Large Amplitude Photocurrent In Photo-emf Experiments In Pure And Doped Absorbing Photorefractive Crystals

We report a mathematical formulation that successfully describes the holographic photocurrent produced in photo-emf experiments, with large oscillation amplitudes, in strongly absorbing photorefractive materials. The large amplitude produces a sensible enhancement of the photocurrent signal and in this way facilitates measurements. Accounting for bulk light absorption of the sample is essential in order to adequately describe the experiment. We measure pure and doped photorefractive Bi12TiO20 (BTO) crystals and show that these data are in excellent agreemnt with theory. From data fitting we are able to determine some material's parameters.4829 II953954Trofimov, G.S., Stepanov, S.I., (1986) Sov. Phys. Solid State, 28, pp. 1559-1562Petrov, M.P., Sokolov, I.A., Stepanov, S.I., Trofimov, G.S., (1990) J. Appl. Phys., 68, pp. 2216-2225Bittner, R., Meerholz, K., Stepanov, S., (1999) Appl. Phys. Lett., 74, pp. 3723-3725Korneev, N.A., Stepanov, S., (1993) J. Appl. Phys., 74, pp. 2736-2741Bryushinin, M.A., Dubrovsky, G.B., Sokolov, L.A., (1999) Appl. Phys. B, 68, pp. 871-87

Treatment of sunitinib-induced hypertension in solid tumor by nitric oxide donors

[Abstract] Vascular endothelial growth factor (VEGF) and its receptor (VEGFR) are overexpressed in the majority of renal cell carcinomas. This characteristic has supported the rationale of targeting VEGF-driven tumour vascularization, especially in clear cell RCC. VEGF-inhibiting strategies include the use of tyrosine kinase inhibitors (sunitinib, axitinib, pazopanib, and sorafenib) and neutralizing antibodies such as bevacizumab. Hypertension (HTN) is one of the most common adverse effects of angiogenesis inhibitors. HTN observed in clinical trials appears to correlate with the potency of VEGF kinase inhibitor against VEGFR-2: agents with higher potency are associated with a higher incidence of HTN. Although the exact mechanism by tyrosine kinase inhibitors induce HTN has not yet been completely clarified, two key hypotheses have been postulated. First, some studies have pointed to a VEGF inhibitors-induced decrease in nitric oxide synthase (NOS) and nitric oxide (NO) production, that can result in vasoconstriction and increased blood pressure. VEGF, mediated by PI3K/Akt and MAPK pathway, upregulates the endothelial nitric oxide synthase enzyme leading to up-regulation of NO production. So inhibition of signaling through the VEGF pathway would lead to a decrease in NO production, resulting in an increase in vascular resistance and blood pressure. Secondly a decrease in the number of microvascular endothelial cells and subsequent depletion of normal microvessel density (rarefaction) occurs upon VEGF signaling inhibition. NO donors could be successfully used not only for the treatment of developed angiogenesis-inhibitor-induced hypertension but also for preventive effects

Enhanced photocurrent in photo-emf experiments in pure and doped absorbing photorefractive crystals

We report a mathematical formulation that successfully describes the holographic photocurrent that is produced, in strongly absorbing photorefractive materials, by the action of a pattern of interference fringes of light vibrating sinusoidally with large amplitude. The large vibrating amplitude produces a sensible enhancement of the photocurrent signal and in this way facilitates measurements. We also show that taking account of the bulk light absorption of the sample is essential for adequately describing the experiment. We measure the first temporal harmonic of the photocurrent, without an externally applied field, as a function of the amplitude and the temporal frequency of the vibrating pattern of fringes and show that these data fit our theoretical model well. From this fit we are able to determine some material parameters for pure and doped photorefractive Bi12TiO20 crystals. (C) 2002 Optical Society of America.19122904291

Nonlinear electrodynamics and the Pioneer 10/11 spacecraft anomaly

The occurrence of the phenomenon known as photon acceleration is a natural prediction of nonlinear electrodynamics (NLED). This would appear as an anomalous frequency shift in any modeling of the electromagnetic field that only takes into account the classical Maxwell theory. Thus, it is tempting to address the unresolved anomalous, steady; but time-dependent, blueshift of the Pioneer 10/11 spacecrafts within the framework of NLED. Here we show that astrophysical data on the strength of the magnetic field in both the Galaxy and the local (super)cluster of galaxies support the view on the major Pioneer anomaly as a consequence of the phenomenon of photon acceleration. If confirmed, through further observations or lab experiments, the reality of this phenomenon should prompt to take it into account in any forthcoming research on both cosmological evolution and origin and dynamical effects of primordial magnetic fields, whose seeds are estimated to be very weak.Comment: Final version accepted for publication in Europhysics Letters, uses EPL style, 7 page

Neutrino Oscillations at Supernova Core Bounce Generate the Strongest Gravitational-Wave Bursts

