Convergence Ratio Research Articles

Mitigation of deceleration-phase Rayleigh–Taylor instability growth in inertial confinement fusion implosions

Rayleigh–Taylor growth during shell deceleration is one of the main limiting factors for target performance in inertial confinement fusion implosions. Using analytical scaling laws and hydrodynamic simulations, we show that such amplification can be mitigated by reducing the initial mass density in the central target region. The perturbation growth reduction is caused by a smaller hot-spot convergence ratio during deceleration, increased density scale length, and enhanced ablation stabilization. The required central density reduction can be achieved using the dynamic shell formation concept.

Numerical investigation on flow and heat transfer of supercritical CO2 in variable cross-section tubes under precooler working conditions

The performance of the precooler in the supercritical CO2 (S-CO2) Brayton cycle may be greatly affected by the interactions between the structure and the thermophysical properties. Variable cross-section tubes, which can effectively enhance heat transfer and reduce pressure drop, can be adopted in the precooler. In this paper, the flow and heat transfer performance of S-CO2 in a circular tube and variable cross-section tubes with different unit length divergent ratio (DR) and convergent ratio (CR) is firstly investigated when the heat transfer area is kept constant. The results show that the converging tubes can effectively enhance the heat transfer compared with the circular tube, and a greater CR is more beneficial for heat transfer. The heat transfer coefficient (htotal) is increased by 84.77% at the maximum. The diverging tubes are found to have a strong advantage in reducing the pressure drop, and a larger DR is more helpful to reduce pressure drop, with a maximum decrease of 84.4%. The heat transfer mechanism is analyzed from the aspects of flow field distribution, thermophysical property changes and buoyancy effect. Furthermore, combined with the performance of different variable cross-section tubes, two new hybrid tubes are proposed based on the idea of partitioned heat transfer enhancement matching the thermophysical property changes under the constant heat transfer area condition. The comprehensive thermal–hydraulic performance of the two hybrid tubes is significantly improved compared with that of the converging tube. A 34.81% higher htotal and a 6.25% lower pressure drop can be obtained when using the hybrid tube A under high heat flux conditions. The hybrid tube B is found to enhance heat transfer by 54.98% and reduced pressure drop by 55.14% under low heat flux conditions. Finally, the flow and heat transfer characteristics of different types of tubes are also further studied under the constant inlet Reynolds number condition. This study can provide some guidance for the design and optimization of precoolers where the thermophysical properties of the working fluid are highly variable.

Effect of Combustor Outlet Geometry on Operating Characteristics of Disk-Shaped Rotating Detonation Engine

A disk-shaped rotating detonation engine with H2/air mixture was tested to identify the impact of combustor outlet geometry on the engine’s operating characteristics. Three combustor outlet diameters and five outlet lengths are employed in the experiments. Results show that with the increase of combustor convergent ratio, the propagation stability of the rotating detonation wave decreases, and the propagation velocity and pressure peak decrease slightly. When the convergent ratio increases to a certain value (1.70 in this study), a “platform zone” with a lower pressure value appears before the sharp rise of the dynamic pressure curve. The propagation mode varies with the increase of mass flow rate at different convergent ratios. As the mass flow rate increases, the wave head number in the combustor increases. But the change rule of propagation mode with mass flow rate is greatly affected by convergent ratio. Increasing the convergent ratio is conducive to the formation of multi-wave modes, and the critical mass flow rate for mode transition drops sharply. When the convergent ratio increases to 1.70, the unstable asymmetric dual-wave mode is obtained. With the increase in the convergent ratio, the engine’s operating range and operating stability decrease significantly. Finally, changing the combustor outlet length has little influence on the engine’s operating characteristics and detonation-wave parameters.

Demonstration of neutron-yield enhancement by laser preheating and magnetization of laser-driven cylindrical implosions

Magnetized liner inertial fusion (MagLIF) is a fusion concept that uses magnetized, preheated fuel to reduce the implosion velocities and convergence ratios required for ignition. A scaled, laser-driven experimental platform to study MagLIF has been demonstrated on the OMEGA laser system, providing comprehensive experimental data on MagLIF scaling, utilizing the higher shot rate on OMEGA compared to the Z machine. Using this platform, a broader experimental space for MagLIF has been studied. Presented in this article are experimental results that demonstrate that the combination of preheat and magnetization enhances the neutron yield by 470% compared to a reference implosion, significantly more than the yield enhancement by the field or preheat alone. These results are achieved while maintaining a relatively low convergence ratio (<20). The experiments were supported by one-, two-, and three-dimensional radiation-hydrodynamics simulations, all of which suggest that multiple sources of mix play different key roles depending on the scale of the MagLIF experiment.

