Archive for January, 2012

A ‘Safe’ Dose?

January 30, 2012
Is there such a thing as a 'safe' exposure level to a hazard?

Is there such a thing as a 'safe' exposure level to a hazard?

In many areas of life we are exposed to hazards in the form of a substance or a process which may harm us. Mobile phones use microwaves – physically similar to those used for microwave cooking – but at a much lower power. We know that microwaves at high power are bad for us – think of microwaved meal . ANd we know that mobile phones are pretty safe – but is the exposure level from using a phone completely safe?

To the best of my knowledge, there is not a single case of a person having been harmed by using a phone (aside from as a result of the inattention they cause). But many people are still convinced that they are harmful. Indeed, for the people for whom this is a concern, the microwave radiation used by phones is intrinsically ‘bad’. And they would consider any level of exposure – no matter how low – to be dangerous. And that led me to wonder if the concept of a ‘safe dose’ really made sense?

One problem with microwaves, is that we can’t see them! And we never receive a large enough dose to sense them directly. This can lead us to either ignore the hazard (“Its all nonsense!”), or to become anxious that we are secretly being over-exposed (“They want to build a phone mast only 100 metres form my children’s school!”). So let’s first learn some lessons from two hazards with which we are more familiar: sound and light. Hazards? Surely exposure to sound and light is completely safe? Well, no. Exposure to loud sounds can cause deafness, and exposure to bright light – such as the Sun – can cause blindness. But it is not just excessively large exposures that cause problems.

Exposure to modestly loud noises does not cause immediate deafness, but prolonged exposure does reduce our hearing acuity, something we don’t usually notice for many decades. “I SAID WE DON’T NOTICE IT FOR DECADES!”. Similarly, exposure to normal sunlight causes a yellowing of the cornea which affects our vision in old age. So it is sensible to consider that exposures to sound and light should be limited so that in the course of our normal lives we are not unduly damaged.

But we also benefit from exposure to light and sound – indeed to withdraw exposure would be – quite literally – torture. As best we can tell, a whole lifetime of listening to sounds which are not-too-loud and exposing ourselves to light which is not-too-bright does us no harm and brings us wonderful benefits. So sound and light are not intrinsically ‘bad for us’ or ‘good for us’. What determines whether exposure to these ‘hazards’ is ‘safe’ is judged quantitatively, not qualitatively. For a hazard of this kind, the concept of a ‘safe dose’ makes sense, we get to enjoy the benefits and avoid the downsides.

What are the numbers for microwaves? The intensity of the microwaves inside a microwave oven is around 100,000 watts per square metre – definitely bad for you. By comparison the intensity of visible light from the full summer Sun is roughly 1,000 watts per square metre. And a mobile phone? A few millimetres from the phone surface the maximum intensity is around 0.1 watts per square metre.

Sound and light are familiar to us, and so it is easy to understand the balance required in terms of reducing our exposure to avoid future harm.  However microwaves are invisible and unfamiliar. So although the concept of determining a ‘safe dose’ quantitatively is reasonable, it is easy to understand why people feel suspicious that we are being secretly harmed. Trusting your health to a regulatory authority is not quite as reassuring as being able to trust your own judgement. But I can’t think of any alternative.


The Elements versus The Periodic Table

January 27, 2012
Elements versus PSE

Two iPhone Apps. Theodore Gray's 'The Elements' (left) or Merck's PSE-HD (right). Both apps are shown displaying basic information for Technetium.

Did I mention I had a new iPhone? Well obviously the first kind of app I downloaded was a periodic table of the elements – it just gave me a comfortable feeling knowing that I had that information close at hand. And what could be better than a Periodic Table app? Well, obviously two Periodic Table apps! And so here I compare the free Merck(TM) PSE HD app with the £6.99 app called ‘The Elements’.

Elements Technetium

'The Elements' page for Technetium. Touching the image allows you to rotate it and the text scrolls for an engaging description of the element.

The Elements is an app written with love by Theodore Gray, co-founder of Wolfram Research who make Mathematica. It is a simple app to understand and navigate. It has an introductory essay, a picture of the periodic table with animated pictures of each element, and splendid animation of the ‘The Elements’ Song by Tom Lehrer. Tapping on an element brings up a screen with a rotatable picture of the element, and an engagingly written essay by the author. I did find a tiny error on the page about Helium, but Theodore said he would fix that in the next release. Each essay links the physical properties and the history of the element and has links to the pages for other relevant elements (this makes it easy to browse and ‘get to know’ the elements).

