Method for evaluation of fractal properties from data with noisy observational errors

In this paper, we propose a method, named cutting detrended fluctuation analysis (cutting DFA), for the evaluation of global and local fractal properties from data containing noisy observational errors. This method evaluates how the Hurst exponent varies by cutting out in the order of the largest deviation from the mean value. An analysis of the simulated fractal signal reveals that cutting DFA exhibits a linear transition of the Hurst exponent with respect to the cutting rate. The mean value and the slope thereof reflect the global and local fractal properties of the time series, respectively. We then analyze the long‐term heart rate variability of congestive heart failure (CHF) patients and healthy subjects with observational errors. It is demonstrated that CHF patients have a higher value in the mean Hurst exponent than healthy subjects, indicating a higher global Hurst exponent. Also, it is demonstrated that healthy subjects have a statistically significant difference in slope from monofractal time series, while CHF patients do not. These results indicate that the local fractal property of healthy subjects is far from monofractal time series, which matches previous findings. Therefore, it is confirmed that cutting DFA extracts fractal properties of original heart rate variability from data containing observational errors. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Design of novel biomimetic polymer gels with self-oscillating function

We report a novel biomimetic gel that undergoes autonomous swelling-deswelling oscillations without on-off switching of external stimuli, similar to heartbeat. The mechanical oscillation of gel was produced via oscillating chemical reaction, called the Belousov-Zhabotinsky (BZ) reaction. We have prepared an ionic gel consisting of the cross-linked poly(N-isopropylacrylamide) chain to which ruthenium tris(2,2′-bipyridine), a catalyst for the BZ reaction, was covalently bonded. The BZ reaction occurring within the gel matrix generates periodic redox changes of the catalyst moiety. This chemical oscillation is converted into the mechanical oscillation of the polymer network. As a result, the gel exhibits a periodical swelling-deswelling change. The self-oscillating behaviors of the gel were investigated in detail. When the gel size is smaller than the chemical wavelength, the redox change occurs homogeneously in the gel. In this case, the volume change is isotropic and the mechanical oscillation synchronizes with chemical oscillation without a phase difference. The period and amplitude can be controlled by changing the outer substrate concentrations. In the case of rectangular shape, chemical wave propagates along the length of the gel. The wavelength and velocity depend on the reaction rate of autocatalytic process as well as the diffusivity of the activator. The dynamic behavior that locally shrunken (or swollen) parts propagate was observed, similar to the peristaltic motion of worms. By using lithography technique, a ciliary motion actuator made of the gel has been demonstrated. These self-oscillating gels may be useful in a number of important applications to intelligent biomaterials such as pulse generator or chemical pacemaker, auto-mobile actuators or micropumps with peristaltic motion, device for signal transmission, etc.     

Bulk ZnO nanorod assemblies fabricated by spin coating of organo-precursor gels on CuO nanowires

Bulk ZnO nanorod assemblies have been successfully fabricated on CuO nanowires through spin coating of organoprecursor gels. A thin film of CuO nanowires was first generated by direct heating of a metallic Cu-foil at 500 °C in an air atmosphere. A stable colloidal organo-precursor sol synthesized by dissolving equimolar zinc acetate dihydrate and monoethanolamine in 2-methoxyethanol was subsequently repeatedly deposited onto the CuO nanowires by spin coating. The formation of ZnO nanorod assemblies was controlled by varying the number of coatings. The average diameter of the ZnO rods was determined to be ～600 nm.     

Evaluation of dioxin-like activities in settled house dust from Vietnamese E-waste recycling sites: relevance of polychlorinated/brominated dibenzo-p-dioxin/furans and dioxin-like PCBs

Few studies have investigated the human exposure to the ensemble of dioxin-related compounds (DRCs) released from uncontrolled e-waste recycling, especially from a toxic effect standpoint. This study evaluated the TCDD toxic equivalents (TEQs) in persistent extracts of settled house dust from two Vietnamese e-waste recycling sites (EWRSs) using the Dioxin-Responsive Chemically Activated LUciferase gene eXpression assay (DR-CALUX), combined with chemical analysis of PCDD/Fs, DL-PCBs, PBDD/Fs, and monobromo PCDD/Fs to determine their TEQ contribution. The CALUX-TEQ levels in house dust ranged from 370 to 1000 pg g(-1) in the EWRSs, approximately 3.5-fold higher than in the urban control site. In EWRS house dust, the concentrations of the unregulated PBDFs were 7.7-63 ng g(-1), an order of magnitude higher than those of regulated DRCs (PCDD/Fs and DL-PCBs), and PBDFs were also principal CALUX-TEQ contributors (4.2-22%), comparable to PCDD/Fs (8.1-29%). The CALUX-TEQ contribution of DRCs varied, possibly depending on thermal processing activities (higher PCDD/F-TEQs) and PBDE content in the waste (higher PBDF-TEQs). However, the percentage of unknown dioxin-like activities was high in all dust samples, indicating large contribution from unidentified DRCs and/or synergy among contaminants. Estimates of TEQ intake from dust ingestion suggest that children in the EWRSs may be adversely affected by DRCs from dust.     

