@phdthesis{68, abstract = {The most common assumption made in statistical learning theory is the assumption of the independent and identically distributed (i.i.d.) data. While being very convenient mathematically, it is often very clearly violated in practice. This disparity between the machine learning theory and applications underlies a growing demand in the development of algorithms that learn from dependent data and theory that can provide generalization guarantees similar to the independent situations. This thesis is dedicated to two variants of dependencies that can arise in practice. One is a dependence on the level of samples in a single learning task. Another dependency type arises in the multi-task setting when the tasks are dependent on each other even though the data for them can be i.i.d. In both cases we model the data (samples or tasks) as stochastic processes and introduce new algorithms for both settings that take into account and exploit the resulting dependencies. We prove the theoretical guarantees on the performance of the introduced algorithms under different evaluation criteria and, in addition, we compliment the theoretical study by the empirical one, where we evaluate some of the algorithms on two real world datasets to highlight their practical applicability.}, author = {Zimin, Alexander}, issn = {2663-337X}, pages = {92}, publisher = {Institute of Science and Technology Austria}, title = {{Learning from dependent data}}, doi = {10.15479/AT:ISTA:TH1048}, year = {2018}, } @phdthesis{83, abstract = {A proof system is a protocol between a prover and a verifier over a common input in which an honest prover convinces the verifier of the validity of true statements. Motivated by the success of decentralized cryptocurrencies, exemplified by Bitcoin, the focus of this thesis will be on proof systems which found applications in some sustainable alternatives to Bitcoin, such as the Spacemint and Chia cryptocurrencies. In particular, we focus on proofs of space and proofs of sequential work. Proofs of space (PoSpace) were suggested as more ecological, economical, and egalitarian alternative to the energy-wasteful proof-of-work mining of Bitcoin. However, the state-of-the-art constructions of PoSpace are based on sophisticated graph pebbling lower bounds, and are therefore complex. Moreover, when these PoSpace are used in cryptocurrencies like Spacemint, miners can only start mining after ensuring that a commitment to their space is already added in a special transaction to the blockchain. Proofs of sequential work (PoSW) are proof systems in which a prover, upon receiving a statement x and a time parameter T, computes a proof which convinces the verifier that T time units had passed since x was received. Whereas Spacemint assumes synchrony to retain some interesting Bitcoin dynamics, Chia requires PoSW with unique proofs, i.e., PoSW in which it is hard to come up with more than one accepting proof for any true statement. In this thesis we construct simple and practically-efficient PoSpace and PoSW. When using our PoSpace in cryptocurrencies, miners can start mining on the fly, like in Bitcoin, and unlike current constructions of PoSW, which either achieve efficient verification of sequential work, or faster-than-recomputing verification of correctness of proofs, but not both at the same time, ours achieve the best of these two worlds.}, author = {Abusalah, Hamza M}, issn = {2663-337X}, pages = {59}, publisher = {Institute of Science and Technology Austria}, title = {{Proof systems for sustainable decentralized cryptocurrencies}}, doi = {10.15479/AT:ISTA:TH_1046}, year = {2018}, } @phdthesis{197, abstract = {Modern computer vision systems heavily rely on statistical machine learning models, which typically require large amounts of labeled data to be learned reliably. Moreover, very recently computer vision research widely adopted techniques for representation learning, which further increase the demand for labeled data. However, for many important practical problems there is relatively small amount of labeled data available, so it is problematic to leverage full potential of the representation learning methods. One way to overcome this obstacle is to invest substantial resources into producing large labelled datasets. Unfortunately, this can be prohibitively expensive in practice. In this thesis we focus on the alternative way of tackling the aforementioned issue. We concentrate on methods, which make use of weakly-labeled or even unlabeled data. Specifically, the first half of the thesis is dedicated to the semantic image segmentation task. We develop