Lifeboat Foundation

White LEDs’ reign as the top light source may soon come to an end with the advent of a new alternative that offers superior directionality.

A photonic crystal or nanoantenna, a 2D structure with periodic arrangement of nano-sized particles, is being developed as a cutting-edge optical control technology. Upon exposure to light, combining a nanoantenna with a phosphor plate produces a harmonious mix of blue and yellow light.

White LEDs have already been improved upon in the form of white laser diodes, or LDs, which consist of yellow phosphors and blue LDs. While the blue LDs are highly directional, the yellow phosphors radiate in all directions, resulting in an undesired mixing of colors.

When waves damp or amplify on resonant particles in a plasma, nonresonant particles experience a recoil force that conserves the total momentum between particles and electromagnetic fields. This force is important to understand, as it can completely negate current drive and rotation drive mechanisms that are predicted on the basis of only resonant particles. Here, the existing electrostatic theory of this recoil force is extended to electromagnetic waves. While the result bears close similarity to historical fluid theories of laser–plasma interactions, it now incorporates both resonant and nonresonant particles, allowing momentum conservation to be self-consistently proven. Furthermore, the result is shown to be generally valid for kinetic plasmas, which is verified through single-particle hot-plasma simulations. The new form of the force provides physical insight into the nature of the generalized Minkowski (plasmon) momentum of geometrical optics, which is shown to correspond to the momentum gained by the field and nonresonant particles as the wave is self-consistently ramped up from vanishing amplitude.

If she hits just the right pitch, a singer can shatter a wine glass. The reason is resonance. While the glass may vibrate slightly in response to most acoustic tones, a pitch that resonates with the material’s own natural frequency can send its vibrations into overdrive, causing the glass to shatter.

Resonance also occurs at the much smaller scale of atoms and molecules. When particles chemically react, it’s partly due to specific conditions that resonate with particles in a way that drives them to chemically link. But atoms and molecules are constantly in motion, inhabiting a blur of vibrating and rotating states. Picking out the exact resonating state that ultimately triggers molecules to react has been nearly impossible.

MIT physicists may have cracked part of this mystery with a new study appearing in the journal Nature. The team reports that they have for the first time observed a resonance in colliding ultracold molecules.

Scientists have found the secret behind a property of solid materials known as ferroelectrics, showing that quasiparticles moving in wave-like patterns among vibrating atoms carry enough heat to turn the material into a thermal switch when an electrical field is applied externally.

A key finding of the study is that this control of thermal conductivity is attributable to the structure of the material rather than any random collisions among atoms. Specifically, the researchers describe quasiparticles called ferrons whose polarization changes as they “wiggle” in between vibrating atoms—and it’s that ordered wiggling and polarization, receptive to the externally applied electrical field, that dictates the material’s ability to transfer the heat at a different rate.

“We figured out that this change in position of these atoms, and the change of the nature of the vibrations, must carry heat, and therefore the external field which changes this vibration must affect the thermal conductivity,” said senior author Joseph Heremans, professor of mechanical and aerospace engineering, materials science and engineering, and physics at The Ohio State University.

Think of bringing a pot of water to the boil: As the temperature reaches the boiling point, bubbles form in the water, burst and evaporate as the water boils. This continues until there is no more water changing phase from liquid to steam.

This is roughly the idea of what happened in the very early universe, right after the Big Bang, 13.7 billion years ago.

The idea comes from particle physicists Martin S. Sloth from the Center for Cosmology and Particle Physics Phenomenology at University of Southern Denmark and Florian Niedermann from the Nordic Institute for Theoretical Physics (NORDITA) in Stockholm. Niedermann is a previous postdoc in Sloth’s research group. In this new scientific article, they present an even stronger basis for their idea.

An international team of space scientists reports that the moon exerts a tidal impact on the plasmasphere. For their paper published in the journal Nature Physics, the group used data from multiple spacecraft over a nearly 40-year period to measure tidal perturbations in the plasmapause. Balázs Heilig, with the Institute of Earth Physics and Space Science, in Hungary, has published a News & Views piece in the same journal issue, explaining the nature of the plasmasphere and outlining the work in this new effort.

Early scientists found a connection between the tides and the movement of the moon thousands of years ago. More recent evidence suggests the moon’s pull acts on the ionosphere as well. In this new study, the researchers wondered if the moon might also have an impact on the plasmasphere.

The plasmasphere is a toroidal mass of plasma that surrounds the Earth. It lies beyond the ionosphere and is made up mostly of electrons and protons. Its particles are charged by the ionosphere, and its outer boundary is known as the plasmapause.

Neutrinos are one of the most abundant particles in our universe, but they are notoriously difficult to detect and study: they don’t have an electrical charge and have nearly no mass. They are often referred to as “ghost particles” because they rarely interact with atoms.

But because they are so abundant, they play a large role in helping scientists answer fundamental questions about the universe.

In groundbreaking research described in Nature —led by researchers from the University of Rochester—scientists from the international collaboration MINERvA have, for the first time, used a beam of neutrinos at the Fermi National Accelerator Laboratory, or Fermilab, to investigate the structure of protons.

With some careful twisting and stacking, MIT physicists have revealed a new and exotic property in “magic-angle” graphene: superconductivity that can be turned on and off with an electric pulse, much like a light switch.

The discovery could lead to ultrafast, energy-efficient superconducting transistors for neuromorphic devices—electronics designed to operate in a way similar to the rapid on/off firing of neurons in the human brain.

Magic-angle graphene refers to a very particular stacking of graphene—an atom-thin material made from carbon atoms that are linked in a hexagonal pattern resembling chicken wire. When one sheet of graphene is stacked atop a second sheet at a precise “magic” angle, the twisted structure creates a slightly offset “moiré” pattern, or superlattice, that is able to support a host of surprising electronic behaviors.

For the first time, physicists have achieved quantum mechanical entanglement of two stable light sources.

Called “spooky action at a distance” by Einstein, quantum entanglement is a seemingly magical phenomenon. Entangled particles, for example light particles called “photons”, share a physical state. Changes to the physical state of one particle in an entangled pair instantaneously causes the same change to occur in its partner – no matter how far apart they are separated.

While quantum mechanical theory is clear on the existence of this effect in the universe, creating entangled pairs of particles is no trivial feat.