Georgian Technical University

The discovery of thermoelectric cobaltites initiated a systematic exploration of these materials for potential applications in thermoelectric generators, which convert waste heat into electricity. This technology may contribute to addressing the current energy crisis. Among the cobaltites studied, p-type Bi2Sr2Co2Oy is a promising thermoelectric material. However, a significant drawback of cobaltites is their low thermoelectric conversion efficiency. To improve thermoelectric performance, it is essential to optimize synthesis techniques, enhance microstructure, and incorporate various dopants and additives, etc. In this work, reference, Co3(BO3)2 and NaF-substituted, as well as Co3(BO3)2/NaF co-substituted Bi2Sr2Co2Oy ceramics were prepared using the sol–gel method. We examined the microstructure and evaluated the power factor (PF) and figure of merit (ZT) through measurements of electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (k). The introduction of substituents reduced the resistivity of Bi2Sr2Co2Oy, leading to improvements in both PF and ZT values. The highest PF and ZT values were achieved for Co3(BO3)2–substituted Bi2Sr2Co2Oy. The incorporation of Co3(BO3)2 significantly increased the material’s grain size and density. The PF enhanced from 0.124 mW/(m⋅K²) at 973 K for the reference sample to 0.228 mW/(m⋅K²) for the Co3(BO3)2 –substituted sample, while ZT raised from 0.054 to 0.072 at 573 K.

Metal alloys are widely used in implantology due to their excellent mechanical properties. However, their biocompatibility can be compromised by corrosion, which releases toxic metal ions that may provoke adverse biological reactions and contribute to implant failure. This study introduces a novel metal-ceramic composite based on a high-chromium FeCrAl alloy, specifically engineered to form a thermally grown α-Al₂O₃ surface layer. This design aims to significantly enhance biocompatibility and corrosion resistance for potential biomedical implant applications. Samples of the Fe-44Cr-5Al alloy were produced using an arc melting process. The mechanically polished alloy coupons were given a mirror-like finish and underwent high-temperature oxidation at 1050 °C for 20 h in laboratory air to develop a dense and adherent α-Al₂O₃ layer. Both bare and oxidized samples were immersed in artificial saliva at 37 °C for two months to assess their corrosion resistance under simulated oral conditions. Biocompatibility was evaluated through cytotoxicity and mitotic activity tests using primary human gingival fibroblasts cultured on both the bare and oxidized samples. The results showed that thermal oxidation effectively produced a uniform, adherent, and stable α-Al₂O₃ layer on the surface of the FeCrAl alloy. The oxidized samples demonstrated superior corrosion resistance, with negligible metal ion release and no formation of corrosion products. In contrast, the bare (unoxidized) alloy exhibited extensive corrosion and significant ion release. Cytotoxicity tests indicated that the oxidized alloy supported normal cell adhesion, proliferation, and morphology comparable to control samples. Although a slight reduction in cell proliferation was noted on the oxidized metal surface, overall bioactivity remained high. Structural and morphological analyses were performed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Grazing Incidence X-ray Diffraction (GIXRD) to confirm the formation and integrity of the oxide layer. Post-immersion corrosion tests in artificial saliva and detailed microscopy further validated the favorable biological responses to the oxidized alloy.

We establish necessary and sufficient conditions for a weight v v guaranteeing the boundedness of multilinear Riemann–Liouville operators from ∏j=1mLpj${\prod}_{j=1}^m{L}^{p_j}$ to Lvq${L}_v^q$.

