Parameters Of Phenomenological Model Research Articles

Pythia8 MC Tuning Validation Using the Professor2 Package

This article presents a method for multi-parameter, simultaneous tuning of the Monte Carlo event generator. It is validated on the Pythia8 Monte Carlo event generator widely used in High Energy Physics (HEP). The obtained results show that the method can be used to constrain the free parameters of phenomenological models while properly taking into account the correlations existing among the parameters.

Particle-based model of liquid crystal skyrmion dynamics.

Motivated by recent experimental results that reveal rich collective dynamics of thousands-to-millions of active liquid crystal skyrmions, we have developed a coarse-grained, particle-based model of the dynamics of skyrmions in a dilute regime. The basic physical mechanism of skyrmion motion is related to squirming undulations of domains with high director twist within the skyrmion cores when the electric field is turned on and off. The motion is not related to mass flow and is caused only by the reorientation dynamics of the director field. Based on the results of the "fine-grained" Frank-Oseen continuum model, we have mapped these squirming director distortions onto an effective force that acts asymmetrically upon switching the electrical field on or off. The resulting model correctly reproduces the skyrmion dynamics, including velocity reversal as a function of the frequency of a pulse width modulated driving voltage. We have also obtained approximate analytical expressions for the phenomenological model parameters encoding their dependence upon the cholesteric pitch and the strength of the electric field. This has been achieved by fitting coarse-grained skyrmion trajectories to those determined in the framework of the Frank-Oseen model.

Diffusion Characteristics of Clusters of Self-Interstitial Atoms in Vanadium: Molecular Dynamics Data

The temperature dependences of diffusion characteristics of the irradiation-induced defects, namely, clusters of self-interstitial atoms (SIAs) containing up to five atoms, in bcc V (vanadium) have been studied by the method of molecular dynamics in the temperature range of 300–1000 K. The diffusion characteristics include the coefficient of diffusion, the tracer correlation factor, the average displacement before changing the direction of migration, and the frequency of changing the direction of migration. The values of the activation energy of diffusion and the activation energy of changing the direction of migration for the considered types of defects in different temperature ranges have been determined. The dependences of the mechanism of (1D vs 3D) diffusion of SIA clusters on the temperature and cluster size and their possible influence on the parameters of phenomenological models of changes in the microstructure of a material under irradiation (sink strengths of spherical absorbers) are discussed.

Precision tests of quantum mechanics and mathcal{CPT} symmetry with entangled neutral kaons at KLOE

The quantum interference between the decays of entangled neutral kaons is studied in the process ϕ → KSKL → π+π−π+π−, which exhibits the characteristic Einstein-Podolsky-Rosen correlations that prevent both kaons to decay into π+π− at the same time. This constitutes a very powerful tool for testing at the utmost precision the quantum coherence of the entangled kaon pair state, and to search for tiny decoherence and mathcal{CPT} violation effects, which may be justified in a quantum gravity framework.The analysed data sample was collected with the KLOE detector at DAΦNE, the Frascati ϕ-factory, and corresponds to an integrated luminosity of about 1.7 fb−1, i.e. to about 1.7 × 109ϕ → KSKL decays produced. From the fit of the observed ∆t distribution, being ∆t the difference of the kaon decay times, the decoherence and mathcal{CPT} violation parameters of various phenomenological models are measured with a largely improved accuracy with respect to previous analyses.The results are consistent with no deviation from quantum mechanics and mathcal{CPT} symmetry, while for some parameters the precision reaches the interesting level at which — in the most optimistic scenarios — quantum gravity effects might show up. They provide the most stringent limits up to date on the considered models.

Phenomenological modeling of low-bias sulfur hexafluoride plasma etching of silicon

Low-bias etching of silicon (Si) using sulfur hexafluoride (SF6) plasma is a valuable tool in the manufacturing of electronic devices and microelectromechanical systems (MEMS). This kind of etching offers an almost isotropic etching behaviour, since the low voltage bias does not provide enough vertical acceleration and kinetic energy to the ions. Due to this near-isotropic behavior, the aforementioned plasma etching finds application as an alternative to wet etching in, e.g., MEMS and optical applications since it provides a cleaner and more precisely controllable process. However, the degree of isotropy and, consequently, the final surface profile remain difficult to control. In this work, we apply a three-dimensional feature-scale topography simulation to low-bias SF6 etching experiments in Si to aid in process development and to investigate the physical etching mechanisms which govern the final surface geometry. We achieve this by accurately reproducing three distinct experimental data sets and by discussing the meaning of the phenomenological model parameters involved in the topography simulation in detail. We show that our phenomenological top-down flux calculation approach more accurately reproduces the experimental results than conventional strictly isotropic and bottom-up approaches. The reactor loading effect is taken into account as a general reduction of the model etch rates, which is supported by comparing simulated to experimentally determined etch depths in different loading regimes. Our model is also able to accurately reproduce reported trench geometries for different mask openings and etch times using a single parameter set for a given reactor configuration. Hence, we propose that the model parameters, in particular the average effective sticking coefficient, can be taken as a proxy of the reactor configuration. We provide an empirical relationship linking the average sticking coefficient of a reactor recipe to a measurable degree of isotropy of etched geometries. This empirical relationship can be used in practice to (i) estimate the average effective sticking coefficient of independent experiments and to (ii) fine-tune the etched geometry.

