341 research outputs found
Multicolor pyrometer for materials processing in space
This report documents the work performed by Physical Sciences Inc. (PSI), under contract to NASA JPL, during a 2.5-year SBIR Phase 2 Program. The program goals were to design, construct, and program a prototype passive imaging pyrometer capable of measuring, as accurately as possible, and controlling the temperature distribution across the surface of a moving object suspended in space. These goals were achieved and the instrument was delivered to JPL in November 1989. The pyrometer utilizes an optical system which operates at short wavelengths compared to the peak of the black-body spectrum for the temperature range of interest, thus minimizing errors associated with a lack of knowledge about the heated sample's emissivity. To cover temperatures from 900 to 2500 K, six wavelengths are available. The preferred wavelength for measurement of a particular temperature decreases as the temperature increases. Images at all six wavelengths are projected onto a single CCD camera concurrently. The camera and optical system have been calibrated to relate the measured intensity at each pixel to the temperature of the heated object. The output of the camera is digitized by a frame grabber installed in a personal computer and analyzed automatically to yield temperature information. The data can be used in a feedback loop to alter the status of computer-activated switches and thereby control a heating system
Understanding hematopoiesis from a single-cell standpoint.
The cellular diversity of the hematopoietic system has been extensively studied, and a plethora of cell surface markers have been used to discriminate and prospectively purify different blood cell types. However, even within phenotypically identical fractions of hematopoietic stem and progenitor cells or lineage-restricted progenitors, significant functional heterogeneity is observed when single cells are analyzed. To address these challenges, researchers are now using techniques to follow single cells and their progeny to improve our understanding of the underlying functional heterogeneity. On November 19, 2015, Dr. David Kent and Dr. Leïla Perié, two emerging young group leaders, presented their recent efforts to dissect the functional properties of individual cells with a webinar series organized by the International Society for Experimental Hematology. Here, we provide a summary of the presented methods for cell labeling and clonal tracking and discuss how these different techniques have been employed to study hematopoiesis.MRC, Wellcome-Trust, BloodwiseThis is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.exphem.2016.03.00
Revealing the Structure of a Pre-Transitional Disk: The Case of the Herbig F Star SAO 206462 (HD 135344B)
SAO 206462 (HD 135344B) has previously been identified as a Herbig F star with a circumstellar disk with a dip in its infrared excess near 10 mum. In combination with a low accretion rate estimated from Br gamma, it may represent a gapped, but otherwise primordial or pre-transitional disk. We test this hypothesis with Hubble Space Telescope coronagraphic imagery, FUV spectroscopy and imagery and archival X-ray data, and spectral energy distribution (SED) modeling constrained by the observed system inclination, disk outer radius, and outer disk radial surface brightness (SB) profile using the Whitney Monte Carlo Radiative Transfer Code. The essentially face-on (i lsim 20°) disk is detected in scattered light from 0farcs4 to 1farcs15 (56-160 AU), with a steep (r -9.6) radial SB profile from 0farcs6 to 0farcs93. Fitting the SB data requires a concave upward or anti-flared outer disk, indicating substantial dust grain growth and settling by 8 ± 4 Myr. The warm dust component is significantly variable in near to mid-IR excess and in temperature. At its warmest, it appears confined to a narrow belt from 0.08 to 0.2 AU. The steep SED for this dust component is consistent with grains with a\u3c= 2.5 mum. For cosmic carbon to silicate dust composition, conspicuous 10 mum silicate emission would be expected and is not observed. This may indicate an elevated carbon to silicate ratio for the warm dust, which is not required to fit the outer disk. At its coolest, the warm dust can be fit with a disk from 0.14 to 0.31 AU, but with a higher inclination than either the outer disk or the gaseous disk, providing confirmation of the high inclination inferred from mid-IR interferometry. In tandem, the compositional and inclination difference between the warm dust and the outer dust disk suggests that the warm dust may be of second-generation origin, rather than a remnant of a primordial disk component. With its near face-on inclination, SAO 206462\u27s disk is a prime location for planet searches
