Radial Density Research Articles

Physical properties of a quintessence anisotropic stellar model in f(Q) gravity and the mass–radius relation

In this article, we present a new family of solutions to the Einstein field equations of an uncharged spherically symmetric anisotropic matter distribution in the context of f(Q) gravity by choosing f(Q)=Q+aQ^2, a being the coupling constant. Along with the fundamental quintessence dark energy defined by the equation of state parameter -1<omega _q<-frac{1}{3}, we have generated the field equations in modified gravity. Using the linear relationship between radial pressure and energy density along with the Krori–Barua (KB) metric potential, we are able to solve the field equations. Next, we discuss the smooth matching between the exterior Schwarzschild spacetime and the interior spherically symmetric spacetime. We have presented a thorough physical analysis of several factors analytically and graphically to show the physical viability of our suggested model. For the compact star SAXJ 1808.4-3658, our entire graphical analysis was carried out in the context of our solutions for various values of the coupling constant connection to the f(Q) gravity. The influence of coupling constant “a” on different model parameters has been numerically determined and is presented in tabular form. We checked the radial and tangential sound speeds, the stability factor, the adiabatic index, etc. to determine whether our model was stable. It is evident from our analysis that the model is potentially stable when coupling constant a in [0,,5]. The maximum allowable mass and radius from our present model have been obtained through the mass–radius (M-R) plot for different values of a.

Translational Tomography with the Wide-field Imager for Parker Solar Probe (WISPR). I. Theoretical Basis and Initial Modeling

In the first of a planned sequence of articles, we present a simple method for reconstructing radial density structures of the solar corona in the vicinity of the Parker Solar Probe (PSP) near and during perihelion passes. We describe how we model the apparent kinematics of stationary K-corona striae from the PSP Wide-field Imager for Parker Solar Probe (WISPR) viewpoint using a simple two-parameter model, form a partial basis of the data space that is a WISPR image sequence, and change the basis from image coordinates to “tomographic coordinates” in order to determine the parameters of such features. We apply the method to a simple three-dimensional model of a WISPR coronal flythrough, demonstrate the ways that it succeeds and fails, and discuss possible improvements to the sensitivity and applicability of the method for real WISPR data.

Study of a sample of faint Be stars in the exofield of CoRoT

Context. The search and interpretation of non-radial pulsations from Be star light curves observed with the CoRoT satellite requires high-quality stellar astrophysical parameters. Aims. The present work is devoted to the spectroscopic study of a sample of faint Be stars observed by CoRoT in the fourth long run (LRA02). Methods. The astrophysical parameters were determined from the spectra in the λλ4000–4500 Å wavelength domain observed with the VLT/FLAMES instruments at ESO. Spectra were fitted with models of stellar atmospheres using our GIRFIT package. Spectra obtained in the λλ6400–7200 Å wavelength domain enabled the confirmation or, otherwise, a first identification of Be star candidates. Results. The apparent parameters (Teff, log g, Vsin i) for a set of 19 B and Be stars were corrected for the effects induced by the rapid rotation. These allowed us to determine: (1) stellar masses that are in agreement with those measured for detached binary systems; (2) spectroscopic distances that agree with the Gaia parallaxes; and (3) centrifugal/gravity equatorial force ratios of ~0.6–0.7, which indicate that our Be stars are subcritical rotators. A study of the Balmer Hα, Hγ and Hδ emission lines produced: (1) extents of the circumstellar disk (CD) emitting regions that agree with the interferometric inferences in other Be stars; (2) R– dependent exponents n(R) = ln[ρ(R)/ρo]/ln(Ro/R) of the CD radial density distributions; and (3) CD base densities ρo similar to those inferred in other recent works. Conclusions. The Hγ and Hδ emission lines are formed in CD layers close to the central star. These lines produced a different value of the exponent n(R) than assumed for Hα. Further detailed studies of Hγ and Hδ emission lines could reveal the physical properties of regions where the viscous transport of angular momentum to the remaining CD regions is likely to originate from. The subcritical rotation of Be stars suggests that their huge discrete mass-ejections and concomitant non-radial pulsations might have a common origin in stellar envelope regions that become unstable to convection due to rotation. If it is proven that the studied Be stars are products of binary mass transfer phases, the errors induced on the estimated Teff by the presence of stripped sub-dwarf O/B companions are not likely to exceed their present uncertainties.

