EMA Model Research Articles

Effect of Carrier Gas on Spray Pyrolysis Deposited SnO2 Thin Films

Nanostructured SnO2 thin films are synthesized by the chemical Spray pyrolysis method in presence of air and nitrogen as carrier gas. The study has emphasized on the impact of carrier gas on the underlying, electrical, and optical properties of the deposited thin films. XRD studies uncover that there is no variation in the crystalline structure of the film. The SnO2 thin films prepared using nitrogen as carrier gas is found more conductive as compared to the film prepared using air as a carrier gas. The change in conductivity is due to the increased oxygen deficiency in the nitrogen atmosphere. The HBM and EMA models are used to calculate particle radius by optical absorption data, showing the particle diameter is low for nitrogen as compared to air as carrier gas. The activation energy is also found to decrease in presence of nitrogen as carrier gas. This may be due to shallow donor and deep acceptor levels of semiconductors. The decrease in particle size increases the number of surface atoms, responsible for a decrease in activation energy of films.

Minimisation of Failure Transients in a Fail-Safe Electro-Mechanical Actuator Employed for the Flap Movables of a High-Speed Helicopter-Plane

The work deals with the model-based characterization of the failure transients of a fail-safe rotary EMA developed by Umbragroup (Italy) for the flap movables of the RACER helicopter-plane by Airbus Helicopters (France). Since the reference application requires quasi-static position-tracking with high disturbance-rejection capability, the attention is focused on control hardover faults which determine an actuator runaway from the commanded setpoint. To perform the study, a high-fidelity nonlinear model of the EMA is developed from physical first principles and the main features of health-monitoring and closed-loop control functions (integrating the conventional nested loops architecture with a deformation feedback loop enhancing the actuator stiffness) are presented. The EMA model is then validated with experiments by identifying its parameters by ad-hoc tests. Simulation results are finally proposed to characterize the failure transients in worst case scenarios by highlighting the importance of using a specifically designed back-electromotive damper circuitry into the EMA power electronics to limit the position deviation after the fault detection.

Electrical Impedance Sensors for Multi-Phase Flow Measurement: A Review

The impedance flow sensors have usually been considered as the competitive components in the multi-flow measurement, primarily due to their advantages of fast response, high dynamic range and sensitivity, non-invasive and/or non-intrusive measurements. In this review, the impedance sensors have been categorized into two categories, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i.e.</i> , the probes for local/average parameter measurement and sensor arrays for distributed parameter measurement. Maxwell’s equations and boundary conditions have been referred as a starting point to understand the measuring principle of impedance sensors, from which the sensitivity distribution can be attained. The sensitivity distribution can be utilized to characterize the sensor and employed as an objective function in optimizing the sensor geometry. The EMA models usually offer a way to relate the impedance measurements to individual phase fraction, which have been critically reviewed. In addition, the application range, spatial and temporal resolutions, advantages and disadvantages of the sensor arrays, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i.e.</i> , the wire mesh sensor, field focusing sensor, electrical resistance and capacitance tomography sensors have also been provided. Finally, the future trends of impedance sensor development have been briefly discussed.

Comparing ecological momentary assessment to sensor-based approaches in predicting dietary lapse.

