143 research outputs found
A Demonstration of Spectral and Spatial Interferometry at THz Frequencies
A laboratory prototype spectral/spatial interferometer has been constructed
to demonstrate the feasibility of the double Fourier technique at Far Infrared
(FIR) wavelengths (0.15 - 1 THz). It is planned to use this demonstrator to
investigate and validate important design features and data processing methods
for future astronomical FIR interferometer instruments. In building this
prototype we have had to address several key technologies to provide an end-end
system demonstration of this double Fourier interferometer. We report on the
first results taken when viewing single slit and double slit sources at the
focus of a large collimator used to simulate real sources at infinity. The
performance of the prototype instrument for these specific field geometries is
analyzed to compare with the observed interferometric fringes and to
demonstrate image reconstruction capabilities.Comment: Accepted for publication in Applied Optic
Segmentación del nodo vesical a partir del plano transversal de imágenes ecográficas de la región suprapúbica
La retención urinaria después de una cirugía anestésica puede
provocar sobre-distensión vesical, impidiendo al paciente
miccionar de forma voluntaria. La cateterización es el método
más utilizado para solucionar este problema. El método es
aplicado cuando el volumen vesical es superior a 300 ml. En este
trabajo propone un método para la binarización y segmentación
del nodo vesical a partir de una imagen ecográfica de la región
suprapúbica transversal. Se han analizado 180 imágenes (80 de
entrenamiento y 100 de validación), segmentadas utilizando el
método de nivel de gris. Las imágenes fueron caracterizadas a
partir de las líneas vertical, horizontal y las dos diagonales. Los
valores obtenidos fueron comparados con los medidos con el
ecógrafo, con un 72% de acierto. Se ha propuesto un método
radial para el cierre de aperturas lateral e interior. Ajustados el
brillo y la profundidad de la imagen, y el control morfológico se
obtuvo hasta un 83% de correcta segmentación del área vesical
en el grupo validación de la muestra. Estos resultados son la base
para el cálculo del volumen de orina en vejiga y la decisión de
cateterizar un paciente con retención urinaria.Postprint (published version
Multimode simulations of a wide field of view double-Fourier far-infrared spatio-spectral interferometer
In the absence of 50-m class space-based observatories, subarcsecond astronomy spanning the full far-infrared wavelength range will require space-based long-baseline interferometry. The long baselines of up to tens of meters are necessary to achieve subarcsecond resolution demanded by science goals. Also, practical observing times command a field of view toward an arcminute (1′) or so, not achievable with a single on-axis coherent detector. This paper is concerned with an application of an end-to-end instrument simulator PyFIInS, developed as part of the FISICA project under funding from the European Commission’s seventh Framework Programme for Research and Technological Development (FP7). Predicted results of wide field of view spatio–spectral interferometry through simulations of a long-baseline, double-Fourier, far-infrared interferometer concept are presented and analyzed. It is shown how such an interferometer, illuminated by a multimode detector can recover a large field of view at subarcsecond angular resolution, resulting in similar image quality as that achieved by illuminating the system with an array of coherent detectors. Through careful analysis, the importance of accounting for the correct number of higher-order optical modes is demonstrated, as well as accounting for both orthogonal polarizations. Given that it is very difficult to manufacture waveguide and feed structures at sub-mm wavelengths, the larger multimode design is recommended over the array of smaller single mode detectors. A brief note is provided in the conclusion of this paper addressing a more elegant solution to modeling far-infrared interferometers, which holds promise for improving the computational efficiency of the simulations presented here
The Wide-Field Spatio-Spectral Interferometer: System Overview, Data Synthesis and Analysis
The Wide-field Imaging Interferometry Testbed (WIIT) is a double Fourier (DF) interferometer operating at optical wavelengths, and provides data that are highly representative of those from a space-based far-infrared interferometer like SPIRIT. We have used the testbed to observe both geometrically simple and astronomically representative test scenes. Here we present an overview of the astronomical importance of high angular resolution at the far infrared, followed by the description of the optical set-up of WIIT, including the source simulator CHIP (Calibrated Hyperspectral Image Projector). We describe our synthesis algorithms used in the reconstruction of the input test scenes via a simulation of the most recent measurements. The updated algorithms, which include instruments artifacts that allow the synthesis of DF experimental data, are presented and the most recent results analyzed
Recent Experiments Conducted with the Wide-Field Imaging Interferometry Testbed (WIIT)
The Wide-field Imaging Interferometry Testbed (WIIT) was developed at NASA's Goddard Space Flight Center to demonstrate and explore the practical limitations inherent in wide field-of-view double Fourier (spatio-spectral) interferometry. The testbed delivers high-quality interferometric data and is capable of observing spatially and spectrally complex hyperspectral test scenes. Although WIIT operates at visible wavelengths, by design the data are representative of those from a space-based far-infrared observatory. We used WIIT to observe a calibrated, independently characterized test scene of modest spatial and spectral complexity, and an astronomically realistic test scene of much greater spatial and spectral complexity. This paper describes the experimental setup, summarizes the performance of the testbed, and presents representative data
Lipid droplet biogenesis induced by stress involves triacylglycerol synthesis that depends on group VIA phospholipase A2