Validation of DSMC mass flow modeling for transsonic gas flows in micro-propulsion systems

Introduction: In the present work, an inflow model for the DSMC method is presented and validated. The approach is based on inflow mass flow rate and temperature and is particularly suitable for arbitrary nozzle flow cases with higher density, subsonic inflow conditions.Methods: The validation is performed on a nozzle test case and the results are compared with experimental and numerical results based on DSMC and Navier-Stokes methods. Calculation of inflow and outflow boundary conditions on an analytical and numerical basis is presented.Results: Results for axial and radial density, temperature, and pressure are in good agreement and reasonable relationships are obtained.Discussion: Since only the inflow mass flow rate and temperature and the vacuum background pressure need to be known to apply the model, the calculation of the inflow velocity from analytical theory can be omitted, potentially eliminating possible sources of error resulting from theorybased calculations.

Stability of a two-electron system under pressure confinement: structural and quantum information theoretical analysis

The stability of a two-electron Zee system trapped inside an impenetrable spherical cavity is analyzed using an explicitly correlated multi-exponent Hylleraas-type basis set in the framework of the Ritz variational method. The wave function is considered to be consistent with Dirichlet’s boundary condition. Four different values are considered, where denotes the critical nuclear charge beyond which the system is embedded in a discrete positive energy continuum due to the impenetrable nature of the cavity. The energy contribution due to the total correlation (in the presence of both radial and angular correlation) effect, the radial correlation limit, and the angular correlation limit are also studied in detail. The thermodynamic pressure felt by the two-electron Zee system inside the cavity is estimated, and a formula replicating the behavior between the pressure and volume of the cavity is deduced by a fitting procedure. Different geometrical properties, e.g. radial moments (, , , , ; p = ), angular moments (, ), and related important physical quantities, are determined. The variation of Kirkwood and Buckingham polarizabilities w.r.t. the pressure felt by the two-electron Zee system is analyzed. A one-electron radial density is estimated for each pair of (), which has been employed to generate the electrostatic potential as well as different information theoretical measures like Shannon entropy, Fisher entropy, Rényi entropy, Tsallis entropy, and Onicescu informational energy. The chosen information theoretical measures have been found to be sensitive tools for describing changes in the electronic structure due to spatial confinement. An interesting interplay between the electronic and nuclear contribution to the classical electrostatic potential is observed, leading to a shift in the position of its characteristic minimum due to compression. Wherever possible, a comparison is made in order to ascertain the high accuracy of our numerical results. The procedure of analytic evaluation of the integrals needed to estimate the atomic properties under consideration is discussed in detail.

Assessment of peripapillary retinal nerve fiber layer thickness and vessel density in newly diagnosed SLE patients without ocular symptoms.

This study aims to assess peripapillary retinal nerve fiber layer thickness (pRNFLT) and peripapillary vessel density (PVD) in patients with newly diagnosed active and inactive systemic lupus erythematosus (SLE) by optical coherence tomography (OCT) and OCT angiography (OCTA). This is a cross-sectional study, in which 77 newly diagnosed SLE patients without ocular symptoms (including 36 active SLE patients and 41 inactive SLE patients) and 72 age- and gender-matched healthy subjects were recruited. All participants underwent OCT and OCTA to evaluate pRNFLT, PVD, and radial peripapillary capillary density (RPCD), respectively. Clinical data at the time of initial diagnosis of SLE, including erythrocyte, leukocyte, platelet, albumin-globulin ratio, erythrocyte sedimentation rate, C-reactive protein, serum complement 3, serum complement 4, anti-dsDNA antibody, and 24-h proteinuria, were collected. No difference was found in pRNFLT between active SLE patients, and healthy controls, average pRNFLT, superonasal RNFLT, and inferonasal pRNFLT were reduced in inactive SLE patients than in healthy controls (p≤0.008). Temporal PVD, inferotemporal PVD, and inferotemporal RPCD in active SLE patients were significantly lower than those in healthy controls (p≤0.043). There also was a trend towards lower temporal RPCD in active SLE than healthy controls (p=0.089). Average PVD, average RPCD, superonasal RPCD, inferonasal RPCD, and inferotemporal RPCD were decreased in inactive SLE patients than in healthy controls (p≤0.047). Additionally, inferotemporal RPCD in active SLE patients was positively associated with albumin-globulin ratio (p=0.041). Temporal RPCD was negatively correlated with anti-dsDNA antibody (p=0.012) and 24-h proteinuria (p=0.006). PRNFL and PVD damage existed in newly diagnosed SLE patients without ocular symptoms. Temporal and inferotemporal RPCD were associated with the laboratory indicators of impaired renal function in active SLE patients, respectively.

