Effect of fast neutron irradiation on magnetic properties of fullerene superconductor Rb3C60

Effects of fast neutron irradiation and post-annealing on magnetic properties of Rb₃C₆₀ were studied through the dc magnetization measurement. Rb₃C₆₀ powder samples were prepared in an evacuated quartz glass tube, and the temperature and the magnetic field dependences of dc magnetization were measured before and after irradiation and after post-annealing. The neutron fluences were 1.0, 1.8 and 3.3 × 10¹⁶ n/cm², and the post-annealing was made at a temperature of 473 K for 3 h. Magnetic hysteresis of the samples irradiated at the fluence of 1.8 and 3.3 × 10¹⁶ n/cm² disappeared, and the hysteresis curves hardly changed at the fluence of 1.0 × 10¹⁶ n/cm². As for the post-annealing effect, the hysteresis curves of the sample irradiated at the fluence of 1.8 × 10¹⁶ n/cm² were completely recovered after annealing, while those of the other samples, which had a magnetic background before irradiation, were not recovered. In this study, it was found that the loss of superconductivity in Rb₃C₆₀ powder is observed when the neutron irradiation fluence exceeds 1.0 × 10¹⁶ n/cm², and the lost superconductivity is completely recovered by the post-annealing at 473 K for 3 h.     

Dynamic melting of driven vortex matter below 1 K

We report on measurements of a mode-locking resonance in amorphous Mo_xGe_1?x films at different temperatures T down to 0.8 K, which is well below the superconducting transition (6 K). We observe dynamic ordering of driven vortex matter for all the temperatures studied. As the field exceeds a certain critical field B_c,dyn at fixed T, moving vortices do not exhibit dynamic ordering. At high T, this field B_c,dyn(T), so-called dynamic melting, nearly coincides with a characteristic field B_c(T) where the linear resistivity vanishes. At low T, however, B_c,dyn(T) is significantly suppressed compared to B_c(T), suggesting intrinsic quantum melting in the absence of pinning.     

Synthesis of Eu x Si6? z Al z O z N8? z green phosphor and?its?luminescent properties

Rare-earth-doped oxynitride or nitride compounds have been reported to be photoluminescent and may then serve as new phosphors because of their good thermal and chemical stabilities. In this work, Eu²⁺-doped β-SiAlON phosphor with a composition of Eu _x Si_6−z Al _z O _z N_8−z (x=0.018, z=0.23) was prepared by gas-pressured solid state reaction. The crystallinity and particle morphology of the prepared phosphor were characterized. The Stokes shift and zero-phonon line were calculated mathematically and estimated from the spectral data. The temperature dependence of photoluminescence was measured from 25 to 250°C. The prepared Eu²⁺-doped β-SiAlON green phosphor showed superior thermal quenching property compared to silicate (SrBaSiO₄:Eu²⁺) green phosphor. The white light-emitting diode (LED) back-lighting unit (BLU) using the prepared β-SiAlON:Eu²⁺ green phosphor exhibited higher color gamut than a commercial silicate phosphor.     

Evaluation and comparison of three novel microbubbles: Enhancement of ultrasound-induced cell death and free radicals production

Three novel lipid-shell-type microbubbles (MBs), AS-0100, BG6356A and BG6356B, have been evaluated for their impact on ultrasound (US)-induced cell death and free radicals production. Previously studied and well-characterized US exposure conditions were employed in which human myelomonocytic lymphoma U937 cells were exposed to 1 MHz pulsed US beam (0.3 W/cm², 10% duty factor) for 1 min with or without MBs. Three different concentrations of each MB were used. Apoptosis and cell lysis were assessed by examining phosphatidylserine externalization and by counting viable cells, respectively, 6 h post-exposure. Free radicals production and scavenging activities were evaluated using electron paramagnetic resonance (EPR)-spin trapping. The results showed that only AS-0100 and BG6356A were able to enhance the US-induced apoptosis, mainly by increasing the secondary necrosis. Apoptosis and cell lysis seemed to depend more on mechanical forces exerted by oscillating MBs while free radicals played a trivial role. BG series MBs exhibited pronounced scavenging activities. Generally, despite the need for further optimization, AS-0100 and BG6356A appear to be promising as adjuncts in cases where US-induced cell death is required.     

Well-crystallized zinc oxide quantum dots with narrow size distribution

In this study, pulsed laser ablation, online annealing, and following size classification using a differential mobility analyzer (DMA) were employed to fabricate quantum dots (QDs) of zinc oxide (ZnO). The irregularly shaped ZnO particles were obtained at annealing temperature less than 873 K, which gradually transformed into spherical QDs with increasing the annealing temperature. Finally, ZnO QDs with narrow size distribution having spherical shapes were successfully obtained at temperatures above 1173 K under the DMA classification at a nominal size of 10 nm. TEM observation demonstrated that the ZnO QDs obtained by this process were well-crystallized single crystallites with a wurtzite structure. Further, ZnO QDs with average sizes in the range of 4.8–8.1 nm were successfully fabricated by reducing the specified sizes of DMA. These features of the fabricated ZnO QDs are favorable for investigation of intrinsic quantum size effect in ZnO.     

SQUID sensor application for small metallic particle detection

High-Tc superconducting quantum interference device (SQUID) is an ultra-sensitive magnetic sensor. Since the performance of the SQUID is improved and stabilized, now it is ready for application. One strong candidate for application is a detection system of magnetic foreign matters in industrial products or beverages. There is a possibility that ultra-small metallic foreign matter has been accidentally mixed with industrial products such as lithium ion batteries. If this happens, the manufacturer of the product suffers a great loss recalling products. The outer dimension of metallic particles less than 100 μm cannot be detected by an X-ray imaging, which is commonly used for the inspection. Ionization of the material is also a big issue for beverages in the case of the X-ray imaging. Therefore a highly sensitive and safety detection system for small foreign matters is required. We developed detection systems based on high-Tc SQUID with a high-performance magnetic shield. We could successfully measure small iron particles of 100 μm on a belt conveyer and stainless steel balls of 300 μm in water. These detection levels were hard to be achieved by a conventional X-ray detection or other methods.     

Coherence effect on decryption characteristics in message modulation type chaos secure communication systems using fiber-optic ring resonators

We numerically investigated the dependence of the decryption characteristics in a message modulation type chaos secure communication system using optical fiber ring resonators (OFRRs) on the coherence condition of carrier light. Since the output dynamics of OFRRs were formed on the basis of interference phenomenon among the circulated components in OFRRs, the coherence condition of input light affected inherently the OFRR output dynamics, resulting in the decryption characteristics. It was found that the decryption characteristics degraded as coherence length increased, i.e., as the spectral width of the input light decreased. The decryption characteristics also grew worse as the parameter differences between the transmitter and the receiver became larger.     

Antiparticle Contribution in the Cross Ladder Diagram for Bethe-Salpeter Equation in the Light-Front

We construct the homogeneous integral equation for the vertex of the bound state in the light front with the kernel approximated to order g ⁴. We will truncate the hierarchical equations from Green functions to construct dynamical equations for the two boson bound state exchanging interacting intermediate σ bosons and including pair creation process contributing to the crossed ladder diagram.