721 research outputs found
The Diversity of High- and Intermediate-Velocity Clouds: Complex C versus IV Arch
We present Far Ultraviolet Spectroscopic Explorer (FUSE) and Space Telescope
Imaging Spectrograph (STIS) observations of interstellar ultraviolet absorption
lines in the Galactic high-velocity cloud Complex C and the Intermediate
Velocity Arch (IV Arch) in direction of the quasar PG 1259+593 (l=120,b=+58
deg). Absorption lines from CII, NI, NII, OI, AlII, SiII, PII, SII, ArI, FeII,
and FeIII are used to study the atomic abundances in these two halo clouds at
V_LSR=-130 km/s (Complex C) and V_LSR=-55 km/s (IV Arch). The OI/HI ratio
provides the best measure of the overall metallicity in the diffuse
interstellar medium, because ionization effects do not alter the ratio, and
oxygen is at most only lightly depleted from the gas into dust grains. For
Complex C, we find an oxygen abundance of 0.093 (+0.125, -0.047) solar,
consistent with the idea that Complex C represents the infall of low
metallicity gas onto the Milky Way. In contrast, the oxygen abundance in the IV
Arch is 0.98 (+1.21,-0.46) solar, which indicates a Galactic origin. We report
the detection of an intermediate- velocity absorption component at +60 km/s
that is not seen in HI 21cm emission. The clouds along the PG 1259+593 sight
line have a variety of properties, proving that multiple processes are
responsible for the creation and circulation of intermediate- and high-velocity
gas in the Milky Way halo.Comment: 12 pages, 3 tables, 3 figures; accepted for publication in Ap
Datastreme Courses: Teacher Enhancement Utilizing Current Environmental Data and the Internet
The American Meteorological Society\u27s (AMS) Educational Program seeks to assist the improvement of science education in K-12 classrooms through implementation of the National Science Education Standards. This goal is being accomplished through the offering of three teacher enhancement courses via blended instruction methods. Following course participation each teacher functions as an Earth system science education resource person for his/her colleagues
Impact of Periodic Unsteadiness on Performance and Heat Load in Axial Flow Turbomachines
Results of an analytical and experimental investigation, directed at the understanding of the impact of periodic unsteadiness on the time-averaged flows in axial flow turbomachines, are presented. Analysis of available experimental data, from a large-scale rotating rig (LSRR) (low speed rig), shows that in the time-averaged axisymmetric equations the magnitude of the terms representing the effect of periodic unsteadiness (deterministic stresses) are as large or larger than those due to random unsteadiness (turbulence). Numerical experiments, conducted to highlight physical mechanisms associated with the migration of combustor generated hot-streaks in turbine rotors, indicated that the effect can be simulated by accounting for deterministic stress like terms in the time-averaged mass and energy conservation equations. The experimental portion of this program shows that the aerodynamic loss for the second stator in a 1-1/2 stage turbine are influenced by the axial spacing between the second stator leading edge and the rotor trailing edge. However, the axial spacing has little impact on the heat transfer coefficient. These performance changes are believed to be associated with the change in deterministic stress at the inlet to the second stator. Data were also acquired to quantify the impact of indexing the first stator relative to the second stator. For the range of parameters examined, this effect was found to be of the same order as the effect of axial spacing
Integrity in democratic politics
The complaint that many professional politicians lack integrity is common. However, it is unclear what such a judgement amounts to. Taking various codes of political ethics in the United Kingdom as my starting point, I examine the extent to which we can understand political integrity as a matter of politicians adhering to the obligations that official codes of ethics prescribe and, in a more general sense, the public-service ethos that underpins these codes. I argue that although this way of approaching the issue usefully draws our attention to an important class of positional duties that apply to politicians, commitment to principled political causes plays a further, indispensable role in coherent assessments of political integrity. In consequence, I claim that politicians of integrity succeed in furthering their deepest political commitments while avoiding malfeasance or misconduct. As such, the ascription of political integrity can often only be made when assessing a long train of action
What is the Total Deuterium Abundance in the Local Galactic Disk?
Analyses of spectra obtained with the Far Ultraviolet Spectroscopic Explorer
(FUSE) satellite, together with spectra from the Copernicus and IMAPS
instruments, reveal an unexplained very wide range in the observed
deuterium/hydrogen (D/H) ratios for interstellar gas in the Galactic disk
beyond the Local Bubble. We argue that spatial variations in the depletion of
deuterium onto dust grains can explain these local variations in the observed
gas-phase D/H ratios. We present a variable deuterium depletion model that
naturally explains the constant measured values of D/H inside the Local Bubble,
the wide range of gas-phase D/H ratios observed in the intermediate regime (log
N(H I} = 19.2-20.7), and the low gas-phase D/H ratios observed at larger
hydrogen column densities. We consider empirical tests of the deuterium
depletion hypothesis: (i) correlations of gas-phase D/H ratios with depletions
of the refractory metals iron and silicon, and (ii) correlation with the
molecular hydrogen rotational temperature. Both of these tests are consistent
with deuterium depletion from the gas phase in cold, not recently shocked,
regions of the ISM, and high gas-phase D/H ratios in gas that has been shocked
or otherwise heated recently. We argue that the most representative value for
the total (gas plus dust) D/H ratio within 1 kpc of the Sun is >=23.1 +/- 2.4
(1 sigma) parts per million (ppm). This ratio constrains Galactic chemical
evolution models to have a very small deuterium astration factor, the ratio of
primordial to total (D/H) ratio in the local region of the Galactic disk, which
we estimate to be f_d <= 1.19 +/-0.16 (1 sigma) or <= 1.12 +/- 0.14 (1 sigma)
depending on the adopted light element nuclear reaction rates.Comment: 19 pages, 9 figure
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