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Comparison between explicit and implicit discretization strategies for a dissipative thermal environment
We investigate strategies for simulating open quantum systems coupled to dissipative baths by comparing explicit wave function-based discretization [via multi-layer multi-configuration time-dependent Hartree (ML-MCTDH)] and the implicit density matrix-based master equation method [via tree tensor network hierarchical equations of motion (TTN-HEOM)]. For dissipative baths characterized by exponentially decaying bath correlation functions, the implicit discretization approach of HEOM—rooted in bath correlation function decompositions—proves significantly more efficient than explicit discretization of the bath into discrete harmonic modes. Explicit methods, like ML-MCTDH, require extensive mode discretization to approximate continuum baths, leading to computational bottlenecks. Case studies for two-level systems and a Fenna–Matthews–Olson complex model highlight TTN-HEOM’s superiority in capturing dissipative dynamics with relaxations with a minimal number of auxiliary modes, while the explicit methods are as exact as the HEOM in pure dephasing regimes. This comparison is enabled by the TENSO package, which has both ML-MCTDH and TTN-HEOM implemented using the same computational structure and propagation strategy.
Faradaic and capacitive charging of an electrolyte-filled pore in response to a small applied potential
Electrochemical devices often charge both through Faradaic reactions and electric double layer formation. Here, we study these coupled processes in a model system of a long electrolyte-filled pore subject to a small suddenly applied potential, close to the equilibrium potential Ψeq at which there is no net Faradaic charge transfer. Specifically, we solve the coupled Poisson–Nernst–Planck and Frumkin–Butler–Volmer equations by asymptotic approximations, using the pore’s small inverse aspect ratio as the small parameter. In the early time limit, the reaction–diffusion equations yield an extended Faradaic transmission line model that includes a voltage source, Ψeq, biasing the Faradaic reactions, captured by the resistance RF. In the long-time limit, the pore exhibits a nontrivial potential of zero total charge, Ψpztc=Ψeq1−Ẑ(0)/RF, where Ẑ(0) is the experimentally accessible zero-frequency impedance of the system. This expression provides a new means to measure the Faradaic contribution to Ψpztc experimentally.
Rethinking the evidence for a liquid–liquid transition in water: What decompression experiments reveal
The possibility of a liquid–liquid transition (LLT) in supercooled water has sparked decades of debate. Recent pump–probe experiments interpret two peaks in the structure factor S(q) during and after decompression of high-density liquid (HDL) as evidence of coexistence with low-density liquid (LDL). However, this interpretation presents a fundamental puzzle: such coexistence is implausible at ambient pressure, below the estimated location of the liquid–liquid critical point (LLCP). Here, we use decompression simulations with ML-BOP to reconcile this contradiction. Even when water decompresses along the LLT, S(q) retains a single peak because HDL and LDL domains remain nanoscopic. We explain the two-peak S(q) observed experimentally as a single evolving liquid peak superimposed on a slower to respond, colder HDL arising from the temperature gradient across the sample. The simulations reveal that the decisive LLT signature is a transient growth and decay of the apparent correlation length ξ at low q, which emerges only when decompression proceeds along the LLT, with maximum ξ near the LLCP. Importantly, ξ remains low when decompressing from T ≥ Tc, or too rapidly. The experimental signatures could be explained by an exponential pressure drop to the LLT in ∼10 ns, the growth of ξ as LDL domains develop, peaking near the LLCP at ∼50 ns, and subsequent entry into the single-phase regime, from which crystallization proceeds. Our findings resolve the contradiction between the LLCP location and structural signatures, identifying the low q region of S(q) evolution—not peak splitting—as the key structural marker of the LLT in water.
