Dr Administrator
Author's posts
Jul 22 2010
The Periodic Table
Understanding the Periodic Table is very much like making love to a beautiful woman, there’s no point rote-learning the location of the different elements if you don’t know what they do… langtry_girl*
The Periodic Table of the Elements is a presentation of the known elements which provides information on the relationships between those elements in terms of their chemical and physical properties. An element is a type of atom: iron, helium, sulphur, aluminium are all examples of elements. Elements cannot be broken down chemically into other elements, but elements can change. An atom is comprised of electrons, protons and neutrons.
This is all very nice, but if you look around you: at the wallpaper, the computer screen, the table – very little of what you see is made from pure elements. They’re made from molecules (pure elements joined together), and the molecules are arranged in different ways which may be completely invisible. So in a sense the periodic table represents the bottom of the tree of knowledge for people interested in materials, other scientists may be more interested in what makes up the elements.
As a design, shown above, the periodic table is a cultural icon which everyone knows. Even if they don’t understand what it means, they know what it stands for – it stands for science. How to make sure people know your scene is set in a lab or your character is a scientist? Bung in a periodic table. It has been purloined to organise other sorts of information, such as Crispian Jago’s rather fine “Periodic Table of Irrational Nonsense“, some more examples here. There is a song.
At various times in my life I’ve been able to name and correctly locate all the elements in the periodic table, normally takes a bit of effort and some mnemonics to help. Increasingly now, I can remember the mnemonics but not the elements they refer to.
Different parts of the periodic table are important to different sorts of scientists. To organic chemists carbon (C), hydrogen (H), oxygen (O), nitrogen (N) hold the majority of their interest with walk on parts for some of the transition metals (the pink ones in a block in the middle) which act as catalysts. Inorganic chemists are more wide ranging, only really forbidden from the Noble Gases (helium (He), neon(Ne), argon (Ar), krypton (Kr), xenon (Xe)) which refuse to react with anything. Semi-conductor physicists are after the odd “semi-metals”: silicon (Si), indium (In), gallium (Ga), germanium (Ge), arsenic (As). For magnets there’s iron (Fe), cobalt (Co), nickel (Ni) along with other transition metals and the Lanthanides. The actinides are for nuclear physicists, radiation scientists and atomic bomb makers. Hydrogen is for cosmologists. In this view, as a soft condensed matter physicist, I am closest to the organic chemists.
I’m rather fond the periodic table, it is the scientist’s badge, but I’m scared of fluorine.
*To be fair to langtry_girl, I pondered on twitter “Trying to finish the sentence: “Understanding the Periodic Table is very much like making love to a beautiful woman…” and I think hers was the best reply. It is, of course, a reference to Swiss Toni.
Jul 20 2010
Some notes on SQL: 5 – database design
This is the fifth in a series of blog posts on SQL, the first covered creating a database, the second selecting information from a database, the third commands to modify the structure and contents of an existing database, the fourth on advanced selection. This post covers database design, as such it is a little lighter on the code examples. No claim of authority is made for these posts, they are mainly intended as my notes on the topic. These notes are based largely on Head First SQL.
The goal of database design is to produce a database which is straightforward and efficient to search. This is done by splitting data into a set of tables, with lookups between those tables used to build the desired output results.
Efficient database design is normally discussed with reference to “normal forms“, the goal being to reach the highest order normal form. In practice, pragmatism is applied which means it may be sensible to hold back a little on this.
(
sid INTEGER,
last_name VARCHAR(30),
first_name VARCHAR(30),
PRIMARY KEY (sid)
);
For a composite key, this form is used:
PRIMARY KEY (column_1,column_2,column_3)
In a normalised relation a non-key field must provide a fact about the key, the whole key and nothing but the key.
