Posted in chemistry, physics, science

How do things glow in the dark?

It is relatively common nowadays to see a plethora of glow-in-the-dark products across a vast spectrum of items. Although most regularly found in toys and watches, there seems to be no end to the types of item that can be modified to glow. So, how does this phenomenon occur?

Firstly, it is important to pin-point what is meant by the term ‘glow-in-the-dark’. In this instance, it is used to describe luminescence. Luminescence is the emission of light from a source that has not been heated; due to the lack of heat, it is a form of spontaneous emission. If heat is involved, then the phenomena is labelled incandescence and is not considered spontaneous. There are several different ways in which luminescence can occur, including through chemical reactions, electric currents and the compression of certain types of crystal.

The type of luminescence encountered most commonly in day-to-day products is phosphorescence. Phosphorescence is a specific type of photoluminescence that involves molecules called phosphors. Usually transition metals or rare earth elements, phosphors absorb energy from electromagnetic radiation and emit it as visible light over timescales between nanoseconds and hours. Funnily enough, phosphorus is not defined as a phosphor – it is chemiluminescent as opposed to photoluminescent.

Underpinning the ability for photoluminescent materials to emit light is quantum mechanics. When a photon collides with the phosphor and is absorbed, it excites an electron to a higher transition state. When the electron drops back down to its usual state, it releases a photon whose energy exactly corresponds to the size of the gap between the levels. This is what we perceive as the emitted ‘glow’. In the majority of photoluminescent events, this excitation and relaxation of electrons occurs over extremely short timescales, often in the region of nanoseconds. This is known as fluorescence. However, when phosphors (such as zinc sulphide and strontium aluminate) are involved, phosphorescence can emit light over much longer periods of time. This is the key difference between fluorescence and phosphorescence – the time taken to re-emit the energy.

So, why is it that phosphorescence can occur over such long timescales? Again, it’s all based on quantum mechanics. As you may know, ‘allowed transition states’ and ‘forbidden transition states’ are key within quantum mechanics. These, along with a rather expansive set of rules, govern the movement of electrons in their respective shells. In normal circumstances, when a ground state electron is excited to a higher energy level, it will transition into an exited singlet state. This means that it has paired up with another electron with an opposite spin (i.e. obeying the Pauli Exclusion Principle). The Pauli Exclusion Principle states that no two particles with a half integer spin (such as electrons) can occupy the same orbital at the same time (think of people on a bus – ideally, people aim to sit on an unoccupied pair of seats before going to sit next to a stranger).

However, in some cases (as in phosphorescence), the excited electron will transition into an excited triplet state. This is where things get a little complicated. In an excited triplet state, the excited electron is spinning parallel to the ground state. This is called intersystem crossing. As having the same spin is considered ‘forbidden’ within quantum mechanics (again, due to our friend Pauli), it means that the excited triplet state electron is in a bit of a pickle. The ‘forbidden’ transitions are less kinetically favourable than the ‘allowed’ transitions, meaning that it is more difficult for the electron to relax back to its normal ground state. This prolongs the relaxation progress, ensuring that the glow of released photons lasts for longer.

So, there it is. Objects glow in the dark due to the phenomena of phosphorescence – the process by which electrons are excited to ‘forbidden’ quantum spin states. As the electrons are allowed to relax, they emit a photon of light corresponding to the distance between the energy levels, producing the subtle glow which is now associated with watch hands and plastic stars. In conclusion, the entire glow-in-the-dark industry is reliant upon a small group of rebellious electrons not doing what they should. Pretty neat, huh?

Tabitha Watson

Posted in biology, science

Is napping bad for you?

Unfortunately, it is often the case that the most enjoyable things in life are also the worst for you. Sweets, coffee, alcohol; the list seems endless. One of the most enjoyable things in life (at least for a student), is a cheeky nap after a particularly trying lecture. However, is it good for you?

There is conflicting evidence surrounding the concept of napping – some suggest that a brief siesta after your 9am lecture could help you lose weight and even boost brain activity, whereas others think that too many naps could increase an individual’s risk of developing Type 2 diabetes. So, which is the truth?

