Electron Density Parameter Research Articles

Extension of Mott Formula in the Linearized Boltzmann Transport Equation to the Study of Thermoelectric Power of Electron in Metal

The focus of this paper is to compute and study thermoelectric power of electron in metals using Mott formula based on free electron theory to get an insight on the effect of strain on electron thermoelectric power in metals. Electron density parameter of strained metals and Poisson ratio of metals is obtained and used in this work unlike some researchers that assumed a value for Poisson ratio of all metals. This assumption make the electron density parameter of strained and unstrained metals to be equal and then reduce the computation to only one input parameter. The experimental and simulated value are in good agreement. This agreement is due to the usefulness of free electron theory in theoretical forecast of some properties of metals. The Poisson ratio is involved in simulation. Result obtained revealed that thermoelectric power of electron in metals goes up as the electron density parameter rises due to high-order contributions from electron scattering theory. Electron thermoelectric power in metals increases as the temperature increases due to electron thermal excitation from their mean position. The electron thermoelectric power rises as strain rises for metals.

Regression fitting megavoltage depth dose curves to determine material relative electron density in radiotherapy.

The relative electron density (RED) parameter is ubiquitous throughout radiotherapy for clinical dosimetry and treatment planning purposes as it provides a more accurate description of the relevant radiological properties over mass density alone. RED is in practice determined indirectly from calibrated CT Hounsfield Units (HU). While CT images provide useful 3D information, the spectral differences between CT and clinical LINAC beams may impact the validity of the CT-ED calibration, especially in the context of novel tissue-mimicking materials where deviations from biologically typical atomic number to atomic weight ratios 〈Z/A〉 occur and/or high-Z materials are present. A theoretical basis for determining material properties directly in a clinical beam spectrum via an electron-density equivalent pathlength (eEPL) method has been previously established. An experimental implementation of this approach is introduced whereby material-specific measured percentage depth dose curves (PDDs) are regressed to a PDD measured in a reference material (water), providing an inference of 〈Z/A〉, which when combined with the physical density provides a determination of RED. This method is validated over a range of tissue-mimicking materials and compared against the standard CT output, as well as compositional information obtained from the manufacturer's specifications. The measured PDD regression method shows consistent results against both manufacturer-provided and CT-derived values between 0.9 and 1.15 RED. Outside of this soft-tissue range a trend was observed whereby the 〈Z/A〉 determined becomes unrealistic indicating the method is no longer reporting RED alone and the assumptions around the eEPL model are constrained. Within the soft-tissue RED range of validity, the regression method provides a practical and robust characterisation for unknown materials in the clinical setting and may be used to improve on the CT derived RED where high Z material components are suspected.

Numerical investigation of the quasi-particles of metals with specific thermodynamic properties at elevated temperatures

The application of the Landau theory of Fermi Liquids to certain thermodynamic properties, like the specific heat of quasi-particles in metals, was investigated in this study. The FORTRAN compiler was used to scientifically coordinate the generation of values of specific heat by writing programs for each thermodynamic property as a function of electron density parameter, temperature, Boltzmann’s constant, and effective mass of the quasi-particle. The results indicate that as the temperature of metals increases, the specific heat of quasi-particles also increases, and the electron density parameter increases for all metals. This suggests that at low densities, the specific heat of quasi-particles is large and there is a large separation between them. Additionally, the ability to absorb heat decreases as the temperature of the quasi-particles increases. The specific heat of quasi-particles calculated in this paper differs greatly from Landau's observations, indicating that the inclusion of the electron density parameter plays a role in the generation of quasi-particles and the observed specific heat of metals. The computed specific heat is close to Laudau’s specific heat but far from the observed specific heat. This research examines the interaction of landau quasi-particles in the overall characteristics of metals and evaluates the reliability of the model used. The results of the calculated specific heat and the actual specific heat demonstrate variations with the model underestimating the specific heat at observed temperatures and higher temperatures.

The Impact of Star-formation-rate Surface Density on the Electron Density and Ionization Parameter of High-redshift Galaxies* *Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W.M. Keck Foundation.

