The measurement of actual acidity in acid sulfate soils and the determination of sulfidic acidity in suspension after peroxide oxidation

Improvements to the routine methods for the determination of actual acidity in suspension for acid sulfate soils (ASS) are introduced. The titratable sulfidic acidity (TSA) results using an improved peroxide-based method were compared with the theoretical acidity predicted by the chromium reducible sulfur method for 9 acid sulfate soils. The regression between these 2 measures of sulfidic acidity was highly significant, the slope of the regression line not significantly different from unity (P = 0.05) and the intercept not significantly different from zero. This contrasts with results of other workers using earlier peroxide oxidation methods, where TSA substantially underestimated the theoretical acidity predicted by reduced inorganic sulfur analysis. Comparison was made between the 2 principal measurements from the improved peroxide method (TSA and S-POS), with S-POS converted to theoretical sulfidic acidity to allow comparison. The relationship between these 2 measurements was highly significant. The effects of titration in suspension, as well as raising titration end points to pH 6.5, were investigated, principally with respect to the titratable actual acidity (TAA) result. TAA results obtained by KCl extraction were compared with those obtained using BaCl2, MgCl2, and water extraction. TAA in 1 M KCl suspensions titrated to pH 6.5 agreed well with titratable actual acidity measured using the 25-h extraction approach of the Lin et al. (2000a) BaCl2 method. Both BaCl2 and KCl solutions were ineffective at fully recovering acidity from synthetic jarosite without repeated extraction and titration. The application of correction factors for the estimation of total actual acidity in ASS is not supported by the results of this investigation. Acid sulfate soils that contain substantial quantities of jarosite or other acid-producing but relatively insoluble sulfate minerals continue to prove problematic to chemically analyse; however, an approach for estimating this component is discussed.

Correction of soil acidity in the subsurface of an oxisol with sandy loam texture under no-tillage

In Rio Grande do Sul State (RS), Southern Brazil, aluminum saturation in many areas under no-till system is high and base saturation low in the 0.10-0.20 m layer (subsurface), which may reduce the grain yield of annual crops. The objective of this study was to evaluate if the occurrence of high aluminum saturation and low base saturation in the subsurface, under a no-till system, represents a restrictive environment for crop production, as well as to evaluate forms of lime incorporation for soil acidity correction in the subsurface. For this purpose, an experiment was carried out with soybean (2005/2006), corn (2006/2007), wheat (2007) and soybean (2007/2008) crops, in a Rhodic Hapludox (USDA, 1999) with sandy loam texture, under no-till for four years in the county of Tupanciretã (RS). The six treatments were: no-tillage with and without lime, plowing with and without lime, and chiseling with and without lime. The values of pH-H2O, aluminum saturation and base saturation were evaluated 24 months after treatment application in the layers 0-0.05; 0.05-0.10; 0.10-0.15; 0.15-0.20 and 0.20-0.30 m. The yields of soybean (2005/2006), corn (2006/2007), wheat (2007) and soybean (2007/2008) were evaluated. Soil acidity in the subsurface did not affect crop yield when the acidity in the layer from 0-0.10 m was at levels for which lime application is not recommended, according to CQFSRS/SC (2004). Lime incorporation through plowing was the most efficient way of correcting acidity at deeper levels.

Monte Carlo simulation of kilovolt electron transport in solids

A Monte Carlo procedure to simulate the penetration and energy loss of low¿energy electron beams through solids is presented. Elastic collisions are described by using the method of partial waves for the screened Coulomb field of the nucleus. The atomic charge density is approximated by an analytical expression with parameters determined from the Dirac¿Hartree¿Fock¿Slater self¿consistent density obtained under Wigner¿Seitz boundary conditions in order to account for solid¿state effects; exchange effects are also accounted for by an energy¿dependent local correction. Elastic differential cross sections are then easily computed by combining the WKB and Born approximations to evaluate the phase shifts. Inelastic collisions are treated on the basis of a generalized oscillator strength model which gives inelastic mean free paths and stopping powers in good agreement with experimental data. This scattering model is accurate in the energy range from a few hundred eV up to about 50 keV. The reliability of the simulation method is analyzed by comparing simulation results and experimental data from backscattering and transmission measurements.

