Interaction Constants Research Articles

Foundations of time-symmetric physics. 2. Quantum field theory

Time symmetric theory (TST), described in the first article and based on the equivalence principle of particle physics, is applied to quantum fields and time-symmetric quantum field theory is formulated. This principle is based on the Zisman-Stückelberg-Feynman interpretation, where antiparticles are described as negative energy particles moving backward in time, and generalizes it to the rest frames of such particles also moving backward in time. In TST, relativistic fields are described by complex field operators, and observables are automatically normally ordered. For this reason, at time-symmetric quantization (TSQ) of fields, the vacuum energy and charge disappear and there is no cosmological constant problem. In TST, the probabilities of states are positive, and the probability currents can have two signs depending on the direction of evolution along the time axis. The operator of interaction current is defined as the product of the probability current and the matrix of interaction constants. Applications of TST to the Standard Model fields and graviton field are considered. In TSQ correctly describes the observable effects, since in terms of ordinary time it leads to a standard diagram technique, transforming mathematical recipes of the latter into logical consequences of physical principles.

Magnetic properties of the frustrated Ising chain

Using the Kramers–Wannier transfer matrix method, we studied several decorated Ising chains. The exact expressions for thermodynamic characteristics, including the ground state characteristics, were obtained. We considered several modeling chains with different signs and absolute values of exchange constants for the nearest- and the next-nearest neighbors. For these models, we calculated the magnetization curves. The critical values of magnetic fields and corresponding magnetization plateau parameters were obtained. Analytic expressions for the ground state entropy were obtained for the chains with different interaction constants. The dependencies of the number of states with minimum energy (the degeneration of the ground state) as the function of the number of particles were found. It was shown that these dependencies are expressed in terms of well-known numerical sequences, namely Lucas numbers and Pell numbers, which, in the limit of a large number of particles, are proportional to the powers of the golden and silver sections. Therefore, the ground state entropy (per particle) of the systems under consideration can be described in terms of these sections and, therefore, is nonzero.

A New Mechanistic Model for Wettability-Altering Surfactant Floods in Carbonates

Summary Surfactants and low-salinity brines have been shown to be effective for enhanced oil recovery in carbonate rocks through wettability alteration (WA). Oil wettability of carbonates is ascribed to the adsorbed organic acid components in oil. The removal of the adsorbed acids leads to WA. Previous experiments with wettability-altering surfactants have shown the following: WA is a slow process; acid removal is irreversible in most cases; surfactants can access the rock surface in water-wet regions and at three-phase contact lines rather than the entire rock surface; surfactant molecules become inactive after interactions with acids. Existing models/simulators do not incorporate the aforementioned observations. In this work, a multiphase, multicomponent, finite-difference reservoir simulator incorporating a new mechanistic model for WA was developed. The model captures the key physicochemical reactions between adsorbed acids and surfactant molecules and honors the four experimental evidences. The model was first tested at the core scale. The simulation results demonstrated that the model can accurately predict waterflood performance in rocks with various wettability. It can also effectively account for the influence of injection rates in surfactant flood experiments. The effectiveness of the surfactant, controlled by an interaction constant in the model, was found to be a dominant factor. The model was also tested for field-scale pilot tests. The results revealed that total quantity of chemicals injected and the injection rate have a more pronounced effect on oil recovery compared to the timing of surfactant treatment and the concentration of surfactant slug.

Fabrication, structural, and enhanced mechanical behavior of MgO substituted PMMA composites for dental applications

