Tag Archives: pressure

Surface displacement.

Scientists have calculated the force of a photon hitting an object

An international team of researchers has finally been able to calculate the momentum of light.

Light night.

Image credits Felix Mittermeier.

Light exerts a minute pressure on the objects it interacts with. Finding the exact value of this pressure is a quest that scientists have pursued for nearly 150 years now. Today, a team of researchers has finally cracked it.

A light touch

Photons, although lacking in mass, do have momentum — so when they hit an object, they apply a force onto it.

This idea first surfaced in science in 1619, in a treatise by the German mathematician and astronomer Johannes Kepler. He believed that the pressure exerted by light was the reason why a comet’s tail always pointed away from the Sun. In 1873, Scottish physicist James Clerk Maxwell proposed that light is a form of electromagnetic radiation — and thus carries momentum, allowing it to exert pressure on matter. Thus, the pressure exerted by light was linked to its momentum.

Maxwell’s hypothesis turned out to be true. However, because the momentum of light is extremely tiny, the pressure it exerts is also exceedingly low — so measuring it directly is next to impossible.

“Until now, we hadn’t determined how this momentum is converted into force or movement,” explains coauthor and engineer Kenneth Chau of the University of British Columbia, Okanagan Campus, Canada.

“Because the amount of momentum carried by light is very small, we haven’t had equipment sensitive enough to solve this.”

We still don’t have any piece of equipment sensitive enough to measure this momentum — which makes the current findings all the more impressive. Chau’s team — which includes members from Slovenia and Brazil — found a way to work around this limitation, however.

The device they built is based around a mirror. The team fitted highly-sensitive acoustic sensors to it and then encased the contraption in several layers of heat shielding material to protect it from outside interferences. The last step was to shoot laser pulses at the mirror.

As photons in the laser hit the mirror, they apply pressure which generates movement (elastic waves) across its surface. The acoustic sensors measured these waves, which the team later used to calculate the pressure generated by individual photons.

Surface displacement.

Surface displacements caused by the laser. “Displacement” is measured in femtometers (quadrillionths of a meter).
Image credits Tomaž Požar et al., 2018, Nature Communications.

“We were able to trace the features of those waves back to the momentum residing in the light pulse itself, which opens the door to finally defining and modeling how light momentum exists inside materials.”

The research provides the framework from which researchers can refine the value. An accurate value of radiation pressure could have wide-ranging applications, from better optical tweezers — scientific instruments that use highly focused laser beams to manipulate particles down to the scale of a single atom — to more efficient solar sails that will let us zip about the universe without the need for fuel.

“We’re not there yet,” Chau said, “but the discovery in this work is an important step and I’m excited to see where it takes us next.”

The paper “Isolated detection of elastic waves driven by the momentum of light” has been published in the journal Nature Communications.

Pressure distribution.

Pressure in protons’ cores is over ten times greater that that in neutron stars

An experiment once thought to be impossible reveals that the protons have incredibly pressurized cores.

Pressure distribution.

Pressure distribution in the proton. The left end of the scale is the proton’s core, the right end corresponds to the proton’s edge.
Image credits V. D. Burkert et al., (2018), Nature.

Protons are the positively-charged elemental blocks of matter — only, they, in turn, consist of three smaller particles called quarks. Each is made up of two ‘up’ quarks and one ‘down’ quark bound by the strong nuclear force. However, beyond that, we simply don’t know much about the internal going-ons of protons. Given how hard it is to split one, it’s obvious that the three quarks are held tightly together.

But they’re bound together so strongly that, in the absence of something to push back, they would just collapse into a single point. To get to the bottom of things, one team of researchers reconciled two theoretical frameworks (one of which was actually considered impossible to implement directly) and then shot an electron through the proton. But the results were worth all the hassle.

“We have the medical 3D imaging technology that now allows the doctors to learn more in a non-invasive manner the structure of the heart,” study co-author Latifa Elouadrhiri from the Thomas Jefferson National Accelerator Facility told Nature. “And this is what we want to do with the new generation of experiments.”

Back in 1966, American physicist Heinz Pagels showed that the energy and momentum of a proton’s internal components can be gleaned from so-called gravitational form factors. However, Pagels himself pointed out that, because the gravitational forces involved would be ludicrously tiny, his findings wouldn’t actually ever be used in practice.

