763 research outputs found
The Adaptive Priority Queue with Elimination and Combining
Priority queues are fundamental abstract data structures, often used to
manage limited resources in parallel programming. Several proposed parallel
priority queue implementations are based on skiplists, harnessing the potential
for parallelism of the add() operations. In addition, methods such as Flat
Combining have been proposed to reduce contention by batching together multiple
operations to be executed by a single thread. While this technique can decrease
lock-switching overhead and the number of pointer changes required by the
removeMin() operations in the priority queue, it can also create a sequential
bottleneck and limit parallelism, especially for non-conflicting add()
operations.
In this paper, we describe a novel priority queue design, harnessing the
scalability of parallel insertions in conjunction with the efficiency of
batched removals. Moreover, we present a new elimination algorithm suitable for
a priority queue, which further increases concurrency on balanced workloads
with similar numbers of add() and removeMin() operations. We implement and
evaluate our design using a variety of techniques including locking, atomic
operations, hardware transactional memory, as well as employing adaptive
heuristics given the workload.Comment: Accepted at DISC'14 - this is the full version with appendices,
including more algorithm
Low EUV Luminosities Impinging on Protoplanetary Disks
The amount of high-energy stellar radiation reaching the surface of
protoplanetary disks is essential to determine their chemistry and physical
evolution. Here, we use millimetric and centimetric radio data to constrain the
EUV luminosity impinging on 14 disks around young (~2-10Myr) sun-like stars.
For each object we identify the long-wavelength emission in excess to the dust
thermal emission, attribute that to free-free disk emission, and thereby
compute an upper limit to the EUV reaching the disk. We find upper limits lower
than 10 photons/s for all sources without jets and lower than photons/s for the three older sources in our sample. These latter
values are low for EUV-driven photoevaporation alone to clear out
protoplanetary material in the timescale inferred by observations. In addition,
our EUV upper limits are too low to reproduce the [NeII] 12.81 micron
luminosities from three disks with slow [NeII]-detected winds. This indicates
that the [NeII] line in these sources primarily traces a mostly neutral wind
where Ne is ionized by 1 keV X-ray photons, implying higher photoevaporative
mass loss rates than those predicted by EUV-driven models alone. In summary,
our results suggest that high-energy stellar photons other than EUV may
dominate the dispersal of protoplanetary disks around sun-like stars.Comment: Accepted for publication to The Astrophysical Journa
Presenting in Virtual Worlds: An Architecture for a 3D Anthropomorphic Presenter
Multiparty-interaction technology is changing entertainment, education, and training. Deployed examples of such technology include embodied agents and robots that act as a museum guide, a news presenter, a teacher, a receptionist, or someone trying to sell you insurance, homes, or tickets. In all these cases, the embodied agent needs to explain and describe. This article describes the design of a 3D virtual presenter that uses different output channels (including speech and animation of posture, pointing, and involuntary movements) to present and explain. The behavior is scripted and synchronized with a 2D display containing associated text and regions (slides, drawings, and paintings) at which the presenter can point. This article is part of a special issue on interactive entertainment
Design Index for Deep Neural Networks
AbstractIn this paper, we propose a Deep Neural Networks (DNN) Design Index which would aid a DNN designer during the designing phase of DNNs. We study the designing aspect of DNNs from model-specific and data-specific perspectives with focus on three performance metrics: training time, training error and, validation error. We use a simple example to illustrate the significance of the DNN design index. To validate it, we calculate the design indices for four benchmark problems. This is an elementary work aimed at setting a direction for creating design indices pertaining to deep learning
Semantic Transformation of Web Services
