@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}, } @article{563, abstract = {In continuous populations with local migration, nearby pairs of individuals have on average more similar genotypes than geographically well separated pairs. A barrier to gene flow distorts this classical pattern of isolation by distance. Genetic similarity is decreased for sample pairs on different sides of the barrier and increased for pairs on the same side near the barrier. Here, we introduce an inference scheme that utilizes this signal to detect and estimate the strength of a linear barrier to gene flow in two-dimensions. We use a diffusion approximation to model the effects of a barrier on the geographical spread of ancestry backwards in time. This approach allows us to calculate the chance of recent coalescence and probability of identity by descent. We introduce an inference scheme that fits these theoretical results to the geographical covariance structure of bialleleic genetic markers. It can estimate the strength of the barrier as well as several demographic parameters. We investigate the power of our inference scheme to detect barriers by applying it to a wide range of simulated data. We also showcase an example application to a Antirrhinum majus (snapdragon) flower color hybrid zone, where we do not detect any signal of a strong genome wide barrier to gene flow.}, author = {Ringbauer, Harald and Kolesnikov, Alexander and Field, David and Barton, Nicholas H}, journal = {Genetics}, number = {3}, pages = {1231--1245}, publisher = {Genetics Society of America}, title = {{Estimating barriers to gene flow from distorted isolation-by-distance patterns}}, doi = {10.1534/genetics.117.300638}, volume = {208}, 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}, } @article{23, abstract = {The strong atomistic spin–orbit coupling of holes makes single-shot spin readout measurements difficult because it reduces the spin lifetimes. By integrating the charge sensor into a high bandwidth radio frequency reflectometry setup, we were able to demonstrate single-shot readout of a germanium quantum dot hole spin and measure the spin lifetime. Hole spin relaxation times of about 90 μs at 500 mT are reported, with a total readout visibility of about 70%. By analyzing separately the spin-to-charge conversion and charge readout fidelities, we have obtained insight into the processes limiting the visibilities of hole spins. The analyses suggest that high hole visibilities are feasible at realistic experimental conditions, underlying the potential of hole spins for the realization of viable qubit devices.}, author = {Vukušić, Lada and Kukucka, Josip and Watzinger, Hannes and Milem, Joshua M and Schäffler, Friedrich and Katsaros, Georgios}, issn = {1530-6984}, journal = {Nano Letters}, number = {11}, pages = {7141 -- 7145}, publisher = {American Chemical Society}, title = {{Single-shot readout of hole spins in Ge}}, doi = {10.1021/acs.nanolett.8b03217}, volume = {18}, year = {2018}, } @phdthesis{69, abstract = {A qubit, a unit of quantum information, is essentially any quantum mechanical two-level system which can be coherently controlled. Still, to be used for computation, it has to fulfill criteria. Qubits, regardless of the system in which they are realized, suffer from decoherence. This leads to loss of the information stored in the qubit. The upper bound of the time scale on which decoherence happens is set by the spin relaxation time. In this thesis I studied a two-level system consisting of a Zeeman-split hole spin confined in a quantum dot formed in a Ge hut wire. Such Ge hut wires have emerged as a promising material system for the realization of spin qubits, due to the combination of two significant properties: long spin coherence time as expected for group IV semiconductors due to the low hyperfine interaction and a strong valence band spin-orbit coupling. Here, I present how to fabricate quantum dot devices suitable for electrical transport measurements. Coupled quantum dot devices allowed the realization of a charge sensor, which is electrostatically and tunnel coupled to a quantum dot. By integrating the charge sensor into a radio-frequency reflectometry setup, I performed for the first time single-shot readout measurements of hole spins and extracted the hole spin relaxation times in Ge hut wires.