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Selected AbstractsKinetic studies on the influence of temperature and growth rate history on crystal growthCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2008P. M. Martins Abstract Crystallization experiments of sucrose were performed in a batch crystallizer to study the effect of temperature and growth rate history on the crystal growth kinetics. In one of the growth methods adopted, the isothermal volumetric growth rate (RV) is determined as a function of supersaturation (S) at 35, 40 and 45 ºC. In the other, crystals are allowed to grow at constant supersaturation by automatically controlling the solution temperature as the solute concentration decreased. Using the latter method RV is calculated as the solution is cooled. The obtained results are interpreted using empirical, engineering and fundamental perspectives of crystal growth. Firstly, the overall activation energy (EA) is determined from the empirical growth constants obtained in the isothermal method. The concept of falsified kinetics, widely used in chemical reaction engineering, is then extended to the crystal growth of sucrose in order to estimate the true activation energy (ET) from the diffusion-affected constant, EA. The differences found in the isothermal and constant supersaturation methods are explained from the viewpoint of the spiral nucleation mechanism, taking into account different crystal surface properties caused by the growth rate history in each method. Finally, the crystal growth curve obtained in the batch crystallizer at 40 ºC is compared with the one obtained in a fluidized bed crystallizer at the same temperature. Apparently divergent results are explained by the effects of crystal size, hydrodynamic conditions and growth rate history on the crystallization kinetics of sucrose. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Comparison of calibration methods for the reconstruction of space-time rainfall fields during a rain enhancement experiment in Southern ItalyENVIRONMETRICS, Issue 7 2009Arianna Orasi Abstract The role of rainfall raingauge observations in calibration of radar derived rainfall estimates is investigated. The final goal is the reconstruction of the rainfall fields over the observed area using both information during a rainfall enhancement experiment. Furthermore, we propose a simple protocol to assess the experiment efficacy. A space-time approach and the use of kriging with external drift are applied and compared. Results are again compared with those one obtained through an ordinary kriging (OK). Data come from a dense raingauge network and a weather radar installed in 1992 for the evaluation of a rain enhancement experiment carried out in Southern Italy. In this paper we report detailed results from one seeding operation carried out on 11 April 1992. The procedure to assess the efficacy of rain enhancement experiment is illustrated for 11 seeding operations. Copyright © 2008 John Wiley & Sons, Ltd. [source] Neural connectivity in hand sensorimotor brain areas: An evaluation by evoked field morphologyHUMAN BRAIN MAPPING, Issue 2 2005Franca Tecchio Abstract The connectivity pattern of the neural network devoted to sensory processing depends on the timing of relay recruitment from receptors to cortical areas. The aim of the present work was to uncover and quantify the way the cortical relay recruitment is reflected in the shape of the brain-evoked responses. We recorded the magnetic somatosensory evoked fields (SEF) generated in 36 volunteers by separate bilateral electrical stimulation of median nerve, thumb, and little fingers. After defining an index that quantifies the shape similarity of two SEF traces, we studied the morphologic characteristics of the recorded SEFs within the 20-ms time window that followed the impulse arrival at the primary sensory cortex. Based on our similarity criterion, the shape of the SEFs obtained stimulating the median nerve was observed to be more similar to the one obtained from the thumb (same median nerve innervation) than to the one obtained from the little finger (ulnar nerve innervation). In addition, SEF shapes associated with different brain regions were more similar within an individual than between subjects. Because the SEF morphologic characteristics turned out to be quite diverse among subjects, we defined similarity levels that allowed us to identify three main classes of SEF shapes in normalcy. We show evidence that the morphology of the evoked response describes the anatomo-functional connectivity pattern in the primary sensory areas. Our findings suggest the possible existence of a thalamo-cortico-thalamic responsiveness loop related to the different classes. Hum Brain Mapp 24:99,108, 2005. © 2004 Wiley-Liss, Inc. [source] Assessing the predictive performance of artifIcial neural network-based classifiers based on different data preprocessing methods, distributions and training mechanismsINTELLIGENT SYSTEMS IN ACCOUNTING, FINANCE & MANAGEMENT, Issue 4 2005Adrian Costea We analyse the