Matter instability in modified gravity

The Dolgov-Kawasaki instability discovered in the matter sector of the modified gravity scenario incorporating a 1/R correction to Einstein gravity is studied in general f(R) theories. A stability condition is found in the metric version of these theories to help ruling out models that are unviable from the theoretical point of view.Comment: 4 pages, revtex, to appear in Phys. Rev. D. In the revised version, an error concerning the Palatini version of these theories has been corrected and the references update

Radar sounding using the Cassini altimeter waveform modeling and Monte Carlo approach for data inversion observations of Titan's seas

Recently, the Cassini RADAR has been used as a sounder to probe the depth and constrain the composition of hydrocarbon seas on Saturn's largest moon, Titan. Altimetry waveforms from observations over the seas are generally composed of two main reflections: the first from the surface of the liquid and the second from the seafloor. The time interval between these two peaks is a measure of sea depth, and the attenuation from the propagation through the liquid is a measure of the dielectric properties, which is a sensitive property of liquid composition. Radar measurements are affected by uncertainties that can include saturation effects, possible receiver distortion, and processing artifacts, in addition to thermal noise and speckle. To rigorously treat these problems, we simulate the Ku-band altimetry echo received from Titan's seas using a two-layer model, where the surface is represented by a specular reflection and the seafloor is modeled using a facet-based synthetic surface. The simulation accounts for the thermal noise, speckle, analog-to-digital conversion, and block adaptive quantization and allows for possible receiver saturation. We use a Monte Carlo method to compare simulated and observed waveforms and retrieve the probability distributions of depth, surface/subsurface intensity ratio, and subsurface roughness for the individual double-peaked waveform of Ligeia Mare acquired by the Cassini spacecraft in May 2013. This new analysis provides an update to the Ku-band attenuation and results in a new estimate for its loss tangent and composition. We also demonstrate the ability to retrieve bathymetric information from saturated altimetry echoes acquired over Ontario Lacus in December 2008

A Lemaitre-Tolman-Bondi cosmological wormhole

We present a new analytical solution of the Einstein field equations describing a wormhole shell of zero thickness joining two Lema{\i}tre-Tolman-Bondi universes, with no radial accretion. The material on the shell satisfies the energy conditions and, at late times, the shell becomes comoving with the dust-dominated cosmic substratum.Comment: 5 pages, latex, no figures, to appear in Phys. Rev.

Antiangiogenic Resistance: Novel Angiogenesis Axes Uncovered by Antiangiogenic Therapies Research

The mechanisms of tumor growth and progression involve the activation of different processes such as neovascularization and angiogenesis. These processes involve tumoral cells and stromal cells. Hence, inhibiting angiogenesis affects tumor growth and proliferation in patients with different types of cancer. Nevertheless, tumoral cells and stromal components are responsible for the resistance to antiangiogenic therapies. The majority of tumors respond to this type of therapy; however, some tumors may be indifferent to antiangiogenic therapies (intrinsic resistance) and other tumors become resistant during treatment (acquired resistance). Different strategies have been proposed to prevent resistance. Preclinical studies and clinical trials are focused to fight this therapeutic approach in order to prevent or delay tumor resistance to antiangiogenic therapies

Angiogenesis and Metabolism: Entwined for Therapy Resistance

Angiogenesis and metabolism are entwined processes that permit tumor growth and progression. Blood vessel supply is necessary for tumor survival by providing oxygen and nutrients for anabolism, but also by removing waste products from cellular metabolism. On the other hand, blocking angiogenesis with antiangiogenic therapies shows clinical benefits in several tumor types. Nevertheless, resistance to therapy emerges over time. In this review, we will discuss a novel mechanism of adaptive resistance involving metabolic adaptation of tumor cells, as well as provide examples of tumor adaptation to therapy, which may represent a new mechanism of resistance in several types of cancer. Thus, targeting this metabolic tumor adaptation could be a way to avoid resistance in cancer patients