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The development of dynamic components for controlling wave fronts in the sub-terahertz region of the electromagnetic spectrum has emerged as a frontier research topic for many applications in sensing and communications. One approach which has attracted much attention involves the use of active metasurfaces, tiled arrays of sub-wavelength elements with properties that can be reconfigured via external actuation. In nearly all cases, these metasurfaces are employed as either transmissive or reflective elements, taking advantage of their strong and tunable interaction with free-space electromagnetic waves. These interactions can be significantly enhanced through the use of surface waves propagating parallel to the metasurface array, although very few studies have exploited this option. Here, we integrate a metasurface into the interior of a parallel-plate waveguide in a configuration explicitly designed to exploit this surface-wave geometry. We show that varying the electrical properties of the active metasurface changes the wave vector of the guided mode, and thereby alters the emission angle of radiation out-coupled through a leaky-wave slot aperture. These results, which are consistent with numerical simulations, represent a new approach to broadband beam steering suitable for the sub-terahertz spectral range. 

Abstract BackgroundClimate change is expected to alter fire return intervals in cold and wet forests in the northwestern United States. This coupled with an expected rise in prescribed fires to restore healthy forests, disproportionately increases risk to saplings of tree species adapted to colder and wetter environments that have low fire resistance. To assess this potential impact, we evaluated the impacts of increasing fire intensity onPicea engelmanniiandThuja plicatasapling physiology, morphology, and mortality. This was achieved using established pyro-ecophysiology experiments where saplings were subjected to controlled surface fires across a range of fire intensities and post-fire growth, physiology and mortality were assessed up to 7 months post-fire. ResultsIn this study we demonstrate that the probability of mortality in the saplings of these two conifer species displays a sigmoidal increase with increasing fire intensity. At fire radiative energy dosage levels < 0.6 MJ m⁻², the observed mortality in both species was lower than predicted by existing crown scorch-based models due to their limited sensitivity at small diameters. Prior to sapling death, chlorophyll fluorescence transiently recovers before a rapid decline, though the timing varies by species and fire intensity dosage. A new general sapling mortality model derived from 7 conifer species is presented. ConclusionsOur results provide predictive tools that managers could use to make informed decisions on the potential impacts of fires on conifer saplings growing in cold and wet environments. Results from both species suggest that chlorophyll fluorescence temporal trends could serve as a potential early warning indicator of fire-induced tree mortality, however, future work should explore whether similar responses are observable using remote sensing data from solar-induced chlorophyll fluorescence and assess potential mechanisms underlying this signal. The general sapling mortality model presented in this paper appears to provide an improved method of predicting conifer sapling mortality over existing approaches, however, research is needed to develop coefficients to adjust the model with tree age and environmental factors. Further studies could also explore whether phenotypic plasticity is driving observed tree responses to fire from plants grown from similar environments. 

We introduce an approach to produce inexpensive linear to circular polarizers for the sub-THz spectral regime with either left or right handedness. Our design consists of a cross-dipole array of slot antennas, fabricated on paper using a fast and inexpensive process. We demonstrate a prototype designed for a frequency of 200 GHz, showing a low axial ratio and acceptable insertion loss. 

The dynamics of photo-excited 4-bromophenolate anions in aqueous solution are investigated using femtosecond extreme ultraviolet (XUV) time-resolved photoelectron spectroscopy (TRPES) in a liquid flat jet. Excitation to the first singlet... 

During fieldwork in Thailand, we observed nearly identical tempos of co-located flashing fireflies and chirping crickets. Motivated by this, we survey published data showing that an abundance of evolutionarily distinct species communicate isochronously at ~0.5–4 Hz, suggesting that this might be a tempo “hotspot.” We hypothesize that this timescale may have a universal basis in the biophysics of the receiver’s neurons. We test this by demonstrating that small receiver circuits constructed from elements representing typical neurons will be most responsive in the observed tempo range. 

Discovering urban functional zones (UFZs) is critical for understanding city spatial structures and supporting effective urban planning. Existing approaches to UFZ discovery typically rely on one of three costly strategies: (1) training large vision models directly on satellite imagery, which demands substantial computational resources; (2) leveraging crowdsourced data such as Points of Interest (POIs) from platforms like OpenStreetMap, which may be incomplete, inconsistent, or unavailable in many regions; or (3) collecting custom labeled data, which requires significant time, expense, and expert effort. Recently, large multi-modal models (LMMs) emerged as a promising alternative, offering strong capabilities in interpreting visual content without requiring extensive data labeling. However, their performance remains limited when applied to the UFZ discovery task, often struggling to capture the complex spatial and functional details and interactions of urban regions. To address this challenge, we propose a new approach that enhances LMMs’ reasoning capability to recognize urban functional zones by keeping LMM encoders frozen while training only lightweight graph-based models, eliminating the need for LMM fine-tuning or additional pre-training. Specifically, our approach first partitions the target area into small regions by road network, where an LMM is used for each region to generate visual and textual embeddings independently using its image and text encoders. Then, two graphs are constructed in which nodes represent regions with features defined by their respective embeddings, and edges encode their spatial adjacency. Message-passing on the two graphs hence captures spatial correlation between the visual and textual modalities. After that, graph clustering will suggest the prototypes representing nearby zones with similar urban functions, where contrastive learning is further leveraged to encourage cross-modal consistency. Evaluation on four city districts, namely Philadelphia (PA, USA), Pudong (Shanghai, China), San Francisco (CA, USA), and Seattle (WA, USA), substantiates the effectiveness of our proposal and that its performance is on par with supervised competitors. 

The rate and impacts of sea level rise vary considerably around the world, but the contribution of human-caused climate change to increases in local and regional flood risks has not yet been systematically explored. Because such information is critical to local decision making, legal proceedings, and loss and damage determinations, we quantify human-caused climate change’s contributions to sea level rise at worldwide locations using budget-based and semiempirical model methods. Results show that human-caused sea level rise is quantifiable at 97% of 519 tide gauge sites and is responsible for 58% (44 to 65%) of the observed daily extreme water level exceedances over 2000–2018. On average, human-caused sea level rise has caused a near-tripling in the number of days with attributable exceedances since the 1970s. 

When a fast droplet impacts a pool, the resulting ejecta sheet dynamics determine the final impact outcome. At low capillary numbers, the ejecta sheet remains separate from a deep static pool, while at higher values, it develops into a lamella. Here, we show that the common natural scenario of a slowly moving deep pool can change the upstream impact outcome, creating highly three-dimensional dynamics no longer characterised by a single descriptor. By considering how pool movement constrains the evolution of the ejecta sheet angle, we reach a length-scale invariant parametrisation for the upstream transition that holds for a wide range of fluids and impact conditions. Direct numerical simulations show similar dynamics for an equivalent oblique impact, indicating that the air boundary layer above a moving pool does not play a decisive role for low pool–droplet speed ratios. Our results also provide insight into the physical mechanisms that underpin pool impact outcomes more generally.