A galaxy-free phenomenological model for the 21-cm power spectrum during reionization
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Jordan Mirocha↗
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Results for “Phenomenological Models”
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Phenomenological model of nuclear primary air showers
The development of proton primary air showers is described in terms of a model based on a hadron core plus an electromagnetic cascade. The muon component is neglected. The model uses three parameters: a rate at which hadron core energy is converted into electromagnetic cascade energy and a two-parameter sea-level shower-age function. By assuming an interaction length for the primary nucleus, the model is extended to nuclear primaries. Both models are applied over the energy range from 10 to the 13th power to 10 to the 21st power eV. Both models describe the size and age structure (neglecting muons) from a depth of 342 to 2052 g/sq cm.
Tompkins, D. R., Jr.↗
A phenomenological model of solar flares
The energy of solar flares is derived from the magnetic energy of fields convected to the sun's surface and subsequently converted to heat and energetic particles within the chromosphere. The circumstances of this conversion in most current models is magnetic flux annihilation at a neutral sheet. An analysis is conducted of the constraints of flux annihilation. It is shown that the present evidence of solar cosmic rays, X-rays, gamma-rays, and total energy suggests a choice of annihilation not at a neutral point, but by an enhanced dissipation of a field-aligned current. The field configuration is related both to its origin and to the extensive theory and laboratory experiments concerned with this configuration in magnetic fusion. The magnetic field model is applied to the August 4 flare. It is shown how the plasma heating in the annihilation region balanced by thermal conduction leads to a plasma temperature of about 20 million deg K.
Colgate, S. A.↗
Phenomenological model describing orificed, hollow cathode operation
(Previously cited in issue 12, p. 1962, Accession no. A81-29564)
Siegfried, D. E.↗
Simulation as an aid to phenomenological modeling
Certain difficulties arise in connection with the development of models for the prediction of turbulent flow characteristics. The present paper is mainly concerned with an approach which provides an aid in such development work by making it possible to test Reynolds average turbulence models. This approach is based on full and large eddy simulations of turbulent flows. Attention is given to details regarding Reynolds average turbulence models, mixing length models, two equation (k-epsilon) models, Reynolds stress models, and passive scalars. It is shown that a great deal about modeling can be learned from simulations of turbulent flows. There is reason to believe that these results will lead to improvements in the quality of predictions of turbulent flows.
Ferziger, J. H.↗
Phenomenological modeling of hardening and thermal recovery in metals
Modeling of hardening and thermal recovery in metals is considered within the context of unified elastic-viscoplastic theories. Specifically, the choices of internal variables and hardening measures, and the resulting hardening response obtained by incorporating saturation-type evolution equations into two general forms of the flow law are examined. Based on the analytical considerations, a procedure for delineating directional and isotropic hardening from uniaxial hardening data has been developed for the Bodner-Partom model and applied to a nickel-base superalloy, B1900 + Hf. Predictions based on the directional hardening properties deduced from the monotonic loading data are shown to be in good agreement with results of cyclic tests.
Chan, K. S.↗
Experimental validation of a phenomenological model of the plasma contacting process
A preliminary model of the plasma coupling process is presented which describes the phenomena observed in ground-based experiments using a hollow cathode plasma contactor to collect electrons from a dilute ambient plasma under conditions where magnetic field effects can be neglected. The locations of the double-sheath region boundaries are estimated and correlated with experimental results. Ion production mechanisms in the plasma plume caused by discharge electrons from the contactor cathode and by electrons streaming into the plasma plume through the double-sheath from the ambient plasma are also discussed.
