Search

Prospective equivalent internal quantum efficiency (eta(int)) of approximately 34% at 300 K was demonstrated for the blue emission peak of nonpolar m-plane (1 (1) over bar 00) InxGa1-xN/GaN multiple quantum well light emitting diodes (LEDs) fabricated on freestanding m-plane GaN substrates. Although the eta(int) value is yet lower than that of conventional c-plane blue LEDs (> 70%), the results encourage one to realize high performance green, amber, and red LEDs by reducing the concentration of nonradiative defects, according to the absence of the quantum-confined Stark effects due to the polarization fields parallel to the quantum well normal. The electric field component of the blue surface emission was polarized perpendicular to the c axis with the in-plane polarization ratio of 0.58 at 300 K. (c) 2006 American Institute of Physics.

Recombination dynamics of the 268 nm photoluminescence (PL) peak in a quaternary Al0.53In0.11Ga0.36N/Al0.58In0.02Ga0.40N multiple quantum well (MQW) grown on relaxed AlGaN templates were studied. Although the polarization field in the compressively strained Al0.53In0.11Ga0.36N wells was as high as 1.6 MV/cm, the value of integrated PL intensity at 300 K divided by that at 8 K (eta(int)) was as high as 1.2%. The value was similar to that obtained for the 285 nm PL peak in an Al0.30Ga0.70N/Al0.70Ga0.30N MQW (1.3%), though the A1N molar fraction in the wells was higher by a factor of 1.7. According to these results and the fact that time-resolved PL signal exhibited a stretched exponential decay shape, the improved eta(int) of the AlInGaN wells was attributed to a beneficial effect of the exciton localization as is the case with InGaN alloys; doping or alloying with InN was confirmed to work also on AlGaN in improving eta(int) to realize deep UV optoelectronic devices.

Abstract The function of a biomacromolecule is not only determined by its three-dimensional structure but also by its electronic state. Quantum chemical calculations are promising non-empirical methods available for determining the electronic state of a given structure. In this study, we used the fragment molecular orbital (FMO) method, which applies to biopolymers such as proteins, to provide physicochemical property values on representative structures in the SCOP2 database of protein families, a subset of the Protein Data Bank. Our dataset was constructed by over 5,000 protein structures, including over 200 million inter-fragment interaction energies (IFIEs) and their energy components obtained by pair interaction energy decomposition analysis (PIEDA) using FMO-MP2/6-31 G*. Moreover, three basis sets, 6-31 G*, 6-31 G**, and cc-pVDZ, were used for the FMO calculations of each structure, making it possible to compare the energies obtained with different basis functions for the same fragment pair. The total data size is approximately 6.7 GB. Our dataset will be useful for functional analyses and machine learning based on the physicochemical property values of proteins.

Abstract In the context of the urgent need to establish sustainable food systems, community-supported agriculture (CSA), in which consumers share risks with producers, has gained increasing attention. Understanding the factors that influence consumer participation in CSA is crucial, yet the complete picture and interrelations of these factors remain unclear in existing studies. This research adopts a scoping review and the KJ method to elucidate the factors influencing consumer participation in CSA and to theorize consumer participation. In particular, we focus on the dynamics of individual decision-making for participation, under the premise that individuals are embedded in socio-cultural environments. We examine the decision-making process based on the seesaw of expected gains and losses from participation, along with the reflexivity to the individual and the process of updating decision-making post-participation. Our study highlights how individual decision-making for participation is influenced by relationships with others within the embedded socio-cultural environment, as well as by attachment and connection to the community. It also shows that discrepancies between expectations and experiences post-participation, and the transformation of the social capital, promote the updating of decision-making processes. In addition, among the factors identified in this study for participation in CSA, the decision to participate was heavily influenced by expectations of “variety of ingredients,” suggesting that other factors such as “food education and learning opportunities,” “contribution to environmental and social issues,” and “connections with people and nature” had little impact. Although there are limitations, the insights gained from this study offer profound implications for stakeholders and provide valuable insights for more sustainable and efficient CSA practices.

This paper presents reverse-phase superimposition method for fault-tolerance in permanent magnet synchronous motor to reduce torque ripple while maintaining torque level. When a motor winding fails, two problems occur: the torque level decreases, and the torque ripple increases. Although previous research solved these problems, maintaining the torque level and reducing the torque ripple simultaneously has not been possible. In the proposed method, the current under the fault condition is separated into zero-, positive-, and reverse-phase, and the reverse-phase current is superimposed on the non-fault phase. By using the proposed method, the torque ripple can be suppressed while maintaining torque levels. To validate the effectiveness, numerical and experimental verification was conducted, and results obtained by the proposed method were compared with the torque performance of the conventional methods. The results revealed that with the proposed method, the advantages of the two conventional methods can be obtained together.

Raman spectroscopy was used to study quasilongitudinal optical phonons in wurtzite gallium nitride.

Quantum well excitons were studied in InGaN single quantum well amber light emitting diodes.

