Consistent Physical Model Research Articles

Reconstructing AGN X-ray spectral parameter distributions with Bayesian methods

We present a new Bayesian method for reconstructing the parent distributions of X-ray spectral parameters of active galactic nuclei (AGN) in large surveys. The method uses the probability distribution function (PDF) of posteriors obtained by fitting a consistent physical model to each object with a Bayesian method. The PDFs are often broadly distributed and may present systematic biases, such that naive point estimators or even some standard parametric modeling are not sufficient to reconstruct the parent population without obvious bias. Our method uses a transfer function computed from a large realistic simulation with the same selection as in the actual sample to redistribute the stacked PDF and then forward-fit a nonparametric model to it in a Bayesian way, so that the biases in the PDFs are properly taken into account. In this way, we are able to accurately reconstruct the parent distributions. We apply our spectral fitting and population inference methods to the XMM-COSMOS survey as a pilot study. For the 819 AGN detected in the COSMOS field, 663 (81%) of which have spectroscopic redshifts (spec-z) and the others high-quality photometric redshifts (photo-z), we find prominent bi-modality with widely separated peaks in the distribution of the absorbing hydrogen column density (NH) and an indication that absorbed AGN have harder photon indices. A clear decreasing trend of the absorbed AGN fraction versus the intrinsic 2–10 keV luminosity is observed, but there is no clear evolution in the absorbed fraction with redshift. Our method is designed to be readily applicable to large AGN samples such as the XXL survey, and eventually eROSITA.

Physical and Mathematical Model of Relaxation Filtration of Undergrounds Water

Earlier, a number of publications presented the results of an experimental study of the free oscillations of the piezometric level of groundwater (pressure in a liquid) in wells with natural frequencies. In this case, the oscillations were initiated by a pulsed action on the aquifer through disturbing wells. The same publications proposed a theoretical interpretation of the established phenomenon. However, a critical analysis of these theoretical constructions showed their incorrectness. Accordingly, a consistent physical and mathematical model of groundwater relaxation filtration is proposed in this work, which provides a theoretical basis for the description and interpretation of the free oscillations of the piezometric level in a disturbing well with natural frequencies. Thus, the proposed physical and mathematical model made it possible to conclude that it is impossible to cause resonance during the initiation of free oscillations of the piezometric groundwater level. An analysis of the experimental data based on the model showed that the implementation of methodological developments based on the theory of relaxation filtration is possible and expedient only on fundamentally different, in comparison with existing, technical and methodological approaches to the experimental study of wave propagation in aquifers.

Hot deformation and dynamic α-globularization of a Ti-17 alloy: Consistent physical model

Ti-17 is exposed to microstructural modifications during thermomechanical treatment. In this work, we focus on the characterisation, analysis and modelling of the modifications during plastic deformation in the one phase and two phases domain. Hot compression tests are carried out between 810 °C and 970 °C and at 0.001 s−1 to 10 s−1 up to 0.85 strain. Metallographic observations and quantifications are done using SEM-EBSD. A physically-based model is developed to describe the deformation mechanisms: dynamic recovery, followed by continuous dynamic recrystallisation, and dynamic globularization of the α-phase. Flow stresses, dislocation densities, and sizes of both phases are predicted as a function of strain rate and temperature for different starting microstructures. The thickness and aspect ratio of the α-phase is predicted as well as the globularization fraction. The flow softening in the α + β domain is attributed to a change in the load transfer mechanism between α and β-phases from isostrain to isostress due to the dynamic globularization of the α-phase. High strain rates promote the formation of finer subgrains of β and less globularization of α-phase. Moreover, cDRX starts at larger strains in the β-domain and is more advanced already at moderate strains for the deformation in the α + β domain.

