Hasil untuk "Nuclear and particle physics. Atomic energy. Radioactivity"

WANG Luyao1, ZHANG Fuhai1, GUO Yi2, CHAO Yilin3, LIU Xiangsong4, MENG Jin1, YUAN Hong5

Aiming at the abnormal low-frequency vibration of the three-bearing reactor coolant pump during the service period of the power station, the ANDRITZ reactor coolant pump was taken as the research object. Based on the calculation methods of fluid dynamics and rotor dynamics, the vibration characteristics of the reactor coolant pump shafting, the generation mechanism of half-frequency whirl of the reactor coolant pump, the key factors affecting the stability of water-lubricated bearings and their physical nature were explored. Then the water-film whirl problem of reactor coolant pump was studied. It is found that the nonlinear dynamic instability of water-lubricated bearing induces the half-frequency whirl phenomenon of reactor coolant pump. Under rated working conditions, the amplitude boundary of the nuclear pump shafting is double horn type, and the center point of the double horn is near the bearing area of the drive end of the motor. The vibration characteristics of the reactor coolant pump shafting in different coaxial segments are significantly different. The half-frequency whirl phenomenon mainly appears in the area near the coupling and the pump shaft side, while the upper shaft section of the motor is mainly power-frequency vibration, and the impeller side shaft section is mainly half-frequency vibration. The tangential force perpendicular to the rotation direction of the rotor is the key force leading to the water-film whirl problem, and the cross-stiffness coefficient and the average circumferential velocity ratio of the liquid film of the water-lubricated bearing are the key physical quantities affecting the tangential force. The research results are helpful to the optimal design of reactor coolant pump, fault diagnosis, and operation and maintenance management of power station.

Tayyab Naseer, M. Sharif, M. Waqas et al.

In this article, we develop two unique singularity-free solutions that describe anisotropic interior fluid configurations in f(R,T) gravity. In this regard, the extended field equations are developed corresponding to a static interior spacetime. This system of equations is facilitated by imposing two novel constraints in order to get a unique solution. We derive two different solutions by choosing specific types of anisotropic pressure. While solving these equations, several constants are involved as a result of performing exact integration. Matching the interior metric to the Schwarzschild exterior metric at the sphere’s boundary in both scenarios yields these integration constants. Another factor that plays an important role in finding the constants is the zero radial pressure. Afterwards, physical feasibility of both compact models is explored under specific conditions. To do so, the predicted data of two stars, named 4U 1820-30 and Cen X-3 is used along with different values of the model parameter. It is reported that both our astrophysical solutions are aligned with the criteria of physical existence of such models under certain parametric values.

Xiaoyun Shao, Carlos A. P. Bengaly, Rodrigo S. Gonçalves et al.

Abstract In this paper, we obtain new measurements of the angular homogeneity scale ( $$\theta _H$$ θ H ) from the BOSS DR12 and eBOSS DR16 catalogs of Luminous Red Galaxies of the Sloan Digital Sky Survey. Considering the flat $$\Lambda $$ Λ CDM model, we use the $$\theta _H(z)$$ θ H ( z ) data to constrain the matter density parameter ( $$\Omega _{m0}$$ Ω m 0 ) and the Hubble constant ( $$H_{0}$$ H 0 ). We find $$H_0 = 65^{+10}_{-7}$$ H 0 = 65 - 7 + 10 km s $$^{-1}$$ - 1 Mpc $$^{-1}$$ - 1 and $$\Omega _{m0}>0.296$$ Ω m 0 > 0.296 . By combining the $$\theta _H$$ θ H measurements with current Baryon Acoustic Oscillations (BAO) and Type Ia Supernova (SN) data, we obtain $$H_{0}= 66.8 \pm 5.0$$ H 0 = 66.8 ± 5.0 km s $$^{-1}$$ - 1 Mpc $$^{-1}$$ - 1 and $$\Omega _{m0} = 0.292^{+0.013}_{-0.015}$$ Ω m 0 = 0 . 292 - 0.015 + 0.013 ( $$\theta _H$$ θ H + BAO) and $$H_{0}=66.8 \pm 5.4 $$ H 0 = 66.8 ± 5.4 km s $$^{-1}$$ - 1 Mpc $$^{-1}$$ - 1 and $$\Omega _{m0}=0.331 \pm 0.018$$ Ω m 0 = 0.331 ± 0.018 ( $$\theta _H$$ θ H + SN). We show that $$\theta _H$$ θ H measurements help break the BAO and SN degeneracies concerning $$H_0$$ H 0 , as they do not depend on the sound horizon scale at the drag epoch or the SN absolute magnitude value obtained from the distance ladder method. Hence, despite those constraints are less stringent compared to other probes, $$\theta _H$$ θ H data may provide an independent cosmological probe of $$H_0$$ H 0 in light of the Hubble tension. For completeness, we also forecast the constraining power of future $$\theta _H$$ θ H data via Monte Carlo simulations. Considering a relative error of the order of 1 $$\%$$ % , we obtain competitive constraints on $$\Omega _{m0}$$ Ω m 0 and $$H_0$$ H 0 ( $$\approx 5\%$$ ≈ 5 % error) from the joint analysis with current SN and BAO measurements.

