Electron transport in Nano‐Gold–Silicon interfaces

The electron transport characteristics of gold–silicon interfaces are studied using a combined ab initio approach of the Green's function for electron transfer and quantum density functional theory (DFT) for finite and extended systems. The Kohn–Sham Hamiltonian of an extended cluster or molecule and the density of states (DOS) of bulk Si and Au are used to construct the interface Hamiltonian to obtain the DOS, electron transmission, and current–voltage characteristics of the interface. Diode behavior is observed with electron conduction when the gold side is positively biased with a threshold of 0.8 V. The presence of molecules trapped at the interface and the geometry of the metal atoms strongly affect the conductance, implying difficult or even impossible theory–experiment validations. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Soft X-ray resonant magnetic scattering study of magnetization reversal in low dimensional magnetic heterostructures

Soft X-ray resonant magnetic scattering (SXRMS) has been used to investigate the microscopic magnetization reversal behavior of complex magnetic systems. SXRMS is a unique technique, providing chemical, spatial and magnetic sensitivity, which is not affected by external magnetic fields. The study of two selected thin magnetic heterostructures is presented, amorphous rare-earth transition metal alloys and perpendicular exchange coupled antiferromagnetic/ferromagnetic films. In the first system, the internal structure of magnetic stripe domains on nanometer length scales is obtained by measuring bi-dimensional (2D) scattering images. In the second system, the element specificity is exploited to identify the role of the uncompensated spins in the antiferromagnetic layer on the exchange coupling phenomena. Future trends are also discussed.     

Conformational Relaxation of p‐Phenylenevinylene Trimers in Solution Studied by Picosecond Time‐Resolved Fluorescence

Two p‐phenylenevinylene (PV) trimers, containing 3′‐methylbutyloxyl (in MBOPV3) and 2′‐ethylhexyloxyl (in EHOPV3) side chains, are used as model compounds of PV‐based conjugated polymers (PPV) with the purpose of clarifying the origin of fast (picosecond time) components observed in the fluorescence decays of poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylenevinylene] (MEH‐PPV). The fluorescence decays of MBOPV3 and EHOPV3 reveal the presence of similar fast components, which are assigned to excited‐state conformational relaxation of the initial population of non‐planar trimer conformers to lower‐energy, more planar conformers. The rate constant of conformational relaxation k_CR is dependent on solvent viscosity and temperature, according to the empirical relationship k_CR=aη_o^?α?exp(?αE_η/RT), where aη_o^?α is the frequency factor, η_o is the pre‐exponential coefficient of viscosity, E_η is the activation energy of viscous flow. The empirical parameter α, relating the solvent microscopic friction involved in the conformational change to the macroscopic solvent friction (α=1), depends on the side chain. The fast component in the fluorescence decays of MEH‐PPV polymers (PPVs), is assigned to resonance energy transfer from short to longer polymer segments. The present results call for revising this assignment/interpretation to account for the occurrence of conformational relaxation, concurrently with energy transfer, in PPVs.     

Existence of nash equilibria for constrained stochastic games

In this paper, we consider constrained noncooperative N-person stochastic games with discounted cost criteria. The state space is assumed to be countable and the action sets are compact metric spaces. We present three main results. The first concerns the sensitivity or approximation of constrained games. The second shows the existence of Nash equilibria for constrained games with a finite state space (and compact actions space), and, finally, in the third one we extend that existence result to a class of constrained games which can be “approximated” by constrained games with finitely many states and compact action spaces. Our results are illustrated with two examples on queueing systems, which clearly show some important differences between constrained and unconstrained games.Mathematics Subject Classification (2000): Primary: 91A15. 91A10; Secondary: 90C40     

Joule heating effects in optimized insulator‐based dielectrophoretic devices: An interplay between post geometry and temperature rise

Insulator‐based dielectrophoresis (iDEP) is the electrokinetic migration of polarized particles when subjected to a non‐uniform electric field generated by the inclusion of insulating structures between two remote electrodes. Electrode spacing is considerable in iDEP systems when compared to electrode‐based DEP systems, therefore, iDEP systems require high voltages to achieve efficient particle manipulation. A consequence of this is the temperature increase within the channel due to Joule heating effects, which, in some cases, can be detrimental when manipulating biological samples. This work presents an experimental and modeling study on the increase in temperature inside iDEP devices. For this, we studied seven distinct channel designs that mainly differ from each other in their post array characteristics: post shape, post size and spacing between posts. Experimental results obtained using a custom‐built copper Resistance Temperature Detector, based on resistance changes, show that the influence of the insulators produces a difference in temperature rise of approximately 4°C between the designs studied. Furthermore, a 3D COMSOL model is also introduced to evaluate heat generation and dissipation, which is in good agreement with the experiments. The model allowed relating the difference in average temperature for the geometries under study to the electric resistance posed by the post array in each design.     

Modification of propylene-α-olefin copolymers by maleic anhydride grafting and blending

Five commercial random propylene-α-olefin copolymers were functionalized with maleic anhydride by reactive mixing. Materials and blends of the original polymers with the grafted ones were characterized by IR, SEC, rheology, XRD, and DSC. The effects of ethylene content and average molecular weights on the effectiveness of scission and grafting reactions were investigated. Functionalization gives place to thermo-rheologically simple materials whose dynamic properties are in agreement with the measured molecular weights. The blends, which stand as miscible ones, display terminal dynamic moduli and crystallization and melting temperatures that show slight positive deviation with respect to linear mixing rules.     

Initial Carbon−Carbon Bond Formation during the Early Stages of Methane Dehydroaromatization

Methane dehydroaromatization (MDA) is among the most challenging processes in catalysis science owing to the inherent harsh reaction conditions and fast catalyst deactivation. To improve this process, understanding the mechanism of the initial C?C bond formation is essential. However, consensus about the actual reaction mechanism is still to be achieved. In this work, using advanced magic‐angle spinning (MAS) solid‐state NMR spectroscopy, we study in detail the early stages of the reaction over a well‐dispersed Mo/H‐ZSM‐5 catalyst. Simultaneous detection of acetylene (i.e., presumably the direct C?C bond‐forming product from methane), methylidene, allenes, acetal, and surface‐formate species, along with the typical olefinic/aromatic species, allow us to conclude the existence of at least two independent C?H activation pathways. Moreover, this study emphasizes the significance of mobility‐dependent host–guest chemistry between an inorganic zeolite and its trapped organic species during heterogeneous catalysis.     

Arched beams of Bresse type: observability and application in thermoelasticity

Nonlinear Dynamics - This is the first paper of a trilogy intended by the authors in what concerns a unified approach to the stability of thermoelastic arched beams of Bresse type under...     

Semigroups of partial transformations with kernel and image restricted by an equivalence

Semigroup Forum - For an arbitrary set X and an equivalence relation $$\mu$$ on X, denote by $$P_\mu (X)$$ the semigroup of partial transformations $$\alpha$$ on X such that $$x\mu \subseteq x(\ker...