5,090 research outputs found
Interactive design of complex time-dependent lighting
Visualizing complicated lighting sequences while designing large theatrical productions proves difficult. The author provides some techniques that achieve fast interaction regardless of scene and lighting complexity, even when used with costly rendering algorithms
Ratiometric fluorescence imaging and marker-free motion tracking of Langendorff perfused beating rabbit hearts
Optical mapping is a fluorescence based imaging technique used extensively
in cardiac research to study the electrophysiological properties of isolated
hearts kept at physiological conditions. The major limitation of optical mapping
studies are the distortions of electrophysiological signals due to the
contractile motion of the hearts. To reduce electrophysiological signal distortions
due to the contractile motion artifacts, the mechanical motion has
been suppressed in optical mapping experiments using electromechanical
uncouplers such as Blebbistatin. Recent studies used marker-free numerical
motion tracking and motion stabilization techniques to record electrophysiological
parameters in the absence of electromechanical uncouplers and
showed that contractile motion of the cardiac tissue is no longer a limitation
in optical mapping studies. However, despite these developments, accurate
measurements of quantities such as action potential duration (APD) and
cardiac restitution are still challenging due to the residual motion artifacts
present in the electrophysiological signals even after numerical motion tracking.
A combination of marker-free motion tracking and ratiometric optical
mapping technique is used in this thesis to minimize motion-related artifacts
from contracting hearts. This combined experimental and numerical technique
reduced motion artifacts significantly and hence, the combination is
used to precisely measure APD, cardiac restitution and ventricular fibrillation
frequencies from Langendorff perfused contracting and deforming rabbit
hearts. A systematic comparison of these electrophysiological parameters
in contracting and Blebbistatin-uncoupled conditions showed, on average,
27 ± 5% (N=5 hearts) shortening of APD in contracting hearts as compared
to Blebbistatin-uncoupled hearts. Ventricular fibrillation frequency significantly
increased in contracting hearts (13 ± 3.5 Hz) in comparison with
Blebbistatin-uncoupled hearts (8 ± 1.5 Hz)
Constraining the Absolute Orientation of Eta Carinae's Binary Orbit: A 3-D Dynamical Model for the Broad [Fe III] Emission
We present a three-dimensional (3-D) dynamical model for the broad [Fe III]
emission observed in Eta Carinae using the Hubble Space Telescope/Space
Telescope Imaging Spectrograph (HST/STIS). This model is based on full 3-D
Smoothed Particle Hydrodynamics (SPH) simulations of Eta Car's binary colliding
winds. Radiative transfer codes are used to generate synthetic spectro-images
of [Fe III] emission line structures at various observed orbital phases and
STIS slit position angles (PAs). Through a parameter study that varies the
orbital inclination i, the PA {\theta} that the orbital plane projection of the
line-of-sight makes with the apastron side of the semi-major axis, and the PA
on the sky of the orbital axis, we are able, for the first time, to tightly
constrain the absolute 3-D orientation of the binary orbit. To simultaneously
reproduce the blue-shifted emission arcs observed at orbital phase 0.976, STIS
slit PA = +38 degrees, and the temporal variations in emission seen at negative
slit PAs, the binary needs to have an i \approx 130 to 145 degrees, {\theta}
\approx -15 to +30 degrees, and an orbital axis projected on the sky at a PA
\approx 302 to 327 degrees east of north. This represents a system with an
orbital axis that is closely aligned with the inferred polar axis of the
Homunculus nebula, in 3-D. The companion star, Eta B, thus orbits clockwise on
the sky and is on the observer's side of the system at apastron. This
orientation has important implications for theories for the formation of the
Homunculus and helps lay the groundwork for orbital modeling to determine the
stellar masses.Comment: 23 pages, 12 color figures, plus 2 online-only appendices (available
in the /anc folder of the Source directory). Accepted for publication in
MNRA
Picosecond electric-field-induced threshold switching in phase-change materials
Many chalcogenide glasses undergo a breakdown in electronic resistance above
a critical field strength. Known as threshold switching, this mechanism enables
field-induced crystallization in emerging phase-change memory. Purely
electronic as well as crystal nucleation assisted models have been employed to
explain the electronic breakdown. Here, picosecond electric pulses are used to
excite amorphous AgInSbTe. Field-dependent reversible
changes in conductivity and pulse-driven crystallization are observed. The
