Eigenmode symmetry assignment of triangular-lattice photonic crystal slabs and their Dirac cones materialized by effective degeneracy in the mid-infrared region.

We measured angle-resolved reflection spectra of triangular-lattice photonic crystal slabs fabricated in a silicon-on-insulator wafer in the mid-infrared region. We achieved a high angle-resolution measurement by means of our homemade optical setup integrated in the sample chamber of an FT-IR spectrometer. By examining the reflection peak frequency as a function of the lateral component of the wave vector of the incident light and applying the selection rules expected from the spatial symmetry of electromagnetic eigenmodes in C6v-symmetric structures, we successfully obtained the dispersion relation and the mode symmetry of the photonic crystal slabs, which agreed well with numerical calculations by the finite element method. We also found the redistribution of diffraction loss between A1- and E1-symmetric modes, which was caused by the Dirac-cone formation due to their effective degeneracy.

Droplet epitaxy of semiconductor nanostructures for quantum photonic devices.

The long dreamed 'quantum internet' would consist of a network of quantum nodes (solid-state or atomic systems) linked by flying qubits, naturally based on photons, travelling over long distances at the speed of light, with negligible decoherence. A key component is a light source, able to provide single or entangled photon pairs. Among the different platforms, semiconductor quantum dots (QDs) are very attractive, as they can be integrated with other photonic and electronic components in miniaturized chips. In the early 1990s two approaches were developed to synthetize self-assembled epitaxial semiconductor QDs, or 'artificial atoms'-namely, the Stranski-Krastanov (SK) and the droplet epitaxy (DE) methods. Because of its robustness and simplicity, the SK method became the workhorse to achieve several breakthroughs in both fundamental and technological areas. The need for specific emission wavelengths or structural and optical properties has nevertheless motivated further research on the DE method and its more recent development, local droplet etching (LDE), as complementary routes to obtain high-quality semiconductor nanostructures. The recent reports on the generation of highly entangled photon pairs, combined with good photon indistinguishability, suggest that DE and LDE QDs may complement (and sometimes even outperform) conventional SK InGaAs QDs as quantum emitters. We present here a critical survey of the state of the art of DE and LDE, highlighting the advantages and weaknesses, the achievements and challenges that are still open, in view of applications in quantum communication and technology.

Mid-IR Dirac-cone dispersion relation materialized in SOI photonic crystal slabs.

We materialized the isotropic Dirac-cone dispersion relation in the mid-infrared range by fabricating photonic crystal slabs of the C4v symmetry in SOI (silicon-on-insulator) wafers by electron beam lithography. The dispersion relation was examined by the angle-resolved reflection spectra with our home-made high-resolution apparatus, which showed a good agreement with the dispersion relation and the reflection spectra calculated by the finite element method. The reflection spectra also agreed with the selection rules derived from the spatial symmetry of the Dirac-cone modes, which proved to be a powerful tool for the mode assignment.

Angle-resolved reflection spectra of Dirac cones in triangular-lattice photonic crystal slabs.

The dispersion relation and the angle-resolved reflection spectra of triangular-lattice photonic crystal slabs of the C6v symmetry were examined by the finite element method. The Dirac-cone dispersion relation on the Γ point of the reciprocal space was confirmed. The reflection spectra showed unique selection rules that agreed with the analytical calculation by the k · p perturbation theory. The distortion of the liner dispersion relation of the Dirac cones due to diffraction loss was also reproduced well by the numerical calculation, while we found distortion-free Dirac cones materialized with E2-symmetric modes.

Ga metal nanoparticle-GaAs quantum molecule complexes for terahertz generation.

A hybrid metal-semiconductor nanosystem for the generation of THz radiation, based on the fabrication of GaAs quantum molecules-Ga metal nanoparticles complexes through a self assembly approach, is proposed. The role of the growth parameters, the substrate temperature, the Ga and As flux during the quantum dot molecule (QDM) fabrication and the metal nanoparticle alignment are discussed. The tuning of the relative positioning of QDMs and metal nanoparticles is obtained through the careful control of Ga droplet nucleation sites via Ga surface diffusion. The electronic structure of a typical QDM was evaluated on the base of the morphological characterizations performed by atomic force microscopy and cross sectional scanning electron microscopy, and the predicted results confirmed by micro-photoluminescence experiments, showing that the Ga metal nanoparticle-GaAs quantum molecule complexes are suitable for terahertz generation from intraband transition.

