arnabocean

— by Arnab Gupta

What advantages does a composite have?

March 15, 2013

Previously, we talked about what composite materials are, in an engineering sense. To recapitulate, composites are materials comprising two or more constituents. The constituents are combined in a way such that they retain their distinct identities in the final material (unlike alloys, for example). In particular, we talked about composites with a homogenous ‘matrix’ material (such as epoxy resin in polymer composites, and metals such as aluminum in metal matrix composites) in which reinforcing fibers (such as carbon fibers or glass fibers) or particulates are embedded. The fibers are the reinforcing material that provides strength to the composite, while the matrix material serves other purposes such as: (a) protecting the fibers (b) binding the fibers together to actually create the composite (c) helping to redistribute stresses if a fiber breaks.

But the key question is: why use composite materials at all? Why not use metals as always? What advantages do composites provide? Turns out, quite a few.

So, what are Composites, again?

March 10, 2013

In the broadest sense, a composite material is one that consists of two or more distinct materials—which retain their individual properties even when the final material is formed! In fact, we’ve all encountered various composite materials in our everyday lives.

Aggregate Concrete

Aggregate Concrete. (Source)

Getting up to speed…

March 05, 2013

Let us get introduced, first, to a class of materials which are highly directional in nature. What does directional mean? Let me give an example. Imagine that you have a sheet of thermocol in your hand. Try to pull the sheet apart—if it’s thin enough, you probably can. Does it matter in what direction you hold the sheet of thermocol? Top-bottom versus left-right? Of course it doesn’t. This is an example of a material that is not directional—it responds in identical fashion, whichever direction you choose to interact with it in.

Thermocol Sheet

Thermocol Sheets. (Source)

It doesn’t matter if global warming is man-made

January 12, 2013

Earth’s climate is changing. If you’re not wearing blinkers, and usually follow the news, this should no longer be a controversial statement to you. (Of course, climate change is a better descriptor than global warming. Earth’s temperatures will not literally rise everywhere all the time. Instead, extremes of climates will become more extreme, and the overall nature of Earth’s climate will shift dramatically.)

For example, from this great New York Times piece:

Especially lately. China is enduring its coldest winter in nearly 30 years. Brazil is in the grip of a dreadful heat spell. Eastern Russia is so freezing — minus 50 degrees Fahrenheit, and counting — that the traffic lights recently stopped working in the city of Yakutsk.

Bush fires are raging across Australia, fueled by a record-shattering heat wave. Pakistan was inundated by unexpected flooding in September. A vicious storm bringing rain, snow and floods just struck the Middle East. And in the United States, scientists confirmed this week what people could have figured out simply by going outside: last year was the hottest since records began.

“Each year we have extreme weather, but it’s unusual to have so many extreme events around the world at once,” said Omar Baddour, chief of the data management applications division at the World Meteorological Organization, in Geneva. “The heat wave in Australia; the flooding in the U.K., and most recently the flooding and extensive snowstorm in the Middle East — it’s already a big year in terms of extreme weather calamity.”

Virgin births… in snakes!

November 01, 2012

Species that reproduce sexually usually need two partners to reproduce, right? Right. What I didn’t know was, females of some species (that usually reproduce sexually) have apparently been observed to be able to reproduce without a mate—rarely, and when they’re in captivity and away from potential mates.

But now, virgin births have been observed in snakes–in the wild, with males present nearby!

They captured pregnant copperhead and cottonmouth female pit-vipers from the field, where males were present.

The snakes gave birth, allowing the scientists to study the physical and genetic characteristics of the litters. […]

“That’s between 2.5 and 5% of litters produced in these populations may be resulting from parthenogenesis.

“That’s quite remarkable for something that has been considered an evolutionary novelty,” he said.

No insights yet on how and why this happens, though, or what implications it may have.

But this is fascinating, nonetheless.

Of Space Worms

July 21, 2012

Found this article recently, where they wanted to check how microscopic worms would do in space. Turns out, they do fine—in fact, they actually live longer in space! Additionally:

“We identified seven genes, which were down-regulated in space and whose inactivation extended lifespan under laboratory conditions,” Szewczyk said in a press release. This basically means that seven C. elegans genes usually associated with muscle aging were suppressed when the worms were exposed to a microgravity environment. Also, it appears spaceflight suppresses the accumulation of toxic proteins that normally gets stored inside aging muscle.

They’re not sure what the biological mechanisms might be behind this phenomenon.

I wonder, though—how much of it can be simple chemistry and fluid dynamics? We know that at small enough length scales (such as those of microscopic organisms) viscosity is a much stronger agent than inertia (governed by mass, and to an extent, gravity). Often, gravitational effects are ignored when doing small scale analyses. How do things change in the actual biology when gravity is really zero, not just as an approximation?

Also from the article:

“Most of us know that muscle tends to shrink in space. These latest results suggest that this is almost certainly an adaptive response rather than a pathological one. Counter-intuitively, muscle in space may age better than on Earth. It may also be that spaceflight slows the process of aging.”

I’m not sure why this seems novel. My thought has always been that muscle atrophy in space is due to lack of use, i.e. adaptation. This is why astronauts take special care to exercise their leg muscles while at the International Space Station. The legs no longer need to support the considerable weight of the human body, and the body efficiently starts optimizing its resources!

But perhaps (and most likely) my lack of knowledge allows me to simplify a phenomenon that a physiologist would find many angles to! I’d love to know those angles though—anyone reading this who can help?

☞ Rethinking Dinosaurs

July 21, 2012

The latest in paleontology:

[…] “a filamentous body covering obviously represents the plesiomorphic state for dinosaurs in general,” wrote Rauhut’s team.

Plesiomorphic is another way of saying “ancestrally typical.” In short, it was feathers all the way down.

What?! All two legged dinosaurs had feathers? What were we thinking all these years? Has this been verified?

Now they’ll have to make Jurassic Park all over again.