Fast and Almost Complete Nitridation of Mesoporous Silica MCM-41 with Ammonia in a Plug-Flow Reactor

The title reaction proceeded well to yield silicon (oxy)nitride at 973–1323 K using a plug-flow reactor. The degree of nitridation was studied as a function of temperature and time of nitridation, the sample weight, and the flow rate of ammonia. It was dependent on the reaction temperature and the amount of ammonia supplied per sample weight. The nitridation at 1273 K for 10–25 h yielded the oxynitride with 36–39 wt% nitrogen, which was very close to 40 wt% of Si₃N₄. Characterization with X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy measurements, and nitrogen adsorption revealed the conversion of MCM-41 to the corresponding oxynitride without essential loss of the mesoporous structure, the decrements of the lattice constant and the pore diameter by 20–35%, and the increments of the wall thickness by ca. 45%. Solid-state ²⁹Si nuclear magnetic resonance spectra during the nitridation clearly showed fast decrease in SiO₄ species and slow in SiO₃(OH). Various intermediate species, SiO _x N _y (NH₂ or NH) _z , were observed to be formed and finally, ca. 70% SiN₄ species, ca. 20% SiN₃(NH₂ or NH), and ca. 10% SiON₂(NH₂ or NH) were produced, being consistent with the results of the above mentioned elemental analysis.     

Improvement of the Nelder-Mead method using Direct Inversion in Iterative Subspace

Optimization and Engineering - The Nelder-Mead (NM) method is a popular derivative-free optimization algorithm owing to its fast convergence and robustness. However, it is known that the method...     

Search for CDW in K metal

The fundamental question of whether the ground state of the alkali metals is a nearly-free-electron state or a charge-density-wave (CDW) state has remained unresolved for over 30 years, ever since Overhauser first suggested the possibility of a CDW ground state in these metals in 1962. For K metal, no evidence for CDW satellites was seen in x-ray measurements at 10 K (You et al., 1987). We made x-ray measurements for a K single crystal down to 50 mK. We observed the satellite-like spots at lower temperatures below about 10 K. We also measured the temperature dependence of the magnetic susceptibility between 1.8 K and 300 K by a SQUID magnetometer. Below about 20 K the magnetic susceptibility starts to decrease and below about 10 K it decreases more rapidly with decreasing temperature. We will discuss the possibility of CDW in K metal from our experimental results.     

Fabricating Nanocrystalline Diamond Ceramics by a Shock Compaction Method

Nanocrystalline diamond ceramics—namely, polycrystalline diamond compact consisting of ultrafine grains (one to hundreds of nanometers)—have been produced without any sintering additives via a shock compaction method using commercial diamond powders which consist of monocrystalline or shock-synthesized polycrystalline particles less than 1 μ in diameter. The method exploits plastic deformation of diamond and requires a precise spatial and timely partitioning of shock-induced thermal energy. Although much yet remains to be done for practical applications, the superior advantages of using ultrafine powders are supported by the experimental results and the theoretical modeling and considerations which are applicable to advanced ceramics.     

A model of Pt-Rh catalyst prepared by electro-chemical deposition of Rh ions on Pt(100) surface

When Pt-Rh(100) alloy surface was exposed to NO or O₂ at temperatures higher than 400 K, a characteristic p(3 × 1) LEED pattern appeared with segregation of Rh atoms on the surface. It was shown that when a Rh-deposited Pt(100) surface is heated in NO or O₂ the same 5 × 10^–8 Torr of H₂ at room temperature, the p(3 × 1) pattern disappears but is readily recovered 5 × 10^–8 Torr of H₂ at room temperature, the p(3 × 1) pattern disappears but is readily recovered by exposing to O₂ of 1 × 10^–7 Torr at room temperature. The growth of a Rh-O overlayer on Pt layer is responsible for the formation of the p(3 × 1) structure on either the Pt-Rh(100) alloy or Pt(100) surface, and this peculiar surface may correspond to the active surface of the Pt-Rh catalyst for NO _x reduction     

Internal tissue displacement measurement based on ultrasonic wave Doppler signal digital detection and its application to fetal movement monitoring

We have developed a fetal movement monitoring system based on small displacement measurement of internal tissues. When ultrasonic pulses are transmitted to the fetus, the reflected ultrasonic waves which have a Doppler frequency shift due to the fetal movements are detected by using an ultrasonic pulsed Doppler technique. In this paper, we propose a displacement measurement method for internal tissues which is based on the Doppler signal digital detection technique. In the method, the received ultrasonic RF signals are sampled with a sampling frequency of four times higher than the centre frequency of the ultrasonic waves; the Doppler frequency shift signals are derived using digital signal processing. From the detected signals, the internal displacements are estimated using the arc-tangent method. The basic algorithm of the detection method has already been used in the area of blood flow sensing, however, we apply the algorithm to the displacement measurement of internal tissues. The comparison between the proposed method and the conventional method is presented. The fetal movement quantitative monitoring system based on the method which has been constructed is shown.     

Noninvasive measurement of instantaneous, radial artery blood pressure

A new prototype system for the noninvasive measurement of instantaneous blood pressure (BP) in the human radial artery has been developed. The system is based on the volume-compensation method, but several components were newly designed, namely, a disk-type cuff for local pressurization and a nozzle-flapper-type electro-pneumatic converter (EPC) for the cuff-pressure control. Results of experiments indicated that, using the disk-type cuff, the radial artery could be completely compressed, and the newly devised EPC had sufficient frequency response for BP measurement in humans. It was also found that the prototype system comprising these components was capable of noninvasively measuring instantaneous BP in the human radial artery, not only under rest conditions but also in a stressful condition, such as during the cold pressor test. In conclusion, the newly developed local pressurization technique appears promising as a useful and helpful means for instantaneous BP monitoring over longer periods of time than have previously been possible. Using this method, it is possible to construct an instrument that is more compact and more comfortable for the subject to use than a conventional commercial instrument. Finally, it has been reported that it may be possible to monitor cardiac output continuously by BP waveform analysis. Thus, continuous cardiac output monitoring might be another potential and important application of the newly designed instrument.     

A New Catalyst for Selective Oxidation of CO in H2: Part 1, Activation by Depositing a Large Amount of FeO x on Pt/Al2O3 and Pt/CeO2 Catalysts

1% Pt/Al₂O₃ and 1% Pt/CeO₂ are markedly activated by the deposition of a large quantity of FeO _x , about 100 wt% in Fe with respect to the supports. In contrast, the activity of a Ru/Al₂O₃ catalyst was completely suppressed by the deposition of FeO _x , but a Ru-Pt/Al₂O₃ was markedly activated by the FeO _x . The activation depends on the sequence of the deposition, that is, no pronounced activation was observed on the Pt supported on a FeO _x /Al₂O₃ as well as on the Pt codeposited with a small amount of Fe on Al₂O₃, that is, the activity was almost equal to that of the Pt/Al₂O₃. The XPS analysis of the Pt/CeO₂ and FeO _x /Pt/CeO₂ proved that the Pt is effectively covered with the FeO _x . Selectivity for the oxidation of CO in H₂ was also improved on the FeO _x /Pt/Al₂O₃ and FeO _x /Pt/CeO₂ catalysts and it is rather independent of the conversion. In conformity with the feature of the FeO _x /Pt/Al₂O₃ and FeO _x /Pt/CeO₂ catalysts, we deduced that the deposited FeO _x is activated by the Pt and the FeO _x is responsible for the selective oxidation of CO.