Spiral Motion Research Articles

A singular vorticity wave packet within a rapidly rotating vortex: spiralling versus oscillating motions

This paper considers a free vorticity wave packet propagating within a rapidly rotating vortex in the quasi-steady regime, a long time after the wave packet strongly and unsteadily interacted with the vortex. We study a singular, nonlinear, helical and asymmetric shear mode inside a linearly stable, columnar and axisymmetric vortex on the $f$-plane. The amplitude-modulated mode enters resonance with the vortex at a certain radius $r_{c}$, where the phase angular speed is equal to the rotation frequency. The singularity in the modal equation at $r_{c}$ strongly modifies the flow in the three-dimensional helical critical layer, the region around $r_{c}$ where the wave/vortex interaction occurs. This interaction generates a vertically sheared three-dimensional mean flow of higher amplitude than the wave packet. The chosen envelope regime assumes the formation of a mean radial velocity of the same order as the wave packet amplitude, leading to the streamlines exhibiting a spiral motion in the neighbourhood of the critical layer. Radar images frequently show such spiral bands in tropical cyclones or tornadoes. Through matched asymptotic expansions, we find an analytical solution of the leading-order equations inside the critical layer. The generalized Batchelor integral condition applied to the quasi-steady, three-dimensional motion inside the separatrices yields a leading-order, non-uniform three-dimensional vorticity. The critical-layer pattern, strongly deformed by the mean radial velocity, loses its symmetries with respect to the azimuthal and radial directions, which makes the leading-order mean radial wave fluxes non-zero. Finally, a stronger wave/vortex interaction occurs with respect to previous studies where a steady neutral vortical mode or an envelope of larger extent was involved.

Mathematical model of the vibration cone crusher with three degrees of freedom

The project of the vibration crusher with three degrees of freedom is proposed. The degrees are limited by the guide rails that hold the crusher body and cone against horizontal and spiral motions. The mathematical model for this project is obtained. The observations for the motion of the body, the cone and the unbalance vibrator are made in a numerical experiment. A fourfold superiority of the cone amplitude over the body amplitude was discovered. When the cone partial frequency exceeds the unbalance rotation frequency, a strongly marked beating in the cone oscillations was observed with a frequency 8 times less than the unbalance rotation frequency. At the same frequencies, a body beating was observed.

Spiral Trajectory Modulation of Rheotaxic Motile Human Sperm in Cylindrical Microfluidic Channels of Different Inner Diameters.

We investigated the relationship between human sperm rheotaxis and motile sperm trajectories by using poly-(dimethylsiloxane) (PDMS)-based cylindrical microfluidic channels with inner diameters of 100 μm, 50 μm, and 70 μm, which corresponded to the inner diameter of the human isthmus, the length of a sperm and a diameter intermediate between the two, respectively. We counted the number of rheotaxic sperm and sperm with spiral motion. We also analyzed motile sperm trajectories. As the cylindrical channel diameter was decreased, the percentage of sperm cells exhibiting rheotaxis, the percentage of sperm cells exhibiting spiral motion, the frequency-to-diameter ratio of the sperm cells' spiral trajectories, and the surface area of the microfluidic channel increased, while the flagellar motion at the channel wall decreased. The percentage of sperm exhibiting a spiral trajectory and the frequency-to-diameter ratio of the sperm cells' spiral trajectories were thus affected by the channel diameter. Our findings suggest that the oviduct structure affects the swimming properties of sperm cells, guiding them from the uterus to the ampulla for egg fertilization. These results could contribute to the development of motile sperm-sorting microfluidic devices for assisted reproductive technologies.

Angular momentum of radiation from a charge in circular and spiral motion

We study theoretically the vortex radiation of a relativistic charged particle. General expressions for the spectral and angular distributions of angular momentum of radiation are derived for an arbitrary moving charge. Special attention is given to calculation of the angular momentum of synchrotron radiation. We obtain the spectrum and the angular distribution of angular momentum carried by synchrotron radiation. Similar expressions for the angular momentum of radiation of a charge moving on a spiral trajectory are derived by use of Lorentz transformations. It is shown that the main part of angular momentum in this case is emitted at a small angle to the vortex axis. Relativistic charged particles at spiral motion are effective source of the vortex photon beams at wave lengths ranging from radio waves to gamma rays. The obtained equations can be used for calculations of the angular momentum emitted by charged particles in the helical undulators and at axial channeling in solid crystal.

