Narrow Results

Located between the Eurasia seismic zone and the circum-Pacific seismic belt, China is the largest continent shallow earthquake area around the world by the frequent earthquake activities. And great quantities of tunnels are located in high earthquake intensity area of China. As one of the main structure of the national lifeline, the seismic analysis methods of tunnel must be paid high attention. Based on seismic response characteristics of the traffic tunnel structure, this paper provides a synthesis of the current state of knowledge in the area of seismic analysis for tunnel, including the seismic design criteria, earthquake effects, tunnel seismic behaviors, and the seismic analysis procedure of tunnel. It focuses on analysis methods of tunnel subjected to seismic motion. There are three major seismic analysis methods normally used in tunnel structures; they are seismic coefficient method, seismic deformation method and dynamic response method. The basic principles of the three methods are described in this paper. Based on the different mechanical characteristics between cross-section and axial direction, the proper seismic analysis methods in the two directions are put forward according to the different construction method of tunnel. The research results will provide reference for seismic analysis of traffic tunnel.

Empirical formulas in determining the cross-sections play an important role at the energies of which there are no experimental data scattered about. The purpose of the present communication is to further improve the formulas of the cross-section of $(n,2n)$ reactions at the energies near 14.6MeV. A systematics for the evaluation of these cross-sections is studied. We present the empirical formulas based on the statistical theory of nuclear reactions in connection with the compound nucleus. The new empirical formulas are found by using the experimental cross-sections as a function of the reaction $Q$-value. Thus, the new formulas provide the best description of the existing measured data compared with systematics suggested earlier by other authors.

Studies on the cross-sections of (n,n$\alpha$) reactions which are energetically possible, about 14 MeV neutrons are quite scarce. In this paper, the cross-sections of (n,n$\alpha )$ nuclear reactions at $E_n=$14–15 MeV are analyzed by using a new empirical formula based on the statistical theory. We show that neutron cross-sections are closely related to the $Q$-value of nuclear reaction, in particular for (n,n$\alpha$) channels. Results obtained with this empirical formula show good agreement with the available measured cross-section values. We hope that the estimations on the cross-sections using the present formalism may be helpful in future studies in this field.

The production of nuclear energy from fusion reaction with no CO₂ emission is one of the most attractive sources for the future. The unprecedented physical and mechanical properties for structural materials are very important in the nuclear fusion reactor design. So, tantalum material is a valuable candidate for plasma-facing materials in the fusion devices. In this paper, nuclear excitation functions for the ${}^{181}\mathrm{\text{Ta}}(p,n){}^{181}\mathrm{\text{W}}$, ${}^{181}\mathrm{\text{Ta}}(p,2n){}^{180}\mathrm{\text{W}}$, ${}^{181}\mathrm{\text{Ta}}(p,4n){}^{178}\mathrm{\text{W}}$, ${}^{181}\mathrm{\text{Ta}}(d,2n){}^{181}\mathrm{\text{W}}$, ${}^{181}\mathrm{\text{Ta}}(\alpha ,n){}^{184}\mathrm{\text{Re}}$ and ${}^{181}\mathrm{\text{Ta}}(\alpha ,2n){}^{183}\mathrm{\text{Re}}$ reactions are obtained using the nuclear codes TALYS 1.8 and ALICE/ASH. The contribution of pre-equilibrium and equilibrium processes in these reactions is investigated. In the calculations, the Weisskopf–Ewing and Hauser–Feshbach formalisms for the equilibrium particle emission, and the two-component exciton, hybrid and geometry-dependent hybrid formalisms for the pre-equilibrium particle emission are used. Hence, the cross-sections calculated are compared with the measured values. It is observed that the cross-section results of the geometry-dependent hybrid model match fairly well with the experimental measurements.

We consider the production of magnetic monopoles via γγ fusion at high energy pp collisions. In the assumption that the monopole spin is equal 0, 1/2, 1, the monopole–antimonopole pair production cross-section by this mechanism at LHC energies is estimated and analyzed.

The category of all 2-dimensional real division algebras is shown to split into four full subcategories, each of which is given by the natural action of a Coxeter group of type 𝔸₁ or 𝔸₂ on the set of all pairs of ellipses in ℝ², which are centred in the origin and have reciprocal axis lengths. Cross-sections for the orbit sets of these group actions are being determined. They yield a classification of all 2-dimensional real division algebras. Moreover all morphisms between the objects in this classifying list are described, and thus an explicit and geometric picture of the category of all 2-dimensional real division algebras is obtained.