Relationships between tables in a database are indicated like this:
(
order_id INTEGER,
order_date DATE,
customer_sid INTEGER,
amount DOUBLE,
PRIMARY KEY (order_id),
FOREIGN KEY (customer_sid) REFERENCES customer(sid)
);
(Example borrowed from here). PRIMARY KEY and FOREIGN KEY are examples of ‘constraints’, primary keys must be unique and a foreign key value cannot be used in a table if it does not exist as a primary key in the referenced table. The CONSTRAINT keyword is used to give a name to a constraint (a constraint being one of NOT NULL, UNIQUE, CHECK, Primary Key, Foreign Key). CHECK is not supported in MySQL.
Keywords: PRIMARY KEY, CONSTRAINT, FOREIGN KEY, REFERENCES, CONSTRAINT
Jul 15 2010
On choice
Choose life. Choose a job. Choose a career. Choose a family. Choose a big fucking television. Choose washing machines, cars, compact disc players and electric tin openers. Choose good health, low cholesterol and dental insurance. Choose fixed interest mortgage payments. Choose a starter home. Choose your friends. Choose leisure wear and matching luggage. Choose a three-piece suite and higher purchase a wide range of fucking fabrics. Choose D.I.Y. and wondering who the fuck you are on Sunday morning. Choose sitting in a large couch watching mind-numbing spirit-crushing game shows stuffing fucking junk food in your mouth. Choose rotting away at the end of it all, pissing your last in a miserable home, nothing more than an embarrassment to the selfish fucked-up brats you’ve sworn to replace yourself. Choose your future, choose life. But why would you want to do a thing like that? I chose not to choose life. I chose something else. – Trainspotting by Irving Welsh (Screenplay by John Hodge)
For the last 20 years or so politicians have been keen on offering us choice, my message is “I don’t want choice”!
Choice of schools is something of an academic question for me since I don’t have any children but I grew up in rural Dorset and there the offer of choice would have been hollow. There were two primary schools in my village : one Roman Catholic and one Church of England, following that we went to the local “Middle School” one mile away – next nearest offering five miles away, followed by an upper school five miles away and the nearest alternative 10 miles and above away (to be honest I don’t even know where the alternative would be)… and this in an area with a rural transport system, not an urban one. A great deal of effort is expended in trying to rank schools, there’s evidence showing this process is not very accurate – the vast majority of schools are statistically indistinguishable. And who says schools are so important for education? My educational success is down, in large part, to the support of my parents but no-one seems to mention that. No one wants to say: actually your child’s education is very much down to you.
We get choice in medical care these days too but how am I supposed to judge the quality of a doctor or a hospital? Set some bright people a target and they’ll do a fine job of hitting it but is the target really representing the thing you want? People are actually quite keen to go to the hospital that’s close to them. Do we really expect patients to make an informed choice of which hospital is best for them from a medical point of view. I’m pretty sure I couldn’t make an accurate choice of the best hospital for medical care. Best hospital for me is easy: it’s the one about half a mile from my house. And what’s the message you’re sending when you’re offering a choice of hospital or doctor and providing data that purports to represent quality?:
“Here’s a bunch of hospitals – make sure you chose the best one. Do you feel lucky?”
I’d much rather you made sure that it didn’t matter which hospitals I went to.
People don’t actually like lots of choice, academic research on jam shows that consumers are more likely to buy jam from a choice of 6 types than from a selection of 24 types, too much choice confuses and causes unhappiness. This chimes with my experience, to a large extent I’ve given up being a rational economic agent, live’s too short to sweat over a choice of 100 different TVs.
This problem of ranking difficult to rank things is quite general, I experience it myself at work in my targets. I’ve come to the tentative conclusion that for people working in areas without clearly quantifiable outputs (number of strawberries picked, widgets sold, football games won), ranking really amounts to three buckets: sack, ok, promote. Your sack and promote buckets should really be pretty small. Yet we expend great effort on making more precise gradings. More interestingly I remember as I sat through an interminable college meeting discussing with an English fellow the marking of students. Normally for degree courses there’s a certain amount of second marking, in physics where there are definite answers second marking works fairly well but for my colleague in English one marker could mark a First and the other a 2.2/3rd, for the same essay!
