University of Central Florida

About: University of Central Florida is a education organization based out in Orlando, Florida, United States. It is known for research contribution in the topics: Laser & Population. The organization has 18822 authors who have published 48679 publications receiving 1234422 citations. The organization is also known as: UCF.

Conductivity and Water Uptake of Aromatic‐Based Proton Exchange Membrane Electrolytes

Abstract: Water uptake and proton conductivity as a function of temperature were determined for three aromatic-based, sulfonic acid-bearing polymers, plus the perfluoroalkyl sulfonic acid Nafion{reg_sign} 117. Water uptake of submerged, equilibrated samples ranged from less than five water molecules per acid group for a high equivalent weight, sulfonated polyethersulfone to almost fifty waters per acid for a low equivalent weight, sulfonated polyetheretherketone. The most conductive aromatic-based polymer, sulfonated polyphenylquinoxaline (S-PPQ), had a room temperature conductivity of 9.8 x 10{sup {minus}3} S/cm, about an order of magnitude less than that of a perfluoroalkyl sulfonic acid under identical conditions. The slope of the S-PPQ Arrhenius conductivity plot was sufficiently steep that at 180 C, the proton conductivity, 1.3 x 10{sup {minus}1} S/cm, was only a factor of two lower than that of Nafion under similar conditions. The lower conductivity of the aromatic-based sulfonic acid polymers can be attributed to chain rigidity, lack of ion channels, and lower acidity.

Prognostic and Warning System for Power-Electronic Modules in Electric, Hybrid Electric, and Fuel-Cell Vehicles

Abstract: Reliability of power-electronic modules is of paramount importance for the commercial success of various types of electric vehicles. In this paper, we study the technical feasibility of detecting and utilizing early symptoms and warning signs of power-module degradation due to thermomechanical stress and fatigue and develop a prognostic system that can monitor the state of health of the power modules in electric, hybrid, and fuel-cell vehicles. A special degradation trace on the VCEsat of the insulated-gate bipolar-transistor modules was observed by a power-cycling accelerated test, which was not reported in literatures. A prognostic system based on utilizing the aforementioned trace is then developed. The system consists of the hardware architecture and current adaptive-algorithm-based software architecture. In addition, this prognostic system hardly increases the hardware cost on existing vehicle-driver system. An extensive simulation based on MATLAB/Simulink verifies the developed prognostic system.

Diffraction-free space–time light sheets

Abstract: Diffraction-free optical beams propagate freely without change in shape and scale. Monochromatic beams that avoid diffractive spreading require two-dimensional transverse profiles and there are no corresponding solutions for profiles restricted to one transverse dimension. Here, we demonstrate that the temporal degree of freedom can be exploited to efficiently synthesize one-dimensional pulsed light sheets that propagate self-similarly in free space, with no need for nonlinearity or dispersion. By introducing programmable conical (hyperbolic, parabolic or elliptical) spectral correlations between the beam’s spatiotemporal degrees of freedom, a continuum of families of propagation-invariant light sheets is generated. The spectral loci of such beams are the reduced-dimensionality trajectories at the intersection of the light-cone with spatiotemporal spectral planes. Far from being exceptional, self-similar axial-propagation in free space is a generic feature of fields whose spatial and temporal degrees of freedom are tightly correlated. These ‘space–time’ light sheets can be useful in microscopy, nonlinear spectroscopy, and non-contact measurements. One-dimensional non-diffracting sheets of light are achieved without exploiting nonlinearity. Such light sheets may be exploited in microscopy and sensing applications.

A spectrum of an extrasolar planet

Abstract: Just detecting an extrasolar planet is quite a feat; but one that has now been achieved over 200 times and astronomers are now developing ways of actually observing them. Of the known extrasolar planets, 14 exhibit transits in front of their parent stars as seen from Earth. For them, spectroscopy can probe the physical conditions of their atmospheres and in theory, subtracting the spectrum seen with the planet 'behind' its star from that seen when it is 'in front', should leave us with the actual spectrum of an extrasolar planet. Practice has now caught up with theory, and using the Spitzer Space Telescope, an infrared spectrum has been obtained for the transiting 'hot Jupiter' HD 209458b. It shows a peak centred near 9.65 µm, attributed to emission by silicate clouds, and a narrow, unidentified feature at 7.78 µm. A measurement of the infrared spectrum (7.5–13.2 micrometres) of the transiting extrasolar planet HD 209458b reveals that there is a broad emission peak centred near 9.65 micrometres, which they attribute to emission by silicate clouds, and a narrow, unidentified feature at 7.78 micrometres. Of the over 200 known extrasolar planets, 14 exhibit transits in front of their parent stars as seen from Earth. Spectroscopic observations of the transiting planets can probe the physical conditions of their atmospheres1,2. One such technique3,4 can be used to derive the planetary spectrum by subtracting the stellar spectrum measured during eclipse (planet hidden behind star) from the combined-light spectrum measured outside eclipse (star + planet). Although several attempts have been made from Earth-based observatories, no spectrum has yet been measured for any of the established extrasolar planets. Here we report a measurement of the infrared spectrum (7.5–13.2 µm) of the transiting extrasolar planet HD 209458b. Our observations reveal a hot thermal continuum for the planetary spectrum, with an approximately constant ratio to the stellar flux over this wavelength range. Superposed on this continuum is a broad emission peak centred near 9.65 µm that we attribute to emission by silicate clouds. We also find a narrow, unidentified emission feature at 7.78 µm. Models of these ‘hot Jupiter’5 planets predict a flux peak6,7,8,9 near 10 µm, where thermal emission from the deep atmosphere emerges relatively unimpeded by water absorption, but models dominated by water fit the observed spectrum poorly.

A Routine Activity Theory Explanation for Women's Stalking Victimizations:

Abstract: Drawing on surveys administered to 861 university women in nine institutions, this article presents a routine activity theory model for predicting stalking victimization likelihood for women. Using routine activity theory, the model highlights lifestyle behaviors and interactions as predictors of stalking victimization. Whereas routine activity theory often highlights the role of demographics and statuses as predictors, this analysis emphasizes the role of women's social interactions and substance use in victimization risk. Significant predictors of victimization likelihood include substance use variables, activities in public settings, and residence off campus.