1,164 research outputs found
The FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later
We have used the VLA FIRST survey and the APM catalog of the POSS-I plates as
the basis for constructing a new radio-selected sample of optically bright
quasars. This is the first radio-selected sample that is competitive in size
with current optically selected quasar surveys. Using only two basic criteria,
radio-optical positional coincidence and optical morphology, quasars and BL
Lacs can be identified with 60% selection efficiency; the efficiency increases
to 70% for objects fainter than magnitude 17. We show that a more sophisticated
selection scheme can predict with better than 85% reliability which candidates
will turn out to be quasars.
This paper presents the second installment of the FIRST Bright Quasar Survey
with a catalog of 636 quasars distributed over 2682 square degrees. The quasar
sample is characterized and all spectra are displayed. The FBQS detects both
radio-loud and radio-quiet quasars out to a redshift z>3. We find a large
population of objects of intermediate radio-loudness; there is no evidence in
our sample for a bimodal distribution of radio characteristics. The sample
includes ~29 broad absorption line quasars, both high and low ionization, and a
number of new objects with remarkable optical spectra.Comment: 41 pages plus 39 gifs which contain all quasar spectra. Accepted for
publication in the Astrophysical Journal Supplement Serie
A conditional form of Bruton's tyrosine kinase is sufficient to activate multiple downstream signaling pathways via PLC Gamma 2 in B cells
BACKGROUND: Bruton's tyrosine kinase (Btk) is essential for B cell development and function. Mutations of Btk elicit X-linked agammaglobulinemia in humans and X-linked immunodeficiency in the mouse. Btk has been proposed to participate in B cell antigen receptor-induced signaling events leading to activation of phospholipase C-Ī³2 (PLCĪ³2) and calcium mobilization. However it is unclear whether Btk activation is alone sufficient for these signaling events, and whether Btk can activate additional pathways that do not involve PLCĪ³2. To address such issues we have generated Btk:ER, a conditionally active form of the kinase, and expressed it in the PLCĪ³2-deficient DT40 B cell line. RESULTS: Activation of Btk:ER was sufficient to induce multiple B cell signaling pathways in PLCĪ³2-sufficient DT40 cells. These included tyrosine phosphorylation of PLCĪ³2, mobilization of intracellular calcium, activation of extracellular signal-regulated kinase (ERK) and c-Jun NH(2)-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) pathways, and apoptosis. In DT40 B cells deficient for PLCĪ³2, Btk:ER activation failed to induce the signaling events described above with the consequence that the cells failed to undergo apoptosis. CONCLUSIONS: These data suggest that Btk:ER regulates downstream signaling pathways primarily via PLCĪ³2 in B cells. While it is not known whether activated Btk:ER precisely mimics activated Btk, this conditional system will likely facilitate the dissection of the role of Btk and its family members in a variety of biological processes in many different cell types
Janus: Launch of a NASA SmallSat Mission to Near-Earth Binary Asteroids
Janus is a two-spacecraft SmallSat mission to fly by two different pairs of binary near Earth asteroids, (175706) 1996 FG3 and (35107) 1991 VH. The two identical Janus spacecraft are scheduled to launch during a launch period opening 1 August 2022 as secondary payloads with the NASA Psyche mission, on a SpaceX Falcon Heavy launch vehicle. Janus is led by principal investigator Dr. Dan Scheeres at the University of Colorado Boulder and managed, built, and operated by Lockheed Martin. These planetary SmallSats share many deep space challenges similar to larger missions: Janus must execute deep space maneuvers to achieve hundreds of meters per second ĪV to reach its destinations, close a telecommunication link at ranges up to 2.4 AU, autonomously manage a several-month-long telecommunications blackout during solar conjunction, operate at a maximum Sun range of 1.62 AU, and survive for approximately four years in interplanetary space before encountering their target asteroids. During the encounters, the spacecraft will return high resolution visible and infra-red images of the asteroids. In getting Janus to the pad, the implementation team successfully managed an aggressive mission schedule despite COVID-19 related supply chain impacts and work environments, all while remaining on target for the SIMPLEx-2 cost cap. Janus is a pathfinder for achievable and affordable SmallSat science missions and demonstrates the valuable partnership between an experienced deep space mission engineering team, the SmallSat commercial component industry, and a forward- looking NASA model for Class-D science missions