Ecological momentary assessment (EMA; brief self-report surveys) of dietary lapse risk factors (e.g., cravings) has shown promise in predicting and preventing dietary lapse (nonadherence to a dietary prescription), which can improve weight loss interventions. Passive sensors also can measure lapse risk factors and may offer advantages over EMA (e.g., objective, automatic, semicontinuous data collection), but currently can measure only a few lapse predictors, a notable limitation. This study preliminarily compared the burden and accuracy of commercially available sensors versus established EMA in lapse prediction. N = 23 adults with overweight/obesity completed a 6-week commercial app-based weight loss program. Participants wore a Fitbit, enabled GPS tracking, completed EMA, and reported on EMA and sensor burden poststudy via a 5-point Likert scale. Sensed risk factors were physical activity and sleep (accelerometer), geolocation (GPS), and time, from which 233 features (measurable characteristics of sensor signals) were extracted. EMA measured 19 risk factors, lapse, and categorized GPS into meaningful geolocations. Two supervised binary classification models (LASSO) were created: the sensor model predicted lapse with 63% sensitivity (true prediction rate of lapse) and 60% specificity (true prediction rate of non-lapse) and EMA model with 59% sensitivity and 72% specificity. EMA model accuracy was higher, but self-reported EMA burden (M = 2.96, SD = 1.02) also was higher (M = 1.50, SD = 0.94). EMA model accuracy was superior, but EMA burden was higher than sensor burden. Findings highlight the promise of sensors in contributing to lapse prediction, and future research may use EMA, sensors, or both depending on prioritization of accuracy versus participant burden.

Estimating Rotational Frequency Response Function Using Mode Expansion and Frequency Response Function Synthesis Method

The rotational frequency response function (RFRF) plays a crucial role in increasing the accuracy of the calculated results of the frequency-based substructuring method. However, RFRFs are often omitted due to the difficulties in the measurement process and limitations of the equipment. This paper presents a scheme of estimating the rotational FRF of an irregular plate structure using the FE model reduction and expansion method. The reduced FE model was introduced using the improved reduction system (IRS) and expanded to the experimental modal model (EMA model) using the system reduction and the expansion (SEREP) method. The FRF expanded method was then employed to derive the translational and rotational FRFs from the expanded EMA model. The accuracy of the expanded FRFs was evaluated with the EMA model of the irregular plate. It was found that the translational and rotational FRFs estimated from the proposed scheme were in good agreement with the EMA counterparts. Furthermore, the patterns of the estimated RFRFs were well correlated with the EMA RFRFs. This work shows that the proposed scheme may offer an attractive alternative way of accurately determining the RFRs of complex structures or structural components.

Static and Dynamic Combined Effects on the Thermal Conductivity of Water Based Ironoxide Nanofluids: Experiments and Theories

ABSTRACT Reasoning of particular mechanism of anomalous thermal transport behaviors is not identified yet for the nanofluids. In this research, the thermal conductivity of maghemite (MH) nanoparticles dispersed deionized water (DW) nanofluids (MH/DW) has been evaluated for the first time using the modified effective medium theories (EMTs). EMTs have been modified with the consideration of static and dynamic effects combinedly for the analysis of anomalous behaviors of thermal conductivity enhancements of the spherical nanoparticles dispersed nanofluids. MH nanoparticles (~20 nm) were synthesized using chemical co-precipitation techniques. MH/DW nanofluids were prepared with the varying MH nanoparticles loading in DW and thermal conductivity was measured using KD2 pro device. The thermal conductivity enhancement (~32 %) was found to be increased linearly with the increasing MH nanoparticle concentration and nonlinearly with the increasing temperature. Existing Maxwell and Maxwell Gantt EMA (MG-EMA) models exhibited awful under-prediction from experimental thermal conductivities of MH/DW nanofluids. Modified model with considering static and dynamic mechanisms of MH nanoparticles combinedly showed reasonably very good agreement with the experimental thermal conductivities of MH/DW nanofluids at elevated temperature. This modified model opens the new windows to analyze the insight of the thermophysical properties of various types of nanofluids by introducing potential parameters.