Web services have become the predominant paradigm for the development of distributed software systems. Web services provide the means to modularize software in a way that functionality can be described, discovered and deployed in a platform independent manner over a network (e.g., intranets, extranets and the Internet). The representation of web services by current industrial practice is predominantly syntactic in nature lacking the fundamental semantic underpinnings required to fulfill the goals of the emerging Semantic Web. This paper proposes a framework aimed at (1) modeling the semantics of syntactically defined web services through a process of interpretation, (2) scop-ing the derived concepts within domain ontologies, and (3) harmonizing the semantic web services with the domain ontologies. The framework was vali-dated through its application to web services developed for a large financial system. The worked example presented in this paper is extracted from the se-mantic modeling of these financial web services
Lace: non-blocking split deque for work-stealing
Work-stealing is an efficient method to implement load balancing in fine-grained task parallelism. Typically, concurrent deques are used for this purpose. A disadvantage of many concurrent deques is that they require expensive memory fences for local deque operations.\ud
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In this paper, we propose a new non-blocking work-stealing deque based on the split task queue. Our design uses a dynamic split point between the shared and the private portions of the deque, and only requires memory fences when shrinking the shared portion.\ud
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We present Lace, an implementation of work-stealing based on this deque, with an interface similar to the work-stealing library Wool, and an evaluation of Lace based on several common benchmarks. We also implement a recent approach using private deques in Lace. We show that the split deque and the private deque in Lace have similar low overhead and high scalability as Wool
An ALMA Survey of faint disks in the Chamaeleon I star-forming region: Why are some Class II disks so faint?
ALMA surveys of nearby star-forming regions have shown that the dust mass in
the disk is correlated with the stellar mass, but with a large scatter. This
scatter could indicate either different evolutionary paths of disks or
different initial conditions within a single cluster. We present ALMA Cycle 3
follow-up observations for 14 Class II disks that were low S/N detections or
non-detections in our Cycle 2 survey of the Myr-old Chamaeleon I
star-forming region. With 5 times better sensitivity, we detect millimeter dust
continuum emission from six more sources and increase the detection rate to
94\% (51/54) for Chamaeleon I disks around stars earlier than M3. The
stellar-disk mass scaling relation reported in \citet{pascucci2016} is
confirmed with these updated measurements. Faint outliers in the
-- plane include three non-detections (CHXR71, CHXR30A, and T54)
with dust mass upper limits of 0.2 M and three very faint disks
(CHXR20, ISO91, and T51) with dust masses M. By
investigating the SED morphology, accretion property and stellar multiplicity,
we suggest for the three millimeter non-detections that tidal interaction by a
close companion (100 AU) and internal photoevaporation may play a role in
hastening the overall disk evolution. The presence of a disk around only the
secondary star in a binary system may explain the observed stellar SEDs and low
disk masses for some systems.Comment: ApJ accepte
An ALMA Survey of CO isotopologue emission from Protoplanetary Disks in Chamaeleon I
The mass of a protoplanetary disk limits the formation and future growth of
any planet. Masses of protoplanetary disks are usually calculated from
measurements of the dust continuum emission by assuming an interstellar
gas-to-dust ratio. To investigate the utility of CO as an alternate probe of
disk mass, we use ALMA to survey CO and CO J = line
emission from a sample of 93 protoplanetary disks around stars and brown dwarfs
with masses from 0.03 -- 2 M in the nearby Chamaeleon I star-forming
region. We detect CO emission from 17 sources and CO from only
one source. Gas masses for disks are then estimated by comparing the CO line
luminosities to results from published disk models that include CO freeze-out
and isotope-selective photodissociation. Under the assumption of a typical ISM
CO-to-H ratios of , the resulting gas masses are implausibly low,
with an average gas mass of 0.05 M as inferred from the average
flux of stacked CO lines. The low gas masses and gas-to-dust ratios for
Cha I disks are both consistent with similar results from disks in the Lupus
star-forming region. The faint CO line emission may instead be explained if
disks have much higher gas masses, but freeze-out of CO or complex C-bearing
molecules is underestimated in disk models. The conversion of CO flux to CO gas
mass also suffers from uncertainties in disk structures, which could affect gas
temperatures. CO emission lines will only be a good tracer of the disk mass
when models for C and CO depletion are confirmed to be accurate.Comment: accepted for publication in Ap
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