diffusion models

Evaluation and Mechanism of the Depolymerization Effect of Aromatic Hydrocarbons on Asphaltene: A Combined Experimental and Molecular Dynamics Simulation Study

While earlier studies examined rejuvenator effects on asphaltenes, detailed mechanistic understanding and quantitative analysis remain limited. In particular, it remains unclear whether different rejuvenators exhibit distinct deagglomeration mechanisms and efficiencies, making it challenging to optimize rejuvenator selection. This study systematically investigates the various depolymerization mechanism and efficiency of different rejuvenators using three representative types of rejuvenators: light aromatic compounds (Benzene-Toluene-Xylene, BTX), polyaromatic hydrocarbons (PAHs), and straight-chain alkanes (BR1 and BR2). We used molecular dynamics simulations to evaluate several key properties. These included radial distribution functions (RDF), fraction of free volume (FFV), self-diffusion coefficients, average aggregation number ( g z ), and intermolecular interaction energies. The analysis was performed under both aging and rejuvenation conditions. The results show that BTX effectively restores the RDF profile of aged asphaltenes by eliminating the additional short-range peak associated with dimer formation. At elevated temperatures, all rejuvenators increase the FFV and self-diffusion coefficients of saturate, aromatics, resins, and asphaltenes (SARA) fractions and reduce the aggregation number. However, BTX consistently exhibits the strongest deagglomeration effect, while PAHs show limited impact and even reduce FFV and mobility at lower temperatures. BTX also significantly lowers the van der Waals and total interaction energies between aged asphaltenes, whereas PAHs exert only minor influence. Small-angle X-ray scattering (SAXS) experiments confirm the simulation findings, showing that both BTX and PAHs reduce the radius of gyration of asphaltene clusters. Notably, only BTX restores the aged asphaltene aggregates to a mass fractal structure, indicating effective structural recovery. A mechanistic model is proposed wherein aromatic rejuvenators intercalate into asphaltene PAH layers, increasing interlayer spacing and promoting exfoliation. BTX compounds, with their smaller molecular size, penetrate these layers more easily. In contrast, bulkier PAHs form stronger π – π interactions, limiting their intercalation and reducing their deagglomeration efficiency.

Lower methane emissions from full-scale stockpiles of the solid fraction of separated digested slurry with biochar amendment

Field application of biochar can be challenging due to loss through dust release and uneven spreading, and incorporation of biochar into organic fertilisers has been proposed as a practical application strategy. If biochar is added to the solid fraction prior to field application, it must be incorporated before or during storage, making its effect on storage emissions important to investigate. This study investigated how biochar addition to the solid fraction from separated digestate affected emissions during storage. Emissions from two full-scale stockpiles were determined over 85 days using the backward Lagrangian stochastic dispersion model combined with up- and downwind concentration measurements. One stockpile was amended with 10% (w/w) biochar, while the other was unamended. The CH 4 emissions were consistently lower from the biochar-amended stockpile during both covered and uncovered periods. Higher oxygen concentrations across depths and elevated core temperatures in the biochar-amended stockpile indicate improved aeration and enhanced aerobic degradation. Emissions of N 2 O and NH 3 were below measurable levels in both treatments. To the best of current knowledge, this is the first field-scale study to quantify the effect of biochar amendment on gas emissions from stockpiled solid fractions of anaerobically digested slurry. The results provide field-scale evidence that biochar enhances gas diffusion and shifts decomposition towards aerobic pathways, suppressing methanogenesis without increasing NH 3 or N 2 O emissions. These findings advance the state of the art beyond small-scale and composting studies by demonstrating that the effect of biochar on CH 4 emissions is detectable and consistent at full scale under practical field conditions.

Investigation of the Expansion Effects on Grout Diffusion and Reinforcement in Fractured Rock Masses

MATHEMATICAL FOUNDATIONS OF AI-ASSISTED AUTOMATED TEXTURING OF 3D OBJECTS

Abstract The article explores the mathematical foundations and architectural solutions for developing an automated texturing system for three-dimensional objects using artificial intelligence. It analyzes the limitations of classical UV mapping and justifies the use of a projection mapping method combined with the developed "Smart Stencil" algorithm to eliminate visual artifacts and texture stretching. Particular attention is given to the integration of latent diffusion models and the ControlNet architecture, which utilizes normalized depth maps to accurately control the spatial structure of textures. The proposed approach enables efficient generation of high-quality seamless textures on consumer-grade hardware in alignment with the actual geometric shape of 3D models.

Lacuna: Cryptic Binding Pocket Discovery via Conformational Ensemble Analysis

Lacuna discovers cryptic binding pockets: sites that are absent or too small to detect in a protein's unbound structure and open only during conformational fluctuation. It generates a conformational ensemble from any input structure, detects pockets independently in every conformer, clusters the detections into persistent sites, and ranks them with a model fitted on within-structure pairs. Ensemble generation is pluggable: normal mode analysis by default, with implicit-solvent molecular dynamics, Boltz-2 diffusion sampling, or a user-supplied ensemble as alternatives. On the designated CryptoBench test fold it recovers 55.6% of cryptic sites in its top five, rising to 66.1% with an optional PLM-assisted ranker, and 73%, 45% and 87% on the PocketMiner set, a curated set of literature apo/holo pairs, and COACH420 respectively. The default backend completes in a median of 2.6 seconds per chain on one CPU core. Outputs are docking-ready Boltz YAML constraints, AutoDock Vina boxes and pseudoatom PDB files.

