TY - JOUR AB - Many algorithms for inferring causality rely heavily on the faithfulness assumption. The main justification for imposing this assumption is that the set of unfaithful distributions has Lebesgue measure zero, since it can be seen as a collection of hypersurfaces in a hypercube. However, due to sampling error the faithfulness condition alone is not sufficient for statistical estimation, and strong-faithfulness has been proposed and assumed to achieve uniform or high-dimensional consistency. In contrast to the plain faithfulness assumption, the set of distributions that is not strong-faithful has nonzero Lebesgue measure and in fact, can be surprisingly large as we show in this paper. We study the strong-faithfulness condition from a geometric and combinatorial point of view and give upper and lower bounds on the Lebesgue measure of strong-faithful distributions for various classes of directed acyclic graphs. Our results imply fundamental limitations for the PC-algorithm and potentially also for other algorithms based on partial correlation testing in the Gaussian case. AU - Uhler, Caroline AU - Raskutti, Garvesh AU - Bühlmann, Peter AU - Yu, Bin ID - 2010 IS - 2 JF - The Annals of Statistics TI - Geometry of the faithfulness assumption in causal inference VL - 41 ER - TY - JOUR AB - Traditional statistical methods for confidentiality protection of statistical databases do not scale well to deal with GWAS databases especially in terms of guarantees regarding protection from linkage to external information. The more recent concept of differential privacy, introduced by the cryptographic community, is an approach which provides a rigorous definition of privacy with meaningful privacy guarantees in the presence of arbitrary external information, although the guarantees may come at a serious price in terms of data utility. Building on such notions, we propose new methods to release aggregate GWAS data without compromising an individual’s privacy. We present methods for releasing differentially private minor allele frequencies, chi-square statistics and p-values. We compare these approaches on simulated data and on a GWAS study of canine hair length involving 685 dogs. We also propose a privacy-preserving method for finding genome-wide associations based on a differentially-private approach to penalized logistic regression. AU - Uhler, Caroline AU - Slavkovic, Aleksandra AU - Fienberg, Stephen ID - 2009 IS - 1 JF - Journal of Privacy and Confidentiality TI - Privacy-preserving data sharing for genome-wide association studies VL - 5 ER - TY - JOUR AB - Sex chromosomes originate from autosomes. The accumulation of sexually antagonistic mutations on protosex chromosomes selects for a loss of recombination and sets in motion the evolutionary processes generating heteromorphic sex chromosomes. Recombination suppression and differentiation are generally viewed as the default path of sex chromosome evolution, and the occurrence of old, homomorphic sex chromosomes, such as those of ratite birds, has remained a mystery. Here, we analyze the genome and transcriptome of emu (Dromaius novaehollandiae) and confirm that most genes on the sex chromosome are shared between the Z and W. Surprisingly, however, levels of gene expression are generally sex-biased for all sex-linked genes relative to autosomes, including those in the pseudoautosomal region, and the male-bias increases after gonad formation. This expression bias suggests that the emu sex chromosomes have become masculinized, even in the absence of ZW differentiation. Thus, birds may have taken different evolutionary solutions to minimize the deleterious effects imposed by sexually antagonistic mutations: some lineages eliminate recombination along the protosex chromosomes to physically restrict sexually antagonistic alleles to one sex, whereas ratites evolved sex-biased expression to confine the product of a sexually antagonistic allele to the sex it benefits. This difference in conflict resolution may explain the preservation of recombining, homomorphic sex chromosomes in other lineages and illustrates the importance of sexually antagonistic mutations driving the evolution of sex chromosomes. AU - Beatriz Vicoso AU - Kaiser, Vera B AU - Bachtrog, Doris ID - 2074 IS - 16 JF - PNAS TI - Sex biased gene expression at homomorphic sex chromosomes in emus and its implication for sex chromosome evolution VL - 110 ER - TY - JOUR AB - 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. AU - Beatriz Vicoso AU - Emerson, Jr J. AU - Zektser, Yulia AU - Mahajan, Shivani AU - Bachtrog, Doris ID - 2076 IS - 8 JF - PLoS Biology TI - Comparative sex chromosome genomics in snakes: Differentiation evolutionary strata and lack of global dosage compensation VL - 11 ER - TY - JOUR AB - 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. AU - Coros, Stelian AU - Thomaszewski, Bernhard AU - Noris, Gioacchino AU - Sueda, Shinjiro AU - Forberg, Moira AU - Sumner, Robert W AU - Matusik, Wojciech AU - Bernd Bickel ID - 2108 IS - 4 JF - ACM Transactions on Graphics TI - Computational design of mechanical characters VL - 32 ER - TY - JOUR AB - 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. AU - Papas, Marios AU - Regg, Christian AU - Jarosz, Wojciech AU - Bernd Bickel AU - Jackson, Philip V AU - Matusik, Wojciech AU - Marschner, Steve