568 research outputs found
Scalable ray tracing with multiple GPGPUs
Rapid development in the field of computer graphics over the last 40 years has brought forth different techniques to render scenes. Rasterization is todayâs most widely used technique, which in its most basic form sequentially draws thousands of polygons and applies texture on them. Ray tracing is an alternative method that mimics light transport by using rays to sample a scene in memory and render the color found at each rayâs scene intersection point. Although mainstream hardware directly supports rasterization, ray tracing would be the preferred technique due to its ability to produce highly crisp and realistic graphics, if hardware were not a limitation. Making an immediate hardware transition from rasterization to ray tracing would have a severe impact on the computer graphics industry since it would require redevelopment of existing 3D graphics-employing software, so any transition to ray tracing would be gradual. Previous efforts to perform ray tracing on mainstream rasterizing hardware platforms with a single processor have performed poorly. This thesis explores how a multiple GPGPU system can be used to render scenes via ray tracing. A ray tracing engine and API groundwork was developed using NVIDIAâs CUDA (Compute Unified Device Architecture) GPGPU programming environment and was used to evaluate performance scalability across a multi-GPGPU system. This engine supports triangle, sphere, disc, rectangle, and torus rendering. It also allows independent activation of graphics features including procedural texturing, Phong illumination, reflections, translucency, and shadows. Correctness of rendered images validates the ray traced results, and timing of rendered scenes benchmarks performance. The main test scene contains all object types, has a total of 32 Abstract objects, and applies all graphics features. Ray tracing this scene using two GPGPUs outperformed the single-GPGPU and single-CPU systems, yielding respective speedups of up to 1.8 and 31.25. The results demonstrate how much potential exists in treating a modern dual-GPU architecture as a dual-GPGPU system in order to facilitate a transition from rasterization to ray tracing
The Magnetic Properties of Heating Events on High-Temperature Active Region Loops
Understanding the relationship between the magnetic field and coronal heating
is one of the central problems of solar physics. However, studies of the
magnetic properties of impulsively heated loops have been rare. We present
results from a study of 34 evolving coronal loops observed in the Fe XVIII line
component of AIA/SDO 94 A filter images from three active regions with
different magnetic conditions. We show that the peak intensity per unit
cross-section of the loops depends on their individual magnetic and geometric
properties. The intensity scales proportionally to the average field strength
along the loop () and inversely with the loop length () for a
combined dependence of . These loop properties are
inferred from magnetic extrapolations of the photospheric HMI/SDO line-of-sight
and vector magnetic field in three approximations: potential and two Non Linear
Force-Free (NLFF) methods. Through hydrodynamic modeling (EBTEL model) we show
that this behavior is compatible with impulsively heated loops with a
volumetric heating rate that scales as .Comment: Astrophysical Journal, in pres
Service level agreement framework for differentiated survivability in GMPLS-based IP-over-optical networks
In the next generation optical internet, GMPLS based IP-over-optical networks, ISPs will be required to support a wide variety of applications each having their own requirements. These requirements are contracted by means of the SLA. This paper describes a recovery framework that may be included in the SLA contract between ISP and customers in order to provide the required level of survivability. A key concern with such a recovery framework is how to present the different survivability alternatives including recovery techniques, failure scenario and layered integration into a transparent manner for customers. In this paper, two issues are investigated. First, the performance of the recovery framework when applying a proposed mapping procedure as an admission control mechanism in the edge router considering a smart-edge simple-core GMPLS-based IP/WDM network is considered. The second issue pertains to the performance of a pre-allocated restoration and its ability to provide protected connections under different failure scenarios
Towards a Quantitative Comparison of Magnetic Field Extrapolations and Observed Coronal Loops
It is widely believed that loops observed in the solar atmosphere trace out
magnetic field lines. However, the degree to which magnetic field
extrapolations yield field lines that actually do follow loops has yet to be
studied systematically. In this paper we apply three different extrapolation
techniques - a simple potential model, a NLFF model based on photospheric
vector data, and a NLFF model based on forward fitting magnetic sources with
vertical currents - to 15 active regions that span a wide range of magnetic
conditions. We use a distance metric to assess how well each of these models is
able to match field lines to the 12,202 loops traced in coronal images. These
distances are typically 1-2". We also compute the misalignment angle between
each traced loop and the local magnetic field vector, and find values of
5-12. We find that the NLFF models generally outperform the potential
extrapolation on these metrics, although the differences between the different
extrapolations are relatively small. The methodology that we employ for this
study suggests a number of ways that both the extrapolations and loop
identification can be improved.Comment: Accepted for publication in Ap
Current sheets at three-dimensional magnetic nulls:effect of compressibility
The nature of current sheet formation in the vicinity of three-dimensional
(3D) magnetic null points is investigated. The particular focus is upon the
effect of the compressibility of the plasma on the qualitative and quantitative
properties of the current sheet. An initially potential 3D null is subjected to
shearing perturbations, as in a previous paper [Pontin et al., Phys. Plasmas,
in press (2007)]. It is found that as the incompressible limit is approached,
the collapse of the null point is suppressed, and an approximately planar
current sheet aligned to the fan plane is present instead. This is the case
regardless of whether the spine or fan of the null is sheared. Both the peak
current and peak reconnection rate are reduced. The results have a bearing on
previous analytical solutions for steady-state reconnection in incompressible
plasmas, implying that fan current sheet solutions are dynamically accessible,
while spine current sheet solutions are not.Comment: to appear in Physics of Plasmas. This version contains updated
figures and references, additional discussion, and typos are fixed. This is
the second in a series of papers - the first of which (by the same authors)
is located at astro-ph/0701462. A version with higher quality figures can be
found at http://www.maths.dundee.ac.uk/~dpontin
Localized Faraday patterns under heterogeneous parametric excitation
Faraday waves are a classic example of a system in which an extended pattern
emerges under spatially uniform forcing. Motivated by systems in which uniform
excitation is not plausible, we study both experimentally and theoretically the
effect of heterogeneous forcing on Faraday waves. Our experiments show that
vibrations restricted to finite regions lead to the formation of localized
subharmonic wave patterns and change the onset of the instability. The
prototype model used for the theoretical calculations is the parametrically
driven and damped nonlinear Schr\"odinger equation, which is known to describe
well Faraday-instability regimes. For an energy injection with a Gaussian
spatial profile, we show that the evolution of the envelope of the wave pattern
can be reduced to a Weber-equation eigenvalue problem. Our theoretical results
provide very good predictions of our experimental observations provided that
the decay length scale of the Gaussian profile is much larger than the pattern
wavelength.Comment: 10 pages, 9 figures, Accepte
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