A model of space debris populations around Earth.

What kinds of problems could debris in space cause? They travel at speeds on the order of tens of thousands of miles per hour, which means that debris of any shape, size, and form will be destructive if it collides with a satellite or space shuttle. Collisions with space debris isn’t unheard of. Also, they could delay space launches if it is known that a large cloud of debris is hovering directly over the launch pad.

Space debris comes from a variety of sources. Nuts and bolts could become loose and float away from spacecraft during normal operation. When rocket stages (or segments) separate in space, they release debris. Also, in-space collisions between satellites, while rare, will create large-sized debris – the same goes for intentional spacecraft destruction, such as the Chinese anti-satellite test that was conducted a few years ago. Some of these events unleashes several thousand pieces of debris, most of which are tiny (less than an inch in size) and are much more difficult to track than larger-sized debris.

Over the past few decades, scientists and engineers have brainstormed possible solutions to decreasing space litter. However, all of the ideas have been technologically and/or economically infeasible. This could change as time goes on, especially as technology advances and/or the cost of launching a vehicle into space decreases. One possible solution is launching a garbage-collecting spacecraft to do just that, but what to do with the collected garbage is a problem. Another solution is somehow colliding objects with the orbiting debris in an effort to reduce their energy enough so that they fall into the Earth’s atmosphere (due to gravity) and burn up, but no one has thought of a feasible means to do that.

(Image from Wikipedia)

The basic gist of how Monte Carlo simulations work is that you randomly select inputs, perform calculations on the randomly-selected inputs, and collect the outputs. This process is repeated several times (perhaps thousands, tens of thousands, or even more! As with any statistical sample, the more, the better), and in the end, all the outputs are gathered together and analyzed. To randomly select inputs, you’ll need to specify boundaries for which inputs can be selected from. A statistical model can help with this, such as a Gaussian distribution, which is a fancy term for the familiar “bell curve.” As for the aggregated outputs, statistical analysis would make sense in order to make sense of thousands of data sets. Basically, statistics is a useful tool that compliments the Monte Carlo technique. Also, generally computers are used to perform a Monte Carlo simulation due to the large number of repetitive calculations required.

This is what a bell curve looks like.

Monte Carlo simulations can be used in space sciences. For example, if one wants to analyze the risk of failure of a spacecraft in orbit, one can perform a Monte Carlo simulation with random inputs for how the spacecraft begins its orbit (speed, physical orientation, etc.), since that state cannot be predetermined accurately and instead can be modeled statistically. Then, the laws of orbital mechanics can be applied to the inputs to produce outputs that can be analyzed later. A more simple example of where the Monte Carlo method is used is the classic game of Battleship. Initially, a player would randomly guess locations for where a battleship is located. After the player scores a hit, the player would follow an algorithm (guess points that are in line with the hit) to sink the battleship (the outcome).

(Image from Wikipedia)

There are three main components to version control: branches, tags, and the trunk. The trunk can be thought of the main sector of a software project: most of the development work stems from the trunk. Tags are for special milestones in a project. Branches are what they sound like: they branch off from the trunk like a tree. All versions of each file in the project, old and new, are stored in what is known as a repository, with version numbers denoting how old a particular revision is.

There are many ways to utilize the branch-tag-trunk combination, but here’s an example. Say you have a team of software engineers working on a project. The trunk would be where known good code lives – code that isn’t broken nor has bugs. When someone wants to modify the code in the trunk (perhaps to make enhancements or add features), they would create a branch in the project and do their work in the branch. After they are done making code modifications in their branch, they would merge their branch back into the trunk. Most of the time, version control software is smart enough to figure out which parts of a particular file were modified, and incorporate those changes when two versions of the same file are merged together. Merging can also occur when two or more people modify one file at the same time, and later on decide to commit their individual changes to the repository. This way, you can have teams of more than one person working on particular parts of a project without the hassle of figuring out who changed what when combining everyone’s contributions into one – that’s what the version control software is there for.

