Category: Articles

What?

Sunscreens contain diverse active ingredients. Some use the inert inorganic mineral pigment, such as zinc oxide and titanium dioxide, primarily to reflect or scatter UV radiation. Others use organic chemicals or a mixture because chemicals can absorb UV rays. For instance, sunscreens also contain carbon-containing molecules that absorb light, such as oxybenzone, octinoxate, octisalate and avobenzone.

The Scientific Committee on Consumer Products (SCCP) has reviewed 27 UV filters approved for Cosmetic Directive, each processes a designation, by which they should be declared on product packaging.

Each sunscreen product has a sunscreen products factor (SPF). It is misleading to interpret SPF as the strength of protection. In fact, SPF refers to the time for the UVB rays to redden the skin with the product compared to that without product. For instance, 15 SPF means using this sunscreen will take 15 times longer for the skin to burn than without using it.

 

How?

Most sunscreen products work by blocking, absorbing, reflecting and scattering UV rays through physical and chemical approaches. Physical method uses particles like titanium dioxide or zinc oxide mentioned above to reflect UV rays away from skins. Meanwhile, many complicated ingredients have chemical reaction with radiation as they contact, absorbing the UV rays, prevent the radiation harming the skins.

Specifically, sunscreens can combat with two types of damaging UV rays: UVA and UVB. Recent researches show that both UVB and UVA radiation will cause sunburn and skin cancer, while UVA rays will also deeply penetrate the skins and cause faster aging, wrinkling and eye damaging.

However, most sunscreen products on the market only block UVB rays while overlook the damage caused by UVA rays. Focusing on efficient UVA protection has a significant prospect in the future.

 

Safety?

Besides SCCP inspections, ingredients used in sunscreen products also must be approved by the Food and Drug Administration (FDA). The FDA has reviewed 17 ingredients that can be used in UV products, including oxybenzone, titanium dioxide and zinc oxide mentioned before.

To guarantee the safety of ingredients, FDA conducts extensive inspections on the ingredients and moreover, regulates the safety and effectiveness of the ingredients until reaching the best performance. For instance, FDA has approved the use of zinc oxide in over-the-counter skin protectants and sunscreen products at concentrations up to 25 percent; active ingredients in sunscreen such as titanium dioxide protect our skin form the harmful UV rays.

 

Experiment!

Now let’s do something interesting using the nature print paper. The nature print paper will become very pale blue after exposure to the sunlight. We can use it to test the effectiveness of UV product by comparing the color.

Step 1: Take one piece of Nature print paper and put it on a piece of corrugated cardboard for support.

Step 2: Smear some sunscreen on part of the paper (the small circle). I used the Shiseido UV product with SPF 50, PF+++.

Step 3: Expose the paper under sunlight until the blue paper turns very pale blue.

Step 4: Check the resulted paper.

We can discover that the whole paper became light blue, except the circle with sunscreen barely changed after 2 hours of exposure. We can see that the sunscreen products do have intensive effect and we can surely believe that sunscreen products can protect our skins against the harmful UV light.

 

Binks, Bernard P., et al. “How the sun protection factor (SPF) of sunscreen films change during solar irradiation.” Journal of Photochemistry and Photobiology A: Chemistry 333 (2017): 186-199.

Holman, Dawn M., et al. “Patterns of sunscreen use on the face and other exposed skin among US adults.” Journal of the American Academy of Dermatology 73.1 (2015): 83-92.

Saini, Ritu, and Andrea Szemplinski. “How to choose the right sunscreen for your skin type.” (2016).

Wahie, S., J. J. Lloyd, and P. M. Farr. “Sunscreen ingredients and labelling: a survey of products available in the UK.” Clinical and Experimental Dermatology: Clinical dermatology 32.4 (2007): 359-364.

Gasparro, Francis P., Mark Mitchnick, and J. Frank Nash. “A review of sunscreen safety and efficacy.” Photochemistry and photobiology 68.3 (1998): 243-256.

Which came first, the chicken or the egg?

A classic philosophical conundrum, intentionally baffling and likely argument-provoking.

“You need a chicken to lay an egg, but chickens come from eggs, so you need an egg to get the chicken… to lay the egg, from which to get a chicken to lay an egg…”

This can (and often does) go on forever, an endlessly frustrating loop of logical fallacy.

I was pretty surprised  then, when the answer was suddenly provided in one of my classes, a course on evolutionary ornithology. We were discussing a phylogenetic tree,  when my professor casually pointed out an easy, glaringly logical, loophole in the age-old query.

So, scientifically speaking, which came first, the chicken or the egg?

Egg Timeline:

The amniotic egg, or cleodic egg as it is also sometimes called, is thought to have evolved between 340-370 million years ago, and is highly conserved across many classes and families, from mammals like us to crocodiles. The classification of amniotes includes all vertebrate animals with four limbs and amniotic eggs, so think all mammals (Synapsida), and reptiles/birds (Reptilia) (Sander 2012).

What exactly is so special about this egg?

The amniotic egg is characterized by its complex of inner membranes. The allantois, which is directly attached to the embryo, primarily holds the waste products, while the yolk sac contains all the nutrients the embryo will need for development. The embryo is bathed in a stable fluid environment, surrounded amniotic fluid and enclosed in amnion membrane. The outermost membrane, the chorion, provides close contact between the eggshell and its internal contents, allowing for the necessary gas exchanges of O₂ and CO₂, and holding the other structures together. Finally, there is the outer shell layer, which can be leathery (as can be seen in some turtle species) or calcified, like the hard eggshells of birds and crocodiles. This outer shell is semi-permeable, again to permit the gas exchanges needed for respiration, and to keep moisture in and harmful microorganisms out (Sander 2012).

Quick aside- yes, mammals generally don’t lay eggs (excepting the monotremes such as platypuses and echidnas). However, the eggs that develop in the uterus before live birth are still considered to be amniotic eggs, since the embryo is surrounded by necessary membranes to encase fluid. They simply lack the outer eggshell and remain inside the mother’s body.  It is also worth noting that while the placental organ does perform some of the functions internal membranes have in other animals, most noticeably the nourishing role of the yolk, mammal embryos still have a yolk sac in early stages of development, as well as the other characteristic structures of the amniotic egg.

This general structure of the amniotic egg is a major landmark in the evolutionary history of life. By providing a way to contain fluid, it eliminated the dependence of reproduction on bodies of water to lay and incubate in, and thus opened up a whole world for vertebrates to expand into. In fact, it’s considered the most defining development allowing for the evolution of life on land! And these eggs are quite old, evolving no later than 310 million years ago with the last common ancestor of mammals and birds. Most estimates place the appearance of the amniotic egg between 340 and 370 million years ago (Sues 2016).

Chicken Timeline:

Alright, now let’s consider the chicken. The modern common domestic fowl (Gallus gallus domesticus), what we know as chickens, have a long and storied evolution like all birds, stretching back into the age of dinosaurs, and more specifically, the therapods. Therapods are thought to have first appeared in the late Carnian age of the late Triassic period, somewhere around 232.4 million years ago, as a clade of saurischian dinosaur. They were a widely diverse group, but main features included hollow, light-weight bones, and bipedality, and they were generally carnivorous. Within the more specialized subsets, there are the Tetanurae, which are further subdivided into Megalosauroidea and the Avetheropoda. The Avetheropoda, contained Carnosauria and the Coelurosauria, from which birds are direct descendants!

If we jump ahead a few million millennia, we can track down the last relative from which our favorite bird diverged. Gallus gallus domesticus, is a subspecies of the junglefowl, Gallus gallus, of the order Galliformes, suborder Galli, and family Phasianidae. Galliformes are originally from Southeast Asia and have been around for an estimated 50 million years. Although there are other jungle fowl with whom the chicken may share genetics, including the gray jungle fowl, Gallus sonneratii, that likely contributed the trait of yellow skin on their feet,  it well accepted that the chicken diverged most directly from the red junglefowl (Potts 2012). In one study by Sawai et al (2010), an analysis of DNA from 19 birds (including red and green junglefowl and several breeds of chickens), found that that the domestic chicken diverged from the red junglefowl  58,000±16,000 years ago, which had in turn diverged from its last common ancestor with the green junglefowl around 3.6 million years ago. This places our oldest chicken between 42,000 and 74,000 years ago (Sawai et al 2010).