Numerical and experimental study on an isolated bubble in the swirling separator

In the online fission gas removal system applied for thorium molten salt reactor, the vane-type gas-liquid separator was developed to separate the dilute dispersed bubbles from the reactor coolant. For the efficient separation, it’s essential to quantitatively describe the bubble trajectory and the separation length of bubble that for the design of the separator. The separation trajectory of sized spherical bubble ranging from 0.22 mm to 1.05 mm produced by the customized isolated bubble generator were preliminary investigated numerically and experimentally in surrogate molten salt of five concentrations of CaCl2 aqueous solution up to 32.91 wt% covering initial inlet velocity of the separator from 0.842 m/s to 2.526 m/s. A promising numerical simulation method was used to effectively and fast predict the isolate bubble motion in the swirling flow, which combines bubble mechanical model with analytical expressions of liquid velocity field. The visualization experiments using high-speed camera and image processing were implemented to record the bubble trajectory during separation under the same conditions. Both numerical and experimental results indicate that the bubble has a convergent spiral movement during separation before captured by the air core. The separation length Ls increases as the bubble diameter decreases or the initial inlet velocity and the concentration of CaCl2 solution increase. The comparison between numerical and experimental data of Ls shows good agreement and the relative errors of Ls between them are bounded to ±10%.

Dislocation and node states in bilayer graphene systems

We investigate the electronic structure of realistic partial dislocation networks in bilayer graphene that feature annihilating, wandering, and intersecting partial lines. We find charge accumulation states at partials that are sensitive to Fermi energy and partial Burgers vector but not to the screw versus edge character of the partial. These states are shown to be current carrying, with the current density executing a spiral motion along the dislocation line with a strong interlayer component to the current. Close to the Dirac point localization on partials switches to localization on intersections of partials, with a corresponding complex current flow around the nodes.

Magnetic Field–Suppressed Lithium Dendrite Growth for Stable Lithium‐Metal Batteries

AbstractLithium metal is the most attractive anode material due to its extremely high specific capacity, minimum potential, and low density. However, uncontrollable growth of lithium dendrite results in severe safety and cycling stability concerns, which hinders the application in next generation secondary batteries. In this paper, a new and facile method imposing a magnetic field to lithium metal anodes is proposed. That is, the lithium ions suffering Lorentz force due to the electromagnetic fields are put into spiral motion causing magnetohydrodynamics (MHD) effect. This MHD effect can effectively promote mass transfer and uniform distribution of lithium ions to suppress the dendrite growth as well as obtain uniform and compact lithium deposition. The results show that the lithium metal electrodes within the magnetic field exhibit excellent cycling and rate performance in a symmetrical battery. Additionally, full batteries using limited lithium metal as anodes and commercial LiFePO4 as cathodes show improved performance within the magnetic field. In summary, a new and facile strategy of suppressing lithium dendrites using the MHD effect by imposing a magnetic field is proposed, which may be generalized to other advanced alkali metal batteries.

Movement of luminous group spots on target and size modification of micro-particles during cathodic vacuum arc deposition

Modification of micro-particle size during cathodic arc deposition is an important issue for the preparation of hard coatings and nanomaterials. In this work, a coil winding and permanent magnets were applied to adjust the magnetic field of a cathodic arc source. The motion of luminous group spots was investigated through high speed imaging method. The average size of the spots was reduced with the decrease of arc current. When the arc current was higher than 80 A, the size probability distributions of the spots presented as bimodal functions. But it turned into unimodal functions at lower arc currents. By changing the coil current three kinds of spots position distributions were observed, such as centered distribution, intermediate and periphery annulus distributions. Their corresponding spots movements were stochastic, spiral and circular motion dominated. The influence of magnetic field on the spots motion was discussed. Although the average spots size was reduced with the increase of coil current to 2.5 A. Further increasing the coil current leaded to a gathering of spots towards the periphery region of the cathode surface, and an increase of the spots size. Finally, a relationship between the spots size and micro-particles size was established.

