Fine Structure Research Articles

Fine-structure changing collisions in 87Rb upon D2 excitation in the hyperfine Paschen-Back regime

Abstract We investigate fine structure changing collisions in 87Rb vapour upon D2 excitation in a thermal vapour at 75 ∘C; the atoms are placed in a 0.6 T axial magnetic field in order to gain access to the hyperfine Pashen-Back regime. Following optical excitation on the D2 line, the exothermic transfer 5P 3 / 2 → 5P 1 / 2 occurs as a consequence of buffer-gas collisions; the 87Rb subsequently emits a photon on the D1 transition. We employ single-photon counting apparatus to monitor the D1 fluorescence, with an etalon filter to provide high spectral resolution. By studying the D1 fluorescence when the D2 excitation laser is scanned, we see that during the collisional transfer process the m J ′ quantum number of the atom changes, but the nuclear spin projection quantum number, m I ′ , is conserved. A simple kinematic model incorporating a coefficient of restitution in the collision accounted for the change in velocity distribution of atoms undergoing collisions, and the resulting fluorescence lineshape. The experiment is conducted with a nominally ‘buffer-gas free’ vapour cell; our results show that fine structure changing collisions are important with such media, and point out possible implications for quantum-optics experiments in thermal vapours producing entangled photon pairs with the double ladder configuration, and solar physics magneto-optical filters.

Numerical study of runaway current impact on sawtooth oscillations in tokamaks

Abstract This study investigates the influence of runaway current in runaway plasmas on the dynamics of sawtooth oscillations and resultant loss of runaway electrons (RE) using the 3D magnetohydrodynamic (MHD) code M3D-C$^{1}$ (Jardin {\it et al} 2012 {\it J. Comput. Sci. Discovery} {\bf 6} 014002). Using an HL-2A-like equilibrium, we confirm that in the linear phase, the impact of REs on resistive internal kink instabilities is consistent with previous research.
In the nonlinear phase, as the runaway current fully replaces the plasmas current, we observe a significant suppression of sawtooth oscillations, with the first sawtooth cycle occurring earlier compared to the case without runaway current. Following the first sawtooth collapse, plasma current density, runaway current density, and safety factor ($q$) flatten within the $q=1$ surface, albeit displaying fine structures. Subsequently, the growing high torodial ($n$) and poloidal ($m$) mode number modes disrupt the magnetic surfaces, leading to the loss of REs outside the $q=1$ surface, while minimally affecting the majority of REs well-confined within it. Thus, in the current model, the physical processes associated with the presence of sawtooth oscillations do not effectively dissipate runaway current, as REs are assumed to be collisionless. In addition, the final profile of runaway current density exhibits increased steepening near the $q=1$ surface in contrast to the initial profile, displaying a distinctive corrugated inhomogeneity influenced by the growing fluctuation of the $n=0$ component. Finally, detailed convergence tests are conducted to validate the numerical simulations.

Measuring 15N and 13C Enrichment Levels in Sparsely Labeled Proteins Using High-Resolution and Tandem Mass Spectrometry.

Isotope labeling of both 15N and 13C in selected amino acids in a protein, known as sparse labeling, is an alternative to uniform labeling and is particularly useful for proteins that must be expressed using mammalian cells, including glycoproteins. High levels of enrichment in the selected amino acids enable multidimensional heteronuclear NMR measurements of glycoprotein three-dimensional structure. Mass spectrometry provides a means to quantify the degree of enrichment. Mass spectrometric measurements of tryptic peptides of a selectively labeled glycoprotein expressed in HEK293 cells revealed complicated isotope patterns which consisted of many overlapping isotope patterns from intermediately labeled peptides, which complicates the determination of the label incorporation. Two challenges are uncovered by these measurements. Metabolic scrambling of amino groups can reduce the 15N content of enriched amino acids or increase the 15N in nontarget amino acids. Also, undefined, unlabeled medium components may dilute the enrichment level of labeled amino acids. The impact of this unexpected metabolic scrambling was overcome by simulating isotope patterns for all isotope-labeled peptide states and generating linear combinations to fit to the data. This method has been used to determine the percent incorporation of 15N and 13C labels and has identified several metabolic scrambling effects that were previously undetected in NMR experiments. Ultrahigh mass resolution is also utilized to obtain isotopic fine structure, from which enrichment levels of 15N and 13C can be assigned unequivocally. Finally, tandem mass spectrometry can be used to confirm the location of heavy isotope labels in the peptides.

