Electronic structure, phase stability and chemical bonding in Th2_2Al and Th2_2AlH4_4

We present the results of theoretical investigation on the electronic structure, bonding nature and ground state properties of Th$_2$Al and Th$_2$AlH$_4$ using generalized-gradient-corrected first-principles full-potential density-functional calculations. Th$_2$AlH$_4$ has been reported to violate the "2 \AA rule" of H-H separation in hydrides. From our total energy as well as force-minimization calculations, we found a shortest H-H separation of 1.95 {\AA} in accordance with recent high resolution powder neutron diffraction experiments. When the Th$_2$Al matrix is hydrogenated, the volume expansion is highly anisotropic, which is quite opposite to other hydrides having the same crystal structure. The bonding nature of these materials are analyzed from the density of states, crystal-orbital Hamiltonian population and valence-charge-density analyses. Our calculation predicts different nature of bonding for the H atoms along $a$ and $c$. The strongest bonding in Th$_2$AlH$_4$ is between Th and H along $c$ which form dumb-bell shaped H-Th-H subunits. Due to this strong covalent interaction there is very small amount of electrons present between H atoms along $c$ which makes repulsive interaction between the H atoms smaller and this is the precise reason why the 2 {\AA} rule is violated. The large difference in the interatomic distances between the interstitial region where one can accommodate H in the $ac$ and $ab$ planes along with the strong covalent interaction between Th and H are the main reasons for highly anisotropic volume expansion on hydrogenation of Th$_2$Al.Comment: 14 pages, 9 figure

Infrastructure for Detector Research and Development towards the International Linear Collider

The EUDET-project was launched to create an infrastructure for developing and testing new and advanced detector technologies to be used at a future linear collider. The aim was to make possible experimentation and analysis of data for institutes, which otherwise could not be realized due to lack of resources. The infrastructure comprised an analysis and software network, and instrumentation infrastructures for tracking detectors as well as for calorimetry.Comment: 54 pages, 48 picture

Interactions between nodes in a physical gel network of telechelic polymers; self-consistent field calculations beyond the cell model

Triblock copolymers, with associative end-groups and a soluble middle block, form flower-like micelles in dilute solutions and a physical gel at higher concentrations. In a gel the middle blocks form bridges between domains/nodes that contain the ends. We combine the self-consistent field theory with a simple molecular model to evaluate the pair potential between the nodes. In this model the end-groups are forced to remain in nodes and the soluble middle blocks are in solution. When the distance between the centres of the nodes is approximately the corona diameter, loops can transform into bridges, and the pair potential is attractive. Due to steric hindrance, the interaction is repulsive at smaller distances. Till now a cell-model has been used wherein a central node interacts through reflecting boundary conditions with its images in a spherical geometry. This artificial approach to estimate pair potentials is here complemented by more realistic three-gradient SCF models. We consider the pair interactions for (i) two isolated nodes, (ii) nodes positioned on a line (iii) a central node surrounded by its neighbours in simple cubic ordering, and (iv) a central node in a face centred cubic configuration of its neighbours. Qualitatively, the cell model is in line with the more refined models, but quantitative differences are significant. We also notice qualitative differences for the pair potentials in the specified geometries, which we interpret as a breakdown of the pairwise additivity of the pair potential. This implies that for course grained Monte Carlo or molecular dynamics simulations the best choice for the pair potentials depends on the expected node density

Interactions between nodes in a physical gel network of telechelic polymers; self-consistent field calculations beyond the cell model

Triblock copolymers, with associative end-groups and a soluble middle block, form flower-like micelles in dilute solutions and a physical gel at higher concentrations. In a gel the middle blocks form bridges between domains/nodes that contain the ends. We combine the self-consistent field theory with a simple molecular model to evaluate the pair potential between the nodes. In this model the end-groups are forced to remain in nodes and the soluble middle blocks are in solution. When the distance between the centres of the nodes is approximately the corona diameter, loops can transform into bridges, and the pair potential is attractive. Due to steric hindrance, the interaction is repulsive at smaller distances. Till now a cell-model has been used wherein a central node interacts through reflecting boundary conditions with its images in a spherical geometry. This artificial approach to estimate pair potentials is here complemented by more realistic three-gradient SCF models. We consider the pair interactions for (i) two isolated nodes, (ii) nodes positioned on a line (iii) a central node surrounded by its neighbours in simple cubic ordering, and (iv) a central node in a face centred cubic configuration of its neighbours. Qualitatively, the cell model is in line with the more refined models, but quantitative differences are significant. We also notice qualitative differences for the pair potentials in the specified geometries, which we interpret as a breakdown of the pairwise additivity of the pair potential. This implies that for course grained Monte Carlo or molecular dynamics simulations the best choice for the pair potentials depends on the expected node density

