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New basis sets of the atomic natural orbital (ANO) type have been developed for the atoms Li–Fr and Be–Ra. The ANOs have been obtained from the average density matrix of the ground states and the lowest excited states of the atom, the positive ion, and the dimer at its equilibirium geometry. Scalar realtivisitc effects are included through the use of a Douglas–Kroll Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second-order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of the ground-state potentials for the dimers. Computed bond energies are accurate to within 0.05 eV for the alkaline dimers and 0.02 eV for the alkaline-earth dimers (except for Be2).

Passive acoustic monitoring of biodiversity is growing fast, as it offers an alternative to traditional aural point count surveys, with the possibility to deploy long‐term acoustic surveys in large and complex natural environments. However, there is still a clear need to evaluate how the frequency‐ and distance‐dependent attenuation of sound as well as the ambient sound level impact the acoustic detection distance of the soniferous species in natural environments over the diel cycles and across seasons. This is of great importance to avoid pseudoreplication and to provide relevant biodiversity indicators, including species richness, species abundance and species density. To address the issue of detection distance, we tested a field‐based protocol in a Neotropical rainforest (French Guiana, France) and in an Alpine coniferous forest (Jura, France). This standardized and repeatable method consists in a recording session of the ambient sound directly followed by an experiment using a calibrated white noise sound broadcast at different positions along a 100 m linear transect. We then used acoustic laws to reveal the basic physics behind sound propagation attenuation. We demonstrate that habitat attenuation in two different kinds of forests can be modelled by an exponential decay law with a linear dependence on frequency and distance. We also report that habitat attenuation, as first approximation, can be summarized by a single value, the coefficient of attenuation of the habitat. Finally, we show that the detection distance can be predicted knowing the contribution of each attenuation factor, the coefficient of attenuation of the habitat, the ambient sound pressure level and the amplitude and frequency bandwidth characteristics of the transmitted sound. We show that the detection distance mostly depends on the ambient sound and may vary by a factor of up to 5 over the diel cycle and across seasons. These results reinforce the need to take into account the variation of the detection distance when performing passive acoustic surveys and producing reliable biodiversity indicators.

With rapid advancements in aerospace technology, research interest in the near-space atmospheric environment has surged. Active space release experiments, known for their high controllability and observational advantages, offer a well-established approach to investigating space physics, particularly in the ionosphere. Extending this technique to near-space is essential for deepening our understanding of its environmental properties and underlying physics. However, significant differences in pressure, chemical reactivity, and constituent distribution between near-space and the ionosphere introduce substantial complexity to active release experiments in this region. This study systematically evaluates the influence of the near-space environment on alkali metal releases. A kinetic model for such releases in near-space is developed, and the feasibility of their implementation is assessed. Numerical simulations demonstrate that releasing 10 kg of alkali metals at an altitude of 100 km can generate an artificial electron cloud that persists for over 30 min. The spatial scale and persistence time of the artificial electron cloud decrease markedly with decreasing release altitude. In the vicinity of an altitude of 70 km, intense recombination reactions rapidly deplete released material within seconds, preventing the formation of a stable electron cloud. This indicates a lower altitude limit for effective application of this technique. Single-point releases yield electron clouds with insufficient spatial extent and duration, employing multipoint release can effectively address this limitation. Ray-tracing simulations further indicate that electron clouds substantially alter radio wave propagation paths, creating a radio shadow region that impedes wave penetration. Crucially, these clouds also establish a new propagation path, forming an \"air bridge\" in near-space with the potential to enable autonomous, reliable long-distance (> 300 km) wireless communication. This work provides a new perspective and approach for near-space research, promising applications in technologies such as artificial communication channels and electromagnetic shielding. Graphical abstract