We use the large spectroscopic data set of the MOSFIRE Deep Evolution Field survey to investigate some of the key factors responsible for the elevated ionization parameters (U) inferred for high-redshift galaxies, focusing in particular on the role of star-formation-rate surface density (ΣSFR). Using a sample of 317 galaxies with spectroscopic redshifts z spec ≃ 1.9–3.7, we construct composite rest-frame optical spectra in bins of ΣSFR and infer electron densities, n e, using the ratio of the [O ii] λ λ3727, 3730 doublet. Our analysis suggests a significant (≃3σ) correlation between n e and ΣSFR. We further find significant correlations between U and ΣSFR for composite spectra of a subsample of 113 galaxies, and for a smaller sample of 25 individual galaxies with inferences of U. The increase in n e—and possibly also the volume filling factor of dense clumps in H ii regions—with ΣSFR appear to be important factors in explaining the relationship between U and ΣSFR. Further, the increase in n e and SFR with redshift at a fixed stellar mass can account for most of the redshift evolution of U. These results suggest that the gas density, which sets n e and the overall level of star formation activity, may play a more important role than metallicity evolution in explaining the elevated ionization parameters of high-redshift galaxies.

Effect of Material-Dependent Boundaries on the Interference Induced Enhancement of the Surface Superconductivity Temperature.

Using the tight-binding Bogoliubov-de Gennes formalism, we describe the influence of the surface potential on the superconducting critical temperature at the surface. Surface details are taken into account within the framework of the self-consistent Lang-Kohn effective potential. The regimes of strong and weak coupling of superconducting correlations are considered. Our study reveals that, although the enhancement of the surface critical temperature, originating from the enhancement of the localized correlation due to the constructive interference between quasiparticle bulk orbits, can be sufficiently affected by the surface potential, this influence, nonetheless, strongly depends on the bulk material parameters, such as the effective electron density parameter and Fermi energy, and is likely to be negligible for some materials, in particular for narrow-band metals. Thus, superconducting properties of a surface can be controlled by the surface/interface potential properties, which offer an additional tuning knob for the superconducting state at the surface/interface.

Wigner crystallization in quasi-one-dimensional quantum wire

We study the ground-state properties of quasi-one-dimensional paramagnetic electron fluid using variational quantum Monte Carlo method. The electrons are transversally confined using the harmonically regularized Coulomb potential with long range order. In this work we have investigated the crossover from liquid to crystalline phase in the finite width paramagnetic quantum wire. The calculated pair correlation function shows the oscillations of period 2r_text {s} a_0, where a_0 is the Bohr’s radius and r_text {s} is Wigner Seitz radius or electron-density parameter which corresponds to a k=4k_text {F} peak with k_text {F} being Fermi wave vector in the static structure factor at finite electron density. It is a signature of the onset of Wigner crystallization. It is found that the cross-over from liquid to a quasi-Wigner phase is due to enhancement of the electron correlation effects as r_text {s} increases or as the wire width b decreases.

Classical and machine learning interatomic potentials for BCC vanadium

BCC transition metals (TMs) exhibit complex temperature and strain-rate dependent plastic deformation behavior controlled by individual crystal lattice defects. Classical empirical and semiempirical interatomic potentials have limited capability in modeling defect properties such as the screw dislocation core structures and Peierls barriers in the BCC structure. Machine learning (ML) potentials, trained on DFT-based datasets, have shown some successes in reproducing dislocation core properties. However, in group VB TMs, the most widely used DFT functionals produce erroneous shear moduli ${C}_{44}$ which are undesirably transferred to machine-learning interatomic potentials, leaving current ML approaches unsuitable for this important class of metals and alloys. Here, we develop two interatomic potentials for BCC vanadium (V) based on (i) an extension of the partial electron density and screening parameter in the classical semiempirical modified embedded-atom method (XMEAM-V) and (ii) a recent hybrid descriptor in the ML Deep Potential framework (DP-HYB-V). We describe distinct features in these two disparate approaches, including their dataset generation, training procedure, weakness and strength in modeling lattice and defect properties in BCC V. Both XMEAM-V and DP-HYB-V reproduce a broad range of defect properties (vacancy, self-interstitials, surface, dislocation) relevant to plastic deformation and fracture. In particular, XMEAM-V reproduces nearly all mechanical and thermodynamic properties at DFT accuracies and with ${C}_{44}$ near the experimental value. XMEAM-V also naturally exhibits the anomalous slip at 77 K widely observed in group VB and VIB TMs and outperforms all existing, publically available interatomic potentials for V. The XMEAM thus provides a practical path to developing accurate and efficient interatomic potentials for nonmagnetic BCC TMs and possibly multiprincipal element TM alloys.