}, author = {Vukušić, Lada}, issn = {2663-337X}, pages = {103}, publisher = {Institute of Science and Technology Austria}, title = {{Charge sensing and spin relaxation times of holes in Ge hut wires}}, doi = {10.15479/AT:ISTA:TH_1047}, year = {2018}, } @phdthesis{149, abstract = {The eigenvalue density of many large random matrices is well approximated by a deterministic measure, the self-consistent density of states. In the present work, we show this behaviour for several classes of random matrices. In fact, we establish that, in each of these classes, the self-consistent density of states approximates the eigenvalue density of the random matrix on all scales slightly above the typical eigenvalue spacing. For large classes of random matrices, the self-consistent density of states exhibits several universal features. We prove that, under suitable assumptions, random Gram matrices and Hermitian random matrices with decaying correlations have a 1/3-Hölder continuous self-consistent density of states ρ on R, which is analytic, where it is positive, and has either a square root edge or a cubic root cusp, where it vanishes. We, thus, extend the validity of the corresponding result for Wigner-type matrices from [4, 5, 7]. We show that ρ is determined as the inverse Stieltjes transform of the normalized trace of the unique solution m(z) to the Dyson equation −m(z) −1 = z − a + S[m(z)] on C N×N with the constraint Im m(z) ≥ 0. Here, z lies in the complex upper half-plane, a is a self-adjoint element of C N×N and S is a positivity-preserving operator on C N×N encoding the first two moments of the random matrix. In order to analyze a possible limit of ρ for N → ∞ and address some applications in free probability theory, we also consider the Dyson equation on infinite dimensional von Neumann algebras. We present two applications to random matrices. We first establish that, under certain assumptions, large random matrices with independent entries have a rotationally symmetric self-consistent density of states which is supported on a centered disk in C. Moreover, it is infinitely often differentiable apart from a jump on the boundary of this disk. Second, we show edge universality at all regular (not necessarily extreme) spectral edges for Hermitian random matrices with decaying correlations.}, author = {Alt, Johannes}, issn = {2663-337X}, pages = {456}, publisher = {Institute of Science and Technology Austria}, title = {{Dyson equation and eigenvalue statistics of random matrices}}, doi = {10.15479/AT:ISTA:TH_1040}, year = {2018}, } @article{566, abstract = {We consider large random matrices X with centered, independent entries which have comparable but not necessarily identical variances. Girko's circular law asserts that the spectrum is supported in a disk and in case of identical variances, the limiting density is uniform. In this special case, the local circular law by Bourgade et. al. [11,12] shows that the empirical density converges even locally on scales slightly above the typical eigenvalue spacing. In the general case, the limiting density is typically inhomogeneous and it is obtained via solving a system of deterministic equations. Our main result is the local inhomogeneous circular law in the bulk spectrum on the optimal scale for a general variance profile of the entries of X. }, author = {Alt, Johannes and Erdös, László and Krüger, Torben H}, journal = {Annals Applied Probability }, number = {1}, pages = {148--203}, publisher = {Institute of Mathematical Statistics}, title = {{Local inhomogeneous circular law}}, doi = {10.1214/17-AAP1302}, volume = {28}, year = {2018}, } @unpublished{6183, abstract = {We study the unique solution $m$ of the Dyson equation \[ -m(z)^{-1} = z - a + S[m(z)] \] on a von Neumann algebra $\mathcal{A}$ with the constraint $\mathrm{Im}\,m\geq 0$. Here, $z$ lies in the complex upper half-plane, $a$ is a self-adjoint element of $\mathcal{A}$ and $S$ is a positivity-preserving linear operator on $\mathcal{A}$. We show that $m$ is the Stieltjes transform of a compactly supported $\mathcal{A}$-valued measure on $\mathbb{R}$. Under suitable assumptions, we establish that this measure has a uniformly $1/3$-H\"{o}lder continuous density with respect to the Lebesgue measure, which is supported on finitely many intervals, called bands. In fact, the density is analytic inside the bands with a square-root growth at the edges and internal cubic root cusps whenever the gap between two bands vanishes. The shape of these singularities is universal and no other singularity may occur. We give a precise asymptotic description of $m$ near the singular points. These asymptotics generalize the analysis at the regular edges given in the companion paper on the Tracy-Widom universality for the edge eigenvalue statistics for correlated random matrices [arXiv:1804.07744] and they play a key role in the proof of the Pearcey universality at the cusp for Wigner-type matrices [arXiv:1809.03971,arXiv:1811.04055]. We also extend the finite dimensional band mass formula from [arXiv:1804.07744] to the von Neumann algebra setting by showing that the spectral mass of the bands is topologically rigid under deformations and we conclude that these masses are quantized in some important cases.