Crystal structure refinement of A-type carbonate apatite by X-ray powder diffraction

Complete carbonate substitution at A-sites (OH) of low-crystallinity hydroxyapatite with near stoichiometric composition (i.e. Ca/P ratio of 1.65) was achieved by heating in a dry carbon dioxide flow at 1173 K for 64 h. The carbonate content was analysed by thermogravimetry and infrared absorption spectrometry; the chemical composition was determined to be Ca_9.9±0.1(PO₄)_6.00±0.1(CO₃)_0.9±0.1. The crystal structure and atomic configuration of the carbonate ion were determined by Rietveld refinement using X-ray powder diffraction data. This analysis revealed that the space group was monoclinic Pb with a = 0.9571(1), b = 1.9085(2), c = 0.68755(3) nm and γ = 119.847(7)°. The triangular planes of the carbonate ions were oriented parallel to the c- and a-axes, though there were two independent carbonate sites with occupancy factors of 0.56(1) and 0.34(1), where the triangles were oppositely rotated about the corresponding carbon atoms by 23° and −18°, respectively. The arrangement of the ions was disordered, which explains the lack of a thermal phase transition below 623 K.     

Improvement in light harvesting and performance of P3HT:PCBM solar cell by using 9,10-diphenylanthracene

We have studied the effect of 9,10-diphenylanthracene (DPA) as a conjugated dye with different concentrations on light harvesting and performance of solar cell composed from poly (3-hexylthiophene) (P3HT):[6,6]-phenyl-C₆₁butyric acid methyl ester (PCBM) blend films. The dye concentration effect was investigated with optical absorption spectroscopy, photocurrent spectroscopy, and current density-voltage characteristic measurements on devices under AM1.5 white light illumination with intensity of 100 mW/cm². The incorporation of the conjugated DPA inside P3HT:PCBM blend improved the light harvesting, slightly, and conjugation length indicated from the optical absorption and external quantum efficiency spectra. By adding specific amounts of the DPA into P3HT:PCBM blend, the external quantum efficiency and solar cell performance parameters, i.e., short circuit current density, fill factor, and power conversion efficiency improved as a result of improvement in the light harvesting and charge carrier transfer taking place between P3HT and PCBM through the conjugated DPA molecules.     

Segmentation of the response of a neuronal network into clusters with similar activity

An important question in the analysis of the electrical activity of a large population of neurons is the detection of families of neurons having a similar pattern of electrical activity, so that the original neuronal network can be decomposed into distinct clusters. This paper describes how it is possible to segment the activity of a neuronal network into clusters of sites with similar patterns of activity. Such a segmentation gives insight on how the network is organized, on how it functions and on its behavior as a dynamical system. Simulation and experiments on real data suggest that the correct approach to solve these problems must use multiresolution analysis. The method has been applied to both synthetic data and real data coming from a network of dissociated cortical neurons from neonatal rat brain.     

Continuous monitoring of developmental activity changes in cultured cortical networks

During development, cortical neurons show highly synchronized spontaneous activity. This spontaneous activity probably reflects the mechanisms underlying proper network formation regulated by activity‐dependent synaptic modification. To see long‐term transitions in this spontaneous activity, we constructed a microelectrode‐array (MEA)‐based continuous monitoring system. Rat cortical neurons were cultured on MEAs with 64 embedded electrodes and maintained in a conventional CO₂ incubator. A perfusion system for medium changes and recording setup for electrical signals were directly connected to the MEA in the incubator. Culture medium was continuously perfused at a very slow rate (0.1 ml/h), which was quite effective at maintaining constant conditions without contamination. Using this system, we succeeded in recording spontaneous activity of cultured cortical networks, almost continuously from 5 days to more than 1 month in vitro. It was revealed that the spontaneous activity patterns showed transition from simple synchronized bursts to a complex mixture of multiple patterns, separated by a brief silent period at approximately 2 weeks in vitro. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(4): 28–37, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10216