Ring Defects Research Articles

Magnetism engineering of nanographene: An enrichment strategy by co-depositing diverse precursors on Au(111)

The magnetism of nanographene is dominated by the structure of its carbon skeleton. However, the magnetism engineering of nanographene is hindered due to finite precursors. Here, we demonstrate an ingenious synthetic strategy to engineer the magnetism of nanographene through hetero-coupling two precursors on Au(111) surface. Bond-resolved scanning tunneling microscopy and spectroscopy results show that two homo-coupled products host a closed-shell structure, while the products with five membered ring defects perform as an open-shell one with the total spin number of 1/2, confirmed by spin-polarized density functional theory calculations. While two hetero precursors on Au(111) substrate, the hetero-coupled products both perform as the magnetic structure with total spin quantum numbers of 1/2 and 1, resulting from carbon skeleton transformations. Our work provides an effective way to engineer the magnetism of nanographene by enriching the magnetic products simultaneous, which could be extended into other controllable magnetic nanographene instruction.

Ring defects-rich and pyridinic N-doped graphene aerogel as floating adsorbent for efficient removal of tetracycline: Evidence from NEXAFS measurements and theoretical calculations

The rational design of carbon-based adsorbents with a high uptake efficiency for polar organic molecules is a key challenge in water purification research. Herein, we report a graphene aerogel that is doped with pyridinic-N and has abundant ring defects (denoted by DNGA). The aerogel sample exhibits a high adsorption capacity of 607.1 mg/g toward tetracycline (TC), a fast adsorption process (20 min), and good reusability (with a declining efficiency < 10.0% after five cycles), while being easy to recycle. C/N K-edge X-ray absorption near-edge structure (XANES) measurements demonstrate that the efficient adsorption capacity of the DNGA sample is related to the presence of ring defects and the pyridinic-N species. Density functional theory (DFT) calculations demonstrate that ring defects of type 5–8–5 and the pyridinic-N species at the edge location are primarily responsible for TC removal. In this study, we resolve a controversial issue regarding the origin of the adsorption performance origin of N-doped carbon-based adsorbents. The findings of this study can guide the development of novel and improved N-doped carbon-based adsorbents for the removal of target contaminants.

HRTEM analysis of the aggregate structure and ultrafine microporous characteristics of Xinjiang Zhundong coal under heat treatment

Understanding the change in coal structure during heat treatment is the basis of efficient and clean utilization of coal. In this study, high-resolution transmission electron microscopy (HRTEM) was used to analyse the changes in the aggregate structure and ultramicropores of Zhungdong coal samples (Xinjiang, China) that were heated from ambient temperature to 800 °C respectively. Then, the relationship between their HRTEM characteristics and the corresponding reaction activation energy were also analyzed. The results show that the length, curvature, order, layer spacing and stacking height of the aromatic layers of the coal sample vary with an increasing temperature, and are related to the activation energy of the reaction. As the temperature reaches 300 °C, the HRTEM characteristics of the heated coal samples are obviously different from those of the raw coal sample. It is shown that the length of lattice fringes is in the range of 0.3–1.15 nm which accounts for approximately 95% of the total number of fringes. The overall orientation of lattice fringes is not good, but there are two main directions. After heating, the number of naphthalenes in the coal samples decreased, while the number of larger aromatic layers increased. The distance between the aromatic layers of the coal sample decreased with an increasing stacking height, the order of the aromatic layers was enhanced, and the number of aromatic sheets with a larger curvature increased. The coal ultramicropores are mainly concentrated from 0.4 to 0.7 nm. Heat treatment reduces the total number of ultramicropores, but the maximum number of pores is increased. The non-six-membered ring and lattice defects lead to the bending of the fringes, the distribution of fatty structures affects the orientation of the fringes, and the relationship between the pore and molecular structure does not exist independently. After heat treatment, the aggregate structure and ultramicropore size of coal have a high correlation with the activation energy. The activation energy is closely related to the 0.6 nmultramicropores. However, the current experiment could not explain the underlying causes of these relationships. The aggregated state in coal is the macromolecular group formed between different aromatic structures, fat structures and other molecules, which is formed by the interaction of internal defects and pores in the molecular group. The structural differences at different temperatures therefore reflect the interaction of different macromolecules in coal.

