On the Jacobi-Metric Stability Criterion

We investigate the exact relation existing between the stability equation for the solutions of a mechanical system and the geodesic deviation equation of the associated geodesic problem in the Jacobi metric constructed via the Maupertuis-Jacobi Principle. We conclude that the dynamical and geometrical approaches to the stability/instability problem are not equivalent.Comment: 14 pages, no figure

Geodesics in a quasispherical spacetime: A case of gravitational repulsion

Geodesics are studied in one of the Weyl metrics, referred to as the M--Q solution. First, arguments are provided, supporting our belief that this space--time is the more suitable (among the known solutions of the Weyl family) for discussing the properties of strong quasi--spherical gravitational fields. Then, the behaviour of geodesics is compared with the spherically symmetric situation, bringing out the sensitivity of the trajectories to deviations from spherical symmetry. Particular attention deserves the change of sign in proper radial acceleration of test particles moving radially along symmetry axis, close to the $r=2M$ surface, and related to the quadrupole moment of the source.Comment: 30 pages late

The Dynamical Behaviour of Test Particles in a Quasi-Spherical Spacetime and the Physical Meaning of Superenergy

We calculate the instantaneous proper radial acceleration of test particles (as measured by a locally defined Lorentzian observer) in a Weyl spacetime, close to the horizon. As expected from the Israel theorem, there appear some bifurcations with respect to the spherically symmetric case (Schwarzschild), which are explained in terms of the behaviour of the superenergy, bringing out the physical relevance of this quantity in the study of general relativistic systems.Comment: 14 pages, Latex. 4 figures. New references added. Typos corrected. To appear in Int. J. Theor. Phy

Thermal Conduction in Systems out of Hydrostatic Equilibrium

We analyse the effects of thermal conduction in a relativistic fluid, just after its departure from hydrostatic equilibrium, on a time scale of the order of thermal relaxation time. It is obtained that the resulting evolution will critically depend on a parameter defined in terms of thermodynamic variables, which is constrained by causality requirements.Comment: 16 pages, emTex (LaTex 2.09). To appear in Classical and Quantum Gravit

Simple solution of DC-offset rejection based phase-locked loop for single-phase grid-connected converters

Distributed Generators (DG) systems based on Renewable Energy Sources (RES) such as hydro, wind, and solar power plants have been spread widely due to their lower cost and the advanced capability of connecting them with the grid. The power generated from the DG must be shaped to be interfaced with the grid employing power electronics converters. The grid-connected power electronics converters must be synchronized with the grid (i.e., the same fundamental component of the grid frequency, phase, amplitude, and sequence). Synchronization techniques are employed to achieve accurate and fast grid synchronization between the converter and the grid. The existence of (DC-offset) in the input of Phase Locked Loop (PLL) caused synchronization problems as it causes oscillations in the estimated fundamental grid phase, frequency, and amplitude. In addition, the closed-loop system stability can be affected. This work proposes a simple technique for grid synchronization based on PLL with a phase angle correction. The proposed method was developed using Transfer Delay (TD) and Delay Signal Cancelation (DSC) operators; then, the small single model and stability analysis was employed. Several scenarios were developed to compare the proposed method with previous methods using MATLAB/Simulink tool. The scenarios involve introducing phase jumps, DC offsets, and amplitude changes to the grid voltage. Additionally, the grid frequency was also changed. The results show that the proposed PLL can solved the DC-offset problem using any delay time and fully synchronized with the grid. Moreover, the proposed PLL has the fastest dynamic response and shortest synchronization time over the other methods from literature

Fluorescence in situ hybridization analysis of CCND3 gene as marker of progression in bladder carcinoma

Supported by the grants SAF2007-64942 (Ministry of Education and Research, Madrid, Spain), P07-CVI-02974 and PI0003/2007 (Junta de Andalucia, Seville, Spain). Work at CIC is also funded by Instituto de Salud Carlos III III-FEDER (PI081828, PI110018, RD06/020/0059). José Luis Oróñez is supported by CSIC (Contratos Postdoctorales JAEDOC).[EN] The aim of this study was to assess patterns of CCND3 gene amplification in bladder cancer and correlate gene status with recurrence-free and progression-free survival. A sequential cohort series of 102 primary bladder tumor samples in which there was enough tissue material to assess CCND3 gene status by fluorescent in situ hybridization (FISH) was the study group. CCND3 gene FISH amplification present in 31.4 percent of bladder carcinomas, was related to tumor progression (p=0.021) and lower time to progression (mean+-SD; 25.75+-15.25 months) as compared to 33.29+-11.0 months in the CCND3 not amplified group (p=0.05). By immunohistochemistry, Cyclin D3 labeling index was higher in the CCND3 amplified group (mean+-SD, 76.69+-27.51) than in not amplified (mean+-SD, 21.57+-7.02) (p less than 0.0001). The univariate survival analysis showed CCND3 gene amplification to be associated to a shorter progression-free survival (p=0.020) together with WHO histological grade (p=0.001) and pT stage category (p less than 0.0001). Cox's regression analysis selected CCND3 amplification as an independent predictor of progression-free survival (p= 0.030, RR3.561, 95 percent CI 1.128-11.236) together with pT category (p less than 0.0001, RR5.834, 95 percent CI 2.364-14.395). Our FISH analysis suggests that CCND3 gene amplification is a marker of aggressiveness and might be a predictor of tumor progression in bladder urothelial carcinoma.Ministry of Education and Research, Madrid, Spain Junta de Andalucia, Seville, Spain Instituto de Salud Carlos III III-FEDER CSI