Determination Of Density Profile Research Articles

Design and characterization of the polychromators for JT-60SA Thomson scattering systems

The Thomson scattering diagnostics are fundamental for a reliable determination of electron density and temperature profiles in Tokamak experiments. In JT-60SA, two systems are currently under development: one is dedicated to the core plasma region, the other to the edge region. They aim to measure the Te and ne profiles with a precision better than 10% and 5%, respectively, at an electron density of 1019 m−3 and with an electron temperature ranging from 10 eV up to 10 keV for the edge system and from 100 eV to 30 keV for the core one. The polychromators design, based on interference filters and APD detectors, is critical to achieve such performance. Each polychromator comprises 6 spectral channels measuring from 1064 nm down to 500 nm for the core system and to 660 nm for the edge one. The design aims at maximizing the efficiency and minimizing the noise under different plasma conditions. About 100 polychromators are manufactured by G.N.R.srl under an F4E contract. In this work, we present the polychromators design and performance. The key features of the optical design and of the mechanical structure are discussed. State of the art interference filters and APD detectors with custom electronics are described. Overall optical transmission measurements of the assembled polychromators and spectral channels calibration are then presented. More specific studies of the APD electrical noise and temperature dependence are discussed. The transmission functions are finally used to predict the error expected in the determination of the electron temperature and density under different levels of plasma light intensity.

A probabilistic deep learning model to distinguish cusps and cores in dwarf galaxies

ABSTRACT Numerical simulations within a cold dark matter (DM) cosmology form haloes whose density profiles have a steep inner slope (‘cusp’), yet observations of galaxies often point towards a flat central ‘core’. We develop a convolutional mixture density neural network model to derive a probability density function (PDF) of the inner density slopes of DM haloes. We train the network on simulated dwarf galaxies from the NIHAO and AURIGA projects, which include both DM cusps and cores: line-of-sight velocities and 2D spatial distributions of their stars are used as inputs to obtain a PDF representing the probability of predicting a specific inner slope. The model recovers accurately the expected DM profiles: $\sim 82{{\ \rm per\ cent}}$ of the galaxies have a derived inner slope within ±0.1 of their true value, while $\sim 98{{\ \rm per\ cent}}$ within ±0.3. We apply our model to four Local Group dwarf spheroidal galaxies and find results consistent with those obtained with the Jeans modelling based code GravSphere: the Fornax dSph has a strong indication of possessing a central DM core, Carina and Sextans have cusps (although the latter with large uncertainties), while Sculptor shows a double peaked PDF indicating that a cusp is preferred, but a core cannot be ruled out. Our results show that simulation-based inference with neural networks provide a innovative and complementary method for the determination of the inner matter density profiles in galaxies, which in turn can help constrain the properties of the elusive DM.

Adsorption of oleic acid on magnetite facets

The microscopic understanding of the atomic structure and interaction at carboxylic acid/oxide interfaces is an important step towards tailoring the mechanical properties of nanocomposite materials assembled from metal oxide nanoparticles functionalized by organic molecules. We have studied the adsorption of oleic acid (C17H33COOH) on the most prominent magnetite (001) and (111) crystal facets at room temperature using low energy electron diffraction, surface X-ray diffraction and infrared vibrational spectroscopy complemented with molecular dynamics simulations used to infer specific hydrogen bonding motifs between oleic acid and oleate. Our experimental and theoretical results give evidence that oleic acid adsorbs dissociatively on both facets at lower coverages. At higher coverages, the more pronounced molecular adsorption causes hydrogen bond formation between the carboxylic groups, leading to a more upright orientation of the molecules on the (111) facet in conjunction with the formation of a denser layer, as compared to the (001) facet. This is evidenced by the C=O double bond infrared line shape, in depth molecular dynamics bond angle orientation and hydrogen bond analysis, as well as X-ray reflectivity layer electron density profile determination. Such a higher density can explain the higher mechanical strength of nanocomposite materials based on magnetite nanoparticles with larger (111) facets.

