On cellulose dissolution and gelation

Cellulose is the World’s most abundant biopolymer and an important renewable raw material for many materials. For applications like textile fibers it is necessary to first dissolve the cellulose pulp. However, dissolving cellulose turns out to be a challenge. This crystalline polymer is insoluble in most classical polar and non-polar solvents, but soluble in certain ionic liquids and also (partly) in concentrated NaOH. Replacing sodium with the larger and more hydrophobic/amphiphilic tetrabutyl ammonium cation, increases the solubility. Cellulose solutions can turn into gels. The reason for this appears to involve the issue of crystal polymorphism. While natural (wood) cellulose, so called Cellulose I dissolves, solutions may become supersaturated with respect to the more stable Cellulose II. Recrystallizing polymers from semi-dilute solutions may lead to gelation as chains can participate in more than one nucleus

Cellulose association in solution

Cellulose is the World’s most abundant biopolymer and hence an important renewable raw material for many materials. It is (semi-)crystalline with a high melting point, and decomposes far before melting can be reached. Processing of cellulose thus require dissolution of the cellulose pulp. But, dissolving cellulose has turned out to be a challenge. Cellulose happens to be fascinatingly insoluble in all classical polar and non-polar solvents, because of its stable crystalline state. Solubility may, however, be obtained for example in certain ionic liquids and also (partly) in a strong base, the latter being the basis for the production of viscose fabrics. There are two major polymorphs of cellulose, native (wood) Cellulose I and the more stable Cellulose II. Dissolving pulp (Cellulose I) therefore may result in a supersaturated solution with respect to Cellulose II, and the association of cellulose in solution. It this talk we will discuss cellulose dissolution and association in solution, with the potential application of textile fiber spinning

Power Properties of Ordinal Regression Models for Likert Type Data

We discuss analysis of 5-grade Likert type data in the two-sample case. Analysis using two-sample t tests, nonparametric Wilcoxon tests, and ordinal regression methods, are compared using simulated data based on an ordinal regression paradigm. One thousand pairs of samples of size n=10 and n=30 were generated, with three different degrees of skewness. For all sample sizes and degrees of skewness, the ordinal probit model has highest power. This is not surprising since the data was generated with this model in mind. Slightly more surprising is that the t test has higher power than the Wilcoxon test in all studied situations, even for skewed data. For n=30, the differences between the methods are small

Gaps and Overlaps in Supervisory Responsibilities: A Case Study of Bachelor’s and Master’s Students’ Thesis Writing in Two Departments

This article focuses on how supervisors and students perceive their responsibilities at the beginning of the thesis writing process. Students in general do little research writing before beginning their Bachelor’s or Master’s programs and they often find academic writing to be a complicated task, which means that many do not complete their thesis writing within the stipulated time. A survey was conducted at the Department of Computer and Systems Sciences (DSV) and the Department of Child and Youth Studies (BUV) at Stockholm University, Sweden. In addition to the distribution of responsibility, participants ranked the importance of four issues: the student’s own collected data in the thesis; language, layout, and correct referencing; the thesis as an excellent product; and the student’s development of his or her competence. In general, students and supervisors agreed on the distribution of responsibilities between them and the importance of some of the issues. The opinions were coherent, considering the survey was conducted early in the thesis writing period. It is suggested that future research includes an in-depth investigation of cultural differences between departments

Safety Culture Onboard Ships

A project focusing on identifying and describing maritime risks is being conducted in the heavily trafficked water area of the Sound, situated in northern Europe between Sweden and Denmark. This paper reports of a test of a first version of a questionnaire constructed for measuring safety culture onboard vessels.48 crew members on a Swedish registered passenger/cargo ship completed and returned the questionnaire. The crew members were able to complete the questionnaire with few unanswered questions. Acceptable homogeneity was obtained for all but one of the nine dimensions of safety culture. Significant differences on several of the safety culture dimensions were found between deck/engine vs catering personnel, men vs women and different age groups, while little differences were found for supervisors vs non-supervisors or people with varying number of years onboard. Such safety culture dimensions need to be studied in relation to reports of accidents and near-misses, to further study the true relevance of safety culture

Ossification of ungular cartilages in front feet of cold-blooded trotters - a clinical radiographic evaluation of development over time

BACKGROUND: It has not yet been shown that ossification of ungular cartilages (OUC) is a pathological condition. Beside heredity, factors such as sex, age, repeated concussion, local trauma, hoof and body size have been suggested as contributing factors for OUC development. By comparing radiographs of front hooves from cold-blooded trotters with different age we wanted to evaluate when development of OUC in cold-blooded trotters occurs and if and when it stabilizes in relation to age and workload. Diagnosis and grading of OUC were based on radiological field examinations of 649 Swedish and Norwegian cold-blooded trotters’ front hooves. A hundred and forty-seven of the horses were re-examined 3-13 years (mean age 9, median 8 years) after the first occasion. All radiographs were evaluated blind, using two different grading systems for OUC. Work load, in form of number of races completed, and body size score were collected from official data. Four statistical ordinal regression models were used, compared and evaluated. RESULTS: We identified a breakpoint at 2.8 ± 0.38 years of age when ossification ends and proposed a simpler grading system with more consistent results. There was no significant correlation between body size and grade of OUC. Comparison of different statistical methods for evaluation of ordinal data revealed a piecewise linear regression model as most suitable. CONCLUSIONS: Individuals with OUC developed this condition during the stage of life when their hooves develop in size. Results from this study can assist equine practitioners when examining and for understanding this condition in their clinical work and is also beneficial for the Scandinavian equine industry when devising breeding programs