基于分布式弹簧-阻尼单元的桥头跳车动力荷载分析

对车辆桥头跳车问题,提出一种分布式弹簧-阻尼单元,该单元可以考虑车轮-路(桥)面接触长度和车轮的动力特性。基于此单元,结合车辆有限元动力分析,可对车辆上、下桥头错台时的竖向动力荷载进行定量研究。实例分析表明:①分布式弹簧-阻尼单元由于考虑了桥头跳车时车轮与桥面的接触长度,所得的车轮竖向动荷载比以往方法有所降低;②桥头错台跳车造成的竖向轮载冲击系数可能超过我国和美国桥梁规范设计值,需要引起重视;③下桥跳车时车轮动荷载降低,可能造成车轮脱空,影响行车安全性;④跳车动力荷载与行车速度、错台高度等因素有关,相关参数分析有利于对桥头错台高度和行车速度进行合理控制。     

Antialiasing filter design for subpixel downsampling via frequency-domain analysis

In this paper, we are concerned with image downsampling using subpixel techniques to achieve superior sharpness for small liquid crystal displays (LCDs). Such a problem exists when a high-resolution image or video is to be displayed on low-resolution display terminals. Limited by the low-resolution display, we have to shrink the image. Signal-processing theory tells us that optimal decimation requires low-pass filtering with a suitable cutoff frequency, followed by downsampling. In doing so, we need to remove many useful image details causing blurring. Subpixel-based downsampling, taking advantage of the fact that each pixel on a color LCD is actually composed of individual red, green, and blue subpixel stripes, can provide apparent higher resolution. In this paper, we use frequency-domain analysis to explain what happens in subpixel-based downsampling and why it is possible to achieve a higher apparent resolution. According to our frequency-domain analysis and observation, the cutoff frequency of the low-pass filter for subpixel-based decimation can be effectively extended beyond the Nyquist frequency using a novel antialiasing filter. Applying the proposed filters to two existing subpixel downsampling schemes called direct subpixel-based downsampling (DSD) and diagonal DSD (DDSD), we obtain two improved schemes, i.e., DSD based on frequency-domain analysis (DSD-FA) and DDSD based on frequency-domain analysis (DDSD-FA). Experimental results verify that the proposed DSD-FA and DDSD-FA can provide superior results, compared with existing subpixel or pixel-based downsampling methods.     

Expanded Reliability-Based Design Approach for Drilled Shafts

This paper develops a more general reliability-based design approach for drilled shafts that formulates the design process as an expanded reliability problem in which Monte Carlo simulations (MCS) are used in the design. Basic design parameters, such as the shaft diameter (B) and depth (D), are formulated as discrete uniform random variables. Then the design process becomes one in which failure probabilities are developed for various combinations of B and D [i.e., conditional probability p(Failure∣B,D)] and are compared with a target probability of failure pT. Equations are derived for this expanded reliability-based design (RBDE) approach, and criteria are established for the minimum number of MCS samples to ensure a desired level of accuracy. Its usefulness is illustrated using a drilled shaft design example. This RBDE approach has the following advantages: (1) it gives results that agree well with current RBD designs, but it improves the resolutions of the designs; (2) it offers design engineers insight into how the expected design performance level changes as B and D change; (3) it gives design engineers the ability to adjust pT, without additional calculation effort, to accommodate specific needs of a particular project; and (4) it is transparent and “visible” to design engineers who are given the flexibility to include uncertainties deemed appropriate. Finally, the effects of uncertainties in the at-rest horizontal soil stress coefficient (K0) and allowable displacement (ya) are illustrated using this approach.     

Performance of 3%Mo/ZSM‐5 catalyst in the presence of water during methane aromatization in supersonic jet expansion

The influence of water in the CH₄ feed on the performance of 3%Mo/ZSM‐5 catalyst during methane direct aromatization under supersonic jet expansion (SJE) condition was investigated. We observed that both surface Mo₂O_xC_y and β‐Mo₂C species are catalytically active for methane aromatization under SJE condition. The presence of water can promote the removal of surface carbon before the generation of aromatic‐type and/or graphitic carbon. In appropriate amount, water can improve the stability of surface Mo₂O_xC_y, and hence resulting in better catalytic performance. The study provided valuable information relevant to the direct utilization of methane hydrate. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Horizontal reactive distillation for multicomponent chiral resolution

