On helical shear of a compressible elastic circular cylindrical tube

In this paper we examine the combined azimuthal and axial shear of a compressible isotropic elastic circular cylindrical tube of finite extent, otherwise referred to as helical shear (which is an isochoric deformation). The equilibrium equations are formulated in terms of the principal stretches, and explicit necessary and sufficient conditions on the strain-energy function for the material to support this deformation are obtained and compared with those obtained previously for this problem. Several classes of strain-energy functions are derived and in some general cases complete solutions of the equilibrium equations are obtained. Existing results are recovered as special cases and some new results for the strain-energy functions derived are determined and discussed.

Plasma-enabled growth of ultralong straight, helical, and branched silica photonic nanowires

This article reports on the lowerature inductively coupled plasma-enabled synthesis of ultralong (up to several millimeters in length) SiO2 nanowires, which were otherwise impossible to synthesize without the presence of a plasma. Depending on the process conditions, the nanowires feature straight, helical, or branched morphologies. The nanowires are amorphous, with a near-stoichiometric elemental composition ([O] / [Si] =2.09) and are very uniform throughout their length. The role of the ionized gas environment is discussed and the growth mechanism is proposed. These nanowires are particularly promising for nanophotonic applications where long-distance and channelled light transmission and polarization control are required.

Indigenous university champion angles for outcomes

The proportion of Australians to finish uni is about 25 per cent. This figure varies dramatically from the amount of Indigenous kids who attain the same result. Only five percent of Aboriginal and Torres Strait Islanders gain a degree. That's why Marnee Shay from Ilkey on the Sunshine Coast is bucking the trend... above and beyond expectations. She's believed to be the first Aboriginal recipient of the Chancellor's Medal at the University of the Sunshine Coast, and she's now starting a PHD at QUT in Brisbane. The ABC's Jon Coghill asked her about her studies and what the medal signifies.

Molecular Origin of the Intrinsic Bending Force for Helical Morphology Observed in Chiral Amphiphilic Assemblies: Concentration and Size Dependence

The formation of the helical morphology in monolayers and bilayers of chiral amphiphilic assemblies is believed to be driven at least partly by the interactions at the chiral centers of the amphiphiles. However, a detailed microscopic understanding of these interactions and their relation with the helix formation is still not clear. In this article a study of the molecular origin of the chirality-driven helix formation is presented by calculating, for the first time, the effective pair potential between a pair of chiral molecules. This effective potential depends on the relative sizes of the groups attached to the two chiral centers, on the orientation of the amphiphile molecules, and also on the distance between them. We find that for the mirror-image isomers (in the racemic modification) the minimum energy conformation is a nearly parallel alignment of the molecules. On the other hand, the same for a pair of molecules of one kind of enantiomer favors a tilt angle between them, thus leading to the formation of a helical morphology of the aggregate. The tilt angle is determined by the size of the groups attached to the chiral centers of the pair of molecules considered and in many cases predicted it to be close to 45 degrees. The present study, therefore, provides a molecular origin of the intrinsic bending force, suggested by Helfrich (J. Chem. Phys. 1986, 85, 1085-1087), to be responsible for the formation of helical structure. This effective potential may explain many of the existing experimental results, such as the size and the concentration dependence of the formation of helical morphology. It is further found that the elastic forces can significantly modify the pitch predicted by the chiral interactions alone and that the modified real pitch is close to the experimentally observed value. The present study is expected to provide a starting point for future microscopic studies.

Beta-Turn Conformations In Crystal-Structures Of Model Peptides Containing Alpha,Alpha-Di-N-Propylglycine And Alpha,Alpha-Di-N-Butylglycine