Diffusing diffusivity model with dichotomous noise

Abstract We study Langevin dynamics with stochastic diffusivity arising from fluctuations of the surrounding medium.The diffusivity is modeled as Ornstein-Uhlenbeck process driven by symmetric dichotomous noise, which confines it to a finite interval. We derive analytical expressions for the short-time probability density function (PDF) of the particle displacement and analyse its asymptotic behaviour. While the PDF retains the characteristic logarithmic divergence at the origin, its tails differ from the Gaussian white-noise case: exponential tails are replaced by Gaussian ones modulated by a power-law with a switching-rate-dependent exponent. At long times, the dynamics converges to ordinary Gaussian diffusion. We determine the variance and covariance of the time-averaged stochastic diffusivity and show that it is self-averaging. The model provides a minimal analytically tractable framework for stochastic transport in environments with bounded or switching fluctuations.

Influence of mass transport near parallel band pumping electrodes and walls on the fate of chemical species in a sample plug introduced onto a redox-magnetohydrodynamics microfluidics chip

Abstract A 3D finite element model is used to investigate the behavior of a small sample volume of molecules inside a redox-magnetohydrodynamics (R-MHD) microfluidic chamber (3.0 cm × 1.7 cm, 429 µm-high), enclosing chip-based, coplanar parallel-band electrodes ( ~ 900 µm wide, 1.5 cm long, and 28 µm thick). A 539-pL cylindrical sample plug is introduced, 20 µm radius, spanning the chamber height, containing 0.10 M molecular species with diffusion coefficient of 8.75 × 10⁻¹⁰ m²·s⁻¹. Fluid motion is driven by the magnetic portion of the Lorentz force by applying ± 400 µA between two pumping electrode pairs, separated by 2760 µm and 4441 µm, and positioned above a 0.37 T permanent magnet. The model tracks how plug trajectory, spreading, and deformation under the combined influence of molecular diffusion and R-MHD-driven convection depends on electrode configuration, pumping direction, wall placement and initial plug position. Different scenarios include transporting the plug toward a chamber wall and sending it around electrode ends while maintaining a closed circulating zone rather than reaching chamber boundaries. The findings demonstrate that sample plugs can be steered, retained, or redirected through electrode activation and current polarity, without external pumps or moving parts, enabling programmable sample manipulation for R-MHD-based lab-on-a-chip systems.

Numerical Investigation of Competitive Methane Transport in Multiborehole Coal Seam Drainage and Its Implications for Borehole Layout Design

Abstract Methane drainage efficiency in coal seams is significantly affected by borehole arrangement, as overlapping pressure sinks in multiborehole systems can redistribute gas migration pathways and reduce the effective performance of individual boreholes. To quantify this interference effect, this study proposes a borehole efficiency coefficient (BEC), defined as the ratio of cumulative methane production from a reference borehole under multiborehole drainage to that under single-borehole drainage under identical geological conditions. A multiphysics numerical model is developed to simulate methane desorption, diffusion, and seepage in a dual-porosity coal seam. The model is validated against field data and further compared with a previously published numerical model. Using the validated model, the effects of borehole spacing, initial gas pressure, initial permeability, and layout pattern on interborehole interference are systematically investigated. The results show that competitive methane transport can reduce methane extraction from a reference borehole by up to 22.39% when the borehole spacing is 5 m. BEC increases with borehole spacing, indicating that larger spacing weakens interborehole interference, although the marginal improvement becomes less significant beyond 15 m. In contrast, BEC decreases with increasing initial gas pressure and permeability, suggesting that interference becomes more pronounced under conditions that favor methane flow. Among the three layout patterns considered, the trapezoidal arrangement yields the highest BEC and the weakest interference, demonstrating better drainage performance than the rectangular and rhombic layouts. Analysis of methane migration pathways further reveals that pressure-sink overlap diverts part of the gas flow away from the reference borehole, which explains the observed reduction in single-borehole efficiency. These findings indicate that BEC can serve as a practical indicator for interference-aware borehole layout design in coal seam methane drainage systems.

