1,461 research outputs found
A Neoclassical Realistâs Analysis Of Sino-U.S. Space Policy
During the Cold War, the United States focused its collective policy acumen on forming a competitive, actor-specific strategy to gain advantage over the Soviet Union. The fragmentation of the Soviet Union resulted in a multi-polar geopolitical environment lacking a near-peer rival for the United States. Overwhelming soft and hard power advantages allowed American policy makers to peruse a general, non-actor specific strategy to maintain its hegemonic position. However, the meteoric rise of China as a near-peer competitor in East Asia has challenged this paradigm. In order to maintain its competitive advantage, or at the very least ensure the safety of its geopolitical objectives through encouraging benign competition, U.S. strategy needs to evolve in both focus and complexity. It is essential for Spacepower, as a key element of national power, to be included in this evolution. In order to do so, this analysis will examine Sino-U.S. space relations using neoclassical realism as a baseline methodology. First, structural elements of the Sino-U.S. relationship will be modeled in a semi-quantitative game theoretical framework, using relative economic and military capabilities as primary independent variables. Second, key assumptions will be tested to ensure that this model accurately represents the current geopolitical environment. Third, the decision making apparatuses of the United States and China will be examined as intervening variables. This will account for imperfect rationality and how it modifies the game theoretical framework. Fourth, this framework will be used to present actionable space policy recommendations for the United States so that space can be incorporated into a competitive strategy for East Asia
Explaining the Rise in Educational Gradients in Mortality
The long-standing inverse relationship between education and mortality strengthened substantially later in the 20th century. This paper examines the reasons for this increase. We show that behavioral risk factors are not of primary importance. Smoking has declined more for the better educated, but not enough to explain the trend. Obesity has risen at similar rates across education groups, and control of blood pressure and cholesterol has increased fairly uniformly as well. Rather, our results show that the mortality returns to risk factors, and conditional on risk factors, the return to education, have grown over time.
The Interaction of 3C401 with the Surrounding Intracluster Medium
We present an observation of the radio-galaxy 3C401 and the surrounding
intracluster medium (ICM) of its host galaxy cluster by the Chandra X-ray
Observatory. This luminous radio-galaxy is notable in that it has
characteristics intermediate between the FRI and FRII morphologies. We clearly
detect point-like emission coincident with the radio-core of 3C401, although
the spatial resolution of even Chandra is only 2kpc at the distance of 3C401
(z=0.201) and so the possibility remains that this is a dense (and rapidly
cooling) thermal gaseous core in the center of the ICM atmosphere. Strong
departures from spherical symmetry in the central 10-20kpc of the ICM clearly
suggest interaction between the ICM and the radio-lobes of 3C401. A central
X-ray bar probably results from the evacuation of two ICM cavities by the
expanding radio lobes. Beyond these central regions, the cluster possesses a
flatter profile than many clusters of comparable mass suggesting the importance
of ICM heating and entropy injection by 3C401. We detect an interesting
cross-like structure in the ICM on 100kpc scales. We speculate that this could
be a radio-galaxy induced disturbance corresponding to a time when 3C401 was
substantially more powerful. A particularly exciting possibility is that this
cross-like structure corresponds to a large scale global g-mode oscillation
excited by a past outburst of 3C401.Comment: 7 pages, 5 postscript figures. Accepted for publication in MNRA
Astrophysical Limits on Very Light Axion-like Particles from Chandra Grating Spectroscopy of NGC 1275
Axions/axion-like particles (ALPs) are a well motivated extension of the
Standard Model and are generic within String Theory. The X-ray transparency of
the intracluster medium (ICM) in galaxy clusters is a powerful probe of light
ALPs (with mass ); as X-ray photons from an embedded or
background source propagate through the magnetized ICM, they may undergo
energy-dependent quantum mechanical conversion into ALPs (and vice versa),
imprinting distortions on the X-ray spectrum. We present Chandra data for the
active galactic nucleus NGC1275 at the center of the Perseus cluster. Employing
a 490ks High-Energy Transmission Gratings (HETG) exposure, we obtain a
high-quality 1-9keV spectrum free from photon pileup and ICM contamination.
Apart from iron-band features, the spectrum is described by a power-law
continuum, with any spectral distortions at the level. We compute photon
survival probabilities as a function of ALP mass and ALP-photon coupling
constant for an ensemble of ICM magnetic field models, and then
use the NGC1275 spectrum to constraint the -plane.
Marginalizing over magnetic field realizations, the 99.7% credible region
limits the ALP-photon coupling to (depending upon magnetic field model) for masses . These are the most stringent limit to date on
for these light ALPs, and have already reached the sensitivity
limits of next-generation helioscopes and light-shining-through-wall
experiments. We highlight the potential of these studies with the
next-generation X-ray observatories Athena and Lynx, but note the critical
importance of advances in relative calibration of these future X-ray
spectrometers.Comment: Published in The Astrophysical Journal, 2020, vol 890, pp59. This
posting corrects typos in equation (2) and the likelihood function just prior
to equation (3). Typos were introduced into the draft at late stage and the
analysis is correc
Polycyclic Aromatic Hydrocarbon and Mid-Infrared Continuum Emission in a z > 4 Submillimeter Galaxy
We report the detection of 6.2 ÎŒm polycyclic aromatic hydrocarbon (PAH) and rest-frame 4-7 ÎŒm continuum emission in the z = 4.055 submillimeter galaxy GN20, using the Infrared Spectrograph on board the Spitzer Space Telescope. This represents the first detection of PAH emission at z > 4. The strength of the PAH emission feature is consistent with a very high star formation rate of ~1600 Mâ yr^(â1). We find that this intense starburst powers at least ~1/3 of the faint underlying 6 ÎŒm continuum emission, with an additional, significant (and perhaps dominant) contribution due to a power-law-like hot dust source, which we interpret to likely be a faint, dust-obscured active galactic nucleus (AGN). The inferred 6 ÎŒm AGN continuum luminosity is consistent with a sensitive upper limit on the hard X-ray emission as measured by the Chandra X-Ray Observatory if the previously undetected AGN is Compton-thick. This is in agreement with the finding at optical/infrared wavelengths that the galaxy and its nucleus are heavily dust-obscured. Despite the strong power-law component enhancing the mid-infrared continuum emission, the intense starburst associated with the photon-dominated regions that give rise to the PAH emission appears to dominate the total energy output in the infrared. GN20 is one of the most luminous starburst galaxies known at any redshift, embedded in a rich protocluster of star-forming galaxies. This investigation provides an improved understanding of the energy sources that power such exceptional systems, which represent the extreme end of massive galaxy formation at early cosmic times
NuSTAR observations of the powerful radio-galaxy Cygnus A
We present NuSTAR observations of the powerful radio galaxy Cygnus A,
focusing on the central absorbed active galactic nucleus (AGN). Cygnus A is
embedded in a cool-core galaxy cluster, and hence we also examine archival
XMM-Newton data to facilitate the decomposition of the spectrum into the AGN
and intracluster medium (ICM) components. NuSTAR gives a source-dominated
spectrum of the AGN out to >70keV. In gross terms, the NuSTAR spectrum of the
AGN has the form of a power law (Gamma~1.6-1.7) absorbed by a neutral column
density of N_H~1.6x10^23 cm^-2. However, we also detect curvature in the hard
(>10keV) spectrum resulting from reflection by Compton-thick matter out of our
line-of-sight to the X-ray source. Compton reflection, possibly from the outer
accretion disk or obscuring torus, is required even permitting a high-energy
cutoff in the continuum source; the limit on the cutoff energy is E_cut>111keV
(90% confidence). Interestingly, the absorbed power-law plus reflection model
leaves residuals suggesting the absorption/emission from a fast
(15,000-26,000km/s), high column-density (N_W>3x10^23 cm^-2), highly ionized
(xi~2,500 erg cm/s) wind. A second, even faster ionized wind component is also
suggested by these data. We show that the ionized wind likely carries a
significant mass and momentum flux, and may carry sufficient kinetic energy to
exercise feedback on the host galaxy. If confirmed, the simultaneous presence
of a strong wind and powerful jets in Cygnus A demonstrates that feedback from
radio-jets and sub-relativistic winds are not mutually exclusive phases of AGN
activity but can occur simultaneously.Comment: 13 pages; accepted for publication in The Astrophysical Journa
Joint analysis of X-ray and Sunyaev Zel'dovich observations of galaxy clusters using an analytic model of the intra-cluster medium
We perform a joint analysis of X-ray and Sunyaev Zel'dovich (SZ) effect data
using an analytic model that describes the gas properties of galaxy clusters.
