Analytical screening criterion for sequencing of distillation columns

This paper is concerned with the development of a quantitative criterion based on the total interstage flowrate in a distillation column. This criterion reflects the total optimum cost of a column and can be used for screening simple column sequences. It has been shown that the interstage flowrate measure is compatible with known heuristics and the results have been compared with those obtained from other methods in the literature.     

Catalytic Total Oxidation of Methane. Part II. Catalytic Processes to Convert Methane: Partial or Total Oxidation

The introduction of solid catalysts into a traditionally non-catalytic free-radical process such as combustion occurred in recent years under the influence of environmental pressures. The major applications of catalytic combustion are two-fold: at low temperatures to eliminate volatile organic compounds (VOCs) and at high temperatures (>1000°C) to reduce NOx emission from gas turbines, jet motors, etc. It is the high temperature application that is reviewed here. Some recent developments in high-temperature catalytic combustion are trend setters in catalysis and hence of particular interest. For instance, novel materials are being developed for catalytic applications above 1000°C for sustained operation longer than one year. Where material/catalyst developments are still inadequate, systems engineering is coming to the rescue by developing multiple-monolith catalyst systems and the so-called hybrid (catalytic + thermal) reactors.     

Mechanism of potassium loss by desorption from an iron oxide catalyst for the styrene process

Several types of experiments have been done with molecular beam and mass spectrometric methods to characterize the desorption processes of potassium from a commercial styrene (potassium promoted iron oxide) catalyst. The loss of potassium as desorption of K is found to be mainly thermal, with an activation energy close to 1.0 eV (97 kJ/mole), which probably is associated with release of K from the initially bound positions in the bulk. The directly measured rate of loss as K appears too small to account for the experimentally observed total rate of loss. A new loss mechanism as electronically excited but not easily field ionizable potassium atoms is detected with an activation barrier of 1.7 eV (164 kJ/mole). Excited states may be important for the total loss both through direct emission of excited K atoms, and since excited states may give rise to cluster formation at the surface and more rapid loss as clusters K_n.     

Role of Interlayer and Intersite Interactions in Superconducting State in High-Tc Layered Cuprates

We studied the role of interlayer and intersite interactions on transition temperature and specific heat of layered high-T _c cuprates. We used double-time Green's function technique in the spirit of mean field approximation in order to obtain the expressions for hole density, transition temperature, and specific heat. These expressions are found to be dependent on the carrier concentration and intersite and interlayer interactions. The numerical analysis shows that the effect of intersite interaction on transition temperature and specific heat is qualitatively similar to that of interlayer interactions and provides favorable conditions to establish long-range order in the superconducting state.     

High temperature superstructural phases of the Sb/Si (5 5 12) interface

The control of adsorption kinetics and post growth treatments yield several stable superstructural phases in heteroepitaxial growth, and are being exploited to form novel nanostructures with controlled shape, size and position assembly. In this paper, we report the study of the interface formation in the sub-monolayer Sb adsorption in UHV on the trenched template of the high index Si (5 5 12) − (2 × 1) reconstructed surface. The interface formation is monitored in-situ by Auger Electron Spectroscopy (AES), Electron Energy Loss Spectroscopy (EELS), and Low Energy Electron Diffraction (LEED). The trenches formed by the (337) and (225) facets separated by primary silicon rows are used to form 1D nanostructures. Performing adsorption, onto substrates held at various temperatures, has enabled us to observe several ordered superstructural phases. Evidence is provided to show that the pathways adopted in the formation of the interface determine the superstructural phases with characteristic electronic properties of this technologically and scientifically important interface.     

Electron Microscopic Study on the Suction Cast In Situ Ti-Fe-Sn Ultrafine Composites

The current investigation reports detailed study on the microstructural evolution in the suction cast hypereutectic Ti₇₁Fe_29?x Sn _x alloys during Sn addition with x = 0, 2, 2.5, 3, 3.85, 4.5, 6, and 10 at. pct and the solidification of these ternary alloys using SEM and TEM. These alloys have been prepared by melting high-purity elements using vacuum arc melting furnace under high-purity argon atmosphere. This was followed by suction casting these alloys in the water-cooled split Cu molds of diameters, ? = 1 and 3 mm, under argon atmosphere. The results indicate the formation of binary eutectic between bcc solid solution ??-Ti and B2 FeTi in all alloys. ??-Ti undergoes eutectoid transformation, ??-Ti ?? ??-Ti + FeTi, during subsequent solid-state cooling, leading to formation of hcp ??-Ti and FeTi. For alloys x < 2, the primary FeTi forms from the liquid before the formation of eutectic with minute scale Ti₃Sn phase. For alloys with 2 ?? x ?? 10, the liquid is found to undergo ternary quasi-peritectic reaction with primary Ti₃Sn, L+Ti₃Sn ?? ??-Ti+FeTi, leading to formation of another kind of FeTi. In all the other alloy compositions (3.85 ?? x ?? 10), Ti₃Sn and FeTi dendrites are observed in the suction cast alloys with profuse amount of Ti₃Sn being formed for alloys with x ?? 4.5. The current study conclusively proves that the liquid undergoes ternary quasi-peritectic reaction involving four phases, L + Ti₃Sn ?? ??-Ti + FeTi, which lies at the invariant point Ti_69.2±0.8Fe_27.4±0.7Sn_3.4±0.2 (denoted by P). Below P, there is one univariant reaction, i.e., L ?? ??-Ti + FeTi for all alloy compositions, whereas above P, liquid undergoes one of the univariant reactions, i.e., L + ??-Ti ?? Ti₃Sn (Sn = 2, 2.5, 3, and 4.5 at. pct) or L + FeTi ?? Ti₃Sn for alloys (Sn = 6, 10 at. pct). For alloy with Sn = 3.85 at. pct, the ternary quasi-peritectic reaction is co-operated by two monovariant eutectic reactions, i.e., L ?? ??-Ti + FeTi below P and L ?? FeTi + Ti₃Sn above P. Detailed microstructural information allows us to construct liquidus projection of the investigated alloys. The results are critically discussed in the light of available literature data.     