Research was conducted to examine the structural and vibrational features of device quality pure GaN substrate grown using a lateral epitaxial ovvergrowth method by x-ray diffraction, Brillouin, Raman and infrared spectroscopy. Lattice constants were observed to be close to bulk GaN and relaxed epilayers on sapphire. Results indicate extremely good structural quality of the GaN substrate with structural coherence length of as long as 1.9 micron along the c axis.

Glacier phototroph blooms on the surfaces of ice sheets and glaciers cause albedo reduction, leading to increased melting rates. We observed seasonal changes in the abundance of phototrophs on the Qaanaaq Ice Cap in northwestern Greenland from June to August 2014, and reproduced these changes using numerical and empirical models. The phototroph community on the ice surface mainly consisted of the glacier alga Ancylonema nordenskioldii and the cyanobacterium Phormidesmis priestleyi. The glacier alga appeared on the ice surface in late June, after which its abundance increased exponentially throughout the melting period. A logistic growth model designed for snow algal growth reproduced the measured exponential increases, suggesting that growth could be explained using the model as a function of the ice melting duration. Cyanobacteria appeared and their abundance increased in late July but did not change exponentially thereafter. The abundance of cyanobacteria was explained with an empirical model expressed as a function of the amount of mineral dust on the bare ice surface. Our numerical and empirical models for reproducing glacier algae and cyanobacteria could be useful for quantifying the albedo reduction caused by their growth and the melt rates of the Greenland ice sheet and glaciers in the future.

Abstract Carbon nanotube (CNT) film photo‐thermoelectric (PTE) imagers are suitable for non‐destructive inspection techniques owing to their functionalities. Simultaneously, their practical application remains a crucial bottleneck due to low yield handling in the device fabrication (e.g., disconnections between photo absorbent channels and readout electrodes). However, studies clarifying the above malfunction mechanism and associated dominant factors in device handling, such as specific fabrication or material selection steps, still need to be completed. To address this issue, this work introduces all‐screen‐coatable fabrication techniques for CNT film PTE imagers to enhance their physical and thermal durabilities. First, this work determined that the transfer of CNT films on supporting substrates dominantly governs the mechanical robustness of the channels and that thermal curing in the subsequent fabrication process is an essential factor in the yields of channel‐electrode connections. The proposed approach ensures a transfer‐free direct coating of the CNT film on diverse substrates and is sufficiently durable against thermal curing‐induced disconnections at the channel‐electrode interfaces. The screen‐coating technique is also available for whole device materials of solution‐processable CNT film PTE imagers, simplifying fabrication processes. All‐screen‐coatable CNT film PTE imagers synergize their inherent functional sensing and high‐yield operations toward versatile applications.

Abstract Variable-temperature cryogenic ion mobility-mass spectrometry (VT-Cryo-IM-MS) was developed to examine the conformations of host-guest complexes. The VT-Cryo-IM-MS consists of an electrospray ionization source, a quadrupole ion trap, a cryogenic ion drift tube, and a time-of-flight mass spectrometer. The ion drift tube was cooled to 83 K with liquid nitrogen. Two sets of ion funnels are installed at the source and the drift tube to focus the ion beam. We used Li+-encapsulated fullerene (Li+@C60) as a reference ion to examine the ion-mobility resolution of the VT-Cryo-IM-MS apparatus because this ion has a rigid structure with a single conformer. The temperature dependence of collision cross section (CCS) of Li+@C60 and the resolution of the apparatus were determined at each temperature. We examined the conformations of host-guest complexes of a series of metal ions (M = Ca2+, Na+, Ag+, K+, Rb+, and Cs+) with dibenzo-24-crown-8 (DB24C8) by Cryo-IM-MS. All CCS distributions were fitted with two Gaussian functions which are assigned to closed and open conformers. These closed and open conformers have different distances between the two benzene rings of DB24C8. The abundance ratio of closed conformers for these M(DB24C8) complex ions depends on the guest M ion with an order, Ca2+ < Na+ < Ag+ < Cs+ < Rb+ < K+. The stability of the closed conformer of K+(DB24C8) originates from the benzene ring positional relationship which is quite close to that of the free benzene dimer. This special benzene dimer-like conformation produces the strong π-π interaction between the benzene rings of K+(DB24C8).

Experiments on gallium nitride, a well-known wide-band gap semiconductor which has a great potential for new applications in electronics and optoelectronics industries, have been made. Efforts for improving the quality of GaN crystals have also been initiated. Findings show that the misalignments between the sapphire base and the GaN layers can affect properties of GaN.