This elementary and self-contained exposition extends Darpö and Dieterich's recent description [14] of the category of all 2-dimensional commutative real division algebras, which in turn is based on Benkart, Britten and Osborn's investigation [4] of the isotopes of ℂ. It also supplements earlier contributions of Althoen and Kugler [2], Burdujan [9], Gottschling [25], Petersson [33], Hübner and Petersson [29], and Doković and Zhao [23] to the problem of classifying all 2-dimensional real division algebras.

A theoretical study of nuclear level density of Thorium nuclei that exist on and off the beta-stability line is carried out using Talys 1.6. The level density parameter a and spin cut-off factor $\sigma$ for Thorium isotopes ${}^{216-270}$Th are estimated. The values of both these parameters decrease towards the neutron drip line and the proton drip line. Cross-sections for $(n,p)$ and $(n,\alpha )$ reactions for Thorium isotopes are also calculated. The estimated and experimental values of cross-sections for ${}^{232}$Th are comparable. These evaluated data are useful in understanding the mechanism of nuclear reactions taking place under extreme conditions including those in nucleosynthesis.

This paper explores the properties of intrinsic gallium nitride (GaN) nanowires (NWs) in terms of formation energy, band structure, density of state (DOS) and optical properties with plane-wave ultrasoft pseudopotential method based on first-principles. Results show that after relaxation, N atoms of the outer layers move outwards, while Ga atoms move inwards, and the relaxation of surface atomic structure appears less obvious with the increasing cross-sectional area. Comparing different cross-sections of GaN NWs, it is found that the formation energy decreases and the stability goes stronger with the increasing size. With the increasing cross-section, the bandgap is decreased. Moreover, through comparative investigation in optical properties between GaN NWs and bulk GaN, a valuable phenomenom is found that the static dielectric constants of GaN NWs are notably lower, which contributes remarkably to the excellent absorbing performance of GaN NWs.

We analyze variance, skewness and kurtosis risk premia and their option-implied and realized components as predictors of excess market returns and of the cross-section of stock returns. We find that the variance risk premium is the only moment-based variable to predict S&P 500 index excess returns, with a monthly out-of-sample $R^2$ above 6% for the period between 2001 and 2014. Nonetheless, all aggregate moment-based variables are effective in predicting the cross-section of stock returns. Self-financed portfolios long on the stocks least exposed to the aggregate moment-based variable and short on the stocks most exposed to it achieve positive and significant Carhart 4-factor alphas and a considerably higher Sharpe ratio than the S&P 500 index, with positive skewness.

We study the associated Higgs production with $Z$ boson at future linear colliders in the framework of the minimal noncommutative standard model. Using the Seiberg–Witten map, we calculate the production cross-section considering all orders of the noncommutative parameter ${\Theta }_{\mu \nu }$. We consider the effect of earth’s rotation on the orientation of ${\Theta }_{\mu \nu }$ with respect to the laboratory frame and thus on the total cross-section, its azimuthal distribution and rapidity distribution for the machine energy ranging from 0.5 TeV to 3 TeV corresponding to the noncommutative scale $\Lambda \ge 0.5\mathrm{\text{TeV}}$.

We study the electron-impact induced ionization of O₂ from threshold to 120 eV using the electron spectroscopy method. Our approach is simple in concept and embodies the ion source with a collision chamber and a mass spectrometer with a quadruple filter as a selector for the product ions. The combination of these two devices makes it possible to unequivocally collect all energetic fragment ions formed in ionization and dissociative processes and to detect them with known efficiency. The ion source allows varying and tuning the electron-impact ionization energy and the target-gas pressure. We demonstrate that for obtaining reliable results of cross-sections for inelastic processes and determining mechanisms for the formation of O${}^{+}{(}^{4}S,{}^{2}D,{}^{2}P)$ ions, it is crucial to control the electron-impact energy for production of ion and the pressure in the ion source. A comparison of our results with other experimental and theoretical data shows good agreement and proves the validity of our approach.

In this work we study the process e⁺+e^-→J/Ψ+η_c at energy observed recently at B-factories whose measurements were made by Babar and Belle groups. We calculate the cross-section for this process in the Bethe–Salpeter formalism under Covariant Instantaneous Anstaz. To simplify our calculation, the heavy quark approximation is employed in the quark and gluon propagators. In the exclusive process of e⁺e^- annihilation into two heavy quarkonia, the cross-section calculated in this scenario is compatible with the experimental data of Babar and Belle.

