29 research outputs found
Hyperprofile-based Computation Offloading for Mobile Edge Networks
In recent studies, researchers have developed various computation offloading
frameworks for bringing cloud services closer to the user via edge networks.
Specifically, an edge device needs to offload computationally intensive tasks
because of energy and processing constraints. These constraints present the
challenge of identifying which edge nodes should receive tasks to reduce
overall resource consumption. We propose a unique solution to this problem
which incorporates elements from Knowledge-Defined Networking (KDN) to make
intelligent predictions about offloading costs based on historical data. Each
server instance can be represented in a multidimensional feature space where
each dimension corresponds to a predicted metric. We compute features for a
"hyperprofile" and position nodes based on the predicted costs of offloading a
particular task. We then perform a k-Nearest Neighbor (kNN) query within the
hyperprofile to select nodes for offloading computation. This paper formalizes
our hyperprofile-based solution and explores the viability of using machine
learning (ML) techniques to predict metrics useful for computation offloading.
We also investigate the effects of using different distance metrics for the
queries. Our results show various network metrics can be modeled accurately
with regression, and there are circumstances where kNN queries using Euclidean
distance as opposed to rectilinear distance is more favorable.Comment: 5 pages, NSF REU Site publicatio
Potential Hazard to Human Health from Exposure to Fragments of Lead Bullets and Shot in the Tissues of Game Animals
Peer reviewedPublisher PD
Discovery of Large-Scale Gravitational Infall in a Massive Protostellar Cluster
We report Mopra (ATNF), Anglo-Australian Telescope, and Atacama Submillimeter
Telescope Experiment observations of a molecular clump in Carina, BYF73 =
G286.21+0.17, which give evidence of large-scale gravitational infall in the
dense gas. From the millimetre and far-infrared data, the clump has mass ~ 2 x
10^4 Msun, luminosity ~ 2-3 x 10^4 Lsun, and diameter ~ 0.9 pc. From radiative
transfer modelling, we derive a mass infall rate ~ 3.4 x 10^-2 Msun yr-1. If
confirmed, this rate for gravitational infall in a molecular core or clump may
be the highest yet seen. The near-infrared K-band imaging shows an adjacent
compact HII region and IR cluster surrounded by a shell-like photodissociation
region showing H2 emission. At the molecular infall peak, the K imaging also
reveals a deeply embedded group of stars with associated H2 emission. The
combination of these features is very unusual and we suggest they indicate the
ongoing formation of a massive star cluster. We discuss the implications of
these data for competing theories of massive star formation.Comment: v1: 23 pages single-column, 6 figures (some multipart) at end v2: 14
pages 2-column, 6 figures interspersed v3: edited to referee's comments with
new sections and new figures; accepted to MNRAS, 20 pages 2-column, 8 figures
(some multipart) intersperse
Radiatively Efficient Magnetized Bondi Accretion
We have carried out a numerical study of the effect of large scale magnetic
fields on the rate of accretion from a uniform, isothermal gas onto a
resistive, stationary point mass. Only mass, not magnetic flux, accretes onto
the point mass. The simulations for this study avoid complications arising from
boundary conditions by keeping the boundaries far from the accreting object.
Our simulations leverage adaptive refinement methodology to attain high spatial
fidelity close to the accreting object. Our results are particularly relevant
to the problem of star formation from a magnetized molecular cloud in which
thermal energy is radiated away on time scales much shorter than the dynamical
time scale. Contrary to the adiabatic case, our simulations show convergence
toward a finite accretion rate in the limit in which the radius of the
accreting object vanishes, regardless of magnetic field strength. For very weak
magnetic fields, the accretion rate first approaches the Bondi value and then
drops by a factor ~ 2 as magnetic flux builds up near the point mass. For
strong magnetic fields, the steady-state accretion rate is reduced by a factor
~ 0.2 \beta^{1/2} compared to the Bondi value, where \beta is the ratio of the
gas pressure to the magnetic pressure. We give a simple expression for the
accretion rate as a function of the magnetic field strength. Approximate
analytic results are given in the Appendixes for both time-dependent accretion
in the limit of weak magnetic fields and steady-state accretion for the case of
strong magnetic fields.Comment: Accepted to Ap
3 to 12 millimetre studies of dense gas towards the western rim of supernova remnant RX J1713.7-3946
The young X-ray and gamma-ray-bright supernova remnant RXJ1713.7-3946 (SNR
G347.3-0.5) is believed to be associated with molecular cores that lie within
regions of the most intense TeV emission. Using the Mopra telescope, four of
the densest cores were observed using high-critical density tracers such as
CS(J=1-0,J=2-1) and its isotopologue counterparts, NH3(1,1) and (2,2) inversion
transitions and N2H+(J=1-0) emission, confirming the presence of dense gas
>10^4cm^-3 in the region. The mass estimates for Core C range from 40M_{\odot}
(from CS(J=1-0)) to 80M_{\odot} (from NH3 and N2H+), an order of magnitude
smaller than published mass estimates from CO(J=1-0) observations. We also
modelled the energy-dependent diffusion of cosmic-ray protons accelerated by
RXJ1713.7-3946 into Core C, approximating the core with average density and
magnetic field values. We find that for considerably suppressed diffusion
coefficients (factors \chi=10^{-3} down to 10^{-5} the galactic average), low
energy cosmic-rays can be prevented from entering the inner core region. Such
an effect could lead to characteristic spectral behaviour in the GeV to TeV
gamma-ray and multi-keV X-ray fluxes across the core. These features may be
measurable with future gamma-ray and multi-keV telescopes offering arcminute or
better angular resolution, and can be a novel way to understand the level of
cosmic-ray acceleration in RXJ1713.7-3946 and the transport properties of
cosmic-rays in the dense molecular cores.Comment: 17 pages, 13 figures and 5 tables. Accepted for publication in MNRAS
2012 February 1
Semantic content outweighs low-level saliency in determining children's and adults' fixation of movies
To make sense of the visual world, we need to move our eyes to focus regions of interest on the high-resolution fovea. Eye movements, therefore, give us a way to infer mechanisms of visual processing and attention allocation. Here, we examined age-related differences in visual processing by recording eye movements from 37 children (aged 6–14 years) and 10 adults while viewing three 5-min dynamic video clips taken from child-friendly movies. The data were analyzed in two complementary ways: (a) gaze based and (b) content based. First, similarity of scanpaths within and across age groups was examined using three different measures of variance (dispersion, clusters, and distance from center). Second, content-based models of fixation were compared to determine which of these provided the best account of our dynamic data. We found that the variance in eye movements decreased as a function of age, suggesting common attentional orienting. Comparison of the different models revealed that a model that relies on faces generally performed better than the other models tested, even for the youngest age group (<10 years). However, the best predictor of a given participant’s eye movements was the average of all other participants’ eye movements both within the same age group and in different age groups. These findings have implications for understanding how children attend to visual information and highlight similarities in viewing strategies across development
Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study
Background Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide.Methods A multimethods analysis was performed as part of the GlobalSurg 3 study-a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital.Findings Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3.85 [95% CI 2.58-5.75]; p<0.0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63.0% vs 82.7%; OR 0.35 [0.23-0.53]; p<0.0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer.Interpretation Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised