Constant Density Research Articles

Putting flat [formula omitted]CDM in the (Redshift) bin

Flat ΛCDM cosmology is specified by two constant fitting parameters at the background level in the late Universe, the Hubble constant H0 and matter density (today) Ωm. Mathematically, H0 and Ωm are either integration constants arising from solving ordinary differential equations or are directly related to integration constants. Seen in this context, if fits of the ΛCDM model to cosmological probes at different redshifts lead to different (H0,Ωm) parameters, this is a mismatch between mathematics and observation. Here, in mock observational Hubble data (OHD) (geometric probes of expansion history) we demonstrate evolution in distributions of best fit parameters with effective redshift. As a result, considerably different (H0,Ωm) best fits from Planck-ΛCDM cannot be precluded in high redshift bins. We explore if OHD, Type Ia supernovae and standardisable quasar samples exhibit redshift evolution of best fit ΛCDM parameters. In all samples, we confirm a decreasing H0 and increasing Ωm trend with increasing bin redshift. Through comparison with mocks, we confirm that similar behaviour can arise randomly within the flat ΛCDM model with probabilities as low as p=0.0021 (3.1σ). We present complementary profile distribution analysis confirming the shifts in cosmological parameters in high redshift bins. In particular, we identify a redshift range where Planck (H0,Ωm) values are disfavoured at 99.6% (2.9σ) confidence level in a combination of OHD and supernovae data.

Fast exact algorithm for neutrino oscillation in constant matter density

A recently published method [1,2] for solving the neutrino evolution equation with constant matter density is further refined and used to lay out an exact algorithm for computing oscillation probabilities, which is moderately faster than previous methods when looping through neutrinos of different energies. In particular, the three examples of ν(−)e survival, ν(−)μ survival and ν(−)e appearance probabilities are written in terms of mixing angles, mass differences and matter electron density. A program based on this new method is found to be roughly twice as fast as, and in agreement with, the leading GLoBES package. Furthermore, the behaviour of all relevant effective parameters is sketched out in terms of a range of neutrino energies, or matter electron densities. For instance, the ν(−)e survival probability in constant matter density is found to have no dependence on the mixing angle θ23 or the CP-violating phase δ13.

AFM-IR study of interfacial nanostructures in high-temperature dilute nanocomposites

The dilute nanocomposite strategy facilitates a promising route for high-temperature polymer dielectrics to achieve high dielectric constant and energy density, robust breakdown strength, and low loss. The dielectric enhancement of the dilute nanocomposites strongly ties to the topological conditions of the nanofiller–polymer interface. Here, atomic force microscopy-based infrared spectroscopy was employed to observe the interfacial region of a high-temperature poly(arylene ether urea) (PEEU) dilute nanocomposite directly. The experimental results showed that the nanoparticles induce morphological changes in PEEU, and the interface region extends over 150 nm away from the nanofiller surfaces. Such nano-morphology changes are highly indicative of generating a large enhancement of the dielectric performance in the PEEU dilute nanocomposite.

Electrophoresis of a weakly charged dielectric fluid droplet in a cylindrical pore.

Electrophoresis of a weakly charged dielectric droplet with constant surface charge density in a chargeless cylindrical pore is investigated theoretically in this study, focusing on the boundary confinement effect of the double layer, which in turn determines the ultimate motion of the droplet. A patched pseudo-spectral method based on the Chebyshev polynomial is adopted to solve the resulting governing fundamental electrokinetic equations. Mobility reversal, among other interesting phenomena, is observed when the droplet is in a narrow cylindrical pore. No such observation was made in the corresponding motion of a rigid particle. The droplet with a thick double layer may even move against the prediction based on the Coulomb electrostatic law, for instance, a positively charged droplet may move against the electric field. The significant enhancement of the motion-deterring double layer polarization due to the severe steric boundary confinement within a narrow cylindrical pore is found to be responsible for this seemingly peculiar phenomenon. Moreover, smaller droplets may move in the opposite direction of the larger ones. The results are useful in capillary electrophoresis involving droplets in particular and migration of droplets through narrow channels in general.

