Lorentzian Vacuum Transitions in Ho\v{r}ava-Lifshitz Gravity

The vacuum transition probabilities for a Friedmann-Lema\^itre-Robertson-Walker universe with positive curvature in Ho\v{r}ava-Lifshitz gravity in the presence of a scalar field potential in the Wentzel-Kramers-Brillouin approximation are studied. We use a general procedure to compute such transition probabilities using a Hamiltonian approach to the Wheeler-DeWitt equation presented in a previous work. We consider two situations of scalar fields, one in which the scalar field depends on all the spacetime variables and other in which the scalar field depends only on the time variable. In both cases analytic expressions for the vacuum transition probabilities are obtained and the infrared and ultraviolet limits are discussed for comparison with the result obtained by using general relativity. For the case in which the scalar field depends on all spacetime variables we obtain that in the infrared limit it is possible to obtain a similar behavior as in general relativity, however in the ultraviolet limit the behavior found is completely opposite. Some few comments about possible phenomenological implications of our results are given. One of them is a plausible resolution of the initial singularity. On the other hand for the case in which the scalar field depends only on the time variable, the behavior coincides with that of general relativity in both limits, although in the intermediate region the probability is slightly altered.Comment: 26 pages, 2 figures. Some references adde

Scalar field inflation driven by a modification of the Heisenberg algebra

We study the modifications induced on scalar field inflation produced by considering a general modification of the Heisenberg algebra. We proceed by modifying the Poisson brackets on the classical theory whenever the corresponding quantum commutator is modified. We do not restrict ourselves to a specific form for such modification, instead we constrain the functions involved by the cosmological behaviour of interest. We present whenever possible the way in which inflation can be realized approximately via three slow roll Hubble parameters that depend on the standard slow roll parameters in a very different form than in the usual case and that can be less restrictive. Furthermore we find a general analytical solution describing an expanding universe with constant Hubble parameter that generalizes the standard cosmological constant case by restricting the form of the modification of the Heisenberg algebra. It is found that even if such modification can be neglected in some limit and the cosmological constant is set to zero in that limit, the exponential expansion is present when the modification is important. Thus an appropriate modification of the Heisenberg algebra is sufficient to produce an exponentially expanding universe without the need of any other source.Comment: 34 pages, 1 figur

Reduced graphene oxides as carbocatalysts in acceptorless dehydrogenation of N-heterocycles

The catalytic properties of graphene-derived materials are evaluated in acceptorless dehydrogenation of N-heterocycles. Among them, reduced graphene oxides (rGOs) are active (quantitative yields in 23 h) under mild conditions (130 °C) and act as efficient heterogeneous carbocatalysts. rGO exhibits reusability and stability at least during eight consecutive runs. Mechanistic investigations supported by experimental evidence (i.e., organic molecules as model compounds, purposely addition of metal impurities and selective functional group masking experiments) suggest a preferential contribution of ketone carbonyl groups as active sites for this transformation.

Características químicas de um latossolo influenciadas por diferentes tipos e doses de cinzas.

O objetivo deste trabalho foi determinar o efeito do tipo e doses de cinza sobre características químicas do solo

Taxa de decomposição de adubos verdes e disponibilidade de N influenciando o feijoeiro comum em sistema agroecológico de produção.

Os objetivos deste trabalho foram avaliar a produção de fitomassa, a quantidade de N fornecida por ela e a taxa de decomposição de adubos verdes e seus efeitos na cultura do feijoeiro comum em sistema de produção agroecológica.bitstream/CNPAF-2010/29763/1/comt-175.pd

Programa computacional de simulação da produtividade para suporte a decisão no plantio de milho.

O objetivo deste trabalho foi desenvolver um programa computacional que simule a produção do milho, sendo utilizado como um suporte a decisão para o produtor. O algoritmo utilizado consta de modelos de regressão obtidos a partir de resultados de uma pesquisa de campo realizada na Embrapa Milho e Sorgo, sob condições de plantio direto e com modelos de estimativas de produção obtidos em tabelas e resultados de outros trabalhos constantes na literatura. O pacote computacional resultante é completo o suficiente para a simulação da produtividade em um determinado solo e implantação e uso por produtores (usuários) como uma ferramenta de Agricultura de Precisão, capaz de auxiliar à tomada de decisão. O programa é de fácil manuseio, onde o usuário pode optar em digitar os valores que representam as condições do solo de plantio, ou resgatar valores de um banco de dados histórico que pode ser implementado pelo próprio usuário, ou obtido através da Embrapa que disponibilizará, através da rede mundial de computadores, condições de solo de todo o país. A saída do programa é de simples interpretação e fornece, entre outros resultados, a produtividade máxima de um solo sob as condições de simulação, auxiliando o produtor na tomada de decisão quanto a aplicação de insumos

Swelling-collapse transition of self-attracting walks

We study the structural properties of self-attracting walks in d dimensions using scaling arguments and Monte Carlo simulations. We find evidence for a transition analogous to the \Theta transition of polymers. Above a critical attractive interaction u_c, the walk collapses and the exponents \nu and k, characterising the scaling with time t of the mean square end-to-end distance ~ t^{2 \nu} and the average number of visited sites ~ t^k, are universal and given by \nu=1/(d+1) and k=d/(d+1). Below u_c, the walk swells and the exponents are as with no interaction, i.e. \nu=1/2 for all d, k=1/2 for d=1 and k=1 for d >= 2. At u_c, the exponents are found to be in a different universality class.Comment: 6 pages, 5 postscript figure

Soil Health – It\u27s Not All Biology

Soil Health research tends to bias to a biology/microbiology emphasis. We believe this bias neglects important physical and chemical interactions in soil that are crucial to soil function. We offer several examples illustrating this bias, and how it may misrepresent management practices that have the greatest influence on Soil Health. Four suggestions are given as approaches to mitigate this bias. By appreciating soil structure as a foundation for Soil Health and its microbial community, we believe better recommendations can be made to assist the farm community in its stewardship of soil as a critical natural resource

Spectroscopic classification of X-ray sources in the Galactic Bulge Survey

We present the classification of 26 optical counterparts to X-ray sources discovered in the Galactic Bulge Survey. We use (time-resolved) photometric and spectroscopic observations to classify the X-ray sources based on their multi-wavelength properties. We find a variety of source classes, spanning different phases of stellar/binary evolution. We classify CX21 as a quiescent cataclysmic variable (CV) below the period gap, and CX118 as a high accretion rate (nova-like) CV. CXB12 displays excess UV emission, and could contain a compact object with a giant star companion, making it a candidate symbiotic binary or quiescent low mass X-ray binary (although other scenarios cannot be ruled out). CXB34 is a magnetic CV (polar) that shows photometric evidence for a change in accretion state. The magnetic classification is based on the detection of X-ray pulsations with a period of 81 $\pm$ 2 min. CXB42 is identified as a young stellar object, namely a weak-lined T Tauri star exhibiting (to date unexplained) UX Ori-like photometric variability. The optical spectrum of CXB43 contains two (resolved) unidentified double-peaked emission lines. No known scenario, such as an AGN or symbiotic binary, can easily explain its characteristics. We additionally classify 20 objects as likely active stars based on optical spectroscopy, their X-ray to optical flux ratios and photometric variability. In 4 cases we identify the sources as binary stars.Comment: Accepted for publication in MNRA