This paper proposes and assesses remedies to the significant storage requirements of unsteady adjoint methods used in gradient-based optimization, in multi-dimensional problems modeled by unsteady ...PDEs. Even if the application domain of the proposed technique(s) is wide, these remedies are herein demonstrated in shape optimization problems with unsteady fluid flows. In these cases, the adjoint equations are integrated backwards in time, requiring the instantaneous flow fields to be available at each time-step of the adjoint solver, and this noticeably increases storage requirements. To avoid extreme treatments, such as the full storage of the computed instantaneous flow fields or their recomputations from scratch during the solution of the adjoint equations, or even the widely used check-pointing technique, lossy compression techniques are proposed. These are implemented within OpenFOAM, which is used to solve the flow and adjoint equations and conduct the optimization. In this paper, (a) the ZFP compression library, (b) the incremental Proper Generalized Decomposition (iPGD) algorithm and (c) an efficient hybridization of them are used. The compression strategies are assessed on aerodynamic shape optimization problems. Their effectiveness in data reduction, computational overhead and representation accuracy is considered, in relation to the continuous adjoint method which uses the decompressed fields to compute the gradient of objective functions as the reference method.
•Memory demands of unsteady adjoint in optimization prevent wide industrial use.•Storage of unsteady flowfields can be relaxed using lossy compression techniques.•ZFP, Incremental Proper Generalized Decomposition incl. hybridization are proposed.•Storage reduced by more than 2 orders of magnitude in shape optimization.•Course of the optimization in fluid mechanics unaffected by the compression error.
Abstract We report a new measurement of the production of electrons from open heavy-flavor hadron decays (HFEs) at mid-rapidity (|y| < 0.7) in Au+Au collisions at s NN $$ \sqrt{s_{\textrm{NN}}} $$ = ...200 GeV. Invariant yields of HFEs are measured for the transverse momentum range of 3.5 < p T < 9 GeV/c in various configurations of the collision geometry. The HFE yields in head-on Au+Au collisions are suppressed by approximately a factor of 2 compared to that in p + p collisions scaled by the average number of binary collisions, indicating strong interactions between heavy quarks and the hot and dense medium created in heavy-ion collisions. Comparison of these results with models provides additional tests of theoretical calculations of heavy quark energy loss in the quark-gluon plasma.
Electron drift parameters in dimethyl ether Burks, Morgan; Trentalange, S; Margetis, S ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/1997, Letnik:
385, Številka:
3
Journal Article
Recenzirano
We have measured electron drift parameters in dimethyl ether gas over distances up to 14 cm and drift fields up to 1600 V/cm. By careful control of impurity levels, the attenuation of signals in the ...gas can be brought to manageable levels. Above 1000 V/cm, the attenuation of ionization signals due to attachment by electro-negative impurities is measured to be less than 0.5%/cm, making this gas an attractive candidate for use in small time projection chambers.
We report precision measurements of hypernuclei _{Λ}^{3}H and _{Λ}^{4}H lifetimes obtained from Au+Au collisions at sqrts_{NN}=3.0 GeV and 7.2 GeV collected by the STAR experiment at the ...Relativistic Heavy Ion Collider, and the first measurement of _{Λ}^{3}H and _{Λ}^{4}H midrapidity yields in Au+Au collisions at sqrts_{NN}=3.0 GeV. _{Λ}^{3}H and _{Λ}^{4}H, being the two simplest bound states composed of hyperons and nucleons, are cornerstones in the field of hypernuclear physics. Their lifetimes are measured to be 221±15(stat)±19(syst) ps for _{Λ}^{3}H and 218±6(stat)±13(syst) ps for _{Λ}^{4}H. The p_{T}-integrated yields of _{Λ}^{3}H and _{Λ}^{4}H are presented in different centrality and rapidity intervals. It is observed that the shape of the rapidity distribution of _{Λ}^{4}H is different for 0%-10% and 10%-50% centrality collisions. Thermal model calculations, using the canonical ensemble for strangeness, describes the _{Λ}^{3}H yield well, while underestimating the _{Λ}^{4}H yield. Transport models, combining baryonic mean-field and coalescence (jam) or utilizing dynamical cluster formation via baryonic interactions (phqmd) for light nuclei and hypernuclei production, approximately describe the measured _{Λ}^{3}H and _{Λ}^{4}H yields. Our measurements provide means to precisely assess our understanding of the fundamental baryonic interactions with strange quarks, which can impact our understanding of more complicated systems involving hyperons, such as the interior of neutron stars or exotic hypernuclei.