The study of virtual source position with the geometric convergent ratio errors prevention management method of spot scanning beam in carbon ion therapy.

We developed a technique including preventing errors management method capable of dealing with the virtual source position delivered by different carbon ion energies from the pattern of spot scanning beam in this study. A homemade large-format complementary metal-oxide-semiconductor (CMOS) sensor and Gaf Chromic EBT3 films were used for the virtual source position measurement. The Gaf films were embedded in a self-designed rectangular plastic frame to tighten the films and set up on a treatment couch for irradiation in the air with the film perpendicular to the carbon ion beam at the nominal source-axis-distance (SAD) as well as upstream and downstream from the SAD. The horizontal carbon ion beam with five energies at a machine opening field size was carried out in this study. The virtual source position was determined mainly with a linear regression by back projecting the full width half maximum (FWHM) to zero at a distance upstream from the various source-film-distance and double checks additionally with a geometric convergent method to avoid any mistakes caused by manual measurement on FWHM. The virtual source position for higher carbon ion energy has an obvious longer distance from the SAD since the more carbon ion beam energy, the less spreading affected by the horizontal and vertical magnetism, therefore, the distance of virtual source positions is decreased from SAD with high to low energy. The method for investigating the virtual source position in the carbon ion beam in this study can also be used for electrons and the proton. We have developed a technique capable of dealing with the virtual source position with a geometric convergent method to avoid any mistakes in spot scanning carbon ion beam.

Los Alamos National Laboratory Double Shell Program Target Development

The Double Shell Program at Los Alamos National Laboratory is studying an alternative platform for achieving robust alpha-particle heating at the National Ignition Facility. Double shells benefit from having a low convergence ratio and lower predicted temperature for achieving volume ignition. The joint required to assemble a double shell has an imperfection in the outer shell that seeds instabilities that can greatly impact the inner capsule’s implosion at bang time. Different variations of the shape and placement of the joint were implemented with improvements in the quality of the machining leading to measurable improvements in yield. High-Z coatings on the outer joint mitigated the impact of the 1- to 2-μm gap sometimes found in double shell assemblies.

High-resolution volumetric imaging constrains compartmental models to explore synaptic integration and temporal processing by cochlear nucleus globular bushy cells.

Globular bushy cells (GBCs) of the cochlear nucleus play central roles in the temporal processing of sound. Despite investigation over many decades, fundamental questions remain about their dendrite structure, afferent innervation, and integration of synaptic inputs. Here, we use volume electron microscopy (EM) of the mouse cochlear nucleus to construct synaptic maps that precisely specify convergence ratios and synaptic weights for auditory nerve innervation and accurate surface areas of all postsynaptic compartments. Detailed biophysically based compartmental models can help develop hypotheses regarding how GBCs integrate inputs to yield their recorded responses to sound. We established a pipeline to export a precise reconstruction of auditory nerve axons and their endbulb terminals together with high-resolution dendrite, soma, and axon reconstructions into biophysically detailed compartmental models that could be activated by a standard cochlear transduction model. With these constraints, the models predict auditory nerve input profiles whereby all endbulbs onto a GBC are subthreshold (coincidence detection mode), or one or two inputs are suprathreshold (mixed mode). The models also predict the relative importance of dendrite geometry, soma size, and axon initial segment length in setting action potential threshold and generating heterogeneity in sound-evoked responses, and thereby propose mechanisms by which GBCs may homeostatically adjust their excitability. Volume EM also reveals new dendritic structures and dendrites that lack innervation. This framework defines a pathway from subcellular morphology to synaptic connectivity, and facilitates investigation into the roles of specific cellular features in sound encoding. We also clarify the need for new experimental measurements to provide missing cellular parameters, and predict responses to sound for further in vivo studies, thereby serving as a template for investigation of other neuron classes.

