Natural and Mathematical Sciences

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

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Open Access
Accelerating discovery of COFs for CO2 capture and H2 purification using structurally guided computational screening
(Elsevier, 2022-01-01) Aksu, G. O.; Fındıkçı, İlknur Eruçar; Haslak, Z. P.; Keskin, S.; Mechanical Engineering; FINDIKÇI, Ilknur Eruçar
Screening of hypothetical covalent organic framework (hypoCOF) database enables to go beyond the current synthesized structures to design high-performance materials for CO2 separation. In this work, we followed a structurally guided computational screening approach to find the most promising candidates of hypoCOF adsorbents and membranes for CO2 capture and H2 purification. Grand canonical Monte Carlo (GCMC) simulations were used to evaluate CO2/H2 separation performance of 3184 hypoCOFs for pressure-swing adsorption (PSA) and vacuum-swing adsorption (VSA) processes. CO2/H2 adsorption selectivities and CO2 working capacities of hypoCOFs were calculated in the range of 6.13–742 (6.39–954) and 0.07–8.68 mol/kg (0.01–3.92 mol/kg), achieving higher values than those of experimentally synthesized COFs at PSA (VSA) conditions. Density functional theory (DFT) calculations revealed that the strength of hydrogen bonding between CO2 and the functional group of linkers is an important factor for determining the CO2 selectivity of hypoCOFs. The most predominant topologies and linker types were identified as bor and pts, linker91 (a triazine linker) and linker92 (a benzene linker) for the top-performing hypoCOF adsorbents, respectively. Molecular dynamics (MD) simulations of 794 hypoCOFs showed that they exceed the Robeson's upper bound by outperforming COF, zeolite, metal organic framework (MOF), and polymer membranes due to their high H2/CO2 selectivities, 2.66–6.14, and high H2 permeabilities, 9×105–4.5×106 Barrer. Results of this work will be useful to guide the synthesis of novel materials by providing molecular-level insights into the structural features of hypothetical COFs to achieve superior CO2 separation performance.
Open Access
Addendum: Measurement and QCD analysis of double-differential inclusive jet cross sections in proton-proton collisions at √s=13 TeV
(Springer, 2022-12-07) Tumasyan, A.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
The QCD analysis at NNLO is repeated by using the NNLO interpolation grids for the double-differential inclusive jet cross section [1], which were released after the journal publication of the original analysis. The NNLOJET calculation used to derive these grids is based on the leading-colour and leading-flavour-number approximation and does not include the most recent subleading colour contributions. However, these contributions were reported in ref. [2] to be very small in inclusive jet production, in particular for a jet size of R = 0.7. The grids also contain an estimate of the numerical integration uncertainty of around 1% or less. To account for point-to-point fluctuations, this uncertainty, after consultation with the authors of NNLOJET, has been increased by a factor of two; however, its impact in the fit is negligible. A comparison of the measurement with predictions using various PDFs is shown in figure 1. Although the PDF parametrisation remains identical, higher precision in PDF and QCD parameters is expected by using NNLO grids consistently in the QCD analysis. These new results supersede those obtained by using the k-factor technique.
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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
Open Access
Analysis of the CP structure of the Yukawa coupling between the Higgs boson and τ leptons in proton-proton collisions at s√ = 13 TeV
(Springer, 2022-06-03) Tumasyan, A.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
The first measurement of the CP structure of the Yukawa coupling between the Higgs boson and τ leptons is presented. The measurement is based on data collected in proton-proton collisions at s = 13 TeV by the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb−1. The analysis uses the angular correlation between the decay planes of τ leptons produced in Higgs boson decays. The effective mixing angle between CP-even and CP-odd τ Yukawa couplings is found to be −1 ± 19°, compared to an expected value of 0 ± 21° at the 68.3% confidence level. The data disfavour the pure CP-odd scenario at 3.0 standard deviations. The results are compatible with predictions for the standard model Higgs boson.
Open Access
Analysis of X(4140) like states and their radial excitations in QCD
(Sissa Medialab Srl, 2017) Türkan, Arzu; Dağ, Hüseyin; Natural and Mathematical Sciences; TÜRKAN, Arzu; DAĞ, Hüseyin
In this work, we investigated the X(4140) and like states and their radial excitations by using molecular and diquark-antidiquark currents which couple to scalar, axial vector and tensor states via QCD sum rules. In operator product expansion, we considered quark, gluon and mixed vacuum condansates up to dimension eight. For the ground states coupling to these currents, we found that masses are almost degenerate with X(4140). For the excited states, we found that scalar and tensor currents are coupling to D∗ sD∗ s threshold. However for the axial vector currents, the mass of the first excited state is compatible with X(4274). Thus we conclude that, X(4274) might be the first radial excitation of X(4140).
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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.
Open Access
Angular analysis of the decay B + → K + μ + μ − in proton-proton collisions at √s =8 TeV
(American Physical Society, 2018-12-01) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
The angular distribution of the flavor-changing neutral current decay B+→K+μ+μ- is studied in proton-proton collisions at a center-of-mass energy of 8 TeV. The analysis is based on data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 20.5 fb-1. The forward-backward asymmetry AFB of the dimuon system and the contribution FH from the pseudoscalar, scalar, and tensor amplitudes to the decay width are measured as a function of the dimuon mass squared. The measurements are consistent with the standard model expectations.
Open Access
Angular analysis of the decay B + → K ∗ (892) +µ +µ − in proton-proton collisions at √s = 8 TeV
(Springer, 2021-01-14) Sirunyan, A. M.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
Angular distributions of the decay B+→ K∗(892)+μ+μ− are studied using events collected with the CMS detector in s = 8 TeV proton-proton collisions at the LHC, corresponding to an integrated luminosity of 20.0 fb−1. The forward-backward asymmetry of the muons and the longitudinal polarization of the K∗(892)+ meson are determined as a function of the square of the dimuon invariant mass. These are the first results from this exclusive decay mode and are in agreement with a standard model prediction.
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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.
Open Access
Author Correction: A portrait of the Higgs boson by the CMS experiment ten years after the discovery
(Nature Research, 2022-11-02) Tumasyan, A.; Işıldak, Bora; The CMS Collaboration; Natural and Mathematical Sciences; IŞILDAK, Bora
In the version of this article initially published, CMS Collaboration author names, affiliations and acknowledgements were omitted and have now been included in the HTML and PDF versions of the article.
Open Access
Axial-tensor meson family at T≠0
(Springer Nature, 2020-10-12) Süngü, J. Y.; Türkan, Arzu; Sertbakan, E.; Veliev, E. V.; Natural and Mathematical Sciences; TÜRKAN, Arzu
The mass and decay constants of rho(2), omega(2) and a missing member in the 2(--) nonet along with their first excited states are analyzed by the Thermal QCD sum rules approach, including QCD condensates up to dimension five. Mass and decay constant values of these mesons are stable from T = 0 up to T congruent to 120 MeV. However, after this threshold point, our numerical analyses indicates that they begin to diminish with increasing temperature. When we compare the hadronic parameters with their vacuum values, masses of these mesons and their first excited states decrease between (1-13%) from the PDG data and (10-26%) for the decay constants. However they diminish in the interval of (9-26%) and (2-34%) respectively with regards to Regge Trajectory Model data. We expect our numerical results will be confirmed by future heavy-ion collision experiments.

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