Since then, however, researchers have developed mathematical models that allow them to produce a 3D model of a proton’s structure by probing its electromagnetic force. These models are known as generalized parton distributions — or GDPs. It was these GDPs that the team used in lieu of the gravitational probe to turn Pagels’ work into something with practical applications.

“This is the beauty of it. You have this map that you think you will never get,” says Elouadrhiri. “But here we are, filling it in with this electromagnetic probe.”

The team used the Compton scattering effect, which describes the interaction between photons and a charged particle (such as an electron) to finally peer into the proton. The team accelerated an electron to massive speeds, in a bid to narrow its wavelength — then shot it at a proton. Then they analyzed the pattern of scattering for the photons produced int he collision to determine how the quarks fared in the impact.

According to the team, the scattering patterns suggest that the center of the proton is pressurized, preventing the particle from collapsing in on itself. An equal pressure from the outside keeps the quarks together. What was surprising, however, was just how immense these pressures were: 100 decillions (35 zeroes) Pascal. To put that into perspective, it’s ten times the pressure inside a neutron star.

Next up, the team plans to continue using this process to further explore the proton’s internal structure and mechanics.

The paper “The pressure distribution inside the proton” has been published in the journal Nature.

What Can Quartz Crystals Really Do?

Image in public domain.

Crystals and quartz

Crystals have caught the eye of humans since the dawn of time. Some scientists have even speculated that the origins of life on Earth may trace its origins to crystals. It shouldn’t come as a surprise that these gleaming mineral formations appear frequently in pop culture often as having supernatural powers (even though they don’t). A few examples of this reoccurring theme are the Silmarils in the Lord of the Rings universe and the sunstones in James Gurney’s Dinotopia.

The atoms which make up a crystal lie in a lattice which repeats itself over and over. There are several methods for generating crystals artificially in a lab, with superheating being the most common process. Likewise, in nature, a hot liquid (eg: magma) cools down, and as this happens, the molecules are attracted to each other, bunching up and forming that repeating pattern which leads to crystal formation.

Quartz is one of the most abundant minerals found on the planet. This mineral is known to be transparent or have the hues of white, yellow, pink, green, blue, or even black. It is also the most common form of crystalline silica which has a rather high melting point and can be extremely dangerous if inhaled in its powdered form. This mineral compound is present in the majority of igneous rocks. Some quartzes are considered semiprecious stones. Aside from mere bedazzlement, they have been used in countless industries.

Industrial, not magical uses

If a pressure is applied to the surface of a quartz crystal, it can give off a small electrical charge. This effect is the result of the electrically charged atoms (the ions) dispersing and spreading away from the area to which the pressure is being applied. This can be done in a number of ways, including simply squeezing the crystal. It also dispenses an electric current if a precise cut is made at an angle to the axis.

Since it possesses this property, quartz has been a component of devices such as radios, TV’s, and radar systems. Some quartz crystals are capable of transmitting ultraviolet light better than glass (by the way, quartz sand is used in making glass). Because of this, low-quality quartz is often used for making specific lenses; optical quartz is made exclusively from quartz crystals. Quartz which is somewhat clouded or which is not as transparent as the stuff used for optics is frequently incorporated into lab instrumentation.

Scientists have employed quartz for many things, and they have considered its role in the Earth sciences a crucial one. Some have stated it directly brings about the reaction which forms mountains and causes earthquakes! It continues to be used in association with modern technology, and it likely will lead us to more discoveries in the future.

Bio-compatible wireless sensors developed to monitor brain injury

An international research team has developed miniaturized devices to monitor living brain tissue. When no longer needed the devices can be deactivated to dissolve and be reabsorbed into the soft tissue. The wireless sensors were implanted into mice brains and successfully took intracranial pressure and temperature readings.

Dissolvable brain implant consisting of pressure and temperature sensors (bottom right) connected to a wireless transmitter. Image via theguardian

Dissolvable brain implant consisting of pressure and temperature sensors (bottom right) connected to a wireless transmitter. Kang et al, 2017

Electronic implants have long been used in the treatment of medical conditions. Ranging from the humble pacemakers and defibrillators given to cardiac patients all the way to futuristic brain-computer interfaces or injectable meshes that fuse with your brain, it’s hard to imagine today’s medical field without these devices.

