"What's (the) Matter?", A Show on Elementary Particle Physics with 28 Demonstration Experiments

We present the screenplay of a physics show on particle physics, by the Physikshow of Bonn University. The show is addressed at non-physicists aged 14+ and communicates basic concepts of elementary particle physics including the discovery of the Higgs boson in an entertaining fashion. It is also demonstrates a successful outreach activity heavily relying on the university physics students. This paper is addressed at anybody interested in particle physics and/or show physics. This paper is also addressed at fellow physicists working in outreach, maybe the experiments and our choice of simple explanations will be helpful. Furthermore, we are very interested in related activities elsewhere, in particular also demonstration experiments relevant to particle physics, as often little of this work is published. Our show involves 28 live demonstration experiments. These are presented in an extensive appendix, including photos and technical details. The show is set up as a quest, where 2 students from Bonn with the aid of a caretaker travel back in time to understand the fundamental nature of matter. They visit Rutherford and Geiger in Manchester around 1911, who recount their famous experiment on the nucleus and show how particle detectors work. They travel forward in time to meet Lawrence at Berkeley around 1950, teaching them about the how and why of accelerators. Next, they visit Wu at DESY, Hamburg, around 1980, who explains the strong force. They end up in the LHC tunnel at CERN, Geneva, Switzerland in 2012. Two experimentalists tell them about colliders and our heroes watch live as the Higgs boson is produced and decays. The show was presented in English at Oxford University and University College London, as well as Padua University and ICTP Trieste. It was 1st performed in German at the Deutsche Museum, Bonn (5/'14). The show has eleven speaking parts and involves in total 20 people.Comment: 113 pages, 88 figures. An up to date version of the paper with high resolution pictures can be found at http://www.th.physik.uni-bonn.de/People/dreiner/Downloads/. In v2 the acknowledgements and a citation are correcte

An FPGA-based Sampling ADC for the Crystal Barrel Calorimeter

The CBELSA/TAPS experiment in Bonn investigates the excitation spectra of protons and neutrons through meson-photoproduction. With its ability to polarize the target nucleons and the incident photon beam, the experiment has contributed significantly to a better understanding of the baryon excitation spectrum, and with that also to the understanding of the strong interaction in the non-perturbative regime. Since a recent upgrade, the experiment's main electromagnetic calorimeter, the Crystal Barrel, is read out by avalanche photo-diodes. Their signal is digitized by integrating Fastbus ADCs, providing a value proportional to the energy deposited in the calorimeter crystals. As a result of long conversion and transfer times, those ADCs have become the limiting factor in the data acquisition, with possible readout rates of less than 2 kHz. Moreover, the possibility to identify pile-up, i.e. quickly-succeeding energy deposits that overlap in the integration window, is presently missing. Already years ago, it has been investigated whether this readout system could be replaced by faster and more modern sampling ADCs, which offer access to the waveform representation for a more sophisticated analysis, but the investigations were limited to commercially available digitizers with high cost and low channel densities. In addition, the firmware (operating system) of such digitizers is usually closed-source, which does not allow for the implementation of experiment-specific algorithms. Due to the above reasons, the investigations had not led to a satisfactory solution, and the Fastbus ADCs are still in operation today. In this thesis, the development and test of a custom (non-commercial) FPGA-based sampling ADC, which will replace the Fastbus ADC, has been driven forward. This so-called CB-SADC (Crystal Barrel Sampling Analog-to-Digital Converter) has been adapted from a prototype of the PANDA experiment in such a way that it is suited to operate within the specific conditions of the CBELSA/TAPS experiment. Apart from the hardware development, the firmware for the FPGA, which processes the digitized data, was designed and tested extensively. Specific algorithms allow not only the determination of the deposited energy and the timestamps of each event, but also an event-wise baseline determination and the detection of pile-up events. An online correction of pileup events, which occur with significant frequency in the forward region of the calorimeter, leads to a higher data quality and improved efficiency and statistics. Apart from the hardware development, the firmware for the FPGA, which processes the digitized data, was designed and tested extensively. Specific algorithms allow not only the determination of the deposited energy and the timestamps of each event, but also an event-wise baseline determination and the detection of pile-up events. An online correction of pileup events, which occur with significant frequency in the forward region of the calorimeter, leads to a higher data quality and improved efficiency and statistics. Two prototype iterations of the CB-SADC have been produced and were tested thoroughly in the laboratory and in connection with the CBELSA/TAPS experiment. The results of those tests, and preliminary analyses of production beam times with 50% of the calorimeter's forward half being read out by the CB-SADCs, showed an improvement of the data quality. The timestamp determination of the CB-SADCs in the energy regime below 10MeV has provided data where the experiment's TDC (Time-to-Digital Converter) either has worse resolution or cannot provide timestamps at all. In addition, standalone tests in the laboratory and tests with the data acquisition system have confirmed a much higher readout speed compared to the integrating Fastbus ADCs. Based on the achieved results, it was finally decided to equip the whole calorimeter with the new CB-SADC readout. At the time of finalizing this thesis, all CB-SADCs have been produced and are prepared for installation in the experimental hall. They will be running in parallel with the integrating Fastbus ADCs during the next production beam times, offering an opportunity to test the CB-SADC readout system as a whole. As soon as it is proven that the new readout works reliably, the limiting integrating Fastbus ADCs will be decommissioned and the CBELSA/TAPS experiment can start taking data with an increased readout rate

