836 research outputs found
Automated Certification of Authorisation Policy Resistance
Attribute-based Access Control (ABAC) extends traditional Access Control by
considering an access request as a set of pairs attribute name-value, making it
particularly useful in the context of open and distributed systems, where
security relevant information can be collected from different sources. However,
ABAC enables attribute hiding attacks, allowing an attacker to gain some access
by withholding information. In this paper, we first introduce the notion of
policy resistance to attribute hiding attacks. We then propose the tool ATRAP
(Automatic Term Rewriting for Authorisation Policies), based on the recent
formal ABAC language PTaCL, which first automatically searches for resistance
counter-examples using Maude, and then automatically searches for an Isabelle
proof of resistance. We illustrate our approach with two simple examples of
policies and propose an evaluation of ATRAP performances.Comment: 20 pages, 4 figures, version including proofs of the paper that will
be presented at ESORICS 201
High-Resolution spectroscopy of the low-mass X-ray binary EXO 0748-67
We present initial results from observations of the low-mass X-ray binary EXO
0748-67 with the Reflection Grating Spectrometer on board the XMM-Newton
Observatory. The spectra exhibit discrete structure due to absorption and
emission from ionized neon, oxygen, and nitrogen. We use the quantitative
constraints imposed by the spectral features to develop an empirical model of
the circumsource material. This consists of a thickened accretion disk with
emission and absorption in the plasma orbiting high above the binary plane.
This model presents challenges to current theories of accretion in X-ray binary
systems.Comment: 5 pages, 4 figures, accepted by A&A letters, XMM special issu
Multi-level Access in Searchable Symmetric Encryption
Remote storage delivers a cost effective solution for data storage. If data is of a sensitive nature, it should be encrypted prior to outsourcing to ensure confidentiality; however, searching then becomes challenging. Searchable encryption is a well-studied solution to this problem. Many schemes only consider the scenario where users can search over the entirety of the encrypted data.
In practice, sensitive data is likely to be classified according to an access control policy and different users should have different access rights.
It is unlikely that all users have unrestricted access to the entire data set.
Current schemes that consider multi-level access to searchable encryption are predominantly based on asymmetric primitives.
We investigate symmetric solutions to multi-level access in searchable encryption where users have different access privileges to portions of the encrypted data and are not permitted to search over, or learn information about, data for which they are not authorised
Protostars and Outflows in the NGC7538 - IRS9 Cloud Core
New high resolution observations of HCO+ J=1-0, H13CN J=1-0, SO 2,2 - 1,1,
and continuum with BIMA at 3.4 mm show that the NGC7538 - IRS9 cloud core is a
site of active ongoing star formation. Our observations reveal at least three
young bipolar molecular outflows, all ~ 10,000 -- 20,000 years old. IRS9 drives
a bipolar, extreme high velocity outflow observed nearly pole on. South of IRS9
we find a cold, protostellar condensation with a size of ~ 14" x 6" with a mass
> 250 Msun. This is the center of one of the outflows and shows deep,
red-shifted self absorption in HCO+, suggesting that there is a protostar
embedded in the core, still in a phase of active accretion. This source is not
detected in the far infrared, suggesting that the luminosity < 10^4 Lsun; yet
the mass of the outflow is ~ 60 Msun. The red-shifted HCO+ self-absorption
profiles observed toward the southern protostar and IRS9 predict accretion
rates of a few times 10^-4 to 10^-3 Msun/yr. Deep VLA continuum observations at
3.6 cm show that IRS9 coincides with a faint thermal VLA source, but no other
young star in the IRS9 region has any detectable free-free emission at a level
of ~ 60 microJy at 3.6 cm. The HCO+ abundance is significantly enhanced in the
hot IRS9 outflow. A direct comparison of mass estimates from HCO+ and CO for
the well-characterized red-shifted IRS9 outflow predicts an HCO+ enhancement of
more than a factor of 30, or [HCO+/H2] >= 6 10^-8.Comment: 40 pages, 3 tables and 10 figures included; to appear in Ap
The Gemini Deep Deep Survey: II. Metals in Star-Forming Galaxies at Redshift 1.3<z<2
The goal of the Gemini Deep Deep Survey (GDDS) is to study an unbiased sample
of K<20.6 galaxies in the redshift range 0.8<z<2.0. Here we determine the
statistical properties of the heavy element enrichment in the interstellar
medium (ISM) of a subsample of 13 galaxies with 1.34<z<1.97 and UV absolute
magnitude M_2000 < -19.65. The sample contains 38% of the total number of
identified galaxies in the first two fields of the survey with z>1.3. The
selected objects have colors typical of irregular and Sbc galaxies. Strong
[OII] emission indicates high star formation activity in the HII regions
(SFR~13-106 M_sun/yr). The high S/N composite spectrum shows strong ISM MgII
and FeII absorption, together with weak MnII and MgI lines. The FeII column
density, derived using the curve of growth analysis, is logN_FeII =
15.54^{+0.23}_{-0.13}. This is considerably larger than typical values found in
damped Ly-alpha systems (DLAs) along QSO sight lines, where only 10 out of 87
(~11%) have logN_FeII > 15.2. High FeII column densities are observed in the
z=2.72 Lyman break galaxy cB58 (logN_FeII ~ 15.25) and in gamma-ray burst host
galaxies (logN_FeII ~ 14.8-15.9). Given our measured FeII column density and
assuming a moderate iron dust depletion (delta_Fe ~ 1 dex), we derive an
optical dust extinction A_V ~ 0.6. If the HI column density is log N(HI)<21.7
