Academic literature on the topic 'Helical Pattern'

The observation of an optical vortex beam at 60 nm wavelength, produced as the second-harmonic radiation from a helical undulator, is reported. The helical wavefront of the optical vortex beam was verified by measuring the interference pattern between the vortex beam from a helical undulator and a normal beam from another undulator. Although the interference patterns were slightly blurred owing to the relatively large electron beam emittance, it was possible to observe the interference features thanks to the helical wavefront of the vortex beam. The experimental results were well reproduced by simulation.

Abstract Motivation The rational design of antimicrobial peptides (AMPs) with increased therapeutic potential requires deep understanding of the determinants of their activities. Inspired by the computational linguistic approach, we hypothesized that sequence patterns may encode the functional features of AMPs. Results We found that α-helical and β-sheet peptides have non-intersecting pattern sets and therefore constructed new sequence templates using only helical patterns. Designed peptides adopted an α-helical conformation upon binding to lipids, confirming that the method captures structural and biophysical properties. In the antimicrobial assay, 5 of 7 designed peptides exhibited activity against Gram(+) and Gram(–) bacteria, with most potent candidate comparable to best natural peptides. We thus conclude that sequence patterns comprise the structural and functional features of α-helical AMPs and guide their efficient design. Supplementary information Supplementary data are available at Bioinformatics online.

AbstractThe jet of BL Lac displays transverse patterns that propagate downstream superluminally. We suggest that they are transverse Alfvén waves propagating on the longitudinal component of a helical magnetic field. The speed of the wave adds relativistically to the speed of the beam, and the apparent speed of the pattern is greater than the beam speed. Models for the jet and the MHD waves give values for the Lorentz factor of the beam of 3–4.4 and pitch angle of the helical magnetic field of 43° - 65°. These are consistent with other estimates, if the beam and pattern speeds are allowed to differ.

The complexity of helical phyllotaxis expressed in diverse phyllotactic patterns and the phenomenon of phyllotactic transformations were investigated theoretically. Two categories of transformations were distinguished: continuous and discontinuous, the latter being interpreted as the consequences of wedge disclinations present at the shoot apex when the number of initials changes. Phyllotaxis triangular unit was described as the common element of all patterns of helical phyllotaxis. It is proposed that the unit plays the same role in a process of the formation of phyllotactic pattern as the crystal basic unit does in a process of crystal growth.

Summary The in-situ upgrading process (IUP) involves very complicated multiphase thermal transport and chemical reactions. Numerical simulation of IUP is computationally expensive, and direct simulation of field-scale IUP models becomes prohibitive. A practical way is to simulate a sector model under proper boundary and initial conditions and then upscale the simulation results to the full field scale with superposition techniques. Because of nonsymmetric pattern configuration and time delay of developing patterns sequentially, interpattern flow may become significant, and its impact on the simulation results cannot be neglected. Therefore, no-flow boundary conditions become inappropriate for such IUP sector models. In this paper, we proposed a new type of “helical” boundary conditions (HBCs) in which pressures and temperatures are periodic in space, except for a shift in time. The HBCs are specifically designed for a field-scale IUP development in which patterns are developed sequentially in time, along a long strip. In such a development, each pattern has exactly the same well configuration and operational schedule, except for a time delay. Because of high viscosity of heavy oil and low heat conductivity of formation rock, the impact of field boundary conditions on interpattern flow will be dampened quickly within only a few patterns, and a repetitive “pseudosteady state” of interpattern flow develops, in which the energy and mass fluxes from the previous pattern to the current pattern are the same as those from the current pattern to the next pattern, except for the delay time. By use of a 1D heat-transfer model, we analytically demonstrate that the pseudosteady state and therefore the HBCs hold for a long strip of patterns. A practical procedure to implement these HBCs in numerical simulation is developed, in which the state variables (pressure, temperature, and fluid composition) are iteratively updated in gridblocks on both edges of a sector model that is composed of two patterns. This iterative approach to impose HBCs was implemented in our in-house simulator. This approach was tested and validated by simulation results of an IUP model that is composed of 59 patterns. Our results show that the full-field boundary conditions only affect the production-rate profiles of the first and the last patterns. Production-rate profiles generated from all other patterns are almost identical except for the interpattern time delay, which also validates the pseudosteady state of interpattern flow for a more-complicated IUP model. The two-pattern sector model with the HBCs converges in three to four iterations. The production-rate profiles of oil, gas, and water generated by the sector model with HBCs are almost identical to those produced from one of those inner patterns in the 59-pattern model. With the 1D example, we also analytically demonstrate the convergence of our numerical implementation of HBCs. In terms of clock-time used, it is possible to achieve 5N time speedup through application of the HBCs, in which N is the number of patterns in a field-scale model. Therefore, the new approach is proved a key enabler for field-scale IUP pattern optimization. Provided that the interpattern-pressure communication that is induced by the pattern delay time is not too severe, we expect that one can also apply HBCs to the simulation of other field-scale thermal processes, such as the in-situ conversion process and steamfloods.

A quantitative electron microscopic (E/M) study of the changes in microtubule arrays and wall microfibril orientation has been done on in vitro grown cotton fibers. Microtubules change orientation during cotton fiber development. During fiber initiation and early elongation, microtubules have a generally random orientation. Microtubules re-orient into shallow pitched helices as elongation and primary wall deposition continue, and into steeply pitched helices during secondary wall deposition. Accompanying the changes in orientation are increases in microtubule length, number, proximity to the plasmalemma and a decreased variability in orientation of the microtubules. Based on these observations, three pivotal stages in microtubule patterns were identified during fiber development: (1) the transition between fiber initiation and elongation, where microtubules develop a shallow pitched helical orientation; (2) the transition between primary and secondary wall synthesis, where microtubules abruptly shift orientation to a steeply pitched helical pattern; and (3) early in secondary wall synthesis, where there is a four fold increase in microtubule number. Microfibrils exhibit changes in orientation similar to the microtubules; however significant differences were found when the precise orientations of microtubules and microfibrils were compared. During secondary wall synthesis, wall microfibrils exhibit some variability in orientation due to inter-fibril bundling, thus indicating that components of the wall may also influence final microfibril orientation.

Abstract Seyfert galaxies with Z-shaped emission filaments in the Narrow Line Region (NLR) are considered. We assume that observable Z-shaped structures and the velocity pattern of the NLR may be explained as tri-dimensional helical waves in the ionization cone.