Browse Articles

The internal and external cost of motor vehicle crashes

Abstract Crash cost estimates are essential for evaluating road safety management policies and assessing the economic benefits of safety improvements. Existing studies often rely on aggregated crash data, assuming an even distribution of incidents, which overlooks significant spatial variations influenced by road characteristics and traffic conditions. This research presents a methodological framework for link-based crash cost analysis that considers both internal and external costs, enabling detailed quantification at a localized level. By employing safety performance functions and ordered probit models, we estimate on-road crash rates by crash type and injury severity, distinguishing between internal costs borne by individuals involved in crashes and external costs that impact victims, insurers, and government agencies. This framework is applied to the Minneapolis-St. Paul metropolitan area for a proof-of-concept. Our findings reveal that the costs incurred by drivers are higher than those imposed on others, and that highways are generally safer than surface streets. However, these crash costs are too low compared to the value of travel time to significantly influence route choices, even when drivers are aware of these costs. To enhance effective decision-making, related policies should consider offering incentives for safe driving practices. Future research on the practical applications of this framework is encouraged to maintain a dynamic dataset that reflects ongoing changes in road safety conditions.

Water intrusion in hydrophobic MOFs with complex topology: A glimpse of the intrusion mechanism of Cu2(tebpz)

Despite water intrusion in microporous materials being extensively investigated, obtaining a detailed overview of the intrusion mechanism in materials with more complex morphology, topology, and physical–chemical characteristics, such as metal–organic frameworks (MOFs), is far from trivial. In this work, we present a qualitative study on the mechanism of water intrusion in a crystallite of hydrophobic Cu2(tebpz) (tebpz = 3,3′,5,5′-tetraethyl-4,4′-bipyrazolate) MOF. This MOF is characterized by a complex morphology; it consists of primary (main channels) and secondary (lateral apertures) porosities. This is similar to some zeolites, such as the so-called ITT-type zeolite framework, but it presents the additional characteristics of high flexibility of the material and non-uniform hydrophobicity. Interestingly, in Cu2(tebpz), water intrusion occurs first for some of the channels lying tangent to the surface of the MOF’s crystallite. This is due to hydrogen bonding bridging with bulk water across the (thin) lateral apertures of these channels. In macroscopic terms, this can be understood as a local reduction of hydrophobicity favoring intrusion. Temperature and pressure influence the average number of hydrogen bonds and the number of intruded water molecules, explaining the effect of these thermodynamic parameters on the intrusion/extrusion characteristics of this porous material. Molecular dynamics simulations allowed us to glimpse liquid intrusion in this complex hydrophobic material, highlighting how the classical models valid for mesoporous systems, namely, Young–Laplace’s law, are not quite appropriate to describe intrusion in such materials.

Extremely low frequency communication using signal modulation of sphere-string structured mechanical antenna

Mechanical antennae have been considered a promising solution for the miniaturization of underwater low-frequency communication. The research on mechanical antennae mainly focuses on the use of strong magnetic fields rather than strong electric fields at present. This paper proposed a method to generate extremely low-frequency (ELF) electromagnetic waves by utilizing the periodic motion of conductive spheres to disturb a strong electrostatic field. Both theoretical analysis and experimental verification demonstrated that this method can effectively generate ELF electromagnetic waves matching the frequency of the conductive spheres. A mechanical antenna system was designed and fabricated combining a sphere-string structure next to a van de Graaff generator, based on the above principle. Leveraging the multi-modal rapid frequency-switching characteristics of the sphere-string structure, an effective information-loading method was proposed and realized for ELF communication. This study provides more options for the radiator and information modulation of mechanical antennae.

Few-shot learning for non-vitrified ice segmentation

Abstract This study introduces Ice Finder, a novel tool for quantifying crystalline ice in cryo-electron tomography, addressing a critical gap in existing methodologies. We present the first application of the meta-learning paradigm to this field, demonstrating that diverse tomographic tasks across datasets can be unified under a single meta-learning framework. By leveraging few-shot learning, our approach enhances domain generalization and adaptability to domain shifts, enabling rapid adaptation to new datasets with minimal examples. Ice Finder’s performance is evaluated on a comprehensive set of in situ datasets from EMPIAR, showcasing its ease of use, fast processing capabilities, and millisecond inference times.