Artificial Intelligence and Future-Oriented Aesthetic Education: Design Thinking in Middle School Art Curriculum

Middle school art curricula in many systems still center on skill reproduction, which sits uneasily with the rapid diffusion of generative AI. This study develops a conceptual instructional model that embeds generative AI within the five-stage design thinking process (empathize, define, ideate, prototype, test) for an eighth-grade visual communication course. AI is assigned differentiated functions across the stages—analytical, retrieval, generative, assistive, and evaluative—while students retain responsibility for aesthetic judgment, justification of selections, and iterative revision. Three learning outcomes anchor the design and are operationalized in parallel measurement instruments: aesthetic judgment, creative problem-solving in visual communication, and stylistic self-awareness. Communicative intent is treated as the core sub-dimension of creative problem-solving rather than as a separate outcome, since intent is observable only through the design products and decisions that enact it. A quasi-experimental pretest-posttest pilot was conducted with 68 eighth-grade students (experimental group n = 34, control group n = 34) over a ten-week intervention at a single school, with both classes taught by the same art teacher. ANCOVA indicated that the experimental group outperformed the control group on aesthetic judgment, F(1, 65) = 8.42, p = .005, ηp² = .115, and creative problem-solving, F(1, 65) = 9.17, p = .003, ηp² = .124, with smaller yet significant gains on stylistic self-awareness. Thematic analysis of journals and interviews surfaced three patterns: shifted attention from execution to selection, prompt-based reasoning, and unease about authorship. Findings are presented as encouraging pilot evidence under specific local conditions, pending replication beyond the present site.

Dependence of the capacitance of trap states at the oxide–semiconductor interface on the interface trap density in nanoscale silicon-on-insulator FinFET transistors and its effect on electrophysical parameters

In this scientific research work, the dependence of the capacitance of trap states at the oxide–semiconductor inter - face ( C it ) on the interface trap density ( D it ) in nano-scale SOI FinFET transistors, as well as its effect on the main electrophysical parameters of the device, was systematically studied. The modeling was carried out on the basis of the drift–diffusion transport model, and quantum corrections based on the density gradient approach were applied to take into account quantum effects at the nanometer scale. The mobility model, the dependence on impurity atom concentration, and the velocity saturation effect occurring under strong electric fields were taken into consideration. The capacitance of trap states at the oxide–semiconductor interface was evaluated based on the relation C it = q²D it , and its effects on the electrostatic field potential, charge carrier concentration, the subthreshold slope (SS) of the current–voltage characteristic, threshold voltage ( V th ), and current–voltage characteristics were comprehensively analyzed. The results show that, with an increase in the interface trap density, an increase in C it is observed, which reduces the electrostatic control of the gate over the channel. As a consequence, the sensitivity of the electrostatic field potential to the gate voltage decreases, the charge carrier concentration along the channel decreases, and the subthreshold regime characteristics deteriorate. The obtained results show that the quality of the oxide–semiconductor interface in nano-scale SOI FinFET transistors is one of the main factors determining the operating characteristics of the device, and they justify the necessity of controlling surface states in the design of high-performance nanoelectronic devices.

Investigation of Position-Dependent Signal Propagation Delay in Large-Pitch AC-LGAD Using a Two-Dimensional Transmission-Line Model

This paper presents a study of position-dependent signal propagation delay in large-pitch pixelated AC-coupled Low-Gain Avalanche Detectors (AC-LGADs). In AC-LGADs, a continuous resistive N+ layer and segmented AC-coupled readout electrodes enable charge sharing and simultaneous timing and position measurements. However, lateral signal transport in the resistive layer can introduce a position-dependent delay in the measured signal arrival time. In this work, an IHEP-designed pixel AC-LGAD was characterized using a two-dimensional picosecond laser scan. The measured leading-edge arrival time shows an approximately linear dependence on an effective propagation distance, with a delay slope of about 194.7±1.3ps/mm for the tested device. After applying a position-dependent delay correction, the sigma of the combined arrival-time distribution over the scanned region is reduced from 88.3 ps to 48.6 ps. To interpret the observed delay, an equivalent two-dimensional lossy transmission-line model is developed for the continuous resistive layer. The model provides a semi-quantitative description of the leading-edge delay and indicates that, within the measured signal bandwidth, the transport is dominated by the resistive term and is therefore dispersive and diffusion-like. A distributed SPICE network including the pad-area response and capacitive charge sharing provides a complementary circuit-level cross-check of the approximately linear distance dependence. These results quantify the propagation-induced timing delay in large-pitch AC-LGADs and provide guidance for timing correction and future optimization of the resistive-layer sheet resistance.

Figure 5 from Counterfactual Diffusion Models Provide Interpretable Explanations of Artificial Intelligence Models in Pathology

Style–morphology decomposition for disentangling structural and staining effects on MSI prediction changes. A, Representative examples of counterfactual manipulation between MSIH and non-MSIH classes. For each original image x and its counterfactual xcf, style-hybrid (xstyle) and morphology-hybrid (xmorph) images were generated using Vahadane stain transfer. Each hybrid isolates the effect of either stain or morphology while controlling for the other. The right-hand bars show the Shapley-style decomposition of the logit change (Δf) into stain (φstyle) and morphology (φmorph) contributions, demonstrating that morphologic differences dominate the model’s predictions. Grad-CAM visualizations below provide region-level attribution under MIL. In contrast, MoPaDi produces class-directed “what-if” edits that offer a complementary view of candidate morphologic and style changes associated with prediction shifts. Scale bar applies to all images within the panel. B, Decomposition results across test-set patients, showing median contributions of φstyle, φmorph, and total (Δf) for manipulations toward (↑) and away from (↓) each class. C, Scatter plot of morphology versus style contributions per patient, illustrating consistent dominance of morphologic effects across both manipulation directions and classes.