A Review on the Sintering and Microstructure Development of Transparent Spinel (MgAl2O4)

A review of the densification mechanisms and the microstructural development for transparent spinel made by free sintering and by hot pressing is given. The paper is divided into two main parts. The first part considers spinel without any sintering additives because there still is some controversy concerning the role of cation stoichiometry on sintering and grain growth. The second part discusses the role of the classic sintering aid, LiF, in processing transparent spinel. LiF is shown to have multiple behaviors: (1) it initially wets spinel and forms a liquid phase at relatively low temperatures, which affects early-stage densification and also grain growth; (2) upon cooling from intermediate temperatures, or even from higher temperatures if microstructure evolution (e.g., formation of closed porosity) prevents volatization, the LiF-containing liquid dewets and resides in isolated pockets; (3) LiF alters the cation stoichiometry, thereby enhancing diffusion via an increase in the concentration of oxygen vacancies; this affects both the densification rate and grain growth; and (4) it reacts with impurities in the system, thereby acting as a cleanser. For the production of transparent spinel, it is critical that LiF or associated reaction products not be retained as a secondary phase.     

Use of Electric Fields to Monitor the Dynamical Aspect of Cell Behavior in Tissue Culture

Mammalian cells can be cultured and therefore studied in vitro. Normally, the cells' morphology and other static properties are observed with the aid of a light microscope. A method is described here that allows observation of the dynamical aspects of cultured cells. Mammalian fibroblasts are cultured in polystyrene dishes that contain evaporated gold electrodes. As the cells attach to the electrodes, their presence and their motion is directly reflected in the measured impedance.     

EFFECT OF PRECIPITATION TEMPERATURE ON THE COMPOSITION OF N-HEPTANE ASPHALTENES Part 2

Petroleum asphaltenes precipitated by n-heptane at temperatures between ambient and 80^°C from two crude oils have been characterized regarding hydrocarbon structures using ¹H and ¹³C nmr, and fluorescence spectroscopy. This indicates a very complex and apparently very small change in structural features except for a molecular weight increase as more material stays in solution at elevated temperature. Aromaticity increase and apparently alkyl chains diminish. The latter trend is however affected by the structural equation used. According to the fluorescence spectroscopy the content of large and complex chromophores increases but a significant effect of the presence of porphyrins on the spectra is also observed. The data is analyzed in combination with previous characterizations of the same asphaltenes presented in the first part of this work (Andersen, 1994). This indicates that as smaller molecules are extracted at elevated temperature the precipitated asphaltenes tend to associate more. This implys that these small molecules block association sites which therefore become available for further association at elevated temperature. For Boscan part of the smaller easy to extract porphyrins may have this behavior.     

Control of food intake in children by reinforcement of relevant verbal behavior.

Amounts consumed of 4 foods were recorded for each child in nursery school. 10 children were randomly selected for repeated sessions of verbal conditioning, which occurred shortly before snack time, and consisted of reinforcing the verbal behavior (food term) denoting the food selected for manipulation. The data give evidence that when positive reinforcement is associated with the verbal response denoting a food, then the consumption of that food increases. Conceptually, food can be considered a stimulus that sets up a class of responses, including verbal and eating responses. If the verbal response in that class is reinforced, hence strengthened, then the other responses of that class will be strengthened as well. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Optimal operation of Petlyuk distillation: steady-state behavior

The “Petlyuk” or “dividing-wall” or “fully thermally coupled” distillation column is an interesting alternative to the conventional cascaded binary columns for separation of multi-component mixtures. However, the industrial use has been limited, and difficulties in operation have been reported as one reason. With three product compositions controlled, the system has two degrees of freedom left for on-line optimization. We show that the steady-state optimal solution surface is quite narrow, and depends strongly on disturbances and design parameters. Thus it seems difficult to achieve the potential energy savings compared to conventional approaches without a good control strategy. We discuss candidate variables which may be used as feedback variables in order to keep the column operation close to optimal in a “self-optimizing” control scheme.     

