544 research outputs found
The path toward a cloud-aware mobile network protocol stack
We are currently observing the softwarization of communication networks, where network functions are translated from monolithic pieces of equipment to programs running over a shared pool of computational, storage, and communication resources. While it is clear that almost any softwarization improves flexibility (eg, the ability to instantiate more servers to cope with increasing traffic demand), in this paper, we advocate for a complete redesign of the communications protocol stack, instead of a mere translation of hardware functions into software. We discuss 2 drivers for this cloud-aware redesign: (1) relaxing the tight interactions between functions and (2) supporting a graceful degradation of the service when resources become scarce. The potential benefits of this redesign are illustrated with the numerical evaluation of one use case.This work has been partially performed within the 5G-MoNArch project, part of the Phase II of the 5th Generation Public Private Partnership (5G-PPP) program partially funded by the European Commission within the Horizon 2020 Framework Program. It has also been partly funded by the Madrid Regional Government through the TIGRE5-CM program
(S2013/ICE-2919) and by the SpanishMinistry of Economy, Industry and Competitiveness of through the 5GCity project (TEC2016-76795-C6-3-R)
Theory of quasi-spherical accretion in X-ray pulsars
A theoretical model for quasi-spherical subsonic accretion onto slowly
rotating magnetized neutron stars is constructed. In this model the accreting
matter subsonically settles down onto the rotating magnetosphere forming an
extended quasi-static shell. This shell mediates the angular momentum removal
from the rotating neutron star magnetosphere during spin-down episodes by
large-scale convective motions. The accretion rate through the shell is
determined by the ability of the plasma to enter the magnetosphere. The
settling regime of accretion can be realized for moderate accretion rates g/s. At higher accretion rates a free-fall
gap above the neutron star magnetosphere appears due to rapid Compton cooling,
and accretion becomes highly non-stationary. From observations of the
spin-up/spin-down rates (the angular rotation frequency derivative , and near the torque reversal)
of X-ray pulsars with known orbital periods, it is possible to determine the
main dimensionless parameters of the model, as well as to estimate the magnetic
field of the neutron star. We illustrate the model by determining these
parameters for three wind-fed X-ray pulsars GX 301-2, Vela X-1, and GX 1+4. The
model explains both the spin-up/spin-down of the pulsar frequency on large
time-scales and the irregular short-term frequency fluctuations, which can
correlate or anti-correlate with the X-ray flux fluctuations in different
systems. It is shown that in real pulsars an almost iso-angular-momentum
rotation law with , due to strongly anisotropic radial
turbulent motions sustained by large-scale convection, is preferred.Comment: 48 pages, 4 figures, accepted for publication in MNRA
Problematising the discourses of the dominant: whiteness and reconciliation
This article investigates how underlying forms of power can affect the political actions of those in the dominant group, in this case white Australians. To do this we identify connections between the discourses used by white Australians involved in Reconciliation, the power and privilege of whiteness in Australia, and participantsâ understandings and actions towards Reconciliation. Using Parkerâs (1992) approach to discourse analysis, four discourses were identified from interviews and focus groups with white Australians involved in Reconciliation. These were labelled âindigenous projectâ, âinstitutional changeâ, âchallenging racismâ, and âbringing them togetherâ. We argue that understanding the power relations that underlie the political actions of those in dominant positions is critical to ensuring the goals of anti-racism are achieved. Discourse analysis may allow us to gain a deeper understanding of the power and the potential impacts that may flow from particular positions and how power may be made more visible to the dominant group
Debris Disks: Probing Planet Formation
Debris disks are the dust disks found around ~20% of nearby main sequence
stars in far-IR surveys. They can be considered as descendants of
protoplanetary disks or components of planetary systems, providing valuable
information on circumstellar disk evolution and the outcome of planet
formation. The debris disk population can be explained by the steady
collisional erosion of planetesimal belts; population models constrain where
(10-100au) and in what quantity (>1Mearth) planetesimals (>10km in size)
typically form in protoplanetary disks. Gas is now seen long into the debris
disk phase. Some of this is secondary implying planetesimals have a Solar
System comet-like composition, but some systems may retain primordial gas.