Increased muscular triglyceride content and hyperglycemia in Goto-Kakizaki rat are decreased by egg white hydrolysate.

We investigated the fat metabolic characteristics in non-obese and diabetic Goto-Kakizaki (GK) rat and the effects of dietary egg white hydrolysate (EWH) on glucose and fat metabolism. Wistar (W) and GK (G) rats were placed into dietary casein (WC and GC) or EWH (WE and GE) group, and fed their respective diet for six weeks. Triglyceride (TG) content and stearoyl-CoA desaturase (SCD) indices in the soleus muscle were higher in the GC group than WC group in parallel with worsening serum glucose metabolic parameters. The glucose metabolic parameters were significantly improved in the GE group. The TG accumulation and SCD indices in the soleus muscle were also significantly lower in the GE group than in the GC group. In conclusion, dietary EWH not only improved glucose metabolism but also reduced both TG accumulation and SCD indices in the soleus muscle of GK rat.

Plasmon-Triggered Ultrafast Operation of Color Centers in Hexagonal Boron Nitride Layers.

High-quality emission centers in two-dimensional materials are promising components for future photonic and optoelectronic applications. Carbon-enriched hexagonal boron nitride (hBN:C) layers host atom-like color-center (CC) defects with strong and robust photoemission up to room temperature. Placing the hBN:C layers on top of Ag triangle nanoparticles (NPs) accelerates the decay of the CC defects down to 46 ps from their reference bulk value of 350 ps. The ultrafast decay is achieved due to the efficient excitation of the plasmon modes of the Ag NPs by the near field of the CCs. Simulations of the CC/Ag NP interaction show that higher Purcell values are expected, although the measured decay of the CCs is limited by the instrument response. The influence of the NP thickness on the Purcell factor of the CCs is analyzed. The ultrafast operation of the CCs in hBN:C layers paves the way for their use in demanding applications, such as single-photon emitters and quantum devices.

A case with anti-galactocerebroside antibody-positive Mycoplasma pneumoniae meningoencephalitis presenting secondary hypersomnia.

Galactocerebroside (Gal-C) is a major myelin component in the central nervous system. The anti-Gal-C antibody induced by mycoplasma infection may therefore be involved in the pathogenic mechanisms of mycoplasma-associated encephalitis. Here we report an adult case of mycoplasma encephalitis developing excessive daytime sleepiness. Brain MRI suggested that hypothalamic involvement was compatible with hypersomnia. This finding was corroborated by decreased hypocretin-1 in cerebrospinal fluid (CSF) and the manifestation of diabetes insipidus. Screening for anti-glycolipid antibody profiles showed the selective increase of serum anti-Gal-C antibody. After treatment with minocyclin, the patient's daytime sleepiness was markedly improved and the CSF hypocretin-1 level became almost normal, as well. It is known that CSF hypocretin-1 is decreased in Guillain-Barré syndrome mediated by anti-glycolipid antibody, suggesting a possible mechanistic link between anti-glycolipid antibodies and hypothalamic involvement. The present case further emphasizes the broad spectrum of neurological complications after mycoplasma infection.

Surface Plasmon Tunability of Core-Shell Au@Mo6 Nanoparticles by Shell Thickness Modification.

Plasmon resonances of noble metal nanoparticles are used to enhance light-matter interactions in the nanoworld. The nanoparticles' optical response depends strongly on the dielectric permittivity of the surrounding medium. We show that the plasmon resonance energy of core-shell Au@Mo6 nanoparticles can be tuned from 2.4 to 1.6 eV by varying the thickness of their Mo6 cluster shells between zero and 70 nm, when the core diameter is fixed at 100 nm. We probe their plasmonic response by performing nanometer-resolution plasmon mapping on individual nanoparticles, using electron energy-loss spectroscopy inside a transmission electron microscope. Our experimental results are corroborated by numerical simulations performed using boundary element methods. The simulations predict a similar dependency for the extinction energy, showing that this effect could also be observed by light-optical experiments outside the electron microscope, although limited by the size distribution of the nanoparticles in solution and the substantial scattering effects.

