Dislocations and torsion in graphene and related systems

A continuum model to study the influence of dislocations on the electronic properties of condensed matter systems is described and analyzed. The model is based on a geometrical formalism that associates a density of dislocations with the torsion tensor and uses the technique of quantum field theory in curved space. When applied to two-dimensional systems with Dirac points like graphene we find that dislocations couple in the form of vector gauge fields similar to these arising from curvature or elastic strain. We also describe the ways to couple dislocations to normal metals with a Fermi surface.     

Ultrastructure of the myotendinous junction of the medial pterygoid muscle of adult and aged Wistar rats

The myotendon junction (MTJ) is a specialised area into the muscle fibers where the sarcoplasmic membranes connect to the collagen fibers bundles. There are few data about plasticity of the MTJ in aging processes. The aim of this study is to analyse the ultrastructure characteristics of MTJ of medial pterygoid muscle of adult and aged rats. Employing the transmission electron microscopy method, twenty male rats Wistar (Rattus norvegicus) were divided into two groups: A (n = 10) with 12 months of age; B (n = 10) 24 months of age. The animals were anaesthetised with overdose the urethane (3 g/kg, i.p.) and sacrified during the perfusion with modified Karnovsky solution. The specimens were post-fixed in a 1% osmium tetroxide solution, dehydrated in ascending concentration of ethanol and embedded in Spurr resin. The thin sections, of 90 nm thick, were counterstained with uranyl acetate and lead citrate solution, and examined in a Jeol 1010 transmission electron microscope. The fine structure of the MTJ of group A revealed the defined interdigitations and disposed in several levels of deep formations containing the collagen fibers. In the group B, such structures did not observed, detecting the projections irregular in shape, and large of extra matrix with in aspect of remodelling. In conclusion it was possible to identify the plasticity of MTJ in the group B which presented several morphological alterations comparing to the adult animals. These data of group B suggested the occurrence of aging processes in the MTJ in rats.     

Detection of hydrogen peroxide produced at a liquid/liquid interface using scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) was used to monitor in situ hydrogen peroxide (H₂O₂) produced at a polarized water/1,2-dichloroethane (DCE) interface. The water/DCE interface was formed between a DCE droplet containing decamethylferrocene (DMFc) supported on a solid electrode and an acidic aqueous solution. H₂O₂ was generated by reducing oxygen with DMFc at the water/DCE interface, and was detected with a SECM tip positioned in the vicinity of the interface using a substrate generation/tip collection mode. This work shows unambiguously how the H₂O₂ generation depends on the polarization of the liquid/liquid interface, and how proton-coupled electron transfer reactions can be controlled at liquid/liquid interfaces.     

Acetylides from Alkyl Propiolates as Building Blocks for C3 Homologation

Three that matter : Metal acetylides from alkyl propiolates allow C₃ homologations with transference of their versatile reactivity profile to products that can then react without further elaboration. Metal‐free acetylides, which are generated by the action of a good nucleophile on the alkyl propiolate, react with suitable electrophiles through different domino reactions to generate skeletal diversity.

     

Direct Synthesis of a Photoactive Inorganic–Organic Mesostructured Hybrid Material and its Application as a Photocatalyst

A direct route : Silylated triphenylmethanol is incorporated into mesoporous material MCM‐41 through a direct synthesis method. Under acidic conditions, this inorganic–organic hybrid generates trityl cations to give the photoactive material Tyl‐MCM41. Tyl‐MCM41 promotes the photosensitized dimerization of 1,3‐cyclohexadiene with an unprecedented selectivity towards the formation of the exo product (see scheme).

     

Control of the Planar Takens–Bogdanov Bifurcation with Applications

It is well-known that on a versal deformation of the Takens–Bogdanov bifurcation is possible to find dynamical systems that undergo saddle-node, Hopf, and homoclinic bifurcations. In this document a nonlinear control system in the plane is considered, whose nominal vector field has a double-zero eigenvalue, and then the idea is to find under which conditions there exists a scalar control law such that be possible establish a priori, that the closed-loop system undergoes any of the three bifurcations: saddle-node, Hopf or homoclinic. We will say then that such system undergoes the controllable Takens–Bogdanov bifurcation. Applications of this result to the averaged forced van der Pol oscillator, a population dynamics, and adaptive control systems are discussed.     

Gellerstedt and Laplace–Beltrami operators relative to a mixed signature metric

Gellerstedt and Laplace–Beltrami operators relative to a certain mixed signature metric share among themselves an interesting and important property: under suitable change of coordinates they can be represented, up to a multiplying factor, in terms of Q _α and R _α singular first order perturbations of the Laplace and D’Alembertian operators. Knowledge of fundamental solutions for Q _α and R _α leads us to finding explicit formulas for fundamental solutions to those operators. J. Barros-Neto’s research partially supported by NSF, Grant # INT 0124940. F. Cardoso’s research partially supported by CNPq (Brazil).     

Nonstationary electroosmotic flow in open cylindrical capillaries

A theoretical model of the EOF established in a wide capillary after the application of a stepwise voltage has been developed. Both periodical and aperiodical flow regimes were studied with arbitrary pulse/pulse or pulse/pause durations and amplitudes. The numerical analysis performed for a few types of periodical regimes showed the peculiarities of the profiles of liquid velocity and its displacement both for the transition to the stationary regime and for the quasi-stationary periodical and aperiodical regimes.