Helical Sections Research Articles

Iteration based calculation of position and orientation of grinding wheel for solid cutting tool flute grinding

End mill cutting tools are widely used in machining of curved surface parts in many areas, e.g. aerospace, automobile, and energy. The parameters of helical groove cross section, influencing chip removal capacity, include rake angle, core radius and edge width. Towards a parametrical control algorithm of the cutting tool flute, this paper proposed an iteration based method. Within the context, the cutting tool parameters and grinding wheel are set firstly. Then, three angle parameters, α,β, and θ in the grinding coordinate system, are looped. In each loop, one of the target flute parameters is compared with the pre-set values, and if the parameter is within the range, the calculation goes the next loop until the parameters are in the target range. Since the loop number is so high that the computing time is too long, the patterns between the flute parameters and looped parameters are used to improve the calculation speed. The method is implemented by using C#, and validated by a set of numeric simulation based on Matlab®.

Spider silk proteome provides insight into the structural characterization of Nephila clavipes flagelliform spidroin

The capture spiral of web from N. clavipes spider consists of a single type of spidroin - the flagelliform silk protein, a natural material representing a combination of strength and high elasticity. Flagelliform spider silk is the most extensible silk fibre produced by orb weaver spiders and the structure of this remarkable material is still largely unknown. In the present study we used a proteomic approach to elucidate the complete sequence and the post-translational modifications of flagelliform silk proteins. The long sequence of flagelliform silk protein presents 45 hydroxylated proline residues, which may contribute to explain the mechanoelastic property of these fibres, since they are located in the GPGGX motif. The 3D-structure of the protein was modelled considering the three domains together, i.e., the N- and C-terminal non-repetitive domains, and the central repetitive domain. In the resulting molecular model there is a predominance of random structures in the solid fibres of the silk protein. The N-terminal domain is composed of three α-helices and the C-terminal domain is composed of one small helical section. Proteomic data reported herein may be relevant for the development of novel approaches for the synthetic or recombinant production of novel silk-based spider polymers.

Magnetic field of heliotron with irregular helical coil pitch

The paper presents the results of numerical calculations on the magnetic field of a heliotron with a helical coil pitch L0, which comprises a helical coil section named as an L-section, where the helical coil pitch L differs from L0, i.e. L < L0. The calculations have shown that within the L-section the real preconditions exist permitting to form both the plasma core of passing plasma particles and of the SOL plasma boundary being at the increased distance from the wall in the high magnetic field region.

Thermal and flow characteristics of helical coils with reversed loops

In this experimental study, flow and heat transfer characteristics of water through a newly designed helical coil heat transfer test section were investigated. A structural modification of the traditional helical coil has been implemented to improve its thermal effectiveness. Specifically, a 360° plastic reversed loop was added after each 180° of the main helical coil loop to redistribute the flow’s velocity profile, which should have a direct effect on the thermal performance of the helical coil heat transfer test section. Results reveal that reversed loops do enhance heat transfer rates by more than 20%, while pressure drop penalty also increases but not at the same rate. The curvature of the reversed loops with respect to the main coil is a critical factor in terms of thermal performance. Furthermore, as the size of the reversed loop decreases, the heat transfer enhancement and pressure drop penalty increment for the modified helical coil test section increase as well. Accordingly, it is suggested that there may exist an optimum helical coil structural modification for which the best tradeoff between pressure drop penalty and heat transfer enhancement can be found.

Fabrication of a helical detonation channel: Effect of initial pressure on the detonation propagation modes of ethylene/oxygen mixtures

