Shape Of String Research Articles

Thermal characteristics of expandable graphite as a burning rate enhancer in hybrid propulsion

AbstractHybrid propulsion, consisting of solid fuel and liquid oxidizer, exhibits major advantage regarding safety, development costs, energetic performance, and controllability. Hence, it has been considered for space and other propulsion programs. One of the characteristic features of hybrid motors, that may be of major disadvantage, is their relatively low thrust due to the characteristic low regression rate of the typical polymeric solid fuels. This research group had revealed that a small fraction of an expandable graphite (EG) additive could double the burning rate and thrust of hybrid motors. EG is an intercalated form of graphite, elongating and swelling, getting a worm‐like string shape at elevated temperatures. In an earlier work it was hypothesized that enhanced heat transfer via conduction through the EG strings protruding from the hot surface, is a significant parameter increasing the burning rate. In the present investigation, thermal analysis revealed that the ignition temperature of polyester fuel containing 5 wt% of EG, is substantially lower than that of the pure polymer, which may promote higher burning rate as well. High‐speed photography of the surface of EG‐containing solid fuels as well as that of individual EG particles during controlled heating, demonstrated the dynamic behavior resulting in the formation of EG strings longer by an order of magnitude compared to the original particles. The different phenomena were related to the observation of enhanced burning rate.

Quantum current dissipation in superconducting strings and vortons

In this work, the current stability is discussed for cosmic strings with the bosonic superconductivity. A non-vanishing curvature of string generally induce the quantum instability of the current-carrying particle. Its decay rates are explored for various types of model parameters, curved string shapes, and decay processes. As a cosmological application, the stability is examined for superconducting strings in the string network and also for cosmic vortons by evaluating their cosmological evolution. The zero mode and hence the vorton cannot be stable in various cases, e.g., with a hierarchy between the current-carrying particle mass off the string and the string tension or with sizable couplings of the current-carrying particle to light species such as the Standard Model particles.

Features of gravitational interaction as the basis of “Dark Energy” in the gas of null strings

In this work, the influence of the shape of the null strings that form the gas on the gravitational properties and evolution of the null string gas was investigated. An interesting result of the study is that the test null string, being in the interaction zone, can only have a shape that exactly repeats the shape of the source string. As a result, null strings having different spatial forms can be located in the gas only outside the zone of interaction with each other. The “size” (width) of the zone of interaction of each null string in the gas is determined by the value of its initial momenta, and for some critical values it can occupy the entire space. The size (width) and “impenetrability” of the interaction zones for null strings having different spatial shapes can be a physical source of “strong” gravitational repulsion in the gas of null strings. In turn, the “strong” gravitational repulsion between null strings with different spatial shapes can be a source of a long-term accelerated expansion of such a gas (a source of “dark energy”).

Wireless Communication for Drilling Using Acoustic Wave Based on MIMO-OFDM

Underground data transmission methods are divided into wired and wireless. Wired transmission includes traditional cable and optical fiber. Wireless transmission includes pressure wave and electromagnetic wave. The limitation of the down-hole data upload rate has become the bottleneck. The wireless transmission system of an acoustic wave using a drilling fluid channel is studied. Drilling fluid channel is a multi-path channel with frequency selective fading characteristics. In the process of drilling, the shape of drill string is spatial spiral bending. This paper provides an exhaustive research in OFDM-MIMO for drilling acoustic telemetry system. The characteristics of drilling fluid channel are discussed. The performances of multiple input multiple output (MIMO), multiple input single output (MISO) and single input single output (SISO) wireless acoustic transmission systems are compared. Acoustic waves transmitted along the drilling fluid channel can realize underground wireless communication with a high transmission rate and a low bit error rate.

