333 research outputs found
Charakterisierung und Signalanalyse von TRD-Prototypen für das CBM Experiment
No full textAls es in den 1920er und 1930er Jahren zur Entdeckung des expandierenden Raums, gemessen über die kosmologische Rotverschiebung, kommt, wird daraus erstmals die Idee eines kleinsten Ursprungspunkts zu Beginn der Zeit postuliert. Es dauerte jedoch weitere 30 Jahre, bis das Konzept des „Big Bang“ als Ursprungsmodell veröffentlicht wurde [Lum07]. Seitdem untersuchen Wissenschaftler fortschreitend die Theorie des Big Bang. Der Zustand der Materie zum Zeitpunkt Null ist nach wie vor ungeklärt, ab ca. 10 exp (-44) Sekunden nach dem Urknall wird in der Theorie des Big Bang davon ausgegangen, dass sich die Materie im Zustand des Quark-Gluon-Plasmas befand. Zunächst galt es eine experimentelle Bestätigung für die generelle Existenz eines solchen Zustands zu finden. Die experimentelle Suche nach dem Quark-Gluon-Plasma im Labor begann vor fast 30 Jahren am Bevalac in Berkley [Gus84], dort konnte bei Niobium-Kollisionen kollektiver Fluss beobachtet werden. Zehn Jahre später begannen die Messungen des Schwerionen-Forschungsprogramms am CERN1. Im Jahr 1994 wurden dort die ersten Schwerionenkollisionen durchgeführt, von denen man sich erhoffte, dass sie zu einer kurzzeitigen Erzeugung des Quark-Gluon-Plasmas führen. Im Jahr 2000 gab es dann eine zusammenfassende Pressemitteilung des CERN, in der die Messungen eines neuartigen Materiezustands beschrieben wurden [CER00]. Weitere fünf Jahre später wurde ein Bericht der bis dahin erreichten Ergebnisse der vier Quark-Gluon-Plasma Experimente am Relativistic Heavy Ion Collider (RHIC) des Brookhaven National Labratory veröffentlicht [BNL05]. Dabei konnten einige Ergebnisse aus den Messungen am CERN bestätigt werden, andere hingegen nicht. Die Annahme, das Quark-Gluon-Plasma verhalte sich wie ein Gas, musste beispielsweise nach den Messungen am RHIC verworfen werden. Diese zeigen, dass das Verhalten des Quark-Gluon-Plasma eher dem von Flüssigkeiten ähnelt [BNL05].
Seit den ersten Schritten zur Untersuchung des Quark-Gluon-Plasma am CERN, in denen vor allem die Messung der Existenz des Quark-Gluon-Plasmas an sich im Vordergrund stand, soll der Phasenübergang nun quantitativ untersucht werden. Dazu werden Dichte und Temperatur der betrachteten Materie variiert und die vorhandene Zustandsphase gemessen. Eines dieser Experimente soll das Compressed Baryonic Matter (CBM) Experiment werden. Das Ziel des Experiments ist die Untersuchung von Materie bei sehr hohen Dichten, aber im Vergleich zu anderen aktuellen Experimenten relativ niedrigen Temperaturen. Im Jahr 2009 wurde der erste Spatenstich auf dem Gelände der Gesellschaft für Schwerionenforschung in Darmstadt für den Bau der Facility for Antiproton and Proton Research (FAIR) getätigt. Mit Hilfe der FAIR-Beschleuniger soll dann das CBM Experiment das Quark-Gluon-Plasma bei hohen Materiedichten mit bisher nicht erreichter Statistik untersuchen können. Jedoch gerade das Erreichen solch hoher Ereignisraten stellt nicht nur eine zentrale Herausforderung an die Beschleuniger dar, sondern auch an die messenden Detektoren. Diese Arbeit beschäftigt sich mit der Entwicklung eines Transition Radiation Detektors für das CBM Experiment.
