153 research outputs found
Vector magnetic hysteresis of hard superconductors
Critical state problems which incorporate more than one component for the
magnetization vector of hard superconductors are investigated. The theory is
based on the minimization of a cost functional
which weighs the changes of the magnetic field vector within the sample. We
show that Bean's simplest prescription of choosing the correct sign for the
critical current density in one dimensional problems is just a particular
case of finding the components of the vector . is
determined by minimizing under the constraint , with a bounded set. Upon the selection of
different sets we discuss existing crossed field measurements and
predict new observable features. It is shown that a complex behavior in the
magnetization curves may be controlled by a single external parameter, i.e.:
the maximum value of the applied magnetic field .Comment: 10 pages, 9 figures, accepted in Phys. Rev.
Critical state theory for nonparallel flux line lattices in type-II superconductors
Coarse-grained flux density profiles in type-II superconductors with
non-parallel vortex configurations are obtained by a proposed phenomenological
least action principle. We introduce a functional , which is minimized
under a constraint of the kind belongs to for the current density
vector, where is a bounded set. This generalizes the concept of
critical current density introduced by C. P. Bean for parallel vortex
configurations. In particular, we choose the isotropic case ( is a
circle), for which the field penetration profiles are derived when a
changing external excitation is applied. Faraday's law, and the principle of
minimum entropy production rate for stationary thermodynamic processes dictate
the evolution of the system. Calculations based on the model can reproduce the
physical phenomena of flux transport and consumption, and the striking effect
of magnetization collapse in crossed field measurements.Comment: The compiled TeX document length is 10 pages. Two figures (one page
each) are also included The paper is accepted for publication in Phys. Rev.
Let
Las poéticas explícitas como género
La abundancia de textos ensayísticos donde los autores literarios describen aspectos de la literatura relacionados con el proceso de creación, la función de la literatura o la imagen del poeta contrasta con la escasez de estudios teóricos sobre el género. Este trabajo indaga en los orígenes y características de estas poéticas explícitas para plantear los rasgos imprescindibles que permiten reconocerlas como un tipo de texto particular.Despite the abundance of texts where writers explain the creation process, the function of literature or the image of the poet, there is a significant lack of studies on the subject. This paper goes into detailed analysis of explicit poetics, from his origin and main characteristics to the essential features that let us recognize explicit poetics as a genre
A variational approach to the macroscopic electrodynamics of anisotropic hard superconductors
We consider the Bean's critical state model for anisotropic superconductors.
A variational problem solved by the quasi--static evolution of the internal
magnetic field is obtained as the -limit of functionals arising from
the Maxwell's equations combined with a power law for the dissipation.
Moreover, the quasi--static approximation of the internal electric field is
recovered, using a first order necessary condition. If the sample is a long
cylinder subjected to an axial uniform external field, the macroscopic
electrodynamics is explicitly determined.Comment: 24 pages, 15 figure
Glyceraldehyde-3-phosphate dehydrogenase is posttranslationally modified by NAD+ in enterohemorrhagic Escherichia coli
Comunicaciones a congreso
Corrosion activity and solubility in polar oils of three bis(trifluoromethylsulfonyl) imide/bis(trifluoromethylsulfonyl) amide ([NTF2]) anion-based ionic liquids.
