Pulse combustion: The mechanisms of NOx production

A study has been performed to elucidate the fundamental mechanisms controlling the production of NO in a Helmholtz-type pulse combustor. Cycle-resolved measurements of velocity and temperature in the combustion chamber were made. These measurements were combined with the Zeldovich NO formation mechanism to explain the mechanism responsible for the low NO formation found in pulse combustors.

The mechanism responsible for low NO formation found in pulsating flow as compared to nonpulsating flow was found to be a short residence time at high temperature. Three different possible mechanisms for this short residence time were investigated: (1) hot products from combustion are cooled by mixing with the cooler exhaust gases entering the combustion chamber from the tail pipe, thus quenching the NO formation reaction (“Automatic Exhaust Gas Recirculation”), (2) hot combustion products are quickly cooled by mixing with the incoming cold reactants, and (3) residual products with a lower overall temperature (due to an increased rate of heat transfer in the combustion chamber) readily mix with hot products producing a short residence time at high temperature. It is shown that the mechanism responsible for the low NO emission in pulse combustors is a result of item 3. A short residence time at high temperature is caused by rapid mixing with cooler residual gases that are lower in temperature due to increased rates of heat transfer in the combustion chamber.     

Family group cognitive–behavioral preventive intervention for families of depressed parents: 18- and 24-month outcomes.

Objective: In a long-term follow-up of a randomized controlled trial (Compas et al., 2009) to examine the effects at 18- and 24-month follow-ups of a family group cognitive–behavioral (FGCB) preventive intervention for mental health outcomes for children and parents from families (N = 111) of parents with a history of major depressive disorder (MDD). Method: Parents with a history of MDD and their 9- to 15-year-old children were randomly assigned to a FGCB intervention or a written information comparison condition. Children's internalizing, externalizing, anxiety/depression, and depressive symptoms; episodes of MDD and other psychiatric diagnoses; and parents' depressive symptoms and episodes of MDD were assessed at 18 and 24 months after randomization. Results: Children in the FGCB condition were significantly lower in self-reports of anxiety/depression and internalizing symptoms at 18 months and were significantly lower in self-reports of externalizing symptoms at 18 and 24 months. Rates of MDD were significantly lower for children in the FGCB intervention over the 24-month follow-up (odds ratio = 2.91). Marginal effects were found for parents' symptoms of depression at 18 and 24 months but not for episodes of MDD. Conclusions: Support was found for a FGCB preventive intervention for children of parents with a history of MDD significantly reducing children's episodes of MDD over a period of 2 years. Significant effects for the FGCB intervention were also found on internalizing and externalizing symptoms, with stronger effects at 18- than at 24-month follow-up. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

DAC应用指南

介绍了DAC的一些典型应用:如CD唱机中的音频DAC,校准和电机控制,说明DAC就像ADC和运算放大器一样,在许多应用中正在及继续发挥关键作用,不会因数字时代而消失。     

Sorption of selenium(IV) and selenium(VI) to mackinawite (FeS): effect of contact time, extent of removal, sorption envelopes

Higher concentrations (127, 253 μM) of Se(IV) at pH 8 were completely removed by 0.5 g/L FeS within 120 min. Removal of Se(VI) by FeS at pH 8 was less extensive than removal of Se(IV). Only 10% of the Se(VI) was removed by 1 g/L FeS within 1h. Removal patterns for Se by FeS depend on pH. Removal patterns of Se at pH 7 and pH 8 were best described by BET models for Se(IV) and Freundlich models for Se(VI), while removal patterns of both at pH 9 and 10 were best described by Langmuir models. Sulfate at 1 and 10 mM had negligible effect on removal of Se(IV) by FeS, while sulfate had little effect on removal of Se(VI) by FeS, but there was some indication that sulfate promoted removal of Se(VI) at intermediate concentrations. The test for the effect of pH on sorption of Se(IV) by FeS showed nearly complete removal at all but the high initial pH. When pH was raised back to initial value, greater removals were observed than initially. Mixtures of Se(VI) and FeS showed moderate removal at low pH, a minimum removal near pH 6 and nearly complete removal at high pH. Very high stability was observed with negligible release as pH decreased.     

Beta zeolite supported sol-gel TiO2 materials for gas phase photocatalytic applications

Beta zeolite supported sol-gel TiO(2) photocatalytic materials were prepared according to a sol-gel route in which high specific surface area Beta zeolite powder was incorporated into the titanium isopropoxide sol during the course of the sol-gel process. This led to an intimate contact between the zeolite surface and the TiO(2) precursors, and resulted in the anchorage of large amounts of dispersed TiO(2) nanoparticles and in the stabilization of TiO(2) in its anatase form, even for high TiO(2) wt. contents and high calcination temperatures. Taking the UV-A photocatalytic oxidation of methanol as gas phase target reaction, high methanol conversions were obtained on the Beta zeolite supported TiO(2) photocatalysts when compared to bulk sol-gel TiO(2), despite lower amounts of TiO(2) within the photoactive materials. The methanol conversion was optimum for about 40 wt.% TiO(2) loading and calcination temperatures of 500-600°C.     