How macrostructures enhance droplet coalescence jumping: A mechanism study

Macrostructures exhibit excellent performance in coalescence-induced droplet jumping enhancement. Previous velocity prediction models were mainly established for flat plain surface, which usually set up the balance relationship between excess surface energy, kinetic energy and dissipation. But these models are no longer appropriate in macrostructure cases due to great variation of oscillational kinetic energy and gravitational potential energy caused by textures. In this work, coalescence-induced droplet jumping on macrostructures was investigated numerically on flat, sidewall, string, ridge and egg shape substrates. An energy conversion model based on energy efficiency rather than energy balance was established for departure velocity by proposing three sub-efficiencies to evaluate jumping enhancement. In this model, oscillational kinetic energy was distinguished from dissipation, gravitational potential energy induced by macrostructures were considered, and the real droplet morphology were used to calculate surface energy. By dividing the whole droplet jumping process into merge and contact stage, the influence of macrostructures on duration of each stage was closely connected to the macrostructure effects on dissipation and kinetic energy conversion. Pressure and velocity distributions near the macrostructure were also discussed to further explore the mechanism for droplet jumping enhancement. Further, the significant increase of initial surface energy for egg case points out a possible new approach to enhance jumping velocity. This model helps us understand the determinants of jumping enhancement with macrostructures and it also applies to flat plain.

Helmholtz vibrations in bowed strings.

For almost 160 years, it has been known that Helmholtz oscillations, unique to vibrating strings in bowed instruments (violin, cello, etc.), have two distinct regimes: "slip" and "stick." During the slip regime, the force at the bow-string interaction is attributed to friction between the sliding bow hair and the vibrating string, with a friction coefficient that decreases with increasing relative velocity. Yet the hair-string interaction during the stick regime is less understood. We propose that the interaction force during the stick regime is proportional to the product of the longitudinal acoustic impedance of the bow hair to the relative bow-string velocity. We validate this hypothesis by solving the string's differential equation of motion, including an enhanced formulation to avoid parasitic high-frequency oscillations. This physical model enables us to analyze, in real time, the characteristics of the Helmholtz oscillations, including the string shape, excitation of harmonics, Schelleng ripples, and string energy, showing that the bowed string gains energy during the stick regime and loses energy during the slip regime.

Bistable kinetic shades actuated with shape memory alloys: prototype development and daylight performance evaluation

Kinetic façade systems can adjust to different environmental conditions, thereby improving daylight performance in buildings. Bistable laminates present large deflections and can maintain their state without continuous energy supply, appealing features for kinetic applications. Nevertheless, these engineered materials have yet to be studied for their potential for improving daylight performance in buildings. This study sought to test the daylight performance of a kinetic bistable screen using a case study approach that combines experimental testing and building performance simulation. This paper details research to design and fabricate the shading screen and the experimental testing of the screens’ daylight performance. First, we focus on the design of a holder mechanism, which relies on a string system and shape memory alloys that actuate bistable flaps. Second, we experimentally collect data on daylight performance and compare it to simulation data to validate a daylight model. Results show that the designed bistable screen can increase the hours of adequate daylight throughout the year versus baseline cases, particularly when oriented south and east. The study suggests that bistable kinetic screens can help improve daylight performance in buildings.

Direct visualization of the three-dimensional shape of skyrmion strings in a noncentrosymmetric magnet.

Magnetic skyrmions are topologically stable swirling spin textures that appear as particle-like objects in two-dimensional (2D) systems. Here, utilizing scalar magnetic X-ray tomography under applied magnetic fields, we report the direct visualization of the three-dimensional (3D) shape of individual skyrmion strings in the room-temperature skyrmion-hosting non-centrosymmetric compound Mn1.4Pt0.9Pd0.1Sn. Through the tomographic reconstruction of the 3D distribution of the [001] magnetization component on the basis of transmission images taken at various angles, we identify a skyrmion string running through the entire thickness of the sample, as well as various defect structures, such as the interrupted and Y-shaped strings. The observed point defect may represent the Bloch point serving as an emergent magnetic monopole, as proposed theoretically. Our tomographic approach with a tunable magnetic field paves the way for direct visualization of the structural dynamics of individual skyrmion strings in 3D space, which will contribute to a better understanding of the creation, annihilation and transfer of these topological objects.

Safety analysis of deep-sea mining pipeline deployment operations considering internal solitary waves

Internal solitary waves bring great challenges to the safety of deep-sea mining pipeline deployment operations. The three-dimensional finite element model of deep-sea mining pipeline system under the action of internal solitary waves is established and solved. The shape, tension, stress, upper rotation, offset, and transient response of the pipe string during the deployment process of the deep-sea mining system under the internal solitary wave environment are analysed, and dangerous stages and risk factors are obtained. The envelopes of deployment operations under different internal solitary waves are calculated, and the technical measures to enlarge the operation envelope are discussed. The results show that the upper rotation and offset at moon pool position are more easily affected by internal wave energy relative to stress and tension, and they are the main factors affecting the safety of operation. The stage that the mining vehicle passes through the high-velocity zone of internal solitary waves is the high-risk stage. The operation envelope is the smallest when the IW-OC direction angle is 0°, and is the largest when the angle is 180°. Strengthening the upper restraint has limited effect on improving the operation envelope, in contrast, turning on the propellers of mining vehicle to resist the internal wave when necessary can effectively expand the operation envelope.