Thermodynamics Model for Mechanochemical Synthesis of Gold Nanoparticles: Implications for Solvent-Free Nanoparticle Production

Mechanochemistry is becoming an established method for the sustainable, solid-phase synthesis of scores of nano-materials and molecules, ranging from active pharmaceutical ingredients to materials for cleantech. Yet we are still lacking a good model to rationalize experimental observations and develop a mechanistic understanding of the factors at play during mechanically assisted, solid-phase nanoparticle synthesis. We propose herein a structural-phase-field-crystal (XPFC) model with a ballistic driving force to describe such a process, with the specific example of the growth of gold nanoparticles in a two component mixture. The reaction path is described in the context of free energy landscape of the model, and dynamical simulations are performed based on phenomenological model parameters closely corresponding to the experimental conditions, so as to draw conclusions on nanoparticle growth dynamics. It is shown that the ballistic term lowers the activation energy barrier of reaction, enabling the reaction in a temperature regime compatible with experimental observations. The model also explains the mechanism of precipitated grain size reduction that is consistent with experimental observations. Our simulation results afford novel mechanistic insights into mechanosynthesis with implications for nanaparticle production and beyond.

Constraining extra dimensions on cosmological scales with LISA future gravitational wave siren data

The Universe is undergoing a late time acceleration. We investigate the idea that this acceleration could be the consequence of gravitational leakage into extra dimensions on cosmological scales rather than the result of a non-zero cosmological constant, and consider the ability of future gravitational-wave (GW) siren observations to probe this phenomenon and constrain the parameters of phenomenological models of this gravitational leakage. A gravitational space interferometer such as LISA will observe massive black hole binary (MBHB) merger events at cosmological distances, and will also provide sky localization information that may permit optical and other electromagnetic (EM) surveys to identify an EM counterpart of these events. In theories that include additional non-compact spacetime dimensions, the gravitational leakage intro extra dimensions leads to a reduction in the amplitude of observed gravitational waves and thereby a systematic discrepancy between the distance inferred to such sources from GW and EM observations. We investigate the capability of LISA to probe this modified gravity on large scales, specifically in the Dvali, Gabadadze and Porrati (DGP) model. Additionally, we include a Supernova Ia sample at lower redshift in order to explore the efficacy of this cosmological probe across a range of redshifts. We then use previously published simulated catalogues of cosmologically distant MBHB merger events detectable by LISA, and which are likely to produce an observable EM counterpart. We find that the extent to which LISA will be able to place limits on the number of spacetime dimensions and other cosmological parameters characterising modified gravity will strongly depend on the actual number and redshift distribution of sources, together with the uncertainty on the GW distance measurements. A relatively small number of sources (∼ 1) and high measurement uncertainties would strongly restrict the ability of LISA to place meaningful constraints on the parameters in cosmological scenarios where gravity is only five-dimensional and modified at scales larger than about ∼ 4 times the Hubble radius. Conversely, if the number of sources observed amounts to a four-year average of ∼ 27, then in the most favourable cosmological scenarios LISA has the potential to place meaningful constraints on the cosmological parameters—with a precision of ∼ 1% on the number of dimensions and ∼ 7.5% on the scale beyond which gravity is modified, thereby probing the late expansion of the universe up to a redshift of ∼ 8, i.e. on scales not yet tested by present EM observations.

