Three-form inflation and non-Gaussianity

We calculate the perturbed action, at second and third order, for a massive three-form field minimally coupled to gravity, and use it to explore the observational predictions of three-form inflation. One intriguing result is that the value of the spectral index is nearly independent of the three-form potential, being fixed solely by the number of e-folds of inflation, with n_s=0.97 for the canonical number of 60. Considering the bispectrum, we employ standard techniques to give explicit results for two models, one of which produces a large non-Gaussianity. Finally, we confirm our results by employing a duality relating the three-form theory to a non-canonical scalar field theory and explicitly re-computing results in this dual picture.Comment: 23 pages, 6 figures. Typos corrected and addition of one appendix. Accepted in JCA

A battery-less, self-sustaining RF energy harvesting circuit with TFETs for µW power applications

This paper proposes a Tunnel FET (TFET) power management circuit for RF energy harvesting applications. In contrast with conventional MOSFET technologies, the improved electrical characteristics of TFETs promise a better behavior in the process of rectification and conversion at ultra-low power (µW) and voltage (sub-0.25 V) levels. RF powered systems can not only benefit from TFETs in front-end rectifiers by harvesting the surrounding energy at levels where conventional technologies cannot operate but also in the minimization of energy required by the power management circuit. In this work we present an energy harvesting circuit for RF sources designed with TFETs. The TFET controller emulates an adequate impedance at the output of the rectifier in order to allow maximum transfer of power from the RF source to the input of the boost converter. The output load is activated once the output capacitor reaches a voltage value of 0.5 V. The results show an efficiency boost of 89 % for an output load consuming 1 µW with an available RF power of -25 dBm.Postprint (published version

Listening to the sound of dark sector interactions with gravitational wave standard sirens

We consider two stable Interacting Dark Matter -- Dark Energy models and confront them against current Cosmic Microwave Background data from the \textit{Planck} satellite. We then generate luminosity distance measurements from ${\cal O}(10^3)$ mock Gravitational Wave events matching the expected sensitivity of the proposed Einstein Telescope. We use these to forecast how the addition of Gravitational Wave standard sirens data can improve current limits on the Dark Matter -- Dark Energy coupling strength ($\xi$). We find that the addition of Gravitational Waves data can reduce the current uncertainty by a factor of $5$. Moreover, if the underlying cosmological model truly features Dark Matter -- Dark Energy interactions with a value of $\xi$ within the currently allowed $1\sigma$ upper limit, the addition of Gravitational Wave data would help disentangle such an interaction from the standard case of no interaction at a significance of more than $3\sigma$.Comment: 16 pages, 3 tables, 4 figures; version published in JCA

Stability of the Period-Doubled Core of the 90-degree Partial in Silicon

In a recent Letter [N. Lehto and S. Oberg, Phys. Rev. Lett. 80, 5568 (1998)], Lehto and Oberg investigated the effects of strain fields on the core structure of the 90-degree partial dislocation in silicon, especially the influence of the choice of supercell periodic boundary conditions in theoretical simulations. We show that their results for the relative stability between the two structures are in disagreement with cell-size converged tight-binding total energy (TBTE) calculations, which suggest the DP core to be more stable, regardless of the choice of boundary condition. Moreover, we argue that this disagreement is due to their use of a Keating potential.Comment: 1 page. Submitted to Comments section of PRL. Also available at http://www.physics.rutgers.edu/~dhv/preprints/rn_dcom/index.htm

Effects of neutrino mass hierarchies on dynamical dark energy models

We investigate how three different possibilities of neutrino mass hierarchies, namely normal, inverted, and degenerate, can affect the observational constraints on three well known dynamical dark energy models, namely the Chevallier-Polarski-Linder, logarithmic, and the Jassal-Bagla-Padmanabhan parametrizations. In order to impose the observational constraints on the models, we performed a robust analysis using Planck 2015 temperature and polarization data, Supernovae type Ia from Joint Light curve analysis, baryon acoustic oscillations distance measurements, redshift space distortion characterized by $f(z)\sigma_8(z)$ data, weak gravitational lensing data from Canada-France-Hawaii Telescope Lensing Survey, and cosmic chronometers data plus the local value of the Hubble parameter. We find that different neutrino mass hierarchies return similar fit on almost all model parameters and mildly change the dynamical dark energy properties.Comment: 10 pages, 5 captioned figures, 4 tables; Published version in Phys. Rev.

Improving Web user experience with document activity sparklines

The temporal dimension of the web has been mostly ignoredwhen designing user interfaces for both searching and document browsing.The dynamic nature of the web is invisible to the typical user despitethe fact that most web documents and sites change at a very rapid pace.In this paper we present and describe visual extensions applied to bothindividual web sites and search engines, that capture content activityover time. This idea is implemented with a prototype that processespublicly available web feeds to generate activity profiles and enhancesselected web sites using sparklines. These proposals bring a temporalperspective to the users browsing experience

Insights into tunnel FET-based charge pumps and rectifiers for energy harvesting applications

In this paper, the electrical characteristics of tunnel field-effect transistor (TFET) devices are explored for energy harvesting front-end circuits with ultralow power consumption. Compared with conventional thermionic technologies, the improved electrical characteristics of TFET devices are expected to increase the power conversion efficiency of front-end charge pumps and rectifiers powered at sub-µW power levels. However, under reverse bias conditions the TFET device presents particular electrical characteristics due to its different carrier injection mechanism. In this paper, it is shown that reverse losses in TFET-based circuits can be attenuated by changing the gate-to-source voltage of reverse-biased TFETs. Therefore, in order to take full advantage of the TFETs in front-end energy harvesting circuits, different circuit approaches are required. In this paper, we propose and discuss different topologies for TFET-based charge pumps and rectifiers for energy harvesting applications.Peer ReviewedPostprint (author's final draft

Using temporal evidence in blog search

In this paper we present a study on the relevance of web documents over time and the use of temporal evidence in blog search tasks. Time is an intrinsic property of social media, most notably in blogs where each post is typically attached with a timestamp representing its publish date. However, due to the challenges in obtaining document collections containing temporal information, research on this field has been scarce. We base our study on the Blog06 collection and the relevance assessments produced in the context of the TREC Blog Track, to investigate the relevance of time-based features in standard retrieval tasks. We observe small, but statistically significant improvements over a BM25 baseline when temporal information is used. Also, we find a direct connection between recency and relevance of documents for ad-hoc retrieval