present results show that threshold switching can take place within the
electric pulse on sub-picosecond time-scales - faster than crystals can
nucleate. This supports purely electronic models of threshold switching and
reveals potential applications as an ultrafast electronic switch.Comment: 6 pages manuscript with 3 figures and 8 pages supplementary materia
Engineering study to determine feasible methods of simulating planetary albedo and radiation effects upon the thermal balance of spacecraft Final report
Planetary radiation and albedo effects on thermal balance of spacecraft orbiting Mars and Venu
Assessing spring phenology of a temperate woodland : a multiscale comparison of ground, unmanned aerial vehicle and Landsat satellite observations
PhD ThesisVegetation phenology is the study of plant natural life cycle stages. Plant phenological events are related to carbon, energy and water cycles within terrestrial ecosystems, operating from local to global scales. As plant phenology events are highly sensitive to climate fluctuations, the timing of these events has been used as an independent indicator of climate change. The monitoring of forest phenology in a cost-effective manner, at a fine spatial scale and over relatively large areas remains a significant challenge. To address this issue, unmanned aerial vehicles (UAVs) appear to be a potential new platform for forest phenology monitoring. The aim of this research is to assess the potential of UAV data to track the temporal dynamics of spring phenology, from the individual tree to woodland scale, and to cross-compare UAV results against ground and satellite observations, in order to better understand characteristics of UAV data and assess potential for use in validation of satellite-derived phenology. A time series of UAV data were acquired in tandem with an intensive ground campaign during the spring season of 2015, over Hanging Leaves Wood, Northumberland, UK. The radiometric quality of the UAV imagery acquired by two consumer-grade cameras was assessed, in terms of the ability to retrieve reflectance and Normalised Difference Vegetation Index (NDVI), and successfully validated against ground (0.84≤R2≥0.96) and Landsat (0.73≤R2≥0.89) measurements, but only NDVI resulted in stable time series. The start (SOS), middle (MOS) and end (EOS) of spring season dates were estimated at an individual tree-level using UAV time series of NDVI and Green Chromatic Coordinate (GCC), with GCC resulting in a clearer and stronger seasonal signal at a tree crown scale. UAV-derived SOS could be predicted more accurately than MOS and EOS, with an accuracy of less than 1 week for deciduous woodland and within 2 weeks for evergreen. The UAV data were used to map phenological events for individual trees across the whole woodland, demonstrating that contrasting canopy phenological events can occur within the extent of a single Landsat pixel. This accounted for the poor relationships found between UAV- and Landsat-derived phenometrics (R2<0.45) in this study. An opportunity is now available to track very fine scale land surface changes over contiguous vegetation communities, information which could improve characterization of vegetation phenology at multiple scales.The Science without Borders program, managed by CAPES-Brazil (Coordenação de Aperfeiçoamento de Pessoal de NÃvel Superior)
Advanced Fluorescence Microscopy Techniques-FRAP, FLIP, FLAP, FRET and FLIM
Fluorescence microscopy provides an efficient and unique approach to study fixed and living cells because of its versatility, specificity, and high sensitivity. Fluorescence microscopes can both detect the fluorescence emitted from labeled molecules in biological samples as images or photometric data from which intensities and emission spectra can be deduced. By exploiting the characteristics of fluorescence, various techniques have been developed that enable the visualization and analysis of complex dynamic events in cells, organelles, and sub-organelle components within the biological specimen. The techniques described here are fluorescence recovery after photobleaching (FRAP), the related fluorescence loss in photobleaching (FLIP), fluorescence localization after photobleaching (FLAP), Forster or fluorescence resonance energy transfer (FRET) and the different ways how to measure FRET, such as acceptor bleaching, sensitized emission, polarization anisotropy, and fluorescence lifetime imaging microscopy (FLIM). First, a brief introduction into the mechanisms underlying fluorescence as a physical phenomenon and fluorescence, confocal, and multiphoton microscopy is given. Subsequently, these advanced microscopy techniques are introduced in more detail, with a description of how these techniques are performed, what needs to be considered, and what practical advantages they can bring to cell biological research
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