Radiative and Magnetically Stimulated Evolution of Nanostructured Complexes in Silicon Surface Layers

The effect of a weak magnetic field (B = 0.17 T) and X-irradiation (D < 520 Gy) on the rearrangement of the defective structure of near-surface p-type silicon layers was studied. It was established that the effect of these external fields increases the positive accumulated charge in the region of spatial charge (RSC) and in the SiO₂ dielectric layer. This can be caused by both defects in the near-surface layer of the semiconductor and impurities contained in the dielectric layer, which can generate charge carriers. It was found that the near-surface layers of the barrier structures contain only one deep level in the silicon band gap, with an activation energy of Ev + 0.38 eV. This energy level corresponds to a complex of silicon interstitial atoms Si_I+Si_I. When X-irradiated with a dose of 520 Gy, a new level with the energy of Ev + 0.45 eV was observed. This level corresponds to a point boron radiation defect in the interstitial site (B_I). These two types of defect are effective in obtaining charge carriers, and cause deterioration of the rectifier properties of the silicon barrier structures. It was established that the silicon surface is quite active, and adsorbs organic atoms and molecules from the atmosphere, forming bonds. It was shown that the effect of a magnetic field causes the decay of adsorbed complexes at the Si–SiO₂ interface. The released hydrogen is captured by acceptor levels and, as a result, the concentration of more complex Si–H₃ complexes increases that of O₃–Si–H.     

Biological Safety Evaluation and Surface Modification of Biocompatible Ti–15Zr–4Nb Alloy

We performed biological safety evaluation tests of three Ti–Zr alloys under accelerated extraction condition. We also conducted histopathological analysis of long-term implantation of pure V, Al, Ni, Zr, Nb, and Ta metals as well as Ni–Ti and high-V-containing Ti–15V–3Al–3Sn alloys in rats. The effect of the dental implant (screw) shape on morphometrical parameters was investigated using rabbits. Moreover, we examined the maximum pullout properties of grit-blasted Ti–Zr alloys after their implantation in rabbits. The biological safety evaluation tests of three Ti–Zr alloys (Ti–15Zr–4Nb, Ti–15Zr–4Nb–1Ta, and Ti–15Zr–4Nb–4Ta) showed no adverse (negative) effects of either normal or accelerated extraction. No bone was formed around the pure V and Ni implants. The Al, Zr, Nb, and Ni–Ti implants were surrounded by new bone. The new bone formed around Ti–Ni and high-V-containing Ti alloys tended to be thinner than that formed around Ti–Zr and Ti–6Al–4V alloys. The rate of bone formation on the threaded portion in the Ti–15Zr–4Nb–4Ta dental implant was the same as that on a smooth surface. The maximum pullout loads of the grit- and shot-blasted Ti–Zr alloys increased linearly with implantation period in rabbits. The pullout load of grit-blasted Ti–Zr alloy rods was higher than that of shot-blasted ones. The surface roughness (Ra) and area ratio of residual Al₂O₃ particles of the Ti–15Zr–4Nb alloy surface grit-blasted with Al₂O₃ particles were the same as those of the grit-blasted Alloclassic stem surface. It was clarified that the grit-blasted Ti–15Zr–4Nb alloy could be used for artificial hip joint stems.     

The Positive Role of Nanometric Molybdenum–Vanadium Carbides in Mitigating Hydrogen Embrittlement in Structural Steels