The application of a fluctuating charge model for boron nitride networks
A fluctuating charge model (FCM) is developed to consider two-dimensional networks of boron nitride. In the FCM, the charge on each atom site is controlled by parameters linked to the atom’s electronegativity and the interactions with other atoms (the coordination environment). The charge held on each atom site is a strong function of the local (first shell) coordination environment. The site charges are shown to be in excellent agreement with those extracted from independent density-functional theory-based calculations. The behavior of the site charges is investigated as a function of the network topology and site disorder. In the first case, specific defects (both site and topological) are introduced, and the spatial “decay” of the local charge to bulk values is assessed. In the second, highly disordered (amorphous) networks are generated, and the distribution of site charges is studied as a function of the degree of topological and site disorder (characterized by the fraction of six-membered rings and mean boron–nitrogen coordination numbers, respectively). Domains of high and low charges are observed to form across a wide range of topological disorder.
Hybrid Monte Carlo metadynamics (hybridMC-MetaD)
We propose the powerful integration of the Hybrid Monte Carlo (hybridMC) algorithm and well-tempered metadynamics. This new algorithm, hybridMC-MetaD, enhances the flexibility and applicability of metadynamics by allowing for the utilization of a wider range of collective variables (CVs), namely non-differentiable CVs. We demonstrate the usage of hybridMC-MetaD through five examples of rare events in molecular dynamics (MD) simulations, including a rare transition in a model potential system, condensation of the argon system, crystallization in a nearly hard sphere system, a nearly hard bipyramid system, and a colloidal suspension. By taking advantage of hybridMC, which combines MD and MC, we are able to bias the transitions along non-differentiable CVs for all five cases, which would be unfeasible with conventional MD simulations. Enabled by metadynamics, we observed significant acceleration of the phase transitions and calculated free energy barriers using the hybridMC-MetaD simulation data. For the nearly hard bipyramid system, whose crystallization is primarily driven by entropy, we report the free energy surface for the first time. Through our case studies, we show that our hybridMC-MetaD scheme reduces the complexity of using metadynamics and increases its accessibility. We believe the hybridMC-MetaD algorithm will stimulate greater interest in and foster broader applications of metadynamics.
Accurate learning of long-range interatomic potentials by coupling Cartesian atomic cluster expansion and sum-of-Gaussians neural networks
Accurately capturing long-range interactions is critical for molecular dynamics simulations based on machine learning interatomic potentials. We recently proposed the sum-of-Gaussians neural network (SOG-Net), which learns long-range energy contributions directly from energy and force data such that the long-range tail of different decay rates can be well fitted. In this work, we incorporate the SOG-Net with a short-range descriptor of the Cartesian atomic cluster expansion, resulting in the CACE-SOG model, to show that the SOG-Net is a general module that can be coupled with different short-range descriptors. We also study new technical developments in the SOG-Net, including improved extrapolation accuracy, handling of different charge states, and faster convergence. We evaluated the CACE-SOG model across a diverse set of systems, including molecular dimers, aqueous salt solutions, charged ionic clusters, and liquid–vapor and Pt(111) interfacial water systems, and compared it with the CACE-based latent Ewald summation and the CACE-only methods. These results demonstrate that the SOG-Net is promising for accurately learning long-range interatomic interactions.
“You could get the best of both breeds or the worst of both”: UK public attitudes towards crossbreeding in dogs - with a specific focus on brachycephalic dogs
Extreme conformation and reduced genetic diversity are recognised to lead to severely reduced health, welfare and longevity in certain dog breeds. There is growing interest in applying strategic crossbreeding to promote more moderate conformations and greater genetic diversity within currently problematic breeds. Crossbreeding could therefore lead to more rapid and effective improvements in welfare compared to current practices of within-breed selection. Deliberate crossbreeding between distinct different dog breeds is not a new concept; it was historically commonly used to create the current pure breeds, to increase genetic diversity and to bring new physical and/or temperament traits into existing breeds. However, a recent surge in the popularity of ‘designer crossbreeds’ (intentional crosses between established purebreds) has elicited fresh interest around the potential positives and negatives of crossbreeding practices. Further research on crossbred brachycephalic dogs is urgently required for a greater understanding of the motivators and barriers to their acquisition. An online survey explored factors that motivate dog breed choice and acquisition of both crossbreed and purebred dogs. In addition, the survey used both closed and open questioning to explore the UK public’s perceptions of crossbreeding, specifically (i) between a brachycephalic breed and a non-brachycephalic breed, and (ii) between two non-brachycephalic breeds. Free-text results were analysed using content analysis and subsequently quantified. Results from 4,899 participants identified that key motivators to acquire a brachycephalic crossbreed vs a brachycephalic purebred included perceptions of improved health, including the reduction in risk of breed and conformation-related disorders, and increased genetic diversity. However, the desire to acquire a purebred dog, or even a specific breed, remained a significant barrier to crossbreed acquisition, alongside concerns surrounding the ethics of crossbreeding. Other barriers included perceived negative changes to appearance and temperament of the offspring from crossbreeding. The current study identified a common set of acquisition decision-making factors across all ownership groups, including desiring a dog who the owner perceives to enjoy being loved and to enjoy physical affection, but further demonstrated that good health is of motivational low priority to some dog owners, particularly to owners of purebred brachycephalic dogs. The mix of positive and negative public perceptions and beliefs around crossbreeding and crossbreed dogs demonstrate the need for further research into the health, temperament and appearance of brachycephalic crossbreed dogs. The suitability of crossbreed dogs as an alternative to certain current purebred breeds with high risk of genetic or conformational disorders depends on both public desire and on evidence-based selection of suitable breeds to encourage crosses which maximise canine welfare.
