Dynamic Snapshot Research Articles

Snapshot Centrality Indices in Dynamic FIFO Networks

The article introduces the concept of snapshot dynamic indices as centrality measures to analyse how the importance of nodes changes over time in dynamic networks. In particular, the dynamic stress-snapshot and dynamic betweenness snapshot are investigated. We present theoretical results on dynamic shortest paths in first-in first-out dynamic networks, and then introduce some algorithms for computing these indices in the discrete-time case. Finally, we present some experimental results exploring the algorithms' efficiency and illustrating the variation of the dynamic betweenness snapshot index for some sample dynamic networks.

Time-Based Software Transactional Memory

Software transactional memory (STM) is a concurrency control mechanism that is widely considered to be easier to use by programmers than other mechanisms such as locking. The first generations of STMs have either relied on visible read designs, which simplify conflict detection while pessimistically ensuring a consistent view of shared data to the application, or optimistic invisible read designs that are significantly more efficient but require incremental validation to preserve consistency, at a cost that increases quadratically with the number of objects read in a transaction. Most of the recent designs now use a “time-based” (or “time stamp-based”) approach to still benefit from the performance advantage of invisible reads without incurring the quadratic overhead of incremental validation. In this paper, we give an overview of the time-based STM approach and discuss its benefits and limitations. We formally introduce the first time-based STM algorithm, the Lazy Snapshot Algorithm (LSA). We study its semantics and the impact of its design parameters, notably multiversioning and dynamic snapshot extension. We compare it against other classical designs and we demonstrate that its performance is highly competitive, both for obstruction-free and lock-based STM designs.

Combining visibilities from the giant meterwave radio telescope and the Nancay radio heliograph

We report first results from an ongoing program of combining visibilities from the Giant Meterwave Radio Telescope () and the Nancay Radio Heliograph () to produce composite snapshot images of the sun at meter wavelengths. We describe the data processing, including a specific multi-scale algorithm. We present results of a) simulations for two models of the sun at 327 MHz, with differing complexity b) observations of a complex noise storm on the sun at 327 MHz on Aug. 27, 2002. Our results illustrate the capacity of this method to produce high dynamic range snapshot images when the solar corona has structures with scales ranging from the image resolution of 49'' to the size of the whole sun. We emphasize that snapshot images of a complex object such as the sun, obtained by combining data from both instruments, are far better than images from either instrument alone, because their uv-coverages are very complementary.

Wide dynamic range snapshot APS for ultra low-power applications

A novel wide dynamic range (WDR) snapshot active pixel sensor for ultra-low power applications is presented. The proposed imager allows capturing of fast moving objects in the field of view and provides WDR by applying adaptive exposure time to each pixel, according to the local illumination intensity level. Driven by low-power dissipation requirements, the proposed pixel is operated by dual low voltage supplies (1.2 and 1.8 V) and utilizes an advanced low-power sensor design methodology. A test chip of a 32*32 array has been implemented in a standard 0.35-/spl mu/m CMOS technology. A single pixel occupies 18*32 /spl mu/m area and is expected to dissipate 18.5 nW at video rate. System architecture and operation are discussed and simulation results are presented.

Dynamic snapshot algorithm and partial rollback algorithm for internet agents

AbstractThis paper considers an Internet agent system in which a tremendous number of agents operate, frequently appearing and disappearing, and discusses the fault‐tolerant algorithm. Application of the snapshot algorithm to the agent system is considered. The snapshot algorithm is used to view the whole situation (snapshot) of the distributed system. The snapshot algorithm of Chandy and Lamport [2] is considered as a representative snapshot algorithm, in terms of the high efficiency and the simplicity of the procedure. It is not practical, however, to apply their snapshot algorithm to the distributed agent system in which a tremendous number of agents operate. From such a viewpoint, this paper extends the idea of Chandy and Lamport's algorithm and proposes a subsnapshot algorithm, in which the snapshot is taken among the agents who are in the causal relation, through message exchange and agent creation. Then, an efficient rollback algorithm is proposed, which is based on the snapshots taken by the subsnapshot algorithm. In the general rollback algorithm utilizing the snapshot, all agents must roll back. In contrast, in the rollback algorithm proposed in this paper, it suffices that only some agents should roll back. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 88(12): 43–57, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20208

