Partially embedded highly dispersed Pt nanoparticles in mesoporous carbon with enhanced leaching stability

Mesoporous carbon materials with highly dispersed platinum nanoparticles have been prepared by a one-pot template-assisted synthesis route. Different amounts of hexachloroplatinic acid were added to a silica-sucrose mixture and heat treated in nitrogen and hydrogen flow. The obtained Pt/C materials have been investigated by means of transmission electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption at 77 K, thermo gravimetric analysis, powder X-ray diffraction, and infrared monitored CO adsorption experiments. Further, Pt/C materials have been used in the liquid-phase oxidation of glucose to gluconic acid to determine their catalytic performance. It has been found that the platinum nanoparticles are partially embedded in the carbon material. However, the Pt sites are accessible for adsorption, and the Pt/C catalysts show good catalytic activity compared to materials prepared by impregnation/reduction. The partial embedding of the Pt nanoparticles accounts for the enhanced leaching stability of the Pt phase during long-term use.     

MONITORING POLYCYCLIC AROMATIC COMPOUNDS IN ENVIRONMENTAL AND WORKPLACE SAMPLES USING CONVENTIONAL METHODS AND THE AMES MUTAGENICITY ASSAY OF THEIR NITRATED DERIVATIVES

The development of sensitive methods for monitoring polycyclic aromatic compounds (PACs) has been a central focus of industrial hygiene studies in those industries where workers are exposed to petroleum oils, bitumen fumes or fuel combustion products. The work reported here focuses on one aspect of that effort—workplace monitoring of airborne PAC levels in the hot-mix asphalt paving industry. During the manufacture, transport, and roadway application of hot-mix asphalt (HMA), workers are exposed to low levels of bitumen fumes emanating from the hot product. Over the last twenty-five years, concerns about the health effects of these exposures have prompted numerous studies of the airborne levels of asphalt fumes in the workplace. By and large, these studies have shown that PAC exposures are extremely low—often below the detection limits of standard analytical techniques. For the present study, we have used standard industrial hygiene methods, together with a newer, biologically based assay called the Nitration Assay to measure relative ambient levels of fumes and/or PACs in various paving workplace settings. The latter assay was also used to test bitumen fumes generated in the laboratory by a new “microfuming” technique and to determine specific activities of the 16 PAHs designated by the US EPA as priority pollutants. The Nitration Assay takes advantage of two properties of 3–7-ring PACs: the ease with which they can be chemically nitrated and the high mutagenic potency of the nitrated products in the Ames Salmonella mutagenicity assay. Measurements of fumes and nitratable PAC levels on seven different hot-mix paving jobs showed reasonable correlations between the various methods, as well as patterns of exposure consistent with proximity to fume source.     

Urinary Bladder Cancer Susceptibility Markers. What Do We Know about Functional Mechanisms?

Genome-wide association studies (GWAS) have been successful in the identification of the several urinary bladder cancer (UBC) susceptibility loci, pointing towards novel genes involved in tumor development. Despite that, functional characterization of the identified variants remains challenging, as they mostly map to poorly understood, non-coding regions. Recently, two of the UBC risk variants (PSCA and UGT1A) were confirmed to have functional consequences. They were shown to modify bladder cancer risk by influencing gene expression in an allele-specific manner. Although the role of the other UBC risk variants is unknown, it can be hypothesized—based on studies from different cancer types—that they influence cancer susceptibility by alterations in regulatory networks. The insight into UBC heritability gained through GWAS and further functional studies can impact on cancer prevention and screening, as well as on the development of new biomarkers and future personalized therapies.     

Rate mechanism and dislocation generation in high density polyethylene and other semicrystalline polymers

The aim of the paper was to use recent experimental dislocation data for the development and testing of a dislocation mediated strength model based on that introduced by Scogna and Register for semicrystalline polymers. It is shown that the model can successfully describe measured and evaluated data of high density polyethylene (PE-HD) on the flow stress as function of strain rate and temperature. Similar coincidences of model fit with experimental yield stress data from literature for polypropylene and polyethylene-ethylenemethacrylic acid co-polymers (E/MAA) were found which suggests prevailing of dislocation mediated plasticity mechanisms also in these materials. It also turned out that two parameters of the model – namely the dislocation density and the lamella size – are not determined by the molecular chemistry but by the conditions of processing and/or sample preparation. Therefore the model allows for a reliable estimation of the dependence of the yield stress on these conditions.     

