Natural and Mathematical Sciences

Permanent URI for this collectionhttps://hdl.handle.net/10679/313

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Now showing 1 - 20 of 524

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Alignment of the CMS tracker with LHC and cosmic ray data
(IOP Publishing, 2014-06) Chatrchyan, S.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
Results are reported from a search for supersymmetry in pp collisions at a center-of-mass energy of 8 TeV, based on events with a single isolated lepton (electron or muon) and multiple jets, at least two of which are identified as b jets. The data sample corresponds to an integrated luminosity of 19.3 fb(-1) recorded by the CMS experiment at the LHC in 2012. The search is motivated by supersymmetric models that involve strong-production processes and cascade decays of new particles. The resulting final states contain multiple jets as well as missing transverse momentum from weakly interacting particles. The event yields, observed across several kinematic regions, are consistent with the expectations from standard model processes. The results are interpreted in the context of simplified supersymmetric scenarios with pair production of gluinos, where each gluino decays to a top quark-antiquark pair and the lightest neutralino. For the case of decays via virtual top squarks, gluinos with a mass smaller than 1.26 TeV are excluded for low neutralino masses
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Angular analysis and branching fraction measurement of the decay B-0 -> K*(0)mu(+)mu(-)
(Elsevier, 2013-11-25) Chatrchyan, S.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
The angular distributions and the differential branching fraction of the decay B0→K⁎(892)0μ+μ− are studied using a data sample corresponding to an integrated luminosity of 5.2 fb−1 collected with the CMS detector at the LHC in pp collisions at View the MathML source. From more than 400 signal decays, the forward–backward asymmetry of the muons, the K⁎(892)0 longitudinal polarization fraction, and the differential branching fraction are determined as a function of the square of the dimuon invariant mass. The measurements are in good agreement with standard model predictions.
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Angular analysis of the decay B0→K*0μ+μ- from pp collisions at s=8 TeV
(Elsevier, 2016-02-10) Khachatryan, V.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
The angular distributions and the differential branching fraction of the decay B0→K⁎(892)0μ+μ− are studied using data corresponding to an integrated luminosity of 20.5 fb−1 collected with the CMS detector at the LHC in pp collisions at View the MathML source. From 1430 signal decays, the forward–backward asymmetry of the muons, the K⁎(892)0 longitudinal polarization fraction, and the differential branching fraction are determined as a function of the dimuon invariant mass squared. The measurements are among the most precise to date and are in good agreement with standard model predictions.
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Angular coefficients of Z bosons produced in pp collisions at s=8 TeV and decaying to μ+μ- as a function of transverse momentum and rapidity
(Elsevier, 2015-11-12) Khachatryan, V.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
Measurements of the five most significant angular coefficients, A0 through A4, for Z bosons produced in pp collisions at View the MathML source and decaying to μ+μ− are presented as a function of the transverse momentum and rapidity of the Z boson. The integrated luminosity of the dataset collected with the CMS detector at the LHC corresponds to View the MathML source. These measurements provide comprehensive information about the Z boson production mechanisms, and are compared to the QCD predictions at leading order, next-to-leading order, and next-to-next-to-leading order in perturbation theory.
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An approach to nonlinear viscoelasticity via metric gradient flows
(SIAM, 2014) Mielke, A.; Ortner, C.; Şengül, Yasemin; Natural and Mathematical Sciences; ŞENGÜL, Yasemin
We formulate quasistatic nonlinear finite-strain viscoelasticity of rate type as a gradient system. Our focus is on nonlinear dissipation functionals and distances that are related to metrics on weak diffeomorphisms and that ensure time-dependent frame indifference of the viscoelastic stress. In the multidimensional case we discuss which dissipation distances allow for the solution of the time-incremental problem. Because of the missing compactness the limit of vanishing timesteps can be obtained only by proving some kind of strong convergence. We show that this is possible in the one-dimensional case by using a suitably generalized convexity in the sense of geodesic convexity of gradient flows. For a general class of distances we derive discrete evolutionary variational inequalities and are able to pass to the time-continuous limit in a specific case.
