Constraints on the infrared behavior of the ghost propagator in Yang-Mills theories

We present rigorous upper and lower bounds for the momentum-space ghost propagator G(p) of Yang-Mills theories in terms of the smallest nonzero eigenvalue (and of the corresponding eigenvector) of the Faddeev-Popov matrix. We apply our analysis to data from simulations of SU(2) lattice gauge theory in Landau gauge, using the largest lattice sizes to date. Our results suggest that, in three and in four space-time dimensions, the Landau gauge ghost propagator is not enhanced as compared to its tree-level behavior. This is also seen in plots and fits of the ghost dressing function. In the two-dimensional case, on the other hand, we find that G(p) diverges as p(-2-2 kappa) with kappa approximate to 0.15, in agreement with A. Maas, Phys. Rev. D 75, 116004 (2007). We note that our discussion is general, although we make an application only to pure gauge theory in Landau gauge. Our simulations have been performed on the IBM supercomputer at the University of Sao Paulo.

Microstructuration induced differences in the thermo-optical and luminescence properties of Nd:YAG fine grain ceramics and crystals

The temperature and compositional dependences of thermo- optical properties of neodymium doped yttrium aluminum garnet (YAG) crystals and fine grain ceramics have been systematically investigated by means of time- resolved thermal lens spectrometry. We have found that Nd:YAG ceramics show a reduced thermal diffusivity compared to Nd:YAG single crystals in the complete temperature range investigated (80-300 K). The analysis of the time- resolved luminescent properties of Nd(3+) has revealed that the reduction in the phonon mean free path taking place in Nd:YAG ceramics cannot be associated with an increment in the density of lattice defects, indicating that phonon scattering at grain boundaries is the origin of the observed reduction in the thermal diffusivity of Nd: YAG ceramics. Finally, our results showed the ability of the time- resolved thermal lens to determine and optimize the thermo- optical properties of Nd: YAG ceramic based lasers. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2975335]

Constraints on the infrared behavior of the gluon propagator in Yang-Mills theories

We present rigorous upper and lower bounds for the zero-momentum gluon propagator D(0) of Yang-Mills theories in terms of the average value of the gluon field. This allows us to perform a controlled extrapolation of lattice data to infinite volume, showing that the infrared limit of the Landau-gauge gluon propagator in SU(2) gauge theory is finite and nonzero in three and in four space-time dimensions. In the two-dimensional case, we find D(0)=0, in agreement with Maas. We suggest an explanation for these results. We note that our discussion is general, although we apply our analysis only to pure gauge theory in the Landau gauge. Simulations have been performed on the IBM supercomputer at the University of Sao Paulo.

Estimation of the thickness and the optical parameters of several stacked thin films using optimization

The reverse engineering problem addressed in the present research consists of estimating the thicknesses and the optical constants of two thin films deposited on a transparent substrate using only transmittance data through the whole stack. No functional dispersion relation assumptions are made on the complex refractive index. Instead, minimal physical constraints are employed, as in previous works of some of the authors where only one film was considered in the retrieval algorithm. To our knowledge this is the first report on the retrieval of the optical constants and the thickness of multiple film structures using only transmittance data that does not make use of dispersion relations. The same methodology may be used if the available data correspond to normal reflectance. The software used in this work is freely available through the PUMA Project web page (http://www.ime.usp.br/similar to egbirgin/puma/). (C) 2008 Optical Society of America

Thermo-solvatochromism in binary mixtures of water and ionic liquids: on the relative importance of solvophobic interactions