PHAT Stellar Cluster Survey I. Year 1 Catalog and Integrated Photometry
The Panchromatic Hubble Andromeda Treasury (PHAT) survey is an on-going
Hubble Space Telescope (HST) multi-cycle program to obtain high spatial
resolution imaging of one-third of the M31 disk at ultraviolet through
near-infrared wavelengths. In this paper, we present the first installment of
the PHAT stellar cluster catalog. When completed, the PHAT cluster catalog will
be among the largest and most comprehensive surveys of resolved star clusters
in any galaxy. The exquisite spatial resolution achieved with HST has allowed
us to identify hundreds of new clusters that were previously inaccessible with
existing ground-based surveys. We identify 601 clusters in the Year 1 sample,
representing more than a factor of four increase over previous catalogs within
the current survey area (390 arcmin^2). This work presents results derived from
the first \sim25% of the survey data; we estimate that the final sample will
include \sim2500 clusters. For the Year 1 objects, we present a catalog with
positions, radii, and six-band integrated photometry. Along with a general
characterization of the cluster luminosities and colors, we discuss the cluster
luminosity function, the cluster size distributions, and highlight a number of
individually interesting clusters found in the Year 1 search.Comment: 26 pages, 22 figures, Accepted by Ap
Relating jet structure to photometric variability: the Herbig Ae star HD 163296
Herbig Ae/Be stars are intermediate-mass pre-main sequence stars surrounded
by circumstellar dust disks. Some are observed to produce jets, whose
appearance as a sequence of shock fronts (knots) suggests a past episodic
outflow variability. This "jet fossil record" can be used to reconstruct the
outflow history. We present the first optical to near-infrared (NIR)
VLT/X-shooter spectra of the jet from the Herbig Ae star HD 163296. We
determine physical conditions in the knots, as well as their kinematic "launch
epochs". Knots are formed simultaneously on either side of the disk, with a
regular interval of ~16 yr. The velocity dispersion versus jet velocity and the
energy input are comparable in both lobes. However, the mass loss rate,
velocity, and shock conditions are asymmetric. We find Mjet/Macc ~ 0.01-0.1,
consistent with magneto-centrifugal jet launching models. No evidence for dust
is found in the high-velocity jet, suggesting it is launched within the
sublimation radius (<0.5 au). The jet inclination measured from proper motions
and radial velocities confirms it is perpendicular to the disk. A tentative
relation is found between the structure of the jet and the photometric
variability of the source. Episodes of NIR brightening were previously detected
and attributed to a dusty disk wind. We report for the first time significant
optical fadings lasting from a few days up to a year, coinciding with the NIR
brightenings. These are likely caused by dust lifted high above the disk plane;
this supports the disk wind scenario. The disk wind is launched at a larger
radius than the high-velocity atomic jet, although their outflow variability
may have a common origin. No significant relation between outflow and accretion
variability could be established. Our findings confirm that this source
undergoes periodic ejection events, which may be coupled with dust ejections
above the disk plane.Comment: 20 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
Distinct p53 acetylation cassettes differentially influence gene-expression patterns and cell fate
The activity of the p53 gene product is regulated by a plethora of posttranslational modifications. An open question is whether such posttranslational changes act redundantly or dependently upon one another. We show that a functional interference between specific acetylated and phosphorylated residues of p53 influences cell fate. Acetylation of lysine 320 (K320) prevents phosphorylation of crucial serines in the NH2-terminal region of p53; only allows activation of genes containing high-affinity p53 binding sites, such as p21/WAF; and promotes cell survival after DNA damage. In contrast, acetylation of K373 leads to hyperphosphorylation of p53 NH2-terminal residues and enhances the interaction with promoters for which p53 possesses low DNA binding affinity, such as those contained in proapoptotic genes, leading to cell death. Further, acetylation of each of these two lysine clusters differentially regulates the interaction of p53 with coactivators and corepressors and produces distinct gene-expression profiles. By analogy with the “histone code” hypothesis, we propose that the multiple biological activities of p53 are orchestrated and deciphered by different “p53 cassettes,” each containing combination patterns of posttranslational modifications and protein–protein interactions
