40 research outputs found
The ^{55}Fe X-ray Energy Response of Mercury Cadmium Telluride Near-Infrared Detector Arrays
A technique involving ^{55}Fe X-rays provides a straightforward method to
measure the response of a detector. The detector's response can lead directly
to a calculation of the conversion gain (e^- ADU^{-1}), as well as aid detector
design and performance studies. We calibrate the ^{55}Fe X-ray energy response
and pair production energy of HgCdTe using 8 HST WFC3 1.7 \micron flight grade
detectors. The results show that each K X-ray generates 2273 \pm 137
electrons, which corresponds to a pair-production energy of 2.61 \pm 0.16 eV.
The uncertainties are dominated by our knowledge of the conversion gain. In
future studies, we plan to eliminate this uncertainty by directly measuring
conversion gain at very low light levels.Comment: 17 pages, 7 Figures, 2 Table. Accepted for publication on PAS
Quantitative analysis of the influence of dust sea surface forcing on the primary production of the subtropical Atlantic Ocean using a ten-year time series of satellite observations
NIMBUS: The Near-Infrared Multi-Band Ultraprecise Spectroimager for SOFIA
We present a new and innovative near-infrared multi-band ultraprecise
spectroimager (NIMBUS) for SOFIA. This design is capable of characterizing a
large sample of extrasolar planet atmospheres by measuring elemental and
molecular abundances during primary transit and occultation. This wide-field
spectroimager would also provide new insights into Trans-Neptunian Objects
(TNO), Solar System occultations, brown dwarf atmospheres, carbon chemistry in
globular clusters, chemical gradients in nearby galaxies, and galaxy
photometric redshifts. NIMBUS would be the premier ultraprecise spectroimager
by taking advantage of the SOFIA observatory and state of the art infrared
technologies.
This optical design splits the beam into eight separate spectral bandpasses,
centered around key molecular bands from 1 to 4 microns. Each spectral channel
has a wide field of view for simultaneous observations of a reference star that
can decorrelate time-variable atmospheric and optical assembly effects,
allowing the instrument to achieve ultraprecise calibration for imaging and
photometry for a wide variety of astrophysical sources. NIMBUS produces the
same data products as a low-resolution integral field spectrograph over a large
spectral bandpass, but this design obviates many of the problems that preclude
high-precision measurements with traditional slit and integral field
spectrographs. This instrument concept is currently not funded for development.Comment: 14 pages, 9 figures, SPIE Astronomical Telescopes and Instrumentation
201
Development of a 2K x 2K GaAs QWIP Focal Plane Array
We are developing the next generation of GaAs Quantum Well Infrared Photodetector (QWIP) focal plane arrays (FPAs) in preparation for future NASA space-borne Earth observing missions. It is anticipated that these missions will require both wider ground spatial coverage as well as higher ground imaging resolution. In order to demonstrate our capability in meeting these future goals we have taken a two-tiered approach in the next stage of advanced QWIP focal plane array development. We will describe our progress in the development of a 512 x 3,200 (512 x 3K) array format for this next generation thermal imaging array for the NASA Landsat project. However, there currently is no existing readout integrated circuit (ROIC) for this format array.so to demonstrate the ability to scale-up an existing ROIC we developed a 1,920 x 2,048 (2K x 2K) array and it hybridized to a Raytheon SB419 CTIA readout integrated circuit that was scaled up from their existing 512 x 640 SB339 ROIC. Two versions of the 512 x 3K QWIP array were fabricated to accommodate a future design scale-up of both the Indigo 9803 ROIC based on a 25 micron pixel dimension and a scale up of the Indigo 9705 ROIC based on a 30 micron pixel dimension. Neither readout for the 512 x 3K has yet to be developed but we have fabricated both versions of the array. We describe the design, development and test results of this effort as well as the specific applications these FPAs are intended to address
New Particle-Induced Single Event Latchup Mechanism Observed in a Cryogenic CMOS Readout Integrated Circuit
No abstract availabl
Snowballs in Euclid and WFIRST Detectors
