Degradation of insulation paper is a key contributor to the failure of power transformers. Insulation degradation accelerates at elevated temperatures, which highlights the potential for better thermal management to prolong life. While several studies have analyzed the benefits of high thermal conductivity oil for reducing temperatures inside a transformer, this study is an initial assessment of the benefits of high thermal conductivity paper on transformer life. Blending particulates with cellulosic fibers offers a pathway for high thermal conductivity paper (with good dielectric properties), which can reduce internal temperatures. Presently, life extensions that can be achieved by the use of such thermally conducting papers were estimated, with the thermal conductivity of the paper being the key parameter under study. The analytical-numerical thermal model used in this study was validated against experimental measurements in a distribution transformer, adding confidence to the utility of the model. This model was then used to provide estimates of hot-spot temperature reduction resulting from the use of papers with higher thermal conductivity than baseline. Transformer life was predicted conventionally by tracking the degree of polymerization of paper over time, based on an Arrhenius model. Results indicate that increasing the thermal conductivity of paper from 0.2 W/mK (baseline) to 1 W/mK reduces the hot spot temperature by 10°C. While degradation significantly depends on the moisture and oxygen content, the model shows that such a temperature reduction can increase life for all conditions, by as much as a factor of three.

1 MoreReceived 8 March 2023DOI:https://doi.org/10.1103/PhysRevC.107.049903©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasParticle & resonance productionRelativistic heavy-ion collisionsNuclear Physics

Elliptic flow measurements from two-, four-, and six-particle correlations are used to investigate flow fluctuations in collisions of U+U at sqrt[s_{NN}]=193  GeV, Cu+Au at sqrt[s_{NN}]=200  GeV and Au+Au spanning the range sqrt[s_{NN}]=11.5-200  GeV. The measurements show a strong dependence of the flow fluctuations on collision centrality, a modest dependence on system size, and very little if any, dependence on particle species and beam energy. The results, when compared to similar LHC measurements, viscous hydrodynamic calculations, and trento model eccentricities, indicate that initial-state-driven fluctuations predominate the flow fluctuations generated in the collisions studied.

Received 22 October 2021DOI:https://doi.org/10.1103/PhysRevC.105.029901©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasParticle correlations & fluctuationsQCD phase transitionsRelativistic heavy-ion collisionsNuclear Physics

Dihadron azimuthal correlations containing a high transverse momentum (p(T)) trigger particle are sensitive to the properties of the nuclear medium created at RHIC through the strong interactions occurring between the traversing parton and the medium, i.e. jet-quenching. Previous measurements revealed a strong modification to dihadron azimuthal correlations in Au+Au collisions with respect to p+p and d+Au collisions. The modification increases with the collision centrality, suggesting a path-length or energy density dependence to the jet-quenching effect. This paper reports STAR measurements of dihadron azimuthal correlations in mid-central (20%-60%) Au+Au collisions at root s(NN)= 200 GeV as a function of the trigger particle's azimuthal angle relative to the event plane, phi(s) = vertical bar phi(t) - psi(EP)vertical bar .The azimuthal correlation is studied as a function of both the trigger and associated particle p(T). The subtractions of the combinatorial background and anisotropic flow, assuming Zero Yield At Minimum (ZYAM), are described. The correlation results are first discussed with subtraction of the even harmonic (elliptic and quadrangular) flow backgrounds. The away-side correlation is strongly modified, and the modification varies with phi(s), with a double-peak structure for out-of-plane trigger particles. The near-side ridge (long range pseudo-rapidity Delta(eta) correlation) appears to drop with increasing phi(s) while the jet-like component remains approximately constant. The correlation functions are further studied with the subtraction of odd harmonic triangular flow background arising from fluctuations. It is found that the triangular flow, while responsible for the majority of the amplitudes, is not sufficient to explain the phi(s)-dependence of the ridge or the away-side double-peak structure. The dropping ridge with phi(s), could be attributed to a phi(s)-dependent elliptic anisotropy; however, the physics mechanism of the ridge remains an open question. Even with a phi(s)-dependent elliptic flow, the away-side correlation structure is robust. These results, with extensive systematic studies of the dihadron correlations as a function of phi(s), trigger and associated particle p(T), and the pseudo-rapidity range Delta(eta), should provide stringent inputs to help understand the underlying physics mechanisms of jet-medium interactions in high energy nuclear collisions.