Small-Scale Cosmology Independent of the Standard Model

‘Small-scale cosmology’ is a theory designed to incorporate the linear redshift versus distance relation, which is inferred from observations, into the theoretical framework independent of the global Robertson–Walker–Friedman (RWF)-type models. The motivation behind this is that the RWF cosmological models, based on the assumptions of homogeneity and a constant matter density, as well as the concept of expanding space inherent to them are not applicable on the scales of observations from which the linear Hubble law is inferred. Therefore, explaining the Hubble law as the small redshift limit of the RWF model or as an effect of expanding space is inconsistent. Thus, the Hubble linear relation between the redshift of an extragalactic object and its distance should be considered an independent law of nature valid in the range of the distances where the RWF cosmology is not valid. In general, the theory, based on that concept, can be developed in different ways. In the present paper, ‘small-scale cosmology’ is formulated as a theory operating in the (redshift–object coordinates) space, which allows developing a conceptual and computational basis of the theory along the lines of that of special relativity. In such a theory, the condition of invariance of the Hubble law with respect to a change in the observer acceleration plays a central role. In pursuing this approach, the effectiveness of group theoretical methods is exploited. Applying the Lie group method yields transformations of the variables (the redshift and space coordinates of a cosmological object) between the reference frames of the accelerated observers. In this paper, the transformations are applied to studying the effects of the solar system observer acceleration on the observed shape, distribution and rotation curves of galaxy clusters.

Exponentially harmonic maps between Kähler manifolds

In this paper, we show Liouville-type theorems for exponentially harmonic maps and p-harmonic maps between Kähler manifolds. We then study the quadratic form of an exponentially harmonic map of Kähler manifolds and its applications. We also prove that if [Formula: see text] is an exponentially harmonic map from a compact Kähler manifold [Formula: see text] into a Kähler manifold [Formula: see text] with constant energy density such that the curvature of [Formula: see text] is strongly semi-negative, then [Formula: see text] is holomorphic or antiholomorphic.

Effect of nanosecond laser pulse width and energy on damage characteristics in carbon fibre reinforced plastic (CFRP) laminates

AbstractThis study explores the effects of laser pulse width and energy on CFRP laminates damage in laser bond inspection technology. Three testing programs were used, including varying laser energy while keeping pulse width constant, altering pulse width while maintaining constant power density, and modifying pulse width while keeping energy constant. The results show that when the pulse width remains constant, increased laser energy has a minimal effect on the initial damage location but leads to gradual interlayer delamination and fiber fracture propagation toward the impact surface. With constant laser energy, a specific threshold for pulse width is observed. When the laser pulse width is below this threshold, it exhibits a positive correlation with the damage characteristics of CFRP laminates, whereas when it exceeds this threshold, it shows a negative correlation. Power density correlates with damage when pulse width is constant, but there is no direct correlation when pulse width varies.Highlights CFRP laminates underwent laser shock tests with varying pulse widths. Power density is positively correlated with damage under specific conditions. There exists a specific threshold for laser pulse width. In single‐sided laser shock, initial damage spreads within a specified range.

Mechanical behavior of multiple-layered gradient cellular scaffolds with constant density: experimental, analytical, and numerical investigation

Mechanical behavior of multiple-layered gradient cellular scaffolds with constant density: experimental, analytical, and numerical investigation

On thermal fluctuations and quantum regularities of (R, ) gravity black holes with constant topological Euler density in nonlinear electrodynamics

