Examination of catalytic roles of inherent metallic species in steam reforming of nascent volatiles from the rapid pyrolysis of a brown coal

In-situ steam reforming of tar from the rapid pyrolysis of a Victorian brown coal was studied, employing a single-stage drop-tube reactor and a particular type of two-stage reactor, in which the nascent tar underwent steam reforming and thermal cracking in the presence and absence of nascent char particles, respectively. Na was the most abundant inherent metallic species contained in the coal, and a significant proportion of Na (60–80%) was volatilized during the pyrolysis. However, the Na dispersed in the vapor phase seemed to have no significant catalytic effect on the steam reforming. Na, and/or Ca remaining on the surface of char particles were responsible for rapid and extensive steam reforming of the nascent tar into gases, resulting in tar yield decrease by nearly 90%. The presence of steam alone was effective for suppressing soot formation from the tar vapor by approx. 80%, but in the absence of char particles containing metallic species, the addition of steam led to an increase in the yield of poly-nuclear aromatics.     

Relationship of indoor and outdoor air pollutants in a naturally ventilated historical building envelope

Concentrations of NO₂, O₃, SO₂, acetic and formic acids, HNO₃ and NH₃ were measured inside and outside a historical building, the Baroque Library Hall (BLH) in the National Library in Prague (Czech Republic). The naturally ventilated system of the building, the restriction of personnel access, reduced groups of visitors and absence of activities which could influence indoor pollutant concentrations are characteristics that make the Baroque Library Hall a suitable location to study the influence of outdoor environment on the indoor air quality. The relationship between indoor and outdoor (I/O) concentration was investigated to assess the infiltration of outdoor generated pollutants. Outdoor and indoor pollution sources were determined and, infiltration of ammonium nitrate and a shift of the equilibrium to the gas phase were the reason for the high concentration of ammonia measured inside the BLH. A significant seasonal variation was observed and interpreted as a consequence of different infiltration regime associated with indoor–outdoor temperature differences, which in addition drives dilution processes of indoor generated pollutants. Based on the indoor air quality assessment performed in the BLH with regard to human and material exposure, there is reason for concern about material preservation and in particular paper at the BLH.     

Relationship between the gas transport properties and the refractive index in high‐free‐volume fluorine‐containing polyimide membranes

The refractive index and gas transport properties (i.e., permeability, diffusivity, and solubility) in the 2,2′‐bis(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)‐based polyimides were systematically investigated in terms of their polymer fractional free volumes (FFVs). The permeability and diffusion coefficients of the 6FDA‐based polyimide membranes to hydrogen, oxygen, nitrogen, methane, and carbon dioxide were correlated with their FFVs, which were estimated with van Krevelen's group contribution method. Linear correlations were also observed between the gas transport properties and the refractive index of these polyimides. We described FFV as a function of the refractive index based on the Lorentz–Lorenz equation. Linear correlations were observed between their refractive‐index‐based FFVs and the gas permeability, diffusivity, and solubility coefficients of these 6FDA‐based polyimides membranes. However, the FFVs of the 6FDA‐based polyimides calculated from refractive index were 1.16–1.37 times larger than their FFV values. This FFV was dependent on the free‐volume space and optical factors, such as the refractive index and molar refraction, which affected the electronic structure and the interactions between the gas molecules and the polymer segments. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of ABA‐type triblock copolymers derived from polyimide and poly(2‐methyl‐2‐adamantyl methacrylate)