This work investigates the metabolic origin of triacylglycerol (TAG) formed during lipid droplet (LD) biogenesis induced by stress. Cytotoxic inhibitors of fatty acid synthase induced TAG synthesis and LD biogenesis in CHO-K1 cells, in the absence of external sources of fatty acids. TAG synthesis was required for LD biogenesis and was sensitive to inhibition and down-regulation of the expression of group VIA phospholipase A2 (iPLA2-VIA). Induction of stress with acidic pH, C2-ceramide, tunicamycin, or deprivation of glucose also stimulated TAG synthesis and LD formation in a manner dependent on iPLA2-VIA. Overexpression of the enzyme enhanced TAG synthesis from endogenous fatty acids and LD occurrence. During stress, LD biogenesis but not TAG synthesis required phosphorylation and activation of group IVA PLA2 (cPLA2α). The results demonstrate that iPLA2-VIA provides fatty acids for TAG synthesis while cPLA2α allows LD biogenesis. LD biogenesis during stress may be a survival strategy, recycling structural phospholipids into energy-generating substrates
Optical and Quasi-Optical Analysis of System Components for a Far-Infrared Space Interferometer
Many important astrophysical processes occur at wavelengths that fall within the far-infrared band of the EM spectrum, and over distance scales that require sub-arc second spatial resolution. It is clear that in order to achieve sub-arc second resolution at these relatively long wavelengths (compared to optical/near-IR), which are strongly absorbed by the atmosphere, a space-based far-IR interferometer will be required. We present analysis of the optical system for a proposed spatial-spectral interferometer, discussing the challenges that arise when designing such a system and the simulation techniques employed that aim to resolve these issues. Many of these specific challenges relate to combining the beams from multiple telescopes where the wavelengths involved are relatively short (compared to radio interferometry), meaning that care must be taken with mirror surface quality, where surface form errors not only present potential degradation of the single system beams, but also serve to reduce fringe visibility when multiple telescope beams are combined. Also, the long baselines required for sub-arc second resolution present challenges when considering propagation of the relatively long wavelengths of the signal beam, where beam divergence becomes significant if the beam demagnification of the telescopes is not carefully considered. Furthermore, detection of the extremely weak far-IR signals demands ultra-sensitive detectors and instruments capable of operating at maximum efficiency. Thus, as will be shown, care must be taken when designing each component of such a complex quasioptical system
Group IVA phospholipase A2 is necessary for the biogenesis of lipid droplets
Lipid droplets (LD) are organelles present in all cell types, consisting of a hydrophobic core of triacylglycerols and cholesteryl esters, surrounded by a monolayer of phospholipids and cholesterol. This work shows that LD biogenesis induced by serum, by long-chain fatty acids, or the combination of both in CHO-K1 cells was prevented by phospholipase A2 inhibitors with a pharmacological profile consistent with the implication of group IVA cytosolic phospholipase A2 (cPLA2α). Knocking down cPLA2α expression with short interfering RNA was similar to pharmacological inhibition in terms of enzyme activity and LD biogenesis. A Chinese hamster ovary cell clone stably expressing an enhanced green fluorescent protein-cPLA2α fusion protein (EGFP-cPLA2) displayed higher LD occurrence under basal conditions and upon LD induction. Induction of LD took place with concurrent phosphorylation of cPLA2α at Ser505. Transfection of a S505A mutant cPLA2α showed that phosphorylation at Ser505 is key for enzyme activity and LD formation. cPLA2α contribution to LD biogenesis was not because of the generation of arachidonic acid, nor was it related to neutral lipid synthesis. cPLA2α inhibition in cells induced to form LD resulted in the appearance of tubulo-vesicular profiles of the smooth endoplasmic reticulum, compatible with a role of cPLA2α in the formation of nascent LD from the endoplasmic reticulum
Adaptive optics performance of a simulated coronagraph instrument on a large, segmented space telescope in steady state
Directly imaging Earth-like exoplanets (``exoEarths'') with a coronagraph
instrument on a space telescope requires a stable wavefront with optical path
differences limited to tens of picometers RMS during exposure times of a few
hours. While the structural dynamics of a segmented mirror can be directly
stabilized with telescope metrology, another possibility is to use a
closed-loop wavefront sensing and control system in the coronagraph instrument
that operates during the science exposures to actively correct the wavefront
and relax the constraints on the stability of the telescope. In this paper, we
present simulations of the temporal filtering provided using the example of
LUVOIR-A, a 15~m segmented telescope concept. Assuming steady-state aberrations
based on a finite element model of the telescope structure, we (1)~optimize the
system to minimize the wavefront residuals, (2)~ use an end-to-end numerical
propagation model to estimate the residual starlight intensity at the science
detector, and (3)~predict the number of exoEarth candidates detected during the
mission. We show that telescope dynamic errors of 100~pm~RMS can be reduced
down to 30~pm~RMS with a magnitude 0 star, improving the contrast performance
by a factor of 15. In scenarios where vibration frequencies are too fast for a
system that uses natural guide stars, laser sources can increase the flux at
the wavefront sensor to increase the servo-loop frequency and mitigate the high
temporal frequency wavefront errors. For example, an external laser with an
effective magnitude of -4 allows the wavefront from a telescope with 100~pm~RMS
dynamic errors and strong vibrations as fast as 16~Hz to be stabilized with
residual errors of 10~pm~RMS thereby increasing the number of detected planets
by at least a factor of 4.Comment: Published in JATIS. arXiv admin note: substantial text overlap with
arXiv:2108.0640
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