We discuss the corrected thermodynamics and naked singularity structure of the topological static spherically symmetric solution in F(R,G) - gravity coupled with Born-Infeld—like nonlinear electrodynamics. Solutions admitting black holes with constant topological Euler density is analyzed in view of various thermodynamical variables. The inclusion of logarithmic correction to the entropy is extended to the other thermodynamical variables and the contribution of corrected variables are displayed on various plots. The stability of black hole under the effect of thermal variables is also studied. As a second scope of this study, solutions admitting timelike naked singularity are probed with bosonic and fermionic quantum wave packets to see if the singularity is quantum mechanically regular or not. In this context, the evolution of these probes remains well-defined if the corresponding spatial Hamiltonian operator is essentially self-adjoint. Our calculations reveal that when the singularity is probed with specific wave modes involving spin—0 and spin—1/2 quantum wave packets, the corresponding wave operators turn out to be essentially self-adjoint, which in turn implies unique well-defined time evolution.

The effect of curved membrane electrode assemblies on performances of parallel and interdigitated flow field PEMFCs with wavelike gas channels

The effect of curved membrane electrode assemblies (MEAs) on performances of parallel and interdigitated flow field PEMFCs with wavelike gas channels (GCs) are for the first time investigated at various curved MEA deformation levels, where the curved MEA is triggered by the pressure difference between anodes and cathodes. The results show that on the cathode side of parallel flow field PEMFCs with wavelike GCs, the oxygen consumption and liquid water generation are small with the increased MEA deformation level at the high operation voltage being larger than 0.8 V, leading to the constant cell performance, that is, leading to the constant output current density. However, the current density is first increased and then decreased with the increased MEA deformation level at the low operation voltage being less than 0.8 V. Because at the low operation voltage, the oxygen consumption and liquid water generation are significantly increased and affected by the increased MEA deformation level. When the MEA deformation level is increased at the high operation voltage being larger than 0.8 V, the current density of interdigitated flow PEMFCs with wavelike GCs is also constant because of small oxygen consumptions and liquid water generations. However the oxygen consumption and liquid water generation are large enough and depend on the oxygen transport and liquid water removal at the low operation voltage being less than 0.8 V. At the low voltage, the oxygen transport and liquid water removal are modified by the increased MEA deformation level. Consequently the current density is first decreased and then increased at the low operation voltage.

Density-based in-orbit collision risk model valid for any impact geometry

Neglecting small fragments in space debris evolutionary models can lead to a significant underestimation of the collision risk for operational satellites. However, when scaling down to the millimetre range, the debris population grows to over a hundred million objects, making deterministic approaches too computationally expensive. On the contrary, probabilistic models provide a more efficient alternative, which however typically works under some simplifying assumptions on the dynamics, limiting their field of applicability. This work proposes an extension of the density-based collision risk models to any orbital dynamics and impact geometry. The impact rate with a target satellite is derived from a multi-dimensional phase space density function in orbital elements, which discretely varies over both phase space and time. The assumption of a bin-wise constant cloud density allows for the analytical transformation of the six-dimensional distribution in orbital elements into the three-dimensional spatial density function, guaranteeing an efficient and accurate evaluation of the fragments flux. The proposed method is applied to the assessment of the collision risk posed by occurred fragmentation events in different orbital regions on a high-risk target object. The effect on the impact rate of the modelling improvements, compared to previous probabilistic formulations, is discussed.

Hydrothermal synthesis of FeCoNi/V3O5 heterojunctions as highly efficient electrocatalysts for the oxygen evolution reaction

To produce green hydrogen in a cost-effective and efficient manner, the research on low-cost, high-performance electrocatalysts is both attractive and challenging. In this study, a heterojunction electrocatalyst containing V3O5 and FeCoNi alloy nanoparticles was introduced. The adsorption and activation of the reactants at the FeCoNi/V3O5 heterointerface are significantly enhanced. The overall performance of the FeCoNi/V3O5 catalyst is excellent, with an OER activity reaching 265 mV at a current density of 10 mA cm−2, nearly 65 mV lower compared to the commercial IrO2 catalyst. Furthermore, it exhibits outstanding durability, remaining stable for 50 h under a constant current density of 100 mA cm−2. Theoretical calculations also revealed a synergistic effect between the FeCoNi alloy (referred to as FeCoNi) nanoparticles and V3O5, thereby enhancing the OER performance, consistent with the experimental findings.