Insight into the significant contribution of intrinsic defects of carbon-based materials for the efficient removal of tetracycline antibiotics

Due to their high adsorption capacity and low cost, carbon-based materials have experienced great progress in the removal of tetracyclines. Unfortunately, the nature of the adsorption site is far from clarified. Especially, it is still a great challenge to systematically explore the impact of intrinsic defects of carbon-based adsorbents on the adsorption of tetracyclines. Herein, carbon-based adsorbents with different defects were designed and prepared, and their adsorption properties of tetracyclines were systematically studied. From microscopic characterization of carbon-based adsorbents and batch adsorption experiments, the intrinsic defects of carbon-based adsorbents facilitated the adsorption performance of tetracyclines. The best adsorbent (SSG-C) had a very high adsorption capacity (526.9 mg/g for tetracycline (TTC); 360.9 mg/g for oxytetracycline (OTC)). Additionally, density functional theory simulation results show that the ring defects of sp2 species promoted the adsorption performance more than sp3 edge defects, and the adsorption performance increased with increasing ring defect of sp2 species. Based on the above analysis, we proposed that intrinsic carbon defects activate the π electrons of sp2 carbon and facilitate π-π interaction between carbon-based adsorbents and tetracyclines, particularly the ring defects of sp2 species. This study provides a decisive contribution to better understanding of the role of intrinsic defects in carbon-based adsorbents for removal of tetracyclines.

Integrated transcriptome and proteome analysis reveals brassinosteroid-mediated regulation of cambium initiation and patterning in woody stem.

Wood formation involves sequential developmental events requiring the coordination of multiple hormones. Brassinosteroids (BRs) play a key role in wood development, but little is known about the cellular and molecular processes that underlie wood formation in tree species. Here, we generated transgenic poplar lines with edited PdBRI1 genes, which are orthologs of Arabidopsis vascular-enriched BR receptors, and showed how inhibition of BR signaling influences wood development at the mRNA and/or proteome level. Six Populus PdBRI1 genes formed three gene pairs, each of which was highly expressed in basal stems. Simultaneous mutation of PdBRI1-1, -2, -3 and- 6, which are orthologs of the Arabidopsis vascular-enriched BR receptors BRI1, BRL1 and BRL3, resulted in severe growth defects. In particular, the stems of these mutant lines displayed a discontinuous cambial ring and patterning defects in derived secondary vascular tissues. Abnormal cambial formation within the cortical parenchyma was also observed in the stems of pdbri1-1;2;3;6. Transgenic poplar plants expressing edited versions of PdBRI1-1 or PdBRI1-1;2;6 exhibited phenotypic alterations in stem development at 4.5months of growth, indicating that there is functional redundancy among these PdBRI1 genes. Integrated analysis of the transcriptome and proteome of pdbri1-1;2;3;6 stems revealed differential expression of a number of genes/proteins associated with wood development and hormones. Concordant (16%) and discordant (84%) regulation of mRNA and protein expression, including wood-associated mRNA/protein expression, was found in pdbri1-1;2;3;6 stems. This study found a dual role of BRs in procambial cell division and xylem differentiation and provides insights into the multiple layers of gene regulation that contribute to wood formation in Populus.

Impact of Gettering and Hydrogenation on Sub-Band-Gap Luminescence from Ring Defects in Czochralski-Grown Silicon

Impact of Gettering and Hydrogenation on Sub-Band-Gap Luminescence from Ring Defects in Czochralski-Grown Silicon

Defect-Photonic Crystal Fiber structure of Zero Chromatic Dispersion and very low Confinement loss

Photonic crystal fibers are being designed with promising results owing to design flexibility and structure geometry. A four-ring structure with ring defects has been proposed. The results show that Photonic crystal fiber with the third ring removed has very low confinement loss of 1.17x10-4dB/km at 1.55µm, chromatic dispersion of - 69ps/km.nm at 0.75µm and zero chromatic dispersion at 0.86µm. The results also show that removing only the third ring reduces chromatic dispersion at shorter wavelengths than at longer wavelengths. Vectorial Finite element method is used for this work. The proposed fiber can be used for short and medium transmission applications.&#x0D; &#x0D; Citation: Agbemabiese, P. A., Agamah, J. D., Nartey, J. A. and Torkudzor, M. K. (2021). Defect-Photonic Crystal Fiber structure of Zero Chromatic Dispersion very low Confinement loss.&#x0D; International Journal of Technology and Management Research (IJTMR), Vol. 6 (2): Pp.96-105.&#x0D; Received: March 20, 2021Accepted: September 1, 2021

Investigation of Ring Rolling Key Parameters for Decreasing Geometrical Ring Defects by 3D Finite Element and Experiments

Investigation of Ring Rolling Key Parameters for Decreasing Geometrical Ring Defects by 3D Finite Element and Experiments

Pinning and rotation of a skyrmion in Co nanodisk with nanoengineered point and ring defects.