a technique, which achieves competitive segmentation performance and only requires annotations in a form of global image-level labels instead of dense segmentation masks. Subsequently, we present a new methodology, which further improves segmentation performance by leveraging tiny additional feedback from a human annotator. By using our methods practitioners can greatly reduce the amount of data annotation effort, which is required to learn modern image segmentation models. In the second half of the thesis we focus on methods for learning from unlabeled visual data. We study a family of autoregressive models for modeling structure of natural images and discuss potential applications of these models. Moreover, we conduct in-depth study of one of these applications, where we develop the state-of-the-art model for the probabilistic image colorization task.}, author = {Kolesnikov, Alexander}, issn = {2663-337X}, pages = {113}, publisher = {Institute of Science and Technology Austria}, title = {{Weakly-Supervised Segmentation and Unsupervised Modeling of Natural Images}}, doi = {10.15479/AT:ISTA:th_1021}, year = {2018}, } @article{6774, abstract = {A central problem of algebraic topology is to understand the homotopy groups πœ‹π‘‘(𝑋) of a topological space X. For the computational version of the problem, it is well known that there is no algorithm to decide whether the fundamental group πœ‹1(𝑋) of a given finite simplicial complex X is trivial. On the other hand, there are several algorithms that, given a finite simplicial complex X that is simply connected (i.e., with πœ‹1(𝑋) trivial), compute the higher homotopy group πœ‹π‘‘(𝑋) for any given 𝑑β‰₯2 . However, these algorithms come with a caveat: They compute the isomorphism type of πœ‹π‘‘(𝑋) , 𝑑β‰₯2 as an abstract finitely generated abelian group given by generators and relations, but they work with very implicit representations of the elements of πœ‹π‘‘(𝑋) . Converting elements of this abstract group into explicit geometric maps from the d-dimensional sphere 𝑆𝑑 to X has been one of the main unsolved problems in the emerging field of computational homotopy theory. Here we present an algorithm that, given a simply connected space X, computes πœ‹π‘‘(𝑋) and represents its elements as simplicial maps from a suitable triangulation of the d-sphere 𝑆𝑑 to X. For fixed d, the algorithm runs in time exponential in size(𝑋) , the number of simplices of X. Moreover, we prove that this is optimal: For every fixed 𝑑β‰₯2 , we construct a family of simply connected spaces X such that for any simplicial map representing a generator of πœ‹π‘‘(𝑋) , the size of the triangulation of 𝑆𝑑 on which the map is defined, is exponential in size(𝑋) .}, author = {FilakovskΓ½, Marek and Franek, Peter and Wagner, Uli and Zhechev, Stephan Y}, issn = {2367-1734}, journal = {Journal of Applied and Computational Topology}, number = {3-4}, pages = {177--231}, publisher = {Springer}, title = {{Computing simplicial representatives of homotopy group elements}}, doi = {10.1007/s41468-018-0021-5}, volume = {2}, year = {2018}, } @inproceedings{133, abstract = {Synchronous programs are easy to specify because the side effects of an operation are finished by the time the invocation of the operation returns to the caller. Asynchronous programs, on the other hand, are difficult to specify because there are side effects due to pending computation scheduled as a result of the invocation of an operation. They are also difficult to verify because of the large number of possible interleavings of concurrent computation threads. We present synchronization, a new proof rule that simplifies the verification of asynchronous programs by introducing the fiction, for proof purposes, that asynchronous operations complete synchronously. Synchronization summarizes an asynchronous computation as immediate atomic effect. Modular verification is enabled via pending asynchronous calls in atomic summaries, and a complementary proof rule that eliminates pending asynchronous calls when components and their specifications are composed. We evaluate synchronization in the context of a multi-layer refinement verification methodology on a collection of benchmark programs.