Production and characterization of activated carbon foams with various activation agents for electrochemical double layer capacitors (EDLCs) applications

Sucrose-based activated carbons were obtained by carbon foams with sugar and cobalt (II) nitrate as precursors, followed by using different chemical activation agents. The effect of Co(NO3)2 concentration, the carbonization temperature and the activation agent on the surface chemistry, porosity were investigated. Textural characterization and electrochemical tests were performed on the activated carbon samples (CF). The results showed that the activated carbon produced by H2SO4 and KOH at 800°C had a surface area of 691 m2/g and 1125 m2/g, 89% and 80% of the sample pore structure was microporous, and specific capacitance of 8.4 F/g and 162.2 F/g at a constant current density of 250 mA/g, respectively. K2CO3-activated carbon had 918 m2/g surface area and 63% of the sample pore structure with microporous and 1.4 F/g specific capacitance, H3PO4-activated carbon and ZnCl2-activated carbon had 1833 m2/g and 1597 m2/g surface area, 53% mesoporous and 50% mesoporous, 222.4 F/g and 149.9 F/g specific capacitance respectively. The most promosing result was observed in the electrochemical storage behavior of the carbon materials with hierarchical pore structure activated with H3PO4 is associated with increasing defect zones at the edges of micro- and mesoporous morphology, resulting in a higher surface area and increased conductivity of the material.

Advancing Lithium-Magnesium Separation: Pioneering Swelling-Embedded Cation Exchange Membranes Based on Sulfonated Poly(ether ether ketone).

With the continuous advancement of electrodialysis (ED) technology, there arises a demand for improved monovalent cation exchange membranes (CEMs). However, limitations in membrane materials and structures have resulted in the low selectivity of monovalent CEMs, posing challenges in the separation of Li+ and Mg2+. In this investigation, a designed CEM with a swelling-embedded structure was created by integrating a polyelectrolyte containing N-oxide Zwitterion into a sulfonated poly(ether ether ketone) (SPEEK) membrane, leveraging the notable solubility characteristic of SPEEK. The membranes were prepared by using N-oxide zwitterionic polyethylenimine (ZPEI) and 1,3,5-benzenetrlcarbonyl trichloride (TMC). The as-prepared membranes underwent systematic characterization and testing, evaluating their structural, physicochemical, electrochemical, and selective ED properties. During ED, the modified membranes demonstrated notable permeability selectivity for Li+ ions in binary (Li+/Mg2+) systems. Notably, at a constant current density of 2.5 mA cm-2, the modified membrane PEI-TMC/SPEEK exhibited significant permeability selectivity in the Li+/Mg2+ system, while ZPEI-TMC/SPEEK outperformed, displaying remarkable permeability selectivity in the Li+/Mg2+ system, surpassing commercial monovalent cation-selective membrane commercial monovalent cation-selective membrane (CIMS). Furthermore, in the Li+/Mg2+ binary system, Li+ flux reached 9.78 × 10-9 mol cm-2 s-1 for ZPEI-TMC/SPEEK, while its Mg2+ flux only reached 2.7 × 10-9 mol cm-2 s-1, showing potential for lithium-magnesium separation. In addition, ZPEI-TMC/SPEEK was tested for performance and stability at high current densities. This work offers a straightforward preparation process and an innovative structural approach, presenting methodological insights for the advancement of lithium and magnesium separation techniques.

