High-frequency Lamb wave device composed of MEMS structure using LiNbO3 thin film and air gap

High-frequency devices operating at 3 GHz or higher are required, for instance, for future 4th generation mobile phone systems in Japan. Using a substrate with a high acoustic velocity is one method to realize a high-frequency acoustic or elastic device. A Lamb wave has a high velocity when the substrate thickness is thin. To realize a high-frequency device operating at 3 GHz or higher using a Lamb wave, a very thin (less than 0.5 μm thick) single-crystal plate must be used. It is difficult to fabricate such a very thin single crystal plate. The authors have attempted to use a c-axis orientated epitaxial LiNbO(3) thin film deposited by a chemical vapor deposition system (CVD) instead of using a thin LiNbO(3) single crystal plate. Lamb wave resonators composed of a interdigital transducer (IDT)/the LiNbO(3) film/air gap/base substrate structure like micro-electromechanical system (MEMS) transducers were fabricated. These resonators have shown a high frequency of 4.5 and 6.3 GHz, which correspond to very high acoustic velocities of 14,000 and 12,500 m/s, respectively, have excellent characteristics such as a ratio of resonant and antiresonant impedance of 52 and 38 dB and a wide band of 7.2% and 3.7%, respectively, and do not have spurious responses caused by the 0th modes of shear horizontal (SH(0)) and symmetric (S(0)) modes.     

Control of cone-jet geometry during electrospray by an electric current

A new electrospray system has been successfully developed by employing a proportional–integral–derivative control action to maintain an electric current at a certain value. A polymer precursor solution containing polyethylene glycol was used to examine the performance of this system. The result showed that cone-jet geometry could be controlled easily by adjusting the electric current. The length of the cone-jet decreased as the electric current was increased, in a correlation that followed power law. We also found that the cone-jet observed during electrospraying was stable and robust with no disturbance during long periods of use (up to 4000 s). The present study is very useful for further development of high precision aerosol generators and particle synthesis.     

Fabrication of conductive porous alumina (CPA) structurally modified with carbon nanotubes (CNT)

A novel binary porous composite nano-carbon networks (NCNs)/alumina, which is denoted as electrically conductive porous alumina (CPA), was structurally modified by carbon nanotubes (CNT) pre-treated with mixed concentrated acids at 60 °C for 6 h in this study. This conductive ceramics (CCs) was fabricated by combination of gelcasting and high temperature reductive sintering (HTRS) in novel atmosphere. CNT pre-treatment leading to the increased hydrophilicity makes it possible to make uniformly dispersed CNT/alumina slurry. And by HTRS in Ar at 1700 °C for 2 h, well-gelled polymer net-paths in green body prepared by gelcasting technology were totally converted to nano-carbon networks (NCNs) without destruction of CNT. NCN with graphitic crystal structure was evaluated by Raman spectroscopy in sintered ceramic body. Moreover, comparing with as-received CNT, the decreased surface defect of detected composite also supported the further graphitization of CNT via HTRS in Ar instead of burning out. With the aid of field-emission scanning electronic microscopy (FE-SEM) observation, the increased alumina grains in sintered ceramic body CNT/NCN/alumina was valid. Moreover, it was demonstrated that there were three components in this composite, which is carbon filler with two different forms (CNT and NCN) and alumina matrix. And these three components CNT covered with Al₂O₃ particles (Al₂O₃/CNT), NCN and alumina grains (alumina) co-exist in four different situations as follows: (a) Al₂O₃/CNT–alumina co-junction, (b) Al₂O₃/CNT–NCN co-junction, (c) Al₂O₃/CNT–alumina–NCN and (d) Al₂O₃/CNT mesh between alumina boundaries. Furthermore, by comparing with binary composite NCN/alumina (CPA), the increased flexural strength of ternary composite CNT/NCN/alumina (CNT/CPA) up to 38 MPa was attributed to the reinforcement CNT acting as elastic bridge in composite.     

