Electric-Field Gradient at Cd Impurities in In2o3. A FLAPW Study

We report an ab initio study of the electric-field gradient tensor (EFG) at Cd impurities located at both inequivalent cationic sites in the semiconductor In2O3. Calculations were performed with the FLAPW method, that allows us to treat the electronic structure of the doped system and the atomic relaxations introduced by the impurities in the host lattice in a fully self-consistent way. From our results for the EFG (in excellent agreement with the experiments), it is clear that the problem of the EFG at impurities in In2O3 cannot be described by the point-charge model and antishielding factors.Comment: 4 pages, 2 figures, and 2 table

Transient jets in the symbiotic prototype Z Andromedae

We present development of the collimated bipolar jets from the symbiotic prototype Z And that appeared and disappeared during its 2006 outburst. In 2006 July Z And reached its historical maximum at U ~ 8.0. During this period, rapid photometric variations with Dm ~ 0.06 mag on the timescale of hours developed. Simultaneously, high-velocity satellite components appeared on both sides of the H-alpha and H-beta emission line profiles. They were launched asymmetrically with the red/blue velocity ratio of 1.2 - 1.3. From about mid-August they became symmetric. Their spectral properties indicated ejection of bipolar jets collimated within an average opening angle of 6.1 degrees. We estimated average outflow rate via jets to dM(jet)/dt ~ 2xE10-6(R(jet)/1AU)**(1/2) M(Sun)/year, during their August - September maximum, which corresponds to the emitting mass in jets, M(jet, emitting) ~ 6xE-10(Rjet)/1AU)^{3/2} M(Sun). During their lifetime, the jets released the total mass of M(jet, total) approx 7.4x1E-7 M(Sun). Evolution in the rapid photometric variability and asymmetric ejection of jets around the optical maximum can be explained by a disruption of the inner parts of the disk caused by radiation-induced warping of the disk.Comment: 31 pages, 9 figures, 2 tables, accepted for Ap

The problem of a metal impurity in an oxide: ab-initio study of electronic and structural properties of Cd in Rutile TiO2

In this work we undertake the problem of a transition metal impurity in an oxide. We present an ab-initio study of the relaxations introduced in TiO2 when a Cd impurity replaces substitutionally a Ti atom. Using the Full-Potential Linearized-Augmented-Plane-Wave method we obtain relaxed structures for different charge states of the impurity and computed the electric-field gradients (EFGs) at the Cd site. We find that EFGs, and also relaxations, are dependent on the charge state of the impurity. This dependence is very remarkable in the case of the EFG and is explained analyzing the electronic structure of the studied system. We predict fairly anisotropic relaxations for the nearest oxygen neighbors of the Cd impurity. The experimental confirmation of this prediction and a brief report of these calculations have recently been presented [P.R.L. 89, 55503 (2002)]. Our results for relaxations and EFGs are in clear contradiction with previous studies of this system that assumed isotropic relaxations and point out that no simple model is viable to describe relaxations and the EFG at Cd in TiO2 even approximately.Comment: 11 pages, 8 figures, Revtex 4, published in Physical Review

Understanding the effects of fungal spillover on tropical forest seedling communities

Deforestation rates of tropical forests have led to a massive increase in forest edge habitats globally. One of the foremost fragmentation types of concern is agriculture, which can introduce new pathogenic fungi into tropical forests via spillover. The long-term effects these spillovers will have on tropical forests are largely unknown but have the potential to influence overall community diversity. This study utilizes both a theoretical model that uses a modified Lotka-Volterra equation and an empirical study in Costa Rican forests to investigate how pathogenic fungal spillover will affect tree seedling diversity. Theoretically, spillover had various effects on plants, depending on a species’ competitive strength, palatability to the pathogen, and overall pathogen strength. In all cases, coexistence of species was inhibited by spillover at the forest edge, however it promoted more instances of coexistence at the interior and rescued weaker plant species when targetting the superior competitor. The study in Costa Rica found that fungal pathogens had no effect on survival but varying effects on overall diversity. This indicates that fungal spillover has the potential to weaken or strengthen mechanisms driving diversity and may be forest-specific, no longer defined by traditional diversity hypotheses. Overall, this study highlights the importance of understanding the effects of fungal spillover and how it may potentially influence the growth and survival of tree seedlings in fragmented tropical forests across the globe

Brewer's Spent Grain to Bioethanol through a Hybrid Saccharification and Fermentation Process

Brewer's spent grain, without being pre-treated, has been investigated for bioethanol production through a Hybrid Saccharification and Fermentation (HSF) process with high solid loading. HSF experiments were performed in a 2 L bioreactor where Cellic ® CTec2 was used to perform the enzymatic hydrolysis, and Saccharomyces Cerevisiae was used for the fermentation. The reaction environment was first set to favour saccharification. Then, after 26 h, the reactor was inoculated with the yeast. The results evidenced the presence of glucose, xylose, and arabinose after the conversion of cellulose and hemicellulose and a rapid depletion of glucose after adding the yeast. The pentoses were also consumed, but with a much slower reaction rate. Almost four hours after adding the yeast, the amount of ethanol had reached a maximum and then began to decrease as microorganisms began to use ethanol as a substrate after glucose depletion. The obtained ethanol yield, evaluated with respect to the theoretical value, was equal to 72%

Chemometric Models Applied to Raman Spectroscopy for Bioprocess Monitoring

This work investigates the development of a Raman spectroscopy-based sensor for the quantitative analysis of products obtained from the fermentation to ethanol of the hydrolyzed product of brewer’s spent grain. Partial least squares (PLS) and variable importance in projection (VIP) methods were applied in order to correlate the information contained in the Raman spectra to the concentration of the compounds investigated