Effect of BaF2 powder addition on the synthesis of YAG phosphor by mechanical method

Here, we report on the effect of BaF₂ powder addition on the mechanical synthesis of Ce³⁺-doped Y₃Al₅O₁₂ (Y_2.97Al₅O₁₂:Ce_0.03³⁺, YAG:Ce³⁺) phosphors for white light emitting diodes. The YAG phosphors were synthesized by the mechanical method using an attrition-type mill. When BaF₂ was added at 6 wt% to the raw powder materials and milled, the synthesis of YAG:Ce³⁺ was favorably achieved at the vessel temperature of 255 °C, which was about 1200 °C lower than the YAG phosphor synthesis temperature by solid-state reaction. The synthesized YAG:Ce³⁺ phosphor revealed the maximum internal quantum yield of 57%.     

Spatio-temporal growth of broken spiral and concentric ringed spherulites in blends of poly(vinylidene fluoride) and ethylene-vinylacetate copolymers

Melting and crystallization behavior in mixtures of poly(vinylidene fluoride) (PVDF) and several ethylene-vinyl acetate copolymers (EVAc) with various ethylene contents have been investigated by means of differential scanning calorimetry, atomic force microscope, and optical microscopy. PVDF/EVAc-80 exhibits the melting point depression of PVDF crystals, suggestive of a miscible character of the pair. Crystallization behavior and morphology development in blends of PVDF/EVAc-80 have been investigated with an emphasis on the spherulitic growth demonstrating the spiral and concentric ringed (or target) patterns. Of particular interest is the break-up of the spiral or concentric ringed patterns at very shallow supercoolings, which may be attributed to instabilities driven by the exclusion of amorphous PVDF and EVAc chains into the emerging inter- and intra-spiral (or target) lamellar regions.     

Development and evaluation of a palm-sized optical PM2.5 sensor

A new palm-sized optical PM_2.5 sensor has been developed and its performance evaluated. The PM_2.5 mass concentration was calculated from the distribution of light scattering intensity by considering the relationship between scattering intensity and particle size. The results of laboratory tests suggested that the sensor can detect particles with diameters as small as ～0.3 µm and can measure PM_2.5mass concentrations as high as ～600 µg/m³. Year-round ambient observations were conducted at four urban and suburban sites in Fukuoka, Kadoma, Kasugai, and Tokyo, Japan. Daily averaged PM_2.5 mass concentration data from our sensors were in good agreement with corresponding data from the collocated standard instrument at the Kadoma site, with slopes of 1.07–1.16 and correlation coefficients (R) of 0.90–0.91, and with those of the nearest observatories of the Ministry of the Environment of Japan, at 1.7–4.1 km away from our observation sites, with slopes of 0.97–1.23 and R of 0.89–0.95. Slightly greater slopes were observed in winter than in summer, except at Tokyo, which was possibly due to the photochemical formation of relatively small secondary particles. Under high relative humidity conditions (>70%), the sensor has a tendency to overestimate the PM_2.5 mass concentrations compared to those measured by the standard instruments, except at Fukuoka, which is probably due to the hygroscopic growth of particles. This study demonstrates that the sensor can provide reasonable PM_2.5 mass concentration data in urban and suburban environments and is applicable to studies on the environmental and health effects of PM_2.5.

Copyright © 2018 American Association for Aerosol Research     

Effect of collagen fibril formation on bioresorbability of hydroxyapatite/collagen composites

Porous hydroxyapatite/collagen (HAp/Col) composite is a promising biomaterial and a scaffold for bone tissue engineering. The effect of fibril formation of Col in the porous composite on bioresorbability and mechanical strength was investigated. The fibril formation, in mixing a self-organized HAp/Col nanocomposite and sodium phosphate buffer at a neutral condition, occurred during incubation at 37 °C, resulting in gelation of the mixture. The porous composites with and without the incubation were obtained by freeze-drying technique, in which macroscopic open pores were formed. The compressive strength of the porous composite with the incubation (34.1 ± 1.6 kPa) was significantly higher than that without the incubation (28.0 ± 3.3 kPa) due to the fibril formation of Col. The implantations of the porous composites treated with a dehydrothermal treatment in bone holes revealed that bioresorption was clearly depended on the fibril formation. The bioresorbability in vivo was almost matched to the in vitro test using enzymatic reaction of collagenase.     

Proper Learning Algorithm for Functions of k Terms under Smooth Distributions

In this paper, we introduce a probabilistic distribution, called a smooth distribution, which is a generalization of variants of the uniform distribution such as q-bounded distribution and product distribution. Then, we give an algorithm that, under the smooth distribution, properly learns the class of functions of k terms given as _k ^k_n={g(f₁(v), …, f_k(v)) | g _k, f₁, …, f_{k n}} in polynomial time for constant k, where _k is the class of all Boolean functions of k variables and _n is the class of terms over n variables. Although class _k ^k_n was shown by Blum and Singh to be learned using DNF as the hypothesis class, it has remained open whether it is properly learnable under a distribution-free setting.     

High Atom Efficiency in Sc(OTf)3‐Catalyzed Allylation of Aldehydes with Tetraallyltin

The high atom efficiency was achieved through addition of Ac₂O in the Sc(OTf)₃‐catalyzed allylation of aldehyde with tetraallytin in a 4 : 1 molar ratio.     

A method of single-phase PWM for an independent power supply in photovoltaic power generation systems

We propose a method of single-phase PWM for an independent power supply in photovoltaic power generation systems. This new PWM is derived by comparing levels of signal waves with one of carrier waves which have bipolar swing different from unipolar swing in the conventional PWM. In this PWM, we can use a battery with lower voltage in combination with the photovoltaic power generation; fundamental level of output voltage is raised by about 11%, though poor in quality of waveforms. © 1998 Scripta Technica. Electr Eng Jpn, 122(4): 55–62, 1998     

Structural and electronic properties of extremely long perylene bisimide nanofibers formed through a stoichiometrically mismatched, hydrogen-bonded complexation

Extremely long nanofibers, whose lengths reach the millimeter regime, are generated via co-aggregation of a melamine-appended perylene bisimide semiconductor and a substituted cyanurate, both of which are ditopic triple-hydrogen-bonding building blocks; they co-aggregate in an unexpected stoichiometrically mismatched 1:2 ratio. Various microscopic and X-ray diffraction studies suggest that hydrogen-bonded polymeric chains are formed along the long axis of the nanofibers by the 1:2 complexation of the two components, which further stack along the short axis of the nanofibers. The photocarrier generation mechanism in the nanofibers is investigated by time-of-flight (TOF) experiments under electric and magnetic fields, revealing the birth and efficient recombination of singlet geminate electron-hole pairs. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements revealed intrinsic 1D electron mobilities up to 0.6 cm(2) V(-1) s(-1) within nanofibers.