Observation of terahertz transitions in iron–molybdenum cofactor from nitrogenase via multiple spectroscopies
Inelastic x-ray scattering spectroscopy (IXS) is a modern synchrotron based vibrational spectroscopy, which measures transitions in the terahertz vibrations. This paper presents the first IXS on a metallo-enzyme derived sample, namely, the iron-molybdenum cofactor (FeMoco) of nitrogenase. We have also measured the corresponding far infrared absorption spectrum (far IR spectrum) of FeMoco and compared these data to previously published nuclear resonant vibrational spectra (NRVS) of FeMoco and far infrared spectra of the model Mo–dioxo–homocitrate complex K2[MoO2(R,S-H2homocitrate)2]·2H2O. Although NRVS offers several clear advantages, IXS can probe vibrations not involving iron motion and is still sensitive to heavier elements. This provides a useful method to study molybdenum vibrations, such as the ν(Mo–O) mode at 530 cm−1 in FeMoco, which is observable by IXS but not by NRVS. The comparison of the vibrational frequencies of FeMoco with those of the Mo-complex supports an earlier proposal that the homocitrate ligand in FeMoco is protonated. This work, which introduces IXS to bioinorganic chemistry, concludes by examining both the opportunities and the challenges of applying IXS to other biologically relevant systems.
A shot in the dark: Comparative morphology of the bioluminescent tube organs in tubeshoulders (Platytroctidae)
Bioluminescence, visible light produced by a living organism, is a key innovation in the diversification of deep-sea fishes. It is useful for a myriad of behaviors and interactions in deep-sea organisms, including communication, predation, camouflage via counterillumination, and predator avoidance. In this study, we investigate the deep-sea tubeshoulders (Platytroctidae), fishes that possess a unique postcleithral tube organ associated with their shoulder girdle that excretes bioluminescent fluid, a feature that unites all members of this poorly studied family. Many tubeshoulders also possess additional bioluminescent structures and luminescent tissues, including a series of tube organs on the caudal peduncle unique to Platytroctes apus that are hypothesized to be similar in structure and function to the postcleithral tube organ. Herein, we present the first histological analysis of the caudal tube organs in P. apus and use histological methods to investigate the morphological diversity in postcleithral tube organ structure across 14 platytroctid species, representing 10 of 13 valid genera. We show that the postcleithral tube organ generally exhibits a conserved morphology across genera and species. However, several species-specific anatomical differences are noted. In some individuals, we observe the presence of luminescent-fluid cells within the tube organ in various stages of development, which may provide evidence for inferring the type of secretory gland found in this novel bioluminescent light organ. We also show that the structure of the caudal tube organs in P. apus are similar to the postcleithral tube organ present in all members of Platytroctidae, likely indicating a similar luminescent fluid emission function.
