Theory of valence mixing for rare-earth compounds

A theory for the mixed valence state of rare-earth compounds is presented. It includes the following features: (1) two types of electronic states-localized, highly correlated states and itinerant, non-correlated states; (2) a very strong Coulomb repulsion between localized states in the same site; (3) a Coulomb interaction between localized and itinerant states which drives the phase transition; and (4) hybridization between localized and itinerant states which produces the mixed valence state. It is shown that this model produces (a) at T = 0, a variation in the number of localized electrons which may vary in a smooth or in a discontinuous fashion as a function of pressure or alloying; (b) transitions at finite temperature which terminate in a classical critical point. Qualitative agreement with experiment is an encouraging feature of the model.     

Magnetic fields and the stability of charge-density-wave ground-states in silicon inversion layers

Earlier work on the stability of charge-density-wave (CDW) ground-states in stressed silicon inversion layers is extended to incorporate the effects of the high magnetic fields normally used in acquiring experimental data. By comparison with the effects of stress, low magnetic fields affect the stability of the CDW only marginally. In the extreme quantum limit, i.e. high magnetic fields and low carrier concentrations, CDW states can be stabilised at significantly lower applied stresses.     

Hole cyclotron masses in silicon MOS devices

Anistropy and non-parabolicity of the hole band structure in silicon, together with bound-state effects, can explain satisfactorily the observed hole cyclotron masses in MOS devices. The calculations presented here show a large increase (of about a factor of 2) in the masses as the carrier concentration varies from 0 to $\text{5 × 10}{}^{12}\text{holes}\text{cm}{}^2$. In approximate terms it can be stated that 40% of the increase is due to pure band-structure effects and the remaining 60% is caused by combined effects of bound-state corrections and band structure.     

Functional neural network analysis in frontotemporal dementia and Alzheimer's disease using EEG and graph theory

Background  

Although a large body of knowledge about both brain structure and function has been gathered over the last decades, we still have a poor understanding of their exact relationship. Graph theory provides a method to study the relation between network structure and function, and its application to neuroscientific data is an emerging research field. We investigated topological changes in large-scale functional brain networks in patients with Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) by means of graph theoretical analysis of resting-state EEG recordings. EEGs of 20 patients with mild to moderate AD, 15 FTLD patients, and 23 non-demented individuals were recorded in an eyes-closed resting-state. The synchronization likelihood (SL), a measure of functional connectivity, was calculated for each sensor pair in 0.5–4 Hz, 4–8 Hz, 8–10 Hz, 10–13 Hz, 13–30 Hz and 30–45 Hz frequency bands. The resulting connectivity matrices were converted to unweighted graphs, whose structure was characterized with several measures: mean clustering coefficient (local connectivity), characteristic path length (global connectivity) and degree correlation (network 'assortativity'). All results were normalized for network size and compared with random control networks.     

Core-level satellite structure in photoemission spectra of transition metals

A theory of the satellite structure of the core-level photoemission spectrum of transition metals is presented. It is applied to the $\text{2}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ level of metallic nickel. The calculation is carried out for both the paramagnetic and ferromagnetic states and is based on two scattering parameters, one intraband and one interband. Agreement with experiment is very good.     

Effects of the 2 × 1 reconstruction on the electronic structure of the (111) surface of Si and Ge

We have studied the electronic surface properties of the (2 × 1) reconstructed (111) surface of a diamond-structure semiconductor with a simple sp³ Hamiltonian. Different models for the reconstruction have been analysed. We conclude that, in order to explain experimental results, both relaxation and reconstruction effects have to be taken into account.