4,363 research outputs found
Performance of the LHCb RICH detectors during the LHC Run II
The LHCb RICH system provides hadron identification over a wide momentum
range (2-100 GeV/c). This detector system is key to LHCb's precision flavour
physics programme, which has unique sensitivity to physics beyond the standard
model. This paper reports on the performance of the LHCb RICH in Run II,
following significant changes in the detector and operating conditions. The
changes include the refurbishment of significant number of photon detectors,
assembled using new vacuum technologies, and the removal of the aerogel
radiator. The start of Run II of the LHC saw the beam energy increase to 6.5
TeV per beam and a new trigger strategy for LHCb with full online detector
calibration. The RICH information has also been made available for all trigger
streams in the High Level Trigger for the first time.Comment: Updated authors' details and DO
The Future of RICH Detectors through the Light of the LHCb RICH
The limitations in performance of the present RICH system in the LHCb
experiment are given by the natural chromatic dispersion of the gaseous
Cherenkov radiator, the aberrations of the optical system and the pixel size of
the photon detectors. Moreover, the overall PID performance can be affected by
high detector occupancy as the pattern recognition becomes more difficult with
high particle multiplicities. This paper shows a way to improve performance by
systematically addressing each of the previously mentioned limitations. These
ideas are applied in the present and future upgrade phases of the LHCb
experiment. Although applied to specific circumstances, they are used as a
paradigm on what is achievable in the development and realisation of high
precision RICH detectors
A hybrid numerical flux for supersonic flows with application to rocket nozzles
The numerical simulation of shock waves in supersonic flows is challenging because of several instabilities which can affect the solution. Among them, the carbuncle phenomenon can introduce nonphysical perturbations in captured shock waves. In the present work, a hybrid numerical flux is proposed for the evaluation of the convective fluxes that avoids carbuncle and keeps high-accuracy on shocks and boundary layers. In particular, the proposed flux is a combination between an upwind approximate Riemann problem solver and the Local Lax-Friedrichs scheme. A simple strategy to mix the two fluxes is proposed and tested in the framework of a discontinuous Galerkin discretisation. The approach is investigated on the subsonic flow in a channel, on the supersonic flow around a cylinder, on the supersonic flow on a flat plate and on the flow in a overexpanded rocket nozzle
Diesel engines equipped with piezoelectric and solenoid injectors: hydraulic performance of the injectors and comparison of the emissions, noise and fuel consumption
A comprehensive comparison between solenoid and indirect acting piezoelectric injectors has been carried out.
The working principle of these injector typologies is illustrated, and their hydraulic performance has been
analysed and discussed on the basis of experimental data collected at a hydraulic test rig. The injector char-
acteristics, injected
fl
ow-rate pro
fi
les, nozzle opening and closure delays, injector leakages and injected volume
fl
uctuations with the dwell time have been compared in order to evaluate the impact of the injector driving
system.
The solenoid and piezoelectric injectors have been installed on a Euro 5 diesel engine, which has been tested
experimentally at a dynamometer cell. Optimized double and triple injection strategies have been considered at
some representative key points of the New European Driving Cycle. Engine-out emissions, brake speci
fi
c fuel
consumption and combustion noise are presented and discussed, with the support of a three-zone, diesel com-
bustion diagnostic model. The research has focused on the cause-and-e
ff
ect relationships between the hydraulic
performance of the injectors and the results of the engine tests. The primary goal has been to assess if the
di
ff
erences in engine performance between the solenoidal and indirect-acting piezoelectric injector setups are
due to the injector driving system or to speci
fi
c features that are present in the hydraulic circuit of the considered
injectors and which are not closely related to the driving system.
A
fi
nal evaluation of the potential of the piezoelectric technology for driving indirect acting injectors is
provided on the basis of real engine result
Can Twitter be a source of information on allergy? Correlation of pollen counts with tweets reporting symptoms of allergic rhinoconjunctivitis and names of antihistamine drugs
Pollen forecasts are in use everywhere to inform therapeutic decisions for patients with allergic rhinoconjunctivitis (ARC). We exploited data derived from Twitter in order to identify tweets reporting a combination of symptoms consistent with a case definition of ARC and those reporting the name of an antihistamine drug. In order to increase the sensitivity of the system, we applied an algorithm aimed at automatically identifying jargon expressions related to medical terms. We compared weekly Twitter trends with National Allergy Bureau weekly pollen counts derived from US stations, and found a high correlation of the sum of the total pollen counts from each stations with tweets reporting ARC symptoms (Pearson's correlation coefficient: 0.95) and with tweets reporting antihistamine drug names (Pearson's correlation coefficient: 0.93). Longitude and latitude of the pollen stations affected the strength of the correlation. Twitter and other social networks may play a role in allergic disease surveillance and in signaling drug consumptions trends
Explaining Central Government’s Tax Revenue Categories through the Bradley-Terry Regression Trunk Model
The Bradley-Terry Regression Trunk (BTRT) model combines the log-linear Bradley-Terry model, including subject-specific covariates, with a particular tree-based model, the so-called regression trunk. It aims to consider simultaneously the main effects and the interaction effects of covariates on data expressed as paired comparisons. We apply this model to financial data expressed as rankings and then transformed into paired comparisons. Tax revenues differentiated by category represent the statistical units of the analysis (i.e., taxes on income, social security contributions, taxes on property, and taxes on goods and services). We combine data from OECD, World Bank, and IMF databases for the year 2018 to investigate the effect size of socio-economic covariates and their interaction on the composition of tax revenues for a set of 100 countries worldwide. We also present a comparison with a more established method proposed in tax determinants literature and with two alternative models used for matched pairs. Finally, we discuss the implications of reported results for stakeholders and policymakers
Utilization of Hydrotreated Vegetable Oil (HVO) in a Euro 6 Dual-Loop EGR Diesel Engine: Behavior as a Drop-In Fuel and Potentialities along Calibration Parameter Sweeps
This study examines the effects on combustion, engine performance and exhaust pollutant emissions of a modern Euro 6, dual-loop EGR, compression ignition engine running on regular EN590-compliant diesel and hydrotreated vegetable oil (HVO). First, the potential of HVO as a "drop-in" fuel, i.e., without changes to the original, baseline diesel-oriented calibration, was highlighted and compared to regular diesel results. This showed how the use of HVO can reduce engine-out emissions of soot (by up to 67%), HC and CO (by up to 40%), while NOx levels remain relatively unchanged. Fuel consumption was also reduced, by about 3%, and slightly lower combustion noise levels were detected, too. HVO has a lower viscosity and a higher cetane number than diesel. Since these parameters have a significant impact on mixture formation and the subsequent combustion process, an engine pre-calibrated for regular diesel fuel could not fully exploit the potential of another sustainable fuel. Therefore, the effects of the most influential calibration parameters available on the tested engine platform, i.e., high-pressure and low-pressure EGR, fuel injection pressure, main injection timing, pilot quantity and dwell-time, were analyzed along single-parameter sweeps. The substantial reduction in engine-out soot, HC and CO levels brought about by HVO could give the possibility to implement additional measures to limit NOx emissions, combustion noise and/or fuel consumption compared to diesel. For example, higher proportion of LP EGR and/or smaller pilot quantity could be exploited with HVO, at low load, to reduce NOx emissions to a greater extent than diesel, without incurring penalties in terms of incomplete combustion species. Conversely, at higher load, delayed main injection timings and reduced rail pressure could reduce combustion noise without exceeding soot levels of the baseline diesel case
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