The phase shift method applied to cross grating moiré measurements

The automatic evaluation of the grating deformation in a moiré image is greatly enhanced by the phase shift method. Based on three or more local grey values of a related number of phase shifted moiré patterns, the local displacement of a deformed grating against a reference grating, and hence the total displacement in one direction, is calculated. In this paper an extension to cross gratings is presented yielding a two- dimensional displacement field.     

Blackbody Infrared Radiative Dissociation of Protonated Oligosaccharides

The dissociation pathways, kinetics, and energetics of protonated oligosaccharides in the gas phase were investigated using blackbody infrared radiative dissociation (BIRD). Time-resolved BIRD measurements were performed on singly protonated ions of cellohexaose (Cel₆), which is composed of β-(1 → 4)-linked glucopyranose rings, and five malto-oligosaccharides (Mal_x, where x = 4–8), which are composed of α-(1 → 4)-linked glucopyranose units. At the temperatures investigated (85–160 °C), the oligosaccharides dissociate at the glycosidic linkages or by the loss of a water molecule to produce B- or Y-type ions. The Y ions dissociate to smaller Y or B ions, while the B ions yield exclusively smaller B ions. The sequential loss of water molecules from the smallest B ions (B₁ and B₂) also occurs. Rate constants for dissociation of the protonated oligosaccharides and the corresponding Arrhenius activation parameters (E_a and A) were determined. The E_a and A-factors measured for protonated Mal_x (x > 4) are indistinguishable within error (~19 kcal mol⁻¹, 10¹⁰ s⁻¹), which is consistent with the ions being in the rapid energy exchange limit. In contrast, the Arrhenius parameters for protonated Cel₆ (24 kcal mol⁻¹, 10¹² s⁻¹) are significantly larger. These results indicate that both the energy and entropy changes associated with the glycosidic bond cleavage are sensitive to the anomeric configuration. Based on the results of this study, it is proposed that formation of B and Y ions occurs through a common dissociation mechanism, with the position of the proton establishing whether a B or Y ion is formed upon glycosidic bond cleavage.     

Highly cross-linked UV-cured siloxane copolymer networks as icephobic coatings

Preventing ice growth on infrastructure, vehicles, and appliances remains a significant engineering challenge. Damage caused by ice growth on these installations can be expensive to repair, and their failure can be dangerous. Materials such as cross-linked polymer networks make effective anti-ice coatings and can prevent ice growth: reducing the cost of infrastructure repairs and limiting downtime. A link between cross-link density and ice adhesion has been demonstrated, such that lower cross-link density materials tend toward lower ice adhesion. Here we describe a method of lowering cross-link density by incorporating the covalently bound comonomers methyl methacrylate, lauryl methacrylate, and styrene into UV-cured PDMS-based polymer networks. Cross-link density, hardness, surface roughness, and ice adhesion on these materials are tested, showing the influence of comonomer proportions on their properties. Durability is found to increase with the addition of 5, 10, and 25 wt% comonomer, with little to no effect on ice adhesion until 25 wt%, where increases in ice adhesion are observed. Coatings show promisingly low ice adhesion of ~50 kPa, maintaining this low adhesion for up to 50 deicing cycles.     

Analysis and Application of the Rational B-Spline Finite Element Method in 2D

Non-Uniform Rational B-Splines (NURBS) are basis functions used in CAD software to describe exact geometric models. The implementation of these basis functions in the context of the Finite Element Analysis (FEA) is known as isogeometric analysis. The concept and definition of NURBS is briefly presented here. Since these functions are implemented as shape functions for the isogeometric analysis, the refinement strategies are discussed. The example of an infinite plate with circular hole serves as a benchmark. Finally, isogeometric analysis is applied to gradient elasticity since NURBS functions are of higher continuity and this is required in gradient elasticity. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A performance comparison study between subroutine packages LINSYS,IBMSSP and IMSL for solving systems of linear equations

A comparison for a range of linear equation problems Ax = b between LINSYS, IBMSSP and IMSL is made.     