On the determination of ionospheric electron density profiles using multi-frequency riometry

Abstract. Radio wave absorption in the ionosphere is a function of electron density, collision frequency, radio wave polarisation, magnetic field and radio wave frequency. Several studies have used multi-frequency measurements of cosmic radio noise absorption to determine electron density profiles. Using the framework of statistical inverse problems, we investigated if an electron density altitude profile can be determined by using multi-frequency, dual-polarisation measurements. It was found that the altitude profile cannot be uniquely determined from a “complete” measurement of radio wave absorption for all frequencies and two polarisation modes. This implies that accurate electron density profile measurements cannot be ascertained using multi-frequency riometer data alone and that the reconstruction requires a strong additional a priori assumption of the electron density profile, such as a parameterised model for the ionisation source. Nevertheless, the spectral index of the absorption could be used to determine if there is a significant component of hard precipitation that ionises the lower part of the D region, but it is not possible to infer the altitude distribution uniquely with this technique alone.

Determination of density profile by using the refractive index in a linearly salt-stratified fluid: An experiment for an advanced undergraduate laboratory

This paper describes a low-cost laboratory experiment designed to demonstrate the applicability of the refractive index to study stratification in fluids. The laser refractography method was applied to a linearly vertical density profile of a salt (NaCl) stratified water column. Next, an image processing procedure was performed, consisting of the binarization and edge detection of the laser beam and its subsequent second-order polynomial best fit. Quantitatively, the whole-field results compared well with the respective measured density profiles. This method allows one to obtain quantitative measurements of density profiles in stratified fluids with good accuracy, making it a suitable experimental method for laboratory demonstrations on fluids.

Direct determination of midplane background neutral density profiles from neutral particle analyzers

Here we present a new method that allows the determination of background neutral density profiles based on measurements from neutral particle analyzers (NPA). Bayesian optimization is used to obtain a reliable 5-parameter representation of the inferred profiles. The method has been benchmarked using forward modelling from FIDASIM against measured data. The systematic errors coming from assumptions made in the analysis were evaluated and they are lower than ≲5%. The new method has been tested using data from the ASDEX Upgrade tokamak. When using reconstructed neutral density profiles, good agreement is found between the measured NPA fluxes of neutralized fast ions with predictions based on TRANSP and FIDASIM. Moreover, a clear drop of neutral density is observed at the plasma boundary after edge localized mode (ELM) activity. As suggested by KN1D simulations, this drop is mainly due to an increase of scrape-off layer (SOL) ionization rate, resulting from higher SOL plasma densities and temperatures after the ELM crash. Moreover, the new method allows calculating the local plasma ionization source which will be important for future transport studies.

Brazilian cerrado species: wood characteristics

The characterization of wood anatomy and proprieties can provide subsidies for rational use of tree species. Enables, oftentimes, the definition of technological potential of wood - and wood products - through the assessment of quality information and also allows it´s correct identification, contributing to the timber production chain. The objective of this study was to contribute to the knowledge about wood properties of the Cerrado biome (Brazilian savanna) species trough the anatomical characterization and determination of density profile. Twenty trees species belonging to thirteen families occurring in Pirenópolis, Goiás and Brasília, Federal District, Brazil, was selected and radial samples were removed from the tree trunks at the DBH (1.30 m) in a non-destructive way using an incremental probe and a motorized extractor. The qualitative and quantitative anatomical parameters of vessels and fibers and the wood density were determined in the collected samples. Species presented fibers with mean values between 900.5 and 2052.9 µm for the length; 18.1 and 27.7 µm for the diameter; and 4.4 to 9.4 µm for the wall thickness. The species presented a variation in the vessel dimensions from 29.2 to 155.6 µm for the diameter; 17.7 to 32.5% for occupied area; and 2.6 to 165 to vessels.mm-2. The apparent density presented mean values between 0.36 and 1.21 g cm-3. The specie that presented the highest variation of wood density was A. fraxinifolium. According to the radial profiles two patterns of increasing and stable variation in the apparent density of the pith to bark were defined as a function of the wood anatomical characteristics.