Temperature-dependent Charpy impact property of 3D printed 15-5 PH stainless steel

In this study, the impact property of 3D printed 15-5 PH stainless steel was investigated at low (77 K), room (298 K), and high temperatures (723 K) using integrated experimental and modelling studies. The finite element model was based on the Johnson-Cook phenomenological material model and fracture parameters. The experimentally measured impact energies are 0.01, 6.78 ± 4.07, and 50.84 ± 3.39 J cm−2, at the low, room, and high temperatures, respectively. The experimental and modelling predicted impact energies are in good agreement. The microstructures show that the steel exhibits a brittle behaviour at low and room temperatures as indicated by a transgranular fracture, but changes to a more ductile behaviour at high temperatures as illustrated by microvoid coalescence induced facture morphology.

Testing CPT Symmetry with Neutral K Mesons: A Review

The neutral kaon system is a very peculiar system that offers unique possibilities to perform precise tests of the CPT symmetry. The entanglement of neutral kaon pairs that are produced at a ϕ-factory opens up new ways and scenarios in order to test this fundamental discrete symmetry. In this paper, the results of the most recent and significant CPT tests are reviewed. Experiments have set stringent limits on the CPT-violating parameters of different phenomenological models, some of them associated to possible decoherence mechanisms or Lorentz symmetry violation which might be justified in a quantum gravity framework. The present results show no violation of CPT symmetry, while their accuracy in some cases reaches the interesting level at which–in the most optimistic scenarios–quantum gravity effects might show up.

Multiparametric MRI in the Diagnosis of Prostate Cancer: Physical Foundations, Limitations, and Prospective Advances ofDiffusion-Weighted MRI.

Diffusion-weighted imaging (DWI) is an essential component of the multiparametric MRI exam for the diagnosis and assessment of prostate cancer (PCa). Over the last two decades, various models have been developed to quantitatively correlate the DWI signal with microstructural characteristics of prostate tissue. The simplest approach (ADC: apparent diffusion coefficient) - currently established as the clinical standard - describes monoexponential decay of the DWI signal. While numerous studies have shown an inverse correlation of ADC values with the Gleason score, the ADC model lacks specificity and is based on water diffusion dynamics that are not true in human tissue. This article aims to explain the biophysical limitations of the standard DWI model and to discuss the potential of more complex, advanced DWI models. This article is a review based on a selective literature review. Four phenomenological DWI models are introduced: diffusion tensor imaging, intravoxel incoherent motion, biexponential model, and diffusion kurtosis imaging. Their parameters may potentially improve PCa diagnostics but show varying degrees of statistical significance with respect to the detection and characterization of PCa in current studies. Phenomenological model parameters lack specificity, which has motivated the development of more descriptive tissue models that directly relate microstructural features to the DWI signal. Finally, we present two of such structural models, i. e. the VERDICT (Vascular, Extracellular, and Restricted Diffusion for Cytometry in Tumors) and RSI (Restriction Spectrum Imaging) model. Both have shown promising results in initial studies regarding the characterization and prognosis of PCa. Recent developments in DWI techniques promise increasing accuracy and more specific statements about microstructural changes of PCa. However, further studies are necessary to establish a standardized DWI protocol for the diagnosis of PCa. · DWI is paramount to the mpMRI exam for the diagnosis of PCa.. · Though of clinical value, the ADC model lacks specificity and oversimplifies tissue complexities.. · Advanced phenomenological and structural models have been developed to describe the DWI signal.. · Phenomenological models may improve diagnostics but show inconsistent results regarding PCa assessment.. · Structural models have demonstrated promising results in initial studies regarding PCa characterization.. · Wichtmann BD, Zöllner FG, Attenberger UI et al. Multiparametric MRI in the Diagnosis of Prostate Cancer: Physical Foundations, Limitations, and Prospective Advances of Diffusion-Weighted MRI. Fortschr Röntgenstr 2021; 193: 399 - 409.

Systematic study of Coulomb displacement energy based on the Coulomb energy empirical formula and mass model

In this study, starting from the nuclear binding energy, we studied the empirical formula of the Coulomb energy systematically. Beginning with the simplest empirical formula, we added the Coulomb exchange term, pairing correlation, and shell correction, to calculate the Coulomb energy more precisely. In addition, we investigated the Coulomb displacement energy of widely used mass models. The discrepancies between the calculation results and experimental data might be caused by the missing of the isospin breaking terms of strong interactions in theory. By investigating these discrepancies, we found that the results obtained by microscopic theories presented a distinctive systematical behavior. Thus, these theories can be improved by including isospin breaking terms. However, in the results obtained by phenomenological models, the systematical behavior is unclear. This occurs because it is difficult for the information of the microscopic nuclear structure to be absorbed into the parameters of phenomenological models.

Comparative Investigation of Phenomenological Modeling for Hysteresis Responses of Magnetorheological Elastomer Devices.

