Intergranular corrosion behavior of the 7075-T6 aluminum alloy under different annealing conditions

The effect of annealing conditions producing various grain sizes on the intergranular corrosion behavior of high-strength aluminum alloy type 7075-T6 was investigated using electrochemical polarization techniques. Aluminum alloy specimens with large grain size exhibited lower breakdown potentials in deaerated 0.5 M NaCl solution. The breakdown potentials decreased with increasing grain size. Microscopic observations of the exposed surfaces during potentiostatic polarization testing showed that the coarse grain structure promotes intergranular crack growth.     

Barrier properties of poly(vinyl alcohol) membranes containing carbon nanotubes or activated carbon

Carbon nanotube addition has been shown to improve the mechanical properties of some polymers. Because of their unique adsorptive properties, carbon nanotubes may also improve the barrier performance of polymers used in contaminant containment. This study compares the barrier performance of poly(vinyl alcohol) (PVA) membranes containing single-walled carbon nanotubes (SWCNTs) to that for PVA containing powdered activated carbon (PAC). Raw and surface-functionalized versions of each sorbent were tested for their abilities to adsorb 1,2,4-trichlorobenzene and Cu(2+), representing the important hydrophobic organic and heavy metal contaminant classes, as they diffused across the PVA. In both cases, PAC (for 1,2,4-trichlorobenzene) and functionalized PAC (for Cu(2+)) outperformed SWCNTs on a per mass basis by trapping more of the contaminants within the barrier membrane. Kinetics of sorption are important in evaluating barrier properties, and poor performance of SWCNT-containing membranes as 1,2,4-TCB barriers is attributed to kinetic limitations.     

Synthesis and characterization of alumina-coated carbon nanotubes and their application for lead removal

Alumina-coated multi-wall carbon nanotubes were synthesized and characterized by scanning electron microscopy, X-ray diffraction, and FTIR. They were used as an adsorbent for the removal of lead ions from aqueous solutions in two modes, batch and fixed bed. In the batch mode, experiments were carried out to investigate the effect of contact time, agitation speed, adsorbent dosage and solution pH on the removal of lead. The coated nanotubes exhibit better removal ability over uncoated. For fixed-bed columns, thickness of the layer and flow rate were investigated. Increasing the thickness and decreasing the flow rate enhanced the removal of lead. The prepared adsorbent displayed the main advantage of separation convenience when a fixed-bed column was used compared to the batch adsorption treatment.     

Augmenting defense-in-depth with the concepts of observability and diagnosability from Control Theory and Discrete Event Systems

Defense-in-depth is a fundamental principle/strategy for achieving system safety. First conceptualized within the nuclear industry, defense-in-depth is the basis for risk-informed decisions by the U.S. Nuclear Regulatory Commission, and is recognized under various names in other industries (e.g., layers of protection in the Chemical industry). Accidents typically result from the absence or breach of defenses or violation of safety constraints. Defense-in-depth is realized by a diversity of safety barriers and a network of redundancies. However, this same redundancy and the intrinsic nature of defense-in-depth - the multiple lines of defense or “protective layers” along a potential accident sequence - may enhance mechanisms concealing the occurrence of incidents, or that the system has transitioned to a hazardous state (accident pathogens) and that an accident is closer to being released. Consequently, the ability to safely operate the system may be hampered and the efficiency of defense-in-depth may be degraded or worse may backfire. Several accidents reports identified hidden failures or degraded observability of accidents pathogens as major contributing factors.In this work, we begin to address this potential theoretical deficiency in defense-in-depth by bringing concepts from Control Theory and Discrete Event Systems to bear on issues of system safety and accident prevention. We introduce the concepts of controllability, observability, and diagnosability, and frame the current understanding of system safety as a “control problem” handled by defense-in-depth and safety barriers (or safety constraints). Observability and diagnosability are information-theoretic concepts, and they provide important complements to the energy model of accident causation from which the defense-in-depth principle derives. We formulate a new safety-diagnosability principle for supporting accident prevention, and propose that defense-in-depth be augmented with this principle, without which defense-in-depth can degenerate into a defense-blind safety strategy. Finally, we provide a detailed discussion and illustrative modeling of the sequence of events that lead to the BP Texas City Refinery accident in 2005 and emphasize how a safety-diagnosable architecture of the refinery could have supported the prevention of this accident or mitigated its consequences. We hope the theoretical concepts here introduced and the safety-diagnosability principle become useful additions to the intellectual toolkit of risk analysts and safety professionals and stimulate further interaction/collaboration between the control and safety communities.     