The internal quantum efficiency (ηint) of the near-band-edge (NBE) excitonic photoluminescence (PL) in ZnO epilayers was significantly improved by eliminating point defects, as well as by the use of ZnO high-temperature-annealed self-buffer layer (HITAB) on a ScAlMgO4 substrate as epitaxial templates. Negatively charged Zn vacancy (VZn) concentration was greatly reduced by high-temperature growth, and slower postgrowth cooling (annealing) under minimum oxygen pressure further reduced the gross concentration of positively and negatively charged and neutral point defects, according to the suppression of nonequilibrium defect quenching. The nonradiative PL lifetime (τnr) at room temperature was increased by decreasing the gross concentration of point defects, as well as by decreasing the concentration of VZn. Accordingly, certain point defect complexes incorporated with VZn (VZn-X complexes) are assigned to the dominant nonradiative recombination centers. As a result of the elimination of point defects, a record long τnr (3.8 ns) at 300 K was demonstrated. Because the radiative lifetime (τr) is in principle constant in bulk and epitaxial ZnO, the increase in τnr gave rise to the increase in ηint. Rich structures originating from exciton-polaritons and excited states of excitons were eventually observed in the low-temperature PL spectrum of the improved ZnO epilayer on HITAB, of which ηint of the NBE emission was 6.3% at 300 K. [ABSTRACT FROM AUTHOR]

Time-integrated and spectrally resolved four-wave mixing (FWM) has been applied to study the impact of the k-linear term on nonlinear optical response of the C-exciton manifold in ZnO. From the excitation wavelength dependence of the FWM signal, we have found possible evidence that the mixing of theΓ 1 anΓ 5L states leads to a three-branch excitonic polariton dispersion but the oscillator strength transfer is small. The energy separation between the lower polariton branch and the extra branch due to the k-linear term has been found to be 3.5 meV. In addition, a binding energy of biexcitons consisting of two C excitons of 1.4 meV has been obtained. [ABSTRACT FROM AUTHOR]

Recombination dynamics of excitons in nearly strain-free Al[SUB1-x]In[SUBx]N alloys on the GaN template were studied. Their band-gap energy showed a nonlinear dependence on the InN molar fraction x, and the bowing parameter was determined to be approximately 23.1 eV. Most of the alloys exhibited an extremely diffused band-edge, and consequently exhibited huge Stokes-type shifts up to 1-2 eV and full width at half maximum of the luminescence peaks up to 0.5 eV. The results suggested enhanced material inhomogeneity in AlInN compared to InGaN alloys. Since the time-resolved photoluminescence signal showed a pronounced stretched exponential decay, the spontaneous emission was assigned as being due to the radiative recombination of excitons localized in disordered quantum nanostructures. The integrated PL intensity at 300 K was as strong as 29% of that at low temperature, showing a potential use of AlInN alloys as infrared-to-UV light emitters. [ABSTRACT FROM AUTHOR]

Polarized Brillouin scattering measurements were carried out for a bulk ZnO single crystal. The whole set of elastic stiffness constants was determined to be c[SUB11]=19.0, c[SUB12]=11.0, c[SUB13]=9.0, c[SUB33]=19.6, c[SUB44]=3.9, and c[SUB66]=4.0 in units of 10[SUP11]dyn/cm[SUP2]. The relationships between photoelastic constants at wavelength of 514.5 nm were also obtained: p[SUB11], p[SUB13], p[SUB44], and p[SUB66]=1.8, 2.3, 0.50, and 0.38, respectively, relative to p[SUB12]. [ABSTRACT FROM AUTHOR]

Recombination dynamics of localized excitons in the best quality strained cubic In[sub x]Ga[sub 1-x]N/GaN multiple quantum wells (MQWs) grown on 3C-SiC (001) were studied as functions of InN mole fraction x and temperature T. The MQWs exhibited large Stokes-type shifts although the full width at half maximum of the photoluminescence (PL) peaks being 80-120 meV is 100-300 meV smaller than those reported previously. Time-resolved PL signal showed stretched exponential decay and spectral redshift with time after excitation up to 300 K. These results are fingerprints that the spontaneous emission is due to the radiative recombination of excitons localized in disordered quantum nanostructures forming extended and localized states. Effective localization depth increased with the increase in x, which gave rise to fast exciton localization. However, nonradiative lifetime in the free states decreased more rapidly with the increase in x and T, giving the emission efficiency maximum at particular x around 0.1. [ABSTRACT FROM AUTHOR]

Studies the forward Raman scattering by quasilongitudinal optical phonons in gallium nitride. Determining frequency variation of quasilongitudinal optical phonons in a relatively wide range of their propagation directions; Selection rules for quasilongitudinal optical phonons which are used to interpret polarized Raman signals.

Stable carbon (C) and nitrogen (N) isotopes (13C and 15N) in water-extractable organic matter (WEOM) derived from air-dried soils may be applicable to elucidate the microbial decomposition of soil organic matter (SOM), which is crucial in terrestrial C cycles. A total of 40 soil samples were collected from a depth of 0–6 cm from a temperate broadleaved forest in Japan with vegetation succession from grassland approximately 150 years ago. Those soil samples were air-dried before the water extraction process and organic matter analysis. The C and N concentrations of WEOM were