Effect of engine-based thermal aging on surface morphology and performance of Lean NOx Traps

A small single-cylinder diesel engine is used to thermally age model (Pt + Rh/Ba/γ-Al₂O₃) lean NO_x traps (LNTs) under lean/rich cycling at target temperatures of 600 °C, 700 °C, and 800 °C. During an aging cycle, fuel is injected into the exhaust to achieve reproducible exotherms under lean and rich conditions with the average temperature approximating the target temperature. Aging is performed until the cycle-average NO_x conversion measured at 400 °C is approximately constant. Engine-based NO_x conversion decreased by 42% after 60 cycles at 600 °C, 36% after 76 cycles at 700 °C and 57% after 46 cycles at 800 °C. The catalyst samples were removed and characterized by XRD and using a microreactor that allowed controlled measurements of surface area, precious metal size, NO_x storage, and reaction rates. Three aging mechanisms responsible for the deactivation of LNTs have been identified: (i) loss of dispersion of the precious metals, (ii) phase transitions in the washcoat materials, and (iii) loss of surface area of the storage component and support. These three mechanisms are accelerated when the aging temperature exceeds 850 °C—the γ to δ transition temperature of Al₂O₃. Normalization of rates of NO reacted at 400 °C to total surface area demonstrates the biggest impact on performance stems from surface area losses rather than from precious metal sintering.     

Temperature and pump power dependent photoluminescence characterization of MBE grown GaAsBi on GaAs

Bulk and quantum well GaAs_1?xBi_x/GaAs layers with Bi mole fractions from 0.02 to 0.10 are grown by molecular-beam epitaxy at temperatures ranging from 280 to 320?°C. The samples are characterized using temperature and pump-power dependent photoluminescence measurements covering 8–300?K and 1–250?mW (7–1,800?W/cm²), respectively. The results indicate that there is strong reduction in bandgap energy with the incorporation of small amounts of Bi and that GaAsBi most likely forms a weak type-I band alignment with GaAs.     

Iron(III)-mediated ATRP systems of n-docosyl acrylate with AIBN and BPO

Well-defined poly(n-docosyl acrylate) (PDA) with narrow molecular weight distribution has been synthesized by atom transfer radical polymerization (ATRP) and reverse ATRP of n-docosyl acrylate (DA) at 80 °C in N,N-dimethylformamide using the carbon tetrabromide/FeCl₃/2,2′-bipyridine (bpy) initiation system in the presence of 2,2′-azobisisobutyronitrile (AIBN) and benzoyl peroxide (BPO) as the source of reducing agent. The rates of polymerization for both the systems exhibit first-order kinetics with respect to the monomer, however, peroxide-initiated system shows slow rate of polymerization as compared to the azo-system. The effect of various reaction parameters on number average molecular weight (M _n ) and molecular weight distribution (M _w/M _n ) have been investigated. The resulting PDA that obtained in presence of AIBN and BPO systems has been compared for both the conventional and reverse ATRP. The reverse ATRP initiated by peroxides behaves differently than that of the azo initiators. In reverse ATRP with BPO, the rate of polymerization (R _p) has been significantly increased with the increase of BPO resulting higher M _n and broader M _w/M _n . The reverse ATRP of DA did not exhibit living characteristics with BPO system. PDA has been characterized by GPC, FTIR, and NMR spectroscopy.     

Rheological studies of two component high build epoxy and polyurethane based high performance coatings

The work presented in this article involves the study of rheometric profile of several rheological additives in two-component (2K) high build epoxy zinc phosphate primer and two-component high build aliphatic polyurethane topcoat. Viscosity profile and thixotropic behavior at different shear rates have been determined for both the paints using Physica MCR 301 Rheometer of Anton Paar. The valuable information derived from these measurements led to better insight into the influence of these rheological additives on important paint properties like flow and leveling, sag control, in-can settling during storage, etc. Rheometric results were also compared with the results obtained during the actual application of these experimental coatings on mild steel panels. From the rheological study it was concluded that the thickeners based on surface-modified clay and organically modified castor oil derivative work well in epoxy zinc phosphate primer whereas polyurea-based thickener showed better results than other rheological additives in the case of the 2K polyurethane system. Measurement of low shear and high shear viscosity response of different thickeners helps in predicting storage and application behavior of these coatings which correlates well with the actual observation.     

钢框架非比例损伤识别

提出能够鉴别损伤位置和截面损伤严重程度的钢框架非比例破坏监测方法。所提出的方法由两部分组成,一是损伤识别,二是损伤严重程度分析。损伤识别和严重程度分析均以结构动力性质的变化作为损伤的判据,以此来确定损伤位置和严重程度。所提方法中损伤判别的重要特点是能够在损伤严重程度分析之前,精确地区分不同的损伤区域。与整个结构尺寸相比,损伤区域相对较小,因此,确定损伤严重程度的计算量更小。检测方法的另一个特点是有些特征值或振型对噪声相对不敏感。采用所提检测方法对几个框架进行验证,结果表明,该方法能够成功地检测及量化截面的损伤。     

Evaluation of error probabilities in the presence of timing errors and fading

Using the approximate Fourier series technique we obtain expressions for the probability of error for bandlimited BPSK signalling in the presence of timing errors and fading. The derived results can be used to compute the error probabilities to any desired accuracy for Nakagami-m and Weibull fading channels. The effect of timing error on the performance of the raised cosine pulse has been evaluated for several fading parameters. We also compare the performance of some useful Nyquist pulses known