String electrospinning based on the standing wave vibration

Preparation of high-quality nanofibers with low applied voltage remains a challenge for needleless electrospinning. In this work, we developed a novel electrospinning technique based on the standing wave vibration of a string. The effects of the process parameters and string parameters on nanofiber diameter and productivity were investigated. The results indicated that standing wave electrospinning is competitive in terms of fiber diameter and productivity when compared with single conventional needle electrospinning. Moreover, the threshold voltage of standing wave electrospinning (18 kV) was approximately 30% lower than most of the current needleless electrospinning techniques (30 kV). The finest nanofiber with a diameter of 173 ± 48 nm was prepared at an applied voltage of 28 kV, a spinning distance of 10 cm, and a standing wave number of 3. The fiber diameter and productivity were significantly influenced by the string diameter and shape instead of the electrical conductivity of the string. The results demonstrated the considerable potential of standing wave electrospinning for fine nanofiber preparation under a low applied voltage.

Shape and dynamics of nonrelativistic vortex strings in parity-breaking media

The shape and dynamics of the nonrelativistic gauge vortex string in the parity-broken media is considered, upon reducing the problem to finding the extremum of the Abelian Higgs model effective action with the fixed B-type helicity of the gauge field. It is shown that in contrast with the case of the fixed A-type helicity, the static solution of the Ginzburg-Landau energy functional in the London limit is the helix with the specific relation between the curvature and torsion of the vortex line depending on the strength of the space parity violating contribution of the Lifshitz invariant. A nonlinear dynamical equation is linearized in case of small oscillations around the helical contour, and the polarization and dispersion law of the propagated waves are obtained.

Dynamic Analysis of Three Bar Tensegrity Structure under Compressive Load for Robotic Application

Tensegrity structures which are comprised of bars and strings are very lightweight structures and they have the capability to deform and remain stable. For these properties they have been utilized in various fields of engineering for various purposes. One of the potential application of tensegrities is in the area of robotics. Three bar tensegrity is a basic unit structure, the dynamics of which can be utilized for tensegrity based robots. Due to its similar geometrical shape and easy control of strings, and by the application of inward compressive load, the movement of whole robot can be controlled. In this paper, the dynamics of three bar tensegrity structure has been studied under compressive load. The mathematical model for the structure has been built; and node matrix and connectivity matrix have been defined to describe the structure. The simulation has been performed on ADAMS software to analyze the movements of bar and deformation in strings under the effect of compressive load. All the strings have been grouped according to the similar deformation experienced by them. In addition to that, compression and twisting of top layer of the structure has been investigated. The obtained results provide the base for the construction of extremely lightweight robotic structure.

Dynamic Analysis of Three Bar Tensegrity Structure under Compressive Load for Robotic Application

Tensegrity structures which are comprised of bars and strings are very lightweight structures and they have the capability to deform and remain stable. For these properties they have been utilized in various fields of engineering for various purposes. One of the potential application of tensegrities is in the area of robotics. Three bar tensegrity is a basic unit structure, the dynamics of which can be utilized for tensegrity based robots. Due to its similar geometrical shape and easy control of strings, and by the application of inward compressive load, the movement of whole robot can be controlled. In this paper, the dynamics of three bar tensegrity structure has been studied under compressive load. The mathematical model for the structure has been built; and node matrix and connectivity matrix have been defined to describe the structure. The simulation has been performed on ADAMS software to analyze the movements of bar and deformation in strings under the effect of compressive load. All the strings have been grouped according to the similar deformation experienced by them. In addition to that, compression and twisting of top layer of the structure has been investigated. The obtained results provide the base for the construction of extremely lightweight robotic structure.