Deciphering Isotopic Fine Structures of Silylated Compounds in Gas Chromatography-Vacuum Photoionization Orbitrap Mass Spectrometry of Bio-Oils.

We introduce vacuum resonance-enhanced multiphoton ionization (REMPI) with high-resolution Orbitrap Fourier transform mass spectrometry (FTMS) for analyzing silylated polar compounds. UV laser radiation at 248 nm sensitively and selectively targets aromatic constituents, while high-resolution mass spectrometry (HRMS) enables high-performance mass spectrometric detection. This workflow enhances the detection confidence of polar constituents by identifying unique isotopologue patterns, including at the isotopic fine structure (IFS) level, in analytical standards and complex bio-oils. A direct and derivatized gas chromatography (GC) procedure on a polar standard component mixture allowed us to explore the general ionization and detection characteristics of REMPI FTMS. HRMS enabled the examination of the complex isotopologue profiles, revealing distinct patterns for the CHOxSiy-class compounds. Particularly in complex mixtures, this isobaric/isonucleonic complexity exceeded the classical mass resolution capabilities of the employed Orbitrap D30 series and prompted the usage of prolonged transients via an external data acquisition system. This procedure substantially improved mass spectrometric results by recording the unreduced time-domain transient data for up to 2 s. Notably, the ability to distinguish diagnostic isotopic pairs, such as 12C/29Si vs 13C/28Si with a mass split of ∼3.79 mDa and 13C12C/28Si29Si vs 13C2/28Si2, with an approximate mass difference of ∼3.32 mDa, demonstrates a significant and expected performance improvement. Finally, we benchmark the GC HRMS methodology to identify silylated oxygenated and nitrogen-containing constituents in ultracomplex bio-oil samples. The presented approach of utilizing the silicon isotope pattern and unique isotopologue mass splits for increasing attribution confidence can be applied beyond bio-oils toward the general GC analyses of polar oxygenates.

JWST observations constrain the time evolution of fine structure constants and dark energy-electromagnetic coupling

Abstract It was hypothesized in the literature that some physical parameters may be time-evolving and the astrophysical data can serve as a probe. Recently, James Webb Space Telescope (JWST) have released its early observations. In this work, we select the JWST spectroscopic observations of the high redshift ($z>7.1$) galaxies with strong [\ion{O}{III}] ($\lambda=4959$\AA \,and $5007$\AA \,in the rest frame) emission lines to constraint the evolution of the fine structure constant ($\alpha$). With the spectra from two galaxies at redshifts of $7.19$ and $8.47$, the deviation of $\alpha$ to its fiducial value is found to be as small as $0.44^{+8.4+1.7}_{-8.3-1.7} \times 10^{-4}$ and $-10.0^{+18+1.5}_{-18-1.5} \times 10^{-4}$, respectively (the first error is statistical and the latter is systematic). The combination of our results with the previous data reveals that $\frac{1}{\alpha} \frac{d \alpha}{dt} = 0.30^{+4.5}_{-4.5} \times 10^{-17}~{\rm yr^{-1}}$. Clearly, there is no evidence for a cosmic evolution of $\alpha$. The prospect of further constraining the time evolution of $\alpha$ is also discussed. The scalar field of dark energy is hypothesized to drive the acceleration of the universe's expansion through an interaction with the electromagnetic field. By integrating the observational data of the fine-structure constant variation, $\frac{\Delta\alpha}{\alpha}(z)$, we have established a stringent upper limit on the coupling strength between dark energy and electromagnetism. Our analysis yields $\zeta \leq 3.92 \times 10^{-7}$ at the 95\% confidence level, representing the most stringent bound to date.