Transition metal silicides are promising materials for improved electronic devices, and this motivates achieving a better understanding of transition metal bonds to silicon. Here we model the ground and excited state bond dissociations of VSi, NbSi, and TaSi using a complete active space (CAS) wave function and a separated-pair (SP) wave function combined with two post-self-consistent field techniques: complete active space with perturbation theory at second order and multiconfiguration pair-density functional theory. The SP approximation is a multiconfiguration self-consistent field method with a selection of configurations based on generalized valence bond theory without the perfect pairing approximation. For both CAS and SP, the active-space composition corresponds to the nominal correlated-participating-orbital scheme. The ground state and low-lying excited states are explored to predict the state ordering for each molecule, and potential energy curves are calculated for the ground state to compare to experiment. The experimental bond dissociation energies of the three diatomic molecules are predicted with eight on-top pair-density functionals with a typical error of 0.2 eV for a CAS wave function and a typical error of 0.3 eV for the SP approximation. We also provide a survey of the accuracy achieved by the SP and extended separated-pair approximations for a broader set of 25 transition metal–ligand bond dissociation energies.

This work explores the electronic structure as well as the reactivity of singlet diradicals, making use of multistate density functional theory (MSDFT). In particular, we show that a minimal active space of two electrons in two orbitals is adequate to treat the relative energies of the singlet and triplet adiabatic ground state as well as the first singlet excited state in many cases. This is plausible because dynamic correlation is included in the first place in the optimization of orbitals in each determinant state via block-localized Kohn–Sham density functional theory. In addition, molecular fragment, i.e., block-localized Kohn–Sham orbitals, are optimized separately for each determinant, providing a variational diabatic representation of valence bond-like states, which are subsequently used in nonorthogonal state interactions (NOSIs). The computational procedure and its performance are illustrated on some prototypical diradical species. It is shown that NOSI calculations in MSDFT can be used to model bond dissociation and hydrogen-atom transfer reactions, employing a minimal number of configuration state functions as the basis states. For p- and s-types of diradicals, the closed-shell diradicals are found to be more reactive than the open-shell ones due to a larger diabatic coupling with the final product state. Such a diabatic representation may be useful to define reaction coordinates for electron transfer, proton transfer and coupled electron and proton transfer reactions in condensed-phase simulations.

The costs of predation may exert significant pressure on the mode of communication used by an animal, and many species balance the benefits of communication (e.g. mate attraction) against the potential risk of predation. Four groups of toothed whales have independently evolved narrowband high-frequency (NBHF) echolocation signals. These signals help NBHF species avoid predation through acoustic crypsis by echolocating and communicating at frequencies inaudible to predators such as mammal-eating killer whales. Heaviside's dolphins (Cephalorhynchus heavisidii) are thought to exclusively produce NBHF echolocation clicks with a centroid frequency around 125 kHz and little to no energy below 100 kHz. To test this, we recorded wild Heaviside's dolphins in a sheltered bay in Namibia. We demonstrate that Heaviside's dolphins produce a second type of click with lower frequency and broader bandwidth in a frequency range that is audible to killer whales. These clicks are used in burst-pulses and occasional click series but not foraging buzzes. We evaluate three different hypotheses and conclude that the most likely benefit of these clicks is to decrease transmission directivity and increase conspecific communication range. The expected increase in active space depends on background noise but ranges from 2.5 (Wenz Sea State 6) to 5 times (Wenz Sea State 1) the active space of NBHF signals. This dual click strategy therefore allows these social dolphins to maintain acoustic crypsis during navigation and foraging, and to selectively relax their crypsis to facilitate communication with conspecifics.