Sound insulation design of the thin partitions on the base of concentrated parameters model

Introduction. The theoretical and practical approach on the base of the discrete parameter's method to the acoustic insulation of the thin partitions by Candidate of Science, Prof. Zakharov A.V. is given in this issue. The method allowed to develop a logically conclusive and consistent physical airborne sound insulation model for one-layered massive and light partitions either. This issue concentrates on providing of the engineer calculation technique of the sound insula-tion for the thin partitions and, also, on comparison of the technique's results with the computations by the current normative documents.
 Materials and methods. The application of the same “Mass Action Law's” formula both for the normal and the oblique noise wave's incidence on the sound isolating plate, regardless the sound waves angles, is mathematically and physically approved. The essence of the concentrated parameters, such as concentrated and reduced material's mass, is revealed. The equations of momentum conservation law and kinetic energy conservation are used to obtain the coefficient of the oscillation velocity transmission. The formulas for airborne sound insulation at the diapasons before and after the sound wave's coincidence frequency are written.
 Results. The damping air property's influence on the thin partition's sound insulation is considered, and it's formulas are represented. The formulas for taking into account the reduction of sound insulation at the resonances in sound protective slab or in a partition are also given. The general equation for the thin partition's sound insulation by the method of localized (discrete) parameters are derived. The example of detailed calculation of the sound isolation of the thin asbestos-cement partition is demonstrated. The comparison between the medial three octave deviations of the sound isolation values and the experimental results in case of the SP (Russian normative document) method and in case of the introduced author's method for the different construction materials is represented.
 Conclusions. The proposedsound insulation calculation method for the thin light partitions, which is based on the concentrated parameters model, gives very close to experiments results. So, it enables to find the insulation figures across the entire standard frequency range, according to the initial physical and technical materials' and constructions' features.

New insight on the far-UV SED and He ii emission from low metallicity galaxies

AbstractUnderstanding the ionizing spectrum of low-metallicity galaxies is of great importance for modeling and interpreting emission line observations of early/distant galaxies.Although a wide suite of stellar evolution, atmosphere, population synthesis, and photoionization models, taking many physical processes into account now exist, all models face a common problem: the inability to explain the presence of nebular Heii emission, which is observed in many low metallicity galaxies, both in UV and optical spectra. Several possible explanations have been proposed in the literature, including Wolf-Rayet (WR) stars, binaries, very massive stars, X-ray sources, or shocks. However, none has so far been able to explain the major observations.We briefly discuss the He ii problem, available empirical data, and observed trends combining X-ray, optical and other studies. We present a simple and consistent physical model showing that X-ray binaries could explain the long-standing nebular Heii problem. Our model, described in Schaerer et al. (2019), successfully explains the observed trends and strength of nebular He ii emission in large samples of low metallicity galaxies and in individual galaxies, which have been studied in detail and with multi-wavelength observations. Our results have in particular important implications for the interpretation of galaxy spectra in the early Universe, which will be obtained with upcoming and future facilities.

Regularities of Nanofocusing of the Electromagnetic Field of a Fractal Rough Surface

A consistent physical and mathematical model of the propagation of electromagnetic waves in an inhomogeneous medium with strong discontinuities of the electromagnetic field at the interface of two media, which is a rough surface, was developed. Mathematical modeling of rough surfaces and their profiles was carried out using fractal geometry, which allows us to display the topology of the object as close as possible to reality. For real heterogeneous rough structures, we have developed a through-counting method that takes into account the continuity of the total current at the interfaces of adjacent media, the effect of induced surface charge and surface current. This approach lets one avoid the necessity to set surface impedances depending on the structure of the field being determined and on the material properties.

Complete generalization of the Ayrton-Perry formula for beam-column buckling problems

The Ayrton-Perry (or Perry-Robertson) formula based stability resistance model (APF) is very popular in steel structural design standards. Although the original version of the model is more than 100 years old, it is still frequently used and continuously researched due to its simplicity and adaptability. The original and most widely accepted version of the APF is valid only for the flexural buckling of compression members yielding the basic formulation of the column buckling curves of several structural design codes. Recently there were more successful attempts for the extension of the APF type resistance model for other buckling modes such as torsional buckling or lateral-torsional buckling. The paper continues this research by deriving a complete closed-form universal APF type solution for steel beam-column stability problems. Rigorous mathematical solution is given for the so-called “fundamental case” which is defined by a simply supported prismatic beam-column with arbitrary cross-section subjected to uniform compression and biaxial bending. The exact interpretation and the universal form of the member slenderness, imperfection and reduction factors are presented for all possible buckling cases. The results of the paper can widen significantly the field of applicability of APF based design methods providing a theoretically consistent physical model for the beam-column stability problems.

