209 research outputs found
Stealthy Deception Attacks Against SCADA Systems
SCADA protocols for Industrial Control Systems (ICS) are vulnerable to
network attacks such as session hijacking. Hence, research focuses on network
anomaly detection based on meta--data (message sizes, timing, command
sequence), or on the state values of the physical process. In this work we
present a class of semantic network-based attacks against SCADA systems that
are undetectable by the above mentioned anomaly detection. After hijacking the
communication channels between the Human Machine Interface (HMI) and
Programmable Logic Controllers (PLCs), our attacks cause the HMI to present a
fake view of the industrial process, deceiving the human operator into taking
manual actions. Our most advanced attack also manipulates the messages
generated by the operator's actions, reversing their semantic meaning while
causing the HMI to present a view that is consistent with the attempted human
actions. The attacks are totaly stealthy because the message sizes and timing,
the command sequences, and the data values of the ICS's state all remain
legitimate.
We implemented and tested several attack scenarios in the test lab of our
local electric company, against a real HMI and real PLCs, separated by a
commercial-grade firewall. We developed a real-time security assessment tool,
that can simultaneously manipulate the communication to multiple PLCs and cause
the HMI to display a coherent system--wide fake view. Our tool is configured
with message-manipulating rules written in an ICS Attack Markup Language (IAML)
we designed, which may be of independent interest. Our semantic attacks all
successfully fooled the operator and brought the system to states of blackout
and possible equipment damage
Commutator Relations Reveal Solvable Structures in Unambiguous State Discrimination
We present a criterion, based on three commutator relations, that allows to
decide whether two self-adjoint matrices with non-overlapping support are
simultaneously unitarily similar to quasidiagonal matrices, i.e., whether they
can be simultaneously brought into a diagonal structure with 2x2-dimensional
blocks. Application of this criterion to unambiguous state discrimination
provides a systematic test whether the given problem is reducible to a solvable
structure. As an example, we discuss unambiguous state comparison.Comment: 5 pages, discussion of related work adde
Bound entangled states fit for robust experimental verification
Preparing and certifying bound entangled states in the laboratory is an
intrinsically hard task, due to both the fact that they typically form narrow
regions in the state space, and that a certificate requires a tomographic
reconstruction of the density matrix. Indeed, the previous experiments that
have reported the preparation of a bound entangled state relied on such
tomographic reconstruction techniques. However, the reliability of these
results crucially depends on the extra assumption of an unbiased
reconstruction. We propose an alternative method for certifying the bound
entangled character of a quantum state that leads to a rigorous claim within a
desired statistical significance, while bypassing a full reconstruction of the
state. The method is comprised by a search for bound entangled states that are
robust for experimental verification, and a hypothesis test tailored for the
detection of bound entanglement that is naturally equipped with a measure of
statistical significance. We apply our method to families of states of and systems, and find that the experimental certification of
bound entangled states is well within reach.Comment: Accepted version in Quantu
A long look at the BALQSO LBQS 2212-1759 with XMM-Newton
Very long (172 ks effective exposure time) observations of the BALQSO LBQS
2212-1759 with XMM-Newton yield a stringent upper-limit on its 0.2-10 keV
(rest- frame 0.64-32.2 keV) flux, F < 6 E-17 erg/cm2/s, while simultaneous UV
and optical observations reveal a rather blue spectrum extending to 650 A in
the source rest frame. These results are used to set a tight upper-limit on its
optical to X-ray spectral index alpha_{ox} < -2.56. Given the HI-BAL nature of
LBQS 212-1759, its X-ray weakness is most likely due to intrinsic absorption.