A novel horizontal reactive distillation apparatus and a new overall process scheme are proposed for continuous multicomponent chiral resolution via reversible enantioselective acylation of a chiral (racemic) substrate by a chiral (racemic) acyl donor. The process enables simultaneous production of up to four enantiomers with enhanced chiral purity. Kinetic studies, miniplant experiments, and process simulation results are described for a model lipase‐catalyzed reaction: (R)‐enantioselective transesterification of (R,S)‐1‐n‐butoxy‐2‐propanol with (R,S)‐1‐methoxy‐2‐acetoxypropane to produce (R)‐1‐n‐butoxy‐2‐acetoxypropane, (R)‐1‐methoxy‐2‐propanol, and the two unreacted (S)‐enantiomers of the (R,S)‐reagents. A horizontal, compartmentalized reactive distillation vessel is specified instead of a conventional reactive distillation column to provide longer liquid‐phase residence time needed for adequate conversion. Low vapor‐traffic pressure drop allows operation under vacuum at reduced temperatures for good enzyme stability and enantioselectivity. The general technology has potential as a means to producing a wide range of chiral synthons used in asymmetric syntheses of chiral pharmaceuticals and other biologically active products. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2603–2620, 2013     

A Path Interval Generation Algorithm in Sculptured Object Machining

The features of a sculptured object are represented by a set of section curves. A fast algorithm is presented to calculate cutting depths based on the scallop height using these curves. The calculated cutting depth can be used for tool-path generation. This tool-path generation approach is particularly useful for constant z level contouring and high-speed machining.     

Effects of metallization characteristics on gold wire bondability of organic printed circuit boards

Organic printed circuit boards (PCBs) with Au/Ni plates on bond pads are widely used in chip-on-board (COB), ball grid array (BGA), and chip-scale packages. These packages are interconnected using thermosonic gold wire bonding. The wire bond yield relies on the bondability of the Ni/Au pads. Several metallization parameters, including elemental composition, thickness, hardness, roughness, and surface contamination, affect the success of the solid state joining process. In this study, various characterization and mechanical testing techniques are employed to evaluate these parameters for different metallization schemes with varying Ni and Au layer thicknesses. The pull force of Au wires is measured as a function of plasma treatment applied before wire bonding to clean the bond pads. Close correlations are established between metallization characteristics and wire bond quality.     

Mechanistic study of borosilicate glass growth by low-pressure chemical vapor deposition from tetraethylorthosilicate and trimethylborate

A reaction mechanism and film morphology as a function of reactor conditions and post growth thermal annealing for borosilicate glass (BSG), (SiO₂)_x(B₂O₃)_1−x, films deposited from tetraethylorthosilicate (TEOS), trimethylborate (TMB), and oxygen (O₂) precursors by low-pressure chemical vapor deposition (LPCVD) was determined. An empirically derived reaction model for BSG film growth is proposed that predicts the growth rate and composition of BSG films up to 70 mole% B₂O₃. The BSG reaction model includes a strongly adsorbed TEOS-derived intermediate that forms SiO₂ and a direct surface reaction of TMB, in O₂, to form B₂O₃. This model is supported by growth rate and mass spectroscopic data. The BSG film morphology, investigated using atomic force microscopy, was found to have a root-mean-square roughness of 0.5 nm, with the precise film morphology being a function of reactor conditions. The BSG film roughness increases with film thickness, temperature, and boron content. Thermal annealing of the films in a water-free environment leads to planarization of the BSG governed by the film composition and anneal temperature.     

Efficacy = endowment × efficiency: Revisiting efficacy and endowment effects in a public goods dilemma.

This article reexamines the efficacy and endowment effects in public good (PG) dilemma by conceptualizing that efficacy = endowment × efficiency. Endowment is the resource that a person can contribute. Efficiency is the impact of a unit of endowment. Efficacy is the total impact of contribution. The authors used a group project scenario to simulate a continuous contribution PG dilemma. The 2 × 2 × 2 × 2 experimental design manipulated own efficiency and own endowment as within-subject variables and the other persons' efficiency and endowment as between-subject variables. Results indicate that cooperation was mainly affected by one's endowment and others' efficiency. The authors distinguished among 3 types of efficiency effects: (a) an own-absolute-efficiency effect that efficient people put in more effort regardless of others' efficiency, (b) an other-absolute-inefficiency effect that people put in more effort when others are inefficient, and (c) a relative-inefficiency effect that inefficient people put in less effort in the presence of efficient people. Contrasting previous robust findings on efficiency, they identified a situation in which efficiency has no effects--when one has more endowment than do others. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An Efficient Approach to Chiral Ferrocene‐Based Secondary Alcohols via Asymmetric Hydrogenation of Ferrocenyl Ketones

P‐Phos‐ruthenium‐DPEN precatalysts have been found to be efficient for the asymmetric hydrogenation of various ferrocenyl ketones. The use of (R)‐xylyl‐P‐PhosRuCl₂(R,R)‐DPEN generated chiral ferrocenylethanol in 99.3% e.e. with >99% conversion in a 150‐g scale.