476 research outputs found
REDUCED ISOTROPIC CRYSTAL MODEL WITH RESPECT TO THE FOURTH-ORDER ELASTIC MODULI
No full textUsing a reduced isotropic crystal model the relationship between the fourth-order elastic moduli of an isotropic medium and the independent components of the fourth-order elastic moduli tensor of real crystals of various crystal systems is found. To calculate the coefficients of these relations, computer algebra systems Redberry and Mathematica for working with high order tensors in the symbolic and explicit form were used, in light of the overly complex computation. In an isotropic medium, there are four independent fourth order elastic moduli. This is due to the presence of four invariants for an eighth-rank tensor in the three-dimensional space, that has symmetries over the pairs of indices. As an example, the moduli of elasticity of an isotropic medium corresponding to certain crystals of cubic system are given (LiF, NaCl, MgO, CaF2). From the obtained results it can be seen that the reduced isotropic crystal model can be most effectively applied to high-symmetry crystal systems
Creep damage anisotropy of thinwalled elements structures
No full textThe paper is devoted to the development and theoretical justification of an anisotropy creep damage material model. For the description of initial anisotropy and damage-induced anisotropy the second-order damage tensor has been used. The numerical method of anisotropy creep damage lifetime prediction in thin-walled elements of structures was elaborated on the basis of the proposed model and FE scheme. The results of anisotropy creep damage analysis in models of plates were discussed
Комплексні числа та їх застосування для представлення кривих і областей на комплексній площині
No full textThe educational-methodological textbook focuses on an important topic in mathematical analysis – the calculus of complex functions with a single variable. This textbook extensively explores the fundamental theoretical concepts and offers solutions to standard problems. It incorporates exercises for study and a series of tasks for individual student work. Tailored for students and lecturers in higher technical educational institutions.Навчально-методичний посібник присвячений важливій темі математичного аналізу – обчисленню функцій комплексної змінної. В ньому детально розглядаються фундаментальні теоретичні концепції та надаються розв'язки стандартних задач. Посібник також включає вправи для вивчення та серію завдань для індивідуальної роботи студентів. Розраховано на студентів і викладачів вищих технічних навчальних закладів
Interaction of atomic systems with quantum vacuum beyond electric dipole approximation
No full textThe photonic environment can significantly influence emission properties and interactions among atomic systems. In such scenarios, frequently the electric dipole approximation is assumed that is justified as long as the spatial extent of the atomic system is negligible compared to the spatial variations of the field. While this holds true for many canonical systems, it ceases to be applicable for more contemporary nanophotonic structures. To go beyond the electric dipole approximation, we propose and develop in this article an analytical framework to describe the impact of the photonic environment on emission and interaction properties of atomic systems beyond the electric dipole approximation. Particularly, we retain explicitly magnetic dipolar and electric quadrupolar contributions to the light-matter interactions. We exploit a field quantization scheme based on electromagnetic Green’s tensors, suited for dispersive materials. We obtain expressions for spontaneous emission rate, Lamb shift, multipole-multipole shift and superradiance rate, all being modified with dispersive environment. The considered influence could be substantial for suitably tailored nanostructured photonic environments, as demonstrated exemplarily
Measurement of the azimuthal anisotropy of charged particles in TeV OO and NeNe collisions with the ATLAS detector
No full textInternational audienceThis paper presents the first measurements of the azimuthal anisotropy coefficients , which quantify the -order Fourier modulation of charged-particle azimuthal distributions, for -4 in TeV and collisions recorded with the ATLAS detector at the Large Hadron Collider in 2025. The coefficients are measured as a function of transverse momentum (), collision centrality, and event multiplicity. They are extracted using two complementary methods: two-particle correlations with a template-fit subtraction of short-range non-flow contributions, and four-particle subevent cumulants, which intrinsically suppress non-flow effects and provide sensitivity to flow fluctuations. The results show a clear hierarchy and a non-monotonic dependence on , reaching a maximum around 2 GeV, consistent with trends observed in heavy-ion collisions. Detailed comparisons between the two collision systems reveal an enhanced in central collisions, consistent with theory expectations based on the predicted prolate deformation of neon nuclei, in contrast to the slightly tetrahedral structure predicted for oxygen. The four-particle cumulant results highlight strong event-by-event fluctuations and provide the greatest sensitivity to nuclear shape effects. These measurements can place new constraints on the initial geometry and the hydrodynamic response in light-ion collisions, offering valuable input for models of nuclear structure
Search for same-charge top-quark pair production in ppcollisions at [sqrt] s = 13 TeV with the ATLAS detector
No full textA search for the production of top-quark pairs with the same electric charge (tt or ¯t¯t) is presented. The analysis uses proton-proton collision data at √s = 13 TeV, recorded by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb−1. Events with two same-charge leptons and at least two b-tagged jets are selected. Neural networks are employed to define two selections sensitive to additional couplings beyond the Standard Model that would enhance the production rate of same-sign top-quark pairs. No significant signal is observed, leading to an upper limit on the total production cross-section of same-sign top-quark pairs of 1.6 fb at 95% confidence level. Corresponding limits on the three Wilson coefficients associated with the O(1)tu , O(1)Qu, and O(8)Qu operators in the Standard Model Effective Field Theory framework are derived
Search for same-charge top-quark pair production in pp collisions at √s = 13 TeV with the ATLAS detector
No full textA search for the production of top-quark pairs with the same electric charge (tt or
t¯t¯) is presented. The analysis uses proton-proton collision data at √
s = 13 TeV, recorded by
the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity
of 140 fb−1
. Events with two same-charge leptons and at least two b-tagged jets are selected.
