Molecular electronics: insight from first-principles transport simulations

Conduction properties of nanoscale contacts can be studied using first-principles simulations. Such calculations give insight into details behind the conductance that is not readily available in experiments. For example, we may learn how the bonding conditions of a molecule to the electrodes affect the electronic transport. Here we describe key computational ingredients and discuss these in relation to simulations for scanning tunneling microscopy (STM) experiments with C60 molecules where the experimental geometry is well characterized. We then show how molecular dynamics simulations may be combined with transport calculations to study more irregular situations, such as the evolution of a nanoscale contact with the mechanically controllable break-junction technique. Finally we discuss calculations of inelastic electron tunnelling spectroscopy as a characterization technique that reveals information about the atomic arrangement and transport channels.     

Experimental investigation of an industrial scale black liquor gasifier. 1. The effect of reactor operation parameters on product gas composition

A novel technology to mitigate the climate changes and improve energy security is Pressurized Entrained flow High Temperature Black Liquor Gasification (PEHT-BLG) in combination with an efficient fuel synthesis using the resulting syngas. In order to optimise the technology for use in a pulp and paper mill based biorefinery, it is of great importance to understand how the operational parameters of the gasifier affect the product gas composition. The present paper is based on experiments where gas samples were withdrawn from the hot part of a 3 MW entrained flow pressurized black liquor gasifier of semi industrial scale using a high temperature gas sampling system. Specifically, the influence of process conditions on product gas composition (CO₂, CO, H₂, CH₄, H₂S, and COS) were examined by systematically varying the operational parameters: system pressure, oxygen to black liquor equivalence ratio, black liquor flow rate to pressure ratio and black liquor pre-heat temperature. Due to the harsh environment inside the gasification reactor, gas sampling is a challenging task. However, for the purpose of the current study, a specially designed high temperature gas sampling system was successfully developed and used. The results, obtained from two separate experimental campaigns, show that all of the investigated operational parameters have a significant influence on the product gas composition and present valuable information about to the process characteristics.     

Cationic peptides that increase the thermal stabilities of 2'-O-MeRNA/RNA duplexes but do not affect DNA/DNA melting

Several different cationic nonapeptides have been synthesized and investigated with respect to how they can influence the thermal melting of 2′‐O‐methylRNA/RNA and DNA/DNA duplexes. Each peptide has a C‐terminal L ‐phenylalanine unit and is otherwise uniformly composed of a sequence of a specific basic D ‐amino acid that in most cases will be largely charged at neutral pH. These N‐terminal octamer stretches are composed variously of the amino acids D ‐lysine, D ‐diaminobutyric acid (D ‐Dab), D ‐diaminopropionic acid (D ‐Dap), or D ‐histidine. None of the peptides substantially affected the thermal melting of DNA/DNA duplexes, which was in sharp contrast with their effects on 2′‐O‐methylRNA/RNA duplexes. In particular, the peptides based on diaminopropionic and diaminobutyric acid units had strong positive effects on the melting temperatures of the 2′‐O‐methylRNA duplexes (up to 16 °C higher with 1 equivalent of peptide) at pH 7, whereas at pH 6 the effect was even more drastic (ΔT_m up to +25 °C). The shorter R groups of the Dap and Dab groups appear to have a better length than lysine for enhancement of the thermal melting of the 2′‐O‐methylRNA/RNA duplex, an effect that is more pronounced at lower pH but substantial even at pH 7, although the Dap derivative is not likely to be fully protonated. The dramatic difference between the influence, or lack thereof, on the 2′‐O‐methylRNA/RNA and the DNA/DNA thermal meltings suggest that, although electrostatic interactions probably play a role, there is another major and structurally dependent component influencing the properties of the duplexes. This is also seen in the observation that the oligo‐Dap and oligo‐Dab peptides give greater melting point enhancements than both the lysine peptide (with a longer side chain) and a β‐linked Dap peptide with a shorter side chain and a longer backbone.     

A New Look at Agenda‐Setting Effects—Comparing the Predictive Power of Overall Political News Consumption and Specific News Media Consumption Across Different Media Channels and Media Types

The purpose of this study was to compare the predictive power of overall political news consumption and media‐specific news consumption, on perceived issue salience across different media channels and media types in the context of the 2006 Swedish parliamentary election. Findings suggest that overall consumption of political news is significantly more important than consumption of specific media outlets in predicting changes in issue salience. Although the study demonstrates that the Swedish news media collectively can exert considerable agenda‐setting influence over their audiences, it could, however, not find any consistent evidence of differences related to media channels or media types. The reasons for and implications of the results are discussed.     

