MrReid.org

Patterns in birthdays

If births were evenly distributed throughout the year (i.e. a 1 in 365 chance of being born on any given day) then the graph of number of births against birth month would look like the one below:

You’re least likely to be born in February, because it only has 28 days, and then slightly more likely to be born in the 31-day months of January, March, May, July, August, October and December than in the 30-day months of April, June, September and November.

I took the data from nearly a thousand pupils and looked at how their dates of birth compared with the expected values. (Included with the data are error bars of one standard deviation.)

The results for April, September and December (particularly December) show birth rates above what would be expected if births are random, and the results for July and August show depressed birth rates.

Considering the months where births are more likely than they should be and working backwards we find the most likely “sex months” to be March, July and December. These seem fairly sensible as all of these months coincide with major holiday periods: Easter, the long Summer Holiday and Christmas/New Year. People are more likely to be “celebrating” and to have more free time during these periods, and March and December have long, cold and dark nights when people are more likely to stay indoors in the evening than go out.

The “sex months” for the lowest birth rates are more puzzling: October and November. I suspect that it has to do with Seasonal Affective Disorder (SAD) and that the generalised depression that comes with SAD includes reduced sex drive; this is combated come December by the general presence of good cheer and plenty of alcohol to lower inhibitions. It is also possible that parents are deliberately choosing when to conceive in order to avoid their child being the youngest in the school year, something that has been shown* to have a negative effect.

Update: Thanks to @S3ym5n I’ve now included national data for 2010.

In the national data it is September and October that show birth rates above what is expected, making December and January the most popular sex months. April appears to be the only month with a significantly lower birth rate, making July, when people are out and about in the nice weather rather than stuck indoors, the least popular sex month.

Continue reading →

Tagged birth, sex | Leave a comment |

Curiosity’s nuclear battery

Posted on 14th December by Mr Reid

The Curiosity rover that is the main part of the Mars Science Laboratory mission is very different from its predecessors Sojourner and the twin rovers Spirit & Opportunity.

L-R: Spirit/Opportunity, Sojourner and Curiosity.

L-R: The wheels of Sojourner, Spirit/Opportunity and Curiosity.

Curiosity is nearly twice as long as Spirit/Opportunity and has more than five times the mass; at 2.1 metres in height it is taller than most of the people that built it.

For me, the most interesting difference between Curiosity and the other Mars rovers is its power source. Both Sojourner and Spirit/Opportunity were powered by solar cells but Curiosity is powered by a radioisotope thermoelectric generator (RTG), in particular the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) built by Pratt & Whitney’s Rocketdyne division.

Curiosity’s RTG is the large unit attached to the rover’s rear.

The main problem with using solar cells for power is that the cells only work during daylight hours and don’t function well at high latitudes where there is less sunlight; Spirit/Opportunity’s cells only worked at full strength for about four hours per day, producing about 900 watt hours (about 3.2 megajoules) per day at best. Mars is covered in fine dust and dust covering solar panels was a problem for the Spirit and Opportunity rovers, though this dust was occasionally blown away by high winds.

Spirit’s solar panels before and after a “cleaning event”.

RTGs work via the Seebeck effect, where a difference in temperature between between the two junctions of a thermocouple cause an electric current to be produced. The heat source in an RTG is the decay of a radioactive isotope; in the case of most RTGs this isotope is plutonium-238 in the form of plutonium dioxide. Pu-238 is a nearly pure alpha emitter and therefore requires only minimal shielding.

A pellet of ²³⁸PuO₂ glows red hot from internal radioactive decay.

The MMRTG uses 32 marshmallow-sized plutonium pellets and will initially produce about 125 watts of electrical power (from 2000 watts of thermal power), but this will drop off over time as the plutonium decays. The MMRTG will consistently produce about 2500 watt hours of electricity per day compared with Spirit/Opportunity’s average of 600 Wh and this will enable Curiosity to operate in all seasons and at all times of day.

Curiosity’s MMRTG before installation.

Tagged mars, nuclear, RTG | 2 Comments |

You’ve already experienced the earliest Easter you’ll ever know

Posted on 12th December by Mr Reid

You may have noticed that the date of Easter Sunday changes every year:

The date of Easter Sunday is calculated using a calendar that is based both on the Sun and the Moon* and takes place “on the first Sunday after the Paschal Full Moon”. Because the Gregorian calendar is based on the Sun only, the date of Easter changes from year to year.

