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91.
92.
Chronis Andrea M.; Lahey Benjamin B.; Pelham William E. Jr.; Williams Stephanie Hall; Baumann Barbara L.; Kipp Heidi; Jones Heather A.; Rathouz Paul J. 《Canadian Metallurgical Quarterly》2007,43(1):70
Children with attention-deficit/hyperactivity disorder (ADHD) are at risk for adverse outcomes such as substance abuse and criminality, particularly if they develop conduct problems. Little is known about early predictors of the developmental course of conduct problems among children with ADHD, however. Parental psychopathology and parenting were assessed in 108 children who first met Diagnostic and Statistical Manual of Mental Disorders (4th ed.) criteria for ADHD at 4-7 years old. When demographic variables and baseline ADHD and conduct problems were controlled, maternal depression predicted conduct problems 2-8 years following the initial assessment, whereas positive parenting during the structured parent- child interaction task predicted fewer future conduct problems. These findings suggest that maternal depression is a risk factor, whereas early positive parenting is a protective factor, for the developmental course of conduct problems among children with ADHD. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
93.
94.
以塔河减压渣油(简称塔河减渣)为原料,在实验室小型试验装置和中型连续试验装置上,对在较高温度条件下催化临氢热转化加工塔河减渣的工艺操作条件及改质效果进行了系统研究。采用高分散的油溶性催化剂,在高压釜反应器中考察了反应温度、反应压力、催化剂添加量、溶剂油添加量、反应时间以及助剂添加量对塔河减渣催化临氢热转化反应的转化率和缩合率的影响,优化了操作参数。在优化的操作条件下,进行了塔河减渣催化临氢热转化中型试验,得到初馏点大于524 ℃组分的裂化率为85.2%,馏分油收率为80%,金属(Ni+V)和沥青质脱除率均大于90%。 相似文献
95.
Synthesis and characterization of acidic properties of Al-SBA-15 materials with varying Si/Al ratios
G. Muthu Kumaran Shelu Garg Kapil Soni Manoj Kumar J.K. Gupta L.D. Sharma K.S. Rama Rao G. Murali Dhar 《Microporous and mesoporous materials》2008,114(1-3):103-109
Al-SBA-15 of varying Si/Al ratios in the range 11.4–78.4 was synthesized using tri-block copolymer P123. The calcined materials were examined by XRD, pore size distribution, surface area, 27Al NMR spectroscopy. The acidity and acid strength distribution were studied using microcalorimetric adsorption of NH3. The acidic properties were also examined by cumene cracking reaction as a function of Si/Al ratios. Systematic variation of acidity and activity was observed as a function of Si/Al ratio. The initial heats of NH3 adsorption correlated well with activity indicate that acid sites with ΔH > 100 kJ/mole is responsible for cumene cracking activity. Linear correlations were obtained with total acidity and cumene cracking activities. The tetrahedral aluminum was found to be responsible for the observed acidities and catalytic activities. 相似文献
96.
Philip Tipping 《International Journal of Pressure Vessels and Piping》1996,66(1-3):17-25
The susceptibility and tendency for nuclear power plant (NPP) components to undergo changes in their mechanical and physical properties in the course of the NPP lifetime is generally termed as “ageing”. The light water reactor (LWR) nuclear environment is not a begnign one; it is characterized not only by fast neutrons, which can degrade metallic structures, but also relatively high temperatures of coolant water (around 300°C) which may contain impurities (e.g. sulphate, chloride, peroxides) which can cause corrosion. The hydrodynamical conditions of the coolant in steam generators, for example, can cause thermal fatigue, erosion and corrosion; suspended particulate matter can accelerate erosion processes which can lead to wall thinning and lowering of safety margins. Ageing is, therefore, a very complex mixture of factors concerned with materials, temperatures, times of exposure to environments which vary with time and with respect to chemical composition and flow charactertistics.
The paper describes a few ageing phenomena which can be considered important due to their impact on nuclear safety issues; their influence on economic aspects (availability) of NPP is outlined. Mitigation measures for NPP component ageing problems are given together with recommendations for addressing such issues in NPP now and in the future. 相似文献
97.
介绍了福建炼油化工有限公司重油催化裂化装置自开工投产以来存在的问题,以及针对这些问题进行改造和改造后所取得的成效,如针对原料重质化、重金属含量高,如何提高产品收率;催化剂跑损,第一、二段再生器烟气混合后发生尾燃的现象以及汽提效率、烧焦效果等问题得到了根本的解决。 相似文献
98.
乙烯裂解炉辐射段流动与燃烧的三维数值模拟 总被引:1,自引:0,他引:1
用计算流体力学软件Fluent6.2对中国石油化工股份有限公司燕山分公司E-BA-107乙烯裂解炉辐射段内的流动和燃烧做了三维数值模拟研究。为保证计算的准确性,使用GAMBIT2.2软件建立了与裂解炉实际尺寸完全一致的几何模型;在计算过程中采用了标准k-ε湍流模型、离散坐标辐射模型和有限速率/涡流耗散燃烧反应模型等计算模型。通过模拟计算得到了裂解炉炉膛内的温度、烟气流速及烟气组成的分布:底部燃烧器和侧壁燃烧器的燃烧使附近的炉墙处于温度分布均匀的高温区,为裂解反应提供了均匀的辐射墙面;炉管底部比其他部位的温度低;底部燃烧器的高速射流产生的旋涡可为炉管提供一定的对流热;出口烟气的平均温度和组成的模拟计算值与设计值接近,表明数值模拟有较高的精度,具有实际意义。 相似文献
99.
The activation of propane using zeolite H-Y and Ga3+ exchanged zeolite Y indicates that in the presence of Ga3+ the mechanism of propane activation is changed from a cracking pathway to a dehydrogenation pathway. The presence of both Ga3+ and H+ are required to achieve this effect. 相似文献
100.
The surface-crack-in-flexure (SCF) method uses a Knoop indenter to create small, semielliptical surface precracks in beam specimens. Lateral cracks may interfere with the primary median crack and cause errors of up to 10% in determination of fracture toughness, particularly for materials for which the fracture toughness is ∼3 MPa·m1/2 or less. Although the residual-stress-damage zone is ground or polished away by hand by removing 4.5–5 times the indentation depth, this amount may not be sufficient to completely remove the lateral cracks in low-fracture-toughness materials. A series of tests were conducted on sintered alpha silicon carbide with different amounts of material removed after indentation. Once the lateral cracks were fully removed, the SCF results concurred with single-edged-precracked-beam and chevron-notched-beam data collected in accordance with ASTM Designation C1421. A simple remedy for the SCF method is to examine the outer ground surface for remnants of lateral cracks before fracture and to remove more material if necessary. 相似文献