Helical Shape Research Articles

Sustainable Dry Machining of Stainless Steel with Microwave-Treated Tungsten Carbide Cutting Tools.

This paper presents a research investigation conducted on the turning of stainless steel 316 material under a dry environment using microwave-treated cutting tool inserts. Plain tungsten carbide WC tool inserts were exposed to microwave treatment for enhancement of their performance characteristics. It was found that a 20-min microwave treatment resulted in the best tool hardness and metallurgical characteristics. These tool inserts have been used to machine SS 316 material following the Taguchi L9 design of experimental techniques. A total of eighteen experiments have been conducted by varying three main machining parameters, i.e., cutting speed, feed rate, and depth of cut, at three levels per parameter. It has been found that tool flank wear increased with all three parameters and surface roughness decreased. At the longest dept of cut, surface roughness increased. An abrasion wear mechanism was found on the tool flank face at a high machining speed and adhesion at low speed. Chips with a helical shape and low serrations have been investigated. Turning SS 316 at optimum machining parameters of 170 m/min cutting speed, 0.2 mm/rev feed rate, and 1 mm depth of cut, as obtained by the multiperformance optimization technique grey relational analysis, resulted in the best values of all machinability indicators: 242.21 µm tool flank wear, 3.81 µm mean roughness depth, and 34,000 mm3/min material removal rate, at a single parameter setting. In terms of research achievements, the percentage reduction in surface roughness is approximately 30% and represents an almost ten-fold improvement in the material removal rate. The combination of machining parameters of 70 m/min cutting speed, 0.1 mm/rev feed rate, and 0.5 mm depth of cut is optimum for the lowest value of tool flank wear when considered for single parameter optimization.

Development of a predictive response surface model for size of silver nanoparticles synthesized in a T-junction microfluidic device

Optimisation of the parameters governing the synthesis of silver nanoparticles (AgNPs) is a critical step in controlling particle size, which facilitates their application in diverse range of industrial and consumer related products. AT-junctionmicrofluidicsystemwas used together with design of experiments, regression-analysis and response surface methodology to build a predictive numerical model for the size of silver nanoparticles (AgNPs). Aqueous solutions of silver-precursor and reducing/stabilizing agent were supplied by two separate channels meeting at the T-junction, withthereaction occurring downstream intheoutlet tube. To improve the mixingof the reagents,the output tube was coiled onto a 3D-printed helical shape device, exploiting the creation of Dean vortices. The effects of both reaction and hydrodynamic conditions including the solution pH, collection temperature, helical curvature, flow rates and concentration of stabilising agent were investigated using a D-optimal experimental design.The obtainedexperimental size distributions for the AgNPs were fittedtoa polynomial model with an average prediction error of around 13% and a 37 % maximum error.The modelpredictedthe optimal synthesis conditionsforthe global and local-minimum sizes of AgNPswith an errorof around 7.0% and 16.1% respectively. The average prediction error of the testing set was estimated to be 6.8% with 16.1% being the maximum error.

Unusual Mooring Oscillations: Apparent Foucault–Wheatstone Device in the Deep Ocean?

A pressure sensor, located for four months in the middle of a 1275 m-long taut deep-ocean mooring in 2380 m water depth above a seamount with sub-surface top-buoys and seafloor anchor-weight, demonstrates narrow-band spectral peaks of deterministic well-predictable signals with equivalent 0.5 m amplitudes at uncommon sub-harmonic frequencies f*/4, f*/2, 3f*/4 of the local near-inertial frequency f* = 1.085f, where f denotes the Coriolis parameter. None of these sub-harmonics can be associated with oceanographic motions, which are dominated by super-inertial internal waves that are more broadband and less predictable. No corresponding peaks are found in spectra of other observables like current velocity (differences), temperature, and pressure in the top buoy of the mooring. The mid-cable pressure sensor was mounted on a nearly 1 kN weighing non-swiveled frame. Its data are hypothesized to reflect a resonant mechanical oscillation of the high-tensioned elastic steel mooring cable under repeated short-scale Strouhal cable vibrations induced by vortex-shedding due to water-flow drag and/or possibly by tidal baroclinic motions that are about 50% larger near the sloping seafloor of the seamount than mid-depth thereby modifying the mooring-cable in a helical shape. Cable dynamics and mooring-motion considerations yield inconclusive results to explain the observations. Hypothesizing, the observations suggest, cable dynamically, sub-harmonic drainage of helix-shape source at non-tidal semidiurnal center-frequency (M2 + S2)/2 = 3f*/2, physically, the measurement of Earth rotation thereby mimicking a Foucault–Wheatstone device, and, oceanographically, the relative vortex-rotation ζ/2 = 0.085f being possibly induced by water-flow interacting quasi-permanently with the nearby seamount by a topographic obstruction, so that total local near-inertial frequency f* = f + ζ/2.