The Paschal Full Moon is based not on an actual astronomical event but on historical tables established by a bunch of religious guys in 325AD, and its date can be up to ± 2 days from the actual astronomical Full Moon. The Paschal Full Moon is selected as the first of the Full Moons recorded in these tables to follow the March Equinox (also known as the vernal equinox as it is the day on which the night and day are the same length when heading into Spring in the northern hemisphere and coming from the Latin ver for spring).

When a line connecting adjacent dates is drawn a pattern becomes obvious, especially when the scale is compressed.

The earliest Easter can possibly fall is March 22nd, though this is very rare, occurring most recently in 1818 and next in 2285. The next earliest date is March 23rd, as it was in 2008 and this will not happen again until 2160, by which time you will be dead.

The latest date Easter can occur is April 25th, which last occurred in 1943 and will next occur in 2038. The cycle for Easter dates repeats every 5 700 000 years exactly, and the most common date within that cycle is April 19th, occurring in 3.9% of cases. Easter moving around to the extent explained above is a real pain and in my opinion we should all just agree that from now on Easter Sunday is always the nearest Sunday to April 19th.

* Lunisolar calendars like this are used by many Jews, Buddhists, and some Hindus as well as those in Burma, China, Korea, Mongolia, Tibet and Vietnam.

Tagged date, easter | 1 Comment |

Logarithmic scales

Posted on 6th December by Mr Reid

Some of the quantities measured in physics cover a very large range of values and this can make displaying measurements of their value difficult or confusing.

pH, traditionally thought of as a measurement of acidity, but actually a measurement of the concentration of hydrogen ions,* is one such quantity. Stomach acid has a concentration of hydrogen ions of 0.1 per mole; bleach has a concentration of hydrogen ions of 0.0000000000001 per mole.

In order to have a sensible scale by which to judge acidity a logarithmic scale is used: pH is the negative of the logarithm of the concentration of hydrogen ions, so for stomach acid pH = −log(0.1) = 1.0 and for bleach pH = −log(0.0000000000001) = 13.

As can be seen from the graph above, it becomes very difficult to tell the difference between H⁺ concentration beyond pH 2 or 3. But on a logarithmic scale the difference is clearly visible:

There has been some fuss on various blogs about a chart from the Minnesota Dental Association (58kB, .PDF) listing the acidity of various sweets. One sweet, WarHeads Sour Spray is listed as having a pH of 1.6, which when compared with battery acid at pH 1.0 sounds very alarming. But when the logarithmic scale is taken into account an increase of 0.6 on the pH scale is equivalent to a four-fold decrease in acidity — Sour Spray is only one-quarter as acidic as battery acid (that’s still pretty acidic, by the way, and not terribly good for your teeth).

The moment magnitude scale used to measure the strength of earthquakes is another logarithmic scale. Earthquakes vary in size (i.e. in the energy they release) from the giant M_W 9.5 earthquake in Chile in 1960 to tiny tremors caused by large vehicles going past and so a logarithmic scale is required. Because of the way that the moment magnitude scale is calculated an increase in moment magnitude of 1.0 indicates a 31.6-fold (10^1.5) increase in the amount of energy released (an increase in moment magnitude of two is equivalent to a 1000-fold (10³) increase).

* For the sake of simplicity I’m ignoring the effect of the activity factor, the tendency of hydrogen ions to interact, on pH.

Tagged logarithmic, pH, scale | Leave a comment |

The Milky Way is shaped like a CD

Posted on 1st December by Mr Reid

The Earth orbits just one of the 200 – 400 billion stars that make up the Milky Way. This star, the Sun, orbits at a distance of about 27000 light years from the Galactic Centre, travelling at 220 km/s (one mile every seven thousandths of a second).

The Milky Way is about 100000 light years across, but only about 1000 light years in height, making it about one hundred times wider than it is tall. To scale, viewed from side on, it would look like the line below:

With a thickness of 1.2 millimetres and a diameter of 120 millimetres a standard CD or DVD has exactly the same thickness:width ratio as the Milky Way; you could correctly describe our galaxy as “CD-shaped”.

Tagged milkyway, space | Leave a comment |

The speed of jet lag

Posted on 28th November by Mr Reid

Jet lag (ICD-10: G47.2) occurs when the body’s internal clock (its circadian rhythm) gets out of sync with the time of day.

