3,411 research outputs found
Node-Centric Detection of Overlapping Communities in Social Networks
We present NECTAR, a community detection algorithm that generalizes Louvain
method's local search heuristic for overlapping community structures. NECTAR
chooses dynamically which objective function to optimize based on the network
on which it is invoked. Our experimental evaluation on both synthetic benchmark
graphs and real-world networks, based on ground-truth communities, shows that
NECTAR provides excellent results as compared with state of the art community
detection algorithms
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
Shared resource control between human and computer
The advantages of an AI system of actively monitoring human control of a shared resource (such as a telerobotic manipulator) are presented. A system is described in which a simple AI planning program gains efficiency by monitoring human actions and recognizing when the actions cause a change in the system's assumed state of the world. This enables the planner to recognize when an interaction occurs between human actions and system goals, and allows maintenance of an up-to-date knowledge of the state of the world and thus informs the operator when human action would undo a goal achieved by the system, when an action would render a system goal unachievable, and efficiently replans the establishment of goals after human intervention
Directional Sensitivity of Echolocation System in Bats Producing Frequency-Modulated Signals
1. Radiation patterns of the 55, 75 and 95 kHz components in frequency-modulated sounds emitted by the grey bat (Myotis grisescens) were studied. FM sounds similar to species-specific orientation sounds were elicited by electrical stimuli applied to the midbrain while the head of the animal was immobilized by a nail cemented to its skull. The main beam was emitted 5-10° downward from the eye-nostril line. The radiation angle at one half of maximum amplitude was 38° lateral, 18° up and 50° down at 55 kHz, 34° lateral, 8° up and 32° down at 75 kHz, and 30° lateral, 5° up and 25° down at 95 kHz. At 95 kHz, two prominent side lobes were present.
2. The directional sensitivity of the auditory system (DSA) measured in terms of the potential evoked in the lateral lemniscus was studied with the grey bat (M. grisescens) and the little brown bat (M. lucifugus). The maximally sensitive direction moved toward the median plane with the increase in frequency from 35-95 kHz. The slope of the DSA curve increased from 0.3-0.6 dB/degree with frequency.
3. The directional sensitivity of the echolocation system (DSE) was calculated using both the DSA curve and the radiation pattern of the emitted sound. The maximally sensitive direction of the echolocation system was 15° lateral to the median plane at 55kHz and 2.5° lateral at 95 kHz. The slope of the DSE curve increased from o.6 to 1.0 dB/degree with frequency. Thus, the higher the frequency of sound, the sharper was the directional sensitivity of the echolocation system.
4. The interaural pressure difference (IPD), which appeared to be the essential cue for echolocation in Myotis, changed linearly with the azimuth angle from 0-30° lateral regardless of the frequency of sound, at respective rates of 0.4, 0.7, 0.3 and 0.4 dB/degree for 35, 55, 75 and 95 kHz sounds. Beyond 30°, the change in IPD was quite different depending on frequency. For 75 and 95 kHz sounds, the IPD stayed nearly the same between 30° and 90°. Thus, the 75-95 kHz components in FM orientation sounds were not superior to the 35 and 55 kHz components in terms of the IPD cue for echolocation.
5. Assuming the just-detectable IPD and ITD to be 0.5 dB and 5”sec respectively, as in man, the just-detectable azimuth difference of Myotis around the median plane would be 0.7-1.7° with the IPD cue and 11° with the ITD cue
Long-Lived Counters with Polylogarithmic Amortized Step Complexity
A shared-memory counter is a well-studied and widely-used concurrent object. It supports two operations: An Inc operation that increases its value by 1 and a Read operation that returns its current value. Jayanti, Tan and Toueg [Jayanti et al., 2000] proved a linear lower bound on the worst-case step complexity of obstruction-free implementations, from read and write operations, of a large class of shared objects that includes counters. The lower bound leaves open the question of finding counter implementations with sub-linear amortized step complexity.
In this paper, we address this gap. We present the first wait-free n-process counter, implemented using only read and write operations, whose amortized operation step complexity is O(log^2 n) in all executions. This is the first non-blocking read/write counter algorithm that provides sub-linear amortized step complexity in executions of arbitrary length. Since a logarithmic lower bound on the amortized step complexity of obstruction-free counter implementations exists, our upper bound is optimal up to a logarithmic factor
Digging Deeper: Art Museums in Las Vegas?
[Excerpt] Las Vegas has been called the âcity of reinventionâ (Douglass and Raento 2003). Part of its more recent reinvention efforts has included the opening of five fine-art venues. However, one of the art museumsââthe Las Vegas Guggenheimââwas shut down in its first year due to low attendance; another, the Bellagio Fine Art Gallery, has seen attendance dwindle (Schemeligian 2004). The question addressed here is whether the museums are bringing the intended intangible benefits to the host resort, or whether the sales and attendance figures represent overall disinterest. More broadly one considers the potential âfitâ between sin-city and the high-art cultural world.
The difficulty in addressing these issues is that tourists might not consciously recognize the value they feel about having a worldclass art museum onsite. Within nonprofit research there has been a call for ââdeeper understandingââ of tourists (Thyne 2001) as reflected within the greater interest in new qualitative methodologies (Riley and Love 2000). The Zaltman metaphor elicitation technique, a patented research method, was chosen to investigate this research issue. Many of the worldâs largest companies (such as Procter & Gamble) have utilized this method for insight on brand meaning and competitive positioning
Capital accumulation and the allocation of residential buildings in African townships on the Witwatersrand, 1980-1985
African Studies Seminar series. Paper presented 30 September, 1985A seemingly interminable shortage of "adequate" shelter haunts the lives of a substantial number of residents of African townshipsâŠ. This paper investigates the activities involved in the accumulation of capital through construction of dwellings in Witwatersrand African townships. It attempts to explain the manner in which building construction, development and financial firms conduct their business, and to crystallise the effects of these business activities on the delivery of residential buildings in the townships. The Witwatersrand was chosen as the area of study because a relatively large amount of building activity occurs there
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