Gas phase dielectric barrier discharge induced reactive species degradation of 2,4-dinitrophenol

The degradation of 2,4-dinitrophenol (DNP) in aqueous solution by reactive species generated from gas-phase dielectric barrier discharge (DBD) was investigated. The effects of various parameters such as gas flow rate, input power and initial concentration of DNP on the degradation of DNP were further examined. The reactive species generated from the DBD system were measured, and the DNP degradation pathway was analyzed. The results indicated that an aqueous solution of 100 mg L⁻¹ DNP was 95.0% degraded and 51% of TOC was removed in 60 min treatment at 60 W input power and 7 L min⁻¹ gas flow rate. The degradation kinetics of DNP was determined to be a pseudo-first-order reaction, which was mainly dependent on the input power, gas flow rate and initial DNP concentrations. The OH· radical was the major reactive species, and played a significant role for the DNP degradation in this study as humid air was used as the gas source.     

Degradation mechanism of Ti---Zr---V---Mn---Ni metal hydride electrodes

The degradation mechanism of Ti---Zr---V---Mn---Ni metal hydride electrodes was investigated because they rapidly degraded within 10 cycles despite having a high discharge capacity of 360464 mAh g⁻¹ at the first cycle. It was observed that Ti-oxide formed and grew on the surface of the alloy powder in the early and later stages of degradation using the scanning electron microscopy (SEM) and the auger electron spectroscopy (AES) analyses. Also, it was found that the contact and the reaction resistances for the electrochemical hydrogenation reaction increased as the number of cycles increased using the EIS (Electrochemical Impedance Spectroscopy) analysis. It was suggested that the reason for the degradation of Ti-based hydride electrodes was because it was extremely difficult for hydrogenation to occur through the Ti-oxide film into the inner part of the alloy. This was due to a high polarization resistance during the electrochemical hydrogenation reaction, which included the resistance of the hydrogen diffusion through the Ti-oxide film and the resistance of the electron conduction between Ti-oxide on the surface of the alloy powder and external circuits, as well as between the Ti-oxide layers on the surface of the alloy powders.     

On preventive maintenance policy of a critical reliability level for system subject to degradation

Conventional preventive maintenance (PM) policies generally hold same time interval for PM actions and are often applied with known failure modes. The same time interval will give unavoidably decreasing reliabilities at the PM actions for degradation system with imperfect PM effect and the known failure modes may be inaccurate in practice. Therefore, field managers would prefer policy with an acceptable reliability level to keep system often at a good state.A PM policy with the critical reliability level is presented to address the preference of field managers. Through assuming that system after a PM action starts a new failure process, a parameter so-called degradation ratio is introduced to represent the imperfect effect. The policy holds a law that there is same number of failures in the time intervals of various PM cycles, and same degradation ratio for the system reliability or benefit parameters such as the optimal time intervals and the hazard rates between the neighboring PM cycles. This law is valid to any of the failure modes that could be appropriately referred as a ‘general isodegrading model’, and the degradation ratio as a ‘general isodegrading ratio’. In addition, life cycle availability and cost functions are derived for system with the policy. An analysis of the field data of a loading and unloading machine indicates that the reliability, availability and cost in life cycle might be well modeled by the present theory and approach.     

Accelerated degradation in amorphous silicon solar cells by a combination of current injection and light insolation

A new degradation technique for amorphous silicon solar cells comprising of a combination of current injection and insolation has been developed. Compared to the conventional light degradation technique, current-induced degradation which involves forward biased current stress, results in a lower stabilized cell parameters including efficiency. This stabilized efficiency is, however, independent of the amount of current injected. The excess degradation is recovered under light illumination. The stabilized value of the conversion efficiency is within experimental error identical to that observed in long term, illumination only degradation. The method is fast, accurate and reliable. Its reliability has also been tested for single junction solar cells having intrinsic layers of different band gaps, as well.     