Impact of ionization and electron density gradients in X-ray reflection spectroscopy measurements

ABSTRACT The models currently used for the analysis of the reflection spectra of black holes usually assume a disc with constant ionization and electron density. However, there is some debate on the impact of these assumptions on the estimate of the properties of the sources, in particular when the fits suggest very steep emissivity profiles in the inner part of the accretion disc. In this work, we re-analyse a selected set of high-quality NuSTAR and Suzaku data of Galactic black holes and we fit the reflection component with three different models: relxill_nk, in which the ionization parameter and the electron density are constant, relxillion_nk, where the electron density is still constant but the ionization profile is described by a power law, and relxilldgrad_nk, where the electron density profile is described by a power law and the ionization profile is calculated self-consistently from the electron density and the emissivity. While relxillion_nk can fit the data better, we do not find any substantial difference in the estimate of the properties of the sources among the three models. Our conclusion is that models with constant electron density and ionization parameter are probably sufficient, in most cases, to fit the currently available X-ray data of accreting black holes.

Wettability of Metals by Water

The wetting behavior of water on metal surfaces is important for a wide range of industries, for example, in the metallurgical industry during the preparation of metallic nanoparticles or electrochemical or electroless coating preparation from aqueous solutions, as well as in the construction industry (e.g., self-cleaning metal surfaces) and in the oil industry, in the case of water–oil separation or corrosion problems. Wettability in water/metal systems has been investigated in the literature; nevertheless, contradictions can be found in the results. Some papers have reported perfect wettability even in water/noble metal systems, while other researchers state that water cannot spread well on the surface of metals, and the contact angle is predicted at around 60°. The purpose of this paper is to resolve this contradiction and find correlations to predict the contact angle for a variety of metals. In our research, the wetting behavior of distilled water on the freshly polished surface of Ag, Au, Cu, Fe, Nb, Ni, Sn, Ti, and W substrates was investigated by the sessile drop method. The contact angle of the water on the metal was determined by KSV software. The contact angle of water is identified as being between 50° and 80°. We found that the contact angle of water on metals decreases linearly with increasing the atomic radius of the substrate. Using our new equation, the contact angle of water was identified on all of the metals in the periodic table. From the measured contact angle values, the adhesion energy of the distilled water/metal substrate interface was also determined and a correlation with the free electron density parameter of substrates was determined.

Effects of a Nonextensive Dust Charge Variation on an Oblique Collision of Dust Acoustic Solitons in a Dusty plasma

In the current study, two-dimensional collision of two dust acoustic solitons in an unmagnetized nonextensive dusty plasma is investigated, including the effect of non-extensive dust charge variation. By using the extended Poincar-Lighthill-Kuo (PLK) method, two Korteweg-de Vries equations that describe the two dust acoustic solitons propagating in two different directions are derived. The phase shifts after a two-dimensional collision of dust acoustic solitons are obtained as well. The effects of parameters of the ratio of ion temperature to electron temperature, the ratio of ion density to electron density and nonextensive parameter of electrons/ions on the phase shifts are discussed with and without dust charge variation. The results show that the phase shift has been significantly influenced by these parameters. Furthermore, the non-extensive dust charge variation has a significant effect on the amplitude, width of a new nonlinear wave, which generates during the oblique collision.