AU - Groß, Markus S ID - 2110 IS - 4 JF - ACM Transactions on Graphics TI - Fabricating translucent materials using continuous pigment mixtures VL - 32 ER - TY - JOUR AB - 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. AU - Bermano, Amit H AU - Bruschweiler, Philipp AU - Grundhöfer, Anselm AU - Iwai, Daisuke AU - Bernd Bickel AU - Groß, Markus S ID - 2111 IS - 6 JF - ACM Transactions on Graphics TI - Augmenting physical avatars using projector-based illumination VL - 32 ER - TY - JOUR AB - 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. AU - Hildebrand, Kristian AU - Bernd Bickel AU - Alexa, Marc ID - 2109 IS - 6 JF - Computers and Graphics (Pergamon) TI - Orthogonal slicing for additive manufacturing VL - 37 ER - TY - JOUR AB - 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. AU - Skouras, Mélina AU - Thomaszewski, Bernhard AU - Coros, Stelian AU - Bernd Bickel AU - Groß, Markus S ID - 2107 IS - 4 JF - ACM Transactions on Graphics TI - Computational design of actuated deformable characters VL - 32 ER - TY - JOUR AB - 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. AU - Miguel, Eder AU - Tamstorf, Rasmus AU - Bradley, Derek J AU - Schvartzman, Sara C AU - Thomaszewski, Bernhard AU - Bernd Bickel AU - Matusik, Wojciech AU - Marschner, Steve AU - Otaduy, Miguel A ID - 2112 IS - 6 JF - ACM Transactions on Graphics TI - Modeling and estimation of internal friction in cloth VL - 32 ER - TY - JOUR AB - 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. AU - Dirksen, Sjoerd AU - Jan Maas AU - van Neerven, Jan M ID - 2117 JF - Electronic Journal of Probability TI - Poisson stochastic integration in Banach spaces VL - 18 ER - TY - JOUR AB - 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. AU - Rouiller, Olivier AU - Bernd Bickel AU - Kautz, Jan AU - Matusik, Wojciech AU - Alexa, Marc ID - 2113 IS - 6 JF - IEEE Computer Graphics and Applications TI - 3D printing spatially varying BRDFs VL - 33 ER - TY - JOUR AB - 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. AU - Bernd Bickel AU - Alexa, Marc ID - 2114 IS - 6 JF - IEEE Computer Graphics and Applications TI - Computational aspects of fabrication: Modeling, design and 3d printing VL - 33 ER - TY - JOUR AB - This paper continues the investigation of `Wasserstein-like' transportation distances for probability measures on discrete sets. We prove that the discrete transportation metrics on the d-dimensional discrete torus with mesh size 1/N converge, when N→∞, to the standard 2-Wasserstein distance W_2 on the continuous torus in the sense of Gromov-Hausdorff. This is the first convergence result for the recently developed discrete transportation metrics. The result shows the compatibility between these metrics and the well-established 2-Wasserstein metric. AU - Gigli, Nicola AU - Jan Maas ID - 2129 IS - 2 JF - SIAM Journal on Mathematical Analysis TI - Gromov-Hausdorff convergence of discrete transportation metrics VL - 45 ER - TY - JOUR AB - Recently it has been shown that pairs of atoms can form metastable bonds due to non-conservative forces induced by dissipation [Lemeshko&Weimer, Nature Comm. 4, 2230 (2013)]. Here we study the dynamics of interaction-induced coherent population trapping - the process responsible for the formation of dissipatively bound molecules. We derive the effective dissipative potentials induced between ultracold atoms by laser light, and study the time evolution of the scattering states. We demonstrate that binding occurs on short timescales of ~10 microseconds, even if the initial kinetic energy of the atoms significantly exceeds the depth of the dissipative potential. Dissipatively-bound molecules with preordained bond lengths and vibrational wavefunctions can be created and detected in current experiments with ultracold atoms. AU - Mikhail Lemeshko ID - 2139 IS - 17 JF - Frontiers Physics TI - Manipulating scattering of ultracold atoms with light-induced dissipation VL - 1 ER - TY - CONF AB - There is a trade-off between performance and correctness in implementing concurrent data structures. Better performance may be achieved at the expense of relaxing correctness, by redefining the semantics of data structures. We address such a redefinition of data structure semantics and present a systematic and formal framework for obtaining new data structures by quantitatively relaxing existing ones. We view a data structure as a sequential specification S containing all "legal" sequences over an alphabet of method calls. Relaxing the data structure corresponds to defining a distance from any sequence over the alphabet to the sequential specification: the k-relaxed sequential specification contains all sequences over the alphabet within distance k from the original specification. In contrast to other existing work, our relaxations are semantic (distance in terms of data structure states). As an instantiation of our framework, we present two simple yet generic relaxation schemes, called out-of-order and stuttering relaxation, along with several ways of computing distances. We show that the out-of-order relaxation, when further instantiated to stacks, queues, and priority queues, amounts to tolerating bounded out-of-order behavior, which cannot be captured by a purely syntactic relaxation (distance in terms of sequence manipulation, e.g. edit distance). We give