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Category: physics – Page 214

A team of Leiden astronomers has managed to calculate the first 100 million years of the history of the Oort cloud in its entirety. Until now, only parts of the history had been studied separately. The cloud, with roughly 100 billion comet-like objects, forms an enormous shell at the edge of our solar system. The astronomers will soon publish their comprehensive simulation and its consequences in the journal Astronomy & Astrophysics.

The Oort cloud was discovered in 1950 by the Dutch Jan Hendrik Oort to explain why there continue to be new comets with elongated orbits in our solar system. The cloud, which starts at more than 3000 times the distance between the Earth and the Sun, should not be confused with the Kuiper belt. This is the rim of rock, grains and ice in which the dwarf planet Pluto is located and which orbits relatively close to the Sun at about 30 to 50 times the Earth-Sun distance.

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Like all metals, silver, copper, and gold are conductors. Electrons flow across them, carrying heat and electricity. While gold is a good conductor under any conditions, some materials have the property of behaving like metal conductors only if temperatures are high enough; at low temperatures, they act like insulators and do not do a good job of carrying electricity. In other words, these unusual materials go from acting like a chunk of gold to acting like a piece of wood as temperatures are lowered. Physicists have developed theories to explain this so-called metal-insulator transition, but the mechanisms behind the transitions are not always clear.

“In some cases, it is not easy to predict whether a material is a or an insulator,” explains Caltech visiting associate Yejun Feng of the Okinawa Institute for Science and Technology Graduate University. “Metals are always good conductors no matter what, but some other so-called apparent metals are insulators for reasons that are not well understood.” Feng has puzzled over this question for at least five years; others on his team, such as collaborator David Mandrus at the University of Tennessee, have thought about the problem for more than two decades.

Now, a new study from Feng and colleagues, published in Nature Communications, offers the cleanest experimental proof yet of a theory proposed 70 years ago by physicist John Slater. According to that theory, magnetism, which results when the so-called “spins” of electrons in a material are organized in an orderly fashion, can solely drive the metal-insulator transition; in other previous experiments, changes in the lattice structure of a material or based on their charges have been deemed responsible.

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China has announced a milestone in the development of clean, sustainable energy by setting a new world record for the longest duration of temperatures needed for fusion to occur.

The Experimental Advanced Superconducting Tokamak (EAST) located in Hefei, Anhui Province, is the successor to HT-7, China’s first superconducting tokamak, which retired in 2013. The Hefei Institutes of Physical Science (HIPS) is conducting the experiment for the Chinese Academy of Sciences (CAS).

Professor Gong Xianzu, a researcher at the CAS Institute of Plasma Physics (IPP) who is leading the project, announced the breakthrough. The reactor achieved not one but two milestones. Firstly it reached a plasma temperature of 120 million degrees Celsius for 101 seconds. This is 20% hotter and five times longer than last year, when EAST managed 100 million degrees Celsius for 20 seconds. Secondly, it reached an even higher peak temperature of 160 million degrees Celsius, lasting for 20 seconds.

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New research is helping to explain one of the big questions that has perplexed astrophysicists for the past 30 years — what causes the changing brightness of distant stars called magnetars.

Magnetars were formed from stellar explosions or supernova e and they have extremely strong magnetic field s, estimated to be around 100 million, million times greater than the magnetic field found on earth.

The magnetic field on each magnetar generates intense heat and x-rays. It is so strong it affects the physical properties of matter, most notably the way that heat is co nducted through the crust of the star and across its surface, creating the variations in brightness which has puzzled astrophysicists and astronomers.

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Scientists have examined the performance of pure boron, boron carbide, high-density carbon and boron nitride ablators—the material that surrounds a fusion fuel and couples with the laser or hohlraum radiation in an experiment—in the polar direct drive exploding pusher (PDXP) platform, which is used at the National Ignition Facility (NIF). The platform uses the polar direct drive configuration to drive high ion temperatures in a room-temperature capsule and has potential applications for plasma physics studies and as a neutron source.

The key findings of the work, featured in High Energy Density Physics, show that these alternate ablators do not improve the symmetry of the PDXP implosion, according to lead author Heather Whitley, associate program director for High Energy Density Science in the Fundamental Weapon Physics section at Lawrence Livermore National Laboratory (LLNL).

“While our simulations predict that the platform is not amenable to the electron-ion coupling measurements due to a lack of implosion symmetry, the alternate materials do enable better coupling between the laser and capsule,” she said. “We plan to test those predicted impacts on future experiments.”

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We know dark matter exists because we can observe its effects on all the stuff that’s swirling around in the universe. Scientists estimate that about 27% of the universe is made of dark matter (68% is dark energy, and the last 5% is ordinary matter and energy). The questions on everyone’s mind: Where exactly is all that elusive stuff located? And how is it distributed throughout the universe?

An international project of over 400 scientists called the Dark Energy Survey is working on answering them. It has just released the largest and most detailed map of dark matter in the universe—with some unexpected findings that don’t yet neatly align with ideas in physics that date all the way back to Albert Einstein and his theory of general relativity.

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Everything is weird on the Sun, where things are not where you’d expect.

This spike in temperature, despite the increased distance from the Sun’s main energy source, has been observed in most stars and represents a fundamental puzzle that astrophysicists have mulled over for decades.

In 1942, the Swedish scientist Hannes Alfvén proposed an explanation. He theorized that magnetized waves of plasma could carry huge amounts of energy along the Sun’s magnetic field from its interior to the corona, bypassing the photosphere before exploding with heat in the Sun’s upper atmosphere.

The theory had been tentatively accepted — but we still needed proof, in the form of empirical observation, that these waves existed. Our recent study has finally achieved this, validating Alfvén’s 80-year-old theory and taking us a step closer to harnessing this high-energy phenomenon here on Earth.

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Great new episode with guest Ben K.D. Pearce on how and why our own genetic code was able to form in Earth’s warm little ponds as early as 4.5 billion years ago. Please have a listen.

Guest Ben K.D. Pearce, a Ph.D student in astrophysics and astrobiology at McMaster University in Toronto, and an expert on the origins of life’s building blocks here on Earth. We discuss the idea that all the genetic components from which life emerged were incredibly readily available biogenically very early in Earth’s evolution. As early as 4.5 billion years ago. Pearce is part of a group making great strides in learning how this all may have happened in Earth’s very ancient warm little ponds.

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Signals can be amplified by an optimum amount of noise, but stochastic resonance is a fragile phenomenon. Researchers at AMOLF were the first to investigate the role of memory for this phenomenon in an oil-filled optical microcavity. The effects of slow non-linearity (i.e. memory) on stochastic resonance were never considered before, but these experiments suggest that stochastic resonance becomes robust to variations in the signal frequency when systems have memory. This has implications in many fields of physics and energy technology. In particular, the scientists numerically show that introducing slow nonlinearity in a mechanical oscillator harvesting energy from noise can increase its efficiency tenfold. They have published their findings in Physical Review Letters on May 27th.

It is not easy to concentrate on a difficult task when two people are having a loud discussion right next to you. However, complete silence is often not the best alternative. Whether it is some soft music, remote traffic or the hum of people chatting in the distance, for many people, an optimum amount of noise enables them to concentrate better. “This is the human equivalent of stochastic ,” says AMOLF group leader Said Rodriguez. “In our scientific labs, stochastic resonance happens in nonlinear systems that are bistable. This means that, for a given input, the output can switch between two possible values. When the input is a periodic signal, the response of a non-linear system can be amplified by an optimum amount of noise using the stochastic resonance condition.”

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