Fine Structure Research Articles

Interpretation of the concepts of dentinal tubule and dentinal canaliculus

The biology of dentin occupies a central place in the theory of tooth integrity as an organ, and knowledge about the microstructure of dentin changes with the development of new research methods, such as scanning electron microscopy. The structures that form dentin, and the odontoblast processes, are an extremely complex biological structure due to cellular polarization. The structure of the dentin of crowns from 30 intact teeth extracted for orthodontic reasons has been studied. Dentin was examined on longitudinal chips using scanning electron microscopy, determining the average number of dentinal tubules per unit area of dentin, the length and diameter of the dentinal canaliculi along the dentinal tubule. Scanning electron microscopy of demineralized teeth showed that numerous fine fibrillar structures were found in the predentin, connecting the odontoblast processes (dentinal canaliculi) and the walls of the dentinal tubules. The odontoblast processes were always in close contact with the microfibrillar network and were located within the dentinal tubule. It was found that the dentinal canaliculi have their own anchoring microfibrillar system, which allows each dentinal canaliculus to be held in a central position. The microfibrils are attached to the wall of the dentinal tubule and form a continuous mesh structure among the dentin tissue and are directly fixed on one side to the wall of the dentinal tubule, and on the other side to the wall of the dentinal canaliculus, which is a derivative of the odontoblast process. In different areas of the dentin, the length, number, and diameter of the microfibrils have a wide variative range. Microstructures were numerous in different regions of the dentinal tubule. Their number decreased with distance from the level of the outer dentin. In the inner third of the dentinal tubule, microfibrillar structures are observed that form a dense network of different types, thicknesses and diameters. The most common direction of the microfibrils was from the surface of the odontoblast process to the wall of the dentinal tubule, and in other cases these microfibrils were attached to both opposite inner surfaces of the dentinal tubule. The base of the microfibril is attached to the wall of the dentinal tubule, as if forming a continuous structure among the dentin tissue and the surface of the odontoblast process. It is shown that the microfibrillar structures may be a previously unknown framework system that ensures the stabilization of odontoblast processes inside the dentinal tubule. In the scientific classification of dentin ultrastructure, it is advisable to use the term "dentinal tubule" and "dentinal canaliculus", since this structure is a derivative of the odontoblast process.

Machine learning molecular dynamics insight into high interface stability and fast kinetics of low-cost magnesium chloride amine electrolyte for rechargeable magnesium batteries

The development of rechargeable magnesium batteries (RMBs) is hindered by the lack of long-lifespan and low-cost electrolytes. Moreover, due to lacking of an in-depth understanding of accurate dynamic solvation structures, the relationship between the interface kinetics behavior and a stable anode interface is still unclear. Herein, we develop a novel low-cost electrolyte containing the MgCl2 salt and the 3-methoxypropylamine solvent (denoted as the MgCl2-S2 electrolyte), which exhibits higher interface stability and faster kinetics compared to the reference Mg(TFSI)2-S2 electrolyte. The powerful machine learning molecular dynamics (MLMD) is employed to systematically investigate the differences of the fine solvation structures and explore the fundamental reason for better interfacial dynamics processes. The results show that the degree of dissociation in MgCl2-S2 electrolyte is less than 1 %, much lower than 95.1 % in Mg(TFSI)2-S2 electrolyte. The solvation structures dominated by Cl− ions can induce Mg2+ ions to preferentially acquire electrons in both kinetics and thermodynamics, which thus improving the deposition kinetics and enhancing the stability of the anode interface. This work inspires a new paradigm from MLMD to investigate the relationship between interface stability and accurate solvation structures for RMBs.