}, author = {Alt, Johannes and Erdös, László and Krüger, Torben H}, booktitle = {arXiv}, title = {{The Dyson equation with linear self-energy: Spectral bands, edges and cusps}}, doi = {10.48550/arXiv.1804.07752}, year = {2018}, } @phdthesis{418, abstract = {The aim of this thesis was the development of new strategies for optical and optogenetic control of proliferative and pro-survival signaling, and characterizing them from the molecular mechanism up to cellular effects. These new light-based methods have unique features, such as red light as an activator, or the avoidance of gene delivery, which enable to overcome current limitations, such as light delivery to target tissues and feasibility as therapeutic approach. A special focus was placed on implementing these new light-based approaches in pancreatic β-cells, as β-cells are the key players in diabetes and especially their loss in number negatively affects disease progression. Currently no treatment options are available to compensate the lack of functional β-cells in diabetic patients. In a first approach, red-light-activated growth factor receptors, in particular receptor tyrosine kinases were engineered and characterized. Receptor activation with light allows spatio-temporal control compared to ligand-based activation, and especially red light exhibits deeper tissue penetration than other wavelengths of the visible spectrum. Red-light-activated receptor tyrosine kinases robustly activated major growth factor related signaling pathways with a high temporal resolution. Moreover, the remote activation of the proliferative MAPK/Erk pathway by red-light-activated receptor tyrosine kinases in a pancreatic β-cell line was also achieved, through one centimeter thick mouse tissue. Although red-light-activated receptor tyrosine kinases are particularly attractive for applications in animal models due to the deep tissue penetration of red light, a drawback, especially with regard to translation into humans, is the requirement of gene therapy. In a second approach an endogenous light-sensitive mechanism was identified and its potential to promote proliferative and pro-survival signals was explored, towards light-based tissue regeneration without the need for gene transfer. Blue-green light illumination was found to be sufficient for the activation of proliferation and survival promoting signaling pathways in primary pancreatic murine and human islets. Blue-green light also led to an increase in proliferation of primary islet cells, an effect which was shown to be mostly β-cell specific in human islets. Moreover, it was demonstrated that this approach of pancreatic β-cell expansion did not have any negative effect on the β-cell function, in particular on their insulin secretion capacity. In contrast, a trend for enhanced insulin secretion under high glucose conditions after illumination was detected. In order to unravel the detailed characteristics of this endogenous light-sensitive mechanism, the precise light requirements were determined. In addition, the expression of light sensing proteins, OPN3 and rhodopsin, was detected. The observed effects were found to be independent of handling effects such as temperature differences and cytochrome c oxidase dependent ATP increase, but they were found to be enhanced through the knockout of OPN3. The exact mechanism of how islets cells sense light and the identity of the photoreceptor remains unknown. Summarized two new light-based systems with unique features were established that enable the activation of proliferative and pro-survival signaling pathways. While red-light-activated receptor tyrosine kinases open a new avenue for optogenetics research, by allowing non-invasive control of signaling in vivo, the identified endogenous light-sensitive mechanism has the potential to be the basis of a gene therapy-free therapeutical approach for light-based β-cell expansion.