208 research outputs found
An SDN-based Approach For Defending Against Reflective DDoS Attacks
Distributed Reflective Denial of Service (DRDoS) attacks are an immanent
threat to Internet services. The potential scale of such attacks became
apparent in March 2018 when a memcached-based attack peaked at 1.7 Tbps. Novel
services built upon UDP increase the need for automated mitigation mechanisms
that react to attacks without prior knowledge of the actual application
protocols used. With the flexibility that software-defined networks offer, we
developed a new approach for defending against DRDoS attacks; it not only
protects against arbitrary DRDoS attacks but is also transparent for the attack
target and can be used without assistance of the target host operator. The
approach provides a robust mitigation system which is protocol-agnostic and
effective in the defense against DRDoS attacks
The Neural Correlates of Face-Voice-Integration in Social Anxiety Disorder
Faces and voices are very important sources of threat in social anxiety disorder (SAD), a common psychiatric disorder where core elements are fears of social exclusion and negative evaluation. Previous research in social anxiety evidenced increased cerebral responses to negative facial or vocal expressions and also generally increased hemodynamic responses to voices and faces. But it is unclear if also the cerebral process of face-voice-integration is altered in SAD. Applying functional magnetic resonance imaging, we investigated the correlates of the audiovisual integration of dynamic faces and voices in SAD as compared to healthy individuals. In the bilateral midsections of the superior temporal sulcus (STS) increased integration effects in SAD were observed driven by greater activation increases during audiovisual stimulation as compared to auditory stimulation. This effect was accompanied by increased functional connectivity with the visual association cortex and a more anterior position of the individual integration maxima along the STS in SAD. These findings demonstrate that the audiovisual integration of facial and vocal cues in SAD is not only systematically altered with regard to intensity and connectivity but also the individual location of the integration areas within the STS. These combined findings offer a novel perspective on the neuronal representation of social signal processing in individuals suffering from SAD
Arraying nonmagnetic colloids by magnetic nanoparticle assemblers
IEEE Transactions On Magnetics, 42(10): pp. 3548-3553.We review our recent work on the manipulation and assembly of nonmagnetic colloidal materials above magnetically programmable
surface templates. The nonmagnetic materials are manipulated by a fluid dispersion of magnetic nanoparticles, known as ferrofluid.
Particle motion is guided by a program of magnetic information stored in a substrate in the form of a lithographically patterned template
of micromagnets. We show how dynamic control over the motion of nonmagnetic particles can be accomplished by applying rotating
external magnetic field. This unexpectedly large degree of control over particle motion can be used to manipulate large ensembles of
particles in parallel, potentially with local control over particle trajectory
A bright, spatially extended lensed galaxy at z = 1.7 behind the cluster RCS2 032727-132623
We present the discovery of an extremely bright and extended lensed source
from the second Red Sequence Cluster Survey (RCS2). RCSGA 032727-132609 is
spectroscopically confirmed as a giant arc and counter-image of a background
galaxy at , strongly-lensed by the foreground galaxy cluster RCS2
032727-132623 at . The giant arc extends over \,\arcsec and
has an integrated -band magnitude of 19.15, making it times larger
and times brighter than the prototypical lensed galaxy MS1512-cB58.
