Elementary Cross Sections Research Articles

Nondiffractive feature of γN → ρ ± N with ρ -meson electromagnetic multipole moments

We investigate photoproduction of charged $\rho$ off the nucleon using $\rho(770)+\pi(140)$ Regge pole exchanges by considering the $\rho$-meson electromagnetic multipole moments. The significance of the Ward identity at the $\gamma\rho\rho$ vertex is emphasized for current conservation in the process. Given $\pi$ exchange with the well-known coupling constants for $\gamma\pi\rho$ and $\pi NN$, we analyze the role of the $\rho$ exchange in the $\gamma p\to \rho^+n$ and $\gamma n\to\rho^-p$ processes without model-dependences except for the magnetic moment $\mu_{\rho^\pm}=\pm2.01$ and electric quadrupole moment ${\cal Q}_{\rho^\pm}=\pm0.027$ fm$^2$ taken from theoretical estimates. The nondiffractive feature of both cross sections is reproduced with a rapid decrease beyond the resonance region by the dominance of $\pi$ exchange over the $\rho$\,. % Cross sections for differential and density matrix elements are presented to compare with existing data. The parity and photon polarization asymmetries are predicted to demonstrate the apparent roles of the $\rho$-meson electromagnetic multipole moments.

Particle production and equilibrium properties within a new hadron transport approach for heavy-ion collisions

The microscopic description of heavy-ion reactions at low beam energies is achieved within hadronic transport approaches. In this article a new approach SMASH (Simulating Many Accelerated Strongly-interacting Hadrons) is introduced and applied to study the production of non-strange particles in heavy-ion reactions at $E_{\rm kin}=0.4-2A$ GeV. First, the model is described including details about the collision criterion, the initial conditions and the resonance formation and decays. To validate the approach, equilibrium properties such as detailed balance are presented and the results are compared to experimental data for elementary cross sections. Finally results for pion and proton production in C+C and Au+Au collisions is confronted with HADES and FOPI data. Predictions for particle production in $\pi+A$ collisions are made.

Development of a beam ion velocity detector for the heavy ion beam probe.

In an axisymmetric plasma, the conservation of canonical angular momentum constrains heavy ion beam probe (HIBP) trajectories such that measurement of the toroidal velocity component of secondary ions provides a localized determination of the poloidal flux at the volume where they originated. We have developed a prototype detector which is designed to determine the beam angle in one dimension through the detection of ion current landing on two parallel planes of detecting elements. A set of apertures creates a pattern of ion current on wires in the first plane and solid metal plates behind them; the relative amounts detected by the wires and plates determine the angle which beam ions enter the detector, which is used to infer the toroidal velocity component. The design evolved from a series of simulations within which we modeled ion beam velocity changes due to equilibrium and fluctuating magnetic fields, along with the ion beam profile and velocity dispersion, and studied how these and characteristics such as the size, cross section, and spacing of the detector elements affect performance.

Dilepton and $ \phi$ meson production in elementary and nuclear collisions at the NICA fixed-target experiment

We argue that the NICA fixed target experiment will be able to provide very important new experimental data on dilepton and $\phi$ meson production in the basically undiscovered energy domain between the SIS and SPS energies. Experimental information about elementary cross sections in this energy region is an essential ingredient of models of nuclear collisions in the same energy range.

Mixed Consolidation Solution for a Reinforced Concrete Structure

During the last years, reinforced concrete structures become subject for rehabilitation due to two factors: their long life span and large change in norms that leaded to a large increase of seismic loads in Eastern Europe. These lead to a necessity for rehabilitation of existing building stock in order to use them during their entire life span at the maximum potential. The present paper proposes a solution for rehabilitation for three reinforced concrete building of a hospital, that consumed a half of their life span and do not correspond anymore to present norms. The chosen solution is a combination between CFRP rehabilitation and increase of structural elements cross section in order to achieve the stiffness balance in the structure nodes that is required by present norms. As a further matter, correction in stiffness of local elements diminished the lateral drifts of the structure and improved the global seismic response of the building.

