Tunable Bragg filter using silicon compound films

In this work, we present the simulation, fabrication and characterization of a tunable Bragg filter employing amorphous dielectric films deposited by plasma enhanced chemical vapor deposition technique on a crystalline silicon substrate. The optical device was built using conventional microelectronic processes and consisted of fifteen periodic intervals of Si3N4 layers separated by air with appropriated thickness and lengths to produce transmittance attenuation peaks in the visible region. For this, previous simulations were realized based in the optical parameters of the dielectric film, which were extracted from ellipsometry and profilometry techniques. For the characterization of the optical interferential filter, a 633 nm monochromatic light was injected on the filter, and then the transmitted output light was collected and conducted to a detector through an optical waveguide made also of amorphous dielectric layers. Afterwards, the optical filter was mounted on a Peltier thermoelectric device in order to control the temperature of the optical device. When the temperature of filter changes, a refractive index variation is originated in the dielectric film due to the thermo-optic effect, producing a shift of attenuation peak, which can be well predicted by numerical simulations. This characteristic allows this device to be used as a thermo-optic sensor. (C) 2007 Elsevier B.V. All rights reserved.

Exploring the random genesis of co-occurrence networks

Using the network random generation models from Gustedt (2009)[23], we simulate and analyze several characteristics (such as the number of components, the degree distribution and the clustering coefficient) of the generated networks. This is done for a variety of distributions (fixed value, Bernoulli, Poisson, binomial) that are used to control the parameters of the generation process. These parameters are in particular the size of newly appearing sets of objects, the number of contexts in which new elements appear initially, the number of objects that are shared with `parent` contexts, and, the time period inside which a context may serve as a parent context (aging). The results show that these models allow to fine-tune the generation process such that the graphs adopt properties as can be found in real world graphs. (C) 2011 Elsevier B.V. All rights reserved.

Electrochemical and spectroscopic characterization of screen-printed gold-based electrodes modified with self-assembled monolayers and Tc85 protein

This work investigates the formation of self-assembled monolayers (SAMs) of cystamine and cystamine-glutaraldehyde on a screen-printed electrode, and the immobilization of the Tc85 protein (from Trypanosoma cruzi) on these monolayers. The methods used included infrared techniques, cyclic voltammetry, and electrochemical impedance spectroscopy. The electrochemical studies were performed at pH 6.9 in 0.1 mol L(-1) phosphate buffer solution containing Fe(CN)(6)(-3/-4) redox species. The surface coverage (0) of the electrode was 0.10 (cystamine), 0.35 (cystamine-glutaraldehyde) and 0.84 (Tc85). Interpretation of electrochemical impedance spectroscopy results was based on a charge-transfer reaction involving Fe(CN)(6)(-3/-4) species at high frequencies, followed by a diffusion through the monolayers at lower frequencies. Estimates of the electrode surface coverage, active site radius, and distance between two adjacent sites assumed that charge transfer occurred at the active sites, and that there was a planar diffusion of redox species to these sites. (C) 2009 Elsevier B.V. All rights reserved.

Animated solid model of the lung constructed from unsynchronized MR sequential images

