Random Sequential Adsorption on Random Trees

When gas molecules bind to a surface they may do so in such a way that the adsorption of one molecule inhibits the arrival of others. Two models which have frequently been studied are the “dimer model” and the “blocking model”, and rather complete solutions for these are known on fixed tree structures or Bethe lattices. In this paper comparisons are made between the occupation probabilities for vertices between fixed and random trees.     

A Framework for Characterizing Middle School Students' Statistical Thinking

People make use of quantitative information on a daily basis. Professional education organizations for mathematics, science, social studies, and geography recommend that students, as early as middle school, have experience collecting, organizing, representing, and interpreting data. However, research on middle school students' statistical thinking is sparse. A cohesive picture of middle school students' statistical thinking is needed to better inform curriculum developers and classroom teachers. The purpose of this study was to develop and validate a framework for characterizing middle school students' thinking across 4 processes: describing data, organizing and reducing data, representing data, and analyzing and interpreting data. The validation process involved interviewing, individually, 12 students across Grades 6 through 8. Results of the study indicate that students progress through 4 levels of thinking within each statistical process. These levels of thinking were consistent with the cognitive levels postulated in a general developmental model by Biggs and Collis (1991).     

Space environmental testing of flexible coverglass alternatives based on siloxanes

With the development of thin-film, high-efficient III–V solar cells using the epitaxial lift-off technique, flexible solar panels for space applications can be designed. Besides new deployment options, this also reduces the mass and thus launch costs of a satellite. One requirement for such a flexible panel configuration is the replacement of the brittle coverglass, which shields the solar cells from the harsh space environment, by a flexible alternative. In this work we have tested several compositions of a polysiloxane candidate material for a flexible shielding layer by exposing them to high energy UV and electron radiation at elevated temperatures. It was found that irradiation by electrons with a fluence corresponding to 15 years in space produces little degradation. UV radiation, on the other hand, has a more pronounced impact on the material properties, causing a discolouration of the transparent material and for some compositions even cracking of the samples.     

Infrared spectroscopic studies of monothiol ligand adsorption on CdS nanocrystal films in aqueous solutions

Probing the surface chemistry of thiol ligand binding to cadmium chalcogenide nanocrystals is important to clarify factors involved in quantum dot stability and surface functionalization. Deposited CdS nanocrystal films have been used in this work as model quantum dot surfaces for ligand adsorption studies. The adsorption of mercaptoacetic acid, mercaptopropionic acid, and mercaptoethanol, from aqueous solution to CdS thin films, has been studied by in situ infrared spectroscopy. The absence of a S-H stretch absorption for the adsorbed species shows that adsorption occurs via the deprotonated thiol group, and the spectrum of the adsorbed carboxylic acid species closely resembles those of the solution ligands. Adsorption of mercaptoacetic acid and of mercaptopropionic acid resulted in pKa(COOH) decreases of 1.5 and 0.5, respectively. Significant changes in the spectrum of mercaptoethanol upon adsorption have been observed, but the present uncertainty in mercaptoethanol spectral interpretation does not provide structural inferences. Adsorption isotherms determined from the spectral data indicate strong thiol adsorption to CdS. The adsorption isotherms have been fitted to both Langmuir and Freundlich equations, with the latter providing a better fit. This may be attributed to a change in the probability of adsorption to vacant surface sites due to the increased CdS surface negative charge as the surface coverage increases.     

Synthesis, structural characterization, in vitro anti-proliferative effect and cell cycle analysis of N-(ferrocenyl)benzoyl dipeptide esters

N-ortho, meta and para-(ferrocenyl)benzoyl dipeptide esters 2-10 were prepared by coupling ferrocenyl benzoic acids 1(ortho, meta and para) to the dipeptide ethyl esters GlyAbu(OEt) 2-4, GlyNva(OEt) 5-7 and GlyNle(OEt) 8-10 in the presence of N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride and 1-hydroxybenzotriazole. The compounds were fully characterized by a range of NMR spectroscopic techniques, mass spectrometry and cyclic voltammetry. The cytotoxicity of 3, 6 and 9 versus H1299 lung cancer cells were 10.5 μM, 19.1 μM and 18.9 μM, respectively, whereas N-{meta-(ferrocenyl)-benzoyl}-glycine-l-alanine ethyl ester 11 and N-{para-(ferrocenyl)-benzoyl}-glycine-l-alanine ethyl ester 12 gave IC₅₀ values of 4.0 and 6.6 μM, respectively. Therefore, an increase in alkyl chain length of the second amino acid also increases the IC₅₀ values. Cell cycle analysis of N-{ortho-(ferrocenyl)-benzoyl}-glycine-l-alanine ethyl ester 13 suggests a block in the G2/M phase of the cell cycle.     

Minimal Euclidean representations of graphs

A simple graph G is representable in a real vector space of dimension m, if there is an embedding of the vertex set in the vector space such that the Euclidean distance between any two distinct vertices is one of only two distinct values, α and β, with distance α if the vertices are adjacent and distance β otherwise. The Euclidean representation number of G is the smallest dimension in which G is representable. In this note, we bound the Euclidean representation number of a graph using multiplicities of the eigenvalues of the adjacency matrix. We also give an exact formula for the Euclidean representation number using the main angles of the graph.     

Highly scalable discrete-particle simulations with novel coarse-graining: accessing the microscale

ABSTRACT

Simulating energetic materials with complex microstructure is a grand challenge, where until recently, an inherent gap in computational capabilities had existed in modelling grain-scale effects at the microscale. We have enabled a critical capability in modelling the multiscale nature of the energy release and propagation mechanisms in advanced energetic materials by implementing, in the widely used LAMMPS molecular dynamics (MD) package, several novel coarse-graining techniques that also treat chemical reactivity. Our innovative algorithmic developments rooted within the dissipative particle dynamics framework, along with performance optimisations and application of acceleration technologies, have enabled extensions in both the length and time scales far beyond those ever realised by atomistic reactive MD simulations. In this paper, we demonstrate these advances by modelling a shockwave propagating through a microstructured material and comparing performance with the state-of-the-art in atomistic reactive MD techniques. As a result of this work, unparalleled explorations in energetic materials research are now possible.