@article{2034, abstract = {Opacity is a generic security property, that has been defined on (non-probabilistic) transition systems and later on Markov chains with labels. For a secret predicate, given as a subset of runs, and a function describing the view of an external observer, the value of interest for opacity is a measure of the set of runs disclosing the secret. We extend this definition to the richer framework of Markov decision processes, where non-deterministicchoice is combined with probabilistic transitions, and we study related decidability problems with partial or complete observation hypotheses for the schedulers. We prove that all questions are decidable with complete observation and ω-regular secrets. With partial observation, we prove that all quantitative questions are undecidable but the question whether a system is almost surely non-opaquebecomes decidable for a restricted class of ω-regular secrets, as well as for all ω-regular secrets under finite-memory schedulers.}, author = {Bérard, Béatrice and Chatterjee, Krishnendu and Sznajder, Nathalie}, journal = { Information Processing Letters}, number = {1}, pages = {52 -- 59}, publisher = {Elsevier}, title = {{Probabilistic opacity for Markov decision processes}}, doi = {10.1016/j.ipl.2014.09.001}, volume = {115}, year = {2015}, } @article{2035, abstract = {Considering a continuous self-map and the induced endomorphism on homology, we study the eigenvalues and eigenspaces of the latter. Taking a filtration of representations, we define the persistence of the eigenspaces, effectively introducing a hierarchical organization of the map. The algorithm that computes this information for a finite sample is proved to be stable, and to give the correct answer for a sufficiently dense sample. Results computed with an implementation of the algorithm provide evidence of its practical utility. }, author = {Edelsbrunner, Herbert and Jablonski, Grzegorz and Mrozek, Marian}, journal = {Foundations of Computational Mathematics}, number = {5}, pages = {1213 -- 1244}, publisher = {Springer}, title = {{The persistent homology of a self-map}}, doi = {10.1007/s10208-014-9223-y}, volume = {15}, year = {2015}, } @inproceedings{10748, abstract = {The study of fluxoid states and fluxoid dynamics in mesoscopic iron-based superconducting rings is valuable for characterizing the basic properties of the superconductor, and may also provide important insight into the superconducting paring symmetry. We report the fabrications of micron-sized rings and disks from thin films of Fe(Se, Te) grown by molecular beam epitaxy. In order to study fluxoid states in rings we developed a custom-tailored version of magnetic force microscopy (MFM). This technique has a number of qualitative advantages for working with mesoscopic superconducting samples in comparison to the conventional MFM and other imaging techniques. We observed metastable fluxoid states in rings of different sizes. Thermally activated fluxoid dynamics of these states was studied and modeled. In addition, we found different regimes of interaction between Fe(Se, Te) ring and MFM tip which are explained. Possibilities of the existence of exotic vortex states and proposals for experiments to test the symmetry of the superconducting order parameter in iron based superconductors are analyzed.}, author = {Polshyn, Hryhoriy and Zhang, Can and Naibert, Tyler and Eckstein, James and Budakian, Raffi}, booktitle = {APS March Meeting 2015}, issn = {0003-0503}, location = {San Antonio, TX, United States}, number = {1}, publisher = {American Physical Society}, title = {{Study of Fe (Se, Te) micron-sized rings by magnetic force microscopy}}, volume = {60}, year = {2015}, } @article{10794, abstract = {Mathematical models are of fundamental importance in the understanding of complex population dynamics. For instance, they can be used to predict the population evolution starting from different initial conditions or to test how a system responds to external perturbations. For this analysis to be meaningful in real applications, however, it is of paramount importance to choose an appropriate model structure and to infer the model parameters from measured data. While many parameter inference methods are available for models based on deterministic ordinary differential equations, the same does not hold for more detailed individual-based models. Here we