Average Cross Section Research Articles

Evaluation and sensitivity analysis of three-dimensional numerical simulation for aerated deflector-generated jets in spillways

Abstract Aeration is an efficient way to prevent cavitation erosion of a discharge structure and alleviate damage to trajectory nappe on the downstream energy dissipator. Due to the complexity of the aeration jet, it is still a big challenge to understand the aeration mechanism at the water-air interface. This study applied the two-fluid model to simulate three-dimensional entrainment characteristics of jet flow, and also analyzed effects of bubble size, wall roughness, drag force model, turbulence model, and numerical model dimension on clear-water length. Results reveal that the two-fluid model can accurately and effectively simulate clear-water length, thickness variation, and average cross-section air concentration of jet flow with maximum error of 4.1%, 6.5% and 4.2% (x = L1, defining clear-water length with 1% air concentration as L1), respectively. Wall roughness height has a crucial influence on clear-water length. Taking L1 as an example, clear-water length decreases by 13.9% when roughness height increases from 0 to 3 mm. The drag models and bubble particle sizes affect clear-water length only when the profile aeration concentration is greater than 15%. Turbulence model and numerical model dimension have a minor effect on clear-water length.

^{74}Ge(n,gamma ) cross section below 70 keV measured at n_TOF CERN

Neutron capture reaction cross sections on ^{74}Ge are of importance to determine ^{74}Ge production during the astrophysical slow neutron capture process. We present new resonance data on ^{74}Ge(n,gamma ) reactions below 70 keV neutron energy. We calculate Maxwellian averaged cross sections, combining our data below 70 keV with evaluated cross sections at higher neutron energies. Our stellar cross sections are in agreement with a previous activation measurement performed at Forschungszentrum Karlsruhe by Marganiec et al., once their data has been re-normalised to account for an update in the reference cross section used in that experiment.

Investigation of photonuclear reactions on isotopes 51V, natCu, natMo, 115In and 207Pb at photon energy Eγmax= 20–70 MeV

The targets with masses in range of 51–207 a.u. have been exposed to the bremsstrahlung photon beam of the electron linear accelerator of AANL (Yerevan Physics Institute). Yields of (γ, α), (γ, αxn) and (γ, xpyn) reactions have been measured at the maximum bremsstrahlung photon energy of 20, 30, 40 and 70 MeV. The yields and the flux-weighted average cross sections of a number of the reactions were compared with the results of calculation in the frames of the TALYS-1.9 model. Agreement between the calculated and experimental data was obtained within a factor of two.

Exploring the self interacting dark matter properties from low redshift observations

We calculate the shear (eta ) and bulk viscosity (zeta ) of Self Interacting Dark Matter (SIDM) fluid using the kinetic theory formalism. Using the astrophysical constraints on dark matter self-interaction cross section over mass sigma /m , we demonstrate that viscous SIDM fluid violates the lower bound on the ratio of shear viscosity to its entropy density, eta /mathfrak {s}=frac{1}{4pi }. Then, considering the eta /mathfrak {s} bound as universal, we derive a theoretical upper limit on the ratio of velocity average dark matter self interaction cross-section to its mass and also estimate an upper limit on SIDM mass. We report that mass of the SIDM particle should be sub-GeV scale. Furthermore, with the assumption of a power-law form of eta and zeta , we study its evolution in the light of low redshift observations. We show that at the large redshift, the SIDM viscosity is small, but at the small redshift, it becomes sufficiently large and contributes significantly to cosmic dissipation. As a consequence, viscous SIDM can explain the low redshift observations and also consistent with the standard cosmological prediction.

Influence of mandrel-cores filling on size effect of cross-section distortion of bimetallic thin-walled composite bending tube

Two new size factors of cross-section hollow coefficient and bending degree are introduced to reveal the size effect of bending forming of bimetallic composite tube. Hollow coefficient and bending degree can limit the commonly used bent tube to the size description range of (0, 2.00). The evolution laws of the cross-section distortion forms in the hollow coefficient-bending degree interval are revealed as well as the action of the mandrel-cores on the size effect. Results show the mandrel-cores filling can expand the forming limit of the bent tube, but also bring two other forming defects of wrinkle and rupture. The identification factor (hollow coefficient multiply bending degree) provides a method for querying the cross-section distortion forms of all composite bending tubes. In the identification factor interval (0, 1.00), the distribution area of bending forming defects of the composite tube is continuous. The thin-walled composite bending tube collapses when identification factor in (0, 0.39), wrinkles when identification factor in [0.39, 0.50), and ruptures when identification factor in [0.50, 1.00). The mathematical model of size effect is derived, by which the average cross-section distortion rate is found to distribute like a radial leaf in the hollow coefficient-bending degree qualified forming space. The best forming zone is hollow coefficient 0.46–0.68, and bending degree 0.25–0.47.