Effects of graphite flake size on the properties of aligned graphene nanoplatelets covered graphite flakes/aluminum composites

Finding out the effects of graphite (Gr) flake size on the properties of Gr (Graphene Nanoplatelet (GNP))/Al composites will be helpful to design and develop various Gr(GNP)/Al composites which need to meet different application requirements. In this work, thermal conductivity (TC) and flexural strength of Gr/Al and Gr(GNP)/Al composites with different Gr flake size were investigated. Through-plane TC of Gr/Al composites is about 50% of the results predicted by EMA model. However, after introducing GNP to Gr flakes, through-plane TC of Gr(GNP)/Al composites reaches about 90% of the results predicted by EMA model. When Gr flake size are 150, 500, 850 μm, respectively, the in-plane TC of Gr/Al composites can be improved by 8.5%, 6.4%, 5.4% after introducing GNP, while the through-plane TC of Gr/Al composites can be improved by 62%, 75%, 83%. So the introduction of GNP to the Gr flake is more effective in improving through-plane TC than in-plane TC. GNP's improvement ratio on the through-plane TC of Gr/Al composites increases with the increase of Gr flake size. Furthermore, as Gr flake size increases, GNP's improvement ratio on the flexural strength of Gr/Al composites increases, which is attributed to the increase of strengthening effect of GNP on the interface region.

Three‐dimensional lattice Boltzmann simulation of the permeability of soil‐rock mixtures and comparison with other prediction models

AbstractWith the discrete element method and the proposed virtual slicing technique for three‐dimensional discrete element model, random pore‐structural models of soil‐rock mixtures (SRMs) are constructed and voxelized. Then, the three‐dimensional lattice Boltzmann method (LBM) is introduced to simulate the seepage flow in SRMs on the pore scale and the influences of rock content, rock size, relative density on the simulated permeability of SRMs are comprehensively investigated. Finally, several theoretical models are introduced to predict the permeability of SRMs, and comparison is made between the results given by these prediction models and the numerical results obtained in this study. The results show that the permeability of SRMs presents a gradually increasing trend with the increase of rock content, and the rate of increase is also getting larger. When the other conditions remain unchanged, the permeability of SRMs decreases with the increase of relative density. When the rock content is lower than a threshold value, the permeability decreases as the rock size increases; however, this trend gets reversed when the rock content exceeds the threshold value. The permeability values of SRMs simulated with the LBM are lower in different levels than those calculated with the HS model, EMA model, and Zhou model, but most of them are very close to those predicted by the Daigle model.

Effects and mechanism of filler surface coating strategy on thermal conductivity of composites: A case study on epoxy/SiO2-coated BN composites

In order to make a systematic understanding of the effects and mechanism of the filler surface coating strategy on the thermal conductivity of composites, the silica coated BN was synthesized via Stöber sol-gel method and then incorporated into epoxy. The thermal conductivities of epoxy/BN@SiO2 composites were investigated experimentally, and it was found that increasing the coating thickness or filler content would decrease the enhanced effect of the strategy on thermal conduction. Fitting the thermal conductivities of composites with the EMA model indicates that the interfacial thermal resistance in the formed BN@SiO2 thermal conduction networks will increase with the increase of filler content, and then deteriorates the thermal conduction enhancement factor. Thus, the concept of the effective filler volume fraction was introduced in the strategy for the first time. Reducing the coating thickness will expand the effective filler volume fraction, but the upper limit of the effective filler volume fraction will not exceed the maximum random packing volume fraction of the fillers. The mechanism research provides an efficient guideline for further studying core-shell particles to improve the thermal conductivity of composites.

Microstructure and thermal properties of Cr7C3 coated graphite flakes/Al composites

Graphite flakes (Gf) were coated with Cr7C3 by salt bathing coating, and the Cr7C3 coated Gf reinforced Al matrix composites were prepared by gas pressure infiltration. Surface morphology of uncoated and Cr7C3 coated Gf, the interfacial characteristics of Cr7C3 coated Gf/Al composites were observed by SEM. Surface of Cr7C3 coated Gf is smooth without defects, the Cr7C3 coating effectively improved the wettability. When volume fraction of Gf is below 50%, the experimental value of thermal conductivity (TC) is basically consistent with the calculated value of the EMA model. When volume fraction of Gf is over 50%, the growth of deviates from the EMA model curve. Coefficient of thermal expansion (CTE) of composite was predicted by Kerner model and Orientation Disc model, because Kerner model does not consider the anisotropy of Gf and inaccurately predict the change of CTE. However, the Orientation Disc model can predict the change of CTE better, but there is certainly deviation.

