Multi-junction III–V solar cells: current status and future potential

Our recent R&D activities of III–V compound multi-junction (MJ) solar cells are presented. Conversion efficiency of InGaP/InGaAs/Ge has been improved up to 31–32% (AM1.5) as a result of technologies development such as double hetero-wide band-gap tunnel junction, InGaP–Ge hetero-face structure bottom cell, and precise lattice-matching of InGaAs middle cell to Ge substrate by adding indium into the conventional GaAs layer. For concentrator applications, grid structure has been designed in order to reduce the energy loss due to series resistance, and world-record efficiency InGaP/InGaAs/Ge 3-junction concentrator solar cell with an efficiency of 37.4% (AM1.5G, 200-suns) has been fabricated. In addition, we have also demonstrated high-efficiency and large-area (7000 cm²) concentrator InGaP/InGaAs/Ge 3-junction solar cell modules of an outdoor efficiency of 27% as a result of developing high-efficiency InGaP/InGaAs/Ge 3-junction cells, low optical loss Fresnel lens and homogenizers, and designing high thermal conductivity modules.Future prospects are also presented. We have proposed concentrator III–V compound MJ solar cells as the 3rd generation solar cells in addition to 1st generation crystalline Si solar cells and 2nd generation thin-film solar cells. We are now developing low-cost and high output power concentrator MJ solar cell modules with an output power of 400 W/m² for terrestrial applications.     

Over 27% efficiency GaAs/InGaAs mechanically stacked solar cell

We have applied an InGaAs solar cell (band GAP = 0.75 eV) to the bottom cell of the super-high-efficiency tandem solar cell aiming an over 35% conversion efficiency. The InGaAs cell which is lattice-matched to the InP substrate showed the efficiency of 5.5% under the GaAs substrate with low carrier concentration. Combining with the GaAs cell by means of a mechanically stacking technique, we obtained an efficiency of 28.8% at air mass (AM) 1.5, 1-sun. This result suggests the possibility of the cells with the efficiency of over 35% with combining a GalnP/GaAs monolithic tandem cell and the InGaAs cell (or InGaAsP cell).     

Fates of foodborne pathogens in raw hams manufactured rapidly using a new patented method

To manufacture raw ham in an efficient manner, we recently developed a new system in which presliced pork loin was used, and the processing time was reduced to 5% of the conventional method. This study aimed to examine whether this raw ham could be as safe as ham produced by the conventional method. Pork loin spiked with enterohemorrhagic Escherichia coli serotype O157:H7, Listeria monocytogenes serotype 1/2c, Salmonella enterica serovar Enteritidis, and Staphylococcus aureus were processed using either the new or conventional method. The fate of the foodborne pathogens and behavior of hygiene indicator bacteria were examined. Whereas nitrite had disappeared during the conventional packaging process, the reduced processing time in the new system allowed for the ham to be vacuum packed with retention of the nitrite (6.9±1.2 ppm, P<0.01). This accounts for the prominent decrease in L. monocytogenes (2.3 log reduction in 35 days) and S. aureus (3.3 log reduction in 13 days) counts during storage. E. coli O157 and Salmonella Enteritidis were likely resistant to the nitrite in the ham. However, they were unable to multiply in the ham and decreased gradually as in the conventionally produced ham. The bacteriostatic nature of the raw ham was also indicated by the gradual decrease in coliforms (1.3 log reduction in 13 days) in nonspiked ham. In conclusion, the raw ham produced using presliced pork loin is practically as safe as conventionally produced raw ham. It is worth validating these results in a small-scale production setting.     

Rapid quantification of coliforms in ready-to-eat foods using lateral-flow immunochromatographic assay

The degree of coliform contamination in pastries was estimated based on culturing times until positive results were obtained with the lateral-flow immunochromatographic assay (LFIA). Coliform genera Citrobacter, Cronobacter, Enterobacter, Klebsiella, Kluyvera, Pantoea, Raoultella, and Serratia were detected in spoiled pastries, as established with next-generation sequencing. A lateral-flow test strip was constructed using antibodies recognizing the above genera. The culture times required for positive detection with LFIA were 0, 3, 6, and 9 hr at initial inoculation concentrations of 3.8, 2.8, 1.8, and 0.8 log₁₀ (cfu/ml), respectively. In pastries contaminated with >5.0, 3.0–5.0, 2.0–3.0 log₁₀ (cfu/g) coliform bacteria, samples became LFIA-positive from 3, 6, and 9 hr culture, respectively. LFIA showed negative for pastries with <2.0 log₁₀ (cfu/g) coliform contamination. The quantitative category of initial coliform content before culture was predictable with 87% accuracy. This novel method can be applied to monitor food safety of other ready-to-eat consumables.     