SPATIALLY LIMITED POLLEN EXCHANGE AND A LONG-RANGE SYNCHRONIZATION OF TREES

Many trees in mature forests show intermittent reproduction. Intensive flowering and seed production occur only once in several years, often synchronized over a long distance. In a previous paper, we showed that the limitation of fruit production by the outcross pollen availability can bring about synchronized reproduction of trees in a constant environment, assuming that pollen availability depends on the mean flowering intensity of the trees. However, pollen exchange normally occurs within a distance much shorter than the extent of the whole forest. We studied a coupled map lattice, in which each tree engages in the chaotic dynamics of energy reserve level, but different trees are coupled by pollen exchange with neighbors. We first derived a relation between two statistics of spatial covariance (dynamic spatial covariance and snapshot spatial covariance). A strong synchronization of tree reproduction can develop over the whole forest that may be orders of magnitude larger than the distance of direct pollen exchange between trees. The fluctuation is close to a cycle with a period of two years. The model of local coupling always generates non-uniform spatial patterns, but the enhanced spatial covariance caused by the spatial heterogeneity is restricted to a short range, only a few times larger than the spatial range of direct interaction. When pollen exchange occurs beyond the nearest neighbors, the local spatial pattern becomes proportionally larger, but the condition for synchronization of the whole forest and its magnitude are the same as for the case with the nearest neighbor pollen exchange. When a fraction of the seeds are sired by globally dispersed pollen and the rest are sired by local pollen, long-range synchronization can occur for a wide-parameter region, and trees may engage in a fluctuation with a masting interval longer than two years. We discuss alternative explanations for the long-range synchronization of beech forests.

Robust velocity computation from a biologically motivated model of motion perception

Current computational models of motion processing in the primate motion pathway do not cope well with image sequences in which a moving pattern is superimposed upon a static texture. The use of non–linear operations and the need for contrast normalization in motion models mean that the separation of the influences of moving and static patterns on the motion computation is not trivial. Therefore, the response to the superposition of static and moving patterns provides an important means of testing various computational strategies. Here we describe a computational model of motion processing in the visual cortex, one of the advantages of which is that it is highly resistant to interference from static patterns.

Differentiation between hepatoma and hemangioma with inversion-recovery snapshot FLASH MRI and Gd-DTPA.

Thirty-eight patients with focal liver tumors (20 hepatomas, 18 hemangiomas) were studied by dynamic sequential inversion recovery (IR) snapshot fast low angle shot (FLASH) MR imaging with Gd-DTPA. Immediately after 0.05 mmol/kg Gd-DTPA was administered intravenously for 2-3 s followed by flushing with normal saline for 4-5 s, 10 images were obtained in the first 20 s (time zero is the end of flush, early phase). Then, one image every 30 s from 1 to 3 min (late phase) and images at 5 min and 7 min (delayed phase) were obtained serially. Hepatomas showed total enhancement in 18 of 20 patients in the early phase, and isointense or low intensity enhancement with respect to the surrounding liver parenchyma in 18 patients in the late to delayed phases. Hemangiomas showed peripheral enhancement in 14 patients in the early phase, but did not show total enhancement (except for two hemangiomas less than 3 cm in size) in the early phase, and showed high intensity enhancement in 15 patients in the late phase. Ninety percent of hepatomas and 82% of hemangiomas showed their characteristic enhancement patterns in the early to delayed phases. We conclude that dynamic sequential IR snapshot FLASH MR images enhanced with Gd-DTPA can facilitate differentiation between hepatomas and hemangiomas.