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Approximate markov-nash equilibria for discrete-time risk-sensitive mean-field games
(Informs, 2020-11) Saldı, Naci; Basar, T.; Raginsky, M.; Natural and Mathematical Sciences; SALDI, Naci
In this paper, we study a class of discrete-time mean-field games under the infinite-horizon risk-sensitive optimality criterion. Risk sensitivity is introduced for each agent (player) via an exponential utility function. In this game model, each agent is coupled with the rest of the population through the empirical distribution of the states, which affects both the agent's individual cost and its state dynamics. Under mild assumptions, we establish the existence of a mean-field equilibrium in the infinite-population limit as the number of agents (N) goes to infinity, and we then show that the policy obtained from the mean-field equilibrium constitutes an approximate Nash equilibrium when N is sufficiently large.
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Approximate nash equilibria in partially observed stochastic games with mean-field interactions
(Informs, 2019-08) Saldı, Naci; Başar, T.; Raginsky, M.; Natural and Mathematical Sciences; SALDI, Naci
Establishing the existence of Nash equilibria for partially observed stochastic dynamic games is known to be quite challenging, with the difficulties stemming from the noisy nature of the measurements available to individual players (agents) and the decentralized nature of this information. When the number of players is sufficiently large and the interactions among agents is of the mean-field type, one way to overcome this challenge is to investigate the infinite-population limit of the problem, which leads to a mean-field game. In this paper, we consider discrete-time partially observed mean-field games with infinite-horizon discounted-cost criteria. Using the technique of converting the original partially observed stochastic control problem to a fully observed one on the belief space and the dynamic programming principle, we establish the existence of Nash equilibria for these game models under very mild technical conditions. Then, we show that the mean-field equilibrium policy, when adopted by each agent, forms an approximate Nash equilibrium for games with sufficiently many agents.
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Approximation by special values of Dirichlet series
(American Mathematical Society, 2020) Çelik, Şermin Çam; Göral, H.; Natural and Mathematical Sciences; ÇAM ÇELİK, Şermin
The classification of the irreducible unitary representations of the stabilizer of the horocycles of a homogeneous tree of finite degree is well-known. In this article we use these stabilizers to form an Olshanski pair and then find all spherical functions of this pair. Finally we give realizations of the corresponding irreducible unitary representations.
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Approximations for constrained Markov decision problems
(Springer, 2018) Saldı, Naci; Linder, T.; Yüksel, S.; Natural and Mathematical Sciences; SALDI, Naci
This chapter studies the finite-state approximation of a discrete-time constrained Markov decision process with compact state space, under the discounted and average cost criteria. Using the linear programming formulation of the constrained discounted problem, we prove the convergence of the optimal value function of the finite-state model to the optimal value function of the original model. Under further continuity conditions on the transition probability of the original discounted model, we also establish a method to compute approximately optimal policies. For the average cost criterion, instead of using the finite-state linear programming approximation method, we use a direct method to establish analogous results under drift and minorization conditions which guarantee the geometric ergodicity of Markov chains induced by stationary policies.
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Approximations for partially observed Markov decision processes
(Birkhäuser Basel, 2018) Saldı, Naci; Linder, T.; Yüksel, S.; Natural and Mathematical Sciences; SALDI, Naci
This chapter studies the finite-model approximation of discrete-time partially observed Markov decision process. We will find that by performing the standard reduction method, where one transforms a partially observed model to a belief-based fully observed model, we can apply and properly generalize the results in the preceding chapters to obtain approximation results. The versatility of approximation results under weak continuity conditions become particularly evident while investigating the applicability of these results to the partially observed case. We also provide systematic procedures for the quantization of the set of probability measures on the state space of POMDPs which is the state space of belief-MDPs.