Suboptimal control for the nonlinear quadratic regulator problem

In this paper a suboptimal solution to the nonlinear quadratic regulator and tracking problem with infinite final time is investigated. The plant may well be time-varying and nonlinear in state and control. The plant is represented by an apparent linearization and the suboptimal control at any given instant is determined by the optimal control law for the linear model valid at the particular instant.It is shown that with certain restrictions the suboptimal control law exists and is a continuous function of state and time. It is further shown that this suboptimal control law results in a closed-loop system which is asymptotically stable in a sufficiently small region.A computational method for obtaining the suboptimal control law is presented which reduces the amount of computations significantly. This suboptimal control law, based on the solution to the linear regulator problem, involves the steady-state solution to the Riccati differential equation. This matrix is expanded in a Taylor series. The terms of this series can be calculated recursively off-line and thus the problem of repeatedly solving the Riccati equation circumvented. It is shown that the control law obtained by using any finite number of terms in this series preserves the stability of the system.     

Estimation of reinforcement in compatibilized polypropylene nanocomposites by extensional rheology

Structural characterization in polymer nanocomposites is usually performed using X‐ray scattering and microscopic techniques, whereas the improvements in processing and mechanical properties are commonly investigated by rotational rheometry and tensile testing. However, all of these techniques are time consuming and require quite expensive scientific equipment. It has been shown that a fast and efficient way of estimating the level of reinforcement in polymer nanocomposites can be performed by melt extensional rheology, because it is possible to correlate the level of melt strength with mechanical properties, which reflect both the 3D network formed by the clay platelets/polymer chains as well as final molecular structure in the filled system. The physical network made of silicate filler and polymer matrix has been evaluated by X‐ray diffraction and transmission electron microscopy. Extensional rheometry and tensile testing have been used to measure efficiency of the compatibilizer amount in a polypropylene‐nanoclay system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of pH on the survival of Listeria innocua in calcium ascorbate solutions and on quality of fresh-cut apples

Fresh-cut apple slices were dipped in calcium ascorbate (CaA) solution at pH values ranging from 2.5 to 7.0 to inhibit browning. After treatment, the cut apples were stored at 4 and 10 degrees C for up to 21 days. Color and texture of the apples were determined on days 1, 14, and 21. In a separate experiement, the pH of CaA solution was adjusted with acetic acid to six different pH levels, and the solution was inoculated with Listeria innocua. The survival of the bacterium and the stability of CaA were determined at 0, 20, and 96 h. The cut apples maintained fresh quality when the pH of the CaA solution was above 4.5, but slight discoloration of apple slices dipped in pH 4.5 solution was observed after 14 days at 10 degrees C. At pH 5.0, the CaA dip maintained the quality of the apples at both temperatures for at least 21 days. The L. innocua population was reduced by 4 to 5 log CFU/ml at pH 4.5 after 96 h. At pH 5, the bacterial population in the CaA solution was reduced by approximately 2 log CFU/ml during the same period. The CaA solution was stable at pH 5 for at least 96 h. Reduction of the pH to between 4.5 and 5.0 might reduce the risk of foodborne illness due to consumption of fresh-cut apples treated with a CaA solution contaminated with Listeria.     

Investigation of the impact of stacking pressure on a double-layer supercapacitor

There are two important steps necessary for the optimization of electrochemical double-layer capacitors (EDLC): maximizing the volumetric capacitance and minimizing the ohmic resistance. The application of force during the assembly of an EDLC cell is one way to achieve this optimization. The effect of the application of force on the performance characteristics of EDLC cells, assembled using porous activated carbon electrodes, was determined. It was shown that applying force to the body of the cell during assembly only provides a significant increase in the performance of the EDLC with the initial application. The results showed that any increase in the applied force beyond that initial stage does not result in a subsequent increase in performance and can result in a substantial decrease in the performance characteristics of the EDLC cell. Furthermore, it was concluded that the substantial decrease shown was attributed to an alteration of the physical structure of the porous material, which produced significant decreases in the accessible surface area and the material resistance of the activated carbon electrodes.     

Application of the psychophysical law to performance evaluation.

In the area of job performance, it was hypothesized that evaluations, e.g., "poor" to "excellent," were based ont the observation of "performance specimens" where a performance specimen is defined as "an incident of relevant performance which at the time of observation was classed as uncommonly effective or uncommonly ineffective." It was further hypothesized that the psychophysical law (y = kxn) would describe the relationship between the number of specimens observed (x) and resulting evaluations (y) of performance. Finally, it was hypothesized that Steven's criterion for prothetic continua would be satisfied—concave downward curve when ratio estimation scale values for sets of performance specimens are plotted against corresponding category scale values. Using simulated performance ratings as well as actual performance evaluations (performance ratings of apprentices, professors, supervisors, and executives) the above hypotheses appear to have been verified. (PsycINFO Database Record (c) 2010 APA, all rights reserved)