}, author = {Kragl, Bernhard and Qadeer, Shaz and Henzinger, Thomas A}, issn = {18688969}, location = {Beijing, China}, publisher = {Schloss Dagstuhl - Leibniz-Zentrum fΓΌr Informatik}, title = {{Synchronizing the asynchronous}}, doi = {10.4230/LIPIcs.CONCUR.2018.21}, volume = {118}, year = {2018}, } @inproceedings{187, abstract = {Given a locally finite X βŠ† ℝd and a radius r β‰₯ 0, the k-fold cover of X and r consists of all points in ℝd that have k or more points of X within distance r. We consider two filtrations - one in scale obtained by fixing k and increasing r, and the other in depth obtained by fixing r and decreasing k - and we compute the persistence diagrams of both. While standard methods suffice for the filtration in scale, we need novel geometric and topological concepts for the filtration in depth. In particular, we introduce a rhomboid tiling in ℝd+1 whose horizontal integer slices are the order-k Delaunay mosaics of X, and construct a zigzag module from Delaunay mosaics that is isomorphic to the persistence module of the multi-covers. }, author = {Edelsbrunner, Herbert and Osang, Georg F}, location = {Budapest, Hungary}, publisher = {Schloss Dagstuhl - Leibniz-Zentrum fΓΌr Informatik}, title = {{The multi-cover persistence of Euclidean balls}}, doi = {10.4230/LIPIcs.SoCG.2018.34}, volume = {99}, year = {2018}, } @article{692, abstract = {We consider families of confocal conics and two pencils of Apollonian circles having the same foci. We will show that these families of curves generate trivial 3-webs and find the exact formulas describing them.}, author = {Akopyan, Arseniy}, journal = {Geometriae Dedicata}, number = {1}, pages = {55 -- 64}, publisher = {Springer}, title = {{3-Webs generated by confocal conics and circles}}, doi = {10.1007/s10711-017-0265-6}, volume = {194}, year = {2018}, } @article{77, abstract = {Holes confined in quantum dots have gained considerable interest in the past few years due to their potential as spin qubits. Here we demonstrate two-axis control of a spin 3/2 qubit in natural Ge. The qubit is formed in a hut wire double quantum dot device. The Pauli spin blockade principle allowed us to demonstrate electric dipole spin resonance by applying a radio frequency electric field to one of the electrodes defining the double quantum dot. Coherent hole spin oscillations with Rabi frequencies reaching 140 MHz are demonstrated and dephasing times of 130 ns are measured. The reported results emphasize the potential of Ge as a platform for fast and electrically tunable hole spin qubit devices.}, author = {Watzinger, Hannes and Kukucka, Josip and Vukusic, Lada and Gao, Fei and Wang, Ting and SchΓ€ffler, Friedrich and Zhang, Jian and Katsaros, Georgios}, journal = {Nature Communications}, number = {3902 }, publisher = {Nature Publishing Group}, title = {{A germanium hole spin qubit}}, doi = {10.1038/s41467-018-06418-4}, volume = {9}, year = {2018}, } @article{401, abstract = {The actomyosin cytoskeleton, a key stress-producing unit in epithelial cells, oscillates spontaneously in a wide variety of systems. Although much of the signal cascade regulating myosin activity has been characterized, the origin of such oscillatory behavior is still unclear. Here, we show that basal myosin II oscillation in Drosophila ovarian epithelium is not controlled by actomyosin cortical tension, but instead relies on a biochemical oscillator involving ROCK and myosin phosphatase. Key to this oscillation is a diffusive ROCK flow, linking junctional Rho1 to medial actomyosin cortex, and dynamically maintained by a self-activation loop reliant on ROCK kinase activity. In response to the resulting myosin II recruitment, myosin phosphatase is locally enriched and shuts off ROCK and myosin II signals. Coupling Drosophila genetics, live imaging, modeling, and optogenetics, we uncover an intrinsic biochemical oscillator at the core of myosin II regulatory network, shedding light on the spatio-temporal dynamics of force generation.}, author = {Qin, Xiang and Hannezo, Edouard B and Mangeat, Thomas and Liu, Chang and Majumder, Pralay and Liu, Jjiaying and Choesmel Cadamuro, Valerie and Mcdonald, Jocelyn and Liu, Yinyao and Yi, Bin and Wang, Xiaobo}, journal = {Nature Communications}, number = {1}, publisher = {Nature Publishing Group}, title = {{A biochemical network controlling basal myosin oscillation}}, doi = {10.1038/s41467-018-03574-5}, volume = {9}, year = {2018}, } @article{318, abstract = {The insect’s fat body combines metabolic and immunological functions. In this issue of Developmental Cell, Franz et al. (2018) show that in Drosophila, cells of the fat body are not static, but can actively β€œswim” toward sites of epithelial injury, where they physically clog the wound and locally secrete antimicrobial peptides.}, author = {Casano, Alessandra M and Sixt, Michael K}, journal = {Developmental Cell}, number = {4}, pages = {405 -- 406}, publisher = {Cell Press}, title = {{A fat lot of good for wound healing}}, doi = {10.1016/j.devcel.2018.02.009}, volume = {44}, year = {2018}, }