The influence of hydrogen on the fracture toughness and fatigue crack propagation rate of two structural steel grades, with and without vanadium, was evaluated by means of tests performed on thermally precharged samples in a hydrogen reactor at 195 bar and 450 °C for 21 h. The degradation of the mechanical properties was directly correlated with the interaction between hydrogen atoms and the steel microstructure. A LECO DH603 hydrogen analyzer was used to study the activation energies of the different microstructural trapping sites, and also to study the hydrogen eggresion kinetics at room temperature. The electrochemical hydrogen permeation technique was employed to estimate the apparent hydrogen diffusion coefficient. Under the mentioned hydrogen precharging conditions, a very high hydrogen concentration was introduced within the V-added steel (4.3 ppm). The V-added grade had stronger trapping sites and much lower apparent diffusion coefficient. Hydrogen embrittlement susceptibility increased significantly due to the presence of internal hydrogen in the V-free steel in comparison with tests carried out in the uncharged condition. However, the V-added steel grade (+0.31%V) was less sensitive to hydrogen embrittlement. This fact was ascribed to the positive effect of the precipitated nanometric (Mo,V)C to alleviate hydrogen embrittlement. Mixed nanometric (Mo,V)C might be considered to be nondiffusible hydrogen-trapping sites, in view of their strong hydrogen-trapping capability (~35 kJ/mol). Hence, mechanical behavior of the V-added grade in the presence of internal hydrogen was notably improved.     

Influence of Alloy Atoms on Substitution Properties of Hydrogen by Helium in ZrCoH3

Intermetallic alloy ZrCo is a good material for storing tritium (T). However, ZrCo is prone to disproportionation reactions during the process of charging and discharging T. Alloying atoms are often added in ZrCo, occupying the Zr or Co site, in order to restrain disproportionation reactions. Meanwhile, T often decays into helium (He), and the purity of T seriously decreases once He escapes from ZrCo. Therefore, it is necessary to understand the influence of alloying atoms on the basic stability property of He. In this work, we perform systematical ab initio calculations to study the stability property of He in ZrCoH₃ (ZrCo adsorbs the H isotope, forming ZrCoH₃). The results suggest that the He atom will undergo displacements of 0.31 and 0.12 Å when it substitutes for Co and Zr, respectively. In contrast, the displacements are very large, at 0.67–1.09 Å, for He replacing H. Then, we introduce more than 20 alloying atoms in ZrCo to replace Co and Zr in order to examine the influence of alloying atoms on the stability of He at H sites. It is found that Ti, V, Cr, Mn, Fe, Zn, Nb, Mo, Tc, Ru, Ta, W, Re, and Os replacing Co can increase the substitution energy of H by the He closest to the alloying atom, whereas only Cr, Mn, Fe, Mo, Tc, Ru, Ta, W, Re, and Os replacing Co can increase the substitution energy of H by the He next closest to the alloying atom. The influence of the alloying atom substituting Zr site on the substitution energies is inconspicuous, and only Nb, Mo, Ru, Ta, and W increase the substitution energies of H by the He closest to the alloying atom. The increase in the substitution energy may suggest that these alloy atoms are conducive to fix the He atom in ZrCo and avoid the reduction in tritium purity.     

Insight into Point Defects and Complex Defects in β-Mo2C and Carbide Evolution from First Principles

In this paper, first principles method was adopted to investigate the point defects, Vanadium-related defects and defect combinations (vacancy (V), substitutional (S) and/or interstitial (I)) in molybdenum β-Mo₂C and explore the use of first principles calculation data in analysing the link between different carbides and the effects of doping elements. Supercell models with different defect types were established and optimized, and the formation energy data of defects was developed. The structure evolution during the optimization process is analysed in detail to establish the main characteristics of changes and the relevant electronic properties. The data for different types of intrinsic defects and combined defects complexes was developed and key results is analysed. The results show that carbon vacancy (V_C) is stable but does not inevitably exist in pure β-Mo₂C. Interstitial site II is a very unstable position for any type of atoms (Mo, V and C), and analysis of the structure evolution shows that the atom always moves to the interface area near the interstitial site I between two layers. In particular, a C atom can expand the lattice structure when it exists between the layer interfaces. One type of the defects studied, the substitution of Mo with V (designated as ‘S_V-Mo’), is the most stable defect among all single point defects. The data for defect complexes shows that the combination of multiple S_V-Mo defects in the super cell being more stable than the combination of other defects (e.g., ‘V_Mo+I_C’, ‘S_V-Mo+V_C’). The data with increasing S_V-Mo in (Mo, V)₂C system is developed, and typical data (e.g., formation energy) for Mo-rich carbides and V carbides are correlated and the potential of the data in analysing transition of different carbides is highlighted. The relevance of using first principles calculation data in the studying of V-doping and the complex carbides (V- and Mo-rich carbides) evolution in different materials systems and future focus of continuous work is also discussed.     