Component-resolved dynamics of glass-forming dipeptide–water-mixtures
We combine differential scanning calorimetry, broadband dielectric spectroscopy, and 1H and 2H nuclear magnetic resonance (NMR) for component-selective studies of molecular reorientation and diffusion in mixtures comprising the dipeptide N-acetyl-glycine-methylamide (NAGMA), which is commonly considered as a protein-backbone model, and deuterated water in a broad temperature range of 140–340 K. For a 7.5 m NAGMA–D2O mixture, crystallization is largely avoided, revealing a separation of the dipeptide-dominated α process, which describes the glassy slowdown, from the water-caused ν process. The latter shows a dynamical crossover at Tg = 175 K and thermally activated motion governed by a temperature-independent Gaussian-like distribution of activation energies with a mean value of Em = 0.49 eV and a standard deviation of σE = 0.035 eV in the glassy state. Detailed NMR analyses show that, despite the time-scale separation, rotational-translational coupling is found for water dynamics at least down into the weakly supercooled regime. Moreover, NMR reveals that the ν process involves a quasi-isotropic reorientation of basically all water molecules even below Tg, while slow or restricted water reorientation does not occur. Based on our findings, we discuss the temperature-dependent coupling of the dipeptide and water motions. For a 2 m NAGMA–D2O mixture, partial crystallization leads to an enhanced temperature dependence. Disentangling the rotational motions of the liquid and crystalline water fractions, we find that the liquid fraction exhibits Arrhenius behavior with Ea = 0.89 eV until a dynamical crossover again occurs upon cooling, while the reorientation of the ice fraction highly resembles that in hexagonal bulk ice.
The impact of school absence on mental health in children and young people: Analysis of an English national birth cohort
Background Given concerns the role of school closures in increasing mental health problems after the Covid-19 pandemic, we used pre-pandemic data to undertake a causal epidemiological analysis of the associations of school absence with later mental health problems. Methods Longitudinal data from the Millennium Cohort Study were collected pre-pandemic at ages 7 (in 2008), 11 (2012) and 14 years (2015), securely linked with English routine educational data on school absence in the 2 years preceding each cohort wave. We constructed marginal structural models for mental health problems (as outcome) and quartiles of absence (exposure), taking account of baseline and time-varying confounding. Results Those in the highest quartile of absence had odds ratios (OR) for experiencing later mental health problems of 2.216 (1.629, 3.014) at age 7 (n = 6383), and in lagged models OR of 1.508 (1.072, 2.122) at age 11 (n = 6102) and 1.903 (1.234, 2.934) at 14 years (n = 5616). Persistent absence (>10% of school year) was associated with OR for later mental health problems of 2.00 (1.56, 2.57) at 7 years, and in lagged models OR of 2.26 (1.62, 3.14) at 11 years and 2.00 (1.27, 3.16) at 14 years. Conclusions School absence above the second quartile doubled the odds of later mental health problems in both primary and secondary school children in pre-pandemic data. Our findings support there being a strong and potentially causal association between absence from school and later mental health problems, and suggest that absence from school is harmful for CYP’s mental health.
Gauge-invariant long-wavelength TDDFT without empty states: From polarizability to Kubo conductivity across heterogeneous materials
Electromagnetic response is commonly computed in two languages: length-gauge molecular polarizabilities and velocity-gauge (Kubo) conductivities for periodic solids. We introduce a compact, gauge-invariant bridge that carries the same microscopic inputs—transition dipoles and interaction kernels—from molecules to crystals and heterogeneous media, with explicit SI prefactors and fine-structure scaling via αfs. The long-wavelength limit is handled through a reduced dielectric matrix that retains local-field mixing; interfaces and 2D layers are treated with sheet boundary conditions (rather than naïve ultrathin films); and length–velocity equivalence is enforced in practice by including the equal-time (diamagnetic/contact) term alongside the paramagnetic current. Finite temperature is addressed on the Matsubara axis with numerically stable real-axis evaluation (complex polarization propagator), preserving unit consistency end-to-end. The framework enables predictive, unit-faithful observables from radio frequency to ultraviolet—RF/microwave heating and penetration depth, dielectric-logging contrast, interfacial optics of thin films and 2D sheets, and adsorption metrics via imaginary-axis polarizabilities. Numerical checks (gauge overlay and optical f-sum saturation) validate the implementation. Immediate priorities include compact, temperature- and salinity-aware kernels with quantified uncertainties and operando interfacial diagnostics for integration into multiphysics digital twins.