Simulation of dry and lubricated contacts in multi-body systems

The present paper investigates the modeling of counterformal elastohydrodynamic lubricated (EHL) contacts in multi-body system (MBS) environments. The aim is to obtain a representation of the dynamic behaviour of machine elements and characteristic values as the lubrication film thickness for lifetime calculations. Two contact models are presented for the study of cam-roller tappet and raceway-roller systems. The first model is a one-dimensional representation of the EHL contact behaviour. It is based on the calculation of the central lubrication film thickness by means of dimensionless values (functions of the operating conditions) and provides a simplified model of the mixed lubrication. The second one, still under development, investigates the modeling of 3D dry and lubricated contacts. The fluid-structure interaction is here fully considered and a discretised form of the contact problem is solved using an iterative algorithm. This paper proposes, in the latter case, some perspectives and a discussion of its implementation

Simulation of dry and lubricated contacts in multi-body systems

International audienceThe present paper investigates the modeling of counterformal elastohydrodynamic lubricated contacts in multi-body system environments. The aim is to obtain a representation of the dynamic behaviour and characteristic values for lifetime calculations. Two contact models are presented for the study of cam-roller tappet and raceway-roller contacts. The first model is a one-dimensional representation of the EHL contact behaviour. It is based on the calculation of the central lubrication film thickness by means of dimensionless values (functions of the operating conditions) and provides a simplified model of the mixed lubrication. The second one, still under development, investigates the modeling of 3D dry and lubricated contacts. This paper proposes, in the latter case, some perspectives and a discussion of its implementation.L'article suivant concerne la modélisation de contacts élastohydrodynamiques entre semi-espaces dans les environnements de systèmes multi-corps dans le but d'obtenir une représentation du comportement dynamique de mécanismes complexes et d'évaluer les grandeurs caractéristiques nécessaires aux calculs de durée de vie. Deux modèles de contact élastohydrodynamique sont ainsi présentés pour l'étude de systèmes du type came-roulement ou piste-roulement. Le premier modèle, qui est une représentation unidimensionnelle du contact, s'appuie sur le calcul de la hauteur du film de lubrifiant au centre du contact, donnée à partir de coefficients sans dimension dépendant des conditions de fonctionnement. Il inclut une modélisation simplifiée du frottement mixte. Le second, encore en cours de développement, concerne la modélisation 3D de contacts secs et lubrifiés. L'article contient, à cet effet, une discussion ainsi que quelques perspectives quant à son implémentation

Deep‐water uptake under drought improved due to locally increased root conductivity in maize, but not in faba bean