Vibrational vs. translational energy in promoting a prototype metal-hydrocarbon insertion reaction

The reaction Y + CH₄ → HYCH₃ → YCH₂ + H₂ is initiated by C–H insertion involving a 20 ± 3 kcal/mol potential energy barrier. The reaction is studied in crossed molecular beams under two different conditions with nearly the same total energy. One experiment is carried out at a collision energy of 15.1 kcal/mol with one quantum of CH₄ antisymmetric (ν₃) stretching vibrational excitation (8.63 kcal/mol), the other at a collision energy of 23.8 kcal/mol. The reaction cross-section for C–H stretch excited methane (σ_s) is found to be at least a factor of 2.2 times larger than for ground-state methane (σ_g) at the same total energy.     

Proven Anti-Wetting Properties of Molybdenum Tested for High-Temperature Corrosion-Resistance with Potential Application in the Aluminum Industry

The behavior of Mo in contact with molten Al was modelled by classical molecular dynamics (CMD) simulation of a pure Mo solid in contact with molten Al at 1200 K using the Materials Studio^®. Results showed that no reaction or cross diffusion of atoms occurs at the Mo(s)–Al(l) interface, and that molten Al atoms exhibit an epitaxial alignment with the exposed solid Mo crystal morphology. Furthermore, the two phases {Mo(s) and Al(l)} are predicted to interact with weak van der Waals forces and give interfacial energy of about 203 mJ/m². Surface energy measurements by the sessile drop experiment using the van Oss–Chaudhury–Good (VCG) theory established a Mo(s)–Al(l) interface energy equivalent to 54 mJ/m², which supports the weak van der Waals interaction. The corrosion resistance of a high purity (99.97%) Mo block was then tested in a molten alloy of 5% Mg mixed in Al (Al-5 wt.%Mg) at 1123 K for 96 h, using the ALCAN’s standard “immersion” test, and the results are presented. No Mo was found to be dissolved in the molten Al-Mg alloy. However, a 20% mass loss in the Mo block was due to intergranular corrosion scissoring the Mo block in the ALCAN test, but not as a result of the reaction of pure Mo with the molten Al-Mg alloy. It was observed that the Al-Mg alloy did not stick to the Mo block.     

Aluminide Diffusion Coatings on IN 718 by Pack Cementation

This paper addressed the issues of both direct and indirect synthesis of Ni aluminides by pack cementation (pure Ni and IN 718 superalloy). On the Al-Ni diffusion twosome under pressure, at temperatures below and above the Al melting temperature, the appearance and evolution of diffusion porosity because of the Kirkendall–Frenkel effect manifestation was highlighted. It has been confirmed that, as the temperature rises above the Al melting temperature, the porosity decreases. Nickel-based superalloys, and in particular IN 718, significantly increase their performance by increasing the aluminides proportion in the top diffusion coating. This is made possible by changing the value of the Al and Ni weight percentage ratio in this area (noted as Al/Ni). In the case of the diffusion twosome between IN 718 and pack aluminizing mixtures, having in their composition as active components Al powder, Ferroaluminum (FeAl40) or mixtures of Al and Fe powders, at processing temperatures above the Al melting temperature, by modifying the active component of the mixture, substantial changes in the Al/Ni values were observed, as well as in the maximum %Al in the diffusion coating and of its thickness. It was found that, when switching from Al to FeAl40 or powder mixture (Al + Fe), the Al/Ni value changes between 3.43 and 1.01, from initial subunit values. The experiments confirmed that the highest %Al in the top aluminized diffusion coating, for IN 718, was obtained if the powder mixture contained 66.34 wt.% Al.     