The most common denture material used for dentistry is poly-methyl-methacrylate (PMMA). Usually, the polymeric PMMA material has numerous biological, mechanical and cost-effective shortcomings. Hence, to resolve such types of drawbacks, attempts have been made to investigate fillers of the PMMA like alumina (Al2O3), silica (SiO2), zirconia (ZrO2) etc. For the enhancement of the PMMA properties a suitable additive is required for its orthopedic applications. Herein, the main motive of this study was to synthesize a magnesium oxide (MgO) reinforced polymer-based hybrid nano-composites by using heat cure method with superior optical, biological and mechanical characteristics. For the structural and vibrational studies of the composites, XRD and FT-IR were carried out. Herein, the percentage of crystallinity for all the fabricated composites were also calculated and found to be 14.79–30.31. Various physical and optical parameters such as density, band gap, Urbach energy, cutoff energy, cutoff wavelength, steepness parameter, electron–phonon interaction, refractive index, and optical dielectric constant were also studied and their values are found to be in the range of 1.21–1.394 g/cm3, 5.44–5.48 eV, 0.167–0.027 eV, 5.68 eV, 218 nm, 0.156–0.962, 4.273–0.693, 1.937–1.932, and 3.752–3.731 respectively. To evaluate the mechanical properties like compressive strength, flexural strength, and fracture toughness of the composites a Universal Testing Machine (UTM) was used and their values were 60.3 and 101 MPa, 78 and 40.3 MPa, 5.85 and 9.8 MPa-m1/2 respectively. Tribological tests of the composites were also carried out. In order to check the toxicity, MTT assay was also carried out for the PM0 and PM15 [(x)MgO + (100 − x) (C5O2H8)n] (x = 0 and 15) composites. This study provides a comprehensive insight into the structural, physical, optical, and biological features of the fabricated PMMA-MgO composites, highlighting the potential of the PM15 composite with its enhanced density, mechanical strength, and excellent biocompatibility for denture applications.

Sparse species interactions reproduce abundance correlation patterns in microbial communities

During the last decades, macroecology has identified broad-scale patterns of abundances and diversity of microbial communities and put forward some potential explanations for them. However, these advances are not paralleled by a full understanding of the dynamical processes behind them. In particular, abundance fluctuations of different species are found to be correlated, both across time and across communities in metagenomic samples. Reproducing such correlations through appropriate population models remains an open challenge. The present paper tackles this problem and points to sparse species interactions as a necessary mechanism to account for them. Specifically, we discuss several possibilities to include interactions in population models and recognize Lotka-Volterra constants as a successful ansatz. For this, we design a Bayesian inference algorithm to extract sets of interaction constants able to reproduce empirical probability distributions of pairwise correlations for diverse biomes. Importantly, the inferred models still reproduce well-known single-species macroecological patterns concerning abundance fluctuations across both species and communities. Endorsed by the agreement with the empirically observed phenomenology, our analyses provide insights into the properties of the networks of microbial interactions, revealing that sparsity is a crucial feature.

Spatially-indirect and hybrid exciton–exciton interaction in MoS2 homobilayers

Interlayer excitons in transition-metal dichalcogenide (TMD) bilayers, alongside their interplay with direct excitonic species, are supposed to offer a pathway towards robust nonlinearity, enabling the exploration of many-body quantum effects. We present a theoretical investigation of interaction among various exciton species within these structures where Coulomb attraction and repulsion are subject to reduced screening. For a homobilayer MoS2, we examine both direct, spatially-indirect, and hybridised excitons, considering the effects of direct and exchange interaction of electrons and holes distributed across one or different layers. Similar physics arises in perfectly aligned twisted TMD heterobilayers which support the direct-to-indirect exciton hybridisation. Deriving the exciton–exciton interaction matrix elements, we unveil a distinct non-monotonic dependence of the interaction on transferred momentum, changing sign from repulsive to attractive even for ground-state excitons, and compare our results with existing calculations for monolayers. Our findings demonstrate that for large momenta involved in high-density effects (strongly correlated phases), the interaction is chiefly governed by the prevailing attractive exchange component. At the same time, at small momenta that are more relevant for rarefied systems, we find that the enhancement of the interaction constant for dipolar species compared to intralayer non-dipolar excitons may be hindered by the surrounding medium. We draw comparisons with existing experiments and discuss the implications of our findings on the collective effects in TMD-based systems of excitons and exciton-polaritons.

Kinetic Study of Coprinus cinereus Peroxidase-Catalyzed Oxidation of 2,2'-Dihydroxyazobenzene.