Accelerated reliability testing of highly aligned single-walled carbon nanotube networks subjected to DC electrical stressing

We investigate the electrical reliability of nanoscale lines of highly aligned, networked, metallic/semiconducting single-walled carbon nanotubes (SWCNTs) fabricated through a template-based fluidic assembly process. We find that these SWCNT networks can withstand DC current densities larger than 10 MA cm(-2) for several hours and, in some cases, several days. We develop test methods that show that the degradation rate, failure predictability and total device lifetime can be linked to the initial resistance. Scanning electron and transmission electron microscopy suggest that fabrication variability plays a critical role in the rate of degradation, and we offer an empirical method of quickly determining the long-term performance of a network. We find that well-fabricated lines subject to constant electrical stress show a linear accumulation of damage reminiscent of electromigration in metallic interconnects, and we explore the underlying physical mechanisms that could cause such behavior.     

A phenomenological analysis of Mode I fracture of adhesively-bonded pultruded GFRP joints

The fracture behavior of adhesively-bonded pultruded joints was experimentally investigated under Mode I loading using double cantilever beam specimens. The pultruded adherends comprised two mat layers on each side with a roving layer in the middle. An epoxy adhesive was used to form the double cantilever beam specimen. The pre-crack was introduced in three different depths in the adherend in order to induce crack initiation and propagation between different layers and thus investigate the effect of these different crack paths on the strain energy release rate. Short-fiber and roving bridging increased the fracture resistance during crack propagation. Specific levels of critical strain energy release rates could be attributed to each of the crack paths, with their levels depending on the amount of short-fiber bridging and the presence of a roving bridge. The different levels of critical strain energy release rate could be correlated to the morphology of the fracture surface and the strain energy release rate can thus be determined visually without any measurement.     

Three dimensional analysis of self-structuring organic thin films using time-of-flight secondary ion mass spectrometry

Selective sub-micrometer structuring of phase-separating organic semiconductor materials has recently got into focus for providing the opportunity of further improvements in optoelectronic device applications. Here we present a 3D-time-of-flight secondary ion mass spectrometry (3D-TOF-SIMS) depth profiling investigation on spin-coated blends consisting of [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) and a cationic cyanine dye (1,1′-diethyl-3,3,3′,3′-tetramethylcarbocyanine iodide). TOF-SIMS provides the required lateral and depth resolution to resolve material and molecular inhomogeneities and phase separation in the blend. The data are illustrating the three-dimensional arrangement of the substances involved and confirm results of earlier studies using atomic force microscopy, UV-vis spectroscopy and x-ray photoelectron spectroscopy, and which have shown well distinguishable morphological features. The formation of this domain structure has been found to be dependent on the absolute as well as the individual film thickness, in accordance with models based on thin liquid two-layer films. Honey-comb like primary structures with micrometer dimension were found in samples containing small amounts of dye molecules in the deposition solution. In this case a thin dye deposit on PCBM was detected, which is well separated from the dye layer at the substrate. For this type of sample, we discuss an extended model of film formation based on partial depletion of dye molecules during film solidification, resulting in two individual dye layers.     

The regionalization of international contracting and its implications for models of construction spending

This paper documents an increasing regionalization of overseas contracting during the 1980s and 1990s. This involved a greater share within richer countries, particularly of intra‐European work. This evidence challenges suggestions that middle‐income countries are particularly appropriate destinations of overseas investment by developed country contractors. The paper therefore re‐evaluates the model underlying such predictions, which relates construction spending to economic development. Reconsidering its empirical basis, it argues that the association between overall levels of per capita income and levels of construction spending is too weak to be of practical utility. It stresses the possibility of different routes to economic development and that this often remained an uncertain process and one within which levels of construction output varied widely. It therefore concludes that research should be informed by a broader political economy approach.     

Community renewal and large public housing estates

Abstract

The extent of social disadvantage in local neighbourhoods has come to the fore in recent years, partly as a result of the problems that State Housing Authorities have faced in managing the concentrations of socially marginalised populations on larger public housing estates. However, a wider understanding of the processes at play in these neighbourhoods is needed to inform policy development. We consider the evolution of local renewal policy in New South Wales at the present time and suggest potential policy options for the future.