This corrects the article DOI: 10.1103/PhysRevLett.92.062301.

High transverse momentum ( \\begin{document}$ p_T $\\end{document} ) particle production is suppressed due to parton (jet) energy loss in the hot dense medium created in relativistic heavy-ion collisions. Redistribution of energy at low-to-modest \\begin{document}$ p_T $\\end{document} has been elusive to measure because of large anisotropic backgrounds. We report a data-driven method for background evaluation and subtraction, exploiting the away-side pseudorapidity gaps, to measure the jetlike correlation shape in Au+Au collisions at \\begin{document}$ \\sqrt{s_{\\rm{NN}}} = 200 $\\end{document} GeV with the STAR experiment. The correlation shapes, for trigger particle \\begin{document}$ p_T\u003e3\\;{\\rm{GeV}}/c $\\end{document} and various associated particle \\begin{document}$ p_T $\\end{document} ranges within \\begin{document}$ 0.5 , are consistent with Gaussians and their widths are found to increase with centrality. The results indicate jet broadening in the medium created in central heavy-ion collisions.

We present STAR measurements of strange hadron (K-S(0), Lambda, (Lambda) over bar, Xi(-), (Xi) over bar (+), Omega(-), (Omega) over bar (+), and phi) production at midrapidity (vertical bar y vertical bar < 0.5) in Au + Au collisions at root S-NN = 7.7-39 GeV from the Beam Energy Scan Program at the Relativistic Heavy Ion Collider (RHIC). Transverse-momentum spectra, averaged transverse mass, and the overall integrated yields of these strange hadrons are presented versus the centrality and collision energy. Antibaryon-to-baryon ratios (<(Lambda)over bar>/Lambda, (Xi) over bar (+)/Xi(-), (Omega) over bar (+)/Omega(-)) are presented as well and used to test a thermal statistical model and to extract the temperature normalized strangeness and baryon chemical potentials at hadronic freeze-out (mu(B)/T-ch and mu(S)/T-ch) in central collisions. Strange baryon-to-pion ratios are compared to various model predictions in central collisions for all energies. The nuclear modification factors (R-CP) and antibaryon-to-meson ratios as a function of transverse momentum are presented for all collision energies. The K-S(0) R-CP shows no suppression for P-T up to 3.5 GeV/c at energies of 7.7 and 11.5 GeV. The (Lambda) over bar /K-S(0) ratio also shows baryon-to-meson enhancement at intermediate p(T) (approximate to 2.5 GeV/c) in central collisions at energies above 19.6 GeV. Both observations suggest that there is likely a change of the underlying strange quark dynamics at collision energies below 19.6 GeV.

We report the energy dependence of mid-rapidity (anti-)deuteron production in Au+Au collisions at root s(NN) = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV, measured by the STAR experiment at the BNL Relativistic Heavy Ion Collider. The yield of deuterons is found to be well described by the thermal model. The collision energy, centrality, and transverse momentum dependence of the coalescence parameter B-2 are discussed. We find that the values of B-2 for antideuterons are systematically lower than those for deuterons, indicating that the correlation volume of antibaryons is larger than that of baryons at root s(NN) from 19.6 to 39 GeV. In addition, values of B-2 are found to vary with collision energy and show a broad minimum around root s(NN) = 20-40 GeV, which might imply a change of the equation of state of the medium in these collisions.

We report systematic measurements of bulk properties of the system created in Au+Au collisions at √(s_NN) = 14.5 GeV recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC).The transverse momentum spectra of π^±, K^± and p(p̅) are studied at mid-rapidity (|y| < 0.1) for nine centrality intervals. The centrality, transverse momentum (p_T),and pseudorapidity (η) dependence of inclusive charged particle elliptic flow (v_2), and rapidity-odd charged particles directed flow (v_1) results near mid-rapidity are also presented. These measurements are compared with the published results from Au+Au collisions at other energies, and from Pb+Pb collisions at √(s_NN) = 2.76 TeV. The results at √(s_NN) = 14.5 GeV show similar behavior as established at other energies and fit well in the energy dependence trend. These results are important as the 14.5 GeV energy fills the gap in μ_B, which is of the order of 100 MeV,between √(s_NN) =11.5 and 19.6 GeV. Comparisons of the data with UrQMD and AMPT models show poor agreement in general.

