Fracture Mechanics of Corrosion Cracking in Concrete by Acoustic Emission

Nucleation of microcracks can be detected and analyzed by acoustic emission (AE), by which crack kinematics of locations, types and rientations are quantitatively estimated. The procedure was applied to clarify mechanisms of corrosion cracking. Based on fracture mechanics, numerical analysis was conducted by the boundary element method (BEM). Relations between the stress intensity factors and crack types were investigated by BEM solutions. In experiments, four types of crack patterns were nucleated by employing expansive agent. Following the surface crack, the diagonal crack and/or the horizontal crack propagated. The internal crack extended after the surface crack was terminated. Depending on the crack types, contributions of mode-I and mode-II were varied. According to AE results, four crack patterns observed differently consisted of tensile, mixed-mode and shear cracks. It is demonstrated that mechanisms of corrosion cracking in concrete are dominantly of mode-I failure along with a minor contribution of mixed-mode and mode-II.     

Emission from a dipole-forbidden energy state in a GaAs quantum-ring induced by dressed photon

The emission intensity from the dipole-forbidden state in a GaAs quantum-ring was increased via close proximity with an aperture fiber probe to induce a near-field interaction between the probe apex and the quantum-ring. As a result, a significant decrease was observed in the decay time of the emission from a dipole-forbidden energy state.     

Optical dynamics of energy-transfer from a CdZnO quantum well to a proximal Ag nanostructure

We studied photoluminescence (PL) and energy-transfer dynamics in a hybrid structure comprising a Cd(0.08)Zn(0.92)O quantum well (QW) and an Ag nanostructure. The observed PL quenching was dependent on the electronic states in the QW. Quenching occurred at low temperature where excited carriers recombined radiatively because of excitonic localization, which disappeared with increasing temperature due to delocalization of excitons. Furthermore, nanostructured Ag surfaces produced local surface plasmon (LSP) absorption that was resonant with the PL peak energy of the QW emission. These results indicate that the recombination energy of excitons transfers nonradiatively to induce LSP excitation, which was revealed using time-resolved PL measurements.     

Self-organized near-field etching of the sidewalls of glass corrugations

Using soda-lime glass with a nano-stripe pattern as a test specimen, we demonstrated self-organized near-field etching with a continuum-wave laser (λ=532 nm) light source. Atomic force microscopy confirmed that near-field etching decreases the flank roughness of the corrugations as well as the roughness of the flat surface.     

Catalytic Four‐Electron Oxidation of Water by Intramolecular Coupling of the Oxo Ligands of a Bis(ruthenium–bipyridine) Complex

A bis(ruthenium–bipyridine) complex bridged by 1,8‐bis(2,2′:6′,2′′‐terpyrid‐4′‐yl)anthracene (btpyan), [Ru₂(μ‐Cl)(bpy)₂(btpyan)](BF₄)₃ ([ 1 ](BF₄)₃; bpy=2,2′‐bipyridine), was prepared. The cyclic voltammogram of [ 1 ](BF₄)₃ in water at pH 1.0 displayed two reversible [Ru^II,Ru^II]³⁺/[Ru^II,Ru^III]⁴⁺ and [Ru^II,Ru^III]⁴⁺/[Ru^III,Ru^III]⁵⁺ redox couples at E_1/2(1)=+0.61 and E_1/2(2)=+0.80 V (vs. Ag/AgCl), respectively, and an irreversible anodic peak at around E=+1.2 V followed by a strong anodic currents as a result of the oxidation of water. The controlled potential electrolysis of [ 1 ]³⁺ ions at E=+1.60 V in water at pH 2.6 (buffered with H₃PO₄/NaH₂PO₄) catalytically evolved dioxygen. Immediately after the electrolysis of the [ 1 ]³⁺ ion in H₂¹⁶O at E=+1.40 V, the resultant solution displayed two resonance Raman bands at $\tilde \nu $ =442 and 824 cm^‐1. These bands shifted to $\tilde \nu $ =426 and 780 cm^?1, respectively, when the same electrolysis was conducted in H₂¹⁸O. The chemical oxidation of the [ 1 ]³⁺ ion by using a Ce^IV species in H₂¹⁶O and H₂¹⁸O also exhibited the same resonance Raman spectra. The observed isotope frequency shifts (Δ$\tilde \nu $ =16 and 44 cm^?1) fully fit the calculated ones based on the Ru? O and O? O stretching modes, respectively. The first successful identification of the metal? O? O? metal stretching band in the oxidation of water indicates that the oxygen–oxygen bond at the stage prior to the evolution of O₂ is formed through the intramolecular coupling of two Ru–oxo groups derived from the [ 1 ]³⁺ ion.     