}, author = {Gschaider-Reichhart, Eva}, issn = {2663-337X}, pages = {107}, publisher = {Institute of Science and Technology Austria}, title = {{Optical and optogenetic control of proliferation and survival }}, doi = {10.15479/AT:ISTA:th_913}, year = {2018}, } @article{616, abstract = {Social insects protect their colonies from infectious disease through collective defences that result in social immunity. In ants, workers first try to prevent infection of colony members. Here, we show that if this fails and a pathogen establishes an infection, ants employ an efficient multicomponent behaviour − "destructive disinfection" − to prevent further spread of disease through the colony. Ants specifically target infected pupae during the pathogen's non-contagious incubation period, relying on chemical 'sickness cues' emitted by pupae. They then remove the pupal cocoon, perforate its cuticle and administer antimicrobial poison, which enters the body and prevents pathogen replication from the inside out. Like the immune system of a body that specifically targets and eliminates infected cells, this social immunity measure sacrifices infected brood to stop the pathogen completing its lifecycle, thus protecting the rest of the colony. Hence, the same principles of disease defence apply at different levels of biological organisation.}, author = {Pull, Christopher and Ugelvig, Line V and Wiesenhofer, Florian and Grasse, Anna V and Tragust, Simon and Schmitt, Thomas and Brown, Mark and Cremer, Sylvia}, journal = {eLife}, publisher = {eLife Sciences Publications}, title = {{Destructive disinfection of infected brood prevents systemic disease spread in ant colonies}}, doi = {10.7554/eLife.32073}, volume = {7}, year = {2018}, } @article{87, abstract = {Using the geodesic distance on the n-dimensional sphere, we study the expected radius function of the Delaunay mosaic of a random set of points. Specifically, we consider the partition of the mosaic into intervals of the radius function and determine the expected number of intervals whose radii are less than or equal to a given threshold. We find that the expectations are essentially the same as for the Poisson–Delaunay mosaic in n-dimensional Euclidean space. Assuming the points are not contained in a hemisphere, the Delaunay mosaic is isomorphic to the boundary complex of the convex hull in Rn+1, so we also get the expected number of faces of a random inscribed polytope. As proved in Antonelli et al. [Adv. in Appl. Probab. 9–12 (1977–1980)], an orthant section of the n-sphere is isometric to the standard n-simplex equipped with the Fisher information metric. It follows that the latter space has similar stochastic properties as the n-dimensional Euclidean space. Our results are therefore relevant in information geometry and in population genetics.}, author = {Edelsbrunner, Herbert and Nikitenko, Anton}, journal = {Annals of Applied Probability}, number = {5}, pages = {3215 -- 3238}, publisher = {Institute of Mathematical Statistics}, title = {{Random inscribed polytopes have similar radius functions as Poisson-Delaunay mosaics}}, doi = {10.1214/18-AAP1389}, volume = {28}, year = {2018}, } @article{806, abstract = {Social insect colonies have evolved many collectively performed adaptations that reduce the impact of infectious disease and that are expected to maximize their fitness. This colony-level protection is termed social immunity, and it enhances the health and survival of the colony. In this review, we address how social immunity emerges from its mechanistic components to produce colony-level disease avoidance, resistance, and tolerance. To understand the evolutionary causes and consequences of social immunity, we highlight the need for studies that evaluate the effects of social immunity on colony fitness. We discuss the role that host life history and ecology have on predicted eco-evolutionary dynamics, which differ among the social insect lineages. Throughout the review, we highlight current gaps in our knowledge and promising avenues for future research, which we hope will bring us closer to an integrated understanding of socio-eco-evo-immunology.