Precise control of water content on the growth kinetics of ZnO quantum dots

The growth kinetics of quantum dots (QDs) is of great importance to control and understand their particle size evolution. Water content is an important parameter for the growth of ZnO QDs during the sol-gel process, which has not been precisely studied until now. Herein, a modified sol-gel method was proposed to prepare uniform and mono-dispersed ZnO QDs. In this method, water content was precisely controlled, which facilitated the thorough investigation concerning the effects of water content on growth kinetics of ZnO QDs. When the water content was low (≤90 mM), the precursor solution was stable and the generation of ZnO QDs could not be triggered. When the water content was too high (3 M), Zn-HDS was generated instead of ZnO. When the water content was in an appropriate range (360 mM-900 mM), the growth of ZnO QDs followed two stages: the oriented attachment (OA) and the Ostwald ripening (OR) stage. Based on our particle size calculation results by Sarma Model, which showed more distinct differentiation and better pertinence than EMA Model, it has been proved that the increase in the water content could not only promote the growth rate of OA stage, but also the OR stage. This results changed our previous thinking that water content has no influence to the OR stage.

Full field optical measurements in experimental modal analysis and model updating

We might doubt if optical measurements and spatially dense datasets are really effective, when dealing with advanced model updating of lightweight structures with complex structural dynamics. Laser Doppler Velocimetry, with its scanning variances, is generally accepted as the reference technology in measuring vibration patterns with high spatial definition. Nonetheless, one must be reminded of the noise shown in the raw signal of some experiments, which poses issues in proficiently exploiting the added data in a fruitful model updating procedure. Instead, native full field measuring technologies, like Hi-Speed DIC and dynamic ESPI, have recently shown intrinsic smoother data fields: their image-based nature and evaluation algorithms of experimental quantities promise advances on model optimisations, having to struggle less against a reduced uncertainty in the references.In this work, a comparison is made by means of all the cited challenging technologies on the same broad frequency band vibration measurement problem, with different spatial resolutions and quality of the measured patterns, in the framework of established procedures for model updating of dynamically excited structures. The identification of EMA models highlights the increasing quality of shapes that can be obtained from native full field high resolution instruments, against that of SLDV (some time unexpectedly poor, as tested).A comparative paradigm is recalled to precisely match the competing measurement technologies on the same physical point of a common grid: model updating results are therefore thoroughly compared between scanning and native full field technologies, with comments and details on the test rig, on the advantages and drawbacks of the approaches. The model updating procedures show a fruitful impact of the native full field technologies in the form of an increased consistency on eigenshapes used to tune the virtual structural model.

Analytical evaluation of the lifetime of a three-axle bogie frame using the analytical model validated through experimental modal analysis

The fatigue strength validation by tests of the railway bogie frames requires existence of an expensive laboratory and a long time for testing, of about 6 to 10 months. Considering these aspects, the european norms admit that fatigue tests can be replaced by finite elementes analysis, with condition that analytical model to be correctly realized and validated by tests. Experimental modal analysis provides a powerful tool for validation of the FEA model through experimental data. The article presents an application for analytical assessment of the fatigue strength for a three-axle locomotive bogie frame, before sending it to the laboratory fatigue tests. Using Ansys, it was carried out the structural analysis of the bogie frame, rezulting the modal model characterized by the modal parameters: eigenfrequencies and eigenshapes. The analytical model was validated through an EMA application carried out on the bogie frame and correlation analysis of the EMA and FEA models. The analytical model and data files containing the simulated vertical, transverse and twist loads, applied to the bogie frame according to EN13749/2011, constitutes the input data for nCode program, that evaluates the bogie frame lifetime using appropriate stress curves and a recognized hypothesis of damage accumulation.

