Extension of the decidability of the marked PCP to instances with unique blocks

In the Post Correspondence Problem (PCP) an instance (h,g)$(h,g)$ consists of two morphisms h$h$ and g$g$, and the problem is to determine whether or not there exists a nonempty word w$w$ such that h(w)=g(w)$h\left(w\right)=g\left(w\right)$. Here we prove that the PCP is decidable for instances with unique blocks using the decidability of the marked PCP. Also, we show that it is decidable whether an instance satisfying the uniqueness condition for continuations has an infinite solution. These results establish a new and larger class of decidable instances of the PCP, including the class of marked instances.     

Fabrication and electrical characterization of integrated nano-scale fluidic channels

We present the fabrication and characterization of nanoscale fluidic channels with embedded electrodes. Arrays of 2.25 μm long and 60 nm tall nanochannels with widths ranging from 60 to 500 nm were microfabricated in SiO₂ with Au electrodes embedded inside and outside of the nanochannels. The built-in electrodes were able to probe nanochannel conductance via a redox reaction of \textFe(\textCN)₆^{3 - /4 -} {\text{Fe}}({\text{CN}})_{6}^{3 - /4 - } . Amperometric characterization showed that conductance of nanochannel arrays varied linearly both with the width and number of nanochannels and was in the 10–100 pS range. Further, we show that electrical current was largely diffusion based and could be predicted from channel geometry using standard diffusion equations. We also discuss the potential of such nanochannel arrays as electronic biomolecular sensors and show preliminary streptavidin detection results.     

直觉模糊粗糙推理的规则库完备性研究

针对规则库检验问题,提出了直觉模糊粗糙规则库的完备性检验方法.首先,引入直觉模糊粗糙集的概念,给出了直觉模糊粗糙规则库的完备性定义;其次,针对直觉模糊粗糙规则库的完备性,提出了完备性检验算法,指出如何设计规则库才能满足完备性要求;最后,通过实例验证了算法的合理性和有效性.     

Evaluating the perceived and estimated quality in use of Web 2.0 applications

Web 2.0 refers to a new generation of web applications where individuals are able to participate, collaborate, and share created artefacts. Despite the fact that Web 2.0 applications are widely used for both educational and professional purposes, a consolidated methodology for their evaluation is still not available. This paper presents and discusses the results of two empirical studies on the case of mind mapping and diagramming Web 2.0 applications. Both studies employed logging actual use method to measure the estimated quality in use, while the retrospective thinking aloud method and an online questionnaire were applied to assess the perceived quality in use. Achieved analytical results showed that the results of the estimated and the perceived quality in use match partially, which indicates that quality in use should be measured with both subjective and objective instruments. The work presented in this paper is the first step towards a comprehensive methodology for evaluating the quality in use of Web 2.0 applications. Consequently, the usage of the proposed quality in use model for other types of Web 2.0 applications as well as contexts of use needs to be investigated in order to draw generalizable conclusions.     

Influence of LPE growth conditions on the electroluminescence properties of InP/InGaAs(P) infrared emitting diodes

Liquid phase epitaxial growth of InP/InGaAs(P) infrared emitting diodes was studied systematically. Small area surface emitting LED chips were prepared to cover completely the 1100–1700 nm wavelength ranges. Nine different diodes were fabricated with optimal spacing of the peak emission wavelengths in order to have sufficient overlapping of their spectra. Efficient LEDs with narrow spectra have been realised by careful selection of the layer structure and growth conditions. Thick active layers with constant composition and abrupt interfaces have been grown for each emission wavelength. The long wavelength diodes (1275–1675 nm) were grown with additional quaternary layer(s) to prevent the melt-back of the active layer by InP melt. Low growth temperature (590°C) was used to prepare the LED structures. In the spectral range of 1250–1520 nm higher growth temperatures (625–645°C) were necessary to improve the device parameters. Such phenomena confirm the existence of the miscibility gap in the InGaAsP quaternary crystal system. Quaternary layers grown in the middle of the immiscibile region showed non-uniform composition and ragged interfaces at the upper heterojunction.     

Specifying Cash-Point with DisCo

We describe how the cash-point service problem of Formal Methods ’99 is specified using DisCo [Dis, JKS91]. Received January 2000 / Accepted in revised form December 2000     

Processing characteristics of tin and tungsten oxides relevant to production of gas sensors

Tungsten trioxide and two types of tin dioxide were compacted at different pressures and then sintered at different temperatures in order to study how the microstructure formed is dependent on these parameters. The structures were studied using dilatometric and porosimetric techniques and also using electron microscopy. X-ray diffraction was used to ascertain the completeness of the decomposition reaction of SnSO₄ being converted to SnO₂. Tin dioxide, which was prepared from tin sulphate by calcining, was characterised by a large specific surface area. For all three materials studied the mean pore size was found to increase and the specific surface area was found to decrease with increasing sintering temperature. In the case of WO₃ the total pore volume decreased markedly as the sintering temperature was increased from 900 to 1000° C. However, in the case of SnO₂, the total pore volume remained almost constant in the sintering temperature range of 600 to 1500° C. In the case of SnO₂ derived from SnSO₄ the sintered density was about 45% of the theoretical value while for the conventionally made SnO₂ the sintered density was about 55% of the theoretical value. The sintered density of WO₃ was found to show a marked increase, from 55% to 70% of the theoretical value, as the sintering temperature was raised from 1000 to 1100° C.     

Methane oxidation on alumina supported palladium catalysts: Effect of Pd precursor and solvent

Palladium precursors and solvents were studied for their effects on the activities of alumina-based palladium catalysts in methane combustion and the resistance of the catalysts to thermal aging. The properties of the catalysts were compared with those of a commercial reference. The palladium precursors were Pd(propionate)₂, Pd(acetate)₂ and Pd(acetyl acetonate)₂ and the solvents were acetone, acetic acid, propionic acid and toluene. Catalysts were prepared by the wet impregnation method.Catalysts were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). The surface areas were measured by Brunauer–Emmett–Teller method (BET). Acidity of the alumina support was measured by NH₃ desorption. Activities of the catalysts in methane oxidation were screened under lean burn conditions.In methane oxidation with fresh catalyst, the best performance was obtained with a combination of Pd(acetate)₂ and acetic or propionic acid. The light-off temperatures of the fresh catalysts (562 K and 557 K, respectively) were slightly lower than the light-off temperature (567 K) of the commercial reference. Differences between the light-off temperatures of the aged and fresh catalysts were least when the catalysts were prepared with Pd(acetyl acetonate)₂ as Pd precursor and in acetic or propionic acid as solvent: +12 K and +18 K, respectively. The corresponding value for the reference was +64 K. For several of the fresh catalysts, conversion in methane oxidation at 623 K was over 90%. A comparison of methane combustion and NH₃ desorption results indicated that acidity of the support material affects catalysts activity.