Electron Microscopic Studies of the Adrenal Gland during Seasonal Cycle of Fruit Eating Bat Pteropus Giganteus giganteus

The fine structure of the adrenal gland is testified in many mammals; whereas, very diminutive information is available on the fine structure of the bat’s adrenal gland. The present work is constrained to the ultrastructural studies of the adrenal gland of Pteropus giganteus giganteus. The adrenal gland of the male bat has two distinct perceptible zonations viz., cortex and medulla. The cortex is divided into three illustrious zones namely, zona glomerulosa, zona fasciculata and zona reticularis. The differences in the zonation under the electron microscope becomes more acute when the studied bat is sexually active. Histoarchitectural study of the adrenal gland designate prominent structures and striking differences in the adrenocortical zone during the sexually active period than the sexually quiescent period. The zona fasciculata is well developed during the sexually active period than that of the sexually quiescent period. Likewise, zona fasciculata is well developed as compared to zona glomerulosa and zona reticularis of the adrenal cortex in both active and quiescent stages. Light microscopic studies on adrenal gland are confirmed by the ultrastructural studies.

Study on 3D printing a fine quality bone-mimetic porous structure with minimized shape error in pore size: a parametric work on key laser parameters in SLM

Study on 3D printing a fine quality bone-mimetic porous structure with minimized shape error in pore size: a parametric work on key laser parameters in SLM

Effect of Annealing Time on Grain Structure Evolution and Superplastic Response of Al-Mg 5xxx Alloys

The impact of annealing on the recrystallized grain structure and superplastic behavior of two Al-Mg 5xxx alloys used for high-speed blow forming (HSBF) was studied. The results revealed that both alloys demonstrated rapid static recrystallization after only a few minutes of annealing at 520 °C, forming fine and equiaxed grain structures. After four min of annealing, Alloy 2 (Al-4.0Mg-1.18Mn) exhibited a higher fraction of small grains (<10 µm) compared to Alloy 1 (Al-4.5Mg-0.74Mn). Moreover, Alloy 2 displayed enhanced resistance to grain coarsening with increasing annealing times, which was attributed to its higher amount of Al6(Mn,Fe) intermetallic particles and a higher number density of Mn dispersoids. Optimizing the annealing time can effectively develop a fine and stable grain structure in Al-Mg 5xxx alloys. During tensile deformation, Alloy 2 consistently showed higher ductility compared to Alloy 1 at low strain rates (170% vs. 138% at 0.001 s−1 and 163% vs. 134% at 0.01 s−1), whereas at a high strain rate of 1 s−1, both alloys displayed comparable tensile elongation. The high superplastic response of Alloy 2 at low strain rates renders it a superior superplastic alloy for HSBF applications.

Unveiling the power of artificial intelligence for image-based diagnosis and treatment in endodontics: An ally or adversary?