Quantum chemical calculation based investigation of synergistic chelating between multiple hydroxyamide ligands and La3+ ion

In this paper, Density Functional Method at B3LYP/SDD level has been implemented in order to study enhanced interaction with lanthanum ion (La3+) in presence of multiple molecules of chelating ligand hydroxyamide (HA) for efficient extraction of lanthanides. Geometrical analysis of optimized structure, thermochemical analysis, potential energy surface study, electron density profile determination and localized orbital locator analysis, molecular orbital analysis, density of states analysis and vibrational spectral (IR spectra) analysis of the complex consisting of one, two, three, and four hydroxyamide ligands with lanthanum have been performed. Calculated geometrical parameters, interaction energies, change in Gibb’s free energy, change in enthalpy, change in entropy, and HOMO-LUMO study indicate the formation feasibility, as well as stability of the complexes, is enhanced while a higher number of hydroxyamide ligand interact with La(III). Structural analysis and vibrational analysis exhibit the formation of hydrogen bond-like non-bonded interaction between hydroxyamide and lanthanum. The orbital analysis provides the underlying reason for the bond formation between lanthanum and doubly bonded oxygen atom with carbon in the hydroxyamide ligand. The above study helps to analyse the interaction of lanthanum with hydroxyamide in order to design chelating extractant for efficient extraction of this rare earth element.

Towards ps-LIBS tritium measurements in W/Al materials

This communication deals with experimental results crucial for the sizing of picosecond LIBS measurements dedicated to the determination of tritium density profiles in the plasma facing components. Ablation properties in single pulse on aluminum (considered as a surrogate of beryllium) and tungsten have been obtained for 532 and 1064 nm picosecond laser pulses. Then, double pulse experiments have been performed to estimate the role played by the second pulse on the spectral radiance observed for lines representative of the ionization degree of the plasma and possible observation of low radiance lines.

Determination of Internal Density Profiles of Smart Acrylamide-Based Microgels by Small-Angle Neutron Scattering: A Multishell Reverse Monte Carlo Approach.

The internal structure of nanometric microgels in water has been studied as a function of temperature, cross-linker content, and level of deuteration. Small-angle neutron scattering from poly( N-isopropylmethacrylamide) (volume phase transition ≈ 44 °C) microgel particles of radius well below 100 nm in D2O has been measured. The intensities have been analyzed with a combination of polymer chain scattering and form-free radial monomer volume fraction profiles defined over spherical shells, taking polydispersity in size of the particles determined by atomic force microscopy into account. A reverse Monte Carlo optimization using a limited number of parameters was developed to obtain smoothly decaying profiles in agreement with the experimentally scattered intensities. The results are compared to the swelling curve of microgel particles in the temperature range from 15 to 55 °C obtained from photon correlation spectroscopy (PCS). In addition to hydrodynamic radii measured by PCS, our analysis provides direct information about the internal water content and gradients, the strongly varying steepness of the density profile at the particle-water interface, the total spatial extension of the particles, and the visibility of chains. The model has also been applied to a variation of the cross-linker content, N, N'-methylenebisacrylamide, from 5 to 15 mol %, providing insight on the impact of chain architecture and cross-linking on water uptake and on the definition of the polymer-water interface. The model can easily be generalized to arbitrary monomer contents and types, in particular mixtures of hydrogenated and deuterated species, paving the way to detailed studies of monomer distributions inside more complex microgels, in particular core-shell particles.

Synthetic helium beam diagnostic and underlying atomic data

We report on synthetic helium beam emission spectroscopy (BES) in fusion edge plasmas, as enabled by the 3D kinetic (neutral particle) transport code EIRENE. We also review and upgrade the underlying atomic helium data base, resorting to the most recent version of the Goto–Fujimoto collisional-radiative code and a recommended and publicly exposed reference cross section data set from an internationally coordinated (IAEA) evaluation activity. On the example of the Wendelstein 7-X (W7-X) stellarator, we use both the upgraded transport code and data base to simulate the penetration of and radiation from thermal helium used for BES in the island divertor region. This allows to evaluate the applicability of the diagnostic in different plasma backgrounds, simulated with the 3D edge plasma Monte Carlo code EMC3-EIRENE, and with different levels of refinement of underlying atomic data. The sensitivity of the diagnostic to the atomic data set—which is crucial for a quantitative determination of electron density and temperature profiles—is investigated and discussed, as well as the effects of p-He beam widening and correlated line-of-sight integration.