Use of mirage effect for the detection of phase transitions in solids

The phenomenon of mirage effect suffered by a He-Ne laser beam has been utilized to detect phase transitions in solids. It has been observed that anomalous fluctuations of large amplitude occur in the signal level near the transition temperature. The mean square value of the fluctuation is found to exhibit a well-defined peak at this point. Results of measurements made in the case of crystals of TGS ((NH2CH2COOH)3.H2SO4) and a ceramic sample (BaTiO3) are given to illustrate this technique.

Theory of laser-induced ultrafast structural changes in solids

The present thesis is a contribution to the study of laser-solid interaction. Despite the numerous applications resulting from the recent use of laser technology, there is still a lack of satisfactory answers to theoretical questions regarding the mechanism leading to the structural changes induced by femtosecond lasers in materials. We provide here theoretical approaches for the description of the structural response of different solids (cerium, samarium sulfide, bismuth and germanium) to femtosecond laser excitation. Particular interest is given to the description of the effects of the laser pulse on the electronic systems and changes of the potential energy surface for the ions. Although the general approach of laser-excited solids remains the same, the potential energy surface which drives the structural changes is calculated with different theoretical models for each material. This is due to the difference of the electronic properties of the studied systems. We use the Falicov model combined with an hydrodynamic method to study photoinduced phase changes in cerium. The local density approximation (LDA) together with the Hubbard-type Hamiltonian (LDA+U) in the framework of density functional theory (DFT) is used to describe the structural properties of samarium sulfide. We parametrize the time-dependent potential energy surface (calculated using DFT+ LDA) of bismuth on which we perform quantum dynamical simulations to study the experimentally observed amplitude collapse and revival of coherent $A_{1g}$ phonons. On the basis of a time-dependent potential energy surface calculated from a non-orthogonal tight binding Hamiltonian, we perform molecular dynamics simulation to analyze the time evolution (coherent phonons, ultrafast nonthermal melting) of germanium under laser excitation. The thermodynamic equilibrium properties of germanium are also reported. With the obtained results we are able to give many clarifications and interpretations of experimental results and also make predictions.

Excitation of Phonons in Solids and Nanostructures by Intense Laser and XUV Pulses and by Low Energy Atomic Collision