Moderate soil drying can cause a strong decrease in the soil-root system conductance. The resulting impact on root water uptake depends on the spatial distribution of the altered conductance relatively to remaining soil water resources, which is largely unknown. Here, we analyzed the vertical distribution of conductance across root systems using a novel, noninvasive sensor technology on pot-grown faba bean and maize plants. Withholding water for 4 days strongly enhanced the vertical gradient in soil water potential. Therefore, roots in upper and deeper soil layers were affected differently: In drier, upper layers, root conductance decreased by 66%–72%, causing an amplification of the drop in leaf water potential. In wetter, deeper layers, root conductance increased in maize but not in faba bean. The consequently facilitated deep-water uptake in maize contributed up to 21% of total water uptake at the end of the measurement. Analysis of root length distributions with MRI indicated that the locally increased conductance was mainly caused by an increased intrinsic conductivity and not by additional root growth. Our findings show that plants can partly compensate for a reduced root conductance in upper, drier soil layers by locally increasing root conductivity in wetter layers, thereby improving deep-water uptake

Stomatal conductance tracks soil-to-leaf hydraulic conductance in faba bean and maize during soil drying

Although regulation of stomatal conductance is widely assumed to be the most important plant response to soil drying, the picture is incomplete when hydraulic conductance from soil to the leaf, upstream of the stomata, is not considered. Here, we investigated to what extent soil drying reduces the conductance between soil and leaf, whether this reduction differs between species, how it affects stomatal regulation, and where in the hydraulic pathway it occurs. To this end, we noninvasively and continuously measured the total root water uptake rate, soil water potential, leaf water potential, and stomatal conductance of 4-week-old, pot-grown maize (Zea mays) and faba bean (Vicia faba) plants during 4 days of water restriction. In both species, the soil–plant conductance, excluding stomatal conductance, declined exponentially with soil drying and was reduced to 50% above a soil water potential of −0.1 MPa, which is far from the permanent wilting point. This loss of conductance has immediate consequences for leaf water potential and the associated stomatal regulation. Both stomatal conductance and soil–plant conductance declined at a higher rate in faba bean than in maize. Estimations of the water potential at the root surface and an incomplete recovery 22 h after rewatering indicate that the loss of conductance, at least partly, occurred inside the plants, for example, through root suberization or altered aquaporin gene expression. Our findings suggest that differences in the stomatal sensitivity among plant species are partly explained by the sensitivity of root hydraulic conductance to soil drying

"What's (the) Matter?", A Show on Elementary Particle Physics with 28 Demonstration Experiments

We present the screenplay of a physics show on particle physics, by the Physikshow of Bonn University. The show is addressed at non-physicists aged 14+ and communicates basic concepts of elementary particle physics including the discovery of the Higgs boson in an entertaining fashion. It is also demonstrates a successful outreach activity heavily relying on the university physics students. This paper is addressed at anybody interested in particle physics and/or show physics. This paper is also addressed at fellow physicists working in outreach, maybe the experiments and our choice of simple explanations will be helpful. Furthermore, we are very interested in related activities elsewhere, in particular also demonstration experiments relevant to particle physics, as often little of this work is published. Our show involves 28 live demonstration experiments. These are presented in an extensive appendix, including photos and technical details. The show is set up as a quest, where 2 students from Bonn with the aid of a caretaker travel back in time to understand the fundamental nature of matter. They visit Rutherford and Geiger in Manchester around 1911, who recount their famous experiment on the nucleus and show how particle detectors work. They travel forward in time to meet Lawrence at Berkeley around 1950, teaching them about the how and why of accelerators. Next, they visit Wu at DESY, Hamburg, around 1980, who explains the strong force. They end up in the LHC tunnel at CERN, Geneva, Switzerland in 2012. Two experimentalists tell them about colliders and our heroes watch live as the Higgs boson is produced and decays. The show was presented in English at Oxford University and University College London, as well as Padua University and ICTP Trieste. It was 1st performed in German at the Deutsche Museum, Bonn (5/'14). The show has eleven speaking parts and involves in total 20 people