168 resultados para Queilite angular
Resumo:
The differential cross-sections for elastic scattering of F-17 and O-17 on Pb-208 have been measured at Radioactive Ion Beam Line at Lanzhou (RIBLL). The variation of the logarithms of differential cross-sections with the square of scattering angles, viz. angulax dispersion plot, shows clearly that there exists a turning point in the range of small scattering angles (6 degrees-20 degrees) for F-17 due to its exotic structure, while no turning point was observed for O-17. The experimental results have been compared with previous data of other groups. Systematical analysis on the available data seems to conclude that there is an exotic behavior of elastic scattering angular dispersion of weakly bound nuclei with halo or skin structure as compared with that of the stable nuclei. Therefore the fact that the turning point of the elastic scattering angular dispersion plot appears at small angle for weakly bound nuclei can be used as a new probe to investigate the halo and skin phenomenon.
Resumo:
We investigate the difference in the angular distribution of Ly-alpha(1) and K alpha(1) photons from hydrogenlike and heliumlike ions of uranium after radiative electron capture to the L shell. The strong anisotropy in the former case is changed to a very small one in the latter case. Our calculations support the observation. The effect takes place even in the limiting case of noninteracting electrons, being caused by the Pauli principle.
Resumo:
The differential cross sections of F-17 and O-17 elastic scattering products on Pb-208 have been measured at the Radioactive Ion Beam Line at Lanzhou (RIBLL). Two angular dispersion plots of ln(d sigma/d theta) versus theta 2 are obtained from the angular distribution of the elastic scattering differential cross sections. The angular dispersion plot exhibits a clear turning point for F-17 in the range of small scattering angles 6 degrees-20 degrees due to its exotic structure, but for O-17, the turning point is not observed in the same angular range. The experimental results have been compared with previous data of other groups. Systematical analysis on the available data supports the above conclusion that there is an exotic behaviour of the angular dispersion plot of weakly bound nuclei with halo or skin structure as compared with that of the ordinary nuclei near stable line. Therefore the turning point of the angular dispersion plot appears at small angle for weakly bound nuclei with halo or skin structure, and can be used as a new probe to investigate the halo and skin phenomena of weakly bound nuclei.
Resumo:
An alternative way to optimize the emission characteristics of a microcavity top-emitting organic light-emitting diode (TOLED) based on a simple device structure is demonstrated via combining a comprehensive theoretical analysis in the microcavity effects with the experimental modification in the carrier injection of both electrodes. It can be seen that the resulting TOLED exhibits much higher efficiencies and a more saturated color than those of the corresponding conventional bottom-emitting device, as well as hardly detectable color shift with viewing angles. Such a strategy may be more feasible in practical application for active-matrix organic light-emitting diode displays.
Resumo:
The Angular Overlap Model (AOM) is applied to the LaOX:Eu3+(X = Cl, Br, I) series involving sigma, pi, delta and phi effects based on the experimental energy levels. The calculations are made in two cases. (1) Consider oxygen and halogen having the same bond-length. (2) Consider the real structure. In both cases, the results show that for sigma-bonding parameters, the values of e(sigma) decrease with increasing charge number of halogen, i.e. Cl- > Br- > I-, this indicates that the bonding ability also decreases with this order. The absolute values of each parameter are much larger than zero-therefore they all must be included in a practical analysis. In the second case, the values of the e(pi) parameter are negative, which means a ''back-bonding'' is formed, and this is profitable for the formation of sigma-bonding, usually referred to as ''synergic effect''.
Resumo:
The angular overlap model (AOM) is applied to 4f6 electron systems. The crystal field parameters are interpreted and covalency between 4f electrons and ligands is investigated based on the experimental energy levels. For Eu3+:Ln2O2S (Ln = Lu, Y, Gd, La) crystal series, we adopt two computational schemes. First of all, we assume that the distances to all ligands are equal, and then the distances to all ligands are divided into two groups, namely, oxygens as one group, sulfurs as the other. Of course, much information about covalency will be obtained from the latter case. Obviously, our results show that the covalency of Ln-O bonding is stronger than that of Ln-S bonding in line with much shorter bondlength for the former than that for the latter. The two schemes yield the same results, that is, for sigma and pi bonding, ligands are strong donors as well as sigma, pi effects are dominant over delta, phi effects.