This work discusses a 4D lung reconstruction method from unsynchronized MR sequential images. The lung, differently from the heart, does not have its own muscles, turning impossible to see its real movements. The visualization of the lung in motion is an actual topic of research in medicine. CT (Computerized Tomography) can obtain spatio-temporal images of the heart by synchronizing with electrocardiographic waves. The FOV of the heart is small when compared to the lung`s FOV. The lung`s movement is not periodic and is susceptible to variations in the degree of respiration. Compared to CT, MR (Magnetic Resonance) imaging involves longer acquisition times and it is not possible to obtain instantaneous 3D images of the lung. For each slice, only one temporal sequence of 2D images can be obtained. However, methods using MR are preferable because they do not involve radiation. In this paper, based on unsynchronized MR images of the lung an animated B-Repsolid model of the lung is created. The 3D animation represents the lung`s motion associated to one selected sequence of MR images. The proposed method can be divided in two parts. First, the lung`s silhouettes moving in time are extracted by detecting the presence of a respiratory pattern on 2D spatio-temporal MR images. This approach enables us to determine the lung`s silhouette for every frame, even on frames with obscure edges. The sequence of extracted lung`s silhouettes are unsynchronized sagittal and coronal silhouettes. Using our algorithm it is possible to reconstruct a 3D lung starting from a silhouette of any type (coronal or sagittal) selected from any instant in time. A wire-frame model of the lung is created by composing coronal and sagittal planar silhouettes representing cross-sections. The silhouette composition is severely underconstrained. Many wire-frame models can be created from the observed sequences of silhouettes in time. Finally, a B-Rep solid model is created using a meshing algorithm. Using the B-Rep solid model the volume in time for the right and left lungs were calculated. It was possible to recognize several characteristics of the 3D real right and left lungs in the shaded model. (C) 2007 Elsevier Ltd. All rights reserved.

Optimization of preservative system in ophthalmic suspension with dexamethasone and polymyxin B

A simplex-lattice statistical project was employed to study an optimization method for a preservative system in an ophthalmic suspension of dexametasone and polymyxin B. The assay matrix generated 17 formulas which were differentiated by the preservatives and EDTA (disodium ethylene diamine-tetraacetate), being the independent variable: X-1 = chlorhexidine digluconate (0.010 % w/v); X-2 = phenylethanol (0.500 % w/v); X-3 = EDTA (0.100 % w/v). The dependent variable was the Dvalue obtained from the microbial challenge of the formulas and calculated when the microbial killing process was modeled by an exponential function. The analysis of the dependent variable, performed using the software Design Expert/W, originated cubic equations with terms derived from stepwise adjustment method for the challenging microorganisms: Pseudomonas aeruginosa, Burkholderia cepacia, Staphylococcus aureus, Candida albicans and Aspergillus niger. Besides the mathematical expressions, the response surfaces and the contour graphics were obtained for each assay. The contour graphs obtained were overlaid in order to permit the identification of a region containing the most adequate formulas (graphic strategy), having as representatives: X-1 = 0.10 ( 0.001 % w/v); X-2 = 0.80 (0.400 % w/v); X-3 = 0.10 (0.010 % w/v). Additionally, in order to minimize responses (Dvalue), a numerical strategy corresponding to the use of the desirability function was used, which resulted in the following independent variables combinations: X-1 = 0.25 (0.0025 % w/v); X-2 = 0.75 (0.375 % w/v); X-3 = 0. These formulas, derived from the two strategies (graphic and numerical), were submitted to microbial challenge, and the experimental Dvalue obtained was compared to the theoretical Dvalue calculated from the cubic equation. Both Dvalues were similar to all the assays except that related to Staphylococcus aureus. This microorganism, as well as Pseudomonas aeruginosa, presented intense susceptibility to the formulas independently from the preservative and EDTA concentrations. Both formulas derived from graphic and numerical strategies attained the recommended criteria adopted by the official method. It was concluded that the model proposed allowed the optimization of the formulas in their preservation aspect.

Rheological behavior, zeta potential, and accelerated stability tests of Buriti oil (Mauritia flexuosa) emulsions containing lyotropic liquid crystals

Background: It is well known that the Amazon region presents a huge biodiversity; therefore, countless natural resources are being employed in the production of phytocosmetics and phytomedicines. Objective: The purpose of this work was to obtain emulsions produced with Buriti oil and nonionic surfactants. Methods: Two surfactant systems were employed (Steareth-2 associated to Ceteareth-5 and to Ceteareth-20) to produce the emulsions using phase diagram method. Emulsions were obtained by echo-planar imaging method at 75 degrees C. Rheological behavior and zeta potential were evaluated, and accelerated stability tests were performed. Results: All emulsions analyzed presented pseudoplastic behavior. Zeta potential values were obtained between -14.2 and -53.3 mV. The formulations did not show changes in either physical stability, pH, or rheological behavior after accelerated stability tests. Significant differences were observed only after temperature cycling test. Conclusion: Based on these results, the emulsions obtained could be considered as promising delivery systems.