Enhanced Solar Coronal Imaging: A GAN Approach with Fused Attention and Perceptual Quality Enhancement

The activity of the solar corona has a significant impact on all aspects of human life. People typically use images obtained from astronomical telescopes to observe coronal activities, among which the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) is particularly widely used. However, due to resolution limitations, we have begun to study the application of generative adversarial network super-resolution techniques to enhance the image data quality for a clearer observation of the fine structures and dynamic processes in the solar atmosphere, which improves the prediction accuracy of solar activities. We aligned SDO/AIA images with images from the High-Resolution Coronal Imager (Hi-C) to create a dataset. This research proposes a new super-resolution method named SAFCSRGAN, which includes a spatial attention module that incorporates channel information, allowing the network model to better capture the corona’s features. A Charbonnier loss function was introduced to enhance the perceptual quality of the super-resolution images. Compared to the original method using ESRGAN, our method achieved an 11.9% increase in Peak Signal-to-Noise Ratio (PSNR) and a 4.8% increase in Structural Similarity (SSIM). Additionally, we introduced two perceptual image quality assessment metrics, the Natural Image Quality Evaluator (NIQE) and Learned Perceptual Image Patch Similarity (LPIPS), which improved perceptual quality by 10.8% and 1.3%, respectively. Finally, our experiments demonstrated that our improved model surpasses other models in restoring the details of coronal images.

Enhanced PET image reconstruction utilizing morphological filtering and MLEM algorithm

Positron Emission Tomography (PET) image reconstruction remains a pivotal area in PET technology, critically influencing clinical diagnostic outcomes. Addressing the need for enhanced image quality, this study introduces a novel algorithm for PET image reconstruction. This algorithm integrates a penalty mechanism, morphological filtering, and the Maximum Likelihood Expectation Maximization (MLEM) algorithm, aiming to improve reconstructed image quality significantly. The operational process of the algorithm within each iteration encompasses two primary phases. Initially, image reconstruction is accomplished via the MLEM algorithm, followed by the application of a morphological filter to attenuate noise in the reconstructed image. Simulation experiments demonstrate that this algorithm effectively mitigates noise while preserving crucial details, such as image edges. Notably, this method presents the dual benefits of straightforward parameter configuration and ease of implementation. The results indicate a substantial enhancement in noise suppression and fine structure preservation in the reconstructed images, marking a significant advancement in PET image reconstruction techniques.

The frequency-following response in late preterm neonates: a pilot study.

Infants born very early preterm are at high risk of language delays. However, less is known about the consequences of late prematurity. Hence, the aim of the present study is to characterize the neural encoding of speech sounds in late preterm neonates in comparison with those born at term. The speech-evoked frequency-following response (FFR) was recorded to a consonant-vowel stimulus /da/ in 36 neonates in three different groups: 12 preterm neonates [mean gestational age (GA) 36.05 weeks], 12 "early term neonates" (mean GA 38.3 weeks), and "late term neonates" (mean GA 41.01 weeks). From the FFR recordings, a delayed neural response and a weaker stimulus F0 encoding in premature neonates compared to neonates born at term was observed. No differences in the response time onset nor in stimulus F0 encoding were observed between the two groups of neonates born at term. No differences between the three groups were observed in the neural encoding of the stimulus temporal fine structure. These results highlight alterations in the neural encoding of speech sounds related to prematurity, which were present for the stimulus F0 but not for its temporal fine structure.

A comparative study on waveform prediction between SPH and S-ALE methods in impact welding

To explore the optimal method for simulating impact welding, we compared detailedly the smoothed particle hydrodynamics (SPH) and structured arbitrary Lagrangian-Eulerian (S-ALE) methods in predicting bonding interface. Based on the experimental results of Cu-Q235 steel atmospheric explosive welding, an in-depth analysis was presented. The results show that the SPH and S-ALE methods converged at element sizes of 2.5 and 2 μm, respectively. When the element size was further reduced to 0.5 % of the wavelength, the errors of both methods were less than 5 %. Benefiting from the gradient mesh, the efficiency of the S-ALE method was 2–4 times that of the SPH method at the same element size. With the addition of the gas medium, the S-ALE method derived the formation mechanism of the gap gas shockwave and indicated that the pressure distribution is not uniform. Furthermore, the local high pressure of the gas shockwave prevents the vortex closure during the wave formation, generating the pore. The calculated pressure and velocity of the wavefront were 20 MPa and 3500 m s−1, respectively. In conclusion, the SPH is suitable for fast previewing waveform interfaces, while the S-ALE method has the advantage of capturing fine waveform structures under various environmental conditions.

