Freckles

Skin colour is determined by a pigment called melanin. When skin is exposed to sunlight, ultraviolet (UV) radiation triggers the production of more melanin. The melanin functions to protect the skin from damage that may be caused by the UV radiation.

There are two types of melanin, namely red pheomelanin and black eumelanin, both of which are present in human skin. However, only eumelanin protects skin from UV damage, while pheomelanin can actually generate free radicals which might contribute to skin damage.

Not every cell in the body produces melanin - skin cells that do, are called melanocytes. In most people melanocytes are spread evenly across the skin, but some people have melanocytes in clumps in the skin. These clumped melanocytes don't produce the UV-protective eumelanin, as they have a mutation in a gene that is essential for regulating the proportions of pheomelanin and eumelanin. Usually this proportion is controlled by a hormone called melanocyte stimulating hormone (MSH). This hormone binds to a specific receptor on the surface of the melanocyte cell called MC1R (A in the illustration on the right). When MSH binds to MC1R signals are sent into the cell to turn pheomelanin into eumelanin. When there is a mutation in MC1R, the MSH can't bind to it, and pheomelanin isn't turned into eumelanin (B in the illustration on the right). This causes the reddish colour of freckles.

The MC1R mutation is dominant, meaning that you only need one copy of the gene to have freckles. However, red hair is a recessive trait, which means that you need two copies of the MC1R gene to have red hair.

A recent interesting paper has determined that variations in MC1R caused variation in hair and skin pigmentation in Neanderthals on a scale that is observed in modern humans.¹


Photo above: Cyclist's tan with freckles. The skin is freckle-free where a watch fits around the wrist and on the hand where cycling gloves cover the skin.

If you want further information on skin pigmentation and melanoma (cancer), you can go here.



¹ Lalueza-Fox C et al.
A Melanocortin 1 Receptor Allele Suggests Varying Pigmentation Among Neanderthals

Cycling

How do you remain upright on a bike? How does steering work? How about those nifty fixie-riders and their track stands at red lights?

Balancing on a bike

The best comparison I've read about balancing on a bicycle is the one that compares it to balancing a stick on your hand, vertically. The moment the stick seems to tilt over right, you move your hand to the right (and slightly over) in order to get the stick to tilt back again. This adjustment is done continuously and leads to the stick "balancing" on your hand. Cycling is the same. As you ride, you fall slightly to the right or left. As you fall to the right, you steer the bike to the right in order to get the wheels under you again. As you fall to the left, you steer left. And so cycling is a continuous adjustment from a tilted position to an upright position - you're actually turning left and right the whole time (albeit small turns). When you look at the track created by a bike you will see these left-and-right swerves created by the wheels.

Track stands

Fixed-gear bikes don't have a freewheel. This means that if you stop pedalling, the wheels stop moving, and if you pedal backwards, the bike moves backwards. When you see a fixie rider standing still at a red light, he always has his wheel turned sharply to one side or the other. What he (or she!) is doing is moving slightly forward or back, or side to side, compensating for the bike leaning in any direction or moving forward or back, in order to stand still. I believe this is a lot easier on a fixed-gear bike as you can control both forward and backward motion.

Steering your bike

When you turn your bike right, centrifugal forces will try to push you towards the left. So in order to turn right, you have to lean your bicycle to the right to counteract the centrifugal forces (see diagram).

If you want to lean your bicycle to the right, you have to actually turn the bars to the left. When you turn the bars to the left, your hips naturally shift towards the right, and the bike leans right. This is called countersteering.

When you turn your bike, this all happens automatically without you having to think about it!

Hygro-, baro-, and thermometers (dial-style)

You might've seen one of these in someone's house, or on a boat. It's a mini weather station consisting of a hygrometer, barometer, and thermometer. The hygrometer measures the relative humidity of the air, barometer measures the air pressure, and thermometer obviously tells you how warm (or cold) it is.

But how do they work? What turns the little dial on the indicator and what acutally measures the moisture, pressure, and temperature? Well, it's all down to really basic physics.

The hygrometer

The hygrometer uses a measuring element - this can be any material that expands when humidity increases, and contracts when humidity decreases. The hygrometer measures and shows the change in length of this element. Since the element is attached to the dial (through a number of levers and axles), the dial turns as humidity changes.
The measuring element is usually a human hair, thread, or paper.

The barometer

The barometer uses a metal capsule called a diaphragm. When air pressure increases, the diaphragm is pressed together, and when air pressure decreases, the diaphragm expands - sort of like a balloon being deflated or inflated. The change in the diaphragm is transformed into a turn of the dial on the meter's face with the help of levers.

The thermometer

You might know thermometers that use mercury or other liquids inside them. When the temperatur of the liquid increases, it expands and moves up in the tube. But dial-type thermometers use a spiral spring made of two different metals. The metals contract with decreasing temperature and expand with increasing temperature, but to different extents. Because the one is less reactive than the other, the spring makes accurate, defined rotating movements. This movement is directly transferred to the dial which indicates what the temperature is.

Reflective material

In the UK cyclists must have a white front light and red rear light to cycle at night. This is required by law. However, these lights are often not sufficient, and so it's advisable to wear clothing with reflective strips on them.

But how does reflective technology work? 3M makes a lot of these products using their Scotchlite technology. They use glass beads and prismatic technology to reflect light rays in a way called "retro reflection".

When a ray of light strikes a reflective surface straight on (at a 90 degree angle), the light is reflected straight back along the same path. However, when light hits the surface at an angle, it's reflected at an angle in an opposite direction. Retro-reflectivity occurs when the reflected ray returns in the direction of the light source, regardless of the angle at which it strikes the reflective surface. This reflection can be obtained in one of two ways:

With the use of three mirrors that are perpendicular to each other.



Or with special beads that bend and reflect light rays in a specific way.


Retro-reflective material reflect the largest amount of light of all reflective materials. The strength of reflective light is measured in candela. White material performs at 0.3 candela while retro-reflective material can measure up to 500 candela.