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.

Characterization of chitosan and polycaprolactone membranes designed for wound repair application

Polycaprolactone (PCL) and chitosan (Ch) are nontoxic, biocompatible, and biodegradable polymers of vast interest for wound repair. The aim of this work was to prepare Ch/PCL membranes in different proportions (90:10 and 80:20 w/w) in the presence and absence of the surfactant Pluronic F68 (PF68). The membranes were evaluated regarding morphology, thermal behavior, and viscoelastic properties. Sample swelling and degradation in phosphate-buffered saline (PBS), simulated body fluid (SBF), and fetal bovine serum (FBS) were determined by differential scanning calorimetry (DSC) and dynamical mechanical analysis (DMA), while cell toxicity to L929 and Vero fibroblasts was evaluated using the MTT reduction assay and cell proliferation, by DNA quantification and confocal laser microscopy. After 60 days in SBF, marked Ch matrix loss and advanced degradation of PCL particles were noticed by scanning electron microscopy (SEM). No significant differences in melting temperature (Tm) and enthalpy (DHm) were detected by DSC. However, the surfactant increased the DHm. After 30 days, the membranes obtained in the presence of PF68 had absorbed more blood serum and were more degraded after exposure to simulated blood fluid for 30 days. All membranes had low cytotoxicity, and higher cell proliferation was noticed for samples obtained in the presence of the surfactant. In conclusion, the Ch/PCL membranes showed satisfactory degradability and biocompatibility, which enhances their potential for application in wound repair.The authors thank the PhD student Sofia Caridade (3B's Research Group-Universidade do Minho, Portugal) for her assistance in the DMA analyses. The financial support provided by the Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq-150984/2009-0) in Brazil is gratefully acknowledged for this work

Revealing the potential of squid chitosan-based structures for biomedical applications

In recent years, much attention has been given to different marine organisms, namely as potential sources of valuable materials with a vast range of properties and characteristics. In this work, β-chitin was isolated from the endoskeleton of the giant squid Dosidicus gigas and further deacetylated to produce chitosan. Then, the squid chitosan was processed into membranes and scaffolds using solvent casting and freeze-drying, respectively, to assess their potential biomedical application. The developed membranes have shown to be stiffer and less hydrophobic than those obtained with commercial chitosan. On the other hand, the morphological characterization of the developed scaffolds, by SEM and micro-computed tomography, revealed that the matrices were formed with a lamellar structure. The findings also indicated that the treatment with ethanol prior to neutralization with sodium hydroxide caused the formation of larger pores and loss of some lamellar features. The in vitro cell culture study has shown that all chitosan scaffolds exhibited a non-cytotoxic effect over the mouse fibroblast-like cell line, L929 cells. Thus, chitosan produced from the endoskeletons of the giant squid Dosidicus gigas has proven to be a valuable alternative to existing commercial materials when considering its use as biomaterial.This work was partially funded by FEDER through INTERREG III A Project Proteus and POCTEP Project IBEROMARE. The Portuguese Foundation for Science and Technology is gratefully acknowledged for post-doctoral grants of THS, JMO and SSS. The authors would also like to acknowledge to Dr Julio Maroto from the Fundacion CETMAR and Roi Vilela from PESCANOVA S.A, Spain, for the kind offer of squid pens and to Dr Ramon Novoa, Professor Ricardo Riguera and Professor Mariana Landin from the University of Santiago of Compostela for the SEC-MALLS measurements

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

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

Cell adhesion and proliferation onto chitosan-based membranes treated by plasma surface modification

Surface properties play a vita role in the functioning of a biomaterial. Cellular adherence and growth onto biomaterials can be enhanced in biomaterial modifications of their surface. In this work, the cell behaviour on chitosan membranes modified by argon and nitron-plasma treatments was investigated. Characterization of the membranes was performed using atomic force microscopy, contact angle measurements, and X-ray photoelectron spectroscopy. Cytotoxicity assessment and direct contact assay were carried out for untreated and treated chitosan membranes using L929 fibroblast-like cells. Cell morphology and cell viability were assessed to evaluate the cell attachment and proliferation. Changes in terms of roughness, surface chemistry, and hydrophilicity/hydrophobic balance of chitosan-modified membranes were observed. Regarding cell studies, the findings revealed that the extracts of all membranes do not induce cytotoxicity effects. Moreover, the in vitro assays evidenced an improvement of the L929 adhesion, and attachment when compared to untreated chitosan membranes. overall, the data obtained clearly demonstrated that plasma treatments constitute an effective way of improving the biocompatibility of chitosan membranes towards to their use in biomedical applications.S. M. Luna acknowledges the support of the Programme Alssan - The European Union Programme of High Level Scholarships for Latin America (scholarship No E04M041362CO) and Silva SS acknowledge the support of the Portuguese Foundation for Science and Technology, (SFRH/BPD/45307/2008). This work was also partially supported by the European Union-funded - STREP project HIPPOCRATES (NMP3-CT-2003-505758) and was carried out under the scope of European NoE EXPERTISSUES (NMP3-CT-2004-500283)

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

COMPARATIVE STUDY FOR MELANOMA SEGMENTATION IN SKIN LESION IMAGES

Melanoma is the leading cause of fatalities among skin can-cers and the discovery of the pathology in the early stagesis essential to increase the chances of cure. Computationalmethods through medical imaging are being developed tofacilitate the detection of melanoma. To interpret informa-tion in these images eciently, it is necessary to isolate theaected region. In our research, a comparison was made be-tween segmentation techniques, rstly a method based onthe Otsu algorithm, secondly the K-means clustering algo-rithm and nally,the U-net deep learning was developed.The tests performed on the PH2 images base had promisingresults, especially U-net

Silk hydrogels from non-mulberry and mulberry silkworm cocoons processed with ionic liquids

Matrices based on silk fibroin from the non-mulberry silkworm Antheraea mylitta and the mulberry silkworm Bombyx mori have demonstrated good applicability in regenerative medicine. However, the cocoons of A. mylitta are underutilized in part due to their lack of solubility in traditional organic solvents. Therefore, the present work investigates the solubilization and processing of degummed fibers obtained from the cocoons of both silkworm species into hydrogels using ionic liquids (ILs). The developed hydrogels exhibited a rubbery consistency, viscoelastic behavior and rapid degradation in the presence of protease XIV. Scanning electron and confocal microscopy images suggest that human adipose stem cells (hASCs) are able to adhere to and migrate at different levels within the hydrogel structures. Moreover, the MTS assay demonstrated the maintenance of cell metabolic activity for up to 28days, while DNA quantification showed that hASCs were able to proliferate on the seeded hydrogels. The findings indicate that complete IL removal from the fabricated hydrogels results in a positive hASCs cellular response. Thus the present approach provides a unique opportunity to broaden the processability and application of silk fibroin obtained from A. mylitta cocoons for regenerative medicine, namely cartilage regeneration.The authors acknowledge financial support from the Portuguese Foundation for Science and Technology (Grants SFRH/BPD/45307/2008 and SFRH/BD/64070/2009), the Fundo Social Europeu, and the Programa Diferencial de Potencial Humano. This work was partially supported by the FEDER through POCTEP 0330_IBERO-MARE_1_P and also by the Department of Biotechnology, Government of India. S.C.K. is grateful to R.L.R. and S.S.S. for their excellent hospitality during his stay at the 3B's laboratory, Guimaraes, Portugal. R.L.R. also offers his sincere thanks to S.C.K. for providing hospitality during his short visits to his laboratory in the Indian Institute of Technology, Kharagpur