Mass spectra of bottom-charm baryons

In this paper, we investigate the mass spectra of bottom-charm baryons systematically, where the relativistic quark model and the infinitesimally shifted Gaussian basis function method are employed. Our calculation shows that the [Formula: see text]-mode appears lower in energy than the other excited modes. According to this feature, the allowed quantum states are selected and a systematic study of the mass spectra for [Formula: see text] ([Formula: see text]) and [Formula: see text] ([Formula: see text]) families is performed. The root mean square radii and quark radial probability density distributions of these baryons are analyzed as well. Next, the Regge trajectories in the [Formula: see text] plane are successfully constructed based on the mass spectra. At last, we present the structures of the mass spectra, and analyze the difficulty and opportunity in searching for the ground states of bottom-charm baryons in experiment.

Estimation of Stator Vibration in DFIM Under Various Types of Rotor Excitation

Variable speed power generation using Doubly Fed Induction Machine requires an adjustable frequency supply at the rotor terminals which can be achieved using power converters. Ideally, a variable frequency sinusoidal voltage should be applied, but it is not possible without the help of power converters. For a typical 250 MW DFIM with a speed variation of -10.73% to +8.33%, excitation power of 25 MW at 3.3kV and 11600 Amps is required. With this much high rotor current at low fundamental rotor frequency (3.75 Hz) electromagnetic forces in the air gap contain harmonic force components. Also, any time harmonic of radial force density in the rotor will be induced in the stator as a distinct time harmonic, modified by the influence of space harmonics in DFIM with regular three phase integral slot winding on both stator and rotor and vice versa. So, if the frequency and order of electromagnetic force components conflicts with mode shape and natural frequencies of the machine stator strong magnification in vibration will occur or more severely develops mechanical resonance. The stator vibration of electrical machine is generated by the electromagnetic forces acting on the surface of the stator tooths. This paper analyzes stator vibration for 250 MW DFIM in multiphysics simulation with its rotor winding excited through pure sinusoidal excitation at fundamental rotor frequency of 3.75 Hz and with two-Level voltage source converter at 3.75 Hz fundamental rotor frequency. Hardware results with supported multiphysics simulation on a laboratory prototype of 2.2 kW rating DFIM.

Enhanced confinement induced by pellet injection in the stellarator TJ-II

Enhanced confinement is observed in neutral beam injector (NBI)-heated hydrogen discharges made in the stellarator TJ-II after the injection of a single cryogenic fuel pellet into the plasma core. In addition to the expected increase in electron density, ne, in the core after pellet injection (PI), the plasma diamagnetic energy content is seen to rise, with respect to similar discharges without PI, by up to 40%. Furthermore, the energy confinement time, τEdiag, as determined using a diamagnetic loop, is enhanced when compared to predictions obtained using the International Stellarator Scaling law [H. Yamada et al., Nucl. Fusion 45, 1684 (2005)] and the triple product, ne · Ti · τEdiag, exhibits a clear bifurcation point toward an improved confinement branch as compared to the branch product predicted by this scaling law. In general, once such a pellet-induced enhanced confinement (PiEC) phase has been established, it is characterized by steepened radial density gradients, by more negative plasma potential in the core, more negative radial electric fields, Er, across a broad plasma region, as well as by reductions in density and plasma potential fluctuations in the density gradient region. In addition, experimental observations show increased peaking of core radiation losses, this pointing to edge/core plasma decoupling. In parallel, neoclassical simulations of reference and PiEC plasmas predict increased particle and energy confinement times during a PiEC phase together with a more negative Er profile. Qualitative rather than quantitative agreement with experimental parameters is found, indicating that turbulence seems to play a significant role here. In summary, single cryogenic pellet injection facilitates the achievement of an enhanced operational regime that was previously not observed in NBI-heated discharges of the TJ-II.