Noble gas signatures constrain oil-field water as the carrier phase of hydrocarbons occurring in shallow aquifers in the San Joaquin Basin, USA
Ā© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Karolyte, R., Barry, P. H., Hunt, A. G., Kulongoski, J. T., Tyne, R. L., Davis, T. A., Wright, M. T., McMahon, P. B., & Ballentine, C. J. Noble gas signatures constrain oil-field water as the carrier phase of hydrocarbons occurring in shallow aquifers in the San Joaquin Basin, USA. Chemical Geology, 584, (2021): 120491, https://doi.org/10.1016/j.chemgeo.2021.120491.Noble gases record fluid interactions in multiphase subsurface environments through fractionation processes during fluid equilibration. Water in the presence of hydrocarbons at the subsurface acquires a distinct elemental signature due to the difference in solubility between these two fluids. We find the atmospheric noble gas signature in produced water is partially preserved after hydrocarbons production and water disposal to unlined ponds at the surface. This signature is distinct from meteoric water and can be used to trace oil-field water seepage into groundwater aquifers. We analyse groundwater (n = 30) and fluid disposal pond (n = 2) samples from areas overlying or adjacent to the Fruitvale, Lost Hills, and South Belridge Oil Fields in the San Joaquin Basin, California, USA. Methane (2.8 Ć 10ā7 to 3 Ć 10ā2 cm3 STP/cm3) was detected in 27 of 30 groundwater samples. Using atmospheric noble gas signatures, the presence of oil-field water was identified in 3 samples, which had equilibrated with thermogenic hydrocarbons in the reservoir. Two (of the three) samples also had a shallow microbial methane component, acquired when produced water was deposited in a disposal pond at the surface. An additional 6 samples contained benzene and toluene, indicative of interaction with oil-field water; however, the noble gas signatures of these samples are not anomalous. Based on low tritium and 14C contents (ā¤ 0.3 TU and 0.87ā6.9 pcm, respectively), the source of oil-field water is likely deep, which could include both anthropogenic and natural processes. Incorporating noble gas analytical techniques into the groundwater monitoring programme allows us to 1) differentiate between thermogenic and microbial hydrocarbon gas sources in instances when methane isotope data are unavailable, 2) identify the carrier phase of oil-field constituents in the aquifer (gas, oil-field water, or a combination), and 3) differentiate between leakage from a surface source (disposal ponds) and from the hydrocarbon reservoir (either along natural or anthropogenic pathways such as faulty wells).This work was supported by the U.S. Geological Survey as part of the California State Water Resources Control Board's Oil and Gas Regional Monitoring Program
SDSS J094604.90+183541.8: A Gravitationally Lensed Quasar at z=4.8
We report the discovery of a gravitationally lensed quasar identified
serendipitously in the Sloan Digital Sky Survey (SDSS). The object, SDSS
J094604.90+183541.8, was initially targeted for spectroscopy as a luminous red
galaxy, but the SDSS spectrum has the features of both a z=0.388 galaxy and a
z=4.8 quasar. We have obtained additional imaging that resolves the system into
two quasar images separated by 3.06 arcsec and a bright galaxy that is strongly
blended with one of the quasar images. We confirm spectroscopically that the
two quasar images represent a single lensed source at z=4.8 with a total
magnification of 3.2, and we derive a model for the lensing galaxy. This is the
highest redshift lensed quasar currently known. We examine the issues
surrounding the selection of such an unusual object from existing data and
briefly discuss implications for lensed quasar surveys.Comment: AJ accepted, 9 pages, 6 figures, referee suggestions include
