25,198 research outputs found
A method for detection of structure
Context. In order to understand the evolution of molecular clouds it is
important to identify the departures from self-similarity associated with the
scales of self-gravity and the driving of turbulence.
Aims. A method is described based on structure functions for determining
whether a region of gas, such as a molecular cloud, is fractal or contains
structure with characteristic scale sizes.
Methods. Using artificial data containing structure it is shown that
derivatives of higher order structure functions provide a powerful way to
detect the presence of characteristic scales should any be present and to
estimate the size of such structures. The method is applied to observations of
hot H2 in the Kleinman-Low nebula, north of the Trapezium stars in the Orion
Molecular Cloud, including both brightness and velocity data. The method is
compared with other techniques such as Fourier transform and histogram
techniques.
Results. It is found that the density structure, represented by H2 emission
brightness in the K-band (2-2.5micron), exhibits mean characteristic sizes of
110, 550, 1700 and 2700AU. The velocity data show the presence of structure at
140, 1500 and 3500AU. Compared with other techniques such as Fourier transform
or histogram, the method appears both more sensitive to characteristic scales
and easier to interpret.Comment: Astronomy and Astrophysics, in pres
Interstellar Sonic and Alfv\'enic Mach Numbers and the Tsallis Distribution
In an effort to characterize the Mach numbers of ISM magnetohydrodynamic
(MHD) turbulence, we study the probability distribution functions (PDFs) of
patial increments of density, velocity, and magnetic field for fourteen ideal
isothermal MHD simulations at resolution 512^3. In particular, we fit the PDFs
using the Tsallis function and study the dependency of fit parameters on the
compressibility and magnetization of the gas. We find that the Tsallis function
fits PDFs of MHD turbulence well, with fit parameters showing sensitivities to
the sonic and Alfven Mach numbers. For 3D density, column density, and
position-position-velocity (PPV) data we find that the amplitude and width of
the PDFs shows a dependency on the sonic Mach number. We also find the width of
the PDF is sensitive to global Alfvenic Mach number especially in cases where
the sonic number is high. These dependencies are also found for mock
observational cases, where cloud-like boundary conditions, smoothing, and noise
are introduced. The ability of Tsallis statistics to characterize sonic and
Alfvenic Mach numbers of simulated ISM turbulence point to it being a useful
tool in the analysis of the observed ISM, especially when used simultaneously
with other statistical techniques.Comment: 20 pages, 16 figures, ApJ submitte
Digital Color Imaging
This paper surveys current technology and research in the area of digital
color imaging. In order to establish the background and lay down terminology,
fundamental concepts of color perception and measurement are first presented
us-ing vector-space notation and terminology. Present-day color recording and
reproduction systems are reviewed along with the common mathematical models
used for representing these devices. Algorithms for processing color images for
display and communication are surveyed, and a forecast of research trends is
attempted. An extensive bibliography is provided
From Big Data to Big Displays: High-Performance Visualization at Blue Brain
Blue Brain has pushed high-performance visualization (HPV) to complement its
HPC strategy since its inception in 2007. In 2011, this strategy has been
accelerated to develop innovative visualization solutions through increased
funding and strategic partnerships with other research institutions.
We present the key elements of this HPV ecosystem, which integrates C++
visualization applications with novel collaborative display systems. We
motivate how our strategy of transforming visualization engines into services
enables a variety of use cases, not only for the integration with high-fidelity
displays, but also to build service oriented architectures, to link into web
applications and to provide remote services to Python applications.Comment: ISC 2017 Visualization at Scale worksho
Adaptive Display Frequency Control for Power Savings
This publication describes systems and techniques directed at adaptive display frequency control for power savings. In aspects, a display manager can adjust a base frequency and/or a driving frequency of display panel circuitry based on determining a number of operating conditions, including an ambient light condition, a current base frequency and driving frequency, a user interaction with the display, and/or a display brightness. Responsive to determining one or more of these conditions, the display manager can implement a base frequency and a driving frequency that can reduce power consumption and eliminate display artifacts commonly associated with automatic driving frequency transition
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