consider, in particular, stochastic models in which the time evolution of the species abundances is described by a continuous-time Markov chain. These models are governed by a master equation that is typically difficult to solve. Consequently, traditional inference methods that rely on iterative evaluation of parameter likelihoods are computationally intractable. The aim of this paper is to present recent advances in parameter inference for continuous-time Markov chain models, based on a moment closure approximation of the parameter likelihood, and to investigate how these results can help in understanding, and ultimately controlling, complex systems in ecology. Specifically, we illustrate through an agricultural pest case study how parameters of a stochastic individual-based model can be identified from measured data and how the resulting model can be used to solve an optimal control problem in a stochastic setting. In particular, we show how the matter of determining the optimal combination of two different pest control methods can be formulated as a chance constrained optimization problem where the control action is modeled as a state reset, leading to a hybrid system formulation.}, author = {Parise, Francesca and Lygeros, John and Ruess, Jakob}, issn = {2296-665X}, journal = {Frontiers in Environmental Science}, keywords = {General Environmental Science}, publisher = {Frontiers}, title = {{Bayesian inference for stochastic individual-based models of ecological systems: a pest control simulation study}}, doi = {10.3389/fenvs.2015.00042}, volume = {3}, year = {2015}, } @inproceedings{10796, abstract = {We consider concurrent mean-payoff games, a very well-studied class of two-player (player 1 vs player 2) zero-sum games on finite-state graphs where every transition is assigned a reward between 0 and 1, and the payoff function is the long-run average of the rewards. The value is the maximal expected payoff that player 1 can guarantee against all strategies of player 2. We consider the computation of the set of states with value 1 under finite-memory strategies for player 1, and our main results for the problem are as follows: (1) we present a polynomial-time algorithm; (2) we show that whenever there is a finite-memory strategy, there is a stationary strategy that does not need memory at all; and (3) we present an optimal bound (which is double exponential) on the patience of stationary strategies (where patience of a distribution is the inverse of the smallest positive probability and represents a complexity measure of a stationary strategy).}, author = {Chatterjee, Krishnendu and Ibsen-Jensen, Rasmus}, booktitle = {Proceedings of the Twenty-Sixth Annual ACM-SIAM Symposium on Discrete Algorithms}, isbn = {978-161197374-7}, location = {San Diego, CA, United States}, number = {1}, pages = {1018--1029}, publisher = {SIAM}, title = {{The value 1 problem under finite-memory strategies for concurrent mean-payoff games}}, doi = {10.1137/1.9781611973730.69}, volume = {2015}, year = {2015}, } @article{333, abstract = {We present a hybrid intercalation battery based on a sodium/magnesium (Na/Mg) dual salt electrolyte, metallic magnesium anode, and a cathode based on FeS2 nanocrystals (NCs). Compared to lithium or sodium, metallic magnesium anode is safer due to dendrite-free electroplating and offers extremely high volumetric (3833 mAh cm-3) and gravimetric capacities (2205 mAh g-1). Na-ion cathodes, FeS2 NCs in the present study, may serve as attractive alternatives to Mg-ion cathodes due to the higher voltage of operation and fast, highly reversible insertion of Na-ions. In this proof-of-concept study, electrochemical cycling of the Na/Mg hybrid battery was characterized by high rate capability, high Coulombic efficiency of 99.8%, and high energy density. In particular, with an average discharge voltage of ∼1.1 V and a cathodic capacity of 189 mAh g-1 at a current of 200 mA g-1, the presented Mg/FeS2 hybrid battery delivers energy densities of up to 210 Wh kg-1, comparable to commercial Li-ion batteries and approximately twice as high as state-of-the-art Mg-ion batteries based on Mo6S8 cathodes. Further significant gains in the energy density are expected from the development of Na/Mg electrolytes with a broader electrochemical stability window. Fully based on Earth-abundant elements, hybrid Na-Mg batteries are highly promising for