We report a new measurement of D-0-meson production at mid-rapidity (vertical bar y vertical bar < 1) in Au + Au collisions at root S-NN= 200 GeV utilizing the heavy flavor tracker, a high resolution silicon detector at the STAR experiment. Invariant yields of D-0 mesons with transverse momentum P-T less than or similar to 9 GeV/c are reported in various centrality bins (0-10%, 10-20%, 20-40%, 40-60%, and 60-80%). Blast-wave thermal models are used to fit the D-0-meson P-T spectra to study D-0 hadron kinetic freeze-out properties. The average radial flow velocity extracted from the fit is considerably smaller than that of light hadrons (pi, K, and p), but comparable to that of hadrons containing multiple strange quarks (phi, Xi(-)), indicating that D-0 mesons kinetically decouple from the system earlier than light hadrons. The calculated D-0 nuclear modification factors reaffirm that charm quarks suffer a large amount of energy loss in the medium, similar to those of light quarks for P-T > 4GeV/c in central 0-10% Au + Au collisions. At low P-T , the nuclear modification factors show a characteristic structure qualitatively consistent with the expectation from model predictions that charm quarks gain sizable collective motion during the medium evolution. The improved measurements are expected to offer new constraints to model calculations and help gain further insights into the hot and dense medium created in these collisions.

We present three-particle mixed-harmonic correlations < cos(m phi(a) + n phi(b) - (m + n)phi(c))> for harmonics n = 1 - 3 for charged particles in root s(NN) = 200 GeV Au+Au collisions at RHIC. These measurements provide information on the three-dimensional structure of the initial collision zone and are important for constraining models of a subsequent low-viscosity quark-gluon plasma expansion phase. We investigate correlations between the first, second and third harmonics predicted as a consequence of fluctuations in the initial state. The dependence of the correlations on the pseudorapidity separation between particles show hints of a breaking of longitudinal invariance. We compare our results to a number of state-of-the art hydrodynamic calculations with different initial states and temperature dependent viscosities. These measurements provide important steps towards constraining the temperature dependent viscosity and longitudinal structure of the initial state at RHIC. (C) 2018 The Author. Published by Elsevier B.V.

The second phase of the Beam Energy Scan at RHIC, BES-II, is scheduled to start in 2019 and will explore the high baryon density region of the QCD phase diagram with precision measurements. The detector upgrades will enhance some of the key measurements by extending STAR's kinematic reach, like the kurtosis of net-protons distribution which could pinpoint the position of a critical point. The upgrades currently under way comprise: the replacement of the inner TPC sectors, the Event Plane Detector (EPD) and the end-cap TOF. Building on these upgrades STAR is planning to further enhance its detector capabilities by installing a Forward Calorimeter System (FCS) integrating an electromagnetic and hadronic calorimeter and a Forward Tracking System (FTS) combining 3 Silicon mini-strip disks and 4 Small-Strip Thin Gap Chamber (sTGC) wheels. The forward upgrades are motivated by studying the initial state of nucleons and nuclei and the exploration of cold QCD physics in the very high and low x regions. This contribution will highlight these upgrades and some of the physics opportunities that they allow.

New STAR measurements of two- and four-particle (c2{4}) azimuthal angle correlations are reported for p+Au collisions at 200 GeV and d+Au collisions from 19.6 to 200 GeV. A negative c2{4}, consistent with collective anisotropic flow, is observed in high multiplicity d+Au events at 62.4 and 200 GeV where the statistical significance of the data allows an analysis. A template fitting method, employed to subtract non-flow contributions to the two-particle correlations, allows the extraction of the anisotropy coefficients (ν2) for these systems at their respective energies. The ν2 results for different energies show a common dependence on the charged particle multiplicity density (〈dNch/dη〉), which provide important insight on the nature of collective behavior in small collision systems.