The radiative processes involving ion-atom alkali systems: The case of hydrogen and potassium

The importance of the symmetric as well as non-symmetric ion-atom absorption processes in broad spectral region within a model of solar photosphere and also within the corresponding sunspot models, has been previously emphasized. This motivated us to study the photo-association, charge-exchange and photo-dissociation absorption processes in the cases of non-symmetric and symmetric systems involving hydrogen and potassium atoms, ions, molecules and molecular-ions. We have calculated the data for molecules and molecular state characterizations needed for current computation. We determined the partial and average cross-sections and corresponding spectral absorption rate coefficients, as the functions of wavelengths, and temperatures (100 nm ⩽λ⩽1000 nm, 400 K ⩽T⩽10 000 K). Our calculations are performed for conditions that exist in different layers of weakly ionized stellar atmospheres. The obtained data are potentially of high impact and may have broad further applications, e.g., for modelling of laboratory plasmas and various astrophysical objects including geocosmical ones.

Native Mass Spectrometry and Collision-Induced Unfolding of Laser-Ablated Proteins.

Infrared laser ablation sample transfer (LAST) was used to collect samples from solid surfaces for mass spectrometry under native spray conditions. Native mass spectrometry was utilized to probe the charge states and collision-induced unfolding (CIU) characteristics of bovine serum albumin (BSA), bovine hemoglobin (BHb), and jack-bean concanavalin A (ConA) via direct injection electrospray, after liquid extraction surface sampling, and after LAST. Each protein was deposited from solution on solid surfaces and laser-ablated for off-line analysis or sampled for online analysis. It was found that the protein ion gas-phase charge-state distributions were comparable for direct infusion, liquid extraction, and laser ablation experiments. Moreover, calculated average collision cross section (CCS) values from direct injection, liquid extraction, and laser ablation experiments were consistent with previously reported literature values. Additionally, an equivalent number of mobility features and conformational turnovers were identified from unfolding pathways from all three methods for all charge states of each protein analyzed in this work. The presented work suggests that laser ablation yields intact proteins (BSA, BHb, and ConA), is compatible with native mass spectrometry, and could be suitable for spatially resolved interrogation of unfolding pathways of proteins.

Bayesian WIMP detection with the Cherenkov Telescope Array

Over the past decades Bayesian methods have become increasingly popular in astronomy and physics as stochastic samplers have enabled efficient investigation of high-dimensional likelihood surfaces.In this work we develop a hierarchical Bayesian inference framework to detect the presence of dark matter annihilation events in data from the Cherenkov Telescope Array (CTA). Gamma-ray events are weighted based on their measured sky position Ω̂ m and energy Em in order to derive a posterior distribution for the dark matter's velocity averaged cross section 〈σv〉. The dark matter signal model and the astrophysical background model are cast as prior distributions for (Ω̂ m , Em ). The shape of these prior distributions can be fixed based on first-principle models; or one may adopt flexible priors to include theoretical uncertainty, for example, in the dark matter annihilation spectrum or the astrophysical distribution of sky location. We demonstrate the utility of this formalism using simulated data with a Galactic Centre signal from scalar singlet dark-matter model. The sensitivity according to our method is comparable to previous estimates of the CTA sensitivity.

Numerical Optimization of Electromagnetic Performance and Aerodynamic Performance for Subsonic S-Duct Intake

In order to improve the performance of subsonic unmanned aerial vehicle (UAV), a knapsack S-duct intake has been designed. The influences of an S-bend diffuser on aerodynamic performance and electromagnetic performance were analyzed firstly. The viscous flow field has been simulated by solving Favre averaged Navier–Stokes equations using a shear stress transport (SST) k-ω turbulence model. The surface current has been simulated by solving Maxwell equations using a multi-level fast multipole method (MLFMM). The multi-objective optimization of the S-duct intake was studied by using the diffuser as the optimized object. The parametric expression of the diffuser model was realized using the fourth order function geometric representation technique. The efficient model based on the Kriging model and non-dominated sorting genetic algorithm-Ⅱ (NSGA-Ⅱ) were used to accelerate the optimization progress. By analyzing the results of an optimal intake chosen from the Pareto front, the total pressure distortion (TPD) index DC60 has decreased by 0.24 at the designed Mach number of 0.9, and the average Radar Cross Section (RCS) has decreased by 2db at the frequency of 3GHz. The optimized S-duct intake could have both excellent aerodynamic performance and electromagnetic performance at various complex conditions.