Nuclear annihilation by antinucleons

We examine the momentum dependence of $\bar p$$p$ and $\bar n$$p$ annihilation cross sections by considering the transmission through a nuclear potential and the $\bar p p$ Coulomb interaction. Compared to the $\bar n p$ annihilation cross section, the $\bar p p$ annihilation cross section is significantly enhanced by the Coulomb interaction for projectile momenta below $p_{\rm lab} <$ 500 MeV/$c$, and the two annihilation cross sections approach the Pomeranchuk's equality limit [JETP Lett. {\bb 30}, 423 (1956)] at $p_{\rm lab}\sim 500$ MeV/$c$. Using these elementary cross sections as the basic input data, the extended Glauber model is employed to evaluate the annihilation cross sections for $\bar n$ and $\bar p$ interaction with nuclei and the results compare well with experimental data.

Inverse estimation of the transient-state stress distribution in the power boiler pressure components

The aim of this work is to present an inverse method of stress estimation in pressure components of power boilers. The proposed algorithm reconstructs the time- and space-dependent temperature, strain and stress distribution in some cross sections of thick-walled cylindrical elements without information concerning the thermal boundary condition on the inner surface. The solution is possible thanks to “measured” temperature histories in easily accessible points located on the component outer surface. In order to stabilize the solution, the data are smoothed out using digital filters based on local polynomial approximation. The material properties of the power boiler elements are assumed as temperature-dependent and the inverse problem is solved iteratively.The proposed method is verified numerically and experimentally in a steam header located on a laboratory stand in the Cracow University of Technology. The presented method may be used in monitoring systems of both conventional and nuclear power plants.

Measurements of neutron radiation and induced radioactivity for the new medical linear accelerator, the Varian TrueBeam

Contemporary linear accelerators applied in radiotherapy generate X-ray and electron beams with energies up to 20 MeV. Such high-energy therapeutic beams induce undesirable photonuclear (γ,n) and electronuclear (e,e'n) reactions in which neutrons and radioisotopes are produced. The originated neutron can also induce reactions such as simple capture, (n,γ), reactions that produce radioisotopes. In this work measurements of the non-therapeutic neutrons and the induced gamma radiation were carried out in the vicinity of a new medical accelerator, namely the Varian TrueBeam. The TrueBeam is a new generation Varian medical linac making it possible to generate the X-ray beams with a dose rate higher than in the case of the previous models by Varian. This work was performed for the X-ray beams with nominal potentials of 10 MV (flattening filter free), 15 MV and 20 MV, and for a 22 MeV electron beam. The neutron measurements were performed by means of a helium chamber and the induced activity method. The identification of radioisotopes produced during emission of the therapeutic beams was based on measurements of the energy spectra of gammas emitted in decays of the produced nuclei. The gamma energy spectra were measured with the use of the high-purity germanium detector. The correlation between the neutron field and the mode and nominal potential was observed. The strongest neutron fluence of 3.1 × 106 cm−2 Gy−1 and 2.0 × 106 cm−2 Gy−1 for the thermal and resonance energies, respectively, was measured during emission of the 20 MV X-ray beam. The thermal and resonance neutron fluence measured for the 15 MV X-rays was somewhat less, at 1.1 × 106 cm−2 Gy−1 for thermal neutrons and 6.7 × 105 cm−2 Gy−1 for resonance neutrons. The thermal and resonance neutron fluences were smallest for the 10 MV FFF beam and the 22 MeV electron beam and were around two orders of magnitude smaller than those of the 20 MV X-ray beam. This work has shown that the neutron reactions are dominant because of relatively high cross sections for many elements used in the accelerator construction. The detailed analysis of the measured spectra made it possible to identify 11 radioisotopes induced during TrueBeam delivery. In this work the following radioisotopes were identified: 56Mn, 122Sb, 124Sb, 131Ba, 82Br, 57Ni, 57Co, 51Cr, 187W, 24Na and 38Cl.