Snowballs are transient events observed in HgCdTe detectors with a sudden increase of charge in a few pixels. They appear between consecutive reads of the detector, after which the affected pixels return to their normal behavior. The origin of the snowballs is unknown, but it was speculated that they could be the result of alpha decay of naturally radioactive contaminants in the detectors, but a cosmic ray origin cannot be ruled out. Even though previous studies predicted a low rate of occurrence of these events, and consequently, a minimal impact on science, it is interesting to investigate the cause or causes that may generate snowballs and their impact in detectors designed for future missions. We searched for the presence of snowballs in the dark current data in Euclid and Wide Field Infrared Survey Telescope (WFIRST) detectors tested in the Detector Characterization Laboratory at Goddard Space Flight Center. Our investigation shows that for Euclid and WFIRST detectors, there are snowballs that appear only one time, and others that repeat in the same spatial localization. For Euclid detectors, there is a correlation between the snowballs that repeat and bad pixels in the operational masks (pixels that do not fulfill the requirements to pass spectroscopy noise, photometry noise, quantum efficiency, and/or linearity). The rate of occurrence for a snowball event is about 0.9 snowballs/hr. in Euclid detectors (for the ones that do not have associated bad pixels in the mask), and about 0.7 snowballs/hr. in PV3 Full Array Lot WFIRST detectors
ACCESS: Design and Sub-System Performance
Establishing improved spectrophotometric standards is important for a broad range of missions and is relevant to many astrophysical problems. ACCESS, "Absolute Color Calibration Experiment for Standard Stars", is a series of rocket-borne sub-orbital missions and ground-based experiments designed to enable improvements in the precision of the astrophysical flux scale through the transfer of absolute laboratory detector standards from the National Institute of Standards and Technology (NIST) to a network of stellar standards with a calibration accuracy of 1% and a spectral resolving power of 500 across the 0.35 -1.7 micrometer bandpass
Acupuncture or low frequency infrared treatment for low back pain in Chinese patients: a discrete choice experiment
Acupuncture is a popular but controversial treatment option for low back pain. In China, it is practised as traditional Chinese medicine; other treatment strategies for low back pain are commonly practised as Western medicine. Research on patient preference for low back-pain treatment options has been mainly conducted in Western countries and is limited to a willingness-to-pay approach. A stated-preference, discrete choice experiment was conducted to determine Chinese patient preferences and trade-offs for acupuncture and low frequency infrared treatment in low back pain from September 2011 to August 2012 after approval from the Department of Scientific Research in the study settings. Eight-six adult outpatients who visited the ‘traditional medicine department’ at a traditional Chinese medicine hospital and the ‘rehabilitation department’ at a Western medicine hospital in Guangdong Province of China for chronic low back pain during study period participated in an interview survey. A questionnaire containing 10 scenarios (5 attributes in each scenario) was used to ask participants' preference for acupuncture, low frequency infrared treatment or neither option. Validated responses were analysed using a nested-logit model. The decision on whether to receive a therapy was not associated with the expected utility of receiving therapy, female gender and higher out-of-pocket payment significantly decreased chance to receive treatments. Of the utility of receiving either acupuncture or low frequency infrared treatment, the treatment sensation was the most important attribute as an indicator of treatment efficacy, followed by the maximum efficacy, maintenance duration and onset of efficacy, and the out-of-pocket payment. The willingness-to-pay for acupuncture and low frequency infrared treatment were about 592.4 USD per course respectively, demonstrated patients' demand of pain management. The treatment sensation was regarded as an indicator of treatment efficacy and the most important attribute for choosing acupuncture or low frequency infrared treatment. The high willingness-to-pay demonstrated patients' demand of pain management. However, there may be other factors influencing patients' preference to receive treatments