#editor anna g
If spending time out in the sun has ever resulted in red, painful, blistering or peeling skin, then you’ve probably had sunburn.
Sunburn is caused by a particular set of light wavelengths emitted from sun. Much of the light produced by the sun is outside the range of human sight, including infraredandultraviolet (UV) light. You can sense infrared light—you feel it as heat on your skin when you step into sunshine. Stay in the sun unprotected for too long, however, and ultraviolet light will leave its mark in the form of a sunburn.
Ultraviolet Radiation
Ultraviolet light is extremely damaging to the DNA of living things. Luckily for us, the Earth’s atmosphere and ozone layer do a great job of blocking a lot of the ultraviolet radiation the sun throws our way. UVAandUVB rays are notable because some of them get through. About 3% of sunlight is made up of UVA/UVB radiation, and of that 3%, about 95% of that is UVA. UVB is what tends to cause you grief every time you get a sunburn, burning the upper layers of your skin, known as the epidermis, to cause the redness we associate with catching the sun. UVA doesn’t cause burns, but unfortunately it does penetrate the skin’s layers much more deeply, getting all the way to the tissues underneath. It is responsible for “photoaging,” the process that accelerates the breakdown of collagen and connective tissue in skin.
Solar Erythema or, Darn it, I got Sunburned!
The effects of a sunburn, or solar erythema, may not be noticeable right away; the full extent of the burn takes anywhere from 6 to 48 hours to appear. However, once the symptoms start, they are difficult to ignore. Sunburn triggers an immune response reaction as the skin tries to heal itself. This is characterized by redness or excessive heat that radiates from the skin, caused by the dilation of blood vessels near the skin’s surface as the body increases blood flow to the burned area, in order to help with the healing process. The pain that accompanies sunburn is caused by cytokines, protein messengers that signal to the body that damage has occurred. White blood cells soon arrive on the scene to attack and remove the harmed skin cells. This part of the healing process is what causes the itching, peeling, and blistering that occurs over the hours or days following getting burned.
Skin Damage and Exposure
UVA and UVB radiation both cause skin damage, but in different ways:
UVA triggers a tanning response in skin, which is a sign that the skin had been exposed to too much UV radiation. Specialized skin cells called melanocytes, or pigment cells, work to guard the skin from UV exposure. If these cells get overwhelmed, they ramp up production of a substance called melanin to produce a tan in order to protect the skin from additional future damage. UVA lights are used in tanning beds for this reason. This is also why there is no such thing as a safe tan, since it is a sign that the skin has already been injured. It is also important to note that UVA rays are constant throughout the year, so people who only apply sunscreen in the summer will still be exposed to UV light over a long period of time.
UVB exposure can vary greatly depending on the time of year. It is easiest to be burned midday in the summer,when the sunlight is most direct and concentrated. However, UVB rays can damage skin year-round, especially at high altitudes (the thinner atmosphere allows more UV radiation through) or in areas with highly reflective surfaces, such as snow or ice. Because UVB damage occurs on the topmost layer of skin, it is a major factor in the development of skin cancer. Skin cells are short lived, with new cells replacing old in a 28 day cycle. This rapid cell growth makes it much more likely that if a mutation occurs, it will get passed on instead of destroyed.
Skin repeatedly damaged by sunburn or tanning lamps is vulnerable to cell mutations which can lead to skin cancers, including basal cell carcinoma,squamous cell carcinoma, and melanoma.
UV Protection
Your skin does provide some natural protection in the form of the melanin produced by melanocytes. The amount of melanin naturally produced by your skin determines skin color: the more melanin in your skin, the darker it is. People with lighter skin will burn much more quickly than people with darker skin, but a higher melanocyte count simply means that person has a greater tolerance to UVB radiation, and it does not make them immune to the damage of UVA radiation.
Seeking shelter between the hours of 10am and 4pm is best if you want to avoid UV rays at their strongest. Keep in mind that windows only block UVB, not UVA rays. Hats and clothing made out of tightly woven materials in darker fabrics can help block or absorb UV rays; some clothing is even manufactured with a UPF (ultraviolet protection factor) rating. UV light can damage your eyes as well, so wear sunglasses that offer UV protection.
Make wearing sunscreen a habit and reapply often! Sunscreens act as a chemical absorber or a physical filter to UV radiation. Only sunscreens labeled with broad spectrum or UVA/UVB protection contain ingredients that protect against both the surface damage of UVB and the deeper tissue damage caused by UVA radiation.
Calculate a sunscreen’s Sun Protection Factor (SPF): The sun protection factor number is a multiplier you combine with how long it takes for you to burn naturally. For example, if you burn after five minutes without protection, putting on SPF 30 will theoretically give you 150 minutes of burn-free fun in the sun. There are a lot of caveats to consider: sunscreen won’t last as long if you swim or sweat a lot, you need to apply it evenly and you need to use at least one and a half ounces (a shot glass full) every time you apply.
