Rippled Cosmological Dark Matter from Damped Oscillating Newton Constant

Let the reciprocal Newton 'constant' be an apparently non-dynamical Brans-Dicke scalar field damped oscillating towards its General Relativistic VEV. We show, without introducing additional matter fields or dust, that the corresponding cosmological evolution averagely resembles, in the Jordan frame, the familiar dark radiation -> dark matter -> dark energy domination sequence. The fingerprints of our theory are fine ripples, hopefully testable, in the FRW scale factor; they die away at the General Relativity limit. The possibility that the Brans-Dicke scalar also serves as the inflaton is favorably examined.Comment: RevTex4, 12 pages, 5 figures; Minor revision, References adde

Writing in your own voice: An intervention that reduces plagiarism and common writing problems in students' scientific writing.

In many of our courses, particularly laboratory courses, students are expected to engage in scientific writing. Despite various efforts by other courses and library resources, as instructors we are often faced with the frustration of student plagiarism and related writing problems. Here, we describe a simple Writing in Your Own Voice intervention designed to help students become more aware of different types of plagiarism and writing problems, avoid those problems, and practice writing in their own voice. In this article, we will introduce the types of plagiarism and writing problems commonly encountered in our molecular biology laboratory course, the intervention, and the results of our study. From the evaluation of 365 student reports, we found the intervention resulted in nearly 50% fewer instances of plagiarism and common writing problems. We also observed significantly fewer instances of severe plagiarism (e.g. several sentences copied from an external source). In addition, we find that the effects last for several weeks after the students complete the intervention assignment. This assignment is particularly easy to implement and can be a very useful tool for teaching students how to write in their own voices. © 2019 International Union of Biochemistry and Molecular Biology, 47(5):589-598, 2019

New Models of f(R) Theories of Gravity

We introduce new models of f(R) theories of gravity that are generalization of Horava-Lifshitz gravity.Comment: 16 pages, typos corrected, v2:minor changes, references adde

Bimetric Gravity Theory, Varying Speed of Light and the Dimming of Supernovae

In the bimetric scalar-tensor gravitational theory there are two frames associated with the two metrics {\hat g}_{\mu\nu} and g_{\mu\nu}, which are linked by the gradients of a scalar field \phi. The choice of a comoving frame for the metric {\hat g}_{\mu\nu} or g_{\mu\nu} has fundamental consequences for local observers in either metric spacetimes, while maintaining diffeomorphism invariance. When the metric g_{\mu\nu} is chosen to be associated with comoving coordinates, then the speed of light varies in the frame with the metric {\hat g}_{\mu\nu}. Observers in this frame see the dimming of supernovae because of the increase of the luminosity distance versus red shift, due to an increasing speed of light in the early universe. Moreover, in this frame the scalar field \phi describes a dark energy component in the Friedmann equation for the cosmic scale without acceleration. If we choose {\hat g}_{\mu\nu} to be associated with comoving coordinates, then an observer in the g_{\mu\nu} metric frame will observe the universe to be accelerating and the supernovae will appear to be farther away. The theory predicts that the gravitational constant G can vary in spacetime, while the fine-structure constant \alpha=e^2/\hbar c does not vary. The problem of cosmological horizons as viewed in the two frames is discussed.Comment: 22 pages, Latex file. No figures. Corrected typos. Added reference. Further references added. Further corrections. To be published in Int. J. Mod. Phys. D, 200

Energy Conditions and Supernovae Observations

In general relativity, the energy conditions are invoked to restrict general energy-momentum tensors on physical grounds. We show that in the standard Friedmann-Lemaitre-Robertson-Walker approach to cosmological modelling where the equation of state of the cosmological fluid is unknown, the energy conditions provide model-independent bounds on the behavior of the distance modulus of cosmic sources as a function of the redshift. We use both the gold and the legacy samples of current type Ia supenovae to carry out a model-independent analysis of the energy conditions violation in the context of standard cosmology.Comment: 4 pages, 2 figures; v2: References added, misprints corrected, published in Phys.Rev.D in the present for

