Pore formation in p-type silicon in solutions containing different types of alcohol

ABSTRACT: Macroporous structure of silicon can be obtained with anodization in HF solution. The macropore formation in the presence of alcohol was studied. Macroporous layer formation in a low-concentration HF solution is stabilized with increasing the number of carbon in alcohol. Dissolution at the topmost part of the porous layer is observed though the behavior depends upon the type of alcohol. Meanwhile the total mass loss of dissolved silicon is almost constant. Such dissolution at the top surface occurs only when the concentration of HF is low. Adding organic solvents to the HF solution also leads to the suppression of the pore wall dissolution. The type of alcohol and HF concentration in solution affect the formation of porous silicon.     

Test for the null hypothesis of cointegration with reduced size distortion

Abstract. This article considers a single‐equation cointegrating model and proposes the locally best invariant and unbiased (LBIU) test for the null hypothesis of cointegration. We derive the local asymptotic power functions and compare them with the standard residual‐based test, and show that the LBIU test is more powerful in a wide range of local alternatives. Then, we conduct a Monte Carlo simulation to investigate the finite sample properties of the tests and show that the LBIU test outperforms the residual‐based test in terms of both size and power. The advantage of the LBIU test is particularly patent when the error is highly autocorrelated. Furthermore, we point out that finite sample performance of existing tests is largely affected by the initial value condition while our tests are immune to it. We propose a simple transformation of data that resolves the problem in the existing tests.     

Hybrid nanostructure of polypyrrole and porous silicon prepared by galvanostatic technique

Nanostructured porous silicon (PS) layer is prepared in a lightly doped p-type substrate (with pores < 5 nm) and used as a working electrode to deposit conducting polypyrrole (PPy) by the electrochemical oxidative polymerization technique in an organic liquid phase. Three distinguishable stages of PPy deposition are observed and recorded under constant applied current: nucleation of polymer at the pore bottom, unidirectional growth of PPy inside the pores, and polymerization outside the PS surface. The hybrid nanostrucutre of PS/PPy shows a significant improvement of electrical conductivity as opposed to the unmodified PS layer. The improved conductivity is observed in spite of the formation of insulating layer of silicon oxides as detected by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) measurements. Systematic study of fabrication and characterization of this organic-inorganic heterosystem, quantification of the PPy in the PS matrix, and the mechanism of filling the nanopores with polymer are presented and thoroughly discussed.     

Improved chemical stability of ascorbic acid and thiamine nitrate in L-HPC granules

The stability of drugs in extruded granules prepared with low substituted hydroxypropylcellulose (L-HPC) and water was investigated using ascorbic acid (AA) and thiamine nitrate (TN) as model drugs. d-Mannitol was used as the control additive for a comparison with L-HPC. The percentage of AA remaining after storage at 60 °C for 14 days in a closed glass bottle was 57% in d-mannitol granules and 89% in L-HPC granules, showing higher stability of AA in L-HPC granules. On powder X-ray diffraction measurement, AA in L-HPC and d-mannitol granules was in an amorphous state. The loss on drying (LOD) (1 g, 105 °C, 2 h) of the granules containing both AA and TN was higher in L-HPC granules (1.96%). The moisture content around AA and TN in granules was calculated. The contents were 1.36% and 4.67% in L-HPC and d-mannitol granules, respectively. Furthermore, the water activities at 25–40 °C were measured in L-HPC and d-mannitol granules, being lower in L-HPC granules at all measurement temperatures. These findings suggested that the superior storage stability of AA in granules prepared with L-HPC was due to L-HPC-induced reduction of the moisture content around AA and TN and water activity of the granules.     