The main attraction of this app is its accessibility – it is simple to use and a pleasure to interact with – one of those apps you will show your friends to make them think that your insanely expensive mobile phone might not have been a complete waste of money. On the down side, it is a bit limited and expensive as apps go. It does have links to Wolfram Alpha’s database on the elements, which is nice, but then you are back to browsing web pages.

Link to UK App Store

The Merck PSE (HD) has more data built-in to the app than The Elements, and it has many different ways to display and interact with the data. The main screen is a picture of the periodic table, and touching an element brings up a panel with basic information. Touching the panel causes it to flip and on its reverse are different categories of information shown in considerable detail, from the history and discovery of the element, to technical data. At this point the app is just ‘really useful’. But there is more: touching the Merck ‘M’ on the home screen brings up a new way of viewing the data where one can view how a property varies across the periodic table.

PSE Melting Temperature

Turning the control increases the temperature, and the periodic table graphically shows which elements are solid, liquid, and gas at that temperature.

For example, selecting ‘state at room temperature’ allows one to view the periodic table colour-coded as to the state (solid, liquid or gas) of the elements. A rotary control allows one to change the temperature and see visually which parts of the table melt and then vaporise in which temperature range: it is delightful. Similarly, selecting electronegativity shows how this property varies across the periodic table. Not sure what electronegativity is? Then select the glossary tab to find out.

PSE Electronegativity

The periodic table graphic shows how the electronegativity of a substance varies with position in the table.

My favourite is the discovery tab which allows you to scroll back through time and see when each element was discovered – and the app displays an image of the discoverer. And there is lots more too.

PSE Discovery

The faces of the people who discovered each element.

This app is data rich and carefully thought out. Having it on your phone gives you that comfortable feeling, knowing that even when your network connection is down, you will still have access to melting point data for the elements

Link to UK Apple App Store and  Android marketplace

Which is best? For people who enjoy tech lore, or if you’re studying Physics or Chemistry, then the Merck PSE app – for free – is a must have . For people who have £6.99 to spare – and are perhaps curious about science – but not professionally involved, ‘The Elements’ is a real pleasure to own.

A Silent National Disaster

January 25, 2012

At Protons for Breakfast I try to make the world of science accessible to ‘normal’ people i.e non-scientists. I use no maths, because the course is about ideas, but I do use words. However many adults in this country can’t read. And so there is universe of ideas to which these people don’t have access.

People who can’t read generally don’t make a fuss: they are embarrassed. And after they have left school, their whole lives are in no-small-part defined by their inability to read. And one in five adults in the UK is functionally illiterate.

Two fantastic friends of mine – Nick Ainley and Libby Coleman – have written a book and started a practical campaign to help any one person teach one other person to read. It’s called Yes we can read. They aim to reach non-readers one by one. At the moment their work is still a ripple, but I think it will become a wave.

Nick and Libby: You are my heroes.

Ground Source Heat Pumps are Solar Powered

January 23, 2012
Amplitude versus time versus depth

A simplified estimate of how the temperature of soil at selected depths varies through the year. Notice that at depth, the variations are minimal and lag behind the variations at the surface. However the average temperature is roughly the same as the average surface temperature, in this case 10 °C. Data are guesstimates adapted from here : please do not trust them! Click for larger version.

Sometimes I astonish myself with how stupid I can be.

At Protons for Breakfast last autumn I stated that geothermal energy supplies could only ever extract around 0.1 watts per square metre of ground. Why? Because that’s the average rate at which heat rises through the Earth. This is a ridiculously low figure, and I couldn’t understand how it made any sense. And then it clicked.

  • Geo-thermal energy isn’t sustainable, at least on a strict definition. It’s a one-shot operation that cools a reservoir over a decade or so, and then waits a few decades for the reservoir to heat up again.
  • Ground Source Heat Pumps don’t capture Geo-thermal energy – they capture Solar Energy and there is on average over the Earth around 240 watts per square metre of solar energy available.