The joint analysis allows the measurement of the cluster gas mass fraction
profile and Hubble constant independent of cosmological parameters. Weak
cosmological priors are used to calculate the overdensity radius within which
the gas mass fractions are reported. Such an analysis can provide direct
constraints on the evolution of the cluster gas mass fraction with redshift. We
validate the model and the joint analysis on high signal-to-noise data from the
Chandra X-ray Observatory and the Sunyaev-Zel'dovich Array for two clusters,
Abell 2631 and Abell 2204.Comment: ApJ in pres
Outcome of Patients After Transcatheter Aortic Valve Embolization
ObjectivesThis study aims to assess the mid- to long-term follow-up of patients after valve embolization at the time of transcatheter aortic valve implantation (TAVI).BackgroundTranscatheter heart valve (THV) embolization is a rare but serious complication during TAVI. Although various techniques have been developed to manage acute complications and reduce periprocedural morbidity/mortality, long-term clinical and hemodynamic consequences after these events are unknown.MethodsPatients who developed THV embolization after TAVI were prospectively assessed. Clinical and echocardiographic characteristics were recorded at baseline and after successful TAVI/surgical aortic valve replacement. The THV migration and strut fractures/degeneration were assessed by computed tomography.ResultsA total of 7 patients had THV embolization, all of which occurred immediately after valve deployment. The embolized THV was repositioned in the aortic arch proximal to the left subclavian artery (n = 2), immediately distal to the left subclavian artery (n = 2), and in the abdominal aorta (n = 3). A second THV was implanted successfully at the same sitting in 4 patients and at the time of a second procedure in 2 patients. Elective conventional aortic valve replacement was performed in 1 patient. Median follow-up was 1,085 days. One patient died during follow-up from an unrelated cause. The remaining 6 survivors were in New York Heart Association functional class I or II at final follow-up. Mid-term computed tomography follow-up (n = 4,591 to 1,548 days) showed that the leaflets of the embolized THV remain open in all phases of the cardiac cycle. There was also no strut fracture or migration of these valves.ConclusionsClinical outcomes remain good when THV embolization is managed effectively. There are no apparent hemodynamic consequences of a second valve placed in the series. These embolized valves remain in a stable position with no evidence of strut fractures at mid-term follow-up
Origins of the Highly Ionized Gas along the Line of Sight towards HD 116852
We present Hubble Space Telescope Imaging Spectrograph (HST/STIS) and Far
Ultraviolet Spectroscopic Explorer (FUSE) observations of high ion interstellar
absorption along the sight line to HD 116852. At a distance of 4.8 kpc, HD
116852 is an O9 III star lying in the low Galactic halo, -1.3 kpc from the
plane of the Galaxy in the direction l = 304.9, b = -16.1. The STIS E140H
grating observations provide high-resolution (FWHM = 2.7 km/s) spectra of the
resonance doublets of Si IV, C IV, and N V. These data are complemented by
medium-resolution (FWHM = 20 km/s) FUSE spectra of O VI. We find evidence for
three distinct types of highly ionized gas present in the data. First, two
narrow absorption components are resolved in the Si IV and C IV profiles, at
approximate LSR velocities of -36 and -10 km/s. These narrow components appear
to be produced in gas associated with the Norma and Sagittarius spiral arms, at
approximate z-distances of -1.0 and -0.5 kpc, respectively. Second, we detect
an intermediate-width component in C IV and Si IV, at 17 km/s, which we propose
could arise at the conductive interface at the boundary between a low column
density neutral or weakly ionized cloud and the surrounding hot medium.
Finally, a broad collisionally ionized component of gas responsible for
producing the smooth N V and O VI profiles is observed; such absorption is also
present to a lesser degree in the profiles of Si IV and C IV. The broad O VI
absorption is observed at a velocity displaced from the broad C IV component by
almost 20 km/s, an amount large enough to suggest that the two ions may not
co-exist in the same physical location.Comment: 39 pages, 6 figures; accepted for publication in January 10, 2003
edition of The Astrophysical Journa
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