Autobiography of Y. Ron Shen

Temperature dependence of polarons in conductive PEDOT:PSS thin films

Organic conductive polymer, Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), has been widely used as an important component in organic optoelectronic devices, and recently it emerged as a promising candidate for novel epsilon-near-zero (ENZ) materials. The presence of polarons and bipolarons, acting as charge carriers in conductive polymers, has a profound influence on the electrical and optical characteristics. In this work, pristine, ethylene glycol-treated (EG-treated hereafter) and acid-treated PEDOT:PSS films were prepared for temperature-dependent spectroscopy measurement to investigate the temperature sensitivity of materials. Spectral fitting method and decomposition of the imaginary part of the permittivity is employed to elucidate the temperature sensitivity of ENZ in thin films treated with various solutions. The pristine PEDOT:PSS film is sensitive to temperature changes (ENZ wavelength changes by 93 nm), while the acid-treated PEDOT:PSS film is less affected by temperature (polarons and bipolarons have been significantly improved, ENZ wavelength changes by 32 nm). Finally, band diagrams are utilized to illustrate the dynamics of polarons and bipolarons within three thin film systems upon temperature excitation, elucidating the underlying physical mechanisms of the thin film's temperature sensitivity. Our research provides a new insight into the study of ENZ photonics in organic materials and the development of temperature-related applications.

Elimination of apoptotic cells by non-professional embryonic phagocytes can be stimulated or inhibited by external stimuli

Inertia effects in the spatial distribution and dynamics of active particles with space-dependent activity

The activity of particles can be modulated by external conditions such as light irradiation. Research on active particles with spatially varying activity has demonstrated that active particles tend to accumulate in low-activity regions and form a polarity layer at the interface, directed from the high-activity to the low-activity region. Here, we investigate the distribution and dynamics of individual or an ideal gas of inertial particles in a space with alternating active and passive regions. Our findings reveal that high inertia leads to a pronounced depletion layer in the passive region. At the interface between the active and passive regions, in addition to the usual polarity layer, an adjacent anti-polarity layer forms on the active-region side. In extreme situations (narrow region width and long persistence times), the interfacial polarity layer can even reverse orientation. Dynamically, we observe long-time peaks in the velocity autocorrelation function of particles within the active region. For particles with high inertia, the peak can even exceed 1. Correspondingly, the mean squared displacement of high-inertia particles in the active region exhibits an unusual superdiffusive behavior (∼t3). In addition, kinetic temperature and pressure differences arise between the active and passive regions. The effective temperature of particles with high inertia exhibits a gradual gradient across the active region. Our study provides new insights into the behavior of inertial active particles under spatially modulated activity and lays the groundwork for further exploration of their collective behaviors when interactions are included.

Improving the growth of pulsed chemical vapor deposition of GaN on Si(100) by <i>in situ</i> ammonia nitriding of the Si surface

The morphology, crystallinity, and photoconductive properties of gallium nitride films grown by pulsed chemical vapor deposition on p-type Si(100) with and without ammonia (NH3) pretreatment are investigated. Ammonia pretreatments were performed at 525 °C and 800 °C, which resulted in GaN film thicknesses of 80 and 140 nm, respectively. An amorphous film of GaN is obtained without pretreatment and a polycrystalline GaN film with pretreatment. X-ray photoelectron spectroscopy showed that the pretreatment results in a 1–2 nm bilayer consisting of SiNx and SiOxNy at the GaN/Si interface. Photoconductive measurements show the 525 °C pretreated GaN film has a responsivity of 72 mA W−1 and a rise time of 0.37 ms, whereas the GaN film with an 800 °C pretreatment has a responsivity of 246 mA W−1 and a rise time of 1.7 ms. Moreover, the photocurrent of the 525 °C pretreated device exhibits superlinear power dependence with a power coefficient of 1.74, whereas the 800 °C pretreated device exhibits sublinear power dependence with a power coefficient of 0.58. The superlinear power dependence of the photoresponse of the 525 °C pretreated film is attributed to the presence of fast and slow recombination centers.

