Dispersion in finlines on semiconductor and the S-parameters of a step discontinuity

The Transverse Transmission Line method is used for the characterization of bilateral and unilateral finlines on a semiconductor substrate and in conjunction with the modal method, for the calculation of the scattering parameters due to a step discontinuity on a unilateral finline with a lossless dielectric substrate.Numerical results of the effective dielectric constant, attenuation constant and characteristic impedance for the bilateral and unilateral finlines on semiconductor substrates, and results of scattering parameters of a step discontinuity for unilateral finline, are presented.     

Unilateral Fin Line Directional Coupler

Photonic band gap (PBG) crystals have been used as a perfectly reflecting substrate for many millimeter wave applications. In this work the fin line directional coupler with substrate PBG was analyzed using the TTL - Transverse Transmission Line - method. Compared to other full wave methods the TTL is an efficient tool to determine the coupler characteristics, making possible a significant algebraic simplification of the equations involved in the process. In order to analyze this structure the effective dielectric constant, the attenuation constant and the coupling were determined. The results obtained for this application and the conclusions are presented. This work was partially financed by CNPQ.     

Review and perspectives on energy dispersive high resolution PIXE and RYIED

Until 2008, high-resolution particle-induced x-ray emission (HR-PIXE) work used mostly wavelength dispersive spectrometers and aimed at fundamental problems and application demonstrations. The method was hardly used for applications in general, mostly due to the small energy window and solid angle of most equipment. In the last 14 years, a few facts pushed HR-PIXE out and beyond this framework. Here, we focus on the developments following the observation of x-ray relative yield ion energy dependence (RYIED) effects on transitions to the same sub-shell, in PIXE experiments, in 2004, and the installation, in 2008, of the first energy dispersive HR-PIXE (EDS HR-PIXE) system. Both facts are among those that were concurrent to the emergence of new problems and perspectives in PIXE and in fundamental atomic physics in the recent past. This review covers these 14 years of results on these issues and the answers they recently led to. Evidence for new problems and perspectives, including the potential access to chemical bonding and/or solid state information, based on EDS HR-PIXE work, are discussed. Furthermore, the grounds for the possibility of developments leading to a new field of atomic solid state physics are presented.     

Time evolution of the eddy viscosity in two-dimensional navier-stokes flow

The time evolution of the eddy viscosity associated with an unforced two-dimensional incompressible Navier-Stokes flow is analyzed by direct numerical simulation. The initial condition is such that the eddy viscosity is isotropic and negative. It is shown by concrete examples that the Navier-Stokes dynamics stabilizes negative eddy viscosity effects. In other words, this dynamics moves monotonically the initial negative eddy viscosity to positive values before relaxation due to viscous term occurs.     

Raman studies in SmCFI* phases

The study of the Raman intensity of the 'breathing' mode of the benzene rings as a function of the temperature in smectic phases revealed strong anomalies of the intensities I_ZZ and I_YY in SmC_FI2* and SmC_FI1* phases, as well as an important shift of the principal optical direction with respect to other smectic phases. The analysis of these results provided evidence for significant structural changes at the SmC*-SmC_FI* and SmC_FI*-SmC_A* phase transitions, because the molecules can no longer be treated as cylindrical rods. No anomalies in the tilt angle were found. Experimental results suggest a relationship between the deviation of the optical axis and the particular structure of the SmC_FI* phases. The deviation of I_ZZ maxima as a function of the rotation angle Ψ and the behaviour evident under an electric field in SmC_FI* and SmC_A* phases clearly excludes the coexistence of SmC_A* and SmC* local domains in SmC_FI* phases.     

Quantum computing with incoherent resources and quantum jumps

Spontaneous emission and the inelastic scattering of photons are two natural processes usually associated with decoherence and the reduction in the capacity to process quantum information. Here we show that, when suitably detected, these photons are sufficient to build all the fundamental blocks needed to perform quantum computation in the emitting qubits while protecting them from deleterious dissipative effects. We exemplify this by showing how to efficiently prepare graph states for the implementation of measurement-based quantum computation.     

Mild Selective Hydrolysis of Acetals in Carbohydrates

A simple and inexpensive methodology for the selective hydrolysis of acetals using hydrogen chloride as catalyst is described.     

H+ and He2 + induced W L X‐rays intensity ratios: part I,Si(Li) data and EDS high resolution insight

Recently, the authors have presented experimental evidences that for some energy windows, proton‐induced W L shell X‐rays intensity ratios of transitions to L₁ subshell depend on the ion beam energy and on the chemical species even after known matrix effects are subtracted. These results, which put in question the assumption of the invariance of the relative intensity of X‐ray transitions to the same atomic subshells, are further exploited in this work, where more data for three different W compounds (W, Li₂WO₄ and P₂O₅.24WO₃.xH₂O) are presented followed by a detailed study using an ultra‐pure (99.995%) W thick foil, used to avoid any possible target contamination interference on the results. Samples were irradiated by H⁺ beams in various conditions in the energy range between 0.25 and 2.38 MeV and by He^{2 +} beams having energies between 3.5 and 5.0 MeV. Spectra were collected using the Si(Li) detector at CTN 2.5 MV Van de Graaff standard Proton‐Induced X‐ray Emission (PIXE) set‐up as well as using the Energy Dispersive Spectrometry (EDS) high resolution X‐ray microcalorimeter spectrometer (XMS) at CTN 3.0 MV Tandetron accelerator high resolution high energy (HRHE) PIXE end station. Results were normalized to the theoretical intensity ratios and plotted as function of the ratio of collision characteristic times allowing the comparison of H⁺ and He^{2 +} results. W L X‐rays intensity ratio variations are presented and compared with theoretical expected results. Radiative Auger emission transitions observed in an EDS high resolution XMS spectra are shown to probably play a crucial role in the highly unexpected results obtained for intensity ratios of transitions to the same subshell. Copyright © 2013 John Wiley & Sons, Ltd.     

SnCl<Subscript>2</Subscript>-catalyzed synthesis of carbamates from renewable origin alcohols

Effects of structure and reactivity of renewable origin alcohols in the conversion and selectivity of the SnCl₂-catalyzed reactions in the presence and absence of urea were assessed. Convenient simple and suitable method for the synthesis of carbamates from renewable origin alcohols and urea in one-step are provided. We have assessed the activity of SnCl₂ catalyst, a commercially affordable Lewis acid, in reactions of urea alcoholysis with different natural origin alcohols (geranyl, neryl, bornyl, cinnamyl, α-terpinyl and benzyl alcohols), aiming to synthesize carbamates, which are biologically active compounds, building blocks in organic synthesis and raw material to synthesize polyurethanes. The low cost of urea, the water tolerant catalyst and phosgene free reaction are positive aspects of this carbamates synthesis process. The different reaction pathways were assessed. A mechanism was proposed based on FT-IR experiments and experimental data.