The Results are in…Eggs are way older

Compared to the egg’s minimum of 310 million years, the chicken is practically a baby in evolutionary terms, somewhere around a mere 58,000 years old.

When you set the comparison in these terms, it is an easy landslide. Of course, you may very well be thinking, “that’s great and all, but that’s not technically a chicken egg. Surely you need a chicken for the egg to be a chicken egg, right?”

And you are not wrong- there are specific enzymes and other proteins that only chickens have which play a crucial role in their eggshell formation, with most people citing ovocledidin-17 as the primary example of this.

When you think of an egg, a hard-shelled egg, the kind of egg  one might decorate at Eastertime, or buy by the dozen at the supermarket, however, the defining features are not of a chicken egg specifically. First and foremost, you are thinking of the massively distinct amniotic egg, which has existed before birds, much less chickens, were around to lay them.

Yes, the question is rigged. It is a false dichotomy, and not meant to have a clear solution. If you are like me, however, this is the most satisfying ending; a supportable conclusion and some great practice in phylogenetic problem-solving.

References:

Amniote Egg. (n.d.). Retrieved from http://www.biologyreference.com/A-Ar/Amniote-Egg.html.Emma.berthold@science.org.au. (2019, September 19). Which came first: the chicken or the egg? Retrieved from https://www.science.org.au/curious/earth-environment/which-came-first-chicken-or-egg.

Potts, A. (2012). Chicken. London: Reaktion.

Sander, P. M. (2012). Reproduction in Early Amniotes. Science, 337(6096), 806–808. doi: 10.1126/science.1224301

Sawai, H., Kim, H., Kuno, K., Suzuki, S., Gotoh, H., Takada, M., . . . Orban, L. (2010). The Origin and Genetic Variation of Domestic Chickens with Special Reference to Junglefowls Gallus g. gallus and G. varius (The Origin of Domestic Chicken). PLoS ONE, 5(5), E10639.

Sues, H.-D. (2016). Amniotes, Diversification of. Encyclopedia of Evolutionary Biology, 56–62. doi: 10.1016/b978-0-12-800049-6.00279-1

Every year I move into a new room on campus at Georgia Tech, I buy a package of sticky putty, hoping that it will be strong enough to hold my large posters of the periodic table and Chance the Rapper, because command strips are just way too expensive. They usually fall down in the middle of the night, waking me up in terror. Recently in my polymers class, I learned about the beauty of spider silks and how they secrete different silks to accomplish different tasks. When I googled “spider silk,” I found articles and youtube videos claiming that spider silk is stronger than steel. I wondered how spiderwebs are able to stick to walls better than my command strips, but when I accidentally run into one, it breaks easily.

After doing some research, I learned that strands of spider silk are actually made of thousands of close-packed, parallel nanostrands, and depending on the gland they are secreted from, their tensile strength is 100-400 kpsi, compared to steel, which is 40 kpsi [1]. The secret is in how the tensile strength is measured. Tensile tests consist of putting a material in tension, essentially stretching it until it breaks. Spider silk is made of semi-crystalline polymer nano strands that can stretch a lot before breaking, and having many strands stacked together makes it even stronger, while steel thread of the same diameter or density has a crystalline structure that doesn’t stretch. This scenario is analogous to breaking a single stick of strong wood versus breaking a bundle of many weaker but stretchier sticks of wood: the bundle wins.