Ontology-guided machine learning outperforms zero-shot foundation models for cardiac ultrasound text reports

Abstract Big data can revolutionize research and quality improvement for cardiac ultrasound. Text reports are a critical part of such analyses. Cardiac ultrasound reports include structured and free text and vary across institutions, hampering attempts to mine text for useful insights. Natural language processing (NLP) can help and includes both statistical- and large language model based techniques. We tested whether we could use NLP to map cardiac ultrasound text to a three-level hierarchical ontology. We used statistical machine learning (EchoMap) and zero-shot inference using GPT. We tested eight datasets from 24 different institutions and compared both methods against clinician-scored ground truth. Despite all adhering to clinical guidelines, institutions differed in their structured reporting. EchoMap performed best with validation accuracy of 98% for the first ontology level, 93% for first and second levels, and 79% for all three. EchoMap retained performance across external test datasets and could extrapolate to examples not included in training. EchoMap’s accuracy was comparable to zero-shot GPT at the first level of the ontology and outperformed GPT at second and third levels. We show that statistical machine learning can map text to structured ontology and may be especially useful for small, specialized text datasets.

Thermo-orientation and anomalous rotational diffusion of cone-shaped particles under a temperature gradient

Thermophoresis, the translational motion of particles in response to temperature gradients, has been well-studied, but the rotational response remains less understood. This work investigates the thermo-orientation and rotational diffusion of non-spherical particles, with special focus on shape asymmetry, through non-equilibrium molecular dynamics simulations. Our results indicate that the degree of thermo-orientation of asymmetric particles (cone-shaped) is positively correlated with both the aspect ratio (R/H) and the temperature gradient; however, the Soret coefficient exhibits a negative correlation with thermo-orientation. To explore the underlying mechanisms further, we analyzed the variation in the torque experienced by the particles. We propose that the thermo-orientation of particles originates from the combined effects of thermophoretic torque and random torque, which in turn lead to anomalous rotational diffusion behavior. Consequently, we investigated the rotational diffusion characteristics of the particles, observing that the probability density functions of angular displacement transition from Gaussian to thin-tailed distributions, with the degree of non-Gaussianity increasing as the R/H values rise. These results could provide a new perspective based on rotational diffusion dynamics for studying the thermo-orientation of asymmetric particles.

Molecular beam epitaxy growth and optoelectronic properties of droplet-free lattice-matched GaInAsSbBi on GaSb with wavelength extension exceeding 5 <i>μ</i>m

GaInAsSbBi alloys are grown lattice-matched on GaSb by molecular beam epitaxy demonstrating smooth surface morphologies, &amp;gt;5 μm wavelength photoluminescence emission, and minority carrier lifetimes &amp;gt;1 μs. At a growth temperature of 400 °C, the Ga flux is systematically increased and the Bi flux systematically decreased to identify GaInAsSbBi growth conditions that yield smooth droplet-free surface morphologies. The minority carrier lifetime is evaluated using time-resolved photoluminescence, where it is observed that GaInAsSbBi samples exhibit minority carrier lifetimes comparable to their Bi-free GaInAsSb counterparts, on the order of 1.5–2 μs. The bandgap and Urbach energy are evaluated from steady-state photoluminescence to gain insight into the impact of the incorporated Bi. Coupled with Rutherford backscattering spectrometry measurements of the Bi mole fraction, bandgap reduction rates of 97 meV/% Bi in InAsSbBi and 150 meV/% Bi in GaInAsSbBi are observed, significantly higher than previous evaluations in InAsSbBi (35–55 meV/% Bi). Detailed comparisons of the Bi mole fraction, bandgap energy, and Urbach energy indicate that the bandgap reduction potential in this alloy system is inhibited by the formation of Bi clusters; however, the inclusion of Ga in the quinary alloy is effective in suppressing Bi's tendency to incorporate in clusters for Ga mole fractions &amp;gt;9%, maximizing the bandgap reduction per unit Bi and overall optoelectronic quality.