Призматическая коррекция остаточного или рецидивирующего косоглазия

Introduction. Recurrent strabismus is a common issue after operations because of heterotrophy. Many scientific works have examined clinical parameters that may predispose to relapse of esotropia after surgery, including poor sensory status, high ratio of accommodative convergence to accommodation, uncorrected farsightedness or combination of these factors. Purpose. To evaluate the effectiveness of prismatic correction of recurrent esotropia in patients after the first stage of surgical treatment. Material and methods. The study group included 24 patients. They were divided into two groups in depends on the postoperative functional treatment. 1st group consisted of 12 patients with partially accommodative esotropia aged 5 to 8 years (6,48 ± 1,12 years) with average hypermetropic refraction +3,10 ± 0,54 diopters. This group of patients was assigned prismatic correction after a relapse of esotropia. 2st group consisted of 12 patients with partially accommodative esotropia aged 5 to 8 years (6,22 ± 1,29 years) with average hypermetropic refraction +3,13 ± 0,61 diopters. This group of patients was assigned orthoptic treatment after a relapse of esotropia. Results. Prismatic correction contributed to recovery binocular vision at 75 % of patients with recurrent esotropia ≤ 20 PD, in the comparison group (orthoptic treatment) – at 50 %. Moreover, the number of patients with stereopsis in the group «EFP» after the treatment was higher than in the group «Synoptophore» (p < 0,05). Conclusion. Prismatic correction ensures optimal motor status while maintaining sufficient sensory balance in most patients with recurrent esotropia after performing recession rectus medialis in combination with median duplication m. rectus lateralis. Keywords: Recurrent strabismus, binocular vision, elastic Frensel prism

Real-Time Kinematically Synchronous Planning for Cooperative Manipulation of Multi-Arms Robot Using the Self-Organizing Competitive Neural Network.

This paper presents a real-time kinematically synchronous planning method for the collaborative manipulation of a multi-arms robot with physical coupling based on the self-organizing competitive neural network. This method defines the sub-bases for the configuration of multi-arms to obtain the Jacobian matrix of common degrees of freedom so that the sub-base motion converges along the direction for the total pose error of the end-effectors (EEs). Such a consideration ensures the uniformity of the EE motion before the error converges completely and contributes to the collaborative manipulation of multi-arms. An unsupervised competitive neural network model is raised to adaptively increase the convergence ratio of multi-arms via the online learning of the rules of the inner star. Then, combining with the defined sub-bases, the synchronous planning method is established to achieve the synchronous movement of multi-arms robot rapidly for collaborative manipulation. Theory analysis proves the stability of the multi-arms system via the Lyapunov theory. Various simulations and experiments demonstrate that the proposed kinematically synchronous planning method is feasible and applicable to different symmetric and asymmetric cooperative manipulation tasks for a multi-arms system.

Effect of sliding speed on the thermohydrodynamic performance of partially slip‐textured slider bearings

AbstractThe present study evaluates the combined use of micro‐textures and ‘wettability gradient’ on the thermohydrodynamic performance of inclined slider bearings. Mass conserving Elrod cavitation model with slip boundary condition has been used to investigate the dimensionless static performance parameters at different convergence ratios and sliding speeds. The most effective location of the wettability gradient and textures has been considered in the present work. It has been observed that with the increase in sliding speed, the load carrying capacity, friction force and volumetric inflow rate of the slip‐textured bearings were improved. The improvements were more pronounced at smaller convergence ratios. Moreover, the slip‐textured bearings exhibited significant improvement in the average pressure and temperature of the lubricant. However, at higher sliding speeds, a substantial increase in friction force and average lubricant temperature was noticed. The square textured slip bearing exhibited maximum improvements towards various performance parameters of the three considered texture shapes.