Intensive, ultrakurze Laserpulse regen Festkörper in einen Zustand an, in dem die Elektronen hohe Temperaturen erlangen, während das Gitter kalt bleibt. Die heißen Elektronen beeinflussen das sog. Laser-angeregte interatomare Potential bzw. die Potentialenergiefläche, auf der die Ionen sich bewegen. Dieses kann neben anderen ultrakurzen Prozessen zu Änderungen der Phononfrequenzen (phonon softening oder phonon hardening) führen. Viele ultrakurze strukturelle Phänomene in Festkörpern hängen bei hohen Laseranregungen von Änderungen der Phononfrequenzen bei niedrigeren Anregungen ab. Um die Laser-bedingten Änderungen des Phononenspektrums von Festkörpern beschreiben zu können, haben wir ein auf Temperatur-abhängiger Dichtefunktionaltheorie basierendes Verfahren entwickelt. Die dramatischen Änderungen nach einer Laseranregung in der Potentialenergiefläche werden durch die starke Veränderung der Zustandsdichte und der Besetzungen der Elektronen hervorgerufen. Diese Änderungen in der Zustandsdichte und den Besetzungszahlen können wir mit unserer Methode berechnen, um dann damit das Verhalten der Phononen nach einer Laseranregung zu analysieren. Auf diese Art und Weise studierten wir den Einfluss einer Anregung mit einem intensiven, ultrakurzen Laserpuls auf repräsentative Phonon Eigenmoden in Magnesium, Kupfer und Aluminium. Wir stellten dabei in manchen Gitterschwingungen entweder eine Abnahme (softening) und in anderen eine Zunahme (hardening) der Eigenfrequenz fest. Manche Moden zeigten bei Variation der Laseranregungsstärke sogar beide Verhaltensweisen. Das eine Phonon-Eigenmode ein hardening und softening zeigen kann, wird durch das Vorhandensein von van Hove Singularitäten in der elektronischen Zustandsdichte des betrachteten Materials erklärt. Für diesen Fall stellt unser Verfahren zusammen mit der Sommerfeld-Entwicklung die Eigenschaften der Festkörper Vibrationen in Verbindung mit den Laser induzierten Veränderungen in den elektronischen Besetzungen für verschiedene Phonon-eingefrorene Atomkonfigurationen. Auch die absolute Größe des softening und hardening wurde berechnet. Wir nehmen an, dass unsere Theorie Licht in die Effekte der Laseranregung von verschiedenen Materialien bringt. Außerdem studierten wir mit Hilfe von Dichtefunktionaltheorie die strukturellen Material-Eigenschaften, die durch kurze XUV Pulse induziert werden. Warme dichte Materie in Ultrakurzpuls angeregten Magnesium wurde analysiert und verglichen mit den Ergebnissen bei durch Laser Anregung bedingten Änderungen. Unter Verwendung von elektronischer-Temperatur-abhängiger Dichtefunktionaltheorie wurden die Änderungen in den Bindungseigenschaften von warmen dichten Magnesium studiert. Wir stellten dabei beide Effekte, Verstärkung und Abschwächung von Bindungen, bei jeweils verschiedenen Phonon Eigenmoden von Magnesium auf Grund von der Erzeugung von Rumpflöchern und dem Vorhandensein von heißen Elektronen fest. Die zusätzliche Erzeugung von heißen Elektronen führt zu einer Änderung der Bindungscharakteristik, die der Änderung, die durch die bereits vorhandenen Rumpflöcher hervorgerufen wurde, entgegen wirkt. Die thermischen Eigenschaften von Nanostrukturen sind teilweise sehr wichtig für elektronische Bauteile. Wir studierten hier ebenfalls den Effekt einer einzelnen Graphen Lage auf Kupfer. Dazu untersuchten wir mit Dichtefunktionaltheorie die strukturellen- und Schwingungseigenschaften von Graphen auf einem Kupfer Substrat. Wir zeigen, dass die schwache Wechselwirkung zwischen Graphen und Kupfer die Frequenz der aus der Ebene gerichteten akustischen Phonon Eigenmode anhebt und die Entartung zwischen den aus der Ebene gerichteten akustischen und optischen Phononen im K-Punkt des Graphen Spektrums aufhebt. Zusätzlich führten wir ab initio Berechnungen zur inelastischen Streuung eines Helium Atoms mit Graphen auf einem Kuper(111) Substrat durch. Wir berechneten dazu das Leistungsspektrum, das uns eine Idee über die verschiedenen Gitterschwingungen des Graphene-Kuper(111) Systems gibt, die durch die Kollision des Helium Atom angeregt werden. Wir brachten die Positionen der Peaks im Leistungsspektrum mit den Phonon Eigenfrequenzen, die wir aus den statischen Rechnungen erhalten haben, in Beziehung. Unsere Ergebnisse werden auch verglichen mit den Ergebnissen experimenteller Daten zur Helium Streuung an Graphen-Kupfer(111) Oberflächen.

Olfactory perception threshold assessment of volatile acidity in Madeira wines

Madeira wine is a fortified wine with impact in the Madeira Island’s economy. Similarly to other wines, its acidity should be well controlled in order to ensure Madeira wine quality, mostly the volatile acidity. Due to Madeira wine complex flavour, it is crucial to get a better knowledge about the volatile acidity impact in its features, namely determine the perception limit of acetic acid and ethyl acetate, as both are the main contributors for volatile acidity. Firstly, the olfactory perception threshold of volatile acidity was assessed by a trained and an untrained panel, using 5 and 10 years-old Sercial and Malvasia wines. Moreover, the current work also presents the evolution of organic acids, acetic acid and ethyl acetate during 540 days of ageing of Madeira wines (Malvasia, Bual, Verdelho and Sercial), comparing the same wines aged by both traditional ageing processes: canteiro and estufagem. Other wine samples, aged in wood casks (canteiro) for at least 5 years, were also evaluated. HS-SPME followed by GC-MS analysis was used to determine ethyl acetate concentration and IEC-HPLC-DAD was used for the organic acids determination, including acetic acid. The results indicated that acetic acid and ethyl acetate olfactory perception threshold depends essentially on wine’s age. Concerning acetic acid, the untrained panel was in average 5.45 g/L (5 years-old) and 6.22 g/L (10 years-old). Training the expert panel to recognize acetic acid odour, the values decreased for 1.44 g/L (5 years-old) and 1.87 g/L (10 years-old), but still remained higher than the established volatile acidity legal limits. Ethyl acetate threshold was similar for both panels (in average 327.97 mg/L). Both compounds tend to increase exponentially with age, being more evident in sweet wines. Organic acids in young Madeira wines depend mostly on the nature of grape varieties, but this difference is minimized with wine ageing.