I realised that I had confused these two sources for years, and browsing the web makes me think a lot of other people have too. Let me explain.

Geothermal energy is the heat flowing outward from the centre of the Earth. It arises in part from the radioactive decay of elements within the Earth, and in part from heat left over from the formation of the Earth. The Earth’s crust is an excellent insulator and the heat only flows out slowly. Across the UK, the average heat flow is just 0.038 watts per square metre, which means that in order to generate the 10 kW one needs to heat a house, one requires an area of around 500 metres x 500 metres – and drilling down doesn’t increase this figure at all. However there are two situations in which we can extract this heat and use it.

  1. In areas of the Earth where the heat flow is stronger than average (e.g. Iceland) it would be perverse not to exploit the gift of heat.
  2. The second situation is more common and involves drilling down to around 3 km depth where the temperature is around 100 ºC. If the rocks are porous at this depth then we can pump cold water in to the rocks, and extract hot water. The porosity of the rock allows the water to accept heat from a large volume of rock. This is not strictly sustainable in that the block of rock will cool down over a few years, and we will need to leave it to warm again. But it will keep warming up for millions of years to come.

Both these schemes extract genuine geothermal energy, which originated on Earth, roughly one half it, nuclear in origin.

Ground Source Heat pumps collect heat in the top few metres of the Earth and here the temperature is strongly affected by the temperature of the surface. And  this is determined by the  local average heating from the Sun, typically around 240 watts per square metre. Even in areas with cold winters, if one digs down more than a few metres, the soil stays warm , and a heat pump can be used to extract this heat. The pump chills a fluid such as ammonia to around 3 °C and then passes it through the buried pipes. Being colder than the surrounding soil, the ammonia absorbs heat from the soil, and evaporates. When compressed, the heat is released at a temperature of around 20 °C which can be used to heat a house.

However the source of the energy is the Sun not the Earth, and so 100% of it comes from nuclear fusion.

Global Warming Mug

January 20, 2012

I got a Global Warming Mug for my birthday!

The blurb:

  • Have you ever wondered what the world would like if the polar ice caps melted?
    •  Now you can ponder the question over a cup of tea 🙂
  • WATCH land mass get swallowed by Atlantic
  • SEE Valuable water front property get turned into a modern day Atlantis

I certainly hope the mug exaggerates the imminent effects of Global Warming.

P.S. Thanks to Andrew & Sharmila

Arctic Sea Ice: Volume and Area

January 18, 2012
Arctic Sea Ice Volume

An estimate of Arctic Sea Ice Volume from 1980 to the end of 2011. Notice that the trend on the minimum volume, which occurs in the Arctic summer, looks as if it will reach zero within the next decade. Click on the graph for a larger version.

I have mentioned previously that the area of sea ice in the arctic is showing a dramatic decline – at the least the Financial Times thinks so. The area of sea ice is relatively straightforward to monitor from satellites, and data is available here. But what about the volume of the sea ice?

If the area is shrinking, one would have to guess that there would be some effect on ice thickness as well. This is not straightforward to measure, or to model, but this week I came across a pretty terrifying estimate of how the sea ice volume is varying. The data from the Polar Science Centre is available here and there is a commentary on the data here. The full dataset is shown on the graph at the head of the page. Shockingly the implication is that the minimum volume of sea ice could reach zero – i.e.no arctic sea ice in the summer – sometime around 2020.

Of  course there is significant uncertainty in this model, and it could be just wrong. Arch climate skeptic and contrarian Anthony Watts certainly thinks so. Personally I am prepared to let time be the judge – it doesn’t look like we will have to wait for many summers before the truth becomes clear.

Looking on the bright side, perhaps this is the shock we need.  As we have seen repeatedly, countries such as the USA and China are able to use scientific uncertainty as an excuse for their understandable reluctance to change. This may not convince climate scientists, but it is enough to convince a fair proportion of their electorate who too are understandably reluctant to change. I think if the entire Arctic ocean melted one summer soon, that this could be a wake up call to us all. Let’s hope so.

Wind Power Wow!