Magnetic skyrmions have been proposed as promising information carriers in the application of spintronics, while the material imperfections are inevitable, thus an understanding of pinning effects on skyrmions in confined geometry is crucial for both fundamental research and development of spintronic devices. Here, we present the interactions of a skyrmion with a point and an extended ring defect, in a Co nanodisk which can be applied in skyrmion oscillator, based on micromagnetic simulations. By comparing with the skyrmion preferred position which is in the nanodisk center without defects, we identify the pinning strength and skyrmion preferred positions with a point defect as a function of skyrmion-defect distance and different local parameters of defect region being considered. The pinning centers range from skyrmion center, domain wall and off-center regions. We find a confinement effect on the skyrmion size with a ring defect. Moreover, we also show the rotation of the skyrmion in the presence of a ring defect, that can lead to a variation of oscillation frequency in a large range. These findings provide a complete understanding of the interaction between skyrmion and defects in a nanodisk and may provide a guidance for the design of skyrmion oscillators.

Dynamics of defects around anisotropic particles in nematic liquid crystals under shear.

Nematic multiparticle collision dynamics is used to simulate disclination ring defects around spherocylinders suspended in a liquid crystal. A solvent-solute interaction potential is integrated over a short-time scale by an auxiliary molecular dynamics procedure that updates the translational and angular coordinates of the spherocylinders. For suspended particles with length in the range ∼(60,160)nm and a fixed aspect ratio, this method is able to simulate static defects reported previously in the literature. It also simulates orientation fluctuations of the elongated colloids that exhibit a broad distribution and a slow relaxation rate. Finally, a nematic host driven from equilibrium by shear flow is simulated, and the consequent dynamic behavior of the colloid-defect pair is studied. Defects under shear present significant structural transformations from chairlike disclination rings to extended defects that cover most of the cylindrical surface of the colloid. This effect results from the hydrodynamic torque on the nematic field caused by the distorted flow around the spherocylinder, and it is present for small Reynolds and Ericksen numbers of order unity.

Morphological changes in and quantitative analysis of macular retinal microvasculature by optical coherence tomography angiography in hypertensive retinopathy.

Hypertension is a serious global health problem. Hypertensive retinopathy is generally considered to be a predictor of vascular disease elsewhere in the human body. In the past few decades, a variety of grading systems have been proposed for hypertensive retinopathy. However, these grading systems have some limitations. This study utilized optical coherence tomography angiography (OCTA) to investigate the morphological changes and macular retinal microvasculature in depth among 100 patients with hypertensive retinopathy and 66 healthy participants. Five main pathological changes were discovered in hypertensive retinopathy, as follows: focal capillary sparsity, scattered microangioma, focal macular arch ring defects, focal capillary disorder, and focal capillary nonperfusion at the levels of the superficial and deep vascular networks. In addition, we have found that the number of various pathological changes shows an increasing trend as hypertensive retinopathy progresses and may be related to renal damage. Finally, deep vessel density tended to decrease with progressive stages of hypertensive retinopathy and could be the best indicator to predict the risk of hypertensive retinopathy. Our study, therefore, proposes 3 stages of hypertensive retinopathy without macular edema according to the pathophysiology found by OCTA: stage 1 (only focal capillary sparsity), taking the place of KWB grade I; stage 2 (focal capillary sparsity and scattered microangioma), taking the place of KWB grade II; and stage 3 (focal capillary sparsity, scattered microangioma, focal capillary disorder, and nonperfusion), taking the place of KWB grade III. Hence, OCTA may be a potentially useful tool for evaluating the pathophysiology and staging of hypertensive retinopathy. Further longitudinal prospective studies are needed to confirm our findings.

Detection of Ring and Adatom Defects in Activated Disordered Carbon via Fluctuation Nanobeam Electron Diffraction.

How the structure of disordered porous carbons evolves during their activation is particularly poorly understood. This problem endures primarily because of a lack of high-resolution 3D techniques for the characterization of amorphous and highly disordered structure. To address this, the measurement of the 3D pair-angle distribution function using nanodiffraction patterns from high-energy electrons is demonstrated. These rich multiatom correlations are measured for a disordered carbon and they clearly show the structural evolution during activation. They provide previously inaccessible bond-angle information and direct evidence for the presence of ring and adatom defects. An increase in the short-range order and the number of fivefold ring defects with activation are observed, indicating stress relaxation by increasing curvature. These observations support models of disordered porous carbons based on curved graphene networks and explain how large amounts of free volume can be created with surprisingly small changes in the average ratios of tetrahedral to graphitic bonding.