Sub-threshold ϕ and production by high mass resonances with UrQMD

We present a possible explanation for the deep sub-threshold, ϕ and production yields measured with the HADES experiment in Ar+KCl reactions at A GeV and present predictions for Au+Au reactions at A GeV. To explain the surprisingly high yields of ϕ and hadrons we propose new decay channels for high mass baryon resonances. These new decay channels are constrained by elementary cross sections, and production in p+Nb. Based on the fits to the elementary reactions one obtains a satisfactorily description of ϕ and production in deep sub-threshold Ar+KCl reactions as well as the observed nuclear transparency ratio in proton-induced ϕ production in cold nuclear matter. The results implicate that no new medium effects are required to describe the rare strange particle production data in low energy nuclear collisions.

RC beams strengthened in shear using the Embedded Through-Section technique: Experimental results and analytical formulation

The Embedded Through-Section (ETS) is a recent strengthening technique that has been developed to retrofit existing reinforced concrete (RC) elements with shear reinforcement deficiencies. This technique is based on the execution of holes drilled through the element cross section, in which steel or fiber reinforced polymer (FRP) bars are inserted and bonded to the surrounding concrete with an epoxy adhesive. An experimental program was carried out with RC T-cross section beams strengthened in shear using steel ETS bars. The influence of the inclination and shear strengthening ratio of ETS on the shear strengthening efficiency was evaluated, as well as the interaction of ETS bars with existing steel stirrups. Two different analytical models are presented in this paper in order to calculate the contribution of ETS to shear resistance. The first model follows an empirical approach (experimentally-based approach), while the second model takes into account the physical and mechanical principles of the technique (mechanically-based approach). The predictive performance of both models is assessed by using experimental results available in literature.

Mathematical simulation of the INR RAS SVZ-100 neutron spectrometer

A mathematical model of the SVZ-100 lead slowing-down neutron spectrometer designed at the Institute for Nuclear Research, Russian Academy of Sciences (Moscow) is presented. The neutron spectra in the SVZ-100 measuring channels are calculated by the Monte Carlo method at different slowing-down times. The influence of the energy resolution of the spectrometer on the shape of the neutron cross sections is demonstrated. The developed model makes it possible to establish agreement between experimental data obtained using neutron spectrometers by different methods and with different resolutions and compare the results of measuring the neutron cross sections of thorium and transuranic elements using the SVZ-100 with recommended international databases.

The valence band electronic structure of rhombohedral-like and tetragonal-like BiFeO3 thin films from hard X-ray photoelectron spectroscopy and first-principles theory

We investigate the electronic structure of rhombohedral-like (R) and tetragonal-like (T) BiFeO3 thin films using high energy X-ray photoelectron spectroscopy and first-principles electronic structure calculations. By exploiting the relative elemental cross sections to selectively probe the elemental composition of the valence band, we identify a strong Bi 6p contribution at the top of the valence band in both phases, overlapping in energy range with the O 2p states; this assignment is confirmed by our electronic structure calculations. We find that the measured occupied Bi 6p signal lies closer to the top of the valence band in the T phase than in the R phase, which we attribute, using our electronic structure calculations, to lower Bi–O hybridization in the T phase. We note, however, that our calculations of the corresponding densities of states underestimate the difference between the phases, suggesting that matrix element effects resulting from the different effective symmetries also contribute. Our results shed light on the chemical nature of the stereochemically active Bi lone pairs, which are responsible for the large ferroelectric polarization of BiFeO3.