Dynamic Analysis of Three Bar Tensegrity Structure under Compressive Load for Robotic Application

Tensegrity structures which are comprised of bars and strings are very lightweight structures and they have the capability to deform and remain stable. For these properties they have been utilized in various fields of engineering for various purposes. One of the potential application of tensegrities is in the area of robotics. Three bar tensegrity is a basic unit structure, the dynamics of which can be utilized for tensegrity based robots. Due to its similar geometrical shape and easy control of strings, and by the application of inward compressive load, the movement of whole robot can be controlled. In this paper, the dynamics of three bar tensegrity structure has been studied under compressive load. The mathematical model for the structure has been built; and node matrix and connectivity matrix have been defined to describe the structure. The simulation has been performed on ADAMS software to analyze the movements of bar and deformation in strings under the effect of compressive load. All the strings have been grouped according to the similar deformation experienced by them. In addition to that, compression and twisting of top layer of the structure has been investigated. The obtained results provide the base for the construction of extremely lightweight robotic structure Keywords- Three bar tensegrity, Dynamics, Compression, Robotic structure, ADAMS

Dynamic manipulation of unknown string by robot arm: realizing momentary string shapes

We propose a method to realize the dynamic manipulation of a string with unknown characteristics via a high-speed robot arm. We use a mass-spring-damper model for the string and repeat three steps: motion generation, real manipulation, and parameter estimation. Robot motion is given by the joint angular velocities expressed by the Bezier curves. Their control points are randomly positioned to generate various robot motion for dynamic string manipulation. The generated motion is performed by a wire-driven robot arm and, real string movement is captured by the camera. These time-series images are used for the parameter estimation of string. The best parameter set is determined via comparison between real and simulated string movement after changing parameter randomly and logarithmically. This parameter set is not unique, but it simulates the actual string movement well. Since the estimated string parameter is used for the robot motion generation after repeating the above 3 steps, the motion generation reflects string property and motion objective can success without special tests in advance. This is an advantage of our method because it is difficult to know all of string property with very complicated non-linearity beforehand. We focus on realizing the momentary string shape in 2 dimensions in this paper. We confirmed the effectiveness of our proposed method by realizing five momentary shapes and 3 kinds of string properties. We also discussed the reproducibility and compatibility of estimated parameters and motion generation.

Moment invariants for cancer classification based on electron–ion interaction pseudo potentials (EIIP)

Cancer is considered one of the most dangerous diseases leading to imminent death during recent decades. It spreads quickly at a frightening pace to all parts of the body and early detection of such diseases may help reduce the risks. Many methods have been used to classify and predict the outcome of cancer, such as image processing techniques, artificial intelligence, and nanotechnology. Out of these methods, artificial intelligence techniques have played an essential role and have provided satisfying results from different investigations in various fields. Considering that cancer is a genetic disease, electron–ion interaction pseudo potential can be used to convert DNA sequences from string shape into number values so that genomic signal processing can be applied for the feature extraction step. In this paper, 51 healthy and 51 cancer genes from multiple cells obtained from the National Center for Biotechnology Information Genbank were used for analysis. Then, 7 invariant moments were extracted into 2 types of learning machine methods: supervised and unsupervised learning. Finally, their results were compared using Receiver Operating Characteristic parameters. From these results, the best accuracy was obtained from the trainable cascade-forward backpropagation network. The calculated parameters were 0.3333, 0.3158, 0.6842, 0.6667, and 67.5% for the Kohonen network, 0.1053, 0.1429, 0.8571, 0.8947, and 87.5% for the feed-forward network, and 0.0000, 0.0909, 0.9091, 1.0000, and 95% for the cascade-forward network for FPR, FNR, TPR, TNR, and accuracy respectively.

Shape and electric performance improvement of an insulator string using particles swarm algorithm

In this study, a particle swarm optimisation (PSO) algorithm coupled with finite-element method (FEM) is implemented to improve the performance of a cap-and-pin insulator by reducing the value of maximum electric field strength. Two goals are set in this work: (i) optimisation of the tangential electric field distribution and magnitude (which is taken as the objectif function to be minimised) to reduce the risk of flashover due to surface pollution, and (ii) reduction of the creepage distance (by adopting adequate constraints) leading to a reduction of the surface area and consequently a decrease in the insulator weight. The investigation is divided into two parts; first, one-unit insulator is optimised with which a chain is constructed, and its performance compared with the reference insulator string. The second part considers a whole chain of four-unit insulator whose performance is optimised and compared to that of a reference insulator string. The main finding of this work indicates that, if an insulator string is constructed using an optimised cap-and-pin unit, the performance of the so-formed string is also optimised. The optimisation of a complete string leads to practically the same performance as that of a string obtained by assembling optimised insulator units.