Vapour–liquid interfacial properties of n-alkanes

The vapour–liquid interfacial properties of linear alkanes (n-hexane, n-heptane, n-octane, n-nonane, and n-decane) were studied via the square gradient theory (SGT) and by molecular dynamics (MD) simulations. The objectives were the determination of interfacial density profiles, surface tensions, molecular orientations, and conformations via order parameters and radii of gyration, the self-diffusion coefficients and free energy profiles. The Soave-Redlich-Kwong (SRK) and Perturbed-Chain SAFT (PC-SAFT) equations of state (EoSs) were combined with SGT to correlate experimental surface tensions and to predict density profiles. SGT-EoSs and MD interfacial density profiles and interface thicknesses are very similar, especially at low reduced temperatures. MD simulations revealed that not only does the density change throughout the interface but also the average molecular orientation and conformation change. The interface can be roughly divided into three main regions: around the Gibbs dividing surface the molecules, on average, lie at the interface; and in the two regions close to the bulk phases they favour a non-parallel orientation. With respect to the self-diffusion coefficients, three different zones were also observed: close to the bulk phases, the diffusivity is a nonlinear function of the local density, whereas in the middle zone it is linear and coincides with the quasi-linear portion of the density profile. Free energy profiles were obtained via umbrella sampling technique, showing an increase of energy at the interfacial region. These profiles show a similar behaviour as the density profiles.

Stabilized density gradient theory algorithm for modeling interfacial properties of pure and mixed systems

Density gradient theory (DGT) allows fast and accurate determination of surface tension and density profile through a phase interface. Several algorithms have been developed to apply this theory in practical calculations. While the conventional algorithm requires a reference substance of the system, a modified “stabilized density gradient theory” (SDGT) algorithm is introduced in our work to solve DGT equations for multiphase pure and mixed systems. This algorithm makes it possible to calculate interfacial properties accurately at any domain size larger than the interface thickness without choosing a reference substance or assuming the functional form of the density profile. As part of DGT inputs, the perturbed chain statistical associating fluid theory (PC-SAFT) equation of state (EoS) was employed with the SDGT algorithm. PC-SAFT has excellent performance in predicting liquid phase properties as well as phase behaviors. The SDGT algorithm with the PC-SAFT EoS was tested and compared with experimental data for several systems. Numerical stability analyses were also included in each calculation to verify the reliability of this approach for future applications.

Investigation of Dual Polarization Reflectometry for Determination of Plasma Density and Magnetic Field in a Spherical Tokamak

The paper deals with dual polarization reflectometry as a method for determination of plasma density and poloidal magnetic field profile in low aspect ratio tokamaks. A numerical iteration algorithm is developed and solutions for integral equations for O- and X-modes are presented. The numerical calculations confirm the use of the iterative algorithm for effective reconstruction of the density and magnetic field profile.

Nanoscale structure of Si/SiO2/organics interfaces.

X-ray reflectivity measurements of increasingly more complex interfaces involving silicon (001) substrates reveal the existence of a thin low-density layer intruding between the single-crystalline silicon and the amorphous native SiO2 terminating it. The importance of accounting for this layer in modeling silicon/liquid interfaces and silicon-supported monolayers is demonstrated by comparing fits of the measured reflectivity curves by models including and excluding this layer. The inclusion of this layer, with 6-8 missing electrons per silicon unit cell area, consistent with one missing oxygen atom whose bonds remain hydrogen passivated, is found to be particularly important for an accurate and high-resolution determination of the surface normal density profile from reflectivities spanning extended momentum transfer ranges, now measurable at modern third-generation synchrotron sources.