Ground-state properties of an electron-phonon coupled quantum wire within the dynamic mean-field approximation

We investigate the ground-state properties of an electron-phonon (e-ph) coupled quantum wire in which the effect of coupling between longitudinal optical (LO) phonons and the wire electrons is considered, in addition to the conventional electron-electron (e-e) interactions. The e-ph coupling is included through the Fröhlich interaction potential and the dynamics of electron correlations using the quantum (dynamic) version of self-consistent mean-field approximation of Singwi et al (the qSTLS approach). Numerical results for static structure factor, pair-correlation function and static density susceptibility are presented over a wide range of electron number density parameter r s . We find that the electrons undergo Wigner crystallization at a critical electron density parameter r s c owing to the dynamics of severely correlated electrons. Notably at a fixed wire width, the inclusion of e-ph coupling tends to increase the value of r s c significantly in comparison to a situation in which only the e-e interactions are considered. Besides this, we compute the plasmon-phonon (pl-ph) coupled modes and the energy contribution of e-ph interactions (E e−ph ) to the ground-state energy of the quantum wire, also known as polaronic energy. We find that pl-ph coupled modes resonantly split into two branches, and ∣E e−ph ∣ monotonically increases with rise in r s then becomes almost constant as . Wherever interesting, we compare our results with the static STLS theory and the lattice regularized diffusion Monte Carlo (LRDMC) simulation data of Casula et al.

Extraction of thermal and optical parameters for As–Se–Te thin films according to phase-change pathways

The technique of thermal evaporation was used to synthesize the As50Se50-xTex (x = 0, 25, and 50 at.%) thin films (∼500 nm). The scenarios of this research were focused on the phase change pathways of the fresh and annealed (at Tc) thin films. By measuring the surface resistance of the studied thin films in the thermal range between 300 and 600 K, the path of phase transitions from the amorphous to the crystalline state was determined. The average activation energy of phase transitions was computed for the entire system. The phase-transition temperature has been determined utilizing the first derivative of the sheet resistance as a function of temperature (Rs–T). The optical bandgap of the fresh and annealed (at Tc) thin films was determined utilizing Kubelka–Munk (K-M) function that was extracted after measuring the diffuse reflectivity spectra in the range of (300–2500 nm). The two molar optical constants (n, k), the molar dispersion and dielectric parameters have been computed. Values of effective plasmon energy (Ψ), Molar volume Vm, the effective number of electrons neff, the electron density parameter rs, the homopolar gap (E‾h), the heteropolar gap (C), the average gap (E‾g), the theoretical static dielectric constant (ε0th) and Phillips ionicity of the glasses under study were calculated according to Penn model. All computed parameters in this work were given to the phase change paths in the studied system to consider the possibility of using the chalcogenide system in the phase-change memory (PCM) applications.

The similarity of elements in multi-principle element alloys based on a new criterion for phase constitution

Prediction of the phase constitution of the multi-principle elements alloys (MPEAs) with various element numbers is important for alloy design and performance optimization. Herein, valence electron density parameter, α, is proposed as an improvement of the valence electron concentration by including the impact of atom volumes. The phase constitution of numerous MPEAs is well predicted by the priori α-ΔHmix(enthalpy of mixing) criterion, evidenced by the distinguishing of FCC single phase, FCC and BCC dual-phase and BCC single phase. The similarity of elements in MPEAs is evaluated by the derivative of α and ΔHmixwith respect to atomic percentage, which successfully predicts the phase constitution of CrFeNi with addition of Ti, Zr, Al, Cr, Fe, Ni, Co and Cu. This work provides valuable insights into priori judgement of the phase constitution of MPEAs in the view of the relationship between elements.

Magnetic Spin Susceptibility of quasi-particles in metals using the Landau Fermi Liquid Theory

    38  In this work, the magnetic spin susceptibility of quasi-particles in metals were computed for some metals based on the modified Landau Fermi Liquids Theory using the electron density parameter. The results showed that for each metal, the Landau magnetic spin susceptibility of quasi-particles is higher than the computed magnetic spin susceptibility of quasi-particles and experimental values. This may be due to the fact that the Landau parameter must have been over estimated in its application. The computed magnetic spin susceptibility of quasi-particles is in good agreement with the experimental values of metals available with a remarkable agreement at. The better estimation of the magnetic spin susceptibility of quasi-particles using the modified Landau Fermi Liquid theory were compared with available experimental values. This show that the introduction of the electron density parameter in the Landau Fermi Liquid theory is promising in predicting the contribution of quasi-particles to the bulk properties of metals. The magnetic spin susceptibility of quasi-particles for transition metals is higher than most of the magnetic spin susceptibility of quasi-particles for alkali metals. This suggests that the magnetic spin susceptibility is considerably higher for most transition metals due to the incomplete inner electronic shells as more quasi-particles can be excited which enhances their susceptibility than the alkali metals.