Example: London to Los Angeles

Leaving London at 1200 you will arrive in Los Angeles ten hours later and your body will feel like the time is 2200. The actual time will be 1400 and so your body expects it to be late night, but it’s actually the middle of the day: an offset of eight hours. Travelling back, leaving Los Angeles at 1200 you will arrive in London ten hours later and again feel like the time is 2200, but it will actually be 0600 the next day; your body expects late evening but gets early morning: an offset of sixteen hours. The difference in these offsets is what gives rise to the fact that travelling west to east causes worse jet lag than travelling in the opposite direction.

Jet lag only occurs when travel causes a difference between the internal and real clocks. If you take anything more than one hour to travel a time difference of one hour then jet lag does not occur. Also, flying north to south doesn’t cross any time zones and therefore jet lag does not occur; flying from Cape Town to Stockholm, for example, is safe for your body clock.

The Earth rotates once per day and therefore contains twenty-four time zones, spaced evenly apart. Turning through 360° in twenty-four hours is equivalent to 15° per hour. At the equator, fifteen degrees of longitude is equivalent to 1670 kilometres so an aeroplane flying along the equator would have to travel at a speed of at least 1670 kilometres per hour (over 1000 mph) for jet lag to occur. At a latitude of 45° (north or south) this 15° is only 1180 kilometres, reducing the speed of jet lag to 734 mph.

Both of the situations above assume that plane fly directly along lines of latitude, but this never happens. In reality planes fly “great circle” paths (see the previous post about geodesics) and travelling along great circle paths, especially those that fly close to or over the poles where time zones are “thinner”, lowers the speed of jet lag to below the 500 – 600 mph speed of an aeroplane.

The narrowing of time zones at northern latitudes is obvious in this map of Western Europe.

Tagged jetlag, time | Leave a comment |

Types of Desert

Posted on 24th November by Mr Reid

A desert is defined as an area that receives a very small amount of precipitation: these areas come in three main forms.

The most recognisable type of desert is the subtropical desert, typified by the Saharan and Arabian deserts. They are the hottest deserts and any rain that does fall often evaporates before it hits the ground.

The Sahara Desert in North Africa.

The Earth has two polar deserts, the Arctic and the Antarctic. At 13.9 million square kilometres the Antarctic Desert is by far Earth’s largest, more than one and a half times the size of the next largest desert, the Sahara.

The Antarctic Desert at the South Pole

Cold winter deserts, like the Gobi Desert in China and Mongolia, are often created by the rain shadow effect in which a tall mountain range causes warm moist air to rise and cool. As the air cools water vapour condenses out and falls as rain or snow, leaving the air dry and creating a desert on the lee (upwind) side of the mountain. For example, the Gobi Desert is created by the Himalaya Mountains; the Patagonian Desert in South America by the Andes; and the Great Basin Desert in the western United States by the Sierra Nevada.

The Gobi Desert, north-east of the Himalaya Mountains.

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UK electricity import and export

Posted on 20th November by Mr Reid

The UK doesn’t have enough electricity.

The amount of electricity that the UK produces (from various sources) is not enough to meet demand, and the UK relies heavily* on imports from France and the Netherlands in order to meet its needs. This energy gap is due to the closure of coal-fired power stations that cannot meet emission standards and the shutdown of aging nuclear power stations.

The import and export of electricty uses submarine high voltage direct current (HVDC) cables. HVDC cables waste less electricity than AC cables (about 3% per 1000km) and are simpler to construct and operate. A 73 km cable connects Bonningues-lès-Calais in France to Sellindge in Kent; a 55 km cable connects Auchencrosh in Scotland and Ballycronan More in Ireland; and a 260 km cable connects Maasvlakte in the Netherlands to Grain in Kent.

The graph below shows electricity import and export (in GWh) for the eight months since February†, when the Britned Interconnector began operating. When the value is positive (when the line is above the origin) the UK is importing electricity and when it is negative electricity is being exported.

One of the most interesting features of the graph is the change in the import/export to Ireland via the Moyle Interconnector. On 26th June at 0417 one of the 250 megawatt cables failed, halving the cable’s capacity, and at 1409 on 24th August the cable failed entirely and has not transferred any electricity since.