T-channel singularities in cosmology and particle physics

The t-channel singularity of a cross section for a binary 2→2 scattering occurs when the particle exchanged in the t-channel is kinematically allowed to be on its mass shell, that is when the process can be viewed as a sequence of two physical subprocesses: a two-body decay 1→2 and an inverse decay 2→1. We derive conditions for the singularity to be present in a binary process. A class of divergent cross sections for Standard Model processes has been determined and illustrated by the weak analog of the Compton scattering Ze−→Ze−. After critically reviewing regularization methods proposed in literature, we discuss singular processes that occur in a medium composed of particles in thermal equilibrium. The medium is shown to regulate the singularities naturally as particles acquire a non-zero width. We demonstrate a possible cosmological application by calculating thermally averaged cross section for an elastic scattering within a simple scalar model. The transition probability, which is divergent in vacuum, becomes finite when the process occurs in a thermal bath due to the imaginary part of the t-channel mediator's self-energy computed within the Keldysh-Schwinger formalism.

Impact of reactor neutron spectrum on measured spectrum averaged cross sections

The cross section averaged over 235U thermal-neutron induced fission spectrum is a fundamental quantity that can be used in evaluation and validation of nuclear data. Many experiments focused on the determination of Spectrum Averaged Cross Sections (SACS) in 235U(nth,f) Prompt Fission Neutron Spectrum (PFNS) in light water reactors using enriched uranium fuel. In these reactors, there is already some amount of water moderator between the uranium fuel and the irradiated sample. Due to the decrease of hydrogen cross-section with neutron energy, the high energy tail of the reactor spectrum in cores with water moderator may be harder than the pure PFNS. This paper aims to compare the shape of the actual reactor spectrum in various core positions of a research light-water reactor differing each from other by the effective water thickness. The spectrum shape is determined both by calculations and experimentally using various high energy threshold reactions.The impact of the photo-nuclear reactions (γ,n) competing with (n,2n) in production of the same residual nucleus was shown to be less than a percent for most of studied dosimeters. An important exception was found for 197Au(n,2n)196Au dosimeter irradiated in the outcore channel where a notable photo-neutron contribution to the production of 196Au is caused by the neutron production from the high energy γ-rays from thermal-neutron capture in 54Fe. The corresponding ENDF/B-VIII.0 data turned out to underestimate such γ-yield by 40 % in comparison with ENDF/B-VI.8. This has improved but however not resolved the disagreement between our measurement and calculations. The remaining deficiency was attributed to the underestimation of the evaluated cross section IAEA/PD-2019 for the 197Au(γ,n) cross section near the reaction threshold. The later was confirmed by comparison with existing measured data.

Properties of 132Xe Neutral Atoms Scattering for 165K and 275K ‎Temperatures

This work aims to use an important method Galitskii-Migdal-Feynman (GMF) for ‎diatomic molecules 132Xe2, to calculate the effective phase shifts which are then used to ‎compute the effective total and viscosity cross sections at low density and temperature . ‎this study has shown that it’s crucial to include partial waves up to ‎ ‎; for ‎ ‎, the ‎effect of the potential becomes negligible .‎‎ Comparing with partial waves cross sections we deduce that the cross section is ‎dominated by S-wave scattering for low energy (wave number k < 0.1 Å-1), otherwise D ‎and G partial waves dominate . The highest peak rises from the partial effective D and G-‎wave resonance, where the system sustains a quasi-bound state trapped by the centrifugal barrier. The average cross section is also determined. ‎

Experimental investigation on the deterioration process and spatial variation of corrosion damage of RC segmental specimens under sustained load

