Automated Exploration of Reaction Network and Mechanism via Meta-dynamics Nanoreactor

We developed an automated approach to construct the complex reaction network and explore the reaction mechanism for several reactant molecules. The nanoreactor type molecular dynamics was employed to generate possible chemical reactions, in which the meta-dynamics was taken to overcome reaction barriers and the semi-empirical GFN2-xTB method was used to reduce computational cost. The identification of reaction events from trajectories was conducted by using the hidden Markov model based on the evolution of the molecular connectivity. This provided the starting points for the further transition state searches at the more accurate electronic structure levels to obtain the reaction mechanism. Then the whole reaction network with multiply pathways was obtained. The feasibility and efficiency of this automated construction of the reaction network was examined by two examples. The first reaction under study was the HCHO + NH3 biomolecular reaction. The second example focused on the reaction network for a multi-species system composed of dozens of HCN and H2O compounds. The result indicated that the proposed approach was a valuable and effective tool for the automated exploration of reaction networks

Semantic-Guided Generative Image Augmentation Method with Diffusion Models for Image Classification

Existing image augmentation methods consist of two categories: perturbation-based methods and generative methods. Perturbation-based methods apply pre-defined perturbations to augment an original image, but only locally vary the image, thus lacking image diversity. In contrast, generative methods bring more image diversity in the augmented images but may not preserve semantic consistency, thus incorrectly changing the essential semantics of the original image. To balance image diversity and semantic consistency in augmented images, we propose SGID, a Semantic-guided Generative Image augmentation method with Diffusion models for image classification. Specifically, SGID employs diffusion models to generate augmented images with good image diversity. More importantly, SGID takes image labels and captions as guidance to maintain semantic consistency between the augmented and original images. Experimental results show that SGID outperforms the best augmentation baseline by 1.72% on ResNet-50 (from scratch), 0.33% on ViT (ImageNet-21k), and 0.14% on CLIP-ViT (LAION-2B). Moreover, SGID can be combined with other image augmentation baselines and further improves the overall performance. We demonstrate the semantic consistency and image diversity of SGID through quantitative human and automated evaluations, as well as qualitative case studies.Comment: AAAI 202

A high resolution MEMS based gas chromatography column for the analysis of benzene and toluene gaseous mixtures

a b s t r a c t his paper reports a high resolution gas chromatography (GC) column based on micro electro mechanical systems (MEMS) technology. This 6.0 m long, 100 m wide, and 100 m deep column was fabricated using deep reactive-ion etching (DRIE) to form channels for gas separation, and the channels were sealed with Pyrex 7740 glass by using anode bonding. After the GC column was coated with dimethyl polysiloxane (OV-1) as the stationary phase, benzene and toluene were successfully separated in less than 185 s. The resolution of benzene and toluene was 6.33, which was higher than any previously reported values to our best knowledge. The tailing factors of benzene and toluene were 1.13 and 1.20, respectively, and the number of theoretical plates of toluene was 4850. The system is applicable as a portable device for ambient air quality monitoring and industrial exhaust gas analysis

Connecting the macroscopic and mesoscopic properties of sintered silver nanoparticles by crystal plasticity finite element method

The stress–strain response of sintered silver nanoparticles (AgNP) materials is precisely characterized in order to adapt for numerical analysis and rational design of electronic packaging structures in this study. A framework of crystal plasticity finite element method (CPFEM) is established based on the mechanism of crystal plastic deformation to describe the mesoscopic structural influence of grain evolution on the macroscopic properties of sintered AgNP materials. Material parameters of crystal plasticity are defined and initial orientations are randomly assigned for sintered AgNP grains. To calibrate the mesoscopic mechanical properties of sintered AgNP by the proposed CPFEM, the results of CPFEM simulations and uniaxial tensile tests subjected to different strain rates and temperatures are compared in terms of the stress–strain curves as the critical macroscopic characteristics. The predicted stress and deformation distributions in the polycrystalline structure demonstrate that the significant inhomogeneity of stress and deformation is caused by the different grain orientations of sintered AgNP. Furthermore, we elucidate the fracture mechanism influenced by the temperature and strain rate and also the effect of initial crystal orientation on the plastic strain of sintered AgNP. This study sheds light on the morphology design of sintered AgNP with optimized mechanical properties and fatigue resistance.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and Material

On-Chip Optical Adder and Differential-Equation-Solver Based on Fourier Optics and Metasurface

Analog optical computing (AOC) has attracted great attention over the past few years, because of its ultra-high speed (potential for real-time processing), ultra-low power consumption, and parallel processing capabilities. In this article, we design an adder and an ordinary differential equation solver (ODE) on chip by Fourier optics and metasurface techniques. The device uses the 4f system consisting of two metalenses on both sides and one middle metasurface (MMS) as the basic structure. The MMS that performs the computing is the core of the device and can be designed for different applications, i.e., the adder and ODE solver in this article. For the adder, through the comparison of the two input and output signals, the effect of the addition can be clearly displayed. For the ODE solver, as a proof-of-concept demonstration, a representative optical signal is well integrated into the desired output distribution. The simulation result fits well with the theoretical expectation, and the similarity coefficient is 98.28%. This solution has the potential to realize more complex and high-speed artificial intelligence computing. Meanwhile, based on the direct-binary-search (DBS) algorithm, we design a signal generator that can achieve power splitting with the phase difference of π between the two output waveguides. The signal generator with the insertion loss of −1.43 dB has an ultra-compact footprint of 3.6 μm× 3.6 μm. It can generate a kind of input signal for experimental verification to replace the hundreds of micrometers of signal generator composed of a multi-mode interference (MMI) combination used in the verification of this type of device in the past

Simultaneous hydrodynamic cavitation and nanosecond pulse discharge plasma enhanced by oxygen injection