Terahertz (THz) technology provides precise monitoring capabilities in dynamic environments, offering unique insights into insect habitats. Our study focuses on environmental monitoring of European honey bees (Apis mellifera) through a combination of measurements and simulations. Initially, the dielectric material properties of honey bee body parts are characterized across the spectral range of 1–500 GHz to collect heterogeneous empirical data. To extend the study, honey bee mockups made from polyamide 12 (PA12) and epoxy resin are employed and validated as effective substitutes for real bees through comparative scattering analyses. The research further explores radar cross-section (RCS), imaging, and spectral properties using advanced THz technologies, including resonant tunneling diodes (RTDs) operating at 250 GHz and THz time-domain spectroscopy (THz-TDS) for frequencies exceeding 250 GHz. High-resolution imaging, utilizing a 450 GHz bandwidth, captures intricate anatomical features of both real and 3D-printed bees, showcasing the potential of THz technology for detailed environmental monitoring. Finally, simulations at 300 GHz assess the dosimetry and feasibility of non-invasive, continuous monitoring approaches based on the heterogeneous honey bee model.

A search is presented for the pair production of new heavy resonances, each decaying into a top quark (t) or antiquark and a gluon (g). The analysis uses data recorded with the CMS detector from proton–proton collisions at a center-of-mass energy of 13 $\,\text {Te}\hspace{-.08em}\text {V}$ Te V at the LHC, corresponding to an integrated luminosity of 138 $\,\text {fb}^{-1}$ fb - 1 . Events with one muon or electron, multiple jets, and missing transverse momentum are selected. After using a deep neural network to enrich the data sample with signal-like events, distributions in the scalar sum of the transverse momenta of all reconstructed objects are analyzed in the search for a signal. No significant deviations from the standard model prediction are found. Upper limits at 95% confidence level are set on the product of cross section and branching fraction squared for the pair production of excited top quarks in the $\text {t}^{*} \rightarrow {\text {t}} {\text {g}}$ t ∗ → tg decay channel. The upper limits range from 120 to 0.8 $\,\text {fb}$ fb for a $\text {t}^{*}$ t ∗ with spin-1/2 and from 15 to 1.0 $\,\text {fb}$ fb for a $\text {t}^{*}$ t ∗ with spin-3/2. These correspond to mass exclusion limits up to 1050 and 1700 $\,\text {Ge}\hspace{-.08em}\text {V}$ Ge V for spin-1/2 and spin-3/2 $\text {t}^{*}$ t ∗ particles, respectively. These are the most stringent limits to date on the existence of $\text {t}^{*} \rightarrow {\text {t}} {\text {g}}$ t ∗ → tg resonances.

A bstract A standard model effective field theory (SMEFT) analysis with dimension-six operators probing nonresonant new physics effects is performed in the Higgs-strahlung process, where the Higgs boson is produced in association with a W or Z boson, in proton-proton collisions at a center-of-mass energy of 13 TeV. The final states in which the W or Z boson decays leptonically and the Higgs boson decays to a pair of bottom quarks are considered. The analyzed data were collected by the CMS experiment between 2016 and 2018 and correspond to an integrated luminosity of 138 fb − 1 . An approach designed to simultaneously optimize the sensitivity to Wilson coefficients of multiple SMEFT operators is employed. Likelihood scans as functions of the Wilson coefficients that carry SMEFT sensitivity in this final state are performed for different expansions in SMEFT. The results are consistent with the predictions of the standard model.

The present investigation reports the content of radionuclides (226Ra, 232Th, 40K, 137Cs, and 235U) in soil samples from active farming lands in Russia. The samples included both control and fertilizer-infused soils. The fertilizers used in the investigation were a combination of two or three of the followings: KCl, K2SO4, KNO3, superphosphate, and ammonium nitrate. HPGe gamma spectrometry was used to measure the content of radionuclides in the soils. Overall, the average content (in Bq/kg) of 40K, 226Ra, 232Th, 137Cs, and 235U in the soil samples was 379, 20.13, 24.65, 2.92, and 1.27, respectively. The highest content of radionuclides was observed in the soil treated with fertilizer of the following composition: K2SO4 + superphosphate + ammonium-nitrate and the lowest was in case of KNO3 + superphosphate + ammonium-nitrate. The content of radionuclides determined in the present study was comparatively lower than in the similar studies from other parts of the world. In addition, the risk assessment indices rules out the possibility of any hazardous situation as these values were lower than the reference limits.