The thermo-solvatochromism of 2,6-dibromo-4-[(E)-2-(1-methylpyridinium-4-yl)ethenyl] phenolate, MePMBr(2), has been studied in mixtures of water, W, with ionic liquids, ILs, in the temperature range of 10 to 60 degrees C, where feasible. The objectives of the study were to test the applicability of a recently introduced solvation model, and to assess the relative importance of solute-solvent solvophobic interactions. The ILs were 1-allyl-3-alkylimidazolium chlorides, where the alkyl groups are methyl, 1-butyl, and 1-hexyl, respectively. The equilibrium constants for the interaction of W and the ILs were calculated from density data; they were found to be linearly dependent on N(C), the number of carbon atoms of the alkyl group; van't Hoff equation (log K versus 1/T) applied satisfactorily. Plots of the empirical solvent polarities, E(T) (MePMBr(2)) in kcal mol(-1), versus the mole fraction of water in the binary mixture, chi(w), showed non-linear, i.e., non-ideal behavior. The dependence of E(T) (MePMBr(2)) on chi(w), has been conveniently quantified in terms of solvation by W, IL, and the ""complex"" solvent IL-W. The non-ideal behavior is due to preferential solvation by the IL and, more efficiently, by IL-W. The deviation from linearity increases as a function of increasing N(C) of the IL, and is stronger than that observed for solvation of MePMBr(2) by aqueous 1-propanol, a solvent whose lipophilicity is 12.8 to 52.1 times larger than those of the ILs investigated. The dependence on N(C) is attributed to solute-solvent solvophobic interactions, whose relative contribution to solvation are presumably greater than that in mixtures of water and 1-propanol.

Evaluation of Several Carbon-Supported Nanostructured Ni-Doped Manganese Oxide Materials for the Electrochemical Reduction of Oxygen

Physical and electrochemical properties of nanostructured Ni-doped manganese oxides (MnO(x)) catalysts supported on different carbon powder substrates were investigated so as to characterize any carbon substrate effect toward the oxygen reduction reaction (ORR) kinetics in alkaline medium. These NiMnO(x)/C materials were characterized using physicochemical analyses. Small insertion of Ni atoms in the MnO(x) lattice was observed, which consists of a true doping of the manganese oxide phase. The corresponding NiMnO(x) phase is present in the form of needles or agglomerates, with crystallite sizes in the order of 1.5-6.7 nm (from x-ray diffraction analyses). Layered manganite (MnOOH) phase has been detected for the Monarch 1000-supported NiMnO(x) material, while different species of MnO(x) phases are present at the E350G and MM225 carbons. Electrochemical studies in thin porous coating active layers in the rotating ring-disk electrode setup revealed that the MnO(x) catalysts present better ORR kinetics and electrochemical stability upon Ni doping. The ORR follows the so-called peroxide mechanism on MnO(x)/C catalysts, with the occurrence of minority HO(2)(-) disproportionation reaction. The HO(2)(-) disproportionation reaction progressively increases with the Ni content in NiMnO(x) materials. The catalysts supported on the MM225 and E350G carbons promote faster disproportionation reaction, thus leading to an overall four-electron ORR pathway. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3528439] All rights reserved.

Sodium piperidine-1-carbodithioate dihydrate

The asymmetric unit of the title compound, Na(+)center dot C(6)H(10)NS(2) center dot 2H(2)O, is composed of a sodium cation, a piperidinedithiocarbamate anion which exhibits positional disorder, and two lattice water molecules. The atoms of the piperidine ring are divided over two sites with occupancy factors of 0.554 (6) and 0.446 (6). In the crystal, the sodium cation (coordination number of 6) and the piperidinedithiocarbamate anion are linked, forming an infinite two-dimensional network extending parallel to (001). O-H center dot center dot center dot S hydrogen bonds, involving the lattice water molecules, also aid in stabilizing the crystal sructure.

Dynamic light scattering and optical absorption spectroscopy study of pH and temperature stabilities of the extracellular hemoglobin of Glossoscolex paulistus

