Micropipelined asynchronous discrete cosine transform (DCT/IDCT)processor

We describe the design and implementation of an asynchronous discrete cosine transform/inverse discrete cosine transform (DCT/IDCT) processor core compliant with the CCITT recommendation H.261. First, a micropipelined implementation with level-sensitive latches is shown. This is improved by replacing the level-sensitive latches with dual-edge triggered flip-flops to save power and using completion-detection adders in the critical stage of the pipeline to exploit the data-dependent processing delay. Gate-level simulation of extracted layouts indicates that the performance of asynchronous implementations is comparable with that of a synchronous implementation based on an identical architecture. This is because part of the penalty introduced by handshaking circuitry in an asynchronous pipeline can be recovered by exploiting data-dependent processing delays with completion-detection circuitry. In pipelines with significant arithmetic processing such as the DCT/IDCT processor, this is easily accomplished. Our results are encouraging because asynchronous designs do not employ global clocking. In the near future when clock generation, clock distribution, and the power consumed in the clock circuitry become limiting factors in the design of large synchronous application specific integrated circuits (ASICs), asynchronous implementation methodology could be pursued as a real alternative     

The Effect of Lanthanum on the Scales Developed on Thin Foils of Fe-20Cr-5Al at Very High Temperatures

A study has been undertaken of the effects oflanthanum on the oxidation of thin foils of Fe-20Cr-5Alin air at 1150°C. The addition of lanthanum causesthe time to breakaway to increase from about 24 hr for Fe-20Cr-5Al to over 400 hr. Oxidationof the lanthanum-containing alloy occurs in threestages. During the first stage, an-Al₂O₃ layer is establishedand thickens with time until the aluminum in the foil is depleted sufficiently for alayer of Cr₂O₃ to become stableand develop at the scale-alloy interface. This continuesto thicken at a relatively slow rate until breakawayoccurs. The main emphasis in the present paper has been anexamination and analysis of the scale established on thelanthanum-containing alloy in cross section in theanalytical transmission electron microscope (TEM), after an exposure period that coincides with thesecond stage of oxidation, prior to breakaway. The scaleat that time consists of three layers. The outer layeris composed of equiaxed Al₂O₃grains. The intermediate and inner layers consist of columnarAl₂O₃ grains and equiaxedCr₂O₃ grains, respectively.Numerous voids are observed in the oxide grainboundaries and at the intermediate-inner layerinterface. Lanthanum segregates in the oxide grain boundaries andits concentration increases toward the outermost surfaceof the scales. These results are consistent with thedynamic segregation model to account for the effects of reactive elements on thegrowth of Al₂O₃ scales.     

Enhanced Oxygen Diffusion Along Internal Oxide–Metal Matrix Interfaces in Ni–Al Alloys During Internal Oxidation

A study of the internal oxidation of dilute Ni–Al alloys in an NiO/Ni Rhines pack was performed at 800, 1000, and 1100°C. Considerable deviations from the classical internal oxidation model have been observed. The rate of internal oxidation depends not only on the concentration of the alloying element but also on its nature, which contributes to determining the size, shape, orientation and distribution of the internal oxide precipitates. For instance, the precipitates in the Ni–Al alloys are continuous rods, arranged in a cone-shaped configuration that extends from the surface to the internal oxide front. The observed depths of internal oxidation for the various concentrations of aluminum are discussed and related to the morphologies of the internal oxide precipitates. The apparent N^(s) _oD_o values determined from internal oxide penetrations increase with increasing solute content in the alloy. It is postulated that diffusivity of oxygen is enhanced along the internal oxide–metal matrix interface compared with that in the metal matrix.     

The early stages of development of α-Al2O3 scales on Fe-Cr-Al and Fe-Cr-Al-Y Alloys at high temperature

The development ofthe oxides on Fe-14%Cr-4%Al, Fe-27%Cr-4%Al, and similar alloys containing 0.008% Y, 0.023% Y, and 0.8% Y has been investigated during the early stages of oxidation in 1 atm oxygen at 1000 and 1200°C. In all cases, a steady-state -Al₂O₃layer is established rapidly, after some initial formation of transient oxides rich in iron and chromium. For the yttrium-free alloys the steady-state situation is achieved more rapidly for the higher chromium-containing alloy and at the higher temperature. The amount of transient oxide formed is also determined by the specimen surface topography since the development of the -Al₂O₃ layer is less rapid at the base of alloy asperities than at a flat alloy-oxide interface. Following establishment of the complete -Al₂O₃layer, the oxide develops a convoluted oxide morphology at temperature, due to high compressive growth stresses in the oxide. These arise following reaction between oxygen ions diffusing inward down the oxide grain boundaries and aluminum ions diffusing outward through the bulk oxide. This results in lateral growth of the oxide and plastic deformation and movement of the alloy in a direction parallel to the alloy-oxide interface. The addition of yttrium to the alloys promotes the selective oxidation of aluminum. Also, the yttrium is incorporated into the growing oxide where it changes the mechanism of growth, reducing the production of the high compressive growth stresses and thus the development of the convoluted oxide morphology.     

The influence of platinum on the maintenance of α-Al2O3 as a protective scale

The influence of externally located platinum on the isothermal stability of -Al₂O₃ scales formed at high temperatures has been examined. It has been observed that a nickel-base alloy forms an external scale of -Al₂O₃ during oxidation at 1200°C, but this scale breaks down isothermally, enabling a faster-growing Cr₂O₃-rich scale to develop. However, in the presence of platinum metal alongside the specimen in the furnace hot zone, the breakdown of the -Al₂O₃ scale is postponed for a substantial period of time. It appears that platinum, as the volatile species PtO₂, is incorporated into the growing -Al₂O₃ scale where it either influences the stress relief mechanism at temperature or reduces oxidation growth stress generation and thus significantly enhances the isothermal stability of the scale.     