Plant-Like Tropisms in Artificial Muscles.

Helical plants have the ability of tropisms to respond to natural stimuli, and biomimicry of such helical shapes into artificial muscles has been vastly popular. However, the shape-mimicked actuators only respond to artificially provided stimulus, they are not adaptive to variable natural conditions, thus being unsuitable for real-life applications where on-demand, autonomous operations are required. Novel artificial muscles made of hierarchically patterned helically wound yarns that are self-adaptive to environmental humidity and temperature changes are demonstrated here. Unlike shape-mimicked artificial muscles, a unique microstructural biomimicking approach is adopted, where the muscle yarns can effectively replicate the hydrotropism and thermotropism of helical plants to their microfibril level using plant-like microstructural memories. Large strokes, with rapid movement, are obtained when the individual microfilament of yarn is inlaid with hydrogel and further twisted into a coil-shaped hierarchical structure. The developed artificial muscle provides an average actuation speed of ≈5.2% s-1 at expansion and ≈3.1% s-1 at contraction cycles, being the fastest amongst previously demonstrated actuators of similar type. It is demonstrated that these muscle yarns can autonomously close a window in wet climates. The building block yarns are washable without any material degradation, making them suitable for smart, reusable textile and soft robotic devices.

Effect of oxyethylene and oxypropylene groups on the interfacial structure and property of extended surfactants: Molecular simulation and experimental study

Extended surfactants including oxyethylene (EO) and oxypropylene (PO) groups have great potential applications in the fields of oil recovery, separation and extraction, fabric washing, medicine and cosmetics vehicles. In this work, the interfacial structure and dynamic property of six alkyl polyoxypropylene polyoxyethylene ether carboxylates (C12POmEOnC, m = 5 and 15, n = 5, 10 and 15) at the water/oil interface were investigated with interfacial tension (IFT) experiments and molecular dynamics (MD) simulations. C12PO15EO5C was found to reduce the experimental IFT value to the order of 10-3 mN/m. Further, the interfacial thickness, stretch degree, hydrogen bond number and radial distribution function were calculated and analyzed in detailed simulations. The simulation results demonstrated that long PO chain curled in a helical shape to wrap hydrophilic oxygen atoms in the oil phase and reached a compact arrangement on the interface but short PO chain could not; long EO chain partially laid flat on the interface (about 5 EO units) and partially extended into the aqueous phase bringing the hydrophilic oxygen atoms close to water molecules while forming vacancies on the water side. Therefore, C12PO15EO5C had the tightest interfacial arrangement. Theoretical and experimental results are in fairly good agreement and they will provide enlightening insights into the design and synthesis of more effective extended surfactants.

