The James Webb space telescope GARDNER, Jonathan P; MATHER, John C; LUNINE, Jonathan I ...
Space science reviews,
01/2006, Letnik:
123, Številka:
4
Journal Article
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Issue Title: The James Webb Space Telescope The James Webb Space Telescope (JWST) is a large (6.6 m), cold (<50 K), infrared (IR)-optimized space observatory that will be launched early in the next ...decade into orbit around the second Earth-Sun Lagrange point. The observatory will have four instruments: a near-IR camera, a near-IR multiobject spectrograph, and a tunable filter imager will cover the wavelength range, 0.6 < ; < 5.0 μ m, while the mid-IR instrument will do both imaging and spectroscopy from 5.0 < ; < 29 μ m. The JWST science goals are divided into four themes. The key objective of The End of the Dark Ages: First Light and Reionization theme is to identify the first luminous sources to form and to determine the ionization history of the early universe. The key objective of The Assembly of Galaxies theme is to determine how galaxies and the dark matter, gas, stars, metals, morphological structures, and active nuclei within them evolved from the epoch of reionization to the present day. The key objective of The Birth of Stars and Protoplanetary Systems theme is to unravel the birth and early evolution of stars, from infall on to dust-enshrouded protostars to the genesis of planetary systems. The key objective of the Planetary Systems and the Origins of Life theme is to determine the physical and chemical properties of planetary systems including our own, and investigate the potential for the origins of life in those systems. Within these themes and objectives, we have derived representative astronomical observations. To enable these observations, JWST consists of a telescope, an instrument package, a spacecraft, and a sunshield. The telescope consists of 18 beryllium segments, some of which are deployed. The segments will be brought into optical alignment on-orbit through a process of periodic wavefront sensing and control. The instrument package contains the four science instruments and a fine guidance sensor. The spacecraft provides pointing, orbit maintenance, and communications. The sunshield provides passive thermal control. The JWST operations plan is based on that used for previous space observatories, and the majority of JWST observing time will be allocated to the international astronomical community through annual peer-reviewed proposal opportunities.PUBLICATION ABSTRACT
The Alpha laser is a hydrogen fluoride laser (2.7 /spl mu/m) that is a ground based testbed for a Space based laser (SBL). Performance of two recent high power tests has been quantified in terms of ...power, spectra, near field intensity and phase, far field intensity, and laser jitter. The conclusions were as follows: (1) Misalignments suggested in earlier analyses were found and corrected with improved precision instrumentation. (2) Alpha power performance improved in recent tests because of improvements in alignment and internal clipper positioning. (3) Alpha intensity profile characteristics were improved by the alignment correction. (4) Alpha spectral characteristics show sensitivity to flow conditions. (5) Alpha phase was relatively unaffected by the alignment and flow modifications. Continued investigation of Alpha includes additional testing to explore a predicted improvement in power performance expected from optimization of the flows.
Space Sci.Rev. 123 (2006) 485 The James Webb Space Telescope (JWST) is a large (6.6m), cold (50K),
infrared-optimized space observatory that will be launched early in the next
decade. The observatory ...will have four instruments: a near-infrared camera, a
near-infrared multi-object spectrograph, and a tunable filter imager will cover
the wavelength range, 0.6 to 5.0 microns, while the mid-infrared instrument
will do both imaging and spectroscopy from 5.0 to 29 microns. The JWST science
goals are divided into four themes. The End of the Dark Ages: First Light and
Reionization theme seeks to identify the first luminous sources to form and to
determine the ionization history of the early universe. The Assembly of
Galaxies theme seeks to determine how galaxies and the dark matter, gas, stars,
metals, morphological structures, and active nuclei within them evolved from
the epoch of reionization to the present day. The Birth of Stars and
Protoplanetary Systems theme seeks to unravel the birth and early evolution of
stars, from infall on to dust-enshrouded protostars to the genesis of planetary
systems. The Planetary Systems and the Origins of Life theme seeks to determine
the physical and chemical properties of planetary systems including our own,
and investigate the potential for the origins of life in those systems. To
enable these observations, JWST consists of a telescope, an instrument package,
a spacecraft and a sunshield. The telescope consists of 18 beryllium segments,
some of which are deployed. The segments will be brought into optical alignment
on-orbit through a process of periodic wavefront sensing and control. The JWST
operations plan is based on that used for previous space observatories, and the
majority of JWST observing time will be allocated to the international
astronomical community through annual peer-reviewed proposal opportunities.