}, author = {Cremer, Sylvia and Pull, Christopher and Fürst, Matthias}, issn = {1545-4487}, journal = {Annual Review of Entomology}, pages = {105 -- 123}, publisher = {Annual Reviews}, title = {{Social immunity: Emergence and evolution of colony-level disease protection}}, doi = {10.1146/annurev-ento-020117-043110}, volume = {63}, year = {2018}, } @article{457, abstract = {Temperate bacteriophages integrate in bacterial genomes as prophages and represent an important source of genetic variation for bacterial evolution, frequently transmitting fitness-augmenting genes such as toxins responsible for virulence of major pathogens. However, only a fraction of bacteriophage infections are lysogenic and lead to prophage acquisition, whereas the majority are lytic and kill the infected bacteria. Unless able to discriminate lytic from lysogenic infections, mechanisms of immunity to bacteriophages are expected to act as a double-edged sword and increase the odds of survival at the cost of depriving bacteria of potentially beneficial prophages. We show that although restriction-modification systems as mechanisms of innate immunity prevent both lytic and lysogenic infections indiscriminately in individual bacteria, they increase the number of prophage-acquiring individuals at the population level. We find that this counterintuitive result is a consequence of phage-host population dynamics, in which restriction-modification systems delay infection onset until bacteria reach densities at which the probability of lysogeny increases. These results underscore the importance of population-level dynamics as a key factor modulating costs and benefits of immunity to temperate bacteriophages}, author = {Pleska, Maros and Lang, Moritz and Refardt, Dominik and Levin, Bruce and Guet, Calin C}, journal = {Nature Ecology and Evolution}, number = {2}, pages = {359 -- 366}, publisher = {Springer Nature}, title = {{Phage-host population dynamics promotes prophage acquisition in bacteria with innate immunity}}, doi = {10.1038/s41559-017-0424-z}, volume = {2}, year = {2018}, } @article{21563, abstract = {Quantum electrodynamics (QED) is one of the most precisely tested theories in the history of science, giving accurate predictions to a wide range of experimental observations. Recent experimental advances allow for the ability to probe physics on extremely short attosecond timescales, enabling ultrafast imaging of quantum dynamics. It is of great interest to extend our understanding of short-time quantum dynamics to QED, where the focus is typically on long-time observables such as 𝑆 matrices, decay rates, and cross sections. That said, solving the short-time dynamics of the QED Hamiltonian can lead to divergences, making it unclear how to arrive at physical predictions. We present an approach to regularize QED at short times and apply it to the problem of free-electron radiation into a medium, known as Cherenkov radiation. Our regularization method, which can be extended to other QED processes, is performed by subtracting the self-energy in free space from the self-energy calculated in the medium. Surprisingly, we find a number of previously unknown phenomena yielding corrections to the conventional Cherenkov effect that could be observed in current experiments. Specifically, the Cherenkov velocity threshold increases relative to the famous conventional theory. This modification to the conventional theory, which can be non-negligible in realistic scenarios, should result in the suppression of spontaneous emission in readily available experiments. Finally, we reveal a bifurcation process creating radiation into new Cherenkov angles, occurring in the strong-coupling regime, which would be realizable by considering the radiation dynamics of highly charged ions. Our results shed light on QED phenomena at short times and reveal surprising new physics in the Cherenkov effect.}, author = {Roques-Carmes, Charles and Rivera, Nicholas and Joannopoulos, John D. and Soljačić, Marin and Kaminer, Ido}, issn = {2160-3308}, journal = {Physical Review X}, number = {4}, publisher = {American Physical Society}, title = {{Nonperturbative quantum electrodynamics in the Cherenkov effect}}, doi = {10.1103/physrevx.8.041013}, volume = {8}, year = {2018}, } @article{21523, abstract = {In this paper, we report dispersion-engineered metasurfaces with distinct functionalities controlled by wavelength. Unlike previous approaches based on spatial multiplexing or vertical stacking of metasurfaces, we utilize a single phase profile with wavelength dependence encoded in the phase shifters’ dispersion. We designed and fabricated a multiwavelength achromatic metalens (MAM) with achromatic focusing for blue (B), green (G), yellow (Y), and red (R) light and two wavelength-controlled beam generators (WCBG): one focuses light with orbital angular momentum (OAM) states (l = 0,1,2) corresponding to three primary colors; the other produces ordinary focal spots (l = 0) for red and green light, while generating a vortex beam (l = 1) in the blue. A full color (RGB) hologram is also demonstrated in simulation. Our approach opens a path to applications ranging from near-eye displays and holography to compact multiwavelength beam generation.