In this paper, quasi-statical boundary contact problems of couple-stress viscoelasticity for inhomogeneous anisotropic bodies with regard to friction are investigated. Non-coercive cases considered, when a friction force acts on the entire boundary of a viscoelastic body. The posed boundary-contact problem equivalently reduced to a spatial variational inequality. After factorization of the main spaces with respect to the vector space of the function of generalized rigid displacements, the necessary condition for the existence of solutions is obtained. This condition, under some additional assumptions, becomes a sufficient condition for the existence of solutions.

A bstract Measurements are presented of inclusive and differential cross sections for Z boson associated production of top quark pairs ( $\textrm{t}\overline{\textrm{t}}\textrm{Z}$ t t ¯ Z ) and single top quarks (tZq or tWZ). The data were recorded in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb − 1 . Events with three or more leptons, electrons or muons, are selected and a multiclass deep neural network is used to separate three event categories, the $\textrm{t}\overline{\textrm{t}}\textrm{Z}$ t t ¯ Z and tWZ processes, the tZq process, and the backgrounds. A profile likelihood approach is used to unfold the differential cross sections, to account for systematic uncertainties, and to determine the correlations between the two signal categories in one global fit. The inclusive cross sections for a dilepton invariant mass between 70 and 110 GeV are measured to be 1.14 ± 0.07 pb for the sum of $\textrm{t}\overline{\textrm{t}}\textrm{Z}$ t t ¯ Z and tWZ, and 0.81 ± 0.10 pb for tZq, in good agreement with theoretical predictions.

A bstract A search is presented for a heavy resonance decaying into a Z boson and a Higgs (H) boson. The analysis is based on data from proton-proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 138 fb − 1 , recorded with the CMS experiment in the years 2016–2018. Resonance masses between 1.4 and 5 TeV are considered, resulting in large transverse momenta of the Z and H bosons. Final states that result from Z boson decays to pairs of electrons, muons, or neutrinos are considered. The H boson is reconstructed as a single large-radius jet, recoiling against the Z boson. Machine-learning flavour-tagging techniques are employed to identify decays of a Lorentz-boosted H boson into pairs of charm or bottom quarks, or into four quarks via the intermediate H → WW * and ZZ * decays. The analysis targets H boson decays that were not generally included in previous searches using the H → $\textrm{b}\overline{\textrm{b}}$ b b ¯ channel. Compared with previous analyses, the sensitivity for high resonance masses is improved significantly in the channel where at most one b quark is tagged.

A bstract A search for dark matter (DM) particles produced in association with bottom quarks is presented. The analysis uses proton-proton collision data at a center-of-mass energy of $\sqrt{s}$ s = 13 TeV, corresponding to an integrated luminosity of 138 fb − 1 . The search is performed in a final state with large missing transverse momentum and a pair of jets originating from bottom quarks. No significant excess of data is observed with respect to the standard model expectation. Results are interpreted in the context of a type-II two-Higgs-doublet model with an additional light pseudoscalar (2HDM+a). An upper limit is set on the mass of the lighter pseudoscalar, probing masses up to 260 GeV at 95% confidence level. Sensitivity to the parameter space with the ratio of the vacuum expectation values of the two Higgs doublets, tan β , greater than 15 is achieved, capitalizing on the enhancement of couplings between pseudoscalars and bottom quarks with high tan β .

A bstract Differential cross sections for top quark pair ( $\textrm{t}\overline{\textrm{t}}$ t t ¯ ) production are measured in proton-proton collisions at a center-of-mass energy of 13 TeV using a sample of events containing two oppositely charged leptons. The data were recorded with the CMS detector at the CERN Large Hadron Collider and correspond to an integrated luminosity of 138 fb − 1 . The differential cross sections are measured as functions of kinematic observables of the $\textrm{t}\overline{\textrm{t}}$ t t ¯ system, the top quark and antiquark and their decay products, as well as of the number of additional jets in the event. The results are presented as functions of up to three variables and are corrected to the parton and particle levels. When compared to standard model predictions based on quantum chromodynamics at different levels of accuracy, it is found that the calculations do not always describe the observed data. The deviations are found to be largest for the multi-differential cross sections.