During the core bounce of a supernova collapse resonant active-to-active ($\nu_a \to \nu_a$), as well as active-to-sterile ($\nu_a \to \nu_s$) neutrino ($\nu$) oscillations can take place. Besides, over this phase weak magnetism increases antineutrino ($\bar{\nu}$) mean free paths, and thus its luminosity. Because the oscillation feeds mass-energy into the target $\nu$ species, the large mass-squared difference between species ($\nu_a \to \nu_s$) implies a huge amount of power to be given off as gravitational waves ($L_{\textrm{GWs}} \sim 10^{49}erg s$^{-1}$), due to anisotropic but coherent$\nu$flow over the oscillation length. This anisotropy in the$\nu$-flux is driven by both the {\it universal spin-rotation} and the spin-magnetic coupling. The new spacetime strain estimated this way is still several orders of magnitude larger than those from$\nu$ diffusion (convection and cooling) or quadrupole moments of the neutron star matter. This new feature turns these bursts the more promising supernova gravitational-wave signal that may be detected by observatories as LIGO, VIRGO, etc., for distances far out to the VIRGO cluster of galaxies.Comment: 10 pages, 1 figure, Proceedings of International Workshop on Astronomy and Relativistic Astrophysics, Olinda (Brazil), October 12-16 (2003), to be published in Int. J. Mod. Phys.

Identificación de las principales fuentes de agua que aportan a la generación de escorrentía en zonas de páramo húmedo: mediante el uso de Deuterium y Oxygen-18

La conservación de las cuencas, manteniendo un caudal que permita el natural funcionamiento de los ecosistemas existentes (caudal ecológico), control de la calidad del agua, control de procesos erosivos, determinación de las fuentes que aportan a la generación de escorrentía dentro de la cuenca, son la base para un manejo sustentable de los recursos naturales (Buytaert et al., 2006a; Mena y Hofstede, 2006). Sin embargo, y a pesar de la gran variedad de servicios ambientales que los ecosistemas de páramo proveen a la sociedad, existen pocos estudios sobre los procesos hidrológicos que gobiernan los mismos (Días-Granados et al., 2005), y aunque en los últimos años, se han realizado esfuerzos significativos para mejorar el conocimiento sobre los mismos, aún hace falta mucha investigación (Crespo et al.,2011a;Buytaert et al., 2006a), razón por la cual existe discrepancia sobre el comportamiento hidrológico del páramo a escala de cuenca (Buytaert et al., 2004), lo que genera un contraste con la importancia socioeconómica que tiene el páramo como fuente primaria de agua. Es por ello y para ello, que se requiere mejorar el conocimiento de los procesos hidrológicos en las zonas de páramo Andino, como son por ejemplo la determinación de la cantidad de agua que aporta cada una de las fuentes que generan la escorrentía en una cuenca. Esto debido principalmente, a que todos los servicios ambientales que proveen estos ecosistemas dependen en gran medida del movimiento del agua dentro de la cuenca, y como esta interactúa con el ambiente circundante (Crespo et al., 2011b)

A Geometric Approach to Massive p-form Duality

Massive theories of abelian p-forms are quantized in a generalized path-representation that leads to a description of the phase space in terms of a pair of dual non-local operators analogous to the Wilson Loop and the 't Hooft disorder operators. Special atention is devoted to the study of the duality between the Topologically Massive and the Self-Dual models in 2+1 dimensions. It is shown that these models share a geometric representation in which just one non local operator suffices to describe the observables.Comment: 26 pages, LaTeX. The discussion about the equivalence between the Proca model and two seldual models, with opposite spins, was eliminated. Typos correcte

Development and operation of a pixel segmented liquid-filled linear array for radiotherapy quality assurance

A liquid isooctane (C$_{8}$H$_{18}$) filled ionization linear array for radiotherapy quality assurance has been designed, built and tested. The detector consists of 128 pixels, each of them with an area of 1.7 mm $\times$ 1.7 mm and a gap of 0.5 mm. The small pixel size makes the detector ideal for high gradient beam profiles like those present in Intensity Modulated Radiation Therapy (IMRT) and radiosurgery. As read-out electronics we use the X-Ray Data Acquisition System (XDAS) with the Xchip developed by the CCLRC. Studies concerning the collection efficiency dependence on the polarization voltage and on the dose rate have been made in order to optimize the device operation. In the first tests we have studied dose rate and energy dependences, and signal reproducibility. Dose rate dependence was found lower than 2.5 % up to 5 Gy min$^{-1}$, and energy dependence lower than 2.1 % up to 20 cm depth in solid water. Output factors and penumbras for several rectangular fields have been measured with the linear array and were compared with the results obtained with a 0.125 cm$^{3}$ air ionization chamber and radiographic film, respectively. Finally, we have acquired profiles for an IMRT field and for a virtual wedge. These profiles have also been compared with radiographic film measurements. All the comparisons show a good correspondence. Signal reproducibility was within a 2% during the test period (around three months). The device has proved its capability to verify on-line therapy beams with good spatial resolution and signal to noise ratio.Comment: 16 pages, 12 figures Submitted to Phys. Med. Bio