Automatic metro map layout using multicriteria optimization

This paper describes an automatic mechanism for drawing metro maps. We apply multicriteria optimization to find effective placement of stations with a good line layout and to label the map unambiguously. A number of metrics are defined, which are used in a weighted sum to find a fitness value for a layout of the map. A hill climbing optimizer is used to reduce the fitness value, and find improved map layouts. To avoid local minima, we apply clustering techniques to the map-the hill climber moves both stations and clusters when finding improved layouts. We show the method applied to a number of metro maps, and describe an empirical study that provides some quantitative evidence that automatically-drawn metro maps can help users to find routes more efficiently than either published maps or undistorted maps. Moreover, we have found that, in these cases, study subjects indicate a preference for automatically-drawn maps over the alternatives.     

The effects of laser-induced modification of surface roughness of Al2O3-based ceramics on fluid contact angle

Laser surface treatment of Al₂O₃-based refractory ceramics, by melting and re-solidification, can be successfully applied to producing surfaces that are pore-free, homogeneous and crack-free. Such treated surfaces can lead to an increase in the corrosion and erosion resistances of the materials, due to lower permeability to corrosive species and higher surface hardness, respectively. Furthermore, the corrosion resistance can be influenced by the wetting characteristics of the treated surfaces in service environment. Therefore, it is important to investigate the effect of laser treatment of ceramic materials on the interaction of the surface with the various environmental elements. This work is concerned with an experimental investigation of the effects of laser surface treatment, by melting and re-solidification, on the fluid contact angles of Al₂O₃-based refractory ceramics. These effects are examined by the modification of the surface roughness characteristics induced by laser treatment. Laser-treated surfaces, both containing cracks and crack-free, are compared with untreated surfaces and the results are reported. The untreated surfaces demonstrated considerable non-uniformity in wetting, in contrast to the treated surfaces. The extent of wetting of the laser-treated surfaces containing cracks was proportional to laser power density. This is due to wetting being enhanced, among other factors, by surface roughness, which increased with power density. The crack-free surfaces were the most smooth and, thereby, exhibited the smallest extent of wettability variations. The reduction in wettability after the laser treatment (crack-free) may have an advantage for corrosion resistance.     

Discharge-based QMRA for estimation of public health risks from exposure to stormwater-borne pathogens in recreational waters in the United States

This study is the first to report a quantitative microbial risk assessment (QMRA) on pathogens detected in stormwater discharges-of-concern, rather than relying on pathogen measurements in receiving waters. The pathogen concentrations include seven “Reference Pathogens” identified by the U.S. EPA: Cryptosporidium, Giardia, Salmonella, Norovirus, Rotavirus, Enterovirus, and Adenovirus. Data were collected from 12 sites representative of seven discharge types (including residential, commercial/industrial runoff, agricultural runoff, combined sewer overflows, and forested land), mainly during wet weather conditions during which times human health risks can be substantially elevated. The risks calculated herein therefore generally apply to short-term conditions (during and just after rainfall events) and so the results can be used by water managers to potentially inform the public, even for waters that comply with current criteria (based as they are on a 30-day mean risk). Using an example waterbody and mixed source, pathogen concentrations were used in QMRA models to generate risk profiles for primary and secondary water contact (or inhalation) by adults and children. A number of critical assumptions and considerations around the QMRA analysis are highlighted, particularly the harmonization of the pathogen concentrations measured in discharges during this project with those measured (using different methods) during the published dose–response clinical trials. Norovirus was the most dominant predicted health risk, though further research on its dose–response for illness (cf. infection) is needed. Even if the example mixed-source concentrations of pathogens had been reduced 30 times (by inactivation and mixing), the predicted swimming-associated illness rates – largely driven by Norovirus infections – can still be appreciable. Rotavirus generally induced the second-highest incidence of risk among the tested pathogens while risks for the other Reference Pathogens (Giardia, Cryptosporidium, Adenovirus, Enterovirus and Salmonella) were considerably lower. Secondary contact or inhalation resulted in considerable reductions in risk compared to primary contact. Measurements of Norovirus and careful incorporation of its concentrations into risk models (harmonization) should be a critical consideration for future QMRA efforts. The discharge-based QMRA approach presented herein is particularly relevant to cases where pathogens cannot be reliably detected in receiving waters with detection limits relevant to human health effects.     

Liquid / liquid ion-transfer processes at the dioctylphosphoric acid (N,N-didodecyl-N',N'-diethylphenylenediamine) / water (electrolyte) interface at graphite and mesoporous TiO2 substrates

Biphasic electrode systems are studied for the case of the oxidation of the water-insoluble liquid N,N-didodecyl-N',N'-diethylphenylenediamine (DDPD) neat and dissolved in bis(2-ethylhexyl) phosphate (HDOP) and immersed in aqueous electrolyte media. The oxidation process in the absence of HDOP is accompanied by transfer of the anion (perchlorate or phosphate) from the water into the organic phase. However, in the presence of HDOP, oxidation is accompanied by proton exchange instead. This electrochemically driven proton exchange process occurs over a wide pH range. Organic microdroplet deposits of DDPD in HDOP at basal plane pyrolytic graphite electrodes are studied by voltammetric techniques and compared in their behavior to organic microphase deposits in mesoporous TiO2 thin films. The mesoporous TiO2 thin film acts as a host for the organic liquid and provides an alternative biphasic electrode system compared to the random microdroplet/graphite system. Two types of mesoporous TiO2 thin-film electrodes, (i) a 300-400-nm film on ITO and (ii) a 300-400-nm film on ITO sputter-coated with a 20-nm porous gold layer, are investigated.