Thermal dissociation of protein-oligosaccharide complexes in the gas phase: mapping the intrinsic intermolecular interactions

Blackbody infrared radiative dissociation (BIRD) and functional group replacement are used to map the location and strength of hydrogen bonds between an antibody single chain fragment (scFv) and its natural trisaccharide receptor, alpha-D-Galp (1-->2)[alpha-D-Abep (1-->3)]alpha-D-Manp1-->OMe (1), in the gaseous, multiply protonated complex. Arrhenius activation parameters (E(a) and A) are reported for the loss of 1 and a series of monodeoxy trisaccharide congeners (5-8 identical with tri) from the (scFv + tri + 10H)(+10) complex. The energetic contribution of the specific oligosaccharide OH groups to the stability of the (scFv + 1 + 10H)(+10) complex is determined from the differences in E(a) measured for the trisaccharide analogues and 1 (55.2 kcal/mol). A decrease of 6 to 11 kcal/mol in E(a), measured for the monodeoxy trisaccharides, indicates that the deleted OH groups interact strongly with the scFv and that they account for a majority of the stabilizing intermolecular interactions. A partial map of the hydrogen bond donor/acceptor groups of 1 and the strength of the interactions is presented for the protonated +10 complex. A comparison of the gas-phase map with the crystal structure indicates that significant structural differences exist. The hydroxyl groups located outside of the binding pocket, and exposed to solvent in solution, participate in new protein-oligosaccharide hydrogen bonds in the gas phase. The decrease in kinetic and energetic stability of the (scFv + 2 + nH)(n)()(+) complex with increasing charge-state is attributed to conformational differences in the binding region induced by electrostatic repulsion. The similarity in the Arrhenius parameters for the +9 and +10 charge states suggests that repulsion effects on the structure of the binding region are negligible below +11.     

A naturally occurring omega current in a Kv3 family potassium channel from a platyhelminth

Background  

Voltage-gated ion channels are membrane proteins containing a selective pore that allows permeable ions to transit the membrane in response to a change in the transmembrane voltage. The typical selectivity filter in potassium channels is formed by a tetrameric arrangement of the carbonyl groups of the conserved amino-acid sequence Gly-Tyr-Gly. This canonical pore is opened or closed by conformational changes that originate in the voltage sensor (S4), a transmembrane helix with a series of positively charged amino acids. This sensor moves through a gating pore formed by elements of the S1, S2 and S3 helices, across the plane of the membrane, without allowing ions to pass through the membrane at that site. Recently, synthetic mutagenesis studies in the Drosophila melanogaster Shaker channel and analysis of human disease-causing mutations in sodium channels have identified amino acid residues that are integral parts of the gating-pore; when these residues are mutated the proteins allow a non-specific cation current, known as the omega current, to pass through the gating-pore with relatively low selectivity.     

Delivering Transmembrane Peptide Complexes to the Gas Phase Using Nanodiscs and Electrospray Ionization

The gas-phase conformations of dimers of the channel-forming membrane peptide gramicidin A (GA), produced from isobutanol or aqueous solutions of GA-containing nanodiscs (NDs), are investigated using electrospray ionization-ion mobility separation-mass spectrometry (ESI-IMS-MS) and molecular dynamics (MD) simulations. The IMS arrival times measured for (2GA + 2Na)²⁺ ions from isobutanol reveal three different conformations, with collision cross-sections (Ω) of 683 Å² (conformation 1, C1), 708 Å² (C2), and 737 Å² (C3). The addition of NH₄CH₃CO₂ produced (2GA + 2Na)²⁺ and (2GA + H + Na)²⁺ ions, with Ω similar to those of C1, C2, and C3, as well as (2GA + 2H)²⁺, (2GA + 2NH₄)²⁺, and (2GA + H + NH₄)²⁺ ions, which adopt a single conformation with a Ω similar to that of C2. These results suggest that the nature of the charging agents, imparted by the ESI process, can influence dimer conformation in the gas phase. Notably, the POPC NDs produced exclusively (2GA + 2NH₄)²⁺ dimer ions; the DMPC NDs produced both (2GA + 2H)²⁺ and (2GA + 2NH₄)²⁺ dimer ions. While the Ω of (2GA + 2H)²⁺ is similar to that of C2, the (2GA + 2NH₄)²⁺ ions from NDs adopt a more compact structure, with a Ω of 656 Å². It is proposed that this compact structure corresponds to the ion conducting single stranded head-to-head helical GA dimer. These findings highlight the potential of NDs, combined with ESI, for transferring transmembrane peptide complexes directly from lipid bilayers to the gas phase.

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