Azo dyes are of concern due to their harmful effects on the environment and human health. The oxidation of 2,2'-dihydroxyazobenzene (DHAB) catalyzed with recombinant Coprinus cinereus (rCiP) peroxidase was investigated. The kinetic measurements were performed using the spectrophotometric and fluorimetric methods. The dependences of the initial reaction rates on enzyme, substrate and hydrogen peroxide concentrations during DHAB oxidation were established, and bimolecular constants of enzyme interaction with DHAB were calculated. This research demonstrated that the initial biocatalytic oxidation rates of DHAB depend on the pH and the estimated pKa values of the active forms of rCip. This study's findings thus contribute to a more comprehensive understanding of the biocatalytic oxidation of DHAB, providing valuable data for assessing the long-term toxicity, carcinogenesis and epigenetic effects of azo dyes in the environment.

PvDBPII elicits multiple antibody-mediated mechanisms that reduce growth in a Plasmodium vivax challenge trial

The receptor-binding domain, region II, of the Plasmodium vivax Duffy binding protein (PvDBPII) binds the Duffy antigen on the reticulocyte surface to mediate invasion. A heterologous vaccine challenge trial recently showed that a delayed dosing regimen with recombinant PvDBPII SalI variant formulated with adjuvant Matrix-MTM reduced the in vivo parasite multiplication rate (PMR) in immunized volunteers challenged with the Thai P. vivax isolate PvW1. Here, we describe extensive analysis of the polyfunctional antibody responses elicited by PvDBPII immunization and identify immune correlates for PMR reduction. A classification algorithm identified antibody features that significantly contribute to PMR reduction. These included antibody titre, receptor-binding inhibitory titre, dissociation constant of the PvDBPII-antibody interaction, complement C1q and Fc gamma receptor binding and specific IgG subclasses. These data suggest that multiple immune mechanisms elicited by PvDBPII immunization are likely to be associated with protection and the immune correlates identified could guide the development of an effective vaccine for P. vivax malaria. Importantly, all the polyfunctional antibody features that correlated with protection cross-reacted with both PvDBPII SalI and PvW1 variants, suggesting that immunization with PvDBPII should protect against diverse P. vivax isolates.

Modulating the ion-transfer electrochemistry of perfluorooctanoate with serum albumin and β-cyclodextrin.

Per- and polyfluoroalkyl substances (PFAS) are durable synthetic pollutants that persist in the environment and resist biodegradation. Ion-transfer electrochemistry at aqueous-organic interfaces is a simple strategy for the detection of ionised PFAS. Herein, we investigate the modulation of the ion transfer voltammetry of perfluorooctanoate (PFOA) at liquid-liquid micro-interface arrays by aqueous phase bovine serum albumin (BSA) or β-cyclodextrin (β-CD) and examine the determination of association constants for these binding interactions. By tracking the ion transfer current due to ionised, uncomplexed PFOA as a function of BSA or β-CD concentration, titration curves are produced. Fitting of a binding isotherm to these data provides the association constants. The association constant of PFOA with the BSA determined in this way was ca. 105 M-1 assuming a 1 : 1 binding. Likewise, the association constant for PFOA with β-CD was ca. 104 M-1 for a 1 : 1 β-CD-PFOA complex. Finally, the simultaneous effect of both BSA and β-CD on the ion transfer voltammetry of PFOA was studied, showing clearly that PFOA bound to BSA is released (de-complexed) upon addition of β-CD. The results presented here show ion transfer voltammetry as a simple strategy for the study of molecular and biomolecular binding of ionised PFAS and is potentially useful in understanding the affinity of different PFAS with aqueous phase binding agents such as proteins and carbohydrates.

SARS-CoV-2S-Protein-Ace2 Binding Analysis Using Surface Plasmon Resonance.

Surface plasmon resonance (SPR) allows for the label-free determination of the binding affinity and rate constants of bimolecular interactions. Here, we describe the method used for the analysis of the Ace2-SARS-CoV2 S-protein interaction using indirect capture of the S-protein onto the SPR surface, and flowing monomeric Ace2. This method will allow for the determination of the rate constants for affinity, with additional analysis that is achievable using S-protein capture levels in conjunction with the sensorgram response for relative activity benchmarking.