concurrent implementations of relaxed data structures and demonstrate that bounded relaxations provide the means for trading correctness for performance in a controlled way. The relaxations are monotonic which further highlights the trade-off: increasing k increases the number of permitted sequences, which as we demonstrate can lead to better performance. Finally, since a relaxed stack or queue also implements a pool, we actually have new concurrent pool implementations that outperform the state-of-the-art ones. AU - Henzinger, Thomas A AU - Kirsch, Christoph AU - Payer, Hannes AU - Sezgin, Ali AU - Sokolova, Ana ID - 2181 SN - 978-1-4503-1832-7 T2 - Proceedings of the 40th annual ACM SIGPLAN-SIGACT symposium on Principles of programming language TI - Quantitative relaxation of concurrent data structures ER - TY - CONF AB - We propose a general framework for abstraction with respect to quantitative properties, such as worst-case execution time, or power consumption. Our framework provides a systematic way for counter-example guided abstraction refinement for quantitative properties. The salient aspect of the framework is that it allows anytime verification, that is, verification algorithms that can be stopped at any time (for example, due to exhaustion of memory), and report approximations that improve monotonically when the algorithms are given more time. We instantiate the framework with a number of quantitative abstractions and refinement schemes, which differ in terms of how much quantitative information they keep from the original system. We introduce both state-based and trace-based quantitative abstractions, and we describe conditions that define classes of quantitative properties for which the abstractions provide over-approximations. We give algorithms for evaluating the quantitative properties on the abstract systems. We present algorithms for counter-example based refinements for quantitative properties for both state-based and segment-based abstractions. We perform a case study on worst-case execution time of executables to evaluate the anytime verification aspect and the quantitative abstractions we proposed. AU - Cerny, Pavol AU - Henzinger, Thomas A AU - Radhakrishna, Arjun ID - 2182 T2 - Proceedings of the 40th annual ACM SIGPLAN-SIGACT symposium on Principles of programming language TI - Quantitative abstraction refinement ER - TY - CONF AB - A straight skeleton is a well-known geometric structure, and several algorithms exist to construct the straight skeleton for a given polygon or planar straight-line graph. In this paper, we ask the reverse question: Given the straight skeleton (in form of a planar straight-line graph, with some rays to infinity), can we reconstruct a planar straight-line graph for which this was the straight skeleton? We show how to reduce this problem to the problem of finding a line that intersects a set of convex polygons. We can find these convex polygons and all such lines in $O(nlog n)$ time in the Real RAM computer model, where $n$ denotes the number of edges of the input graph. We also explain how our approach can be used for recognizing Voronoi diagrams of points, thereby completing a partial solution provided by Ash and Bolker in 1985. AU - Biedl, Therese AU - Held, Martin AU - Huber, Stefan ID - 2209 TI - Recognizing straight skeletons and Voronoi diagrams and reconstructing their input ER - TY - JOUR AB - We introduce a new platform for quantum simulation of many-body systems based on nonspherical atoms or molecules with zero dipole moments but possessing a significant value of electric quadrupole moments. We consider a quadrupolar Fermi gas trapped in a 2D square optical lattice, and show that the peculiar symmetry and broad tunability of the quadrupole-quadrupole interaction results in a rich phase diagram encompassing unconventional BCS and charge density wave phases, and opens up a perspective to create a topological superfluid. Quadrupolar species, such as metastable alkaline-earth atoms and homonuclear molecules, are stable against chemical reactions and collapse and are readily available in experiment at high densities. AU - Bhongale, Satyan AU - Mathey, Ludwig AU - Zhao, Erhai AU - Yelin, Susanne AU - Lemeshko, Mikhail ID - 2204 IS - 15 JF - Physical Review Letters TI - Quantum phases of quadrupolar fermi gases in optical lattices VL - 110 ER - TY - JOUR AB - Magnetic impurities embedded in inert solids can exhibit long coherence times and interact with one another via their intrinsic anisotropic dipolar interaction. We argue that, as a consequence of these properties, disordered ensembles of magnetic impurities provide an effective platform for realizing a controllable, tunable version of the dipolar quantum spin glass seen in LiHoxY1-xF4. Specifically, we propose and analyze a system composed of dysprosium atoms embedded in solid helium. We describe the phase diagram of the system and discuss the realizability and detectability of the quantum spin glass and antiglass phases. AU - Mikhail Lemeshko AU - Yao, Norman Y AU - Gorshkov, Alexey V AU - Weimer, Hendrik AU - Bennett, Steven D AU - Momose, Takamasa AU - Gopalakrishnan, Sarang ID - 2206 IS - 1 JF - Physical Review B - Condensed Matter and Materials Physics TI - Controllable quantum spin glasses with magnetic impurities embedded in quantum solids VL - 88 ER -