Characteristic Diagrams Research Articles

Periodic orbits of multiplicity higher than one in an N-body barred galaxy potential

Aims. Periodic orbits (POs) have been exhaustively studied. On the contrary, to our knowledge, no complete and systematic study of higher-multiplicity (ℳ) POs, that is, orbits that close after more than one revolution in phase space, exists. Here, we fill this gap and also extend the standard tools used for studies of the x1 POs to studies of higher multiplicity POs. Methods. We adopted a multi-aspect approach, using surfaces of section, stability diagrams, characteristic diagrams, studies of the shapes of individual orbits, and other properties of the POs. We modified and extended the standard tools used for ℳ = 1, to ℳ > 1 cases, allowing them to use the snapshot information more fully. Our potential is more realistic than those of most previous studies, as it is obtained directly from a snapshot of a fully self-consistent, high-resolution numerical simulation. Results. We find five main pairs of PO families with ℳ = 2. Two of these bifurcate from the x1 family and are direct rotators, and one bifurcates from the x4 family and rotates retrograde. We suggest that the remaining families do not bifurcate, but form parts of bubbles. The POs of the x1 family have four-fold symmetry, while all the ℳ = 2 POs have only two-fold symmetry, with respect to either the x or the y axis. Furthermore, two orbits of the same Jacobi constant and from families of the same PO pair are mirror images of each other. Thus, by considering them together, it is possible to achieve four-fold symmetry. All results obtained here will be used in a following paper to study the effect of including ℳ orbits in the disc. We also show that a given family can include orbits of more than one multiplicity.

Frequency domain analysis of density wave oscillations for two-phase flow in a vertical tube

In order to investigate the boundary characteristics of density wave oscillations in nuclear reactor steam generators and boiler water-cooled wall tubes, a frequency domain method numerical calculation model applicable to different geometrical structures and operating parameters was developed. In order to make the results of the model more accurate, the state of the fluid at the outlet of the heated pipe and the time delay were fully considered on the basis of the traditional model. Depending on the physical properties of the fluid at the outlet of the heated pipe, the model calculation area was divided into single-phase, two-phase and superheated zones. Small-perturbation linearization and Laplace transform were performed on the conservation equations in the three regions. The Nyquist stability criterion was used in matlab software to judge the stability of the flow, and by varying the working parameters the flow instability boundary can be calculated. For a more in-depth study of density wave oscillations in heated pipes, the unstable boundary characteristics were analysed computationally for different influences such as pressure, mass flow rate, inlet subcooling degree and pipe geometry on the basis of model validation. In addition, the Nyquist function was used in Matlab to plot the Nyquist curve for different influencing factors and to analyse the stability margins for specific operating conditions. The unstable boundary characteristic diagram was obtained when the pressure was 5–10 MPa and the mass flux was 300–1300 kg·m−2·s−1. The calculated data was collated and mass flow rate and heat load boundary diagrams were plotted, which could visualise the boundary characteristics of the density wave oscillations under different operating conditions. In order to make the calculation results more applicable, Nsub and Npch were used to construct the dimensionless unstable boundary characteristic diagram. Results showed that the influence of inlet subcooling degree on flow stability is non-monotonic. In addition, the effects of factors such as pressure, mass flow rate and inlet throttling coefficient are monotonic.