Enhancing drought tolerance in blackgram (Vigna mungo L. Hepper) through physiological and biochemical modulation by peanut shell carbon dots

Bats on film: scientific storytelling from a recovering academic

Transcorrelated methods applied to second row elements

We explore the applicability of the transcorrelated method to the elements in the second row of the periodic table. We use transcorrelated Hamiltonians in conjunction with full configuration interaction quantum Monte Carlo and coupled cluster techniques to obtain total energies and ionization potentials, investigating their dependence on the nature and size of the basis sets used. Transcorrelation accelerates convergence to the complete basis set limit relative to conventional approaches, and chemically accurate results can generally be obtained with the cc-pVTZ basis, even with a frozen Ne core in the post-Hartree–Fock treatment.

Stiffness characteristic of HTS pinning maglev system with electromagnetic compensation device

The high-temperature superconducting (HTS) pinning magnet levitation (maglev) train, with its unique self-stabilizing and levitation-guidance integration, holds great potential for high-speed transportation. The levitation stiffness between the train and permanent magnet guideway (PMG) is crucial for studying HTS maglev dynamics and vibration reduction design. However, the magnetic hysteresis characteristics of HTS bulk can alter levitation stiffness. During high-speed operation, the high-frequency magnetic field excitation from PMG induces eddy current losses in the HTS bulk, reducing levitation force and levitation stiffness, thereby compromising train safety and increasing vibrations. Therefore, this paper investigates the HTS maglev system with an electromagnetic compensation (EMC) device to compensate for this loss, measuring and analyzing its levitation stiffness. First, a quasi-static stiffness experiment was designed to analyze and summarize the variation of levitation stiffness under different current intensities. Second, based on the experimental results, a vertical motion model was proposed and validated using the Lyapunov method. Then, dynamic experiments were designed to analyze the dynamic response of the system at different frequencies. Finally, the model simulations were combined with dynamic experiments to analyze the phenomena and dynamic characteristics of levitation stiffness changes in the system. This paper shows that the EMC device can effectively enhance levitation stiffness and improve the stability of the system under high-frequency vibrations. The levitation stiffness characteristics proposed in this study can provide relevant references for subsequent stiffness optimization and shock absorber design.

Small traffic sign recognition method based on improved YOLOv7

‘Researching climate change feels like standing in the path of an approaching train’

Transport coefficients from equilibrium molecular dynamics

The determination of transport coefficients through the time-honored Green–Kubo theory of linear response and equilibrium molecular dynamics requires significantly longer simulation times than those of equilibrium properties while being further hindered by the lack of well-established data-analysis techniques to evaluate the statistical accuracy of the results. Leveraging recent advances in the spectral analysis of the current time series associated with molecular trajectories, we introduce a new method to estimate the full (diagonal as well as off-diagonal) Onsager matrix of transport coefficients from a single statistical model. This approach, based on the knowledge of the statistical distribution of the Onsager-matrix samples in the frequency domain, unifies the evaluation of diagonal (conductivities and viscosities) and off-diagonal (e.g., thermoelectric) transport coefficients within a comprehensive framework, significantly improving the reliability of transport coefficient estimation for materials ranging from molten salts to solid-state electrolytes. We validate the accuracy of this method against existing approaches using benchmark data on molten cesium fluoride and liquid water and conclude our presentation with the computation of various transport coefficients of the Li3PS4 solid-state electrolyte.

Electron mixing performance of a magnetron sputtering cathode

The motions of electrons near a direct current magnetron sputtering cathode are analyzed, focusing on mixing performance in balanced and two unbalanced configurations, both with and without plasma. Electron–gas collisions are modeled using a Monte Carlo approach. The study investigates the impacts of field profiles on the cathode’s performance in mixing electrons by examining snapshots of electron motions at various time intervals and Poincaré maps of electron trajectories across different cut planes. The findings demonstrate that the range of axial and radial positions traversed by electrons remains remarkably stable, regardless of plasma conditions. However, significant divergence in the range of electron positions is observed in the Poincaré maps for the different configurations. In the balanced configuration, electron density is primarily concentrated in the middle region above the target. Conversely, in the unbalanced configurations, electrons predominantly accumulate near the side walls or within the central region above the target. These disparities in the distribution arise from the distinct magnetic field line arrangements. Moreover, temporal analysis of the Poincaré maps indicates that high-energy electrons, primarily emitted from the target, exhibit a distribution across a wider range of axial–radial locations, while low-energy electrons, generated via impact ionization, are more concentrated within a limited region.