Predicting the Rate of Degradation Related to Oxygen Electrode Delamination in Solid Oxide-Ion Electrolyzers

One of the leading causes for the performance degradation in H2-producing solid oxide electrolytic cells (SOECs) is the gradual delamination of oxygen electrode (OE) from the electrolyte under a strong anodic polarization. Identification of the key factor that controls the rate of OE delamination is of paramount importance to achieve long-term stable operation of SOECs. Here we show from thousands of hours of testing data that the exchange current density (i°) of OE can be leveraged as a predictor for the rate of delamination. To obtain i°, we apply DC-biased electrochemical impedance spectroscopy on a three-electrode symmetrical cell to measure polarization resistance (Rp) of OE as a function of current density (i) and time (t). The collected Rp-i-t raw data are then converted to overpotential (η)-i-t, from which i° is extracted from the “low-field” approximation. An analytical relationship between i° and time-to-delamination (TTD) is further established from the established i°-i-t relationship. We show that under a constant anodic polarization current density i, the greater the ratio i/i°, the faster the delamination. Therefore, we conclude that the exchange current density of an OE, i°, can be used to predict the rate of OE degradation in solid oxide-ion electrolyzers.

A numerical study of thermal shrinkage influence on the impact dynamics of alumina droplets thermally sprayed on flat, grit-blasted and laser treated surfaces

Thermal spray splat morphology and its microstructure are of significance to the coating resulting properties. Depending on the material, the changes in density as the droplet solidifies during splat development and solidification could have a substantial role in the particle deformation dynamics, formation of porosity and subsequent adhesion to the flat or rough target surface.In the current study, the effect of shrinkage on the final splat shape is numerically investigated for collisions occurring under several high-speed impact conditions using the Volume-of-Fluid (VOF) method on real surface topography. This influence is also studied for the interaction of two successive impacting particles. The developed models study the splat impact, development and dynamics of heat transfer on flat, laser-patterned, grit-blasted surfaces and numerically designed features. The results of droplet material variable density cases are compared with those assuming constant density. Experimentally obtained single splat depositions are also used to validate the developed models and obtained numerical results.Findings show that micro substrate surface features lead to splat stretching, porosity and limited finger creation subsequent to improved solidification through interfacial contact area increase. Macro surface characteristics, however, lead to splashing and separation from the substrate surface driven by fluid instabilities. Irrespective of the interface topography, shrinkage processes reduce droplet spreading and accentuate splat feature discontinuities such as porosity.

Assessment of captan pesticide stability by thermal and spectroelectrochemical analysis

In this study, thermal analysis and electrochemical methods were used to evaluate the stability of captan pesticide (CPTN). Simultaneous Thermogravimetry (TG), Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC) were successfully applied to study the stability of CPTN in the temperature range from 20 to 600 °C. The stability evaluation of CPTN by spectroelectrochemical analysis was carried out using cyclic voltammetry (CV) and electrolysis at constant current density in association with UV−Vis spectrophotometry. Thermoanalytical results revealed a relative stability of CPTN up to a temperature of 154 °C, and above this temperature the pesticide molecule undergoes irreversible degradation. The kinetic approach of the electrochemical results on the electrochemical degradation of CPTN showed a rate constant of 0.02 min−1 in the presence of chloride ions and 0.089 min−1 in the presence of bromide ions. Thermal and electrochemical methods are considered effective strategies applied in order to eliminate pesticides from polluted waters, and the choice of optimal parameters can considerably increase the efficiency of decontamination. The study also aims to provide insights into electrode processes to address the mechanism of electrochemical degradation.

Exploring plasma phenomena with the Nizhnik–Novikov–Veselov formula: Analyzing ion-acoustic waves, solitons, and shocks

This paper delves into the intricacies of the ([Formula: see text])-dimensional asymmetric Nizhnik–Novikov–Veselov ([Formula: see text]) model, a nonlinear partial differential equation governing ion-acoustic wave propagation in plasma. By employing advanced analytical and numerical approaches, the study explores innovative solitary wave solutions, particularly focusing on the dynamics of isochoric flow. Isochoric flow analysis is crucial for unraveling the complex behaviors exhibited by incompressible fluids like elastomers and bio-elastomers, which maintain a constant density. The derivation of the ([Formula: see text])-dimensional [Formula: see text] equation stems from fluid equations governing plasma dynamics. This model serves as a valuable tool for simulating experimental observations of plasma waves. The computational methodology applied in this research demonstrates a commendable level of precision and consistency, yielding novel solitary wave solutions previously unreported in the [Formula: see text] model. These results underscore the study’s importance and novelty. The outcomes not only contribute to our understanding of incompressible fluid dynamics, but also lay the groundwork for future investigations in this domain. The revealed solitary wave solutions have the potential to inform the development of more accurate models for predicting fluid dynamics, thereby advancing the field.