ANALYSIS OF THE METHODS FOR BENDING SMALL-SIZED DISKS ON A RING SUPPORT

A number of methods for testing bending of thin discs on an annular support designed to determine the tensile strength of brittle materials, are considered. The methods differ in the type of a loading indenter (with flat, spherical, or toroidal tips), support devices, and calculation equations for determination of the breaking stress. The results of testing samples on an annular support made of two model materials which differ in the degree of brittleness, i.e., cast iron and graphite, are presented. It is shown that the calculated strength of the tested materials depends on the character of the sample destruction and on the type of bending diagram. Cast iron samples were destructed under a significant plastic deformation (characteristic bending diagram passed through the maximum), and the tensile strength of the samples corresponded to the compressive strength of the material being several times higher than the tensile strength of the material. Graphite samples underwent brittle fracture (within the linear section of the bending diagram), and the calculated strength value was comparable to the tensile strength of the material. A conclusion is made that the use of the test method of thin disk samples on an annular support for determination of the tensile strength of the material is substantiated only in the case of absolutely brittle fracture of samples with a bending diagram similar to the fracture diagram of graphite samples. Disk samples made of aluminum oxide obtained by electro-pulse sintering were tested using two methods (with flat and spherical tips). In both cases, the bending diagram of aluminum oxide samples was similar to that of graphite samples, i.e., their destruction occurred at the initial linear section of the diagram and was absolutely brittle. The results of comparative testing of the samples made of aluminum oxide, taking into account the results of testing samples made of model materials (cast iron and graphite), showed that tests on the annular support of disks using a flat-tipped indenter are the most grounded. The samples should be made of brittle materials having a linear bending diagram up to the sample destruction.

Parameter study on characteristic pulse diagram of polycystic ovary syndrome based on logistic regression analysis

This study aimed to explore the parameters of the independent predictive characteristic pulse diagram of polycystic ovary syndrome (PCOS) by analysing the pulse characteristics between healthy women and the PCOS group. A total of 278 women were recruited for this study. Pulse wave parameters were collected by the pulse spectrum analyser. The single-factor analysis of the pulse diagram parameters was used to identify significant indicators, and the logistic regression analysis was carried out on the above indicators with statistical differences to obtain independent predictors. According to the single-factor and multi-factor analyses, h1, h5, h3/h1, t, t1 and t5 were independent predictors of PCOS diagnosis. The results showed that PCOS patients had a faster heart rate, decreased left ventricular systolic function and decreased aortic compliance compared to healthy individuals. These findings suggested that the characteristic pulse parameters screened out are valuable for the diagnosis of PCOS. IMPACT STATEMENT What is already known on this subject? Polycystic ovary syndrome (PCOS) is a common gynecological reproductive endocrine and metabolic disease, which is significant for screening and early intervention in the disease. However, due to the lack of pulse’s diagnostic evidence of PCOS, there is still an unknown area in the research on the correlation between PCOS and pulse diagram parameters. What do the results of this study add? This study fills the gap between the research on PCOS and pulse wave. The study also shows that the pulse characteristic parameters h1, h5, h3/h1, t, t1, and t5 are independent predictors of PCOS, suggesting that the patients have a higher heart rate, lower ventricular systolic function, and aortic compliance than healthy individuals. What are the implications of these findings for clinical practice and/or further research? Prominent risk factors for pulse parameters associated with the occurrence of PCOS facilitate early screening and diagnosis of the disease. The objectification of pulse diagnosis helps to establish a health management model, which can be used for the accurate assessment and treatment of PCOS by traditional Chinese medicine (TCM). It provides a clinical reference for the study of pulse diagnosis objectification.

A Fault Identification Method of Mechanical Element Action Unit Based on CWT-2DCNN

Aiming at the problems of low recognition rate and human intervention in the traditional fault diagnosis of mechanical equipment, a fault identification method based on continuous wavelet transform (CWT) and two-dimensional convolutional neural network (2DCNN) is proposed. By collecting the vibration signals of four kinds of fault states and normal states of the worm rotation unit of the CNC machine tool, the data are preprocessed and identified. Firstly, the vibration signals of each fault state of the element action unit are CWT transformed into the corresponding two-dimensional time-frequency diagram; then, the 2DCNN fault identification model is established, and the time-frequency diagrams of various faults are input to the network as characteristic diagrams for training and testing. Through the adjustment of network parameters, the network performance is gradually optimized; finally, the hybrid domain attention module CBAM is added to further improve the network structure, and the recognition effect is compared with the initial 2DCNN. The results show that the CWT-2DCNN meta-action unit fault recognition model with an attention module can recognize the different states of meta-action units more effectively, and the fault recognition effect is better. By using this method, the different fault types of mechanical element action units can be accurately identified, which has a certain application in the field of mechanical fault identification and diagnosis.