Pressure oscillation suppression by air admission in a Francis turbine draft tube

When Francis turbine operated at part-load conditions, there is strong vortex rope in the draft tube, which may induce violent pressure oscillation, mechanical vibration and noise. This paper treats the pressure oscillations at a part-load operation by analyzing the unsteady multiphase flow in a Francis turbine. Air admission is used to alleviate pressure oscillation under different cavitation number. In order to improve the numerical accuracy, a modified method including the Level-set based method and FBDCM model is applied in the calculation. The simulation results indicate that the modified method can reasonably predict the pressure oscillations in turbine with good agreement with experimental data. The method can reflect more detailed flow characteristics and capture a clearer phase interface compared to the conventional method. It is noted that air admission with suitable ventilation rate does suppress the pressure oscillation in the turbine. The pressure oscillation in the vaneless area due to rotor-stator interaction cannot be depressed completely. Further, the mechanism on the pressure oscillation suppression in the draft tube is due to the spiral motion depression of vortex rope by air admission. As the increase of air admission, the pressure and its gradient distributions become much homogeneous. The homogeneous distribution of pressure in the draft tube would be favourable for the suppression of pressure oscillation

Robust Cochlear Modiolar Axis Detection in CT.

The cochlea, the auditory part of the inner ear, is a spiral-shaped organ with large morphological variability. An individualized assessment of its shape is essential for clinical applications related to tonotopy and cochlear implantation. To unambiguously reference morphological parameters, reliable recognition of the cochlear modiolar axis in computed tomography (CT) images is required. The conventional method introduces measurement uncertainties, as it is based on manually selected and difficult to identify landmarks. Herein, we present an algorithm for robust modiolar axis detection in clinical CT images. We define the modiolar axis as the rotation component of the kinematic spiral motion inherent in the cochlear shape. For surface fitting, we use a compact shape representation in a 7-dimensional kinematic parameter space based on extended Plücker coordinates. It is the first time such a kinematic representation is used for shape analysis in medical images. Robust surface fitting is achieved with an adapted approximate maximum likelihood method assuming a Student-t distribution, enabling axis detection even in partially available surface data. We verify the algorithm performance on a synthetic data set with cochlear surface subsets. In addition, we perform an experimental study with four experts in 23 human cochlea CT data sets to compare the automated detection with the manually found axes. Axes found from co-registered high resolution μCT scans are used for reference. Our experiments show that the algorithm reduces the alignment error providing more reliable modiolar axis detection for clinical and research applications.

Deterrence under nuclear asymmetry: THAAD and the prospects for missile defense on the Korean peninsula

ABSTRACTThe 2016 decision to deploy Terminal High Altitude Area Defense (THAAD) to South Korea has generated multitude of intensely politicized issues and has proved highly controversial. This has made it challenging to alleviate, let alone clarify, points of analytical and policy tensions. We instead disaggregate and revisit two fundamental questions. One is whether THAAD could really defend South Korea from North Korean missiles. We challenge the conventional “qualified optimism” by giving analytical primacy to three countermeasures available to defeat THAAD–use of decoys, tumbling and spiral motion, and outnumbering. These countermeasures are relatively inexpensive to create but exceedingly difficult to offset. Second, we assess the optimal way to ensure South Korean national security against North Korean missiles. By examining the balance of capability and issues of credibility/commitment, we show that the U.S. extended deterrence by punishment remains plentiful and sufficiently credible even without enhancing the current defense capability.

Broken interference structure during ionization process of H atom in strong laser fields

In this paper we investigate the carpetlike structures in the photoelectron momentum distributions (PMDs) of hydrogen atom driven by a linear polarization laser with different optical cycle numbers and an elliptical polarization laser with different ellipticity values. We find that for linear polarization with the optical cycle number nc = 3, the ionized electrons undergo few half cycles, the carpetlike structures in the PMDs are not clearly seen. As the optical cycle number increases, the carpetlike structure becomes more obvious because that the contribution from the constructive and destructive interference. For elliptical polarization laser pulses, the ionized electrons are accelerated along the perpendicular direction along the other elliptical axis. And then the electrons have a spiral movement, which destroys the conditions resulting in the constructive and destructive interference. So the carpetlike structures gradually disappear with the increasing of ellipticity values.

Impact of Lèvy flight on modern meta-heuristic optimizers

In this paper, a variant based on Lèvy flight was proposed to enhance the performance of two recently proposed optimizers. The first optimizer used in the study is Sine-Cosine Algorithm (SCA) while the second is Whale Optimization Algorithm (WOA). Both optimizers are composed of two phases of random walks in each optimization iteration and both have stagnation and premature convergence problems. Lèvy flight is used to replace the walk based on cosine function in the SCA and the spiral motion in the WOA as well. The Lèvy-based search guarantees a fraction of solutions to be generated apart from the current best solution and hence tolerates for optimizer stagnation, premature convergence, and allows for local optima avoidance. A smooth control of the scale of the Lèvy random walk is also proposed to ensure a smooth adaptation of exploration to exploitation switching. The proposed variants, as well as the original algorithms, were benchmarked using a set of unimodal, multimodal, fixed-dimension multimodal and composite benchmark functions. The evaluation is performed using a set of assessment indicators and results prove the capability of the proposed variants to outperform the original optimizers.