• Early deterioration damage of a bearing segment is investigated via AE technique. • Effect of sustained load on spatial variability of steel corrosion is studied. • Spatial correlation between steel corrosion and surface corrosion cracks is studied. For the reinforced concrete (RC) shield tunnel in coastal regions, premature corrosion damages are always investigated after construction because of the combined effects of sustained earth and water pressures and marine chloride attacks. To evaluate the performance of these deteriorated shield tunnels, the effect of sustained load on structural performance degradation must be considered. In this paper, an experiment was conducted using the corrosion-accelerated specimens of a tunnel segment. The deteriorating damage processes of the RC segmental specimens were illustrated via acoustic emission (AE) with an emphasis on the influence of sustained load. Based on AE intensity analysis, intensive cracking damages for a bearing segment were identified when the average steel cross-section area losses increased from 0.5% to 2%. Meanwhile, the spatial variations of corrosion damage were discussed incorporating the impact of tensile load. The effect of tensile load on spatial correlation of distribution between steel cross-section area loss and surface corrosion cracks was experimentally verified. The experimental outcomings can help in modelling a random field-based probabilistic model associated with non-uniform steel corrosion in the bearing segmental linings.

Cross-sections of photonuclear reactions 65Cu(γ, n)64Cu and 63Cu(γ, xn)63−xCu in the energy range E γmax = 35–94 MeV

The flux-averaged cross-sections for the reactions , , , and have been measured within the bremsstrahlung end-point energy range of 35–94 MeV. The experiments were performed with the electron beam from the NSC KIPT linear accelerator LUE-40 with the use of the activation and off-line γ-ray spectrometric techniques. Theoretical calculation of the flux-average cross-sections was conducted using the cross-section values from the TALYS1.95 code, run with default options. It is shown that the experimental average cross-sections for the reactions , , and are systematically higher than the theoretical estimates based on the TALYS1.95 code. The obtained values supplement the data of different laboratories for the and reactions of and . For the reaction , the values of were measured for the first time.

Cross sections of photoneutron reactions on Ta181 at Eγmax up to 95 MeV

The total bremsstrahlung flux-averaged cross-sections $\langle{\sigma(E_{\rm{\gamma max}})}\rangle$ for the photonuclear reactions $^{181}\rm{Ta}(\gamma,\textit{x}n; \textit{x} \leq 8)^{181-\textit{x}}\rm{Ta}$ have been measured in the range of end-point energies $E_{\rm \gamma max}$ up to 95 MeV. The experiments were performed with the beam from the NSC KIPT electron linear accelerator LUE-40 with the use of the activation and off-line $\gamma$-ray spectrometric technique. The calculation of average cross-sections was carried out using the cross-section values computed with the TALYS1.95 code for different level density models $LD$ 1-6. A comparison between the experimental total cross-sections $\langle{\sigma(E_{\rm{\gamma max}})}\rangle$ and the theoretical values has shown satisfactory agreement for the $^{181}\rm{Ta}(\gamma,\textit{x}n)$ reactions with the escape of 1-4, 6 and 7 neutrons. The closest agreement with the measured data is observed with the $LD$5 computation version, which represents the microscopic level density model taking into account Hilaire's combinatorial tables.

Semi-empirical formula for (n, α) reaction cross sections at 14–15 MeV neutrons

Semi-empirical formula for calculating the average (n, α) reaction cross-section was derived by using the EXFOR experimental data at 14–15 MeV neutron energies for 133 target nuclei in the mass number range 9≤A≤209. In this new systematic, the non-elastic cross-section portion has been modified by (A13+1)−0.5196∗(BEA), while the asymmetry parameter-dependent term has been maintained. Using EMPIRE 3.2.3 and TALYS 1.95, the (n, α) cross sections for selected nuclei within the same energy range were calculated. The experimental data can be predicted with greater precision when the cross sections derived from the proposed formula are compared to those derived from codes and earlier systematics.

TWO-STEP ESTIMATION OF QUANTILE PANEL DATA MODELS WITH INTERACTIVE FIXED EFFECTS

This paper considers the estimation of panel data models with interactive fixed effects where the idiosyncratic errors are subject to conditional quantile restrictions. An easy-to-implement two-step estimator is proposed for the coefficients of the observed regressors. In the first step, the principal component analysis is applied to the cross-sectional averages of the regressors to estimate the latent factors. In the second step, the smoothed quantile regression is used to estimate the coefficients of the observed regressors and the factor loadings jointly. The consistency and asymptotic normality of the estimator are established under large $N,T$ asymptotics. It is found that the asymptotic distribution of the estimator suffers from asymptotic biases, and this paper shows how to correct the biases using both analytical and split-panel jackknife bias corrections. Simulation studies confirm that the proposed estimator performs well with moderate sample sizes.