The effect of the initial gas mixture pressure on curved detonation propagation modes has been extensively investigated in the present study using a stoichiometric ethylene–oxygen mixture in a new experimental facility consisting of a straight channel section joined to a helical channel section. Flame propagation through the helical channel was observed by high-speed CCD camera, and the trajectories of triple points on the detonation waves were obtained using a soot-deposition plate. The results clearly identify three detonation propagation modes, namely, a stabilized propagation mode, critical mode, and non-stabilized propagation mode, that vary according to the ratio of the radius of curvature of the inside wall ri to the normal detonation cell width λ. For the stabilized propagation mode (ri/λ > 27), the detonation velocity at the inner wall in the curved section asymptotically approaches the detonation velocity in the straight section with increasing initial pressure due to competition between the weakening and strengthening effects characteristic of the curved channel geometry. A definite flame shape, which is perpendicular to the inner wall of the channel, is observed. For the critical mode (16 ≤ ri/λ ≤ 27), the shape of the flame front is observed to be more irregular and unstable than that of the stabilized propagation mode. This mode can be considered as a transition zone, where the stabilized propagation mode transits to the non-stabilized propagation mode with decreasing initial pressure. For the non-stabilized propagation mode (ri/λ < 16), two types of periodic detonation propagation behavior are observed. The first is analogous to single-headed spinning detonation in a circular tube, which is observed in an initial pressure range of 5.5–11 kPa. Soot-coated foil records show that the cellular structure has specific features of the periodic variation, such as re-generation, decrease, and partial disappearance of detonation near the inner wall. The angular interval of consecutive cycles for sinning-like detonation decreases with increasing initial pressure. The second is galloping detonation near the detonation propagation limit. In one cycle of galloping detonation, a change from multi-headed to single-headed cellular structure is observed. However, as the galloping detonation further decays to the low velocity phase of the galloping cycle, the cellular structure vanishes. The angular interval of consecutive cycles for galloping detonation is observed to be random. Although both spinning-like and galloping detonations periodically undergo the process of re-generation, decrease, and failure, they exhibit two different propagation behaviors. The former partially fails near the inner wall, and is re-initiated by transverse detonation from the outer wall, while the latter fails completely, and re-generates by local explosion at the outer wall.

Mono-Substituted Hydrocarbon Diastereomer Combinations Reveal Stapled Peptides with High Structural Fidelity.

Modified peptides, such as stapled peptides, which replicate the structure of α-helical protein segments, represent a potential therapeutic advance. However, the 3D solution structure of these stapled peptides is rarely explored beyond the acquisition of circular dichroism (CD) data to quantify bulk peptide helicity; the detailed backbone structure, which underlies this, is typically undefined. Diastereomeric stapled peptides based on helical sections of three proteins (αSyn, Cks1 and CK1α) were generated; their overall helicity was quantified by CD; and the most helical peptide from each series was selected for structural analysis. Solution-phase models for the optimised peptides were generated using NMR-derived restraints and a modified CHARMM22 force field. Comparing these models with PDB structures allowed deviation between the stapled peptides and critical helical regions to be evaluated. These studies demonstrate that CD alone is not sufficient to assess the structural fidelity of a stapled peptide.

Boiling pressure drop, local heat transfer distribution and critical heat flux in helical coils with R123

The objectives of the present work are to study the influence of curvature on local heat transfer coefficient, two-phase pressure drop and CHF in helical coils. The curvature of coil generates secondary flow of fluid which affects the mechanism inside helical coils. Very less information is available on the influence of curvature on flow boiling system. The present work investigates the characteristics of single phase flow and flow boiling in helical coils. Infra-red thermal imaging technique is used to measure the local wall temperature in the axial direction (along the length of coil) and in the circumferential direction. Experiments are performed with six helical coil test sections made of SS 304 circular tubes having three different tube diameters with two different coil diameters. The tube inner diameters are varying from 5.5 to 9.5 mm with wall thickness of 0.25 mm. The coil diameter to the tube diameter ratio ranges from 14 to 58 and coil pitch is 50 mm. The system pressure is varying from 1.1 bar to 3.6 bar. The analysis is performed for different heated lengths of test section. The experimental data of pressure drop and CHF are compared with available helical coil correlations. In fully developed flow boiling region, the circumferential averaged heat transfer coefficient in helical coils is same as in straight tubes. Correlations are suggested to predict local heat transfer coefficient in single phase and in flow boiling process, two-phase pressure drop and CHF in helical coils.

