Zigzag Path Research Articles

(Invited) Can Phosphorus-Doped Graphene be a Good Anode for Na-Ion Batteries? A First-Principles Study

Secondary energy storage technologies based on sodium ions are an important emerging alternative to lithium ion batteries (LIBs). Sodium is less expensive than lithium, with its supplies being much wider and more democratically distributed throughout the globe. There are fundamental physical differences between Na and Li, and it is clear the knowledge available from extensive research on LIBs does not translate to sodium. However, the understanding of Na-based systems is at their infancy, and their complexities are just beginning to be understood. In this talk, we theoretically investigated the possibility of using phosphorus-doped (P-doped) graphene as an anode material in sodium ion batteries (NIBs). We reveal some fundamental physical properties of sodium adsorption on P-doped graphene by calculating formation and adsorption energies, voltage vs. capacity curves, migration for Na transport, and electron density of states and mobility. Our calculations suggest that Na adsorption on the same side of protrudent P is the preferred configuration for application in NIBs. This particular configuration possesses very large Na capacity (~582 mAh/g). More importantly, Na has to cross a diffusion barrier (~0.3 eV) and it diffuses in a zigzag path on the P-doped structures due to the presence of protrudent P with larger atomic size compared with the size of a carbon. We will also present electronic movements and accumulations during sodiation. Though carrier mobility may be not as fast as in metals or pristine graphene because P-doped graphene with Na adsorbed on it becomes a semiconductor, the calculated carrier mobility is still significantly large with the order of 103 to 105 cm2/V/s. Lastly, we will discuss the guidelines for the efficient design of P-doped graphene as a promising anode for NIBs.

Path instability of a compressible air bubble rising in quiescent water with consideration of variable thermophysical properties

A numerical study of a compressible air bubble rising in water with variable thermophysical properties is conducted. The coupled level set and volume of fluid method is adopted to track the interface. Empirical correlations in terms of temperature for thermophysical properties and equation of state for air are considered in the simulations. We simulate a compressible 3D static air bubble in water for the first time. The volume change of the bubble and the pressure difference between the inside and outside of the static bubble agree well with the theoretical solutions. We study the zigzag motion of a compressible air bubble considering the temperature difference with respect to the surrounding water. The mechanism of the zigzag motion is clarified by analyzing the shape evolution and the wake structure. The periodic shedding of hairpin vortex with 2R mode is observed during the zigzag motion. There are two periods of the bubble shape oscillation within one zigzag cycle. We obtain the relation between the oscillation frequency of the aspect ratio (fE), the zigzag path (fp) and vorticity component in X and Y direction accumulated on the bubble surface (fv) as fE=2fp=2fv.

Magneto-Capillary Particle Dynamics at Curved Interfaces: Time-Varying Fields and Drop Mixing.

Spatially uniform magnetic fields induce nonzero forces on magnetic particles adsorbed at curved liquid interfaces thereby driving their motion. Such motions, prohibited in bulk fluids, arise due to interfacial constraints that couple magnetic torques to capillary forces at curved interfaces. Here, we show that time-varying (spatially uniform) magnetic fields can be used to drive a variety of steady particle motions on water drops in decane. Upon application of a precessing field, magnetic Janus particles with amphiphilic surface chemistry move either along circular orbits at the drop poles or along zigzag paths at the drop equator. The different magneto-capillary motions depend on the frequency and precession angle of the field as well as the initial position of the particle on the drop surface. Our experimental observations are reproduced and explained by a mathematical model that accounts for the relevant magnetic, capillary, and hydrodynamic forces and torques that contribute to particle motion. In addition to ferromagnetic Janus particles, we show that similar dynamics can be achieved using superparamagnetic carbonyl iron particles, which are manufactured on industrial scales and respond to even weaker magnetic fields. We demonstrate how the field-driven motion of such particles at the drop interface can induce fluid flows that effectively mix the drop interior. These results suggest that magneto-capillary particle motions could be used to enhance mass transfer within emulsions stabilized by magnetic particles.

High-Level Path Planning for an Autonomous Sailboat Robot Using Q-Learning.