Nach einer kurzen Einführung in die generelle Untersuchung des Quark-Gluon-Plasmas folgt die Beschreibung des geplanten Aufbaus des CBM Experiments mit dessen Subsystemen. Danach wird die theoretische und praktische Funktionsweise eines Transition-Radiation Detektors (TRD) erklärt, um darauf aufbauend die Charakterisierung und Signalanalyse der entwickelten TRD-Prototypen darzustellen. Abschließend werden die Ergebnisse in Bezug auf den für das CBM Experiment zu entwickelnden Detektor diskutiert
Quarkonium measurements in nucleus--nucleus collisions with ALICE
No full textQuarkonia, i.e. bound states of bb‾ and cc‾ quarks, are powerful observables to study the properties of nuclear matter under extreme conditions. The formation of a Quark-Gluon Plasma (QGP), which is predicted by lattice QCD calculations at high temperatures as reached at the LHC energies, has a strong influence on the production and behavior of quarkonia. The latest ALICE results on bottomonium and charmonium production in nucleus−nucleus collisions are presented. This includes measurements of the ϒ(1S) and ϒ(2S) nuclear modification factor ( R AA ) at forward rapidity and the J/ψ R AA and ν2 as a function of centrality, p T and rapidity in Pb–Pb collisions at sNN=5.02TeV . Also, first results from J/ψ measurements in Xe–Xe collisions at sNN=5.44TeV are presented. Further on, the experimental results are compared to various calculations from theoretical models.Quarkonia, i.e. bound states of and quarks, are powerful observables to study the properties of nuclear matter under extreme conditions. The formation of a Quark-Gluon Plasma (QGP), which is predicted by lattice QCD calculations at high temperatures as reached at LHC energies, has a strong influence on the production and behavior of quarkonia. The latest ALICE results on bottomonium and charmonium production in nucleusnucleus collisions are presented. This includes measurements of the (1S) and (2S) nuclear modification factors () at forward rapidity and the J/ and as a function of centrality, and rapidity in PbPb collisions at = 5.02 TeV. Also, first results from J/ measurements in XeXe collisions at = 5.44 TeV are presented. Further on, the experimental results are compared to various calculations from theoretical models
Image-guided therapy: evolution and breakthrough.
No full textInternational audienceBeyond the advances made in computer-assisted interventions and robotic systems, the demand for more efficient and safer therapies remains challenging. Thus, if it is possible to improve the instrument tracking, steering, and target localization, to miniaturize the sensors and actuators, and to conduct preoperatively planned minimally invasive therapies, we still need new resources to achieve permanent destruction of abnormal tissues or suppression of pathological processes. Most of the physics-based (or energy-based) therapeutic principles at our disposal have been established a long time ago, but their actions on basic cellular and molecular mechanisms are not yet fully understood. They all have a wide spectrum of clinical targets in terms of organs and pathologies, modes of application (external, interstitial, intraluminal, etc.) with advantages and side-effect drawbacks, proven indications, and contraindications. Some of them may still face controversies regarding their outcomes. This short article, mainly focused on tumor destruction, briefly reviews in its first part some of these techniques and sketches the next generation under investigation. The former include radio frequency (RF), high-intensity focused ultrasound (HiFU), microwaves, and cryotherapy, of which all are temperature based. Laser-based approaches [e.g., photodynamic therapy (PDT) at large] are also discussed. Radiotherapy and its variants (hadrontherapy, brachytherapy, Gamma Knife, and CyberKnife) remain, of course, as the reference technique in cancer treatment. The next breakthroughs are examined in the second part of the article. They are based on the close association between imaging agents, drugs, and some stimulation techniques. The ongoing research efforts in that direction show that, if they are still far from clinical applications, strong expectations are made. From the point of view of interventional planning and image guidance, all of them share a lot of concerns
A few critical issues in biomedical imaging and therapy
No full textInternational audienceThis introductory chapter does not pretend to give a full overview of the biomedical imaging and therapeutic resources but some ideas about the problems to face and the breakthroughs that are on the way or will happen tomorrow. It will emphasize the importance to look outside its own field and understand how the new advances made elsewhere can help in solving specific problems or, and perhaps more, be the source of inspirations. It attempts to emphasize the efforts to make on therapy if we want to be coherent with the trend toward early diagnosis in caring patients