Onset of ring defects in n-type Czochralski-grown silicon wafers

This paper presents experimental studies on the formation of ring defects during high-temperature annealing in both electronic-grade and upgraded metallurgical-grade (UMG) Czochralski-grown silicon wafers. Generally, a faster onset of ring defects, or shorter incubation time, was observed in the UMG samples ([Oi] = 6.3 × 1017 cm−3) in comparison to the electronic-grade samples ([Oi] = 3.9 × 1017 cm−3) used in this work. By applying a tabula rasa (TR) treatment prior to annealing, the incubation time can be increased for both types of wafers. We show that TR temperatures above 1000 °C are necessary to effectively dissolve grown-in oxygen precipitate nuclei and limit the subsequent formation of ring defects. A 30 min TR treatment at 1000 °C resulted in the longest incubation time for both types of samples used in this work, as it achieved the best balance between precipitate nuclei dissolution and precipitate re-growth/ripening. Finally, a nitrogen ambient TR step showed a short incubation time for the formation of ring defects in comparison to an oxygen ambient TR step.

Assessment of SPECT images using UHRFB and other low-energy collimators in brain study by Hoffman phantom and manufactured defects

The performance of collimators was investigated using low-energy high-resolution (LEHR) and low-energy ultra-high-resolution (LEUHR) collimators in SPECT system to study the brain physiology by injecting 99mTc-HMPAO radionuclide. Ultra-high-resolution fan beam (UHRFB) images were compared to other low-energy collimator images by constructed defects embedded into Hoffman brain phantom as lateral, deepness and metastasis designs with slices of Perspex. The defects were constructed by CNC machine as circular slices and ring flaws ranging in size from 2 to 16 mm to detect low-concentration regions. The data acquisition was done in tomographic mode with minimum radii and different matrix sizes, data acquisition time and number of projections. The collected data were reconstructed using two methods, filtered backprojection and ordered subset expectation maximization (OSEM). By two radiologists and via thallium and V-shaped markers, the minimum diameters of the constructed flaws inside the abnormal area of the brain phantom were diagnosed to 4.0 ± 0.4, 6.0 ± 0.7 and 8.0 ± 0.9 mm for UHRFB, LEUHR and LEHR, respectively. In OSEM method, the desirable ranges of the filter parameters were 4–8 iterations and 2–4 subsets for FB collimator. The outcomes showed that FB collimator provides the better resolution in axial, coronal and sagittal views using brain perfusion phantom and data from eight patients on tinnitus disease. The UHRFB with converging geometry confirmed the better detection of defect regions due to the lowest ratio of cold/background counts. This study may be useful for early detection of disease transference, monitoring of treatment response and disease progression. A CNC machine was used to make disks for Hoffman brain phantom as metastases and ring defects in evaluation of SPECT images.

Defect formation-induced tunable evolution of oxygen functional groups for sodium storage in porous graphene

The coinciding effects of carbon defects and oxygen functional groups in porous graphene were demonstrated in this work. The species and distributions of oxygen functional groups evolved with the types of defects, especially those containing C[double bond, length as m-dash]O bonds mainly distributed along the edge of ring defects, and enhanced Na+ storage.

Defects around nanocolloids in nematic solvents simulated by Multi-particle Collision Dynamics

Colloids of nanometric size dispersed in a nematic environment are simulated using a hybrid algorithm that combines rules from Multi-particle Collision Dynamics and Molecular Dynamics. Coupling between flow and orientation fields is incorporated through the application of the Leslie–Ericksen theory for reorientation of slender rods under flow. It is found that Multi-particle Collision Dynamics sustains Saturn ring defects in the solvent when homeotropic anchoring on the colloids is considered. Changes on these topological structures induced by different anchoring strengths and spontaneous fluctuating flows are quantified. Stable defect structures around two close colloidal particles are observed that coincide with those obtained in experiments and alternative numerical techniques. Simulations of uniform nematic flow around the suspended colloid are conducted. It is found that Saturn rings are displaced along the stream direction. Large flows can separate the Saturn ring from the colloid, though the motion of the defect and the suspended particle reaches a steady state where disclinations are aligned with the streamlines.

