8,303 research outputs found
BIC extensions for order-constrained model selection
The Schwarz or Bayesian information criterion (BIC) is one of the most widely used tools for model comparison in social science research. The BIC, however, is not suitable for evaluating models with order constraints on the parameters of interest. This article explores two extensions of the BIC for evaluating order-constrained models, one where a truncated unit information prior is used under the order-constrained model and the other where a truncated local unit information prior is used. The first prior is centered on the maximum likelihood estimate, and the latter prior is centered on a null value. Several analyses show that the order-constrained BIC based on the local unit information prior works better as an Occamâs razor for evaluating order-constrained models and results in lower error probabilities. The methodology based on the local unit information prior is implemented in the R package âBICpackâ which allows researchers to easily apply the method for order-constrained model selection. The usefulness of the methodology is illustrated using data from the European Values Study
The SseC translocon component in Salmonella enterica serovar Typhimurium is chaperoned by SscA
Background: Salmonella enterica is a causative agent of foodborne gastroenteritis and the systemic disease known as typhoid fever. This bacterium uses two type three secretion systems (T3SSs) to translocate protein effectors into host cells to manipulate cellular function. Salmonella pathogenicity island (SPI)-2 encodes a T3SS required for intracellular survival of the pathogen. Genes in SPI-2 include apparatus components, secreted effectors and chaperones that bind to secreted cargo to coordinate their release from the bacterial cell. Although the effector repertoire secreted by the SPI-2 T3SS is large, only three virulence-associated chaperones have been characterized. Results: Here we report that SscA is the chaperone for the SseC translocon component. We show that SscA and SseC interact in bacterial cells and that deletion of sscA results in a loss of SseC secretion, which compromises intracellular replication and leads to a loss of competitive fitness in mice. Conclusions: This work completes the characterization of the chaperone complement within SPI-2 and identifies SscA as the chaperone for the SseC translocon
Status of National Open Spatial Data Infrastructures: a Comparison Across Continents
The increasing need for geospatial information demands for well-organised management among all levels of society. A Spatial Data Infrastructure (SDI) is a multidisciplinary and dynamic instrument that facilitates access and sharing of geospatial information. The current trend towards open data initiatives is influencing the development of these infrastructures. In order to examine this effect, this article addresses the following question: what is the current state of SDI openness of four best practice open data countries Canada, The Netherlands, Australia and Brazil, and how do they compare? The question is answered through a qualitative literature study and the application of a newly developed Open SDI Assessment Framework to the countries. The Netherlands and Canada show a high performance on all assessment dimensions; data discovery, data access and data properties. Australia and Brazil show a poor open SDI performance, as they could not meet the requirements set for the assessed datasets. General conclusions of the assessment are that data is currently fragmented and scattered among the web in all four countries, which strongly negatively influences the user experience. It is crucial that a strict legal framework is embedded in a country, which ensures that current SDI objectives and propositions regarding an user-centred approach and open data availability are achieved
Neural Attention and Evaluative Responses to Gay and Lesbian Couples
The goal of the current study was to examine whether differential neural attentional capture and evaluative responses for out-group homosexual relative to in-group heterosexual targets occur during social categorization. To this end, 36 heterosexual participants were presented with pictures of heterosexual and homosexual couples in a picture-viewing task that was designed to assess implicit levels of discomfort toward homosexuality and explicit evaluations of pleasantness toward the images. Neural activity in the form of electroencephalogram was recorded during the presentation of the pictures, and event-related potentials resulting from these stimuli were examined. Participants also completed questionnaires that assessed the degree to which they socialized with gays and lesbians. Results demonstrated that relative to straight couples, larger P2 amplitude was observed in response to gay but not to lesbian couples. However, both gay and lesbian couples yielded a larger late positive potential than straight couples. Moreover, the degree to which participants differentially directed early neural attention to out-group lesbian versus in-group straight couples was related to their familiarity with homosexual individuals. This work, which provides an initial understanding of the neural underpinnings of attention toward homosexual couples, suggests that differences in the processing of sexual orientation can occur as early as 200 ms and may be moderated by familiarity
The Effect of the Outer Lindblad Resonance of the Galactic Bar on the Local Stellar Velocity Distribution
Hydro-dynamical modeling of the inner Galaxy suggest that the radius of the
outer Lindblad resonance (OLR) of the Galactic bar lies in the vicinity of the
Sun. How does this resonance affect the distribution function in the outer
parts of a barred disk, and can we identify any effect of the resonance in the
velocity distribution f(v) actually observed in the solar neighborhood? To
answer these questions, detailed simulations of f(v) in the outer parts of an
exponential stellar disks with nearly flat rotation curves and a rotating
central bar have been performed. For a model resembling the old stellar disk,
the OLR causes a distinct feature in f(v) over a significant fraction of the
outer disk. For positions <2kpc outside the OLR radius and at bar angles of
\~10-70 degrees, f(v) inhibits a bi-modality between the low-velocity stars
moving like the local standard of rest (LSR) and a secondary mode of stars
predominantly moving outward and rotating more slowly than the LSR.
Such a bi-modality is indeed present in f(v) inferred from the Hipparcos data
for late-type stars in the solar neighborhood. If one interpretes this observed
bi-modality as induced by the OLR -- and there are hardly any viable
alternatives -- then one is forced to deduce that the OLR radius is slightly
smaller than Ro. Moreover, by a quantitative comparison of the observed with
the simulated distributions one finds that the pattern speed of the bar is
1.85+/-0.15 times the local circular frequency, where the error is dominated by
the uncertainty in bar angle and local circular speed.