Magnetorheological elastomer (MRE) is a type of magnetic soft material consisting of ferromagnetic particles embedded in a polymeric matrix. MRE-based devices have characteristics of adjustable stiffness and damping properties, and highly nonlinear and hysteretic force–displacement responses that are dependent on external excitations and applied magnetic fields. To effectively implement the devices in mitigating the hazard vibrations of structures, numerically traceable and computationally efficient models should be firstly developed to accurately present the unique behaviors of MREs, including the typical Payne effect and strain stiffening of rubbers etc. In this study, the up-to-date phenomenological models for describing hysteresis response of MRE devices are experimentally investigated. A prototype of MRE isolator is dynamically tested using a shaking table in the laboratory, and the tests are conducted based on displacement control using harmonic inputs with various loading frequencies, amplitudes and applied current levels. Then, the test results are used to identify the parameters of different phenomenological models for model performance evaluation. The procedure of model identification can be considered as solving a global minimization optimization problem, in which the fitness function is the root mean square error between the experimental data and the model prediction. The genetic algorithm (GA) is employed to solve the optimization problem for optimal model parameters due to its advantages of easy coding and fast convergence. Finally, several evaluation indices are adopted to compare the performances of different models, and the result shows that the improved LuGre friction model outperforms other models and has optimal accuracy in predicting the hysteresis response of the MRE device.

Issue: Selected paper of OIPE 2016 on modeling and optimal design of electromagnetic and electronic devices

Issue: Selected paper of OIPE 2016 on modeling and optimal design of electromagnetic and electronic devices

Dynamic simulation of the effect of time-dependent variation of pH on response variable of the tailing thickener of coal washing plant

Dynamic simulation approach can be used for understanding the nonlinear behavior in mineral processing circuits. In this study, the gel point, the main parameters of batch flux density function and the main parameters of effective solid stress were determined at different conditions (pH, flocculant dosage and particle size). Therefore, the main parameters of phenomenological model of sedimentation and thickening were determined as a function of particle size, pH and flocculant dosages using the result of experimental tests and Curve expert professional software. Then, the dynamic simulation was carried out for the industrial thickener of coal washing plant and the time-dependent variation of response variables was investigated by time-dependent variation of pH of input feed to thickener using the obtained equations. It was observed that it is possible to predict the thickener behavior as a function of time for time dependent variation of pH of input feed to the thickener of coal washing plant using obtained equations that it was not possible using phenomenological model of thickener alone.

Comparative analysis on the influence of the MAAP4 phenomenological model parameters for the severe accident source term for different plant designs and accident scenarios

Considerable efforts have been taken to estimate the radioactive source term by using integrated computer models, but uncertainties exist in using these models, partly due to the fact that the results cannot be validated using real-world large-scale experiments. The purpose of this research is to identify the MAAP4 phenomenological model parameters with large influences in predicting environmental releases. The identified parameters were compared for different accident scenarios and plant configurations. Two-step screening of the influential model parameters through the Latin hypercube-rank correlation and the one-at-time method was used for the comparative analysis. From the integral analyses, it was found that the source term error propagation was much larger in the containment and in the secondary system. However, error propagation was not necessarily larger inside the containment than in the secondary system. There are common phenomenological parameters with significant influences on the source term simulations: primary depressurization, molten core-concrete interaction, and cladding oxidation models. More focused research regarding the effect of aforementioned identified phenomenological models on the source term calculations would be necessary to better predict the amount of environmental radionuclides release for the severe accidents. However, the detailed uncertainty and sensitivity analysis involving phenomenological model parameters may have to be done in a plant-specific way. Some phenomenological model parameters that showed significant impact on the global source term uncertainty in one plant type did not necessarily have the same impact on another plant. A sensitivity study involving a typical PWR may not have same implications in other designs, even if a same accident scenario with similar accident phenomena is analyzed. Such sensitivity study would be much more beneficial for standardized plant designs.

Level density of the [formula omitted]-nuclei—Statistical shell-model predictions

Accurate knowledge of the nuclear level density is important both from a theoretical viewpoint as a powerful instrument for studying nuclear structure and for numerous applications. For example, astrophysical reactions responsible for the nucleosynthesis in the universe can be understood only if we know the nuclear level density. We use the configuration-interaction nuclear shell model to predict nuclear level density for all nuclei in the sd-shell, both total and for individual spins (only with positive parity). To avoid the diagonalization in large model spaces we use the moments method based on statistical properties of nuclear many-body systems. In the cases where the diagonalization is possible, the results of the moments method practically coincide with those from the shell-model calculations. Using the computed level densities, we fit the parameters of the Constant Temperature phenomenological model, which can be used by practitioners in their studies of nuclear reactions at excitation energies appropriate for the sd-shell nuclei.