A study conducted at the University of Tokyo in Japan found that those who napped for longer than an hour per day were 45% more likely to contract Type 2 diabetes than those who did not nap or who napped for less than an hour. Despite this seemingly damning evidence, all is not lost for those who enjoy a longer snooze. It is very likely that the data gathered by the Japanese research team could have been influenced by external factors not recorded in the distributed questionnaire – in fact, it is almost certain. A more recent research project presented at the European Association for the Study of Diabetes suggested that the correlation between obesity and napping is likely to have influenced the apparent link to diabetes. They argued that the existing obesity epidemic and not the act of napping itself was to blame for the raised diabetes risk.

The claim that napping can help with weight loss can also be swiftly debunked: on average, people who sleep around 5 hours per night tend to gain less than 2kg of weight per year, which is on par with those who sleep around 7 hours per night.

After examining both sides of the argument, it appears that napping is a fairly neutral pastime. When the evidence is weighed up, the correlations between extra sleep and the proposed health benefits and/or detriments seem to be built on rather spurious connections, vastly influenced by external variables. Finally, a pleasure that can be enjoyed sans-guilt.

Tabitha Watson

Image Credit: [https://i.kinja-img.com/gawker-media/image/upload/s–1FvmwsTr–/c_scale,fl_progressive,q_80,w_800/191dbvjco20mbjpg.jpg]

Posted in science

What causes colour-blindness?

Colour-blindness is a relatively common human condition – 8% of men are born colour-blind, as are 4.5% of women. This discrepancy between the genders is due to the gene linked to colour-blindness being on the X chromosome (i.e. women inherit two copies so both of the inherited genes must be faulty for them to be impacted). That being said, although the majority of cases of colour-blindness are genetic, a percentage of people can develop colour-blindness later in life. Colour vision tends to decline past the age of 60, and ill-managed chronic conditions such as diabetes, strokes, chronic alcoholism and Parkinson’s disease can all lead to eventual colour-blindness.

So what exactly causes people to be unable to see colour? It’s all linked to the many complex structures within the eye. There are two main light-sensitive cells within the human eye, both found in the retina. These cells are rods and cones. Both are found in vast numbers – in each individual retina there is in excess of 90 million rods and between 6 to 7 million cones. Despite their apparent similarities, rods and cones have very different and distinct roles when it comes to detecting light and processing images.

Rods are able to function in less light and are more sensitive than cones, and therefore they are mainly used for night vision. They are capable of responding to a single photon of light, making them around 100 times more sensitive than cones. However, they only contain one type of colour pigment. Rods are concentrated around the outer edges of the retina, and are used in peripheral vision during the daylight. However, as there are so many rod cells in the retina, multiple cells tend to share a neuron in order to amplify their signals. This makes the resolution of images detected by rods much less clear.

Despite there being many, many fewer cones than rods, they are responsible for much of the clarity of colour we experience. The exact opposite to rods, they function best in bright light. Three different varieties of cones are found in the retina of typical humans, L-cones, M-cones and S-cones. This means that as a species we are said to have ‘trichromatic vision’. Each different type of cone detects a different wavelength of light, and these wavelengths combine to give the large spectrum of visible colour seen by the majority of people. This range varies from species to species – amazingly, it has been reported that some types of snake can observe some wavelengths in the infrared spectrum.

There are three main pigments in the eye that allow us to observe colour, and – bizarrely enough – they vary from person to person due to genetic mutation and other factors. This means that everyone sees colour differently.

This intricate network of different receptors and pigments within the eye is very fragile, making it susceptible to damage and mutation. If a combination of rods and/or cones are faulty, then not all wavelengths of light can be absorbed. This leads to some colours appearing differently to the affected person, or perhaps not appearing at all. The most common form of colour-blindness is ‘red-green colour-blindness’. This is an umbrella term for people with either deuteranomaly or protanomaly. This is caused by one type of cone being slightly faulty, which causes the spectrum of visible colour to shift, rendering some colours slightly out-of-whack.

However, my parting thought is this: as no-one sees colour in exactly the same way, who’s to say who’s version of colour is correct?

Tabitha Watson

Image Credit: [http://www.colourblindawareness.org/wp-content/themes/outreach/images/slider/types/xeye.jpg.pagespeed.ic.mmcI6be7ml.jpg]

Posted in science

Why do leaves change colour?