Application of the EMA Model to Tourism Entrepreneurs: Motivation as a Mediator

This research uses the expectation, motivation, and attitude (EMA) model, originally developed for tourists/consumers, to provide a better understanding of what guides the actions of entrepreneurs. These entrepreneurs have not been a focus in the hospitality literature therefore their desire to start the business, expectations about the business, and resulting attitudes are not fully understood. The study uses bed and breakfast entrepreneurs as the population and finds that motivation is a mediator of the relationship between expectations and attitudes. Additionally, using the model in this new setting, with a new population supports the model as providing the underlying relationships at work when the population investigated is expending resources for a desired outcome. The EMA model should continue to be used in future research.

Broad frequency band full field measurements for advanced applications: Point-wise comparisons between optical technologies

Abstract The progress of optical systems gives nowadays at disposal on lightweight structures complex dynamic measurements and modal tests, each with its own advantages, drawbacks and preferred usage domains. It is thus more easy than before to obtain highly spatially defined vibration patterns for many applications in vibration engineering, testing and general product development. The potential of three completely different technologies is here benchmarked on a common test rig and advanced applications. SLDV, dynamic ESPI and hi-speed DIC are here first deployed in a complex and unique test on the estimation of FRFs with high spatial accuracy from a thin vibrating plate. The latter exhibits a broad band dynamics and high modal density in the common frequency domain where the techniques can find an operative intersection. A peculiar point-wise comparison is here addressed by means of discrete geometry transforms to put all the three technologies on trial at each physical point of the surface. Full field measurement technologies cannot estimate only displacement fields on a refined grid, but can exploit the spatial consistency of the results through neighbouring locations by means of numerical differentiation operators in the spatial domain to obtain rotational degrees of freedom and superficial dynamic strain distributions, with enhanced quality, compared to other technologies in literature. Approaching the task with the aid of superior quality receptance maps from the three different full field gears, this work calculates and compares rotational and dynamic strain FRFs. Dynamic stress FRFs can be modelled directly from the latter, by means of a constitutive model, avoiding the costly and time-consuming steps of building and tuning a numerical dynamic model of a flexible component or a structure in real life conditions. Once dynamic stress FRFs are obtained, spectral fatigue approaches can try to predict the life of a component in many excitation conditions. Different spectral shaping of the excitation can easily be used to enhance the comparison in the framework of any of the spectral approaches for fatigue life calculations, highlighting benefits and drawbacks of a direct experimental approach to failure and risk assessment in structural dynamics when dealing with complex patterns in real-life testing. Are optical measurements and spatially dense datasets really effective in advanced model updating of lightweight structures with complex structural dynamics? The noise shown in the raw signal of some experiments may pose issues in proficiently exploiting the added data in a fruitful model updating procedure. Model updating results are here compared between scanning and native full field technologies, with comments and details on the test rig, on the advantages and drawbacks of the approaches. The identification of EMA models highlights the increasing quality of shapes that can be obtained from native full field high resolution gears, against that (some time unexpectedly poor) of SLDV tested.

Environmental management accounting: A conceptual model for the reporting of environmental costs

The overall aim of this study was to identify factors that affect the use of EMA by the hotel sector in South Africa. The research was an exploratory study and qualitative in nature using a single case study with embedded units approach. ABC Hotel Management Group along its 3 hotels located in the province of KwaZulu-Natal, South Africa, met the selection criteria and thus formed part of this study. There were 10 participants in this case study. Additional documents were analysed which included financial statements, policy documents, the Group website, the hotels’ websites, Group Energy Profile Analysis (GEPA) programme, and Building Monitoring Systems (BMS). The results of this research established a number of factors that affect the use of EMA by the hotel sector in South Africa. The adoption of a prototype EMA model by the hotel sector is then suggested by the study.