Energy conditions of traversable wormhole in the deformed f(R) gravitational model

One of the most important issues in cosmology is the study of a series of hypothetical objects called wormholes. Recently, researchers have studied these hypothetical objects under different conditions. In this paper, we aim to evaluate the traversable wormhole according to a modified [Formula: see text] gravitational model, specifically [Formula: see text], from the perspective of two essential functions in wormhole structure: shape and redshift function. These hypothetical objects can solve Einstein’s equations by tolerating the violation of null energy conditions (NEC). With respect to these concepts, we examine various energy conditions such as the NEC, weak energy condition (WEC), dominant energy condition (DEC) and strong energy condition (SEC) using radial pressure, tangential pressure and energy density obtained from the wormhole equations. Finally, we evaluate different energy conditions by plotting some figures and checking for satisfaction or violation. We will analyze the results and present the conclusions in tables.

Compressible convection in super-earths

The radial density of planets increases with depth due to compressibility, leading to impacts on their convective dynamics. To account for these effects, including the presence of a quasi-adiabatic temperature profile and entropy sources due to dissipation, the compressibility is expressed through a dissipation number, D, proportional to the planet's radius and gravity. In Earth's mantle, compressibility effects are moderate, but in large rocky or liquid exoplanets (super-earths), the dissipation number can become very large. This paper explores the properties of compressible convection when the dissipation number is significant. We start by selecting a simple Murnaghan equation of state that embodies the fundamental properties of condensed matter at planetary conditions. Next, we analyze the characteristics of adiabatic profiles and demonstrate that the ratio between the bottom and top adiabatic temperatures is relatively small and probably less than 2. We examine the marginal stability of compressible mantles and reveal that they can undergo convection with either positive or negative superadiabatic Rayleigh numbers. Lastly, we delve into simulations of convection in 2D Cartesian geometry performed using the exact equations of mechanics, neglecting inertia (infinite Prandtl number case), and examine their consequences for super-earth dynamics.

Design and assessments on graded metal foam in heat storage tank: An experimental and numerical study

The effectiveness of solidification in latent heat storage (LHS) systems has been restricted by the low thermal conductivity of pure phase change materials (PCMs). To address this challenge, an innovative composite PCM impregnated with metal foam has been introduced. This study investigates a vertical thermal energy storage (TES unit) filling with foamed copper with radial gradient pore density, with a focus on enhancing energy storage and heat conduction mixing through natural convection. Experiments and numerical models are employed to research the variation of liquid fraction, solid-liquid interfaces, temperature field, and velocity field, as well as to assess heat release properties, including thermal transfer distribution and heat release quantity. Results indicate a 14.3% reduction in solidification duration for both positive and negative radially graded pore density arrangements, compared to a homogeneous structure. In addition, temperature uniformity is improved by 4.0% in these two optimization structures, due to the influence of varied pore density. Findings from this work offer guidance for building more efficient latent energy storage tanks.

Systematic analysis of doubly charmed baryons $$\Xi _{cc}$$ and $$\Omega _{cc}$$

In this work, we perform a systematic study of the mass spectra, the root mean square(r.m.s.) radii and the radial density distributions of the doubly charmed baryons $\Xi_{cc}$ and $\Omega_{cc}$. The calculations are carried out in the frame work of Godfrey-Isgur (GI) relativized quark model, where the baryon is regarded as a real three-body system of quarks. Our results show that the excited energy of doubly charmed baryon with $\rho$-mode is lower than those of the $\lambda$-mode and $\lambda$-$\rho$ mixing mode, which indicates that the lowest state is dominated by the $\rho$-mode. According to this conclusion, we systematically investigate the mass spectra, the r.m.s. radii of the ground and excited states($1S\sim4S$, $1P\sim4P$, $1D\sim4D$, $1F\sim4F$ and $1G\sim4G$) with $\rho$-mode. Using the wave functions obtained from quark model, we also study the radial density distributions. Finally, with the predicated mass spectra, the Regge trajectories of $\Xi_{cc}$ and $\Omega_{cc}$ in the ($J$,$M^{2}$) plane are constructed, and the slopes, intercepts are determined by linear fitting. It is found that model predicted masses fit nicely to the constructed Regge trajectories.

