Thermal behavior and decomposition kinetics of rifampicin polymorphs under isothermal and non-isothermal conditions

The thermal behavior of two polymorphic forms of rifampicin was studied by DSC and TG/DTG. The thermoanalytical results clearly showed the differences between the two crystalline forms. Polymorph I was the most thermally stable form, the DSC curve showed no fusion for this species and the thermal decomposition process occurred around 245 ºC. The DSC curve of polymorph II showed two consecutive events, an endothermic event (Tpeak = 193.9 ºC) and one exothermic event (Tpeak = 209.4 ºC), due to a melting process followed by recrystallization, which was attributed to the conversion of form II to form I. Isothermal and non-isothermal thermogravimetric methods were used to determine the kinetic parameters of the thermal decomposition process. For non-isothermal experiments, the activation energy (Ea) was derived from the plot of Log β vs 1/T, yielding values for polymorph form I and II of 154 and 123 kJ mol-1, respectively. In the isothermal experiments, the Ea was obtained from the plot of lnt vs 1/T at a constant conversion level. The mean values found for form I and form II were 137 and 144 kJ mol-1, respectively.

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.%).

Effect of HMEC on the consolidation of cement pastes: Isothermal calorimetry versus oscillatory rheometry

Chemical admixtures increase the theological complexity of cement pastes owing to their chemical and physical interactions with particles, which affects cement hydration and agglomeration kinetics. Using oscillatory rheometry and isothermal calorimetry, this article shows that the cellulose ether HMEC (hydroxymethyl ethylcellulose), widely used as a viscosity modifying agent in self-compacting concretes and dry-set mortars, displayed a steric dispersant barrier effect during the first 2 h of hydration associated to a cement retarding nature, consequently reducing the setting speed. However, despite this stabilization effect, the polymer increased the cohesion strength when comparing cement particles with the same hydration degree. (C) 2009 Elsevier Ltd. All rights reserved.

A method for simultaneous detection and identification of Brazilian dog- and vampire bat-related rabies virus by reverse transcription loop-mediated isothermal amplification assay

At present, the sporadic occurrence of human rabies in Brazil can be attributed primarily to dog- and vampire bat-related rabies viruses. Reverse transcription loop-mediated isothermal amplification (RT-LAMP) was employed as a simultaneous detection method for both rabies field variants within 60 min. Vampire bat-related rabies viruses could be distinguished from dog variants by digesting amplicons of the RT-LAMP reaction using the restriction enzyme Alwl. Amplification and digestion could both be completed within 120 min after RNA extraction. In addition, the RI-LAMP assay also detected rabies virus in isolates from Brazilian frugivorous bats and Ugandan dog, bovine and goat samples. In contrast, there were false negative results from several Brazilian insectivorous bats and all of Chinese dog, pig, and bovine samples using the RI-LAMP assay. This study showed that the RT-LAMP assay is effective for the rapid detection of rabies virus isolates from the primary reservoir in Brazil. Further improvements are necessary so that the RT-LAMP assay can be employed for the universal detection of genetic variants of rabies virus in the field. (C) 2010 Elsevier B.V. All rights reserved.

Rotation effect on geodesic and zonal flow modes in tokamak plasmas with isothermal magnetic surfaces

The electrostatic geodesic mode oscillations are investigated in rotating large aspect ratio tokamak plasmas with circular isothermal magnetic surfaces. The analysis is carried out within the magnetohydrodynamic model including heat flux to compensate for the non-adiabatic pressure distribution along the magnetic surfaces in plasmas with poloidal rotation. Instead of two standard geodesic modes, three geodesic continua are found. The two higher branches of the geodesic modes have a small frequency up-shift from ordinary geodesic acoustic and sonic modes due to rotation. The lower geodesic continuum is a newzonal flowmode (geodesic Doppler mode) in plasmas with mainly poloidal rotation. Limits to standard geodesic modes are found. Bifurcation of Alfven continuum by geodesic modes at the rational surfaces is also discussed. Due to that, the frequency of combined geodesic continuum extends from the poloidal rotation frequency to the ion-sound band that can have an important role in suppressing plasma turbulence.