Effects of Different Types of Interlayers on the Interfacial Reaction Mechanism at the Cu Side of Al/Cu Lap Joints Obtained by Laser Welding/Brazing

The influence of tin foil and Ni coatings on microstructures, mechanical properties, and the interfacial reaction mechanism was investigated during laser welding/brazing of Al/Cu lap joints. In the presence of a Zn-based filler, tin foil as well as Ni coating strengthened the Al/Cu joints. The tin foil only slightly influenced the joint strength. It considerably improved the spreading/wetting ability of the weld filler; however, it weakened the bonding between the seam and the Al base metal. The Ni coating considerably strengthened the Al/Cu lap joints; the highest tensile strength was 171 MPa, which was higher by 15.5% than that of a joint without any interlayer. Microstructure analysis revealed that composite layers of Ni₃Zn₁₄–(τ₂ Zn–Ni–Al ternary phase)–(α-Zn solid solution)–Al₃Ni formed at the fusion zone (FZ)/Cu interface. Based on the inferences about the microstructures at the interfaces, thermodynamic results were calculated to analyze the interfacial reaction mechanism. The diffusion of Cu was limited by the Ni coating and the mutual attraction between the Al and Ni atoms. The microstructure comprised Zn, Ni, and Al, and they replaced the brittle Cu–Zn intermetallic compounds, successfully strengthening the bonding of the FZ/Cu interface.     

Trp replacements for tightly interacting Gly–Gly pairs in LacY stabilize an outward-facing conformation

Trp replacements for conserved Gly–Gly pairs between the N- and C-terminal six-helix bundles on the periplasmic side of lactose permease (LacY) cause complete loss of transport activity with little or no effect on sugar binding. Moreover, the detergent-solubilized mutants exhibit much greater thermal stability than WT LacY. A Cys replacement for Asn245, which is inaccessible/unreactive in WT LacY, alkylates readily in the Gly→Trp mutants, indicating that the periplasmic cavity is patent. Stopped-flow kinetic measurements of sugar binding with the Gly→Trp mutants in detergent reveal linear dependence of binding rates on sugar concentration, as observed with WT or the C154G mutant of LacY, and are compatible with free access to the sugar-binding site in the middle of the molecule. Remarkably, after reconstitution of the Gly→Trp mutants into proteoliposomes, the concentration dependence of sugar-binding rates increases sharply with even faster rates than measured in detergent. Such behavior is strikingly different from that observed for reconstituted WT LacY, in which sugar-binding rates are independent of sugar concentration because opening of the periplasmic cavity is limiting for sugar binding. The observations clearly indicate that Gly→Trp replacements, which introduce bulky residues into tight Gly–Gly interdomain interactions on the periplasmic side of LacY, prevent closure of the periplasmic cavity and, as a result, shift the distribution of LacY toward an outward-open conformation.     

Molecular defects of the glycine 41 variants of alanine glyoxylate aminotransferase associated with primary hyperoxaluria type I

G41 is an interfacial residue located within the α-helix 34–42 of alanine:glyoxylate aminotransferase (AGT). Its mutations on the major (AGT-Ma) or the minor (AGT-Mi) allele give rise to the variants G41R-Ma, G41R-Mi, and G41V-Ma causing hyperoxaluria type 1. Impairment of dimerization in these variants has been suggested to be responsible for immunoreactivity deficiency, intraperoxisomal aggregation, and sensitivity to proteasomal degradation. However, no experimental evidence supports this view. Here we report that G41 mutations, besides increasing the dimer-monomer equilibrium dissociation constant, affect the protein conformation and stability, and perturb its active site. As compared to AGT-Ma or AGT-Mi, G41 variants display different near-UV CD and intrinsic emission fluorescence spectra, larger exposure of hydrophobic surfaces, sensitivity to Met53-Tyr54 peptide bond cleavage by proteinase K, decreased thermostability, reduced coenzyme binding affinity, and catalytic efficiency. Additionally, unlike AGT-Ma and AGT-Mi, G41 variants under physiological conditions form insoluble inactive high-order aggregates (∼5,000 nm) through intermolecular electrostatic interactions. A comparative molecular dynamics study of the putative structures of AGT-Mi and G41R-Mi predicts that G41 → R mutation causes a partial unwinding of the 34–42 α-helix and a displacement of the first 44 N-terminal residues including the active site loop 24–32. These simulations help us to envisage the possible structural basis of AGT dysfunction associated with G41 mutations. The detailed insight into how G41 mutations act on the structure-function of AGT may contribute to achieve the ultimate goal of correcting the effects of these mutations.     