Effect of SARA fractions on the physical, structural and dynamic properties of bitumen using molecular dynamics simulation

The utilization of molecular dynamics simulation on bituminous materials usually adopts three classical bitumen models (AAA-1, AAK-1, AAM-1). However, the chemical compositions of bitumen, namely SARA fractions, vary significantly in reality, depending on the source of bitumen. In this regard, this study investigated the influence of SARA fractions on the simulated properties of bitumen. To this end, 21 bitumen models with different SARA fractions collected from the literature were established. The radial distribution function (RDF), density, and self-diffusion coefficient (SDC) were derived to characterize the structural, physical, and dynamic properties, respectively. Results indicated that the SARA fractions would not significantly influence the density and radial distribution function of bitumen models. However, the influence of heavy components on the equilibrium of dynamic sampling was pronounced. In the MSD analysis, the temperature variation contributed little to the self-diffusion capability of bitumen when the asphaltene index was close to one. The correlation between SDC and asphaltene index varied depending on the value of the asphaltene index. Specifically, the correlation was positive when the asphaltene index was larger than one, and negative when it was smaller than one.

Investigation of heavy gas dispersion characteristics in a static environment: Spatial distribution and volume flux prediction

The unexpected release of hazardous gases due to natural/industrial accidents or man-made disasters can have tragic consequences. Compared with other gaseous pollutants, heavy gases easily accumulate in personnel working areas and are more difficult to eliminate through existing mechanical ventilation systems. In this paper, to improve air quality in enclosed environments, the spatial characteristics of heavy gas dispersion were obtained based on an analysis of the basic properties of heavy gas dispersion. Schlieren experiments and image processing were conducted with shadow correction and noise reduction. The computational fluid dynamics (CFD) was used for predicting the dispersion of heavy gas. The numerical simulations cover a wide range of the densimetric Froude number (Fr) from 6.45 to 25.79, and a best-fit relation of Fr and the height of heavy gas fountain was provided. The radial velocity, radial density and axial density at cross-section of heavy gas dispersion were normalized using the unified scaling law. The axial density reached a minimum value at a height of 10 times the inlet diameter. Further decreases in the inertial force or decreases in the buoyant force can reduce the dilution of heavy gas by ambient fluids, which means that heavy gases diffuse faster and farther. An alternative method for estimating volume flux during gas dispersion using Fr was also proposed.

Evaluation and validation of radial impurity density profiles from CXRS using neutral beam modelling in W7-X

Absolute radial impurity density profiles in the Wendelstein 7-X stellarator (W7-X) are derived from charge exchange recombination spectroscopy using modelling of the neutral beam. The approach is validated via cross comparisons of the neutral beam attenuation, the radial localization of ion temperature measurements, as well as a comparison of the effective plasma charge determined by other diagnostics. The latter implies the validity of the obtained absolute density levels. The simulation based approach novel to W7-X allows to assess the neutral beam halo population, introducing corrections to the shape and amplitude of determined impurity density profiles. To illustrate the capabilities of the derived impurity density profiles, the particle transport properties in a W7-X discharge heated by electron cyclotron resonance heating were assessed. Density profiles for various impurities are found to be flat, consistent with dominant anomalous diffusion in the range 0.1–5.0 m2 s−1. This range of the anomalous transport in such plasmas is in line with other impurity diagnostics at W7-X.

