@article{2076, abstract = {Snakes exhibit genetic sex determination, with female heterogametic sex chromosomes (ZZ males, ZW females). Extensive cytogenetic work has suggested that the level of sex chromosome heteromorphism varies among species, with Boidae having entirely homomorphic sex chromosomes, Viperidae having completely heteromorphic sex chromosomes, and Colubridae showing partial differentiation. Here, we take a genomic approach to compare sex chromosome differentiation in these three snake families. We identify homomorphic sex chromosomes in boas (Boidae), but completely heteromorphic sex chromosomes in both garter snakes (Colubridae) and pygmy rattlesnake (Viperidae). Detection of W-linked gametologs enables us to establish the presence of evolutionary strata on garter and pygmy rattlesnake sex chromosomes where recombination was abolished at different time points. Sequence analysis shows that all strata are shared between pygmy rattlesnake and garter snake, i.e., recombination was abolished between the sex chromosomes before the two lineages diverged. The sex-biased transmission of the Z and its hemizygosity in females can impact patterns of molecular evolution, and we show that rates of evolution for Z-linked genes are increased relative to their pseudoautosomal homologs, both at synonymous and amino acid sites (even after controlling for mutational biases). This demonstrates that mutation rates are male-biased in snakes (male-driven evolution), but also supports faster-Z evolution due to differential selective effects on the Z. Finally, we perform a transcriptome analysis in boa and pygmy rattlesnake to establish baseline levels of sex-biased expression in homomorphic sex chromosomes, and show that heteromorphic ZW chromosomes in rattlesnakes lack chromosome-wide dosage compensation. Our study provides the first full scale overview of the evolution of snake sex chromosomes at the genomic level, thus greatly expanding our knowledge of reptilian and vertebrate sex chromosomes evolution. }, author = {Beatriz Vicoso and Emerson, Jr J. and Zektser, Yulia and Mahajan, Shivani and Bachtrog, Doris}, journal = {PLoS Biology}, number = {8}, publisher = {Public Library of Science}, title = {{Comparative sex chromosome genomics in snakes: Differentiation evolutionary strata and lack of global dosage compensation}}, doi = {10.1371/journal.pbio.1001643}, volume = {11}, year = {2013}, } @article{2108, abstract = {We present an interactive design system that allows non-expert users to create animated mechanical characters. Given an articulated character as input, the user iteratively creates an animation by sketching motion curves indicating how different parts of the character should move. For each motion curve, our framework creates an optimized mechanism that reproduces it as closely as possible. The resulting mechanisms are attached to the character and then connected to each other using gear trains, which are created in a semi-automated fashion. The mechanical assemblies generated with our system can be driven with a single input driver, such as a hand-operated crank or an electric motor, and they can be fabricated using rapid prototyping devices. We demonstrate the versatility of our approach by designing a wide range of mechanical characters, several of which we manufactured using 3D printing. While our pipeline is designed for characters driven by planar mechanisms, significant parts of it extend directly to non-planar mechanisms, allowing us to create characters with compelling 3D motions. }, author = {Coros, Stelian and Thomaszewski, Bernhard and Noris, Gioacchino and Sueda, Shinjiro and Forberg, Moira and Sumner, Robert W and Matusik, Wojciech and Bernd Bickel}, journal = {ACM Transactions on Graphics}, number = {4}, publisher = {ACM}, title = {{Computational design of mechanical characters}}, doi = {10.1145/2461912.2461953}, volume = {32}, year = {2013}, } @article{2110, abstract = {We present a method for practical physical reproduction and design of homogeneous materials with desired subsurface scattering. Our process uses a collection of different pigments that can be suspended in a clear base material. Our goal is to determine pigment concentrations that best reproduce the appearance and subsurface scattering of a given target material. In order to achieve this task we first fabricate a collection of material samples composed of known mixtures of the available pigments with the base material. We then acquire their reflectance profiles using a custom-built measurement device. We use the same device to measure the reflectance profile of a target material. Based on the database of mappings from pigment concentrations to reflectance profiles, we use an optimization process to compute the concentration of pigments to best replicate the target material appearance. We demonstrate the practicality of our method by reproducing a variety of different translucent materials. We also present a tool that allows the user to explore the range of achievable appearances for a given set of pigments. }, author = {Papas, Marios and Regg, Christian and Jarosz, Wojciech and Bernd Bickel and Jackson, Philip V and Matusik, Wojciech and Marschner, Steve and Groß, Markus S}, journal = {ACM Transactions on Graphics}, number = {4}, publisher = {ACM}, title = {{Fabricating translucent materials using continuous pigment mixtures}}, doi = {10.1145/2461912.2461974}, volume = {32}, year = {2013}, } @article{2111, abstract = {Animated animatronic figures are a unique way to give physical presence to a character. However, their movement and expressions are often limited due to mechanical constraints. In this paper, we propose a complete process for augmenting physical avatars using projector-based illumination, significantly increasing their expressiveness. Given an input animation, the system decomposes the motion into low-frequency motion that can be physically reproduced by the animatronic head and high-frequency details that are added using projected shading. At the core is a spatio-temporal optimization process that compresses the motion in gradient space, ensuring faithful motion replay while respecting the physical limitations of the system. We also propose a complete multi-camera and projection system, including a novel defocused projection and subsurface scattering compensation scheme. The result of our system is a highly expressive physical avatar that features facial details and motion otherwise unattainable due to physical constraints.