Charged black holes: Wave equations for gravitational and electromagnetic perturbations

A pair of wave equations for the electromagnetic and gravitational perturbations of the charged Kerr black hole are derived. The perturbed Einstein-Maxwell equations in a new gauge are employed in the derivation. The wave equations refer to the perturbed Maxwell spinor $\Phi_0$ and to the shear $\sigma$ of a principal null direction of the Weyl curvature. The whole construction rests on the tripod of three distinct derivatives of the first curvature $\kappa$ of a principal null direction.Comment: 12 pages, to appear in Ap.

Dark-bright mixing of interband transitions in symmetric semiconductor quantum dots

In photoluminescence spectra of symmetric [111] grown GaAs/AlGaAs quantum dots in longitudinal magnetic fields applied along the growth axis we observe in addition to the expected bright states also nominally dark transitions for both charged and neutral excitons. We uncover a strongly non-monotonous, sign changing field dependence of the bright neutral exciton splitting resulting from the interplay between exchange and Zeeman effects. Our theory shows quantitatively that these surprising experimental results are due to magnetic-field-induced \pm 3/2 heavy-hole mixing, an inherent property of systems with C_3v point-group symmetry.Comment: 5 pages, 3 figure

Designing silk fibroin-based matrices with ionic liquids for tissue engineering strategies using human adipose stem cells

Silk (SF) is an attractive biomaterial to be used in tissue engineering applications because of its excellent mechanical properties and biocompatibility [1, 2]. In this work, the cellular response of silk hydrogels produced through dissolution of this protein in ionic liquids (ILs) was investigated. For that, degummed fibers obtained from the cocoons of mulberry silkworm (Bombyx mori) were dissolved in an IL and the solution was gelified in ethanol, followed by IL removal from gels using soxhlet extraction. The fabricated hydrogels were characterized biochemically and biophysically by detecting amino acid composition, FTIR, SEM and mechanical testing (DMA). For in vitro assessment, human adipose stem cells (hASCs) were seeded in the hydrogels and cultured for different time periods. The resulting hydrogels have a rubbery consistency, homogeneous surface and viscoelastic behavior. Additionally, no differences on amino acid composition were found, indicating that the silk composition was kept. Confocal images confirmed cell attachment and alignment of actin filaments within the hydrogel matrix with well-develop nuclei. The MTS assay demonstrated the metabolic activity of hASCs in contact with hydrogels up to 28 days. Furthermore, the results of DNA quantification showed that hASCs are able to proliferate during studied period. These results indicated that (i) the efficiency of IL removal resulted in hydrogels with minimal cytotoxicity; and (ii) positive cellular response of the materials surface for the adhesion and proliferation of hASCs. SEM observations corroborated with the results obtained from MTS and DNA suggested that cells are able to migrate at different levels within the structure. These findings indicated that silk hydrogels produced using ILs may be potential candidates for tissue engineering strategies, namely cartilage regeneration

Mineralization of chitosan membrane using a double diffusion system for bone related applications

Chitosan membranes were subjected to a pre-treatment in a double diffusion system, with a calcium solution in one chamber and a phosphate solution in the other chamber. Both chambers were separated by the chitosan membrane and subject to three mineralization periods (5, 10 and 15 minutes). After this pre-treatment the bioactivity of the different calcium phosphate coatings formed was tested for different periods of immersion time, 7, 14 and 21 days at room temperature and 37ºC, in acellular simulated body fluid (1.0x). The results obtained demonstrated that the calcium phosphate coatings formed during the pre-treatment process are bioactive. It was found that the calcification is effective just in the side of the membrane exposed to the calcium solution chamber. This enabled to develop membranes with asymmetric osteoinductive properties that can be useful in different orthopedic applications

Electromagnetic waves in NUT space: Solutions to the Maxwell equations

In this paper, using the Newman-Penrose formalism, we find the Maxwell equations in NUT space and after separation into angular and radial components solve them analytically. All the angular equations are solved in terms of Jaccobi polynomials. The radial equations are transformed into Hypergeometric and Heun's equations with the right hand sides including terms of different order in the frequency of the perturbation which allow solutions in the expansion of this parameter.Comment: 19 pages, Revtex format, Minor changes including an extention of the discussion and typos correction, (Extended version of the article presented to the GR16 conference, July 15-21 2001, Durban, South Africa

The transferencial relation beyond the interpretation : reflections from the theory of Winnicott.