}, author = {Shi, Zhujun and Khorasaninejad, Mohammadreza and Huang, Yao-Wei and Roques-Carmes, Charles and Zhu, Alexander Y. and Chen, Wei Ting and Sanjeev, Vyshakh and Ding, Zhao-Wei and Tamagnone, Michele and Chaudhary, Kundan and Devlin, Robert C. and Qiu, Cheng-Wei and Capasso, Federico}, issn = {1530-6992}, journal = {Nano Letters}, keywords = {Metasurface, dispersion engineering, visible spectrum, titanium dioxide, orbital angular momentum states, achromatic metalens}, number = {4}, pages = {2420--2427}, publisher = {American Chemical Society }, title = {{Single-layer metasurface with controllable multiwavelength functions}}, doi = {10.1021/acs.nanolett.7b05458}, volume = {18}, year = {2018}, } @article{21545, abstract = {Free-electron radiation such as Cerenkov1, Smith–Purcell2 and transition radiation3,4 can be greatly affected by structured optical environments, as has been demonstrated in a variety of polaritonic5,6, photonic-crystal7 and metamaterial8,9,10 systems. However, the amount of radiation that can ultimately be extracted from free electrons near an arbitrary material structure has remained elusive. Here we derive a fundamental upper limit to the spontaneous photon emission and energy loss of free electrons, regardless of geometry, which illuminates the effects of material properties and electron velocities. We obtain experimental evidence for our theory with quantitative measurements of Smith–Purcell radiation. Our framework allows us to make two predictions. One is a new regime of radiation operation—at subwavelength separations, slower (non-relativistic) electrons can achieve stronger radiation than fast (relativistic) electrons. The other is a divergence of the emission probability in the limit of lossless materials. We further reveal that such divergences can be approached by coupling free electrons to photonic bound states in the continuum11,12,13. Our findings suggest that compact and efficient free-electron radiation sources from microwaves to the soft X-ray regime may be achievable without requiring ultrahigh accelerating voltages.}, author = {Yang, Yi and Massuda, Aviram and Roques-Carmes, Charles and Kooi, Steven E. and Christensen, Thomas and Johnson, Steven G. and Joannopoulos, John D. and Miller, Owen D. and Kaminer, Ido and Soljačić, Marin}, issn = {1745-2481}, journal = {Nature Physics}, pages = {894--899}, publisher = {Springer Nature}, title = {{Maximal spontaneous photon emission and energy loss from free electrons}}, doi = {10.1038/s41567-018-0180-2}, volume = {14}, year = {2018}, } @article{21533, abstract = {Recent advances in the fabrication of nanostructures and nanoscale features in metasurfaces offer new prospects for generating visible light emission from low-energy electrons. Here we present the experimental observation of visible light emission from low-energy free electrons interacting with nanoscale periodic surfaces through the Smith–Purcell (SP) effect. We demonstrate SP light emission from nanoscale gratings with periodicity as small as 50 nm, enabling the observation of tunable visible radiation from low-energy electrons (1.5 to 6 keV), an order of magnitude lower in energy than previously reported. We study the emission wavelength and intensity dependence on the grating pitch and electron energy, showing agreement between experiment and theory. Our results open the way to the production of SP-based nanophotonics integrated devices. Built inside electron microscopes, SP sources could enable the development of novel electron–optical correlated spectroscopic techniques and facilitate the observation of new quantum effects in light sources.}, author = {Massuda, Aviram and Roques-Carmes, Charles and Yang, Yujia and Kooi, Steven E. and Yang, Yi and Murdia, Chitraang and Berggren, Karl K. and Kaminer, Ido and Soljačić, Marin}, issn = {2330-4022}, journal = {ACS Photonics}, keywords = {light−matter interactions, periodic structures, nanophotonics, free-electron light sources}, number = {9}, pages = {3513--3518}, publisher = {American Chemical Society }, title = {{Smith–Purcell radiation from low-energy electrons}}, doi = {10.1021/acsphotonics.8b00743}, volume = {5}, year = {2018}, } @inproceedings{433, abstract = {A thrackle is a graph drawn in the plane so that every pair of its edges meet exactly once: either at a common end vertex or in a proper crossing. We prove that any thrackle of n vertices has at most 1.3984n edges. Quasi-thrackles are defined similarly, except that every pair of edges that do not share a vertex are allowed to cross an odd number of times. It is also shown that the maximum number of edges of a quasi-thrackle on n vertices is 3/2(n-1), and that this bound is best possible for infinitely many values of n.