University of California, Santa Barbara

About: University of California, Santa Barbara is a education organization based out in Santa Barbara, California, United States. It is known for research contribution in the topics: Population & Laser. The organization has 30281 authors who have published 80852 publications receiving 4626827 citations. The organization is also known as: UC Santa Barbara & UCSB.

Analysis of Fluid Flows via Spectral Properties of the Koopman Operator

Abstract: This article reviews theory and applications of Koopman modes in fluid mechanics. Koopman mode decomposition is based on the surprising fact, discovered in Mezic (2005), that normal modes of linear oscillations have their natural analogs—Koopman modes—in the context of nonlinear dynamics. To pursue this analogy, one must change the representation of the system from the state-space representation to the dynamics governed by the linear Koopman operator on an infinite-dimensional space of observables. Whereas Koopman in his original paper dealt only with measure-preserving transformations, the discussion here is predominantly on dissipative systems arising from Navier-Stokes evolution. The analysis is based on spectral properties of the Koopman operator. Aspects of point and continuous parts of the spectrum are discussed. The point spectrum corresponds to isolated frequencies of oscillation present in the fluid flow, and also to growth rates of stable and unstable modes. The continuous part of the spectrum c...

Interference-Aware Channel Assignment in Multi-Radio Wireless Mesh Networks

Abstract: The capacity problem in wireless mesh networks can be alleviated by equipping the mesh routers with multiple radios tuned to non-overlapping channels However, channel assignment presents a challenge because co-located wireless networks are likely to be tuned to the same channels The resulting increase in interference can adversely affect performance This paper presents an interference-aware channel assignment algorithm and protocol for multi-radio wireless mesh networks that address this interference problem The proposed solution intelligently assigns channels to radios to minimize interference within the mesh network and between the mesh network and co-located wireless networks It utilizes a novel interference estimation technique implemented at each mesh router An extension to the conflict graph model, the multi-radio conflict graph, is used to model the interference between the routers We demonstrate our solution’s practicality through the evaluation of a prototype implementation in a IEEE 80211 testbed We also report on an extensive evaluation via simulations In a sample multi-radio scenario, our solution yields performance gains in excess of 40% compared to a static assignment of channels

Organic thermoelectric materials for energy harvesting and temperature control

Abstract: Conjugated polymers and related processing techniques have been developed for organic electronic devices ranging from lightweight photovoltaics to flexible displays. These breakthroughs have recently been used to create organic thermoelectric materials, which have potential for wearable heating and cooling devices, and near-room-temperature energy generation. So far, the best thermoelectric materials have been inorganic compounds (such as Bi2Te3) that have relatively low Earth abundance and are fabricated through highly complex vacuum processing routes. Molecular materials and hybrid organic–inorganic materials now demonstrate figures of merit approaching those of these inorganic materials, while also exhibiting unique transport behaviours that are suggestive of optimization pathways and device geometries that were not previously possible. In this Review, we discuss recent breakthroughs for organic materials with high thermoelectric figures of merit and indicate how these materials may be incorporated into new module designs that take advantage of their mechanical and thermoelectric properties. Thermoelectrics can be used to harvest energy and control temperature. Organic semiconducting materials have thermoelectric performance comparable to many inorganic materials near room temperature. Better understanding of their performance will provide a pathway to new types of conformal thermoelectric modules.

Exploring the Optical Transient Sky with the Palomar Transient Factory

Abstract: The Palomar Transient Factory (PTF) is a wide-field experiment designed to investigate the optical transient and variable sky on time scales from minutes to years. PTF uses the CFH12k mosaic camera, with a field of view of 7.9 deg^2 and a plate scale of 1″ pixel^(-1), mounted on the Palomar Observatory 48 inch Samuel Oschin Telescope. The PTF operation strategy is devised to probe the existing gaps in the transient phase space and to search for theoretically predicted, but not yet detected, phenomena, such as fallback supernovae, macronovae, .Ia supernovae, and the orphan afterglows of gamma-ray bursts. PTF will also discover many new members of known source classes, from cataclysmic variables in their various avatars to supernovae and active galactic nuclei, and will provide important insights into understanding galactic dynamics (through RR Lyrae stars) and the solar system (asteroids and near-Earth objects). The lessons that can be learned from PTF will be essential for the preparation of future large synoptic sky surveys like the Large Synoptic Survey Telescope. In this article we present the scientific motivation for PTF and describe in detail the goals and expectations for this experiment.

Optics of liquid crystal displays

Abstract: This tutorial covers an introduction to liquid crystal technology and principles of operation of various modes of liquid crystal displays as well as the development of birefringent optical thin film technologies (e.g., polarizers, compensators) for improving the viewing quality of these displays.