A detailed analysis of structure growth in f(R)f(R) theories of gravity

We investigate the connection between dark energy and fourth order gravity by analyzing the behavior of scalar perturbations around a Friedmann-Robertson-Walker background. The evolution equations for scalar perturbation are derived using the covariant and gauge invariant approach and applied to two widely studied $f(R)$ gravity models. The structure of the general fourth order perturbation equations and the analysis of scalar perturbations lead to the discovery of a characteristic signature of fourth order gravity in the matter power spectrum, the details of which have not seen before in other works in this area. This could provide a crucial test for fourth order gravity on cosmological scales.Comment: 27 pages and 35 figure

A Program Evaluation of Intersession Tutoring

This study examined one program which was in place in a multi-track year-round elementary school, a tutoring program delivered during the students\u27 intersession. Through interviews, surveys, and analysis of grades recorded on report cards, the program was evaluated to determine whether goals for the program were met. Survey data revealed that students, parents, and teachers all felt overwhelmingly that the program was effective at meeting stated program goals. Report card data did not show a statistically significant increase in grades after students attended the program, but many intervening variables were not controlled for. Additional convenience factors, such as transportation, cost, and timing contributed to the program benefit

The cosmological gravitational wave background from primordial density perturbations

We discuss the gravitational wave background generated by primordial density perturbations evolving during the radiation era. At second-order in a perturbative expansion, density fluctuations produce gravitational waves. We calculate the power spectra of gravitational waves from this mechanism, and show that, in principle, future gravitational wave detectors could be used to constrain the primordial power spectrum on scales vastly different from those currently being probed by large-scale structure. As examples we compute the gravitational wave background generated by both a power-law spectrum on all scales, and a delta-function power spectrum on a single scale.Comment: 8 Page

Cosmo-dynamics and dark energy with a quadratic EoS: anisotropic models, large-scale perturbations and cosmological singularities

In general relativity, for fluids with a linear equation of state (EoS) or scalar fields, the high isotropy of the universe requires special initial conditions, and singularities are anisotropic in general. In the brane world scenario anisotropy at the singularity is suppressed by an effective quadratic equation of state. There is no reason why the effective EoS of matter should be linear at the highest energies, and a non-linear EoS may describe dark energy or unified dark matter (Paper I, astro-ph/0512224). In view of this, here we study the effects of a quadratic EoS in homogenous and inhomogeneous cosmological models in general relativity, in order to understand if in this context the quadratic EoS can isotropize the universe at early times. With respect to Paper I, here we use the simplified EoS P=alpha rho + rho^2/rho_c, which still allows for an effective cosmological constant and phantom behavior, and is general enough to analyze the dynamics at high energies. We first study anisotropic Bianchi I and V models, focusing on singularities. Using dynamical systems methods, we find the fixed points of the system and study their stability. We find that models with standard non-phantom behavior are in general asymptotic in the past to an isotropic fixed point IS, i.e. in these models even an arbitrarily large anisotropy is suppressed in the past: the singularity is matter dominated. Using covariant and gauge invariant variables, we then study linear perturbations about the homogenous and isotropic spatially flat models with a quadratic EoS. We find that, in the large scale limit, all perturbations decay asymptotically in the past, indicating that the isotropic fixed point IS is the general asymptotic past attractor for non phantom inhomogeneous models with a quadratic EoS. (Abridged)Comment: 16 pages, 6 figure

Utilizing Open Source in Terrestrial Digital TV Broadcasting

Indonesian terrestrial TV broadcasting has just started its migration to digital standard. Digitalization offers more roles for software development in various functional blocks of digital TV system. This paper presents utilization of open-source softwares in assessing some aspects of terrestrial digital TV system. We propose technical specification and measurement standard operating procedure for basic services using DVB-T standard, and set-up a softwarebased platform based on open source softwares for testing a DVB-T set-top-box

Species Diversity and Distribution of Sponges in the Coastal Area of Kasiak Island Pariaman Regency Sumatera Barat Province

Sponges are the most primitive multicellular animals that live in various types of waters from freshwater, brackish and sea. Sponges live in bottom waters that typically stick themselves on hard substrate such as rock or coral and compete with other tacks organism to obtain a food hall. The research was conducted in Kasiak Island Pariaman regency West Sumatera in February-March 2019, aims to find outthe type, density, frequency of occurrence, diversity index, dominance index, the distribution pattern of sponge, To support the research data is also observed the characteristics of the environment such as water quality. The method used is survey method, where sampling using belt transect method performed on three stations. The research found 14 genus / species of sponge consisting of 11 families in island waters Kasiak with sponge density values obtained in each research station ranges from 1458-4208 ind / ha. The highest frequency of occurrence of the type Jaspis sp. with the frequency of occurrence of 100%. Diversity index values ranged from 1.8921 to 1.9488, dominance index value obtained was from 0.3163 to 0.3396, and the value of the distribution pattern of the sponge ranges from 0.2941 to 0.3015