Selected news from the latest edition of The Engineer

Physicists seek to determine the origin of cosmic X-rays

The NuSTAR satellite will include an extendable telescope to look for cosmic X-rays

UK researchers are hoping to determine the origin of cosmic X-rays using new satellite technology launched by NASA earlier this month.

Physicists from Durham University want to use the first space telescope that can focus high-energy X-rays using specially coated mirrors — part of the $170m (£110m) NuSTAR satellite — to confirm whether background radiation in space comes from black holes.

These X-rays aren’t detectable on Earth and were first discovered in space in 1962, but scientists have so far been unable to focus the radiation sufficiently to pinpoint its origin.

‘Black holes can pull in gas off nearby stars, and this gas gets very hot and emits strong X-rays,’ Prof David Alexander, the research project’s co-ordinator at Durham, told The Engineer.

‘We’ve known from telescopes that look at lower-energy X-rays that this is likely to be the case, but you don’t know [for sure] until you’ve looked [at higher energy levels] and you don’t know what the exact properties of the objects will be.’

High-energy X-rays can penetrate the gas and dust surrounding black holes so the scientists should be able to track them to their source, but this high penetration rate also makes them very difficult to reflect with focusing mirrors.

Conventional X-ray mirrors are made from high-density materials and are placed almost parallel to the beam’s direction of travel so the X-ray just grazes the surface, increasing the amount of reflection.

But these materials are not so good for reflecting high-energy X-rays, so NuSTAR will use mirrors that alternate the high-density platinum and tungsten with low-density silicon and siliconcarbite in hundreds of layers to form a ‘depth-graded multilayer’.

As the waves hit the different material layers, they produce slightly different patterns that interfere with one another and enhance the beam as it is reflected.

‘When previously we’d have an out-of-focus image, we’ll see things clearly for the first time at these energies,’ said Alexander.

‘We’ll be able to pinpoint where this X-ray emission is coming from and at the same time we can go about 100 times deeper than we’ve been before in the sense that we can see fainter objects.’

Several teams of academics from across the US and Europe helped to develop the telescope, which consists of 130 concentric mirror shells made by depositing the multilayer coating on a flexible glass substrate heated to give it the desired curvature.

The telescope is due to be deployed using a mast that folds out from the satellite once it is in orbit, extending up to 10m in order to position the optics at the right distance from the X-ray detectors to achieve the desired focus.

After a one-month calibration period, the satellite will collect data for an initial period of two years. But Alexander said he hoped the team would begin to make discoveries after just one month of data gathering.

Technology could monitor hip replacements for signs of wear

A new device could monitor hip replacements for signs of wear, powered only by the movement of the user’s walk.

The technology, designed to fit inside a typical prosthetic hip joint, uses a piezo-electric device that generates up to 3.7V of electricity as the user walks to power a strain gauge and a transmitter.

By using the strain gauge to monitor the distance between the prosthesis and the femur leg bone, doctors will able to tell if the replacement is starting to break down and advise the patient on lifestyle changes or the potential need for another operation.

‘Thirty per cent of hip replacements within six years start to show signs of osteolysis,’ said Brunel University student Luke Kavanagh, who developed the device.

‘As the joint comes loose it starts to work away at the plastic cement and these little particles then travel around the body and can actually start to corrode the rest of the femur and the hip.’

The device contains a ball bearing that rolls back and forth as the user walks along and strikes a substrate covered on one side with piezo-electric material (known as a unimorph) to produce electricity.

Kavanagh said the challenge was adjusting the rigidity of the unimorph so that it bent enough to produce sufficient power but was durable enough to survive this repetitive process.

He added that the device could be customised to adjust its output and durability depending on how active the user was.

‘An older person isn’t going to move with any real vigour, so you could put a much thinner unimorph in and get all the electricity from big deflections,’ Kavanagh said.

‘With a young person who’s going to be running around, you can put a much thicker one in, but because the velocity you’re hitting the unimorphs with is going to be so much greater you’d get the electricity you need either way.’

Material could enable cheaper method of carbon capture

A cheaper method of carbon capture could emerge from the creation of a unique porous material by UK researchers.

A team of scientists from Nottingham and Newcastle universities has designed a honeycomb-like metal organic framework (MOF) known as NOTT-202a to adsorb and release carbon dioxide (CO₂) gas at lower temperatures than existing capture methods.

The material adsorbs CO₂ under pressure and releases it as the pressure is decreased, while allowing other chemicals such as hydrogen, nitrogen and methane to pass out of it first.

NOTT-202a could avoid the need for the amine solutions that are commonly used in carbon capture but must be heated to release the CO₂ and can also be toxic.

‘The most novel aspect of this paper is the structure of the material itself,’ said Prof Marin Schröder, head of inorganic chemistry at Nottingham and one of the authors of a paper on the research published in Nature Materials.

The material consists of two interpenetrating networks formed from organic ligand molecules attached to a central indium metal atom, but with holes or defects in one of the networks to create more space in which to hold CO₂.

‘So you have a more porous network than what you would normally expect while the interpenetration means you have greater interactions between the pore walls and therefore you get stronger interactions with gases,’ said Schröder.

‘It’s a contradiction. You need narrow pores to maximise the interaction with gases but you also want the pores to be bigger so each can hold more gas.’

The researchers used the Diamond Light Source synchrotron at the Science and Technology Facilities Council’s Rutherford Apple Laboratory to take X-ray powder diffraction measurements that allowed them to see inside the material’s structure.

They have also developed a computer simulation that will allow them to test new designs of the material as they go through the process of optimising it so it can be scaled up for use in real carbon capture systems.

‘There are all manner of issues about scale-up of this material,’ said Schröder. ‘Can we make this material cheaply? Can we develop the ligand synthesis to be more green?’

These articles first appeared on The Engineer.