Spiders have different glands that secrete silks with different properties as protein structures to accomplish different tasks [2]. The tubuliform gland creates the silk to make the hard outer shell for an egg sac, and the aciniform gland makes the inner lining of the egg sac. The aggregate and flagelliform glands produce the sticky droplets and capture spiral threads, respectively, to catch prey.  The major ampullate gland makes the frame of the web as well as the dragline silk that allows the spider to move around. Lastly, the pyriform silk gland is responsible for the silk that attaches the web to the walls, trees, your bedroom window, etc. Pyriform silk is described as a “protein glue” or a “glue-like cement” that holds small amino acid fibroins, which then connect larger dragline silks, and are sometimes reinforced by aciniform silk [3]. Together, all of these components create a very strong network of silks that makes the overall product very adhesive. 

In this picture from a study that took Scanning Electron Microscope (SEM) images of a single attachment point of a web, it looks like the pyriform silk is a splat of glue with the dragline silk (white arrow) stuck in it [4]. Looking closer, the “glue” looks like a network with many, smaller attachments to the surface of the wall. 

Meanwhile, the sticky putty that I use to try to hang up my posters isn’t as robust as the spider silk glue. The formula for sticky putty is a trade secret, but it is known that it works as a pressure-sensitive adhesive, so the extent of adhesion depends on the amount of pressure you apply to it, as well as the shape and geometry. So even though I add a lot of pressure to the poster when I first apply it, depending on the weight of the poster and the amount of putty I used, the poster will slowly pull the putty off the wall, depending on how much I used and the temperature of my room [5]. 

If spider silks are so strong and perform so many tasks well, why don’t we make adhesives or other high performance materials out of it? There have been many ideas for potential uses of spider silk in body armor due to its mechanical properties. It is also antimicrobial, so there are many ideas for biomedical applications, such as scaffolding for tissue generation [2]. However, spider silk is extremely difficult to harvest. This is because spiders are inherently cannibalistic and produce a small amount of silk in comparison to silk worms, which are typically used to harvest silk for textiles. Scientists have attempted to put spider genes in silkworms, but the silk they produce still isn’t of the same quality [6]. So unfortunately, I probably can’t get a spider as a pet and harvest the silk for my dorm posters. But doing all this research made me curious: How is Spiderman’s silk compared to actual spider’s silk? And where are the silk glands?

 

References:

[1]Hayashi, C. Y., Shipley, N. H., & Lewis, R. V. (1999). Hypotheses that correlate the sequence, structure, and mechanical properties of spider silk proteins. International journal of biological macromolecules, 24(2-3), 271-275.

[2] TED. (Dec 7, 2011). Hayashi, Cheryl: The Magnificence of Spider Silk [Video file]. Retrieved from https://www.youtube.com/watch?v=xossR6eHv3I&t=248s

[3]Hardy, John & Römer, Lin & Scheibel, Thomas. (2008). Polymeric materials based on silk proteins. Polymer. 49. 4309-4327. 10.1016/j.polymer.2008.08.006.

[4]Blasingame, Eric et al. “Pyriform spidroin 1, a novel member of the silk gene family that anchors dragline silk fibers in attachment discs of the black widow spider, Latrodectus hesperus.” The Journal of biological chemistry vol. 284,42 (2009): 29097-108. doi:10.1074/jbc.M109.021378

[5] “Blu Tack FAQs.” Blu Tack, Wayback Machine Internet Archive, 2010, web.archive.org/web/20100418062649/http://www.blutack.com/faq.htm.

[6] SciShow (Feb 4, 2019). Green, Hank: Why Can’t We Make Spider Silk? [Video file]. Retrieved from https://www.youtube.com/watch?v=UX2LHcLxjio

It is a truth universally acknowledged that any homework of significant difficulty is in want of long hours to completion. In this case, twenty hours, give or take some breaks to re-hydrate from where the tears slipped away unnoticed among the frustration and eye strain. Even then, the outcome isn’t what you wanted and you may not make the deadline at all.

May whatever powers-that-be bless professors that give their students who fail part one of a multi-part homework a working version to complete the next section.

All dramatics and literary reference aside, animation is hard. I know this for a fact, I’ve been doing frame-by-frame animation since middle school and, while that can get tedious, it is much, much more straightforward than the computer graphics assignment I was referencing above. However, I’m getting ahead of myself; this is a story about learning, frustration, trial, error, failure, success, and at the end of it all, the final product.