High accuracy, high resolution 235U(n,f) cross section from n_TOF (CERN) from 18 meV to 10 keV

The 235U(n,f) cross section was measured in a wide energy range (18 meV–170 keV) at the n_TOF facility at CERN, relative to 6Li(n,t) and 10B(n,α) standard reactions, with high resolution and accuracy, with a setup based on a stack of six samples and six silicon detectors placed in the neutron beam. In this paper we report on the results in the region between 18 meV and 10 keV neutron energy. A resonance analysis has been performed up to 200 eV, with the code SAMMY. The resulting fission kernels are compared with the ones extracted on the basis of the resonance parameters of the most recent major evaluated data libraries. A comparison of the n_TOF data with the evaluated cross sections is also performed from thermal to 10 keV neutron energy for the energy-averaged cross section in energy groups of suitably chosen width. A good agreement, within 0.5%, is found on average between the new results and the latest evaluated data files ENDF/B-VIII.0 and JEFF-3.3, as well as with respect to the broad group average fission cross section established in the framework of the standard working group of IAEA (the so-called reference file). However, some discrepancies, of up to 4%, are still present in some specific energy regions. The new dataset here presented, characterized by a unique combination of high resolution and accuracy, low background and wide energy range, can help to improve the evaluations from the Resolved Resonance Region up to 10 keV, also reducing the uncertainties that affect this region.

Absorption caused by potassium molecules in astrophysical plasmas: Data needed for modeling

In this study, the processes of photo-dissociation in the cases of symmetric and strongly non-symmetric systems which involve hydrogen and potassium are investigated. The aim of this study was to calculate data for those small molecules and molecular state characterizations as well as to obtain the corresponding partial and average cross-sections. Moreover, the corresponding spectral absorption rate coefficients for symmetric and strongly non-symmetric cases i.e. for K2+ and KH+ cases are given in tables as a function of temperatures and wavelengths allowing potential modeling. The current research and presented results can be of interest for astrophysical plasma research and laboratory plasma investigation.

Measurement of neutron-capture cross sections of Ge70,72 using the DANCE facility

Background: Approximately half of all atomic nuclei heavier than iron are synthesized by the slow neutron-capture process. The weak component of this process is not well understood and the reaction rates of each isotope in the s-process path affect nucleosynthesis abundances downstream.Purpose: To measure the neutron-capture cross sections of two weak s-process nuclei, $^{70,72}\mathrm{Ge}$, using the neutron time-of-flight technique. Measuring the capture cross sections for isotopes in this region of the chart of nuclides has proven challenging due to dominant scattering cross sections.Method: Samples consisted of pellets made of pressed enriched metallic powders. The $^{70,72}\mathrm{Ge}$ neutron-capture cross sections were measured as a function of neutron energy using the Detector for Advanced Neutron Capture Experiments at Los Alamos National Laboratory.Results: Neutron-capture cross sections were measured from 10 eV to 1 MeV. These are the first measurements for $^{70,72}\mathrm{Ge}$ between 300 keV and 1 MeV neutron energy. Maxwellian-averaged cross sections were calculated in the astrophysically relevant neutron energy range (5 keV $\ensuremath{\le}kT\ensuremath{\le}$ 100 keV). Their value at $kT=30$ keV was found to be $89\ifmmode\pm\else\textpm\fi{}11$ mb for $^{70}\mathrm{Ge}$ and $58\ifmmode\pm\else\textpm\fi{}5$ mb for $^{72}\mathrm{Ge}$. Both values are in agreement with recent time-of-flight measurements at n_TOF (neutron Time-Of-Flight facility at the European Organization for Nuclear Research).Conclusions: The average cross section results from this work for $^{70}\mathrm{Ge}$ show minor ($&lt;1\ensuremath{\sigma}$) disagreement with a recent measurement by the n_TOF collaboration at higher neutron energies. This corresponds to the neutron energy region that had previously never been measured ($&gt;300$ keV). Two reaction library databases underestimate the $^{72}\mathrm{Ge}$ average cross section below 30 keV according to n_TOF and DANCE. This is likely due to capture resonances that are missing from the theoretical cross sections in the databases that were identified in both time-of-flight measurements. Additionally, a rudimentary analysis of the impact of both cross section measurements on stellar nucleosynthesis abundances using the NETZ nucleosynthesis tool is presented.