Whether implanted permanently or only for short periods of time, the procedure always carries some risk — the devices can hurt surrounding tissues during implantation and their metallic components are prime real estate for bacteria, possibly leading to infections in the area. Not to mention the added risk and distress involved in removing these devices.

The novel device, developed by a research team with members from America and South Korea, is described in the journal Nature and could potentially overcome these limitations. Each device houses a pressure and a temperature sensor, each one smaller than a grain of rice. They’re housed in a biodegradable silicone chip that rests on the brain and sends data via wireless transmitters attached to the outside of the skull.

The devices were successfully tested on live rats and recorded pressure and temperature changes that occurred as the animals drifted in and out of consciousness under anesthesia. They proved to be at least as or more accurate than other devices currently available.

The team showed that by tweaking the sensors they could take measurements either from the surface of the brain up to about 5mm below it. The researchers say the device can easily be modified to monitor a wide range of other important physiological parameters of brain function, such as acidity and the motion of fluids. It could also be used to deliver drugs to the brain, and, with the incorporation of microelectrodes, to stimulate or record neuronal activity.

However, what truly makes this sensor unique is the materials that go into building them, the so-called “green electronics.” These materials are designed to be stable for a few weeks then dissolve. If immersed in watery fluids (such as cerebrospinal fluid) these fully biodegradable and bio-compatible materials take about a day to fully dissipate. When the team examined the animal’s brains after the tests, they found no indication of inflammation or scarring around the implantation site.

As well as being safer for the patient the fabrication process is also cheaper and more environmentally-friendly than that employed in existing technologies.

The next step in development is to test the devices in human clinical trials, the researchers said.

The full paper describing these devices is available online in the journal Nature.

Artificial skin can feel pressure, then tell your brain about it

Prosthetics has come a long way from its humble beginnings – the crude wooden legs of yore are a far cry from the technological marvels we can create to replace our limbs today. However, there is one thing that, with all our know-how, we haven’t yet been able to incorporate in them: a sense of touch. A research team from Stanford University aims to fix this shortcoming, and has developed technology that can “feel” when force is exerted upon it, then transmit the sensory data to neurons – in essence, they’ve created an artificial skin.

Image via factor-tech

Image via factor-tech

Tactile sense is a very important source of information for our brains, and having an otherwise functioning limb that doesn’t feel what it’s touching is something most of us can’t even imagine. Sit on your hand till it goes numb, then try to tie your laces – it’s frustratingly hard, and personally, I find the sensation disturbing.

Now imagine that numbness persists for your whole life. That’s what prosthetic users have to live with, a serious limitation imposed on even the most effective prosthetic. Without tactile sensitivity, it’s hard to maintain optimal motor control, and it’s impossible to know how much force you’re exerting on an object, or it’s temperature and texture, for example. To make matters worse, having a sense of touch (even the illusion of it) is one of the best ways to alleviate phantom limb pain, which affects nearly 80% of amputees.

The human skin is a superbly complex and well tuned sensory organ – so much so in fact, that we may never be capable of creating something that reacts to stimulus in quite the same way it does. But the Stanford team, led by electrical engineer Benjamin Tee, recently performed a proof-of-concept experiment that brought artificial tactile sense from the realm of sci-fi one step closer to reality. They used flexible organic circuits and innovative pressure sensors to create a skin-like interface that can sense the force of static objects. Data recorded by the device was transmitted via optogenetic to cultured mice brain cells. Their work was published in the journal Science.

The DiTact

Artificial mechanoreceptors mounted on the fingers of a model robotic hand.
Image via phys

The system, dubbed “DiTact” (Digital Tactile System) relies on low-power, flexible organic transistor circuitry, that can translate pressure into the same signals our natural mechanoreceptors generate. To make the sensors precise and to give them a wide enough range of pressure recording, the team created them out of carbon nanotubes shaped into tiny pyramidal structures.

“Our sensor was made of tiny pyramids of rubber with carbon nanotubes distributed in it,” noted study co-author Alex Chortos. “This structure was very useful because it allowed us to easily change a few things, like the distance between the pyramids, the size of the pyramids, and the concentration of carbon nanotubes in order to get the ideal pressure sensing characteristics in the right range.”

The nanostructure of the pyramids allowed the researchers to increase the sensors’ precision close to the levels of our own cutaneous receptors.