Interaction of magnetized electrons with a boundary sheath: investigation of a specular reflection model

This publication reports analytical and numerical results concerning the interaction of gyrating electrons with a plasma boundary sheath, with focus on partially magnetized technological plasmas. It is assumed that the electron Debye length is much smaller than the electron gyroradius , and in turn much smaller than the mean free path λ and the gradient length L of the fields. Focusing on the scale of the gyroradius, the sheath is assumed as infinitesimally thin (), collisions are neglected (), the magnetic field is taken as homogeneous, and electric fields (=potential gradients) in the bulk are neglected (). The interaction of an electron with the electric field of the plasma boundary sheath is represented by a specular reflection of the velocity at the plane z = 0 of a naturally oriented Cartesian coordinate system . The electron trajectory is then given as sequences of helical sections, with the kinetic energy ϵ and the canonical momenta px and py conserved, but not the position of the axis (base point ), the slope (pitch angle χ), and the phase (gyrophase φ). A ‘virtual interaction’ which directly maps the incoming electrons to the outgoing ones is introduced and studied in dependence of the angle γ between the field and the sheath normal . The corresponding scattering operator is constructed, mathematically characterized, and given as an infinite matrix. An equivalent boundary condition for a transformed kinetic model is derived.

Response analysis of longitudinal vibration of sucker rod string considering rod buckling

Considering the limitation of simulation model of the deep well and ultra-deep well, an improved simulation model of sucker rod pumping system (SRPS) is presented. The main innovations of the simulation model are nonlinear longitudinal vibration model of sucker rod string (SRS) and numerical integral model of nonlinear system with pump time varying parameters. In the detail, the relationship of rod buckling and plunger load is analyzed using a finite element preprocessor module of ANSYS. Based on analysis results and experimental results, the change rule of equivalent stiffness is studied. Using parameters of oil well, the response of longitudinal vibration of SRS is analyzed. The new model is verified by comparing it with the available analytical solution, and good agreement is found. The simulation results show that the instantaneous equivalent stiffness of helical buckling section of SRS follows exponential distribution. The equivalent stiffness is affected by some parameters, among them, the values of water cut, density of crude oil and pump depth have a significant effect. With new model presented in this paper, the subharmonic resonance is found, which is characteristic of nonlinear vibration. Comparing with the steel rod, carbon fiber rod and fiberglass rod, the resonant phenomenon of single rod is more likely to happen for the wire rope sucker rod. However, when sucker rod is double stage rod, the resonant phenomenon of fiberglass rod is more likely to happen than other rods. The above results are significant to the optimization of SRS.

Helical Defect Packings in a Quasi-One-Dimensional System of Cylindrically Confined Hard Spheres.

We use a combination of analytical theory and molecular dynamics simulation to study the inherent structure landscape of a system of hard spheres confined to narrow cylindrical channels of diameter 1+√[3]/2<H(d)/σ<1+4√[3]/7. The most dense packing is a perfect, symmetrical single helix. The presence of topological defects that change the local chirality of the helix lowers the packing density and alters the local packing structure. The helical sections between defects become asymmetrical and are better described as a double helix with angular twists between the first and second nearest neighbors that are determined by the defect separation distance. Increasing the fraction of defects unwinds the two helical strands so that the least dense structure is a nonhelical packing of two zigzag chains. We also show that the packing effects of the helical section induce a long-range, entropically driven attraction between the defects.

Effect of Helix Parameter Modification onFlow Characteristics of CIDI Diesel EngineHelical Intake Port

This project work involves experimental investigation of helical inlet port flow characteristics for cylinder head of Direct Injection (D.I) diesel engine. The average flow coefficient and swirl number is obtained using a paddle wheel test bench. Intake port helix parameters, i.e., distance between peripheral side wall and valve axis ‘Dp’, width of helical section parallel to valve axis ‘W’ and initial width of the helix ‘Wh’ are measured for different flow boxes for selected different bore and stroke engines. These parameters are modified and detailed analysis has been done to establish the effect on swirl number and average flow coefficient. The second part of work focused on the Computation Fluid Dynamics (CFD) to study flow velocity, flow distribution inside cylinder and to analyze effect of helix parameter change. The experimental study of combined effect of helix parameters, ‘W’, ‘Wh’ and ‘Dp’ indicates that this modification can be initiated for improving flow characteristics if change required in average flow coefficient is small as compared to higher amount of change required in swirl number. The CFD analysis with this modification also shows improvement in swirl generation and flow distribution.