The cause of the failure is unknown and the MV North Sea Giant, the world’s longest offshore construction vessel, is currently moored in the Irish Sea investigating the fault. The cable has been dug out of the seabed 200m below the surface, cut in half, and both ends raised to the surface so the cause of the fault can be investigated. The fault is expected to take up to six months to fix and were a similar fate to befall the Cross-Channel or Britned interconnector the UK would have a very serious energy problem.

If it is to close the growing energy gap the UK must accelerate the pace of construction of energy infrastructure, in particular the construction of safe, zero-carbon nuclear power stations.

* The UK is the world’s sixth largest importer of electricity despite being eleventh in terms of electricity production and twenty-second in terms of population.

† The graph shows a seven day moving average of import/export values. For half-hourly data you can download the full dataset as an Excel spreadsheet.

Tagged electricity, energy | Leave a comment |

The Moses Bridge

Posted on 14th November by Mr Reid

The Moses Bridge, designed by Ro & Ad Architects in the Netherlands is my new favourite water crossing (taking over from the Magdeburg Water Bridge). The bridge allows visitors to cross the West Brabantse Waterline to reach Fort de Roovere.

Tagged architecture, bridge | Leave a comment |

Why does metal feel cold?

Posted on 8th November by Mr Reid

One adjective commonly used to describe metals, along with the adjectives like “shiny” and “silvery”, is “cold”.

But this doesn’t makes any sense when you take the Zeroth Law of Thermodynamics into account. Over a long enough period, everything in the same location will tend* to the same temperature, so any metal must be at the same temperature as its surroundings.

So why does metal feel cold?

Metals feel cold because they are very good conductors. Both the metal blade and wooden handle of a shovel left out in the Sun will be at the same temperature but the blade will feel colder because the metal is a good conductor: it “sucks” the heat out of your fingers and this heat leaving your fingers is what makes them feel cold.

Fifteen minute timelapse of melting ice cubes.

In the video above identical ice cubes placed on a wooden board and a metal heatsink removed from a broken laptop computer melt at vastly different rates. The wood is a poor conductor and so the ice cube takes a long time to melt; the opposite is true for the metal heatsink.

* I’m using “tend” in the physics sense of “to approach” rather than the general public sense of “to occur frequently” or “to look after”.

Star traveller etymology

Posted on 2nd November by Mr Reid

The term astronaut comes from the two Greek words: ástron (star) and nautes (traveller), making an astronaut a “star traveller”. In Russia astronauts have always been known as cosmonauts, an anglicised version of the Russian word kosmonavt (originally from the Greek kosmos meaning “universe”) and the difference between the two terms used seems to have encouraged other nations.

Officially the Chinese use “astronaut” when writing in English and “cosmonaut” when writing in Russian but the term taikonaut (from the Chinese taikong for “space”) has often been used by non-Chinese media. The French have used spationaut, from the Latin word for space spatium and some have suggested that the Indian space program should use anthanaut from the Hindi anthariksh, also meaning “space”.

Tagged language, space | 1 Comment |

Looking at constellations from a different angle

Posted on 30th October by Mr Reid

You are probably familiar with the constellation of Orion (The Hunter), in particular with the asterism that makes up Orion’s Belt.

Because of the way the right ascension data is plotted the images shown here are how they would appear to a distant observer looking at Orion towards Earth.

Because stars are so far away we tend to think of them as being painted onto a surface at a fixed distance — “like a huge picture painted on the sphere of the sky”. But if you look at the stars in three dimensions then Orion looks very different.

From above it’s difficult to recognise Orion’s shape as the lines connecting the two rightmost stars (Betelgeuse and Saiph) to the rightmost star of Orion’s belt (Alnitak) overlap:

From the side the shape is more obvious. Alnilam, the middle star of Orion’s belt is by far the furthest star, more than 1300 light years away from Earth:

This post was inspired by an arXiv paper* by Dr Daniel Brown from the School of Science and Technology at Nottingham Trent University. You can download the data I used as an Excel spreadsheet (.XLS, 29 kB).

* Daniel Brown (2011) “The Orion constellation becomes installation: An innovative three dimensional teaching and learning environment”, arXiv:1110.3469v1 [physics.ed-ph].

Tagged space, stars | Leave a comment |

Dating a common ancestor

Posted on 26th October by Mr Reid

Time Tree is a website that allows you to search for the point in time at which the genetic code of two organisms diverged; the time at which their last common ancestor lived.