The NA49 large acceptance hadron detector Afanasiev, S.; Alber, T.; Appelshäuser, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/1999, Letnik:
430, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The NA49 detector is a wide acceptance spectrometer for the study of hadron production in p+p, p+A, and A+A collisions at the CERN SPS. The main components are 4 large-volume TPCs for tracking and ...particle identification via d
E/d
x. TOF scintillator arrays complement particle identification. Calorimeters for transverse energy determination and triggering, a detector for centrality selection in p+A collisions, and beam definition detectors complete the set-up. A description of all detector components is given with emphasis on new technical realizations. Performance and operational experience are discussed in particular with respect to the high track density environment of central Pb+Pb collisions.
Abstract We report on the measurement of the Central Exclusive Production of charged particle pairs h + h − (h = π, K, p) with the STAR detector at RHIC in proton-proton collisions at s $$ \sqrt{s} ...$$ = 200 GeV. The charged particle pairs produced in the reaction pp → p′ + h + h − + p′ are reconstructed from the tracks in the central detector and identified using the specific energy loss and the time of flight method, while the forward-scattered protons are measured in the Roman Pot system. Exclusivity of the event is guaranteed by requiring the transverse momentum balance of all four final-state particles. Differential cross sections are measured as functions of observables related to the central hadronic final state and to the forward-scattered protons. They are measured in a fiducial region corresponding to the acceptance of the STAR detector and determined by the central particles’ transverse momenta and pseudorapidities as well as by the forward-scattered protons’ momenta. This fiducial region roughly corresponds to the square of the four-momentum transfers at the proton vertices in the range 0.04 GeV2 < −t 1 , −t 2 < 0.2 GeV2, invariant masses of the charged particle pairs up to a few GeV and pseudorapidities of the centrally-produced hadrons in the range |η| < 0.7. The measured cross sections are compared to phenomenological predictions based on the Double Pomeron Exchange (DPE) model. Structures observed in the mass spectra of π + π − and K + K − pairs are consistent with the DPE model, while angular distributions of pions suggest a dominant spin-0 contribution to π + π − production. For π + π − production, the fiducial cross section is extrapolated to the Lorentz-invariant region, which allows decomposition of the invariant mass spectrum into continuum and resonant contributions. The extrapolated cross section is well described by the continuum production and at least three resonances, the f 0(980), f 2(1270) and f 0(1500), with a possible small contribution from the f 0(1370). Fits to the extrapolated differential cross section as a function of t 1 and t 2 enable extraction of the exponential slope parameters in several bins of the invariant mass of π + π − pairs. These parameters are sensitive to the size of the interaction region.
We present first data on event-by-event fluctuations in the average transverse momentum of charged particles produced in Pb+Pb collisions at the CERN SPS. This measurement provides previously ...unavailable information allowing sensitive tests of microscopic and thermodynamic collision models and to search for fluctuations expected to occur in the vicinity of the predicted QCD phase transition. We find that the observed variance of the event-by-event average transverse momentum is consistent with independent particle production modified by the known two-particle correlations due to quantum statistics and final state interactions and folded with the resolution of the NA49 apparatus. For two specific models of non-statistical fluctuations in transverse momentum limits are derived in terms of fluctuation amplitude. We show that a significant part of the parameter space for a model of isospin fluctuations predicted as a consequence of chiral symmetry restoration in a non-equilibrium scenario is excluded by our measurement.
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