Investigation of the performance of cathode supported solid oxide fuel cell with energy and exergy analysis at different operating temperatures

In this research, the performance analysis of a cathode-supported solid oxide fuel cell (SOFC) with an active cell area of 0.0834 m2 and a cathode thickness of 750 µm was carried out under three different operating temperatures (973 K, 1073 K and 1173 K). The power density and cell potential were calculated by determining the losses in the cell at 8 different current densities (1500 A/m2 - 5000 A/m2) for each operating temperature. It was observed that ohmic losses in SOFC have a lower effect on the cell potential compared to other losses. An increase of the operating temperature by 100 K resulted in a decrease in ohmic losses of 3.36×10-8 V under constant current density (CD). In addition, the rise in CD negatively affected all the losses in the cell and decreased the cell voltage. The exergy and energy analysis of SOFC was carried out by calculating the thermal efficiency, exergy destruction, entropy production and exergy efficiency for various operating parameters. An increment of 200 K in the operating temperature increased the thermal efficiency by approximately 2 times at a CD of 5000 A/m2. Also, the minimum entropy production was obtained at an operating temperature of 1173 K and a CD of 1500 A/m2. In this case, the entropy production was calculated as 2.63 kW/K, resulting in a maximum exergy efficiency of 66.93%.

Effect of Gd3+ ion doping on structural, optical, magnetic and dielectric properties on superparamagnetic Mg0.5Zn0.5Fe2−xGdxO4 (0 ≤ x ≤ 1) nanoparticles synthesized via oleic acid assisted chemical co-precipitation method

In the present study, different compositions having general formula Mg0.5Zn0.5GdxFe2−xO4, (x = 0, 0.025, 0.050, 0.075, 0.1) were synthesized using chemical co-precipitation method. The substitution of Gd3+ ions have exhibited profound impacts on the structural, morphological, magnetic, and optical parameters of Mg-Zn ferrites. Single-phase cubic spinel structure has been substantiated by X-ray diffractometer (X-ray diffraction, XRD) analysis for all compositions without any contamination peak. The values of the lattice constant and X-ray density both show an increasing trend when the Gd3+ ion concentration increases. (Fourier transformed infrared spectroscopy) FTIR spectra recorded in the mid-infrared region (4000–400 cm−1) exhibit two main absorption bands associated with the Oh and Td sites within the frequency range of 400–600 cm−1. Morphological studies using (High-resolution transmission electron microscopy) HR-TEM analysis reveal agglomeration of nanoparticles and the average particle size lies between 8 and 9 nm. Maximum magnetization displays an erratic trend with increasing Gd3+ ion concentration, although both retentivity and coercivity decreases. The hysteresis curve for samples of differing ratios of Gd3+ ions demonstrated the superparamagnetic nature. Tauc’s plot was employed to calculate the energy bandgap (Eg) of synthesized nanoparticles and Eg value were observed to decline from 3.563 eV to 3.521 eV with an increasing Gd3+ ion concentration. Impedance analyzer was used in the frequency range of 100 Hz–100 MHz to study dielectric properties at room temperature. The dielectric parameters declined as the frequency values increased. Due to lower values of dielectric parameters in Gd3+ ion doped Mg–Zn nano-ferrite, these materials are suitable in the fabrication of devices that need to operate at high frequencies such as switching memory storage devices. Moreover, these materials are appropriate for application in ferrofluids and medicinal treatments such as magnetic hyperthermia because of their low coercive field value.