Archive for May, 2022

May 03 2022

Using the Sun as a Lens

Published by under Astronomy

Is it even theoretically possible to image in any detail the surface of an exoplanet light years away? An optical telescope would need to be many times the diameter of the Earth to produce such images. This “brute force” method of just building a giant telescope is probably never going to happen. Instead we need to find a more clever way, a method of exploiting the laws of physics to magnify distant images orders of magnitude beyond current technology. One idea gaining attention is using the sun as a giant gravitational lens.

In 1916 Einstein published his theory of General Relativity, which conceptualized gravity as a distortion of spacetime. He predicted that an object with a large gravitational field would even bend light. His predictions were validated with the 1919 total solar eclipse. During totality stars could be seen around the edge of the sun, and their apparent positions indicated that light from those stars had been bent as they passed near the sun. That validation gave a huge boost to acceptance of Einstein’s theory and made him a scientific superstar. Building on this idea he later predicted that a distant massive object with a light source directly behind it from the perspective of Earth would be surrounded by a ring of light from that more distant object – called an Einstein ring. Although relatively rare because they require a precise alignment, Hubble has found many examples.

In 1979 Von R. Eshleman wrote a paper in which he proposed that Einstein’s gravitational lens effect could be leveraged to image objects at interstellar distances. He wrote:

“The gravitational field of the sun acts as a spherical lens to magnify the intensity of radiation from a distant source along a semi-infinite focal line. A spacecraft anywhere on that line in principle could observe, eavesdrop, and communicate over interstellar distances, using equipment comparable in size and power with what is now used for interplanetary distances.”

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May 02 2022

Portable Desalination

Published by under Technology

According to the WHO, one third of the people in the world lack access to safe drinking water. They report that, “Globally, at least 2 billion people use a drinking water source contaminated with faeces.” Some locations (like the island of Bermuda) lack any supply of fresh water, and depend largely on rainwater. While a lot of progress has been made over the last few decades, this remains a huge problem. It is also likely to be exacerbated by global warming and an increasing population. A proper sanitation infrastructure is the ideal solution, but in the meantime anything that can supplement supplies of drinkable water will help.

One technology that has been around for decades and is often pointed to as a potential solution is desalination, taking the salt out of salt water. If we can economically do this, then we could just get our fresh water supply from the ocean or from brackish sources. There are plenty of commercial options available, like this one, that uses reverse osmosis and filtration to desalinate and purify water. Even in developed nations desalination plants are becoming more common, as demand increases, and also to create a reliable local source even during times of drought. California has 11 such plants, like this one north of San Diego that produces 50 million gallons of fresh water per day.

There is also a use for small portable desalination options in poor or remote regions that lack access to centralized sources of clean water. Portable options can also be useful during disasters, or when demand spikes due to heat waves or droughts. Portable “suitcase” sized desalination devices already exist and can be purchased commercially. The SeaWater Pro, for example, costs about $6,000 and comes in a portable hard case. It comes in two options, a plug-in and one run by a lithium-ion battery. The battery option could also be paired with a portable solar panel, which range from a couple of hundred to a few thousand dollars depending on how much power you need. This device produces 10 gallons of fresh water per hour, or 240 gallons per day (if plugged in). That is enough to serve a few families or even a small village.

A recent study examines a new approach to portable desalination, using “multistage electromembrane processes, composed of two-stage ion concentration polarization and one-stage electrodialysis.”  The study demonstrates that the technology works, producing drinkable water up to the WHO standard starting with either brackish water or sea water. The advantage of this system is that it does not require filters, so nothing that needs to be regularly replaced. It is therefore a more independent system. A battery-based system has been field tested, and the authors report that: “The demonstrated portable desalination system is unprecedented in size, efficiency, and operational flexibility.” Continue Reading »

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