The extracellular hemoglobin of Glossoscolex paulistus (HbGp) is constituted of subunits containing heme groups, monomers and trimers, and nonheme structures, called linkers, and the whole protein has a minimum molecular mass near 3.1 x 10(6) Da. This and other proteins of the same family are useful model systems for developing blood substitutes due to their extracellular nature, large size, and resistance to oxidation. HbGp samples were studied by dynamic light scattering (DLS). In the pH range 6.0-8.0, HbGp is stable and has a monodisperse size distribution with a z-average hydrodynamic diameter (D-h) of 27 +/- 1 nm. A more alkaline pH induced an irreversible dissociation process, resulting in a smaller D-h of 10 +/- 1 nm. The decrease in D-h suggests a complete hemoglobin dissociation. Gel filtration chromatography was used to show unequivocally the oligomeric dissociation observed at alkaline pH. At pH 9.0, the dissociation kinetics is slow, taking a minimum of 24 h to be completed. Dissociation rate constants progressively increase at higher pH, becoming, at pH 10.5, not detectable by DILS. Protein temperature stability was also pH-dependent. Melting curves for HbGp showed oligomeric dissociation and protein denaturation as a function of pH. Dissociation temperatures were lower at higher pH. Kinetic studies were also performed using ultraviolet-visible absorption at the Soret band. Optical absorption monitors the hemoglobin autoxidation while DLS gives information regarding particle size changes in the process of protein dissociation. Absorption was analyzed at different pH values in the range 9.0-9.8 and at two temperatures, 25 degrees C and 38 degrees C. At 25 degrees C, for pH 9.0 and 9.3, the kinetics monitored by ultraviolet-visible absorption presents a monoexponential behavior, whereas for pH 9.6 and 9.8, a biexponential behavior was observed, consistent with heme heterogeneity at more alkaline pH. The kinetics at 38 degrees C is faster than that at 25 degrees C and is biexponential in the whole pH range. DLS dissociation rates are faster than the autoxidation dissociation rates at 25 degrees C. Autoxiclation and dissociation processes are intimately related, so that oligomeric protein dissociation promotes the increase of autoxidation rate and vice versa. The effect of dissociation is to change the kinetic character of the autoxidation of hemes from monoexponential to biexponential, whereas the reverse change is not as effective. This work shows that DLS can be used to follow, quantitatively and in real time, the kinetics of changes in the oligomerization of biologic complex supramolecular systems. Such information is relevant for the development of mimetic systems to be used as blood substitutes.

Mechanistic studies of the 'blue' Cu enzyme, bilirubin oxidase, as a highly efficient electrocatalyst for the oxygen reduction reaction

The 'blue copper' enzyme bilirubin oxidase from Myrothecium verrucaria shows significantly enhanced adsorption on a pyrolytic graphite 'edge' (PGE) electrode that has been covalently modified with naphthyl-2-carboxylate functionalities by diazonium coupling. Modified electrodes coated with bilirubin oxidase show electrocatalytic voltammograms for the direct, four-electron reduction of O(2) by bilirubin oxidase with up to four times the current density of an unmodified PGE electrode. Electrocatalytic voltammograms measured with a rapidly rotating electrode (to remove effects of O(2) diffusion limitation) have a complex shape (an almost linear dependence of current on potential below pH 6) that is similar regardless of how PGE is chemically modified. Importantly, the same waveform is observed if bilirubin oxidase is adsorbed on Au(111) or Pt(111) single-crystal electrodes (at which activity is short-lived). The electrocatalytic behavior of bilirubin oxidase, including its enhanced response on chemically-modified PGE, therefore reflects inherent properties that do not depend on the electrode material. The variation of voltammetric waveshapes and potential-dependent (O(2)) Michaelis constants with pH and analysis in terms of the dispersion model are consistent with a change in rate-determining step over the pH range 5-8: at pH 5, the high activity is limited by the rate of interfacial redox cycling of the Type 1 copper whereas at pH 8 activity is much lower and a sigmoidal shape is approached, showing that interfacial electron transfer is no longer a limiting factor. The electrocatalytic activity of bilirubin oxidase on Pt(111) appears as a prominent pre-wave to electrocatalysis by Pt surface atoms, thus substantiating in a single, direct experiment that the minimum overpotential required for O(2) reduction by the enzyme is substantially smaller than required at Pt. At pH 8, the onset of O(2) reduction lies within 0.14 V of the four-electron O(2)/2H(2)O potential.

ON TWO-DIMENSIONAL QUASITOPOLOGICAL FIELD THEORIES

We study a class of lattice field theories in two dimensions that includes gauge theories. We show that in these theories it is possible to implement a broader notion of local symmetry, based on semisimple Hopf algebras. A character expansion is developed for the quasitopological field theories, and partition functions are calculated with this tool. Expected values of generalized Wilson loops are defined and studied with the character expansion.