A mem-element Wien-Bridge circuit with amplitude modulation and three kinds of offset boosting

In the field of information processing, peripherals are often required to modulate the signal in terms of amplitude and position. At present, amplitude and offset boosting control of chaotic signals are mainly achieved by introducing additional constants or functions, and few systems rely on their parameters. In this work, a Wien-Bridge circuit is designed based on a voltage-controlled memristor. In addition to implementing the boosting control by introducing additional constants, the system exhibits both linear and nonlinear offset boosting behavior and amplitude control by changing the system’s parameters. This facilitates the reduction of the number of external devices for signal modulation. Besides, the system also presents coexisting symmetric attractors and bistability. These dynamic characteristics are investigated using Lyapunov exponents, bifurcation diagram, attractor projection, frequency spectra, attraction basin, and chaotic characteristic diagram. Finally, the system is implemented using DSP, which provides the basis for the application of chaotic modulation.

Magnetoelastic primary resonance and bifurcation of an axially moving ferromagnetic plate under harmonic magnetic force

The magnetoelastic primary resonance and bifurcation of an axially moving ferromagnetic plate under harmonic magnetic force are investigated. In harmonic magnetic field, the ferromagnetic plate is subjected to harmonic magnetic force generated by magnetization. Based on the Hamilton principle, the nonlinear magnetoelastic transverse vibration equation of the plate under the combined action of mechanical load and harmonic magnetic force is derived. For simply supported boundary conditions, the discretized vibration differential equation is obtained by Galerkin method. The multi-scale method is used to solve the nonlinear primary resonance, and obtain the resonance characteristic equation under steady-state response. According to Lyapunov stability theory, the stability criterion of constant solutions is determined. Through numerical calculation, two-dimensional and three-dimensional characteristic diagrams of amplitude are plotted, and the parameter ranges corresponding to multivalued solution regions and stable solution regions are determined. Global bifurcation diagrams and maximum Lyapunov exponent spectrums are plotted for different control parameters, and the effects of control parameters on the dynamic response and stability of the system are analyzed. The results show that magnetic field strength, axial velocity and mechanical load have significant effects on the vibration characteristics of the system, and tiny variation of control parameters can lead to the dramatic change of system motion characteristics.

Simulating the magnetorotational instability on a moving mesh with the shearing box approximation

ABSTRACT The magnetorotational instability (MRI) is an important process in sufficiently ionized accretion discs, as it can create turbulence that acts as an effective viscosity, mediating angular momentum transport. Due to its local nature, it is often analysed in the shearing box approximation with Eulerian methods, which otherwise would suffer from large advection errors in global disc simulations. In this work, we report on an extensive study that applies the quasi-Lagrangian, moving-mesh code arepo, combined with the Dedner cleaning scheme to control deviations from $\nabla \cdot \boldsymbol B=0$, to the problem of magnetized flows in shearing boxes. We find that we can resolve the analytical linear growth rate of the MRI with mean background magnetic field well. In the zero net flux case, there is a threshold value for the strength of the divergence cleaning above which the turbulence eventually dies out, and in contrast to previous Eulerian simulations, the strength of the MRI does not decrease with increasing resolution. In boxes with larger vertical aspect ratio we find a mean-field dynamo, as well as an active shear current effect that can sustain MRI turbulence for at least 200 orbits. In stratified simulations, we obtain an active αω dynamo and the characteristic butterfly diagram. Our results compare well with previous results obtained with static grid codes such as athena. We thus conclude that arepo represents an attractive approach for global disc simulations due to its quasi-Lagrangian nature, and for shearing box simulations with large density variations due to its continuously adaptive resolution.

DEFORMATION-HARDENING FIBER COMPOSITES: DEFINITION, PRINCIPLES OF PREPARATION AND PROSPECTS OF APPLICATION

The article presents the results of a study of the effect of microfiber based on high - density polyethylene and polybenzoxazole on the axial stretching of fibrocomposites. The definition of the phenomenon of deformation hardening of a hydration hardening fibrocomposite is proposed. Characteristic deformation diagrams of various fiber - reinforced composites are obtained and analyzed. The ranges of values of deformation hardening and plastic deformation are determined, as well as the factors that determine these characteristics are stated. From a practical point of view the increase of the resistance of fibrocomposite while maintaining its integrity in conditions of high values of plastic deformations opens up the possibility of using such materials for repairing damaged superstructures and ceilings, durable (heat and bio - resistant) sealing of joints of precast reinforced concrete structures.

