Nanoelectromechanical systems

Nanoelectromechanical systems (NEMS) are nano-to-micrometer scale mechanical resonators coupled to electronic devices of similar dimensions. NEMS show promise for fast, ultrasensitive force microscopy and for deepening our understanding of how classical dynamics arises by approximation to quantum dynamics. This article begins with a survey of NEMS and then describes certain aspects of their classical dynamics. In particular, we show that for weak coupling the action of the electronic device on the mechanical resonator can be effectively that of a thermal bath, this despite the device being a driven, far-from-equilibrium system.     

Anatomy of a polarization switch of a vertical-cavity semiconductor laser

Using a streak camera we have measured the three Stokes polarization parameters during a polarization switch of a vertical-cavity semiconductor laser. The switch occurs along a corkscrew path on the Poincare sphere and takes on average a few nanoseconds; this value agrees with a theoretical treatment based upon the Fokker-Planck equation.     

p-tert-Butylcalix[8]arene: a support for sodium and sodium-manganese clusters that exhibit interesting self-assembly properties

A series of new sodium and mixed sodium/manganese clusters have been formed using p-tert-butylcalix[8]arene as a support. In all cases the calixarene adopts the pleated-loop conformation, and the resulting complexes show interesting self-assembly properties depending on the ligated solvent molecules around individual cluster cores.     

Infiltration of initially dry, deformable porous media

The present paper studies the infiltration of an incompressible liquid in an initially dry (or partially dry), deformable sponge-like material made of an incompressible constituent in the slug-flow approximation having in mind the application to some industrial processes involving flow through sponge-like materials and, in particular, some composite materials manufacturing processes. The resulting initial-boundary value problem is of Stefan type, with suitable interface conditions and evolution equations describing the position of the interfaces delimiting the saturated region within the porous material. Different models are then suggested in the saturated region, depending on the importance of the inertial terms and on the constitutive equation for the stress. Comparison of the simulation with known experimental results is satisfactory.     

The matrix sign function and computations in systems

The matrix sign function has several interesting properties which form the basis of new solution algorithms for problems which occur frequently in systems and control theory applications. Presented in this paper are new algorithms, based on the matrix sign function, for the solution of algebraic matrix Riccati equations, Lyapunov equations, coupled Riccati equations, spectral factorization, matrix square roots, pole assignment, and the algebraic eigenvalue-eigenvector problem. Examples of the application of each algorithm are also presented.     

Crystallographic X-ray analyses of Yb@C(2v)(3)-C80 reveal a feasible rule that governs the location of a rare earth metal inside a medium-sized fullerene

Single crystal X-ray diffraction studies of Yb@C(2v)(3)-C(80)·Ni(II)(OEP)·CS(2)·1.5C(6)H(6) (OEP = octaethylporphinate) reveal that a relatively flat region of the fullerene interacts with the Ni(II)(OEP) molecule, featuring shape-matching interactions. Surprisingly, it is found that the internal metal is located under a hexagonal carbon ring apart from the 2-fold axis of the C(2v)(3)-C(80) cage, presenting the first example of metallofullerenes with an asymmetrically positioned metal. Such an anomalous location of Yb(2+) is associated with its strong ability to pursue a large coordination number and the lack of hexagon along the C(2) axis of C(2v)(3)-C(80). It is accordingly assumed that a suitable cage hexagon is most likely to be preferred by the single rare earth metal to stay behind inside a medium-sized fullerene, such as C(80) and C(82).