly happened. I had been pacing the poop as usual with old Thompson when suddenly he stopped and looked up at the mizzen royal which had just begun to flap against the mast. He glanced at the wind-vane near him, then ruffled his hat back and stared at the sea.
'"Wind's droppin', mister. There'll be trouble tonight," he said. "D'you see yon?" And he pointed away to windward. '"What?" I asked, staring with a curious little thrill that was due to more than curiosity. "Where?"
'"Right off the beam," he said. "Comin' from under the sun." "I don't see anything," I explained after a long stare at the wide-spreading silence of the sea that was already glassing into a dead calm surface now that the wind had died. "Yon shadow fixin'" said the old man, reaching for his glasses.
He focussed them and took a long look, then passed them across to me and pointed with his finger. "Just under the sun," he repeated. "Comin' towards us at the rate o' knots." He was curiously calm and matter-of-fact and yet I felt that a certain excitement had him in the throat; so that I took the glasses eagerly and stared according to his directions.
After a minute I saw it - a vague shadow upon the still surface of the sea that seemed to move towards us as I stared. For a moment I gazed fascinated, yet ready every moment to swear that I saw nothing and in the same instant to be assured that there was truly something out there upon the water, apparently coming towards the ship.
'"It's only a shadow, captain," I said at length...."
More http://www.forgottenfutures.com/game/ff4/jarvee.htm

Torino, Piazza San Carlo, Il cavallo di bronzo

Rattling "guests" in atomic cages

"In addition to their ground state, diamond structure, Si, Ge and Sn can form crystalline solids called clathrates. As in the diamond structure, in the clathrates, the Group IV atoms are tetrahedrally coordinated and sp3 covalently bonded to their neighbors. However, the clathrates contain pentagonal atomic rings and have open-framework lattices containing 20-, 24- and 28-atom “cages”. ... The pure clathrates are semiconductors.
The cages can contain weakly bound impurities (“guests”), usually alkali or alkaline earth atoms. The choice of guest may be used to tune the material properties. The guests are electronic donors, but because of their weak bonding, they have small effects on the electronic band structures. However, they can produce low frequency vibrational (“rattling”) modes which can strongly affect the vibrational properties. Some guest-containing clathrates have been shown to be excellent candidates for thermoelectric applications precisely because the guests only perturb the electronic properties weakly, while strongly affecting the vibrational (heat transport) properties. For thermoelectric applications, semiconductor materials are needed. When all cages are filled, the clathrates become semi-metallic due to the excess valence electrons of the guests. To compensate for this, Group III atoms (usually Ga or In) are substituted on the framework sites."
More at Physica B: Condensed Matter, Volumes 401-402, 15 December 2007, Pages 695-698, Proceedings of the 24th International Conference on Defects in Semiconductors
Rattling “guest” impurities in Si and Ge clathrate semiconductors
C.W. Myles, K. Biswas and E. Nenghabi

The Latin word clatrum means lattices; bars; grate; railings -> Clatratus

Monday, December 27, 2010

Arthur Machen - The Novel of the Black Seal

This evening, a novel of a black seal engraved with "characters, shaped somewhat like wedges or daggers, as strange and outlandish as the Hebrew alphabet". Starting from the seal, a man gradually uncovers the secrets of a race of pre-humans hiding in the Welsh hills.


Night at the Museum - 3 - China

One of the finest collection of neolithic artifacts outside of China is at MAO, Museo d'Arte Orientale, Via San Domenico 11, Torino. Here a movie showing some potteries

The Wilberforce pendulum

A Wilberforce pendulum, invented by Lionel Robert Wilberforce around 1896, consists of a mass suspended by a  helical spring and free to turn on its vertical axis, twisting the spring. Despite the name, this pendulum does not swing back and forth as the Galileo's pendulum does. The mass usually has symmetric pairs of radial 'arms' sticking out horizontally, with small weights on them. These small masses are used to tune the moment of inertia and then the torsional vibration period of the pendulum.
Look the movie1 or movie2 .When correctly adjusted and set in motion, it exhibits a curious motion. One is the familiar up and down bounce of the spring, the other is the twist causing the mass to rotate. Note that the  energy is transferred from pure up and down to pure rotational and back again (coupled mechanical oscillator).  in which periods of purely rotational oscillation gradually alternate with periods of purely up and down oscillation. That is, the energy stored in the device shifts between  'up and down' and  'clockwise and counterclockwise' oscillations.

A little bit of theory: http://online.redwoods.cc.ca.us/instruct/darnold/deproj/sp04/stevemisay/Project1.pdf

How did Georg do it?

An article by L A  Geddes and L.E.  Geddes, explains how Georg Ohm discovered the  Ohm’s law. As the authors tell, Georg Ohm  lived  at a time when  there were no calibrated indicators for electric current:  no volt or amp, because these were established much later.  The resources available  to Ohm were:  1) the discovery of Oersted, who in 1820 showed that a magnetic field surrounded a wire carrying electric current; 2) the electrochemical cell, described by Volta in 1800; and 3) the thermoelectric effect, discovered by Seebeck in 1822. In fact, the Seebeck effect is giving a quite stable source of current.
More  http://deltat.pro.br/Arquivos/notas/Lei%20de%20Ohm%20IEEE.pdf

Sunday, December 26, 2010

Night at the Museum - 2 - Crystals

Una collezione di minerali, Museo regionale di scienze naturali, Torino
Here a movie showing some crystals:

Crystals and light, it is enough!
Some crystals from the collection of the Museum of Natural Science.