Este artigo reflete sobre a importância de pensar a relação transferencial na clínica psicanalítica para além da interpretação. Para isso, utiliza-se a concepção de Winnicott como referencial teórico, sendo ressaltadas a noção de holding, a regressão à dependência e a questão do uso de objetos e sua influência sobre a técnica da interpretação. Winnicott revela que na clínica com alguns pacientes, em especial os autistas e psicóticos, o objetivo da análise, antes de fornecer interpretações, é proporcionar um ambiente suficientemente bom a partir do qual o sujeito pode retomar o processo de constituição de si mesmo e da externalidade do mundo.This article reflects about the importance of thinking the transferencial relation in the psychoanalytic clinic beyond the interpretation. For this, the Winnicott’s concept is used as theoretical reference, highlighting the concept of holding, regression to dependence and the question of the use of objects and its influence on the technique of interpretation. Winnicott shows that in the clinic, with some patients, particularly autistic and psychotic, before providing interpretation, the objective of the analysis is to provide a good environment from which the subject can retake the constitution process of himself/herself and of the externality of the world

Stem cell factor induces phosphatidylinositol 3'-kinase-dependent Lyn/Tec/Dok-1 complex formation in hematopoietic cells

Stem cell factor (SCF) has an important role in the proliferation, differentiation, survival, and migration of hematopoietic cells. SCF exerts its effects by binding to cKit, a receptor with intrinsic tyrosine kinase activity. Activation of phosphatidylinositol 3'-kinase (PI3-K) by cKit was previously shown to contribute to many SCF-induced cellular responses. Therefore, PI3-K-dependent signaling pathways activated by SCF were investigated. The PI3-K-dependent activation and phosphorylation of the tyrosine kinase Tec and the adapter molecule p62Dok-1 are reported. The study shows that Tec and Dok-1 form a stable complex with Lyn and 2 unidentified phosphoproteins of 56 and 140 kd. Both the Tec homology and the SH2 domain of Tec were identified as being required for the interaction with Dok-1, whereas 2 domains in Dok-1 appeared to mediate the association with Tec. In addition, Tec and Lyn were shown to phosphorylate Dok-1, whereas phosphorylated Dok-1 was demonstrated to bind to the SH2 domains of several signaling molecules activated by SCF, including Abl, CrkL, SHIP, and PLCgamma-1, but not those of Vav and Shc. These findings suggest that p62Dok-1 may function as an important scaffold molecule in cKit-mediated signaling

Radiative multipole moments of integer-spin fields in curved spacetime

Radiative multipole moments of scalar, electromagnetic, and linearized gravitational fields in Schwarzschild spacetime are computed to third order in v in a weak-field, slow-motion approximation, where v is a characteristic velocity associated with the motion of the source. To zeroth order in v, a radiative moment of order l is given by the corresponding source moment differentiated l times with respect to retarded time. At second order in v, additional terms appear inside the spatial integrals. These are near-zone corrections which depend on the detailed behavior of the source. At third order in v, the correction terms occur outside the spatial integrals, so that they do not depend on the detailed behavior of the source. These are wave-propagation corrections which are heuristically understood as arising from the scattering of the radiation by the spacetime curvature surrounding the source. Our calculations show that the wave-propagation corrections take a universal form which is independent of multipole order and field type. We also show that in general relativity, temporal and spatial curvatures contribute equally to the wave-propagation corrections.Comment: 34 pages, ReVTe