SOURCE APPORTIONMENT OF POLYCYCLIC AROMATIC HYDROCARBONS IN ROAD DUST IN TOKYO

This study was aimed at investigating source apportionment of PAHs in urban road dust. Seven kinds of PAHs sources were defined: diesel vehicle exhaust, gasoline vehicle exhaust, tire, asphalt-pavement, asphalt or bitumen, petroleum products excluding tire and asphalt, and the combustion products except for those in vehicle engines. Using cluster analysis combined with principal component analysis, 189 source data were classified into 11 source groups (S1–S11) based on the content percentage of 12 individual PAHs (12-PAH profiles). Thirty-seven dust samples on nine streets in Tokyo were collected and analyzed for 12-PAH profiles. In order to estimate the PAHs, contributions of S1–S11 to dust samples, the multiple regression analysis was performed. The 12-PAH profiles of each dust sample and those of 11 source groups were applied as dependent and independent variables, respectively. We defined the comparative contribution of each source group as the ratio of each regression coefficient to the sum of them. The result revealed that diesel vehicle exhaust, tire, and pavement were the major contributors of PAHs in the road dust.     

Size Control of Monodisperse Prussian Blue Nanoparticles by Enforced-Nucleation and Additional-Growth Procedures in a Citrate Reduction System

Synthesis procedures of monodisperse Prussian blue nanoparticles have been investigated to control their size in a citric acid reduction system. Two different procedures, enforced-nucleation and additional-growth ones, are applied to decrease and to increase the particle size, respectively. In the former, small amount of ascorbic acid is added in the citric acid solution as the enforced-nucleation agent, which varies the number of nuclei and thus the particle size depending on its amount. In the latter, a part of Prussian blue dispersion preliminarily prepared is introduced into the reactant solution that provides additional reaction resources for the further growth. As a result, Prussian blue nanoparticles are prepared in the range of 20?100 nm in the mean size with narrow size distribution.     

Selected mapping with symbol re‐mapping for OFDM/TDM using MMSE‐FDE

Orthogonal frequency division multiplexing (OFDM) signals have a problem with a high peak‐to‐average power ratio (PAPR). A distortionless selected mapping (SLM) has been proposed to reduce the PAPR, but a high computational complexity prohibits its application to an OFDM system with a large number of subcarriers. Recently, we proposed OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error frequency‐domain equalization (MMSE‐FDE) to improve the bit error rate (BER) performance of conventional OFDM with a lower PAPR. The PAPR problem, however, cannot be completely eliminated. In this paper, we present an SLM combined with symbol re‐mapping for OFDM/TDM using MMSE‐FDE. Unlike the conventional OFDM, where SLM is applied over subcarriers in the frequency domain, we exploit both time and frequency dimensions of OFDM/TDM signal to improve the performance with respect to PAPR and BER. A mathematical model for PAPR distribution of OFDM/TDM with SLM is presented to complement the computer simulation results. It is shown that proposed SLM can further reduce the PAPR without sacrificing the BER performance with the same or reduced computational complexity. Copyright © 2010 John Wiley & Sons, Ltd.     

Iterative decision‐directed estimation and compensation of nonlinear distortion effects for OFDM systems

Orthogonal frequency division multiplexing (OFDM) has been adopted for several wireless network standards due to its robustness against multipath fading. Main drawback of OFDM is its high peak‐to‐average power ratio (PAPR) that causes a signal degradation in a peak‐limiting (e.g., clipping) channel leading to a higher bit error rate (BER). At the receiver end, the effect of peak limitation can be removed to some extent to improve the system performance. In this paper, a joint iterative channel estimation/equalization and clipping noise reduction technique based on minimum mean square error (MMSE) criterion is presented. The equalization weight that minimizes the mean square error (MSE) between the signal after channel equalization and feedback signal after clipping noise reduction is derived assuming imperfect channel state information (CSI). The MSE performance of the proposed technique is theoretically evaluated. It is shown that the BER performance of OFDM with proposed technique can be significantly improved in a peak‐limited and doubly‐selective (i.e., time‐ and frequency‐selective) fading channel. Copyright © 2011 John Wiley & Sons, Ltd.     