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Asymptotic optimality of finite model approximations for partially observed markov decision processes with discounted cost
(IEEE, 2020-01) Saldı, Naci; Yuksel, S.; Linder, T.; Natural and Mathematical Sciences; SALDI, Naci
We consider finite model approximations of discrete-time partially observed Markov decision processes (POMDPs) under the discounted cost criterion. After converting the original partially observed stochastic control problem to a fully observed one on the belief space, the finite models are obtained through the uniform quantization of the state and action spaces of the belief space Markov decision process (MDP). Under mild assumptions on the components of the original model, it is established that the policies obtained from these finite models are nearly optimal for the belief space MDP, and so, for the original partially observed problem. The assumptions essentially require that the belief space MDP satisfies a mild weak continuity condition. We provide an example and introduce explicit approximation procedures for the quantization of the set of probability measures on the state space of POMDP (i.e., belief space).
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Asymptotic optimality of finite models for witsenhausen’s counterexample and beyond
(Birkhäuser Basel, 2018) Saldı, Naci; Linder, T.; Yüksel, S.; Natural and Mathematical Sciences; SALDI, Naci
In this chapter, we study the approximation of Witsenhausen’s counterexample and the Gaussian relay channel problem by using the results of the previous chapter. In particular, our goal is to establish that finite models obtained through the uniform quantization of the observation and action spaces result in a sequence of policies whose costs converge to the value function. We note that the operation of quantization has typically been the method to show that a non-linear policy can perform better than an optimal linear policy, both for Witsenhausen’s counterexample [10, 86] and the Gaussian relay channel problem [88, 152]. Our findings show that for a large class of problems, quantized policies not only may perform better than linear policies, but that they are actually almost optimal.
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Azimuthal decorrelation of jets widely separated in rapidity in pp collisions at s√=7s=7 TeV
(Springer International Publishing, 2018) Khachatryan, V.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
The decorrelation in the azimuthal angle between the most forward and the most backward jets (Mueller-Navelet jets) is measured in data collected in pp collisions with the CMS detector at the LHC at s√=7s=7 TeV. The measurement is presented in the form of distributions of azimuthal-angle differences, Δϕ, between the Mueller-Navelet jets, the average cosines of (π − Δϕ), 2(π − Δϕ), and 3(π − Δϕ), and ratios of these cosines. The jets are required to have transverse momenta, pT, in excess of 35 GeV and rapidities, |y|, of less than 4.7. The results are presented as a function of the rapidity separation, Δy, between the Mueller-Navelet jets, reaching Δy up to 9.4 for the first time. The results are compared to predictions of various Monte Carlo event generators and to analytical predictions based on the DGLAP and BFKL parton evolution schemes.
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Biocompatible MOFs for storage and separation of O2: A molecular simulation study
(American Chemical Society, 2019-02-27) Gülçay, Ezgi; Fındıkçı, İlknur Eruçar; Mechanical Engineering; FINDIKÇI, Ilknur Eruçar; Gülçay, Ezgi
Metal organic frameworks (MOFs) are great candidates for capturing 02 due to their highly porous structures and tunable physical and chemical properties. In this study, we assessed the performance of 1525 biocompatible MOFs which have endogenous linkers and nontoxic metal centers for adsorption-based and membrane-based O-2 separation and also for high-pressure O-2 storage. We initially computed Henry's constants of O-2 and N-2 at zero coverage and 298 K by performing Grand Canonical Monte Carlo (GCMC) simulations and estimated infinite dilution adsorption selectivities for O-2/N-2 mixture. We performed binary mixture GCMC simulations for the top 15 candidates at various pressures and 298 K and compared mixture adsorption selectivities with those obtained from infinite dilution. We then estimated O-2 working capacities of 315 biocompatible MOFs obtained at 298 K and 140 bar for storage and 5 bar for release pressures. Our results showed that 15 biocompatible MOFs outperform gravimetric O-2 working capacities of the traditional adsorbent materials such as activated carbon and NaX and some common MOFs such as NU-125 and UMCM-152 at 298 K. We finally calculated O-2 and N-2 permeabilities and membrane selectivities of 45 promising MOF candidates for O-2/N-2 separation. Seventeen biocompatible MOF membranes were identified to exceed the Robeson's upper bound established for polymers. This computational study will be useful to identify the promising biocompatible MOFs for storage and separation of O-2. The bio-MOF library constructed in this study will also guide both experimental and computational studies for design and development of biocompatible MOFs for various medical applications.