Faster but less accurate: An explorative study on the effects of three weeks of ketogenic diet on cognitive functions in undergraduate students
The ketogenic diet (KD) is a low-carbohydrate diet that induces and sustains a ketosis state and minimizes somatic glucose levels. Several psychological studies have described the positive effects of ketosis on cognitive functions for a wide range of neuropsychiatric conditions (e.g., Alzheimer’s disease; epilepsy), leading to greater interest in the KD today. However, the psychological and cognitive effects of inducing ketosis via diet remain unclear, especially in healthy people. From an initial pool of thirty participants, eight undergraduate students performed a cognitive assessment before (baseline) and after three weeks (follow-up) of an isocaloric ketogenic diet. Several neuropsychological measures and psychometric tests have been administered to investigate psychological chronotype, sleep quality, eating habits, anxiety and cognitive components of attention, inhibition, and memory. Non-parametric Bayesian analysis showed that the ketogenic diet affected cognitive functions. Participants performed cognitive tests faster at follow-up than at baseline, showing improvements in visual-motor cognitive and processing speed components. However, they were less accurate on working memory tasks, suggesting a decreasing performance of higher cognitive functions. Finally, no differences in anxiety levels were found between baseline and follow-up. The results could have significant implications for identifying specific cognitive models of students based on specific lifestyle habits and nutritional patterns, allowing the implementation of targeted interventions to improve university learning conditions.
A four-component relativistic perspective on an <i>E</i> ⊗ <i>e</i> Jahn–Teller model
Most advances in electronic spin-dependent non-adiabatic dynamics focus on refining the underlying dynamics methods. In contrast, this work considers an improved description of spin–orbit coupling by explicitly accounting for its relativistic origins. To this end, we extend a standard one-electron triatomic Jahn–Teller model to the four-component relativistic domain. In our formulation, the electron is treated using the Dirac–Coulomb Hamiltonian, while the nuclei remain non-relativistic, departing from the conventional formulation that incorporates the Pauli spin–orbit coupling as a perturbation. The most striking difference between our relativistic model and the conventional one is the presence of vibronic coupling terms on the anti-diagonal of the diabatic potential matrix. These terms scale as 1/c2 and, although nominally small, they can be amplified near avoided-crossings or in systems with heavy nuclei. Furthermore, their presence implies that nuclear motion can affect the direction of the electron spin, a feature entirely absent in the non-relativistic formulation of our model. In the adiabatic representation, the couplings translate to non-Abelian characteristics of the non-adiabatic coupling matrix that persist even in the Born–Oppenheimer approximation. Within our model setting, a relativistic formulation allows for a more intricate interplay between the electronic spin and nuclear degrees of freedom.
Health and lifestyle in the Iron Age Italian community of Pontecagnano (Campania, Italy, 7th-6th century BCE)
This study investigates health, dental development, diet, and human-environment interactions in individuals buried in the necropolises of Pontecagnano (Campania, Italy, 7th-6th century BCE), using an integrated approach merging dental histomorphometry and calculus micro-residue analysis. The sample consists of 30 permanent teeth (canines, first and second molars) from 10 individuals. Histomorphometric analysis of dental thin sections allowed the estimation of crown formation times, initial cusp formation, crown completion, and enamel extension rates. The prevalence of Accentuated Lines, marking physiological stress events, was analyzed chronologically across tooth classes. Dental calculus analysis was performed on five individuals, identifying plant micro-remains and fungal spores. Crown formation times varied by tooth class, with canines forming the longest (mean = 1,977 ± 295 days), followed by second molars (mean = 1,176 ± 179 days) and first molars (mean = 1,094 ± 154 days). Initial cusp formation values, estimated through chronological overlap between teeth, allowed for a more accurate reconstruction of crown completion timing. Accentuated Lines prevalence peaked at 12 and 44 months, likely reflecting early childhood dietary transitions and the differential recording of stress events across different crown regions. Calculus analysis identified starch granules from cereals (Triticeae) and legumes (Fabaceae), fungal spores ( Saccharomyces ), and plant fibers, indicating diverse dietary practices, food processing, and extra-masticatory activities. This interdisciplinary approach reinforces the validity of combining histomorphometric and micro-residue analyses to reconstruct childhood health, adult diet, and lifestyle. Our findings align with previous research while emphasizing population-specific variations. This study enhances understanding of Iron Age biocultural adaptations, offering insights into developmental and dietary behaviors in this ancient Italian community.
