Adaptive divided difference filtering for simultaneous state and parameter estimation

A novel adaptive version of the divided difference filter (DDF) applicable to non-linear systems with a linear output equation is presented in this work. In order to make the filter robust to modeling errors, upper bounds on the state covariance matrix are derived. The parameters of this upper bound are then estimated using a combination of offline tuning and online optimization with a linear matrix inequality (LMI) constraint, which ensures that the predicted output error covariance is larger than the observed output error covariance. The resulting sub-optimal, high-gain filter is applied to the problem of joint state and parameter estimation. Simulation results demonstrate the superior performance of the proposed filter as compared to the standard DDF.     

Catalytic activity of cobalt deposited on nanostructured poly(p-xylylene) films

Nanostructured and planar films of poly(p-xylylene) (PPX) are fabricated by an oblique angle polymerization method and coated with cobalt using electroless deposition. The catalytic activity of cobalt coated on the nanostructured and planar PPX films is studied by measuring the rate of hydrogen evolution by the hydrolysis of alkaline-stabilized sodium borohydride (NaBH₄) solution. The hydrogen release rate data show an asymptotic increase for the structured PPX film as a function of the electroless bath time, but the planar PPX films show a lower catalytic activity due to the inefficiency of cobalt deposition. The hydrogen release rate of the cobalt-coated nanostructured PPX film shows a rate between 2000 and 4250 mL(g min)⁻¹ (i.e., rate of hydrogen gas per cobalt mass at room temperature and pressure), which is comparable to the values obtained on platinum, and ruthenium systems.     

An immunoelectrochemical sensor for salivary cortisol measurement

An immunoelectrochemical sensor based on alkaline phosphatase (AP) enzyme for determination of salivary cortisol concentration is reported. Microfabricated Au electrodes encased in a microfluidic chamber were functionalized to immobilize the cortisol capture antibodies. The reaction product p-nitrophenol (pNP) generated by reacting the AP enzyme attached to the cortisol antigen via detector antibodies with the p-nitrophenyl phosphate (pNPP) solution. pNP was detected as an oxidative peak between 0.9 and 1.1 V (vs. Ag pseudo-reference electrode) using cyclic voltammetry (CV) at room temperature. The magnitude of the peak varies linearly with the cortisol concentration, and was used to quantify the concentration of cortisol in real saliva samples. This immunoelectrochemical detection method accurately measured cortisol in the collected saliva samples achieved to a concentration of 0.76 nmol/L with an incubation time of 10 min. We demonstrate successfully the approach for establishing diurnal cortisol concentration behavior for clinical purposes with numerous advantages: a much higher throughput capability, significantly lower amounts of the sample, sub-pmol/L range sensitivity, higher resolution at low mass ranges, and easy to use.     

Sequential Bayesian decoding with a population of neurons

Population coding is a simplified model of distributed information processing in the brain. This study investigates the performance and implementation of a sequential Bayesian decoding (SBD) paradigm in the framework of population coding. In the first step of decoding, when no prior knowledge is available, maximum likelihood inference is used; the result forms the prior knowledge of stimulus for the second step of decoding. Estimates are propagated sequentially to apply maximum a posteriori (MAP) decoding in which prior knowledge for any step is taken from estimates from the previous step. Not only do we analyze the performance of SBD, obtaining the optimal form of prior knowledge that achieves the best estimation result, but we also investigate its possible biological realization, in the sense that all operations are performed by the dynamics of a recurrent network. In order to achieve MAP, a crucial point is to identify a mechanism that propagates prior knowledge. We find that this could be achieved by short-term adaptation of network weights according to the Hebbian learning rule. Simulation results on both constant and time-varying stimulus support the analysis.     

Open-circuit to short-circuit switching: method for lifetime measurement in solar cells

A new method is suggested for measurement of lifetime of photoinjected carriers in the base layer of a p-n junction solar cell. The cell is switched from the open-circuit to the shortcircuit mode of operation by using a negative voltage pulse. C.R.O. trace of the output voltage pulse provides a direct means for lifetime measurement.     