Folding potentials of the elastic scattering drip-line nuclei at various incident energies is one method to study nuclear matter density distributions and nuclear radii. The nuclei with density distributions consisting of a bulk (core) and an outer layer (halo), dilute and spatially extended are called the halo nuclei caused for the weak particle binding. Several halo nuclei are studied and many potential candidates are identified. All the cross-sections of the elastic scattering for the drip-line nuclei ¹¹Be and ⁶He, are calculated to understand the exotic properties of these nuclei starting from its structure, extended radius, nuclear size till the large total reaction cross-sections for these nuclei when it interact with a stable target ¹²C.

Proton elastic scattering at various incident energies is one method to study nuclear density distributions and nuclear radii. Single folding potential describing the p-scattering on ⁴⁰Ca over a broad energy range 9–48.4 MeV is constructed. The resulting potential does not need any renormalization to fit the measured elastic scattering angular distributions and total reaction cross-sections. Furthermore, correlation between volume integral and proton incident energy is discussed. Theoretical calculations are in a good agreement with existing experimental data.

In this work, we explore the possibility that the motion of the deuterium ions emitted from Coulomb cluster explosions is highly disordered enough to resemble thermalization. We analyze the process of nuclear fusion reactions driven by laser–cluster interactions in experiments conducted at the Texas Petawatt laser facility using a mixture of D₂+³He and CD₄+³He cluster targets. When clusters explode by Coulomb repulsion, the emission of the energetic ions is “nearly” isotropic. In the framework of cluster Coulomb explosions, we analyze the energy distributions of the ions using a Maxwell–Boltzmann (MB) distribution, a shifted MB distribution (sMB), and the energy distribution derived from a log-normal (LN) size distribution of clusters. We show that the first two distributions reproduce well the experimentally measured ion energy distributions and the number of fusions from d–d and d-³He reactions. The LN distribution is a good representation of the ion kinetic energy distribution well up to high momenta where the noise becomes dominant, but overestimates both the neutron and the proton yields. If the parameters of the LN distributions are chosen to reproduce the fusion yields correctly, the experimentally measured high energy ion spectrum is not well represented. We conclude that the ion kinetic energy distribution is highly disordered and practically not distinguishable from a thermalized one.

Isomeric yields ratios and energy differential cross-section of metastable state excitation in the ${}^{138}\mathrm{\text{Ce}}(\gamma ,n){}^{137m,g}\mathrm{\text{Ce}}$ reaction has been studied in the 10–22MeV end-point energy range of bremsstrahlung beams. Experimental data are compared with Hauser–Feshbach calculations performed with TALYS-1.6 statistical model code.

Nuclear fusion reactions at low energies ($E\sim 1$eV to few KeV) are crucial for the primordial nucleosynthesis of light elements. Nuclear fusion reactions in this energy window can be understood fruitfully in terms of quantum mechanical tunneling through the mutual Coulomb barrier of interacting nuclei. In this work, we studied the fusion cross-section, $\sigma$ and astrophysical S-factor in the selective resonant tunneling model (SRTM) approach for the $\mathrm{\text{p}}{+}^{15}$N and $\alpha {+}^{12}$C nuclear fusion reactions. We used space varying complex Gaussian type nuclear potential here. The quantum mechanical findings of the fusion cross-section, $\sigma$ and S-factor are in excellent agreement with the experimentally observed results found in the literature. The improved value of astrophysical S-factors for light nuclei may give a more clear picture of the elemental abundance in primordial nucleosynthesis.

Theoretical nuclear reaction codes are crucial for studying cross-section and S-factors of nuclear reactions required for the thermonuclear reaction rate calculations. We analyze two reactions ⁸Li($\alpha ,n$)¹¹B and ¹⁴N($p,\gamma$)¹⁵O, using both TALYS and EMPIRE codes. We stress that these reactions are highly important for CNO cycle but the extent of involvement of experimental datasets are meager and conflicting. For the first reaction, the trend of experimental data has been predicted satisfactorily by the codes. The reaction rate is also matched with REACLIB calculation. However, in ¹⁴N($p,\gamma$)¹⁵O, none of the codes could predict the resonant structures in the experimental data at the lower energies. The importance of our work is a sincere attempt to validate the TALYS and EMPIRE predictions for cross-section, S-factor and the reaction rate, simultaneously.

We review here recent results on $e^{+}{e}^{-}$ annihilation to hadrons below 2 GeV obtained with the SND detector at the VEPP-2000 collider. Among others we report cross sections and dynamics properties for the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$, $e^{+}{e}^{-}\to n\bar{n}$, $e^{+}{e}^{-}\to \eta {\pi }^0\gamma$, and $e^{+}{e}^{-}\to \eta \eta \gamma$.