A few critical issues in biomedical imaging and therapy
No full textInternational audienceThis introductory chapter does not pretend to give a full overview of the biomedical imaging and therapeutic resources but some ideas about the problems to face and the breakthroughs that are on the way or will happen tomorrow. It will emphasize the importance to look outside its own field and understand how the new advances made elsewhere can help in solving specific problems or, and perhaps more, be the source of inspirations. It attempts to emphasize the efforts to make on therapy if we want to be coherent with the trend toward early diagnosis in caring patients
Dense biased networks with deep priori anatomy and hard region adaptation: Semi-supervised learning for fine renal artery segmentation
No full textInternational audienceFine renal artery segmentation on abdominal CT angiography (CTA) image is one of the most important tasks for kidney disease diagnosis and pre-operative planning. It will help clinicians locate each interlobar artery's blood-feeding region via providing the complete 3D renal artery tree masks. However, it is still a task of great challenges due to the large intra-scale changes, large inter-anatomy variation, thin structures, small volume ratio and small labeled dataset of the fine renal artery. In this paper, we propose the first semi-supervised 3D fine re-nal artery segmentation framework, DPA-DenseBiasNet, which combines deep prior anatomy (DPA), dense biased network (DenseBiasNet) and hard region adaptation loss (HRA): 1) Based on our proposed dense biased connection, the DenseBiasNet fuses multi-receptive field and multi-resolution feature maps for large intra-scale changes. This dense biased connection also obtains a dense * Corresponding author information flow and dense gradient flow so that the training is accelerated and the accuracy is enhanced. 2) DPA features extracted from an autoencoder (AE) are embedded in DenseBiasNet to cope with the challenge of large inter-anatomy variation and thin structures. The AE is pre-trained (unsupervised) by numerous unlabeled data to achieve the representation ability of anatomy features and these features are embedded in DenseBiasNet. This process will not introduce incorrect labels as optimization targets and thus contributes to a stable semi-supervised training strategy that is suitable for sensitive thin structures. 3) The HRA selects the loss value calculation region dynamically according to the segmentation quality so the network will pay attention to the hard regions in the training process and keep the class balanced. Experiments demonstrated that DPA-DenseBiasNet had high predictive accuracy and generalization with the Dice coefficient of 0.884 which increased by 0.083 compared with 3D U-Net (Ç içek et al., 2016). This revealed our framework with great potential for the 3D fine renal artery segmentation in clinical practice
Publisher Correction: Unveiling the strong interaction among hadrons at the LHC (Nature, (2020), 588, 7837, (232-238), 10.1038/s41586-020-3001-6)
No full textIn Fig. 1c of this Article, owing to an error during the production process, the equation incorrectly began ‘C(k*, r*) = …’ instead of ‘C(k*) = …’. In addition, in affiliation 71 ‘Dipartimento di Fisica dell’Università degli studi di Bari Aldo Moro’ has been corrected to read ‘Dipartimento di Fisica dell’Università degli studi di Cagliari’. The original Article has been corrected online. *A list of authors and their affiliations appears online. © 2021, The Author(s), under exclusive licence to Springer Nature Limited
Neutral pion production at midrapidity in pp and Pb–Pb collisions at √ sNN TeV
No full textInvariant yields of neutral pions at midrapidity in the transverse momentum range (Formula presented.)c measured in Pb–Pb collisions at (Formula presented.) TeV are presented for six centrality classes. The pp reference spectrum was measured in the range (Formula presented.)c at the same center-of-mass energy. The nuclear modification factor, (Formula presented.), shows a suppression of neutral pions in central Pb–Pb collisions by a factor of up to about (Formula presented.) for (Formula presented.) ≲(Formula presented.)c. The presented measurements are compared with results at lower center-of-mass energies and with theoretical calculations. © 2014, The Author(s)
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