Cold Welding

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Welding is the joining together of two materials, usually two metals. This is usually done through the application of heat: the two metals melt, their liquid stages coalesce and mix, and then the combined liquid stage is left to re-solidify by cooling down.

Welding

But what if you just placed two pieces of metal on top of each other? The two sets of metal atoms at the interface between the two pieces of metal wouldn’t know which atoms belonged to which piece of metal. As Richard Feynman wrote:

“When the atoms in contact are all of the same kind, there is no way for the atoms to ‘know’ that they are in different pieces of [metal]. When there are other atoms, in the oxides and greases and more complicated thin surface layers of contaminants in between, the atoms ‘know’ when they are not on the same part.”

So if you take two very clean and very flat pieces of metal, and place them in contact with each other, in a vacuum (so that there is no air between the two pieces) they will join themselves together, in the same manner as they would if they were welded together conventionally using heat. (Usually the application of large pressures is required, so that the two pieces of metal are fully in contact throughout the entire overlapping area.)

Space is a very good vacuum, and spontaneous cold welding of metal parts aboard spacecraft is something that spacecraft designers have to plan to avoid. It is suggested that the failure of the Galileo spacecraft’s high-gain antenna was due to cold welding that had not been spotted in ground testing due to the quick formation of a protective oxide layer, which did not form in space due to the absence of oxygen.

Names

There is an understandable tendency to believe that all names work like your own, but this isn’t the case. I can’t hope to cover all the minutiae of naming in different countries and cultures, so this article is, at best, a collection of interesting facts about names in different cultures.

To make this post easier to understand I’ll be sticking to some simple terminology: the first name is the name that is written first when the name is written down, and the second name is the name that is written second when the name is written down.

In the “Western system” the first name is a given name, and the second name is a family name (AKA a “surname”). People are also frequently given a second given name, which is placed in between the first and second names (i.e. a middle name). In the “Eastern system” the order is reversed, so the family name is the first name and the given name is the second name. For example, the President of China is Xi Jinping and is referred to as “Mr Xi”, and his daughter is Xi Mingze and is referred to as “Ms Xi”. To avoid confusion, in lists where both Western and Eastern system names appear, it is common to capitalise the name that should be used formally.* It is also common for Eastern system names that do not use the Latin alphabet to be converted to the Western order when the name is transliterated. For example, the Prime Minister of Japan is Shinzō Abe, where “Abe” is the family name and comes first when written in Japanese.

In a large number of countries, when a man and woman are married, the woman takes the man’s family name. Thus if Jane Doe marries John Smith, she becomes Jane Smith. Sometimes the family names are joined or “double-barrelled”, so Jane Doe and John Smith could become Jane and John Smith-Doe, or Jane and John Doe-Smith. In many Spanish and Latin American countries double-barrelled family names are obligatory, and children take the first of each of their parents’ family names. The President of Spain, Mariano Rajoy Brey and his wife, Elvira Fernández Balboa, have two children: Mariano and Juan Rajoy Fernández. In practice, most use only their first family name, so names are patrilinear as with most other countries.

Patronymic and matronymic second names take themselves from the name of the father and mother respectively, and women generally do not change their names when they are married. Perhaps the most well-known example of a qpatronymic name system are Icelandic names, where sons and daughters take a different second name to their parents (i.e. they do not continue-on a “family name”). For example, if a man named Jón (the most common Icelandic first name) had a son, Sigurður, and a daughter, Guðrún, they would take the names “Sigurður Jónsson” (literally “Sigurður, Jón’s son”) and “Guðrún Jónsdottir” (“Guðrún, Jón’s daughter”) respectively. Phonebooks in Iceland list people alphabetically by first name, and people are usually addressed formally by their first name (so the siblings above would never be introduced as “Mr Jónsson” or “Ms Jónsson”). Within in a large family there will therefore be a wide range of second names, and this occasionally causes trouble for Icelanders in foreign countries where people expect children to have the same second name as their parents. The other Nordic/Scandinavian countries, who used to use the same naming system, have generally moved away from it, but in those countries there are a smaller number of surnames and people are often referred to by both their first and second given (middle) names.

In some Eastern Slavic countries (Russia, Belarus, Ukraine, Macedonia, Bulgaria and Kazakhstan) a patronymic name is usually used as a middle name. In Russian, Abram, the son of Anatoly Ivanov, would have the full name Abram Anatolyevich Ivanov, and Anatoly’s daughter Darya would be Darya Anatolyevna Ivanov. In at least Russian, Ukraine and Belarus a person must have three names, including a patronymic.

Arabic names do not follow a given name and family name, or first name and second name system. Rather they indicate the heritage of a person and that person’s hoped-for characteristics. For example, the ruler of Dubai is Mohammed bin Rashid Al Maktoum. “Mohammed” is a religious given name literally meaning “praised”, “bin” is the colloquial form of “ibn” meaning “son of”, “Rashid” is his father’s (Rashid bin Saeed Al Maktoum) given name (meaning “integrity”) and “Al Maktoum” is the “House of Maktoum”, a de-facto family name. Some Arabic names are very long and contain a miniature family history with lots of “bin”s.

* For example, the leaders of the G22 countries are: Stephen HARPER, François HOLLANDE, Angela MERKEL, Pietro GRASSO, Shinzō ABE, Vladimir PUTIN, David CAMERON, Barack OBAMA, Cristina FERNÁNDEZ DE KIRCHNER, Tony ABBOTT, Dilma ROUSSEFF, XI Jinping, LEUNG Chun-ying, Pranab MUKHERJEE, Joko WIDODO, NAJIB Razak (“Najib” is the given name, and “Razak” is a patronym), Enrique PEÑA NIETO, Bronisław KOMOROWSKI, Tony TAN, Jacob ZUMA, PARK Geun-hye and PRAYUT Chan-ocha (Chan-ocha is the family name, but according to Thai custom he is referred to by his given name).

Ranking Things Properly

I keep seeing things ranked improperly, so here is how to do it right.

Imagine that we have six candidates for an exam, and they score as follows. Ranking these candidates is very easy.

Name Score Rank
Abel 90% 1
Bohr 80% 2
Curie 70% 3
Dirac 60% 4
Einstein 50% 5
Feynman 40% 6

But what if two candidates have the same score? The correct way of ranking is to give both of these candidates the same rank, but then the next rank is one place lower. In the example below, Abel and Bohr both score 90% and are therefore ranked in first place; Curie then remains in third place, rather than being elevated to second.

Name Score Rank
Abel 90% 1
Bohr 90% 1
Curie 70% 3
Dirac 60% 4
Einstein 50% 5
Feynman 40% 6

This prevents a situation in which we have six participants, but the person with the lowest score is ranked fifth. If more than two participants have the same score, or if this situation occurs more than once, the same rule is applied.

Name Score Rank
Abel 90% 1
Bohr 90% 1
Curie 90% 1
Dirac 60% 4
Einstein 60% 4
Feynman 40% 6

Microscope Types

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Microscopes come in many forms.

Optical microscopes use visible light and glass lenses to image samples, and are limited to around two-thousand-times magnification and imaging samples down to 200 nanometres.

Electron microscopes use a fine beam of electrons to image samples by measuring how the beam is transmitted (or more rarely reflected) by the surface. Because the wavelength of an electron is much smaller than the wavelength of visible light, electron microscopes can magnify by ten million times and image samples down to 50 picometres (fifty trillionths of a metre). Electron microscopes use electrostatic and electromagnetic lenses to focus the electron beam and detect images with CCDs.

Scanning probe microscopes image a sample by running a physical object over the surface; the two most common types are the atomic force microscope (AFM) and the scanning tunnelling microscope (STM). Both AFM and STM can magnify by one hundred million times, and AFM produces a three-dimensional image of the sample being studied.

An AFM works by running a tiny sharp point attached to the end of a thin metal bar (a cantilever) over a surface and measuring the deflection of the cantilever. In Contact AFM the probe is in actual contact with the sample and deflection of the cantilever is measured directly. In Non-Contact AFM the probe is vibrated above the sample and changes in the vibration of the cantilever due to van der Waal’s forces between the probe and the sample are measured to create an image. Non-contact AFM has the advantage that is does not damage the AFM probe.

afm-probe-used

Used AFM probe.

A scanning tunnelling microscope makes use of a quantum mechanical effect known as quantum tunnelling. A conducting probe is brought close to the sample, and a voltage is applied between the sample and the probe. This causes electrons to “tunnel” through the vacuum between sample and probe, and this flow of electrons constitutes an electric current. As the probe is moved across the sample the current changes, and this changing current is used to create an image. STMs can only image conducting materials, so a very thin coating of a heavy metal like gold is usually applied. STMs are also more difficult to run, requiring a very good vacuum, but they can image larger areas and do so more quickly than an AFM.

STMs can also be used to move individual atoms, dragging them across a surface. IBM famously created a version of their logo by moving around thirty-five xenon atoms on a copper surface.

ibm-stm

Diamond Types and Colours

Diamonds can be classified as one of four types (Type Ia, Type Ib, Type IIa and Type IIb) according to the impurities that they contain. These impurities lend colour to the diamond, (though this colour can be artificially enhanced, for example by treating with ionising radiation).

diamond-colours

Type Ia diamonds are most common, making up about 98% of all natural diamonds. They contain small concentrations (0.3%) of nitrogen impurities. Type IaA diamonds contain pairs of nitrogen atoms, and are therefore colourless, and Type IaB diamonds contain large “clumps” of nitrogen atoms and absorb blue light, giving them a pale yellow/brown colour depending on the concentration of nitrogen.

Type Ib diamonds make up about 0.1% of natural diamonds, and contain a much lower concentration (0.05%) of nitrogen impurities, with the impurities clustered rather than widespread as in Type Ia diamonds. They absorb both blue and some green light, giving them a stronger yellow or brown colour. Synthetic diamonds are generally of Type Ib.

Type IIa diamonds (2% of natural diamonds) contain almost no impurities at all, and are therefore usually colourless.

Type IIb diamonds (0.1% of natural diamonds) contain almost no nitrogen impurities, but do contain significant quantities of boron which yields a light blue or grey colour. They are among the most expensive gem diamonds due to their rarity.

During the formation of any type of diamond a deformation of the lattice of carbon atoms that makes up the diamond can occur, which can lead to a wide range of colourings: red, pink, orange, yellow, brown and purple. This colouring can be removed by treating the diamond with high temperatures and pressures to remove the deformation, but this is often not done to retain the “fancy” colouring, which can demand the highest prices.