An Analytical Lidar Sensor Model Based on Ray Path Information

Two core competencies of a mobile robot are to build a map of the environment and to estimate its own pose on the basis of this map and incoming sensor readings. To account for the uncertainties in this process, one typically employs probabilistic state estimation approaches combined with a model of the specific sensor. Over the past years, lidar sensors have become a popular choice for mapping and localization. However, many common lidar models perform poorly in unstructured, unpredictable environments, they lack a consistent physical model for both mapping and localization, and they do not exploit all the information the sensor provides, e.g. out-of-range measurements. In this paper, we introduce a consistent physical model that can be applied to mapping as well as to localization. It naturally deals with unstructured environments and makes use of both out-of-range measurements and information about the ray path. The approach can be seen as a generalization of the well-established reflection model, but in addition to counting ray reflections and traversals in a specific map cell, it considers the distances that all rays travel inside this cell. We prove that the resulting map maximizes the data likelihood and demonstrate that our model outperforms state-of-the-art sensor models in extensive real-world experiments.

Modelling deuterium release from tungsten after high flux high temperature deuterium plasma exposure

Tungsten is a primary candidate for plasma facing materials for future fusion devices. An important safety concern in the design of plasma facing components is the retention of hydrogen isotopes. Available experimental data is vast and scattered, and a consistent physical model of retention of hydrogen isotopes in tungsten is still missing. In this work we propose a model of non-equilibrium hydrogen isotopes trapping under fusion relevant plasma exposure conditions. The model is coupled to a diffusion-trapping simulation tool and is used to interpret recent experiments involving high plasma flux exposures. From the computational analysis performed, it is concluded that high flux high temperature exposures (T = 1000 K, flux = 1024 D/m2/s and fluence of 1026 D/m2) result in generation of sub-surface damage and bulk diffusion, so that the retention is driven by both sub-surface plasma-induced defects (bubbles) and trapping at natural defects. On the basis of the non-equilibrium trapping model we have estimated the amount of H stored in the sub-surface region to be ∼10−5 at−1, while the bulk retention is about 4 × 10−7 at−1, calculated by assuming the sub-surface layer thickness of about 10 μm and adjusting the trap concentration to comply with the experimental results for the integral retention.

Rotation, inflation, and lithium in the Pleiades

The rapidly rotating cool dwarfs of the Pleiades are rich in lithium relative to their slowly rotating counterparts. Motivated by observations of inflated radii in young, active stars, and by calculations showing that radius inflation inhibits pre-main sequence (pre-MS) Li destruction, we test whether this pattern could arise from a connection between stellar rotation rate and radius inflation on the pre-MS. We demonstrate that pre-MS radius inflation can efficiently suppress lithium destruction by rotationally induced mixing in evolutionary models, and that the net effect of inflation and rotational mixing is a pattern where rotation correlates with lithium abundance for $M_{*} < {\rm M}_{\odot}$, and anti-correlates with lithium abundance for $M_{*} > {\rm M}_{\odot}$, similar to the empirical trend in the Pleiades. Next, we adopt different prescriptions for the dependence of inflation on rotation, and compare their predictions to the Pleiades lithium/rotation pattern. We find that if a connection between rotation and radius inflation exists, then the important qualitative features of this pattern naturally and generically emerge in our models. This is the first consistent physical model to date that explains the Li--rotation correlation in the Pleiades. We discuss plausible mechanisms for inducing this correlation and suggest an observational test using granulation.