Coupled Nanomechanical Motions: Metal-Ion-Effected, pH-Modulated, Simultaneous Extension/Contraction Motions of Double-Domain Helical/Linear Molecular Strands

A new class of shape-enforced synthetic polyheterocyclic molecular strands, containing both a helical and a linear domain, has been designed and synthesized. On reaction with Pb(II), under the effect of cation binding to the coordination subunits, the helical section unfolds into a linear shape in the complex and the linear domain folds into a helical ligand wrapped around the bound cations. Such double-domain ligand strands are thus able to undergo a combined unfolding-folding interconversion on binding and release of metal cations. These changes can be modulated through coupling to a competing ligand that reversibly binds and releases metal cations, when respectively unprotonated and protonated, on effecting alternate pH changes. The resulting process thus performs nanomechanical extension/contraction molecular motions of a linear motor type, which is fueled by acid-base neutralization.

Studies on the Effect of Pellet Size on Positive Conveying in Helically Grooved Single Screw Extruders

The helical grooved barrel feed section permits, when the barrel channel aspect ratio and the barrel channel helical angle are properly designed, an operating mode where the positive conveying is prevailing. While the pellet size of materials is varied, different dimension relationships of the barrel channel depth and pellet size could induce different equivalent barrel channel aspect ratios with the transformation of solids conveying mechanisms from the positive conveying to the friction-drag conveying. Considering the effect of dimension relationships on the solids conveying mechanism, a novel pellet-size physical model was established to guide the available design of the barrel channel geometry for positive conveying. In the pellet-size model, one or two shear interfaces were identified inside the solid-plug resulting in different equivalent barrel channel aspect ratios, based on which the solids conveying mechanism on the shear interfaces was detailed by the boundary condition equations for positive conveying. Besides, the theoretical simulations are also compared with the on-line measuring experimental data. The results show that the equivalent barrel channel aspect ratio on the shear interfaces exists indeed and determines the solids conveying mechanism, which is well confirmed by the excellent consistence between the predicted and measured data.

Computational Modelling of the Hydride Generation Reaction in a Tubular Reactor and Atomization in a Quartz Cell Atomizer

In this study, we present a model whereby the centre of the atomization channel is shown to be the optimal location for the spectrometric data acquisition in a quartz cell atomizer. The study aims to explore the hydride generation technique which is normally coupled with efficient thermal source to apply determination of heavy metals in water samples via spectrometric analysis. The arsenic hydride generation process and the atomization of the generated hydride in a quartz cell atomizer were studied analytically as model case studies. The hydride generation (HG) process was analyzed by adopting two hypotheses, the nascent hydrogen and formation of intermediate hydroboron species, where the results based on the second hypothesis are found to be more realistic for design purposes. Moreover, the release of the generated hydride from the liquid phase and their transport to the gas phase is simulated in a helical tubular section, in which the actual tubular section length required for separation is deduced. The analytical results have been verified experimentally by measuring the signal intensity for the free arsenic atoms against several reaction tube lengths, in which increasing the tubular section length from 12 cm to 100 cm results in signal amelioration by no more than 6.6%. Furthermore, the atomization of the hydride and the distribution of the generated free atoms are deduced in two configurations of tubular quartz atomizers. The results obtained from both studied cases illustrate that a high concentration of the free analyte atoms is generated in the first part of the atomization channel, saturates to a maximum in a position at the atomizer centre, and dissipates at the inside wall of the tubular atomizer before reaching the atomizer outlet edge, which is found to be in total agreement with the current understanding of atomization mechanism in tubular atomizer and emphasizes the fact that the centre of the quartz cell atomizer is the best location for the spectrometric data acquisition.

Spontaneous and deterministic three-dimensional curling of pre-strained elastomeric bi-strips

Three dimensional curls (“hemi-helices”) consisting of multiple, periodic and alternating helical sections of opposite chiralities, separated by perversions, are one of a variety of complex shapes that can be produced by a simple generic process consisting of pre-straining one elastomeric strip, joining it side-by-side to another and then releasing the bi-strip. The initial wavelength of the hemi-helix and the number of perversions are determined by the strip cross-section, the constitutive behavior of the elastomer and the value of the pre-strain. The hemi-helix has no net twist. Topologically, the perversions separate regions of the hemi-helix deforming principally by bending from those where twisting dominates.

In silico analysis of IRES RNAs of foot-and-mouth disease virus and related picornaviruses

Foot-and-mouth disease virus (FMDV) uses an internal ribosome entry site (IRES), a highly structured segment of its genomic RNA, to hijack the translational apparatus of an infected host. Computational analysis of 162 type II picornavirus IRES RNA sequences yielded secondary structures that included only base pairs supported by comparative or experimental evidence. The deduced helical sections provided the foundation for a hypothetical three-dimensional model of FMDV IRES RNA. The model was further constrained by incorporation of data derived from chemical modification and enzymatic probing of IRES RNAs as well as high-resolution information about IRES RNA-bound proteins.

