Competing periodicities in fractionally filled one-dimensional bands

We present a variable temperature Scanning Tunneling Microscopy and Spectroscopy (STM and STS) study of the Si(553)-Au atomic chain reconstruction. This quasi one-dimensional (1D) system undergoes at least two charge density wave (CDW) transitions at low temperature, which can be attributed to electronic instabilities in the fractionally-filled 1D bands of the high-symmetry phase. Upon cooling, Si(553)-Au first undergoes a single-band Peierls distortion, resulting in period doubling along the imaged chains. This Peierls state is ultimately overcome by a competing tripleperiod CDW, which in turn is accompanied by a x2 periodicity in between the chains. These locked-in periodicities indicate small charge transfer between the nearly half-filled and quarter-filled 1D bands. The presence and the mobility of atomic scale dislocations in the x3 CDW state indicates the possibility of manipulating phase solitons carrying a (spin,charge) of (1/2,+-e/3) or (0,+-2e/3).Comment: submitted, accepted for publication in Phys. Rev. Let

Formation of atom wires on vicinal silicon

The formation of atomic wires via pseudomorphic step-edge decoration on vicinal silicon surfaces has been analyzed for Ga on the Si(112) surface using Scanning Tunneling Microscopy and Density Functional Theory calculations. Based on a chemical potential analysis involving more than thirty candidate structures and considering various fabrication procedures, it is concluded that pseudomorphic growth on stepped Si(112), both under equilibrium and non-equilibrium conditions, must favor formation of Ga zig-zag chains rather than linear atom chains. The surface is non-metallic and presents quasi-one dimensional character in the lowest conduction band.Comment: submitte

Triphasic finite element model for swelling porous media

The equations describing the mechanical behaviour of intervertebral disc tissue and other swelling porous media are three coupled partial differential equations in which geometric and physical non-linearities occur. To solve the equations for an arbitrary geometry and arbitrary boundary conditions, we use the finite element (FE) method. The differential equations are rewritten in an integral form by means of the weighted residual method. The domain of the integral is defined via a set of shape functions. By applying the Gauss theorem and rewriting with respect to the reference state (total Lagrange), non-linear equations are obtained. In order to get a finite set of equations, the weighted residual equations are discretized. The shape functions are chosen as weighting functions (Galerkin method). A general description is given for the elements implemented into the commercial FE package DIANA. The numerical results of unconfined compression of a schematic intervertebral disc with varying proteoglycan concentration are given. (from Authors

Recent advances in the assessment and treatment of falls in Parkinson's disease

Falls are among the most incapacitating features of Parkinson's disease. Prevention of falls requires a systematic assessment of all contributing factors (with emphasis on freezing of gait and frontal executive dysfunction), and a multidisciplinary treatment approach tailored to the specific pathophysiology of falls for each individual patient