A First-Principles Study of the Cu-Containing β″ Precipitates in Al-Mg-Si-Cu Alloy

The nanostructured β″ precipitates are critical for the strength of Al-Mg-Si-(Cu) aluminum alloys. However, there are still controversial reports about the composition of Cu-containing β″ phases. In this work, first-principles calculations based on density functional theory were used to investigate the composition, mechanical properties, and electronic structure of Cu-containing β″ phases. The results predict that the Cu-containing β″ precipitates with a stoichiometry of Mg_4+xAl_2−xCuSi₄ (x = 0, 1) are energetically favorable. As the concentration of Cu atoms increases, Cu-containing β″ phases with different compositions will appear, such as Mg₄AlCu₂Si₄ and Mg₄Cu₃Si₄. The replacement order of Cu atoms in β″ phases can be summarized as one Si3/Al site → two Si3/Al sites → two Si3/Al sites and one Mg1 site. The calculated elastic constants of the considered β″ phases suggest that they are all mechanically stable, and all β″ phases are ductile. When Cu atoms replace Al atoms at Si3/Al sites in β″ phases, the values of bulk modulus (B), shear modulus (G), and Young’s modulus (E) all increase. The calculation of the phonon spectrum shows that Mg_4+xAl_2−xCuSi₄ (x = 0, 1) are also dynamically stable. The electronic structure analysis shows that the bond between the Si atom and the Cu atom has a covalent like property. The incorporation of the Cu atom enhances the electron interaction between the Mg2 and the Si3 atom so that the Mg2 atom also joins the Si network, which may be one of the reasons why Cu atoms increase the structure stability of the β″ phases.     

The Surface of Nanoparticle Silicon as Studied by Solid-State NMR

The surface structure and adjacent interior of commercially available silicon nanopowder (np-Si) was studied using multinuclear, solid-state NMR spectroscopy. The results are consistent with an overall picture in which the bulk of the np-Si interior consists of highly ordered (“crystalline”) silicon atoms, each bound tetrahedrally to four other silicon atoms. From a combination of ¹H, ²⁹Si and ²H magic-angle-spinning (MAS) NMR results and quantum mechanical ²⁹Si chemical shift calculations, silicon atoms on the surface of “as-received” np-Si were found to exist in a variety of chemical structures, with apparent populations in the order (a) (Si–O–)₃Si–H > (b) (Si–O–)₃SiOH > (c) (HO–)_nSi(Si)_m(–OSi)_4−m−n ≈ (d) (Si–O–)₂Si(H)OH > (e) (Si–O–)₂Si(–OH)₂ > (f) (Si–O–)₄Si, where Si stands for a surface silicon atom and Si represents another silicon atom that is attached to Si by either a Si–Si bond or a Si–O–Si linkage. The relative populations of each of these structures can be modified by chemical treatment, including with O₂ gas at elevated temperature. A deliberately oxidized sample displays an increased population of (Si–O–)₃Si–H, as well as (Si–O–)₃SiOH sites. Considerable heterogeneity of some surface structures was observed. A combination of ¹H and ²H MAS experiments provide evidence for a substantial population of silanol (Si–OH) moieties, some of which are not readily H-exchangeable, along with the dominant Si–H sites, on the surface of “as-received” np-Si; the silanol moieties are enhanced by deliberate oxidation. An extension of the DEPTH background suppression method is also demonstrated that permits measurement of the T₂ relaxation parameter simultaneously with background suppression.     

