Possibilidades e limitações no uso da temperatura em cromatografia líquida de fase reversa

High-temperature liquid chromatography (HTLC) is a technique that presents a series of advantages in liquid phase separations, such as: reduced analysis time, reduced pressure drop, reduced asymmetry factors, modified retentions, controlled selectivities, better efficiencies and improved detectivities, as well as permitting green chromatography. The practical limitations that relate to instrumentation and to stationary phase instability are being resolved and this technique is now ready to be applied for routine determinations.

Determinação de substitutos da manteiga de cacau em coberturas de chocolate através da análise de triacilgliceróis

Brazilian regulations prohibit the addition of cocoa butter replacements to chocolate, in total or partial substitution. The objective of the present work was to check the quality standards of four of coating bitter Brasilian chocolate bars and five of coating milk chocolate bars, commercialized in Campinas. In order to check the possible addition of substitutes, the triacylglycerol composition was determined, and the results were analysed by Padley & Timms mathematical method. The triacylglycerol composition of each sample was determined by high temperature gas chromatography (HTGC). The presence of cocoa butter replacements was not detected in the brands of coating chocolate.

Atividade de plasmina e plasminogênio no leite longa vida com alta e baixa contagem de células somáticas durante o armazenamento

O objetivo deste estudo foi avaliar o efeito da contagem de células somáticas (CCS) do leite na atividade de plasmina e plasminogênio durante o período de armazenamento do leite longa vida integral. Os leites crus foram categorizados em grupos de CCS de baixa (342.000-487.000 células mL-1) e alta contagem (603.000-808.000 células mL-1). Dois lotes de leite longa vida em cada categoria de CCS foram analisados para determinação de plasmina e plasminogênio após 10, 30, 60, 90 e 120 dias de armazenamento em temperatura ambiente. Para a fabricação do leite longa vida, o leite cru foi submetido à pasteurização rápida seguida da esterilização industrial do leite por injeção de vapor pelo método direto e embalagem asséptica do produto. A CCS não apresentou efeitos sobre as características físico-químicas do leite cru, e nem sobre a atividade de plasmina e plasminogênio nos leites cru e longa vida, armazenados por 120 dias. Entretanto, independentemente da CCS, a atividade de plasmina e plasminogênio aumentou no leite longa vida ao longo do armazenamento, indicando a possibilidade de aumento da proteólise no produto durante sua vida de prateleira.

Hidrólise do óleo de Azadirachta indica em água subcrítica e determinação da composição dos triacilglicerídeos e ácidos graxos por cromatografia gasosa de alta resolução a alta temperatura e cromatografia gasosa de alta resolução acoplada à espectrometria de massas

The development of modern analytical tools plays an important role in quality control. The main purpose of this study was to explore the use of subcritical water as a versatile analytical tool, employed simultaneously as a reagent and solvent, as well as the application of high temperature-high resolution gas chromatography (HT-HRGC) to develop a procedure for the analysis of triacylglycerides and fatty acids in Azadirachta indica A. Juss. (Neem) oil without the need for solvents, chemical reagents, or catalytic agents. The developed method presented satisfactory results and is in agreement with the concepts of Green Analytical Chemistry (GAC).

Evaluation of Ti(3)Si Phase Stability from Heat-Treated, Rapidly Solidified Ti-Si Alloys

Ti-base alloys containing significant amounts of silicon have been considered for high temperature structural applications. Thus, information concerning phase stability on the Ti-Si system is fundamental and there are not many investigations covering the phase stability of the Ti(3)Si phase, specially its dependence on oxygen/nitrogen contamination. In this work the stability of this phase has been evaluated through heat-treatment of rapidly solidified Ti-rich Ti-Si alloys at 700 A degrees C and 1000 A degrees C. The rapidly solidified splats presented nanometric scale microstructures which facilitated the attainment of equilibrium conditions. The destabilization of Ti(3)Si due to oxygen/nitrogen contamination has been noted.