THERMAL BEHAVIOR STUDY AND DECOMPOSITION KINETICS OF SALBUTAMOL UNDER ISOTHERMAL AND NON-ISOTHERMAL CONDITIONS

The thermal decomposition of salbutamol (beta(2) - selective adrenoreceptor) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry (TG/DTG). It was observed that the commercial sample showed a different thermal profile than the standard sample caused by the presence of excipients. These compounds increase the thermal stability of the drug. Moreover, higher activation energy was calculated for the pharmaceutical sample, which was estimated by isothermal and non-isothermal methods for the first stage of the thermal decomposition process. For isothermal experiments the average values were E(act) = 130 kJ mol(-1) (for standard sample) and E(act) = 252 kJ mol(-1) (for pharmaceutical sample) in a dynamic nitrogen atmosphere (50 mL min(-1)). For non-isothermal method, activation energy was obtained from the plot of log heating rates vs. 1/T in dynamic air atmosphere (50 mL min(-1)). The calculated values were E(act) = 134 kJ mol(-1) (for standard sample) and E(act) (=) 139 kJ mol(-1) (for pharmaceutical sample).

A new bianthron glycoside as inhibitor of Trypanosoma cruzi glyceraldehyde 3-phosphate dehydrogenase activity

A phytochemical investigation of the ethanolic extract of stalks of Senna martiana Benth. (Leguminoseae), native specie of northeast Brazil, resulted in the isolation and spectroscopic characterization of a new bianthrone glycoside, martianine 1 (10,10'-il-chrysophanol-10-oxi10,10'-bi-glucosyl). Its identification was established by HRMS, IR and 2D NMR experiments. The evaluation of martianine trypanocidal activity was carried out against gliceraldehyde 3-phosphate dehydrogenase enzyme from Trypanosoma cruzi. Its inhibitory constant (Ki) is in the low micromolar concentration and it was determined by isothermal titration calorimetry to be 27.3 ± 2.47 µmol L-1. The non-competitive mechanism is asserted to be putative of the mode of action martianine displays against T. cruzi GAPDH. Results show that martianine has a great potential to become new lead molecule by inhibiting this key enzyme and for the development of new drugs against Chagas disease.

Turbulence in collisionless plasmas: statistical analysis from numerical simulations with pressure anisotropy

In recent years, we have experienced increasing interest in the understanding of the physical properties of collisionless plasmas, mostly because of the large number of astrophysical environments (e. g. the intracluster medium (ICM)) containing magnetic fields that are strong enough to be coupled with the ionized gas and characterized by densities sufficiently low to prevent the pressure isotropization with respect to the magnetic line direction. Under these conditions, a new class of kinetic instabilities arises, such as firehose and mirror instabilities, which have been studied extensively in the literature. Their role in the turbulence evolution and cascade process in the presence of pressure anisotropy, however, is still unclear. In this work, we present the first statistical analysis of turbulence in collisionless plasmas using three-dimensional numerical simulations and solving double-isothermal magnetohydrodynamic equations with the Chew-Goldberger-Low laws closure (CGL-MHD). We study models with different initial conditions to account for the firehose and mirror instabilities and to obtain different turbulent regimes. We found that the CGL-MHD subsonic and supersonic turbulences show small differences compared to the MHD models in most cases. However, in the regimes of strong kinetic instabilities, the statistics, i.e. the probability distribution functions (PDFs) of density and velocity, are very different. In subsonic models, the instabilities cause an increase in the dispersion of density, while the dispersion of velocity is increased by a large factor in some cases. Moreover, the spectra of density and velocity show increased power at small scales explained by the high growth rate of the instabilities. Finally, we calculated the structure functions of velocity and density fluctuations in the local reference frame defined by the direction of magnetic lines. The results indicate that in some cases the instabilities significantly increase the anisotropy of fluctuations. These results, even though preliminary and restricted to very specific conditions, show that the physical properties of turbulence in collisionless plasmas, as those found in the ICM, may be very different from what has been largely believed.

