3,758 research outputs found
Opto-fluidic third order distributed feed-back dye laser
This letter describes the design and operation of a polymer-based third order
distributed feed-back (DFB) microfluidic dye laser. The device relies on
light-confinement in a nano-structured polymer film where an array of
nanofluidic channels is filled by capillary action with a liquid dye solution
which has a refractive index lower than that of the polymer. In combination
with a third order DFB grating, formed by the array of nanofluidic channels,
this yields a low threshold for lasing. The laser is straight-forward to
integrate on Lab-on-a-Chip micro-systems where coherent, tunable light in the
visible range is desired.Comment: 4 pages, 3 figure
Comparing transnational organizational innovation in state administration and local government
Probiotic Lactobacillus acidophilus NCFM and Bifidobacterium animalis subsp lactis Bl-04 interactions with prebiotic carbohydrates using differential proteomics and protein characterization
Modal dynamics of structures with bladed isotropic rotors and its complexity for 2-bladed rotors
Abstract. The modal dynamics of structures with bladed isotropic rotors is analyzed using Hill's method. First, analytical derivation of the periodic system matrix shows that isotropic rotors with more than two blades can be represented by an exact Fourier series with 3/rev as the highest order. For 2-bladed rotors, the inverse mass matrix has an infinite Fourier series with harmonic components of decreasing norm, thus the system matrix can be approximated by a truncated Fourier series of predictable accuracy. Second, a novel method for automatically identifying the principal solutions of Hill's eigenvalue problem is introduced. The corresponding periodic eigenvectors can be used to compute symmetric and anti-symmetric components of the 2-bladed rotor motion, and the additional forward and backward whirling components for rotors with more than two blades. Finally, the generic methods are used on a simple wind turbine model consisting of three degrees of freedom for each blade and seven degrees of freedom for the nacelle and drivetrain. The modal dynamics of a 3-bladed 10MW turbine from previous studies is recaptured. Removing one blade, the larger and higher harmonic terms in the system matrix lead to resonant modal couplings for the 2-bladed turbine that do not exist for the 3-bladed turbine, and that excitation of a single mode of a 2-bladed turbine leads to responses at several frequencies in both the ground-fixed and rotating blade frames of reference which complicates the interpretation of simulated or measured turbine responses.
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Near-Optimal Detection in MIMO Systems using Gibbs Sampling
In this paper we study a Markov Chain Monte Carlo (MCMC) Gibbs sampler for
solving the integer least-squares problem. In digital communication the problem
is equivalent to performing Maximum Likelihood (ML) detection in Multiple-Input
Multiple-Output (MIMO) systems. While the use of MCMC methods for such problems
has already been proposed, our method is novel in that we optimize the
"temperature" parameter so that in steady state, i.e. after the Markov chain
has mixed, there is only polynomially (rather than exponentially) small
probability of encountering the optimal solution. More precisely, we obtain the
largest value of the temperature parameter for this to occur, since the higher
the temperature, the faster the mixing. This is in contrast to simulated
annealing techniques where, rather than being held fixed, the temperature
parameter is tended to zero. Simulations suggest that the resulting Gibbs
sampler provides a computationally efficient way of achieving approximative ML
detection in MIMO systems having a huge number of transmit and receive
dimensions. In fact, they further suggest that the Markov chain is rapidly
mixing. Thus, it has been observed that even in cases were ML detection using,
e.g. sphere decoding becomes infeasible, the Gibbs sampler can still offer a
near-optimal solution using much less computations.Comment: To appear in Globecom 200
IST Austria Thesis
Computer graphics is an extremely exciting field for two reasons. On the one hand,
there is a healthy injection of pragmatism coming from the visual effects industry
that want robust algorithms that work so they can produce results at an increasingly
frantic pace. On the other hand, they must always try to push the envelope and
achieve the impossible to wow their audiences in the next blockbuster, which means
that the industry has not succumb to conservatism, and there is plenty of room to
try out new and crazy ideas if there is a chance that it will pan into something
useful.
Water simulation has been in visual effects for decades, however it still remains
extremely challenging because of its high computational cost and difficult artdirectability.
The work in this thesis tries to address some of these difficulties.
Specifically, we make the following three novel contributions to the state-of-the-art
in water simulation for visual effects.
First, we develop the first algorithm that can convert any sequence of closed
surfaces in time into a moving triangle mesh. State-of-the-art methods at the time
could only handle surfaces with fixed connectivity, but we are the first to be able to
handle surfaces that merge and split apart. This is important for water simulation
practitioners, because it allows them to convert splashy water surfaces extracted
from particles or simulated using grid-based level sets into triangle meshes that can
be either textured and enhanced with extra surface dynamics as a post-process.
We also apply our algorithm to other phenomena that merge and split apart, such
as morphs and noisy reconstructions of human performances.
Second, we formulate a surface-based energy that measures the deviation of a
water surface froma physically valid state. Such discrepancies arise when there is a
mismatch in the degrees of freedom between the water surface and the underlying
physics solver. This commonly happens when practitioners use a moving triangle
mesh with a grid-based physics solver, or when high-resolution grid-based surfaces
are combined with low-resolution physics. Following the direction of steepest
descent on our surface-based energy, we can either smooth these artifacts or turn
them into high-resolution waves by interpreting the energy as a physical potential.
Third, we extend state-of-the-art techniques in non-reflecting boundaries to handle spatially and time-varying background flows. This allows a novel new
workflow where practitioners can re-simulate part of an existing simulation, such
as removing a solid obstacle, adding a new splash or locally changing the resolution.
Such changes can easily lead to new waves in the re-simulated region that would
reflect off of the new simulation boundary, effectively ruining the illusion of a
seamless simulation boundary between the existing and new simulations. Our
non-reflecting boundaries makes sure that such waves are absorbed
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