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The size and strength of the momentum bandgap improve as the quality factor of the metasurface increases. Figure 3f shows that metasurfaces with a higher Q-factor provide wider momentum bandgaps for surface waves with larger amplification rates, assuming the same modulation function. In comparison, the metasurface discussed in Fig. 3b–e has a quality factor of Q = 2.44. Moreover, for sufficiently large Q-factors (Q ≥ 9.75), a second momentum bandgap opens inside the light cone, that is, for propagating waves. The size of the second bandgap grows with the quality factor of the metasurface because resonances with longer lifetimes suffer from smaller radiation losses and require weaker modulation to maintain the same amplification rate. When the quality factor takes sufficiently large values, the two bandgaps merge and the metasurface can amplify incident waves with all possible momenta k _{∣ ∣} (see Fig. 3f).

We place a dipole emitter above the metasurface to demonstrate this infinite momentum bandgap (see Fig. 3g). The dipole radiation includes a wide spectrum of momenta, as shown in the upper panel of the figure. Once the temporal modulation of the metasurface is on, waves with all different momenta are amplified and radiated in the specular and retro-directions with respect to the source; see the lower panel in Fig. 3g. This leads to interesting possibilities such as amplified emission and lasing of light from a radiation source⁶. In contrast to the idea suggested in ref. ⁶, due to the substantially enhanced bandgap, it is possible here to amplify emission with a large and, in principle, tunable spectrum of wavenumbers. This provides opportunities for beam shaping of the amplified signal and for creating perfect lenses³¹. Indeed, the evanescent wave content of the source radiation can be reconstructed effectively thanks to the amplification of the wide range of k _{∣ ∣}. In Supplementary Section 5, we demonstrate that evanescent and propagating wave components of the radiating dipole are amplified by the metasurface in reflection and transmission regimes.

To provide a feasible optical realization of the resonant PTC, we consider a penetrable metasurface surrounded by air and consisting of dielectric nanospheres that are made of a material with a time-varying permittivity (see Fig. 4a). Each nanosphere effectively behaves as an LC resonator as it supports Mie resonances³². For simplicity, we initially ignore material dispersion. The permittivity associated with each nanosphere reads \(\varepsilon (t)=1+{\chi }_{0}[1+m\cos ({\omega }_{{\rm{m}}}t)]\). Varying the permittivity in time modulates the Mie resonance frequencies of the nanospheres (see Fig. 2b). In the following, we rely on the T-matrix method to study the optical response from such a metasurface³³ (see Methods and Supplementary Section 6 for details).

Research from Washington University shows that glioblastoma, a type of brain cancer, has its own internal clock that synchronizes with the host’s circadian rhythms to optimize its growth by responding to daily hormone releases like cortisol.

Targeting these circadian signals in treatment slowed tumor growth significantly in both lab and animal studies. This synchronization could explain the mixed effects of dexamethasone, a common treatment, depending on the timing of its administration. The study highlights the potential of chronotherapy, aligning treatment with the body’s natural rhythms, to improve cancer outcomes.

Circadian Rhythms and Human Biology.

Air pollution is associated with increased risk of venous thromboembolism: the Multi-Ethnic Study of Atherosclerosis https://ashpublications.org/blood/article/doi/10.1182/blood.…ed-risk-of

A comprehensive longitudinal study has shown a clear link between long-term exposure to air pollution and an increased risk of developing blood clots in deep veins, known as venous thromboembolism.

The study, which followed over 6,000 U.S. adults across major cities, revealed that exposure to particulate matter, oxides of nitrogen, and nitrogen dioxide significantly heightened the risk, with those in the highest quartile of exposure facing the most severe risks.

Continue reading “New Study Finds Alarming Link Between Air Pollution and Dangerous Blood Clots” »

An unusual approach to spotting tiny asteroids uses James Webb Space Telescope data in a boost for planetary defense research.

Stars are born, live and die in spectacular ways, with their deaths marked by one of the biggest known explosions in the universe. Like a campfire needs wood to keep burning, a star relies on nuclear fusion—primarily using hydrogen as fuel—to generate energy and counteract the crushing force of its own gravity.

But when the fuel runs out, the outward pressure vanishes, and the star collapses under its own weight, falling at nearly the speed of light, crashing into the core and rebounding outward. Within seconds, the star is violently blown apart, hurling stellar debris into space at speeds thousands of times faster than the most powerful rocket ever built. This is a supernova explosion.

Astronomers aim to understand what types of stars produce different kinds of explosions. Do more massive stars result in brighter explosions? What happens if a star is surrounded by dust and gas when it explodes?

Regarding oral HSV-1 infections, the global prevalence in 2020 among individuals aged 0–49 years was 58.6% (95% UI: 53.5–62.1%), equating to approximately 3.4 billion people. The African region exhibited the highest oral HSV-1 prevalence, while the Western Pacific had the largest number of infected individuals.

Conclusions

To summarize, in 2020, 26 million individuals aged 15–49 acquired new HSV-2 infections, with 520 million living with HSV-2 and 188 million experiencing HSV-2-related GUD. Similarly, 17 million acquired new genital HSV-1 infections, with 376 million living with genital HSV-1 and 17 million experiencing HSV-1-related GUD.

A radical research program in deep design.

Scientists have accidentally discovered a particle that has mass when it’s traveling in one direction, but no mass while traveling in a different direction. Known as semi-Dirac fermions, particles with this bizarre behavior were first predicted 16 years ago.

The discovery was made in a semi-metal material called ZrSiS, made up of zirconium, silicon and sulfur, while studying the properties of quasiparticles. These emerge from the collective behavior of many particles within a solid material.

“This was totally unexpected,” said Yinming Shao, lead author on the study. “We weren’t even looking for a semi-Dirac fermion when we started working with this material, but we were seeing signatures we didn’t understand – and it turns out we had made the first observation of these wild quasiparticles that sometimes move like they have mass and sometimes move like they have none.”

Researchers show that large language models exhibit social identity biases similar to humans, having favoritism toward ingroups and hostility toward outgroups. These biases persist across models, training data and real-world human–LLM conversations.