Universality classes of Anderson localization transitions in disordered three-dimensional non-Hermitian systems with exceptional points
We conduct a numerical study of wave localization in disordered three-dimensional non-Hermitian systems featuring exceptional points. The energy spectrum of a disordered non-Hermitian Hamiltonian, exhibiting both parity-time and parity-particle-hole symmetries, forms a cross in the complex energy plane, with an exceptional point fixed at the origin. Near the exceptional point, the system undergoes a disorder-driven quantum phase transition from extended to localized states, which is characterized as an Anderson localization transition in non-Hermitian systems. Notably, we identify a universal critical exponent that remains independent of the distribution of random variables. The model also supports Anderson localization transitions away from the exceptional points, albeit with different critical exponents. Furthermore, we investigate wave localization in a non-Hermitian system lacking parity-time symmetry, revealing distinct universality classes. By comparing the obtained critical exponents with those reported in the literature, we conclude that the presence of exceptional points introduces new universality classes that extend beyond the established 38-fold symmetry classification for non-Hermitian systems.
Anal HPV shedding assessed by self-sampling and multiplex real-time PCR among men who have sex with men in N’Djamena, Chad: a feasibility and acceptability study
Background High-risk (HR) human papillomavirus (HPV) infection remains a great concern in sub-Saharan Africa in men who have sex with men (MSM). The prevalence of anal shedding of HPV and associated risk factors was estimated for the first time in a cross-sectional observational study covering MSM living in N’Djamena, the capital city of Chad. Methods MSM were recruited from the community in 21 sites in neighborhoods of 5 districts randomly selected in N’Djamena by respondent-driven sampling (RDS) method. Anal Collector V-Veil UP2™ device was used for anal canal self-sampling. Manual silica-extracted DNA was subjected for HPV detection and genotyping using BMRT Human Papillomavirus Genotyping Real Time PCR assay (Jiangsu Bioperfectus Technologies Co., Ltd., Taizhou, China). HIV serostatus was assessed using two rapid tests in series. Results A total of 70 MSM (mean age: 29.9 years; range, 18–50) were included. The overall acceptability to practice veil-based anal self-sampling was 95.9%. The usability of the veil collector device was high (92.3%), with easy understandable instructions for use and correct placement in the anal canal. Satisfaction questionnaire reported high overall feeling, intimacy respect and lack of shame. The majority of MSM (44/70, 62.8%) showed anal shedding of HPV DNA, with HR-HPV frequently detected (38,70, 54.3%), including HPV-33 (30/70, 42.9%) HPV-68 (16/70, 22.9%), HPV-18 (4/70, 5.7%), HPV-35 (3/70, 4.3%), HPV-58 (2/70, 2.9%), and HPV-45 (1/70, 1.4%). The distribution of genotypes in HR-HPV DNA-positive MSM revealed that HPV-33 (30/70; 42.9%) was the predominant genotype, followed by the HPV-68 (16/70; 22.9%), HPV-18 (4/70; 5.7%), HPV-35 (3/70; 4.3%), HPV-58 (2/70; 2.9%), and HPV-45, HPV-51 and HPV-56 (each type, 1/70;1.4%). Among all HPV detected, only 42 HPV (36.8%) were covered by Gardasil-9 ® vaccine, including the HR-HPV-33, −18, −58 and −45, and the low risk-HPV-6 (5.7%) and HPV-11 (1.4%). The majority of detected HPV were non-covered by Gardasil-9 ® vaccine (63.1%). Overall HIV prevalence was 5.7%. Conclusions Taken together, these observations point the MSM population in N’Djamena as a very particular core group of HIV and HPV transmission. HIV prevalence was higher than that of general adult population, but limited to only one MSM of twenty. The RDS method of recruitment allowed to include MSM likely belonging to the same sexual network of HPV transmission leading to the selection of an atypical and specific profile of anal HPV distribution. The potential efficacy of HPV prophylactic vaccination in this population can be estimated at relatively weak.