The changing colours of the leaves is many people’s favourite part of autumn – the gorgeous hues are pretty much synonymous with the changing of the seasons. There is so much variation as well; many trees display a wide array of yellows, golds, oranges, reds and everything in-between. So, what causes this transformation to occur?

As the days get shorter and darker, there is less light intensity falling on the leaves of trees. This reduced light intensity initiates the breakdown of chlorophyll, a green pigment which is responsible for absorbing light to facilitate photosynthesis. As the chlorophyll begins to break down and be removed from the leaves, other pigments start to become visible. Funnily enough, it is these secondary pigments that cause the vibrant (and picturesque) autumnal colours. The main compounds which are revealed are xanthophyll, carotene and anthocyanins. Xanthophyll and carotene are responsible for the more orange shades, and any red colours are attributed to the anthocyanins.

At the same time as the chlorophyll is being broken down, a specialist layer of cells named ‘cork cells’ build up at the base of the leaf. These cells shut off the veins in the leaf from the rest of the tree, forming a leaf scar which protects the overall plant when the leaf is eventually severed.

The overall colours of the leaves are determined by a combination of environmental factors. Light intensity, temperature and the abundance of water all play roles. For example: the colder the temperature, the redder the leaves. This is due to the anthocyanins being more visible.

Currently there are two main theories as to why leaves change colour; photoprotection and coevolution. The idea behind the photoprotection theory is that as the chlorophyll breaks down and exposes more anthocyanins, they are then able to protect the leaves from damage caused by high light intensity at low temperatures. This helps to reduce photo-oxidation and photo-inhibition, therefore (theoretically) making the reabsorption of nutrients more efficient.

The coevolution theory states that the brighter red the leaves turn, the more toxic the tree is to certain types of insect. This would act as an indicator to the creatures affected, reducing the parasite load of the tree for the onset of winter. Equally, the vibrant colours could attract certain types of insect or bird. This said, neither of these theories has been fully proven, and neither of them provide a justifiable explanation as to how the colour change links to the inevitable dropping of the leaves.

So, to conclude: the fantastic autumnal colours of leaves are produced as chlorophyll breaks down, and no one fully understands why this occurs.

Tabitha Watson

Image credit: http://www.mrwallpaper.com/wallpapers/Autumn-Leaves-Background-851×315.jpg

Posted in science

Smoking – how fast will it kill you?

As of 2015, around 19% of the adult population in the UK were regular smokers, and 1.1 million people labelled themselves as social smokers. Assuming that these are two separate groups of people, that means that 13497621.79 people in the UK smoke. Now, it’s pretty common knowledge that smoking is bad, but what does that actually mean? How ‘bad’ is bad, and how quickly do the negatives take effect?

One of the most well-known effects of long term smoking is, of course, cancer. More specifically, lung cancer (although other areas such as the bladder, kidneys and liver can also be affected). The cancers are caused by structural damage in the DNA of cells. This structural damage then triggers mutations, which can be malignant. This damage and the resultant mutations has been linked to tiny chemicals called polycyclic aromatic hydrocarbons by researchers at the University of Minnesota. When they enter the body, they are able to form metabolites that then attack cells and cause irreparable structural damage. Studies have shown that the concentration of these metabolites in the body peaks between 15 and 30 minutes after the first inhale, meaning that the damage begins to occur almost immediately.

Recent research conducted by the Los Alamos National Laboratory in New Mexico has managed to quantify just how fast these harmful mutations occur. According to their data, every 50 cigarettes carries with it the potential for one serious (i.e. cancerous) mutation. On average, a heavy smoker would consume approximately 20 cigarettes a day. If this is multiplied out, that’s 140 a week. If this is extrapolated again, it can be assumed that they would smoke, on average, 7280 cigarettes in a year. This means that each smoker will experience roughly 145.6 serious mutations per year, and whether or not they are cancerous is completely up to chance. Think Russian Roulette, but with lung cancer.

Scarily, once these changes to the DNA have been made, they cannot be reversed. No amount of avocado and kale smoothies can erase the permanent cellular damage. However, all is not lost. A 50-year-long study of smokers and their habits has recently been concluded by researchers at the University of Oxford, and their findings are fairly positive. Despite smoking knocking approximately 10 years off a person’s average lifespan, if smokers quit before the age of 30 then the risk of dying prematurely is ‘virtually eliminated’.