Synthesis and Electroluminescence of Silver Doped ZnS/PVK Nanocomposite

Sulfide based luminescent materials have attracted a lot of attention for a wide range of photo-and electroluminescence applications. Among the sulfides, ZnS is promising host material for development of phosphors in different visible emission bands. Doping of Ag can affect the electroluminescence of the host material. Incorporation of host ZnS into the polymer matrix is one of the best method to display their special functions, which stabilize the nanoparticles. Here we report a synthesis and electroluminescence of silver doped ZnS/PVK nanocomposites thin films. Reported films were prepared by using chemical route with varying Ag doping and ZnS loading in the composite. Structural and morphological characterization were carried out through XRD and SEM techniques, which confirmed the particles in nanoregime. Though optical absorption spectra and band gap of ZnS semiconductor nanoparticles in ZnS:Ag/PVK matrix were estimated, and using EMA model, particle size was calculated which supports the results of XRD. Electroluminescence of nanocomposite samples was studied and it was found that threshold voltage depends on doping of Ag and also on loading of ZnS. Voltage brightness characteristics support the production of EL by acceleration-collision mechanism.Contents of Paper

XPS and Spectroscopic Ellipsometry Study of Composite SiNx/DLC Prepared by Co-Deposition of RF Magnetron and Filtered Cathodic Arc

Composite SiNx/DLC films were deposited on silicon substrate by co-deposition system. The carbon plasma was generated by filtered cathodic arc source, simultaneously incorporated with silicon nitride from RF magnetron sputtering. The silicon nitride sputtering rate was maintained by fixed RF power at 100W while the arc current of FCA was varied from 20 to 80A.The SiNx/DLC film composition and optical properties were investigated by X-ray photoelectron spectroscopy and spectroscopic ellipsometry respectively. The results revealed that the atomic concentration of carbon increased while those of silicon and nitrogen decreased with increasing arc current. The oxidation was found on the film surface and related to the atomic concentration of silicon. The optical properties can be changed as a function of carbon concentration by setting different arc current. In this work, the volume percentage of carbon obtained from spectroscopic ellipsometry using Bruggeman EMA model showed good numerical correlation with the atomic percentage of carbon from XPS analysis with the range spanning across 75-95 at. %.

Empirical Study on B-S Model Based Pricing of Warrants in China

This article valuated theoretical prices of covered warrants in china through fitting temporal series of target warrant prices and market information of corresponding underlying securities. Furthermore, the author surveyed the deviation between market price and theoretical price of warrant. In order to eliminate the inaccuracy caused by constant volatility assumption of B-S Model, the author creatively used Modified Exponentially Moving Average (Modified EMA) Model to calculate the historical volatility of market prices of warrants and fixed the best dilution factor through Grid Search Technique. Also, validities of calculation of historical volatility by Modified EMA Model and original EMA Model are compared. Original data came from market information during the period 2005-2008 supported by security trading software and calculation was done via Excel. At the same time when Chinese government was going to revive covered warrant market, this article provided a more accurate method of pricing covered warrant, also known as modified B-S Model.

Expectation, Motivation, and Attitude: A Tourist Behavioral Model

This study focuses on the previsit stage of tourists by modeling the behavioral process incorporating expectation, motivation, and attitude in the context of Chinese outbound travelers. An expectation, motivation, and attitude (EMA) model is proposed based on a comprehensive literature review. An instrument is developed based on previous tourism and marketing studies as well as focus groups to measure the variables in the EMA model. Data are collected from 1,514 Beijing, Shanghai, and Guangzhou residents. Results of the study confirm the proposed relations that expectation of visiting an outbound destination has a direct effect on motivation to visit the destination; motivation has a direct effect on attitude toward visiting the destination; expectation of visiting the outbound destination has a direct effect on attitude toward visiting the destination; and motivation has a mediating effect on the relationship between expectation and attitude. Practical and theoretical contributions are discussed, with future research suggested.