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  • 1
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    Chemical stability of levoglucosan: an isotopic perspective (2016)
    Wiley
    Details
    Publication Date: 2016-05-03
    Description: The chemical stability of levoglucosan was studied by exploring its isotopic fractionation during the oxidation by hydroxyl radicals. Aqueous solutions as well as mixed (NH 4 ) 2 SO 4 − levoglucosan particles were exposed to OH. In both cases, samples experiencing different extents of processing were isotopically analyzed by Thermal Desorption - Gas Chromatography - Isotope Ratio Mass Spectrometry (TD-GC-IRMS). From the dependence of levoglucosan δ 13 C and concentration on the reaction extent, the kinetic isotope effect (KIE) of the OH oxidation reactions was determined to be 1.00187±0.00027 and 1.00229±0.00018, respectively. Both show good agreement within the uncertainty range. For the heterogeneous oxidation of particulate levoglucosan by gas-phase OH, a reaction rate constant of (2.67±0.03)·10 −12 molec cm −3 s −1 was derived. The laboratory kinetic data, together with isotopic source and ambient observations give information on the extent of aerosol chemical processing in the atmosphere.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Fatty acid analogs act antiarrhythmically [Cell Biology] (2015)
    National Academy of Sciences
    Details
    Publication Date: 2015-05-06
    Description: Polyunsaturated fatty acids (PUFAs) affect cardiac excitability. Kv7.1 and the β-subunit KCNE1 form the cardiac IKs channel that is central for cardiac repolarization. In this study, we explore the prospects of PUFAs as IKs channel modulators. We report that PUFAs open Kv7.1 via an electrostatic mechanism. Both the polyunsaturated acyl...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 3
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    CK2 balances TH17 and iTreg development [Immunology and Inflammation] (2016)
    National Academy of Sciences
    Details
    Publication Date: 2016-09-07
    Description: T helper 17 (TH17) cells represent a discrete TH cell subset instrumental in the immune response to extracellular bacteria and fungi. However, TH17 cells are considered to be detrimentally involved in autoimmune diseases like multiple sclerosis (MS). In contrast to TH17 cells, regulatory T (Treg) cells were shown to be...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 4
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    ROSAT Detection of an X-ray Shadow in the 1/4-keV Diffuse Background in the Draco Nebula (1991)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1991-06-14
    Description: The detection by the Roentgen satellite (ROSAT) x-ray telescope of a shadow in the 1/4-kiloelectron volt (C band, 0.1 to 0.284 kiloelectron volt) cosmic diffuse background is reported. The location and morphology of the local minimum in x-rays are in clear agreement with a discrete H I cloud. The shadow is very deep with a minimum level at 50 percent of the surrounding emission; therefore, a minimum of 50 percent of the observed off-cloud flux must originate on the far side of the cloud. The analysis of H I velocity components links the cloud with the Draco nebula (distance approximately 600 parsecs); it then follows that there is significant 1/4-kiloelectron volt x-ray emission at a large distance (〉400 parsecs) from the galactic plane along this line of sight. The extent of the distant emission region is uncertain, and, if it indicates the existence of a hot galactic corona, it must be patchy in nature.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Snowden, S L -- Mebold, U -- Hirth, W -- Herbstmeier, U -- Schmitt, J H -- New York, N.Y. -- Science. 1991 Jun 14;252(5012):1529-32.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17834877" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    A Lunar Occultation of the Dust-Scattering Halo Around GX 5-1 Observed with ROSAT (1992)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1992-08-14
    Description: The x-ray source GX 5-1 in the galactic bulge has been observed with the position-sensitive proportional counter onboard the Rontgen satellite (ROSAT) during and after a lunar occultation. Extended emission around the source was unambiguously discovered while the central source was behind the lunar rim. This emission is interpreted as a dust-scattering halo around GX 5-1 that has a fractional intensity of 28 percent, implying a grain column density between GX 5-1 and Earth of approximately 3 x 10(10) per square centimeter. The halo derived from imaging during the ROSAT all-sky survey is identical to that obtained from the lunar occultation, thus demonstrating that the ROSAT x-ray mirror scattering has not changed as compared with the mirror properties as measured in preflight calibrations.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Predehl, P -- Schmitt, J H -- Snowden, S L -- Trumper, J -- New York, N.Y. -- Science. 1992 Aug 14;257(5072):935-7.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17789635" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    Making a case for humans in space (2004)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2004-05-08
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schmitt, Harrison H -- New York, N.Y. -- Science. 2004 May 7;304(5672):822.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15131288" target="_blank"〉PubMed〈/a〉
    Keywords: *Astronauts ; Humans ; *Space Flight
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 7
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    A Spatially Resolved X-ray Image of a Star Like the Sun (1993)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1993-10-08