Neural networks are employed to define two selections sensitive to additional couplings beyond
the Standard Model that would enhance the production rate of same-sign top-quark pairs. No
significant signal is observed, leading to an upper limit on the total production cross-section
of same-sign top-quark pairs of 1.6 fb at 95% confidence level. Corresponding limits on the
three Wilson coefficients associated with the O
(1)
tu , O
(1)
Qu, and O
(8)
Qu operators in the Standard
Model Effective Field Theory framework are derived
Configuration, performance, and commissioning of the ATLAS b-jet triggers for the 2022 and 2023 LHC data-taking periods
No full textIn 2022 and 2023, the Large Hadron Collider produced approximately two billion hadronic
interactions each second from bunches of protons that collide at a rate of 40 MHz. The ATLAS trigger
system is used to reduce this rate to a few kHz for recording. Selections based on hadronic jets,
their energy, and event topology reduce the rate to O (10) kHz while maintaining high efficiencies
for important signatures resulting in b-quarks, but to reach the desired recording rate of hundreds of
Hz, additional real-time selections based on the identification of jets containing b-hadrons (b-jets)
are employed to achieve low thresholds on the jet transverse momentum at the High-Level Trigger.
The configuration, commissioning, and performance of the real-time ATLAS b-jet identification
algorithms for the early LHC Run 3 collision data are presented. These recent developments provide
substantial gains in signal efficiency for critical signatures; for the Standard Model production of
Higgs boson pairs, a 50% improvement in selection efficiency is observed in final states with four
b-quarks or two b-quarks and two hadronically decaying τ-leptons
Search for events with one displaced vertex from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in collisions at TeV
No full textA search for events with one displaced vertex from long-lived particles using data collected by the ATLAS detector at the Large Hadron Collider is presented, using 140 fb of proton-proton collision data at TeV recorded in 2015-2018. The search employs techniques for reconstructing vertices of long-lived particles decaying into hadronic jets in the muon spectrometer displaced between 3 m and 14 m from the primary interaction vertex. The observed number of events is consistent with the expected background and limits for several benchmark signals are determined. A scalar-portal model and a Higgs-boson-portal baryogenesis model are considered. A dedicated analysis channel is employed to target Z-boson associated long-lived particle production, including an axion-like particle and a dark photon model. For the Higgs boson model, branching fractions above 1% are excluded at 95% confidence level for long-lived particle proper decay lengths ranging from 5 cm to 40 m. For the photo-phobic axion-like particle model considered, this search produces the strongest limits to date for proper decay lengths greater than cm.A search for events with one displaced vertex from long-lived particles using data collected by the ATLAS detector at the Large Hadron Collider is presented, using 140 fb-1 of proton-proton collision data at s=13 TeV recorded in 2015–2018. The search employs techniques for reconstructing vertices of long-lived particles decaying into hadronic jets in the muon spectrometer displaced between 3 m and 14 m from the primary interaction vertex. The observed number of events is consistent with the expected background and limits for several benchmark signals are determined. A scalar-portal model and a Higgs-boson-portal baryogenesis model are considered. A dedicated analysis channel is employed to target Z-boson associated long-lived particle production, including an axionlike particle and a dark photon model. For the Higgs boson model, branching fractions above 1% are excluded at 95% confidence level for long-lived particle proper decay lengths ranging from 5 cm to 40 m. For the photophobic axionlike particle model considered, this search produces the strongest limits to date for proper decay lengths greater than O(10) cm.A search for events with one displaced vertex from long-lived particles using data collected by the ATLAS detector at the Large Hadron Collider is presented, using 140 fb of proton-proton collision data at TeV recorded in 2015-2018. The search employs techniques for reconstructing vertices of long-lived particles decaying into hadronic jets in the muon spectrometer displaced between 3 m and 14 m from the primary interaction vertex. The observed number of events is consistent with the expected background and limits for several benchmark signals are determined. A scalar-portal model and a Higgs-boson-portal baryogenesis model are considered. A dedicated analysis channel is employed to target Z-boson associated long-lived particle production, including an axion-like particle and a dark photon model. For the Higgs boson model, branching fractions above 1% are excluded at 95% confidence level for long-lived particle proper decay lengths ranging from 5 cm to 40 m. For the photo-phobic axion-like particle model considered, this search produces the strongest limits to date for proper decay lengths greater than cm
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