Guo Pu, Jintao Zhang, Bingsheng Li et al.

Exploring novel plasma-facing materials with exceptional irradiation resistance is a pivotal and challenging endeavor for applications in the harsh environment of energetic ion irradiation in future fusion reactors. In this work, tungsten-containing WTaTiVCr refractory high-entropy alloys (RHEAs) featuring nano-columnar crystalline structures were subjected to irradiation with 60 keV helium ion (He ^+ ) beams at fluences ranging from 1 × 10 ^16 cm ^−2 to 2 × 10 ^17 to elucidate the fundamental mechanisms governing He behavior and superficial swelling height. After irradiation, the WTaTiVCr RHEAs demonstrated remarkable micro-structural stability, exhibiting only minimal grain growth while maintaining their characteristic columnar architecture. At the highest fluence (2 × 10 ^17 cm ^−2 ), detailed characterization revealed the preferential formation of distinctive ribbon-like He bubbles along grain boundaries, confirming these interfacial regions as favorable nucleation sites. While the overall phase structure remained stable throughout the irradiation process, advanced micro-structural analysis detected localized elemental segregation phenomena. This segregation behavior appears to be directly correlated with the development of highly pressurized bubbles and associated micro-crack formation within the columnar grain boundaries. Meanwhile, this study provides comprehensive insights into the complex interactions between internal bubble formation and surface blister development, revealing that these mechanisms collectively contribute to the observed irradiation-induced swelling behavior.

Georg Bergner, Stefano Piemonte, Mithat Ünsal

Abstract We present our investigations of SU(N) adjoint QCD in two dimensions with one Majorana fermion on the lattice. We determine the relevant parameter range for the simulations with Wilson fermions and present results for Polyakov loop, chiral condensate, and string tension. In the theory with massive fermions, all observables we checked show qualitative agreement between numerical lattice data and theory, while the massless limit is more subtle since chiral and non-invertible symmetry of the continuum theory are explicitly broken by lattice regularization. In thermal compactification, we observe N perturbative vacua for the holonomy potential at high-T with instanton events connecting them, and a unique vacuum at low-T. At finite-N, this is a cross-over and it turns to a phase transition at large-N thermodynamic limit. In circle compactification with periodic boundary conditions, we observe a unique center-symmetric minimum at any radius. In continuum, the instantons in the thermal case carry zero modes (for even N) and indeed, in the lattice simulations, we observe that chiral condensate is dominated by instanton centers, where zero modes are localized. We present lattice results on the issue of confinement vs. screening in the theory and comment on the roles of chiral symmetry and non-invertible symmetry.

T.O.S.J. Bosman, M. Bernert, L. Ceelen et al.

Control of heat exhaust is essential for the operation of power producing fusion reactors. Here, we present results of heat exhaust feedback control experiments in JET and AUG. In JET, we demonstrate the first X-point radiator (XPR) control in DD and DT discharges using argon seeding. In AUG, we improve the XPR control with nitrogen seeding, resulting in achieving the first detached L-H and H-L transition (in a single discharge). The controllers are designed using a model-based design procedure. The required models are obtained experimentally using perturbative (system identification) experiments. We study the dynamic response of the XPR to various seeding species and varying operating conditions. We find that the sensitivity (relative gain) of the XPR varies as function the height of the radiator inside the confined region but that the relative phase is consistent for all operating points. In AUG, the XPR is also less sensitive to impurity seeding changes for higher heating powers. In JET, we show that the XPR dynamics are the same for DD and DT plasmas. However, we observe that XPR control is only possible with argon and not with neon. The results show that a controller might well be designed in earlier stages of operation of a future device, but remains applicable and can be further tuned for full power operation.

Simon Caron-Huot, Yue-Zhou Li, Julio Parra-Martinez et al.

