Quantum Aspects of Massive Gravity

We consider the effect of quantum interactions on Pauli-Fierz massive gravity. With generic graviton cubic interactions, we observe that the 1-loop counterterms do not conform to the tree level structure of Pauli-Fierz action, resulting in the reappearance of the 6th mode ghost. Then to explore the quantum effects to the full extent, we calculate the resummed graviton propagator with an arbitrary interaction and analyze its complete structure, from which a minimal condition for the absence of the ghost is obtained.Comment: 1+18p

Sudden variations in the speed of sound during inflation: features in the power spectrum and bispectrum

We employ the formalism of the effective field theory of inflation to study the effects of a sudden change in the speed of sound of the inflationary perturbations. Such an event generates a feature with high frequency oscillations both in the two- and in the three-point functions of the curvature fluctuations. We study, at first order in the magnitude of the change of the speed of sound, the dependence of the power spectrum and of the bispectrum on the duration of the change. In the limit of a very short duration, the oscillations in the power spectrum persist up to very large momenta and the amplitude of the feature in the bispectrum diverges while its location moves to increasing momenta.Comment: 7 pp, 2 figure

Rigorous Approach to the Gravitational Lensing

We revisit a weak gravitational lensing problem by constructing a setup which describes the actual system as accurately as possible and solving the null geodesic equations. Details are given for the case of a Universe driven only by a cosmological constant, \Lambda, which confirm the conventional results: The conventional lensing analysis is correct as it is, without any need for correction of O(\Lambda). We also treat the cases of the lensing in generic FRW backgrounds.Comment: 6 pages, the discussion is revise

Practicable Soundmapping: JavaScript enabled Edge Compute

In this paper, we report on developments of the Citygram, a comprehensive sensor network platform for capturing, streaming, analyzing, mapping, visualizing, and providing easy access to spatiotemporal soundscape data. Launched in 2011, Citygram’s recent strategic decision has resulted in system redesign to enable migration from a codebase built on multiple computer languages to a cross-platform single JavaScript codebase. Citygram now runs on V8 engines including standard web-browsers and in the node.js environment. The Citygram sensor network significantly alleviates problems concerning soundmapping complexities including operating system limitations, hardware dependency, software update and dissemination issues, data access mechanism, data visualization, and cost. This strategy has made practicable a key design philosophy for soundmapping: rapid sensor network growth for capturing spatiotemporally granular soundscapes. We summarize research and development for the following Citygram modules (1) cost-effective sensor module allowing high-value data transmission through edge compute paradigms, (2) machine learning module focusing on environmental sound classification, and (3) visualization and data access prototypes

Materials and Chemistry for Redox Flow Batteries

Department of Energy Engineering(Battery Science and Technology)Vanadium redox reactions have been considered as a key factor affecting the energy efficiency of the all-vanadium redox flow batteries (VRFBs). This redox reaction determines the reaction kinetics of whole cells. However, poor kinetic reversibility and catalytic activity towards of V2+/V3+ and VO2+/VO2+ redox couples on commonly used carbon substrate limit broader applications of VRFBs. Consequently, modified carbon substrates have been extensively investigated to improve vanadium redox reactions. In this Focus Review, recent progress of metal- and carbon-based nanomaterials as an electrocatalyst for VRFBs is discussed in detail, not intending a comprehensive review on whole components of system. The focus is mainly placed on redox chemistry of vanadium ions at a surface of various metals, different dimensional carbons, nitrogen-doped carbon nanostructures, and metal carbon composites. Spatial separation of the electrolyte and electrode is the main characteristic of the redox flow battery technology that liberates them from constraints of overall energy content and energy/power ratio. The concept of flowing electrolyte not only present a cost-effective approach for large-scale energy storage, but recently being embraced to develop a wide range of new hybrid energy storage and conversion systems. The advent of flow based Li-ion, organic redox, metal-air, and photo-electrochemical batteries promise new opportunities for advancing the electrical energy storage technologies. In this review, we present a critical overview of recent progress in conventional aqueous redox flow batteries (RFBs) and next-generation RFB systems, highlighting the latest innovative alternative materials and chemistries. Finally, we outline their technical feasibility for use in long-term and large-scale electrical energy-storage devices as well as the limitations that need to be overcome, providing an overview of future research direction in the field of RFBs.ope

Unified approach to cosmic acceleration

We present a unified framework for the study of late time cosmic acceleration. Using methods of effective field theory, we show that existing proposals for late time acceleration can be subsumed in a single framework, rather than many compartmentalized theories. We construct the most general action consistent with symmetry principles, derive the background and perturbation evolution equations, and demonstrate that for special choices of our parameters we can reproduce results already existing in the literature. Lastly, we lay the foundation for future work placing phenomenological constraints on the parameters of the effective theory. Although in this paper we focus on late time acceleration, our construction also generalizes the effective field theory of inflation to the scalar-tensor and multifield case for perturbatively constructed backgrounds