This is the brightest distant lensed galaxy in the Universe known to date. Its
location in the `redshift desert' provides unique opportunities to connect
between the large samples of galaxies known at and . We have
collected photometry in 9 bands, ranging from to , which densely
sample the rest-frame UV and optical light, including the age-sensitive
4000\AA\ break. A lens model is constructed for the system, and results in a
robust total magnification of for the counter-image; we
estimate an average magnification of for the giant arc based on
the relative physical scales of the arc and counter-image. Fits of
single-component spectral energy distribution (SED) models to the photometry
result in a moderately young age, \,Myr, small amounts of dust,
, and an exponentially declining star formation history with
\textit{e}-folding time \,Myr. After correcting for the lensing
magnification, we find a stellar mass of
. Allowing for episodic star
formation, an underlying old burst could contain up to twice the mass inferred
from single-component modeling. This stellar mass estimate is consistent with
the average stellar mass of a sample of `BM' galaxies () studied
by Reddy et al. (2006).Comment: 13 pages, 8 figures, abstract abridge
A CANDELS WFC3 Grism Study of Emission-Line Galaxies at z~2: A Mix of Nuclear Activity and Low-Metallicity Star Formation
We present Hubble Space Telescope Wide Field Camera 3 slitless grism
spectroscopy of 28 emission-line galaxies at z~2, in the GOODS-S region of the
Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). The
high sensitivity of these grism observations, with 1-sigma detections of
emission lines to f > 2.5x10^{-18} erg/s/cm^2, means that the galaxies in the
sample are typically ~7 times less massive (median M_* = 10^{9.5} M_sun) than
previously studied z~2 emission-line galaxies. Despite their lower mass, the
galaxies have OIII/Hb ratios which are very similar to previously studied z~2
galaxies and much higher than the typical emission-line ratios of local
galaxies. The WFC3 grism allows for unique studies of spatial gradients in
emission lines, and we stack the two-dimensional spectra of the galaxies for
this purpose. In the stacked data the OIII emission line is more spatially
concentrated than the Hb emission line with 98.1 confidence. We additionally
stack the X-ray data (all sources are individually undetected), and find that
the average L(OIII)/L(0.5-10 keV) ratio is intermediate between typical z~0
obscured active galaxies and star-forming galaxies. Together the compactness of
the stacked OIII spatial profile and the stacked X-ray data suggest that at
least some of these low-mass, low-metallicity galaxies harbor weak active
galactic nuclei.Comment: ApJ accepted. 8 pages, 6 figure
Short-lived star-forming giant clumps in cosmological simulations of z~2 disks
Many observed massive star-forming z\approx2 galaxies are large disks that
exhibit irregular morphologies, with \sim1kpc, \sim10^(8-10)Msun clumps. We
present the largest sample to date of high-resolution cosmological SPH
simulations that zoom-in on the formation of individual M*\sim10^(10.5)Msun
galaxies in \sim10^(12)Msun halos at z\approx2. Our code includes strong
stellar feedback parameterized as momentum-driven galactic winds. This model
reproduces many characteristic features of this observed class of galaxies,
such as their clumpy morphologies, smooth and monotonic velocity gradients,
high gas fractions (f_g\sim50%) and high specific star-formation rates
(\gtrsim1Gyr^(-1)). In accord with recent models, giant clumps
(Mclump\sim(5x10^8-10^9)Msun) form in-situ via gravitational instabilities.
However, the galactic winds are critical for their subsequent evolution. The
giant clumps we obtain are short-lived and are disrupted by wind-driven mass
loss. They do not virialise or migrate to the galaxy centers as suggested in
recent work neglecting strong winds. By phenomenologically implementing the
winds that are observed from high-redshift galaxies and in particular from
individual clumps, our simulations reproduce well new observational constraints
on clump kinematics and clump ages. In particular, the observation that older
clumps appear closer to their galaxy centers is reproduced in our simulations,
as a result of inside-out formation of the disks rather than inward clump
migration.Comment: 11 pages, 6 figures, 1 table. Accepted for publication in the
Astrophysical Journa
The Cosmic Evolution of Metallicity from the SDSS Fossil Record
We present the time evolution of the stellar metallicity for SDSS galaxies, a
sample that spans five orders of magnitude in stellar mass (10^7 - 10^{12}
Msun). Assuming the BC03 stellar population models, we find that more massive
galaxies are more metal-rich than less massive ones at all redshifts; the
mass-metallicity relation is imprinted in galaxies from the epoch of formation.
For galaxies with present stellar masses > 10^{10} Msun, the time evolution of
stellar metallicity is very weak, with at most 0.2-0.3 dex over a Hubble time-
for this reason the mass-metallicity relation evolves little with redshift.
However, for galaxies with present stellar masses < 10^{10} Msun, the evolution
is significant, with metallicity increasing by more than a decade from redshift
3 to the present. By being able to recover the metallicity history, we have
managed to identify the origin of a recent discrepancy between the metallicity
recovered from nebular lines and absorption lines. As expected, we show that
the young population dominates the former while the old population the latter.
We have investigated the dependence on the stellar models used and find that
older stellar population synthesis codes do not produce a clear result.