基于近地表相分析的全局约束近地表建模方法

针对复杂地表地区近地表地质、地球物理条件变化剧烈、结构复杂等特点,提出近地表相和近地表相分析的概念和理论方法,在完成近地表相分析的基础上,充分利用可控震源地震采集、近地表调查等所得到的多种地学数据,进行了近地表黏弹性参数反演并提出了拟微测井的概念,进而建立了高精度的极浅近地表层模型,最后结合地震波初至层析反演实现了各种地学数据及多种近地表建模方法之间宏观与微观的全局约束,建立了具有明确地质、地球物理意义的近地表模型。微测井和VSP数据标定结果表明：该模型精度较高,实际资料处理应用中较好地解决了中长波长静校正问题。该方法代表了目前近地表模型研究的一个方向,为复杂地表地区近地表建模提供了一种新的思路与方法。     

On the grain boundary internal friction peak of α-brasses

A conventional Ke pendulum was used to investigate the temperature dependence of internal friction for thoroughly annealed samples of Cu-30% Zn. The relaxation peak observed at 330° C at a frequency of vibration 0.60 Hz was attributed to grain boundary diffusion. The energy activating the process amounted to 1.84 eV and characterized the activation energy for self diffusion in copper. The relaxation strength showed strain amplitude dependence, however, the activation energy and peak temperature did not show any amplitude dependence. The effect of solute atom concentration, cold work and vacancies was also tested.     

Distributed Antennas for Indoor Radio Communications

The idea of implementing an indoor radio communications system serving an entire building from a single central antenna appears to be an attractive proposition. However, based on various indoor propagation measurements of the signal attenuation and the multipath delay spread, such a centralized approach appears to be limited to small buildings and to narrow-band FDMA-type systems with limited reliability and flexibility. In this paper, we present the results of indoor radio propagation measurements of two signal distribution approaches that improve the picture dramatically. In the first, the building is divided into many small cells, each served from an antenna located in its own center, and with adjacent cells operating in different frequency bands. In the second approach, the building is divided into one or more large cells, each served from a distributed antenna system or a "leaky feeder" that winds its way through the hallways. This approach eliminates the frequency cell handoff problem that is bound to exist in the first approach, while still preserving the dramatic reductions in multipath delay spread and signal attenuation compared to a centralized system. For example, the measurements show that, with either approach, the signal attenuation can be reduced by as much as a few tens of decibels and the rms delay spread becomes limited to 20 to 50 us, even in large buildings. This can make possible the implementation of sophisticated broad-band TDMA-type systems that are flexible, robust, and virtually building-independent.     

A Statistical Model for Indoor Multipath Propagation

The results of indoor multipath propagation measurements using 10 ns, 1.5 GHz, radarlike pulses are presented for a medium-size office building. The observed channel was very slowly time varying, with the delay spread extending over a range up to about 200 ns and rms values of up to about 50 ns. The attenuation varied over a 60 dB dynamic range. A simple statistical multipath model of the indoor radio channel is also presented, which fits our measurements well, and more importantly, appears to be extendable to other buildings. With this model, the received signal rays arrive in clusters. The rays have independent uniform phases, and independent Rayleigh amplitudes with variances that decay exponentially with cluster and ray delays. The clusters, and the rays within the cluster, form Poisson arrival processes with different, but fixed, rates. The clusters are formed by the building superstructure, while the individual rays are formed by objects in the vicinities of the transmitter and the receiver.