Also other, less prominent but still significant, features in the observed
f(v) resemble properties of the simulated velocity distributions, in particular
a ripple caused by orbits trapped in the outer 1:1 resonance.Comment: 14 pages, 10 figures (Fig.2 in full resolution available upon
request), accepted for publication in A
Tracking Cyber Adversaries with Adaptive Indicators of Compromise
A forensics investigation after a breach often uncovers network and host
indicators of compromise (IOCs) that can be deployed to sensors to allow early
detection of the adversary in the future. Over time, the adversary will change
tactics, techniques, and procedures (TTPs), which will also change the data
generated. If the IOCs are not kept up-to-date with the adversary's new TTPs,
the adversary will no longer be detected once all of the IOCs become invalid.
Tracking the Known (TTK) is the problem of keeping IOCs, in this case regular
expressions (regexes), up-to-date with a dynamic adversary. Our framework
solves the TTK problem in an automated, cyclic fashion to bracket a previously
discovered adversary. This tracking is accomplished through a data-driven
approach of self-adapting a given model based on its own detection
capabilities.
In our initial experiments, we found that the true positive rate (TPR) of the
adaptive solution degrades much less significantly over time than the naive
solution, suggesting that self-updating the model allows the continued
detection of positives (i.e., adversaries). The cost for this performance is in
the false positive rate (FPR), which increases over time for the adaptive
solution, but remains constant for the naive solution. However, the difference
in overall detection performance, as measured by the area under the curve
(AUC), between the two methods is negligible. This result suggests that
self-updating the model over time should be done in practice to continue to
detect known, evolving adversaries.Comment: This was presented at the 4th Annual Conf. on Computational Science &
Computational Intelligence (CSCI'17) held Dec 14-16, 2017 in Las Vegas,
Nevada, US
Dark matter within high surface brightness spiral galaxies
We present results from a detailed dynamical analysis of five high surface
brightness, late type spirals, studied with the aim to quantify the
luminous-to-dark matter ratio inside their optical radii. The galaxies' stellar
light distribution and gas kinematics have been observed and compared to
hydrodynamic gas simulations, which predict the 2D gas dynamics arising in
response to empirical gravitational potentials, which are combinations of
differing stellar disk and dark halo contributions. The gravitational potential
of the stellar disk was derived from near-infrared photometry, color-corrected
to constant (M/L); the dark halo was modelled by an isothermal sphere with a
core. Hydrodynamic gas simulations were performed for each galaxy for a
sequence of five different mass fractions of the stellar disk and for a wide
range of spiral pattern speeds. These two parameters mainly determine the
modelled gas distribution and kinematics. The agreement between the
non-axisymmetric part of the simulated and observed gas kinematics permitted us
to conclude that the galaxies with the highest rotation velocities tend to
possess near-maximal stellar disks. In less massive galaxies, with v_max<200
km/s, the mass of the dark halo at least equals the stellar mass within 2-3
R_disk. The simulated gas morphology provides a powerful tool to determine the
dominant spiral pattern speed. The corotation radius for all galaxies was found
to be constant at R_corotation ~ 3 R_disk and encloses the strong part of the
stellar spiral in all cases.Comment: 28 pages, 7 figures; to appear in the Astrophysical Journal, Vol.
586, March 200
Density Waves Inside Inner Lindblad Resonance: Nuclear Spirals in Disk Galaxies
We analyze formation of grand-design two-arm spiral structure in the nuclear
regions of disk galaxies. Such morphology has been recently detected in a
number of objects using high-resolution near-infrared observations. Motivated
by the observed (1) continuity between the nuclear and kpc-scale spiral
structures, and by (2) low arm-interarm contrast, we apply the density wave
theory to explain the basic properties of the spiral nuclear morphology. In
particular, we address the mechanism for the formation, maintenance and the
detailed shape of nuclear spirals. We find, that the latter depends mostly on
the shape of the underlying gravitational potential and the sound speed in the
gas. Detection of nuclear spiral arms provides diagnostics of mass distribution
within the central kpc of disk galaxies. Our results are supported by 2D
numerical simulations of gas response to the background gravitational potential
of a barred stellar disk. We investigate the parameter space allowed for the
formation of nuclear spirals using a new method for constructing a
gravitational potential in a barred galaxy, where positions of resonances are
prescribed.Comment: 18 pages, 9 figures, higher resolution available at
http://www.pa.uky.edu/~ppe/papers/nucsp.ps.g
SPH Simulations of Galactic Gaseous Disk with Bar: Distribution and Kinematic Structure of Molecular Clouds toward the Galactic Center
We have performed Smoothed Particle Hydrodynamic (SPH) simulations to study
the response of molecular clouds in the Galactic disk to a rotating bar and
their subsequent evolution in the Galactic Center (GC) region. The Galactic
potential in our models is contributed by three axisymmetric components
(massive halo, exponential disk, compact bulge) and a non-axisymmetric bar.
These components are assumed to be invariant in time in the frame corotating
with the bar. Some noticeable features such as an elliptical outer ring, spiral
arms, a gas-depletion region, and a central concentration have been developed
due to the influence of the bar. The rotating bar induces non-circular motions
of the SPH particles, but hydrodynamic collisions tend to suppress the random
components of the velocity. The velocity field of the SPH particles is
consistent with the kinematics of molecular clouds observed in HCN (1-0)
transition; these clouds are thought to be very dense clouds. However, the l-v
diagram of the clouds traced by CO is quite different from that of our SPH
simulation, being more similar to that obtained from simulations using
collisionless particles. The diagram of a mixture of collisional and
collisionless particles gives better reproduction of the kinematic structures
of the GC clouds observed in the CO line. The fact that the kinematics of HCN
clouds can be reproduced by the SPH particles suggests that the dense clouds in
the GC are formed via cloud collisions induced by rotating bar.Comment: 31 pages, 10 pigures, accepted for publication in Ap
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