Highly accurate measurements within the international system of units

Physics today presents a consistent model of natural phenomena based upon a coherent system of units of physical quantities. Knowledge of the most accurate values of the most important fundamental constants is essential for the traceability of units and for the refinement of theory. Of the four base units in the International System of units relevant to electrodynamics, the ampere can as yet only be realized with poor relative uncertainty of the order of 10^-6; the same holds true for the derived electric and magnetic units with the exception of the ohm. The accurate measurement of the gyromagnetic ratio of the proton γppromises to yield a more accurate realization of the ampere than that achieved using the traditional current balance.     

Preparative Protein Crystallization

Preparative protein crystallization can possibly replace one or more chromatographic steps in downstream processing. The development of such crystallization processes is demanding: first, promising principal crystallization conditions must be identified; second, details about the process must be defined; and third, the crystals have to be separated from the mother liquor without putting harm of their crystalline integrity. State‐of‐the‐art about these three steps is developing fast by (i) employing new screening methods which are based on fundamental understanding of the interaction of the protein molecules, (ii) application of existing concepts of technical bulk crystallization of small molecules to preparative protein crystallization, and (iii) making available specific gentle separation machinery.     

Meeting the Challenge of Chemical Language Barriers in University Level Chemistry Education

The specific yet varied challenges chemical language presents to students learning the subject are widely recognised. However, to effectively engage a student population becoming increasingly diverse in terms of culture, language and prior knowledge chemistry educators must develop pedagogical strategies that address issues of language comprehension. In this paper we discuss the body of literature that provides evidence of the multiple challenges that the language of chemistry presents students. These include: words in a scientific context, words with dual meaning, similar words and symbolic language. The chemistry learning triplet is used to illustrate how students must use chemical language to move between the macroscopic, sub‐microscopic and symbolic levels. Combining evidence from our research and the wider literature we describe a novel model of linguistic demand in multiple dimensions that represents the challenge of chemical language. This model can be used to assess the linguistic demand of teaching resources and to focus the appropriate use of language and literacy informed pedagogical strategies.     

Attrition and secondary nucleation in crystallizers

The mean crystal size of coarse crystalline products is determined by secondary nucleation and crystal growth. Secondary unclei are mainly produced by contacts of crystals with parts of the crystallizer or with other crystals. As a consequence, attrition effects are very important. In this paper, a model is proposed in order to calculate the attrition rate of crystals, depending on the physical properties of the crystalline product, the geometry of the crystallizer and on the operating conditions such as the stirrer speed or the suspension density. The effective rate of secondary nucleation can be expressed in terms of the attrition rate by introducing effective values for number and size of attrition particles. Finally, a scale-up criterion based on this model is derived. This criterion allows to predict effective rates of secondary nucleation and mean crystal sizes if data obtained in a laboratory crystallizer are available.     

Methodological and statistical issues of quality of life (QoL) and economic evaluation in cancer clinical trials: report of a workshop

In recent years, quality of life (QoL) and economic evaluations have become increasingly important as additional outcome measures in cancer clinical trials. However, both fields of research are relatively new and in need of finding solutions to a substantial number of specific methodological problems. This paper reports on the proceedings of a symposium aimed at summarising and discussing some of the most contentious methodological and statistical issues in QoL and economic evaluations. In addition, possible solutions are indicated and the most pertinent areas of research are identified. Issues specific to QoL evaluations that are addressed include clinically meaningful changes in QoL scores; how to analyse QoL data and to handle missing and censored data and integration of length of life and QoL outcomes. Issues specific to economic evaluations are the advantages and disadvantages of various outcome measures; statistical methods to analyse economic data and choice of decision criteria and analytical perspective. How to perform QoL and economic evaluations in large and simple trials and whether the gap between QoL and utility measures can be bridged are also discussed.     

Inorganic Precipitated Silica Gel. Part 2: Fragmentation by Mechanical Energy

Precipitated silica (SiO₂) is industrially produced by mixing a silicate solution with acid in a semi‐batch process. Polycondensation of monomeric silica leads to the formation of particles which aggregate and eventually form a particulate gel. However, this is instantly fragmented by the mechanical energy input caused by the stirrer. Shrinkage and compaction of these fragments lead to the final product aggregates. It is the aim of this study to enable tailoring of the structure and size of these product particles via the process parameters. In the present paper this is achieved by varying the stirrer speed. It can be shown that there is an analogy between the behavior of the gel and that of highly viscous liquids. Unexpectedly, however, the fragment size can not be reversibly controlled by the power input. The influence of the process parameters on the strength of the gel has been described in the first part of this series [1].