10,021 research outputs found
Localization phase diagram of two-dimensional quantum percolation
We examine quantum percolation on a square lattice with random dilution up to
and energy (measured in units of the hopping
matrix element), using numerical calculations of the transmission coefficient
at a much larger scale than previously. Our results confirm the previous
finding that the two dimensional quantum percolation model exhibits
localization-delocalization transitions, where the localized region splits into
an exponentially localized region and a power-law localization region. We
determine a fuller phase diagram confirming all three regions for energies as
low as , and the delocalized and exponentially localized regions for
energies down to . We also examine the scaling behavior of the
residual transmission coefficient in the delocalized region, the power law
exponent in the power-law localized region, and the localization length in the
exponentially localized region. Our results suggest that the residual
transmission at the delocalized to power-law localized phase boundary may be
discontinuous, and that the localization length is likely not to diverge with a
power-law at the exponentially localized to power-law localized phase boundary.
However, further work is needed to definitively assess the characters of the
two phase transitions as well as the nature of the intermediate power-law
regime
Using Fuzzy Linguistic Representations to Provide Explanatory Semantics for Data Warehouses
A data warehouse integrates large amounts of extracted and summarized data from multiple sources for direct querying and analysis. While it provides decision makers with easy access to such historical and aggregate data, the real meaning of the data has been ignored. For example, "whether a total sales amount 1,000 items indicates a good or bad sales performance" is still unclear. From the decision makers' point of view, the semantics rather than raw numbers which convey the meaning of the data is very important. In this paper, we explore the use of fuzzy technology to provide this semantics for the summarizations and aggregates developed in data warehousing systems. A three layered data warehouse semantic model, consisting of quantitative (numerical) summarization, qualitative (categorical) summarization, and quantifier summarization, is proposed for capturing and explicating the semantics of warehoused data. Based on the model, several algebraic operators are defined. We also extend the SQL language to allow for flexible queries against such enhanced data warehouses
Redundant Array Configurations for 21 cm Cosmology
Realizing the potential of 21 cm tomography to statistically probe the
intergalactic medium before and during the Epoch of Reionization requires large
telescopes and precise control of systematics. Next-generation telescopes are
now being designed and built to meet these challenges, drawing lessons from
first-generation experiments that showed the benefits of densely packed, highly
redundant arrays--in which the same mode on the sky is sampled by many antenna
pairs--for achieving high sensitivity, precise calibration, and robust
foreground mitigation. In this work, we focus on the Hydrogen Epoch of
Reionization Array (HERA) as an interferometer with a dense, redundant core
designed following these lessons to be optimized for 21 cm cosmology. We show
how modestly supplementing or modifying a compact design like HERA's can still
deliver high sensitivity while enhancing strategies for calibration and
foreground mitigation. In particular, we compare the imaging capability of
several array configurations, both instantaneously (to address instrumental and
ionospheric effects) and with rotation synthesis (for foreground removal). We
also examine the effects that configuration has on calibratability using
instantaneous redundancy. We find that improved imaging with sub-aperture
sampling via "off-grid" antennas and increased angular resolution via far-flung
"outrigger" antennas is possible with a redundantly calibratable array
configuration.Comment: 19 pages, 11 figures. Revised to match the accepted ApJ versio
Conceptual modeling of knowledge based systems for digital ecosystems
The agents or entities frequently require intelligence in the form of knowledge based systems(KBS) to support many of their functions. In this Paper we discuss how these KBSs are conceptual are conceptually modeled as a first step towards their development. In particular, we show to effectively model all the different knowledge constructs using an extended definition of an object. The notation used to express this is UML [Booch 2005]
Research, development and application of noncombustible Beta fiber structures
Beta fiber was selected as the primary material for flexible fibrous structures used in spacecraft and crew systems applications in the Apollo program because it was noncombustible in a 100 percent oxygen atmosphere up to 16.5 psia. It met NASA criteria for outgassing, toxicity, odor, and crew comfort, and possessed sufficient durability to last through the mission. Topics discussed include: study of spacecraft applications; design of Beta fiber textile structures to meet the requirements; selection of surface treatments (finishes, coatings, and printing systems) to impart the required durability and special functional use to the textile structures; development of sewing and fabrication techniques; and testing and evaluation programs, and development of production sources
Use and modeling of multi-agent systems in medicine
Multi-Agent System (MAS), and more specifically, ontology-based MAS, are increasingly being proposed and used within the medical domain. In this paper we represent an ontology-based multi-agent system specifically designed to intelligently retrieve information about human diseases. Thehuman disease ontology is organized according to the four dimensions: disease types, symptoms, causes and treatments. The multi-agent system consists of four different types of agent: Interface, Manger, Information and Smart agent. We use of UML 2.1 to model social and goal-driven nature of agents. We believe that UML 2.1 has not only provided a way for standardized notation of MAS, but also for effective representation of the dynamic processes associated with these MAS
Detecting the 21 cm Forest in the 21 cm Power Spectrum
We describe a new technique for constraining the radio loud population of
active galactic nuclei at high redshift by measuring the imprint of 21 cm
spectral absorption features (the 21 cm forest) on the 21 cm power spectrum.
Using semi-numerical simulations of the intergalactic medium and a
semi-empirical source population we show that the 21 cm forest dominates a
distinctive region of -space, . By simulating
foregrounds and noise for current and potential radio arrays, we find that a
next generation instrument with a collecting area on the order of (such as the Hydrogen Epoch of Reionization Array) may
separately constrain the X-ray heating history at large spatial scales and
radio loud active galactic nuclei of the model we study at small ones. We
extrapolate our detectability predictions for a single radio loud active
galactic nuclei population to arbitrary source scenarios by analytically
relating the 21 cm forest power spectrum to the optical depth power spectrum
and an integral over the radio luminosity function.Comment: 20 pages, 17 figures, accepted for publication in MNRA
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