Bloch-Redfield equations for modeling light-harvesting complexes.

We challenge the misconception that Bloch-Redfield equations are a less powerful tool than phenomenological Lindblad equations for modeling exciton transport in photosynthetic complexes. This view predominantly originates from an indiscriminate use of the secular approximation. We provide a detailed description of how to model both coherent oscillations and several types of noise, giving explicit examples. All issues with non-positivity are overcome by a consistent straightforward physical noise model. Herein also lies the strength of the Bloch-Redfield approach because it facilitates the analysis of noise-effects by linking them back to physical parameters of the noise environment. This includes temporal and spatial correlations and the strength and type of interaction between the noise and the system of interest. Finally, we analyze a prototypical dimer system as well as a 7-site Fenna-Matthews-Olson complex in regards to spatial correlation length of the noise, noise strength, temperature, and their connection to the transfer time and transfer probability.

Simulation of Yield Strength in Allvac&lt;sup&gt;®&lt;/sup&gt; 718Plus&lt;sup&gt;TM&lt;/sup&gt;

In the present study, we describe a comprehensive and consistent physical model for the yield strength change in Allvac® 718PlusTM caused by precipitation strengthening. The model incorporates the effect of different shearing and non-shearing mechanisms with respect to atomic continuity between the lattices of precipitates and matrix. We demonstrate that coherency and anti-phase boundary effects are the major strengthening mechanisms in this alloy. The final yield strength of Allvac® 718PlusTM during aging is investigated using the thermo-kinetic software MatCalc. The calculated final yield strength evolution is consistent with experimental results.

A Unified Channel Thermal Noise Model for Short Channel MOS Transistors

A unified channel thermal noise model valid in all operation regions is presented for short channel MOS transistors. It is based on smooth interpolation between weak and strong inversion models and consistent physical model including velocity saturation, channel length modulation, and carrier heating. From testing for noise benchmark and comparing with published noise data, it is shown that the proposed noise model could be useful in simulating the MOSFET channel thermal noise in all operation regions.

FORECASTING COSMOLOGICAL PARAMETER CONSTRAINTS FROM NEAR-FUTURE SPACE-BASED GALAXY SURVEYS

The next generation of space-based galaxy surveys are expected to measure the growth rate of structure to about a percent level over a range of redshifts. The rate of growth of structure as a function of redshift depends on the behaviour of dark energy and so can be used to constrain parameters of dark energy models. In this work we investigate how well these future data will be able to constrain the time dependence of the dark energy density. We consider parameterizations of the dark energy equation of state, such as XCDM and wCDM, as well as a consistent physical model of time-evolving scalar field dark energy, \phi CDM. We show that if the standard, specially-flat cosmological model is taken as a fiducial model of the Universe, these near-future measurements of structure growth will be able to constrain the time-dependence of scalar field dark energy density to a precision of about 10%, which is almost an order of magnitude better than what can be achieved from a compilation of currently available data sets.

Application of the Mole-8.5 supercomputer: Probing the whole influenza virion at the atomic level

Discrete computer simulations are quite helpful in understanding dynamic structures in complex systems. Recently, using the Mole-8.5 supercomputer and molecular dynamics simulations as a microscope, we simulated the dynamic structure of a whole H1N1 influenza virion in solution for the first time at the atomic level. In total, 300 million atoms in a periodic cube with an edge length of 148.5 nm were simulated. Using 288 low level hybrids with 1728 C2050 GPUs and a software package developed specifically for the hardware, the simulation executed 770 ps/d with an integration time step of 1 fs, and analyzed the dynamic structure. With the tremendous computational power of GPUs, efficient software packages for various hardware designs, and consistent physical models, more challenging applications will be carried out in the near future.