Observability analysis of cooperative orbit determination using inertial inter-spacecraft angle measurements

The cooperative orbit determination (OD) using inertial inter-spacecraft measurements is of great value for the constellation. Previous studies concluded that the cooperative OD system in the two-body dynamics is observable using the inertial angle measurement. This paper performs an observability analysis for the inertial angle-only cooperative OD system based on the observability matrix (OM), and finds that the previous conclusions do not hold for some special configurations. Eight special configurations are proposed, and for each configuration, the unobservable orbit elements are analytically revealed by analyzing the linear relationship among different columns of the OM. Moreover, a method of improving the observability of the two-spacecraft system is proposed by adding another spacecraft. An extended Kalman filter is employed to numerically illustrate the observability of the proposed special configurations and to show the relationship between the observability and the convergence ratio of estimations. Monte Carlo simulations show that the convergence ratios of the observable orbit elements and state combinations are higher than 97%, while convergence ratios of the unobservable states are lower than 70%. With one non-planar elliptic orbit added, all the elements of the three-spacecraft system are observable, and the estimated errors converge within 6 h. The results found in this paper can provide a reference for the design and management of the constellation.

Accelerated Arithmetic Optimization Algorithm by Cuckoo Search for Solving Engineering Design Problems

Several metaheuristic algorithms have been implemented to solve global optimization issues. Nevertheless, these approaches require more enhancement to strike a suitable harmony between exploration and exploitation. Consequently, this paper proposes improving the arithmetic optimization algorithm (AOA) to solve engineering optimization issues based on the cuckoo search algorithm called AOACS. The developed approach uses cuckoo search algorithm operators to improve the ability of the exploitation operations of AOA. AOACS enhances the convergence ratio of the presented technique to find the optimum solution. The performance of the AOACS is examined using 23 benchmark functions and CEC-2019 functions to show the ability of the proposed work to solve different numerical optimization problems. The proposed AOACS is evaluated using four engineering design problems: the welded beam, the three-bar truss, the stepped cantilever beam, and the speed reducer design. Finally, the results of the proposed approach are compared with state-of-the-art approaches to prove the performance of the proposed AOACS approach. The results illustrated an outperformance of AOACS compared to other methods of performance measurement.

IFRS ADOPTION AND KEY ACCOUNTING RATIOS: AN EVIDENCE FROM COLOMBO STOCK EXCHANGE

The purpose of this study is to investigate the impact of International Financial Reporting Standards (IFRS) adoption on key accounting ratios of firms listed in the Colombo Stock Exchange (CSE). The study also sought to test if the entity’s sector discriminates the impact that the IFRS adoption has on accounting ratios being evaluated. Descriptive statistics and non-parametric univariate analysis (Mann Whitney U test) were used to compare pre and post IFRS convergence ratios. The researchers tested eleven accounting ratios falling under profitability, liquidity, leverage, and market performance. We randomly sampled 40 firms listed in CSE, 20 each from the service and manufacturing sectors. The study period was ten years from 2007 through 2016, whereby the periods corresponding to pre-IFRS convergence were from 2007 through 2011, and post-IFRS convergence was captured from 2012 through 2016.. We showed that all profitability measures we tested were significantly impacted by IFRS adoption. We infer that the direct comparability of the profitability measures across pre and post-IFRS periods is no longer useful for decision making. In contrast, all liquidity ratios investigated were significantly indifferent between the pre and post-IFRS adoption. We have argued that liquidity measures have not changed considerably due to IFRS adoption and may thus still be comparable across pre and post-IFRS periods. Leverage and market ratios returned mixed results. We also document that the IFRS convergence’s impact on profitability and leverage ratios tends to be influenced by the sector in which firms operate, while its impact is not evidenced in relation to liquidity measures and market ratios. The limitation of this paper is that the effects of firm-specific variables and macro-economic factors on accounting ratios were not controlled. The results are useful for those interested in analyzing the long-term trends of accounting ratios. Our findings will also help the policymakers, standards setters, financial analysts, and future researchers about the behaviors of accounting ratios and quality financial reporting due to convergence to IFRS-based accounting regimes. This study is one of very few works on this topic in Sri Lanka, an IFRS jurisdiction with a developing economy.

Practical implications of the erroneous treatment of exposure time in the Eulerian hemolysis power law model.

