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.     

High-Temperature Indentation Studies on the {110} Plane of Single-crystal Magnesium Oxide

The indentation behavior (Vickers) of Single-crystal MgO was studied as a function of temperature (20° to 1000°C). Indentations were made on the {110} plane, with the indents oriented such that one indent diagonal was parallel to the 〈001〉 direction. Using etchant techniques, the dislocation etch pit structures were examined both in the plane of the indentation and in cross section. All the observed slip traces were found to be consistent with primary slip ({110}〈 1 10〉), with no evidence of secondary slip, even at 1000°C. Radial cracking was observed only at the pair of indent corners joined by the indent diagonal parallel to 〈001〉. The crack length increased with temperature ( T ) for indentations conducted at T < 800°C. For indents made at 800°C or higher, however, no cracking occurred. These results are discussed both with respect to an existing slip-induced crack nucleation model, and the change in crack driving force and toughness with indentation temperature.     

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.     

Enzymatic process for extracting oil and protein from rice bran

Enzymatic extraction of oil and protein from rice bran, using a commercial protease (Alcalase), was investigated and evaluated by response surface methodology. The effect of enzyme concentration was most significant on oil and protein extraction yields, whereas incubation time and temperature had no significant effect. The maximal extraction yields of oil and protein were 79 and 68%, respectively. Further, the quality of oil recovered from the process in terms of free fatty acid, iodine value, and saponification value was comparable with solvent-extracted oil and commercial rice bran oil, but the peroxide value was higher.     

Synthesis of Biopolymer‐Derived Zirconium Carbide Powder by Facile One‐Pot Reaction

Zirconium carbide (ZrC) was synthesized by polycondensation and carbothermal reduction reactions from an organic–inorganic hybrid complex. A natural biopolymer Gum Karaya (GK) and zirconyl oxychloride octahydrate (ZOO) were used as the sources of carbon and zirconium, respectively. FTIR of as‐synthesized dried complexes revealed formation of Zr–O. Pyrolysis of the complexes at 1200°C/1 h under argon resulted in tetragonal and monoclinic zirconia which after heat treatment at 1400°C–1550°C transformed to zirconium carbide. Thermal analysis shows that the GK–ZOO complexes lost less mass than the pristine GK to 600°C. The intensity of exothermic decomposition decreases and shifted to higher temperature for the hybrid complexes indicating that zirconia induced thermal stability. A maximum ZrC yield of ~60 wt% is obtained for the intermediate GK–ZOO ratio of 1:2. Particles pyrolyzed for 1 h at 1550°C were coarser (5–10 μm) with flakes for lower GK–ZOO weight ratio, but were spheroidal with narrow size distribution (~1 μm) with increasing GK–ZOO weight ratio.     

Study of dynamic viscoelastic behavior of polystyrene films on addition of oleic acid

We have investigated the dynamic mechanical behavior of films prepared from polystyrene solutions in chloroform containing oleic acid as an additive. The response of the films has been measured by means of a dynamic mechanical analyzer operated in tension mode over a temperature range of 30-150 °C, using sinusoidal motion with a maximum strain of 0.04% and a frequency of 2 Hz. The long term creep behavior has also been evaluated. Our results show that the oleic acid softens and disentangles the polystyrene chains backbone, resulting in a decrease in the dynamic mechanical properties of the polystyrene films.