8,417 research outputs found
Intrinsic Differences in the Inner Jets of High- and Low-Optically Polarized Radio Quasars
A significant fraction of compact radio-loud quasars display most of the
characteristics of relativistically beamed, high-optical polarization blazars,
yet are weakly polarized in the optical regime. We have used the VLBA at 22 and
43 GHz to look for differences in the parsec-scale magnetic field structures of
18 high- and low-optically polarized, compact radio-loud quasars (HPQs and
LPRQs, respectively). We find a strong correlation between the polarization
level of the unresolved parsec-scale radio core at 43 GHz and overall optical
polarization of the source, which suggests a common (possibly co-spatial)
origin for the emission at these two wavelengths. The magnetic fields of the
polarized 43 GHz radio cores are aligned roughly transverse to the jet axis.
Similar orientations are seen in the optical, suggesting that the polarized
flux at both wavelengths is due to one or more strong transverse shocks located
very close to the base of the jet. In LPRQs, these shocks appear to be weak
near the core, and gradually increase in strength down the jet. The LPRQs in
our sample tend to have less luminous radio cores than the HPQs, and jet
components with magnetic fields predominantly parallel to the flow. The
components in HPQ jets, on the other hand, tend to have transverse alignments.
These differences cannot be accounted for by a simple model in which HPQs and
LPRQs are the same type of object, seen at different angles to the line of
sight. A more likely scenario is that LPRQs represent a quiescent phase of
blazar activity, in which the inner jet flow does not undergo strong shocks.Comment: 29 pages, includes 25 figures and 6 tables. Uses emulateapj5.sty.
Accepted for publication in the Astrophysical Journal. A version with better
quality figures (785Kb, gzipped) can be found at
http://sgra.jpl.nasa.gov/html_lister/LPQ
Bone fracture toughness of estrogen deficient rabbits
Bone mass is commonly used as an indicator of fracture risk. It has been shown in numerous studies that bone loss causes increased bone fragility and risk of fracture. It has also been shown that 50% of patients with osteoporotic vertebral compression fractures have the same bone mass as normal age matched controls. Thus, bone mass alone is not the only indicator of bone quality and ability to resist fracture.;The objective of this study was to qualitatively assess bone\u27s mechanical and histomorphometric changes with drug treatment, and estrogen deficiency, using fracture toughness, femoral neck fracture and histomorphometric analysis in an ovarectomized rabbit model.;No significant differences were found in fracture toughness, porosity, or femoral neck ultimate strength for any treatment group, which may have be from a lack sufficient time for the difference caused by estrogen deficiency and drug treatment to manifest in the rabbit model
When Does Mental Health Coercion Constitute Torture?: Implications of Unpublished U.S. Immigration Judge Decisions Denying Non-Refoulement Protection
KSZ tomography and the bispectrum
Several statistics have been proposed for measuring the kSZ effect by
combining the small-scale CMB with galaxy surveys. We review five such
statistics, and show that they are all mathematically equivalent to the optimal
bispectrum estimator of type . Reinterpreting these kSZ
statistics as special cases of bispectrum estimation makes many aspects
transparent, for example optimally weighting the estimator, or incorporating
photometric redshift errors. We analyze the information content of the
bispectrum and show that there are two observables: the small-scale
galaxy-electron power spectrum , and the large-scale
galaxy-velocity power spectrum . The cosmological constraining power
of the kSZ arises from its sensitivity to fluctuations on large length scales,
where its effective noise level can be much better than galaxy surveys.Comment: 39 page
BacillOndex: An Integrated Data Resource for Systems and Synthetic Biology
BacillOndex is an extension of the Ondex data integration system, providing a semantically annotated, integrated knowledge base for the model Gram-positive bacterium Bacillus subtilis. This application allows a user to mine a variety of B. subtilis data sources, and analyse the resulting integrated dataset, which contains data about genes, gene products and their interactions. The data can be analysed either manually, by browsing using Ondex, or computationally via a Web services interface. We describe the process of creating a BacillOndex instance, and describe the use of the system for the analysis of single nucleotide polymorphisms in B. subtilis Marburg. The Marburg strain is the progenitor of the widely-used laboratory strain B. subtilis 168. We identified 27 SNPs with predictable phenotypic effects, including genetic traits for known phenotypes. We conclude that BacillOndex is a valuable tool for the systems-level investigation of, and hypothesis generation about, this important biotechnology workhorse. Such understanding contributes to our ability to construct synthetic genetic circuits in this organism
Field testing a novel high residence positioning system for monitoring the fine‐scale movements of aquatic organisms
1. Acoustic telemetry is an important tool for studying the behaviour of aquatic organisms in the wild.
2. VEMCO high residence (HR) tags and receivers are a recent introduction in the field of acoustic telemetry and can be paired with existing algorithms (e.g. VEMCO positioning system [VPS]) to obtain high‐resolution two‐dimensional positioning data.