Path planning for sailboat robots is a challenging task particularly due to the kinematics and dynamics modelling of such kinds of wind propelled boats. The problem is divided into two layers. The first one is global where a general trajectory composed of waypoints is planned, which can be done automatically based on some variables such as weather conditions or defined by hand using some human–robot interface (a ground-station). In the second local layer, at execution time, the global route should be followed by making the sailboat proceed between each pair of consecutive waypoints. Our proposal in this paper is an algorithm for the global, path generation layer, which has been developed for the N-Boat (The Sailboat Robot project), in order to compute feasible sailing routes between a start and a target point while avoiding dangerous situations such as obstacles and borders. A reinforcement learning approach (Q-Learning) is used based on a reward matrix and a set of actions that changes according to wind directions to account for the dead zone, which is the region against the wind where the sailboat can not gain velocity. Our algorithm generates straight and zigzag paths accounting for wind direction. The path generated also guarantees the sailboat safety and robustness, enabling it to sail for long periods of time, depending only on the start and target points defined for this global planning. The result is the development of a complete path planner algorithm that, together with the local planner solved in previous work, can be used to allow the final developments of an N-Boat making it a fully autonomous sailboat.

The Structural Origins of Wood Cell Wall Toughness.

The remarkable mechanical stability of wood is primarily attributed to the hierarchical fibrous arrangement of the polymeric components. While the mechanisms by which fibrous cell structure and cellulose microfibril arrangements lend stiffness and strength to wood have been intensively studied, the structural origins of the relatively high splitting fracture toughness remain unclear. This study relates cellulose microfibril arrangements to splitting fracture toughness in pine wood cell walls using in situ electron microscopy and reveals a previously unknown toughening mechanism: the specific arrangement of cellulose microfibrils in the cell wall deflects cracks from the S2 layer to the S1/S2 interface, and, once there, causes the crack to be repetitively arrested and shunted along the interface in a zig-zag path. It is suggested that this natural adaptation of wood to achieve tough interfaces and then deflect and trap cracks at them can be generalized to provide design guidelines to improve toughness of high-performance and renewable engineering materials.

Coverage Mission for UAVs Using Differential Evolution and Fast Marching Square Methods

This research presents a novel approach for missions of coverage path planning (CPP) carried out by unmanned aerial vehicles (UAVs) in a three-dimensional environment. These missions are focused on path planning to cover a certain area in an environment in order to carry out tracking, search, or rescue tasks. The methodology followed uses an optimization process based on the differential evolution (DE) algorithm in combination with the Fast Marching Square (FM2) planner. The DE algorithm evaluates a cost function to determine what the zigzag path with the minimum cost is, according to the steering angle of the zigzag bands (α). This optimization process allows achieving the most optimal zigzag path in terms of distance traveled by the UAV to cover the whole area. Then, the FM2 method is applied to generate the final path according to the steering angle of the zigzag bands resulting from the DE algorithm. The approach generates a feasible path free from obstacles, keeping a fixed altitude flight over the ground. The flight level, smoothness, and safety of the path can be modified by two adjustment parameters included in our approach. Simulated experiments carried out in this work demonstrate that the proposed approach generates the most optimal zigzag path in terms of distance, safety, and smoothness to cover a certain whole area, keeping a determined flight level with successful results.

A path planning and sharp corner correction strategy for wire and arc additive manufacturing of solid components with polygonal cross-sections

Pores can easily form in the geometric center and sharp corner lap joints of solid components with polygonal cross-sections fabricated by wire and arc additive manufacturing. To solve these problems, this paper proposes a composite path planning method and a sharp corner correction strategy. The composite path planning method consists of the zigzag path and the contour offsetting path. The zigzag path is used to fill the interior of the component and eliminates pores formed by traditional filling paths. The contour offset path is used to improve the geometric precision of the component. Filling paths are connected to create a closed path, which reduces arc striking and arc extinguishing during the manufacturing process. By exploring the distance between two vertices of a sharp corner lap of the outer contour path, it was found that pores form in the sharp corner lap when the angle of the sharp corner is less than 58.65°; therefore, the sharp corner correction strategy is proposed to correct the sharp corner lap path in the outer contour path. Experimental results show that the composite path filling method and the sharp corner correction strategy can eliminate pores between the geometric center and the sharp corner lap joints of components, thereby improving surface morphology and forming quality of components with complex polygonal cross-sections.

Weeds Associated with Banana Crops in Magdalena Department, Colombia

ABSTRACT: This study was conducted to determine the richness and composition of weed communities associated with banana plantations in Magdalena department, Colombia. Between September 2016 and May 2017, a total of 164 hectares were assessed over four agroecological zones (Alta, Media, Baja and Norte); in each zone, three representative farms were selected where, through zigzag paths, botanical collections were made in cultivated lots. Information on life cycle, growth habit and origin of each species was included. The floristic composition was represented by 204 species distributed among 143 genera and 54 families. Poaceae, with 31 species, was the family with the highest species richness, followed by Fabaceae (12) and Asteraceae (11). From the total species recorded, 113 are perennial (55%) and 91 are annual (45%); 141 species are herbaceous (68%), 38 are climbers (20%), and 25 are arboreal or shrubby (12%). Native species predominate over introduced species. The species richness does not differ significantly between the sampling zones, but the weed community composition does. The presence of common species reported as important weeds worldwide was recorded in the four zones. However, some species were recorded in only one of the zones, generating a differential composition pattern. Comparison with local inventories showed changes in the composition of the weed complex over time. The presence of various species not previously considered weeds in the banana crops of this region is highlighted.