So, in conclusion, quit while you’re ahead.

Tabitha Watson

 

 

Posted in science

How does artificial gravity work?

As a self-confessed lover of sci-fi, something that has always intrigued me is the presence of artificial gravity aboard vessels such as Star Trek’s USS Enterprise and the Death Star. According to the website Memory-Alpha, the USS Enterprise and other Starfleet vessels use ‘gravity plates’ to get around the issue, and in the Star Wars universe the use of ‘artificial gravity generators’ is widespread. Alas, as the elements required to make either of the aforementioned devices are fictional, we cannot recreate the technology for our own spacecraft.

Seeing as we are not yet as technologically advanced as our fictional counterparts, the only way to simulate the effects of gravity (at the moment) is by using centripetal force, much like that experienced on some types of vintage fairground rides such as ‘The Rotor’ and the ‘Gravitron’ (they’re the ones where the floor drops out from under you and you stick to the wall). This works incredibly well when applied to something as small and uncomplicated as a fairground ride, but what happens when you want to scale it up to the size of a space station? Will the concept still work? Well, worry not, for that is what we are about to find out (after a quick whistle-stop explanation of centripetal force so that we’re all on the same page).

Centripetal force is often described as ‘a force which acts on a body moving in a circular path and is directed towards the centre around which the body is moving’ (thanks Wikipedia.com). In other words, any type of motion in a curved path represents accelerated motion, which in turn requires a force directed towards the centre of the curved path. In the case of artificial gravity, it would be this force that would mimic the natural pull of the Earth and thereby stick everything to the floor. That being said, the ‘floor’ would no longer be pointing vertically downwards – due to the nature of centripetal force, everything would be sucked towards what would stereotypically be described as the wall (if everything were stationary). Essentially, everyone would be walking parallel to the ‘floor’ around the inner wall of the ship (imagine a sideways hamster wheel and you’re on the right track).

So, in theory, we do have the method to facilitate the production of artificial gravity. However, as with many things, it is easier said than done. In order for the centripetal force to match that produced by the Earth’s gravity, any potential spacecraft would have to spin unrealistically quickly. Actually, that being said, it isn’t entirely true – the rate of rotation would be proportional to size, and therefore if the ship was massive enough then it could slow the minimum speed to a more manageable pace. Again though, this solution has its own issues. In order for the speed to be sufficiently slowed, the spaceship would have to rival the Death Star in size. This would be hugely expensive to build, seeing as we would be unable to launch anything of that sheer gigantic-ness. Each component would have to be launched from Earth and assembled in situ (i.e. the entire construction would be ludicrously expensive). Along with this, the nauseating rotation of the ship would mean that windows would be an impossibility in order to avoid crippling motion sickness.

I can’t help but conclude that, at this point in time, the construction of a spaceship with artificial gravity is rather fanciful. That doesn’t necessarily mean that the technology/resources/insanely rich person with limited common sense won’t come along and make it reality, but for the time being we are still destined to float around unfettered in the great chasm of space. So, in answer to my original question, artificial gravity really doesn’t work.

Tabitha Watson

(photo cred: starwars.wikia.com)

Posted in science

Why are horsefly bites so painful?

Like most students, I have the mixed blessing of moving back home for the duration of the summer holidays. On the one hand, I get to catch up with my family, there’s no rent and I can indulge in large amounts of free food. However, as with everything, there are downsides to returning to the rural idyll that is the countryside. Ranking only slightly below the lack of public transport in my local area, the ridiculous abundance of horseflies is very high on my list of utter nuisances. I don’t know about you, but when I am bitten by one of those godforsaken creatures I swell up like a balloon and itch like you wouldn’t believe. So, obviously, I wanted to find out why.

According to the rather dubious source that is Wikipedia, horseflies have appeared in literature since someone in Ancient Greece complained about them ‘driving people to madness through their persistent pursuit’. Personally, I entirely relate to this historical experience. They are known by a large number of common names, such as gad-flies, dun-flies and breeze-flies to name but a few. Rather terrifyingly, it has been recorded that they can fly at speeds of up to 15 mph (although I cannot verify the veracity of this information).

