Subcritical drying of silica gels

Silica aerogel is a sol-gel prepared material characterized by high porosity and large inner surface area. Aerogels can be prepared with a high transparency and low thermal conductivity, giving a material excellent for application as transparent thermal insulator. The traditional route to prepare silica aerogels is by formation of an alcogel by hydrolysis and condensation of silicon alkoxides followed by supercritical drying in an autoclave at high pressure (–100 atm). Unfortunately, this process is expensive and might be dangerous, so drying methods have been developed that operate under ambient conditions. In previous work, we have shown that gels can be strengthened and stiffened by providing new monomers to the alcogel giving xerogels with similar properties as aerogels by drying at ambient pressure (porosity up to 90%). This method of obtaining ambient pressure dried aerogels will be described and special emphasis will be given on the effect of the initial gel structure on the preparation of the xerogels.     

Determination of the vapor pressures of moth sex pheromone components by a gas chromatographic method

The vapor pressures of decyl acetate, five decenyl acetate isomers, (Z)-7-dodecenyl acetate, and (Z)-9-tetradecenyl acetate have been determined at three to six temperatures in the interval 25–45 °C by a gas Chromatographic method suitable for accurate measurements of the low vapor pressures of moth sex pheromone components at biologically relevant temperatures. The vapor pressure values at 30.5 °C are 3.80 Pa for decyl acetate, 4.08–5.40 Pa for the decenyl acetate isomers, 0.562 Pa for (Z)-7-dodecenyl acetate, and 0.094 Pa for (Z)-9-tetradecenyl acetate. The vapor pressures of the decenyl acetates show a small but significant dependence on the double bond position. Four of the compounds in this study, 10Ac,Z5–10Ac,Z7–12Ac, andZ9–14Ac have recently been identified as sex pheromone components of the turnip moth,Agrotis segetum. Large differences between the mole percentages of the component as found in liquid extracts of female abdominal tips and the corresponding mole percentages in the vapor phase are predicted.     

Preparation of fetal rat brains for light and electron microscopy

To study cellular shapes, growth patterns, and fine structure during early stages of CNS development in rat embryos, preparative procedures were evaluated and modified to meet two criteria: (1) Coronal semithin sections should reveal undeformed telencephalic hemispheres that were symmetrically expanded on both sides of midline structures and were surrounded by contiguous mesenchyme. (2) In electron micrographs, cells should have intact, undistorted surface membranes, evenly distributed nucleoplasm and well preserved cytoplasmic organelles. To meet these criteria, 378 fetuses with a gestational age of 11–20 days (E11–E20) were used to test and modify procedures for anesthesia, embryo removal and handling, dissection, fixation, dehydration, and embedding of the embryonic CNS. Most specimens were in an early stage of development (E11–E13), which, in case of the neopallial wall, is the preneural period. The tests produced methods that met the above criteria and identified the most common artifacts and their causes. Deformities of the cerebral hemispheres and separations between the brain and its coverings were usually caused by trauma during embryo removal and during handling before fixation. Changes in cellular volumes, especially swelling during fixation and dehydration, were the most important causes of histological artifacts. The procedures and methods that consistently produced the best light and electron microscopic preservation of the E11–E13 rat CNS are described. Fixation was best when the brains were treated with glutaraldehyde and s-collidine buffer, followed by osmium tetroxide in s-collidine buffer. A surprisingly beneficial effect of sodium chloride in the dehydrating alcohol was noted.     

Frequency-domain properties of Kalman filters

This paper explores the frequency-domain characteristics of the steady-state Kalman filter. It gives insight into the properties of the filter that are useful for analysis and design. The results are illustrated by a number of industrial applications.     

Contents of dietary fibre components and their relation to associated bioactive components in whole grain wheat samples from the HEALTHGRAIN diversity screen

A large and diverse material collection of whole grain wheat samples (n = 129) was analysed for total dietary fibre (TDF) content and composition, including fructan (11.5–15.5%). Correlations between the dietary fibre components, associated bioactive components (e.g. tocols, sterols, phenolic acids and folates) and agronomic properties previously determined on the same samples were found with multivariate analysis (PCA). Samples from the same countries had similar characteristics. The first PC described variation in components concentrated in the starchy endosperm (e.g. starch, β-glucan and fructan) and the dietary fibre components concentrated in the bran (e.g. TDF, arabinoxylan and cellulose). The second PC described the variation in kernel weight and other bran components such as alkylresorcinols, tocols and sterols. Interestingly, there was no correlation among these different groups of bran components, which reflected their concentration in different bran tissues. The results are of importance for plant breeders who wish to develop varieties with health-promoting effects.     

Interphase precipitation in niobium-microalloyed steels

The interphase precipitation in niobium steel has been investigated. In the present work, the austenite/ferrite transformation speed should be fast due to hot deformations, and interphase precipitation can be observed after 10 s isothermal holding in the temperature range 923–1023 K. The dominant interphase precipitation is planar and is not oriented on the {1 1 0}α plane suggested by the ledge mechanism but on other planes.     

Evaluation of herd-level sampling strategies for control of Salmonella in Swedish cattle

Based on Swedish legislation, all herds where Salmonella of any serotype is detected are put under restrictions, and measures aiming at eradication are required. Costs for sampling and control have increased in recent years and the aim of this study was to investigate the efficiency of different sampling strategies. We also compiled test results from recent surveillance activities and used these to complement and compare with calculated results. Sensitivities and specificities at group and herd level were calculated for different test strategies. A scenario-tree modeling approach was used to account for the hierarchy of animals within herds, and different relative risk of salmonella in different age groups. Negative and positive predictive values (NPV and PPV), and probability of freedom from Salmonella were calculated to compare the added value of different sampling strategies. Results showed that more fecal samples than serological samples per group are needed to reach a group sensitivity >0.50. This also means that serological testing leads to a higher NPV. For example, with 10 negative test-results from a group of 25 animals in a herd with a suspicion of Salmonella, the NPV based on serology was 0.75 and based on culture was 0.56. For the PPV, testing based on culture from fecal sampling was superior, as specificity of such testing was close to perfect. By changing the threshold for considering a group positive, from 1 test-positive animal to 2, the PPV of serological results could be increased without substantial loss in NPV. The herd sensitivity based on (1) bulk milk sampling, (2) fecal sampling of all animals, and (3) bulk milk sampling and individual sera from 20 animals within each age group was 0.53, 0.88, and 0.95, respectively. In low-prevalence regions, this sensitivity was enough to verify a high probability of freedom (>0.99), as the probability of infection in such Swedish regions has been shown to be 0.01. For herds with a higher prior probability of infection, repeated sampling (2–9 sampling occasions) was needed to reach the same level of confidence. Analysis of surveillance data indicated that boot swabs can be used to replace the standard fecal sampling presently used in Sweden. It was also confirmed that the individual specificity of the tests used for serological testing of Swedish calves is high (0.99). The results can form a basis for fit-for-purpose testing strategies (e.g., surveillance or prepurchase testing).