MĚŘENÍ HUSTOTNÍHO PROFILU NEROVNOMĚRNĚ SLISOVANÉHO DŘEVA OSIKY OBECNÉ POMOCÍ PŘÍSTROJE X - RAY DENSE - LAB

The paper deals with the measuring of the density profile of unevenly pressed wood of European aspen (Populus tremula L.). The main aim of the work is to examine in an experimental way the possibilities of using the X – RAY DENSE – LAB laboratory equipment designed for the determination of density profiles of agglomerated and plied large-area materials. The work uses the X – RAY DENSE – LAB equipment to determine the density profile of the cross-section of unevenly pressed aspen wood, plasticized hydrothermically, without the presence of chemical substances. The work also presents calculations of the level of compression/densification in dependence on the density and it describes the factors that can influence the density profile of compressed/densified wood; at the same time, it presents the possible ways to determine the density profile in the cross-section. Further, it includes the creation of the methodology for sample preparation so that the results do not get distorted during measuring. It describes the preparation of sample pieces, the orientation of the anatomic structure, the methodology of pressing, air conditioning, sample preparation, their measuring and analysis. The paper also describes the theory and the principles of measuring with use of X – RAY DENSE – LAB and its calibration. The paper analyses the obtained results of density profiles and searches for and describes the causes of the uneven distribution of the density in the cross-section. It concludes by summarizing the results and recommending the procedure for future measuring.

Structural and morphological characterization of molecular beam epitaxy grown Si/Ge multilayer using x-ray scattering techniques

Si/Ge multilayers are of great technological importance as is evident from the research studies of the past two decades. Here, we have presented a method for the morphological and structural characterization of such MBE grown epitaxial Si/Ge superlattice structures using simultaneous analysis of x-ray reflectivity and x-ray diffraction data, respectively. The consistent analysis of the data collected in the Indian Beamline at Photon Factory Synchrotron have allowed for the determination of electron density and strain profile as a function of depth.

Determination of Electron Density Profiles and Area from Simulations of Undulating Membranes

The traditional method for extracting electron density and other transmembrane profiles from molecular dynamics simulations of lipid bilayers fails for large bilayer systems, because it assumes a flat reference surface that does not take into account long wavelength undulations. We have developed what we believe to be a novel set of methods to characterize these undulations and extract the underlying profiles in the large systems. Our approach first obtains an undulation reference surface for each frame in the simulation and subsequently isolates the long-wavelength undulations by filtering out the intrinsic short wavelength modes. We then describe two methods to obtain the appropriate profiles from the undulating reference surface. Most combinations of methods give similar results for the electron density profiles of our simulations of 1024 DMPC lipids. From simulations of smaller systems, we also characterize the finite size effect related to the boundary conditions of the simulation box. In addition, we have developed a set of methods that use the undulation reference surface to determine the true area per lipid which, due to undulations, is larger than the projected area commonly reported from simulations.

Theory of X-ray microcomputed tomography in dental research: application for the caries research

Caries remains prevalent throughout modern society and is the main disease in the field of dentistry. Although studies of this disease have used diverse methodology, recently, X-ray microtomography has gained popularity as a non-destructive, 3-dimensional (3D) analytical technique, and has several advantages over the conventional methods. According to X-ray source, it is classified as monochromatic or polychromatic with the latter being more widely used due to the high cost of the monochromatic source despite some advantages. The determination of mineral density profiles based on changes in X-ray attenuation is the principle of this method and calibration and image processing procedures are needed for the better image and reproducible measurements. Using this tool, 3D reconstruction is also possible and it enables to visualize the internal structures of dental caries. With the advances in the computer technology, more diverse applications are being studied, such automated caries assessment algorithms.

Active spectroscopic measurements using the ITER diagnostic system

Active (beam-based) spectroscopic measurements are intended to provide a number of crucial parameters for the ITER device being built in Cadarache, France. These measurements include the determination of impurity ion temperatures, absolute densities, and velocity profiles, as well as the determination of the plasma current density profile. Because ITER will be the first experiment to study long timescale (∼1 h) fusion burn plasmas, of particular interest is the ability to study the profile of the thermalized helium ash resulting from the slowing down and confinement of the fusion alphas. These measurements will utilize both the 1 MeV heating neutral beams and a dedicated 100 keV hydrogen diagnostic neutral beam. A number of separate instruments are being designed and built by several of the ITER partners to meet the different spectroscopic measurement needs and to provide the maximum physics information. In this paper, we describe the planned measurements, the intended diagnostic ensemble, and we will discuss specific physics and engineering challenges for these measurements in ITER.