Abstract We study constraints from causality and unitarity on 2 → 2 graviton scattering in four-dimensional weakly-coupled effective field theories. Together, causality and unitarity imply dispersion relations that connect low-energy observables to high-energy data. Using such dispersion relations, we derive two-sided bounds on gravitational Wilson coefficients in terms of the mass M of new higher-spin states. Our bounds imply that gravitational interactions must shut off uniformly in the limit G → 0, and prove the scaling with M expected from dimensional analysis (up to an infrared logarithm). We speculate that causality, together with the non-observation of gravitationally-coupled higher spin states at colliders, severely restricts modifications to Einstein gravity that could be probed by experiments in the near future.

DONG Tao;LIU Ximing;XING Guilai;WANG Zhentao;HUANG Yibin;LIU Jinhui;WU Zhifang

In large object radiation imaging system, the interaction between medium and high energy (MeV) X/γ-ray and matter is dominated by Compton scattering, which produces a large number of the scattered particles. And the influence of the scattered particles on the radiographic images has always been a tough problem that plagues the developers. And the rear collimator is commonly used to reduce the influence of the scattered particles and improve the quality of the radiographic images. At present, the relevant research mainly analyzes the distribution of the scattered particles in the detector array, but there is a lack of research on the distribution of the scattered particles on the surface of the inspected object. Based on the Monte-Carlo simulation model of the 60Co large object radiation imaging system, a common medium-density substance (iron plate) was selected as the inspected object, and the number distribution and energy distribution of the scattered particles were analyzed in detail when γ-ray penetrates iron plates from different positions and with different thicknesses. Also, the diffusion effect of the scattered particles and the shielding effect of the rear collimator on the scattered particles were analyzed. There are some results drawn in this paper. In the horizontal direction, the diffusion effect of the scattered particles caused by multiple Compton scattering is limited, and most of the scattered particles come from the area covered by the initial γ-ray beam on the object. About 90% of the scattered particles have a horizontal distribution range of 40-70 mm on the surface of the object, which will limit the shielding effect of the rear collimator. When the distance S between the iron plate (with the thickness of 100 mm) and the detector array is reduced to the limit of 500 mm for safe driving, there is approximately 39.74% of the scattered particles shielded by the rear collimator (Fe) with the collimation ratio of 20∶1 and the best thickness of 5 mm, while the ideal rear collimator absorbing all incident particles can shield about 63.21% of the scattered particles. When the distance S increases to 1 750 mm or more, the scattering effect of the rear collimator will be severe and cause an increase in the number of the scattered particles instead of performing its function of shielding the scattered particles, and a wider rear collimator may cause more serious scattering interference. Therefore, in the large object radiation imaging system, the scattering effect of the rear collimator cannot be ignored, and its shielding effect on the scattered particles is also limited.

D. Silvagni, P.T. Lang, T. Happel et al.

This letter reports on the efforts carried out at the ASDEX Upgrade tokamak to integrate I-mode plasmas with pellet fueling and to increase the I-mode Greenwald fraction $f_{\mathrm{GW}}$ , two important requirements for any DEMO operational scenario. For the first time, stationary I-mode plasmas have been achieved with pellet fueling and the core Greenwald fraction has been increased up to 0.8. Larger $f_{\mathrm{GW}}$ were not achieved due to technical constraints rather than to a physics-based limit. Pellet-fueled I-mode plasmas exhibit enhanced core and edge density, while core and edge temperature are reduced. Nonetheless, edge normalized gradients remain I-mode-like, namely shallow for the density and steep for the temperature. The I-mode energy confinement time is found to obey two distinct density dependencies: for $f_{\mathrm{GW}}\lt0.4$ it rises with increasing $f_{\mathrm{GW}}$ , while for $f_{\mathrm{GW}} \gt 0.4$ the energy confinement time plateaus with increasing $f_{\mathrm{GW}}$ , or even decreases with $f_{\mathrm{GW}}$ for the pellet-fueled plasmas. Similarities with Ohmic and L-mode energy confinement time dependency on density are discussed.

Andréa Vidal Ferreira, Ana Carolina Araujo Bispo, Christiane Silva Leite et al.

Small animals, such as mice, are used in radiopharmaceutical biodistribution studies and innumerous others preclinical investigations involving ionizing radiation. Longitudinal preclinical studies with five or more image procedures, involving radiopharmaceuticals injection and/or X-radiation, are not uncommon. However, a suitable dosimetric evaluation is not always available and, sometimes, absorbed doses in animal organs or tissues and their influence in experimental results were not appropriately taken into account. Accurate calculation of absorbed doses in mice organs are needed to evaluate potential radiobiological effects that may interfere with in vivo experiments. In this work, we perform a preliminary 16α-[18F]-fluoro-17β-estradiol (18F-FES) radiation dosimetry estimates for female mice. The obtained animal dosimetric results can be useful for evaluating animal doses during the design of longitudinal preclinical studies.

