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Institution

Jet Propulsion Laboratory

FacilityLa Cañada Flintridge, California, United States
About: Jet Propulsion Laboratory is a facility organization based out in La Cañada Flintridge, California, United States. It is known for research contribution in the topics: Mars Exploration Program & Telescope. The organization has 8801 authors who have published 14333 publications receiving 548163 citations. The organization is also known as: JPL & NASA JPL.


Papers
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Journal ArticleDOI
TL;DR: In this article, the authors present simulations of coronagraphs matched to adaptive optics (AO) systems on the Calypso 1.2 m, Palomar Hale 5 m, and Gemini 8 m telescopes under various atmospheric conditions and identify useful parameter ranges for AO coronagraphy.
Abstract: We summarize the theory of coronagraphic optics and identify a dimensionless —ne-tuning parameter, F, which we use to describe the Lyot stop size in the natural units of the coronagraphic optical train and the observing wavelength. We then present simulations of coronagraphs matched to adaptive optics (AO) systems on the Calypso 1.2 m, Palomar Hale 5 m, and Gemini 8 m telescopes under various atmospheric conditions and identify useful parameter ranges for AO coronagraphy on these telescopes. Our simulations employ a tapered, high-pass —lter in spatial frequency space to mimic the action of adaptive wave front correction. We test the validity of this representation of AO correction by comparing our simulations with recent K-band data from the 241 channel Palomar Hale AO system and its dedicated Palomar High Angular Resolution Observer (PHARO) science camera in coronagraphic mode. Our choice of monochromatic modeling enables us to distinguish between underlying halo suppression and ★ b)

141 citations

Journal ArticleDOI
TL;DR: In this paper, internal flow measurements in transonic region of supersonic nozzle with small throat radius of curvature compared with prediction data were used to estimate the internal flow of a supersonically-charged supersonica nozzle.
Abstract: Internal flow measurements in transonic region of supersonic nozzle with small throat radius of curvature compared with prediction data

141 citations

Journal ArticleDOI
12 Jul 1984-Nature
TL;DR: A series of automated instruments that use state-of-the-art chemical methods has been developed for high-sensitivity protein sequencing, DNA synthesis and peptide synthesis and their use for the study of a variety of biologically interesting problems.
Abstract: A series of automated instruments that use state-of-the-art chemical methods has been developed for high-sensitivity protein sequencing, DNA synthesis and peptide synthesis. These intruments have been integrated into a centralized microchemical facility in order to promote their use for the study of a variety of biologically interesting problems. This facility has as one of its major functions the development of new chemistries and instrumentation for the structural analysis and synthesis of genes and proteins.

141 citations

Journal ArticleDOI
TL;DR: In this paper, the authors examined the sky variation at intermediate latitudes using a cross-correlation technique and compared the observed emission in 15 selected sky regions to three'standard' templates.
Abstract: Wilkinson Microwave Anisotropy Probe (WMAP) data when combined with ancillary data on free-free, synchrotron and dust allow an improved understanding of the spectrum of emission from each of these components. Here, we examine the sky variation at intermediate latitudes using a cross-correlation technique. In particular, we compare the observed emission in 15 selected sky regions to three 'standard' templates. The free-free emission of the diffuse ionized gas is fitted by a well-known spectrum at K and Ka band, but the derived emissivity corresponds to a mean electron temperature of similar to 4000-5000 K. This is inconsistent with estimates from Galactic H II regions although a variation in the derived ratio of H alpha to free-free intensity by a factor of similar to 2 is also found from region to region. The origin of the discrepancy is unclear. The anomalous emission associated with dust is clearly detected in most of the 15 fields studied. The anomalous emission correlates well with the Finkbeiner, Davis & Schlegel model 8 predictions (FDS8) at 94 GHz, with an effective spectral index between 20 and 60 GHz, of beta similar to -2.85. Furthermore, the emissivity varies by a factor of similar to 2 from cloud to cloud. A modestly improved fit to the anomalous dust at K band is provided by modulating the template by an estimate of the dust colour temperature, specifically FDS8 x T^n. We find a preferred value n similar to 1.6, although there is a scatter from region to region. Nevertheless, the preferred index drops to zero at higher frequencies where the thermal dust emission dominates. The synchrotron emission steepens between GHz frequencies and the WMAP bands. There are indications of spectral index variations across the sky but the current data are not precise enough to accurately quantify this from region to region. Our analysis of the WMAP data indicates strongly that the dust-correlated emission at the low WMAP frequencies has a spectrum which is compatible with spinning dust; we find no evidence for a synchrotron component correlated with dust. The importance of these results for the correction of cosmic microwave background data for Galactic foreground emission is discussed.

141 citations

Journal ArticleDOI
TL;DR: In this article, a simple model of a bubble of synchrotron-emitting electrons cooling via adiabatic expansion can explain the time delay between various wavelengths, the asymmetric shape of the light curves, and the observed polarization of the flare emission at 43 and 22 GHz.
Abstract: Sgr A*, the massive black hole at the center of the Galaxy, varies in radio through X-ray emission on hourly timescales. The flare activity is thought to arise from the innermost region of an accretion flow onto Sgr A*. We present simultaneous light curves of Sgr A* in radio, submillimeter and X-rays that show a possible time delay of -->110 ? 17 minutes between X-ray and 850 ?m suggesting that the submillimeter flare emission is optically thick. At radio wavelengths, we detect time lags of -->20.4 ? 6.8, -->30 ? 12, and -->20 ? 6 minutes between the flare peaks observed at 13 and 7 mm (22 and 43 GHz) in three different epochs using the VLA. Linear polarization of -->1% ? 0.2% and -->0.7 ? 0.1% is detected at 7 and 13 mm, respectively, when averaged over the entire observation on 2006 July 17. A simple model of a bubble of synchrotron-emitting electrons cooling via adiabatic expansion can explain the time delay between various wavelengths, the asymmetric shape of the light curves, and the observed polarization of the flare emission at 43 and 22 GHz. The derived physical quantities that characterize the emission give an expansion speed of -->vexp ~ 0.003?0.1 c, magnetic field of -->B ~ 10?70 G, and particle spectral index -->p ~ 1?2. These parameters suggest that the associated plasma cannot escape from Sgr A* unless it has a large bulk motion.

141 citations


Authors

Showing all 9033 results

NameH-indexPapersCitations
B. P. Crill148486111895
George Helou14466296338
H. K. Eriksen141474104208
Charles R. Lawrence141528104948
W. C. Jones14039597629
Gianluca Morgante13847898223
Jean-Paul Kneib13880589287
Kevin M. Huffenberger13840293452
Robert H. Brown136117479247
Federico Capasso134118976957
Krzysztof M. Gorski132380105912
Olivier Doré130427104737
Mark E. Thompson12852777399
Clive Dickinson12350180701
Daniel Stern12178869283
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
2023177
2022416
2021359
2020348
2019384
2018445