3. Here, we present results of the first documented field test of a VPS composed of HR receivers (hereafter, HR‐VPS). We performed a series of stationary and moving trials with HR tags (mean HR transmission period = 1.5 s) to evaluate the precision, accuracy and temporal capabilities of this positioning technology. In addition, we present a sample of data obtained for five European perch Perca fluviatilis implanted with HR tags (mean HR transmission period = 4 s) to illustrate how this technology can estimate the fine‐scale behaviour of aquatic animals.
4. Accuracy and precision estimates (median [5th–95th percentile]) of HR‐VPS positions for all stationary trials were 5.6 m (4.2–10.8 m) and 0.1 m (0.02–0.07 m), respectively, and depended on the location of tags within the receiver array. In moving tests, tracks generated by HR‐VPS closely mimicked those produced by a handheld GPS held over the tag, but these differed in location by an average of ≈9 m.
5. We found that estimates of animal speed and distance travelled for perch declined when positional data for acoustically tagged perch were thinned to mimic longer transmission periods. These data also revealed a trade‐off between capturing real nonlinear animal movements and the inclusion of positioning error.
6. Our results suggested that HR‐VPS can provide more representative estimates of movement metrics and offer an advancement for studying fine‐scale movements of aquatic organisms, but high‐precision survey techniques may be needed to test these systems
Spatially Continuous Depletion Algorithm for Monte Carlo Simulations
To correctly predict reactor behavior during cycle operations, the evolution of nuclide number densities throughout the core must be accurately modeled. The time-varying spatial distribution of nuclide number densities is typically resolved by discretizing the Monte Carlo geometry into smaller cells over which number densities are assumed to be spatially invariant.
The nuclide number densities in these smaller cells are integrated through time using reaction rate tallies on the same discretized geometry. However, detailed distributions of nuclide number densities in a full three dimensional simulation can require a prohibitive amount of tallies, and the spatial
discretization of the base geometry makes coupling to external multiphysics tools difficult. In this paper a method for solving for spatially continuous number density distributions during depletion calculations
will be described. The spatially continuous number densities can be used in the transport method proposed by Brown and Martin which allows for transporting neutrons through a material with continuously varying properties such as temperature and nuclide number densities. Coupled with the ability of Functional Expansion Tallies (FETs) [2] to represent tallied quantities as continuous functions, it is possible to both solve for and make use of spatially continuous nuclide number densities. The need for this capability was alluded to by Brown et. al., but no solution has yet been proposed. With a continuous depletion method, recent work which utilized
FETs and continuous material tracking to incorporate multiphysics
feedback in Monte Carlo simulations can be extended to simulations that include depletion analysis.United States. Department of Energy (Nuclear Energy University Programs Graduate Fellowship
Measuring Three-Dimensional Temperature Distributions in Steel-Concrete Composite Slabs Subjected to Fire using Distributed Fiber Optic Sensors
Detailed information about temperature distribution can be important to understand structural behavior in fire. This study develops a method to image three-dimensional temperature distributions in steel–concrete composite slabs using distributed fiber optic sensors. The feasibility of the method is explored using six 1.2 m × 0.9 m steel–concrete composite slabs instrumented with distributed sensors and thermocouples subjected to fire for over 3 h. Dense point clouds of temperature in the slabs were measured using the distributed sensors. The results show that the distributed sensors operated at material temperatures up to 960◦C with acceptable accuracy for many structural fire applications. The measured non-uniform temperature distributions indicate a spatially distributed thermal response in steel–concrete composite slabs, which can only be adequately captured using approaches that provide a high density of through-depth data points
A theoretical explanation for the Central Molecular Zone asymmetry
It has been known for more than thirty years that the distribution of
molecular gas in the innermost 300 parsecs of the Milky Way, the Central
Molecular Zone, is strongly asymmetric. Indeed, approximately three quarters of
molecular emission comes from positive longitudes, and only one quarter from
negative longitudes. However, despite much theoretical effort, the origin of
this asymmetry has remained a mystery. Here we show that the asymmetry can be
neatly explained by unsteady flow of gas in a barred potential. We use
high-resolution 3D hydrodynamical simulations coupled to a state-of-the-art
chemical network. Despite the initial conditions and the bar potential being
point-symmetric with respect to the Galactic Centre, asymmetries develop
spontaneously due to the combination of a hydrodynamical instability known as
the "wiggle instability" and the thermal instability. The observed asymmetry
must be transient: observations made tens of megayears in the past or in the
future would often show an asymmetry in the opposite sense. Fluctuations of
amplitude comparable to the observed asymmetry occur for a large fraction of
the time in our simulations, and suggest that the present is not an exceptional
moment in the life of our Galaxy.Comment: Accepted for publication in MNRAS. Videos of the simulations are
available at http://www.ita.uni-heidelberg.de/~mattia/download.htm
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