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The Camassa-Holm approximation to the double dispersion equation for arbitrarily long times
(Springer, 2022-09) Erbay, Saadet; Erkip, A.; Kuruk, G.; Natural and Mathematical Sciences; ERBAY, Saadet
In the present paper we prove the validity of the Camassa-Holm equation as a long wave limit to the double dispersion equation which describes the propagation of bidirectional weakly nonlinear and dispersive waves in an infinite elastic medium. First we show formally that the right-going wave solutions of the double dispersion equation can be approximated by the solutions of the Camassa-Holm equation in the long wave limit. Then we rigorously prove that the solutions of the double dispersion and the Camassa-Holm equations remain close over a long time interval, determined by two small parameters measuring the effects of nonlinearity and dispersion.
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The Camassa-Holm equation as the long-wave limit of the improved Boussinesq equation and of a class of nonlocal wave equations
(AIMS, 2016-11) Erbay, Hüsnü Ata; Erbay, Saadet; Erkip, A.; Natural and Mathematical Sciences; ERBAY, Hüsnü Ata; ERBAY, Saadet
In the present study we prove rigorously that in the long-wave limit, the unidirectional solutions of a class of nonlocal wave equations to which the improved Boussinesq equation belongs are well approximated by the solutions of the Camassa-Holm equation over a long time scale. This general class of nonlocal wave equations model bidirectional wave propagation in a nonlocally and nonlinearly elastic medium whose constitutive equation is given by a convolution integral. To justify the Camassa-Holm approximation we show that approximation errors remain small over a long time interval. To be more precise, we obtain error estimates in terms of two independent, small, positive parameters \epsilon and \delta measuring the effect of nonlinearity and dispersion, respectively. We further show that similar conclusions are also valid for the lower order approximations: the Benjamin-Bona-Mahony approximation and the Korteweg-de Vries approximation.
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Charged-particle nuclear modification factors in PbPb and pPb collisions at root s(NN)=5.02 TeV
(Springer International Publishing, 2017) Khachatryan, V.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
The spectra of charged particles produced within the pseudorapidity window |η| < 1 at sNN−−−−√=5.02sNN=5.02 TeV are measured using 404 μb−1 of PbPb and 27.4 pb−1 of pp data collected by the CMS detector at the LHC in 2015. The spectra are presented over the transverse momentum ranges spanning 0.5 < pT< 400 GeV in pp and 0.7 < pT< 400 GeV in PbPb collisions. The corresponding nuclear modification factor, RAA, is measured in bins of collision centrality. The RAA in the 5% most central collisions shows a maximal suppression by a factor of 7-8 in the pT region of 6-9 GeV. This dip is followed by an increase, which continues up to the highest pT measured, and approaches unity in the vicinity of pT = 200 GeV. The RAA is compared to theoretical predictions and earlier experimental results at lower collision energies. The newly measured pp spectrum is combined with the pPb spectrum previously published by the CMS collaboration to construct the pPb nuclear modification factor, RpA, up to 120 GeV. For pT> 20 GeV, RpA exhibits weak momentum dependence and shows a moderate enhancement above unity.
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Choquet-Monge-Ampère classes
(Springer Nature, 2017) Guedj, V.; Şahin, Sibel; Zeriahi, A.; Natural and Mathematical Sciences; ŞAHİN, Sibel
We introduce and study Choquet-Monge-Ampère classes on compact Kähler manifolds. They consist of quasi-plurisubharmonic functions whose sublevel sets have small enough asymptotic Monge-Ampère capacity. We compare them with finite energy classes, which have recently played an important role in Kähler Geometry.
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CMS Collaboration
(Elsevier, 2014-11) Khachatryan, V.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
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CMS Collaboration
(Elsevier, 2014-12) Chatrchyan, S.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora

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