Intelligent Traffic Control System with Priority to Emergency Vehicles

Traffic is the most critical problem in metropolitan cities. Traffic control becomes more necessary to provide problem-less, peaceful driving and pollution-less life to people. The work is designed to develop a density based dynamic traffic signal system. The signal timing changes automatically on sensing the traffic density at the junction. The traffic system is structured with a camera. The image captured by the camera is processed in order to calculate the number of vehicles present in the image. The camera also identifies the siren and allows the green light for emergency vehicles like ambulance, fire engine etc. In this paper, masking algorithm is used to process the image and find the vehicle count on the road. This algorithm shows only the required portion of the image and masks the unnecessary details. The visual basic programming is used to control the glowing time of traffic light based on the vehicle count on the road. The Arduino controller is a single board microcontroller used for instructing the LED to glow. This method can be used to detect road accidents and identify violations of the spiral movements of cars. The whole system when installed on road, provides a way for easy traffic clearance for emergency vehicles without a need of sergeant.

Dusting Efficiency of the Moses Holmium Laser: An Automated In Vitro Assessment.

Moses technology is a novel Holmium:YAG laser system designed to minimize stone retropulsion and improve stone ablation when the laser is not in direct contact with the stone. Our aim was to assess the efficiency of Moses technology relative to short- and long-pulse lithotripsy using an automated in vitro "dusting model" of stone comminution. All tests were conducted using a Lumenis Pulse 120H Holmium:YAG laser with a 365 μm Moses D/F/L fiber. "Hard" (15:3) and "soft" (15:6) Begostones mimicking calcium oxalate monohydrate and uric acid stones, respectively, were used. To assess ablation efficiency and fiber tip degradation, a dusting model was employed: the laser was moved by a three-dimensional positioning system in a spiral motion across a flat Begostone surface submerged in water. Ablation efficiency was measured as stone mass loss after 4 kJ of energy delivery. Fiber tip degradation was measured at 1 kJ intervals. Comparative trials with short pulse, long pulse, Moses contact, and Moses distance settings were completed with the laser tip positioned at 0, 1, and 2 mm distances from the stone at energy settings of 0.4 J delivered at 70 Hz. In our dusting model, stone ablation was significantly greater the closer the laser was to the stone. On hard stones, pulse type did not have a significant impact on ablation at any distance. On soft stones at 0 mm, Moses contact produced the greatest ablation, significantly greater than long pulse (p < 0.05). At 1 mm, Moses distance produced significantly greater ablation than all other settings (p = 0.025) and was as effective as long or short pulse at 0 mm. At 2 mm distance, no pulse type demonstrated significantly different ablation. Fiber tip degradation was minimal and not significant between settings. Moses technology delivers greater ablation of soft stones when in contact and 1mm from the stone surface.

Non-isothermal bubble rise dynamics in a self-rewetting fluid: three-dimensional effects

The dynamics of a gas bubble in a square channel with a linearly increasing temperature at the walls in the vertical direction is investigated via three-dimensional numerical simulations. The channel contains a so-called ‘self-rewetting’ fluid whose surface tension exhibits a parabolic dependence on temperature with a well-defined minimum. The main objectives of the present study are to investigate the effect of Marangoni stresses on bubble rise in a self-rewetting fluid using a consistent model fully accounting for the tangential surface tension forces, and to highlight the effects of three-dimensionality on the bubble rise dynamics. In the case of isothermal and non-isothermal systems filled with a ‘linear’ fluid, the bubble moves in the upward direction in an almost vertical path. In contrast, strikingly different behaviours are observed when the channel is filled with a self-rewetting fluid. In this case, as the bubble crosses the location of minimum surface tension, the buoyancy-induced upward motion of the bubble is retarded by a thermocapillary-driven flow acting in the opposite direction, which in some situations, when thermocapillarity outweighs buoyancy, results in the migration of the bubble in the downward direction. In the later stages of this downward motion, as the bubble reaches the position of arrest, its vertical motion decelerates and the bubble encounters regions of horizontal temperature gradients, which ultimately lead to the bubble migration towards one of the channel walls. These phenomena are observed at sufficiently small Bond numbers (high surface tension). For stronger self-rewetting behaviour, the bubble undergoes spiralling motion. The mechanisms underlying these three-dimensional effects are elucidated by considering how the surface tension dependence on temperature affects the thermocapillary stresses in the flow. The effects of other dimensionless numbers, such as Reynolds and Froude numbers, are also investigated.