A Molecular Dynamics Study Employing Bimetallic Co–CuHAB Nanosheets for Seawater Desalination

Bimetallic MOFs, which contain two different types of metal nodes within their porous structures, have emerged as a novel class of materials that exhibit tunable properties, rendering them suitable for various applications. In this research, molecular dynamics (MD) simulations are conducted to assess the performance of 2D Hexaaminobenzene (HAB)-derived MOF membranes in reverse osmosis seawater desalination. The membranes display different Co:Cu metal node ratios and degrees of offset nanosheets, and their ion rejection rates and water flux values are compared. In particular, their behaviors are explained through the corresponding radial distribution functions, density distributions, and interaction energy values. Our findings reveal that of the four MOF membranes studied, CuHAB exhibits the best performance in terms of water flux. In addition, the pore diameter of the MOFs is dependent on the ratio of the Co and Cu nodes inside their respective MOF membranes. To achieve high water flux, it is recommended for the membranes to have large hydrophobic pores, while the membrane must display poor salt adsorption to prevent salt ions from permeating through. It is also observed that Co nodes exhibit greater affinity toward the O atoms of the water molecules and the Cl– ions than the Cu nodes. Due to the hydrophobic nature of the small CoHAB pores, offsetting the nanosheets that constitute the membranes can improve salt rejection but show no significant effect on water flux. Overall, this study shows that MD simulations can effectively determine the optimal ratio of metal nodes in bimetallic 2D MOF membranes to achieve desirable water flux values and ensure excellent salt rejection.

Universal Multistream Radial Structures of Cold Dark Matter Halos

Virialized halos of cold dark matter generically exhibit multistream structures of accreted dark matter within an outermost radial caustic known as the splashback radius. By tracking the particle trajectories that accrete onto the halos in cosmological N-body simulations, we count their number of apocenter passages (p) and use them to characterize the multistream structure of dark matter particles. We find that the radial density profile for each stream, classified by the number of apocenter passages, exhibits universal features and can be described by a double power-law function comprising shallow inner slopes and steep outer slopes of indices of −1 and −8, respectively. Surprisingly, these properties hold over a wide range of halo masses. The double power-law feature is persistent when dividing the sample by concentration or accretion rate. The dependence of the characteristic scale and amplitude of the profile on p cannot be replicated by known self-similar solutions, requiring consideration of complexities such as the distribution of angular momentum or mergers.

The Use of Black Pine Bark for Improving the Properties of Wood Pellets

The requirement for alternative raw materials for fuel pellets that would enable the use of readily available low-cost renewable resources and waste materials, such as bark, has always attracted interest. The aim of the current work was to assess the effect of black pine (Pinus nigra L.) bark content (0%–100%) as well as densification temperature on the properties of black pine wood pellets produced in a single pellet die. The quality assessment of the pellets was carried out by the determination of radial compression strength, density, moisture content, ash content, and surface roughness. The results showed that adding black pine bark to the pellet feedstock resulted in the production of substantially smoother and moderately denser pellets, which also exhibited higher mechanical strength than that of the respective pellets of pure wood. Finally, it was shown that black pine bark can be a valuable raw material, which can induce improved bonding of biomass particles and may provide the opportunity to create pellets of favorable characteristics at a lower temperature compared to those made of pure wood.

The S- and P-wave fully charmed tetraquark states and their radial excitations

Inspired by recent progresses in observations of the fully charmed tetraquark states by LHCb, CMS, and ATLAS collaborations, we perform a systematic study of the ground states and the first radial excitations of the S- and P-wave textrm{cc}bar{textrm{c}}bar{textrm{c}} system. Their mass spectra, root mean square (r.m.s.) radii and radial density distributions are studied with the relativized quark model. The calculations show that there is no stable bound states for the fully charmed tetraquark states, and the r.m.s. radii of these tetraquark states are smaller than 1 fm. Our results support assigning X(6600) structure, M_{X(6600)}=6552pm 10pm 12 MeV, as one of the 0^{++}(1S) and 2^{++}(1S) states or their mixtures. Another structure also named as X(6600) by CMS Collaboration, M_{X(6600)}=6.62pm 0.03^{+0.02}_{-0.01} GeV, may arise from the lowest 1P states with J^{PC}=0^{-+}, 1^{-+}, and 2^{-+}. The possible assignments for X(6900) include the 0^{++}(2S), 2^{++}(2S) states, and the highest 1P state with J^{PC}=0^{-+}. As for X(7200), it can be interpreted as one of the highest 2P states with J^{PC}=0^{-+}, 1^{-+}, and 2^{-+}, and the 3S states can not be completely excluded from the candidates.