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Position-dependent three-dimensional reciprocal space mapping (RSM) by nanobeam x-ray diffraction (nanoXRD) was performed to reveal the strain fields produced around individual threading dislocations (TDs) in GaN substrates. The distribution and Burgers vector of TDs for the nanoXRD measurements were confirmed by prerequisite analysis of multi-photon excited photoluminescence and etch pit methods. The present results demonstrated that the nanoXRD can identify change in the lattice plane structure for all types of TDs, i.e., edge-, screw-, and mixed TDs with the Burgers vector of b = 1a, 1c and 1m + 1c. Strain tensor components related to edge and/or screw components of the TDs analyzed from the three-dimensional RSM data showed a nearly symmetrical strained region centered on the TD positions, which were in good agreements with simulation results based on the isotropic elastic theory using a particular Burgers vector. The present method is beneficial in that it allows non-destructive analysis of screw components of TDs that tend to contribute to leakage characteristics and are not routinely accessible by conventional structural analysis. These results indicate that nanoXRD could be a powerful way to reveal three-dimensional strain fields associated with arbitrary types of TDs in semiconductor materials, such as GaN and SiC. [ABSTRACT FROM AUTHOR]

The propagation behavior of threading dislocations (TDs) and the effects of Burgers vectors in hydride vapor phase epitaxy (HVPE) GaN bulk crystals generated on Na-flux-grown GaN and in a commercially available HVPE-grown GaN bulk crystal were investigated. Analyses based on chemical etching and transmission electron microscopy (TEM) revealed a close correlation between the etch pit sizes and the Burgers vector of these TDs. The existence of TDs with the unique Burgers vector b = 1m + 1c was observed for the first time ever using a large-angle convergent-beam electron diffraction technique and plan-view bright-field scanning TEM. Multi-photon excitation photoluminescence microscopy observations showed that TDs with b = 1c had a meandering morphology in contrast to the linear morphology of TDs with b = 1a, 1a + 1c, or 1m + 1c in both types of HVPE-grown GaN crystals. The inclinations of TDs with b = 1a and 1a + 1c in HVPE-grown GaN on Na-flux-grown GaN were greatly affected by large symmetrical hexagonal hillocks. The TDs with b = 1a were inclined in the slope directions of the hillock planes, while those with b = 1a + 1c were inclined in the a directions parallel or antiparallel to the a component in their Burgers vector. These inclinations were readily explained by the isotropic elastic theory of an individual TD. The hillocks were produced around pairs of parallel mixed TDs for which the a components were opposite to one another. This phenomenon was attributed to inclusions at the interface between the Na-flux-grown GaN substrate and the HVPE-grown layer. The origins of other TDs including unusual ones having b = 1m + 1c are also discussed herein. [ABSTRACT FROM AUTHOR]

The local piezoelectricity of a Na-flux GaN crystal grown on a multipoint-seed-GaN template is investigated using piezoresponse force microscopy. The piezoresponse is critically dependent on two types of growth regions that are dominantly formed in the Na-flux GaN crystal: the c-growth sector (cGS), which is grown on top of the point-seed GaN surface with a growth front of (0001) planes, and the facet-growth sector (FGS), which is grown on the side of cGS with { 10 1 ¯ 1 } facets. Quantitative analyses reveal the GaN surface displacements at cGS that result from the piezoresponses increase with the applied AC voltage: the measured values well reflect the piezoelectric constant of d33 in GaN. The piezoresponses at the FGS and the boundary between the cGS and FGS are less sensitive than that at the cGS. A combination of cathodoluminescence and multiphoton excitation photoluminescence techniques clarifies that a local reduction of the piezoresponse observed in cGS is attributed to microscale FGSs that exist randomly in cGS. The dependence of the piezoresponse on the growth regions is quantitatively discussed from three possible viewpoints that potentially affect the polarization properties of GaN: residual strain, local crystallographic tilting, and inherent carrier distribution. As a result, a carrier screening effect is the most probable candidate to induce reduction of the piezoresponse in the FGSs of GaN crystals. [ABSTRACT FROM AUTHOR]