Ongoing planet formation processes are invoked for some debris disks, such as
the continued growth of dwarf planets in an unstirred disk, or the growth of
terrestrial planets through giant impacts. Planets imprint structure on debris
disks in many ways; images of gaps, clumps, warps, eccentricities and other
disk asymmetries, are readily explained by planets at >>5au. Hot dust in the
region planets are commonly found (<5au) is seen for a growing number of stars.
This dust usually originates in an outer belt (e.g., from exocomets), although
an asteroid belt or recent collision is sometimes inferred.Comment: Invited review, accepted for publication in the 'Handbook of
Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018
Evaluation of polygenic risk scores for breast and ovarian cancer risk prediction in BRCA1 and BRCA2 mutation carriers
Background: Genome-wide association studies (GWAS) have identified 94 common single-nucleotide polymorphisms (SNPs) associated with breast cancer (BC) risk and 18 associated with ovarian cancer (OC) risk. Several of these are also associated with risk of BC or OC for women who carry a pathogenic mutation in the high-risk BC and OC genes BRCA1 or BRCA2. The combined effects of these variants on BC or OC risk for BRCA1 and BRCA2 mutation carriers have not yet been assessed while their clinical management could benefit from improved personalized risk estimates.
Methods: We constructed polygenic risk scores (PRS) using BC and OC susceptibility SNPs identified through population-based GWAS: for BC (overall, estrogen receptor [ER]-positive, and ER-negative) and for OC. Using data from 15 252 female BRCA1 and 8211 BRCA2 carriers, the association of each PRS with BC or OC risk was evaluated using a weighted cohort approach, with time to diagnosis as the outcome and estimation of the hazard ratios (HRs) per standard deviation increase in the PRS.
Results: The PRS for ER-negative BC displayed the strongest association with BC risk in BRCA1 carriers (HR = 1.27, 95% confidence interval [CI] = 1.23 to 1.31, P = 8.2 x 10(53)). In BRCA2 carriers, the strongest association with BC risk was seen for the overall BC PRS (HR = 1.22, 95% CI = 1.17 to 1.28, P = 7.2 x 10(-20)). The OC PRS was strongly associated with OC risk for both BRCA1 and BRCA2 carriers. These translate to differences in absolute risks (more than 10% in each case) between the top and bottom deciles of the PRS distribution; for example, the OC risk was 6% by age 80 years for BRCA2 carriers at the 10th percentile of the OC PRS compared with 19% risk for those at the 90th percentile of PRS.
Conclusions: BC and OC PRS are predictive of cancer risk in BRCA1 and BRCA2 carriers. Incorporation of the PRS into risk prediction models has promise to better inform decisions on cancer risk management
Accreting Millisecond X-Ray Pulsars
Accreting Millisecond X-Ray Pulsars (AMXPs) are astrophysical laboratories
without parallel in the study of extreme physics. In this chapter we review the
past fifteen years of discoveries in the field. We summarize the observations
of the fifteen known AMXPs, with a particular emphasis on the multi-wavelength
observations that have been carried out since the discovery of the first AMXP
in 1998. We review accretion torque theory, the pulse formation process, and
how AMXP observations have changed our view on the interaction of plasma and
magnetic fields in strong gravity. We also explain how the AMXPs have deepened
our understanding of the thermonuclear burst process, in particular the
phenomenon of burst oscillations. We conclude with a discussion of the open
problems that remain to be addressed in the future.Comment: Review to appear in "Timing neutron stars: pulsations, oscillations
and explosions", T. Belloni, M. Mendez, C.M. Zhang Eds., ASSL, Springer;
[revision with literature updated, several typos removed, 1 new AMXP added
BRCA2 polymorphic stop codon K3326X and the risk of breast, prostate, and ovarian cancers
Background: The K3326X variant in BRCA2 (BRCA2*c.9976A>T; p.Lys3326*; rs11571833) has been found to be associated with small increased risks of breast cancer. However, it is not clear to what extent linkage disequilibrium with fully pathogenic mutations might account for this association. There is scant information about the effect of K3326X in other hormone-related cancers.