Niobium hydrogenation process Effect of temperature and cooling rate from the hydrogenation temperature

High-purity niobium powder can be produced via the hydrogenation and dehydrogenation processes The present work aimed at the effect of temperature and cooling rate conditions on the niobium hydrogenation process using hydrogen gas The hydrogen contents of the materials were evaluated by weight change and chemical analysis X ray diffraction (XRD) was performed to identify and determine the lattice parameters of the formed hydride phases No hydrogenation took place under isothermal conditions only during cooling of the materials Significant hydrogenation occurred in the 500 C and 700 C experiments leading to the formation of a beta NbH(x) single phase material (C) 2010 Elsevier Ltd All rights reserved

Extending the kinetic solution of the classic Michaelis-Menten model of enzyme action

The principal aim of studies of enzyme-mediated reactions has been to provide comparative and quantitative information on enzyme-catalyzed reactions under distinct conditions. The classic Michaelis-Menten model (Biochem Zeit 49:333, 1913) for enzyme kinetic has been widely used to determine important parameters involved in enzyme catalysis, particularly the Michaelis-Menten constant (K (M) ) and the maximum velocity of reaction (V (max) ). Subsequently, a detailed treatment of the mechanisms of enzyme catalysis was undertaken by Briggs-Haldane (Biochem J 19:338, 1925). These authors proposed the steady-state treatment, since its applicability was constrained to this condition. The present work describes an extending solution of the Michaelis-Menten model without the need for such a steady-state restriction. We provide the first analysis of all of the individual reaction constants calculated analytically. Using this approach, it is possible to accurately predict the results under new experimental conditions and to characterize and optimize industrial processes in the fields of chemical and food engineering, pharmaceuticals and biotechnology.

Solution Polymerization of N-vinylcaprolactam in 1,4-dioxane. Kinetic Dependence on Temperature, Monomer, and Initiator Concentrations

The kinetics of the solution free radical polymerization of N-vinylcaprolactam, in 1,4-dioxane and under various polymerization conditions was studied. Azobisisobutyronitrile and 3-mercaptopropionic acid were used as initiator and as chain transfer agent (CTA), respectively. The influence of monomer and initiator concentrations and polymerization temperature on the rate of polymerizations (R(p)) was investigated. In general, high conversions were obtained. The order with respect to initiator was consistent with the classical kinetic rate equation, while the order with respect to the monomer was greater than unity. The overall activation energy of 53.6 kJ mol(-1) was obtained in the temperature range 60-80 degrees C. The decreasing of the absolute molecular weights when increasing the CIA concentration was confirmed by GPC/SEC/LALS analyses. It was confirmed by UV-visible analyses the effect of molecular weights on the lower critical solution temperature of the polymers. It was also verified that the addition of the CTA influenced the kinetic of the polymerizations. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 229-240, 2010

EBSD characterization of an ECAP deformed Nb single crystal

A niobium single crystal was subjected to equal channel angular pressing (ECAP) at room temperature after orienting the crystal such that [1 -1 -1] ayen ND, [0 1 -1] ayen ED, and [-2 -1 -1] ayen TD. Electron backscatter diffraction (EBSD) was used to characterize the microstructures both on the transverse and the longitudinal sections of the deformed sample. After one pass of ECAP the single crystal exhibits a group of homogeneously distributed large misorientation sheets and a well formed cell structure in the matrix. The traces of the large misorientation sheets match very well with the most favorably oriented slip plane and one of the slip directions is macroscopically aligned with the simple shear plane. The lattice rotation during deformation was quantitatively estimated through comparison of the orientations parallel to three macroscopic axes before and after deformation. An effort has been made to link the microstructure with the initial crystal orientation. Collinear slip systems are believed to be activated during deformation. The full constraints Taylor model was used to simulate the orientation evolution during ECAP. The result matched only partially with the experimental observation.

Evaluation of the catalytic properties of Burkholderia cepacia lipase immobilized on non-commercial matrices to be used in biodiesel synthesis from different feedstocks

The objective of this work was to produce an immobilized form of lipase from Burkholderia cepacia (lipase PS) with advantageous catalytic properties and stability to be used in the ethanolysis of different feedstocks, mainly babassu oil and tallow beef. For this purpose lipase PS was immobilized on two different non-commercial matrices, such as inorganic matrix (niobium oxide, Nb(2)O(5)) and a hybrid matrix (polysiloxane-polyvinyl alcohol, SiO(2)-PVA) by covalent binding. The properties of free and immobilized enzymes were searched and compared. The best performance regarding all the analyzed parameters (biochemical properties, kinetic constants and thermal stability) were obtained when the lipase was immobilized on SiO(2)-PVA. The superiority of this immobilized system was also confirmed in the transe-sterification of both feedstocks, attained higher yields and productivities. (C) 2010 Elsevier Ltd. All rights reserved.