The mechanisms associated with electrical conduction through individual threading dislocations (TDs) in a Na-flux GaN crystal grown with a multipoint-seed-GaN technique were investigated by conductive atomic force microscopy (C-AFM). To focus on individual TDs, dislocation-related etch pits (DREPs) were formed on the Na-flux GaN surface by wet chemical etching, after which microscopic Pt electrodes were locally fabricated on the DREPs to form conformal contacts to the Na-flux GaN crystal, using electron beam assisted deposition. The C-AFM data clearly demonstrate that the leakage current flows through the individual TD sites. It is also evident that the leakage current and the electrical conduction mechanism vary significantly based on the area within the Na-flux GaN crystal where the TDs are formed. These regions include the c-growth sector (cGS) in which the GaN grows in the [ 0001 ] direction on top of the point-seed with a c-plane growth front, the facet-growth sector (FGS) in which the GaN grows with { 10 1 ¯ 1 } facets on the side of the cGS, the boundary region between the cGS and FGS (BR), and the coalescence boundary region between FGSs (CBR). The local current-voltage (I–V) characteristics of the specimen demonstrate space charge limited current conduction and conduction related to band-like trap states associated with TDs in the FGS, BR, and CBR. A detailed analysis of the I–V data indicates that the electrical conduction through TDs in the cGS may proceed via the Poole-Frenkel emission mechanism. [ABSTRACT FROM AUTHOR]

Natural competence is the ability of bacteria to incorporate extracellular DNA into their genomes. This competence is affected by a number of factors, including Ca2+ utilization and biofilm formation. As bacteria can form thick biofilms in the presence of extracellular Ca2+, the additive effects of Ca2+-promoted biofilm formation on natural competence should be examined. We evaluated natural competence in Aggregatibacter actinomycetemcomitans, an important periodontal pathogen, in the context of Ca2+-promoted biofilms, and examined whether the pga gene cluster, required for bacterial cell aggregation, is necessary for competence development. The A. actinomycetemcomitans cells grown in the presence of 1 m m CaCl2 exhibited enhanced cell aggregation and increased levels of cell-associated Ca2+. Biofilm-derived cells grown in the presence of Ca2+ exhibited the highest levels of natural transformation frequency and enhanced expression of the competence regulator gene, tfoX. Natural competence was enhanced by the additive effects of Ca2+-promoted biofilms, in which high levels of pga gene expression were also detected. Mutation of the pga gene cluster disrupted biofilm formation and competence development, suggesting that these genes play a critical role in the ability of A. actinomycetemcomitans to adapt to its natural environment. The Ca2+-promoted biofilms may enhance the ability of bacteria to acquire extracellular DNA. [ABSTRACT FROM AUTHOR]

The efficacy of the local application of recombinant human fibroblast growth factor-2 (FGF-2) in periodontal regeneration has been investigated. In this study, a randomized, double-blind, placebo-controlled clinical trial was conducted in 253 adult patients with periodontitis. Modified Widman periodontal surgery was performed, during which 200 µL of the investigational formulation containing 0% (vehicle alone), 0.2%, 0.3%, or 0.4% FGF-2 was administered to 2- or 3-walled vertical bone defects. Each dose of FGF-2 showed significant superiority over vehicle alone (p < 0.01) for the percentage of bone fill at 36 wks after administration, and the percentage peaked in the 0.3% FGF-2 group. No significant differences among groups were observed in clinical attachment regained, scoring approximately 2 mm. No clinical safety problems, including an abnormal increase in alveolar bone or ankylosis, were identified. These results strongly suggest that topical application of FGF-2 can be efficacious in the regeneration of human periodontal tissue that has been destroyed by periodontitis. [ABSTRACT FROM PUBLISHER]