ABA‐type triblock copolymers derived from 4,4‐(hexafluoroisopropylidene)diphthalic anhydride‐2,3,5,6‐tetramethyl‐1,4‐phenylenediamine and 2‐methyl‐2‐adamantyl methacrylate (2‐MAdMA) were synthesized via atom transfer radical polymerization. The component ratios of polyimide (PI) and poly(2‐MAdMA) (PMAdMA) were about 8/2, 6/4 and 3/7, as determined using ¹H NMR spectroscopy and thermogravimetric analysis (TGA). The film structure of the triblock copolymers was dependent on the PI structure. Hydrophobicity increased as the component ratio of PMAdMA increased. Based on TGA, three‐step decomposition behaviors of all triblock copolymers derived from PI and PMAdMA in nitrogen and air atmosphere were observed. The gas permeability of the triblock copolymers was lower than that of PI. This finding can be attributed to the decrease in fractional free volume by the adamantane component and the decrease in permeability of the triblock copolymers compared with PI. The dielectric constant of the triblock copolymers was lower than that of PI. The dielectric constant was dependent on molar volume and molar porlarizability, and the dielectric constant derived from the symmetric structure of adamantane was reduced. The ABA‐type triblock copolymers derived from PI and PMAdMA can be considered as new polymer materials with high hydrophobicity, high H₂/CO₂ selectivity and low dielectric constant. © 2013 Society of Chemical Industry     

Three-dimensional interconnect with excellent moisture resistance for low-cost MMICs

The moisture resistance of three-dimensional (3-D) interconnects using organic insulator films and Au metals has been investigated to ascertain the feasibility of housing monolithic-microwave integrated circuits with these interconnects in inexpensive nonhermetic packages. By comparing polyimide and benzocyclobutene (BCB) for organic insulator films, it was found that although polyimide has higher moisture absorption than BCB, it has a greater moisture resistance. This suggests that moisture absorption is not the dominant factor in moisture resistance and that BCB has higher water permeability than polyimide. As an adhesion layer between Au metal and insulator film, W and WN have better moisture resistance than WSi and WSiN; adhesion layer compositions containing Si oxidize easily. Further, the metal patterning method has an effect on moisture resistance in terms of leakage current. Reactive ion etching (RIE) with SF/sub 6/ gas is necessary in order to completely remove the metal atom residue left after ion milling with Ar gas. An interconnect using polyimide insulator film, W or WN adhesion metal, and metal patterned by ion milling and RIE, did not fail in terms of contact resistance and leakage current under stress of 85/spl deg/C and 85% relative humidity with a bias for 1000 h.     

Path-following with a bounded-curvature vehicle: a hybrid control approach

In this paper, we consider the problem of stabilizing the kinematic model of a car to a path in the plane under rather general conditions. The path is subject to very mild restrictions, while the car model, although rather simplified, contains the most relevant limitations inherent in wheeled robots kinematics. Namely, the car can only move forward, its steering radius is lower bounded and a limited sensory information only provides a partial knowledge of some state parameters. In particular, we consider the case that the current distance and the heading angle error with respect to the closest point on the reference path can be measured but only the sign of the path curvature is detected. These constraints are such to make classical control techniques inefficient. As the feedback information is both continuous and discrete, the hybrid systems formalism turns out to be well appropriate to model the problem. The proposed approach is based on optimal control techniques successfully applied in a previous work for following rectilinear paths. We propose here an extension to the tracking of more general paths with moderate curvature. The stability of the closed-loop system is proved by means of hybrid system formalisms and hybrid formal verification techniques. Finally, the practicality of the proposed approach, in spite of non-idealities in real-world applications, is discussed by reporting experimental results.     

Fabrication and characterization of high-T(c) YBa(2)Cu(3)O(7-x) nanoSQUIDs made by focused ion beam milling

We have fabricated high-T(c)?nanoscale superconducting quantum interference devices (nanoSQUIDs) with a hole size of 250?nm × 250?nm based on a 100?nm bridge at 77?K by focused ion beam milling and ion implantation. At 78?K, the curve of the voltage branch became roughly linear and agreed with the Josephson-like behavior. The sample exhibited strong flux flow behavior at temperatures under 76?K. The voltage flux characteristic curves, V -I(mod), of the nanoSQUID at different bias currents at 78?K were observed. Typically, critical currents of 15?μA and peak-to-peak values of the voltage flux transfer function of 3.7?μV were measured. The measured data strongly suggest that the weak link structure could be a superconducting metal with a critical temperature T(c)' smaller than that (T(c)) of other YBa(2)Cu(3)O(7-x) (YBCO) films. This fabrication method of combining a nanobridge and ion implantation can improve the yield of nanojunctions and nanoSQUIDs.