Cosmic distance duality relation and the shape of galaxy clusters

Context. Observations in the cosmological domain are heavily dependent on the validity of the cosmic distance-duality (DD) relation, eta = D(L)(z)(1+ z)(2)/D(A)(z) = 1, an exact result required by the Etherington reciprocity theorem where D(L)(z) and D(A)(z) are, respectively, the luminosity and angular diameter distances. In the limit of very small redshifts D(A)(z) = D(L)(z) and this ratio is trivially satisfied. Measurements of Sunyaev-Zeldovich effect (SZE) and X-rays combined with the DD relation have been used to determine D(A)(z) from galaxy clusters. This combination offers the possibility of testing the validity of the DD relation, as well as determining which physical processes occur in galaxy clusters via their shapes. Aims. We use WMAP (7 years) results by fixing the conventional Lambda CDM model to verify the consistence between the validity of DD relation and different assumptions about galaxy cluster geometries usually adopted in the literature. Methods. We assume that. is a function of the redshift parametrized by two different relations: eta(z) = 1+eta(0)z, and eta(z) = 1+eta(0)z/(1+z), where eta(0) is a constant parameter quantifying the possible departure from the strict validity of the DD relation. In order to determine the probability density function (PDF) of eta(0), we consider the angular diameter distances from galaxy clusters recently studied by two different groups by assuming elliptical (isothermal) and spherical (non-isothermal) beta models. The strict validity of the DD relation will occur only if the maximum value of eta(0) PDF is centered on eta(0) = 0. Results. It was found that the elliptical beta model is in good agreement with the data, showing no violation of the DD relation (PDF peaked close to eta(0) = 0 at 1 sigma), while the spherical (non-isothermal) one is only marginally compatible at 3 sigma. Conclusions. The present results derived by combining the SZE and X-ray surface brightness data from galaxy clusters with the latest WMAP results (7-years) favors the elliptical geometry for galaxy clusters. It is remarkable that a local property like the geometry of galaxy clusters might be constrained by a global argument provided by the cosmic DD relation.

MASS DISTRIBUTION IN HICKSON COMPACT GROUPS OF GALAXIES

This study presents the mass distribution for a sample of 18 late-type galaxies in nine Hickson compact groups. We used Ha rotation curves (RCs) from high-resolution two-dimensional velocity fields of Fabry-Perot observations and the J-band photometry from the Two Micron All Sky Survey, in order to determine the dark halo and the visible matter distributions. The study compares two halo density profiles, an isothermal core-like distribution, and a cuspy one. We also compare their visible and dark matter distributions with those of galaxies belonging to cluster and field galaxies coming from two samples: 40 cluster galaxies of Barnes et al. and 35 field galaxies of Spano et al. The central halo surface density is found to be constant with respect to the total absolute magnitude similar to what is found for the isolated galaxies. This suggests that the halo density is independent of galaxy type and environment. We have found that core-like density profiles better fit the RCs than cuspy-like ones. No major differences have been found between field, cluster, and compact group galaxies with respect to their dark halo density profiles.

Hydro-kinetic approach to relativistic heavy ion collisions

We develop a combined hydro-kinetic approach which incorporates a hydrodynamical expansion of the systems formed in A + A collisions and their dynamical decoupling described by escape probabilities. The method corresponds to a generalized relaxation time (tau(rel)) approximation for the Boltzmann equation applied to inhomogeneous expanding systems; at small tau(rel) it also allows one to catch the viscous effects in hadronic component-hadron-resonance gas. We demonstrate how the approximation of sudden freeze-out can be obtained within this dynamical picture of continuous emission and find that hypersurfaces, corresponding to a sharp freeze-out limit, are momentum dependent. The pion m(T) spectra are computed in the developed hydro-kinetic model, and compared with those obtained from ideal hydrodynamics with the Cooper-Frye isothermal prescription. Our results indicate that there does not exist a universal freeze-out temperature for pions with different momenta, and support an earlier decoupling of higher p(T) particles. By performing numerical simulations for various initial conditions and equations of state we identify several characteristic features of the bulk QCD matter evolution preferred in view of the current analysis of heavy ion collisions at RHIC energies.