Investigating human beings is quite fun: the last common ancestor that we shared with chimpanzees lived 6.3 million years ago and we shared an ancestor with gorillas 8.6 million years ago. We are much closer to cats and dogs (95.2 million years ago) than we are to ducks (292 million years ago).

If we start to look at more obviously different organisms we find much older most recent common ancestors: we shared an ancestor with jellyfish 892 million years ago and with the northern red oak tree 1.43 billion years ago.

It isn’t just humans that you can find the most recent common ancestors for. Horses and camels shared an ancestor 84.2 million years ago and cats and dogs a mere 55.7 million years ago.

Tagged dating, genetics | 2 Comments |

R₀

Posted on 23rd October by Mr Reid

R₀, also known as the basic reproduction number, is a measure of the ability of an infection to reproduce and spread in an unimmunised population. If R₀ is less than one, each infected person infects (on average) less than one secondary person and the infection will die out. If R₀ is greater than one then each infected person infects more than one secondary person and the infection will spread.

R₀varies greatly between diseases:

From the R₀ figure the proportion of a population that must be immunised to prevent the spread of a disease can be calculated. If we use the population of the UK (61 838 154 according to 2009 figures from the World Bank) then we get the following graph:

You can see that for the most infectious disease on our list, measles, more than 93% (on average) of the population need to be immunised to prevent the disease from spreading (to prevent an epidemic). This is alarming in light of the failure of many parents to immunise their children due to unfounded fears about the MMR vaccine.

Tagged disease, vaccination | Leave a comment |

Spherical ice cubes and surface area to volume ratio

Posted on 20th October by Mr Reid

I’ve recently been experimenting with making spherical ice cubes for cocktails.

But why go to all the fuss of making spherical ice cubes? What’s wrong with regular ice cubes? The answer is surface area to volume ratio: the volume of the ice provides the cooling effect but the surface area controls how fast the ice melts — the lower the surface area to volume ratio the longer the ice will take to melt for the same cooling effect. Essentially, a lower surface area to volume ratio keeps your drink cold, but stops it from becoming too diluted.

A cube with sides of length x will have a volume of x³ and a surface area of 6x². The surface area to volume ratio for a cube is therefore 6 to 1 (6:1). Of all the Platonic solids (solids with identical faces) the icosahedron has the lowest surface area to volume ratio.

Of all the regular shapes a sphere has the lowest possible surface area to volume ratio. That is what makes it particularly well suited for cooling drinks.

The production of spherical ice cubes is also quite interesting. They’re usually made in an extremely elaborate process using large blocks of ice that are then shaped using metal “presses” (usually made of copper or aluminium as they are very good conductors of heat).

Tagged ice, mathematics | 1 Comment |

Does your weight change in a lift?

Posted on 17th October by Mr Reid

The simplest answer to the question of whether your weight changes when you ride in a lift is ‘no’. Your weight, being the force with which the Earth pulls down upon you due to gravity, does not vary with speed or acceleration.

It does, however, feel like your weight changes when you ride in a lift. Because your weight is the force between you and the Earth (and between the Earth and you) you cannot actually feel your own weight; what you feel is the ground pushing up against you (the normal reaction force). Because of Newton’s Third Law (“each force has an equal but opposite reaction force”) this force is equal to your weight pushing down on the Earth.

When the lift accelerates and decelerates the force that the cables and motors exert on the lift is either added to, or subtracted from, the force with which the floor of the lift pushes up on you. This is what makes you feel heavier and lighter.

I used a PASCO force platform and a SPARK datalogger to measure the apparent change in my weight as I rode downwards in a lift.

You can see a drop in apparent weight as the lift accelerates downwards, this then returns to normal as the lift travels at constant speed before rising again as the lift decelerates. By measuring the peak forces and using Newton’s Second Law of Motion I can calculate some approximate values for the maximum acceleration and deceleration of the lift in question: for the lift at school these values were 0.569 m/s² and −0.625 m/s², showing the lift decelerates at a significantly higher rate than it accelerates.

Were you in a lift that was accelerating downwards at the same rate as gravity (9.81 metres per second per second) you would feel weightless; were you in a lift that was accelerating upwards at the same rate you would feel like you weighed twice as much.

Tagged gravity, lift, weight | 2 Comments |

Why 80mph is not a good idea

Posted on 3rd October by Mr Reid

The UK government has announced that it is beginning a consultation on raising the speed limit on UK motorways from 70 mph to 80 mph. I don’t think this is a very good idea, and my reasons are listed below.