Structural studies on methylated starch granules

Granules of potato starch and amylopectin potato starch were methylated in aqueous alkaline suspension. Here, an overview is given of all structural aspects that have been studied with respect to the determination of the location of the substituents. Methods, which are generally applicable, were developed for the separation of different areas of derivatised starch granules, followed by determination of the substitution level. For methylated starch granules it was found that methyl groups are predominantly present in branched regions and amorphous domains, and that amylose is higher substituted than amylopectin. No differences were found between substitution levels of granules of various sizes, nor radially across the granule

Substituent distribution in highly branched dextrins from methylated starches

Granular potato starch and amylopectin potato starch were methylated to molar substitutions (MS) up to 0.29. Extensive alpha-amylase digestion gave mixtures of partially methylated oligomers. Precipitation of larger fragments by methanol yielded mainly alpha-limit dextrins (8499%). Methanol precipitates were extensively digested with beta-amylase yielding alpha,beta-limit dextrins. The average substitution level of branched glucose residues in the dextrins thus obtained was determined after per deuteriomethylation by using FAB mass spectrometry, and compared with that of the linearly linked glucose residues. The present work demonstrates that methylation does not show any preference for substitution at either branched or linearly linked glucose residues, taking into account the inherently lower amount of substitution sites at branched residues. The results corroborate earlier studies wherein it was found that substituents in branched regions are distributed almost randomly. In addition, the data enable the determination of the average degree of branching of partially methylated dextrins

Distribution of methyl substituents over crystalline and amorphous domains in methylated starches

Granular potato starch and amylopectin potato starch were methylated in aqueous suspension with dimethyl sulfate to molar substitution (MS) up to 0.29. The percentage of amorphous starch compared with crystalline domains increased with increasing MS. Prolonged treatment of these methylated starches with hydrochloric acid below the swelling temperature resulted in the release of D-glucose and small D-glucose-oligomers from the amorphous domains. The granular structure was maintained during the acidic treatment, indicating that the crystalline lamellae were less affected by acid. The amorphous domains contained on average about twice as many substituents per glucose unit as the remaining crystalline network. The distributions of methyl substituents in trimers and tetramers, released from amorphous domains and prepared from crystalline fractions, were determined by FABMS and compared to the outcome of a statistically random distribution. Quantification of the degree of heterogeneity of the thus-obtained trimers and tetramers showed a much larger deviation from random substitution in the crystalline fractions compared with the amorphous ones. These results are in agreement with our previous study that describes substitution patterns in branched and linear regions of methylated starch granules

FAB CIDMS/MS analysis of partially methylated maltotrioses derived from methylated amylose : a study of the substituent distribution

Amylose was methylated with CH3I in alkaline aqueous suspension, yielding methylated amylose (MeAl) with a degree of substitution of 1.44 (s<0.01). Determination of the monomer composition showed that HO-6 and HO-2 were highly substituted in contrast to HO-3 (7:2:5.5, HO-2:HO-3:HO-6). By using partial acid hydrolysis, oligomers were prepared that varied both in degree of polymerisation and in methyl-content. Studies on the distribution of substituents in trimers showed large deviations from random distributions. By using CID tandem mass spectrometry, the substituent distribution in these trimers was determined in more detail. Various sets of trimers with equal amounts of methyl-groups but differing in substituted positions were quantified. From the monomer composition of MeAl, the probability of each trimer was calculated and compared to the outcome of the measured distributions. It was concluded that trimers with terminal tri- or non-substituted glucose monomers at the non-reducing end were formed preferentially during partial hydrolysis and that partial hydrolysis of MeAl yielded oligomers in a non-random way. This is the first study that describes the partial hydrolysis of MeAl in such detail

Distribution of methyl substituents in amylose and amylopectin from methylated potato starches

Granular potato starches were methylated in aqueous suspension with dimethyl sulfate to molar substitution (MS) values up to 0.29. Fractions containing mainly amylose or amylopectin were obtained after aqueous leaching of the derivatised starch granules. Amylopectin in these fractions was precipitated with Concanavalin A to separate it from amylose. Amylose remained in solution and was enzymatically converted into D-glucose for quantification, thereby taking into account the decreased digestibility due to the presence of methyl substituents. It was found that the MS of amylose was 1.61.9 times higher than that of amylopectin in methylated starch granules. The distributions of methyl substituents in trimers and tetramers, prepared from amylose- or amylopectin-enriched fractions, were determined by FAB mass spectrometry and compared with the outcome of a statistically random distribution. It turned out that substituents in amylopectin were distributed heterogeneously, whereas substitution of amylose was almost random. The results are rationalised on the basis of an organised framework that is built up from amylopectin side chains. The crystalline lamellae are less accessible for substitution than amorphous branching points and amylose