Extended finite element method (XFEM) modeling of fracture in additively manufactured polymers

The fracture of additively manufactured polymer materials with various layer orientations is studied using the extended finite element method (XFEM) in an anisotropic cohesive zone model (CZM). The single edge notched bending (SENB) specimens made of acrylonitrile-butadiene-styrene (ABS) materials through fused filament fabrications with various crack tip/layer orientations are considered. The XFEM coupled with anisotropic CZM is employed to model the brittle fracture (fracture between layers), ductile fracture (fracture through layers), as well as kinked fracture behaviors of ABS specimens printed with vertical, horizontal, and oblique layer orientations, respectively. Both elastic and elastoplastic fracture models, coupled with linear or exponential traction-separation laws, are developed for the inter-layer and cross-layer fracture, respectively. For mixed inter-/cross- layer fracture, an anisotropic cohesive zone model is developed to predict the kinked crack propagations. Two crack initiation and evolution criteria are defined to include both crack propagation between layers (weak plane failure) and crack penetration through layers (maximum principal stress failure) that jointly determine the zig-zag crack growth paths. The anisotropic cohesive zone model with XFEM developed in this study is able to capture different fracture behaviors of additively manufactured ABS samples with different layer orientations.

Flexure Behaviors of ABS-Based Composites Containing Carbon and Kevlar Fibers by Material Extrusion 3D Printing.

Short-fiber-reinforced thermoplastics are popular for improving the mechanical properties exhibited by pristine thermoplastic materials. Due to the inherent conflict between strength and ductility, there are only a few successful cases of simultaneous enhancement of these two properties in polymer composite components. The objective of this work was to explore the feasibility of simultaneous enhancement of strength and ductility in ABS-based composites with short-carbon and Kevlar fiber reinforcement by material extrusion 3D printing (ME3DP). Microstructure characterization and measurement of thermal and mechanical properties were conducted to evaluate the fiber-reinforced ABS. The influence of printing raster orientation and build direction on the mechanical properties of material extrusion of 3D-printed composites was analyzed. Experimental results demonstrated that the reinforcement of the ABS-based composites by short-carbon and Kevlar fibers under optimized 3D-printing conditions led to balanced flexural strength and ductility. The ABS-based composites with a raster orientation of ±45° and side build direction presented the highest flexural behaviors among the samples in the current study. The main reason was attributed to the printed contour layers and the irregular zigzag paths, which could delay the initiation and propagation of microcracks.

Routing Acoustic Waves via a Metamaterial with Extreme Anisotropy

Routing acoustic waves without backscattering losses is presently of great interest. Unlike both conventional approaches using defects in sonic crystals and emerging approaches based on topological edge states, this study proposes a radically different theoretical framework that utilizes extremely anisotropic media to engineer backscattering-immune waveguides. The exact condition for one-way wave propagation along zigzag paths is derived. The proposal is experimentally validated using spoof surface acoustic waves, and the results could have implications for on-chip wave manipulation, as well as noise control.

Cluster integrable systems and spin chains

We discuss relation between the cluster integrable systems and spin chains in the context of their correspondence with 5d supersymmetric gauge theories. It is shown that {mathfrak{gl}}_N XXZ-type spin chain on M sites is isomorphic to a cluster integrable system with N × M rectangular Newton polygon and N × M fundamental domain of a ‘fence net’ bipartite graph. The Casimir functions of the Poisson bracket, labeled by the zig-zag paths on the graph, correspond to the inhomogeneities, on-site Casimirs and twists of the chain, supplemented by total spin. The symmetricity of cluster formulation implies natural spectral duality, relating {mathfrak{gl}}_N -chain on M sites with the {mathfrak{gl}}_M -chain on N sites. For these systems we construct explicitly a subgroup of the cluster mapping class group {mathcal{G}}_{mathcal{Q}} and show that it acts by permutations of zig-zags and, as a consequence, by permutations of twists and inhomogeneities. Finally, we derive Hirota bilinear equations, describing dynamics of the tau-functions or A-cluster variables under the action of some generators of {mathcal{G}}_{mathcal{Q}} .