large-scale stationary energy storage. }, author = {Walter, Marc and Kravchyk, Kostiantyn and Ibáñez, Maria and Kovalenko, Maksym}, journal = {Chemistry of Materials}, number = {21}, pages = {7452 -- 7458}, publisher = {ACS}, title = {{Efficient and inexpensive sodium magnesium hybrid battery}}, doi = {10.1021/acs.chemmater.5b03531}, volume = {27}, year = {2015}, } @article{334, abstract = {A cation exchange-based route was used to produce Cu2ZnSnS4 (CZTS)-Ag2S nanoparticles with controlled composition. We report a detailed study of the formation of such CZTS-Ag2S nanoheterostructures and of their photocatalytic properties. When compared to pure CZTS, the use of nanoscale p-n heterostructures as light absorbers for photocatalytic water splitting provides superior photocurrents. We associate this experimental fact to a higher separation efficiency of the photogenerated electron-hole pairs. We believe this and other type-II nanoheterostructures will open the door to the use of CZTS, with excellent light absorption properties and made of abundant and environmental friendly elements, to the field of photocatalysis.}, author = {Yu, Xuelian and Liu, Jingjing and Genç, Aziz and Ibáñez, Maria and Luo, Zhishan and Shavel, Alexey and Arbiol, Jordi and Zhang, Guangjin and Zhang, Yihe and Cabot, Andreu}, journal = {Langmuir}, number = {38}, pages = {10555 -- 10561}, publisher = {American Chemical Society}, title = {{Cu2ZnSnS4–Ag2S Nanoscale p–n heterostructures as sensitizers for photoelectrochemical water splitting}}, doi = {10.1021/acs.langmuir.5b02490}, volume = {31}, year = {2015}, } @article{354, abstract = {A simple and effective method to introduce precise amounts of doping in nanomaterials produced from the bottom-up assembly of colloidal nanoparticles (NPs) is described. The procedure takes advantage of a ligand displacement step to incorporate controlled concentrations of halide ions while removing carboxylic acids from the NP surface. Upon consolidation of the NPs into dense pellets, halide ions diffuse within the crystal structure, doping the anion sublattice and achieving n-type electrical doping. Through the characterization of the thermoelectric properties of nanocrystalline PbS, we demonstrate this strategy to be effective to control charge transport properties on thermoelectric nanomaterials assembled from NP building blocks. This approach is subsequently extended to PbTexSe1-x@PbS core-shell NPs, where a significant enhancement of the thermoelectric figure of merit is achieved. }, author = {Ibáñez, Maria and Korkosz, Rachel and Luo, Zhishan and Riba, Pau and Cadavid, Doris and Ortega, Silvia and Cabot, Andreu and Kanatzidis, Mercouri}, journal = {Journal of the American Chemical Society}, number = {12}, pages = {4046 -- 4049}, publisher = {American Chemical Society}, title = {{Electron doping in bottom up engineered thermoelectric nanomaterials through HCl mediated ligand displacement}}, doi = {10.1021/jacs.5b00091}, volume = {137}, year = {2015}, } @article{361, abstract = {We report the synthesis and photocatalytic and magnetic characterization of colloidal nanoheterostructures formed by combining a Pt-based magnetic metal alloy (PtCo, PtNi) with Cu2ZnSnS4 (CZTS). While CZTS is one of the main candidate materials for solar energy conversion, the introduction of a Pt-based alloy on its surface strongly influences its chemical and electronic properties, ultimately determining its functionality. In this regard, up to a 15-fold increase of the photocatalytic hydrogen evolution activity was obtained with CZTS–PtCo when compared with CZTS. Furthermore, two times higher hydrogen evolution rates were obtained for CZTS–PtCo when compared with CZTS–Pt, in spite of the lower precious metal loading of the former. Besides, the magnetic properties of the PtCo nanoparticles attached to the CZTS nanocrystals were retained in the heterostructures, which could facilitate catalyst purification and recovery for its posterior recycling and/or reutilization.