HopScotch - a low-power renewable energy base station network for rural broadband access
The provision of adequate broadband access to communities in sparsely populated rural areas has in the past been severely restricted. In this paper, we present a wireless broadband access test bed running in the Scottish Highlands and Islands which is based on a relay network of low-power base stations. Base stations are powered by a combination of renewable sources creating a low cost and scalable solution suitable for community ownership. The use of the 5~GHz bands allows the network to offer large data rates and the testing of ultra high frequency ``white space'' bands allow expansive coverage whilst reducing the number of base stations or required transmission power. We argue that the reliance on renewable power and the intelligent use of frequency bands makes this approach an economic green radio technology which can address the problem of rural broadband access
Selective inhibition of HIV-1 reverse transcriptase-associated ribonuclease H activity by hydroxylated tropolones
High-throughput screening of a National Cancer Institute library of pure natural products identified the hydroxylated tropolone derivatives Ī²-thujaplicinol (2,7-dihydroxy-4-1(methylethyl)-2,4,6-cycloheptatrien-1-one) and manicol (1,2,3,4-tetrahydro-5-7-dihydroxy-9-methyl-2-(1-methylethenyl)-6H-benzocyclohepten-6-one) as potent and selective inhibitors of the ribonuclease H (RNase H) activity of human immunodeficiency virus-type 1 reverse transcriptase (HIV-1 RT). Ī²-Thujaplicinol inhibited HIV-1 RNase H in vitro with an IC(50) of 0.2 Ī¼M, while the IC(50) for Escherichia coli and human RNases H was 50 Ī¼M and 5.7 Ī¼M, respectively. In contrast, the related tropolone analog Ī²-thujaplicin (2-hydroxy-4-(methylethyl)-2,4,6-cycloheptatrien-1-one), which lacks the 7-OH group of the heptatriene ring, was inactive, while manicol, which possesses a 7-OH group, inhibited HIV-1 and E.coli RNases H with IC(50) = 1.5 Ī¼M and 40 Ī¼M, respectively. Such a result highlights the importance of the 2,7-dihydroxy function of these tropolone analogs, possibly through a role in metal chelation at the RNase H active site. Inhibition of HIV-2 RT-associated RNase H indirectly indicates that these compounds do not occupy the nonnucleoside inhibitor-binding pocket in the vicinity of the DNA polymerase domain. Both Ī²-thujaplicinol and manicol failed to inhibit DNA-dependent DNA polymerase activity of HIV-1 RT at a concentration of 50 Ī¼M, suggesting that they are specific for the C-terminal RNase H domain, while surface plasmon resonance studies indicated that the inhibition was not due to intercalation of the analog into the nucleic acid substrate. Finally, we have demonstrated synergy between Ī²-thujaplicinol and calanolide A, a nonnucleoside inhibitor of HIV-1 RT, raising the possibility that both enzymatic activities of HIV-1 RT can be simultaneously targeted
CCAT-prime: a novel telescope for submillimeter astronomy
The CCAT-prime telescope is a 6-meter aperture, crossed-Dragone telescope,
designed for millimeter and sub-millimeter wavelength observations. It will be
located at an altitude of 5600 meters, just below the summit of Cerro
Chajnantor in the high Atacama region of Chile. The telescope's unobscured
optics deliver a field of view of almost 8 degrees over a large, flat focal
plane, enabling it to accommodate current and future instrumentation fielding
>100k diffraction-limited beams for wavelengths less than a millimeter. The
mount is a novel design with the aluminum-tiled mirrors nested inside the
telescope structure. The elevation housing has an integrated shutter that can
enclose the mirrors, protecting them from inclement weather. The telescope is
designed to co-host multiple instruments over its nominal 15 year lifetime. It
will be operated remotely, requiring minimum maintenance and on-site activities
due to the harsh working conditions on the mountain. The design utilizes
nickel-iron alloy (Invar) and carbon-fiber-reinforced polymer (CFRP) materials
in the mirror support structure, achieving a relatively temperature-insensitive
mount. We discuss requirements, specifications, critical design elements, and
the expected performance of the CCAT-prime telescope. The telescope is being
built by CCAT Observatory, Inc., a corporation formed by an international
