A Load Balancing Tool for Distributed Parallel Loops

Large scale applications typically contain parallel loops with many iterates. The iterates of a parallel loop may have variable execution times which translate into performance degradation of an application due to load imbalance. This paper describes a tool for load balancing parallel loops on distributed-memory systems. The tool assumes that the data for a parallel loop to be executed is already partitioned among the participating processors. The tool utilizes the MPI library for interprocessor coordination, and determines processor workloads by loop scheduling techniques. The tool was designed independent of any application; hence, it must be supplied with a routine that encapsulates the computations for a chunk of loop iterates, as well as the routines to transfer data and results between processors. Performance evaluation on a Linux cluster indicates that the tool reduces the cost of executing a simulated irregular loop without load balancing by up to 81%. The tool is useful for parallelizing sequential applications with parallel loops, or as an alternate load balancing routine for existing parallel applications.     

Performance Evaluation of the Deadline Credit Scheduling Algorithm for Soft-Real-Time Applications in Distributed Video-on-Demand Systems

Video-on-Demand (VoD) systems are expected to support a variety of multimedia services to the users, such as tele-education, teleconference, remote working, videotelephony, high-definition TV, etc. These applications necessitate abundant bandwidth and buffer space as well as appropriate software and hardware for the efficient manipulation of the networks resources. In this work we investigate a promising scheduling algorithm referred to as the Deadline Credit (DC) algorithm, which exploits the available bandwidth and buffer space to serve a diverse class of prerecorded video applications. We provide simulation results when the DC algorithm is applied to a hierarchical architecture distributed VoD network, which fits the existing tree topology used in todays cable TV systems. The issues investigated via the simulations are: the system utilization, the influence of the buffer space on the delivered Quality of Service, and the fairness of the scheduling mechanism. We examine cases with homogenous as well as diverse video streams, and extend our system to support interactive VCR-like functions. We also contribute a modification to the DC algorithm so that in cases when the video applications have different displaying periods, the video streams obtain a fair share of the networks resources. Finally, we validate our results by simulating actual videos encoded in MPEG-4 and H.263 formats.     

A Dynamic Workflow Approach for the Integration of Bioinformatics Services

Modern biological and chemical studies rely on life science databases as well as sophisticated software tools (e.g., homology search tools, modeling and visualization tools). These tools often have to be combined and integrated in order to support a given study. SIBIOS (System for the Integration of Bioinformatics Services) serves this purpose. The services are both life science database search services and software tools. The task engine is the core component of SIBIOS. It supports the execution of dynamic workflows that incorporate multiple bioinformatics services. The architecture of SIBIOS, the approaches to addressing the heterogeneity as well as interoperability of bioinformatics services, including data integration are presented in this paper.     

On the use of cellular telephony for audio interaction with animals

Playback is an important method of surveying animals, assessing habitats and studying animal communication. However, conventional playback methods require on-site observers and therefore become labour-intensive when covering large areas. Such limitations could be circumvented by the use of cellular telephony, a ubiquitous technology with increasing biological applications. In addressing concerns about the low audio quality of cellular telephones, this paper presents experimental data to show that owls of two species (Strix varia and Megascops asio) respond similarly to calls played through cellular telephones as to calls played through conventional playback technology. In addition, the telephone audio recordings are of sufficient quality to detect most of the two owl species' responses. These findings are a first important step towards large-scale applications where networks of cellular phones conduct real-time monitoring tasks.     

Molecular Modeling Study of the PtCl2 Complexes of Unsaturated S2On+1-Coronands: Dynamic Simulations and Investigation of the Ring Interconversion

Maleonitrile-dithiacrown ethers mn-12S₂O₂ - mn-21S₂O₅ (mn = maleonitrile) are preorganized S₂O_n+1-coronands (n = 1–4) which force B, AB and A class metal ions into mixed S/O coordination spheres. Moreover, they form chelate complexes with MX₂ salts (M = Pd, Pt; X = Cl, Br), which were studied in this paper. The structures of mn-S₂O_n+1 and [PtCl₂(mn-S₂O_n+1)] (n = 2, 3) were investigated theoretically by empirical and semiempirical methods using SYBYL (TRIPOS force field) and MSI/DISCOVER97 (ESFF force field). mn-12S₂O₂ was investigated experimentally by X-ray analysis and 1D and 2D NMR spectroscopy in solution and the complex formation was studied by ¹H, ¹³C and ¹⁹⁵Pt NMR titration experiments, respectively. S-inversion was also investigated in order to determine the ring corresponding interconversional barriers. Different orientations of the macrocyclic ring system mn-18S₂O₄ and of its transition states are shown.Electronic Supplementary Material available.     

On the reproductive value and the spectrum of a population projection matrix with implications for dynamic population models

The eigenvalues of a population projection matrix-except for the Lotka coefficient-are uniquely determined by the reproductive values and the survival. This relation (proposed earlier, but not really well known in western literature) follows from another useful relation between fertility, reproductive values, survival, and Lotka’s coefficient. These results are applied to provide demographic interpretations to the intrinsically dynamic and metastable population models by Schoen and co-workers.