}, author = {Yu, Xuelian and An, Xiaoqiang and Genç, Aziz and Ibáñez, Maria and Arbiol, Jordi and Zhang, Yihe and Cabot, Andreu}, journal = {Journal of Physical Chemistry C}, number = {38}, pages = {21882 -- 21888}, publisher = {American Chemical Society}, title = {{Cu2ZnSnS4–PtM (M = Co, Ni) nanoheterostructures for photocatalytic hydrogen evolution}}, doi = {10.1021/acs.jpcc.5b06199}, volume = {119}, year = {2015}, } @article{362, abstract = {Monodisperse Pd2Sn nanorods with tuned size and aspect ratio were prepared by co-reduction of metal salts in the presence of trioctylphosphine, amine, and chloride ions. Asymmetric Pd2Sn nanostructures were achieved by the selective desorption of a surfactant mediated by chlorine ions. A preliminary evaluation of the geometry influence on catalytic properties evidenced Pd2Sn nanorods to have improved catalytic performance. In view of these results, Pd2Sn nanorods were also evaluated for water denitration. }, author = {Lu, Zhishan and Ibáñez, Maria and Antolín, Ana and Genç, Aziz and Shavel, Alexey and Contreras, Sandra and Medina, Francesc and Arbiol, Jordi and Cabot, Andreu}, issn = {1520-5827}, journal = {Langmuir}, number = {13}, pages = {3952 -- 3957}, publisher = {American Chemical Society}, title = {{Size and aspect ratio control of Pd inf 2 inf Sn nanorods and their water denitration properties}}, doi = {10.1021/la504906q}, volume = {31}, year = {2015}, } @article{388, abstract = {We use ultrafast optical spectroscopy to observe binding of charged single-particle excitations (SE) in the magnetically frustrated Mott insulator Na2IrO3. Above the antiferromagnetic ordering temperature (TN) the system response is due to both Hubbard excitons (HE) and their constituent unpaired SE. The SE response becomes strongly suppressed immediately below TN. We argue that this increase in binding energy is due to a unique interplay between the frustrated Kitaev and the weak Heisenberg-type ordering term in the Hamiltonian, mediating an effective interaction between the spin-singlet SE. This interaction grows with distance causing the SE to become trapped in the HE, similar to quark confinement inside hadrons. This binding of charged particles, induced by magnetic ordering, is a result of a confinement-deconfinement transition of spin excitations. This observation provides evidence for spin liquid type behavior which is expected in Na2IrO3.}, author = {Alpichshev, Zhanybek and Mahmood, Fahad and Cao, Gang and Gedik, Nuh}, journal = {Physical Review Letters}, number = {1}, publisher = {American Physical Society}, title = {{Confinement deconfinement transition as an indication of spin liquid type behavior in Na2IrO3}}, doi = {10.1103/PhysRevLett.114.017203}, volume = {114}, year = {2015}, } @article{1728, abstract = {In the vertebrate neural tube, the morphogen Sonic Hedgehog (Shh) establishes a characteristic pattern of gene expression. Here we quantify the Shh gradient in the developing mouse neural tube and show that while the amplitude of the gradient increases over time, the activity of the pathway transcriptional effectors, Gli proteins, initially increases but later decreases. Computational analysis of the pathway suggests three mechanisms that could contribute to this adaptation: transcriptional upregulation of the inhibitory receptor Ptch1, transcriptional downregulation of Gli and the differential stability of active and inactive Gli isoforms. Consistent with this, Gli2 protein expression is downregulated during neural tube patterning and adaptation continues when the pathway is stimulated downstream of Ptch1. Moreover, the Shh-induced upregulation of Gli2 transcription prevents Gli activity levels from adapting in a different cell type, NIH3T3 fibroblasts, despite the upregulation of Ptch1. Multiple mechanisms therefore contribute to the intracellular dynamics of Shh signalling, resulting in different signalling dynamics in different cell types.}, author = {Cohen, Michael and Kicheva, Anna and Ribeiro, Ana and Blassberg, Robert and Page, Karen and Barnes, Chris and Briscoe, James}, issn = {2041-1723}, journal = {Nature Communications}, publisher = {Springer Nature}, title = {{Ptch1 and Gli regulate Shh signalling dynamics via multiple mechanisms}}, doi = {10.1038/ncomms7709}, volume = {6}, year = {2015}, } @inproceedings{1729, abstract = {We present a computer-aided programming approach to concurrency. The approach allows programmers to program assuming a friendly, non-preemptive scheduler, and our synthesis procedure inserts synchronization to ensure that the final program works even with a preemptive scheduler. The correctness specification is implicit, inferred from the non-preemptive behavior. Let us consider sequences of calls that the program makes to an external