Influence of 3D helical microstructure shape deviations on the properties of a vortex beam generated in the near diffraction zone

Influence of 3D helical microstructure shape deviations on the properties of a vortex beam generated in the near diffraction zone

Mixed convection phenomena in tubes with wire coil inserts

A numerical investigation of the flow and heat transfer in a helical coil in laminar and transitional flow regime under mixed convection conditions is presented. The continuous separation and reattachment of the boundary layer caused by the wire coil, that interrupts the flow near the tube all, and the swirl induced by the helical shape of the insert, are identified as the mechanism for heat transfer enhancement. Simulations in the Reynolds number range 200<Re<1500 show the role of mixed convection on heat transfer, as the flow dynamics is sensitive to the buoyancy forced induced by the tube wall heating. The interaction of the secondary swirl flow with the buoyancy motion is investigated in this work, with the aim of clarifying the range where heat transfer could be worsened by the presence of the helical coil. The investigation has been undertaken considering a helical coil of geometrical characteristics e/D=0.071 and p/D=1.5 and water as working fluid. Validation with experimental results of friction factor and Nusselt number is also presented.

Electret Molecular Configuration Induced Programmable Photonic Memory for Advanced Logic Operation and Data Encryption

AbstractNonvolatile organic photonic transistor (OPT) memories have attracted widespread attention due to their nondestructive readout, remote controllability, and robust tunability. Developing electrets with similar molecular structures but different memory behaviors and light‐responsive features is crucial for light‐wavelength‐modulated data encryption. However, reported OPT memories have yet to meet this challenge. Here a new electret molecule (“H‐PDI”) is developed via reconfiguring the linear perylene diimide molecule (“L‐PDI”) to a helical shape. Respectively incorporating H‐PDI and L‐PDI into the floating gate layer results to H‐PDI OPT and L‐PDI OPT. Attributing to their remarkably different electronic structures and energy bandgaps, H‐PDI OPT and L‐PDI OPT preferably respond to 405 and 532 nm light irradiation, respectively. Upon electrical programming, data can be written and stored in both memories with good retention features and a high “1”/“0” state current ratio over 105, though the data can only be erased by light with correct wavelengths, rather than the electrical field. Moreover, data stored in a memory array consisting of both H‐PDI OPT and L‐PDI OPT can only be read out by correct inputs, and wrong inputs will lead to highly deceptive outputs. This study provides a general design strategy of OPT for advanced data encryption and protection.

Catalyst-Substrate Helical Character Matching Determines the Enantioselectivity in the Ishihara-Type Iodoarenes Catalyzed Asymmetric Kita-Dearomative Spirolactonization.

Catalyst design has traditionally focused on rigid structural elements to prevent conformational flexibility. Ishihara's elegant design of conformationally flexible C2-symmetric iodoarenes, a new class of privileged organocatalysts, for the catalytic asymmetric dearomatization (CADA) of naphthols is a notable exception. Despite the widespread use of the Ishihara catalysts for CADAs, the reaction mechanism remains the subject of debate, and the mode of asymmetric induction has not been well established. Here, we report an in-depth computational investigation of three possible mechanisms in the literature. Our results, however, reveal that this reaction is best rationalized by a fourth mechanism called "proton-transfer-coupled-dearomatization (PTCD)", which is predicted to be strongly favored over other competing pathways. The PTCD mechanism is consistent with a control experiment and further validated by applying it to rationalize the enantioselectivities. Oxidation of the flexible I(I) catalyst to catalytic active I(III) species induces a defined C2-symmetric helical chiral environment with a delicate balance between flexibility and rigidity. A match/mismatch effect between the active catalyst and the substrate's helical shape in the dearomatization transition states was observed. The helical shape match allows the active catalyst to adapt its conformation to maximize attractive noncovalent interactions, including I(III)···O halogen bond, N-H···O hydrogen bond, and π···π stacking, to stabilize the favored transition state. A stereochemical model capable of rationalizing the effect of catalyst structural variation on the enantioselectivities is developed. The present study enriches our understanding of how flexible catalysts achieve high stereoinduction and may serve as an inspiration for the future exploration of conformational flexibility for new catalyst designs.