Thermodynamic model for voltammetric responses in conducting redox polymers.

Electroactive polymer materials are known to play important roles in a vast spectrum of modern applications such as in supercapacitors, fuel cells, batteries, medicine, and smart materials, etc. They are usually divided into two main groups: first, conducting π-conjugated organic polymers, which conduct electricity by cation-radicals delocalized over a polymer chain; second, redox polymers, which conduct electricity via an electron-hopping mechanism. Polymer materials belonging to these two main groups have been thoroughly studied and their thermodynamic and kinetic models have been built. However, in recent decades a lot of mixed-type materials have been discovered and investigated. To the best of our knowledge, a thermodynamic-based description of conducting redox polymers (CRPs) has not been provided yet. In this work, we present a thermodynamic model for voltammetric responses of conducting redox polymers. The derived model allows one to extract thermodynamic parameters of a CRP including the polaron delocalization degree and redox active groups interaction constant. The model was verified with voltammetric experiments on three recently synthesized CRPs and showed a satisfactory predictive ability. The simulated data are in good agreement with the experiment. We believe that developing theoretical descriptions for CRPs and other types of electroactive materials with the ability to simulate their electrochemical responses may help in future realization of new systems with superior characteristics for electrochemical energy storage, chemical sensors, pharmacological applications, etc.

Novel ternary AgIICoIIIF5 fluoride: synthesis, structure and magnetic characteristics.

We present a new compound in the silver-cobalt-fluoride system, featuring paramagnetic silver (d9) and high-spin cobalt (d6), synthesized by solid-state method in an autoclave under F2 overpressure. Based on powder X-ray diffraction, we determined that AgIICoIIIF5 crystallizes in a monoclinic system with space group C2/c. The calculated fundamental band-gap falls in the visible range of the electromagnetic spectrum, and the compound has the character of charge-transfer insulator. AgCoF5 is likely a ferrimagnet with one predominant superexchange magnetic interaction constant between mixed spin cations (Ag-Co) of -62 meV (SCAN result). Magnetometric measurements conducted on a powdered sample allowed the identification of a transition at 128 K, which could indicate magnetic ordering.

К вопросу определения точки контакта в силовых измерениях методами атомно-силовой микроскопии

Atomic force microscopy (AFM) is a widely used technique for obtaining information about the three-dimensional structure and physical and mechanical properties of surfaces. In nanoindentation methods, an AFM probe is brought to the sample from a distance and then interacts with the surface. Accurate determination of the point of contact of the probe tip with the surface in these measurements is necessary for reliable calculation of both the non-contact interaction constants and the structural and mechanical properties of the material. The tip-surface contact is preceded by a rapid jump of the probe to the surface due to attractive forces in experiments conducted in ambient conditions. If the stiffness of the probe beam or the sample does not allow the probe to deform the surface, then the end of the probe jump (minimum deflection of the beam as the probe approaches the material) is usually taken as the start of the contact. If the surface is soft enough, contact may occur earlier than the end of the rapid jump, i.e., the tip will begin to penetrate into the surface before the jump is complete. In this work it is shown that the contact of the tip with a deformable polymer surface occurs before the completion of the jump of the tip to the surface. It is reasonable to take the point corresponding to the maximum change in the beam deflection as the beginning of the contact between the probe and the material. The significant speed of the approach of the tip to the surface under the action of attractive forces leads to a loss of experimental data in the section of the curve near the transition from non-contact to contact interaction. Insufficient rate of data capture and high approach velocity can cause significant points of the force curve to be missed, i.e., lead to errors in determining the beginning of the contact both for soft and hard surfaces.

The 235-360 GHz Rotational Spectrum of 1-Oxaspiro[2.5]octa-4,7-dien-6-one─Analysis of the Ground Vibrational State and Its 10 Lowest-Energy Vibrationally Excited States.