Don’t give me choice, give me uniformity!
Jul 14 2010
Some notes on SQL: 4 – Advanced select
This is the fourth in a series of blog posts on SQL, the first covered creating a database, the second selecting information from a database, the third commands to modify the structure and contents of an existing database. This post covers more advanced commands for selecting information from a database and ways of manipulating the results returned. No claim of authority is made for these posts, they are mainly intended as my notes on the topic.
SQL supports CASE statements, similar to those which are found in a range of programming languages, they are used to write multiple comparison sequences more compactly:
UPDATE my_table
SET new_column = CASE
WHEN column1 = somevalue1 THEN newvalue1
WHEN column2 = somevalue2 THEN newvalue2
ELSE newvalue3
END;
The CASE statement can also be used in a SELECT:
SELECT title,
price,
budget = CASE price
WHEN price > 20.00 THEN ‘Expensive’
WHEN price BETWEEN 10.00 AND 19.99 THEN ‘Moderate’
WHEN price < 10.00 THEN ‘Inexpensive’
ELSE ‘Unknown’
END,
FROM titles
(This second example is from here)
The way in which results are returned from a SELECT statement can be controlled by the ORDER BY keyword with the ASC (or ASCENDING) and DESC (or DESCENDING) modifiers. Results can be ordered by multiple keys. The sort order is numbers before letters, and uppercase letters before lowercase letters.
SELECT title,purchased
FROM movie_table
ORDER BY title ASC, purchased DESC;
ASCENDING order is assumed in the absence of the explicit keyword.
There are various functions that can be applied to sets of rows returned in a query to produce a single value these include MIN, MAX, AVG, COUNT and SUM. The functions are used like this:
SELECT SUM(sales)
FROM cookie_sales
WHERE first_name = ‘Nicole’;
This returns a sum of all of the “sales” values returned by the WHERE clause. Related is DISTINCT which is a keyword rather than a function so the syntax is slightly different:
SELECT DISTINCT sale_date
FROM cookie_sales
ORDER BY sale_date;
This returns a set of unique dates in the sale_date column.
The GROUP BY keyword is used to facilitate the use of functions such as SUM etc which take multiple arguments to produce a single output, or to reduce a list to distinct elements (in these circumstances it is identical to the DISTINCT keyword but execution may be faster). The format for GROUP BY is shown, by example below:
SELECT first_name, SUM(sales)
FROM cookie_sales
GROUP BY first_name;
This will return a sum of the “sales” by each person identified by “first_name”. A final keyword used to control the output of a SELECT statement is the LIMIT keyword which can take one or two parameters the behaviour for the two forms is quite different. One parameter form:
SELECT * FROM your_table LIMIT 5;
This returns the first five results from a SELECT. Two parameter form:
SELECT * FROM your_table LIMIT 5, 5;
This returns results 6,7,8,9 and 10 from the SELECT. The first parameter is the index of the first result to return (starting at 0 for the first position) and the second parameter is the number of results to return.
Keywords: CASE, WHEN, THEN, ELSE, ORDER BY, ASC, DESC, DISTINCT, MIN, MAX, AVG, COUNT, SUM, GROUP BY, LIMIT
Jul 12 2010
How does a magnet work?
How does a magnet work? This question arose on “I’m a Scientist, Get me out of here“, a fine piece of science communication which involved putting scientists in contact with school children. This is my attempt at an answer, which says a bit more about science in general but is utterly untimely. The short answer to the question is that magnets are made from atoms which act like little magnets and in a proper magnet are all lined up, but as an answer this is somewhat unsatisfactory.
From a scientific point of view, what you’d commonly call magnets are just one group of magnetic materials – the ferromagnets. They are accompanied in early magnetism courses for aspiring physics students by paramagnetic and diamagnetic materials. A ferromagnetic material, like iron, is strongly attracted to a magnet, a paramagnetic material is weakly attracted and a diamagnetic material is very weakly repelled. Diamagnetism and paramagnetism are useful for scientific research but it is ferromagnetism where all the practical applications are found. Iron, cobolt and nickel are the only ferromagnetic elements.