The James Webb Space Telescope (JWST) is a large (6.6m), cold (50K), infrared-optimized space observatory that will be launched early in the next decade. The observatory will have four instruments: a ...near-infrared camera, a near-infrared multi-object spectrograph, and a tunable filter imager will cover the wavelength range, 0.6 to 5.0 microns, while the mid-infrared instrument will do both imaging and spectroscopy from 5.0 to 29 microns. The JWST science goals are divided into four themes. The End of the Dark Ages: First Light and Reionization theme seeks to identify the first luminous sources to form and to determine the ionization history of the early universe. The Assembly of Galaxies theme seeks to determine how galaxies and the dark matter, gas, stars, metals, morphological structures, and active nuclei within them evolved from the epoch of reionization to the present day. The Birth of Stars and Protoplanetary Systems theme seeks to unravel the birth and early evolution of stars, from infall on to dust-enshrouded protostars to the genesis of planetary systems. The Planetary Systems and the Origins of Life theme seeks to determine the physical and chemical properties of planetary systems including our own, and investigate the potential for the origins of life in those systems. To enable these observations, JWST consists of a telescope, an instrument package, a spacecraft and a sunshield. The telescope consists of 18 beryllium segments, some of which are deployed. The segments will be brought into optical alignment on-orbit through a process of periodic wavefront sensing and control. The JWST operations plan is based on that used for previous space observatories, and the majority of JWST observing time will be allocated to the international astronomical community through annual peer-reviewed proposal opportunities.
We report the observation of the xenon isotope spectrum using saturation spectroscopy on a gain cell external to a He-Xe laser. Six resonances centered about 3.508mum are observed over the limited ...tuning range of the laser. These resonances are assigned to the Xe(128)Xe(130)Xe(131)Xe(132)Xe(134)and Xe(136)isotopes. The observed homogeneous linewidth is 9 +/- 1 MHz, and the pressure broadening of the homogeneous linewidth is experimentally determined to be 71 +/- 20 MHz/ torr.
Water-splitting dye-sensitized photoelectrochemical cells (WS-DSPECs) utilize high surface area TiO2 electrodes functionalized with light absorbing sensitizers and water oxidation catalysts. Because ...water splitting requires vectorial electron transfer from the catalyst to the sensitizer to the TiO2 surface, attaching both sensitizer and catalyst to TiO2 in the correct sequence and stabilizing them under photoelectrochemical conditions has been a challenging problem. Rutile-phase IrO2 nanoparticles can be deposited directly on the TiO2 electrode by adsorbing citrate-capped amorphous IrO x and then sintering at 450 °C. Electrodes functionalized with these nanocrystalline particles show higher activity than those made from ligand-capped amorphous IrO x without sintering. In the WS-DSPEC, the Coulombic efficiency for oxygen evolution from the sintered nanoparticle photoelectrodes was near unity. The loading of colloidal IrO x and IrO2 particles onto the porous TiO2 electrodes was quantified by neutron activation analysis. Photovoltage measurements suggest that at high catalyst loading the dominant charge recombination pathway is from photoinjected electrons to IrO2.
Two‐dimensional photosynthetic protein crystals provide a high density of aligned reaction centers. We reconstitute the robust light harvesting protein Photosystem I into a 2D crystal with lipids and ...integrate the crystals into a photo‐electrochemical device. A 4‐fold photocurrent enhancement is measured by incorporating conjugated oligoelectrolytes to form a supporting conductive bilayer in the device which produces a high photocurrent of ∼600 μA per mg PSI deposited.
Millions of patients present to US EDs each year with symptoms concerning for acute coronary syndrome (ACS), but fewer than 10% are ultimately diagnosed with ACS. Well-tested and externally validated ...accelerated diagnostic protocols were developed to aid providers in risk stratifying patients with possible ACS and have become central components of current ED practice guidelines. Nevertheless, the fear of missing ACS continues to be a strong motivator for ED providers to pursue further testing for their patients. An ethical dilemma arises when the provider must balance the risk of ACS if the patient is discharged compared with the potential harms caused by a cardiac workup. Providers should be familiar with the ethical principles relevant to this dilemma in order to determine what is in the best interests of the patient.
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