Multi-axial fatigue behavior of high-strength structural bolts

In this study, the fatigue failure of high-strength bolts (galvanized and regular) was experimentally and analytically explored under different tension-to-shear cyclic loading ratios. The observed cracking mechanisms were found to be a function of the bolt types and loading conditions. Though the cracks in the galvanized bolts followed the helical shape of the threads, the cracks for the regular bolts were parallel to the shear plan. The predicted fatigue lives under the combined tension and shear loads using the analytical approach matched the experimental results. Utilizing Eurocode SN curves for independent tension and shear demands overestimated the fatigue life of bolts under multi-axial stresses. The resulting SN curves obtained from this study can aid engineers in designing connections where bolts are subjected to multi-axial fatigue load.

A mechanical model for compaction of strands for wire ropes

Steel wire ropes are used for numerous industrial applications such as ships, elevators, cranes and bridges. A wire rope consists of numerous thin, steel wires and its geometrical construction can be explained in two steps. First, several wires are wrapped together in a helical shape called a strand. Second, several strands are wrapped together in a helical shape to form the final wire rope. In most cases, each strand is compacted before they are wrapped together to form the final wire rope. Compaction generally reduces contact stresses and thereby, extends ropes’ service life. Not many models have been proposed to predict the compaction process and its influence on the strand’s mechanical behavior during service. This contribution proposes a computationally efficient approach that consists of two elastoplastic mechanical models. The first model, describing the compaction process, is of a 2D plane strain nature and is therefore fast. Subsequently, the 2D geometry and plastic variables predicted by the compaction model are used to generate the initial geometry and initial plastic state of a 3D model, that is subsequently used to describe the strand’s mechanical behavior during service (we limit ourselves to tension). The results of the approach, with and without the mapping of the plastic variables, are compared to experimental measurements and the results without compaction. This is investigated for two real world strands.

Motility of Different Gastric Helicobacter spp.

Helicobacter spp., including the well-known human gastric pathogen H. pylori, can cause gastric diseases in humans and other mammals. They are Gram-negative bacteria that colonize the gastric epithelium and use their multiple flagella to move across the protective gastric mucus layer. The flagella of different Helicobacter spp. vary in their location and number. This review focuses on the swimming characteristics of different species with different flagellar architectures and cell shapes. All Helicobacter spp. use a run-reverse-reorient mechanism to swim in aqueous solutions, as well as in gastric mucin. Comparisons of different strains and mutants of H. pylori varying in cell shape and the number of flagella show that their swimming speed increases with an increasing number of flagella and is somewhat enhanced with a helical cell body shape. The swimming mechanism of H. suis, which has bipolar flagella, is more complex than that of unipolar H. pylori. H. suis exhibits multiple modes of flagellar orientation while swimming. The pH-dependent viscosity and gelation of gastric mucin significantly impact the motility of Helicobacter spp. In the absence of urea, these bacteria do not swim in mucin gel at pH < 4, even though their flagellar bundle rotates.

Bipolar Electrochemical Analysis of Chirality in Complex Media through Miniaturized Stereoselective Light-Emitting Systems

Environmentally relevant contaminants endowed with chirality may include pharmaceutical compounds, flame retardants, perfluoroalkyl chemicals, pesticides, and polychlorinated biphenyls. Despite having similar physicochemical properties, enantiomers may differ in their biochemical interactions with enzymes, receptors, and other chiral molecules leading to different biological responses. In this work, we have designed a wireless miniaturized stereoselective light-emitting system able to qualitatively detect a chiral contaminant (3,4-dihydroxyphenylalanine, DOPA) dissolved in reduced volumes (in the microliters range), through bipolar electrochemistry. The diastereomeric environment was created by mixing the enantiomers of an inherently chiral inductor endowed with helical shape (7,8-dipropyltetrathia[7]helicene) and the chiral probe (DOPA) in micro-solutions of a commercial ionic liquid. The synergy between the inductor, the applied electric field, and the chiral pollutant was transduced by the light emission produced from a miniaturized light-emitting diode (LED) exploited in such an approach as a bipolar electrode.