Methods: Using weighted logistic regression, we analyzed data from the large iCOGS study including 76 637 cancer case patients and 83 796 control patients to estimate odds ratios (ORw) and 95% confidence intervals (CIs) for K3326X variant carriers in relation to breast, ovarian, and prostate cancer risks, with weights defined as probability of not having a pathogenic BRCA2 variant. Using Cox proportional hazards modeling, we also examined the associations of K3326X with breast and ovarian cancer risks among 7183 BRCA1 variant carriers. All statistical tests were two-sided.
Results: The K3326X variant was associated with breast (ORw = 1.28, 95% CI = 1.17 to 1.40, P = 5.9x10- 6) and invasive ovarian cancer (ORw = 1.26, 95% CI = 1.10 to 1.43, P = 3.8x10-3). These associations were stronger for serous ovarian cancer and for estrogen receptorânegative breast cancer (ORw = 1.46, 95% CI = 1.2 to 1.70, P = 3.4x10-5 and ORw = 1.50, 95% CI = 1.28 to 1.76, P = 4.1x10-5, respectively). For BRCA1 mutation carriers, there was a statistically significant inverse association of the K3326X variant with risk of ovarian cancer (HR = 0.43, 95% CI = 0.22 to 0.84, P = .013) but no association with breast cancer. No association with prostate cancer was observed.
Conclusions: Our study provides evidence that the K3326X variant is associated with risk of developing breast and ovarian cancers independent of other pathogenic variants in BRCA2. Further studies are needed to determine the biological mechanism of action responsible for these associations
Properties of discrete X-ray sources in the starburst spiral galaxy M83
We have identified 127 discrete sources in a Chandra observation of M83, with
a detection limit of ~ 3 x 10^{36} erg/s in the 0.3-8.0 keV band. We discuss
the individual properties of about 20 bright sources with L_x >~ 10^{38} erg/s,
and the statistical properties of the whole sample. About 1/3 of the bright
sources show X-ray spectra with a bb component at kT <~ 1 keV, plus a p-law
component with Gamma ~ 2.5, typical of X-ray binaries (XRBs) in a soft state;
another third have p-law spectra with Gamma ~ 1.5, consistent with XRBs in a
hard state. Two bright sources show emission lines on a hard p-law continuum,
and are probably XRBs surrounded by a photo-ionized nebula or stellar wind.
Among the other bright sources, we also identified two SNR candidates, with
optically-thin thermal plasma spectra at kT ~ 0.5 keV. The two brightest
supersoft sources have T_bb ~ 70 eV and L_x ~ 10^{38} erg/s. Two candidate
X-ray pulsars are detected with periods ~ 200 s. Another source corresponds to
the core of a background FRII radio galaxy. The discrete sources can be divided
into three groups, based on their spatial, color and luminosity distributions.
The first group comprises supersoft sources with no detected emission above 1
keV. The second group consists of soft sources with little or no detected
emission above 2 keV. They are strongly correlated with H-alpha emission in the
spiral arms and starburst nucleus, tracing a young population. Their relative
abundance depends on the current level of star-formation. Most of them are
likely to be SNRs. The sources in the third group are mostly XRBs (in a soft or
hard state), reaching higher X-ray luminosities than sources in the other two
groups. Being a mixture of old low-mass and young high-mass systems, the whole
group appears to be of intermediate age when correlated with H-alpha.Comment: 25 pages, A&A, in press (submitted december 2002, accepted july 2003
Corporate cash holdings: causes and consequences
The considerable growth in corporate cash holdings around the world has prompted scholarly interest. Consequently, there is now a large academic literature examining cash holdings and their impact on corporate outcomes and firm values. This article reviews and synthesizes the literature to offer insight into two primary motives to hold cash: precautionary and agency. We first present a stylized model that explores the trade-off in holding cash between these two motives and then examine empirical studies to determine how existing theories are supported by evidence using data from a variety of countries. In addition, we examine the effectiveness of a variety of corporate governance devices in curtailing cash holdings and also the extent to which these devices offer investors' confidence that cash will not be wasted. Finally, we discuss methodological and measurement issues associated with empirical cash holdings studies
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