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Category: physics – Page 63

Thermal photonics advances enable efficient subambient daytime radiative cooling for vertical surfaces

Radiative heat transfer is one of the most critical energy transfer mechanisms in nature. However, traditional blackbody radiation, due to its inherent characteristics, such as its non-directional, incoherent, broad-spectrum, and unpolarized nature, results in energy exchange between the radiating body and all surrounding objects, significantly limiting heat transfer efficiency and thermal flow control. These limitations hinder its practical application.

A recent study published in Science utilized thermal photonics to achieve cross-band synergistic control of thermal radiation in both angle and spectrum. The researchers then designed a directional emitter with cross-scale symmetry-breaking, angularly asymmetric and spectrally selective thermal emission, achieving daytime subambient radiative cooling on vertical surfaces.

The research team was led by Prof. Wei Li from the Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences, in collaboration with Prof. Shanhui Fan’s team from Stanford University and Prof. Andrea Alu’s team from the City University of New York.

Study finds ZnO nanorods achieve 98.3% Faraday efficiency in CO₂ reduction

Nano-ZnO is a potential catalyst material for carbon dioxide electrocatalytic reduction (CO2RR), but its effective Faraday efficiency (FE) is still below 90% and the current density is less than 300 mA cm-2, which is not enough to meet industrial requirements.

A new study published in Chem Catalysis reported on ZnO nanorods for electrocatalytic CO2RR, which after 500°C heat-treatment, achieved the highest vacancy content, the highest FECO of 98.3%, and a partial of 786.56 mA cm-2 in a 3 M KCl electrolyte.

The research was conducted by Prof. Wu Zhonghua and Dr. Xing Xueqing from the Institute of High Energy Physics of the Chinese Academy of Sciences (CAS) and Prof. Han Buxing from the Institute of Chemistry of CAS.

Record-breaking run on Frontier sets new bar for simulating the universe in exascale era

The universe just got a whole lot bigger—or at least in the world of computer simulations, that is. In early November, researchers at the Department of Energy’s Argonne National Laboratory used the fastest supercomputer on the planet to run the largest astrophysical simulation of the universe ever conducted.

The achievement was made using the Frontier supercomputer at Oak Ridge National Laboratory. The calculations set a new benchmark for cosmological hydrodynamics simulations and provide a new foundation for simulating the physics of atomic matter and dark matter simultaneously. The simulation size corresponds to surveys undertaken by large telescope observatories, a feat that until now has not been possible at this scale.

“There are two components in the universe: —which as far as we know, only interacts gravitationally—and conventional matter, or atomic matter,” said project lead Salman Habib, division director for Computational Sciences at Argonne.

Cyanobacterial circadian clock uses an AM radio-like mechanism to control cellular processes

Cyanobacteria, an ancient lineage of bacteria that perform photosynthesis, have been found to regulate their genes using the same physics principle used in AM radio transmission.

New research published in Current Biology has found that cyanobacteria use variations in the amplitude (strength) of a pulse to convey information in single cells. The finding sheds light on how biological rhythms work together to regulate cellular processes.

In AM (amplitude modulation) radio, a wave with constant strength and frequency—called a carrier wave—is generated from the oscillation of an electric current. The audio signal, which contains the information (such as music or speech) to transmit, is superimposed onto the carrier wave. This is done by varying the amplitude of the carrier wave in accordance with the frequency of the .

X-ray diffraction enables measurement of in-situ ablation depth in aluminum

When laser energy is deposited in a target material, numerous complex processes take place at length and time scales that are too small to visually observe. To study and ultimately fine-tune such processes, researchers look to computer modeling. However, these simulations rely on accurate equation of state (EOS) models to describe the thermodynamic properties—such as pressure, density and temperature—of a target material under the extreme conditions generated by the intense heat of a laser pulse.

One process that is insufficiently addressed in current EOS models is ablation, where the irradiation from the laser beam removes solid material from the target either by means of vaporization or plasma formation (the fourth state of matter). It is this mechanism that launches a shock into the material, ultimately resulting in the high densities required for high pressure experiments such as (ICF).