Experimental and numerical investigation of a novel fractal tube configuration in helically tube heat exchanger

The effects of innovative fractal configuration in helically tubular heat exchangers on thermal and hydraulic performance are investigated using numerical and experimental methods in this work. With Reynolds (Re) numbers ranging from 12,025 to 21,220, the overall heat transfer coefficient (U), pressure drop (ΔP), and performance factor (PF) are investigated. The fluid flow within and outside the tubes is studied using temperature, velocity, and pressure distributions. The numerical model was validated by comparing the simulation results and the experimental data where the difference between the results was found to be acceptable and trustworthy. In comparison to the standard helically tube heat exchanger (HTHE), the results showed that the fractal tube heat exchanger (FTHE) is more favorable to heat transmission. The overall heat transfer coefficient enhancement ratio is around 289%. The exergy efficiency increases with the rise of the Re number where the fractal tube configuration has the highest exergy efficiency. The fractal tree-like structure is more beneficial in decreasing pumping powers than typical HTHE, with a reduction ratio of ΔP of roughly 57%. At the same Re number range, the FTHE has a higher PF than the HTHE, indicating that fractal tree-like heat exchangers are preferable to standard HTHEs. The fractal-like tree form is greater than the helical shape for velocity, according to velocity contours and streamlines.

Numerical study of the compression of tightly constrained slender rods

Compression of a slender rod, tightly confined in a bore, is an archetypal problem that has relevance in a wide variety of situations ranging from worm like macromolecular chains and microtubules to drill strings in wellbores. If persistence length quantifies the stiffness of the rod, these problems span over cases where persistence length is of the order of the contour length to where it is many orders larger. In spite of this wide spread, all of these problems adopt the Kirchhoff rod theory, whereby, with appropriate normalisations, the force displacement response becomes independent of stiffness. This is true for unconstrained rods but not for rods constrained in bores. In fact, when the bore dimensions are much smaller compared to the length of the rod, i.e. the rod is ‘tightly’ constrained, post Euler buckling responses are characterised by abrupt large configurational adjustments or so-called ‘jump-instabilities’. The large and repeated configurational adjustments render the numerical simulation of the post-buckling force displacement responses difficult. We have used a geometrically exact 3-dimensional beam theory with rough constraining walls in order to successfully simulate the force displacement response of constrained rods up to large strains. In particular, we have simulated rods with stiffness values ranging over 6 orders of magnitude — starting from values comparable to microtubules in the cytoskeleton to those applicable to large scale engineering structures. Our results show that, unlike what is expected from the Kirchhoff rod theory, the geometry of the bore, and its size, play a significant role in rendering the compression response stiffness dependent. Moreover, nature and degree of confinement also dictate the stable 3-dimensional configuration to which the rod eventually evolves. In circular bores, the rod evolves to an almost perfect helical shape while in square ones, it does not.

Preferential molecular recognition of heterochiral guests within a cyclophane receptor

The discrimination of enantiomers by natural receptors is a well-established phenomenon. In contrast the number of synthetic receptors with the capability for enantioselective molecular recognition of chiral substrates is scarce and for chiral cyclophanes indicative for a preferential binding of homochiral guests. Here we introduce a cyclophane composed of two homochiral core-twisted perylene bisimide (PBI) units connected by p-xylylene spacers and demonstrate its preference for the complexation of [5]helicene of opposite helicity compared to the PBI units of the host. The pronounced enantio-differentiation of this molecular receptor for heterochiral guests can be utilized for the enrichment of the P-PBI-M-helicene-P-PBI epimeric bimolecular complex. Our experimental results are supported by DFT calculations, which reveal that the sterically demanding bay substituents attached to the PBI chromophores disturb the helical shape match of the perylene core and homochiral substrates and thereby enforce the formation of syndiotactic host-guest complex structures. Hence, the most efficient substrate binding is observed for those aromatic guests, e. g. perylene, [4]helicene, phenanthrene and biphenyl, that can easily adapt in non-planar axially chiral conformations due to their inherent conformational flexibility. In all cases the induced chirality for the guest is opposed to those of the embedding PBI units, leading to heterochiral host-guest structures.

