613 research outputs found
Anti-aliasing with stratified B-spline filters of arbitrary degree
A simple and elegant method is presented to perform anti-aliasing in raytraced images. The method uses stratified
sampling to reduce the occurrence of artefacts in an image and features a B-spline filter to compute the final
luminous intensity at each pixel. The method is scalable through the specification of the filter degree. A B-spline
filter of degree one amounts to a simple anti-aliasing scheme with box filtering. Increasing the degree of the B-spline generates progressively smoother filters. Computation of the filter values is done in a recursive way, as part of a sequence of Newton-Raphson iterations, to obtain the optimal sample positions in screen space. The proposed method can perform both anti-aliasing in space and in time, the latter being more commonly known as motion blur. We show an application of the method to the ray casting of implicit procedural surfaces
Linear scaling computation of the Fock matrix VII. Periodic Density Functional Theory at the -point
Linear scaling quantum chemical methods for Density Functional Theory are
extended to the condensed phase at the -point. For the two-electron
Coulomb matrix, this is achieved with a tree-code algorithm for fast Coulomb
summation [J. Chem. Phys. {\bf 106}, 5526 (1997)], together with multipole
representation of the crystal field [J. Chem. Phys. {\bf 107}, 10131 (1997)]. A
periodic version of the hierarchical cubature algorithm [J. Chem. Phys. {\bf
113}, 10037 (2000)], which builds a telescoping adaptive grid for numerical
integration of the exchange-correlation matrix, is shown to be efficient when
the problem is posed as integration over the unit cell. Commonalities between
the Coulomb and exchange-correlation algorithms are discussed, with an emphasis
on achieving linear scaling through the use of modern data structures. With
these developments, convergence of the -point supercell approximation
to the -space integration limit is demonstrated for MgO and NaCl.
Linear scaling construction of the Fockian and control of error is demonstrated
for RBLYP/6-21G* diamond up to 512 atoms
Progressive Transient Photon Beams
In this work we introduce a novel algorithm for transient rendering in
participating media. Our method is consistent, robust, and is able to generate
animations of time-resolved light transport featuring complex caustic light
paths in media. We base our method on the observation that the spatial
continuity provides an increased coverage of the temporal domain, and
generalize photon beams to transient-state. We extend the beam steady-state
radiance estimates to include the temporal domain. Then, we develop a
progressive version of spatio-temporal density estimations, that converges to
the correct solution with finite memory requirements by iteratively averaging
several realizations of independent renders with a progressively reduced kernel
bandwidth. We derive the optimal convergence rates accounting for space and
time kernels, and demonstrate our method against previous consistent transient
rendering methods for participating media
Heavy Quark Physics in Nf=2 QCD
We present a preliminary analysis of the heavy-heavy spectrum and heavy-light
decay constants in full QCD, using a tadpole-improved SW quark action and an
RG-improved gauge action on a 16^3 x 32 lattice with four sea quark masses
corresponding to m_pi/m_rho = 0.8, 0.75, 0.7, 0.6 and a^-1 = 1.3 GeV. We focus
particularly on the effect of sea quarks on these observables.Comment: 3 pages Latex, 3 eps figures. Uses espcrc2.sty and epsf.sty . To
appear in the Proceedings of Lattice 98 (Heavy Quarks
Hetero-DielsâAlder Cycloaddition with RAFT Polymers as Bioconjugation Platform
We introduce the bioconjugation of polymers synthesized by RAFT polymerization, bearing no specific functional end group, by means of heteroâDielsâAlder cycloaddition through their inherent terminal thiocarbonylthio moiety with a dieneâmodified model protein. Quantitative conjugation occurs over the course of a few hours, at ambient temperature and neutral pH, and in the absence of any catalyst. Our technology platform affords thermoresponsive bioconjugates, whose aggregation is solely controlled by the polymer chains
Hetero-Diels-Alder-Cycloaddition mit RAFT-Polymeren als Biokonjugationsplattform
Wir stellen die Biokonjugation von Polymeren vor, die durch RAFTâPolymerisation mittels HeteroâDielsâAlderâCycloaddition durch ihren inhĂ€renten terminalen Thiocarbonylthiorest mit einem dienmodifizierten Modellprotein synthetisiert wurden und keine spezifische funktionelle Endgruppe tragen. Die quantitative Konjugation erfolgt im Verlauf einiger Stunden bei Raumtemperatur und nahezu neutralem pHâWert und in Abwesenheit jeglichen Katalysators. Unsere Technologieplattform liefert thermoresponsive Biokonjugate, deren Aggregation allein durch die Polymerketten gesteuert wird
Sub-Doppler spectroscopy of Rb atoms in a sub-micron vapor cell in the presence of a magnetic field
We report the first use of an extremely thin vapor cell (thickness ~ 400 nm)
to study the magnetic-field dependence of laser-induced-fluorescence excitation
spectra of alkali atoms. This thin cell allows for sub-Doppler resolution
without the complexity of atomic beam or laser cooling techniques. This
technique is used to study the laser-induced-fluorescence excitation spectra of
Rb in a 50 G magnetic field. At this field strength the electronic angular
momentum J and nuclear angular momentum I are only partially decoupled. As a
result of the mixing of wavefunctions of different hyperfine states, we observe
a nonlinear Zeeman effect for each sublevel, a substantial modification of the
transition probabilities between different magnetic sublevels, and the
appearance of transitions that are strictly forbidden in the absence of the
magnetic field. For the case of right- and left- handed circularly polarized
laser excitation, the fluorescence spectra differs qualitatively. Well
pronounced magnetic field induced circular dichroism is observed. These
observations are explained with a standard approach that describes the partial
decoupling of I and J states
A Temporal Image-Based Approach to Motion Reconstruction for Globally Illuminated Animated Environments
Enhancing Perception of Complex Sculptural Forms using Interactive Real-time Ray tracing
This paper looks at experiments into using real-time ray tracing to significantly enhance shape perception of complex three-dimensional digitally created structures. The author is a computational artist whose artistic practice explores the creation of intricate organic three-dimensional forms using simulation of morphogenesis. The generated forms are often extremely detailed, comprising tens of millions of cellular primitives. This often makes depth perception of the resulting structures difficult. His practice has explored various techniques to create presentable artefacts from the data, including high resolution prints, animated videos, stereoscopic installations, 3D printing and virtual reality.
The author uses ray tracing techniques to turn the 3D data created from his morphogenetic simulations into visible artefacts. This is typically a time-consuming process, taking from seconds to minutes to create a single frame. The latest generation of graphics processing units offer dedicated hardware to accelerate ray tracing calculations. This potentially allows the generation of ray traced images, including self-shadowed complex structures and multiple levels of transparency, from new viewpoints at frame rates capable of real-time interaction. The author presents the results of his experiments using this technology with the aim of providing significantly enhanced perception of his generated three-dimensional structures by allowing user-initiated interaction to generate novel views, and utilizing depth cues such as stereopsis, depth from motion and defocus blurring.
The intention is for these techniques to be usable to present new exhibitable works in a gallery context
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