Many animals produce long-distance acoustic signals to mediate a variety of social interactions, and the efficacy of transmission depends in part on environmental attenuation. Vocalizing from positions that optimize transmission is one key solution to minimizing attenuation, though few studies assess the magnitude of this effect in relation to receiver position. In this study, we assessed how transmission of high-frequency vocalizations produced by pinyon mice (Peromyscus truei) varied based on the position of senders and receivers. Pinyon mice are semi-arboreal rodents that produce sustained vocalizations to advertise to conspecifics. Synthesized signals derived from a population-sample-average of fundamental frequency, duration, and amplitude were broadcast and recorded at different heights (0, 1, and 2 m) and distances (1, 2, 4, and 8 m) in a full factorial design to mimic hypothetical senders and receivers. We also measured receiver hearing sensitivity using auditory brainstem responses (ABR) to quantify the audible distance (active space) of vocalizations at different heights. Vocalizations showed less attenuation when emitted and received from an elevation compared to the ground if the signal was received at least 4 m from the sender. Vocalizations emitted from a 1 m height had an approximately 3 times greater audible distance compared to the ground. Additionally, less attenuation occurred when both senders and receivers were elevated at the same height and when receivers were elevated, regardless of sender height. Our results highlight the importance of considering receiver position in animal communication, especially when senders produce highly directional signals.Significance statementVocalizing animals often position themselves in locations that maximize sound transmission. However, the magnitude of this effect is not often quantified, especially in relation to the position of intended receivers. In this study, we combined acoustic recording, hearing experiments, and modelling of sound attenuation to quantify how sending and receiving vocalizations from trees impacts sound transmission in a semi-arboreal mouse. We found that vocalizations produced from 1 m above the ground could be heard by receivers at 3 times the distance compared to ground level. We also found that no matter the sender position, receivers benefitted from being at elevated positions. Finally, we found that the least attenuation occurred when senders and receivers were elevated at the same height. Our results highlight the importance of considering receiver position in animal communication, especially when senders produce highly directional signals.

Quantum computing leverages the principles of quantum mechanics in novel ways to tackle complex chemistry problems that cannot be accurately addressed using traditional quantum chemistry methods. However, the high computational cost and available number of physical qubits with high fidelity limit its application to small chemical systems. This work employed a quantum-classical framework which features a quantum active space-embedding approach to perform simulations of chemical reactions that require up to 14 qubits. This framework was applied to prototypical example metal hydrogenation reactions: the coupling between hydrogen and Li2, Li3, and Li4 clusters. Particular attention was paid to the computation of barriers and reaction energies. The predicted reaction profiles compare well with advanced classical quantum chemistry methods, demonstrating the potential of the quantum embedding algorithm to map out reaction profiles of realistic gas-phase chemical reactions to ascertain qualitative energetic trends. Additionally, the predicted potential energy curves provide a benchmark to compare against both current and future quantum embedding approaches.

Purpose This paper aims to study the encounter issues of the Tethered-Space Net Robot System (TSNRS) with non-target objects on orbit during the maneuver, including the collision issues with small space debris and the obstacle avoidance from large obstacles. Design/methodology/approach For the collision of TSNRS with small debris, the available collision model of the tethered net and its limitation is discussed, and the collision detection method is improved. Then the dynamic response of TSNRS is studied and a closed-loop controller is designed. For the obstacle avoidance, the variable enveloping circle of the TSNRS has coupled with the artificial potential field (APF) method. In addition, the APF is improved with a local trajectory correction method to avoid the overbending segment of the trajectory. Findings The collision model coupled with the improved collision detection method solves the detection failure and speeds up calculation efficiency by 12 times. Collisions of TSNRS with small debris make the local thread stretch and deforms finally making the net a mess. The boundary of the disturbance is obtained by a series of collision tests, and the designed controller not only achieved the tracking control of the TSNRS but also suppressed the disturbance of the net. Practical implications This paper fills the gap in the research on the collision of the tethered net with small debris and makes the collision model more general and efficient by improving the collision detection method. And the coupled obstacle avoidance method makes the process of obstacle avoidance safer and smoother. Originality/value The work in this paper provides a reference for the on-orbit application of TSNRS in the active space debris removal mission.

The behavioural, physiological, and energetic repercussions for wildlife that result from changes in their soundscapes are increasingly being realized. To understand the effects of changing acoustic landscapes, we first must establish the importance of the acoustic sense for species to transfer information between the environment, con- and heterospecifics, and a receiver, and the functional role of calling in behaviours such as foraging, navigation, mate attraction, and weaning. This review begins with a discussion of the use of calling and the acquisition of the vocal repertoire, before providing examples from multiple taxa on the functional applications of signals and communication. The acoustic sensory mode adds to, if not being inherent in, many critical life history stages over a range of species. The potential effects on an animal resulting from a change in its perceived soundscape and disturbance on its acoustics use is outlined. This can then be used to consider the implications of an altered acoustic niche or active space in the success and survival of an individual or species. Furthermore, we discuss briefly metrics that could be used to understand the implications of these changes, or could be used to guide mitigation action to lessen the impact.