A simple diagram showing how version control works.

Continuing with the above example, let’s imagine a major milestone for the project has been attained (perhaps Version 1.0 of the software is complete and ready for release). The code would then be tagged as a tag, and would sit as that particular tagged version in the repository. This is an example of how all three components of version control software is used, and hopefully this article sheds some light onto the underworkings of large-scale software projects.

(Image from Wikipedia)

In most cases, conductive heat transfer happens more rapidly than convective heat transfer. That is, heat transfer through solid materials is more profound than that in liquids or gases. You’ve probably experienced this in your everyday lives, knowing that we can “sense” heat transfer when we feel warm or cold ourselves. The heat or cold that we feel is known as heat flux, which is heat transfer per unit area. Therefore, in most cases if we have a metallic object and a roomful of air at the same temperature, touching the metallic object will feel warmer (be careful of burns!) than simply standing in the room and absorbing the ambient temperature.

Wear gloves when touching hot metal surfaces!

Why does this happen? Intuitively, solids are denser than liquids and gases, meaning the molecules in solids are more closely-packed. This means that it is easier for heat to be transferred from molecule to molecule in solids, which would explain why heat transfers faster in solids.

When designing an apparatus for heat transfer purposes, one must consider two things: cost and effectiveness. Natural convection (such as with air) is relatively inexpensive because air is everywhere, but it isn’t as effective as using a metallic solid for heat transfer purposes. However, metals can be expensive. Therefore, some form of middle-ground is often desireable. This can be seen in computers, where fins conduct heat away from, say, a processor, and a fan blows the heat away in a process called forced convection.

(Image from WellBake)

The main goal of the contact lens (or glasses for that matter) is to simply bend light, or refract light, differently that our eye normally does. For someone with good vision, light enters the person’s eye where the lens, which is actually several layers of transparent cells, inside of the eye bend this light so it is well focused for the all-important receptor at the back of the eye, the retina. For people with poor vision, this light is progressively more and more poorly focused as eyesight gets worse and worse. We can liken this to the effect of a magnifying glass. Clearly we can place the magnifying glass at an optimal point between ourselves and the object we want to view, and the object will be magnified and very detailed. A slight disturbance in this distance ratio causes the image to lose focus, or refractive error, essentially allowing you to see what a person with not so perfect vision sees.

Now, let’s say that in our system we move toward magnifying glass a few centimeters. And lets assume that our eye can be considered the “retina,” since we’re working on a large scale here. The goal here is to place another lens in front of the magnifying glass to get that image to be focused again for this new location of the magnifying glass. And that, on a simple level, is the job of our contact lens.

That’s the technical. The practical is shown well in this image:

Where the lines meet is the focal point.

Optimally, we want the light to focus as in the center photo. However, due to different shapes in the eye (this is caused mainly through genetics, NOT sitting with your nose stuck to the TV for a long period of time. The latter has no effect on your vision, contrary to what seems to be popular belief.) the retina is not where the lens’ focal point is. It is as if in our system described above we moved toward or away from the “magnifying glass”, which in this case is the lens inside of our eye. To fix this, we place a contact lens on our cornea, or wear glasses in order to pass light through the eyes inner lens in a way such that the focal point will be on the retina of the eye.

That’s all there really is to it. For those still interested, The following links are rather interesting:

http://www.enotes.com/how-products-encyclopedia/contact-lens

- This link has a particularly interesting history section. Contacts have been around for about a hundred years, though back then, they were made with actual glass and supposedly, “To fit these early lenses, an impression had to be made of the patient’s eyeball”. Ouch.

http://www.youtube.com/watch?v=62tha1Kxa2c

- This link is a video that explains how contact lenses are made. Really thorough, and supposedly the actual process to make a contact lens takes only 15 minutes. Pretty short considering its a pretty complicated process, and everything needs to be perfectly done.

Image from : Vision Associates