Williams, John D.↗
A parametric study of slow dynamic nonlinear elasticity with comparisons to models
Several phenomenological models that aspire to quantitative description of anomalous nonlinear mesoscopic elasticity are reviewed and compared with laboratory measurements. This class of nonlinearity, best known perhaps for slow dynamics and aging, is seen widely in imperfectly consolidated granular solids but is not well understood. Typical slow dynamic tests show that a modest conditioning oscillatory "pump" strain depresses material stiffness, which then recovers like the logarithm of time after conditioning ceases. Several phenomenological models based on physical arguments have been proposed that predict the material stiffness response to arbitrary pump strain histories during conditioning and recovery. Approximate closed form and numerical solutions to the models are presented that predict the quantitative influence of three key pump parameters: the pump's strain amplitude, the pump's strain rate, and the pump’s duration. Laboratory measurements on Berea sandstone, concrete and a confined single aluminum bead find that slow dynamic responses are linear in pump strain and independent of pump frequency. Measurements also show that, after pump-off, stiffness recovers over times far longer than the pump duration. These observations and others are compared to model predictions. One of the considered models, based on a picture of fast brittle damage and slow healing, successfully matches all these behaviors.
36 MATERIALS SCIENCE↗
Varied phenomenology of models displaying dynamical large-deviation singularities
Singularities of dynamical large-deviation functions are often interpreted as the signal of a dynamical phase transition and the coexistence of distinct dynamical phases, by analogy with the correspondence between singularities of free energies and equilibrium phase behavior. Here we study models of driven random walkers on a lattice. These models display large-deviation singularities in the limit of large lattice size, but the extent to which each model's phenomenology resembles a phase transition depends on the details of the driving. We also compare the behavior of ergodic and nonergodic models that present large-deviation singularities. Finally, we argue that dynamical large-deviation singularities indicate the divergence of a model timescale, but not necessarily one associated with cooperative behavior or the existence of distinct phases.
74 ATOMIC AND MOLECULAR PHYSICS↗
A phenomenological wobbling model for isolated pulsars and the braking index
ABSTRACT An isolated pulsar is a rotating neutron star possessing a very high magnetic dipole moment, thus providing a powerful radiating mechanism. These stars loose rotational energy E through various processes, including a plasma wind originating from a highly magnetized magnetosphere and the emission of magnetic dipole radiation (MDR). Such phenomena produce a time decreasing angular velocity Ω(t) of the pulsar that is usually quantified in terms of its braking index. Although these mechanisms are widely acknowledged as the primary drivers of the spin evolution of isolated pulsars, it is plausible that other contributing factors influencing this effect have yet to be comprehensively investigated. Most of young isolated pulsars present a braking index different from that given by the MDR and plasma wind processes. Working in the weak field (Newtonian) limit, we take in this work a step forward in describing the evolution of such a system by allowing the star’s shape to wobble around an ellipsoidal configuration as a backreaction effect produced by its rotational deceleration. It is assumed that an internal damping of the oscillations occurs, thus introducing another form of energy loss in the system, and this phenomenon may be related to the deviation of the braking index from the models based on $\dot{E} \sim -\Omega ^4$ predictions. Numerical calculations suggest that the average braking index for typical isolated pulsars can be thus explained by a simple phenomenological model.
Araujo, E. C. A. (ORCID:0000000213520879)↗
A Phenomenological Durability Model for Environmental Barrier Coating Systems Subjected to Steam Oxidation
Environmental barrier coatings (EBC) are used to protect the silicon carbide fiber reinforced silicon carbide matrix (SiC/SiC) ceramic matrix composites (CMC) from rapid surface recession due to volatization by water vapor in a steam oxidation environment. A phenomenological modeling approach is outlined to estimate the durability of a given EBC system when exposed to steam oxidation. The report provides a step-by-step procedure to estimate the life of a given EBC system subjected to thermal loads only. Once calibrated, the methodology can predict the critical thickness of an oxide layer that will cause failure initiation/spallation as well as the remaining strength or stress that the EBC system can take for a given oxide layer thickness
Subodh K Mital↗
Interlayer fusion bonding of semi-crystalline polymer composites in extrusion deposition additive manufacturing
This work focuses on the evolution of interlayer fracture toughness properties of fiber-reinforced, semi-crystalline polymers in the extrusion deposition additive manufacturing (EDAM) process. Further, this work bridges the gap between the additive process conditions (time-temperature history) and the effective layer-to-layer fracture properties developed within a printed component. This is the first step to predict delamination that can occur during printing, during cooling to room temperature after printing, and during service performance of an additively manufactured geometry. A phenomenological model is developed for fusion bonding of semi-crystalline polymer matrix composites by coupling the interdiffusion of polymer chains with the evolution of polymer crystallinity. While the interdiffusion is captured by reptation theory of polymer dynamics, the evolution of crystallinity is modeled by phenomenological crystallization kinetics and crystal melting dynamics. Further, a methodology is developed to determine the critical strain energy release rate, G IC of the interlayer interface and experiments are conducted utilizing the double cantilever beam fracture test geometry. In conclusion, predictions of GIC as a function of thermal history are compared with experiments.