Airway mechanics, gas exchange, and blood flow in a nonlinear model of the normal human lung

A model integrating airway/lung mechanics, pulmonary blood flow, and gas exchange for a normal human subject executing the forced vital capacity (FVC) maneuver is presented. It requires as input the intrapleural pressure measured during the maneuver. Selected model-generated output variables are compared against measured data (flow at the mouth, change in lung volume, and expired O2 and CO2 concentrations at the mouth). A nonlinear parameter-estimation algorithm is employed to vary selected sensitive model parameters to obtain reasonable least squares fits to the data. This study indicates that 1) all three components of the respiratory model are necessary to characterize the FVC maneuver; 2) changes in pulmonary blood flow rate are associated with changes in alveolar and intrapleural pressures and affect gas exchange and the time course of expired gas concentrations; and 3) a collapsible midairway segment must be included to match airflow during a forced expiration. Model simulations suggest that the resistances to airflow offered by the collapsible segment and the small airways are significant throughout forced expiration; their combined effect is needed to adequately match the inspiratory and expiratory flow-volume loops. Despite the limitations of this lumped single-compartment model, a remarkable agreement with airflow and expired gas concentration measurements is obtained for normal subjects. Furthermore, the model provides insight into the important dynamic interactions between ventilation and perfusion during the FVC maneuver.     

Image quality assessment based on a degradation model

We model a degraded image as an original image that has been subject to linear frequency distortion and additive noise injection. Since the psychovisual effects of frequency distortion and noise injection are independent, we decouple these two sources of degradation and measure their effect on the human visual system. We develop a distortion measure (DM) of the effect of frequency distortion, and a noise quality measure (NQM) of the effect of additive noise. The NQM, which is based on Peli's (1990) contrast pyramid, takes into account the following: 1) variation in contrast sensitivity with distance, image dimensions, and spatial frequency; 2) variation in the local luminance mean; 3) contrast interaction between spatial frequencies; 4) contrast masking effects. For additive noise, we demonstrate that the nonlinear NQM is a better measure of visual quality than peak signal-to noise ratio (PSNR) and linear quality measures. We compute the DM in three steps. First, we find the frequency distortion in the degraded image. Second, we compute the deviation of this frequency distortion from an allpass response of unity gain (no distortion). Finally, we weight the deviation by a model of the frequency response of the human visual system and integrate over the visible frequencies. We demonstrate how to decouple distortion and additive noise degradation in a practical image restoration system     

Observation of Crack Propagation in Glass Using X-ray Phase Contrast Imaging

High-speed X-ray phase contrast imaging synchronized with a Kolsky bar apparatus was utilized to investigate the cracking behavior of a borosilicate glass, a soda lime glass, and a glass ceramic in front of a cylindrical projectile with an impact velocity of 5 ms⁻¹. For each material, three different surface conditions were prepared for the impacted edge of the specimen. Angular cracking was observed in front of the projectile for borosilicate glass. For soda lime glass, straight cracking was observed. For glass ceramic, curved cracking was observed in front of the projectile. Cracking behavior was observed to be independent of the surface condition on the impacted edge.     

Decolourization of Methyl Orange using Fenton-like mesoporous Fe(2)O(3)-SiO(2) composite

Rapid decolourization of Methyl Orange by Fenton-like mesoporous Fe(2)O(3)-SiO(2) catalyst has been reported. The effect of various parameters such as initial pH, initial H(2)O(2) concentration, Fe content in the catalyst and initial dye concentration on decolourization process were studied. The results show that 20mg of mesoporous Fe(2)O(3)/SiO(2) composite (with Si/Fe=10) was sufficient to decolourize 0.6 mg/ml of Methyl Orange in presence of 2 ml of H(2)O(2) at an initial pH of 2.93 within 20 min. The pH range for effective decolourization (≥90%) was found to be 1-3. Leaching tests indicated that the activity of the catalyst was almost unaffected up to three consecutive cycles although ≤0.2 ppm of Fe ion was leached into treated water in each run.