Polarization Anisotropies in Strain-Free, Asymmetric, and Symmetric Quantum Dots Grown by Droplet Epitaxy.

We provide an extensive and systematic investigation of exciton dynamics in droplet epitaxial quantum dots comparing the cases of (311)A, (001), and (111)A surfaces. Despite a similar s-shell exciton structure common to the three cases, the absence of a wetting layer for (311)A and (111)A samples leads to a larger carrier confinement compared to (001), where a wetting layer is present. This leads to a more pronounced dependence of the binding energies of s-shell excitons on the quantum dot size and to the strong anti-binding character of the positive-charged exciton for smaller quantum dots. In-plane geometrical anisotropies of (311)A and (001) quantum dots lead to a large electron-hole fine interaction (fine structure splitting (FSS) ∼100 µeV), whereas for the three-fold symmetric (111)A counterpart, this figure of merit is reduced by about one order of magnitude. In all these cases, we do not observe any size dependence of the fine structure splitting. Heavy-hole/light-hole mixing is present in all the studied cases, leading to a broad spread of linear polarization anisotropy (from 0 up to about 50%) irrespective of surface orientation (symmetry of the confinement), fine structure splitting, and nanostructure size. These results are important for the further development of ideal single and entangled photon sources based on semiconductor quantum dots.

Apparatus for High-Precision Angle-Resolved Reflection Spectroscopy in the Mid-Infrared Region.

Fourier transform (FT) spectroscopy is a versatile technique for studying the infrared (IR) optical response of solid-, liquid-, and gas-phase samples. In standard Fourier transform infrared (FT-IR) spectrometers, a light beam passing through a Michelson interferometer is focused onto a sample with condenser optics. This design enables us to examine relatively small samples, but the large solid angle of the focused infrared beam makes it difficult to analyze angle-dependent characteristics. Here, we design and construct a high-precision angle-resolved reflection setup compatible with a commercial FT-IR spectrometer. Our setup converts the focused beam into an achromatically collimated beam with an angle dispersion as high as 0.25°. The setup also permits us to scan the incident angle over ∼8° across zero (normal incidence). The beam diameter can be reduced to ∼1 mm, which is limited by the sensitivity of an HgCdTe detector. The small-footprint apparatus is easily installed in an FT-IR sample compartment. As a demonstration of the capability of our reflection setup, we measure the angle-dependent mid-infrared reflectance of two-dimensional photonic crystal slabs and determine the in-plane dispersion relation in the vicinity of the Γ point in momentum space. We observe the formation of photonic Dirac cones, i.e., linear dispersions with an accidental degeneracy at Γ, in an ideally designed sample. Our apparatus is useful for characterizing various systems that have a strong in-plane anisotropy, including photonic crystal waveguides, plasmonic metasurfaces, and molecular crystalline films.

Facial nerve reconstruction using a vascularized lateral femoral cutaneous nerve graft based on the superficial circumflex iliac artery system: an application of the inferolateral extension of the groin flap.

The use of an inferolateral extension technique of a groin flap has previously been reported. This technique involves harvesting an extended portion from the anterolateral thigh, including the lateral femoral cutaneous nerve (LFCN) and its accompanying vessels, attached to a groin flap via communications between the LFCN-accompanying vessels and the superficial circumflex iliac artery (SCIA) system. In this study, we used this technique involving a vascularized LFCN combined with a groin flap to reconstruct a facial nerve defect. The patient was a 58-year-old man with a salivary duct carcinoma in the left parotid gland. Tumor ablation resulted in a defect of the skin and soft tissue including all branches of the facial nerve. A free groin flap was harvested based on the SCIA system, composed of the LFCN and a small monitoring flap, which were nourished by the LFCN-accompanying vessels and by communication with the SCIA system. The LFCN was transplanted into the gaps in the facial nerve branches as a cable graft, and the skin flap was used to cover and fill the soft tissue defect. The postoperative course was uneventful and satisfactory facial animation was obtained. This represents a possible technique for nerve reconstruction using a vascularized nerve graft.