    Description: Observations made with the x-ray satellite ROSAT (Roentgen Satellite) have produced the first spatially resolved x-ray image of a corona around a star like our sun. The star is the secondary in the eclipsing binary system alpha Coronae Borealis (CrB), which consists of one star of spectral type A0V and one of type G5V. The x-ray light curve of alpha CrB shows a total x-ray eclipse during secondary optical minimum, with the G star behind the A star. The totality of the eclipse demonstrates that the A-type component in alpha CrB is x-ray dark and that the x-ray flux arises exclusively from the later-type companion. The x-ray eclipse ingress and egress are highly asymmetric compared with the optical eclipse, indicating a highly asymmetric x-ray intensity distribution on the surface of the G star. From a detailed modeling of the ingress and egress of the x-ray light curve, an eclipse map of the G star was constructed by a method based on an optimization by simulated annealing.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schmitt, J H -- Kurster, M -- New York, N.Y. -- Science. 1993 Oct 8;262(5131):215-8.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17841866" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 8
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    The Elemental Composition of the Corona of Procyon: Evidence for the Absence of the FIP Effect (1995)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1995-03-10
    Description: The chemical composition of the solar corona is not the same as that of the underlying photosphere. In the corona, elements with a first ionization potential (FIP) of 〈/=10 electron volts (for example, iron, magnesium, silicon, and calcium) are overabundant relative to those with an FIP of 〉/=10 electron volts (for example, oxygen, neon, and sulfur) by factors of 3 to 10 with respect to the photosphere. The origin of this FIP effect is unknown. The launch of the Extreme Ultraviolet Explorer Satellite (EUVE) opened up the spectroscopic capability required to determine elemental abundances in the coronae of other stars. Spectroscopic observations of the corona of the nearby F5 IV star Procyon obtained with EUVE have yielded estimates of the relative abundances of high- and low-FIP species. The results provide evidence that Procyon, unlike the sun, does not exhibit the FIP effect. Whether the sun or Procyon is more typical of the general late-type stellar population is of fundamental interest to the physics of stellar outer atmospheres and has a bearing on the origin of cosmic rays.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Drake, J J -- Laming, J M -- Widing, K G -- Schmitt, J H -- Haisch, B -- Bowyer, S -- New York, N.Y. -- Science. 1995 Mar 10;267(5203):1470-3.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17743544" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 9
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    Solar-Like M-Class X-ray Flares on Proxima Centauri Observed by the ASCA Satellite (1995)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1995-06-02
    Description: Because of instrumental sensitivity limits and stellar distances, the types of x-ray flares observable on stars have been intrinsically much more energetic than those on the sun. Such enormous events are a useful extrapolation of the solar phenomenon if the underlying assumption is correct that they form a continuous sequence involving similar physical processes as on the sun. The Advanced Satellite for Cosmology and Astrophysics (ASCA), with its greater sensitivity and high-energy response, is now able to test this hypothesis. Direct comparison with solar flares measured by the x-ray-monitoring Geostationary Operational Environmental Satellites (GOES) is possible. The detection of flares on Proxima Centauri that correspond to GOES M-class events on the sun are reported.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Haisch, B -- Antunes, A -- Schmitt, J H -- New York, N.Y. -- Science. 1995 Jun 2;268(5215):1327-9.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17778978" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 10
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    X-ray Variability in the Hot Supergiant zgr Orionis (1994)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1994-09-16
    Description: Hot massive stars represent only a small fraction of the stellar population of the galaxy, but their enormous luminosities make them visible over large distances. Therefore, they are ideal standard candles, used to determine distances of near galaxies. Their mass loss due to supersonic winds driven by radiation pressure contributes significantly to the interstellar medium and thus to the chemical evolution of galaxies. All hot stars are soft x-ray sources; in contrast to the sun with its highly variable x-ray flux, long time scale x-ray variability is not common among hot stars. An analysis is presented here of an unusual increase in x-ray flux observed with the roentgen observatory satellite during a period of 2 days for the hot supergiant zeta Orionis, the only episode of x-ray variability that has been found in a hot star. These observations provide the most direct evidence so far for the scenario of shock-heated gas in the winds of hot stars.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Berghofer, T W -- Schmitt, J H -- New York, N.Y. -- Science. 1994 Sep 16;265(5179):1689-91.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17770897" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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