Coexisting single-atomic Fe and Fe2O3 on nitrogen-deficient g-C3N4 with enriched Fenton-like oxidation and photocatalytic performances for tetracycline degradation: DFT calculation, degradation mechanism and toxicity evaluation

The regulation of heterogeneous material properties to strengthen the peroxymonosulfate activation to destroy refractory pharmaceuticals remains a challenge. Herein, a promising nitrogen-deficient catalyst (FeCN) with single atom Fe and Fe2O3 nanoparticles dispersing on g-C3N4 matrix was synthesized and applied as a competent peroxydisulfate (PDS) activator for tetracycline (TC) degradation under visible light. The K-edge X-ray absorption fine structures and 57Fe Mössbauer measurements confirmed the unique configuration of Fe2O3 and single atom Fe active sites (pyrrolic and pyridinic FeN4) induced by the neighbouring nitrogen vacancies. The theory calculations and experiments provided a deep insight into the PDS activation and TC degradation via radical and non-radical pathways. The pyrrolic FeN4 active sites dominated the electron transfer, while the pyridinic FeN4 and Fe2O3 decomposed PDS to produce free radicals. The synergistic effect between the Fenton-like oxidation and photocatalysis is responsible for efficient TC degradation. This study offers a new strategy by integrating novel catalysts and advanced oxidation technology for effective wastewater purification.

Mesoscale Auroral Curls in Antarctica

AbstractThe morphology and motion of auroras have been widely studied due to their indications on magnetospheric processes. Here, we report a new kind of “auroral curls,” which have wavelengths in the mesoscale (∼100 km) and propagate azimuthally. Utilizing data from the Chinese Antarctic Zhongshan Station (the all‐sky imager and the high‐frequency radar), the Active Magnetosphere and Planetary Electrodynamics Response Experiment and the Defense Meteorological Satellite Program, we analyze an event occurred on 23 April 2019. We find these curls are fine structures in the poleward boundary of multiple arcs. Corresponding field‐aligned currents manifest as a series of longitudinally arranged pairs, while ionospheric flow velocities nearby oscillate with periods in the Pc 5 band. Observational evidence suggests these curls are connected with ultra‐low frequency (ULF) waves, which opens the possibility of using auroras to globally image ULF waves.

Microstructural characteristics and properties of wire arc additive manufactured 304L austenitic stainless steel cylindrical components by different arc welding processes

Wire arc additive manufacturing (WAAM) is an advanced additive manufacturing (AM) technology that offers low cost and high deposition rates, making it suitable for building large metal parts for structural engineering applications. However, various welding procedures result in differing heat inputs and repetitive heating treatments throughout the deposition process, which can affect the microstructural and mechanical characteristics of the parts. In the current study, cylindrical parts made of 304L austenitic stainless steel (ASS) were manufactured using the WAAM technique, employing both gas metal arc welding (GMAW) and cold metal transfer (CMT) processes. This study explores the correlation between WAAM techniques and their effects on the bead geometry, microstructure and mechanical properties. The microstructure of the cylinders consisted of vertically growing austenite dendrites with residual ferrite (δ) within the austenite (γ) matrix. Compared to the bottom region (region ①), the top region (region ②) contained more residual ferrite. Although the microstructural characteristics from region ① to region ② are similar, they exhibit different ferrite morphologies. The rapid cooling rate in the CMT-AM process resulted in finer structures and a greater presence of ferrite phases in both regions compared to the GMAW-AM method. Cylinders produced by the CMT process displayed nearly uniform properties across both regions and demonstrated superior tensile properties, hardness, and impact toughness relative to those made using the GMAW technique. The WAAM 304L ASS cylinders also showed enhanced performance compared to stainless steel manufactured using traditional industrial forging standards, indicating that WAAM-processed 304L ASS cylinders are suitable for industrial applications.