Adsorption of Organic Acids and Phosphate to an Iron (Oxyhydr)oxide Mineral: A Combined Experimental and Density Functional Theory Study.

The interaction of soil organic matter with mineral surfaces is a critical reaction involved in many ecosystem services, including stabilization of organic matter in the terrestrial carbon pool and bioavailability of plant nutrients. Using model organic acids typically present in soil solutions, this study couples laboratory adsorption studies with density functional theory (DFT) to provide physical insights into the nature of the chemical bonding between carboxylate functional groups and a model FeOOH cluster. Topological determination of electron density at bond critical points using quantum theory of atoms in molecules (QTAIM) analysis revealed that the presence of multiple bonding paths between the organic acid and the FeOOH cluster is essential in determining the competitive adsorption of organic acids and phosphate for FeOOH surface adsorption sites. The electron density and Laplacian parameter values from QTAIM indicated that the primary carboxylate-FeOOH bond was more ionic than covalent in nature. The experimental and computational results provide molecular-level evidence of the important role of electrostatic forces in the bonding between carboxylic acids and Fe-hydroxides. This knowledge may assist in the formulation of management studies to meet the challenges of maintaining ecosystems services in the face of a changing climate.

Local Density Approximation for the Short-Range Exchange Free Energy Functional.

Analytical expressions for the exchange free energy per particle of the uniform electron gas (UEG) associated with the short-range (SR) interelectronic interaction at the low- and high-temperature limits are examined, yielding an accurate analytical parametrization for the SR exchange free energy per particle of the UEG as a function of the uniform electron density, temperature, and range-separation parameter. This parametrization constitutes the local density approximation for the SR exchange free energy functional, which can be the first step toward finding generally accurate range-separated hybrid functionals in both finite-temperature density functional theory and thermally assisted-occupation density functional theory.

Effects of Linear Deformation on Relaxation Time and Some Fermi Properties of Metals

In this work, a model for computing the relaxation time, Fermi velocity and Fermi temperature of deformed metals was developed based on free electron theory. This study generalized the work of Kiejna and Pogosov (2000) due to the shortcomings of the electron density parameter of deformed metals. They failed to account for metal dilation by assuming a constant value for the Poisson ratio of metals which leads to neglect of the uniaxial strain (deformation) in their computation. This causes the electron density parameter of both deformed and undeformed metals to be equal. The result obtained in this work revealed that there is an agreement between the experimental and computed values of the Fermi velocity, Fermi temperature and relaxation time of some of the metals calculated which shows the validity of the model used in the study. The experimental value used in this work is theoretically obtained by substituting the experimental value of Fermi energy obtained from solid state Physics by Charles Kittel (1976) into the model used in the computation. The Fermi velocity, Fermi temperature and relaxation time of all the metals subjected to different deformation decreases as deformation increases. This seems to suggest that as deformation increases the collision frequency between the interacting electron decreases which forces the relaxation time, Fermi velocity and Fermi temperature to decrease as deformation increases. This behavior could also be due to an increase in the inter-atomic spacing between the interacting electrons in the metals during deformation which reduces the strength of interaction between the electrons in metal and their-by forces the relaxation time, Fermi velocity and Fermi temperature to decrease as deformation increases. Keywords: relaxation time, Fermi velocity, Fermi temperature, mean free path, deformation, Fermi surface DOI : 10.7176/JNSR/9-8-04 Publication date : April 30 th 2019

Nequick2 Model Behaviour for Global Ionospheric Delay Mitigation During Solar Cycle-24