Engineering subunit association of multisubunit proteins: A dimeric streptavidin

A dimeric streptavidin has been designed by molecular modeling using effective binding free energy calculations that decompose the binding free energy into electrostatic, desolvation, and side chain entropy loss terms. A histidine-127 → aspartic acid (H127D) mutation was sufficient to introduce electrostatic repulsion between subunits that prevents the formation of the natural tetramer. However, the high hydrophobicity of the dimer–dimer interface, which would be exposed to solvent in a dimeric streptavidin, suggests that the resulting molecule would have very low solubility in aqueous media. In agreement with the calculations, a streptavidin containing the H127D mutation formed insoluble aggregates. Thus, the major design goal was to reduce the hydrophobicity of the dimer–dimer interface while maintaining the fundamental structure. Free energy calculations suggested that the hydrophobicity of the dimer–dimer interface could be reduced significantly by deleting a loop from G113 through W120 that should have no apparent contact with biotin in a dimeric molecule. The resulting protein, containing both the H127D mutation and the loop deletion, formed a soluble dimeric streptavidin in the presence of biotin.     

The Characteristic of Fe as a β-Ti Stabilizer in Ti Alloys

It is well known that adding elements, especially β-Ti stabilizers, are holding a significant effect on titanium alloy strength due to the solution and precipitate strengthening mechanisms. In order to reveal the Fe strengthening mechanism in titanium, this study investigate the effect of Fe on the stability of β-Ti and the phase transition between α, β and ω phase with first-principle calculations. According to our study, Fe is a strong β-Ti phase stabilizer could owe to the 3d orbital into e_g and t_2g states which results in strong hybridization between Fe-d orbital and Ti-d orbital. The phase transition from ω to β or from α to β becomes easier for Fe-doped Ti compared to pure titanium. Based on our results, it is found that one added Fe atom can lead the phase transition (ω → β) of at least nine titanium atoms, which further proves that Fe has a strong stabilizing effect on β-Ti phase. This result provides a solid guide for the future design of high-strength titanium with the addition of Fe.     

Effect of Ag on Properties,Microstructure, and Thermostability of Cu–Cr Alloy

Cu–Cr-based alloys exhibit excellent electrical conductivity and strength, but their poor thermal stability limits their application in industry. In this paper, Cu–0.2Cr (at. %) and Cu–0.2Cr–0.12Ag (at. %) alloys were prepared to study the effect of Ag on the properties, microstructure, and thermal stability of the Cu–Cr alloy. Microstructure and precipitation were observed by an optical microscope (OM) and a transmission–electron microscope (TEM). After cold-drawing by 99.9% and aging at 450 °C for 2 h, the peak hardness and electric conductivity of the Cu–Cr alloy were 120.3 HV and 99.5% IACS, respectively, and those of the Cu–Cr–Ag alloy were 135.8 HV and 98.3% IACS, respectively. The softening temperature of the Cu–Cr alloy was 500~525 °C, and that of the Cu–Cr–Ag alloy was about 550 °C. The creep strains of the Cu–Cr and Cu–Cr–Ag alloys at 40 MPa and 400 ℃ for 50 h were 0.18% and 0.05%, respectively. Ag elements improved the thermal stability of the Cu–Cr alloy. Recovery and recrystallization occurred before the coarsening of precipitates during the softening process. Ag atoms mainly improved the softening resistance of the alloy by delaying recrystallization, and mainly increased creep resistance by preventing the increase in mobile-dislocation density.     

Preparation and Characterization of Cu and Ni on Alumina Supports and Their Use in the Synthesis of Low-Temperature Metal-Phthalocyanine Using a Parallel-Plate Reactor

Ni- and Cu/alumina powders were prepared and characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM), and N₂ physisorption isotherms were also determined. The Ni/Al₂O₃ sample reveled agglomerated (1 μm) of nanoparticles of Ni (30–80 nm) however, NiO particles were also identified, probably for the low temperature during the H₂ reduction treatment (350 °C), the Cu/Al₂O₃ sample presented agglomerates (1–1.5 μm) of nanoparticles (70–150 nm), but only of pure copper. Both surface morphologies were different, but resulted in mesoporous material, with a higher specificity for the Ni sample. The surfaces were used in a new proposal for producing copper and nickel phthalocyanines using a parallel-plate reactor. Phthalonitrile was used and metallic particles were deposited on alumina in ethanol solution with CH₃ONa at low temperatures; ≤60 °C. The mass-transfer was evaluated in reaction testing with a recent three-resistance model. The kinetics were studied with a Langmuir-Hinshelwood model. The activation energy and Thiele modulus revealed a slow surface reaction. The nickel sample was the most active, influenced by the NiO morphology and phthalonitrile adsorption.     