interface. The specification requires that any such sequence produced under a preemptive scheduler should be included in the set of such sequences produced under a non-preemptive scheduler. The solution is based on a finitary abstraction, an algorithm for bounded language inclusion modulo an independence relation, and rules for inserting synchronization. We apply the approach to device-driver programming, where the driver threads call the software interface of the device and the API provided by the operating system. Our experiments demonstrate that our synthesis method is precise and efficient, and, since it does not require explicit specifications, is more practical than the conventional approach based on user-provided assertions.}, author = {Cerny, Pavol and Clarke, Edmund and Henzinger, Thomas A and Radhakrishna, Arjun and Ryzhyk, Leonid and Samanta, Roopsha and Tarrach, Thorsten}, location = {San Francisco, CA, United States}, pages = {180 -- 197}, publisher = {Springer}, title = {{From non-preemptive to preemptive scheduling using synchronization synthesis}}, doi = {10.1007/978-3-319-21668-3_11}, volume = {9207}, year = {2015}, } @article{1730, abstract = {How much cutting is needed to simplify the topology of a surface? We provide bounds for several instances of this question, for the minimum length of topologically non-trivial closed curves, pants decompositions, and cut graphs with a given combinatorial map in triangulated combinatorial surfaces (or their dual cross-metric counterpart). Our work builds upon Riemannian systolic inequalities, which bound the minimum length of non-trivial closed curves in terms of the genus and the area of the surface. We first describe a systematic way to translate Riemannian systolic inequalities to a discrete setting, and vice-versa. This implies a conjecture by Przytycka and Przytycki (Graph structure theory. Contemporary Mathematics, vol. 147, 1993), a number of new systolic inequalities in the discrete setting, and the fact that a theorem of Hutchinson on the edge-width of triangulated surfaces and Gromov’s systolic inequality for surfaces are essentially equivalent. We also discuss how these proofs generalize to higher dimensions. Then we focus on topological decompositions of surfaces. Relying on ideas of Buser, we prove the existence of pants decompositions of length O(g^(3/2)n^(1/2)) for any triangulated combinatorial surface of genus g with n triangles, and describe an O(gn)-time algorithm to compute such a decomposition. Finally, we consider the problem of embedding a cut graph (or more generally a cellular graph) with a given combinatorial map on a given surface. Using random triangulations, we prove (essentially) that, for any choice of a combinatorial map, there are some surfaces on which any cellular embedding with that combinatorial map has length superlinear in the number of triangles of the triangulated combinatorial surface. There is also a similar result for graphs embedded on polyhedral triangulations.}, author = {Colin De Verdière, Éric and Hubard, Alfredo and De Mesmay, Arnaud N}, journal = {Discrete & Computational Geometry}, number = {3}, pages = {587 -- 620}, publisher = {Springer}, title = {{Discrete systolic inequalities and decompositions of triangulated surfaces}}, doi = {10.1007/s00454-015-9679-9}, volume = {53}, year = {2015}, } @article{1731, abstract = {We consider two-player zero-sum games on graphs. These games can be classified on the basis of the information of the players and on the mode of interaction between them. On the basis of information the classification is as follows: (a) partial-observation (both players have partial view of the game); (b) one-sided complete-observation (one player has complete observation); and (c) complete-observation (both players have complete view of the game). On the basis of mode of interaction we have the following classification: (a) concurrent (both players interact simultaneously); and (b) turn-based (both players interact in turn). The two sources of randomness in these games are randomness in transition function and randomness in strategies. In general, randomized strategies are more powerful than deterministic strategies, and randomness in transitions gives more general classes of games. In this work we present a complete characterization for the classes of games where randomness is not helpful in: (a) the transition