Isothermal Section of the V-Si-B System at 1600 A degrees C in the V-VSi(2)-VB Region

In recent years, the Me-Si-B (Me-metal) ternary systems have received considerable attention aiming at the development of high-temperature structural materials. Assuming that any real application of these materials will rely on multicomponent alloys, as is the case of Ni-base superalloys, phase equilibria data of these systems become very important. In this work, results are reported on phase equilibria in the V-Si-B system, and are summarized in the form of an isothermal section at 1600 A degrees C for the V-VSi(2)-VB region. Several alloys of different compositions were prepared via arc melting and then heat-treated at 1600 A degrees C under high vacuum. All the materials in both as-cast and heat-treated conditions were characterized through x-ray diffraction, scanning electron microscopy, and selected alloys via wavelength dispersive spectroscopy. A negligible solubility of B in the V(3)Si, V(5)Si(3) (T(1)), and V(6)Si(5) phases as well as of Si in V(3)B(2) and VB phases was noted. Two ternary phases presenting the structures known as T(2) (Cr(5)B(3)-prototype) and D8(8) (Mn(5)Si(3)-prototype) were observed in both as-cast and heat-treated samples. It is proposed that at 1600 A degrees C the homogeneity range of T(2) extends approximately from 5 at.% to 12 at.% Si at constant vanadium content and the composition of D8(8) phase is close to V(59.5)Si(33)B(7.5) (at.%).

Internal stresses and textures of nanostructured alumina scales growing on polycrystalline Fe(3)Al alloy

The evolution of internal stresses in oxide scales growing on polycrystalline Fe(3)Al alloy in atmospheric air at 700 degrees C was determined using in situ energy-dispersive synchrotron X-ray diffraction. Ex situ texture analyses were performed after 5 h of oxidation at 700 degrees C. Under these conditions, the oxide-scale thickness, as determined by X-ray photoelectron spectroscopy, lies between 80 and 100 nm. The main phase present in the oxide scales is alpha-Al(2)O(3), with minor quantities of metastable theta-Al(2)O(3) detected in the first minutes of oxidation, as well as alpha-Fe(2)O(3). alpha-Al(2)O(3) grows with a weak (0001) fiber texture in the normal direction. During the initial stages of oxidation the scale develops, increasing levels of compressive stresses which later evolve to a steady state condition situated around -300 MPa. (C) 2010 International Centre for Diffraction Data. [DOI: 10.1154/1.3402764]

Evaluation technique for determining wheel performance in the grinding of aerospace materials

Nickel-based super alloys are used in a variety of applications in which high-temperature strength and resistance to creep, corrosion, and oxidation are required, such as in aircraft gas turbines, combustion chambers, and automotive engine valves. The properties that make these materials suitable for these applications also make them difficult to grind. Grinding systems for such materials are often built around vitrified cBN (cubic boron nitride) wheels to realize maximum productivity and minimum cost per part. Conditions that yield the most economical combination of stock removal rate and wheel wear are key to the successful implementation of the grinding system. Identifying the transition point for excessive wheel wear is important. The aim of this study is to compare the performance of different cBN wheels when grinding difficult-to-grind (DTG) materials by determining the 'wheel wear characteristic curve', which correlates the G-ratio to the calculated tangential force per abrasive grain. With the proposed methodology, a threshold force per grit above which the wheel wear rate increases rapidly can be quickly identified. A comparison of performance for two abrasive product formulations in the grinding of three materials is presented. The obtained results can be applied for the development of grinding applications for DTG materials.