On the computation of moments in the Super-Transition-Arrays model for radiative opacity calculations

In the Super-Transition-Array statistical method for the computation of radiative opacity of hot dense matter, the moments of the absorption or emission features involve partition functions with reduced degeneracies, occurring through the calculation of averages of products of subshell populations. In the present work, we discuss several aspects of the computation of such peculiar partition functions, insisting on the precautions that must be taken in order to avoid numerical difficulties. In a previous work, we derived a formula for supershell partition functions, which takes the form of a functional of the distribution of energies within the supershell and allows for fast and accurate computations, truncating the number of terms in the expansion. The latter involves coefficients for which we obtained a recursion relation and an explicit formula. We show that such an expansion can be combined with the recurrence relation for shifted partition functions. We also propose, neglecting the effect of fine structure as a first step, a positive-definite formula for the Super-Transition-Array moments of any order, providing an insight into the asymmetry and sharpness of the latter. The corresponding formulas are free of alternating sums. Several ways to speed up the calculations are also presented.

Imaging of biological tissues with terahertz microscopy based on a cross-filament

Terahertz (THz) imaging technology has shown powerful potential for applications in biological sensing due to characteristics of the THz radiation. However, the measurement accuracy is always restricted by the low spatial resolution of THz imaging. In this work, a THz microscopy based on a cross-filament was utilized to inspect different biological tissues. A quasi sub-wavelength resolution was realized without approaching the sampe surface with any actual devices. By using the technique, fine tissue structures of two plant leaves and two animal bodies were precisely identified and analyzed from their temporal, spectral, and absorption images. Furthermore, possible optimization solutions were also discussed in detail for enhancing the imaging performance. This work demonstrated a novel and practical inspection method for pushing the development of THz biological applications.

Parameter optimization, microstructural and mechanical properties of fiber laser lap welds of DP1200 steel sheets

In this research, the effects of laser power, laser welding speed and laser incidence angle were evaluated in terms of weld geometry, microstructure, microhardness, fracture surfaces and tensile shear load in fiber laser welding joints of DP1200 steel sheets. Response Surface Methodology (RSM) was utilized to derive mathematical relationships between the process parameters and the tensile shear load after the tensile test. The optimum combination of process parameters was a laser power of 2800 W, a laser welding speed of 40 mm/s, and a laser incidence angle of 70°. A thermal camera was used to record the laser welding process, and the cooling rates were evaluated by analyzing this data. The influence of cooling rate upon microstructure phase formation for DP1200 steel is investigated, with continuous cooling transformation (CCT) diagrams. Also, post-welding stress and displacement were simulated by Simufact Welding software. At high heat input (55.79 J/mm) occurred coarse dendritic martensitic lath growth while at low heat input (37.6 J/mm) fine dendritic martensitic structure was observed in the weld zone was obtained owing to the high rate of cooling. The microstructure consists of full martensite at a higher than 10 °C/s cooling rate. The findings reveal that the phases in FZ and HAZ, the morphology and martensite/bainite constituents differed related to the heat input and laser incidence angle, which ultimately affects the joint’s microhardness, fracture dynamics and tensile shear load.

Electron Precipitation Driven by EMIC Waves: Two Types of Energy Dispersion

AbstractElectromagnetic ion cyclotron (EMIC) waves can very rapidly and effectively scatter relativistic electrons into the atmosphere. EMIC‐driven precipitation bursts can be detected by low‐altitude spacecraft, and analysis of the fine structure of such bursts may reveal unique information about the near‐equatorial EMIC source region. In this study, we report, for the first time, observations of EMIC‐driven electron precipitation exhibiting energy, E, dispersion as a function of latitude (and hence L‐shell): two predominant categories exhibit dE/dL > 0 and dE/dL < 0. We interpret precipitation with dE/dL < 0 as due to the typical inward radial gradient of cold plasma density and equatorial magnetic field (∼65% of the statistics). Precipitation with dE/dL > 0 is interpreted as due to an outward radial gradient of the equatorial magnetic field, likely produced by energetic ions freshly injected into the ring current (∼35% of the statistics). The observed energy dispersion of EMIC‐driven electron precipitation was reproduced in simulations.

