Showing papers by "Josua P. Meyer published in 2013"
TL;DR: In this article, the luminosity calibration for the ATLAS detector at the LHC during pp collisions at root s = 7 TeV in 2010 and 2011 is presented, and a luminosity uncertainty of delta L/L = +/- 3.5 % is obtained.
Abstract: The luminosity calibration for the ATLAS detector at the LHC during pp collisions at root s = 7 TeV in 2010 and 2011 is presented. Evaluation of the luminosity scale is performed using several luminosity-sensitive detectors, and comparisons are made of the long-term stability and accuracy of this calibration applied to the pp collisions at root s = 7 TeV. A luminosity uncertainty of delta L/L = +/- 3.5 % is obtained for the 47 pb(-1) of data delivered to ATLAS in 2010, and an uncertainty of delta L/L = +/- 1.8 % is obtained for the 5.5 fb(-1) delivered in 2011.
499 citations
TL;DR: In this article, a search for a charged Higgs boson (H+) in t (t) over bar decays is presented, where one of the top quarks decays via t -> H(+)b, followed by H+ -> two jets (c (s) over bars).
Abstract: A search for a charged Higgs boson (H+) in t (t) over bar decays is presented, where one of the top quarks decays via t -> H(+)b, followed by H+ -> two jets (c (s) over bar). The other top qu ...
119 citations
TL;DR: In this paper, the convective heat transfer enhancement of aqueous suspensions of multi-walled carbon nanotubes flowing through a straight horizontal tube was investigated experimentally for a Reynolds number range of 1000-8000, which included the transitional flow regime.
119 citations
TL;DR: In this paper, the authors presented the double-differential cross-section of the jet transverse momentum and the dimensionless quantity x(T) = 2p(T)/root s, in bins of jet rapidity.
Abstract: The inclusive jet cross-section has been measured in proton-proton collisions at root s = 2.76 TeV in a dataset corresponding to an integrated luminosity of 0.20 pb(-1) collected with the ATLAS detector at the Large Hadron Collider in 2011. Jets are identified using the anti-k(t) algorithm with two radius parameters of 0.4 and 0.6. The inclusive jet double-differential cross-section is presented as a function of the jet transverse momentum p(T) and jet rapidity y, covering a range of 20 <= p(T) < 430 GeV and vertical bar y vertical bar < 4.4. The ratio of the cross-section to the inclusive jet cross-section measurement at root s = 7 TeV, published by the ATLAS Collaboration, is calculated as a function of both transverse momentum and the dimensionless quantity x(T) = 2p(T)/root s, in bins of jet rapidity. The systematic uncertainties on the ratios are significantly reduced due to the cancellation of correlated uncertainties in the two measurements. Results are compared to the prediction from next-to-leading order perturbative QCD calculations corrected for non-perturbative effects, and next-to-leading order Monte Carlo simulation. Furthermore, the ATLAS jet cross-section measurements at root s = 2.76 TeV and root s = 7 TeV are analysed within a framework of next-to-leading order perturbative QCD calculations to determine parton distribution functions of the proton, taking into account the correlations between the measurements.
115 citations
TL;DR: In this article, the authors derived the uncertainty on the calorimeter energy response to jets of particles for the ATLAS experiment at the Large Hadron Collider (LHC) and compared the Monte Carlo simulation using proton-proton collisions at centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009 and 2010.
Abstract: The uncertainty on the calorimeter energy response to jets of particles is derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the calorimeter response to single isolated charged hadrons is measured and compared to the Monte Carlo simulation using proton-proton collisions at centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009 and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter response to specific types of particles (positively and negatively charged pions, protons, and anti-protons) is measured and compared to the Monte Carlo predictions. Finally, the jet energy scale uncertainty is determined by propagating the response uncertainty for single charged and neutral particles to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3% for the final calorimeter jet energy scale.
103 citations
TL;DR: In this article, the integrated and differential fiducial cross sections for the production of a W or Z boson in association with a high-energy photon are measured using pp collisions at root s = 7 TeV.
Abstract: The integrated and differential fiducial cross sections for the production of a W or Z boson in association with a high-energy photon are measured using pp collisions at root s = 7 TeV. The analyse ...
88 citations
TL;DR: In this article, the authors reconstructed the Z boson via dielectron and dimuon decay channels, with a background contamination of less than 3% and combined results from two channels are consistent and are combined.