The millimeter-wave rotational spectrum of 1-oxaspiro[2.5]octa-4,7-dien-6-one (1) was collected from 235 to 360 GHz. With the rotational spectrum of this compound available for the first time, more than 5500 a- and c-type transitions were observed and assigned for the vibrational ground state. These transitions were least-squares fit to S- and A-reduced, sextic distorted-rotor Hamiltonians in the Ir representation (σfit = 37 kHz). Additionally, transitions of four fundamental states (ν22, ν21, ν39, and ν38), four overtone states (2ν22, 3ν22, 4ν22, and 5ν22), and two combination states (ν22 + ν21 and ν22 + ν39) were measured, assigned, and least-squares fit to single-state, S- and A-reduced, sextic distorted-rotor Hamiltonians in the Ir representation (σfit < 42 kHz). The computed vibration-rotation interaction constants (B0 - Bv) (MP2 and B3LYP/6-311+G(2d,p)) were compared to their corresponding experimental values, showing excellent agreement for all fundamental states. Based on the intensities of the transitions from six members of the v ν22 series, the fundamental frequency of ν22 was determined to be 79.0 (2.1) cm-1.

Measurement of Acefylline Piperazine Interaction and Dissociation Constants in Polymer Solvent Systems

In this study the physicochemical interactions of acefylline piperazine drug (APD) were examined in aqueous and aqueous polymer systems viz., aqueous polyethylene glycol (1.0 %w/v) and aqueous polyvinyl pyrrolidone (1.0% w/v). The study was carried within the concentration ranges from 2.0×10-2 to 10.0 ×10-2 mol/dm3 at different temperatures (293.15 to 318.15 K with the difference of 5 K). Various analytical methods such as conductometric, refractometry, and liquid chromatographic (RP-HPLC) were applied. In order to observe the interaction of APD, o m was calculated to evaluate the structural influence of polymers on the mobility of solute (APD) at different temperatures. α, Kd and Walden product of APD were also assessed in aqueous polyethylene glycol and aqueous polyvinyl pyrrolidone. Solvation was observed by Walden's product showing strong solvation of APD in water-soluble polymer systems. Thermodynamic parameters for APD such as * E , ΔG*, ΔH*and ΔS* have also been evaluated as a function of temperature to determine the exo/endothermic nature of the drug dissociation process. Specific refraction, molar refraction and polarizability of APD in aqueous and aqueous polymer systems were calculated using the Lorentz-Lorentz equation and various interactions were interpreted. Drug's compatibility studies were also performed by HPLC in aqueous and aqueous polymer systems.

Hermitian and pseudo-Hermitian Hamiltonians of [formula omitted] system—Spectrum, exceptional point, quantum–classical correspondence

We in this paper study the relation of hermiticity and energy spectrum for Hamiltonians consisting of SU(1,1) generators. In contrast with the common belief, the transition from real to imaginary spectra can appear at an exceptional point for the Hermitian Hamiltonian of a conservative system. The imaginary domain of spectrum resulted from an inverted potential well unbounded from below. An outward force applies on the particle, which moves acceleratingly away from the central point similar to the minisuperspace model of expanding universe. The Hamiltonian remains Hermitian beyond the exceptional point in a price that the boson-operator realization of SU(1,1) generator Ŝz becomes non-Hermitian. Oppositely a non-Hermitian Hamiltonian (called pseudo-Hermitian) possesses real eigenvalues in the entire region of interaction constant, which increases the gradient of potential well. While the Hermitian interaction decreases the gradient continuously to zero, namely the exceptional point, where eigenstates are degenerate. We extend the non-Hermitian Hamiltonian to the periodically time-dependent and two-dimensional system. The probability density of wave function coincides with classical orbits, which are derived from the corresponding classical-counterpart of the non-Hermitian quantum Hamiltonian.

Multiferroic Properties of Co, Ru, and La Ion Doped KBiFe2O5.

