Measurement of global polarization of {\Lambda} hyperons in few-GeV heavy-ion collisions

The global polarization of {\Lambda} hyperons along the total orbital angular momentum of a relativistic heavy-ion collision is presented based on the high statistics data samples collected in Au+Au collisions at \sqrt{s_{NN}} = 2.4 GeV and Ag+Ag at 2.55 GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at GSI, Darmstadt. This is the first measurement below the strangeness production threshold in nucleon-nucleon collisions. Results are reported as a function of the collision centrality as well as a function of the hyperon transverse momentum (p_T) and rapidity (y_{CM}) for the range of centrality 0--40%. We observe a strong centrality dependence of the polarization with an increasing signal towards peripheral collisions. For mid-central (20--40%) collisions the polarization magnitudes are (%) = 6.0 \pm 1.3 (stat.) \pm 2.0 (syst.) for Au+Au and (%) = 4.6 \pm 0.4 (stat.) \pm 0.5 (syst.) for Ag+Ag, which are the largest values observed so far. This observation thus provides a continuation of the increasing trend previously observed by STAR and contrasts expectations from recent theoretical calculations predicting a maximum in the region of collision energies about 3 GeV. The observed polarization is of a similar magnitude as predicted by 3D fluid dynamics and the UrQMD plus thermal vorticity model and significantly above results from the AMPT model.Comment: 8 pages, 4 figure

Inclusive e+^+e−^- production in collisions of pions with protons and nuclei in the second resonance region of baryons

Inclusive e$^+$e$^-$ production has been studied with HADES in $\pi^-$ + p, $\pi^-$ + C and $\pi^- + \mathrm{CH}_2$ reactions, using the GSI pion beam at $\sqrt{s_{\pi p}}$ = 1.49 GeV. Invariant mass and transverse momentum distributions have been measured and reveal contributions from Dalitz decays of $\pi^0$, $\eta$ mesons and baryon resonances. The transverse momentum distributions are very sensitive to the underlying kinematics of the various processes. The baryon contribution exhibits a deviation up to a factor seven from the QED reference expected for the dielectron decay of a hypothetical point-like baryon with the production cross section constrained from the inverse $\gamma$ n$\rightarrow \pi^-$ p reaction. The enhancement is attributed to a strong four-momentum squared dependence of the time-like electromagnetic transition form factors as suggested by Vector Meson Dominance (VMD). Two versions of the VMD, that differ in the photon-baryon coupling, have been applied in simulations and compared to data. VMD1 (or two-component VMD) assumes a coupling via the $\rho$ meson and a direct coupling of the photon, while in VMD2 (or strict VMD) the coupling is only mediated via the $\rho$ meson. The VMD2 model, frequently used in transport calculations for dilepton decays, is found to overestimate the measured dielectron yields, while a good description of the data can be obtained with the VMD1 model assuming no phase difference between the two amplitudes. Similar descriptions have also been obtained using a time-like baryon transition form factor model where the pion cloud plays the major role.Comment: (HADES collaboration

Analysis of the impact of sex and age on the variation in the prevalence of antinuclear autoantibodies in Polish population: a nationwide observational, cross-sectional study

The detection of antinuclear autoantibody (ANA) is dependent on many factors and varies between the populations. The aim of the study was first to assess the prevalence of ANA in the Polish adult population depending on age, sex and the cutoff threshold used for the results obtained. Second, we estimated the occurrence of individual types of ANA-staining patterns. We tested 1731 patient samples using commercially available IIFA using two cutoff thresholds of 1:100 and 1:160. We found ANA in 260 participants (15.0%), but the percentage of positive results strongly depended on the cutoff level. For a cutoff threshold 1:100, the positive population was 19.5% and for the 1:160 cutoff threshold, it was 11.7%. The most prevalent ANA-staining pattern was AC-2 Dense Fine speckled (50%), followed by AC-21 Reticular/AMA (14.38%) ANA more common in women (72%); 64% of ANA-positive patients were over 50 years of age. ANA prevalence in the Polish population is at a level observed in other highly developed countries and is more prevalent in women and elderly individuals. To reduce the number of positive results released, we suggest that Polish laboratories should set 1:160 as the cutoff threshold

The effect of alternative fuels injection timing on toxic substances formation in CI engines

The present study describes selected issues associated with the emission level in toxic exhaust gases and fuel injection timing. The study was focused on the following types of fuels: Diesel oil (the base fuel) and the other fuels were the mixture of fatty acid methyl ester with Camelina (L10 – diesel fuel with 10% V/V FAME of Camelina and L20 – diesel fuel with 10% V/V FAME of Camelina) was used. Fuel injection advanced angle was set for three different values – the factory setting – 12° before TDC, later injection – 7° and earlier injection – 17°. The most important conclusion is that in most measurement points registered in the same engine operating conditions, the concentration of fuel NOx in L10 and L20 increased but PM emissions decreased which is caused by active oxygen located in the internal structure of the fuel. This fact contributes to the rise in temperature during the combustion process. At the same time factory settings of the angle makes NOx emissions lower and close to reference fuel

Hydroxyl radicals as an indicator of knocking combustion in the dual-fuel compression-ignition engine

The occurrence of knocking combustion is one of the basic problems of dual-fuel compression-ignition engines supplied with diesel oil and gaseous fuel. In order to detect this phenomenon and evaluate its intensity, several methods are commonly used, including the analysis of pressure of working medium in the combustion chamber of the engine or vibrations of certain engine components. This paper discusses the concept of using mass fraction of hydroxyl radicals as the indicator of the occurrence of knocking combustion. Current knowledge on the conditions of hydroxyl radical formation in the engine combustion chamber has been systematized and the results of research on this subject have been presented. Theoretical considerations are illustrated by exemplary results of simulation studies of the combustion process in a dual-fuel compression-ignition engine supplied with diesel oil and methane. The conclusions drawn may be useful for the development of dual-fuel engine control systems

Evaluation of emission level of biofuels from waste-free production in compression-ignition engines

This article presents the impact of biofuel for compression-ignition engines, produced with the use of innovative production technology, on the emission of toxic substances. The innovative production technology of biodiesel does not generate by-products, eliminating the need for development glycerol fraction and toxic methanol, substances inconvenient for environment. This technology is not currently well known and not used on an industrial scale. The essence of this technology is to carry out the transesterification of triglycerides and methyl acetate in special conditions and with using an alkaline catalyst. The only product of this technology is a mixture of fatty acid methyl esters and glycerol triacetate (no by-products). In the first part of the article, selected physical and chemical properties of such biofuel in comparison to the limits specified in the standard quality requirements for this type of products (EN 14214) were discussed. In the next part, the results of empirical studies were evaluated, showing the influence of speed and load conditions in test engine Perkins 1104C-E44TA on concentrations of harmful components in the exhaust gases such as carbon monoxide, nitrogen oxides, hydrocarbons, particulates. Engine tests were performed with using biofuels selected by the authors. The measurement system, consisted of an AVL CEB II gas analyser and MEXA-1230PM device for measure of particulate matter in real time, to measure the concentrations of toxic exhaust components was used. Based on the concentration of toxic components of exhaust gases according to Test C1 according to ISO 8178, the emission of the above-mentioned normalized toxic components of exhaust gases was determined. In the final part of the article, the results of empirical studies on the concentrations of toxic exhaust gases in the linear-point diagrams, and emission in the bar chart diagrams were presented