If this is the case, and assuming that the intrinsic alpha_{ox} of LBQS
2212-1759 is -1.63 - a value appropriate for a radio-quiet quasar of this
luminosity - one can set a lower limit on the X-ray absorbing column N_{H} >
3.4 E25 cm-2. Such a large column has a Thomson optical depth to electron
scattering tau > 23, sufficient to extinguish the optical and UV emission. The
problem only gets worse if the gas is neutral since the opacity in the Lyman
continuum becomes extremely large, > 2 E8, conflicting with the source
detection below 912 A. This apparent contradiction probably means that our
lines-of-sight to the X-ray and to the UV emitting regions are different, such
that the gas covers completely the compact X-ray source but only partially the
more extended source of ultraviolet photons. An extended (~ 1') X-ray source is
detected 2' to the south-east of the QSO. Given its thermal spectrum and
temperature (1.5 < T < 3.0 keV}, it is probably a foreground (0.29 < z < 0.46)
cluster of galaxies.Comment: 9 pages, 3 figures, A&A latex, accepted for publication in Astronomy
& Astrophysic
An evolutionary catalogue of Galactic post-AGB and related objects
With the ongoing AKARI infrared sky survey, of much greater sensitivity than
IRAS, a wealth of post-AGB objects may be discovered. It is thus time to
organize our present knowledge of known post-AGB stars in th galaxy with a view
to using it to search for new post-AGB objects among AKARI sources. We searched
the literature available on the NASA Astrophysics Data System up to 1 October
2006, and defined criteria for classifying sources into three categories: "very
likely", "possible" and "disqualified" post-AGB objects. The category of "very
likely" post-AGB objects is made up of several classes. We have created an
evolutionary, on-line catalogue of Galactic post-AGB objects, to be referred to
as "The Torun catalogue of Galactic post-AGB and related objects". The present
version of the catalogue contains 326 "very likely", 107 "possible" and 64
"disqualified" objects. For the very likely post-AGB objects, the catalogue
gives the available optical and infrared photometry, infrared spectroscopy and
spectral types, and links to finding charts and bibliography.Comment: 9 pages, 6 figures, accepted for publication in A&
Selection of ULIRGs in Infrared and Submm Surveys
We examine the selection characteristics of infrared and sub-mm surveys with
IRAS, Spitzer, BLAST, Herschel and SCUBA and identify the range of dust
temperatures these surveys are sensitive to, for galaxies in the ULIRG
luminosity range (12<log(LIR)<13), between z=0 and z=4. We find that the extent
of the redshift range over which surveys are unbiased is a function of the
wavelength of selection, flux density limit and ULIRG luminosity. Short
wavelength (<200{\mu}m) surveys with IRAS, Spitzer/MIPS and Herschel/PACS are
sensitive to all SED types in a large temperature interval (17-87K), over a
substantial fraction of their accessible redshift range. On the other hand,
long wavelength (>200{\mu}m) surveys with BLAST, Herschel/ SPIRE and SCUBA are
significantly more sensitive to cold ULIRGs, disfavouring warmer SEDs even at
low redshifts. We evaluate observations in the context of survey selection
effects, finding that the lack of cold ULIRGs in the local (z<0.1) Universe is
not a consequence of selection and that the range of ULIRG temperatures seen
locally is only a subset of a much larger range which exists at high redshift.
We demonstrate that the local luminosity-temperature (L-T) relation, which
indicates that more luminous sources are also hotter, is not applicable in the
distant Universe when extrapolated to the ULIRG regime, because the scatter in
observed temperatures is too large. Finally, we show that the difference
between the ULIRG temperature distributions locally and at high redshift is not
the result of galaxies becoming colder due to an L-T relation which evolves as
a function of redshift. Instead, they are consistent with a picture where the
evolution of the infrared luminosity function is temperature dependent, i.e.
cold galaxies evolve at a faster rate than their warm counterparts.Comment: 11 pages, 6 figures, accepted for publication in MNRA
Herschel observations of EXtra-Ordinary Sources: The Terahertz spectrum of Orion KL seen at high spectral resolution
We present the first high spectral resolution observations of Orion KL in the
frequency ranges 1573.4 - 1702.8 GHz (band 6b) and 1788.4 - 1906.8 GHz (band
7b) obtained using the HIFI instrument on board the Herschel Space Observatory.
We characterize the main emission lines found in the spectrum, which primarily
arise from a range of components associated with Orion KL including the hot
core, but also see widespread emission from components associated with
molecular outflows traced by H2O, SO2, and OH. We find that the density of
observed emission lines is significantly diminished in these bands compared to
lower frequency Herschel/HIFI bands.Comment: Accepted for publication in the Herschel HIFI special issue of
Astronomy and Astrophysics Letters, 5 pages, 3 figure
Extreme infrared variables from UKIDSS-I. A concentration in star-forming regions
We present initial results of the first panoramic search for high-amplitude near-infrared variability in theGalactic plane.We analyse the widely separated two-epoch K-band photometry in the fifth and seventh data releases of the UKIDSS Galactic plane survey.We find 45 stars with δK > 1 mag, including two previously known OH/IR stars and a Nova. Even though the midplane is not yet included in the data set, we find the majority (66 per cent) of our sample to be within known star-forming regions (SFRs), with two large concentrations in the Serpens OB2 association (11 stars) and the Cygnus-X complex (12 stars). Sources in SFRs show spectral energy distributions that support classification as young stellar objects (YSOs). This indicates that YSOs dominate the Galactic population of high-amplitude infrared variable stars at low luminosities and therefore likely dominate the total high-amplitude population. Spectroscopic follow up of the DR5 sample shows at least four stars with clear characteristics of eruptive premain- sequence variables, two of which are deeply embedded. Our results support the recent concept of eruptive variability comprising a continuum of outburst events with different timescales and luminosities, but triggered by a similar physical mechanism involving unsteady accretion. Also, we find what appears to be one of the most variable classical Be stars. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Ten Million Degree Gas in M 17 and the Rosette Nebula: X-ray Flows in Galactic H II Regions
We present the first high-spatial-resolution X-ray images of two high-mass
star forming regions, the Omega Nebula (M 17) and the Rosette Nebula (NGC
2237--2246), obtained with the Chandra X-ray Observatory Advanced CCD Imaging
Spectrometer (ACIS) instrument. The massive clusters powering these H II
regions are resolved at the arcsecond level into >900 (M 17) and >300 (Rosette)
stellar sources similar to those seen in closer young stellar clusters.
However, we also detect soft diffuse X-ray emission on parsec scales that is
spatially and spectrally distinct from the point source population. The diffuse
emission has luminosity L_x ~ 3.4e33 ergs/s in M~17 with plasma energy
components at kT ~0.13 and ~0.6 keV (1.5 and 7 MK), while in Rosette it has L_x
\~6e32 ergs/s with plasma energy components at kT ~0.06 and ~0.8 keV (0.7 and 9
MK). This extended emission most likely arises from the fast O-star winds
thermalized either by wind-wind collisions or by a termination shock against
the surrounding media. We establish that only a small portion of the wind
energy and mass appears in the observed diffuse X-ray plasma; in these blister
H II regions, we suspect that most of it flows without cooling into the
low-density interstellar medium. These data provide compelling observational
evidence that strong wind shocks are present in H II regions.Comment: 35 pages, including 11 figures; to appear in ApJ, August 20, 2003. A
version with high-resolution figures is available at
ftp://ftp.astro.psu.edu/pub/townsley/diffuse.ps.g
A line confusion limited millimeter survey of Orion KL. II: Silicon-bearing species
We present a study of the Silicon-bearing species detected in a line
confusion limited survey towards Orion KL performed with the IRAM 30-m
telescope, which ranges from 80 to 280 GHz. Our aim is to derive physical and
chemical conditions for each family taking into account all observed lines from
all isotopologues of each species. We have modeled the lines of the detected
molecules using a radiative transfer code, which permit us to choose between
LVG and LTE approximations depending on the physical conditions of the gas. We
have used appropriate collisional rates for the LVG calculations. For the v=1
state of SiO we have detected the J=2-1 line and, for the first time in this
source, emission in the J=4-3 transition, both of them showing strong masering
effect. For SiO v=0, we have detected 28SiO, 29SiO, and 30SiO; in addition, we
have mapped the J = 5-4 SiO line. For SiS, we have detected the main species,
29SiS, and SiS v=1. Unlikely other species detected in Orion KL (IRc2), the
emission peak of SiS appears at a velocity of ~15.5 km s-1; a study of the 5-4
SiO line around IRc2 shows this feature as an extended component that probably
arises from the interaction of the outflow with the ambient cloud. We derive a
SiO/SiS column density ratio of ~13 in the plateau component. Besides, we
provide upper limits to the column density of several non-detected
Silicon-bearing species. The results of our chemical models show that while it
is possible to reproduce SiO in the gas phase (as well as on the grains), SiS
is a product of surface reactions, most likely involving direct reactions of S
with Si.Comment: Astronomy and Astrophysics, in pres
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