Exciton Dynamics in Droplet Epitaxial Quantum Dots Grown on (311)A-Oriented Substrates.

Droplet epitaxy allows the efficient fabrication of a plethora of 3D, III-V-based nanostructures on different crystalline orientations. Quantum dots grown on a (311)A-oriented surface are obtained with record surface density, with or without a wetting layer. These are appealing features for quantum dot lasing, thanks to the large density of quantum emitters and a truly 3D lateral confinement. However, the intimate photophysics of this class of nanostructures has not yet been investigated. Here, we address the main optical and electronic properties of s-shell excitons in individual quantum dots grown on (311)A substrates with photoluminescence spectroscopy experiments. We show the presence of neutral exciton and biexciton as well as positive and negative charged excitons. We investigate the origins of spectral broadening, identifying them in spectral diffusion at low temperature and phonon interaction at higher temperature, the presence of fine interactions between electron and hole spin, and a relevant heavy-hole/light-hole mixing. We interpret the level filling with a simple Poissonian model reproducing the power excitation dependence of the s-shell excitons. These results are relevant for the further improvement of this class of quantum emitters and their exploitation as single-photon sources for low-density samples as well as for efficient lasers for high-density samples.

Distinct roles of ezrin, radixin and moesin in maintaining the plasma membrane localizations and functions of human blood-brain barrier transporters.

The purpose of this study was to clarify the roles of ERM proteins (ezrin/radixin/moesin) in the regulation of membrane localization and transport activity of transporters at the human blood-brain barrier (BBB). Ezrin or moesin knockdown in a human in vitro BBB model cell line (hCMEC/D3) reduced both BCRP and GLUT1 protein expression levels on the plasma membrane. Radixin knockdown reduced not only BCRP and GLUT1, but also P-gp membrane expression. These results indicate that P-gp, BCRP and GLUT1 proteins are maintained on the plasma membrane via different ERM proteins. Furthermore, moesin knockdown caused the largest decrease of P-gp and BCRP efflux activity among the ERM proteins, whereas GLUT1 influx activity was similarly reduced by knockdown of each ERM protein. To investigate how moesin knockdown reduced P-gp efflux activity without loss of P-gp from the plasma membrane, we examined the role of PKCßI. PKCßI increased P-gp phosphorylation and reduced P-gp efflux activity. Radixin and moesin proteins were detected in isolated human brain capillaries, and their protein abundances were within a 3-fold range, compared with those in hCMEC/D3 cell line. These findings may mean that ezrin, radixin and moesin maintain the functions of different transporters in different ways at the human BBB.

Doubly enhanced spontaneous emission due to increased photon density of states at photonic band edge frequencies.

Double enhancement of spontaneous emission due to increased photon density of states at the emission frequency and the small group velocity of light at the excitation frequency was clearly demonstrated by angle-resolved photoluminescence experiments for dielectric multilayers composed of Ta2O5 and SiO2 with oxygen vacancies as light emitters. Theoretical emission profiles given by the weak modulation approximation agreed well with the experimental observations.

Coherent anti-Stokes Raman scattering of two-phonon complexes in diamond.

Coherent anti-Stokes Raman scattering (CARS) associated with the second-order Raman process has been confirmed in diamond. Frequency dependence of CARS was analyzed using two-color synchronously-generated picosecond pulses. Resonance enhancement of chi((3)) was observed at an energy shift corresponding to the overtone Sigma branch (K point) phonon, as well as the fundamental Raman-active Gamma((25+)) phonon. The excitation spectrum of CARS at the two-phonon resonance region showed dispersive dependence, reflecting the interference of resonant CARS and nonresonant four-wave mixing scattering.

