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  • 1
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    A method for estimating the height of a mesospheric density level using meteor radar (2015)
    Wiley
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    Publikationsdatum: 2015-07-08
    Beschreibung: A new technique for determining the height of a constant density surface at altitudes of 78–85 km is presented. The first results are derived from a decade of observations by a meteor radar located at Davis Station in Antarctica and are compared with observations from the Microwave Limb Sounder instrument aboard the Aura satellite. The density of the neutral atmosphere in the mesosphere/lower thermosphere region around 70–110 km is an essential parameter for interpreting airglow derived atmospheric temperatures, planning atmospheric entry maneuvers of returning spacecraft, and understanding the response of climate to different stimuli. This region is not well characterized however, due to inaccessibility combined with a lack of consistent strong atmospheric radar scattering mechanisms. Recent advances in the analysis of detection records from high performance meteor radars provide new opportunities to obtain atmospheric density estimates at high time resolutions in the MLT region using the durations and heights of faint radar echoes from meteor trails. Previous studies have indicated that the expected increase in underdense meteor radar echo decay times with decreasing altitude is reversed in the lower part of the meteor ablation region due to the neutralization of meteor plasma. The height at which the gradient of meteor echo decay times reverses is found to occur at a fixed atmospheric density. Thus, the gradient reversal height of meteor radar diffusion coefficient profiles can be used to infer the height of a constant density level, enabling the observation of mesospheric density variations using meteor radar.
    Print ISSN: 0094-8276
    Digitale ISSN: 1944-8007
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 2
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    In vitro evidence for senescent multinucleated melanocytes as a source for tumor-initiating cells (2015)
    Springer Nature
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    Publikationsdatum: 2015-04-03
    Beschreibung: In vitro evidence for senescent multinucleated melanocytes as a source for tumor-initiating cells Cell Death and Disease 6, e1711 (April 2015). doi:10.1038/cddis.2015.71 Authors: C Leikam, A L Hufnagel, C Otto, D J Murphy, B Mühling, S Kneitz, I Nanda, M Schmid, T U Wagner, S Haferkamp, E-B Bröcker, M Schartl & S Meierjohann
    Digitale ISSN: 2041-4889
    Thema: Biologie , Medizin
    Publiziert von Springer Nature
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  • 3
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    STEM faculty who believe ability is fixed have larger racial achievement gaps and inspire less student motivation in their classes (2019)
    American Association for the Advancement of Science (AAAS)
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    Publikationsdatum: 2019
    Beschreibung: 〈p〉An important goal of the scientific community is broadening the achievement and participation of racial minorities in STEM fields. Yet, professors’ beliefs about the fixedness of ability may be an unwitting and overlooked barrier for stigmatized students. Results from a longitudinal university-wide sample (150 STEM professors and more than 15,000 students) revealed that the racial achievement gaps in courses taught by more fixed mindset faculty were twice as large as the achievement gaps in courses taught by more growth mindset faculty. Course evaluations revealed that students were demotivated and had more negative experiences in classes taught by fixed (versus growth) mindset faculty. Faculty mindset beliefs predicted student achievement and motivation above and beyond any other faculty characteristic, including their gender, race/ethnicity, age, teaching experience, or tenure status. These findings suggest that faculty mindset beliefs have important implications for the classroom experiences and achievement of underrepresented minority students in STEM.〈/p〉
    Digitale ISSN: 2375-2548
    Thema: Allgemeine Naturwissenschaft
    Publiziert von American Association for the Advancement of Science (AAAS)
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  • 4
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    Low energy constants of SU(2) partially quenched chiral perturbation theory from N_{f} =2+1 domain wall QCD (2016)
    American Physical Society (APS)
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    Publikationsdatum: 2016-03-11