Artificial intelligence (AI), a field within computer science, uses algorithms to replicate human intelligence tasks such as pattern recognition, decision-making and problem-solving through complex datasets. In endodontics, AI is transforming diagnosis and treatment by applying deep learning algorithms, notably convolutional neural networks, which mimic human brain function to analyse two-dimensional (2D) and three-dimensional (3D) data. This article provides an overview of AI applications in endodontics, evaluating its use in 2D and 3D imaging and examining its role as a beneficial tool or potential challenge. Through a narrative review, the article explores AI's use in 2D and 3D imaging modalities, discusses their limitations and examines future directions in the field. AI significantly enhances endodontic practice by improving diagnostic accuracy, workflow efficiency, and treatment planning. In 2D imaging, AI excels at detecting periapical lesions on both periapical and panoramic radiographs, surpassing expert radiologists in accuracy, sensitivity and specificity. AI also accurately detects and classifies radiolucent lesions, such as radicular cysts and periapical granulomas, matching the precision of histopathology analysis. In 3D imaging, AI automates the segmentation of fine structures such as pulp chambers and root canals on cone-beam computed tomography scans, thereby supporting personalized treatment planning. However, a significant limitation highlighted in some studies is the reliance on in vitro or ex vivo datasets for training AI models. These datasets do not replicate the complexities of clinical environments, potentially compromising the reliability of AI applications in endodontics. Despite advancements, challenges remain in dataset variability, algorithm generalization, and ethical considerations such as data security and privacy. Addressing these is essential for integrating AI effectively into clinical practice and unlocking its transformative potential in endodontic care. Integrating radiomics with AI shows promise for enhancing diagnostic accuracy and predictive analytics, potentially enabling automated decision support systems to enhance treatment outcomes and patient care. Although AI enhances endodontic capabilities through advanced imaging analyses, addressing current limitations and fostering collaboration between AI developers and dental professionals are essential. These efforts will unlock AI's potential to achieve more predictable and personalized treatment outcomes in endodontics, ultimately benefiting both clinicians and patients alike.

First discovery of the podocytes in the circulatory system of enigmatic Echiurids (Annelida: Thalassematidae)

Fine structure of echiurid blood vessels in the proboscis is known in details, but the circulatory system of the trunk remains studied mainly at the level of general anatomy. The investigation of the trunk circulatory system in Bonellia viridis females revealed the presence of specialized podocytes in the ring vessel and anterior part of the ventral vessel. This study allowed to describe podocytes in echiurid circulatory system for the first time. Podocytes of B. viridis are characterized by a typical cellular architecture, which is known for other bilaterians: they consist of a cell body, primary processes, and pedicels that are interconnected via specialized slit diaphragms. The presence of podocytes in the ventral and ring vessels indicates these parts of circulatory system as sites of ultrafiltration in echiurids, i.e., exactly in these palaces, the filtration of plasma occurs through the basal lamina to the body cavity.

Synthesis, Characterization, and Hydrogen Evolution Reaction Activity of MoS2 Nanostructures Prepared Using Nonionic Surfactant

Molybdenum disulfide (MoS2) has garnered significant interest as an auspicious catalytic material for the hydrogen evolution reaction (HER). Here, MoS2 nanostructures are synthesized using the hydrothermal method with ammonium molybdate tetrahydrate ((NH4)6Mo7O24∙4H2O) as the Mo source; thioacetamide (CH3CSNH2) as the reducing agent and S source; and nonylphenols 9, nonylphenols 40, and polysorbate 80 as the surfactants. The impact of the different nonionic surfactants on the materials is comprehensively investigated. Moreover, the MoS2 fine structure was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, scanning electron microscopy (SEM), and transmission scanning microscopy (TEM). The HER characteristics of the MoS2 composites are assessed through electrochemical experiments, including linear sweep voltammetry and chronoamperometry measurements. Among the prepared specimens, MoS2/NP 9 exhibits the best electrocatalytic performance in a neutral medium. Furthermore, 240 mV is required to reach the current density of 10 mAcm−2.

Skin and hair of the Tibetan Hamster (<i>Urocricetus kamensis</i>, Cricetidae, Rodentia): A comparative morphological analysis

For the first time, using light and scanning electron microscopy, the fine structure of the skin and its derivatives (glands, hairs, whiskers) was studied in adult male and female Tibetan hamsters (Urocricetus kamensis Satunin 1903), a unique species of the subfamily Cricetinae that lives only in the highlands of the Tibetan Plateau. A comparative morphological analysis of the skin, along with features of its similarity with the skin of other hamsters, revealed a number of characteristic features in the Tibetan hamster that contribute to the adaptation of this species to the harsh mountain climate conditions with sharp seasonal and daily temperature fluctuations: abundant subcutaneous fatty tissue, a special hair structure that provides effective heat protection due to a significant change in the volume of inert air in the fur: significant hair density, wavy arrangement of rows of hairs and the profile of the lower sections of the guard hairs. The presence of relatively long and thick guide hairs in the fur serves to protect the coat in rocky habitats. The array of specific skin glands is little compared to other Cricetinae; no mid-ventral and flank glands were found, this being unique for representatives of the subfamily, but this requires confirmation based on more abundant material.