Roberto Emparan, David Licht, Ryotaku Suzuki et al.

Abstract We study the evolution of the Gregory-Laflamme instability for black strings in global AdS spacetime, and investigate the CFT dual of the formation of a bulk naked singularity. Using an effective theory in the large D limit, we uncover a rich variety of dynamical behaviour, depending on the thickness of the string and on initial perturbations. These include: large inflows of horizon generators from the asymptotic boundary (a ‘black tsunami’); a pinch-off of the horizon that likely reveals a naked singularity; and competition between these two behaviours, such as a nakedly singular pinch-off that subsequently gets covered by a black tsunami. The holographic dual describes different patterns of heat flow due to the Hawking radiation of two black holes placed at the antipodes of a spherical universe. We also present a model that describes, in any D, the burst in the holographic stress-energy tensor when the signal from a bulk self-similar naked singularity reaches the boundary. The model shows that the shear components of the boundary stress diverge in finite time, while the energy density and pressures from the burst vanish.

Paul Caucal, Farid Salazar, Björn Schenke et al.

Abstract Back-to-back dijet cross-sections in deeply inelastic scattering (DIS) at small x Bj are suppressed by many-body multiple scattering and screening effects arising from gluon saturation at high parton densities. They are similarly sensitive in these kinematics to large Sudakov logarithms from soft gluon radiation. Uncovering novel physics in this DIS channel therefore requires understanding the interplay of the two phenomena. In this work, we compute the small x Bj inclusive dijet DIS cross-section in back-to-back kinematics at next-to-leading order (NLO) in the Color Glass Condensate effective field theory (CGC EFT). Our result includes, for the first time, all real and virtual NLO contributions to the impact factor. These include all Sudakov double and single logarithm contributions, as well as all other finite O $$ \mathcal{O} $$ (α s ) terms that contribute at this order. We demonstrate explicitly that resummations of small x and Sudakov logarithms can be performed simultaneously in the CGC EFT. This requires that the JIMWLK kernel for small x evolution of the Weizsäcker-Williams (WW) gluon distribution satisfies a kinematic constraint imposed by lifetime ordering of successive gluon emissions; the corresponding modifications to the kernel, corresponding to resummations of large double transverse logarithms, are precisely of the type required to stabilize JIMWLK evolution beyond leading logarithmicaccuracy. We compute the azimuthal harmonics of the NLO back-to-back distributions and show their sensitivity to both the unpolarized and linearly polarized WW gluon distributions. Finally, we discuss how TMD factorization is broken by an emergent saturation scale at small x.

B. Blok, R. Segev

Abstract We study the influence of quantum interference and colour flow on three point correlations described by asymmetric cumulants in high multiplicity events in pp collisions. We use the model previously developed for the study of the collectivity in symmetric cumulants. We show that the resulting three point asymmetric cumulant is in qualitative agreement with the experimental data for the same parameters of the model as it was with the symmetric cumulants. Our results show that the initial state correlations must play a major role and may be even dominant in the explanation of the correlations in high multiplicity pp events.

Sujay Kr. Biswas, Atreyee Biswas

Abstract In this work interacting Umami Chaplygin gas has been studied in flat FRW model of universe in context of it’s thermodynamic and dynamical behaviour. In particular, considering Umami fluid as dark energy interacting with dark matter, irreversible thermodynamics has been studied both for apparent and event horizon as bounding horizon in two separate cases. Also the model has been investigated in purview of dynamical systems analysis by converting the cosmological evolution equations to an autonomous system of ordinary differential equations. With some restrictions on model parameter $$\omega $$ ω and coupling parameter $$\lambda $$ λ , some cosmologically interesting critical points describing late time accelerated evolution of the universe attracted by cosmological constant and accelerated scaling attractor in quintessence era have been found to alleviate coincidence problem.

Victor I. Danchev, Daniela D. Doneva, Stoytcho S. Yazadjiev

Abstract In the modern era of abundant X-ray detections and the increasing momentum of gravitational waves astronomy, tests of general relativity in strong field regime become increasingly feasible and their importance for probing gravity cannot be understated. To this end, we study the characteristics of slowly rotating topological neutron stars in the tensor-multi-scalar theories of gravity following the static study of this new type of compact objects by two of the authors. We explore the moment of inertia and verify that universal relations known from general relativity hold for this new class of compact objects. Furthermore, we study the properties of their innermost stable circular orbits and the epicyclic frequencies due to the latter’s hinted link to observational quantities such as quasi-periodic X-ray spectrum features.