implications of three different factors (preprocessing method, data distribution and training mechanism) on the classification performance of artificial neural networks (ANNs). We use three preprocessing approaches: no preprocessing, division by the maximum absolute values and normalization. We study the implications of input data distributions by using five datasets with different distributions: the real data, uniform, normal, logistic and Laplace distributions. We test two training mechanisms: one belonging to the gradient-descent techniques, improved by a retraining procedure, and the other is a genetic algorithm (GA), which is based on the principles of natural evolution. The results show statistically significant influences of all individual and combined factors on both training and testing performances. A major difference with other related studies is the fact that for both training mechanisms we train the network using as starting solution the one obtained when constructing the network architecture. In other words we use a hybrid approach by refining a previously obtained solution. We found that when the starting solution has relatively low accuracy rates (80,90%) the GA clearly outperformed the retraining procedure, whereas the difference was smaller to non-existent when the starting solution had relatively high accuracy rates (95,98%). As reported in other studies, we found little to no evidence of crossover operator influence on the GA performance. Copyright © 2005 John Wiley & Sons, Ltd. [source] Energetic stability of boron nitride nanostructures doped with one carbon atomINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 9 2010Rebeca D. Gonçalves Abstract We have investigated, using first-principles calculations, the role of a substitutional carbon atom on the geometric stability of boron nitride monolayers, nanotubes, and nanocones. It is shown that the formation of energy depends on the number of atoms for the monolayers and on the diameter for the tubes. It is also found, for the carbon-doped boron nitride nanotubes, that the value for the strain energy approaches the one obtained for nondoped tubes with increasing diameter. For the structural stability, we have verified that the doping, which introduces an excess of nitrogen or boron, makes each structure more favorable in its reverse atmosphere, i.e., excess of nitrogen is more stable in a boron-rich growth environment, whereas excess of boron is preferred in a nitrogen-rich condition. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Impact of habitat disturbance in the wetland forests of East Usambara, TanzaniaAFRICAN JOURNAL OF ECOLOGY, Issue 2 2010Ramadhani Senzota Abstract We evaluated habitat characteristics of East Usambara wetland forests. The abundance and species composition in the tree, shrub and herbaceous layers were enumerated in two sets of nested plots, one set in a natural wetland forest and the second in a wetland forest that had been disturbed by small-scale gold mining activities. Each set had thirty-six 1 m × 1 m plots for herbs, inside nine 5 m × 5 m plots for shrubs, in three 20 m × 20 m plots for trees. The habitat profile of herbaceous , shrub , tree layers was found to be sharply different from one obtained in previous studies at the surrounding nonwetland forests as were species composition and abundance. Unlike in the nonwetland forests, the herbaceous layer was thick, the shrub layer very thin and the woody species density and richness much lower. Disturbance significantly reduced woody cover and changed species composition in the herbaceous layer. Recovery of the woody vegetation was low. Wetland forests in the East Usambaras form a small fraction of the total area, but they are a unique biodiversity repository, they appear to be an important carbon dioxide sink and to reserve and purify water. They are sensitive to disturbance and need protection. Résumé Nous avons évalué les caractéristiques de l'habitat des forêts humides d'East Usambara. L'abondance et la composition des espèces dans les étages d'arbres, d'arbustes et d'herbes furent dénombrées dans deux ensembles de parcelles emboitées, un situé dans une forêt humide naturelle, l'autre dans une forêt humide qui avait été perturbée par les activités d'orpaillage à petite échelle. Chaque ensemble se composait de 36 carrés de 1 m² pour les herbes, situés dans neuf carrés de 5 m × 5 m pour les buissons, eux-mêmes situés à l'intérieur de trois carrés de 20 m × 20 m pour les arbres. Le profil des habitats pour les trois couches d'herbes , d'arbustes , d'arbres s'est révélé très différent de celui qui avait été obtenu lors d'études précédentes réalisées dans des forêts environnantes non humides; il en était de même pour la composition et l'abondance des espèces. Contrairement aux forêts non humides, la couche herbeuse était épaisse, la couche des arbustes très claire et la densité et la richesse des espèces ligneuses étaient beaucoup plus faibles. La perturbation avait significativement réduit le couvert ligneux et changé la composition des espèces