To better understand laser–matter interactions with regard to ablation, researchers from Lawrence Livermore National Laboratory (LLNL), the University of California, San Diego (UCSD), SLAC National Accelerator Laboratory and other collaborating institutions conducted a study that represents the first example of using X-ray diffraction to make direct time-resolved measurements of an aluminum sample’s ablation depth. The research appears in Applied Physics Letters.

Plasma pursuits: HEDS Center fellows illuminate the fourth state of matter

In 2019, the High Energy Density Science (HEDS) Center at Lawrence Livermore National Laboratory (LLNL) launched its postdoctoral fellowship program, welcoming one new scientist annually to come and conduct research for a two-year term. Supported by LLNL’s Weapons Physics and Design program, HEDS fellows are encouraged to pursue their own research agenda as it relates to the study of matter and energy under extreme conditions.

The most recent postdoctoral fellows, physicist Elizabeth “Liz” Grace (2022 fellow) and plasma physicist Graeme Sutcliffe (2023 fellow), are using high-intensity lasers and advanced diagnostics to observe the behaviors of plasma. A plasma, known as the “fourth state of matter,” is a superheated, ionized gas that makes up the majority of visible matter in the universe, like stars and nebulae. Replicating these conditions is a key step to achieving robust igniting inertial fusion designs for energy resilience.

Why the [expletive] can’t we travel back in time?

Observations of the cosmic microwave background, leftover light from when the Universe was only 380,000 years old, reveal that our cosmos is not rotating. Infinitely long cylinders don’t exist. The interiors of black holes throw up singularities, telling us that the math of GR is breaking down and can’t be trusted. And wormholes? They’re frighteningly unstable. A single photon passing down the throat of a wormhole will cause it to collapse faster than the speed of light. Attempts to stabilize wormholes require exotic matter (as in, matter with negative mass, which isn’t a thing), and so their existence is just as debatable as time travel itself.

This is the point where physicists get antsy. General relativity is telling us exactly where time travel into the past can be allowed. But every single example runs into other issues that have nothing to do with the math of GR. There is no consistency, no coherence among all these smackdowns. It’s just one random rule over here, and another random fact over there, none of them related to either GR or each other.

If the inability to time travel were a fundamental part of our Universe, you’d expect equally fundamental physics behind that rule. Yet every time we discover a CTC in general relativity, we find some reason it’s im possible (or at the very least, implausible), and the reason seems ad hoc. There isn’t anything tying together any of the “no time travel for you” explanations.

Dead and Alive: Astronomers Uncover Star Pairs Transforming Our Universe

Astronomers have made a groundbreaking discovery of binary star systems, consisting of a white dwarf and a main sequence star, within young star clusters.

This discovery opens up new avenues for understanding stellar evolution and could provide insights into the origins of phenomena such as supernovas and gravitational waves.

Breakthrough Discovery in Star Clusters.

You Can Time Travel Without Worrying About Changing the Present. Theoretically, at Least

Good news for anyone with a hankerin’ for going back in time to kill their grandfather before he had kids: a physicist named Germain Tobar from the University of Queensland in Australia says go for it since time travel paradoxes aren’t real. So feel free to kill your grandpappy without fear of deleting your own existence.

He didn’t explicitly frame it that way, but he does think that time travel paradoxes are bullshit. Tobar’s work uses Einstein’s theory of general relativity as a foundation and then builds from there. He says that, according to his calculations, events can exist both in the past and in the future simultaneously, independent of one another. Space-time will adjust itself to avoid paradoxes, thus allowing you to cause whatever mayhem you want throughout time without creating contradictions.

If true, famous time travel stories like The Terminator and Back to the Future wouldn’t be possible. A Terminator sent to the past to kill John Connor would not be killing John Connor in the future, theoretically. It would only kill John Connor in the past and space-time would find some way to adjust to ensure that John Connor is still alive in the future to continue to be a pain in every robot’s shiny metal ass.

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