NEAR INFRARED SPECTROSCOPY FOR ESTIMATING SUGARCANE BAGASSE CONTENT IN MEDIUM DENSITY FIBERBOARD

Medium density fiberboard (MDF) is an engineered wood product formed by breaking down selected lignin-cellulosic material residuals into fibers, combining it with wax and a resin binder, and then forming panels by applying high temperature and pressure. Because the raw material in the industrial process is ever-changing, the panel industry requires methods for monitoring the composition of their products. The aim of this study was to estimate the ratio of sugarcane (SC) bagasse to Eucalyptus wood in MDF panels using near infrared (NIR) spectroscopy. Principal component analysis (PCA) and partial least square (PLS) regressions were performed. MDF panels having different bagasse contents were easily distinguished from each other by the PCA of their NIR spectra with clearly different patterns of response. The PLS-R models for SC content of these MDF samples presented a strong coefficient of determination (0.96) between the NIR-predicted and Lab-determined values and a low standard error of prediction (similar to 1.5%) in the cross-validations. A key role of resins (adhesives), cellulose, and lignin for such PLS-R calibrations was shown. PLS-DA model correctly classified ninety-four percent of MDF samples by cross-validations and ninety-eight percent of the panels by independent test set. These NIR-based models can be useful to quickly estimate sugarcane bagasse vs. Eucalyptus wood content ratio in unknown MDF samples and to verify the quality of these engineered wood products in an online process.

H(2) infrared line emission from the ionized region of planetary nebulae

Context. The analysis and interpretation of the H(2) line emission from planetary nebulae have been done in the literature by assuming that the molecule survives only in regions where the hydrogen is neutral, as in photodissociation, neutral clumps, or shocked regions. However, there is strong observational and theoretical evidence that at least part of the H(2) emission is produced inside the ionized region of these objects. Aims. The aim of the present work is to calculate and analyze the infrared line emission of H(2) produced inside the ionized region of planetary nebulae using a one-dimensional photoionization code. Methods. The photoionization code Aangaba was improved in order to calculate the statistical population of the H(2) energy levels, as well as the intensity of the H(2) infrared emission lines in the physical conditions typical of planetary nebulae. A grid of models was obtained and the results then analyzed and compared with the observational data. Results. We show that the contribution of the ionized region to the H(2) line emission can be important, particularly in the case of nebulae with high-temperature central stars. This result explains why H(2) emission is more frequently observed in bipolar planetary nebulae (Gatley's rule), since this kind of object typically has hotter stars. Collisional excitation plays an important role in populating the rovibrational levels of the electronic ground state of H(2) molecules. Radiative mechanisms are also important, particularly for the upper vibrational levels. Formation pumping can have minor effects on the line intensities produced by de-excitation from very high rotational levels, especially in dense and dusty environments. We included the effect of the H(2) molecule on the thermal equilibrium of the gas, concluding that, in the ionized region, H(2) only contributes to the thermal equilibrium in the case of a very high temperature of the central star or a high dust-to-gas ratio, mainly through collisional de-excitation.

Cluster and cluster galaxy evolution history from IR to X-ray observations of the young cluster RX J1257.2+4738 at z=0.866

Context. The cosmic time around the z similar to 1 redshift range appears crucial in the cluster and galaxy evolution, since it is probably the epoch of the first mature galaxy clusters. Our knowledge of the properties of the galaxy populations in these clusters is limited because only a handful of z similar to 1 clusters are presently known. Aims. In this framework, we report the discovery of a z similar to 0.87 cluster and study its properties at various wavelengths. Methods. We gathered X-ray and optical data (imaging and spectroscopy), and near and far infrared data (imaging) in order to confirm the cluster nature of our candidate, to determine its dynamical state, and to give insight on its galaxy population evolution. Results. Our candidate structure appears to be a massive z similar to 0.87 dynamically young cluster with an atypically high X-ray temperature as compared to its X-ray luminosity. It exhibits a significant percentage (similar to 90%) of galaxies that are also detected in the 24 mu m band. Conclusions. The cluster RXJ1257.2+4738 appears to be still in the process of collapsing. Its relatively high temperature is probably the consequence of significant energy input into the intracluster medium besides the regular gravitational infall contribution. A significant part of its galaxies are red objects that are probably dusty with on-going star formation.