Optical skyrmions and tunable fine spin structures in deep-subwavelength scale at metal/graded index material interface

Optical skyrmions and tunable fine spin structures in deep-subwavelength scale at metal/graded index material interface

Visualizing the Structure and Dynamics of Transition Metal-Based Electrocatalysts Using Synchrotron X-Ray Absorption Spectroscopy.

As the global energy structure evolves and clean energy technologies advance, electrocatalysis has become a focal point as a critical conversion pathway in the new energy sector. Transitional metal electrocatalysts (TMEs) with their distinctive electronic structures and redox properties show great potential in electrocatalytic reactions. However, complex reaction mechanisms and kinetic limitations hinder the improvement of energy conversion efficiency, highlighting the necessity for comprehensive studies on structure and performance of electrocatalysts. X-ray Absorption Fine Structure (XAFS) spectra stand out as a robust tool for examining the electrocatalyst's structures and performance due to its atomic selectivity and sensitivity to local environments. This review delves into the application of XAFS technology in characterizing TMEs, providing in-depth analyses of X-ray Absorption Near-Edge Structure (XANES) spectra, and Extended XAFS (EXAFS) spectra in both R-space and k-space. These analyses reveal intrinsic structural information, electronic interactions, catalyst stability, and aggregation morphology. Furthermore, the paper examines advancements in in-situ XAFS techniques for real-time monitoring of active site changes, capturing critical intermediate and transitional states, and elucidating the evolution of active species during electrocatalytic reactions. These insights deepen our understanding on structure-activity relationship of electrocatalysts and offer valuable guidance for designing and developing highly active and stable electrocatalysts.

Infinitely rugged intra-cage potential energy landscape in metallic glasses caused by many-body interaction

The absence of translational symmetry in glassy materials poses a significant challenge in establishing effective structure-property relationships in real space. Consequently, the potential energy landscape (PEL) in phase space is widely utilized to comprehend the complex phenomena in glasses. The classical PEL features a two-scale profile comprising mega-basins and sub-basins, corresponding to α-relaxations (e.g. glass transition) and β-relaxations (e.g. local cage-breaking atomic rearrangements), respectively. Recent studies, however, reveal that sub-basins are not smooth and contain finer structures, the origins of which remain elusive. Here we probe the smoothness of sub-basin bottoms in glasses' PEL by introducing small intra-cage cyclic loading and then measuring the net changes in atomic-level stresses. Compared to glasses with pair interaction, glasses with many-body interaction exhibit orders-of-magnitude larger and loading-dependent stress changes even before the first cage-breaking event takes place, which reflect much more feature-rich sub-basins. We further demonstrate this stark contrast stems from the spatial distribution of individual atom's constraining force field. Specifically, at vanishing perturbations, many-body interactions disrupt the positive-definite synchrony in energy variations of the perturbed atom and the whole system, causing inherently less confined atomic responses and infinitely rugged sub-basins. The implications of these findings for the selective addition or removal of fine structures in the PEL and the subsequent tuning of glassy materials' responses to external stimuli are also explored.

Ambient Noise‐Derived SmS Splitting: A New Approach to Constraining Crustal Radial Anisotropy

AbstractRecent studies have shown that crustal body wave phases, such as PmP or SmS, can be effectively retrieved from ambient noise cross‐correlations. However, few studies have used these phases to constrain crustal structures. In this study, we successfully retrieve SmS signals from ambient noise data and observe SmS splitting caused by crustal radial anisotropy. Furthermore, through simulations of synthetic tests and application to field data, we demonstrate that these SmS signals can be used to constrain crustal radial anisotropy structures through joint inversion with surface waves. Our findings suggest that SmS signals obtained from noise data can significantly enhance the understanding of fine crustal radial anisotropic structures.