de l'étage herbacé. La restauration de la végétation ligneuse était faible. Les forêts humides des East Usambara ne constituent qu'une petite fraction de la superficie totale, mais elles sont un sanctuaire unique pour sa biodiversité, elles semblent être un puits de carbone important et aussi retenir et purifier l'eau. Elles sont sensibles à toute perturbation et doivent être protégées. [source] Class I ribonucleotide reductase revisited: The effect of removing a proton on Glu441JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2004Vladimir Pelmenschikov Abstract The substrate mechanism of class I ribonucleotide reductase has been revisited using the hybrid density functional B3LYP method. The molecular model used is based on the X-ray structure and includes all the residues of the R1 subunit commonly considered in the RNR substrate conversion scheme: Cys439 initiating the reaction as a thiyl radical, the redox-active cysteines Cys225 and Cys462, and the catalytically important Glu441 and Asn437. In contrast to previous theoretical studies of the overall mechanism, Glu441 is added as an anion. All relevant transition states have been optimized, including one where an electron is transferred 8 Å from the disulfide to the substrate simultaneously with a proton transfer from Glu441. The calculated barrier for this step is 19.1 kcal/mol, which can be compared to the rate-limiting barrier indicated by experiments of about 17 kcal/mol. Even though the calculated barrier is somewhat higher than the experimental limit, the discrepancy is within the normal error bounds of B3LYP. The suggestion from the present modeling study is thus that a protonated Glu441 does not need to be present at the active site from the beginning of the catalytic cycle. However, the previously suggested mechanism with an initial protonation of Glu441 cannot be ruled out, because even with the cost added for protonation of Glu441 with a typical pKa of 4, the barrier for that mechanism is lower than the one obtained for the present mechanism. The results are compared to experimental results and suggestions. © 2003 Wiley Periodicals, Inc. J Comput Chem 25: 311,321, 2004 [source] Lobby Groups and the Financial Support of Election CampaignsJOURNAL OF PUBLIC ECONOMIC THEORY, Issue 3 2000M. Socorro Puy We study a model of competition between two political parties with policy compromise. There is a special interest group with well-defined preferences on political issues. Voters are of two kinds: impressionable and knowledgeable. The impressionable voters are influenced by the election campaigns. The objective of the parties is to obtain the maximum votes. Parties compete for financial support from a given interest group. Each party proposes a platform in exchange for an amount of campaign funds, and the interest group decides whether to accept or reject each of these proposals. We show that parties' competition resembles, to a certain extent, Bertrand competition. Furthermore, in equilibrium only one party gets funds from the interest group. This result differs from the one obtained in a similar model by Grossman and Helpman in which, in equilibrium, both parties are financed by the interest group. This difference arises because Grossman and Helpman assume that it is the interest group who makes the proposals to the political parties. [source] An analysis of the composite stellar population in M32,MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009P. Coelho ABSTRACT We obtained long-slit spectra of high signal-to-noise ratio of the galaxy M32 with the Gemini Multi-Object Spectrograph at the Gemini-North telescope. We analysed the integrated spectra by means of full spectral fitting in order to extract the mixture of stellar populations that best represents its composite nature. Three different galactic radii were analysed, from the nuclear region out to 2 arcmin from the centre. This allows us to compare, for the first time, the results of integrated light spectroscopy with those of resolved colour,magnitude diagrams from the literature. As a main result we propose that an ancient and an intermediate-age population co-exist in M32, and that the balance between these two populations change between the nucleus and outside one effective radius (1reff) in the sense that the contribution from the intermediate population is larger at the nuclear region. We retrieve a smaller signal of a young population at all radii whose origin is unclear and may be a contamination from horizontal branch stars, such as the ones identified by Brown et al. in the nuclear region. We compare our metallicity distribution function for a region 1 to 2 arcmin from the centre to the one obtained with photometric data by Grillmair et al. Both distributions are broad, but our spectroscopically derived distribution has a significant component with [Z/Z,],,1, which is not found by Grillmair et al. [source] Measuring the spin up of the accreting millisecond pulsar XTE J1751,305MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008A. Papitto ABSTRACT We perform a