Actions of a Proline Analogue, L-Thiazolidine-4-Carboxylic Acid (T4C), on Trypanosoma cruzi

It is well established that L-proline has several roles in the biology of trypanosomatids. In Trypanosoma cruzi, the etiological agent of Chagas' disease, this amino acid is involved in energy metabolism, differentiation processes and resistance to osmotic stress. In this study, we analyzed the effects of interfering with L-proline metabolism on the viability and on other aspects of the T. cruzi life cycle using the proline analogue L- thiazolidine-4-carboxylic acid (T4C). The growth of epimastigotes was evaluated using different concentrations of T4C in standard culture conditions and at high temperature or acidic pH. We also evaluated possible interactions of this analogue with stress conditions such as those produced by nutrient starvation and oxidative stress. T4C showed a dose-response effect on epimastigote growth (IC(50) = 0.89+/-0.02 mM at 28 degrees C), and the inhibitory effect of this analogue was synergistic (p<0.05) with temperature (0.54+/-0.01 mM at 37 degrees C). T4C significantly diminished parasite survival (p<0.05) in combination with nutrient starvation and oxidative stress conditions. Pre-incubation of the parasites with L-proline resulted in a protective effect against oxidative stress, but this was not seen in the presence of the drug. Finally, the trypomastigote bursting from infected mammalian cells was evaluated and found to be inhibited by up to 56% when cells were treated with non-toxic concentrations of T4C (between 1 and 10 mM). All these data together suggest that T4C could be an interesting therapeutic drug if combined with others that affect, for example, oxidative stress. The data also support the participation of proline metabolism in the resistance to oxidative stress.

Local atomic structure in tetragonal pure ZrO(2) nanopowders

The local atomic structures around the Zr atom of pure (undoped) ZrO(2) nanopowders with different average crystallite sizes, ranging from 7 to 40 nm, have been investigated. The nanopowders were synthesized by different wet-chemical routes, but all exhibit the high-temperature tetragonal phase stabilized at room temperature, as established by synchrotron radiation X-ray diffraction. The extended X-ray absorption fine structure (EXAFS) technique was applied to analyze the local structure around the Zr atoms. Several authors have studied this system using the EXAFS technique without obtaining a good agreement between crystallographic and EXAFS data. In this work, it is shown that the local structure of ZrO(2) nanopowders can be described by a model consisting of two oxygen subshells (4 + 4 atoms) with different Zr-O distances, in agreement with those independently determined by X-ray diffraction. However, the EXAFS study shows that the second oxygen subshell exhibits a Debye-Waller (DW) parameter much higher than that of the first oxygen subshell, a result that cannot be explained by the crystallographic model accepted for the tetragonal phase of zirconia-based materials. However, as proposed by other authors, the difference in the DW parameters between the two oxygen subshells around the Zr atoms can be explained by the existence of oxygen displacements perpendicular to the z direction; these mainly affect the second oxygen subshell because of the directional character of the EXAFS DW parameter, in contradiction to the crystallographic value. It is also established that this model is similar to another model having three oxygen subshells, with a 4 + 2 + 2 distribution of atoms, with only one DW parameter for all oxygen subshells. Both models are in good agreement with the crystal structure determined by X-ray diffraction experiments.

Synchrotron X-ray powder diffraction study of the tetragonal-cubic phase transition in nanostructured ZrO2-Sc2O3 solid solutions

The transition between tetragonal and cubic phases in nanostructured ZrO2-Sc2O3 solid solutions by high-temperature X-ray powder diffraction using synchrotron radiation is presented. ZrO2-8 and 11 mol% Sc2O3 nanopowders that exhibit the t'- and t ''-forms of the tetragonal phase, respectively, were synthesized by a stoichiometric nitrate-lysine gel-combustion route. The average crystallite size treated at 900 degrees C was about 25 nm for both compositions. Our results showed that t'-t '' and t ''-cubic transitions take place for the 8 and 11 mol% Sc2O3 samples, respectively. (C) 2008 International Centre for Diffraction Data.

Thermal instability in a gravity-like scalar theory

We study the question of stability of the ground state of a scalar theory which is a generalization of the phi(3) theory and has some similarity to gravity with a cosmological constant. We show that the ground state of the theory at zero temperature becomes unstable above a certain critical temperature, which is evaluated in closed form at high temperature.