The first thing to note is that Computer Graphics is a known grade killing class, and has been that way for at least five years, if not since it’s conceit. You talk to any Georgia Tech student who has taken the course and they’ll tremble in horror, either fake or very real, the reaction is the same at its core. I, unfortunately, didn’t know this until after I had begun.

The second thing to note is that the professor that I had for the class was infinitely preferable to previous holders of the position, as referenced by the second paragraph.

The third thing to note is that I’m still not entirely sure what a scene graph is. Of course, I understand what it is in concept — a data structure designed to keep graphic elements organised in a certain configuration for ease of use. Say you had a character with the parts: body, head, left arm, right arm, left leg, right leg, left hand, right hand, left foot, and right foot. The graph would be organized something like this:

Body
/           |            |            |             \
Head    left arm   right arm      left leg     right leg
|               |              |            |
Left hand    right hand    left foot    right foot

The character would then be connected to the world of the scene through the Body node. Using this construction, all of the pieces of the scene graph of the character are moved relative to its parent nodes– the nodes above it and connected to it within the scene graph. It’s fairly simple for anyone with a basic knowledge of coding languages, but understanding a scene graph and implementing one are two entirely separate things. It’s the implementation where I stumbled and was left in the dust on the side of the road.

However, homework waits for no one, especially not a homework with multiple parts. Part two of the homework was to create a character using the scene graph implementation from part one, and to connect the pieces appropriately to make a recognizable image of at least ten parts and three levels like the scene graph above. This was accomplished mostly by trial, error, and begging my fellow students to take pity and help me. If there is one thing I can say about college, it really does destroy any pride you may have once had when it comes to school work.

The third and final part of the homework was to take the character from part two and create an animation in the scene graph. Camera movements, movement of at least one part of the character, and one part of the surrounding scene were required. This part came the easiest to me, but it was still an exercise in frustrated guess-and-check. Moving the camera a few degrees only to find you turned it the wrong direction, making sure that the piece of your character that you decided to move doesn’t visually disconnect itself and become a floating arm spinning into the distance.

I’ll admit, I laughed aloud at some of the things my errors caused, but it felt more hysterical than anything at the time. When your entire animation starts spinning into the endless void, you have to start laughing, or you’ll cry. Still, I lived in the TA office hours until I finally managed to create a working product. It isn’t what I wanted, not nearly as good as it could have been, but remember what I said earlier about pride. If it completes all of the requirements and doesn’t look like hot garbage, it is a success.

You can view the finished version that took 20 hours out of my life by clicking the link below.

https://dj-baker.github.io/charged-animation/

A Tale of Binge-Watching and You

After years of saying ‘I don’t need it’ or ‘it will waste my time,’ I finally caved last year and started using Netflix. My friend decided to celebrate the occasion by trying to hook me on the show, You. We huddled on her couch and watched the first two episodes together. Afterwards, she left it up to me to finish the season. However, like I tend to do with many things, I put it off. Over a month passed before I finally decided to finish the show. I sat down the following Saturday afternoon to begin episode three and came to my senses hours later when I realized I had finished the entire series. I had been so eager to feel the rush of the story and not be left on cliffhangers that I gave up my entire afternoon to gain some closure. While part of me felt a little empty inside due to forking over so much continuous time to the show, I did actually enjoy its contents and was eager to discuss it with my friend. However, I was not able to see her until 2 weeks later. When this chance finally arose for me to devour every detail of the show and its story, I suddenly started drawing up blanks. I could remember those first two episodes fairly well, but when it came to the nine episodes I watched in the same day, I could really only remember the ending and a few select events in detail. Everything else blurred together. He did what in which episode? Wait, did she actually do that? My memory was foggy and nothing stood out clearly but those first two episodes. Why did I remember those so well even though it had been well over a month since I had seen them and yet all the more recent episodes I watched were already well-faded in my memories? Besides just wasting my time, did binge-watching have some unforeseen consequences on me?