Crystallization and melting behaviour of photodegraded polypropylene - I. Chemi-crystallization

An investigation has been conducted into the effects of photodegradation on the crystallinity and melting behaviour of isotactic polypropylene (PP). PP samples having different structural characteristics were prepared and exposed to ultraviolet radiation (u.v.) in the laboratory for periods of up to 48 weeks. The changes in crystallinity during exposure were followed by X-ray diffraction and differential scanning calorimetry (d.s.c.), whereas the chemical degradation of the specimens sampled was evaluated by gel permeation chromatography (g.p.c.) and Fourier transform infrared spectroscopy (f.t.i.r.). An increase in fractional crystallinity during u.v. exposure was noted for all types of samples studied, and the gain in crystallinity was usually between 6% and 7% and was virtually independent of the initial structure of the polymer. Measurements conducted at different depths within the test bars indicated that the fractional crystallinity increased during u.v. exposure due to crystal growth using molecule segments released by the scission of molecules (probably taut molecules). This process, called chemi-crystallization, is restricted by the chemical defects introduced into the molecules by the photodegradation. Possible mechanisms for the chemi-crystallization process are discussed. The melting thermograms of most types of samples exhibited single peaks with melting range increasing with exposure time. The broadening of the melting thermograms occurred during the period between the commencement and the completion of the chemi-crystallization. Secondary crystallization proceeded much more slowly in the interior of the test bars because of the limited oxygen supply, but the final crystallinity was the same as the plateau value, which was attained more rapidly when the material in the interior was exposed by machining away the surface prior to u.v. exposure. © 1997 Elsevier Science Ltd.     

Development and Validation of a Generalized Biaxial Hysteresis Model

Biaxial flexural interaction has been known to significantly affect, in many cases magnify, structural response in the inelastic range. Compared to uniaxial cases, the distinct characteristics of biaxial hysteresis curves often observed are negative stiffness and rounded corners of the curves near the time instants of unloading. Developed based on the widely used Bouc-Wen model, this paper presents a generalized biaxial smooth hysteresis model that takes into account the commonly observed hysteretic characteristics of strength and stiffness degradation, asymmetry in ultimate positive and negative forces, pinching, and those exclusively found in biaxial interaction. The capabilities of the developed model are illustrated by comparing the model results to the results of two cyclic and two quasi-static reinforced concrete column tests.     

Interpretation of Secant Shear Modulus Degradation Characteristics from Pressuremeter Tests

Nonlinear shear modulus degradation characteristics are of interest in many geotechnical engineering applications, such as ground deformation caused by seismic shaking and deep excavations in clay, weathered rock, and stabilized soil. This paper presents an approach to derive the secant shear modulus degradation characteristics from in situ pressuremeter tests, which is based on a digital filter algorithm. The algorithm is described, and data preparation procedures are presented. Use of the algorithm is illustrated by means of pressuremeter data for soils stabilized with deep mixing methods on the Boston central artery/tunnel (CA/T). The nonlinear secant shear modulus degradation characteristics from the digital filter approach are shown to be in good agreement with those from the curve fitting and transformed-strain approaches. They also compare favorably with the results of other in situ and laboratory tests performed in conjunction with the CA/T stabilized soils. The algorithm is implemented by a 26-line MATLAB code in an appendix of the paper.     

Numerical Method to Elucidate Likely Target Positions of Chlorine Removal in Anaerobic Sediments Undergoing Polychlorinated Biphenyl Dechlorination

Polychlorinated biphenyl (PCB) contamination in the United States is predominately from commercially manufactured Aroclor mixtures. These mixtures consist of approximately 150 congeners and are characterized by chlorination level and congener distribution profile, with some congeners maintaining a constant relative abundance across the chlorination levels. Once introduced into the environment, changes in congener profiles occur, in some cases altering the relative abundance of congeners correlated in the commercial Aroclors. The shifts in the relationships of the correlated congener pairs (trackers) are used to quantify the likelihood of natural remediation processes occurring in the anaerobic sediment and to identify positions where chlorine removal is likely. A numerical model for elucidating the most likely chlorine positions was developed, implemented, and tested on Hudson River sediment data. The model results show that flanked chlorines were most likely to have been removed, followed by meta chlorines. These results are consistent with those reported by laboratory investigation of Hudson River sediments. The findings suggest that the model can successfully determine the most likely positions of chlorine removal, even in the absence of a priori knowledge of the sediment contamination (source Aroclors) or the dechlorinating organisms. Thus the model can be applied, even where limited knowledge exists regarding the contamination source and the nature of the biogeochemical reactions affecting the fate of PCBs in a particular sediment system.