Precisely folding nanographene

Nanomaterials Graphene nanostructures that would result from folding or rolling graphene monolayers or bilayers have been predicted to have a number of interesting electronic properties, but control over such folding processes has been limited. Chen et al. used a scanning tunneling microscope tip to fold and unfold graphene nanoislands etched on graphite surfaces at low temperatures (4 kelvin). The fold angle could be precisely controlled to create different twist angles in bilayer graphene and a tubelike edge in folded graphene. They also folded 5 ring–7 ring defects and explored this heterojunction with scanning tunneling spectroscopy. Science , this issue p. [1036][1] [1]: /lookup/doi/10.1126/science.aax7864

Health Monitoring on the Spacecraft Bearings in High-Speed Rotating Systems by Using the Clustering Fusion of Normal Acoustic Parameters

The rolling bearings in moment wheel assemblies (MWAs) or control moment gyros (CMGs) are not only the core components in spacecrafts but also prone to failure. Therefore, a high reliability is the critical characteristic for spacecraft bearings, and long-life testing on the ground is one of the main means for bearing reliability assessment. In practical applications, a convenient and reliable method is required for monitoring the health status of abnormal bearings in MWAs during the long-life test. In this paper, a monitoring method based on the clustering fusion of normal operation acoustic parameters is proposed for the identification of abnormal bearings. Firstly, the characteristics of MWA’s acoustic signal and its feasibility as a monitoring medium are clarified based on tests and modal analysis. Then statistical parameters and sound quality parameters are introduced to characterize the changes caused by bearing faults, and the root mean square (RMS), kurtosis, and sharpness parameters are selected to construct the feature vectors. The K-medoids clustering technology is used to fuse the characteristic parameters, and the safety distance for normal bearing operation can be obtained by a suitable method. Finally, the abnormal index is presented based on the excess rate and excess distance to judge the abnormal states of several types of bearings through tests. The research results indicate that the presented monitoring method based on the clustering of the normal operation acoustic parameters can not only identify various faults of the spacecraft bearing (ball defects, outer ring defects, cage instability, etc.) effectively but also give a quantitative evaluation of the severity of the abnormality.

Microstructures and mechanical behaviors of CVI-based C/C composites containing h-BN powdered additives

Hexagonal boron nitride (h-BN) powders were introduced into carbon fiber preform by powder addition and subsequent combined with chemical vapor infiltration (CVI) for densification to prepare carbon fiber reinforced/carbon and boron nitride dual matrix composites (C/C-BN). Microstructures and mechanical properties of C/C composites with three different volume contents of h-BN powders were investigated in comparison to pure C/C composites. Results indicated that the introduction of h-BN powders into C/C composites significantly reduced the size of PyC and the anisotropy of thermal contraction in matrix, leading to a gradual disappearance of ring defects as the h-BN content increased. In addition, an enhanced interfacial bonding between fiber and matrix obtained due to higher-textured PyC and rougher fiber surface. Thereby, the flexural strengths and modulus of as-prepared composites decreased firstly and then increased, while the impact toughness presented a decreasing tendency as the content of BN powders increased. Furthermore, with the increasing of h-BN content, anisotropies of compressive properties were weakened, and the compressive strength of C/C-BN composites were always higher than that of pure C/C composit. However, when C/C composites modified by 13.5 vol% content of h-BN, excessive loose BN aggregates appeared in C/C-BN composites, leading to a relatively slight reduction of compressive strength.

Frontal Lobe Signs Caused by Migration of a Burr Hole Cap into the Brain after Deep Brain Stimulation Surgery:A Case Report

We report a rare complication in a patient with Parkinson's disease who underwent deep brain stimulation(DBS)surgery. The patient was a 60-year-old woman who presented with frontal lobe signs, including ataxic gait and memory disturbance, that were caused by the unexpected migration of a burr hole cap into the brain three to four months after surgery. The patient had no incidence of a head injury prior to development of symptoms. The patient underwent surgery to extract the migrated cap from the frontal lobe, and her symptoms improved several months after the operation. The cap serves to fix the DBS lead to the skull using an adjunctive burr hole ring. It was intraoperatively confirmed that only the cap detached from the ring, and no cap or ring defects were detected in a postoperative quality check by the manufacturer. We have previously utilized a burr hole ring and cap, which are packaged along with the DBS electrode, when employing the product made by Medtronic Inc. No previous report has described the cap packed in the official DBS kit to have migrated into the intracranial space. It seems unlikely that the cap migration into the intracranial space would occur without the cap and/or ring breaking through either traumatic injury or from manufacturing defects. It is important to consider the migration of a burr hole cap into the intracranial space in the absence of head injury as a possible device complication after DBS surgery.