Measurement of multimode coherent phonons in nanometric spaces in a homojunction-structured silicon light emitting diode

We review the recent advances in integrated quantum optical technologies, with specific emphasis on the femtosecond laser direct-write technique. We present a comparative study of the processing windows which produce low-loss waveguides in two glasses, Schott AF-45 and Corning Eagle-2000. We report the losses at wavelengths 800 and 1,550 nm, the two most critical wavelengths for quantum information science. We find the iron absorption in Eagle-2000 to be the limiting factor for propagation losses, suggesting that low Fe $^{2+}$ glasses are better suited for quantum optical science.     

Fixed-distance coupling and encapsulation of heterogeneous quantum dots using phonon-assisted photo-curing

We propose a novel method of coupling heterogeneous quantum dots at fixed distances and capsulating the coupled quantum dots by utilizing nanometric local curing of a photo-curable polymer caused by multistep electronic transitions based on a phonon-assisted optical near-field process between quantum dots. Because the coupling and the capsulating processes are triggered only when heterogeneous quantum dots floating in a solution closely approach each other to induce optical near-field interactions between them, the distances between the coupled quantum dots are physically guaranteed to be equal to the scale of the optical near fields. To experimentally verify our idea, we fabricated coupled quantum dots, consisting of CdSe and ZnO quantum dots and a UV-curable polymer. We also measured the photoluminescence properties due to the quantum-dot coupling and showed that the individual photoluminescences from the CdSe and ZnO quantum dots exhibited a trade-off relationship.     

The unprecedented role of a Cu<Superscript>II</Superscript> cryptand in the luminescence properties of a Eu<Superscript>III</Superscript> cryptate complex

Abstract  A Eu^III cryptate complex constructed from a Cu^II cryptand with an L ^tBu ligand, [Eu^IIICu₂^II(L ^tBu)₂(NO₃)₃(MeOH)], and the corresponding Ca^II and Na^I cryptates, [Ca^IICu₂^II(L ^tBu)₂(NO₃)₂(MeOH)₂] and [Na^ICu₂^II(L ^tBu)₂(Me₂CO)](BPh₄), have been synthesized and characterized in order to shed light on the essential role of Cu^II in the luminescence of a Eu^III cryptate. The unprecedented role of a Cu^II cryptand makes it possible to produce lanthanide luminescence in a Eu^III cryptate complex and is successfully elucidated by comparison with the corresponding Ca^II and Na^I cryptates. Graphical abstract   Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Frequency stabilization in semiconductor lasers

Three promising methods of improving temporal coherence in semiconductor lasers are reviewed. They are the development of novel laser devices, a technique of optical feedback and a technique of electrical feedback. The main discussion in this paper is focused on the technique of electrical feedback. The theoretical limit of frequency stability and recent experimental results are presented with respect to the following five subjects which are indispensable in the realization of highly coherent lasers: (a) frequency stabilization; (b) improvements in frequency reproducibility; (c) linewidth reduction; (d) frequency tracking; and (e) stable, accurate and wideband frequency sweep.     

Direct observation of optically forbidden energy transfer between CuCl quantum cubes via near-field optical spectroscopy

We report, for the first time, evidence of near-field energy transfer among CuCl quantum cubes using an ultrahigh-resolution near-field optical microscopy and spectroscopy in the near UV region at 15 K. The sample was high-density CuCl quantum cubes embedded in a NaCl matrix. Measured spatial distributions of the luminescence intensities from 4.6-nm and 6.3-nm quantum cubes clearly established anticorrelation features. This is thought to be a manifestation of the energy transfer from the lowest state of exciton in 4.6-nm quantum cubes to the first dipole-forbidden excited state of exciton in 6.3-nm quantum cubes, which is attributed to the resonant optical near-field interaction.