Eulerian and Lagrangian power-law formulations are both widely used for computational fluid dynamics (CFD) to predict flow-induced hemolysis in blood-contacting medical devices. Both are based on the same empirical power-law correlation between hemolysis and the shear stress and exposure time. In the Lagrangian approach, blood damage is predicted by tracking both the stress and exposure time along a finite number of pathlines in the domain. In the Eulerian approach, a scalar transport equation is solved for a time-linearized damage index within the entire domain. Previous analytical work has demonstrated that there is a fundamental problem with the treatment of exposure time in the Eulerian model formulation such that the only condition under which the model correctly represents the true exposure time is in a flow field with no streamwise velocity variation. However, the practical implications of this limitation have yet to be thoroughly investigated. In this study, we demonstrate the inaccuracy of Eulerian hemolysis power-law model predictions due to the erroneous treatment of exposure time by systematically considering four benchmark test cases with increasing degrees of flow acceleration: Poiseuille flow through a straight tube, inclined Couette flow, and flow through a converging tube with two different convergence ratios. Compared with Lagrangian predictions, we show that, as flow acceleration becomes more pronounced, the resultant inaccuracy in the Eulerian predictions increases. For the inclined Couette flow case, there is a small degree of flow acceleration that yields a discrepancy in the range of 10% between Lagrangian and Eulerian predictions. For flows with a larger degree of acceleration, as occurs in the converging tube flow cases, the discrepancy is considerably larger (up to 257%). The inaccuracy of hemolysis predictions due to the erroneous treatment of exposure time in the Eulerian power-law model can be significant when there is streamwise velocity variation in the flow field. These results may partially explain the extremely large variability in CFD hemolysis predictions reported in the literature between Lagrangian and Eulerian models.

Observer‐based neural adaptive fixed‐time tracking control for multi‐input multi‐output nonlinear systems with actuator faults

SummaryThis study developed a new strategy for adaptive fixed‐time output feedback control of multi‐input multi‐output (MIMO) nonlinear systems involving unmeasurable external disturbances and actuator faults. Two actuator faults, loss of effectiveness and lock‐in‐place were simultaneously considered. Furthermore, a composite observer was used in MIMO systems to estimate unmeasurable states and external disturbances simultaneously, and radial basis function neural networks were employed to identify unknown internal nonlinearities. Additionally, the command‐filtered backstepping approach was applied to avoid tedious analytic calculations of the backstepping framework, and a compensation item was constructed to attenuate the filter error. A fault‐tolerant controller was developed to ensure that the overall states of the controlled system were practically fixed‐time bounded while the tracking error was regulated to the equilibrium region having a fixed‐time convergence ratio. Illustrative studies showed the validity and practicability of the proposed theory.

Estimation of NOx pollutants in a spark engine fueled by mixed methane and hydrogen using neural networks and genetic algorithm

Nowadays, due to stricter pollution standards, more attention has been focused on pollutants emitted from cars. As a very dangerous pollutant, NOx has always triggered the sensitivity of the related organizations. In the process of developing and designing the engine, estimating the amount of this pollutant is of great importance to reduce future expenses. Calculating the amount of this pollutant has usually been complicated and prone to error. In the present paper, neural networks have been used to find the coefficients of correcting NOx calculation. The Zeldovich method calculated the value of NOx with 20% error. By applying the progressive neural network and correcting the equation coefficient, this value decreased. The related model has been validated with other fuel equivalence ratios. The neural network model has fitted the experimental points with a convergence ratio of 0.99 and a squared error of 0.0019. Finally, the value of NOx anticipated by the neural network has been calculated and validated according to empirical data by applying maximum genetic algorithm. The maximum point for the fuel composed of 20% hydrogen and 80% methane occurred in the equivalence ratio of 0.9; and the maximum point for the fuel composed of 40% hydrogen occurred in equivalence ratio of 0.92. The consistency of the model findings with the empirical data shows the potential of the neural network in anticipating the amount of NOx.

Implementing Optimization Techniques in PSS Design for Multi-Machine Smart Power Systems: A Comparative Study

This study performed a comparative analysis of five new meta-heuristic algorithms specifically adopted based on two general classifications; namely, nature-inspired, which includes artificial eco-system optimization (AEO), African vulture optimization algorithm (AVOA), gorilla troop optimization (GTO), and non-nature-inspired or based on mathematical and physics concepts, which includes gradient-based optimization (GBO) and Runge Kutta optimization (RUN) for optimal tuning of multi-machine power system stabilizers (PSSs). To achieve this aim, the algorithms were applied in the PSS design for a multi-machine smart power system. The PSS design was formulated as an optimization problem, and the eigenvalue-based objective function was adopted to improve the damping of electromechanical modes. The expressed objective function helped to determine the stabilizer parameters and enhanced the dynamic performance of the multi-machine power system. The performance of the algorithms in the PSS’s design was evaluated using the Western System Coordinating Council (WSCC) multi-machine power test system. The results obtained were compared with each other. When compared to nature-inspired algorithms (AEO, AVOA, and GTO), non-nature-inspired algorithms (GBO and RUN) reduced low-frequency oscillations faster by improving the damping of electromechanical modes and providing a better convergence ratio and statistical performance.