36 MATERIALS SCIENCE↗
Coherent anti-Stokes Raman spectroscopic modeling for combustion diagnostics
The status of modelling the coherent anti-Stokes Raman spectroscopy (CARS) spectra of molecules important in combustion, such as N2, H2O, and CO2, is reviewed. It is shown that accurate modelling generally requires highly precise knowledge of line positions and reasonable estimates of Raman linewidths, and the sources of these data are discussed. CARS technique and theory is reviewed, and the status of modelling the phenomenon of collisional narrowing at pressures well above atmospheric for N2, H2O, and CO2 is described. It is shown that good agreement with experiment can be achieved using either the Gordon rotational diffusion model or phenomenological models for inelastic energy transfer rates.
Hall, R. J.↗
Three-Dimensional High Fidelity Progressive Failure Damage Modeling of NCF Composites
Performance prediction of off-axis laminates is of significant interest in designing composite structures for energy absorption. Phenomenological models available in most of the commercial programs, where the fiber and resin properties are smeared, are very efficient for large scale structural analysis, but lack the ability to model the complex nonlinear behavior of the resin and fail to capture the complex load transfer mechanisms between the fiber and the resin matrix. On the other hand, high fidelity mesoscale models, where the fiber tows and matrix regions are explicitly modeled, have the ability to account for the complex behavior in each of the constituents of the composite. However, creating a finite element model of a larger scale composite component could be very time consuming and computationally very expensive. In the present study, a three-dimensional mesoscale model of non-crimp composite laminates was developed for various laminate schemes. The resin material was modeled as an elastic-plastic material with nonlinear hardening. The fiber tows were modeled with an orthotropic material model with brittle failure. In parallel, new stress based failure criteria combined with several damage evolution laws for matrix stresses were proposed for a phenomenological model. The results from both the mesoscale and phenomenological models were compared with the experiments for a variety of off-axis laminates.
Aitharaju, Venkat↗
Comprehensive silicon solar cell computer modeling
Phenomenological submodels of the optical absorption coefficient of solar cells and of the optimum grid contact design are presented and discussed.