The official dictionary definition of a horsefly (or gad-fly or whatever you want to call it) is as follows: ‘a stoutly built fly, the female of which is a bloodsucker and inflicts painful bites on horses, humans, and other large mammals’. Painful? Damn right. Most of the time, both genders of horsefly consume plant nectar in order to survive. However, when it comes to reproducing, the females of the species need the protein found in blood to produce their eggs. As such, they then turn into evil creatures that attack unsuspecting bystanders.

Unlike mosquitoes (which pierce the skin with a needle-like projection instead of inflicting a genuine bite) horseflies use sharp mandibles to tear open the skin. This provides easier access to the blood underneath, and it also has a very beneficial evolutionary side effect – because the bite is more painful, the poor mammal is usually more concerned with tending to the newly inflicted wound than it is with killing the perpetrator. Once it has bitten, the horsefly will return in order to drink the blood with its sponge-like mouthparts. Yuck. When it is feeding, salvia containing an anticoagulant is injected into the wound in order to maximise blood flow. It is this saliva that causes the intense allergic reaction in some people; the main symptoms are painful weals, itching, dizziness, weakness and wheezing. The reactions are caused by the increased production of histamine by the body, which then floods the area.

Unfortunately, there is no fool-proof way to get rid of/avoid being bitten by the ever-present horror that are horseflies. Never fear though, because there are ways to minimise the likelihood of being turned into a walking buffet. Horseflies tend to be most active during the day, especially around noon and in warm, sunlit areas. They tend to avoid shady areas, and are completely inactive at night. My recommendation is to avoid the areas/times they frequent. They seem to be attracted to potential victims in a number of ways, such as movement, warmth, the pattern/colour of the clothing/hide and the amount of carbon dioxide exhaled. There is some evidence to suggest that horseflies may be deterred by stripes, but this has not been extensively researched. I think stripes might be in this season? Fashionable and functional?

So to conclude, the reason why horsefly bites are so damn itchy and painful is this: they tear open your skin to form a wound, which is then filled with a mixture of saliva and anticoagulant which triggers an intense histamine reaction from the body. Fabulous.

Tabitha Watson

Posted in general

Why are tattoos permanent?

Tattoos have been a part of human culture for over five thousand years, and having recently gone under the needle myself (I got a little rocket on my upper back, if you’re interested), I found myself wondering what it is that makes tattoos permanent. In my search for information, it became apparent that there are two main factors: the composition of the tattoo ink and the depth at which it is injected.

As you probably know, tattoos are drawn using a mechanised needle that repeatedly punctures the skin at a rate of anywhere between fifty to three thousand times a second. This needle penetrates to a depth of around two millimetres, depositing the ink into the layer of skin known as the dermis. The skin is made up of three main layers, and as the thickest layer, the dermis is sandwiched between the others (the epidermis and the subcutis). It is made up of a variety of fibrous and dense connective tissues, and unlike the epidermis, it does not shed cells. Due to this, the ink deposited there is not degenerated by the day-to-day shedding of skin cells (usually at a rate of around forty thousand cells per day). However, this does not mean that the dermis does not undergo constant degeneration. One of the reasons that tattoos fade over time is the cyclical process of cell death and regeneration that occurs in all parts of the body.

Now, we all know that the body does not necessarily take kindly to being repeatedly attacked with an ink-filled needle. As soon as the nerves send reports of the invasion to the central nervous system, thousands of white blood cells are deployed in order to remove the invading ink particles and heal the wounds. Normally, white blood cells break down any offending foreign bodies and transport them to the lymph nodes where they can be disposed. However, tattoo ink is made up of a variety of compounds, and the majority of them are too large for white blood cells to remove. This doesn’t stop them from trying though; tattoos are constantly under attack from the immune system, and this is part of why they tend to fade and blur over time. Interestingly, this plays a large role in how laser removal procedures get rid of unwanted tattoos. The laser is used to break down the embedded ink into little pieces that are small enough for the white blood cells to naturally remove.

So, there you have it. The creation of a permanent piece of art relies on two main factors –  the chemical composition of the ink used and the depth at which it is embedded into the skin. Pretty funky.

Tabitha Watson