Go Vegan

La méthode de mesure, due à Vernotte, des caractéristiques thermophysiques d'une plaque d'un matériau donné par application d'un film chauffant sur une face de la plaque et enregistrement en fonction du temps de l'évolution des températures de la face opposée, et éventuellement de la face chauffée, a été souvent mise en application. On précise ici quelles conditions doivent être remplies et quelles sont les incidences de divers défauts éventuels du montage quand on applique la variante due à Krischer de cette méthode. Un dispositif expérimental très simple a permis de corroborer ces considérations théoriques

Soil Moisture and Porosity Affects the Abundance and Distribution of Ageratum houstonianum

Introduction: Ageratum houstonianum is an herbaceous, drought-tolerant plant also known as Blue billygoat weed. It grows well in drained soil and shaded areas. Soil moisture and porosity are two abiotic factors that affect the abundance and distribution of A. houstonianum. An ideal condition for plants to grow includes a greater amount of soil moisture and porosity. Higher porosity would mean that there is a greater number of pores, which would result in more significant plant nutrients because of its ability to retain more water. The purpose of this research was to see how soil moisture and porosity based on the gradient with regards to distance from the tree impact the abundance and distribution of A. houstonianum. Materials and Methods: The belt transect method was used to test the soil moisture and porosity, and three belts with four quadrants in each were formed. For each of the belts, the first two quadrants closer to the tree were called zone 1, and the last two quadrants were labeled as zone 2. We hypothesized that there was an increase in abundance and distribution further away from the tree. Abundance was calculated by finding the density of the total number of species over each quadrant area. Soil samples were collected to test the soil moisture and porosity. Paired two-sample t-tests and ANOVA single factor tests were performed. Results and Conclusion: The t-tests showed a difference between the relationship of abundance/moisture, abundance/porosity, and moisture/porosity. The ANOVA test compared the means of density/moisture/porosity between zone 1 and 2 to see if they were statistically different from each other. Based on the results, there was a decrease in the density as the distance from the tree increased. Soil moisture and porosity also decreased as the distance from the tree increased, which rejected the hypothesis. Closer to the tree, there was an increase in moisture, density, and porosity, which led to the abundance of A. houstonianum species because the ideal conditions were met

Covariant theory of asymptotic symmetries, conservation laws and central charges

Under suitable assumptions on the boundary conditions, it is shown that there is a bijective correspondence between equivalence classes of asymptotic reducibility parameters and asymptotically conserved n-2 forms in the context of Lagrangian gauge theories. The asymptotic reducibility parameters can be interpreted as asymptotic Killing vector fields of the background, with asymptotic behaviour determined by a new dynamical condition. A universal formula for asymptotically conserved n-2 forms in terms of the reducibility parameters is derived. Sufficient conditions for finiteness of the charges built out of the asymptotically conserved n-2 forms and for the existence of a Lie algebra g among equivalence classes of asymptotic reducibility parameters are given. The representation of g in terms of the charges may be centrally extended. An explicit and covariant formula for the central charges is constructed. They are shown to be 2-cocycles on the Lie algebra g. The general considerations and formulas are applied to electrodynamics, Yang-Mills theory and Einstein gravity.Comment: 86 pages Latex file; minor correction

Preoperative predictors of sternotomy need in mediastinal goiter management

BACKGROUND: The objective of this study was to identify the preoperative risk factors for patients in need of a sternotomy in the management of mediastinal goiters in order to provide better preoperative planning and patient consent. METHODS: We analyzed 98 patients who underwent surgery for mediastinal goiters (goiters extending below the thoracic inlet > or =3 cm with the neck in hyperextension) between 1995 and 2008. Twelve (12.2%) of the patients required a sternotomy. The patients' features were analyzed by the surgical approach performed. Logistic regression analysis was used to study which variables were influencing the surgical strategy. The receiver operating characteristic (ROC) curves were designed when appropriate. RESULTS: The analysis disclosed the following risk factors: radiologic extension of mediastinal goiters below the aortic arch (odds ratio [OR] = 32.87; 95% confidence interval [CI] = 4.04-267.12; p 160 months: OR = 22.8; 95% CI = 5.28-98.53; p < .0001). CONCLUSIONS: Sternotomy need for mediastinal goiter removal can be predicted; in such cases surgeons should not hesitate to perform it for minimizing complications

Characteristic cohomology of pp-form gauge theories

The characteristic cohomology $H^k_{char}(d)$ for an arbitrary set of free $p$-form gauge fields is explicitly worked out in all form degrees $k<n-1$, where $n$ is the spacetime dimension. It is shown that this cohomology is finite-dimensional and completely generated by the forms dual to the field strengths. The gauge invariant characteristic cohomology is also computed. The results are extended to interacting $p$-form gauge theories with gauge invariant interactions. Implications for the BRST cohomology are mentioned.Comment: Latex file, no figures, 44 page

Paraxial and nonparaxial polynomial beams and the analytic approach to propagation

We construct solutions of the paraxial and Helmholtz equations which are polynomials in their spatial variables. These are derived explicitly using the angular spectrum method and generating functions. Paraxial polynomials have the form of homogeneous Hermite and Laguerre polynomials in Cartesian and cylindrical coordinates respectively, analogous to heat polynomials for the diffusion equation. Nonparaxial polynomials are found by substituting monomials in the propagation variable $z$ with reverse Bessel polynomials. These explicit analytic forms give insight into the mathematical structure of paraxially and nonparaxially propagating beams, especially in regards to the divergence of nonparaxial analogs to familiar paraxial beams.Comment: 3 pages, Optics Letters styl

Gauge theories of spacetime symmetries

Gauge theories of conformal spacetime symmetries are presented which merge features of Yang-Mills theory and general relativity in a new way. The models are local but nonpolynomial in the gauge fields, with a nonpolynomial structure that can be elegantly written in terms of a metric (or vielbein) composed of the gauge fields. General relativity itself emerges from the construction as a gauge theory of spacetime translations. The role of the models within a general classification of consistent interactions of gauge fields is discussed as well.Comment: 8 pages, revtex; v2: minor improvements of text and formulas; v3: typo in formula after eq. (35) correcte

Nothing is in the air

It has often been argued that “there is something in the air” which makes firms in high-density environments—such as cities or clusters—more innovative. The co-location of firms facilitates the emergence of serendipity and casual encounters which promote innovation in firms. We assess this hypothesis using data from a survey of Norwegian firms engaged in innovation partnerships. The results indicate that there may be “much less in the air” than is generally assumed in the literature. The relationships conducive to innovation by Norwegian firms emerged as a consequence of purpose-built searches and had little to do with chance, serendipity, or “being there.”acceptedVersio