Moments of inertia for solids of revolution and variational methods

We present some formulae for the moments of inertia of homogeneous solids of revolution in terms of the functions that generate the solids. The development of these expressions exploits the cylindrical symmetry of these objects, and avoids the explicit use of multiple integration, providing an easy and pedagogical approach. The explicit use of the functions that generate the solid gives the possibility of writing the moment of inertia as a functional, which in turn allows us to utilize the calculus of variations to obtain a new insight into some properties of this fundamental quantity. In particular, minimization of moments of inertia under certain restrictions is possible by using variational methods.Comment: 6 pages, 6 figures, LaTeX2e. Two paragraphs added. Minor typos corrected. Version to appear in European Journal of Physic

Space-time inhomogeneity, anisotropy and gravitational collapse

We investigate the evolution of non-adiabatic collapse of a shear-free spherically symmetric stellar configuration with anisotropic stresses accompanied with radial heat flux. The collapse begins from a curvature singularity with infinite mass and size on an inhomogeneous space-time background. The collapse is found to proceed without formation of an even horizon to singularity when the collapsing configuration radiates all its mass energy. The impact of inhomogeneity on various parameters of the collapsing stellar configuration is examined in some specific space-time backgrounds.Comment: To appear in Gen. Relativ. Gra

The nature of domain walls in ultrathin ferromagnets revealed by scanning nanomagnetometry

The recent observation of current-induced domain wall (DW) motion with large velocity in ultrathin magnetic wires has opened new opportunities for spintronic devices. However, there is still no consensus on the underlying mechanisms of DW motion. Key to this debate is the DW structure, which can be of Bloch or N\'eel type, and dramatically affects the efficiency of the different proposed mechanisms. To date, most experiments aiming to address this question have relied on deducing the DW structure and chirality from its motion under additional in-plane applied fields, which is indirect and involves strong assumptions on its dynamics. Here we introduce a general method enabling direct, in situ, determination of the DW structure in ultrathin ferromagnets. It relies on local measurements of the stray field distribution above the DW using a scanning nanomagnetometer based on the Nitrogen-Vacancy defect in diamond. We first apply the method to a Ta/Co40Fe40B20(1 nm)/MgO magnetic wire and find clear signature of pure Bloch DWs. In contrast, we observe left-handed N\'eel DWs in a Pt/Co(0.6 nm)/AlOx wire, providing direct evidence for the presence of a sizable Dzyaloshinskii-Moriya interaction (DMI) at the Pt/Co interface. This method offers a new path for exploring interfacial DMI in ultrathin ferromagnets and elucidating the physics of DW motion under current.Comment: Main text and Supplementary Information, 33 pages and 12 figure

Does rotation generate a massive string ?

The properties of a stationary massive string endowed with intrinsic angular momentum are investigated. The spacetime is generated by an "improper" time translation combined with uniform rotation. The mass per unit length of the string is proportional to the angular velocity $\omega$. The spacetime is Minkowskian geometrically but the topology is nontrivial thanks to the event horizon located on the surface $r = 0$ (similar with Rindler's spacetime) and to the deficit angle generated by rotation. The Sagnac time delay is calculated. It proves to be nonvanishing even when $\omega = 0$ due to the intrinsic spin of the string.Comment: 4 pages, minor changes, talk given at the XXIXth Spanish Relativity Meeting (ERE 2006), Palma de Mallorca, Spain, Sept. 4 - 8, 2006, appeared in Jour. Phys. : Conf. Ser. 66 (2007) 01205

Efecto de dos dietas: alimento comercial más complemento (semolina, melaza y lactobacillus acidophilus) vs. alimento comercial para el crecimiento de post-larvas de camarón litopenaeus vannamei