January 16, 2012
Wind Turbines off Llandudno in North Wales

Wind Turbines off Llandudno in North Wales: Click for larger Image

In my humble opinion, wind power is one of the simplest, most inoffensive ways to generate renewable electricity. Libertarians with country cottages in the Lake District  🙂 criticise wind power because it is (a) not very effective, (b) offensive to the eye, and (c) more expensive than burning coal. I disagree with all these criticisms.

  • Firstly it is effective. Reuters report that at the height of storms in December 2011, wind power provided 12% of UK electricity requirements. Wow! And more significantly, on average in 2011 it provided 5% of UK electricity requirements. That is a pretty effective generation on any terms and it should grow in the coming decade.
  • Secondly, I think wind turbines are beautiful – breathtaking engineering structures that are the embodiment of our respect and understanding of the natural world. They say loud and clear that we have understood that carbon dioxide emissions are pollution and that we are going to reduce the damage we do to our climate and try to live sustainably
  • And finally, although it is more expensive than burning coal, I think our collective choice to generate electricity this way is real sign of our civilisation – something to be proud of.

Body Weight Simulator

January 13, 2012
Body Weight Simulator

Screenshot of the Body Weight Simulator. At last a piece of software that explains why its hard to keep the weight off - and uses realistic numbers. Click for larger image: See text for link.

As I mentioned back in November 2011 (The Mass of Sisyphus) I don’t seem to be able to keep my weight stable at a level with which I am comfortable. Since I wrote that, I have lost around 6 kg but I seem to be stuck at about 80 kg. Now I have at last found an explanation based on physiology and physics.

The Body Weight Simulator is available is a piece of ‘java’ software from the US National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The software runs directly from your web browser and requires various inputs (mainly initial weight, height, age and level of activity) that allows it to estimate how many food calories you require each day. Significantly this number differs from the standard numbers for adults (e.g. 2500 calories for an adult male).

One of the insights embodied in the software is that heavier people have a higher calorific requirement. So if you restrict your diet by 500 calories per day, your weight will not fall indefinitely, but stabilise at a new lower value. This is what I have observed previously, but never really understood.

For example it tells me to that get from 80 kg to 75 kg in 50 days I need to restrict my diet by around 713 calories per day (if I don’t do any extra exercise). Additionally it tells me that in order to maintain a weight of 75kg, I need to restrict my calorie intake permanently by 87 calories a day compared to what I am doing now.

It’s possible to cut and paste the predicted weight data and so I can compare theory and experiment – see below – and the numbers are sort of plausible.

Dieting Graph

I have been on a diet since 16th October 2011 and the graph below shows my weight versus the prediction of the body weight simulator for a 700 calorie restriction in my diet which stopped after 70 days. The agreement is plausible.

So now I will sit at my computer for even longer and consider strategies which will allow me to reach – and maintain – a body weight of 75 kg. Mmmm. Or maybe I should just go for a run…

Mobile Phone Safety: An Interesting Graph

January 11, 2012

Incidence of Cancers of the Central Nervous System: This graph is featured at the head of an article about increases in brain tumours arising from the use of mobile phones.

I came across the graph at the head of the page while looking at an article which asserted that there was evidence that mobile phones do indeed cause cancer. I was at first shocked – I had searched for data of this kind and found only data showing no detectable trend.  And then I was angered – because the rise seen in this graph very obviously has nothing to do with mobile phones!

The offending page (The million dollar question: What is the risk of brain cancer from cell phone radiation?)is authored by one Dariusz Leszczynski and he comments on it thus:

The graph presented above, which has been generated by the Finnish Cancer Registry, shows a steady increase in brain and nervous system cancer cases among Finnish women and, to a lesser extent, among Finnish men. Therefore, the “urban legend” that there has been no increase in brain cancer cases in recent years should be put to rest.

The implication in this context is clear: that this rise is in someway connected with mobile phone use. Now Dariusz does go on to say…

…we should remain cautious and not jump to the easy conclusion that cell phone radiation is responsible. Cell phone radiation may be the cause for the increase, but there have been other changes to the way we live and our environment, and so it might not be.

My problem with this is that contrary his assertion, Cell phone radiation could not possibly be the cause of the rise.  Look at the dates! There is a clear rise in cancers of the brain and central nervous system starting in around 1960. Yes 1960. A quick browse of Wikipedia confirms that something called a ‘mobile phone’ did exist in the 1960’s, but it was rare and could not conceivably be the cause of the observed rise.