The structure of DNA fragments: Quantum-chemical modelling

In this review, we analyze and systematize our computational studies of the nucleic acid duplex formations and thermodynamic stability under the different factors of investigation. The proposed structural models of mini-helix contains N nucleobase pairs (N = 3-5); QM structural data suggest that the helical conformations of mini-helix adopt geometrical parameters comparable to those of natural A- and B-DNA forms under specific conditions as micro hydration and charge compensation. The gas-phase models adopt non regular conformations between the helical form and a ladder form.. The natural helical shape of DNA mini-helix is stabilized by the presence of counterions or by explicit micro-hydration of the major and minor groves. The presence of aqueous solution is shown as a minor factor for the helical shape formation. The studies are performed at the level of density functional theory.

Experimental investigation of flow-induced sound of kite lines

In times of increasing importance of renewable energies, airborne wind energy (AWE) systems represent an emerging extension to conventional wind turbines. Many AWE systems use powerful kites to provide tether traction to mechanically unwind the tether, generating electricity on the ground. In addition to the traction tether, a large number of kite lines spanning the kite are moved through the air at high speed. This can produce a loud unpleasant whistling noise on the ground, which is due to a superposition of the aeolian tones of the many different lines. In the present work, differently structured kite lines were investigated in the aeroacoustic wind tunnel with respect to their sound radiation when they were exposed to a flow at up to 34 ms−1 resulting in Re ≦ 7300 and angles of attack (AOA) in the range of 90° ≧ AOA ≧ 45°. It was found that greater surface roughness increases sound radiation while line tension has negligible influence. By weaving a single-helix-shaped protrusion into the sheath of the kite line, the total radiated sound pressure level can be reduced by up to 9 dB. If the line itself has a helical contour, even a reduction of up to 11.5 dB is reachable. For decreasing AOA the noise suppression effect of helical surface protrusions and helical line shape is significantly reduced. The results provide initial guidelines on how to effectively reduce sound radiation from aircraft kites. Further investigations should consider the individual contributions of fluid and structural sounds to the total radiated sound of a flying kite.

Mechanism of low-temperature helical streamer discharge driven by pulsed electromagnetic field

Under the condition of specific pulsed discharge parameters, the discharge mode conversion of the low-temperature plasma jet discharge channel that originally propagates along a straight line will occur, forming a three-dimensional helical plasma channel. Unlike the traditional helical wave discharge, there are no factors such as an external constant magnetic field that destroys the poloidal symmetry of the dielectric tube, and the chiral direction of the helical streamer will change with the discharge parameters. In order to understand in depth the electromagnetic mechanism of the helical structure in the plasma jet, and the source and influencing factors of the poloidal electric field that leads to the helical shape and determines the chirality in this new type of discharge, we analyze the complex characteristics and electromagnetic mechanism of the helical streamer, such as the chiral direction, pitch, branching, by establishing a self-consistent plasma theoretical model. It is found that the phase of the poloidal wave mode has an effect on the chiral selection of the helical streamer, that the electron density has an influence on the pitch of the streamer, and that the repetition frequency has an effect on the bifurcation point. The above discharge characteristics and their influencing factors are of scientific significance in exploring the interaction mechanism of electromagnetic wave and plasma, and also in providing experimental and theoretical support for the chiral application of low-temperature plasma.

メーターガス栓および灯外内管・供給管への挿通・撤収が可能な空気圧駆動型ガス管内移動ロボットの開発

To observe the inside of gas pipes, we have been developing a pneumatically driven inspection robot that can locomote in service line including bended areas. In this paper, the robot accomplished insertion from a meter gas cock and shortage of the transmit time. To enable it to insert from a meter gas cock, the diameter of the robot is decreased to 12 [mm]. Furthermore, to shorten the transit time, we developed a way to increase the airflow rate of the robot by applying a wider tube stored in a helical shape inside the body. Finally, the robot could insert from the meter gas cock throughout a 7[m] service line within 81[min].