Preliminary Study of the Gastric Acidity in Thoroughbred Horses at Rest after Enteral Administration of Esomeprazole Magnesium (Nexium)

The regulation of gastric secretion is of crucial importance to the equilibrium of the gastroenteric system. Despite the large number of factors involved in the causes of peptic illnesses, pH = 4 is considered the threshold between physiologic and deleterious effects of stomach acid secretion. With the aim of maintaining pH greater than 4, proton-pump inhibitors, such as esomeprazole magnesium (NEXIUM), have shown excellent results in the control of acid secretion. Aimed at examining the action of this drug in the control of pH levels of gastric secretion in thoroughbreds, a single dose of 40 or 80 mg of esomeprazole magnesium was administered daily, and pH was determined serially for 5 consecutive days. The results obtained corroborated the efficacy of esomeprazole magnesium in the control of gastric pH at both doses tested, with 100% of the mean pH being greater than 5. Moreover, no statistical difference was noted between the two doses tested.

Correction of soil acidity in the subsurface of an oxisol with sandy loam texture under no-tillage

No Rio Grande do Sul (RS), muitas áreas sob plantio direto apresentam elevada saturação por Al e baixa saturação por bases na camada de 0,10-0,20 m (subsuperfície), e isso pode diminuir a produção de grãos de culturas anuais. O objetivo do presente trabalho foi avaliar se a ocorrência de alta saturação por Al e baixa saturação por bases em subsuperfície (0,10-0,20 m), no plantio direto, pode representar um ambiente restritivo para a produção de culturas, bem como avaliar os modos de incorporação de calcário na correção da acidez do solo em subsuperfície. Para isso, foi realizado um experimento com os cultivos de soja (2005/ 2006), milho (2006/2007), trigo (2007) e soja (2007/2008), em um Latossolo Vermelho distrófico típico (Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA), 2006) de textura franco arenosa, há quatro anos sob plantio direto, no município de Tupanciretã (RS). Os seis tratamentos foram: sem revolvimento com ou sem calcário; lavração com ou sem calcário; e escarificação com ou sem calcário. Aos 24 meses após a aplicação dos tratamentos e nas camadas de 0-0,05, 0,05-0,10, 0,10-0,15, 0,15-0,20 e 0,20-0,30 m, foram avaliados os valores de pH-H2O, saturação por Al e por bases. Avaliou-se a produtividade de soja (2005/2006), milho (2006/2007), trigo (2007) e soja (2007/2008). A acidez do solo em subsuperfície não alterou a produtividade das culturas quando as propriedades de acidez na camada de 0-0,10 m estavam em níveis em que não se recomenda a aplicação de calcário, segundo a CQFSRS/SC (2004). A incorporação de calcário com aração foi o modo mais eficiente de corrigir a acidez em profundidade.