Abstract: The ATLAS experiment has observed 1995 Z boson candidates in data corresponding to 0.15 nb(-1) of integrated luminosity obtained in the 2011 LHC Pb + Pb run at root s(NN) = 2.76 TeV. The Z bosons are reconstructed via dielectron and dimuon decay channels, with a background contamination of less than 3%. Results from the two channels are consistent and are combined. Within the statistical and systematic uncertainties, the per-event Z boson yield is proportional to the number of binary collisions estimated by the Glauber model. The elliptic anisotropy of the azimuthal distribution of the Z boson with respect to the event plane is found to be consistent with zero. DOI: 10.1103/PhysRevLett.110.022301
80 citations
TL;DR: In this article, the authors recommend the use of the total entropy generation minimization method for the modeling of a system and can serve as validation when compared with first-law modelling.
Abstract: Many studies have been published on the performance and optimisation of the Brayton cycle and solar thermal Brayton cycle showing the potential, merits and challenges of this technology. Solar thermal Brayton systems have potential to be used as power plants in many sun-drenched countries. It can be very competitive in terms of efficiency, cost and environmental impact. When designing a system such as a recuperative Brayton cycle there is always a compromise between allowing effective heat transfer and keeping pressure losses in components small. The high temperatures required in especially the receiver of the system present a challenge in terms of irreversibilities due to heat loss. In this paper, the authors recommend the use of the total entropy generation minimisation method. This method can be applied for the modelling of a system and can serve as validation when compared with first-law modelling. The authors review various modelling perspectives required to develop an objective function for solar thermal power optimisation, including modelling of the sun as an exergy source, the Gouy–Stodola theorem and turbine modelling. With recommendations, the authors of this paper wish to clarify and simplify the optimisation and modelling of the solar thermal Brayton cycle for future work. The work is applicable to solar thermal studies in general but focuses on the small-scale recuperated solar thermal Brayton cycle.
71 citations
TL;DR: In this article, a numerical analysis of entropy generation in a parabolic trough receiver at different concentration ratios, inlet temperatures and flow rates is presented, and the optimal flow rates at which the entropy generated is minimum are presented for different flow rate and concentration ratio.
68 citations
TL;DR: In this article, the authors presented a study on the use of SANERI/SANEDI and EEDSM Hub and NAC in the NAC NAC Challenge.
66 citations
TL;DR: In this article, an adaptive neuro-fuzzy inference system (FCM-ANFIS) and a set of experimental data were developed to predict the effective viscosity of nanofluids.
TL;DR: In this article, a measurement of the top quark pair production cross section in the final state with a hadronically decaying tau lepton and jets is presented, based on proton-proton collision data recorded by the ATLAS experiment at the LHC, with a centre-of-mass energy of 7 TeV.
Abstract: A measurement of the top quark pair production cross section in the final state with a hadronically decaying tau lepton and jets is presented. The analysis is based on proton-proton collision data recorded by the ATLAS experiment at the LHC, with a centre-of-mass energy of 7 TeV. The data sample corresponds to an integrated luminosity of 1.67 fb(-1). The cross section is measured to be sigma(t (t) over bar) = 194 +/- 18 (stat.) +/- 46 (syst.) pb and is in agreement with other measurements and with the Standard Model prediction.
TL;DR: In this article, a physical discussion of the flow-induced vibration of two circular cylinders in view of the time-mean lift force on stationary cylinders and interaction mechanisms is presented, and the whole regime is classified into seven interaction regimes.
TL;DR: In this paper, the authors investigated three-dimensional topology optimisation with regard to heat conduction for the volume-to-point or volume to-surface problem in a cubic 3D domain, where the positioning of high conductive material in a solid with low thermal conductivity and high heat generation was optimized via the method of moving asymptotes (MMA) algorithm.
TL;DR: In this article, an analytical and numerical thermodynamic optimization of a downhole coaxial heat exchanger used to extract the maximum possible energy from the Earth's deep underground (2 km and deeper below the surface) for direct usage, and subject to a nearly linear increase in geothermal gradient with depth.
TL;DR: In this paper, the authors used the modified Wilson plot method, a nonlinear regression scheme, and the logarithmic mean temperature difference method to determine the mean Nusselt number of a tube-in-tube heat exchanger with annular diameter ratios.
Abstract: Varying diameter ratios associated with smooth concentric tube-in-tube heat exchangers are known to have an effect on their convective heat transfer capabilities. Linear and nonlinear regression models exist for determining the heat transfer coefficients; however, these are complex and time-consuming, and require much experimental data in order to obtain accurate solutions. A large data set of experimental measurements on heat exchangers with annular diameter ratios of 0.483, 0.579, 0.593, and 0.712 with respective hydraulic diameters of 17.01 mm, 13.84 mm, 10.88 mm, and 7.71 mm was gathered. Mean Nusselt numbers were determined using the modified Wilson plot method, a nonlinear regression scheme, and the logarithmic mean temperature difference method. These three methods presented disagreements with existing correlations based on local wall temperatures. The local Nusselt numbers were determined using the logarithmic mean temperature difference method. Local wall temperature measurements were made using ...
