Ricci dark energy in Chern-Simons modified gravity

In this work, we have considered the Ricci dark energy model, where the energy density of the universe is proportional to the Ricci scalar curvature, in the dynamic Chern-Simons modified gravity. We show that in this context the evolution of the scale factor is similar to that displayed by the modified Chaplygin gas.Comment: 7 pages; to appear in EPJ

A coordinate-dependent superspace deformation from string theory

Starting from a type II superstring model defined on $R^{2,2}\times CY_6$ in a linear graviphoton background, we derive a coordinate dependent $C$-deformed ${\cal N}=1$, $d=2+2$ superspace. The chiral fermionic coordinates $\theta$ satisfy a Clifford algebra, while the other coordinate algebra remains unchanged. We find a linear relation between the graviphoton field strength and the deformation parameter. The null coordinate dependence of the graviphoton background allows to extend the results to all orders in $\alpha'$.Comment: 14 pages, reference added, accepted for publication in JHE

Simulation of Chua's Circuit by Means of Interval Analysis

The Chua's circuit is a paradigm for nonlinear scientific studies. It is usually simulated by means of numerical methods under IEEE 754-2008 standard. Although the error propagation problem is well known, little attention has been given to the relationship between this error and inequalities presented in Chua's circuit model. Taking the average of round mode towards $+\infty$ and $-\infty$, we showed a qualitative change on the dynamics of Chua's circuit.Comment: 6th International Conference on Nonlinear Science and Complexity - S\~ao Jos\'e dos Campos, 2016, p. 1-

Are z>2 Herschel galaxies proto-spheroids?

We present a backward approach for the interpretation of the evolution of the near-infrared and the far-infrared luminosity functions across the redshift range 0<z<3. In our method, late-type galaxies are treated by means of a parametric phenomenological method based on PEP/HerMES data up to z~4, whereas spheroids are described by means of a physically motivated backward model. The spectral evolution of spheroids is modelled by means of a single-mass model, associated to a present-day elliptical with K-band luminosity comparable to the break of the local early-type luminosity function. The formation of proto-spheroids is assumed to occurr across the redshift range 1< z < 5. The key parameter is represented by the redshift z_0.5 at which half proto-spheroids are already formed. A statistical study indicates for this parameter values between z_0.5=1.5 and z_0.5=3. We assume as fiducial value z_0.5~2, and show that this assumption allows us to describe accourately the redshift distributions and the source counts. By assuming z_0.5 ~ 2 at the far-IR flux limit of the PEP-COSMOS survey, the PEP-selected sources observed at z>2 can be explained as progenitors of local spheroids caught during their formation. We also test the effects of mass downsizing by dividing the spheroids into three populations of different present-day stellar masses. The results obtained in this case confirm the validity of our approach, i.e. that the bulk of proto-spheroids can be modelled by means of a single model which describes the evolution of galaxies at the break of the present-day early type K-band LF.Comment: Accepted for publication in ApJ; 26 pages; 13 figure

Spin dependent transport in organic light-emitting diodes

Electrically Detected Magnetic Resonance (EDMR) was used to study a series of multilayer organic devices based on aluminum (III) 8-hydroxyquinoline. These devices were designed to identify the micoscopic origin of different spin dependent process, i.e. hopping and exciton formation. EDMR is demonstrated to probe molecular orbitals of charge, and thus indirectly explore interfaces, exciton formation, charge accumalation and electric fields in operating organic based devices

On FRW Model in Conformal Teleparallel Gravity

In this paper we use the conformal teleparallel gravity to study an isotropic and homogeneous Universe which is settled by the FRW metric. We solve the field equations and we obtain the behavior of some cosmological parameters such as scale factor, deceleration parameter and the energy density of the perfect fluid which is the matter field of our model. The field equations, that we called modified Friedmann equations, allow us to define a dark fluid, with dark energy density and dark pressure, responsible for the acceleration in the Universe.Comment: Accepted in EPJ

A photometric and spectroscopic survey of solar twin stars within 50 parsecs of the Sun: I. Atmospheric parameters and color similarity to the Sun

Solar twins and analogs are fundamental in the characterization of the Sun's place in the context of stellar measurements, as they are in understanding how typical the solar properties are in its neighborhood. They are also important for representing sunlight observable in the night sky for diverse photometric and spectroscopic tasks, besides being natural candidates for harboring planetary systems similar to ours and possibly even life-bearing environments. We report a photometric and spectroscopic survey of solar twin stars within 50 pc of the Sun. Hipparcos absolute magnitudes and (B-V)_Tycho colors were used to define a 2 sigma box around the solar values, where 133 stars were considered. Additional stars resembling the solar UBV colors in a broad sense, plus stars present in the lists of Hardorp, were also selected. All objects were ranked by a color-similarity index with respect to the Sun, defined by uvby and BV photometry. Moderately high-resolution, high-S/N spectra were used for a subsample of equatorial-southern stars to derive Teff, log g, and [Fe/H] with average internal errors better than 50 K, 0.20 dex, and 0.08 dex, respectively. Ages and masses were estimated from theoretical HR diagrams. The color-similarity index proved very successful. We identify and rank new excellent solar analogs, which are fit to represent the Sun in the night sky. Some of them are faint enough to be of interest for moderately large telescopes. We also identify two stars with near-UV spectra indistinguishable from the Sun's. We present five new "probable" solar twin stars, besides five new "possible" twins. Masses and ages for the best solar twin candidates lie very close to the solar values, but chromospheric activity levels range somewhat. We propose that the solar twins be emphasized in the ongoing searches for extra-solar planets and SETI searches.Comment: 25 pages, 15 figures, 14 table