Reflood oxidation performances of Cr-coated Zr-Sn-Nb alloy cladding tubes at 1000 °C∼1200 °C

Reflood plays an important role in preventing the serious accident process. In this paper, the reflood oxidation performances of Cr-coated Zr-Sn-Nb alloy cladding tubes at 1000 °C, 1100 °C and 1200 °C were studied by high-temperature steam oxidation followed by in-situ water quenching. The oxidation kinetics, macroscopic morphology, phase transformation and microstructural evolution were investigated. Cr coating can provide excellent anti-reflood oxidation protection for Zr-Sn-Nb alloy, resulting in an oxidation rate constant of only 1/4–1/7 of that of uncoated Zr-Sn-Nb alloys. However, the cladding tube degraded into fragments due to excessive thermal stress during the in-situ water quenching after reflood oxidation at 1200 °C for 4000 s. After reflood oxidation at 1000 °C and 1100 °C, the most prominent feature of the surface is a porous flocculation structure main due to the formation of volatile products, while after 1200 °C, it is a fine mackerel scale-like structure accompanied by protruding whiskers main owing to Cr3+ rapidly migrates outward to the outer surface via short circuit paths. After oxidation, the cross-section of Cr-coated Zr-Sn-Nb alloys exhibits a multi-layer structure. The thickness of each layer changes approximately linearly with oxidation time. However, due to the redox reaction, compared to that after oxidation for 2000s, the Cr2O3 layer becomes thinner and the residual Cr coating becomes thicker after oxidation at 1200 °C for 4000 s.

Rotational Spectrum of the Phenoxy Radical.

We report the hyperfine-resolved rotational spectrum of the gas-phase phenoxy radical in the 8-25 GHz frequency range using cavity Fourier transform microwave spectroscopy. A complete assignment of its complex but well-resolved fine and hyperfine splittings yielded a precisely determined set of rotational constants, spin-rotation parameters, and nuclear hyperfine coupling constants. These results are interpreted with support from high-level quantum chemical calculations to gain detailed insight into the distribution of the unpaired π electron in this prototypical resonance-stabilized radical. The accurate laboratory rest frequencies enable studies of the chemistry of phenoxy in both the laboratory and space. The prospects of extending the present experimental and theoretical techniques to investigate the rotational spectra of isotopic variants and structural isomers of phenoxy and other important gas-phase radical intermediates that are yet undetected at radio wavelengths are discussed.

The fine structure of pygmy and giant multipole resonances in nuclei

In connection with the program of planned work on the megascience installation "Intensive Reverse Compton"(INOC) at the Scientific Center of Physics and Mathematics in Sarov, a brief overview of experimental and theoretical results in the field of pygmy- and giant resonance energies is presented. Considered: 1) pygmy-dipole resonance in 208Pb, for which the limit of experimental resolution has already been reached and separate 1 − levels have been identified, 2) the most important physical results of experiments with a resolution of (50–200) keV both for gamma strenght functions, that determine the characteristics of nuclear reactions, and for analysis of non–statistical mechanisms of formation of widths of giant resonances («doorway» states) in the framework of wavelet analysis. Some results in the field of excitation energies (1–5) MeV are also discussed.

The microstructures and mechanical properties of the TC4 titanium alloy fabricated by laser composite manufacturing technology

The effective combination of traditional forging and laser three-dimensional forming technology can play a crucial role in the preparation of large metal part with fine structures, thereby accelerating the manufacturing cycle of parts and reducing costs. This study used laser composite manufacturing technology to perform complete annealing heat treatment on TC4 titanium alloy structural part produced from traditional forgings. The analysis of microscopic structure, chemical composition, and mechanical properties has verified that the overall mechanical properties consistency of the composite manufacturing part has been effectively improved. The results indicate that laser composite manufacturing part have good metallurgical bonding, and there is no component segregation phenomenon in the composite manufacturing area. After complete annealing, the α lath in the composite manufacturing part is coarsened, the strength of the laser forming area is reduced, and the consistency of mechanical properties of the forging area and the laser forming area is enhanced. The consistency of strength of the two areas is increased from 78% before heat treatment to 84%.