Inactivation kinetics of polyphenol oxidase using a two-stage method with low pressurized carbon dioxide microbubbles

Inactivation kinetics of polyphenol oxidase (PPO) by a two-stage method which was additionally pressurized at ambient temperature after carbon dioxide microbubbles (MB-CO₂) was mixed with a solution at low temperature and pressure (two-stage MB-CO₂) was analyzed. The PPO inactivation efficiency of the two-stage MB-CO₂ treatment was higher than that of heat treatment. A decrease in the decimal reduction time (D value) and activation energy during PPO inactivation using the two-stage MB-CO₂ treatment was observed as the temperature of the heating coil and the pressure in the mixing vessel increased. The temperature rise required for a 90% reduction in the D value was increased. Furthermore, the pressure rise required for a 90% reduction in the D value and activation volume increased with the temperature of the heating coil. These results showed that PPO inactivation using the two-stage MB-CO₂ treatment could be achieved with less energy than heat treatment.     

Nanoscale potential measurements in liquid by frequency modulation atomic force microscopy

We have developed a method for local potential measurements in liquid using frequency modulation atomic force microscopy. In this method, local potential is calculated from the first and second harmonic vibrations of a cantilever induced by applying an ac bias voltage between a tip and a sample. The use of an ac bias voltage with a relatively high frequency prevents uncontrolled electrochemical reactions and redistribution of ions and water. The nanoscale resolution of the method is demonstrated by imaging potential distribution of a dodecylamine thin film deposited on a graphite surface in 1 mM NaCl solution.     

Evaluation of crack nucleation site and mechanical properties for friction stir welded butt joint in 2024-T3 aluminum alloy

In this paper, metallographic observations, hardness measurement, and static and fatigue tests were conducted to investigate the discontinuity states which become crack nucleation sites in friction stir welded butt joints in 2-mm-thick 2024-T3 aluminum alloy and static and fatigue properties of the joint. Because different types of surface finish can be used depending on the application of the joint, several types of surface conditions were tested to evaluate their effect on crack nucleation sites and static and fatigue life. Indentation hardness tests revealed that typical hardness reduction is not necessarily observed on the section of the welding line. Based on fatigue test results, it was confirmed that there are several types of crack nucleation sites for friction stir welding (FSW) joints depending on the surface finish, and the features of the fracture surface also differ depending on the site. Furthermore, the type of discontinuity state affects the fatigue life of the FSW joint.     

Corrosion monitoring of nickel-containing steels in marine atmospheric environment

Corrosion monitoring of nickel-containing steels has been performed in a natural atmospheric environment using AC impedance technique. A pair of identical comb-shape steel electrodes embedded in epoxy resin was used as a probe electrode for the corrosion monitoring. Three different probes of ordinary carbon steel, 2.5%Ni- and 5%Ni-containing steels were exposed to a natural marine atmosphere for the period of 14 months. The instantaneous corrosion rate of the steels was monitored by continuous measurements of the polarization resistance, and time of wetness of the steel surface was determined from high frequency impedance. The measurement was automatically carried out with an AC corrosion monitor placed at the exposure site, and data transmission between the exposure site and laboratory was performed through cellular phones.     

Generation of Compositional‐Gradient Structures in Biodegradable,Immiscible, Polymer Blends by Intermolecular Hydrogen‐Bonding Interactions

A biodegradable, immiscible poly(butylenes adipate‐co‐butylenes terephthalate) [P(BA‐co‐BT)]/poly(ethylene oxide) (PEO) polymer blend film with compositional gradient in the film‐thickness direction has been successfully prepared in the presence of a low‐molecular‐weight compound 4,4′‐thiodiphenal (TDP), which is used as a miscibility‐enhancing agent. The miscibilities of the P(BA‐co‐BT)/PEO/TDP ternary blend films and the P(BA‐co‐BT)/PEO/TDP gradient film were investigated by differential scanning calorimetry (DSC). The compositional gradient structure of the P(BA‐co‐BT)/PEO/TDP (46/46/8 w/w/w) film has been confirmed by microscopic mapping measurement of Fourier‐transform infrared spectra and dynamic mechanical thermal analysis. We have developed a new strategy for generating gradient‐phase structures in immiscible polymer‐blend systems by homogenization, i.e., adding a third agent that can enhance the miscibility of the two immiscible polymers through simultaneous formation of hydrogen bonds with two component polymers.