Interfacing

But just having sensors isn’t enough, all the magic happens in the brain. To create sensation, the researchers took the signals from the piezometers and transferred them via optic cables to mouse cortical neurons – as the technology is still in an early stage of development, the cells were cultured in vitro rather than use the brains of live animals.

But using the same technique, signals from a prosthesis coated with DiTact could be fed directly to the brain of a living human – optogenetics has been successfully used on live subjects before. All that is needed is for a number of neurons to be genetically altered to respond to light signals. Using a transgene obtained from certain algae strands, neurons can be made to fire electrical signals when exposed to blue light, or to yellow light using a bacterial transgene.

However, because of the rate at which sensory information is processed by neurons, the team had to implement a few of their own changes to the classical method.

“Biological mechanoreceptors are able to produce signals as fast as several hundred electrical pulses per second,” says Chortos. “Previous optogenetic technologies were only capable of stimulating brain cells much slower than we need to mimic real mechanoreceptors.”

Luckily, Chortos knew of the work of Andre Berndt and Karl Deisseroth who developed a new type of optogenetic treatment that allows brain cells to be stimulated very rapidly so that they’re compatible with the speed of real mechanoreceptors. Using the new optogenetic proteins, the neurons were able to sustain longer intervals of stimulation, suggesting that the system could also work with other fast-firing neurons, including peripheral nerves. This, the team says, means that DiTact will likely work with live mice or humans, and the good results they’ve seen up to know means that they will test the system on a live mouse as soon as possible.

Getting a feel for the future

“We could validate that our sensor is conveying the correct information to [a live] animal by using behavioral cues, i.e. how the animal behaves in response to pressure,” said Chortos. “The ultimate test will be to attach the sensor to a human and ask them what they feel. In order to get truly natural touch sensing, we may need to modify and tweak our design.”

“We envision our artificial mechanoreceptors making the greatest impact via integration for sensory feedback with prosthetic systems in development by other groups,” noted co-author Amanda Nguyen. “As our sensor would be mounted alongside artificial limb systems, the primary safety concerns are centered around nerve stimulation patterns and interface.”

Nguyen notes that while the early work on sensory feedback with neurally interfaced prosthetics shows great promise, we need to truly understand how to effectively and safely stimulate nerves in order to provide realistic sensory feedback.

“As a greater understanding of stimulation parameters is gained, the output of our artificial mechanoreceptor will be tuned to follow these stimulation paradigms,” she said. “With demonstrated efficacy and safety, the potential for improving the quality of life for individuals with tactile impairments can be balanced with the ethical concerns raised by neuroprosthetics. Accessibility of this type of technology in humans will grow as both our understanding of neuroscience grows and prosthetic technology advances to provide nuanced sensory perceptions.”

 

At a few million atmospheric pressures, Hydrogen nears metal conductivity

Hydrogen is the most common element in the Universe. It’s the first element in the periodic table, and it has but one proton and one electron. Understanding how it behaves at very large pressures is crucial to our understanding of matter and the nature of hydrogen-rich planets.

hydrogen

Under typical conditions, Hydrogen is a diatomic molecule (H2); but as pressure increases, these molecules start to change – these different forms are called phases, and hydrogen as three well known solid phases. But it has also been speculated that at very large pressures, it starts acting like a metal, conducting electricity. As a matter of fact, a few more bold physicists believe that it can even become a superconductor or a superfluid that never freezes–a completely new and exotic state of matter.

In this new paper, a team from Carnegie’s Geophysical Laboratory examined the structure, bonding and electronic properties of highly compressed hydrogen using a technique called infrared radiation.

The team found the new form to occur between 2.2 million atmospheres at about 25 degrees Celsius (80 Fahrenheit) to at least 3.4 million times atmospheric pressure and about -70 degrees Celsius (-100 Fahrenheit).

Their results showed that in these conditions, hydrogen acts like no other structure that we know of. It has two very different types molecules in its structure – one which interacts very weakly with its neighboring molecules (highly unusual for matter at such high pressures), and another which bonds with its neighbors, forming surprising planar sheets.

“This simple element–with only one electron and one proton–continues to surprise us with its richness and complexity when it is subjected to high pressures,” Russell Hemley, Director of the Geophysical Laboratory, said. “The results provide an important testing ground for fundamental theory.”

Via Carnegie