Vibrational state control of HPCO photodissociation in the S1 band
Control of molecular photodissociation process is expected to be achieved owing to its relatively fast and direct dynamics that fulfill the criteria to achieve mode specificity in chemical reactions. HPCO is a typical tetra-atomic system with different atoms, which may have an obvious mode-specific character in its photodissociation process HPCO(S1) → H + PCO/HP + CO. In this work, the control of the photodissociation dynamics of HPCO was investigated by both the quantum mechanical (QM) and quasi-classical trajectory (QCT) dynamical methods, in which a scheme of vibrational excitation for the initial state was utilized. By and large, the QM and QCT results are reasonably consistent and some energy-dependent differences caused by quantum effects exist. It was found that the excitation of the H–P stretching (v1) mode promotes the yield of the product H + PCO to the greatest extent. While, for the HP + CO channel, the excitation of the C–O stretching (v2) mode was found to promote the production of HP + CO more efficiently than the P–C stretching (v4) mode, stemming from the bottleneck in the exit channel and intramolecular vibrational energy redistribution caused by the relatively long-lived resonances in the wells on the S1 potential energy surface. Simultaneously, the photon energy is found to greatly affect the quantum yield of H + PCO due to the asymptote of the product HP + CO ∼ 1.0 eV lower than that of the product H + PCO in energy, as well as large differences between the frequencies of the H–P stretching and P–C stretching modes.
Observations of marine animal interactions with a small tidal turbine
The risk of collisions between animals and operating tidal turbines remains a concern in the scientific and regulatory communities. A sensor package including optical cameras was deployed to monitor animal interactions with a small-scale (1 m 2 ) cross-flow tidal turbine. The turbine was deployed in Washington State, USA for 141 days at a site with peak flow speeds of 2.5 m/s. We analyze optical camera imagery spanning 109 days of turbine operation. The analyzed images contain 1044 observations of fish, fish schools, seabirds, or seals in the vicinity of the turbine. No instances of collision with seabirds or seals were observed. Seabirds were only observed during daylight hours and while the turbine was stationary. Both seals and fish were observed during both day and night and while the turbine was stationary and rotating. Four fish were observed colliding with the moving turbine and in all but one case the animals swam away following the collision. Over the same period of time, over fifty times more fish (224 individual fish and 5 fish schools) were observed passing the moving turbine without collision. Fish encounters were likely under counted due to the difficulty in discerning small fish from plant matter in the water column. These observations represent the first optical camera imagery showing fish, bird, and marine mammal interactions with a tidal turbine in North America. In addition to quantitative and qualitative discussion of the implications of our observations for collision risk, we discuss lessons learned on sampling schemes and deployment of machine learning for detection of animals to inform future data collection strategies in future monitoring campaigns.
The simplest planar tetracoordinate carbon: CLi3H+
Although numerous planar hypercoordinate atoms have been reported, we describe the first planar tetracoordinate carbon (ptC) stabilized by a distinct electronic mechanism. In the global minimum C2v structure of CLi3H+, the ptC is bonded to one hydrogen and three lithium atoms. This structure lies over 39 kcal/mol below the next isomer on the potential energy surface. Its stabilization arises solely from direct carbon ligand interactions, without contributions from ligand–ligand bonding. The carbon atom adopts a 2s22pσ12pπ22pπ′1 configuration, forming a strong C–H σ bond, while the C–Li interactions are weak and polar. CLi3H+ is therefore the smallest electron-deficient planar hypercoordinate species known, revealing a new bonding motif in cluster chemistry.