Radii and Binding Energies of Nuclei in the Alpha-Cluster Model

The alpha-cluster model is based on two assumptions that the proton-neutron pair interactions are responsible for adherence between alpha-clusters and that the NN-interaction in the alpha-clusters is isospin independent. It allows one to estimate the Coulomb energy and the short range inter-cluster bond energy in dependence on the number of clusters. The charge radii are calculated on the number of alpha-clusters too. Unlike the Weizsacker formula in this model the binding energies of alpha-clusters and excess neutrons are estimated separately. The calculated values are in a good agreement with the experimental data.Comment: Latex2e 2.09, 13 pages, 4 figure

Charge Radii of beta-Stable Nuclei

In previous work it was shown that the radius of nucleus R is determined by the alpha-cluster structure and can be estimated on the number of alpha-clusters disregarding to the number of excess neutrons. A hypothesis also was made that the radius R_m of a beta-stable isotope, which is actually measured at electron scattering experiments, is determined by the volume occupied by the matter of the core plus the volume occupied by the peripheral alpha-clusters. In this paper it is shown that the condition R_m = R restricts the number of excess neutrons filling the core to provide the beta-stability. The number of peripheral clusters can vary from 1 to 5 and the value of R for heavy nuclei almost do not change, whereas the number of excess neutrons should change with the number of peripheral clusters to get the value of R_m close to R. It can explain the path of the beta-stability and its width. The radii R_m of the stable isotopes with 12 =< Z =< 83 and the alpha-decay isotopes with 84 =< Z =< 116 that are stable to beta-decay have been calculated.Comment: Latex2e 2.09, 10 pages, 3 figure

Masses and Radii of the Nuclei with N>=Z in an Alpha-Cluster Model

In the framework of a recently developed alpha-cluster model a nucleus is represented as a core (alpha-cluster liquid drop with dissolved excess neutron pairs in it) and a nuclear molecule on its surface. From analysis of experimental nuclear binding energies one can find the number of alpha-clusters in the molecule and calculate the nuclear charge radii. It was shown that for isotopes of one Z with growing A the number of alpha-clusters in the molecule decreases to three, which corresponds to the nucleus 12C for even Z and 15N for odd Z, and the specific density of the core binding energy \rho grows and reaches its saturation value. In this paper it is shown that the value \rho=2.55 MeV/fm^3 explains the particular number of excess neutrons in stable nuclei.Comment: 7 pages, 3 eps figures, submitted as a contribution to the Proceedings of the International Conference, Messina, Italy, October 5-9, 200

Simulations of an energy dechirper based on dielectric lined waveguides

Terahertz frequency wakefields can be excited by ultra-short relativistic electron bunches travelling through dielectric lined waveguide (DLW) structures. These wakefields can either accelerate a witness bunch with high gradient, or modulate the energy of the driving bunch. In this paper, we study a passive dechirper based on the DLW to compensate the correlated energy spread of the bunches accelerated by the laser plasma wakefield accelerator (LWFA). A rectangular waveguide structure was employed taking advantage of its continuously tunable gap during operation. The assumed 200 MeV driving bunch had a Gaussian distribution with a bunch length of 3.0 {\mu}m, a relative correlated energy spread of 1%, and a total charge of 10 pC. Both of the CST Wakefield Solver and PIC Solver were used to simulate and optimize such a dechirper. Effect of the time-dependent self-wake on the driving bunch was analyzed in terms of the energy modulation and the transverse phase space

Open educational practices for curriculum enhancement

Open educational resources (OER) and open educational practices (OEP) are relatively new areas in educational research. How OER and OEP can help practitioners enhance curricula is one of a number of under-researched topics. This article aims to enable practitioners to identify and implement appropriate open practices to enhance higher education curricula. To that aim, we put forward a framework of four open educational practices based on patterns of OER reuse (‘as is’ or adapted), mapped against the processes of curriculum design and delivery. The framework was developed from the in-depth analysis of 20 cases of higher education practitioners, which revealed patterns of OER reuse across disciplines, institutions and needs. For each open practice we offer evidence, examples and ideas for application by practitioners. We also put forward recommendations for institutional policies on OER and OE

Differential quadrature method for space-fractional diffusion equations on 2D irregular domains

In mathematical physics, the space-fractional diffusion equations are of particular interest in the studies of physical phenomena modelled by L\'{e}vy processes, which are sometimes called super-diffusion equations. In this article, we develop the differential quadrature (DQ) methods for solving the 2D space-fractional diffusion equations on irregular domains. The methods in presence reduce the original equation into a set of ordinary differential equations (ODEs) by introducing valid DQ formulations to fractional directional derivatives based on the functional values at scattered nodal points on problem domain. The required weighted coefficients are calculated by using radial basis functions (RBFs) as trial functions, and the resultant ODEs are discretized by the Crank-Nicolson scheme. The main advantages of our methods lie in their flexibility and applicability to arbitrary domains. A series of illustrated examples are finally provided to support these points.Comment: 25 pages, 25 figures, 7 table