Articles by David Appell
Phys.org / Measuring a previously mysterious imaginary component of wave scattering
There has long been a mystery when calculating how an incoming light wave scatters off an object and becomes a modified, outgoing light wave. In particular, the time delay of the transition from one to the other comes out ...
Phys.org / What's the lifetime of a Dyson megaswarm?
In 2015, astronomer Tabetha Boyajian and colleagues announced the discovery of unusual light fluctuations coming from a star about 1,500 light-years away. It came to be known as "Tabby's star" or "Boyajian's star," and the ...
Phys.org / Your ketchup will see you now: Solid-phase properties reveal when yield stress fluids start to flow
Pounding on the bottom of a glass bottle of ketchup is one of life's small annoyances. Getting that sweet, red concoction from its solid phase to a liquid takes too long when you're hungry and could even require messy strategies ...
Phys.org / New research determines the thermodynamic properties of the quark gluon plasma
Very soon after the Big Bang, the universe enjoyed a brief phase where quarks and gluons roamed freely, not yet joined up into hadrons such as protons, neutrons and mesons. This state, called a quark-gluon plasma, existed ...
Phys.org / Detecting the primordial black holes that could be today's dark matter
Besides particles like sterile neutrinos, axions and weakly interacting massive particles (WIMPs), a leading candidate for the cold dark matter of the universe are primordial black holes—black holes created from extremely ...
Phys.org / When a comet hits a tidally locked exo-Earth
Comets that have hit Earth have been a mixed bag. Early in Earth's history, during the solar system's chaotic beginning, they were likely the source of our planet's water, ultimately making up about 0.02% of the planet's ...
Phys.org / Hey, what are these curved green flashes above my polymer semiconductor?
In every scientific discovery in the movies, a scientist observes something unexpected, scratches the side of his or her forehead and says "hmmmmm." In just such a moment in real life, scientists from Canada observed unexpected ...
Phys.org / Researchers propose a simple magnetic switch using altermagnets
Controlling magnetism in a device is not easy; unusually large magnetic fields or lots of electricity are needed, which are bulky, slow, expensive and/or waste energy. But that looks soon to change, thanks to the recent discovery ...
Phys.org / Might the proton decay in other places or at other times?
Does the proton decay? While this was a famous prediction of Grand Unified Theories (GUTS) developed in the 1970s and 1980s, experimentalists have ruled it out—or rather, put lower limits on its mean lifetime of about 1034 ...
Phys.org / Surprisingly, some Dyson spheres and ringworlds can be stable
In the realm of science fiction, Dyson spheres and ringworlds have been staples for decades. But it is well known that the simplest designs are unstable against gravitational forces and would thus be torn apart. Now a scientist ...
Phys.org / A new law gives the energy needed to fracture stretchable networks
Interconnected materials containing networks are ubiquitous in the world around us—rubber, car tires, human and engineered tissues, woven sheets and chain mail armor. Engineers often want these networks to be as strong as ...
Phys.org / How will artificial intelligence affect wealth equality?
How will artificial intelligence affect the distribution of income and wealth this century? After falling through much of the 20th century, income inequality, measured as the fraction of income going to the richest 1% of ...
Phys.org / Findings reveal an important link to Northern Hemisphere extreme temperatures
Heat waves have gotten hotter in the Northern Hemisphere in recent decades. Home to about 90% of the world's population, with the largest fraction living in the mid-latitudes, more frequent and more severe heat waves and ...
Phys.org / An equation of state for dense nuclear matter such as neutron stars
Neutron stars are some of the densest objects in the universe. They are the core of a collapsed megastar that went supernova, have a typical radius of 10 km—just slightly more than the altitude of Mt. Everest—and their density ...
Phys.org / Relativistic spin-orbit coupling may lead to unconventional superconductivity type
Observing the effects of special relativity doesn't necessarily require objects moving at a significant fraction of the speed of light. In fact, length contraction in special relativity explains how electromagnets work. A ...