The crystal state conformations of three peptides containing the alpha, alpha-dialkylated residues, alpha,alpha-di-n-propylglycine (Dpg) and alpha,alpha-di-n-butylglycine (Dbg), have been established by x-ray diffraction. Boc-Ala-Dpg-Ala-OMe (I) and Boc-Ala-Dbg-Ala-OMe (III) adopt distorted type II beta-turn conformations with Ala (1) and Dpg/Dbg (2) as the corner residues. In both peptides the conformational angles at the Dxg residue (I: phi = 66.2 degrees, psi = 19.3 degrees; III: phi = 66.5 degrees, psi = 21.1 degrees) deviate appreciably from ideal values for the i + 2 residue in a type II beta-turn. In both peptides the observed (N...O) distances between the Boc CO and Ala(3) NH groups are far too long (I: 3.44 Angstrom; III: 3.63 Angstrom) for an intramolecular 4 --> 1 hydrogen bond. Boc-Ala-Dpg-Ala-NHMe (II) crystallizes with two independent molecules in the asymmetric unit. Both molecules IIA and IIB adopt consecutive beta-turn (type III-III in IIA and type III-I in IIB) or incipient 3(10)-helical structures, stabilized by two intramolecular 4 --> 1 hydrogen bonds. In all four molecules the bond angle N-C-alpha-C' (tau) at the Dxg residues are greater than or equal to 110 degrees. The observation of conformational angles in the helical region of phi,psi space at these residues is consistent with theoretical predictions.

Energy-based guidance of an underactuated unmanned underwater vehicle on a helical trajectory

This paper presents a motion control system for guidance of an underactuated Unmanned Underwater Vehicle (UUV) on a helical trajectory. The control strategy is developed using Port-Hamiltonian theory and interconnection and damping assignment passivity-based control. Using energy routing, the trajectory of a virtual fully actuated plant is guided onto a vector field. A tracking controller is then used that commands the underactuated plant to follow the velocity of the virtual plant. An integral control is inserted between the two control layers, which adds robustness and disturbance rejection to the design.

Effect of inflow and outflow angles on the computational hemodynamics in abdominal aortic aneurysm

To help with the clinical screening and diagnosis of abdominal aortic aneurysm (AAA), we evaluated the effect of inflow angle (IA) and outflow bifurcation angle (BA) on the distribution of blood flow and wall shear stress (WSS) in an idealized AAA model. A 2D incompressible Newtonian flow is assumed and the computational simulation is performed using finite volume method. The results showed that the largest WSS often located at the proximal and the distal end of the AAA. An increase in IA resulted in an increase in maximum WSS. We also found that WSS was maximal when BA was 90°. IA and BA are two important geometrical factors, they may help with AAA risk assessment along with the commonly used AAA diameter.

Fibre diffraction of lithium DNA shows structural variability and deviation from a regular helical structure for the B-form

Recently, reports have appeared which show structural variations in B-DNA and indicate deviations from a uniform helical structure. We report for the first time that these indications are also present in the B-form fibre diffraction patterns for the lithium salt of natural DNA. We have used an improved method of controlling the salt concentration in the fibres. Our results are based on the appearance and disappearance of meridional reflections on different layer lines depending upon the salt.

Image reconstruction with laterally truncated projections in helical cone-beam CT: Linear prediction based projection completion techniques

Lateral or transaxial truncation of cone-beam data can occur either due to the field of view limitation of the scanning apparatus or iregion-of-interest tomography. In this paper, we Suggest two new methods to handle lateral truncation in helical scan CT. It is seen that reconstruction with laterally truncated projection data, assuming it to be complete, gives severe artifacts which even penetrates into the field of view. A row-by-row data completion approach using linear prediction is introduced for helical scan truncated data. An extension of this technique known as windowed linear prediction approach is introduced. Efficacy of the two techniques are shown using simulation with standard phantoms. A quantitative image quality measure of the resulting reconstructed images are used to evaluate the performance of the proposed methods against an extension of a standard existing technique.

The helical conformations of 14- and 16-residue fragments of suzukacillin, a membrane channel-forming polypeptide

The suzukacillin fragments, Boc-Ala-Aib-Aib-Gln-Aib-Leu-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-OMe (14), Boc-Ala-Aib-Ala-Aib-Aib-Gln-Aib-Leu-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-OMe (16G) and the completely apolar 16-residue peptide in which the glutamine residue has been replaced by alanine (16A) have been studied by 270 MHz 1H-HMR, in C2HCl3 and (C2H3)2SO solution. Intramolecularly hydrogen-bonded NH groups have been identified by temperature and solvent dependence of chemical shifts. Peptides 14 and 16A adopt folded 310 helical conformations stabilized by 11 and 13 hydrogen bonds, respectively. In peptide 16G there are 12 intramolecular hydrogen bonds, with the glycine NH being solvent-exposed, in contrast to 14 and 16A.