Hamiltonian mappings and circle packing phase spaces.

We introduce three area preserving maps with phase space structures which resemble circle packings. Each mapping is derived from a kicked Hamiltonian system with one of the three different phase space geometries (planar, hyperbolic or spherical) and exhibits an infinite number of coexisting stable periodic orbits which appear to ‘pack’ the phase space with circular resonances.

On the nonlinear Neumann problem with critical and supercritical nonlinearities

We investigate the solvability of the Neumann problem (1.1) involving a critical Sobolev exponent. In the first part of this work it is assumed that the coeffcients Q and h are at least continuous. Moreover Q is positive on overline Omega and lambda > 0 is a parameter. We examine the common effect of the mean curvature and the shape of the graphs of the coeffcients Q and h on the existence of low energy solutions. In the second part of this work we consider the same problem with Q replaced by - Q. In this case the problem can be supercritical and the existence results depend on integrability conditions on Q and h.

Velocimetry and thermometry of supersonic flow around a cylindrical body

The supersonic flow around a cylindrical body has been studied using two optical techniques. For both sets of measurements, the cylinder was mounted from the side of the tunnel, allowing investigation of the bow shock region as well as in the wake. A new technique, laser-enhanced ionization flow tagging, was used for streamwise velocity determinations behind the body. From these measurements, it was found that the downstream velocity outside the wake was (1.90 +/- 0.06) km/s, whereas inside the wake the velocity was about 0-500 m/s in the upstream direction. Planar laser induced fluorescence of nitric oxide was employed for temperature determinations. It was established that the freestream temperature was (2120 +/- 100) K, decreasing to around (1550 +/- 400) K in the wake.

Sharp vibronic spectra of Cu(II) doped Cs2ZrCl6

The low temperature electronic spectrum of Cu(II) doped Cs2ZrCl6 is reported. It is found that Cu(II) is incorporated as the square planar copper tetrachloride ion, CuCl42-, which substitutes at the Zr(IV) site in the Cs2ZrCl6 lattice. There is a complete absence of axial coordination. The optical spectrum shows vibronic structure with peak widths as small as 8 cm(-1), far narrower than previously seen for this ion. The energy of the observed transitions and the Franck-Condon intensity pattern suggest that there is a substantial relaxation of the host lattice about the impurity ion. The relative intensity of the magnetic dipole component of the bands appears to be considerably greater than for pure copper(II) compounds containing the CuCl42- ion. (C) 1998 Elsevier Science B.V. All rights reserved.

Thermochromism and structure of piperazinium tetrachlorocuprate(II) complexes

The tetrachlorocuprate(II) ion can crystallize in two different structures with the piperazinium dication (pipzH(2)). Both structures contain discrete CuCl42- species. A yellow compound (pipzH(2))[CuCl4]. 2H(2)O (1) is monoclinic (C2/c, Z = 4, a = 10.538(3) Angstrom, b = 7.4312(5) Angstrom, c = 17.281(4) Angstrom, beta = 111.900(10)degrees) and contains the CuCl42- ion as a distorted tetrahedron. A green compound (pipzH(2))(2)[CuCl4]. Cl-2. 3H(2)O (2) is triclinic (P (1) over bar, Z = 2, a = 9.264(3) Angstrom, b = 10.447(2) Angstrom, c = 11.366(2) Angstrom, alpha = 68.38 degrees, beta = 82.86(2)degrees, gamma = 83.05(2)degrees) and contains the CuCl42- ion with a square planar geometry. This latter compound shows thermo/photochromism, changing from green to yellow upon heating or laser irradiation.