Reflectance reduction of InP wafers after high-temperature annealing

Broadband reduction of light reflection from the surface of InP wafers after high-temperature annealing in air has been observed. In the transparency region of the material, the reflection drop is accompanied by increasing transmission of light through the wafer. The spectral position of a deep minimum of the reflection coefficient can be tuned, by varying the temperature and the time of annealing, in a wide spectral range from ultraviolet to infrared. The effect is due to formation of thermal oxide layers on the surfaces of the wafer with optical parameters favorable for antireflection.     

Measuring cosmic-ray exposure in aircraft using real-time personal dosemeters

Aircrew exposure to radiation was measured on several long-haul flights using two small commercial electronic personal dosemeters: one was a photon dosemeter, the NRF20; the other was a neutron dosemeter, the NRY21-both manufactured by Fuji Electric Systems Co. Ltd. for radiation protection at nuclear facilities. Non-neutron doses were measured using the photon dosemeter, and neutron doses were measured using the neutron dosemeter. The measured non-neutron doses at commercial aviation altitudes agree with the EPCARD (European Program Package for the Calculation of Aviation Route Doses) dose calculation within a difference of 8 %. However, the recorded neutron doses were 5-15 times larger than the EPCARD calculation. These over-measurements are dependent on cut-off rigidities.     

Rank 2 proximal Cantor systems are residually scrambled

Downarowicz and Maass [7 T. Downarowicz and A. Maass, Finite-rank Bratteli–Vershik diagrams are expansive, Ergod. Th. Dynam. Sys. 28 (2008), pp. 739–747.[Web of Science ®] , [Google Scholar]] proposed topological ranks for all homeomorphic Cantor minimal dynamical systems using properly ordered Bratteli diagrams. In this study, we adopt this definition to the case of the essentially minimal zero-dimensional systems. We consider the cases in which topological ranks are 2 and unique minimal sets are fixed points. Akin and Kolyada [2 E. Akin and S. Kolyada, Li–Yorke sensitivity, Nonlinearity 16(4) (2003), pp. 1421–1433.[Crossref], [Web of Science ®] , [Google Scholar]], had shown that if the unique minimal set of an essentially minimal system is a fixed point, then the system must be proximal. The finite topological rank implies expansiveness; furthermore, in the case of proximal Cantor systems with topological rank 2, the expansiveness is always from the lowest degree. Rank 2 proximal Cantor systems are residually scrambled. We present a necessary and sufficient condition for the unique ergodicity of these systems. In addition, we show that the number of ergodic measures of the systems that are topologically mixing can be 1 and 2. Moreover, we present examples that are topologically weakly mixing, not topologically mixing, and uniquely ergodic. Finally, we show that the number of ergodic measures of the systems that are not weakly mixing can be 1 and 2.     

Synthesis of Various Water-Soluble G60 Derivatives and Their Superoxide-Quenching Activity

Abstract

In order to examine the utility of fullerene as a medicinal application, we evaluated the reaction between fullerene derivatives and active oxygen species in vitro. This paper describes the synthesis of various water-soluble C₆₀ derivatives (cationic and anionic) and evaluation of their superoxide (O₂ ^?) quenching activity. Cationic C₆₀ derivatives showed fairly high efficiency.     

High-precision transfer-printing and integration of vertically oriented semiconductor arrays for flexible device fabrication

Flexible electronics utilizing single crystalline semiconductors typically require post-growth processes to assemble and incorporate the crystalline materials onto flexible substrates. Here we present a high-precision transfer-printing method for vertical arrays of single crystalline semiconductor materials with widely varying aspect ratios and densities enabling the assembly of arrays on flexible substrates in a vertical fashion. Complementary fabrication processes for integrating transferred arrays into flexible devices are also presented and characterized. Robust contacts to transferred silicon wire arrays are demonstrated and shown to be stable under flexing stress down to bending radii of 20 mm. The fabricated devices exhibit a reversible tactile response enabling silicon based, nonpiezoelectric, and flexible tactile sensors. The presented system leads the way towards high-throughput, manufacturable, and scalable fabrication of flexible devices.