Effects of auditory and tactile warning on response to visual hazards under a noisy environment.

A warning signal presented via a visual or an auditory cue might interfere with auditory or visual information inside and outside a vehicle. On the other hand, such interference would be certainly reduced if a tactile cue is used. Therefore, it is expected that tactile cues would be promising as warning signals, especially in a noisy environment. In order to determine the most suitable modality of cue (warning) to a visual hazard in noisy environments, auditory and tactile cues were examined in this study. The condition of stimulus onset asynchrony (SOA) was set to 0ms, 500ms, and 1000ms. Two types of noises were used: white noise and noise outside a vehicle recorded in a real-world driving environment. The noise level LAeq (equivalent continuous A-weighted sound pressure level) inside the experimental chamber of each type of noise was adjusted to approximately 60 dB (A), 70 dB (A), and 80 dB (A). As a result, it was verified that tactile warning was more effective than auditory warning. When the noise outside a vehicle from a real-driving environment was used as the noise inside the experimental chamber, the reaction time to the auditory warning was not affected by the noise level.

Excitonic Aharonov-Bohm effect in QD-on-ring nanostructures.

We show by the first-order perturbation theory and the configuration interaction method that the Coulomb interaction in quantum rings mixes electron-hole pair states with the same total angular momentum, which makes it difficult to observe a clear excitonic Aharonov-Bohm (A-B) effect. To avoid this situation, we propose the use of a combined structure of a quantum dot on the top of a quantum ring with an applied static electric field. Under moderate experimental conditions with respect to the applied electric and magnetic fields, we show that we can observe the excitonic A-B effect due to the reduction of the Coulomb interaction and an increase in the difference between the average radii of the electron and hole trajectories.

Effect of thermal cycling on bond strengths of single-step self-etch adhesives to bovine dentin.

The purpose of this study was to clarify the effect of thermal cycling on dentin bond strengths of single-step self-etch adhesives. Five commercially available single-step self-etch systems were used. The adhesives were applied to the dentin surfaces of bovine incisors, and then light-irradiated. Resin composites were condensed into a mold and light-irradiated. Bonded specimens were divided into two groups and stored in water at 37 degrees C for 24 h without thermal cycling, or in water at 37 degrees C for 24 h followed by 10,000 thermal cycles between 5 degrees C and 60 degrees C. Ten samples per group were tested for shear strength at a crosshead speed of 1.0 mm/min. The data were analyzed by Student's t test and Tukey HSD test at a probability level of 0.05. After 24 h of storage in water, the mean dentin bond strengths ranged from 9.3 MPa to 14.0 MPa. After 10,000 thermal cycles, the mean bond strengths remained unchanged. Failure after the test was commonly due to adhesive breakdown associated with partial cohesive failure of the resin. The present results suggest that the benefit of using single-step self-etch systems, in terms of simplifying the clinical procedure, might be acceptable even after thermal stresses.

Influence of light intensity on dentin bond strength of self-etch systems.

The purpose of this study was to investigate the influence of light intensity on dentin bond strengths of four self-etch adhesive systems. The light intensities used to polymerize specimens were controlled at levels of 150, 300, 600, and 900 mW/cm2. The two-step self-etch adhesive systems Imperva Fluoro Bond and Mac Bond II, and the one-step self-etch systems Fluoro Bond Shake-One and One-Up Bond F Plus were used with their corresponding light-cured resins. Labial surfaces of lower bovine incisors were ground with #600 grit SiC paper to expose the dentin. The dentin surfaces were treated according to each manufacturer's instructions and bonded with resin composites. A shear bond strength test was performed and the data were analyzed by one-way ANOVA followed by Newman-Keuls multiple comparison at a level of 0.05. Statistical analysis of the data indicated that light intensity affected the dentin bond strengths of the adhesive systems tested. Significantly lower bond strengths were obtained by exposure to 150 mW/cm2, and there were no differences between the bond strengths obtained at 600 and 900 mW/cm2 for all the adhesive systems used. Further research will be required to clarify the irradiance-dependent properties of light-cured resin adhesive systems.