Surface states and resonances in field emission from low-index facets of clean tungsten

The energies, widths, and shapes of features observed in the total energy distributions in field emission from W(1 0 0) and W(1 1 1) are compared with the results of a full-potential LAPW calculation of the surface density of states based on a supercell model of the crystal structure at the metal–vacuum interface. The Swanson hump on W(1 0 0) is attributed to two bands of surface states and surface resonances of d_z² symmetry that are highly localised at , and a second peak observed at lower energy is attributed to a band of surface resonances, also of d_z² symmetry, centred at from along . The energy scale of the calculated total energy distribution is compressed by about 20% relative to the experimental data. The present calculation yields strong evidence that the broad asymmetric peak observed on W(1 1 1) is due to emission from a band of surface resonances. Further calculations for W(1 1 1) are proposed both to test the accuracy of the band model and to take into account the velocity factor that enters in a calculation of the emission current.     

High magnetic field properties and ESR of the compounds

compounds have a layered structure made of alternating Ni-O and Li-O slabs. An amount z of extra divalent Ni ions is always present in the Li-O layers. We show, using high field magnetisation, static and dynamic susceptibility and high frequency ESR, that the magnetic properties are driven by the z parameter. The compounds can be described as ferromagnetic Ni-O layers, bridged by clusters possessing a net ferromagnetic moment. Received: 24 July 1998 / Revised and Accepted: 23 September 1998     

Substrate-Modulated Electromagnetic Resonances in Colloidal Cu2O Nanospheres

Dielectric nanoparticles are expected to complement or even replace plasmonic nanoparticles in many optical and optoelectronic applications, because they exhibit small absorption losses and support strong electric and magnetic resonances simultaneously. Dielectric nanoparticles need to be deposited on various substrates in many applications. Understanding the substrate effect on the electromagnetic resonances of dielectric nanoparticles is of great importance for engineering their resonance properties and designing optical devices. In this study, moderate-refractive-index cuprous oxide nanospheres with uniform sizes and shapes are synthesized. The scattering spectra and images of the nanospheres deposited on three types of substrates are analyzed experimentally and theoretically. When supported on indium tin oxide–coated glass slides and Si wafers, the color of the nanospheres varies from blue, cyan, green, yellow, orange and red, covering almost the entire visible region. When deposited on gold films, the electromagnetic resonances of the nanospheres redshift intensively and a new effective magnetic resonance mode appears. The enhanced Raman scattering reveals that large electromagnetic field enhancements are produced in the gap region between the nanosphere and the substrate. The results shed light on the manipulation of the electromagnetic responses of dielectric nanoparticles and the design of dielectric metamaterials in the presence of various substrates.     

Resonances and O-curves in Hamiltonian systems

We investigate the problem of the existence of trajectories asymptotic to elliptic equilibria of Hamiltonian systems in the presence of resonances.      

Influence of the moment of inertia of the pendulum on the internal friction (loss tangent) measured by free decay

Summary The internal friction (loss tangent) of solids is normally measured, as a function of temperature, with a torsion pendulum operating in free decay. Curves of the internal friction and the oscillation frequency, against temperature, are obtained at various moments of inertia, to extract the parameters characteristic of the relaxation process (relaxation time and strength). In all these experiments only the temperature is considered as an independent variable and the moment of inertia of the pendulum is mainly used to shift the internal friction peaks in the temperature scale. It is pointed out in the paper that the moment of inertia is also an independent variable which can be used to determine, with high accuracy, if the measured peak is of the Debye type or not. A new torsion pendulum, with continuously variable moment of inertia is presented, which allows measurements of the partial derivative of the internal friction and the oscillation frequency with respect to the moment of inertia, at constant temperature. Finally, some measurements of the Snoek relaxation in Nb-O alloys are presented, to show the applicability of the concepts developed in the paper. The authors of this paper have agreed to not receive the proofs for correction.     

Characterization of non-exponential relaxation via linear ESR

Summary The effect of non-exponential relaxation on the lineshape of the linear Electron Spin Resonance spectroscopy is discussed. In the simple case of a paramagnetic system withS=1/2 it is found that the lineshape is mainly affected by the tails of the correlation function. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Identification of baryon resonances in central heavy-ion collisions at energies between 1 and 2 AGeV

The mass distributions of baryon resonances populated in near-central collisions of Au on Au and Ni on Ni are deduced by defolding the p_t spectra of charged pions by a method which does not depend on a specific resonance shape. In addition the mass distributions of resonances are obtained from the invariant masses of (p, π^±) pairs. With both methods the deduced mass distributions are shifted by an average value of −60 MeV/c² relative to the mass distribution of the free Δ(1232) resonance, the distributions descent almost exponentially towards mass values of 2000 MeV/c². The observed differences between (p, π⁻) and (p, π⁺) pairs indicate a contribution of isospin I = 1/2 resonances. The attempt to consistently describe the deduced mass distributions and the reconstructed kinetic energy spectra of the resonances leads to new insights about the freeze out conditions, i.e. to rather low temperatures and large expansion velocities. Received: 26 June 1998 / Revised version: 2 September 1998     

xc0→BB^-MM衰变中的重子共振态

基于SU（3）对称性研究了Xc0的遍举多体衰变xc0→BB^-MM（B：重子，M：介子），通过同位旋耦合常数构造了xc0→BB^-→BB^-MM衰变的跃迁振幅．基于这些跃迁振幅，发现N^＊共振态对xc0→BB^-ππ的贡献相对较大，这个衰变道可以在实验上用来研究N^＊共振态．     

重子五夸克波函数与核子磁矩

依据ＳＵＦ（３）味对称性并运用群论方法提出了一个简单的重子夸克模型（ｑｑｑ）＋（ｑｑｑｑｑ），计算了核子的磁矩，得到了静态核子磁矩的一般表达式；并由质子、中子磁矩的实验值定出了静态核子内各夸克组分的权重，从而得到了核子的静态波函数．     

Study of the first-excited K π=0+ and 2+ bands in 228Th in the 226Ra(α,2n) reaction

Excited bands of ²²⁸Th were studied in the ²²⁶Ra(α,2n) reaction by gamma-ray and conversion-electron spectroscopy. The first-excited K ^π=0⁺ and 2⁺ bands were identified up to I ^π= 12⁺ and 10⁺, respectively. The spin dependence of the moments of inertia is discussed. The experimental data indicate a structural change of these bands from ²²⁸Th to ²³⁰Th and ²³²Th. Received: 11 August 1997 / Revised version: 19 September 1997