Application of proteomics to understand the molecular mechanisms behind meat quality

The proteome is expressed from the genome, influenced by environmental and processing conditions, and can be seen as the molecular link between the genome and the functional quality characteristics of the meat. In contrast to traditional biochemical methods where one protein is studied at a time, several hundred proteins can be studied simultaneously. Proteomics is a promising and powerful tool in meat science and this is reflected by the increasing number of studies emerging in the literature using proteomics as the key tool to unleash the molecular mechanisms behind different genetic backgrounds or processing techniques of meat. Thus understanding the variations and different components of the proteome with regard to a certain meat quality or process parameter will lead to knowledge that can be used in optimising the conversion of muscles to meat. At present, there has been focus on development of techniques and mapping of proteomes according to genotypes and muscle types. In the future, focus should be more towards understanding and finding markers for meat quality traits. This review will focus on the methods used in the published proteome analyses of meat, with emphasis on the challenges related to statistical analysis of proteome data, and on the different topics of meat science that are investigated.     

Local entropy generation and entropy fluxes of a transient flame during head-on quenching towards solid and hydrogen-permeable porous walls

Premixed H₂-air flames are studied in a one-dimensional wall-bounded configuration. The laminar flame propagates towards and quenches at a wall that is either solid or permeable. Entropy generation by each of 19 elementary reactions is evaluated. Their total contribution remains the most important up to the quenching instance. Close to quenching, the conduction entropy generation grows considerable. Mass diffusion has a modest contribution, which decreases towards quenching. Viscous forces are negligible as a source of entropy. Effects of unburnt-mixture temperature and fuel-air ratio are investigated, and also dilution with nitrogen (inert) and water vapour. The diffusive entropy flux changed direction away from the permeating wall compared that of the solid wall. A major finding is that fuel permeation through the wall tends to decrease the entropy generation per unit of converted fuel, in particular for initially lean mixtures.     

Plant quality and harvest in old meadows grazed by reindeer in spring

Dry matter (DM) production and nutritional quality of plants were recorded on an old meadow before, during and after it was grazed by reindeer (Rangifer tarandus tarandus; 15 reindeer ha⁻¹) in the spring of 1996 and 1997 in northern Norway. Mean herbage harvest after 54 and 50 days of growth including 25 and 24 days of reindeer grazing was 1217 ± 320 kg DM ha⁻¹ in 1996 and 2297 ± 495 kg DM ha⁻¹ in 1997 respectively. On ungrazed old meadow, in contrast (P < 0.05), mean herbage harvest after 54 and 50 days of growth was 4159 ± 1164 kg DM ha⁻¹ in 1996 and 3791 ± 275 kg DM ha⁻¹ in 1997 respectively. In 1997, mean herbage harvest after 50 days of growth including 7 days of grazing by reindeer was as high as 3441 ± 180 kg DM ha⁻¹ (P > 0.05). Crude protein content (% of DM) was 25% early in the growing season in both 1996 and 1997. After 54 and 50 days of growth including 25 and 24 days of reindeer grazing, crude protein content was about 17% of DM in both 1996 and 1997 respectively, compared with about 12% of DM in ungrazed old meadow in both years. In 1997, crude protein content was 13.3% of DM after 50 days of growth including 7 days of reindeer grazing. The grazed and ungrazed old meadow contained about 20% (of DM) water‐soluble carbohydrates throughout the summer in both years. Mean plant cell wall content in ungrazed plants harvested after about 50 days was higher (51.5 and 49.1% of DM; P > 0.05) compared with plant cell wall content in grazed meadow (49.0 and 46.4% of DM) in 1996 and 1997 respectively. In vitro dry matter digestibility (%) of herbage harvest using rumen fluid from domestic ruminants was about 10% higher (73.4 ± 0.30 and 75.7 ± 0.28) in samples from grazed meadow compared with ungrazed meadow (66.2 ± 0.93 and 65.4 ± 1.19) in 1996 and 1997 respectively. Reindeer grazing of old meadow in spring maintains the vegetation at a younger phenological stage during the growing season when compared with ungrazed meadow. Therefore grazing increased the quality of the herbage, but decreased herbage harvest under conditions of high grazing intensity. © 2000 Society of Chemical Industry     

Semat—Three Year Vision

The purpose of writing this Three Year Vision paper is threefold. Firstly, it briefly recaps the progress Semat has made thus far; secondly, it lays out the future directions for people working actively within the Semat community; thirdly, it provides the background for seeking funding support from agencies, such as the European Community and the like. Funding support is necessary to sustain the ongoing activities of Semat and its growth into a broader community effort, as most people working within Semat are volunteers. As such, the paper may be both too much and too little for the wider supporter base. However, we intend to make our work fully transparent, hence, we publish it widely. We seek feedback and comments from supporters and signatories in order to improve the vision. In this context, other companion papers are being written to better address the specific needs for the practitioners, the industry and the academia.