Abstract The ionospheric delay is the major current source of potential range delay for single-frequency GNSS users. Different ionospheric delay mitigation methods have been developed to mitigate the ionospheric delay effects for single-frequency users. The NeQuick is a quick-run ionospheric electron density model particularly designed for trans-ionospheric propagation applications developed at the Aeronomy and Radio propagation Laboratory of the Abdus Salam International Centre for Theoretical Physics (ICTP), Italy. NeQuick2 is the latest version of the NeQuick ionosphere electron density model. NeQuick model been used by the European Space Agency (ESA) European Geostationary Navigation Overlay Service (EGNOS) project for assessment analysis and has been adopted for single-frequency positioning applications in the frame work of the European satellite navigation system (Galileo). NeQuick2 model adopted modifications related to the modeling of the F1 layer peak electron density, height and thickness parameter. Also, a new formulation of the shape parameter k has been adopted. This paper presents a global study for the behavior of the modified NeQuick2 model. The zenith ionospheric range delay correction by the model has been assessed using the highly accurate IGS-Global Ionospheric Maps (IGS-GIMs) for two different-latitude stations (Aswan, Egypt) (low-latitude) (24.1o N) and (Helsinki, Finland) (high-latitude) (60.2o N). The study was carried out during current solar cycle-24 over three different months that each of them reflects a different state of solar activity. It can be concluded that NeQuick2 model globally presents overestimation for ionospheric delay for quiet and medium ionospheric activity states respectively, while the model presents underestimation for high activity state of the ionosphere layer.

Quasi-particle Contribution in Thermal Expansion and Thermal Conductivity in Metals

In this paper the modified Landau theory of Fermi Liquids was used to compute the thermal expansion and thermal conductivity of quasi-particles in metals. The result revealed that as temperature increases the thermal expansion of quasi-particles in metals increases in all the metals investigated. It is also observed that as the electron density parameter increases the thermal expansion of quasi-particles increases. This shows that at low density region the thermal expansion of quasi-particles is large. The result obtained for the thermal conductivity of quasi-particles in metals revealed that for all the metals computed the thermal conductivity of quasi-particles decreases as temperature increases. This seems to suggest that as temperature increases the separation between quasi-particles increases because they are not heavy particles hence, the rate of absorbing heat decreases. The computed thermal expansion and thermal conductivity of quasi-particles are in better agreement with experimental values. This suggests that the introduction of the electron density parameter is promising in predicting the contribution of quasi-particles to the bulk properties of metals. This study revealed the extent to which quasi-particles contribute to the bulk properties of metals, which assisted their potential applications in materials science and engineering development.

Positron probing of disordered regions in neutron‐irradiated silicon

The vacancy‐rich disordered regions (DR) playing a key role in improving the thermoelectric figure‐of‐merit of silicon thermoelectric generators by reducing (by ∼90%) the thermal conductivity, have been probed with positrons. The DR were created by irradiating n‐Cz‐Si(P) material with the fast reactor neutrons. The parameter of the electron density rs′ ≈ 2.18 a.u. contacting positrons in DR has been reconstructed using the data of the angular correlation of the annihilation radiation (ACAR); the amendments to the rs′ value associated with the ion core electrons were taken into account. It is argued that the ion cores of atoms of silicon as well as the ones of the as‐grown impurities (O, C) are involved in the open vacancy volume to be probed with positrons: a relaxation of the ion cores directed inward toward the vacancy volume seems to take place. These positron traps are formed beyond the vacancy‐rich area of the disordered region. In the course of isochronal annealing, the traps are stable up to Tanneal. ≈ 520 °C when a recovery of ACAR parameters begins and then it continues up to ∼1050 °C.A vacancy center containing positrons in the open vacancy volume beyond the vacancy‐rich area of the disordered region is shown schematically. The emission of electron–positron annihilation gamma‐quanta dominates from within these positron traps. The values of both the electron–positron ion core radius (rm) and electron density (parameter rs′) suggest a relaxation directed toward inwards the open vacancy volume: the impurity atoms of oxygen and carbon are, perhaps, involved in the center.