1,559 research outputs found
Doctor of Philosophy
dissertationDataflow pipeline models are widely used in visualization systems. Despite recent advancements in parallel architecture, most systems still support only a single CPU or a small collection of CPUs such as a SMP workstation. Even for systems that are specifically tuned towards parallel visualization, their execution models only provide support for data-parallelism while ignoring taskparallelism and pipeline-parallelism. With the recent popularization of machines equipped with multicore CPUs and multi-GPU units, these visualization systems are undoubtedly falling further behind in reaching maximum efficiency. On the other hand, there exist several libraries that can schedule program executions on multiple CPUs and/or multiple GPUs. However, due to differences in executing a task graph and a pipeline along with their APIs being considerably low-level, it still remains a challenge to integrate these run-time libraries into current visualization systems. Thus, there is a need for a redesigned dataflow architecture to fully support and exploit the power of highly parallel machines in large-scale visualization. The new design must be able to schedule executions on heterogeneous platforms while at the same time supporting arbitrarily large datasets through the use of streaming data structures. The primary goal of this dissertation work is to develop a parallel dataflow architecture for streaming large-scale visualizations. The framework includes supports for platforms ranging from multicore processors to clusters consisting of thousands CPUs and GPUs. We achieve this in our system by introducing the notion of Virtual Processing Elements and Task-Oriented Modules along with a highly customizable scheduler that controls the assignment of tasks to elements dynamically. This creates an intuitive way to maintain multiple CPU/GPU kernels yet still provide coherency and synchronization across module executions. We have implemented these techniques into HyperFlow which is made of an API with all basic dataflow constructs described in the dissertation, and a distributed run-time library that can be used to deploy those pipelines on multicore, multi-GPU and cluster-based platforms
INDEX STRATEGIES FOR EFFICIENT AND EFFECTIVE ENTITY SEARCH
The volume of structured data has rapidly grown in recent years, when data-entity emerged as an abstraction that captures almost every data pieces. As a result, searching for a desired piece of information on the web could be a challenge in term of time and relevancy because the number of matching entities could be very large for a given query. This project concerns with the efficiency and effectiveness of such entity queries. The work contains two major parts: implement inverted indexing strategies so that queries can be searched in minimal time, and rank results based on features that are independent of the query itself
Extremely Large and Anisotropic Upper Critical Field and the Ferromagnetic Instability in UCoGe
Magnetoresistivity measurements with fine tuning of the field direction on
high quality single crystals of the ferromagnetic superconductor UCoGe show
anomalous anisotropy of the upper critical field H_c2. H_c2 for H // b-axis
(H_c2^b) in the orthorhombic crystal structure is strongly enhanced with
decreasing temperature with an S-shape and reaches nearly 20 T at 0 K. The
temperature dependence of H_c2^a shows upward curvature with a low temperature
value exceeding 30 T, while H_c2^c at 0 K is very small (~ 0.6 T). Contrary to
conventional ferromagnets, the decrease of the Curie temperature with
increasing field for H // b-axis marked by an enhancement of the effective mass
of the conduction electrons appears to be the origin of the S-shaped H_c2^b
curve. These results indicate that the field-induced ferromagnetic instability
or magnetic quantum criticality reinforces superconductivity.Comment: 5 pages, 4 figures, accepted for publication in J. Phys. Soc. Jp
Microscopic Coexistence of Ferromagnetism and Superconductivity in Single-Crystal UCoGe
Unambiguous evidence for the microscopic coexistence of ferromagnetism and
superconductivity in UCoGe ( K and
0.6 K) is reported from Co nuclear quadrupole resonance (NQR). The
Co-NQR signal below 1 K indicates ferromagnetism throughout the sample
volume, while nuclear spin-lattice relaxation rate in the ferromagnetic
(FM) phase decreases below due to the opening of the
superconducting(SC) gap. The SC state was found to be inhomogeneous, suggestive
of a self-induced vortex state, potentially realizable in a FM superconductor.
In addition, the Co-NQR spectrum around show that the FM
transition in UCoGe possesses a first-order character, which is consistent with
the theoretical prediction that the low-temperature FM transition in itinerant
magnets is generically of first-order.Comment: 5 pages, 5 figure
Pressure-temperature Phase Diagram of Polycrystalline UCoGe Studied by Resistivity Measurement
Recently, coexistence of ferromagnetism (T_Curie = 2.8K) and
superconductivity (T_sc = 0.8K) has been reported in UCoGe, a compound close to
a ferromagnetic instability at ambient pressure P. Here we present resistivity
measurements under pressure on a UCoGe polycrystal. The phase diagram obtained
from resistivity measurements on a polycrystalline sample is found to be
qualitatively different to those of all other ferromagnetic superconductors. By
applying high pressure, ferromagnetism is suppressed at a rate of 1.4 K/GPa. No
indication of ferromagnetic order has been observed above P ~ 1GPa. The
resistive superconducting transition is, however, quite stable in temperature
and persists up to the highest measured pressure of about 2.4GPa.
Superconductivity would therefore appear also in the paramagnetic phase.
However, the appearance of superconductivity seems to change at a
characteristic pressure P* ~ 0.8GPa. Close to a ferromagnetic instability, the
homogeneity of the sample can influence strongly the electronic and magnetic
properties and therefore bulk phase transitions may differ from the
determination by resistivity measurements.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jp
Detection of Phase Jumps of Free Core Nutation of the Earth and their Concurrence with Geomagnetic Jerks
We detected phase jumps of the Free Core Nutation (FCN) of the Earth directly
from the analysis of the Very Long Baseline Interferometer (VLBI) observation
of the Earth rotation for the period 1984-2003 by applying the Weighted Wavelet
Z-Transform (WWZ) method and the Short-time Periodogram with the Gabor function
(SPG) method. During the period, the FCN had two significant phase jumps in
1992 and 1998. These epochs coincide with the reported occurrence of
geomagnetic jerks.Comment: 8 pages, 4 figure
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