Numerical simulations on material flow behaviors in whole process of friction stir welding

Abstract A finite element model based on solid mechanics was developed with ABAQUS to study the material flow in whole process of friction stir welding (FSW), with the technique of tracer particles. Simulation results indicate that the flow pattern of the tracer particles around the pin is spiral movement. There are very different flow patterns at the upper and lower parts of the weld. The material on the upper surface has the spiral downward movement that is affected by the shoulder and the lower material has the spiral upward movement that is affected by the pin. The velocity of the material flow on the periphery of the stirring pin is higher than that at the bottom of the stirring pin. The material can be rotated with a stirring pin a few times, agreeing well with the previous experimental observation by tungsten tracer particles.

Improving formability of sheet metals in incremental forming by equal diameter spiral tool path

In order to improve formability of sheet metal in incremental forming, a new tool path strategy is proposed. When using the tool path strategy, the tool feeds at each layer while making an equal diameter spiral movement around the forward direction. A detailed procedure for generating the tool path is described. The procedure includes the use of commercial CAD/CAM software to generate a common tool path, outputting the common tool path in the form of tool path points, interpolating the output tool path points, and transforming the interpolated tool path points in space. A series of experiments for forming varying wall angle conical frustums were carried out by the spiral tool paths with different spiral directions, spiral diameters, and spiral leads, respectively. The experimental results show that the method of generating equal diameter spiral tool path proposed in this paper is feasible. Within the experimental range, the spiral tool path in both directions can improve the sheet formability, compared with the common tool path in incremental sheet forming. And, the formability with the anti-right-hand spiral direction is better than that with the right-hand spiral direction when the tool moves counter clockwise; the formability increases with the decrease of the spiral lead and the increase of the spiral diameter. In addition, the influence of spiral parameters on the surface quality of the sheet metal was also experimentally studied. The results show that the surface quality of parts decreases with the increase of spiral lead, while the effect of spiral diameter is not significant.

Introduction to The Spiral Dynamics and The Spiral Coriolis Force

The spiral dynamics of a point-like body of mass m in spiral differential geometry are introduced. New ideal motions have been studied, the uniform spiral motion and the uniform spiral-polar motion. The analysis is proposed by comparing the ideal spiral motions with the ideal circular motions. The theoretical forces acting on a point-like body of mass m moving in spiral frames were analyzed. The spiral and polar components of the Coriolis forces were compared.

A Pink Wave for Breast Cancer Awareness and Prevention

Background and context: Integrated in the Pink October Movement, we decided since 2014 to challenge people and institutions to use the color pink as a way to raise awareness concerning breast cancer prevention. Aim: Raise awareness and reinforce the idea that breast cancer prevention is possible, namely with screening. Strategy/Tactics: We present a list of possibilities to be done individually or in community, indoor or outdoor, in one day or several, with family, friends and colleagues or with the anonymous community. Program/Policy process: We disseminate this idea to all our partners: schools, municipalities, enterprises and, of course, mass media. Between the 15th and 31st October hundreds of institutions join us in this Pink Wave. Outcomes: Each year we raise the number of partners which develop creative and dynamic activities, engaging themselves a high number of participants. Information sessions, awareness workshops, gymnastics challenges, arts and crafts initiatives, call for partnerships throughout the rest of the year and fundraising. All of this empowers community and turns out to be totally impossible to run away from this wave and consequently from the theme of breast cancer prevention. What was learned: First, we learnt that sometimes less is more. We started to do a list of activities and we didn´t offered anything more. And the truth is people didn´t need it because the list was the trigger for their creativity and originality. Secondly, the spiral movement is reinforcement and each year we add new activities that were done successfully in the past by partners. This way people believe is possible and try it also. Finally, it´s very important to listen to the community: which kind of activities they enjoy the most and how can we help them... and of course to share with the community the good results, disseminating the best practices on social and mass media, stressing the idea that without them nothing (or nearly nothing) could be done!