The answer is yes. A recent study has linked binge-watching to the reduction of long-term memories of basic details related to watched shows (Hattie, Horto, Horvath & Lodge, 2017). When compared to normal television viewers who tend to watch one new episode per week, binge-watchers scored lower on basic assessments regarding common details of specific episodes and characters of the shows they’ve seen. Why though does binge-watching have this effect on individuals? The science behind this is connected with memory consolidation and a little phenomenon called the temporal distinctiveness theory.

Memory Consolidation and Your Brain

Memory consolidation refers to the process of converting a temporary memory into a long-lasting one. For a memory to become permanent, the memory must be transported from the hippocampus (the part of the brain related to short-term gains and instinct) to the neocortex (part of the brain connected to rational thought/deeper thinking)(Squire, Genzel, Wixted & Morris, 2015).During this transfer, the long-term memory is established by increasing the complexity, distribution, and connectivity of the neocortex with respect to the other parts of the brain. Without this transfer and shifts in the neocortex, the initial memory becomes lost to the person within a short period of time. 

A couple of different factors can influence how well someone can consolidate a memory. For example, the amount of prior knowledge one has on a topic can influence the strength of one’s ability to make these long-term memories. Another factor that affects this process of consolidation is time, and this time factor can be explained by the temporal distinctness theory.

Temporal Distinctiveness Theory: The Gap Between Memories

Temporal distinctiveness theory essentially states that by increasing the time gap between solidifying new long-term memories, you can better recall them more distinctly at a later time (Cowan, 2008). When a single item/event has been given time to be isolated by itself, then that memory can be transferred into the neocortex as a much more distinct and identifiable memory versus if multiple consecutive memories are trying to be stored in the neocortex at once. This “downtime” for memories to be installed into the neocortex is called neutral memory consolidation (Brown, Ecker & Lewandowsky, 2014). During neutral consolidation, the brain is either doing low mental activities or sleep, giving it a chance to successfully transfer the memories from the hippocampus to the neocortex. When I watched the first two episodes of You and then gave myself time to absorb what occurred in those episodes, I was able to better create distinct long-term memories from those experiences and recall more specific details from the show. However, when I binged-watched the other nine episodes, I did not give myself time between each episode to consolidate my memories, which is why all of my memories regarding those episodes (barring the very end) were foggy and jumbled together. Binge-watching my show, while enjoyable at the time, stripped me away from my ability to better remember what happened in it in the future. 

So Netflix or TV?

We all hate that feeling of watching a captivating show on TV and then being forced to wait a week or month for its conclusion. It feels so rewarding to just get that immediate answer to a question without being forced to suffer and mull over all the possibilities of what’s going to happen to your favorite character. However, for this quick satisfaction, we relinquish part of our ability to better remember the content that we witness. Binge-watching does not give you brain the chance to transfer that event into long-term memory. Though, at the end of the day, it is still up to you to decide your viewing experience. Which part of the trade-off will you accept: binge-watching’s instantaneous enjoyment but long-term haziness, or TV’s long-lasting remembrance but painful wait time? I’ve already decided my choice for the next series on my Netflix list: Bojack Horseman season 6. I’ll be taking it one episode at a time, so I can make distinct memories to stay with me well after I finish the show. What about you?  

 

Citations

• Brown, G. D. A., Ecker, U. K. H. & Lewandowsky, S. (2014). Memory Without Consolidation: Temporal Distinctiveness Explains Retroactive Interference. Cognitive Science. Volume 39. Issue 7. https://doi.org/10.1111/cogs.12214 
• Cowan N. (2008). What are the differences between long-term, short-term, and working memory?. Progress in brain research, 169, 323–338. doi:10.1016/S0079-6123(07)00020-9
• Hattie, J.A.C., Horto, A. J., Horvath, J.C., & Lodge, J. M. (2017). The impact of binge-watching on memory and perceived comprehension. First Monday. Volume 22. Number 9. https://firstmonday.org/ojs/index.php/fm/article/view/7729/6532 
• Squire, L. R., Genzel, L., Wixted, J. T., & Morris, R. G. (2015). Memory consolidation. Cold Spring Harbor perspectives in biology, 7(8), a021766. doi:10.1101/cshperspect.a021766