N=2 superparticle near horizon of extreme Kerr-Newman-AdS-dS black hole

Conformal mechanics related to the near horizon extreme Kerr-Newman-AdS-dS black hole is studied. A unique N=2 supersymmetric extension of the conformal mechanics is constructed.Comment: V2: the version to appear in NP

Avalanche: A communication and memory architecture for scalable parallel computing

technical reportAs the gap between processor and memory speeds widens, system designers will inevitably incorporate increasingly deep memory hierarchies to maintain the balance between processor and memory system performance. At the same time, most communication subsystems are permitted access only to main memory and not a processor's top level cache. As memory latencies increase, this lack of integration between the memory and communication systems will seriously impede interprocessor communication performance and limit effective scalability. In the Avalanche project we are redesigning the memory architecture of a commercial RISC multiprocessor, the HP PA-RISC 7100, to include a new multi-level context sensitive cache that is tightly coupled to the communication fabric. The primary goal of Avalanche's integrated cache and communication controller is attacking end to end communication latency in all of its forms. This includes cache misses induced by excessive invalidations and reloading of shared data by write-invalidate coherence protocols and cache misses induced by depositing incoming message data in main memory and faulting it into the cache. An execution-driven simulation study of Avalanche's architecture indicates that it can reduce cache stalls by 5-60% and overall execution times by 10-28%

Fast Locality-Sensitive Hashing Frameworks for Approximate Near Neighbor Search

The Indyk-Motwani Locality-Sensitive Hashing (LSH) framework (STOC 1998) is a general technique for constructing a data structure to answer approximate near neighbor queries by using a distribution $\mathcal{H}$ over locality-sensitive hash functions that partition space. For a collection of $n$ points, after preprocessing, the query time is dominated by $O(n^{\rho} \log n)$ evaluations of hash functions from $\mathcal{H}$ and $O(n^{\rho})$ hash table lookups and distance computations where $\rho \in (0,1)$ is determined by the locality-sensitivity properties of $\mathcal{H}$. It follows from a recent result by Dahlgaard et al. (FOCS 2017) that the number of locality-sensitive hash functions can be reduced to $O(\log^2 n)$, leaving the query time to be dominated by $O(n^{\rho})$ distance computations and $O(n^{\rho} \log n)$ additional word-RAM operations. We state this result as a general framework and provide a simpler analysis showing that the number of lookups and distance computations closely match the Indyk-Motwani framework, making it a viable replacement in practice. Using ideas from another locality-sensitive hashing framework by Andoni and Indyk (SODA 2006) we are able to reduce the number of additional word-RAM operations to $O(n^\rho)$.Comment: 15 pages, 3 figure

Rotor loss reduction using segmented inverter in surface-mounted permanent magnet drive

In this paper, the influence of different switching modulation arrangements, i.e. current waveform modulation- and phase-shift, on the resultant current waveform of an electrical machine drive consisting of a two segment inter-leaved inverter feeding a surface-mounted permanent magnet (SPM) machine with two identical sets of three phase windings is investigated. The modulation- and phase-shift have been illustrated and the influence of the different modulation and frequency indices have been studied. Furthermore, the torque, and rotor eddy currents and core losses are calculated using FEA when either modulation-shifted or phase-shifted current waveforms are generated and fed to the machine. It is found that using modulation-shift can reduce the current harmonic substantially however the inverter requires two sets of input signals. On the other hand, although the current harmonic reduction is less than that of the modulation-shift, the phase-shift layout can be employed using one set of input signals with a signal delay

Electromagnetic and Mechanical Analysis of High Speed SPM Rotor with Copper Shield

For high-speed applications, the surface-mounted permanent magnet (SPM) machine is preferred due to its high torque density and efficiency. However, induced eddy currents in the rotor conductive parts result in a loss of efficiency and rotor heating. Therefore, several methods to reduce such losses have been proposed in the literature including copper shielding. In this paper, a high-speed SPM machine rotor with a copper shield is designed and investigated both electromagnetically and mechanically. Several quantitative investigations including placing the copper sheet around the retaining sleeve or magnets, different copper sheet and airgap thicknesses, different retaining sleeve materials, different harmonic contents in the current waveform, i.e. pulse amplitude modulation (PAM) and pulse width modulation (PWM) generated waveforms, and different frequencies and current levels are reported. Additionally, a mechanical analysis investigating possible failure modes of the rotor with the copper sheet is reported

A Hybrid Approach for Supporting Adaptivity in E-learning Environments

Purpose: The purpose of this paper is to identify a framework to support adaptivity in e-learning environments. The framework reflects a novel hybrid approach incorporating the concept of the ECA model and intelligent agents. Moreover, a system prototype is developed reflecting the hybrid approach to supporting adaptivity in any given Learning Management System based on learners’ learning styles. Design/methodology/approach: This paper offers a brief review of current frameworks and systems to support adaptivity in e-learning environments. A framework to support adaptivity is designed and discussed, reflecting the hybrid approach in detail. A system prototype is developed incorporating different adaptive features based on the Felder-Silverman learning styles model. Finally, the prototype is implemented in Moodle. Findings: The system prototype supports real-time adaptivity in any given Learning Management System based on learners’ learning styles. It can deal with any type of content provided by course designers and instructors in the Learning Management System. Moreover, it can support adaptivity at both course and learner levels. Research limitations/implications: Practical implications: Social implications: Originality/value: To the best of our knowledge, no previous work has been done incorporating the concept of the ECA model and intelligent agents as hybrid architecture to support adaptivity in e-learning environments. The system prototype has wider applicability and can be adapted to support different types of adaptivity