A physics-based model for maintenance of the pH gradient in the gastric mucus layer.

It is generally accepted that the gastric mucus layer provides a protective barrier between the lumen and the mucosa, shielding the mucosa from acid and digestive enzymes and preventing autodigestion of the stomach epithelium. However, the precise mechanisms that contribute to this protective function are still up for debate. In particular, it is not clear what physical processes are responsible for transporting hydrogen protons, secreted within the gastric pits, across the mucus layer to the lumen without acidifying the environment adjacent to the epithelium. One hypothesis is that hydrogen may be bound to the mucin polymers themselves as they are convected away from the mucosal surface and eventually degraded in the stomach lumen. It is also not clear what mechanisms prevent hydrogen from diffusing back toward the mucosal surface, thereby lowering the local pH. In this work we investigate a physics-based model of ion transport within the mucosal layer based on a Nernst-Planck-like equation. Analysis of this model shows that the mechanism of transporting protons bound to the mucus gel is capable of reproducing the trans-mucus pH gradients reported in the literature. Furthermore, when coupled with ion exchange at the epithelial surface, our analysis shows that bicarbonate secretion alone is capable of neutralizing the epithelial pH, even in the face of enormous diffusive gradients of hydrogen. Maintenance of the pH gradient is found to be robust to a wide array of perturbations in both physiological and phenomenological model parameters, suggesting a robust physiological control mechanism.NEW & NOTEWORTHY This work combines modeling techniques based on physical principles, as well as novel numerical simulations to test the plausibility of one hypothesized mechanism for proton transport across the gastric mucus layer. Results show that this mechanism is able to maintain the extreme pH gradient seen in in vivo experiments and suggests a highly robust regulation mechanism to maintain this gradient in the face of dynamic lumen composition.

Vinča – Garden of Eden

Accurate knowledge of the nuclear level density is important both from a theoretical viewpoint as a powerful instrument for studying nuclear structure and for numerous applications. For example, astrophysical reactions responsible for the nucleosynthesis in the universe can be understood only if we know the nuclear level density. We use the configuration-interaction nuclear shell model to predict nuclear level density for all nuclei in the sd-shell, both total and for individual spins (only with positive parity). To avoid the diagonalization in large model spaces we use the moments method based on statistical properties of nuclear many-body systems. In the cases where the diagonalization is possible, the results of the moments method practically coincide with those from the shell-model calculations. Using the computed level densities, we fit the parameters of the Constant Temperature phenomenological model, which can be used by practitioners in their studies of nuclear reactions at excitation energies appropriate for the sd-shell nuclei.

Holographic study of the QCD matter under external conditions

Holographic QCD is based on the AdS/CFT duality and offers new nonperturbative approaches to understand the strongly interacting regime of gauge theories. One of the primary questions in Quantum Chromodynamics is the clarification of the whole phase diagram of matter out of quarks and gluons as a function of temperature, baryon or quark chemical potential, and other external parameters.We use methods of the bottom-up AdS/QCD approach to bring out the phase structure of several holographic models in which transition to a deconfined phase is related to a (first order) Hawking-Page phase transition. The impact of phenomenological model parameters on the critical temperature and chemical potential is studied in detail. Comparison of the model predictions with results of experimental investigations, lattice QCD simulations and other methods is also done.

Evaluation of phenomenological model parameters using density dependent laws for prediction of mechanical response of cellular materials

Abstract Cellular materials have found wide-spread attention in structural applications involving impact energy absorption. The choice of the most suitable density of a cellular material, for a particular impact application, is based on its mechanical response, which may be obtained through experimental tests and/or models. A current study is focused on prediction of a mechanical response of a wide range of densities of a cellular material using available experimental data of very few densities. Best fitting-parameters of four selected phenomenological models, to fit the available experimental response of three distinct aluminum foam densities, are evaluated. The relationship between the best-fitting parameters and density of the foam is established by using two types of functions. The first function is based on a power law relationship between each parameter and foam density ρ, while the second function assumes each parameter as a linear combination of ρn and ρ, where n is any real number. The former function is found reasonable in the cases of both parameter interpolation and extrapolation while the latter is found reasonable for a parameter interpolation only. The findings of a current study emphasize for a conscious approach during selection of density dependent laws for phenomenological model parameters to avoid any erroneous or misleading design decision.