  • If a tiny number of phones in the 1960’s immediately caused an increase in cancer rates as shown, then the millions of phones we use now would cause the above graph to skyrocket.
  • Alternatively, if there was a latency period – as one would predict if mobile phone use did indeed cause cancer – then where is it? The data would be flat and then show rise after perhaps twenty years of use – that’s the typical latency between starting smoking and getting cancer.
  • Finally, notice that in the period since 1990 when mobile phone use has exploded, all that can be seen is exactly the same trend as seen in the 1960’s – but possibly flattening off.

So the the rise seen in the graph above cannot possibly be associated with mobile phone use. So what did cause it? Well, I don’t know, but I would suggest it arises as the product of improved healthcare resulting improved diagnosis, coupled with improved life expectancy – the graph below shows life expectancy for Finland using data from the wonderful  Gap Minder. The data are nominally age compensated but as this page explains, the compensation is complicated.

I am not saying that mobile phones do not cause cancer: I don’t know whether they do or they don’t. I feel sure that time will tell. However, having looked for evidence that they do cause harm, I have never found any evidence of harm. And indeed the graph shown at the head of the page is actually evidence that the exponential increase in mobile phone use was not the cause of the observed rise.

LIfe Expectancy in Finland: Data from Gapminder.org

Looking closer at Argon

January 9, 2012
Graph showing the relative mass of atoms as the number of protons - the atomic number - increases. Notice that Argon is out of sequence - it is heavier than the element with one more proton. Why?
Graph showing the relative mass of atoms as the number of protons – the atomic number – increases. Roughly speaking the relative atomic mass increases linearly with the number of protons – but notice that argon is unusual. It is heavier than the element with one more proton – potassium. Why?

It never fails to amaze me how dumb I can be!

I have just spent three years making all kinds of precision measurements on argon gas, but it took a chance remark from Andrew Marmary in a short movie on the RI Channel to alert me to a simple astonishing fact: argon atoms – with 18 protons in each nucleus are on average heavier than potassium atoms which have one more proton in each nucleus. It’s a simple fact that hides a remarkable story!

The relative mass of atoms of each element is tabulated at the end of this article, and shown as a graph at the top of the page. The Atomic Number is the number of protons in the nucleus of each atom and the relative atomic mass is – very roughly – the combined number of neutrons and protons in the nucleus. So for example, a hydrogen atom has 1 proton and no neutrons has a relative atomic mass of 1. Helium atoms have 2 protons and 2 neutrons a relative atomic mass of 4. The graph shows that atoms with more protons in the nucleus tend to have around one extra neutron for each extra proton – but not exactly one. Notice that the relative atomic masses do not fall exactly on the red dotted line, but ‘wiggle’ a little. And some atoms such as chlorine – with 17 protons – have a relative atomic mass of 35.45 no where near an integer. Does a chlorine nucleus contain a fraction of a neutron? No. But to understand this we need to learn about isotopes

Even pure elements contain atoms with different numbers of neutrons. Naturally occurring chlorine, for example, has two isotopes both with 17 protons, but one has 18 neutrons and a relative mass of approximately 35 and the other has 20 neutrons and a relative mass of approximately 37. The former type outnumbers the latter by approximately 3 to 1 so the average mass of chlorine atoms turns out to be roughly 35.5.

So what about argon? Does that have isotopes too? Yes. Argon in the atmosphere has three isotopes, all with 18 protons – but one type (called 36Ar) has 18 neutrons and a relative mass of approximately 36 ; a second type (called 38Ar) has 20 neutrons and a relative mass of approximately 38, and the final and most common type (called 40Ar) one has 22 neutrons and a relative mass of approximately 40. Measurements made by my colleagues at the Scottish Universities Environmental Research Centre have shown that in normal argon there is roughly 300 times more 40Ar than 36Ar – and that  38Ar is even rarer. That is why the average atomic mass is just a little less than 40.

The astonishing fact is is that if we had made this measurement 4 billion years ago as the Earth formed, or if we made the measurement on argon gas from another planet – we would get a different answer – an answer much closer to 36. That is because the ‘natural’ argon is actually the 36Ar. If we re-plot the experimental data from the head of the page, but with a mass of of 36 for argon instead of the experimental value, then we see that the point fits neatly on the line.