In-medium and isospin effects on particle production near threshold energies in heavy-ion collisions

Dynamics of pseudoscalar mesons ($\pi$, $\eta$, $K$ and $\overline{K}$ ) and hyperons ($\Lambda$ and $\Sigma$) produced in heavy-ion collisions near threshold energies has been investigated within the Lanzhou quantum molecular dynamics (LQMD) transport model. The in-medium modifications on particle production in dense nuclear matter are implemented in the model through corrections on the elementary cross sections and by inclusion of the meson (hyperon)-nucleon potentials, in which the isospin effects are considered. It is found that the transportation of particles are influenced with the in-medium corrections. The total number of pions is reduced with an isospin, density and momentum dependent pion-nucleon potential. However, the ratios of charged pions is enhanced with inclusion of the potential. The production of eta in the domain of mid-rapidities and high momenta is sensitive to the $\eta$-nucleon potential, but weakly depends on symmetry energy. The attractive antikaon-nucleon potential enhances the subthreshold $\overline{K}$ production and also influences the structure of phase-space distributions. Dynamics of etas, kaons, antikaons and hyperons is also influenced by the pion potential because of collisions between pions and nucleons (resonances). The impacts of mean-field potentials on particle dynamics are investigated, such as the phase-space distributions from rapidity and transverse momentum spectra, inclusive invariant spectra, collective flows etc.

Impact of External Heat Insulation on Drying Process of Autoclaved Aerated Concrete Masonry Constructions

In the time when sustainable construction as well as cost saving on heating and cooling of buildings is one of the most important construction trends, it is important to acknowledge the possibilities of application of construction materials with high heat insulation parameters and the ways in which these parameters can be obtained. Autoclaved aerated concrete (AAC) is a load bearing construction material, which has high heat insulation parameters, although it has one significant disadvantage. If the AAC masonry construction has high moisture content, it loses its heat insulation properties. This is the reason why it is important to detect the humidity distribution throughout the cross section of the masonry elements in order to conduct the drying process of the AAC construction. Therefore, the question about non-destructive detection of humidity distribution throughout the cross section of the material arises. Humidity distribution throughout the cross section of AAC masonry constructions has a significant impact on its heat resistivity properties. Application of electrical impedance spectrometry (EIS) method for determination of humidity distribution throughout the cross section of AAC constructions has been a subject of research recently. The EIS method is an easily applicable non-destructive testing method for detection of the humidity distribution throughout the cross section of a construction. Research on the impact of the external heat insulation layer on the speed of humidity distribution changes is described in this paper.

The model of a temporary temperature field during multi-pass arc weld surfacing. Part II: Example of computations

Journal of Applied Mathematics and Computational Mechanics, Prace Naukowe Instytutu Matematyki i Informatyki, Politechnika Częstochowska, Scientific Research of the Institute of Mathematics and Computer Science, Czestochowa University of Technology

Continuum Mechanics Based Bilinear Shear Deformable Shell Element Using Absolute Nodal Coordinate Formulation

In this investigation, a continuum mechanics based bilinear shear deformable shell element is developed using the absolute nodal coordinate formulation (ANCF) for the large deformation analysis of multibody shell structures. The element consists of four nodes, each of which has the global position coordinates and the transverse gradient coordinates along the thickness introduced for describing the orientation and deformation of the cross section of the shell element. The global position field on the middle surface and the position vector gradient at a material point in the element are interpolated by bilinear polynomials. The continuum mechanics approach is used to formulate the generalized elastic forces, allowing for the consideration of nonlinear constitutive models in a straightforward manner. The element lockings exhibited in the element are eliminated using the assumed natural strain (ANS) and enhanced assumed strain (EAS) approaches. In particular, the combined ANS and EAS approach is introduced to alleviate the thickness locking arising from the erroneous transverse normal strain distribution. Several numerical examples are presented in order to demonstrate the accuracy and the rate of convergence of numerical solutions obtained by the continuum mechanics based bilinear shear deformable ANCF shell element proposed in this investigation.

L shell fluorescence yields and total ionization and x-ray production cross sections for elements with 40≤Z≤92

Abstract Existing experimental compilation (till 2014) for a wide range of elements (40≤Z≤92) by proton impact (up to 10.0 MeV) is used to deduce empirical ionization and x-ray production cross sections. The reliability of the obtained cross sections is then exploited to derive new values of L shell average fluorescence yield. This was based on the fact that ratio of ionization to x-ray production cross sections is independent of the excitation energy of proton ranging from 0.02 to 10.0 MeV, for a given element. The obtained values are compared with earlier theoretical and experimental results, where a good agreement is observed for all elements under investigation.