01 Jun 2013
TL;DR: The integrated and differential cross sections for the production of a W or Z boson in association with a high-energy photon are measured using pp collisions atfined as the difference between N obs Z(cid:3) and the total number of expected background events.
Abstract: The integrated and differential fiducial cross sections for the production of a W or Z boson in association with a high-energy photon are measured using pp collisions at root s = 7 TeV. The analyse ...
TL;DR: In this article, the authors investigated the thermal behavior of an assembly of multi scale cylinders in a staggered counter-rotating configuration cooled by natural convection with the objective of maximizing the heat transfer density rate (heat transfer rate per unit volume).
TL;DR: In this article, the authors proposed a new correlation for the estimation of optimal hub height for harnessing the power of the wind on an economically competitive basis, and the optimal hub heights for Dhahran, Dhulom, Gassim, Juaymah and Rawdat Ben Habbas were found to be 64, 66, 81, 70 and 82 m, respectively.
TL;DR: In this article, a three-dimensional flow architecture of conjugate cooling channels in forced convection with internal heat generation within the solid for an array of circular cooling channels with different flow orientation was developed.
TL;DR: In this paper, the National Research Foundation and the Solar Hub between the University of Pretoria and Stellenbosch were supported by the Department of Energy for the development of a photovoltaic system.
Abstract: National Research Foundation and the Solar Hub between the University of Pretoria and Stellenbosch which is supported by the Department of Energy
TL;DR: In this paper, a GA-PNN hybrid system was used for modeling the convective heat transfer characteristics and pressure drop of TiO2-water a nanofluid in a fully developed turbulent flow based on an experimentally obtained train and test data set.
TL;DR: In this article, a measurement of the flavour composition of dijet events produced in pp collisions at sqrt{s}=7 TeV using the ATLAS detector is described. But the measurement uses the full 2010 data sample, corresponding to an integrated luminosity of 39 pb^-1.
Abstract: This paper describes a measurement of the flavour composition of dijet events produced in pp collisions at sqrt{s}=7 TeV using the ATLAS detector. The measurement uses the full 2010 data sample, corresponding to an integrated luminosity of 39 pb^-1. Six possible combinations of light, charm and bottom jets are identified in the dijet events, where the jet flavour is defined by the presence of bottom, charm or solely light flavour hadrons in the jet. Kinematic variables, based on the properties of displaced decay vertices and optimised for jet flavour identification, are used in a multidimensional template fit to measure the fractions of these dijet flavour states as functions of the leading jet transverse momentum in the range 40 GeV to 500 GeV and jet rapidity |y| < 2.1. The fit results agree with the predictions of leading- and next-to-leading-order calculations, with the exception of the dijet fraction composed of bottom and light flavour jets, which is underestimated by all models at large transverse jet momenta. The ability to identify jets containing two b-hadrons, originating from e.g. gluon splitting, is demonstrated. The difference between bottom jet production rates in leading and subleading jets is consistent with the next-to-leading-order predictions.
15 Nov 2013
TL;DR: In this article, a parabolic trough receiver with twisted tape inserts detached from the absorber tube's wall is numerically studied, which shows a significant increase in the heat transfer and fluid friction performance of the receiver.
Abstract: In this paper, heat transfer and fluid friction performance of a parabolic trough receiver with twisted tape inserts detached from the absorber tube’s wall is numerically studied. The numerical investigations were conducted for twist ratios in the range 0.30 ≤ y ≤ 2.40, width ratios in the range 0.53 ≤ w ≤ 0.91 and Reynolds numbers in the range 10,260 ≤ Re ≤ 320,000. The numerical simulations were performed using a finite volume method with the realisable k-e turbulence model and Syltherm 800 as the heat transfer fluid. The use of twisted tape inserts shows a significant increase in the heat transfer and fluid friction performance of the receiver. The study also reveals significant reduction in absorber tube’s circumferential temperature difference due to the improved heat transfer performance. For the range of parameters considered, the Nusselt number, fluid friction and thermal enhancement factor are 1.01–3.36, 1.32–21.8, and 0.74–1.25 times those in a receiver with a plain absorber tube respectively. The absorber tube’s circumferential temperature difference reduces between 4–76% compared with a plain absorber tube. Correlations for Nusselt number and fluid friction are also reported for the range of parameters considered.Copyright © 2013 by ASME
TL;DR: In this article, the effect of the vibrations on heat convection over a wide range of parameter values is analyzed using the Nusselt number, which provides an answer to how the heat transfer is affected by the vibrations.
TL;DR: In this article, the boundary layer solution is obtained using the two-integral method to solve displacement thickness point by point with a local Newton method, at a fraction of the cost of a conventional mesh-based, full viscous solution.