timing analysis on RXTE data of the accreting millisecond pulsar XTE J1751,305 observed during the 2002 April outburst. After having corrected for Doppler effects on the pulse phases due to the orbital motion of the source, we performed a timing analysis on the phase delays, which gives, for the first time for this source, an estimate of the average spin frequency derivative . We discuss the torque resulting from the spin-up of the neutron star deriving a dynamical estimate of the mass accretion rate and comparing it with the one obtained from X-ray flux. Constraints on the distance to the source are discussed, leading to a lower limit of , 6.7 kpc. [source] Thin films of Co3O4, MnCo2O4 and their solid solution as electrocatalyst: study of their magnetic propertiesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S1 2004E. Ríos Abstract We present magnetic measurements performed on the MnxCo3,xO4 (0 , x , 1) solid solution, prepared by spray pyrolysis. Thin films of about 20 ,m thickness were obtained after depositing aqueous metal nitrates precursors on Ti or conducting glass substrates. Powder material scratched from the substrate's surface was used for physico-chemical characterization. Presence of two oxidation states for each metal ion (Mn3+,Mn4+; Co2+,Co3+) triggers specific conduction mechanisms and double-exchange magnetic interactions. The ferromagnetic components are enhanced when x(Mn) increases, in detriment of the antiferromagnetic interactions. The ordering temperature Tc changes with x (from 22 K up to room temperature, for x = 0 up to x = 1). Based in the paramagnetic moment ,eff obtained at T > Tc, we propose a cationic distribution which can be nicely compared to the one obtained from crystallographic analyses. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Counts with an endogenous binary regressor: A series expansion approachTHE ECONOMETRICS JOURNAL, Issue 1 2005Andrés Romeu Summary, We propose an estimator for count data regression models where a binary regressor is endogenously determined. This estimator departs from previous approaches by using a flexible form for the conditional probability function of the counts. Using a Monte Carlo experiment we show that our estimator improves the fit and provides a more reliable estimate of the impact of regressors on the count when compared to alternatives which do restrict the mean to be linear-exponential. In an application to the number of trips by households in the United States, we find that the estimate of the treatment effect obtained is considerably different from the one obtained under a linear-exponential mean specification. [source] Dissecting galaxies with quantitative spectroscopy of the brightest stars in the UniverseASTRONOMISCHE NACHRICHTEN, Issue 5 2010R.-P. KudritzkiArticle first published online: 20 MAY 2010 Abstract Measuring distances to galaxies, determining their chemical composition, investigating the nature of their stellar populations and the absorbing properties of their interstellar medium are fundamental activities in modern extragalactic astronomy helping to understand the evolution of galaxies and the expanding universe. The optically brightest stars in the universe, blue supergiants of spectral A and B, are unique tools for these purposes. With absolute visual magnitudes up to MV , -9.5 they are ideal to obtain accurate quantitative information about galaxies through the powerful modern methods of quantitative stellar spectroscopy. The spectral analysis of individual blue supergiant targets provides invaluable information about chemical abundances and abundance gradients, which is more comprehensive than the one obtained from HII regions, as it includes additional atomic species, and which is also more accurate, since it avoids the systematic uncertainties inherent in the strong line studies usually applied to the HII regions of spiral galaxies beyond the Local Group. Simultaneously, the spectral analysis yields stellar parameters and interstellar extinction for each individual supergiant target, which provides an alternative very accurate way to determine extragalactic distances through a newly developed method, called the Flux-weighted Gravity,Luminosity Relationship (FGLR). With the present generation of 10 m-class telescopes these spectroscopic studies can reach out to distances of 10 Mpc. The new generation of 30 m-class telescopes will allow to extend this work out to 30 Mpc, a substantial volume of the local universe (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Role of the cholinergic system and of apamin-sensitive Ca2+ -activated K+ channels on rabbit jejunum spontaneous activity and on the inhibitory effects of adrenoceptor agonistsAUTONOMIC & AUTACOID PHARMACOLOGY, Issue 2 2003L. Romanelli Summary 1 One reason why rabbit jejunum is suitable for studying the mechanisms underlying the actions of the various neurotransmitters and their interactions is its spontaneous motility. The main regulator of spontaneous motility is the cholinergic system. How the cholinergic system regulates the spontaneous activity in the rabbit jejunum and how it affects the inhibitory action of , - and , -adrenoceptor agonists remains unclear. 