Extended studies of degradation mechanisms in the refractory lining of a rotary kiln for iron ore pellet production

Changes, over a period of 8 years, in the chemical composition and morphology of deposit and lining materials in a production rotary kiln for iron ore pellet manufacture are described. The following have been studied: two types of refractory brick used as lining material; deposited chunk materials from the lining; the interaction zones between deposits and linings. Morphological changes at the deposit/lining interface, and the active chemical reactions, are established. Larger hematite grains in the deposit material (5–50 μm) primarily remain at the original deposit/lining interface. The remainder penetrates fissures, voids and brick joints, forms a laminar structure with corundum from the bricks, and migrates in grains in the lining material. Potassium penetrates more deeply into the bricks than hematite, resulting in the formation of kalsilite, leucite and potassium β-alumina, which contribute to degradation of the lining.     

Effect of Silver Loading on the Lean NOx Reduction with Methanol Over Ag–Al2O3

The influence of silver loading on the lean NO_x reduction activity using methanol as reductant has been studied for alumina supported silver catalysts. In general, increasing the silver loading (0–3 wt%), in Ag–Al₂O₃, shifts or extends the activity window, for lean NO_x reduction towards lower temperatures. In particular Ag–Al₂O₃ with 3 wt% silver is active for NO_x reduction under methanol-SCR conditions in a broad temperature interval (200–500 °C), with high activity in the low temperature range (maximum around 300 °C) typical for exhaust gases from diesel and other lean burn engines. Furthermore, increasing the C/N molar ratio enhances the reduction of NO_x. However, too high C/N ratios results in poor selectivity to N₂.     

STEAM DRYLNG OF WOOD FUELS

ABSTRACT

The objective of this work is to investigate some of the important aspects in the design of a steam band dryer for wood fuels. For this purpose the drying of the material in a bench-scale fixed bed dryer has been studied.

Drying times and thermal efficiencies for experiments conducted under different conditions are compared. The investigated materials are soft-and hardwood chips and softwood bark.

The thermal efficiency, the part of the sensible heat which is used during one passage of the steam through the bed, increases with increasing mass load (mass of dry matter per unit area) and with decreasing steam mass flux. At a mass load of 30 kg/m the thermal efficiency is about 0.85 even at steam mass fluxes as high as 0.6 kg/m² s (1.2 m/s). The thermal efficiency proves to be almost independent of pressure and temperature of the steam.

Due to the very inhomogeneous materials the steam mass flow distribution was uneven. This causes a decreased thermal efficiency. When bark     

Topology optimization of structures with manufacturing and unilateral contact constraints by minimizing an adjustable compliance–volume product

In this paper the concept of extended optimality, or hyperoptimality, is adopted. By following this idea, a new compliance–volume product is suggested as objective. The volume appearing in the product is also raised to the power of a new design parameter which can be set to different values. In such manner design concepts with different volume fractions can be generated by using the approach of extended optimality. Both manufacturing constraints and unilateral contact constraints are included in the proposed method. The manufacturing constraints are implemented by adjusting the move limits such that the draw directions are satisfied. Both one draw direction as well as split draw constraints are considered. The contact conditions are modeled by the augmented Lagrangian approach such that the Jacobian in the Newton algorithm as well as in the adjoint equation becomes symmetric. The design parametrization is done by the SIMP model and Sigmund’s filter is utilized when the sensitivities are calculated. The proposed method is very robust and efficient. This is demonstrated by solving problems in both 2D and 3D. The numerical results are also compared to solutions obtained by performing compliance optimization with a constraint on the volume fraction.     

Multivariable data analysis of a cold rolling control system to minimise defects

This paper focuses on the application of principal component analysis (PCA) to thoroughly analyse and interpret multidimensional data from a cold rolling process. The analysis includes the effects of variables on the final properties of strips in a cold rolling mill. Unscrambler software was used to analyse and identify hidden variables. Variable correlations were also used to derive correlations between the control parameters. The results of this research will be used to improve the selection of material in order to reduce the occurrence of defects in the cold rolling process and to improve the adjustment of the set points that are performed in every pass or section of the cold rolling process. The hot rolled strips that enter the cold rolling mill are made of different materials and are produced by different strip manufacturers. Some strips break during the thickness reduction process in the cold rolling mill. This paper focuses on two possible causes of breakage: non-uniform strip material properties and failures in the rolling mill process. Two types of rolled strips (those that break and those that do not break) were compared to identify causes of breakage. The results indicate that breakages are caused by material or process failures. PCA was applied to the dataset in order to identify and analyse the relationships between the variables in the process. This information was used to interpret and diagnose the process behaviour. Swarm analysis and relating observations to process behaviour were able to distinguish between different start-up conditions, and between desirable and undesirable process conditions.