partnership of universities. More information about CCAT and the CCAT-prime
telescope can be found at www.ccatobservatory.org.Comment: Event: SPIE Astronomical Telescope + Instrumentation, 2018, Austin,
Texas, USA; Proceedings Volume 10700, Ground-based and Airborne Telescopes
VII; 107005X (2018
Combining Dark Energy Survey Science Verification data with near-infrared data from the ESO VISTA Hemisphere Survey
We present the combination of optical data from the Science Verification phase of the Dark
Energy Survey (DES) with near-infrared (NIR) data from the European Southern Observatory
VISTA Hemisphere Survey (VHS). The deep optical detections from DES are used to
extract fluxes and associated errors from the shallower VHS data. Joint seven-band (grizYJK)
photometric catalogues are produced in a single 3 sq-deg dedicated camera field centred at
02h26mā04d36m where the availability of ancillary multiwavelength photometry and spectroscopy
allows us to test the data quality. Dual photometry increases the number of DES
galaxies with measured VHS fluxes by a factor of ā¼4.5 relative to a simple catalogue level
matching and results in a ā¼1.5 mag increase in the 80 per cent completeness limit of the NIR
data. Almost 70 per cent of DES sources have useful NIR flux measurements in this initial
catalogue. Photometric redshifts are estimated for a subset of galaxies with spectroscopic
redshifts and initial results, although currently limited by small number statistics, indicate that
the VHS data can help reduce the photometric redshift scatter at both z 1. We
present example DES+VHS colour selection criteria for high-redshift luminous red galaxies
(LRGs) at z ā¼ 0.7 as well as luminous quasars. Using spectroscopic observations in this field
we show that the additional VHS fluxes enable a cleaner selection of both populations with
<10 per cent contamination from galactic stars in the case of spectroscopically confirme
Occurrence and sources of radium in groundwater associated with oil fields in the southern San Joaquin Valley, California
Author Posting. Ā© American Chemical Society, 2019. This is an open access article published under an ACS AuthorChoice License. The definitive version was published in Environmental Science and Technology 53(16), (2019): 9398-9406, doi:10.1021/acs.est.9b02395.Geochemical data from 40 water wells were used to examine the occurrence and sources of radium (Ra) in groundwater associated with three oil fields in California (Fruitvale, Lost Hills, South Belridge). 226Ra+228Ra activities (range = 0.010ā0.51 Bq/L) exceeded the 0.185 Bq/L drinking-water standard in 18% of the wells (not drinking-water wells). Radium activities were correlated with TDS concentrations (p < 0.001, Ļ = 0.90, range = 145ā15,900 mg/L), Mn + Fe concentrations (p < 0.001, Ļ = 0.82, range = <0.005ā18.5 mg/L), and pH (p < 0.001, Ļ = ā0.67, range = 6.2ā9.2), indicating Ra in groundwater was influenced by salinity, redox, and pH. Ra-rich groundwater was mixed with up to 45% oil-field water at some locations, primarily infiltrating through unlined disposal ponds, based on Cl, Li, noble-gas, and other data. Yet 228Ra/226Ra ratios in pond-impacted groundwater (median = 3.1) differed from those in oil-field water (median = 0.51). PHREEQC mixing calculations and spatial geochemical variations suggest that the Ra in the oil-field water was removed by coprecipitation with secondary barite and adsorption on MnāFe precipitates in the near-pond environment. The saline, organic-rich oil-field water subsequently mobilized Ra from downgradient aquifer sediments via Ra-desorption and Mn/Fe-reduction processes. This study demonstrates that infiltration of oil-field water may leach Ra into groundwater by changing salinity and redox conditions in the subsurface rather than by mixing with a high-Ra source.This article was improved by the reviews of John Izbicki and anonymous reviewers for the journal. This work was funded by the California State Water Resources Control Boardās Regional Groundwater Monitoring in Areas of Oil and Gas Production Program and the USGS Cooperative Water Program. A.V., A.J.K., and Z.W were supported by USDA-NIFA grant (#2017-68007-26308). Any use of trade, firm, or product names is for description purposes only and does not imply endorsement by the U.S. Government
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