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Category: materials – Page 250

Metalens Retinal Projection Using The Eye’s Inherent Structure

The human eye does not work like a camera, contrary to common belief. Consider the following key factors:

1) Both the cornea and the lens COMBINE to give the focusing effect. Thus it is TWO lenses, not one that allow human vision. In fact the cornea is responsible for two-thirds or more of the focusing effect. The lens compounds that focusing, projecting it from past the pupil onto the curved retina at the back of the eye.

2) The eye corrects for CHROMATIC ABERATION by having a central pit, the FOVEA, where the blue cells are concentrated along the outer rim and the red cells concentrated in the center. Blue light focusses slightly closer to an objective lens and red light slightly further. Thus the red cells are concentrated further back, at the base of the pit, so that the human eye has a natural color correction without the need for complex color corrected lenses.

3) The retina is a curved “screen” at the back of the eye, allowing human vision to encompass an entire hemisphere of 180 degrees in the forwards direction. The retina is mostly rod cells except for at the central fovea, for seeing light but not color and detail, which is why it is easier to see faint objects through a telescope by using what astronomers call “averted vision,” not looking straight at it.

There are thus several factors in trying to use metamaterial lenses to create retinal projection, including:

1) Since the cornea is curved, a tailored curved contact metalens, instead of a flat metalens is ideal.

2) That lens must be able to project a wide-angled view through the lens of the eye, in such a way that the lens distributes the image widely onto the curved retinal screen.

3) If using a third exterior projection system onto that metalens, as with a pair of glasses, googles, or another metalens on top of the first one, it will be a four-lens projection system: projector metalens, contact metalens, human cornea lens, human eye lens. These elements will have to be coordinated into a single system with the final effect.

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Rippling graphene harvests thermal energy

New technology could deliver “clean, limitless, low-voltage power for small devices”.

The rippling thermal motion of a tiny piece of graphene has been harnessed by a special circuit that delivers low-voltage electrical energy. The system was created by researchers in US and Spain, who say that if it could be duplicated enough times on a chip, it could deliver “clean, limitless, low-voltage power for small devices”.

Brownian motion is the random movement of a tiny particle that is buffeted by atoms or molecules in a liquid or gas – and the idea of harnessing this motion to do useful work has a long and chequered history. In the early 1960s, the Nobel laureate Richard Feynman popularized a thought experiment known as the “Brownian ratchet”, which had been conceived in 1912 by the Polish physicist Marian Smoluchowski. This involves a paddle wheel that is connected by an axle to a ratcheted gear. Both the paddle wheel and the ratchet are immersed in fluids. The system is imagined as being small enough so that the impact of a single molecule is sufficient to turn the paddle. Because of the ratchet, the paddle can only turn in one direction and therefore it appears that the Brownian motion of the paddle can be harnessed to do the work of turning the axle.

However, Feynman showed that if the two fluids were at the same temperature, collisions throughout the system would prevent this from happening. The only way work could be done, argued Feynman, is if the fluids are a different temperature, making the Brownian ratchet a heat engine.

Researchers print rainbow colorants on shimmering chocolate

ETH researchers are making chocolates shimmer in rainbow colors without the addition of colorants. They have found a way to imprint a special structure on the surface of the chocolate to create a targeted color effect.

Traditional methods for coloring have been around for a long time. But the ETH researchers are able to create the rainbow effect without artificial colorants. The effect is achieved simply through a surface imprint that produces what the scientists refer to as a structural color. The process is similar to a chameleon, whose skin surface modulates and disperses light to display specific colors.

The story begins in the shared corridor of a university building. The food scientist Patrick Rühs, the materials scientist Etienne Jeoffroy and the physicist Henning Galinski chat about chocolate during their coffee break. Although they work in different research groups, their offices are next to each other. They wonder how—and whether—it might be possible to make colored chocolate. Rühs is studying the material properties of foodstuffs, Jeoffroy specializes in complex materials and Galinski has already done in-depth research into optical materials.

New Neutron Detector Can Fit in Your Pocket – Critical for Catching Smuggled Nuclear Materials

Homeland Security might soon have a new tool to add to its arsenal.

Researchers at Northwestern University and Argonne National Laboratory have developed a new material that opens doors for a new class of neutron detectors.

With the ability to sense smuggled nuclear materials, highly efficient neutron detectors are critical for national security. Currently, there are two classes of detectors which either use helium gas or flashes of light. These detectors are very large — sometimes the size of a wall.

For The First Time, Physicists Have Achieved Superconductivity at Room Temperature

A major new milestone has just been achieved in the quest for superconductivity. For the first time, physicists have achieved the resistance-free flow of an electrical current at room temperature — a positively balmy 15 degrees Celsius (59 degrees Fahrenheit).

This has smashed the previous record of −23 degrees Celsius (−9.4 degrees Fahrenheit), and has brought the prospect of functional superconductivity a huge step forward.

“Because of the limits of low temperature, materials with such extraordinary properties have not quite transformed the world in the way that many might have imagined,” physicist Ranga Dias of the University of Rochester said in a press statement.

NASA is getting ready to land on an asteroid that may hold the building blocks of life

With NASA getting ready to land a spacecraft on the asteroid Bennu in just a few short days, the mysterious space rock is already revealing some of its secrets, including the presence of carbon-bearing materials.

Several studies were published on the matter in the journals Science and Science Advances, noting that carbon-bearing, organic material is “widespread” on the surface of the asteroid. This includes the area where NASA’s OSIRIS-REx spacecraft will take its first sample from, known as Nightingale, on Oct. 20.

“The abundance of carbon-bearing material is a major scientific triumph for the mission. We are now optimistic that we will collect and return a sample with organic material – a central goal of the OSIRIS-REx mission,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona in Tucson, in a statement.

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