Time Saving

You simply don’t save that much time by increasing your speed to 80 mph. If you drove the 400 mile distance from London to Edinburgh, you would only save three-quarters of an hour, and that assumes that you maintain a constant speed of 80 mph the entire time, neither accelerating or decellerating.

Assuming no acceleration or deceleration is entirely unrealistic and as it takes longer to accelerate to 80 mph than it does to get to 70 mph, the graphs above represent a best case scenario. The real time savings are likely to be much lower.

Kinetic Energy and Stopping Distance

Kinetic energy at different speeds for my car, a Peugeot 207 with a mass just over 1000 kg.

The kinetic energy of a vehicle is what makes it dangerous; transferring that kinetic energy to an object — be it a pedestrian or another car — is what causes damage. Kinetic energy depends on the square of the speed; if you double the speed of an object you quadruple its kinetic energy. An increase in speed from 70 mph to 80 mph is a 14% increase in speed but this results in a 31% increase in kinetic energy, making the car — in a sense — 31% more dangerous to other road users.

Increasing kinetic energy also increases stopping distance. Increasing the speed limit to 80 mph would increase the average stopping distance on motorways to 120 metres (30 car lengths!), a 25% increase on the 96 metre stopping distance found at 70 mph.

Fuel Economy

The relationship between speed and fuel economy is not linear; fuel economy is poor at both low and high speeds and peaks somewhere between 40 and 60 mph. Driving at 80 mph will decrease fuel economy and therefore increase fuel consumption; fuel costs will be higher and CO₂ (and other harmful gas) output will be higher. Our limited supply of petrol will be depleted faster if we all drive at 80 mph than if we drive at 70 mph.

Tagged energy, transport | 3 Comments |

SkySails

Posted on 19th September by Mr Reid

On July 7th the German company SkySails GmbH was awarded the Sustainable Shipping Environmental Technology of the Year Award (for the second time) for its SkySail technology.

The SkySails system uses a computer controlled kite with an area of more than 160 square metres to harness the power of wind as an auxilliary power system for large marine vessels. The SkySails company claims it can reduce fuel consumption over long journeys by between ten and fifteen percent.

The SkySails system is a form of high altitude wind power (HAWP). HAWP systems are viable because the power available to wind power systems increases with the cube of the wind’s speed (e.g. if you double the speed the energy produced increases by a factor of eight) and wind speed increases rapidly with height. Companies like KiteGen are even working on using HAWP systems for electricity generation.

Tagged transport, wind | 2 Comments |

Lactose tolerance

Posted on 9th September by Mr Reid

Because most in the western world are able to digest dairy products it is often assumed that this condition (lactose persistence) is the norm. But if you are able to tolerate lactose then you are actually in a minority: ninety-eight percent of Southeast Asians and ninety-five percent of Chinese are lactose intolerant. Between them these two ethnic groups make up more than 28% of the world’s population.

The graph below shows some of the ethnic groups with over 50% of the population lactose intolerant:

Tagged disease, genetics, population | Leave a comment |

Liquid cooling

Posted on 2nd September by Mr Reid

Computer hardware produces a huge amount of heat when operating. Usually this heat is removed by a combination of heatsinks and fans

The grey heatsink conducts the heat away from the processor and the sink’s fins give the heatsink a larger surface area for the air moved by the fan to blow over. Some computers use very large heatsinks in order to do away with the need for a fan entirely, relying only on natural convection currents for cooling.

Some computers do away with fans by pumping water past the heatsink; water is a much better absorber of heat than air* and therefore the system uses less power for cooling.

Green Revolution Cooling have gone one step further — they actually submerge the computing hardware in a special non-conductive liquid. This liquid then circulates, transferring the heat away to an external evaporation tower.

They claim that their cooling system will pay for itself within 1 – 3 years.

* The specific heat capacity of air is 1.007 joules per gram per kelvin and the specific heat capacity of water is 4.187 J/g/K. This means that water will absorb more than four times the energy of the same amount of air for the same increase in temperature. Green Revolution don’t say what the specific heat capacity of the fluid they use is, but it’s likely to be greater than water’s.

Tagged computing, cooling, thermodynamics | 8 Comments |

Patterns in birthdays

Curiosity’s nuclear battery

You’ve already experienced the earliest Easter you’ll ever know

Logarithmic scales

The Milky Way is shaped like a CD