A novel Hydrodynamic Cavitation-Assisted Oxygen Plasma (HCAOP) process, which employs a venturi tube and oxygen injection, has been developed for enhancing the production and utilization of hydroxyl radicals (·OH) in the degradation of organic pollutants. This study has systematically investigated the fluid characteristics and discharge properties of the gas–liquid two-phase body in the venturi tube. The hydraulic cavitation two-phase body discharge is initiated by the bridging of the cavitation cloud between the electrodes. The discharge mode transitions from diffuse to spark to corona as the oxygen flow rate increases. The spark discharge has the highest current and discharge energy. Excessive oxygen results in the change of the flow from bubbly to annular and a subsequent decrease in discharge energy. The effects of cavitation intensity, oxygen flow rate, and power polarity on discharge characteristics and ·OH production were evaluated using terephthalic acid as a fluorescent probe. It was found that injecting 3 standard liter per minute (SLPM) of oxygen increased the ·OH yield by 6 times with only 1.2 times increase in power, whereas<0.5 SLPM of oxygen did not improve the ·OH yield due to lower breakdown voltage. Negative polarity voltage increased the breakdown voltage and ·OH yield due to asymmetric density and pressure distribution in the throat tube. This polarity effect was explained by numerical simulation. Using indigo carmine (E132) as a model pollutant, the HCAOP process degraded 20 mg/L of dye in 5 L water within 2 min following a first-order reaction. The lowest electric energy per order (EEO) was 0.26 (kWh/m3/order). The HCAOP process is a highly efficient flow-type advanced oxidation process with potential industrial applications

Solvation effect on the ESIPT mechanism of 2-(4 '-amino-2 '-hydroxyphenyl)-1H-imidazo- [4,5-c]pyridine

The excited-state intramolecular proton transfer (ESIPT) dynamics of 2-(4'-Amino-2'-hydroxyphenyI)-1H-imidazo-[4,5-c]pyridine (AHPIP-c) has been studied by using density-functional theory and time-dependent density-functional theory method. Three kinds of different polar aprotic solvents, including acetonitrile (strong polar), tetrahydrofuran (weak polar) and methylcyclohexane (non-polar) have been chosen to explore solvent effects on these molecules. The calculated absorption and fluorescence spectra agree well with the experimental results for the three solvents and the dual fluorescence emission mechanism is well explained. The electron density p(r) and Laplacian del(2)rho(r) at the bond critical point (BCP) have been calculated using the Atoms-In-Molecule (AIM) theory, which prove that the intramolecular hydrogen bond (O-1-H-2 center dot center dot center dot N-3) exists in the S-0 state. The geometric parameters and the infrared vibrational spectra in the O-H stretching vibrational region have been calculated, which manifests the hydrogen-bond is strengthened in the S-1 state. The molecular electrostatic potential surface and frontier molecular orbitals analysis demonstrate that the proton transfer prefer occurring on excited state because of the charge redistribution upon photo-excitation. The results of potential energy curves, further confirm that the proton transfer process is more likely to conduct in the S-1 state due to the lower potential energy barrier than that in the S-0 state. In addition, we also find that ESIPT reaction is more easily to occur as the solvent polarity decreases. Therefore, we believe that solvent effect could play an important role in controlling excited state behaviors of AHPIP-c molecules

Oxidation Behavior of Matrix Graphite and Its Effect on Compressive Strength

Matrix graphite (MG) with incompletely graphitized binder used in high-temperature gas-cooled reactors (HTGRs) is commonly suspected to exhibit lower oxidation resistance in air. In order to reveal the oxidation performance, the oxidation behavior of newly developed A3-3 MG at the temperature range from 500 to 950°C in air was studied and the effect of oxidation on the compressive strength of oxidized MG specimens was characterized. Results show that temperature has a significant influence on the oxidation behavior of MG. The transition temperature between Regimes I and II is ~700°C and the activation energy (Ea) in Regime I is around 185 kJ/mol, a little lower than that of nuclear graphite, which indicates MG is more vulnerable to oxidation. Oxidation at 550°C causes more damage to compressive strength of MG than oxidation at 900°C. Comparing with the strength of pristine MG specimens, the rate of compressive strength loss is 77.3% after oxidation at 550°C and only 12.5% for oxidation at 900°C. Microstructure images of SEM and porosity measurement by Mercury Porosimetry indicate that the significant compressive strength loss of MG oxidized at 550°C may be attributed to both the uniform pore formation throughout the bulk and the preferential oxidation of the binder

Thermo-elasto-plastic phase-field modelling of mechanical behaviours of sintered nano-silver with randomly distributed micro-pores

Nano-silver paste is an emerging lead-free bonding material in power electronics, and has excellent mechanical properties, thermal conductivity and long-term reliability. However, it is extremely challenging to model the mechanical and failure behaviours of sintered nano-silver paste due to its random micro-porous structures and the coupled thermomechanical loading conditions. In this study, a novel computational framework was proposed to generate the random micro-porous structures and simulate their effects on mechanical properties and fracture behaviour based on the one-cut gaussian random field model and the thermo-elasto-plastic phase-field model. The elastic modulus, ultimate tensile strength and strain to failure are computed statistically, showing good agreement with the experimental results. Further, the framework was applied to model the fracture of sintered nano-silver paste under thermal cyclic conditions, demonstrating the formation of distinctive crack patterns and complex crack networks. The cracking behaviours observed in the experiments and simulations are remarkably similar to each other. The framework was implemented within Abaqus via a combination of subroutines and Python scripts, automating the process of model generation and subsequent computation. This study provides an efficient and reliable approach to simulate the mechanical and failure behaviours of sintered nano-silver paste with random micro-porous structures