Resonant ion-pair formation in electron recombination with HF^+

The cross section for resonant ion-pair formation in the collision of low-energy electrons with HF^+ is calculated by the solution of the time-dependent Schrodinger equation with multiple coupled states using a wave packet method. A diabatization procedure is proposed to obtain the electronic couplings between quasidiabatic potentials of ^1Sigma^+ symmetry for HF. By including these couplings between the neutral states, the cross section for ion-pair formation increases with about two orders of magnitude compared with the cross section for direct dissociation. Qualitative agreement with the measured cross section is obtained. The oscillations in the calculated cross section are analyzed. The cross section for ion-pair formation in electron recombination with DF^+ is calculated to determine the effect of isotopic substitution.Comment: 12 pages, 12 figure

Growth and symbiosis of plants with arbuscular mycorrhizal fungi in soil submitted to biochar application.

Arbuscular mycorrhizal fungi (AMF), which is intrinsically present or may be introduced in soils by inoculation, is an example of natural and renewable resource to increase plant nutrient uptake. This kind of fungi produces structures (hyphae, arbuscles and sometimes vesicles) inside the plant root cortex. This mutualistic relationship promotes plant gains in terms of water and nutrient absorption (mainly phosphorus). Biochar can benefit plant interaction with AMF, however, it can contain potentially toxic compounds such as heavy metals and organic compounds (e.g. dioxins, furans and polycyclic aromatic hydrocarbons), depending on the feedstock and pyrolysis conditions, which may damage organisms. For these reasons, the present work will approach the impacts of biochar application on soil attributes, AMF-plant symbiosis and its responses in plant growth and phosphorus uptake. Eucalyptus biochar produced at high temperatures increases sorghum growth; symbiosis with AMF; and enhances spore germination. Enhanced plant growth in the presence of high temperature biochar and AMF is a response of root branching stimulated by an additive effect between biochar characteristics and root colonization. Biochar obtained at low temperature reduces AMF spore germination; however it does not affect plant growth and symbiosis in soil

Avaliação espectroscópica de carvão derivado do bagaço da cana-de-açúcar sob diferentes temperaturas de pirólise e doses de fósforo.

As Terras Pretas de Índio são solos antrópicos que frequentemente apresentam elevado teor de P disponível. Visto que a origem desse P provavelmente seja da atividade humana pré-Colombiana, surge a dúvida de que mecanismo garantiu a persistência desse P numa forma disponível em um ambiente susceptível à lixiviação e fixação de P. Nesse contexto, o C pirogênico, abundante nas Terras Pretas de Índios, pode desempenhar papel central. O objetivo deste trabalho foi avaliar a capacidade adsorvente de carvões preparados a partir de bagaço da cana-deaçúcar a diferentes temperaturas. Para isso, a biomassa foi submetida a pirólise a temperaturas de 250 °C; 450 °C e 650 °C, carvão comercial de eucalipto foi utilizado como padrão. As isotermas de adsorção foram obtidas com concentrações de P variando de 0 a 300 mg L-1. Os carvões estudados não adsorveram P, ao contrário, foram fontes de P solúvel. A espectroscopia na região do infravermelho médio foi capaz de diferenciar os carvões produzidos a diferentes temperaturas, sendo que o material produzido a 250 °C ainda preserva algumas estruturas termolábeis, tais como estruturas alifáticas e carboidratos (celulose) enquanto que na maior temperatura observa-se um aumento da condensação dos anéis aromáticos. Adicionalmente se propõe o uso da espectroscopia vibracional para a determinação da natureza dos grupos reativos (carboxílicos aromáticos ou alifáticos) e do grau de carbonização de biomassas como um método de menor custo e mais rápido que a Ressonância Magnética Nuclear

An analytical model for the detection of levitated nanoparticles in optomechanics

Interferometric position detection of levitated particles is crucial for the centre-of-mass (CM) motion cooling and manipulation of levitated particles. In combination with balanced detection and feedback cooling, this system has provided picometer scale position sensitivity, zeptonewton force detection, and sub-millikelvin CM temperatures. In this article, we develop an analytical model of this detection system and compare its performance with experimental results allowing us to explain the presence of spurious frequencies in the spectra

Solid-state 13C NMR studies of activated carbons prepared from biomass using different chemical agents.

Activated carbons are largely employed in several chemical and physical processes nowadays, including water treatment, catalysis, gas storage and others [1]. The surface properties of the porous carbons are determinant for most of such applications. Oxygenated functional groups present at the edges of the aromatic lamellae are known to influence decisively the surface chemistry of these materials [2]. In this work, solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy was used for the analysis of a series of activated carbons prepared from a lignocellulosic precursor, using different chemical activating agents

Dynamic of polycyclic aromatic hydrocarbons in soils treated with biochar.

In recent years the interest in pyrogenic carbon for agricultural use (biochar, i.e. carbonized biomass for agricultural use) has sharply increased. However biochar contain dangerous compounds such as Polycyclic Aromatic Hydrocarbons (PAHs), many of them potentially carcinogenic and mutagenic. They are organic compounds formed from incomplete combustion of organic materials and are persistent pollutants. Therefore, PAHs concentrations and their dynamic must be evaluated in soils amended with biochar. For this, soil samples were collected in three experimental areas in different years (1, 3, 5 or 6) after the application of 0 (control) or 16 Mg ha-1 of biochar. This is the first report of PAHs persistence up to six years in soil treated with biochar. The biochar application increased total PAHs concentrations up to five years after the application, however the levels have always been an order of magnitude lower the limits of prevention established by International Environmental Agencies for soils. Thus, under the evaluated conditions ,the use of biochar was safe concerning PAHs contamination, besides, after six years of the application, the levels found were similar to the control treatment, making it possible to define a safe frequency of application based on the persistence of PAHs in soil