(as in 98% of DLAs), then the mean metallicity is Z/Z_sun > 0.2. The high
completeness of the GDDS sample implies that these results are typical of
star-forming galaxies in the 1<z<2 redshift range, an epoch which has
heretofore been particularly challenging for observational programs.Comment: ApJ in press, corrected HI column density estimat
An efficient and robust laboratory workflow and tetrapod database for larger scale environmental DNA studies
BACKGROUND: The use of environmental DNA for species detection via metabarcoding is growing rapidly. We present a co-designed lab workflow and bioinformatic pipeline to mitigate the 2 most important risks of environmental DNA use: sample contamination and taxonomic misassignment. These risks arise from the need for polymerase chain reaction (PCR) amplification to detect the trace amounts of DNA combined with the necessity of using short target regions due to DNA degradation. FINDINGS: Our high-throughput workflow minimizes these risks via a 4-step strategy: (i) technical replication with 2 PCR replicates and 2 extraction replicates; (ii) using multi-markers (12S,16S,CytB); (iii) a "twin-tagging," 2-step PCR protocol; and (iv) use of the probabilistic taxonomic assignment method PROTAX, which can account for incomplete reference databases. Because annotation errors in the reference sequences can result in taxonomic misassignment, we supply a protocol for curating sequence datasets. For some taxonomic groups and some markers, curation resulted in >50% of sequences being deleted from public reference databases, owing to (i) limited overlap between our target amplicon and reference sequences, (ii) mislabelling of reference sequences, and (iii) redundancy. Finally, we provide a bioinformatic pipeline to process amplicons and conduct PROTAX assignment and tested it on an invertebrate-derived DNA dataset from 1,532 leeches from Sabah, Malaysia. Twin-tagging allowed us to detect and exclude sequences with non-matching tags. The smallest DNA fragment (16S) amplified most frequently for all samples but was less powerful for discriminating at species rank. Using a stringent and lax acceptance criterion we found 162 (stringent) and 190 (lax) vertebrate detections of 95 (stringent) and 109 (lax) leech samples. CONCLUSIONS: Our metabarcoding workflow should help research groups increase the robustness of their results and therefore facilitate wider use of environmental and invertebrate-derived DNA, which is turning into a valuable source of ecological and conservation information on tetrapods
RXJ0142.0+2131: I. The galaxy content of an X-ray-luminous galaxy cluster at z=0.28
We present a photometric and spectroscopic study of stellar populations in
the X-ray-luminous cluster of galaxies RXJ0142.0+2131 at z=0.280. This paper
analyses the results of high signal-to-noise spectroscopy, as well as g'-, r'-,
and i'-band imaging, using the Gemini Multi-Object Spectrograph on Gemini
North. Of 43 spectroscopic targets, we find 30 cluster members over a range in
color. Central velocity dispersions and absorption-line strengths for lines in
the range 3700A < lambda_rest < 5800A are derived for cluster members, and are
compared with a low-redshift sample of cluster galaxies, and single stellar
population (SSP) models. We use a combination of these indicators to estimate
luminosity-weighted mean ages, metallicities ([M/H]), and alpha-element
abundance ratios ([alpha/Fe]).
RXJ0142.0+2131 is a relatively poor cluster and lacks galaxies with high
central velocity dispersions. Although the red sequence and the Faber-Jackson
relation are consistent with pure passive evolution of the early-type
population with a formation redshift of z_form = 2, the strengths of the 4000A
break and scaling relations between metal line indices and velocity dispersion
reject this model with high significance. By inverting SSP models for the
Hbeta_G, Mgb, and line indices, we calculate that, at a given velocity
dispersion and metallicity, galaxies in RXJ0142.0+2131 have luminosity-weighted
mean ages 0.14 +- 0.07 dex older than the low-redshift sample. We also find
that [alpha/Fe] in stellar populations in RXJ0142.0+2131 is 0.14 +- 0.03
greater than at low redshift. All scaling relations are consistent with these
estimated offsets. (abridged)Comment: AJ, accepted. 31 pages, 13 figures, uses emulateapj.cls.
High-resolution figures available on request from first autho
NGC 3576 and NGC 3603: Two Luminous Southern HII Regions Observed at High Resolution with the Australia Telescope Compact Array
NGC 3576 (G291.28-0.71; l=291.3o, b=-0.7o) and NGC 3603 (G291.58-0.43;
l=291.6o, b=-0.5o) are optically visible, luminous HII regions located at
distances of 3.0 kpc and 6.1 kpc, respectively. We present 3.4 cm Australian
Telescope Compact Array (ATCA) observations of these two sources in the
continuum and the H90a, He90a, C90a and H113b recombination lines with an
angular resolution of 7" and a velocity resolution of 2.6 km/s. All four
recombination lines are detected in the integrated profiles of the two sources.
Broad radio recombination lines are detected in both NGC 3576 (DV_{FWHM}>= 50
km/s) and NGC 3603 (DV_{FWHM}>=70 km/s). In NGC 3576 a prominent N-S velocity
gradient (~30 km/s/pc) is observed, and a clear temperature gradient (6000 K to
8000 K) is found from east to west, consistent with a known IR color gradient
in the source. In NGC 3603, the H90a, He90a and the H113b lines are detected
from 13 individual sources. The Y^+ (He/H) ratios in the two sources range from
0.08+/-0.04 to 0.26+/-0.10. We compare the morphology and kinematics of the
ionized gas at 3.4 cm with the distribution of stars, 10 micron emission and
H_2O, OH, and CH_3OH maser emission. These comparisons suggest that both NGC
3576 and NGC 3603 have undergone sequential star formation.Comment: 24 pages, 12 Postscript figure
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