    Beschreibung: Author(s): P. A. Boyle, N. H. Christ, N. Garron, C. Jung, A. Jüttner, C. Kelly, R. D. Mawhinney, G. McGlynn, D. J. Murphy, S. Ohta (太田滋生), A. Portelli, and C. T. Sachrajda We have performed fits of the pseudoscalar masses and decay constants, from a variety of the RBC-UKQCD Collaboration’s domain wall fermion ensembles, to S U ( 2 ) partially quenched chiral perturbation theory at next-to-leading order (NLO) and next-to-next-to-leading order (NNLO). We report values for n… [Phys. Rev. D 93, 054502] Published Wed Mar 09, 2016
    Schlagwort(e): Lattice Methods
    Print ISSN: 0556-2821
    Digitale ISSN: 1089-4918
    Thema: Physik
    Publiziert von American Physical Society (APS)
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  • 5
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    Domain wall QCD with physical quark masses (2016)
    American Physical Society (APS)
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    Publikationsdatum: 2016-04-13
    Beschreibung: Author(s): T. Blum, P. A. Boyle, N. H. Christ, J. Frison, N. Garron, R. J. Hudspith, T. Izubuchi, T. Janowski, C. Jung, A. Jüttner, C. Kelly, R. D. Kenway, C. Lehner, M. Marinkovic, R. D. Mawhinney, G. McGlynn, D. J. Murphy, S. Ohta ((太田滋生)), A. Portelli, C. T. Sachrajda, and A. Soni (RBC and UKQCD Collaborations) We present results for several light hadronic quantities ( f π , f K , B K , m u d , m s , t 0 1 / 2 , w 0 ) obtained from simulations of 2 + 1 flavor domain wall lattice QCD with large physical volumes and nearly physical pion masses at two lattice spacings. We perform a short, O ( 3 ) % , extrapolation in pion mass to the … [Phys. Rev. D 93, 074505] Published Tue Apr 12, 2016
    Schlagwort(e): Lattice Methods
    Print ISSN: 0556-2821
    Digitale ISSN: 1089-4918
    Thema: Physik
    Publiziert von American Physical Society (APS)
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  • 6
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    A climatological study of short-period gravity waves and ripples at Davis Station, Antarctica (68 °S, 78 °E) during the (austral winter February-October) period 1999-2013 (2017)
    Wiley
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    Publikationsdatum: 2017-10-15
    Beschreibung: A scanning radiometer deployed at Davis Station, Antarctica (68 ° S, 78 ° E) has been recording infrared (1.10-1.65 μm) images of a small region (24 km × 24 km) of the zenith night sky once per minute each austral winter night since February 1999. These images have been processed to extract information on the passage of gravity waves (GWs) (horizontal wavelength, λ h 〉 15 km) and ripples ( λ h ≤ 15 km) over the observing station. Phase speeds, periods, horizontal wavelengths, and predominant propagation directions have been deduced. Observed speeds were found to be highly correlated with horizontal wavelengths as has been reported in previous studies. Reverse ray-tracing of the detected GWs only enabled us to identify four distinct groups. On average only 15% of waves detected can be traced back to the troposphere, and a large proportion ( ~ 45%) were not successfully reverse traced substantially below the airglow layer. Two smaller groups were found to reach a termination condition for reverse ray-tracing at altitudes near 50 km and 75 km. Of those that reached the termination altitude in the troposphere (10 km), most of the end points fell within a radius of 300 km of the station, with a very pronounced concentration of wave initiation to the north west at approximately of the observing point. The predominant direction of propagation was southward, and they were observed throughout the year. Recent reports suggest the interaction of planetary waves with the background wind field as a potential source for these waves.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 7
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    Domain wall fermion QCD with the exact one flavor algorithm (2018)
    American Physical Society (APS)
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    Publikationsdatum: 2018-03-14
    Beschreibung: Author(s): C. Jung, C. Kelly, R. D. Mawhinney, and D. J. Murphy Lattice QCD calculations including the effects of one or more nondegenerate sea quark flavors are conventionally performed using the rational hybrid Monte Carlo (RHMC) algorithm, which computes the square root of the determinant of D † D , where D is the Dirac operator. The special case of two degenera... [Phys. Rev. D 97, 054503] Published Tue Mar 13, 2018
    Schlagwort(e): Lattice field theories, lattice QCD
    Print ISSN: 0556-2821
    Digitale ISSN: 1089-4918
    Thema: Physik
    Publiziert von American Physical Society (APS)
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  • 8
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    Trends and Variability in Vertical Winds in the Southern Hemisphere Summer Polar Mesosphere and Lower Thermosphere (2019)
    Wiley
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    Publikationsdatum: 2019