Comparative structural studies of bovine viral diarrhea virus IRES RNA

The internal ribosomal entry site (IRES) RNA of bovine viral diarrhea virus (BVDV) has been implicated in virus propagation. To gain insight into the structure and potential function of the BVDV IRES RNA, we collected and aligned 663 of its sequences. Compensatory Watson–Crick and wobble G·U pairs were investigated to establish phylogenetically supported secondary structures for each of the BVDV IRES RNA sequences. The extensively folded BVDV IRES RNAs were composed of helices 2, 3 and 4. Helix 2 consisted of five helical sections. Helix 3 contained sections 3a to 3j as well as six helical insertions 3.1–3.6. Sections 3a and 3b together with helices 3.6 and 4 formed an RNA pseudoknot. Two highly variable regions corresponded to hairpins 3j and 3.4. Three-dimensional modeling of the BVDV-1b strain Osloss IRES RNA predicted an elongated structure with approximate dimensions of 170Å by 65Å by 90Å. The model of the IRES RNA-ribosome complex suggested proximity between helix 2 of the BVDV IRES and ribosomal proteins S5 and S25.

Behavior of Grouted Shaft Helical Anchors in Clay

AbstractSome years ago, a method was developed to incorporate a grout column around square-shaft helical screw-piles and anchors to increase shaft buckling resistance under compression loading. An additional benefit of this grouted shaft is to increase the load capacity in both compression and tension, depending on the geometry of the lead helical section and the soil conditions. Because of the unique construction procedure, the contribution of the shaft to the total capacity has largely been unknown. The behavior of grouted shaft helical anchors in clay was investigated by performing full-scale axial uplift (tension) load tests on a series of anchors installed at the University of Massachusetts Geotechnical Test Site. In order to isolate the contribution of the grouted shaft to the total load capacity, anchors were installed with a wooden dowel connection between the lead helical section and extension sections on three of the four anchors so that only the shaft resistance would be measured during the loa...

Tryptophan Fluorescence Modulated by Histidine Quenching During Folding of Small Alpha Helical Peptides: Distance and Solvation Effects

8oct10-11:30 am prc changes.Tryptophan (Trp) fluorescence has been extensively used to study the folding kinetics of small alpha helical proteins including: the villin headpiece N68H (1yrf), villin headpiece K65(NLE) N68H K70(NLE) (2f4k) and a peptide Ac-Trp-(Ala)3-His+-NH2(WH5). In these three cases a histidine (His) has been placed in an alpha helical section of the protein four amino acids away from Trp, so that His will quench the fluorescence of Trp as the protein folds. His+ quenches the fluorescence of free Trp in solution at a diffusion limited rate by electron transfer from the Trp ring to the His+ ring. The rate of electron transfer is known to fall off exponentially due to the exponential decay of the electronic coupling Vel with distance. In this work we show that this decay also depends on how the energy gap is affected by distance. Solvation around the imidazole cation at large distances increases the energy gap, since waters around the cation point their dipoles towards the ring, destabilizing the charge transfer state. At short distances, the decreased water accessibility reduces the destabilization of the charge transfer state, enhancing electron transfer from the Trp ring to the His+ ring. This is seen in five different proteins: 1yrf, 2f4k, barnase (1a2p), T4-lysozyme (1lyd) and WH5. We also examine the ability of Trp fluorescence to determine folding rates for 1yrf, 2f4k and WH5 by using QM/MM simulations to determine the electron transfer rates in the folded and unfolded states.

TERRESTRIAL MODE QUADRIFILAR HELIX ANTENNA

In this paper we present a modiflcation to the QHA whereby a gap is introduced at the current minima points at the centre of the helical sections of the QHA. The linear and rotational movement between the two halves of the QHA against each other is optimised to get current distribution, so that when tilted 90 - , it generates omnidirectional radiation pattern required for land communications in addition to hemispherical radiation pattern for space mode which is obtainable in conventional conflguration. This makes it possible to use the single antenna for both terrestrial and satellite communications. The simulated results are validated by experimental measurements.