}, author = {Bermano, Amit H and Bruschweiler, Philipp and Grundhöfer, Anselm and Iwai, Daisuke and Bernd Bickel and Groß, Markus S}, journal = {ACM Transactions on Graphics}, number = {6}, publisher = {ACM}, title = {{Augmenting physical avatars using projector-based illumination}}, doi = {10.1145/2508363.2508416}, volume = {32}, year = {2013}, } @article{2109, abstract = {Most additive manufacturing technologies work by layering, i.e. slicing the shape and then generating each slice independently. This introduces an anisotropy into the process, often as different accuracies in the tangential and normal directions, but also in terms of other parameters such as build speed or tensile strength and strain. We model this as an anisotropic cubic element. Our approach then finds a compromise between modeling each part of the shape individually in the best possible direction and using one direction for the whole shape part. In particular, we compute an orthogonal basis and consider only the three basis vectors as slice normals (i.e. fabrication directions). Then we optimize a decomposition of the shape along this basis so that each part can be consistently sliced along one of the basis vectors. In simulation, we show that this approach is superior to slicing the whole shape in one direction, only. It also has clear benefits if the shape is larger than the build volume of the available equipment.}, author = {Hildebrand, Kristian and Bernd Bickel and Alexa, Marc}, journal = {Computers and Graphics (Pergamon)}, number = {6}, pages = {669 -- 675}, publisher = {Elsevier}, title = {{Orthogonal slicing for additive manufacturing}}, doi = {10.1016/j.cag.2013.05.011}, volume = {37}, year = {2013}, } @article{2107, abstract = {We present a method for fabrication-oriented design of actuated deformable characters that allows a user to automatically create physical replicas of digitally designed characters using rapid manufacturing technologies. Given a deformable character and a set of target poses as input, our method computes a small set of actuators along with their locations on the surface and optimizes the internal material distribution such that the resulting character exhibits the desired deformation behavior. We approach this problem with a dedicated algorithm that combines finite-element analysis, sparse regularization, and constrained optimization. We validate our pipeline on a set of two- and three-dimensional example characters and present results in simulation and physically-fabricated prototypes.}, author = {Skouras, Mélina and Thomaszewski, Bernhard and Coros, Stelian and Bernd Bickel and Groß, Markus S}, journal = {ACM Transactions on Graphics}, number = {4}, publisher = {ACM}, title = {{Computational design of actuated deformable characters}}, doi = {10.1145/2461912.2461979}, volume = {32}, year = {2013}, } @article{2112, abstract = {Force-deformation measurements of cloth exhibit significant hysteresis, and many researchers have identified internal friction as the source of this effect. However, it has not been incorporated into computer animation models of cloth. In this paper, we propose a model of internal friction based on an augmented reparameterization of Dahl's model, and we show that this model provides a good match to several important features of cloth hysteresis even with a minimal set of parameters. We also propose novel parameter estimation procedures that are based on simple and inexpensive setups and need only sparse data, as opposed to the complex hardware and dense data acquisition of previous methods. Finally, we provide an algorithm for the efficient simulation of internal friction, and we demonstrate it on simulation examples that show disparate behavior with and without internal friction.}, author = {Miguel, Eder and Tamstorf, Rasmus and Bradley, Derek J and Schvartzman, Sara C and Thomaszewski, Bernhard and Bernd Bickel and Matusik, Wojciech and Marschner, Steve and Otaduy, Miguel A}, journal = {ACM Transactions on Graphics}, number = {6}, publisher = {ACM}, title = {{Modeling and estimation of internal friction in cloth}}, doi = {10.1145/2508363.2508389 }, volume = {32}, year = {2013}, } @article{2117, abstract = {We prove new upper and lower bounds for Banach space-valued stochastic integrals with respect to a compensated Poisson random measure. Our estimates apply to Banach spaces with non-trivial martingale (co)type and extend various results in the literature. We also develop a Malliavin framework to interpret Poisson stochastic integrals as vector-valued Skorohod integrals, and prove a Clark-Ocone representation formula.}, author = {Dirksen, Sjoerd and Jan Maas and van Neerven, Jan M}, journal = {Electronic Journal of Probability}, publisher = {Institute of Mathematical Statistics}, title = {{Poisson stochastic integration in Banach spaces}}, doi = {10.1214/EJP.v18-2945 }, volume = {18}, year = {2013}, } @article{2113, abstract = {A new method fabricates custom surface reflectance and spatially varying bidirectional reflectance distribution functions (svBRDFs). Researchers optimize a microgeometry for a range of normal distribution functions and simulate the resulting surface's effective reflectance. Using the simulation's results, they reproduce an input svBRDF's appearance by distributing the microgeometry on the printed material's surface. This method lets people print svBRDFs on planar samples with current 3D printing technology, even with a limited set of printing materials. It extends naturally to printing svBRDFs on arbitrary shapes.}, author = {Rouiller, Olivier and Bernd Bickel and Kautz, Jan and Matusik, Wojciech and Alexa, Marc}, journal = {IEEE Computer Graphics and Applications}, number = {6}, pages = {48 -- 57}, publisher = {IEEE}, title = {{3D printing spatially varying BRDFs}}, doi = {10.1109/MCG.2013.82 }, volume = {33}, year = {2013}, } @article{2114, abstract = {3D printing is considered a disruptive technology with a potentially tremendous socioeconomic impact. The three articles in this special issue illustrate how novel computer graphics approaches are advancing such digital fabrication.}, author = {Bernd Bickel and Alexa, Marc}, journal = {IEEE Computer Graphics and Applications}, number = {6}, pages = {24 -- 25}, publisher = {IEEE}, title = {{Computational aspects of fabrication: Modeling, design and 3d printing}}, doi = {10.1109/MCG.2013.89}, volume = {33}, year = {2013}, }