Feed constitutes the main element of the production cost in shrimp farming and due to this fact it is considered as the factor of greatest economic importance in this activity. Much has been studied about the nutritional requirements of the different species of shrimp that are farmed in the world, and we are getting closer to designing a diet that guarantees meeting all the needs of these organisms. (Vega, et al. 2000). With the completion of this research, it is necessary to verify which of the two types of diets is more profitable with respect to their growth, if using commercial feed plus supplement (semolina, molasses, Lactobacillus acidophilus) vs. Commercial food. That is why with this work it is intended to provide alternatives to the producer, since this has a great importance in the aquaculture field with respect to food. Shrimp farming is one of the fastest growing aquaculture sectors. Therefore, the need to create a diet that improves the quality, growth and development of organisms is essential, which would benefit producers with a more efficient food in the rearing of organisms, obtaining a higher rate of growth, productive yield , growth rate and survival.La alimentación constituye el elemento principal del costo de producción en la camaronicultura y debido a este hecho es considerado como el factor de mayor importancia económica en esta actividad. Mucho se ha estudiado acerca de los requerimientos nutricios de las diferentes especies de camarón que se cultivan en el mundo, y cada vez estamos más cerca del diseño de una dieta que garantice cumplir con todos las necesidades de estos organismos. (Vega,  et al. 2000).Con la realización de esta investigación se requiere comprobar cuáles de los dos tipos de dietas es más rentable con respecto a su crecimiento, si utilizando  Alimento comercial más complemento (semolina, melaza, Lactobacillus acidophilus) vs. Alimento comercial.Es por esto que con este trabajo se pretende brindar alternativas al productor, ya que este posee una gran importancia en el ámbito acuícola con respecto a la alimentación.La crianza de camarón es uno de los sectores de la acuicultura con más rápido crecimiento. Por lo tanto la necesidad de crear una dieta que mejore la calidad, el crecimiento y desarrollo de los organismos es indispensable, lo que beneficiaría a los productores con un alimento más eficiente en la crianza de los organismos obteniendo un mayor ritmo de crecimiento, rendimiento productivo, tasa de crecimiento y sobrevivencia

Test results for the V0 detector in ALICE

ALIC

Application of Chlorella sp. and Scenedesmus sp. in the bioconversion of urban leachates into industrially relevant metabolites

This paper explores the ability of Chlorella sp. and Scenedesmus sp. to convert landfill leachates into usable metabolites. Different concentrations (0.5, 1, 5, and 10% v/v) of leachate coupled with an inorganic carbon source (Na2CO3, and NaHCO3) were tested to improve biomass production, metabolites synthesis, and removal of NO3 and PO4 . The result shows that both strains can effectively grow in media with up to 5% (v/v) leachate, while significantly reducing the concentrations of NO3, and PO4 (80 and 50%, respectively). The addition of NaHCO3 as a carbon source improved the final concentration of biomass, lipids, carbohydrates, and the removal of NO3 and PO4 in both strains

Argentine plant extracts active against polymerase and ribonuclease H activities of HIV-1 reverse transcriptase

Lipophilic and hydrophilic extracts of four Argentine plants (Gamochaeta simplicaulis Cabr. 1, Achyrocline flaccida Wein. D. C. 2, Eupatorium buniifolium H. et A. 3, and Phyllanthus sellowianus Muell. Arg. 4) were examined in vitro for their ability to inhibit the polymerase and ribonuclease H (RNase H) activities of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) (wild and Y181C mutant types). The active extracts were also examined as inhibitors of viral replication in HLT4LacZ-1IIIB cell cultures, evaluating their cytotoxicity in parallel. Infusions 2I and 4I, among the crude extracts, showed the highest activity. These extracts were refractioned into four fractions; 2I4 and 4I4 were active as inhibitors of DNA-polymerase (wild and Y181C types) and RNase H activities. These fractions were potent as inhibitors of viral replication and were not cytotoxic. Refractionation of 2I4 yielded five new fractions, two of which, 2I4-4 and 2I4-5, showed notable activity. Refractionation of 4I4 yielded for new fractions; of these, 4I4-3 and 4I4-4 were active. The marked biological activity found in the infusion of A. flaccida and P. sellowianus makes them sufficiently attractive to be considered in the combined chemotherapy of the disease