A comparative study of the fluidized-bed coating of cylindrical metal surfaces with various thermoplastic polymer powders

This paper reports the results of an experimental investigation into the fluidized-bed coating of cylindrical metal specimens using two types of thermoplastic powders, Rilsan(R) PA11, a nylon-11 powder produced by Elf Atochem, France and Cotene(TM) 4612, a linear low density polyethylene powder produced by J.R Courtenay (New Zealand). The effects of dipping time, preheat temperature and particle size distribution on coating thickness and surface finish were investigated. Consistent trends in coating thickness growth with dipping time were obtained for both nylon-11 and polyethylene powders with increases in coating thickness with preheat temperature. For the same preheat temperature, the lower melting point of polyethylene results in thicker coatings compared to those of nylon-11. There is a negligible change in the coating thickness for sieved powders compared to that for unsieved powders. A pre-heat temperatures of between 240 degrees C and 300 degrees C is necessary to achieve an acceptable surface finish with both nylon-11 and polyethylene powders. To minimize errors in achieving the desired coating thickness, dipping times shorter than 2 s are not recommended. The use of graphs of coating thickness versus dipping time in combination with the coating surface roughness plots presented in this paper enable the optimal choice of pre-heat temperature and dipping time to achieve acceptable surface finish. (C) 1999 Elsevier Science S.A. All rights reserved.

Maximal sets of Hamilton cycles in Kn,n

In this article, we prove that there exists a maximal set of m Hamilton cycles in K-n,K-n if and only if n/4 < m less than or equal to n/2. (C) 2000 John Wiley & Sons, Inc.

Conformations of cyclic octapeptides and the influence of heterocyclic ring constraints upon calcium binding

A comparison is made between the structures and calcium binding properties of four cyclic octapeptides that differ in the number of heterocyclic thiazole and oxazoline ring constraints. The conformations of the naturally occurring cyclic octapeptides ascidiacyclamide 1 and patellamide D 2, which each contain two oxazoline and two thiazole rings, are compared by H-1 NMR spectroscopy with the analogues cyclo(Thr-D-Val(Thz)-Ile)(2) 3 with just two thiazoles, and cyclo(Thr-D-Val-alpha Abu-Ile)(2) 4, with no 5-membered rings. The conformations observed in the solid state for ascidiacyclamide (saddle) and patellamide D (twisted figure of eight) were retained in solution, whilst peptide 3 was found to have a chair shape and peptide 4 displayed a range of conformations. The solid state structure of 4 revealed that the peptide takes a relatively planar conformation with a number of transannular hydrogen bonds, which are apparently retained in solution. Complexation studies utilising H-1 NMR and CD spectroscopy yielded 1∶1 calcium-peptide binding constants (log K) for the four peptides (2.9 (1), 2.8 (2), 4.0 (3) and 5.5 (4)) as well as a 1 : 2 metal-peptide binding constant for 3 (log K = 4.5). The affinity for Ca2+ thus decreases with increasing number of 5-membered ring constraints in the macrocycle (4 > 3 > 2 approximate to 1).

Characterization of the sequential non-covalent and covalent interactions of the antitumour antibiotic hedamycin with double stranded DNA by NMR spectroscopy

Hedamycin, a member of the pluramycin class of antitumour antibiotics, consists of a planar anthrapyrantrione chromophore to which is attached two aminosugar rings at one end and a bisepoxide-containing sidechain at the other end, Binding to double-stranded DNA is known to involve both reversible and non-reversible modes of interaction. As a part of studies directed towards elucidating the structural basis for the observed 5'-pyGT-3' sequence selectivity of hedamycin, we conducted one-dimensional NMR titration experiments at low temperature using the hexadeoxyribonucleotide duplexes d(CACGTG)(2) and d(CGTACG)(2). Spectral changes which occurred during these titrations are consistent with hedamycin initially forming a reversible complex in slow exchange on the NMR timescale and binding through intercalation of the chromophore. Monitoring of this reversible complex over a period of hours revealed a second type of spectral change which corresponds with formation of a non-reversible complex. Copyright (C) 1999 John Wiley & Sons, Ltd.