• Computation of parton distributions from the quasi-PDF approach at the physical point

      Alexandrou, C; Bacchio, S; Cichy, K; Constantinou, M; Hadjiyiannakou, K; Jansen, K; Koutsou, G; Scapellato, A; Steffens, F (2018-03-26)
      © The Authors, published by EDP Sciences, 2018. We show the first results for parton distribution functions within the proton at the physical pion mass, employing the method of quasi-distributions. In particular, we present the matrix elements for the iso-vector combination of the unpolarized, helicity and transversity quasi-distributions, obtained with Nf = 2 twisted mass cloverimproved fermions and a proton boosted with momentum p→ = 0.83 GeV. The momentum smearing technique has been applied to improve the overlap with the proton boosted state. Moreover, we present the renormalized helicity matrix elements in the RI' scheme, following the non-perturbative renormalization prescription recently developed by our group.
    • Constraining sea quark distributions through W<sup>±</sup> cross section ratios measured at STAR

      Posik, M (2015-01-01)
      © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). Over the past several years the STAR experiment at RHIC has been contributing to our understanding of the proton structure. Through its instrumentation, STAR is well equipped to measure W → v + e in √s = 500/510 GeV proton-proton collisions at mid-rapidity (-1.1 ≤ η ≤ 1.1). The W cross section ratio (W+/W-) is sensitive to unpolarized u, d, ū, and d quark distributions. At these kinematics, STAR is able to measure the quark distributions near Bjorken-x values of 0.1. The RHIC runs in 2011, 2012 and 2013 at √s = 500/510 GeV saw a significant increase in delivered luminosity from previous years. This resulted in a total data sample being collected of about 352 pb-1 of integrated luminosity. The increased statistics will lead to a higher precision measurement of the W+/W- cross section ratio than was previously measured by STAR's 2009 run, as well as allow for a measurement of its η dependence at mid-rapidity. Presented here is an update of the W cross section ratio analysis from the STAR 2011, 2012 and 2013 runs.
    • Constraining the sea quark distributions through w<sup>±</sup> cross section ratio measurements at STAR

      Posik, M (2019-01-01)
      © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). Over the past several years, parton distribution functions (PDFs) have become more precise. However there are still kinematic regions where more data are needed to help constrain global PDF extractions, such as the ratio of the sea quark distributions d¯/ū near the valence region. Furthermore, current measurements appear to suggest different high-x behaviors of this ratio. The W cross section ratio (W+/W−) is sensitive to the unpolarized quark distributions at large Q2 set by the W mass. Such a measurement can be used to help constrain the d¯/ū ratio. The STAR experiment at RHIC is well equipped to measure the leptonic decays of W bosons, in the midpseudorapdity range (|η| ≤ 1), produced in proton-proton collisions at √s = 500/510 GeV. At these kinematics STAR is sensitive to quark distributions near x of 0.16. STAR can also measure W+/W− in a more forward region ranging from 1.0 < η <1.5, which extends the sea quark sensitivity to higher x. RHIC runs from 2011 through 2013 have collected about 350 pb−1 of integrated luminosity, and an additional 350 pb−1 from the 2017 run. These proceedings will present preliminary results of the 2011-2013 W+/W− cross section ratio measurements. Additionally, the W/Z cross section ratio, differential and total W and Z cross sections are presented.
    • Constraining the sea quark distributions through W<sup>±</sup> cross section ratio measurements at STAR

      Posik, M (2017-01-01)
      © 2017 Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). Over the past several years, parton distribution functions (PDFs) have become more precise. However there are still kinematic regions where more data are needed to help constrain global PDF extractions, such as the sea quark distributions d/ū near the valence region (Bjorken-x ≈ 0.1 - 0.3). Current measurements appear to suggest different high-x behaviors of these distributions, leading to large uncertainties in global fits. The charged W cross section ratio (W+/W-) is sensitive to the unpolarized u; d; ū; and d quark distributions at large Q2 set by theW mass and could help shed light on this discrepancy. The STAR experiment at RHIC is well equipped to measure the leptonic decays of W bosons, in the mid-rapidity range (|η| ≤ 1), produced in proton+proton collisions at √s = 500/510 GeV. At these kinematics STAR is sensitive to quark distributions near Bjorken-x of 0.16. STAR can also measure the W cross section ratio in a more forward bin ranging from 1.1 < η < 2.0, which extends the sea quark sensitivity to higher x. RHIC runs from 2011 through 2013 have collected about 350 pb-1 of integrated luminosity, and a 2017 run is expected to provide an additional 400 pb-1. Presented here are preliminary results for the 2011-2012 charged W cross section ratios (∼100pb-1) and an update on the 2013 charged W cross section analysis (∼250 pb-1).
    • Disconnected diagrams with twisted-mass fermions