The clusters Abell 222 and Abell 223: a multi-wavelength view

Context. The Abell 222 and 223 clusters are located at an average redshift z similar to 0.21 and are separated by 0.26 deg. Signatures of mergers have been previously found in these clusters, both in X-rays and at optical wavelengths, thus motivating our study. In X-rays, they are relatively bright, and Abell 223 shows a double structure. A filament has also been detected between the clusters both at optical and X-ray wavelengths. Aims. We analyse the optical properties of these two clusters based on deep imaging in two bands, derive their galaxy luminosity functions (GLFs) and correlate these properties with X-ray characteristics derived from XMM-Newton data. Methods. The optical part of our study is based on archive images obtained with the CFHT Megaprime/Megacam camera, covering a total region of about 1 deg(2), or 12.3 x 12.3 Mpc(2) at a redshift of 0.21. The X-ray analysis is based on archive XMM-Newton images. Results. The GLFs of Abell 222 in the g' and r' bands are well fit by a Schechter function; the GLF is steeper in r' than in g'. For Abell 223, the GLFs in both bands require a second component at bright magnitudes, added to a Schechter function; they are similar in both bands. The Serna & Gerbal method allows to separate well the two clusters. No obvious filamentary structures are detected at very large scales around the clusters, but a third cluster at the same redshift, Abell 209, is located at a projected distance of 19.2 Mpc. X-ray temperature and metallicity maps reveal that the temperature and metallicity of the X-ray gas are quite homogeneous in Abell 222, while they are very perturbed in Abell 223. Conclusions. The Abell 222/Abell 223 system is complex. The two clusters that form this structure present very different dynamical states. Abell 222 is a smaller, less massive and almost isothermal cluster. On the other hand, Abell 223 is more massive and has most probably been crossed by a subcluster on its way to the northeast. As a consequence, the temperature distribution is very inhomogeneous. Signs of recent interactions are also detected in the optical data where this cluster shows a ""perturbed"" GLF. In summary, the multiwavelength analyses of Abell 222 and Abell 223 are used to investigate the connection between the ICM and the cluster galaxy properties in an interacting system.

Rapid solidification and phase stability evaluation of Ti-Si-B alloys

Ti-rich Ti-Si-B alloys can be considered for structural applications at high temperatures (max. 700 degrees C), however, phase equilibria data is reported only for T = 1250 degrees C. Thus, in this work the phase stability of this system has been evaluated at 700 degrees C. In order to attain equilibrium conditions in shorter time, rapid solidified samples have been prepared and carefully characterized. The microstructural characterization of the produced materials were based on X-ray diffraction (XRD), scanning electron microscopy (SEM-BSE), high resolution transmission electron microscopy (HRTEM), High Temperature X-ray diffraction with Synchrotron radiation (XRDSR) and Differential Scanning Calorimetry (DSC). Amorphous and amorphous with embedded nanocrystals have been observed after rapid solidification from specific alloy compositions. The values of the crystallization temperature (Tx) of the alloys were in the 509-647 degrees C temperature range. After Differential Scanning Calorimetry and High Temperature X-ray Diffraction with Synchrotron radiation, the alloys showed crystalline and basically formed by two or three of the following phases: alpha Ti, Ti(6)Si(2)B; Ti(5)Si(3); Ti(3)Si and TiB. It has been shown the stability of the Ti(3)Si and Ti(6)Si(2)B phases at 700 degrees C and the proposition of an isothermal section at this temperature. (C) 2011 Elsevier B.V. All rights reserved.

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

Three-layer piezoelectrets from fluorinated ethylene-propylene (FEP) copolymer films

A process for preparing three-layer piezoelectrets from fluorinated ethylene-propylene (FEP) copolymer films is introduced. Samples are made from commercial FEP films by means of laser cutting, laser bonding, electrode evaporation, and high-field poling. The observed dielectric-resonance spectra demonstrate the piezoelectricity of the FEP sandwiches. Piezoelectric d (33) coefficients up to a few hundred pC/N are achieved. Charging at elevated temperatures can increase the thermal stability of the piezoelectrets. Isothermal experiments for approximately 15 min demonstrate that samples charged at 140A degrees C keep their piezoelectric activity up to at least 120A degrees C and retain 70% of their initial d (33) even at 130A degrees C. Acoustical measurements show a relatively flat frequency response in the range between 300 Hz and 20 kHz.