2 We studied the influence of the cholinergic system and apamin-sensitive Ca2+ -activated K+ channels on spontaneous contractions in the rabbit jejunum and on the inhibitory effects of,1 - and , -adrenoceptor agonists. 3 In naïve tissues, atropine (ATR, 7.4 × 10,8 m) and tetrodotoxin (8 × 10,8 m) almost completely inhibited , to a similar extent , the amplitude of spontaneous activity. Despite the presence of ATR or TDX, tissue contraction gradually recovered to about 50% of the baseline amplitude within 5,10 min. When ATR or TDX, respectively, were added to the TDX- or ATR-treated tissues, the recovered activity decreased weakly but significantly. After washout and a 45-min rest the contraction amplitude returned to baseline values. A further exposure to ATR or TDX reduced the contraction to a level significantly lower than the one obtained after TDX or ATR added 5 min after ATR or TDX, respectively. In preparations prestimulated for 10 min with acetylcholine (ACh), ATR abolished the TDX-resistant recovered spontaneous activity. 4 Adrenaline (ADR, 0.5,5 × 10,7 m) and phenylephrine (PHE, 1,10 × 10,7 m) inhibited tissue motility in naïve and in ATR- and in TDX-exposed preparations. But whereas in naïve preparations the ,1 -adrenoceptor antagonists completely antagonized inhibition induced by both drugs, in ATR- and TDX-exposed tissues they did so only partially for ADR. Agonist-induced inhibition had a rapid onset but rapidly faded; pendular movements took significantly longer to recover in ATR- and TDX-treated tissues than in naïve tissues. In tissues exposed for 2 min to ADR (0.5,5 × 10,7 m) or PHE (1,10 × 10,7 m), washout or addition of ,1 -adrenoceptor antagonists caused an immediate short-lasting increase in contraction amplitude. 5 Apamin (APAM, 5 × 10,9 m) caused a rapid and persistent increase in the amplitude of contractions. It also blocked the inhibitory responses to ADR and PHE, and removed washout-induced contractions. The APAM-induced increase in the contraction amplitude correlated with the increase obtained by washing out ADR or PHE. 6 Isoprenaline (at concentrations up to 2.8 × 10,7 m) produced no inhibitory response in naïve tissues, but it invariably blocked (at a concentration of 0.7 × 10,7 m) the recovered spontaneous activity (and sometimes depressed muscletone) in tissues exposed to ATR or TDX. Neither propranolol (3.4 × 10,7 m) nor APAM (5 × 10,9 m) counteracted these inhibitory effects. 7 These results indicate that spontaneous motility in the rabbit jejunum is predominantly mediated by neuronal release of ACh and by some other unidentified neuronal activity. Released ACh inhibits myogenic activity and strongly antagonizes , -adrenoceptor-induced APAM-insensitive inhibition but leaves ,1 agonist-induced APAM-sensitive inhibition unchanged. [source] Fluorene and phenanthrene uptake by Pseudomonas putida ATCC 17514: Kinetics and physiological aspectsBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2005Ana C. Rodrigues Abstract Pseudomonas putida ATCC 17514 was used as a model strain to investigate the characteristics of bacterial growth in the presence of solid fluorene and phenanthrene. Despite the lower water-solubility of phenanthrene, P. putida degraded this polycyclic aromatic hydrocarbon (PAH) at a maximum observed rate of 1.4 ± 0.1 mg L,1 h,1, higher than the apparent degradation rate of fluorene, 0.8 ± 0.07 mg L,1 h,1. The role of physiological processes on the biodegradation of these PAHs was analyzed and two different uptake strategies were identified. Zeta potential measurements revealed that phenanthrene-grown cells were slightly more negatively charged (,57.5 ± 4.7 mV) than fluorene-grown cells (,51.6 ± 4.9 mV), but much more negatively charged than glucose-grown cells (,26.8 ± 3.3 mV), suggesting that the PAH substrate induced modifications on the physical properties of bacterial surfaces. Furthermore, protein-to-exopolysaccharide ratios detected during bacterial growth on phenanthrene were typical of biofilms developed under physicochemical stress conditions, caused by the presence of sparingly water-soluble chemicals as the sole carbon and energy source for growth, the maximum value for TP/EPS during growth on phenanthrene (1.9) being lower than the one obtained with fluorene (5.5). Finally, confocal laser microscopy observations using a gfp -labeled derivative strain revealed that, in the presence of phenanthrene, P. putida::gfp cells formed a biofilm on accessible crystal surfaces, whereas in the presence of fluorene the strain grew randomly between the crystal clusters. The results showed that P. putida was able to overcome the lower aqueous solubility of phenanthrene by adhering to the solid PAH throughout the production of extracellular polymeric substances, thus promoting the availability and uptake of such a hydrophobic compound. © 2005 Wiley Periodicals, Inc. 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