Charged Nariai black holes on the dark bubble

Abstract In this paper, we realise the charged Nariai black hole on a braneworld from a
nucleated bubble in AdS5, known as the dark bubble model. Geometrically, the black hole
takes the form of a cylindrical spacetime pulling on the dark bubble. This is realised by a
brane embedding in an AdS5 black string background. Identifying the brane with a D3-brane
in string theory allows us to determine a relation between the fine structure constant and the
string coupling, αEM = 3 gs/2, which was previously obtained for a microscopic black hole. We
also speculate on the consequences for the Festina Lente bound and neutrino masses.

Impact of cochlear detailed morphology on insertion results and intracochlear trauma of a slim pre-curved electrode array: a micro-CT study.

This study aimed to evaluate the impact of detailed cochlear dimensions, assessed using micro-CT (µCT) imaging, on insertion outcomes and associated trauma with a new slim, precurved electrode array. Eleven temporal bone specimens underwent implantation of a 22-electrode slim precurved array via the round window. High-resolution µCT scans post-implantation enabled visualization of cochlear structures and electrode positioning. Combination with subsequent scans taken after electrodes removal, we analyzed angular insertion depth (AID), insertion length, number of electrodes inserted, cochlear dimensions (specifically cochlear duct length (CDL), basal turn diameter, scala tympani dimension), and intracochlear trauma of fine structures. Statistical analyses were performed to correlate cochlear detailed dimensions and morphology with insertion outcomes and trauma. The mean AID was 351.82°, and the mean insertion length was 21.07mm. CDL showed positive correlations with AID and insertion length. Basal turn diameter (value B) positively correlated with AID and insertion length, unlike value A. Middle-basal turn (M/B) relationships (angle and height) significantly influenced insertion depth. The cochleae with smaller M/B heights and specific angles were more susceptible to insertion trauma. Larger basal turn diameters correlated with increased trauma and electrode translocation into the scala vestibuli. This study highlights the importance of precise cochlear measurements in predicting and optimizing cochlear implant outcomes. Specific cochlear dimensions and anatomical shapes were identified as critical factors affecting insertion depth, trauma risk, and electrode positioning. Utilizing micro-CT provided detailed insights into cochlear anatomy and insertion outcomes, offering valuable data for advancing cochlear implant technology and surgical practices.

Effects of aging on the fine structure, chain conformation, and morphology of Chenpi polysaccharides

Effects of aging on the fine structure, chain conformation, and morphology of Chenpi polysaccharides

Spectral Characteristics of Fundamental–Harmonic Pairs of Interplanetary Type III Radio Bursts Observed by PSP

Based on the observations by the Parker Solar Probe (PSP) during its encounter phases of approaching the Sun, I. C. Jebaraj et al. found that fundamental–harmonic (F-H) pairs constitute a majority of interplanetary (IP) type III radio bursts. In the present Letter, spectral characteristics of the IP F-H pairs are identified and analyzed further. The observations were made with the Radio Frequency Spectrometer (RFS) experiment on the PSP spacecraft in its encounter phase from the first to the ninth orbit as it traveled from 0.17 to 0.074 au from the Sun. The result shows that the occurrence rate of F-H pairs rises significantly with the rise in the number of IP type III radio bursts detected by the PSP or the enhancement in the time resolution of the RFS instrument. In particular, we compare the relationship between F and H spectral characteristics, such as the frequency-drift rate, emission intensity, relative bandwidth, duration, and fine structure. The results will be helpful for us to understand the physics underlying the generation and evolution of the IP F-H pairs as well as other IP type III radio bursts.