Parareal Neural Networks Emulating a Parallel-in-Time Algorithm.

As deep neural networks (DNNs) become deeper, the training time increases. In this perspective, multi-GPU parallel computing has become a key tool in accelerating the training of DNNs. In this article, we introduce a novel methodology to construct a parallel neural network that can utilize multiple GPUs simultaneously from a given DNN. We observe that layers of DNN can be interpreted as the time steps of a time-dependent problem and can be parallelized by emulating a parallel-in-time algorithm called parareal. The parareal algorithm consists of fine structures which can be implemented in parallel and a coarse structure that gives suitable approximations to the fine structures. By emulating it, the layers of DNN are torn to form a parallel structure, which is connected using a suitable coarse network. We report accelerated and accuracy-preserved results of the proposed methodology applied to VGG-16 and ResNet-1001 on several datasets.

Selective laser melting of Hastelloy-X alloy and cerium oxide reinforced Hastelloy-X composite: Microstructural examination and corrosion behavior

The study investigated the microstructures and corrosion behaviors of Hastelloy X (HX) and HX reinforced by cerium oxide particles (HX-C) produced by selective laser melting (SLM) and compared to the wrought equivalent (HX-W). The aim was to eliminate hot cracking and investigate the HX's corrosion behavior in the presence of cerium oxide particles. The HX samples showed fine cellular and columnar solidification structures with uniform-size sub-cells and severe microcracking. Incorporating cerium oxide particles (1 wt%) resulted in finer and relatively equiaxed grains without microcracking. The HX-W alloy contained a micron-sized carbide (Mo-rich M6C type) within the matrix. The HX-C sample displayed higher porosities compared to the HX sample (1.8 % against 0.3 %). Potentiodynamic polarization and electrochemical impedance spectroscopy tests were conducted in a standard NaCl solution at temperatures of 25, 50, and 70 °C to assess the corrosion behavior of Hastelloy samples. The HX-C matrix showed superior corrosion resistance compared to the HX-W and HX samples due to its finer grain structure and stable passive layer formation. Cerium oxide particles were found to be efficient in decreasing hot cracking and improving corrosion resistance.

A multidisciplinary approach to describe population structure of Solea solea in the Mediterranean Sea

Investigating marine species population structure in a multidisciplinary framework can reveal signatures of potential local adaptation and the consequences for management and conservation. In this study we delineate the population structure of common sole (Solea solea) in the Mediterranean Sea using genomic and otolith data, based on single nucleotide polymorphism (SNPs) markers, otolith shape and otolith trace element composition data. We correlated SNPs with environmental and spatial variables to evaluate the impact of the selected features on the actual population structure. Specifically, we used a seascape genetics approach with redundancy (RDA) and genetic-environmental association (GEA) analysis to identify loci potentially involved in local adaptation. Finally, putative functional annotation was investigated to detect genes associated with the detected patterns of neutral and adaptive genetic variation. Results from both genetic and otolith data suggested significant divergence among putative populations of common sole, confirming a clear separation between the Western and Eastern Mediterranean Sea, as well as a distinct genetic cluster corresponding to the Adriatic Sea. Evidence of fine-scale population structure in the Western Mediterranean Sea was observed at outlier loci level and further differentiation in the Adriatic. Longitude and salinity variation accounted for most of the wide and fine spatial structure. The GEA detected significant associated outlier loci potentially involved in local adaptation processes under highly structured differentiation. In the RDA both spatial distribution and environmental features could partially explain the genetic structure. Our study not only indicates that separation among Mediterranean sole population is led primarily by neutral processes because of low connectivity due to spatial segregation and limited dispersal, but it also suggests the presence of local adaptation. These results should be taken into account to support and optimize the assessment of stock units, including a review and possible redefinition of fishery management units.