Catalytic double ring-opening polyaddition of spiro orthoester with acid chloride for shrinkage-controlled molding

In order to develop a casting resin for precision molding, a curing method without shrinkage during the polymerization was achieved by the double ring-opening addition reaction of spiro orthoester (SOE) and acid chloride using cationic catalysts. Tetraphenylphosphonium halides (TPPXs) were found to be effective catalysts for the reaction. The catalytic reaction of SOE with acid chloride proceeded even at 25 °C to give the corresponding adduct. Polyaddition of a bifunctional SOE-XII with trifunctional 1,3,5-pentanetricarbonyl trichloride gave a cured material at 30 °C in the presence of tetraphenylphosphonium bromide (TPPB) of 1 mol%, accompanied by a negligible shrinkage of 0.21%. Gelation time was shortened with increase in the amount of catalyst and reaction temperature in the curing process. The obtained products were crosslinked copolymers that showed variable mechanical properties dependent on the curing temperature and monomer structure. This is the first demonstration of shrinkage-controlled molding in the absence of heating or cooling process.     

Selective hydroxylation of benzene to phenol by photocatalysis of molybdenum complexes grafted on mesoporous FSM‐16

Mo complexes with Mo₁–Mo₄ nuclearities were grafted on mesoporous silica FSM‐16, and their catalytic performances were studied in the hydroxylation of benzene. A trinuclear Mo oxo complex grafted on FSM‐16 exhibits the highest catalytic activity in the hydroxylation of benzene to phenol using hydrogen peroxide as an oxidant under the irradiation of UV‐light. The turnover numbers for phenol are over 700 at 300 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Lax-Phillips scattering theory and well-posed linear systems: a coordinate-free approach

We give a further elaboration of the fundamental connections between Lax-Phillips scattering, conservative input/state/output linear systems and Sz.-Nagy-Foias model theory for both the discrete- and continuous-time settings. In particular, for the continuous-time setting, we show how to locate a scattering-conservative L ²-well-posed linear system (in the sense of Staffans and Weiss) embedded in a Lax-Phillips scattering system presented in axiomatic form; conversely, given a scattering-conservative linear system, we show how one can view the space of finite-energy input-state-output trajectories of the system as the ambient space for an associated Lax-Phillips scattering system. We use these connections to give a simple, conceptual proof of the identity of the scattering function of the scattering system with the transfer function of the input-state-output linear system. As an application we show how system-theoretic ideas can be used to arrive at the spectral analysis of the scattering function.     

Optimal slip ratio estimator for traction control system of electric vehicle based on fuzzy inference

In this paper we propose an optimal slip ratio estimation method based on fuzzy inference. One of the major advantages of electric vehicles is the quick and precise torque response of the electric motor, which realizes a novel traction control system. To prevent skidding, optimal slip ratio control has been successfully developed. It maintains the slip ratio at the optimum value that gives the maximum driving force. The remaining problem is how to generate the optimal slip ratio command sent to the controller. First we show that effective estimation of the optimal slip ratio is difficult to perform by the simple gradient method, which is a well‐known optimization method. But various experimentally obtained data can be easily incorporated into fuzzy inference, and therefore its estimation performance can be easily improved by the accumulation of human experience. This is a major advantage in the nonlinear estimation of real road‐tire characteristics. The effectiveness of the proposed estimation and control methods is confirmed by numerical simulation. © 2001 Scripta Technica, Electr Eng Jpn, 135(3): 56–63, 2001     

Benzene oxidation with ozone over supported manganese oxide catalysts: effect of catalyst support and reaction conditions

Catalytic oxidation of gaseous benzene with ozone was carried out over supported manganese oxides to investigate the factors controlling the catalytic activities. The rate for benzene oxidation linearly increased with the surface area of catalyst, regardless of the kinds of catalyst support, whereas the ratio of ozone decomposition rate to benzene oxidation rate was larger for SiO(2)-supported catalyst than Al(2)O(3)-, TiO(2)-, and ZrO(2)-supported catalysts. The rate for benzene oxidation and CO(x) selectivity increased with the reaction temperature (22-100 degrees C) and were improved by the addition of water vapor to reaction gases. Benzene conversion and carbon balance increased with ozone concentration.