Resumo:
Photodissociation dynamics of ketene following excitation at 208.59 and 213.24 nm have been investigated using the velocity map ion-imaging method. Both the angular distribution and translational energy distribution of the CO products at different rotational and vibrational states have been obtained. No significant difference in the translational energy distributions for different CO rotational state products has been observed at both excitation wavelengths. The anisotropy parameter beta is, however, noticeably different for different CO rotational state products at both excitation wavelengths. For lower rotational states of the CO product, beta is smaller than zero, while beta is larger than zero for CO at higher rotational states. The observed rotational dependence of angular anisotropy is interpreted as the dynamical influence of a peculiar conical intersection between the B-1(1) excited state and (1)A(2) state along the C-S-I coordinate.
Resumo:
A new phenomenological strain gradient theory for crystalline solid is proposed. It fits within the framework of general couple stress theory and involves a single material length scale Ics. In the present theory three rotational degrees of freedom omega (i) are introduced, which denote part of the material angular displacement theta (i) and are induced accompanying the plastic deformation. omega (i) has no direct dependence upon u(i) while theta = (1 /2) curl u. The strain energy density omega is assumed to consist of two parts: one is a function of the strain tensor epsilon (ij) and the curvature tensor chi (ij), where chi (ij) = omega (i,j); the other is a function of the relative rotation tensor alpha (ij). alpha (ij) = e(ijk) (omega (k) - theta (k)) plays the role of elastic rotation reason The anti-symmetric part of Cauchy stress tau (ij) is only the function of alpha (ij) and alpha (ij) has no effect on the symmetric part of Cauchy stress sigma (ij) and the couple stress m(ij). A minimum potential principle is developed for the strain gradient deformation theory. In the limit of vanishing l(cs), it reduces to the conventional counterparts: J(2) deformation theory. Equilibrium equations, constitutive relations and boundary conditions are given in detail. For simplicity, the elastic relation between the anti-symmetric part of Cauchy stress tau (ij), and alpha (ij) is established and only one elastic constant exists between the two tensors. Combining the same hardening law as that used in previously by other groups, the present theory is used to investigate two typical examples, i.e., thin metallic wire torsion and ultra-thin metallic beam bend, the analytical results agree well with the experiment results. While considering the, stretching gradient, a new hardening law is presented and used to analyze the two typical problems. The flow theory version of the present theory is also given.
Resumo:
It is shown that for a particle with suitable angular moments in the screened Coulomb potential or isotropic harmonic potential, there still exist closed orbits rather than ellipse, characterized by the conserved aphelion and perihelion vectors, i.e. extended Runge-Lenz vector, which implies a higher dynamical symmetry than the geometrical symmetry O-3. The closeness of a planar orbit implies the radial and angular motional frequencies are commensurable.
Resumo:
The strain gradient effect becomes significant when the size of fracture process zone around a crack tip is comparable to the intrinsic material length l, typically of the order of microns. Using the new strain gradient deformation theory given by Chen and Wang, the asymptotic fields near a crack tip in an elastic-plastic material with strain gradient effects are investigated. It is established that the dominant strain field is irrotational. For mode I plane stress crack tip asymptotic field, the stress asymptotic field and the couple stress asymptotic field can not exist simultaneously. In the stress dominated asymptotic field, the angular distributions of stresses are consistent with the classical plane stress HRR field; In the couple stress dominated asymptotic field, the angular distributions of couple stresses are consistent with that obtained by Huang et al. For mode II plane stress and plane strain crack tip asymptotic fields, only the stress-dominated asymptotic fields exist. The couple stress asymptotic field is less singular than the stress asymptotic fields. The stress asymptotic fields are the same as mode II plane stress and plane strain HRR fields, respectively. The increase in stresses is not observed in strain gradient plasticity for mode I and mode II, because the present theory is based only on the rotational gradient of deformation and the crack tip asymptotic fields are irrotational and dominated by the stretching gradient.
Resumo:
A plane strain mode I crack tip field with strain gradient effects is investigated. A new strain gradient theory is used. An elastic-power law hardening strain gradient material is considered and two hardening laws, i.e. a separation law and an integration Law are used respectively. As for the material with the separation law hardening, the angular distributions of stresses are consistent with the HRR field, which differs from the stress results([19]); the angular distributions of couple stresses are the same as the couple stress results([19]). For the material with the integration law hardening, the stress field and the couple stress field can not exist simultaneously, which is the same as the conclusion([19]), but for the stress dominated field, the angular distributions of stresses are consistent with the HRR field; for the couple stress dominated field, the angular distributions of couple stresses are consistent with those in Ref. [19]. However, the increase in stresses is not observed in strain gradient plasticity because the present theory is based on the rotation gradient of the deformation only, while the crack tip field of mode I is dominated by the tension gradient, which will be shown in another paper.