    Beschreibung: Abstract Direct measurement of mean vertical velocities in the mesosphere‐lower thermosphere (60–110 km) is not possible due to their small values. Here we derive vertical velocities using the divergence of the mean meridional wind over the Antarctic summer pole using MF radar wind measurements made at Davis Station (69°S, 78°E) between 1994 and 2018. Estimates of vertical velocity are restricted to a 21‐day period centered just after solstice when the equatorward wind reaches its maximum value of about 15 m s−1 at heights near 90 km. The Medium Frequency (MF) radar winds are calibrated against colocated meteor wind radar observations. Neutral densities required for the vertical wind calculations are obtained from zonally averaged temperature measurements obtained by the MLS instrument aboard the AURA satellite. The estimated vertical velocities have peak values varying between 2 and 6 cm s−1 with significant interannual variability. While the peak values do not show significant long‐term change, there is a long‐term decrease in the mean height of maximum winds of about 0.6 km per decade that is statistically significant. The interannual variability is linked to the date of transition in the stratospheric zonal circulation from winter eastward to summer westward flow. Meridional and vertical velocities are smaller and peak at lower altitudes during early transitions (20–30 days prior to solstice) than is the case for late transitions that occur at solstice or later.
    Print ISSN: 2169-897X
    Digitale ISSN: 2169-8996
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 9
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    Tides in the mesopause region over Antarctica: Comparison of Whole Atmosphere Model (WAM) simulations with ground-based observations (2016)
    Wiley
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    Publikationsdatum: 2016-01-09
    Beschreibung: Almost a quarter century ago first optical and radar observations from the South Pole revealed rich dynamics unexpected from classical tidal theory. A strong semidiurnal wind oscillation was detected near the mesopause implying substantial deviations from the classical view that the semidiurnal variation is dominated by the migrating tide. Subsequent systematic observations exhibited large seasonal variations of both the diurnal and semidiurnal tide with dramatic reduction in amplitude from summer to winter. First numerical simulations with a realistic general circulation model extending into the lower thermosphere indicated the presence of nonmigrating tides with substantial amplitudes in the polar regions. However, direct model-data comparisons have been limited to idealized linear models. Here Whole Atmosphere Model (WAM) simulations for January and July are compared with available wind climatologies based on multi-year radar observations at different locations in Antarctica as well as with first summertime lidar measurements of temperature. The diurnal tide simulation agrees well with most of the independent radar and satellite wind observations in both seasons. The strong semidiurnal tide comprised of migrating and nonmigrating components is well reproduced in summer, while in winter the model tends to overestimate the amplitudes over the continental edge. Besides model validation, a self-consistent numerical solution also enables cross-validation of observations made with different instruments at different locales.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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  • 10
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    Observations and fine-scale model simulations of gravity waves over Davis, East Antarctica (69∘S, 78∘E) (2017)
    Wiley
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    Publikationsdatum: 2017-06-30
    Beschreibung: Large vertical velocities were observed throughout the troposphere at Davis, East Antarctica on 18 February 2014 by a VHF wind-profiling radar. Simulations using the Met Office Unified Model at 2.2, 0.5, and 0.1 km horizontal grid spacing were able to broadly capture the location, timing, and magnitude of the observed velocities, as well as reveal that they are due to small-scale orographic gravity waves resulting from the interaction between the coastal topography and strong easterly winds associated with a synoptic-scale cyclone situated to the north. The simulations indicated that the gravity waves are responsible for: i) temperature fluctuations which coincided with satellite-observed cloud variations in the vicinity of Davis, suggesting that they have a crucial role in the formation of cirrus clouds, and ii) large vertical momentum fluxes in the troposphere. The waves are prevented from propagating into the stratosphere by the background winds turning from near-surface easterlies to lower-stratospheric northerlies. As well as illuminating and quantifying the role that weather systems have in producing orographic gravity waves along the East Antarctic coastline, studies such as this should be exploited to improve the representation of key localised atmospheric processes in global climate models.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
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