A Methodology for Evaluating and Scheduling Preventive Maintenance for a Thermo-Electric Unit Using Artificial Intelligence

Flow-production systems whose pieces are connected in a row may not have maintenance scheduling procedures fixed because problems occur at different times (electricity plants, cement plants, water desalination plants). Contemporary software and artificial intelligence (AI) technologies are used to fulfill the research objectives by developing a predictive maintenance program. The data of the fifth thermal unit of the power station for the electricity of Al Dora/Baghdad are used in this study. Three stages of research were conducted. First, missing data without temporal sequences were processed. The data were filled using time series hour after hour and the times were filled as system working hours, making the volume of the data relatively high for 2015-2016-2017. 2018 was utilized as a test year to assess the modeling work and validate the experimental results. In the second step, the artificial neural networks approach employs the python program as an AI, and the affinity ratio of real data using the performance measurement of the mean absolute error (MAE) was 0.005. To improve and reduce the value of absolute error, the genetic algorithm uses the python program and the convergence ratio became 0.001. It inferred that the algorithm is efficient in improving results. Thus, the genetic algorithm provided better results with fewer errors than the neural network alone. This concludes that the shown network has superior performance over others and the possibility of its long-term predictions for 2030. A Sing time series helped detect future cases by reading and inferring system data. The development of appropriate work plans will lower internal and external expenses of the systems and help integrate other capabilities by giving correct data sources of raw materials, costs, etc. To facilitate prediction for maintenance workers, an interface has been created that facilitates users to apply them using the python program represented by entering the times, an hour, a day, a month, a year, to predict the type and place of failure.

Measuring the principal Hugoniot of inertial-confinement-fusion-relevant TMPTA plastic foams.

Wetted-foam layers are of significant interest for inertial-confinement-fusion capsules, due to the control they provide over the convergence ratio of the implosion and the opportunity this affords to minimize hydrodynamic instability growth. However, the equationof state for fusion-relevant foams are not well characterized, and many simulations rely on modeling such foams as a homogeneous medium with the foam average density. To address this issue, an experiment was performed using the VULCAN Nd:glass laser at the Central Laser Facility. The aim was to measure the principal Hugoniot of TMPTA plastic foams at 260mg/cm^{3}, corresponding to the density of liquid DT-wetted-foam layers, and their "hydrodynamic equivalent" capsules. A VISAR was used to obtain the shock velocity of both the foam and an α-quartz reference layer, while streaked optical pyrometry provided the temperature of the shocked material. The measurements confirm that, for the 20-120 GPa pressure range accessed, this material can indeed be well described using the equationof state of the homogeneous medium at the foam density.

Study on optimization of the dynamic performance of the robot bonnet polishing system

To solve the problem of processing quality degradation due to vibration in the robot bonnet polishing system (RBPS), the vibration generation mechanism of the polishing system is revealed based on the modal analysis and dynamic modeling of the RBPS. The modal analysis results showed that the operating frequency of the system is near the natural frequency, which makes the system susceptible to resonance. On the other hand, the forced vibration caused by the polishing force leads to high vibration at the end of the robot during the polishing process. In order to suppress the vibration generated by the polishing system and optimize the dynamic characteristics of the polishing system, a vibration suppression method to increase the damping ratio of the system was proposed. The experiments of SiC fixed point polishing were performed using both vibration suppression bonnet and original bonnet. The surfaces RMS and PV of the parts polished by the vibration suppression bonnet were generally better than those of the original bonnet. The vibration suppression bonnet has improved the convergence ratio of RMS and PV by 42.59% and 19.56% respectively over the original bonnet in the whole surface polishing experiments. The PSD analysis illustrated that the vibration suppression bonnet can better suppress the intermediate frequency errors. The effectiveness of the method in suppressing vibration and improving machining quality is demonstrated.