So where did all the 40Ar come from? The answer is that it came from the radioactive decay of potassium-40 (40K). Most potassium on Earth has 20 neutrons (39K) giving potassium a relative mass close to 39. However, there is a small amount of potassium with 22 neutrons (41K) giving of potassium a relative mass slightly greater than 39. Additionally there is an even tinier amount of potassium with 21 neutrons (40K) and this isotope is radioactive, and decays into 40Ar with a half-life of around 1.2 billion years. So over the course of the Earth’s 4 billion year history around 90% of our original gift of  40K has decayed into 40Ar

In the solar system, argon is actually more common than potassium but on Earth potassium if far more abundant than argon. And so even though  (40K) is a tiny fraction of the potassium atoms on Earth – there is so much potassium (its about 1/500th part of the Earth by weight) that 40Ar from the radioactive decay of 40K is now the dominant isotope of argon on Earth.

So the graph at the head of the page seems mute, but if one can read the data and spot the patterns, one finds that the graph speaks volumes. It speaks of the history of the Earth and of the birth of the elements in the death throes of stars (Nucleosynthesis). Wow! And how could I not have noticed?

Data I took the data below from Wikipedia, so I know it must be correct 🙂

Atomic Number Symbol Name Relative Mass
1 H Hydrogen 1.01
2 He Helium 4.00
3 Li Lithium 6.94
4 Be Beryllium 9.01
5 B Boron 10.81
6 C Carbon 12.01
7 N Nitrogen 14.01
8 O Oxygen 16.00
9 F Fluorine 19.00
10 Ne Neon 20.18
11 Na Sodium 22.99
12 Mg Magnesium 24.31
13 Al Aluminium 26.98
14 Si Silicon 28.09
15 P Phosphorus 30.97
16 S Sulfur 32.07
17 Cl Chlorine 35.45
18 Ar Argon 39.95
19 K Potassium 39.10
20 Ca Calcium 40.08
21 Sc Scandium 44.96
22 Ti Titanium 47.87
23 V Vanadium 50.94
24 Cr Chromium 52.00
25 Mn Manganese 54.94
26 Fe Iron 55.85
27 Co Cobalt 58.93
28 Ni Nickel 58.69
29 Cu Copper 63.55
30 Zn Zinc 65.38
31 Ga Gallium 69.72
32 Ge Germanium 72.64
33 As Arsenic 74.92
34 Se Selenium 78.96
35 Br Bromine 79.90
36 Kr Krypton 83.80
37 Rb Rubidium 85.47
38 Sr Strontium 87.62
39 Y Yttrium 88.91
40 Zr Zirconium 91.22
41 Nb Niobium 92.91
42 Mo Molybdenum 95.96
43 Tc Technetium
44 Ru Ruthenium 101.07
45 Rh Rhodium 102.91
46 Pd Palladium 106.42
47 Ag Silver 107.87
48 Cd Cadmium 112.41
49 In Indium 114.82
50 Sn Tin 118.71
51 Sb Antimony 121.76
52 Te Tellurium 127.60
53 I Iodine 126.90
54 Xe Xenon 131.29
55 Cs Caesium 132.91
56 Ba Barium 137.33
57 La Lanthanum 138.91
58 Ce Cerium 140.12
59 Pr Praseodymium 140.91
60 Nd Neodymium 144.24
61 Pm Promethium
62 Sm Samarium 150.36
63 Eu Europium 151.96
64 Gd Gadolinium 157.25
65 Tb Terbium 158.93
66 Dy Dysprosium 162.50
67 Ho Holmium 164.93
68 Er Erbium 167.26
69 Tm Thulium 168.93
70 Yb Ytterbium 173.05
71 Lu Lutetium 174.97
72 Hf Hafnium 178.49
73 Ta Tantalum 180.95
74 W Tungsten 183.84
75 Re Rhenium 186.21
76 Os Osmium 190.23
77 Ir Iridium 192.22
78 Pt Platinum 195.08
79 Au Gold 196.97
80 Hg Mercury 200.59
81 Tl Thallium 204.38
82 Pb Lead 207.21
83 Bi Bismuth 208.98

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