Background and Objective: Emdogain® gel is clinically used as a periodontal regenerative material. However, the mechanism of the regeneration has not been completely elucidated. Although many studies have focused on the regenerative effect of Emdogain on connective tissue attachment and alveolar bone, the role of macrophages and the expression of growth factors remains unclear in the regeneration stimulated by Emdogain gel in vivo. The aim of this study was to investigate the effect of Emdogain gel on the expression of cytokines and growth factors by macrophages in vivo using a newly devised rat experimental periodontitis model. Material and Methods: Rat experimental periodontitis was induced by elevating a full-thickness gingival flap and ligating silk threads around the first molars of the mandible. At 14 d after inducing experimental periodontitis, Emdogain gel or propylene glycol alginate was applied to the furcation area. The rats were killed 7 and 14 d after treatment with propylene glycol alginate or Emdogain gel. The expression of cytokines and growth factors, and the regeneration of periodontal tissue, were examined by histochemical and immunohistochemical methods. Results: Fourteen days after the induction of periodontitis, the resorption of alveolar bone at furcation was observed and cytokines such as interleukin-1β, transforming growth factor-β1, receptor activator of nuclear factor-κB ligand, receptor activator of nuclear factor-κB and osteoprotegerin were found. In the Emdogain-treatment group, the formation of new acellular cementum and, more remarkably, recovery of the bone, were observed. The new bone formation ratio in the Emdogain treatment group was significantly higher than that of the propylene glycol alginate treatment group. Although the expression of cytokines such as interleukin-1β, transforming growth factor-β1, receptor activator of nuclear factor-κB ligand and receptor activator of nuclear factor-κB was very low, bone morphogenetic protein-2- and bone morphogenetic protein-4-expressing macrophages were observed close to the root, and bone morphogenetic protein-4-expressing macrophages were mainly observed close to the bone surface at the furcation in the Emdogain-treatment group. Conclusion: These results suggest that wound-healing macrophages may express bone morphogenetic protein and play an important role in the regeneration of periodontal tissue at the furcation following the application of Emdogain gel. [ABSTRACT FROM AUTHOR]

In spite of a lack of sequence 'homology' between HLA-B27 and the bacterial Omp/K outer membrane proteins, they both react with the Ye-2 monoclonal anti-HLA-B27 antibody. The Ye-2 antibody also reacted positively in ELISA with a synthetic peptide derived from the segment spanning residues 63-84 of B*2705. The critical peptide residues were determined by testing first with overlapping peptides, followed by a replacement set made according to the determined epitope. The results were compared with those with overlapping eight mers made to span a carboxyl fragment of the Escherichia coli OmpA protein. They indicate the reason why Ye-2 reacts with both sets of peptides is because it has a preference for polymers of arginine. [ABSTRACT FROM AUTHOR]

We developed a colorimetric microtiter plate-based assay for the detection and quantification of polymerase chain reaction-amplified DNA fragment specific for Actinobacillus actinomycetemcomitans. We amplified the 396-bp leukotoxin-specific DNA fragment by using two oligonucleotide primers, one carrying a biotin group at the 5' end and another one with a digoxigenin at the 5' end. Following amplification, the biotinylated polymerase chain reaction products were applied to a microtiter well precoated with avidin. The colorimetric detection and quantification were achieved by an enzyme-linked immunosorbent assay using alkaline phosphatase-conjugated anti-digoxigenin antibody. The detection limit of the colorimetric assay was found to be as little as 500 fg of purified A. aclinomycetemcomitans DNA and as few as 50 A. actinomycetemcomitans cells. The absorbance values in the colorimetric assays were log-linear between 500 fg and 1 ng of purified DNA and between 50 and 105 cells of A. actinomycetemcomitans. Therefore, this colorimetric assay was able to estimate the amount of A. actinomycetemcomitans in subgingival plaque samples. We concluded that the colorimetric assay of the PCR product is a very useful method not only to detect the presence of A. actinomyceIemcomitans but also to quantify the amount of A. actinomycetemcomitans in large numbers of subgingival plaque samples. [ABSTRACT FROM AUTHOR]

Dynamic nuclear polarization (DNP) is a method for achieving high levels of nuclear spin polarization by transferring spin polarization from electrons to nuclei by microwave irradiation, resulting in higher sensitivity in NMR/MRI. In particular, DNP using photoexcited triplet electron spins (triplet-DNP) can provide a hyperpolarized nuclear spin state at room temperature and in low magnetic field. In this review article, we highlight recent developments in materials and instrumentation for the application of triplet-DNP. First, a brief history and principles of triplet-DNP will be presented. Next, important advances in recent years will be outlined: new materials to hyperpolarize water and biomolecules; high-sensitivity solution NMR by dissolution triplet-DNP; and strategies for further improvement of the polarization. In view of these developments, future directions to widen the range of applications of triplet-DNP will be discussed., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