Interacting dark energy, holographic principle and coincidence problem

The interacting and holographic dark energy models involve two important quantities. One is the characteristic size of the holographic bound and the other is the coupling term of the interaction between dark energy and dark matter. Rather than fixing either of them, we present a detailed study of theoretical relationships among these quantities and cosmological parameters as well as observational constraints in a very general formalism. In particular, we argue that the ratio of dark matter to dark energy density depends on the choice of these two quantities, thus providing a mechanism to change the evolution history of the ratio from that in standard cosmology such that the coincidence problem may be solved. We investigate this problem in detail and construct explicit models to demonstrate that it may be alleviated provided that the interacting term and the characteristic size of holographic bound are appropriately specified. Furthermore, these models are well fitted with the current observation at least in the low red-shift region.Comment: 20 pages, 3 figure

Speech and language difficulties in children with and without a family history of dyslexia

Comorbidity between SLI and dyslexia is well documented. Researchers have variously argued that dyslexia is a separate disorder from SLI, or that children with dyslexia show a subset of the difficulties shown in SLI. This study examines these hypotheses by assessing whether family history of dyslexia and speech and language difficulties are separable risk factors for literacy difficulties. Forty-six children with a family risk of dyslexia (FRD) and 36 children receiving speech therapy (SLT) were compared to 128 typically developing children. A substantial number (41.3%) of the children with FRD had received SLT. The nature of their difficulties did not differ in severity or form from those shown by the other children in SLT. However, both SLT and FRD were independent risk factors in predicting reading difficulties both concurrently and 6 months later. It is argued that the results are best explained in terms of Pennington's (2006) multiple deficits model

Lookback time bounds from energy conditions

In general relativity, the energy conditions are invoked to restrict general energy-momentum tensors on physical grounds. We show that in the standard Friedmann-Lemaitre-Robertson-Walker (FLRW) approach to cosmological modeling, where the energy and matter components of the cosmic fluid are unknown, the energy conditions provide model-independent bounds on the behavior of the lookback time of cosmic sources as a function of the redshift for any value of the spatial curvature. We also confront such bounds with a lookback time sample which is built from the age estimates of 32 galaxies lying in the interval $0.11 \lesssim z \lesssim 1.84$ and by assuming the total expanding age of the Universe to be $13.7 \pm 0.2$ Gyr, as obtained from current cosmic microwave background experiments. In agreement with previous results, we show that all energy conditions seem to have been violated at some point of the recent past of cosmic evolution.Comment: 7 pages, 3 figures. v2: Minor changes, published in Phys.Rev.D in the present for

Energy Conditions and Cosmic Acceleration

In general relativity, the energy conditions are invoked to restrict general energy-momentum tensors $T_{\mu\nu}$ in different frameworks, and to derive general results that hold in a variety of general contexts on physical grounds. We show that in the standard Friedmann-Lemaitre-Robertson-Walker (FLRW) approach, where the equation of state of the cosmological fluid is unknown, the energy conditions provide model-independent bounds on the behavior of the distance modulus of cosmic sources as a function of the redshift for any spatial curvature. We use the most recent type Ia supernovae (SNe Ia) observations, which include the new Hubble Space Telescope SNe Ia events, to carry out a model-independent analysis of the energy conditions violation in the context of the standard cosmology. We show that both the null (NEC), weak (WEC) and dominant (DEC) conditions, which are associated with the existence of the so-called phantom fields, seem to have been violated only recently ($z \lesssim 0.2$), whereas the condition for attractive gravity, i.e., the strong energy condition (SEC) was firstly violated billions of years ago, at $z \gtrsim 1$.Comment: 6 pages, 3 figures. v2: References added, misprints corrected, published in Phys.Rev.D in the present for

Dual interacting cosmologies and late accelerated expansion

In this paper we show that by considering a universe dominated by two interacting components a superaccelerated expansion can be obtained from a decelerated one by applying a dual transformation that leaves the Einstein's field equations invariant.Comment: 13 pages, 1 figura, version to match published articl