Abstract: Purpose – The purpose of this paper is to introduce a unique technique to couple the two-integral boundary layer solutions to a generic inviscid solver in an iterative fashion. Design/methodology/approach – The boundary layer solution is obtained using the two-integral method to solve displacement thickness point by point with a local Newton method, at a fraction of the cost of a conventional mesh-based, full viscous solution. The boundary layer solution is coupled with an existing inviscid solver. Coupling occurs by moving the wall to a streamline at the computed boundary layer thickness and treating it as a slip boundary, then solving the flow again and iterating. The Goldstein singularity present when solving boundary layer equations is overcome by solving an auxiliary velocity equation along with the displacement thickness. Findings – The proposed method obtained favourable results when compared with the analytical solutions for flat and inclined plates. Further, it was applied to modelling the flow a...
14 Jul 2013
TL;DR: In this article, the effects of saturation temperature and inclination angle on convective heat transfer during condensation of R134a in an inclined smooth copper tube of inner diameter of 8.38 mm were investigated.
Abstract: This paper presents the effects of saturation temperature and inclination angle on convective heat transfer during condensation of R134a in an inclined smooth copper tube of inner diameter of 8.38 mm. Experiments were conducted for inclination angles ranging from −90° (vertical downward) to +90° (vertical upward) for mass fluxes between 100 kg/m2s and 400 kg/m2s and vapour qualities between 0.1 and 0.9 for saturation temperatures ranging between 30 °C and 50 °C. The results show that saturation temperature and inclination angles strongly influence the heat transfer coefficient. With respect to saturation temperature, an increase in saturation temperature generally leads to a decrease in heat transfer coefficient irrespective of the inclination angle. The effect of inclination angle was found to be more pronounced at mass fluxes of 100 kg/m2s and 200 kg/m2s for the range of vapour qualities considered. Within the region of influence of inclination there is an optimum angle which is between 15° and −30° (downward flow). The inclination effect corresponds to the predominance of the effect of gravity on the flow distribution.© 2013 ASME
Journal Article•
TL;DR: In this paper, a typical shaft configuration was analyzed and the primary energy consumers of typical shaft systems were identified, and a total of five shafts were instrumented and the actual pressure losses over the shafts plotted against time.
Abstract: Synopsis As a result of the rising electrical energy costs in South Africa, a method was sought to reduce the overall electrical consumption of typical shaft systems. A typical shaft configuration was analysed and the primary energy consumers were identified. The ventilation fans for this system were found to consume 15% of the total energy of the shaft system. It was calculated that more than 50% of this energy is consumed by the shaft itself, more specifically, by the pressure losses that occur in the shaft as the ventilation air passes through it. In order to ensure that the theory being used for the evaluation of these shaft systems is accurate, a total of five shafts were instrumented and the actual pressure losses over the shafts plotted against time. These shafts were then analysed from a theoretical perspective. Finally, in order to ensure a thorough understanding of the behaviour of the ventilation air in shaft systems, the systems were simulated using computational fluid dynamics (CFD) techniques. There were significant discrepancies between the theoretical analysis and the CFD simulation during the initial comparisons. This discrepancy lessened as the complexity of the CFD models increased, until when the complete shaft was modelled using the full bunton sets, the pipes, and the flanges, the difference between the theoretical evaluation and the CFD simulation was small. This result demonstrates that the theory is insufficient and that the interrelated effect of the buntons and fittings has not been fully appreciated by current theory. The final phase of the work presented here was to evaluate the costeffectiveness of using different bunton shapes and shaft configurations. It is shown that the increase in the pressure losses and therefore the direct operating costs of the shaft can vary by as much as 80%, depending on the bunton configuration chosen. The placement of the piping in the shaft can increase the pressure losses, and therefore the direct operating costs of the shaft, by as much as 12%, depending on the placement of the piping in the shaft; this effect includes the use of flanges. The use of fairings on a large cage can reduce the resistance that the cage offers to the ventilation flow by as much as 30%. This, however, does not translate into a direct saving because as the cage moves through the shaft, the overall effect is transitory. These savings can be significant when the items highlighted in this work are applied correctly.
03 Apr 2013
TL;DR: In this article, a model of an existing water heating product, using paraffin as the energy source, is presented to better understand how such products work and can then be used to optimise the current design or to redesign the product from scratch.
Abstract: The provision of electricity to many rural areas has not been adequately addressed. The means to warm water can thus be a problem in such areas. An opportunity for a product to fulfil the water heating needs of the rural community exists. Current market products are not engineered well enough to provide realistic solutions to this problem. The modelling of an existing water heating product, using paraffin as the energy source, will allow for better understanding of how such products work. The model can then be used to optimise the current design or to redesign the product from scratch.