Kasteleyn operators from mirror symmetry

Given a consistent bipartite graph $$\Gamma $$ in $$T^2$$ with a complex-valued edge weighting $$\mathcal {E}$$ we show the following two constructions are the same. The first is to form the Kasteleyn operator of $$(\Gamma , \mathcal {E})$$ and pass to its spectral transform, a coherent sheaf supported on a spectral curve in $$(\mathbb {C}^\times )^2$$ . The second is to form the conjugate Lagrangian $$L \subset T^* T^2$$ of $$\Gamma $$ , equip it with a brane structure prescribed by $$\mathcal {E}$$ , and pass to its mirror coherent sheaf. This lives on a stacky toric compactification of $$(\mathbb {C}^\times )^2$$ determined by the Legendrian link which lifts the zig-zag paths of $$\Gamma $$ (and to which the noncompact Lagrangian L is asymptotic). We work in the setting of the coherent–constructible correspondence, a sheaf-theoretic model of toric mirror symmetry. We also show that tensoring with line bundles on the compactification is mirror to certain Legendrian autoisotopies of the asymptotic boundary of L.

A New Bursting Liability Evaluation Index for Coal –The Effective Elastic Strain Energy Release Rate

Because both faults and cleats exist in coal, sharp stress drops occur during loading when coal is deformed. These drops occur during the pre-peak stage and are accompanied by sudden energy releases. After a stress drop, the stress climbs slowly following a zigzag path and the energy accumulated during the pre-peak stage is unstable. A stress–strain curve is the basic tool used to evaluate the bursting liability of coal. Based on energy accumulation in an unsteady state, the pre-peak stress–strain curve is divided into three stages: pre-extreme, stress drop, and re-rising stage. The energy evolution of the specimen during each stage is analyzed. In this paper, an index called the effective elastic strain energy release rate (EESERR) index is proposed and used to evaluate the coal’s bursting liability. The paper shows that the propagation and coalescence of cracks is accompanied by energy release. The stress climb following a zigzag path prolongs the plastic deformation stage. This causes a significant difference between the work done by a hydraulic press during a laboratory uniaxial compression experiment and the elastic strain energy stored in the specimen during the experiment, so the evaluation result of the burst energy index would be too high. The determination of bursting liability is a comprehensive evaluation of the elastic strain energy accumulated in coal that is released when the specimen is damaged. The index proposed in this paper fully integrates the energy evolution of coal samples being damaged by loading, the amount of elastic strain energy released during the sample failure divided by the failure time is the energy release rate. The calculation method is simplified so that the uniaxial compressive strength and elastic modulus are included which makes the new index more universal and comprehensive. Theoretical analysis and physical compression experiments validate the reliability of the evaluation.

Beam quality improvement in an end-pumped Nd:YAG slab amplifier by the increase of the super-Gaussian order of laser diode beam profile

This work focuses on a new estimation to pave the way for an easier optical design of a slab amplifier according to optical path difference (OPD) distribution via laser diode (LD) as a pump source. In general, the output of LD consists of super-Gaussian beams with order 1 in the fast axis and order 3 in the slow axis. The thermal lens (TL) effect is the most important challenge in the optical design of the slab amplifier chain for transferring light from one single-module slab to the next. The formed TL in the slab volume is compensated via the zigzag path of the seed laser in the slab thickness direction. Aforementioned, to improve the output beam quality (BQ) of the slab amplifier, TL effect must be covered by using external optical elements in the slab width direction. In the present paper, the OPD spatial distribution of LD pumped Nd:YAG slab (0.6% Nd3+ dopant) is estimated by using math functions that can be matched. It follows both aspheric and super-Gaussian functions in the slab width direction. Our results show that the super-Gaussian estimation could portray a better understanding of OPD changes and create the conditions for optimizing the slab amplifier output BQ which relates to the super-Gaussian parameter of LD beam in the slow axis. Experimental measurement of TL-diopter in the slab thickness direction proves our simulation results.