Developing a Clinical Decision Support System for Prediction Postoperative Coronary Artery Bypass Grafting Infection in Diabetic Patients.

Postoperative infection in Coronary Artery Bypass Graft (CABG) is one of the most common complications for diabetic patients, due to an increase in the hospitalization and cost. To address these issues, it is necessary to apply some solutions. The study aimed to the development of a Clinical Decision Support System (CDSS) for predicting the CABG postoperative infection in diabetic patients. This developmental study is conducted on a private hospital in Tehran in 2016. From 1061 CABG surgery medical records, we selected 210 cases randomly. After data gathering, we used statistical tests for selecting related features. Then an Artificial Neural Network (ANN), which was a one-layer perceptron network model and a supervised training algorithm with gradient descent, was constructed using MATLAB software. The software was then developed and tested using the receiver operating characteristic (ROC) diagram and the confusion matrix. Based on the correlation analysis, from 28 variables in the data, 20 variables had a significant relationship with infection after CABG (P<0.05). The results of the confusion matrix showed that the sensitivity of the system was 69%, and the specificity and the accuracy were 97% and 84%, respectively. The Receiver Operating Characteristic (ROC) diagram shows the appropriate performance of the CDSS. The use of CDSS can play an important role in predicting infection after CABG in patients with diabetes. The designed software can be used as a supporting tool for physicians to predict infections caused by CABG in diabetic patients as a susceptible group. However, other factors affecting infection must also be considered for accurate prediction.

Theoretical and experimental research on damping characteristics of CDC shock absorber

CDC (Continuous Damping Control) shock absorber is the typical representative of the stepless valve-controlled type, which has the advantages of low cost and stable performance. Based on the throttling characteristics of the CDC valve, the damping force mathematical model of the CDC shock absorber is established. Through simulation analysis, the indicator characteristics and speed characteristics of the CDC shock absorber under different input currents and speeds are obtained. A CDC shock absorber testbed is built to study damping characteristics, and the results are compared with the simulation results. The results show that the indicator diagram obtained by simulation and experiment is smooth without distortion, and the speed characteristic diagram is smooth without a large mutation point. The experimental values of damping force are slightly larger than the simulation values. The relative error between the simulation data and the experimental data is basically less than 10% and the model has high accuracy. When the input current is the same, the damping force increases with the increase of piston rod speed. When the speed of the piston rod is the same, the damping force of the rebound and compression stroke decreases with the increase of input current.

Design and Testing of a Multimode Capable Passive Battery Management System

A customized passive battery management system (BMS), which offers a selection of different operating configurations regarding the connection of external sources and loads, has been developed. The device supports balance, charge, de-balance, discharge and permanent storage battery processes. The control unit is run by its own written algorithm (code). Suggestions for potential hardware and software changes that can be made to expand the capabilities of the device are listed. The device is tested in five different operating configurations and the output data (battery-cell voltages and balancing currents) are plotted in characteristic diagrams. The output data is analyzed and the unique capabilities of the device are explained. The detailed PCB design, code, and output measurement data files are included within the paper.

Vibration characteristics of cracked compressor blades with different materials

Aiming at the influence of different material properties on the vibration characteristics of cracked gas turbine compressor blades, the vibration characteristics of cracked compressor blades with three different materials were studied by numerical calculation. The first order bending vibration of a cracked cantilever beam was simplified to a single degree of freedom system. The breathing crack stiffness model was introduced to change the elastic modulus and other parameters of the material. The fourth-order Runge-Kutta method and fast Fourier transform were used to obtain the cantilever beam vibration characteristic diagram, and the relationship between the material properties and the structural vibration was analyzed. The results show that the elastic modulus of the material is proportional to the stiffness, and the stiffness of the material affects the vibration displacement response of the cantilever beam, and the larger the stiffness is, the smaller the vibration displacement is.