The magnetic, electric, dielectric, and optical (band gap) properties of ion doped multiferroic KBiFe2O5 (KBFO) have been systematically investigated utilizing a microscopic model and the Green's function theory. Doping with Co at the Fe site and Ru at the Bi site induces changes in magnetization, coercive field, and band gap energy. Specifically, an increase in magnetization is observed, while the coercive field and band gap energy decrease. This behavior is attributed to the distinct ionic radii of the doped and host ions, leading to alterations in the exchange interaction constants. The temperature dependence of the polarization P reveals a distinctive kink at the Neel temperature TN, which shifts to higher temperatures with an increase in the applied magnetic field h. Furthermore, doping with Ru and La leads to an increase in polarization. The temperature dependence of the dielectric constant exhibits two peaks at the Neel temperature TN and the Curie temperature TC. Notably, these peaks diminish with increasing frequency. Additionally, the dielectric constant demonstrates a decrease with the rise in the applied magnetic field h. This study sheds light on the intricate interplay between ion doping, structural modifications, and multifunctional properties in KBFO, offering valuable insights into the underlying mechanisms governing its behavior across various physical domains.

Advancing understanding of structural, electronic, and magnetic properties in 3d-transition-metal TM-doped α-Ga2O3 (TM = V, Cr, Mn, and Fe): A first-principles and Monte Carlo study

In this paper, we investigated the properties of transition metal (TM)-doped α-Ga2O3 using first-principles calculations and Monte Carlo simulations. α-Ga2O3 is a wide-bandgap semiconductor material with enhanced performance and lower fabrication costs on sapphire substrates compared to β-Ga2O3. Doping with TMs can modify electrical transport, optical absorption, and magnetic properties, yet theoretical studies on this are scarce. Our study focused on V, Cr, Mn, and Fe impurities. We introduced a newly proposed scheme for efficiently determining the ground-state defect configuration during structural relaxation. We adopt a recent, novel image charge correction method to accurately calculate formation enthalpy and thermodynamic transition levels for spin-polarized transition metal ion doping, without employing the empirical dielectric constant. Results showed Cr ions tend to neutral substitutional Ga, while V, Mn, and Fe impurity ions tend to carry a negative charge in common n-type α-Ga2O3. Magnetic moments and spin-splitting impurity levels primarily arise from transition metal impurities and their d orbitals. We used the generalized four-state method to calculate exchange interaction constants between substitution lattice sites and identified (anti) ferromagnetic couplings at specific distances in a 120-atom supercell, which are negligible in total energy calculations. Monte Carlo simulations indicated a Curie temperature of 360 K in n-type α-Ga2O3: Mn system with 12.5% doping, suggesting intrinsic ferromagnetic ordering based on the Heisenberg model. Our study contributes to understanding TM-doped α-Ga2O3 electronic structure and magnetic properties through improved methodologies. The approach can be applied in research involving other TM-doped oxides or wide-bandgap semiconductors.

Vibration spectra of benzene-like models with Hooke’s law interactions

The harmonic oscillations of a spring-ball model of benzene-like nanosystems with Hooke’s law interactions between nearest, second, and third neighbors are explored. We show that in the cylindrical coordinates the dynamics of this cyclic hexagonal system is described by the Lagrange equations similar to those of the one-dimensional two-component crystal model. We demonstrate that the vibration frequencies of the hexagonal model lie on the branches of the dispersion law of the associated lattice model, and their positions are determined by the cyclic Born-Von Karman condition. The hexagonal model is generalized to one describing the benzene molecule and the fully deuterated and halogenated benzenes. The effect of hybridization of vibration modes and pushing apart of spectral branches in the crossover situation is revealed. All the discrete frequency spectrum and normal modes of oscillations and their explicit dependencies on all the constants of elastic interactions are exactly found.

Phenomenology of dark tensor currents

In this work we suggest a dark mediator model which extends the usual U(1) Lagrangian by including new degrees of freedom coupling to Standard Model fermions. Such dark particles can contribute to the neutral pion decay. For interaction constant and the dark particle mass consistent with the observed anomalies in the nuclear decays by the ATOMKI group we show that the dark tensor particles naturally incorporate lepton universality violation which introduces sizable effect on the muon anomalous magnetic moment.