A bstract A search for long-lived heavy neutral leptons (HNLs) using proton-proton collision data corresponding to an integrated luminosity of 138 fb − 1 collected at $\sqrt{s}$ s = 13 TeV with the CMS detector at the CERN LHC is presented. Events are selected with a charged lepton originating from the primary vertex associated with the proton-proton interaction, as well as a second charged lepton and a hadronic jet associated with a secondary vertex that corresponds to the semileptonic decay of a long-lived HNL. No excess of events above the standard model expectation is observed. Exclusion limits at 95% confidence level are evaluated for HNLs that mix with electron and/or muon neutrinos. Limits are presented in the mass range of 1–16.5 GeV, with excluded square mixing parameter values reaching as low as 2 × 10 − 7 . For masses above 11 GeV, the presented limits exceed all previous results in the semileptonic decay channel, and for some of the considered scenarios are the strongest to date.

In the present paper, the models of structural analysis and evaluation of efficiency indicators (reliability, fault tolerance, viability, and flexibility) of a multi-core processor with variable structure, equipped with multi-functional cores, are considered. Using logical–probabilistic methods, the following has been developed: models for evaluating the reliability and fault tolerance of processor cores as multi-functional elements; logical–probabilistic models of the shortest paths, flexibility, and performance conditions for successful operation of multi-core processors based on multi-functional cores; and models for estimating the reliability, fault tolerance, and lifetime of multi-core processors considering all possible states of performance. The results of the structural analysis of two-core and four-core processors and the trends of increasing the efficiency indicators of multi-core processors are presented.

This paper presents one of the most interesting generalizations of Gaver’s basic two-unit parallel system sustained by a cold standby unit and attended by a repairman with multiple vacations. The system was studied using the supplementary variables technique, like many other similar semi-Markov systems. D.P. Gaver, Jr. was the first to apply this method for constructing and studying reliability models, and since then it has been then widely used by other researchers to study various reliability problems. As a result, non-classical boundary value problem of mathematical physics with nonlocal boundary conditions has been obtained. Until now, a solution to this problem was obtained in terms of Laplace transforms. Naturally, the most significant part of the problem is a system of partial differential equations (Kolmogorov forward equations). In this study, we demonstrate that Kolmogorov equations are redundant and we can solve the problem by avoiding the necessity of using them. We present here a novel, purely probabilistic approach. The results are formulated as rigorous mathematical statements, offering a significant simplification in the reliability analysis of stochastic systems. Our findings show that this novel approach can be applied to study both semi-Markov and some non semi-Markov models where the supplementary variables technique is used.

A bstract A search is presented for the resonant production of a pair of standard model-like Higgs bosons using data from proton-proton collisions at a centre-of-mass energy of 13 TeV, collected by the CMS experiment at the CERN LHC in 2016–2018, corresponding to an integrated luminosity of 138 fb − 1 . The final state consists of two b quark-antiquark pairs. The search is conducted in the region of phase space where at least one of the pairs is highly Lorentz-boosted and is reconstructed as a single large-area jet. The other pair may be either similarly merged or resolved, the latter reconstructed using two b-tagged jets. The data are found to be consistent with standard model processes and are interpreted as 95% confidence level upper limits on the product of the cross sections and the branching fractions of the spin-0 radion and the spin-2 bulk graviton that arise in warped extradimensional models. The limits set are in the range 9.74–0.29 fb and 4.94–0.19 fb for a narrow radion and a graviton, respectively, with masses between 1 and 3 TeV. For a radion and for a bulk graviton with widths 10% of their masses, the limits are in the range 12.5–0.35 fb and 8.23–0.23 fb, respectively, for the same masses. These limits result in the exclusion of a narrow-width graviton with a mass below 1.2 TeV, and of narrow and 10%-width radions with masses below 2.6, and 2.9 TeV, respectively.