Conformations Of Peptides Containing 1-Aminocyclohexane-Carboxylic Acid (Acc6) - Crystal-Structures Of 2 Model Peptides

The crystal structures of two peptides containing 1-aminocyclohexanecarboxylic acid (Acc6) are described. Boc-Aib-Acc6-NHMe · H2O adopts a β-turn conformation in the solid state, stabilized by an intramolecular 4 → 1 hydrogen bond between the Boc CO and methylamide NH groups. The backbone conformational angles (φAib = – 50.3°, ψAib = – 45.8°; φAcc6 = – 68.4°, ψAcc6 = – 15°) lie in between the values expected for ideal Type I or III β-turns. In Boc-Aib-Acc6-OMe, the Aib residue adopts a partially extended conformation (φAib = – 62.2°, ψAib = 143°) while the Acc6residue maintains a helical conformation (φAcc6 = 48°, ψAcc6= 42.6°). 1H n.m.r. studies in CDCl3 and (CD3)2SO suggest that Boc-Aib-Acc6-NHMe maintains the β-turn conformation in solution.

Cyclic Peptide Disulfides - Solution And Solid-State Conformation Of Boc-Cys-Pro-Aib-Cys-S-S-Bridge-Nhme,A Disulfide-Bridged Peptide Helix

The solution and solid-state conformations of the peptide disulfide Boc-Cys-Pro-Aib-Cys-NHMe have been determined by NMR spectroscopy and X-ray diffraction. The Cys(4) and methylamide NH groups are solvent shielded in CDCI3 and (CD,),SO, suggesting their involvement in intramolecular hydrogen bonding. On the basis of known stereochemical preferences of Pro and Aib residues, a consecutive @-turn structure is favored in solution. X-ray diffraction analysis reveals a highly folded 310 helical conformation for the peptide, with the S-S bridge lying approximately parallel to the helix axis, linking residues 1 and 4. The backbone conformational angles are Cys(1) 4 = -121.1', $ = 65.6"; Pro(2) 4 = -58.9', 4 = -34.0'; Aib(3) 4 = -61.8', $ = -17.9'; Cys(4) 4 = -70.5', $ = -18.6'. Two intramolecular hydrogen bonds are observed between Cys(1) CO--HN Cys(4) and Pro(2) CO--HNMe. The disulfide bond has a right-handed chirality, with a dihedral angle (xss) of 82'.

Sequence-dependent conformation of an A-DNA double helix: The crystal structure of the octamer d(G-G-T-A-T-A-C-C)

The crystal structures of the synthetic self-complementary octamer d(G-G-T-A-T-A-C-C) and its 5-bromouracil-containing analogue have been refined to R values of 20% and 14% at resolutions of 1·8 and 2·25 Å, respectively. The molecules adopt an A-DNA type double-helical conformation, which is minimally affected by crystal forces. A detailed analysis of the structure shows a considerable influence of the nucleotide sequence on the base-pair stacking patterns. In particular, the electrostatic stacking interactions between adjacent guanine and thymine bases produce symmetric bending of the double helix and a major-groove widening. The sugar-phosphate backbone appears to be only slightly affected by the base sequence. The local variations in the base-pair orientation are brought about by correlated adjustments in the backbone torsion angles and the glycosidic orientation. Sequence-dependent conformational variations of the type observed here may contribute to the specificity of certain protein-DNA interactions.

Helical conformations of three crystalline pentapeptide fragments of suzukacillin, a membrane channel forming polypeptide

The crystal structures of three pentapeptide fragments of suzukacillin-A have been determined. Boc-Aib-Pro-Val-Aib-Val-OMe (peptide 1–5) adopts a distorted helical conformation, stabilized by three intramolecular hydrogen bonds (two 5→1, one 4→1). Boc-Ala-Aib-Ala-Aib-Aib-OMe (peptide 6–10) and Boc-Leu-Aib-Pro-Val-Aib-OMe (peptide 16–20) adopt 310 helical structures stabilized by three and two 4→1 intramolecular hydrogen bonds, respectively. These structures provide substantial support for a largely helical conformation for the suzukacillin membrane channel.