Video: Animation - Short and Long Term Effects of UV exposure
http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/Tanning/ucm135889.htm
References:
U.S. Food and Drug Administration. The Risks of Tanning. http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/Tanning/ucm116432.htm#1
JAMA Patient Page | July 02, 2015. Suntan and Sunburn. http://jamanetwork.com/article.aspx?doi=10.1001/jama.2015.8045
Skin Cancer Foundation. Understanding UVA and UVB. http://www.skincancer.org/prevention/uva-and-uvb/understanding-uva-and-uvb
Wired Magazine. Big Question: How Does Sunscreen Shield Your Skin With Science? http://www.wired.com/2015/07/big-question-sunscreen-shield-skin-science/
By Jenna L., Writer.
Edited by Anna G.
The more we understand the history of Earth’s climate, the better we understand the complexities of its future. A massive collaboration involving scientists from around the world, led by the Desert Research Institute in Nevada, has helped show the impact volcanoes have had on the climate.
When a volcano erupts, it spews tons of material into the air, which gets into the atmosphere and blocks some of the Sun’s radiation, causing a cooling effect. One example of this was in 1991, when Mt. Pinatubo in the Philippines erupted. The eruption caused a cooling of 0.5 ᵒC in the North Hemisphere. This kind of cooling can have massive consequences in predicting climate change, so a greater understanding of the effect is incredibly important.
We are able to gain this understanding by analyzing our environment.
The sulfur that volcanoes eject will always eventually land on Earth; this is taken up by trees and can be seen in tree rings. It also lands on ice and is incorporated into the ice sheets. Scientists drill into the ice and extract long cylinders of ice called ice cores, which are so sensitive to change that a drop in lead can be seen in when unleaded petrol became the norm.
It can be hard to accurately pin records from ice cores to records from tree rings, as it’s often done by simply judging that a change of sulfur in both the ice and the trees were from the same event. Using different timescales from each can often make things inaccurate.
Recently, sudden changes in an isotope of carbon, carbon-14, have been found in tree rings very soon after volcanic eruptions. We’ve been able to accurately date this using an eruption from 775 AD, and using multiple trees from all over the Northern Hemisphere. The scientists in this new study assumed that a radioactive isotope of beryllium, beryllium-10, would also be created in greater quantities during an eruption, because this isotope is made when cosmic rays interact with particles in the atmosphere. This gives us a way to pin tree data to ice core data, using independent but simultaneous events. Using this information, scientists went back through previous records of ice cores and found them to be inaccurate. Some eruptions in Greenland were found to be seven years out of line with the tree ring data.
This data allowed the scientists to create a new model spanning the last 2,500 years. The model shows hundreds of eruptions that influenced the climate, and shows that tropical eruptions were the cause of numerous cooling events. It has been found that between 500 BC and 1000 AD, 15 of the 16 coldest summers were after tropical eruptions.
They were also able to solve a mystery: there were a number of strange cooling occurrences in the early part of the sixth century. A dust cloud was observed in records in 536 AD; this was thought to have been due to an eruption, but was never proven. The new paper shows that it must have been caused by at least two tropical eruptions. This new understanding of previous events will greatly help our planning for future change.
Sources
Link to article: http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14565.html
Study on carbon 14 in tree rings: http://www.nature.com/nature/journal/v486/n7402/full/nature11123.html
Mt. Pinatubo data: http://pubs.usgs.gov/pinatubo/self/
Lead in ice cores: http://www.sciencewa.net.au/topics/environment-a-conservation/item/1271-mt-everest-ice-core-reveals-atmospheric-lead-history/1271-mt-everest-ice-core-reveals-atmospheric-lead-history
More info on paleoclimatology: http://serc.carleton.edu/microbelife/topics/proxies/paleoclimate.html
By Adam M., Discoverer.
Edited by Anna G.
Question:
How does a 3D printer work?
Asked by anonymous
Answer:
While 2D printing, a process familiar to many, is used to draw images on a flat surface, 3D printing – also called additive manufacturing – is a process used to create three-dimensional objects. In additive processes, successive layers of materials are laid down under computer control until an entire object is created. This method of 3D printing has many applications, ranging from mass production of machine parts to building food models.
Initially, the digital 3D model is generated from a Computer Aided Design (CAD) program or a 3D scanner before printing software divides it into very small horizontal layers and uploads it into the printer, which proceeds to create each layer one at a time, blending them together so that no signs of the layering remain visible. A wide range of materials can be used for 3D printing, including plastic, glass, metal, wax, even edible food.
There are many different additive processes available: in some, materials are melted in order to create the layers(e.g.electron beam melting,selective laser melting,selective laser sintering), while other processes cure liquid materials using different technologies(e.g.stereolithography). Another way to print 3D objects is by cutting thin layers to shape and join them together. This is called laminated object manufacturing.
To summarize, 3D printing can be done in different ways depending on the purpose, number of items, materials used, and complexity of the objects. For more information about 3D printing, click here.
Answered by Juan Chau, Expert Leader.
Edited by Anna G.