Finally, we have explored the relationship between cluster environment and
metallicity, and find a strong correlation in the sense that galaxies in high
density regions have high metallicity.Comment: Submitted to MNRA
Spectroscopic Confirmation of Three z-Dropout Galaxies at z = 6.844 - 7.213: Demographics of Lyman-Alpha Emission in z ~ 7 Galaxies
We present the results of our ultra-deep Keck/DEIMOS spectroscopy of
z-dropout galaxies in the SDF and GOODS-N. For 3 out of 11 objects, we detect
an emission line at ~ 1um with a signal-to-noise ratio of ~ 10. The lines show
asymmetric profiles with high weighted skewness values, consistent with being
Lya, yielding redshifts of z=7.213, 6.965, and 6.844. Specifically, we confirm
the z=7.213 object in two independent DEIMOS runs with different spectroscopic
configurations. The z=6.965 object is a known Lya emitter, IOK-1, for which our
improved spectrum at a higher resolution yields a robust skewness measurement.
The three z-dropouts have Lya fluxes of 3 x 10^-17 erg s^-1 cm^-2 and
rest-frame equivalent widths EW_0^Lya = 33-43A. Based on the largest
spectroscopic sample of 43 z-dropouts that is the combination of our and
previous data, we find that the fraction of Lya-emitting galaxies (EW_0^Lya >
25A) is low at z ~ 7; 17 +- 10% and 24 +- 12% for bright (Muv ~= -21) and faint
(Muv ~= -19.5) galaxies, respectively. The fractions of Lya-emitting galaxies
drop from z ~ 6 to 7 and the amplitude of the drop is larger for faint galaxies
than for bright galaxies. These two pieces of evidence would indicate that the
neutral hydrogen fraction of the IGM increases from z ~ 6 to 7, and that the
reionization proceeds from high- to low-density environments, as suggested by
an inside-out reionization model.Comment: 15 pages, 9 figures, accepted for publication in Ap
An Analytic Model for the Evolution of the Stellar, Gas, and Metal Content of Galaxies
We present an analytic formalism that describes the evolution of the stellar,
gas, and metal content of galaxies. It is based on the idea, inspired by
hydrodynamic simulations, that galaxies live in a slowly-evolving equilibrium
between inflow, outflow, and star formation. We argue that this formalism
broadly captures the behavior of galaxy properties evolving in simulations. The
resulting equilibrium equations for the star formation rate, gas fraction, and
metallicity depend on three key free parameters that represent ejective
feedback, preventive feedback, and re-accretion of ejected material. We
schematically describe how these parameters are constrained by models and
observations. Galaxies perturbed off the equilibrium relations owing to inflow
stochasticity tend to be driven back towards equilibrium, such that deviations
in star formation rate at a given mass are correlated with gas fraction and
anti-correlated with metallicity. After an early gas accumulation epoch,
quiescently star-forming galaxies are expected to be in equilibrium over most
of cosmic time. The equilibrium model provides a simple intuitive framework for
understanding the cosmic evolution of galaxy properties, and centrally features
the cycle of baryons between galaxies and surrounding gas as the driver of
galaxy growth.Comment: 11 pages, MNRAS, accepte
Constraints on Physical Properties of z~6 Galaxies Using Cosmological Hydrodynamic Simulations
We conduct a detailed comparison of broad-band spectral energy distributions
of six z >= 5.5 galaxies against galaxies drawn from cosmological hydrodynamic
simulations. We employ a new tool called SPOC, which constrains the physical
properties of observed galaxies through a Bayesian likelihood comparison with
model galaxies. For five out of six observed z>=5.5 objects, our simulated
galaxies match the observations at least as well as simple star formation
histories such as tau-models, with similar favored values obtained for the
intrinsic physical parameters such as stellar mass and star formation rate, but
with substantially smaller uncertainties. Our results are broadly insensitive
to simulation choices for galactic outflows and dust reddening. Hence the
existence of early galaxies as observed is broadly consistent with current
hierarchical structure formation models. However, one of the six objects has
photometry that is best fit by a bursty SFH unlike anything produced in our
simulations, driven primarily by a high K-band flux. These findings illustrate
how SPOC provides a robust tool for optimally utilizing hydrodynamic
simulations (or any model that predicts galaxy SFHs) to constrain the physical
properties of individual galaxies having only photometric data, as well as
identify objects that challenge current models. (abridged)Comment: 22 pages, 11 figures, accepted by MNRAS. Added discussions of dust,
numerical resolution; clarified conclusion
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