Sources of atmospheric acidity in an agricultural-industrial region of São Paulo State, Brazil

[1] Surface-based measurements of atmospheric formic acid (HCOOH), acetic acid (CH3COOH), sulfur dioxide (SO2), hydrogen chloride (HCl), and nitric acid (HNO3) were made in central São Paulo State, Brazil, between April 1999 and March 2000. Mean concentrations were 9.0 ppb (HCOOH), 1.3 ppb (CH3COOH), 4.9 ppb (SO2), 0.3 ppb (HCl), and 0.5 ppb (HNO3). Concentrations in sugar cane burning plumes were 1160-4230 ppb (HCOOH), 360-1750 ppb (CH3COOH), 10-630 ppb (SO2), 4-210 ppb (HCl), and 14-90 ppb (HNO3). Higher ambient concentrations of SO2, HCl and HNO3 were measured during the burning season (May-November). Concentrations of SO2 and HCl increased during the evening, and of HCOOH and CH3COOH were lowest in the morning, with peak levels in the afternoon. Ratios obtained between different species showed either nighttime maxima (SO2/HCOOH, SO2/CH3COOH, SO2/HNO3, CH3COOH/HNO3, SO2/HCl and HCOOH/HNO3), daytime maxima (HCOOH/HCl, CH3COOH/HCl and HNO3/HCl), or no clear trends (HCOOH/CH3COOH). Correlation analysis showed that SO2 and HCl were primary emissions from biomass burning and road transport; HCOOH, HNO3 and CH3COOH were products of photochemistry; HCOOH and CH3COOH were emitted directly during combustion as well as from biogenic sources. Biomass burning affected atmospheric acidity on a regional scale, while vehicular emissions had greater impact in urban and adjacent areas. Atmospheric ammonia levels were insufficient to neutralize atmospheric acidity, which was mainly removed by deposition to the surface.

An implicit BEM formulation to model strong discontinuities in solids

A boundary element method (BEM) formulation to predict the behavior of solids exhibiting displacement (strong) discontinuity is presented. In this formulation, the effects of the displacement jump of a discontinuity interface embedded in an internal cell are reproduced by an equivalent strain field over the cell. To compute the stresses, this equivalent strain field is assumed as the inelastic part of the total strain. As a consequence, the non-linear BEM integral equations that result from the proposed approach are similar to those of the implicit BEM based on initial strains. Since discontinuity interfaces can be introduced inside the cell independently on the cell boundaries, the proposed BEM formulation, combined with a tracking scheme to trace the discontinuity path during the analysis, allows for arbitrary discontinuity propagation using a fixed mesh. A simple technique to track the crack path is outlined. This technique is based on the construction of a polygonal line formed by segments inside the cells, in which the assumed failure criterion is reached. Two experimental concrete fracture tests were analyzed to assess the performance of the proposed formulation.

Evaluation of the acidity in the juice from different parts of the stem of sugarcane, cycle 2010/2011

The acidity levels present in the juice of sugarcane can cause problems in its processing. This study aimed to compare the values of total, volatile and fixed acidity in the juice of the stem nodes and internodes of sugarcane. The experimental design was a completely randomized, 3x2 factorial arrangement with four replications, using three varieties of sugarcane (IAC91-1099; ISC95 and CTC7-5000) divided into node and internode. The stems were collected and separated in node and internode. After extraction of juice from each part, total, volatile and fix acidities were determined. The results were subjected to variance analysis the by F test and compared by the Tukey test at 5% probability. The cultivar CTC7 had the lowest levels of total and fixed acidity. Cultivar IAC91-1099 showed high levels of fixed acidity on both parts of the stem, and high volatile acidity at the node. In the stem, the values of volatile acidity showed no definite pattern between cultivars. The node has, in general, a higher fixed acidity, but some cultivars have shown opposite results.

Relativistic high-current electron-beam stopping-power characterization in solids and plasmas: collisional versus resistive effects.

We present experimental and numerical results on intense-laser-pulse-produced fast electron beams transport through aluminum samples, either solid or compressed and heated by laser-induced planar shock propagation. Thanks to absolute K� yield measurements and its very good agreement with results from numerical simulations, we quantify the collisional and resistive fast electron stopping powers: for electron current densities of � 8 � 1010 A=cm2 they reach 1:5 keV=�m and 0:8 keV=�m, respectively. For higher current densities up to 1012 A=cm2, numerical simulations show resistive and collisional energy losses at comparable levels. Analytical estimations predict the resistive stopping power will be kept on the level of 1 keV=�m for electron current densities of 1014 A=cm2, representative of the full-scale conditions in the fast ignition of inertially confined fusion targets.