      Abdel-Rehim, A; Alexandrou, C; Constantinou, M; Finkenrath, J; Hadjiyiannakou, K; Jansen, K; Kallidonis, C; Koutsou, G; Avilés-Casco, AV; Volmer, J (2016-01-01)
      © Copyright owned by the author(s). The latest results from the Twisted-Mass collaboration on disconnected diagrams at the physical value of the pion mass are presented. In particular, we focus on the sigma terms, the axial charges and the momentum fraction, all of them for the nucleon. A detailed error analysis for each observable follows, showing the strengths and weaknesses of the one-end trick. Alternatives are discussed.
    • Disconnected quark loop contributions to nucleon observables using N<inf>f</inf> = 2 twisted clover fermions at the physical value of the light quark mass

      Abdel-Rehim, A; Alexandrou, C; Constantinou, M; Hadjiyiannakou, K; Jansen, K; Kallidonis, C; Koutsou, G; Avilés-Casco, AV (2015-01-01)
      We compute the disconnected quark loops contributions entering the determination of nucleon observables, by using a Nf = 2 ensemble of twisted mass fermions with a clover term at a pION mass mπ = 133 MeV. We employ exact deflation and implement all calculations in GPUs, enabling us to achieve large statistics and a good signal.
    • Evolution enters the genomic era

      Liberles, DA; Liberles, David A|0000-0003-3487-8826 (2001-12-01)
      A report on the 18th Congress of the European Society for Evolutionary Biology (ESEB), Aarhus, Denmark, 20-25 August, 2001.
    • Extraction of the isovector magnetic form factor of the nucleon at zero momentum

      Alexandrou, C; Constantinou, M; Koutsou, G; Ottnad, K; Petschlies, M (2014-01-01)
      © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. The extraction of the magnetic form factor of the nucleon at zero momentum transfer is usually performed by adopting a parametrization for its momentum dependence and fitting the results obtained at finite momenta. We present position space methods that rely on taking the derivative of relevant correlators to extract directly the magnetic form factor at zero momentum without the need to assume a functional form for its momentum dependence. These methods are explored on one ensemble using Nf = 2+1+1 Wilson twisted mass fermions.
    • Future prospects of di-jet production constraining Dg(x) at low x at STAR at RHIC

      Surrow, B (2014-01-01)
      © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial Share like Licence. One of the main objectives of the high-energy spin physics program at RHIC at BNL is the precis determination of the polarized gluon distribution function, δg(x). Polarized p+p collision at ps = 200GeV and at √ = 500GeV at RHIC provide an unique way to probe the proton spi structure. Inclusive measurements, such as inclusive jet and hadron production, have so far bee the prime focus of various results at radic; = 200GeV constraining δg(x) for 0:05 < x < 0:2. A recen global analysis provides for the first time evidence of a non-zero value of the gluon polarizatio 10:05 δg(x)dx (Q2 =10GeV2)=0:20+0:006+0.07 First results of di-jet production at ps=200Ge by the STAR collaboration will allow a better constraint of the underlying event kinematics. Extendin the current program to smaller values of x is a key goal for the future high-energy spi physics program at RHIC. Forward di-jet production measurements at STAR beyond the curren acceptance from 1< <+2 to +2:5< <+4, in particular those carried out atps=500GeV provides access to low x values at the level of 103 where current uncertainties of Dg(x) remai very large. Those measurements will eventually be complemented by a future Electron-Ion Collide facility probing δg(x) in polarized e+p collisions.
    • GIFT: A real-time and scalable 3D shape search engine