Enhanced visible light photocatalytic activity of CdS through controllable self-assembly compositing with ZIF-67

Enhanced light absorption, improved separation of photoelectrons and holes, and controllable electron transfer paths are important ways to improve photocatalyst performance. In this work, a convenient but more efficient method is adopted to prepare composite photocatalysts integrating narrow gap semiconductors and zeolitic imidazolate frameworks (ZIFs). We chose ZIF-67, a typical ZIF, as the model and integrate it with CdS to self-assemble into highly crystalline ZIF-67@CdS composites. Extensive characterization methods (e.g., XRD, FE-SEM, UV–vis DRS, Raman, XPS, HRTEM, TEM, M–S, EIS and FT-IR) were applied to understand the correlations between performance and interface structure and morphology of the composite catalysts. Results demonstrate that the performances of the composite catalysts were greatly improved. ZIF2@CdS100 with optimized particle size (200 nm), limited shell thickness (less than 100 nm) and the shape of sugar gourd strings with Z-scheme interface structures was the best. Its H2 evolution rate and degradation rate constant of methylene blue (MB) under visible light irradiation were up to 6.7 and 3.1 times over those of bare CdS nanorods, respectively. Possible mechanisms of structure-morphology-performance were proposed. Optimizing the size and shape of composites can be used to regulate the morphology and interface structures of the composite catalysts to enhance their visible light photocatalytic activities.

Solution of Einstein’s Equations for a Closed Null String with Axial Symmetry that Is Radially Increasing Its Size

A solution to the Einstein equations for a closed null string with axial symmetry that is radially increases its size is found. The possibility of choosing the ideal gas of null strings as a dominant source of gravity is confirmed in the study of the null string inflation mechanism in Friedmann–Robertson–Walker spaces. The absence of a limit transition between the solution that is found and the solution for a closed circular null string that is radially changing its size is shown. This indicates the stability of the configuration of a closed circular null string during its motion in an external gravitational field. It is noted that part of the characteristics of the null string gas, such as the ability to form a domain structure and existence of stable polarized states (multi-string systems), are independent of the shape of null string, but the dynamics of the test null string in a field of such multi-string system has singularities.

Methods for computation of flow-driven string dynamics in a pump and residence time

We present methods for computation of flow-driven string dynamics in a pump and related residence time. The string dynamics computations help us understand how the strings carried by a fluid interact with the pump surfaces, including the blades, and get stuck on or around those surfaces. The residence time computations help us to have a simplified but quick understanding of the string behavior. The core computational method is the Space–Time Variational Multiscale (ST-VMS) method, and the other key methods are the ST Isogeometric Analysis (ST-IGA), ST Slip Interface (ST-SI) method, ST/NURBS Mesh Update Method (STNMUM), a general-purpose NURBS mesh generation method for complex geometries, and a one-way-dependence model for the string dynamics. The ST-IGA with NURBS basis functions in space is used in both fluid mechanics and string structural dynamics. The ST framework provides higher-order accuracy. The VMS feature of the ST-VMS addresses the computational challenges associated with the turbulent nature of the unsteady flow, and the moving-mesh feature of the ST framework enables high-resolution computation near the rotor surface. The ST-SI enables moving-mesh computation of the spinning rotor. The mesh covering the rotor spins with it, and the SI between the spinning mesh and the rest of the mesh accurately connects the two sides of the solution. The ST-IGA enables more accurate representation of the pump geometry and increased accuracy in the flow solution. The IGA discretization also enables increased accuracy in the structural dynamics solution, as well as smoothness in the string shape and fluid dynamics forces computed on the string. The STNMUM enables exact representation of the mesh rotation. The general-purpose NURBS mesh generation method makes it easier to deal with the complex geometry we have here. With the one-way-dependence model, we compute the influence of the flow on the string dynamics, while avoiding the formidable task of computing the influence of the string on the flow, which we expect to be small.