An Earthquake-Clustering Model in North Aegean Area (Greece)

The investigation of short-term earthquake-clustering features is made feasible through the application of a purely stochastic Epidemic-Type Aftershock Sequence (ETAS) model. The learning period that is used for the estimation of the parameters is composed by earthquakes with M ≥ 2.6 that occurred between January 2008 and May 2017. The model predictability is retrospectively examined for the 12 June 2017 Lesvos earthquake (Mw6.4) and the subsequent events. The construction of time-dependent seismicity maps and comparison between the observed and expected earthquake number are performed in order to temporally and spatially test the evolution of the sequence, respectively. The generation of 127 target events with M ≥ 3.0 in the period June–July 2017, just before the main shock occurrence, is examined in a quantitative evaluation. The statistical criteria used for assessing the model performance are the Relative Operating Characteristic Diagram, the R-score, and the probability gain. Reliable forecasts are provided through the epidemic model testifying its superiority towards a time-invariant Poisson model.

Generalized State-Plane Analysis of Bidirectional CLLC Resonant Converter

The <i>CLLC</i> resonant converter is a promising candidate for high efficient, bidirectional power transfer applications, such as vehicle-to-grid on-board charger and hybrid vehicle dc&#x2013;dc converter. Nevertheless, the analysis of <i>CLLC</i> still remains challenging because of its complex multiresonant nature and several storage elements. In this article, a circuit analysis method based on change of variables is presented that maps the state-space equations into two decoupled sets of equations. The analyses are carried out in two state-plane coordinate systems, then the results are mapped onto the original region. The proposed method is then used to thoroughly analyze the <i>CLLC</i> resonant converter operating in the continuous conduction mode (CCM). The voltage and current stresses of components, zero voltage switching condition, output voltage gain, output characteristic diagram, and mode boundary of CCM&#x002F; discontinuous conduction mode are then obtained. The accuracy of the proposed approach is verified by the experiments on a 3 kW bidirectional <i>CLLC</i> resonant converter with GaN transistors as the primary and secondary side switches. The results confirm the accuracy of the proposed state-plane analysis of the <i>CLLC</i> resonant converter operating in either direction of power transferring.

Sensitivity analysis of the process parameters of laser cladding NiCrCoAlY

This research aims to explore the forming quality of Laser Cladding NiCrCoAlY. The small changes in process parameters on the geometric characteristics of cladding layer was investigated. Mathematical models were established based on the linear regression analysis, and the influence of process parameters on the geometric morphology was obtained through the sensitivity analysis. The results show that the mathematical models have remarkable fitting accuracy. The laser power is positively correlated with clad height, width, and dilution rate; while the scanning speed is negatively correlated with clad height and width but positively with dilution rate. The powder feeding voltage has a positive correlation with clad height and a negative with clad width and dilution rate. In addition, the clad height has the greatest negative sensitivity to scanning speed, while the clad width is most sensitive to laser power and nearly insensitive to powder feeding voltage, which indicates that the clad width cannot be controlled effectively by powder feeding voltage. The dilution rate is most sensitive to laser power. The findings of this research provide a characteristic diagram of sensitivity for the geometric characteristics of laser cladding NiCrCoAlY, and also provide a theoretical basis for the further effective control on the forming quality of cladding layer.

Improved design of experiments method for machine-learning-based modelling of gearbox efficiency in a test rig environment

Knowledge of the efficiency of the subsystems in the drive train is essential for development in drive technology. Experiments have confirmed that the efficiency gradient of gearboxes is particularly high in the partial load range. Conventional test planning does not adequately reflect the influence of the efficiency gradient in the partial load range. To adequately represent the partial load range, it must be recorded with a particularly high number of measuring points. Map ranges with a low gradient are recorded with a smaller number of measuring points. This paper describes a method for the design of experiments, not with but for neural networks, with regard to modelling the efficiency of a two-stage spur transmission. In order to determine the test data, an optimized design of experiments is carried out. The test planning is divided into preliminary tests and main tests. The measuring points are optimally distributed in the characteristic diagram for use in neural networks. The measurement data is generated with the planned test data on a road to rig vehicle test rig. Suitable methods are used to prepare the data for further processing. The modelling is done experimentally with the help of neural networks. The result is a function for the continuous description of the efficiency at each operating point. The procedure is compared with the conventional method and validated with statistical methods. It was proven that the optimised experimental design method for neural networks gives better results than the conventional approach.