On the approximation of protein threading

In this paper, we study the protein threading problem, which was proposed for predicting a folded 3D protein structure from an amino acid sequence. Since this problem was already proved to be NP-hard, we study polynomial time approximation algorithms. We show several hardness results for the approximation, which includes a MAX SNP-hardness result. We also show approximation algorithms for a special case and a general case, where a graph representing interactions between amino acid residues is restricted to be planar in a special case. For this special case, we obtain a constant approximation ratio.     

A Highly Active 4‐Siloxyproline Catalyst for Asymmetric Synthesis

trans‐4‐tert‐Butyldimethylsiloxy‐L ‐proline displays a greater catalytic activity than the parent proline without compromising the enantioselectivity, which widens the substrate scope in the α‐aminoxylation of carbonyl compounds, as well as O‐nitroso‐aldol/Michael, and Mannich reactions.     

Robust stability evaluation of sampled-data control systems with a sector nonlinearity in a gain-phase plane

This paper describes a graphical evaluation of the robust stability in a frequency domain based on the results from our previous paper in which the extension of Popov's criterion to discrete-time systems was expressed in an explicit form. The control system described herein is a sampled-data control system with one time-invariant nonlinear element (sector nonlinearity) in the forward path. For the purpose of application to a computer-aided control system design (CACSD), we will present an evaluation method of the robust stability in connection with the size of sector nonlinearity and the gain margin on a gain-phase diagram (i.e. a modified Nichols chart). We will show two results as numerical examples: one where Aizerman's conjecture was approved, and one where it was not. Copyright © 1999 John Wiley & Sons Ltd.     

Synthesis of Red-Light-Responsive Pheophorbide-a Tryptamine Conjugated Photosensitizers for Photodynamic Therapy

Six methyl pheophorbide-a derivatives were prepared by linking a tryptamine side chain at the C-13 ¹ , C-15 ² and C-17 ³ positions of pheophorbide-a. P repared conjugates were characterized and evaluated for their photocytotoxicity against A549 cells. The conjugate 6 a with strong absorption at 413 nm (Soret band), 663–671 nm (Q bands) and comparable fluorescence quantum yield (0.26) was found to exhibit significant cytotoxicity (659 nM). Molecular integration of pheophorbide-a and tryptamines showed synergistic effects as the most potent conjugate 6 a was identified with enhanced photocytotoxicity when compared to methyl pheophorbide-a. T he conjugate 6 a was smoothly taken up by A549 cells and exhibited intracellular localization predominantly to lysosome in the cytoplasm. Upon photoirradiation 6 a generated singlet oxygen to show potent cytotoxicity toward A549 cells.     

Effect of degree of neutralization of sodium-based ionomers on hot-tack properties

The hot-tack properties of ethylene-methacrylic acid copolymers neutralized with sodium (Na) cations to produce ionomers were investigated. Specimens with neutralization degrees of 20%, 54%, and 70% were examined. After testing at low sealing temperatures (<130°C), the highest hot-tack strength was obtained from a specimen with a neutralization degree of 20%. In contrast, at high sealing temperatures (>140°C), the hot-tack strength increased with an increasing degree of neutralization. Observations of the surfaces of samples tested at low sealing temperatures after hot-tack tests showed that specimens having a neutralization degree of 20% exhibited cohesive breakdown while the 54% and 70% specimens underwent interfacial delamination. The effect of sealing temperature on hot-tack strength was determined by assessing the rheological properties of molten ionomers. The results suggested that, when testing at low sealing temperatures, a low melt viscosity provided high hot-tack strength by allowing flow diffusivity of the resin at the sealed interface. At high sealing temperatures, uniaxial elongational viscosity related to strain hardening contributed to the high hot-tack strength of these Na-based ionomers. The present study highlights the important effect of ionic aggregates on hot-tack properties.     

A RaPID Macrocyclic Peptide That Inhibits the Formation of α-Synuclein Amyloid Fibrils

There is considerable interest in drug discovery targeting the aggregation of α-synuclein (αSyn) since this molecular process is closely associated with Parkinson's disease. However, inhibiting αSyn aggregation remains a major challenge because of its highly dynamic nature which makes it difficult to form a stable binding complex with a drug molecule. Here, by exploiting Random non-standard Peptides Integrated Discovery (RaPID) system, we identified a macrocyclic peptide, BD1, that could interact with immobilized αSyn and inhibit the formation of fibrils. Furthermore, improving the solubility of BD1 suppresses the co-aggregation with αSyn fibrils while it kinetically inhibits more effectively without change in their morphology. We also revealed the molecular mechanism of kinetic inhibition, where peptides bind to fibril ends of αSyn, thereby preventing further growth of fibrils. These results suggest that our approach for generating non-standard macrocyclic peptides is a promising approach for developing potential therapeutics against neurodegeneration.