3,987 research outputs found
The space density distribution of galaxies in the absolute magnitude - rotation velocity plane: a volume-complete Tully-Fisher relation from CALIFA stellar kinematics
The space density distribution of galaxies in the absolute magnitude -
rotation velocity plane: a volume-complete Tully-Fisher relation from CALIFA
stellar kinematicsComment: Accepted to A&
Achromatizing a liquid-crystal spectropolarimeter: Retardance vs Stokes-based calibration of HiVIS
Astronomical spectropolarimeters can be subject to many sources of systematic
error which limit the precision and accuracy of the instrument. We present a
calibration method for observing high-resolution polarized spectra using
chromatic liquid-crystal variable retarders (LCVRs). These LCVRs allow for
polarimetric modulation of the incident light without any moving optics at
frequencies >10Hz. We demonstrate a calibration method using pure Stokes input
states that enables an achromatization of the system. This Stokes-based
deprojection method reproduces input polarization even though highly chromatic
instrument effects exist. This process is first demonstrated in a laboratory
spectropolarimeter where we characterize the LCVRs and show example
deprojections. The process is then implemented the a newly upgraded HiVIS
spectropolarimeter on the 3.67m AEOS telescope. The HiVIS spectropolarimeter
has also been expanded to include broad-band full-Stokes spectropolarimetry
using achromatic wave-plates in addition to the tunable full-Stokes
polarimetric mode using LCVRs. These two new polarimetric modes in combination
with a new polarimetric calibration unit provide a much more sensitive
polarimetric package with greatly reduced systematic error.Comment: Accepted in PAS
Development of a glucose sensor based on competitive binding and laser-excited fluorescence
An optical glucose sensor has been developed using competitive binding in conjunction with energy transfer. Sensor response is based on competition between glucose and dextran for a limited number of binding sites on the protein concanavalin A (conA). The system is optically monitored using fluorescent donor-acceptor dye pairs labeled to concanavalin A and dextran. When the dyes are sufficiently close, on the order of 50 A, energy is transferred from the donor emission band to the overlapping excitation band of the acceptor. This nonradiative, singlet-singlet transfer of energy enhances the acceptor emission at the expense of donor emission.
In absence of glucose, the conA and dextran are bound together and energy transfer takes place. Upon addition of glucose, the dextran is displaced, and energy transfer is disrupted. The ratio of the two emission intensities can be related to glucose concentration. Donor-acceptor systems investigated included energy transfer from fluorescein (FITC) to three different types of rhodamine, TRITC, XRITC, and Texas Red, and both coumarin and fluorescamine donating energy to FITC. The system that gave the largest change in intensity involved FITC labeled conA as the donor and TRITC labeled dextran as the donor.
Fluorescence was measured with both conventional fluorescence instrumentation and a computer controlled, laser excited spectrometer. The laser instrument was developed specifically for the optical glucose sensor, but was designed to support a wide range of fiber optic sensors. Instrument components include a nitrogen pumped dye laser, fiber optic beam splitters, photomultiplier tubes fitted with interference filters for wavelength selection, and boxcar averagers.
Instrument development included calibration of the dye laser, evaluation of different fiber optic beam splitter arrangements, reduction of stray light, and evaluation of the boxcar averagers. The spectrometer was interfaced to an Apple IIc computer which was programmed to collect the data, perform baseline corrections, ratio the two channels, and trigger the laser to initiate the next data point.
The instrument\u27s detection level, using Rhodamine 6G standards, is 1.0 10\sp{-9}molar and is limited by stray light. Precision of the instrument is approximately 3% and is limited by drift of the boxcar averagers
On motion in dynamic magnetic resonance imaging: Applications in cardiac function and abdominal diffusion
La imagen por resonancia magnética (MRI), hoy en día, representa una potente herramienta para el diagnóstico clínico debido a su flexibilidad y sensibilidad a un amplio rango de propiedades del tejido. Sus principales ventajas son su sobresaliente versatilidad y su capacidad para proporcionar alto contraste entre tejidos blandos. Gracias a esa versatilidad, la MRI se puede emplear para observar diferentes fenómenos físicos dentro del cuerpo humano combinando distintos tipos de pulsos dentro de la secuencia. Esto ha permitido crear distintas modalidades con múltiples aplicaciones tanto biológicas como clínicas. La adquisición de MR es, sin embargo, un proceso lento, lo que conlleva una solución de compromiso entre resolución y tiempo de adquisición (Lima da Cruz, 2016; Royuela-del Val, 2017). Debido a esto, la presencia de movimiento fisiológico durante la adquisición puede conllevar una grave degradación de la calidad de imagen, así como un incremento del tiempo de adquisición, aumentando así tambien la incomodidad del paciente. Esta limitación práctica representa un gran obstáculo para la viabilidad clínica de la MRI. En esta Tesis Doctoral se abordan dos problemas de interés en el campo de la MRI en los que el movimiento fisiológico tiene un papel protagonista. Éstos son, por un lado, la estimación robusta de parámetros de rotación y esfuerzo miocárdico a partir de imágenes de MR-Tagging dinámica para el diagnóstico y clasificación de cardiomiopatías y, por otro, la reconstrucción de mapas del coeficiente de difusión aparente (ADC) a alta resolución y con alta relación señal a ruido (SNR) a partir de adquisiciones de imagen ponderada en difusión (DWI) multiparamétrica en el hígado.Departamento de Teoría de la Señal y Comunicaciones e Ingeniería TelemáticaDoctorado en Tecnologías de la Información y las Telecomunicacione
High-resolution remote thermography using luminescent low-dimensional tin-halide perovskites
While metal-halide perovskites have recently revolutionized research in
optoelectronics through a unique combination of performance and synthetic
simplicity, their low-dimensional counterparts can further expand the field
with hitherto unknown and practically useful optical functionalities. In this
context, we present the strong temperature dependence of the photoluminescence
(PL) lifetime of low-dimensional, perovskite-like tin-halides, and apply this
property to thermal imaging with a high precision of 0.05 {\deg}C. The PL
lifetimes are governed by the heat-assisted de-trapping of self-trapped
excitons, and their values can be varied over several orders of magnitude by
adjusting the temperature (up to 20 ns {\deg}C-1). Typically, this sensitive
range spans up to one hundred centigrade, and it is both compound-specific and
shown to be compositionally and structurally tunable from -100 to 110 {\deg} C
going from [C(NH2)3]2SnBr4 to Cs4SnBr6 and (C4N2H14I)4SnI6. Finally, through
the innovative implementation of cost-effective hardware for fluorescence
lifetime imaging (FLI), based on time-of-flight (ToF) technology, these novel
thermoluminophores have been used to record thermographic videos with high
spatial and thermal resolution.Comment: 25 pages, 4 figure
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