The corrosion behaviour and solubility of three bis(trifluoromethylsulfonyl)amide1 ([NTf2]) anion-based ionic liquids: 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([C12MIM][NTf2]), tributylmethylammonium bis(trifluoromethylsulfonyl)amide ([N4441][NTf2]), and methyltrioctylammonium bis(trifluoromethylsulfonyl)amide ([N1888][NTf2]), as a component in a mixture with different base oils were analysed. Six polar oils suitable for use in lubrication were utilized as base oil. Solubility tests were performed by using turbidimetry, and corrosion was checked at 4 v/v% by examining the roughness and chemical composition of the surface after 21 days. The results showed that long carbon chains in the cation improve the solubility greatly in diesters and slightly in polyolesters. Corrosion was not detected at this concentration
Modelo de aprovechamiento de aguas lluvias en zonas de pobreza extrema
Las ventajas de captar agua lluvia en un entorno natural son: agua extremadamente limpia en comparación con otras fuentes de agua dulce disponibles, recurso esencialmente gratuito e independiente de empresas suministradoras habituales y que requiere de infraestructura sencilla para su captación, almacenamiento y distribución. El sistema de captación del agua lluvia permite almacenarla y posteriormente someter a tratamiento la que se utilizará para el consumo humano. A este sistema se le denomina CATDALL, que fue el prototipo resultado final del desarrollo del proyecto, gracias al apoyo del Fondo para la Investigación en Educación Superior (FIES) y la Universidad Tecnológica de El Salvador (UTEC). El prototipo puede ser replicable en otros centros escolares, que presenten escasez de agua bajo las circunstancias que fueren o como simple alternativa de ahorro aprovechando un recurso natural que es gratuito.Investigación desarrollada bajo el convenio FIES-UTEC, 2008-2009Universidad Tecnológica de El Salvado
General critical states in type-II superconductors
The magnetic flux dynamics of type-II superconductors within the critical
state regime is posed in a generalized framework, by using a variational theory
supported by well established physical principles. The equivalence between the
variational statement and more conventional treatments, based on the solution
of the differential Maxwell equations together with appropriate conductivity
laws is shown. Advantages of the variational method are emphasized, focusing on
its numerical performance, that allows to explore new physical scenarios. In
particular, we present the extension of the so-called double critical state
model to three dimensional configurations in which only flux transport
(T-states), cutting (C-states) or both mechanisms (CT-states) occur. The theory
is applied to several problems. First, we show the features of the transition
from T to CT states. Second, we give a generalized expression for the flux
cutting threshold in 3-D and show its relevance in the slab geometry. In
addition, several models that allow to treat flux depinning and cutting
mechanisms are compared. Finally, the longitudinal transport problem (current
is applied parallel to the external magnetic field) is analyzed both under T
and CT conditions. The complex interaction between shielding and transport is
solved.Comment: 21 figures, submitted for publicatio
Cyclopalladated Benzophenone Imines: Synthesis, Antitumor Activity, Cell Accumulation, DNA Interaction, and Cathepsin B Inhibition.
The synthesis of the endo five-membered cyclo-ortho-palladated benzophenone imines [Pd{C6H4(Ph)C═NR}]2(μ-X)2 [1 (X = OAc), 2 (X = Cl), a (R = phenyl), b (R = 1-naphthyl), c (R = benzyl), d (R = α-methylbenzyl)], and trans-N,P-[Pd{C6H4(Ph)C═NR}X(PPh3)] [3 (X = OAc), 4 (X = Cl), a (R = phenyl), b (R = 1-naphthyl), c (R = benzyl), d (R = α-methylbenzyl)] and the X-ray molecular structure of 1a, 1c, 1d, 4a, 4b, and 4c are reported. The antitumor activity, DNA interaction, and cathepsin B inhibition of palladium compounds a-d were studied and compared with those previously reported for palladium compounds e with R = H and compound 4f analogous to 4e but with a platinum(II) center. The IC50 values against a panel of human cancer cell lines allowed the establishment of a qualitative relationship between their structure and antitumor activity. Compounds 3e, 4e, and 4f were the most active ones in relation to their in vitro anticancer activity. Compounds 3e and 4e were about 4 times more active than cisplatin against the MDA-MB-231 and MCF-7 breast human cancer lines, and compound 4f was about 4 times more active than cisplatin against the cisplatin-resistant HCT-116 colon human cancer cell line. In addition, compound 3e was 3 times less cytotoxic than cisplatin toward the quiescent HUVEC cells. Accumulation of palladium compounds e and b in the MDA-MB-231 cell line was considerably greater than that of cisplatin in the same cell line, but palladium compounds b were noncytotoxic. Some of these complexes altered the DNA tertiary structure in a similar way to cisplatin but at higher concentration, and most cytotoxic ones did not present a high efficiency as cathepsin B inhibitors
- …