      Bai, S; Bai, X; Zhou, Z; Zhang, Z; Latecki, LJ (2016-12-09)
      © 2016 IEEE. Projective analysis is an important solution for 3D shape retrieval, since human visual perceptions of 3D shapes rely on various 2D observations from different view points. Although multiple informative and discriminative views are utilized, most projection-based retrieval systems suffer from heavy computational cost, thus cannot satisfy the basic requirement of scalability for search engines. In this paper, we present a real-time 3D shape search engine based on the projective images of 3D shapes. The real-time property of our search engine results from the following aspects: (1) efficient projection and view feature extraction using GPU acceleration, (2) the first inverted file, referred as F-IF, is utilized to speed up the procedure of multi-view matching, (3) the second inverted file (S-IF), which captures a local distribution of 3D shapes in the feature manifold, is adopted for efficient context-based reranking. As a result, for each query the retrieval task can be finished within one second despite the necessary cost of IO overhead. We name the proposed 3D shape search engine, which combines GPU acceleration and Inverted File (Twice), as GIFT. Besides its high efficiency, GIFT also outperforms the state-of-the-art methods significantly in retrieval accuracy on various shape benchmarks and competitions.
    • Hadron structure

      Constantinou, M (2014-01-01)
      © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. This is a review of recent developments in hadron structure within the framework of Lattice QCD. The main focus is on recent achievements in the evaluation of nucleon quantities, such as the axial charge, electromagnetic form factors, the Dirac and Pauli radii, the quark momentum fraction and the spin content of the nucleon, in view of simulations at pion masses very close to their physical value. A discussion of the systematic uncertainties and the computation of the disconnected contributions using dynamical simulations is also included. Results emerging the propetries of particles other than the nucleon are summarized, highlighting selected hyperon and meson form factors.
    • Intrinsic disorder in putative protein sequences

      Midic, U; Obradovic, Z (2012-01-01)
      © 2012 Midic and Obradovic; licensee BioMed Central Ltd. Background: Intrinsically disordered proteins (IDPs) and regions (IDRs) perform a variety of crucial biological functions despite lacking stable tertiary structure under physiological conditions in vitro. State-of-the-art sequencebased predictors of intrinsic disorder are achieving per-residue accuracies over 80%. In a genome-wide study of intrinsic disorder in human genome we observed a big difference in predicted disorder content between confirmed and putative human proteins. We investigated a hypothesis that this discrepancy is not correct, and that it is due to incorrectly annotated parts of the putative protein sequences that exhibit some similarities to confirmed IDRs, which lead to high predicted disorder content. Methods: To test this hypothesis we trained a predictor to discriminate sequences of real proteins from synthetic sequences that mimic errors of gene finding algorithms. We developed a procedure to create synthetic peptide sequences by translation of non-coding regions of genomic sequences and translation of coding regions with incorrect codon alignment. Results: Application of the developed predictor to putative human protein sequences showed that they contain a substantial fraction of incorrectly assigned regions. These regions are predicted to have higher levels of disorder content than correctly assigned regions. This partially, albeit not completely, explains the observed discrepancy in predicted disorder content between confirmed and putative human proteins. Conclusions: Our findings provide the first evidence that current practice of predicting disorder content in putative sequences should be reconsidered, as such estimates may be biased.
    • Modeling the mutualistic interactions between tubeworms and microbial consortia

      Cordes, EE; Arthur, MA; Shea, K; Arvidson, RS; Fisher, CR; Cordes, Erik|0000-0002-6989-2348 (2005-03-01)
      The deep-sea vestimentiferan tubeworm Lamellibrachia luymesi forms large aggregations at hydrocarbon seeps in the Gulf of Mexico that may persist for over 250 y. Here, we present the results of a diagenetic model in which tubeworm aggregation persistence is achieved through augmentation of the supply of sulfate to hydrocarbon seep sediments. In the model, L. luymesi releases the sulfate generated by its internal, chemoautotrophic, sulfide-oxidizing symbionts through posterior root-like extensions of its body. The sulfate fuels sulfate reduction, commonly coupled to anaerobic methane oxidation and hydrocarbon degradation by bacterial-archaeal consortia. If sulfate is released by the tubeworms, sulfide generation mainly by hydrocarbon degradation is sufficient to support moderate-sized aggregations of L. luymesi for hundreds of years. The results of this model expand our concept of the potential benefits derived from complex interspecific relationships, in this case involving members of all three domains of life. © 2005 Cordes et al.
    • Multi-task feature selection in microarray data by binary integer programming