Comparative Study of Structural Behaviour for Rolled and Castellated Steel Beams with Different Strengthening Techniques

Currently, the castellated steel beams are used widely because of their useful structural applications and serviceable performance due to their good significant properties such as light weight, facility in construction, materials economize and strength. The castellated steel beam fabricated from its origin solid beam (I-beam) by cutting its web in a zigzag path and then re-joined the two halve by welding so the height of the castellated beam expanded about 50%. The aim of this paper is to study the effect of castellation with and without strengthening on the structural behaviour of castellated beams and compare the results with the origin solid steel beam. Three castellated beams with deferent configuration in addition to solid beam subjected to two equal point loads at mid third of span with simple support condition were analysed numerically using finite element analysis by Abaqus software virgin (6.14.5) .The results show that the load carrying capacity values of castellated steel beams that represent (second, third& fourth) models were increased by (39.11,105.95&124.77) % respectively compared with origin solid beam due to increase beams stiffness after castellation and strengthening process, while mid-span deflection values at service load were decreased by (36.36,9.10&27.27) % respectively comparing with the origin solid steel beam due to increasing section dimensions and stiffness after castellation process and using strengthening technique respectively. Also it was seen that the maximum ultimate moment and ductility were observed in the fourth model that strengthened by high strength concrete and lacing reinforcement so they increased by 124.79% and 165.65% respectively as compare to reference beam, while the third model that strengthened by high strength concrete was stiffer than other beams.

Visually meaningful image encryption using data hiding and chaotic compressive sensing

A visually secure multiple image encryption using chaotic map and compressive sensing is proposed. The existing image encryption algorithms transform a secret image into a random noise like cipher image which can lead to cryptanalysis by an intruder. In the proposed method, compressive sampling is done using a chaos based, key controlled measurement matrix. An image dependent key generation scheme is used to generate the parameters of the chaotic map. The secret images are transformed into wavelet coefficients, and scrambled along a zigzag path, so that the high correlation among them can be reduced and thereby provide increased security level. The sparse coefficients are measured using the chaotic map-based measurement matrix, whose initial parameters are obtained from the keys generated. Then the reduced measurements are embedded into the sub-bands of the wavelet transformed cover image. Therefore, the proposed algorithm is highly sensitive to the secret images and can effectively withstand known-plaintext and chosen-plaintext attacks. Additionally, the cipher image and the secret images are of same size and do not require additional transmission bandwidth and storage space.

Efficiency of germination inhibition after treatment of an air-water plasma jet: the effect of pulsating DC power

Pulsating direct current (PDC) power consisting of AC power and a diode connected in series was adopted to produce an atmospheric pressure plasma jet. The PDC power is a high-voltage half-wave rectified AC power. During the experiments, the gas temperature of the PDC plasma was in the range of 45.0 °C–59.7 °C. P. digitatum spores spread on a glass slide were directly treated by the plasma plume and a germination inhibition rate was adopted to evaluate the inhibition efficiency. In order to ensure that the plasma plume touched as many spores as possible, the glass slide was fixed on a programmable 3D mobile platform and moved in a zigzag path during the treatment process. The maximum germination inhibition rate reaches 0.701 by the PDC plasma jet at a discharge current of −7.5 mA and water content of 9.58 mg l−1.

On the Relationship Between Dislocation Creep Strength and Microstructure of a Solid-Solution-Strengthened Ni-Base Superalloy

It is shown that the dislocation creep strength of a solid-solution-strengthened Ni-base superalloy is critically dependent upon the cooling rate from the annealing temperature. This behavior is correlated with the effect of cooling rate on the morphology of M23C6-type carbide which precipitates at grain boundaries during cooling. Experiment shows that the creep strength is enhanced by rapid cooling which results in discrete carbide particles with irregular shape following a zigzag path along the grain boundaries. However, the creep strength is degraded as the morphology is changed into lamellar type by a discontinuous grain boundary reaction which occurs during slower cooling rates. Due to the transition from the discrete particle into the lamellar morphology, plastic deformation becomes more localized alongside the grain boundaries which accelerates the creep rate leading to premature intergranular failure. On the other hand, it is also shown that the stacking fault energy of the alloy increases with temperature which can allow dislocations to rearrange themselves into subgrain structure with relative ease during steady-state creep.

GPU-accelerated scanning path optimization in particle cancer therapy

When using the beam scanning method for particle beam therapy, the target volume is divided into many iso-energy slices and is irradiated slice by slice. Each slice may comprise thousands of discrete scanning beam positions. An optimized scanning path can decrease the transit dose and may bypass important organs. The minimization of the scanning path length can be considered as a variation of the traveling salesman problem; the simulated annealing algorithm is adopted to solve this problem. The initial scanning path is assumed as a simple zigzag path; subsequently, random searches for accepted new paths are performed through cost evaluation and criteria-based judging. To reduce the optimization time of a given slice, random searches are parallelized by employing thousands of threads. The simultaneous optimization of multiple slices is realized by using many thread blocks of general-purpose computing on graphics processing units hardware. Running on a computer with an Intel i7-4790 CPU and NVIDIA K2200 GPU, our new method required only 1.3 s to obtain optimized scanning paths with a total of 40 slices in typically studied cases. The procedure and optimization results of this new method are presented in this work.