Dirac's hole theory versus quantum field theory

Dirac's hole theory and quantum field theory are usually considered equivalent to each other. For models of a certain type, however, the equivalence may not hold as we discuss in this Letter. This problem is closely related to the validity of the Pauli principle in intermediate states of perturbation theory.Comment: No figure

The difference between Dirac's hole theory and quantum field theory

Dirac's hole theory and quantum field theory are generally thought to be equivalent. In fact field theory can be derived from hole theory through the process of second quantization. However, it can be shown that problems worked in both theories yield different results. The reason for the difference between the two theories will be examined and the effect the this difference has on the way calculations are done in quantum theory will be examined.Comment: Accepted as a chapter in "Progress in Quantum Physics Research" Nova Science Publishers. 62 page

Controlling a resonant transmission across the δ′\delta'-potential: the inverse problem

Recently, the non-zero transmission of a quantum particle through the one-dimensional singular potential given in the form of the derivative of Dirac's delta function, $\lambda \delta'(x)$, with $\lambda \in \R$, being a potential strength constant, has been discussed by several authors. The transmission occurs at certain discrete values of $\lambda$ forming a resonance set ${\lambda_n}_{n=1}^\infty$. For $\lambda \notin {\lambda_n}_{n=1}^\infty$ this potential has been shown to be a perfectly reflecting wall. However, this resonant transmission takes place only in the case when the regularization of the distribution $\delta'(x)$ is constructed in a specific way. Otherwise, the $\delta'$-potential is fully non-transparent. Moreover, when the transmission is non-zero, the structure of a resonant set depends on a regularizing sequence $\Delta'_\varepsilon(x)$ that tends to $\delta'(x)$ in the sense of distributions as $\varepsilon \to 0$. Therefore, from a practical point of view, it would be interesting to have an inverse solution, i.e. for a given $\bar{\lambda} \in \R$ to construct such a regularizing sequence $\Delta'_\varepsilon(x)$ that the $\delta'$-potential at this value is transparent. If such a procedure is possible, then this value $\bar{\lambda}$ has to belong to a corresponding resonance set. The present paper is devoted to solving this problem and, as a result, the family of regularizing sequences is constructed by tuning adjustable parameters in the equations that provide a resonance transmission across the $\delta'$-potential.Comment: 21 pages, 4 figures. Corrections to the published version added; http://iopscience.iop.org/1751-8121/44/37/37530

Relação entre poda verde e o uso de material refletivo com a qualidade de pêssegos ´Eldorado´.

bitstream/item/33532/1/documento-134.pd

Comparación del crecimiento, propiedades del suelo y análisis químico del follaje entre masas puras y mixtas

Ecosystems with mixed species compared to the ones with pure compositions provide a broader range of options in the fields of biodiversity, conservation, protection and restoration. Industrial plantations in Portugal are mostly monocultures with the predominance of coniferous forests, so the introduction of broadleaves could be important for the biodiversity and sustainability of Portuguese forests. This study aims to present and discuss field data from pure and mixed-species plantations of European chestnut (Castanea sativa Mill.) and douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] with different intercropping densities in a total of 5 treatments with two replicate blocks. In respect to growth, the results showed significant difference (P < 0.05, Scheffe) between treatments for survival and basal area. Diameter breast height (DBH), total and top height of the individual Castanea tree was positively affected by the presence of Pseudotsuga. In general, soil properties results showed a higher fertility for mixed treatments compared with pure ones. Statistically differences (P < 0.05, Scheffe) were observed in pH, P, Mn and in the exchangeable acidity. Results for foliar analysis in N, P, Ca and K concentrations are higher for mixed treatments. The obtained results from this study indicate that mixed plantations have a positive effect in the productivity of the Castanea.Los ecosistemas con especies mixtas, en comparación con las masas puras, proporcionan una gama más amplia de opciones en el campo de la biodiversidad, la conservación, la protección y la restauración. Las plantaciones industriales de Portugal son en su mayoría monocultivos con predominio de bosques de coníferas, por lo que la introducción de frondosas podría ser importante para la biodiversidad y la sostenibilidad de los bosques portugueses. Este estudio tiene como objetivo presentar y discutir los datos de campo de plantaciones puras y mixtas de especies de castaño y de abeto de Douglas con diferentes densidades de cultivo intercalado en un total de 5 tratamientos con dos bloques. En lo que respecta al crecimiento, los resultados mostraron diferencias significativas (P < 0,05) entre los tratamientos para la supervivencia y el área basal. El diámetro normal (DAP), la altura total y la altura dominante del Castaño se vio afectado positivamente por la presencia de Pseudotsuga. En general, las propiedades del suelo mostraron una mayor fecundidad de los tratamientos mixtos en comparación con los puros. Se observaron diferencias estadísticamente significativas (P < 0,05) en el pH, P, Mn y en la acidez intercambiable. Los resultados de los análisis foliares de N, P, Ca y la concentración de K son mayores para los tratamientos mixtos. Los resultados obtenidos de este estudio indican que las plantaciones mixtas tienen un efecto positivo en la productividad del Castaño

Impact of cattle slurry treatment by separation and acidification on gaseous emissions after soil application

Objectives: Cattle-slurry management became a priority in many livestock farms and slurry treatment is used to increase the fertilizer value of slurry and/or minimize its environmental impact. Indeed, significant emissions of ammonia (NH3) and greenhouse gases (GHG) as nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) can occur during and after slurry application to soil. Application of acidified slurry or liquid fraction (LF) obtained by solid-liquid separation are two alternatives to raw slurry application that have proven to be efficient to minimize ammonia emissions. However, few is known about its effect on GHG emissions. The aim of the present work was to assess the efficiency of cattle slurry treatment by acidification and/or solid liquid separation to mitigate ammonia (NH3) and greenhouse gases (GHG) emissions following surface application to a sandy loam soil

Uso combinado de dados NDVI/MODIS dos satélites Terra e Aqua no monitoramento multi-temporal de áreas agrícolas.

O objetivo deste estudo foi analisar a utilização combinada de dados de NDVI do sensor MODIS (Moderate-resolution Imaging Spectroradiometer) provenientes de duas plataformas orbitais - Terra e Aqua - na geração de perfis temporais em áreas agrícolas.SBSR 2013