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Katerina Doka Dimitrios Tsoumakos Nectarios KozirisAuthor vitae 《Journal of Parallel and Distributed Computing》2011,71(11):1434-1446
In this paper we present the Brown Dwarf, a distributed data analytics system designed to efficiently store, query and update multidimensional data over commodity network nodes, without the use of any proprietary tool. Brown Dwarf distributes a centralized indexing structure among peers on-the-fly, reducing cube creation and querying times by enforcing parallelization. Analytical queries are naturally performed on-line through cooperating nodes that form an unstructured Peer-to-Peer overlay. Updates are also performed on-line, eliminating the usually costly over-night process. Moreover, the system employs an adaptive replication scheme that adjusts to the workload skew as well as the network churn by expanding or shrinking the units of the distributed data structure. Our system has been thoroughly evaluated on an actual testbed: it manages to accelerate cube creation up and querying up to several tens of times compared to the centralized solution by exploiting the capabilities of the available network nodes working in parallel. It also manages to quickly adapt even after sudden bursts in load and remains unaffected with a considerable fraction of frequent node failures. These advantages are even more apparent for dense and skewed data cubes and workloads. 相似文献
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Katerina Diamantaki Charalampos Rizopoulos Dimitris Charitos Nikos Tsianos 《Personal and Ubiquitous Computing》2011,15(1):37-49
Multiuser location-aware applications present a new form of mediated communication that takes place within a digital as well
as a physical spatial context. The inherently hybrid character of locative media use necessitates that the designers of such
applications take into account the way communication and social interaction is influenced by contextual elements. In this
paper, an investigation into the communicational and social practices of users who participate in a location-based game is
presented, with an emphasis on group formation and dynamics, interpersonal communication, and experienced sense of immersion.
This investigation employs a methodological approach that is reliant on both qualitative and quantitative data analysis. A
series of this user experience study’s results are presented and discussed. 相似文献
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Katerina Raleva Dragica Vasileska Stephen M. Goodnick Tomislav Dzekov 《Journal of Computational Electronics》2008,7(3):226-230
For the purpose of investigating the role of self-heating effects on the electrical characteristics of nano-scale devices,
we implemented a two-dimensional Monte Carlo device simulator that self-consistently includes the solution of the energy balance
equations for both, acoustic and optical phonons. We find less degradation in the current in smaller device structures because
of the more pronounced velocity overshoot. 相似文献
27.
Viktor Dan’ko Katerina Michailovska Ivan Indutnyi Petro Shepeliavyi 《Nanoscale research letters》2014,9(1):165
We investigated plasmon-assisted enhancement of emission from silicon nanoparticles (ncs-Si) embedded into porous SiO
x
matrix in the 500- to 820-nm wavelength range. In the presence in the near-surface region of gold nanoisland film, ncs-Si exhibited up to twofold luminescence enhancement at emission frequencies that correspond to the plasmon resonance frequency of Au nanoparticles. Enhancement of the photoluminescence (PL) intensity was attributed to coupling with the localized surface plasmons (LSPs) excited in Au nanoparticles and to increase in the radiative decay rate of ncs-Si. It has been shown that spontaneous emission decay rate of ncs-Si modified by thin Au film over the wide emission spectral range was accelerated. The emission decay rate distribution was determined by fitting the experimental decay curves to the stretched exponential model. The observed increase of the PL decay rate distribution width for the Au-coated nc-Si-SiO
x
sample in comparison with the uncoated one was explained by fluctuations in the surface-plasmon excitation rate.
PACS
78. 67. Bf; 78.55.-m 相似文献28.
We report on experimental results of the thermal conductivity k of
highly porous Si in the temperature range 4.2 to 20 K, obtained using the
direct current (dc) method combined with thermal finite element simulations. The
reported results are the first in the literature for this temperature range. It
was found that porous Si thermal conductivity at these temperatures shows a
plateau-like temperature dependence similar to that obtained in glasses, with a
constant k value as low as 0.04 W/m.K. This behavior is attributed
to the presence of a majority of non-propagating vibrational modes, resulting
from the nanoscale fractal structure of the material. By examining the fractal
geometry of porous Si and its fractal dimensionality, which was smaller than two
for the specific porous Si material used, we propose that a band of fractons
(the localized vibrational excitations of a fractal lattice) is responsible for
the observed plateau. The above results complement previous results by the
authors in the temperature range 20 to 350 K. In this temperature range, a
monotonic increase of k with temperature is observed, fitted with
simplified classical models. The extremely low thermal conductivity of porous
Si, especially at cryogenic temperatures, makes this material an excellent
substrate for Si-integrated microcooling devices (micro-coldplate).
PACS
61.43.-j; 63.22.-m; 65.8.-g 相似文献29.
Being aware of negative health effects of radon exposure, many countries aim for the reduction of the radon exposure of their population. The Czech radon programme was commenced >20 y ago. Since then experts have gathered a lot of knowledge, necessary legislation has been enacted, tens of thousands of inhabitants have been offered free measurement and subsidy for the mitigation. Despite the effort, the effectiveness of the radon programme seems to be poor. Newly built houses still exhibit elevated radon concentrations and the number of houses mitigated is very low. Is it possible to enhance the effectivity of radon programme while keeping it on a voluntary basis? One possible way is to employ health marketing that draws together traditional marketing theories and science-based strategies to prevention. The potential of using marketing principles in communication and delivery of radon information will be discussed. 相似文献
30.
The mechanical and morphological degradation that human dentin undergoes after prolonged exposure in cola drinks was examined using nanoindentation and AFM. The elastic modulus of the dentin prior cola exposure was 18.28 ± 1.7 GPa, while after exposure it had decreased to 4.25 ± 1.4 GPa on the surface that was in direct contact with the drink, and to 13.38 ± 2.9 GPa on the surface that was in indirect contact with the drink. AFM documented the corrosion effects of the cola through topography images and histograms of the RMS roughness. 相似文献