Lamorte, M. F.↗
Quasisteady evolution of fast neutrino-flavor conversions
In astrophysical environments such as core-collapse supernovae (CCSNe) and binary neutron star mergers (BNSMs), neutrinos potentially experience substantial flavor mixing due to the refractive effects of neutrino self-interactions. Determining the survival probability of neutrinos in asymptotic states is paramount to incorporating flavor conversions’ effects in the theoretical modeling of CCSN and BNSM. Some phenomenological schemes have shown good performance in approximating asymptotic states of fast neutrino-flavor conversions (FFCs), known as one of the collective neutrino oscillation modes induced by neutrino self-interactions. However, a recent study showed that they would yield qualitatively different asymptotic states of FFC if the neutrino number is forced to evolve. It is not yet fully understood why the canonical phenomenological models fail to predict asymptotic states. In this paper, we perform detailed investigations through numerical simulations and then provide an intuitive explanation with a quasihomogeneous analysis. Based on the analysis, we propose a new phenomenological model, in which the quasisteady evolution of FFCs is analytically determined. The model also allows us to express the convolution term of spatial wave number as a concise form, which corresponds to useful information on analyses for the nonlinear feedback from small-scale flavor conversions to large-scale ones. Furthermore, our model yields excellent agreement with numerical simulations, which lends support to our interpretation.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Application of machine learning to estimate fireball characteristics and their uncertainty from infrared spectral data
Experiments or events involving high explosives (HE) can be monitored remotely by infrared (IR) sensors to gather information about the configuration or materials involved in the device. Researchers at the Air Force Institute of Technology (AFIT) developed a phenomenological model for HE fireball spectra in the IR range that allows for parameters to be extracted from Fourier transform infrared (FTIR) data. This model includes parameters tied to physical characteristics of the fireball: temperature, size, soot, and gas concentrations. Previous works have sought to recover these parameters by the fitting of either whole spectra or select wavenumber bands to this phenomenological model. Difficulties arise due to the complex relationships between the parameters to be fit. Uncertainty quantification of the estimated fireball parameters is also problematic since HE experiments do not have any ground truth information on the parameters. It is suggested that artificial neural network (ANN) based approaches may be well suited to this problem, because of their ability to capture complex and highly nonlinear relationships. As such, this work seeks to explore the efficacy of deep artificial neural networks (DNNs) for this problem of parameter recovery from spectra and to also investigate the uncertainty of recovering the fireball parameters from FTIR data. Networks are designed using the hyperparameter optimization tool Hyperopt and trained/tested on artificial data generated using the phenomenological model developed by AFIT. The results of applying the network to the artificial data set are compared to a physics-based band approach that uses a selected number of bands based on their physical properties. Information on the uncertainty of estimating parameters from remotely sensed experimental data is obtained by treating the accuracy of the DNN model on artificial data as an upper bound and by examining the impact of emissivity due to soot on parameter estimation error; the results for artificial data are likely to be optimistic as compared to recovering parameters from experimental data.
42 ENGINEERING↗
Analytic MHD Theory for Earth's Bow Shock at Low Mach Numbers
A previous MHD theory for the density jump at the Earth's bow shock, which assumed the Alfven M(A) and sonic M(s) Mach numbers are both much greater than 1, is reanalyzed and generalized. It is shown that the MHD jump equation can be analytically solved much more directly using perturbation theory, with the ordering determined by M(A) and M(s), and that the first-order perturbation solution is identical to the solution found in the earlier theory. The second-order perturbation solution is calculated, whereas the earlier approach cannot be used to obtain it. The second-order terms generally are important over most of the range of M(A) and M(s) in the solar wind when the angle theta between the normal to the bow shock and magnetic field is not close to 0 deg or 180 deg (the solutions are symmetric about 90 deg). This new perturbation solution is generally accurate under most solar wind conditions at 1 AU, with the exception of low Mach numbers when theta is close to 90 deg. In this exceptional case the new solution does not improve on the first-order solutions obtained earlier, and the predicted density ratio can vary by 10-20% from the exact numerical MHD solutions. For theta approx. = 90 deg another perturbation solution is derived that predicts the density ratio much more accurately. This second solution is typically accurate for quasi-perpendicular conditions. Taken together, these two analytical solutions are generally accurate for the Earth's bow shock, except in the rare circumstance that M(A) is less than or = 2. MHD and gasdynamic simulations have produced empirical models in which the shock's standoff distance a(s) is linearly related to the density jump ratio X at the subsolar point. Using an empirical relationship between a(s) and X obtained from MHD simulations, a(s) values predicted using the MHD solutions for X are compared with the predictions of phenomenological models commonly used for modeling observational data, and with the predictions of a modified phenomenological model proposed recently. The similarities and differences between these results are illustrated using plots of X and a(s) predicted for the Earth's bow shock. The plots show that the new analytic solutions agree very well with the exact numerical MHD solutions and that these MHD solutions should replace the corresponding phenomenological relations in comparisons with data. Furthermore, significant differences exist between the standoff distances predicted at low M(A) using the MHD models versus those predicted by the new modified phenomenological model. These differences should be amenable to observational testing.
Grabbe, Crockett L.↗