function probabilistic transition can be simulated by deterministic transition); and (b) strategies (pure strategies are as powerful as randomized strategies). As consequence of our characterization we obtain new undecidability results for these games. }, author = {Chatterjee, Krishnendu and Doyen, Laurent and Gimbert, Hugo and Henzinger, Thomas A}, journal = {Information and Computation}, number = {12}, pages = {3 -- 16}, publisher = {Elsevier}, title = {{Randomness for free}}, doi = {10.1016/j.ic.2015.06.003}, volume = {245}, year = {2015}, } @inproceedings{1732, abstract = {We consider partially observable Markov decision processes (POMDPs), that are a standard framework for robotics applications to model uncertainties present in the real world, with temporal logic specifications. All temporal logic specifications in linear-time temporal logic (LTL) can be expressed as parity objectives. We study the qualitative analysis problem for POMDPs with parity objectives that asks whether there is a controller (policy) to ensure that the objective holds with probability 1 (almost-surely). While the qualitative analysis of POMDPs with parity objectives is undecidable, recent results show that when restricted to finite-memory policies the problem is EXPTIME-complete. While the problem is intractable in theory, we present a practical approach to solve the qualitative analysis problem. We designed several heuristics to deal with the exponential complexity, and have used our implementation on a number of well-known POMDP examples for robotics applications. Our results provide the first practical approach to solve the qualitative analysis of robot motion planning with LTL properties in the presence of uncertainty.}, author = {Chatterjee, Krishnendu and Chmelik, Martin and Gupta, Raghav and Kanodia, Ayush}, location = {Seattle, WA, United States}, pages = {325 -- 330}, publisher = {IEEE}, title = {{Qualitative analysis of POMDPs with temporal logic specifications for robotics applications}}, doi = {10.1109/ICRA.2015.7139019}, year = {2015}, } @article{1734, abstract = {Facial appearance capture is now firmly established within academic research and used extensively across various application domains, perhaps most prominently in the entertainment industry through the design of virtual characters in video games and films. While significant progress has occurred over the last two decades, no single survey currently exists that discusses the similarities, differences, and practical considerations of the available appearance capture techniques as applied to human faces. A central difficulty of facial appearance capture is the way light interacts with skin-which has a complex multi-layered structure-and the interactions that occur below the skin surface can, by definition, only be observed indirectly. In this report, we distinguish between two broad strategies for dealing with this complexity. "Image-based methods" try to exhaustively capture the exact face appearance under different lighting and viewing conditions, and then render the face through weighted image combinations. "Parametric methods" instead fit the captured reflectance data to some parametric appearance model used during rendering, allowing for a more lightweight and flexible representation but at the cost of potentially increased rendering complexity or inexact reproduction. The goal of this report is to provide an overview that can guide practitioners and researchers in assessing the tradeoffs between current approaches and identifying directions for future advances in facial appearance capture.}, author = {Klehm, Oliver and Rousselle, Fabrice and Papas, Marios and Bradley, Derek and Hery, Christophe and Bickel, Bernd and Jarosz, Wojciech and Beeler, Thabo}, journal = {Computer Graphics Forum}, number = {2}, pages = {709 -- 733}, publisher = {Wiley-Blackwell}, title = {{Recent advances in facial appearance capture}}, doi = {10.1111/cgf.12594}, volume = {34}, year = {2015}, } @article{1735, abstract = {This work presents a method for efficiently simplifying the pressure projection step in a liquid simulation. We first devise a straightforward dimension reduction technique that dramatically reduces the cost of solving the pressure projection. Next, we introduce a novel change of basis that satisfies free-surface boundary conditions exactly, regardless of the accuracy of the pressure solve. When combined, these ideas greatly reduce the computational complexity of the pressure solve without compromising free surface boundary conditions at the highest level of detail. Our techniques are easy to parallelize, and they effectively eliminate the computational bottleneck for large liquid simulations.