      Lan, L; Vucetic, S (2013-12-20)
      © 2013 Lan and Vucetic; licensee BioMed Central Ltd. A major challenge in microarray classification is that the number of features is typically orders of magnitude larger than the number of examples. In this paper, we propose a novel feature filter algorithm to select the feature subset with maximal discriminative power and minimal redundancy by solving a quadratic objective function with binary integer constraints. To improve the computational efficiency, the binary integer constraints are relaxed and a low-rank approximation to the quadratic term is applied. The proposed feature selection algorithm was extended to solve multi-task microarray classification problems. We compared the single-task version of the proposed feature selection algorithm with 9 existing feature selection methods on 4 benchmark microarray data sets. The empirical results show that the proposed method achieved the most accurate predictions overall. We also evaluated the multi-task version of the proposed algorithm on 8 multi-task microarray datasets. The multi-task feature selection algorithm resulted in significantly higher accuracy than when using the single-task feature selection methods.
    • New Physics Searches from Nucleon Matrix Elements in Lattice QCD

      Constantinou, M (2017-03-22)
      © The Authors, published by EDP Sciences, 2017. In this paper we review recent progress in hadron structure using lattice QCD simulations, with main focus in the evaluation of nucleon matrix elements. We highlight developments that may guide new Physics searches, such as the scalar and tensor charges, as well as, the neutron electric dipole moment.
    • Nucleon electromagnetic and axial form factors with N<inf>f</inf>=2 twisted mass fermions at the physical point

      Alexandrou, C; Constantinou, M; Hadjiyiannakou, K; Kallidonis, C; Koutsou, G; Jansen, K; Ottnad, K; Vaquero, A (2016-01-01)
      © Copyright owned by the author(s). We present results for the nucleon electromagnetic and axial form factors using an Nf=2 twisted mass fermion ensemble with pion mass of about 131 MeV. We use multiple sink-source separations to identify excited state contamination. Dipole masses for the momentum dependence of the form factors are extracted and compared to experiment, as is the nucleon magnetic moment and charge and magnetic radii.
    • Nucleon generalized form factors with twisted mass fermions

      Alexandrou, C; Constantinou, M; Drach, V; Jansen, K; Kallidonis, C; Koutsou, G (2013-01-01)
      We present results on the nucleon form factors, momentum fraction and helicity moment for Nf = 2 and Nf = 2+1+1 twisted mass fermions for a number of lattice volumes and lattice spacings. First results for a new Nf = 2 ensemble at the physical pion mass are also included. The implications of these results on the spin content of the nucleon are discussed taking into account the disconnected contributions at one pion mass.
    • Nucleon observables and axial charges of other baryons using twisted mass fermions

      Alexandrou, C; Constantinou, M; Hadjiyiannakou, K; Jansen, K; Kallidonis, C; Koutsou, G (2014-01-01)
      © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. We present results on the nucleon scalar, axial and tensor charges, as well as, on the first moments of the unpolarized, polarized and transversity parton distributions using Nf = 2 and Nf = 2+1+1 twisted mass fermions. These include an ensemble that yields the physical value of the ratio of the nucleon to the pion mass. Results on the axial charges of hyperons and charmed baryons are also presented for a range of pion masses including the physical one.
    • Nucleon spin and quark content at the physical point

      Alexandrou, C; Constantinou, M; Hadjiyiannakou, K; Kallidonis, C; Koutsou, G; Jansen, K; Wiese, C; Avilés-Casco, AV (2016-01-01)
      © Copyright owned by the author(s). We present results on the spin and quark content of the nucleon using Nf =2 twisted mass cloverimproved fermion simulations with a pion mass close to its physical value. We use recently developed methods to obtain accurate results for both connected and disconnected contributions. We provide results for the axial charge, quark and gluon momentum fraction as well as the light, strange and charm sσ-terms.
    • Parton distributions from lattice QCD with momentum smearing

      Alexandrou, C; Cichy, K; Constantinou, M; Hadjiyiannakou, K; Jansen, K; Steffens, F; Wiese, C (2016-01-01)
      © Copyright owned by the author(s). In this work we continue our effort to explore a recent proposal, which allows light-cone distributions to be extracted from purely spatial correlations, being thus accessible to lattice methods. In order to test the feasibility of this method, we present our latest results from a twisted mass lattice calculation of the flavor non-singlet momentum, helicity and transversity distributions of the nucleon. Furthermore, we apply a newly proposed momentum improved smearing, which has the potential to reach higher nucleon momenta as required for a safe matching procedure to the physical distribution functions.