Improving the Flexibility of Dynamic Prosody Modification Using Instants of Significant Excitation

Modification of suprasegmental features such as pitch and duration of original speech by fixed scaling factors is referred to as static prosody modification. In dynamic prosody modification, the prosodic scaling factors (time-varying modification factors) are defined for all the pitch cycles present in the original speech. The present work is focused on improving the naturalness of the prosody modified speech by reducing the generation of piecewise constant segments in the modified pitch contour. The prosody modification is performed by anchoring around the accurate instants of significant excitation estimated from the original speech. The division of longer pitch intervals into many equal intervals over long speech segments introduces step-like discontinuities in the form of piecewise constant segments in the modified pitch contours. The effectiveness of proposed dynamic modification method is initially confirmed from the smooth modified pitch contour plot obtained for finer static prosody scaling factors, waveforms, spectrogram plots and comparison subjective evaluations. Also, the average \(F_0\) jitter computed from the pitch segments of each glottal activity region in the modified speech is proposed as an objective measure for the prosody modification. The naturalness of the prosody modified speech using the proposed method is objectively and subjectively compared with that of the existing zero frequency filtered signal-based dynamic prosody modification. Also, the proposed algorithm effectively preserves the dynamics of the prosodic patterns in singing voices where in the \(F_0\) parameters rapidly and continuously fluctuate within a higher \(F_0\) range.     

Mapping tree and shrub leaf area indices in an ombrotrophic peatland through multiple endmember spectral unmixing

Leaf area index (LAI) is an important parameter used by most process-oriented ecosystem models. LAI of forest ecosystems has routinely been mapped using spectral vegetation indices (SVI) derived from remote sensing imagery. The application of SVI-based approaches to map LAI in peatlands presents a challenge, mainly due to peatlands characteristic multi-layer canopy comprising shrubs and open, discontinuous tree canopies underlain by a continuous ground cover of different moss species, which reduces the greenness contrast between the canopy and the background.Our goal is to develop a methodology to map tree and shrub LAI in peatlands and similar ecosystems based on multiple endmember spectral mixture analysis (MESMA). This new mapping method is validated using LAI field measurements from a precipitation-fed (ombrotrophic) peatland near Ottawa, Ontario, Canada. We demonstrate first that three commonly applied SVI are not suitable for tree and shrub LAI mapping in ombrotrophic peatlands. Secondly, we demonstrate for a three-endmember model the limitations of traditional linear spectral mixture analysis (SMA) due to the unique and widely varying spectral characteristics of Sphagnum mosses, which are significantly different from vascular plants. Next, by using a geometric-optical radiative transfer model, we determine the nature of the equation describing the empirical relationship between shadow fraction and tree LAI using nonlinear ordinary least square (OLS) regression. We then apply this equation to describe the empirical relationships between shadow and shrub fractions obtained from mixture decomposition with SMA and MESMA, respectively, and tree and shrub LAI, respectively. Less accurate fractions obtained from SMA result in weaker relationships between shadow fraction and tree LAI (R² = 0.61) and shrub fraction and shrub LAI (R² = 0.49) compared to the same relationships based on fractions obtained from MESMA with R² = 0.75 and R² = 0.68, respectively. Cross-validation of tree LAI (R² = 0.74; RMSE = 0.48) and shrub LAI (R² = 0.68; RMSE = 0.42) maps using fractions from MESMA shows the suitability of this approach for mapping tree and shrub LAI in ombrotrophic peatlands. The ability to account for a spectrally varying, unique Sphagnum moss ground cover during mixture decomposition and a two layer canopy is particularly important.     

Processing and Consolidation of Nanocrystalline Cu-Zn-Ti-Fe-Cr High-Entropy Alloys via Mechanical Alloying

In the current investigation, nanocrystalline multicomponent high-entropy alloys (HEAs) have been synthesized in the Cu _x Zn _y Ti₂₀Fe₂₀Cr₂₀ system (x/y = 1/0, 3/1, 1; and x + y = 40) by mechanical alloying and subsequently consolidated using spark plasma sintering (SPS) in argon atmosphere at a pressure of 50 MPa. A detailed X-ray diffraction and transmission electron microscopy study reveals the presence of both FCC copper solid-solution, (Cu)_ss and BCC chromium solid-solution, (Cr)_ss phases in both the mechanically alloyed powders as well as the sintered compacts. The phase formation and stability of the sintered multicomponent Cu _x Zn _y Ti₂₀Fe₂₀Cr₂₀ with x/y = 3/1 and x + y = 40 pellet have been studied at different sintering temperatures, i.e., 873 K, 973 K, 1073 K, and 1173 K (600 °C, 700 °C, 800 °C, and 900 °C). The important findings include that high Vickers bulk hardness of around 6 GPa and relative density of around 95 pct reported in the Cu _x Zn _y Ti₂₀Fe₂₀Cr₂₀ with x/y = 3/1 and x + y = 40 HEAs, SPSed at 1173 K (900 °C). The formation, consolidation, and microstructural details are analyzed critically and discussed.