Transmission of a detonation wave across an inert layer

The transmission of a detonation wave across a layer of inert gas is studied via one- and two-dimensional numerical simulations based on the reactive Euler equations. The resulting transient transmission process from the one-dimensional simulations is first explored in detail, and is analyzed via distance-time characteristic diagrams. The physics of this transient process is the same until the end of a quasi-steady period. Afterward, the energy release from the combustion may couple to the gas dynamics. Through this coupling, the pressure pulse accompanying the energy release can be rapidly amplified, and consequently, leads to detonation onset. If the inert layer is too thick, the detonation cannot be successfully re-initiated downstream. This inert-layer thickness beyond which a detonation fails to be re-initiated is determined as the critical thickness, δi,cr. The mechanisms underlying the scenarios with a successful and unsuccessful re-initiation are demonstrated in detail. A parametric study considering simplified and detailed chemical kinetics (i.e., a stoichiometric mixture of hydrogen and air at various initial pressure from 0.1−1atm) demonstrate that δi,cr normalized by the intrinsic ZND induction length, ΔI, asymptotically decreases with an increase of the effective activation energy, Ea. The one-dimensional simulations under-predict the experimental results [1, 2] of δi,cr/ΔI by at least one order of magnitude. In the two-dimensional scenarios, transverse-wave instabilities are present and allow the detonation wave to re-initiate in cases where re-initiation is unsuccessful in one dimension. The two-dimensional results of δi,cr are in a closer agreement with the experimental findings.

Determination of Boussinesq and Coriolis coefficients for pipelines operating with discharge connection along the path

Peculiarities of the diagrams of averaged fluid velocities in the cross-sections of pressure collecting perforated pipelines were determined on the basis of the experimental studies conducted by the authors.&#x0D; The most characteristic typical diagrams of averaged velocities in the pipelines cross-sections with their different design characteristics were given. A comparative analysis of the obtained diagrams with the diagrams of velocities that occur during uniform motion in pressure pipelines with solid walls was carried out. It is shown that the main difference between them occurs in the flow zones, which are located near the pipeline walls. It was explained by the connected liquid jets effect on the main flow. The degree of diagrams deformation was estimated by the value of the momentum coefficient α0 (Boussinesq coefficient) and the coefficient of kinetic energy α (Coriolis coefficient). It was determined that in the general case these coefficients will be variable in magnitude along the length of the studied pipes. Nevertheless, these coefficients are recommended to be constant in magnitude in engineering calculations. The limits of the structural characteristics of collecting perforated pipes for which this non-uniformity of the diagrams must be taken into account, and for which it can be neglected were determined on the basis of the analysis of the equation of fluid motion with a variable flow rate.

Perspectives on Clustering and Declustering of Earthquakes

Abstract Clustering is a fundamental feature of earthquakes that impacts basic and applied analyses of seismicity. Events included in the existing short-duration instrumental catalogs are concentrated strongly within a very small fraction of the space–time volume, which is highly amplified by activity associated with the largest recorded events. The earthquakes that are included in instrumental catalogs are unlikely to be fully representative of the long-term behavior of regional seismicity. We illustrate this and other aspects of space–time earthquake clustering, and propose a quantitative clustering measure based on the receiver operating characteristic diagram. The proposed approach allows eliminating effects of marginal space and time inhomogeneities related to the geometry of the fault network and regionwide changes in earthquake rates, and quantifying coupled space–time variations that include aftershocks, swarms, and other forms of clusters. The proposed measure is used to quantify and compare earthquake clustering in southern California, western United States, central and eastern United States, Alaska, Japan, and epidemic-type aftershock sequence model results. All examined cases show a high degree of coupled space–time clustering, with the marginal space clustering dominating the marginal time clustering. Declustering earthquake catalogs can help clarify long-term aspects of regional seismicity and increase the signal-to-noise ratio of effects that are subtler than the strong clustering signatures. We illustrate how the high coupled space–time clustering can be decreased or removed using a data-adaptive parsimonious nearest-neighbor declustering approach, and emphasize basic unresolved issues on the proper outcome and quality metrics of declustering. At present, declustering remains an exploratory tool, rather than a rigorous optimization problem, and selecting an appropriate declustering method should depend on the data and problem at hand.