Modelling the behaviour of microbulk Micromegas in xenon/trimethylamine gas

We model the response of a state of the art micro-hole single-stage charge amplification device (‘microbulk’ Micromegas) in a gaseous atmosphere consisting of xenon/trimethylamine at various concentrations and pressures. The amplifying structure, made with photo-lithographic techniques similar to those followed in the fabrication of gas electron multipliers (GEMs), consisted of a 100μm-side equilateral-triangle pattern with 50μm-diameter holes placed at its vertexes. Once the primary electrons are guided into the holes by virtue of an optimized field configuration, avalanches develop along the 50μm-height channels etched out of the original doubly copper-clad polyimide foil. In order to properly account for the strong field gradients at the holes׳ entrance as well as for the fluctuations of the avalanche process (that ultimately determine the achievable energy resolution), we abandoned the hydrodynamic framework, resorting to a purely microscopic description of the electron trajectories as obtained from elementary cross-sections. We show that achieving a satisfactory description needs additional assumptions about atom–molecule (Penning) transfer reactions and charge recombination to be made.

A demo solar thermoelectric conversion device based on Bi2Te3 and carbon nanotubes

It is known that carbon nanotubes (CNTs) possess a high light absorption coefficient with a very broad spectrum, showing good potential for solar-thermal conversion. Bi2Te3 is a typical thermoelectric material with high thermoelectric conversion efficiency. In this study, we first fabricated several simple elements based on p- and n-type Bi2Te3 respectively. By integrating p- and n-type elements in series, we constructed a novel solar thermoelectric conversion device covered with 0.32g/m2 CNT sheets, which showed a high light absorption coefficient and generated a large short-circuit current (Isc) of 200mA. The size of the cross section of each series element was 0.19×0.19cm2. Thus, the short-circuit current density (Jsc) was as high as 5520mA/cm2. The open-circuit voltage (Voc) of the device reached 400mV. Each element of the device displayed a power conversion efficiency (PCE) of 2.1% in the near-infrared (NIR) region by a narrow band diode laser source with light flux of 100mW/cm2 without using any optical or thermal concentrator. Furthermore, the device is stable, durable and capable of operating at high temperatures and thus is promising for converting sunlight into electricity. This work provides a simple and convenient approach to prepare solar-energy conversion devices for large-scale applications in the future.

Dual-energy X-ray analysis using synchrotron computed tomography at 35 and 60 keV for the estimation of photon interaction coefficients describing attenuation and energy absorption.

A novel method for dual-energy X-ray analysis (DEXA) is tested using measurements of the X-ray linear attenuation coefficient μ. The key is a mathematical model that describes elemental cross sections using a polynomial in atomic number. The model is combined with the mixture rule to describe μ for materials, using the same polynomial coefficients. Materials are characterized by their electron density Ne and statistical moments Rk describing their distribution of elements, analogous to the concept of effective atomic number. In an experiment with materials of known density and composition, measurements of μ are written as a system of linear simultaneous equations, which is solved for the polynomial coefficients. DEXA itself involves computed tomography (CT) scans at two energies to provide a system of non-linear simultaneous equations that are solved for Ne and the fourth statistical moment R4. Results are presented for phantoms containing dilute salt solutions and for a biological specimen. The experiment identifies 1% systematic errors in the CT measurements, arising from third-harmonic radiation, and 20-30% noise, which is reduced to 3-5% by pre-processing with the median filter and careful choice of reconstruction parameters. DEXA accuracy is quantified for the phantom as the mean absolute differences for Ne and R4: 0.8% and 1.0% for soft tissue and 1.2% and 0.8% for bone-like samples, respectively. The DEXA results for the biological specimen are combined with model coefficients obtained from the tabulations to predict μ and the mass energy absorption coefficient at energies of 10 keV to 20 MeV.