Dynamic nuclear polarization (DNP) significantly improves the sensitivity of magnetic resonance imaging, and its most important medical application is cancer diagnosis via hyperpolarized 13 C-labeled pyruvate. Unlike cryogenic DNP, triplet-DNP uses photoexcited triplet electrons under mild conditions. However, triplet-DNP of pyruvate has not been observed because of incompatibility of the hydrophobic polarizing agent with hydrophilic pyruvate. This work demonstrates that supramolecular complexation with β-cyclodextrin can disperse 4,4'-(pentacene-6,13-diyl)dibenzoate (NaPDBA), a pentacene derivative with hydrophilic substituents, even in the presence of high sodium pyruvate concentrations. The polarization of photoexcited triplet electron spins in NaPDBA was transferred to the 13 C spins of sodium pyruvate via triplet-DNP of 1 H spins in water and 1 H-to- 13 C cross-polarization. This provides an important step toward the widespread use of ultra-sensitive MRI for cancer diagnosis., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Triplet dynamic nuclear polarization (triplet-DNP) is a technique that can obtain high nuclear polarization under moderate conditions. However, in order to obtain practically useful polarization, large single crystals doped with a polarizing agent must be strictly oriented with respect to the magnetic field to sharpen the electron spin resonance (ESR) spectra, which is a fatal problem that prevents its application to truly useful biomolecular targets. Instead of this conventional physical approach of controlling crystal orientation, here, we propose a chemical approach, i.e., molecular design of polarizing agents; pentacene molecules, the most typical triplet-DNP polarizing agent, are modified so as to make the triplet electron distribution wider and more isotropic without loss of the triplet polarization. The thiophene-modified pentacene exhibits a sharper and stronger ESR spectrum than the parent pentacene, and state-of-the-art quantum chemical calculations revealed that the direction of the spin polarization is altered by the modification with thiophene moieties and the size of D and E parameters are reduced from parent pentacene due to the partial delocalization of spin densities on the thiophene moieties. The triplet-DNP with the new polarizing agent successfully exceeds the previous highest 1 H polarization of glassy materials by a factor of 5. This demonstrates the feasibility of a polarizing agent that can surpass pentacene, the best polarizing agent for more than 30 y since triplet-DNP was first reported, in the unoriented state. This work provides a pathway toward practically useful high nuclear polarization of various biomolecules by triplet-DNP.

The photoexcited triplet state of dyes can generate highly polarized electron spins for sensing and dynamic nuclear polarization. However, while triplets exhibit long spin-lattice relaxation times ( T 1 ) on the microsecond scale in solids, the polarization quickly relaxes on the nanosecond scale in solution due to the rotational motion of chromophores. Here, we report that the immobilization of dye molecules on a solid surface allows molecular contact with a liquid while maintaining high polarization and long T 1 as in a solid. By adsorbing anionic porphyrins on cationic mesoporous silica gel, porphyrin triplets exhibit high polarization and long T 1 at the solid-liquid interface of silica and toluene. Furthermore, porphyrin triplets on the solid surface can exchange spin polarization with TEMPO radicals in solution. This simple and versatile method using the solid-liquid interface will open the door for utilizing the photoinduced triplet spin polarization in solution, which has been mainly limited to the solid-state.

Micro- and nanostructures in vapor-phase-grown AlN on face-to-face annealed sputtered AlN (FFA Sp-AlN) templates formed on nanopatterned sapphire substrates (NPSS) were comprehensively analyzed using transmission electron microscopy. The comparison between metal-organic vapor-phase epitaxy-grown AlN/FFA Sp-AlN/hole-type NPSS (Sample MOH) and hydride vapor-phase epitaxy-grown AlN/FFA Sp-AlN/cone-type NPSS (Sample HVC) showed apparent differences in the morphology of dislocation propagation, presence of voids, shape of polarity inversion boundaries, and crystal structure on the slope region of NPSS. Notably, cross-sectional and plan-view observations revealed that the quality of FFA Sp-AlN significantly affects the threading dislocation density in the vapor-phase-grown layer. At the slope region of the AlN/NPSS interface, γ -AlON was observed in the MOH sample, while highly misaligned AlN grains were observed in the HVC sample. These characteristic crystal structures affect the occurrence of dislocations via different mechanisms in each sample. This study provides practical information for strategically controlling the micro- and nanostructures formed in AlN/NPSS structures for high-performance AlGaN-based deep-ultraviolet emitters., Supplementary Information: The online version contains supplementary material available at 10.1007/s11664-023-10348-3., Competing Interests: Conflict of interestThe authors declare that they have no conflict of interest., (© The Minerals, Metals & Materials Society 2023, Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.)