Variability of disk emission in pre-main sequence and related stars. II. Variability in the gas and dust emission of the Herbig Fe star SAO 206462
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.We present 13 epochs of near-infrared (0.8-5 μm) spectroscopic observations of the pre-transitional, "gapped" disk system in SAO 206462 (=HD 135344B). In all, six gas emission lines (Brα, Brγ, Paβ, Paγ, Paδ, Paepsilon, and the 0.8446 μm line of O I) along with continuum measurements made near the standard J, H, K, and L photometric bands were measured. A mass accretion rate of approximately 2 × 10–8 M ☉ yr–1 was derived from the Brγ and Paβ lines. However, the fluxes of these lines varied by a factor of over two during the course of a few months. The continuum also varied, but by only ~30%, and even decreased at a time when the gas emission was increasing. The H I line at 1.083 μm was also found to vary in a manner inconsistent with that of either the hydrogen lines or the dust. Both the gas and dust variabilities indicate significant changes in the region of the inner gas and the inner dust belt that may be common to many young disk systems. If planets are responsible for defining the inner edge of the gap, they could interact with the material on timescales commensurate with what is observed for the variations in the dust, while other disk instabilities (thermal, magnetorotational) would operate there on longer timescales than we observe for the inner dust belt. For SAO 206462, the orbital period would likely be 1-3 years. If the changes are being induced in the disk material closer to the star than the gap, a variety of mechanisms (disk instabilities, interactions via planets) might be responsible for the changes seen. The He I feature is most likely due to a wind whose orientation changes with respect to the observer on timescales of a day or less. To further constrain the origin of the gas and dust emission will require multiple spectroscopic and interferometric observations on both shorter and longer timescales that have been sampled so far.This work was supported by NASA ADP grants NNH06CC28C and NNX09AC73G, Hubble Space Telescope grants HST-GO-10764 and HST-GO-10864, Chilean National TAC grants CNTAC-010A-064
Heatshield for Extreme Entry Environment Technology (HEEET) - Enabling Missions Beyond Heritage Carbon Phenolic
This poster provides an overview of the requirements, design, development and testing of the 3D Woven TPS being developed under NASA's Heatshield for Extreme Entry Environment Technology (HEEET) project. Under this current program, NASA is working to develop a Thermal Protection System (TPS) capable of surviving entry into Venus or Saturn. A primary goal of the project is to build and test an Engineering Test Unit (ETU) to establish a Technical Readiness Level (TRL) of 6 for this technology by 2017
High-Contrast NIR Polarization Imaging of MWC480
One of the key predictions of modeling from the IR excess of Herbig Ae stars
is that for protoplanetary disks, where significant grain growth and settling
has occurred, the dust disk has flattened to the point that it can be partially
or largely shadowed by the innermost material at or near the dust sublimation
radius. When the self-shadowing has already started, the outer disk is expected
to be detected in scattered light only in the exceptional cases that the scale
height of the dust disk at the sublimation radius is smaller than usual.
High-contrast imaging combined with the IR spectral energy distribution allow
us to measure the degree of flattening of the disk, as well as to determine the
properties of the outer disk. We present polarimetric differential imaging in
band obtained with Subaru/HiCIAO of one such system, MWC 480. The HiCIAO
data were obtained at a historic minimum of the NIR excess. The disk is
detected in scattered light from 0\farcs2-1\farcs0 (27.4-137AU). Together with
the marginal detection of the disk from 1998 February 24 by HST/NICMOS, our
data constrain the opening half angle for the disk to lie between
1.3. When compared with similar measures in CO for
the gas disk from the literature, the dust disk subtends only 30% of the
gas disk scale height (H/R0.03). Such a dust disk is a factor of 5-7
flatter than transitional disks, which have structural signatures that giant
planets have formed.Comment: 21 pages, 6 figures, 1 table, ApJ accepted 2012-05-0
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