At this point I am ashamed to admit I nearly missed out on a tortured analogy to explain magnetism but fortunately I caught myself in time! Imagine, if you will, a crowd bearing vuvuzelas. Individuals in this crowd can blow their vuvuzelas in any direction they please, however much we might wish they didn’t. In a ferromagnet groups of vuvuzela players spotting their neighbours spontaneously face the same direction to play their devilish instruments. The whole crowd may not be blowing them in the same direction but groups of them will. They can be marshalled to all blow their horns in the same direction by a band leader, and once pointing in the same direction they will continue to face that way, even in the absence of the band leader.
The individuals in this group are atoms in a material, and the vuvuzelas represent the magnetic field of a single atom. Groups of players facing in the same direction represent magnetic domains and the band leader represents an applied magnetic field. The point about ferromagnets is they massively enhance an a magnetic field applied by something like a coil of wire with a current flowing through it – this is how you make an electromagnet. The difference between a “magnet” and any old bit of ferromagnet is that in a “magnet” all the domains have been lined up to face the same way.
In paramagnetic materials vuvuzelas players ignore their neighbours and play away in random directions, they respond in a somewhat feeble fashion to the directions of the band leader.
In diamagnetic materials the crowd have no vuvuzelas but use their hands as a substitute, rather petulantly they face the opposite direction to that proposed by the band leader. In scientific language the hands represent induced magnetic dipole moments.
But why is an atom magnetic? An atom could be magnetic because the electron orbiting the nucleus acts like a little current loop, which gives it a magnetic field like a little bar magnet (posh name for “little bar magnet” is “magnetic dipole moment”) but actually the majority of the magnetic dipole moment of an atom comes from the intrinsic magnetic dipole moment of individual electrons.
We really don’t know why the electron acts as a magnetic dipole, it is ascribed to a property known as ‘spin’ but it can’t be spin as we normally define it since electrons are, as far as we can tell, point-like – nobody has every managed to measure the diameter of an electron. Therefore how can we meaningfully describe it as spinning? In a sense the origin of the electron magnetic dipole moment is not important, it exists, we know what it is and we can use the measured value in our calculations for designing magnetic materials. This question of the “why” of fundamental properties of sub-atomic particles is what string theory seeks to address. For most scientists the answer is unimportant for practical applications, but for physicists in particular it is a nagging unpleasantness that we don’t know why.
Magnetism and electricity have been known since antiquity but as two very separate phenomena, and unsurprisingly really. Magnetism is a property of some funny rocks (lodestone) whilst electricity is a property of rubbed materials, and lemons. The connection between the two is far from obvious, the link was made in the early part of the 19th century. This is a recurring theme in science, we blithely teach that such and such is true, implying that it’s truth is pretty much self-evident and elide the fact that for most of history we have not believed these things and that it has taken the painstaking work of a number of very great minds to reveal these self-evident truths. I must admit to being a little unsure of the history in this area, taught in England the key figures were Michael Faraday who did much of the experimental work in linking electricity and magnetism followed by James Clerk Maxwell who formulated a mathematical theory. In the experimental area in particular there were many other participants in the story, I suspect who takes centre stage depends on where you are taught.
So there you have it: magnets work because the vuvuzela players copy each other and play in the same direction.
About
I've worked as a scientist for the last 30 years, at various universities, a large home and personal care company, a startup in Liverpool called The Sensible Code Company (formerly ScraperWiki Ltd), GBG and now as a consultant in data science.
I write about:
* the books I have read, typically science and history (or both), partly as a reminder to myself and partly as a review;
* science, things I have done or things I find interesting;
* technology, programming and gadgets;
politics, and current affairs;
* ...and other stuff as it takes my fancy - holidays, photographs and things I want to remember.