}, author = {Ando, Ryoichi and Thürey, Nils and Wojtan, Christopher J}, journal = {Computer Graphics Forum}, number = {2}, pages = {473 -- 480}, publisher = {Wiley}, title = {{A dimension-reduced pressure solver for liquid simulations}}, doi = {10.1111/cgf.12576}, volume = {34}, year = {2015}, } @article{17615, abstract = {Graham et al. have detected a 5.2 yr periodic optical variability of the quasar PG 1302-102 at redshift z = 0.3, which they interpret as the redshifted orbital period (1 + z)tbin of a putative supermassive black hole binary (SMBHB). Here, we consider the implications of a 3–8 times shorter orbital period, suggested by hydrodynamical simulations of circumbinary discs (CBDs) with nearly equal-mass SMBHBs (q ≡ M2/M1 ≳ 0.3). With the corresponding 2–4 times tighter binary separation, PG 1302 would be undergoing gravitational wave dominated inspiral, and serve as a proof that the BHs can be fuelled and produce bright emission even in this late stage of the merger. The expected fraction of binaries with the shorter tbin, among bright quasars, would be reduced by one to two orders of magnitude, compared to the 5.2 yr period, in better agreement with the rarity of candidates reported by Graham et al. Finally, shorter periods would imply higher binary speeds, possibly imprinting periodicity on the light curves from relativistic beaming, as well as measurable relativistic effects on the Fe K α line. The CBD model predicts additional periodic variability on time-scales of tbin and ≈0.5tbin, as well as periodic variation of broad line widths and offsets relative to the narrow lines, which are consistent with the observations. Future observations will be able to test these predictions and hence the binary+CBD hypothesis for PG 1302.}, author = {D'Orazio, D. J. and Haiman, Zoltán and Duffell, P. and Farris, B. D. and MacFadyen, A. I.}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {3}, pages = {2540--2545}, publisher = {Oxford University Press}, title = {{A reduced orbital period for the supermassive black hole binary candidate in the quasar PG 1302-102?}}, doi = {10.1093/mnras/stv1457}, volume = {452}, year = {2015}, } @article{17622, abstract = {Graham et al. discovered a supermassive black hole binary (SMBHB) candidate and identified the detected 5.2 yr period of the optical variability as the orbital period of the binary. Hydrodynamical simulations predict multiple periodic components for the variability of SMBHBs, thus raising the possibility that the true period of the binary is different from 5.2 yr. We analyse the periodogram of PG1302 and find no compelling evidence for additional peaks. We also point out that, despite the 5.2 yr peak being significant if a single source is considered, further analysis is required to account for the fact that PG1302 was selected among a large sample of 247 000 quasars. We derive upper limits on any additional periodic modulations in the available data, by modelling the light curve as the sum of stochastic noise and the known 5.2 yr periodic component, and injecting additional sinusoidal signals. We find that, with the current data, we would be able to detect with high significance (false alarm probability <1 per cent) secondary periodic terms, with periods in the range predicted by the simulations, if the amplitude of the variability was at least ∼0.06 mag (compared to 0.14 mag for the main sinusoid). A three-year follow-up monitoring campaign with weekly observations can increase the sensitivity for detecting secondary peaks by ≈50 per cent, and would allow a more robust test of predictions from hydrodynamical simulations.}, author = {Charisi, M. and Bartos, I. and Haiman, Zoltán and Price-Whelan, A. M. and Márka, S.}, issn = {1745-3933}, journal = {Monthly Notices of the Royal Astronomical Society: Letters}, number = {1}, pages = {L21--L25}, publisher = {Oxford University Press}, title = {{Multiple periods in the variability of the supermassive black hole binary candidate quasar PG1302-102?}}, doi = {10.1093/mnrasl/slv111}, volume = {454}, year = {2015}, }