Hans Hartung - Lo slancio

At the Museo Regionale di Scienze Naturali, via Giolitti  36, Torino, until 30 January, the exhibition of  Hans Hartung.


W H Hodgson - The Voice in the Night

William Hope Hodgson was born in 1877. At the age of thirteen, Hodgson ran away from school in an effort to become a sailor. Caught, he returned to family but eventually received his father's permission to begin an apprenticeship as a cabin boy. After receiving the mate certificate, he was a sailor for several years. During his period as sailor, he was awarded the Royal Humane Society medal for heroism. During his voyages,  Hodgson practised photography, taking, among others, photographs of atmospheric phenomena such as cyclones, lightning and aurora borealis. Back from sailing, he opened in 1899 a school of physical culture, in Blackburn, England, offering personal training. In this period he began writing articles on physical culture. After, Hodgson turned his attention to fiction, publishing his first short stories. He wrote poems too, many posthumously published by his widow. In 1907 he published "The Voice in the Night", a horror sea story, and "The House on the Borderland"; in 1909, "Out of the Storm", and the novel "The Ghost Pirates". After, he invented a recurring character, Carnacki,  .... see Wiki for more.

From "the Voice in the Night"

It was a dark, starless night. We were becalmed in the northern Pacific. Our exact position I do not know; for the sun had been hidden during the course of a weary, breathless week by a thin haze which had seemed to float above us, about the height of our mastheads, at whiles descending and shrouding the surrounding sea.
With there being no wind, we had steadied the tiller, and I was the only man on deck. The crew, consisting of two men and a boy, were sleeping forward in their den, while Will—my friend, and the master of our little craft—was aft in his bunk on the port side of the little cabin.
Suddenly, from out of the surrounding darkness, there came a hail:
“Schooner, ahoy!”
The cry was so unexpected that I gave no immediate answer, because of my surprise.
It came again—a voice curiously throaty and inhuman, calling from somewhere upon the dark sea away on our port broadside:
“Schooner, ahoy!”
“Hullo!” I sang out, having gathered my wits somewhat. “What are you? What do you want?”
“You need not be afraid,” answered the queer voice, having probably noticed some trace of confusion in my tone. “I am only an old—man.”

Saturday, December 25, 2010

M R James - Lost Hearts

Montague Rhodes James, (1862 – 1936), used the publication name M R James. He was an English mediaeval scholar and provost of King's College, Cambridge and of Eton College. He is well-known for his ghost stories. James's ghost stories were published in a series of collections: among them, the "Ghost Stories of an Antiquary". Many of the ghost tales were created as a Christmas Eve entertainment and read aloud to friends.

This evening, Lost Hearts

"It was a day of curious experiences for Stephen: a windy, noisy day, which filled the house and the gardens with a restless impression. As Stephen stood by the fence of the grounds, and looked out into the park, he felt as if an endless procession of unseen people were sweeping past him on the wind, borne on resistlessly and aimlessly, vainly striving to stop themselves, to catch at something that might arrest their flight and bring them once again into contact with the living world of which they had formed a part."

Night at the Museum - 1 - Egypt

Here a film showing some statues you can see visiting the Egyptian Museum, Torino

In occasion of the Winter Olympic Games, Torino 2006, the exibition space of the  Museum hosting the statues gained a new stage design created by Dante Ferretti (two times awared by the Academy for Best Art Direction).  Visitors entering the room were  plunged in a dark space where only the statues were lighted. Dark walls and mirrors on them, background music of flutes with the rattling of a sistrum, created a suggestive feeling of being in Egypt.

The Merowe Dam on the Nile

The artificial lake (reservoir) created by the Merowe Dam on the Nile has been photographed by the crew of the International Space Station. This image is recent, dating 5 October 2010. The dam is on the Nile near the Fourth Cataract, in that part of Nubia desert where the river Nile is creating the Great Bend, a contorted path through the bedrocks of Bayuda Massif. The satellite imagery of Google Maps, which is a few years old, shows the region, when the dam was under construction. Using Google, we see the Nile and river banks creating a fertile strip of land with many villages. 
We can compare the region before and after the spill gates have been closed.
Comparison shows that the lake created itself through the paleochannes, the old dry riverbeds. 

More at


Friday, December 24, 2010

Human, All Too Human - 1 - New

The sequencing of the nuclear genome from an ancient finger bone found in a Siberian cave shows that the cave dwellers were neither Neanderthals nor modern humans.
An international team of researchers led by Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig (Germany) has sequenced the nuclear genome from a finger bone of an extinct hominin that is at least 30,000 years old and was excavated by archaeologists from the Russian Academy of Sciences in Denisova Cave in southern Siberia, Russia, in 2008.

Read more

The thermal rectifier

From Wiki: A thermal rectifier is a device that preferentially passes heat in one direction; a "one-way valve" for heat. The name is by analogy with an electrical rectifier, which performs a similar function for electric current.

More information