Reconstruction of solar spectral irradiance since the Maunder minimum

Solar irradiance is the main external driver of the Earth's climate. Whereas the total solar irradiance is the main source of energy input into the climate system, solar UV irradiance exerts control over chemical and physical processes in the Earth's upper atmosphere. The time series of accurate irradiance measurements are, however, relatively short and limit the assessment of the solar contribution to the climate change. Here we reconstruct solar total and spectral irradiance in the range 115–160,000 nm since 1610. The evolution of the solar photospheric magnetic flux, which is a central input to the model, is appraised from the historical record of the sunspot number using a simple but consistent physical model. The model predicts an increase of 1.25 W/m2, or about 0.09%, in the 11‐year averaged solar total irradiance since the Maunder minimum. Also, irradiance in individual spectral intervals has generally increased during the past four centuries, the magnitude of the trend being higher toward shorter wavelengths. In particular, the 11‐year averaged Ly‐α irradiance has increased by almost 50%. An exception is the spectral interval between about 1500 and 2500 nm, where irradiance has slightly decreased (by about 0.02%).

Electrodynamics of layered media with boundary conditions corresponding to the total-current continuum

A consistent physical and mathematical model of propagation of electromagnetic waves in layered media, in which the induced surface charge is not explicitly taken into account, has been constructed on the basis of Maxwell equations, the total-current continuum equation, and the Dirichlet theorem. A numerical method of through counting for solving the system of equations defining layered media has been developed and substantiated. Examples of numerical simulation of the propagation of an electromagnetic wave in a two-dimensional cellular structure and the propagation of a modulated signal in a one-dimensional layered medium on condition that the current flows at the interfaces between the adjacent media are dependent are presented.

Observation of surface enhanced IR absorption coefficient in alkanethiol based self-assembled monolayers on GaAs(001)

Alkanethiol self-assembled monolayers (SAMs) of various methylene group chain lengths [HS–(CH2)n–CH3] (n=9,11,13,15,17) were fabricated on the GaAs(001) surface followed by characterization using Fourier transform infrared spectroscopy. Modal analysis of the CH2 stretching mode region (2800–3000 cm−1) showed that linear scaling of the n-dependent factors accurately reproduced the spectral data, supporting a chain-length consistent physical model upon which a measurement of the absorption coefficient was based. Evaluated from the linearity of the absorbance data, a peak coefficient of 3.5×104 cm−1 was obtained and a domain for ordered self-assembly was assigned for values n&amp;gt;9. Compared with measurements of the absorption coefficient made in the liquid phase, the SAM phase coefficient was determined to be about six times greater. This enhancement effect is discussed in terms of contributions relating to the locally ordered environment and is largely attributed to the chemical properties of the interface. We believe this to be the first demonstration of IR spectral enhancement of a molecular species chemisorbed on the semiconductor surface.

Acoustic Kramers–Kronig relations in the ultrasonic frequency band.

Physical manifestations of the principle of causality, Kramers–Kronig (KK) relations, have proven to be adaptable to a wide array of tasks which include measuring fundamental material parameters, establishing the consistency of laboratory data, and building causally consistent physical models. This talk is concerned with the use of finite bandwidth KK relations between and among the components and derivatives of the complex wavenumber in the low megahertz ultrasound band. Special focus is given to their applicability to data from suspensions of resonant scatterers and media exhibiting attenuation with a power‐law dependence on frequency. One recent development is the validation of a KK relation for the direct prediction of the group velocity from the attenuation coefficient, which has demonstrated great utility for suspensions with resonant type dispersion. The roles of KK analysis in other recent issues are also discussed, including the apparent negative dispersion in cancellous bone.

Reconstruction of solar irradiance using the Group sunspot number

We present a reconstruction of total solar irradiance since 1610 to the present based on variations of the surface distribution of the solar magnetic field. The latter is calculated from the historical record of the Group sunspot number using a simple but consistent physical model. Our model successfully reproduces three independent data sets: total solar irradiance measurements available since 1978, total photospheric magnetic flux from 1974 and the open magnetic flux since 1868 (as empirically reconstructed from the geomagnetic aa-index). The model predicts an increase in the total solar irradiance since the Maunder Minimum of about 1.3 Wm −2.