Dissimilar Brazing of Ti–15Mo–5Zr–3Al and Commercially Pure Titanium Using Ti–Cu–Ni Foil

Dissimilar brazing of Ti–15Mo–5Zr–3Al (Ti-1553) to commercially pure titanium (CP-Ti) using Ti–15Cu–15Ni foil was performed in this work. The microstructures in different sites of the brazed joint showed distinct morphologies, which resulted from the distributions of Mo, Cu, and Ni. In the brazed zone adhered to the Ti-1553 substrate, the partitioning of Mo from the Ti-1553 into the molten braze caused the formation of stabilized β-Ti without Ti₂Cu/Ti₂Ni precipitates. In the CP-Ti side, the brazed joint displayed a predominantly lamellar structure, composed of the elongated primary α-Ti and β-transformed eutectoid. The decrease in the Mo concentration in the brazed zone caused the eutectoid transformation of β-Ti to Ti₂Cu + α-Ti in that zone. The diffusion of Cu and Ni from the molten braze into the CP-Ti accounted for the precipitation of Ti₂Cu/Ti₂Ni in the transformed zone therein. The variation in the shear strength of the joints was related to the amount and distribution of brittle Ti₂Ni compounds. Prolonging the brazing time, the wider transformed zone, consisting of coarse elongated CP-Ti interspersed with sparse Ti₂Ni precipitates, was responsible for the improved shear strength of the joint.     

Substitutions in Penicillin-Binding Protein 1 in Amoxicillin-Resistant Helicobacter pylori Strains Isolated from Korean Patients

Background/Aims

A worldwide increase in amoxicillin resistance in Helicobacter pylori is having an adverse effect on eradication therapy. In this study, we investigated the mechanism of the amoxicillin resistance of H. pylori in terms of amino acid substitutions in penicillin-binding protein 1 (PBP1).

Methods

In total, 150 H. pylori strains were isolated from 144 patients with chronic gastritis, peptic ulcers, or stomach cancer. The minimum inhibitory concentrations (MICs) of the strains were determined with a serial 2-fold agar dilution method. The resistance breakpoint for amoxicillin was defined as >0.5 µg/mL.

Results

Nine of 150 H. pylori strains showed amoxicillin resistance (6%). The MIC values of the resistant strains ranged from 1 to 4 µg/mL. A PBP1 sequence analysis of the resistant strains revealed multiple amino acid substitutions: Val16→Ile, Val45→Ile, Ser414→Arg, Asn562→Tyr, Thr593→Ala, Gly595→Ser, and Ala599→Thr. The natural transformation of these mutated genes into amoxicillin-sensitive strains was performed in two separate pbp1 gene segments. A moderate increase in the amoxicillin MIC was observed in the segment that contained the penicillin-binding motif of the C-terminal portion, the transpeptidase domain.

Conclusions

pbp1 mutation affects the amoxicillin resistance of H. pylori through the transfer of the penicillin-binding motif.     

Microscopic Understanding of the Growth and Structural Evolution of Narrow Bandgap III–V Nanostructures

III–V group nanomaterials with a narrow bandgap have been demonstrated to be promising building blocks in future electronic and optoelectronic devices. Thus, revealing the underlying structural evolutions under various external stimuli is quite necessary. To present a clear view about the structure–property relationship of III–V nanowires (NWs), this review mainly focuses on key procedures involved in the synthesis, fabrication, and application of III–V materials-based devices. We summarized the influence of synthesis methods on the nanostructures (NWs, nanodots and nanosheets) and presented the role of catalyst/droplet on their synthesis process through in situ techniques. To provide valuable guidance for device design, we further summarize the influence of structural parameters (phase, defects and orientation) on their electrical, optical, mechanical and electromechanical properties. Moreover, the dissolution and contact formation processes under heat, electric field and ionic water environments are further demonstrated at the atomic level for the evaluation of structural stability of III–V NWs. Finally, the promising applications of III–V materials in the energy-storage field are introduced.