}, author = {Fulek, Radoslav and Pach, János}, location = {Boston, MA, United States}, pages = {160 -- 166}, publisher = {Springer}, title = {{Thrackles: An improved upper bound}}, doi = {10.1007/978-3-319-73915-1_14}, volume = {10692}, year = {2018}, } @article{536, abstract = {We consider the problem of consensus in the challenging classic model. In this model, the adversary is adaptive; it can choose which processors crash at any point during the course of the algorithm. Further, communication is via asynchronous message passing: there is no known upper bound on the time to send a message from one processor to another, and all messages and coin flips are seen by the adversary. We describe a new randomized consensus protocol with expected message complexity O(n2log2n) when fewer than n / 2 processes may fail by crashing. This is an almost-linear improvement over the best previously known protocol, and within logarithmic factors of a known Ω(n2) message lower bound. The protocol further ensures that no process sends more than O(nlog3n) messages in expectation, which is again within logarithmic factors of optimal. We also present a generalization of the algorithm to an arbitrary number of failures t, which uses expected O(nt+t2log2t) total messages. Our approach is to build a message-efficient, resilient mechanism for aggregating individual processor votes, implementing the message-passing equivalent of a weak shared coin. Roughly, in our protocol, a processor first announces its votes to small groups, then propagates them to increasingly larger groups as it generates more and more votes. To bound the number of messages that an individual process might have to send or receive, the protocol progressively increases the weight of generated votes. The main technical challenge is bounding the impact of votes that are still “in flight” (generated, but not fully propagated) on the final outcome of the shared coin, especially since such votes might have different weights. We achieve this by leveraging the structure of the algorithm, and a technical argument based on martingale concentration bounds. Overall, we show that it is possible to build an efficient message-passing implementation of a shared coin, and in the process (almost-optimally) solve the classic consensus problem in the asynchronous message-passing model.}, author = {Alistarh, Dan-Adrian and Aspnes, James and King, Valerie and Saia, Jared}, issn = {0178-2770}, journal = {Distributed Computing}, number = {6}, pages = {489--501}, publisher = {Springer}, title = {{Communication-efficient randomized consensus}}, doi = {10.1007/s00446-017-0315-1}, volume = {31}, year = {2018}, } @inproceedings{85, abstract = {Concurrent accesses to shared data structures must be synchronized to avoid data races. Coarse-grained synchronization, which locks the entire data structure, is easy to implement but does not scale. Fine-grained synchronization can scale well, but can be hard to reason about. Hand-over-hand locking, in which operations are pipelined as they traverse the data structure, combines fine-grained synchronization with ease of use. However, the traditional implementation suffers from inherent overheads. This paper introduces snapshot-based synchronization (SBS), a novel hand-over-hand locking mechanism. SBS decouples the synchronization state from the data, significantly improving cache utilization. Further, it relies on guarantees provided by pipelining to minimize synchronization that requires cross-thread communication. Snapshot-based synchronization thus scales much better than traditional hand-over-hand locking, while maintaining the same ease of use.}, author = {Gilad, Eran and Brown, Trevor A and Oskin, Mark and Etsion, Yoav}, issn = {0302-9743}, location = {Turin, Italy}, pages = {465 -- 479}, publisher = {Springer}, title = {{Snapshot based synchronization: A fast replacement for Hand-over-Hand locking}}, doi = {10.1007/978-3-319-96983-1_33}, volume = {11014}, year = {2018}, }